Accepted Manuscript Title: Recovery of oil from oil-in-water emulsion using biopolymers by adsorptive method Author: S.S.D. Elanchezhiyan N. Sivasurian S. Meenakshi PII: DOI: Reference:
S0141-8130(14)00443-7 http://dx.doi.org/doi:10.1016/j.ijbiomac.2014.07.002 BIOMAC 4461
To appear in:
International Journal of Biological Macromolecules
Received date: Revised date: Accepted date:
12-5-2014 16-6-2014 3-7-2014
Please cite this article as: S.S.D. Elanchezhiyan, N. Sivasurian, S. Meenakshi, Recovery of oil from oil-in-water emulsion using biopolymers by adsorptive method, International Journal of Biological Macromolecules (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.07.002 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Recovery of oil from oil-in-water emulsion using biopolymers by adsorptive method S. SD. Elanchezhiyan, N. Sivasurian, S. Meenakshi*
Gandhigram- 624 302, Tamil Nadu, India
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Department of Chemistry, The Gandhigram Rural Institute-Deemed University,
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*Corresponding author. Tel.: +91-451-2452371; Fax: +91-451-2454466.
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E-mail address: [email protected]
Abstract
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In the present study, it is aimed to identify, a low cost sorbent for the recovery of oil from oil-in-water emulsion using biopolymers such as chitin and chitosan. Chitin has the greater adsorption capacity than chitosan due to its hydrophobic nature. The characterizations of chitin and chitosan were done using FTIR, SEM, EDAX, XRD, TGA and DSC techniques. Under
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batch equilibrium mode, a systematic study was performed to optimize the various equilibrium parameters viz., contact time, pH, dosage, initial concentration of oil, and temperature. The
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adsorption process reached equilibrium at 40 min of contact time and the percentage removal of
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oil was found to be higher (90 %) in the acidic medium. The Freundlich and Langmuir models were applied to describe the equilibrium isotherms and the isotherm constants were calculated.
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Thermodynamic parameters such as ΔGº, ΔHº and ΔSº were calculated to find out the nature of the sorption mechanism. The kinetic studies were investigated with reaction-based and diffusion-
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based models. The suitable mechanism for the removal of oil has been established.
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Keywords: Oil removal; Chitin; Chitosan; Adsorption; Isotherms.
1. Introduction
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In the modern society, the release of wastewater containing oil into the environment increases due to urbanization and industrial development. Oils that are found in contaminated water can be fats, lubricants, cutting liquids, heavy hydrocarbons such as tars, grease, crude oils, diesel oils, and light hydrocarbons viz., kerosene, jet fuel and gasoline. Foremost industrial
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sources of oily wastewater include petroleum refineries, metal manufacturing and machining and food processors. These industries have augmented the threats of oil pollution to the environment
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and their discharges to the natural environment, create a major ecological problem throughout
oil-in-water emulsions among their basic contaminants.
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the world [1]. Unlike free or floating oil spilled at sea, most of the industrial wastewaters contain
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Cutting fluid is used in the production process elements of machining operation, including turning, drilling, grinding, and milling and provides better surface finishes. The type of
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cutting fluid used for machining operations is oil based and water-based. The oil-based fluid
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consists of natural oil or synthetic oil. The water-based fluids are soluble oil, which may be
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synthetic and semisynthetic and are mixed with water to form oil-in-water emulsion. A Material used as a lubrication matter in soluble oil, synthetic and semisynthetic cutting fluid is mineral oil,
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organic compounds of poly-alpha-olefins and the mixture of mineral oil and organic compounds, respectively [2]. Typical additives in the water-based cutting fluid is emulsifiers, surfactants, corrosion inhibitors and biocides. After a long use, cutting fluid loses its lubricating property and generates a toxic waste. It contains heavy metals, biocides, microorganisms and harmful decomposition products.
Oil emulsions are deleterious to the environment as they impede penetration of sunlight and absorption of oxygen from the air by the water bodies contaminated by oil, and in many cases are toxic to the aquatic life. Because of these reasons, the Ministry of Environment and Forests, Government of India has prescribed the discharge wastewater quality stating that the oil
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concentration should not exceed 5 mg/L [3]. The concentration of oil in effluents from different industrial sources is found to be as high as 40,000 mg/L [4]. Emulsified oil wastewater can lead to severe problems in different treatment stages. Therefore, it is essential to remove oil from wastewater. Numerous methods have been proposed to remove residual oil from wastewater,
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such as adsorption [5-7], flocculation [8], electro-coagulation [9] and electro-flotation [10, 11]. It is difficult to use biological method to treat the cutting fluid due to its toxicity. Conventional
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treatment methods of oil-in-water emulsions are skimming, gravity setting, emulsion breaking
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[12], chemical de-emulsification [13], the combination of destabilization and flotation [14] and membrane [15]. Adsorption is a far and wide accepted technology for both organic and inorganic
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contaminants such as cutting fluid [2], dyes [16], fluoride [17], nitrate [18], phosphate [19], perchlorate [20] etc. It is a promising technology to remove oil from oil-in-water emulsion using
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adsorbents such as peat [21], mixture of Ca and Mg oxides [22] activated carbon, etc. Natural
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materials and natural polymers such as chitin and chitosan, certain waste products such as fly
many countries.
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ash, oxides and sludges are considered as low cost adsorbents due to their local availability in
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Chitin (β-(1 → 4)-linked 2-acetamido-2-deoxy-D-glucan) is the main component in the cuticles of crustaceans, insects, mollusks and in the cell walls of fungi. It is the second most abundant polysaccharide found on earth next to cellulose [23]. The exoskeletons of shrimps have long since attracted attention as a source of raw material for chitin production as the dry arthropod exoskeletons contained about 20 % to 50 % chitin (natural chelating polymers). The deacetylated form of chitin is chitosan. The flakes of chitin and chitosan could be considered as an alternative carrier material for immobilizing microorganisms for bioremediation purposes. Chitin is highly hydrophobic and is insoluble in water and most organic solvents [24]. At neutral and alkaline pH values, chitosan is insoluble, but the salt formation is observed with organic and
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inorganic acids [25, 26]. Chitin and chitosan are cost effective, non-toxic, non-polluting and sustainable since fishery wastes are freely and abundantly available. Hence, in the present study, sequences of adsorption experiments were conducted to evaluate the possibility of the use of chitin and chitosan powder as adsorbents for oil removal
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from oil-in-water emulsion. The isotherm and kinetic models were used to describe the experimental data. This information will be useful for further application in the treatment of oily
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waste effluents.
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2. Materials and methods 2.1. Materials
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Chitin and chitosan (85% deacetylated) were supplied from Pelican Biotech and Chemicals Labs, Kerala (India). The cutting oil was commercially obtained and the
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characteristics of oil are given in Table 1. Base oil used is for making cutting oil which consists
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of 66.9 % saturated compounds, 27.5 % aromatic compounds and 5.5 % sulphur compounds.
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The following analytical grade chemicals were used in the experimental work: n-hexane (Merck, Mumbai) HCl and NaOH (Central Drug House, New Delhi). Double distilled water was used
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throughout the study.
Table 1
2.2. pH zero point charge measurements The pH at the potential of zero point charge (pHzpc) of chitin and chitosan was measured using pH drift method [27]. The pH of a solution of 0.01M NaCl was adjusted between 2 and 12 by adding either HCl or NaOH. Sorbent (0.15 g) was added to 50 mL of the solution. After the pH had stabilized (typically after 24 h), the final pH was recorded. The graphs of final versus initial pH were used to determine the points at which initial pH and final pH values were equal. This was taken as the pHzpc of the sorbent used.
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2.3. Measurement of Hydrophobic property Hydrophobic property of chitin and chitosan was investigated by hydrophobic index. For hydrophobic index, 1.0 g of adsorbent was soaked in cutting oil or deionized water until equilibrium had been reached. The adsorption capacity was calculated as {(weight of the
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adsorbed adsorbate/weight of the adsorbent) × 100}. Hydrophobic index was then computed as
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the adsorption capacity of cutting fluid/adsorption capacity of deionized water [2]. 2.4. Characterization
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Fourier Transform Infra-red (FTIR) spectra of the samples as solid by diluting in KBr pellets were recorded with JASCO-460 plus model within the wavelength range of 400 – 4000
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cm−1. The results of FTIR spectrometer were used to confirm the functional groups present in the
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sorbent before and after sorption of oil. The surface morphology of chitin and chitosan before and after treatment with oil was studied by scanning electron microscope (SEM) with
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VEGA3TESCAN model and the elemental analysis was made by energy dispersive analysis of
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X-ray (EDAX) spectroscopy with Bruker Nano Gmbh, Germany. The crystalline natures of biopolymers were analyzed by X-ray powder diffraction (XRD, X’per PRO model – PANalytical
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make). Thermal stability of the sorbents were determined using a Thermo gravimetric analyzer (TGA, Model 2960, Universal V2.4F TA instruments, USA) and Differential Scanning Calorimetry (DSC, Model 2920, Universal V2. 4F TA Instruments, USA). The pH measurements were done using expandable ion analyzer EA940 with the pH electrode. 2.5. Sorption experiments
Sorption studies of oil from oil emulsion have been carried out with the sorbents to assess the suitability of its application towards oil removal. Studies were performed to assess how sorption rates depended on the concentrations of sorbate in solution and how rates were influenced by various parameters like contact time, pH and temperature. Various concentrations
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of oil-in-water emulsion were obtained by diluting the prepared stock solution and used for oil sorption experiments. The batch adsorption experiments were carried out with the required quantity of the sorbent along with oil-in-water emulsion. The contents were shaken thoroughly using a thermostated shaker rotating at a speed of 200 rpm. The isotherm and thermodynamic
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parameters of sorption was established by conducting the experiments at different initial oil concentrations viz., 1140, 2830, 5560 and 7620 mg/L at 303, 313 and 323 K in a thermally
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controlled mechanical shaker. Then the solution was filtered at the appropriate time and the
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residual oil concentration was measured. Duplicate experiments were performed by the batch equilibrium method.
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The percentage of oil removal can be calculated according to the following equation:
(1)
2.6. Analysis
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where, Ci is initial oil concentration (mg/L), Ce is equilibrium oil concentration (mg/L)
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The concentration of oil was measured using oil and grease method recommended by
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APHA, AWWA, WPCF (2005) Standard method of examination of water and wastewater, with n-Hexane being used as the oil-extraction solvent [28]. The oil content in the suspension was determined for each sample of oil-in-water emulsion, both before and after the experiment. All the experiments were carried out twice and the average values of the results have been reported. 3. Results and discussion
3.1. Characterisation of the sorbents 3.1.1. FTIR analysis Fig. 1 depicts the respective FTIR spectra of chitin before and after oil sorption. In Fig. 1a, the raw chitin before sorption of oil showed the -NH group in the ranges 3442 and 1657 cm-1. The bands at 2926, 1421 and 1378 cm-1 are attributed to the vibration of -CH group of chitin.
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The band at 1629 cm-1 is due to an amide type of CO group of chitin. The interaction between oil and chitin was confirmed in the spectrum taken for oil sorbed chitin (Fig. 1b). After oil adsorption, the peaks for CH groups were shifted to 2923 and 2857 cm-1 for sharp intense peak corresponds to respective CH strong and medium peaks. The band around 3442 cm-1 has also
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been shifted to 3450 cm-1 which indicates the oil adsorption onto the chitin surface.
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Fig. 2 shows the FT-IR spectrum of chitosan before and after oil sorption. In Fig. 2a, the
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raw chitosan before sorption of oil showed the –OH and –NH2 group in the ranges 3005 and 3989 cm-1. The peaks at 2928 and 1368 cm-1 are ascribed to the -CH stretching and bending
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modes of vibration. After oil adsorption the peaks for CH groups are shifted to 2922 and 2859
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cm-1 for sharp intense peak corresponds to respective CH strong and medium peaks (Fig. 2b). Figure 2
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3.1.2. Morphology and elemental analysis
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SEM images of respective raw chitin, oil-adsorbed chitin, chitosan and oil-adsorbed chitosan are shown in Fig. 3 a-d. The change in the SEM micrographs of the sorbent indicates
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that there are threads like structure and surface is not smooth. But after oil-adsorption, the surface was fully occupied by oil, which has formed a layer over the surface. This covered layer Figure 3 like structure may be due to oil-adsorption onto the chitin and chitosan surfaces (Fig. 3 b & d). This is further supported by EDAX methods. The EDAX spectra of oil sorbed chitin and chitosan showed higher percentage of carbon when compared to raw chitin and chitosan as shown in Fig. 4. Also, as shown in Fig. 4b and d, the presence of peaks showing sulfur after oil adsorption by chitin and chitosan clearly proves that oil (sulfur compounds present in base oil) is adsorbed by both the sorbents chitin and chitosan. Figure 4
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3.1.3. XRD analysis XRD study was applied to detect the crystallinity of chitin and chitosan which are shown in Fig. 5 Chitin has 2θ diffraction peaks at 19.20º and 26.21º together with a few other peaks with much weaker intensity. Peaks corresponding to 20.3º in XRD of chitosan were less resolved and
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shifted to higher 2θ [29]. It is observed that the sharpness of the band is superior in chitin than in chitosan which shows the higher crystalline nature of chitin than chitosan [30].
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3.1.4. TGA and DSC analysis
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Figure 5
Thermogravimetric curves of chitin and chitosan are shown in Fig. 6 a and b. There are
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two degradation steps observed for chitin and chitosan. The first step noticed at temperatures lower than 40 °C – 90 °C for chitin and 40 °C – 150 °C for chitosan indicating the loss of water
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[31]. The second step takes place in the range of 200 °C – 390 °C for chitin and 200 °C – 330 °C
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for chitosan. This could be attributed to the decomposition of pyranose ring structure of chitin
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and chitosan [32]. As the decomposition temperature is higher in chitin than in chitosan, chitin exists as a stable structure towards thermal decomposition when compared to chitosan.
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Fig. 6 c and d shows the DSC thermograms of chitin and chitosan within the temperature range of 50 °C – 500 °C at a heating rate of 10 °Cmin-1. The DSC thermograms of chitin and chitosan were characterized by two thermal events; the first endothermic and the second exothermic. The endothermic event appeared at 46.63 °C for chitin and 68.91 °C for chitosan which are attributed to the evaporation of water. A wide exothermic peak appeared at 407.48 °C for chitin and a sharp exothermic peak comes out for chitosan at 308.88 °C are almost nearer to the temperature reported in the literature [31]. These exothermic peaks were owing to the thermal decomposition of chitin and chitosan. Figure 6 3.2. Effect of contact time
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For determining oil removal percentage using chitin and chitosan, the contact time is varied in the range of 10-60 min. About 200 mg of the sorbent was added in 25 mL of 1140 mg/L initial concentration of oil. Fig. 7a shows the effect of contact time on the cutting oil uptake on chitin and chitosan at pH 3. The plots show that the adsorption of cutting oil increases with time and
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then reaches a value beyond which no more oil was further removed from the solution leading to saturation. The adsorption of oil reached saturation at 40 min. The maximum removal of cutting
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oil was found to be 81.6 % using chitin and 45.1 % using chitosan as adsorbents. At the
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equilibrium point, the amount of oil desorbed from the chitin was in a state of dynamic equilibrium with the amount of oil being adsorbed on both the sorbents. The results revealed that
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the oil adsorption was fast at the initial stages of the contact period, and thereafter it became slower near the equilibrium. This phenomenon was due to the fact that a large number of vacant
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surface sites were available for adsorption during the initial stage, and after a lapse of time, the
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remaining vacant surface sites were difficult to be occupied due to repulsive forces between the
the further experiments.
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solute molecules on the solid and bulk phases. Hence, 40 min was fixed as the contact time for
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3.3. Effect of adsorbent dosage
The percentage of oil removal was determined by varying the dose of chitin and chitosan in the range from 50, 100, 150, 200 and 250 mg to find the maximum oil removal percentage by fixing the contact time of 40 min, at pH 3. As shown in Fig. 7b, it was observed that chitin needed an adsorbent dosage of 200 mg to achieve the highest percentage of 81.6 % removal of oil, while in case of chitosan the maximum percentage of oil removal was found to be 45 % at an adsorbent dosage of 200mg. It was noticed that when the weight dosage of sorbents increased, the percentage of cutting oil removal also improved due to the availability of more surface sites. 3.4. Effect of pH
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pH plays a vital role in the sorption of oil. Fig. 7c shows the effect of pH on the percentage of oil removal using chitin and chitosan. Before adsorption, the oil in the form of emulsion has to be made available for the sorption and this emulsion breaking is usually brought about by changing the pH value or inorganic coagulants [33]. Therefore, pH adjustments in the
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range of 3, 5, 7, 9 and 11 were also done to study the effect of adsorption of oil onto chitin and chitosan. In strong acidic condition, chitin and chitosan provokes a physico-chemical effect,
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apparently serving to demulsify and enhances the adsorption of oil. Thus acidic medium acts as a
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catalyst to catalyze the reaction between the oil molecules and the sorbent. As pH increases, the percentage of oil removal decreased. This may be due to the destabilization of sorbents and also
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the low degree of de-emulsification at a basic medium.
Hence, throughout the study, the pH of the medium was maintained at pH 3. In basic
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condition, the adsorption of cutting oil on chitin and chitosan decreased due to deprotonation of
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adsorbents and electrostatic repulsive interactions.
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Oil is mainly consisting of a mixture of hydrocarbons and hence the driving force between the oil and sorbents sorption may be due to the hydrogen bonding between them. pHZPC
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of chitin was found to be 6.8. At pH lower than pHZPC, the surface of chitin is positively charged and the adsorption of oil is favoured resulting in the highest percentage of oil removal in addition to the availability of oil due to de-emulsification. At pH higher than pHZPC, the surface of chitin is negatively charged which limits the chances for hydrogen bonding. Further, the degree of de-emulsification is less pronounced at this higher pH, which restricts the release of oil for sorption. The same reason is applicable to the oil removal using chitosan which has the pHZPC of 5.6. Out of the sorbents chitin and chitosan used for the removal of oil from oil-in-water emulsion, the oil removal percentage at 40 min of
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contact time, using 200 mg chitin was found to be 81.6 % at pH 3 which was higher than that observed for chitosan. Hence, further studies were limited to chitin alone. 3.5. Effect of initial oil concentration It is obvious that oil adsorption is significantly influenced by the initial concentration of
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the oil in aqueous solution at 40 min of contact time using 200 mg chitin for various initial concentrations viz., 1140, 2830, 5560 and 7620 mg/L as the percentage of oil removal decreases
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which is shown in Fig. 7d. The decreasing trend of percentage removal of oil can be explained
above a certain oil concentration.
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Figure 7
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by the fact that chitin had a limited number of active sites, which would have become saturated
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3.6. Sorption isotherms
To quantify the sorption capacity of the sorbents studied for the oil removal, the most
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commonly used isotherms, namely Freundlich and Langmuir isotherms have been adopted.
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Freundlich [34] isotherm is an empirical equation employed to describe heterogeneous systems. The well known logarithmic form of the Freundlich isotherm is given by the following equation:
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log qe = log kF + (1/n) log Ce
(2)
Where Ce is the equilibrium concentration of the adsorbate (mg/L) and qe is the amount of adsorbate adsorbed per unit weight of adsorbent, kF and n are Freundlich constants with n giving an indication of how favorable the adsorption process. Table 2 presents the values of Freundlich isotherm constants for chitin that was calculated from the linear plot of log qe vs. log Ce which is shown in Fig. S1. The favorable condition for adsorption is confirmed as the values of 1/n prevail between 0 and 1. The kF values of chitin were found to decrease with the increase in temperature. This
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confirms the exothermic nature of sorption. The higher r values obtained for all the sorbents demonstrate the applicability of Freundlich isotherm for oil removal. The Langmuir [35] equation is given as follows, (Ce/qe) = (1/Qob) + (Ce/Qo)
(3)
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Where Ce is the equilibrium concentration (mg/L) and qe is the amount adsorbed at
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equilibrium (mg/g) and Qo and b is Langmuir constants related to the energy of adsorption (L/mg) and adsorption capacity (mg/g), respectively. The Langmuir isotherm constant that
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relates to the energy of adsorption was calculated from the respective slope and intercept of the linear plot of Ce/qe vs. Ce and the values are presented in Table 2. The values of Qo were found to
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decrease with the increase in temperature, which further confirms the exothermic nature and
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temperature dependence of the sorption process.
In order to find out the feasibility of the isotherm, the essential characteristics of the
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Langmuir isotherm can be expressed in terms of the dimensionless constant separation factor or
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equilibrium parameter.
1 1 + bC
(4) o
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RL =
where b is the Langmuir isotherm constant and Co is the initial concentration of oil (mg/L). The RL values lying between 0 and 1 indicated that the conditions were favorable for adsorption. The higher r values of Freundlich over Langmuir, suggested that the Freundlich isotherm was more suitable than the Langmuir isotherm for oil removal using chitin as adsorbent. This fact was further supported by the low chi square values of Freundlich isotherm as shown in Table 2. In order to identify the suitable isotherm model for the sorption of oil on the chitin, this analysis has been carried out. The equivalent mathematical statement is
χ2 = ∑
(q e − q e,m ) 2 qe,m
(5)
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where qe,m is equilibrium capacity obtained by calculating from the model (mg/g) and qe is experimental data of the equilibrium capacity (mg/g). If data from the model are similar to the experimental data, χ2 will be a small number, where as if they differ, χ2 will be higher number. Therefore, it is also necessary to analyze the data set using the non-linear chi-square test to
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confirm the best fit isotherm for the sorption system [36]. The results of chi-square analysis are
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presented in Table 2. The lower χ2 values of Freundlich isotherm indicate the best fitting model for the sorption of oil onto chitin.
3.7. Thermodynamic treatment of the sorption process
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Table 2
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The thermodynamic parameters associated with the adsorption, viz., standard free energy
determined using the following equations.
ΔS o Δ H o − R RT
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ln K o =
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∆Go = -RT lnKo
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change (∆Go), standard enthalpy change (∆Ho) and standard entropy change (∆So), were
(6) (7)
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where ∆Go is the free energy of sorption (kJ/mol), ∆Ho is the standard enthalpy change (kJ/mol) and ∆So is standard entropy change (kJ/mol.K) T is the temperature in Kelvin and R is the universal gas constant (8.314 J mol-1K-1). The sorption distribution coefficient Ko was determined from the slope of the plot ln (qe/Ce) against Ce at different temperature and extrapolating to zero Ce according to Khan and Singh method [37]. ∆Ho and ∆So were calculated from the slope and intercept of van’t Hoff plot of ln Ko against 1/T. The values of thermodynamic parameters for chitin were calculated and are shown in Table 3. The spontaneous nature of the oil sorption by chitin is confirmed by the negative values of ΔGº. The positive value of ΔSº denotes that the freedom of oil is not much restricted in the
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sorbent, chitin. The negative value of ΔHº for oil removal confirms the exothermic nature [38] of the sorption process by chitin. Table 3
3.8. Sorption dynamics
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In this study, the two main types of sorption kinetic models, namely reaction-based and diffusion-based models, were adopted to fit the experimental data. The initial sorbate
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concentration and the reaction temperature are considered for examining the influence of
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sorption capacity on the rate of the reaction. 3.8.1. Reaction-based models
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To investigate the sorption mechanism of oil sorption on chitin, pseudo-first-order [39] and pseudo-second-order [40] kinetic models have been used in different experimental
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conditions. A simple pseudo-first-order kinetic model is represented as, (8)
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log (qe - qt) = log (qe) − (kad t) / 2.303
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Where qe and qt are the adsorption capacity at equilibrium and at time t, respectively (mg/g), kad is the rate constant of pseudo-first order adsorption (1/min). The slope of the straight-
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line plot of log (qe-qt) against t for different experimental conditions will give the value of the rate constant (kad). Linear plots of log (qe-qt) against t gives a straight line that indicates the applicability of Lagergren equation. The values of kad and the correlation coefficient (r) computed from these plots for oil sorption on chitin is given in Table 4. The fitness of the pseudo second order model was also analyzed. The most popular linear form is as follows: (t/qt) = (1/ h) + (t/qe)
(9)
The fitness of the data and the values of qe, k, and h were obtained from the plots of t/qt vs t for oil sorption at different temperatures viz., 303, 313 and 323 K on chitin, which are
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presented in Table 4. The plot of pseudo-second-order model of oil sorption onto chitin at 303 K is shown in Fig. S2. The decreasing qe values of the sorption of oil on chitin with the increase in temperature suggest the temperature dependence of the sorption process which in turn confirms the physisorption process.
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The plot of t/qt vs t gives a straight line with high correlation coefficient r values which is highthan that observed for pseudo-first-order model. This indicates the applicability of pseudo-
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second-order than pseudo-first-order model for the sorption of oil on chitin.
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3.8.2. Diffusion-based models
For a solid-liquid sorption process, the solute transfer is usually characterized either by
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particle diffusion [41] or by intraparticle diffusion [42, 43] control.
A simple equation for the particle diffusion controlled sorption process is as follows,
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ln (1- Ct/Ce) = kp t
(10)
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Where kp is the particle diffusion coefficient (mg/ g min). The value of the particle diffusion
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coefficient is obtained by the slope of ln (1- Ct/Ce) against t. The intra-particle diffusion model used here to refer to the theory proposed by Weber and
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Morris. The intra-particle diffusion equation, qt = ki t½
(11)
Where ki is the intra-particle diffusion coefficient (mg/g min0.5). The slope of the plot of qt against t1/2 will give the value of the intra-particle diffusion coefficient which is depicted in Fig. S3.
The kp, ki and r values of particle and intraparticle diffusion models are illustrated in Table 4. The higher r values obtained for intraparticle diffusion model indicates that the oil sorption on chitin prefers intraparticle diffusion model rather than particle diffusion model. Table 4
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3.9. Mechanism of cutting oil removal using chitin via adsorption process The oil removal consists of two steps. 1. De-emulsification of oil which makes oil free. 2. Sorption of oil by chitin.
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De-emulsification could be brought about by maintaining at pH 3. Next step is sorption of oil by the sorbents. The interaction of oil and the sorbents is mainly due to the hydrogen
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bonding. The Oil used for study is mainly consisting of a mixture of hydrocarbons which is
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hydrophobic in nature and could be attracted by the sorbent only due to van der Waals forces. Further, chitin exhibits higher hydrophobic nature as indicated by its value, when compared to
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chitosan which makes it more selective for hydrocarbon. Nevertheless, the mechanism of cutting oil adsorption on chitin powder involves two steps: (1) diffusion of cutting oil to the boundary
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surface of adsorbent; (2) diffusion through a liquid film at the surface to the pores of adsorbent.
4. Conclusions
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onto chitin.
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FT-IR spectra and SEM micrographs are used to prove the adsorption performance of cutting oil
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Biosorbents such as chitin and chitosan were used for the sorption of oil from oil-in-water emulsion with a minimum contact time of 40 min. The oil uptake by both chitin and chitosan was influenced by the pH of the medium. The sorption of the oil on the chitin and chitosan was higher at acidic pH and gradually decreases at basic pH values. The optimum pH for the removal of oil is pH 3 where de-emulsification occurs and also the surface acquires a positive charge. The lower χ2 values of Freundlich isotherm indicate the best fitting model for the sorption of oil onto chitin. This predicts the fitness of Freundlich isotherm than Langmuir isotherm for oil sorption by chitin, which confirms that the mechanism of oil sorption by chitin was mainly governed by physical forces. The negative standard free energy change and positive standard entropy change
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values show the spontaneity of the sorption process. The negative standard enthalpy change value for oil sorption using chitin confirms the exothermic nature of the process. The kinetics of sorption of oil on chitin followed the pseudo-second-order and intra-particle diffusion kinetic models.
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Acknowledgements
The First author is thankful to UGC-BSR for the Fellowship in the category of Research
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Fellowship in Science for Meritorious Students.
V. Singh, R.J. Kendall, K. Hake, S. Ramkumar, Crude oil sorption by raw cotton, Ind. Eng. Chem. Res. 52 (2013) 6277–6281.
[2]
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[1]
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Publishing, CRC Press, Washington, DC 2003. A.L. Ahmad, S. Sumathi, B.H. Hameed, Adsorption of residue oil from palm oil mill effluent using powder and flake chitosan: equilibrium and kinetic studies, Water Res. 39 (2005) 2483–2494. [6]
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[16] M.H. Farzana, S. Meenakshi, Removal of Acid blue 158 from aqueous media by adsorption onto cross-linked chitosan beads, J. Chitin Chitosan Sci. 1 (2013) 50–58. [17] S.M. Prabhu, S. Meenakshi, Enriched fluoride sorption using chitosan supported mixed metal
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[18] P. Ganesan, R. Kamaraj, S. Vasudevan, Application of isotherm, kinetic and thermodynamic models for the adsorption of nitrate ions on graphene from aqueous solution, J. Taiwan Inst. Chem. Eng. 44 (2013) 808–8144. [19] S. Vasudevan, J. Lakshmi, The adsorption of phosphate by graphene from aqueous
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solution, RSC Adv. 2 (2012) 5234–5242.
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[21] T. Viraraghavan, G.N. Mathavan, Treatment of oil-in-water emulsions using peat, Oil Chem. Pollut. 4 (1988) 261–280.
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[22] C. Solisio, A. Lodi, A. Converti, M.D. Borghi, Removal of exhausted oils by adsorption on mixed Ca and Mg oxides, Water Res. 36 (2002) 899–904.
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[23] M.N.V. Ravikumar, Chitin and chitosan fibers: An overview on chitin and Chitosan
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[24] A.V. Ilina, S.N. Kulikov, G.I. Chalenko, N.G. Gerasimova, V.P. Varlamov, Obtaining and study of monosaccharide derivatives of low-molecular-weight chitosan, Appl. Biochem.
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Microbiol. 44 (2008) 551–558.
[25] K.A. Alkhamis, M.S. Salem, M.S. Khanfar, The sorption of ketotifen fumarate by chitosan, AAPS Pharm. Sci. Technol. 9 (2008) 866–869. [26] N.V.R.K. Majeti, A review of chitin and chitosan applications, React. Funct. Polym. 46 (2000) 1–27.
[27] M.V. Lopez-Ramon, F. Stoeckli, C. Moreno-Castilla, F. Carrasco-Marin, On the characterization of acidic and basic surface sites on carbons by various techniques, Carbon. 37 (1999) 1215–1221.
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[28] APHA, Standard methods for the examination of water and wastewater, 21st ed., (2005) 5– 35. [29] M. Rajiv Gandhi, N. Viswanathan, S. Meenakshi, Int. J. Biol. Macromol. 47 (2010) 146– 154.
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[30] D. Saravanan, R. Hemalatha, P.N. Sudha, Synthesis and characterization of cross linked chitin/bentonite polymer blend and adsorption studies of Cu (II) and Cr (VI) on chitin, Der
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[31] S. Tripathi, G.K. Mehrotra, P.K. Dutta, Physicochemical and bioactivity of cross-linked chitosan–PVA film for food packaging applications, Int. J. Biol. Macromol. 45 (2009)
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properties of chitosan, Colloid. Polym. Sci. 276 (1998) 1159–1165. [34] H.M.F. Freundlich, Over the adsorption in solution, J Phys Chem. 57A (1906) 385–470.
Ac ce p
[35] I. Langmuir, The constitution and fundamental properties of solids and liquids, J. Am. Chem. Soc. 38 (1916) 2221–2295. [36] Y.S. Ho, Selection of optimum sorption isotherm, Carbon 42 (2004) 2115–2116. [37] A.A. Khan, R.P. Singh, Adsorption thermodynamics of carbofuran on Sn(IV) arsenosilicate in H+, Na+ and Ca2+ forms, Colloid Surf. 24 (1987) 33–42. [38] B.H. Hameed, M.I. El-Khaiary, Removal of cationic dye from aqueous solution using jackfruit peel as non-conventional low-cost adsorbent, J. Hazard. Mater. 162 (2009) 344– 350.
Page 21 of 35
[39] S. Lagergren, Zur theorie der sogenannten adsorption gelöster stoffe, K. Sven. Vetenskapsakad. Handl. 24 (1898) 1–39. [40] Y.S. Ho, Second-order kinetic model for the sorption of cadmium onto tree fern: A comparison of linear and non-linear methods, Water Res. 40 (2006) 119–125.
ip t
[41] D. Wankasi, M. Horsfall, A.I. Spiff, Retention of Pb(II) ion from aqueous solution by nipah palm (nypa fruticans wurmb) petiole biomass, J. Chil. Chem. Soc. 50 (2005) 691–
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Eng. Div. Am. Soc. Civ. Eng., 90 (1964) 79–91.
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[42] W.J. Weber, J.C. Morris, Equilibrium and capacities for adsorption on carbon, J. Sanit.
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[43] S. Meenakshi, N. Viswanathan, Identification of selective ion-exchange resin for fluoride
Ac ce p
te
d
M
sorption, J. Colloid Interface Sci. 308 (2007) 438–450.
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Figure captions Fig. 1. FT-IR Spectra of (a) chitin and (b) oil-adsorbed chitin. Fig. 2. FT-IR Spectra of (a) chitosan and (b) oil-adsorbed chitosan.
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Fig. 3. SEM images of (a) chitin (b) oil-adsorbed chitin (c) chitosan (d) oil-adsorbed chitosan.
Fig. 5. X – ray diffraction (XRD) patterns of Chitin and Chitosan.
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Fig. 4. EDAX spectra of (a) chitin (b) oil-adsorbed chitin (c) chitosan (d) oil-adsorbed chitosan.
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Fig. 6. Thermogravimetric analyses of (a) Chitin (b) Chitosan and DSC of (c) Chitin (d) Chitosan.
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Fig. 7. (a) Effect of contact time on the removal of cutting oil using chitin and chitosan (b) Effect of dosage of chitin and chitosan on the removal of cutting oil (c) Influence of pH on the
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adsorption of cutting oil using chitin and chitosan (d) Effect of cutting oil concentration using
Ac ce p
te
d
chitin.
Page 23 of 35
Table 1: Characteristics of cutting oil S. No.
Characteristics
Specification
1.
Appearance at 30 0C
Clear & bright
2.
Density @ 29.5 oC
3.
Viscosity index
99
4.
Water content, % wt
Nil
Ac ce p
te
d
M
an
us
cr
ip t
0.8550
Page 24 of 35
Table 2: Freundlich and Langmuir isotherms constants for cutting oil removal using chitin
Langmuir
Temperature 303 K
313 K
323 K
0.685
0.621
0.639
n
1.461
1.061
1.566
kF (mg/g) (L/mg)1/n
0.028
0.006
0.005
r
0.998
0.999
0.998
sd
0.026
χ2
0.745
cr
ip t
1/n
0.0253
0.030
0.667
0.211
us
Freundlich
Parameters
Qo(mg/g)
456.62
448.43
671.14
b (L/g)
0.0003
0.0004
0.0005
0.994
0.995
0.996
0.994
0.988
0.983
0.073
0.019
0.317
0.770
0.864
0.997
an
Isotherms
RL r
M
sd
Ac ce p
te
d
χ2
Page 25 of 35
Table 3: Thermodynamic parameter of chitin on the removal of cutting oil
Chitin
303 K
-18.03
313 K
-18.65
323 K
-20.12
∆H˚ (kJ mol-1)
ip t
∆G˚ (kJ mol-1)
Parameters
cr
Thermodynamic
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13.42
0.10
Ac ce p
te
d
M
an
∆S˚ (kJ K-1 mol-1)
Page 26 of 35
ip t
313 K
303 K
Pseudosecond-order
2830 mg/L
5560 mg/L
7620 mg/L
1140 mg/L
28300 mg/L
5560 mg/L
7620 mg/L
1140 mg/L
2830 mg/L
5560 mg/L
7620 mg/L
kad (min-1)
0.064
0.079
0.117
0.096
0.090
0.108
0.097
0.111
0.210
0.121
0.196
0.290
r
0.986
0.920
0.940
0.886
0.969
0.923
0.875
0.919
0.957
0.996
0.924
0.978
sd
0.062
0.192
0.244
0.287
0.132
0.257
0.308
0.272
0.366
0.070
0.465
0.352
qe (mg/g)
108.4
282.49
613.50
884.96
157.98
286.53
584.80
847.96
147.06
257.07
531.91
1074.89
k (g/mg min)
0.009
0.0062
0.0006
0.0002
0.0002
0.0006
0.0004
0.0003
0.0003
0.0005
0.0004
5.0E-5
h (mg/g min)
103.2
497.51
225.22
157.73
5.42
49.19
128.87
185.19
4.50
27.60
109.17
58.04
r
0.999
0.999
0.999
0.989
0.996
0.997
0.994
0.999
0.997
0.996
0.995
0.991
sd kp (min-1) Particle diffusion
r
Intra-particle diffusion
M an
0.002
6.1E-4
9.7E-4
0.002
0.007
0.004
0.003
7.3E-4
0.007
0.004
0.002
0.002
0.064
0.079
0.117
0.096
0.090
0.108
0.097
0.111
0.091
0.053
0.085
0.126
0.986
0.920
0.940
0.886
0.969
0.923
0.875
0.919
0.958
0.995
0.924
0.978
0.143
0.416
0.561
0.665
0.305
0.592
0.709
0.627
0.366
0.069
0.465
0.352
Ac
sd
us
1140 mg/L
ed
Pseudo-firstorder
323 K
Parameters
ce pt
Kinetic models
cr
Table 4: Kinetic models of oil sorption on chitin
ki (mg/g min0.5)
2.807
3.749
32.586
64.692
16.037
24.798
38.420
69.022
15.085
27.041
39.605
124.19
r
0.991
0.998
0.996
0.696
0.998
0.998
0.975
0.962
0.997
0.997
0.995
0.982
sd
0.578
0.351
0.996
26.384
1.452
2.396
13.172
29.568
1.643
3.353
6.276
36.081
Page 27 of 35
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ed
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Figure(s)
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Figure(s)
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ed
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Figure(s)
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ed
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Figure(s)
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ed
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Figure(s)
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ed
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Figure(s)
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Ac
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Figure(s)
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HIGHLIGHTS Removal of oil using raw chitin has not been reported elsewhere
•
The percentage of oil removal was found to be higher at acidic pH
•
Hydrophobicity plays an important role for cutting fluid removal
•
It is an economical and efficient material for oil removal
Ac ce p
te
d
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an
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•
28 Page 35 of 35
S0141-8130(14)00443-7 http://dx.doi.org/doi:10.1016/j.ijbiomac.2014.07.002 BIOMAC 4461
To appear in:
International Journal of Biological Macromolecules
Received date: Revised date: Accepted date:
12-5-2014 16-6-2014 3-7-2014
Please cite this article as: S.S.D. Elanchezhiyan, N. Sivasurian, S. Meenakshi, Recovery of oil from oil-in-water emulsion using biopolymers by adsorptive method, International Journal of Biological Macromolecules (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.07.002 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Recovery of oil from oil-in-water emulsion using biopolymers by adsorptive method S. SD. Elanchezhiyan, N. Sivasurian, S. Meenakshi*
Gandhigram- 624 302, Tamil Nadu, India
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Department of Chemistry, The Gandhigram Rural Institute-Deemed University,
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*Corresponding author. Tel.: +91-451-2452371; Fax: +91-451-2454466.
Ac ce p
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E-mail address: [email protected]
Abstract
Page 1 of 35
In the present study, it is aimed to identify, a low cost sorbent for the recovery of oil from oil-in-water emulsion using biopolymers such as chitin and chitosan. Chitin has the greater adsorption capacity than chitosan due to its hydrophobic nature. The characterizations of chitin and chitosan were done using FTIR, SEM, EDAX, XRD, TGA and DSC techniques. Under
ip t
batch equilibrium mode, a systematic study was performed to optimize the various equilibrium parameters viz., contact time, pH, dosage, initial concentration of oil, and temperature. The
cr
adsorption process reached equilibrium at 40 min of contact time and the percentage removal of
us
oil was found to be higher (90 %) in the acidic medium. The Freundlich and Langmuir models were applied to describe the equilibrium isotherms and the isotherm constants were calculated.
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Thermodynamic parameters such as ΔGº, ΔHº and ΔSº were calculated to find out the nature of the sorption mechanism. The kinetic studies were investigated with reaction-based and diffusion-
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based models. The suitable mechanism for the removal of oil has been established.
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Keywords: Oil removal; Chitin; Chitosan; Adsorption; Isotherms.
1. Introduction
Page 2 of 35
In the modern society, the release of wastewater containing oil into the environment increases due to urbanization and industrial development. Oils that are found in contaminated water can be fats, lubricants, cutting liquids, heavy hydrocarbons such as tars, grease, crude oils, diesel oils, and light hydrocarbons viz., kerosene, jet fuel and gasoline. Foremost industrial
ip t
sources of oily wastewater include petroleum refineries, metal manufacturing and machining and food processors. These industries have augmented the threats of oil pollution to the environment
cr
and their discharges to the natural environment, create a major ecological problem throughout
oil-in-water emulsions among their basic contaminants.
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the world [1]. Unlike free or floating oil spilled at sea, most of the industrial wastewaters contain
an
Cutting fluid is used in the production process elements of machining operation, including turning, drilling, grinding, and milling and provides better surface finishes. The type of
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cutting fluid used for machining operations is oil based and water-based. The oil-based fluid
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consists of natural oil or synthetic oil. The water-based fluids are soluble oil, which may be
te
synthetic and semisynthetic and are mixed with water to form oil-in-water emulsion. A Material used as a lubrication matter in soluble oil, synthetic and semisynthetic cutting fluid is mineral oil,
Ac ce p
organic compounds of poly-alpha-olefins and the mixture of mineral oil and organic compounds, respectively [2]. Typical additives in the water-based cutting fluid is emulsifiers, surfactants, corrosion inhibitors and biocides. After a long use, cutting fluid loses its lubricating property and generates a toxic waste. It contains heavy metals, biocides, microorganisms and harmful decomposition products.
Oil emulsions are deleterious to the environment as they impede penetration of sunlight and absorption of oxygen from the air by the water bodies contaminated by oil, and in many cases are toxic to the aquatic life. Because of these reasons, the Ministry of Environment and Forests, Government of India has prescribed the discharge wastewater quality stating that the oil
Page 3 of 35
concentration should not exceed 5 mg/L [3]. The concentration of oil in effluents from different industrial sources is found to be as high as 40,000 mg/L [4]. Emulsified oil wastewater can lead to severe problems in different treatment stages. Therefore, it is essential to remove oil from wastewater. Numerous methods have been proposed to remove residual oil from wastewater,
ip t
such as adsorption [5-7], flocculation [8], electro-coagulation [9] and electro-flotation [10, 11]. It is difficult to use biological method to treat the cutting fluid due to its toxicity. Conventional
cr
treatment methods of oil-in-water emulsions are skimming, gravity setting, emulsion breaking
us
[12], chemical de-emulsification [13], the combination of destabilization and flotation [14] and membrane [15]. Adsorption is a far and wide accepted technology for both organic and inorganic
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contaminants such as cutting fluid [2], dyes [16], fluoride [17], nitrate [18], phosphate [19], perchlorate [20] etc. It is a promising technology to remove oil from oil-in-water emulsion using
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adsorbents such as peat [21], mixture of Ca and Mg oxides [22] activated carbon, etc. Natural
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materials and natural polymers such as chitin and chitosan, certain waste products such as fly
many countries.
te
ash, oxides and sludges are considered as low cost adsorbents due to their local availability in
Ac ce p
Chitin (β-(1 → 4)-linked 2-acetamido-2-deoxy-D-glucan) is the main component in the cuticles of crustaceans, insects, mollusks and in the cell walls of fungi. It is the second most abundant polysaccharide found on earth next to cellulose [23]. The exoskeletons of shrimps have long since attracted attention as a source of raw material for chitin production as the dry arthropod exoskeletons contained about 20 % to 50 % chitin (natural chelating polymers). The deacetylated form of chitin is chitosan. The flakes of chitin and chitosan could be considered as an alternative carrier material for immobilizing microorganisms for bioremediation purposes. Chitin is highly hydrophobic and is insoluble in water and most organic solvents [24]. At neutral and alkaline pH values, chitosan is insoluble, but the salt formation is observed with organic and
Page 4 of 35
inorganic acids [25, 26]. Chitin and chitosan are cost effective, non-toxic, non-polluting and sustainable since fishery wastes are freely and abundantly available. Hence, in the present study, sequences of adsorption experiments were conducted to evaluate the possibility of the use of chitin and chitosan powder as adsorbents for oil removal
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from oil-in-water emulsion. The isotherm and kinetic models were used to describe the experimental data. This information will be useful for further application in the treatment of oily
cr
waste effluents.
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2. Materials and methods 2.1. Materials
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Chitin and chitosan (85% deacetylated) were supplied from Pelican Biotech and Chemicals Labs, Kerala (India). The cutting oil was commercially obtained and the
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characteristics of oil are given in Table 1. Base oil used is for making cutting oil which consists
d
of 66.9 % saturated compounds, 27.5 % aromatic compounds and 5.5 % sulphur compounds.
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The following analytical grade chemicals were used in the experimental work: n-hexane (Merck, Mumbai) HCl and NaOH (Central Drug House, New Delhi). Double distilled water was used
Ac ce p
throughout the study.
Table 1
2.2. pH zero point charge measurements The pH at the potential of zero point charge (pHzpc) of chitin and chitosan was measured using pH drift method [27]. The pH of a solution of 0.01M NaCl was adjusted between 2 and 12 by adding either HCl or NaOH. Sorbent (0.15 g) was added to 50 mL of the solution. After the pH had stabilized (typically after 24 h), the final pH was recorded. The graphs of final versus initial pH were used to determine the points at which initial pH and final pH values were equal. This was taken as the pHzpc of the sorbent used.
Page 5 of 35
2.3. Measurement of Hydrophobic property Hydrophobic property of chitin and chitosan was investigated by hydrophobic index. For hydrophobic index, 1.0 g of adsorbent was soaked in cutting oil or deionized water until equilibrium had been reached. The adsorption capacity was calculated as {(weight of the
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adsorbed adsorbate/weight of the adsorbent) × 100}. Hydrophobic index was then computed as
cr
the adsorption capacity of cutting fluid/adsorption capacity of deionized water [2]. 2.4. Characterization
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Fourier Transform Infra-red (FTIR) spectra of the samples as solid by diluting in KBr pellets were recorded with JASCO-460 plus model within the wavelength range of 400 – 4000
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cm−1. The results of FTIR spectrometer were used to confirm the functional groups present in the
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sorbent before and after sorption of oil. The surface morphology of chitin and chitosan before and after treatment with oil was studied by scanning electron microscope (SEM) with
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VEGA3TESCAN model and the elemental analysis was made by energy dispersive analysis of
te
X-ray (EDAX) spectroscopy with Bruker Nano Gmbh, Germany. The crystalline natures of biopolymers were analyzed by X-ray powder diffraction (XRD, X’per PRO model – PANalytical
Ac ce p
make). Thermal stability of the sorbents were determined using a Thermo gravimetric analyzer (TGA, Model 2960, Universal V2.4F TA instruments, USA) and Differential Scanning Calorimetry (DSC, Model 2920, Universal V2. 4F TA Instruments, USA). The pH measurements were done using expandable ion analyzer EA940 with the pH electrode. 2.5. Sorption experiments
Sorption studies of oil from oil emulsion have been carried out with the sorbents to assess the suitability of its application towards oil removal. Studies were performed to assess how sorption rates depended on the concentrations of sorbate in solution and how rates were influenced by various parameters like contact time, pH and temperature. Various concentrations
Page 6 of 35
of oil-in-water emulsion were obtained by diluting the prepared stock solution and used for oil sorption experiments. The batch adsorption experiments were carried out with the required quantity of the sorbent along with oil-in-water emulsion. The contents were shaken thoroughly using a thermostated shaker rotating at a speed of 200 rpm. The isotherm and thermodynamic
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parameters of sorption was established by conducting the experiments at different initial oil concentrations viz., 1140, 2830, 5560 and 7620 mg/L at 303, 313 and 323 K in a thermally
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controlled mechanical shaker. Then the solution was filtered at the appropriate time and the
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residual oil concentration was measured. Duplicate experiments were performed by the batch equilibrium method.
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The percentage of oil removal can be calculated according to the following equation:
(1)
2.6. Analysis
d
where, Ci is initial oil concentration (mg/L), Ce is equilibrium oil concentration (mg/L)
te
The concentration of oil was measured using oil and grease method recommended by
Ac ce p
APHA, AWWA, WPCF (2005) Standard method of examination of water and wastewater, with n-Hexane being used as the oil-extraction solvent [28]. The oil content in the suspension was determined for each sample of oil-in-water emulsion, both before and after the experiment. All the experiments were carried out twice and the average values of the results have been reported. 3. Results and discussion
3.1. Characterisation of the sorbents 3.1.1. FTIR analysis Fig. 1 depicts the respective FTIR spectra of chitin before and after oil sorption. In Fig. 1a, the raw chitin before sorption of oil showed the -NH group in the ranges 3442 and 1657 cm-1. The bands at 2926, 1421 and 1378 cm-1 are attributed to the vibration of -CH group of chitin.
Page 7 of 35
The band at 1629 cm-1 is due to an amide type of CO group of chitin. The interaction between oil and chitin was confirmed in the spectrum taken for oil sorbed chitin (Fig. 1b). After oil adsorption, the peaks for CH groups were shifted to 2923 and 2857 cm-1 for sharp intense peak corresponds to respective CH strong and medium peaks. The band around 3442 cm-1 has also
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been shifted to 3450 cm-1 which indicates the oil adsorption onto the chitin surface.
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Fig. 2 shows the FT-IR spectrum of chitosan before and after oil sorption. In Fig. 2a, the
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raw chitosan before sorption of oil showed the –OH and –NH2 group in the ranges 3005 and 3989 cm-1. The peaks at 2928 and 1368 cm-1 are ascribed to the -CH stretching and bending
an
modes of vibration. After oil adsorption the peaks for CH groups are shifted to 2922 and 2859
M
cm-1 for sharp intense peak corresponds to respective CH strong and medium peaks (Fig. 2b). Figure 2
d
3.1.2. Morphology and elemental analysis
te
SEM images of respective raw chitin, oil-adsorbed chitin, chitosan and oil-adsorbed chitosan are shown in Fig. 3 a-d. The change in the SEM micrographs of the sorbent indicates
Ac ce p
that there are threads like structure and surface is not smooth. But after oil-adsorption, the surface was fully occupied by oil, which has formed a layer over the surface. This covered layer Figure 3 like structure may be due to oil-adsorption onto the chitin and chitosan surfaces (Fig. 3 b & d). This is further supported by EDAX methods. The EDAX spectra of oil sorbed chitin and chitosan showed higher percentage of carbon when compared to raw chitin and chitosan as shown in Fig. 4. Also, as shown in Fig. 4b and d, the presence of peaks showing sulfur after oil adsorption by chitin and chitosan clearly proves that oil (sulfur compounds present in base oil) is adsorbed by both the sorbents chitin and chitosan. Figure 4
Page 8 of 35
3.1.3. XRD analysis XRD study was applied to detect the crystallinity of chitin and chitosan which are shown in Fig. 5 Chitin has 2θ diffraction peaks at 19.20º and 26.21º together with a few other peaks with much weaker intensity. Peaks corresponding to 20.3º in XRD of chitosan were less resolved and
ip t
shifted to higher 2θ [29]. It is observed that the sharpness of the band is superior in chitin than in chitosan which shows the higher crystalline nature of chitin than chitosan [30].
us
3.1.4. TGA and DSC analysis
cr
Figure 5
Thermogravimetric curves of chitin and chitosan are shown in Fig. 6 a and b. There are
an
two degradation steps observed for chitin and chitosan. The first step noticed at temperatures lower than 40 °C – 90 °C for chitin and 40 °C – 150 °C for chitosan indicating the loss of water
M
[31]. The second step takes place in the range of 200 °C – 390 °C for chitin and 200 °C – 330 °C
d
for chitosan. This could be attributed to the decomposition of pyranose ring structure of chitin
te
and chitosan [32]. As the decomposition temperature is higher in chitin than in chitosan, chitin exists as a stable structure towards thermal decomposition when compared to chitosan.
Ac ce p
Fig. 6 c and d shows the DSC thermograms of chitin and chitosan within the temperature range of 50 °C – 500 °C at a heating rate of 10 °Cmin-1. The DSC thermograms of chitin and chitosan were characterized by two thermal events; the first endothermic and the second exothermic. The endothermic event appeared at 46.63 °C for chitin and 68.91 °C for chitosan which are attributed to the evaporation of water. A wide exothermic peak appeared at 407.48 °C for chitin and a sharp exothermic peak comes out for chitosan at 308.88 °C are almost nearer to the temperature reported in the literature [31]. These exothermic peaks were owing to the thermal decomposition of chitin and chitosan. Figure 6 3.2. Effect of contact time
Page 9 of 35
For determining oil removal percentage using chitin and chitosan, the contact time is varied in the range of 10-60 min. About 200 mg of the sorbent was added in 25 mL of 1140 mg/L initial concentration of oil. Fig. 7a shows the effect of contact time on the cutting oil uptake on chitin and chitosan at pH 3. The plots show that the adsorption of cutting oil increases with time and
ip t
then reaches a value beyond which no more oil was further removed from the solution leading to saturation. The adsorption of oil reached saturation at 40 min. The maximum removal of cutting
cr
oil was found to be 81.6 % using chitin and 45.1 % using chitosan as adsorbents. At the
us
equilibrium point, the amount of oil desorbed from the chitin was in a state of dynamic equilibrium with the amount of oil being adsorbed on both the sorbents. The results revealed that
an
the oil adsorption was fast at the initial stages of the contact period, and thereafter it became slower near the equilibrium. This phenomenon was due to the fact that a large number of vacant
M
surface sites were available for adsorption during the initial stage, and after a lapse of time, the
d
remaining vacant surface sites were difficult to be occupied due to repulsive forces between the
the further experiments.
te
solute molecules on the solid and bulk phases. Hence, 40 min was fixed as the contact time for
Ac ce p
3.3. Effect of adsorbent dosage
The percentage of oil removal was determined by varying the dose of chitin and chitosan in the range from 50, 100, 150, 200 and 250 mg to find the maximum oil removal percentage by fixing the contact time of 40 min, at pH 3. As shown in Fig. 7b, it was observed that chitin needed an adsorbent dosage of 200 mg to achieve the highest percentage of 81.6 % removal of oil, while in case of chitosan the maximum percentage of oil removal was found to be 45 % at an adsorbent dosage of 200mg. It was noticed that when the weight dosage of sorbents increased, the percentage of cutting oil removal also improved due to the availability of more surface sites. 3.4. Effect of pH
Page 10 of 35
pH plays a vital role in the sorption of oil. Fig. 7c shows the effect of pH on the percentage of oil removal using chitin and chitosan. Before adsorption, the oil in the form of emulsion has to be made available for the sorption and this emulsion breaking is usually brought about by changing the pH value or inorganic coagulants [33]. Therefore, pH adjustments in the
ip t
range of 3, 5, 7, 9 and 11 were also done to study the effect of adsorption of oil onto chitin and chitosan. In strong acidic condition, chitin and chitosan provokes a physico-chemical effect,
cr
apparently serving to demulsify and enhances the adsorption of oil. Thus acidic medium acts as a
us
catalyst to catalyze the reaction between the oil molecules and the sorbent. As pH increases, the percentage of oil removal decreased. This may be due to the destabilization of sorbents and also
an
the low degree of de-emulsification at a basic medium.
Hence, throughout the study, the pH of the medium was maintained at pH 3. In basic
M
condition, the adsorption of cutting oil on chitin and chitosan decreased due to deprotonation of
d
adsorbents and electrostatic repulsive interactions.
te
Oil is mainly consisting of a mixture of hydrocarbons and hence the driving force between the oil and sorbents sorption may be due to the hydrogen bonding between them. pHZPC
Ac ce p
of chitin was found to be 6.8. At pH lower than pHZPC, the surface of chitin is positively charged and the adsorption of oil is favoured resulting in the highest percentage of oil removal in addition to the availability of oil due to de-emulsification. At pH higher than pHZPC, the surface of chitin is negatively charged which limits the chances for hydrogen bonding. Further, the degree of de-emulsification is less pronounced at this higher pH, which restricts the release of oil for sorption. The same reason is applicable to the oil removal using chitosan which has the pHZPC of 5.6. Out of the sorbents chitin and chitosan used for the removal of oil from oil-in-water emulsion, the oil removal percentage at 40 min of
Page 11 of 35
contact time, using 200 mg chitin was found to be 81.6 % at pH 3 which was higher than that observed for chitosan. Hence, further studies were limited to chitin alone. 3.5. Effect of initial oil concentration It is obvious that oil adsorption is significantly influenced by the initial concentration of
ip t
the oil in aqueous solution at 40 min of contact time using 200 mg chitin for various initial concentrations viz., 1140, 2830, 5560 and 7620 mg/L as the percentage of oil removal decreases
cr
which is shown in Fig. 7d. The decreasing trend of percentage removal of oil can be explained
above a certain oil concentration.
an
Figure 7
us
by the fact that chitin had a limited number of active sites, which would have become saturated
M
3.6. Sorption isotherms
To quantify the sorption capacity of the sorbents studied for the oil removal, the most
d
commonly used isotherms, namely Freundlich and Langmuir isotherms have been adopted.
te
Freundlich [34] isotherm is an empirical equation employed to describe heterogeneous systems. The well known logarithmic form of the Freundlich isotherm is given by the following equation:
Ac ce p
log qe = log kF + (1/n) log Ce
(2)
Where Ce is the equilibrium concentration of the adsorbate (mg/L) and qe is the amount of adsorbate adsorbed per unit weight of adsorbent, kF and n are Freundlich constants with n giving an indication of how favorable the adsorption process. Table 2 presents the values of Freundlich isotherm constants for chitin that was calculated from the linear plot of log qe vs. log Ce which is shown in Fig. S1. The favorable condition for adsorption is confirmed as the values of 1/n prevail between 0 and 1. The kF values of chitin were found to decrease with the increase in temperature. This
Page 12 of 35
confirms the exothermic nature of sorption. The higher r values obtained for all the sorbents demonstrate the applicability of Freundlich isotherm for oil removal. The Langmuir [35] equation is given as follows, (Ce/qe) = (1/Qob) + (Ce/Qo)
(3)
ip t
Where Ce is the equilibrium concentration (mg/L) and qe is the amount adsorbed at
cr
equilibrium (mg/g) and Qo and b is Langmuir constants related to the energy of adsorption (L/mg) and adsorption capacity (mg/g), respectively. The Langmuir isotherm constant that
us
relates to the energy of adsorption was calculated from the respective slope and intercept of the linear plot of Ce/qe vs. Ce and the values are presented in Table 2. The values of Qo were found to
an
decrease with the increase in temperature, which further confirms the exothermic nature and
M
temperature dependence of the sorption process.
In order to find out the feasibility of the isotherm, the essential characteristics of the
d
Langmuir isotherm can be expressed in terms of the dimensionless constant separation factor or
te
equilibrium parameter.
1 1 + bC
(4) o
Ac ce p
RL =
where b is the Langmuir isotherm constant and Co is the initial concentration of oil (mg/L). The RL values lying between 0 and 1 indicated that the conditions were favorable for adsorption. The higher r values of Freundlich over Langmuir, suggested that the Freundlich isotherm was more suitable than the Langmuir isotherm for oil removal using chitin as adsorbent. This fact was further supported by the low chi square values of Freundlich isotherm as shown in Table 2. In order to identify the suitable isotherm model for the sorption of oil on the chitin, this analysis has been carried out. The equivalent mathematical statement is
χ2 = ∑
(q e − q e,m ) 2 qe,m
(5)
Page 13 of 35
where qe,m is equilibrium capacity obtained by calculating from the model (mg/g) and qe is experimental data of the equilibrium capacity (mg/g). If data from the model are similar to the experimental data, χ2 will be a small number, where as if they differ, χ2 will be higher number. Therefore, it is also necessary to analyze the data set using the non-linear chi-square test to
ip t
confirm the best fit isotherm for the sorption system [36]. The results of chi-square analysis are
cr
presented in Table 2. The lower χ2 values of Freundlich isotherm indicate the best fitting model for the sorption of oil onto chitin.
3.7. Thermodynamic treatment of the sorption process
us
Table 2
an
The thermodynamic parameters associated with the adsorption, viz., standard free energy
determined using the following equations.
ΔS o Δ H o − R RT
te
ln K o =
d
∆Go = -RT lnKo
M
change (∆Go), standard enthalpy change (∆Ho) and standard entropy change (∆So), were
(6) (7)
Ac ce p
where ∆Go is the free energy of sorption (kJ/mol), ∆Ho is the standard enthalpy change (kJ/mol) and ∆So is standard entropy change (kJ/mol.K) T is the temperature in Kelvin and R is the universal gas constant (8.314 J mol-1K-1). The sorption distribution coefficient Ko was determined from the slope of the plot ln (qe/Ce) against Ce at different temperature and extrapolating to zero Ce according to Khan and Singh method [37]. ∆Ho and ∆So were calculated from the slope and intercept of van’t Hoff plot of ln Ko against 1/T. The values of thermodynamic parameters for chitin were calculated and are shown in Table 3. The spontaneous nature of the oil sorption by chitin is confirmed by the negative values of ΔGº. The positive value of ΔSº denotes that the freedom of oil is not much restricted in the
Page 14 of 35
sorbent, chitin. The negative value of ΔHº for oil removal confirms the exothermic nature [38] of the sorption process by chitin. Table 3
3.8. Sorption dynamics
ip t
In this study, the two main types of sorption kinetic models, namely reaction-based and diffusion-based models, were adopted to fit the experimental data. The initial sorbate
cr
concentration and the reaction temperature are considered for examining the influence of
us
sorption capacity on the rate of the reaction. 3.8.1. Reaction-based models
an
To investigate the sorption mechanism of oil sorption on chitin, pseudo-first-order [39] and pseudo-second-order [40] kinetic models have been used in different experimental
M
conditions. A simple pseudo-first-order kinetic model is represented as, (8)
d
log (qe - qt) = log (qe) − (kad t) / 2.303
te
Where qe and qt are the adsorption capacity at equilibrium and at time t, respectively (mg/g), kad is the rate constant of pseudo-first order adsorption (1/min). The slope of the straight-
Ac ce p
line plot of log (qe-qt) against t for different experimental conditions will give the value of the rate constant (kad). Linear plots of log (qe-qt) against t gives a straight line that indicates the applicability of Lagergren equation. The values of kad and the correlation coefficient (r) computed from these plots for oil sorption on chitin is given in Table 4. The fitness of the pseudo second order model was also analyzed. The most popular linear form is as follows: (t/qt) = (1/ h) + (t/qe)
(9)
The fitness of the data and the values of qe, k, and h were obtained from the plots of t/qt vs t for oil sorption at different temperatures viz., 303, 313 and 323 K on chitin, which are
Page 15 of 35
presented in Table 4. The plot of pseudo-second-order model of oil sorption onto chitin at 303 K is shown in Fig. S2. The decreasing qe values of the sorption of oil on chitin with the increase in temperature suggest the temperature dependence of the sorption process which in turn confirms the physisorption process.
ip t
The plot of t/qt vs t gives a straight line with high correlation coefficient r values which is highthan that observed for pseudo-first-order model. This indicates the applicability of pseudo-
cr
second-order than pseudo-first-order model for the sorption of oil on chitin.
us
3.8.2. Diffusion-based models
For a solid-liquid sorption process, the solute transfer is usually characterized either by
an
particle diffusion [41] or by intraparticle diffusion [42, 43] control.
A simple equation for the particle diffusion controlled sorption process is as follows,
M
ln (1- Ct/Ce) = kp t
(10)
d
Where kp is the particle diffusion coefficient (mg/ g min). The value of the particle diffusion
te
coefficient is obtained by the slope of ln (1- Ct/Ce) against t. The intra-particle diffusion model used here to refer to the theory proposed by Weber and
Ac ce p
Morris. The intra-particle diffusion equation, qt = ki t½
(11)
Where ki is the intra-particle diffusion coefficient (mg/g min0.5). The slope of the plot of qt against t1/2 will give the value of the intra-particle diffusion coefficient which is depicted in Fig. S3.
The kp, ki and r values of particle and intraparticle diffusion models are illustrated in Table 4. The higher r values obtained for intraparticle diffusion model indicates that the oil sorption on chitin prefers intraparticle diffusion model rather than particle diffusion model. Table 4
Page 16 of 35
3.9. Mechanism of cutting oil removal using chitin via adsorption process The oil removal consists of two steps. 1. De-emulsification of oil which makes oil free. 2. Sorption of oil by chitin.
ip t
De-emulsification could be brought about by maintaining at pH 3. Next step is sorption of oil by the sorbents. The interaction of oil and the sorbents is mainly due to the hydrogen
cr
bonding. The Oil used for study is mainly consisting of a mixture of hydrocarbons which is
us
hydrophobic in nature and could be attracted by the sorbent only due to van der Waals forces. Further, chitin exhibits higher hydrophobic nature as indicated by its value, when compared to
an
chitosan which makes it more selective for hydrocarbon. Nevertheless, the mechanism of cutting oil adsorption on chitin powder involves two steps: (1) diffusion of cutting oil to the boundary
M
surface of adsorbent; (2) diffusion through a liquid film at the surface to the pores of adsorbent.
4. Conclusions
te
onto chitin.
d
FT-IR spectra and SEM micrographs are used to prove the adsorption performance of cutting oil
Ac ce p
Biosorbents such as chitin and chitosan were used for the sorption of oil from oil-in-water emulsion with a minimum contact time of 40 min. The oil uptake by both chitin and chitosan was influenced by the pH of the medium. The sorption of the oil on the chitin and chitosan was higher at acidic pH and gradually decreases at basic pH values. The optimum pH for the removal of oil is pH 3 where de-emulsification occurs and also the surface acquires a positive charge. The lower χ2 values of Freundlich isotherm indicate the best fitting model for the sorption of oil onto chitin. This predicts the fitness of Freundlich isotherm than Langmuir isotherm for oil sorption by chitin, which confirms that the mechanism of oil sorption by chitin was mainly governed by physical forces. The negative standard free energy change and positive standard entropy change
Page 17 of 35
values show the spontaneity of the sorption process. The negative standard enthalpy change value for oil sorption using chitin confirms the exothermic nature of the process. The kinetics of sorption of oil on chitin followed the pseudo-second-order and intra-particle diffusion kinetic models.
ip t
Acknowledgements
The First author is thankful to UGC-BSR for the Fellowship in the category of Research
cr
Fellowship in Science for Meritorious Students.
V. Singh, R.J. Kendall, K. Hake, S. Ramkumar, Crude oil sorption by raw cotton, Ind. Eng. Chem. Res. 52 (2013) 6277–6281.
[2]
an
[1]
us
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ip t
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ip t
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ip t
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properties of chitosan, Colloid. Polym. Sci. 276 (1998) 1159–1165. [34] H.M.F. Freundlich, Over the adsorption in solution, J Phys Chem. 57A (1906) 385–470.
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[39] S. Lagergren, Zur theorie der sogenannten adsorption gelöster stoffe, K. Sven. Vetenskapsakad. Handl. 24 (1898) 1–39. [40] Y.S. Ho, Second-order kinetic model for the sorption of cadmium onto tree fern: A comparison of linear and non-linear methods, Water Res. 40 (2006) 119–125.
ip t
[41] D. Wankasi, M. Horsfall, A.I. Spiff, Retention of Pb(II) ion from aqueous solution by nipah palm (nypa fruticans wurmb) petiole biomass, J. Chil. Chem. Soc. 50 (2005) 691–
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Page 22 of 35
Figure captions Fig. 1. FT-IR Spectra of (a) chitin and (b) oil-adsorbed chitin. Fig. 2. FT-IR Spectra of (a) chitosan and (b) oil-adsorbed chitosan.
ip t
Fig. 3. SEM images of (a) chitin (b) oil-adsorbed chitin (c) chitosan (d) oil-adsorbed chitosan.
Fig. 5. X – ray diffraction (XRD) patterns of Chitin and Chitosan.
cr
Fig. 4. EDAX spectra of (a) chitin (b) oil-adsorbed chitin (c) chitosan (d) oil-adsorbed chitosan.
us
Fig. 6. Thermogravimetric analyses of (a) Chitin (b) Chitosan and DSC of (c) Chitin (d) Chitosan.
an
Fig. 7. (a) Effect of contact time on the removal of cutting oil using chitin and chitosan (b) Effect of dosage of chitin and chitosan on the removal of cutting oil (c) Influence of pH on the
M
adsorption of cutting oil using chitin and chitosan (d) Effect of cutting oil concentration using
Ac ce p
te
d
chitin.
Page 23 of 35
Table 1: Characteristics of cutting oil S. No.
Characteristics
Specification
1.
Appearance at 30 0C
Clear & bright
2.
Density @ 29.5 oC
3.
Viscosity index
99
4.
Water content, % wt
Nil
Ac ce p
te
d
M
an
us
cr
ip t
0.8550
Page 24 of 35
Table 2: Freundlich and Langmuir isotherms constants for cutting oil removal using chitin
Langmuir
Temperature 303 K
313 K
323 K
0.685
0.621
0.639
n
1.461
1.061
1.566
kF (mg/g) (L/mg)1/n
0.028
0.006
0.005
r
0.998
0.999
0.998
sd
0.026
χ2
0.745
cr
ip t
1/n
0.0253
0.030
0.667
0.211
us
Freundlich
Parameters
Qo(mg/g)
456.62
448.43
671.14
b (L/g)
0.0003
0.0004
0.0005
0.994
0.995
0.996
0.994
0.988
0.983
0.073
0.019
0.317
0.770
0.864
0.997
an
Isotherms
RL r
M
sd
Ac ce p
te
d
χ2
Page 25 of 35
Table 3: Thermodynamic parameter of chitin on the removal of cutting oil
Chitin
303 K
-18.03
313 K
-18.65
323 K
-20.12
∆H˚ (kJ mol-1)
ip t
∆G˚ (kJ mol-1)
Parameters
cr
Thermodynamic
us
13.42
0.10
Ac ce p
te
d
M
an
∆S˚ (kJ K-1 mol-1)
Page 26 of 35
ip t
313 K
303 K
Pseudosecond-order
2830 mg/L
5560 mg/L
7620 mg/L
1140 mg/L
28300 mg/L
5560 mg/L
7620 mg/L
1140 mg/L
2830 mg/L
5560 mg/L
7620 mg/L
kad (min-1)
0.064
0.079
0.117
0.096
0.090
0.108
0.097
0.111
0.210
0.121
0.196
0.290
r
0.986
0.920
0.940
0.886
0.969
0.923
0.875
0.919
0.957
0.996
0.924
0.978
sd
0.062
0.192
0.244
0.287
0.132
0.257
0.308
0.272
0.366
0.070
0.465
0.352
qe (mg/g)
108.4
282.49
613.50
884.96
157.98
286.53
584.80
847.96
147.06
257.07
531.91
1074.89
k (g/mg min)
0.009
0.0062
0.0006
0.0002
0.0002
0.0006
0.0004
0.0003
0.0003
0.0005
0.0004
5.0E-5
h (mg/g min)
103.2
497.51
225.22
157.73
5.42
49.19
128.87
185.19
4.50
27.60
109.17
58.04
r
0.999
0.999
0.999
0.989
0.996
0.997
0.994
0.999
0.997
0.996
0.995
0.991
sd kp (min-1) Particle diffusion
r
Intra-particle diffusion
M an
0.002
6.1E-4
9.7E-4
0.002
0.007
0.004
0.003
7.3E-4
0.007
0.004
0.002
0.002
0.064
0.079
0.117
0.096
0.090
0.108
0.097
0.111
0.091
0.053
0.085
0.126
0.986
0.920
0.940
0.886
0.969
0.923
0.875
0.919
0.958
0.995
0.924
0.978
0.143
0.416
0.561
0.665
0.305
0.592
0.709
0.627
0.366
0.069
0.465
0.352
Ac
sd
us
1140 mg/L
ed
Pseudo-firstorder
323 K
Parameters
ce pt
Kinetic models
cr
Table 4: Kinetic models of oil sorption on chitin
ki (mg/g min0.5)
2.807
3.749
32.586
64.692
16.037
24.798
38.420
69.022
15.085
27.041
39.605
124.19
r
0.991
0.998
0.996
0.696
0.998
0.998
0.975
0.962
0.997
0.997
0.995
0.982
sd
0.578
0.351
0.996
26.384
1.452
2.396
13.172
29.568
1.643
3.353
6.276
36.081
Page 27 of 35
Ac
ce
pt
ed
M
an
us
cr
i
Figure(s)
Page 28 of 35
Ac
ce
pt
ed
M
an
us
cr
i
Figure(s)
Page 29 of 35
Ac
ce
pt
ed
M
an
us
cr
i
Figure(s)
Page 30 of 35
Ac
ce
pt
ed
M
an
us
cr
i
Figure(s)
Page 31 of 35
Ac
ce
pt
ed
M
an
us
cr
i
Figure(s)
Page 32 of 35
Ac
ce
pt
ed
M
an
us
cr
i
Figure(s)
Page 33 of 35
Ac
ce
pt
ed
M
an
us
cr
i
Figure(s)
Page 34 of 35
HIGHLIGHTS Removal of oil using raw chitin has not been reported elsewhere
•
The percentage of oil removal was found to be higher at acidic pH
•
Hydrophobicity plays an important role for cutting fluid removal
•
It is an economical and efficient material for oil removal
Ac ce p
te
d
M
an
us
cr
ip t
•
28 Page 35 of 35
