Accepted Manuscript Short Communication Biodiesel production from waste cooking oil using copper doped zinc oxide nanocomposite as heterogeneous catalyst Gurunathn Baskar, Ravi Aiswarya PII: DOI: Reference:

S0960-8524(15)00023-1 http://dx.doi.org/10.1016/j.biortech.2015.01.012 BITE 14444

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Bioresource Technology

Received Date: Revised Date: Accepted Date:

21 November 2014 5 January 2015 6 January 2015

Please cite this article as: Baskar, G., Aiswarya, R., Biodiesel production from waste cooking oil using copper doped zinc oxide nanocomposite as heterogeneous catalyst, Bioresource Technology (2015), doi: http://dx.doi.org/ 10.1016/j.biortech.2015.01.012

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Biodiesel production from waste cooking oil using copper doped zinc oxide nanocomposite as heterogeneous catalyst Gurunathn Baskar*, Ravi Aiswarya Department of Biotechnology, St. Joseph’s College of Engineering, Chennai – 600 119. India. *Email id: [email protected] Abstract A novel CZO nanocomposite was synthesized and used as heterogeneous catalyst for transesterification of waste cooking oil into biodiesel using methanol as acyl acceptor. The synthesized CZO nanocomposite was characterized in FESEM with an average size of 80 nm as nanorods. The XRD patterns indicated the substitution of ZnO in the hexagonal lattice of Cu nanoparticles. The 12% (w/w) nanocatalyst concentration, 1:8 (v/v) O/M ratio, 55°C temperature and 50 min of reaction time were found as optimum for maximum biodiesel yield of 97.71% (w/w). Hence, the use of CZO nanocomposite can be used as heterogeneous catalyst for biodiesel production from waste cooking oil. Keywords: Nanocomposite; Heterogeneous catalyst; Transesterification; Biodiesel. 1. Introduction Renewable biofuels has gained more importance in the transport sector due its properties such as low emission of sulfur, carbon monoxide and hydrocarbons. Biodiesel is a fatty acid monoesters derived from renewable feedstock. Biodiesel is a clean and renewable form of energy, has emerged as substitute for conventional fuels. The high growth in industrial sector tends to increase the pollution where it is necessary to develop renewable sources which are technically feasible, economically feasible and available

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where one among renewable source is the biodiesel (Meher et al., 2004). Biodiesel has got attention due to its detrimental effects of reducing pollutants associated with the environment when compared to the conventional diesel derived from petroleum (Xin Deng et al., 2011). Biodiesel tends to be one of the sustainable fuel helps to reduce the global warming in the environment (Fjerbaek et al., 2009). Biodiesel is produced from feedstocks by transesterification process in the presence of catalyst. Wide ranges of catalysts are used for the production of biodiesel such as homogeneous catalyst, heterogeneous catalyst and enzymes as catalyst. Traditionally homogeneous catalysts are reported sensitive to free fatty acid and leads to soap formation. Enzymatic catalyst slows down the reaction rate and deactivated when alcohol is used as acyl acceptor. In addition, the production cost is also high when enzymes are used as catalyst. Hence heterogeneous catalysts are tends to overcome the problem with homogeneous and enzymes as catalyst. These heterogeneous catalysts can be used for the production of biodiesel from low-grade oil with less purification step (Lam et al., 2010; Bharathiraja et al., 2014). Heterogeneous catalyst has great advantages such as it requires mild conditions, easy to separate, reuse and regenerate, thus the production cost can be reduced to a great extent. Technology has been developed to overcome the problem with heterogeneous catalyst (Lam et al., 2010). Heterogeneous catalyst such as alkali earth oxides, hydrotalcites, alkali-doped oxides, mixed metal oxides and ion resins were reported to be used for the transesterfication process. The catalytic activity of heterogeneous catalyst was improved by doping these elements (Yu et al., 2011). Nanocomposite was reported to have good catalytic activity and recovery rate with transesterification reaction (Deng et al., 2011). The various factors influencing the production process include reaction time,

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temperature, Oil-Methanol ratio, catalyst concentration (Suganya et al., 2013). The reaction conditions and kinetics of transesterfication reaction have to be investigated to develop an efficient biodiesel production process (Sivakumar et al., 2013). Transesterification involves the displacement of alcohol from an ester where the preferred alcohol is methanol due to cheaper cost and polar nature. Understanding the reaction mechanism tend to design the reaction conditions for maximum biodiesel production. Transesterification tends be to more complex as it contains two immiscible phases such as oil and methanol. The active site of the catalyst is most important in heterogeneous catalyst. The metal oxide heterogeneous catalyst consists of positive metal ions which act as electron acceptors and negative oxygen ions which act as proton acceptors. This makes it efficient for transesterfication and provides adsorptive sites for methanol, where the (O-H) bonds readily break into methoxide anions and hydrogen cations. The methoxide anion in heterogeneous catalyst reacts with triglyceride molecules to yield methyl esters (Refaat, 2011). The present work was focused on synthesis of novel heterogeneous catalyst for transesterification process using copper doped zinc oxide (CZO) nanocomposite for efficient production of biodiesel from waste cooking oil. The produced nanocatalyst was characterized using Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD). Various process parameters were also studied and optimized along with the kinetic study. The purity of produced biodiesel was characterized using gas chromatography and compared with the standard.

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2. Materials and Methods 2.1 Materials used Chemicals used for the synthesis of nanocatalyst and production of biodiesel such as Cupric Sulphate, Zinc Sulphate, Sodium Carbonate and Methanol were purchased from Sd fine Chemicals, India and Merck, India of analytical grade and used without further purification. The waste cooking oil used for biodiesel production was obtained from commercial cooking unit in Chennai, India. The collected oil was subjected to pretreatment to remove suspended solid materials. 2.2 Synthesis of CZO nanocomposite The CZO nanocomposite was synthesized by co-precipitation method. Solution I was prepared by dissolving 14.3% (w/v) of zinc sulfate with 0.76% (w/v) of cupric sulfate in 50 ml of distilled water. Solution II was prepared by dissolving 2.64% of sodium carbonate in 50 ml of distilled water. Solution I was added in drops into solution II under continuous stirring. The temperature was maintained as constant at 60°C and the pH was around 11. The resultant bluish white precipitate was filtered and dried in hot air oven at 80°C. The dried precipitate of CZO nanocomposite was calcinated at 500°C in muffle furnace for 2 h to activate into nanocatalyst (Milenova et al., 2013). 2.3 Characterization of synthesized CZO nanocomposite The morphological structure, size, shape and elemental composition of synthesized CZO nanocomposite were analyzed using FESEM (CARL ZEISS, GERMANY) and EDS (OXFORD Instruments, United Kingdom). The phase structure of the calcinated nanocatalyst was studied using XRD (RIKAGU, JAPAN) analysis at Bragg angle 2θ ranging from 10° to 80° using Cu as anode material at radiation Kα radiation

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(λ=1.541A°). 2.4 Transesterification of waste cooking oil using CZO nanocomposite Transesterifiction of waste cooking oil was carried in batch process in a 100 ml Erlenmeyer flask equipped with external beaker and heating magnetic stirrer. The process was carried out mixing desired amount of catalyst, methanol and preheated (50°C) waste cooking oil. The reaction mixture was mixed at constant speed using magnetic stirrer. Transesterfication reaction was repeated for varied catalyst concentration (2-14% w/w), Oil/Methanol (O/M) ratio (1:3-1:9 v:v), temperature (35-60°C) and reaction time (10-70 min). After the desired duration the reaction mixture was allowed to settle, the bottom catalyst layer (solid) was removed carefully. The catalyst was dried to remove the residues and excessive methanol for regeneration and used in successive cycles. The top liquid mixture was separated into lighter phase and denser phase using separating funnel. The mixture was left undisturbed in the separating funnel for 2 h to separate lighter phase (biodiesel) and denser phase (glycerol). The biodiesel yield was calculated using eq. (1).

Yield ,% = ( VVOB ××ρρOB ××MM OB ) ×100

(1)

Where, VB is volume of the product, VO is volume of oil, ρB is density of biodiesel, ρO is density of oil, MB is molecular mass of biodiesel and MB is molecular mass of oil. The produced biodiesel was characterized by Gas Chromatography. 3. Results and Discussions 3.1 Characterization of CZO nanocomposite using Field Emission Scanning Electron Microscopy and Energy Dispersive Spectroscopy The FESEM analysis of synthesized CZO nanocomposite indicated that the nanocomposite has different size and the morphology at different position and found as 5

heterogeneous. The obtained nanocomposites were found compact and well structured. The change in morphology at different position was might be due dopant effect resulted in aggregation. Aggregations were observed with uniform small particle in low magnification of nanorods with size of 80 nm. The CZO nanocomposites were reported to form nanorod shaped aggregates when it was synthesized by wet method at low concentration (Kalantar et al., 2013). The surface was found as compact and uniform due to the presence of hydroxide ions (Yuan et al., 2014). The presence of metal oxides posses basic surface sites and large surface area to the nanocomposite and made it efficient for transesterification process with high activity. The nanocomposite was identified to be transition doped metal oxide using EDS analysis. The dopants were found to be in respective spectrum where more addition of Cu induces a dominant effect on the optical, structural, morphological properties of ZnO. The presence of the other materials did not inhibit the original catalytic activity of nanocomposite. The concentration of Cu was within limit as reported by (Drmosh et al., 2013). 3.2 Characterization of CZO nanocomposite using X-Ray Diffraction spectroscopy The crystalline nature of the CZO nanocomposite was confirmed with the singlephase structure using XRD analysis. On doping Cu on ZnO, there were changes in lattice parameters with respect to intensity where increase in concentration of Cu tends to decrease the intensity, which resulted due to the doping procedures. The use of precursors plays a vital role in crystalline structure where doping at low concentration tends to create a shift with the peak of orientation (002). At the orientation (101) the position of the peak has changed due to angular displacement and the shift over the diffraction peak towards lower and higher range. This might be due to the presence of Cu and Zn. The absence of

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the diffraction peaks of Cu phase structure in the XRD pattern indicates the Cu doped on ZnO by substitution of Zn in the hexagonal lattice, which indicates that Cu ions occupied interstitial position without change in the structure. 3.3 Transesterification of waste cooking oil using synthesized CZO nanocatalyst 3.3.1 Effect of catalyst concentration and oil to methanol ratio Transesterification reaction is strongly dependent upon the catalyst concentration. The effect of catalyst concentration was investigated with wide range from 2 to 14% with an interval of 2% (w/w). The reaction was carried out at 55°C for 60 min and 1:8 (v/v) O/M ratio. The increase in biodiesel yield was observed with increase in catalyst concentration upto 12% as shown in Table 1. The maximum biodiesel yield of 97.73% was obtained at 12% catalyst concentration. The increase in catalyst concentration tends to increase the yield as it facilitates the interaction between the catalyst and the reactants (Deng et al., 2011). The decrease in biodiesel yield was observed when catalyst concentration was increased beyond 12%. This may be due to the increase in slurry viscosity and emulsification of O/M mixture. Another important factor affecting the biodiesel yield is oil to methanol ratio. Minimum stoichiometric ratio of oil to methanol required is 1:3 (v/v) to yield fatty acid esters. Since the transesterification reaction being reversible, it requires excess methanol to shift the reaction and O/M ratio interferes the separation of glycerol due to increase in solubility. The O/M ratio was varied from 1:3 to 1:9 (v:v) ratio under constant catalyst concentration of 12% at 55°C for 60 min. The biodiesel yield was found to increase from 43% to 96% when the O/M ration was varied from 1:3 to 1:8 (v/v) (Table 1). The yield was decreased from 96% to 94% when the O/M ratio was further increased to 1:9 (v:v). This may be due to the accumulation of methanol

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and viscous nature of the reaction mixture (Meher et al., 2006). 3.3.2 Effect of reaction temperature and reaction time Transesterification reaction can occur at different temperature depending upon the type of oil and catalyst used. In order to study the effect of reaction temperature on biodiesel yield, the temperature was varied from 35 to 60°C with an interval of 5°C using constant catalyst concentration, O/M ratio and reaction time. The reaction was carried out for 60 min with 12% catalyst concentration and 1:8 O/M ratio. Table 1 indicates that the increase in temperature upto 55°C increased the biodiesel yield. This might be due to the increase in solubility of the solvent with enhanced diffusion rate. Then the biodiesel yield was decreased when the temperature was further increased from 55 to 60°C. This might be due to the vaporization of methanol which inhibits the reaction on three phase interface (Meher et al., 2006). The effect of reaction time on biodiesel yield was studied at different time ranging from 10-70 min using 1:8 (v:v) O/M ratio and 12% catalyst concentration at 55°C (Table 1). The biodiesel yield was increased with reaction time upto 50 min, the maximum 97.71% biodiesel yield was obtained at the end of 50 min. No significant increase in biodiesel yield was observed after 50 min of reaction time. The biodiesel yield was found to increase with increase in reaction time (Freedman et al., 1984). 3.4 Effect of reusability of CZO nanocatalyst One of the most important factors in designing the catalyst is its reusability. The effect of reusability was studied by carrying out the reaction under optimized conditions. The catalyst used after the first cycle was collected, dried and regenerated for next cycle. The activity of CZO nanocatalyst was found to remain stable upto five cycles. 10

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percentage decrease in yield was observed after 5 cycles. Thus the CZO nanoparticles can be effectively recollected and reused for production of biodiesel from waste cooking oil. 3.5 Production kinetics of biodiesel from waste cooking oil using CZO nanocatalyst The temperature dependency of transesterification of waste cooking oil using CZO nanocatalyst was studied using to understand the kinetics of the reaction. The production kinetics of transesterification reaction tends to follow the first order reaction (eq. 2) as the product formations (methyl esters) are studied as function of time.

d [ P] dt

= k[ P]

(2)

Where P is methyl esters in terms of yield (%), t is the reaction time (min), and of the reaction (min1). The plot of

ln(P)

versus

ln (d [ P] dt )

is rate

at different interval

of time and temperature was found to be linear where rate constant was determined from intercept and slope. The first order kinetic model tends fit with the experimental data on transesterfication of waste cooking oil by CZO nanocatalyst. The yield tends to increase with respect to reaction time and temperature, where the reaction rate increases with increase to temperature (Suganya et al., 2012). Arrhenius relationship and the activation energy were studied for the transesterfication of waste cooking oil by CZO nanocatalyst. Thus the reaction rate was dependent on the temperature and time. The activation energy was calculated from Arrhenius plot. The activation energy requirement was found to be 480.87 J/mol. 3.6 Characterization of the biodiesel by Gas Chromatography-Mass Spectroscopy The produced biodiesel from waste cooking oil was confirmed by Thin Layer Chromatography (TLC). Gas chromatography was used to determine the concentration of

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of glycerol, mono, di and tri-glycerides and absolute saturated fatty acid methyl esters (C14-18). GC-MS was carried out by Agilent 6890 gas chromatograph equipped with a straight deactivated 2 mm direct injector liner and a 15m Alltech EC-5 column (250µ I.D., 0.25µ film thickness). The oven temperature was programmed at 35°C with held for 2 min. It was then ramped at 20°C per minute to 300°C and held for 5 min. The helium carrier gas was set to 2 ml/min flow rate at constant flow mode. Mass spectrometry was carried by JEOL GC mate II bench top double-focusing magnetic sector mass spectrometer operating in electron ionization (EI) mode with TSS-20001. The peaks in chromatogram represent the presence of methyl esters where the maximum peak represent the presence of pentadecenoic acid, 13-methyl ester with the retention time at 16.83 min. The components matched with the data bank mass spectra of NIST library V11 provided by the instruments software. 4. Conclusions The biodiesel production using waste cooking oil was effectively investigated using CZO nanocomposite as heterogeneous catalyst. The CZO nanocomposite was found to be an efficient catalyst for the transesterification and found to increase the yield due to the presence of large surface area and site of exposure during the chemical reaction. The CZO nanocatalyst has showed good reusability and catalytic activity over five recycle. References 1. Bharathiraja,

B.,

Chakravarthy,

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RanjithKumar,

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Jayamuthunagai, J., Praveen Kumar, R., Palani, S., 2014. Biodiesel production using chemical and biological methods – A review of process, catalyst, acyl

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acceptor, source and process variables. Renew. Sust. Energ. Rev. 38, 368–382. 2. Deng, X., Fang, Z., Liu, Y., Yu, C.L., 2011. Production of biodiesel from Jatropha oil catalyzed by nanosized solid basic catalyst. Energy. 36, 1–8. 3. Drmosh, Q.A., Rao, S.G., Yamani, Z.H., Gondal, M.A., 2013. Crystalline nanostructed Cu doped ZnO thin films grown at room temperature by pulsed laser deposition technique and their characterization. Appl. Surf. Sci. 270, 104–108. 4. Fjerbaek, L., Christensen, K.V., Norddahl, B., 2009. A review of the current state of biodiesel production using enzymatic transesterification. Biotechnol. Bioeng. 102, 1298–1315. 5. Freedman, B., Pryde, E.H., Mounts, T.L., 1984. Variables affecting the yield of fatty acid from transesterified vegetable oils. J. Am. oil Chem. Soc. 61, 1638– 1643. 6. Kalantar, E., Kabir, K., Gharibi, F., Hatami, S., Maleki, A., 2013. Effect and Properties of Surface-Modified Copper Doped ZnO Nanoparticles (Cu:ZnO NPs) on Killing Curves of Bacterial Pathogens, J. Med. Bacteriol. 2, 20–26. 7. Lam, M.K., Lee, K.T., Mohamed, A.R., 2010. Homogeneous, heterogeneous and enzymatic catalysis for transesterification of high free fatty acid oil (waste cooking oil) to biodiesel: A review. Biotechnol. Adv. 28, 500–518. 8. Meher, L.C., Vidya Sagar, D., Naik, S.N., 2006. Technical aspects of biodiesel production by transesterification- A review. Renew. Sust. Energ. Rev. 10, 248–268. 9. Milenova, K., Stambolova, I., Blaskov, V., Eliyas, A., Vassilev, S., Shipochka, M., 2013. The effect of introducing copper dopant on the photocatalytic activity of ZnO nanoparticles. J. Chem. Technol. Metall. 48, 259–264.

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10. Refaat, A.A., 2011. Biodiesel production using solid metal oxide catalysts. 2011. Int. J. Environ. Sci. Technol. 8, 203-221. 11. Sivakumar, P., Sankaranarayanan, S., Renganathan, S., Sivakumar, P., 2013. Studies on sono-chemical biodiesel production using smoke deposited nano MgO catalyst. B. Chem. React. Eng. Catal. 8, 89–96. 12. Suganya, T., Nagendra Gandhi, N., Sahadevan, R., 2013. Production of algal biodiesel from marine microalgae Enteromorpha compressa by two-step process: Optimization and kinetic study. Bioresour. Technol.128, 392–400. 13. Suganya, T., Renganathan, S., 2012. Optimization and kinetic studies on algal oil extraction from marine macroalgae Ulva lactuca. Bioresour. Technol. 107, 310– 326. 14. Yu, X., Wen, Z., Li, H., Tu, S.T., Yan, J., 2011. Transesterification of Pistacia chinensis oil for biodiesel catalyzed by CaO–CeO2 mixed oxides, Fuel. 90, 1868– 1874. 15. Yuan, H., Xu, M., Huang, Q.Z., 2014. Effects of pH of the precursor sol on structural and optical properties of Cu-doped ZnO thin films. J. Alloy. Comp. 616, 401–407.

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Table 1. Effect of catalyst concentration, O/M ratio, reaction temperature and reaction time on biodiesel production from waste cooking oil using CZO nanocomposite as heterogeneous catalyst Catalyst concentration, %, (w/w)

Biodiesel yield, % (w/w)

O/M ratio, % (v/v)

Biodiesel yield, % (w/w)

Temperature, °C

Biodiesel yield, % (w/w)

Reaction time, min

Biodiesel yield, % (w/w)

2 4 6 8 10 12 14

36.12 57.36 87.11 93.48 95.61 97.73 93.48

1:3 1:4 1:5 1:6 1:7 1:8 1:9

43.60 43.90 56.88 72.24 84.77 96.33 93.85

35 40 45 50 55 60 -

35.78 68.81 81.19 88.07 96.33 88.07 -

10 20 30 40 50 60 70

57.80 72.94 85.32 93.58 97.71 97.71 97.71

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Highlights:  Synthesized CZO nanocomposite was found as nanorods with an average size of 80 nm.  The presence of metal oxides in nanocomposite possesses more active sites.  The maximum biodiesel yield obtained was 97.71%.  CZO nanocomposite was found to be efficient catalysts for biodiesel production.

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Biodiesel production from waste cooking oil using copper doped zinc oxide nanocomposite as heterogeneous catalyst.

A novel CZO nanocomposite was synthesized and used as heterogeneous catalyst for transesterification of waste cooking oil into biodiesel using methano...
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