Accepted Manuscript Title: Joint action of ultrasonic and Fe3+ to improve selectivity of acid hydrolysis for microcrystalline cellulose Author: Jinbao Li Dandan Qiang Meiyun Zhang Huijuan Xiu Xiangrong Zhang PII: DOI: Reference:

S0144-8617(15)00350-1 http://dx.doi.org/doi:10.1016/j.carbpol.2015.04.034 CARP 9865

To appear in: Received date: Revised date: Accepted date:

23-2-2015 8-4-2015 10-4-2015

Please cite this article as: Li, J., Qiang, D., Zhang, M., Xiu, H., and Zhang, X.,Joint action of ultrasonic and Fe3+ to improve selectivity of acid hydrolysis for microcrystalline cellulose, Carbohydrate Polymers (2015), http://dx.doi.org/10.1016/j.carbpol.2015.04.034 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.

Jinbao Li et al

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Highlights

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Ultrasonic was applied to the Fe3+/HCl system to selectively hydrolyze cellulose.

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The hydrocellulose was obtained with higher crystallinity and specific surface area.

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The reuse of hydrolysate could save chemicals dosage and reduce environment

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pollution.

The total reducing sugar after reuse may be used as source of biofuels.

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Joint action of ultrasonic and Fe3+ to improve selectivity of

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acid hydrolysis for microcrystalline cellulose Jinbao Li, College of Light Industry & Energy, Shaanxi Key Laboratory on Paper Technology and Specialty Papers, Shaanxi University of Science & Technology, Weiyang University Zone, Xi’an, Shaanxi 710021, China Email: [email protected] Tel: +86-29-86168575

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Dandan Qiang, College of Light Industry & Energy, Shaanxi Key Laboratory on Paper Technology and Specialty Papers, Shaanxi University of Science & Technology, Weiyang University Zone, Xi’an, Shaanxi 710021, China Email: [email protected] Tel: +86-15029987821

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Meiyun Zhang, College of Light Industry & Energy, Shaanxi Key Laboratory on Paper Technology and Specialty Papers, Shaanxi University of Science & Technology, Weiyang University Zone, Xi’an, Shaanxi 710021, China

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Huijuan Xiu, College of Light Industry & Energy, Shaanxi Key Laboratory on Paper Technology and Specialty Papers, Shaanxi University of Science & Technology, Weiyang University Zone, Xi’an, Shaanxi 710021, China

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Xiangrong Zhang, College of Light Industry & Energy, Shaanxi Key Laboratory on Paper Technology and Specialty Papers, Shaanxi University of Science & Technology, Weiyang University Zone, Xi’an, Shaanxi 710021, China

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Abstract: In this study, the combination of Fe3+/HCl and ultrasonic treatment was

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applied to selectively hydrolyze cellulose for the preparation of microcrystalline

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cellulose (MCC). It was found that the crystallinity and specific surface area of

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hydrocellulose samples were higher (78.92% and 2.23581m2·g-1, respectively)

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compared with the method only used Fe3+/HCl catalyst without ultrasonic treatment.

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Meanwhile, the hydrolysate can be extracted and reused for cellulose hydrolysis three

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runs, which was effective in saving the dosage of chemicals and reducing the pollution

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of the environment without affecting the properties of hydrocellulose. Moreover, the

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increased concentration of total reducing sugar (TRS) after three runs may be used as a

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valuable source in biofuels production. The technology of cellulose hydrolysis by

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retaining crystalline region for MCC products while promoting hydrolysis of

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amorphous region for further utilization is of great novelty, which may prove valuable

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in converting biomass into chemicals and biofuels environmentally and economically.

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Keywords: Cellulose hydrolysis; Ultrasonic treatment; Microcrystalline cellulose;

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Crystallinity; Hydrolysate reuse

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Chemical compounds studied in this article

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Hydrochloric acid (PubChem CID: 313); Ferric chloride (PubChem CID: 24380)

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Introduction Cellulose, one of the most abundant biomass resources, has become a promising

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alternative to process into the sustainable production of chemicals and fuels (Wang et al.,

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2006; Klemm, Heublein, Fink, & Bohn, 2005). It is a linear polysaccharide with

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repeating units D-glucose (C6H10O5)n via β-1,4-glucosidic bonds. The cellulose

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molecular chains are composed of crystalline and amorphous region. The arrangement

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of cellulose molecular chains in crystalline region is neater and more compact compared

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with that in amorphous region, so the accessibility of two regions are different by

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reagents (Jeoh et al., 2007). Microcrystalline cellulose (MCC), prepared from natural

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cellulose through acid hydrolysis along with series of post-treatment processes, has

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been widely used in the light industry, chemical industry, daily chemical due to its high

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degree of crystallinity, high specific surface area, narrower dimension (20-80μm), and

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other characteristics (Nada, El-Kady, El-Sayed, & Amine, 2009).

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To promote acid hydrolysis of cellulose for microcrystalline cellulose (MCC), it is

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essential to protect crystalline region and selectively promote hydrolysis of amorphous

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region. Otherwise, the hydrolysis of amorphous area in cellulose will lead degradation

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of crystalline region at the same time and finally affect the yield and quality of the

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product (Mohamad, Eichhorn, Hassan, & Jawaid, 2013). In recent years, extensive

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attention and research have been paid worldwide to develop high efficiency methods for

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producing MCC. These include solvent/metal-ion systems (Ma, Ji, Zhu, Tian, & Wan,

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2012; Tao, Song, & Chou, 2010), ultrasonic techniques (Tang, Yang, Zhang, & Zhang,

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2014; Wang, Fang, & Hu, 2007) and other coupled methods (Agblevor, Ibrahim, &

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El-Zawawy, 2007). It has been proved that metal ion can reduce activation energy of the

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hydrolysis reaction, thus enhance the catalytic activity and accelerate the hydrolysis of

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cellulose (Wang et al., 2014; Kamireddy, Li, & Tucker, 2013). By application of

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ultrasonic treatment, cavitation generated by ultrasound leads to micro-jet in a liquid

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medium, with which the fiber surface and internal structure can be damaged, this in turn

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increases reaction rate due to the more contact between acid and fibers (Melissa &

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David, 2015; Preeti, Narmadha, & Parag, 2015; Zhou, Huang, & Wang, 2008).

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Though much attention has been paid in promoting acid hydrolysis of cellulose for

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MCC, the combination of ultrasonic treatment and metal-ion applied to acid hydrolysis

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of cellulose has been rarely reported. Moreover, the hydrolysate after hydrolysis is

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always discarded instead of further reutilization. This leads to the waste of chemicals

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and environmental pollution. We have found that added mental-ion or pretreated

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cellulose by ultrasound was effective to selectively improve hydrolysis of amorphous

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region of cellulose in previous studies, and the high crystallinity of hydrocellulose could

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be obtained under the condition of 2.5 mol·L-1 HCl, 0.3 mol·L-1 FeCl3 in 80℃ for

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70min. (Li, Zhang, Zhang, Xiu, & He, 2015; Li, Zhang, Zhang, & He, 2014). Hence, the

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combination of ultrasound and metal-ion method was applied to the acid hydrolysis of

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cellulose for MCC in this study. And the ultrasonic was carried out and occurred with

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acid simultaneously in the whole process of cellulose hydrolysis, which was different

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with the acid hydrolysis of cellulose by ultrasonic pretreatment. Moreover, the

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hydrolysate was also extracted to explore its reusability based on the premise of

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guaranteeing the quality of MCC products, which has not been reported in previous

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literatures before and may provide a way in high value-added utilization of cellulose.

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With the purpose of comparing the hydrocellulose produced from Fe3+/HCl system with

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and without ultrasonic treated synergistically, the properties of hydrocellulose such as

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microstructure, special surface area, crystalline and chemical structure were done by

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SEM, EDS, XRD and FT-IR, respectively. Meanwhile, HPLC and DNS were applied to

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discuss the feasibility and times of hydrolysate reuse process.

Materials and methods

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Materials

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Dissolved Kraft eucalyptus pulp was received from Shan Dong Pulp & Paper Co.,

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Ltd., China. The chemical compositions of pulp analyzed according to Technical

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Association of Pulp and Paper Industry (TAPPI) standards were shown in Table 1.

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3,5-Dinitrosalicylic acid (DNS) was prepared according to a glucose standard (Miller,

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1959). Other chemicals were analytical grade and used as received.

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Table 1.

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Material

Wood pulp

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Chemical compositions of the dissolved pulp.

α-cellulose

Hemicellulose

Lignin

Ash

Moisture

Degree of

Crystallinity

(%)

(%)

(%)

(%)

content (%)

polymerization

(%)

92.66

4.75

1.19

0.08

5.27

661

58.92

Ultrasonic-assisted acid hydrolysis of cellulose

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The hydrolysis reaction was carried out in a flask equipped with a stirrer and reflux

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condenser. The flask containing 10g pulp (oven dry weight) , 150mL of acid solution

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(2.5mol·L-1 HCl and 0.3mol·L-1 FeCl3) were placed into the ultrasonic generator

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(KQ-2000, Kunshan ultrasonic instrument Co., Ltd., China) with a constant power of

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80W, which is a synergistic effect to improve the cellulose hydrolysis selectivity. The

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reaction was applied and operated at 80℃ for 70min. After hydrolysis, the flask was

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immersed in cold water to terminate the reaction. Then the reaction mixture was

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centrifuged to separate hydrocellulose samples and hydrolysate liquid. The supernatant

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was decanted for further analyzation, following this deionized water was used to wash

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the precipitation of hydrocellulose samples until the pH was neutral. The schematic

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procedure of acid hydrolysis by using ultrasonic method for the production of

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hydrocellulose was shown in Fig. 1. The yield of hydrocellulose was calculated from

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the Eq. (1):

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Yield of hydrocellulose (%) = (weight of hydrocellulose) / (weight of pulp put into the

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reactor) ×100%

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Pulp

HCl FeCl3

Reuse

Hydrolysis

Ultrasonic generator

(1)

3+

Reducing sugar

Fe /HCl hydrolysate

Separate

Centrifugal machine

Precipitation Hydrocellulose

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Fig. 1.

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hydrocellulose.

Schematic procedure of acid hydrolysis by using ultrasonic method for the production of

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Characteristic analysis of hydrocellulose The fracture surface morphology of hydrocellulose with and without ultrasonic

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cooperation was characterized with a HITACHI S-4800 (Hitachi, Tokyo, Japan)

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scanning electron microscope (SEM) at 3KV. Energy dispersive X-ray spectra (EDS)

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was attached on the SEM to elemental analysis on the surface of the samples. Surface of

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the samples were coated with gold under vacuum before observation.

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Samples with and without ultrasonic treatment were analyzed on a D/max-2200 PC

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automatic X-ray diffraction (XRD) (Rigaku Co. Ltd., Tokyo, Japan) using a Ni-filtered

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Cu-Kα radiation source (λ =0.1518 nm). The X-ray diffractograms were recorded from

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6° to 50° (2θ) with a scanning rate of 2°·min-1. Then the peak fitting software (MDI

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Jade 5.0) was used to obtain the area of each region through repeated fitting according

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Gaussian functions. The degree of hydrocellulose crystallinity (CI) was calculated used

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via Eq. (2) (Sun et al., 2008):

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CI (%) 

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Fa  100% Fa  Fc

(2)

Fa and Fc are the area of crystalline and amorphous regions, respectively. Brunauer-Emmett-Teller (BET) analysis (Micrometritics Co. Ltd., USA) was

carried out to detect the specific areas of hydrocellulose samples.

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Fourier transform infrared (FT-IR) spectra of hydrocellulose samples were detected

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on a Bruker (Germany) FT-IR spectrometer with a resolution of 4 cm-1 in the range of

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4000–400 cm-1 using KBr.

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Compositional analysis of hydrolysate

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The concentration of monosaccharides and oligosaccharides, as well as other

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byproducts were determined using High Performance Liquid Chromatography (HPLC)

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with a RI detector and NH2 column operated at 35℃, based on the standard procedure

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by National Renewable Energy Laboratory (NREL) No. 002 (Sluiter, 2005). The

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hydrolysate was filtered with 0.45μm syringe filters and degassed. The mobile phase

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consisted of acetonitrile and water mixture (the ratio of acetonitrile to water was 4:1)

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with a flow rate of 0.6mL·min-1.

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The amount of reducing sugar obtained from hydrolysate after hydrolyzing

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cellulose under ultrasonic treatment was determined by the DNS method (Zhang, Liu, &

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Zhao, 2012).

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Results and discussion

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Microstructure and elemental contents of hydrocellulose

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The morphology and microstructure of freeze-dried samples were investigated by

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SEM (Fig. 2). From Fig. 2 a-d, it was found that both of the samples turned into

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rod–like structure after hydrolysis, and the particle size of hydrocellulose (Fig. 2 c and d)

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become smaller after ultrasonic treatment. It was said that the cavitation bubbles

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generated by ultrasound can accumulate energy from the positive and negative pressure

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in the ultrasonic propagation direction, and they will collapse and further produce a very

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brief, strong pressure pulse when the accumulated energy reaches to a certain value. The

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pulse will work on the surface of fibers at great speed and then make the surface eroded

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and cracked (Yunus, Salleh, Abdullah, & Biak, 2010; Tang, Zhang, Chen, Liu, & Xie,

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2005), which enhance the penetration of Fe3+ and HCl to selectively hydrolyze the less

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dense amorphous and defective crystalline regions into saccharide, resulting in the

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acquisition of samples with smaller size. To prove the effect of ultrasound obviously,

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raw fibers and pretreated fibers by ultrasound (80W, for 20 min at room temperature)

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were showed in Fig. 2 e-h. It can be seen clearly that some fibrillation, delamination and

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erosion emerged on the surface morphology of fibers pretreated by ultrasound. And the

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erosive region has been hydrolyzed by the acid, so it was difficult to detect the extent of

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the damage on fiber surface by ultrasound in the Fig. 2 c and d.

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179 180

Fig. 2.

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(a, b) and with ultrasonic treated synergistically (c, d). raw fibers (e, f) and treated with ultrasound (g, h).

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SEM images of hydrocellulose samples hydrolyzed by Fe3+/HCl hydrolysis without treatment

Given that the presence of Fe3+ residue may affect the purity of hydrocellulose,

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further analysis of micro district of samples after hydrolyzing assisted with ultrasonic

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treatment was carried out by EDS (Fig. 3). The content of total C and O elements were

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72.54% (weight percentage constitutes), while the content of Fe element (0.02%) was

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too little to be shown in Fig. 3, resulting in almost no Fe residues in the hydrocellulose

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samples. The reason of high content of Au was due to the surface of samples coated

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with gold before observation. Thus, it can be concluded the elemental composition of

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fibers did not change and the product had been washed cleanly after hydrolysis.

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8000

4000 C O

Au

Fe

0 0

cr

2000

Au

2

4 Energy (keV)

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6000

Atom/ % 64.83 32.66 0.01 2.50

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Element Weight/ % C 43.41 O 29.13 Fe 0.02 Au 27.44 Total 100.00

6

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Fig. 3.

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cellulose with ultrasonic treated synergistically.

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Crystalline structure and special surface area of hydrocellulose

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The EDS curve of micro district of hydrocellulose samples after Fe3+/HCl hydrolysis of

The X-ray patterns of hydrocellulose (Fig. 4) showed the typical diffraction peaks

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of cellulose at about 2θ=15.1°, 16.4°, 22.7°and 34.6°due to 101, 10 , and 002 ,040

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planes, respectively, indicating the crystallographic form of cellulose I (Jahan, Saeed,

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He, & Ni, 2011; Ciolacu, 2007). The calculated crystallinity of hydrocellulose samples

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with and without ultrasonic treatment were 78.92% and 69.50%. As the ultrasonic

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selectively damaged the amorphous regions and defective crystalline regions, the (002)

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plane of hydrocellulose became sharper, in addition, the peak for the (101) plane

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became more intense and separated from the (10 ) plane for hydrocellulose samples

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assisted with ultrasonic treatment, as reported previously (Han, Zhou, Wu, Liu, & Wu,

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2013), which resulted in a more compact and ordered chain arrangements of crystalline

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structure (Liu et al., 2014).

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3500

Hydrocellose (untreated) Hydrocellulose (ultrasonic treated) 002

3000

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2000 1500 101 101

1000

040

500

5

10

15

20

25

2 Theta(degree)

205 206

Fig. 4.

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and without ultrasonic treated synergistically.

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Intensity

2500

30

35

40

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X-ray diffraction spectra of hydrocellulose samples by Fe3+/HCl hydrolysis of cellulose with

After detected the specific surface area of hydrocellulose by the BET method, the

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specific surface area of samples after hydrolyzing with and without ultrasonic treatment

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were 2.2358m2·g-1 and 1.6574m2·g-1, respectively. This may be because the rising

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degree of crystallinity led to the increasing order of structure and eventually made the

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specific surface area higher. The higher specific surface area reflected the better surface

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adsorption property, which also indicated the possibility of their application as efficient

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additives in various fields such as drug carrier and cosmetic filler (Adel, Abd El-Wahab,

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Ibrahim, & Al-Shemy, 2011).

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Chemical structure of hydrocellulose

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The chemical groups of hydrocellulose carried by FT-IR spectra (Fig. 5) also

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showed no change of chemical structure of hydrocellulose under ultrasonic treatment, as

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with XRD analysis. The absorption band at 3346 cm-1 was associated with the

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intermolecular, and intramolecular O-H stretching vibration band, the peaks at 2902

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cm-1 and 1375 cm-1 are methyl, methylene and methyne stretching vibrational bands.

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The bands at 1432 cm-1 and 1320 cm-1 are attributed to the saturated C-H bending and

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wagging vibration, respectively. The absorption bands at 1164 cm-1, 1109 cm-1, 1058

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cm-1, and 1034 cm-1, which are due to C-O-C stretching vibrational were considered to

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be the typical bonds of cellulose (Liu, Qiu, & Xu, 2009; Leung et al., 2011). It can be

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seen that the intensity of peaks marked in Fig. 5 reduced obviously after cellulose

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hydrolysis with ultrasonic treated synergistically. This indicated the surface structure of

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the cellulose was destroyed by ultrasound, the hydrogen bonds were broken, as a result,

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more C–OH, C–H and C–O–C bonds were exposed, which improved the effective

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contact between the Fe3+/HCl acid system and cellulose, therefore the absorbency

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increased (Nada, El-Kady, El-Sayed, & Amine, 2009; Sun, Zhuang, Lin, & Ouyang,

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2009).

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Hydrocellulose (ultrasonic treated) Hydrocellulose (untreated)

1.1

Transmittance (%)

1.0 0.9 0.8 0.7

2902

1432 1375 1320

0.6 1164 0.5 0.4 4000

1109

3500

1034

1059

3346 3000

2500 2000 1500 -1 Wavenumber (cm )

1000

500

233 234

Fig. 5.

FT-IR spectra of hydrocellulose samples by Fe3+/HCl hydrolysis of cellulose with and without

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ultrasonic treated synergistically.

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Compositional and recycling of hydrolysate After hydrolysis, the hydrolysate was analyzed by HPLC. It can be seen from Fig. 6,

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the concentrations of glucose, fructose were determined, and the peaks of

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oligosaccharides such as cellotetrose, cellotriose and cellobiose were also detected in

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their turn within 2.8-6.6 minutes. In addition, there were unknown mixsture in the

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hydrolysate system, which may be some formic acid, acetic acid, glucuronic acid and

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other acids from the degradation of monosaccharides during the process of hydrolysis

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(Ma, Ji, Zhu, Tian, & Wan, 2012; Zhuang, Wang, Yuan, Yao, & Luo, 2007). The

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highest content of glucose indicated a main product of glucose among cellulose

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hydrolysis. The yield of reducing sugar (1.08g·L-1) was further tested by DNS method.

600

MV

400

1 - unknown mixsture 2 - glucose 3 - fructose

3 - 7.559

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1 - 2.835

500

2 - 6.629

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300 200 100

0

0

5

10 Time (min)

15

20

246 247

Fig. 6.

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treated synergistically.

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HPLC analysis of hydrolysate extracted after Fe3+/HCl hydrolysis of cellulose with ultrasonic

From above analysis, it was observed that there were reducing sugar, acid and Fe3+

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in the hydrolysate system, so the recycling of hydrolysate is necessary for commercial

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benefit. In this work, the obtained hydrolysate were around 110mL after each run, so the

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amount of fresh HCl and Fe3+ were added proportionally to make sure the solid-liquid

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ratio constant, other conditions were the same as above. Fig. 7 showed the recycling of

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hydrolysate over 5 runs. It can be seen that no further obvious decrease in yield and

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crystallinity of hydrocellulose were found in the following 3 runs, and the amount of

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reducing sugar could reach to 3.32 g·L-1. However, the composition of hydrolysate

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system may be more complex, besides, the accumulated monosaccharides degraded

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sharply to byproducts such as levulinic acid and 5-Hydroxymethylfurfural under

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prolonged ultrasonic treatment afterwards (Modig, Almeida, Gorwa-Grauslund, &

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Liden, 2008; Zhou, 2008), Therefore, the hydrolysate can be reused up to an optimal

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value of 3 runs.

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250

100 90

Concentration of TRS (g/L)

80 70

3

60 50 40

2

30

1

20

Concentration of TRS (g/L) Yield of hydrocellulose (%) CI of hydrocellulose (%)

10

Yield and CI of hydrocellulose (%)

4

0

0 0

1

2

3

4

5

Numbers of run

262 263

Fig. 7.

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synergistically for hydrocellulose.

Reuse of hydrolysate after Fe3+/HCl hydrolysis of cellulose with ultrasonic treated

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Conclusions Ultrasonic-assisted Fe3+/HCl hydrolysis of cellulose for the production of MCC

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from Dissolved Kraft eucalyptus pulp was demonstrated. From this study, the

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introduction of ultrasonic-assisted method in Fe3+/HCl hydrolysis system turned out to

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be effective in improving the selectively hydrolysis of amorphous region of cellulose.

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The solid product, namely hydrocellulose mainly came from the crystalline region of

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cellulose, which showed better properties such as crystallinity and special surface area

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compared to hydrolysis without ultrasound. The liquid product, namely hydrolysate

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came from the less dense amorphous and defective crystalline regions of cellulose,

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which can be reused in the cellulose hydrolysis system without affecting the yield and

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crystallinity of hydrocellulose. In addition, HPLC detected the existence of some

276

content of saccharides especially glucose in hydrolysate after hydrolysis. The reuse of

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hydrolysate showed not only the feasibility of recycling trial but also an accumulation

278

of TRS. So the attempt on total utilization of cellulose in this study is feasible and

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effective. However, a detailed mechanism in the coordination of ultrasonic-assisted,

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metal-ion catalyzed and acid in cellulose hydrolysis, as well as the greater optimization

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of reaction conditions should be considered in future studies. Thus, it may facilitate the

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conversion of lignocellulose into valuable chemicals and biofuels more environmental

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and energy-efficient.

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Acknowledgments

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This work was supported by the Doctoral Program of Higher Education of China

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(grant NO.20126125130001) and the Doctoral Scientific Research Fund by Shaanxi

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University of Science & Technology (grant NO.BJ13-02).

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References

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Adel, A. M., Abd El-Wahab, Z. H., Ibrahim, A. A., & Al-Shemy, M. T. (2011).

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676–687.

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cotton gin waste. Cellulose, 14, 247–256.

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Ciolacu, D. (2007). On the supramolecular structure of cellulose allomorphs after

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Figures caption

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Fig. 1.

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hydrocellulose.

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Fig. 2.

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(a, b) and with ultrasonic treated synergistically (c, d). raw fibers (e, f) and treated with ultrasound (g, h).

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Fig. 3.

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cellulose with ultrasonic treated synergistically.

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Fig. 4.

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and without ultrasonic treated synergistically.

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Fig. 5.

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ultrasonic treated synergistically.

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Fig. 6.

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treated synergistically.

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Fig. 7.

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synergistically for hydrocellulose.

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Schematic procedure of acid hydrolysis by using ultrasonic method for the production of

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SEM images of hydrocellulose samples hydrolyzed by Fe3+/HCl hydrolysis without treatment

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The EDS curve of micro district of hydrocellulose samples after Fe3+/HCl hydrolysis of

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X-ray diffraction spectra of hydrocellulose samples by Fe3+/HCl hydrolysis of cellulose with

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FT-IR spectra of hydrocellulose samples by Fe3+/HCl hydrolysis of cellulose with and without

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HPLC analysis of hydrolysate extracted after Fe3+/HCl hydrolysis of cellulose with ultrasonic

Reuse of hydrolysate after Fe3+/HCl hydrolysis of cellulose with ultrasonic treated

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Joint action of ultrasonic and Fe³⁺ to improve selectivity of acid hydrolysis for microcrystalline cellulose.

In this study, the combination of Fe(3+)/HCl and ultrasonic treatment was applied to selectively hydrolyze cellulose for the preparation of microcryst...
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