Cationic Hemicellulose As a Product of Dissolving Pulp Based

Jan 19, 2015 - Chemical Engineering Department, Lakehead University, Thunder Bay, Ontario P7B 5E1, Canada. •S Supporting Information. ABSTRACT: In ...
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Cationic Hemicellulose As a Product of Dissolving Pulp Based Biorefinery Jing Shen,† Robin Singh,‡ Mohan Konduri,§ and Pedram Fatehi*,‡,§ †

Key Laboratory of Bio-based Material Science and Technology of Ministry of Education, Material Science, and Engineering College, Northeast Forestry University, Harbin 150040, China ‡ Chemical Engineering Department, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada § Chemical Engineering Department, Lakehead University, Thunder Bay, Ontario P7B 5E1, Canada S Supporting Information *

ABSTRACT: In the present technology practiced, hemicelluloses dissolved in the prehydrolysis liquor (PHL) of the kraft-based dissolving pulp production process is mixed with black liquor and incinerated in the kraft mill. In this study, solvent precipitation was used for isolating lignin and hemicelluloses from PHL. The results showed that acetone was a more effective and selective solvent than ethanol to isolate hemicelluloses. Furthermore, the cationization of hemicelluloses with glycidyltrimethylammonium chloride resulted in cationic hemicelluloses with the charge density of 2.3 meq/g and molecular weight of 6330 g/mol. Based on these results, an integrated dissolving pulp-based biorefining process was proposed that would produce dissolving pulp and cationic hemicellulose as main products.

1. INTRODUCTION Forest biorefinery has been regarded as a new concept to revisit the pulping industry.1,2 In forest biorefinery, value-added chemicals will be produced from woody materials and can be substituted for fossil-based products worldwide. One approach to convert traditional pulping processes to forest biorefineries is to utilize their wasted lignocelluloses in the production of highvalue products.1,3,4 Wood chips are pretreated with steam in order to remove hemicelluloses from wood chips in the kraft-based dissolving pulp production process. The treated wood chips will be cooked via kraft process and then bleached to produce dissolving pulp with a purity that is higher than 98%.5−12 The prehydrolysis liquor (PHL) that is generated via steaming of wood chips contains lignin and hemicelluloses, but it is mixed with black liquor of the kraft process and sent to the recovery cycle; thus, the lignin and hemicelluloses dissolved in PHL are wasted.3,9 However, lignin and hemicelluloses can be separated from PHL and then converted to value-added products. In this regard, the efficient recovery of lignin and hemicelluloses from PHL and their value-added utilization are keys to successful implementation of dissolving pulp-based biorefinery. Generally, more than 50% of hemicelluloses and about 10% lignin contained in wood chips are dissolved in PHL during the hydrolysis process, thus a considerable amount of wood chips is dissolved in PHL. To recover the dissolved organics from PHL, various separation pathways including adsorption, extraction, polymer flocculation, membrane filtration, ion-exchange resin and acidification were proposed in the past.9,12−16 Adsorption and flocculation are efficient and industrially attractive, but the application of adsorbent in PHL may increase the complexity and cost of the adsorbent’s recovery process.13 Membrane filtration was used in the past to concentrate spent liquors.9,15 Although it can effectively isolate lignocelluloses based on their molecular weights, the practical © 2015 American Chemical Society

application of membrane technology is limited due to its frequent blockage in the process.9,15 Ion exchange resin can be used for isolating charged lignocelluloses from spent liquors, but not all of the lignocelluloses in PHL have charges and ion exchange resins are expensive and their practical application may significantly add to the operational cost of the process.12,16 In contrast, solvent precipitation has been regarded as an efficient method to recover the lignocelluloses from various pulping spent liquors. In this regard, it is important to develop an extraction process with a solvent that has an efficient, simple and industrially applicable recovery process. In the past, ethanol was introduced as a solvent to recover lignocelluloses from PHL.6,7,17,18 However, there is still a need to identify a more efficient solvent for this purpose, which may open the door for better extraction (and eventually utilization) of the dissolved organics of PHL. The first objective of this work was to access the efficiency of acetone as an alternative solvent for recovering hemicelluloses from PHL. Once recovered, hemicelluloses can be transformed to furfural, xylitol, ethanol, and other bioproducts.3,19−21 Alternatively, they can be used as papermaking additives for increasing the basis weight of papers6,7 or as dry strength or retention aids.22 However, the lack of cationic charges on hemicelluloses may constrain their practical use, as their adsorption on cellulose fibers would be limited.6,23 Cationization has been regarded as an efficient method to improve the adsorption of organic materials and thus promoting the end-use application of hemicelluloses. This is due to the fact that cationic polymers can readily adsorb to negative charges of cellulose fibers (i.e., originating mainly from carboxylic group Received: Revised: Accepted: Published: 1426

November 4, 2014 January 11, 2015 January 19, 2015 January 19, 2015 DOI: 10.1021/ie504363j Ind. Eng. Chem. Res. 2015, 54, 1426−1432

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Industrial & Engineering Chemistry Research Table 1. Properties of Prehydrolysis Liquor (PHL) pH concn. in PHL, g/L fraction based on dried mass, wt %

3.6

oligomeric sugars (hemicelluloses) (g/L)

monomeric sugars (g/L)

lignin (g/L)

acetic acid (g/L)

furfural (g/L)

12.1 23.8

6.3 12.3

10.1 19.9

18.1 35.6

4.3 8.4

were centrifuged at 2000 rpm for 15 min and the filtrates were collected for lignin and hemicellulose analyses, while precipitates were collected for cationization. 2.3. Cationization of the Recovered Hemicelluloses. In this set of experiments, 1 g of hemicellulosic precipitates (HP) was added to a 250 mL three neck glass flask and dissolved in deionized distilled water, and then, various amounts of NaOH solution (5 wt %) were added to the solution. The HP concentration was maintained at 1 wt % in solution. Finally, GTMAC was added to the system, and the reaction was conducted under different reaction temperatures and times but at constant stirring (100 rpm). In this work, temperature (55− 90 °C) and time (1−4 h) of reaction, NaOH dosage (5−20 wt %), and GTMAC/HP molar ratio (1−3 mol/mol) were variables of the reaction. After the reaction, the solutions were cooled to room temperature and neutralized with sulfuric acid (5 wt %). Unreacted monomers were separated from the products by a membrane dialysis with a molecular weight cutoff of 1000, while changing water every 2 h for the first 6 h and then once a day for 2 days. The product of this cationization reaction was denoted cationic hemicellulosic precipitates (CHP) in this study. 2.4. Hemicellulose Analysis. The concentration of hemicelluloses was determined by using an ion chromatography (IC) unit equipped with CarboPac PA1 column (Dionex-300, Dionex Corporation, Canada) and a pulsed amperometric detector (PAD). The PAD settings were E1 = 0.1 V, E2 = 0.6 V, and E3 = −0.8 V. Deionized water was used as eluant with a flow rate of 1 mL/min, 0.2 M NaOH was used as the regeneration agent with 1 mL/min flow rate, and 0.5 M NaOH was used as the supporting electrolyte with 1 mL/min flow rate. As only monomeric sugars can be detected by the IC, the oligomeric sugars (i.e., hemicelluloses) dissolved in the samples were initially converted to monomeric sugars via acid hydrolysis. Generally, the conversion of oligomeric sugars to monomeric sugars under acidic conditions may results in uronic acid generation, in particular for xylan of PHL.27 However, it was reported that the acid treatment under the conditions of 4% sulfuric acid at 121 °C for 1 h would result the minimum amount of byproducts (uronic acid) and the maximum amount of monomeric sugars, and these conditions were used in the acid treatment of PHL using an oil bath (Neslab Instruments Inc., Portsmouth, NH, U.S.A.).3,27,28 The concentration of monomeric sugars was detected by the IC. The IC analysis before this acid hydrolysis reflected the monomeric sugars in the samples (as IC cannot detect the oligomeric sugars) and the IC analysis after this acid hydrolysis reflected the total sugars in the samples. The amount of oligomeric sugars, which was reported as hemicelluloses in this work, was determined by subtracting the amount of monomeric sugars from total sugars.14,28 Meanwhile, the HP that was collected via acetone treatment (acetone in PHL mixture 80%) was acid hydrolyzed, and its oligomeric sugars were determined according to the above procedure. 2.5. Lignin, Acetic Acid, and Furfural Analyses. The lignin content of the PHL samples was measured based on the

attached to fibers) based on electrostatic charge interaction.22,24 This cationization would enhance the affinity of hemicelluloses in interacting with various substrates such as cellulosic fibers and fine particles.22,25,26 It could also improve the interaction of hemicelluloses with materials dissolved in wastewater effluent of pulp mills and thus can be used as a flocculant. The second objective of this research was to investigate the cationization of hemicellulose precipitated from PHL to produce cationic hemicelluloses. In this research, hemicelluloses were recovered via acetone or ethanol from PHL. The recovered hemicelluloses were cationized under different conditions to induce cationic hemicelluloses with the highest possible charge density. Based on the results, an integrated process for producing cationic hemicelluloses from the PHL of a kraft-based dissolving pulp process was proposed, and its advantages and disadvantages were comprehensively discussed. In fact, this is the first report to assess the efficiency of acetone in recovering hemicelluloses from PHL and in cationizing the precipitated hemicelluloses to produce cationic products.

2. EXPERIMENTAL SECTION 2.1. Materials. Acetone and ethanol (both analytical grades), as well as glycidyl-trimethylammonium chloride (GTMAC, 75% in water), sulfuric acid (98 wt %), and NaOH pellets (analytical grade) were all obtained from Sigma Aldrich and used as received. Anionic polyvinyl sulfate (PVSK) with MW of 100 000−200 000 g/mol (97.7% esterified) was provided by Wako Pure Chem. Ltd. Japan. Prehydrolysis liquor (PHL) was collected from a kraft-based dissolving pulp process located in Eastern Canada. The raw material of this process was mixed hardwood (70 wt % maple, 20 wt % poplar, and 10 wt % birch). The PHL was centrifuged at 2000 rpm for 15 min to remove undissolved materials, and the centrifuged PHL was used as raw material in this research. The properties of the centrifuged PHL are shown in Table 1. As seen, the PHL contained 12 g/L of hemicelluloses and 10 g/L of lignin. The acetic acid content of PHL (18.1 g/L) was, in fact, more than the other components. The acetic acid of PHL is originated from the conversion of acetyl groups, which are attached to cellulose and hemicelluloses of wood chips, to acetic acid in autohydrolysis process.5,14 Furfural is also a byproduct of the decomposition of hemicelluloses of wood chips under acidic conditions in the autohydrolysis process.5,14 Also, PHL contained 5.2 wt % dried mass, and this amount is very close (5.09 wt %) to the overall amount of oligomeric and monomeric sugars, lignin, acetic acid, and furfural of PHL presented in Table 1. The results also showed that the dried fraction of lignin and oligomeric sugar in PHL were close (approximately 20%), while acetic acid was higher (35%). 2.2. Treatment of PHL with Solvent. In one set of experiments, various dosages of ethanol or acetone were added to 500 mL of PHL in order to produce solvent/PHL mixtures with altered mass ratios in glass beakers at room temperature, and the mixtures were shaken for 30 min in a New Brunswick water bath shaker at room temperature. Then, the mixtures 1427

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Industrial & Engineering Chemistry Research UV/vis spectrometric method at a wavelength of 205 nm (TAPPI UM 250). A Varian 300 1H NMR spectrometer was employed for determining the concentrations of furfural and acetic acid of the PHL samples.6,14 Calibration curves were established for both furfural and acetic acid. The details of furfural and acetic acid analyses with NMR were provided in our previous work.29 2.6. Molecular Weight Analysis. The weight-average (Mw) and number-average molecular (Mn) weights of the lignin and hemicelluloses samples were determined by a Gel Permeation Chromatography (GPC) on a Sodex KF-802.5 column. The samples (10 μL) were dissolved in tetrahydrofuran (THF). The column was operated at 30 °C and eluted with THF at a flow rate of 1 mL/min. The column was calibrated by polystyrene standard samples. 2.7. Determination of Charge Density and Degree of Substitution. To identify the charge density of CHP, their solutions (1% wt.) were titrated against a PVSK standard solution (0.5 mM) by using a particle charge detector Mütek, PCD 03 (Herrsching, Germany). Degree of substitution (DS) is an indicator (based on mole percentage) of hydroxyl groups that were substituted with GTMAC group. This can directly show the yield of reaction as the DS of 100% implies that all of the hydroxyl groups were substituted with GTMAC. To quantify the degree of substitution (DS) of hydroxyl group with GTMAC on cationic hemicellulosic precipitates (CHP), CHPs were dried at 105 °C overnight, and their 1H NMR spectra were recorded in D2O at 25 °C using an Oxford 300 MHz spectrometer operating at 300.13 MHz.30 The areas under the peaks at 3.2 (cationic group), 4.3−4.9, 4.9−5.60 (hemicelluloses backbone) ppm were used for determining the DS in this work. The NMR spectra of HP and one CHP sample are provided in Supporting Information.

3. RESULTS AND DISCUSSION 3.1. Precipitation of Lignocelluloses from PHL. Figure 1 shows the concentration of the dissolved organics of PHL in acetone/PHL or ethanol/PHL mixture as a function of solvent percentage in PHL. It is clear that the concentration of hemicelluloses significantly decreased upon increasing the solvent percentage, which is in agreement with previous work.6,17 Also, the concentrations of furfural, acetic acid, and lignin were marginally changed by altering the solvent percentage in solvent/PHL mixture. The solubility of organic materials in solutions was theoretically discussed by considering solubility parameter (δ) of solute and solvent in the literature.31 It was postulated that the closer the δ values of solutions and organic materials, the greater the solubility of organic materials will be in the solutions (i.e., less precipitation).31,32 In general, the main component of hardwood hemicellulose is xylan (O-acetyl-4-O-methylglucuronoxylan) and glucomannan.14 The δ values of xylan and glucomannan are 17.49 and 24.71 (cal/cm3)1/2, respectively.33 The δ value of solvent/ water mixtures are listed in Table 2. The data in Table 2 implies that, by increasing the ratio of solvent in solvent/water mixture, the δ value of the mixture will generally drop, as the δ values of acetone and ethanol are smaller than that of water (Table 2). Considering the δ values of glucomannan and solvent/water mixture, it can be understood that, by increasing the ratio of solvent in the mixture, the difference between the δ values of glucomannan and mixture will increase, which leads to the precipitation of

Figure 1. Concentration of hemicellulose, lignin, and furfural as a function of solvent weight percentage in solvent/PHL mixture.

Table 2. δ Value Of Solvent/Water Mixture (cal/cm3)1/2 According to a Previous Work33 solvent/water ratio wt/wt

0/100

25/75

50/50

75/25

100/0

acetone ethanol

22.31 22.31

20.75 20.87

18.06 18.43

14.43 15.59

9.19 12.25

glucomannan. Therefore, the decrease in the concentration of hemicelluloses from 0 to 50% solvent concentration in Figure 1a could be attributed to the precipitation of glucomannan (but further study is needed to prove this). By increasing the solvent ratio up to 50 wt % in the mixtures, the δ values of xylan and the solvent/water mixture will become closer, reflecting that the 1428

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Figure 2. Reaction scheme of pentose (as a representative of hemicelluloses) with GTMAC.

concentration reduction, the HP precipitates contained approximately 75 wt % hemicelluloses, 12.5 wt % lignin, and 12.5 wt % furfural. 3.2. Cationization of the Recovered Hemicelluloses. In this study, glycidyl trimethylammonium chloride (GTMAC) was used as a cationic reagent for the preparation of cationic products from HP. As is well-known, hemicelluloses of mixed hardwood contain mainly pentoses.5 Figure 2 shows the reaction scheme of pentose units of hemicelluloses with GTMAC. It is clear that the epoxy ring of GTMAC is opened under alkaline conditions and provides the linkage to pentose (as a representative of mixed hardwood hemicellulose). Figure 3 presents the charge density and degree of substitution (DS) of the cationic hemicellulosic precipitate

solubility of xylan can increase. However, this does not mean that the concentration of xylan in the solvent/PHL mixture will increase, as there is no undissolved xylan in the mixture to become soluble. By further increasing the percentage of solvent in solvent/PHL, the difference between the δ values of xylan and solvent/water will increase and this will lead to the precipitation of xylan. Therefore, the decrease in the hemicellulose concentration at the solvent/PHL ratio of less than 50% may be due to glucomannan precipitation, while the decrease at the ratio of higher than 50% may be due to xylan and glucomannan precipitations, but further studies need to prove this. Furthermore, Table 2 shows that the δ value of the acetone/water mixture is lower than that of ethanol/water mixture, leading to more precipitation of hemicelluloses. The δ value of lignin was reported to be in the range 13.5− 14.2 (cal/cm3)1/2.32 The δ of acetic acid and furfural are 10.1 and 11.2 (cal/cm3)1/2, respectively.33,34 As seen in Table 2, the δ value of the mixture would drop by increasing the percentage of solvent, which would be closer to that of lignin, acetic acid, and furfural; thus, their solubility could not significantly be affected in the solvent/water mixture. In fact, only the δ value of large lignin polymers or lignin−carbohydrate (i.e., lignin− hemicellulose) complexes might be affected by the addition of solvent to PHL, and thus, these large complexes would be precipitated from the PHL.18,35 Therefore, the small reduction in the concentration of lignin could be due to the removal of lignin−carbohydrate complexes from the PHL, which was reported in the past.36 As the main objective of this work was to precipitate hemicelluloses from PHL, the results in Figure 1 showed (1) a high precipitation yield (at 60% solvent in solvent/PHL mixture), as all hemicelluloses were removed from PHL, and (2) a reasonable selectivity, as limited amounts of lignin and furfural were precipitated along with hemicelluloses from the PHL, were achieved. A change in the concentrations of acetic acid and monomeric sugars in PHL was also undetected via changing the percentage of solvent in solvent/PHL mixtures. The precipitates that were generated via mixing acetone (80 wt %) and PHL (20 wt %) were selected for cationization analysis. As shown in Figure 1, the HP that was precipitated with acetone (acetone in PHL mixture 80%) contained all of the hemicelluloses of PHL. As stated above, acetone treatment helps the precipitation of oligomers. Therefore, HP contained all the oligomers of PHL. To prove this, the HP that was collected via acetone treatment (acetone in PHL mixture 80%) was acid hydrolyzed, and its oligomeric sugars were determined. Interestingly, the results confirmed that the oligomeric sugar content of the precipitated HP was 11.6 g/L, which was close to the oligomeric sugars of HL in Table 1 (12.1 g/L). The results in Figure 1 also showed that the concentration of lignin and furfural were decreased by 3 g/L. Therefore, based on the

Figure 3. Charge density (CD) and degree of substitution (DS) of CHP as a function of time of reaction, experimental conditions: 1/1 mol/mol GTMAC/hemicellulose ratio, 65 °C, NaOH 5 wt %.

(CHP) as a function of reaction time. It is apparent that the maximum charge density and DS were obtained at 1 h of reaction, and with extending the reaction time, the charge density and the DS of CHP decreased. A similar trend was reported for the cationization of poly(vinyl alcohol) under the optimal conditions of 95 °C, 1 h, GTMAC/PVA molar ratio of 0.5, and 5% (mol) NaOH concentration, which resulted in a charge density of 1.3 meq/g.3 The increases in the charge density and DS were due to the enhancement in the grafting of GTMAC to the polymer backbone,24 while decreases in charge density and the DS at prolonged time might be related to the hydrolysis of CHP and/or hydrolysis of GTMAC under strong alkaline conditions.3,7 Figure 4 presents the charge density and DS of CHP versus the GTMAC/hemicelluloses molar ratio. Apparently, the increase in the ratio resulted in an increase in charge density and the DS, which is basically due to enhanced availability of the cationic reagent (GTMAC) for the cationization reaction. A 1429

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Figure 6. Charge density and degree of substitution (DS) of CHP as a function of reaction temperature, 1/1 mol/mol GTMAC/hemicellulose ratio, 1 h, NaOH 5 wt %.

Figure 4. Charge density and degree of substitution of CHP as a function of GTMAC/hemicellulose in reaction, experimental conditions: 1 h, NaOH 5 wt %, 65 °C.

Table 3. Properties Of Hemicelluloses after Precipitation and Cationization

similar trend was reported in the cationization of poly(vinyl alcohol).24 Figure 5 presents the charge density and DS of CHP as a function of NaOH dosage. As seen, the charge density and DS

sample HP via acetone treatment HP via ethanol treatment hemicellulose18 hemicellulose38 CHP a

Mn, g/mol

charge density, meq/g

6100

4420

NDa

5800

4346

N/A

6600 8000−19600 6330

3200

N/A

4720

2.5

Mw, g/mol

Not detectable.

Furthermore, the molecular weight of hemicelluloses precipitated with acetone was similar to that precipitated via ethanol treatment and to that reported in the literature.18 The charge density of HP was not detectable, which may imply that it contained very limited amount of carboxylic group. The molecular weight and charge density of CHP shows that it can potentially be an effective fixation agent and basic weight additive for papermaking. 3.4. Proposed Process. Figure 7 shows a process for producing cationic hemicellulosic precipitates (CHP) in an

Figure 5. Charge density and degree of substitution of CHP as a function of NaOH in reaction, experimental conditions: 1/1 mol/mol GTMAC/hemicellulose ratio, 65 °C.

of CHP were the maximum at 5% NaOH concentration. This implies that the amount of sodium hydroxide should be optimized to catalyze the reaction; however, its high amount would probably lead to the hydrolysis of GTMAC or CHP.37 Figure 6 depicts the charge density and DS of CHP as a function of temperature of the reaction. It was found that 65 °C was an optimum temperature for an efficient cationization.3 A high temperature (e.g., 90 °C) impaired the cationization, probably due to the hydrolysis of GTMAC or CHP, as described earlier. Therefore, it can be concluded that the cationization reaction can be optimized under the conditions of GTMAC/hemicelluloses molar ratio of 1, NaOH dosage of 5%, temperature of 65 °C, and 1 h reaction time. 3.3. Property Analysis. Table 3 presents the properties of CHP (under the optimized conditions), HP, and hemicelluloses precipitated from spent liquors in the literature. The tabulated results showed that the molecular weight of CHP was similar to that of HP, implying that cationization had a limited effect on the molecular weight of hemicelluloses.

Figure 7. Proposed process for producing cationic hemicellulosic precipitates (CHP) in an integrated dissolving pulp-based biorefinery.

integrated dissolving pulp-based biorefinery. In this process, wood chips are pretreated with steam for hemicellulose removal. The precipitated hemicellulose will be dissolved in PHL. The treated wood chips are cooked in a kraft process to produce unbleached pulp and then bleached to produce 1430

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this work. This material is available free of charge via the Internet at http://pubs.acs.org.

dissolving pulp. The PHL is initially mixed with acetone, which leads to the precipitation of hemicellulosic materials, as was illustrated in Figures 1−3. The precipitated material (HP) can be collected via a filter or clarifier. Acetone/PHL solution will be sent to a distillation column to recover acetone for reuse in the precipitation stage, while the PHL is directed to wastewater system. The filtered/precipitated hemicelluloses will be transferred to another reactor. A part of NaOH that is generated in the recovery cycle of the kraft process is added to this reactor in order to provide the required pH of the cationic reaction. GTMAC will be added to the reactor, and the product will pass through another filter so that the product with a desired concentration and purity is produced for the market. The main advantage of this process is that (1) it is truly integrated into the existing facilities of the kraft-based dissolving pulp production process and (2) it uses acetone with boiling point of 56 °C for the precipitation of hemicelluloses from PHL; thus, the heat demand for the distillation tower is relatively insignificant. In the proposed process, one raw material (PHL) is free of charge, NaOH is already used in the kraft process, and GTMAC is the cationic agent that is widely used for the cationization of starch commercially (i.e., not very expensive). This process reduces the load to the recovery boiler, as the treated PHL will be sent to the wastewater after the process instead of being treated in the recovery unit of kraft process (i.e., reduces the cost of evaporation), which can benefit the mill by reducing the overall operating cost of the kraft process. On the other hand, the main disadvantage of this process is the introduction of a solvent to PHL, which may imply that the design of the distillation tower should be such that the amount of acetone in PHL directed to wastewater treatment should be controlled at a minimum level, and this may be expensive. Also, part of the acetone may be converted to other products via acid catalyzed aldol reactions, which may reduce the efficiency of acetone recovery. The efficiency of acetone recovery will be investigated in future studies. A detailed analysis is required to estimate the production cost of CHP and the impact of this process on the overall economy of the proposed kraft mill operation, which needs future studies.

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Corresponding Author

*E-mail: [email protected]. Tel: 807-343-8697. Fax: 807346-7943. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank NSERC Canada for supporting this research.

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REFERENCES

(1) Reardon, K. F. Lignocellulosic Biorefineries: Concepts and Possibilities. Plants and Bioenergy. Adv. Plant Biol. 2014, 4, 255. (2) Van Heiningen, A. R. P. Converting a Kraft Pulp Mill into an Integrated Forest Biorefinery. Pulp Pap. Can. 2006, 107, 38. (3) Fatehi, P.; Ni, Y. Integrated Forest BiorefineryPrehydrolysis/ Dissolving Pulping Process. Sustainable Production of Fuels, Chemicals, and Fibers from Forest Biomass; American Chemical Society: Washington, DC, 2011; Chapter 18, p 475. (4) Sanglard, M.; Chirat, C.; Jarman, B.; Lachenal, D. Biorefinery in a Pulp Mill: Simultaneous Production of Cellulosic Fibers from Eucalyptus Globulus by Soda-Anthraquinone Cooking and SurfaceActive Agents. Holzforschung 2013, 67, 481. (5) Li, H.; Saeed, A.; Ni, Y.; Van Heiningen, A. R. P. Hemicellulose Removal from Hardwood Chips in the Pre-Hydrolysis Step of the Kraft-Based Dissolving Pulp Production Process. J. Wood Chem. Technol. 2010, 30, 48. (6) Liu, Z.; Fatehi, P.; Jahan, M. S.; Ni, Y. Separation of Lignocellulosic Materials by Combined Processes of Pre-Hydrolysis and Ethanol Extraction. Bioresour. Technol. 2011, 102, 1264. (7) Liu, Z.; Fatehi, P.; Sadeghi, S.; Ni, Y. Application of Hemicelluloses Precipitated via Ethanol Treatment of Pre-Hydrolysis Liquor in High-Yield Pulp. Bioresour. Technol. 2011, 102, 9613. (8) Miao, Q.; Chen, L.; Huang, L.; Tian, C.; Zheng, L.; Ni, Y. A Process for Enhancing the Accessibility and Reactivity of Hardwood Kraft-Based Dissolving Pulp for Viscose Rayon Production by Cellulase Treatment. Bioresour. Technol. 2013, 154, 109. (9) Shen, J.; Kaur, I.; Baktash, M. M.; He, Z.; Ni, Y. A Combined Process of Activated Carbon Adsorption, Ion Exchange Resin Treatment and Membrane Concentration for Recovery of Dissolved Organics in Pre-Hydrolysis Liquor of the Kraft-Based Dissolving Pulp Production Process. Bioresour. Technol. 2013, 127, 59. (10) Shi, H.; Fatehi, P.; Xiao, H.; Ni, Y. A Combined Acidification/ PEO Flocculation Process to Improve the Lignin Removal from the Pre-Hydrolysis Liquor of Kraft-Based Dissolving Pulp Production Process. Bioresour. Technol. 2011, 102, 5177. (11) Yang, G.; Jahan, M. S.; Ahsan, L.; Zheng, L.; Ni, Y. Recovery of Acetic Acid from Pre-Hydrolysis Liquor of Hardwood Kraft-Based Dissolving Pulp Production Process by Reactive Extraction with Triisooctylamine. Bioresou. Technol. 2013, 138, 253. (12) Yang, G.; Jahan, M. S.; Ahsan, L.; Ni, Y. Influence of the Diluent on the Extraction of Acetic Acid from the Prehydrolysis Liquor of Kraft Based Dissolving Pulp Production Process by Tertiary Amine. Sep. Pur. Technol. 2013, 120, 341. (13) Liu, S.; Amidon, T. E.; Wood, C. D. Membrane Filtration: Concentration and Purification of Hydrolyzates from Biomass. J. Biobased Mater. Bioenergy 2008, 2, 121. (14) Saeed, A.; Fatehi, P.; Ni, Y. An Integrated Process for Removing the Inhibitors of the Pre-Hydrolysis Liquor of Kraft-Based Dissolving Pulp Process via Cationic Polymer Treatment. Biotechnol. Prog. 2012, 28, 19.

4. CONCLUSIONS Solvent precipitation can be an effective and fast process to isolate hemicelluloses from PHL. In this case, acetone was a more effective and selective solvent than ethanol to isolate hemicelluloses. The optimal conditions for the cationization of precipitated hemicellulosic were GTMAC/hemicellulose mole ratio of 1, temperature of 65 °C, 5 wt % NaOH, and 1 h reaction, which induced cationic hemicellulosic precipitates with the charge density of 2.3 meq/g and molecular weight of 6330 g/mol. Based on these results, an integrated dissolving pulp-based biorefinery were discussed that produces dissolving pulp and cationic hemicelluloses as main products.

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AUTHOR INFORMATION

ASSOCIATED CONTENT

S Supporting Information *

NMR spectra of unmodified hemicellulose and modified hemicellulose, which was prepared under the conditions of pH 10, 2 h, 65 °C, and 2 mol/mol GTMAC/CHP ratio (Figure S1). Areas under the peaks at 3.2 (cationic group), 4.3−4.9 (hemicellulose backbone), and 4.9−5.60 (hemicellulose backbone) ppm used for determining the degree of substitution in 1431

DOI: 10.1021/ie504363j Ind. Eng. Chem. Res. 2015, 54, 1426−1432

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DOI: 10.1021/ie504363j Ind. Eng. Chem. Res. 2015, 54, 1426−1432