The purpose of this research project is to increase the reactivity of prehydrolyzed kraft pulp using prehydrolyzate and sulfuric acid during prehydrolysis cooking. First, we determined the chemical composition of the wood of two different species of hardwood (Acacia crassicarpus and Eucalyptus hybrids) and related it to the pre-hydrolysis process of kraft cellulose. This research project showed that prehydrolyzate and sulfuric acid prehydrolysis of kraft pulp improved Fock reactivity compared to water prehydrolysis under similar pulping conditions.
Acid-based prehydrolysis kraft cooking provided lower pentosan and extractive content, but lower viscosity values. Meanwhile, the prehydrolyzate kraft pulp had the intermediate values between water and sulfuric acid prehydrolysis kraft pulping. Moreover, Eucalyptus hybrids before hydrolysis kraft pulping had higher Fock reactivity, lower pentosan content, lower extractants and higher viscosity than Acacia crassicarpa.
INTRODUCTION
Research questions
What is the difference between the wood chemical composition of Acacia crassicarpa and Eucalyptus hybrids. What is the difference between the pulp quality of Acacia crassicarpa and eucalyptus hybrids during water prehydrolysis, sulfuric acid prehydrolysis and prehydrolyzate prehydrolysis. Can the reactivity of PHK pulp from Acacia crassicarpa and Eucalyptus hybrids be improved using sulfuric acid and prehydrolyzate prehydrolysis?
BACKGROUND
Hardwood
- Celluloses
- Hardwood Hemicelluloses
- Hardwood Lignin
- Extractives
Celluloses are the most abundant polysaccharides in lignocellulosic biomass, which make up about 40-50% of the wood. The glucose residues are rotated 180o towards each other, creating the repeating unit in cellulose as a cellobiose residue instead of a glucose residue as shown in Figure 2. Hemicelluloses are one of the main components of wood, which is about 20-35% of the wood.
Different hemicelluloses and concentrations can be found in softwood and hardwood, the most abundant hemicellulose in hardwood is glucuronoxylan, usually found between 15-35%, followed by a small amount (2-5%) of glucomannan in wood. In terms of reactivity, both acetyl groups in glucuronoxylan and glucomannans are readily cleaved by alkali to form acetate. Unlike cellulose and hemicellulose, lignin is considered as a network structure, as shown in Figure 5.
Prehydrolysis Kraft pulp
The prehydrolysis liberates organic acids (eg acetic and formic acid) from the xylan which selectively hydrolyze the glycosidic bonds of hemicellulose to produce water-soluble carbohydrates. Addition of mineral acid catalyst will significantly increase the rate of solubilization of the xylan, which is usually applied for wood saccharification, to emphasize the yield and quality of the released sugars. Pre-hydrolysis with aqueous solution of 0.4% sulfuric acid at 170oC gave a higher yield of monomeric xylose compared to pure water hydrolysis (Springer & Harris, 1982).
Pre-hydrolysis is influenced by the wood sources, liquor to wood ratio, and also temperature and time (P-factor) with constant steam pressure. An increasing liquor-to-wood ratio improves solubility of xylan degradation products (Sixta, Potthast, & Krotschek, 2006). A prehydrolysis factor called P-Factor was also proposed by Brasch and Free to control the prehydrolysis step (Brasch & Free, 1964).
Using the same principle as the H factor, Lin applied an activation energy to the cleavage of glycosidic bonds of the carbohydrates in wood (Lin, 1979). After the wood chips are pre-hydrolyzed, they will undergo power cooking where delignification occurs, before further delignification in oxygen delignification and bleaching to increase and stabilize brightness. Currently, there is no commercial exploitation and economically feasible separation of the prehydrolyzate's valuable carbohydrates and acid compounds (Sixta, Potthast, & Krotschek, 2006).
Kraft dissolving pulp of Acacia mangium with prehydrolysis of pH 4 using sulfuric acid gave the highest yield of a-cellulose, lowest hemicellulose and ash content compared to pH 7 and 10 (Siagi, S, T, & Purba, 1989). The prehydrolysis temperature or sulfuric acid concentration can improve the α-cellulose content and reduce the pulp yield, kappa number and viscosity (Jahan, 2009). Prehydrolysis of Eucalyptus globulus with sulfuric acid reduced treatment temperatures and provided better selectivity in hemicellulose removal at 80% wood yield than regular autohydrolysis (Gutsch, Nousiainen, & Sixta, 2012).
Furthermore, for bagasse solution pulp, where the prehydrolysis was carried out with 0.1% sulfuric acid dosage at 150oC for 90 minutes, pentosan reduced by 14.49% and increased cellulose content by 18.45% (Zheng, Li, Jiang, & Cheng, 2014).
Cellulose Reactivity
EXPERIMENTAL
Raw Materials
- Hardwood Chips
- Chemicals
Experiments
- Prehydrolysis Kraft cooking
- Oxygen Delignification
- Bleaching
12 When the reaction was complete, the autoclaves were allowed to cool and the slurry was carefully washed with deionized water until the filtrate was clear and the pH was neutral. Unbleached kraft pulp was subjected to elemental chlorine-free bleaching (ECF) with the sequence D0-(EP)-D1. After each bleaching step, the pulp was thoroughly washed with deionized water until the filtrate was clear and the pH was neutral.
Fock reactivity, α-cellulose, pentosan, extractives and ash content were also determined for the final bleached pre-hydrolyzed kraft cellulose.
Wood and Pulp Characterization
- Holocellulose
- a-cellulose
- Pentosan
- Extractives
- Carbohydrates and Lignin
- Ash
- Syringyl/Guaiacyl (S/G) ratio
- Pulp hand sheet
- Kappa Number
- Pulp intrinsic viscosity
- Brightness
- Fock Reactivity
When the cellulose was completely dispersed, a volume of 25 ml of 17.5% sodium hydroxide was added and the magnetic stirrer was rinsed. The amount of 25 mL of filtrate was transferred to a 250 mL Erlenmeyer flask with the addition of 10 mL of 0.5 N potassium dichromate. A quantity of 50 mL of concentrated sulfuric acid was slowly added while rotating the flask.
An amount of test sample as shown in Table 2 was placed in the flask. After distillation for 90 ± 5 minutes, a volume of 225 ± 10 ml of distillate was collected and brought to room temperature. After the distillate was diluted in 250 ml with 3.85 N hydrochloric acid, a 5 ml amount of the distillate was pipetted into a 50 ml volumetric flask and mixed with 25 ml of orcinol reagent.
At the beginning, an amount of 150 ml of dichloromethane was used, which was followed the next day by 150 ml of a mixture of ethanol:acetone (1:2). An amount of 20 g of 60-mesh Wiley-ground wood powder was extracted with a Soxhlet extractor using acetone. The cellulose solution was mixed well and the desired amount of g of the cellulose solution was transferred to the hand sheet former to form the hand sheet.
An amount of 25 ml of deionized water and 10 pieces of copper wire were added to the solution bottle. Then, an amount of 25 ml of cupri-ethylenediamine solution was added and the remaining air was expelled by squeezing the bottle. An amount of 10 ml of 1 N potassium dichromate was added to the flask and the mixture was refluxed for 1 hour to completely oxidize the regenerated cellulose.
An amount of 40 ml of solution was transferred to a 250 ml Erlenmeyer flask and 5 ml of potassium iodide (10% w/w) was added.
RESULTS AND DISCUSSION
- Wood chemical composition
- Prehydrolysis kraft cooking results
- Oxygen delignification and bleaching results
- Prehydrolysis kraft pulp results
Prehydrolysis kraft cooking was performed using prehydrolyzate and sulfuric acid in two different concentrations compared to water prehydrolysis as the references to observe the pulp quality impacts. The pulp quality of different prehydrolysis kraft cooking during experiments can be seen in Figure 7. Effect of prehydrolysis kraft cooking using prehydrolyzate and sulfuric acid (a) screened pulp yield, (b) pentosan, (c) intrinsic viscosity, (d) kappa number, ( e) clarity, (f) pH starting pre-hydrolysis.
From Figure 7(a) it can be seen that both prehydrolysis kraft pulping using prehydrolyzate and sulfuric acid had lower sieved pulp yields compared to water prehydrolysis; the yield was more severely reduced with sulfuric acid than with prehydrolyzate-prehydrolysis-kraft pulping. From Figure 7(b), it can be seen that both prehydrolysis kraft pulping using prehydrolyzate and sulfuric acid benefited more pentosan removal due to the higher acidity during prehydrolysis. Taking into account the pulping results of pentosan, the viscosity and sieved pulp yield compared with water prehydrolysis kraft pulp as reference pulp, prehydrolyzate 10% (v/v) and sulfuric acid 0.1% OD prehydrolysis kraft pulp were considered to have sufficient pulp quality for processing in fully deligitized and bleached pulps for determining Fock reactivity and other important dissolving pulp qualities.
After pre-hydrolysis kraft cooking, the brown pulp was further processed using oxygen delignification and D0-EP-D1 bleaching series to achieve brightness values of 89%. The brightness of each sample at each stage increased accordingly in fairly similar range in Figure 9, but there was a slightly lower brightness increase during O and D0 stages for prehydrolyzate and sulfuric acid prehydrolysis kraft pulp. Kappa number of Acacia crassicarpa and Eucalyptus hybrids for water prehydrolysis, prehydrolyzate and sulfuric acid during OD0EPD1 stages.
Prehydrolysis kraft pulp generally has a very high α-cellulose content (>90%) with a low hemicellulose content (3 to 6%), a trace amount of lignin and other impurities (Sixta, Potthast, & Krotschek, 2006). DCM extracts were slightly lower in sulfuric acid and prehydrolysis kraft pulp compared to water prehydrolysis kraft pulp. In this study, sulfuric acid prehydrolysis kraft pulping increased Fock reactivity about 60% for eucalyptus hybrids and 15% for acacia crassicarpa.
Overall, acid pre-hydrolyzed eucalyptus kraft pulp showed interesting Fock reactivity results with lower screened pulp yield, but further investigation into the reasons for the improvement in Fock reactivity as well as the yield improvements is needed.
CONCLUSIONS
FUTURE WORK
ACKNOWLEDGEMENT
Outlook for the Global Wood Pulp Industry China still dominates the global market despite a trade war. Retrieved from Intrado Globe Newswire: https://www.globenewswire.com/news-release en/Global-Dissolving-Wood-Pulp-Industry-Outlook China-Still-Dominates-the-Global-Market-Despite-a-Trade- War.html Gutsch, J. Impact of within-family variation on the growth superiority of improved seeds of Eucalyptus pellita observed in genetic gain studies.
Estimates of genetic parameters for growth and wood traits in Eucalyptus pellita F.Muell to support tree breeding in Vietnam. Behavior of different single-component endoglucanases on the accessibility and reactivity of soluble grade cellulose for the viscous process. Studies on the effect of pre-hydrolysis and amine in the cooking liquid on the production of dissolved cellulose from jute (Corchorus capsularis).
Methods to increase the reactivity of dissolving pulp in the viscose rayon production process: a review. Chemical properties and fiber dimension of Eucalyptus pellita from 2nd generation progeny tests in Pelaihari, South Borneo, Indonesia. A process for improving the availability and reactivity of kraft dissolving hardwood pulp for viscose rayon production by cellulase treatment.
Paper, board and brick - Measurement of blue diffuse reflectance factor - Part 1: Indoor daylight conditions (ISO brightness).
APPENDIX
