Guang Wei Sun

Structural changes of poplar wood lignin after supercritical pretreatment using carbon dioxide and ethanol–water as co-solvents

To delineate the structural changes of lignin during supercritical carbon dioxide pretreatment with ethanol–water as co-solvents (SCEP), enzymatic hydrolysis lignin (EHL) in original poplar chips, residual lignin in SCEP pretreated residues (SCEP-RL) and lignin dissolved in the SCEP liquors (SCEP-DL) were sequentially isolated and systematically characterized by GPC, quantitative 13C-NMR, 31P-NMR, 2D-HSQC NMR and TGA. After SCEP process, 19.2% of lignin was degraded and dissolved into SCEP liquors, while 4.8% of lignin was still present in the pretreated residues. It was also convinced that parts of the β-O-4 aryl ether linkages were cleaved and some of the stilbene, resinol (β–β) and phenylcoumaran (β-5) units were increased during SCEP process. Furthermore, the contents of free phenolic hydroxyl groups and carboxylic acids in SCEP-RL and SCEP-DL were higher than that of EHL.

Depolymerization of Lignin with Supercritical Fluids: A Review

Biomass has attracted keen interest as a renewable resource and an environmental friendly material that is essential to realize a sustainable world. Lignin as biomass has been long labeled with waste material. But now the innate chemistry of lignin and a phenolic heteropolymer, has allowed it to make inroads into the high value polymer and natural biomass material industries. Supercritical fluids (SCF) have been shown to be a promising technique for future large-scale biofuel and base-chemicals production, especially for depolymerization production from lignin. This paper reviews the research progress of lignin-depolymerization processes, including effects of process parameters, such as reaction time, temperature, pressure and catalyst, product analysis, and reaction mechanism with different supercritical fluids. The problems of depolymerization with supercritical fluid technology and its development direction are also briefly discussed. Compared with conventional lignin production methods, the SCF technology processes of lignin can produce smaller fragments through breakage of the ether linkages and produce larger fragments through cross linking between the reactive fragments, and the depolymerization lignin processes are typically conducted at mild operating conditions, and the monomeric products have a high economic value because the aromatic products can be readily blended into current transportation fuels or used in chemical industry.

Extraction of Hemicellulose from Corn Stover by KOH Solution Pretreatment and its Characterization

In this work, hemicellulose was extracted from corn stover by pretreatment with potassium hydroxide (KOH) solution, and the influences of pretreatment conditions on hemicellulose extraction were investigated. The dissolution rate of xylan from the raw material was used to indicate the extraction yield of the hemicellulose. The results showed that under the conditions of temperature 85 °C, alkali concentration 6%, liquor/solid ratio 8:1 and time 120 min, high xylan extraction yield of 43.74% (based on the xylose content of raw material) was achieved. The content of saccharides and uronic acids in the hemicellulose was 80.22%. The hemicellulose was characterized by FT-IR and TG/DTG after being separated from the hydrolysates by precipitation of the neutralized hydrolysate with 3 times volumes of ethanol.

The optimum delignification conditions and delignification course during the pretreatment process of poplar kraft pluping with green liquor pretreatment

In this paper, optimal pretreatment conditions were obtained by investigating the influences of temperature, time and green liquor doses on delignification during pretreatment stage in poplar green liquor pretreatment-Kraft pulping process with orthogonal experiments firstly. Then delignification course during pretreatment stage was obtained by conditional experiments after orthogonal experiments. Finally reaction course was analyzed by the changes of OH- and HS- in the pretreatment liquor. The results showed that the optimal conditions of delignification were as follows: maximum temperature, 120°C; green liquor dose, 1L/kg; holding time, 1h; liquor ratio, 1:4. The delignification process had three periods, which were the initial delignification stage, mass delignification stage and residual delignification stage. During the pretreatment the main function of NaOH was to open the channels for ion penetration, and provided suitable environment for the reaction between HS- and lignin. The main function of HS- was to react with lignin molecular and made it dissolvable after fragmentation.

Study on TCF Bleaching of Reed Displacement Cooking Pulp

With the improvement of environmental protection requirements, paper-making enterprises are imperative to eliminate pollution directly in production. This paper aims to adopt environment-friendly bleaching method, yield good quality pulp products. Op-Pa-P bleaching process of reed displacement cooking pulp is studied in this paper (O-oxygen, P-hydrogen peroxide, Pa-peracetic acid ). The experimental conditions of Op and Pa stage were optimized respectively. It included oxygen pressure, temperature, time in Op stage and charge of peracetic acid, temperature, time in Pa stage. The results show that the optimal technological conditions of Op are: 0.9Mpa, 100°C, 70min, Op stage can make brightness increase by 57.3%, viscosity decrease by 25% and KMnO4 number reduce to 2.6. Pa stage optimal conditions are Pa charge 1.5%, 70°C, 75min, brightness reached to 79.1 %ISO, KMnO4 number to 1.0, viscosity to 631mL.g-1. The brightness of P bleached pulp reached to 84.8%ISO, viscosity 601 mL.g-1, KMnO4 number 0.8.

Comparison between Green Liquor Pretreatment-Kraft Pulping and Conventional Kraft Pulping

This paper studied the differences of pulping performances, beating characteristics and strength properties between green liquor pretreatment-Kraft pulping and conventional Kraft pulping based on previous optimized pulping conditions. The green liquor pretreatment-Kraft pulping has higher yield, lower Kappa number, reduced residual effective alkali and decreased viscosity. Green liquor pretreatment improves pulp strength properties although green liquor pretreatment-Kraft pulp has beating characteristics similar to conventional Kraft pulp.

Reed Soda Pulping Modified by Green Liquor Pretreatment

The soda pulping modified by green liquor pretreatment was adopted to explore optimal green liquor pretreatment conditions. Results shows that optimum pretreatment conditions are as follows: max temperature, 130°C; holding time, 90min; wood to liquor ratio, 1:4; and green liquor charge, 0.9L/kg. Pretreated reed was pulped under following conditions: heating-up time, 60min; maximum temperature, 160°C; holding time, 60min; NaOH charge, 20% (pretreatment alkali included). Results shows that this process produces pulp with screened yield of 49.05%, Kappa number of 14.6, and viscosity of 1274mL/g. Compared with the results of industrial simulation pulping (21% NaOH), screened yield increases by 2.14%, Kappa number decreases by 5.6 and viscosity rises by 556 mL/g. Therefore, green liquor pretreatment before soda pulping improves pulp performance and yield. Meanwhile the pretreatment utilizes material effectively, thus has practical significance to decrease alkaline consumption and pulping cost.

Etherifying Modification of Xylan-Type Hemicellulose and its Characterization

The reaction of the xylan-type hemicellulose with 2,3-epoxypropyltrimethylammonium chloride and acrylamide in ethanol-water-alkali slurry yielded water-soluble, cationic etherified xylan-type hemicellulose derivatives. The degree of substitution (DS) value reaches up to 0.40 by adjusting the mass ratios (NaOH/hemicellulose, total etherifying agents/hemicellulose and 2,3-epoxypropyltrimethylammonium chloride/acrylamide), the reaction temperature and the reaction time in a one-step synthesis. The etherified hemicellulose was characterized by infrared spectroscopic analysis (FT-IR), Zeta potential analysis, charge density analysis and thermogravimetric analysis (TGA). It is found that Zeta potential is promoted from-30.50mv to +35.81mv and charge density is promoted from-0.50mmol/g to +0.88mmol/g during etherification under the conditions used. The thermal stability of the etherified hemicellulose is lower than that of the unmodified xylan-type hemicellulose polymers.

Study on Pre-Hydrolysis Technology of Reed Artificial Fiber Pulp

The main materials of artificial fiber pulp are natural fiber from wood and linters etc. However, it will be more and more difficult to make this pulp in China because of the scarcity of forest resource and cotton field. Reed is widely distributed with high yield in china. Therefore, exploitation and utilization of reed in artificial fiber pulping have an important social significance. The artificial pulp made from reed was studied in this paper. The pulping method adopted pre-hydrolysis followed by Kraft cooking. The results showed that the great influence factors of pre-hydrolysis were the highest temperature and holding time. The optimal pre-hydrolysis conditions were: 175 °C, 75min, solid-to-liquid ratio 1:6. Under the conditions, semi-slurry yield was 60.8%. Compared with the chemical composition of reed materials, the pentosan decreased from 20.33% to 7.37%, the lignin decreased from 26.46% to 21.14%, ash decreased from 5.56% to 4.05%, besides the relative holocellulose increased from 75.95% to 81.26%. The dissolving pulp obtained after cooking and bleaching of semi-slurry met with pulp performance index requirement.

New Strength Agent: Corn Stalk Pulp Applied on Package Board

The feasibility of making new strength agent by cooking corn stalk rich in hemicellulose was studied. Corn stalk was cooked by normal ethanol pulping with best process parameters obtained by early discovery. The effect of corn stalk agent on physical strength of package board (made by 20% mineral fibre and 80% recycled fibre) was discussed as well. After cooked, all of the corn stalk suspension was added into the mixed pulp directly. Results showed that the package boards physical properties improved greatly. Tensile index, ring crush index, bursting index and folding index increased by 39.6%, 35.4%, 26.6% and 100% respectively at dosage of 5% while tear index and tightness changed slightly under the same conditions.