Ethanol production from steam-explosion pretreated wheat straw

Bioconversion of cereal straw to bioethanol is becoming an attractive alternative to conventional fuel ethanol production from grains. In this work, the best operational conditions for steam-explosion pretreatment of wheat straw for ethanol production by a simultaneous saccharification and fermentation process were studied, using diluted acid [H₂SO₄ 0.9% (w/w)] and water as preimpregnation agents. Acid-or water-impregnated biomass was steam-exploded at different temperatures (160–200°C) and residence times (5, 10, and 20 min). Composition of solid and filtrate obtained after pretreatment, enzymatic digestibility and ethanol production of pretreated wheat straw at different experimental conditions was analyzed. The best pretreatment conditions to obtain high conversion yield to ethanol (approx 80% of theoretical) of cellulose-rich residue after steam-explosion were 190°C and 10 min or 200°C and 5 min, in acid-impregnated straw. However, 180°C for 10 min in acid-impregnated biomass provided the highest ethanol yield referred to raw material (140 L/t wheat straw), and sugars recovery yield in the filtrate (300 g/kg wheat straw).     

Preliminary results on optimization of pilot scale pretreatment of wheat straw used in coproduction of bioethanol and electricity

The overall objective in this European Union-project is to develop cost and energy effective production systems for coproduction of bioethanol and electricity based on integrated biomass utilization. A pilot plan reactor for hydrothermal pretreatment (including weak acid hydrolysis, wet oxidation, and steam pretreatment) with a capacity of 100 kg/h was constructed and tested for pretreatment of wheat straw for ethanol production. Highest hemicellulose (C5 sugar) recovery and extraction of hemicellulose sugars was obtained at 190°C whereas highest C6 sugar yield was obtained at 200°C. Lowest toxicity of hydrolysates was observed at 190°C; however, addition of H₂O₂ improved the fermentability and sugar recoveries at the higher temperatures. The estimated total ethanol production was 223 kg/t straw assuming utilisation of both C6 and C5 during fermentation, and 0.5 g ethanol/g sugar.     

Lime pretreatment of crop residues bagasse and wheat straw

Lime (calcium hydroxide) was used as a pretreatment agent to enhance the enzymatic digestibility of two common crop residues: bagasse and wheat straw. A systematic study of pretreatment conditions suggested that for short pretreatment times (1–3 h), high temperatures (85-135°C) were required to achieve high sugar yields, whereas for long pretreatment times (e.g., 24 h), low temperatures (50–65°C) were effective. The recommended lime loading is 0.1 g Ca(OH)₂/g dry biomass. Water loading had little effect on the digestibility. Under the recommended conditions, the 3-d reducing sugar yield of the pretreated bagasse increased from 153 to 659 mg Eq glucose/g dry biomass, and that of the pretreated wheat straw increased from 65 to 650 mg Eq glucose/g dry biomass. A material balance study on bagasse showed that the biomass yield after lime pretreatment is 93.6%. No glucan or xylan was removed from bagasse by the pretreatment, whereas 14% of lignin became solubilized. A lime recovery study showed that 86% of added calcium was removed from the pretreated bagasse by ten washings and could be recovered by carbonating the wash water with CO₂ at pH 9.5.     

Plasma-Assisted Pretreatment of Wheat Straw

O₃ generated in a plasma at atmospheric pressure and room temperature, fed with dried air (or oxygen-enriched dried air), has been used for the degradation of lignin in wheat straw to optimize the enzymatic hydrolysis and to get more fermentable sugars. A fixed bed reactor was used combined with a CO₂ detector and an online technique for O₃ measurement in the fed and exhaust gas allowing continuous measurement of the consumption of O₃. This rendered it possible for us to determine the progress of the pretreatment in real time (online analysis). The process time can be adjusted to produce wheat straw with desired lignin content because of the online analysis. The O₃ consumption of wheat straw and its polymeric components, i.e., cellulose, hemicellulose, and lignin, as well as a mixture of these, dry as well as with 50% water, were studied. Furthermore, the process parameters dry matter content and milled particle size (the extent to which the wheat straw was milled) were investigated and optimized. The developed methodology offered the advantage of a simple and relatively fast (0.5–2 h) pretreatment allowing a dry matter concentration of 45–60%. FTIR measurements did not suggest any structural effects on cellulose and hemicellulose by the O₃ treatment. The cost and the energy consumption for lignin degradation of 100 g of wheat straw were calculated.     

Ensiling Agricultural Residues for Bioethanol Production

The potential of using ensiling, with and without supplemental enzymes, as a cost-effective pretreatment for bioethanol production from agricultural residues was investigated. Ensiling did not significantly affect the lignin content of barley straw, cotton stalk, and triticale hay ensiled without enzyme, but slightly increased the lignin content in triticale straw, wheat straw, and triticale hay ensiled with enzyme. The holocellulose (cellulose plus hemicellulose) losses in the feedstocks, as a result of ensiling, ranged from 1.31 to 9.93%. The percent holocellulose loss in hays during ensiling was lower than in straws and stalks. Ensiling of barley, triticale, wheat straws, and cotton stalk significantly increased the conversion of holocellulose to sugars during subsequent hydrolysis with two enzyme combinations. Enzymatic hydrolysis of ensiled and untreated feedstocks by Celluclast 1.5 L-Novozyme 188 enzyme combination resulted in equal or higher saccharification than with Spezyme CP-xylanase combination. Enzyme loadings of 40 and 60 FPU/g reducing sugars gave similar sugar yields. The percent saccharification with Celluclast 1.5 L-Novozyme 188 at 40 FPU/g reducing sugars was 17.1 to 43.6%, 22.4 to 46.9%, and 23.2 to 32.2% for untreated feedstocks, feedstocks ensiled with, and without enzymes, respectively. Fermentation of the hydrolysates from ensiled feedstocks resulted in ethanol yields ranging from 0.21 to 0.28 g/g reducing sugars.     

Evaluation and Optimization of Organic Acid Pretreatment of Cotton Gin Waste for Enzymatic Hydrolysis and Bioethanol Production

This paper investigates the efficiency of the organic acids on the pretreatment of an industrially generated cotton gin waste for the removal of lignin, thereby releasing cellulose and hemicellulose as fermentable sugar components. Cotton gin waste was pretreated with various organic acids namely lactic acid, oxalic acid, citric acid, and maleic acid. Among these, maleic acid was found to be the most efficient producing maximum xylose sugar (126.05?±?0.74 g/g) at the optimum pretreatment condition of 150 °C, 500 mM, and 45 min. The pretreatment efficiency was comparable to the conventional dilute sulfuric acid pretreatment. A lignin removal of 88% was achieved by treating maleic acid pretreated biomass in a mixture of sodium sulfite and sodium chlorite. The pretreated biomass was further evaluated for the release of sugar by enzymatic hydrolysis and subsequently bioethanol production from hydrolysates. The maximum 686.13 g/g saccharification yield was achieved with maleic acid pretreated biomass which was slightly higher than the sulfuric acid (675.26 g/g) pretreated waste. The fermentation of mixed hydrolysates(41.75 g/l) produced 18.74 g/l bioethanol concentration with 2.25 g/l/h ethanol productivity and 0.48 g/g ethanol yield using sequential use of Saccharomyces cerevisiae and Pichia stipitis yeast strains. The production of bioethanol was higher than the ethanol produced using co-culture in comparison to sequential culture. Thus, it has been demonstrated that the maleic acid pretreatment and fermentation using sequential use of yeast strains are efficient for bioethanol production from cotton gin waste.     

Potential of Agricultural Residues and Hay for Bioethanol Production

Production of bioethanol from agricultural residues and hays (wheat, barley, and triticale straws, and barley, triticale, pearl millet, and sweet sorghum hays) through a series of chemical pretreatment, enzymatic hydrolysis, and fermentation processes was investigated in this study. Composition analysis suggested that the agricultural straws and hays studied contained approximately 28.62-38.58% glucan, 11.19-20.78% xylan, and 22.01-27.57% lignin, making them good candidates for bioethanol production. Chemical pretreatment with sulfuric acid or sodium hydroxide at concentrations of 0.5, 1.0, and 2.0% indicated that concentration and treatment agent play a significant role during pretreatment. After 2.0% sulfuric acid pretreatment at 121 degrees C/15 psi for 60 min, 78.10-81.27% of the xylan in untreated feedstocks was solubilized, while 75.09-84.52% of the lignin was reduced after 2.0% sodium hydroxide pretreatment under similar conditions. Enzymatic hydrolysis of chemically pretreated (2.0% NaOH or H2SO4) solids with Celluclast 1.5 L-Novozym 188 (cellobiase) enzyme combination resulted in equal or higher glucan and xylan conversion than with Spezyme(R) CP- xylanase combination. The glucan and xylan conversions during hydrolysis with Celluclast 1.5 L-cellobiase at 40 FPU/g glucan were 78.09 to 100.36% and 74.03 to 84.89%, respectively. Increasing the enzyme loading from 40 to 60 FPU/g glucan did not significantly increase sugar yield. The ethanol yield after fermentation of the hydrolyzate from different feedstocks with Saccharomyces cerevisiae ranged from 0.27 to 0.34 g/g glucose or 52.00-65.82% of the theoretical maximum ethanol yield.     

Characterisation of degraded organosolv hemicelluloses from wheat straw

Treatment of the dewaxed wheat straw with acetic acid-H₂O (65/35, v/v), acetic acid-H₂O (80/20), acetic acid-H₂O (90/10), formic acid-acetic acid-H₂O (20/60/20), formic acid-acetic acid-H₂O (30/60/10), methanol-H₂O (60/40), and ethanol-H₂O (60/40) using 0.1% HCl as a catalyst at 85 °C for 4 h degraded 42.4, 58.7, 70.0, 65.1, 76.5, 14.2, and 22.2% of the original hemicelluloses and 78.2, 80.0, 88.2, 89.4, 94.1, 23.5, and 37.4% of the original lignin, respectively. It was found that substantial hemicelluloses and lignin were degraded during the treatment with organic acids. The optimum condition for degradation of hemicelluloses was found to use a mixture of formic acid-acetic acid-H₂O (30/60/10), which yielded 76.5% of the original hemicelluloses from wheat straw. Xylose was a major constituent in all the degraded hemicellulosic preparations. Glucose and arabinose appeared in noticeable amounts. Uronic acids, principally 4-O-methyl-d-glucuronic acid occurred in a small amount. Galactose, mannose, and rhamnose were present as minor components. In comparison, the five degraded hemicellulosic preparations isolated during the treatment with organic acids were more linear and partially acetylated, whereas the two acidic alcohol-degradable hemicelluloses were more branched. The FT-IR and liquid-state ¹³C NMR analyses revealed that the organosolv treatments under the acidic conditions substantially degraded the hemicellulosic polymers as shown by their lower molecular weights ranging between 8480 and 18,940 g mol⁻¹. The thermal stability of the hemicellulosic preparations, degraded during the aqueous organic acids, was lower than that of the hemicellulosic preparations, degraded during the aqueous alcohols.     

Ethanol/water pulps from sugar cane straw and their biobleaching with xylanase from Bacillus pumilus

The influence of independent variables (temperature and time) on the cooking of sugar cane straw with ethanol/water mixtures was studied to determine operating conditions that obtain pulp with high cellulose contents and a low lignin content. An experimental 2(2) design was applied for temperatures of 185 and 215 degrees C, and time of 1 and 2.5 h with the ethanol/water mixture concentration and constant straw-to-solvent ratio. The system was scaled-up at 200 degrees C cooking temperature for 2 h with 50% ethanol-water concentration, and 1:10 (w/v) straw-to-solvent ratio to obtain a pulp with 3.14 cP viscosity, 58.09 kappa-number, and the chemical composition of the pulps were 3.2% pentosan and 31.5% lignin. Xylanase from Bacillus pumilus was then applied at a loading of 5-150 IU/g dry pulp in the sugar cane straw ethanol/water pulp at 50 degrees C for 2 and 20 h. To ethanol/water pulps, the best enzyme dosage was found to be 20 IU/g dry pulp at 20 h, and a high enzyme dosage of 150 IU/g dry pulp did not decrease the kappa-number of the pulp.     

Comparison of Different Pretreatment Strategies for Enzymatic Hydrolysis of Wheat and Barley Straw

In biomass-to-ethanol processes a physico-chemical pretreatment of the lignocellulosic biomass is a critical requirement for enhancing the accessibility of the cellulose substrate to enzymatic attack. This report evaluates the efficacy on barley and wheat straw of three different pretreatment procedures: acid or water impregnation followed by steam explosion versus hot water extraction. The pretreatments were compared after enzyme treatment using a cellulase enzyme system, Celluclast 1.5 L from Trichoderma reesei, and a beta-glucosidase, Novozyme 188 from Aspergillus niger. Barley straw generally produced higher glucose concentrations after enzymatic hydrolysis than wheat straw. Acid or water impregnation followed by steam explosion of barley straw was the best pretreatment in terms of resulting glucose concentration in the liquid hydrolysate after enzymatic hydrolysis. When the glucose concentrations obtained after enzymatic hydrolyses were related to the potential glucose present in the pretreated residues, the highest yield, approximately 48% (g g-1), was obtained with hot water extraction pretreatment of barley straw; this pretreatment also produced highest yields for wheat straw, producing a glucose yield of approximately 39% (g g-1). Addition of extra enzyme (Celluclast 1.5 L+Novozyme 188) during enzymatic hydrolysis resulted in the highest total glucose concentrations from barley straw, 32-39 g L-1, but the relative increases in glucose yields were higher on wheat straw than on barley straw. Maldi-TOF MS analyses of supernatants of pretreated barley and wheat straw samples subjected to acid and water impregnation, respectively, and steam explosion, revealed that the water impregnated + steam-exploded samples gave a wider range of pentose oligomers than the corresponding acid-impregnated samples.     

Fermentation of Biologically Pretreated Wheat Straw for Ethanol Production: Comparison of Fermentative Microorganisms and Process Configurations

The pretreatment of lignocellulosic biomass with white-rot fungi to produce bioethanol is an environmentally friendly alternative to the commonly used physico-chemical processes. After biological pretreatment, a solid substrate composed of cellulose, hemicellulose and lignin, the two latter with a composition lower than that of the initial substrate, is obtained. In this study, six microorganisms and four process configurations were utilised to ferment a hydrolysate obtained from wheat straw pretreated with the white-rot fungus Irpex lacteus. To enhance total sugars utilisation, five of these microorganisms are able to metabolise, in addition to glucose, most of the pentoses obtained after the hydrolysis of wheat straw by the application of a mixture of hemicellulolytic and cellulolytic enzymes. The highest overall ethanol yield was obtained with the yeast Pachysolen tannophilus. Its application in combination with the best process configuration yielded 163 mg ethanol per gram of raw wheat straw, which was between 23 and 35 % greater than the yields typically obtained with a conventional bioethanol process, in which wheat straw is pretreated using steam explosion and fermented with the yeast Saccharomyces cerevisiae.     

Xylanase and Ultrasound Assisted Pulping of Wheat Straw

In the present work, a novel approach to pretreat wheat straw pulping was investigated with ultrasound and xylanase to achieve maximum reduction in lignin content. Sequential xylanase pretreatment and alkaline pulping was found to reduce kappa number by 0.31 to 4.84?% compared with only alkaline pulping alone at different pulping conditions. Although Klason lignin of ultrasound-treated straw was found to be 7.37?% less compared with untreated straw, sequential ultrasound pretreatment and alkaline pulping could not show any significant reduction in kappa number compared with alkaline pulping alone. Also, sequential xylanase and ultrasound pretreatment could not show any significant reduction in kappa number. Total yield of the pulp was found to be less in ultrasound-assisted processing compared with both alkaline pulping alone and sequential xylanase pretreatment and alkaline pulping.     

High solids simultaneous saccharification and fermentation of pretreated wheat straw to ethanol

Wheat straw was pretreated with dilute (0.5%) sulfuric acid at 140°C for 1 h. Pretreated straw solids were washed with deionized water to neutrality and then stored frozen at –20°C. The approximate composition of the pretreated straw solids was 64% cellulose, 33% lignin, and 2% xylan. The cellulose in the pretreated wheat straw solids was converted to ethanol in batch simultaneous saccharification and fermentation experiments at 37°C using cellulase enzyme fromTrichoderma reesei (Genencor 150 L) with or without supplementation with β–glucosidase fromAspergillus niger (Novozyme 188) to produce glucose sugar and the yeastSaccharomyces cerevisiae to ferment the glucose into ethanol. The initial cellulose concentrations were adjusted to 7.5, 10, 12.5, 15, 17.5, and 20% (w/w). Since wheat straw particles do not form slurries at these concentrations and cannot be mixed with conventional impeller mixers used in laboratory fermenters, a simple rotary fermenter was designed and fabricated for these experiments. The results of the simultaneous saccharification and fermentation (SSF) experiments indicate that the cellulose in pretreated wheat straw can be efficiently fermented into ethanol for up to a 15% cellulose concentration (24.4% straw concentration).     

Fungal Pretreatment by Phanerochaete chrysosporium for Enhancement of Biogas Production from Corn Stover Silage

Corn stover silage (CSS) was pretreated by Phanerochaete chrysosporium in solid-state fermentation (SSF), to enhance methane production via subsequent anaerobic digestion (AD). Effects of washing of corn stover silage (WCSS) on the lignocellulosic biodegradability in the fungal pretreatment step and on methane production in the AD step were investigated with comparison to the CSS. It was found that P. chrysosporium had the degradation of cellulose, hemicellulose, and lignin of CSS up to 19.9, 32.4, and 22.6 %, respectively. Consequently, CSS pretreated by 25 days achieved the highest methane yield of 265.1 mL/g volatile solid (VS), which was 23.0 % higher than the untreated CSS. However, the degradation of cellulose, hemicellulose, and lignin in WCSS after 30 days of SSF increased to 45.9, 48.4, and 39.0 %, respectively. Surface morphology and Fourier-transform infrared spectroscopy analyses also demonstrated that the WCSS improved degradation of cell wall components during SSF. Correspondingly, the pretreatment of WCSS improved methane production by 19.6 to 32.6 %, as compared with untreated CSS. Hence, washing and reducing organic acids (such as lactic acid, acetic acid, propionic acid, and butyric acid) present in CSS has been proven to further improve biodegradability in SSF and methane production in the AD step.     

The enzymatic hydrolysis of pretreated agricultural residues and the fermentation of the liberated sugars to ethanol

Agricultural residues were pretreated by steam explosion and the cellulosic component of these substrates were converted to ethanol using a combined enzymatic hydrolysis and fermentation (CHF) process. The enzymatic hydrolysis was carried out using culture filtrates ofTrichoderma harzianum E58 while the liberated sugars were fermented to ethanol byS. cerevisiae. Initially, pretreatment conditions were optimized to ensure that the substrates were readily hydrolyzed and fermented. The agricultural residues were steamed for various times between 30 and 120 s at approximately 240‡C prior to rapid decompression (explosion) in a small masonite-type gun. The various substrates were selectively extracted by water and alkali to see whether the enzymatic hydrolysis and fermentability of the substrates were enhanced. A comparison between the overall conversion of wheat and barley straw was made since these are the two most readily available agricultural residues in Canada. Steam explosion did not affect the hexosan content of the residues, although the pentosan content of the substrates decreased with increasing duration of steaming. The hexosan (cellulose) content of wheat straw was 50.7% of the total substrate while a slightly higher 52.9% cellulose content was detected in the barley straw. Wheat straw was more efficiently hydrolyzed after it had been steamed for 90 s while optimum hydrolysis of the barley straw was detected after 60 s. Steam exploded wheat and barley straw that was subsequently extracted with water was readily hydrolyzed to their component sugars.S. cerevisiae could almost quantitatively convert these sugars to ethanol. This indicated that water washing not only enhanced the enzymatic hydrolysis of the steam exploded substrates, it also removed inhibitory material that restricted the growth of S.cerevisiae. Maximum hydrolysis (78.5%) and ethanol yields (10 mg/mL) were obtained when wheat straw was steamed for 90 s. Slightly lower hydrolysis (76.0%) and ethanol yields (9.5 mg/mL) were obtained with barley straw that had been steamed for 120 s.     

Evaluation and Characterization of Forage Sorghum as Feedstock for Fermentable Sugar Production

Sorghum is a tropical grass grown primarily in semiarid and drier parts of the world, especially areas too dry for corn. Sorghum production also leaves about 58 million tons of by-products composed mainly of cellulose, hemicellulose, and lignin. The low lignin content of some forage sorghums such as brown midrib makes them more digestible for ethanol production. Successful use of biomass for biofuel production depends on not only pretreatment methods and efficient processing conditions but also physical and chemical properties of the biomass. In this study, four varieties of forage sorghum (stems and leaves) were characterized and evaluated as feedstock for fermentable sugar production. Fourier transform infrared spectroscopy and X-ray diffraction were used to determine changes in structure and chemical composition of forage sorghum before and after pretreatment and the enzymatic hydrolysis process. Forage sorghums with a low syringyl/guaiacyl ratio in their lignin structure were easy to hydrolyze after pretreatment despite the initial lignin content. Enzymatic hydrolysis was also more effective for forage sorghums with a low crystallinity index and easily transformed crystalline cellulose to amorphous cellulose, despite initial cellulose content. Up to 72% hexose yield and 94% pentose yield were obtained using modified steam explosion with 2% sulfuric acid at 140 °C for 30 min and enzymatic hydrolysis with cellulase (15 filter per unit (FPU)/g cellulose) and β-glucosidase (50 cellobiose units (CBU)/g cellulose).     

Enhanced Enzymatic Saccharification of Barley Straw Pretreated by Ethanosolv Technology

The fermentable sugars in lignocellulosic biomass are derived from cellulose and hemicellulose, which are not readily accessible to enzymatic saccharification because of their recalcitrance. An ethanosolv pretreatment method was applied for the enzymatic saccharification of barley straw with an inorganic acid. The effects of four process variables (temperature, time, catalyst dose, and ethanol concentration) on the barley straw pretreatment were analyzed over a broad range using a small composite design and a response surface methodology. The yield of the residual solid and composition of the solid fraction differed as ethanosolv conditions varied within the experimental range. A glucan recovery, xylan recovery, and delignification were 85%, 14%, and 69% at center point conditions (170°C, 60 min, 1.0% (w/w) H₂SO₄, and 50% (w/w) ethanol), respectively. Ethanosolv pretreatment removed lignin effectively. Additionally, the highest enzymatic digestibility of 85.3% was obtained after 72 h at center point conditions.     

Biodegradation of cotton straw byPleutorus florida

Cotton straw is an unutilized waste product containing 25% lignin, thus making it unsuitable for use as animal feed. This material was found to be an excellent substrate for the growth of the edible mushroomPleurotus florida. A growth-promoting flavonoid was isolated from the water-soluble fraction of the straw (Platt et al., 1983). After 3 wk of fungal growth on native cotton straw, an 18% decrease in dry weight occurred. Lignin (insoluble in 72% H₂SO₄) was degraded from the 8th d of growth up to a total of 65% of the original content after 21 d. Prior to lignin degradation, sugars and other water-soluble materials were removed and laccase activity (substrate, 2,6-dimethoxyphenol) was detected. This activity disappeared after the eighth day of growth. In all our experiments it appears that laccase activity precedes the onset of lignin degradation. Cellulase activity reached a maximum after 8 d of fungal growth and immediately disappeared. Total fungal activity was estimated by measuring hydrolysis of fluorescein diacetate (FDA), which indicated a gradual increase during the first 8 d and then reached a plateau. Release of glucose from the straw by commercial cellulase increased with duration of fungal growth from 28 (Μ/g/h^-1 to 250 Μg/g/h^-1. These results are corroborated by information from artificial rumen experiments showing an increase of in vitro dry matter digestability from 26 to 38%. In comparison, on washed straw, FDA and laccase activity was three-fold smaller. Final dry weight reduction was 10.1%, while total lignin loss was only 33% of the original lignin content. It seems that the water-soluble materials are responsible for the rapid growth, increased enzymatic activity, and total degradation of cotton straw byP. florida.     

碱木质素超/亚临界乙醇体系解聚机理研究

采用微型高温高压反应釜,在超/亚临界乙醇体系,进行麦草碱木质素的解聚实验,通过扫描电子显微镜(SEM)、气相色谱/质谱联用仪(GC/MS)及红外光谱仪(FT-IR)对解聚产物进行分析,探讨大分子结构的解聚机理。结果表明,碱木质素在乙醇临界点条件(240℃,7.2 MPa)解聚获得最低残焦得率,数值为16.5%。碱木质素在亚临界乙醇体系解聚过程,碱木质素熔融形成直径1.0-2.0μm的微球分散于乙醇中,结构单体间少量醚键和苯环侧链Cα均裂断裂,形成酚类、酯类、酮类和酸类产物;碱木质素在超临界乙醇体系解聚过程,熔融微球直径明显缩小,解聚时发生大量结构单体间醚键、苯环侧链Cα断裂及酯类产物的二次分解反应,解聚产物中酯类产物含量(11.94%)降低,酚类产物得率(52.14%)提高。     

Pyrolytic behaviour of different biomasses (angiosperms) (maize plants,straws, and wood) in low temperature pyrolysis

The thermal degradation of agricultural products and by-products (two kinds of maize plants, wheat, and barley straw) has been investigated by means of thermogravimetric/mass spectrometric analysis at heating rates from 1 to 10 °C/min. Large differences were found in the pyrolytic behaviour of the untreated samples, mainly caused by the high content of inorganics (ash content of about 4–6 wt%). These differences could be reduced by washing the samples with cold water. A kinetic model based on the formal kinetic parameters for the pyrolysis of the main components (hemicelluloses, lignin, and cellulose) and their degradable amounts was applied. To reduce the complexity of the model, only largely ash reduced samples were used. The formal kinetic parameters for the main components of barley straw and Gavott were individually determined. Although, different monomeric lignin degradation products were found for the angiosperms of grassy biomass in comparison to woody biomass, the formal kinetic parameters for lignin degradation are similar. The transferability of the formal kinetic parameters was successfully tested by applying them to a different straw type (wheat) and to a different maize cultivar (Doge) using the results of the biochemical analysis for the main components (hemicelluloses, lignin, and cellulose).