汽爆秸秆漆酶协同作用提取木质素

组分分离是秸秆炼制的关键技术。本文建立了汽爆耦合漆酶协同作用工艺,研究其对秸秆物理形态、化学组成以及木质素碱提取过程的影响。研究结果表明汽爆破坏秸秆表面致密结构,提高比表面积,促进漆酶对秸秆木质素的氧化作用;红外分析表明,漆酶破坏了汽爆秸秆中半纤维素酯键,且愈创木基吸收峰减弱,漆酶削弱了木质素与纤维素间相互作用;汽爆漆酶协同作用后的秸秆木质素提取率提高约20%(70℃,120 min)。Nuclei Growth模型分析温和条件下秸秆木质素提取过程,动力学结果表明,汽爆漆酶协同预处理增加了汽爆秸秆木质素碱提过程中反应起始作用位点,并提高了该过程对温度的敏感性。汽爆-漆酶协同预处理是一种有效的分离木质素的方法,将在木质纤维素原料的生物炼制中发挥重要作用。     

Characteristics of degraded cellulose obtained from steam-exploded wheat straw

The isolation of cellulose from wheat straw was studied using a two-stage process based on steam explosion pre-treatment followed by alkaline peroxide post-treatment. Straw was steamed at 200 degrees C, 15 bar for 10 and 33 min, and 220 degrees C, 22 bar for 3, 5 and 8 min with a solid to liquid ratio of 2:1 (w/w) and 220 degrees C, 22 bar for 5 min with a solid to liquid ratio of 10:1, respectively. The steamed straw was washed with hot water to yield a solution rich in hemicelluloses-derived mono- and oligosaccharides and gave 61.3%, 60.2%, 66.2%, 63.1%, 60.3% and 61.3% of the straw residue, respectively. The washed fibre was delignified and bleached by 2% H2O2 at 50 degrees C for 5 h under pH 11.5, which yielded 34.9%, 32.6%, 40.0%, 36.9%, 30.9% and 36.1% (% dry wheat straw) of the cellulose preparation, respectively. The optimum cellulose yield (40.0%) was obtained when the steam explosion pre-treatment was performed at 220 degrees C, 22 bar for 3 min with a solid to liquid ratio of 2:1, in which the cellulose fraction obtained had a viscosity average degree of polymerisation of 587 and contained 14.6% hemicelluloses and 1.2% klason lignin. The steam explosion pre-treatment led to a significant loss in hemicelluloses and alkaline peroxide post-treatment resulted in substantial dissolution of lignin and an increase in cellulose crystallinity. The six isolated cellulose samples were further characterised by FT-IR and 13C-CP/MAS NMR spectroscopy and thermal analysis.     

Unpolluted fractionation of wheat straw by steam explosion and ethanol extraction

An unpolluted process of wheat straw fractionation by steam explosion coupled with ethanol extraction was studied. The wheat straw was steam exploded for 4.5 min with moisture of 34.01%, a pressure of 1.5 MPa without acid or alkali. Hemicellulose sugars were recovered by water countercurrent extraction and decolored with chelating ion exchange resin D412. The gas chromatography (GC) and high-performance liquid chromatography (HPLC) analysis results indicated that there were organic acids in the hemicellulose sugars and the ratio of monosaccharides to oligosaccharides was 1:9 and the main component, xylose, was 85.9% in content. The total recovery rate of hemicellulose was 80%. Water washed materials were subsequently extracted with ethanol. The optimum extraction conditions in this work were 40% ethanol, fiber/liquor ratio 1:50 (w/v), severity log(R)=3.657 (180 degrees C for 20 min), 0.1% NaOH. The lignin yield was 75% by acid precipitation and 85% ethanol solvent was recovered. The lignin was purified using Bj?rkman method. Infrared spectrometry (IR) results indicated that the lignin belonged to GSH (guaiacyl (G) syringyl (S) and p-hydroxyphenyl (H)) lignin and its purity rate reached 85.3%. The cellulose recovery rate was 94% and the results of electron spectroscopy for chemical analysis (ESCA) and infrared spectrometry (IR) showed that hemicellulose and lignin content decreased after steam explosion and ethanol extraction.     

Pretreatment efficiency and structural characterization of rice straw by an integrated process of dilute-acid and steam explosion for bioethanol production

The combined pretreatment of rice straw using dilute-acid and steam explosion followed by enzymatic hydrolysis was investigated and compared with acid-catalyzed steam explosion pretreatment. In addition to measuring the chemical composition, including glucan, xylan and lignin content, changes in rice straw features after pretreatment were investigated in terms of the straw's physical properties. These properties included crystallinity, surface area, mean particle size and scanning electron microscopy imagery. The effect of acid concentration on the acid-catalyzed steam explosion was studied in a range between 1% and 15% acid at 180°C for 2 min. We also investigated the influence of the residence time of the steam explosion in the combined pretreatment and the optimum conditions for the dilute-acid hydrolysis step in order to develop an integrated process for the dilute-acid and steam explosion. The optimum operational conditions for the first dilute-acid hydrolysis step were determined to be 165°C for 2 min with 2% H(2)SO(4) and for the second steam explosion step was to be carried out at 180°C for 20 min; this gave the most favorable combination in terms of an integrated process. We found that rice straw pretreated by the dilute-acid/steam explosions had a higher xylose yield, a lower level of inhibitor in the hydrolysate and a greater degree of enzymatic hydrolysis; this resulted in a 1.5-fold increase in the overall sugar yield when compared to the acid-catalyzed steam explosion.     

Cellulase production from the corn stover fraction based on the organ and tissue

In this study, the biodegradation of fractionated corn stover in solid-state fermentation by Trichoderma reesei YG3 was investigated. Fractions of miscellaneous cells (MC) and fasciculi (FC) tissue from leaf, shell or core were separated using the combined pretreatment method of carding classification after steam explosion. The highest enzyme activities including the filter paper activity, endoglucanase, exoglucanase and β-glucosidase activities, weight loss rate of dry material and biodegradation rate were all observed in the MC tissue fraction from the leaf, which was more nutritious, while lowest activity was observed in the FC tissue fraction from the shell. The maximum filter paper activity and weight loss rate of the dry material were 4.56 and 1.89 times the minimum and the cellulose and hemicellulose biodegradation rates were 51.22 and 39.38% versus 23.85 and 26.51%, respectively. These variances maybe attributed to the heterogeneity of the component in the fractions. A higher weight loss rate corresponded to higher enzymatic activities, whereas cellulose biodegradation was not proportional to cellulase activities. Hemicellulose biodegradation was much slower than cellulose degradation. Here, we demonstrated the importance of fractionation in component biodegradation and utilization of straw.     

Solid-state production of biopulp by Phanerochaete chrysosporium using steam-exploded wheat straw as substrate.

A novel material for biopulp-making, steam-exploded wheat straw (SEWS), was studied. During the steam explosion process, the hemicellulose was partly degraded and became water-soluble sugar as the carbon resource of the chosen microbe growth, and compared with non-SEWS, the degradation amount of cellulose decreased and the degradation amount of lignin increased for the fermented steam-exploded wheat straw (FSEWS) cultured with Phanerochaete chrysosporium ME-446. Under the optimum conditions of solid-state ferrmentation (SSF), the degradation amount of lignin reached 60% on the 5th day and the fermented straw residue could be used directly as the material for pulp making.     

Alkali-explosion pretreatment of straw and bagasse for enzymic hydrolysis

Sugarcane bagasse and wheat straw were subjected to alkali treatment at 200 degrees C for 5 min and at 3.45 MPa gas pressure (steam and nitrogen), followed by an explosive discharge through a defibrating nozzle, in an attempt to improve the rate and extent of digestibility. The treatment resulted in the solubilization of 40-45% of the components and in the production of a pulp that gave saccharification yields of 80 and 65% in 8 h for bagasse and wheat straw, respectively. By comparison, alkali steaming at 200 degrees C (1.72 MPa) for 5 min gave saccharification yields of only 58 and 52% in 48 h. The increase in temperature from 140 to 200 degrees C resulted in a gradual increase in in vitro organic matter digestibility (IVOMD) for both the substrates. Also, the extent of alkalinity during pretreatment appears to effect the reactivity of the final product towards enzymes. Pretreatment times ranging from 5 to 60 caused a progressive decline in the IVOMD of bagasse and wheat straw by the alkali explosion method and this was accompanied by a progressive decrease in pH values after explosion. In the alkali-steaming method, pretreatment time had no apparent effect with either substrate. An analysis of the alkali-exploded products showed that substantial amounts of hemicellulose and a small proportion of the lignin were solubilized. The percentage crystallinity of the cellulose did not alter in either substrate but there was a substantial reduction in the degree of polymerization. The superiority of the alkali-explosion pretreatment is attributed to the efficacy of fiber separation and disintegration; this increases the surface area and reduces the degree of polymerization.     

Efficient conversion of wheat straw wastes into biohydrogen gas by cow dung compost

Efficient conversion of wheat straw wastes into biohydrogen gas by cow dung compost was reported for the first time. Batch tests were carried out to analyze influences of several environmental factors on biohydrogen production from wheat straw wastes. The performance of biohydrogen production using the raw wheat straw and HCl pretreated wheat straw was then compared in batch fermentation tests. The maximum cumulative hydrogen yield of 68.1 ml H2/g TVS was observed at 126.5 h, the value is about 136-fold as compared with that of raw wheat straw wastes. The maximum hydrogen production rate of 10.14 ml H2/g TVS h was obtained by a modified Gompertz equation. The hydrogen content in the biogas was 52.0% and there was no significant methane observed in this study. In addition, biodegradation characteristics of the substrate were also discussed. The experimental results showed that the pretreatment of the substrate plays a key role in the conversion of the wheat straw wastes into biohydrogen by the composts generating hydrogen.     

Biological pretreatment of wheat straw by Phanerochaete chrysosporium supplemented with inorganic salts

Inorganic salts and tween 80 are known to induce the lignin degrading peroxidase expression of Phanerochaete chrysosporium in submerged culture. In this study, the wheat straw pretreatment supplemented with inorganic salts (salts group), tween 80 (plus) and no supplementation to the biomass (minus) were examined. Among the solid state fermentation groups, salts group resulted in a substantial degradation of wheat straw within one week, along with the highest lignin loss (25%) and ～250% higher efficiency for the total sugar release through enzymatic hydrolysis. The results were correlated with pyrolysis GC-MS (Py-GC-MS), thermogravimetric (TG)/differential thermogravimetric (DTG) and X-ray diffraction (XRD). The results suggested that the supplementation of inorganic salts in the solid state fermentation of wheat straw significantly enhances the degradation rate of the biomass by P. chrysosporium which can be exploited as an alternative means to existing pretreatment technologies.     

Synergistic effects of mixing hybrid poplar and wheat straw biomass for bioconversion processes

Background

Low cost of raw materials and good process yields are necessary for future lignocellulosic biomass biorefineries to be sustainable and profitable. A low cost feedstock will be diverse, changing as a function of seasonality and price and will most likely be available from multiple sources to the biorefinery. The efficacy of the bioconversion process using mixed biomass, however, has not been thoroughly investigated. Considering the seasonal availability of wheat straw and the year round availability of hybrid poplar in the Pacific Northwest, this study aims to determine the impact of mixing wheat straw and hybrid poplar biomass on the overall sugar production via steam pretreatment and enzymatic saccharification.

Results

Steam pretreatment proved to be effective for processing different mixtures of hybrid poplar and wheat straw. Following SO₂-catalyzed steam explosion pretreatment, on average 22 % more sugar monomers were recovered using mixed feedstock than either single biomass. Improved sugar recovery with mixtures of poplar and wheat straw continued through enzymatic hydrolysis. After steam pretreatment and saccharification, the mixtures showed 20 % higher sugar yields than that produced from hybrid poplar and wheat straw alone.

Conclusions

Blending hybrid poplar and wheat straw resulted in more monomeric sugar recovery and less sugar degradation. This synergistic effect is attributable to interaction of hybrid poplar’s high acetic acid content and the presence of ash supplied by wheat straw. As a consequence on average 20 % more sugar was yielded by using the different biomass mixtures. Combining hybrid poplar and wheat straw enables sourcing of the lowest cost biomass, reduces seasonal dependency, and results in increasing biofuels and chemicals productivity in a cellulosic biorefinery.