乙醇预处理麦秆的酶解性能研究

采用H2SO4催化和自催化乙醇法对麦秆进行预处理,比较预处理后麦秆的主要化学组成、纤维素酶解性能和半同步糖化发酵生产乙醇特性,并进行物料衡算。结果表明:H2SO4催化和自催化乙醇预处理过程中纤维素固体回收率大于90%。添加非离子表面活性剂吐温20和吐温80没有显著提高H2SO4催化乙醇预处理后纤维素的酶解葡萄糖得率及半同步糖化发酵过程中乙醇的产量,而对自催化乙醇处理后麦秆的酶解和半同步糖化发酵过程有一定程度的促进作用,相应的酶解葡聚糖转化率由72.7%提高到85.0%,而半同步糖化发酵过程中乙醇质量浓度提高了11.4%。物料衡算结果表明:酸催化和自催化乙醇预处理后葡聚糖回收率分别为91.0%和95.4%;半同步糖化发酵生产乙醇的得率分别为10.4和11.6 g(按100 g原料计)。     

常压甘油自催化预处理麦草浓醪发酵纤维素乙醇

目前纤维素乙醇成本偏高的根本原因在于没有达到淀粉质乙醇发酵水平的"三高"(高浓度、高转化率和高效率)指标,提高水解糖液浓度和避免发酵抑制物来实现浓醪发酵,是解决问题的关键。文中以常压甘油自催化预处理麦草为底物,尝试采用不同发酵策略,探讨其浓醪发酵产纤维素乙醇的可行性。在优化培养条件(15%底物浓度,加酶量30 FPU/g干底物,温度37℃,接种量10%)下同步糖化发酵72 h,纤维素乙醇产量为31.2 g/L,转化率为73%,发酵效率0.43 g/(L·h);采用半同步(预酶解24 h)糖化发酵72 h,纤维素乙醇浓度达到33.7 g/L,转化率为79%,发酵效率为0.47 g/(L·h),其中(半)同步糖化发酵中90%以上纤维素已被糖化水解用于发酵;采用分批补料式半同步糖化发酵,补料到基质浓度相当于30%,发酵72 h时纤维素乙醇产量达到51.2 g/L,转化率为62%,发酵效率为0.71 g/(L·h)。在所有浓醪发酵中乙酸不足3 g/L,无糠醛和羟甲基糠醛等发酵抑制物。以上结果表明,常压甘油自催化预处理木质纤维素基质适用于纤维素乙醇发酵;分批补料式半同步糖化发酵策略可用来进行浓醪纤维素乙醇发酵;未来工作中提高基质纯度和强化酶解产糖是浓醪纤维素乙醇达到"三高"指标的关键。     

稀碱预处理棕榈残渣制备纤维乙醇

以棕榈残渣(Empty fruit bunch,EFB)为原料,通过预处理、酶解、发酵等过程制备纤维乙醇.首先对比了碱、碱/过氧化氢等预处理条件对棕榈残渣组成及酶解的影响,结果表明稀碱预处理效果较好.适宜的稀碱预处理条件为:NaOH浓度为1％,固液比为1∶10,在40℃浸泡24 h后于121℃下保温30 min,在该条件下,EFB的固体回收率为74.09％,纤维素、半纤维素和木质素的含量分别为44.08％、25.74％和13.89％.对该条件下预处理后的固体样品,以底物浓度5％、酶载量30 FPU/g底物酶解72 h,纤维素和半纤维素的酶解率分别达到84.44％和89.28％.进一步考察了酶载量和底物浓度对酶解的影响以及乙醇批式同步糖化发酵,当酶载量为30 FPU/g底物,底物浓度由5％增加至25％时,利用酿酒酵母Saccharomyces cerevisiae(接种量为5％,VIV)发酵72 h后乙醇的浓度分别为9.76 g/L和35.25 g/L,可分别达到理论得率的79.09％和56.96％.     

木薯纤维素乙醇发酵的纤维素酶成本评价

木薯中的纤维素成分约占木薯干重的10％(W/W).文中以木薯燃料乙醇生产的木薯纤维素酒渣为原料,从纤维素酶成本角度评估了三种利用木薯纤维素组分发酵生产乙醇的方法,包括木薯纤维素酒渣的直接糖化和乙醇发酵、木薯纤维素酒渣预处理后的糖化与乙醇发酵、木薯乙醇发酵中同步淀粉与纤维素糖化以及乙醇发酵.结果表明,前两种方法的纤维素利用效率不高,酶成本分别达到13602、11659元/吨乙醇.第三种方法,即在木薯乙醇发酵过程同时加入糖化酶和纤维素酶,进行同步淀粉与纤维素糖化,进而进行乙醇发酵,木薯纤维素乙醇的收益最高.发酵结束时的乙醇浓度从101.5g/L提高到107.0g/L,纤维素酶成本为3 589元/吨乙醇.此方法利用木薯纤维素与木薯淀粉同时进行,不会带来额外的设备及操作投入,酶成本低于产品乙醇价格,可实现盈利,因此第三种方法为木薯纤维用于乙醇发酵的最适方法,本研究结果将为木薯乙醇产业深度利用木薯纤维提供依据.     

湿氧化爆破稻秆的同步糖化发酵条件研究

探讨了木质纤维素经过湿氧化爆破后在同步糖化发酵过程中酵母产乙醇的基本规律.采用单因素方法对湿氧化爆破条件、酶系组成和添加量以及预酶解时间和温度进行了优化.不同湿氧化爆破预处理条件下的稻秆对同步糖化发酵工艺的影响较大,在预处理温度160 ℃,进氧压力为4×105 Pa,碱用量为6%(w/w),反应时间为20 min的条件...     

螺带桨搅拌在木质纤维素酸预处理反应器中的应用简

在干式稀酸预处理的反应器中采用螺带桨搅拌器,对秸秆预处理体系进行混合。在带有螺带式搅拌的预处理过程中,在质量分数2.0％和2.5％的H2 SO4用量条件下,预处理后72 h秸秆的酶解糖化得率分别为77.55％和87.11％,比静态预处理得到的得率分别增长了7.6％和2.4％,抑制物的生成显著降低。通过计算流体力学方法验证,螺带桨搅拌器可以有效地改善玉米秸秆在稀酸预处理过程中的蒸汽和秸秆两相的混合情况。     

乙醇-酶体系预处理结合水提法提取灵芝中β-葡聚糖的研究

采用乙醇-酶预处理体系,结合水提法较系统地研究了灵芝子实体中β-葡聚糖的提取技术。结果表明,乙醇-酶体系预处理的关键参数为:乙醇质量分数60%(V/V),加酶量1.5%(M/V,g/m L)、酶解温度45℃、酶解p H8.0;在乙醇-酶体系预处理的基础上,进一步采用单因素试验和Box-Benhnken试验设计与响应面分析法对灵芝子实体中β-葡聚糖的热水提取工艺进行了优化。结果显示水提温度、提取时间、水料比3个因素及水提温度与水料比二者的交互作用对β-葡聚糖的提取有显著影响。经优化后获得3个核心因素的最佳水平为:提取温度80℃、提取时间2.5h、水料比35:1。在乙醇-酶预处理结合水提取条件下,灵芝子实体中β-葡聚糖的提取得率可达0.412mg/g,是传统无水乙醇回流预处理结合水提法提取β-葡聚糖得率的2.1倍。本研究为灵芝β-葡聚糖的进一步提取放大试验奠定了技术基础。     

白腐真菌Pleurotus sajor-caju预处理对红麻秸秆发酵乙醇的影响

为研究微生物法预处理对红麻秸秆中木质素的降解及后续的红麻纤维素酶促糖化和发酵效率的影响,将白腐真菌Pleurotus sajor-caju接种在红麻秸秆培养基上固态培养,对红麻秸秆进行预处理。经P. sajor-caju培养25~35 d后,有效转化红麻秸秆中的木质素,转化率最高可达50.20％,并提高红麻纤维素的酶促水解效率,糖化率达69.33％~78.64％,与对照组相比提高了3.5~4.1倍。以微生物法预处理后的红麻秸秆样品为底物的同步糖化发酵实验表明,发酵72 h,发酵液中乙醇浓度达到18.35~     

一株乳杆菌对蒸汽爆破处理纤维物料的乳酸发酵研究

用筛选得到的一株乳酸杆菌ZJU-1(Lactobacillus sp．)对蒸汽爆破预处理纤维物料的乳酸发酵进行了研究,结果表明该菌株能对蒸汽爆破处理的纤维物料酶解液进行乳酸发酵,在还原糖质量浓度为52．1mg/mL时,乳酸量为42．1mg/mL;与纤维素酶的酶解过程相耦合,对蒸汽爆破处理的物料进行同时糖化乳酸发酵。其发酵周期比分步糖化发酵的过程周期短,在底物质量分数为80mg/mL,接种量为10％,温度为45％时,乳酸量为45．3mg/mL。     

预处理苎麻秆和红麻秆糖化发酵生产燃料乙醇

苎麻和红麻是我国传统纤维作物,皮部纤维在造纸、纺织等工业具有广泛用途,但剥皮后剩余的茎秆部分并没有被有效利用。由于其中含有较多纤维素,可望被生物转化生产燃料乙醇。比较了几种不同化学预处理方法对苎麻秆和红麻秆纤维素酶解性能的改善效果,进而选择碱法预处理后原料,进行半同步糖化发酵产乙醇实验。结果表明,苎麻秆和红麻秆经4%NaOH和0.02%蒽醌-2-磺酸钠盐(AQSS),在170℃下处理1 h,继而在固形物底物浓度18%时发酵168 h,发酵液中乙醇浓度达到51 g/L。采用少量多次补料至20%的底物浓度,乙醇浓度都能达到63 g/L,纤维素转化率分别为77%和79%。红麻秆经5.2%NaHSO3和0.2%H2SO4,在170℃下处理1 h,补料至20%的底物浓度时,乙醇浓度可达到65 g/L,纤维素转化率为72%。     

Fungal pretreatment of lignocellulose by Phanerochaete chrysosporium to produce ethanol from rice straw

Phanerochaete chrysosporium is a wood‐rot fungus that is capable of degrading lignin via its lignolytic system. In this study, an environmentally friendly fungal pretreatment process that produces less inhibitory substances than conventional methods was developed using P. chrysosporium and then evaluated by various analytical methods. To maximize the production of manganese peroxidase, which is the primary lignin‐degrading enzyme, culture medium was optimized using response surface methodologies including the Plackett–Burman design and the Box–Behnken design. Fermentation of 100 g of rice straw feedstock containing 35.7 g of glucan (mainly in the form of cellulose) by cultivation with P. chrysosporium for 15 days in the media optimized by response surface methodology was resulted in a yield of 29.0 g of glucan that had an enzymatic digestibility of 64.9% of the theoretical maximum glucose yield. In addition, scanning electronic microscopy, confocal laser scanning microscopy, and X‐ray diffractometry revealed significant microstructural changes, fungal growth, and a reduction of the crystallinity index in the pretreated rice straw, respectively. When the fungal‐pretreated rice straw was used as a substrate for ethanol production in simultaneous saccharification and fermentation (SSF) for 24 h, the ethanol concentration, production yield and the productivity were 9.49 g/L, 58.2% of the theoretical maximum, and 0.40 g/L/h, respectively. Based on these experimental data, if 100 g of rice straw are subjected to fungal pretreatment and SSF, 9.9 g of ethanol can be produced after 96 h, which is 62.7% of the theoretical maximum ethanol yield. Biotechnol. Bioeng. 2009; 104: 471–482 © 2009 Wiley Periodicals, Inc.     

Aqueous ammonia pretreatment of oil palm empty fruit bunches for ethanol production

Oil palm empty fruit bunches (EFB) were pretreated by aqueous ammonia soaking for ethanol production. Pretreated EFB, which were pretreated at the optimal conditions of 60 °C, 12 h, and 21% (w/w) aqueous ammonia, showed 19.5% and 41.4% glucose yields during an enzymatic digestibility test for 96 h when using 15 and 60 FPU of cellulase, respectively. Using the pretreated EFB, simultaneous saccharification and fermentation for 168 h with 5% (w/v) glucan loading and 60 FPU of cellulase and 30 CBU of β-glucosidase per gram glucan resulted in ethanol production of 18.6 g/L titer, 65.6% of theoretical maximum yield, and 0.11 g/L/h of productivity.     

Two-stage pretreatment of rice straw using aqueous ammonia and dilute acid

Liberation of fermentable sugars from recalcitrant lignocellulosic biomass is one of the key challenges in production of cellulosic ethanol. Here we developed a two-stage pretreatment process using aqueous ammonia and dilute sulfuric acid in a percolation mode to improve production of fermentable sugars from rice straw. Aqueous NH? was used in the first stage which removed lignin selectively but left most of cellulose (97%) and hemicellulose (77%). Dilute acid was applied in the second stage which removed most of hemicellulose, partially disrupted the crystalline structure of cellulose, and thus enhanced enzymatic digestibility of cellulose in the solids remaining. Under the optimal pretreatment conditions, the enzymatic hydrolysis yields of the two-stage treated samples were 96.9% and 90.8% with enzyme loadings of 60 and 15FPU/g of glucan, respectively. The overall sugar conversions of cellulose and hemicellulose into glucose and xylose by enzymatic and acid hydrolysis reached 89.0% and 71.7%, respectively.     

Bioethanol production from ammonia percolated wheat straw

This study examined the effectiveness of ammonia percolation pretreatment of wheat straw for ethanol production. Ground wheat straw at a 10% (w/v) loading was pretreated with a 15% (v/v) ammonia solution. The experiments were performed at treatment temperature of 50∼170°C and residence time of 10∼150 min. The solids treated with the ammonia solution showed high lignin degradation and sugar availability. The pretreated wheat straw was hydrolyzed by a cellulase complex (NS50013) and β-glucosidase (NS50010) at 45°C. After saccharification, Saccharomyces cerevisiae was added for fermentation. The incubator was rotated at 120 rpm at 35°C. As a result of the pretreatment, the delignification efficiency was > 70% (170°C, 30 min) and temperature was found to be a significant factor in the removal of lignin than the reaction time. In addition, the saccharification results showed an enzymatic digestibility of > 90% when 40 FPU/g cellulose was used. The ethanol concentration reached 24.15 g/L in 24 h. This paper reports a total process for bioethanol production from agricultural biomass and an efficient pretreatment of lignocellulosic material.     

稀酸和稀碱预处理对四种不同生物质资源制备还原糖的影响

本论文探讨了不同浓度的稀H_2SO_4和稀NaOH预处理对大豆秸秆、水稻秸秆、象草和狼尾草四种不同生物质酶解制备还原糖的影响。结果表明,大豆秸秆、水稻秸秆、象草和狼尾草具有较高的纤维素和半纤维素含量,是制备还原糖的理想原料。与稀H_2SO_4预处理相比,经稀NaOH预处理后的样品表现出较好的酶解性能。通过使用4%的NaOH对大豆秸秆和狼尾草进行预处理,还原糖产量分别为145.8 mg/mL和319.2 mg/mL。此外,以1%NaOH预处理后的水稻秸秆和象草为原料,可以分别获得385.2 mg/mL和231.6 mg/mL还原糖产量。     

Isolation of xylose isomerases by sequence- and function-based screening from a soil metagenomic library

Background

The recent development of improved enzymes and pentose-using yeast for cellulosic ethanol processes calls for new attention to the lignocellulose pretreatment step. This study assessed the influence of pretreatment pH, temperature, and time, and their interactions on the enzymatic glucose and xylose yields from mildly pretreated wheat straw in multivariate experimental designs of acid and alkaline pretreatments.

Results

The pretreatment pH was the most significant factor affecting both the enzymatic glucose and xylose yields after mild thermal pretreatments at maximum 140°C for 10 min. The maximal enzymatic glucose and xylose yields from the solid, pretreated wheat straw fraction were obtained after pretreatments at the most extreme pH values (pH 1 or pH 13) at the maximum pretreatment temperature of 140°C. Surface response models revealed significantly correlating interactions of the pretreatment pH and temperature on the enzymatic liberation of both glucose and xylose from pretreated, solid wheat straw. The influence of temperature was most pronounced with the acidic pretreatments, but the highest enzymatic monosaccharide yields were obtained after alkaline pretreatments. Alkaline pretreatments also solubilized most of the lignin.

Conclusions

Pretreatment pH exerted significant effects and factor interactions on the enzymatic glucose and xylose releases. Quite extreme pH values were necessary with mild thermal pretreatment strategies (T ≤ 140°C, time ≤ 10 min). Alkaline pretreatments generally induced higher enzymatic glucose and xylose release and did so at lower pretreatment temperatures than required with acidic pretreatments.     

Dilute acid pretreatment, enzymatic saccharification and fermentation of wheat straw to ethanol

Wheat straw consists of 48.57 ± 0.30% cellulose and 27.70 ± 0.12% hemicellulose on dry solid (DS) basis and has the potential to serve as a low cost feedstock for production of ethanol. Dilute acid pretreatment at varied temperature and enzymatic saccharification were evaluated for conversion of wheat straw cellulose and hemicellulose to monomeric sugars. The maximum yield of monomeric sugars from wheat straw (7.83%, w/v, DS) by dilute H₂SO₄ (0.75%, v/v) pretreatment and enzymatic saccharification (45 °C, pH 5.0, 72 h) using cellulase, β-glucosidase, xylanase and esterase was 565 ± 10 mg/g. Under this condition, no measurable quantities of furfural and hydroxymethyl furfural were produced. The yield of ethanol (per litre) from acid pretreated enzyme saccharified wheat straw (78.3 g) hydrolyzate by recombinant Escherichia coli strain FBR5 was 19 ± 1 g with a yield of 0.24 g/g DS. Detoxification of the acid and enzyme treated wheat straw hydrolyzate by overliming reduced the fermentation time from 118 to 39 h in the case of separate hydrolysis and fermentation (35 °C, pH 6.5), and increased the ethanol yield from 13 ± 2 to 17 ± 0 g/l and decreased the fermentation time from 136 to 112 h in the case of simultaneous saccharification and fermentation (35 °C, pH 6.0).     

Effect of organosolv pretreatment on mechanically pretreated biomass by use of concentrated ethanol as the solvent

In this study, we determined the effect of organosolv pretreatment on herbaceous biomasses corn stover and wheat straw, by using high-concentration ethanol as the solvent. A high-concentration of ethanol allows for the easy reuse and recycling of the solvent. First, we tested the effects of ethanol pretreatments at 60 and 99.5% (w/w) and found that highest solvent concentration resulted in low glucose digestibility. The maximum enzymatic glucose digestibility with 60% ethanol was 92.6% at 190°C for 120 min (using corn stover) and 86.9% at 190°C for 120 min (using wheat straw). In contrast, the digestion rates with 99.5% ethanol were 68.8 and 77.4% under the same conditions, respectively, indicating that there is a limit to the use of high-concentration ethanol as the solvent. To overcome this limitation, we applied a mechanical pretreatment step before the chemical pretreatment. Subsequently, glucose digestibility increased significantly to 93.1% with 99.5% ethanol as the solvent. Additionally the enzymatic digestibility of mechanically pretreated corn stover was higher than that of non-pretreated corn stover by about 40%. Taken together, these results confirm the efficacy of using high-concentration ethanol as a solvent for organosolv pretreatment when done in conjunction with mechanical pretreatment.     

Aqueous ammonia pretreatment, saccharification, and fermentation evaluation of oil palm fronds for ethanol production

Oil palm fronds are the most abundant lignocellulosic biomass in Malaysia. In this study, fronds were tested as the potential renewable biomass for ethanol production. The soaking in aqueous ammonia pretreatment was applied, and the fermentability of pretreated fronds was evaluated using simultaneous saccharification and fermentation. The optimal pretreatment conditions were 7?% (w/w) ammonia, 80?°C, 20?h of pretreatment, and 1:12 S/L ratio, where the enzymatic digestibility was 41.4?% with cellulase of 60?FPU/g-glucan. When increasing the cellulase loading in the hydrolysis of pretreated fronds, the enzymatic digestibility increased until the enzyme loading reached 60?FPU/g-glucan. With 3?% glucan loading in the SSF of pretreated fronds, the ethanol concentration and yield based on the theoretical maximum after 12 and 48?h of the SSF were 7.5 and 9.7?g/L and 43.8 and 56.8?%, respectively. The ethanol productivities found at 12 and 24?h from pretreated fronds were 0.62 and 0.36?g/L/h, respectively.     

Low temperature alkali pretreatment for improving enzymatic digestibility of sweet sorghum bagasse for ethanol production

A low temperature alkali pretreatment method was proposed for improving the enzymatic hydrolysis efficiency of lignocellulosic biomass for ethanol production. The effects of the pretreatment on the composition, structure and enzymatic digestibility of sweet sorghum bagasse were investigated. The mechanisms involved in the digestibility improvement were discussed with regard to the major factors contributing to the biomass recalcitrance. The pretreatment caused slight glucan loss but significantly reduced the lignin and xylan contents of the bagasse. Changes in cellulose crystal structure occurred under certain treatment conditions. The pretreated bagasse exhibited greatly improved enzymatic digestibility, with 24-h glucan saccharification yield reaching as high as 98% using commercially available cellulase and β-glucosidase. The digestibility improvement was largely attributed to the disruption of the lignin-carbohydrate matrix. The bagasse from a brown midrib (BMR) mutant was more susceptible to the pretreatment than a non-BMR variety tested, and consequently gave higher efficiency of enzymatic hydrolysis.