【作者】 周娜；

【导师】 王务林； 张毅民；

【作者基本信息】 天津大学 ， 环境化工， 2012， 博士

【摘要】 将生物质转化生成糖类中间体是生物质资源转化过程中重要研究内容。本研究选用藻类生物质(小球藻)、木质纤维素类生物质(玉米秸秆)和草本纤维生物质(龙须草)三种较为典型的生物质原料为研究对象,针对不同原料在组成和结构上的差异,采用不同技术手段将其降解生成可发酵糖,并对生成的可发酵糖在发酵生产生物乙醇方面的应用进行了评价。研究了小球藻生物质在无机酸HCl、H2SO4以及Lewis酸MgCl2中水解生产可发酵糖的工艺。结果表明,HCl催化水解小球藻生产可发酵糖的能力大于H2SO4和MgCl2。在此基础上,研究了小球藻在HCl/MgCl2协同催化剂中的水解特性,研究发现,当2%HCl与2.5%MgCl2协同催化小球藻时,生成的可发酵糖产率高于单独以2%HCl和2.5%MgCl2作催化剂时可发酵糖产率的总和。对生成的可发酵糖进行微生物发酵实验,乙醇产率为0.47 g/g。采用新型绿色溶剂离子液体[EMIM]Cl为催化剂,对小球藻进行催化水解。研究了溶解温度、溶解时间、催化剂HCl的用量、水解温度和水解时间等因素对小球藻在[EMIM]Cl中水解生成可发酵糖的影响。得出当溶解温度为105℃、溶解时间为3h、催化剂HCl的用量为小球藻质量的7 Wt%、水解温度为105℃、水解时间为3h时,小球藻在[EMIM]Cl中生成的可发酵糖产率最大,为88.02%。采用离子排阻色谱技术对水解液中[EMIM]Cl和糖类物质进行分离回收,离子液体可重复利用,糖类物质的回收率为92%。对分离回收的可发酵糖进行微生物发酵实验,乙醇产率为0.496 g/g。采用响应曲面法对玉米秸秆的蒸汽爆破条件进行优化,得到当汽爆压力为2.4 MPa、保压时间为8.5 min、物料含水率为60%时,汽爆处理后的秸秆中纤维素含量为46.97%,半纤维素含量为5.24%,酶解率为81.51%。对优化条件下得到的汽爆秸秆进行酶解和工艺放大研究,在150 L反应体系中,采用补料方式以24%总底物浓度对汽爆秸秆酶解72 h时,总糖浓度可达100.7g/L,酶解率为70.2%。选用高温酿酒酵母在40℃条件下对汽爆秸秆的酶解液清液和带渣酶解液进行乙醇发酵,72 h后酶解液清液的乙醇产率为0.49g/g；带渣酶解液为0.37 g/g。选用某生物制浆公司提供的不同工艺段龙须草物料为原料,对其进行结构、组分及酶解研究。结果表明,龙须草物料中的木质素结构逐步变形、破坏,含量逐渐减小,而酶解产率却逐渐增大。与木质素没有被降解的原料相比,木质素降解掉71.55%的样品,酶解率可以提高9.58倍。然而,由于纤维素的晶体结构并未被破坏,物料的最终酶解产率低于40%。向纤维素酶中加入少量木聚糖酶,可以同时提高酶解速率和酶解产率。更多还原

【Abstract】 In recent years, utilization of biomass materials as potential biofuel feedstocks to convert carbohydrates to sugars has attracted significant attention. In this thesis, Chlorella biomass, corn stover and Chinese alpine rush were selected as biomass materials to produce fermentable sugars by the technology of acid/salt, ionic liquid, steam explosion as well as enzymatic hydrolysis. The performance of fermentable sugars in the hydrolysate was evalutated by conversing to ethanol.A novel chemical hydrolysis technology was developed to obtain high-yielding fermentable sugars from Chlorella biomass. Using a mixed catalyst of HCl and MgCl2, the highest sugar concentration was close to 12%, and the highest sugar recovery was about 83%, more than the sum of sugar recovery with HCl or MgCl2 as the catalyst, respectively. The results suggested a synergic effect of HCl and MgCl2 during the chemical hydrolysis of Chlorella biomass. Fermentation experiments demonstrated that glucose in the Chlorella biomass hydrolysates was conversed into bioethanol by Sccharomyces cerevisiae with the yield of 0.47 g/g, which is 92% of the theoretical yield. This chemical hydrolysis technology indicated the potential to provide a novel route for biomass to fermentable sugars.Chlorella biomass was then hydrolyzed in the presence of [EMIM]Cl. The effects of dissolution temperature and dissolution time, HCl loading, hydrolysis temperature and hydrolysis time on the formation of fermentable sugars from Chlorella biomass were investigated. After 3 h’s dissolution in [EMIM]Cl and then 3 h’s hydrolysis in 7 wt% HCl at 105℃,75% of Chlorella biomass could be dissolved, with 48% of total sugar released from Chlorella biomass, a second hydrolysis of the hydrolysates in the presence of 8% H2SO4 would enhance the final sugar yield to nearly 90%. [EMIM]Cl and sugars in the hydrolysate was recovered by using ion-exclusion chromatography, with the recovery of 94% of glucose and 87% of xylose and arabinose. Fermentation experiments demonstrated that the approach used could not introduce much inhibitor that interfered with bioethanol production.Corn stover was treated under different steam explosion pressure (1.5 MPa-2.5 MPa), pressure-retention time (3 min-10 min) and water content (0%-60%), on the base of cellulose content, hemicelluloses content, and enzymatic yield of the treated corn stover, the optimization condition was obtained by using the software of Design Expert, with the steam explosion pressure of 2.4 MPa,8.5 min and 60% of water content. Using the steam explosion treated corn stover obtained at the above condition, enzymatic hydrolysis experiment was carried out in order to get high concentration of fermentable sugar for ethanol production, and the system was gradually increased from 0.5 L,4 Lto 150 L. In 150 L enzymatic hydrolysis system,12%,6%, and 6% of feedstock were introduced at 0 h,24 h and 48 h, with the total sugar concentration increased all the time, while for enzymatic hydrolysis yield and compositions in solid residue, the phenomenon of decrease and increase was observed alternatively. At the end of enzymatic hydrolysis,100.7 g/L of total sugar with the yield of 70.2% was obtained.Different samples of Chinese alpine rush material with different lignin content from a biopulping process was selected as biomass materials to produce fermentable sugars. The enzymatic hydrolysis experiments showed that lignin content in the biomass materials would significantly affect the biomass saccharification. Compared to the sample without lignin degradation, the enzymatic hydrolysis yield of the sample with 71.55% lignin degradation would enhance about 9.58 fold. The addition of xylanse would further enhace the efficiency of enzymatic hydrolysis. However, due to almost intact crystalline structure of cellulose in the test samples, the overall enzymatic hydrolysis yield was less than 40%, which implicated that disrupting the crystalline structure of cellulose in the biomass material was an important key to further enhance the enzymatic hydrolysis of biomass.更多还原