Department of Biological Systems Engineering, Bioproducts, Sciences and Engineering Laboratory, Washington State University, Richland, WA 99354, USA.
Biotechnol Biofuels. 2014 May 23;7:76. doi: 10.1186/1754-6834-7-76. eCollection 2014.
Pretreatment is a vital but expensive step in biomass biofuel production. Overall, most of this past effort has been directed at maximizing sugar yields from hemicellulose and cellulose through trials with different chemicals, operating conditions, and equipment configurations. Flowthrough pretreatment provides a promising platform to dissolution of lignocellulosic biomass to generate high yields of fermentable sugars and lignin for biofuels productions.
Dissolution of xylan, lignin, and cellulose from poplar wood were significantly enhanced by water-only and dilute acid (0.05% w/w, H2SO4) flowthrough pretreatment when the temperature was raised from 200°C to 280°C over a range of flow rates 10-62.5 mL/min, resulting in more than 98% solid removal. Up to 40% of original xylan was converted to xylose in the hydrolyzate and the rest xylan was solubilized into xylooligomers with negligible furfural formation. Up to 100% cellulose was removed into hydrolyzate with the highest glucose yield of 60% and low 5-hydroxymethylfurfural (5-HMF) formation. The maximal recovered insoluble lignin and soluble lignin were 98% and 15% of original lignin, respectively. In addition, enzymatic hydrolysis of pretreated whole slurries was characterized under various enzyme loadings with or without Bovine serum albumin (BSA) treatment. More than 90% glucose yield and 95% xylose yield were obtained from enzymatic hydrolysis of dilute acid pretreated whole slurries with 10 mg protein Ctec 2 with 2 mg Htec2/g glucan + xylan.
Nearly complete dissolution of whole biomass was realized through water-only and dilute acid flowthrough pretreatment under tested conditions. Temperature was considered as the most significant factor for cellulose degradation. The cellulose removal significantly increased as temperature reached 240°C for water-only and 220°C for dilute acid. Dilute acid pretreatment resulted in higher yields of recovered xylan and cellulose as monomeric sugars in the hydrolyzate than that for water-only pretreatment. Enzymes readily hydrolyzed the degraded cellulose and xylooligomers in pretreatment hydrolysate. Results suggested that kinetics controlled the flowthrough pretreatment of biomass dissolution, which was also affected by flow rate to certain extent.
预处理是生物质生物燃料生产中至关重要但昂贵的步骤。总的来说，过去的大部分努力都集中在通过不同的化学物质、操作条件和设备配置来尝试从半纤维素和纤维素中最大限度地提高糖产量。流通过预处理为溶解木质纤维素生物质提供了一个很有前途的平台，可产生高产量的可发酵糖和木质素用于生物燃料生产。
在温度从 200°C 升高到 280°C 的范围内，在 10-62.5 mL/min 的不同流速下，只用水和稀酸（0.05%w/w，H2SO4）进行流通过预处理，显著增强了杨木中木聚糖、木质素和纤维素的溶解，固体去除率超过 98%。多达 40%的原始木聚糖在水解物中转化为木糖，其余木聚糖溶解为低聚木糖，糠醛形成可忽略不计。多达 100%的纤维素被转化为水解物，葡萄糖收率最高为 60%，5-羟甲基糠醛（5-HMF）形成率低。可回收的不溶性木质素和可溶性木质素分别为原始木质素的 98%和 15%。此外，还在有无牛血清白蛋白（BSA）处理的情况下，在不同的酶负荷下对预处理的全浆进行了酶水解特性研究。在 10mg 蛋白 Ctec 2 和 2mg Htec2/（葡聚糖+木聚糖）的条件下，用稀酸预处理的全浆进行酶水解，可获得超过 90%的葡萄糖收率和 95%的木糖收率。
在测试条件下，通过只用水和稀酸的流通过预处理实现了全生物质的几乎完全溶解。温度被认为是纤维素降解的最主要因素。只用水时，温度达到 240°C，稀酸时达到 220°C，纤维素的去除率显著增加。稀酸预处理导致水解物中回收木聚糖和纤维素作为单体糖的产量高于只用水预处理。酶容易水解预处理水解物中的降解纤维素和木寡糖。结果表明，动力学控制了生物质溶解的流通过预处理，这也在一定程度上受到流速的影响。
