Patri Abhishek S, McAlister Laura, Cai Charles M, Kumar Rajeev, Wyman Charles E
1Department of Chemical and Environmental Engineering, Bourns College of Engineering, University of California, Riverside, 900 University Ave, Riverside, CA 92521 USA.
2BioEnergy Science Center (BESC), Oak Ridge National Laboratory (ORNL), Oak Ridge, TN 37831 USA.
Biotechnol Biofuels. 2019 Jul 10;12:177. doi: 10.1186/s13068-019-1515-7. eCollection 2019.
Pretreatment is effective in reducing the natural recalcitrance of plant biomass so polysaccharides in cell walls can be accessed for conversion to sugars. Furthermore, lignocellulosic biomass must typically be reduced in size to increase the pretreatment effectiveness and realize high sugar yields. However, biomass size reduction is a very energy-intensive operation and contributes significantly to the overall capital cost.
In this study, the effect of particle size reduction and biomass presoaking on the deconstruction of Alamo switchgrass was examined prior to pretreatment by dilute sulfuric acid (DSA) and Co-solvent Enhanced Lignocellulosic Fractionation (CELF) at pretreatment conditions optimized for maximum sugar release by each pretreatment coupled with subsequent enzymatic hydrolysis. Sugar yields by enzymatic hydrolysis were measured over a range of enzyme loadings. In general, DSA successfully solubilized hemicellulose, while CELF removed nearly 80% of Klason lignin from switchgrass in addition to the majority of hemicellulose. Presoaking and particle size reduction did not have a significant impact on biomass compositions after pretreatment for both DSA and CELF. However, presoaking for 4 h slightly increased sugar yields by enzymatic hydrolysis of DSA-pretreated switchgrass compared to unsoaked samples, whereas sugar yields from enzymatic hydrolysis of CELF solids continued to increase substantially for up to 18 h of presoaking time. Of particular importance, DSA required particle size reduction by knife milling to < 2 mm in order to achieve adequate sugar yields by subsequent enzymatic hydrolysis. CELF solids, on the other hand, realized nearly identical sugar yields from unmilled and milled switchgrass even at very low enzyme loadings.
CELF was capable of achieving nearly theoretical sugar yields from enzymatic hydrolysis of pretreated switchgrass solids without size reduction, unlike DSA. These results indicate that CELF may be able to eliminate particle size reduction prior to pretreatment and thereby reduce overall costs of biological processing of biomass to fuels. In addition, presoaking proved much more effective for CELF than for DSA, particularly at low enzyme loadings.
预处理对于降低植物生物质的天然抗降解性有效，这样细胞壁中的多糖就能被提取出来用于转化为糖。此外，木质纤维素生物质通常必须减小尺寸以提高预处理效果并实现高糖产量。然而，生物质的尺寸减小是一项能源密集型操作，并且在总体资本成本中占很大比例。
在本研究中，在通过稀硫酸（DSA）和共溶剂强化木质纤维素分级分离（CELF）进行预处理之前，研究了粒度减小和生物质预浸泡对阿拉莫柳枝稷解构的影响，这两种预处理在各自优化以实现最大糖释放的条件下进行，并随后进行酶水解。在一系列酶负载量下测量了酶水解的糖产量。一般来说，DSA成功溶解了半纤维素，而CELF除了去除了大部分半纤维素外，还从柳枝稷中去除了近80%的克拉森木质素。对于DSA和CELF预处理后的生物质组成，预浸泡和粒度减小没有显著影响。然而，与未浸泡的样品相比，预浸泡4小时使DSA预处理的柳枝稷酶水解的糖产量略有增加，而CELF固体的酶水解糖产量在预浸泡长达18小时的时间内持续大幅增加。特别重要的是，DSA需要通过刀磨将粒度减小至<2毫米，以便通过随后的酶水解获得足够的糖产量。另一方面，即使在非常低的酶负载量下，CELF固体从未研磨和研磨的柳枝稷中获得的糖产量几乎相同。
与DSA不同，CELF能够在不减小粒度的情况下，从预处理的柳枝稷固体的酶水解中实现接近理论的糖产量。这些结果表明，CELF或许能够在预处理之前消除粒度减小，从而降低生物质生物加工成燃料的总体成本。此外，事实证明预浸泡对CELF比对DSA更有效，特别是在低酶负载量时。
