Novozymes North America, Franklinton, NC 27525, USA.
J Ind Microbiol Biotechnol. 2012 May;39(5):691-700. doi: 10.1007/s10295-011-1068-7. Epub 2011 Dec 14.
Dilute acid pretreatment is a leading pretreatment technology for biomass to ethanol conversion due to the comparatively low chemical cost and effective hemicellulose solubilization. The conventional dilute acid pretreatment processes use relatively large quantities of sulfuric acid and require alkali for pH adjustment afterwards. Significant amounts of sulfate salts are generated as by-products, which have to be properly treated before disposal. Wastewater treatment is an expensive, yet indispensable part of commercial level biomass-to-ethanol plants. Therefore, reducing acid use to the lowest level possible would be of great interest to the emerging biomass-to-ethanol industry. In this study, a dilute acid pretreatment process was developed for the pretreatment of corn stover. The pretreatment was conducted at lower acid levels than the conventional process reported in the literature while using longer residence times. The study indicates that a 50% reduction in acid consumption can be achieved without compromising pretreatment efficiency when the pretreatment time was extended from 1-5 min to 15-20 min. To avoid undesirable sugar degradation and inhibitor generation, temperatures should be controlled below 170°C. When the sulfuric acid-to-lignocellulosic biomass ratio was kept at 0.025 g acid/g dry biomass, a cellulose-to-glucose conversion of 72.7% can be achieved at an enzyme loading of 0.016 g/g corn stover. It was also found that acid loading based on total solids (g acid/g dry biomass) governs the pretreatment efficiency rather than the acid concentration (g acid/g pretreatment liquid). While the acid loading on lignocellulosic biomass may be achieved through various combinations of solids loading and acid concentration in the pretreatment step, this work shows that it is unlikely to reduce acid use without undermining pretreatment efficiency simply by increasing the solid content in pretreatment reactors, therefore acid loading on biomass is indicated to be the key factor in effective dilute acid pretreatment.
稀酸预处理是生物质转化为乙醇的主要预处理技术，因为其化学成本相对较低，且能有效溶解半纤维素。传统的稀酸预处理工艺使用相对大量的硫酸，并且需要碱来调节 pH 值。作为副产物会产生大量的硫酸盐盐，在处置之前必须进行适当的处理。废水处理是商业级生物质制乙醇工厂不可或缺的昂贵部分。因此，尽可能将酸的使用量降低到最低水平将对新兴的生物质制乙醇产业具有重要意义。在这项研究中，开发了一种用于玉米秸秆预处理的稀酸预处理工艺。与文献中报道的传统工艺相比，该预处理工艺使用的酸水平较低，停留时间较长。研究表明，当预处理时间从 1-5 分钟延长至 15-20 分钟时，通过延长预处理时间可以实现酸消耗减少 50%，而不会影响预处理效率。为避免不必要的糖降解和抑制剂生成，温度应控制在 170°C 以下。当硫酸与木质纤维素生物质的比例保持在 0.025g 酸/g 干生物质时，在酶用量为 0.016g/g 玉米秸秆的情况下，可以实现纤维素至葡萄糖的转化率为 72.7%。还发现，基于总固体（g 酸/g 干生物质）的酸负荷比酸浓度（g 酸/g 预处理液）更能控制预处理效率。虽然可以通过预处理步骤中固体负荷和酸浓度的各种组合来实现对木质纤维素生物质的酸负荷，但这项工作表明，仅通过增加预处理反应器中的固体含量而不损害预处理效率来降低酸的使用量是不太可能的，因此，生物质上的酸负荷被认为是有效稀酸预处理的关键因素。
