Department of Paper and Bioprocess Engineering, SUNY College of Environmental Science and Forestry,1 Forestry Drive, Syracuse, NY 13210, USA.
Biotechnol Adv. 2012 Jul-Aug;30(4):785-810. doi: 10.1016/j.biotechadv.2012.01.013. Epub 2012 Jan 27.
Woody biomass is renewable only if sustainable production is imposed. An optimum and sustainable biomass stand production rate is found to be one with the incremental growth rate at harvest equal to the average overall growth rate. Utilization of woody biomass leads to a sustainable economy. Woody biomass is comprised of at least four components: extractives, hemicellulose, lignin and cellulose. While extractives and hemicellulose are least resistant to chemical and thermal degradation, cellulose is most resistant to chemical, thermal, and biological attack. The difference or heterogeneity in reactivity leads to the recalcitrance of woody biomass at conversion. A selection of processes is presented together as a biorefinery based on incremental sequential deconstruction, fractionation/conversion of woody biomass to achieve efficient separation of major components. A preference is given to a biorefinery absent of pretreatment and detoxification process that produce waste byproducts. While numerous biorefinery approaches are known, a focused review on the integrated studies of water-based biorefinery processes is presented. Hot-water extraction is the first process step to extract value from woody biomass while improving the quality of the remaining solid material. This first step removes extractives and hemicellulose fractions from woody biomass. While extractives and hemicellulose are largely removed in the extraction liquor, cellulose and lignin largely remain in the residual woody structure. Xylo-oligomers, aromatics and acetic acid in the hardwood extract are the major components having the greatest potential value for development. Higher temperature and longer residence time lead to higher mass removal. While high temperature (>200°C) can lead to nearly total dissolution, the amount of sugars present in the extraction liquor decreases rapidly with temperature. Dilute acid hydrolysis of concentrated wood extracts renders the wood extract with monomeric sugars. At higher acid concentration and higher temperature the hydrolysis produced more xylose monomers in a comparatively shorter period of reaction time. Xylose is the most abundant monomeric sugar in the hydrolysate. The other comparatively small amounts of monomeric sugars include arabinose, glucose, rhamnose, mannose and galactose. Acetic acid, formic acid, furfural, HMF and other byproducts are inevitably generated during the acid hydrolysis process. Short reaction time is preferred for the hydrolysis of hot-water wood extracts. Acid hydrolysis presents a perfect opportunity for the removal or separation of aromatic materials from the wood extract/hydrolysate. The hot-water wood extract hydrolysate, after solid-removal, can be purified by Nano-membrane filtration to yield a fermentable sugar stream. Fermentation products such as ethanol can be produced from the sugar stream without a detoxification step.
木质生物质只有在可持续生产的情况下才是可再生的。研究发现，最佳和可持续的生物质林分生产速率是收获时的增量增长率等于平均总增长率。木质生物质的利用带来了可持续的经济。木质生物质由至少四个组成部分组成：提取物、半纤维素、木质素和纤维素。虽然提取物和半纤维素对化学和热降解的抵抗力最小，但纤维素对化学、热和生物攻击的抵抗力最大。反应性的差异或不均匀性导致木质生物质在转化过程中的顽固性。本文提出了一系列工艺，作为基于增量顺序解构的生物炼制厂，对木质生物质进行分馏/转化，以实现主要成分的有效分离。生物炼制厂最好没有预处理和解毒过程，因为这些过程会产生废物副产物。虽然有许多生物炼制厂的方法，但本文重点对基于水的生物炼制厂工艺的综合研究进行了综述。热水提取是从木质生物质中提取价值并提高剩余固体材料质量的第一步。这第一步从木质生物质中提取提取物和半纤维素部分。虽然提取物和半纤维素在提取液中大部分被去除，但纤维素和木质素在残余木质结构中大部分保留。硬木提取物中的木寡糖、芳烃和乙酸是开发价值最大的主要成分。较高的温度和较长的停留时间会导致更高的质量去除。虽然高温（>200°C）几乎可以完全溶解，但提取液中的糖含量会随着温度的升高而迅速下降。浓缩木材提取物的稀酸水解使木材提取物具有单糖。在较高的酸浓度和较高的温度下，反应时间较短，水解生成更多的木糖单体。木糖是水解物中最丰富的单糖。其他相对少量的单糖包括阿拉伯糖、葡萄糖、鼠李糖、甘露糖和半乳糖。在酸水解过程中，不可避免地会产生乙酸、甲酸、糠醛、HMF 和其他副产物。热水木材提取物的水解反应时间越短越好。酸水解为从木材提取物/水解物中去除或分离芳烃材料提供了绝佳机会。在固体去除后，热水木材提取物水解液可以通过纳滤进行纯化，以得到可发酵的糖流。发酵产物，如乙醇，可以从糖流中生产而无需解毒步骤。
