Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, People's Republic of China.
Biotechnol Biofuels. 2013 Nov 29;6(1):174. doi: 10.1186/1754-6834-6-174.
Sweet sorghum is regarded as a very promising energy crop for ethanol production because it not only supplies grain and sugar, but also offers lignocellulosic resource. Cost-competitive ethanol production requires bioconversion of all carbohydrates in stalks including of both sucrose and lignocellulose hydrolyzed into fermentable sugars. However, it is still a main challenge to reduce ethanol production cost and improve feasibility of industrial application. An integration of the different operations within the whole process is a potential solution.
An integrated process combined advanced solid-state fermentation technology (ASSF) and alkaline pretreatment was presented in this work. Soluble sugars in sweet sorghum stalks were firstly converted into ethanol by ASSF using crushed stalks directly. Then, the operation combining ethanol distillation and alkaline pretreatment was performed in one distillation-reactor simultaneously. The corresponding investigation indicated that the addition of alkali did not affect the ethanol recovery. The effect of three alkalis, NaOH, KOH and Ca(OH)2 on pretreatment were investigated. The results indicated the delignification of lignocellulose by NaOH and KOH was more significant than that by Ca(OH)2, and the highest removal of xylan was caused by NaOH. Moreover, an optimized alkali loading of 10% (w/w DM) NaOH was determined. Under this favorable pretreatment condition, enzymatic hydrolysis of sweet sorghum bagasse following pretreatment was investigated. 92.0% of glucan and 53.3% of xylan conversion were obtained at enzyme loading of 10 FPU/g glucan. The fermentation of hydrolyzed slurry was performed using an engineered stain, Zymomonas mobilis TSH-01. A mass balance of the overall process was calculated, and 91.9 kg was achieved from one tonne of fresh sweet sorghum stalk.
A low energy-consumption integrated technology for ethanol production from sweet sorghum stalks was presented in this work. Energy consumption for raw materials preparation and pretreatment were reduced or avoided in our process. Based on this technology, the recalcitrance of lignocellulose was destructed via a cost-efficient process and all sugars in sweet sorghum stalks lignocellulose were hydrolysed into fermentable sugars. Bioconversion of fermentable sugars released from sweet sorghum bagasse into different products except ethanol, such as butanol, biogas, and chemicals was feasible to operate under low energy-consumption conditions.
甜高粱被认为是一种很有前途的生产乙醇的能源作物，因为它不仅提供谷物和糖，还提供木质纤维素资源。具有成本竞争力的乙醇生产需要生物转化茎秆中的所有碳水化合物，包括蔗糖和木质纤维素水解成可发酵糖。然而，降低乙醇生产成本和提高工业应用可行性仍然是一个主要挑战。在整个过程中整合不同的操作是一个潜在的解决方案。
本工作提出了一种集成工艺，将先进的固态发酵技术（ASSF）和碱性预处理相结合。首先，使用粉碎的茎秆，通过 ASSF 将甜高粱茎秆中的可溶性糖直接转化为乙醇。然后，在一个蒸馏-反应器中同时进行乙醇蒸馏和碱性预处理的联合操作。相应的研究表明，添加碱并不影响乙醇的回收。考察了三种碱，NaOH、KOH 和 Ca(OH)2 对预处理的影响。结果表明，NaOH 和 KOH 对木质纤维素的脱木质素作用比 Ca(OH)2 更为显著，NaOH 引起的木聚糖去除率最高。此外，确定了 10%（w/w DM）NaOH 的最佳碱用量。在这种有利的预处理条件下，对预处理后的甜高粱渣进行了酶水解研究。在酶用量为 10 FPU/g 葡聚糖的情况下，获得了 92.0%的葡聚糖和 53.3%的木聚糖转化率。水解浆液的发酵采用工程菌 Zymomonas mobilis TSH-01 进行。对整个工艺进行了物料衡算，从 1 吨新鲜甜高粱茎秆中获得了 91.9 千克乙醇。
本工作提出了一种从甜高粱茎秆生产乙醇的低能耗集成技术。在我们的工艺中，减少或避免了原料准备和预处理的能耗。基于这项技术，通过一种经济高效的工艺破坏木质纤维素的抗降解性，将甜高粱茎秆木质纤维素中的所有糖水解成可发酵糖。在低能耗条件下，从甜高粱渣中释放的可发酵糖转化为除乙醇以外的不同产品，如丁醇、沼气和化学品，是可行的。
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