Luque Luis, Oudenhoven Stijn, Westerhof Roel, van Rossum Guus, Berruti Franco, Kersten Sascha, Rehmann Lars
Department of Chemical and Biochemical Engineering, University of Western Ontario, 1151 Richmond Street, London, ON Canada.
Institute for Chemicals and Fuels from Alternative Resources, University of Western Ontario, 22312 Wonderland Road, Ilderton, ON Canada.
Biotechnol Biofuels. 2016 Nov 9;9:242. doi: 10.1186/s13068-016-0661-4. eCollection 2016.
One of the main obstacles in lignocellulosic ethanol production is the necessity of pretreatment and fractionation of the biomass feedstocks to produce sufficiently pure fermentable carbohydrates. In addition, the by-products (hemicellulose and lignin fraction) are of low value, when compared to dried distillers grains (DDG), the main by-product of corn ethanol. Fast pyrolysis is an alternative thermal conversion technology for processing biomass. It has recently been optimized to produce a stream rich in levoglucosan, a fermentable glucose precursor for biofuel production. Additional product streams might be of value to the petrochemical industry. However, biomass heterogeneity is known to impact the composition of pyrolytic product streams, as a complex mixture of aromatic compounds is recovered with the sugars, interfering with subsequent fermentation. The present study investigates the feasibility of fast pyrolysis to produce fermentable pyrolytic glucose from two abundant lignocellulosic biomass sources in Ontario, switchgrass (potential energy crop) and corn cobs (by-product of corn industry).
Demineralization of biomass removes catalytic centers and increases the levoglucosan yield during pyrolysis. The ash content of biomass was significantly decreased by 82-90% in corn cobs when demineralized with acetic or nitric acid, respectively. In switchgrass, a reduction of only 50% for both acids could be achieved. Conversely, levoglucosan production increased 9- and 14-fold in corn cobs when rinsed with acetic and nitric acid, respectively, and increased 11-fold in switchgrass regardless of the acid used. After pyrolysis, different configurations for upgrading the pyrolytic sugars were assessed and the presence of potentially inhibitory compounds was approximated at each step as double integral of the UV spectrum signal of an HPLC assay. The results showed that water extraction followed by acid hydrolysis and solvent extraction was the best upgrading strategy. Ethanol yields achieved based on initial cellulose fraction were 27.8% in switchgrass and 27.0% in corn cobs.
This study demonstrates that ethanol production from switchgrass and corn cobs is possible following a combined thermochemical and fermentative biorefinery approach, with ethanol yields comparable to results in conventional pretreatments and fermentation processes. The feedstock-independent fermentation ability can easily be assessed with a simple assay.
木质纤维素乙醇生产的主要障碍之一是需要对生物质原料进行预处理和分馏，以生产足够纯净的可发酵碳水化合物。此外，与玉米乙醇的主要副产品干酒糟（DDG）相比，副产品（半纤维素和木质素部分）价值较低。快速热解是一种用于处理生物质的替代热转化技术。最近对其进行了优化，以生产富含左旋葡聚糖的物流，左旋葡聚糖是用于生物燃料生产的可发酵葡萄糖前体。其他产品物流可能对石化行业有价值。然而，众所周知，生物质的异质性会影响热解产物物流的组成，因为在回收糖类时会得到芳香族化合物的复杂混合物，这会干扰后续发酵。本研究调查了快速热解从安大略省两种丰富的木质纤维素生物质来源柳枝稷（潜在能源作物）和玉米芯（玉米产业副产品）生产可发酵热解葡萄糖的可行性。
生物质脱矿可去除催化中心并提高热解过程中左旋葡聚糖的产率。当分别用乙酸或硝酸脱矿时，玉米芯中生物质的灰分含量显著降低了82% - 90%。在柳枝稷中，两种酸只能使灰分含量降低50%。相反，用乙酸和硝酸冲洗后，玉米芯中左旋葡聚糖的产量分别增加了9倍和14倍，而在柳枝稷中，无论使用哪种酸，产量都增加了11倍。热解后，评估了升级热解糖的不同配置，并在每个步骤中通过高效液相色谱分析的紫外光谱信号的二重积分来估算潜在抑制性化合物的存在。结果表明，水提取后进行酸水解和溶剂提取是最佳的升级策略。基于初始纤维素部分的乙醇产率在柳枝稷中为27.8%，在玉米芯中为27.0%。
本研究表明，采用热化学和发酵生物精炼相结合的方法，从柳枝稷和玉米芯生产乙醇是可行的，乙醇产率与传统预处理和发酵过程中的结果相当。原料无关的发酵能力可以通过简单的分析轻松评估。
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