Co-pretreatment of spruce and poplar for ethanol production - Effects of mixed feedstocks on pretreatment and enzymatic hydrolysis efficiency
Abstract: Oil is very important for today’s society and the transportation sector is almost completely dependent on this material. Unfortunately, it affects the level of greenhouse gases negatively which in turn contribute to global warming. Therefore, it is necessary to reduce greenhouse gas emissions, especially in the sectors that emit the most, as transportation sector. The European Parliament has decided that by year 2020, 20 % of all fuels used in European transportation sector should be based on renewable energy sources. However, it is not easy to find an energy source that will replace oil, but one of the leading alternatives is ethanol produced from biomass. There are many different raw materials that can serve as feedstock in ethanol production process, both first generation and second generation. However, within the same plant, usually the feedstock is not mixed and the ethanol process is optimized for one material. Diversifying feedstock base may lead to improved supply efficiency and, thus improved profitability. However, the heterogeneity of feedstock mixtures makes the concurrent processing of multiple feedstocks more challenging, which requires further investigations. This study concentrates on exploring the possibility to co-pretreat spruce (softwood) and poplar (hardwood) to enable to utilize mixed feedstock blends for ethanol production in a second generation process. In this study it has been showed that there are no huge effects or synergies by mixing poplar and spruce on enzymatic hydrolysis. Although, if a 50% blend of spruce and poplar not possible to separate is to be pretreated, there is a wide range of conditions that can be applied and still obtain the same glucose yield after enzymatic hydrolysis. Also, the study has showed that glucan amount was increasing and the concentrations of monomeric glucose were decreasing with higher percentage of poplar in the feedstock mixtures. From the pretreatment step it was concluded that poplar needs more severe pretreatment than spruce in order to dissolve hemicelluloses to the same extent. The main conclusion from the study is that it is not effective to mix poplar and spruce considering sugar recoveries after enzymatic hydrolysis. When poplar and spruce are mixed, lower glucose recoveries than for pure materials are obtained after enzymatic hydrolysis. The mixtures have to be further test for fermentability in order to draw any conclusion on ethanol yield.
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