Matsakas Leonidas, Nitsos Christos, Raghavendran Vijayendran, Yakimenko Olga, Persson Gustav, Olsson Eva, Rova Ulrika, Olsson Lisbeth, Christakopoulos Paul
1Biochemical Process Engineering, Division of Chemical Engineering, Department of Civil, Environmental, and Natural Resources Engineering, Luleå University of Technology, 971-87 Luleå, Sweden.
2Division of Industrial Biotechnology, Department of Biology and Biological Engineering, Chalmers University of Technology, Kemivägen 10, 412 96 Göteborg, Sweden.
Biotechnol Biofuels. 2018 Jun 8;11:160. doi: 10.1186/s13068-018-1163-3. eCollection 2018.
The main role of pretreatment is to reduce the natural biomass recalcitrance and thus enhance saccharification yield. A further prerequisite for efficient utilization of all biomass components is their efficient fractionation into well-defined process streams. Currently available pretreatment methods only partially fulfill these criteria. Steam explosion, for example, excels as a pretreatment method but has limited potential for fractionation, whereas organosolv is excellent for delignification but offers poor biomass deconstruction.
In this article, a hybrid method combining the cooking and fractionation of conventional organosolv pretreatment with the implementation of an explosive discharge of the cooking mixture at the end of pretreatment was developed. The effects of various pretreatment parameters (ethanol content, duration, and addition of sulfuric acid) were evaluated. Pretreatment of birch at 200 °C with 60% v/v ethanol and 1% w/w HSO was proven to be the most efficient pretreatment condition yielding pretreated solids with 77.9% w/w cellulose, 8.9% w/w hemicellulose, and 7.0 w/w lignin content. Under these conditions, high delignification of 86.2% was demonstrated. The recovered lignin was of high purity, with cellulose and hemicellulose contents not exceeding 0.31 and 3.25% w/w, respectively, and ash to be < 0.17% w/w in all cases, making it suitable for various applications. The pretreated solids presented high saccharification yields, reaching 68% at low enzyme load (6 FPU/g) and complete saccharification at high enzyme load (22.5 FPU/g). Finally, simultaneous saccharification and fermentation (SSF) at 20% w/w solids yielded an ethanol titer of 80 g/L after 192 h, corresponding to 90% of the theoretical maximum.
The novel hybrid method developed in this study allowed for the efficient fractionation of birch biomass and production of pretreated solids with high cellulose and low lignin contents. Moreover, the explosive discharge at the end of pretreatment had a positive effect on enzymatic saccharification, resulting in high hydrolyzability of the pretreated solids and elevated ethanol titers in the following high-gravity SSF. To the best of our knowledge, the ethanol concentration obtained with this method is the highest so far for birch biomass.
预处理的主要作用是降低天然生物质的抗降解性，从而提高糖化产率。有效利用所有生物质成分的另一个前提条件是将它们有效地分离成明确的工艺流。目前可用的预处理方法仅部分满足这些标准。例如，蒸汽爆破作为一种预处理方法表现出色，但分离潜力有限，而有机溶剂法在脱木质素方面表现出色，但生物质解构效果不佳。
在本文中，开发了一种混合方法，该方法将传统有机溶剂预处理的蒸煮和分离与在预处理结束时对蒸煮混合物进行爆炸排放相结合。评估了各种预处理参数（乙醇含量、持续时间和硫酸添加量）的影响。事实证明，在200°C下用60% v/v乙醇和1% w/w H₂SO₄对桦木进行预处理是最有效的预处理条件，得到的预处理固体中纤维素含量为77.9% w/w、半纤维素含量为8.9% w/w、木质素含量为7.0% w/w。在这些条件下，脱木质素率高达86.2%。回收的木质素纯度高，纤维素和半纤维素含量分别不超过0.31% w/w和3.25% w/w，且所有情况下灰分均<0.17% w/w，适用于各种应用。预处理后的固体具有较高的糖化产率，在低酶负载量（6 FPU/g）下达到68%，在高酶负载量（22.5 FPU/g）下实现完全糖化。最后，在20% w/w固体含量下进行同步糖化发酵（SSF），192小时后乙醇浓度达到80 g/L，相当于理论最大值的90%。
本研究开发的新型混合方法能够有效地分离桦木生物质，并生产出纤维素含量高、木质素含量低的预处理固体。此外，预处理结束时的爆炸排放对酶促糖化有积极影响，导致预处理固体具有高水解性，并在随后的高浓度SSF中提高了乙醇浓度。据我们所知，用这种方法获得的乙醇浓度是迄今为止桦木生物质中最高的。
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