Pielhop Thomas, Amgarten Janick, Studer Michael H, von Rohr Philipp Rudolf
Institute of Process Engineering, ETH Zurich, Sonneggstrasse 3, 8092 Zurich, Switzerland.
School of Agricultural, Forest and Food Sciences, Bern University of Applied Sciences, Länggasse 85, 3052 Zollikofen, Switzerland.
Biotechnol Biofuels. 2017 May 18;10:130. doi: 10.1186/s13068-017-0816-y. eCollection 2017.
Steam explosion pretreatment has been examined in many studies for enhancing the enzymatic digestibility of lignocellulosic biomass and is currently the most common pretreatment method in commercial biorefineries. It is however not effective for overcoming the extremely high recalcitrance of softwood to biochemical conversion. Recent fundamental research in small-scale liquid hot water pretreatment has shown, though, that the addition of a carbocation scavenger like 2-naphthol can prevent lignin repolymerization and thus enhance the enzymatic digestibility of softwood cellulose. This work studies the technical application potential of this approach in a larger steam explosion pilot plant for surmounting softwood recalcitrance.
The addition of 35.36 g 2-naphthol to the steam explosion pretreatment of 1.5 kg spruce wood chips allowed to considerably enhance the enzymatic cellulose digestibility. Different ways of adding the solid 2-naphthol to steam pretreatment were tested. Mixing with the biomass before pretreatment could enhance digestibility by up to 55% compared to control experiments. Impregnation of the biomass with 2-naphthol was yet more effective. Acetone and ethanol were tested to dissolve 2-naphthol and impregnate the biomass. The solvents were then removed again by evaporation before the pretreatment. The impregnation allowed to enhance digestibility by up to 179 and 192%, respectively. A comparison to prevalent acid-catalyzed steam explosion pretreatments for softwood revealed that the scavenger approach allows for obtaining exceptionally high yields in enzymatic hydrolysis. The biomass impregnation with 2-naphthol even renders a complete enzymatic cellulose conversion possible, which is remarkable for a softwood pretreatment not removing lignin. Steam pretreatment experiments without explosive decompression revealed that the enhancing effects of the explosion and the scavenger complement each other well. The explosion enhances the accessibility of the cellulose while the use of the scavenger reduces particularly the deactivation of enzymes.
This is the first study to show that a carbocation scavenger in steam pretreatment can enhance the enzymatic digestibility of lignocellulosic biomass. The approach opens up a novel possibility for overcoming the high softwood recalcitrance in a process that does not require an acid catalyst or the removal of lignin from the biomass.
蒸汽爆破预处理已在许多研究中被用于提高木质纤维素生物质的酶解消化率，并且是目前商业生物精炼厂中最常见的预处理方法。然而，它对于克服软木对生物化学转化的极高抗性并不有效。不过，最近在小规模液态热水预处理方面的基础研究表明，添加像2-萘酚这样的碳正离子清除剂可以防止木质素再聚合，从而提高软木纤维素的酶解消化率。这项工作研究了这种方法在更大规模的蒸汽爆破中试装置中克服软木抗性的技术应用潜力。
向1.5千克云杉木屑的蒸汽爆破预处理中添加35.36克2-萘酚能够显著提高纤维素的酶解消化率。测试了将固体2-萘酚添加到蒸汽预处理中的不同方式。与对照实验相比，预处理前与生物质混合可使消化率提高多达55%。用2-萘酚浸渍生物质更有效。测试了用丙酮和乙醇溶解2-萘酚并浸渍生物质。然后在预处理前通过蒸发再次除去溶剂。浸渍分别可使消化率提高多达179%和192%。与用于软木的普遍酸催化蒸汽爆破预处理相比，清除剂方法能够在酶水解中获得极高的产率。用2-萘酚浸渍生物质甚至使纤维素的完全酶转化成为可能，这对于未去除木质素的软木预处理来说是显著的。无爆炸减压的蒸汽预处理实验表明，爆炸和清除剂的增强作用相互补充良好。爆炸提高了纤维素的可及性，而使用清除剂尤其降低了酶的失活。
这是第一项表明蒸汽预处理中的碳正离子清除剂可提高木质纤维素生物质酶解消化率的研究。该方法为在不需要酸催化剂或从生物质中去除木质素的过程中克服软木的高抗性开辟了一种新的可能性。
