The industrial production of sugar syrups from lignocellulosic materials requires the conduction of the enzymatic hydrolysis step at high-solids loadings (i.e., with over 15% solids [w/w] in the reaction mixture). Such conditions result in sugar syrups with increased concentrations and in improvements in both capital and operational costs, making the process more economically feasible. However, this approach still poses several technical hindrances that impact the process efficiency, known as the “high-solids effect” (i.e., the decrease in glucan conversion yields as solids load increases). The purpose of this review was to present the findings on the main limitations and advances in high-solids enzymatic hydrolysis in an updated and comprehensive manner. The causes for the rheological limitations at the onset of the high-solids operation as well as those influencing the “high-solids effect” will be discussed. The subject of water constraint, which results in a highly viscous system and impairs mixing, and by extension, mass and heat transfer, will be analyzed under the perspective of the limitations imposed to the action of the cellulolytic enzymes. The “high-solids effect” will be further discussed vis-à-vis enzymes end-product inhibition and the inhibitory effect of compounds formed during the biomass pretreatment as well as the enzymes’ unproductive adsorption to lignin. This review also presents the scientific and technological advances being introduced to lessen high-solids hydrolysis hindrances, such as the development of more efficient enzyme formulations, biomass and enzyme feeding strategies, reactor and impeller designs as well as process strategies to alleviate the end-product inhibition. We surveyed the academic literature in the form of scientific papers as well as patents to showcase the efforts on technological development and industrial implementation of the use of lignocellulosic materials as renewable feedstocks. Using a critical approach, we expect that this review will aid in the identification of areas with higher demand for scientific and technological efforts.

中文翻译：

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木质纤维素生物质高固体酶水解的制约因素和进展：一项重要综述

由木质纤维素材料的工业生产糖浆需要在高固体含量下（即反应混合物中固体含量超过15％[w / w]）进行酶促水解步骤。这样的条件导致糖浆的浓度增加，资本成本和运营成本均得到改善，从而使该过程在经济上更加可行。但是，这种方法仍然存在一些影响工艺效率的技术障碍，称为“高固含量效应”（即，随着固含量的增加，葡聚糖转化率的降低）。这篇综述的目的是以更新和全面的方式介绍有关高固体酶水解的主要限制和进展的发现。将讨论高固含量操作开始时流变学限制的原因以及影响“高固含量效应”的原因。水分限制的问题会导致高粘度的体系并损害混合，进而扩展质量和传热的角度，将在对纤维素分解酶的作用受到限制的情况下进行分析。相对于酶的终产物抑制作用和在生物质预处理过程中形成的化合物的抑制作用以及酶对木质素的非生产性吸附，将进一步讨论“高固含量效应”。这篇评论还介绍了为减少高固体份水解障碍而引入的科学技术进步，例如开发更有效的酶制剂，生物质和酶的进料策略，反应器和叶轮设计以及减轻最终产物抑制的工艺策略。我们以科学论文和专利的形式对学术文献进行了调查，以展示使用木质纤维素材料作为可再生原料的技术开发和工业实施方面的努力。我们希望采用一种关键的方法，这项审查将有助于确定对科学和技术工作有更高要求的领域。我们以科学论文和专利的形式对学术文献进行了调查，以展示使用木质纤维素材料作为可再生原料的技术开发和工业实施方面的努力。我们希望采用一种关键的方法，这项审查将有助于确定对科学和技术工作有更高要求的领域。我们以科学论文和专利的形式对学术文献进行了调查，以展示使用木质纤维素材料作为可再生原料的技术开发和工业实施方面的努力。我们希望采用一种关键的方法，这项审查将有助于确定对科学和技术工作有更高要求的领域。