Lignocellulosic Biomass Transformations via Greener Oxidative Pretreatment Processes: Access to Energy and Value-Added Chemicals.
Lignocellulosic Biomass Transformations via Greener Oxidative Pretreatment Processes: Access to Energy and Value-Added Chemicals.
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DOI：
10.3389/fchem.2018.00141
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发表时间：
2018
影响因子：
5.5
通讯作者：
Varma RS
中科院分区：
文献类型：
--
作者：
Den W;Sharma VK;Lee M;Nadadur G;Varma RS
人为气候变化主要是由化石燃料驱动的全球经济排放的大量二氧化碳引起的，已被观察到并被科学证明是对文明的主要威胁。与此同时，化石燃料的枯竭已被确定为未来的挑战。有机残渣形式的木质纤维生物质似乎是生产能源和平台化学品的最有希望的可再生原料。到目前为止，与淀粉和甘蔗等原料相比，来自木质纤维生物质的生物质能源相对较少，主要是因为生产成本较高，需要通过破坏这些刚性聚合物的天然顽固结构来粉碎生物质组分；耐火原料的酶解效率低是一个重大挑战。木质素和纤维素的价态转化为能源产品或化学产品取决于前处理过程的选择性解聚的有效性，这通常涉及在腐蚀性酸或碱性试剂的辅助下进行苛刻的热解和溶剂热过程。这些非选择性的方法将木质素分解成许多可能在能量或化学上没有价值，甚至在生物上具有抑制性的产物。因此，在过去的十年里，探索更温和、更有选择性和更绿色的工艺已成为这些材料价态研究的关键课题。正在探索高效的替代活化工艺，如微波和超声波照射，以替代热解和水热分解，而较温和的选择，如高级氧化和催化工艺，应被视为更苛刻的酸和碱性工艺的选择。在此，我们严格限制了木质纤维素化学氧化技术的研究，明确的目的是使生物质前处理步骤的目标和与常规工艺相关的问题合理化。综述了臭氧分解、光催化、氧化催化、电化学氧化、Fenton或类Fenton反应等绿色工艺应用于木质纤维生物质解聚的反应途径、最终产物的选择性和效率的机理，并在生命周期评估的背景下讨论了采用更绿色预处理工艺的生物精炼的未来前景。
Anthropogenic climate change, principally induced by the large volume of carbon dioxide emission from the global economy driven by fossil fuels, has been observed and scientifically proven as a major threat to civilization. Meanwhile, fossil fuel depletion has been identified as a future challenge. Lignocellulosic biomass in the form of organic residues appears to be the most promising option as renewable feedstock for the generation of energy and platform chemicals. As of today, relatively little bioenergy comes from lignocellulosic biomass as compared to feedstock such as starch and sugarcane, primarily due to high cost of production involving pretreatment steps required to fragment biomass components via disruption of the natural recalcitrant structure of these rigid polymers; low efficiency of enzymatic hydrolysis of refractory feedstock presents a major challenge. The valorization of lignin and cellulose into energy products or chemical products is contingent on the effectiveness of selective depolymerization of the pretreatment regime which typically involve harsh pyrolytic and solvothermal processes assisted by corrosive acids or alkaline reagents. These unselective methods decompose lignin into many products that may not be energetically or chemically valuable, or even biologically inhibitory. Exploring milder, selective and greener processes, therefore, has become a critical subject of study for the valorization of these materials in the last decade. Efficient alternative activation processes such as microwave- and ultrasound irradiation are being explored as replacements for pyrolysis and hydrothermolysis, while milder options such as advanced oxidative and catalytic processes should be considered as choices to harsher acid and alkaline processes. Herein, we critically abridge the research on chemical oxidative techniques for the pretreatment of lignocellulosics with the explicit aim to rationalize the objectives of the biomass pretreatment step and the problems associated with the conventional processes. The mechanisms of reaction pathways, selectivity and efficiency of end-products obtained using greener processes such as ozonolysis, photocatalysis, oxidative catalysis, electrochemical oxidation, and Fenton or Fenton-like reactions, as applied to depolymerization of lignocellulosic biomass are summarized with deliberation on future prospects of biorefineries with greener pretreatment processes in the context of the life cycle assessment.