SusChEM: Drop-in Hydrocarbon Fuels through Novel Integration of Biological and Catalytic Conversion of Cellulosic Biomass-Derived Sugars

PI名称：Ian Wheeldon建议编号：1510697植物生物质是一种丰富的国内资源，可用于可持续和大规模生产液体运输燃料。这种生物质转化为燃料的系统减少了对化石燃料的依赖，降低了温室气体排放，并改善了能源安全。目前将植物生物质转化为燃料的过程通常涉及生物过程，如使用微生物将纤维素部分转化为糖，然后发酵为生物乙醇，或者通常将生物质转化为活性气体，然后再升级为各种燃料化合物的化学过程。该项目的目标是将生物和化学过程的最佳特性结合成一个单一的综合过程，有选择地将生物质糖转化为类似于汽油的液态碳氢燃料。该项目的创新方面是通过乙酸乙酯将这两个过程联系在一起，乙酸乙酯是一种由酵母产生的中间化合物，很容易分离并催化转化为高产量和高纯度的汽油。基础研究将使用基因工程，使酵母能够专门生产乙酸乙酯，而不是乙醇，然后定制催化剂系统，从乙酸乙酯生产汽油。这项研究将包括来自代表性不足背景的本科生参加加州河滨县当地社区大学的学习。拟议研究的总体目标是探索将选择性生物转化过程和催化转化过程相结合，将植物生物质衍生糖转化为液体燃料的可行性。总的概念是最大限度地利用这两个过程的独特特点，使生物质糖能够选择性地转化为碳氢化合物。选择的基础研究体系主要集中在酵母菌对乙酸乙酯生物合成的代谢工程，以及在汽油范围内乙酸乙酯的催化转化为碳氢化合物。乙酸乙酯被选为有效连接生物和化学转化步骤的中间产物，因为它的高挥发性允许以蒸汽产物的形式从发酵液中回收，并对催化转化为碳氢化合物起反应。K.maxiumus是一株可进行基因工程的工业酵母菌，具有从发酵液中回收乙酸乙酯所需的50℃的耐热性，并能代谢来自木质纤维生物质的C5和C6糖，因此被选为乙酸乙酯生物合成的模式生物。该研究计划有两个主要目标。第一个目标是鉴定马克克鲁维酵母中乙酸乙酯的生物合成途径，并利用这一知识通过代谢工程最大限度地提高乙酸乙酯的产量。为此，假设乙酸乙酯是通过三种途径之一合成的，包括通过乙醇-乙酰基转移酶(AATase)合成、反转酯酶活性或乙醇脱氢酶(ADH)活性合成半缩醛。途径将针对C5和C6糖类进行优化。第二个目标是开发和表征一种新的催化乙酸乙酯水蒸气转化为汽油烃的反应途径，即使用纳米颗粒贵金属/氧化铝氢解催化剂将乙酸乙酯转化为二乙醚，以及使用择形固体酸沸石催化剂将二乙醚转化为碳氢化合物。

PI Name: Ian WheeldonProposal Number: 1510697 Plant biomass is an abundant, domestic resource for the sustainable and large-scale production of liquid transportation fuels. Such biomass-to-fuel systems reduce dependence on fossil fuels, lower greenhouse gas production, and improve energy security. Present processes for converting plant biomass into fuels usually involve biological processes, such as using microorganisms to convert the cellulosic fractions to sugars which are fermented into bioethanol, or chemical processes, which typically convert the biomass to a reactive gas which is then upgraded to a wide range of fuel compounds. The goal of this project is combine the best attributes of biological and chemical processes into a single integrated process that selectively converts biomass sugars into liquid hydrocarbon fuels similar to gasoline. The innovative aspect of this project is that it ties both processes together through ethyl acetate, an intermediate compound produced by yeast which is readily separated and catalytically converted to gasoline with high yield and purity. The fundamental research will use genetic engineering to enable the yeast to exclusively make ethyl acetate instead of ethanol, and then tailor the catalyst systems to make gasoline from ethyl acetate. The research will include undergraduate student participants from under-represented backgrounds attending local community colleges in Riverside County, California.The overall goal of the proposed research is to explore the feasibility of integrating selective biological and catalytic conversion processes to convert plant biomass derived sugars into liquid fuels. The overall concept is to take best advantage of the unique features of both processes to enable selective conversion of biomass sugars to hydrocarbons. The particular system chosen for fundamental study focuses on the metabolic engineering of the yeast Kluyveromyces marxianus for ethyl acetate biosynthesis, followed by the catalytic conversion of ethyl acetate to hydrocarbons in the gasoline range. Ethyl acetate is selected as the intermediate product to efficiently link the biological and chemical conversion steps, since its high volatility allows for recovery as vapor product from the fermentation broth, and is reactive towards catalytic conversion to hydrocarbons. K. maxiumus is selected as the model organism for ethyl acetate biosynthesis, as it is an industrial yeast strain amenable to genetic engineering, exhibits thermal tolerance at 50 C needed for ethyl acetate vapor recovery from the fermentation broth, and can metabolize both C5 and C6 sugars derived from lignocellulosic biomass. The research plan has two primary objectives. The first objective is to identify ethyl acetate biosynthesis pathways in Kluyveromyces marxianus, and use this knowledge to maximize ethyl acetate production through metabolic engineering. Towards this end, it is hypothesized that ethyl acetate is synthesized by one of three pathways, including synthesis by alcohol-Oacetyltransferase (AATase), reverse esterase activity, or alcohol dehydrogenase (Adh) activity towards hemiacetal. Pathways will be optimized for both C5 and C6 sugars. The second objective is to develop and characterize a new catalytic reaction pathway for conversion of ethyl acetate vapor to gasoline hydrocarbons, using nanoparticle based noble metal/alumina hydrogenolysis catalysts to convert ethyl acetate to diethyl ether, and shape-selective, solid-acid zeolite catalysts to convert diethyl ether to hydrocarbons.