Fine chemicals from lignocellulosic fermentation residues using heterogeneous catalysis

人们普遍认为，化石燃料需要被可再生能源替代品所取代。用于汽车的生物乙醇现在是由玉米和甘蔗等粮食作物制成的。然而，这对全球粮食市场产生了破坏性影响。从生物质（即木材、秸秆和不可食用的草作物）开始的新工艺现已进入商业阶段。生物质材料由木质素和纤维素等坚韧的聚合物组成。纤维素很难分解成葡萄糖，葡萄糖又发酵成乙醇。木质素更难分解，它不产生葡萄糖或任何其他碳水化合物，因此不能发酵。通常，发酵后留下的残渣主要由木质素组成，并被燃烧。如果木质素能被分解成它的组成部分，那么这些组成部分就很像目前从石油中提取的一些工业化学品，例如苯。一个非常广泛的化学过程，主要涉及催化剂，用于相互转换石油衍生的化学品，如苯。原则上，这些方法可以用来从木质素中制造类似的化学品。这几乎从未成功过，因为木质素是一种固体，通常不溶于水或任何其他液体。工业催化剂只对液体或气体起作用。今天，由木质素制成的唯一有用的产品是调味物质香草醛，这是构成木质素聚合物的一种单元的严重降解版本。香草醛是由木质素磺酸盐制成的，木质素磺酸盐是牛皮纸生产过程中的含硫可溶性副产品。香草醛的生产过程是一个苛刻的氧化过程，缺乏催化改性所能实现的灵活性。我们提出的创新是从生物燃料生产后剩余的发酵残留物中分离木质素，使用所谓的有机溶剂过程的改进版本。在这个过程中，木质素被轻轻地分解成大的聚合物碎片，溶解在乙醇等溶剂中。这些有机溶剂木质素片段可以以非常适合于受控催化转化成单个单元并且然后潜在地转化成目前由油制成的广泛的其它产品的纯的可溶形式回收。有机溶剂法已经被用于不同的目的，从原料中去除木质素，使纤维素更容易分解。不过，还有其他方法可以改善纤维素的获取，目前这些方法是首选：最重要的问题是可以从纤维素中制备乙醇的量。因为我们建议将有机溶剂法的一种变体应用于发酵后的残留物，所以这个问题不再相关。我们的建议在利用催化过程将木质素分解为单个单元并将这些产物转化为有用的化学品方面也是新颖的。有机溶剂木质素的纯度和溶解度是允许催化方法的关键特征。为了将这一想法付诸实践，我们需要改变有机溶剂法，使其适用于发酵后残留物中发现的更具抗性的木质素。我们还需要设计催化方法来完成木质素分解成单个单元并将其转化为其他产品。将不尝试催化转化成全范围的其它产物，仅一个实例。其目的是，这项研究将导致其他项目，其中更广泛的产品可以与工业合作。这两位研究人员为英国生物燃料界带来了新的技能。贾维斯博士在食品和木材工业中的纤维素材料分析方面有着毕生的经验，而杰克逊教授在催化方面的专业知识是在以石油为基础的化学工业中积累起来的。这些互补的技能将是完成项目所必需的，但也将是IBTI俱乐部其他活动的资产。

It is widely agreed that fossil fuels need to be replaced by renewable alternatives. Bioethanol for cars is now being made from food crops like maize and sugarcane. However this has had a disruptive effect on global food markets. New processes starting from biomass, meaning wood, straw and inedible grass crops, are now reaching commercial stage. Biomass materials consist of tough polymers like lignin and cellulose. Cellulose can with difficulty be broken down to glucose, which in turn is fermented to ethanol. Lignin is even more difficult to break down and it does not yield glucose or any other carbohydrate, so it cannot be fermented. Usually the residues left over after fermentation consist mostly of lignin, and are burnt. If lignin can be broken down into its constituent parts, these are rather like some of the industrial chemicals derived at present from oil, benzene for example. A very wide range of chemical processes, mostly involving catalysts, are in use to interconvert oil-derived chemicals like benzene. In principle processes like these could be used to make similar chemicals from lignin. This has hardly ever been done successfully, because lignin is a solid that does not usually dissolve in water or any other liquid. Industrial catalysts only work on liquids or gases. The only useful product made from lignin today is the flavouring substance vanillin, a severely degraded version of one of the units making up the lignin polymer. Vanillin is made from lignosulphonates, sulphur-containing soluble by-products of the Kraft process from which brown paper is made. The process of vanillin manufacture is a harsh oxidative one, lacking the flexibility that can be achieved by catalytic modification. The innovation that we propose is to isolate lignin from the fermentation residues remaining after biofuel production, using a modified version of what is called the organosolv process. In this process lignin is broken down gently into large, polymeric fragments that dissolve in solvents like ethanol. These organosolv lignin fragments can be recovered in a pure, soluble form very suitable for controlled catalytic conversion to single units and then, potentially, to a wide range of other products that are made at present from oil. The organosolv process has been used already with a different aim, to remove lignin from the raw material so that the cellulose can be broken down more readily. There are other ways to improve access to cellulose, though, and currently these are preferred: the most important issue is the amount of ethanol that can be made from the cellulose. Because we propose to apply a variant of the organosolv process to the residue after fermentation this problem is no longer relevant. Our proposal is also novel in making use of catalytic processes to break down the lignin to single units and to convert these products to useful chemicals. The purity and solubility of the organosolv lignin are the key features that permit the catalytic approach. To put this idea into practice we shall need to alter the organosolv process to make it suitable for the more resistant lignin that will be found in the residues after fermentation. We also need to devise catalytic methods for completing the breakdown of lignin to single units and for converting these to other products. The catalytic conversion to a full range of other products will not be attempted, only one example. The intention is that the research will lead to other projects in which a wider variety of products can be made in collaboration with industry. The two investigators bring new skills to the UK biofuels community. Dr Jarvis has a lifetime's experience of the analysis of cellulosic materials in the food and timber industries, while Prof Jackson's expertise in catalysis has been accumulated within a chemical industry founded on oil. These complementary skills will be necessary to complete the project but will also be an asset in the IBTI Club's other activities.