Center for Energy, Indian Institute of Technology Guwahati, Guwahati, Assam, India.
Crit Rev Biotechnol. 2012 Sep;32(3):235-62. doi: 10.3109/07388551.2011.604839. Epub 2011 Sep 27.
Biodiesel has emerged as a potential alternate renewable liquid fuel in the past two decades. Total annual production of biodiesel stands at 6.96 million tons and 11.2 million tons in USA and Europe, respectively. In other countries, Asia and Latin America, biodiesel production has increased at unprecedented rate. Despite this, the economy of biodiesel is not attractive. An obvious solution for boosting the economy of the biodiesel industry is to look for markets for side products of the transesterification process of biodiesel synthesis. The main by-product is glycerol. However, this glycerol is contaminated with alkali/acid catalyst and alcohol, and thus, is not useful for conventional applications such as in toothpaste, drugs, paints and cosmetics. Conversion of this glycerol to value-added product is a viable solution for effective and economic utilization, which would also generate additional revenue for the biodiesel industry. Intensive research has taken place in area of conversion of glycerol to numerous products. The conventional catalytic route of glycerol transformation employs prohibitively harsh conditions of temperature and pressure, and thus, has slim potential for large-scale implementation. In addition, the selectivity of the process is rather small with formation of many undesired side products. The bioconversion processes, on the other hand, are highly selective although with slower kinetics. In this review, we have given an assessment and overview of the literature on bioconversion of glycerol. We have assessed as many as 23 products from glycerol bioconversion, and have reviewed the literature in terms of microorganism used, mode of fermentation, type of fermentor, yield and productivity of the process and recovery/purification of the products. The metabolic pathway of conversion of glycerol to various products has been discussed. We have also pondered over economic and engineering issues of large-scale implementation of process and have outlined the constraints and limitations of the process. We hope that this review will be a useful source of information for biochemists, biotechnologists, microbiologists and chemical engineers working in the area of glycerol bioconversion.
在过去的二十年中，生物柴油已成为一种有潜力的可再生液体燃料。美国和欧洲的生物柴油总产量分别达到了 696 万吨和 1120 万吨。在其他国家，如亚洲和拉丁美洲，生物柴油的产量也以前所未有的速度增长。尽管如此，生物柴油的经济性并不吸引人。提高生物柴油行业经济的一个明显解决方案是为生物柴油合成酯交换过程的副产物寻找市场。主要的副产品是甘油。然而，这种甘油被碱/酸催化剂和酒精污染，因此，不适用于传统应用，如牙膏、药物、油漆和化妆品。将这种甘油转化为高附加值产品是有效和经济利用的可行解决方案，也将为生物柴油行业带来额外的收入。在将甘油转化为众多产品的领域，已经进行了大量的研究。甘油转化的传统催化途径需要极其苛刻的温度和压力条件，因此，大规模实施的潜力很小。此外，该过程的选择性相当小，会形成许多不期望的副产物。另一方面，生物转化过程虽然动力学较慢，但具有高度的选择性。在这篇综述中，我们对甘油生物转化的文献进行了评估和概述。我们评估了多达 23 种来自甘油生物转化的产品，并根据所用微生物、发酵方式、发酵罐类型、过程的产率和生产率以及产品的回收/纯化等方面对文献进行了综述。讨论了甘油转化为各种产品的代谢途径。我们还考虑了大规模实施该过程的经济和工程问题，并概述了该过程的限制和局限性。我们希望这篇综述能为从事甘油生物转化研究的生物化学家、生物技术专家、微生物学家和化学工程师提供有用的信息来源。
