Production of bio-plastics from organic acids derived from brown coal

褐煤是一种丰富的化石资源，但由于其热值较低，尚未得到大量利用。考虑到褐煤含有小芳环结构和多官能团，应探索反映其结构的利用方法。另一方面，生产生物塑料的成本非常高，因为原材料非常昂贵。如果生物塑料可以从低成本的原料中生产出来，它们可能作为一种环保材料被广泛利用。从这个角度出发，我们提出了一种以褐煤为原料，在温和条件下生产生物塑料原料的新方法。研究了几种褐煤在30% h_2o_2水溶液中，在25 ~ 80℃的常压下氧化。当澳大利亚褐煤在60℃下氧化24小时时，80%的煤分解成水溶性有机物，其中38%是草酸、甲酸、乙酸、乙醇酸和丙二酸等化学物质。接下来，利用Aladcligenes enthrophahas从这些有机酸中生产聚羟基丁酸（一种生物塑料，PHB）。结果表明，为了高产PHB，有机酸总浓度应保持在5 g/l以下。仅以乙酸为原料时，PHB的产率可达33%。该反应由柠檬酸在TCA循环中生成的NADPH控制。丙二酸完全不发生反应，因此可以通过生产PHB从有机酸混合物中高选择性地回收丙二酸。结果表明，该方法是利用褐煤制备生物塑料的有效方法。

Brown coals are abundant fossil resources, but they have not been utilized in a large amount because of their low calorific values. Condidering that brown coals consist of small aromatic ring structure and many functional groups, utilization methods reflecting the structure should be explored. On the other hand, the cost for producing bio-plastics is very high because raw materials are verr expensive. If bio-plastics can ve produced from a feedstock of low cost, they may be utilized widely as a environmentally benign material.From this viewpoint we have presented a new method to produce a feedstock for bio-plastics from brown coals under mild conditions. Several brown coals were oxidized in 30%-H_2O_2 aqueous solution at between 25 and 80ﾟC under atmospheric pressure. When an Australian brown coal was oxidized for 24h at 60ﾟC,80wt% of the coal decomposed to water soluble organics, 38% of which were, surprisingly, chemicals such as oxalic acid, formic acid, acetic acid, glycolic acid, and malonic acid.Next, poly hydroxyl butylic acid (a bio-plastics, PHB) was produced from these organic acids using Aladcligenes enthrophas. It was found that total concentration of organic acids should be kept less than 5 g/l in order to produce PHB in high yield. The yield of PHB reached 33% when only acetic acid was used as a feedstock. The reaction was controlled by NADPH produced from citric acid in TCA cycle. Malonic acid did not react at all, so it can be recovered in high selectivity from the mixture of the organic acids through producing PHB.Thus it was clarified that the proposed method is effective to produce bioplastics from brown coals.