PET decomposition in supercritical water to recover telephthalic acid

以生产聚酯的原料--邻苯二甲酸为原料，开发超临界水中分解聚酯回收邻苯二甲酸的新工艺，进行了一些基础研究。首先，利用管式炸弹反应器对反应机理进行了研究。在亚临界水和超临界水中，对苯二甲酸和乙二醇水解制取对苯二甲酸和乙二醇酯。在超临界条件下(673K，40 Mpa)，PET可在5min内分解。当反应时间为12.5min时，苯二甲酸的纯度为97%，产率为91%。反应温度对PET的分解有显著影响。在573K时，对苯二甲酸的回收率为90%，约需90min。在超临界条件下，压力对反应的影响很大。随着反应压力的增加，结焦受到抑制。在PET分解过程中产生的二氧化碳也受到抑制，这可能是由于电话邻苯二甲酸的脱羧基造成的。在此基础上，开发了浆料喂料器，为连续反应奠定了基础。我们认为，在超临界水中对苯二甲酸的非催化水解法将是一种很有前途的化学循环方法，因为1)这不需要废水处理，2)对苯二甲酸的提纯可以在PET水解后的冷却过程中进行。

For the development of a new process of PET decomposition in supercritical water to recover telephthalic acid wihch is a raw material for producing PET,some basic studies were conducted. First, mechanism of the reaction was studied by using a tube bomb reactor. Hydrolysis of PET to produce telephthalic acid and ethyleneglycol took place in both sub and supercritical water. In supercritical condition (673 K,40 MPa), PET could be decomposed in 5 min. The yield of telephthalic acid whose purity was 97% reached to 91% at the reaction time of 12.5 min. Reaction temperature influenced signifidantly the PET decomposition. At 573 K,it took around 90 min for the 90% of telephthalic acid recovery. Supercritical condition, the effect of pressure on the reaction was significant. With increasing reaction pressure, char formation could be suppressed. Carbon dioxide production during the PET decomposition which is probably due to the decarboxylation from telephthalic acid, has been also suppressed. Besides this fundamental study for the PET decomposition, development of slurry feeder was also conducted and thus the basis of the continuous reaction has established. We think the process of non catalytic hydrolysis of PET in supercritical water will be a promising method for the chemical recycle, since 1) this require no waste water treatment, 2) purification of terlephthalic acid can be done during the cooling process after the PET hydrolysis.