PET decomposition in supercritical water to recover telephthalic acid

为了开发超临界水分解PET回收对苯二甲酸的新工艺，进行了一些基础性研究。首先，利用管式弹反应器研究了反应机理。PET在亚临界和超临界水中水解制备对苯二甲酸和乙二醇。在超临界条件下（673 K，40 MPa），PET在5 min内即可完全分解，在反应12.5 min时，纯度为97%的对苯二甲酸产率可达91%。在573 K下，需要约90 min才能回收90%的对苯二甲酸。超临界条件下，压力对反应的影响显著。随着反应压力的增加，焦炭的形成受到抑制。PET分解过程中可能由于对苯二甲酸脱羧而产生的二氧化碳也得到了抑制。除了对PET的分解进行了基础性的研究外，还进行了料浆加料器的研制，为实现连续化反应奠定了基础。超临界水中PET非催化水解工艺是一种很有前途的化学品回收方法，因为1）该工艺不需要废水处理，2）在PET水解后的冷却过程中可以进行对苯二甲酸的纯化。

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.