The Value-added Utilization Of PET Monomer Bis(2-hydroxyethylene Terephthalate)

With the extensive use of PET, the disposal of waste plastics has caused a huge resource waste and heavy pressure on society and ecological environment. The corresponding monomers can be easily obtained through chemical degradation of waste PET, and ethylene terephthalate(BHET) with high purity is obtained by glycolysis of waste PET under mild condition. Currently, there is no other application of BHET for commerce besides re-polymerization.1,4-cyclohexanedimethanol(CHDM) is one of the important synthetic raw materials and widely used in high-performance polyester industry, which causes great market demand. In order to improve the value of the recycling of waste PET, the conversion of BHET into CHDM by a two-step hydrogenation method has been studied.However, it is difficult to separate the intermediate product for further hydrogenation. Besides, the operation process is so complicated that leads to high production costs.Herein, an one-pot conversion process of BHET into CHDM by selective hydrogenation is introduced. In the experiment, a series of catalysts were prepared with impregnation method, and the catalysts were characterized by BET, SEM, EDS.The incorporation of the third component such as Pt, Ni, Co and Pd into RuSn catalyst could significantly improve the performance of the catalyst, among which Pt performed the best. Based on the above, RuSnPt catalyst was used in the following experiments. The effect of the reaction conditions on the conversion of BHET into CHDM were studied, and the optimal reaction conditions including reaction temperature, pressure and time were also studied. At the same time, the possibility of hydrogenating BHET into CHDM by single reaction temperature was verified. Since the hydrogenation conditions of the phenyl group and the carbonyl group were quite different, desire result was not obtained. In addition, according to the distribution of the products, the possible reaction pathway was proposed, which was beneficial to the further exploration of the reaction mechanism. Moreover, different methods for the preparation of CHDM were compared and the conversion of BHET into CHDMby one-pot method was of great potential.P-xylene(PX) is one of the important chemicals, which is widely used in many fields such as polyester fiber, plastic, pesticide, pharmaceuticals and so on. In recent years, due to the rapid development of polyester fiber, the demand for p-xylene greatly increases for its use in the synthesis of the polyester fibers.In this study, RuSnPt catalyst was found to show superior performance for the hydrolysis of waste PET into p-xylene(PX).The decomposition temperature,melting point and molecular weight of PET material were determined by TGA, DSC and GPC analysis, respectively. The catalysts before and after using were characterized by XRD, SEM and TEM and so on. The results showed that the agglomeration of catalyst after using appeared due to the high temperature and the effect of the reactants and products. The reaction conditions including reaction temperature and time were optimized. Nearly 100% conversion of PET and 91.0%selectivity of PX were obtained at 300℃, 5MPa for 7h. In addition, the kinetic study of the reaction was carried out, and the activation energy Ea and the Arrhenius constant A were obtained. The study not only broadens the sources of raw materials for the preparation of PX, but also has great significance for environmental protection and recycling of resource.