Preparation Of 1, 4-cyclohexanedimethanol By Selective Hydrogenation Of The Waste PET Monomer Bis(2-hydroxyethylene Terephthalate)

With the wide application of high performance polyesters, the demand of 1,4-cyclohexanedimethanol(CHDM) wich is an important raw material in the synthetic of high performance polyesters,therefore, the studies on the synthetic of CHDM will be increasing. Industrially, CHDM is prepared by two-step hydrogenation of dimethyl terephthalate(DMT). However, DMT is derived from petroleum industries and the cost of raw material is high. So, it is imperative to develop a new approach for the preparation of CHDM. Additionally, bis(2-hydroxyethylene terephthalate)(BHET)obtained from the waste poly(ethylene terephthalate) PET has no application in the market currently, therefore, we produced the 1, 4-cyclohexanedimethanol by the hydrogenation of BHET, which not only improves the economy of the waste PET recycling, resulting in the high-valued of the waste PET monomer BHET, but also reduces the cost of the procuction of CHDM effectively, which contributes to the recycling of resources.Herein, a new method for the preparation of CHDM using the BHET without solvent was established. We not only explored the two-step and one-step hydrogenation process, but also optimized the catalysts and reaction conditions. The catalysts were characterized and the catalytic mechanism was suggested.In the two-step preparation of CHDM by BHET without solvent, the first step is the selective hydrogenation of phenyl group to cyclohexane group, which was catalyzed by Pd/C catalyst. From the optimization of reaction conditions, the conversion of BHET and the yield of bis(2-hydroxyethyl) cyclohexane-1,4-dicarboxylate(BHCD) have reached 100% and 95%, respectively. The second step is the selective hydrogenation of ester group to hydroxyl group catalyzed by Cu-based catalysts. By optimizing the reaction conditions, the conversion of BHCD and the two-step yield of CHDM have reached 100% and 78%, respectively. Addtionally, theH2-TPR, XRD, SEM, XPS, TEM, BET were used to characterize the Cu-based catalysts, demonstrating that the Cu+/Cu0 species are the active sites.In the one-step solvent-free preparation of CHDM by BHET, we firstly prepared the Ru Pt/γAl2O3 or Si O2 catalysts containing different third elements(Sn, Cu, Zn, Pb and Mn), and selectived the third element Sn and the γAl2O3 carrier which showed the best activity. The single metal element, bimetal element and three metallic elements containing Ru, Pt, Sn suppoted on the γAl2O3 catalysts were prepared, the catalytic activity evaluation of the catalysts showed that only the three metallic catalysts have effect.The further studies on the catalytic activity of the Ru Pt Sn/Al2O3 series catalyts with diffrient Ru content were carried out.It displayed that with the increase of the ratio of Ru, the yield of CHDM increased, however, the yield of CHDM became unchanged when the ritio of Ru exceeds 6. The conversion of BHET and yield of CHDM reached 100% and 87%, respectively, catalyzed by the Ru6 Pt Sn4/Al2O3 catalyst.The H2-TPR, XRD, SEM, XPS, TEM, BET were used to characterize the Ru Pt Sn/Al2O3 series catalyts, demonstrating that Ru0, Ru O2, Pt0, Pt O2 and Sn O2 exist in the catalysts. From the characterization of catalysts and the catalytic activity evaluation, the catalytic mechanism was speculated that the interaction between Ru O2 and Al2O3 forms the co-catalyst, Pt shows the supporting role to Ru in the selective hydrogenation of phenyl group to cyclohexane group, in the selective hydrogenation of ester group to hydroxyl group, Ru0 is the active sites,and the Sn O2 plays as acid which reduces the effect of carbon-oxygen double bond of the ester groups, thus promoting the selective hydrogenation of ester group.