Depolymerization Of Polyethylene Naphthalate In Subcritical Water

In this article, phase behaviors of polyethylene naphthalate (PEN) in subcritical water with and without catalyst were investigated in a fused silica capillary reactor (FSCR), respectively. Depolymerization of PEN in SBW with and without catalyst was explored in a autoclave reactor. GC, GC-MS, HPLC, LC-MS, FT-IR and Raman spectroscopy were used to analyze the depolymerization products qualitatively and quantitatively, studying the effects of reaction conditions on depolymerization yield of PEN and yields of main products 2,6-NDA and EG. According to the analysis of depolymerization products and the phase behaviors of PEN, depolymerization mechanisms of PEN in SBW with and without catalyst were proposed.Phase changes of PEN in water with and without catalyst were investigated in different FSCRs. The datas showed that PEN gradually melted in both mediums with reaction temperature and time increasing. In the subcritical water (250℃,260℃,270℃), PEN ultimately dissolved in water becoming a homogeneous aqueous solution and catalyst zinc acetate accelerated the rate of dissolution, shortening the reaction time of polymerization. Meanwhile, in FSCRs, the vapor-liquid-solid phases turned into vapor-liquid phases finally. In the cooling process,2,6-NDA gradually separated out from the water and the size and number of it increased gradually with the drop of temperature. The results of phase changes provide a basis for the choices of reaction conditions and the analysis of mechanisms of PEN depolymerization in SBW with and without catalyst.Under the conditions of mass ratio of water/PEN (8.0-16.0), reaction temperature (240-280℃), reaction pressure (3.2-5.9 MPa) and reaction time (5-60 min), the depolymerization of PEN in SBW was studied. The results showed that the depolymerization of PEN had little relationship with the mass ratio but was mainly influenced by reaction temperature and time. At the optimal reaction condition (water/PEN ratio of 12:1 (w/w), reaction temperature 280℃ and reaction time 45 min), PEN was depolymerized completely and the yields of 2,6-NDA and EG reached 82.25% and 77.08%, respectively. Associated with the experimental datas, it was found that the activation energy of PEN depolymerization was 92.56 kJ·mol01.Under the conditions of mass ratio of water/PEN (12.0), reaction temperature (220-250℃), reaction pressure (2.1-3.9 MPa), reaction time (5-60 min) and mass of zinc acetate (0-0.04 g,0-4%), we also studied the catalytic depolymerization of PEN. The results showed that zinc acetate was beneficial to the depolymerization in SBW. At the optimal reaction condition (water/PEN ratio of 12:1 (w/w), reaction temperature 250℃, reaction time 60 min and the mass of zinc acetate 0.04 g), PEN was depolymerized completely and the yields of 2,6-NDA and EG reached 87.90% and 73.77%, respectively. The activation energy of PEN catalytic depolymerization was 59.48 kJ·mol-1, less than the activation energy in SBW 92.56 kJ·mol-1.