Catalytic depolymerization of high-density polyethylene and postconsumer plastic waste: Process development and process kinetics

Catalytic effects of various hydrogenation-hydrocracking catalysts on the coliquefaction of coal with HDPE or CP#2 were systematically investigated in tubing reactors or autoclave under typical liquefaction conditions: 430{dollar}spcirc{dollar}C, {dollar}sim{dollar}2000 psig H{dollar}sb2,{dollar} at reaction time of 60 minutes. Silica-alumina impregnated with Pt, Ni, Pd, or Fe showed higher catalytic activities for oil conversion than did metal-free catalysts. Both fresh and spent Ni/SiO{dollar}sb2{dollar}-Al{dollar}sb2{dollar}O{dollar}sb3{dollar} catalysts were subject to EXANES and EXAFS studies. Ni K-edge EXANES and EXAFS spectra showed that Ni was present as NiO with nanoscale particles. The effects of reactor type (autoclave and tubing reactor), reaction temperature (400-450{dollar}spcirc{dollar}C), reaction time (0 to 90 minutes), solvents (tetralin and waste oil), and coal ranks on coliquefaction of coal and HDPE with Ni/SiO{dollar}sb2{dollar}-Al{dollar}sb2{dollar}O{dollar}sb3{dollar} as catalyst were also investigated.; Two-stage coprocessing of plastic with coal was developed to produce liquid fuels. In the first stage, HDPE or CP#2 was degraded in a 150-cm{dollar}sb3{dollar} autoclave reactor at 435{dollar}spcirc{dollar}C, 1 hour, with stirring at 800 rpm, under N{dollar}sb2{dollar} or H{dollar}sb2{dollar}. For HDPE, the optimum oil yield (88.7%) was obtained over TiCl{dollar}sb3{dollar} catalyst, whereas maximum gas yield (21.2%) was produced on HZSM-5. In the second stage, the resulting oil was used as solvent for liquefaction of DECS-6 coal or Fe loaded DECS-6 coal in a tubing reactor at 400{dollar}spcirc{dollar}C, 1 hour, at 160 rpm, {dollar}sim{dollar}2000 psig H{dollar}sb2{dollar}. For Fe loaded coal liquefaction, when the oil, obtained from the degradation of HDPE at 435{dollar}spcirc{dollar}C under N{dollar}sb2{dollar}, was used as solvent, yields and total conversion were about the same as those with tetralin as solvent. The final oil products contained 70% lower-boiling fractions (b.p. up to 325{dollar}spcirc{dollar}).; Results of a kinetic study of thermal and catalytic (Fe impregnated on coal) liquefaction of DECS-6 coal with plastic-derived-liquids (PDL) as solvent have been obtained. The experimental work was conducted in 27-cm{dollar}sp3{dollar} horizontally shaken microreactors at temperatures of 360 to 400{dollar}spcirc{dollar}C with isothermal reaction times ranging from 0 to 180 minutes. The reaction pressure was about 2000 psig H{dollar}sb2{dollar} and solvent-to-coal weight ratio was 2:1. Experimental data were correlated by a kinetic model which assumed the reaction pathways: coal to preasphaltenes, coal to asphaltenes, coal to gas + oil, preasphaltenes to asphaltenes, preasphaltenes to gas + oil, and asphaltenes to gas + oil. It was shown that this reaction model fit experimental data reasonably well at the conditions used, and the six rate constants exhibited Arrhenius-type temperature dependence.