Converting plastic wastes into value-added products through energy-efficient pyrolysis is essential, and it requires lower pyrolysis temperatures and shorter processing times than that of other processes. An exothermic phenomenon was observed during the process high-pressure polyethylene pyrolysis. It was proven for the first time that the exotherm is caused by a pressure-induced phase transition, in which colossal heat release can be driven by relatively small pressures. A large temperature change (> 100 °C) leads to the deep cracking of polyethylene, although the set temperature is far lower than the required temperature for thermal cracking. Importantly, the heat input stops immediately when the set temperature is reached; thus, the external heating time is short. Polyethylene can be completely converted into liquid products in ~90 wt% yield and with a small number of gases. The self-exothermic phase transition only occurs within a certain range of material thickness, which is related to the corresponding phase behavior. In the self-exothermic pyrolysis process, with an increase in the thickness of polyethylene, the proportion of low-value olefins in oil products decreases gradually, while alkanes, isoalkanes and aromatics show an increasing trend, making the product composition closer to the fuel standard. This work provides a viable approach for plastic recycling at low pyrolysis temperatures and short external heating times with the help of a self-exothermic phase transition in the absence of a catalyst.
Jia Wang,Jianchun Jiang,Xianzhi Meng,Su Shiung Lam,Arthur J. Ragauskas,Yanqin Wang
Chemical upcycling rubber wastes into hydrocarbon fuels offers a promising approach toward achieving carbon neutrality . To generate fuel-range cycloalkanes and isoalkanes from natural rubber glove wastes (NRGWs), the depolymerization of NRGWs was performed by integrating hydropyrolysis with vapor-phase hydrogenation over a bifunctional Ni/Al 2 O 3 -SiO 2 catalyst. Isoprene and limonene were the primary alkenes obtained from the non-catalytic hydropyrolysis of NRGWs, and these intermediates were vapor-phase hydrotreated over Ni/Al 2 O 3 -SiO 2 producing C 10 cycloalkane as the dominant fuel-range products. Complete hydrogenation of isoprene and limonene was achieved under a catalyst to feedstock mass ratio of 2.0, giving a maximum gasoline yield of 92 wt% under 225 °C hydrogenation temperature at 0.2 MPa H 2 . A low hydropyrolysis temperature of 450 °C maximized C 10 cycloalkane yield at 72.3 wt% with 80.1% selectivity, while a high temperature of 600 °C yielded 76.6 wt% C 5 isoalkane. A deconstruction mechanism in the catalytic cascade upcycling of NRGWs was proposed by employing limonene hydrogenation as a probe reaction. The results demonstrate that upcycling polymer wastes by cascade hydropyrolysis‑hydrogenation is a promising approach to produce alternative fuels with improved properties.
危险品化学品经营许可证（带存储）