High Olefin Yield in Pyrolysis of Heavier Hydrocarbon Liquids Using Microwave as Heat Supplier

Abstract

In order to expand the scope of C 2 H 4 pyrolysis material and recycle the waste polyolefin, this study has employed microwave pyrolysis of heavier hydrocarbon liquids. Microwave pyrolysis not only maintains a stable energy supply to the reaction materials for obtaining a high conversion rate, but also avoids coking caused by local overheating. Steam may serve a dual role as diluent and heat carrier. Thus, this study has obtained higher olefin yield, higher olefin selectivity, and better operational continuity than conventional steam cracking. Light olefins (C 2  −C 4  ) reached 50.65−68.64 mol% in the pyrolysis gas. The yields of C 2 H 4 and C 3 H 6 for heavier hydrocarbons pyrolysis were 42.80−44.76 and 12.98−13.91 wt% of the feedstock, respectively, while the maximum yields of C 2 H 4 and C 3 H 6 for pyrolysis of liquid products of polyolefin cracking were 47.00 and 22.83 wt%, respectively. Analysis of the pyrolysis mechanism indicates that the β-scission reactions of free radicals are predominant, while the secondary reactions are significantly inhibited due to the enhanced heat transfer between the steam and the hydrocarbons.

Recent Trends in the Pyrolysis of Non‐Degradable Waste Plastics

“…In another study by Jing et al, a mixture of LDPE:PP (60 : 40) was pyrolyzed using a semi-batch reactor under atmospheric pressure applying a microwave heater. [190] They reported that high contents and selectivity towards olefins (50.65-68.64 mol %) were achieved in the process. Based on their findings, they proposed the reaction mechanism as follows: when the temperature has increased, CÀ C bond cleavage occurs to generate free radicals.…”

“…In another study by Jing et al, a mixture of LDPE:PP (60 : 40) was pyrolyzed using a semi‐batch reactor under atmospheric pressure applying a microwave heater [190] . They reported that high contents and selectivity towards olefins (50.65–68.64 mol %) were achieved in the process.…”

Plasma-Assisted Catalytic Cracking as an Advanced Process for Vegetable Oils Conversion to Biofuels: A Mini Review

“…This initiation process is followed by random scission and chain-end scission (secondary degradation) . The free radicals produced in the initiation process are generated through the C–C bond cleavage, generally random scission, which is activated at high temperature. , In the microwave-assisted cracking, the C–C bond cleavage is activated by the energy input of the microwaves. With the presence of a catalyst, the cracking temperature of the C–C bond is reduced by inducing the carbenium ion mechanism .…”

“…Second, the long-chain free radicals can generate more-stable free-radical molecules, secondary or tertiary free radicals, through the intramolecular hydrogen transfer process (labeled (II) in Figure ). Furthermore, these new radicals can produce α-olefins and new free radicals by subsequent β-scission reactions . Third, the long-chain free radicals molecules can generate alkanes and new secondary or tertiary free radicals through intermolecular hydrogen transfer process (labeled (III) in Figure ).…”

“…Proposed pyrolysis mechanism for microwave pyrolysis of heavier hydrocarbon liquids, where R p is the primary radical; R s is the secondary radical; and R t is the tertiary radical. [Reprinted (adapted) with permission from ref . Copyright 2017, American Chemical Society, Washington, DC.…”