Production of monocyclic aromatic hydrocarbons by segmented in situ and ex situ two-stage coupled catalytic co-pyrolysis of biomass and waste plastics

Co-pyrolysis of biomass and waste plastics has the potential to produce high-quality chemicals and these resources are recycled to realize their clean and efficient utilization. However, the current co-pyrolysis technology often mixes them physically, which can cause key problems, such as large differences in pyrolysis characteristics, restricting the synergistic effect of co-pyrolysis intermediates. The purpose of this study was to construct a segmented co-pyrolysis system and use FeCl₃ and MCM-41 as in situ catalysts for Choerospondias axillaris seeds (CAS) and low-density polyethylene (LDPE), respectively, to analyze the relationship between different in situ catalyst addition ratios (0%, 3%, 5%, 7% and 10%) and pyrolysis products. In addition, the product distribution of the various parts of the segmented co-pyrolysis system as well as the comparison of segmented and traditional mixed co-pyrolysis were investigated. The results showed that FeCl₃ can help in promoting the conversion of hemicellulose and cellulose to furans from CAS. The relative content of furans in the liquid product reached 61.08 wt% when its addition was 7%. MCM-41 can achieve its best catalytic effect when its addition was 5% in LDPE. Furthermore, segmented co-pyrolysis can promote the Diels-Alder reaction between furans and olefins and result in the content of monocyclic aromatic hydrocarbons (MAHs) in the liquid product reaching up to 72.01 wt%. Compared with traditional mixed co-pyrolysis, the relative content of MAHs of segmented co-pyrolysis was 13.53 wt% higher and the wax yield was 14.49 wt% lower. Therefore, segmented co-pyrolysis can offer potential benefits for future industrial application, compared to a traditional co-pyrolysis process.