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Producing aromatic-enriched oil from mixed plastics through catalytic pyrolysis has been experimentally studied. The effect of biochar catalysts has been investigated, and the possible dominating catalytic mechanisms of biochars activated with different chemical agents have been discussed. Results indicated that when waste plastics were pyrolyzed with raw biochar, the alkene fraction in the oil product increased to 54.9%. When biochar was activated by ZnCl2, KOH, and H3PO4, the oil product showed high selectively toward aromatics, and the proportions of aromatics were up to 47.6, 44.7, and 66.0%, respectively. Benzene, 1,1′-(1,3-propanediyl) bis- was the main composition in aromatics, the proportion of which could be up to 25.1% when KOH-activated biochar was used. The enrichment part of aromatics was mainly bicyclic aromatics and C15–C16 compositions, the maximum proportions of which could reach 92.5 and 28.1% by KOH-activated biochar. High surface functional group (e.g., C═O) content and low metal content of KOH-activated biochar promoted hydrogen transfer reaction of alkenes to alkanes and aromatics, whereas the aromatization process promoted by Lewis acid sites and Brønsted acid sites on ZnCl2- and H3PO4-activated biochar, respectively, significantly increased aromatic yield.
Sun et al. (Tue,) studied this question.