Jet fuel range hydrocarbon generation from catalytic pyrolysis of lignin and polypropylene with iron-modified activated carbon

In this study, iron was used to modify pyrolytic activated carbon (AC) to synthesize a bifunctional catalyst (Fe/AC). It was applied to the catalytic co-pyrolysis of lignin with polypropylene (PP) for the preparation of jet fuel range hydrocarbons. Relationships between iron loading, reaction temperature, catalyst/feedstock ratio, and lignin/PP ratio were investigated in connection to the yield, component distribution, carbon number distribution, and chain structure of pyrolysis products. The results indicated that the hydrocarbons with carbon numbers in the jet fuel range dominated the products obtained from the catalytic co-pyrolysis of lignin and polypropylene. Owing to the oxytropism of Fe3+, the selectivity of oxygenated chemicals in pyrolysis oil decreased as the Fe loading rose. Consequently, the production of hydrocarbons in the jet fuel range was increased. Furthermore, the deoxygenation and alkylation reactions of phenols to high-carbon aromatics were facilitated by Fe3+. The cyclization and dehydrogenation reactions were promoted with the reaction temperature increased, thus enhancing the selectivity of cyclic hydrocarbons (cycloalkanes and aromatics) in the jet fuel range. However, secondary reactions were boosted with the excessive temperature, reducing the yield of hydrocarbons and the percentage of high-carbon hydrocarbons in the jet fuel range. The reduction of the proportion of oxygenated compounds was facilitated by the use of catalysts. Thus, the selectivity of hydrocarbons in the jet fuel range was improved, but the yield of high-carbon hydrocarbons would be reduced. In addition, the cleavage of PP-derived chain hydrocarbons was promoted by the hydrogen abstraction reaction of lignin-derived oxygenates during co-pyrolysis. The hydrogen transfer reaction between hydrocarbons and phenols was enhanced, it was pushed for phenols to convert to aromatics. Thus, the yield of hydrocarbons in the range of jet fuel was improved. A new approach to the efficient application of lignin with PP might be offered by the current work.