Perspectives of Biomass Catalytic Fast Pyrolysis for Co-Refining: Review and Correlation of Literature Data From Continuously Operated Setups

Abstract

For the co-processing of pyrolysis-based biocrudes within petroleum refineries, a degree of conditioning/upgrading involving the cracking of the oligomers and (partial) removal of oxygen could be operationally beneficial. By inducing a complex set of reactions in biomass-derived fast pyrolysis vapors, catalytic fast pyrolysis (CFP) ensures significant changes in oxygen functionalities and alleviates oxygen concentration in the resulting liquid intermediate (CFP-oil). Due to its reduced oxygen content and acidity, CFP-oil could be considered suitable for co-feeding in FCC units and/or for co-hydrotreatment (co-HT) with gas oils within the existing crude oil processing infrastructure. On the operational side, however, research concerning CFP of biomass has shown poor results: deoxygenation of pyrolysis vapors goes along with a progressive reduction in CFP-oil yield. Apart from any control over catalyst activity, selectivity, and lifetime, the other critical issue is in the process design, which is complicated by rapid catalyst deactivation through coke formation and catalyst poisoning by biomass-originated minerals. This review analyzes the outcome of research efforts concerning in- and ex situ CFP of biomass based on carefully selected literature studies reporting the results obtained from meso- and macrolevel laboratory-scale setups, pilot, process development units (PDU), and (semi-) commercial process units, wherein the biomass feedstock and catalyst is fed continuously. Key operational aspects such as the reactor technology, reactive medium, processing mode, and optimization of process parameters are addressed. The performances of continuously operated CFP units were benchmarked through a comparison of yields and elemental compositions of (by-)products. Despite the considerable research efforts related to CFP technology development, the co-processing of CFP-oil is still in its infancy. However, in close collaboration with refinery professionals, it could be made a serious candidate for biobased co-feeding. For refinery integration, quality parameters of CFP-oil, e.g., acidity, stability, and miscibility, should be considered as crucial as its oxygen content.