Separation of BTX chemicals from biomass pyrolysis oils via continuous flash distillation

Authors: MCVEY, MATTHEW - Pennsylvania State University; Elkasabi, Yaseen; CIOLKOSZ, DANIEL - Pennsylvania State University

Submitted to: Biomass Conversion and Biorefinery
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2019
Publication Date: 2/12/2020
Citation: Mcvey, M., Elkasabi, Y.M., Ciolkosz, D. 2020. Separation of BTX chemicals from biomass pyrolysis oils via continuous flash distillation. Biomass Conversion and Biorefinery. 10(1):15-23. https://doi.org/10.1007/s13399-019-00409-1.
DOI: https://doi.org/10.1007/s13399-019-00409-1

Interpretive Summary: One method of making renewable fuel involves the conversion of biomass into a liquid that resembles petroleum (termed ‘bio-oil’). This method, termed ‘pyrolysis’, relies on high temperature in the absence of oxygen. Like petroleum, this oil needs to be purified and refined into products using typical processes found in commercial petroleum refineries. Distillation is one important process, since it is the first step before the oil enters other reactors. Distillation separates the oil into lighter and heavier fractions. Generally, bio-oil cannot distill very easily, due to its highly reactive nature. However, a modified pyrolysis procedure (tail-gas reactive pyrolysis, TGRP) can produce oils with less oxygen, which results in greater stability. This work examines the feasibility of distilling TGRP oils, and using computer simulation, with both model bio-oils and actual bio-oils. Model bio-oils consisted of mixtures of compounds found in the TGRP oil. The distillation process was tested at different oil flow rates and different process temperatures. It was found that both the model and actual oils distilled continuously without clogging or malfunction of the process. Particular components benzene, toluene, and xylene (‘BTX’, all critical petrochemicals) were separated while also separating water and highly reactive components in the water. The relative amounts of BTX collected were slightly less in the actual oil than in the model oil. These results are important for understanding how biofuels can be refined in existing petrochemical to refineries.

Technical Abstract: Partially deoxygenated pyrolysis oils, such as those produced by Tail Gas Reactive Pyrolysis (TGRP), show promise for use in biorefineries if they can integrate into standard refinery operations, one of which is distillation. A feasible method for modeling the process and for removing aqueous components will advance progress. This study investigated the potential of continuous flash distillation for fractionating partially deoxygenated bio-oil component chemicals benzene, toluene, and xylene (BTX), which are critical feedstocks for producing many refinery products. A model bio-oil mixture was used to evaluate process performance, and process conditions were investigated with respect to separation efficiency (temperature = 120, 130, and 140 degree C; input flow rate = 2 or 3 mL min-1). Mean BTX yield (gout/gin) for an oil flow rate of 2 mL min-1 ranged between 13.4 – 22.2 %, while for 3 mL min-1 yields ranged from 13.5 – 40 wt%. In all treatments, the measured amounts of BTX from model bio-oil were less than those from ASPEN simulations. From the distillates, aqueous fractions phase-separated while sequestering acetic acid from the organics. Residence time within the drum was positively correlated with concentration of BTX in the distillates. At no point did solid residues form within the flash drum. When compared with analogous experiments at optimal conditions, BTX yields from real TGRP oil were comparable but less than the analogous model experiment. These results suggest that continuous, atmospheric pressure distillation of low-oxygen bio-oils can be used for separating commodity, refinery-grade chemicals such as BTEX from biomass pyrolysis-derived bio-oils.