Hydrotreatment of supercritical carbon dioxide extracts of hydrothermal liquefaction lignocellulosic biocrude

Authors: MONTESANTOS, NIKOLAOS - Aalborg University; KOHLI, KIRTIKA - Council Of Scientific And Industrial Research (CSIR); Sharma, Brajendra - Bk; MASCHIETTI, MARCO - Aalborg University

Submitted to: Industrial and Engineering Chemistry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2022
Publication Date: 10/6/2022
Citation: Montesantos, N., Kohli, K., Sharma, B.K., Maschietti, M. 2022. Hydrotreatment of supercritical carbon dioxide extracts of hydrothermal liquefaction lignocellulosic biocrude. Industrial and Engineering Chemistry Research. https://doi.org/10.1021/acs.iecr.2c02109.
DOI: https://doi.org/10.1021/acs.iecr.2c02109

Interpretive Summary: Biomass conversion through thermochemical conversion processes produced liquid products called biocrude oil, which needs to be upgraded to produce biofuels directly or co-refined with petroleum crude oils in refineries to produce fuels and chemicals. One of the challenges in the upgradation of biocrude oil is the reduction of the oxygen content. Catalytic hydrotreatment, a well-established technology in crude oil refining could be an effective technology for oxygen removal. However, hydrotreatment suffers from high hydrogen requirements, catalyst deactivation, corrosion, the high viscosity of the feed, etc. Prefractionation of the biocrude oil could produce fractions more suitable for hydrotreatment than the whole biocrude. This work investigates the hydrotreatment of supercritical carbon dioxide extract of biocrude oil and the results are compared with biocrude oil to show that some of the problems could be avoided this way to produce biofuels. The outcome from this work will help improve the economics of biofuel production through the thermochemical conversion route and thereby help farmers by increasing the value of waste biomass generated on the farms.

Technical Abstract: Catalytic hydrotreatment was applied on the supercritical carbon dioxide extract (SE) of a biocrude produced by hydrothermal liquefaction of pinewood. The process was also applied on the raw biocrude (BC) for benchmarking. The hydrotreatment reactions were carried out at temperatures 350-400 °C, and reaction times between 2 and 6 h. Commercial CoMo and NiMo catalysts were utilized. The hydrotreated SE (HSE) samples were characterized by much lower oxygen content than the SE, with values down to 1.6 wt %, while the minimum oxygen content attained on the hydrotreated BC (HBC) was 3.1 wt %. No coke formation was observed operating on the SE, while the yield of coke was 13 wt % in the operation on the BC. The HSE samples exhibited number-average molecular weights 24-61 % lower than the HBC samples, with larger low-boiling fractions (up to Diesel). The better quality of the hydrotreated products, together with the lower metal content of SE (0.2 g/kg) vs. BC (8.5 g/kg) and the absence of coke in the operation on the SE, suggests that the use of SE extracts of biocrude is a better option for operations on conventional hydrotreatment catalysts.