Catalytic upgrading of hydrothermal liquefaction biocrudes: Different challenges for different feedstocks

TL;DR

This study explores the catalytic upgrading of biocrudes from various biomass sources via hydrothermal liquefaction and hydrotreating, highlighting feedstock-specific challenges and optimizing conditions for producing diesel and gasoline-range hydrocarbons.

Contribution

It provides a comparative analysis of biocrude upgrading from different feedstocks using NiMo/Al2O3 catalysts, revealing feedstock-dependent challenges and optimal operational parameters.

Findings

Sewage sludge biocrude yields straight-chain hydrocarbons with effective heteroatoms removal.

Algal biocrude shows promising results but faces challenges in complete denitrogenation.

Lignocellulosic biocrude produces high gasoline-range yields with significant aromatics content.

Abstract

Hydrothermal liquefaction (HTL) followed by catalytic hydrotreating of the produced biocrude is increasingly gaining ground as an effective technology for the conversion of biomass into liquid biofuels. A strong advantage of HTL resides in its great flexibility towards the feedstock, since it is able to treat a large number of different organic substrates, ranging from dry to wet residual biomass. Nevertheless, the characteristics of biocrudes from different typologies of organic materials result in different challenges to be met during the hydrotreating step, leading to differences in heteroatoms removal and in the typology and composition of the targeted products. In this work, biocrudes were catalytically hydrotreated with a commercial NiMo/Al2O3 catalyst at different temperatures and pressures. Sewage sludge biocrude was found to be very promising for the production of straight-chain hydrocarbons in the diesel range, with considerable heteroatoms removal even at mild hydrotreating conditions. Similar results were shown by algal biocrude, although complete denitrogenation is challenging. Upgraded biocrudes from lignocellulosic feedstock (miscanthus) showed high yields in the gasoline range, with a remarkable content of aromatics. Operating at a higher H2 pressure was found to be crucial to prevent coking and decarboxylation reactions.