CO2 capture and cleaning of HTL gas stream using the HTL solid fraction as adsorbents

Reducing greenhouse gas emissions and achieving energy sovereignty requires minimising the reliance on imported fossil fuels. Leveraging local carbon sources contributes to these goals. The gaseous stream from agricultural biomass hydrothermal liquefaction (HTL) contains a high CO 2 content, which can be valorised as a carbon feedstock for the synthesis of renewable fuels. The feasibility of using the solid by-product from the HTL process as a selective adsorbent is evaluated, as it can remove impurities from the gas stream. These contaminants may deactivate downstream catalytic processes. Activated carbons were synthesised from the solid fraction obtained after HTL of a 50:50 mixture of straw and manure through high-temperature thermal treatment and physical activation with CO 2 , as well as chemical activation with ZnCl 2 and subsequent surface modification with ZnO and alkaline treatment to tailor porosity and surface reactivity. The proposed separation process has been divided into three adsorption stages using different adsorbents and selectivity mechanisms: the first involves eliminating sulphur compounds using ZnO-based materials and Zn-modified HTL solids under fixed-bed conditions; the second stage consists of a pressure swing adsorption (PSA) process operating between 0.3 and 3 bar using HTL-derived activated carbons to remove light compounds and increase CO 2 purity based on equilibrium and kinetic effects; the third stage involves an additional purification step based on fixed-bed adsorption to retain heavy hydrocarbons. The results demonstrate that the solids obtained from HTL can effectively purify the gas stream, achieving CO 2 purities of up to 99.7 % and an overall CO 2 recovery rate of 97.0 %.