Co-solvent effects on hydrothermal co-gasification of coal/biomass mixtures for hydrogen production

The use of low-rank coals for hydrogen production by gasification can create advantageous options to overcome a potential energy crisis. In this study, the effects of 8 different solvents on gasification and hydrogen yield in coal/biomass co-solvent hydrothermal gasification were investigated. The most effective co-solvent on product conversion and high hydrogen yield was found N-methyl pyrrolidone (NMP) and tetrahydrofuran (THF). Total gas volumes and hydrogen yields obtained from the co-solvent gasification of coal/sorghum blends were higher than the arithmetical sum of the average values of the yields from individual solvent and coal/sorghum blend gasifications. The increase in the hydrogen yield was 11 mol H-2/kg feed with the co-solvent THF due to the synergistic effects of THF on hydrogen production. Solvent concentration was effective on both total gas volumes and hydrogen yields. In the catalytic (K2CO3/CaO) runs with a concentration of 20 % (v/v) NMP co-solvent 98.8 +/- 0.1 mol H-2/kg feed was achieved with a dramatic decrease of CO content in the produced gas mixture. The comparison of the results obtained from subcritical and supercritical water conditions showed that in catalytic processes co-solvent was more effective towards feedstock conversion and almost the same hydrogen yields obtained at lower pressures under the subcritical water conditions.

Automated summary

This study investigated the effects of different solvents on gasification and hydrogen yield in coal/biomass co-solvent hydrothermal gasification. The results showed that NMP and THF were the most effective solvents, increasing product conversion and hydrogen yield. Comparing subcritical and supercritical water conditions, the study found that the solvent was more effective in catalytic processes.