Upgrading peat to gas and liquid fuels in supercritical water with catalysts

Peat was effectively upgraded into gas and liquid fuels by supercritical water treatment at 380–440 °C with and without catalyst. Treatment of the peat without using catalyst at a temperature ranging from 350 °C to 440 °C generally led to 5–10 wt% yield of water soluble oil (WSO), about 15 wt% yield of heavy oil (HO), 20–27 wt% yield of Gas and 20–30 wt% yield of Char. As expected, the Gas yield increased and the yields of oils and Char generally decreased at a higher operation temperature. The optimal conditions for a greater HO yield appeared to be a lower residence time and a lower water-to-peat ratio (i.e., a higher initial biomass concentration). Among all the catalysts tested including 0.1 M K2CO3, 0.1 M FeSO4, 0.1 M RuO2, and 0.1 M and 1.0 M Ca(OH)2, 0.1 M Ca(OH)2 was found the most effective for enhancing the production of liquid oils of both HO and WSO. The presence of 1.0 M Ca(OH)2 at 410 °C produced extremely low CO2 yield, due to the adsorption reaction of CO2 over the Ca(OH)2 catalyst, and a fourfold increase in H2, resulting in a high quality gas product with a HHV of 27.7 MJ/kg, as oppose to only 2.81 MJ/kg for the gas product without catalyst. Among all the catalysts tested, RuO2 proved to be the best catalyst for upgrading peat to H2-rich gas products, and the formation of H2 attained as high as 2.44 mmol/g with 0.1 M RuO2 at 410 °C, compared with 0.05 mmol/g without catalyst. The HOs obtained from the SCW treatments, rich in phenolic compounds and fatty acids, possess much greater caloric values (with a HHV of >33–35 MJ/kg) than the dried peat powder used (with a HHV of about 21 MJ/kg).