Effect of mineral matter on product yield in supercritical water extraction of lignite at different temperatures

The effect of demineralization on conversion of Soma Lignite in supercritical water extraction was studied using a batch autoclave operated at 400, 450 and 500 °C under nitrogen atmosphere. The experiments were carried out to investigate the effect of mineral matter and temperature on gaseous, liquid, residue yield and composition of gaseous products. According to the results, main product in gaseous state is CO2. Temperature is key factor affecting product distribution when compared the effect of minerals in lignite. As temperature was increased, yield of gas and solid residue increased, while yields of liquid decreased for raw and demineralized lignite samples. The removal of mineral matter caused to decrease the conversion for all lignite samples and to increase the carbon content of solid residue in supercritical water extraction.

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► The gaseous products composed of mainly CO2, CO, CH4, H2 and C2–C3 groups.
► As temperature was increased, yield of gas and residue increased, while yields of liquid decreased for raw and demineralized lignite samples.
► The increase in temperature caused decrease in evolution of CO2 in contrast to increase in evolution of the CH4 and H2.
► The effect of temperature is greater than the effect of demineralization on product yield.