Conversion of carbon monoxide in supercritical water and the influence of alkaline potassium salts

The conversion of carbon monoxide in supercritical water was investigated in a continuous reaction system which could dissolve carbon monoxide in water at high pressure. Meanwhile, due to the diversity of potassium salts in biomass supercritical water gasification, the influence of various alkaline potassium salts (KHCO₃, K₂CO₃ and KOH) on the water gas shift reaction were investigated at 450-600 ℃, 23-29 MPa and with a residence time of 3-6 s. The results show that under non-catalytic conditions, the increases in reaction temperature and residence time both lead to higher CO conversion. The effect of pressure on CO conversion is distinct at low pressure (23-25 MPa), but rather minor at higher pressure (25-29 MPa). The rate expression for the non-catalytic water gas shift reaction is k=10^3.75×exp(-0.66×10⁵/RT)(s^-1). The potassium salts can promote the CO conversion significantly and the activity of three salts follows the order of KHCO₃ > K₂CO₃ > KOH; the conversion of CO is enhanced at higher temperature and longer reaction time, whereas the effect of pressure on CO conversion is much complicated. The catalytic effect of alkaline potassium salts in the CO conversion may be explained by the formation of oxalate (HC₂O₄^-) and formate (HCOO^-) intermediates.