Pyrolysis of a high-ash peat in supercritical water

The effects of the addition of CaO, temperature, and residence time on the conversion and product yields of a high-ash peat in supercritical water was investigated. The experiments were carried out in an autoclave in the temperature range of 623–773 K at pressure up to 30 MPa. At a Ca/C molar ratio of 0.46, almost no CO2 remained in gas phase. It was found that CaO facilitates the extraction of volatile matter from peat and the decomposition of volatile matter to small molecular compounds. Moreover, CaO catalyses the steam reforming reaction of hydrocarbons and the water-shift reaction. The addition of KOH might favor the reforming reaction of oil product to hydrogen and carbon dioxide. Furthermore, the yield of oil reaches a maximum at the temperature approximately 723 K. A threefold increase in the yield of oil product was observed under 36.5 MPa compared with pyrolysis. However, the polar compounds decomposed with the prolongation of reaction time.