Char suppression mechanism using recycled intermediate phenol in supercritical water gasification of coal

Supercritical water gasification (SCWG) is a novel thermochemical technique to convert wet feedstock into hydrogen-rich gas products with near zero emission. However, char formation during SCWG of coal could reduce production efficiency and operational stability. In this paper, the influence of recycled intermediate phenol on coal gasification and coal char inhibition mechanism was investigated. The results indicated that phenol had positive influence on the gas yield and char inhibition. Carbon gasification efficiency of coal increased from 65.18% to 99.36% and H₂ yield increased by 59% with the optimal experimental parameters (phenol concentration of 1 wt% and temperature of 750 °C. The experimental results demonstrated that phenol suppressed char formation effectively and strengthened the char reactivity since no solid produced in the reactor after reaction. Coal char microstructure characteristics were detected to analyze the migration of functional groups. The results of Fourier transform infra-red spectroscopy showed the presence of phenol enhanced the exchange of –OH between the char and supercritical water circumstances and promoted the conversion of –CH₃ in char to methane. The suppression mechanism of char was further studied, which could be beneficial for regulating the product distribution and promote the oriented conversion of coal in SCW.