Hydrogen production by catalytic gasification of coal in supercritical water with alkaline catalysts: Explore the way to complete gasification of coal

摘要

Supercritical water gasification (SCWG) of coal is a promising technology for clean coal utilization. In this paper, hydrogen production by catalytic gasification of coal in supercritical water (SCW) was carried out in a micro batch reactor with various alkaline catalysts: Na_2CO_3, K_2CO_3, Ca(OH)_2, NaOH and KOH. H_2 yield in relation to the alkaline catalyst was in the following order: K_2CO_3 ≈ KOH ≈ NaOH ＞ Na_2CO_3 ＞ Ca(OH)_2. Then, hydrogen production by catalytic gasification of coal with K_2CO_3 was systematically investigated in supercritical water. The influences of the main operating parameters including feed concentration, catalyst loading and reaction temperature on the gasification characteristics of coal were investigated. The experimental results showed that carbon gasification efficiency (CE, mass of carbon in gaseous product/mass of carbon in coal × 100%) and H_2 yield increased with increasing catalyst loading, increasing temperature, and decreasing coal concentration. In particular, coal was completely gasified at 700 ℃ when the weight ratio of K_2CO_3 to coal was 1, and it was encouraging that raw coal was converted into white residual. At last, a reaction mechanism based on oxygen transfer and intermediate hybrid mechanism was proposed to understand coal gasification in supercritical water.