Catalytic effect of K₂CO₃ in steam gasification of lignite char on mole ratio of H₂/CO in syngas

To fulfill the requirement for synthetic fuel (synfuel) production in the Fischer-Tropsch process, in which syngas fed to the process has a H₂/CO mole ratio approaching 2, gasification of lignite coal is needed. In this research, char particles were prepared by pyrolysis of lignite coal at controlled heating rates to obtain the highest possible surface area for gasification. In the gasification process, char with a surface area of 172.5 m²/g was used, along with the catalyst K₂CO₃ in a fixed bed reactor. In this research, there were variations in the steam/char mass ratio (2.0, 3.0, and 4.0) and in gasification temperature (675°C, 750°C, and 825°C, respectively). Results of this research showed that the highest H₂/CO mole ratio of 2.07 corresponding to the mole ratio of gas yield/carbon of 1.13 was achieved at the gasification temperature of 675°C using the catalyst K₂CO₂; the steam/char mass ratio was 2.0. However, at the same gasification conditions-but without a catalyst-the H₂/CO mole ratio and corresponding mole ratio of gas yield/carbon were 3.02 and 0.42, respectively. A finding of this research was that the addition of the catalyst K₂CO₃ to gasification of lignite char adversely reduced the mole ratio of H₂/CO compared to gasification without catalysis. It is suspected that the high composition of mineral ash in coal ash reacted with the K₂CO₃ catalyst, thus causing the Boudouard reaction to compete considerably with the water-gas reaction. The increases in gasification temperature and the steam/carbon ratio lowered the mole ratio of H₂/CO in syngas.