Behavior of Alkaline‐Metal Catalysts in Supercritical Water Gasification of Lignite

Abstract

The efficient utilization of abundant low‐rank coals, which show high moisture and ash content, is significant for coal‐based energy systems. The gasification of Zhaotong lignite was performed with different alkaline‐metal catalysts, such as KOH, NaOH, K2CO3, and Na2CO3, in supercritical water. The behavior of the alkaline metal was also investigated. Potassium shows better catalytic activity than sodium. KOH not only promotes breakage of chemical bonds in the coal matrix to generate low‐molecular‐weight gases, but also alters the pore structure of the char to improve the gasification of carbon in the residue. However, potassium is partly inactivated upon reaction with minerals in coal in supercritical water gasification. In situ protection of potassium is realized by adding Ca(OH)2 under supercritical conditions.

Catalytic Supercritical Water Gasification of Canola Straw with Promoted and Supported Nickel-Based Catalysts

“…These reactions have high activation energies which require catalysts for rapid reaction rates, explaining low gas yields and hydrogen selectivity in non-catalytic gasification. Usually, homogenous alkali metal salt catalysts, namely potassium carbonate (K 2 CO 3 ), sodium hydroxide (NaOH), potassium hydroxide (KOH), and sodium carbonate (Na 2 CO 3 ), are utilized for SCWG of biomass [ 17 , 18 , 19 ]. Alkali metal salts promote a water–gas shift (WGS) reaction by forming a formate intermediate compound to shift the equilibrium towards the product side and enhance hydrogen yield.…”

Experimental Investigation of the Effects of Inorganic Components on the Supercritical Water Gasification of Semi-Coke

“…This enables SCW to achieve low mass resistance, high solubility of produced gases, easy separation of salts and impurities, and high reaction rate when used as a gasification medium [9,10]. In recent years, the supercritical water gasification (SCWG) of coal, a novel coal gasification technology, has received extensive attention and in-depth research due to its clean, efficient, and low-cost characteristics [11][12][13][14][15][16][17]. In the SCWG of coal, elements such as C, H, and O will be converted into gas-phase products, mainly existing in the form of H 2 and CO 2 [18].…”