The catalytic effect of calcium and potassium on CO2 gasification of Shengli lignite: the role of carboxyl.

Yanpeng Ban,Quansheng Liu,Runxia He,Na Li,Keduan Zhi,Yan Wang

doi:10.1098/rsos.180717

Abstract

The CO2 gasification of Chinese Shengli lignite (SL) catalysed by K+ and Ca2+ was studied. The results showed that calcium could greatly decrease the gasification reaction temperature of SL, and the gasification reaction rates of acid-treated SL catalysed by calcium were significantly higher than that catalysed by potassium. Kinetic analysis showed that the activation energy of the reaction catalysed by calcium was much lower than that catalysed by potassium, which was the reason for the higher catalytic activity of calcium. Fourier transform infrared characterization showed that, compared with acid-treated SL, the addition of K+/Ca2+ resulted in the significant weakening of C=O bond, and new peaks attributed to carboxylate species appeared. X-ray photoelectron spectroscopy results indicated that the numbers of C=O decreased after the metal ions were added, indicating the formation of metal–carboxylate complexes. Raman characterization showed that the ID1/IG values increased, suggesting more structural defects, which indicated that the reactivity of coal samples had a close relation with amorphous carbon structures. Ca2+ could interact with the carboxyl structure in lignite by both ionic forces and polycarboxylic coordination, while K+ interacted with carboxyl structure mainly via ionic forces.

Highlights

Efficient and clean utilization of the low rank coals (LRCs) has attracted wide attention around the world due to the large reserves of LRCs
Kþ interacted with the carboxyl structure in lignite in the form of ionic forces, while Ca2þ interacted with the lignite in the form of both ionic forces and polycarboxylic coordination
It was proved that Ca2þ and Kþ could significantly promote the CO2 gasification, and Ca2þ exhibited higher activity than potassium

Summary

Introduction

Efficient and clean utilization of the low rank coals (LRCs) has attracted wide attention around the world due to the large reserves of LRCs. The coal gasification can be divided into three main steps: pyrolysis, volatile matter reforming, and char gasification, and the last step is considered to be the rate-controlling step because it is kinetically slower compared with the other two steps [1,2]. Char is formed simultaneously with the coal gasification reaction. The reaction between char and H2O or CO2 is the rate-determining step. Boudouard reaction is generally considered as the rate-determining step in the gasification process [6]. Increasing the Boudouard reaction rate below 9008C is the key step for low-temperature gasification, which can decrease the energy consumption of the gasification process [7]

Methods

Results

Conclusion