Catalytic combustion of low-concentration coal bed methane over CuO/γ-Al2O3 catalyst: effect of SO2

Abstract

The purpose of this work is to report the results of an experimental study devoted to investigate the effects of SO₂ in feed gas on the catalytic combustion of low-concentration coal bed methane (1 vol%) over CuO/γ-Al₂O₃ catalyst with 10 wt% Cu prepared by incipient wetness impregnation in a fix-bed reactor. The study deals with researching a regular low-concentration coal bed methane combustion with lean SO₂, which is vital in utilizing low-concentration coal bed methane and in eliminating greenhouse emissions. The concentration of SO₂ varied from 0 ppm to 200 ppm, and the accumulation of sulfur on the catalyst surface was examined by X-ray fluorescence (XRF) and Scanning electron microscopy (SEM). The reaction temperature was in the range of 450–700 °C controlled by an electric heater, and at two key reaction temperatures (550 °C and 650 °C), the effect of altering SO₂ concentration on low-concentration coal bed methane combustion was studied experimentally. A sulfur poisoning mechanism of CuO/γ-Al₂O₃ catalyst was proposed. The results showed that the presence of SO₂ in feed gas led to the phenomena of sulfur poisoning over CuO/γ-Al₂O₃ catalyst, and the effect of sulfur poisoning aggravated with increased SO₂ concentration. Meanwhile, it had significant influence when temperature was below 575 °C due to the faster decomposition of sulfates at higher temperatures. A high reaction temperature promoted the decomposition of sulfates produced simultaneously, which provided more activating sites on the catalyst for methane catalytic combustion. Sulfates (CuSO₄ and Al₂(SO₄)₃) were detected by Fourier transform-infrared spectroscopy (FT-IR) and X-ray diffraction (XRD), resulting in both the reduction of activating sites and specific surface area of the catalyst. The absorption of methane molecules on activated sites was hindered and the catalyst activity decreased.