Equilibrium and experimental study on carbothermal reduction of sulfur dioxide to elemental sulfur

In order to solve the problem of low utilization value of flue gas desulfurization by-product, reduction of sulfur dioxide to elemental sulfur has emerged as a new process for resource utilization of SO₂ with promising application prospects. Herein, the thermodynamic equilibrium calculation was carried out to study the influence of temperatures and C/SO₂ molar ratios on the C-SO₂ reaction. The effects of reaction temperature, carbon mass, and CO concentration on SO₂ reduction by coke and activated carbon were studied on a fixed bed reaction system. The theoretical results demonstrated that the highest equilibrium S yield occurred when the C/SO₂ molar ratio is 1, with higher ratios resulting in the formation of COS, CS₂, and CO. Experimental data revealed that at temperatures below 700°C, both SO₂ conversion and S yield are notably low. As the temperature increases, both the conversion and yield gradually increase and approach the thermodynamic equilibrium value. The evolution of carbon surface chemical properties under the action of CO was analyzed by FTIR and XPS, which indicated that the presence of CO promotes the decarboxylation reaction, and then increases SO₂ conversion and S yield. The conclusion of this study provides guidance for the development of high efficiency SO₂ reduction technology.