Effect of temperature on non-catalytic reduction of CO₂ by semi-coke

China emitted nearly 12 billion tons of CO₂ in 2021, and there will be a huge pressure on carbon emission reduction. To realize carbon peaking and carbon neutrality, converting CO₂ into basic chemical raw materials such as CO is an important way to reduce CO₂ emissions and realize its resource utilization. Based on an independently designed continuous feeding fluidized vertical furnace apparatus, the Yulin semi-coke was used as raw material to investigate the effect of temperature (900-1 100℃)on the non-catalytic reduction of CO₂ in semi-coke in CO₂ atmosphere, and the physical and chemical properties of bottom char (BC) and fly char (FC) were characterized. The results showed that with the increase of temperature, the reduction rate and conversion yield of CO₂, the volume fraction of CO, the carbon conversion rate, and the lower heating value (LHV)of gas all increased, while the volume percent of CO₂ decreased greatly. CO₂ was effectively converted to CO, but the trend slowed down when the temperature was over 1 050℃. When the temperature was 1 050℃, CO accounted for about 64% and CO₂ accounted for about 30%, the reduction rate of CO₂ was 50.37%, and the conversion yield of CO₂ was 0.72 m³/kg. With the increase in temperature, the smooth and dense surface of the semi-coke turned porous and spongy, and then became rough, the specific surface area of BC was higher than 300 m²/g, and the area of both FC and BC increased at first and then decreased. The maximum specific surface area of FC was 36 times higher than that of semi-coke, while the maximum specific surface area of BC was 63 times higher, and the average pore diameter of FC and BC was reduced by more than 50%. Raman spectrum analysis showed that after the reaction with CO₂, the active sites of FC increased, and the ordered carbon structure decreased, due to the different reaction environment, BC had more ordered carbon structure than FC. With the increase in temperature, the reaction between CO₂ and carbon intensified, the active sites of FC and BC were easy to be consumed, the ordered carbon structure of FC and BC was relatively low and the active sites were relatively more between 1 000-1 050℃. The reaction activity of FC and BC was better than that of the Yulin semi-coke. Kinetic analysis showed that the reaction activation energy of FC with CO₂ was lower, which provided favorable conditions for further high-temperature conversion.