CO2 capture using carbide slag modified by propionic acid in calcium looping process for hydrogen production

Lime enhanced gasification (LEGS) process based on calcium looping in which CaO is employed as CO₂ sorbent is an emerging technology for hydrogen production and CO₂ capture. In this work, carbide slag which was an industrial solid waste was utilized as CO₂ sorbent in hydrogen production process. Modification of carbide slag by propionic acid was proposed to improve its reactivity. The CO₂ capture behavior of raw and modified carbide slags was investigated in a dual fixed-bed reactor (DFR) and a thermo-gravimetric analyzer (TGA). The results show that modification of carbide slag by propionic acid enhances its CO₂ capture capacity in the multiple calcination/carbonation cycles. The favorable carbonation temperature and calcination temperature for modified carbide slag are 680–700 °C and 850–950 °C, respectively. Prolonged carbonation treatment is beneficial to CO₂ capture of raw and modified carbide slags. The prolonged carbonation for 9 h in the 21st cycle increases the conversions of raw and modified carbide slags in this cycle. And then the carbonation conversions of the two sorbents were also improved in the subsequent cycles. Calcined modified carbide slag shows more porous microstructure compared with calcined raw one for the same number of cycles. Modification of carbide slag by propionic acid increases the surface area, pore volume and pore area. In addition, the volume and area of the pores in 20–100 nm in diameter were improved, which had been proved to be more effective to capture CO₂. The microstructure of calcined modified carbide slag favors its higher CO₂ capture capacity in the multiple calcination/carbonation cycles.