Novel nonaqueous solvent for carbon capture: Effects of glycol and water on CO2 absorption, desorption and energy penalty

Amidine-alcohol solution is an efficient absorbent for CO2 capture with high CO2 loading and low regeneration temperature compared with 30 wt% monoethanolamine (MEA) solution. However, the high viscosity restricts its further utilization in the industry. To decrease the viscosity of amidine-alcohol solutions during the absorption of CO2, different glycols including ethylene glycol, 1,3-propanediol, 1,2-propanediol, 1,3-butanediol and 1,4-butanediol were adopted in 1,5-diazabicyclo [4,3,0] non-5-ene (DBN)-glycol solutions for CO2 absorption. Both the absorption and desorption performances of those absorbents in the reaction with CO2 were investigated including the viscosity and regeneration energy. The CO2 loading can reach as high as 5.87 mol·kg-1 in DBN-1,3-propanediol solution, which is more than 3 times higher than that of 30 wt% MEA. Meanwhile, the viscosities for DBN-glycol-CO2 systems can be decreased more than 95% compared with 1,8-diazabicyclo [5,4,0] undec-7-ene (DBU)-glycerol-CO2 system. And DBN-ethylene glycol-CO2 system shows the lowest viscosity among the five glycols systems. With DBN-1,4-butanediol solution as an absorbent, the regeneration energy can be decreased as low as 1.38 GJ·ton-1 CO2, which is 62% lower than that of 30 wt% MEA. After 9 cycles of absorption-desorption process, the CO2 loading can be kept about 72% of the initial loading. Furthermore, the effect of water on absorption, desorption, viscosity and regeneration energy was also studied. It shows that the presence of water can increase the absorption rate and has little effect on the final CO2 loading while decreasing the desorption rate. Meanwhile, the presence of water increases the regeneration energy of DBN-ethylene glycol-H2O-CO2 system. However, considering the regeneration energy and viscosity, DBN-ethylene glycol solution is a promising solution for carbon capture and the regeneration energy can be decreased about 51 % even with 5 wt% water compared with 30 wt% MEA.