Absorption of carbon dioxide into aqueous potassium carbonate promoted by boric acid

Abstract

Abstract The absorption of carbon dioxide with alkanolamine or potassium carbonate solvents has gained widespre ad acceptance for the removal of CO2 from natural gas and H 2. However, alkanolamine solutions are prone to oxidative degradation at high temperature. The main advantages of potassium carbonate solution for CO2 removal are the high chemical solubility of CO2 in the carbonate/ bicarbonate system, low solvent costs and the low energy requirement for solvent regeneration. The major challenge concerning absorption of CO2 into aqueous solutions of potassium carbonate is a relatively slow rate of reaction in the liquid phase causing low mass transfer rates. It is often advantageous to add a promoter to increase the absorption rate. While piperazine is often used for this purpose, there are some environmental health concerns with this approach. In this work we consider boric acid as an alternative promoter. Absorption of CO2 in a wetted -wall column by aqueous potassium carbonate solution with and without various concentrations of boric acid as promoter was measured under conditions in which the reaction of CO2 was of pseudo-first order. The equilibrium partial pressure and the rate of absorption of CO2 were measured in 30.0 wt% potassium carbonate and 1.0 to 5.0 wt% of boric acid at 50 to 80 ∘C. The overall pseudo -first-order reaction rate constants were determined fro m the kinetic measurements. The addition of small amounts of boric acid to potassium carbonate resulted in a significant enhancement of CO2 absorption rates.