Vapor-Liquid Equilibrium (VLE) Study of CO2 with MEA and Ammonia Solvents

In the carbon capture and sequestration (CCS )scenario, vapor liquid equilibrium (VLE) curves represent the theoretical relationship between local gaseous CO2 vapor pressure and the respective carbon loading in solution for a given operating temperature. It determines the maximum carbon content in the lean solution to achieve 90% removal efficiency in the absorption process, and the minimum carrier gas flowrate required in the stripper for solvent regeneration at operating temperature. Unfortunately, the equilibrium between liquid and vapor phases can be very difficult to accurately quantify with simulation calculations, which use a combination of physical and thermodynamic equations along with post-experimental data for reference. Simulations can often yield results which are not a true reflection of what is observed in reality. In order to measure the VLE accurately, a CSTR equilibrium cell in conjunction with an on-line gas-sampling gas chromatograph (GC) for analyzing the vapor phase composition at equilibrium have been assembled. This apparatus will allow the engineer to test various solvents and determine the optimum operating conditions suitable for CCS. In this research effort, we report on initial gas equilibrium results that will be useful for designing CO2 scrubbers and associated stripping units using various aqueous ammonia and amine-based solvents. The results are reported at different CO2 loadings, temperatures, and pressures to obtain “true” vapor-liquid equilibrium curves for use in analysis and process design.