Vapor-liquid equilibrium (VLE) study of CO₂ with MEA and ammonia solvents

In the carbon capture and sequestration (CCS )scenario, 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. To measure the VLE accurately, a CSTR equilibrium cell in conjunction with an on-line gas-sampling GC for analyzing the vapor phase composition at equilibrium was developed. This apparatus will allow the engineer to test various solvents and determine the optimum operating conditions suitable for CCS. Initial gas equilibrium results that will be useful for designing CO₂ scrubbers and associated stripping units using various aqueous ammonia and amine-based solvents are presented. The results are reported at different CO₂ loadings, temperatures, and pressures to obtain true VLE curves for use in analysis and process design. This is an abstract of a paper presented at the AIChE 2010 Spring National Meeting (San Antonio, TX 3/21-25/2010).