(702d) Pressure Swing Membrane Absorption for Pre-Combustion CO2 Capture From Shifted Syngas

An advanced pressure swing membrane absorption (PSMAB) technology utilizing a hollow fiber membrane contactor device and a cyclic absorption-desorption process is being developed to produce purified hydrogen at a high pressure for IGCC-CCS plant’s combustion turbine from low temperature (L-T) post-shift reactor synthesis gas and simultaneously obtain a purified CO₂ stream suitable for sequestration. The low temperature water gas shift reactor product stream is likely to be available at ~20 atm and around 150-200⁰C. The experimental studies are employing He as a surrogate for H₂. Studies have been carried out with a 40%CO₂-60% He feed gas mixture coming in at temperatures up to 100⁰C and pressures varying from 100 to 250 psig (689-1723 kPag). The nonvolatile absorbent liquid consists of an ionic liquid 1-butyl-3-methylimidazolium dicyanamide ([bmim][DCA]) (among others) containing nonvolatile amines. Two different cyclic processes have been studied; most of the performance will focus on a 5-valve cycle. Process performance studies have focused on the duration of various parts of the cycle, the effects of pressure and temperature variation, and the effect of hollow fiber membrane module design on the quality of the two product streams namely, the He-rich stream and the CO₂-rich stream. A numerical model has been developed to predict the process performance of the simpler 3-valve cycle for pure ionic liquid as the absorbent. Solubility and diffusion coefficient data for the gases are needed in this model; these were determined for the pure ionic liquid absorbent using a pressure-decay-dual transducer apparatus at temperatures of 323, 353, 363, and 373 K and at pressures up to 1.38 MPa (~200 psig).