Pressure Swing Membrane Absorption Process for CO2 Removal From Precombustion Syngas

In this work, we carried out studies for CO₂ removal from simulated pre-combustion syngas by a pressure swing membrane absorption (PSMAB) process. In the PSMAB-based cyclic separation process, a well-packed membrane module containing either a hydrophobized porous ceramic tubule or hydrophobized polyether ether ketone (PEEK) porous hollow fiber membranes was used to achieve non-dispersive gas absorption from a high-pressure high-temperature feed gas into a stationary absorbent liquid on the module shell side during a certain part of the cycle followed by desorption of absorbed gases from the liquid in the rest of the cycle. Helium was used as a surrogate for H₂. Separation of the feed gas mixture containing 40% CO₂-He balance was implemented using pure ionic liquid, 1-butyl-3-methylimidazolium dicyanamide ([bmim][DCA]), and its solution containing poly(amidoamine) (PAMAM) dendrimer Gen 0 primarily with a dry feed gas. A numerical model was developed to predict the extent of purification of the gas by pure ionic liquid [bmim][DCA] in the PSMAB device. We needed information on CO₂ solubility and diffusivity in the ionic liquid to predict this performance. Therefore, measurements of the solubilities of pure carbon dioxide, pure helium, and a feed mixture of 40% CO₂-He balance were also carried out in the ionic liquid, ([bmim][DCA]), and in its solution containing 20 wt% and 30 wt% poly(amidoamine) (PAMAM) dendrimer Gen 0 with and without water. A pressure-decay-dual transducer apparatus was employed at temperatures of 323, 353, 363, and 373 K and at pressures up to 1.38 MPa (~200 psig). Henry’s law constants of pure CO₂ and pure He were determined at different temperatures for the ionic liquid. Pseudo Henry’s law constants for each of CO₂ and He in a 40-60% feed gas mixture were also determined. Solubility selectivities of carbon dioxide to helium for all liquid absorbents were also calculated at each temperature.