This presentation will consider novel membrane absorption and stripping based processes and devices for CO2 absorption and stripping for carbon capture and sequestration. Two feed streams are considered: (1) lower temperature (L-T) post-shift reactor synthesis gas at high pressures and temperature up to 100oC where He was used as a surrogate for H2; (2) simulated flue gas at ̴ 40-50oC.
An advanced pressure swing membrane absorption (PSMAB) technology utilizing a hollow fiber membrane contactor and a cyclic absorption-desorption process is being developed to separate H2 from the low temperature (L-T) post-shift reactor synthesis gas and simultaneously obtain a purified CO2 stream. Studies have been carried out with ̴ 40% CO2-rest He feed gas mixture coming in at temperatures up to 1000C and pressures varying from 100 to 250 psig (689-1723kPag). The nonvolatile absorbent consists of a solvent and a suitable amine; the solvent is either polyethylene glycol (PEG) 400 or an ionic liquid (IL), 1-butyl-3-methylimidazolium dicyanamide ([bmim][DCA]). Studies were carried out with microporous hydrophobized polyether ether ketone (PEEK) hollow fiber membrane modules of small sizes having different characteristics. Reducing the dead volume on the module tube side and decreasing the fiber packing density greatly enhanced gas absorption and improved product qualities while increasing temperature had a negative impact on product qualities with absorbents without the amine. Adding a nonvolatile amine such as polyamidoamine (PAMAM) dendrimer Gen 0 to the ionic liquid or PEG 400 improved CO2 absorption capability especially at higher temperatures. The measured CO2 concentration in the CO2-rich product stream from the less-than-optimum membrane modules using such mixed absorbents went up to 93-94%. A model has been developed and numerically solved to predict the cyclic process performance of pure IL as the absorbent. Solubility and diffusion coefficient data for the gases needed in this model were determined for the pure IL 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). The CO2/He solubility selectivity was determined for various compositions.
Studies for CO2 separation from flue gas employed advanced hollow fiber membrane contactors and a nonvolatile absorbent circulating between an absorber and a stripper. The loaded absorbent is heated before it enters the stripper. Preliminary studies were also implemented with a novel integrated absorber-stripper. The observed separation behavior will be illustrated. The deficiencies of the design will be pointed out. The issues of energy consumption and capital costs are of great importance here.
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