Integrated gasification combined cycle (IGCC) with CO2 capture and sequestration (CCS) offers a promising approach for cleanly using abundant coal reserves of the world to generate electricity. The present state-of-the-art synthesis gas (syngas) cleanup technologies in IGCC involve cooling the syngas from the gasifier to room temperature or lower for removing sulfur, carbon dioxide, and other pollutants, leading to a large efficiency loss. Here we assess the suitability of various alternative syngas cleanup technologies for IGCC with CCS through computational simulations. We model multicomponent gas separation for CO2 capture in IGCC using polymeric membranes and H-2 separation from the syngas using both Pd-alloy based composite metallic membranes and polymeric membranes. In addition, we develop a pressure swing adsorption model to estimate the energy efficiency of regenerable sorbent beds for CO2 capture. We use our models with Aspen Plus simulations to identify promising design and operating conditions for membrane and adsorption processes in an IGCC plant. On the basis of our analysis, the benefits of warm gas cleanup are not as great as previously reported in the literature, and only CO2 separations performed using H-2-permeable Pd-alloy membranes and CO2 adsorbents produce overall higher heating value (HHV) efficiencies higher than that of Selexol. In addition, many of the technologies surveyed require a narrow operating range of process parameters in order to be viable alternatives. We identify desired material properties of membranes and thermodynamic properties of sorbents that are needed to make these technologies successful, providing direction for ongoing experimental efforts to develop these materials.