in Wiley InterScience (www.interscience.wiley.com).A synopsis of the published literature on removal of CO 2 from a flue gas is given. A novel thermal swing chemisorption (TSC) process concept is proposed for removal and recovery of compressed CO 2 from a flue gas without precompression, predrying, or precooling. The process uses Na 2 O promoted alumina as a reversible CO 2 selective chemisorbent in conjunction with the principles of rapid thermal swing adsorption for direct production of compressed CO 2 from a flue gas. Several complementary process steps are used in the design to compress the product CO 2 and to achieve high CO 2 recovery and sorbent capacity utilization. Judicious steam purge steps are used for highly efficient sorbent regeneration and to minimize the steam requirement. The CO 2 chemisorption characteristics of the sorbent are reviewed and a model simulation of the TSC process performance is reported.

New equilibrium and column dynamic data for chemisorption of carbon dioxide from inert nitrogen at 250, 350, and 4508C were measured on a sample of sodium oxide promoted alumina, which was found to be a reversible chemisorbent for CO 2 . The equilibrium chemisorption isotherms were Langmuirian in the low pressure region (p CO 2 \2.0 kPa) with a large gas-solid interaction parameter. The isotherms deviated from the Langmuirian behavior in the higher pressure region. A new analytical model which simultaneously accounted for Langmuirian chemisorption of CO 2 on the adsorbent surface and additional reaction between the gaseous and sorbed CO 2 molecules was used to describe the measured equilibrium data. The heats of CO 2 chemisorption and the additional surface reaction were, respectively, 64.9 and 37.5 kJ/mol. The column breakthrough curves for CO 2 sorption from inert N 2 on the chemisorbent as well as the desorption of CO 2 from the chemisorbent by N 2 purge at 3508C could be described by the linear driving force (LDF) model in conjunction with the new sorption isotherm. The same LDF mass transfer coefficients can be used to describe both sorption and desorption processes. The CO 2 mass transfer coefficients were (i) independent of feed gas CO 2 concentration in the range of the data at a given temperature, and (ii) a weak function of temperature. The ratio of the mass transfer zone length to the column length was very small due to highly favorable CO 2 sorption equilibrium. Several sequential cyclic CO 2 sorption-desorption column dynamic tests were conducted to demonstrate the apparent stability of the material.

One vision of clean energy for the future is to produce hydrogen from coal in an ultra-clean plant. The conventional route consists of reacting the coal gasification product (after removal of trace impurities) with steam in a water gas shift (WGS) reactor to convert CO to CO 2 and H 2 , followed by purification of the effluent gas in a pressure swing adsorption (PSA) unit to produce a high purity hydrogen product. PSA processes can also be designed to produce a CO 2 by-product at ambient pressure. This work proposes a novel concept called "Thermal Swing Sorption Enhanced Reaction (TSSER)" which simultaneously carries out the WGS reaction and the removal of CO 2 from the reaction zone by using a CO 2 chemisorbent in a single unit operation. The concept directly produces a fuel-cell grade H 2 and compressed CO 2 as a by-product gas. Removal of CO 2 from the reaction zone circumvents the equilibrium limitations of the reversible WGS reaction and enhances its forward rate of reaction. Recently measured sorption-desorption characteristics of two novel, reversible CO 2 chemisorbents (K 2 CO 3 promoted hydrotalcite and Na 2 O promoted alumina) are reviewed and the simulated performance of the proposed TSSER concept using the promoted hydrotalcite as the chemisorbent is reported.