Micron-sized CaO, obtained by calcination of mesoporous CaCO3, attained 36 wt % CO2 sorption capacity after 100 cycles of carbonation and calcination reactions at 700 °C. The extent of simultaneous carbonation (X CO 2 ) and sulfation (X SO 2 ) of CaO at 700 °C was obtained under simulated flue gas conditions (10% CO2, 3000 ppm of SO2, 4% O2 in N2). CaO reacts with SO2 to form thermally stable CaSO4, which leads to a reduction in the CO2 capture capacity of CaO. Whereas X SO 2 increases monotonically with the residence time, X CO 2 goes through a maximum and eventually drops as a result of direct sulfation of CaCO3. The maximum value attained by X CO 2 was 50% in 10 min in the first cycle. The highest X CO 2 /X SO 2 ratio of 5 is attained at a residence time of 5 min. X SO 2 is higher under simultaneous carbonation and sulfation conditions compared to sulfation of CaO or direct sulfation of CaCO3.

Increasing concerns over growing CO 2 levels in the atmosphere have led to a worldwide demand for efficient, cost-effective, and clean carbon capture technologies. One of these technologies is the Carbonation-Calcination Reaction (CCR) process, which utilizes a calcium-based sorbent in a high-temperature reaction (carbonation) to capture the CO 2 from the flue gas stream and releases a pure stream of CO 2 in the subsequent calcination reaction that can be sequestered. A 120 KWth subpilot-scale combustion plant utilizing coal at 20 pph along with natural gas has been established at The Ohio State University to test the CCR process. Experimental studies on CO 2 capture using calcium-based sorbents have been performed at this facility. Greater than 99% CO 2 and SO 2 capture has been achieved at the subpilot-scale facility on a once-through basis at a Ca:C mole ratio of 1.6. In addition, the sorbent reactivity is maintained over multiple cycles by the incorporation of a sorbent reactivation hydration step in the carbonation-calcination cycle.

The influence of several process parameters on the calcination of a naturally occurring limestone and a precipitated mesoporous calcium carbonate (CaCO3) sorbent structure to calcium oxide (CaO) is detailed in this study. CaCO3 calcination is an integral part of a multicyclic carbonation−calcination reaction (CCR) process that separates carbon dioxide (CO2) from high-temperature gas mixtures into a pure CO2 stream. Maintenance of high sorbent reactivity over repeated CCR cycles reduces the capital and operating cost of the CCR process. A lower calcination temperature, required to maintain high sorbent reactivity, reduces the calcination rate of CaCO3. This study investigates various process conditions such as subatmospheric calcination, sorbent dispersion in a rotary calciner, use of a high thermal conductivity sweep gas, etc. in enhancing the calcination rate at lower calcination temperatures. The high-temperature gas−solid carbonation studies of the resulting CaO sorbent prove the necessity to maintain a high porosity structure during limestone calcination.

A cobalt-tungsten η-carbide material [Co 6 W 6 C] was investigated as a precursor for a stable and active catalyst for the dry reforming of methane to produce synthesis gas. The kinetics of CH 4 /CO 2 reforming were studied under differential conditions over a temperature range of 500-600 °C, based on a detailed experimental design. The observed rates qualitatively follow a Langmuir-Hinshelwood type of reaction mechanism. Such a scheme is considered quantitatively, with four reactions: methane reforming, reverse water-gas shift, carbon deposition, and carbon removal by a reverse Boudouard reaction. Of these, carbon deposition and carbon removal are generally disregarded in most of the reported kinetic models. The parameters of the model were successfully estimated for all of the experimental data. The comparison plots of the observed data and the predicted model show generally a good fit for all of the product species.

Enhancement in the production of high purity hydrogen (H 2 ) from fuel gas, obtained from coal gasification, is limited by thermodynamics of the water gas shift reaction. However, this constraint can be overcome by the concurrent water gas shift and CaO carbonation reaction to enhance H 2 production by incessantly driving the equilibrium-limited water gas shift reaction forward and in situ removing the carbon dioxide (CO 2 ) product from the gas mixture. The in situ removal of CO 2 is achieved by using a calcium oxide (CaO) sorbent which also reacts with and removes sulfur and halide contaminants present in the syngas stream. The water gas shift reaction is achieved by the high temperature shift (HTS) iron oxide catalyst while the CO 2 capture is achieved using CaO sorbent. The spent sorbent from the system is regenerated by calcining it to produce a pure stream of CO 2 and CaO which can be reused. The steam addition for the water gas shift reaction is reduced to a large extent in this process which aids in reducing the parasitic energy consumption. In addition, the extent of sulfur removal by the CaO sorbent is also enhanced by operating at lower steam partial pressures. Experiments conducted in a bench scale facility have revealed that high purity H 2 of 99.7% purity can be produced by this calcium looping process.