Raghubir Gupta

Mixed Gas Permeation of Syngas Components in Poly (dimethylsiloxane) and Poly (1-trimethylsilyl-1-propyne) at Elevated Temperatures:

Abstract The permeability of poly(dimethylsiloxane) (PDMS) and poly(1-trimethylsilyl-1-propyne) (PTMSP) to a simulated syngas feed containing H 2 , CO, CO 2 , and H 2 S was determined as a function of temperature up to 240°C (464°F). The permeation properties of rarely studied CO and H 2 S were found to be consistent with their molecular properties (i.e. critical temperature) in both rubbery PDMS and high free volume, glassy PTMSP. At room temperature, PDMS and PTMSP are more permeable to the more condensable gases CO 2 and H 2 S than to H 2 . However, both polymers become hydrogen selective at elevated temperatures. Activation energies of permeation are highest for H 2 in both polymers and decrease regularly with increasing gas condensability. PTMSP exhibits evidence of accelerated physical aging at high temperature.

Capture of carbon dioxide from flue gas using solid regenerable sorbents

Carbon dioxide emissions from the combustion of fossil fuels are a significant factor in global climate change. Large stationary sources such as coal-fired electric generating plants are likely to be the most cost-effective targets for carbon dioxide capture. At present, liquid amine-based scrubbing systems are the only processes available for this application. Processes based on regenerable solids that absorb carbon dioxide from flue gas and release it in concentrated form have the potential to be less expensive to operate. This paper summarises the results of studies conducted at RTI and Louisiana State University (LSU) to investigate the feasibility of using sodium or potassium carbonate as a sorbent. Upon reaction with carbon dioxide and water (also present in flue gas), this material is converted to sodium or potassium bicarbonate. Upon heating (ideally with low grade heat from the generating plant), carbon dioxide and water vapour are released and the solid carbonate can be reused. Work to date has focused on thermogravimetry (TG) and bench scale fluidised-bed testing, as well as characterisation of materials and thermodynamic and kinetic analyses. TG studies with sodium carbonate have indicated that the sorption reaction takes place rapidly at approximately 60°C and that the sorbent can be regenerated at temperatures less than 120°C. A five-cycle test conducted in a bench scale fluid bed reactor system indicated that the sorbent could be regenerated and reused. The process implications of compound salts and hydrates in the sodium carbonate system on the useful capacity of the sorbent and heat removal requirements were also investigated.

Carbon Dioxide Capture from Flue Gas Using Dry, Regenerable Sorbents

This report describes research conducted between October 1, 2004 and December 31, 2004 on the use of dry regenerable sorbents for removal of carbon dioxide from flue gas. Two supported sorbents were tested in a bench scale fluidized bed reactor system. The sorbents were prepared by impregnation of sodium carbonate on to an inert support at a commercial catalyst manufacturing facility. One sorbent, tested through five cycles of carbon dioxide sorption in an atmosphere of 3% water vapor and 0.8 to 3% carbon dioxide showed consistent reactivity with sodium carbonate utilization of 7 to 14%. A second, similarly prepared material, showed comparable reactivity in one cycle of testing. Batches of 5 other materials were prepared in laboratory scale quantities (primarily by spray drying). These materials generally have significantly greater surface areas than calcined sodium bicarbonate. Small scale testing showed no significant adsorption of mercury on representative carbon dioxide sorbent materials under expected flue gas conditions.

CARBON DIOXIDE CAPTURE FROM FLUE GAS USING DRY REGENERABLE SORBENTS

Electrobalance studies of calcination and carbonation of sodium bicarbonate materials were conducted at Louisiana State University. Calcination in an inert atmosphere was rapid and complete at 120 C. Carbonation was temperature dependent, and both the initial rate and the extent of reaction were found to decrease as temperature was increased between 60 and 80 C. A fluidization test apparatus was constructed at RTI and two sodium bicarbonate materials were fluidized in dry nitrogen at 22 C. The bed was completely fluidized at between 9 and 11 in. of water pressure drop. Kinetic rate expression derivations and thermodynamic calculations were conducted at RTI. Based on literature data, a simple reaction rate expression, which is zero order in carbon dioxide and water, was found to provide the best fit against reciprocal temperature. Simulations based on process thermodynamics suggested that approximately 26 percent of the carbon dioxide in flue gas could be recovered using waste heat available at 240 C.