(420b) High Reactivity and Enhanced Capacity Carbon Dioxide Removal Agents with Low Susceptibility to Deactivation

The first step of forming hydrogen from carbonaceous solid fuels is gasification, followed by water gas shift reaction and separation of the carbon dioxide and hydrogen. Capture of carbon dioxide in situ will result in increased production of hydrogen by the water gas shift reaction. Separation of H2 from the coal gasification products supports existing H2 markets (such as refineries and power production) and makes hydrogen economy a distinct possibility. The sequestration-ready aspect of hydrogen/carbon dioxide separation will be of consequence in power applications in the future. The capture of acid and greenhouse gases from process streams is a major concern. One of the most common methods is the absorption of the gases in liquid solvents.

The initial and the ultimate carbon dioxide capture by sorption/reaction in repeated calcinations-carbonation cycles is strongly influenced by its surface area, pore size, and volume characteristics of calcium oxide. The commercially mined-limestone/dolomite powders exhibit a very low initial surface area and porosity. In an effort to increase the purity of hydrogen in the product stream by separation of the product gases from gasification, a new process to produce Ca-based carbon dioxide sorbent with enhanced sorption capacities and life has been developed. The method allows customizing the particle sizes for use in both packed bed and fluidized bed reactors. Samples with mean sizes ranging from 5 to 85 microns were produced. The fundamental carbon dioxide sorption on modified calcium oxide samples were studied using TGA reactor. Repetitive calcinations-carbonation reactions in pure nitrogen and carbon dioxide, respectively, were performed. Correlation of the removal efficiencies with BET surface area, pore size distribution, and particle size distribution are presented. The data from experiments with lab-synthesized removal agents is presented and compared with commercially available calcium carbonate and calcium oxide. The uptake by commercial CaO was less than 40 %, while that by the commercial calcium carbonate decreased monotonously from an initial value of 52 % to nearly 20 % after 11 cycles. On the other hand, the uptake by the laboratory synthesized samples showed nearly 100 % uptake of the theoretical maximum. Repeated cycling for over 11 cycles showed only a 5 % decrease in the capacity. The reactivities of the lab-synthesized removal agents were found to be greater than 10 times that of the commercially available Ca-based sorbents.