Archive | 2019
Intermediate Temperature CO2 Capture for Future Clean Energy Production
Abstract
The establishment of CO2 emission-free, low energy penalty chemical production processes for clean energies, such as hydrogen and electricity, is a critical challenge for the mitigation of serious ongoing global warming. For hydrogen, most of the world-wide demand, which exceeds 65 million tons, is covered currently by steam methane reforming coupled with the water-gas shift reaction. Here, over 300 million tons of CO2 are co-produced and released into the atmosphere due to the lack of appropriate low energy cost CO2 capture technologies. For electricity generation, combined cycle technologies have been developed as a new class of high-efficiency power generation processes. However, the capture of CO2 from these power plants by conventional aqueous amine absorbents is not economically feasible for commercial operations. We present our recent work and progress on advanced CO2 capture technologies based on new, high capacity, metal oxide-based CO2 adsorbents that can operate over moderate to intermediate temperature ranges for the establishment of new CO2 emission-free, clean energy production processes. Since the first invention of amine-scrubbing process by Bottoms in 1930,[1] a variety of molecular and solid sorbents for CO2 capture have been developed.[2] The sorbents are classified into two groups depending on the temperatures at which they are active. Materials belonging to the first group are usually used at temperatures lower than 150 oC, and capture CO2 by either acid-base reactions or surface adsorption on porous solid materials. Aqueous amines, zeolites, porous silica, activated carbon, and MOFs are included in this group. In contrast, materials in the second group are suitable for capture at high temperatures, usually 650 to 800 oC, through the formation of metal carbonates on reaction with CO2. CaO, Li2ZrO3, and Li4SiO4, among others, are included in this group. For the development of new CO2 emission-free, low energy penalty chemical production processes for hydrogen and electricity, however, optimum process temperatures for CO2 capture are usually in the range of 200-650 oC and not covered by the materials listed in the above two groups. The sorbents we explored are materials that can be used for CO2 capture at such intermediate temperatures. We have examined first methods to enhance the reaction kinetics of CO2 on solid basic oxides by surface functionalization with ionic molten salts and fabrication of clustered nanoparticles to increase the active surface area for the reaction with CO2. Second, we explored the design of new metal oxide compounds with different equilibrium parameters for CO2 capture at different temperatures. As shown in Figure 1, these works have delivered new classes of high capacity and highly-regenerable CO2 adsorbents operative over the target temperature ranges.[3-5] In our presentation, we will demonstrate our new adsorbent design strategy for the preparation of high capacity CO2 adsorbents that operate at intermediate temperatures, and discuss early results on the application of these new adsorbents for the development of advanced CO2 emission-free, high efficiency production processes for hydrogen (via methane steam reforming) and electricity (by combined cycle processing).