June, 2005
Vol 1 Chapter 9: Self-assembled nanoporous materials for CO2 capture
Part 2: Experimental studies
Ripudaman Malhotra et al, Chemical Science and Technology Laboratory, SRI International, USA
Abstract: Adsorption tests verified the expected high capacity of copper terephthalate complex for adsorbing CO2. The CO2 isotherm did not level off up to CO2 partial pressures of 25 psig. The selectivity of the material for CO2 over N2 is about 8. Analogous tests with a silicalite (Hisiv 3000) showed saturation behavior above CO2 partial pressures of 10 psig. Based on laboratory measurements and simulations, a PSA process was designed to capture the CO2 from a 400 MW gas-fired power plant that would meet the specifications of 90% capture and 96% CO2 purity. Because pressurizing the total plant exhaust (1586.1 MMSCFD) would place a very high parasitic load (about 260 MW), we opted for a design in which the beds are charged at the pressure of the exhaust, and the CO2 product is recovered by pulling vacuum. The highest purity obtained in the experiments was 67.9% CO2 with 34.1% recovery. The production rate was 0.0113 sL/min. Additional simulations of the PSA process revealed that CO2-rich product with 97% purity is achievable by a 2-bed/5-step PSA process using the copper terephthalate adsorbent; however, it would require a long rinse (with part of the CO2-rich stream) and purging at low absolute pressure to obtain a high-purity CO2-rich product.
A rough economic analysis, accounting for capital and power consumption of the PSA system, gave estimated costs, per ton of CO2 captured, of $406 for the powdered copper terephthalate adsorbent, $495 for the granulated material, and $393 for UOP Hisiv 3000. Considering that the former adsorbents were experimentally obtained from batch syntheses and were not optimized, it is likely that they show good potential for this application, relative to the existing commercial product.
The most striking result though was that the power requirements for CO2 capture are enormous, about 1 GW or more than twice that of the power plant for which this capture system was being designed. It did not matter whether the adsorbent was copper terephthalate or Hisiv 3000, although it should be pointed out that under the operating conditions, the benefits of the large capacity of copper terephthalate were not being realized. In any case, in order to meet the stipulated requirements, the adsorbent for a PSA-based system must be able to deliver about two orders of magnitude better performance. That goal seems unlikely, and other scenarios in which some of the constraints are relaxed should also be considered.
Carbon Dioxide Capture for Storage in Deep Geologic Formations – Results from the CO2 Capture Project Capture and Separation of Carbon Dioxide from Combustion Sources - Volume 1
Edited by: David C. Thomas, Senior Technical Advisor, Advanced Resources International Inc, USA
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