Optimized adsorption processes for CO2 capture

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Carbon capture and storage (CCS) from industrial flue gas is identified by the Canadian government as an important technology to reduce CO2 emissions. For example, a 500 MW coal-based power plant produce ca. 16,000 tonnes of CO2 per day. Capturing CO2 from a dilute flue gas stream (CO2 composition is 12 -15%) and concentrating it to high purities (>90%), using current technologies, e.g., amine-based absorption, is expensive and there is a need to develop alternatives. Adsorption using solid sorbents has been identified as a promising option. The main challenges in adsorptive CO2 capture are: 1. development of novel adsorbents; 2. design and optimization of novel process configurations (cycles) to achieve regulatory targets on purity & recovery > 90%; and 3. experimental demonstration (using wet flue gas) and cost estimation to compare with other technologies. This proposal develops enabling tools for challenge #1 and solutions for #2 & 3. Two projects are proposed under the research program. The distinctive feature of the projects is that they integrate experimental+modelling approaches to find practical CCS solutions. PROJECT 1: CO2 CAPTURE FROM WET FLUE GAS: Most reports on adsorptive CO2 capture have considered a dry flue gas feed. However, industrial flue gas is saturated with moisture (12.5 mol%) which can adversely affect CO2 adsorption capacity of most adsorbents. It is indeed surprising that not enough attention has been paid to the understanding of the effect of H2O on adsorptive CO2 capture. Project 1 will study the fundamentals of adsorption under high H2O concentrations and develop processes for wet flue-gas CO2 capture and quantify the costs involved. PROJECT 2: RATIONAL PROCESS DESIGN & ADSORBENT SELECTION: Adsorption processes have two important constituents: the cycle and the adsorbent. Adsorption cycles are designed based on past experience and limited simulations+experiments. This approach neither guarantees that a process is optimized nor that all possible configurations have been explored. On materials front, there has been an explosive growth of new adsrbents, e.g., metal-organic frameworks (MOFs). Many performance metrics, typically based on equilibrium information, have been proposed to select the right adsorbent for a particular application. Since adsorption is a fairly complex operation involving simultaneous heat/mass transfer, together with intricate configurations, we have recently shown that these metrics do not correlate with process performance and using them is rather misleading. Project 2 will address these challenges through the development of superstructure based optimization techniques which will automatically synthesize complex adsorption cycles; optimize their operating conditions and choose the best process+adsorbent combination for a particular separation. The research program outlined here, will not only be applicable to CO2 capture, but also to other important gas separations, natural and shale gas purification e.g., CO2/CH4, CH4/N2 separations and hydrocarbon separations. All these separations are vital to the economy of Alberta and Canada; each representing a business of the order of millions of dollars. Two PhD and four undergraduate students will be trained. HQP involved in this project will receive training that combines both experimentation and mathematical modelling, a rather rare combination. They will also receive an unique opportunity to design, construct and commission a multi-column pressure/vacuum swing adsorption system. HQP will be trained in design and optimization of separation processes, chemical process design and strong communication skills; attributes that will enable them to be successful in their chosen career paths.