Overview of CO2 Capture from Flue Gas Streams by Vacuum Pressure Swing Adsorption Technology

Review Article

Austin J Chem Eng. 2014;1(2): 1009.

Overview of CO2 Capture from Flue Gas Streams by Vacuum Pressure Swing Adsorption Technology

Jianghua Ling,sup>1,2

, Augustine Ntiamoah2, Penny Xiao2*, Dong Xu3, Paul A Webley2, Yuchun Zhai1

1School of Materials and Metallurgy, Northeastern University, China

2Department of Chemical and Bimolecular Engineering, University of Melbourne, Australia

3Guodian New Energy Technology Research Institute, China Guodian Corporation, China

*Corresponding author: Penny Xiao, Department of Chemical and Bimolecular Engineering, University of Melbourne, Victoria 3010, Australia

Received: May 31, 2014; Accepted: August 08, 2014; Published: August 12, 2014


With increasing concerns about CO2 emissions and their impact on global warming, CO2 capture technologies have been widely studied. Adsorption technology, as an important process for gas separation, has also been studied for CO2 capture from flue gas for more than two decades. Because the pressure of most flue gas streams is approximately atmospheric, vacuum swing adsorption process (VSA) is preferred. This paper provides an overview of the development of VSA processes for CO2 capture based on commercial adsorbent materials. We discuss the general trends in process performance with respect to adsorbent characteristics, cycle design and operating conditions. We have also discussed the impact of impurities in feed gases on VSA processes and strategies for dealing with the negative impacts. Finally, energy consumption in CO2VSA processes is summarized. The review of process performance is mainly based on simulation and laboratory scale work.

Keywords: CO2 capture; Vacuum swing adsorption; TSA


CO2 is a major greenhouse gas and hence, contributes significantly to global warming. The development and deployment of CCS (CO2 capture and storage) technologies is considered the most important option to make much deeper cuts in greenhouse gas emissions, and CO2 concentration of greater than 95% is commonly required for sequestration [1]. Currently three major separation technologies namely absorption, membranes and adsorption are being developed to capture and concentrate CO2 from flue gases for CSS applications [2, 3]. Absorption is the most mature of these technologies, and has long been used for CO2 capture, though not from power plants. However, it results in high energy consumption during the high temperature absorbent regeneration [4].

Adsorption technology is increasingly becoming popular for CO2 capture because of its potential low energy consumption, simple operation, easy maintenance and flexibility in design to meet different demand requirements [5-7]. Each of the different adsorption processes such as TSA (temperature swing adsorption), PSA (pressure swing adsorption), VSA (vacuum swing adsorption), and ESA (electrical swing adsorption) may be most suitable for treating feed gases with different CO2 concentrations [8]. The TSA can be designed to directly utilize cheaper, low-grade thermal energy resources from power plants for regeneration to reduce the operating cost. However, the longer time required for heating/cooling limits its application for CO2 capture. With the long cycle time, productivity will be lower compared to other adsorption technologies. The product may also be diluted by the purge gas if regeneration is performed by direct hot gas purge as used in conventional systems [9-12]. Because the pressure in flue gas streams is approximately equal to 1.0 bar and CO2 concentration in the feed gas is commonly higher than 10%, VSA is considered more economical for CO2 capture than PSA (where significant compression of the feed gas is required) [13,14]. The temperature range of flue gases varies by their sources and pre-treatment processes that may be available. Taking a typical coal-based power plant for instance, the flue gas stream may be available at a temperature ranging from 30 to 80°C or even higher, depending on the extent of heat recovery from the stream [15]. The VSA performance is sensitive to the feed gas temperature, so a further heat treatment may be required to condition the flue gas before feeding it to the VSA plant, which will inevitably impact on the separation efficiency and economics of the process.

Adsorbents play a key role in adsorption technology. The adsorbent determines the overall CO2 capture performance in VSA technology [16,17]. The key elements for a good adsorbent in CO2VSA technology are high selectivity of CO2 over N2, high adsorption capacity of CO2, rapid adsorption/desorption kinetics, stable adsorption capacity after repeated cycles, and adequate mechanical strength of the particles [18]. Many adsorbents with high CO2 adsorption capacity and selectivity have been developed recently such as MOFs, amine modified adsorbents, etc. [19]. While the number of new adsorbent materials reported has proliferated, only a very select few will undergo bench-top testing and even fewer will pass on to pilot testing stage, partly due to limited availability of production materials since large scale production is often not the goal of initial materials research. Therefore, VSA process design for CO2 capture still focuses on commercially available materials such as zeolites, activated carbon and CMS which can be purchased in bulk and tested in pilot or field installations [20-24]. This paper provides a review of VSA process development for CO2 capture, and specifically discusses how adsorbent characteristics, process design and operating conditions impact the overall process performance.

Commercial CO2 Adsorbents

In capture processes of CO2 from flue gas streams, it is assumed that the impurities in the feed gases including water are removed through flue gas pre-treatment processes so that CO2 separation from flue gases can be represented as that from a mixture of CO2 and N2. Zeolite materials have been widely studied for CO2 capture from flue gases in fossil fuel power plants, natural gas and biogas facilities [5,14,25,26]. According to the literature on CO2 capture using different types of natural and various types of synthetic zeolites such as Y, X, A, 13X zeolite shows superior performance for CO2 separation from N2 at relatively low temperatures [27]. Some researchers have considered 5A in TSA processes because of its higher volumetric capacity and high working capacity between low and high temperatures [28,29]. Zeolite 13X, studied for more than two decades, is the benchmark material for CO2VSA systems because of its high working capacity and selectivity for CO2 at the prevailing conditions of the process. From the isotherms of CO2 and N2 on 13X [22,30], both CO2 and N2 adsorption amount increases as their partial pressures increase (Figure 1) in the usual way as expected for a physic-sorbent. As the temperature increases, the adsorption amount for both CO2 and N2 decreases, indicative of exothermic adsorption. Although 13X is a physic-sorbent for CO2 and as such should be restricted to modest temperature application, we have found that it presents a relatively high CO2 working capacity even over 120°C. Therefore, it is an ideal adsorbent for CO2 and N2 separation as it has a wide operating temperature range.