2 nd Mercosur Congress on Chemical Engineering 4 th Mercosur Congress on Process Systems Engineering PRESSURE SWING ADSORPTION FOR CARBON DIOXIDE SEQUESTRATION Carlos A. Grande * , Simone Cavenati, Alírio E. Rodrigues Laboratory of Separation and Reaction Engineering (LSRE), Departamento de Engenharia Química, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias (4200-465), Porto, Portugal. Abstract. The members of the MERCOSUR as well as the European Union have agreed in the Kyoto protocol to diminish 12% the emissions of carbon dioxide up to 2010. Carbon dioxide emissions are quite high in the entire European continent with many countries being in the top 20 larger polluting countries of the world. Co-generation of electricity and heat has proved to be one of the most efficient and less polluting technologies for power generation. Even though, these centrals are still based on the combustion of fossil fuels, requiring additional processes for carbon dioxide sequestration and concentration for further uses. Many alternatives are already available for CO 2 capture from flue gases: cryogenic process, absorption with monoethanolamine, MEA and membranes. Up to 1995, Pressure Swing Adsorption (PSA) adsorption technologies were the ones having the higher capture efficiency, although was penalized by global economics. In this work we studied the feasibility of concentration and capture of carbon dioxide from flue gases of electric power centrals by Pressure Swing Adsorption (PSA) units. Two different adsorbents, zeolite 13X and activated carbon, were used as selective adsorbents for carbon dioxide. We used a four-step cycle comprising pressurization, feed, counter-current blowdown and purge at temperature around 373 K, conditions of a typical co-generation exhaust stream. Following, scale-up and process economics (installation and operational costs and its impact in energy price) were evaluated. Keywords: Carbon Dioxide, Sequestration and Pressure Swing Adsorption. 1. Introduction Earth's atmosphere is roughly 78% nitrogen, 21% oxygen, and 1% other gases. Water vapor (varying in amount from 0 to 2%), carbon dioxide (around 260 ppmv) and some other minor gases present in the atmosphere absorb some of the solar thermal radiation keeping an energetic balance that allows Earth to be warmer than it should be (around –20C). These gases are known as greenhouse gases (GHG) because they act as a partial blanket for thermal radiation. This blanketing is a natural greenhouse effect. A higher concentration of any GHG due to human activities (anthropogenic GHG), implies that the greenhouse effect will increase changing this energetic balance with still unknown consequences in global weather. It was observed that in the last century the ocean level has increased in a direct relationship with an increase in average ground temperature. To avoid serious catastrophes, many countries agreed in some commitments (Kyoto protocol) to stabilize the GHG concentration in the atmosphere, for carbon dioxide, methane, NO x , SO x , etc. As the country emissions of GHG are not uniform and as local economic factors have to be also taken into account, the commitments are not equal to all countries. As an example, in Figure 1 we show the CO 2 emissions per capita in European countries. * To whom all correspondence should be addressed. Address: Laboratory of Separation and Reaction Engineering (LSRE), Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias (4200-465), Porto, Portugal Email: cgrande@fe.up.pt 1