Removal of Carbon Dioxide from Natural Gas by Vacuum Pressure Swing Adsorption

A vacuum pressure swing adsorption (VSA-PSA) process is studied for the removal of carbon dioxide in a contaminated stream of natural gas to achieve fuel grade methane. The adsorbent used was zeolite 13X (CECA) where CO 2 is strongly adsorbed. A Skarstrom-type cycle comprising pressurization with product, feed, countercurrent blowdown, and countercurrent purge was employed. A mixture having 60% CH 4 /20% CO 2 /20% N 2 was used, and two different temperatures were evaluated in a single-column VSA-PSA unit. Under the conditions tested, CO 2 was removed to levels lower than 2% as required by fuel grade methane with methane recovery higher than 80% without recycle. This separation process also helps in the CH 4 −N 2 separation. A bidisperse (macropore−micropore) model also including distributed energy balances in gas, solid, and column wall considering heat and mass transfer resistance at the gas−solid interface was used to simulate the VSA-PSA behavior and compare with experiments. Also, some scale-up considerations are considered and evaluated by simulations of the process.