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 CO2 is strongly adsorbed. A Skarstrom-type cycle comprising pressurization with product, feed, countercurrent blowdown, and countercurrent purge was employed. A mixture having 60% CH4/20% CO2/ 20% N-2 was used, and two different temperatures were evaluated in a single-column VSA-PSA unit. Under the conditions tested, CO2 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 CH4-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.