Membrane Technologies for CO2 Capture

This thesis investigates the potential of membrane technology for the effective CO2/CH4 separation. The work focuses on two different membrane processes to accomplish the separation: 1) The use of a gas-liquid membrane contactor for the selective absorption of CO2 from CH4 2) The use of thin, dense gas separation membranes to establish the separation Porous (PP) and asymmetric (PPO) hollow fiber membranes have been used in a membrane contactor with the traditional absorption liquid monoethanolamine (MEA) and the influence of different process parameters has been evaluated. The PP membranes outperform the PPO membranes in terms of productivity and selectivity, but the PPO membranes are much less sensitive towards variations in feed pressure, which increases the operating window. Amino acid salt solutions have similar reactivity and CO2 absorption capacity as alkanol amines, but in addition they can be made non-volatile and are therefore a competitive alternative. The kinetics of the CO2 absorption in an amino acid salt solution (sarcosine) have been studied. Reaction rate constants significantly higher than those found for MEA were obtained for the absorption of CO2 in aqueous sarcosine salt solutions showing the potential of this new absorption liquid. The performance of this amino acid salt solution in a membrane contactor showed very high CO2/CH4 selectivities due to very low CH4 permeances. These high selectivities for sarcosine salt solutions can already be achieved without a temperature difference between absorber and desorber, which is a step forward towards energy-efficient CO2 absorption. In addition, the use of gas separation membranes with improved plasticization resistance has been investigated. An imidazolium-based poly(RTIL) is used as base material and the length of the alkyl chain serves as a tool to strengthen or weaken the ionic interactions within the poly(RTIL). Furthermore a promising high selective polymeric membrane (ODPA PEI) is tested and its sorption, swelling and permeation behavior at high pressure are analyzed. High CO2/CH4 selectivities for the ODPA PEI films even at elevated pressure and therewith high potential of this material for the effective CO2 removal were found.