Novel Membrane contactor using ionic liquids for pre-combustion CO₂ capture

The project entitled MCIL-CO₂ - Novel membrane contactor using ionic liquids (ILs) for pre-combustion CO₂ capture, is aimed to develop an environmentally friendly new solution with high separation efficiency and low energy consumption for CO₂ capture from pre-combustion power plant emission. In pre-combustion process, CO₂/H2 separation is an important step to purify H2 from the water-gas shift reaction products and hence avoid CO₂ emission. The selective separation of CO₂ from H2 at elevated temperatures is the key challenge for this process since this reaction is equilibrium limited and only occurs at appreciable rates at 15-20 bar and temperatures 190-210oC. As an approach to the CO₂/H2 separation at elevated temperature and pressures, a membrane contactor process using specifically tailored ILs as CO₂ absorbents is proposed. This ILs membrane contactor process takes advantages of membrane separation, absorption and ILs, and is expected to have high CO₂/H2 separation efficiency (with high CO₂, H2 purity and H2 recovery), small footprint, low energy consumption and reduced pollution, bringing in clearly positive impact not only on the climate, but also to the natural environment in a long term. Despite of all these advantages, reports on membrane contactors with ILs as absorbents for CO₂/H2 separation at elevated temperature and pressures can barely be found.
Goal of project:
To develop an environmentally friendly new solution with high separation efficiency and low energy consumption for CO₂ capture from pre-combustion power plant emission.
Technical content:
This project is to develop a membrane contactor process using ILs as CO₂ absorbents for CO₂/H2 separation at the pre-combustion conditions.
The research is carried out as four work packages:
-    Optimization of ILs as absorbents
-    Optimization of membrane materials and modules
-    Lab scale experimental rig for separation performance testing
-    Optimization of the process and separation conditions
Technical advantages:
-    High separation efficiency: The use of ILs as absorbents in the membrane contactor process can result in high CO₂ purity, H2 recovery and H2 purity at the same time.
-    Energy saving: The regeneration of absorbents in this process is low energy demanding- no evaporation of solvent is involved. The purified H2 in the retentate is kept at high pressures, which is beneficial for the downstream utilizations of H2.
-    Environmentally friendly: ILs are green solvents with undetectable vapour pressure, hence no harmful effect on the environment in a long term.
R&D challenges:
The pre-combustion conditions is the key challenge for this process as the reaction is equilibrium limited and only occurs at appreciable rates at 15-20 bar and temperatures 190-210oC.
-    High temperature may cause problems such as the reduced CO₂ sorption capacity and increased the corrosion to the metallic materials. The concern on the long term stability and durability of the ILs at high temperature also limits the use of certain types of high performance ILs.
-    The sealing of the membrane modules at high temperature and high pressure is difficult.
-    To maintain a small pressure difference between gas and liquid phase and prevent membrane wetting at elevated pressures are complicated.
Results to date:
The following research tasks have been successful completed during the past year:
(1)    Commercially available ILs screened and two ILs, [Bmim][TCM] and [Emim][AC] were selected for further investigation;
(2)    5 different series, 13 different kinds of structure specific ionic liquids with high CO₂ absorption capacities were successfully synthesized and characterized.
(3)    AAIL-PEG (amino acid ionic liquid and low molecular weight Polyethylene glycol) Blend solvent optimized and properties determined.
(4)    Suitable ionic liquids-based solvents for the process were optimized with respect to CO₂ sorption capacity and physical properties (e.g. viscosity), and evaluated at operating conditions.
(5)    Suitable membrane and membrane module were selected. The chosen SPG glass membrane has high porosity, shape pore size distribution, high thermal and chemical stability.
(6)    Composite membranes with dense coating layer (i.e., Teflon AF 2400) have been also prepared as membrane contactor. These membranes show superior chemical stability, mechanical strength and good thermal stability. Composite membrane can eliminate membrane wetting.
(7)    Selected membranes were modified and characterized.
(8)    The in-house made lab scale experiment rig has been commissioned and put into use.
(9)    Separation performances of glass membrane and [Bmim][TCM] has been tested and operating parameter been optimized.
(10)    Membrane contactors using two polymeric membranes, porous PTFE membrane and Teflon-polypropylene hollow fiber composite membranes have been tested and optimized.
(11)    Long-term stability of the two polymeric membrane contactors has been investigated in a period of 2 weeks.
(12)    Mass and heat transfer modeling of IL membrane contactor has been completed using literature reported data of IL. The modeling study is now going on with the experimental data of aforementioned ILs for validation with the tested separation performance.