3rd GENERATION SOLVENT MEMBRANE CONTACTOR

During the last years there has been significant development in new solvents for chemical absorption of CO2. These new solvents, often called 3rd generation solvents, require lower temperatures in the desorber and/or less heat to reverse the reactions making them economically more feasible. However, the 3rd generation solvents suggested are partly quite volatile and this has been pointed out as an obstacle to their use industrially in a traditional absorption tower. In an absorption tower there is no physical boundary between gas and liquid and all volatile components can freely move between the phases. This can increase the solvent molecule emissions. In this project a membrane contactor is proposed as a viable solution to fully exploit the potential of the highly volatile 3rd generation solvents. Non-porous composite membranes with high CO2 permeation but limited amine permeation towards the gas phase will be developed and optimized for the membrane contactor. The 3rd generation solvents will be further optimized to improve the separation performance and reduce the energy penalty associated with the amine regeneration step. In view of the smaller footprint and the easier scalability compared to traditional absorption columns, the 3rd generation solvent membrane contactors could have a faster and more accessible commercialization of the CO2 capture technology for post combustion applications. The following results have been achieved: (1) 5 different new solvent systems with better energy efficiency compare to the benchmark solvents (i.e., 5M MEA and 5M DEEA 2M MAPA) have been identified. The new solvents showed a larger CO2 partial pressure at high temperature (120 °C), suggesting an easier and more energy efficient regeneration. The lowest energy penalty of 2.5 MJ/kgCO2 has been estimated. (2) A polymer family (e.g., AF2400), which is found durable in the 3rd generation solvents and stable in a long term operation, has been identified as the thin coating layer materials for the non-porous membrane contactor. AF2400 composite membranes have high CO2 permeation rate, and the presence of the liquid phase in the contactor shows a limited effect on the transport properties of the membranes. Pervaporation of various amine mixtures have been tested, and the membranes achieved high selectivity (> 100) in the considered operating conditions (25 - 60 °C); (3) A procedure has been determined to coat a thin (1 µm) layer of AF2400 on porous PP hollow fibers. Several membrane modules have been prepared and tested in the lab.

We believe that the development of the technology will continue and hopefully eventually will lead into commercialization. Currently the following activities are planned: ? EU-project proposal TESLA: The results from the project are so promising, that we were invited to join an EU-project proposal (coordinated by SINTEF) where the membrane contactor developed will be tested first in the laboratory scale and when successful in a real industrial site. The application was submitted in September 2018 ? To apply the concept (coated membrane contactor) has also been proposed for another application. We are currently discussing the testing possibilities with TNO.

The idea of the proposed project is to try combine the properties of membrane contactors and 3rd generation solvents so a process can be developed that will provide regeneration energy numbers below 2 MJ steam/kg CO2 captured and at the same time reduce footprint, cost and avoid problems associated with solvents losses through physical volatility and mist/aerosol formation. The challenges in this project can be summed up in two major points: 1) To select/develop a 3rd generation solvent system that has the potential for low energy demand and at the same time shows long term compatibility with the chosen membrane material 2) To develop a membrane material, compatible with the solvent, that has low mass transfer resistance for CO2 and water, and at the same time prevents solvent molecules from entering the gas phase. The project will start with testing of solvents and membrane materials for compatibility.When a potential combination is found, membrane development and solvent testing will be performed. At the end of the project process modeling and cost analyses will be done to evaluate the process.