Summary
The project aims at the use of moist CO2 gas streams, such as those generated during the upgrading of biogas to biomethane or natural gas. The drying of these gas streams is an essential requirement for many applications. In the project, a membrane drying process will be developed and tested. This process has the advantage of being more energy-efficient than adsorption and absorption processes. In addition, the use of a temperature-stable, inorganic microporous or mesoporous separation membrane should enable operation at high temperatures, so that the permeate (water or water vapour) can be used for heat recovery.
In the project so-called MFI (Mobile Five) membranes were produced and tested. Commercially available, asymmetric corundum carriers were used as carriers. The carriers were tested in the laboratory at 120 °C and feed streams of 3-21 l/h to quantify the factors influencing the separation properties of the membrane.
Results:
- Water vapor condensation in the pores of the membrane considerably reduces the permeability for CO2 (capillary condensation). This effect is utilised for the separation process.
- Below an H2O:CO2 ratio of 0.5 the selectivity is very low, because not enough water is available for capillary condensation.
- The permeability for water vapor remains constantly high, regardless of the H2O:CO2 ratio. The permeability for CO2 drops abruptly at an H2O:CO2 ratio of 0.4-0.7 depending on the feed stream.
- The useful working range (pressure, temperature) for this process is based on the conditions of an amine wash.
- In a pilot plant the laboratory results could be confirmed. With a water content in the feed of 198 g/h and a CO2 inflow of 600 l/h, approx. 72 % of the water could be removed.
