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Supercritical CO 2 (scCO 2 ), used in the food industry as a water extraction agent, requires dehydration units for regeneration. The present study assesses the economics of membrane-based dehydration of scCO 2 . In contrast to earlier studies, the contribution, next to the membrane, also the contributions of the mass transfer resistances of the feed and permeate boundary are included, which have a dominant effect on the final process design and economics. In addition, our work also extrapolates the process to industrial scale evaluating different configurations and process conditions. Specifically, the contribution of the membrane and membrane unit costs is discussed in more detail. Including the mass transfer resistances of feed and permeate boundary layer reduces the water flux across the membrane up to a factor 150, implying a larger required membrane surface area for a given water removal rate, and thus higher costs. Using a SPEEK-based membrane, the total drying costs, normalized for the amount of water removed, minimize around a skin layer thickness of 1 μm, i.e., not too thin to permeate and thus spill too much CO 2 and not too thick to hamper the H 2 O flux. Because the feed boundary layer dominates water transport, conditions that minimize its thickness reduce total costs. A reduction of the feed boundary layer dominance can be achieved by adjusting channel height, cross-flow velocity and the density and viscosity of scCO 2 , the latter two by increasing the operational temperature from 45 to 65 °C (at 130 bar). Compared to the benchmark zeolite process currently available, the membrane-based process for drying scCO 2 outlined and optimized in the present study results in a 50% saving of total drying costs. These savings can be achieved by using a dense polymeric membrane with a H 2 O permeability of at least 10,000 Barrer and a CO 2 permeability of at most 10 Barrer.

Continuous drying processes using supercritical CO2 (scCO2) as a water extraction agent require 24/7 operational dehydration units for scCO2 regeneration. Dehydration units using dense polymeric membranes are considered a cost effective, sustainable alternative to the current zeolite-based units. The focus of previous studies on the membrane-based dehydration of scCO2 was always on the membrane itself whereas boundary layer effects, e.g., concentration polarization, were not taken into account. To quantify the boundary layer effects, simulations were performed using three different membrane materials: SPEEK, Nafion® 117, and PEBAX® 1074. Process conditions during the simulations ranged from 8.0 to 18.0 MPa and 40 to 100 °C. Even though the three types of membranes examined differ in their H2O permeability and H2O over CO2 selectivity, in all cases 80% of the total mass-transfer resistance can be assigned to concentration polarization effects, making it the dominant parameter for water transport. Despite high but differing intrinsic water permeabilities of all three membranes materials, the H2O transport, thus H2O flux through the membrane is significantly reduced by concentration polarization down to similar levels. This makes it necessary to use larger membrane areas, that result in higher CO2 fluxes. As a consequence, material selection is predominantly based on the ability to reject CO2. Optimization of process conditions other than membrane material is briefly discussed.