Recovery of Liquid CO2 from Cleaning Solutions Without Phase Change Using Ultrafiltration and Microfiltration Membranes

Abstract

Recovery of liquid and supercritical fluid (SCF) CO2 in the application of CO2 as processing solvent in extraction, chemical, and biochemical reactions is an important issue. Membrane-based separation may provide an option in recovering CO2 in liquid and/or SCF phase without expensive, energy intensive recompression. The potential application of microporous inorganic membranes in separating liquid CO2 without phase change was investigated. A high-pressure membrane filtration unit was designed, built, and tested. Microporous stainless steel (0.2 μm) and ceramic (0.02 μm, and 1000 Dalton) tubular elements were retrofitted into in-house designed, high-pressure housings to test the functionality of the system using Triton X-100 solute in liquid CO2 as feed. In-house designed fiberoptic cells coupled with a UV–VIS spectrophotometer was used for on-line measurement of solute Triton X-100 in the feed and permeate streams. The fiberoptic cell coupled with UV–VIS spectrophotometer was capable of providing on-line concentration measurement of Triton X-100 at operating pressures up to 100 bar. Two different path-length fiberoptic cells, 5.0 mm and 0.5 mm, were designed and built to cover a wide range of solute concentrations. Membrane filtration experiments with ceramic membranes showed that 1000-Dalton membrane offered a solute rejectivity of about 80%. The coarse ceramic membrane (0.02 μm) had a lower rejectivity, which was about 55%. The 0.2-μm stainless steel membrane provided very little solute rejectivity.