Solvent recovery membrane application

The commercial membrane separation processes are offered in the areas of nitrogen production and waste treatment applications (1). Developing membrane applications in oil milling and edible oil processing are (1) solvent recovery, (2) degumming, (3) free fatty acid removal, (4) catalyst recovery, (5) recovery of wash water from second centrifuge, (6) coohng tower water recovery, (7) protein purification, and (8) tocopherol separation. 

Because caffeine extraction is an important industrial application of SC CO2 technology, different studies have been recently conducted on solvent recovery by membrane separation. As the molecular weight (MW) (194 g moP ) of caffeine is higher than CO2 (44 g moP ), classical suitable membrane for this application needs to reject caffeine while letting CO2 cross through the membrane. Thus, pure CO2 can be obtained on permeate side and recycled. 

Other methods for forming blends such as by evaporation of a solvent or by polymerization of a monomer in the presence of a polymer involve at least three components in the preparation process. Mixing in a common solvent followed by its removal is a convenient way of making blends on a laboratory scale, but has obvious commercial disadvantages due to the cost and difficulty of solvent recovery as well as the potential environmental hazards associated with handling large volumes of often toxic chemicals. In specific applications, however, such as membrane formation or paints and coatings where thin films are required, the use of solvents is unavoidable. 

Membranes are among the most important industrial applications today, and every year, the use of this technology in processes such as water purification, industrial wastewater treatment, dehydration solvent recovery of volatile organic compounds, and protein concentration is increasing [1]. 

Kuk et al. [55] applied a PA membrane with molar weight cutoff of 1000 Da in a mixture containing ethanol and crude cotton seed oil. The recovery of solvent was 99% with an operational pressure of 2-4 bar, temperature of 25°C, and permeate flow ranging between 1 and 4 L m h. The authors conclude that small pore diameters result in low permeate flows. Typically, low permeate flux can be correlated with fouling consolidation (Figures 23.14 and 23.15), which limits an industrial application of NF processes by polymeric membranes to solvent recovery from micelle (usually ranging between 20% and 40% w/w or v/v of oil in hexane or another organic solvent) in coupled UF/ NF processes. 

The recovery of organic vapors from waste gas streams using polymeric membranes is a well established process (7). Typically, composite membranes are used for this process. These membranes consist of a diin, selective rubbery layer coated onto a microporous support material. The selectivities of these membranes for organic vapors over nitrogen are typically about 10-100. Currently, commercial vapor separation membrane applications include small systems (10-100 scfin) to recover fluorinated hydrocarbons (Freons) and other high-value solvent vapors from process vent streams to large systems (100-1,000 scfin) for recovery of hydrocarbon vapors in the petrochemical industry (7). 

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