Effects of baffles on separation of aqueous ethanol solution with hollow fibers

Abstract

The effects of baffles on the operation and mass-transfer characteristics in novel hollow fiber membrane contactor used in distillation were investigated. Hollow fiber membranes, coated with a 7 μm polydimethyl-siloxane, were operated as structural packing in the separation of ethanol-water solutions. The parallel flow mode was chosen for separation due to the stronger driving force of the concentration difference, in which liquid flows through the lumens of the fibers and vapor flows countercurrent-wise outside the fibers. Two baffles were installed on the shell side of the membrane contactors to enhance separation, which had a round shape with a semi-lunar hole. The results show that both baffled and unbaffled membrane contactors gave better, more productive separations than traditional packing in distillation, such as the excellent Sulzer Gauze BX structured packing. The baffled membrane contactors performed better than unbaffled ones, especially at high vapor velocities. The minimal HTU of membrane contactor with baffles could reach as low as 4.5 cm, and almost all the contactors could work well above the limit where flooding normally occurs in conventional cases. Theoretical analysis predicted that baffles helped membrane module to obtain a higher mass-transfer coefficient and a smaller mass-transfer resistance. Finally, theoretical mass-transfer coefficient and experimental value were compared as well as the contribution of each individual mass-transfer coefficients among liquid, gas and membrane.

Keywords

hollow fiber / membrane contactor / baffle / mass-transfer / ethanol-water

References

[1] Kreulen H, Smolers C A, Versteeg G F, Van Swaai W P M. Microporous hollow fiber membrane modules as gas-liquid contactors. Part 2. Physical mass transfer with processes. J Membr Sci, 1993, 78: 217-238

[2] Prasad R, Sirkar K K. Hollow fiber solvent extraction: Performance and design. J Membr Sci, 1990, 50: 153-175

[3] Alan G, Hwang S T. Hollow fiber membrane contactors. J Membr Sci, 1999, 159: 61-106

[4] Majumdar S, Guha A K, Sirkar K K. Fule oil desalting by hydrogel hollow fiber membrane. J Membr Sci, 2002, 202: 253-256

[5] Zhang G, Cussler E L. Distillation in hollow fibers. AIChE J, 2003, 49: 2344-2351

[6] Zhang G, Cussler E L. Hollow fibers as structured distillation packing. J Membr Sci, 2003, 215: 185-193

[7] Zhang G, Lin L, Meng Q. Distillation of methanol-water solution in hollow fibers. Sep & Purif Technol, 2007, 56: 143-149

[8] Zhang G, Lin L, Meng Q. Separation of alcohol-water solution by distillation through hollow fibers. Ind Eng Chem Res, 2007, 46: 7820-7825

[9] TreybalR E. Mass Transfer Operations, 3rd ed., McGrawHill, New York, 1980

[10] Keller K H, Stein T R. A two-dimensional analysis of porous membrane transport. Math Biosci, 1967, 1: 421-437

[11] Mahmud H, Kumar A, Narbaitz R M, Matsuura T. Highly VOC-selective hollow fiber membranes for separation by vapor permeation. J Membr Sci, 2000, 217: 99-116

[12] Johnson D W, Semmens M J, Gulliver J S. Diffusive transport across unconfined hollow fiber membranes, J Membr Sci, 1997, 128: 67-81

[13] Kister H Z. Distillation Design. New York: McGraw-Hill, 1992

[14] Sulzer Chemtech. Structural packings for distillation and absorption, Product Bulletin. 22.13.06.40-111, 00-70

[15] Cussler E L. Diffusion: Mass transfer in fluid systems. London: Cambridge University Press, 1984

[16] Yang D, Barbero R S, Devlin D J, Cussler E L, Colling C W, Carrera Martin E. Hollow fibers as structured packing for olefin/paraffin separations. J Membr Sci, 2006, 279: 61-69

[17] Steiner L, Hartland S. A new type of agitated liquid/liquid extraction column with enhanced coalescence plates. Sep Sci Technol, 1980, 15: 907-923

Acknowledgements

The authors thanks to Dr. E. L. Cussler for the useful discussions while visiting CEMS, UMN. This work was primarily funded by the Research Fund of the National Natural Science Foundation of China (Grants Nos. 20476096, 20776133). Other financial support came from the Research Fund from the Bureau of Education (Key Discipline of Environmental Engineering grants 56310503014).

RIGHTS & PERMISSIONS

2014 Higher Education Press and Springer-Verlag Berlin Heidelberg