Cellulose acetate membrane hydrogen recovery

A similar application is the processing of fuel gas, whose major components are hydrogen (about 80%) and methane (about 20%). Asymmetric cellulose acetate membranes have been used successfully to extract the more valuable hydrogen at high purity. New membrane materials more resistant to harsh conditions will accelerate the application of other H2 recovery schemes for... 

Cellulose acetate membranes have been suggested for hydrogen recovery, C02/CH4 separations, gas dehydration and for nitrogen enrichment.41"43... 

Commercial membranes for CO2 removal are polymer based, and the materials of choice are cellulose acetate, polyimides, polyamides, polysulfone, polycarbonates, and polyeth-erimide [12]. The most tested and used material is cellulose acetate, although polyimide has also some potential in certain CO2 removal applications. The properties of polyimides and other polymers can be modified to enhance the performance of the membrane. For instance, polyimide membranes were initially used for hydrogen recovery, but they were then modified for CO2 removal [13]. Cellulose acetate membranes were initially developed for reverse osmosis [14], and now they are the most popular CO2 removal membrane. To overcome state-of-the-art membranes for CO2 separation, new polymers, copolymers, block copolymers, blends and nanocomposites (mixed matrix membranes) have been developed [15-22]. However, many of them have failed during application because of different reasons (expensive materials, weak mechanical and chemical stability, etc.). 

Figure 15.1 A gas treatment skid for hydrogen recovery from the 1980 s containing cellulose acetate membranes as spiral wound modules. Image courtesy of W. R. Grace, Copyright (1988) W. R. Grace...

Gas permeation systems typically use hollow-fiber or spiral-wound membranes, although hollow-fiber systems are more common tBaker. 2004k Cellulose acetate membranes are used for carbon dioxide recovery, polysulfone coated with silicone rubber is used for hydrogen purification, and conposite membranes are used for air separation. The feed gas is forced into the membrane module under pressure. Retentate, which does not go through the membrane, will become concentrated in the less permeable gas. Retentate exits at a pressure that will be close to the input pressure. The more permeable species will be concentrated in permeate. Permeate, which has passed through the membrane, exits at low pressure. The operating cost for a gas permeator is the cost of conpression of the feed gas and the irreversible pressure difference that occurs for the gas that permeates the membrane. A typical hollow-fiber unit will contain 5000 m membrane area per m at a cost of approximately 200/m. ... 

The last section Applied Aspects of Membrane Gas Separation contains three chapters. Brunetti et al. start their contribution with a brief review of membrane materials and membranes used in gas separation and survey the main directions of industrial applications of gas separation (hydrogen recovery, air separation, etc.). In the second part of their chapter they present a new concept for comparison of membrane and other, more traditional, methods for gas separation. Their approach includes a consideration of engineering, economical, environmental and social indicators. Something similar had been written 15 years ago [2] but this analysis is now rather outdated. White (Chapter 15) focuses on a specific but very important problem in industrial gas separation membrane separation of natural gas. The main emphasis is on cellulose acetate based membranes that have the longest history of practical applications. This chapter also contains the results of field tests of these membranes and considers approaches how to reduce the size and cost of industrial membrane systems. The final chapter is an example of detailed engineering... 

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