Oxygen-selective membranes

In contrast to past environmental problems associated with fluorocarbon refrigerants, the exceptional properties of fluorine in polymers have great environmental value. Some fluoropolymers are enabling green technologies such as hydrogen fuel cells for automobiles and oxygen-selective membranes for cleaner diesel combustion. 

The packed bed ceramic membrane reactor configuration (PBMR) has been chosen as the reactor set-up (see Section 14.2.2). In the PBMR configuration three possible sub-configurations can be envisioned for a specific sweep gas in combination with a hydrogen or oxygen selective membrane for the dehydrogenation of ethylbenzene. These sub-configurations are shown in Fig. 14.10. 

A large part of the cost of a syngas production plant based on partial oxidation is for the air separation unit. Continuous research efforts are going on for reducing the cost of this step. One possibility is to use oxygen-selective membranes integrated in a partial oxidation reactor, as illustrated in Fig. 13. Air is introduced... 

Techno-economic evaluations [12] have shown that oxygen selective membranes are required that can deliver oxygen at a rate of over 10 ml/cm min. This value will be used as a base case for all our considerations. 

Oxygen permeates through the oxygen-selective membrane into the reaction mixture. By oxidative dehydrogenation, the oxygen burns the hydrogen that is formed (C). 

In the packed bed the catalyst is in a fixed configuration and in contact with a hydrogen permselective membrane. The most used packed bed configuration is the tubular one where the catalyst may be packed either inside the membrane tube or in the shell side, while the permeation stream is collected on the other side of the membrane (in case of hydrogen selective membranes) or one reactant is fed at the other side of the membrane (in case of oxygen selective membrane). 

Fig. 27. Syngas production in an oxygen-selective membrane reactor. Courtesy Air Products..

Oxygen permselective membranes. Oxygen selective membranes are used to supply the oxygen along the height of the reformer for the oxidative reforming reaction. 

The permeation and selectivity of different commercial hydrogen and oxygen selective membranes as well as membranes developed by the students should (if possible) be determined using permeation cells and the rate of permeation equations will be developed. 

The main challenges for the exploitation of the oxygen-selective membranes for membrane reactors remain in the possibility to produce stable membranes under reactive conditions with high flux and high stability. 

Another interesting application of oxygen-selective membrane reactors is proposed by Zhang et al, who used this kind of membrane reactors to convert via partial oxidation the methane in coke oven gas (COG) to syngas [67]. 

Oxygen-selective membranes integrated with oxy-fuel combustion. 

There is a strong industrial interest in a process such as POM using oxygen selective membranes, since this would avoid the use of expensive cryogenic units for the separation of oxygen from air. In addition, the operation temperatures required... 

---