Membrane reactors operation

It is evident, that in any membrane reactor operation mode there are important parameters which determine the performance of the process (Shah, Remmen and Chiang 1970). These are (1) the total and partial pressures on both sides of the membrane, (2) the total and partial pressure differences across the membrane, (3) the diffusion mechanism through the support and the membrane layer (membrane structure), (4) the thickness of the membrane, (5) the reactant configuration (i.e. whether the reactants are supplied from the same or from opposite sides of the membrane, in counter or co-current flow) and (6) the catalyst distribution. 

The utilization of enzyme membrane reactors with soluble, homogeneous enzymes has been reviewed on several occasions (Bommarius, 1992 Kragl, 1992). The principal advantages and disadvantages of an enzyme-membrane reactor operated as a CSTR are listed in Table 5.2. 

The present work will mainly focus on biochemical membrane reactors operate at the production scale and give an overview of systems of potential interest studied at the laboratory level. 

Figure 17.7 % Conversion at steady state ( ) and reactor capacity (o) as a function of cell loading in UF-membrane reactors operated at 50°C with substrate feed lOOmM Nicotinamide in buffered solution.

The unusual interaction of hydrogen with palladium-based membrane materials opens up the possibility of oxidative hydrogen pump for tritium recovery from breeder blankets. The feasibility for this potential commercial application hinges on the hot-fusion and cold-fusion technology under development [Saracco and Specchia, 1994]. At first, Yoshida et al. [1983] suggested membrane separation of this radioactive isotope of hydrogen followed by its oxidation to form water. Subsequently, Hsu and Bauxbaum [1986] and Drioli et al. [1990] successfully tested the concept of combining the separation and reaction steps into a membrane reactor operation. 

Introducing a significant quantity of the carrier (or sweep) gas to the permeate side of the membrane, however, has two major implications. One is that it may necessitate the need to separate the permeate from the carrier gas downstream of the membrane reactor operation if the permeate is a valuable product. The other is the cost associated with the sweep gas. If chemically compatible, air can be used as the least expensive sweep gas available. 

Despite the growing interest in S EM Rs during the past 25 years, there is at present no industrial application of these reactors, except in the case of potentiometric sensors. Examples of the application of membrane reactors operating under closed-circuit conditions are briefly described in the following sections, with special emphasis on the laboratory set-ups used for materials studies and on membrane reactors presently in the pre-commercial phase, such as SOFCs or oxygen generators. 

Fig. 17.4 Comparison of ethane conversion in conventional and membrane reactor operated with CO- and counter-current sweep...

Fig. 17.6 Hydrogen concentration gradients in membrane reactor operated in co- and counter-current sweep modes...

S. Battersby, M. C. Duke, S. Liu, V. Rudolph, J. C. Diniz da Costa, Metal doped sihca membrane reactor operational effects of reaction and permeation for the water gas shift reaction, J. Membr. Sci. 316 (2008) 46-52. 

M. E. Adrover, A. Anzola, S. Schbib, M. Pedemera, D. Borio, Effect of flow ctmfiguration on the behavior of a membrane reactor operating without sweep gas, Catal. Today 156 (2010) 223-228. 

As seen from Equ. 6.155, if Prf > Pcstr f then the productivity ratio jRp > 1. Thus, by suitable choice of operating conditions for Fp > Fg so that Fp is maximized while Prp > Pcstr is maintained, about 10 times greater ethanol productivity was experimentally found in the rotor fermenter from a CSTR, thus illustrating the advantage of membrane reactor operation. 

The pressure difference between the two membrane sides, namely the transmembrane pressure, determines the position of the gas-liquid interface along the membrane cross-section, since the phase-phase displacement will take place only in pores where the transmembrane pressure is greater than the breakthrough pressure. Therefore, in catalytic membrane reactors operating in contactor mode a strict control of the transmembrane pressure is very important. 

The overall effectiveness for a catalytic membrane reactor operating in the mode described in Fig. 4.3b can be defined as... 

In 1994, Serralheiro and coworkers deseribed the a-chymotrypsin catalyzed synthesis of A-acetyl-L-phenylalanine-L-leucinamide in a reverse micellar membrane reactor operated in a batch mode [65]. The reverse micelles were formulated with TTAB, heptane, and hexanol. An ultrafUtration ceramic membrane was used to retain the enzyme and separate the peptide. The reactor was operated for four days without any loss of enzyme activity and the yield of the produced dipeptide was around 80%. 

Figure 7-24. Schematic representation of a membrane reactor operating with dense ionic conducting membranes for syngas production (a) tubular reactor using a MIEC membrane (b) Electrochemical cell using a purely ion conducting membrane.

Battersby, S., Duke, M.C., Liu, S., Rudolph, V. and da Costa, J.C.D. (2008) Metal doped silica membrane reactor Operational effects of reaction and permeation for the water gas shift reaction. Journal of Membrane Science, 316,46-52. 

The catalytic membranes were successfully applied in the aerobic photooxidation of phenol, one of the main organic pollutants in wastewater, providing stable and recyclable photoeatalytic systems. The catalytic tests were carried out in a photoeatalytic membrane reactor operating with flow-through at different transmembrane pressures (TMP). 

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