Membrane differential operators

Harold M.R, Zaspalis V.T., Keizer K. and Burggraaf A.J., Intermediate product yield enhancement with a catalytic inorganic membrane—I. Analytical model for the case of isothermal and differential operation, Chem. Eng. ScL 48 2105 (1993). 

All the aforementioned SILMs were prepared using microflltration membranes and operated with low varying pressure differential (<2 bar). To avoid the pitfaU of liquid instability associated with microporous membranes, nanofiltration membranes were used in SILMs, which greatly reduce the instability problem only at the expense of increased gas transport resistance provided by the nanofiltration (NF) membranes [87]. Experimental stability tests demonstrated that the impregnated ILs did not discharge from the NF membrane structure even under a high transmembrane... 

Harold, M., Zaspalis, V., Keizer, K., etal (1993). Intermediate Product Yield Enhancement with a Catalytic Inorganic Membrane. 1. Analytical Model for the Case of Isothermal and Differential Operation, Chem. Eng. ScL, 48, pp. 2705-2725. 

The ability of living organisms to differentiate between the chemically similar sodium and potassium ions must depend upon some difference between these two ions in aqueous solution. Essentially, this difference is one of size of the hydrated ions, which in turn means a difference in the force of electrostatic (coulombic) attraction between the hydrated cation and a negatively-charged site in the cell membrane thus a site may be able to accept the smaller ion Na (aq) and reject the larger K (aq). This same mechanism of selectivity operates in other ion-selection processes, notably in ion-exchange resins. 

The porous electrodes in PEFCs are bonded to the surface of the ion-exchange membranes which are 0.12- to 0.25-mm thick by pressure and at a temperature usually between the glass-transition temperature and the thermal degradation temperature of the membrane. These conditions provide the necessary environment to produce an intimate contact between the electrocatalyst and the membrane surface. The early PEFCs contained Nafton membranes and about 4 mg/cm of Pt black in both the cathode and anode. Such electrode/membrane combinations, using the appropriate current coUectors and supporting stmcture in PEFCs and water electrolysis ceUs, are capable of operating at pressures up to 20.7 MPa (3000 psi), differential pressures up to 3.5 MPa (500 psi), and current densities of 2000 m A/cm. ... 

The driving force for the separation is differential pressure. CO2 tends to diffuse quickly through membranes and thus can be removed from the bulk gas stream. The low pressure side of the membrane that is rich in CO2 is normally operated at 10 to 20% of the feed pressure. 

Novel Processing Schemes Various separators have been proposed to separate the hydrogen-rich fuel in the reformate for cell use or to remove harmful species. At present, the separators are expensive, brittle, require large pressure differential, and are attacked by some hydrocarbons. There is a need to develop thinner, lower pressure drop, low cost membranes that can withstand separation from their support structure under changing thermal loads. Plasma reactors offer independence of reaction chemistry and optimum operating conditions that can be maintained over a wide range of feed rates and H2 composition. These processors have no catalyst and are compact. However, they are preliminary and have only been tested at a laboratory scale. 

For higher temperature operation, a polybenzimid-azole-based polymer electrolyte may be preferred. The PEMFC structures have good mechanical integrity under compression and expansion from differential temperature and pressure gradients that occur during operation. This system has minimal materials problems, except for the cost and operation characteristics of the membrane. The PEMFC operates at 1 A/cm at 0.7 V. The electrode reactions in acidic media have been discussed above. 

Both types of Bourdon gauge are most suitable for use with corrosive gases and both can be used most effectively as null-point instruments. Several types of mechanical gauge are available commercially which use electrical capacitance or induction to magnify the mechanical movement of a membrane. Such gauges are easily operated in a differential mode and can be used for measuring pressure differences down to ca. 10 Torr. 

In the membrane tlisiilluliim process, combined use of distillation and membranes is made. Salt water is warmed to produce vapor. This vapor passes through porous membranes, which are permeable to vapor but not to the liquid phase. The vapor is condensed on a cooled surface to produce fresh water. The main advantage of this process is jts simplicity and the need for only small temperature differentials to operate. 

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