Composition membrane for separating water from fluids containing

Details Composition membrane for separating water from fluids containing Composition membrane for separating water from fluids containing

1991-10-01

1994-08-02

Spear, Frank

Liquid purification or separation

Processes

Liquid/liquid solvent or colloidal extraction or diffusing...

21050042, B01D 6136

Patent

active

053343140

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a composite membrane for separating water from fluid mixtures containing organic components by means of pervaporation, a pervaporation process as well as the use of the composite membrane in pervaporation processes.
It is known that water can be separated from fluid mixtures containing organic components by various processes. One such conventional process employed especially for dehydration of fluids is the distillation method, by which a separation takes place corresponding to the volatility of the components. Distillation columns are necessary for this with auxiliary equipment, pumps, heat exchangers for heating and condensation, etc., which require a considerable capital investment. In addition, distillation methods require extensive instrumentation and control systems, as distillation columns can only be operated in a narrow utilization range.
When only a small amount of water is to be separated by distillation from a fluid mixture, in which water is the higher boiling point component, the entire remaining, non-aqueous portion must be evaporated and condensed at the head of the distillation column. Depending on the form of the distillation curve (liquid-vapor equilibrium) it may become necessary to multiply evaporate the entire non-aqueous portion to achieve the desired separation. The energy input required for this leads to considerable costs.
If the boiling point of the non-aqueous components of the mixture is at a higher temperature than the boiling point of water, then in principle only the water must is be distilled and condensed at the column head. The entire non-aqueous portion, however, must in any case be heated to its boiling point, which can lead to an undesired thermal loading and to decomposition of the organic components. The energy input in this case can also be considerable due to the high enthalpy of evaporation of water and the necessity of operating the distillation column with a certain amount of reflux.
Increasingly stringent environmental protection provisions make it necessary in both cases to separate the purest possible water, so that it can be discarded without further treatment, i.e. can be diverted into naturally occurring waters. This needed purity of the separated water in many cases requires disproportionatly higher costs for equipment, instrumentation and control means and energy in distillation methods, to remove the remaining small amounts of high or low boiling point components from the separated water.
When the mixture to be separated contains organic components with both a higher and a lower boiling point than water, the removal of water through simple distillation is no longer possible. Moreover, a multi-stage repetitive distillation is necessary, combined with an increased investment and use of energy.
Many mixtures of organic liquids with water in certain compositions have azeotropic points, at which the liquid has the same composition as the vapor in equilibrium with it. Such mixtures cannot be separated by normal distillation, but only through complicated processes. Frequently, an additional substance is added to break down the azeotropy. This additional substance must subsequently be completely removed and recovered from both product streams.
Similar difficulties as in distillation also arise in the removal of water by adsorption or absorption from organic components. The amount of adsorption agents increases strongly with increasing amounts of water to be removed and with decreasing final concentration of water in the product. In addition, the difficulties in regeneration of the adsorption agent increase.
The pervaporation method is a method for dehydration of fluid mixtures containing organic components, which substantially avoids the above-mentioned draw-backs. According to this method, the mixture to be dehydrated is contacted with the side of a non-porous membrane, where this membrane has a particularly high permeability to water, while organic components are non-permeable or pass only to a very small degree. If the chemical poten

REFERENCES:
patent: 4802988 (1989-02-01), Bartels et al.
patent: 4915834 (1990-04-01), Bruschke
patent: 5019261 (1991-05-01), Stengaard
patent: 5039421 (1991-08-01), Linder et al.

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