WO2000072948A1

WO2000072948A1 - Oil dehydrator

Info

Publication number: WO2000072948A1
Application number: PCT/US2000/014640
Authority: WO
Inventors: Michael R. Spearman; John H. Burban; Mathews Thundyil; Majid Zia
Original assignee: Porous Media Corporation
Priority date: 1999-05-27
Filing date: 2000-05-26
Publication date: 2000-12-07
Also published as: AU5298400A

Abstract

A method and apparatus for the removal of free, emulsified, or dissolved water from liquids of low volatility, such as oil, is shown. The liquid of low volatility is removed by contacting the fluid stream (40) of concern with one side of a semi-permeable membrane (18). The membrane (18) divides a separation chamber (42) into a feed side into which the stream of liquid (40) is fed, and a permeate side from which the water is removed. The permeate side is maintained at a low partial pressure of water through presence of vacuum, or by use of a sweep gas.

Description

TITLE OIL DEHYDRATOR

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to the lubrication and hydraulic industry, and particularly to an apparatus and a process used for the removal of free, emulsified, or dissolved water from oil, and more generally, from liquids of low volatility.

2. Discussion of the Related Art

Oil is used in lubrication and hydraulic systems. It is widely recognized that the presence of water has deleterious effects on the oil in such systems, the components in the systems, and the operation of the systems. It is well known that corrosion, oil oxidation, chemical wear and tear, reduced bearing fatigue life and loss of lubricity may result when water contamination enters a lubrication or hydraulic system. These deleterious effects can be directly attributed to water present in free, emulsified or dissolved form.

As a result, significant efforts have been made to remove water from oil in order to provide optimal performance of lubrication and hydraulic systems. The devices and systems that have been used to remove water contamination include settling tanks or reservoirs, centrifuges, water absorbing filters, and vacuum dehydration oil purifiers. However, these have had significant limitations in either their water removal capabilities, ease of operation, capital costs, or operating costs, as will be discussed. Settling tanks remove bulk quantities of "free" water from oil based on the difference in their densities and gravitational settling. To be effective in removing "free" water, settling tanks require large residence times and a significant amount of floor space. However, they are ineffective in separating oil-water emulsions and are not capable of removing dissolved water.

Centrifuges accelerate the gravitational settling of water from oil by imposing centrifugal force on the fluid that, in effect, elevates the gravitational force.

Centrifuges are effective in removing free water from the oil. However, these centrifuges are generally expensive, and also have limited capability of separating oil-water emulsions. They cannot remove dissolved water from the oil.

Water absorbing filters utilize special filter media that absorbs water from the oil. As the water is absorbed, the media swells, the flow is restricted, and the pressure drop across the filter rises. When the pressure drop reaches a predetermined level, the water absorbing filter is removed, disposed of, and a new filter is installed. These water-absorbing filters are effective in removing free water but have marginal effect in removing emulsified or dissolved water from the oil. In addition, water-absorbing filters have a limited capacity and must be discarded once that capacity of water is absorbed. As a result, they are typically only used in applications where trace amounts of water are present. In applications where water concentrations are higher, the cost of continuously replacing water-absorbing filters becomes very high.

There have been several types of vacuum dehydration oil purifiers that have been used for water removal from oil. These generally operate under the principle of vacuum distillation, mass transfer of moisture from the oil to dry air, or a combination of the two.

In vacuum distillation, a vacuum is applied to reduce the boiling point of the water. For example, while the boiling point of water is 100°C(212°F) at 1013 mm H₂0 (29.92"Hg) barometric pressure (standard atmospheric pressure) , its boiling point at 100 mm H₂0 (approximately 26" Hg of vacuum) is only 50°C(122°F). By applying a sufficient vacuum relative to the temperature of the oil, the water in the oil will evaporate from the oil into the low-pressure air (vacuum), thus dehydrating the oil.

Flowing the oil into a contactor vessel which has a vacuum applied to it by means of a vacuum pump is the typical means by which this is achieved. In order to maximize the water vaporization rate in a given vessel, large surface area-to-volume ratios of oil are preferred. This can be accomplished by means of flowing the oil over structured packing, random packing, cascading plates, spinning discs, or other methods well known in the vacuum distillation and contactor fields. The oil usually enters at the top of the contactor and flows gravitationally downward over the packing, spreading into relatively thin films. The oil collects in the bottom of the vessel where it must be pumped out by means of an oil pump. Examples of these are U.S. Patent No. 4,604,109 by Koslow and U.S. Patent No. 5,133,880 by Lundquist, et al . Heat may be added to the oil in order to reduce the amount of vacuum needed. Vacuum is applied to lower the water boiling point, and also to increase the water removal rate. Heat may also be applied to increase the water removal rate. However, great care must be taken in not applying too much heat and/or vacuum because more and more of the lower molecular weight hydrocarbons in the oil will also be vaporized as the temperature and/or vacuum is increased to levels below their boiling points. It should be understood that any liquid with a boiling point less than water will also be removed. This may, or may not be desirable, depending upon the application.

Mass transfer-based systems use similar contactor vessels. However, rather than relying on distillation for removal of the water, dry air or gas is continuously passed countercurrently upwards across the oil that flows downward. Water molecules in the oil will move via a concentration gradient into the relatively drier air. The now humid air is drawn from the contactor by a vacuum pump or blower and exhausted to atmosphere. It is not necessary to heat the oil in excess of the boiling point of water in order for the water to vaporize. Therefore, less heat and/or vacuum can be used for water removal with a mass transfer-based system than in vacuum distillation systems.

While vacuum distillation and mass transfer systems do remove free, emulsified and dissolved water, they have several drawbacks that have prevented their widespread use. In both systems, liquid level controls are used within the vessel in order to ensure that the oil level does not become so low so that the oil pump runs dry. The liquid level controls also function to ensure that the oil level does not become so high that the vacuum vessel fills with oil. This would reduce or eliminate the water removal efficiency of the vessel and may even lead to the oil entirely filling the vessel and overflowing into the vacuum pump. Vacuum purifiers are also subject to foaming within the vessels as water is vaporized within the oil. This foam has a lower specific gravity than the oil, and can cause malfunctioning of the liquid level controls and a reduction in the performance of the purifier.

Due to the very nature of the use of heaters, controls, pumps, etc., purifiers are relatively complex pieces of equipment. In addition, the type of packing used, the viscosity of the oil, and the airflow rate, limit the flow rates through contactor vessels. This usually results in very large vessels being used relative to the amount of flow. When packaged with all of the necessary oil pumps, vacuum pumps, heaters, controls, electrical panels and connections, the system becomes quite large and expensive. With the number of components and complexity of these systems, the maintenance and operating costs are usually quite high as well.

Due to their ability to remove free, emulsified or dissolved water from oil, vacuum dehydration oil purifiers have become the desired method for water removal from oil. However, the drawbacks associated with vacuum oil purifiers have prohibited these purifiers from being widely used and/or are not practical on the majority of lubrication or hydraulic systems. As a result of their relatively large size and costs, they are limited to non- mobile, stationary applications, and are not practical for use on mobile equipment.

Due to their high capital cost, they are typically not permanently installed in a system unless it is a relatively large, expensive lubrication or hydraulic system. Instead, they are usually shared by several systems by using one to purify the oil on one machine or reservoir for a period of time, and then move it to another machine, etc. However, when the purifier is being used in this manner, the oil in the machines which are not connected to the purifier can become contaminated with water, and remain so until the purifier can be reattached to them and the oil dehydrated once again.

SUMMARY OF THE INVENTION The present invention provides a process for removing free, emulsified or dissolved water from oils or other liquids of low volatility. This process is such that it may be used on mobile equipment while in operation and moving, as well as on stationary equipment and processes. The operation of this process is simple, while the equipment in question is small and compact making it practical and cost effective for systems of all sizes.

Specifically, this invention relates to the process of using a membrane to selectively remove water from oils. More particularly, the process consists of removing water from the oil stream of concern by contacting the oil with one side ("feed side") of a semi-permeable membrane. The membrane divides a separation chamber into the feed side into which the oil is fed, and a permeate side from which the water is removed. The permeate side is maintained at a low partial pressure of water through presence of vacuum, or by use of a sweep gas. The water in the oil may be either in the dissolved form, or, as a separate phase, either emulsified, dispersed or "free". The membrane material is one that is of the appropriate chemical compatibility with the oil, while selectively permitting the transport of water across it.

Thus one of the objects of the present invention is to overcome the shortcomings of conventional oil dehydration techniques, and provide a new apparatus and a process for dehydrating oil that overcomes these limitations .

Another object of this invention is to provide an oil dehydrator which removes free, emulsified or dissolved water from oils.

A further object of the present invention is to provide an oil dehydrator which is simple to operate. A further object of the present invention is to provide an oil dehydrator which is relatively small and compact.

A further object of the present invention is to provide an oil dehydrator which is cost effective.

A further object of the present invention is to provide an oil dehydrator which is practical to use on small and large systems.

A further object of the present invention is to provide an oil dehydrator which may be used on mobile equipment while in operation and moving.

Further objects and advantages of the present invention will be apparent from the following description and appended claims, reference being made to the accompanying drawings forming a part of the specification, wherein like reference characters designate corresponding parts in the several views.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a membrane construction used in the present invention.

Fig. 2 is a perspective view of a modification of a membrane useful for the present invention.

Fig. 3 is a perspective view of a further modification of a membrane useful for the present invention. Fig. 4A is a plan view of a plurality of hollow fiber membranes, as shown in Fig. 3, woven into a mat.

Fig. 4B is a cross sectional view, taken in the direction of the arrows, along the section line B-B of Fig. 4A.

Fig. 4C is a schematic diagram of the mat shown in Fig. 4B after being spirally wound.

Fig. 4D is a perspective view of two hollow fiber semi-permeable membrane constructions, such as illustrated in Fig. 3, after being helically wound.

Fig. 5 is a schematic view of the construction shown in Fig. 1 after being spirally wound.

Fig. 6 is a schematic view of an exemplary membrane separation process embodying the present invention, wherein the water is removed by means of a vacuum pump.

Fig. 7 is a schematic view of a modification of separation process shown in Fig. 6, wherein the water is removed by means of a sweep gas stream.

Fig. 8 is a schematic of a further modification of the separation process shown in Fig. 6, wherein the membrane is protected from contaminants in the feed stream by means of an upstream filter.

Fig. 9 is an elevational view of a hollow fiber membrane device embodying the construction of the present invention, wherein the feed flows in the bore of the fibers.

Fig. 10 is an elevational view of a hollow fiber membrane device embodying the construction of the present invention, wherein the feed flows on the outside of the fibers.

Fig. 11 is an elevational view of a hollow fiber membrane device embodying the construction of the present invention, wherein the feed flows on the outside of the fibers and the water is removed countercurrent to the exiting oil. The oil is extracted by means of a perforated core.

Fig. 12 is an elevational view of a hollow fiber membrane device embodying the construction of the present invention, wherein the water is removed by means of a sweep gas.

Fig. 13 is a perspective view of a modification of the construction shown in Fig. 1 wherein the membrane has an integrally formed skin.

Fig. 14 is a fragmentary end elevational view of the construction shown in Fig. 13.

Fig. 15 is a perspective view of a modification of the construction shown in Fig. 3 wherein the membrane has an integrally formed skin.

Fig. 16 is a fragmentary end elevational view of the construction shown in Fig. 15.

DETAILED DESCRIPTION OF THE INVENTION It is to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following description, are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein should not be considered as limiting, unless the claims expressly state otherwise.

Before describing the preferred embodiment of the invention, incorporated herein as if fully rewritten are the Membrane Handbook, pages 3-15, published by Van

Nostrand Reinhold, 1992 and the Handbook of Industrial Membranes First Edi tion, pages 56-59, 1995. According to the present invention, there is an apparatus and a process with utility in the discriminating removal of water, or highly volatile solvents, from a broad class of liquids of low volatility. A liquid of low volatility is defined as a liquid with a normal boiling point greater than that of water (100°C) . Water may also be categorized as a liquid of high volatility.

More specifically, the process of dehydrating the oil consists of the following steps: contacting one side of a semi-permeable membrane with a liquid stream containing at least oil and water, wherein the membrane divides a separation chamber into a feed-side, into which the feed liquid mixture is fed, and a permeate side, from which the water is withdrawn; maintaining a partial chemical potential gradient for water such that the water preferentially permeates through the membrane from the feed side to the permeate side; removing, from the permeate side, the water that has permeated; and removing, from the feed side of the membrane the oil that is dehydrated. The term "chemical potential gradient" may also be referred to as an "activity gradient" or as a "partial potential gradient". The term "partial pressure gradient" implies the difference between the water vapor pressure on the permeate side and the equilibrium water vapor pressure corresponding to the water concentration in the oil.

The device for dehydrating the oil consists of a vessel containing at least a nonporous, semi-permeable membrane interposed in said vessel in such a fashion as to divide the interior of the vessel into at least one feed- side space and one permeate space; at least one inlet opening to the feed space; at least one outlet opening to the feed space; and at least one outlet opening to the permeate space. Such an apparatus would enable flowing the oil-water mixture in through the inlet opening, and contacting at least one side of the semi-permeable membrane; maintaining a chemical potential gradient for water such that the water preferentially permeates through the membrane from the feed side to the permeate side; removing, from the permeate side, the water that has permeated through the outlet opening; and removing from the feed side of the membrane, the oil that is dehydrated, through the outlet opening.

The membrane used is made, at least in part, of a thin, dense, nonporous, discriminating layer (the term "discriminating layer" may also be referred to as "skin") and a support structure. In an alternate embodiment, the discriminating layer may be self-supporting, however, this is not required to practice the invention.

The thin, dense, nonporous, discriminating layer may be a separate layer. It may also be formed at nominally the same time, and integrally with, the support structure. It may consist of the same material as the support structure, or a different material in a composite form. The dense, nonporous, discriminating layer may be formed as a separate step at a later time.

Porous membranes such as those used for micro- filtration, ultra-filtration, and dialysis are not suitable, as the low volatility fluid will permeate the pores and foul the membrane. Included as suitable membranes are dense, nonporous polymer films or asymmetric membranes with relatively dense discriminating layers, or skins, on one, or both, surfaces of a support structure. The support structure may be porous or nonporous . The dense nonporous skin, and/or the support structure, may be polymeric in nature. The dense nonporous skin, and/or the support structure, may be oligomeric in nature. The dense nonporous skin, and/or the support structure, may also be elastomeric in nature. The dense nonporous skin, and/or support structure, may be an inorganic or organic polymer. The dense nonporous skin, and/or support structure may be a ceramic. The polymer may be a linear polymer, a branched polymer, a crosslinked polymer, a cyclolinear polymer, a ladder polymer, a cyclomatrix polymer, a copolymer, a terpolymer, a graft polymer, or a blend thereof.

The support structure and the nonporous skin may be made from any combination of materials listed above. For instance, the support structure may consist of a ceramic, while the skin may be a crosslinked polymer. Another example would be a skin composed of a certain blend of materials, and a support composed of the same or a different blend of materials.

The membrane can be in any form or shape as long as a surface suitable for separation is provided. Common examples of this include self-supported films, hollow fibers, composite sheets and composite hollow fibers. The hollow fiber membranes may be potted or otherwise disposed so that the fibers are nominally parallel to each other. The fibers of the composite hollow fiber membrane or the hollow fiber membrane may be helically wound or twisted. Alternatively, the fibers may also be woven into a mat. In the case of a membrane that is composed of flat sheets or mats of fibers, the sheets or mats may be spirally wound. Also, the sheets or mats may be separated by spacers.

The composite membrane has a dense layer that is attached to the support structure. These composite films, fibers, or sheets may be porous or nonporous. The sheets, preferably, are flat, though this is not required to practice the invention. These fibers, films or sheets may be potted on one or more sides to separate the feed from the permeate space. The discriminating layer in such a membrane may be identical to or different from the support structure that may be composed of porous organic or inorganic polymer, ceramic or glass. The preferred embodiment would be a composite sheet or composite hollow fiber with a thin, dense discriminating layer of polymer on one or both faces of the support. In the case of a symmetric or asymmetric membrane, the liquid may contact the membrane on either side, although the preferred embodiment would be the one that minimizes the boundary layer on the feed side. The dense nonporous layer, or skin, may also be an integral part of the membrane. The invention may also be practiced by forming the dense nonporous layer, or skin, as a component (A.K.A. composite part) of the membrane. The dense nonporous layer, or skin, may be formed at the same time, or at a different time than the support structure. The dense nonporous layer, or skin, and the support may consist of the same material or blend of materials. The skin and support may consist of different materials or blend of materials. This may be done by forming an asymmetric fiber with a skin, by coextruding an asymmetric fiber with a selective layer that is also asymmetric, or by other methods known to those skilled in the art.

The porous support structure may be wetted by the liquid of low volatility. Alternatively, the porous support structure may be treated so that the structure is wetted by the liquid of low volatility. However, this is not required to practice the invention. The invention may still be practiced when the porous support structure is not wetted with the liquid of low volatility.

Furthermore, the invention may still be practiced when the porous support structure is treated such that the structure is not wetted with the liquid of low volatility. Preferably, the porous support structure is of such a nature that the low volatility liquid does not wet the structure.

In the situation wherein the membrane consists of a dense, nonporous layer, or skin, on only one side, the presence of defects in the dense, nonporous layer may result in passage of the oil. If the oil permeates through the membrane it may evaporate at a slower rate than the water, or not at all, thus fouling the membrane and reducing dehydration rates. Consequently, the preferred embodiment would be one that has a defect free, dense, nonporous, discriminating layer, or skin, on one or both sides of the porous support structure. An advantage of having a defect free, dense, nonporous, discriminating layer on a second side is that the second non-porous layer will not allow the oil to permeate through the membrane. In the case of hollow fibers, the feed may contact the membrane in the bore of the fiber, or on the outside of the fiber, although the preferred embodiment would be the one where the liquid is fed on the outside to provide lower operating pressure drop.

The discriminating layer, or skin, may be composed of any family of polymers that is chemically compatible with the feed as long as the dense, nonporous layer does not permit the transport of the oil in substantial quantities. The dense, nonporous layer may be composed of polymers including, but not restricted to, polymers such as polyimides, polysulfones, polycarbonates, polyesters, polyamides, polyureas, poly (ether-amides) , amorphous Teflon, polyorganosilanes, and polyolefins.

The liquid may be contacted with the membrane in a countercurrent, co-current, crossflow or radial crossflow configuration. The flow may be such that either, none, or both streams (i.e., feed and permeate) are well mixed or unmixed. The feed stream is preferably well mixed.

The liquid stream containing the low volatility liquid (e.g. oil) and the water may be fed into the vessel to contact the dense nonporous layer of the membrane.

However, the operation of the invention is not limited to feeding the liquid into the vessel to contact the dense nonporous layer. The invention may also be practiced by feeding the liquid into the vessel to contact the membrane on the side without the dense nonporous layer or skin.

The water partial pressure on the permeate side may be reduced by the application of vacuum, or by the use of a sweep gas with a low water vapor partial pressure, such as carbon dioxide, argon, hydrogen, helium, nitrogen, methane, or preferably air. The permeate flow, including the sweep, is preferably in the countercurrent, crossflow or radial crossflow mode. The pressure of the permeate may be equal to or less than the pressure of the feed. Alternatively, the pressure of the permeate may be greater than the pressure of the feed. An example of when the pressure of the permeate is greater than the pressure of the feed would be when the permeate is removed by a sweep gas. The sweep gas may be comprised of dehydrated compressed air or nitrogen such that the pressure on the permeate side is greater than the pressure on the feed side of the vessel. Typically in this scenario, the activity of the high volatility liquid being removed from the feed is locally greater on the feed side than on the permeate side.

In connection with the membrane based oil dehydration invention, it is preferable to filter the incoming fluid. Filtration may be used to remove particulate matter or bulk water entrained in the stream. Any type of known techniques to filter a fluid are suitable. This can prevent the destruction of the discriminating layer by particulate matter entrained in this stream. In the preferred embodiment the membrane consists of a hollow fiber with a dense, defect-free, nonporous discriminating layer on one or both sides of the porous support structure. In the preferred embodiment, the feed side boundary layer is minimized. Also, in the preferred embodiment, the pressure drop across the feed side is minimized. The water may be withdrawn, from the permeate side, by means of a vacuum or a sweep. The sweep may be in the form of a gas or a liquid. Also, the sweep may have a lower activity for water than that of the low volatility liquid.

This device may be applied in situations where vacuum purifiers and other conventional dehydrators are used. This process or device may be used to treat oil in a "kidney-loop" system, where the oil dehydrator is connected to a reservoir which is part of a piece of equipment. The oil is withdrawn from the process reservoir, processed through the dehydrator, and then returned to the reservoir. The oil is withdrawn from the process reservoir, processed through the dehydrator, and then returned to the reservoir. The oil dehydrator may be operated continuously or intermittently while the main system is operating, or while it is at rest. This device may also be used "off-line" to treat the fluid in a reservoir. This reservoir is not connected to any piece of operating equipment and serves as a container for conditioning the fluid. In addition to conventional applications, this device may be used "in-line". Since the feed and permeate spaces are separated by a dense, nonporous barrier, it is possible to operate the device such that the feed and permeate are at different pressures. As a result, the device may be operated in such a way that the oil is at the pressure of the system in which it is used. Consequently, this opens the possibility of utilizing such a device and process "in-line", which is the preferred embodiment of this invention. The need for conventional off-line, or kidney-loop systems, is reduced, and may be eliminated. Being able to use the present invention inline and at system pressure allows it to be compact and lightweight and useful on virtually all hydraulic or lubrication equipment. In addition, it can be used on stationery or mobile equipment since additional power, pumps and controls are not required.

Referring now to the drawings, wherein like numerals refer to the same elements, Fig. 1 is a flat sheet embodiment 16 of a semi-permeable membrane 18. The membrane 18 includes the discriminating layer or skin, 22 and the support structure 24. The discriminating layer or skin 22 may be present on either, or both, sides of the support structure 24.

Referring to Figs. 13-14, a modification of the semi- permeable membrane 18 is shown wherein the discriminating layer or skin 22 is formed integrally with the support structure 24 by methods known in the membrane art. As before, the discriminating layer or skin 22 may be present on either, or both, sides of the support structure 24.

In Fig. 2, two flat sheet semi-permeable membranes 18 are separated by a plurality of feed channel spacers 34. The spacers 34 may be made or formed of a wide variety of materials well known in the art, including potting compounds. Each membrane 18 has skin 22 and support structure 24. Permeate collection spacer 25, which is constructed so as to prevent the feed and permeate streams from mixing, is interposed between membrane 18 and spacers 34. Membranes 18 are separated by feed channel spacers 34.

Depicted in Fig. 3 is a hollow fiber embodiment 20 of the semi-permeable membrane 18. In this embodiment, hollow fiber membrane 20 includes the discriminating layer or skin 22 and the support structure 24. The discriminating layer may be on the inside or outside of the fiber, or both sides of it.

Referring to Figs. 15-16, there is shown a modification of the hollow fiber membrane 20 wherein the discriminating layer or skin 22 is formed integrally with the support structure 24 by methods known in the membrane art. As before, the discriminating layer or skin 22 may be present on either, or both, sides of the support structure 24.

Shown in Fig. 4A is a plurality of the hollow fiber semi-permeable membranes 20 woven into a mat 30. In terms of weaving or web technology, the hollow fiber membranes 20 would typically constitute the weft of the mat 30. A plurality of fillers 28 are used to weave the hollow fiber membranes 20 into a mat. The fillers 28 are used in the traditional sense of weaving a mat or web. A cross sectional view along section line B-B of Fig. 4A is shown in Fig. 4B. The reference numerals used in Fig. 4B indicate the same elements as previously identified. Any weaving type process may be used to create hollow fiber mats, provided it doesn't damage the fibers .

In Fig. 4C mat 30 is shown spirally wound. Typically, a feed channel spacer 34, such as a potting compound 35, will have been applied proximate the ends of mat 30, and will fill the spaces between the hollow fibers 20, as will be discussed further below.

In Fig. 4D, two hollow fiber semi-permeable membranes 20 are helically wound to form a "rope" 32.

In Fig. 5, a flat sheet embodiment 16 of a semi- permeable membrane 18 is spirally wound utilizing known spiral-wound configurations and techniques which provide for a feed space and a permeate space in the spiral wound module. Prior to spirally winding the membrane 18, a feed channel spacer 34 was disposed on the discriminating layer 22. More than one flat sheet semi-permeable membrane 16 may be spirally wound at the same time. Typically, a plurality of flat sheet membranes 16 will be disposed horizontally to each other. The flat sheet membranes 16 may or may not be separated by spacers 34. The assembly of the horizontally disposed plurality of flat sheet membranes 16 is then spirally wound on to core 60 (if used) . Typically, the spiral would be wound tighter, and the feed channel spacer 34 would communicate with the permeate collection spacer 25. In Fig 6, the invention with a vacuum permeate mode is depicted. A water containing feed 40 is introduced to the feed side of a membrane separator vessel 42 so that the oil is efficiently contacted with the semi-permeable membrane 18. The feed 40 may optionally be heated before coming in contact with the membrane 18. The dehydrated low volatility liquid is removed from the vessel 42 in an effluent 44. The permeate 46 is withdrawn by means of a vacuum pump 48. Optionally, the feed 40 may flow parallel or perpendicular to the membrane 18 and the permeate 46 may also flow parallel or perpendicular to the membrane 18 or any combination thereof. Optionally, the vessel 42 may be heated. Clearly, the vessel 42 should be sized appropriately to the desired flow rate of the feed 40, the desired operating pressure drop, and the amount of water to be removed. The permeate 46 is illustrated in the crossflow configuration, but, the feed 40 and the permeate 46 may also flow in relation to each other in countercurrent flow, co-current flow, or radial cross flow.

The sweep gas mode is demonstrated in Figs. 7 and 8 where there is an inlet on the permeate side of semi- permeable membrane 18 for a sweep fluid 50. The feed stream can be filtered as shown in Fig. 8 by means of a filter 52.

In Figs. 9, 10, 11, and 12 there are shown modifications of the present invention wherein the membrane separator vessel contains multiple hollow fiber embodiments 20 of the semi-permeable membrane 18 in various configurations. In Figs. 9-12 the fluid on the bore side of the hollow fiber 20 is separated from the fluid on the shell side by means of a potting compound 34. In Fig. 11, the oil exits by means of a perforated core 60. The perforated core 60 is a conventional perforated core with a housing 62 having a perforated section 64 and an outlet 68. The perforated section includes a plurality of perforations 66. The outlet 68 is in communication with the effluent 44 of the vessel 42. The perforations may be any suitable size or configuration. The liquid of low volatility flows over the housing 62 and the perforated section 64. The low volatility liquid enters the housing 62 through the perforations 66. The low volatility liquid exits the perforated core 60 through the outlet 68.

In addition to lubricating oils, this device and process may also be used for dehydrating other fluids, such as vegetable or food grade oils, silicones, or other fluids of low volatility.

The terms and expressions that have been used in the foregoing specification are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof. It is recognized that the scope of the invention is defined and limited only by the claims that follow.

Claims

WHAT IS CLAIMED IS:

1. A device for the dehydration of liquid streams of low volatility comprising: a) a fluid-containing vessel; b) a nonporous, semi-permeable membrane interposed in said vessel dividing the interior of said vessel into at least one feed-side space and one permeate space; c) at least one inlet opening to the feed-side space; d) at least one outlet opening to the feed- side space; and e) at least one outlet opening to the permeate space.

2. A process for the dehydration of liquid streams of low volatility, comprising the following steps: a) contacting one side of a nonporous, semi- permeable membrane with a liquid stream containing at least water and a low volatility liquid, wherein the membrane divides a separation chamber into a feed- side, into which the liquid stream is fed, and a permeate side, from which the water is withdrawn; b) maintaining a partial pressure differential for water such that the water selectively permeates through the membrane from the feed side to the permeate side; c) removing the water that has permeated from the permeate side; and d) removing the dehydrated liquid from the feed side of the membrane.

3. A process as defined in claim 2, wherein the low volatility liquid is oil.

4. The process defined in claim 2, wherein the semi-permeable non-porous membrane is defect-free.

5. The process defined in claim 2, wherein the nonporous semi-permeable membrane has an integrally formed skin on at least one side of the support structure.

6. The process defined in claim 2, wherein the liquid of low volatility is defined as a liquid with a normal boiling point greater than that of water.

7. The process defined in claim 2, wherein water is present in the liquid of low volatility in the dissolved, dispersed or emulsified form, or as a separate phase.

8. The process defined in claim 2, wherein the semi-permeable membrane consists of a dense, nonporous, self supported layer.

9. The process defined in claim 2, wherein the semi-permeable membrane consists of one or more dense, nonporous layers on a porous or nonporous hollow fiber.

10. The process defined in claim 2, wherein the semi-permeable membrane consists of one or more, dense nonporous layers on a porous or nonporous flat sheet.

11. The process defined in claim 2, wherein the semi-permeable membrane includes a dense, nonporous layer as an integral part of a hollow fiber, the dense, nonporous layer being formed nominally at the same time as a support structure in the hollow fiber.

12. The process defined in claim 2, wherein the semi-permeable membrane includes a dense, nonporous layer as an integral part of a flat sheet, the dense, nonporous layer being formed nominally at the same time as a support structure in the flat sheet.

13. The process defined in claim 2, wherein the semi- permeable membrane includes a dense, nonporous layer as a composite part of a hollow fiber, the dense, nonporous layer being formed at a different time than a support structure in the hollow fiber.

14. The process defined in claim 2, wherein the semi-permeable membrane includes a dense, nonporous layer as a composite part of a flat sheet, the dense, nonporous layer being formed at a different time than a support structure in the flat sheet.

15. The process defined in claim 2, wherein the semi-permeable membrane includes a support structure in a hollow fiber, the hollow fiber having a dense, nonporous layer on one of the bore or outside faces.

16. The process defined in claim 2, wherein the semi-permeable membrane includes a support structure in a flat sheet, the flat sheet having a dense, nonporous layer on one of its sides.

17. The process defined in claim 2, wherein the semi-permeable membrane includes a support structure in a hollow fiber, the hollow fiber having a dense, nonporous layer on both of its bore and outside faces.

18. The process defined in claim 2, wherein the semi-permeable membrane includes a support structure in a flat sheet, the flat sheet having a dense, nonporous layer on both of its sides.

19. The process defined in claim 2, wherein the semi-permeable membrane consists of a dense, nonporous layer on a porous or nonporous hollow fiber, and the liquid of low volatility is fed on the side with the dense, nonporous layer.

20. The process defined in claim 2, wherein the semi-permeable membrane consists of a dense nonporous layer on a porous or nonporous flat sheet, and the liquid of low volatility is fed on the side without the dense, nonporous layer.

21. The process defined in claim 2, wherein the semi-permeable membrane consists of one or more dense, nonporous layers on a porous or nonporous hollow fiber, wherein the liquid of low volatility is fed on the outside of the fibers.

22. The process defined in claim 2, wherein the semi-permeable membrane consists of one or more dense, nonporous layers on a porous or nonporous hollow fiber, wherein the liquid of low volatility is fed on the inside of the fibers.

23. The process defined in claim 2, wherein the semi-permeable membrane consists of one or more dense nonporous layers on a porous or nonporous hollow fiber, wherein the fibers are helically wound.

24. The process defined in claim 2, wherein the semi-permeable membrane consists of one or more dense nonporous layers on a porous or nonporous flat sheet, wherein the flat sheets are spirally wound.

25. The process defined in claim 2, wherein the semi-permeable membrane consists of one or more dense nonporous layers on a porous or nonporous flat sheet, wherein spacers separate the flat sheets.

26. The process defined in claim 2, wherein the liquid stream is well mixed.

27. The process defined in claim 2, wherein the liquid stream is not well mixed.

28. The process defined in claim 2, wherein the process is in line in another system wherein at least a part of the entire flow of the liquid of low volatility is continually fed through the said process.

29. The process defined in claim 2, wherein the process operates as a "kidney loop" in another system wherein a fraction of the total flow of the liquid of low volatility is continually fed through the said process.

30. The process defined in claim 2, wherein the process operates offline in another system, and wherein the liquid of low volatility is fed through the said process from a storage device.

31. The process defined in claim 2, wherein the feed flows parallel to the surface of the semi-permeable membrane .

32. The process defined in claim 2, wherein the feed flows perpendicular to surface of the semi-permeable membrane .

33. The process defined in claim 29, wherein the flow on the permeate side is parallel to the surface of the semi-permeable membrane.

34. The process defined in claim 29, wherein the flow on the permeate side is perpendicular to the surface of the semi-permeable membrane.

35. The process defined in claim 30, wherein the flow on the permeate side is parallel to the surface of the semi-permeable membrane.

36. The process defined in claim 30, wherein the flow on the permeate side is perpendicular to the surface of the semi-permeable membrane.

37. The process defined in claim 2, wherein the semi-permeable membrane consists of one or more dense, nonporous layers on a porous or nonporous hollow fiber, and the feed flows parallel to the hollow fiber.

38. The process defined in claim 2, wherein the semi-permeable membrane consists of at least one dense, nonporous layer on a porous or nonporous hollow fiber, and the flow on the permeate side is parallel to the hollow fiber.

39. The process defined in claim 2, wherein the semi-permeable membrane consists of at least one dense, nonporous layer on a porous or nonporous hollow fiber, and the flow on the permeate side is perpendicular to the hollow fiber.

40. The process defined in claim 2, wherein the semi-permeable membrane consists of at least one dense nonporous layer on a porous or nonporous hollow fiber, and the feed flows perpendicular to the hollow fiber.

41. The process defined in claim 2, wherein the semi-permeable membrane consists of at least one dense nonporous layer on a porous or nonporous flat sheet, and the feed flows parallel to the flat sheet.

42. The process defined in claim 2, wherein the semi-permeable membrane consists of at least one dense nonporous layer on a porous or nonporous flat sheet and the flow on the permeate side is parallel to the flat sheet.

43. The process defined in claim 2, wherein the semi-permeable membrane consists of at least one dense nonporous layer on a porous or nonporous flat sheet, and the flow on the permeate side is perpendicular to the flat sheet.

44. The process defined in claim 2, wherein the semi-permeable membrane consists of at least one dense nonporous layer on a porous or nonporous flat sheet and the feed flows perpendicular to the flat sheet.

45. The process defined in claim 2, wherein the flows on the feed side and on the permeate side are countercurrent .

46. The process defined in claim 2, wherein the flows on the feed side and on the permeate side are co- current .

47. The process defined in claim 2, wherein the flows on the feed side and on the permeate side are crossflow.

48. The process defined in claim 2, wherein the flows on the feed side and on the permeate side are radial crossflow.

49. The process defined in claim 2, wherein the semi-permeable membrane includes a porous support structure, and the porous support structure is wetted by the liquid of low volatility.

50. The process defined in claim 2, wherein the semi-permeable membrane includes a porous support structure, and the porous support structure is treated so that it is wetted by the liquid of low volatility.

51. The process defined in claim 2, wherein the semi-permeable membrane includes a porous support structure, and the porous support structure is not wetted by the liquid of low volatility.

52. The process defined in claim 2, wherein the semi-permeable membrane includes a porous support structure, and the porous support structure is treated so that it is not wetted by the liquid of low volatility.

53. The process defined in claim 2, wherein the permeate side is at a pressure greater than that of the feed side.

54. The process defined in claim 2, wherein the permeate side is at the same pressure or lower than the feed side.

55. The process defined in claim 2, wherein there is a sweep of gas or liquid through the permeate side.

56. The process defined in claim 2, wherein there is a sweep of gas through the permeate side, and said sweep gas is selected from the group consisting of argon, methane, nitrogen, air, carbon dioxide, helium, or hydrogen or any mixture thereof.

57. The process defined in claim 2, wherein said there is a sweep of gas through the permeate side, and said sweep gas has a lower activity for water than that of the low volatility liquid.

58. The process defined in claim 2, wherein the semi-permeable membrane includes a dense nonporous layer, and said non-porous layer is polymeric in nature.

59. The process defined in claim 55, wherein the semi-permeable membrane includes a dense porous support, and the dense porous support is polymeric in nature.

60. The process defined in claim 2, wherein the semi-permeable membrane includes a dense nonporous layer, and the dense non-porous layer is oligomeric in nature.

61. The process defined in claim 55, wherein the semi-permeable membrane includes a dense porous support, and the dense porous support is oligomeric in nature.

62. The process defined in claim 2, wherein the semi-permeable membrane includes a dense nonporous layer, and the dense nonporous layer is elastomeric in nature.

63. The process defined in claim 55, wherein the semi-permeable membrane includes a dense porous support, and the dense porous support is elastomeric in nature.

64. The process defined in claim 2, wherein the semi-permeable membrane includes a porous support and the porous support is an inorganic polymer.

65. The process defined in claim 2, wherein the semi-permeable membrane includes a porous support, and the porous support is ceramic.

66. The process defined in claim 2, wherein the semi-permeable membrane includes a porous support, and the porous support is glass.

67. The process defined in claim 2, wherein the liquid of low volatility is filtered before it contacts the semi-permeable membrane.

68. The process defined in claim 2, wherein the semi-permeable membrane consists of a plurality of hollow fibers and the hollow fibers are woven in a mat.

69. The device defined in claim 1, wherein the fluid containing vessel is heated.

70. The process defined in claim 2, wherein the liquid stream is heated before contacting the membrane.

71. The process defined in claim 2, wherein the liquid of low volatility is intercepted in the droplet form, permeated as liquid, and removed as liquid.

72. The device defined in claim 1, wherein said nonporous, semi-permeable membrane has an integrally formed skin on at least one side of a support structure.

73. The process defined in claim 2, wherein said nonporous, semi-permeable membrane has an integrally formed skin on at least one side of a support structure.