Process Of Removing Oil From Mixtures Of Oil And Aqueous Media

Abstract

A device for separating water-immiscible oils from a mixture of said oils and an aqueous medium and a process for utilization of the device is described. The device comprises a flexible web and a frame used to support the web. The frame has retaining means attached to hold at least a portion of the edge of the web allowing the remaining portion of the web to form a receptacle for containing the separated oil. The process provides for the separation and removal of water-immiscible oil from a mixture of oil and an aqueous medium. The process is comprised of first, forming a receptacle with a fibrous web, and then placing the web in contact with an oil and water mixture. The web and the oil and water mixture define a separation system in which the work of adhesion for the system as a whole is greater than one-half to one times the value of the work of cohesion for the oil-water portion of said system and the contact angle formed by the oil in an oil-water mixture with a smooth surface of a fiber-forming polymer is less than 90.degree.. The oil is preferentially absorbed into the web until the web is substantially saturated. The receptacle formed by the web then becomes filled with oil as a result of the hydrostatic pressure imparted to the substantially saturated web.

Description

The present invention relates to a method for removal and separation of oil from water and a device useful for accomplishing said removal.

More particularly, this invention relates to the utilization of a receptacle formed by a fibrous web by means of a device to retain and support the web to accomplish such separation. The web is oleophilic in character and, therefore, can preferentially absorb oil to the exclusion of water. When the web is completely saturated, the hydrostatic pressure throughout the area of the saturated web is such that oil will appear on the inside surface of the web. The web in combination with the supporting frame, may be used to not only remove oil from an oil and water mixture but actually physically separate the oil by simply emptying the receptacle formed by the web.

For example, the removal of fats or fatty layers from soup or gravies may be readily accomplished by the teachings of this invention. The invention also has many obvious industrial uses, for example, removing oil slicks from water, as well as several others, which will be readily apparent to those skilled in the art.

The term "oil" as used herein is to be the generally construed as defined in Hackh's Chemical Dictionary, Third Edition, Blackiston Company, Inc., New York, Toronto 1953. The term "oil" as used herein, however, is not limited to the group of compounds which are liquid at room temperature. Oleophilic materials which are solid at room temperature but will become liquid at elevated temperatures which have the same general structure and properties, as described in Hackh's referred to above, are also meant to be included within the scope of the term "oil." The polymeric web at extremely elevated temperatures may decompose or be substantially weakened. Oils which are solid at such temperatures obviously cannot be separated by the device and process of this invention.

There have been numerous prior art attempts to separate oil from water. Some are effective, but not particularly efficient; and some are efficient but relatively expensive and cumbersome. For example, it has long been known that soups, gravies, or broths may be cooled, thus congealing a layer of fat on the surface of these liquids and the fat may then be physically removed. Other prior art, such as U.S. Pat. Nos. 3,146,192; 3,314,540; 3,259,245; 3,358,838; 3,265,616; 3,215,623; 3,219,910; and 3,214,368 are all concerned with the removal of fat or oil from an aqueous solution. The prior art attempts, however, involve a blotting concept, where the oleophilic surface is contacted with a sheet of the material and the material absorbs certain amounts of the oil present at the oil-material interface. To the best of applicant's knowledge, there has been no process described which provides for the separation and recovery of oils from an oil-water mixture as easily and efficiently as applicant's. Merely by contacting the mixture with applicant's receptacle, allowing the receptacle to fill and emptying it (either manually or mechanically) oil which is physically and chemically unchanged may be recovered.

The preferred device for carrying out the process of this invention is comprised of flexible fibrous web and a frame adapted to support the web. The frame has retaining means attached for the engagement of at least a portion of the web with the remainder of the web thereby forming a receptacle for the oil. In one embodiment illustrated in the accompanying drawings, the retaining means is a pivotally mounted member adapted to impinge upon the frame.

The preferred embodiment of this device provides a locking means designed to clamp the web between the frame and a pivotally mounted member which serves as a retaining means. It may also be desirable to support the interior and/or exterior of the receptacle by other members bridging the opposite sides of the receptacle. The embodiment illustrated by the drawings also illustrates a base with the bridging members radiating from it attached to the frame to provide a bottom support for the fiber-made receptacle. Of course, as the size of the receptacle is increased, the need for internal and possibly external support is also increased.

While, as illustrated by the drawings, the retaining member may be movable, it need not be. For example, the member may be comprised of multiple layers or laminates of paper or the like with open areas into which the fibrous web has been previously inserted. An alternative to the above is to provide paper or other similar mounting component with open areas and attach the web to the paper by means of an adherent such as adhesives or heat fusible thermoplastics. In the latter embodiment, the adherent provides the retaining means while in the former embodiment either the paper or an adherent may be used to form the retaining means.

In both of these configurations, the paper may define part of the receptacle. The frame may also be made of paper or other mounting component and a continuous sheet of the mounting component with open areas or apertures to which the web has been attached may be shaped from such continuous sheet of the component so that part of the component forms part of the reservoir while another part forms the frame.

A further embodiment involves the use of the web only to make the device of this invention. By forming a receptacle from the polymeric web and then fusing the edges of the web, a smooth solid thermoplastic frame essentially incapable of oil absorption is formed by the fused edges of the web with the fusion itself providing the frame and retaining means.

The fiber-forming materials which are effective as fibrous webs in carrying out the process of this invention are those which are preferentially wetted by the oil with an oil-water mixture to the extent that water will be rejected from the internal voids of the web while the oil will still be retained. While not all fiber-forming materials are useful for this purpose, it has been observed that a large variety of fiber-forming materials will function within the scope of this disclosure. These materials may be defined broadly as those materials (normally polymeric) which when immersed in an oil-water mixture, allow the oil to displace water from a smooth surface thereof to form a contact angle with said surface of less than 90.degree.. Generally the effectiveness of the fiber-forming material has an inverse relationship to the size of the above-described contact angle. Polypropylene and polyethylene surfaces are two materials which are preferred because they allow the oil to assume the contact angle of substantially 0.degree.. Surface energy parameters for the components of the particular system (the system being defined as the combination of water, oil and the fiber) are known or determinable by methods well known in the art. The following criteria are employed to determine whether a particular fibrous material will function within the scope of the invention.

The work of adhesion (W.sub.a) of an oil/solid (i.e. fiber) interface is first calculated. Then, the work of cohesion (W.sub.c) of the oil/water interface is calculated. The following mathematical relationships may be applied to determine the usefulness of the particular fiber-forming material in practicing the invention:

1. If: W.sub. a -W.sub.c is 0 then, substantially unlimited wetting of oil in a smooth film surface of the fiber-forming material occurs in the presence of water.

2. If: W.sub. a - W.sub.c is 0 then, in a substantially uniform capillary of the fiber-forming material, oil will disrupt the water/solid, i.e. fiber interface, wet the capillary surface and cause rejection of the water. In other words, whenever W.sub.a is greater than 1/2 to 1 times the value of W.sub.c in the system under consideration, the fibrous material is considered to be useful in the practice of this invention. It must be borne in mind, however, that in selecting the fibrous web of this invention, the materials selected must not melt at the highest temperature anticipated in the oil-water mixture during the removal operation. Polymeric fibers found to provide adequate results in falling within the criteria defined above include polyolefin fibers, such as polypropylene, polyethylene and copolymers thereof, poly 4-methylpentene, arylene and styrene polymers, as well as polyesters, polyamides and polycarbonates.

The work of adhesion (W.sub.a) may be characterized as the interfacial tension between water and the oil in question plus the interfacial tension between water and the solid fiber-forming material minus the interfacial tension between the oil and the solid fiber-forming material. The work of cohesion may be characterized as twice the interfacial tension between the oil and water. These interfacial tension values may be computed from a knowledge of the contributing factors apparent to those skilled in the art of physical chemistry, of dispersion forces of polar interactions to the surface energies of the components of the system, see, e.g. Contact Angle Wettability and Adhesion, Advances in Chemistry Series, Chapter 6, p. 99 ff, American Chemical Society, Washington, D.C., 1964. Thus, fiber-forming materials useful in practicing the invention may be defined as those interacting within an oil-water system to satisfy the relationships mentioned earlier. The preferred relationship is that defined by W.sub.a -W.sub.c is 0. This relationship defines materials which are substantially totally hydrophobic in which, when employed in practicing the invention reject water vigorously from web voids and retain oil. Examples of fibrous materials satisfying this relationship include polypropylene, polyethylene, polytrifluorochloroethylene, and polytetrafluoroethylene. The other formula, i.e. W.sub. a -W.sub.c is 0 includes both the preferred materials exemplified above and other less preferred materials, i.e. those exhibiting lower levels of hydrophobicity. These materials which satisfy the less stringent relationship only may have to be prewet with oil in order to function according to the process of this invention. Prewetting may be accomplished by soaking in oil immediately prior to setting up the system. If the oil is in the form of a discrete layer on top of the water, then this wetting may be accomplished by placing the device initially only in the oil layer. There is a possibility that some water may also be found within the web voids with the less preferred materials, if these materials are not prewet with oil.

Webs may be formed employing one of several processes well known in the art. Particularly useful webs may be formed according to the teachings of U.S. Pat. Nos. 2,571,457 and 3,231,639. It is to be understood that within the scope of this invention fiber diameters and web densities may be varied over a considerably wide range depending upon the particular oil-separating operation involved. For most operations, webs including fibers ranging in diameter from 0.1 microns to 250 microns have proved effective; acceptable web density, expressed as a percent of fiber density, ranges from about 2 to 65 and preferably 4 to 35. It will be apparent to those skilled in the art that at any given fiber diameter the density of the web will affect the rate of oil uptake for any given mixture. However, a balance is generally struck between the optimal density for oil passage and web strength required for efficient use in the particular system. For example, if the device is designed to be used to separate oil in a deep vessel it may be necessary to use a web having high fiber density and/or a device which will not allow the web to "ride" at great depths in the mixture.

Generally for degreasing liquid foods, webs are employed comprised of fibers having diameters ranging from 0.1 microns to approximately 100 microns; web density, expressed as percentage of fiber density may range from 2 to 35 percent. Preferably in this type of application 90 percent of the fiber comprising the web are within the diameter ranging from between 1 to about 11 microns and the preferred density, expressed as the percentage of fiber density, ranges between about 4 to about 10. While, of course, the specific character of the web will vary with the particular use, it has been generally found that parameters above discussed are preferred for most food usages.

The process of this invention is comprised of forming a receptacle with a fibrous web thereby establishing a separation system comprising the fibrous web and a water-immiscible oil in an aqueous medium. The separation system is defined as one in which the work of adhesion for the system as a whole is greater than 1/2 to 1 times the value of the work of cohesion for the oil-water portion of the system. The system is further defined as one in which the contact angle formed by the oil in the presence and a smooth surface of the fiber-forming material is less than 90.degree.. After the system has been formed, the web is substantially saturated with oil by absorption. After, substantial saturation has taken place, the oil is forced into the receptacle defined by the web by hydrostatic pressure.

It is preferable for esthetic reasons that the dry device of this invention float on the surface of the oil and water mixture. As the oil is absorbed in the web, the device becomes heavier and slowly sinks. After complete absorption, it is preferred that the receptacle portion of the device above the area of the web be the only part above the surface of the liquid. In general, the lower the device "rides" in the mixture the more hydrostatic pressure is generated upon the web as a whole and the quicker will be the flow of oil into the receptacle defined by the web. Removal of oil from the receptacle is quite easy to accomplish. Depending upon the size of the receptacle it may be manually lifted and poured or it may be pumped out by any conventional pumping means.

For removing oil slicks from fairly large bodies of water or for other applications involving large surface areas larger webs may be used. With larger devices, however, better support for the receptacle should be provided. Support for the external as well as the internal portion of the web may be preferred when for example the device is used on open water, such as a lake or pond. The process for removal of oil can be made continuous by using a vacuum pump attached to one or a group of receptacles. The pump may remove the oil to a central reservoir and also serves to increase the rate of flow of the oil to the receptacle by building negative pressure. While the vacuum pump will function if the oil inlet is placed in the oil it may be desired to provide a sealed cover for the receptacle with an opening only for the oil inlet portion of the pump. The covering provides for an even more greatly increased rate of flow of oil because the vacuum pressure is present to help draw the oil into the receptacle initially. The pump aids in increasing the rate before any oil is present in the receptacle. With vacuum pressure applied, the receptacle will generally start to fill without complete saturation of the web.

An example of the device is found in the drawings,

FIGS. 1 and 3 are isometric views showing the fibrous web retained between the frame 7 and the second member 6.

FIGS. 2 and 4 are cross-sectional views of the device with the latter view illustrating the position of the device in an oil-water mixture after substantial oil absorption by the web has taken place.

FIG. 3 is an isometric view of the device in an open position prior to the insertion of the web 10.

To prepare the device for use the web 10 is disposed about the base 12 and the bridging member 8 attached to the frame 6. The retaining member 7 is then positioned to retain the web by rotating it about pivot 14. The releasable locking means 4 is then inserted through the opening 16 in the frame 6 with the lip 5 resting upon the ledge 15 of opening 16. The web is now firmly retained and the device is ready for use as illustrated in FIGS. 1 and 2. The device is then placed in an oil-water mixture as in FIG. 4 by means of the handle 2 and the web either prewet with oil or not depending upon the fiber, and the separation process is started.

EXAMPLE 1

250 g. of mineral oil was mixed with approximately 1,500 ml. of water at room temperature in a cylindrical glass vessel having a depth of 10.0 cm. and a diameter of 19.0 cm. The oil had a viscosity of 15.67/18.14 centistokes at 100.degree. F. A web of polypropylene microfibers having a density expressed as a percentage of fiber density of 9 percent and having 90 percent of the fibers with a diameter between 1 and 11 microns was used. The web measured 10.16 by 10.16 cm. and weighed 1.35 g. and was securely anchored in a device illustrated by the drawings. The fibers, when in the device, formed a receptacle of 7.62 cm. in diameter and 3.81 cm. in depth. The receptacle was then lowered into the oil and water mixture and it floated on the surface of the mixture. The oil passed through the fibers to the inside of the receptacle to the exclusion of the water. After approximately 15 minutes, most of the oil appeared to have been removed from the mixture. The mass of oil collected and removed was found to be 238 g. and the microfiber web contained 10 g. of oil. The total mass of oil removed from the mixture, therefore, was 248 g. or 99.2 percent of the oil originally present.

EXAMPLE 2

200 g. of rendered beef kidney fat was mixed with approximately 3,000 ml. of water at 190.degree. F. in a 4,000 ml. metal beaker 15.2 cm. diameter and 20.3 cm. in depth. The mixture was held at a temperature between 190.degree. and 200.degree. F. A web of polypropylene microfibers measuring 10.16 by 10.16 cm. and weighing 1.3 g. was securely fastened around the device described in example 1. The microfibers had a density expressed as a percent of fiber density of 6.8 percent and 90 percent of the fibers had a diameter of between 1 and 5 microns. The device was then floated in the fat and water and the mixture and the beef fat passed through the fibers to the inside of the receptacle to the exclusion of the water. The device was emptied periodically when the oil level was 1.27 to 1.905 cm. from the top of the vessel. After 45 minutes, most of the oil appeared to have been removed from the mixture. The mass of fat collected was 186 g. and the web contained 12 g. of fat. Thus, 198 g. or 99 percent of the fat was removed from the mixture.

EXAMPLE 3

The web of example 1 was employed with the ingredients of example 2. The same procedure was followed and the amount of fat collected was measured after 10 minutes. 195 g. of fat were separated which amounted to 97.5 percent of the fat originally available.

EXAMPLE 4

200 g. of white mineral oil (viscosity of 15.67/18.14 centistokes at 100.degree. F.) and 100 g. of water were mixed with a high shear mixer until a homogeneous suspension was achieved. This suspension was poured into the device used in the preceding examples having a depth of 6.35 cm. and a diameter of 7.62 cm. The fiber used was polypropylene microfiber, having an area of 20.3 by 15.2 cm. and weighing 5.2 g. 291 g. of the suspension was put into the device, i.e., 97 g. of water and 195 g. of mineral oil. Only the oil passed through the fibers. The oil was collected in a metal beaker. The amount of oil collected in a period of 10 minutes was found to be 189.8 g. or 97.8 of the oil initially present.

EXAMPLES 5-10

These examples were designated to illustrate a variety of other fibers that which may be used to practice the teachings of this invention. One of the materials, nylon, is a member of the class of fibers which must be preset with oil prior to use. In this instance, the web was placed in the oil layer of the mixtures and the layer itself preset the fibers. Some of the fibers which require prewetting with oil prior to use may be preferred for certain applications where specific properties, e.g., flexibility, heat resistance, shear strength, etc. are particularly useful; and, as indicated in the table below, these fibers still remove extremely great amounts of oil especially when compared to other separation means currently available. In all of the examples 1,500 ml. of water and 200 g. of oil were added to a cylindrical glass vessel having a depth of 10.0 cm. and a diameter of 19.0 cm. The device was then placed in the mixtures as in the earlier examples with each of the fiber samples used in examples 5 to 10 with the results as indicated in the table below: ##SPC1##

EXAMPLE 11

This example illustrates the use of the device of this invention to solve a problem common to the serving and preparation of many foods which contain within them solid oleophilic materials. When these foods are cooked, some of these materials contained within the food melt and enter the surrounding liquid medium, e.g. soup, sauce or gravy, reducing the flavor and esthetic appeal of the medium.

To illustrate the removal of oil from such a product, the device of this invention as illustrated in the drawings was used to remove liquefied oleophilic materials during the preparation of barbequed hamburger. A polypropylene microfiber web 10.16 by 10.16 cm. and weighing 1.2 g. was used in the device. 90 percent of the fibers had diameters between 1 and 10 microns and a density expressed as percent of fiber density of 8.1 percent.

The sample was prepared in the following manner. Part of a portion of ground beef was set aside for subsequent fat extraction and the remainder was combined with the following ingredients to produce a typical barbequed hamburger recipe:

Ingredient Amount Ground beef 810 g. v-8 vegetable juice 610.4 g. Chopped onions 35 ml. Spices 15 ml.

(V-8 is a trademark of Campbell Soup Co. and, according to the label, contains vegetable juices, salt, monosodium glutamate, vitamin C and flavoring. Therefore, essentially all of the oleophilic material present in the recipe mixture is from the ground beef).

The ingredients were placed in a 2-liter sauce pan and brought rapidly to a boil. After heating for 15 minutes, the device was placed in the mixture while boiling was maintained. As the reservoir formed by the web was filled with oleophilic material it was emptied and the material was collected. At periodic intervals the oleophilic material was weighed to determine the relationship between the process time and the amount of oleophilic material removed. The table below indicates the results of such determinations. ---------------------------------------------------------------------------

Process Time Period in G. Fat Removed Within Time Minutes Period __________________________________________________________________________ 0-5 24 5-9 21.4 9-15 22.6 15-25 20.9 25-40 18.4 40-55 12.3 55-60 4.6 __________________________________________________________________________

As is apparent from the table, removal takes place at a more rapid rate in the early stages of the process than at the latter stages. As a matter of fact, including oleophilic material present in the web, over 60 percent of the material removed by the process is removed after 15 minutes and over 70 percent is removed after 25 minutes process time. Fat removal from gravies, soups and other totally liquid foods will follow essentially the same pattern of accelerated rate of removal at the beginning of the process with decreasing rates of removal as the total amount of fat removal approaches 100 percent. At the end of 60 minutes, the device was removed and the web was taken out of the device and weighed to determine the amount of oleophilic material contained therein. The web was found to contain 17 g. making the total amount of oleophilic material removed 141.2 g.

The ground beef not used in the recipe was weighed and then placed in a soxhlet extraction apparatus. The oleophilic material was subjected to extraction with petroleum ether by refluxing for 15 hours. The meat was then removed from the apparatus, reground and subjected to extraction for another hour. The meat was found to contain 22.2 percent oleophilic material. The meat in the recipe, therefore, contained 178 g. of oleophilic material and the process removed a total of 79.5 percent.

While the percentage of removal seems relatively low when compared with the percentage of removal found in the preceding examples, it should be noted that some of the oleophilic material present in the ground beef is either physically or chemically bound to the beef and will not be leached out into the sauce. However, substantially all of the oleophilic material present in the sample to be extracted will be removed by the vigorous extraction procedure. This means that the actual amount of oleophilic material in the liquid phase, i.e. the sauce fraction of the recipe and, indeed, visual observation indicated that substantially all of the oleophilic material present in the sauce was removed.

The preceding examples are illustrative and not definitive of the scope of this invention. A wide variety of alternatives will readily suggest themselves to those skilled in the art as a result of the teachings embodied within this disclosure.

Claims

I claim:

1. A process for separating water-immiscible oils from a mixture of said oils and an aqueous medium, said process comprising:

a. providing a receptacle comprising a fibrous web formed from an oleophilic polymeric material which is hydrophobic in the presence of oil, the fibers being of such diameter and density and the web being of such mesh as to allow oil to pass through said web without allowing water to pass therethrough,

b. contacting said mixture with said web by partially immersing said receptacle in said mixture, while leaving some appreciable area of said web exposed to the atmosphere,

c. substantially saturating the immersed portion of said web with oil, and

d. maintaining said receptacle in contact with said mixture of a time sufficient to permit the hydrostatic pressure to cause the oil to pass through said web and thereby at least partially fill said receptacle.

2. A process in accordance with claim 1, wherein said receptacle is removed from said mixture after being filled with the desired amount of oil.

3. A process in accordance with claim 2, wherein said web is constructed from polyolefin fibers.

4. A process in accordance with claim 1, wherein said web is constructed from polymeric materials selected from the group consisting from polyolefin, polyarylene, polystyrene, polyester, polyamide, polycarbonate, polytrifluorochloroethylene, polytetrafluoroethylene, and poly(4-methylpentene) fibers.

5. A process for separating water-immiscible oils from a mixture of said oils and an aqueous medium, said process comprising:

a. providing a cup-shaped receptacle comprising a fibrous web formed from an oleophilic polymeric material which is hydrophobic in the presence of oil, the fibers being of such diameter in density and the web being of such mesh as to allow oil to pass through said web without allowing water to pass therethrough,

b. contacting said mixture with said web by partially immersing said receptacle in said mixture,

c. substantially saturating the immersed portion of said web with oil, and

d. maintaining said receptacle in contact with said mixture for a time sufficient to permit the hydrostatic pressure to cause the oil to pass through said web and thereby at least partially fill said receptacle.

6. A process in accordance with claim 5, wherein said web is constructed from polymeric materials selected from the group consisting of polyolefin, polyarylene, polystyrene, polyester, polyamide, polycarbonate, polytrifluorochloroethylene, polytetrafluoroethylene, and poly(4-methylpentene) fibers.

7. A process in accordance with claim 6, wherein said web is constructed from polyolefin fibers.

8. A process in accordance with claim 5, wherein said web comprises polyolefin fibers having diameters in the range of about 0.1 to about 250 microns, the density of said web, expressed as percentage of fiber density, being in the range of about 2 to about 65 percent.