CA1067416A - Ultrafiltration apparatus and process for treatment of liquids - Google Patents

Abstract

Abstract of the Disclosure An apparatus and process are provided for the concentration and separation of components contained in liquids. The apparatus is comprised of, in part, a module containing a plurality of axially aligned, hollow tubular members having a well defined porosity and a substantially uniform, continuous, adherent, porous coating of preformed, aggregated, inorganic metal oxide particles on their interior or exterior surface. The low molecular weight dissolved phases permeate the walls of the tubes while the larger diameter molecules are retained in the liquid. The apparatus can be operated for long periods of time with a high degree of concentration and separation of liquids. The apparatus is particularly suited for the concentration and separation of oil from mixtures of oil, water and detergents. It is also useful in textile, paper making and food industries.

Description

" ~ 0 6'~

This invention relates in general to an ultrafiltration apparatus and process ~or the treatment of liquids. In another aspect, this inven~ion is directed to an apparatus and a process for the concentration and`
separation of components contained in liquids. In a further aspect, this invention is directed to a process for the treatment of chemically stabilized emulsified oils and other liquids containing large diameter molecules.
In recent years a variety of processes have been disclosad in the literature relating to ultra-filtration techniques. A majority of work in the ultrafiltration area was developed at the Oak Ridge National Laboratories of the United States Atomic Energy Commission where extensive studies of ultra-filtration, or cross-flow filtration, as it is some-times called~ have been carried out. The work there was primarily concerned with high pressure (500-9SO psi) systems using porous tubular support structures of carbon or alumino~silicates or a microporous membrane on a perforated stainless steel sleeve.
The investigators at Oak Ridge found that for some aqueous systems, a bed of particles uniformly dispersed onto a porous substrate functions as an eficient filter medium which rejects the passage of particles and moleculPs whose size exceed the openings between adjacent particles ~9172 .
~ ~ 67 ~1 ~

in the porous bed. It was suggested that the partlcles deposited on the substrate surface may be of any material inert to the solutions in contact with the surface. A
variety of materials such as diatomaceou$ earth, perlite, asbestos flbers, cellulose fibers, dr~ed silica gel, and carbon have been used.
In other experiments at Oak R~dge it was shown that colloidal hydrous oxides may be used as permeation barriers for the hyperfiltration ln raverse osmosis treatment of solutions, thereby c~ntrating still lower molecular weight solutes in water, provided that the aqueous solution is pumped over the surface of the permeable membrane under high pressure (50-1000 psi).
In this case the colloids are fonmed from polyvalent metal salts by heating an aqueous solution of the salt until a turbid solution is obtained. To form the membrane, small concentrations of the turbid solution (greater than 10 ppm) are circulated over the support structure at moderate velocity and at pressure. This procedure resuits in the formation of a thin boundary layer (thickness up to O.05 millimeters) which serves as an interface between the waste solution and the porous substrate. (See, for example, U.S. Patents 3,413,219; 3 9 449,245; and 3,537,988).
It is indicated in U.S. Patent 3,413,21g at column 2, lines 43 et seq., that membranes formed from 1~674~6 the colloidal hydrous oxides will continue to have rejecting properties for a day or more, thou~h rejection gradually decreases. However, :Lt is indicated that the continued presence of an additivl~ in ~he solution will improve the rejection properties and repair defects which might occur in ~he membrane. In addition ta the necessity for the continued presence of an additive to maintain the desired properties, it has also been found that many of the prior art methods are useful only for the treatment of certain types of liquids. For example, prior to the present invention no completely satisfactory method was available for the treatment of liquids such as those containing chemically stabilized emulsified oils. Thus, while the pr~or art discloses a variety of ultrafiltration methods, to date no completely satisfactory method has been provided which avoids or minimizes many of the difficulties inherent with such processes.
Accordingly, one or more of the following objects will be achieved by the practice of this invention.
It is an object of this invention to provide an ultra-filtration apparatus which is useful for the separation and concentration of components contained in liquids.
Another object of this invention is to provide an ultra-filtration apparatus which is useful for the separation and concentration of waste liquids fr~m lndus-trial processes. A further object is to provide a novel, ~`: 9172 ~OG74~L6 e~onomical and continuous ultrafiltration process for the separation and concentration of llquids containing molecules o~ a relatively large diameter from those of a relatively small d~ameter. Another object is to provide a process for the separation of large, dissolved polymeric molecules, such as proteins from solutions. A further object of this invention is to provide an ultrafiltration apparatus which is useful for separating emulsified oil, dirt and various other suspended materials from solution~.
Another object is to provide a process for the concentra-tion and separation of components contained in textile mill liquids. A still further object is to provide a process for the separation and concentration of poly-vinyl alcohol from textile mill liquids. A still further object is to provide a process for the separation and concentration of materials employed in processing paper pulp. A further object is to provide a process for the separation of materials employed in electropaint primer operations.
Ano~her object of this invèntion i9 to provide a process for coating the surfaces of the tubular members contained in the ultrafiltration module. A
still further object is to provide a process for coating the inner surfaces of carbon tubes with a preformed metal oxide. Another object is to provide a process for coa~ing the inner surfaces of carbon tubes with zirconia.
A further object is to provide a process for coating the outer surface of carbon tubes with a preformed metal oxide.

Another object is to provlde a process for coating the outer surfaces of carbon tubes with zirconia.

A further ob~ect is ~o provide a process for seallng the tubular members in the ultrafiltration module. These and othar objects will readily become apparent to those skilled in the art in the light of the teachings herein set ~orth.
In its broad aspect, this i~vention ls directed to an ultrafiltration apparatus and a ~rocess for the treatment of liquids. The apparatus i.s comprised of, in combination:
(a~ at least one module having:
(i) at least one entranee port, (ii) at least one exit port, (iii) a permeate collection zone having at least one exit port (iv) a multiplicity of axially aligned hollow tubular members disposed in the zone in close proximity to one another, said members having a pore volume of at least about 0.08 cc/gm in the distributlon peak in the pore diameter range wherein the majority of the pores are from about 0.1 to about 2.0 microns in diameter, the members being supported and sealably mounted in the zone so that fluid entering the module must contact the members and any components o~ the fluid which permeat~ the walls of the members collect in the permeate zone, and 1067~16 (v) contained on one selected sur~ace o the members a substantially uniorm, continuous, adherent porous coating of preonned, aggregated metal oxide particles ha-ving an average mean size of less than about 5.0 microns, and a coating of from about 0.01 to about 10 . O
microns in`thickness without substantial --penetration into the members of more than about 5.0 micron.
(b) means for supplying a feed liquid to the module, (c) means for withdrawing a concentrated liquid from the module, and (d) means for withdrawing a permeate liquid from the permeate collection zone.
:

~ The objects of the invention and the preferred :~ - embodiments thereof will best be understood by reference to the accompanying drawings. Figure 1 illustrates one form of the ultrafiltration system of this invention.
Figures 2 shows a cut away view of the multi-tube ultra-filtration module. Figures 3-6 show methods for assembling the tubular ultrafiltration module.
Figure 7 is a drawing depicting a longikudinal, cross-sectional view of one of the hollow tubular members.
Figure 8 depicts an enlarged view of a portion of th~
cross-sectional view showing thepcrous substrate and metal oxide coating.

With reference to the drawings, the ul tra-filtration system of this invention as shown in Figure 1 ~i74~6 is comprised of the ultra~ltration module 10, a tank 12, pumps 14 and 16, and valve control means 18. The liquid to be concentrated and separated is pumped from tank 12 via conduits 20, 22, 24 and 26 into the ultrafiltratlon module 10. As shown in l:he cut-away view of Figure 2 module 10 is comprised of a pluraLity of closely packed tubes 32 which are held in place at each end by tube sheets 34 and 36. The tubes are positioned in the module in such a manner that li~uid entering the module via Fonduit 26 must pass through the tubes. The liquid and low molecular weight .!1 dissolved phases, i.e., small diameter molecules, permeate the walls of the tubes into chamber 38 and pass out via conduit 28. The high molecular weight dissolved phases, i.e., large diameter molecules, as well as any non-dissolved material pass out through conduit 30.
Figure 3 shows one means for positioning tubes 32 in the module shell 40. Tube sheet 42 has a plurality of openings 44 of sufficient diameter to receive the ends of the tubes. 0-rings 46 are then inserted over the ends of the tubes and plate 48 posi-tioned over the tube ends. Cap 50 is then affixed to the tube sheet 42 compressing the 0 rings to form a tight seal.
Figures 4, 5 and 6 show another method for positioning the tubes 32 in the module shell. The tube ~o67~l6 sheet 34 has openings through which the tubes 32 can be inserted. The outer sid~ of the tube sheet has openings of greater diamater than the tubes which pxovides a recess for gasket seal 52 whic]h can be composed o rubber or rubber-like material. The module shell 56 containing the tubes 32 and equipped with a permeate port 54 is shown in Figure 4 with a portion of its end 58 removed to view the interior.
Figure 7 illustrates a cross-seceional view taken longitudinally along the axis of one of the hollow tubular members 32. Feed liquid enters at location 60, passes through the tubular member 32 and exists at location 62. The low molecular weight dissolved phases permeate the walls 64 of the tubular member into permea-tion zone 66.

Figure 8 illustrates an enalrged cross-sectional view, approximately 2000 X, o a portion of the tubular member 32 taken, for example, at location 68. The tubular member 32, for example a carbon tube, is composed of bonded carbon particles 70 and has essentially continuous coating of aggregated metal oxide particles 72. The particles 72 only partially penetrate into pores 74 which pores are characteristic of the carbon tubes employed in this invention.
invention. The aggregated metal oxide particles typically penetrate to a depth M. of no more than about 5.0 ' ~o67~6 micron. ~he pores below about 0.05 micron ln diameter are essentially free of the rnetal oxide coatings. When in use a filter cake 76 composed of higher molecular we:Lght dissolved phases,i.e.,large diameter molecules or undissolved particles may form on the coated surface.

~- The module of the apparatus can be designed and assembled in such a manner that the metal oxide coating can be either on the inner hollow interior surface or on the outer surface of the tubular members. In either case~ the coating of metal oxide particles is on that surface of the tubular member which is in direct contact with the feed liqu;d. For example~ if the module is designed as shown in Figure 2 where the feed liquid enters through conduit 26 and leaves at eonduit 30, the metal oxide coating is on the hollow interior of the tubular members. If the coating is on the ou~er surface of the tubular members, then the feed liquid would enter through conduit 28, contact the outer surface of the tubular members and exit from module 10 through a conduit not shown in Figure 2. The permeate which passed through the walls of the tubular members could then be withdrawn through conduit 30.
- Of the two types of modules, the one shown in Figure

2 is preferred, because of enhanced hydrodynamic character-istics compared to the arrangement where~he feed liquid contacts the outer surface of the mPmbers. The feed fluid passes through the inner hollow portion of the tubular members and the permeate collects in the permea~e zone and can be withdrawn ~hrough conduit 28.

~0674~6 As hereinbe~ore indicated the apparatus o this invention is ideally suited for operation over extended periods of time with a high degree of concentra-tion and separation of components contained in l~quids.
In contrast to many of the ultrafiltrati.on units currently available, the apparatus of this invention maintains a high level of throughput without the need for additives.
As previously mentioned ~he apparatus of this invention is comprised of an ultrafiltration module together with means for supplying feed liquid and means for collecting and withdrawings a concentrate liquid and a permeate liquid. The module itself is comprised of a multiplicity of axially aligned hollow tubular members disposed in the permeate collection zone of the module. As set forth in Figure 2 the tubular members 32 are aligned in a parallel fashion and supported and sealably mounted in place by tube sheets 34 and 36.
Although the tubular members can be fabricated from a varlety of material, it is preferred that they be largely inorganic in composition. It has been observed .. .. _ _ ... .... ... .
that tubular members composed of inorganic materials are more resistant to abrasion and can wi~hstand higher temperatures than those largely composed of organic materials. In practice, it has been found that tubular members composed of carbon, alumina, alumino silicate, and the like, can be utilized in the apparatus of this invention.

~067~6 It is critical for the s~ccess~ul practLce of this invention that the tubular members~have ~ well defined poroslty. If the pore diameter iS too large-separation will not be selective and the lnner pores may even become blocked by the larger diameter molecules.
If the pore diameter is too small ~he rate at whlch liquid passes to the permeate collection zone wi:Ll be greatly reduced and thus the overall efficiency of the apparatus lowered.
It has been found that tubular members which~are ~~
characterized by a pore volume of at least about 0.08 cc/gm in the distribution peak in the pore diameter range wherein the majority of the pores are from about 0.1 to about 2.0 microns in diameter, are ideally suited for use in the ultrafiltration apparatus. Particularly preferred are tubular members composed of carbon and which have the majority of pore diameters within the above range. Pore size measurements on samples of carbon tubes employed in the modules indicate that they are sharply peaked in the range of 0.10=0.50 microns. Pores in this size range account for nearly 50 per cent of the distribution through-out the tube. The preferred tubular members are fabricated by a binder-coking process followed by a subsequent heat treatment. The carbon tubes employed are known in the art~ for example, those normally used for the fabrication of commercial cored arc carbons for motion picture projection machines. The carbon tubes serve as the outer shell which is subsequently filled with graphite and rare earth oxides to provide the desired light intensity.

` 9172 i~i7~

The size of the tubular members and the length to diameter ratio can vary over a wide range. The particular slze chosen will undoubtedly be influenced by the overall size o~ thf.~Ddule as well as the type of liquid and components to be separated. In practice, however, tubular members having an internal diameter of from about 0.10 inch to about l.0 inch and a wall thickness of from about 0.03 to about 0.25 inch and a length of about 48 inches have been employed with excellent results.
10 Tubular members having an internal diameter of 0.25 inch, a wall thickness of about 0.06 inch and a length of about 48 inches are particularly preferred.
In addition to the well defined poro~sity of ~he~
tubular members, it has been found that optimum ultra-filtration can be achieved if the inner surface of the porous tubular members is coated with certain aggregated metal oxide particles as hereinafter defined. The utili-zation of a selected size range, metal oxide coating represents a significant improvement over the prior art with respect to the development of a microporous ultra-filtration filter for cros~-flow filtration. Based upon the use of carbon, alumina or other porous tubular members as substrate materials, with the addition of aggregated metal oxide particles, i.e., a microporous metal oxide coating, it has been discovered that several different industrial process and waste streams can be treated in which suspended solids, collids, oils, or high molecular weight polymers are separated by ultrafiltration at rates ~067~L6 ,.
several times higher than the bare ~ube or the previously preferred hydrous zirconia oxide membrane of the prior art.
The present invention utilizes as the coating aggregated metal oxide particles having a narrow size range below about 5 microns and largely between about 0.1 and about 2.0 microns. The aggregated particles can be further sized and classified as fine (less than 0.1 microns), medium (0.1 to 1.0 micron) and coarse ~l.0 micron and largèr). Particularly preferred are aggregated metal oxide particles wherein a sizeable portion, i.e., at least about 50 per cent, is from about 0.1 to about 1.0 microns in size.
- Although commercially available metal oxides powders can be employed, in some instances they may require prolonged grinding times to reduce the particle size to the proper range. Particularly preferred metal oxide powders which have been found to be id~lly suited for use in this invention are those prepared by the so called "precursor procsss." This process comprises first contacting a metal compound with a carbohydrate material, igniting the material to decompose and remove the carbo-hydrate material and to insure conversion of substantially all of said metal compound to fragile agglomerates of its metal oxide, followed by comminution of ~he thus formed agglomerates to give the finer microporous aggregatecl particle employed in the invention.

`` 9172 ~067~

For example, a supply of the metal oxide powder aggregate, prepared by the precursor process, such as zirconia containing about 8 to 10 per cent yttria, can be ball milled by placing 1500 grams ln a one gallon contalner and adding zirconia beads. The container is then filled about three-quarters full with deionized water and acidified to a pH of 4 with acetic acid. Thereafter, the contents are milled for about 18 hours.
The particles prepared by the precursor process are so small that settling rates are slow, thus aggregates which have not been completely disrupted during wet ball milling can be separated from dispersed suspension of liberated particles by sedimentation, centrifugation, or other separation procedures based on particle size or mass.
For example, sizing can be effected by centrifuging from a broad distribution of particles sizes to obtain aggregated metal oxide particles largely within thë desired range ~ - ~
as hereinafter indicated. Once the separation has been made, the liberated particles remaining in suspension can - 20 be conveniently collect~d by treatments that reduce the surface charge and render the colloidal suspension unstable.
Typical treatments are the addition of an acid to lower the pH of the suspension, or the addition of a salt having a multivalentanion. The suspensions treated in this manner revert ~o a flocculated condition, and in this form, the powder can be separated from the bulk of the suspending medium by filtration or sedimentation.

'i~67~L6 It has been observed that tha mean individual particle size from which the preferred Q.l to 1.0 micron aggregates are obtained, is below 1.0 micron, and usually below 0.1 micron. The individual particles remain un-resolved at 11,000 magnification. X-ray powder di~frac~ion analysis indicates an ultimate par~icle size within the range of from about 0.01 to about 0.1 microns.

A variety of metal oxide particles can be employed as the coating in this invention. For e~ample, the metal of the metal oxide can, either singly or in mixtures thereof, include beryllium, magnesium, calcium, aluminum, titanium5 strontium, yttrium, lanthanum, zirconium, hafnium, thorium, iron, manganese, sillcon, and the like.

When the metal oxide powder employed is zirconia, in many cases it is preferred to produce the zirconia powder in a stabilized form. Therefore; a compound of yttrium, calcium, magnesium, rare earth metal or other known me~al that forms a stabilizer oxide can be employed along with the zirconium containing compound in producing the loaded material.
The proportions of the zirconium compound and ~ 0674~6 stabilizer metal compound should be selected to produce the type of stabilized zirconia desired.
A ~urther and more detailed description of the precursor process for making the metal oxide powders employed in ~ present invention is set orth in Belgiàn Patent No. 766,962 entitled "Finely Divided Metal Oxides and Sintered Objects Therefrom" by B.H.
H~mling and A.W. Naumann.
In practice, ~e metal oxide coating is applied to the tubular members by circulating and aqueous suspension of the aggregated particles through the tubes at linear flow velocities of from about 0.5 feet per second to about 40 feet per second, and at pressures from 30 to 500 psi. The concentration ~f aggregated particles in the suspension typically ranges from about 10 to about 100 milligrams per liter. The suspension is generally maintained at a pH sufficient to maintain a stable suspension of the aggregates. As the water filters through the pores of the tubes, the particles are filtered out and cover the pore opening of the substrat~
with a very fine pored layer. It is thisuniorm, continuous, highly porous, very fine pore structure which provides the higher throughput and improved resistance to fouling as compared to either bare tubes or tubes coated with less porous materials. For ` 9172 ~067416 optimum efficiency and throughput, it has been found that t~e coating should be from about 0.01 to about 10,0 microns in thickness without substantial pene-tration into the tubular member of more than about 5.0 microns, It is also desirable but not necessary to coat the tubular members at pressures at least equal to, and at flow rates no greater than, those which will be employed when the module is in operation.
For most applications the tubular members are coated with the aggregated metal oxide particles to provide an average coating of about 8.5 milligrams per square inch of the surface of the tubular member. ~or certain applications it may be desirable to add a second coating on top of the first of the fine size particles.
For the majority of applications, it has been found that a level of about 1 milligram of aggregated metal oxide particles per square inch tube surEace is the minimum amount that should be applied. Higher amounts yield higher and more stable flux levels. For example, while an average metal oxide coating o~ 8.5 milligrams is useful, it may be desirable to coat as much as 30 milligrams per square inch.
The coating of the tubular members with the metal oxides preferably is effected within a selected ` 9172 ~o67~6 pH range. The particular pH range chosell -19 that range in which the metal oxide particles remain in suspension.
For example, when the tubular members are coated with zirconia particles, the preferred pH range is from about 1 to about 5 and more preferably from about 2 to about 3.5. Ad~ustment of the pH can be accomplished by the addition of an acid such as acetic, oxalic~
hydrochloric and the like. In practice~ oxalic acid or hydroehloric acid is preferred since it tends to keep in solution any iron which might be present.
It should be noted that in contrast to methods disclosed in the prior art, it is not necessary to form a colloid before depositing the metal oxide on the surface of the tubular member such as is disclosed for the hydrous zirconia gel (3,413,219). The metal oxide aggregates are preformed and separated into the proper particle size range prior to the coating step. The coating is mainly a mechanical step with ~he metal oxide aggregates penetrating to a degree the pores of the tubular members and building up the desired coating on the surface. The aggregated metal oxide particles do not "fill" the pores of the tubular members in the sense that they are plugged, but "brldge" the pores which permits the small diameter molecules of the feed stream to pass through at a hlgh rate.

~ L9 -~74~6 As previously indicated the ultrafiltration apparatus of this invention can operate efficiently at pressures o~ about 500 psi and lower. Various ~ac~ors such as temperature, pressure and flow velocities, will, of course~ vary depending upon the particular ~eed stream.
Additionally, the actual geometric configuration of the interior of the tubular members wilL also be a ~actor.
For example, the interior of the members need not be cylindrical but can be star-shaped, hexagonal, octagonal, saw tooth, or the like.
It has been found that for the concentration and separation of certain dissolved phases, optimum results are obtained if the hollow tubular members containing the metal oxide coating are covered with an additional coating, such as for example, the fine grade of metal oxide powder (C 0.1 microns) or a hydrous zirconia gel. Method for applying hydrous zirconia gel coating are known in the art and are disclosed, for example, in U.S. Patent 3,537,988.
It should be no~ed that such coatings are in addition to the metal oxide coating. Attemped use of the hydrous zirconia gels alone on the tubular members doesnOt prov-ide the high degree of concentration and separation as in the present invention. For instance, examples 4 and 5 of this invention are directed to the use of the ultrafiltration apparatus for the concentration of polyvinyl alcohol in a textile liquids. As ind;cated in Table V of example 5 both the metal oxide coated carbon tube and the tubes having an addition hydrous _- 917z ~ 0674'L6 metal oxide coating gave markedly improved resuLts over the uncoated carbon tube.

As illustrated in Figure 8, when ln operation a ~ilter cake composed of the larger diameter molecules as well as solid or suspended ma~ter in the feed liquid will form initially on the coated tubular members. When the ultrafiltration appara~us is in operation, the feed stream, such as an aqueous oil emulsion, is fed, under pressure, over the filter surface at velocities high enough to shear away most of the accumulated filtered substances.
Since this flow is perpendicular to the direction of flow of the filtered liquid through the filtering surface, the term "cross-flow" filtration is employed. I~ is important that the flow rate through ~e tubular members be such that turbulent conditions are achieved. The liquid should pass through the tubular members at a rate of at least about 1.0 linear feet per second and at a Reynolds Number of at least about 2000.
~or instance, an ultrafiltration apparatus containing a single module with approximately 151 tubular members (0.25 inch internal d~ameter and 48 inches in Length) can process over 3,000 gallons per day at a pressure of 100 psi and a feed stream temperature of abou~ 72 F.

~67416 ~hen two or more modules are employed in the same apparatus, or when ~he num~er of tubular members is increasad, voLumes as large a~ tens of thousands of gallons per da~, and higher, can be processed efficiently.
In conventional ~iltration the filtered material would build up as thick ~ilter cake whiclh greatly reduces the filtration rate. Depending on the geometry of the system and the type of material being ~iltered, the velocities parallel to the filtering surface may be from about 0.5 ~o about 40 feet per second. A most significant feature of the present process is that the f~lter interface is such that di~solved, colloidal or suspend~d particles of the feed liquid in the size range of 10 microns and higher to as low as 0.002 microns may be removed at iltratio~
rates through th~ surface as high as several hundred gallons per day per square foot at pressures ~f 100 psi or lower.
Whereas ultrafiltration has been used for ~he removal of suspensions, colloids and high moLecular weight materials dissolved in aqueous solutions, the discovery that oil emulsions could be concentrated a~d separated from the bulk aqueous phase by ultrafiltration through coated fine pored tubes was unexpected. Such oil emulsions are, for example, those used in ~he preparation of steel and rolling mill coolants and lubri-cants or such e~ulsions as used in eutting, drawing, stamping, or other metal-working operations. In addition, the types of oil-water-dirt-metal chip emulsions obtained - 2~ -in the detergent washing of fabricated metal parts, etc., may also be separa~ed into a concentrated oil~dirt-particle retentate solution plus a clear water plus solubla detergent filtrate phase.
At present, accumulations of oil~ dirt and various other suspended solids in an aqueous system are removed by additions of acid and/or other chemicals at relatively high temperatures to break the emulsion and separate the oil from the suspension; the water is then settled in large storage tanks to remove particulate matter and the remaining soluble components are either neutralized or otherwise chemically treated by additions of acid or a~kali and then directed to a sewer or trans-ported to a suitable dumplng or processing site.
Transportation is relatively costly and in no cases are water soluble components of the waste water separated cleanly for recycling. Further, the costs of the processing with chemicals are substantial, both for materials and labor as well as for the processing facilities. Sewer surcharges for the chemiGal laden water phase are often quite high. In an increasing number of localities, such discharges are being pro-hibited by pollution control laws. As a result still further treatment of the aqueous phase is required before the water itself may be discarded.

~067416 9172 The ultrafiltration process of this lnvention can reduce the volu~e of the oil-dirt-water phase b~ as much as a actor of five to thirty or higher depending on the oil content of the starting mat:erial. m us, the volume o material requiring furthar ~.reatment for disposal is greatly reduced. Further5 because the oil level i~ this concentrate phs~e may typically be brought to a level of 20 to 40 per cent, which iB a high enough level to typically sustain combustion without ad~itional fuel be~ng added, the disposal problem can be greatly simplified by burning. This also permits the recovery of the bulk of the heating energy of the oil.
The oil-free aqueous phase may be rejected into a se~er or recycled back into the process. The r~use of the water promotes closed cycle operation, highly desirable from the water conservation standpoint. In ad~ition, where there are valuable wate~ soluble substances, such as detergents, which are carried through with the filtrate, an operating economy is r~ali7ab~e by avoid~ng the loss of these materials in the usual waste stream.

_ . .
~ nother maJor advantage accruing from the use of the process of the invention to continuously remove the dirt and oil from a metal washer on a paint line, for example, is that the cleaner washer liquid improves the cleanlinsss of the following rinse and other `` 9172 ~ OG74~6 commonly used pre-paint processing baths. As a result, ~he quality of the paint coating on the cleaner metal part may be improved considerably.
A fuxther embodiment, of the present invention is directed to the ultrafiltration module itself and to methods or assembling the tubular mem~ers. Although , .;
even a ~ingle tubular member can effect concentration and separation, it is, or course, more practical to construct ; a module having a multiplicity of tubes. The number of tubular members employed will vary depending upon a variety of factors. Modules containing as few as 25 or less, or up to 1000 or more tubular members have been constructed.
As indicated in Figure 2, the tubular members are~aligned in a parallel fashion and in close proximity to one another. Each tubular member is held in place by tube sheets 34 and 36. The tube sheets themselves are moun~ed in the module so as to provide a permeate zone 38 which is sealed from feed fluid entering the entrance port via conduit 26. ~he only liquid which ~an enter the penmeate zone is that which filters through the walls of the tubular members.
The ~uter shell of the module and the ~ube sheets can be fabricated from a variety of materials. For example, a wide variety of plastics, such as polyvinyl chloride and the like, or metals such as stainless steel can be used. Due to the wide variety of liquids which can be treated and ~emperature ~ariations of the feed streams, it is preferred to construct the module oE

` 9172 ~0674~t;

stainless steel or other material which is compatible with the feed liquid and operating conditions.
As hereinbefore indlcated, Figures 3 and 4 illustrate two types of methods for assembl~ng the tubular members in the tube sheets so that a liquid-tight seal is o~tai~ed. In both instances the ends of the tubular members are sealed and cushioned by a rubber or rubber-like seal. As opposed to a cemented or other fixed sealing means, the assembly method employed ln this invention provides somewhat of a "floating seal" so that brittle tubular members, for example, those composed of carbon~ can withstand a certain amount of shock.
The assembly shown in Figure 3, utilizes "O"
rings 46 which are fitted over the ends of the tubular members. The plate 48 is then placed over the tube ends and "O" rings. When the cap 50 is attached to end sheet 42 the "O" rings are compressed, sealing and securing the tu~ular members in place.
Figures 4-6 illustrate'a more preferred assembly of the tubular members in the ultrafiltration module.

As shown in Figure 6, the end sheet 34 contains openings of sufficient diameter to admit the tubular members. The surface of the end sheet opposite the per~eate zone is recessed to permit a gasket seal 52 to be placed over the end of the tube and forced into the recessed area. Th~ seals and secures the tubular ~674~L6 members in pLace. An advantage of this type of assembly over the previous one is that iLt penmits the tùbular members to be aligned in very cLose proximity to one another. For certain applications and due to space requirements it may be advantageous to fabricate a relatively co~act module wi~hout sacr~icing the desired number of tubular members.
For the most ef~icient utilization o~ the ~ ultrafiltration apparatus of this invention it is often preferred to operate a çlosed loop system, that is, the J
feed stream after passing through the module where it becomes slightly more concentrated with the larger molecular we~ght molecules~ is recycled back to the module. As ~he liquid increases to a sufficient concentration, it can then be drawn off from the system.
A variety of automatic control means can be utilized in removal of concentrate as well as circulating the feed stream.

Although Figure 1 illustra~es an ultra~
filtration apparatus employing a single module 10, for certain applicatlons it may be desirable to use t~o or more modules in the same apparatus. In such instances, the modules can be arranged in series, i.e., the concentrate from a first module serving as the feed stream to a second, and so on, or in parallel wherein the same feed stream simultaneously enters all moclules.

' 9172 ~ ,o674~6 A variety of factors can influence which arrangement - will optimize the concentration and separation o~
components for a particular application.
Due to the excellent features of tha apparatus of this invention, it i8 ideally suited for the separation and concentration of components contained in a wide variety of liquids. As previously inldica~ed, a parti-cularly attractive application of the ultrafiltration apparatus of this invention is in ~he concentration and separation o oil-water emulsions. Such emulsions are encountered in a wide variety of metal-working and metal-washing operations. Prior to the present invention there was no sa~isfactory method for concentrating such liquids efficiently ln order to minimizing waste disposal and reclaimed many of the useful components in the liquids.
However, the apparatus of this invention has been outstand-ingly successful in the treatment of a wide variety of liquids which contain emulsified and/or chemically stabilized oil.

As demonstrated in the examples, the ultra-filtration apparatus is also useful for the concentration and separation of solutions employed in textile operations.

For example, polyvinyl alcohol is readily concentrated and separated from textile sizing solutions with a high degree of efficiency.
The apparatus is also useful for recovering and recycling detergents from a variety of wash waters, such as car washes~ laundries, and the like.

~. 9172 74~6 It has also been noted that the ultrafiltration apparatus of this invention is useful in electrophoretic coating operations. For example, after a painted article is removed from an electro-painting bath in many instances it is sprayed with water to remove excess drag-out. By passing this wa~h wat~r containing paint through the apparatus of this invention paint sollds can be concentrated and returned to the psint bath. The apparatus is a~so useful in removing excess waterj soluble salts, or excess solubilizers from the paint bath. As indicated in Example 6, the xejection o~ the pigment phase can be as high as 99.95 per cent. In contrast to methods disclosed in the prior art such as, for example, in U.S. Patent 3,663,399, the penmeation rates obtained with the apparatus of this invention are much higher.
Additionally the apparatus of this invention has been found to be useful in the treatment of a variety of food and beverage products. For instance, the apparatus is useful in the concentration and separation of spent grain liquors in ~ preparation of beer and ale. It has also been found to be useful in concentrating proteins from cheese whey, clarification of vinegar, and the like.
In certain applications such as in the desali-nization of sea water, the ultrafiltration apparatus can ~e employed as an initial step to clarify the water prior to its passage through a reverse osmosls unit.

,--. 9172 1067~1~

It has also been observed that the ultra-filtration apparatus is useful for the concentration and separation of bovill3 animal blood serum, egg albumin, enzymes and the like.

~0674~i The following ex~mples are illustrative:
Example 1 An aqueous solution (solution A) containing approximately 2 per cent by weight of tramp and so1uble oil~ with about 3 per cent by we~ght of soluble indus-trial detergent and caustic soda was circulated through an ultrafiltration module at various pressures and flow velocities. me waste itself can~from the holding - tank for an industrial washer which is used to clean the dirt, metal chips and remnants of oil from the metal parts after they are fabricated. Various oils are on the finished parts including lubricating oils used ~or the drawing operation7 soluble oils from the shaping operation~ and various cutting olls from the machining operation. The concentration of total oil - in ~ feed material was determined by sulfuric acid addition and subsequent separation.

me operating condltions and results obtained are set forth in Table I below:
2Q Table I
O eratin~ Conditions of Ultrafiltration Solution A
Operating pressure 100 psi Circulation velocity 18 ft/sec ~ 31 -~067~
Filtrate flux 90 GFD ~gallons per square foot per day) Operating temperature 140F
Total Operating time 30 hours Characteristics of Feed, Filtrate and Concentrate _ _ __ Feed Filtrate Concentrate pH 12.5 12.5 12.5 Oil content 2% C100 ppm 16%
Detergent content 3% 3% 3%

As is evident from the Table there was an eight-fold concentration of the feed. The filtrate had less than 100 ppm of oil but still had the same detergent concentration as the feed making it suitable for reuse.

Example 2 A second oil-water-detergent solution (solution B) was tested in which the main oil constituent consisted of the soluble oil used in a metal stamping operation. In this case the feed stream contained about 0.4% of oil by volume as determined by sulfuric acid ~eparation. Operating characteristics and characteristics of the feed, filtrate and concentrate are indicated in Table II
below. Flux values greater than 100 GFD were measured over operating periods greater than 30 days at various " ~

~;
~67416 9172 concentrations of oil. A 55-fold concentration was achieved, Table II
Charac~eristics of Ultrafiltration System for Processin~ Oil-Water-Detergent Solution_B
Operating pressure 100 psi Circulation velocity 15 ftlsec Operating temperature 150F
Filtrate flux 1~4 GFD
Total operating time 720 hours Characteristics of Feed, Filtrate and Concentrate Feed Filtrate Concentrate pH 9.5 9.5 9.5 Oil content 0.4 ~ 100 ppm 22%
Detergent content 3% 3% 3%

.
Example 3 In a third experiment Texaco Soluble Oil type C was run in a single tube system at a feed concentration of about 5 per cent. Data o Table III
indicate operating charcteristcs for a 30-hour run, during which time the concentration of oil was increased from 5 per cent to 20 per cent.
Table III
Operating Conditions of Ultrafiltration System for Processing Texaco-C Oil/Water Emulsion , Operating pressure 100 psi ~0674~6 Circulation veloci~y 22 t/sec Average filtrate flux 138 GFD
Average operating tempera~ure 130F
Total operating time 24 hours Characteri~t~s of Feed, Filtrate and Concentrate _ _ Feed Filtrate Concentrate Oil Content 5% C 100 ppm 29%

Example 4 To illustrate the versatility of the ultra-filtration system for various other industrial wastes9 samples of polyvinyl alcohol-water solutions were run at concen~rations of l.O to 4.0 per cent. Data of Table IV indicate the operating characteristics of the system and the properties of eed, filtrate and concentrate. m e polyvinyl alcohol was within the molecular size range 50,000-lOO,OOO such as used in a textile sizing bath. In this case a particulate bed coating of zirconia was covered with a second coating of a hydrous zirconium oxide gel. The hydrous zirconium oxide was prepared by boiling a 0.25 M ZrOC12 solution for 30 hours to hydrolyze tha oxy-chloride. For the 37" long, 1/4 in. I.D. tube, 12.5 milllliters of tk~s stock solution was added to 3 li~ers of distilled water to produce the feed which was fed through the tube at 100 psi for approximately . ~ 917~

~,o67~6 an hour, with the permeate being returned to the reservoir, to deposit the hydrous zirconia gel on top o~ the previous coatlng. In use, the apparatus provided grea~er ~han 97 per cent rejection o~ the polyvinyl alcohol.
Table IV

Operating Conditions of Ultraflltration System wi h I~Ly~ __ohnl Solution Operat~ng Pressure 100 psig Circulation velocity 20 ftlsec Average filtrate flux at 1% concentration 70GFD
at 4% concentration 21GFD
Average operating temperature 180F
Total operating time 112 hours Characteristics of Feed9 Filtrate, Concentrate_ _ Feed Filtrate Concentrate p~ 6.8 6.8 6.8 PVA 1% 0.03% 4~/O

Experiment 5 Comparison experiments in the concentration of polyvinyl alchohol were performed with carbon tubes uncoated 9 with carbon tubes coated wlth a particula~e bed, and with carbon tubes coated with a part~culate bed plus the hydrous zirconia. All measurements were performed at 100 psi inlet pressure and flow velocity near 20fps. Data of Table V indicate comparative rejection and flux characteristics fo~ the thrlee experiments, showing the grea~ly improved flux afforded by the zirconia particle and the improved ~067~6 rejection with sustained high flux when the hydrous zirconia gel layer was added.

.. .... .. . _ .
Table V
Comparison of Reject~on and Flux Characteristics for Carbon Tube Permeator, Carbon Tube-Particula~e Bed P~rmea~or, Carbon Tu~e - Particulate Bed -Hydrous Metal Oxide Permeator Using 1% PVA
Solution as Feed . .

.
Flux Rejection Temperature . ~ 10 ~GFD? ~%~ ( F2 Carbon tube alone 15 0-50 134 Carbon tube - particulate 100 63-66 188 Carbon tube - particulate -hydrous met~l ~xide100 97-99 177 . ~ 9172 ~L0~74~L6 Example 6 The ultrafiltration apparatus of this invention was employe~ ~or the concentration of a primer pain~ from an electrodeposition system.
A porous carbon tube with a pore volume of about 0.2 g/cc and the majority of the pores in the 0.1 to 1.0~ diameter range, as detenmined by Hg poro-simetry, was coated with 6 mg/cm2 of precursor ZrO2 particleæ, sized in the 0.1 to 1.~ range by centri-fuging. The coating was performed by adding the Zr2 to about 3 liters of acidified water and circulating the water through the interior of the ; tube at 100 psi for 1 hour whLle the water permeating through the tube waLl was returned to the circulating feed. The tube was th~n insert d in a circulation syst~m in which a 7-1/2% solid solution of an electro-depositable paint, Forbes 2000, was fed at 100 psi and 80F through the tuke at a linear flow velocity of 15 to 25 ft/sec. Over a 214 hour period, the permeation rate held between 85 and 100 (GFD). In other experiments with this paint and this tube extending over 412 more hours, the flux held between 50 a~d 65 GFD.
Rejection of the pigment phase was 99. 95% and of ~he ionic constitu~nts, was 48.8%. Typical permeation rates ~or film type ultrafiltration systems on this type of paint is lQ-30 GFD.

. - 37 -:

~674~16 Example 7 In another e~ample in which a different type of high porosity, high ~ur~ace area powder was used as a pre-coat, a slurry of y-alumnla, ground in size to appro~imately the same range as the precursor 2irconia, tha~ ~s, from 0.1 to 1.~ was used. I~e carbon tube was of the same type as in the previous example. Its flux at 100 psi with pure water was over 400 GFD at 110F. With the pre-coat applied it had dropped to 280 GFD at an operating ~emperature of 160F. mis tube was used to process a sample of the black liquor from wood pulp digestion. Fluxes of the : order of 70 to 80 GFD were obtained with color reJec-tion greater than 90% and about 30% rejection of the , ionlc constituents.

Example 8 In another experiment wi~h the paper mill black liquor, a carbon tube as above was coated first wieh the par~iculate zirconia and ~hen wi~h the hydrous zirconia oxide from the zrocQ,2 solution as indicated in example 4. After ntnning the black liquor overnight at 100 psi and 140F, the permeation rate was 80 GFD with greater than 90% rejection of the color. The ~eed had a conductivity of 32,000 mhos while the permeate had a conductivity of approximately 17,000 mhos, indicating an ionic rejection of the order of 47%.

~~~

1~)674~6 Exam~le 9 A comparison was made on a (number of carbon and alumina tubes to ~emonstrate the wide variety in characteristics which are related to pore diameter, pore volume and air and water permeabi:Lity. As indicated previously, tubular members having a pore diameter of from about 0.1 to about 2.0 micron~ such as sample numbers 1-7 of Table VI, have b~en found to provide optimum concentratlon and separation of components from liquids.
Those tubular members having pore diameters generally larger than about 2.0 microns (sample number 8-15) tended to plug the pores in dep~h with the metal oxide particles and ultrafiltered materials in the retentate and give undesirably low permeation rates.
Additionally, when the bulk of the pore volume had pore diameters less ~han about 0.1 micron the water flow rate of the uncoated tube was too low and ~herefore the permeation rate was unacceptably low. In contrast sample numbers 1-7 having a pore volume in the distri-bution peak of about 0.08 cubic centimeters per gram Gr greater, in the pore diameter range primarily of from about 0.1 to about 2.0 microns gave excellent results. Such carbon tubes are also distinguished by having a bulk density of less than about 1.60 grams per cubic centimeters.

67~ lL6 Sample Number 7 was a useful tubular member compos~d of alumina wheraas the others were composed of carbon.
hll measurements were made using standard techniques for the determlnation o~ pore volume, pore diame~er, air and water flow rates and bulk densities.

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~0~7~ 9172 Exam~ 10 The ultrafiltration apparatus of this invention ~as also employed for the concentration and separation of the protein fraction of cottage chee~se whey from the bulk of the water, lactose and dissolved salts.
Porous carbon tubes with pore volumes w:ithin the preferred range previously indicated were coated with a "precursor" magnesium-aluminum spinel in a manner similar to that of ~xample 6. A feed solution with 90 per cent of the liquid phase extracted was passed through the apparatus of 120F for 20 hours keeping essentially all of the protein in the concentrate. The permeation rate at the end of the run was 60 GFD. The tubes were cleaned with distilled water and a new feed solution passed through the apparatus. After 6.5 hours of operation the permeation rate dropped from 51 to 33 GFD. After washing with a Tergitol(l) 15-S-5 wash the permeation rate of the feed solution returned to 57 GFD. The tubular members were then cleaned with the Tergitol(l) wash and purged with steam at 8 psig. to sterilize the tubes and remove particulate matter.
A new feed solution was fed to the apparatus and the initial permeation rate was 63 GFD. After 2 hours of continuous operation the permeation rate was 51 GFD
and after 24 hours, 36 GFD. It was therefore evident (l)Trademark oE Union Carbide Corporation for a group of higher sodi~m alkyl sulfates.

~0 67 ~ ~

that the tubular membex and metal oxide coating could be cleaned and sterilizad with ste~l to return the performance to a high level.

Although the invention has been illustrated by the preceding examples it is not to be construed as being limited to the materials etnployed thereln, but rather, the invention relates to t~e ganerlc area as hereinbefore disclosed. Various modifications and embodiments can be made without departing ~orm the spirit and scope thereof.

- ~3

Claims (31)

WHAT IS CLAIMED IS:

1. An ultrafiltration apparatus for the concentration and separation of components contained in liquids, said apparatus comprised of, in combination:
(a) at least one module having (i) at least one entrance port, (ii) at least one exit port, (iii) a permeate collection zone, having at least one exit port, (iv) a multiplicity of axially aligned hollow tubular members disposed in said zone in close proximity to one another, said members having a pore volume of at least about 0.08 cc/gm in the distri-bution peak in the pore diameter range wherein the majority of the pores are from about 0.1 to about 2.0 microns in diameter, said members being supported and sealably mounted in said zone so that liquid entering said module must contact said members and any components of said liquid which permeate the walls of said members collect in said permeate collection zone, and (v) contained on the surface of said members which is in direct contact with said liquid a substantially uniform continuous adherent porous coating of preformed, aggregated metal oxide particles said aggregated particles having an average mean size of less than about 5.0 microns, said coating being from about 0.01 to about 10.0 microns in thickness without substantial penetration into said members, (b) means for supplying a feed liquid to said module, (c) means for withdrawing a concentrated liquid from said module, and (d) means for withdrawing a permeate liquid from said permeate collection zone.

2. The apparatus of claim 1 having conduit means connected to the exit port and the entrance port of said module, whereby said concentrated liquid is recycled through said module.

3. The apparatus of claim 2 having means connected to said conduit means whereby at least a portion of said concentrated liquid is withdrawn.

4. The apparatus of claim 1 having two or more modules disposed so that said feed liquid passes through said modules sequentially.

5. The apparatus of claim 1 having two or more modules disposed so that said feed passes through said modules simultaneously.

6. The apparatus of claim 1 wherein said tubular members have a length to diameter ratio of at least about 20 to 1.

7. The apparatus of claim 1 wherein said tubular members have an internal diameter of from about 0.10 inch to about 1.0 inch.

8. The apparatus of claim 1 wherein said tubular members have average pore diameters, at least 50 per cent of which are within the range of from about 0.1 to about 0.50 microns.

9. The apparatus of claim 1 wherein said tubular members are composed of carbon.

10. The apparatus of claim 1 wherein said tubular members are composed of alumina.

11. The apparatus of claim 1 wherein said tubular members are composed of alumino silicate.

12. The apparatus of claim 1 wherein said aggregated metal oxide particles have an average mean size of from about 0.1 to about 1.0 microns.

13. The apparatus of claim 1 wherein said coating is comprised of a precoat of aggregated metal oxide particles having an average mean particle size of from about 0.1 to about 1.0 microns, and a second coating of metal oxide particles having an average mean particle size of less than about 0.1 microns.

14. The apparatus of claim 1 wherein said coating is comprised of a precoat of aggregated metal oxide particles having an average mean particle size of from about 0.1 to about 1.0 microns, and a second coating of hydrous zirconia.

15. The apparatus of claim 1 wherein said metal oxide is zirconia.

16. The apparatus of claim 1 wherein said metal oxide is gamma alumina.

17. The apparatus of claim 1 wherein said metal oxide is magnesium-alumina spinel.

18. A module, useful in an ultrafiltration apparatus for the concentration and separation of components contained in liquids, said module comprised of in combination:
(i) at least one entrance port, (ii) at least one exit port, (iii) a permeate collection zone, having at least one exit port, (iv) a multiplicity of axially aligned hollow tubular members disposed in said zone in close proximity to one another, said members having a pore volume of at least about 0.08 cc/gm in the distribution peak in the pore diameter range wherein the majority of the pores are from about 0.1 to about 2.0 microns in diameter, said members being supported and sealably mounted in said zone so that liquid entering said module must pass through the interior of said members and any components of said liquid which permeate the walls of said members collect in said permeate collection zone, and (v) contained on the surface of said members a substantially uniform continuous adherent porous coating of said preformed, aggregated metal oxide particles, said particles having an average mean size of less than about 5.0 microns, said coating being from about 0.01 to about 10.0 microns in thickness without substantial penetration into said members.

19. The module of claim 18 wherein said tubular members have a length to diameter ratio of at least about 20 to 1.

20. The module of claim 18 wherein said tubular members have an internal diameter of from about 0.10 inch to about 1.0 inch.

21. The module of claim 18 wherein said tubular members have average pore diameters, at least 50 per cent of which are within the range of from about 0.1 to about 0.50 microns.

22. The module of claim 18 wherein said tubular members are composed of carbon.

23. The module of claim 18 wherein said tubular members are composed of alumina.

24. The module of claim 18 wherein said tubular members are composed of alumino silicate.

25. The module of claim 18 wherein said metal oxide particles have an average mean particle size of from about 0.1 to about 1.0 microns.

26. The module of claim 18 wherein said coating is comprised of a precoat of aggregated metal oxide particles having an average mean particle size of from about 0.1 to about 1.0 microns, and a second coating of metal oxide particles having an average me n particle size of less than about 0.1 microns.

27. me module of claim 18 wherein said coating is comprised of a precoat of aggregated metal oxide particles having an average mean size of from about 0.1 to about 1.0 microns and a second coating of hydrous zirconia.

28. The module of claim 18 wherein said metal oxide is zirconia.

29. The module of claim 18 wherein said metal oxide is gamma alumina.

30. The module of claim 18 wherein said metal oxide is magnesium-alumina spinel.

31. A process for the concentration and separa-tion of polyvinyl alcohol from textile liquids containing said polyvinyl alcohol which comprises supplying said liquid containing polyvinyl alcohol to the ultrafiltration apparatus of claim 1 and withdrawing a liquid concentrated with polyvinyl alcohol from said apparatus.