CA1058525A

CA1058525A - Membrane separation of phenols from aqueous streams

Info

Publication number: CA1058525A
Application number: CA232,897A
Authority: CA
Inventors: Eli Perry
Original assignee: Monsanto Co
Current assignee: Monsanto Co
Priority date: 1974-08-05
Filing date: 1975-08-04
Publication date: 1979-07-17
Also published as: FR2281322B1; JPS5141333A; BE832078A; GB1480018A; IT1040350B; AU8363975A; SU865123A3; FR2281322A1; DE2534780A1; SU704451A3; NL7509076A

Abstract

APPLICATION FOR

LETTERS PATENT

FOR

MEMBRANE SEPARATION OF PHENOLS

FROM AQUEOUS STREAMS

Abstract of the Disclosure Phenols are separated from aqueous streams by contacting the aqueous streams with a first surface of of polymeric membrane which is selectively permeable -to phenols, maintaining d second and opposite membrane surface at a lower chemical potential than the fist surface, and withdrawing, from the second membrane surface a mixture having a higher concentration of phenols than the aqueous feed stream.

Description

~C1585Z5 The invention relates to the membrane separation of phenols from aqueous streams. In another aspect the invention relates to the membrane separation of phenols from aqueous streams in combination with a solution sink which provides a lower chemical potential on the permeate side of the membrane.
In yet another aspect, the invention relates to a process where-in phenols can be recovered from aqueous streams. Still another aspect of the invention relates to a process for the removal of environmental contaminants such as phenols from waste water streams.
The separation of phenols from aqueous streams has been accomplished by various means, for example, distillation, filtration, solvent extraction, and combinations of these and other means. A major pollution problem associated with indus-trial waste is the phenols content of waste water streams.
Ona source of industrial phenols pollution results from crack-ing processes o~ partial oxidation techniques where there is a chance of aromatic and oxygen-containing compounds raacting at elevated temperatures. Another source of phenols-containing waste water streams results from those processes which use phenols as extraction or extractive distillation solvents for the preparation of hydrocarbon compounds. Phenols are often present in these waste water streams in relatively large amounts which has presented difficulty in effeative removal.
The removal of phenols from waste water has been d!ifficult in the past because of the lack of suitable technology. These technological problems arise because, for example, even though phenol and water are immiscible between the limits of about 9 and 70 weight percent phenol at 25C, it is difficult to re-cover phenol from the lower than 9 weight percent solutions i. e. the concentration of the water-phenol azeotrope. Phenol - 1 - ~q~

can be removed from aqueous streams through the use of benzene extraction systems, however, the phenol removal by this method is limited as to both large concentrations and trace amounts.
These limitations result from economic considerations in the case of large concentrations of phenol and recovery efficiency in the case of trace amounts of phenol.
Solvent extraction systems utiliæing benzene hav0 been used by industry for the purposes of recovering phenol from various streams, but these systems suffer from poor effi-ciency, particularly when the phenols content of the feedstream is low. Solvent extraction methods frequently result in an exchange of one solvent for another thus presenting a continuing need for phenol separation from the mixture or solu-tion. Frequentlythe mixtures, such as phenol water form azeo-- tropic mixtures. Because of these azeotropic mixtures produ-cing vapors having the same compositions as t~e liquid, the individual components of the mi~ture cannot be separated by ordinary distillation means.
Dilute phenol-containing aqueous streams have also been treated by feeding the streams to secondary purge treat-ment basins where appropriate micro-organism can metabolize the phenol, provided the phenol content is low enough. How-ever, at best this is a sensitive operation, even requiring occasional intentional phenol spills during times of low phenol admission in order to keep the microbil population in the purge ponds properly balanced to handle phenolic waters. Moreover, in addition to its limited usefulness, biological oxidation is a relatively laborious process. As can be seen the disadvan-tages of existing methods for the separation of phenol from aqueous streams necessitates a simple, inexpensive process which is adaptable for various aqueous phenolic mixtures and concentrations.

~58S~S

Mambrane separation techniques have been utilized to separate mixtures of two or more different molecules, for example, aqueous mixtures, mixed hydrocarbons, azeotropic mix-tures, and the like. However, known membrane separation techniques utili~ed in separation of aqueous mixtures, fre-quently are followed by secondary procedures such as distilla-tion, and the like. Because of the disadvantages of existing separation methods which principally involve a substantial energy input of a thermal or mechanical nature, a simple mem-brane separation process for separating phenols of varying con-centrations from aqueous mixtures is needed.
Phenolic contaminants of waste water streams can be present in amounts of from 1 part per million to 10,000 parts per million or more, even up to substantial percentages by weight. Typically, these parts per million phenol concentra-tions are present in refinery effluence, but also originate from chemical plants which produce for example, oxygenated com-pounds by partial oxidation of hydrocarbons, pulp and paper mills, -food processing plants, drug manufacturing facilities, and other process industry installations.
The increasing need to recover phenols from aqueous streams is founded on the cost of replacing these phenols as well as modern environmental requirements. In addition, trace amounts of phenols in aqueous discharge streams can cre-ate fish kills and biological imbalances in fresh water lakes and streams. Substantial efforts have been made in improving phenols recovery from aqueous streams through known methods;
However, even with improvement such known procedures require complex equipment and expenditures, significant energy and chemical input. Known methods xemain inflexible, particu-larly in dealing with varying phenolic concentrations, i. e.

~S85ZS

from up to 50 percent by weight and as low as trace amounts in the parts per million range. In order to achieve an eficient, flexible phenols separation system, techniques must be devel-oped which can deal with trace amounts up to substantial weight percent concentration with corresponding energy, chemical and eq~ipment conservation.
In a preferred embodiment of the present invention there is provided a process for separating phenols from aqueous solutions, characteri7ed b~
lQ contacting a phenols-containing aqueous solution of less than 9 weight percent phenols with a first surface of an organic polymeric membrane selectively permeable to phenols;
maintaining a second and opposite membrane surface at a lower chemical potential than the first membrane surface;
permeating a portion of the phenols into and through the membrane;
withdrawing at the second membrane surface a solution having a higher concentration of phenols than the phenols con-centration in the aqueous solution.
It has been discovered in accordance with the pre-sent invention that phenols are effectively separated from aqueous streams through the use of polymeric membranes selec-tively permeable to phenols wherein the permeate side of the membrane is maintained at a lower chemical potential than the permeant or feed zone of the membrane through chemical or phys-ical means~ ~n essential feature of the polymeric membrane separation of phenols from aqueous streams is that the poly-meric membrane be selectively permeable to phenols. The process according to the invention separates phenols from aqueous streams having various concentrations of phenols through the steps of (a) contacting the phenols-containing ~1:9585Z5 aqueous streams with a first surface of an organic polymeric membrane which is selectively permeable to phenols; ~b) main-taining a second and opposite membrane surface at a lower chemical. potential than the first membrane surface through chemical or physical means; (c) permeating a portion of the phenols into and through the membrane; and (d) withdrawing at the second membrane surface a mixture having a higher concen-tration of phenols than the phenols concentration inthe aqueous stream. In addition, an optional feature of the invention is the utilization of a solution sink as the chemical means for maintaining a lower chemical potential on the permeate side of the membrane. This solution sink can be selected from poten-tial solvents for phenols and/or phenolic complexing solutions.
The process of the instant invention comprises the utilization of polymeric membranes which are selectively per-meable to phenols and substantially impermeable to other compo-nents of an aqueous waste stream, phenols solvents, or phen-olic complexing solutions which are in contact with the mem-brane. The process according to the invention can utilize a phenol solution or a vapor vacuum mode on the permeate side of the membrane for maintaining the lower chemical potential which is an essential feature of the invention. The lower chemical potential provides a force which drives the phenols permeate through the selective membrane and arises from the phenols solution or vapor vacuum mode having additional capa-city for phenols permeate. Multiple stage operations are feasi~le as scale-up utilization of the invention since indi-vidual stages permit various concentrat.ions and temperatures in order to achieve optimum driving forces.
Continuous processing according to the invention is achievable wherein an a~ueous stream passes on one side of ~5~35~5 and in contact with a selective membrane and a solution sink or vapor vacuum is present on the other side of and in contact with the membrane. The lower chemical potential of, for example, the phenols solution sink together with countercurrent relationship of the phenols-containing aqueous stream, provides a driving force for permeating phenols through the selective membrane to enrich the phenols solution sink. The phenols enriched solution sink, i. e. pheno~c complexes, solvent, or vapor can be swept or moved by physical means to suitable pro cessing which promotes a recycling of the solvents or complex-ing solutions.
For each individual stage the effectiveness of the separation is shown by the separation factor (S.F.). The sep-aration factor (S.F.) is defined as the ratio of the concentra-tion of two substances, A and B, to be separated, divided into the ratio of the concentrations of the corresponding substances in the permeate S. F (Ca/Cb) in permeate = (Ca/Cb) in permeate where Ca and Cb are the concentration of the preferentially permeable component and any other component of the ~xture or the sum of other components respectively.
In the pervaporiæation or vapor vacuum embodiment of the invention, the first or feed side of the membrane is usu-ally under a positive pressure, while the second side is under a negative pressure, relative to atmospheric pressure. An-other preferred mode of the pervaporization phenol separation is where the second side of the membrane is maintained at a vacuum of 0.2 mm to about 759 mm of mercury.
The term "chemical potential" is employed herein as described by Olaf A. Hougen and K. M. Watson ("Chemical 10S~5ZS
Process Principles, Part II," John Wiley, New York, 1947~) The term is related to the escaping tendency of a substance from any particular phase. For an ideal vapor or gas, this escaping tendency is equal to the partial pressure so that it varies greatly with changes in the total pressure. For a liquid, change in escaping tendency as a function of total pressure is small. The escaping tendency of a liquid always depends upon the temperature and concentration. In the pres~
; ent invention, the feed substance is typically a liquid solu-tion and the permeate side of the membrane is maintained such that a vapor or liquid phase exists. A vapor feed may be em-ployed when the mixture to be separated is available in that form from an industrial process or when heat economies are to be effected in multi-stage.
In a preferred embodiment of this inventive process, the first or feed surface of the membrane is contacted with a phenols-containing aqueous stream in the liquid phase, while the second sur~ace of the membrane is contacted with a phenol solvent ox complexing agent solution. However, the aqueous feed stream can be in the vapor pha~ wherein it is preferable that the feed side of the membrane be under a positive pressure in relation to the permeate side. In order for permeation of the phenols to occur, there must be a chemical potential gradient between the two zones, i. e. the feed side of the mem-brane as compared to the permeate side of the membrane. The chemical potential gradient for purposes of this invention re-quires that the chemical potential of the feed zone be higher than the chemical potential in the permeate zone. Under such conditions a portion of the phenols in the stream aqueous feed will dissolve within the membrane and permeate therethrough, since an essential feature of the invention is that~he membrane be selectively permeable to phenols.

9.[3585Z5 The permeation step is conducted by contacting the phenols-containing aqueous feed stream in either the liquid or vapor phase with the membrane and reco,vering a phenols-e~iched permeate fraction from the other side of the membrane. The permeate is in the form of a phenols vapor, phenols solution, or phenols complex solution. To facilitate rapid permeation of the phenols, the chemical potential of the permeated phenols at the surface of the membrane on the permeate side can be kept at a relatively low level through the rapid removal of the per-meate fraction, for example, through a continuous process where-in the phenols-enriched vapor, phenols-solvent or phenols com-plex solution are continually removed and replaced by vacuum or non-enriched phenols solvent and~or complexing agent.
The term "solution sink" for purposes of this dis~
closure defines a liquid sweep utilized on the permeate side of the membrane and is inclusive of both solvents for phenols and solut~ons of phenolic complexing agents or both. Suitable solvents for phenols used as a solution sink can be selected from solvents which permit the total concentration of phenolic bodies to be greater on the permeate side than on the feed or permeant side of the membrane. An illustrative list of suit-able sweep solvents is presented in Table I and Table II below, however, the limited list of solvents does not represent a com-plete list of operable solvents according to the invention.
TABLE I
SOhVENT K(a) % EXTRACTED (b) Benzene 5 55 5 Toluene 3 50.0 Chlorobenzene 1 21.6 Nitrobenzene 12 75.0 n-Butyl Acetate 38 90.5 - - J
5~5 TAB~E I ~continued) SOLVENT K( ) ~ EXTRACTED (b~
iso~Butyl Acetate . 60 93.8 sec-Butyl Acetate 56 93.3 tert-Butyl Acetate 45 91.5 Dimethyl Phthalate 49 92.4 Dibutyl Maleate 44 91.7 Dibutyl Fumarate 24 85.7 Tributyl Phosphate 276 98.6 Dibutyl Phenyl Phosphate 160 97.6 Methyl Diphenyl Phosphate 120 96.8

2-Ethyl Hexanol 14 77.8 (a3 K ~ Distribution Coefficient ~ Phenol conc~in Solv~nt Phenol Conc.Ln Water (b) % Extracted - PK X 100%
- 1 + PK
p _ Solvent Volume, ~ o 25 in all tests Water Volume TABLE II
-- . Conc. of Phenol atA~prox. Sol~
Equilibrium - (à) of Solute in Solvent in Solvent ln Water K Water (C) tgm7100 cc) - -l-methylnaphthalene 0.66 0.411'1.60 low diphenyl ether 0.74 0.3352.20 low triisopropylbenzene 0.77 0.3052.50 low N,N-diethylaniline 0.88 0.1884.70 slightly m-chloroaniline 1.01 0.06 17 0.92 (70C) isodecanol 1.03 0.04 24 <0.01 (25C) benzyl alcohol 1.04 0.03 35 ~4 (25C~
monodecylamine 1.06 0.01106 81~ o-chloronitrobenzene~ ~ About (40C) o.05 (25C) - ~ 1.07 ~ 0 100 3019% isodecanol J J (40C~ <0.01 (25C) (a) K ~ (Cp)~/(Cp)w where Cp is the concentration of phenol in grams/cc in 0 (organic~ and W (waterj phases _ g _ r Solutions of phenols complexing agents suitable according to the invention as a solution sink or sweep material may be selected from those complexing agents which in solution form permit the total concentration of phenolic bodies to be greater on the permeate side than on the feed or permeant side of the membrane. Complexing agents such as the hydroxides of alkaline earth and alkali metals in solution readily form phenolates and provide a satisfactory solution sink. Various solution concentrations, for example, of sodium hydroxide, potassium hydroxide and the like may be utilized as a solution sink; however, it is essential that the solution sink be com-patible with the separation membrane and not cause swelling, rupture or other physical weakness over a use period, and not permeate the membrane significantly.
Phenols are defined for purposes of this disclosure as a class of aromatic organic compounds in which one or more ~ydroxy groups are attached directly to the benzene ring.
Examples include phenol, the cresols, cumyl phenol, nonyl phenol, xylenols, resorcinol, naphthols and the like as well as substituted phenols.
The aqueous feed stream may be continuously or inter-mittently introduced into the membrane feed zone. The perme-ated phenols are removed from the opposite side of the membrane~;
in a batch or continuous manner through the use of the various sweep forms, vapor, complexing solutions or solvent sinks.
The rate of introduction of the aqueous feed stream and the re-moval of the permeant fraction may be a~usted to provide the desired proportions of permeate and permeant fraction. A
number of permeation stages may be employed and the permeate and permeant ~ractions may be rec~cled to various stages. In each permeation zone the membrane may be used in the form of -- 10 -- .

~L058S2S

sheets, tubes, hollow ibers, or other structures which prefer-entially provide a maximum amount of membrane surface while utilizing a minimum volume of space.
The absolute pressure on the feed and the permeate zones may vary considerably. Negative and positive pressures of from a few mi~imeters of mercury to ashig~ as 35 to 70 kg/
cm2 or higher may be used according to the ~vention depending upon the strength of the membrane and the separation require-ment i. e. a vapor versus a liquid system or a com~ination liquid-vapor system. When the permeate zone is under the liquid phase conditions, pressure is generally not an important factor. However, when gas or vapor feed mixtures or pervapor-ation conditions are utilized, higher pressures on the feed zone can result in greater chemical potential and is desirable.
The membrane permeation step is preferably operated under conditions of temperature which can vary over a wide range from about 0C to about 150C or more depending upon the selection of the phenols permeate, solution sink, or pervapor-ization mode and the thermal condition of the a~ueous feed mixture~ ~igher operating temperatures are frequently desir-able because of the increased rates of permeation: however, the present invention is also concerned with energy input efficiency and minimum temperature change for the purpose of separating phenols from aqueous streams.
The permeation membran~ usedin the inventive process is non-porous, that is, free from holes and tears and the like, which destroy the continuity of the membrane surface. Useful membranes according to the invention are comprised of organic, polymeric materials. The membranes are preferably in as thin a form as possi~le which permits sufficient strength and stab-ility for use in the permeation process. Generally separation ~358525 membranes from about 2.54 x 10 to about .0381 cm or somewhat more are utilized according to the invention. High rates of permeation are obtained with thinner membranes which can be supported with structures such as fine mesh wire, screen, porous metals, porous polymers, and ceramic materials. The membrane may be a simple disc or sheet of the membrane sub-stance which is suitably mounted in a duct or pipe, or mounted in a plat~ and framed filter press. Other ~rms of membrane ; may also be employed such as hollow tubes and fibers through which or around which the feed is applied or is recirculated with the permeate being removed at the other side of the tube as a phenols~enriched sweep solution or complex. Various other useful shapes and sizes are readily adaptable to commer-cial installations. The membrane polymeric components may be - linear or crosslinked and vary over a wide range of molecular weight. The membrane, of course, must be insoluble in the aqueous feed mixture or the various sweep liquid solvents and/
or complexing agents. Membrane insolubility as used herein is taken to include that the membEane material is not substan-tially soluble or sufficiently weakened by i~s presence in thesweep solvent or aqueous feed stream to impart rubbery charac-teristics which can cause creep and rupturelunder the condi-tions of use, in~cluding high pressure. The organic membranes~
may be polymers which have been polymerized or treated so that various end groups are present in the polymeric ma~erials.
The membranes according to the inventive process may be pre-pared by any suitable feature such as, for example, the casting of film or spinning of hollow fibers from a "dope" containing organic polymer and solvent. Such preparations are well known in the art. An important control of the separation capacity of a particular organic membrane is exercised by the method -- .

- 12 - ~

~585;~

used to form and solidify the membrane, e, g. casting from a melt into controlled atmospheres or from so~ution at various concentrations and temperatures. The art of membrane use is known with substantial literature being available on membrane support, fluid flow and the like. The present inventlon is practices with such conventional apparatus. The membranQ must, of coursel be sufficiently thin' to permit permeation as desired but sufficiently thick so as not,to rupture under operating conditions. The memhrane according to'the invention must be selectively permeable to phenols in comparison to the other components of the a~ueous feed stream or take up solutions and complexing agents.
The following examples as listed in Table III illus-trate suitable membranes for the selective pervaporation of phenol from an aqueous feed stream wherein the ~henol repre-, sented 0.1% by weight of the stream. It should be noted that a separation factor (S. F.) as defined in Table III of less than 1.0 is representative of a membrane exhibiting selectivity for phenol over water.
The results of Examples 1 through 12 demonstrate that for the selective pervaporation of phenol from any aqueous streams containing 0.1~ by weight phenol amorphous aliphatic hydrocarbons are very selective for phenol. For example, the butadiene polym~,r beiny completely amorphous is very selective, and low density polyethylene is more selective than high density polyethylene with high crystalline polypropylene being least selective. The data of Table III is based on very specific conditions, thus variation of conditions such as temperature, downstream pressure and the~like c~uld modify the results of Examples 1 through 12. However, the cited membranes maintain a selectivity for phenol over a broad range o~ these variables.

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b. film~ ca. .00254 cm thick unless noted otherwise.
c. distribution coefficient between 1%
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-5~3525 Various membranes were utilized according to the in-vention under li~uid to liquid sepaxation conditions with a tributyl phosphate solution sink present on the downstream or second side of the membrane. Separation factor could not be measured since the tributyl phosphate solution sink was water saturated, thus no measurable water passed through the mem-branes. Examples 31 through 35 illustrate the use of diff-erent membranes under liquid to liquid solution sink condi-tions with results and conditions tabulated in Table VII below.
Li~uid-liquid permeation of phenol may be preferred to pervaporation because of the low-vapor pressure of phenol, depending on the specific operation conditions. Selective membrane separation of phenols from aqueous streams in combin-ation with a solution sink provides advantages over the direct contact liquid-liquid extractions in that the solvent is con-tained in the solut~on sink and emulsification is generally avoided. Six solvents suitable for use according to the invention as solution sink media were considered for phenols permeation separation and are present in Table VIII below.
ThP minimum value of the distribution coefficient~ K, for phenol between water and the solvents at 23~ is 10 and K
remains unchanged over the range of 1 to 7% phenol for all the solvents. K was calculated assuming (1) the volumes of the components were ideally additive, ~2) solubility of water in the solvents was negligible, (3) the density of tXe phenolic component trans~erred was unity, and (4) the solubility of solvent in water was so small that it could be neglected. The values of K are correct to better than + 5%.

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1~5~25 An industrial ~aste stream having the approximate composition:
~ by weight NaCl 9.3~
Water 85.5%
Esters 2.5%
Phenols 2~7~
was treated with concentrated, i. e. 37~ HCl until a solution pH of 4.2 was achieved. As the pH was lowered, phenolic derivatives separated out leaving a clear liquid. This clear liquid was used for the aqueous feed streams for Examples 36 through 42 as reported in Table IX belowO The aqueous ~eed stream provided on analysls the following approximate phenols proportions:
Parts per ~illion N-methylpyrrolidone420 Phenol 15,600 Cumylphenol 180 Nonylphenol 20 2Q Samples of the two phenols containing ~ees ~treams were adjusted to pH of 1 to 2 ~ith hydrochloric acid and allo~ed to settle. Permeations at 70C were carried out on both resulting clear supe~na~ent liquids using 30~ NaOH and 40% sodium phenate plus 10% NaOH as the solution sink.
Stream I contained phenol, cumylphenol and nonylphenol plus partial esters and salts. ~t,ream I~ contained phenol and butyl alcohol plus the partial esters and salts. .00254 cm low den-sity polyethylene was chosen as the membrane material.
~Xa~le 43 An aqueous ~eed strea~ containing 1.8 percent by weight phenols was treated accoxding to the above conditions ~ 23 -~ 8~25 .,, . _~ O ~ tD

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35;;~5 and the system was found to have a permeability (p)(a) of 8.8 x 10 8 cc - cm~sec-cm2. (~VF) The P was the same for both basic solvents and the feed pH was unchanged after 150 hours. At that time the phenol had been reduced from the initial value of 18,300 to 200-300 ppm and the nonyl and cumylphenol contents were less than l0 ppm.
A repeat run gave the same P (30% NaOH as the solvent). In each case the film was intact and no or neyligible solids were observed in the solutions at 70C.
(a) P in cc-cm~cm -sec-~F in the expression Rate - (P~ hVF) where ~ is the film thickness and ~VF is the "volume fraction difference"
which is used to represent the driving force.
All densities taken as unity~
Example 44 An aqueous feed stream conta~ning 0.75 percent by weight phenol was heated according to the above conditions and the system was found to have a permeability (p)~a) of 9.5 X 10 8 cc - cm/sec-cm . (~VF) There was no pH-change and the phenol had been reduced from 750n to 200 ppm after 150 hours. All solutions were crystal clear at 70C. The films were strong but slight pitting was observed for the 30% NaOH run and severepitting was observed for the phenate plus NaOH run. Apparently, that particular film was defective because a repeat run using fresh film for 120 hours with the "phenate plus NaOH" solvent did not show any indications of attack on the poly (ethylenei film. Also, film soaking in Stream II feed for 360 hours at 70C remained intact and showed no signs of pitting.
(a) P in cc-cm~cm -sec-~VF in the expression Rate = (P/~ VF) where ~ is the film thicknes~

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which is used to represent the driving force.
All densities taken as unity.
In Examples 45 through 57 as reported in Table X
below, variation as to membranes, feedstreams, and concentra-tions of sodium hydroxide in the complexing solution sink are demonstrated. The p~ of the aqueous phénolic feed streams was set at from about 2 to about 4 and remained unch~nged through-out the permeation periodsO The volume of the caustic stream remained unchanged, showing thatnegligible amounts of NaOH and water were permeated during the selective permeation of the phenols.
Several grades of polyethylene and one silicone carbonate separation membranes are presented according to the invention as Examples 58 through 63 in Table XI. The results as illustrated in Table XI demonstrate the suitability of poly-ethylen~ having a range of polymer characteristics.
Hollow fibers spun from low density polyethylene were utilized according to the invention for the selective liquia-liquid permeation of phenol. Examples 65 through 72 as presented in Table XII illustrate and compare the use of flat films and hollow fibers of two low density polyethylene polymers. Examples 64 through 72 utilized a feed stream com-prised of a 3% by weight phenol, 97~ by weight water at 70~C
and a solution sink of a 40% solution of sodium hydroxide.
The results as reported in Table XII clearly demonstrate that a selective membrane can be utilized in any physical configur-ation, such as a hollow fiber.

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(a) A is Plant Stream #2 ~757376-2? pH = 4-5 N-methylpyrrolidone 450 ppm phenol (P) 15,250 ppm nonylphenol (NP~ 20 ppm cumylphenol (CP) 132 ppm B has nominally 10,000 ppm phenol pH = 3; synthetic mixture.
C has 9730 ppm P, 36 ppm CP, 2 ppm NP; pH = 3-4;
synthetic mixture, D has 1019 ppm P, 15 ppm CP, ~ 0 ppm NP; pH = 3-4;
sy-nthetic mixture.
(b) bVF is driving force as volume fraction difference in the equation: rate of transfer of a species = P/~ (~VF) where æ = thickness. At 70C, unless otherwise indicated, with all densities taken as unity.
(c) NaO0 i5 sodium phenate.
~d) Film split.

TABLE XI
LiquidjL~quid Permeàtion of i% Phenol/Water Streams(a) . ~. ..
Examples Resin Melt Density p(c) at (~C~
Index for 1% Phenol~
,.
58 Rexene PE-126* 30 ~.~24 2.0 x 10 B (70C) 59 Rexene PE-127* 55 0.024 3.2 x 10 B (70C) Petrothene NA-224* 0.6 0.919 5.0 x 10 ~(70C) 61 Alathon 20* 1.90.920 3.6 x 10 ~70C) 62 Alathon 2560~ 2.650.920 1 x 10 ~(70C) 63 G. E.- Silicone _ _ 1 5 x 10 (Z2C) Carbonate - MEM 213 Notes:
(a) All feeds about 1% phenol in water, pH adjusted to one.
Fluid on downstream side of membrane was always 10% NaOH.
(b) First five films are various ~rades of poly(ethylene).
Films made by pressing pellets in a 15.24 cm Carver press at 150 to 170C and cooling rapidly with tap water.
(c) P calculated from the expression Rate = P, bVF where Rate is in cc/cm2-sec, P is in cc-cm/cm2-sec-bVF, ~ is film thick-ness in centimeters and ~VF is the concentration differ-rence across the film in units of volume fraction. All densities assumed to be unity.

*_Txade Maxk TAB E XII
Results on Polyethylene Hollow Fibers for Phenol/Water Separation by Liquid-Liquid Separation ExamplePolyethylene Membrane OD/ID 10 p : Sample Form microns 64 P 126 film -- 2.0 P 126 fiber 0.38 66 P 126 fiber 109/62 1.0 67 P 127 film -- 3.2 68 P 127 fiber 85/55 0.12 69 P 127 fiber 110/66 2.1 P 127 fiber 105/62 1.0 71 P 127 fiber 0.23 72 P 127 fiber 0.65 (a) Melt Index of P 126 = 30; Melt Index of P 127 = 5S
(b) P is the intrinsic permeability coefficient which, if calculated assuming isotropic structure, should be : independent o~ membrane thickness and geometrical shape.
The defining relationships are:
for films and fibers: J = P ~v A
where J is flux of phenol in g/cm2.-sec and hv is .
volume fraction of phenol (equal to weight fraction when density is unity) driving force.
for films: P = PA 1 where 1 is membrane thickness for fibers: P = (PA/2)/(IDj ~n(OD/ID) where PA is expressed on the ID area basis for fiber, and ln i~ logarithm to the base e.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for separating phenols from aqueous solutions, characterized by contacting a phenols-containing aqueous solution of less than 9 weight percent phenols with a first surface of an organic polymeric mem-brane selectively permeable to phenols;
maintaining a second and opposite membrane surface at a lower chemical potential than the first membrane surface by contacting the second membrane surface with a solution sink;
permeating a portion of the phenols into and through the membrane into the solution sink;
and withdrawing at the second membrane surface a solution having a higher concentration of phenols than the phenols concentration in the aqueous solution.

2. The process of Claim 2 characterized in that the polymeric membrane is low density polyethylene having a density of 0.91 to 0.925 grams per cubic centimeter.

3. The process of Claim 1 characterized in that the aqueous solution is comprised of from 10 parts per million to 3 weight percent phenols and the polymeric membrane is selected from the groups consisting of polypropylene, poly-ethylene, copolymer of ethylene and acrylic acid, ethylene-trimethyl vinyl ammonium chloride copolymer, polybutadiene, polysilicone carbonate, methyl silicone resin, polyvinyl-fluoride, nylon 66, nylon 12 and polyurethane.

4. The process of Claim 1 characterized in that the aqueous solution is comprised of from 10 parts per million to 0.1 weight percent phenols and the polymeric membrane is selected from the group consisting of methyl-phenyl silicone resin, nylon 6, nylon 6-nylon 9 blend, nylon 6-nylon 10 blend, nylon 11, polypropylene, polyethylene, copolymer of ethylene and acrylic acid, ethylene-trimethyl vinyl ammonium chloride copolymer, polybutadiene, polysilicone carbonate, methyl silicone resin, polyvinylfluoride. nylon 66, nylon 12 and polyurethane.

5. The process of Claim 1 characterized in that the solution sink is comprised of a phenols solvent.

6. The process of Claim 5 characterized in that the solvent is at least one of nonylphenyl cumylphenyl diphenyl phosphate, mixture of alkyl phthalates having from seven to eleven carbons per molecule, butyl benzyl phthalate, mixture of nonylphenyl cumylphenyl diphenyl phosphate and triphenyl phosphate, benzene, toluene, nitrobenzene n-butyl acetate, dimethyl phthalate, dibutyl maleate, dibutyl fumarate, tributyl phosphate, dibutyl phenyl phosphate, methyl diphenyl phosphate, 2-ethyl mexanol, 1-methylnaphthalene, diphenyl ether, triiso-propyl-benzene, N, N-diethylaniline, m-chloroaniline, isodecanol, benzyl alcohol, monodecylamine, and o-chloronitrobenzene.

7. The process of Claim 1 characterized in that the solu-tion sink is comprised of a phenols complexing solution having total concentrations of phenolic bodies which permit a lower chemical potential on the second membrane surface than on the first membrane surface.

8. The process of Claim 7 characterized in that the com-plexing solution is comprised of the hydroxides of at least one of lithium, sodium, potassium, ribidium, and cesium.

31 g. The process of Claim 1 characterized in that the pH
of the phenols-containing solution is lowered to a pH of 1 to 6 before contacting with the membrane.

10. The process of Claim 5 characterized in that the organic polymeric membrane selectively permeable to phenols is selected from the group consisting of polyethylene, nylon 12, polyethylene sulfide, polybutadiene, polyvinyl fluoride, natural gum rubber, ethylene-vinyl acetate copolymer, ethy-lene-tetra-fluoroethylene copolymer, polypropylene, polyiso-prene, chloro-trifluoro-ethylene-vinylidene fluoride copoly-mers, vinylidene fluoride-tetrafluoroethylene copolymers and urethane resins.

11. A process of Claim 7 characterized in that the organic polymeric membrane selectively permeable to phenols is selected from the group consisting of polyethylene, nylon

12, polyethylene sulfide, polybutadiene, polyvinyl fluoride, natural gum rubber, ethylene-vinyl acetate copolymer, ethyl-ene-tetrafluoroethylene copolymer, polypropylene, polyiso-prene chlorotrifluoroethylene-vinylidene fluoride copolymers, vinylidene fluoridetetrafluoroethylene copolymers and urethane resins.