CA1312550C - Pervaporation of phenols - Google Patents

Abstract

Abstract of the Disclosure Aqueous phenolic solutions are separated by pervaporation to yield a phenol-depleted retentate and a phenol-enriched permeate. The separation effect is enhanced by phase segregation into two immiscible phases, "phenol in water" (approximately 10% phenol), and "water in phenol" (approximately 70% phenol). Membranes capable of enriching phenols by pervaporation include anion exchange membranes and block copolymers of either polyether polyamide or diol terephthalate polyether diol membrane selection and process design is guided by pervaporation performance and chemical stability towards phenolic solutions. Single- and multiple-state processes are disclosed, both for the enrichment of phenols and for purification of water from phenolic contamination.

Description

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PERVAPORATION OF PHENOLS

Backqround of the Invention Phenol-contaminated water as a by-product of various chemical proce~seq i~ a recognized industrial problem, both in term~ of water toxicity and recovery phenol3. ~ to toxlcity~ it i~ known that ph~nol~ are ~oxic to ~l~h ~t: conc~ntra~lon~ a~ low ~ 0.1 ppmt whil~
at 0.01 ppm, an extremcly disagreeable t~ste ls imparted to water treated by hypochlorite to render it potable, owing to the formation of chlorophenols. Residual phenol concentrations from such source~ a~ ga~works, coking plant~, refineries, coal processing plant~, tar processing plants, pesticide plant~, phenol conver~ion plant~, and phenoplast plastics material~ plant~ vary from a few ppm to a~ high a~ 10~.
Known processes for the purification of pheno-lated water are few, and may be broadly characterized a~
falling into one of two categorie~: (1) recovery pro-ces~e3, or (2) chemical/biological destruction proce~se~.
In the first category, there are included processes such a~ liquid-liquid solvent extraction (see, for example, U.SO Patent No. 3,673,070), steam di~t~llation, absorp-tion on activated charcoal or ion-exchange resins, and foaming with surfactants. In the second category are included processes such a~ treatment by activitated ~3~

sludges and bacterial bed~, oxidation by o~one, per-manganate, chlorine, catalyzed hydrogen peroxide, and electrolysis (see U.S. Patent No. 3,730,864). Another process not falling into either category is that dis-closed in U.S. Patent No. 3,931,000, comprising passing an aqueous polysubstituted phenolic feed stream around the outside of a bundle of hollow fibers while passing sodium hydroxide solution into the hollow fibers, the phenols passing through the fibers to form insoluble sodium phenate salts which concentrate inside the hollow fiber membrane, and are ~wept out o the ~yatem wlth tlle qoclium hydroxldo ~lolution ~tream.
~ low~v~r~ none Oe tho above proce~se~ have been totally effective, leaving a significant residual phenol content, and all suffer from various serious drawbacks, such as strict monitoring of the content and pH of the feed stream in the case of bacterial bed treatment, regeneration of absorbents, high cost of reactant~ in the case of oxidation treatment, and production of unde-~irable by-products (chlorophenols) in the case of chlorination treatment.
Use of membranes for pervaporation ha~ been limited. The only known commercially useful pervapora-tion membrane is one for dehydrating ethanol and propanol which comprises a composite of polyvinyl alco-hol on a porou~ support of polyacrylonitrile. See 53 Desalination 327 (1985). Ion-exchange membrane3 have _ been investigated as to pervaporation e~fects on aqueous ethanol and lower carboxylic acid mixtures, with the water having pervaporated preferentially. Boddeker, !

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Proc. 1st Int. Symp. Pervapo_ation ~Feb. 1986). And ~ilicone rubber membranes have been used for the selec-tive pervaporation of halogenated hydrocarbons and butanol from aqueous ~olutions thereof. See 8 J. Membr.
Sci 177 (1983). However, none of these membrane~ have been incorporated into a pervaporation process that is technically feasible.
It i8 therefore a principal objective of the present invention to provide a ~imple, hi~hly efficient, and inexpenlive method o~ purl~yin~ phenol-contamlnated water.
It .L~ qually .tmportant ob~ect.tva o~ tha present invention to provide a simple, highly efficient and inexpensive method of recovering phenols from aqueous phenolic solutions.
These and other objects that will become apparent are achieved by the method of the present invention, which is summarized and described in detail below.
~0 Summary of the Invention The present invention is based on the discovery that certain cla~ses of nonporous polymeric membranes, when used in a pervaporation mode, will selectively transport and thereby enrich the phenols content in the permeate of the process. This selective permeation of phenols is unexpected in view of the much lower volatility of phenols relative to that of water, baqed upon which one would predict precieely the oppo3ite ~3~2~

order of transport. An integral part of the invention lies in the related discovery that the phenolic enrich-ment factor strongly increases with decreasing phenolic - concentration of the feed stream, thus permitting a pro-cess by which, through a limited number of consecutive pervaporation steps, the phenolic content of the per-meate can be raised to a concentration at which natural phase separation spontaneously occurs. Still another unique aspect of the present invention iq the di~covery that, with increa~ing feed concentration~ the phenolic enrichment ~ctor remain~ relatively con~tant an(l~ In Aome ca~3a~ actual.ly incr~a~eA~
The present invention accordingly comprisQs a single-or multiple-step method for both ridding water of phenolic contaminants and recovering phenols of rela-tively high concentration. The method includes two distinct steps: (1) a pervaporation step, followed by (2) a phase separation step.
The pervaporation step essentially comprises contacting the feed side of a nonporous polymeric membrane having certain characteristics detailed below with an a~ueous phenol-containing feed stream while maintaining on the permeate side of the membrane either a sweep stream or a coarse vacuum, whereupon phenols in the feed stream preferentially diffuse through the mem-brane to form a phenol-rich permeate comprising phenols and water in a vapor state and leaving a phenol-depleted water retentate on the feed side of the membrane.

~3~5~

The phase separation step essentially comprises condensing the pervaporated phenol-rich per-meate of a certain concentration, that concentration exceeding the concentration at which spontaneous phase separation occurs into an upper phenol-poor fraction and a lower phenol-rich fraction.
A }arge number of variations of the pervapora-tion step and the phase separation step and combinations of the two steps are feasible by combining and recycling permeate~, retentates and separated fraction~ a9 feed~
and by con~ecutlv~ pervaporatlon ~eps~ thu~ permitting custom-mado ~ppllc~tlon~ Oe th~ method to achl~vo a deslred degree oE puriflcation of water or concentration of phenols. And, as one skilled in the art will readily appreciate, the present invention may be utilized in connection with other known phenol separation methods.

Brief Descri~tion of the Drawings FIGS. 1-5 comprise schematic flow diagrams of exemplary applications of the present invention.
FIGS. 6-8 comprise graphs showing the per-vaporation performance of three exemplary membranes of the present invention.

Detailed Description of the Invention According to the present invention, there is provided a simple, efficient and inexpensive method for the recovery of both phenols and phenol-purified water from phenol-contaminated water, the method comprising a ~.3~2~

single- or multiple-step pervaporation separation or a combination of pervaporation separation and phase separation steps.
The pervaporation step comprises contacting the feed side of a nonporou~ polymeric membrane having a feed side and a permeate side with an aqueous phenol-containing feed ~tream, said membrane not being degraded by phenols and selected from the group consisting essen-tially of elastomeric polymers and anion exchange poly-mers, and maintaining on the permeate side o~ saidmombrane either an inert ga~ sweep strRam or a prea~ur~
oE 10 mm~lg or l~a~ wh~r~y ph~nol~ in ~id ~ r~am sel~ctively diEfusc through ~id membrane to Eorm a phenol-rich permeate comprising phenol and water in a vapor state on the permeate side of said membrane, and leaving a phenol-depleted water retentate on the feed side of said membrane, followed by recovery of the phenol-depleted water retentate.
The phase separation step may be utilized when the phenolic concentration in the permeate has exceeded a threshold concentration (about 10% by weight, depend-ing upon the temperature of the condensate) at which spontaneous phase separation of the condensed permeate occurs into a phenol-poor fraction (also about 10% by weight phenol) and a phenol rich fraction (about 70% by weight phenol). The "phenol-poor" fraction is often also referred to as "phenol in water, n while the "phenol-rich" fraction is also referred to as "water in phenol."

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The terms "phenol," "phenols," and "phenolic"
are intended to include phenol, pyrocatechol, resorci-nol, hydroquinone, naphthols, as well as substituted phenols such as phlorol, cresols, and xyIenol~
sy "nonporous" membranes is meant membranes capable of separations that are best described by the solution-diffu~ion model, the class of membranes generally comprehending tho~e with no discernable pore~
having a dlameter greater than 5 Angstroms~ Membl-anes usable ln the prqclenk invenkion m~y no~ bo ~u3copl:ibl~
~o deg~adakiol~ by phnnol~ in ~ny concentration ~or obviou~ rea~on~ Clas3~s o~ Qlastomeric polymer~
include silicone rubbers, polyesters, polyurethanes, and soft segment copolymers containing flexible groupings such as chains of rigid polyamide with flexible poly-ether segments. Preferred examples of such elastomeric polymers are a silicone-polycarbonate copolymer made by General Electric Co. of Schenectedy, New York and sold under the trade name "MEM-213,*" a polyether-polyamide block copolymer made by Atochem S.A. of Paris, France, and sold under the trade name "Pebax 5533,*" a polyester base polyurethane made by Lord Corporation of Erie, Pennsylvania, and sold under the trade name "Tuftane TF-312," a polyether base polyurethane also made by Lord Corporation and ~old under the trade name "Tuftane TF-410," and a diol terephthalate-polyether diol terephthalate block copolymer made by DuPont Company of Wilmington, Delaware and 301d under the trade name *

"Hytrel 5556."

* Trade-marks 3L3~255~

Anion exchange polymers include virtually any polymer containing in 30me fashion the well-known anion exchange functionality of a quaternized ammonium group, as well as weak base anion exchange of the tertiary amine types. Preferred example~ are a ~erie~ of polymer films containing quaternized vinylbenzylamine groups grafted onto polyethylene or polytetrafluoroethylene made by RAI Research Corporation and sold under the trade name "Raipore,*" includin~ "Raipore R-1035, n "Ralpore R-4035~l "Raipore R-5035~" and "Ralpore R-S035~1 ~k~
Membrarlo~ useful in the presQnt inventlon may be either flat or tubular, such as tubular membranes and hollow fibers, including asymmetric membrane~. In the lS case of flat sheets, the dry thickness of the membranes may vary from 2 to 200 micrometers~ 5-S0 micrometers being preferred, the e~sentlal criterion being that the membrane withstand the low pre~sure applied to it on the perm~ate side of the membrane. Incorporation into pervaporation modules or series of modules comprises a convenient way of using membranes in the method of the present invention. In the case of hollow ~ibers, incor-poration into modules by potted bundles i9 the preferred form of use, in the same fashion as such fibers are used in the reverse osmosis art. Hollow fibers are best used with a lumen-side feed.
The proces~ of the present invention may be used on aqueous solutions of phenols having virtually any phenolic concentration from a few ppm up to about * Trade-marks ~L3~2~

10~ by weight* (all concentrations hereafter, when specified a~ a percentage, refer to percent by weight).
Under pervaporation conditions, the membrane is in a state of extreme anisotropic swellinl~, ranging from fully swollen near the feed ~ide to near dryness at the permeate side, resulting in an extremely steep concen-tration profile within the membrane from very high at the feed side to very low at the permeate side.
Subject to the stability of the membranes, the aqueou~ phenollc feed solution may be at temperatures rangin~ anywhore ~rom ~lbout 20C up to the boiltn~
pOillt oE w~ter~ htly ~lovnt~d t~mpera~ureY Oe 4so to 90C being preferred. The process of the present inven-tion is therefore highly efficient, allowing the use of low-grade, waste-type heat (temperatures of less than 100C) to be utilized to produce a relatively high grade product. The linear crossflow velocity of the feed may range from 10 to 100 cm/sec. When a sweep stream is used on the permeate side of the membrane, the gas should be both inert to phenols and water and noncon-densableO Examples include air, nitrogen, argon and helium. When a vacuum is maintained on the permeate side, it should be les~ than 10 mmHg. It should be noted that, in the process of the present invention, the downstream or permeate side pressure is entirely independent of the feed side pressure.

_ *The concentration above which, at 40C or below, spontaneous phase separation occurs~

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Conden~ation of the vaporized permeate emerging from the permeate ~ide of the membrane may be accomplished by any number of known method~, including collection on a cold surface such as in a cold trap, or ~ubjecting the same to elevated pressurs.
Referring now to the drawings, FIG. 1 comprise~ a schematic diagram illustrating both the pervaporation step and the pha~e separation qtep of the present invention, having the objectives of (a) removal o~ phenol~ from wa~te water or proce3s water to produce wat~r me~ting ~A~e dl~po~al or reu~e purlt~ reqllir~mon~7 and tb) cnrichm~nk an~ rocovery oE phenol to a "w~lter in phenol" solution comprising roughly 70~ phenol and 30%
water. As shown therein, the aqueous phenolic feed solution is directed to the feed side of a nonporous polymeric membrane of the type described herein, repre-sented by the diagonal line in the "Pervaporation" box.
An inert gas sweep stream or coar~e vacuum of 10 mmHg or les3 is maintained on the downstream or permeate side of the membrane, causing permeation or diffusion of the liquid phase feed stream from the feed side of the mem-brane to the permeate side of the membrane, the phenols in the feed being transported in preference to water, 30 as to form a phenol-enriched vaporized permeate on the permeate side of the membrane, and leaving on the feed 3ide of the membrane a phenol-depleted liquid retentate, or phenol-purified water, the degree of purification depending upon the particular separation characteristic~
of the membrane used, the membrane surface area, and the --10-- , ~L 3 ~

duration of contact of the feed with the membrane~ The vaporized permeate is continually condensed in, for example, a cold trap (not shown) into a phenol-enrichsd aqueous liquid. When the concentration of phenols in the permeate is about 10%, upon condensation of the permeate, separation into two immiscible phases spon-taneously occurs, shown schematically by the dashed horizontal line in the 'IPhase Separation~ box of FIG. 1, into an upper phenol-poor or "phenol in water" pha~e comprising about 10~ phenol and ~0% water, and a lower phenol-rich or "wa~er in phenol" pha~e compri~ing about 70~ ptlenol and 3Q~ w~to~ Tlle lower ph~3e may bQ
withdrawn from the procQs~, representing recovery of a highly concentrated aqueous phenolic solution.
FIG. 2 schematically illu~trates a multi~stage arrangement of pervaporation modules, allowing repeated processing of the permeate resulting from each pervapo-ration step wherein the condensed permeate of a given stage con3titutes the feed of the next ~tage. As ~hown in FIG. 2, the resulting retentate of each stage may be combined to produce a single retentate exiting the pro-cess stream and recoverable as phenol-depleted water, while a single phenol-enriched permeate, that of the last stage, is produced.
FIG. 3 shows a serial arrangement of pervapo-ration modules, which, for the sake of simplicity in illustration, represents two pervaporation steps, wherein the retentate of a first pervaporation step ~C~2~5~

serve~ as the feed of a ~econd pervaporation step and the downstream second permeate is recycled as part of the feed to the first pervaporation ~tepO A~ may be readily seen, such a serial arrangement need not be limited to two pervaporation modules.
FIG. 4 illustrate~ another important advantage of the method of the present invention, combining per-vaporation and phase ~eparation, wherein the phenol-poor (or "phenol in water") fraction from a first phase ~epa-ration step comprises the f~ed to a second se~uel ofpervaporation and pha~ ~eparation ~tep~. In thi~
~cheme~ the "phonol in wa~r" eraction rQsul~ing ~rom a combination of pervaporation and phase separation steps such as shown in FIG. 1 comprises the "phenol in water"
feed having a phenolic concentration of about 10%, this "phenol in water'l feed being pervaporated to yield a phenol-enriched permeate which, upon condensation and upon reaching a phenol concentration of about 10~, undergoes spontaneous phase separation into an upper phenol-poor (or "phenol In water") fraction comprising about a 10~ aqueous phenolic solutiQn, and a lower phenol-rich (or "water in phenol") fraction. The "phenol in water" fraction, being identical in com-position to the feed of the pervaporation step shown at the left hand ~ide of FIGr 4, may be recycled to that ~ame feed.
Simultaneously with the production of the phenol-enriched permeate, the pervaporation ~tep shown in FIG~ 4 leaves a phenol-depleted retentate which, due ~2~

to its relatively low phenol concentration, i~ suited to be recycled as feed to the initial pervaporation ~tage, as shown in FIG. 5, FIG. 5 essentially comprising the combination of the ~cheme shown in FIG. 1 with that shown in FIG. 4.
As mentioned above, the process of the present invention, by virtue of the large number of permutation~
of steps available, may be used to tailor a predeter-mined degree oP either phenol-purified water or phenolic values. 0~ course, the ~electivity and Elux clensity o~
th~ mombrall~ chosen al~o con~ikut~ ~actor~ in:eluoncin~
the degre~ oE ~eparatlon achieved~
As is the case wlth membrane separations in general, selectivity and flux in the membrane per-vaporation separation of the present invention haveopposite tendencies, the greatest phenolic enrichment being generally ob~erved at the lowest flux density.
For convenience herein, the selectivity of a giverl membrane iq expressed as an "enrichment Eactor," that factor comprising the ratio oE phenolic concentration in the permeate to phenolic concentration in the feedr The elastomeric polymeric membranes useful in the present invention generally exhibit a moderately increasing enrichment at high phenol concentration, followed by a ~ignificant increase in enrichment with a low residual phenol concentration, while flux density remains nearly independent of phenol concentration, declining ~lightly a~ phenolic depletion progre~ses.

The anion exchange membranes u~eful in the present invention behave differently than the elasto-meric membranes in that enrichment i~3 generally lower and flux density generally higher than with the elasto-meric membranes. Both phenol enrichment and fluxdensity increase at low phenolic concentrations in the feed. But, when viewed as a function of the total con-centration range entailed, the enrichment factor passes through a minimum, whereas the flux denqity ~teadily increases with phenol depletion of the feed~
In general, an increase of the temperature at which porvaporation 1~ ~on~lc~ed ha~ the a~ect o~
lowerirlg the enrichlnont Eacto~ and increa~ing ~lux density. Flux density is inver~ely proportional to membrane thickne~s, while thickness appears to have no impact on enrichment capability. Suitable phenol depletion in a single stage pervaporation step may be accomplished by highly selective membranes, wherea~ a multi-stage pervaporation process i9 required to achieve the same degree of phenol depletion with a le8s selec-tive, more permeable membrane. In a multi-stage per-vaporation process, each pervaporation ~tage is designed to produce a retentate of a targeted residual phenol concentration high yield of phenol-depleted retentate.
Example 1 Aqueous phenolic feed solutlons comprising 200 ppm of each of phenol (b.p. 181C), phlorol ~b.p.
196C) and xylenol (b.p. 212C), for a combined total phenolic concentration of 600 ppm was fed at lo 2 L/min 13~2~

and 50C for about 2 hours via a rotary feed pump with a flowmeter through two pervaporation cells in parallel, the functional part of each cell comprising the non-porou~ polymeric membranes noted in Table 1~ each S membrane having a surface area of 45.5 cm2, and a dry thicknes~ varying from 1 to 2 mils. The downstream or permeate ~ide of each cell was connected via cold traps to a vacuum pump which maintained a pressure of 5-10 mmHg on that 3ide of the cell, the cold trap~ being immersed in liquid nitrogen to effect condensation of the permeate. Down~tream pr~ure wa9 monitored by a mercury manomotor ln clo~ proximity to the down~t:re~m ~ide oE the pervaporaton cell. Analysis for phenolic enrichment was by both high pressure liquid chroma-tography and by ultraviolet spectroscopy. The resultsare shown in Table 1, the enrichment factors being expres~ed as noted above, and flux density being expressed in kg/m2-day.

Table 1 Enrichment Flux Membrane Factor Density Hytrel 5556 24 4.9 MEM-213 60 5.5 Pebax 5533 150 5.2 Tuftane TF 312 14 2.8 Tuftane TF 410 30 3.8 Raipore R-1035 3 68 Raipore R-4035 6 18 Raipore R-5035L 3 32 Raipore R-5035H 5 13 13~2~

Example 2 Three of the membranes of Example l were evaluated assuming two pervaporation cell3 in ~erie3, as schematically shown in FIG. 3, and further as~uming the continuation of pervaporation in discrete step~ of increasing phenolic concentration of the feed just until spontaneous phase separation of the condensed permeate took place, the qeparation being one of an upper phenol-poor pha~e ("phenol in water") comprising about 10%
phenol in waker and a lower phenol-rich pha~a ("water in phonol") comprl~ing about 70~ phenol ln WatQr~ Th~
re~ult~ ar~ shown in Table 2~ with fe~d conc~ntration being given in ppm phenols.
Table 2 Feed Concentration Enrichment Factor Membrane Yielding Pha~e Sep'n at Phase Se~'n Pebax 5533 1,700 57 MEM-213 3,200 31 Raipore ~-~035 11,500 8.5 Example 3 The ~ame three membranes of Example 2 were used in a single pervaporation ~tage to determine the relation~hip between the concentration of phenolics in the feed and enrichment and flux den3ity. The values obtained were plotted in the graph~ comprising FIGS. 6-8.
As 3een in FIGS. 6 and 7, the two ela~tomeric membranes show a fairly ~imilar pattern of enrichment and flux with progres3ing phenol depletion of the feed, ~2~

i.e., there was a moderately increasing enrichment at high phenol concentration in the feecl, followed by a marked increa~e in enrichment toward low residual phenol concentration, while flux density remained nearly inde-pendent of phenol concentration in the feed, slightlydeclining as phenol depletion progre~lsed.
As seen in FIG. 8, the anion exchange membrane exhibited a generally lower enrichment and higher flux than the elastomeric membrane~. Both enrichment and ~lux incr~ed with decrea~ing eced concantr~tion~
~nrichm~nt paa~ g khrou~h a minimum, whlle ~lux stQadily increa~ed.
Example 4 U~ing the data of Example 3, single-stage pervaporation of aqueous phenolic feea ~olutions with initial concentrationq of 5000 ppm, 1000 ppm and 200 ppm were evaluated assuming an elastomeric nonporous poly-meric membrane ~Pebax 5533) and the ~ame apparatus a~
that of Example 1 for examination of the pattern of phenol depletion. The result~ are ~hown in Table 4, with all concentration3 in ppm (mg/kg), the membrane area in m2/1000 kg-day, and ~howing the fraction of feed recovered as phenol-depleted retentate ~% Feed in Retentate). As is apparent from Table 4, phenol deple-tion i~ readily accompli~hed in a ~ingle ~tage.

~.3~2~

Table 4 Feed RetentateMembrane ~ Feed in Conc. Conc~ Area Retentate 5000 0.1 49 89 1000 0.1 36 92 200 10 1~ 97 200 0.1 26 9S

Example 5 Multi-stage pervaporation of feed solution~
having the same concentrations as those of Example 4 was : evaluated as~uming an anion exchange membrane of the pre~ent invention (Raipore R-4035) in a series arrange-ment of the type depicted in FIG. 2. Each stage wa~
de~gned to produce a retentate having the targeted re~idual phenol concentration~ of 10 ppm and 1 ppm. The results are shown in Table 5, the units of which are the same as for Table 4 except that the membrane area given comprises the combined areas of the membrane~ for each . . . . .
~tage of pervaporation nece~ary to achieve the phenol depletion shown.

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Table_5 Feed Retentate Membrane ~ Feed in Number of Co Conc. Area Retentate Stages Required ~ Slmult,lnQou~ anrlchmQnt oE ph~nol to ~ per-meate concentration of 10~ (lOO,Q00 ppm), so as to cause phase separation as discussed above, and depletion of phenol from a water fraction was evaluated on feed solution~ having the same concentrations a~ those of Example 4 by an arrangement of the type shown in FIG. 3 assuming an elastomeric nonporous polymeric membrane (Pebax 5533)~ Membrane areas ~or the two modules are given separately in Table 6 in the same unit~ as in Table 4. By recycling the phenol-enriched down~tream permeate (permeate 2) to the feed stream, the phenol concentration o~ the feed is increased such that single-stage pervaporation yielded the targeted 10% phenolic concentration. Thus, as seen in Table 6, the fraction of the total membrane area required to deliver permeate for recycling increa~ed as the initial feed con-centration decreased.

~311 2~

Table 6 Feed Retentate Permeate Membrane Area % Feed in Conc. Conc. Conc. _odule 1 Module 2 Retentate 5000 10 100,000 18 20 95 55000 1 100,000 18 26 95 5000 0.1 100,000 18 27 95 1000 10 100,000 4 2~ 99 1000 1 100,000 4 37 99 1000 0.1 100,000 ~ 4~ 99 10200 10 100,000 0.7 31 99 ' 200 1 100~000 0.7 3~ 9 200 0.1 100,000 0.7 50 99 Example 7 Using actual data obtained in the previous example3, an idealized process scheme of the type illustrated in FIG. 5 utilizing both elastomeric and anion exchange-type membranes of the present invention was evaluated. An elastomeric-type membrane with high qelectivity is used in a flrst pervaporation stage on a dilute feed solution, while an anion exchange-type membrane with moderate selectivity is used in a second pervaporation stage to treat the "phenol in water" solu-tion comprising the supernatant of the spontaneous phase separation occurring in the first phase separation step.
Since thi~ "phenol in water" solution is to be subjected to a second pervaporation stage as shown in FIG. 5, phenol enrichment of the first pervaporation stage may be limited to the concentration level of "phenol in ~3~2~

water" (about 10~ phenol), implying that very litle "water in phenol" is being produced at this first per-vaporation stage. Given appropriate procesq control, the first phase separation step may be eliminated alto-S gether, feeding the condensed first qtage permeate of "phenol in waterN concentration directly into the ~econd pervaporation stageO As would be expected given the low initial phenol concentrations considered, the fraction of the feed appearing as phenol-enriched permeate, to be processed in the ~econd pervaporation ~tage~ mall.
~ed on the ~eparation charactoris~ic o tha anion exchange m~mbrane Ralpore ~-~035~ the ~ollowln~ ma~
balance for the ~econd stage pervaporation is obtained:
Pervaporation of 100 kg of "phenol in water"
lS (10% phenol) at 50C yields - 16 kg of permeate (60% phenol) - 84 kg of retentate (0.5% phenol) The retentate is recycled into the original feed stream and thus remains in the proceq9. The permeate undergoes phase separation as follows:
Pha~e separation of 16 kg of the above permeate (60% phenol) yields - 13.3 kg of "water in phenol" (70% phenol~
- 2.7 kg of "phenol in water" (10~ phenol) The "phenol in water" fraction is recycled to the second pervaporation ~tep, as shown in FIG. 5. The "water in æhenol" fraction, combined with the corresponding frac-tion of the first phase separation step, is con~idered to be the phenol-enriched product of the overall separation process.

The overall enrichment of phenol in the pro-ces~ envisioned depends solely on the initial phenol concentration of the feed stream, the exit concentration of the phenol-enriched process stream being fixed by the nature of the immi~cible water-phenol phases. The over-all enrichment realized by such a process i3 illustrated by the figure~ in Table 7, concentration again being given in ppm phenol.

Table 7 Initial Overal.l Feed Concenkration~nrichmenk Factor 200 3~S00 1,000 700 2,000 350 155,000 140 lOO,000 (10%) 7 The term.s and expressions which have been employed in the foregoing specification are used therein a~ terms of description and not of limitation, and there is no intention, in the use of such terms and expres-sions, of excluding equivalents of the features shownand described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.

Claims (13)

1. A method of separating phenol-depleted and phenol-enriched water from aqueous phenolic solutions characterized by the pervaporation step of (a) contacting the feed side of a nonporous polymeric membrane having a feed side and a permeate side with an aqueous phenol-containing feed stream, said membrane not being degraded by phenols and selected from the group consisting essentially of anion exchange polymers and block copolymers of either polyether-polyamide or diol terephthalate-polyether diol, and (b) maintaining on the permeate side of said membrane either an inert gas sweep stream or a pressure of .10 mmHg or less, whereby phenols in said feed stream preferentially permeate said membrane to form a phenol-enriched permeate comprising vaporized phenol and water on the permeate side of said membrane, and leaving a phenol-depleted water retentate on the feed side of said membrane.

2. The method of claim 1 further including subjecting said phenol-depleted water retentate to at least one additional pervaporation step.

3. The method of claim 1 combined with a phase separation step, said phase separation step comprising condensing said permeate at a concentration at which spontaneous phase separation of said condensed permeate occurs into a phenol-poor fraction and a phenol-rich fraction.

4. The method of claim 1, including recovering either or both of said phenol-depleted retentate and said phenol-enriched permeate.

5. The method of claim 5 wherein said phenol-enriched permeate is condensed.

6. The method of claim 5 combined with at least one phase separation step, said phase separation step comprising condensing said permeate at a phenol concentration at which spontaneous phase separation of said condensed permeate occurs into a phenol-poor frac-tion and a phenol-rich fraction, and recovering said phenol-rich fraction.

7. The method of claim 4 further including subjecting said phenol-enriched permeate to at least one additional pervaporation step.

8. The method of claim 7 including combining the resulting phenol-depleted retentates.

9. The method of claim 1 combined with the phase separation step of condensing said permeate at a phenol concentration at which spontaneous phase separation of said condensed permeate occurs into a phenol-poor fraction and a phenol-rich fraction, and further combined with the recovery steps of recovering said phenol-depleted water retentate and said separated phenol-rich fraction.

10. The method of claim 9 further including subjecting said separated phenol-poor fraction to at least one additional pervaporation step.

11, The method of claim 10 further including subjecting the phenol-enriched permeate from said at least one additional pervaporation step to at least one additional phase separation step.

12. The method of claim 10 or 11 wherein said separated phenol-poor fraction is subjected to a second pervaporation step, the phenol-enriched permeate from said second pervaporation step is subjected to a second phase separation step, and wherein the phenol-depleted water retentate from said second pervaporation step is recycled to the feed stream of the first pervaporation step, said separated phenol-poor fraction from said second phase separation step is recycled to the feed stream of said second pervaporation step, and the separated phenol rich fraction from the first phase separation step is combined with the separated phenol-rich fraction from the second phase separation step.

13. The method of claim 1 or 4 or 9 wherein said pervaporation step is conducted only until the con-centration of phenol in said phenol-enriched permeate corresponds to the phenol concentration of a phenol-poor fraction resulting from a naturally-occuring spontaneous phase separation of an aqueous phenolic solution into a phenol-rich fraction and a phenol-poor fraction.