Note: Descriptions are shown in the official language in which they were submitted.
~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~
1058525
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.
-- 2 --
~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.
- 3
~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
-- 4 --
~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.
-- 7 --
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
3585Z5
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.
- 13 -
3L6~585Z5
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-- 14 ~`
. ~ i852S
Notes:
a. the few experiments at other than 70C
are so indicated in the table.
b. film~ ca. .00254 cm thick unless noted
otherwise.
c. distribution coefficient between 1%
phenol solution and the resin at
22-2~C;
K (gm phenol/gm resin)
(gm phenol/gm water)
d. aH~O = 0 5 =( Cw )/(Cw ) (at 0-1% phenol)
phenol p p
a in the relative volatility based on
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SF ~( cw ) / ( cw ) and
permeate permeant
is based on kinetic rather than thermo-
dynamic quantities.
Pervaporation of an aqueous stream containing 3.0% by weight
phenol through various membranes, according to the ~vention
is reported in Table IV.
- 15 -
~ 852~
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--19--
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 -
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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~
S~35ZS
and ~VF is the "volume fraction difference"
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.
- 26 -
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- 27 -
~5~iZ5
TABLE X ~continued)
Notes:
(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
- 28 -
SZ5
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.
- - 29 -
