Note: Descriptions are shown in the official language in which they were submitted.
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PRODUCTION OF POLYSACCHARIDE ETHERS
Field of the Invention
The present invention relates to processes for producing
polysaccharide ethers. More' specifically, the present invention relates
to improved processes for producing polysaccharide ethers wherein
salts formed in the processes can be converted to their corresponding
acids and bases, e.g., by electrodialysis.
Background of the Invention
Typical commercial processes for the manufacture of
polysaccharide ethers, e.g. hydroxyethyl cellulose, require the use of
acids and bases. For example, a base such as, e.g., sodium hydroxide,
is typically used to promote the swelling of the polysaccharide, which
in turn facilitates th.e subsequent reaction with an alkylene oxide, e.g.,
ethylene oxide. After the polysaccharide is reacted with the alkylene
oxide to form the polysaccharide ether, the reaction mixture is
typically neutralized with a mineral acid or an organic acid, e.g., nitric
acid or acetic acid. As a result of the neutralization, a salt, e.g.,
sodium nitrate or sodium acetate, is formed. Typically, the salt is
comprised in an aqueous waste stream which also contains organic
solvents used in the process and residues of the polysaccharide.
Often, the salts are recovered from the waste stream and
disposed of. HowevE~r, the disposal of such salts may not be
,, environmentally desirable or feasible. Therefore, improved processes
i
for the production of polysaccharide ethers are desired which can
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convert the salts formed in the processes to their corresponding acids
and bases. Preferably, the acids and bases recovered from the
processes can be recycled for use in the production of the
polysaccharide ethers.
Summary of the Invention
By the present invention, improved processes for the production
of polysaccharide ethers, e.g., hydroxyethyl cellulose, are provided.
The improvements are directed to the conversion of salts formed
during the manufacture of the polysaccharide ethers to their
corresponding acids and bases. In accordance with the present
invention, the conversion of the salts to their corresponding acids and
bases is achieved by subjecting the salts to an electric current effective
to promote the conversion of the salts to the acids and bases.
Preferably, a separation means, e.g., a bipolar membrane, is utilized to
isolate the acids and bases as they are converted from the salt.
Prior to the conversion of the salts to their corresponding acids
and bases, it is preferred in accordance with the present invention to
remove organic solvents and residues of the polysaccharide from the
salt-containing stream in order to avoid fouling of the bipolar
membranes. Electrodialysis is a convenient means for removing such
materials in accordance with the present invention because the salts
are more strongly ionized than the other materials. However, these
other ~aterials~, the residues of the polysaccharides in particular, can
cause fouling of the membranes used in the electrodialysis process.
tauite surprisingly, in accordance with the present invention, it has
been found that by conducting the electrodialysis at a alkaline pH, the
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degree of fouling of the membrane can be reduced and the ionic
mobility of the salt through the membrane can be enhanced.
Brief Description of the DrawlnE
Figure 1 is a schematic of a process for the conversion of a salt to
as corresponding acid and base in accordance with ~he present
invention.
Detailed Description of the Invention
The polysaccharide starting materials suitable for use in
accordance with the present invention include naturally occurring,
biosynthesized and derivatized carbohydrate polymers or mixtures
thereof. Such materials encompass high molecular weight polymers
composed of monosac:charide units joined by glycosidic bonds. These
materials may include, for example, the entire starch and cellulose
families; pectin, chitosan; chitin; the seaweed products such as agar
and carrageenan; alginate; the natural gums such as guar, arabic and
tragacanth; bio-derived gums such as xanthan; and the like. Preferred
starting materials include cellulosics conventionally employed for the
preparation of cellulose ethers, such as, for example, chemical cotton,
cotton linters, wood pulp, alkali cellulose and the like. Such materials
are commercially available.
The molecular weight of the polysaccharides suitable for use in
accordance with the present invention typically ranges from about
10,000 to 2,000,000 grams per gram mole and preferably ranges from
about 20,000 to 250,000 grams per gram mole. As used herein, the
term "molecular weight" means weight average molecular weight.
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Methods for determining weight average molecular weight of cellulose
ethers are known to those skilled in the art. One preferred method for
determining molecular weight is low angle laser light scattering.
The particular derivatizing agent, e.g., alkyl halides or alkylene
oxides, used to derivatize the polysaccharides is not critical to the
present invention. Suitable alkylene oxides for use in accordance with
the present invention comprise from about 2 to 24, preferably from
about 2 to 5 carbon atoms per molecule. Examples include ethylene
oxide, propylene oxide and butylene oxide. Typically, the ether
substituent is derivatized onto the cellulose by reacting the
polysaccharide with an alkylene oxide, preferably ethylene oxide. The
amount of ether substitution is typically from about 1.5 to 6 and
preferably from about 2 to 4 moles of ether substituent per mole of
polysaccharide ether. Suitable alkyl halides include, for example,
ethyl chloride or methyl chloride.
The polysaccharide ethers may be substituted with one or more
desired substituents, e.g., cationic, anionic and/or hydrophobic
substituents. Hydrophobic substituents. are known in the art and
typically comprise alkyl, alkene, aryl-alkene or aryl-alkyl groups
having about 8 to 24 carbon atoms per molecule. Hydrophobically-
modified cellulose ethers are described, for example, in U.S. Patent
Nos. 4,228,2??, 5,120,328 and 5,504,123 and European Patent
Publication 0 384 16? B1. Cationic, hydrophobically modified cellulose
ethers are described, for example, in U.S. Patent No. 4,663,159. The
substitution level of each such substituent on the polysaccharide ether
is typically from about 0.001 to 0.1 and preferably from about 0.004 to
about 0.05 moles of substituent per mole of polysaccharide ether. More
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than one particular substituent can be substituted onto the
polysaccharide ether.
The polysaccharide ethers of the present invention can be water-
soluble or water-insoluble. As used herein, the term "water-soluble"
means that at least 1 gram, and preferably at least 2 grams of the
polysaccharide ether are soluble in 100 grams of distilled water at -
25°C and 1 atmosphere. The extent of water-solubility can be varied
by adjusting the extent of ether substitution on the polysaccharide
ether and by adjusting the substitution level of the various
substituents, when present. Techniques for varying the water
solubility of polysaccharide ethers are known to those skilled in the
art.
The viscosity of the polysaccharide ethers typically ranges from
about 1 to 8000 centipoise, preferably from about 100 to 3000
centipoise. Unless otherwise indicated, as used herein the term
"viscosity" refers to the viscosity of a 1.0 weight percent aqueous
solution of the polymer measured at 25°C with a Brookfield
viscometer. Such viscosity measuring techniques are known in the art
and are described in .ASTM D 2364-89. The average particle size of the
polysaccharide ethers is not critical, but is preferably from about 0.01
to 1000 microns and :more preferably from about 50 to 400 microns.
Preferred polysaccharide ethers produced in accordance with the
present invention, are cellulose ethers, including for example,
hydroXyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, ethyl
cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl
cellulose, carboxymethyl cellulose, hydroxyethyl carboxylmethyl
cellulose, and derivatives thereof.
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In general, typical processes for producing polysaccharide ethers
comprise:
(i) treating a polysaccharide with a basic compound to
promote swelling of the polysaccharide;
(ii) reacting the polysaccharide with a derivatizing
agents) in a liquid medium under co :3itions effective to
promote a reaction between the polysaccharide and the
derivatizing agent and form a reaction product comprising a
polysaccharide ether and the basic compound;
(iii) treating at least a portion of the reaction product
comprising the basic compound with an acidic compound to
provide a neutralized liquid comprising a salt of the acidic
compound and the basic compound (It is noted that the term
"neutralized liquid" is not intended to mean that the product
necessarily has a neutral pH. The pH can be 7.0 or above or
below 7.0); and
(iv) separating the polysaccharide ether from at least
one of the reaction product or the neutralized liquid.
The basic compounds suitable for use in accordance with the
present invention include any base effective to promote the swelling of
the polysaccharide. Typical basic compounds include, for example,
sodium hydroxide, potassium hydroxide, calcium hydroxide,
magnesium hydroxide, lithium hydroxide, ammonium hydroxide and
mixtui es thereof.
The acidic compounds suitable for use in accordance with the
present invention include any acids which are effective to neutralize
the polysaccharide ether. Typical acidic compounds include, for
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example, nitric acid, acetic acid, hydrochloric acid, sulfuric acid,
phosphoric acid and mixture thereof.
Typically, the liquid medium in which the etherification is
conducted comprises from about 5 to 25 wt °/, preferably from about 10
to 20 wt % water, from about 75 to 95 wt %, preferably from about 80
to 90 wt % of at least; one organic solvent. The particular organic
solvents used in the processes of the present invention, are not critical
and may include, far example, t- butyl alcohol, acetone, isopropyl
alcohol, ethanol, dioxane , glycol ethers and mixtures thereof.
Typically, the etherification of polysaccharides is conducted in a
batch mode, although semi-batch and continuous processes may be
employed. The process conditions typically include a reaction
temperature of about 50 to 100 °C, preferably from about 70 to 90
°C, a
pressure of from about 1 to 5 atmospheres, and the reaction time of
from about 30 to 400 minutes. Further details concerning the
etherification of cellulose are known in the art and disclosed, for
example, in U.S. Pat,ent Nos. 2,010,818, 4,228,277 and 4,663,159.
Typical salts which are formed when the acidic compound is
added to neutralize the reaction product include, for example, sodium
nitrate, sodium acetate and other salts produced by combination of the
acids and bases listed above. The concentration of the salts in the
neutralized reaction product, i.e., the neutralized liquid, is typically
from about 2 to 20 moles per kilogram of polysaccharide ether and
preferably from about 5 to 10 moles per kilogram of polysaccharide
ether.
In accordance with the improved processes of the present
invention, the neutralized liquid, which comprises the salt, is subjected
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to an electric current and suitable means effective to promote the
conversion of the salt to the acidic compound and the basic compound,
e.g., a suitable separation means and a source of hydrogen ions and
hydroxyl ions. Preferably, the step of subjecting the neutralized liquid
to an electric current is conducted with a suitable separation means to
isolate the acidic compound and the basic compound as they are
converted from the salt. Any suitable means can be used to effect the
isolation. A preferred separation means is by semi-permeable
membranes, i.e., electrodialyis. Electrodialysis, sometimes referred to
herein as "ED", is a well known separation process wherein ionized
compounds are separated from non-ionized or weakly ionized
compounds in aqueous solutions based on transport through ionic
exchange membranes in an electric field. Details concerning suitable
apparatus and process conditions for conducting electrodialysis are
known to those skilled in the art.
Especially preferred membranes for use in accordance with the
present invention to isolate the acids and bases from the salts are
bipolar membranes. The use of bipolar membranes in conjunction with
an electric current to perform a separation is referred to in the art as
"water-splitting electrodialysis". Further details concerning suitable
apparatus and process conditions for conducting water-splitting
electrodialysis ar a known to those skilled in the art. See, for example,
U.S. Patent Nos. 4,885,247 and 5,143,839. The particular
composition of the bipolar membranes is not critical. Examples of
materials which comprise such membranes include cationic and
anionic polymers, e.g., sulfonated polystyrene, polystyrene with amine
functionality and polysulfone. Bipolar membranes are described for
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' example, in U.S. Patent Nos. 4,116,889 and 4,766,161. Preferred by
commercially available bipolar membranes for use in accordance with
the present invention, include the following: BP1 from Tokuyama
Corporation Tokyo" Japan and AQPS and BA06 from Aqualytics
Corporation, Warren, NJ. Other suitable bipolar membranes are
commercially available.
Preferably, the electric current used to facilitate the conversion
of the salt to its corresponding acid and base has a current density of
from about 500 to 2000 amps/square meter ("A/sq. m.") and preferably
from about 800 to 1200 amps per square meter. Current density is
the current per unit area of available membrane through which the
current passes measured when the current is initially applied to the
membrane. The higher the applied current density, the lower the cell
area required to achieve a specific degree of ion transfer.
Pr eferably, in accordance with the present invention, the
neutralized liquid is subjected to a separation prior to the water-
splitting electrodia:lysis to separate the salt from the organic solvents
and any residue of the polysaccharide remaining from the
etherification. Typically, distillation can be used to remove any
volatile organics from the salt solution and to concentrate the salt to
the appropriate concentration for further processing, typically about 5
to 20 wt %. Any suitable means can be used to effect the separation of
the salt from the high boiling organic solvents and the residue of the
polysaccharide, e.g. membrane separation, filtration, ultra-filtration,
electrolysis, electrodialysis. Electrodialysis is a preferred means of
separating the salts from the organic solvents and the residues of the
polysaccharide. In this type of electrodialysis, known in the art as
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"desalting electrodialysis", the salt does not convert to its
corresponding acid and base. It remains intact. Any semi-permeable
membranes effective to promote the separation of the salts from the
organic solvents and the residue of the polysaccharides can be used in
accordance with the present invention. Typical membranes, for
example, comprise films of crosslin~ :~d polymers comprising either
positively or negatively charged groups. Examples include polystyrene
divinylbenzene copolymers containing sulfonic acid groups (negatively
charged, allowing transport of positive ions) or quaternary amine
groups (positively charged, allowing transport of negative ions).
Preferred commercially available semi-permeable membranes for the
desalting electrodialysis step include, for example, cation membranes
CM-2, CMX and CMB and anion membranes AM-1, AM-2 and AM-3
from Tokuyama Corporation. Other suitable membranes are
commercially available. Further details concerning the apparatus and
process for conducting desalting electrodialysis axe known to those
skilled in the art.
Quite surprisingly, in accordance with the present invention, it
has been found that the efficiency of the salt recovery in the desalting
electrodialysis step can be surprisingly enhanced by conducting the
separation under alkaline conditions. Preferably, the alkaline
conditions are effective to inhibit the deposition of the residue of the
polysaccharide on the membrane. In addition, it is preferred that the
alkaline conditions are effective to enhance the ionic mobility of the
salt through the membrane. In a preferred aspect of the invention, the
pH is greater than about 10, more preferably from about 10.5 to 14,
even more preferably from about 10.5 to 13 and most preferably from
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about 10.5 to 11.5. At a pH below about 10, it has been found that
significant fouling of the membranes can occur.
In addition to the specific unit operations described herein,
those skilled in the art will recognize that additional unit operations,
such as, for example, filtration, chelation, distillation, etc., can be used
to enhance the overall process of the present invention.
The polysaccharide ethers of the present invention can have a
variety of end-use applications, such as, for example, industrial
applications and personal care applications. Typical industrial
applications for polysaccharide ethers include, for example, use as
viscosity adjusters, suspension aids, oil field drilling and fracturing
materials, adhesion promoters for siliceous substrates, e.g., glass
panels and ceramics, coating materials for plastic and metal
substrates, protective colloids and building materials, e.g., wallboard
compound and latex grout additive. Typical personal care applications
include, for example, pharmaceutical and cosmetic compositions, e.g.,
ointments, skin creams, lotions, soaps, shampoos, conditioners and the
like.
A preferred end-use application for polysaccharide ethers of the
present invention, especially cellulose ethers such as hs droxyethyl
cellulose and its derivatives, is as an additive in latex compositions.
Typical latex compositions comprise as essential components:
water; latex polymer; and the cellulose ether. The kind and amount of
latex polymer is not critical, and may be provided based on well
established procedures. Typical latex polymers include, but are not
limited to, various types such as the following: acrylics; alkyds;
celluloses; coumarone-indenes; epoxys, esters; hydrocarbons; maleics;
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melamines; natural resins; oleo resins; phenolics; polyamides;
polyesters; rosins; silicones; styrenes; terpenes; areas; urethanes;
vinyls; vinyl acrylics; and the like. Illustrative latex polymers include,
but are not limited to, one or more homo- or copolymers containing one
or more of the following monomers: (meth)acrylates; vinyl acetate;
styrene; ethylene; vinyl chloride butadiene; vinylidene chloride; vinyl
versatate; vinyl propionate; t-butyl acrylate; acrylonitrile; neoprene;
maleates; fumarates; and the like, including plasticized or other
derivatives thereof.
The amount of cellulose ether which may be used in the latex
composition is not narrowly critical. In the broadest sense, the amount
of cellulose ether is that which is an effective amount in providing the
desired thickening and rheological properties to the latex composition.
Typically, the amount of cellulose ether is at least about 0.05,
preferably from about 0.15 to about 3, and more preferably from about
0.25 to about 1.5 weight percent of the latex composition.
The selection and amount of latex polymer used in the latex
composition can be determined by those skilled in the art is not
critical. Typically, the amount of dry latex polymer is at least about 1,
preferably from about 2 to about 50, and most preferably from about 3
to about 40 weight percent of the total latex composition.
The latex composition may optionally contain other components
such as those generally used in latex compositions. Typical
compofients include, but are not limited to, one or more of the
following: solvents such as aliphatic or aromatic hydrocarbons,
alcohols, esters, ketones, giycols, glycol ethers, nitroparaffins or the
like; pigments; fillers, dryers, flatting agents; plasticizers; stabilizers;
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dispersants; surfactants; viscosifiers including other polymeric
additives, cellulose ether based thickeners and so on; suspension
agents; flow control agents; defoamers; anti-skinning agents;
preseratives; extenders; filming aids; other crosslinkers; surface
improvers; corrosion inhibitors; and other ingredients useful in latex
compositions.
Further details concerning the preparation of latex compositions
are known to those skilled in the art.
The invention is hereinafter described with reference to Figure 1
which is provided for purposes of illustration and is not intended to
limit the scope of the claims.
A hazy, dark brown feedstream 10 (neutralized liquid)
containing about 8-10 wt % sodium acetate, about 0.5 wt % sodium
hydroxide, about 4-5 wt % of a mixture of ethylene glycol, diethylene
glycol and triethylene glycol, 1-2wt % of partially soluble cellulosic
material and the remainder water is passed to an ultrafiltration unit
100 wherein suspended materials and soluble materials with
molecular weights above about 100,000 grams/gram mole are removed.
Ultrafiltration unit 1.00 is comprised of a metal housing containing
tubular membranes which are permeable to materials with molecular
weights below 100,000 grams/gram mole. Examples of suitable
membranes include ceramic membranes and polymeric membranes,
e.g., polyamide, cellulose acetate, polyethersulfone, polyacrylonitrite,
polyvirfylidene fluoride and polyvinylchloride. A waste stream 11
comprising material which does not pass through the ultrafiltration
unit is withdrawn by a stream 11. A clear brown filtrate stream 12
comprising essentially the same components as stream 10 but with the
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suspended matter and possibly some high molecular weight dissolved
material removed is withdrawn from ultrafiltration unit 100,
combined with sodium hydroxide via line 13, the source of which is
hereinafter described, and introduced via line 14 to a desalting
electrodialysis unit 101 which is comprised of a TS-2 ED stack from
Tokuyama Corporation-:,ontaining 6 ED cells comprised of AMl anion
exchange membranes and CM2 and CMX cation exchange membranes.
The desalting electrodialysis unit 101 is operated at a pH of
from about 11 to 11.5. The amount of sodium hydroxide introduced via
line 13 is controlled in order to provide the desired pH in the desalting
electrodialysis unit 101. A stream 15 comprising material which does
not pass through the membranes in the desalting electrodialysis unit
101 is combined with stream 11 as described previously and
withdrawn from the process via line 16. A permeate stream 17
comprising about 18-20 wt % sodium acetate, about 1 wt % sodium
hydroxide, about 0.5 wt % glycols and the remainder water is
withdrawn from the desalting electrodialysis unit 101. The desalting
electrodialysis unit 101 operates in a batch mode under the following
conditions: a temperature of about 45°C, a feed flowrate (line 14) of
about 3-4 liters/minute, an initial current density of about 500 A/sq.
m., with a 3 wt % sodium sulfate electrode rinse solution.
Stream 17 is passed to a chelation unit 102 which is a 2-Iiter
column with an internal diameter of 2 inches containing Duolite C-467
sodium form ion exchange resin available from Rohm and Haas,
Philadelphia, PA. The purpose of the chelation unit is to reduce
multivalent cation (Ca++, Mg++, Fe+++,etc.) concentrations to <
lppmw. An effluent stream 18 is withdrawn from chelation unit 102
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' and passed to a water-splitting electrodialysis unit 103 which
comprises a 2-compartment ED stack (TS-2, Tokuyama Corporation)
equipped with cation exchange membrane CM-1 and bipolar
membrane BP1(4 cell pairs), both from Tokuyama Corporation. The
water-splitting electrodialysis unit 103 operates in a batch mode under
the following conditions: a temperature of ~l~out 45°C, a feed flowrate
(line 18) of about 2-3 liters/minute, an initial current density of about
1000 A/sq. m., with a. normal sodium hydroxide electrode rinse
solution.
Water is introduced to the water-splitting electrodialysis unit
103 via line 19.
A base product stream 20 comprising from about 5 to 15 weight
percent sodium hydroxide is produced. A portion of the sodium
hydroxide product stream is recycled to the desalting electrodialysis
unit 101 via line 13 as described previously. The remainder of the
stream is withdrawn from the process via line 21.
An acid produca stream 22 comprising from about 10 to 20
weight percent acetic; acid, is also produced. This stream also contains
some residual sodium acetate e.g., about 0.5 to 2 wt % and glycols
present in the feed e.g., about 0.5 to 1 wt %.
Further details concerning the apparatus, process condition
and operation of the ;process described in Figure 1 are known to those
skilled in the art.
EXAMPLES
The following Examples are provided for illustrative purposes
and are not intended to limit the scope of the claims which follow.
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The following materials were used in the Examples. '
INGREDIENT DESCRIPTION
Wood pulp Improved Ethenier-F wood pulp sheets
available from ITT Rayonier, Stamford, CT,
and flocked in the laboratory by techniques
known in the art.
Ethylene oxide: Obtained from Praxair, Inc., Danbury, CT,
distilled under nitrogen before use.
Obtained from Tokuyama Corporation,
TS-2 ED Stack Shibuya Konno Bldg., 3-chome Shibuya,
Shibuya-ku, Tokyo 150, Japan
Membranes AM-1, CM- Obtained from Tokuyama Corporation,
2, CM-X, BP-1 Shibuya Konno Bldg., 3-chome Shibuya,
Shibuya-ku, Tokyo 150, Japan
Duolite C-467 Ion A chelating resin comprised of a polystyrene
Exchange Resin divinylbenzene copolymer with
aminophosphonic functional groups.
Obtained from Rohm and Haas,
Philadelphia, PA
B-1 Ultrafiltration PCI Membrane Systems Ltd., 123 South
module Division Street, Zelienople, PA
FP-100 Tubular OF A polyvinylidene fluoride membrane
Membranes available. PCI Membrane Systems Ltd., 123
South Division Street, Zelienople, PA
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EXAMPLE 1
PREPARATION OF HYDROXYETHYL CELLULOSE
A three pint, glass ChemcoTM pressure reactor was charged with
Improved Ethenier-F wood pulp (32.4 g contained), 317 g of acetone, 41
g of ethanol and 47 g of water. The mixture was stirred for one hour
while purging the headspace of the reactor with nitrogen at a rate of
400 ml/min to remove any entrained oxygen. The reactor was fitted
with an ice water condenser to prevent evaporative losses of the
diluent during the nitrogen purge.
After purging for one hour the slurry was heated to 35°C and held
for 15 minutes. 47 g of 22 wt. % (by weight) aqueous sodium hydroxide
solution were added to the slurry by syringe. The slurry was stirred for
one hour at 35°C, while continuing the nitrogen headspace purge.
Ethylene oxide (34 g) was added to the reactor by syringe, and with
continuous stirring, the reactor was sealed. The slurry was heated with a
water bath to 75°C (typical heat-up time is 60 minutes). The
temperature
was held at 75°C for 1.5 hours to react out the ethylene oxide.
The slurry was cooled to room temperature and 16.2 g of glacial
acetic acid were added by syringe. After stirring for 15 minutes, the
polymer was collected by vacuum filtration through a fritted metal
Buchner funnel. The polymer was washed four times with 500 ml of 7:1
(by volume) acetone/water, twice with 500 ml of 5:1 acetone/water, and
twice with 500 ml o:f pure acetone. In the second pure acetone wash, 1.00
g of 40% aqueous gl;yoxal and 2.00 g of glacial acetic acid was included in
the acetone wash to surface-treat the polymer. The polymer was dried
overnight in vacuo at 50°C, affording 50-55 g of a white granular
solid.
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The ash content was found to be 4-8% (as sodium acetate), and the mass
gain EO MS was found to be 2-2.5.
CONTROL EXAMPLE 2
A stream containing about 8wt °/ sodium acetate, 0.5 wt
sodium hydroxide, 4 wt % glycols, a_:3 0.5 wt % cellulosic material (the
remainder water), recovered by distillation of organics and some water
from a combined diluentlwash solution from the process described
above, was processed in a TS-2 ED stack containing 6 cell pairs made
up of AM-1, CM-2, and CMX membranes. This stream was dark brown
in color but clear to the naked eye. It had previously been ultrafiltered
using an apparatus consisting of a feed tank and pump connected to a
membrane module with a B-1 housing and 18 FP-100 tubular
membranes (PCI Membranes, 100,000 molecular weight cutoff) to
remove suspended and high molecular weight components. Initial
current density was 500A/sq.m.The run proceeded normally until the
pH of the feed stream dropped from the initial value of 11.5 to about
10.x. At this point only about 77wt % of the acetate had been
transferred and cell resistance was increasing. Therefore the run was
ended.
EXA.12PLE 3
A stream identical to the one used in Control Example 2 was
processed as described above except that the pH of the feed was raised
to ~ 11.5 by addition of 40wt % sodium hydroxide whenever the pH
dropped to ~11. As a result of this pH control, ~9lwt % of the acetate
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' was transferred and cell resistance was kept under control. Sodium
acetate concentration in the concentrate was about 20 wt % by weight.
The product from the ED step was then processed through a
column containing Duolite C-46? to remove multivalent cations. Ca++
and Mg++ were below 1 ppm in the resulting stream. This product
stream was then subjected to water splitting electrodialy..~'.s using a 2-
compartment TS-2 stack equipped with BP1, CM-1, and CMX ion
exchange membranes. The stream processed with no difficulty and
produced an acid/salt; product containing about l6wt % acetic acid and
a sodium hydroxide product with a concentration of about 10 wt %.
There was no evidence of irreversible membrane fouling and cell
voltage remained low (~1.2 voltslcell pair) throughout the run.
EXAMPLE 4
A stream from the distillation of the diluent and wash solutions
from example 1 containing about l2wt % sodium acetate was
ultrafiltered and passed through a chelation column as described in
example 3. The resulting solution was processed using the water
splitting electrodialysis process described in example 3. Cell voltage
was about 1.5 volts/cell pair within a half hour. After 6-8 hours of
operation the syste~~ began to plug up, pressure increased and cell
voltage increased to over 2 volts/cell pair (constant current operating
mode) . An oily, tarry material was seen floating on the top of the feed
tank. The base was brown in color. The entire system, including tanks
and pipes, had to be cleaned after this test
° 1 Although the invention has been described with respect to
specific aspects, those skilled in the art will recognize that other
CA 02339374 2001-02-02
WO 00/08059 PCT/US99/17597
-20-
aspects are intended to be included within the scope of the claims
which follow.
