Note: Descriptions are shown in the official language in which they were submitted.
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Method of Rapidly
Dissolving Polymers in Water
BACI~GROUND OF T~I~ INVENTION
Field of the Invention
This invention relates to water~soluble polymers
and, more particularly, to a method of rapidly dis-
solving such polymers in water.
Description of the Prior Art
The use of solutions of water-soluble polymers in
thickening and flocculating applications is well known
~uch applications include the clarification of aqueous
solutions in papermaking, and in treatment of sewage and
industrial wastes. Such solutions of polymers are also
useful as stabilizers for drilling muds, and in the
secondary recovery of petroleum by waterflooding.
Although these polymers are most often available
commercially as powders or as finely divided solids,
they are most frequently utilized in aqueous solutions.
This necessitates that the solid polymer materia' be
dissolved in water. Although the various polymers are
more or less soluble in water, difficulty is often
experienced in preparing aqueous polymer solutions
because of their slow dissolution and because the solid
polymer is not readily dispersible in water.
Furthermore, dispersion of solid polymers in water
is hindered by their tendency to clump or remain as
agglomerates on contact with water. Lumps of solid
polymer immediately form by the encapsulation of
undissolved solids in an outer coating of water-wet
polymer which retards the penetration of additional
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watcr into the a~glomeratc. Although many of these
lumps arc eventually dissolved by continued agitation,
it is frequently impractical to agitate the solution for
a sufficiently long period to obtain complete
dissolution.
The foregoing problems are described in U.S.
patents Re. 2~,474 (July 8, 1974) and Re. 28,576
~October 21, 1975) issued to Anderson et al.
The above-identified Anderson et al reissue patents
describe a method of rapidly dissolving water-soluble
polymers in which a polymer is dispersed lnto a
water-in-oil emulsion, which emulsion is then inverted
in water to release the polymer into solution. The
Anderscn et al disclosures require an oil-to-water ratio
15 between 5:1 and 1:10.
Accordins to the Anderson et al disclosures,
emulsions containing between 5 and 75 weight percent
polymer dispersed therein can be prepared and inverted
into aqueous solution. However, it has been found in
practice that the upper limit of the polymer content of
an emulsion made according to the Anderson et al process
is much lower than 75 weight percent, and usually is in
the 10-35 weight percent range, depending upon the
characteristics of the particular emulsion.
Further, the Anderson et al system, in practice,
requires substantial amounts (e.g. 20 wt. ~, or more,
based on oil) of an emulsifier in the oil/water/polymer
emulsion to provide a.stable product.
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SUMMARY OF THE INVENTION
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The invention seeks to overcome one or more of
the problems described above.
The invention as broadly claimed in one aspect
pertains to a method of rapidly dissolving a water soluble
polymer or gum in water which comprises the steps of
preparing finely-divided particles of the polymer or gum by
comminuting the polymer or gum under substantially non-
molecularly destructive conditions, dispersing the particles
in a substantially water-free liquid carrier in which the
polymer or gum is substantially insoluble to form a suspension,
and adding the suspension to water with sufficient mixing to
disperse and rapldly dissolve the particles in the water.
A preferred polymer is a polyacrylamide polymer,
and the finely-divided particles of polyacrylamide are
prepared by comminuting the polymer under cryogenic grinding
conditions.
The suspension may be added to water in the presence
of an emulsifier or a surfactant. Alternatively, an emul-
sifier may be added to the liquid carrier before additionof the polymer or gum to the carrier~ The liquid carrier
may be soluble or insoluble in water.
The polymer or gum particles are prepared by a
comminution process which does not degrade the molecular
structure of the polymer or gum. Only very low levels of
emulsi~ier and/or surfactant, or none at all, are required
to provide a stable product.
Other aspects and advantages will be apparent from
the following detailed description.
DETAILED DESCRIPTION OF THE INVENTION
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The Water Soluble Polymers
These polymers are well known in the art and have
been described in numerous publications and patents. They
include, but are not limited to, naturally occurring
galactomannan gums such as guar and locust bean gums,
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alginate salts, biologically produced polymers (e.g.
~anthan gum), polyethylene o~ides, water soluble
condensation polymers, and vinyl addition polymers such
as polyacrylamides and copolymeric derivatives of
acryIamide with, for example, acrylic acid, m~leic
anhydride, acrylonitrile, styrene, allyl or diallyl
amines or dimethylaminoethylmethacrylate (D~EM). Such
polymers may be nonionic, anionic or cationic.
The~-gums are well-known water-soluble polymers,
and include those described in Volume lO of the En-
cyclopedia of Chemical Technology, 2nd Edition,
Interscience Publishers, 1966.
The molecular weight of the polymers described
above may vary over a wide range, e.g. between about
10,000-25,000,000, and molecular weight is not a
- critical parameter in this invention. The invention
finds-~its greatest usefulness in preparing aqueous
solutions or dispersions of these polymers and is
particularly useful with respect to acrylamidé polymers,
the molecular weights of which are in excess of 1
million.
` Polymers havin~ relatively high molecular weights
previously were dissolved in water only with difficulty
and tended to form extremely viscous solutions at
relatively low concentrations. The polymers may be
produced by any suitable me~hod of conducting
polymerization reactions. Thus, solution, suspension or
emulsion polymerization techniques may be used.
As used herein, the term "polymer" is`understood to
include polymers and gums which are soluble in water to
a significant degree. The polymers are solid, but may
have a substantiàl water content. ~
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The invention i5 capable of rapidly producing
aqueous solutions of water soluble synthetic or natural
polymers having polymer concentrations within the ranye
of 0.1-10% by weight, with preferred concentrations
within the range of 0.2-2.0~ by weight.
The Commlnution Process
The rate of polymer dissolution in water is a
function of surface aréa and, consequently, particle
size. Polymers produced by most manufacturing processes
are in the form of powders or lump-like agglomerates.
Largeiparticle sizes minimize handling and dusting
problèms and reduce the formation of gel particles
during dissolution in water. However, large prarticle
size~increases dissolving time when dry particles are
added dlrectly to water.
Therefore, it is desirabLe that the particles be
comminuted by grinding, abrading or slicing so as
develop the large surface area which promotes rapid
dissolution when the polymer particles subsequently
contact water. The preferred particle size of the
polymer or gum is determined by the desired improvement
in dissolùtion rate in water and will genera~lly be less
than 100 microns and preferably less than 7~0 microns.
~ - Small particle size also promotes suspension stability.
Many of the polymers amenable to this process are
subject to molecular degradation by heat generation
during comminution. For such heat sensitive polymers,
comminution without molecular degradation may be
achieved through cryogenic grinding, such as by the use
of carbon dioxide or liquid~nitrogen to reduce the
temperature of the polymer prior to and/or during the
grinding or sliclng process. Certain polymers that
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become plastic or sticky at temperatures developed in
ambient temperature grinding processes can also benefit
~rom cryogenic grinding.
Such cryogenic processes employ pulverizing
equipment such as that marketed by Pulverizin~ ~achinery
Company of Summit, NJ under the trademark "~ikroPul".
Comminuting equipment that employs a slicing action,
such as that sold by Urschel Laboratories of
Valparaiso, IN under the trademark "Comitrol" may be
additionally employed to further reduce particle size in
the polymer suspension itself. The comminuting process
and equipment are chosen to protect the polymer from
significant molecular degradation and to produce the
desired dissolution rate when the polymer suspension is
introduced into water with mixing.
The Suspension
From a commercial standpoint it is beneficial that
the suspension of polymer be stable so that agitation
of the stored suspension is minimal or not required, and
that polymer concentration be`as high as possible to
minimize~freight costs. Suspensions as high as about
70-75 wt.~ polymer solids may be produced according to
this invention, depending on particle size, carrier
viscosity and the effect of suspending or dispersing
agents on suspension viscosity. The preferred range of
polymer solids in the suspension is about 50g~-70gO by
weight. Suspension stability is enhanced by relatively
fine comminution of the polymer or gum and by a high
viscosity li~uid carrier. Additionally the carrier may
be treated with suitable thickening, dispersing,
suspending or viscosity modifying agents such as those
well known in the art.
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A particularly advanta~eous method of increasing
stability with hydrocar~on oil carriers is to add an
oil-in-~ater emulsifier such as the
isooctylphenoxypo1yethoxyethanol product sold by ~ohm &
Haas under the trademark "Triton X-100." When this
oil-in-water emulsi~ier is added to a hydroc~rbon
carrier it performs the dual functio~s of increaslng
suspension stabili~y and emulsifying the hydrocarbon in
the water in which the polymer is ~o subsequently
dissolve, thus speeding dissolution of the polymer by
exposing oil-free polymer surfaces to the water.
The polymer must not be soluble in the liquid
carrier, and the carrier should be substantially
water-free. However, the liquid carrier may be either
soluble or insoluble in water.
Since the liquid carrier is substantially
water-~ree, a water-in-oil emulsion is not formed, in
contrast to the process o Anderson et al reissue
patents 28,474 and 28,576, identified above. Although
the solid polymer may have a substantial water content,
this water content does not result in the formation of a
water-in-oil emulsion.
Suitable hydrocarbon oil carriers include, but are
not limited to, parif~in-based oils such an Conoco's
LOPS (low order para~f~n solvent) and Exxon's Faxam.
Exxon's Isopar M, a deodorized high purity isoparaffinic
material, is also suita~le, as are the hydrocarbon
liquids disclosed .in Anderson et al~ Re. 28,474 and
28,576.
Water-soluble or water-dispersible carriers in
which the polymer is insoiuble under practical
conditions may also be used in producing ~he polymer
suspension. In the case wherein the liquid c~rrier is
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water soluble, no surfactant is needed. ~xamples of
such carriers include, but not limited to, higher
alcohols, glycols and glycol ethers.
Dissolving The Polymer
When a polymer-containing suspension of the type
described herein is dispersed in water the polymer
rapidly dissolves in the water. The polymer con-taining
suspension will produce a water solution in a very short
time when compared to the amount of time required to
dissolve the conventional solid form of the polymer.
The polymer-containing suspension may be dispersed
in water by any suitable means. Where a ~ater insoluble
carrier is used, the most convenient means is to use a
surfactant present in either the polymer containing
suspension or the water in which the polymer is to be
dissolved. The surfactant causes the carrier to rapidly
emulsify in the water (forming an oil-in-water
emulsion), thus expediting formation of the aqueous
solution of the polymer. When this technique is used
to invert the polymer-containing suspension to an
aqueous solution the amount of surfactant present in the
water may vary over a range of 0.01~ to 30% based on
polymer. Good conversion often occurs within the range
of 1.0~ to 8~ based on carrier.
The preferred surfactants for use with a polymer
suspension in a hydrocarbon liquid carrier are
hydrophilic and water soluble. Any anionic, cationic or
nonionic hydrophilic compound can be used as the
surfactant although it is~best to choose a surfactant
whose ionic properties do not react with those of the
polymer in solution.
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In addition to using water-soluble surfactants with
hydrocarbon carriers, other surfactants such as
silicones, clays and the like may be used since in
certain instances they tend to emulsify a hydrocarbon
carrier even though they are not themselves
water-soluble.
By the use of this process different polymers may
he com~ined into a single suspension so that when the
polymers of the suspension are dissolved in water as a
co-solution the technical performance of the mixture is
enhanced. Such combinations include, but are not
limited to, nonionic polyacrylamide with either anionic
or cationic polyacrylamide copolymers, anionic poly-
acrylamide copolymer with biopolysaccharide, poly-
ethylene oxide with nonionic polyacrylamide, poly-
ethylene oxide with cationic or anionic polycrylamide
copolymers, or biopolysaccharide with galactomannan
gums.
Examples
Examples 1-26
To illustrate the invention, Examples 1-26 are
summarized below in the Table. A variety of suspensions
were prepared containing different water-soluble
polymers and gums and using differing types of liquid
carriers. The suspensions were then converted to
polymer solutions in water using different conversion
techniques and the time for polymer dissolution was
compared to that for dissolution of the dry polymer or
gum in its commercially available form. In all cases
significant reductions in dissolving time were noted and
the usual problems associated with handling and dis-
persing dry polymer or gum were eliminated.
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In those Examples in which the liquid carrier was ahydrocarbon oil, the hydrocarbon oil was a mixture
comprising #2 diesel oil (50~) and Faxa~Z2 (S0~).
(Faxam~22 is a general purpose para~fin based oil
marketed by Exxon.) In those Examples in which a
surfactant was present, ~he sur~actant was Triton X-100
and was present in the suspension or water in an amount
calcula~ed to give a nominal 2 wt % surfactant content,
based on product. Where an emulsifier was used, the
emulsifier was Triton X-100 , and was present in the
suspension in an amount calculated to give an emulsifier
concentration of about 2 wt %, based on suspension.
In Example 26, a small amount (about 1% by weight,
based on suspension) Bentone SD-l ~a clay dispersant
sold by NL Industries) was added to the suspension in
order to enhance stability.
All percentages of carrier and polymer or gum are
based on the total suspension. In each Example,
sufficient suspensio~ was mixed with water to give an
aqueous solution polymer concentration of about 0.2 wt
%.
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Example 27
A sample of dry polyacrylamide (~00-~00 ~icron
particle size) was dissolved directly in water by
agitation to form a O.lS wt. ~ solution. Dissolution
required mixing for 75 minutes. The solution viscosity
was measured as 23.6 cps.
Two samples of polymer from the same batch were
ground to 70 microns using a cryogenic process, and an
ambient grinding process in an air classifying mill
tACM) pulverizer sold by MikroPul, Inc., respectively.
Both ground samples were suspended in surfactant--
containing hydrocarbon oil and converted in water,
according to the procedure of Example 4. Both samples
of polymer dissolved in less than 10 minutes. Aqueous
polymer solutions (0.15 wt. ~ polymer) from the two
grinds had viscosities of 24.2 cps (cryogenic grind) and
1~.2 cps (ambient temperature grind).
This Example demonstrates one advantage of
comminution by cryogenic grinding over comminution by
molecularly-destructive a~bient temperature grinding.
The foregoing detailed description is given for
clearness of understanding, and no unnecessary
limitations should be inferred therefrom, as variations
within the scope of the invention will be obvious to
those skilled in the art.
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