Process for the production of concentrated emulsion polymers

The present invention relates to a process for the production of concentrated, water-soluble or water swellable emulsion polymers by the polymerization of at least one water-soluble monomer in a water-in-oil dispersion by means of polymerization initiators, preferably in presence of bi- or multi-function vinyl- or allyl compounds in which a water-in-oil dispersion of the starting monomers is polymerized while being stirred so that the heat of polymeriaation is eliminated by distillation removal of the water contained in the reaction mixture. The polymerisation temperature is preferably adjusted and controlled by means of the pressure in the system.

Polyelectrolytes in the form of liquid dispersions, designated as emulsion 
polymers, are used in technology, in water and waste-water processing and 
in various manufacturing processes as flocculating, water-removal, and 
retention aids, as viscosity-intensifying additives in exploration and 
crude oil extraction, in the production of textiles, and, more recently, 
in cosmetic preparations 
As described in DE-PS No. 1089173 the production of emulsion polymers takes 
place by the radical polymerisation of water-soluble monomers. Preferably 
acrylamide and other acrylic acid derivatives that are contained in the 
disperse, aqueous phase of finely divided water-in-oil emulsions. 
These products are economically produced if the polymer fraction in the 
product (dissolved in water) possesses the required effectiveness in its 
intended application, and if the polymer fractions within the product, 
apart from the non-effective portions (the hydrophobic phase formed from 
the liquid hydrocarbons and emulsifiers and water), is sufficiently high 
For this reason, it is desirable to prepare emulsion polymers that are as 
highly concentrated as possible. 
During the production of the emulsion polymers the concentration of the 
polymer portion is determined--in addition to the solubility of the 
monomers--by the fact that the radical polymerisation of the quoted 
monomers is a rapid, strongly exothermic process, so that the reaction 
heat that is generated in proportion to the concentration of the monomers 
and to the speed of polymerisation has to be eliminated. In addition to 
the known monomer-supply process, several other production methods are 
described as solutions to this problem. U.S. Pat. No. 3,767,629 proposes 
the inhibition of polymerisation by a sporadic air supply to the monomer 
emulsion as a means of controlling the course of polymerisation. DE-OS No. 
28 11 422 proposes a reduction of the speed of polymerisation by the 
addition of heavy-metal ions in the monomer phase. However, all of these 
processes entail the disadvantage that the polymerisation reaction is very 
often too strongly inhibited, so that polymerisation as a whole is 
impaired and the quality of the polymers does not reach the optimal 
possible level. 
According to U.S. Pat. No. 4,070,321, the reaction is controlled by 
adjusting the pH value of the monomer phase for producing high-molecular 
anionic polymers. However, regulation of polymerisation by way of the pH 
value of the aqueous phase is inadequate for the production of 
concentrated products. 
It is already known that work can be carried on in two stages in order to 
produce concentrated products. 
In the first stage, low-concentrated products are produced by the adiabatic 
process, and in the second stage an increase in the polymer content is 
achieved by distillation with the renewed addition of heat, optionally 
with the addition of hydrocarbons distilled azeotropically, by the 
separation of water and with a small proportion of the hydrocarbons (U.S. 
Pat. Nos. 4,021,399 and 4,090,992). However, this process entails 
additional expenditures of energy and time. Furthermore, the polymers have 
to be stabilized by special additives (U.S. Pat. No. 3,507,840), in order 
that they retain their effectiveness for technical applications for a 
longer period of time. In addition, it is also known that the 
polymerisation heat can be eliminated by distillate reflux cooling at low 
pressure (DD-PS No. 145 401 and U.S. Pat. No. 4,078,133). This process 
entails the disadvantage that the refluxing free quantity of water can 
lead to inhomogeneity in the water-in-oil polymer dispersion and dilute 
the polymer portion that is effective in the product. 
The technique of concentration by means of azeotropic distillation of 
prepared polymer dispersions has been improved recently by DE-OS No. 
3224994, in particular by suitable changes in the apparatus used but 
without the elimination of the disadvantages inherent in such a two-stage 
process. 
Proceeding from the preceding described prior art it is an object of the 
present invention to create a process with which emulsion polymers with a 
high polymer content of high quality can be produced in one process step. 
According to the present disclosure this object is achieved by special 
management of the polymerisation, by which both control of the speed of 
the radical polymerisation of the water-soluble monomers in the 
water-in-oil emulsion as well as an increase in the polymer concentration 
in the end product is achieved. 
Thus, here described is a process for the production of concentrated 
emulsion polymers by the polymerisation of at least one water-soluble 
monomer in a water-in-oil dispersion by means of polymerisation 
initiators, preferably in the presence of bi- or multifunctional vinyl or 
allyl compounds, this being characterized in that a water-in-oil 
dispersion of the starting monomers is polymerized whilst being stirred 
such that the polymerisation heat is eliminated by the distillative 
removal of the water contained in the reaction mixture. 
The fact that by using the mode of operation according to the present 
disclosure it is possible, starting from water-in-oil monomer emulsions, 
to control the polymerisation and at the same time separate a mixture 
consisting of water and, preferably, small fractions of the liquid 
hydrocarbons of the emulsion as a distillate, without destroying the 
monomer or polymer dispersion or changing the proportions during 
polymerisation by removal of the component water, without prejudicing the 
quality of the product, must be regarded as surprising. The polymerisation 
temperature is adjusted or controlled by the prevailing pressure in the 
reaction vessel. 
It is preferred that the pressure in the reaction system be so adjusted 
that the polymerisation temperature lies in the range of 
20.degree.-70.degree., preferably 30.degree.-50.degree. C. The 
polymerisation takes place at a reduced pressure, preferably in the range 
of 10-150 mbar. According to a further embodiment, polymerisation takes 
place under at least approximately isothermic conditions. However, 
according to a further embodiment of the present invention it can take 
place in a first phase almost isothermically at lower temperatures in the 
range of 30.degree. C. to 50.degree. C., and then either approximately 
isothermically at higher temperatures of 50.degree. C. to 80.degree. C., 
preferably 50.degree. to 70.degree. C. or be concluded under adiabatic 
conditions. Polymerisation under adiabatic conditions can then occur if 
the polymerisation has progressed to the point that the polymerisation 
heat that is liberated for a brief period does not lead to the batch being 
heated to the boiling point of the dispersion (monomer emulsion and 
emulsion polymer). Polymerisation under adiabatic conditions is precluded 
if high temperatures during polymerisation have a negative influence on 
the characteristics of the product. 
The emulsion of the starting monomers is formed in the known manner from 
the aqueous monomer solution and the hydrophobic phase. When this is done, 
the monomer concentration in the aqueous solution is so selected that high 
polymer fractions are obtained in the end product and the stability of the 
dispersion is retained in all phases of production. According to the 
present disclosure it is possible to start from concentrated monomer 
solutions. Typical concentrations lie in the range of 40-80%-wt. However, 
it is possible to start from solutions at lower concentrations that are 
then concentrated to form concentrated polymer dispersions in the course 
of the process described. This method of proceeding makes it possible to 
use economical raw materials in the form of low-concentration monomer 
solutions. Typical concentrations of such low concentration monomer 
solutions lie in the range of 15-40%, preferably from 30-40%. 
Water-soluble, radically polymerizable compounds are suitable as monomers. 
Examples of non-ionogenic monomers are acryl- and methacrylamide, the 
hydroxyalkyl esters of the acryl- or methacrylic acid, preferably 
2-hydroxyethyl- and 2-hydroxypropyl ester, vinyl pyrrolidon and N-vinyl 
acetamide. Examples of anionic monomers are .alpha.-.beta.-unsaturated 
mono- and/or dicarboxylic acids, such as acrylic, methacrylic, itaconic, 
maleic and fumaric acids, their water-soluble salts, vinyl sulfonic acid, 
acrylamide alkane sulfonic acids, phenylvinyl phosphonic acids and their 
salts. Cationically effective monomers are amino-alkyl esters and amino 
alkylamides of unsaturated radically polymerizable carboxylic acids, for 
example 2-dimethyl- or 2-dietyl-aminoethyl-, 2-dimethyl-aminopropyl-, 
4-dimethylaminobutyl-, 3-dimethyl-aminoneopentyl, morpholinoethyl- and 
piperidinethyl ester of the acryl- or methacrylic acid as well as 
vinylpyridin, vinylimadazol, vinylimidazolin, and vinylimidazolidine, as 
well as their quaternary products and salts. 
Fractions of monomers which are water-soluble either only slightly or not 
at all are usable if the monomer mixture as a whole remains water-soluble. 
Bi- or multifunctional vinyl or allyl compounds, for example, methylene 
bisacrylamide can be used to produce polymer dispersions that are 
insoluble in water but which can however swell in water. 
As a basis for the hydrophobic phase it is possible to use paraffinic, 
isoparaffinic, naphthenic, and aromatic liquid hydrocarbons, optionally 
their halogenized derivatives, e.g., n-paraffins as well as mixtures of 
the quoted hydrocarbons, amongst others. Preferably, sorbitane fatty-acid 
esters, and glycerine fatty-acid esters are used as emulsifiers to form 
the water-in-oil emulsion, although, however, other water-in-oil 
emulsifiers, for example, according to DE-OS No.2455 287 emulsifiers that 
can be produced from fatty alcohol glycidyl ethers with polyvalent 
alcohols can be used. Furthermore, the stability of the monomer emulsion 
can be achieved by combining water-in-oil emulsifiers with oil-in-water 
emulsifiers, for example, of sorbitane mono-oleate with ethoxylized fatty 
acids or fatty alcohols as is cited in DE-OS No. 23 33 927. The 
water-in-oil emulsion formed from the components is optionally homogenized 
by a separate process until a specific viscosity number of the emulsion 
has been achieved. 
A container that is suitable for the polymerisation process is provided 
with a stirring mechanism, a distillation stage, and a cooler as well as 
with gas supply lines, an immersion tube, with a temperature sensor and a 
suitable indicator as well as a pressure indicator. 
Prior to polymerisation the emulsion is washed with an inert gas, e.g., 
with nitrogen or carbon dioxide, so as to remove the oxygen. The oxygen 
can also be removed by repeated evacuation and rinsing of the emulsion 
with nitrogen. 
Polymerisation can be started with the known radical initiators, by heating 
the monomer emulsion, e.g., with 2,2-azoisobutyrodinitrile, 
2,2-azo-bis-(2-amidineopropane) dichloride, 4,4-azo-bis-(4-cyanvaleric 
acid), peroxocarbonates, and peroxides such as tert-butylhydroperoxide, 
dibenzoyl peroxide, and persulfates such as potassium peroxide disulfate. 
Proceeding from monomer emulsions at room temperature or in the cooled 
state, polymerisation can be initiated by the addition of a redox system 
as a starter, e.g., by the addition of aqueous solutions of sodium 
dithionite and potassium peroxide sulfate. When this is done, the monomer 
emulsion is heated by the exothermic polymerisation and polymerisation is 
continued by the thermal decomposition of a second starter in the 
emulsion. 
The desired polymerisation temperature in the range of 
20.degree.-70.degree. C. is adjusted or controlled by the pressure in the 
polymerisation vessel. Once the polymerisation vessel has been evacuated 
polymerisation is started at the appropriate low pressure and continued, 
in which connection pressures in the range of 10-150 mbar have been found 
to be advantageous. The polymerisation temperature or pressure in the 
reaction system are so selected that polymerisation takes place at 
sufficient reaction speed. With the start of polymerisation the partial 
vapour pressure of the water and the liquid hydrocarbons increases above 
the monomer emulsion. When the low pressure that has been selected is 
reached the water begins to distill off from the polymerizing emulsion. In 
order to maintain the desired low pressure within the reaction vessel the 
water vapour is drawn off through an effective cooling system and 
condensed in a receiver, preferably together with small fractions of the 
liquid hydrocarbons. In this way, the heat that is liberated during 
polymerisation is eliminated from the system. At the same time, the 
concentration of the resulting polymer dispersion is increased by the 
separation of the distillate. 
If needs be, polymerisation can also be influenced by known measures such 
as external cooling, inhibition by air injection, etc. After the removal 
of atmospheric oxygen that has been introduced in limited quantities, by 
the renewed application of the vacuum, polymerisation proceeds 
automatically, i.e., without the renewed addition of a starter. 
If no other measures for heat exchange are carried out during distillation, 
the reaction yield can be controlled quite simply on the basis of the 
quantity of distillate. The reaction is concluded with the cessation of 
the heat tone and distillation. 
The distillate can be divided into water and preferably small fractions of 
liquid hydrocarbons both of which can be reused as raw material. If 
2,2-azoisobutyro dinitrile is used as a starter before being used again 
the distillate must be filtered so as to cleanse it of fractions of this 
substance, which make the transition with the steam during distillation. 
In the process according to the present disclosure stable emulsion polymers 
with a high polymer content are produced in one process stage by 
polymerisation of water-soluble monomers in the form of the water-in-oil 
emulsion; in this stage the polymerisation heat is used as vapourizing 
heat to distill off the water from the reaction system during 
polymerisation. In contrast to processes known up to the present time and 
used to produce water-soluble polymerisation products no additional 
thermal energy is used to boost the concentration. 
This process permits the use of inexpensive raw materials in the form of 
low concentration solutions of the monomers to produce concentrated 
polymer dispersions. 
In this process, the control of polymerisation by the selection of suitable 
temperature and pressure conditions, and the effective removal of 
polymerisation heat permits the large scale production of polymers that 
are extremely effective from the point of view of technical applications 
and which are particularly well suited, amongst other things, as 
flocculating, retention and de-watering agents as well as additives to 
flood water during the extraction of crude oil.

Most surprising, it was found that, according to the present disclosure, 
very effective polymerisation was achieved by stirring, particularly by 
stirring with a high level of turbulence, without there being any 
interruption in the reaction. In contrast to this, in other processes, 
e.g., as in DE-OS No. 32 07 113, brisk stirring is a disadvantage since it 
causes the polymerisation reaction to break down. 
EXAMPLE 1 
The reaction vessel is provided with a stirrer, a thermometer, a descending 
cooler, a vacuum connection, and a RTC vacuum controller (Reichelt 
Chemietechnik GmbH & Co., Heidelberg, Catalogue No. 95412). 
A solution of 220.20 g acrylamide, 190.02 g water and 119.44 g acrylic acid 
was neutralized and adjusted to pH 7.8 by the addition of 204.77 g 45% 
caustic potach. 
35.39 g sorbitane monoisostereate were dissolved in a beaker in 216.47 g 
iospar M (Esso.TM.; isoparaffin hydrocarbon mixture with a boiling range 
of 204.degree.-247.degree. and a density of 0.786 g/cm.sup.3 at 12.degree. 
C.) to form the hydrophobic phase. The water-in-oil emulsion was formed by 
pouring the aqueous monomer solution (concentration 54.8%) into the 
hydrophobic phase whilst stirring. The emulsion was homogenized with a 
mixing rod (Krups.TM.-3-Mix) for 60 seconds whereupon it displayed a 
viscosity of 4.560 mPa.S. 
After the addition of 0.34 g 2.2'-azoisobutyro dinitrile the emulsion was 
added to the reaction vessel and rinsed for 30 minutes with nitrogen 
whilst being stirred. Next, the emulsion was heated slowly in a bath, 
stirring speed 300 rpm, and the pressure in the vessel was adjusted to 55 
mbar by connection to a water-jet pump through the RTC controller. After a 
brief period the emulsion was heated to 48.degree. C. and polymerisation 
began, which is recognizable at the start of distillation. At 58.degree. 
C. the bath was removed and the reaction mixture isolated. The progress of 
the polymerisation can be seen from the data shown in the following table. 
______________________________________ 
Time Temp. Bath Temp. Pressure 
(Min) (.degree.C.) 
(.degree.C.) 
(mbar) 
______________________________________ 
0 36,0 65 55 
2 40,0 64 .dwnarw. 
Batch begins to 
7 46,0 61 .dwnarw. 
boil; start of 
13 48,0 58 .dwnarw. 
distillation 
15 48,0 isolated 55 
18 46,0 " 50 
21 47,0 " .dwnarw. 
28 49,0 " .dwnarw. 
34 47,0 " .dwnarw. 
38 46,0 " 50 
41 50,0 " 45 
43 48,0 " .dwnarw. 
51 47,0 " .dwnarw. End of distillation 
55 48,0 " .dwnarw. 
62 48,0 " 45 
72 48,0 " 50 
77 47,5 " 50 
83 46,5 " 45 
105 44,0 " ventilated 
______________________________________ 
Once the reaction has ceased, the reaction vessel is ventilated and the 
polymer dispersion is drawn off. 171.0 g distillate is obtained during 
polymerisation. 
The polymer dispersion has a viscosity of 2.000 mPa.S. The 0.5-% solution 
(relative to polymer) obtained with the use of a wetting agent, e.g., 
nonylphenol-9 EO has a viscosity of 8.700 mPa.S. The product is effective 
as a flocculating agent in aqueous heavy liquids that contain solids. For 
purposes of description the flocculating behaviour and the sedimentation 
can be determined in a sample liquid. 
To this end, a 250-ml test cylinder (diameter 50 mm) was filled with a clay 
slurry (Stammberge I) produced by the intensive mixing of 20 g blue clay 
from the Witterschlick mine (near Bonn) and one liter of water. The liquid 
was stirred with a simple angled rod stirrer at 300 rpm and a solution of 
the polymer was added by pipette in ppm-quantities. After the stirring 
machine had been stopped the time taken for the surface of the flocculant 
bed to fall from the 250 ml marking to the 170 ml marking of the test 
cylinder was measured in seconds. Time so measured is quoted as the 
flocculating value. 
In order to test the cationic polyelectrolytes, 1.25 ml of a 20-% solution 
of Al.sub.2 (SO.sub.4).sub.3.18H.sub.2 O (Stammberge II) was added to the 
clay slurry in the test cylinder. (The flocculating values for Stammberge 
I (Witterschlick clay), determined from a 0.01-% solution are as follows 
at 1 ppm 3.5 seconds, 
at 0.5 ppm 7.3 seconds) 
The polymer content of the dispersion amounts to 49.3%, and the water 
content, 19.8%. 
EXAMPLE 2 
Production is carried on using the same apparatus as in example 1. 
The aqueous monomer solution is produced from 336.56 g water, 337.44 g 
acrylamide and 311.72 g of an 80-% aqueous solution of acrylic 
acid-trimethylammonium ethylester chloride and adjusted to pH 4.4 with 6.5 
ml 30-% hydrochloric acid. The hydrophobic phase was obtained by mixing 
14.0 g sorbitane monoisostereate and 396.0 g isopar M (Esso). 
The water-in-oil emulsion was formed by adding the aqueous solution to the 
hydrophobic phase, which was homogenized for 60 seconds with a Krups-3 
mixer and adjusted to a viscosity of 840 mPa.S. 1.240 g of the emulsion 
added to the reaction vessel together with 0.3 g 2,2'-azoisobutyro 
dinitrile and freed of atmospheric oxygen by connection to water-jet pump 
whilst being stirred at 250 rpm for 20 minutes. The pressure in the 
reaction vessel at the beginning of polymerisation was adjusted to 70 mbar 
through the RTC vacuum controller and the reaction was started by the 
addition of 0.23 ml of a 0.5-% sodium dithionite solution. The temperature 
and pressure values that occurred during the course of polymerisation can 
be seen in the table. 
______________________________________ 
Time Temp. Pressure 
(Min) (.degree.C.) 
(mbar) 
______________________________________ 
0 23 70 +0,23 ml 0,5% Na.sub.2 S.sub.2 O.sub.4 in water 
4 34,5 44 
18 37,5 64 
27 40 64 
34 44,5 64 Start of distillation 
46 44,5 64 
66 44 62 
81 41,5 59 
114 43 58 approx. 80 ml distillate 
125 50 1.000 ventilated with N.sub.2 
132 58,5 1.000 
145 70,5 1.000 end of polymerisation 
______________________________________ 
The distillation phase begins at 44.5.degree. C. and 64 mbar; once 
approximately 80 ml of distillate have been obtained, the pressure is 
raised through the RTC vacuum controller and polymerisation is carried on 
adiabatically under a temperature increase up to 70.5.degree. C. until the 
end. The polymer dispersion is then cooled by renewed distillation at 50 
mbar. Altogether, 121.0 g distillate was separated off. 11.2 g of a 20-% 
aqueous solution of sodium dithionite was added to the polymer dispersion 
while stirring and then 11.2 g of a C.sub.12 -C.sub.18 fatty alcohol-5-EO 
oxethylate was added. The product has a viscosity of 2.200 mPa.S. The 1-% 
solution (relative to the polymer fraction) in completely desalinated 
water has a viscosity of 3.800 mPa.S. (Flocculation value in Stammberge II 
(Witterschlick clay) determined from a 0.1-% solution amounts to 3.4 
seconds at an addition of 2 ppm). 
The polymer content of the dispersion amounts to 45.7%, and the water 
content amounts to 20.4%. 
EXAMPLE 3 
Production is carried on with the same apparatus as example 1. The aqueous 
monomer solution is produced from 193.2 g water, 207.0 g acrylic acid, 
179.7 g 25-% ammonia, 0.045 g methylenebisacrylamide and 0.13 g 
2,2'-azo-bis-(2-amidinopropane) hydrochloride. The pH value of the 
solution was adjusted to 5.84. 
The hydrophobic phase was formed by mixing 200.1 g of an isoparaffinic 
hydrocarbon mixture (boiling range 204.degree.-247.degree. C.) with 17.3 g 
sorbitane monoisostereate. 
The water-in-oil emulsion is formed by adding the aqueous monomer solution 
to the hydrophobic phase while stirring and this was homogenized for 20 
seconds with a Krupps-3 mixer and adjusted to a viscosity of 1400 mPa.S. 
780 g of the monomer emulsion were added to the reaction vessel and whilst 
being stirred (250 rpm) were freed of oxygen for 20 minutes by connection 
to a water-jet pump. At the beginning of polymerisation pressure in the 
reaction vessel was adjusted through the RTC vacuum controller to 70 mbar 
and the water-in-oil emulsion was heated to 42.degree. C. After this the 
reaction vessel was isolated. 
The temperature and pressure values during the polymerisation process are 
seen in the following table. 
______________________________________ 
Time Temp. Pressure 
(Min.) (.degree.C.) 
(mbar) 
______________________________________ 
0 21 70 
9 42 Isolation without heating 
10 42 Start of distillation 
20 44 
23 45 
24 45,5 78 
66 44,5 70 approx. 45 ml distillate 
79 60 
85 74 
126 78,5 
134 78,0 70 
______________________________________ 
The emulsion polymer was cooled to 30.degree. C. by distilling off the 
water. Altogether, a total of 80 g was separated off as distillate. 
3.0 g ethoxylated monylphenol and 3.0 g 25-% ammonia were added during 
stirring. The polymer content of the homogeneous dispersion amounted to 
33.7%. 
On the addition of 0.5% polymer to water viscosity increased to 4600 mPa.S.