GB2046279A - Process for polymerising dialkyl ammonium compounds - Google Patents

Abstract

Polymers of the general formula:- <IMAGE> in which R<1> and R<2> are the same or different alkyl radicals, which can also be joined together to form a ring, X<-> is an anion, n, which corresponds to the valency of the anion, is a small whole number and y is the degree of polymerisation, are prepared by a polymerisation process wherein a 30 to 70% aqueous solution of a dialkyldiallylammonium salt of the general formula:- <IMAGE> in which R<1>, R<2>, X<-> and n have the same meanings as above, is mixed at a pH value of from 6.7 to 10.3 with a peroxydisulphate initiator and, if X<-> is not chloride or bromide, with a soluble chloride and reacted either discontinuously at a temperature of from 10 to 80 DEG C. or continuously at a temperature of from 40 to 90 DEG C. in an apparatus which provides a residence time sufficient for the polymer to be obtained in yields of over 90%. The polymerisation process is less sensitive to oxygen than previous processes and is easily controllable.

Description

SPECIFICATION Process for the production of polymeric tetraalkylammonium compounds The present invention is concerned with a process for the production of polymeric tetraalkylammonium compounds by the discontinuous or continuous polymerisation of dialkyl-diallylammonium compounds.

Polymeric tetraalkylammonium compounds are used, inter alia, as electrically-conductive coatings and as precipitation and flocculation agents.

Discontinuous processes for the polymerisation of diallylammonium compounds, these processes depending either upon a thermal-radical or on a redox-initiated polymerisation.

Apart from other initiators, there has, inter alia, been used ammonium peroxydisulphate for the thermal-radically-initiated polymerisation of diallylammonium compounds in oxygen-free monomer solutions (see U.S. Patent Specification No. 3,472,740). Copolymers can be prepared similarly by thermal-radical initiation (see U.S. Patent Specification No. 3,639,208) or by redox initiation (see Federal Republic of Germany Patent Specification No. 2,738,758).

It is known that the properties of water-soluble polymeric tetraalkylammonium compounds become better, when used as precipitation, flocculation and coating agents, with increasing molecular weight, the molecular weight obtained of the polymers depending substantially upon the degree of purity of the monomers, upon the initiator system, upon the concentration ratios, upon the reaction temperature and upon disturbing influences, for example the action of atmospheric oxygen.

Since polymerisation in the presence of atmospheric oxygen gives rise to products with lower molecular weights and thus to low viscosities of the polymer solution, which are technically disadvantageous for use, it has been suggested to compensate this influence by copolymerisation with up to 5% by weight of cross-linking agents, (see German Democratic Republic Patent Specification No. 127,729). However, from the point of view of technical use, high molecular weight linear homopolymers are more valuable.

The disadvantages of the thermal-radically initiated discontinuous polymerisation are that, in the case of a high reaction temperature of from 80 to 110"C., due to continuous dosing in of initiator, the thermal controllability of up to batch sizes of at most 100 mol of monomer is reached and only average molecular weights are thereby achieved.

For a continuous carrying out of the reaction, that would mean, in order to be able to add the initiator continuously, dosing in via numerous dosing points distributed over the residence length, i.e. the length of the reaction apparatus in which the reaction mixture remains during the reaction, which would mean a considerable technological expenditure.

The polymerisation is very sensitive to oxygen. The polymerisation taking place in the presence of the acid-reacting ammonium peroxydisulphate, which forms acid in the course of the reaction, is also very sensitive to traces of heavy metals and definitely requires the use of chelating agents. Furthermore, there is an undesired negative influence of impurities, for example in the monomers, on the molecular weight of the product formed. Due to the narrow temperature range of the thermal-radical-initiated polymerisation, there is only a limited possibility of influencing the end value of the viscosity of the product by temperature control.

The disadvantages of the known redox-initiated polymerisation are that, in the often long reaction times, only incomplete conversions are achieved. For the reduction of the negative influence of oxygen, up to 5 mol % of cross-linker must be added in order to achieve products with the same viscosity as are obtained with the exclusion of oxygen and the initiator concentration and the necessary concentration of the chelating agent must also be simultaneolusly increased.

In the case of a combination of redox initiation and thermal initiation by the use of so called "double catalysts" (see Federal Republic of Germany Patent Specification No. 2,544,840), high conversions are admittedly achieved but the polymers obtained have a very low viscosity.

Continuous processes for the preparation of polymeric tetraalkylammonium compounds have hitherto not been described.

The previously known discontinuous processes for the polymerisation of diallylammonium compounds are not suitable for carrying out the reaction continuously.

It is an object of the present invention to provide a polymerisation process which has a low oxygen sensitivity, proceeds at relatively low temperatures and gives yields of over 90%.

It is also an object of the present invention to provide for a variable carrying out of the reaction in devices which permit the necessary residence times and are thermally easy to control.

Thus, according to the present invention, there is provided a process for the production of polymeric tetraalkylammonium compounds of the general formula:-

in which R1 and R2 are the same or different alkyl radicals, which can also be joined together to form a ring, X is an anion, n, which corresponds to the valency of the anion, is a small whose number and y is the degree of polymerisation, by polymerisation of a diallyldialkylammonium salt with the use of a peroxydisulphate as initiator, wherein a 30 to 70% solution of a dialkyldiallylammonium salt of the general formula::-

in which R', R2, X- and n have the same meanings as above, is mixed at a pH value of from 6.7 to 10.3, which can be adjusted by the addition of an appropriate solution and preferably of a buffer solution, with a peroxydisulphate and, if X- is not chloride or bromide, with a soluble chloride and reacted either discontinuously at a temperature of from 10 to 80"C. or continuously at a temperature of from 40 to 90"C. in an apparatus which provides a residence time sufficient for the polymerisation.

The dialkyldiallylammonium salts used are those which contain the same or different alkyl radicals, which can also be joined to form a ring. The anions present in these salts can be inorganic anions, for example, chlorine, bromine, sulphate, phosphate or fluoride anions, or also anions derived from organic acids, for example acetate anions.

The pH of the reaction mixture is preferably adjusted by the addition of a buffer substance. The pH-regulating buffer substances can be alkali metal or ammonium salts of weak acids, for example carbonates, bicarbonates, borates or phosphates, or salts of organic acids, the buffer action of which is generally known, for example acetates, or also mixtures of such materials. The amount of the buffer substances is such that the resulting buffer capacity is sufficient for the adjustment of the desired pH range. Ammonia can also be used in combination with buffering salts, for example with ammonium peroxydisulphate, ammonium sulphate or ammonium chloride, or also in combination with the above-mentioned salts of weak acids. Apart from the buffer systems here mentioned, other combinations can also be employed.Carbonates and bicarbonates have the advantage that, from the bicarbonate stage, even at 80"C., due to the giving off of carbon dioxide, the reformation of carbonate takes place; the buffer capacity of such systems is, therefore, high. Furthermore, the liberated carbon dioxide brings about a mixing up of the reaction solution and provides an advantageous inert atmosphere.

When the process is carried out discontinuously, the adjustment of the pH value can take place by the continuous and precise dosing in of ammonia, of an aqueous alkali metal hydroxide solution or of another base, in dependence upon the continuously measured pH value of the reaction mixture.

In the case of thermal-radical initiation, traces of heavy metals and especially traces of iron have a very disadvantageous effect; by the use of acid-reacting (and, in the course of the reaction, also acid-forming) initiators, such as ammonium peroxydisulphate, the traces of heavy metals remain dissolved in the reaction mixture. The carrying out of the process according to the present invention requires the adjustment of pH values at which, for example, iron becomes insoluble as ferric hydroxide or as a basic salt. Therefore, there is no need to use a chelating agent. If, however, a pH value of from 6.7 to 7.5 is used, it is recommended to add, per 25 kg.

of monomer, about 10 g. of a condensed phosphate, for example sodium hexametaphosphate, or of a geminal bis-phosphate acid or of a soluble salt thereof, for example etidronic acid or dimethylaminomethanebisphosphonic acid. Such additives can also be advantageously used even at higher pH values. They promote a uniformly stable reaction and avoid disturbing influences due to the take up of traces of heavy metals during the polymerisation reaction, for example from metal parts of the reaction vessels used for the reaction.

The process according to the present invention makes possible, by means of an appropriate buffer, the adjustment of pH values at which the polymerisation already takes place at 10 to 20"C. If provision is made for maintaining this temperature by cooling, then, in the case of prolonged reaction times, polymer solutions are produced with very high viscosities, which is a further important advantage in comparison with the known processes since the reaction products obtained are unbranched polymers which are more useful. By selection of the pH value and of the temperature, it is possible to influence the molecular weight of the resultant polymer.

The initiator used can be, for example, sodium, ammonium or potassium peroxydisulphate or polydimethyldiallylammonium peroxydisulphate. The two last-mentioned initiators are soluble in the solution of the monomers in the necessary amount of up to 2 mol %, in contradistinction to their substantially lower solubility in water. The peroxydisulphate initiator is preferably used in an amount of from 1 to 2 mol %.

We have found that the improved initiation with S208- - and buffer substances in a pH range of from 6.7 to 10.3 is, surprisingly, only possible in the case of compounds of general formula (I) when X- is chloride or bromide. In order to achieve the same effect with, for example, the corresponding sulphates, phosphates, fluorides and acetates, it is necessary to add a soluble chloride, for example an alkali metal chloride or ammonium chloride. The addition of the corresponding bromides is possible but is does not provide any advantages with regard to the reaction and the molecular weights which can be achieved; furthermore, the bromides of the corresponding polymers have a lower solubility.An increase of the pH value above 10.3 is also not advantageous because a lower degree of conversion is achieved and the speed of reaction becomes so great that it becomes difficult to remove the heat of reaction.

With the use, by way of example, of dimethyldiallylammonium chloride, not only by the discontinuous process but also by the continuous process, with comparable initiator, concentration and temperature conditions, in the case of the polymerisation of 61.85 mole batches, the buffer system was varied and the degree of conversion obtained determined by NMR spectroscopy. The investigations were carried out in the presence of atmospheric oxygen. The temperature control was such that the temperature was maintained for one hour periods at 50, 60, 70 and 80"C. In each case, the final concentration of polymer was 48%. The amount of peroxydisulphate was, in each case, 0.02 mol peroxydisulphate/mole of monomer. The buffer systems, the initial pH values and the degrees of conversion are shown in the following Table.

TABLE System initial degree of (Mol basic components/ pH conversion mol persulphate) 1.1 K2CO3/Na2S208 10.90 88.0 KOH + 1.1 K2CO3/(N H4)2S208 9.90 91.0 1.1 K2C03/0.5 Na2S208+0.5(NH4)S208 9.55 92.0 2.2 NH3/(NH4)2S208 9.45 93.0 1.1 K2CO3/(NH4)2S208 9.10 95.5 1.1 (NH4)2CO3/(NH4)2S208 8.65 98.0 2.2 KHCO3/Na2S208 8.25 98.5 2.2 KHCO3/(NH4)2S208 7.80 98.5 2.2 NH4HCO3/(NH4)2S208 7.65 98.5 2.2 CH3COOK/(NH4)2S208 7.00 98.3 2.2 CH3COO(NH4)/(NH4)2S2Q 6.70 98.0 The temperature control in the case of the examples given in the above Table was kept constant for the sake of comparability of the conditions. Other temperature controls have an influence on the final conversion. However, the maximum conversion remains in the pH range of 6.7 to 10.3.

When using very large batches in the discontinuous process, it proved to be advantageous, for ensuring the removal of heat, to dilute the monomer solution or a part thereof with already pre-polymerised product.

It is possible not only to dissolve the buffer substance in the monomer solution and to dose the solution of the peroxydisulphate into the current of product, as well as vice versa, but also to introduce both substances into the current of product. When potassium peroxydisulphate or polymeric dimethyldiallylammonium peroxydisulphate is to be used, this can be previously dissolved in the monomer solution and the buffer substance dosed into the current of product.

We have found that increasing the pH value in the range of 6.7 to 10.3 has a surprisingly favourable action on the carrying out of the polymerisation: in this pH range, the polymerisation already begins at a low temperature at technically satisfactory rates, for example at pH 6.7 already at about 60"C., at the pH 9.1 at 30"C. and above pH 9.45 even at 20 to 10"C.; the rates of polymerisation increase in the same manner: for example, the reaction times shorten (in order to achieve 50% conversion) in solutions with comparatively high initial pH values in the following ratio: pH 7.8: pH 9.9: pH 12.7=2.6:1.7:1, i.e. the conversion/time ratio increases with increasing pH value.

The technical result of this observation is that, by adjustment of the pH which advantageously takes place by means of buffer systems, the reaction temperature and the reaction rate can be determined, which is a prerequisite for the removal of the considerable heat of polymerisation.

The process thereby makes possible the continuous polymerisation of diallylammonium compounds on a technical scale.

One of the most important technical-economic effects obtained with the process according to the present invention is that, in the pH range of 6.7 to 10.3, high yields of polymer of from 91 to 98.5% are achieved.

The following Examples are given for the first purpose of illustrating the present invention, the first six Examples being of the discontinuous process and the last five Examples being of the continuous process: Example 1.

In a 250 litre stirrer apparatus with a built-in cooling coil of chromium-nickel steel (1.25 m2 cooling surface) are mixed 190 kg. (618.5 mol) of a 52.5% by weight solution of dimethyldiallylammonium chloride (with a sodium chloride content of 4.85% by weight), 2.82 kg. (2 mol %) ammonium peroxydisulphate (APS) in 7 litres of water, 1.85 kg. (4.4 mol %) 25% by weight ammonia solution in 6 litres of water and 40 g. technical grade sodium hexametaphosphate dissolved in 0.5 litres of water, the monomer concentration in the mixture being 48% by weight.While stirring, the reaction mixture is heated for half an hour at 40"C., the internal temperature being carefully observed (the temperature indication should have practically no lag) and then maintained for 1.5 hours at 40 + 2"C. by intensive cooling (cooling water inlet temperature 13"C). The temperature is then maintained for further one hour periods at 50"C.

and at 60"C., whereafter the reaction mixture is heated for 1.5 hours at 70"C. and finally for 1 hour at 80"C. After the S208- - detection is found to be negative, the degree of conversion is found to be 95% by NMR spectroscopy. The final pH value is 8.

Example 2.

The procedure according to Example 1 is followed except that, instead of ammonia, there is added 1.87 kg. (2.2 mol %) potassium carbonate in 6.5 litres of water. While stirring, the reaction mixture is heated in the course of 3 hours from 27"C. to 50"C. and is then maintained, by cooling, at 50 + 2"C. for 1.5 hours. Subsequently, the reaction mixture is heated for 2 hour periods at 60 and 70"C. and then for 1 hour at 80"C. The converison is 98%.

Example 3. (production of a highly viscous product) The same components are used as in Example 2 and the reaction mixture is kept at 15"C. for 80 hours by careful cooling. After 16 hours, the conversion is 55%. Thereafter, in the course of 8 hours, the temperature is increased slowly and continuously to 80"C., whereby, because of still occurring self-heating, the supply of heat has to be cut off from time to time and occasionally it is necessary to cool for a short time. The degree of conversion is 99%. The product obtained has a very high viscosity.

Example 4.

In a 40 litre stirrer kettle made of chromium-nickel steel with an incorporated cooling coil (cooling surface area 0.4 m2) and heating means, there are mixed 19 kg. (61.85 mol) of a 52.6% by weight dimethyldiallylammonium chloride solution and 1 31 g. (2.2 mol %) ammonium carbonate in 700 g. water and the mixture is pre-heated, while stirring, to 50"C.

282 g. Ammonium peroxydisulphate (2.0 mol %) dissolved in 700 g. water are then added thereto all at once and the temperature of the reaction mixture is kept constant at 50"C. for 1 hour, by cooling. By briefly heating and possibly subsequently cooling, the reaction temperature is kept for a further hour at 60"C. The temperature is then kept for 1 hour at 70"C. and thereafter, within the course of a further hour, brought to 80"C. until 5208 - can no longer be detected. The 48% polymer solution obtained has a degree of conversion of 98%, determined by NMR spectroscopy.

Example 5.

The procedure of Example 4 is repeated except that, instead of ammonium carbonate, there are added 210 g. (4.4 mol %) ammonium acetate in 630 g. water and in this case, the reaction mixture is pre-heated to 60"C. The 48% polymer solution obtained has a degree of conversion of 98%, determined by NMR spectroscopy.

Example 6.

Into an enamelled 3 m3 stirrer vessel with a double-wall cooling, there are placed 500 kg.

(3092.5 mol) polydimethyldiallylammonium chloride in the form of a 48% by weight solution and mixed with 950 kg. (3092.5 mol) of a 52.6% by weight dimethyldiallylammonium chloride solution containing 4.85% by weight dissolved sodium chloride, with solutions of 14.1 kg. (2 mol %) ammonium peroxydisulphate in 30 litres water, of 9.4 kg. (2.2 mol %) potassium carbonate in 30 litres water and of 200 g. sodium hexametaphosphate in 7.3 litres water. While stirring, the reaction mixture is carefully pre-heated to 35"C., the internal temperature being carefully observed, and the temperature then allowed to increase, while cooling, to 50"C. in the course of 5 hours.Thereafter, in the course of a further 5 hours, the reaction mixture is slowly and continuously heated to 80"C., using alternating cooling and heating periods. The final pH value is 8. The degree of conversion is found to be 96% by NMR spectroscopy.

Example 7.

A 100 litre stirrer kettle (A) is connected by a swan-necked overflow (overflow at 75 litres) with a second 250 litre kettle (B). Kettle A is filled with 75 litres of pre-polymerised polydimethyldiallylammonium chloride solution (obtained from a 52.6% by weight solution of dimethyldiallylammonium chloride by polymerisation with the use of peroxydisulphate as initiator). The pre-polymerised solution is heated to 45 to 60"C. and then, via a mixing device, per hour and by means of 3 dosing pumps, there are added thereto the following 3 solutions: 1. 57 kg. (188.5 mol) of a 52.6% by weight dimethyldiallylammonium chloride solution, 2. 564 g. (2.2 mol %) potassium carbonate and 10 g. sodium hexametaphosphate, dissolved in 2.4 litres water, and 3. 846 g. (2 mol %) ammonium peroxydisulphate, dissolved in 2.1 litres water.

Kettle A is warmed to allow 45 to 60"C. and kettle B to 50 to 80"C. The overflow from kettle B shows a conversion of 90 to 95%. A 48% by weight solution of polydimethyldiallylammonium chloride solution is obtained with a pH value of 8. The viscosity of the polymer solution can be influenced by the degree of conversion of the polymer solution initially employed and by dividing up the addition of the initiator solution to kettle A. By means of appropriate dilution of the components, in the case of practically the same conversion, there is obtained, for example a polymer concentration of 40% by weight.

Example 8.

The procedure described in Example 7 is repeated except that kettle A is replaced by a tube reactor, the temperature of which can be controlled. The conversion is 90 to 95%.

Example 9.

As residence length, there is used a flow reactor which consists of twelve 1.75 metre long chromium-nickel steel tubes of 26mm. diameter surrounded with cooling mantles which tubes are joined by standardised flanged tube angle pieces of Jena laboratory glass in such a manner that the resulting residence length ascends spirally. The gradient of the tube connections is so dimensioned that the individual flow tube, from the lower to the upper end thereof, is raised by an amount at least equal to the diameter of the tube. The cooling mantles are, from below upwardly, either connected in 4 groups each of 3 tubes to the temperature-controlling water circulation in such a manner that there is obtained a temperature gradation of 50, 60, 70 and 804C., or in 3 groups each of 4 tubes providing a temperature gradation of 55, 65 and 80"C.

For mixing the flow of product, the reactor is packed with filler bodies, for example with glass Raschig rings.

In a temperature-controllable storage vessel, to 190 kg. (6.18 g. mol) of a 52.6% by weight dimethyldiallylammonium chloride solution are added a solution of 1.88 kg. potassium carbonate (0.022 mol/mol monomer) in 7 litres water and a solution of 40 g. sodium hexametaphosphate in 0.33 litres water. The mixture obtained is stirred and a temperature is maintained in the solution which is above 32"C.

In a second storage vessel, there is prepared a solution of 2.83 kg. (0.02 mol/mol monomer) of ammonium peroxydisulphate in 6.18 litres water. By means of two dosing pumps, the components are brought together in a mixing device in such a manner that a monomer concentration of 48% by weight results. The capacity of both pumps is 3.22 kg./hour for the monomer solution and 0.1455 kg./hour for the peroxydisulphate solution.

The mixing device is directly connected with the flow reactor. The polymer solution leaving the flow reactor is 48% by weight and has a pH value of 8. The degree of conversion, determined by NMR spectroscopy, is 93 to 95%. The reactor remains free of all salt deposits during the whole of an operating period of 11 7.5 hours.

Example 10.

The procedure described in Example 9 is repeated except that, instead of potassium carbonate, there is used a solution of 1.31 kg. (2.2 mol %) ammonium carbonate in 7.26 litres water. There is obtained a 48% by weight polymer solution with a degree of conversion of 96 to 98%.

Example ii The procedure described in Example 9 is repeated except that instead of the potassium carbonate and ammonium peroxydisulphate solutions, there are used solutions of 2.15 kg. (4.4 mol %) ammonium bicarbonate in 12.18 litres water (15% by weight solution) and 2.82 kg. (2 mol %) ammonium peroxydisulphate in 2.82 litres water (50% by weight solution). There is obtained a 47.6% by weight polymer solution with a degree of conversion of 96 to 98%. The final pH value is 8.

Claims (19)

1. Process for the production of polymeric tetraalkylammonium compounds of the general formula:

in which R' and R' are the same or different alkyl radicals, which can also be joined together to form a ring, X- is an anion, n, which corresponds to the valency of the anion, is a small whole number and y is the degree of polymerisation, by the polymerisation of a diallyldialkylammonium salt with the use of a peroxydisulphate as initiator, wherein a 30 to 70% solution of a dialkyldiallylammonium salt of the general formula::-

in which R', R2, X- and n have the same meanings as above, is mixed at a pH value of from 6.7 to 10.3 with a peroxydisulphate and, if X- is not chloride or bromide, with a soluble chloride and reacted either discontinuously at a temperature of from 10 to 80"C. or continuously at a temperature of from 40 to 90"C. in an apparatus which provides a residence time sufficient for the polymerisation.

2. Process according to claim 1, wherein the pH value is adjusted by means of a buffer solution.

3. Process according to claim 1 or 2, wherein a dialkylallylammonium salt is used in which X- is a chloride, fluoride, bromide, sulphate or phosphate anion or an organic anion.

4. Process according to claim 3, wherein the organic anion is an acetate anion.

5. Process according to any of the preceding claims, wherein the peroxydisulphate used is sodium, potassium or ammonium peroxydisulphate or polymeric diallyldimethylammonium peroxydisulphate.

6. Process according to any of the preceding claims, wherein the peroxydisulphate initiator is used in an amount of from 1 to 2 mol %.

7. Process according to any of the preceding claims, wherein the pH is regulated with an alkali metal or ammonium salt of a weak acid or with a mixture thereof in an amount such that the resulting buffer capacity is sufficient for the adjustment of the pH range.

8. Process according to claim 7, wherein the salt used for regulating the pH is a carbonate, bicarbonate, borate, phosphate or acetate.

9. Process according to any of claims 2 to 6, wherein buffering is obtained with the use of ammonia in combination with a buffering salt.

10. Process according to claim 9, wherein the buffering salt is ammonium peroxydisulphate, ammonium sulphate or ammonium chloride.

11. Process according to any of claims 1 to 6, wherein, when carrying out the process discontinuously, the adjustment of the pH value takes place by the continuous and precise dosing in of ammonia, of an aqueous alkali metal hydroxide solution or of another base, in dependence upon the continuously measured pH value of the reaction mixture.

1 2. Process according to any of claims 2 to 10, wherein the buffer substance and optionally the peroxydisulphate are dosed in portionwise or continuously in the course of the polymerisation.

1 3. Process according to any of claims 2 to 12, wherein the buffer substance is dissolved in the solution of the monomer and the solution of peroxydisulphate is dosed into the current of product.

1 4. Process according to any of claims 2 to 12, wherein the solution of the buffer substance and the solution of the peroxydisulphate are dosed as a mixture into the monomer solution.

1 5. Process according to any of the preceding claims, wherein the temperature of the reaction mixture is gradually or stepwise increased in the course of the progressing polymerisation.

1 6. Process according to any of the preceding claims, wherein the monomer solution to be polymerised is diluted with pre-polymerised product.

17. Process according to any of claims 2 to 10, wherein continuous polymerisation is carried out in a device which provides the residence time and the temperature control necessary for the polymerisation.

1 8. Process according to claim 1 for the production of polymeric tetraalkylammonium compounds, substantially as hereinbefore described and exemplified.

19. Polymeric tetraalkylammonium compounds, whenever produced by the process according to any of claims 1 to 18.