Polymerization process

DESCRIPTIVE MEMORY

This invention relates to a new process for the polymerization of monomers that polymerize exothermically in a solvent, especially monomers soluble in polar solvents, particularly acrylamide and copolymers of acrylamide with other vinyl monomers soluble in 'polar solvents.

One of the problems encountered so far in the manufacture of polymers has been the difficulty of moving viscous masses. As the polymerization takes place, viscous masses form that cannot be handled

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easily. This causes a problem in drying, and as a consequence it is only commercially possible, in most cases, to keep the polymers in a liquid state. In addition, in the majority of the polymerization processes, the presence of atmospheric oxygen or air has so far been considered undesirable and interfering with the polymerization. To avoid this, purging the reaction polymerization mixture with nitrogen has been used.

One of the characteristics of the present invention is to provide a new and improved type of polymerization process in which the resulting polymers are obtained directly as dry products.

Another feature is to provide a new and improved polymerization method that can be carried out in the presence of air or atmospheric oxygen.

A more specific feature of the invention is to provide a new and improved method of polymerizing monomers soluble in polar solvents, preferably acrylamide or mixtures of acrylamide with other vinyl monomers soluble in polar solvents.

Another specific feature of the invention is to provide a new and improved method of producing polyacrylamide. Other features will appear as follows.

According to the invention, monomers soluble in polar solvents are polymerized, for example water

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and / or methanol, capable of undergoing polymerization exothermically, by j (1) Formation of a solution of at least one monomer and a catalyst, (2) converting the solution prepared in this way into the form of a thin film5. the, (3) heating the thin film formed to a temperature sufficient to initiate polymerization and start this polymerization, and (4) maintain the polymerization temperature until the desired polymerization is completed. The product can be recovered as a solid. by adjusting the temperature of the polymerization solution enough to remove the solvent from the system.

The thickness of the film or layer is a factor in the satisfactory operation of the process. I know

fifteen. it has obtained good results when the thickness of the film or layer is between 1 and 30 mm, and, in most cases it is preferable to operate with a layer thickness of approximately 13 mm (0.5 inch). Satisfactory results have also been obtained with a grue20. so about 1.5 mm layer, 3 raa and 6 mm. You can use thinner layers.

The concentration of the monomer in the solution to be polymerized will depend on the heat of reaction. In general, as the concentration of monomer is increased in

25. The polymerization reaction mixture will generate a greater amount of heat. The monomer concentration must therefore be controlled so that the reaction heat vaporizes at least a part of the solvent, but

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that does not break down the resulting polymer or produce side reactions. Thus, when polymerizing the acrylamide it is convenient to maintain a concentration of monomer within the range of about 20 to 30 fi by weight of the polymerization reaction mixture. This concentration can be as low as in certain cases, and high enough to reach saturation at polymerization temperatures in other cases, but is usually £ 10 to £ 5. The thickness of the layer can also be varied depending on the concentration of monomer used.

According to a preferred embodiment of the invention, the process is carried out in a closed system, where the atmosphere above the reaction film or layer is heated. It can be used, for example, in an apparatus such as a humidifier cabinet, where the system is initially heated by means of hot air. After starting the polymerization, the temperature of the reaction mixture is, in fact, higher than that of the heated air, and the latter acts, therefore, as a refrigerant. When the reaction is carried out in a stationary, closed chamber or cabinet, it is convenient to form the reaction mixture film or layer on trays. However, instead of this type of arrangement, the reaction mixture film or layer can be formed in a conveyor dryer where a continuous band carrying the film or layer is continuously displaced through a se chamber25.

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lamb In both cases the product is dried in situ, without removing it from the place where it was previously formed,^¡

The invention is especially useful for making water-soluble polymers of ethylenically unsaturated monomers and soluble in polar solvents, for example to make polyacrylamide by polymerization of acrylamide in an aqueous solution containing an azo-bis-iso-butyronitrile catalyst dissolved with the aid of methanol, the acrylamide concentration being within the range of 10 to 50% by weight of the polymerization reaction mixture, preferably 20 a by weight of this mixture, and the concentration of the catalyst included within the range of 0.03 to 2% by weight of the acrylamide, preferably about 0.5 / s or weight of the dry monomer. The amount of methanol used to dissolve the catalyst may vary, and is usually within the range of about 0.5 to 40 / by weight of the monomer, preferably 5 / of said monomer.

Preferably, the catalyst is prepared as an independent solution and then added to an aqueous solution of the monomer, under temperature conditions such that the catalyst remains in solution but at an insufficiently high temperature to initiate the polymerization reaction. With an azocatalyst of the type previously described, the catalyst begins to separate from the solution at a temperature below 38 ° C, and is pre25.

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It is possible to maintain a temperature of at least this value when the catalyst is mixed with the aqueous monomer solution.

A preferred way of carrying out the procedure5. The solution consists in placing the monomer solution mixed with the catalyst on metal trays coated with an inert layer, for example polytetrafluoroethylene (Teflon). Eas trays are placed in a dryer unit where the temperature can be increased

10. in any suitable way, this unit being provided with an exhaust and an output damper that can be closed. Under these conditions, the exhaust is stopped and the damper is closed in order to saturate the air above the trays, and thereby reduce it to me15. I encourage evaporation of the solvent while the monomer-catalyst solution is heated to the reaction temperature. Then the temperature of the dryer is increased until the solution reaches the reaction temperature. When the reaction takes place, the solution of mo20. The number thickens and the temperature of the reaction mixture rises above the boiling point. When the reaction is over, the exhaust damper opens and starts the exhaust. Then the temperature of the dryer is increased again, preferably to about 105 ° C.

25. When drying is complete, the product usually contains about 10 to 15 fi of moisture. The polymer sheets are sufficiently dry when they exhibit a net and easy separability of the coated surface of

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Teflon of the trays, and are soft at the drying temperature, but harden when cooled to room temperature. The product; it can be ground to a state of finer subdivision in any suitable way.

The same general procedure can be used to prepare many different types of polymers, but the one described is especially useful for preparing many different types of polymers and copolymers in which one of the monomers is acrylamide. Further examples of such polymers are copolymers made of 30 # of acrylic acid monomer and 70 fi of acrylamide monomer, and copolymers made of 50 # of acrylic acid monomer and 50 # of acrylamide monomer.

The invention will be further illustrated, but not limited, by the following examples where the amounts are indicated by weight unless otherwise specified.

EXAMPLE 1.

A 30 # solution of acrylamide is prepared by mixing the acrylamide monomer with deionized water and adjusting the pH to 5.0 with sodium hydroxide. Separately^:A catalyst solution is prepared by dissolving 5 # by weight of azo-bis-isobutyronitrile in methanol. The acrylamide solution is heated to a temperature of 46 ° C and maintained at this temperature. Then the catalyst and acrylamide solutions are mixed in a storage tank in the appropriate proportions to give an amount of azo-bis-isobutyronitrile equal to

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0.5 / by weight of the acrylamine (based on dry weight) contained in the solution. A series of rectangular Teflon-coated aluminum trays are placed in a dryer equipped with an exhauster and a damper

5, escape. The dryer is previously heated at 49 ° C with the exhaust stopped and the damper closed. Then the monomer-catalyst solution is loaded into the trays so that they are filled to a level of 13 mm. When the trays are full

XO The temperature is raised to 77 ° C to the desired level, which causes the solution contained therein to be heated to between 49 and 68 ° C in about 45 minutes, and that the polymerization reaction is initiated. The reaction is essentially complete after approximately 15, - half an hour after the beginning. During the reaction, the catalyst-monomer solution of all trays clicks and explodes with a considerable release of water vapor due to the heat of reaction; the reaction temperature rises to a point of approximately

twenty. 113-119 ° 0. Once the reaction is over, the exhaust damper is opened and the exhaust is connected. Half an hour after the end of the reaction, the temperature of the dryer rises to 104 ° 0. Drying takes about 15-17 hours and once the · are finished, trays are removed from the dry $ 2_t dero and left^? at rest at room temperature. The resulting polymer sheets are sufficiently dry when they have a net and easy separability from the coated surface of the trays. The content w »« i »¿.

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of moisture in the dry state is approximately 1015 #. The dried leaves are soft at the drying temperature, but harden at^!be cooled to room temperature.

EXAMPLE 2

The procedure is the same as in example 1, except: in which a 50 # solution of aorilamide in deionized water is used, the amount of catalyst, based on aorilamide, is. 0.25 # and the amount of. Methanol, based on aorilamide, is 5 #. The. initiation temperature is 60 ° C. A 1 # solution of dry product in deionized water at room temperature (25 ° 0) gives a viscosity of 20.7 centipoise. EXAMPLE 3

The same procedure is used as in Example 1, except that the aorilamide solution contains 20 # of aorilamide and 30 # of deionized water. The polymerization initiation temperature is 60-61 ° 0 and the polymerization time is 30 minutes.

The viscosity of a 1 # solution of product in deionized water is 47 centipoise at 25 ° C.

EXAMPLE 4

• The procedure is the same as in Example 1, except that the monomer solution is made by mixing 14 parts of acrylamide and 6 parts of acrylic acid with 30 parts of deionized water and the pH is adjusted to 3.4. The catalyst solution consists of 1 # 'of azo-bis-isobutyronitrile in 20 # of methanol, based on so-ιο-

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About the total weight of monomer. the initiation temperature is 60-56 ° 0, the reaction time is 1.75 hours, the drying temperature 75 ° 0 and the drying time 22 hours.

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EXAMPLE 5

The procedure is the same as in Example 4- except that the monomer solution consists of 10 parts of acrylamide, 10 parts of acrylic acid and 80 parts of deionized water, the pH being adjusted to 3/5.

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The process is the same as in Example 5 except that a mixture in (NH4) 2 is used as catalyst^S2°8 ^{and Ka}2^S2°5 ³¹¹ P^r° P^orcion3s based on the total monomer of 0.025 and $ 0.10 respectively as catalyst. The pH of the monomer solution is 8.5 the 60 ° 0 ingestion temperature, the reaction time 0.75 hour and the drying time 16 hours.

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The procedure is the same as in Example 6 except that the catalyst consists of 0.25 $ of (ΠΗ ^) 2 ^ 2θ8 ^sor^lamea^³· 'AXIS II PL 0 8.

The procedure is the same as in Example 6 except that the relative amounts of the catalyst ingredients are 0.10 and $ 0.40 respectively, based on the total monomer, and 0.1 $ is added, also based on the total monomer, of the tetrasodium salt

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of ethylenediaminetetraacetic acid, as a chelate agent. hot The initiation temperature is 60 ° 0, the * time. reaction time 1 hour, drying temperature 75 ° C and drying time 15 hours.

It should be recognized that the above examples are illustrative and subject to various variations. Thus, different types of catalyst systems can be used, the process can be carried out at different pH values ​​and several film thicknesses can be used. The pressure on the reaction mixture layer during the reaction or after, during drying, can be atmospheric, subatmospheric or superatmospheric. The process can also be performed in a manner similar to that described in the examples but using a nitrogen purge on the monomer solution. However, as indicated above, an advantage of the process is that it can be carried out without nitrogen purge and at atmospheric pressure.

The products of the examples are especially useful for coagulation and sedimentation of suspensions. Preferred products are soluble in water, and small amounts thereof, in the order of

1-15 ppm, when added to aqueous suspensions of suspended solids, for example turbid waters containing silica, basin wash waters, and waters containing iron oxide suspended from the steel mills, are effective in orovocation of the orecipitation. of the oue solids

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they can then be separated from the aqueous layer by decantation, filtration or in any other way.

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