RU2076873C1 - Process for preparing powdered acrylamide polymers - Google Patents

Abstract

FIELD: chemistry of high-molecular compounds, more particularly preparation of powdered acrylamide polymers. SUBSTANCE: the claimed process comprises polymerizing acrylamide in concentrated aqueous solutions using chemical initiators in the presence of 0.01-7.5 wt.-% of sodium or potassium or ammonium carbonate or bicarbonate and antiadhesion additive such as sodium alkylbenzene sulfonate in amount of 0.02-0.01 wt%. Reduced adhesion of polymer makes it possible to avoid sticking of polymer to the surface of equipment and also eliminate formation of agglomerates at drying stage. EFFECT: increased yield of the desired product and greater process efficiency.

Description

 The invention relates to the chemistry of macromolecular compounds, namely to the production of powdered polymers of acrylamide, which can be used as a flocculant in various production processes, water thickeners for oil production.

 One of the methods for producing powdered polymers is the radical polymerization of acrylamide in concentrated aqueous solutions under the action of chemical initiators, followed by grinding the gel-like polymer, drying and crushing the dry granules of the obtained polymer.

 Typically, the 30% gel rubber-like polymer obtained at the polymerization stage 20 is sticky, resulting in difficulties in unloading the polymer from the polymerization reactor. Due to the increased elasticity and adhesive ability, noticeable polymer deposits are formed on the walls of the polymerization reactor and on the surface of technological process apparatuses for processing a gel-like rubber-like polymer into a target powdery product: at the stages of grinding and drying, this leads to a significant decrease in the yield of the product. Moreover, the resulting polymer particles at the stage of grinding the gel-like block during drying significantly stick together, forming agglomerates, so that the drying time increases several times, reducing the productivity of the process of obtaining powder products. After drying, the obtained large polymer granules are crushed to obtain particles of a given size, due to mechanical loads, mechanical degradation of polymer macromolecules is observed, and the quality of the obtained product is deteriorated.

Known methods for producing powdered acrylic polymers without loss of product on the surface of technological equipment by polymerization of acrylamide or acrylic monomers in concentrated aqueous solutions in a polymerization reactor with a special fluoroplastic coating, preventing the polymer from sticking to the walls of the reactor [1] or by drying the gel-like polymer in the form of aggregated particles with hot air in a dryer with chrome parts to prevent polymer from sticking to the surface of the dryer [2]
The yield of the target product is high. However, the productivity of the process is relatively low due to the increase in the duration of the grinding process of the elastic high molecular weight gel polymer through dies with small hole sizes (less than 3 mm) and the increase in the duration of the drying process of agglomerates formed due to the high adhesive ability of the polymer when gel particles adhere to each other . When crushing large agglomerated polymer granules, a loss of viscosity properties is observed due to the mechanical degradation of polymer macromolecules, resulting in a decrease in the efficiency of the use of powder polymer. In addition, the manufacture of special equipment for a polymerization reactor with a fluoroplastic coating and a drying device with chrome parts is required.

A known method of producing powdered polymers during the polymerization of acrylic monomers in concentrated aqueous solutions in a polymerization reactor, the surface of which is treated with various special substances that reduce the adhesion of the polymer to the walls of the reactor. The inner surface of the reactor is covered with a layer of a release agent that is not miscible with polymer, silicone or liquid paraffin, or stearic or lauric acid [3]. A gel-like, highly viscous polymer with satisfactory adhesive properties is obtained at the polymerization stage, which allows the polymer to be unloaded under its own gravity as through the bottom reactor, and through the top of a 90 ^° tilted reactor with a high yield of product.

 However, the polymer yield decreases at the stage of drying the gelled polymer particles due to its deposition on the surface of the drying device. The drying time is increased due to the agglomeration of polymer particles, the quality of the powder product is deteriorated as a result of mechanical destruction at the crushing stage.

A more effective and simpler technological solution to the problem of obtaining powdered polymers is the introduction of special release agents in the reaction monomer mixture before polymerization, which allows to obtain an intermediate gel polymer with satisfactory structural and mechanical properties: low elasticity and adhesion to the surface of technological equipment. So, there is a known method of producing powdered polyacrylamide by radical polymerization of acrylamide in concentrated aqueous solutions in the presence of a release agent - ammonium sulfate in an amount of 0.2 2% (by weight of acrylamide) [4] The obtained gel-like polyacrylamide in the presence of this inorganic salt - (NH ₄ ) ₂ SO ₄ does not deposit on the surface of the polymerization reactor.

However, at the stage of drying the obtained gel-like polymer particles, they agglomerate and adhere to the surface of the drying device. As a result, the yield of the product (powdered polyacrylamide) is 90% of the drying time at 65 ^{° C. for} 16 hours.

The closest in technical essence is the method of obtaining powdered acrylic copolymers by polymerization of acrylamide in the presence of alkali metal carbonates [5] The polymerization is carried out in aqueous solutions of acrylamide with a mass fraction of 5 to 20% under the action of initiators. Use 10 67% (by weight of acrylamide) of alkali metal carbonates, such as sodium carbonate. Peroxides, hydroperoxides, alkali metal persulfates are used as initiators. The polymerization is carried out at a temperature of 20 55 ^o C. Obtained in the presence of alkali metal carbonates gel polyacrylamide does not stick to the surface of the polymerization reactor. Isolation of the target product of powdered partially hydrolyzed polyacrylamide is carried out by a known method of grinding and drying gel-like polymer particles, for example, in a tumble dryer.

However, during drying, gel-like polymer particles adhere to agglomerates and adhere to the surface of the drying apparatus. As a result, the yield of the target product is 90% (of the calculated amount), and the drying time at 65 ^{° C. is} increased to 16 hours.

 The method of the present invention reduces the adhesion of the polymer, which eliminates the sticking of the polymer to the surface of the processing equipment not only at the stage of polymerization, but also at the stages of separation of the powdered product, and also eliminates the formation of agglomerates during adhesion of gel-like particles at the drying stage, thereby increasing the yield of the product and process performance.

A method of obtaining a powdered polymer of acrylamide involves the polymerization of acrylamide in concentrated aqueous solutions under the action of chemical initiators in the presence of 0.01 to 7.5 wt. sodium carbonate or bicarbonate, or potassium, or ammonium and a release agent - sodium alkylbenzenesulfonate (TU 6-01-1001-75 and 6-01-0161283-34-89), sulfonol preparation in an amount of 0.002 0.01 wt. The reaction mixture is deoxygenated by purging with nitrogen and aqueous initiator solutions are added. The initial polymerization temperature is 10-40 ^o С, the polymerization temperature varies from 10 to 100 ^o С, the polymerization time is up to 6 10 hours. After the polymerization is completed, the bottom of the reactor is opened (in the form of a sliding gate) and after a few minutes gel-like under the influence of its own gravity a polymer block in the form of a polymerization reactor is recovered. Isolation of the target product is carried out by coarse grinding of the polymer block into pieces of size 20x20x70 mm (for example, on a device of the guillotine type), grinding of pieces on a grinder with a grating with a hole size of 2 10 mm at the outlet (for example, on a grinder like a meat grinder), drying gelled polymer particles (for example, in a “continuous tape” type dryer with hot air at 40 ^° -70 ^{° C.} ), crushing dry polymer granules to a predetermined size of 1.5 mm (for example, on a disk crusher).

 The initiators used are: peroxides, hydroperoxides, azo compounds, redox catalysts, initiating redox systems, including persulfates, hydrosulfites, metabisulfites of ammonium, potassium, sodium, metal ions of variable valence (e.g., Fe, Cu), etc. constituting 0.003 0.1% (by weight of acrylamide).

 The effectiveness of the proposed method for producing powdered acrylamide polymers is evaluated by the yield of the target product, by the duration of drying of the gel-like particles of the polymer.

 The yield of the target product (in 100% of the calculated amount) is calculated by determining the weight of the dry polymer and the content of the main substance (non-volatile substances) in it.

The duration of the drying stage is determined by drying the gel-like polymer particles obtained by grinding while passing through a die with a hole size of 2 mm, at 65 ^o With a constant speed of hot air. Drying is completed after reaching a moisture content of less than 10 wt. The shorter the drying time, the less agglomeration of the particles; therefore, the solution to the problem of reducing the adhesive properties of the polymer is achieved.

 Distinctive features are the additional introduction before polymerization in a concentrated aqueous solution of acrylamide 0.002 to 0.01 wt. sodium alkylbenzenesulfonate; and alkali metal or ammonium carbonates or bicarbonates.

 When using sodium alkylbenzenesulfonate less than 0.002 wt. powdery acrylamide polymers are obtained with a low yield of the product (less than 90%), with a low productivity of the process (drying time increases to 10 hours).

 When using sodium alkylbenzenesulfonate more than 0.01 wt. undesirable because of the significant foaming in the monomer reaction mixture when the desired result is achieved in the proposed method for producing powdered acrylamide polymers.

 When using alkali metal or ammonium carbonates or bicarbonates of less than 0.01%, polyacrylamide powder is obtained with a low yield (less than 80%) due to the sticking of the gel polymer on the walls of the polymerization reactor, with low productivity (due to the possibility of grinding the gel polymer during passage through a die with holes larger than 3 mm) and an increase in the drying time of larger granules by 2 times (up to 10 hours).

 The use of carbonates or bicarbonates of alkali metals or ammonium more than 7.6 wt. it is impractical, since the desired result has been achieved: a powdery acrylamide polymer is obtained with a high yield of the product (more than 96%), with a high productivity of the process (drying time 8 hours) and with a maximum degree of hydrolysis.

 The invention is illustrated by the following examples.

Example 1 (prototype). 3200 ml of a 50% solution of acrylamide, 3000 ml of distilled water, 1760 g of a 10% solution of sodium carbonate (0.1 mol per 1 mol of acrylamide) or, respectively, 20 are introduced into a reactor equipped with a stirrer, a bubbler for nitrogen purging. wt. acrylamide and 2.2 wt. sodium carbonate. Purge the reaction mixture with nitrogen for 30 minutes and introduce oxygen-free solutions of potassium persulfate (0.003% by weight of acrylamide) and sodium metabisulfite (0.015% by weight of acrylamide). The initial polymerization temperature is 25 ^o C. After 2 hours of polymerization, the temperature reaches 84 ^o C. The obtained gel-like polymer block is easily removed through the bottom of the reactor, cut into pieces 20x20x70 mm in size, then crushed in a grinder with a grating with an opening size of 2 mm , on gel-like polymer particles with a size of 2 × 5 × 10 mm. The obtained polymer particles are dried in a drying device such as a tape dryer with hot air at 65 ^o C, controlling the drying time. Dry granules are crushed on a mechanical rotary crusher to particles of a given size (less than 1.4 mm). The resulting polymer powder is weighed. The moisture content of the sampled powder polymer is determined.

 The test results in the process of obtaining powdered acrylamide polymers are presented in the table.

Example 2. In a reactor equipped with a stirrer, a nitrogen bubbler, 3200 ml of a 50% solution of acrylamide (20 wt.), 3000 ml of distilled water, 1760 g of a 10% solution of sodium carbonate (2.2 wt. Or 0.1 mol per 1 mol of acrylamide), 100 ml of 0.25% sodium alkylbenzenesulfonate solution (0.003 wt.). Purge the mixture with nitrogen for 30 minutes and introduce oxygen-free solutions of potassium persulfate and sodium metabisulfite (0.03 and 0.015% by weight of acrylamide, respectively). The initial polymerization temperature is 25 ^o C. After 2 hours of polymerization, the temperature reaches 84 ^o C. The obtained gel-like polymer block is removed through the bottom of the reactor (it falls under its own gravity), crushed in the same manner as in example 1 and dried with hot air at 65 ^o C, controlling drying time. The resulting dry granules are crushed to a predetermined size. The powdered polymer is weighed, the content of the basic substance is determined in it.

 The test results are shown in the table.

Example 3. Analogously to example 2, acrylamide is polymerized in a reaction mixture obtained by mixing 4800 ml of a 50% solution of acrylamide (30 wt.), 9.6 g of a 10% solution of ammonium carbonate (0.01 wt. Or 0.005 mol per 1 mol of acrylamide), 60 ml of a 0.25% solution (0.002 wt.) sodium alkylbenzenesulfonate, 3100 ml of distilled water in the presence of 0.007% (by weight acrylamide) potassium persulfate and 0.005% (by weight acrylamide) sodium metabisulfite. The polymerization temperature for 1.5 hours varies from 25 to 100 ^o C.

 Analogously to example 1, powdered polyacrylamide is isolated by grinding and drying gelled polymer particles and crushing dry granules. The content of the basic substance is determined and the obtained polyacrylamide powder is weighed.

 The test results for the production of powdered polyacrylamide are shown in the table.

Example 4. Analogously to example 2, acrylamide is polymerized in a reaction mixture obtained by mixing 4000 ml of a 50% solution of acrylamide (25 wt.), 2240 g of a 20% solution of potassium carbonate (5.6 wt. Or 0.3 mol per 1 mol of acrylamide), 200 ml of 0.25% sodium alkylbenzenesulfonate solution (0.006 wt.), 1600 ml of distilled water, 0.04% of sodium persulfate acrylamide and 0.025 of sodium metabisulfite acrylamide. The temperature of the reaction mass during 10 hours of polymerization varies from 25 to 84 ^o C.

Analogously to example 1, a powdery polymer is isolated by drying the crushed gel-like polymer particles at 65 ^{° C.} , controlling the drying time, followed by crushing of the dry polymer granules. The obtained polyacrylamide powder is weighed and the content of the basic substance is determined in it.

 The results of tests to obtain powdered acrylamide polymers are shown in the table.

Example 5. Analogously to example 2, acrylamide is polymerized in a reaction mixture obtained by mixing 3200 ml of a 50% solution of acrylamide (20 wt.), 100 g of a 10% solution of sodium bicarbonate and 1900 g of a 20% solution of sodium carbonate (total 7 , 5 wt. Or 0.5 mol per 1 mol of acrylamide), 320 ml of 0.25% sodium alkylbenzenesulfonate solution (0.01 wt.), 1500 ml of distilled water, in the presence of 0.07% by weight of potassium persulfate acrylamide and 0.05% by weight of sodium metabisulfite acrylamide. The temperature of the reaction mixture during 8 hours of polymerization varies from 25 to 75 ^o C.

Analogously to example 1, a powdery product is isolated by drying the crushed gel-like polymer particles at 65 ^o C, controlling the drying time, followed by crushing of the dry polymer granules. The obtained powdery product is weighed and the content of the basic substance is determined in it.

 The test results for the production of powdered acrylamide polymers are shown in the table.

Claims (1)

 A method for producing powdered acrylamide polymers by radical polymerization of acrylamide in a concentrated aqueous solution in the presence of mono- and disubstituted carbonic acid salts and a chemical initiator, grinding the obtained gel-like polymer and drying followed by crushing, characterized in that carbonate is used as mono- and disubstituted carbonic salts or sodium bicarbonate, potassium or ammonium in an amount of 0.01 to 7.50 wt. and sodium alkylbenzenesulfonate is additionally added to the solution in an amount of 0.002 to 0.010 wt.

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