A system and method for continuous production of polyacrylamide

Abstract

The present application relates to the chemical technology field, specifically to a kind of continuous preparation polyacrylamide system and method.The continuous preparation polyacrylamide system includes batching tank, batching tank is connected with first reactor, the output end of first reactor is communicated with the upper portion of second reactor, and the output end of second reactor is connected with dryer.The present application divides the polymerization of polyacrylamide into two reactions, which are the strong exothermic rapid polymerization reaction of first reactor and the heat preservation reaction of second reactor respectively;The strong exothermic rapid polymerization reaction can realize the effective transmission of reaction heat, and the heat preservation reaction improves the conversion rate of raw materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the chemical technology field, and in particular to a system and method for continuously preparing polyacrylamide. BACKGROUND

[0002] The information disclosed in this Background section is only for the purpose of increasing the understanding of the general background of the application and does not necessarily constitute an admission by the patent applicant or the patent owner that this information constitutes prior art.

[0003] Polyacrylamide (PAM) is a linear polymer with the chemical formula (C3H5NO) n , which has good water solubility and thermal stability. It is a hard glassy solid at room temperature and can be dissolved in water in any proportion to form a uniform transparent liquid. Polyacrylamide has a wide range of applications in various fields, including but not limited to oilfield chemicals, water treatment, papermaking, textiles, pharmaceuticals, and agriculture.

[0004] The method of using free radical polymerization in aqueous solution to produce polyacrylamide products is the earliest industrialized and still used method of producing polyacrylamide. The initiator is mostly an oxidation-reduction initiator system composed of persulfate and sulfite to reduce the initiation temperature. The principle of free radical polymerization of polyacrylamide is that at a certain temperature, the initiator decomposes to produce primary free radicals to initiate polymerization, the primary free radicals combine with acrylamide monomers, and through chain growth reaction, long-chain free radicals are formed. Chain termination reaction is completed by means of bimolecular termination or coupling termination between long-chain free radicals, and high polymer polyacrylamide is obtained.

[0005] In the industrialized production process of polyacrylamide, acrylamide aqueous solution and initiator are first premixed in a kettle stirrer, and then polymerization reaction is initiated by heating. Since the polymerization reaction heat of acrylamide is as high as 82.8 kJ / mol, and the viscosity of the polymer solution gradually increases as the polymerization reaction proceeds, the mixing and heat exchange performance of traditional kettle reactors for high-viscosity polymer solutions is poor, which can easily lead to uneven distribution of monomer concentration, local temperature too high, and even autoacceleration effect or explosive polymerization during the reaction, ultimately resulting in poor batch stability of the product. Therefore, the current method of reducing the effective concentration of monomers in acrylamide aqueous solution and initiating polymerization at low temperature is used to solve the above problems, but after polymerization by this method, the gel block contains a large amount of water, and a large amount of energy is consumed in the evaporation process. At the same time, most of the current production of polyacrylamide uses batch reaction process, which has low production efficiency and poor product stability. SUMMARY

[0006] In order to overcome the above problems, the present application provides a system and method for continuously preparing polyacrylamide.

[0007] To achieve the above technical purposes, the present application adopts the following technical solutions:

[0008] In a first aspect of the present application, a system for continuously preparing polyacrylamide is provided, which comprises a batching tank, the batching tank being connected to a first reactor, the output end of the first reactor being in communication with the upper part of a second reactor, and the output end of the second reactor being connected to a dryer.

[0009] In one or more embodiments, the batching tank is connected to a vacuum system, and a stirring device is arranged in the batching tank; the batching tank is connected to the first reactor through a feed pump.

[0010] In one or more embodiments, the first reactor is a plate-and-shell reactor or a tube-in-tube reactor; the plate-and-shell reactor is a plate-and-shell heat exchanger, which is composed of a plate bundle and a shell; the tube-in-tube reactor is a tube-in-tube heat exchanger, which is composed of a tube and a shell. The reaction liquid performs polymerization reaction in the plate bundle of the plate-and-shell heat exchanger or the tube of the tube-in-tube heat exchanger, and the heat exchange medium in the shell absorbs heat and then leaves, so that the polymerization heat in the first reactor can be removed in time.

[0011] In one or more embodiments, when the first reactor is distributed horizontally, the output end of the first reactor is in vertical communication with the upper part of the side wall of the second reactor, and a cutting device is arranged at the output end of the first reactor, which can cut the material after the reaction in the first reactor into small pieces.

[0012] In one or more embodiments, when the first reactor is distributed vertically, the output end of the first reactor is in vertical communication with the top of the second reactor.

[0013] In one or more embodiments, the first reactor is provided with a heat exchange medium input end and a heat exchange medium output end; the medium output end is connected to the dryer.

[0014] In one or more embodiments, the dryer is an air dryer, and an air heater is arranged at the inlet of the dryer; the air dryer uses the hot air generated by the air heater to dry the wet material.

[0015] Preferably, an air preheater is arranged at the inlet of the air heater, and the heat exchange medium output end is connected to the air preheater; the air enters the air heater after being exchanged with the heat exchange medium, so that the reaction heat in the first reactor is fully utilized, thereby achieving energy saving and consumption reduction.

[0016] In one or more embodiments, the output end of the second reactor is connected to the dryer through a granulator.

[0017] In one or more embodiments, a cyclone separator is arranged at the gas phase outlet of the dryer for recovering the material entrained in the dry tail gas.

[0018] In a second aspect of the present application, a method for continuously preparing polyacrylamide is provided, comprising:

[0019] The reaction solution containing acrylamide, initiator and other additives is deoxygenated and then introduced into the first reactor for strong exothermic rapid polymerization, in which the heat exchange medium in the shell of the first reactor absorbs the reaction heat and leaves the first reactor to control the temperature of the polymerization;

[0020] The material after rapid polymerization is directly introduced into the second reactor for heat preservation reaction, and then dried in the dryer to obtain polyacrylamide.

[0021] In one or more embodiments, after the heat preservation reaction is completed, the material is introduced into a granulator for granulation, then introduced into a dryer for drying, and finally crushed and packaged.

[0022] In one or more embodiments, the heat exchange medium after being heated exchanges heat with air, and the hot air is introduced into the dryer to dry the wet polyacrylamide.

[0023] In one or more embodiments, the concentration of acrylamide in the reaction solution is 10-50 wt.%.

[0024] In one or more embodiments, the temperature in the first reactor and the second reactor is 50-90℃; the residence time in the first reactor is 1-60 min, and the residence time in the second reactor is 60-480 min.

[0025] In one or more embodiments, the heat exchange medium is water, methanol, ethanol, paraffin, cyclohexane, or a mixture of two or more thereof.

[0026] In one or more embodiments, the initiator is a persulfate salt and / or an azo initiator. The persulfate salt includes ammonium persulfate, potassium persulfate and sodium persulfate. The azo initiator includes azobis isobutyronitrile, azobis isohexyl nitrile and azobis isobutylimidazoline hydrochloride.

[0027] In one or more embodiments, the other additives include disodium ethylenediaminetetraacetate, sodium bicarbonate and urea. The disodium ethylenediaminetetraacetate as a chelating agent can avoid the influence of metal ions on the reaction; the sodium bicarbonate is an initiation promoter; and the addition of urea can increase the solubility of the product.

[0028] The present application has the following beneficial effects:

[0029] (1) The present application divides the polymerization reaction of polyacrylamide into two-stage reactions, which are strong exothermic rapid polymerization reaction of the first reactor and heat preservation reaction of the second reactor respectively; the strong exothermic rapid polymerization reaction can realize effective transfer of reaction heat, and the heat preservation reaction improves the conversion rate of raw materials. Specifically, the reaction liquid in the first reactor is subjected to polymerization reaction in the plate bundle of the plate and shell heat exchanger or the column tube of the column tube heat exchanger, the plate bundle of the plate and shell heat exchanger or the column tube of the column tube heat exchanger has a relatively short transverse distance, and the heat transfer medium in the shell removes the reaction heat in time, thereby controlling the temperature of the polymerization reaction and avoiding the problem of explosive polymerization, thereby affecting the molecular weight and solubility of the product. The heat preservation reaction in the second reactor can make the monomer reaction complete and improve the conversion rate of raw materials.

[0030] (2) In the present application, the preparation of polyacrylamide is realized by continuous reaction, and after the reaction in the first reactor is completed, the material can enter the second reactor for reaction, and at the same time, new material enters the first reactor for reaction, so that the continuous preparation of polyacrylamide is realized, and the problems of low production efficiency and poor product stability caused by batch reaction process are avoided.

[0031] (3) The concentration of acrylamide in the reaction liquid in the present application has a wide application range, and can be reacted under low concentration conditions or high concentration conditions. The production process under high concentration conditions greatly reduces the water content in the reaction liquid, thereby reducing the energy consumption during drying.

[0032] (4) In the present application, the polymerization heat in the first reactor can be absorbed by the heat transfer medium and exchanged with air, and the hot air enters the dryer to dry the wet polyacrylamide, thereby realizing energy saving and consumption reduction. BRIEF DESCRIPTION OF DRAWINGS

[0033] The drawings accompanying the specification of the present application serve to provide a further understanding of the present application, and the schematic embodiments of the present application and the description thereof serve to explain the present application, and do not constitute an improper limitation on the present application.

[0034] Figure 1 It is a system structure schematic diagram for continuously preparing polyacrylamide in Example 1 of the present application;

[0035] Figure 2 It is a system structure schematic diagram for continuously preparing polyacrylamide in Example 2 of the present application;

[0036] Figure 3 It is a system structure schematic diagram for continuously preparing polyacrylamide in Example 3 of the present application;

[0037] Wherein, 1 is a batching tank, 2 is a feed pump, 3 is a first reactor, 4 is a cutting device, 5 is a second reactor, 6 is an air preheater, 7 is an extrusion granulator, 8 is an air heater, 9 is a dryer, and 10 is a cyclone separator. DETAILED DESCRIPTION

[0038] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0039] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0040] In order to enable persons skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in combination with specific examples.

[0041] Example 1

[0042] Reference Figure 1 A system for continuously preparing polyacrylamide includes a batching tank 1, the batching tank 1 is connected with a first reactor 3 through a feed pump 2, an output end of the first reactor 3 is communicated with an upper portion of a second reactor 5, and an output end of the second reactor 5 is connected with a dryer 9.

[0043] The batching tank 1 is connected with a vacuum system for discharging oxygen in the batching tank 1. A stirring device is arranged in the batching tank 1, the stirring device includes a stirring rod and a stirring paddle, and the stirring rod is connected with an output end of a motor. The stirring device can uniformly mix the materials.

[0044] In the embodiment, the first reactor 3 is a plate-shell reactor, the plate-shell reactor is a plate-shell heat exchanger, and the plate-shell heat exchanger is composed of a plate tube bundle and a shell. Meanwhile, the plate-shell reactor is distributed in the transverse direction in the embodiment, the reaction liquid performs a polymerization reaction in the plate tube bundle of the plate-shell heat exchanger, the transverse distance of the plate tube bundle of the plate-shell heat exchanger is short, the heat exchange medium in the shell absorbs heat and then leaves, and the reaction heat is removed in time, thereby controlling the temperature of the polymerization reaction and avoiding the problem of explosive polymerization, and further affecting the quality of the product.

[0045] The output end of the first reactor 3 is communicated with the upper part of the sidewall of the second reactor 5 vertically, and the output end of the first reactor 3 is provided with a cutting device 4 which can cut the material reacted in the first reactor 3 into small pieces to improve the dispersibility of the material reacted. The output end of the first reactor 3 is communicated with the upper part of the second reactor 5 to directly send the material reacted in the first reactor into the second reactor for heat preservation reaction, so that the preparation is continuous.

[0046] The first reactor 3 is provided with a heat exchange medium input end and a heat exchange medium output end; the medium output end is connected with the dryer. The heat exchange medium enters into the shell of the first reactor 3 from the heat exchange medium input end, absorbs the heat of polymerization reaction, and then is output from the heat exchange medium output end.

[0047] The dryer 9 is an air dryer, and the inlet of the dryer is provided with an air heater 8. The air dryer uses the hot air generated by the air heater 8 to dry the wet material. The inlet of the air heater is provided with an air preheater 6, the heat exchange medium output end is connected with the air preheater 6, and the heat source of the air preheater 6 is the heat in the first reactor 3. The air is heated after being exchanged with the heat exchange medium and then enters the air heater 8. The heat exchange medium which has absorbed the heat of polymerization reaction is output from the medium output end of the first reactor 3, and then is exchanged with the air at the air preheater 6. The hot air enters the dryer 9 to dry the wet polyacrylamide, so that energy saving and consumption reduction can be realized. The gas phase outlet of the dryer is provided with a cyclone separator 10 for recovering the material entrained in the dry tail gas.

[0048] The output end of the second reactor 5 is connected with the dryer 9 through a granulator 7. After the heat preservation reaction is completed, the material enters the granulator 7 to be granulated. The surface area of the small granular polyacrylamide increases, so that the polyacrylamide can be quickly dried. The granulated polyacrylamide enters the dryer 9 to be dried, and then is crushed and packaged.

[0049] The system structure of the continuous preparation of polyacrylamide in the embodiment is used for reaction:

[0050] 500g of acrylamide, 389g of water, 10g of disodium ethylenediaminetetraacetate, 80g of sodium bicarbonate and 20g of urea are added into a batching tank 1. After the material is stirred and dissolved, vacuum deoxygenation is performed. 1g of azobisimidozolinium hydrochloride is added, and the mixture is uniformly mixed to form a reaction liquid. The content of monomers in the reaction liquid is 50%.

[0051] The material in the ingredient tank 1 is continuously sent into the plate tube bundle of the first reactor 3 through the feed pump 2, and the residence time is 10 min. The shell side of the first reactor 3 is ethanol, and the temperature is 75℃. The vaporized ethanol is cooled and recycled through the air preheater 6. The material in the first reactor 3 is cut into small pieces by the cutting device 4 at the output end of the plate tube bundle and then falls into the second reactor 5. The reaction temperature of the second reactor 5 is 80℃, and the residence time is 3h. After the material is reacted, it is granulated by the extrusion granulator 7 connected to the bottom of the second reactor 5, and then sent to the dryer 9. After drying, it is crushed and packaged. The material entrained in the tail gas of the dryer is recovered by the cyclone separator 10.

[0052] The product obtained after drying has a viscosity average molecular weight of 31 million, a monomer conversion rate of 99.3%, and a solid content of 99.2%.

[0053] Example 2

[0054] Reference Figure 2 A system for continuously preparing polyacrylamide, compared with example 1, the first reactor 3 is a column tube reactor, and the other structures are the same as those of example 1.

[0055] The column tube heat exchanger is composed of two parts of column tube and shell. The reaction liquid performs polymerization reaction in the column tube of the column tube heat exchanger. The column tube of the column tube heat exchanger has a relatively short transverse distance. The heat transfer medium in the shell removes the reaction heat in time, thereby controlling the temperature of the polymerization reaction and avoiding the problem of explosive polymerization, which further affects the quality of the product.

[0056] 500g of acrylamide, 469g of water, 10g of disodium ethylenediaminetetraacetate, and 20g of urea are added to the ingredient tank 1. After stirring and dissolving, vacuum deoxygenation is performed. 1g of azobisdimethylimidazole hydrochloride is added, and the mixture is uniformly mixed to form a reaction liquid. The content of monomers in the reaction liquid is 50%.

[0057] The material in the ingredient tank 1 is continuously sent into the plate tube bundle of the first reactor 3 through the feed pump 2, and the residence time is 10 min. The shell side of the first reactor 3 is ethanol, and the temperature is 75℃. The vaporized ethanol is cooled and recycled through the air preheater 6. The material in the first reactor 3 is cut into small pieces by the cutting device 4 at the output end of the plate tube bundle and then falls into the second reactor 5. The reaction temperature of the second reactor 5 is 80℃, and the residence time is 3h. After the material is reacted, it is granulated by the extrusion granulator 7 connected to the bottom of the second reactor 5, and then sent to the dryer 9. After drying, it is crushed and packaged. The material entrained in the tail gas of the dryer is recovered by the cyclone separator 10.

[0058] The product obtained after drying has a viscosity average molecular weight of 31 million, a monomer conversion rate of 99.3%, and a solid content of 99.2%.

[0059] Example 3

[0060] Reference Figure 3 A system for continuously preparing polyacrylamide, the system of the embodiment is completely same as that of embodiment 1. The difference of the process flow is that the shell of the first reactor 3 is ethanol, the temperature is 55℃, and the residence time of the material in the first reactor 3 is 30 min. The other process flow is same as that of embodiment 1.

[0061] The product obtained after drying has a viscosity average molecular weight of 31.9 million, a monomer conversion rate of 99.0%, and a solid content of 98.7%.

[0062] Embodiment 4

[0063] Compared with embodiment 1, the first reactor 3 is vertical, the output end of the first reactor 3 is vertically communicated with the top of the second reactor 5, and the other system structure and process flow are same as those of embodiment 1.

[0064] The product obtained after drying has a viscosity average molecular weight of 29.3 million, a monomer conversion rate of 99.1%, and a solid content of 99.2%.

[0065] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An apparatus for continuous preparation of polyacrylamide, characterized in that, It includes a mixing tank, which is connected to a first reactor. The output end of the first reactor is connected to the upper part of a second reactor. The output end of the second reactor is connected to a dryer via a granulator. The first reactor is a plate-and-shell reactor or a shell-and-tube reactor; the plate-and-shell reactor is a plate-and-shell heat exchanger, which consists of a plate-and-tube bundle and a shell; the shell-and-tube reactor is a shell-and-tube heat exchanger, which consists of a tube bundle and a shell. The first reactor is horizontally distributed, and its output end is vertically connected to the upper part of the side wall of the second reactor. A cutting device is provided at the output end of the first reactor, which can cut the material after the reaction in the first reactor into small segments to improve the dispersibility of the material after the reaction. The first reactor is provided with a heat exchange medium inlet and a heat exchange medium outlet; the dryer is an air dryer, and an air heater is provided at the inlet of the dryer; an air preheater is provided at the inlet of the air heater, and the air preheater is connected to the heat exchange medium outlet. The heat exchange medium enters the shell of the first reactor from the heat exchange medium inlet end, absorbs the heat of polymerization reaction, and then exits from the heat exchange medium outlet end. It exchanges heat with air at the air preheater, and the hot air enters the dryer to dry the wet polyacrylamide, which can achieve energy saving and consumption reduction.

2. The apparatus as claimed in claim 1, characterized in that, The mixing tank is connected to a vacuum system, and a stirring device is installed inside the mixing tank; the mixing tank is connected to the first reactor via a feed pump.

3. The apparatus as described in claim 1, characterized in that, A cyclone separator is installed at the gas phase outlet of the dryer.

4. A method for continuous preparation of polyacrylamide using the apparatus according to any one of claims 1-3, characterized in that, include: After deoxygenation, the reaction solution containing acrylamide, initiator and other additives is introduced into the first reactor to carry out a strong exothermic rapid polymerization reaction. During the strong exothermic rapid polymerization reaction, the heat exchange medium in the shell of the first reactor absorbs the heat of reaction and leaves the first reactor to control the temperature of the polymerization reaction. After rapid polymerization, the material is directly fed into the second reactor for a heat preservation reaction. After the heat preservation reaction is completed, it is dried in a dryer to obtain polyacrylamide.

5. The method as described in claim 4, characterized in that, After the heat preservation reaction is completed, the material enters the granulator for granulation, then enters the dryer for drying, and finally is crushed and packaged. The heated heat exchange medium exchanges heat with the air, and the hot air enters the dryer to dry the wet polyacrylamide.

6. The method as described in claim 4, characterized in that, The concentration of acrylamide in the reaction solution is 10~50 wt.%; Alternatively, the reaction temperature in the first reactor and the second reactor is 50~90 ℃; the residence time in the first reactor is 1~60 min, and the residence time in the second reactor is 60~480 min.

7. The method as described in claim 4, characterized in that, The heat exchange medium is a mixture of two or more of the following: water, methanol, ethanol, paraffin, and cyclohexane. Alternatively, the initiator may be a persulfate and / or an azo initiator; wherein the persulfate includes ammonium persulfate, potassium persulfate, and sodium persulfate; and the azo initiator includes azobisisobutyronitrile, azobisisoheptanenitrile, and azobisisobutyramidoline hydrochloride.

8. The method as described in claim 4, characterized in that, The other additives include disodium ethylenediaminetetraacetate, sodium bicarbonate, and urea.

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