Device and method for preparing latex

Abstract

The invention belongs to the field of latex preparation, and particularly relates to a device and method for preparing latex, oil-in-water type emulsion is guided into multiple stages of steam stripping kettles which are sequentially connected, the solvent content is gradually reduced to obtain the latex, the temperature of the second-stage steam stripping kettle is higher than the steam stripping temperature of the first-stage steam stripping kettle, and the method is characterized in that the temperature of the second-stage steam stripping kettle is higher than that of the first-stage steam stripping kettle. And returning at least a part of the latex obtained by the second-stage stripping kettle to the first-stage stripping kettle. According to the invention, the operation difficulty of emulsion desolvation can be obviously reduced, the problems of emulsion particle precipitation and equipment scale deposition are reduced, and the working efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the field of latex preparation, and in particular relates to a device and a method for preparing latex. Background Art

[0002] Synthetic latex is usually prepared by mixing emulsification of a rubber solution and water containing an emulsifier, desolventizing, and then concentrating and dehydrating. The desolventizing step mostly adopts the method of atmospheric distillation and vacuum distillation, which has low desolventizing efficiency and takes a long time. Patent document CN200980126521.9 discloses a method for preparing artificial latex, which adopts two or more desolventizing stages to prepare artificial latex, and a part of the latex heated to a boiling point higher than the solvent is mixed with the emulsion, and the solvent is evaporated to remove the solvent. The heating method of the emulsion includes two methods: steam is directly added to the emulsion evaporator and steam is indirectly heated to the emulsion through a heat exchanger. However, this method still has the problems of low efficiency, long time and polymer degradation, and there is also the risk of rubber precipitation of the emulsion on the heat exchange wall with a large temperature difference due to the use of steam for indirect heating of the heat exchanger. Summary of the invention

[0003] In order to improve the deficiencies of the prior art, the present invention provides a device for preparing latex and a method for preparing latex, wherein the method and the device have many advantages such as high desolventizing efficiency and thorough desolventizing.

[0004] A method for preparing latex, the method comprising the following steps: introducing an oil-in-water emulsion into a plurality of sequentially connected stripping kettles, gradually reducing the solvent content to obtain latex, wherein the temperature of the second stripping kettle is higher than the stripping temperature of the first stripping kettle, and returning at least a portion of the latex obtained in the second stripping kettle to the first stripping kettle.

[0005] A stripping device comprises a first-stage stripping kettle and a second-stage stripping kettle connected in sequence, wherein the first-stage stripping kettle is provided with a first material inlet, a first steam inlet, a first air outlet and a first latex outlet, and the second-stage stripping kettle is provided with a second material inlet, a second steam inlet, a second air outlet and a second latex outlet; the second latex outlet of the second-stage stripping kettle is connected with the first material inlet of the first-stage stripping kettle, so as to introduce the heated latex into the first-stage stripping kettle.

[0006] A device for preparing latex comprises an emulsifying device and the above-mentioned stripping device, wherein the emulsion outlet of the emulsifying device is connected to the first material inlet of the first-stage stripping kettle.

[0007] Beneficial Effects

[0008] The present invention provides a device for preparing latex and a method for preparing latex. The method adopts at least two-stage stripping kettles to strip and remove solvents, thereby obtaining a polymer latex with reduced solvent and a gas containing an organic solvent, wherein the stripping temperature of the second-stage stripping kettle is higher than the stripping temperature of the first-stage stripping kettle, and in addition, a part of the latex obtained by stripping in the second-stage stripping kettle is recycled back to the first-stage stripping kettle to provide 50-100% of the required heat for the evaporation of the solvent in the first-stage stripping kettle. In the method, the heat source is directly and gently provided by the second-stage circulating emulsion, which reduces or even avoids the direct contact between the first-stage emulsion and the water vapor with a large temperature difference, avoids the risk of overheating and precipitation of the latex due to the heating of the heat exchanger, significantly reduces the difficulty of emulsion desolventization, reduces the precipitation of emulsion particles and equipment fouling, improves work efficiency, and has a low solvent content in the obtained latex and a low emulsion rubber loss rate (for example, not higher than 5% or less). BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 The figure is a schematic diagram of the structure and logistics of the device for preparing latex in the present invention.

[0010] Figure symbols: C1 is the first-stage stripping kettle, C2 is the second-stage stripping kettle, P1 is the first-stage emulsion circulation pump, P2 is the second-stage emulsion circulation pump, 1. Water-in-oil emulsion, 2. First-stage stripping gas phase, 3. First-stage stripping kettle entering steam, 4. Second-stage stripping latex circulated back to the first stage, 5. First-stage stripping latex, 6. Second-stage stripping gas phase, 7. Second-stage stripping kettle entering steam, 8. Second-stage stripping latex. DETAILED DESCRIPTION

[0011] As described above, the present invention provides a stripping device, which includes a first-stage stripping kettle and a second-stage stripping kettle connected in sequence, the first-stage stripping kettle is provided with a first material inlet, a first steam inlet, a first air outlet and a first latex outlet, and the second-stage stripping kettle is provided with a second material inlet, a second steam inlet, a second air outlet and a second latex outlet; the second latex outlet of the second-stage stripping kettle is connected to the first material inlet of the first-stage stripping kettle, so as to introduce the heated latex into the first-stage stripping kettle.

[0012] According to an embodiment of the present invention, after the heated latex from the second stage stripping kettle enters the first stage stripping kettle, it provides a heat source for the raw material water-in-oil emulsion, which can reduce or even avoid direct contact between the raw material water-in-oil emulsion and steam.

[0013] According to an embodiment of the present invention, the stripping device also includes a plurality of third-stage stripping kettles, and the plurality of third-stage stripping kettles are connected in sequence, and the third-stage stripping kettle close to the second-stage stripping kettle is connected to the second-stage stripping kettle, and the third-stage stripping kettle is provided with a third material inlet, a third steam inlet, a third air outlet and a third latex outlet, and the second latex outlet of the second-stage stripping kettle is connected to the third material inlet of the third-stage stripping kettle close to the second-stage stripping kettle.

[0014] According to an embodiment of the present invention, when the temperature of the latex discharged from the third latex outlet is higher than the emulsion temperature in the first-stage stripping kettle, the third latex outlet is connected to the first material inlet of the first-stage stripping kettle to introduce the heated latex into the first-stage stripping kettle.

[0015] According to an embodiment of the present invention, the filling amount of liquid in the first-stage stripping kettle is less than or equal to 25%, preferably the filling amount of liquid in the first-stage stripping kettle is less than or equal to 20%, and further preferably, the filling amount of liquid in the first-stage stripping kettle is less than or equal to 18%. Studies have found that the gas volatilization amount in the first-stage stripping kettle is large, the foam amount is large, and a large gas phase space is required. When the liquid filling amount is too large, it will lead to defects such as large latex particle size.

[0016] In the present invention, the first-stage stripping kettle, the second-stage stripping kettle and the third-stage stripping kettle may also be collectively referred to as stripping kettles.

[0017] According to an embodiment of the present invention, the material inlet is arranged at the lower part of the corresponding stripping tank.

[0018] According to an embodiment of the present invention, the steam inlet and the latex outlet are arranged at the bottom of the corresponding stripping tank.

[0019] According to an embodiment of the present invention, the gas outlet is arranged at the top of the corresponding stripping tank.

[0020] According to an embodiment of the present invention, an emulsion circulation pump is provided between adjacent stripping kettles, and the emulsion circulation pump is connected to the corresponding stripping kettles through pipelines to achieve communication between different stripping kettles.

[0021] According to an embodiment of the present invention, the inlet of the emulsion circulation pump is connected to the bottom of the stripping kettle, and the outlet of the emulsion circulation pump is connected to the upper part of the stripping kettle for internal circulation of the latex in the stripping kettle.

[0022] According to an embodiment of the present invention, the outlet of the emulsion circulation pump of the second-stage stripping kettle is also connected to the water-in-oil emulsion inlet pipe of the first-stage stripping kettle, so as to introduce the circulating latex of the second-stage stripping kettle into the first-stage stripping kettle.

[0023] According to an embodiment of the present invention, the outlet of the emulsion circulation pump of part of the third-stage stripping kettle is also connected to the water-in-oil emulsion inlet pipe of the first-stage stripping kettle, so as to introduce the circulating latex of the third-stage stripping kettle that meets the requirements into the first-stage stripping kettle.

[0024] According to an embodiment of the present invention, the steam inlet of the stripping kettle is connected to a steam pipeline for passing steam into the stripping kettle to heat the emulsion.

[0025] According to an embodiment of the present invention, a stirrer is provided in the stripping kettle.

[0026] According to an embodiment of the present invention, a temperature sensor is provided in the stripping kettle.

[0027] The present invention also provides a device for preparing latex, which comprises an emulsifying device and the stripping device as described above, wherein the emulsion outlet of the emulsifying device is connected to the first material inlet of the first-stage stripping kettle.

[0028] According to an embodiment of the present invention, the emulsification device is used to mix and emulsify the polymer solution and the solution containing the emulsifier to form an oil-in-water emulsion. Specifically, the emulsification device is, for example, a homogenizer.

[0029] According to the embodiment of the present invention, the material of the pipeline can be selected according to actual needs, such as plastic, glass, stainless steel and other materials that are not corroded by emulsions or solvents. Stainless steel is preferred.

[0030] According to the embodiment of the present invention, the diameter of the pipeline is also selected according to actual needs.

[0031] The present invention also provides a method for preparing latex, which comprises the following steps:

[0032] An oil-in-water emulsion is introduced into a multi-stage stripping kettle connected in series, and the solvent content is gradually reduced to obtain a latex, wherein the temperature of the second stage stripping kettle is higher than the stripping temperature of the first stage stripping kettle, and it is characterized in that at least a portion of the latex obtained in the second stage stripping kettle is returned to the first stage stripping kettle.

[0033] According to an embodiment of the present invention, an oil-in-water emulsion is introduced into the stripping device as described above to gradually reduce the solvent content to obtain a latex, wherein the temperature of the second-stage stripping kettle is at least 3 degrees Celsius higher than the stripping temperature of the first-stage stripping kettle, and at the same time, at least a portion of the latex obtained in the second-stage stripping kettle is returned to the first-stage stripping kettle.

[0034] According to an embodiment of the present invention, the removal temperature of the second stripping kettle is at least 5 degrees Celsius higher than the removal temperature of the first stripping kettle, preferably at least 10 degrees Celsius higher, further preferably at least 20 degrees Celsius higher, and further preferably at least 30 degrees Celsius higher.

[0035] According to an embodiment of the present invention, at least 50% of the heat used for stripping in the first-stage stripping kettle is provided by the latex returned from the second-stage stripping kettle, and preferably all the heat used for stripping in the first-stage stripping kettle is provided by the latex returned from the second-stage stripping kettle.

[0036] According to an embodiment of the present invention, the removal temperature of the first-stage stripping tank is higher than the boiling point of the solvent in the oil-in-water emulsion.

[0037] According to an embodiment of the present invention, the removal temperature of the second-stage stripping kettle and the removal temperature of the third-stage stripping kettle may be the same or different. For example, generally, as the number of stages increases, the operating pressure decreases, and the temperature is the same or increases. For example, the removal pressure of the third-stage stripping kettle is less than that of the second-stage stripping kettle, and the removal temperature of the third-stage stripping kettle is greater than or equal to the removal temperature of the second-stage stripping kettle.

[0038] According to an embodiment of the present invention, the removal temperature of the first-stage stripping kettle is 40-90°C, illustratively 50°C, 60°C, 70°C, 80°C, 90°C.

[0039] According to an embodiment of the present invention, the removal pressure of the first-stage stripping kettle is 0.1-0.2 MPa, exemplarily 0.1 MPa, 0.11 MPa, 0.12 MPa, 0.13 MPa, 0.14 MPa, 0.15 MPa, 0.16 MPa, 0.17 MPa, 0.18 MPa, 0.19 MPa, and 0.2 MPa.

[0040] According to an embodiment of the present invention, the removal temperature of the second-stage stripping kettle is 50-90°C, illustratively 50°C, 60°C, 70°C, 80°C, 90°C.

[0041] According to an embodiment of the present invention, the removal pressure of the second-stage stripping kettle is 0.11-0.2 MPa, exemplarily 0.11 MPa, 0.12 MPa, 0.13 MPa, 0.14 MPa, 0.15 MPa, 0.16 MPa, 0.17 MPa, 0.18 MPa, 0.19 MPa, and 0.2 MPa.

[0042] According to an embodiment of the present invention, the removal temperature of the third-stage stripping kettle is 50-90°C, illustratively 50°C, 60°C, 70°C, 80°C, 90°C.

[0043] According to an embodiment of the present invention, the removal pressure of the third-stage stripping kettle is 0.02-0.099 MPa, illustratively 0.02 MPa, 0.04 MPa, 0.06 MPa, 0.07 MPa, 0.08 MPa, 0.09 MPa, and 0.099 MPa.

[0044] According to an embodiment of the present invention, the steam inlet of the stripping kettle is connected to a steam pipeline for passing steam into the stripping kettle to heat the emulsion.

[0045] According to an embodiment of the present invention, the steam is water vapor with a temperature ≥ 100°C.

[0046] Steam According to an embodiment of the present invention, the pressure of the water vapor is 0.3-2.0 MPa, preferably 0.5-0.7 MPa.

[0047] According to an embodiment of the present invention, the mass ratio of the latex returned from the second-stage stripping kettle to the first-stage stripping kettle to the oil-in-water emulsion is 0.1-40:1, preferably 1-15:1, more preferably 2-10:1, for example 5:1 or 8:1.

[0048] According to an embodiment of the present invention, the temperature in the stripping kettle is 40-90°C, preferably 50-80°C, for example, the temperature in the first-stage stripping kettle is 50°C, and the temperature in the second-stage stripping kettle is 80°C.

[0049] According to an embodiment of the present invention, the oil-in-water emulsion is prepared by the following method:

[0050] The polymer solution and the aqueous solution containing an emulsifier are mixed and emulsified to form an oil-in-water emulsion.

[0051] According to an embodiment of the present invention, the polymer in the polymer solution is a modified or unmodified olefin homopolymer or olefin copolymer, and the polymer is, for example, at least one of polyisoprene, styrene block copolymer, styrene-butadiene rubber, hydrogenated nitrile rubber, butyl rubber, halogenated butyl rubber, polyisobutylene, ethylene-propylene rubber, polybutadiene rubber, chlorosulfonated polyethylene, etc.

[0052] According to an embodiment of the present invention, the room temperature viscosity of the polymer solution is lower than 20,000 centipoise.

[0053] According to an embodiment of the present invention, the concentration of the polymer solution is lower than 20 wt %, preferably the concentration of the polymer solution is 8-15 wt %.

[0054] Exemplarily, the concentration of the polyisoprene rubber solution is lower than 20 wt %, and preferably the concentration of the polyisoprene rubber solution is 8 to 15 wt %.

[0055] According to an embodiment of the present invention, the solvent in the polymer solution is selected from a solvent having a boiling point below 100°C. Preferably, the solvent is selected from at least one of alkanes having a boiling point below 100°C, cycloalkanes having a boiling point below 100°C or aromatics having a boiling point below 100°C. Further preferably, the solvent is selected from at least one of pentane, hexane, heptane, cyclohexane, benzene, etc., for example, pentane and / or hexane.

[0056] According to an embodiment of the present invention, the concentration of the aqueous solution containing the emulsifier is 0.5-5.0wt%, preferably the concentration of the aqueous solution containing the emulsifier is 0.5-3.0wt%, exemplarily 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt% or 3wt%.

[0057] According to an embodiment of the present invention, the volume ratio of the polymer solution to the aqueous solution containing the emulsifier is 1.5-3.0:1, preferably 2.0-2.5:1.

[0058] According to an embodiment of the present invention, the emulsifier in the aqueous solution containing an emulsifier is selected from at least one or more mixtures of anionic surfactants such as potassium disproportionate rosin acid, potassium rosin acid, sodium dodecylbenzene sulfonate, and non-ionic surfactants such as SPAN80 and Tween 60.

[0059] According to an embodiment of the present invention, in the oil-in-water emulsion, the content of the solvent is 40-65wt%, exemplarily 40wt%, 45wt%, 50wt%, 55wt%, 60wt% or 65wt%, wherein the solvent is derived from the solvent in the polymer solution.

[0060] According to an embodiment of the present invention, the latex obtained after desolventizing in the first-stage stripping kettle has a solvent content of 0.01-10 wt %.

[0061] According to an embodiment of the present invention, the latex obtained after desolventizing in the second-stage stripping kettle has a solvent content of 0.01-1 wt %.

[0062] According to an embodiment of the present invention, the solvent content in the latex obtained after desolventizing in the third-stage stripping reactor is less than or equal to 150 ppm.

[0063] According to an embodiment of the present invention, the median particle size of the latex prepared by the method is 0.5 μm to 2 μm, preferably the median particle size of the latex is 0.8 μm to 1.5 μm, for example, 1.0 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.8 μm.

[0064] According to an embodiment of the present invention, in the latex prepared by the method, the latex rubber loss rate is not higher than 5%, preferably the latex rubber loss rate is not higher than 3%, for example, 4%, 3.5%, 2.5%, 2%, 1.5%, 1.2%, 1%.

[0065] According to an embodiment of the present invention, the oil-in-water emulsion is treated in the stripping kettle to obtain an evaporated solvent and latex; specifically, the evaporated solvent is discharged from the gas outlet at the top of the stripping kettle, and the latex is discharged from the latex outlet at the bottom of the stripping kettle.

[0066] The study found that after desolventizing in the first-stage stripping reactor, the amount of solvent in the emulsion was greatly reduced, which greatly reduced the amount of steam required for subsequent desolventizing. A conventional stripping reactor with multiple independent feed ports can be used to remove the solvent.

[0067] The following will be further described in detail with reference to specific examples of the general formula compound of the present invention and its preparation method and application. It should be understood that the following examples are only for exemplary description and explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies realized based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0068] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0069] During the emulsion desolventizing process, the loss rate of rubber in the emulsion is analyzed to determine the quality of the desolventizing effect. The higher the rubber loss rate, the worse the desolventizing effect.

[0070] Emulsion rubber loss rate χ = 100 × (M1-M2) / M2.

[0071] Wherein, M1 is the rubber content in the oil-in-water latex (unit: gram), and M2 is the rubber content in the latex obtained after desolventization (unit: gram).

[0072] Example 1

[0073] A device for preparing latex, comprising an emulsifying mechanism (i.e. the emulsifying device mentioned above) and a solvent removing mechanism (i.e. the stripping device mentioned above) connected to each other,

[0074] The emulsifying mechanism is used to mix and emulsify the polymer solution and the emulsifier solution to form an oil-in-water emulsion. The emulsifying mechanism is, for example, a homogenizer. The emulsifying mechanism includes a liquid outlet 1 .

[0075] The solvent removal mechanism includes a plurality of stripping kettles, wherein the number of the stripping kettles is selected according to actual needs, and is usually greater than or equal to 2, and the sizes of different stripping kettles are the same or different.

[0076] See also Figure 1 As shown, taking a preparation device including two stripping kettles as an example, the solvent removal mechanism includes a first-stage stripping kettle C1 and a second-stage stripping kettle C2, and the first-stage stripping kettle C1 is provided with an agitator, a temperature sensor, a first material inlet at the bottom, a first air outlet 2 at the top, a first steam inlet 3 and a first latex outlet 4 at the bottom, wherein the first material inlet is connected to the liquid outlet 1 of the emulsification mechanism, and the first steam inlet 3 is used to introduce steam with a temperature higher than the boiling point of the solvent into the first-stage stripping kettle C1, mix with the emulsion and evaporate the solvent in the emulsion, and the evaporated solvent is discharged from the first air outlet 2, and the latex with part of the solvent removed is discharged from the first latex outlet 4.

[0077] The second-stage stripping kettle C2 is provided with an agitator, a temperature sensor, a second material inlet at the bottom, a second air outlet 6 at the top, a second steam inlet 7 and a second latex outlet 5 at the bottom, wherein the second material inlet is connected to the first latex outlet 4, and the second steam inlet 7 is used to introduce steam with a temperature higher than the boiling point of the solvent into the second-stage stripping kettle C2 to mix with the latex and evaporate the solvent in the latex, and the evaporated solvent is discharged from the second air outlet 6, and the latex from which the solvent is further removed is discharged from the second latex outlet 5.

[0078] Among them, a first-stage emulsion circulation pump P1 is arranged between the first-stage stripping kettle C1 and the second-stage stripping kettle C2. The latex discharged from the second latex outlet 5 of the second-stage stripping kettle C2 is introduced into the first material inlet after passing through the second-stage emulsion circulation pump P2. The temperature of the latex discharged from the second-stage stripping kettle C2 is higher than the emulsion temperature in the first stripping kettle C1, and can provide evaporation heat for the first stripping kettle C1, meeting 50% to 100% of the heat requirement of the first stripping kettle C1.

[0079] Wherein, the steam is selected from water vapor with a temperature greater than or equal to 100°C. In actual use, the number of stripping kettles can be multiple. When the number of stripping kettles is greater than two, the other stripping kettles are used as the third stripping kettle, which are connected in sequence after the second-stage stripping kettle C2. The third stripping kettle is provided with a third material inlet at the lower side, a third gas outlet at the top, a third steam inlet and a latex outlet at the bottom. The third material inlet is connected to the latex outlet of the previous-stage stripping kettle, and an emulsion circulation pump is provided on the connecting passage. The third steam inlet is used to introduce steam with a temperature higher than the boiling point of the solvent into the third stripping kettle, mix with the latex and evaporate the solvent in the latex. The evaporated solvent is discharged from the third gas outlet, and the latex with part of the solvent removed is discharged from the latex outlet to the next-stage stripping kettle or the first stripping kettle (when the temperature of the latex discharged from the latex outlet of the third stripping kettle is higher than the temperature in the first stripping kettle, the corresponding latex can be discharged into the first stripping kettle as a heat source).

[0080] The emulsion circulation pump is connected to the corresponding stripping kettle through a pipeline to achieve connectivity between different stripping kettles, wherein the pipeline diameter is selected according to actual needs, and the pipeline material can be selected according to actual needs, such as plastic, stainless steel and other materials that are not corroded by emulsions or solvents.

[0081] Example 2

[0082] A three-stage stripping reactor is used to remove the solvent in a preparation device having three stripping reactors (the structure of the preparation device is as described in Example 1), wherein the first-stage stripping reactor, the second-stage stripping reactor and the third-stage stripping reactor are connected in sequence.

[0083] A polyisoprene rubber (Mn=1.72 million, molecular weight distribution of 1.7, obtained by anionic polymerization catalyzed by n-butyl lithium) with a 1,4-cis content of 91% was dissolved in n-pentane to obtain a 10wt% polyisoprene glue solution, a disproportionate potassium rosin acid emulsifier was dissolved in deionized water to obtain an emulsifier solution with a concentration of 1.5wt%, and the glue solution and the emulsifier aqueous solution were mixed and emulsified in a volume ratio of 2.5:1 to obtain an oil-in-water emulsion, in which the n-pentane solvent content in the emulsion was about 60wt%, and the emulsion was introduced into the first-stage stripping reactor C1 of the preparation device at 2260kg / h, and the steam used was 0.6MPa water vapor for stripping.

[0084] In this embodiment, the solvent content of the latex obtained by desolventizing in the first-stage stripping kettle C1 is about 1wt%; the solvent content of the latex obtained by desolventizing in the second-stage stripping kettle is about 0.05wt%; the solvent content of the latex obtained by desolventizing in the third-stage stripping kettle is about 150ppm, and the emulsion rubber loss rate is 1.2%.

[0085] The specific operating parameters of the oil-in-water emulsion passing through the above three-stage stripping reactor are shown in Table 1 below.

[0086] Table 1 Operating parameters of the stripping reactor

[0087]

[0088] In this embodiment, the latex after three-stage desolventization is centrifuged and dehydrated to obtain a latex with a rubber content of 64 wt%, a median particle size of 1.4 μm, and a residual solvent of 150 ppm in the latex.

[0089] Comparative Example 1

[0090] A three-stage conventional stripping kettle is used to replace the three-stage stripping kettle in Example 2.

[0091] The device used in this comparative example includes three conventional stripping kettles connected in sequence: a first-stage conventional stripping kettle, a second-stage conventional stripping kettle, and a third-stage conventional stripping kettle. Compared with the device in Example 1, the first-stage conventional stripping kettle, the second-stage conventional stripping kettle, and the third-stage conventional stripping kettle have the same structure except that there is no structure for returning the latex flowing out of the latex outlets in the second-stage conventional stripping kettle and the third-stage conventional stripping kettle to the first conventional stripping kettle.

[0092] Among them, the latex outlet of the first-stage conventional stripping kettle is connected to the feed port in the second-stage conventional stripping kettle, the latex outlet of the second-stage conventional stripping kettle is connected to the feed port in the third-stage conventional stripping kettle, and the bottoms of the first-stage conventional stripping kettle, the second-stage conventional stripping kettle and the third-stage conventional stripping kettle are all provided with steam inlets for introducing steam.

[0093] After the three-stage solvent removal of the water-in-oil emulsion, steam is directly introduced into the kettle. Due to uneven heating, the steam feed rate needs to be controlled to a lower level to prevent the foam in the kettle from rushing out of the stirring kettle.

[0094] A polyisoprene rubber (Mn=1.72 million, molecular weight distribution of 1.7, obtained by anionic polymerization catalyzed by n-butyl lithium) with a 1,4-cis content of 91% was dissolved in n-pentane to obtain a 10wt% polyisoprene glue solution, a disproportionate potassium rosin acid emulsifier was dissolved in deionized water to obtain an emulsifier solution with a concentration of 1.5wt%, and the glue solution and the emulsifier aqueous solution were mixed and emulsified in a ratio of 2.5:1 by volume to obtain an oil-in-water emulsion, in which the n-pentane solvent content in the emulsion was about 60wt%, and the emulsion was introduced into a first-stage conventional stripping kettle at 2260kg / h, and the steam used was 0.6MPa water vapor for stripping.

[0095] In this comparative example, the solvent content of the latex obtained by desolventizing in the first stage conventional stripping kettle is about 4wt%; the solvent content of the latex obtained by desolventizing in the second stage conventional stripping kettle is about 0.5wt%; the solvent content of the latex obtained by desolventizing in the third stage conventional stripping kettle is about 200ppm. The operating parameters are shown in Table 2 below.

[0096] The latex after the three-stage desolventization was centrifugally dehydrated to obtain a latex with a rubber content of 64wt%, a median particle size of 1.9μm, a residual solvent in the latex greater than 200ppm, and a latex rubber loss rate of 15%.

[0097] Table 2 Operating parameters of conventional stripping reactor

[0098] series Temperature(℃) Pressure(MPa) 1 55 0.18 2 80 0.18 3 80 0.07

[0099] The solvent removal of the oil-in-water emulsion is completed by more than 90% in the first-stage stripping, so the first-stage conventional stripping kettle operation has the characteristics of large gas-liquid phase change of the material system and large solvent volatilization. In the first-stage conventional stripping kettle, steam is directly used as a heat source, which makes it difficult to add steam, the system is prone to violent foaming, and gas-liquid separation is difficult. The gas phase mixed latex rushes out of the stripping kettle and enters the gas phase condenser and other subsequent equipment, causing the equipment to stop. Comparative Example 1 has the disadvantages of large particle size of the obtained latex product, large residual solvent, and high latex rubber loss rate.

[0100] The above examples are used to illustrate the specific implementation of the present invention. However, the protection scope of the present invention is not limited to the above exemplary implementation. Any modification, equivalent substitution, improvement, etc. made by those skilled in the art within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing latex, characterized in that: The method comprises the following steps: introducing an oil-in-water emulsion into a plurality of sequentially connected stripping kettles, gradually reducing the solvent content to obtain a latex, wherein the temperature of the second stripping kettle is higher than the stripping temperature of the first stripping kettle, and returning at least a portion of the latex obtained in the second stripping kettle to the first stripping kettle.

2. The preparation method according to claim 1, characterized in that: The removal temperature of the second-stage stripping kettle is at least 3 degrees Celsius higher than the removal temperature of the first-stage stripping kettle; preferably, the removal temperature of the second-stage stripping kettle is at least 8 degrees Celsius higher than the removal temperature of the first-stage stripping kettle. Preferably, at least 50% of the heat used for stripping in the first-stage stripping kettle is provided by the latex returned from the second-stage stripping kettle; preferably, all the heat used for stripping in the first-stage stripping kettle is provided by the latex returned from the second-stage stripping kettle.

3. The preparation method according to claim 1 or 2, characterized in that: The removal temperature of the first-stage stripping kettle is 40-90°C, and the removal pressure of the first-stage stripping kettle is 0.1-0.2MPa. Preferably, the removal temperature of the second-stage stripping kettle is 50-90° C., and the removal pressure of the second-stage stripping kettle is 0.11-0.2 MPa.

4. The preparation method according to any one of claims 1 to 3, characterized in that When the temperature of the latex discharged from the third latex outlet in the third stage stripping kettle is higher than the emulsion temperature in the first stage stripping kettle, the third latex outlet is connected to the first material inlet of the first stage stripping kettle, so that part of the latex returned from the third stage stripping kettle can be introduced into the first stage stripping kettle to provide a heat source for the stripping of the first stage stripping kettle.

5. The preparation method according to claim 4, characterized in that: The removal temperature of the third-stage stripping kettle is 50-90°C, and the removal pressure of the third-stage stripping kettle is 0.02-0.099MPa.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The mass ratio of the latex returned from the second-stage stripping kettle to the first-stage stripping kettle to the emulsion is 0.1 to 40:

1.

7. The preparation method according to any one of claims 1 to 6, characterized in that: In the oil-in-water emulsion, the content of the solvent is 40-65 wt %. Preferably, the solvent content of the latex obtained after desolventizing in the first-stage stripping reactor is 0.01-10wt%; Preferably, the solvent content of the latex obtained after desolventizing in the second-stage stripping reactor is 0.01-1wt%; Preferably, the solvent content in the latex obtained after desolventizing in the third-stage stripping reactor is less than or equal to 150 ppm.

8. A stripping device, comprising a first-stage stripping kettle and a second-stage stripping kettle connected in sequence, characterized in that: The first-stage stripping kettle is provided with a first material inlet, a first steam inlet, a first air outlet and a first latex outlet, and the second-stage stripping kettle is provided with a second material inlet, a second steam inlet, a second air outlet and a second latex outlet; the second latex outlet of the second-stage stripping kettle is connected to the first material inlet of the first-stage stripping kettle, so as to introduce the heated latex into the first-stage stripping kettle.

9. The stripping device according to claim 8, characterized in that The stripping device also includes a plurality of third-stage stripping kettles, which are connected in sequence, and the third-stage stripping kettle close to the second-stage stripping kettle is connected to the second-stage stripping kettle, and the third-stage stripping kettle is provided with a third material inlet, a third steam inlet, a third air outlet and a third latex outlet, and the second latex outlet of the second-stage stripping kettle is connected to the third material inlet of the third-stage stripping kettle close to the second-stage stripping kettle.

10. A device for preparing latex, characterized in that: The device for preparing latex comprises an emulsifying device and the stripping device according to claim 8 or 9, and the emulsion outlet of the emulsifying device is connected to the first material inlet of the first-stage stripping kettle.

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