A process for odorless stripping treatment of styrene-acrylic emulsion

Abstract

The present invention relates to a styrene-acrylic emulsion odor-removing stripping process. The specific method comprises the following steps: thoroughly mixing an organic solvent with the emulsion; employing a packed stripping tower as the emulsion stripping equipment to strip the emulsion mixed with the organic solvent. The emulsion is fed from the upper portion of the packing layer of the stripping tower, and low-temperature steam is fed from the lower portion of the packing layer of the stripping tower. The temperature of the emulsion when fed is controlled to be 55-65°C, and the temperature of the steam when fed is controlled to be 70-130°C. The stripping tower is maintained in a vacuum negative pressure state. Prior to stripping, the emulsion is mixed with the organic solvent, and then stripped using the packed stripping tower. The organic solvent, when added to the emulsion as a stripping aid, has a good dissolving and stripping effect on residual monomers, impurities, and VOCs. It can dissolve and adsorb residual monomers and organic impurities remaining in latex particles. After stripping in the packed stripping tower, the residual monomers and VOCs are more effectively removed.

Description

Technical Field

[0001] The invention relates to the field of emulsion odor removal stripping technology, in particular to a styrene-acrylic emulsion odor removal stripping treatment technology. Background Art

[0002] Styrene acrylic emulsion, a milky white liquid with a bluish sheen, is produced through the emulsion copolymerization of styrene and acrylate monomers. It exhibits excellent adhesion, film transparency, and resistance to water, oil, heat, and aging. Due to its exceptionally high cost-effectiveness, styrene acrylic emulsion has become a key intermediate chemical product, widely used in various fields, including architectural coatings, metal latex coatings, floor coatings, paper binders, and adhesives.

[0003] Styrene-acrylic emulsions typically have a certain odor after preparation. When used as high-quality coatings, they require odor removal treatment to eliminate residual phenols and reduce the VOC content. Existing technologies can remove residual phenols and VOCs through physical or chemical methods. For example, patent CN 105169730 A discloses a method and apparatus for removing VOCs from an acrylic emulsion. The method involves preheating a crude extract of the acrylic emulsion and passing it through an evaporator. A mixed gas containing water vapor and an inert gas is then introduced into the evaporator to remove the VOCs.

[0004] However, it is difficult to achieve a more thorough odor removal of styrene acrylic emulsion. This is because a large amount of styrene monomer is used in the preparation process of styrene acrylic emulsion, and the monomer raw materials including styrene monomer are difficult to be 100% consumed in the polymerization process. Due to the high boiling point of the monomer, it is difficult to effectively remove it through the conventional stripping process when removing the residual monomers. It often requires a long stripping process and a large amount of steam. In addition, the residual monomer raw materials mainly composed of styrene contain odorous hydrocarbon impurities (ethylbenzene, p-toluene, m-diphenylene, o-xylene, isopropylbenzene, n-propylbenzene, m-ethylethylbenzene, p-methylethylbenzene, α-methylstyrene, phenylacetylene, m-methylstyrene, p-methylstyrene, etc.), which makes it difficult for styrene acrylic emulsions to achieve more demanding odor removal effects and cannot meet higher quality usage requirements. Summary of the Invention

[0005] The purpose of the present invention is to provide a styrene acrylic emulsion odor-free stripping treatment process in order to solve the above problems. This method can effectively achieve ultra-clean odor treatment of styrene acrylic emulsion.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A styrene-acrylic emulsion odor-removing process, specifically comprising:

[0008] The organic solvent is thoroughly mixed with the emulsion;

[0009] A packed stripping tower is used as the stripping equipment, and the emulsion mixed with the organic solvent is fed into the stripping tower from the upper part of the packing layer, and low-temperature steam is fed into the stripping tower from the lower part of the packing layer;

[0010] The temperature of the emulsion mixed with the organic solvent is controlled at 55-65°C when it is introduced, and the temperature of the steam is controlled at 70-130°C when it is introduced. The stripping tower is in a vacuum negative pressure state.

[0011] In the packing layer, the emulsion from top to bottom is fully in contact with the steam from bottom to top, and the stripped emulsion is collected at the bottom of the stripping tower and discharged.

[0012] The inventors discovered through research that water-insoluble residual monomers in styrene-acrylic emulsions primarily remain within the polymer latex particles, making them difficult to remove through stripping. The present invention addresses this difficulty in completely removing styrene monomer and its hydrocarbon impurities from styrene-acrylic emulsions. By adding a certain amount of an organic solvent capable of dissolving residual monomers and organic odor impurities as a stripping aid, the organic solvent dissolves and adsorbs the residual monomers and organic impurities remaining within the latex particles, removing them from the polymer latex particles. Combined with stripping in a packed stripping tower, the present invention effectively removes the residual monomers and VOCs.

[0013] As a preferred technical solution of the present invention, the organic solvent is an organic solvent having a boiling point lower than that of water. Preferably, the organic solvent can be selected from one or more combinations of n-hexane, cyclohexane, and ethanol.

[0014] In the present invention, the organic solvent is introduced as a liquid and can fully volatilize at the temperature and pressure maintained in the stripping tower during stripping. After the organic solvent mixes with the residual monomers and VOC components in the emulsion, the residual monomers and VOCs can be stripped from the emulsion by the organic solvent, completely separating the residual monomers and VOCs that are difficult to separate by water vapor during stripping. Furthermore, the added organic solvent itself has no substantial harmful effect on the emulsion.

[0015] As a preferred technical solution of the present invention, the amount of organic solvent used is 0.1-5% of the weight of the emulsion. After the organic solvent is added, it is mixed with the emulsion by mechanical stirring or ultrasonic dispersion for 5-15 minutes.

[0016] The present invention utilizes a packed stripping tower as the stripping equipment. Within the packing layer of a defined thickness, the contact area between the emulsion and the water vapor is large, ensuring full contact between the emulsion and the water vapor, significantly improving the efficiency of removing monomers and VOCs from the emulsion. The emulsion spreads across the cross-section of the stripping tower, coming into extensive contact with the steam within the tower. After the emulsion is steamed, residual monomers, VOCs, and organic solvents are removed by the steam.

[0017] The inlet temperature of the emulsion mixed with an organic solvent in the present invention is controlled to be 55-65°C. At this temperature, the emulsion has good fluidity and can keep the organic solvent in a liquid state, which is conducive to the dissolution of residual monomers and VOCs. At the same time, the temperature when the steam is sent in is controlled to be 70-130°C, the stripping tower is kept in a vacuum negative pressure state, and the pressure is controlled below the saturated vapor pressure of water at the corresponding temperature when the steam enters. The water vapor under this condition accelerates the demulsification speed of the emulsion and does not cause the emulsion to break, slag and form a crust, and does not affect the quality of the emulsion. If the steam temperature is too low, it is difficult to effectively remove the high-boiling point monomer components and organic solvents; and if the temperature is too high, the high-temperature steam and the material are in direct contact, which is likely to cause the temperature-sensitive emulsion properties to change. At high temperatures, the emulsion is prone to breakage and slag and form a crust, and energy consumption will also increase.

[0018] As a preferred technical solution of the present invention, the temperature of the emulsion mixed with the organic solvent is controlled at 60-65°C when it is introduced, and the temperature of the steam is controlled at 75-95°C when it is introduced.

[0019] As a preferred technical solution of the present invention, the filler material in the packing layer can be selected from at least one of metal, plastic, ceramic, and carbon fiber, and the filler adopts structured packing or bulk packing. For example, in practical applications, the structured packing can specifically be selected from one or more of perforated plate corrugated packing, plate corrugated packing, perforated plate corrugated packing, wire mesh corrugated packing, and mesh corrugated packing. The bulk packing type can specifically be selected from one or more of ball rings, Raschig rings, iso-saddle rings, rectangular saddle rings, ladder rings, Haier rings, Taylor rosettes, snowflake rings, and 84 inner arc rings. The filler has a large specific surface area, and after the emulsion passes through a packing layer with a certain height, it can be in more thorough and sufficient contact with the steam in the packing, so that the residual monomers and VOCs in the emulsion are reduced to extremely low levels.

[0020] In some preferred embodiments, the equivalent diameter of the plate corrugated packing is Φ5 to Φ25; further preferably, the equivalent diameter of the plate corrugated packing is Φ5 to Φ15; for example, the equivalent diameter of the plate corrugated packing may be Φ10.

[0021] As a preferred technical solution of the present invention, per unit time, the steam flow rate is 1 / 5 to 1 / 20 of the total emulsion flow rate by weight. More preferably, the total steam flow rate is 1 / 5 to 1 / 10 of the total emulsion flow rate. Even more preferably, the steam flow rate is 1 / 5 to 1 / 8 of the emulsion flow rate.

[0022] As a preferred technical solution of the present invention, the residence time of the emulsion in the stripping tower is 0.1 to 20 minutes. Further preferably, the residence time of the emulsion in the stripping tower is 0.1 to 10 minutes. Even more preferably, the residence time of the emulsion in the stripping tower is 1 to 8 minutes, for example, the residence time is 3 to 7 minutes.

[0023] As a preferred technical solution of the present invention, the stripping tower comprises multiple packing layers arranged in a vertical sequence, with steam flowing through the lower portion of each packing layer, preferably 2 to 6 layers. In this case, the emulsion to be treated can be stripped by multiple packing layers, which can further improve treatment efficiency. Especially for emulsions with high odor requirements, the provision of multiple packing layers can remove residual monohydrate and VOCs in the emulsion to lower levels, meeting more stringent requirements.

[0024] As a preferred technical solution of the present invention, the stripping process comprises the following steps:

[0025] S1. The bottom of the stripping tower is passed through a steam cooling buffer tank into the steam;

[0026] S2. The emulsion mixed with an organic solvent is fed into a stripping tower through a feed pump. The emulsion is distributed from top to bottom in the stripping tower packing layer and is in countercurrent contact with steam;

[0027] S3. The treated emulsion is discharged through a discharge pump and collected to obtain the treated emulsion;

[0028] S4. A condenser and a high-level tank are installed on the top of the stripping tower. The tail gas is collected by a vacuum pump, and the wastewater is collected by a wastewater pump.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] Due to the low water solubility of monomers, most of the residues of monomers such as styrene are present in the emulsion polymer colloid particles, establishing a controlled equilibrium between the continuous phase (water) and the particles, making it difficult for the residual monomers to be further removed by stripping. The present invention addresses this problem through in-depth research and process optimization. Before stripping, the emulsion is first mixed with a certain amount of organic solvent, and then the emulsion is stripped using a packed stripping tower. After the organic solvent is added to the emulsion as a stripping aid, the organic solvent has a good dissolving and stripping effect on the residual monomers and their impurities and VOCs, and can dissolve and adsorb the residual monomers and organic impurities remaining in the latex particles. After this step, the residual monomers and organic impurities are removed more effectively by stripping treatment in a packed stripping tower combined with a packed stripping tower.

[0031] In addition, the temperature of the emulsion to be treated is controlled at 55-65°C, and the temperature of the steam is controlled at 70-130°C. Under these process conditions, not only can the emulsion be effectively deodorized and the residual monohydrate content and VOC content be greatly reduced, but the emulsion will not break, produce slag, or form a crust, thus ensuring the stability of the emulsion quality properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a process flow chart for removing emulsion residues and VOCs by steam stripping;

[0033] In the figure: 1-mixing tank; 2-feed pump; 3-stripping tower; 4-condenser; 5-vacuum pump; 6-high-level tank; 7-wastewater pump; 8-discharge pump; 9-steam cooling buffer tank;

[0034] 100-emulsion before treatment; 200-process water; 300-steam; 400-steam condensate; 500-tail gas; 600-wastewater; 700-cleaning pipeline; 800-emulsion after treatment; 900-organic solvent. DETAILED DESCRIPTION

[0035] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] Reference Figure 1 , which is a process flow chart for removing residual monohydrate and VOC from emulsion by a stripping method. When the emulsion is subjected to odor-free stripping treatment, the specific steps are as follows:

[0037] S1. The bottom of the stripping tower 3 is passed through the steam cooling buffer tank 9, steam 300 and process water 200 are passed into the steam cooling buffer tank 9, the steam temperature is controlled by controlling the process water 200, and the steam condensate 400 is discharged from the bottom of the steam cooling buffer tank 9;

[0038] S2. The emulsion 100 to be treated is passed into a mixing tank 1. A certain amount of organic solvent 900 is added to the mixing tank 1 and mechanically stirred for a certain period of time. The uniformly dispersed emulsion is then fed into a stripping tower 3 via a feed pump 2. The emulsion is distributed from top to bottom in stripping tower 3, where it is countercurrently contacted by steam flowing from bottom to top. The stripping tower is a packed stripping tower, and the packing in the packed stripping tower is a corrugated plate packing with an equivalent diameter of Φ10.

[0039] S3. The treated emulsion is discharged through the discharge pump 8, the pressure of the discharge pump is 2.5Mpa (A), and the treated emulsion 800 is collected;

[0040] S4. A condenser 4 and a header tank 6 are sequentially provided at the top of the stripping column 3. The upper portion of the header tank 6 is connected to a vacuum pump 5, and the tail gas 500 is collected by the vacuum pump 5. The lower portion of the header tank 6 is provided with a wastewater pump 7 to collect wastewater 600, wherein the temperature of the header tank is 35°C and the pressure is -80KPa (G);

[0041] S5. After completion, the stripping device is cleaned by connecting the cleaning line 700 for next use. The cleaning line 700 can be directly connected to the upper part of the stripping tower 3 or to the upper part of the mixing tank 1 to facilitate cleaning of the entire device.

[0042] The present invention will be further described below with reference to a specific processed emulsion.

[0043] The emulsion treated in the embodiment of the present invention is a styrene-acrylic emulsion prepared by Shanghai Baolijia New Materials Co., Ltd. The synthesis process is described as follows: water, emulsifier or seed emulsion are added to the reactor and stirred evenly. After the temperature rises to 60-90°C, the initial initiator solution is added and the monomer emulsion and initiator solution are added dropwise. After the addition is completed, the temperature is kept for a certain period of time, and the temperature is lowered to 80-50°C. At the same time, an aqueous solution of an oxidant and an aqueous solution of a reducing agent are added dropwise. After the addition is completed, the temperature is kept for a certain period of time, and the temperature is lowered to below 50°C. The gel that may be generated is removed by filtering through a 200-mesh filter cloth. If necessary, the pH of the emulsion can be adjusted to neutral with an alkaline solution.

[0044] Monomers used include, but are not limited to, butyl acrylate, isooctyl acrylate, styrene, hydroxyethyl acrylate, acrylic acid, and methacrylic acid. The initiator solution can be either a redox system or a thermal initiation system; oxidizing agents include, but are not limited to, sodium persulfate, ammonium persulfate, potassium persulfate, hydrogen peroxide, and tert-butyl hydroperoxide; reducing agents include, but are not limited to, sodium bisulfite, sodium thiosulfate, and FF6.

[0045] Anionic emulsifiers include phosphate anionic emulsifiers and / or sulfate anionic emulsifiers; preferably, the phosphate anionic emulsifier includes fatty phosphate; preferably, the sulfate anionic emulsifier includes any one or more of ethoxylated alkyl sulfates, alkyl sulfates and fatty alcohol ether sulfates, more preferably any one or more of ethoxylated alkyl sulfate sodium salts, ethoxylated alkyl sulfate ammonium salts, alkyl sulfate sodium salts and fatty alcohol ether sulfate sodium salts; nonionic emulsifiers include fatty alcohol polyoxyethylene ether emulsifiers.

[0046] The obtained emulsion has the following properties: solid content of 30-60%, viscosity (mPa·s) of 50-5000, Tg (°C) of -20-50, residual monomer content of the emulsion ≤2000ppm, and VOC content ≤10000ppm. The emulsion generally has a strong odor before odor removal. The inventors tested it by gas chromatography and found that the main residual monomer in the emulsion is styrene (≥200ppm). It is speculated that the main source of the odor is styrene monomer and its accompanying hydrocarbon impurities.

[0047] In the following, emulsions 1, 2, 3 and 4 prepared by Shanghai Baolijia New Materials Co., Ltd. are selected as the treatment objects for stripping treatment. Table 1 shows the specific composition raw materials and physical property parameters of the emulsions to be treated.

[0048] Table 1 Emulsion monomer raw materials to be treated and their main physical properties

[0049]

[0050] Note: Viscosity tests were performed at 25°C using a Brookfield LV spindle.

[0051] The main process parameters of the stripping treatment process of Examples 1 to 6 are shown in Table 2.

[0052] Table 2 Specific parameters of the main process of stripping in Example

[0053]

[0054]

[0055] Experimental results

[0056] The residual monohydrate content of the emulsion in the example before and after treatment was measured according to Appendix A of the standard GB / T 20623-2006, and the VOC content of the emulsion in the example was tested according to the standard GB / T 18582-2020.

[0057] The specific method for evaluating lotion odor is as follows: the lotion is placed in a clean, frosted wide-mouth bottle with the liquid level at half the height of the bottle body, covered with a glass lid, and left to stand for 24 hours. Five odor assessors then evaluate the odor intensity level on a scale of 0-5, with 0 being no odor, 1 being noticeable, non-disturbing, and mild, 2 being clearly noticeable, non-disturbing, and moderate, 3 being clearly noticeable, with a disturbing odor and a strong intensity, 4 being clearly noticeable, with a strongly disturbing odor and a very strong intensity, and 5 being an unbearable odor.

[0058] The test results are shown in Table 3.

[0059] Table 3 Experimental results of the examples

[0060]

[0061] As can be seen from Table 3, the embodiments of the present invention can effectively deodorize styrene acrylic emulsion, and the VOC content and residual monolactic acid content are greatly reduced. After treatment, the VOC content is reduced to below 600 ppm, and the total residual monolactic acid content is reduced to below 100 ppm, and most of it is below 50 ppm. Most of the emulsion reaches the level of being odorless (or slightly perceptible), meeting the requirements of high-quality emulsion.

[0062] The present invention also provides the following comparative examples.

[0063] Comparative Example 1

[0064] Emulsion 1 was treated by vacuum extraction (no organic solvent was added to the emulsion before vaporization) at a temperature of 50° C., an extraction pressure of −0.1 MPa, and an extraction time of 2 hours.

[0065] Comparative Example 2

[0066] Emulsion 1 was treated by vacuum extraction (no organic solvent was added to the emulsion before vaporization) at a temperature of 50° C., an extraction pressure of −0.1 MPa, and an extraction time of 4 hours.

[0067] Comparative Example 3

[0068] Emulsion 1 was treated by vacuum extraction at a temperature of 60° C., an extraction pressure of −0.1 MPa, and an extraction time of 4 hours.

[0069] Comparative Example 4

[0070] Compared with Example 1, no organic solvent was added before the emulsion vaporization, and the rest was the same as Example 1.

[0071] Comparative Example 5

[0072] Compared with Example 2, no organic solvent was added before the emulsion vaporization, and the rest was the same as Example 2.

[0073] Comparative Example 6

[0074] Compared with Example 1, the water vapor inlet temperature is controlled to 135° C., and the rest are the same as Example 1.

[0075] The experimental results of Comparative Examples 1 to 6 are shown in Table 4.

[0076] Table 4 Experimental results after treatment

[0077]

[0078] As shown in Table 4, comparative examples 1 to 3 used vacuum extraction to treat the emulsion, but the removal effect of VOC content and the total amount of residual monomers was poor, the emulsion still had a strong odor, and the emulsion had varying degrees of crusting, and the treatment effect was not ideal.

[0079] In Comparative Examples 4 and 5, when no organic solvent is added to the emulsion before steam stripping, although the VOC content and the total residual monomers are reduced significantly, they cannot reach a lower level. That is, it is difficult to achieve deep odor removal of styrene-acrylic emulsion only through steam stripping treatment in a packed steam stripping tower.

[0080] In Comparative Example 6, although VOC and residual monomers in the emulsion were effectively removed, the emulsion showed a certain degree of crusting and even slagging. It is speculated that the possible reason is that the steam temperature is too high, which affects the properties of the emulsion.

[0081] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A styrene-acrylic emulsion odor-removing process, characterized in that: The organic solvent is thoroughly mixed with the emulsion; A packed stripping tower is used as the emulsion stripping equipment. The emulsion mixed with the organic solvent is fed into the stripping tower from the upper packing layer, and low-temperature steam is fed into the stripping tower from the lower packing layer. The temperature of the emulsion mixed with the organic solvent is controlled at 55-65°C when it is introduced, and the temperature of the steam is controlled at 70-130°C when it is introduced. The stripping tower is in a vacuum negative pressure state. The organic solvent is selected from one or more combinations of n-hexane, cyclohexane, and ethanol; The amount of the organic solvent used is 0.1-5% of the weight of the emulsion. After the organic solvent is added, it is fully mixed with the emulsion by mechanical stirring or ultrasonic dispersion for 5-15 minutes.

2. A styrene-acrylic emulsion odor-free stripping process according to claim 1, characterized in that: The temperature of the emulsion when it is fed in is controlled at 60-65°C, and the temperature of the steam when it is fed in is controlled at 75-95°C.

3. A styrene-acrylic emulsion odor-free stripping process according to claim 1, characterized in that: The filler material in the filler layer is selected from at least one of metal, plastic, ceramic, and carbon fiber, and the filler is a structured filler or a bulk filler.

4. A styrene-acrylic emulsion odor-free stripping process according to claim 1, characterized in that: In unit time, the flow rate of steam is 1 / 5 to 1 / 20 of the total flow rate of the emulsion by weight.

5. A styrene-acrylic emulsion odor-free stripping process according to claim 1, characterized in that: The residence time of the emulsion in the stripping tower is 0.1 to 20 minutes.

6. A styrene-acrylic emulsion odor-removing treatment process according to claim 1, characterized in that: The packing layers in the stripping tower are arranged in layers in sequence, and steam is introduced into the lower part of each packing layer.

7. A styrene-acrylic emulsion odor-free stripping process according to claim 1, characterized in that: The specific steps include: S1. The bottom of the stripping tower is passed through a steam cooling buffer tank into the steam; S2. The emulsion mixed with an organic solvent is fed into a stripping tower through a feed pump. The emulsion is distributed from top to bottom in the stripping tower packing layer and is in countercurrent contact with steam; S3. The treated emulsion is discharged through a discharge pump and collected to obtain the treated emulsion; S4. A condenser and a high-level tank are installed on the top of the stripping tower. The tail gas is collected by a vacuum pump, and the wastewater is collected by a wastewater pump.

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