Continuous preparation method of hydroxypropyl methacrylate

Abstract

The invention discloses a continuous preparation method of hydroxypropyl methacrylate, which comprises the following steps: (1) mixing, heating and dissolving a catalyst chromium acetate, a polymerization inhibitor, water and methacrylic acid to obtain a catalyst solution; and (2) reacting methacrylic acid, epoxypropane and the catalyst solution in a continuous flooded reactor to generate hydroxypropyl methacrylate. Quantitative water is added into methacrylic acid to realize uniform dissolution of the catalyst chromium acetate, the ratio X% of water to the catalyst meets the following inequality: 5 < = X < = 21.2-2.5% A-1.7% B, and A and B are respectively water (ppm) in methacrylic acid and epoxypropane. The method solves the problem that the catalyst is difficult to dissolve or the content of light component impurities in the product is high due to excessive moisture in the traditional production process, and is suitable for industrial production.

Description

Technical Field

[0001] The invention belongs to the field of chemical synthesis and relates to a continuous preparation method of hydroxypropyl methacrylate. Background Art

[0002] Hydroxypropyl methacrylate, referred to as HPMA, is a colorless transparent liquid with two functional groups: carbon-carbon double bonds and hydroxyl groups. Therefore, it has active properties and is widely used as active diluents and adhesives in the fields of fiber processing, coatings, photocurable resins, rubber, etc.

[0003] At present, the main synthesis process of HMPA is the intermittent ring-opening reaction method, which is prepared by the reaction of methacrylic acid and propylene oxide under the action of a catalyst and an inhibitor. Inhibitors include hydroquinone, p-hydroxyanisole, phenothiazine, copper dibutyl dithiocarbamate, etc., and catalysts commonly used include pyridine, chromium trichloride, chromium acetate, chromium acetylacetonate, ferric chloride or organic iron compounds, etc. In actual industrial production, chromium acetate catalyst is mostly used.

[0004] Patent CN102584580A discloses a method for preparing hydroxypropyl methacrylate, which is prepared by reaction under vacuum and nitrogen protection in the presence of a preferred chromium acetate catalyst and hydroquinone or p-hydroxyanisole inhibition; the process is an intermittent operation, and propylene oxide is relatively volatile. A large amount of propylene oxide vaporizes under vacuum conditions, affecting the reaction rate. At the same time, the volatilization of methacrylic acid easily leads to gas-phase condensation polymerization on the reactor wall, requiring frequent cleaning of the reactor.

[0005] Patent US6465681B2 uses chromium acetate as a catalyst, phenothiazine as an inhibitor, a reaction temperature of 80-90°C, a reaction time of 7h, and a yield of 96.7% for preparing HPMA; wherein the chromium catalyst exhibits good catalytic activity and selectivity, but is also an intermittent operation and cannot be produced continuously.

[0006] Patent CN113861025A discloses a continuous synthesis method of hydroxypropyl methacrylate, using magnetic zeolite molecular sieve and tetraisopropyl titanate as catalysts to generate hydroxypropyl methacrylate in a continuous microchannel reactor, and the HPMA yield can reach more than 96%. In the present invention, the catalyst can be recycled without the need to add an additional inhibitor; in fact, the catalyst still needs to be recycled after calcination, and long-term continuous operation in industry cannot be achieved; at the same time, tetraisopropyl titanate is added as a co-catalyst, resulting in increased separation energy consumption.

[0007] Patent CN114634414A discloses a method for synthesizing hydroxypropyl methacrylate, wherein ferric chloride is dissolved in a water-alcohol mixed solvent to catalyze the reaction of methacrylic acid and propylene oxide, and no additional polymerization inhibitor is required during the reaction process. In the present invention, the moisture content exceeds 2% and the methyl (ethyl) alcohol content exceeds 10% based on the mass of methacrylic acid. Excessive moisture and methyl (ethyl) alcohol react with the raw materials propylene oxide and methacrylic acid, which not only increases the unit consumption, but also produces light components that affect product quality and downstream applications.

[0008] In the prior art, in the process of preparing hydroxypropyl methacrylate with methacrylic acid and propylene oxide as starting materials, technicians mainly study new catalysts or inhibitor-free applications, but most of them are intermittent kettle operations, which require frequent temperature rise and fall operations and have low reaction efficiency; and due to the presence of gas phase space in the kettle, methacrylic acid is easy to condense and polymerize, causing scaling of the kettle wall after long-term operation, resulting in shutdown and maintenance; in addition, in the prior art, excessive water is added during the production process to inhibit the formation of dimethacrylate. In fact, excessive water not only increases the ring-opening side reaction of propylene oxide, resulting in an increase in the unit consumption of propylene oxide, but also the generated diol impurities will affect the product quality more. This is because diol has higher hydroxyl activity than HPMA and will react preferentially during the resin polymerization process, thereby affecting the resin performance; therefore, in the disclosed patent literature (such as CN104284880A), the water content of the reaction solution is preferably less than 0.05%.

[0009] Although chromium acetate has good catalytic properties, it has poor solubility in methacrylic acid, especially when the catalyst content is higher than 4%. It still cannot be dissolved when heated to 70°C, and even agglomerates, affecting the stirring power. In severe cases, it causes the stirring machine to jump. Low catalyst concentrations require larger catalyst dissolution tanks, which is also a difficulty in current industrialization. Summary of the invention

[0010] In order to solve the above technical problems, the present invention proposes a continuous preparation method of hydroxypropyl methacrylate: in the dissolution process of the catalyst chromium acetate, a controlled amount of water is added to methacrylic acid to uniformly dissolve the chromium acetate, and then mixed with the raw materials to react in a reactor, thereby solving the problem of difficult catalyst dissolution in the traditional production process or high light component impurity content of the product caused by excessive water, and the method is suitable for industrial production.

[0011] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0012] A continuous production method for hydroxypropyl methacrylate comprises the following steps:

[0013] (1) mixing and heating a catalyst, chromium acetate, a polymerization inhibitor, water and methacrylic acid to dissolve the mixture and prepare a uniform catalyst solution;

[0014] (2) The catalyst solution, methacrylic acid and propylene oxide are continuously introduced into a continuous reactor to continuously produce hydroxypropyl methacrylate.

[0015] Preferably, in step (1), the mass ratio of chromium acetate, polymerization inhibitor and methacrylic acid is 6-10:1-3:100.

[0016] Preferably, in the step (1), the mass ratio X% of the added water to the catalyst satisfies the following relationship: 5≤X≤21.2-2.5%A-1.7%B, wherein A and B are the water content (ppm) in methacrylic acid and propylene oxide, respectively;

[0017] Preferably, A≤300, B≤100, in accordance with the national standard GB / T 6283-2008 moisture testing method.

[0018] In the present invention, by controlling the mass ratio of added water to the catalyst within a certain range, on the one hand, the addition of a small amount of water plays a phase transfer role, so that solid chromium acetate and methacrylic acid are fully contacted and dissolved, and the parallel side reaction of HPMA dehydration esterification is inhibited to improve the product selectivity; on the other hand, the upper limit of the amount of water added is controlled to prevent the catalyst solution from being unevenly distributed due to emulsification, and at the same time reduce the diol impurities formed by the ring-opening reaction with PO (propylene oxide), without affecting PO consumption and product quality.

[0019] Preferably, in step (1), the heating temperature of the catalyst dissolution process is 45-80°C, specifically 45, 50, 55, 60, 65, 70, 75, 80°C; the catalyst dissolution time is 1-6h, specifically 1, 2, 3, 4, 5, 6h.

[0020] Preferably, the inhibitor in step (1) includes one or more of tetramethylpiperidinyl nitroxide free radical, tetramethylpiperidone nitroxide free radical, tetramethylpiperidinol nitroxide free radical, di(2,2,6,6-tetramethylpiperidinyl nitroxide free radical) sebacate, and tri(2,2,6,6-tetramethylpiperidinyl nitroxide free radical) phosphite; more preferably, tetramethylpiperidinol nitroxide free radical.

[0021] Preferably, in step (2), the mass ratio of the catalyst solution to the methacrylic acid added in step (2) is 4-8:100.

[0022] In the present invention, the catalyst solution obtained in step (1) is continuously introduced into the reactor, and the mass ratio of propylene oxide to methacrylic acid is controlled to be 69-73:100, wherein methacrylic acid is the total mass of methacrylic acid in the catalyst solution in step (2) and newly added methacrylic acid.

[0023] Preferably, in step (2), the reaction temperature of methacrylic acid and propylene oxide is 70-100° C., more preferably 80-95° C.; the pressure is 0.3-0.7 MPaG; and the reaction residence time is 2-6 hours.

[0024] Preferably, in step (2), the continuous reactor is selected from any one of a PFR tubular reactor (plug flow tubular reactor), a CSTR tank reactor (continuous stirred tank reactor) or a CSTR tank reactor connected in series with a PFR tubular reactor.

[0025] Preferably, the continuous reactor can be selected in the form of multi-stage series connection according to actual production, and the kettle reactor and the tubular reactor can be selected in combination. In a specific embodiment, for example, 3-stage kettle reactors are connected in series, 2-stage kettle reactors are connected in series with 1-stage tubular reactor, etc.

[0026] Preferably, in the present invention, by adopting the above-mentioned continuous reactor, full liquid operation is performed, and the material is discharged from the top of the reactor. Compared with the overflow operation adopted in the prior art, the liquid level in the reactor usually does not exceed 80%. The full liquid operation can eliminate the gas phase space of the traditional kettle reaction, greatly reduce the polymerization generation, and improve the production stability.

[0027] Preferably, in step (2) of the present invention, the reaction liquid at the reactor outlet is subjected to gas stripping, scraper evaporation and distillation to obtain the HPMA product.

[0028] Specifically, the gas stripping, scraper evaporation and negative pressure distillation are conventional steps for removing light and heavy substances. The gas stripping removes the residual propylene oxide. After the scraper evaporation removes the heavy substances, the distillation can obtain a hydroxypropyl methacrylate product with a content of more than 99.4wt%;

[0029] In a specific embodiment, the gas stripping operating pressure is preferably 10-50 KpaA, the scraper operating pressure is preferably 1-2 KpaA, and the distillation pressure is preferably 0.1-1 KpaA.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The addition of a small amount of water in the present invention plays a phase transfer role, so that the solid chromium acetate and methacrylic acid are fully contacted and dissolved, which can achieve high catalytic activity and continuous production; avoid the dissolving slurry state of the traditional intermittent process, causing valve wear and catalyst dosage fluctuation.

[0032] 2. The present invention controls the addition of a small amount of water, and while suppressing the parallel side reaction of HPMA dehydration esterification, avoids excessive water from causing the catalyst solution to emulsify and affect the catalyst distribution, and reduces the ring-opening side reaction of propylene oxide, reduces the diol impurity content, and has high product quality.

[0033] 3. The present invention adopts a full liquid continuous reaction with mild reaction conditions, a methacrylic acid conversion rate of ≥99.9%, and a hydroxypropyl methacrylate selectivity of ≥98%. It eliminates the gas phase space of the traditional kettle reaction, greatly reduces polymerization production, improves production stability and convenience, reduces production costs, and is suitable for industrial production. DETAILED DESCRIPTION

[0034] The present invention is further described below by means of specific examples. The examples described in the present invention are only used to illustrate the present invention and do not limit the scope of the present invention.

[0035] Unless otherwise specified, the main raw materials and reagents involved in the present invention were purchased from commercially available products.

[0036] Reagents Specification Manufacturer Tetramethylpiperidinol nitroxide free radical 99％ Jilin Changyuan Technology Chromium acetate 99.9％ Xia County Transport Capacity Methacrylic acid 99.9％ Wanhua Chemical produces Propylene oxide 99％ Aladdin Reagent

[0037] Gas chromatography (GC): analysis of reaction liquid composition, model Shimadzu GC-2010-plus; parameters: chromatographic column DB-5, column temperature: starting temperature 135°C, heating to 240°C, maintaining for 9 min, injection port temperature: 250°C, detector temperature: 260°C, air flow rate: 350 ml / min, hydrogen flow rate: 36 ml / min, carrier gas flow rate: 1 ml / min, split ratio 1:60.

[0038] Moisture content: Determined in accordance with GB / T 6283-2008.

[0039] [Example 1]

[0040] Hydroxypropyl methacrylate was prepared according to the following continuous process:

[0041] Add 6 g of catalyst chromium acetate, 3 g of tetramethylpiperidinol nitroxide free radical, and 0.3 g of water to 100 g of MAA (water content 300 ppm, the same below), stir at 45° C. for 6 h to dissolve into a catalyst solution for use;

[0042] 42.41 g of the above catalyst solution was mixed evenly with 543.23 g of methacrylic acid and 401.6 g of propylene oxide (water content 100 ppm) and then pumped into the bottom of a coil reactor (outer diameter 6 mm, inner diameter 4 mm, length 3000 mm) at 0.105 g / min by a horizontal flow pump. The residence time was 6 hours. The reaction liquid was discharged from the top. The oil bath outside the reaction tube was heated to 70° C. and the reaction pressure was 0.3 MPaG. After continuous operation for 157 hours, the outlet sampling analysis showed that the conversion rate of methacrylic acid was 99.95%, the selectivity of the product HPMA was 98.1%, and the water content was 324 ppm.

[0043] The reaction liquid was stripped with nitrogen at 10KpaA to remove residual PO, and then the heavy components were removed by scraper evaporation at 1KpaA. The vacuum distillation was continued at 300PaA, and the top component (74°C) was condensed to obtain HPMA product with a purity of 99.4%.

[0044] [Example 2]

[0045] Hydroxypropyl methacrylate was prepared according to the following continuous process:

[0046] 200 g of catalyst chromium acetate, 20 g of di(2,2,6,6-tetramethylpiperidinylnitroxide) sebacate, and 25 g of water were added to 2000 g of MAA (water content: 300 ppm, the same below), and stirred at 80° C. for 1 h to dissolve into a catalyst solution for later use;

[0047] 1976g of the above catalyst solution was mixed evenly with 42.25kg of methacrylic acid and 32.13kg of propylene oxide (water content 100ppm) and then pumped into a series of autoclave reactors (500ml*3) at 8.33g / min through a horizontal flow pump. The top of the reactor was discharged, and the reactor was heated to 100°C in an oil bath, the reaction pressure was 0.7MpaG, and the single reactor residence time was 1h. After continuous operation for 152h, the outlet sampling analysis showed that the conversion rate of methacrylic acid was 99.98%, the selectivity of the product HPMA was 99.2%, and the water content was 496ppm.

[0048] The reaction liquid was stripped with nitrogen at 10KpaA to remove residual PO, and then the heavy components were removed by scraper evaporation at 1KpaA. The vacuum distillation at 300Pa was continued, and the top component (74°C) was condensed to obtain HPMA product with a purity of 99.8%.

[0049] [Example 3]

[0050] Hydroxypropyl methacrylate was prepared as follows:

[0051] 200 g of catalyst chromium acetate, 50 g of tetramethyl piperidine alcohol nitrogen oxide free radical, and 14 g of water were added to 2500 g of MAA (water content 300 ppm, the same below), and stirred at 60° C. for 2.5 h to dissolve into a catalyst solution for use;

[0052] The above catalyst solution 2378.25g was mixed with 40.88kg of methacrylic acid and 30.12kg of propylene oxide (water content 100ppm) and then pumped into a continuous kettle reactor (500ml*2) in series with a tubular reactor (outer diameter 10mm, inner diameter 8mm, length 2000mm) at 8.33g / min through a horizontal flow pump. The reactor was top discharge, full liquid operation, the reactor and the reaction tube were heated to 95°C in an oil bath, the reaction pressure was 0.5MpaG, and the total residence time was 2.2h. After continuous operation for 146h, the outlet sampling analysis showed that the conversion rate of methacrylic acid was 99.95%, the selectivity of the product HPMA was 98.5%, and the water content was 372ppm.

[0053] The reaction liquid was stripped with nitrogen at 10KpaA to remove residual PO, and then the heavy components were removed by scraper evaporation at 1KpaA. The vacuum distillation was continued at 300Pa, and the top component (74°C) was condensed to obtain HPMA product with a purity of 99.52%.

[0054] [Example 4]

[0055] Hydroxypropyl methacrylate was prepared according to the following continuous process:

[0056] Add 10 g of catalyst chromium acetate, 1.2 g of tris(2,2,6,6-tetramethylpiperidinyl nitroxide) phosphite and 2.12 g of water to 100 g of MAA (water content 10 ppm, the same below), stir at 70° C. for 1.5 h to dissolve into a catalyst solution for use;

[0057] 30.34g of the above catalyst solution was mixed evenly with 642.56g of methacrylic acid and 481.92g of propylene oxide (water content 10ppm) and then pumped into the bottom of a coil reactor (outer diameter 6mm, inner diameter 4mm, length 3000mm) at 0.157g / min by a horizontal flow pump. The residence time was 4h. The reaction liquid was discharged from the top. The oil bath outside the reaction tube was heated to 80°C and the reaction pressure was 0.4MpaG. After continuous operation for 122h, the outlet sampling analysis showed that the conversion rate of methacrylic acid was 99.97%, the selectivity of the product HPMA was 98.6%, and the water content was 500ppm.

[0058] The reaction liquid was stripped with nitrogen at 10KpaA to remove residual PO, and then the heavy components were removed by scraper evaporation at 1KpaA. The vacuum distillation was continued at 300PaA, and the top component (74°C) was condensed to obtain HPMA product with a purity of 99.1%.

[0059] [Comparative Example 1]

[0060] Referring to the synthesis method of hydroxypropyl methacrylate in Example 3, the difference is that the ratio of water to catalyst added during the catalyst dissolution process is 4%, other operating conditions and proportions remain unchanged, and the catalyst is continuously stirred for 24 hours without being completely dissolved; after filtering out the residue, the catalyst solution is continuously reacted with methacrylic acid and propylene oxide as mixed ingredients in Example 3, and the residence time is controlled to be 2.2 hours. The outlet sampling analysis shows that the conversion rate of methacrylic acid is 91.2%, the selectivity of the product HPMA is 87.2%, the water content is 302 ppm, and the reaction conversion rate and selectivity are significantly reduced.

[0061] [Comparative Example 2]

[0062] Referring to Example 3, the method for synthesizing hydroxypropyl methacrylate was described, except that the ratio of water to catalyst added during the catalyst dissolution process was 25%, other operating conditions and proportions remained unchanged, and the catalyst was completely dissolved by stirring at 60° C. for 1.5 h, but it was found that the solution was partially emulsified during standing; the catalyst solution, methacrylic acid and propylene oxide were mixed and continuously reacted, and the residence time was controlled to be 2.2 h. The outlet sampling analysis showed that the methacrylic acid conversion rate was 98.2%, the product HPMA selectivity was 94.9%, the water content was 794 ppm, and the reaction indicators were unqualified.

[0063] [Comparative Example 3]

[0064] Referring to the synthesis method of hydroxypropyl methacrylate in Example 3, the raw materials were mixed uniformly according to the ratio of Example 3, and then pumped into a continuous autoclave reactor (500ml*2) in series with a tubular reactor (outer diameter 10mm, inner diameter 8mm, length 2000mm) at 6.82g / min by a horizontal flow pump. The reactor was changed from top discharge to side overflow discharge, non-full liquid operation, the reactor and the reaction tube oil bath were heated to 95°C, the reaction pressure was 0.5MpaG, the total residence time was 2.2h, and the outlet sampling analysis showed that the methacrylic acid conversion rate was 99.92%, the product HPMA selectivity was 98.3%, and the water content was 372ppm; in the subsequent continuous operation process, due to the slow polymerization of methacrylic acid and hydroxypropyl methacrylate on the gas phase wall of the autoclave reactor, the formed gel polymer accumulated in the series tubular reactor, and the raw material conversion rate and product selectivity gradually decreased; after 90h of continuous operation, the methacrylic acid conversion rate dropped to 96.1%, the product selectivity was 95.2%, and the reaction index was unqualified; after continuing to run for 26h, the reaction tube was blocked and the reaction stopped.

[0065] [Comparative Example 4]

[0066] The catalyst solution was prepared by referring to the method of Example 3, except that the addition of water during the catalyst dissolution process was omitted, and other operations and conditions remained unchanged. During the heating and stirring dissolution process, the catalyst agglomerated, stirring was stopped, and subsequent reaction could not be carried out.

[0067] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention.

Claims

1. A continuous preparation method of hydroxypropyl methacrylate, characterized in that: The following steps are involved: (1) Mixing catalyst chromium acetate, polymerization inhibitor, water and methacrylic acid, heating and dissolving to prepare a catalyst solution; wherein the mass ratio of water to catalyst chromium acetate is X% and satisfies the following relationship: 5≤X≤ 21.2-2.5%A-1.7%B, A≤300, B≤100; (2) The catalyst solution, methacrylic acid and propylene oxide are continuously introduced into a reactor to produce hydroxypropyl methacrylate.

2. The method according to claim 1, characterized in that In step (1), the inhibitor includes one or more of tetramethylpiperidinyl nitroxide free radical, tetramethylpiperidone nitroxide free radical, tetramethylpiperidinol nitroxide free radical, di(2,2,6,6-tetramethylpiperidinyl nitroxide free radical) sebacate, and tri(2,2,6,6-tetramethylpiperidinyl nitroxide free radical) phosphite.

3. The method according to claim 1 or 2, characterized in that: In step (1), the mass ratio of chromium acetate, polymerization inhibitor and methacrylic acid is 6-10:1-3:

100.

4. The method according to any one of claims 1 to 3, characterized in that: In step (1), the heating temperature during the catalyst dissolution process is 45-80° C. and the dissolution time is 1-6 h.

5. The method according to claim 1, characterized in that In step (2), the mass ratio of the catalyst solution to the methacrylic acid added in step (2) is 4-8:

100.

6. The method according to claim 1 or 5, characterized in that: In step (2), the mass ratio of propylene oxide to methacrylic acid is 69-73:100 based on the mass of the total methacrylic acid.

7. The method according to claim 1, characterized in that In step (2), the reaction temperature of methacrylic acid and propylene oxide is 70-100° C., preferably 80-95° C., the pressure is 0.3-0.7 MPaG, and the reaction residence time is 2-6 hours.

8. The method according to claim 1, characterized in that: In step (2), the continuous reactor includes any one of a PFR tubular reactor, a CSTR kettle reactor or a CSTR kettle reactor connected in series with a PFR tubular reactor.

9. The method according to any one of claims 1 to 8, characterized in that: In step (2), the continuous reactor is operated with full liquid, and the material is discharged from the top of the reactor.

10. The method according to claim 1, characterized in that In step (2), the reaction liquid at the reactor outlet is subjected to gas stripping, scraper evaporation and distillation to obtain the hydroxypropyl methacrylate product.