A process for the production of dimethyl sebacate

Abstract

The application discloses a method for producing dimethyl sebacate, which uses p-toluene sulfonic acid as a catalyst and realizes two-stage esterification. The first stage is a liquid-solid reaction of solid sebacic acid and methanol at low temperature, which is carried out in a stirring kettle. The second stage is a gas-liquid reaction of crude ester (a mixture of sebacic acid, sebacic acid monomethyl ester and dimethyl sebacate) after pre-esterification and methanol steam at high temperature, which is carried out in a bubble column. The method solves the problem of height dispersion in the tower through the pre-esterification reaction in the stirring kettle. Meanwhile, the methanol steam and the crude ester are countercurrently flowed and reacted in the bubble column, so as to improve the mass transfer driving force, break through the reaction balance, accelerate the reaction rate, improve the esterification rate and reduce the product acid value. The reactor structure adopted by the method is simple, the operation is stable, the investment and maintenance cost are low, and the method is suitable for large-scale continuous production in industry.

Description

Technical Field

[0001] This invention relates to a method for producing dimethyl sebacate. Background Technology

[0002] Dimethyl sebacate, a widely used organic chemical product, is commonly used in the preparation of surfactants, plasticizers, softeners, leather additives, textile auxiliaries, and as a light stabilizer. Currently, there is limited literature on the preparation of dimethyl sebacate; existing literature mainly focuses on the esterification reaction of sebaic acid and methanol. The key aspects of dimethyl sebacate production are: 1) the catalyst; and 2) the production process and equipment. CN102351692A and CN113443983B use solid acid as a catalyst, while CN1070395A uses concentrated sulfuric acid. Concentrated sulfuric acid has strong oxidizing, corrosive, and dehydrating properties, requiring high corrosion resistance in reaction equipment and easily causing product carbonization and color darkening. Solid acid offers good safety and is easy to recover, but it has low acid content, high mass transfer resistance, and low catalytic efficiency. Existing literature mainly mentions two types of equipment for dimethyl sebacate production: stirred tank reactors and fixed-bed reactors. CN1070395A and CN102351692A both use stirred esterification reactors. Stirred reactors provide macroscopic mixing, resulting in poor mixing effects, making industrial scale-up difficult and yielding poor scale-up results. Furthermore, esterification is a reversible reaction, and the reaction in a stirred reactor struggles to overcome equilibrium limitations, leading to low single-stage esterification rates. CN113443983B employs a two-stage esterification process to produce dimethyl sebacate. The first stage takes place in a stirred reactor, where most of the sebacate is esterified, and the generated water is removed by vaporization. The second stage takes place in a fixed bed, where countercurrent flow of alcohol and oil reduces the impact of reaction equilibrium on the esterification reaction, thus refining the small amount of carboxyl groups remaining in the first-stage esterification product. Fixed-bed reactors suffer from large axial bed pressure drop, flooding, and uneven radial concentration and temperature distribution. Summary of the Invention

[0003] To address the aforementioned technical problems in the existing technology, the present invention aims to provide a method for producing dimethyl sebacate. The method of the present invention uses p-toluenesulfonic acid as a catalyst and employs a two-stage esterification process. The first stage involves a liquid-solid reaction between solid sebacate and methanol at low temperature, carried out in a stirred tank. The second stage involves a gas-liquid reaction between the pre-esterified crude ester (a mixture of sebacate, monomethyl sebacate, and dimethyl sebacate) and methanol vapor at high temperature, carried out in a bubble column.

[0004] The technical solution adopted in this invention is as follows:

[0005] A method for producing dimethyl sebacate, using p-toluenesulfonic acid as a catalyst, employs a two-stage esterification reaction: the first stage is a pre-esterification reaction in a stirred tank, and the second stage is an esterification reaction in a bubble column. The method specifically includes the following steps:

[0006] 1) Pre-esterification: Solid sebacic acid, methanol and p-toluenesulfonic acid are added to a stirred tank, heated to reflux, and stirred to carry out the pre-esterification reaction. The acid value is reduced to below 75 mg KOH / g and the esterification rate is above 85%.

[0007] 2) The material after the pre-esterification reaction in step 1) is pumped to the crude ester dehydration kettle, where methanol and water are removed by distillation to obtain a mixture containing monomethyl sebacate, dimethyl sebacate, and a small amount of unreacted sebacate, which is the crude ester; the mixed vapor of distilled methanol and water enters the methanol recovery tower to recover methanol, and the crude ester after removing methanol and water enters the bubble column. The bubble column is equipped with a stirrer with 2-8 stages of flat blade impellers to provide a stirring radial flow effect on the liquid material in the bubble column;

[0008] 3) Bubble tower reaction: Crude ester enters from the top of the bubble tower, and liquid methanol, after being heated and vaporized in the vaporization kettle, enters from the bottom of the bubble tower. The crude ester and methanol vapor are further heated in the bubble tower, and the two phases flow and react in countercurrent. The dimethyl sebacate product obtained after the reaction flows out from the bottom of the bubble tower and enters the product storage tank. The mixed vapor formed by unreacted methanol and generated water is distilled out from the top of the bubble tower and enters the methanol recovery tower to recover methanol.

[0009] 4) The methanol recovered by the methanol recovery tower is recycled for the pre-esterification reaction.

[0010] Further, in step 1), the mass ratio of methanol to sebacic acid in the pre-esterification reaction is (0.6–1):1, the amount of p-toluenesulfonic acid is 0.2–0.4 wt% of the amount of sebacic acid, the reaction temperature is the reflux temperature of methanol, and the reaction time is 240–

[0011] 480min.

[0012] Further, step 2) is the dehydration process of the primary esterified product. The primary esterified product obtained after pre-esterification contains unreacted sebacic acid and methanol, as well as the reacted monomethyl sebacic acid, dimethyl sebacic acid, and water. The esterification reaction is reversible. At the end of the pre-esterification reaction, the reaction is close to equilibrium. To promote further reaction, the water in the primary esterified product must be removed before it enters the secondary esterification reaction. The crude ester dehydration reactor adopts a continuous flash evaporation dehydration process with a dehydration temperature of 95℃-150℃ to control the water content in the crude ester to below 1%.

[0013] Further, step 3) is a secondary esterification reaction, which is carried out in a bubble column. The reaction conditions are as follows: methanol vapor enters the bubble column through a gas distributor located at the bottom of the bubble column, and crude ester enters the bubble column through a liquid distributor located at the top of the bubble column. Methanol vapor and crude ester flow countercurrently and react. During the reaction, the mass ratio of methanol vapor to crude ester is controlled at (0.8~1.2):1, the reaction temperature is 95~115℃, the operating pressure is atmospheric pressure, the stirring speed is set at 50 rpm, and the residence time of crude ester in the bubble column is 60 min~480 min.

[0014] Furthermore, a heat exchange jacket is provided on the outside of the bubbling tower, and high-temperature steam is introduced into the heat exchange jacket to heat the bubbling tower; the bubbling tower has a cylindrical structure, and an agitator, a liquid distributor, and a gas distributor are provided inside; the liquid distributor is located at the top of the bubbling tower reactor and is connected to the crude ester feed pipe; the gas distributor is located at the bottom of the bubbling tower reactor and is connected to the methanol vapor feed pipe; the agitator includes an agitator shaft passing through the center of the cylinder, the upper end of the agitator shaft passing through the top of the bubbling tower and connected to the motor, and 2-8 stages of flat-blade agitators are provided on the part of the agitator shaft inside the bubbling tower.

[0015] Furthermore, the portion of the stirring shaft located inside the bubble column is equipped with at least 3-5 stages of flat-blade stirring paddles from top to bottom, with the stirring radius of the flat-blade stirring paddles being 0.2-0.3 times the diameter of the bubble column.

[0016] Furthermore, each stage of the flat-blade agitator includes 3-4 evenly spaced blades, which are elongated rectangles with their surfaces vertically aligned and the long side perpendicular to the agitator shaft. The aspect ratio of the blades is 1.5 to 3:1.

[0017] Furthermore, the stirring speed of the flat-blade agitator is 50-100 rpm.

[0018] Furthermore, in step 3), the acid value of the dimethyl sebacate product is less than 2.22 mg KOH / g.

[0019] Furthermore, in step 4), the mixed vapor of methanol and water generated during the reaction is recycled for the pre-esterification reaction after passing through a methanol recovery tower, so as to reduce the amount of methanol used in the production process and reduce waste emissions.

[0020] The beneficial effects achieved by this invention are:

[0021] (1) The bubble column of this invention has 2-8 stages of flat-blade agitators, which provide radial flow stirring for the liquid material inside the bubble column. This ensures good radial mixing of the crude ester liquid while minimizing axial mixing. Multi-stage reactions occur within the bubble column under the stirring action of the multi-stage flat-blade agitators. The crude ester liquid generally exhibits a plug flow. By simply increasing the methanol dosage to a certain extent, the mass transfer driving force can be significantly improved, the reaction equilibrium can be broken, thereby accelerating the reaction rate, increasing the esterification rate, and reducing the product acid value. The combined effect of the bubble column reaction and the multi-stage reactor in series in this invention significantly reduces equipment costs compared to existing technologies.

[0022] (2) The method described in this invention enables continuous and efficient production of dimethyl sebacate, producing a product with high purity and low acid value. The reactor used in this invention has a simple structure, stable operation, and low investment and maintenance costs, making it suitable for large-scale industrial production. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the apparatus used in the method for producing dimethyl sebacate according to the present invention.

[0024] In the diagram: 1. Stirring vessel; 2. Crude ester transfer pump; 3. Crude ester dehydration vessel; 4. Methanol feed pump; 5. Vaporization vessel; 6. Bubbling tower; 7. Methanol recovery tower; 8. Product storage tank. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0026] Example:

[0027] Comparison Figure 1 This is a schematic diagram of the apparatus used in the method of the present invention. Solid sebacic acid, methanol, and p-toluenesulfonic acid are added to a stirred tank 1, heated to reflux, and stirred for a pre-esterification reaction. The reacted material is transported to a crude ester dehydration tank 3 by a crude ester transfer pump 2, where methanol and water are distilled off (the mixed vapor of distilled methanol and water enters a methanol recovery tower 7 to recover methanol). The resulting crude ester is fed into a liquid distributor at the top of a bubble column 6, where it is distributed throughout the upper part of the bubble column 6. Liquid methanol is transported to a vaporization tank 5 by a methanol feed pump 4, heated and vaporized, and then enters a gas distributor at the bottom of the bubble column 6. The dimethyl sebacic acid product obtained after the reaction flows out from the bottom of the bubble column 6 into a product storage tank 8. The mixed vapor formed by unreacted methanol and generated water is distilled off from the top of the bubble column and enters a methanol recovery tower 7 to recover methanol.

[0028] The bubble column 6 of the present invention is provided with a heat exchange jacket on its outer side, and high-temperature steam is introduced into the heat exchange jacket to heat the bubble column 6. The bubble column has a cylindrical structure and is provided with an agitator, a liquid distributor and a gas distributor inside. The liquid distributor is located at the top of the bubble column reactor and is connected to the crude ester feed pipe. The gas distributor is located at the bottom of the bubble column reactor and is connected to the methanol vapor feed pipe. The agitator includes an agitator shaft that passes through the center of the cylinder. The upper end of the agitator shaft passes through the top of the bubble column and is connected to a motor. The part of the agitator shaft located inside the bubble column is provided with 2-8 stages of flat blade agitators.

[0029] In the following embodiments and comparative examples of this invention, the portion of the stirring shaft located inside the bubble column is equipped with three stages of flat-blade stirring paddles from top to bottom. These three stages of flat-blade stirring paddles are evenly installed at the upper, middle, and lower positions of the rotating shaft. Each stage of the flat-blade stirring paddle includes four evenly spaced blades (arranged in a cross shape). The blades are elongated rectangles with their surfaces vertically aligned. The long side of each blade is perpendicular to the stirring shaft, and the aspect ratio of the blade is 2.5:1. The stirring radius of the flat-blade stirring paddle is 0.25 times the diameter of the bubble column.

[0030] Example 1

[0031] 1) First, solid sebacic acid with an acid value of 541.42 mg KOH / g and liquid methanol were added to a pre-esterification reactor at a mass ratio of 1:1. p-Toluenesulfonic acid was added as a catalyst at a dosage of 0.2% of the sebacic acid mass. The pre-esterification reactor was heated to 64°C, and the mixture was stirred to ensure full contact and reaction between the solid sebacic acid and liquid methanol for 8 hours. A sample was taken and the product acid value was measured to be 45.52 mg KOH / g, corresponding to an esterification rate of 91.65%.

[0032] 2) The pre-esterification reaction material is pumped to a crude ester dehydration reactor to remove methanol and water, yielding crude ester. The mixed vapor of distilled methanol and water enters a methanol recovery tower to recover methanol; the crude ester after methanol and water removal enters a bubbling tower.

[0033] 3) Methanol and crude ester were fed at a mass ratio of 1:1. The crude ester entered from the top of the bubble column, while the liquid methanol, after being vaporized in a vaporization kettle, entered from the bottom of the bubble column. The two phases were further heated to 105°C in the bubble column and reacted in a countercurrent flow. The flow rate of the crude ester was adjusted to ensure a residence time of 8 hours in the bubble column, and the agitator speed was set to 50 rpm. The resulting dimethyl sebacate product flowed out from the bottom of the bubble column into a product storage tank. The product had an acid value of 2.17 mg KOH / g and a yield of 99.60%.

[0034] 4) The mixed vapor formed by unreacted methanol and generated water is distilled from the top of the bubble column and enters the methanol recovery column to recover methanol, which is then recycled for the pre-esterification reaction.

[0035] Example 2

[0036] 1) Add 11wt% solid sebacic acid to the dimethyl sebacic acid product with a conversion rate of 98.66%, start stirring, and heat to 85℃ until the sebacic acid is completely dissolved in the dimethyl sebacic acid liquid and the solution is homogeneous. The acid value is measured to be 37.08mgKOH / g.

[0037] 2) The pre-esterification reaction material is pumped to a crude ester dehydration reactor to remove methanol and water, yielding crude ester. The mixed vapor of distilled methanol and water enters a methanol recovery tower to recover methanol; the crude ester after methanol and water removal enters a bubbling tower.

[0038] 3) Methanol and crude ester were fed at a mass ratio of 1:1. The crude ester entered from the top of the bubble column, while the liquid methanol, after being vaporized in a vaporization kettle, entered from the bottom of the bubble column. The two phases were further heated to 105°C in the bubble column and reacted in a countercurrent flow. The flow rate of the crude ester was adjusted to ensure a residence time of 8 hours in the bubble column, and the agitator speed was set to 50 rpm. The resulting dimethyl sebacate product flowed out from the bottom of the bubble column into a product storage tank. The product had an acid value of 1.68 mg KOH / g and a yield of 99.69%.

[0039] 4) The mixed vapor formed by unreacted methanol and generated water is distilled from the top of the bubble column and enters the methanol recovery column to recover methanol, which is then recycled for the pre-esterification reaction.

[0040] Example 3

[0041] 1) First, solid sebacic acid with an acid value of 541.42 mg KOH / g and liquid methanol were added to a pre-esterification reactor at a mass ratio of 1:0.8. p-Toluenesulfonic acid was added as a catalyst at a dosage of 0.2% of the sebacic acid mass. The pre-esterification reactor was heated to 64°C, and the mixture was stirred to ensure full contact and reaction between the solid sebacic acid and liquid methanol for 8 hours. A sample was taken and the product acid value was measured to be 62.54 mg KOH / g, corresponding to an esterification rate of 88.45%.

[0042] 2) The pre-esterification reaction material is pumped to a crude ester dehydration reactor to remove methanol and water, yielding crude ester. The mixed vapor of distilled methanol and water enters a methanol recovery tower to recover methanol; the crude ester after methanol and water removal enters a bubbling tower.

[0043] 3) Methanol and crude ester were fed at a mass ratio of 1.2:1. The crude ester entered from the top of the bubble column, while the liquid methanol, after being vaporized in a vaporization kettle, entered from the bottom of the bubble column. The two phases were further heated to 105°C in the bubble column and reacted in a countercurrent flow. The flow rate of the crude ester was adjusted to ensure a residence time of 8 hours in the bubble column, and the agitator speed was set to 50 rpm. The resulting dimethyl sebacate product flowed out from the bottom of the bubble column into a product storage tank. The product had an acid value of 1.84 mg KOH / g and a yield of 99.66%.

[0044] 4) The mixed vapor formed by unreacted methanol and generated water is distilled from the top of the bubble column and enters the methanol recovery column to recover methanol, which is then recycled for the pre-esterification reaction.

[0045] Example 4

[0046] 1) First, solid sebacic acid with an acid value of 541.42 mg KOH / g and liquid methanol were added to a pre-esterification reactor at a mass ratio of 1:1. p-Toluenesulfonic acid was added as a catalyst at a dosage of 0.2% of the sebacic acid mass. The pre-esterification reactor was heated to 84°C, and the mixture was stirred to ensure full contact and reaction between the solid sebacic acid and liquid methanol for 8 hours. A sample was taken and the product acid value was measured to be 74.29 mg KOH / g, corresponding to an esterification rate of 86.28%.

[0047] 2) The pre-esterification reaction material is pumped to a crude ester dehydration reactor to remove methanol and water, yielding crude ester. The mixed vapor of distilled methanol and water enters a methanol recovery tower to recover methanol; the crude ester after methanol and water removal enters a bubbling tower.

[0048] 3) Methanol and crude ester were fed at a mass ratio of 1:1. The crude ester entered from the top of the bubble column, while the liquid methanol, after being vaporized in a vaporization kettle, entered from the bottom of the bubble column. The two phases were further heated to 105°C in the bubble column and subjected to countercurrent flow and reaction. The flow rate of the crude ester was adjusted to ensure a residence time of 6 hours in the bubble column, and the agitator speed was set to 50 rpm. The resulting dimethyl sebacate product flowed out from the bottom of the bubble column into a product storage tank. The product had an acid value of 2.22 mg KOH / g and a yield of 99.59%.

[0049] 4) The mixed vapor formed by unreacted methanol and generated water is distilled from the top of the bubble column and enters the methanol recovery column to recover methanol, which is then recycled for the pre-esterification reaction.

[0050] Compare with Example 1:

[0051] To demonstrate the effectiveness of the stirring paddle in this device, a control example is provided for comparison.

[0052] 1) First, solid sebacic acid with an acid value of 541.42 mg KOH / g and liquid methanol were added to a pre-esterification reactor at a mass ratio of 1:1. p-Toluenesulfonic acid was added as a catalyst at a dosage of 0.2% of the sebacic acid mass. The pre-esterification reactor was heated to 84°C, and the mixture was stirred to ensure full contact and reaction between the solid sebacic acid and liquid methanol for 6 hours. A sample was taken and the product acid value was measured to be 56.31 mg KOH / g, corresponding to an esterification rate of 89.60%.

[0053] 2) The pre-esterification reaction material is pumped to a crude ester dehydration reactor to remove methanol and water, yielding crude ester. The mixed vapor of distilled methanol and water enters a methanol recovery tower to recover methanol; the crude ester after methanol and water removal enters a bubbling tower.

[0054] 3) Methanol and crude ester were fed at a mass ratio of 1:1. The crude ester entered from the top of the bubble column, while the liquid methanol, after being vaporized in a vaporization kettle, entered from the bottom of the bubble column. The two phases were further heated to 105°C in the bubble column and reacted in a countercurrent flow. The flow rate of the crude ester was adjusted to ensure a residence time of 8 hours in the bubble column, without stirring. The resulting dimethyl sebacate product flowed out from the bottom of the bubble column into a product storage tank. The acid value of the product was 11.07 mgKOH / g, and the product yield was 97.95%, which did not meet the product requirements.

[0055] 4) The mixed vapor formed by unreacted methanol and generated water is distilled from the top of the bubble column and enters the methanol recovery column to recover methanol, which is then recycled for the pre-esterification reaction.

[0056] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A method for producing dimethyl sebacate, characterized in that... This method uses p-toluenesulfonic acid as a catalyst and employs a two-stage esterification reaction. The first stage is a pre-esterification reaction in a stirred tank, and the second stage is an esterification reaction in a bubble column. The specific steps include: 1) Pre-esterification: Solid sebacic acid, methanol and p-toluenesulfonic acid are added to a stirred tank, heated to reflux, stirred and pre-esterified to reduce the acid value to below 75 mg KOH / g and the esterification rate to above 85%. 2) The material after the pre-esterification reaction in step 1) is pumped to the crude ester dehydration kettle, where methanol and water are removed by distillation to obtain a mixture containing monomethyl sebacate, dimethyl sebacate, and a small amount of unreacted sebacate, which is the crude ester; the mixed vapor of distilled methanol and water enters the methanol recovery tower to recover methanol, and the crude ester after removing methanol and water enters the bubble column. The bubble column is equipped with a stirrer with 2-8 stages of flat blade impellers to provide a stirring radial flow effect for the liquid material in the bubble column; 3) Bubble tower reaction: Crude ester enters from the top of the bubble tower, and liquid methanol, after being heated and vaporized in the vaporization kettle, enters from the bottom of the bubble tower. The crude ester and methanol vapor are further heated in the bubble tower, and the two phases flow and react in countercurrent. The dimethyl sebacate product obtained after the reaction flows out from the bottom of the bubble tower and enters the product storage tank. The mixed vapor formed by unreacted methanol and generated water is distilled out from the top of the bubble tower and enters the methanol recovery tower to recover methanol. 4) The methanol recovered by the methanol recovery tower is recycled for the pre-esterification reaction.

2. The method for producing dimethyl sebacate as described in claim 1, characterized in that... Step 1) The mass ratio of methanol to sebacic acid in the pre-esterification reaction is (0.6~1):1, the amount of p-toluenesulfonic acid is 0.2~0.4wt% of the amount of sebacic acid, the reaction temperature is the reflux temperature of methanol, and the reaction time is 240~480min.

3. The method for producing dimethyl sebacate as described in claim 1, characterized in that... In step 2), the crude ester dehydration kettle adopts a continuous flash dehydration process with a dehydration temperature of 95℃-150℃, so that the water content in the crude ester is controlled below 1%.

4. The method for producing dimethyl sebacate as described in claim 1, characterized in that... Step 3) The conditions for the bubbling tower reaction are: the mass ratio of methanol to crude ester is (0.8~1.2):1, the reaction temperature is 95~115℃, the operating pressure is atmospheric pressure, and the residence time of crude ester in the bubbling tower is 60min~480min.

5. The method for producing dimethyl sebacate as described in claim 1, characterized in that... The bubbling tower is equipped with a heat exchange jacket on its outside, through which high-temperature steam is introduced to heat the bubbling tower. The bubbling tower has a cylindrical structure, and is equipped with an agitator, a liquid distributor, and a gas distributor inside. The liquid distributor is located at the top of the bubbling tower reactor and is connected to the crude ester feed pipe. The gas distributor is located at the bottom of the bubbling tower reactor and is connected to the methanol vapor feed pipe. The agitator includes an agitator shaft that passes through the center of the cylinder. The upper end of the agitator shaft passes through the top of the bubbling tower and is connected to a motor. The part of the agitator shaft located inside the bubbling tower is equipped with 2-8 stages of flat-blade agitators.

6. The method for producing dimethyl sebacate as described in claim 5, characterized in that... The section of the stirring shaft inside the bubble column is equipped with at least 3-5 stages of flat-blade agitators from top to bottom. The stirring radius of the flat-blade agitators is 0.2-0.3 times the diameter of the bubble column.

7. The method for producing dimethyl sebacate as described in claim 5, characterized in that... Each stage of the flat-blade agitator includes 3-4 evenly spaced blades. The blades are long rectangles with their surfaces vertically aligned and the long side of the blades perpendicular to the agitator shaft. The aspect ratio of the blades is 1.5 to 3:

1.

8. The method for producing dimethyl sebacate as described in claim 5, characterized in that... The stirring speed of the flat-blade agitator is 50-100 rpm.

9. The method for producing dimethyl sebacate as described in claim 1, characterized in that... In step 3), the acid value of the dimethyl sebacate product is less than 2.22 mg KOH / g.

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