Continuous production process of trimethyl borate

Abstract

The invention relates to a continuous production process of trimethyl borate, which comprises the following steps: 1) mixing methanol and boric acid according to the molar ratio of (4.0-4.5): 1, feeding into a pre-reactor, and dissolving and pre-reacting at 64-66 DEG C; (2) continuously feeding the pre-reacted material into the middle upper part of an esterification rectifying tower, continuously carrying out esterification reaction and rectifying separation, controlling the tower top temperature at 53-55 DEG C, and extracting an azeotrope of trimethyl borate and methanol; (3) conveying a methanol-water mixed solution discharged from the bottom of the esterification rectifying tower to a methanol recovery tower, controlling the temperature of the tower top at 62-64 DEG C, directly introducing the extracted gas-phase methanol into the middle part or the lower part of the esterification rectifying tower, and discharging the total amount lt of boric acid / trimethyl borate from the tower bottom; and 0.5% of water. Compared with the prior art, the energy consumption can be saved by more than 50% under the condition of ensuring that the one-time conversion rate of boric acid is greater than or equal to 99.6%, the diameter and the height of the esterification rectifying tower are greatly reduced under the same productivity, and the equipment cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a continuous production process for trimethyl borate. Background Technology

[0002] Trimethyl borate (B(OCH3)3) is an important organoboroester with wide applications in various fields, serving as a solvent, plasticizer, catalyst, welding aid, and flame retardant. With the rise of new energy sources, the demand for trimethyl borate is increasing.

[0003] The main synthetic method for trimethyl borate involves the reaction of boric acid and methanol in a stoichiometric molar ratio to synthesize trimethyl borate, as shown in the following reaction equation: H3BO3 + 3CH3OH → B(OCH3)3+ 3H2O Direct esterification of boric acid and methanol is the most suitable industrial method for producing trimethyl borate. However, the reaction produces water, and trimethyl borate is highly susceptible to hydrolysis, resulting in a slow reaction and low yield. Furthermore, both trimethyl borate and methanol are more volatile than water, so the water formed during esterification cannot be separated as a distillate as in other esterification processes. Therefore, in important industrial methods for preparing trimethyl borate, distillation is used to remove the trimethyl borate. Trimethyl borate and methanol form a low-boiling azeotrope at 54.9°C under normal pressure. Therefore, anhydrous trimethyl borate can be distilled from the reaction mixture as an azeotrope.

[0004] Improving the yield of trimethyl borate, reducing production costs, and solving pollution problems in the process have become key research areas in this field.

[0005] US2813115A discloses a method for producing trimethyl borate, in which the feedstock is introduced in the middle of a fractionating column in the form of a methanol solution of boric acid or boron trioxide, and anhydrous trimethyl borate-methanol mixture is recovered by controlling the reflux ratio. The molar ratio of methanol to boric acid is 6:1 to 8:1. In a 2-inch, 30-plate glass distillation column, the experimental boric acid conversion rate was 98.2%. However, in practical production, the single-pass boric acid conversion rate of this process can only reach about 95%, and the energy consumption is high.

[0006] CN103833780A discloses a novel process for preparing trimethyl borate by continuous reactive distillation: methanol and boric acid are continuously fed into a reactor in a specific ratio for initial reaction. The reaction solution is continuously evaporated in a crude distillation vessel, and the methanol, trimethyl borate, and water are distilled into a reactive distillation column in a mixed gas phase. Water generated during the reaction of methanol and trimethyl borate is continuously discharged from the bottom of the column. Due to the discharge of water, the reaction proceeds in the direction of trimethyl borate formation until all boric acid has reacted. The trimethyl borate distilled from the reactive distillation column and methanol are fed into an azeotropic distillation column. The anhydrous methanol at the bottom of the azeotropic distillation column is cooled and reused, and the azeotrope of trimethyl borate and methanol is collected from the top of the column. The azeotrope is then separated to obtain trimethyl borate. The molar ratio of methanol to boric acid is 6–10:1, and the primary conversion rate of boric acid can reach over 99.5%.

[0007] CN114195815A discloses a continuous esterification process for producing trimethyl borate. Methanol and boric acid are mixed and pre-reacted in a pre-reactor before entering an esterification tower. 30-40% crude trimethyl borate is collected from the top of the esterification tower, along with water. The crude trimethyl borate gaseous product enters a purification tower, where a trimethyl borate-methanol azeotrope is collected from the top, and methanol is recovered from the bottom and returned to the reaction system for recycling. In Example 2, with a methanol to boric acid molar ratio of 5:1, the boric acid conversion rate reaches 99.7% in a single step.

[0008] However, this process has the following drawbacks: First, it has high energy consumption, requiring 2.574 tons of steam to produce one ton of trimethyl borate azeotrope; second, excess methanol needs to be distilled and separated multiple times before being reused, leading to an accumulation of system heat load; and third, it requires significant equipment investment, requiring an esterification distillation column with a diameter of 1400 mm and a height of 23200 mm for a 5000-ton-per-year trimethyl borate plant.

[0009] Therefore, there is an urgent need to develop production processes that can significantly reduce energy consumption and equipment investment while ensuring high conversion rates. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention provides a continuous production process for trimethyl borate, which can simultaneously solve the problems of high energy consumption, low material utilization, and large equipment investment, while ensuring high conversion rates and significantly reducing energy consumption and equipment investment.

[0011] Therefore, the present invention provides a continuous production process for trimethyl borate, comprising the following steps: 1) Methanol and boric acid are mixed at a molar ratio of 4.0 to 4.5:1 and then fed into a pre-reactor for dissolution and pre-reaction at 64 to 66°C; 2) The pre-reacted material is continuously fed into the upper part of the esterification distillation column to continue the esterification reaction and distillation separation. The reflux ratio is controlled in the range of 1 to 3, and the top temperature of the column is controlled at 53 to 55°C. The azeotrope of trimethyl borate and methanol is collected. 3) The methanol-water mixture discharged from the bottom of the esterification distillation column is transported to the methanol recovery column. The temperature at the top of the column is controlled at 62-64℃. The collected vapor methanol is directly introduced into the middle or lower part of the esterification distillation column. Water with a total boric acid / trimethyl borate content of <0.5% is discharged from the bottom of the column.

[0012] In a preferred embodiment, the molar ratio of methanol to boric acid is in the range of 4.2:1 to 4.3:1.

[0013] In a preferred embodiment, methanol and boric acid are mixed at a molar ratio of 4.26:1.

[0014] In a preferred embodiment, the temperature of the pre-reactor is controlled at 65°C.

[0015] In a preferred embodiment, the reflux ratio of the esterification distillation column is in the range of 1 to 2.

[0016] In a preferred embodiment, the reflux ratio of the esterification distillation column is 1.

[0017] In a preferred embodiment, the reflux ratio of the methanol recovery tower is controlled within the range of 1 to 2.

[0018] In a preferred embodiment, the reflux ratio of the methanol recovery tower is 2.

[0019] In a preferred embodiment, the bottom temperature of the methanol recovery tower is 100-102°C.

[0020] The continuous production process of trimethyl borate of the present invention, by collecting the azeotrope of trimethyl borate and methanol from the top of the esterification distillation column, using a lower methanol / boric acid molar ratio, a lower reflux ratio, and directly recycling the gaseous methanol obtained from the methanol recovery column back to the esterification distillation column, can save more than 50% of energy consumption compared with the prior art while ensuring a boric acid primary conversion rate of ≥99.6%. Moreover, the column diameter and height of the esterification distillation column are significantly reduced under the same production capacity, thus reducing equipment costs. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the process flow of one embodiment of the continuous production process of trimethyl borate of the present invention.

[0022] The components are: 1. Pre-reactor; 2. Esterification distillation column top condenser; 3. Esterification distillation column reflux tank; 4. Esterification distillation column; 5. Esterification distillation column reboiler; 6. Esterification distillation column bottom condenser; 7. Methanol recovery column top condenser; 8. Methanol recovery column reflux tank; 9. Methanol recovery column; 10. Methanol recovery column reboiler; 11. Methanol recovery column top condenser; 12. Methanol; 13. Boric acid; 14. Methanol recovery column feed; 15. Trimethyl borate-methanol azeotrope; 16. Wastewater; 17. Recycled gaseous methanol. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments and examples. The embodiments and examples given are only for better illustrating the present invention and are not intended to limit the scope of the present invention. Therefore, the numerical values, shapes, materials, constituent elements, the arrangement and connection of constituent elements, and steps (processes) and the order of steps shown in the following embodiments are merely examples and are not intended to limit the present invention. Thus, any constituent elements in the following embodiments that are not described in the independent claims representing the highest concept of the present invention are arbitrary constituent elements. In addition, all the drawings are schematic diagrams, in which substantially identical structures are given the same reference numerals, and repeated descriptions are omitted or simplified. Furthermore, in the following embodiments, the terms "about" or "approximately" not only mean approximately, but also include manufacturing errors or dimensional tolerances.

[0024] This invention provides a continuous production process for trimethyl borate, comprising the following steps: 1) Methanol and boric acid are mixed at a molar ratio of 4.0 to 4.5:1 and then fed into a pre-reactor for dissolution and pre-reaction at 64 to 66°C; 2) The pre-reacted material is continuously fed into the upper part of the esterification distillation column to continue the esterification reaction and distillation separation. The reflux ratio is controlled in the range of 1 to 2, and the top temperature of the column is controlled at 53 to 55°C. The azeotrope of trimethyl borate and methanol is collected. 3) The methanol-water mixture discharged from the bottom of the esterification distillation column is transported to the methanol recovery column. The temperature at the top of the column is controlled at 62-64℃. The collected vapor methanol is directly introduced into the middle or lower part of the esterification distillation column. Water with a total boric acid / trimethyl borate content of <0.5% is discharged from the bottom of the column.

[0025] refer to Figure 1Methanol 12 and boric acid 13 are mixed in a specific ratio and fed into pre-reactor 1 for dissolution and pre-reaction under heating. The pre-reacted material is continuously fed into the upper part of esterification distillation column 4 for further autocatalytic esterification. Heating is provided through reboiler 5 at the bottom of the column, creating temperature and concentration gradients within the column. The reflux ratio of the column is controlled within the range of 1 to 2, and the top temperature is controlled at 53–55°C. Under these conditions, the azeotrope of trimethyl borate and methanol is collected as the product, which can be used directly as a welding aid.

[0026] The methanol-water mixture from the bottom of the esterification distillation column is fed to the methanol recovery column 9 as feed 14. The top temperature is controlled at 62-64℃, and the bottom temperature at 100-102℃. The methanol-rich gaseous stream obtained from the top is directly returned to the middle of the esterification distillation column 4 as recycled gaseous methanol 17. Wastewater 16, which contains almost no methanol, is discharged from the bottom.

[0027] The continuous production process of trimethyl borate of the present invention, by collecting the azeotrope of trimethyl borate and methanol from the top of the esterification distillation column, using a lower methanol / boric acid molar ratio, a lower reflux ratio, and directly recycling the gaseous methanol obtained from the methanol recovery column back to the esterification distillation column, can save more than 50% of energy consumption compared with the prior art while ensuring a boric acid primary conversion rate of ≥99.6%. Moreover, the column diameter and height of the esterification distillation column are significantly reduced under the same production capacity, thus reducing equipment costs.

[0028] Example 1

[0029] An esterification distillation column with a diameter of 1000×15000mm was used.

[0030] Methanol and boric acid were mixed in a molar ratio of 4.26:1 and heated to 65°C in a pre-reactor for dissolution and pre-reaction.

[0031] The pre-reacted material is continuously fed into an esterification distillation column for autocatalytic esterification and distillation separation. The esterification distillation column operates with a reflux ratio of 2, and the top temperature is controlled at 53–55°C. The product collected from the top of the column is a trimethyl borate / methanol azeotrope.

[0032] The methanol-water mixture discharged from the bottom of the esterification distillation column is sent to the methanol recovery column. The methanol recovery column operates with a reflux ratio of 2, with the top temperature controlled at 62-64℃ and the bottom temperature controlled at 100-102℃. The methanol-rich vapor stream obtained from the top is directly returned to the lower part of the esterification distillation column. Wastewater containing almost no methanol is discharged from the bottom.

[0033] During stable operation, the obtained trimethyl borate / methanol azeotrope contains ≥72% trimethyl borate and ≤0.05% moisture. The total boric acid / trimethyl borate content in the discharged wastewater is <0.5%. The primary conversion rate of boric acid is 99.7%. Producing one kilogram of trimethyl borate consumes 0.9 kg of steam. Based on a steam price of 280 yuan / ton, the energy consumption is approximately 0.25 yuan / kg of product.

[0034] Example 2

[0035] An esterification distillation column with a diameter of 1000×15000mm was used.

[0036] Methanol and boric acid were mixed in a molar ratio of 4.26:1 and heated to 65°C in a pre-reactor for dissolution and pre-reaction.

[0037] The pre-reacted material is continuously fed into an esterification distillation column for autocatalytic esterification and distillation separation. The esterification distillation column operates with a reflux ratio of 1, and the top temperature is controlled at 53–55°C. The product collected from the top of the column is a trimethyl borate / methanol azeotrope.

[0038] The methanol-water mixture discharged from the bottom of the esterification distillation column is sent to the methanol recovery column. The methanol recovery column operates with a reflux ratio of 2, with the top temperature controlled at 62-64℃ and the bottom temperature controlled at 100-102℃. The methanol-rich vapor stream obtained from the top is directly returned to the lower part of the esterification distillation column. Wastewater containing almost no methanol is discharged from the bottom.

[0039] During stable operation, the obtained trimethyl borate / methanol azeotrope contains ≥72% trimethyl borate and ≤0.05% moisture. The total boric acid / trimethyl borate content in the discharged wastewater is <0.5%. The primary conversion rate of boric acid is 99.6%. 0.85 kg of steam is consumed to produce each kg of trimethyl borate. Based on a steam price of 280 yuan / ton, the energy consumption is approximately 0.24 yuan / kg of product.

[0040] Comparative Example 1 Example 2 was repeated, except that, referring to US2813115A, boric acid and methanol were mixed in a molar ratio of 7:1, and the recovered methanol was condensed and introduced into the pre-reactor.

[0041] During stable operation, the obtained trimethyl borate / methanol azeotrope contains ≥72% trimethyl borate and ≤0.05% moisture. The total boric acid / trimethyl borate content in the discharged wastewater is <0.5%. The primary conversion rate of boric acid is 95.0%. Producing one kilogram of trimethyl borate consumes 1.80 kg of steam. Based on a steam price of 280 yuan / ton, the energy consumption is approximately 0.50 yuan / kg of product.

[0042] Comparative Example 2 An esterification tower with a diameter of 1400×23200mm was used, and the process was carried out according to Example 1 in CN114195815A. The production of one kilogram of trimethyl borate product consumed 2.57 kg of steam. Based on a steam price of 280 yuan / ton, the energy consumption was approximately 0.72 yuan / kg of product.

[0043] Experiments show that the continuous production process of trimethyl borate of the present invention can save more than 50% of energy consumption compared with the prior art while ensuring a boric acid conversion rate of ≥99.6%. Moreover, the diameter and height of the esterification distillation column are significantly reduced under the same capacity, thus reducing equipment costs.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A continuous production process of trimethyl borate, comprising the following steps: 1) methanol and boric acid are mixed in a molar ratio of 4.0-4.5:1 and then fed into a pre-reactor for dissolution and pre-reaction at 64-66℃; 2) the pre-reacted material is continuously fed into the middle or upper part of an esterification rectifying tower for further esterification reaction and rectification separation, the reflux ratio is controlled in the range of 1 to 3, the tower top temperature is controlled in the range of 53-55℃, and azeotrope of trimethyl borate and methanol is collected; 3) the methanol-water mixed solution discharged from the bottom of the esterification rectifying tower is transported to a methanol recovery tower, the tower top temperature is controlled in the range of 62-64℃, the collected gas phase methanol is directly introduced into the middle or lower part of the esterification rectifying tower, and the water discharged from the bottom of the tower is less than 0.5% of the total amount of boric acid / trimethyl borate.

2. A continuous process for the production of trimethyl borate as claimed in claim 1, wherein: The molar ratio of methanol and boric acid is in the range of 4.2:1 to 4.3:

1.

3. A continuous process for the production of trimethyl borate as claimed in claim 2, wherein: Methanol and boric acid are mixed in a molar ratio of 4.26:

1.

4. A continuous process for the production of trimethyl borate as claimed in claim 1, wherein: The pre-reactor temperature is controlled at 65℃.

5. A continuous process for the production of trimethyl borate according to any one of claims 1 to 4, characterised in that: The reflux ratio of the esterification rectifying tower is in the range of 1 to 2.

6. A continuous process for the production of trimethyl borate as claimed in claim 5 wherein: The reflux ratio of the esterification rectifying tower is 1.

7. A continuous process for the production of trimethyl borate according to any one of claims 1 to 4, characterised in that: The reflux ratio of the methanol recovery tower is controlled in the range of 1 to 2.

8. A continuous process for the production of trimethyl borate as claimed in claim 7, wherein: The reflux ratio of the methanol recovery tower is 2.

9. A continuous process for the production of trimethyl borate according to any one of claims 1 to 4, characterised in that: The methanol recovery tower bottom temperature is 100-102℃.

Images