Process for the preparation of 3-methyl-2-buten-1-al diisopentyl acetal by continuous reaction rectification

Abstract

The application discloses a process for preparing 3-methyl-2-buten-1-al diisopentyl acetal by continuous reaction rectification. The process comprises the following steps: reacting and rectifying isopentenyl alcohol and isopentenyl aldehyde in a reaction rectification tower to prepare 3-methyl-2-buten-1-al diisopentyl acetal, characterized in that the content of 2-methyl-3-buten-2-al in the liquid phase of the third to fifth trays of the reaction rectification tower from bottom to top is less than or equal to 1 wt%. By the continuous reaction rectification process, the device can be stably operated for more than 7200 hours, and the economic benefit of the enterprise can be remarkably improved.

Description

Technical Field

[0001] This invention relates to a reaction process, and more particularly to a process for preparing 3-methyl-2-buten-1-aldehyde diisopentenyl acetal by continuous reactive distillation. Background Technology

[0002] 3-Methyl-2-buten-1-aldehyde diisopentenyl acetal is a key intermediate in the synthesis of citral. Its efficient synthesis can significantly reduce the production cost of citral and has extremely important commercial value.

[0003] Currently, the industrial production of 3-methyl-2-buten-1-aldehyde diisopentenyl acetal mainly relies on reactive distillation. For example, patent US4133836A discloses a scheme using nitric acid as a catalyst to reactively distill isopentenol and isopentenal to prepare 3-methyl-2-buten-1-aldehyde diisopentenyl acetal, achieving a selectivity of over 93%. Subsequent improvements include US2002035298A1, which employs a two-stage evaporator, significantly improving reaction controllability; US4933500A, which uses lithium chloride as a catalyst for the condensation reaction, achieving an isopentenal conversion rate greater than 75%; and US5177265A, which uses phosphoric acid as a catalyst for the condensation reaction and toluene as an azeotropic solvent for dehydration, achieving an isopentenal conversion rate of 83%.

[0004] It can be seen that most of the existing research focuses on how to improve product selectivity and raw material conversion rate. However, for reactive distillation processes, ensuring the long-term stable operation of the reaction is the key to maximizing the economic benefits of enterprises, and no relevant reports have been found in this regard. Summary of the Invention

[0005] To address the above technical problems, this invention proposes a process for preparing 3-methyl-2-buten-1-aldehyde diisopentenyl acetal via continuous reactive distillation, wherein the condensation reaction apparatus can operate continuously and stably for more than 7200 hours.

[0006] A process for preparing 3-methyl-2-buten-1-aldehyde diisopentenyl acetal by continuous reactive distillation includes the process of preparing 3-methyl-2-buten-1-aldehyde diisopentenyl acetal by reactive distillation of isopentenol and isopentenal in a reactive distillation column, characterized in that the content of 2-methyl-3-buten-2-ol in the liquid phase of the 3rd to 5th trays from the bottom of the reactive distillation column is controlled to be less than 1 wt%.

[0007] As a preferred embodiment of the present invention, the reactive distillation column is a packed column or a plate column, more preferably a packed column.

[0008] During reactive distillation, the feedstocks isopentenol and isopentenal are fed from the upper middle part of the reactive distillation column, and the product 3-methyl-2-buten-1-aldehyde diisopentenyl acetal is discharged from the bottom of the reactive distillation column. At the same time, during the reactive distillation process, light components (mainly water) are continuously collected from the top of the column, and unreacted feedstocks isopentenol and isopentenal are separated and reused.

[0009] The reaction process in this invention is expressed as follows:

[0010]

[0011] In a preferred embodiment of the present invention, the feed mass ratio of isopentenol to isopentenal is (2-5):1. In a preferred embodiment of the present invention, the reactive distillation is carried out in the presence of an acid catalyst.

[0012] Preferably, the acid catalyst is selected from one or more of nitric acid, phosphoric acid, p-toluenesulfonic acid, and isopentenic acid;

[0013] Preferably, the amount of acid catalyst is 0.001-0.1 wt% of the total mass of isopentenol and isopentenal, more preferably 0.04-0.08 wt%. As a preferred embodiment of the present invention, the conditions for reactive distillation are: bottom temperature of 90-110°C and reaction pressure of 6-14 kPa (absolute pressure).

[0014] Through continuous research, this invention discovered that under acidic conditions, a small amount of isopentenol undergoes an isomerization reaction to form 2-methyl-3-buten-2-ol. However, 2-methyl-3-buten-2-ol is sterically hindered and does not readily react with isopentenal to form the corresponding acetal. Therefore, its accumulation in the system significantly reduces reaction efficiency, becoming a major factor affecting the long-term stable operation of the apparatus. Surprisingly, when the content of 2-methyl-3-buten-2-ol in the liquid phase of the 3rd to 5th trays from the bottom of the reactive distillation column is controlled to be below 1 wt%, the operating cycle of the apparatus can be significantly extended, ensuring a consistently high reaction efficiency over the long term, thus completing this invention.

[0015] In this invention, the method for controlling the content of 2-methyl-3-buten-2-ol in the liquid phase of the 3rd to 5th trays from the bottom of the reactive distillation column is not limited in any way. However, as a preferred embodiment of this invention, the content control can be achieved through the following process:

[0016] During reactive distillation, the vapor phase collected from the top of the column is condensed and enters the oil-water separator. Part of the separated oil phase is directly returned to the reactive distillation column, while the other part is collected, distilled, and then reused. Through this process, the content of 2-methyl-3-buten-2-ol in the liquid phase of the 3rd to 5th trays from the bottom of the reactive distillation column is controlled within the required range.

[0017] As a preferred embodiment of the present invention, the separation of the oil phase is processed under the following conditions: the number of packed trays in the distillation column is 30-50, the operating pressure is 4-10 kPa, the reflux ratio is (2-6):1, the top temperature is 26-30°C, and the bottom temperature is 58-62°C.

[0018] As a preferred embodiment of the present invention

[0019] Of the oil phase separated by the oil-water separator, the mass of the oil phase directly refluxed to the reactive distillation column is 1-3 times the total feed amount of the raw materials isopentenol and isopentenal, and the mass of the oil phase that is first distilled and then reused is 0.5-10 wt% of the total feed amount of the raw materials isopentenol and isopentenal, preferably 1.5-5 wt%.

[0020] The continuous reactive distillation process provided by this invention can ensure stable operation of the equipment for more than 7200 hours, which is beneficial to significantly improving the economic benefits of enterprises. Detailed Implementation

[0021] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0022] The main raw material information in this invention is as follows:

[0023] Isopentenol, Wanhua Chemical, ≥99.5%,

[0024] Isopentenal, Wanhua Chemical, ≥99.0%,

[0025] Nitric acid, Sinopharm Chemical Reagent Co., Ltd., ≥65.0%;

[0026] Phosphoric acid, Sinopharm Chemical Reagent Co., Ltd., ≥85.0%;

[0027] p-Toluenesulfonic acid, Xilong Chemical, ≥99.0%;

[0028] Isoprenic acid, Beijing Innocare Technology Co., Ltd., ≥98.0%;

[0029] Unless otherwise specified, other raw materials and reagents can be purchased through commercial channels.

[0030] The main analytical and characterization instruments / methods used in the following embodiments of the present invention are as follows:

[0031] Gas chromatograph instrument: Agilent 7890A; column model: HP-5; inner diameter: 320.00 μm; length: 30.0 m; maximum temperature: 325.0℃; injection port temperature: 280℃; split ratio: 30:1.

[0032] The heating program first maintains 50°C for 1 minute, then increases the temperature to 140°C at 10°C / min and maintains it for 5 minutes, then increases the temperature to 280°C at 20°C / min and maintains it for 8 minutes, with a total running time of 30 minutes.

[0033] Unless otherwise specified, "%" in the following examples refers to mass percentage.

[0034]

Example 1

[0035] The reactive distillation column is a 25mm inner diameter column with a height of 1.5m, packed with Raschig rings, and contains 20 trays. The feedstocks, isopentenol and isopentenal, are mixed in a 3:1 mass ratio, and 0.0615% (by mass) of 65% nitric acid is added. This mixture is fed into the reactive distillation column from the third tray from the top, and the acetal reaction is carried out at a reboiler temperature of 98℃ and a pressure of 8kPa.

[0036] The water generated in the reaction is collected from the top of the column, condensed, and separated into an oil phase using an oil-water separator. The oil phase refluxed to the reactive distillation column has a mass ratio of 3:1 to the total feed of isopentenol and isopentenal. The portion that is first distilled and then reused is 5 wt% of the total feed of isopentenol and isopentenal. The distillation conditions for this portion of the oil phase are: 40 packed trays, operating pressure of 7 kPa, reflux ratio of 4:1, top temperature of 28°C, and bottom temperature of 60°C. The content of 2-methyl-3-buten-2-ol in the liquid phase at the third tray from the bottom of the reactive distillation column is measured to be 0.25 wt%.

[0037] After the device operated continuously and stably for 8500 hours, the product composition was analyzed. Based on isopentenal, the conversion rate of the condensation reaction remained above 78%.

[0038]

Example 2

[0039] The reactive distillation column is a 25mm inner diameter column with a height of 1.5m, packed with Raschig rings, and contains 20 trays. The feedstocks, isopentenol and isopentenal, are mixed in a 2:1 mass ratio, and 0.07% (by mass) of 85% nitric acid is added. This mixture is fed into the reactive distillation column from the third tray from the top, and the acetal reaction is carried out at a reboiler temperature of 110℃ and a pressure of 14kPa.

[0040] The water generated in the reaction is collected from the top of the column, condensed, and separated into an oil phase using an oil-water separator. The oil phase refluxed to the reactive distillation column has a mass ratio of 1:1 to the total feed of isopentenol and isopentenal. The portion that is first distilled and then reused is 1.5 wt% of the total feed of isopentenol and isopentenal. The distillation conditions for this portion of the oil phase are: 50 packed trays, operating pressure of 4 kPa, reflux ratio of 2:1, top temperature of 26°C, and bottom temperature of 58°C. The content of 2-methyl-3-buten-2-ol in the liquid phase at the 5th tray from the bottom of the reactive distillation column is measured to be 1 wt%.

[0041] After the device operated continuously and stably for 7200 hours, the product composition was analyzed. Based on isopentenal, the conversion rate of the condensation reaction remained above 75%.

[0042]

Example 3

[0043] The reactive distillation column is a 25mm inner diameter column with a height of 1.5m, packed with Raschig rings, and contains 20 trays. The feedstocks, isopentenol and isopentenal, are mixed in a 5:1 mass ratio, and 0.08wt% of isopentenic acid is added. This mixture is fed into the reactive distillation column from the fourth tray from the top, and the acetal reaction is carried out at a reboiler temperature of 110℃ and a pressure of 14kPa.

[0044] The water generated in the reaction is collected from the top of the column, condensed, and separated into an oil phase using an oil-water separator. The oil phase refluxed to the reactive distillation column has a mass ratio of 2:1 to the total feed of isopentenol and isopentenal. The portion that is first distilled and then reused is 3 wt% of the total feed of isopentenol and isopentenal. The distillation conditions for this portion of the oil phase are: 30 packed trays, operating pressure of 10 kPa, reflux ratio of 6:1, top temperature of 30°C, and bottom temperature of 62°C. The content of 2-methyl-3-buten-2-ol in the liquid phase at the third tray from the bottom of the reactive distillation column is measured to be 0.42 wt%.

[0045] After the device operated continuously and stably for 7400 hours, the product composition was analyzed. Based on isopentenal, the conversion rate of the condensation reaction remained above 76%.

[0046]

Example 4

[0047] The reactive distillation column is a 25mm inner diameter column with a height of 1.5m, packed with Raschig rings, and contains 20 trays. The feedstocks, isopentenol and isopentenal, are mixed in a mass ratio of 3.5:1, and 0.05wt% of p-toluenesulfonic acid is added. This mixture is fed into the reactive distillation column from the fifth tray from the top, and the acetal reaction is carried out at a reboiler temperature of 90℃ and a pressure of 6kPa.

[0048] The water generated in the reaction is collected from the top of the column, condensed, and separated into an oil phase using an oil-water separator. The oil phase refluxed to the reactive distillation column has a mass ratio of 3:1 to the total feed of isopentenol and isopentenal. The portion that is first distilled and then reused is 3.5 wt% of the total feed of isopentenol and isopentenal. The distillation conditions for this portion of the oil phase are: 40 packed trays, operating pressure of 7 kPa, reflux ratio of 4:1, top temperature of 28°C, and bottom temperature of 60°C. The content of 2-methyl-3-buten-2-ol in the liquid phase at the third tray from the bottom of the reactive distillation column is measured to be 0.29 wt%.

[0049] After the device operated continuously and stably for 8200 hours, the product composition was analyzed. Based on isopentenal, the conversion rate of the condensation reaction remained above 77%.

[0050] Comparative Example 1

[0051] The reaction was carried out using essentially the same method as in Example 1, except that the oil phase obtained from the oil-water separator was entirely returned to the reactive distillation column. The content of 2-methyl-3-buten-2-ol in the bottom liquid phase of the reactive distillation column (the third tray from the bottom) was measured to be 2.3 wt%.

[0052] After the device operated continuously and stably for 1540 hours, the product composition was analyzed. Based on isopentenal, the conversion rate of the condensation reaction was <10%.

[0053] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A process for preparing 3-methyl-2-buten-1-aldehyde diisopentenyl acetal by continuous reactive distillation, comprising a process of preparing 3-methyl-2-buten-1-aldehyde diisopentenyl acetal by reactive distillation of isopentenol and isopentenal in a reactive distillation column, characterized in that, The content of 2-methyl-3-buten-2-ol in the liquid phase of the 3rd to 5th trays from the bottom of the reactive distillation column is controlled to be less than 1 wt%; the isopentenol refers to 3-methyl-2-buten-1-ol, and the isopentenal refers to 3-methyl-2-butenal. The reactive distillation is carried out in the presence of an acid catalyst; During reactive distillation, the vapor phase collected from the top of the column is condensed and then enters the oil-water separator. Part of the separated oil phase is directly refluxed back to the reactive distillation column, while the other part is collected, first distilled and then reused. Through this process, the content of 2-methyl-3-buten-2-ol in the liquid phase of the 3rd to 5th trays from the bottom of the reactive distillation column is controlled within the required range. Of the oil phase separated by the oil-water separator, the mass of the oil phase directly refluxed to the reactive distillation column is 1-3 times the total feed amount of the raw materials isopentenol and isopentenal, while the mass of the oil phase that is first distilled and then reused is 0.5-10 wt% of the total feed amount of the raw materials isopentenol and isopentenal.

2. The process for preparing 3-methyl-2-buten-1-aldehyde diisopentenyl acetal by continuous reactive distillation according to claim 1, characterized in that, The feed mass ratio of isopentenol and isopentenaldehyde is (2-5):

1.

3. The process for preparing 3-methyl-2-buten-1-aldehyde diisopentenyl acetal by continuous reactive distillation according to claim 1, characterized in that, The acid catalyst is selected from one or more of nitric acid, phosphoric acid, p-toluenesulfonic acid, and isopentenyl acid.

4. The process for preparing 3-methyl-2-buten-1-aldehyde diisopentenyl acetal by continuous reactive distillation according to claim 3, characterized in that, The amount of the acid catalyst used is 0.001-0.1 wt% of the total mass of isopentenol and isopentenal.

5. The process for preparing 3-methyl-2-buten-1-aldehyde diisopentenyl acetal by continuous reactive distillation according to claim 4, characterized in that, The amount of the acid catalyst used is 0.04-0.08 wt% of the total mass of isopentenol and isopentenal.

6. The process for preparing 3-methyl-2-buten-1-aldehyde diisopentenyl acetal by continuous reactive distillation according to any one of claims 1-5, characterized in that, The conditions for reactive distillation are: reboiler temperature of 90-110℃ and reaction pressure of 6-14 kPa absolute.

7. The process for preparing 3-methyl-2-buten-1-aldehyde diisopentenyl acetal by continuous reactive distillation according to claim 1, characterized in that, The conditions for the separation of the oil phase by distillation are as follows: the number of packed trays in the distillation column is 30-50, the operating pressure is 4-10 kPa, the reflux ratio is (2-6):1, the top temperature is 26-30℃, and the bottom temperature is 58-62℃.

8. The process for preparing 3-methyl-2-buten-1-aldehyde diisopentenyl acetal by continuous reactive distillation according to claim 1 or 7, characterized in that, Of the oil phase separated by the oil-water separator, the mass of the oil phase that is first distilled and then reused is 1.5-5 wt% of the total feed of the raw materials isopentenol and isopentenaldehyde.

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