CN109485544B

CN109485544B - Method for continuously preparing trimethylolpropane

Info

Publication number: CN109485544B
Application number: CN201710810798.XA
Authority: CN
Inventors: 陈光文; 王克军; 焦凤军; 周峰
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2017-09-11
Filing date: 2017-09-11
Publication date: 2021-12-14
Anticipated expiration: 2037-09-11
Also published as: CN109485544A

Abstract

A method for continuously preparing trimethylolpropane uses a mixture of formaldehyde and butyraldehyde as raw materials, absolute ethyl alcohol as a solvent, and sodium hydroxide aqueous solution as a reagent, the mixture and a catalyst flow and are mixed in a capillary, a reaction mixture is formed in the capillary, and the reaction mixture generates a product containing trimethylolpropane in the capillary through aldol condensation and disproportionation, wherein the temperature of the reaction mixture is controlled to be 25-75 ℃, and the length and/or volume of the capillary is increased or the flow rate of the reaction mixture is reduced, so that the reaction residence time is 2-25 min. The method shortens the synthesis reaction time of the trimethylolpropane (4-6 h in the prior art), and improves the yield from about 75% to 90%.

Description

Method for continuously preparing trimethylolpropane

Technical Field

The present invention relates to a method for continuously preparing trimethylolpropane, and particularly to a method for continuously preparing trimethylolpropane in a capillary tube.

Background

Trimethylolpropane (TMP) is a polyol containing alpha-methyl neopentyl structure, has unique physicochemical characteristics due to the particularity of the molecular structure, and is widely applied to surfactants, coatings, high-grade lubricating oil, printing ink, high-grade aviation grease, plasticizers and glass fiber reinforced plastics. In the production of paint, the performance of alkyd resin prepared by TMP is superior to that of resin prepared by glycerol, neopentyl glycol, pentaerythritol and the like. With the development of the industries such as automobiles, household electrical appliances, ships, transportation and the like in China, the demand of high-grade coatings is greatly increased.

At present, the yield of trimethylolpropane in China is little, the quality needs to be improved, the gap is large, and most of trimethylolpropane is imported. The synthesis of TMP is usually carried out by using an alkaline solution as a catalyst, and formaldehyde and butyraldehyde are subjected to aldol condensation reaction and disproportionation reaction to generate the TMP.

The first step is as follows: aldol condensation reaction of formaldehyde and butyraldehyde

The second step is that: cannizzaro disproportionation of 2, 2-dimethylolbutyraldehyde and formaldehyde

In the prior art, the method for synthesizing TMP is intermittently carried out in a kettle type reactor, and the TMP is reacted for 4-6 hours in a slow dripping mode, so that the yield is limited by a long production period. Therefore, a new process for efficiently and continuously producing TMP is required.

Disclosure of Invention

In order to overcome the defects of difficult control of reaction temperature, long reaction time, low yield and the like in the kettle type reactor for preparing the TMP, the invention provides the method for continuously preparing the TMP by utilizing the micro-reaction technology, which not only can quickly and efficiently prepare the TMP, but also has simple process operation and convenient process regulation.

The specific method of the invention is as follows:

using absolute ethyl alcohol as a solvent, and mixing formaldehyde and n-butyl aldehyde according to a molar ratio of 3-6: 1 to prepare a raw material, wherein the molar concentration of the formaldehyde is 1.5-12 mol/L, and the molar concentration of the n-butyl aldehyde is 0.5-2 mol/L for later use; preparing a sodium hydroxide aqueous solution with the molar concentration of 0.5-2 mol/L for later use; the mixed starting material of formaldehyde and n-butyraldehyde and an aqueous solution of sodium hydroxide were fed into a capillary having a diameter of 0.8 mm by means of an HPLC pump at such a flow rate that the molar ratio of sodium hydroxide to n-butyraldehyde in the reaction mixture was 1: 1. In a capillary tube, a mixed raw material of formaldehyde and n-butyl aldehyde and a sodium hydroxide aqueous solution are respectively preheated to 25-75 ℃ in respective preheating pipelines, preferably to 45-55 ℃; and then the mixture enters a capillary tube to be mixed and reacted, the temperature of the reaction mixture is controlled within the range of 25-75 ℃, the flow rate enables the residence time of the reaction mixture in the capillary tube to be 2-25 minutes, in a preferred or alternative embodiment, the residence time of the reaction mixture in the capillary tube is 5-10 minutes, so that the trimethylolpropane is continuously prepared, and cold fluid with the temperature of-5 ℃ is adopted in an ice water temperature control area, such as cold brine for heat exchange, so as to terminate the reaction.

Adjusting the pH value of the obtained reaction product to about 7 by using formic acid, distilling under reduced pressure to remove ethanol, water, unreacted formaldehyde, n-butyl aldehyde and the like, stopping distillation when a large amount of white solid is separated out, adding a proper amount of absolute ethanol as a solvent, filtering and desalting, continuously distilling the filtrate under reduced pressure to remove the solvent to obtain a crude product. Dissolving the crude product in appropriate amount of anhydrous ethanol, cooling, recrystallizing to obtain white fluid product, vacuum filtering, and drying to obtain white powder product.

Because the n-butyraldehyde is difficult to dissolve in water, the invention takes the absolute ethyl alcohol as the solvent when preparing the mixed solution of the formaldehyde and the n-butyraldehyde, ensures that the formaldehyde and the n-butyraldehyde are uniformly mixed, and simultaneously the absolute ethyl alcohol does not participate in the reaction,

the reaction mixture produces a trimethylolpropane-containing product in the capillary by aldol condensation and disproportionation reactions.

Compared with the prior art, the method can shorten the reaction process time for synthesizing the trimethylolpropane within 30 minutes from the original 6 hours, improve the yield from 75 percent to 90 percent and realize the continuous preparation of the TMP.

Drawings

FIG. 1 is a process flow diagram for synthesizing trimethylolpropane, wherein a 1-liquid caustic soda liquid storage tank, a 2-formaldehyde and n-butyraldehyde mixed solution liquid storage tank, a 3, 4-advection pump, a 5-water bath temperature control area, a 6-sample collection tank and a 7-ice water heat preservation area are adopted.

Detailed Description

The capillary tube was constructed in the reaction system shown in FIG. 1 and used in the following implementation.

Example 1

The method comprises the steps of taking absolute ethyl alcohol as a solvent, preparing a mixed raw material 1 from a formaldehyde aqueous solution and n-butyl aldehyde, wherein the molar concentration of formaldehyde is 10mol/L, the molar concentration of the n-butyl aldehyde is 2mol/L, preparing a sodium hydroxide aqueous solution 2 with the molar concentration of 2mol/L, conveying two materials into a capillary tube at a flow rate of 0.5ml/min by using an HPLC (high performance liquid chromatography) pump 3, controlling the temperature at 55 ℃ in a water bath temperature control region, mixing the two materials after entering the capillary tube from an inlet respectively, reacting in the capillary tube, keeping the materials for 5 ml/(1 ml/min) ═ 5min, and collecting the product to a sample collection tank at an outlet. Adding formic acid into the collected sample to neutralize the pH value to 7, then carrying out reduced pressure distillation, removing water, unreacted n-butyl aldehyde, formaldehyde and the like, dissolving the obtained solid in absolute ethyl alcohol, carrying out suction filtration, carrying out reduced pressure rotary evaporation on the filtrate to remove the ethyl alcohol, cooling and recrystallizing to obtain a solid product. The filtrate was analyzed by gas chromatography, and the yield of trimethylolpropane was calculated to be 90%.

Example 2

The procedure is as in example 1, with only the molar concentrations of the reactants formaldehyde with n-butyraldehyde and catalyst being varied: preparing a mixed raw material from a formaldehyde aqueous solution and n-butyl aldehyde, wherein the molar concentration of the formaldehyde is 5mol/L, the molar concentration of the n-butyl aldehyde is 1mol/L, a sodium hydroxide aqueous solution with the molar concentration of 1mol/L is used as a catalyst, the reaction temperature is 55 ℃, and the material retention time is 5 minutes. The yield of trimethylolpropane obtained was 76%.

Example 3

The process is the same as example 1, only the mixture ratio and molar concentration of the reactants formaldehyde and n-butyraldehyde are changed: the formaldehyde aqueous solution and n-butyl aldehyde are prepared into a mixed raw material, wherein the molar concentration of formaldehyde is 3mol/L, the molar concentration of n-butyl aldehyde is 1mol/L, a sodium hydroxide aqueous solution with the molar concentration of 1mol/L is used as a catalyst, and the material retention time is 5 minutes. The yield of trimethylolpropane obtained was 53%.

Example 4

The procedure is as in example 1, with only the residence times of the reactants formaldehyde and n-butyraldehyde being varied: the formaldehyde aqueous solution and n-butyl aldehyde are prepared into a mixed raw material, wherein the molar concentration of formaldehyde is 3mol/L, the molar concentration of n-butyl aldehyde is 1mol/L, a sodium hydroxide aqueous solution with the molar concentration of 1mol/L is used as a catalyst, the reaction temperature is 55 ℃, and the material retention time is 2.5 minutes. The yield of trimethylolpropane obtained was 46%.

Example 5

The procedure is as in example 1, with only the temperatures of the reactants formaldehyde and n-butyraldehyde being varied: preparing a mixed raw material from a formaldehyde aqueous solution and n-butyl aldehyde, wherein the molar concentration of the formaldehyde is 3mol/L, the molar concentration of the n-butyl aldehyde is 1mol/L, a sodium hydroxide aqueous solution with the molar concentration of 1mol/L is used as a catalyst, the reaction temperature is 45 ℃, and the material retention time is 5 minutes. The yield of trimethylolpropane obtained was 45%.

Claims

1. A method for continuously preparing trimethylolpropane, the method comprising:

using absolute ethyl alcohol as a solvent, and mixing formaldehyde and n-butyl aldehyde according to a molar ratio of (3-6) to 1 to prepare a mixed raw material; sodium hydroxide aqueous solution is used as a catalyst;

flowing and mixing the mixed feedstock and the catalyst in a capillary to form a reaction mixture;

heating the reaction mixture flowing in the capillary tube to 25-75 ℃, and carrying out aldol condensation and disproportionation reaction on the reaction mixture at the temperature to generate a trimethylolpropane-containing product;

wherein the residence time of the reaction mixture in the capillary is 2-25 minutes;

the molar concentration of sodium hydroxide in the catalyst is 0.5-2 mol/L.

2. The method according to claim 1, characterized in that anhydrous ethanol is used as a solvent, and formaldehyde and n-butyl aldehyde are mixed according to a molar ratio of 5:1 to prepare a mixed raw material;

heating the reaction mixture flowing in the capillary to 55 deg.C, and subjecting the reaction mixture to aldol condensation and disproportionation reaction at the temperature to obtain trimethylolpropane-containing product;

wherein the residence time of the reaction mixture in the capillary is 5 minutes.

3. The method according to claim 1, wherein the molar concentration of formaldehyde in the mixed raw material is 1.5-12 mol/L; the molar concentration of the n-butyraldehyde is 0.5-2 mol/L.

4. The method according to claim 3, wherein the molar concentration of formaldehyde in the mixed raw materials is 10 mol/L; the molar concentration of n-butyraldehyde was 2 mol/L.

5. The method of claim 1, wherein the molar concentration of sodium hydroxide in the catalyst is 2 mol/L.

6. The method according to any one of claims 1 to 5, wherein the mixed raw material and the catalyst flow through the capillary at a volume flow rate such that the molar ratio of sodium hydroxide to n-butyraldehyde in the reaction mixture is 0.5 to 2: 1.

7. The method of claim 1, wherein the step of formulating the blended feedstock comprises: mixing formaldehyde and n-butyraldehyde in a preposed capillary, preheating to 25-75 ℃, and introducing into a reaction capillary to contact and react with a catalyst.

8. The method of claim 7, wherein the step of formulating the blended feedstock comprises: mixing formaldehyde and n-butyraldehyde in a preposed capillary, preheating to 55 ℃, and then introducing into a reaction capillary to contact and react with a catalyst.

9. The method according to claim 1, wherein the mixed raw material of formaldehyde and n-butyraldehyde is preheated to 25-75 ℃ before being mixed with the aqueous sodium hydroxide solution, and then the aqueous sodium hydroxide solution is introduced into a reaction capillary tube to contact and react with the raw material.

10. The method according to claim 9, wherein the mixed raw material of formaldehyde and n-butyraldehyde is preheated to 55 ℃ before being mixed with the aqueous sodium hydroxide solution, and then introduced into a reaction capillary to be contacted with the raw material for reaction.