Improved method for synthesizing trimethylolpropane

Abstract

The invention relates to an improved method for synthesizing trimethylolpropane. The method comprises the following steps: under an ice bath condition, adjusting a formaldehyde aqueous solution with a molar ratio of 2.2-2.5 to a pH value of 11-12 by using a catalytic amount of a calcium hydroxide aqueous solution, slowly dropwise adding n-butyraldehyde with a molar ratio of 1.0 to carry out aldol condensation reaction, and synchronously dropwise adding a condensation reaction solution and the calcium hydroxide aqueous solution with a molar ratio of 0.50-0.51 to the formaldehyde aqueous solution with a molar ratio of 1.0 to carry out disproportionation reaction, the content of the trimethylolpropane in the organic matter in the reaction solution can reach 93.4%, the content of cyclic trimethylolpropane formal (CTF) is 0.4%, and the content of bis (trimethylolpropane) (DTMP) is 1.1%.

Description

Technical Field

[0001] The invention belongs to the chemical synthesis technology of polyols, and specifically relates to a method for preparing trimethylolpropane by taking formaldehyde and n-butyraldehyde as raw materials. Background Art

[0002] Trimethylolpropane (TMP) is a polyol containing three hydroxymethyl structures. Like glycerol, neopentyl glycol, pentaerythritol and other polyols, it is mainly used in the synthesis of various alkyd resins, polyesters and polyurethanes. It is also widely used in advanced lubricants, plasticizers, surfactants, resin chain extenders, explosives, fireproof materials and adhesives. With the expansion of the application scope of trimethylolpropane, the demand for trimethylolpropane in domestic and foreign markets continues to increase, and it has a good market prospect.

[0003] The current industrial production methods are mainly divided into two types: 1. Hydrogenation reduction method, firstly, n-butyraldehyde and formaldehyde aqueous solution are subjected to aldol condensation reaction under the action of organic base to obtain the intermediate 2,2-dihydroxymethylbutyraldehyde (DMB), and then the intermediate is hydrogenated and reduced to TMP. Its representative patents include CN 116874349 A; CN 102304022 A; CN 114409520 A; CN 102432430 A; CN 104892364 A; Henan Chemical Industry, 2016, 33:22-24; Guangzhou Chemical Industry, 2013, 41(6):102-105; CN 102391070 A, etc. The hydrogenation reduction method can save formaldehyde and a large amount of alkali, has relatively few side reaction products, good product quality, simple purification and refining process, and can obtain a higher TMP yield. However, this method also has problems such as strong organic alkali odor, the use of high-pressure equipment, the need for hydrogenation equipment, high investment, high risk factor, high requirements for catalysts, and high production technology requirements.2. Cannizzaro disproportionation method: n-butyraldehyde and formaldehyde aqueous solution directly undergo aldol condensation and disproportionation reaction under the action of inorganic base to produce TMP. This synthesis method often has the disadvantages of low reaction selectivity, many by-products, and poor product color, but it has low equipment investment, simple operation, and low production cost. Therefore, most TMP companies still use this synthesis method for production. According to the different types of bases, it is mainly divided into sodium method and calcium method. Among them, the sodium method using sodium hydroxide as the inorganic base has representative documents such as CN 110372475 A; CN 102617285 A; CN 101102986 B; CN 114524712 A; Shandong Chemical Industry, 2009, 38(09): 1-5. Since the sodium hydroxide aqueous solution is highly alkaline, a high pH value will lead to an increase in by-products (such as di(trimethylol)propane DTMP, and cyclic trimethylolpropane formal CTF and ditrimethylolpropane formal TMP-MBLF and other cyclic methylals and linear methylal compounds). Finally, not only is the process of removing sodium formate complicated and difficult, but the product quality will also decrease. It has been reported that the use of microreactor synthesis to improve the sodium method can effectively alleviate the problem of many by-products. Its representative document is CN 109485544 A and Chemical Reaction Engineering and Technology, 2017, 33(6): 841-846. However, its reaction selectivity is still not high, and the use of a large excess of formaldehyde also increases the pressure of environmental protection treatment. The calcium method using calcium hydroxide as an inorganic base, its representative documents are CN 102795964 A; CN 115745742 A; CN 108997082 A; CN 102795963 A; China High-tech Enterprise, 2017(08):32-33, due to the low solubility of calcium hydroxide in water, the pH value of the reaction solution is relatively stable, the reaction process is more stable, and no large excess of formaldehyde is required. However, due to the low solubility of calcium hydroxide in water and the need for a higher temperature to promote the reaction, there will be problems such as excessive alkalinity in the reaction area, many side reactions, darker color of the reaction solution, equipment scaling, and poor product color. Therefore, it is a very meaningful research work to develop a new and improved process for the synthesis of trimethylolpropane, which can not only increase the content of TMP in the reaction solution, but also reduce the color of the reaction solution to avoid affecting the later purification process. Summary of the invention

[0004] The purpose of the present invention is to provide an improved method for synthesizing trimethylolpropane with high selectivity and light-colored reaction liquid, which effectively inhibits the generation of DTMP and controls the reaction liquid to be substantially colorless in the later stage, so that the reaction liquid will not generate some undesirable by-products in the subsequent purification process, thereby improving the product quality.

[0005] To solve the above problems, the technical solution provided by the present invention is: an improved method for synthesizing trimethylolpropane, comprising the following steps: (1) Aldol condensation reaction: At low temperature (2-5°C, the same below), adjust the pH value of the formaldehyde aqueous solution to 10-12 with a catalytic amount of alkali solution, slowly add n-butyraldehyde, and react at low temperature for 0.5-1h after the addition is completed. Then gradually and slowly raise the temperature to room temperature and react for 2-3h.

[0006] (2) Cannizzaro disproportionation reaction: the above reaction solution and calcium hydroxide suspension are simultaneously added dropwise to a pre-low-temperature treated formaldehyde aqueous solution, the dropping temperature is maintained below 5°C, and the reaction is continued at this temperature for 0.5 h after the addition is completed, and the temperature is gradually raised to room temperature for 1-2 h, and then raised to 40-45°C for 1 h, wherein the molar ratio of calcium hydroxide to formaldehyde is 0.50-0.51:1; (3) The reaction solution is neutralized with formic acid to a pH value of 6.5-7 to terminate the reaction and obtain a crude trimethylolpropane solution.

[0007] In the condensation reaction stage of the present invention, the mass fraction of formaldehyde is 18-30% aqueous solution, the content of n-butyraldehyde is 98% (mass fraction), the molar ratio of formaldehyde to butyraldehyde is 2.2-2.5:1, and the reaction needs to be dropped at a low temperature of about 5°C.

[0008] Preferably, in the condensation reaction stage of the present invention, a catalytic amount of alkali solution is used to adjust the pH value of the reaction liquid to 11-12 at low temperature for condensation reaction, and the dripping stage is first carried out at low temperature, the reaction temperature is about 5°C, the reaction time is 0.5-1 h, and then the temperature is gradually raised to room temperature for reaction for 2-3 h. The test in the experiment shows that when the pH value of the condensation reaction liquid is adjusted to 10-11 at low temperature, the condensation reaction is very slow by TLC detection, and the conversion rate of n-butyraldehyde is often not high after 5-6 hours of temperature reaction; when the pH value is greater than 12, condensation and disproportionation reactions occur simultaneously, and the reaction selectivity is low, and when the pH value is adjusted to 11-12, the condensation reaction can proceed smoothly by TLC detection at a reaction temperature of 5°C, especially when the pH value is adjusted to 11.5-12, the condensation reaction is relatively rapid and no obvious disproportionation reaction impurities are produced. After rising to room temperature for 1-2 hours, the reaction liquid is conventionally treated and the n-butyraldehyde conversion rate is about 95% by gas chromatography, but if the reaction time is further extended, the TLC detection shows that the disproportionation reaction will obviously occur.

[0009] The disproportionation reaction of the present invention is carried out by dropping the condensation reaction liquid and the calcium hydroxide suspension liquid synchronously under low temperature conditions. Because the disproportionation reaction has an obvious exothermic effect, the pH value of the entire system will rise rapidly when the calcium hydroxide aqueous solution is dropped, and the n-butyraldehyde and the intermediate 2-hydroxymethylbutyraldehyde that have not been completely reacted in the condensation reaction will react rapidly with the local heat release and the increase of the pH value, thereby generating a large amount of by-products, which will lead to a decrease in the reaction selectivity and increase the color of the reaction liquid. Therefore, the entire dropping process needs to be carried out under the conditions of low temperature and slow dropping.

[0010] In the disproportionation reaction stage, the present invention can use an appropriate amount of formaldehyde water as a primer, and the formaldehyde solution used for the primer is an 18-30% aqueous solution, and the molar ratio of the formaldehyde solution to the amount of n-butyraldehyde is 1.0:1, which not only facilitates stirring in the initial stage of the reaction and promotes the smooth conversion of unreacted trace n-butyraldehyde in the condensation reaction liquid, but more importantly, increases the local concentration of formaldehyde in the disproportionation reaction liquid, thereby improving the disproportionation selectivity of the intermediate 2,2-dihydroxymethylbutyraldehyde.

[0011] After the dropwise addition in the disproportionation reaction stage of the present invention is completed, the reaction needs to be continued at low temperature, and the reaction temperature is maintained for 0.5 h, and then the temperature is gradually and slowly raised to room temperature for 1-2 h, and the reaction is carried out at 40-45 ° C for 1 h. The pH value of the formic acid neutralization reaction liquid is 6.5-7 to obtain a colorless trimethylolpropane crude solution. After conventional treatment, the solution is detected by gas chromatography, and its content can reach 91.1-93.4% of TMP, 0.4-0.6% of CTF, and 0.4-1.2% of DTMP. This result is significantly better than the 85.9-90.0% TMP selectivity of the microreactor sodium method, and there is no problem that the reaction liquid of the calcium method for synthesizing TMP is easy to change color and the product color is low in the literature, indicating that the improved trimethylolpropane synthesis method of the present invention can improve the reaction selectivity and control the color of the reaction liquid, and its effect is very obvious.

[0012] Compared with the prior art, the invention is characterized in that the alkalinity of the reaction system is reduced by accurately controlling the pH value of the reaction liquid to 11.5-12 during the condensation stage. This method not only ensures that the condensation reaction generates the DMB intermediate smoothly and steadily, reduces the occurrence of various formal and hemiformal side reactions, but also greatly reduces the generation of 2-ethylacrolein, a product of the E1cb alkaline elimination reaction in the reaction system, reduces the generation of DTMP, improves the reaction selectivity, and also alleviates the problem of the darkening of the color of the reaction system of the reaction liquid during the disproportionation stage. The improvement effect is significant. DETAILED DESCRIPTION

[0013] The technical solution of the present invention is further described in detail below through specific examples, but the present invention is not limited to these examples. The preparation process under other conditions can be achieved by referring to the methods of the following examples. Example

[0014] Add 1.95 g of 95% Ca(OH)2 powder into a 25 mL single-necked flask, then add 15 g of water and stir to prepare a 12% Ca(OH)2 suspension for later use.

[0015] Add 10g of 30% formaldehyde solution to a 50mL single-necked flask, place it in an ice-salt bath and stir to precool, when the temperature of the liquid in the flask drops to about 5°C, gradually add a catalytic amount of Ca(OH)2 suspension to adjust the pH to 11.5, then slowly drop 3.68g of 98% n-butyraldehyde, after about 0.5h of dropwise addition, maintain this temperature and continue to react for 0.5h, then naturally rise to room temperature (20-25°C) and stir to react for 2h, place aside and stir for later use. At this time, using thin layer chromatography, it can be observed that there are obvious intermediate product DMB dots.

[0016] Add 5g of 30% formaldehyde solution to another 100mL three-necked flask, place it in an ice-salt bath and stir to precool, when the solution temperature drops below 5°C, add the above condensation solution and the prepared 17g 12% Ca(OH)2 suspension solution at the same time, add the solution in about 1 hour, maintain this temperature and continue to react for 0.5 hours, gradually rise to room temperature for about 1 hour, and finally react at 40°C for about 1 hour, neutralize with formic acid to pH 6.5-7, and obtain a colorless trimethylolpropane reaction solution. After conventional treatment, the solution is tested by gas chromatography, which contains 90.6% TMP, 0.5% CTF, and 1.3% DTMP. Example

[0017] Add 55.0 g of 30% formaldehyde solution to a 250 mL single-necked flask, place it in an ice-salt bath and stir to pre-cool, when the temperature of the liquid in the flask drops to about 5°C, gradually add a catalytic amount of Ca(OH)2 suspension to adjust the pH to 11.5-12, then slowly drop 18.4 g of 98% n-butyraldehyde, after about 0.5 h of dropwise addition, maintain this temperature and continue to react for 0.5 h, then naturally rise to room temperature and stir to react for 2 h, place aside and stir for later use. At this time, using thin layer chromatography, it can be observed that there are obvious intermediate product DMB dots.

[0018] Add 25.0 g of 30% formaldehyde solution to another 100 mL three-necked flask, place it in an ice-salt bath and stir to precool, and when the solution temperature drops below 5°C, add the above condensation solution and the prepared 84.8 g 12% Ca(OH)2 suspension dropwise at the same time, and complete the addition in about 1 hour. Maintain this temperature and continue to react for 0.5 hours, gradually rise to room temperature for about 1 hour, and finally react at 40°C for about 1 hour, neutralize with formic acid to a pH of 6.7-7, and obtain a colorless trimethylolpropane reaction solution. After conventional treatment, the solution is tested by gas chromatography, which contains 93.4% TMP, 0.4% CTF, and 1.1% DTMP. Example

[0019] Add 12.5g of 30% formaldehyde solution to a 50mL single-necked flask, place it in an ice-salt bath and stir to precool, when the liquid temperature in the flask drops to about 5°C, gradually add a catalytic amount of Ca(OH)2 suspension to adjust the pH to 11.5-12, then slowly drop 3.68g of 98% n-butyraldehyde, after about 0.5h of dropwise addition, maintain this temperature and continue to react for 0.5h, then naturally warm to room temperature and stir to react for 2h, place aside and stir for later use. At this time, using thin layer chromatography, it can be observed that there are obvious intermediate product DMB dots.

[0020] Add 5g of 30% formaldehyde solution to another 100mL three-necked flask, place it in an ice-salt bath and stir to precool, when the solution temperature drops below 5°C, add the above condensation solution and the prepared 17g 12% Ca(OH)2 suspension solution at the same time, add the solution in about 1 hour, maintain this temperature and continue to react for 0.5 hour, gradually rise to room temperature for about 1 hour, and finally react at 40°C for about 1 hour, neutralize with formic acid to pH 6.5-7, and obtain a colorless trimethylolpropane reaction solution. After conventional treatment, the solution is tested by gas chromatography, which contains 92.8% TMP, 0.4% CTF, and 0.4% DTMP. Example

[0021] Add 15.0 g of 30% formaldehyde solution to a 50 mL single-necked flask, place it in an ice-salt bath and stir to pre-cool, when the temperature of the liquid in the flask drops to about 5°C, gradually add a catalytic amount of Ca(OH)2 suspension to adjust the pH to 11.0, then slowly drop 3.68 g of 98% n-butyraldehyde, after about 0.5 h of dropwise addition, maintain this temperature and continue to react for 0.5 h, then naturally rise to room temperature and stir to react for 2 h, place aside and stir for later use. At this time, using thin layer chromatography, it can be observed that there are obvious intermediate product DMB dots.

[0022] Add 5g of 30% formaldehyde solution to another 100mL three-necked flask, place it in an ice-salt bath and stir to precool, when the solution temperature drops below 5°C, add the above condensation solution and the prepared 17g 12% Ca(OH)2 suspension solution at the same time, add the solution in about 1 hour, maintain this temperature and continue to react for 0.5 hours, gradually rise to room temperature for about 1 hour, and finally react at 40°C for about 1 hour, neutralize with formic acid to pH 7.0, and obtain a colorless trimethylolpropane reaction solution. After conventional treatment, the solution is tested by gas chromatography, which contains 89.2% TMP, 0.4% CTF, and 0.6% DTMP. Example

[0023] Add 18.77g of 20% formaldehyde solution to a 50mL single-necked flask, place it in an ice bath and stir to precool, when the temperature of the liquid in the flask drops below 10°C, gradually add 20% NaOH aqueous solution to adjust the pH to 11.5-12, then slowly drop 3.68g of 98% n-butyraldehyde for about 15 minutes, after the dropwise addition is complete, maintain this temperature and continue to react for about 15 minutes, then gradually heat to room temperature and react for about 3 hours, place aside and stir for use. At this time, using thin layer chromatography, it can be observed that there are obvious intermediate product DMB dots.

[0024] Add 7.5g of 20% formaldehyde solution to another 100mL three-necked flask, place it in an ice bath and stir to precool, and when the temperature of the liquid in the flask drops to about 8°C, add the above condensation solution and the prepared 17g 12% Ca(OH)2 suspension dropwise at the same time, and complete the addition in about 1 hour. Maintain this temperature and continue to react for 0.5 hours, gradually rise to room temperature for about 1 hour, and finally react at 40°C for about 1 hour, neutralize with formic acid to a pH of 6.5-7.0, and obtain a colorless trimethylolpropane reaction solution. After conventional treatment, the solution is tested by gas chromatography, which contains 0.5% CTF, 91.1% TMP, and 0.9% DTMP.

[0025] Comparative Example 1: Add 18.77g of 20% formaldehyde solution to a 50mL single-necked flask, place it in an ice-salt bath and stir to pre-cool, when the temperature of the liquid in the flask drops to about 5°C, gradually add Ca(OH)2 aqueous solution to adjust the pH to 12.5, then slowly drop 3.68g of 98% n-butyraldehyde for about 15 minutes, after the addition is complete, maintain this temperature and continue to react for 15 minutes, then gradually heat to room temperature to react for about 2 hours, and place aside to stir for use. At this time, using thin layer chromatography, it can be observed that there are obvious intermediate product DMB dots.

[0026] Add 7.5g of 20% formaldehyde solution to another 100mL three-necked flask, place it in an ice-salt bath and stir to precool, when the temperature of the liquid in the flask drops to about 5°C, add the above condensation liquid and the Ca(OH)2 aqueous solution prepared according to Example 1 dropwise for about 0.5 h, maintain this temperature after the addition is complete, and continue to react for 0.5 h, then gradually heat to room temperature for about 1 h, react at 40°C for about 1 h, neutralize with formic acid to pH 7.0, and obtain a colorless trimethylolpropane solution. After conventional treatment, the solution is tested by gas chromatography, which contains 88.5% TMP, 0.8% CTF, and 1.9% DTMP.

[0027] Comparative Example 2: 18.77g of 20% formaldehyde solution was added to a 50mL single-necked flask, and it was placed in an ice bath and stirred to pre-cool. When the temperature of the liquid in the flask dropped to about 5°C, 10% NaOH aqueous solution was gradually added to adjust the pH value to 11.5, and then 3.68g of 98% n-butyraldehyde was slowly added dropwise for about 20 minutes. After the addition was completed, the temperature was maintained to continue the reaction for about 0.5 hours, and then the temperature was gradually raised to room temperature for about 3 hours, and it was placed aside for stirring. At this time, the generation of obvious intermediate product DMB dots can be observed by thin layer chromatography.

[0028] Add 7.5g of 20% formaldehyde solution to another 100mL three-necked flask, place it in an ice bath and stir to precool, when the temperature of the liquid in the flask drops to about 5°C, add the above condensation solution and 10mL of 2.2g NaOH aqueous solution, add the solution dropwise for about 0.5h, keep the ice bath and continue the reaction for 0.5h, then gradually warm to room temperature for about 1h, react at 40°C for about 1h, neutralize with formic acid to pH 7.0, and obtain a colorless trimethylolpropane solution with a slight precipitate. After conventional treatment, the solution is tested by gas chromatography, which contains 0.6% CTF, 86.8% TMP, and 3.2% DTMP.

[0029] Comparative Example 3: Take 60g of 8% formaldehyde aqueous solution and place it in a cryogenic pump to cool it to 10°C, then divide 3.39g of 98% n-butyraldehyde and 7.23g of 32% sodium hydroxide alkali solution into two parts, the first part of n-butyraldehyde is 3 / 4 of the calculated mass of n-butyraldehyde, that is, 2.54g, and the rest is the second part, the first part of the alkali solution is 1 / 3 of the calculated mass of the alkali solution, that is, 2.41g, and the rest is the second part. In the first hour, the first part of n-butyraldehyde and the alkali solution are added at a uniform speed of 2.54g / h and 2.41g / h, respectively, and in the next 0.5 h, the second part of n-butyraldehyde and the alkali solution are added at a uniform speed of 1.70g / h and 9.64g / h, respectively. After the feeding is completed, the stirring state is maintained for 0.5 h, and then formic acid was added dropwise to the condensation liquid until the pH value of the condensation liquid reached 5.5 to obtain a crude reaction solution of trimethylolpropane. After conventional treatment, the solution was tested for content by gas chromatography, which showed that it contained 87.2% TMP, 0.4% CTF and 3.6% DTMP.

[0030] Comparative Example 4: In a 100mL single-necked flask, 51.3g of formaldehyde with a mass fraction of 18.8%, 7.21g of n-butyraldehyde with a content of 98% and 4.67g of Ca(OH)2 with a content of 95% were added at one time, and water was added to control the bottom water concentration to 110g / L. The temperature was raised to 50-60℃ for condensation reaction. During the reaction, the reaction liquid gradually turned yellow. After the reaction was completed, formic acid was added to neutralize to a pH value of 6.5. At this time, the entire reaction liquid turned yellowish brown to obtain a crude trimethylolpropane reaction liquid. After conventional treatment, the solution was tested by gas chromatography, which contained 88.6% TMP, 0.5% CTF and 4.0% DTMP.

[0031] Comparative Example 5: In a 250mL single-necked flask, 4.96g of 95% Ca(OH)2 and 32.84g of water were added to prepare a Ca(OH)2 aqueous solution, which was added to 50.75g of 18.8% formaldehyde aqueous solution. The temperature of the reaction solution was lowered to 15°C, and 7.21g of n-butyraldehyde was gradually added dropwise for about 2 hours. After the addition was completed, the temperature was gradually raised to 45°C and the reaction was carried out for 2 hours. During the reaction, the reaction solution gradually turned yellow. After the reaction was completed, formic acid was added to neutralize it to a pH value of 6.5. At this time, the entire reaction solution turned yellow-brown, and a crude trimethylolpropane reaction solution was obtained. After conventional treatment, the solution was tested by gas chromatography, which contained 0.4% CTF, 90.6% TMP, and 2.8% DTMP.

Claims

1. An improved method for synthesizing trimethylolpropane, comprising the steps of: (1) Aldol condensation reaction: adjust the pH value of the formaldehyde aqueous solution to 10-12 with a catalytic amount of alkali solution under ice bath conditions, slowly add n-butyraldehyde, react at low temperature for 0.5-1 h after the addition is complete, then gradually and slowly heat to room temperature and react for 2-3 h for use; (2) Cannizzaro disproportionation reaction: The above reaction solution and calcium hydroxide suspension are simultaneously added dropwise to a pre-low-temperature treated formaldehyde aqueous solution, and the dropping temperature is maintained below 5°C. After the dropping is completed, the reaction is continued in an ice bath for 0.5 h, and then the temperature is slowly raised to room temperature and stirred for 1-2 h, and then the temperature is raised to 40-45°C for 1 h, wherein: The molar ratio of calcium hydroxide to formaldehyde is 0.50~0.51:1; (3) The reaction solution is neutralized with formic acid to a pH value of 6.5 to 7.0 to terminate the reaction and obtain a trimethylolpropane reaction solution.

2. The improved method according to claim 1, characterized in that: The alkali solution used is a calcium hydroxide aqueous solution, a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution, which ensures that the disproportionation reaction occurs almost asynchronously in the aldol condensation reaction stage.

3. The improved method according to claim 1 or 2, characterized in that: The mass fraction of the formaldehyde aqueous solution in the aldol condensation reaction stage is 18%~30%, the content of n-butyraldehyde is 98%, and the molar ratio of formaldehyde to n-butyraldehyde is 2.2~2.5:

1.

4. The improved method according to claim 1 or 2, characterized in that: The reaction temperature of the aldol condensation reaction is 2-5°C.

5. The improved method according to claim 1 or 2, characterized in that: The synchronous addition time of step (2) is about 0.5~1h.