Method for inhibiting generation of polysaccharide impurities in condensation reaction process of trimethylolpropane by calcium method

Abstract

The invention discloses a method for inhibiting generation of polysaccharide impurities in a condensation reaction process of trimethylolpropane by a calcium method. The method comprises the following steps: 1) adding a formaldehyde solution into a condensation kettle; 2) putting a calcium hydroxide solution into a condensation kettle; (3) uniformly mixing n-butyraldehyde and an alcoholic solution to form an n-butyraldehyde solution, and adding the n-butyraldehyde solution into the reaction kettle after the calcium hydroxide solution is added for 5 minutes; the molar ratio of the formaldehyde solution to the n-butyraldehyde solution is 3.1-3.5; the molar ratio of the calcium hydroxide solution to the n-butyraldehyde solution is 0.5-0.6; the preparation method comprises the following steps of 1, adding an n-butyraldehyde solution into a condensation kettle, 2, adding the n-butyraldehyde solution into the condensation kettle, 4, adding a hydroquinone aqueous solution into the condensation kettle for 60 min when the n-butyraldehyde solution is added, 5, carrying out a constant temperature reaction at 40 DEG C for 30-50 min after n-butyraldehyde is added so that a full reaction is ensured, 6, adding hydrogen peroxide into the condensation liquid at a constant temperature to remove unreacted formaldehyde, and 7, adding formic acid into the condensation liquid to adjust the pH value of the condensation liquid to 6.8.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical technology, specifically relating to a method for suppressing the generation of polysaccharide impurities during the calcium-based trimethylolpropane condensation reaction. Background Technology

[0002] The core reaction principle of the calcium condensation process for preparing trimethylolpropane (TMP) is that formaldehyde and n-butyraldehyde undergo aldol condensation-cannizaro reaction under the catalysis of calcium hydroxide to produce the target product TMP, while calcium formate is produced as a byproduct. This reaction system is prone to a series of side reactions. Formaldehyde and n-butyraldehyde undergo self-polymerization under alkaline conditions to generate polysaccharide impurities. The degree of polymerization of these polysaccharides gradually increases with the reaction progress, gradually exhibiting a distinct color that directly affects the color index of the final TMP product, negatively impacting its quality.

[0003] In existing industrial production processes of trimethylolpropane (TMP) using the calcium-based method, the high content of colored impurities and the dark color of the finished product are common problems. Therefore, there is an urgent need for a method to suppress the generation of polysaccharide impurities during the condensation reaction of TMP using the calcium-based method, which is of great significance for improving the product quality of TMP. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for suppressing the generation of polysaccharide impurities during the calcium-based trimethylolpropane condensation reaction.

[0005] The objective of this invention is achieved through the following technical solution: a method for suppressing the generation of polysaccharide impurities during the calcium-based trimethylolpropane condensation reaction, comprising the following steps: 1) Add a 20% (w / w) formaldehyde solution to the condensation vessel at once as the reaction base liquid; 2) Continuously add a 10%-12% calcium hydroxide solution to the condensation vessel over a period of 90-110 minutes, maintaining the pH of the reaction system at 10-11. 3) Mix n-butyraldehyde and alcohol solution at a volume ratio of 1:1-2 until homogeneous. The n-butyraldehyde dissolves in the alcohol solution to form a n-butyraldehyde solution. After adding the calcium hydroxide solution for 5 minutes, continuously add the n-butyraldehyde solution to the reactor over a period of 120 minutes. The molar ratio of formaldehyde solution to n-butyraldehyde solution is 3.1-3.5; the molar ratio of calcium hydroxide solution to n-butyraldehyde solution is 0.5-0.6. 4) When the n-butyraldehyde solution is fed for 60 minutes, add hydroquinone aqueous solution to the condensation kettle at once as an inhibitor of self-polymerization reaction. The amount of hydroquinone added is 100-200 ppm of the total raw material, which can significantly reduce the content of polysaccharide impurities in the condensation liquid. 5) After the n-butyraldehyde is added, maintain a constant temperature of 40℃ for 30-50 minutes to ensure a complete reaction; 6) Add hydrogen peroxide to the condensation solution after it has been kept at a constant temperature to remove unreacted formaldehyde; 7) Add formic acid to adjust the pH of the condensation solution to 6.8.

[0006] Furthermore, the alcohol solution is a methanol solution or an ethanol solution.

[0007] Furthermore, in step 4), the amount of hydroquinone added is 200 ppm of the total amount of raw materials.

[0008] The raw material systems in the calcium condensation process exhibit significant phase differences: n-butyraldehyde is a colorless, oily liquid, poorly soluble in water; formaldehyde is added as an aqueous solution; and calcium hydroxide participates in the reaction as a solid suspension. In traditional reaction systems, n-butyraldehyde tends to float to the surface of the aqueous solution, resulting in insufficient contact between it and formaldehyde in the aqueous phase, severely hindering the efficient reaction. By dissolving n-butyraldehyde in methanol or ethanol, the following multiple effects can be achieved: First, it improves the miscibility between oily n-butyraldehyde and formaldehyde aqueous solution, promoting sufficient contact of reactants and homogeneous reaction, significantly improving reaction efficiency; Second, methanol or ethanol can act as a proton transfer medium, promoting the generation of enol anions, thereby increasing the conversion rate of trimethylolpropane; Third, alcohol solvents can inhibit the excessive condensation of aldehydes and reaction intermediates, reducing side reactions from the source; Fourth, it can reduce the probability of n-butyraldehyde oxidizing to form n-butyric acid, an organic acid impurity, effectively controlling the total amount of impurities in the system; Fifth, it can inhibit the self-polymerization of n-butyraldehyde to form 2-ethylhexenal byproduct. In addition, adding hydroquinone in the middle of the reaction can further suppress the generation of polysaccharide impurities by blocking the self-condensation pathway of 2-ethylpropenal.

[0009] The beneficial effects of this invention are as follows: By dissolving n-butyraldehyde in methanol or ethanol and then adding it to the reaction system, the generation of polysaccharide impurities can be significantly inhibited, thereby reducing the content of colored impurities in the trihydroxy condensation solution; by adding hydroquinone during the condensation stage, the generation of polysaccharide impurities is further inhibited. The polysaccharide content in the condensation solution of this invention is reduced to 0.1-0.2%, and the trihydroxy content is increased to over 88.6%. Detailed Implementation

[0010] The present invention will now be described in detail. Example 1

[0011] A method for suppressing the generation of polysaccharide impurities during the calcium-based trimethylolpropane condensation reaction includes the following steps: 1) Add a 20% (w / w) formaldehyde solution to the condensation vessel at once as the reaction base liquid; 2) Continuously add a 10% calcium hydroxide solution to the condensation vessel over a period of 110 minutes, maintaining the pH of the reaction system at 11.0. 3) Mix n-butyraldehyde and methanol solution at a volume ratio of 1:2 until homogeneous. The n-butyraldehyde dissolves in the methanol solution to form a n-butyraldehyde solution. After adding calcium hydroxide solution for 5 minutes, continuously add the n-butyraldehyde solution into the reactor. The feeding time is 120 minutes. The molar ratio of formaldehyde solution to n-butyraldehyde solution is 3.5. The molar ratio of calcium hydroxide solution to n-butyraldehyde solution is 0.5. 4) When the n-butyraldehyde solution has been fed for 60 minutes, add hydroquinone aqueous solution to the condensation vessel all at once. The amount of hydroquinone added is 200 ppm of the total amount of raw materials, and react for 1 hour. 5) After the n-butyraldehyde is added, maintain the temperature at 40℃ for 30 minutes to ensure a complete reaction; 6) Add hydrogen peroxide to the condensation solution after it has been kept at a constant temperature to remove unreacted formaldehyde; 7) Add formic acid to adjust the pH of the condensation solution to 6.8.

[0012] After the above steps, the polysaccharide content in the condensation solution decreased to 0.1%, and the trihydroxy content increased to 89.6%. Example 2

[0013] A method for suppressing the generation of polysaccharide impurities during the calcium-based trimethylolpropane condensation reaction includes the following steps: 1) Add a 20% (w / w) formaldehyde solution to the condensation vessel at once as the reaction base liquid; 2) Continuously add a 12% calcium hydroxide solution to the condensation vessel over a period of 90 minutes, maintaining the pH of the reaction system at 10.0. 3) Mix n-butyraldehyde and ethanol solution at a volume ratio of 1:1 until homogeneous. The n-butyraldehyde dissolves in the ethanol solution to form a n-butyraldehyde solution. After adding calcium hydroxide solution for 5 minutes, continuously add the n-butyraldehyde solution into the reactor. The feeding time is 120 minutes. The molar ratio of formaldehyde solution to n-butyraldehyde solution is 3.1. The molar ratio of calcium hydroxide solution to n-butyraldehyde solution is 0.6. 4) When the n-butyraldehyde solution is fed for 60 minutes, add hydroquinone aqueous solution into the condensation vessel all at once. The amount of hydroquinone added is 100 ppm of the total amount of raw materials, and react for 1 hour. 5) After the n-butyraldehyde is added, maintain the temperature at 40℃ for 50 minutes to ensure a complete reaction; 6) Add hydrogen peroxide to the condensation solution after it has been kept at a constant temperature to remove unreacted formaldehyde; 7) Add formic acid to adjust the pH of the condensation solution to 6.8.

[0014] After the above steps, the polysaccharide content in the condensation solution decreased to 0.2%, and the trihydroxy content increased to 88.6%.

[0015] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for suppressing the generation of polysaccharide impurities during the calcium-based trimethylolpropane condensation reaction, characterized in that... Includes the following steps: 1) Add a 20% (w / w) formaldehyde solution to the condensation vessel at once as the reaction base liquid; 2) Continuously add a 10%-12% calcium hydroxide solution to the condensation vessel over a period of 90-110 minutes, maintaining the pH of the reaction system at 10-11. 3) Mix n-butyraldehyde and alcohol solution at a volume ratio of 1:1-2 until homogeneous. The n-butyraldehyde dissolves in the alcohol solution to form a n-butyraldehyde solution. After adding the calcium hydroxide solution for 5 minutes, continuously add the n-butyraldehyde solution to the reactor over a period of 120 minutes. The molar ratio of formaldehyde solution to n-butyraldehyde solution is 3.1-3.5; the molar ratio of calcium hydroxide solution to n-butyraldehyde solution is 0.5-0.

6. 4) When the n-butyraldehyde solution is fed for 60 minutes, add hydroquinone aqueous solution into the condensation vessel all at once. The amount of hydroquinone added is 100-200 ppm of the total amount of raw materials. 5) After the n-butyraldehyde is added, maintain a constant temperature of 40℃ for 30-50 minutes to ensure a complete reaction; 6) Add hydrogen peroxide to the condensation solution after it has been kept at a constant temperature to remove unreacted formaldehyde; 7) Add formic acid to adjust the pH of the condensation solution to 6.

8.

2. The method for suppressing the generation of polysaccharide impurities during the calcium-based trimethylolpropane condensation reaction according to claim 1, characterized in that: The alcohol solution is a methanol solution or an ethanol solution.

3. The method for suppressing the generation of polysaccharide impurities during the calcium-based trimethylolpropane condensation reaction according to claim 2, characterized in that: In step 4), the amount of hydroquinone added is 200 ppm of the total amount of raw materials.