Low-energy-consumption salt-free etherified amino resin production method

Abstract

The invention discloses a low-energy-consumption salt-free etherified amino resin production method, which comprises the following steps of: adopting acid (oxalic acid, citric acid, carbonic acid, sulfuric acid and the like) capable of forming precipitates as an acid catalyst of etherification reaction, simultaneously adopting alkali (calcium hydroxide, barium hydroxide and the like) capable of forming precipitates in cooperation with the acid catalyst to terminate the reaction, and neutralizing the acid and the alkali to generate insoluble salt; and insoluble salt can be directly filtered out, so that an etherified amino resin product which is basically free of salt is obtained. Evaporation desalination is not needed, energy consumption is reduced, and desalination is more thorough. Especially for a water-based amino resin product, part of water can be reserved as a solvent, so that the energy consumption is greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of amino resins, and in particular relates to a method for producing a low-energy-consumption salt-free etherified amino resin. Background Art

[0002] As a downstream product of melamine, etherified amino resin is mainly used as a coating crosslinker. When used with polyester resin, acrylic resin, epoxy resin, epoxy resin, etc., it can give the coating film excellent gloss, color retention, hardness, chemical resistance, water resistance and weather resistance, etc. It can be widely used in industrial coatings such as automobiles, rigid furniture, household appliances and metal pre-coating.

[0003] Etherified amino resin is a multifunctional compound, which is a product obtained by the addition condensation of melamine and aldehydes (mainly formaldehyde) to generate polymethylol melamine containing 3 to 6 hydroxymethyl groups (-CH2OH), and polymethylol melamine is partially or fully etherified with aliphatic monohydric alcohol. The following formula shows a fully methylated amino resin, in which all 6 hydroxymethyl groups react with alcohol to generate hexaalkoxymethyl melamine. In fact, 1 to 6 hydroxymethyl groups can be controlled to react with alcohol, so there is a partially or fully etherified amino resin.

[0004]

[0005] It is an existing technology in the art to synthesize etherified amino resins using hydroxymethyl melamine, pentahydroxymethyl melamine, tetrahydroxymethyl melamine, trihydroxymethyl melamine, etc. For example, CN103739563A discloses a method for synthesizing iminobutyl etherified amino resin using tetrahydroxymethyl melamine as a raw material, CN103709111A discloses a method for synthesizing a mixed high-etherified amino resin using hexahydroxymethyl melamine as a raw material, and CN113061222A discloses a method for producing etherified amino resin using alkyl alcohol and polyhydroxymethyl melamine as raw materials.

[0006] In the prior art, liquid acid such as hydrochloric acid or nitric acid is generally used as an acid catalyst in the production of etherified amino resins. After the reaction is completed, an alkaline solution such as sodium hydroxide, sodium carbonate, sodium bicarbonate, etc. needs to be used to terminate the reaction and adjust the pH value to alkaline. A large amount of salt (such as sodium salt) will be generated in the system after acid-base neutralization. It is necessary to remove excess alcohol and water by vacuum distillation, so that the salt is precipitated in the form of crystals, and then filter to completely remove the salt to obtain a clear and transparent etherified amino resin product. However, this desalination method brings great troubles to enterprises. First, the process of vacuum distillation to precipitate salt is energy-intensive, and second, the salt is not easy to remove cleanly, and the salt-containing etherified amino resin will greatly affect the performance. Summary of the invention

[0007] In view of this, the object of the present invention is to provide a method for producing a low-energy salt-free etherified amino resin to solve the problem of high energy consumption and incomplete desalination in the production process.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] The invention discloses a method for producing a low-energy-consumption salt-free etherified amino resin, comprising the following steps:

[0010] (1) adding polymethylol melamine and monohydric alcohol into a reaction kettle, adding acid to control the pH value of the system to 2-5, and performing etherification reaction;

[0011] (2) After the reaction is completed, a base is added to adjust the pH value of the system to 8-10, and the acid and base react in the system to form a sparingly soluble salt;

[0012] (3) Filtration to remove insoluble salts and impurities in the system;

[0013] (4) removing excess monohydric alcohol and / or water in the system to obtain an etherified amino resin product.

[0014] As a preferred technical solution, in the step (1), the polymethylol melamine is selected from one or more of hexamethylol melamine, pentamethylol melamine, tetramethylol melamine and trimethylol melamine.

[0015] As a preferred technical solution, in step (1), the monohydric alcohol is selected from one or more of methanol, ethanol, butanol and propanol.

[0016] As a preferred technical solution, in the step (1), the molar ratio of polymethylol melamine to monohydric alcohol is 1:8-30.

[0017] As a preferred technical solution, in step (1), the etherification reaction temperature is 40-80°C.

[0018] As a preferred technical solution, in the step (3), diatomaceous earth is added during filtration, and then the filtration is carried out through a filter press.

[0019] As a preferred technical solution, in step (4), the method for removing excess monohydric alcohol and / or water in the system is reduced pressure distillation.

[0020] As a preferred technical solution, the acid is selected from one or more of oxalic acid, citric acid, carbonic acid, and sulfuric acid; the base is selected from one or more of calcium hydroxide and barium hydroxide.

[0021] The beneficial effects of the present invention are:

[0022] The present invention uses an acid (oxalic acid, citric acid, carbonic acid, sulfuric acid, etc.) that can form a precipitate as an acid catalyst for the etherification reaction, and uses a base (calcium hydroxide, barium hydroxide, etc.) that can form a precipitate to terminate the reaction. After acid-base neutralization, a sparingly soluble salt (as shown in Table 1) is generated, and the sparingly soluble salt can be directly filtered out to obtain an etherified amino resin product that is substantially free of salt.

[0023] Table 1 Comparison table of sparingly soluble salts

[0024]

[0025]

[0026] Therefore, the present invention does not need to remove salt by evaporation, reduces energy consumption and removes salt more thoroughly. Especially for water-based amino resin products, the present invention can retain part of the water as a solvent, greatly reducing energy consumption. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0028] Example 1

[0029] (1) adding 3230 kg of methanol and 3088 kg of hexamethylolmelamine into a reaction kettle at a molar ratio of hexamethylolmelamine:methanol=1:10, starting the agitator and steam circulation, raising the temperature to 55° C., and then adding 15 kg of oxalic acid to control the pH value of the system to 2-5, and performing an etherification reaction;

[0030] (2) When the hexahydroxymethylmelamine is completely dissolved, the reaction is completed, and 42.5 kg of barium hydroxide is added to adjust the pH value of the system to 8-10 to terminate the reaction. Oxalic acid and barium hydroxide react to form barium hydroxide;

[0031] (3) Add 10 kg of diatomaceous earth into the reaction kettle, maintain stirring, start the material pump, filter the material through the filter press, and after observing that the material is clear and transparent through the sight glass, pump the material to the post-treatment kettle;

[0032] (4) Open the post-treatment kettle to heat steam, start the agitator, and start the vacuum pump to perform reduced pressure distillation on the material to remove reaction water and excess methanol;

[0033] (5) After the vacuum distillation is completed, 500 kg of isobutanol is added, stirred evenly, and the discharged material is barreled.

[0034] The product of Example 1 is an oily etherified amino resin, so after filtering and desalting, it is still necessary to remove the reaction water and excess methanol. The steam consumption does not change, but the product is clear and transparent without salt precipitation when discharged.

[0035] Example 2

[0036] (1) adding 4740 kg of methanol and 2000 kg of trimethylol melamine to a reaction kettle in a molar ratio of trimethylol melamine:methanol=1:16, starting a stirrer and steam circulation, raising the temperature to 64° C., and then adding 15 kg of oxalic acid to control the pH value of the system to 2-5, and performing an etherification reaction;

[0037] (2) When the trimethylol melamine is completely dissolved, the reaction is complete, and 42.5 kg of calcium hydroxide is added to adjust the pH value of the system to 8-10 to terminate the reaction. Oxalic acid and barium hydroxide react to generate calcium hydroxide;

[0038] (3) Add 10 kg of diatomaceous earth into the reaction kettle, maintain stirring, start the material pump, filter the material through the filter press, and after observing that the material is clear and transparent through the sight glass, pump the material to the post-treatment kettle;

[0039] (4) Open the post-treatment kettle to heat steam, start the agitator, and start the vacuum pump to perform vacuum distillation on the material to remove excess methanol;

[0040] (5) After the vacuum distillation is completed, the material is discharged and loaded into barrels.

[0041] The product of Example 2 is an aqueous etherified amino resin, so part of the water is retained as a solvent after filtering and removing salt, and the steam consumption is reduced by 40%. The product is clear and transparent when discharged without salt precipitation.

[0042] The above embodiments only take the reaction of oxalic acid with calcium hydroxide and barium hydroxide to form insoluble salts as an example. Other acids that can form precipitates (oxalic acid, citric acid, carbonic acid, sulfuric acid, etc.) and bases that can form precipitates with them (calcium hydroxide, barium hydroxide, etc.) can all achieve the purpose of the present invention and are within the scope of protection of the present invention.

[0043] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A method for producing a low-energy salt-free etherified amino resin, characterized in that: The following steps are involved: (1) adding polymethylol melamine and monohydric alcohol into a reaction kettle, adding acid to control the pH value of the system to 2-5, and performing etherification reaction; (2) After the reaction is completed, a base is added to adjust the pH value of the system to 8-10, and the acid and base react in the system to form a sparingly soluble salt; (3) Filtration to remove insoluble salts and impurities in the system; (4) removing excess monohydric alcohol and / or water in the system to obtain an etherified amino resin product.

2. The method for producing a low-energy consumption salt-free etherified amino resin according to claim 1, characterized in that: In the step (1), the polymethylol melamine is selected from one or more of hexamethylol melamine, pentamethylol melamine, tetramethylol melamine and trimethylol melamine.

3. The method for producing a low-energy consumption salt-free etherified amino resin according to claim 1, characterized in that: In the step (1), the monohydric alcohol is selected from one or more of methanol, ethanol, butanol and propanol.

4. The method for producing a low-energy consumption salt-free etherified amino resin according to claim 1, characterized in that: In the step (1), the molar ratio of polymethylol melamine to monohydric alcohol is 1:8-30.

5. The method for producing a low-energy consumption salt-free etherified amino resin according to claim 1, characterized in that: In the step (1), the etherification reaction temperature is 40-80°C.

6. The method for producing a low-energy consumption salt-free etherified amino resin according to claim 1, characterized in that: In the step (3), diatomaceous earth is added during filtration, and then the filtration is performed through a filter press.

7. The method for producing a low-energy consumption salt-free etherified amino resin according to claim 1, characterized in that: In the step (4), the method for removing excess monohydric alcohol and / or water in the system is vacuum distillation.

8. The method for producing a low-energy consumption salt-free etherified amino resin according to any one of claims 1 to 7, characterized in that: The acid is selected from one or more of oxalic acid, citric acid, carbonic acid and sulfuric acid; the alkali is selected from one or more of calcium hydroxide and barium hydroxide.

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