A preparation method of dipropylene glycol monoalkyl ether formal

Abstract

The invention provides a preparation method of dipropylene glycol monoalkyl ether formal, belonging to the technical field of organic synthesis. The invention adopts a homogeneous catalyst to catalyze the acetalization reaction. Compared with a heterogeneous catalyst, the catalyst only participates in the reaction part. The catalyst is subsequently separated by thin film evaporation, which greatly reduces the occurrence of side reactions and reverse reactions in the subsequent sections, and ensures the high conversion rate of the reaction part; the invention adopts a thin film evaporation de-weighting method to remove the homogeneous catalyst, does not adopt a water washing extraction method, generates less waste water, and reduces the loss of the product dissolved in water. The removed catalyst can be reused in the acetalization reaction, which is green and economical, has little environmental pollution, and conforms to the concept of green development; the invention adopts a vacuum distillation de-lighting method to remove unreacted raw materials. The preparation method of the invention is simple, has a fast reaction rate, high catalytic activity, is convenient for post-processing, is suitable for industrial continuous production, and has high product purity, low acidity, and can be stored for a long time.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, and in particular to a method for preparing dipropylene glycol monoalkyl ether formal. Background Art

[0002] Acetal compounds play a very important role in industry. Dipropylene glycol monoalkyl ether formal has a unique glycol ether structure and is widely used in the fields of inks, coatings, plasticizers, and diluents. For example, diethylene glycol methyl ether formal, also known as bis(2-methoxyethoxy)methane, CAS No. 4431-83-8, is a colorless transparent liquid with low odor and a boiling point of 181.3°C. It is easily soluble in water and can be used as a solvent in coatings, inks, adhesives, pesticides and other industries. Di(diethylene glycol butyl ether) formal can be used as a non-reactive plasticizer and a diluent in coatings such as electrophoretic paints.

[0003] The traditional acetalization reaction uses a catalyst such as sulfuric acid, which is highly corrosive to the equipment, difficult to effectively separate, and cannot be recycled. In addition, since the acetalization reaction is a reversible reaction, the catalyst is left in the reaction solution and is prone to reverse reaction and other side reactions during the refining stage. Therefore, in order to facilitate the separation of the catalyst, the prior art often uses a heterogeneous catalyst, which is easy to separate. The disadvantage is that the heterogeneous catalyst is cumbersome to prepare, has a high price, a general yield, and a short lifespan, which makes the cost of industrial production of acetal compounds high.

[0004] Patent CN 110511124A discloses a method for preparing bis(dimethoxyethoxy)methane, which is filtered, neutralized with a catalyst, then extracted with water, and the product is obtained by distillation of the oil phase. This increases the generation of waste water on the one hand, and on the other hand, dipropylene glycol monoalkyl ether formal has good water solubility, and the product loss is large when extracted with water, and the yield is low, about 60-90%. In addition, patent CN107827717A discloses a method for preparing diglycol monoalkyl ether formal, which is prepared by acetal exchange reaction, and the catalyst is recycled, but the product is also refined by washing with water, and there are also problems of large product loss and low yield. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a method for preparing dipropylene glycol monoalkyl ether formal. The preparation method provided by the present invention is green and economical, and the yield of the obtained dipropylene glycol monoalkyl ether formal is high.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The invention provides a method for preparing dipropylene glycol monoalkyl ether formal, comprising the following steps:

[0008] (1) mixing a formaldehyde compound, propylene glycol monoalkyl ether, a homogeneous catalyst and a water-carrying agent to carry out an acetalization reaction to obtain an acetalization reaction liquid;

[0009] (2) subjecting the acetal reaction liquid to thin film evaporation to separate heavy components, and collecting light components evaporated by the thin film;

[0010] The light components of the thin film evaporation are subjected to reduced pressure distillation to separate the light components and obtain a crude product of dipropylene glycol monoalkyl ether formal;

[0011] Alternatively, the acetal reaction liquid is subjected to vacuum distillation to separate the light components, and the obtained vacuum distillate is collected;

[0012] The vacuum distillate is subjected to thin film evaporation to separate heavy components to obtain a crude product of dipropylene glycol monoalkyl ether formal;

[0013] (3) subjecting the crude dipropylene glycol monoalkyl ether formal to vacuum distillation to obtain a pure dipropylene glycol monoalkyl ether formal.

[0014] Preferably, in step (2), the vacuum degree of the thin film evaporation is 0.5-100 kPa and the temperature is 60-200°C.

[0015] Preferably, in step (2), the thin film evaporation separation and recombinant fractionation are:

[0016] During the thin film evaporation, the heavy components are separated and reused in the thin film evaporation until the mass of the heavy components is less than or equal to 5% of the mass of the acetal reaction liquid and does not increase any more, and the thin film evaporation is terminated.

[0017] Preferably, in the step (2), the vacuum distillation is carried out in a lightness removal tower, the vacuum degree of the vacuum distillation is 1 to 100 kPa, the tower top temperature is 60 to 150°C, and the kettle temperature is 90 to 180°C.

[0018] Preferably, in the step (3), the vacuum distillation is carried out in a distillation tower, the vacuum degree of the vacuum distillation is 0.1-30 kPa, the top temperature is 80-220°C, and the kettle temperature is 110-250°C.

[0019] Preferably, in step (1), the homogeneous catalyst is one or more of titanate compounds, sulfates, chlorides, organic acids and organic acid salts;

[0020] The mass of the homogeneous catalyst is 0.02-5% of the total mass of the acetal reaction liquid.

[0021] Preferably, the titanate compound is one or more of tetraisopropyl titanate, tetraethyl titanate and tetrabutyl titanate;

[0022] The sulfate is one or more of sodium bisulfate, potassium bisulfate, ferrous sulfate, ferrous sulfate, zinc sulfate and copper sulfate;

[0023] The chloride salt is one or more of zinc chloride, ferric chloride and tin tetrachloride;

[0024] The organic acid is one or more of p-toluenesulfonic acid, acetic acid and aminosulfonic acid;

[0025] The organic acid salt is one or more of zinc acetate, manganese acetate, chromium acetate, iron acetate, aminosulfonate and ammonium ferric sulfate dodecahydrate.

[0026] Preferably, the formaldehyde compound is one or more of formaldehyde, trioxymethylene and polyformaldehyde;

[0027] The molar ratio of the formaldehyde compound to propylene glycol monoalkyl ether is 1:(2-5).

[0028] Preferably, the water-carrying agent is one or more of petroleum ether, toluene and cyclohexane;

[0029] The mass of the water-carrying agent is 1 to 30% of the total mass of the acetal reaction liquid.

[0030] Preferably, the temperature of the acetalization reaction is 70-170°C.

[0031] The invention provides a method for preparing dipropylene glycol monoalkyl ether formal. According to the method, formaldehyde compounds, propylene glycol monoalkyl ether, a homogeneous catalyst and a water-carrying agent are mixed to carry out acetalization reaction to obtain acetalization reaction liquid; then, the acetalization reaction liquid is subjected to thin film evaporation to remove weight and reduced pressure distillation to remove light, or the acetalization reaction liquid is subjected to reduced pressure distillation to remove light and thin film evaporation to remove weight to obtain a crude dipropylene glycol monoalkyl ether formal; finally, the crude dipropylene glycol monoalkyl ether formal is subjected to reduced pressure rectification to obtain a pure dipropylene glycol monoalkyl ether formal. The preparation method provided by the present invention adopts a homogeneous catalyst to catalyze the acetalization reaction. Compared with a heterogeneous catalyst, it only participates in the reaction part. The catalyst is subsequently separated by thin film evaporation, which greatly reduces the occurrence of side reactions and reverse reactions in the subsequent sections, and ensures the efficient conversion rate of the reaction part; the present invention adopts a thin film evaporation method to remove the homogeneous catalyst, does not adopt a water washing extraction method, produces less waste water, and reduces the loss of the product dissolved in water. The removed catalyst can be reused in the acetalization reaction, which is green and economical, has little environmental pollution, and conforms to the concept of green development; the present invention adopts a vacuum distillation method to remove light, which can remove unreacted raw materials. The preparation method of the present invention is simple, has a fast reaction rate, high catalytic activity, is convenient for post-processing, is suitable for continuous production in industry, and has high product purity, low acidity, and can be stored for a long time. The results of the embodiment show that the yield of dipropylene glycol monoalkyl ether formal obtained by the preparation method of the present invention is 85.6-95.6%. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention is a process flow chart for preparing dipropylene glycol monoalkyl ether formal. DETAILED DESCRIPTION

[0033] The invention provides a method for preparing dipropylene glycol monoalkyl ether formal, comprising the following steps:

[0034] (1) mixing a formaldehyde compound, propylene glycol monoalkyl ether, a homogeneous catalyst and a water-carrying agent to carry out an acetalization reaction to obtain an acetalization reaction liquid;

[0035] (2) subjecting the acetal reaction liquid to thin film evaporation to separate heavy components, and collecting light components evaporated by the thin film;

[0036] The light components of the thin film evaporation are subjected to reduced pressure distillation to separate the light components and obtain a crude product of dipropylene glycol monoalkyl ether formal;

[0037] Alternatively, the acetal reaction liquid is subjected to vacuum distillation to separate the light components, and the obtained vacuum distillate is collected;

[0038] The vacuum distillate is subjected to thin film evaporation to separate heavy components to obtain a crude product of dipropylene glycol monoalkyl ether formal;

[0039] (3) subjecting the crude dipropylene glycol monoalkyl ether formal to vacuum distillation to obtain a pure dipropylene glycol monoalkyl ether formal.

[0040] The present invention mixes a formaldehyde compound, propylene glycol monoalkyl ether, a homogeneous catalyst and a water-carrying agent, performs acetalization reaction, and obtains an acetalization reaction liquid. In the present invention, the formaldehyde compound is preferably one or more of formaldehyde, trioxymethylene and polyformaldehyde. In the present invention, the propylene glycol monoalkyl ether represents propylene glycol monoalkyl ether or ethylene glycol monoalkyl ether.

[0041] In the present invention, the structural formula of the propylene (ethylene) glycol monoalkyl ether is shown in Formula 1:

[0042]

[0043] In formula 1, R1 = C1-4 alkyl, R2 = H or CH3, and n = 1-3.

[0044] In the present invention, the molar ratio of the formaldehyde compound to propylene glycol monoalkyl ether is preferably 1:(2-5), more preferably 1:(3-4).

[0045] In the present invention, the homogeneous catalyst is preferably one or more of titanate compounds, sulfates, chlorides, organic acids and organic acid salts; the titanate compounds are preferably one or more of tetraisopropyl titanate, tetraethyl titanate and tetrabutyl titanate; the sulfate is preferably one or more of sodium hydrogen sulfate, potassium hydrogen sulfate, ferrous sulfate, ferrous sulfate, zinc sulfate and copper sulfate; the chloride is preferably one or more of zinc chloride, ferric chloride and tin tetrachloride; the organic acid is preferably one or more of p-toluenesulfonic acid, acetic acid and aminosulfonic acid; the organic acid salt is preferably one or more of zinc acetate, manganese acetate, chromium acetate, ferrous acetate, aminosulfonate and ammonium ferric sulfate dodecahydrate. In the present invention, the aminosulfonate is preferably one or more of potassium aminosulfonate, sodium aminosulfonate, zinc aminosulfonate and ammonium aminosulfonate.

[0046] In the present invention, the mass of the homogeneous catalyst is preferably 0.02-5% of the total mass of the acetalization reaction solution, more preferably 0.05-3%, further preferably 0.1-2%, and further preferably 0.5-1%.

[0047] In the present invention, the water-carrying agent is preferably one or more of petroleum ether, toluene and cyclohexane; the mass of the water-carrying agent is preferably 1-30% of the total mass of the acetal reaction liquid, more preferably 5-20%, and further preferably 10-15%.

[0048] In the present invention, the mixing method is preferably stirring and mixing; the present invention has no special requirements for the stirring and mixing method, and the stirring and mixing method well known to those skilled in the art can be used.

[0049] In the present invention, the acetalization reaction is preferably carried out in a reactor; in the present invention, the temperature of the acetalization reaction is preferably 70 to 170° C., more preferably 100 to 150° C., and further preferably 120 to 140° C. In the present invention, the acetalization reaction is preferably:

[0050] The mixed solution of formaldehyde compound, propylene glycol monoalkyl ether, homogeneous catalyst and water-carrying agent is heated to boiling, and the boiling reflux state is maintained to separate water. When no more water is generated, the acetal reaction is finished.

[0051] The present invention preferably performs organic matter recovery and wastewater collection treatment on the separated water. The present invention has no special requirements on the methods of organic matter recovery and wastewater collection treatment, and the above operations well known to those skilled in the art can be used.

[0052] In the present invention, the reaction formula of the acetal reaction is shown in Formula 2:

[0053]

[0054] In formula 2, R1 = C1-4 alkyl, R2 = H or CH3, and n = 1-3.

[0055] After obtaining the acetal reaction liquid, the present invention performs thin film evaporation on the acetal reaction liquid to separate the heavy components and collect the light components of the thin film evaporation. In the present invention, the thin film evaporation is preferably performed in a thin film evaporator; in the present invention, the feeding method of the thin film evaporation is preferably continuous feeding. In the present invention, the vacuum degree of the thin film evaporation is preferably 0.5 to 100 kPa, more preferably 1 to 80 kPa, further preferably 10 to 60 kPa, and further preferably 20 to 50 kPa.

[0056] In the present invention, the temperature of the thin film evaporation is preferably 60 to 200°C, more preferably 80 to 150°C, and further preferably 100 to 120°C.

[0057] In the present invention, the thin film evaporation separation to remove heavy components is preferably:

[0058] During the thin film evaporation, the heavy components are separated and reused in the thin film evaporation until the mass of the heavy components is less than or equal to 5% of the mass of the acetal reaction liquid and does not increase any more, and the thin film evaporation is terminated.

[0059] The present invention preferably separates the heavy component from the residual liquid outlet of the thin film evaporator; in the present invention, the heavy component is reused in the thin film evaporation for preferably 2 to 5 times, more preferably 3 to 4 times.

[0060] In the present invention, the final heavy component is in a viscous semi-solid state, and its components are mainly homogeneous catalysts, which can be reused in acetalization reaction.

[0061] The present invention preferably collects the light components evaporated from the thin film from the light component outlet of the thin film evaporator.

[0062] After obtaining the light components of the thin film evaporation, the present invention performs reduced pressure distillation on the light components of the thin film evaporation to separate the light components and obtain a crude product of dipropylene glycol monoalkyl ether formal. In the present invention, the reduced pressure distillation is preferably carried out in a light removal tower, and the vacuum degree of the reduced pressure distillation is preferably 1 to 100 kPa, more preferably 5 to 80 kPa, and further preferably 10 to 50 kPa. In the present invention, the tower top temperature of the reduced pressure distillation is preferably 60 to 150°C, more preferably 80 to 120°C; the kettle temperature is preferably 90 to 180°C, more preferably 120 to 150°C.

[0063] In the present invention, after the light component is separated, the obtained light component is preferably used as a raw material for acetalization reaction. In the present invention, when the light component is used as a raw material for acetalization reaction, the present invention preferably performs chromatographic analysis on the light component to obtain the contents of formaldehyde, propylene (ethylene) glycol monoalkyl ether, and propylene (ethylene) glycol monoalkyl ether formal in the light component, and calculates the amount of the light component in the raw material based on the obtained contents.

[0064] In the present invention, the crude product of dipropylene glycol monoalkyl ether formal is preferably collected in the bottom of the lightness removal tower.

[0065] Alternatively, the present invention performs vacuum distillation on the acetal reaction liquid to separate the light components, and collects the vacuum distillate obtained;

[0066] The reduced pressure distillate is subjected to thin film evaporation to separate heavy components to obtain a crude product of dipropylene glycol monoalkyl ether formal.

[0067] In the present invention, the method of vacuum distillation to separate the light components and thin film evaporation to separate the heavy components is the same as above, the only difference is the order, which will not be repeated here.

[0068] After obtaining the crude product of dipropylene glycol monoalkyl ether formal, the present invention performs vacuum distillation on the crude product of dipropylene glycol monoalkyl ether formal to obtain pure dipropylene glycol monoalkyl ether formal. In the present invention, the vacuum distillation is preferably carried out in a distillation tower, and the vacuum degree of the vacuum distillation is preferably 0.1 to 30 kPa, more preferably 0.5 to 20 kPa, and further preferably 1 to 10 kPa; the top temperature is preferably 80 to 220°C, more preferably 100 to 200°C, and more preferably 140 to 180°C; the kettle temperature is preferably 110 to 250°C, and more preferably 150 to 200°C.

[0069] The present invention preferably collects light components from the top of the distillation tower, and the obtained light components are preferably used as raw materials for acetalization reaction. The present invention preferably collects pure dipropylene glycol monoalkyl ether formal from the discharge port of the distillation tower.

[0070] The preparation method of the dipropylene glycol monoalkyl ether formal provided by the present invention is described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0071] The raw materials trioxymethylene, polyoxymethylene and propylene glycol monoalkyl ether used in the present invention are all of industrial grade.

[0072] The concentration of each substance in the final product was quantitatively analyzed by gas chromatograph area normalization method. A GC9890 gas chromatograph was used, and the detection conditions were as follows: SE-54 column: 30m×0.32mm×0.4μm, vaporization temperature 260℃, FID detector temperature 250℃, column temperature 130℃, retention time 2min, program temperature rise 15℃ / min to 260℃, retention time 10min.

[0073] Example 1

[0074] Add 120g of paraformaldehyde, 608g of ethylene glycol monomethyl ether, 5g of catalyst tetrabutyl titanate, and 200g of water-carrying agent cyclohexane into a 2000mL three-necked flask, and heat to cyclohexane reflux with water until no more water is produced. The reaction solution is evaporated by a thin film evaporator, the temperature of the thin film evaporator is 100°C, the vacuum degree is 3kPa, the heavy phase residual liquid of the thin film evaporator is returned to the thin film evaporator for distillation, and the cycle is repeated twice until the heavy component is viscous semi-solid, the light phase of the thin film evaporator is subjected to vacuum distillation under the conditions of vacuum 100KPa, top temperature 120°C, and kettle temperature 125°C, the light component ethylene glycol methyl ether is extracted from the tower top for reuse, and the obtained tower bottom liquid is subjected to vacuum distillation under the conditions of vacuum degree 300Pa, top temperature 85°C, and kettle temperature 125°C, and the product diethylene glycol methyl ether formal is extracted, the product is 592.2g, the content is 99.71%, the acidity is 0.02%, and the comprehensive yield is 90.3%.

[0075] The obtained product was characterized and was consistent with the commercially available diethylene glycol methyl ether formal standard product.

[0076] Example 2

[0077] Add 120g of paraformaldehyde, 608g of ethylene glycol monomethyl ether, 5g of p-toluenesulfonic acid, and 200g of water-carrying cyclohexane into a 2000mL three-necked flask, and heat to cyclohexane reflux with water until no more water is produced. The reaction solution is evaporated by a thin film evaporator, the temperature of the thin film evaporator is 110°C, the vacuum degree is 10kPa, the heavy phase residual liquid of the thin film evaporator is returned to the thin film evaporator for distillation, and the cycle is repeated 3 times until the heavy component is viscous semi-solid, the light phase of the thin film evaporator is subjected to reduced pressure distillation under the conditions of vacuum 80KPa, top temperature 100°C, and kettle temperature 108°C, the light component ethylene glycol methyl ether is extracted from the tower top for reuse, and the obtained tower bottom liquid is extracted under the conditions of vacuum degree 300Pa, top temperature 85°C, and kettle temperature 125°C, the product diethylene glycol methyl ether formal is extracted, the product is 606g, the content is 99.71%, the acidity is 0.02%, and the comprehensive yield is 92.4%.

[0078] Example 3

[0079] Add 120g of paraformaldehyde, 720g of ethylene glycol monomethyl ether, 10g of p-toluenesulfonic acid, and 200g of water-carrying cyclohexane into a 2000mL three-necked flask, and heat to cyclohexane reflux with water until no more water is produced. The reaction solution is evaporated by a thin film evaporator, the temperature of the thin film evaporator is 100°C, the vacuum degree is 3kPa, the heavy phase residual liquid of the thin film evaporator is returned to the thin film evaporator for distillation, and the cycle is repeated 3 times until the heavy component is viscous semi-solid, the light phase of the thin film evaporator is extracted under vacuum 63KPa, top temperature 90°C, and the kettle temperature is 100°C. The light component ethylene glycol methyl ether is extracted from the tower top for reuse, and the obtained tower bottom liquid is extracted under vacuum 1kPa, top temperature 95°C, and kettle temperature 128°C. The product diethylene glycol methyl ether formal is extracted, the product is 621g, the content is 99.75%, the acidity is 0.02%, and the comprehensive yield is 94.7%.

[0080] Example 4

[0081] In 2000mL three-necked flask, add paraformaldehyde 120g, ethylene glycol monomethyl ether 720g, p-toluenesulfonic acid 1g, thin film evaporator residual liquid 30g in embodiment 3, water-carrying agent cyclohexane 200g, be warming up to cyclohexane reflux with water, to no longer having water to produce.Reaction solution evaporates by thin film evaporator, thin film evaporator temperature 120 ℃, vacuum 1.5kPa, thin film evaporator heavy phase residual liquid returns thin film evaporator distillation, circulates 3 times to heavy component and is viscous semi-solid, thin film evaporator light phase carries out underpressure distillation under vacuum degree 63kPa, top temperature 90 ℃, still temperature 100 ℃ condition, tower top extraction light component ethylene glycol methyl ether reuse, gained tower bottom liquid under vacuum degree 300Pa, top temperature 85 ℃, still temperature 125 ℃ condition, extraction product diethylene glycol methyl ether formal, product 645g, content 99.68%, acidity 0.03%, comprehensive yield 98.4%.

[0082] Example 5

[0083] Add 120g of paraformaldehyde, 720g of propylene glycol monomethyl ether, 5g of tetrabutyl titanate catalyst, and 200g of cyclohexane with water in a 2000mL three-necked flask, and heat to cyclohexane reflux with water until no more water is produced. The reaction solution is evaporated by a thin film evaporator, the temperature of the thin film evaporator is 185°C, the vacuum degree is 100kPa, the heavy phase residual liquid of the thin film evaporator is returned to the thin film evaporator for distillation, and the cycle is repeated twice until the heavy component is viscous semi-solid, the light phase of the thin film evaporator is subjected to reduced pressure distillation under the conditions of vacuum 63KPa, top temperature 93°C, and kettle temperature 105°C, the light component propylene glycol methyl ether is extracted from the tower top for reuse, and the obtained tower bottom liquid is extracted under the conditions of vacuum degree 200Pa, top temperature 130°C, and kettle temperature 145°C, the product dipropylene glycol methyl ether formal is extracted, the product is 695g, the content is 99.81%, the acidity is 0.01%, and the comprehensive yield is 90.5%.

[0084] Example 6

[0085] Add 120g of paraformaldehyde, 720g of propylene glycol monomethyl ether, 5g of p-toluenesulfonic acid as catalyst, and 200g of cyclohexane as water-carrying agent into a 2000mL three-necked flask, and heat to cyclohexane reflux with water until no more water is produced. The reaction solution is evaporated by a thin film evaporator, the temperature of the thin film evaporator is 100°C, the vacuum degree is 3kPa, the heavy phase residual liquid of the thin film evaporator is returned to the thin film evaporator for distillation, and the cycle is repeated 4 times until the heavy component is viscous semi-solid, the light phase of the thin film evaporator is subjected to reduced pressure distillation under the conditions of vacuum 100KPa, top temperature 122°C, and kettle temperature 130°C, the light component propylene glycol methyl ether is extracted from the tower top for reuse, and the obtained tower bottom liquid is extracted under the conditions of vacuum degree 200Pa, top temperature 130°C, and kettle temperature 145°C, the product dipropylene glycol methyl ether formal is extracted, the product is 702.7g, the content is 99.73%, the acidity is 0.02%, and the comprehensive yield is 91.5%.

[0086] Example 7

[0087] Add 120g of paraformaldehyde, 840g of propylene glycol monomethyl ether, 10g of p-toluenesulfonic acid catalyst, and 200g of cyclohexane with water in a 2000mL three-necked flask, and heat to cyclohexane reflux with water until no more water is produced. The reaction solution is evaporated by a thin film evaporator, the temperature of the thin film evaporator is 120°C, the vacuum degree is 3kPa, the heavy phase residual liquid of the thin film evaporator is returned to the thin film evaporator for distillation, and the cycle is repeated 3 times until the heavy component is viscous semi-solid, the light phase of the thin film evaporator is subjected to reduced pressure distillation under the conditions of vacuum 3KPa, top temperature 70°C, and kettle temperature 90°C, the light component propylene glycol methyl ether is extracted from the tower top for reuse, and the obtained tower bottom liquid is extracted under the conditions of vacuum degree 2kPa, top temperature 155°C, and kettle temperature 180°C, the product dipropylene glycol methyl ether formal is extracted, the product is 718g, the content is 99.77%, the acidity is 0.01%, and the comprehensive yield is 93.5%.

[0088] Example 8

[0089] In 2000mL three-necked flask, add paraformaldehyde 120g, propylene glycol monomethyl ether 840g, thin film evaporator residual liquid 36g in embodiment 7, water-carrying agent cyclohexane 200g, warm up to cyclohexane reflux with water, until no more water is produced.Reaction solution is evaporated by thin film evaporator, thin film evaporator temperature 140 ℃, vacuum 5kPa, thin film evaporator heavy phase residual liquid returns thin film evaporator distillation, circulates 3 times to heavy component in sticky semi-solid state, thin film evaporator light phase is under vacuum 3kPa, top temperature 70 ℃, still temperature 90 ℃ condition, carries out underpressure distillation, tower top extraction light component propylene glycol monomethyl ether is reused, gained tower bottom liquid is under vacuum 200Pa, top temperature 130 ℃, still temperature 150 ℃ condition, extraction product dipropylene glycol monomethyl ether formal, product 734.2g, content 99.72%, acidity 0.01%, comprehensive yield 95.6%.

[0090] Example 9

[0091] Add 120g of paraformaldehyde, 608g of ethylene glycol monomethyl ether, 5g of catalyst tetrabutyl titanate, and 200g of water-carrying agent cyclohexane into a 2000mL three-necked flask, and heat to cyclohexane reflux with water until no more water is produced. The reaction solution is subjected to reduced pressure distillation under the conditions of vacuum degree 100kPa, top temperature 120°C, and kettle temperature 125°C. The light component ethylene glycol methyl ether is extracted from the tower top for reuse, and the tower bottom liquid is evaporated by a thin film evaporator, the temperature of the thin film evaporator is 120°C, the vacuum is 3kPa, and the heavy phase residual liquid of the thin film evaporator is returned to the thin film evaporator for distillation, and the cycle is repeated 2 times until the heavy component is viscous semi-solid. The light phase extraction of the thin film evaporator is subjected to reduced pressure distillation under the conditions of vacuum degree 300Pa, top temperature 85°C, and kettle temperature 125°C, and the product diethylene glycol methyl ether formal is extracted, the product is 595.5g, the content is 99.76%, the acidity is 0.02%, and the comprehensive yield is 90.8%.

[0092] Example 10

[0093] Add 120g of paraformaldehyde, 608g of ethylene glycol monomethyl ether, 5g of p-toluenesulfonic acid, and 200g of water-carrying cyclohexane into a 2000mL three-necked flask, and heat to cyclohexane reflux with water until no more water is produced. The reaction solution is subjected to reduced pressure distillation under the conditions of vacuum degree 80kPa, top temperature 100°C, and kettle temperature 108°C. The light component ethylene glycol methyl ether is extracted from the tower top for reuse. The tower bottom liquid is evaporated by a thin film evaporator, the temperature of the thin film evaporator is 130°C, the vacuum is 10kPa, and the heavy phase residual liquid of the thin film evaporator is returned to the thin film evaporator for distillation. The cycle is repeated 3 times until the heavy component is viscous semi-solid. The light phase of the thin film evaporator is extracted under the conditions of vacuum degree 1kPa, top temperature 96°C, and kettle temperature 140°C. The product diethylene glycol methyl ether formal is extracted, the product is 599g, the content is 99.78%, the acidity is 0.02%, and the comprehensive yield is 91.3%.

[0094] Embodiment 11

[0095] Add 120g of paraformaldehyde, 720g of propylene glycol monomethyl ether, 5g of tetrabutyl titanate catalyst, and 200g of cyclohexane with water in a 2000mL three-necked flask, and heat to cyclohexane reflux with water until no more water is produced. The reaction solution is subjected to reduced pressure distillation under the conditions of vacuum degree 63kPa, top temperature 93°C, and kettle temperature 105°C. The light component propylene glycol methyl ether is extracted from the top of the tower for reuse. The bottom liquid of the tower is evaporated by a thin film evaporator, the temperature of the thin film evaporator is 185°C, the vacuum is 100kPa, and the heavy phase residual liquid of the thin film evaporator is returned to the thin film evaporator for distillation, and the cycle is repeated twice until the heavy component is viscous semi-solid. The light phase of the thin film evaporator is extracted under the conditions of vacuum degree 200Pa, top temperature 130°C, and kettle temperature 145°C. The product dipropylene glycol methyl ether formal is 703g, the content is 99.78%, the acidity is 0.01%, and the comprehensive yield is 91.5%.

[0096] Example 12

[0097] Add 120g of paraformaldehyde, 720g of propylene glycol monomethyl ether, 5g of p-toluenesulfonic acid as catalyst, and 200g of cyclohexane as water-carrying agent into a 2000mL three-necked flask, and heat to cyclohexane reflux with water until no more water is produced. The light phase of the reaction liquid is extracted and distilled under reduced pressure under the conditions of vacuum degree 100kPa, top temperature 122℃, and kettle temperature 130℃. The light component propylene glycol methyl ether is extracted from the top of the tower for reuse. The bottom liquid of the tower is evaporated by a thin film evaporator, the temperature of the thin film evaporator is 120℃, and the vacuum is 3kPa. The heavy phase residual liquid of the thin film evaporator is returned to the thin film evaporator for distillation, and the cycle is repeated 4 times until the heavy component is viscous semi-solid. The light phase of the thin film evaporator is extracted under the conditions of vacuum degree 200Pa, top temperature 130℃, and kettle temperature 145℃, and the product dipropylene glycol methyl ether formal is extracted, the product is 699.5g, the content is 99.76%, the acidity is 0.02%, and the comprehensive yield is 91.0%.

[0098] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing dipropylene glycol monoalkyl ether formal, comprising the following steps: (1) mixing a formaldehyde compound, propylene glycol monoalkyl ether, a homogeneous catalyst and a water-carrying agent to carry out an acetalization reaction to obtain an acetalization reaction liquid; (2) subjecting the acetal reaction liquid to thin film evaporation to separate heavy components, and collecting light components evaporated by the thin film; The light components of the thin film evaporation are subjected to reduced pressure distillation to separate the light components and obtain a crude product of dipropylene glycol monoalkyl ether formal; Alternatively, the acetal reaction liquid is subjected to vacuum distillation to separate the light components, and the obtained vacuum distillate is collected; The vacuum distillate is subjected to thin film evaporation to separate heavy components to obtain a crude product of dipropylene glycol monoalkyl ether formal; (3) subjecting the crude dipropylene glycol monoalkyl ether formal to vacuum distillation to obtain a pure dipropylene glycol monoalkyl ether formal; The vacuum degree of the thin film evaporation is 0.5-100 kPa and the temperature is 60-200° C.; The vacuum distillation is carried out in a light removal tower, the vacuum degree of the vacuum distillation is 1-100 kPa, the tower top temperature is 60-150° C., and the kettle temperature is 90-180° C.; The structural formula of the propylene (ethylene) glycol monoalkyl ether is shown in Formula 1: In formula 1, R1 = C1-4 alkyl, R2 = H or CH3, n = 1-3; The formaldehyde compound is one or more of formaldehyde, trioxymethylene and polyformaldehyde; The homogeneous catalyst is one or more of titanate compounds, sulfates, chlorides, organic acids and organic acid salts; the titanate compounds are one or more of tetraisopropyl titanate, tetraethyl titanate and tetrabutyl titanate; the sulfates are one or more of sodium hydrogen sulfate, potassium hydrogen sulfate, ferrous sulfate, ferrous sulfate, zinc sulfate and copper sulfate; the chlorides are one or more of zinc chloride, ferric chloride and tin tetrachloride; the organic acids are one or more of p-toluenesulfonic acid and acetic acid; the organic acid salts are one or more of zinc acetate, manganese acetate, chromium acetate and ferric acetate; The mass of the homogeneous catalyst is 0.02-5% of the total mass of the acetal reaction liquid.

2. The preparation method according to claim 1, characterized in that: The thin film evaporation separation in step (2) is followed by recombinant components: During the thin film evaporation, the heavy components are separated and reused in the thin film evaporation until the mass of the heavy components is less than or equal to 5% of the mass of the acetal reaction liquid and does not increase any more, and the thin film evaporation is terminated.

3. The preparation method according to claim 1, characterized in that: In the step (3), the vacuum distillation is carried out in a distillation tower, the vacuum degree of the vacuum distillation is 0.1-30 kPa, the top temperature is 80-220°C, and the kettle temperature is 110-250°C.

4. The preparation method according to claim 1, characterized in that: The molar ratio of the formaldehyde compound to propylene glycol monoalkyl ether is 1:(2-5).

5. The preparation method according to claim 1 or 4, characterized in that: The water-carrying agent is one or more of petroleum ether, toluene and cyclohexane; The mass of the water-carrying agent is 1 to 30% of the total mass of the acetal reaction liquid.

6. The preparation method according to claim 1, characterized in that: The temperature of the acetalization reaction is 70-170°C.

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