High-selectivity continuous synthesis method of dipentaerythritol

Abstract

The invention relates to a high-selectivity continuous synthesis method of dipentaerythritol. According to the invention, pentaerythritol is introduced, so that more dipentaerythritol intermediates can be effectively generated at the initial stage of reaction, and the selectivity of dipentaerythritol is greatly improved. The reaction product solution can be separated through a conventional separation method, the separation cost is low, the obtained crude product pentaerythritol can serve as an additive to participate in the reaction again and be recycled, and high selectivity of dipentaerythritol is guaranteed. Besides, a continuous reactor is used for condensation reaction under the high-temperature condition, compared with a conventional method, the reaction rate is higher, the reaction time can be shortened to be within 1 hour, the selectivity of dipentaerythritol is improved, and the yield even reaches 30% or above.

Description

Technical Field

[0001] The invention belongs to the technical field of chemistry and chemical engineering, and particularly relates to a high-selectivity continuous synthesis method of dipentaerythritol. Background Art

[0002] Pentaerythritol and dipentaerythritol are polyol products with excellent performance and are important fine chemical intermediates. Among them, pentaerythritol contains 4 hydroxyl groups in the molecule, which can form a polyester structure and is widely used in polymer materials such as alkyd resins and polyurethanes. Dipentaerythritol contains 6 hydroxyl groups in the molecule and is widely used in light-cured coatings, advanced lubricants, flame retardant materials and other fields.

[0003] In industry, formaldehyde, acetaldehyde and sodium hydroxide are used to obtain mono-, di- and tripentaerythritol and sodium formate through condensation reaction, and pentaerythritol and dipentaerythritol products are obtained after evaporation, crystallization, filtration and drying. At present, there is no other method for directly synthesizing dipentaerythritol in industry. The existing process mainly adopts a kettle process of adding reactants under low temperature conditions, which has a slow reaction rate and a long reaction time. In addition, the selectivity of dipentaerythritol in the synthesis process is low, which cannot meet its huge market demand.

[0004] Patent CN 112771014 A discloses a production method for increasing the yield of dipentaerythritol, based on calcium hydroxide as a reaction base, reducing the reaction ratio of formaldehyde to acetaldehyde, adding a formaldehyde polysaccharide inhibitor, and using a method of continuously metering and adding part of the formaldehyde to reduce the ratio of formaldehyde to acetaldehyde during the reaction. The yield of dipentaerythritol obtained by this method is 8% relative to acetaldehyde, which is slightly higher than that of conventional methods, but it is obvious that such an increase is still difficult to meet the demand.

[0005] Patent CN 115231990 B discloses a method for preparing high-purity dipentaerythritol, which adopts a medium-temperature high-formaldehyde ratio tubular reaction, uses extraction and adsorption to remove impurities, and separates and recrystallizes to purify high-purity dipentaerythritol through a high-efficiency settler. The reaction temperature of this method is 40-60°C, the reaction time is still relatively long, and the reaction time and space yield is low. This method is also mainly an innovation in the downstream separation and purification method, and the innovation in the reaction is still obviously insufficient.

[0006] Patent CN 102807477 A discloses a method for synthesizing dipentaerythritol by using monopentaerythritol as raw material through three-step continuous reactions of esterification, intermolecular condensation and transesterification of pentaerythritol. Although the yield of dipentaerythritol is high, 10-30% of tripentaerythritol is produced as a byproduct. Since tripentaerythritol is a very fine, sticky and difficult to separate polyol, the separation and purification cost is high. In addition, the method has complicated reaction steps, long reaction time and low efficiency. The reaction temperature of the intermolecular condensation step is high, and the equipment cost and safety requirements are high.

[0007] In summary, the conventional methods usually have a reaction time of more than 1 hour, a yield of dipentaerythritol of less than 10%, or the reaction steps are complicated and the by-products are difficult to separate, which cannot meet the market demand for dipentaerythritol products. Therefore, it is very necessary to invent a production process for dipentaerythritol with high selectivity and which can be separated using conventional separation methods. Summary of the invention

[0008] Problem that the invention aims to solve

[0009] In view of the problems existing in the current production method of dipentaerythritol, such as long reaction time, more by-products, low dipentaerythritol yield and selectivity, and difficulty in separation and purification, it is necessary to provide a dipentaerythritol synthesis method which can shorten the reaction time, has higher dipentaerythritol yield and selectivity, has fewer by-products and is easy to separate.

[0010] Solutions for solving problems

[0011] The present invention provides a high-selectivity continuous synthesis method of dipentaerythritol, which comprises the following steps:

[0012] (1) preparing a mixed aldehyde solution A, a pentaerythritol aqueous solution B and a sodium hydroxide aqueous solution C respectively;

[0013] Wherein, the mixed aldehyde solution A is obtained by mixing a formaldehyde aqueous solution with acetaldehyde;

[0014] (2) respectively conveying the mixed aldehyde solution A, the pentaerythritol aqueous solution B and the sodium hydroxide aqueous solution C to a preheating pipe section for preheating;

[0015] (3) mixing the mixed aldehyde solution A with the pentaerythritol aqueous solution B, and then mixing with the sodium hydroxide aqueous solution C, thereby performing a continuous condensation reaction to obtain a reaction product solution D;

[0016] (4) Separating the reaction product solution D to obtain pentaerythritol and dipentaerythritol.

[0017] According to the method described above, in step (1), the molar ratio of formaldehyde to acetaldehyde in the mixed aldehyde solution A is 4:1 to 15:1.

[0018] According to the above method, in step (1), the mass fraction of the pentaerythritol aqueous solution B is 1 to 10%.

[0019] According to the above method, in step (1), the mass fraction of the sodium hydroxide aqueous solution C is 10-30%.

[0020] According to the method described above, in step (2), the preheating temperature is 40-130°C.

[0021] According to the method described above, in step (3), the molar ratio of acetaldehyde in the mixed aldehyde solution A to pentaerythritol in the pentaerythritol aqueous solution B is 1:0.5 to 1:10.

[0022] According to the method described above, in step (3), the molar ratio of acetaldehyde in the mixed aldehyde solution A to sodium hydroxide in the sodium hydroxide aqueous solution C is 1:1 to 1:3.

[0023] According to the method described above, in step (3), the temperature of the condensation reaction is 40 to 130° C.; and / or,

[0024] The condensation reaction time is 5-60 minutes.

[0025] According to the method described above, it also includes the following steps: (5) recycling the pentaerythritol obtained in step (4) for the preparation of the pentaerythritol aqueous solution B in step (1).

[0026] According to the method described above, in step (4), the separation treatment includes neutralization to weak acidity, formaldehyde stripping and fractional crystallization steps.

[0027] Effects of the Invention

[0028] (1) In the present invention, due to the introduction of pentaerythritol, more dipentaerythritol intermediates can be effectively generated in the early stage of the reaction, greatly improving the selectivity of dipentaerythritol; the crude pentaerythritol obtained after the reaction product solution is separated and treated can be used as an additive to participate in the reaction again and be recycled, thereby ensuring the high selectivity of dipentaerythritol.

[0029] (2) The present invention uses a continuous reactor to carry out the condensation reaction under high temperature conditions. Compared with the conventional method, the reaction rate is faster and the reaction time can be shortened to less than 1 hour. The selectivity of dipentaerythritol is improved and the yield can even reach more than 30%.

[0030] (3) The reaction product solution of the present invention can be separated by conventional separation methods, and the separation cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a process flow chart of the present invention.

[0032] Figure 2 It is a diagram of the reaction device of the present invention.

[0033] Description of Reference Numerals

[0034] 1-mixed aldehyde solution A storage bottle; 2-pentaerythritol aqueous solution B storage bottle; 3-sodium hydroxide aqueous solution C storage bottle; 4-preheating pipe section; 5-mixer; 5'-mixer; 6-reactor; 7-reaction product solution D storage bottle. DETAILED DESCRIPTION

[0035] Various exemplary embodiments, features and aspects of the present invention will be described in detail below. The word "exemplary" used here means "used as an example, embodiment or illustrative". Any embodiment described here as "exemplary" is not necessarily interpreted as being superior or better than other embodiments.

[0036] In addition, in order to better illustrate the present invention, numerous specific details are provided in the following specific embodiments. It should be understood by those skilled in the art that the present invention can be implemented without certain specific details. In other examples, methods, means, equipment and steps well known to those skilled in the art are not described in detail in order to highlight the subject matter of the present invention.

[0037] Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values ​​and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0038] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0039] In this specification, the references to "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0040] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints numerical values ​​A and B.

[0041] The present invention provides a highly selective synthesis method of dipentaerythritol, which is characterized by comprising the following steps:

[0042] (1) preparing a mixed aldehyde solution A, a pentaerythritol aqueous solution B and a sodium hydroxide aqueous solution C respectively;

[0043] Wherein, the mixed aldehyde solution A is obtained by mixing a formaldehyde aqueous solution with acetaldehyde;

[0044] (2) respectively conveying the mixed aldehyde solution A, the pentaerythritol aqueous solution B and the sodium hydroxide aqueous solution C to a preheating pipe section for preheating;

[0045] (3) mixing the mixed aldehyde solution A with the pentaerythritol aqueous solution B, and then mixing with the sodium hydroxide aqueous solution C, thereby performing a continuous condensation reaction to obtain a reaction product solution D;

[0046] (4) separating the reaction product solution D to obtain pentaerythritol and dipentaerythritol;

[0047] Preferably, it also includes the following steps:

[0048] (5) The pentaerythritol obtained in step (4) is recycled for the preparation of the pentaerythritol aqueous solution B in step (1).

[0049] The following combination Figure 1 and Figure 2 Each step is explained in detail.

[0050] Step (1)

[0051] First, formaldehyde aqueous solution and liquid acetaldehyde are mixed in proportion to form a mixed aldehyde solution A; pentaerythritol is prepared with water to form a pentaerythritol aqueous solution B; sodium hydroxide is prepared with water to form a sodium hydroxide aqueous solution C; and the following are added respectively: Figure 2 The storage bottles 1, 2 and 3 are shown for storage.

[0052] In the present invention, the mass fraction of the formaldehyde aqueous solution is 20-50%, for example, 25%, 30%, 35%, 37.5%, 40%, 45%, etc.

[0053] In some specific embodiments of the present invention, the mass fraction of the formaldehyde aqueous solution is 37.5%.

[0054] In the present invention, the molar ratio of formaldehyde to acetaldehyde in the mixed aldehyde solution A is 4:1 to 15:1, for example, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, etc.

[0055] In the present invention, the mass fraction of the pentaerythritol aqueous solution B is 1-10%, for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, etc.

[0056] In the present invention, the mass fraction of the sodium hydroxide aqueous solution C is 10% to 30%, for example, 12%, 15%, 18%, 20%, 22%, 24%, 25%, 28%, etc.

[0057] Step (2)

[0058] like Figure 2 As shown, the mixed aldehyde solution A in the storage bottle 1, the pentaerythritol aqueous solution B in the storage bottle 2 and the sodium hydroxide aqueous solution C in the storage bottle 3 are respectively transported to the preheating pipe section, and preheated in the preheating pipe section 4 to reach the set temperature.

[0059] In the present invention, the preheating temperature is 40 to 130°C, for example, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, etc.

[0060] Step (3)

[0061] like Figure 1 and Figure 2 As shown, the mixed aldehyde solution A and the pentaerythritol aqueous solution B are first mixed uniformly in a mixer 5, and then further mixed rapidly with the sodium hydroxide aqueous solution C in a mixer 5', and then a continuous condensation reaction is carried out in a reactor 6 to obtain a reaction product solution D, and the reaction product solution D is transferred to a storage bottle 7 for storage.

[0062] In the present invention, the molar ratio of acetaldehyde in the mixed aldehyde solution A to pentaerythritol in the pentaerythritol aqueous solution B is 1:0.5 to 1:10, for example, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, etc.

[0063] In the present invention, the molar ratio of acetaldehyde in the mixed aldehyde solution A to sodium hydroxide in the sodium hydroxide aqueous solution C is 1:1 to 1:3, for example, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.8, 1:2.0, 1:2.2, 1:2.4, 1:2.5, 1:2.6, 1:2.8, etc.

[0064] In the present invention, the temperature of the condensation reaction is 40 to 130°C, for example, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, etc.

[0065] In the present invention, the condensation reaction time is 5-60 minutes, for example, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, etc.

[0066] In the present invention, the reactor 6 is a continuous reactor, including but not limited to a continuous tank reactor (including a multi-stage stirred tank), a continuous tubular reactor, a microreactor, and the like.

[0067] The method of the present invention can be used Figure 2 The reaction system shown implements, but is not limited to Figure 2 The system shown.

[0068] Step (4)

[0069] like Figure 1 As shown, after the reaction, the reaction product solution D is subjected to conventional separation treatment to obtain pentaerythritol and dipentaerythritol.

[0070] In the present invention, the conventional separation treatment includes neutralization to weak acidity, formaldehyde stripping and fractional crystallization steps.

[0071] In the present invention, weak acidity refers to a pH value of 5.0-6.5, for example, 5.5, 6.0, etc.

[0072] In some embodiments of the present invention, formic acid is used to adjust the pH to 6.0.

[0073] In some specific embodiments of the present invention, the reaction product solution D is neutralized to weak acidity, then sent to a multiple-effect evaporation system to remove formaldehyde, and then concentrated and fractional crystallized. The concentrated solution can also be called mother liquor. The steps of fractional crystallization include:

[0074] S1: cooling the mother liquor for crystallization, centrifugation, filtering and drying to obtain dipentaerythritol;

[0075] S2: cooling and crystallizing the mother liquor, centrifuging, filtering and drying to obtain pentaerythritol.

[0076] In the present invention, in step S1, the temperature of cooling crystallization is 35-45°C, for example, 38°C, 40°C, 42°C, 44°C, etc.

[0077] In the present invention, in step S1, the drying temperature is 60-90°C, for example, 65°C, 70°C, 75°C, 80°C, 85°C, etc.

[0078] In the present invention, in step S2, the temperature of cooling crystallization is 15-25°C, for example, 18°C, 20°C, 22°C, 24°C, etc.

[0079] In the present invention, in step S2, the drying temperature is 60-90°C, for example, 65°C, 70°C, 75°C, 80°C, 85°C, etc.

[0080] Step (5)

[0081] like Figure 1 As shown, the obtained pentaerythritol product is recycled for the preparation of the pentaerythritol aqueous solution B in step (1).

[0082] Example

[0083] The embodiments of the present invention will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0084] Example 1

[0085] (1) 44.05 g of liquid acetaldehyde was added to 320.32 g of a 37.5% formaldehyde aqueous solution to obtain a mixed aldehyde solution A having a molar ratio of formaldehyde to acetaldehyde of 4:1, and the solution was added to storage bottle 1. 136.15 g of pentaerythritol was prepared with deionized water to obtain a 5% pentaerythritol solution B, and the solution was added to storage bottle 2. 40.00 g of sodium hydroxide was prepared with deionized water to obtain a 20% sodium hydroxide solution C, and the solution was added to storage bottle 3.

[0086] (2) The mixed aldehyde solution A, the pentaerythritol aqueous solution B and the sodium hydroxide aqueous solution C are respectively transported to the preheating section and reach a set temperature of 50° C. in the preheating section 4.

[0087] (3) After the mixed aldehyde solution A and the pentaerythritol aqueous solution B are uniformly mixed in the mixer 5, they are further quickly mixed with the sodium hydroxide solution C in the mixer 5', and reacted in the microreactor 6 at a set temperature of 50°C for 20 minutes to obtain a reaction product solution D, which is transferred to the storage bottle 7.

[0088] (4) The reaction product solution D is adjusted to a pH value of 6.0 with formic acid, sent to a multi-effect evaporation system to remove formaldehyde, concentrated, cooled, cooled to 40° C. for crystallization, centrifuged, filtered, and dried at 70° C. to obtain dipentaerythritol; the mother liquor is then cooled to 20° C. for crystallization, centrifuged, filtered, and dried at 70° C. to obtain pentaerythritol.

[0089] The liquid chromatography test results of the product prepared in Example 1 are as follows: relative to acetaldehyde, the yield of pentaerythritol is 56.8%, and the yield of dipentaerythritol is 33.7%.

[0090] Example 2

[0091] (1) 44.05 g of liquid acetaldehyde was added to 640.64 g of a 37.5% formaldehyde aqueous solution to obtain a mixed solution A having a molar ratio of formaldehyde to acetaldehyde of 8:1, and the mixed solution A was added to storage bottle 1. 68.07 g of pentaerythritol was prepared with deionized water to form a 1% pentaerythritol solution B, and the mixed solution B was added to storage bottle 2. 48.00 g of sodium hydroxide was prepared with deionized water to form a 10% sodium hydroxide solution C, and the mixed solution C was added to storage bottle 3.

[0092] (2) The mixed aldehyde solution A, the pentaerythritol aqueous solution B and the sodium hydroxide aqueous solution C are respectively transported to the preheating section and reach a set temperature of 90° C. in the preheating section 4.

[0093] (3) After the mixed aldehyde solution A and the pentaerythritol aqueous solution B are uniformly mixed in the mixer 5, they are further quickly mixed with the sodium hydroxide solution C in the mixer 5', and reacted in the microreactor 6 at a set temperature of 90°C for 10 minutes to obtain a reaction product solution D, which is transferred to the storage bottle 7.

[0094] (4) The reaction product solution D is adjusted to a pH value of 6.0 with formic acid, sent to a multi-effect evaporation system to remove formaldehyde, concentrated, cooled, cooled to 40° C. for crystallization, centrifuged, filtered, and dried at 70° C. to obtain dipentaerythritol; the mother liquor is then cooled to 20° C. for crystallization, centrifuged, filtered, and dried at 70° C. to obtain pentaerythritol.

[0095] The liquid chromatography test results of the product prepared in Example 2 showed that the yield of pentaerythritol was 50.7% and the yield of dipentaerythritol was 38.2% relative to acetaldehyde.

[0096] Example 3

[0097] (1) 44.05 g of liquid acetaldehyde was added to 960.96 g of a 37.5% formaldehyde aqueous solution to obtain a mixed solution A having a molar ratio of formaldehyde to acetaldehyde of 12:1, and the mixed solution A was added to storage bottle 1. 544.58 g of pentaerythritol was prepared with deionized water to obtain a pentaerythritol solution B having a mass fraction of 7%, and the mixed solution B was added to storage bottle 2. 44.00 g of sodium hydroxide was prepared with deionized water to obtain a sodium hydroxide solution C having a mass fraction of 20%, and the mixed solution C was added to storage bottle 3.

[0098] (2) The mixed aldehyde solution A, the pentaerythritol aqueous solution B and the sodium hydroxide aqueous solution C are respectively transported to the preheating section and reach a set temperature of 40° C. in the preheating section 4.

[0099] (3) After the mixed aldehyde solution A and the pentaerythritol aqueous solution B are uniformly mixed in the mixer 5, they are further quickly mixed with the sodium hydroxide solution C in the mixer 5', and reacted in the microreactor 6 at a set temperature of 40°C for 20 minutes to obtain a reaction product solution D, which is transferred to the storage bottle 7.

[0100] (4) The reaction product solution D is adjusted to a pH value of 6.0 with formic acid, sent to a multi-effect evaporation system to remove formaldehyde, concentrated, cooled, cooled to 40° C. for crystallization, centrifuged, filtered, and dried at 70° C. to obtain dipentaerythritol; the mother liquor is then cooled to 20° C. for crystallization, centrifuged, filtered, and dried at 70° C. to obtain pentaerythritol.

[0101] The liquid chromatography test results of the product prepared in Example 3 showed that relative to acetaldehyde, the yield of pentaerythritol was 66.9%, and the yield of dipentaerythritol was 24.4%.

[0102] Example 4

[0103] (1) 44.05 g of liquid acetaldehyde was added to 400.40 g of a 37.5% formaldehyde aqueous solution to obtain a mixed solution A having a molar ratio of formaldehyde to acetaldehyde of 5:1, and the mixed solution A was added to storage bottle 1. 408.44 g of pentaerythritol was prepared with deionized water to obtain a 5% pentaerythritol solution B, and the mixed solution was added to storage bottle 2. 60.00 g of sodium hydroxide was prepared with deionized water to obtain a 30% sodium hydroxide solution C, and the mixed solution was added to storage bottle 3.

[0104] (2) The mixed aldehyde solution A, the pentaerythritol aqueous solution B and the sodium hydroxide aqueous solution C are respectively transported to the preheating section and reach a set temperature of 80° C. in the preheating section 4.

[0105] (3) After the mixed aldehyde solution A and the pentaerythritol aqueous solution B are uniformly mixed in the mixer 5, they are further quickly mixed with the sodium hydroxide solution C in the mixer 5', and reacted in the microreactor 6 at a set temperature of 80°C for 20 minutes to obtain a reaction product solution D, which is transferred to the storage bottle 7.

[0106] (4) The reaction product solution D is adjusted to a pH value of 6.0 with formic acid, sent to a multi-effect evaporation system to remove formaldehyde, concentrated, cooled, cooled to 40° C. for crystallization, centrifuged, filtered, and dried at 70° C. to obtain dipentaerythritol; the mother liquor is then cooled to 20° C. for crystallization, centrifuged, filtered, and dried at 70° C. to obtain pentaerythritol.

[0107] The liquid chromatography test results of the product prepared in Example 4 were as follows: relative to acetaldehyde, the yield of pentaerythritol was 54.1%, and the yield of dipentaerythritol was 36.7%.

[0108] Example 5

[0109] (1) 44.05 g of liquid acetaldehyde was added to 720.72 g of a 37.5% formaldehyde aqueous solution to obtain a mixed solution A having a molar ratio of formaldehyde to acetaldehyde of 9:1, and the mixed solution A was added to storage bottle 1. 272.29 g of pentaerythritol was prepared with deionized water to obtain a 5% pentaerythritol solution B, and the mixed solution was added to storage bottle 2. 52.00 g of sodium hydroxide was prepared with deionized water to obtain a 20% sodium hydroxide solution C, and the mixed solution was added to storage bottle 3.

[0110] (2) The mixed aldehyde solution A, the pentaerythritol aqueous solution B and the sodium hydroxide aqueous solution C are respectively transported to the preheating section and reach a set temperature of 70° C. in the preheating section 4.

[0111] (3) After the mixed aldehyde solution A and the pentaerythritol aqueous solution B are uniformly mixed in the mixer 5, they are further quickly mixed with the sodium hydroxide solution C in the mixer 5', and reacted in the microreactor 6 at a set temperature of 70°C for 20 minutes to obtain a reaction product solution D, which is transferred to the storage bottle 7.

[0112] (4) The reaction product solution D is adjusted to a pH value of 6.0 with formic acid, sent to a multi-effect evaporation system to remove formaldehyde, concentrated, cooled, cooled to 40° C. for crystallization, centrifuged, filtered, and dried at 70° C. to obtain dipentaerythritol; the mother liquor is then cooled to 20° C. for crystallization, centrifuged, filtered, and dried at 70° C. to obtain pentaerythritol.

[0113] The liquid chromatography test results of the product prepared in Example 5 are as follows: relative to acetaldehyde, the yield of pentaerythritol is 55.9%, and the yield of dipentaerythritol is 33.6%.

[0114] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A highly selective continuous synthesis method of dipentaerythritol, characterized in that: The following steps are involved: (1) preparing a mixed aldehyde solution A, a pentaerythritol aqueous solution B and a sodium hydroxide aqueous solution C respectively; Wherein, the mixed aldehyde solution A is obtained by mixing a formaldehyde aqueous solution with acetaldehyde; (2) respectively conveying the mixed aldehyde solution A, the pentaerythritol aqueous solution B and the sodium hydroxide aqueous solution C to a preheating pipe section for preheating; (3) mixing the mixed aldehyde solution A with the pentaerythritol aqueous solution B, and then mixing with the sodium hydroxide aqueous solution C, thereby performing a continuous condensation reaction to obtain a reaction product solution D; (4) Separating the reaction product solution D to obtain pentaerythritol and dipentaerythritol.

2. The method according to claim 1, wherein in step (1), The molar ratio of formaldehyde to acetaldehyde in the mixed aldehyde solution A is 4:1 to 15:

1.

3. The method according to claim 1 or 2, wherein in step (1), The mass fraction of the pentaerythritol aqueous solution B is 1-10%.

4. The method according to any one of claims 1 to 3, wherein in step (1), The mass fraction of the sodium hydroxide aqueous solution C is 10-30%.

5. The method according to any one of claims 1 to 4, wherein in step (2), The preheating temperature is 40-130°C.

6. The method according to any one of claims 1 to 5, wherein in step (3), The molar ratio of acetaldehyde in the mixed aldehyde solution A to pentaerythritol in the pentaerythritol aqueous solution B is 1:0.5 to 1:

10.

7. The method according to any one of claims 1 to 6, wherein in step (3), The molar ratio of acetaldehyde in the mixed aldehyde solution A to sodium hydroxide in the sodium hydroxide aqueous solution C is 1:1 to 1:

3.

8. The method according to any one of claims 1 to 7, wherein in step (3), The condensation reaction temperature is 40 to 130° C.; and / or, The condensation reaction time is 5-60 minutes.

9. The method according to any one of claims 1 to 8, further comprising the following steps: (5) The pentaerythritol obtained in step (4) is recycled for the preparation of the pentaerythritol aqueous solution B in step (1).

10. The method according to any one of claims 1 to 9, wherein in step (4), The separation process includes neutralization to weak acidity, formaldehyde stripping and fractional crystallization steps.

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