Preparation method of 2, 2-dimethoxypropane

Abstract

The invention discloses a preparation method of 2, 2-dimethoxy propane. The method comprises the following steps: in the presence of a catalyst, enabling acetone and methanol to react in a molar ratio of 1: 2 to 1: 6 in a reaction temperature range of-50 DEG C to-80 DEG C; reacting the acetone with the methanol for about 12 hours to 7 days in a reaction temperature range of-50 DEG C to-80 DEG C to obtain a reaction mixture containing 2, 2-dimethoxypropane crystals; and quenching the reaction mixture containing the 2, 2-dimethoxypropane crystal with an alkali to obtain a slurry containing the 2, 2-dimethoxypropane crystal. And treating the slurry containing the 2, 2-dimethoxypropane crystal, so as to obtain the liquid 2, 2-dimethoxypropane.

Description

Technical Field

[0001] The present application relates to a method for preparing 2,2 - dimethoxypropane (commonly known as DMP), and specifically, to an economical, efficient and energy - saving method for preparing 2,2 - dimethoxypropane by preparing 2,2 - dimethoxypropane crystals. Background Art

[0002] 2,2 - Dimethoxypropane is an organic compound with various uses, including but not limited to: as a water remover in moisture - sensitive reactions, as an intermediate for synthesizing 2 - methoxypropene, for the production of pesticides and fungicides, for dehydrating animal tissues in histology, and for producing 2 - methoxypropene required for the production of vitamins D and E.

[0003] 2,2 - Dimethoxypropane is a product formed by the condensation reaction of acetone and methanol in the presence of an acid catalyst. However, this reaction is reversible, and at normal temperature or higher temperatures, the reaction equilibrium shifts towards the raw material side. Since the reaction equilibrium favors the raw material side, it is necessary to remove water through low temperature, a high methanol / acetone ratio, and a cumbersome pervaporation technique to shift the equilibrium towards the formation of 2,2 - dimethoxypropane to increase its yield. Nevertheless, in the prior art, the conversion rate from reactants to 2,2 - dimethoxypropane mostly fails to reach an ideal level. In addition, due to the formation of azeotropes among the components of the reaction mixture, the separation or purification process of 2,2 - dimethoxypropane in the prior art is very cumbersome. The prior art has not effectively broken through the technical bottleneck of the azeotropic mixture.

[0004] U.S. Patents US9309177 and US9309178 disclose a method for preparing 2,2 - dimethoxypropane, which involves reacting a ketone with ethanol at a reaction temperature below - 40°C in the presence of a solid acid to form a reaction product mixture, and then removing water and methanol from the reaction product mixture through a hydrophilic membrane pervaporation technique.

[0005] In another alternative method, it is known that a large amount of desiccant calcium sulfate can be used to change the reaction equilibrium in the preparation process of 2,2 - dimethoxypropane. Calcium sulfate can remove the water generated in the reaction. However, this means additional costs for replacing or regenerating the used calcium sulfate.

[0006] U.S. Patent US4775447 discloses a process for preparing 2,2 - dimethoxypropane by reacting acetone with methanol at a molar ratio of 1:1 to 1:3 in the presence of a strongly acidic ion - exchange resin at room temperature. Subsequently, 2,2 - dimethoxypropane can be recovered in the form of an azeotrope with methanol. However, the conversion rate of 2,2 - dimethoxypropane at room temperature is extremely low, and the concentration of 2,2 - dimethoxypropane obtained is less than 6 - 8%. In addition, the subsequent distillation step is not only costly but also requires a large amount of acetone to separate and purify 2,2 - dimethoxypropane. Summary of the Invention

[0007] This application discloses a method for preparing 2,2 - dimethoxypropane, which includes: reacting acetone with methanol at a molar ratio of 1:2 to 1:6 in the presence of a catalyst within a reaction temperature range of - 50°C to - 80°C; reacting acetone and methanol within the reaction temperature range of - 50°C to - 80°C for about 12 hours to 7 days to obtain a reaction mixture containing 2,2 - dimethoxypropane crystals; quenching the reaction mixture containing 2,2 - dimethoxypropane crystals with an alkali to obtain a slurry containing 2,2 - dimethoxypropane crystals; and treating the slurry containing 2,2 - dimethoxypropane crystals to obtain liquid 2,2 - dimethoxypropane. Brief Description of the Drawings

[0008] Figure 1 shows the influence of different reaction times on the conversion rate of 2,2 - dimethoxypropane in one embodiment of this application.

[0009] Figure 2 shows the influence of different reaction temperatures on the conversion rate of 2,2 - dimethoxypropane in one embodiment of this application.

[0010] Figure 3 shows the white 2,2 - dimethoxypropane crystals formed in an intermediate step in one embodiment of this application.

[0011] Figure 4A and 4B shows the white 2,2 - dimethoxypropane crystals formed after quenching the reaction mixture in one embodiment of this application. Detailed Description of the Invention

[0012] For ease of understanding the technical principle of this application, the following will be described in detail with specific embodiments. It should be particularly noted that these embodiments are only for illustration and not for limiting the protection scope of this application. Any reasonable adjustment or improvement made by those skilled in the art to the process parameters and reaction conditions based on the technical solutions disclosed in this application, as well as other applications of the principle of this application, shall be regarded as falling within the protection scope of this application.

[0013] Those skilled in the art should understand that the foregoing general description and the following detailed description are both exemplary descriptions, aiming to explain rather than limit the technical solutions of the present application.

[0014] Throughout this specification, the terms "one embodiment", "an embodiment" or similar expressions mean that the specific technical features, structures or characteristics described are included in at least one embodiment of the present application. Therefore, the embodiments referred to by the similar expressions such as "in one embodiment" and "in an embodiment" appearing throughout the specification may be the same or different.

[0015] Broadly speaking, the present application relates to a method for preparing 2,2-dimethoxypropane. Specifically, the method comprises the following steps:

[0016] In the presence of a catalyst, acetone and methanol are reacted at a molar ratio of 1:2 to 1:6 within a reaction temperature range of -50°C to -80°C;

[0017] Acetone and methanol are reacted within a reaction temperature range of -50°C to -80°C for about 12 hours to 7 days to obtain a reaction mixture containing 2,2-dimethoxypropane crystals;

[0018] The reaction mixture containing 2,2-dimethoxypropane crystals is quenched with a base to obtain a slurry containing 2,2-dimethoxypropane crystals; and

[0019] The slurry containing 2,2-dimethoxypropane crystals is processed to obtain liquid 2,2-dimethoxypropane.

[0020] The applicant has found that through the above crystallization method, the conversion rate of 2,2-dimethoxypropane can be increased to approximately 60-70%.

[0021] In one embodiment, acetone and methanol are reacted at a molar ratio of 1:2 to 1:4. In some embodiments, acetone and methanol are reacted at a molar ratio of 1:4.

[0022] In the method disclosed in the present application, acetone reacts with methanol at a very low reaction temperature. In one embodiment, the reaction temperature for the reaction of acetone and methanol is controlled within the range of -60°C to -65°C. In some embodiments, the reaction temperature for the reaction of acetone and methanol is -65°C.

[0023] In one embodiment, the reaction between acetone and methanol is carried out in an environment of nitrogen (N2) at 1 atmosphere.

[0024] After the reaction of acetone and methanol starts, the formation of 2,2-dimethoxypropane crystals in the reaction mixture occurs at least 24 hours after the start of the reaction. In one embodiment, acetone and methanol react for 24 to 72 hours to obtain a reaction mixture containing 2,2-dimethoxypropane crystals. In some embodiments, acetone and methanol react for 48 hours.

[0025] In one embodiment, the formation of 2,2-dimethoxypropane crystals occurs in the range of -60 °C to -75 °C. In some embodiments, 2,2-dimethoxypropane crystals are formed at -65 °C.

[0026] In one embodiment, the reaction of acetone and methanol is not stirred during the reaction process. In another embodiment, the reaction of acetone and methanol is dynamically stirred at a rotational speed in the range of 40 - 200 revolutions per minute during the reaction process.

[0027] Subsequently, at a temperature condition of -50 °C to -80 °C, the reaction mixture containing 2,2-dimethoxypropane crystals is quenched with a base to obtain a slurry containing 2,2-dimethoxypropane crystals. In one embodiment, the reaction mixture containing 2,2-dimethoxypropane crystals is quenched with a base within a time range of 1 minute to 1 hour. In some embodiments, at a temperature of -65 °C, the reaction mixture containing 2,2-dimethoxypropane crystals is quenched with a base for 5 to 15 minutes.

[0028] In one embodiment, the quenching base is selected from the group consisting of triethylamine, sodium hydroxide, sodium carbonate, potassium hydroxide, sodium methoxide, triethanolamine, and trimethylamine. In some embodiments, triethylamine is used as the quenching base. In one embodiment, the base is added to the reaction mixture containing 2,2-dimethoxypropane crystals at a weight ratio (w / w) of 0.5% to 5%. In some embodiments, the base is added to the reaction mixture containing 2,2-dimethoxypropane crystals at a weight ratio (w / w) of 1 - 2%.

[0029] The slurry containing 2,2-dimethoxypropane crystals is processed to obtain liquid 2,2-dimethoxypropane. In one embodiment, the processing of the slurry includes filtering the slurry to recover purified 2,2-dimethoxypropane crystals and the filtrate therefrom. In one embodiment, the slurry containing 2,2-dimethoxypropane crystals is filtered within a temperature range of -60 °C to -75 °C to recover purified 2,2-dimethoxypropane crystals. In some embodiments, the slurry containing 2,2-dimethoxypropane crystals is filtered within a temperature range of -60 °C to -65 °C to recover purified 2,2-dimethoxypropane crystals. Filtration can be carried out using any known or future-developed process. In some embodiments, filtration is performed through a pre-cooled single-layer filter.

[0030] Subsequently, the purified 2,2 - dimethoxypropane crystals are heated to a temperature above - 55°C to melt them, thereby obtaining liquid 2,2 - dimethoxypropane. In one embodiment, the purified 2,2 - dimethoxypropane crystals are brought to room temperature to melt them.

[0031] In one embodiment, after recovering the purified 2,2 - dimethoxypropane crystals from the slurry, a recovery step is performed on the filtrate to recover one or more of acetone, methanol, and water. The recovery can be carried out using any process known in the art or developed in the future.

[0032] In one embodiment, the filtrate is recovered by distillation. Examples of distillation methods include, but are not limited to, simple distillation, fractional distillation, steam distillation, vacuum distillation, and zone distillation.

[0033] In another embodiment, the treatment of the slurry to obtain 2,2 - dimethoxypropane crystals includes adding a sodium hydroxide solution to the slurry containing 2,2 - dimethoxypropane crystals. In one embodiment, the slurry is treated with the sodium hydroxide solution at a temperature in the range of - 20°C to - 60°C for 0.5 to 2 hours to obtain liquid 2,2 - dimethoxypropane. Adding the sodium hydroxide solution to the slurry containing 2,2 - dimethoxypropane crystals causes the 2,2 - dimethoxypropane crystals to melt, thereby obtaining liquid 2,2 - dimethoxypropane. In one embodiment, the liquid 2,2 - dimethoxypropane is obtained as a separate top layer of the bottom alkaline layer of the sodium hydroxide solution.

[0034] In one embodiment, the concentration of the sodium hydroxide solution in water ranges from 20 - 50% w / w. In some embodiments, the concentration of the sodium hydroxide solution in water is 35% w / w. In one embodiment, the addition amount of the sodium hydroxide solution is 50% to 500% w / w of the total mass of the slurry containing 2,2 - dimethoxypropane crystals. In some embodiments, the addition amount of the sodium hydroxide solution is 150 - 250% w / w of the total mass of the slurry containing 2,2 - dimethoxymethylpropane crystals.

[0035] In one embodiment, the addition amount of the catalyst is 0.5% - 5% of the total mass of acetone and methanol. In some embodiments, the addition amount of the catalyst is 1% w / w of the total mass of acetone and methanol. In one embodiment, the catalyst is selected from the group consisting of acidic ion exchange resins and acids.

[0036] Any known acidic ion exchange resin that can be used for the preparation of 2,2 - dimethoxypropane can be used. In one embodiment, the acidic ion exchange resin is selected from the group consisting of polystyrene copolymers with sulfonic acid functional groups and styrene - divinylbenzene copolymers with sulfonic acid functional groups. In some embodiments, the acidic ion exchange resin can be a styrene - divinylbenzene copolymer with sulfonic acid functional groups.

[0037] Any known acid that can be used to prepare 2,2 - dimethoxypropane can be used. In one embodiment, the acid is selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, p - toluenesulfonic acid, methanesulfonic acid, phosphoric acid, and acetic acid. In some embodiments, sulfuric acid can be used as the acid.

[0038] In one embodiment, the yield of the liquid 2,2 - dimethoxypropane obtained by this method can reach 20 - 40% of the total mass of the reaction materials.

[0039] The present application will be described below by way of examples, and these examples are for illustration only and do not limit the scope of protection of the present application. Those skilled in the art can make various modifications and changes to the method / process without departing from the substantial content of the present application. By reading this specification and practicing the method / process disclosed herein, other embodiments will be apparent to those skilled in the art. This specification and the examples should be considered exemplary, and the actual scope of the present application is defined by the appended claims and their equivalents.

[0040] Examples

[0041] Example 1: Preparation of 2,2 - dimethoxypropane according to an embodiment of the present application

[0042] 58 grams of acetone, 128 grams of methanol (molar ratio 1:4), and 10 grams of Tulsion T - 62MP were added to a jacketed reactor to form a reaction mixture. The reactor containing the reaction mixture was cooled to - 60 °C to - 65 °C. The jacket of the reactor was insulated with liquid nitrogen to maintain the low - temperature reaction conditions. Within 24 hours after the start of the reaction, the conversion rate measured by gas chromatography (GC) analysis reached up to 40%. After the reaction of acetone and methanol for 24 hours, 2,2 - dimethoxypropane crystals began to form and a reaction mixture containing 2,2 - dimethoxypropane crystals was obtained. In the next 24 hours, the formation process of 2,2 - dimethoxypropane crystals continued slowly. The reaction mixture containing 2,2 - dimethoxypropane crystals was quenched with 1% triethylamine to obtain a slurry containing 2,2 - dimethoxypropane crystals. The slurry containing 2,2 - dimethoxypropane crystals was filtered to recover the purified 2,2 - dimethoxypropane crystals. The purified 2,2 - dimethoxypropane crystals were melted at room temperature to obtain liquid 2,2 - dimethoxypropane. After recovering the purified 2,2 - dimethoxypropane crystals from the slurry containing 2,2 - dimethoxypropane crystals, the filtrate was recovered to obtain one or more of acetone, methanol, and water. The prepared 2,2 - dimethoxypropane was characterized by GC analysis. Table 1 shows the effect of the reaction time (obtained by GC analysis) on the conversion rate of 2,2 - dimethoxypropane.

[0043] Table 1: Influence of reaction time on the conversion rate of 2,2-dimethoxypropane

[0044]

[0045]

[0046] Observation results: It was experimentally observed that when acetone and methanol with a molar ratio of 1:4 reacted at a reaction temperature of -60 °C for more than 24 hours, 2,2-dimethoxypropane crystals could be formed. Further observation found that when the reaction time reached 42 hours, the conversion rate of 2,2-dimethoxypropane could be increased to 68%.

[0047] An experiment on a 5-liter scale was carried out in the same manner as in Example 1. At a reaction temperature of -60 °C, acetone and methanol were reacted at a molar ratio of 1:4 for 48 hours. Table 2 summarizes the influence of reaction time on the conversion rate of 2,2-dimethoxypropane.

[0048] Table 2: Influence of reaction time on the conversion rate of 2,2-dimethoxypropane

[0049]

[0050] Observation results: It was experimentally observed that when the reaction time reached 48 hours, 2,2-dimethoxypropane crystals could be formed. Further observation found that when the reaction time reached 48 hours, the conversion rate of 2,2-dimethoxypropane increased to 60%.

[0051] Figure 1 The influence of reaction time on the conversion rate under the conditions of a molar ratio of 1:4 and a reaction temperature of -60 °C is shown. The experimental observation results show that when the reaction time exceeds 40 hours, the conversion rate of 2,2-dimethoxypropane increases with the prolongation of the reaction time.

[0052] Example 2: Preparation of 2,2-dimethoxypropane according to an embodiment of the present application

[0053] 2.0 kg of acetone, 4.41 kg of methanol and 64 g of sulfuric acid were added to a jacketed reactor to form a reaction mixture. The reactor included cooling the reaction mixture first to -20 °C and maintaining it for 2 hours, then cooling it to -40 °C and maintaining it for 2 hours, and finally cooling it to -60 °C to -65 °C and maintaining it for 48 hours. The reactor used a liquid nitrogen-cooled jacket to maintain the low temperature. After the acetone and methanol reacted for 24 hours, 2,2-dimethoxypropane crystals began to form and a reaction mixture containing 2,2-dimethoxypropane crystals was obtained. According to the GC analysis results, the reaction conversion rate reached 40% in the first 24 hours. In the subsequent 24 hours, the formation process of 2,2-dimethoxypropane crystals proceeded slowly. The reaction mixture containing 2,2-dimethoxypropane crystals was quenched with 1% triethylamine to obtain a crystal slurry containing 2,2-dimethoxypropane crystals. The crystal slurry containing 2,2-dimethoxypropane crystals was filtered to recover the purified 2,2-dimethoxypropane crystals. The purified 2,2-dimethoxypropane crystals were melted at room temperature to obtain liquid 2,2-dimethoxypropane. After the purified 2,2-dimethoxypropane crystals were recovered from the crystal slurry, the filtrate was recovered to obtain one or more of acetone, methanol and water. The prepared 2,2-dimethoxypropane was characterized by GC analysis. Table 3 shows the effect of reaction time (obtained by GC analysis) on the conversion rate of 2,2-dimethoxypropane.

[0054] Table 3: Effect of reaction time and reaction temperature on the conversion rate of 2,2-dimethoxypropane

[0055]

[0056]

[0057] Observation results: It was experimentally observed that when the reaction time reached 48 hours, the conversion rate of 2,2-dimethoxypropane could be increased to 60%.

[0058] Figure 2 It shows the effect of different reaction temperatures on the conversion rate of 2,2-dimethoxypropane under the conditions of a molar ratio of 1:4 and a reaction time of 1 hour. It was experimentally observed that as the reaction temperature decreased, the conversion rate of 2,2-dimethoxypropane increased.

[0059] Example 3: Preparation of 2,2-dimethoxypropane according to the prior art

[0060] 2,2 - dimethoxypropane was prepared using acetone and methanol in three molar ratios of 1:1, 1:2, and 1:4. As shown in Table 3 below, specific amounts of acidic ion exchange resin catalyst were added respectively, and the reaction was carried out under different reaction temperatures and reaction times specified in Table 3. In the comparative examples provided in this embodiment, the reaction duration was less than 24 hours, and the conditions involved were all typical parameters in the prior art.

[0061] Table 4: GC analysis of preparing 2,2 - dimethoxypropane according to the prior art

[0062]

[0063]

[0064]

[0065] Observation results: It was observed through experiments that under the conditions where the ratio of acetone to methanol was 1:1, 1:2, and 1:4 respectively, compared with - 60 °C, the conversion rate of 2,2 - dimethoxypropylene was lower at room temperature, 0 °C, and 20 °C. Among them, at - 60 °C, the acetone - methanol molar ratio of 1:4 showed the optimal conversion rate.

[0066] The following Table 5 shows the comparison data of the reaction of acetone and methanol with a molar ratio of 1:4 at - 20 °C for 1 hour and 12 hours.

[0067] Table 5: Influence of reaction time on the conversion rate of 2,2 - dimethoxypropane

[0068]

[0069] Observation results: It was observed through experiments that at 1 hour of reaction, the conversion rate of 2,2 - dimethoxypropane was 30.49%, and at 12 hours of reaction, the conversion rate of 2,2 - dimethoxypropane was 30.62%. When the reaction time changed from 1 hour to 12 hours, the increase in the conversion rate of 2,2 - dimethoxypropane was negligible.

[0070] Industrial applicability

[0071] This application provides a method for preparing 2,2 - dimethoxypropylene that is efficient, simple, and has a high yield. This method can achieve a conversion rate of more than 60% of 2,2 - dimethoxypropane in a single operation.

[0072] The method disclosed in this application does not require the multi - stage heating and cooling operations and pervaporation steps required in the prior art to achieve a high conversion rate, thus effectively overcoming the defects of the prior art such as high carbon dioxide emissions and high production costs, which mainly stem from the pervaporation and distillation steps used in the prior art.

Claims

1. A method for preparing 2,2 - dimethoxypropane, which comprises: Reacting acetone with methanol in a molar ratio of 1:2 to 1:6 in the reaction temperature range of - 50°C to - 80°C in the presence of a catalyst; Reacting the acetone with the methanol in the reaction temperature range of - 50°C to - 80°C for about 12 hours to 7 days to obtain a reaction mixture containing 2,2 - dimethoxypropane crystals; Quenching the reaction mixture containing 2,2 - dimethoxypropane crystals with a base to obtain a slurry containing 2,2 - dimethoxypropane crystals; and Processing the slurry containing 2,2 - dimethoxypropane crystals to obtain liquid 2,2 - dimethoxypropane.

2. The method according to claim 1, characterized in that, The acetone reacts with the methanol in a molar ratio of 1:

4.

3. The method according to claim 1, wherein The acetone reacts with the methanol in the reaction temperature range of - 60°C to - 65°C.

4. The method according to claim 1, characterized in that The processing of the slurry containing 2,2 - dimethoxypropane crystals includes: Filtering the slurry to recover purified 2,2 - dimethoxypropane crystals and a filtrate therefrom; and Melting the purified 2,2 - dimethoxypropane crystals to obtain liquid 2,2 - dimethoxypropane.

5. The method according to claim 4, characterized in that, After recovering the purified 2,2 - dimethoxypropane crystals, the filtrate is subjected to a recovery treatment to obtain one or more of acetone, methanol, and water.

6. The method according to claim 1, wherein The processing of the slurry containing 2,2 - dimethoxypropane crystals includes: Adding a sodium hydroxide solution to the slurry containing 2,2 - dimethoxypropane crystals to obtain liquid 2,2 - dimethoxypropane as a separated top layer.

7. The method according to claim 6, wherein The sodium hydroxide solution has a concentration in water of 20 - 50%, and its addition amount accounts for 50% to 500% w / w of the total mass of the slurry containing 2,2 - dimethoxypropane crystals.

8. The method according to claim 1, characterized in that, The addition amount of the catalyst accounts for 0.5% to 5% w / w of the total mass of the acetone and the methanol.

9. The method according to any one of claims 1 or 8, characterized in that The catalyst is selected from the group consisting of acidic ion - exchange resins and acids.

10. The method according to any one of claims 1 or 9, characterized in that, The acidic ion - exchange resin as the catalyst is selected from the group consisting of polystyrene copolymers with sulfonic acid groups and styrene - divinylbenzene copolymers.

11. The method according to any one of claims 1 or 9, characterized in that, The acid as the catalyst is selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, p - toluenesulfonic acid, methanesulfonic acid, phosphoric acid, and acetic acid.

12. The method according to claim 1, characterized in that, The reaction of the acetone with the methanol is not stirred during the process.

13. The method according to claim 1, characterized in that, The quenching of the reaction mixture with the base is carried out in the reaction temperature range of - 50°C to - 80°C for 1 minute to 1 hour.

14. The method according to any one of claims 1 or 13, characterized in that, The base is selected from the group consisting of triethylamine, sodium hydroxide, sodium carbonate, potassium hydroxide, sodium methoxide, triethanolamine, and trimethylamine.

15. The method according to any one of claims 1 or 13, characterized in that The addition amount of the base is 0.5% to 5% w / w of the mass of the reaction mixture containing 2,2 - dimethoxypropane crystals.

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