CN106045850A - Method for catalytic synthesis of citrate through composite doped phosphowolframate - Google Patents

Abstract

The invention relates to a method for catalyzing the synthesis of citric acid ester with compound doped phosphotungstate, which uses the compound doped phosphotungstate as a catalyst to synthesize citric acid ester through the esterification reaction of citric acid and fatty alcohol. The simplified structural formula of the composite doped phosphotungstate used in the present invention is: (NH ₄ ) _x Al _(3-x-y)/3 H _y PW ₁₂ O ₄₀ , where x=0.4~1.1, y=0.4 ~1.1. The method provided by the invention has the advantages of low catalyst cost, easy preparation, high catalytic efficiency, simple separation of catalyst and product, and excellent catalyst reusability.

Description

A kind of compound doped phosphotungstate catalyzes the method for synthesizing citrate

technical field

The invention relates to a method for synthesizing citrate, in particular to a method for catalyzing the synthesis of citrate by composite doping phosphotungstate.

Background technique

Citrate is a non-toxic plasticizer with a wide range of uses. It has the advantages of non-toxicity, low volatility, high plasticizing efficiency and good compatibility. As one of the green alternatives to traditional phthalate plasticizers, the U.S. Food and Drug Administration has approved the use of citrate plasticizers in food packaging materials, medical appliances and personal hygiene products, etc. . In recent years, citric acid esters have become the first environmentally friendly plasticizers at home and abroad.

In the traditional production process of citrate, concentrated sulfuric acid is mainly used as a catalyst. Concentrated sulfuric acid is cheap and has high catalytic activity. However, there are many by-products in the reaction, which cause great difficulties in the separation and purification of the product. In addition, sulfuric acid severely corrodes equipment and produces a large amount of acid-containing wastewater, causing serious environmental pollution. In order to overcome the above defects, researchers at home and abroad have developed a series of solid acid catalysts for the synthesis of citric acid esters, such as molecular sieves, solid superacids, inorganic salts, cation exchange resins, and heteropolyacids. Among them, heteropolyacids have the characteristics of green, non-toxic, high activity and selectivity, and are widely used in the reaction of synthesizing citric acid esters. However, heteropolyacids also have problems such as easy solubility in polar reaction media, low specific surface area, and poor thermal stability. The method to solve the above problems is to immobilize or transform the heteropolyacid into an insoluble heteropolyacid salt catalyst. Compared with supported heteropolyacids, heteropolyacids have the advantages of strong acidity, high surface acid center density and easy preparation. They are a type of high-efficiency solid acid catalysts that have received widespread attention, such as aluminum phosphotungstate (Chen Ping et al. , Industrial Catalysis, 2007, 15, 46-49), 1-(3-sulfonic acid) propyl-3-methylimidazolium phosphotungstate (Yu Shengjian et al., Industrial Catalysis, 2012, 20, 52-55), etc. Heteropolyacid salt catalysts have been applied in the reaction system of synthesizing citric acid ester. However, the above-mentioned heteropolyacid salt catalysts have defects such as low activity, complicated preparation process, large dosage or poor reusability.

CN 105061204 A uses ammonium and silver composite doped phosphotungstate to catalyze the synthesis of citrate with molecular formula (NH ₄ ) _x Ag _y H _3-xy PW ₁₂ O ₄₀ (x=0.3～0.8, y=0.3～0.8) , the activity of the catalyst is higher than that of the traditional single-type ion-doped phosphotungstic acid, the yield of the product is high, the catalyst is easy to separate, and the reusability is better. However, its application is limited due to the high price of silver. Therefore, it is an urgent technical problem for those skilled in the art to develop a cheap, efficient, stable and easy-to-prepare solid acid catalyst suitable for industrial production of citric acid esters.

Contents of the invention

The purpose of the present invention is to provide a method for catalyzing the synthesis of citric acid ester by compound doping phosphotungstate, which has the advantages of low production cost, high efficiency and environmental protection.

The method for catalyzing the synthesis of citric acid ester with composite doped phosphotungstate provided by the present invention uses composite doped phosphotungstate as a catalyst to synthesize citric acid ester by esterification reaction of citric acid and fatty alcohol, and the composite doped The simplified structural formula of phosphotungstate is: (NH ₄ ) _x Al _(3-xy)/3 H _y PW ₁₂ O ₄₀ , where x=0.4~1.1, y=0.4~1.1.

Further, the fatty alcohol is a C ₄ -C ₁₆ straight chain or branched chain fatty alcohol, more preferably n-butanol, n-hexanol, 2-ethylhexanol, n-octanol, n-decyl alcohol or lauryl alcohol.

Further, the preparation process of the composite doped phosphotungstate catalyst comprises steps:

(1) Mix ammonium salt, aluminum salt and phosphotungstic acid in the solution;

(2) After the reaction, the composite doped phosphotungstate is obtained by separation.

Further, the step (1) is specifically:

Add the aluminum salt to the aqueous solution of phosphotungstic acid;

Ammonium salt was added to the aforementioned mixed solution.

Further, the ammonium salt is ammonium carbonate, ammonium bicarbonate, ammonium chloride or ammonium nitrate.

Further, the aluminum salt is aluminum nitrate, aluminum sulfate or aluminum chloride.

Further, the temperature of the esterification reaction is 120-170°C.

Further, the ratio of citric acid to fatty alcohol is 1:2-5.

Further, the mass ratio of catalyst to citric acid is 0.5-3:100.

Further, the reaction time is 2 to 5 hours.

The technical solution provided by the invention has the following advantages: (1) The catalyst component does not contain precious metals, is low in cost, easy to prepare, and has high catalytic efficiency; (2) The separation of the catalyst and the product is simple, and the catalyst can be reused; ( 3) The yield of citric acid ester is high.

detailed description

Specific embodiments of the present invention will be further described in detail below. The above and other objects, features and advantages of the present invention will be apparent to those skilled in the art from the detailed description of the present invention.

Example 1:

Catalyst preparation: Weigh 0.375 mmol of ammonium carbonate, 0.5 mmol of aluminum nitrate and 1 mmol of phosphotungstic acid and dissolve them in 20 ml of deionized water; after dissolving, slowly add the aluminum nitrate solution dropwise to In the phosphotungstic acid solution, react for 0.5 hours, then slowly add ammonium carbonate solution dropwise, and gradually form a white precipitate; after the dropwise addition, continue to stir and react for 0.5 hours, let stand and age for 1 hour, the precipitate is separated by filtration, dried, The composite doped phosphotungstate with molecular formula (NH ₄ ) _0.75 Al _0.5 H _0.75 PW ₁₂ O ₄₀ can be obtained.

Example 2:

Catalyst preparation: The preparation process is the same as in Example 1, except that the amount of ammonium carbonate added is changed to 0.2 mmol, and a composite doped phosphotungstate with the molecular formula (NH ₄ ) _0.4 Al _0.5 H _1.1 PW ₁₂ O ₄₀ can be obtained.

Example 3:

Catalyst preparation: The preparation process is the same as in Example 1, except that the amount of ammonium carbonate added is changed to 0.55 mmol, and a composite doped phosphotungstate with the molecular formula (NH ₄ ) _1.1 Al _0.5 H _0.4 PW ₁₂ O ₄₀ can be obtained.

Example 4:

Preparation of the catalyst: the preparation process is the same as in Example 1, only the ammonium salt is changed to 0.6 mmol of ammonium bicarbonate, and the amount of aluminum nitrate is changed to 0.6 mmol, and the molecular formula can be obtained as (NH ₄ ) _0.6 Al _0.6 H _0.6 PW ₁₂ O ₄₀ Composite doped phosphotungstate.

Example 5:

Catalyst preparation: The preparation process is the same as in Example 4, except that the ammonium salt is changed to 0.6 mmol ammonium chloride, and a composite doped phosphotungstate with the molecular formula (NH ₄ ) _0.6 Al _0.6 H _0.6 PW ₁₂ O ₄₀ can be obtained.

Embodiment 6:

Catalyst preparation: The preparation process is the same as in Example 4, except that the aluminum salt is changed to 0.6 mmol aluminum chloride, and a composite doped phosphotungstate with the molecular formula (NH ₄ ) _0.6 Al _0.6 H _0.6 PW ₁₂ O ₄₀ can be obtained.

Embodiment 7:

Add 19.21 g of citric acid (0.1 mol), 29.6 g of n-butanol (0.4 mol) and 0.29 g of (NH ₄ ) prepared in Example 1 into a reactor equipped with a thermometer, water separator and condenser tube _0.75 Al _0.5 H _0.75 PW ₁₂ O ₄₀ catalyst, start stirring, raise the temperature to 150°C, start timing when the reflux phenomenon starts to appear in the condenser tube, and react for 3 hours. After the reaction system was cooled to room temperature, it was separated by filtration, and the filtrate was detected by gas chromatography. The product yields are shown in Table 1.

Embodiment 8:

Using the same reaction conditions and detection methods as in Example 7, only the catalyst was changed to (NH ₄ ) _0.4 Al _0.5 H _1.1 PW ₁₂ O ₄₀ prepared in Example 2. The product yields are shown in Table 1.

Embodiment 9:

Using the same reaction conditions and detection methods as in Example 7, only changing the catalyst to (NH ₄ ) _1.1 Al _0.5 H _0.4 PW ₁₂ O ₄₀ prepared in Example 3, the product yields are shown in Table 1.

Example 10:

Using the same reaction conditions and detection methods as in Example 7, only the catalyst was changed to (NH ₄ ) _0.6 Al _0.6 H _0.6 PW ₁₂ O ₄₀ prepared in Example 4. The product yields are shown in Table 1.

Example 11:

Using the same reaction conditions and detection methods as in Example 7, only changing the catalyst to (NH ₄ ) _0.6 Al _0.6 H _0.6 PW ₁₂ O ₄₀ prepared in Example 5, the product yields are shown in Table 1.

Example 12:

Using the same reaction conditions and detection methods as in Example 7, only the catalyst was changed to (NH ₄ ) _0.6 Al _0.6 H _0.6 PW ₁₂ O ₄₀ prepared in Example 6. The product yields are shown in Table 1.

Example 13:

Add 19.21 g of citric acid (0.1 mol), 26.05 g of n-octanol (0.2 mol), 5 mL of water-carrying agent cyclohexane and 0.29 g of The (NH ₄ ) _0.75 Al _0.5 H _0.75 PW ₁₂ O ₄₀ catalyst was prepared, and the stirring was started, and the temperature was raised to 160°C. When the reflux phenomenon began to appear in the condenser tube, the timer was started, and the reaction was carried out for 3 h. After the reaction system was cooled to room temperature, it was separated by filtration, and the filtrate was detected by gas chromatography. The product yields are shown in Table 1.

Example 14:

Using the same reaction conditions and detection method as in Example 13, only the raw material n-octanol was changed to 26.05 g iso-octanol (0.2 mol). The product yield is shown in Table 1.

Example 15:

Add 19.21 g of citric acid (0.1 mol), 37.26 g of dodecyl alcohol (0.2 mol), 5 mL of water-carrying agent cyclohexane and 0.29 g of For the prepared (NH ₄ ) _0.75 Al _0.5 H _0.75 PW ₁₂ O ₄₀ catalyst, start the stirring, raise the temperature to 165°C, start timing when the reflux phenomenon starts to appear in the condenser tube, and react for 4 hours. After the reaction system was cooled to room temperature, it was separated by filtration, and the filtrate was detected by liquid chromatography. The product yields are shown in Table 1.

Example 16:

Add 19.21 g of citric acid (0.1 mol), 48.5 g of cetyl alcohol (0.2 mol), 5 mL of water-carrying agent cyclohexane and 0.29 g of For the prepared (NH ₄ ) _0.75 Al _0.5 H _0.75 PW ₁₂ O ₄₀ catalyst, start the stirring, raise the temperature to 170°C, start timing when the reflux phenomenon starts to appear in the condenser tube, and react for 5 hours. After the reaction system was cooled to room temperature, it was separated by filtration, and the filtrate was detected by liquid chromatography. The product yields are shown in Table 1.

Example 17:

Using the same reaction conditions and detection method as in Example 10, only the amount of n-butanol was changed to 14.8 g (0.2 mol), and the product yield is shown in Table 1.

Example 18:

Using the same reaction conditions and detection method as in Example 10, only the amount of n-butanol was changed to 22.2 g (0.3 mol), and the product yield is shown in Table 1.

Example 19:

Using the same reaction conditions and detection method as in Example 10, only the amount of n-butanol was changed to 37 g (0.5 mol), and the product yield is shown in Table 1.

Example 20:

Using the same reaction conditions and detection method as in Example 11, only changing the amount of catalyst to 0.1 g, the product yield is shown in Table 1.

Example 21:

Using the same reaction conditions and detection method as in Example 11, only the amount of catalyst was changed to 0.38 g, and the product yield is shown in Table 1.

Example 22:

Using the same reaction conditions and detection methods as in Example 12, only changing the reaction temperature to 130°C, the product yields are shown in Table 1.

Example 23:

Using the same reaction conditions and detection method as in Example 7, only changing the reaction time to 5 hours, the product yield is shown in Table 1.

Example 24:

The catalyst used in Example 7 was filtered and separated without any treatment, and was used for the next batch of cyclic reactions. The reaction conditions and detection methods of the cyclic reactions were the same as in Example 7. After 15 times of recycling, the product yield Rates are shown in Table 1.

Comparative example 1:

Using the same reaction conditions and detection methods as in Example 10, only changing the catalyst to (NH ₄ ) _2.4 H _0.6 PW ₁₂ O ₄₀ , the product yields are shown in Table 1.

Comparative example 2:

Using the same reaction conditions and detection methods as in Example 10, only changing the catalyst to Al _0.8 H _0.6 PW ₁₂ O ₄₀ , the product yields are shown in Table 1.

Table 1: Product yields of Examples and Comparative Examples.

According to the results in Table 1, the compound-doped phosphotungstate involved in the present invention has very excellent catalytic performance for the reaction of esterification into citrate, and its catalytic activity is better than that of the traditional single-type ion-doped phosphotungstate. The activity of the catalyst did not decrease significantly after 15 times of repeated use. In addition, the catalyst is cheap and easy to prepare. Therefore, the technical solution involved in the present invention is suitable for industrial application. It should be clear to those skilled in the art that the ammonium salt adopts ammonium carbonate, ammonium bicarbonate, ammonium chloride or ammonium nitrate, and the aluminum salt adopts aluminum nitrate, aluminum sulfate or aluminum chloride, all of which can realize the technical effect of the present invention. Fatty alcohols suitable for the present invention include C4-C16 straight chain or branched chain fatty alcohols.

It should be understood that although the present invention has been clearly described through the above embodiments, those skilled in the art can make various corresponding changes and modifications according to the present invention without departing from the spirit and essence of the present invention. But these corresponding changes and amendments should all belong to the protection scope of the claims of the present invention.

Claims (10)

1. A method for compound-doped phosphotungstate to catalyze the synthesis of citric acid esters, using compound-doped phosphotungstate as a catalyst to synthesize citric acid esters from citric acid and fatty alcohol through esterification, characterized in that, The simplified structural formula of the composite doped phosphotungstate is: (NH ₄ ) _x Al _(3-xy)/3 H _y PW ₁₂ O ₄₀ , where x=0.4~1.1, y=0.4~1.1. 2. the method for catalytic synthesis of citrate according to claim 1, is characterized in that, described fatty alcohol is n-butanol, n-hexanol, 2-ethylhexanol, n-octanol, n-decyl alcohol or lauryl alcohol . 3. the method for catalytic synthesis citrate according to claim 1, is characterized in that, the preparation process of described composite doping phosphotungstate catalyst comprises steps: (1) Mix ammonium salt, aluminum salt and phosphotungstic acid in the solution; (2) After the reaction, the composite doped phosphotungstate is obtained by separation. 4. the method for catalytic synthesis of citrate according to claim 3, is characterized in that, described step (1) is specifically: Add the aluminum salt to the aqueous solution of phosphotungstic acid; Ammonium salt was added to the aforementioned mixed solution. 5. the method for catalytic synthesis of citrate according to claim 3, is characterized in that, described ammonium salt is ammonium carbonate, ammonium bicarbonate, ammonium chloride or ammonium nitrate. 6. the method for catalytic synthesis citrate according to claim 3, is characterized in that, described aluminum salt is aluminum nitrate, aluminum sulfate or aluminum chloride. 7. The method for catalytically synthesizing citrate according to any one of claims 1-6, wherein the temperature of the esterification reaction is 120 to 170°C. 8. according to the method for catalytic synthesis of citric acid ester described in any one of claim 1-6, it is characterized in that, the ratio of the amount of substance of citric acid and fatty alcohol is 1: 2～5. 9. according to the method for the catalytic synthesis of citric acid ester described in any one of claim 1-6, it is characterized in that, the mass ratio of catalyst and citric acid is 0.5～3:100. 10. according to the method for catalytic synthesis citrate described in any one of claim 1-6, it is characterized in that, the reaction times is 2～5 hours.