Preparation method of malate and solid acid catalyst

Abstract

The invention relates to the technical field of organic synthesis, and provides a preparation method of malate and a solid acid catalyst. The method comprises the following steps: mixing fatty alcohol, malic acid, a solid acid catalyst and water for esterification reaction to obtain malate; the solid acid catalyst comprises an alumina carrier, and methanesulfonic acid and hypophosphorous acid which are loaded on the alumina carrier. The solid acid catalyst adopted by the method is high in catalytic activity and can be repeatedly used, the conversion rate of malic acid can be greatly increased, and the product quality is improved; in addition, a small amount of water is added as a medium, the reaction is carried out under normal pressure, then esterification reaction is promoted through vacuum dehydration, and the malic acid conversion rate is increased. Results of the embodiment show that the chromatic value of the malate prepared by the method is less than or equal to 35, the acid value is less than or equal to 0.56 mg / gKOH, and the conversion rate of malic acid can reach 98.4% or above.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, and in particular to a method for preparing malic acid ester and a solid acid catalyst. Background Art

[0002] Malic acid esters have excellent lubrication, dispersing, emulsifying and solubilizing properties and are widely used in the fields of medicine, food and daily chemicals. Among them, diisostearyl malate is a surfactant with good wetting effect and can be used as a raw material for cosmetics. The preparation methods of malic acid esters mainly include direct esterification, transesterification, acyl chloride, anhydride acylation and coupling agent method, among which the most widely used synthesis method is direct esterification.

[0003] The direct esterification method uses malic acid and alcohol as raw materials and performs an esterification reaction under the action of a catalyst. A method for preparing malic acid ester using malic acid and diisostearyl alcohol is reported in the related art, wherein a composite oxide (composed of non-metallic P, alkali metal Cs, transition metal V, Cu, Mo, rare earth metal La, Nd and other composite oxides) is used as a catalyst, cyclohexane is used as a water-carrying agent, and malic diisostearyl alcohol malate is obtained by reaction at 180-240°C. The raw materials for the preparation of the catalyst of this method are expensive, the cost is high, and the reaction needs to be carried out under cyclohexane with water, the operation is complicated, and the conversion rate of malic acid can only reach about 90%. In addition, the malic acid ester prepared by the current traditional method is prone to the problem of excessive chromaticity and acid value, and the product quality is not high.

[0004] In summary, there is an urgent need to provide a method for preparing malic acid esters with simple operation, low cost, high conversion rate and good product quality. Summary of the invention

[0005] In view of this, the present invention provides a preparation method of malic acid ester and a solid acid catalyst. The preparation method provided by the present invention is simple to operate, low in cost, high in malic acid conversion rate, and the acid value and chromaticity value of the obtained product are low, and the product quality is good.

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

[0007] A method for preparing malic acid ester comprises the following steps: mixing fatty alcohol, malic acid, a solid acid catalyst and water for esterification reaction to obtain malic acid ester; the solid acid catalyst comprises an alumina carrier and methylsulfonic acid and hypophosphorous acid loaded on the alumina carrier; the esterification reaction comprises sequentially performing a normal pressure reaction stage and a vacuum dehydration stage.

[0008] Preferably, the preparation method of the solid acid catalyst comprises:

[0009] The aluminum oxide powder is first immersed in a methanesulfonic acid aqueous solution and then subjected to a first microwave heat treatment to obtain acidic aluminum oxide;

[0010] The acidic aluminum oxide is immersed in a hypophosphorous acid aqueous solution for a second time and then subjected to a second microwave heat treatment to obtain the solid acid catalyst.

[0011] Preferably, the concentration of the methanesulfonic acid aqueous solution is 8-15 wt %, the first immersion time is 24-72 h; the temperature of the first microwave heat treatment is 60-120° C., and the time is 2-5 h;

[0012] The concentration of the hypophosphorous acid aqueous solution is 8-15wt%; the second immersion time is 24-72h; the temperature of the second microwave heat treatment is 60-120°C, and the time is 2-5h.

[0013] Preferably, the method for preparing the alumina powder comprises: mixing an aluminum salt solution and a urea solution under ultrasonic conditions to perform a precipitation reaction, and calcining the obtained solid product to obtain the alumina powder.

[0014] Preferably, the precipitation reaction time is 2 to 5 hours; the calcination temperature is 800 to 1200° C., the time is 4 to 8 hours, and the calcination is carried out under the action of a microwave field.

[0015] Preferably, the fatty alcohol is an isomeric fatty alcohol, and the number of carbon atoms of the isomeric fatty alcohol is greater than or equal to 10; the molar ratio of the fatty alcohol to malic acid is 1.9-2.2:1.

[0016] Preferably, the amount of the solid acid catalyst is 0.2-0.8% of the total mass of the fatty alcohol and the malic acid; and the mass of the water is less than or equal to 12% of the mass of the malic acid.

[0017] Preferably, the temperature of the normal pressure reaction stage is 100-105°C, and the time is 2-4 hours; the temperature of the vacuum dehydration stage is 105-115°C, and the time is 4-8 hours, and the vacuum degree is -0.04 to -0.085 MPa.

[0018] Preferably, after the esterification reaction is completed, the process further comprises separating the obtained reaction liquid into solid and liquid to obtain a recovered catalyst, and applying the recovered catalyst.

[0019] The invention also provides a solid acid catalyst, comprising an alumina carrier and methanesulfonic acid and hypophosphorous acid loaded on the alumina carrier.

[0020] The present invention provides a method for preparing malic acid ester, comprising the following steps: mixing fatty alcohol, malic acid, a solid acid catalyst and water for esterification reaction to obtain malic acid ester; the solid acid catalyst comprises an alumina carrier and methylsulfonic acid and hypophosphorous acid loaded on the alumina carrier. The solid acid catalyst used in the present invention contains a methylsulfonic acid group and a hypophosphorous acid group, has a synergistic catalytic effect, high catalytic activity, can be reused, can effectively reduce costs, and has mild reaction conditions, and general reaction equipment can meet the requirements; the hypophosphorous acid group in the solid acid catalyst used in the present invention can also effectively prevent the occurrence of oxidation reaction during the reaction, so that the prepared product has low chromaticity.

[0021] In addition, malic acid has a relatively high melting point and is not easily soluble in general organic solvents. It is easy to form sticky reactants during the reaction, resulting in a low conversion rate of malic acid esters and unqualified indicators such as the acid value of the product. The present invention adds a small amount of water as a medium and first reacts under normal pressure. After most of the malic acid reacts with the isomeric fatty alcohols, water is distilled off by reduced pressure distillation to promote esterification and improve the conversion rate of malic acid. The results of the embodiment show that the color value of the malic acid ester prepared by the present invention is ≤35, the acid value is ≤0.56mg / gKOH, and the conversion rate of malic acid can reach more than 98.4%.

[0022] Furthermore, when preparing malic acid esters by the traditional direct esterification method, it is usually necessary to use a large excess of fatty alcohol to promote the conversion rate of malic acid in the esterification reaction. The solid acid catalyst of the present invention contains a sulfonic acid group and a hypophosphorous acid group, which has a synergistic catalytic effect and can promote a more thorough reaction when a small excess of alcohol is used. Therefore, the present invention can adjust the amount of fatty alcohol according to actual needs, so that the esterification reaction can be carried out under the condition of a slight excess of fatty alcohol, without the step of recovering the fatty alcohol, and the operation is simpler.

[0023] The present invention also provides a solid acid catalyst. The solid acid catalyst provided by the present invention has high catalytic activity, simple composition, low cost, no need to use organic solvents, no excessive alcohol recovery, and can be reused. It is green, pollution-free and environmentally friendly. Using it to prepare malic acid ester can greatly improve the conversion rate of malic acid and obtain high-quality products. DETAILED DESCRIPTION

[0024] The invention provides a method for preparing malic acid ester, comprising the following steps: mixing fatty alcohol, malic acid, a solid acid catalyst and water for esterification reaction to obtain malic acid ester; the solid acid catalyst comprises an alumina carrier and methylsulfonic acid and hypophosphorous acid loaded on the alumina carrier; the esterification reaction comprises sequentially performing a normal pressure reaction stage and a vacuum dehydration stage.

[0025] In the present invention, the content of methanesulfonic acid in the solid acid catalyst is preferably 5 to 15 wt %, and the content of hypophosphorous acid is preferably 5 to 15 wt %.

[0026] In the present invention, the preparation method of the solid acid catalyst preferably comprises: soaking alumina powder in a methanesulfonic acid aqueous solution for a first time and then performing a first microwave heat treatment to obtain acidic alumina; soaking the acidic alumina in a hypophosphorous acid aqueous solution for a second time and then performing a second microwave heat treatment to obtain the solid acid catalyst.

[0027] In the present invention, the preparation method of the alumina powder preferably comprises: mixing an aluminum salt solution and a urea solution under ultrasonic conditions for precipitation reaction, and calcining the obtained solid product to obtain the alumina powder; the aluminum salt is preferably aluminum nitrate, and the concentration of the aluminum salt solution is preferably 45-55wt%, specifically 48wt% or 50wt%; the concentration of the urea solution is preferably 40-50wt%, specifically 45wt% or 50wt%; the power of the ultrasonic condition is preferably 30-40W, specifically 35W or 40W; the aluminum salt and urea solution are preferably mixed in a manner of: under ultrasonic conditions, dripping the urea solution into The aluminum salt solution is added until the pH value of the system reaches 9 to 10; the precipitation reaction time is preferably 2 to 5 hours, specifically 3 hours or 4 hours, the precipitation reaction temperature is preferably room temperature, and the precipitation reaction time is counted from the completion of the dropwise addition of the urea solution; after the precipitation reaction is completed, the obtained reaction solution is preferably filtered, and the obtained filter cake is rinsed with deionized water and collected in a crucible, and then calcined; the calcination temperature is preferably 800 to 1200°C, specifically 800°C, 900°C or 1000°C, the calcination time is preferably 4 to 8 hours, specifically 4 hours, 6 hours or 7 hours; the calcination is preferably carried out under microwave field conditions. Microwave heating is more uniform and rapid. The present invention performs calcination under microwave field conditions, which can effectively reduce the agglomeration of powder materials and make the obtained alumina powder particle size more uniform.

[0028] After obtaining the alumina powder, the present invention first soaks the alumina powder in a methanesulfonic acid aqueous solution and then performs a first microwave heat treatment to obtain acidic alumina. In the present invention, the concentration of the methanesulfonic acid aqueous solution is preferably 8-15wt%, specifically 8wt%, 10wt%, 12wt% or 15wt%; the first soaking time is preferably 24h, and the temperature is preferably room temperature; after the first soaking, it is preferably filtered, and then the obtained solid product is subjected to a first microwave heat treatment; the temperature of the first microwave heat treatment is preferably 60-120°C, specifically 60°C, 80°C, 100°C or 120°C, and the time of the first microwave heat treatment is preferably 2-5h, specifically 2h, 3h, 4h or 5h.

[0029] After obtaining the acidic alumina, the present invention performs a second microwave heat treatment after soaking the acidic alumina in a hypophosphorous acid aqueous solution for a second time to obtain the solid acid catalyst. In the present invention, the concentration of the hypophosphorous acid aqueous solution is preferably 8-15wt%, specifically 8wt%, 10wt%, 12wt% or 15wt%; the second soaking time is preferably 24h, and the temperature is preferably room temperature; after the second soaking, it is preferably filtered, and then the obtained solid product is subjected to a second microwave heat treatment; the temperature of the second microwave heat treatment is preferably 60-120°C, specifically 60°C, 80°C, 100°C or 120°C, and the time of the second microwave heat treatment is preferably 2-5h, specifically 2h, 3h, 4h or 5h. The present invention can accelerate the volatilization of water, reduce the agglomeration of material particles, and make methylsulfonic acid and hypophosphorous acid adhere more firmly to alumina and not easy to desorb through the first microwave heat treatment and the second microwave heat treatment.

[0030] In the present invention, the fatty alcohol is preferably an isomeric fatty alcohol, and the number of carbon atoms of the isomeric fatty alcohol is preferably greater than or equal to 10, more preferably 10 to 20, and specifically can be 12, 13, 15, 16, 18 or 20; specifically, the isomeric fatty alcohol preferably includes one or more of isomeric C12-13 alcohol, isomeric C12-15 alcohol, isomeric hexadecanol, isomeric octadecyl alcohol and isomeric eicosanol; the malic acid is preferably food grade malic acid; the molar ratio of the fatty alcohol to malic acid is preferably 1.9 to 2.2:1, specifically 1.9:1, 2:1, 2.1:1 or 2.2:1. The present invention can achieve a thorough reaction in the case of a small excess of alcohol, and the amount of fatty alcohol can be adjusted according to actual needs, so that the esterification reaction can be carried out under the condition of a slight excess of fatty alcohol, without the step of recovering the fatty alcohol, and the operation is simpler.

[0031] In the present invention, the amount of the solid acid catalyst is preferably 0.2-0.8% of the total mass of the fatty alcohol and malic acid, specifically 0.3%, 0.4%, 0.5% or 0.6%.

[0032] In the present invention, the water is preferably distilled water, and the mass of the water is preferably less than or equal to 12% of the mass of the malic acid, more preferably 8-12% of the mass of the malic acid, and specifically can be 9%, 10% or 11%. In the present invention, adding a small amount of water can prevent malic acid from generating sticky reactants during the reaction process and improve the conversion rate.

[0033] In the present invention, the esterification reaction comprises a normal pressure reaction stage and a vacuum dehydration stage in sequence; the temperature of the normal pressure reaction stage is preferably 100-105°C, and the time is preferably 2-4h, specifically 2h, 3h or 4h; the temperature of the vacuum dehydration stage is preferably 105-115°C, specifically 105°C, 110°C or 112°C, the time of the vacuum dehydration stage is preferably 4-8h, specifically 4h, 5h, 6h or 7h, and the vacuum degree of the vacuum dehydration stage is preferably -0.04 to -0.085MPa, specifically -0.05MPa, -0.06MPa, -0.07MPa or -0.08MPa. In a specific embodiment of the present invention, it is preferred to first add fatty alcohol, malic acid, a solid acid catalyst and water into a reaction device, then start stirring and cooling water, heat the feed liquid to 100-105°C, keep the temperature at normal pressure for reaction, then heat to 105-115°C, adjust the vacuum to -0.04MPa, then gradually adjust the vacuum of the system to -0.085MPa, then continue to react for 4-8h, and stop the reaction after no obvious water is generated. The present invention first reacts at normal pressure for a period of time, and then distills water out by reduced pressure distillation after most of the malic acid reacts with the fatty alcohol, promotes esterification, and improves the conversion rate of malic acid.

[0034] After the esterification reaction is completed, the present invention preferably performs solid-liquid separation on the obtained reaction liquid, and the obtained solid is a recovered catalyst, and the recovered catalyst is applied; in a specific embodiment of the present invention, the solid obtained by solid-liquid separation is preferably added to ethanol, stirred and soaked, and then filtered, and then the obtained filter cake is subjected to microwave heating to obtain a recovered catalyst; the volume fraction of the ethanol is preferably 90-95%, the soaking time is preferably 24-72h, the temperature of the microwave heating treatment is preferably 60-120°C, and the time is preferably 2-5h.

[0035] In the present invention, the liquid obtained after the solid-liquid separation of the obtained reaction liquid is the crude filtrate. The present invention preferably mixes the crude filtrate and a baking soda solution, then centrifuges, and takes the oil phase for drying to obtain the malic ester; the concentration of the baking soda solution is preferably 8 to 10 wt%; the mixing temperature is preferably 75°C, the time is preferably 10 to 30 min, and the amount of the baking soda solution is based on neutralizing the pH value of the mixed liquid to 7 to 8; the drying is preferably vacuum drying; the vacuum drying temperature is preferably 115 to 120°C, the insulation time is preferably 15 to 25 min, and the vacuum degree is preferably -0.095 to -0.01 MPa.

[0036] In the present invention, the structural formula of the malate is as shown in Formula I:

[0037]

[0038] In formula I, R represents an alkyl group, specifically an isomeric alkyl group.

[0039] The present invention also provides a solid acid catalyst, comprising an alumina carrier and methanesulfonic acid and hypophosphorous acid supported on the alumina carrier. The specific preparation method of the solid acid catalyst is consistent with the above scheme, which is not repeated here. The solid acid catalyst provided by the present invention has high catalytic activity, simple composition, low cost, and can be reused. The solid acid catalyst is used to prepare malic acid ester, which can greatly improve the conversion rate of malic acid and obtain high-quality products.

[0040] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] Example 1

[0042] A 50 wt% aluminum nitrate solution was added to an ultrasonic reactor, and a 50 wt% urea solution was added dropwise under the action of 30 W ultrasonic waves. The addition was stopped when the pH reached 9. After the reaction was continued at room temperature for 2 h, the filter cake was filtered and washed with deionized water. The filter cake was collected in a crucible and calcined at 800 ° C for 4 h under the action of a microwave field. The calcined alumina was collected and slightly ground for later use.

[0043] Alumina powder was added to a 10 wt % methanesulfonic acid aqueous solution, stirred and soaked for 24 h, filtered, and microwaved and heated at 120° C. for 2 h to obtain acidic alumina.

[0044] Acidic alumina was added to a 10 wt % hypophosphorous acid aqueous solution, stirred and soaked for 24 h, filtered, and microwaved for 2 h at 120° C. to obtain a solid acid catalyst, wherein the content of methanesulfonic acid was 8.8 wt % and the content of hypophosphorous acid was 9.2 wt %.

[0045] The solid acid catalyst prepared in Example 1 was applied in subsequent examples.

[0046] Example 2

[0047] Add 108g of isomeric 13-ol, 35g of malic acid, 0.5g of solid acid catalyst and 3.5g of distilled water into a three-necked flask, stir, cool the condenser, raise the material temperature to 102°C and keep the reaction for 4 hours, then raise the material temperature to 110°C and keep the reaction, adjust the vacuum degree to -0.04MPa, adjust the vacuum degree to -0.085MPa within 1 hour, and then continue the reaction for 4 hours, no obvious water is generated, sample the acid value to be 1.67mg / g KOH, stop heating, filter to obtain the crude product filtrate and recover the catalyst filter cake. Heat the crude product filtrate to 75°C, add 7g of 10wt% sodium bicarbonate solution and neutralize for 10min, centrifuge the oil phase and keep it at 115°C for 15min under vacuum -0.095MPa, filter to obtain the finished product, and the acid value of the finished product is 0.31mg / g KOH.

[0048] Example 3

[0049] Add 108g of isomeric C12-15 alcohol, 35g of malic acid, 0.5g of solid acid catalyst and 3.5g of distilled water into a three-necked flask, stir, cool the condenser, raise the material temperature to 102°C and keep the reaction for 4h, then raise the material temperature to 110°C, adjust the vacuum degree to -0.04MPa, adjust the vacuum degree to -0.085MPa within 1h, and continue the reaction for 4h, no obvious water is generated, sample the acid value to be 1.92mg / g KOH, stop heating, filter to obtain the crude product filtrate and recover the catalyst filter cake. Heat the crude product filtrate to 75°C, add 6g of 10wt% sodium bicarbonate solution and neutralize for 10min, centrifuge the oil phase and keep it at 115°C for 15min under vacuum -0.095MPa, filter to obtain the finished product, and the acid value of the finished product is 0.56mg / g KOH.

[0050] Example 4

[0051] Add 121g isomeric hexadecanol, 35g malic acid, 0.6g solid acid catalyst and 3.5g distilled water into a three-necked flask, stir, cool the condenser, raise the material temperature to 102℃ and keep the reaction for 4h, then raise the material temperature to 115℃ and keep the reaction, adjust the vacuum degree to -0.04MPa, adjust the vacuum degree to -0.085MPa within 1h, and then continue the reaction for 8h, no obvious water is generated, sample the acid value to 2.35mg / g KOH, stop heating, filter to obtain the crude product filtrate and recover the catalyst filter cake. Heat the crude product filtrate to 75℃, add 4.5g 10wt% sodium bicarbonate solution and neutralize for 10min, centrifuge the oil phase and keep it at 115℃ for 15min under vacuum -0.095MPa, filter to obtain the finished product, the acid value of the finished product is 0.48mg / g KOH.

[0052] Example 5

[0053] Add 135g of isomeric octadecyl alcohol, 35g of malic acid, 0.6g of homemade solid acid catalyst and 3.5g of distilled water into a three-necked flask, stir, cool the condenser tube, raise the material temperature to 102°C and keep the reaction for 4h, then raise the material temperature to 115°C, adjust the vacuum degree to -0.04MPa, adjust the vacuum degree to -0.085MPa for 1h, and continue the reaction for 8h, no obvious water is generated, sample the acid value to be 2.88mg / g KOH, stop heating, filter to obtain the crude product filtrate and recover the catalyst filter cake. Heat the crude product filtrate to 75°C, add 6.5g of 10wt% sodium bicarbonate solution and neutralize for 10min, centrifuge the oil phase and keep it at 115°C for 15min under vacuum -0.095MPa, filter to obtain the finished product, and the acid value of the finished product is 0.38mg / g KOH.

[0054] Example 6

[0055] Add 155g of isomeric octadecyl alcohol, 35g of malic acid, 0.6g of solid acid catalyst and 3.5g of distilled water into a three-necked flask, stir, cool the condenser tube, raise the material temperature to 102°C and keep the reaction for 3h, then raise the material temperature to 115°C, adjust the vacuum to -0.04MPa, adjust the vacuum to -0.085MPa for 1h, and continue the reaction for 4h. No obvious water is generated. The acid value of the sample is 2.15mg / g KOH. Stop heating and filter to obtain a crude filtrate and a catalyst filter cake. Heat the crude filtrate to 75°C, add 4.5g of 10wt% sodium bicarbonate solution and neutralize for 10min, centrifuge and take the oil phase under vacuum -0.095MPa, keep it at 115°C for 15min, filter to obtain the finished product, and the acid value of the finished product is 0.55mg / g KOH.

[0056] Example 7

[0057] The catalyst filter cake obtained in Example 6 was added to 95% ethanol and stirred and soaked for one day, then filtered. After collecting the filter cake, microwave heating treatment was performed at 120°C for 2h to obtain a recovered catalyst for standby use. 155g isomeric octadecyl alcohol, 35g malic acid, 0.6g recovered catalyst and 3.5g distilled water were added to a three-necked flask, stirring was started, cooling water was turned on the condenser, the material temperature was raised to 102°C and kept warm for 4h, the material temperature was raised to 115°C and kept warm, the vacuum was adjusted to -0.04MPa, and the vacuum was adjusted to -0.085MPa for 1h, and then the reaction was continued for 6h, no obvious water was generated, and the acid value of the sample was 2.53mg / g KOH, the heating was stopped, and the crude product filtrate and the recovered catalyst filter cake were obtained by filtration. The crude filtrate was heated to 75°C, and 7.3 g of 10 wt% baking soda solution was added for neutralization for 10 min. After centrifugation, the oil phase was taken out and kept warm at 115°C for 15 min under vacuum -0.095 MPa, and the finished product was obtained by filtration. The acid value of the finished product was 0.53 mg / g KOH.

[0058] The chromaticity and acid value of the crude products in Examples 2 to 7 and the chromaticity, acid value, saponification value and hydroxyl value of the finished products were tested, and the malic acid conversion rate was calculated. The results are shown in Table 1.

[0059] Table 1 Test results of Examples 2 to 7

[0060] index Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Crude color (hazen) 25 25 30 50 30 40 Crude acid value (mg / gKOH) 1.67 1.92 2.35 2.88 2.15 2.53 Finished product color (hazen) 20 20 25 35 30 35 Finished product acid value (mg / gKOH) 0.31 0.56 0.48 0.38 0.55 0.53 Finished product saponification value (mg / gKOH) 215.3 214.7 196.5 181.8 160.4 159.4 Finished product hydroxyl value (mg / gKOH) 125.8 118.2 92.8 84.8 97.7 96.3 Malic acid conversion rate (%) 99.3 99.1 98.8 98.4 98.7 98.4

[0061] It can be seen from Table 1 that the malate prepared by the present invention has low chroma and acid value, and high conversion rate of malic acid. At the same time, it can be seen from Example 7 that the malate prepared by recycling the catalyst can still obtain a high conversion rate of malic acid, and the product quality is good, which shows that the catalyst of the present invention has good reusability.

[0062] Comparative Example 1: Using p-toluenesulfonic acid as catalyst

[0063] Add 155g of isomeric octadecyl alcohol, 35g of malic acid, 0.95g of p-toluenesulfonic acid and 3.5g of distilled water into a three-necked flask, stir, cool the condenser, raise the material temperature to 102°C and keep the reaction for 4h, then raise the material temperature to 115°C, adjust the vacuum degree to -0.04MPa, adjust the vacuum degree to -0.085MPa for 1h, continue the reaction for 10h, no obvious water is generated, sample the acid value to 7.33mg / g KOH, stop heating, filter to obtain the crude filtrate and catalyst filter cake. Heat the crude filtrate to 75°C, add 15.3g of 10wt% sodium bicarbonate solution to neutralize for 10min, centrifuge the oil phase, keep it at 115°C for 15min under vacuum -0.095MPa, filter to obtain the finished product, the acid value of the finished product is 0.59mg / g KOH.

[0064] Comparative Example 2: Reaction without adding distilled water

[0065] Add 155g of isomeric octadecyl alcohol, 35g of malic acid and 0.6g of solid acid catalyst to a three-necked flask, stir, turn on cooling water on the condenser, raise the material temperature to 102°C and keep the reaction for 4h, then raise the material temperature to 115°C, adjust the vacuum to -0.04MPa, adjust the vacuum to -0.085MPa for 1h, continue the reaction for 3h, no obvious water is generated, the acid value of the sample is 8.72mg / gKOH (there is a sticky precipitate at the bottom, which can be partially dissolved after adding distilled water, and the acid value of the stirred sample is 14.8), stop heating, filter to obtain the crude filtrate, catalyst and sticky filter cake. Heat the crude filtrate to 75°C, add 31g of 10wt% sodium bicarbonate solution and neutralize for 10min, centrifuge and take the oil phase under vacuum -0.095MPa, keep it at 115°C for 15min, filter to obtain the finished product, and the acid value of the finished product is 1.08mg / g KOH.

[0066] Comparative Example 3: The amount of distilled water is 100% of the mass of malic acid

[0067] Add 155g of isomeric octadecyl alcohol, 35g of malic acid, 0.6g of solid acid catalyst and 35g of distilled water into a three-necked flask, stir, cool the condenser tube, raise the material temperature to 102°C and keep the reaction for 4h, then raise the material temperature to 115°C, adjust the vacuum to -0.01MPa, adjust the vacuum to -0.085MPa for 5h, continue the reaction for 4h (because more water is added, there is emulsification, and the vacuum adjustment is slow), no obvious water is generated, the acid value of the sample is 2.42mg / g KOH, stop heating, filter to obtain the crude filtrate and catalyst filter cake. Heat the crude filtrate to 75°C, add 5g of 10wt% sodium bicarbonate solution and neutralize for 10min, centrifuge and take the oil phase under vacuum -0.095MPa, keep it at 115°C for 15min, filter to obtain the finished product, and the acid value of the finished product is 0.46mg / gKOH.

[0068] The chromaticity and acid value of the crude products in Comparative Examples 1 to 3 and the chromaticity, acid value, saponification value and hydroxyl value of the finished products were tested, and the malic acid conversion rate was calculated. The results are shown in Table 2.

[0069] Table 2 Test results of comparative examples 1 to 3

[0070] index Comparative Example 1 Comparative Example 2 Comparative Example 3 Crude color (hazen) 100 30 35 Crude acid value (mg / gKOH) 7.33 8.72 2.42 Finished product color (hazen) 75 20 25 Finished product acid value (mg / gKOH) 0.59 1.08 0.46 Finished product saponification value (mg / gKOH) 155.5 132.7 160.8 Finished product hydroxyl value (mg / gKOH) 97.7 126.1 97.6 Malic acid conversion rate (%) 95.5 81.9 98.5

[0071] According to the data in Table 2, it can be seen that when p-toluenesulfonic acid is used as a catalyst (Comparative Example 1), the chromaticity and acid value of the obtained product are higher, and the conversion rate of malic acid is reduced; when no distilled water is added during the esterification reaction (Comparative Example 2), the acid value of the obtained product is also higher, and the conversion rate of malic acid is significantly reduced; when a large amount of distilled water is used (Comparative Example 3), the vacuum degree during vacuum dehydration is difficult to increase, the reaction time is prolonged, and the energy consumption for dehydration is large.

[0072] 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 malic acid ester, characterized in that: The following steps are involved: Fatty alcohol, malic acid, a solid acid catalyst and water are mixed for esterification reaction to obtain malic acid ester; the solid acid catalyst comprises an alumina carrier and methanesulfonic acid and hypophosphorous acid loaded on the alumina carrier; the esterification reaction comprises a normal pressure reaction stage and a vacuum dehydration stage in sequence.

2. The preparation method according to claim 1, characterized in that: The preparation method of the solid acid catalyst comprises: The aluminum oxide powder is first immersed in a methanesulfonic acid aqueous solution and then subjected to a first microwave heat treatment to obtain acidic aluminum oxide; The acidic aluminum oxide is immersed in a hypophosphorous acid aqueous solution for a second time and then subjected to a second microwave heat treatment to obtain the solid acid catalyst.

3. The preparation method according to claim 2, characterized in that: The concentration of the methanesulfonic acid aqueous solution is 8-15 wt %, and the first soaking time is 24-72 h; the temperature of the first microwave heat treatment is 60-120° C., and the time is 2-5 h; The concentration of the hypophosphorous acid aqueous solution is 8-15wt%; the second immersion time is 24-72h; the temperature of the second microwave heat treatment is 60-120°C, and the time is 2-5h.

4. The preparation method according to claim 2, characterized in that: The preparation method of the alumina powder comprises: mixing an aluminum salt solution and a urea solution under ultrasonic conditions to carry out a precipitation reaction, and calcining the obtained solid product to obtain the alumina powder.

5. The preparation method according to claim 4, characterized in that: The precipitation reaction time is 2 to 5 hours; the calcination temperature is 800 to 1200° C., the time is 4 to 8 hours, and the calcination is carried out under the action of a microwave field.

6. The preparation method according to claim 1, characterized in that: The fatty alcohol is an isomeric fatty alcohol, and the number of carbon atoms of the isomeric fatty alcohol is greater than or equal to 10; the molar ratio of the fatty alcohol to malic acid is 1.9-2.2:

1.

7. The preparation method according to claim 1, characterized in that: The dosage of the solid acid catalyst is 0.2-0.8% of the total weight of the fatty alcohol and the malic acid; the weight of the water is less than or equal to 12% of the weight of the malic acid.

8. The preparation method according to claim 1, characterized in that: The temperature of the normal pressure reaction stage is 100-105° C., and the time is 2-4 hours; the temperature of the vacuum dehydration stage is 105-115° C., and the time is 4-8 hours, and the vacuum degree is -0.04 to -0.085 MPa.

9. The preparation method according to claim 1, characterized in that: After the esterification reaction is completed, the obtained reaction liquid is separated into solid and liquid to obtain a recovered catalyst, and the recovered catalyst is applied.

10. A solid acid catalyst, characterized in that The invention comprises an alumina carrier and methanesulfonic acid and hypophosphorous acid supported on the alumina carrier.

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