CN109453784B - Catalyst for synthesizing p-dimethylaminobenzoate and preparation method and application thereof - Google Patents
Catalyst for synthesizing p-dimethylaminobenzoate and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a catalyst for synthesizing p-dimethylaminobenzoate, a preparation method and application thereof, wherein the catalyst comprises metal Ni, Pd and carrier alumina, wherein the mass percent of Ni in the catalyst is 0.8-1.1%, the mass percent of Pd in the catalyst is 0.2-0.5%, and the balance is alumina. The invention also discloses a preparation method and application of the catalyst. The prepared catalyst takes p-nitrobenzoate and formaldehyde as raw materials, nitro hydrogenation and methyl reaction are completed in one step to generate a target product, and the molar yield is high; the preparation method is characterized in that a sectional filling and sectional feeding mode is adopted, the catalyst mainly performs a nitro hydrogenation reaction at the upper end of the reaction tube, the reaction is violent, the material reacted at the upper end enters the catalyst at the lower end with reaction heat, the material mainly comprises an amino compound and reacts with formaldehyde to form a methyl group, and the rest of unreacted nitro compound is quickly converted into the amino compound on the undiluted catalyst.
Description
Technical Field
The invention belongs to the technical field of catalysts, and particularly relates to a catalyst for synthesizing p-dimethylaminobenzoate and a preparation method and application thereof.
Background
The common p-dimethylaminobenzoic acid ester compounds mainly comprise methyl p-dimethylaminobenzoate, ethyl p-dimethylaminobenzoate, n-butyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate and isooctyl p-dimethylaminobenzoate, and the p-dimethylaminobenzoate compounds have good ultraviolet resistance, so the p-dimethylaminobenzoate compounds are widely used as ultraviolet resistance additives and can play a good sun-screening effect when being added into cosmetics and sun-screening creams, and particularly the isooctyl p-dimethylaminobenzoate is recommended as a first-class sun-screening agent by the United states food and drug administration. The p-dimethylaminobenzoate compounds are used as ultraviolet initiators and also high-efficiency amine accelerators, are usually used together with photoinitiators and matched with free radical type II photoinitiators, are widely applied to the aspects of papermaking ink, metal or polymer coatings, wood varnish and the like, and play a role in ultraviolet curing. In addition, p-dimethylaminobenzoate compounds can also be used as preservatives.
In the relatively laggard age of catalytic hydrogenation catalyst technology, the routes for producing p-dimethylaminobenzoate compounds mainly include 3: firstly, the method comprises the following steps: performing esterification reaction on dimethylaminobenzoic acid and corresponding alcohol directly, and using acid as a catalyst; secondly, the method comprises the following steps: performing nitrogen methylation on the aminobenzoate directly, wherein dimethyl sulfate, formaldehyde sodium cyanoborohydride or methyl iodide is generally adopted as a methylation reagent; thirdly, the method comprises the following steps: p-dimethylaminobenzaldehyde is used as a raw material, p-dimethylaminobenzoic acid is prepared under the action of a catalyst, and then esterification reaction is carried out under the action of an acid catalyst. The three methods have the defects of low production efficiency, high toxicity, low product yield and the like, can not meet the current domestic environment-friendly requirement, and the traditional strong acid type catalyst and the environment-unfriendly homogeneous catalyst are gradually updated and replaced by a novel catalyst along with the development of the catalytic technology and the progress of the catalyst.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a catalyst for synthesizing p-dimethylaminobenzoate and a preparation method and application thereof.
The catalyst for synthesizing p-dimethylaminobenzoate comprises metal Ni, Pd and carrier alumina, wherein the mass percent of Ni in the catalyst is 0.8-1.1%, the mass percent of Pd in the catalyst is 0.2-0.5%, and the balance is alumina.
Preferably, the alumina is hollow bar-shaped gamma alumina, the length of the gamma alumina is 3-6mm, the diameter of the gamma alumina is 1.5mm, and the inner diameter of the middle cavity is 0.8 mm.
The preparation method of the catalyst comprises the following steps:
(1) pretreatment of a carrier: soaking alumina in a hydrochloric acid solution for 2h, taking out, drying at 120 ℃ for 12h, then soaking in ethanol until the adsorption is saturated, taking out, drying at 120 ℃ for 12h, and then roasting in a muffle furnace at 800-900 ℃ for 0.5-1.5h to obtain a pretreated alumina carrier;
(2) preparing a Ni-loaded catalyst precursor by an isometric impregnation method: dissolving nickel nitrate hexahydrate into an ethanol water solution, adding an alumina carrier into the ethanol water solution, uniformly stirring, drying and drying at 120 ℃ for 12h, roasting in a muffle furnace at 400-600 ℃ for 0.5-1h, and then reducing for 2h by using hydrogen at 400-600 ℃ to obtain a Ni-loaded catalyst precursor;
(3) impregnating Pd: adding sponge palladium into aqua regia, heating to 60-90 ℃, dissolving, naturally cooling to room temperature, diluting with deionized water, and fixing the volume to 0.004-0.01g/mL of palladium ion concentration to obtain a Pd solution; filling a catalyst precursor into a reaction tube, dropwise adding a Pd solution from the upper end of the reaction tube under the protection of nitrogen, allowing the Pd solution to flow through the catalyst precursor and flow out from the lower end of the reaction tube, recycling the flowing Pd solution to the upper end of the reaction tube, dropwise adding, circulating, stopping dropwise adding the Pd solution when the Pd solution flowing out from the lower end of the reaction tube is colorless, changing nitrogen into hydrogen, heating to 100 ℃, keeping for 2h, heating to 200-500 ℃, activating for 2h, and cooling to obtain the catalyst for synthesizing the p-dimethylaminobenzoate.
Preferably, the volume concentration of the hydrochloric acid solution in the step (1) is 5-10%.
Preferably, the ethanol solution in step (2) has a volume concentration of 50%.
Preferably, the ratio of sponge palladium to aqua regia is (2-5) g: 10 mL.
A method for preparing p-dimethylaminobenzoate using the above catalyst, the method comprising: in a fixed bed reactor, dividing a catalyst into a catalyst A and a catalyst B with equal mass, wherein the catalyst A is filled at the lower end of a reaction tube, and the catalyst B is mixed with quartz sand with equal mass and then filled at the upper end of the reaction tube; the top of the reaction tube is provided with a first inlet, and the lower end of the reaction tube and the junction of the catalyst A and the catalyst B are provided with a second inlet; dividing hydrogen into a hydrogen A part and a hydrogen B part according to a ratio of 4: 6; mixing the p-nitrobenzoate serving as a raw material with a solvent, preheating to a reaction temperature, and feeding the mixture and hydrogen B together from a first inlet; preheating formaldehyde to the reaction temperature, feeding the formaldehyde and hydrogen A together from a second feeding hole, allowing a reaction product to flow out from the bottom of the reaction tube, and performing gas-liquid separation to obtain a target product p-dimethylaminobenzoate, a solvent and excessive hydrogen for recycling; wherein the reaction temperature is 40-70 ℃, the reaction pressure is 0.5-1MPa, and the space velocity of the p-nitrobenzoate is 0.4-0.8 g/(g.h).
Preferably, the molar ratio of the p-nitrobenzoate to the formaldehyde to the hydrogen to the solvent is 1: (2.2-2.6): (5.5-7): 2.
preferably, when the target product p-dimethylaminobenzoate is ethyl p-dimethylaminobenzoate (EDB), the raw material p-nitrobenzoate is ethyl p-nitrobenzoate, and the solvent is ethanol;
when the target product p-dimethylaminobenzoate is isoamyl p-dimethylaminobenzoate (IADB), the p-nitrobenzoate serving as the raw material is isoamyl p-nitrobenzoate, and the solvent is isoamyl alcohol;
when the target product p-dimethylaminobenzoate is isooctyl p-dimethylaminobenzoate (EHA), the raw material p-nitrobenzoate is isooctyl p-nitrobenzoate, and the solvent is isooctanol;
when the target product p-dimethylaminobenzoate is methyl p-dimethylaminobenzoate, the p-nitrobenzoate serving as the raw material is methyl p-nitrobenzoate, and the solvent is methanol;
when the target product p-dimethylaminobenzoic acid ester is n-butyl p-dimethylaminobenzoate, the p-nitrobenzoate serving as the raw material is n-butyl p-nitrobenzoate, and the solvent is n-butanol.
Preferably, in the fixed bed reactor, the reaction tube is a stainless steel tube lined with a quartz tube, and the inner diameter of the quartz tube is 15-25 mm.
The invention has the advantages that:
1. the catalyst provided by the invention has high nickel content, replaces part of noble metals, can reduce the cost of the catalyst on the premise of not influencing the catalytic effect, and improves the cost performance;
2. the alumina carrier is treated by hydrochloric acid, ethanol and high temperature, so that the acidity of the carrier can be improved, the impurity content in the alumina carrier is reduced, impurities adsorbed by alumina are removed, the crystal form of the alumina is changed, and the surface pulverized alumina is removed, so that the catalyst carrier has strong acidity, can meet the requirement of methyl, does not need to additionally add sulfuric acid, and is environment-friendly; moreover, the hollow strip-shaped alumina carrier has large external specific surface area, can provide more contact area for catalyst preparation and catalytic reaction, and can play a good role in uniformly distributing or avoiding bias current in gas-liquid-solid three-phase reaction;
3. the prepared catalyst takes p-nitrobenzoate and formaldehyde as raw materials, nitro hydrogenation and methyl reaction are completed in one step to generate a target product, and the molar yield is high; the preparation method is characterized in that a sectional filling and sectional feeding mode is adopted, the catalyst mainly performs a nitro hydrogenation reaction at the upper end of the reaction tube, the reaction is violent, the material reacted at the upper end enters the catalyst at the lower end with reaction heat, the material mainly comprises an amino compound and reacts with formaldehyde to form a methyl group, and the rest of unreacted nitro compound is quickly converted into the amino compound on the undiluted catalyst.
Detailed Description
Example 1
1. The catalyst for synthesizing p-dimethylaminobenzoate comprises metal Ni, Pd and carrier alumina, wherein the mass percent of Ni in the catalyst is 0.8%, the mass percent of Pd in the catalyst is 0.3%, and the balance is alumina; wherein the alumina is hollow bar-shaped gamma alumina, the length of the alumina is 3-6mm, the outer diameter of the alumina is 1.5mm, and the inner diameter of the middle cavity is 0.8 mm.
2. A preparation method of a catalyst for synthesizing p-dimethylaminobenzoate comprises the following steps:
(1) pretreatment of a carrier: soaking alumina in a hydrochloric acid solution with the volume concentration of 10% for 2h, taking out, drying at 120 ℃ for 12h, then soaking in ethanol until the alumina is saturated, taking out, drying at 120 ℃ for 12h, and then roasting in a muffle furnace at 800 ℃ for 1.5h to obtain a pretreated alumina carrier;
(2) preparing a Ni-loaded catalyst precursor by an isometric impregnation method: dissolving 3.96g of nickel nitrate hexahydrate into 49.5mL of ethanol water solution with the volume concentration of 50%, adding 98.9g of alumina carrier, uniformly stirring, drying at 120 ℃ for 12h, roasting in a muffle furnace at 500 ℃ for 0.5h, and then reducing for 2h at 500 ℃ by using hydrogen to obtain a Ni-loaded catalyst precursor;
(3) impregnating Pd: adding 0.3g of sponge palladium into 1mL of aqua regia, heating to 70 ℃ to dissolve, naturally cooling to room temperature, diluting with deionized water to a constant volume of 500mL to obtain a Pd solution; filling a catalyst precursor into a reaction tube, dropwise adding a Pd solution from the upper end of the reaction tube under the protection of nitrogen, allowing the Pd solution to flow through the catalyst precursor and flow out from the lower end of the reaction tube, recycling the flowing Pd solution to the upper end of the reaction tube, dropwise adding, circulating, stopping dropwise adding the Pd solution when the Pd solution flowing out from the lower end of the reaction tube is colorless, changing nitrogen into hydrogen, heating to 100 ℃, keeping for 2h, heating to 200 ℃, activating for 2h, and cooling to obtain the catalyst for synthesizing the p-dimethylaminobenzoate.
3. A process for preparing methyl p-dimethylaminobenzoate using the catalyst, the process comprising: in a fixed bed reactor, dividing a catalyst into a catalyst A and a catalyst B with equal mass, wherein the catalyst A is filled at the lower end of a reaction tube, and the catalyst B is mixed with quartz sand with equal mass and then filled at the upper end of the reaction tube; the top of the reaction tube is provided with a first inlet, and the lower end of the reaction tube and the junction of the catalyst A and the catalyst B are provided with a second inlet; dividing hydrogen into a hydrogen A part and a hydrogen B part according to a ratio of 4: 6; mixing the raw material methyl p-nitrobenzoate with a solvent methanol, preheating to a reaction temperature, and feeding the mixture and hydrogen B together from a first inlet; preheating formaldehyde to the reaction temperature, feeding the formaldehyde and hydrogen A together from a second feeding hole, allowing a reaction product to flow out from the bottom of the reaction tube, and performing gas-liquid separation to obtain a target product methyl p-dimethylaminobenzoate, a solvent and excessive hydrogen for recycling; wherein the reaction temperature is 70 ℃, the reaction pressure is 0.8MPa, and the space velocity of the p-nitrobenzoate is 0.5 g/(g.h); the molar ratio of the methyl p-nitrobenzoate to the formaldehyde to the hydrogen to the methanol solvent is 1: 2.5: 6: 2; in the fixed bed reactor, a reaction tube is a stainless steel tube with a quartz tube inside, and the inner diameter of the quartz tube is 18 mm;
the molar yield of the target product methyl p-dimethylaminobenzoate is 99.1%.
Example 2
1. A catalyst for synthesizing p-dimethylaminobenzoate comprises metal Ni, Pd and carrier alumina, wherein the mass percent of Ni in the catalyst is 1%, the mass percent of Pd in the catalyst is 0.2%, and the balance is alumina; wherein the alumina is hollow bar-shaped gamma alumina, the length of the alumina is 3-6mm, the outer diameter of the alumina is 1.5mm, and the inner diameter of the middle cavity is 0.8 mm.
2. A preparation method of a catalyst for synthesizing p-dimethylaminobenzoate comprises the following steps:
(1) pretreatment of a carrier: soaking alumina in a hydrochloric acid solution with the volume concentration of 9% for 2h, taking out, drying at 120 ℃ for 12h, then soaking in ethanol until the alumina is saturated, taking out, drying at 120 ℃ for 12h, and then roasting in a muffle furnace at 900 ℃ for 0.5h to obtain a pretreated alumina carrier;
(2) preparing a Ni-loaded catalyst precursor by an isometric impregnation method: dissolving 4.95g of nickel nitrate hexahydrate into 49.5mL of ethanol aqueous solution with the volume concentration of 50%, adding 98.8g of alumina carrier, uniformly stirring, drying at 120 ℃ for 12h, roasting in a muffle furnace at 600 ℃ for 0.5h, and then reducing with hydrogen at 500 ℃ for 2h to obtain a Ni-loaded catalyst precursor;
(3) impregnating Pd: adding 0.2g of sponge palladium into 1mL of aqua regia, heating to 60 ℃ to dissolve, naturally cooling to room temperature, diluting with deionized water to a constant volume of 500mL to obtain a Pd solution; filling a catalyst precursor into a reaction tube, dropwise adding a Pd solution from the upper end of the reaction tube under the protection of nitrogen, allowing the Pd solution to flow through the catalyst precursor and flow out from the lower end of the reaction tube, recycling the flowing Pd solution to the upper end of the reaction tube, dropwise adding, circulating, stopping dropwise adding the Pd solution when the Pd solution flowing out from the lower end of the reaction tube is colorless, changing nitrogen into hydrogen, heating to 100 ℃, keeping for 2h, heating to 500 ℃, activating for 2h, and cooling to obtain the catalyst for synthesizing the p-dimethylaminobenzoate.
3. A process for preparing n-butyl p-dimethylaminobenzoate using the catalyst, the process comprising: in a fixed bed reactor, dividing a catalyst into a catalyst A and a catalyst B with equal mass, wherein the catalyst A is filled at the lower end of a reaction tube, and the catalyst B is mixed with quartz sand with equal mass and then filled at the upper end of the reaction tube; the top of the reaction tube is provided with a first inlet, and the lower end of the reaction tube and the junction of the catalyst A and the catalyst B are provided with a second inlet; dividing hydrogen into a hydrogen A part and a hydrogen B part according to a ratio of 4: 6; mixing the raw material of n-butyl p-nitrobenzoate and solvent of n-butyl alcohol, preheating to the reaction temperature, and feeding the mixture and hydrogen B from a first inlet; preheating formaldehyde to the reaction temperature, feeding the formaldehyde and hydrogen A together from a second feeding hole, allowing a reaction product to flow out from the bottom of the reaction tube, and performing gas-liquid separation to obtain a target product, namely n-butyl p-dimethylaminobenzoate, a solvent and excessive hydrogen for recycling; wherein the reaction temperature is 40 ℃, the reaction pressure is 0.5MPa, and the space velocity of the p-nitrobenzoate is 0.5 g/(g.h); the molar ratio of the p-nitrobenzoic acid n-butyl ester to the formaldehyde to the hydrogen to the solvent n-butanol is 1: 2.6: 6.5: 2; in the fixed bed reactor, a reaction tube is a stainless steel tube with a quartz tube inside, and the inner diameter of the quartz tube is 22 mm;
the molar yield of the target product, n-butyl p-dimethylaminobenzoate, is 95.7%.
Example 3
1. A catalyst for synthesizing p-dimethylaminobenzoate comprises metal Ni, Pd and carrier alumina, wherein the mass percent of Ni in the catalyst is 1%, the mass percent of Pd in the catalyst is 0.3%, and the balance is alumina; wherein the alumina is hollow bar-shaped gamma alumina, the length of the alumina is 3-6mm, the outer diameter of the alumina is 1.5mm, and the inner diameter of the middle cavity is 0.8 mm.
2. A preparation method of a catalyst for synthesizing p-dimethylaminobenzoate comprises the following steps:
(1) pretreatment of a carrier: soaking alumina in a hydrochloric acid solution with the volume concentration of 6% for 2h, taking out, drying at 120 ℃ for 12h, then soaking in ethanol until the alumina is saturated, taking out, drying at 120 ℃ for 12h, and then roasting in a muffle furnace at 900 ℃ for 1h to obtain a pretreated alumina carrier;
(2) preparing a Ni-loaded catalyst precursor by an isometric impregnation method: dissolving 4.95g of nickel nitrate hexahydrate into 49.5mL of ethanol aqueous solution with the volume concentration of 50%, adding 98.7g of alumina carrier by adopting an equal-volume impregnation method, uniformly stirring, drying at 120 ℃ for 12h, roasting in a muffle furnace at 400 ℃ for 1h, and then reducing by using hydrogen at 500 ℃ for 2h to obtain a Ni-loaded catalyst precursor;
(3) impregnating Pd: adding 0.3g of sponge palladium into 1mL of aqua regia, heating to 70 ℃ to dissolve, naturally cooling to room temperature, diluting with deionized water to a constant volume of 500mL to obtain a Pd solution; filling a catalyst precursor into a reaction tube, dropwise adding a Pd solution from the upper end of the reaction tube under the protection of nitrogen, allowing the Pd solution to flow through the catalyst precursor and flow out from the lower end of the reaction tube, recycling the flowing Pd solution to the upper end of the reaction tube, dropwise adding, circulating, stopping dropwise adding the Pd solution when the Pd solution flowing out from the lower end of the reaction tube is colorless, changing nitrogen into hydrogen, heating to 100 ℃, keeping for 2h, heating to 450 ℃, activating for 2h, and cooling to obtain the catalyst for synthesizing the p-dimethylaminobenzoate.
3. A method for preparing isoamyl p-dimethylaminobenzoate using the catalyst, the method comprising: in a fixed bed reactor, dividing a catalyst into a catalyst A and a catalyst B with equal mass, wherein the catalyst A is filled at the lower end of a reaction tube, and the catalyst B is mixed with quartz sand with equal mass and then filled at the upper end of the reaction tube; the top of the reaction tube is provided with a first inlet, and the lower end of the reaction tube and the junction of the catalyst A and the catalyst B are provided with a second inlet; dividing hydrogen into a hydrogen A part and a hydrogen B part according to a ratio of 4: 6; mixing raw material isoamyl p-nitrobenzoate and solvent isoamyl alcohol, preheating to reaction temperature, and feeding the mixture and hydrogen B together from a first inlet; preheating formaldehyde to the reaction temperature, feeding the formaldehyde and hydrogen A together from a second feeding hole, allowing a reaction product to flow out from the bottom of the reaction tube, and performing gas-liquid separation to obtain a target product isoamyl p-dimethylaminobenzoate, and recycling the solvent and excessive hydrogen; wherein the reaction temperature is 50 ℃, the reaction pressure is 0.9MPa, and the space velocity of the p-nitrobenzoate is 0.5 g/(g.h); the molar ratio of the isoamyl p-nitrobenzoate to the formaldehyde to the hydrogen to the solvent isoamyl alcohol is 1: 2.2: 6.5: 2; in the fixed bed reactor, a reaction tube is a stainless steel tube with a quartz tube inside, and the inner diameter of the quartz tube is 25 mm;
the molar yield of the target product isoamyl p-dimethylaminobenzoate is 96.9%.
Example 4
1. The catalyst for synthesizing p-dimethylaminobenzoate comprises metal Ni, Pd and carrier alumina, wherein the mass percent of Ni in the catalyst is 0.9%, the mass percent of Pd in the catalyst is 0.5%, and the balance is alumina; wherein the alumina is hollow bar-shaped gamma alumina, the length of the alumina is 3-6mm, the outer diameter of the alumina is 1.5mm, and the inner diameter of the middle cavity is 0.8 mm.
2. A preparation method of a catalyst for synthesizing p-dimethylaminobenzoate comprises the following steps:
(1) pretreatment of a carrier: soaking alumina in a hydrochloric acid solution with the volume concentration of 5% for 2h, taking out, drying at 120 ℃ for 12h, then soaking in ethanol until adsorption saturation, taking out, drying at 120 ℃ for 12h, and then roasting in a muffle furnace at 800 ℃ for 0.5h to obtain a pretreated alumina carrier;
(2) preparing a Ni-loaded catalyst precursor by an isometric impregnation method: dissolving 4.46g of nickel nitrate hexahydrate into 49.5mL of ethanol water solution with volume concentration of 50%, adding 98.6g of alumina carrier by adopting an equal-volume impregnation method, uniformly stirring, drying at 120 ℃ for 12h, roasting in a muffle furnace at 600 ℃ for 1h, and then reducing by using hydrogen at 400 ℃ for 2h to obtain a Ni-loaded catalyst precursor;
(3) impregnating Pd: adding 0.5g of sponge palladium into 1mL of aqua regia, heating to 90 ℃, dissolving, naturally cooling to room temperature, diluting with deionized water, and fixing the volume to 500mL to obtain a Pd solution; filling a catalyst precursor into a reaction tube, dropwise adding a Pd solution from the upper end of the reaction tube under the protection of nitrogen, allowing the Pd solution to flow through the catalyst precursor and flow out from the lower end of the reaction tube, recycling the flowing Pd solution to the upper end of the reaction tube, dropwise adding, circulating, stopping dropwise adding the Pd solution when the Pd solution flowing out from the lower end of the reaction tube is colorless, changing nitrogen into hydrogen, heating to 100 ℃, keeping for 2h, heating to 300 ℃, activating for 2h, and cooling to obtain the catalyst for synthesizing the p-dimethylaminobenzoate.
3. A process for preparing ethyl p-dimethylaminobenzoate using the catalyst, the process comprising: in a fixed bed reactor, dividing a catalyst into a catalyst A and a catalyst B with equal mass, wherein the catalyst A is filled at the lower end of a reaction tube, and the catalyst B is mixed with quartz sand with equal mass and then filled at the upper end of the reaction tube; the top of the reaction tube is provided with a first inlet, and the lower end of the reaction tube and the junction of the catalyst A and the catalyst B are provided with a second inlet; dividing hydrogen into a hydrogen A part and a hydrogen B part according to a ratio of 4: 6; mixing the raw material ethyl p-nitrobenzoate and solvent ethanol, preheating to the reaction temperature, and feeding the mixture and hydrogen B together from a first inlet; preheating formaldehyde to the reaction temperature, feeding the formaldehyde and hydrogen A together from a second feeding hole, allowing a reaction product to flow out from the bottom of the reaction tube, and performing gas-liquid separation to obtain a target product ethyl p-dimethylaminobenzoate, a solvent and excessive hydrogen for recycling; wherein the reaction temperature is 70 ℃, the reaction pressure is 0.6MPa, and the space velocity of the p-nitrobenzoate is 0.7 g/(g.h); the molar ratio of the ethyl p-nitrobenzoate to the formaldehyde to the hydrogen to the solvent ethanol is 1: 2.3: 5.5: 2; in the fixed bed reactor, a reaction tube is a stainless steel tube with a quartz tube inside, and the inner diameter of the quartz tube is 15 mm;
the molar yield of the target product ethyl p-dimethylaminobenzoate is 99.7%.
Example 5
1. The catalyst for synthesizing p-dimethylaminobenzoate comprises metal Ni, Pd and carrier alumina, wherein the mass percent of Ni in the catalyst is 0.9%, the mass percent of Pd in the catalyst is 0.4%, and the balance is alumina; wherein the alumina is hollow bar-shaped gamma alumina, the length of the alumina is 3-6mm, the outer diameter of the alumina is 1.5mm, and the inner diameter of the middle cavity is 0.8 mm.
2. A preparation method of a catalyst for synthesizing p-dimethylaminobenzoate comprises the following steps:
(1) pretreatment of a carrier: soaking alumina in a hydrochloric acid solution with the volume concentration of 6% for 2h, taking out, drying at 120 ℃ for 12h, then soaking in ethanol until the alumina is saturated, taking out, drying at 120 ℃ for 12h, and then roasting in a muffle furnace at 850 ℃ for 1h to obtain a pretreated alumina carrier;
(2) preparing a Ni-loaded catalyst precursor by an isometric impregnation method: dissolving 4.46g of nickel nitrate hexahydrate into 49.5mL of ethanol water solution with volume concentration of 50%, adding 98.7g of alumina carrier by adopting an equal-volume impregnation method, uniformly stirring, drying at 120 ℃ for 12h, roasting in a muffle furnace at 500 ℃ for 1h, and then reducing by using hydrogen at 550 ℃ for 2h to obtain a Ni-loaded catalyst precursor;
(3) impregnating Pd: adding 0.4g of sponge palladium into 1mL of aqua regia, heating to 80 ℃ to dissolve, naturally cooling to room temperature, diluting with deionized water and fixing the volume to 500mL to obtain a Pd solution; filling a catalyst precursor into a reaction tube, dropwise adding a Pd solution from the upper end of the reaction tube under the protection of nitrogen, allowing the Pd solution to flow through the catalyst precursor and flow out from the lower end of the reaction tube, recycling the flowing Pd solution to the upper end of the reaction tube, dropwise adding, circulating, stopping dropwise adding the Pd solution when the Pd solution flowing out from the lower end of the reaction tube is colorless, changing nitrogen into hydrogen, heating to 100 ℃, keeping for 2h, heating to 300 ℃, activating for 2h, and cooling to obtain the catalyst for synthesizing the p-dimethylaminobenzoate.
3. A process for preparing ethyl p-dimethylaminobenzoate using the catalyst, the process comprising: in a fixed bed reactor, dividing a catalyst into a catalyst A and a catalyst B with equal mass, wherein the catalyst A is filled at the lower end of a reaction tube, and the catalyst B is mixed with quartz sand with equal mass and then filled at the upper end of the reaction tube; the top of the reaction tube is provided with a first inlet, and the lower end of the reaction tube and the junction of the catalyst A and the catalyst B are provided with a second inlet; dividing hydrogen into a hydrogen A part and a hydrogen B part according to a ratio of 4: 6; mixing the raw material ethyl p-nitrobenzoate and solvent ethanol, preheating to the reaction temperature, and feeding the mixture and hydrogen B together from a first inlet; preheating formaldehyde to the reaction temperature, feeding the formaldehyde and hydrogen A together from a second feeding hole, allowing a reaction product to flow out from the bottom of the reaction tube, and performing gas-liquid separation to obtain a target product ethyl p-dimethylaminobenzoate, a solvent and excessive hydrogen for recycling; wherein the reaction temperature is 70 ℃, the reaction pressure is 1MPa, and the space velocity of the p-nitrobenzoate is 0.8 g/(g.h); the molar ratio of the ethyl p-nitrobenzoate to the formaldehyde to the hydrogen to the solvent ethanol is 1: 2.6: 7: 2; in the fixed bed reactor, a reaction tube is a stainless steel tube with a quartz tube inside, and the inner diameter of the quartz tube is 18 mm;
the molar yield of the target product ethyl p-dimethylaminobenzoate is 99.5%.
Example 6
1. A catalyst for synthesizing p-dimethylaminobenzoate comprises metal Ni, Pd and carrier alumina, wherein the mass percent of Ni in the catalyst is 1.1%, the mass percent of Pd in the catalyst is 0.3%, and the balance is alumina; wherein the alumina is hollow bar-shaped gamma alumina, the length of the alumina is 3-6mm, the outer diameter of the alumina is 1.5mm, and the inner diameter of the middle cavity is 0.8 mm.
2. A preparation method of a catalyst for synthesizing p-dimethylaminobenzoate comprises the following steps:
(1) pretreatment of a carrier: soaking alumina in a hydrochloric acid solution with the volume concentration of 8% for 2h, taking out, drying at 120 ℃ for 12h, then soaking in ethanol until adsorption saturation, taking out, drying at 120 ℃ for 12h, and then roasting in a muffle furnace at 850 ℃ for 1h to obtain a pretreated alumina carrier;
(2) preparing a Ni-loaded catalyst precursor by an isometric impregnation method: dissolving 5.45g of nickel nitrate hexahydrate into 49.5mL of ethanol water solution with volume concentration of 50%, adding 98.6g of alumina carrier by adopting an equal-volume impregnation method, uniformly stirring, drying at 120 ℃ for 12h, roasting in a muffle furnace at 400 ℃ for 1h, and then reducing by using hydrogen at 450 ℃ for 2h to obtain a Ni-loaded catalyst precursor;
(3) impregnating Pd: adding 0.3g of sponge palladium into 1mL of aqua regia, heating to 70 ℃ for dissolution, naturally cooling to room temperature, diluting with deionized water and fixing the volume to 500mL to obtain a Pd solution; filling a catalyst precursor into a reaction tube, dropwise adding a Pd solution from the upper end of the reaction tube under the protection of nitrogen, allowing the Pd solution to flow through the catalyst precursor and flow out from the lower end of the reaction tube, recycling the flowing Pd solution to the upper end of the reaction tube, dropwise adding, circulating, stopping dropwise adding the Pd solution when the Pd solution flowing out from the lower end of the reaction tube is colorless, changing nitrogen into hydrogen, heating to 100 ℃, keeping for 2h, heating to 250 ℃, activating for 2h, and cooling to obtain the catalyst for synthesizing the p-dimethylaminobenzoate.
3. A method for preparing isooctyl p-dimethylaminobenzoate using the catalyst, the method comprising: in a fixed bed reactor, dividing a catalyst into a catalyst A and a catalyst B with equal mass, wherein the catalyst A is filled at the lower end of a reaction tube, and the catalyst B is mixed with quartz sand with equal mass and then filled at the upper end of the reaction tube; the top of the reaction tube is provided with a first inlet, and the lower end of the reaction tube and the junction of the catalyst A and the catalyst B are provided with a second inlet; dividing hydrogen into a hydrogen A part and a hydrogen B part according to a ratio of 4: 6; mixing raw material isooctyl p-nitrobenzoate and solvent isooctyl alcohol, preheating to reaction temperature, and feeding the mixture and hydrogen B together from a first inlet; preheating formaldehyde to the reaction temperature, feeding the formaldehyde and hydrogen A together from a second feeding hole, allowing a reaction product to flow out of the bottom of the reaction tube, and performing gas-liquid separation to obtain a target product isooctyl p-dimethylaminobenzoate, and recycling the solvent and excessive hydrogen; wherein the reaction temperature is 60 ℃, the reaction pressure is 0.8MPa, and the space velocity of the p-nitrobenzoate is 0.5 g/(g.h); the molar ratio of the isooctyl p-nitrobenzoate to the formaldehyde to the hydrogen to the solvent isooctyl alcohol is 1: 2.5: 6: 2; in the fixed bed reactor, a reaction tube is a stainless steel tube with a quartz tube inside, and the inner diameter of the quartz tube is 20 mm;
the molar yield of the target product isooctyl p-dimethylaminobenzoate is 98.5%.
Claims (8)
1. A method for preparing p-dimethylaminobenzoate using a catalyst, comprising: the method comprises the following steps: in a fixed bed reactor, dividing a catalyst into a catalyst A and a catalyst B with equal mass, wherein the catalyst A is filled at the lower end of a reaction tube, and the catalyst B is mixed with quartz sand with equal mass and then filled at the upper end of the reaction tube; the top of the reaction tube is provided with a first inlet, and the lower end of the reaction tube and the junction of the catalyst A and the catalyst B are provided with a second inlet; dividing hydrogen into a hydrogen A part and a hydrogen B part according to a ratio of 4: 6; mixing the p-nitrobenzoate serving as a raw material with a solvent, preheating to a reaction temperature, and feeding the mixture and hydrogen B together from a first inlet; preheating formaldehyde to the reaction temperature, feeding the formaldehyde and hydrogen A together from a second feeding hole, allowing a reaction product to flow out from the bottom of the reaction tube, and performing gas-liquid separation to obtain a target product p-dimethylaminobenzoate, a solvent and excessive hydrogen for recycling; wherein the reaction temperature is 40-70 ℃, the reaction pressure is 0.5-1MPa, and the space velocity of the p-nitrobenzoate is 0.4-0.8 g/(g.h);
the catalyst comprises metal Ni, Pd and carrier alumina, wherein the mass percent of Ni in the catalyst is 0.8-1.1%, the mass percent of Pd in the catalyst is 0.2-0.5%, and the balance is alumina;
the catalyst is obtained by the following preparation method:
(1) pretreatment of a carrier: soaking alumina in a hydrochloric acid solution for 2h, taking out, drying at 120 ℃ for 12h, then soaking in ethanol until the adsorption is saturated, taking out, drying at 120 ℃ for 12h, and then roasting in a muffle furnace at 800-900 ℃ for 0.5-1.5h to obtain a pretreated alumina carrier;
(2) preparing a Ni-loaded catalyst precursor by an isometric impregnation method: dissolving nickel nitrate hexahydrate into an ethanol water solution, adding an alumina carrier into the ethanol water solution, uniformly stirring, drying and drying at 120 ℃ for 12h, roasting in a muffle furnace at 400-600 ℃ for 0.5-1h, and then reducing for 2h by using hydrogen at 400-600 ℃ to obtain a Ni-loaded catalyst precursor;
(3) impregnating Pd: adding sponge palladium into aqua regia, heating to 60-90 ℃, dissolving, naturally cooling to room temperature, diluting with deionized water, and fixing the volume to 0.004-0.01g/mL of palladium ion concentration to obtain a Pd solution; filling a catalyst precursor into a reaction tube, dropwise adding a Pd solution from the upper end of the reaction tube under the protection of nitrogen, allowing the Pd solution to flow through the catalyst precursor and flow out from the lower end of the reaction tube, recycling the flowing Pd solution to the upper end of the reaction tube, dropwise adding, circulating, stopping dropwise adding the Pd solution when the Pd solution flowing out from the lower end of the reaction tube is colorless, changing nitrogen into hydrogen, heating to 100 ℃, keeping for 2h, heating to 200-500 ℃, activating for 2h, and cooling to obtain the catalyst for synthesizing the p-dimethylaminobenzoate.
2. The process for producing p-dimethylaminobenzoate using a catalyst according to claim 1, wherein: the alumina is hollow bar-shaped gamma alumina, the length of the alumina is 3-6mm, the diameter of the alumina is 1.5mm, and the inner diameter of the middle cavity is 0.8 mm.
3. The process for producing p-dimethylaminobenzoate using a catalyst according to claim 1, wherein: the volume concentration of the hydrochloric acid solution in the step (1) is 5-10%.
4. The process for producing p-dimethylaminobenzoate using a catalyst according to claim 1, wherein: the volume concentration of the ethanol water solution in the step (2) is 50%.
5. The process for producing p-dimethylaminobenzoate using a catalyst according to claim 1, wherein: the ratio of the sponge palladium to the aqua regia is (2-5) g: 10 mL.
6. The process for producing p-dimethylaminobenzoate using a catalyst according to claim 1 or 2, characterized in that: the molar ratio of the p-nitrobenzoate to the formaldehyde to the hydrogen to the solvent is 1: (2.2-2.6): (5.5-7): 2.
7. the process for producing p-dimethylaminobenzoate using a catalyst according to claim 6, wherein: when the target product p-dimethylaminobenzoate is ethyl p-dimethylaminobenzoate, the p-nitrobenzoate serving as the raw material is ethyl p-nitrobenzoate, and the solvent is ethanol;
when the target product p-dimethylaminobenzoate is isoamyl p-dimethylaminobenzoate, the p-nitrobenzoate serving as the raw material is isoamyl p-nitrobenzoate, and the solvent is isoamyl alcohol;
when the target product p-dimethylaminobenzoate is isooctyl p-dimethylaminobenzoate, the p-nitrobenzoate serving as the raw material is isooctyl p-nitrobenzoate, and the solvent is isooctanol;
when the target product p-dimethylaminobenzoate is methyl p-dimethylaminobenzoate, the p-nitrobenzoate serving as the raw material is methyl p-nitrobenzoate, and the solvent is methanol;
when the target product p-dimethylaminobenzoic acid ester is n-butyl p-dimethylaminobenzoate, the p-nitrobenzoate serving as the raw material is n-butyl p-nitrobenzoate, and the solvent is n-butanol.
8. The process for producing p-dimethylaminobenzoate using a catalyst according to claim 1 or 2, characterized in that: in the fixed bed reactor, the reaction tube is a stainless steel tube with a quartz tube inside, and the inner diameter of the quartz tube is 15-25 mm.
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