CN117658796A - Synthesis and purification method of p-hydroxybenzoic acid - Google Patents
Synthesis and purification method of p-hydroxybenzoic acid Download PDFInfo
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- FJKROLUGYXJWQN-UHFFFAOYSA-N 4-hydroxybenzoic acid Chemical compound OC(=O)C1=CC=C(O)C=C1 FJKROLUGYXJWQN-UHFFFAOYSA-N 0.000 title claims abstract description 72
- 229940090248 4-hydroxybenzoic acid Drugs 0.000 title claims abstract description 36
- 238000000034 method Methods 0.000 title claims abstract description 25
- 238000000746 purification Methods 0.000 title claims description 5
- 238000003786 synthesis reaction Methods 0.000 title abstract description 6
- 230000015572 biosynthetic process Effects 0.000 title abstract description 5
- 238000006243 chemical reaction Methods 0.000 claims abstract description 40
- 238000005984 hydrogenation reaction Methods 0.000 claims abstract description 17
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 15
- 239000003054 catalyst Substances 0.000 claims abstract description 13
- 230000002194 synthesizing effect Effects 0.000 claims abstract description 10
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 30
- 238000001816 cooling Methods 0.000 claims description 26
- 238000001914 filtration Methods 0.000 claims description 24
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 22
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 19
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 19
- 239000007787 solid Substances 0.000 claims description 19
- OHEPMXOERTVRMN-UHFFFAOYSA-L dipotassium;4-carboxyphenolate Chemical compound [K+].[K+].OC(=O)C1=CC=C([O-])C=C1.OC(=O)C1=CC=C([O-])C=C1 OHEPMXOERTVRMN-UHFFFAOYSA-L 0.000 claims description 18
- 239000007864 aqueous solution Substances 0.000 claims description 17
- 238000010438 heat treatment Methods 0.000 claims description 17
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims description 16
- 239000001257 hydrogen Substances 0.000 claims description 16
- 229910052739 hydrogen Inorganic materials 0.000 claims description 16
- ISWSIDIOOBJBQZ-UHFFFAOYSA-N Phenol Chemical compound OC1=CC=CC=C1 ISWSIDIOOBJBQZ-UHFFFAOYSA-N 0.000 claims description 15
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 14
- 239000012452 mother liquor Substances 0.000 claims description 12
- OTYBMLCTZGSZBG-UHFFFAOYSA-L potassium sulfate Chemical group [K+].[K+].[O-]S([O-])(=O)=O OTYBMLCTZGSZBG-UHFFFAOYSA-L 0.000 claims description 12
- 238000003756 stirring Methods 0.000 claims description 12
- 229910052939 potassium sulfate Inorganic materials 0.000 claims description 11
- 235000011151 potassium sulphates Nutrition 0.000 claims description 11
- 239000000243 solution Substances 0.000 claims description 11
- 229910052757 nitrogen Inorganic materials 0.000 claims description 10
- 239000002253 acid Substances 0.000 claims description 9
- 238000001035 drying Methods 0.000 claims description 9
- UKVIEHSSVKSQBA-UHFFFAOYSA-N methane;palladium Chemical compound C.[Pd] UKVIEHSSVKSQBA-UHFFFAOYSA-N 0.000 claims description 9
- 238000007599 discharging Methods 0.000 claims description 8
- 239000011261 inert gas Substances 0.000 claims description 8
- 239000007868 Raney catalyst Substances 0.000 claims description 7
- NPXOKRUENSOPAO-UHFFFAOYSA-N Raney nickel Chemical compound [Al].[Ni] NPXOKRUENSOPAO-UHFFFAOYSA-N 0.000 claims description 7
- 229910000564 Raney nickel Inorganic materials 0.000 claims description 7
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 7
- 229910052782 aluminium Inorganic materials 0.000 claims description 7
- 239000001569 carbon dioxide Substances 0.000 claims description 7
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 7
- 229910052763 palladium Inorganic materials 0.000 claims description 7
- 238000006473 carboxylation reaction Methods 0.000 claims description 6
- XAEFZNCEHLXOMS-UHFFFAOYSA-M potassium benzoate Chemical compound [K+].[O-]C(=O)C1=CC=CC=C1 XAEFZNCEHLXOMS-UHFFFAOYSA-M 0.000 claims description 6
- 238000010521 absorption reaction Methods 0.000 claims description 4
- 238000002844 melting Methods 0.000 claims description 4
- 230000008018 melting Effects 0.000 claims description 4
- ZGJADVGJIVEEGF-UHFFFAOYSA-M potassium;phenoxide Chemical compound [K+].[O-]C1=CC=CC=C1 ZGJADVGJIVEEGF-UHFFFAOYSA-M 0.000 claims description 4
- 239000000843 powder Substances 0.000 claims description 4
- 230000035484 reaction time Effects 0.000 claims description 4
- 238000002834 transmittance Methods 0.000 claims description 4
- 235000014101 wine Nutrition 0.000 claims description 4
- 239000012153 distilled water Substances 0.000 claims description 3
- 239000012266 salt solution Substances 0.000 claims 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 abstract description 18
- AZQWKYJCGOJGHM-UHFFFAOYSA-N 1,4-benzoquinone Chemical compound O=C1C=CC(=O)C=C1 AZQWKYJCGOJGHM-UHFFFAOYSA-N 0.000 abstract description 6
- 229910052799 carbon Inorganic materials 0.000 abstract description 4
- 230000000694 effects Effects 0.000 abstract description 4
- 238000012797 qualification Methods 0.000 abstract description 2
- 239000002910 solid waste Substances 0.000 abstract description 2
- 238000001179 sorption measurement Methods 0.000 abstract description 2
- 238000009903 catalytic hydrogenation reaction Methods 0.000 abstract 1
- 239000003638 chemical reducing agent Substances 0.000 abstract 1
- 239000000047 product Substances 0.000 description 23
- 238000002360 preparation method Methods 0.000 description 7
- 239000000126 substance Substances 0.000 description 5
- 229910000831 Steel Inorganic materials 0.000 description 4
- 239000012265 solid product Substances 0.000 description 4
- 239000010959 steel Substances 0.000 description 4
- 230000020477 pH reduction Effects 0.000 description 3
- 238000001953 recrystallisation Methods 0.000 description 3
- JVBXVOWTABLYPX-UHFFFAOYSA-L sodium dithionite Chemical compound [Na+].[Na+].[O-]S(=O)S([O-])=O JVBXVOWTABLYPX-UHFFFAOYSA-L 0.000 description 3
- FJKROLUGYXJWQN-UHFFFAOYSA-M 4-hydroxybenzoate Chemical compound OC1=CC=C(C([O-])=O)C=C1 FJKROLUGYXJWQN-UHFFFAOYSA-M 0.000 description 2
- 229920000106 Liquid crystal polymer Polymers 0.000 description 2
- 239000004977 Liquid-crystal polymers (LCPs) Substances 0.000 description 2
- 229910001873 dinitrogen Inorganic materials 0.000 description 2
- KCIDZIIHRGYJAE-YGFYJFDDSA-L dipotassium;[(2r,3r,4s,5r,6r)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl] phosphate Chemical compound [K+].[K+].OC[C@H]1O[C@H](OP([O-])([O-])=O)[C@H](O)[C@@H](O)[C@H]1O KCIDZIIHRGYJAE-YGFYJFDDSA-L 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000008213 purified water Substances 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- 230000002378 acidificating effect Effects 0.000 description 1
- 150000001298 alcohols Chemical class 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000003086 colorant Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000004042 decolorization Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 239000004973 liquid crystal related substance Substances 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 239000010413 mother solution Substances 0.000 description 1
- -1 nipagin ester Chemical class 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 239000000575 pesticide Substances 0.000 description 1
- 238000011020 pilot scale process Methods 0.000 description 1
- DKGFIVSGQRBSOG-UHFFFAOYSA-M potassium;4-hydroxybenzoate Chemical compound [K+].OC1=CC=C(C([O-])=O)C=C1 DKGFIVSGQRBSOG-UHFFFAOYSA-M 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 239000003755 preservative agent Substances 0.000 description 1
- 230000002335 preservative effect Effects 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 235000020095 red wine Nutrition 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 238000012795 verification Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Landscapes
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
The invention discloses a method for synthesizing and purifying p-hydroxybenzoic acid, which improves the traditional method for separating by decolorizing with active carbon, and avoids the problems of separating active carbon and decolorizing protection by adding a reducing agent in the prior method; by adding a hydrogenation device in the process and utilizing a catalytic hydrogenation reduction mode, 1) the hydrogenation catalyst can be used mechanically, and the reduction selectivity of the p-benzoquinone is good; 2) The adsorption of the activated carbon to the product is reduced, the yield is improved, and the generation of solid waste is reduced; 3) The safety of hydrogenation reduction in a water system is high; 4) The product has better appearance and color than the active carbon, and meets the standard and specification requirements. The invention can solve the similar problems of high cost and the like by improving the synthesis process, and achieves the effects of increased yield, improved qualification rate and better reaction effect.
Description
Technical Field
The invention belongs to the field of organic synthesis, and particularly relates to a synthetic purification method of p-hydroxybenzoic acid.
Background
The conventional synthesis process generally proceeds by the following procedure:
adding carbonized dipotassium p-hydroxybenzoate solution into a stainless steel kettle, and then adding sodium hydrosulfite and activated carbon to finish; heating to 90 ℃, stirring and decoloring for 30 minutes at 90 ℃, filtering out activated carbon to obtain a light (brown) red transparent solution, adding acid to adjust the pH value to 6.5-8.0, cooling to 40-60 ℃, separating out solid potassium salt by filtration, continuously acidifying the obtained mother solution to pH 2.0-4.0, separating out a large amount of light yellow parahydroxybenzoic acid product, cooling to 25 ℃, separating out the light yellow solid product by filtration, and drying to obtain the light yellow solid product with the chromaticity of 40-60Hazen and the light transmittance of 425nm of 73.5-82.5%. The quality standard requirements of the industrial quality are not met. The water recrystallization preparation is needed, a large amount of waste liquid is caused, the environment is polluted, and the production cost is increased.
According to the patent application 201210056215.6, potassium hydroxide solution and phenol react in a salifying reaction kettle to obtain potassium salt of phenol, then carbon dioxide is introduced into a carboxylating reaction kettle to carry out carboxylation reaction to obtain a potassium p-hydroxybenzoate aqueous solution, activated carbon is used for decolorization, sulfuric acid acidification is carried out, and finally, a product is obtained by filtering, washing and drying; repeating the above process to obtain the p-hydroxybenzoic acid product with chromaticity less than 20Hazen.
As the parahydroxybenzoic acid product is an important intermediate in chemical industry, the parahydroxybenzoic acid product can be used as a preservative, a dye, a medicine and an injection intermediate, and can be esterified with alcohols to obtain the nipagin ester, which is also a main raw material of a high molecular liquid crystal polymer and a raw material of a pesticide intermediate. Particularly, the high-purity colorless transparent p-hydroxybenzoic acid is used for preparing high-molecular liquid crystal polymers, and the high chromaticity and impurities have great influence on the liquid crystal yield.
Thus, there is a need in the art for a simple, low cost method of purifying parahydroxybenzoic acid, particularly to remove the color of impurities, and to increase the purity of the product.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for synthesizing and purifying p-hydroxybenzoic acid, which is simple to operate, low in cost, green and pollution-free. The substances which are analyzed to produce the (brown) red color of the wine are substances which are inevitably oxidized during the high-temperature salification and carboxylation reaction of phenol to produce benzoquinone colors. The applicant researches find that the benzoquinone can be reduced into phenol colorless substances through the hydrogenation reaction of the hydrogenation catalyst through experimental verification, and the phenol colorless substances are separated out through a subsequent separation system according to the dissolution property of potassium sulfate in an acidic aqueous solution.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
s1: adding carboxylated dipotassium p-hydroxybenzoate aqueous solution into a reaction kettle, adding a hydrogenation catalyst, and removing air in the reaction kettle by using inert gas;
s2: heating by program, stirring, introducing hydrogen for replacement until the internal pressure is 0.2-1.5MPa, and observing the inside of the reaction kettle until no hydrogen is absorbed in the kettle, wherein no hydrogen absorption is the end point;
s3: cooling the reaction kettle, discharging inert gas into the reaction kettle, discharging the solution out of the reaction kettle, and separating out the hydrogenation catalyst to obtain a nearly colorless transparent solution;
s4: adding acid into the nearly colorless transparent solution to adjust the pH value to 6.0-8.0, and continuously cooling to 30-60 ℃ to precipitate solid potassium salt;
s5: filtering and separating to obtain mother liquor, and continuously adjusting the pH value of the mother liquor to 2.0-4.0 by using acid, wherein a white parahydroxybenzoic acid product is separated out; cooling, filtering, separating and drying to obtain white product.
Preferably, the aqueous solution of the dipotassium p-hydroxybenzoate in the step S1 has wine/brown red color and chromaticity of more than 300Hazen; the inert gas is nitrogen;
preferably, the hydrogenation catalyst comprises at least one of Raney nickel, palladium carbon and palladium aluminum;
preferably, the mass volume ratio of the hydrogenation catalyst to the aqueous solution of the dipotassium p-hydroxybenzoate is 0.002-0.008:1g/mL.
Preferably, the pressure of the reaction kettle in the step S2 is 0.5-1.5Mpa; the temperature is programmed to be 80-100 ℃.
Preferably, in the step S3, the temperature is reduced to 60-80 ℃; the inert gas is nitrogen, and the hydrogenation catalyst separated by filtration is recycled.
Preferably, the pH value in the step S4 is 6.5-8.0, and the temperature is reduced to 40-60 ℃.
Preferably, in the step S4, the acid is 20-40% sulfuric acid, and the potassium salt is potassium sulfate.
Preferably, in the step S5, the temperature is reduced to room temperature; adjusting the pH value to 2.5-4.0; the acid is 20-40% sulfuric acid.
Preferably, the chromaticity of the dried white product in the step S5 is 0-10Hazen, and the light transmittance of 425nm reaches 96.2-98%.
Preferably, the number of times of recycling the hydrogenation catalyst in the step S3 is 20-30.
Preferably, the equation of the acidification process in the step S4 is as follows:
acidification in step S5:
the preparation of the dipotassium p-hydroxybenzoate solution is obtained by the following steps:
a1, adding phenol into a reaction kettle, heating and melting, adding potassium hydroxide powder, stirring and heating to 220-250 ℃ at the same time, reacting to obtain molten potassium phenoxide, and removing water in vacuum;
preferably, the temperature of the heating and melting in the step A1 is 50-65 ℃; heating to 230-250 ℃; the mass ratio of phenol to potassium hydroxide is 1:0.90-1.10.
Preferably, the reaction time in the step A1 is 30-100 minutes.
A2, introducing carbon dioxide into the reaction kettle to carry out carboxylation reaction, and stopping after a period of reaction
Reacting;
preferably, the flow rate of the carbon dioxide in the step A2 is 300-500mL/min, and the reaction time is
60-150 minutes.
A3, cooling the steps to 200-230 ℃, distilling to remove phenol to obtain solid dipotassium p-hydroxybenzoate, and adding distilled water to obtain the aqueous solution of the dipotassium p-hydroxybenzoate.
Preferably, the temperature in the step A3 is reduced to 200-220 ℃.
The invention has the beneficial effects that:
1) The hydrogenation catalyst can be used for at least 20 times, and the reduction selectivity of the quinone is good; 2) The adsorption of the activated carbon to the product is reduced, the yield is improved, the generation of solid waste is reduced, the recrystallization of an organic solvent is avoided, the generation of waste liquid is reduced, and the production cost is lower; 3) The safety of hydrogenation reduction in a water system is high; 4) The product has better appearance and color than that of sodium hydrosulfite and active carbon, and the chromaticity of the product is 0-10Hazen, thereby meeting the standard and specification requirements of subsequent products.
The invention can solve the similar problems of high cost and the like by improving the synthesis process, and achieves the effects of increased yield, improved qualification rate and better reaction effect.
The specific embodiment is as follows:
the invention is further described by the following specific examples, which are not intended to limit the scope of the invention.
Example 1: preparation of dipotassium p-hydroxybenzoate
300g of phenol is added into 1000mL of autoclave with a stirring device, the mixture is heated to 60 ℃ to be melted, 280g of potassium hydroxide powder is added, meanwhile, the mixture is stirred and heated to 80 ℃ to remove water completely under reduced pressure, the temperature is further raised to 240 ℃, the reaction is carried out for 60 minutes, molten potassium phenoxide is obtained, and water generated in the reaction kettle is removed in vacuum.
Introducing CO into a reaction kettle by using a high-purity carbon dioxide steel bottle 2 Carboxylation reaction is carried out, the flow is controlled at 300mL/min, after 100 minutes of reaction, the valve of the steel cylinder is closed,stopping the reaction;
the reaction vessel was cooled to about 200℃and phenol produced by the reaction was distilled off to give 455g of solid dipotassium parahydroxybenzoate, and 430g of distilled water was added to give an aqueous solution of dipotassium parahydroxybenzoate in the form of a (brown) red wine, cooled to room temperature and measured for a hue of 330Hazen, used in the following examples.
Example 2: preparation of parahydroxybenzoic acid
Into a 1000mL autoclave, 300mL of the dipotassium p-hydroxybenzoate aqueous solution obtained in example 1 was introduced, 0.5g of Raney nickel was added, and nitrogen was introduced to replace the air in the autoclave, followed by rapid stirring and heating to about 90℃at which time the hydrogen gas introduced into the autoclave was maintained at 1.0MPa in the autoclave and was not absorbed until the reaction was completed.
Cooling to about 60 ℃, evacuating hydrogen in the autoclave by nitrogen, discharging out of the autoclave, filtering to separate Raney nickel, and reserving for next use; adding 30% dilute sulfuric acid into the colorless transparent aqueous solution to adjust the pH to 6.5, and continuously cooling to 45 ℃, wherein 16g of precipitated solid potassium sulfate is obtained;
separating solid potassium sulfate by filtration to obtain 450g of mother liquor, continuously adjusting the pH value of the mother liquor to 2.5 by 30% dilute sulfuric acid, separating out white parahydroxybenzoic acid product at the moment, and waiting for no solid to be separated out; cooling to about 30 ℃, filtering and separating, and drying to obtain 28g of white product, namely parahydroxybenzoic acid with the chromaticity of 8Hazen.
The recovered Raney nickel is reused, and then the Raney nickel with small loss is needed to be replenished, and the Raney nickel can be reused at least 20 times.
Example 3: preparation of parahydroxybenzoic acid
Into a 1000mL autoclave, 300mL of the dipotassium p-hydroxybenzoate aqueous solution in example 1 was introduced, 1g of 0.5% palladium on carbon Pb/C was added, the air in the autoclave was replaced with nitrogen gas, the autoclave was rapidly stirred and heated to about 80℃at which time the hydrogen gas introduced into the autoclave was maintained at 0.5MPa and the autoclave was terminated without hydrogen absorption.
Cooling to about 65 ℃, evacuating hydrogen in the autoclave by nitrogen, discharging the hydrogen out of the autoclave, filtering and separating palladium carbon, and reserving the palladium carbon for next use; adding 30% dilute sulfuric acid into the colorless transparent aqueous solution to adjust the pH to 6.6, and continuously cooling to 45 ℃ to precipitate 17g of solid potassium sulfate;
separating out solid potassium sulfate by filtration to obtain 448g of mother liquor, continuously adjusting the pH value of the mother liquor by 30% dilute sulfuric acid to 2.5, at the moment, starting to precipitate a white parahydroxybenzoic acid product, and waiting for no solid precipitation; cooling to room temperature, filtering and separating, and drying to obtain 27.5g of white product, namely parahydroxybenzoic acid with chromaticity of 6Hazen.
The recovered palladium carbon is recycled, almost no replenishment is needed, and the recovered palladium carbon can be reused at least 20 times.
Example 4: preparation of parahydroxybenzoic acid
Into a 1000mL autoclave, 300mL of the dipotassium p-hydroxybenzoate aqueous solution in example 1 was introduced, 1g of 0.5% palladium aluminum Pb/Al was added, the air in the autoclave was replaced with nitrogen gas, the autoclave was rapidly stirred and heated to about 80℃at which time the hydrogen gas introduced into the autoclave was maintained at 0.5MPa and the autoclave was terminated without hydrogen absorption.
Cooling to about 60 ℃, evacuating hydrogen in the autoclave by nitrogen, discharging the hydrogen out of the autoclave, filtering and separating palladium and aluminum, and reserving the palladium and aluminum for next use; adding 30% dilute sulfuric acid into the colorless transparent aqueous solution to adjust the pH to 6.7, and continuously cooling to 45 ℃, wherein 17.3g of precipitated solid potassium sulfate is obtained;
the solid potassium sulfate is separated out by filtration, 451g of mother liquor is obtained, the mother liquor is continuously adjusted to pH value of 2.5 by 30% dilute sulfuric acid, at the moment, white parahydroxybenzoic acid product starts to be separated out, and the solid is not separated out any more; cooling to room temperature, filtering and separating, and drying to obtain 28.2g of white product, namely parahydroxybenzoic acid with chromaticity of 8Hazen.
The recovered palladium aluminum is recycled, almost no replenishment is needed, and the palladium aluminum can be reused at least 20 times.
Example 5: pilot scale up preparation of parahydroxybenzoic acid
In a 500L reaction kettle with a stirring device, adding 120KG of potassium hydroxide powder and 128.5KG of phenol, heating to 65 ℃ to melt, stirring and heating to 170 ℃ to slowly decompress and remove water, heating to 240 ℃ to react for 2 hours to obtain molten potassium phenoxide, and removing water generated in the reaction kettle in vacuum.
Opening a high-purity carbon dioxide steel bottle, and introducing CO into the reaction kettle 2 Carboxylation reaction is carried out, the flow is controlled at 30L/min, after 120 minutes of reaction, the valve of the steel cylinder is closed, phenol is removed completely under reduced pressure, and the reaction is stopped;
cooling the reaction kettle to about 130 ℃, pumping purified water by 200KG, stirring to obtain a wine (brown) red aqueous solution of dipotassium p-hydroxybenzoate, and cooling to 80 ℃; transferred to another 500L autoclave,
adding 0.5% palladium carbon Pb/C with 2.5KG, introducing nitrogen to replace air in the reaction kettle, rapidly stirring, heating to about 80 ℃, and maintaining the pressure in the autoclave at 0.5MPa without absorbing hydrogen.
Cooling to about 60 ℃, evacuating hydrogen in the autoclave by nitrogen, discharging the hydrogen out of the autoclave, filtering and separating palladium carbon, and reserving the palladium carbon for next use; adding 30% dilute sulfuric acid into the colorless transparent aqueous solution to adjust the pH to 6.0, and continuously cooling to 50 ℃, wherein the precipitated solid potassium sulfate is 53KG;
filtering to separate out solid potassium sulfate, regulating the pH value of the obtained mother liquor to 2.5 by 30% dilute sulfuric acid, wherein a white parahydroxybenzoic acid product is separated out at the moment, and waiting for no solid to be separated out; cooling to room temperature, filtering and separating, and drying to obtain white product, namely parahydroxybenzoic acid with chromaticity of 7Hazen.
Comparative example 1:
300mL of the dipotassium p-hydroxybenzoate solution obtained in example 1 was added to a 1000mL autoclave, followed by 1g of sodium hydrosulfite and 3g of activated carbon, thereby completing the reaction; heating to 90 ℃, stirring and decoloring for 30 minutes at 90 ℃, filtering out activated carbon to obtain a light (light brown) red transparent solution, regulating the pH value to 6.8 by adding 30% of dilute sulfuric acid, cooling to 45 ℃, separating 17g of precipitated solid potassium sulfate salt, filtering and separating the obtained mother liquor, continuing to acidify to pH2.4 by 30% of dilute sulfuric acid, separating a large amount of light yellow parahydroxybenzoic acid product, cooling to 30 ℃, filtering and separating to obtain 33.3g of light yellow solid product, drying to obtain 26.5g of light yellow gray solid product, and ensuring that the light transmittance of 43Hazen and 425nm reaches 81.5%. Recrystallization using 80mL of purified water produced a product with a color of 8Hazen.
The foregoing examples represent only a few preferred embodiments of the present invention, which are described in more detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.
Claims (10)
1. The synthetic purification method of the parahydroxybenzoic acid is characterized by comprising the following steps of:
s1: adding carboxylated dipotassium p-hydroxybenzoate aqueous solution into a reaction kettle, adding a hydrogenation catalyst, and removing air in the reaction kettle by using inert gas;
s2: heating by program, stirring, introducing hydrogen for replacement until the internal pressure is 0.2-1.5MPa, and observing the inside of the reaction kettle until no hydrogen is absorbed in the kettle, wherein no hydrogen absorption is the end point;
s3: cooling the reaction kettle, discharging inert gas into the reaction kettle, discharging the solution out of the reaction kettle, and separating out the hydrogenation catalyst to obtain a nearly colorless transparent solution;
s4: adding acid into the nearly colorless transparent solution to adjust the pH value to 6.0-8.0, and continuously cooling to 30-60 ℃ to precipitate solid potassium salt;
s5: filtering and separating to obtain mother liquor, and continuously adjusting the pH value of the mother liquor to 2.0-4.0 by using acid, wherein a white parahydroxybenzoic acid product is separated out; cooling, filtering, separating and drying to obtain white product.
2. The method for synthesizing and purifying p-hydroxybenzoic acid according to claim 1, wherein the carboxylated p-hydroxybenzoic acid dipotassium salt solution is obtained by the steps of:
a1, adding phenol into a reaction kettle, heating and melting, adding potassium hydroxide powder, decompressing and removing water, stirring and heating up, reacting to obtain molten potassium phenoxide, stopping reacting after a period of time, and removing water in vacuum;
a2, introducing carbon dioxide into the reaction kettle to carry out carboxylation reaction, and stopping the reaction after reacting for a period of time;
a3, cooling the steps to 200-230 ℃, distilling to remove phenol to obtain solid dipotassium p-hydroxybenzoate, and adding distilled water to obtain the aqueous solution of the dipotassium p-hydroxybenzoate.
3. The synthetic purification method of p-hydroxybenzoic acid according to claim 2, wherein the temperature of the heating and melting in step A1 is 50-65 ℃; heating to 230-250 ℃; the mass ratio of phenol to potassium hydroxide is 1:0.9-1.1; the reaction time in the step A1 is 30-100 minutes;
the flow rate of the carbon dioxide in the step A2 is 300-500mL/min, and the reaction time is 60-150 minutes;
the temperature reduction in the step A3 is 200-220 ℃.
4. The method for synthesizing and purifying p-hydroxybenzoic acid according to claim 1, wherein the dipotassium p-hydroxybenzoate salt solution in step S1 is reddish wine or brown; the inert gas is nitrogen; the hydrogenation catalyst comprises at least one of Raney nickel, palladium carbon and palladium aluminum.
5. The method for synthesizing and purifying p-hydroxybenzoic acid according to claim 1, wherein the pressure of the reaction vessel in the step S2 is 0.5 to 1.5MPa; the temperature is programmed to be 80-100 ℃.
6. The method for synthesizing and purifying p-hydroxybenzoic acid according to claim 1, wherein in step S3, the temperature is lowered to 60-85 ℃; the inert gas is nitrogen.
7. The method for synthesizing and purifying p-hydroxybenzoic acid according to claim 1, wherein in the step S4, the pH is 6.5-8.0, and the temperature is reduced to 40-60 ℃; the acid is sulfuric acid with the concentration of 20-40%, and the potassium salt is potassium sulfate.
8. The method for synthesizing and purifying p-hydroxybenzoic acid according to claim 1, wherein in step S5, the temperature is lowered to room temperature; adjusting the pH value to 2.5-4.0; the acid is sulfuric acid with the concentration of 20-40%.
9. The method for synthesizing and purifying p-hydroxybenzoic acid according to claim 1, wherein the chromaticity of the dried white product in step S5 is 0-10hazen, and the light transmittance at 425nm is 96.2-98%.
10. The method for synthesizing and purifying p-hydroxybenzoic acid according to claim 1, wherein the number of cycles of the hydrogenation catalyst in step S3 is 20 to 30.
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