A method for purifying solid benzoic acid

Abstract

The present invention proposes a method for purifying solid benzoic acid, which comprises the following steps: step 1, detecting a sample of solid benzoic acid to be purified, including benzoic acid and several impurity components, and determining the content percentage of benzoic acid and each impurity component in the solid benzoic acid to be purified; step 2, adding a low eutectic component to a solid benzoic acid raw material to be purified to obtain a mixed material, wherein the low eutectic component includes one or several impurity components, and the mass ratio of each impurity component in the mixed material is 0-100; step 3, purifying the mixed material by a volatilization purification method to obtain a purified product and a volatile component, performing subsequent treatment on the volatile component to obtain a by-product, and the by-product is recovered or used as a source of the solid benzoic acid raw material to be purified; by adjusting the mass ratio of each component of the low eutectic component, the low eutectic component can have a higher saturated vapor pressure at a specific temperature, thereby separating it from the solid benzoic acid, and only the low eutectic component undergoes a phase change.

Description

Technical Field

[0001] The invention relates to the technical field of chemical purification, and in particular to a method for purifying solid benzoic acid. Background Art

[0002] At present, benzoic acid is usually produced by direct liquid phase oxidation of toluene. Due to the complex mechanism of the oxidation reaction, the presence of impurities generated during the process affects the quality of benzoic acid and limits the use of benzoic acid, so it is necessary to purify the crude benzoic acid.

[0003] At present, the crude benzoic acid produced by the direct liquid phase oxidation of toluene usually contains by-products such as benzaldehyde, benzyl alcohol, methyl benzoate, biphenyl, benzyl benzoate, etc. In view of the large difference in relative volatility between them, the purification of benzoic acid generally uses a multi-tower distillation process. That is, after removing the low-boiling substances before benzoic acid, the finished benzoic acid is obtained from the top of the distillation tower or the side line. In addition, the purification process of benzoic acid can also adopt methods such as dissolution crystallization, sublimation crystallization and melt crystallization.

[0004] However, the common methods for industrial purification of benzoic acid mentioned above, no matter which process, require benzoic acid to undergo phase change operations such as melting, sublimation, and vaporization, and the phase change heat is usually large, such as the melting enthalpy of benzoic acid is 147 kj / kg, the vaporization enthalpy of benzoic acid at 170°C is 544 kj / kg, the sublimation enthalpy of benzoic acid at 100°C is about 737.7 kj / kg, and the specific heat capacity of solid benzoic acid is only 1.229 kj / (kg*°C). Therefore, the purification of benzoic acid by phase change consumes a lot of energy, and the purification effect is only unsatisfactory. In addition, the residual liquid and sweat produced after multiple purifications in the crystallization process have many impurities, which affect the wall hanging performance of the material on the surface of the crystallizer, making it very difficult to continue purification, resulting in a low product yield and poor atom economy. Summary of the invention

[0005] In view of this, the present invention proposes a method for purifying solid benzoic acid with high product purity, high yield, no need for product phase change, and low separation energy consumption.

[0006] The technical solution of the present invention is achieved as follows: The present invention provides a method for purifying solid benzoic acid, comprising the following steps: step 1, detecting a sample of solid benzoic acid to be purified, including benzoic acid and several impurity components, and determining the content percentage of benzoic acid and each impurity component in the solid benzoic acid to be purified; step 2, adding a low eutectic component to the solid benzoic acid raw material to be purified to obtain a mixed material, the low eutectic component including one or several impurity components, so that the mass ratio of each impurity component in the mixed material is 0 to 100; step 3, purifying the mixed material by a volatilization purification method to obtain a purified product and a volatile component, performing subsequent treatment on the volatile component to obtain a by-product, and the by-product is recovered or used as a source of the solid benzoic acid raw material to be purified.

[0007] On the basis of the above technical scheme, preferably, in step 1, the impurity components include benzaldehyde, benzyl alcohol, phthalic acid, biphenyls and benzyl benzoate.

[0008] More preferably, in step 2, the impurity components in the mixed material include benzaldehyde, benzyl alcohol, phthalic acid, biphenyls and benzyl benzoate, and the mass ratio of the impurity components is 1.5:1:10:40:3.

[0009] On the basis of the above technical scheme, preferably, step three includes drying equipment and hot air equipment, the mixed material is continuously input into the drying equipment for sweating volatilization and outputting the purified product, the volatile components fill the drying equipment, the hot air equipment is used to increase the internal temperature of the drying equipment and promote the volatilization and purification of the mixed material, and at the same time the volatile components are discharged from the drying equipment for collection.

[0010] More preferably, in step 2, the solid benzoic acid raw material and the low eutectic component are melted and fully mixed to obtain a mixed material which is input into a drying device.

[0011] More preferably, step 2 also includes a conveying device, which is used to carry the mixed material, input the mixed material into the drying device, and output the purified product from the drying device, and a first coating of a low eutectic component is arranged on the carrying surface of the conveying device, and a second coating of the mixed material is arranged on the first coating.

[0012] On the basis of the above technical solution, preferably, in step three, the volatile components are collected and condensed to obtain a condensate, and the condensate can be used as a source of the solid benzoic acid raw material to be purified in step one.

[0013] On the basis of the above technical solution, preferably, in step three, the volatile components are repeatedly washed to obtain purified gas phase and liquid phase wastewater, the purified gas phase is emptied, and the liquid phase wastewater is recovered.

[0014] The solid benzoic acid purification method of the present invention has the following beneficial effects compared with the prior art:

[0015] The present invention utilizes the low eutectic component composed of various impurity components, which has a lower melting point than solid benzoic acid. By adjusting the mass ratio of each component of the low eutectic component, the low eutectic component can have a higher saturated vapor pressure at a specific temperature, thereby separating it from the solid benzoic acid and achieving the purpose of purifying benzoic acid. During the purification process, only the low eutectic component undergoes a phase change, and there is no need to consume a large amount of phase change heat, which can greatly reduce the production cost. The process is simple and can be used in combination with purification processes such as distillation, crystallization, and sublimation or used alone. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 It is a schematic diagram of the process flow of the present invention;

[0018] Figure 2 The figure is a schematic diagram of the process of subsequent treatment of volatile components in the process of the present invention. DETAILED DESCRIPTION

[0019] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments 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.

[0020] A eutectic component, also known as a eutectic mixture, is a mixture that shows wetting or liquefaction after mixing two or more materials. The principle is that in a two-component solid-liquid two-phase equilibrium system, at a temperature lower than the melting points of both pure components, a uniform solid mixture with the same composition as the liquid phase is precipitated. This precipitation temperature is called the eutectic temperature or eutectic point. Eutectic mixtures are not limited to two components. For example, Wood's alloy is a eutectic alloy formed by four metals: 50% bismuth (Bi), 25% lead (Pb), 12.5% ​​tin (Sn) and 12.5% ​​cadmium (Cd). Its melting point (65.5°C) is lower than the melting points of the four pure metals.

[0021] In addition, the low eutectic solvent used in some fields refers to a two-component or three-component low eutectic mixture composed of a certain stoichiometric ratio of hydrogen bond acceptors (such as quaternary ammonium salts) and hydrogen bond donors (such as amides, carboxylic acids, polyols and other compounds). It is one of the applications of low eutectic components.

[0022] Based on the low phase transition heat property of the low eutectic component, which can become an effective basis for the technical solution of the present invention, the first embodiment of the present invention is designed.

[0023] A method for purifying solid benzoic acid of the present invention comprises the following steps:

[0024] Step 1: Detecting a sample of solid benzoic acid to be purified, including benzoic acid and several impurity components, specifically, the impurity components include benzaldehyde, benzyl alcohol, phthalic acid, biphenyls and benzyl benzoate, and then determining the content percentages of benzoic acid, benzaldehyde, benzyl alcohol, phthalic acid, biphenyls and benzyl benzoate in the solid benzoic acid to be purified.

[0025] Step 2, adding a eutectic component to the solid benzoic acid raw material to be purified to obtain a mixed material, the eutectic component includes one or more of benzaldehyde, benzyl alcohol, phthalic acid, biphenyls and benzyl benzoate, so that the mass ratio of each impurity component in the mixed material is 0-100, preferably 0-50; in fact, benzaldehyde, benzyl alcohol, phthalic acid, biphenyls and benzyl benzoate, no matter how much the five mass ratios are, the mixture can form a eutectic component, but the eutectic components of different component mass ratios have different eutectic points, so the purpose of the present invention is to adjust the component mass ratio of the eutectic component so that the eutectic point of the eutectic component is low and the melting point of solid benzoic acid is large. In addition, when adding a eutectic component to the solid benzoic acid raw material according to the detection result of step 1, atom economy should be followed, that is, based on the most impurity component contained in the sample, the remaining components are added accordingly. The mass ratio of benzaldehyde, benzyl alcohol, phthalic acid, biphenyls and benzyl benzoate in the mixed material is preferably 1.5: 1: 10: 40: 3. Biphenyls include biphenyl, methyl biphenyl, dimethyl biphenyl and 2,4-dimethyl biphenyl.

[0026] Step three, purify the mixed material by volatilization purification to obtain a purified product and a volatile component, perform subsequent treatment on the volatile component to obtain a by-product, and the by-product is recovered or used as a source of solid benzoic acid raw material to be purified.

[0027] Specifically, the purification step in step three is divided into sweating and volatilization steps, wherein the volatilization step can improve efficiency by reducing the saturated partial pressure of the eutectic component, including the use of industrially commonly used equipment including drying equipment and hot air equipment, the mixed material is continuously input into the drying equipment for sweating volatilization and outputting the purified product, the volatile component fills the drying equipment, the hot air equipment is used to increase the internal temperature of the drying equipment and promote the volatilization and purification of the mixed material, and at the same time the volatile component is discharged from the drying equipment for collection. The benzoic acid sample containing the low eutectic component is heated to a certain temperature and then kept warm. The low eutectic component can gradually move from the inside of the benzoic acid solid to the surface and liquefy and wet on the solid surface. The principle is that the low eutectic component has a different melting point from benzoic acid, causing the low eutectic component to precipitate from the solid benzoic acid and adhere to the surface of the solid benzoic acid. At this time, the low eutectic component is liquefied, and a saturated vapor pressure much greater than the volatility of solid benzoic acid is generated. The hot air is transported by the hot air equipment into the drying equipment. On the one hand, the volatilized low eutectic component is discharged and collected, and on the other hand, the saturated partial pressure of the low eutectic combination above the benzoic acid solid is reduced, so that the liquefied low eutectic component can continue to volatilize.

[0028] The drying equipment generally adopts fluidized bed drying equipment, and the hot air equipment can adopt Roots blower to send air and flow through the preheater to generate hot air to be input into the drying equipment.

[0029] As the low eutectic components evaporate, the mass ratio of the low eutectic components in the solid benzoic acid is greatly reduced, that is, the mass of each impurity component is greatly reduced, thereby achieving the purpose of purifying solid benzoic acid. Therefore, in fact, the purification method and principle of the present invention are also applicable to the purification of other solids that can form low eutectic components.

[0030] However, technicians have noticed that in order to achieve efficient sweating and volatilization of the low-eutectic component, it is necessary to fully and evenly mix the low-eutectic component in the solid state of benzoic acid with the benzoic acid. In order to solve the problem of sufficient mixing between the solid-phase materials, Examples 2 and 3 of the present invention provide ideas respectively.

[0031] In Example 2, the technicians found that it is not difficult to reach the melting point of the solid benzoic acid raw material and the low eutectic component with the required phase change heat. Therefore, it is possible to first melt the solid benzoic acid raw material and the low eutectic component and then fully mix them to obtain a mixed material and then input it into a drying equipment for volatilization and purification.

[0032] However, for some solid-phase materials that require a higher phase change heat to reach the melting point, the method of embodiment 3 can be used to achieve this.

[0033] Among them, step 2 also includes a conveying device, which is used to carry the mixed material, input the mixed material into the drying device, and output the purified product from the drying device. A first coating of a low eutectic component is set on the bearing surface of the conveying device, and a second coating of the mixed material is set on the first coating, so that the low eutectic component is continuously generated on the contact surface of the first coating and the second coating. In the process of moving to the solid phase surface, the low eutectic component will spontaneously drive and guide the unevenly distributed impurity components to combine to form a new low eutectic component, thereby realizing the continuous generation of the low eutectic component. The conveying device can be a screw conveyor.

[0034] In addition, in order to process the recovered volatile components, the technicians designed Example 4 and Example 5.

[0035] In Example 4, in step 3, the volatile components are collected and condensed to obtain a condensate, which can be used as a source of the solid benzoic acid raw material to be purified in step 1; the volatiles of the low eutectic component will contain a certain proportion of benzoic acid, so it can be used in the volatilization and purification process with the next batch or the latter part of the benzoic acid sample to be purified, and can also be used for other purposes.

[0036] In Example 5, in step 3, the volatile components are repeatedly washed to obtain purified gas phase and liquid phase wastewater, the purified gas phase is emptied, and the liquid phase wastewater is recovered, which is a conventional waste gas treatment process. Specifically, the waste gas containing volatile components is generally reversely washed with an alkaline washing liquid through a washing tower, and the air after washing is discharged. The washing liquid can be repeatedly used for washing through a circulation mechanism, and after production is completed, it is uniformly treated.

[0037] After the purification method of the present invention was applied to actual production, Example 6, Example 7 and Example 8 were obtained.

[0038] Embodiment six:

[0039] A solid benzoic acid raw material produced by a benzoic acid distillation device, wherein the benzoic acid content is 99.58% (GC), is taken. The purification method of Example 1 of the present invention is adopted to detect the content of benzoic acid and various impurity components therein after each time interval.

[0040]

[0041] Embodiment seven:

[0042] 750.0 kg of solid benzoic acid raw material produced by a benzoic acid distillation device was taken, wherein the benzoic acid content was 99.53% (GC), and the purification method of Example 1 of the present invention was adopted to finally obtain a total of 738.6 kg of finished products. The contents of benzoic acid and various impurity components therein were detected after each period of time.

[0043]

[0044] Embodiment eight:

[0045] A solid benzoic acid raw material produced by a benzoic acid crystallization device is taken, wherein the benzoic acid content is 96.21% (GC). No low eutectic components are added to the benzoic acid solid for configuration according to various impurity components. Instead, step three of Example 1 of the present invention is directly performed for volatilization purification, and the content is re-detected after each interval.

[0046]

[0047] The 36h benzoic acid sample is heated and melted, and a small amount of biphenyl and benzyl benzoate are added to prepare a low eutectic component with a preferred mass ratio, and the components are mixed evenly. The purification method of Example 1 of the present invention is used, and the content is re-detected after a certain period of time.

[0048]

[0049] It can be seen that even if one or more of the impurity components are not added to the solid benzoic acid raw material, the impurity components present in the solid benzoic acid raw material can still form a low eutectic component, thereby sweating and volatilizing, but the efficiency is low; therefore, when a small amount of biphenyl and benzyl benzoate are added to the solid benzoic acid sample to configure a low eutectic component with a preferred mass ratio, the efficiency of its volatilization and purification is greatly improved.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for purifying solid benzoic acid, Features: The following steps are included: Step 1, detecting a sample of solid benzoic acid to be purified, including benzoic acid and several impurity components, and determining the content percentage of benzoic acid and each impurity component in the solid benzoic acid to be purified; Step 2, adding a low eutectic component to the solid benzoic acid raw material to be purified to obtain a mixed material, the low eutectic component includes one or more impurity components, the impurity components include benzaldehyde, benzyl alcohol, phthalic acid, biphenyl and benzyl benzoate, and the mass ratio of the impurity components in the mixed material is 1.5:1:10:40:3; the equipment used includes a drying device, a hot air device and a conveying device, the solid benzoic acid raw material and the low eutectic component are melted and fully mixed to obtain a mixed material and continuously input the drying device for sweating volatilization and outputting a purified product, the volatile components fill the drying device, the hot air device is used to increase the internal temperature of the drying device and promote the volatilization and purification of the mixed material, and at the same time, the volatile components are discharged from the drying device for collection; the conveying device is used to carry the mixed material, and the mixed material is input into the drying device, and the purified product is output from the drying device, a first coating of the low eutectic component is arranged on the bearing surface of the conveying device, and a second coating of the mixed material is arranged on the first coating; Step three, purify the mixed material by volatilization purification to obtain a purified product and a volatile component, perform subsequent treatment on the volatile component to obtain a by-product, and the by-product is recovered or used as a source of solid benzoic acid raw material to be purified.

2. A method for purifying solid benzoic acid according to claim 1, Features: In the step three, the volatile components are collected and condensed to obtain a condensate, which can be used as a source of the solid benzoic acid raw material to be purified in the step one.

3. A method for purifying solid benzoic acid according to claim 1, Features: In the step three, the volatile components are repeatedly washed to obtain purified gas phase and liquid phase wastewater, the purified gas phase is emptied, and the liquid phase wastewater is recovered.

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