阅读说明：本技术 熔融结晶高效回收低含量苯甲酸的方法 (Method for efficiently recovering low-content benzoic acid by melt crystallization ) 是由 王彦飞 杨鹏辉 许史杰 张凯丽 朱亮 杨立斌 赵晓昱 赵文立 韩梅 贾原媛 杨静 于 2021-09-28 设计创作，主要内容包括：本发明属于化学提纯领域,具体涉及一种熔融结晶高效回收低含量苯甲酸的方法。包括以下步骤：1)液相进料：将质量百分含量40～85％的固态苯甲酸粗料加入到层式熔融结晶器在熔化温度进行化料,熔化到液态；2)降温结晶：对质量百分含量≥40％的液态苯甲酸粗料进行降温,降温速率为1～30K/h；降温终温为70～80℃；恒温0.5h；3)升温发汗：待排出未结晶母液后,对晶体进行发汗,升温速率为1～20K/h,升温至110～125℃,恒温0.5h,将发汗液排出；4)化料。本发明的方法适用于质量百分含量≥40％,优先适用于质量百分含量≥50％苯甲酸粗品,不外加溶剂,降低了操作成本,简化了操作,环境友好无三废产生,得到纯度大于93％的苯甲酸。(The invention belongs to the field of chemical purification, and particularly relates to a method for efficiently recovering low-content benzoic acid through melt crystallization. The method comprises the following steps: 1) liquid-phase feeding: adding solid benzoic acid coarse materials with the mass percentage of 40-85% into a layer-type melting crystallizer, melting at a melting temperature, and melting to a liquid state; 2) cooling and crystallizing: cooling the liquid benzoic acid coarse material with the mass percentage content of more than or equal to 40%, wherein the cooling rate is 1-30K/h; the final temperature of the cooling is 70-80 ℃; keeping the temperature for 0.5 h; 3) warming and sweating: after discharging the non-crystallized mother liquor, sweating the crystals at a heating rate of 1-20K/h to 110-125 ℃, keeping the temperature for 0.5h, and discharging the sweating liquid; 4) and (5) melting materials. The method is suitable for the benzoic acid crude product with the mass percentage of more than or equal to 40 percent, preferably more than or equal to 50 percent, does not add any solvent, reduces the operation cost, simplifies the operation, is environment-friendly, does not generate three wastes, and obtains the benzoic acid with the purity of more than 93 percent.)

1. A method for efficiently recovering low-content benzoic acid by melt crystallization is characterized by comprising the following steps: the method comprises the following steps:

step 1) liquid phase feeding: adding 40-85% by mass of solid benzoic acid coarse material into a layer-type melting crystallizer, melting at a melting temperature, and melting to a liquid state;

step 2), cooling and crystallizing: cooling, wherein the cooling rate is 1-30K/h; the final temperature of the cooling is 70-80 ℃; keeping the temperature for 0.5-1 h;

step 3), sweating: after discharging the non-crystallized mother liquor, sweating the crystals at a heating rate of 1-20K/h to 110-125 ℃, keeping the temperature for 0.5-1 h, and discharging the sweating liquid;

step 4), material melting: after the sweat is discharged, the material is heated to be completely melted, and the benzoic acid with the product purity of more than 93 percent is obtained.

2. The method of claim 1, wherein: step 1) the melting temperature is 110-.

3. The method of claim 1, wherein: and 2) the cooling rate is 1-10K/h.

4. The method of claim 1, wherein: and 2) cooling to the final temperature of 73-75 ℃.

5. The recycling method according to claim 1, wherein: and 3) the heating rate is 1-10K/h.

6. The recycling method according to claim 1, wherein: and 3) heating to a final temperature of 110-122 ℃.

Technical Field

The invention belongs to the field of chemical purification, and relates to a method for efficiently recovering low-content benzoic acid by melt crystallization.

Background

Benzoic acid is an organic compound of aromatic acids, also the simplest aromatic acid, and is a white needle-like or scaly crystal in appearance, widely existing in nature in the form of free acid, ester or its derivative. The method is mainly used for preparing the sodium benzoate preservative and synthesizing medicaments and dyes; it is also used for preparing plasticizer, mordant, bactericide, perfume, etc. The commercial value of benzoic acid is enormous and it would be of great value if low levels of benzoic acid could be recovered to obtain a high purity product.

Benzoic acid is initially prepared by dry distillation of benzoin gum or hydrolysis with alkaline water, or by hydrolysis with hippuric acid. In industry, toluene, o-xylene or naphthalene are commonly used as raw materials for preparing benzoic acid, and the raw materials can be obtained from coal tar or petroleum. Further, benzoic acid can be by-produced when benzaldehyde is produced from toluene. The industrial production methods of benzoic acid mainly include a toluene liquid phase air oxidation method, a trichlorotoluene hydrolysis method, a phthalic anhydride decarboxylation method, and a benzyl halide oxidation method. Patents CN101492368 and CN111892494A describe the production and preparation methods of benzoic acid. Patent CN208814920U describes an apparatus for recovering benzoic acid from benzoic acid waste water. Patent CN106892811B describes a method for purifying benzoic acid.

Patent CN101492368 uses cobalt naphthenate as a catalyst, toluene is subjected to oxidation reaction, and a product obtained by the oxidation reaction is rectified to obtain a final product. The patent CN111892494A uses acetic acid, toluene, tetraphenyl cobalt porphyrin and ethyl diacetylacetate as raw materials, and the raw materials are put into a reaction kettle to be uniformly stirred, then oxygen is introduced into the reaction kettle, the temperature and the pressure of the reaction kettle are adjusted and controlled, and the benzoic acid is prepared by reaction, wherein the purity of the obtained benzoic acid is not mentioned. Patent CN208814920U provides an apparatus for extracting benzoic acid from benzoic acid.

The purification method of benzoic acid introduced in CN106892811B is to fully dissolve crude benzoic acid in deionized water in a reaction kettle to obtain a crude benzoic acid solution in a slightly boiling molten state, add activated carbon into the reaction kettle to adsorb impurities, enter a filter press through a gear pump to filter the crude benzoic acid solution, enter a melting kettle to melt the filtered benzoic acid solution, enter a crystallization kettle to crystallize the upper layer melting solution, enter a dryer to dry the crystallized benzoic acid solid, and enter a crystallization kettle to re-crystallize the crystallized residual benzoic acid liquid. The purity of the obtained product can reach 99.5 percent, and the yield can reach more than 90 percent. However, the method does not indicate the purity of the raw materials, the dissolving amount of the solvent is limited, and the process is more complicated and uses more equipment.

Therefore, the benzoic acid purification process with less equipment investment, convenient operation and relative environmental protection meets the market demand, and the application of the benzoic acid purification process can generate great economic benefit and social benefit and has important significance. The substances and homologues reported in the literature and the patent are purified by adopting modes of rectification, solution crystallization and the like. The melt crystallization process was the first time applied to the purification of this material.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a method for efficiently recovering low-content benzoic acid by layered melt crystallization, which does not add a solvent, reduces the operation cost, simplifies the operation, is environment-friendly, does not generate three wastes and obtains the benzoic acid with the purity of more than 93 percent.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for efficiently recovering low-content benzoic acid by melt crystallization comprises the following steps:

step 1) liquid phase feeding: adding 40-85% by mass of solid benzoic acid coarse material into a layer-type melting crystallizer, melting at a melting temperature, and melting to a liquid state;

step 2), cooling and crystallizing: cooling, wherein the cooling rate is 1-30K/h; the final temperature of the cooling is 70-80 ℃; keeping the temperature for 0.5-1 h;

step 3), sweating: after discharging the non-crystallized mother liquor, sweating the crystals at a heating rate of 1-20K/h to 110-125 ℃, keeping the temperature for 0.5-1 h, and discharging the sweating liquid;

step 4), material melting: after the sweat is discharged, the material is heated to be completely melted, and the benzoic acid with the product purity of more than 93 percent is obtained.

Further, it is preferable that the melting temperature in step 1) is 110-.

Further, preferably, the cooling rate of the step 2) is 1-10K/h.

Further, preferably, the final temperature of the cooling in the step 2) is 73-75 ℃.

Further, preferably, the temperature rising rate of the step 3) is 1-10K/h.

Further, preferably, the temperature in the step 3) is raised to a final temperature of 110-122 ℃.

The invention has the advantages and beneficial effects that:

the method is suitable for crude benzoic acid products (the mass percentage content is more than or equal to 40 percent, and preferably more than or equal to 50 percent), raw materials of the process enter a separation process, and materials with the mass percentage content of more than or equal to 40 percent of benzoic acid obtained in each step can be used as primary raw materials. Most of benzoic acid in the whole system can be recovered, and the total yield is about 80%. In addition, the process does not add a solvent, reduces the operation cost, simplifies the operation, is environment-friendly, does not generate three wastes, and obtains the benzoic acid with the purity of more than 93 percent.

Detailed Description

In order to make those skilled in the art better understand the technical solution of the present invention, the following detailed description of the present invention is provided in conjunction with the best embodiment.

Example 1

260.29g of 67.15 percent benzoic acid crude product is put into a 500ml layer type melt crystallizer, the temperature is raised to 115 ℃ until the material is completely melted into liquid, the temperature is reduced according to the cooling rate of 20K/h, and the final temperature of the temperature reduction is 73 ℃; discharging the mother liquor, and heating the materials to 122 ℃ at the temperature rise rate of 15K/h for sweating; discharging the perspiration; heating and melting, and discharging. The purity of the product obtained was 94.91%. The single-pass yield was 36.46%.

Example 2

388.8g of benzoic acid crude product with the content of 51.57 percent is put into a 500ml layer type melt crystallizer, the temperature is raised to 110 ℃ until the material is completely melted into liquid, the temperature is reduced according to the cooling rate of 22K/h, and the final temperature of the temperature reduction is 75 ℃; discharging the mother liquor, and heating the materials to 109 ℃ at the temperature rise rate of 16K/h for sweating; discharging the perspiration; heating and melting, and discharging. The purity of the obtained product is 93.11%. The one-way yield is 37.37%, and if mother liquor and perspiration are used together, the total yield can reach 97.3%.

The foregoing is only a preferred embodiment of the invention, and the description should not be construed as limiting the invention as described herein, since variations in the detailed description and the scope of the application will occur to those skilled in the art and may be made in accordance with the teachings of the present invention.