Properties and uses of benzoic acid preservatives and their salts

Preservative is a food additive that can prevent food spoilage caused by microorganisms and extend the shelf life of food. It also It has the function of preventing food poisoning. There are many types of preservatives. The main ones allowed to be used in my country are benzoic acidPreservatives and its salts, hydroxybenzoic acid, sorbic acid and its salts, etc.

Benzoic acid and its salts

Properties and uses of benzoic acid and its salts

Benzoic acidPreservativesBennzoic acid is named after it was originally produced from benzoylamine (a plant-based spice whose main components are benzoic acid, cinnamic acid, vanillic acid and resin). It is colorless or white crystal. Relative density 1.2659 (15/4℃. ​​Melting point 122℃. Boiling point 249℃, at 100℃℃sublimates when time passes, is slightly soluble in water, and is easily soluble in hexanol, hexyl ether, chloroform, benzene and other solvents. Benzoic acid can combine with aminocaproic acid in the human body to generate hippuric acid, which is excreted in the urine. There is no accumulation. Function. The advantage is low cost, good effect in acidic foods, and effective against yeast, mold and bacteria. The disadvantage is that the antiseptic effect is greatly affected by the pH value. When pH>4, the effect decreases significantly, and there is a bad taste.

Benzoic acid has low solubility and is inconvenient to use. In actual production, most of its sodium salt, namely sodium benzoate, is used. During use, sodium benzoate can be converted into effective Form benzoic acid. It is an odorless powdery solid with a commonly used sweet and astringent taste, and is soluble in water and ethanol.

Benzoic acid and its sodium salt are generally used in acidic foods, especially beverages, such as apple juice, grape juice, etc. According to the hygienic standards for the use of food additives, the maximum usage of benzoic acid in soy sauce, vinegar, jams and cans is 1g/kg. The maximum usage in fruit juices and wines is 0.8g/kg. The maximum usage in soda and sparkling wine is 0.2g/kg. Concentrated juice shall not exceed 2g/kg.

Production of benzoic acid and sodium salt

(1) Method Toluene is carried out in the presence of a catalyst (commonly used manganese dioxide) Direct oxidation method; it can be obtained by heating decarboxylation of phthalic acid in the presence of catalysts aluminum oxide and zinc oxide; it can also be obtained by hydrolysis of dichlorotoluene in the presence of lime milk and iron powder; the commonly used method in industry is toluene oxidation method .And its sodium salt benzoic acid is prepared by neutralizing benzoic acid and sodium carbonate solution, filtering, evaporating and crystallizing.

(2) Process flow This process mainly consists of five processes:

①Toluene oxidation;

②Debenzene removal by oxidizing liquid;

③Distillation of benzoic acid after benzene removal;

④ Neutralize benzoic acid with soda ash;

⑤Dry product sodium benzoate.

Put 2200kg of toluene and 2.2kg of naphthoic acid into the oxidation tower with a pump. The jacket is heated to 120°C with steam. At this time, the toluene boils and starts. In a 6.0m³ air compressor, the compressed air enters the toluene liquid from the bottom of the tower through the buffer tank, and an oxidation reaction occurs. This oxidation reaction is an exothermic reaction. As the reaction proceeds, the temperature rises, but Note that the temperature cannot exceed 170°C. Therefore, the tower top jacket must not only stop heating, but also switch to water cooling. During the oxidation reaction, a large amount of toluene vapor and water vapor are discharged from the top of the tower, enter the 20㎡ coil condenser, condense into liquid and then enter the water separator (2). Toluene returns to the oxidation tower from the upper part of the water separator, and the water flows from the separator. The lower part of the water vesselseparates out. Then enters the water metering tank (14), and separates There is an exhaust gas discharge pipe on the cover of the water device. The exhaust gas passes through the discharge pipe to the buffer tank (13) Enter the activated carbon adsorption tower(15).to adsorb the toluene. Direct steam is passed into the tower at regular intervals to desorb the adsorbed toluene. . Then it is condensed, separated, dried and recycled for reuse. At 170°C, the oxidation time of toluene is about 12 to 16 hours, and the toluene conversion rate can reach 70% or more.

Picture2-1 Sodium benzoate process Process

1 – condenser; 2 – water separator, 3 – debenzene pot, 4 – distillation pot; 5 —Distillation column, 6—Measuring tank, 7—Neutralization pot, 8 —Filter;

9-filtrate tank, 10-sodium benzoate storage tank; 11-drum dryer, 12-oxidation tower; 13 One buffer tank, 14 and one water metering tank

15-adsorption tower; 16-dryer, 17-toluene storage tank: a-steam, b-electric heating ,c-who,d-compressed air

Put the oxidizing liquid into the debenzene pot (3) (15OOL jacketed), heat it to 100-110°C with steam through the jacket under a vacuum of 0.08MPa, and use The unreacted toluene is steamed out by bubbling compressed air and enters the 10㎡ condenser. The condensate enters the water separator for recycling and reuse.

The benzoic acid after benzene removal also contains impurities and organic pigments and needs to be distilled again. Put the material liquid into the distillation pot（4)Heat and control the temperature of the feed liquid to 190°C, and the benzoic acid will evaporate and enter the distillation tower. (5). Control the temperature at the top of the tower to 160°C, and the distillate will be cooled through the jacket and enter the neutralization pot(7), pure jasmine acid is obtained.

After the pure benzoic acid enters the neutralization pot, add the prepared soda ash solution in time for neutralization (300L distilled water plus 140kg of soda ash can neutralize about 200kg of benzoic acid ). The neutralization temperature is preferably 70 C, and the neutralization material should have a pH of 7.5 as the end point. And add activated carbon to decolorize 3% of the neutralized material, and then filter through vacuum suction to obtain a colorless and transparent sodium benzoate solution (content 50%).

The solution containing 50% sodium benzoate is drum dried or box spray dried to obtain a powdery finished product.