Melting point: 153-159℃(lit.)
Boiling point: 248.08℃
Vapor density: 7.26 (air)
Vapor pressure: <0.1hPa(20℃)
Refractive index: 1.493~1.509
Flash point: 100℃
Storage conditions: 2-8℃
Anhydrous citric acid is a natural component and an intermediate product of physiological metabolism in animals and plants. It is also one of the most widely used organic acids in food, medicine, chemical industry and other fields. It is colorless, transparent or translucent crystal, or granular and particulate powder, odorless. Although it has a strong sour taste, it is pleasant and slightly astringent. It is gradually weathered in warm air and slightly deliquescent in humid air.
Citric acid is widely distributed in nature. It exists in fruits of plants such as lemon, citrus, pineapple, currant, raspberry, grape juice and animal bones, muscles and blood. Synthetic citric acid is produced by fermentation of sugar containing substances such as granulated sugar, molasses, starch and grapes. It can be divided into anhydrous and hydrate. Pure citric acid is colorless, transparent crystal or white powder, odorless and has an attractive sour taste.
Many kinds of fruits and vegetables, especially citrus fruits, contain more citric acid, especially lemon and lime - they contain a lot of citric acid, which can reach 8% after drying (about 47g / L in fruit juice). In citrus fruits, the content of citric acid is between 0.005mol/l of orange and grape and 0.30mol/l of lemon and lime. This content varies with the growth of different cultivated species and plants.
1.In the food industry, shallow sour agents, solubilizers, buffers, antimicrobial agents, sterilizing deodorants, binding agents, etc. are extremely widely used. The specific uses are numerous.
2. Effervescence is a popular drug delivery system for oral ingredients. Citric acid reacts with sodium carbonate or sodium bicarbonate aqueous solution to produce a large amount of CO2 (ie effervescence) and sodium citrate, which can quickly dissolve the active ingredients in the drug and enhance the taste ability. For example, it has a solubilizing effect on laxatives and analgesics. Citric acid syrup is a refreshing drink for patients with fever, which has the effects of correcting, cooling and detoxifying. Citric acid is commonly used in various nutritional oral liquids, etc., to buffer pH 3.5-4.5, maintain the stability of active ingredients, and enhance the effect of preservatives. Citric acid is used in combination with fruit flavors to give people a favorite flavor to mask the bitter taste of drugs, especially in traditional Chinese medicine preparations. Adding 0.02% citric acid to liquid ingredients can form a trace of iron and copper complexes, delaying the degradation of active ingredients effect. Using 0.1% to 0.2% citric acid in chewing tablets can improve the flavor of the tablets and make them have a lemon flavor.
3. The metal purification formula based on citric acid can effectively remove the oxides formed on the surface of ferrous and non-ferrous metals. As a weak organic acid, it can cause slight damage to the surface of the metal, but as a metal ion Chelating agents accelerate the migration of metal oxides. In many steel pickling systems, in order to eliminate metal oxide stress cracks and minimize the corrosion and brittleness of high-strength steels, citric acid is used to remove rust instead of strong inorganic acids.
Citric acid can be extracted from fruits such as lemons and oranges, as well as synthetic methods using oxaloacetate and ketene as raw materials. However, the industrial production methods currently used at home and abroad are all fermentation methods. There are solid fermentation, shallow plate fermentation and deep fermentation processes in the fermentation method. More than 80% of the citric acid in my country is made from dried potato powder through deep fermentation of Aspergillus niger, neutralization of calcium carbonate, acidolysis with sulfuric acid, refining, concentration, crystallization and drying. (1) Fermentation: Prepare dried potato powder into a slurry of 18%-22%, and send it to a fermenter that has been steam sterilized (0.2MPa, 40-60min). Use steam to heat to 110°C for 20min sterilization, and use 0.05% amylase for liquefaction. After cooling to 35°C, it was inoculated with Aspergillus niger for fermentation. The fermentation temperature is 36～38℃ in the early stage and 34～36℃ in the later stage; the ventilation rate is 1:(0.1～0.2); the pH value is not lower than 2.5; the fermentation period is 96h. The acid production level is 10% to 14%, and the conversion rate is 95%. (2) After the neutralization fermentation is completed, the fermentation broth is heated to 80°C to kill the mold, and then sent to the plate and frame to obtain a clear liquid by pressure filtration. The filtrate was neutralized by adding calcium carbonate powder at 80°C to a pH of 5.0-5.5, and kept for 0.5h. Then it was filtered by vacuum suction and washed with hot water at 80°C to obtain calcium citrate. (3) Acid hydrolysis and refining Under constant stirring, add calcium citrate to water or dilute acid, then slowly add sulfuric acid until the pH value is 1.8, heat to 90°C, and use the double tube method to determine the end point. Then add 1% to 3% activated carbon of the amount of citric acid, keep it warm for 0.5h, put it in a suction filter bucket to absorb dry, and wash the acid with 90℃ hot water until the residual acid is below 0.5%, and the washing water (ie dilute acid) is used for the next acid Deuse. Finally, 732 cationic resin is used for ion exchange to remove various cations. (4) The clear liquid after concentration, crystallization, drying and ion exchange contains about 15%-20% citric acid. At 55～600C: Concentrate under vacuum to a relative density of 1.335～1.340, and put it into a crystallization pot. Cooled with chilled brine to below 36.6°C to precipitate water crystals. After the crystals are separated, they are washed with a small amount of distilled water until the sulfuric acid content is less than 200×10", and finally dried with hot air at 35°C to obtain the finished product.