SU42644A1 - The method of obtaining alizarin - Google Patents

Description

The preparation of alizarin by direct oxidation of anthraquinone according to the method described in Soviet patent No. 14118 presents considerable technological difficulties. First of all, it is necessary to note a very long reaction time. In order to achieve a complete or almost complete transfer of anthraquinone to alizarin, it is necessary to react with repeated additions of nitrate solution (under a pressure of 30-40 atmospheres) for 3-5 days. Then, the calcium lacide alizarin formed under these conditions is released in a colloidal state and is completely unsuitable for filtration. It is necessary to treat hydrochloric acid not only with the most calcium lacquer of alizarin, but also with all of the melt, which is due to the excessive consumption of hydrochloric acid and the conversion of caustic soda to such a low-value product as sodium chloride. In addition, with this method of operation, along with alizarin, from 5 to the heavily contaminated ugly oxyanthraquinones formed during the reaction, which adversely respond to the quality of alizarin, are precipitated. All this makes the method of obtaining alizarin described in patent A 14118 technologically unacceptable.

The authors of the present invention have found that the oxidation reaction of anthraquinone to alizarin should be carried out in 2 phases.

1) Recovery of anthraquinone in an alkaline medium and hydroanthraquinone.

2) Alkali oxidation of hydroanthraquinone formed in alizarin.

Both of these phases can be carried out in a single operation, with the simultaneous introduction of both a reducing agent and an oxidizing agent. As a reducing agent, cheap sodium sulphide gives the best results, as calcium nitrate oxidizing agent. The duration of the reaction under these conditions with the complete transition of anthraquinone to alizarin does not exceed 18 hours.

The reduction phase is maintained at a temperature of 200-210 ° for 2-3 hours.

The oxidative phase requires additional heating to 220-225 ° for 12-15 hours.

The process is regulated by the release of pressure, which is maintained at a level of 25-26 atm.

Under the conditions described, calcium nitrate was found to be the most suitable oxidizing agent.

Calcium lacizum of alizarin precipitated under these conditions has a crystalline structure and perfectly filters. This circumstance leads, firstly, to the minimum consumption of hydrochloric acid (not required to neutralize the entire alkaline water, as is the case with the work described in patent No. 14118, but only for the decomposition of calcium varnish); secondly, alizarin is free from ugly impurities; thirdly, the ability to almost quantitatively regenerate - (90-95 / 0) caustic soda taken into operation.

The use of the new method enables the technical preparation of alizarin free from obscure impurities with excellent yields (90-95 / o theory and above).

Example. 95 kg of anthraquinone is loaded into a 300-liter ball mill. There, in 3 receptions, 150 l of a solution of 296 kg of caustic soda with 600 l of water are added to 3 doses. After stirring for 40 minutes, the anthraquinone pulp paste is sucked into a 2.2 cubic meter autoclave. The rest of the amount indicated is a solution of sodium hydroxide solution and a solution of 87 kg (100 ° / o) of sodium sulphide freed from suspended particles in 190 liters of water is discharged into the autoclave. 203 l of a solution (counting on anhydrous salt) of calcium nitrate are last loaded into the autoclave. Total autoclave loading 1000 l.

The mass is heated with stirring to 210 (pressure 16-18 atm.) And then made at that temperature — a 2-hour vyderchka. Then the temperature rises to 220-225 °, the pressure at the level of 25-26 atm for the retractor. (if the generated nitrogen is not lowered, the pressure, without compromising the quality and yield of alizarin, rises to 40 atm.). Heating at this stage of the process (oxidative stage 2) continues for about 12 hours until the complete transfer of the anthraquinone to alizarin (sampling under pressure).

At the end of the reaction, the contents of the autoclave are cooled to a temperature of 100 and the residual pressure (1-2 atm.) Is lowered through the drain valve, the autoclave is filled with water and the mass is discharged into a 4 cubic meter vat. m. Then the autoclave is washed twice with 1000 liters of hot water, the washings flow

in the same vat. Filling of Chan-3500 tg. The mass in the tank is heated to 50-60 and drained to suck off the calcium lacquer of alizarin on the floor. The filtration of the crystalline precipitate proceeds extremely quickly. The calcium lacquer is washed with water until colorless. The appearance of the crystalline precipitate is dark blue. The conversion of calcium varnish to alizarin is carried out in aqueous suspension by heating with hydrochloric acid. The alizarin that has landed is filtered on a filterpress and washed with water. The resulting alizarin contains yellow marks and is free from obscure impurities, i.e., meets the requirements for an alizarin of extra blue mark. Output 90-93% of theory.

The use of anthraquinone is usually complete and the resulting alizarin is free of anthraquinone impurities. Sometimes, in the course of heating in a certain amount, the anthraquinone, which is partially aggravated on the lid of the autoclave, is partially crushed into the mass, resulting in alizarin (1-2% anthraquinone). In this case, the release of the calcium lacquer of alizarin from the admixture of anthraquinone is best achieved by passing superheated to 200 water vapor through a wet calcium varnish at a mass temperature of 100-110 °.

Alkaline mother liquors containing a large amount of caustic soda, after evaporation and separation of inorganic salts (thiosulphate, sulphate, sodium sulphite) are evaporated and separated, are utilized with the addition of 10% of fresh caustic soda for further operations.

The subject matter of the invention.

1. Modification of the method of producing alizarin from anthraquinone by heating with caustic alkalis under pressure in the presence of calcium compounds according to the author's certificate No. 14118, with an increase in the melt of sulfuric alkalis, characterized in that calcium nitrate and calcium oxidant in the melt use calcium nitrate.

2. Acceptance of the method mentioned in claim 1, characterized in that the melting is carried out in 2 phases, keeping the melt first for 2 to 3 hours at 200 - 210 ° and then for 12-18 hours at 220-225 °.