A method of co-producing citric acid and calcium sulfate dihydrate

Abstract

The invention discloses a method for the co-production of citric acid and calcium sulfate dihydrate. The method comprises the following steps: (1) carrying out contact reaction on calcium citrate and sulfuric acid aqueous solution to obtain a mixed liquid of citric acid and calcium sulfate hemihydrate, wherein the temperature of the contact reaction between the calcium citrate and the sulfuric acid aqueous solution is higher than the transition temperature at which calcium sulfate hemihydrate is converted into calcium sulfate dihydrate; (2) cooling the mixed liquid of citric acid and calcium sulfate hemihydrate to a temperature lower than the transition temperature at which calcium sulfate hemihydrate is converted into calcium sulfate dihydrate, so that calcium sulfate hemihydrate is converted into calcium sulfate dihydrate, thus obtaining a mixed liquid of citric acid and calcium sulfate dihydrate; and (3) carrying out solid-liquid separation on the mixed liquid of citric acid and calcium sulfate dihydrate to obtain citric acid solution and solid-phase calcium sulfate dihydrate. Through the method disclosed by the invention, the content of free water is low in the produced calcium sulfate dihydrate while ensuring low citric acid residues, and the produced citric acid has high concentration (up to 0.6 g / ml or above). The method disclosed by the invention can be widely used in industrial production.

Description

technical field [0001] The invention relates to a method for co-producing citric acid and calcium sulfate dihydrate. Background technique [0002] Calcium sulfate has a wide range of uses, but the calcium sulfate produced by the reaction of calcium citrate and sulfuric acid contains residual citric acid and more free water, which restricts the application of the product calcium sulfate and cannot exert its due value. [0003] The acid hydrolysis of calcium citrate and sulfuric acid produces citric acid and calcium sulfate. There are two traditional methods and ideas. One is to obtain citric acid and calcium sulfate hemihydrate, and the other is to obtain citric acid and calcium sulfate dihydrate. There are three crystal forms of calcium sulfate, which are anhydrous calcium sulfate, hemihydrate calcium sulfate, and dihydrate calcium sulfate. Which crystal form of calcium sulfate is obtained depends on factors such as reaction temperature, reaction time, and reactant concentra...

AI Technical Summary

Problems solved by technology

But its disadvantages are also obvious. Due to the need to react at a higher temperature, the easy carbides entrained in calcium citrate will be carbonized by concentrated sulfuric acid, and the chroma of the citric acid solution obtained by the reaction will increase; The solubility of calcium sulfate dihydrate in citric acid aqueous solution is higher than the solubility of calcium sulfate dihydrate in citric acid aqueous solution. After solid-liquid separation, the content of calcium ions and sulfate ion in citric acid aqueous solution is high, which will pollute the resin and increase the regeneration frequency; the temperature of the reaction solution is high, Improve the equipment and environment requirements for subsequent solid-liquid separation. At the same time, there are potential safety hazards caused by high temperature during solid-liquid separation, and relevant safety precautions are required.

[0006] The reactant calcium citrate is solid, and the product calcium sulfate is also solid. When the sulfuric acid is added too fast, too slowly, stopped midway or stirred unevenly during the reaction, calcium sulfate will embed calcium citrate. In severe cases, there will be agglomeration (caking) of materials in the reaction tank

The entrapment of calcium citrate salt reduces the purity of calcium sulfate and causes the loss of citric acid yield, which makes subsequent solid-liquid separation difficult. This phenomenon cannot be completely avoided by the above two production processes.

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