SU1001660A1 - Method for controlling crystallization of ascorbic acid - Google Patents

Abstract

A METHOD FOR CONTROLLING THE CRYSTALLIZATION PROCESS OF ASCORBINIC ACID from its aqueous saturated solution i: when cooled from 60 to 4 ° C by measuring the concentration of crystals in the solution, characterized in that, in order to simplify the process, the concentration of crystals in the solution is measured by passing through continuously a stirred solution of ultrasonic oscillations at a frequency of 2–3 MHz with the subsequent determination of the concentration of ultrasound oscillations by the magnitude of the absorption coefficient of ultrasonic vibrations.

Description

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The invention relates to the production of chemical-pharmaceutical preparations, namely, to an improved process control method for the ascorbic acid's crystallization during its preparation and purification. Ascorbic acid is used not only as a drug, but also to find wide application in the chemical industry.

A known method of controlling the crystallization process of ascorbic acid from its saturated aqueous solution upon cooling from 60 to by spectrophotometric measurement of the concentration of crystals in the solution.

The method is based on the absorption of light of a certain frequency by a substance. For ascorbic acid, the maximum absorption of light in a neutral aqueous solution is 265 nm. The concentration of crystalline ascorbic acid (Scr) is determined by the difference between the initial concentration of the solution (Scx.) At the beginning of crystallization and the concentration of the mother liquor (C) "at,) / which is determined by a spectrophotometric method. The mother liquor is obtained by centrifuging or filtering a sample taken during the crystallization process.

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Prior to measurements using this method, the calibration dependence of the optical density (D) on the concentration of an aqueous solution of ascorbic acid at a wavelength of 5,265 nm l is used.

The spectrophotometric method has the following disadvantages:

The crystal concentration is determined by the residual concentration of the solute, for which sampling and filtering are necessary;

this method is a destructive control method;

continuous instantaneous monitoring of suspended matter concentration is not possible.

The aim of the invention is to simplify the process by allowing the continuous monitoring of the crystallization process of ascorbic acid directly in the working volume and instant determination of the end of the process.

The goal is achieved by the fact that during the implementation of the method of controlling the process of crystallization of ascorbic acid from its aqueous saturated solution upon cooling from 60 to ° C by measuring the concentration of crystals in the solution, this measurement is carried out by passing through

a constantly stirred solution of ultrasonic oscillations of a frequency of 2-3 MHz with the subsequent determination of the concentration of crystals by the magnitude of the absorption coefficient of ultrasonic oscillations.

The use of ultrasonic vibrations to determine the concentration of particles in dispersed systems is known 2.

However, these methods cannot be used to control crystallization processes, since, as a rule, not only the crystal concentration changes, but also the crystal size of the crystal f coagulates, and this changes the amount and size of coagulants. and the number of crystals forming coagulums A, since the absorption coefficient of ultrasound depends both on the concentrations of particles and on their size and degree of coagulation fsj, unambiguous measurements of the concentration of crystals in the process of crista tion of impossible due to the influence of confounding factors were higher.

A detailed microscopic study of the crystallization process of ascorbic acid made it possible to establish that this process has a number of special features, which make it possible to use high frequency ultrasound to control the concentration of crystals. These features include the following:

in the range from 60 to, i.e. in the practically feasible temperature range, the size of the crystals varies so slightly that this does not affect the value of l;

in the same temperature range, ascorbic acid crystals do not coagulate at all.

It is established that the measurement of concentration using ultrasonic oscillations in a wide range of concentrations is optimal at a frequency of 2 to 3 MHz.

At a frequency of less than 2 MHz, the dependence (C) is expressed very weakly, which prevents quantitative measurements. At frequencies greater than 3 MHz in the region of high concentrations of the crystalline substance (10-30 wt.%) Measurements are impossible due to significant non-linear distortions.

The calculation of the concentration, wt.% Of ascorbic acid crystals is carried out using the formula

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, oo where gb is the ultrasound absorption coefficient; and k is the coefficient depending on the frequency of the ultrasonic vibrations. To determine the end of crystallization, the absorption coefficient of the ultrasound is measured and, if the two values measured after 5 minutes do not change, the crystallization process can be considered complete. Construction of a calibration curve. A blue water solution of ascorbic acid i is prepared at a concentration of 12.6 wt.% At 3 ° C. The ultra is then transmitted; the sound frequency oscillations are at 2 MHz and the absorption coefficient of ultrasound (oi) is measured. For these conditions "(. Next, a certain amount of crystalline ascorbic acid (e.g., 20 wt.%) Is added with continuous stirring with continuous stirring. And ultrasound absorption coefficient (L) is measured. At a frequency of 2 MHz at a concentration of crystals C20 wt.% Ultrasound absorption coefficient: equal to 0.45 cm. From these data, a calibration curve is constructed (graph) and the coefficient K is determined by the formula et-Wo (0.45-0) -1, (0 ../o .O.-Z

Ultrasound absorption coefficient,

The concentration of precipitated crystals, wt.% The drawing shows a caliber on the dependence of the absorption coefficient of ultrasound on the concentration of ascorbic acid crystals f (C) at 40.21,. The measurement of the absorption coefficient of ultrasound is carried out using the power of the known device b. Example. The original saturated solution of ascorbic acid at 60 ° C is cooled for 1 h to. The concentration of precipitated ascorbic acid crystals was monitored 30 minutes after the start of cooling of the crystallized system. At constant mixing of the system, ultrasonic oscillations with a frequency of 2 MHz are passed through it, and the absorption coefficient of the ultra-eugue is measured, which in this case is equal to 0.30. The concentration of precipitated crystals is calculated by the formula, .0.30 / 5.751 · 0.44 wt.%. To determine the end of the crystallization process, the subsequent measurements are carried out with an interval of 5 minutes. Similarly, each time the absorption coefficient of the ultrasound is measured and the concentration of ascorbic acid crystals precipitated is calculated. . The data obtained are given fi table.

0.37 0.51 0.65 0.67 0.68 0.68

If, when measuring the absorption coefficient of ultrasound, after 5 min the value does not change, then the crystallization process is over (see table and drawing, section BC).

Thus, the process of crystallization of ascorbic acid in this example is for 1 hour.

As a result of research, it has been established that for ascorbic acid with a concentration of crystals

16.4 22.4 28.6 29.4 30, P 30.0

From 0 to 30% by weight, the dependence on {(c) is linear, the temperature change in the range from 40 to no effect on the magnitude of the absorption coefficient of ultrasound (see drawing).

Thus, the determination of the numerical value of the concentration of ascorbic acid crystals is possible by analytical calculation using formula (1) and graphically using a graph.

The use of the method of continuous control of the concentration of ascorbic acid in the process of its crystallization at the stages of preparation and purification as compared with the known methods provides the following advantages: reduction of the process time from 6 to 1-2 hours;

the ability to determine the concentration of crystals of a substance directly in the working volume. without sampling and additional processing of samples, which allows reducing the time of control; possibility of correct and timely determination of the end of the crystallization process.

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Claims (1)

METHOD FOR MONITORING THE CRYSTALLIZATION PROCESS OF ASCORBIC ACID from its aqueous saturated solution upon cooling from 60 to 4 ° С by measuring the concentration of crystals in the solution, different from flea in that, in order to simplify the process, the concentration of crystals in the solution is carried out by passing through a constantly mixed solution of ultrasonic vibrations with a frequency of 2–3 MHz with subsequent determination of the concentration of stalls by the value of the absorption coefficient of ultrasonic vibrations. SU,. ,, 100166