DETERMINATION OF SOME PHYSICOCHEMICAL PROPERTIES OF STARTING MATERIALS IN THE PRODUCTION OF AMIDOPYRINE

V. I. Redekop, G. D. Spetstsi, I. P. Chashchin, M. S. Lantsman

(Presented by the scientific seminar of the Department of Processes, Apparatus, and Cybernetics of Chemical Production)

The ever-increasing demand for amidopyrine preparations presupposes an increase in its production either by increasing production capacities or by intensifying production processes.

The problem of process intensification can be solved by transferring production to a continuous scheme. The associated calculation and design work, primarily for the first stage—methylation—required the determination of certain physicochemical properties of the starting substances: 1-phenyl-3-methylpyrazolone-5 (PhMP), methyl ester of benzenesulfonic acid, and the methylation product: antipyrine benzenesulfonate (ABSA), because such data are absent from literary sources.

Technical raw material and product directly used in production were taken for the determinations.

The bulk density was determined by the standard method for air-dry materials.

The bulk density of PhMP was 663 kgf/m³, and that of ABSA was 806 kgf/m³.

The density of melts of PhMP and ABSA was determined by the pycnometric method in the temperature interval 130–210°C. The densities of greatest technological interest are those for PhMP at 130°C and for ABSA at 210°C, which are respectively equal to 1190 and 995 kg/m³.

For melts of PhMP and ABSA, as well as for the methyl ester of benzenesulfonic acid, viscosity was determined using a capillary viscometer of the VPZh-2 type, GOST 1002–62.

The viscometer was placed in a transparent thermostat filled with a high-boiling liquid.

For PhMP in the temperature interval 140–210°C, the dynamic viscosity decreases from 5.49 to 1.69 cP; for ABSA in the interval 145–225°C, from 32.7 to 6.06 cP; for the ester, the viscosity measured at 20°C is 6.01 cP.

The melting temperatures of PhMP and ABSA were determined by the standard method and were found to be, respectively, 124–125°C and 93–94°C.

The studies established that PhMP and ABSA practically do not sublime. When held in the molten state, PhMP and ABSA change their melting temperature, evidently because of changes in the composition of the main product.

The coefficients of thermal diffusivity \((a)\) and thermal conductivity

\((\lambda)\) for FMP and BSKA were determined by the regular-regime method [1].

The results are given in Table 1.

Table 1

To select construction materials for the equipment design of the processes, the contact angle of wetting of these materials by FMP and BSKA was determined on an instrument designed by P. A. Rebinder, into which design modifications had been introduced that made it possible to keep FMP and BSKA in the molten state. Determinations were carried out for metals (steel, cast iron, copper, brass, aluminum) and Teflon. Only Teflon is not wetted by these substances.

The results obtained are necessary in calculations and in the design of apparatus for the production of antipyrine.

The second part of the work is devoted to investigation of the BSKA crystallization process. The investigation was carried out in order to establish the optimum process conditions needed for conducting pilot-scale tests and for drawing up the design specification for the design of an industrial continuous-action crystallizer. These conditions include: type of solvent, temperature, cooling rate, stirring rate, initial concentration of the solution, duration of the crystallization process, the presence and nature of the influence of impurities, and various physicochemical and physical effects.

At present, BSKA crystallization is carried out in batch apparatus from a solution obtained by mixing the melt with water. In total, the crystallization process lasts about 24 hours, with stirring and with stoppages of the apparatus for cleaning the walls of a layer of encrustation. From the crystallizer the mass goes to centrifugation. For the normal course of the centrifugation process, formation of crystals that are as large as possible and uniform in size is desirable.

Since there are no ready data on the BSKA crystallization process—apart from the results of determination of solubility in the range 20–40°C—the task arose of experimentally studying the course of the process under various conditions and determining the influence of various factors on it. A total of 8 series of experiments were set up.

Technical BSKA obtained from the plant was used for the investigations.

Aqueous BSKA solutions were prepared at temperatures determined from a previously obtained solubility curve, with different ratios of the amounts of substance and solvent, ranging from 3:5 to 4:1.

The experiments were carried out at different times, at different stirrer rotation speeds, and under different temperature conditions. For each experiment, the following were kept constant: the stirrer speed and the temperature of the cooling water; to this end, the beaker with the solution was placed in a thermostat. The temperature range of the experiments was 0–90°C. Cooling of the solutions proceeded at different rates. Frame and propeller stirrers made of various materials were used.

After drying, the crystals obtained were subjected to sieve analysis. The data obtained were entered into tables and analyzed—

were plotted graphically as integral and differential distribution curves.

The results of analysis of the data obtained are given below.

1. Increasing the duration of crystallization leads to an increase in the size of the crystals. Under the experimental conditions, the best time may be considered to be 60 min. A further increase in duration does not give any substantial improvement in the granulometric composition of the crystallization product.

2. To determine the nature of the effect of the stirring rate on the granulometric composition of the crystals, experiments were carried out at stirrer speeds from 24 to 72 rpm. It was found that as the stirring rate of the solution increases, the yield of coarse fractions decreases and the yield of fine fractions increases, owing to the destructive action of the stirrer and the mutual friction of the crystals, which become more pronounced as the viscosity of the stirred mass increases.

For dilute solutions (BSCA:water = 3:5), an improvement in the granulometric composition of the crystals was observed when the stirrer speed was increased, apparently owing to an increase in the crystal growth rate under conditions of enhanced mass transfer.

For the two tested types of stirrers, frame and propeller, the difference in the yields of coarse and fine crystal fractions is insignificant.

The results of some experiments carried out to determine the effect of the initial concentration of the solution on the granulometric composition of the crystals are given in Table 2.

Table 2

Analysis of the results presented leads to the following conclusions:

a) for each experimental time there is an optimum value of the solution concentration; at higher and lower concentrations the granulometric composition of the crystals is worse;

b) at crystallization durations of 60 and 90 min, the best results were obtained for the ratio 2:1.

With greater dilution, apparently, the degree of supersaturation of the solution was insufficient, while with less dilution it was very high, which accelerated the formation of nuclei and, to a lesser extent, their growth rate; as a result, the size of the crystals decreased. An increase in the viscosity of the stirred mass, it should be assumed, also played a negative role.

1. At a crystallization duration of 15 min, the best results were obtained for the ratio 3:1, which confirms a significant

but the effect of the increase in viscosity, which in a short experiment does not have time to manifest itself.

1. To determine the dependence of the particle-size composition of the crystals on temperature, crystallization was carried out at various temperatures, from 0 to 90°C, at 15° intervals. The results of the experiments showed that, as the temperature increases, the yield of coarse fractions increases, probably owing to an increase in the rate of crystal growth.

The total yield of fractions larger than 1 mm, when the initial temperature of the cooling water was raised from 15 to 75°C, increased from 37.9 to 55.1%.

It was found that particles 2 mm and larger are formed at a cooling-medium temperature above 20°C. As the temperature corresponding to saturation of the solution is raised, the particle-size composition of the crystals deteriorates noticeably.

1. The dependence of the particle-size composition of the crystals formed on the rate of temperature decrease was checked under various conditions of cooling the solution: in air, in cold and heated still water, and in cold running water.

For all experiments the stirrer speed was 32 rpm, the time was 60 min, and the ratio of the amounts BSKA:water was 2:1.

The results of the experiments are given in Table 3, in order of increasing cooling rate of the solution.

Table 3

From the first experiment to the last, the yield of coarse fractions decreases and the yield of fines increases. Thus, the crystal size increases as the rate of cooling of the solution decreases.

On the basis of the results of the five series of experiments presented, a general conclusion can be drawn: the character of the main dependences for BSKA does not differ from those generally known for solutions [2, 3, 4].

The last three series of experiments were carried out in order to determine the effect of impurities on the crystallization process of BSKA, the degree of encrustation of various materials by it, and the pH value of the solution medium.

Experiments with technical BSKA and BSKA washed free of impurities showed that, in practice, the presence of impurities does not affect the quality of the product and there is no need to remove them.

BSKA belongs to substances that strongly encrust heat-transfer surfaces. Encrustation is promoted by certain temperature and hydrodynamic conditions, as well as by the nature of the surface being encrusted. Glass, polished steel, and Teflon stirrers were used in the experiments. Teflon is encrusted to the least degree, followed by glass and steel.

The medium most suitable for the crystallization process proved to be that arising when BSKA is dissolved in water, pH = 1.5.

Similar experiments on crystallization with sulgin, caffeine, and antipyrine were carried out under pilot-plant conditions.

On the basis of the results obtained, recommendations were prepared for pilot-plant testing of the crystallization process for BSKA and other products.

REFERENCES

1. M. A. Mikheev. Fundamentals of Heat Transfer. 3rd ed. Gosenergoizdat, 1956.
2. L. N. Matusevich. Crystallization from Solutions in the Chemical Industry. “Khimiya,” 1968.
3. A. V. Bamforth. Industrial Crystallization. “Khimiya,” 1969.
4. N. V. Caldwell. Theoretical and industrial aspects of crystallization. Chem. Met. Eng. 49, No. 5, 116, 1952.