CS198810B1 - Method of continuous determination of cnoversion stage by manufacture of water solutions of resins - Google Patents

Description

( ⁵⁴ ) A method for continuously determining the degree of conversion in the manufacture of aqueous resin solutions

The invention relates to the continuous determination of the degree of conversion in the manufacture of aqueous resin solutions.

For the production of aqueous solutions of urea-formaldehyde, phenol-formaldehyde or melamine-formaldehyde resins, urea, phenol or melamine with formaldehyde are condensed at 70 to 100 ° C, depending on the type of resin, in a duplicator reactor equipped with a stirrer or reflux condenser. The polycondensation reaction is interrupted by cooling the reaction mixture when the prescribed parameters are reached. During the polycondensation reaction, changes in pressure, local temperature, viscosity, degree of conversion and other physicochemical variables occur, whereby only the temperature and pressure of the interacting mixture and the temperature of the tempering water in the duplicator are continuously measured and recorded. The degree of conversion of the reaction mixture is an important quantity indicating the amount of reacted resin. In addition to other physicochemical variables, the continuous determination of the degree of conversion of resins during the polycondensation reaction is desirable for the most complete information about the polycondensation process in the case of self-control. In addition, the ongoing knowledge of the degree of conversion of urea, phenol or melamine during polycondensation allows an efficient determination of the end of the polycondensation reaction and thereby rationalization of the resin production.

Hitherto known methods for determining the degree of conversion of urea, phenol or melamine during

198 810

198 810 their condensation with formaldehyde is largely based on taking samples from the reacting mixture at various moments of polycondensation and subsequently measuring the degree of conversion by known physico-chemical methods. Determining the degree of conversion by these methods is very laborious and time consuming. The actual sampling of the reacting mixture as well as the determination of the degree of conversion in these samples usually requires human service. In addition, in order to consider the value of the conversion rate at the time of sampling as the value of the conversion rate obtained after a period of time necessary for sample handling and measurement, further polycondensation needs to be stopped in the sample.

These drawbacks are eliminated by the method of continuously determining the degree of conversion in the production of the aqueous resin solutions according to the invention, which comprises introducing ultrasonic waves at a frequency of 10 * to 10 Hz into the reaction condensation mixture, measuring ultrasonic wave propagation velocity in the reaction mixture. the duration of the polycondensation reaction.

Continuously measured ultrasonic wave propagation velocities are recorded and correlated with the calibration dependence of the ultrasonic propagation velocity at a given frequency on the reaction mixture conversion rate during an exemplary polycondensation reaction. Since the velocity of propagation of ultrasonic waves whose wavelength is much greater than the mean value of the structural parameter of the reacting mixture is a continuous and unambiguous function of the concentration of reacted resin in the reaction mixture, the correlation between these variables can be performed continuously and unambiguously.

The advantages of the process according to the invention are that it permits continuous determination of the degree of conversion during the polycondensation reaction, an efficient and, optionally, automatic determination of the end of the polycondensation reaction for the prescribed conversion degree. In addition, it also permits monitoring of possible variations in the degree of conversion during the polycondensation due to different parameters of the polycondensation reaction, different batch composition and polycondensation process conditions, such as stirring speed, temperature, etc. The process of the invention can be carried out using known ultrasonic devices. such as ultrasonic flaw detectors or hydrolocators, echolots, whose specific ultrasonic probes are pressure- and electro-spark resistant.

The method according to the invention is described by way of example of a continuous determination of the degree of conversion of urea during polycondensation with formaldehyde to urea-formaldehyde resin.

Exemplary embodiment

Longitudinal ultrasonic waves in the form of quasi-monochromatic pulses with a mean frequency of 1 MHz, a length of 5 / US and a repetition rate of 50 Hz were introduced into the reactor by means of ultrasonic equipment, a flaw detector and ultrasonic transducers with delay lines, using ultrasonic transducers. the rate at which the reaction mixture passes through the polycondensation time. The measured value of the ultrasonic wave propagation speed was compared with the calibration dependence of the propagation speed

AND

198 810 ultrasonic waves at the reaction mixture conversion stage during polycondensation. This dependence was obtained on the basis of simultaneous measurements of the ultrasound propagation rate as described above and the degree of conversion by the sampling method and are shown in Table 1.

Claims (1)

SUBJECT MATTER Process for continuously determining the degree of conversion in the manufacture of aqueous resin solutions, characterized in that ultrasonic waves of 10 to 10 Hz are introduced into the reaction condensation mixture and the ultrasonic wave propagation rate is measured in dependence on the duration of the polycondensation reaction.