DE4142117A1 - Determining conversion deg. in aq. polymerisation of gaseous monomers - by expanding latex sample and measuring foam density, by radiometric method - Google Patents

Abstract

Process is for determining the degree of conversion in the polymerisation of gaseous monomers in a liq. medium. The process involves determination of the density of foam by a radiometric method. Measurement is performed in an appts. attached to the outside of the reactor, in which a sample of latex is expanded to produce the foam. The method is applicable esp. to the continuous polymerisation of vinyl chloride in aq. emulsion, opt, with other comonomers. USE/ADVANTAGE - For (co)polymerisation of vinyl chloride. Process is simple and rapid (ony one parameter measured), and is used to monitor polymerisation over the whole reaction time, enabling trouble-free control of polymerisation and uniform quality of prod.. Unlike other methods, it is not sensitive to temp. variation and non-homogeneity of the reaction mixt.

Description

The determination of the turnover in the polymerization gaseous monomer is especially in continuous Process an important reaction parameter. So is from the DE 27 14 948 C2 discloses that in the polymerization of Vinyl chloride sales by measuring the foam density of Dispersion samples taken from the polymerization kettle can determine. The method allows precise Measurements, but the ongoing taking of samples labor-intensive and in the case of physiologically questionable Monomer only under special safety precautions possible, which is why several alternative methods for whose replacements have been worked out:

DE 36 27 287 A1 discloses the turnover of the Polymerization of vinyl chloride over the Calculate polymerization pressure. Likewise, in the DE 38 18 249 A1 describes the degree of implementation from the Condensation temperature of the monomer in the gas space of the Reactor and the temperature of the polymerizing To determine dispersion. Have processes of this type however, the disadvantage that they face Temperature fluctuations are very sensitive as well against inhomogeneities in the polymerization vessel, the can occur especially in large reactors.

Product quality is becoming increasingly demanding posed and thus also to the accuracy and Reproducibility of the required measuring and control processes.  

It has now been found that the determination of sales is about the determination of the foam density then a simple and represents exact method if this density determination done radiometrically. You can do the rich use positive experiences with this method without the to have to accept previous disadvantages.

The foam density is measured by using a Latex sample from the polymerization vessel in a measuring tube relaxed and the resulting foam radiometrically shines through.

As a measuring effect for the density measurement is according to the Lambert-Beer law weakening of Gamma rays when passing through the medium to be measured exploited. If the measuring path is constant, it is still at the detector incoming residual radiation a measure of the density of the measuring product.

Further details can be found in the brochure "Operating Instructions / Operating Manual Foam Measurement LB 386-11C ", laboratory Prof. Dr. Berthold GmbH & Co., D-7547 Wildbad 1.

The method according to the invention can in particular in the Polymerization of vinyl chloride, optionally with other comonomers find application. Particularly suitable it is for the processes for polymerizing vinyl chloride in aqueous emulsion, such as in the European patent specification 00 73 015 are described.

Radiometric density measurement brings a number of Advantages with it: It happens very quickly, because only one Parameters must be determined so that the measurement over the total response time or at any time can be done. You can, for example, the  Control monomer feed or any operating parameters. Emissions of the monomer into the environment and with it associated health burden of Operating personnel are completely avoided. Furthermore can pressure compensation in the method according to the invention be provided.

The method according to the invention thus permits a faultless one Control of the polymerization process and thus the Generation of constant qualities of the polymer. In many cases it can also be controlled precisely the space-time yield can be increased.

The invention is illustrated in the following examples explained. Percentages refer to the weight.

example 1

In an upright cylindrical polymerization vessel with a volume of 1.5 m ³ , equipped with a jacket cooler and blade stirrer, the following quantities are fed continuously on an hourly basis:
70 l vinyl chloride
77 l aqueous solution containing 0.23% of an alkanesulfonate (with a carbon cut of 15), 1.28% di-isodecyl ester of the sulfosuccinic acid sodium salt and 0.1% sodium bicarbonate and 0.015% sodium bisulfite
2 l of 2% potassium peroxodisulfate solution.

By appropriate discharge of the polymerized dispersion the level of the liquid will be 90% of the inner Container height kept. At regular intervals now a latex sample from the polymerization kettle for about 1 minute  long into a previously evacuated measuring tube against one constant pressure relaxes and the foam formed Radiometrically irradiated to measure the foam weight.

Table 1

The turnover can, as in DE 27 14 948 C2 described, calculate from the measured foam weight.

Example 2

The procedure is as described in Example 1. The following quantities are entered on an hourly average:
70 l vinyl chloride
77 l aqueous solution containing 2.02% ammonium laurate, after 137 hours only 1.88%
2 l of 2% potassium peroxodisulfate solution.

Table 2

The turnover can, as in DE 27 14 948 C2 described, calculate from the measured foam weight.

Claims (5)

1. A method for determining the degree of conversion in the polymerization of gaseous monomers in a liquid medium by foam density determination, characterized in that the determination is carried out radiometrically. 2. The method according to claim 1, characterized in that the measurement in an outside of the reactor Apparatus takes place into which the latex sample expands becomes. 3. The method according to claim 1 or 2, characterized characterized in that the polymerization in aqueous Emulsion takes place. 4. The method according to claim 1, 2 or 3, characterized characterized in that vinyl chloride, optionally with other comonomers is polymerized. 5. Method according to one or more of the preceding Claims, characterized in that the Polymerization process carried out continuously becomes.