A kind of detection method of paraformaldehyde polymerization degree

Abstract

The invention relates to a method for detecting the degree of polymerization of paraformaldehyde, which belongs to the technical field of chemical production. Put the solvent and dispersant methanol into the reaction pool 1, add paraformaldehyde, stir well to obtain the mixed solution 1, use a trace moisture analyzer to measure the water content of the mixed solution 1, and record it as h1; put the auxiliary agent into the mixed solution In solution 1, mix well to obtain mixed solution 2, use a trace moisture analyzer to measure the water content of mixed solution 2, and record it as h2; the degree of polymerization of paraformaldehyde n=M (water) / M (formaldehyde)*q / { [h2·(w+x‑y+z)‑h1·(w+x)‑z·hz] / x} to get the degree of polymerization. This process uses additives to treat paraformaldehyde samples, which can continuously and accurately measure free water and bound water in paraformaldehyde at one time. The amount of bound water is not affected by various impurities such as formic acid, metal ions, and mechanical impurities in paraformaldehyde. Due to the influence of components, the determination of the degree of polymerization of paraformaldehyde is fast and accurate.

Description

technical field [0001] The invention relates to a method for detecting the degree of polymerization of paraformaldehyde, which belongs to the technical field of chemical production. Background technique [0002] Introduction to Paraformaldehyde [0003] Paraformaldehyde (molecular formula HO-(CH 2 O)n-H, where n is the degree of polymerization, and the value of n ranges from 8 to 100), also known as polyformaldehyde, polyoxymethylene, polyacetal, solid formaldehyde, is a white amorphous particle or powder with formaldehyde odor, easily soluble in Hot water, slightly soluble in cold water, soluble in dilute acids and alkalis. Its harm to the human body is the same as that of formaldehyde, and there is also a dust hazard. The chemical properties and uses are basically similar to formaldehyde. It is an excellent substitute for industrial formaldehyde aqueous solution. It is mainly used to replace high-concentration formaldehyde aqueous solution to participate in various reac...

AI Technical Summary

Problems solved by technology

However, it is not suitable for measuring the amount of bound water in a system with a large amount of water such as a water system.

[0014] In non-aqueous systems, the depolymerization effect of paraformaldehyde is not satisfactory, mainly because the depolymerization is not complete, and the release of bound water is not complete, resulting in inaccurate results.

Although traditional depolymerization catalysts such as triethylamine have certain effects, they also have the problem of slow and incomplete depolymerization. Even if heated, the effect of rapid and complete depolymerization cannot be achieved, resulting in inaccurate measurement of bound water.

[0015] The aforementioned methods have large errors and poor accuracy in the results of the degree of polymerization inspection, and are of little significance to the manufacturer’s process control and downstream customers’ inspection guidance, resulting in large fluctuations in the quality of paraformaldehyde (polymerization degree index) in the production enterprise, and the depolymerization of the enterprise is difficult to control. Great impact on the yield and quality of the next process

[0016] The reason for the large error in method 1 is that the bound water content is indirectly estimated and inaccurate.

(1) The moisture calculation method does not consider the influence of other water-insoluble substances and impurities in paraformaldehyde except formic acid and other known impurity components; (2) The process of measuring the moisture content (free water) of paraformaldehyde with a moisture analyzer In the middle, the reaction end point is unstable and shifts continuously, which further increases the detection error

(3) In the complex system of paraformaldehyde solution, when measuring the content of known impurities such as formic acid, iron, sodium, etc., the inspection of each impurity will affect the accuracy of the degree of polymerization

[0017] The reason for the large error in method 2 is mainly because the bound water content is indirectly estimated and inaccurate

One is that the volatilization of formaldehyde during the drying (drying) process of paraformaldehyde and the incomplete drying of free water lead to inaccurate results of bound water; the higher the drying temperature and the longer the drying time, the greater the deviation

Conversely, if the drying temperature is not too high and the drying time is not too long, the decomposition and volatilization of paraformaldehyde will be slowed down, but the water in paraformaldehyde will not be completely removed, resulting in distortion of the results of moisture and polymerization degree

Second, during the drying process, the paraformaldehyde sample will further polymerize, resulting in distortion of the test results of the main aldehyde content and bound water content

In addition, during the inspection process, the formaldehyde smell at the operation site is strong, which is not conducive to health

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