RU2292355C2 - Method for applying agent against overgrowing - Google Patents

Abstract

FIELD: organic chemistry, special agents.

SUBSTANCE: invention relates to a method for applying agent used against overgrowing on internal walls of reactor for polymerization of vinyl chloride, vinyl acetate or their mixtures. Agent against overgrowing represents an aqueous solution containing salt of this agent that comprises product of condensation of aldehyde, phenolic compound and aromatic carboxylic acid hydroxylated by aromatic ring. Value of pH of this aqueous solution is changed during applying to pH value less and, preferably, in the range from 2.5 to 4.5 by acidification with organic and/or inorganic acid aqueous solution. Proposed agent provides practically complete prevention of deposits formation being even after prolonged time of reactor exploitation that allows minimizing the necessary for breaking the industrial cycle for treatment of the device.

EFFECT: improved applying method.

15 cl, 2 dwg, 8 ex

Description

The present invention relates to a method for applying anti-fouling agents used in the polymerization of vinyl chloride, vinyl acetate or mixtures thereof.

Prior level

Anti-fouling agents commonly used in the polymerization of vinyl chloride and / or vinyl acetate are products that can be obtained by condensation of formaldehyde and 1-naphthol, such as those described in European patent application EP-52412.

European patent application EP-942936, incorporated by reference, describes anti-fouling agents that include the condensation product of an aldehyde, phenolic compound and aromatic hydroxylated carboxylic acid at the aromatic nucleus. Preferably, the aldehyde is formaldehyde, the phenolic compound is 1-naphthol, and the aromatic carboxylic acid hydroxylated at the aromatic nucleus is selected from salicylic acid, 4-hydroxybenzoic acid, α, β, or γ-resorcylic acid, 2,3-dihydroxybenzoic acid, 2 5-dihydroxybenzoic acid, 2-hydroxy-5-methoxybenzoic acid or 6-hydroxy-2-naphthoic acid; of these, β-resorcylic acid (i.e., 2,4-dihydroxybenzoic acid) is particularly preferred.

SUMMARY OF THE INVENTION

To be effective and economically suitable for the production of PVC in suspension (PVC / C), an anti-pollution agent (or anti-fouling agent) must satisfy the following conditions:

- it must be stable, easily dosed and easily applicable with steam under pressure (the reactor-polymerizer must be virtually closed to avoid very dangerous contaminants due to the release of gaseous vinyl chloride);

- it should have an increased ability to quickly coagulate when the pH value changes at the moment when it comes into contact with steam (which usually has a pH value of 9-10);

- it should be able to form a gel-like coagulum and, if possible, be colorless (to avoid contamination of the final product).

The coagulum should preferably be of the “sticky gel” type to adhere to the inner walls of the reactors and form a protective film (coating) due to the action of steam heat.

The gel deposited on the walls must, in addition, be able to uniformly penetrate micropores on the surface of the steel in order to prevent the formation of PVC microparticles, which can cause deposits.

In addition, there is no need to heat the inner walls of the reactor to facilitate the formation of a protective film; such actions would actually lead to a delay in the production cycle; after application, the protective film should, among other things, be strong enough so that it can be washed with water (pH value 7) to remove residual contaminants from the reactor; finally, the total application time should be as short as possible, the coating equipment should be simple and ensure reliable and uniform application of the material.

This type of result is usually achieved by applying an aqueous solution under pressure with steam, while the aqueous solution contains 4-8 wt.% Anti-pollution agent, of which at least 12-18% should remain on the inner walls of the reactor in the form of a protective film (such a method is described, for example, in the publication "Fine Chemicals for PVC / S", Chapter 5, 1999, published by CIRS Spa, incorporated herein by reference); the method under consideration actually makes possible extended and economical deposition cycles, while mechanical or gas-powered spraying apparatuses are currently not able to achieve the above objectives.

The present invention relates to a new method for applying the antifouling agent, known as EVERCLEAN ^® 104NS. The preparation of this anti-fouling agent currently sold by the owners of 3V Sigma Spa is described in detail in Example 25 of the already mentioned European Patent Application EP-942936; this agent relates to a basic aqueous solution having a brown color and a pH value of from 11 to 12.4 (usually 11.54), which, as is known in the art, is applied to the inner walls of reactors for the polymerization of vinyl chloride and / or vinyl acetate by spraying in steam flow using equipment that is similar to that shown in figure 1.

However, this application method allows to achieve the desired anti-fouling effect only partially. In fact, when working in such conditions, a coagulum that would adhere sufficiently to the inner walls of the reactors, thus forming the necessary protective film, is not obtained; on the contrary, most of the anti-fouling agent deposited in this way (approximately 99%) accumulates unchanged at the bottom of the reactor before the polymerization reaction begins, so subsequent application is required.

It has now been surprisingly found that by using acidifying before application the solution EVERCLEAN ^® 104NS to a pH less than 5 and preferably in the range from 2.5 to 4.5, is obtained coagulation of the antifouling agents which can therefore be applied on the walls of the reactor with greater efficiency. Therefore, it is an object of the present invention to provide a method for applying an aqueous solution containing an alkali metal and / or alkaline earth metal salt, preferably an anti-fouling sodium salt, containing the condensation product of an aldehyde, phenolic compound and aromatic carboxylic acid hydroxylated at an aromatic core, characterized in that the pH of this aqueous solution changes to a pH of less than 5 and, preferably, in the range from 2.5 to 4.5.

Preferably, the aldehyde is formaldehyde, the phenolic compound is 1-naphthol, and the aromatic carboxylic acid hydroxylated at the aromatic nucleus is 2,4-dihydroxybenzoic acid; the aqueous solution usually contains 4-8 wt.% salt of an alkali metal and / or alkaline earth metal of this anti-fouling agent and has a pH in the range from 11 to 12.4.

The method according to the present invention provides on the wall (i.e. on the inner walls of the polymerization reactor) or in the mixer a contact between the solution of the anti-fouling agent and the solution of organic and / or inorganic acid, for example citric, oxalyl, tartaric, hydrochloric, nitric and / or sulfuric acid which, in the presence of steam, provides a decrease in pH sufficient to allow coagulation and the formation of a protective film. This aqueous solution preferably contains from 1 to 10 wt.% Citric acid, preferably 5%.

According to a particularly preferred embodiment of the present invention, the anti-fouling salt and an aqueous solution of an organic and / or inorganic acid are mixed before being applied to the inner walls of the polymerization reactor; the mixture of gel and condensate thus obtained is applied to the inner walls of the polymerization reactor in a steam stream. Suitable application equipment according to the present invention is shown, for example, in figure 2 (where the valves are indicated using the letter V). The vapor pressure is not limiting for the purposes of the present invention and may vary according to the type of installation; however, typically a pressure in the range of about 2 to 20 bar is used; application time is usually 15 to 45 seconds.

As will be understood from the examples below, which should not be considered as limiting the present invention, the method claimed here has the advantage that it provides an anti-fouling agent according to European patent application EP-942936 as a coagulation product. Therefore, this product can be easily applied to the inner walls of the polymerization reactor of vinyl chloride and / or vinyl acetate, thereby forming a protective film that adheres to the walls in a ratio of more than 12 wt.% Of the loaded amount. Thus, it is possible to sufficiently protect the reactor, almost completely preventing the formation of deposits even after a long period of operation, thereby minimizing the need to interrupt the production cycle to clean the installation; in addition, the large amount of anti-fouling agent remaining on the wall makes it possible to reduce the amount of anti-fouling agent needed for use, with obvious economic advantages.

EXAMPLES

Example 1

In a reactor with a volume of 10 m ³ with stainless steel walls, equipped with application equipment, of the type shown schematically in FIG. 1, 1 kg of an aqueous solution containing 6 wt.% Sodium salt of the anti-fouling agent obtained as described in Example 25 was loaded European Patent Application EP-942936. The product was sprayed for 30 seconds inside the reactor with steam at a pressure of 5 atmospheres.

After application, condensate was collected at the bottom of the reactor. Condensate was analyzed to determine the pH value and the possible presence of coagulate. The pH value was 10, and the condensate did not contain precipitated gel.

The condensate was then treated again with hydrochloric acid until a pH of 3.8 was reached, at the end a dark brown / black coagulum was observed, which was found to correspond to more than 99 wt.% Of the initially loaded anti-fouling agent.

Example 2

The procedure described in Example 1 was repeated and the apparatus schematically shown in FIG. 2 was used (where 1 liter of citric acid at a concentration of 5 wt.% Was loaded into reservoir B).

After spraying in the reactor, condensate was collected; it was found that the condensate had a pH of 3.2 and contained 85% of a coagulated anti-fouling agent (while the remaining 15% remained deposited on the inner walls of the reactor as a protective film).

Examples 3-4

The procedure of Examples 1 and 2 was repeated with similar results when operating at a vapor pressure of 18 atmospheres.

Examples 5-8

The procedure of Examples 1-4 was repeated with similar results using EVERCLEAN ^® 104NS, commercially available, instead of the product obtained according to Example 25 of European application EP-942 936 patent.

Claims (15)

1. The method of applying an aqueous solution to the inner walls of the reactor for the polymerization of vinyl chloride and / or vinyl acetate, and the aqueous solution contains a salt anti-fouling agent, which includes the condensation product of an aldehyde, phenolic compound and aromatic carboxylic acid hydroxylated at the aromatic core, characterized in that the value The pH of this aqueous solution is changed to a pH value of less than 5 by acidification of an organic and / or inorganic acid with an aqueous solution. 2. The method according to claim 1, characterized in that the pH of the aqueous solution changes to a pH value in the range from 2.5 to 4.5. 3. The method according to claim 1, characterized in that the salt of the anti-fouling agent is a salt of an alkali metal and / or alkaline earth metal, preferably sodium. 4. The method according to claim 1, characterized in that the acid is selected from citric, oxalic, tartaric, hydrochloric, nitric and / or sulfuric acid, preferably citric acid. 5. The method according to claim 5, characterized in that the aqueous solution contains from 1 to 10 wt.% Citric acid, preferably 5%. 6. The method according to any one of claims 1 to 5, characterized in that the aqueous solution that contains the salt of the anti-fouling agent and the aqueous solution of an organic and / or inorganic acid are mixed with each other before the polymerization reaction. 7. The method according to claim 6, characterized in that the aqueous solution containing the salt of the anti-fouling agent and the aqueous solution of an organic and / or inorganic acid are mixed with each other before application to the inner walls of the polymerization reactor. 8. The method according to claim 7, characterized in that the mixture thus obtained is applied to the inner walls of the polymerization reactor in a steam stream. 9. The method according to claim 8, characterized in that the aqueous solution thus obtained is applied to the inner walls of the polymerization reactor at a pressure in the range from 2 to 20 bar. 10. The method according to claim 9, characterized in that the aqueous solution thus obtained is applied to the inner walls of the polymerization reactor for a period of 15 to 45 seconds. 11. The method according to claim 6, characterized in that the aqueous solution containing a salt of anti-fouling, and an aqueous solution of organic and / or inorganic acid are mixed with each other on the wall. 12. The method according to claim 1, characterized in that the aldehyde is formaldehyde, the phenolic compound is 1-naphthol, and the aromatic carboxylic acid hydroxylated at the aromatic nucleus is 2,4-dihydroxybenzoic acid. 13. The method according to claim 1, characterized in that the anti-fouling agent is EVERCLEAN ^® 104NS. 14. The method according to claim 1, characterized in that the aqueous solution contains 4-8 wt.% Salts of alkali metal and / or alkaline earth metal anti-fouling. 15. The method according to claim 1, characterized in that the aqueous solution has a pH value in the range from 7 to 12.4.

Images