WO2003068826A1

WO2003068826A1 - A method for suppressing build-up in vinyl chloride polymerization processes

Info

Publication number: WO2003068826A1
Application number: PCT/EP2003/001169
Authority: WO
Inventors: Massimo Quintini
Original assignee: 3V Sigma S.P.A.
Priority date: 2002-02-12
Filing date: 2003-02-06
Publication date: 2003-08-21
Also published as: TW200304442A; ITMI20020271A0; AU2003206849A1; ITMI20020271A1

Abstract

The present invention relates to a method for suppressing the formation of build-up during the polymerization processes of monomer vinyl chloride, alone or in mixture with other copolymerizable vinyl monomers, which processes are effected in aqueous suspension, aqueous emulsion or in bulk.

Description

A METHOD FOR SUPPRESSING BUILD-UP IN VINYL CHLORIDE POLYMERIZATION PROCESSES

The present invention relates to a method for suppressing the formation of build-up during the polymerization processes of monomer vinyl chloride, alone or in mixture with other copolymerizable vinyl monomers, which processes are effected in aqueous suspension, aqueous emulsion or in bulk. In all the above mentioned polymerization processes, part of the formed polymer tenaciously adheres to the reactor walls, thus forming "buildup" (deposits), with deleterious effects on both the final product itself, due to small fragments of build-up which, when detached from the reactor walls, can be included in the polymerized product, and the safety of the reaction, as the build-up slows down the thermal exchange of the reactor walls, giving rise to safety problems due to overheating.

This build-up is a drawback since it makes it necessary to clean the reactor walls after each polymerization run. This cleaning operation is costly, as it decreases the plant output, as well as dangerous for the operators due to the toxicity of the monomers, particularly vinyl chloride.

A number of products and techniques have been developed to mitigate this problem, all of which are based on coating the reactor walls with products which should inhibit adhesion of the build-up or even its formation, or anyway promote its removal. Condensation products of compounds containing phenol groups with formaldehyde or formaldehyde-releasing compounds (see for example GB 1439339; JP 54-107991; CA 1181899; EP 0052421 ; EP 0695761; EP 0942936; EP 847404; EP 830383) or dye mixtures (alizarin, xanthones, natural flavonoids, naphthoquinones, hydroxyanthraquinones and others) with film-forming products such as polysaccharides, polyvinyl alcohols, polyvinylpyrrolidone, were proposed as reactor wall coating (see for example patents JP 04342701; JP 04154804; JP 04154801; JP 04154805; JP 04108805; JP 04159302 and JP 04031402) have been suggested as reactor wall coating.

All these build-up suppressors can be applied in a number of manners, which depend on the nature of the product and on their capacity of adhering to the reactor walls. The more common methods comprise coating by hand painting with brushes or, more usually, spraying aqueous solutions of suitable concentration. In case of spraying, nitrogen or water vapor at 5-15 bar pressures can be used as propellant. In the case of polymerization in aqueous suspension or emulsion, any traces of build-up formed are usually filtered off the polymer suspension/emulsion at the end of the polymerization, while the fraction still adhering to the reactor walls is mechanically removed by means of pressurized water jets. The final purpose of such operations is to make the reactor walls and inner structures as clean as possible. It has now been found that the condensation products of compounds containing phenol groups with formaldehyde or formaldehyde-releasing compounds claimed in the above cited patents are able to exert their anti build-up action simply by addition to the polymerization mass, with no need for walls coating, which is cost-saving in terms of time and spraying systems involved. Furthermore, no need for walls coating also means that no film- forming products such as polysaccharides or polyvinyl alcohols are required.

Particularly suitable proved (a) compounds obtainable by condensation of aromatic acids having one or more phenol groups with formaldehyde and other phenols, for example those described in EP 0942936, or (b) aromatic phenols, such as formaldehyde-condensed alpha-naphthols, for example those described in EP 0052421, optionally subsequently reacted with hydroxylated aliphatic acids as described in EP 0695751, or (c) alpha-naphthols and the condensation product of formaldehyde with sodium hydrosulphite or with hydroxymethanesulfinic acid or the salts thereof, or with hydroxymethanesulfonic acid or the salts thereof, for example those described in O97/08210. Particularly suited for the purposes of the present invention, most of all for obtaining particularly clean walls after the standard mechanical cleaning procedures, is the condensation product of 2,4- dihydroxybenzoic acid with formaldehyde and alpha-naphthol disclosed in EP 0942936.

The above mentioned products may be used alone or in mixtures thereof. The present invention further comprises a process for the polymerization of vinyl chloride, alone or in mixture with other copolymerizable vinyl monomers, in aqueous suspension, in aqueous emulsion o in mass, characterized by the addition of a build-up suppressor described above to the polymerization mass. The compounds able to exert this build-up inhibiting action can be used in the solid state or in solution. The use of such compounds in the form of solution is preferred; aqueous solutions at the pH necessary to solubilize the build-up suppressor being further preferred.

The amount of the active compound for use as build-up suppressor according to the invention ranges from 1 to 50 ppm based on the monomers weight, preferably from 3 to 25 ppm.

The following examples further illustrate the invention. EXAMPLES

Three build-up suppressors were prepared according to processes known procedures:

Product A: prepared as described in Example 1 of EP0052421. The resulting 20% w/w solution was subsequently diluted to 5% w/w for use.

Product B: prepared as described in Example 25 of EP 0942936. The resulting 16% solution was subsequently diluted to 5% w/w for use.

Product C: prepared as described in Example 1 of WO 97/08210 (EP 847404), but omitting the addition of the polyvinyl alcohol solution, to obtain a 5% w/w solution for use. Polymerization reactions in the presence or without build-up suppressors were carried out in a 1000 liters stainless steel reactor, using the following formulation:

Monomer vinyl chloride 330 kg

Demineralized water 495 kg Primary suspending agent Polivic SP 808TM 0.132* kg

Secondary suspending agent Polivic S 404WTM 0.132* kg Methylhydroxypropyl cellulose 0.132 kg

Bis(4-tert-butyl-cyclohexyl)peroxi-di-carbonate 0.132 kg build-up suppressor: according to the indications in the following examples.

*as active substance The polymerization temperature was 68°C; the polymerization time was around 300 minutes.

In each test, both the amount of build-up filtered off the polyvinyl chloride slurry through a suitable net and that recovered upon washing the reactor walls and shaft with pressurized water, were weighed. The build-up total amount collected, which means the build-up removed, was expressed in grams. Example 1

Example 2

Example 3

Example 4

Example 5

Example 6

Example 7

Example 8

Claims

1. A method for inhibiting build-up formation in the polymerization processes of monomer vinyl chloride, alone or in mixture with other copolymerizable vinyl monomers, in aqueous suspension, in aqueous emulsion or in mass, characterized in that an effective amount of condensation products of compounds containing phenol groups with formaldehyde or with formaldehyde-releasing compounds is added as buildup suppressor to the polymerization mass.

2. A method as claimed in claim 1 wherein the amount of build-up suppressor ranges from 1 to 50 ppm, preferably from 3 to 25 ppm, based on the weight of polymerization monomer.

3. A method as claimed in claims 1 and 2 wherein the condensation product of claim 1 is the condensation product of 2,4-dihydroxy-benzoic acid with formaldehyde and alpha-naphthol in the molar ratios substantially of 1 :2:1.

4. A method as claimed in claims 1 and 2 wherein the condensation product of claim 1 is the condensation product of alpha-naphthol with formaldehyde in molar ratio substantially of 1 : 1.

5. A method as claimed in claims 1 and 2 wherein the condensation product of claim 1 is the condensation product of alpha-naphthol with the reaction product of formaldehyde with hydrosulphite.

6. A method as claimed in claims 1 and 2 wherein the condensation product of claim 1 is the condensation product of alpha-naphthol with hydroxymethanesulfinic acid or salts thereof.

7. A method as claimed in claim 1 wherein the condensation product of claim 1 is the condensation product of alpha-naphthol with hydroxymethanesulfonic acid or the salts thereof.

8. A method as claimed in claim 1 wherein the condensation product of claim 1 is the condensation product of alpha-naphthol with formaldehyde subsequently modified by reaction with hydroxylated aliphatic polycarboxylic acids.

9. A process of polymerization in aqueous suspension of monomer vinyl chloride, alone or in mixture with other copolymerizable vinyl monomers, characterized in one or more condensation products of claim 1 is added to the polymerization mass in amounts from 1 to 50 ppm, preferably from 3 to 25 ppm, based on the monomers weight.

10. A process as claimed in claim 9 wherein the condensation product of claim 1 is the condensation product of 2,4-dihydroxy-benzoic acid with formaldehyde and alpha-naphthol in molar ratios substantially of 1:2: 1.

11. A process as claimed in claim 9 wherein the condensation product of claim 1 is the condensation product of alpha-naphthol with formaldehyde in molar ratio substantially of 1 : 1.

12. A process as claimed in claim 9 wherein the condensation product of claim 1 is the condensation product of alpha-naphthol with the reaction product of the formaldehyde with sodium hydrosulphite.

13. A process as claimed in claim 9 wherein the condensation product of claim 1 is the condensation product of alpha-naphthol with hydroxymethanesulfinic acid or salts thereof.

14. A process as claimed in claim 9 wherein the condensation product of claim 1 is the condensation product of alpha-naphthol with hydroxymethanesulfonic acid or salts thereof.

15. A process as claimed in claim 9 wherein the condensation product of claim 1 is the condensation product of alpha-naphthol with formaldehyde subsequently modified by reaction with hydroxylated aliphatic polycarboxylic acids.