IE42205B1

IE42205B1 - Process for the suspension polymerisation of vinyl chloride

Info

Publication number: IE42205B1
Application number: IE2688/75A
Authority: IE
Original assignee: Anic Spa
Priority date: 1974-12-10
Filing date: 1975-12-10
Publication date: 1980-06-18
Also published as: GB1496058A; IN144911B; IT1026902B; NL7514358A; DE2555568A1; ES443586A1; AU500593B2; IL48589A0; DD122981A5; CA1068046A; TR18667A; HU172316B; NO145763B; DE2555568C2; FR2294189B1; IL48589A; RO67271A; BG34188A3; NO145763C; YU311975A

Abstract

The technical problem of the suspension polymerisation of vinyl chloride, alone or in a mixture with other monomers, without it being adversely affected by the formation of encrustations in the polymerisation reactor, is solved by carrying out the polymerisation in the presence of a mixture of polyvinyl alcohols having a mean saponification number between 300 and 500, accompanied by substances of hydroxylic character, such as clays, bentonites and natural or artificial inorganic colloids.

Description

The present invention relates to a process for the production of a polymer of vinyl chloride.

It is known that in the conventional suspension polymerisation of vinyT chloride, either alone or in admixture with other monomers, remarkable amounts of polymer accumulate on the walls of the autoclave. The quantity of such accumulation normally depends on the type of stirring, on the formulations which are used (type and amount of suspending agents and of catalysts) on the impurities present in the monomers and on the number of polymerisation runs carried out in the particular autoclave.

Such deposits on the walls of the autoclave reduce the heat transmission through the walls of the autoclave and give rise to difficulties in controlling the reaction; moreover the product is highly contaminated by hard and vitreous crystals. As a rule the scales are removed after each polymerisation run, manually or with water at high pressure, in each case the time required being one hour or longer. Moreover, in the case of the manual technique, problems of environment hygiene arise for the personnel attending to the descaling operation.

Italian Patent No. 874,456 (Goodrich) relates to a process for the suspension polymerisation of vinyl chloride, according to which the aforementioned drawbacks are mitigated by the addition, during the reaction, of - 2 42205 magnesium hydroxide in a maximum proportion of 1000 ppm based on the monomers.

An essential reduction of the deposit is obtained, but at the same time there is a worsening of the porosity and of the heat stability of the polymer. The addition of magnesium hydroxide in a proportion greater than 1000 ppm causes an intolerable deterioration of the product.

According to the present invention there is provided a process for the production of a polymer of vinyl chloride, which process comprises polymerising a suspension comprising monomeric vinyl chloride in the presence of an additive comprising (a) a first component which is poly vinyl alcohol having a saponification number of from 300 to 500 and (b) a second component which is a natural colloidal material or a hydroxyl compound of an element of group IIA, IIB, IIIA, IVA, or VIII of the periodic classification of the elements (as hereinafter defined), which hydroxyl compound exhibits colloidal behaviour, to produce the desired polymer.

The periodic classification of elements referred to above may be found, for example, in The Hand Book of Chemistry and Physics, 39th edition, Chemical Rubber Publishing Company at pages 400-401.

The polymers of vinyl chloride produced according to the invention may be granular homopolymers of vinyl chloride or copolymers of vinyl chloride, in which case the suspension comprises an additional monomer other than vinyl chloride. Such copolymers preferably contain at least 80% by weight of vinyl chloride or preferably not more than 20% by weight of vinylidene compounds including a terminal group CH2 = C zL . Any vinylidene compound which is copolymerisable with vinyl chloride may be used, for example other vinyl halides, vinylidene chloride, vinyl esters such as vinyl acetate or vinyl butyrate, esters of acrylic or methacrylic acid such as methyl acrylate, butyl acrylates, isooctyl acrylate, methyl methacrylate or hexyl methacrylate, maleic or fumaric esters such as diethyl maleate or dipropyl fumarate, aromatic vinyl monomers such as styrene, mono-olefins such as ethylene, propylene or butylene, vinyl ethers such as - 3 4SS05 vinyl ethyl ether, allyl esters such as allyl acetate or di allyl phthalate, acrylonitrile or methacrylonitrile.

The amount of polyvinyl alcohol having a saponification number of from 300 to 500 which is present is preferably in the range 0.01 to 0.5% by weight with respect to the total weight of the monomer or monomers. In one embodiment the first component comprises an admixture of polyvinyl alcohols having an average saponification number of from 300 to 500.

The amount of the natural colloidal material or hydroxyl compound used is preferably in the range 0.1 to 0.5% by weight with respect to the monomer oi monomers used. The natural colloidal material is preferably a clay, for example bentonite. A preferred hydroxyl compound is magnesium hydroxide.

In the case where the second component is a hydroxyl compound which exhibits colloidal behaviour, the polymer of vinyl chloride produced by the process is afterwards treated with a strong inorganic acid or hydrolysable salt thereof, for example ammonium sulphate.

The polymerisation reaction is preferably carried out under pressure in the presence of a catalyst soluble in the monomer (oil) at a temperature lower than 100°C, preferably in the range 40 to 60°C.

Oil soluble catalysts which may be used are for example, lauryl 20 peroxide, peroxydicarbonates including di isopropyl peroxydicarbonate, caprylyl peroxide or azodiisobutyronitrile. The amount of catalyst used is preferred to be as low as possible, preferably less than one part by weight relative to 100 parts by weight of monomer, consistent with providing a good polymerisation velocity. For example the polymerisation can be satisfactorily carried out with 0.2 parts by weight of lauryl peroxide or 0.02 parts by weight of diisopropyl peroxydicarbonate. The catalyst can be used as it is or directly prepared in the polymerisation autoclave.

In a preferred embodiment the polymerisation is carried out in the presence of a suspending agent. The suspending agent used may comprise any one - 4 42205 of the well known materials used for such purpose, including gelatin, polyvinyl alcohol with a low saponification number, and water soluble cellulose ethers such as methyl cellulose.

The following examples illustrate the invention.

EXAMPLE 1.

A 25 cu.m reactor, provided with a stirrer and a Pfaudler wavebreaker, was charged with the following mixture, relative to 100 parts by weight of vinyl chloride (VC): VC 100 H20 150 methyl cellulose 0.035 Sodium bicarbonate 0.02 tert.-butylcyclohexyl peroxydicarbonate 0.03 The stirrer was rotated at a speed of 120 RPM and the reaction mixture was maintained at 55°C. After 9 hours it was no longer possible to control the reaction, at which stage residual monomer was removed by distillation. There was found to have been a conversion of about 70% by weight. The incrustations, which were manually removed, weighed about 8 kg. The density of the polymerised vinyl chloride product was 490 g/1.

EXAMPLE 2.

The reaction mixture of Example 1 was supplemented with 0.06 parts by weight of Mg(OH),,. 5 runs were carried out before the cleaning operation, kg of incrustations being then removed. The conversion rate, which was higher for the initial batches and gradually decreased, was on average about 78% by weight.

EXAMPLE 3.

In the same reaction mixture as Example 2 the amount of Mg(OH)2 was increased to 0.2 parts by weight. After 15 batches, 11 kg of scale were removed. - 5 4320 5 The average conversion was about 87% by weight. In this series of runs too, the conversion rate decreased as the deposits on the walls increased. Compared with Example 1, the average density of the polymerised vinyl chloride product was higher (530 g/1) and the thermal stability was worse.

A sample of the product of this series of runs, treated with 0.02 Parts by weight of (NH^SO^ and washed, gave a normal heat stability. Such a treatment was always used in the subsequent Examples with Mg(0H)2· EXAMPLE 4.

Example 3 was repeated, except that 0.07 parts by weight of polyvinyl alcohol having a saponification number of 420 were added before polymerisation. After 50 batches without cleaning, the walls appeared completely free from incrustation. The conversion was 93% by weight in all the batches and the densi ty of the product was 480 g/1.

An identical reaction mixture, tested in a reactor having smaller size and a variable stirring speed, gave the same results.

Of course it was necessary in this case to adjust the proportions of the primary suspending agents so as to obtain the desired morphological characteristics.

EXAMPLE 5.

The procedure of Example 4 was repeated except that 0.05 parts by weight of a commercial bentonite (Ultragel 300) was substituted for the Mg(0H)2. After 30 batches, 5 kg of incrustations were removed.

The average conversion was 92% by weight and the density of the product was 460 g/1. The heat stability was optimal even without post-treatment with ammonium sulphate.

Claims

1. A process for the production of a polymer of vinyl chloride, which process comprises polymerising a suspension comprising monomeric vinyl chloride in the presence of an additive comprising (a) a first component which is polyvinyl alcohol having a saponification number of from 300 to 500 and (b) a second component which is a natural colloidal material or a hydroxyl compound of an element of group IIA, IIB, IIIA, IVA or VIII of the periodic classification of the elements (as hereinbefore defined) which hydroxyl compound exhibits colloidal behaviour, to produce the desired polymer.

2. A process according to Claim 1 wherein the first component is an admixture of polyvinyl alcohols having an average saponification number of from 300 to 500.

3. A process according to Claim 1 or 2 wherein the natural colloid material is clay.

4. A process according to Claim 3 wherein the clay is bentonite.

5. A process according to any one of the preceding claims wherein the hydroxyl compound is magnesium hydroxide.

6. A process according to any one of the preceding claims wherein, when the second component is a hydroxyl compound, and the polymer of vinyl chloride produced is treated with a strong inorganic acid or hydrolysable salt thereof.

7. A process according to Claim 6 wherein the salt is ammonium sulphate.

8. A process according to any one of the preceding claims wherein the polymer of vinyl chloride is a homopolymer.

9. A process according to any one of Claims 1 to 7 wherein the suspension includes a monomer other than vinyl chloride and the polymer of vinyl chloride produced is a copolymer.

10. A process according to Claim 9 wherein the copolymer contains not less than 80% by weight of vinyl chloride.

11. A process according to any one of the preceding claims wherein the - 7 <5330 5 first component is present in a proportion of from 0.01 to 0.5% by weight based on the total weight of monomer or monomers.

12. A process according to any one of the preceding claims wherein the second component is present in a proportion of from 0.1 to 0.5% by weight 5 based on the total weight of monomer or monomers.

13. A process according to Claim 1 substantially as hereinbefore described with reference to Example 4 or 5.

14. A polymer of vinyl chloride whenever produced by the process according to any one of the preceding claims.