FI57423C - SAETT ATT AVLAEGSNA VINYLKLORID VILKEN AER NAERVARANDE SAOSOM REST I EN VINYLKLORIDPOLYMER - Google Patents

Description

ΓβΙ <1 ANNOUNCEMENT, EXTERNAL, SU ^ H L O "K

lBJ (") UTLÄGGN I NGSSKRI FT u H ^ 0 C (45) Fate :, i ti:.;, fnr 'i te 11 03 10 10'« S® '(51) X ^ 11 F 6/10, 14 / 06 FINLAND —FINLAND (il) P * t.fittih «k« mu «—P« * nt »ni0tcnln | 21Ö1 / 73 (22) Haktmlspllvi - Ameknln | * d« g 09 · 07 · 73 (23) Alkuplivt— GlltlfhMadif 09.07.73 (41) Tullut julklMluI - Bllvlt offantllg 20.01.74 ^ exam and registered Nihuvik .. ^ j. Kuui.jullc.taun p ™. -

Patent and registration authorities of the United Kingdom and other Member States * krft «n public · ™ * 30.04.80 (32) (33) (31) Requested« tuolktu * —Begird prlorltet 19.07.72 29.12.72 Belgium-Belgium (BE) 120023 125979 (71) Solvay & Cie, rue du Prince Albert 33, 1050 Brussels, Belgium-Belgium (BE) (72) Jean Golstein, Brussels, Guillaume Coppens, Brussels, Jean Claude Davoine, Brussels, Belgium-Belgium (BE) (74) Oy Kolster Ab (54) Method of removing vinyl chloride present as a residue in vinyl chloride polymer - Sätt att avlägsna vinylklorid, vilken är närvarande säsom rest i en vinylkloridpolymer

The invention relates to an economical and rapid way of removing one or more residual monomers present in polyvinyl chloride prepared by a known polymerization process, in particular a gas-phase process.

The polymer recovered at the end of the polymerization after the unpolymerized monomer has been removed as a gas contains, as is known, some still absorbed monomer, the amount of which varies according to the nature of the polymer produced.

When the amount of residual monomer present in the polymer is greater than about 0.5% w / w, the mechanical properties of the injection molded products deteriorate considerably, especially due to the presence of bubbles formed by the gaseous monomer.

Various means of removing this residual monomer have already been proposed, but these means have so far proved to be rather inefficient and, above all, very economical. By way of example, it is known that 57423 removes the last residues of the residual monomer by stripping with steam.

However, the disadvantage of this method is that, after treatment, an aqueous suspension of the resin is dealt with, from which the aqueous phase must be taken. The resin must then be dried by conventional methods.

A known method for removing residual monomer from a vinyl chloride polymer by water vapor stripping is described, for example, in Iyle F. Albright, Chem. Eng., June 5, 1967, ρ · 1U5 ~ 152. According to the prior art, stripping was performed at a temperature below 65-70 ° C due to the fear of thermal degradation of the vinyl chloride polymer.

It has now been found that stripping at any temperature is not sufficient to remove residual monomer in polyvinyl chloride at industrially acceptable yields and rates. The invention is based on the surprising finding that the efficiency of stripping is considerably improved when the temperature is at least the glass transition temperature of the polymer.

According to the invention, the residual monomer present in the polymer can be removed and recovered quickly, efficiently and economically so that the polymer product is obtained by dry dewatering and drying.

The invention relates to a method for removing vinyl chloride and optionally comonomers present in a vinyl chloride homopolymer or copolymer, whereby the polymer is heated by condensing water vapor, after which the polymer is cooled by evaporation of water.

The invention is characterized in that water vapor is condensed until the polymer reaches a temperature between the glass transition temperature of the polymer and 180 ° C, and that the polymer is maintained at this temperature for a time sufficient to remove most of the monomer or monomers, after which the polymer is cooled to a polymer temperature. below the glass transition temperature.

By vinyl chloride polymer is meant homopolymers of vinyl chloride and copolymers containing at least 50% by weight of one or more copolymerizable monomers and which may optionally contain additives added during the polymerization or immediately before the treatment according to the invention. These additives may be stabilizers, plasticizers, colorants, reinforcing agents and / or ease of use, etc.

When the vinyl chloride polymer is treated according to the invention at a temperature at which there is a risk of irreversible decomposition of the polymer, it is necessary to add a thermal stabilizer. This addition can be made during the polymerization of the poly-57423 or immediately before the treatment according to the invention. In this case, conventional heat stabilizers for vinyl chloride polymers or mixtures thereof can be used, and in particular metal salts of organic or inorganic acids, such as Zn, Pb, Ba, Ca, Cd salts, organometallic salts, such as organotin salts or epoxides, for example epoxy played oils.

The first step of the method according to the invention is based on heating the polymer by introducing water vapor which condenses directly on the polymer.

"The polymer may also be heated by adding one or more conventional heating methods to the steam-fired heating, in which case hot gas, a double jacket or heating tubes may be used, as well as mechanical means of generating heat, in particular suitable mixers. These secondary heat sources may be use heating as a useful complement in the event that they are incorporated into the process of the invention cannot be used alone because of the economic and practical disadvantages involved.

The amount of heat added by these secondary sources must not significantly exceed the amount of heat necessary to evaporate the residual monomer, as it is important that the amount of condensed water be large enough to rapidly cool the polymer in the next treatment step. On the other hand, the amount of condensed water vapor must be such that it is sufficient to heat the polymer to a temperature between the glass transition temperature and 180 ° C, taking into account possible other heat sources. These results are generally obtained by condensing an amount of water vapor corresponding to 1-10% by weight of the treated polymer. Amounts of 2 to 6% by weight are preferably used. Once the temperature of the polymer has been reached, this temperature is allowed to act for as long as most of the monomer entrapped in the polymer is removed. The length of this time depends on the selected temperature and is shorter the higher the temperature. Preferably operated at 80-130 ° C. The length of the treatment is preferably 5 minutes to 2 hours, especially 10 to 60 minutes.

In the case where the temperature to which the polymer is heated is below the glass transition temperature, the removal of the residual monomer takes place very slowly and the treatment is no longer economical or meaningful on an industrial scale either.

In the event that the 1+ 57423 polymer, which may contain a thermal stabilizer, is heated to more than 180 ° C over a relatively long period of time, it no longer has the properties required for use after treatment.

The polymer is then cooled below the glass transition temperature by evaporating the water condensed during heating. This rapid evaporation can be carried out by applying conventional means, and in particular by evaporating in a vacuum and / or blowing a gas such as nitrogen or air.

In two steps of the process according to the invention, i.e. during the heating and subsequent cooling of the vinyl chloride polymer, the temperature is controlled by adjusting the pressure.

The polymer obtained after treatment can be stored immediately and used without subsequent drying. The released monomer can be recovered after the water vapor has been condensed.

The method which is the subject of the invention can be practiced either using a tank equipped with a stirrer or using a bed in a fluidized state. When using a fluidized bed, water vapor can be suitably condensed on a polymer maintained in the fluidized state by another gas, especially a monomer to be polymerized. Once the desired temperature is reached, the water vapor is no longer completely condensed, but can now be used as a fluidizing gas so that the supply of the original fluidizing gas can be reduced.

The process according to the invention can be applied to such polymers of vinyl chloride which have been prepared by applying known polymerization methods, in particular by carrying out bulk polymerization, suspension emulsion polymerization or polymerization in the gas phase, in a fluidized bed or by mechanical mixing.

The process according to the invention has numerous advantages over known methods, and in particular the heating and rapid cooling of the polymer can be easily carried out, so that the temperature required to remove the residual monomer can be maintained for a certain time so that most of the closed residual monomer can be removed without polymer degradation.

In addition, according to the invention, the residual monomer encapsulated in the polymer can be completely and very economically recovered and the polymer can be obtained dry and thus storable and usable without further processing.

Examples 1 and 2

The process according to the invention is applied to polyvinyl chloride which, after the gas has been removed from the autoclave used for polymerization and after it has been blown clean, contains 3 g of residual vinyl chloride per kilogram of polyvinyl chloride.

5 57423

Polyvinyl chloride has been prepared by polymerization in the gas phase so that the temperature has been 60 ° C and the partial pressure of vinyl chloride has been 9 kp / cm.

In this case, the method described in Example 1 of BE patent 786 k62 has been applied.

The glass transition temperature of this polyvinyl chloride is 80 ° C.

Place 1 kg of polyvinyl chloride in an autoclave equipped with a double jacket and a stirrer. A vacuum is obtained such that the residual pressure is 1 * 30 mm Hg »after which water vapor with a temperature s * of 90 ° C is introduced into the autoclave. Polyvinyl chloride, which had an initial temperature of 30 ° C, heats rapidly when it comes into contact with condensing water vapor. When the polyvinyl chloride has reached a temperature of 85 ° C, i.e. corresponding to the condensation point of the water vapor at operating pressure, the water vapor is practically no longer condensed, whereby the steam is removed directly by placing the system under reduced pressure.

To avoid secondary condensations on the autoclave walls, these are kept at the same temperature as the polymer during the heating cycle of the polymer. After the heat treatment, the polyvinyl chloride contains about 3% by weight of? condensed water.

After 30 minutes, the polyvinyl chloride is cooled to a temperature below its glass transition temperature, namely U0 ° C, by applying a vacuum to the autoclave so that the residual pressure is 55 mm Hg.

steam and vinyl chloride are separated by condensation to give 28 g of water and 31 g of vinyl chloride.

The polyvinyl chloride obtained contains only 3 g of residual vinyl chloride, so that in other words more than 90% of the residual vinyl chloride enclosed in the polyvinyl chloride has been removed.

For comparison, the same experiment is repeated by heating the polymer for 30 minutes and 2 hours at 60 ° C, i.e. below the glass transition temperature of the polymer, by feeding water vapor at 65 ° C and maintaining the autoclave at 155 mm, which corresponds to water vapor condensation point at 60 ° C.

The polyvinyl chloride, which is recovered after heating for 30 minutes at 60 [deg.] C., contains a further 32 g of vinyl chloride, corresponding to less than 10% of residual vinyl chloride removed.

The polyvinyl chloride recovered after heating for 2 hours at 60 ° C contains 29 g of vinyl chloride, so that less than 20% of the residual vinyl chloride has been removed.

Examples 3 and H

The process according to the invention is applied to a copolymer of vinyl chloride and propylene containing 3% of copolymerized propylene obtained by polymerizing in the gas phase at 53 ° C using the method described in Example 1 of BE patent 785 608. temperature is 75 ° C.

1 kg of a copolymer of vinyl chloride and propylene containing 28 g of vinyl chloride and 15 g of propylene as residual monomers is introduced into the autoclave. Then, to 100 parts of the resin, 2 parts of tribasic lead sulfate, 1 part of dibasic lead stearate, 0.5 part of calcium stearate and 0.3 part of stearic acid are added.

The product is heated to 115 ° C by the addition of water vapor superheated to 120 ° C, maintaining the autoclave pressure at 1270 mm Hg, which corresponds to the condensation point of the water vapor at 115 ° C. When the temperature of 115 ° C is reached, the water vapor no longer condenses, so the water vapor supply is stopped. The product is allowed to stand for 10 minutes at 115 ° C, after which it is placed under reduced pressure and cooled to 50 ° C.

The product obtained contains only 0.5 g of residual vinyl chloride and 0.1 g of residual propylene, which corresponds to the order of magnitude of the residual monomer of 98 # and 99 #, respectively.

For comparison, the same experiment is repeated by supplying steam at 65 ° C and maintaining a pressure of 150 mm Hg, which corresponds to the condensation point of water vapor at 60 ° C.

After 10 minutes, the product containing 27 g of vinyl chloride and 13 g of propylene is recovered, so that only a negligible amount has been removed from the residual monomers.

Examples 5 ~ 10

The experiments were performed under the same conditions as in Example 1. Examples 5 and 6 relate to the treatment of a polyvinyl chloride (homopolymer) prepared by gas phase polymerization and identical to the polymer used in Example 1.

Examples 7 and 8 relate to the treatment of a polyvinyl chloride prepared by polymerization in an aqueous suspension at 70 ° C and separated from the polymerization medium in a conventional manner. At the end of the polymerization, the polyvinyl chloride was separated by drying most of the polymerization medium. The resulting cake, which contained about 17% by weight of water, was dried in a fluid bed dryer with an average drying time of one hour. Upon removal of the polymer from the dryer, the temperature of the polymer was about 65 ° C. The dried polyvinyl chloride contained 0.25% by weight of water.

Examples 9 and 10 dealt with commercial, bulk polymerized * polyvinyl chloride.

The glass oven temperature of the polyvinyl chloride used in all Examples 5 to 10 was about 80 ° C.

Residual vinyl chloride was determined by gas chromatography.

The results are shown in the following table.

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Claims (1)

Claim: A method of removing vinyl chloride and optionally comonomers present in a vinyl chloride homopolymer or copolymer, wherein the polymer is heated by condensing water vapor, after which the polymer is cooled by evaporation of water, characterized in that the water vaporizes C, and that the polymer is maintained at this temperature for a time sufficient to remove most of the monomer or monomers, after which the polymer is cooled to a temperature below the glass transition temperature of the polymer.