DE4109527A1 - METHOD FOR CLEANING A POLYMER - Google Patents

Description

The present invention relates to a method for Purification of a polymer, and in particular a process for extracting volatile materials contained in a polymer are contained in the melted state under high pressure, where at being removed.

Background of the Invention

As a method of removing volatile materials from a Polymer has been published, for example, in Japanese Patent Publications No. 29 245/1986 and 52 163/1986 procedure beat in which a melted thermoplastic resin in a degassing screw press is processed, or in the Japanese Patent Application (OPI) No. 1 66 506/1984 a process proposed in which a liquid polymer composition is continuous of volatile substances by means of a volatilization Gungsseparators is freed, to which a vertical bubble the preheater and a vacuum tank are connected directly. In recent years, a high pressure extraction process using a supercritical fluid, suggested and Japanese Patent Publication No. 46 972/1984 net as a process for reducing oligomeric cyclic ethers, which in tetrahydrofuran polymers, alkylene oxide polymers or Tetrahydrofuran / alkylene oxide copolymers are included, a ver drive, in which such a polymer with a gas, which is is in the supercritical state, is brought into contact. However, in the procedures described in the above ge named Japanese Patent Publications No. 29 245/1986 and 52 163/1986 and Japanese Patent Application (OPI) No. 1 66 506/1984 the concentration of volatile materials which in the processed polymer, at best one Order of magnitude reduced by about 400 ppm, and this process could meet the market requirements where the concentration of  volatile components must be less than 400 ppm, do not withstand. Furthermore, although the process, which is disclosed in Japanese Patent Publication No. 46 972/1984 describes a method for extracting Impurities from a polymer in the liquid state Represents room temperature under high pressure, with the impurity removed, this procedure does not apply to a high-grade extraction, where the conc tration of impurities remaining in the polymer at or below a certain concentration (thousands of ppm) must be lowered.

Summary of the invention

The first object of the present invention is a Process for the effective purification of a polymer in ge to provide molten state.

The second object of the present invention is a Process for the purification of a polymer by extraction volatile materials from the polymer in the molten state to provide, the degree of extraction very high is.

Other and further objects, properties and pre Parts of the invention will be apparent from the following detail lated description of the invention, together with the accompanying tendency figure.

Brief description of the figure

Fig. 1 is a flow chart showing an embodiment of the present invention.

Detailed description of the invention

The inventors have intensively researched the above Overcome problems associated with cleaning polymers  are socialized and they found that if to melt a polymer with an extract contacting agent, the removal of volatile Materials can be carried out effectively and the Concentration of volatile materials in the polymer remain, can be reduced to or below about 100 ppm, which leads to the completion of the invention.

This means that the present invention is a method for Purification of a polymer by treating the polymer with egg provides an extractant under high pressure, removing volatile materials contained in the polymer are characterized in that the polymer in molten zenem condition with the extractant in a weight Ratio of said polymer to the extractant, which in the Range between 1: 0.1 to 1: a value less than 20, in Is brought into contact.

When carrying out the present method, preferred poly mere thermoplastic, moldable resins, which by ge melted and liquefied, but at room temperature rigid, such as polyethylene, polypropylene, polysty rol, acrylonitrile / styrene copolymer, acrylonitrile / butadiene / sty rolterpolymer, polyvinyl acetate, polyacrylate, polymethacrylate, Polyvinyl chloride, polyvinylidene chloride, fluoroplastic, poly acrylonitrile, polyvinyl ether, polyvinyl ketones, polyether, ther plastic polyesters, polyamides, diene type plastics and Polyurethane plastics, and as heat-resistant polymers poly xylylene, polycarbonate, polyphenylene oxide and polysulfone. Here is with "polymer in the molten state" for example wise a lot of a liquid, polymeric composition of the above-mentioned polymer, a melt which is heated by heating the polymer is obtained in powder or tablet form, or a mixture of a liquid, essentially polymeric composition and a melt, which is obtained by heating a Polymer is obtained in powder or tablet form, ge means.

The extractant used in the present invention will match the polymer in the molten state from which should be extracted, selected, and as a specific case games are (a) carbon dioxide, nitrous oxide, carbon di  sulfide, aliphatic hydrocarbons such as ethane, Ethylene, propane, butane, pentane and hexane, halogenated Hydrocarbons, aromatic hydrocarbons such as play benzene, toluene and xylene, and alcohols such as Methanol and ethanol, and (b) a mixture of two or more of the substances mentioned. For reference, the kri table constants etc. of the typical extraction medium mentioned listed in Table 1.

Table 1

Critical constants

In the present invention, the ratio of the ge melted polymer in the extractor to the extractant, which is introduced into the extractor, by weight in a range from 1: 0.1 to 1: a value less than 20. Im Case of the continuous process, which is usually a Countercurrent process is used, it is preferably between  1: 1 to 1: a value less than 20, and in particular be preferably between 1: 1 to 1: a value less than 15. If too we little extractant is present, none can be sufficient effective extraction can be achieved. If too much extraction medium is present, the energy consumption for compresses increases sion of the extractant or the like because of the enlarger ten volume of the extractant very strongly, the Extraction efficiency is only slightly increased.

The extractant used in the present invention is in the liquid or supercritical state, and the use of the supercritical state is preferred. If it is considered that the extractant should be separated from the purified polymer, it is preferred to use an extractant which is gaseous at room temperature and normal pressure or an extractant which has a boiling point at normal pressure of 150 ° C or below, and in particular the use of the supercritical state is preferred. When the extractant is used in the supercritical state, although pressure and temperature in the extractor may differ depending on the type of the polymer to be purified and the extractant, the pressure is generally preferably 0.8 to 10 times, and more preferably 1.0 to 5 times the critical pressure of the extractant; it is preferably 20 to 500 kg / cm ² G, and more preferably 100 to 350 kg / cm ² G. The temperature is usually 0.9 to 2.0 times the critical temperature of the extractant or the melting temperature of the polymer to be purified and is preferably between 80 and 250 ° C, and more preferably between 150 and 220 ° C. The upper limit represents the melting temperature of the polymer to be cleaned. The temperature causes destruction of the polymer. In this case, although the temperature in the extractor could be at or above the melting temperature of the polymer and below the critical temperature of the extraction medium, the temperature in the extractor is preferably at or above the critical temperature of the extractant.

Volatile materials that ex are to be traced are volatile impurities which  are contained in the polymer in the molten state, such as Example of unreacted monomers, solvents and oligo mere.

While practicing the present invention exist, though the extractor used suitably is an apparatus from the packed column type, from the bottom column type, from the spray tower type or of the boiler type, no particular restrictions obviously the type of extractor as long as it has a good con clock of the polymer in the molten state, which is extracted should, with the extractant to be used safely poses. Several extractors can be arranged in parallel to continuously influence the extraction, or they can be arranged in series, for example the polymer and the extractant in opposite directions flow to continuously influence the extraction.

Furthermore, the melt of the polymer, which by Mas senpolymerization or solution polymerization was obtained, and the coarse of volatile substances (from the solvents) was freed, or the melt of the polymer, which by Emulsion polymerization or by suspension polymerization was obtained and dehydrated (from liquid medium freit) was loaded directly into the extraction tank, or it can first solidify in tablet form or the like and then loaded directly into the extraction tank or only be loaded after the solid substance has melted.

An embodiment of the invention will now be described with reference to FIG Figure described.

Fig. 1 is a flowchart showing an embodiment of this invention using a filling column type extractor.

In Fig. 1 the reference number 1 points to a polymerisation tion reactor equipped with an agitator. The monomer to be polymerized is fed via a line 10 into the reactor 1 and polymerized therein continuously by a known method. The polymeric product is continuously withdrawn from the reactor together with volatile substances via a line 12 and reaches a heat exchanger 2 in order to raise the temperature and make it suitable for volatilization, and it is then introduced into a volatilization apparatus 3 via a line 13 to evaporate the volatile material contained in the polymer by a conventional method. If, considering the concentration in the extracted product, the proportion of volatile substances in the polymer is low enough, the volatilization apparatus 3 can also be omitted or bypassed.

In general, the concentration of volatile impurities in the polymer thus freed from volatile substances ranges from about 400 ppm to a few thousand ppm. Again according to Figure 1 , the polymer, freed from volatile substances in a conventional manner, is fed via a line 15 to a pump 4 in order to increase the pressure of the molten polymer, and then fed via line 16 into an extractor 5 , the pressure of which is by means of a pressure booster 7 was increased to a pressure suitable for extraction.

The pressure booster 7 is a compressor when the extraction medium is in gaseous form, or a pump when the extraction medium is in liquid form. The molten polymer is continuously fed via a line 16 into the upper part of the extractor 5 , which is kept at a certain pressure and a certain temperature, and flows through it downwards towards the bottom, while the extractant, which is continuous via a Line 19 is introduced by means of the amplifier 7 in the lower part of the extractor, in countercurrent and in contact with the downward flowing ge molten polymer, flows upwards towards the tip of the extractor and from there is continuously removed via a line 17 .

During contact with the extractant, volatile impurities are extracted from the molten polymer, which, after contact with the extractant, is withdrawn from the bottom of the extractor through a line 20 and fed into the subsequent process.

Via the line 17 , the extractant, which contains the extra volatile substances, leads into a separator 6 , in which the volatile substances are separated from the extractant by using a low pressure and / or a temperature increase (not shown). As a separation method, a conventional method can be used, such as a liquefaction separation, a separation by a distillation column or a separation by an absorption column.

The cleaned in this way in the separator 6 extraction medium is cycled through a line 18 , a line 26 , the pressure booster 7 and line 19 in the bottom of the extractor 5 re. If necessary, a prepared extracting agent can be introduced into the extractor via a line 26 , the pressure booster 7 and line 19 .

Volatile substances, which can be added to the extractant in the gas phase and which have been separated in the separator 6 , are drawn off via a line 21 and flow in this example into a line 14 , which contains volatile substances from the volatilization apparatus 3 , and the volatile materials from both lines are introduced via a line 11 into a process (not shown) which recovers the non-polymerized monomers.

According to the method presented here, a polymer in ge molten state can be cleaned effectively, and from egg A polymer in the molten state can contain volatile materials extracted to a very high degree. The molded one Product of the polymer obtained by the present method can withstand the high demands of the market the remaining concentration of volatile mate remaining restrict materials.

Now, the present invention will be described in detail with reference to Examples and comparative examples are described.

example 1

Melted polystyrene at a temperature of 220 ° C with a concentration of 2,500 ppm of volatile substances was subjected to a pressure of 245 kg / cm ² G with a tooth pump and continuously introduced into the upper part of a column-type extractor at a rate of 1 kg / h and kept there at 245 kg / cm ² G. The molten polystyrene flowed down towards the bottom of the column through a screen head attached to the top of the column and came into contact with the counter-current carbon dioxide which was the extractant. The height of the extractor (contact zone) was 5 meters.

The carbon dioxide was fed to the bottom of the extractor at a flow rate of 5 Nm ³ / h, this amount being 10 times the weight of the melted polystyrene supplied as explained above.

The melted polystyrene and carbon dioxide were from the Ex tractor from the ground or at the top with the subtracted at the same speed as fed.

The concentration of volatile materials in the polystyrene, which is removed from the extraction tower as described above was 40 ppm.

Comparative Example 1

The same melted polystyrene as that in Example 1 was treated in the same manner as described in Example 1, except that the rate of supply of carbon dioxide was changed. That is, a molten polystyrene of a temperature of 220 ° C was continuously introduced into the upper part of an extractor (height: 5 meters) at a rate of 1 kg / h and held there at 245 kg / cm ² , and the carbon dioxide gas was initiated in the lower part of the extractor at a rate of 2511 / h. The weight ratio of polymer to extractant was 1: 0.05.

The melted polystyrene that comes from the lower part of the Ex out of the tractor was analyzed and it was found that the concentration of volatile materials be 2,100 ppm wore.  

Example 2

Tablet-form polystyrene, which had a concentration of volatile materials of 400 ppm, was heated to 220 ° C. and the molten polystyrene was exposed to a pressure of 200 kg / cm ² G with a tooth pump and at a speed of 1 kg / h continuously introduced into the upper part of a filling column type tractor and held there at 200 kg / cm ² G. The molten polystyrene flowed down towards the bottom of the column through a screen head which had been placed in the upper part of the column and came into contact with the carbon dioxide flowing in the opposite direction, which was the extraction medium. The height of the extractor (contact zone) was 5 meters.

The carbon dioxide was at a flow rate of 250 N1 / h the Bo that of the extractor supplied, this amount being 0.5 times Amount of weight of the melted feed as explained above corresponded to melted polystyrene.

The melted polystyrene and carbon dioxide were from the Ex tractor from the ground or at the top with the subtracted at the same speed as fed.

The concentration of volatile materials in the polystyrene, which is removed from the extraction tower as described above was 100 ppm.

After describing our invention with reference to its Embodiment we express our intention here that the invention by no detail of the description if not otherwise specified, should not be restricted, son on the contrary, it should be within its meaning and its Scope of action set out in the following claims be interpreted in a broad way.

Claims (15)

1. Process for purifying a polymer by treatment of the polymer with an extractant under high pressure to to remove volatile materials contained therein the improvement being the contacting of the polymer in ge molten state with the extractant in a ratio nis, where the weight ratio of polymer to extraction medium in a range from 1: 0.1 to 1: a value less than 20 lies. 2. The method of claim 1, wherein the polymer is a is thermoplastic resin. 3. The method of claim 1, wherein the polymer is molten zenem condition a liquid, essentially polymeric Kom position of a polymer, a melt produced by heating an egg the polymer was obtained in powder or tablet form, or a mixture of them. 4. The method of claim 1, wherein the extractant from the group consisting of carbon dioxide, nitrous oxide, Koh lenstoffdisufid, an aliphatic hydrocarbon, one halogenated hydrocarbon, an aromatic hydrocarbon hydrogen, and a mixture thereof. 5. The method of claim 1, wherein the extraction by a counter flow of the polymer flow and the extractant river is running. 6. The method of claim 1, wherein the extractant in liquid state is used. 7. The method of claim 1, wherein the extractant in supercritical state is used. 8. The method of claim 1, wherein the pressure in the extractor is in the range of 20 to 500 kg / cm ² G. 9. The method of claim 1, wherein the pressure in the extractor in Range from 0.8 to 10 times the critical pressure of the Ex traction agent lies. 10. The method of claim 1, wherein the ratio of the poly mers to the extractant by weight parts in the range from 1: 1 to 1: a value less than 20 in a continuous Process in which a countercurrent is used. 11. The method of claim 1, wherein the temperature in the extract tor is the critical temperature of the extractant or above. 12. The method of claim 1, wherein the temperature in the extract gate is in the range of 80 to 250 ° C. 13. The method of claim 1, wherein the ones to be extracted volatile materials impurities, such as a unreacted monomer, solvent or an oligomer are. 14. The method according to claim 1, wherein several Ex tractors are arranged in parallel. 15. The method according to claim 1, wherein as an extractor several Ex tractors are arranged in series.