SE502884C2 - Process and appts. for recovery of plastics and/or metal - Google Patents

Abstract

Method for the recovery of metal and/or plastic from an opt. fragmented mixed material comprises heating to melt the plastic, then subjecting the melt to centrifugal force to enrich the metal and plastic content, and then treating the opt. solidified enriched melt to recover the metal and/or plastic. The appts. for carrying out the method is also claimed.

Description

502 884 2 to dissolve the plastic and recycle the insoluble components.

A similar procedure is described in Rohstoff / Rundschau 18/1992 s667-668. There, the polyethylene part is dissolved in a solvent at elevated temperature, after which the aluminum part is separated by filtration.

The further treatment of the viscous polyethylene solution is stated to be cumbersome and difficult. A further method is described in JP 51020159 where a flotation process is used to separate plastic and aluminum derived from an aluminum / plastic laminate.

Obviously, these methods have not found any major use, which in addition to inadequate source sorting of used packaging in waste can probably be explained by the fact that the methods have technical shortcomings. The use of solvents according to JP 51020976 is thus likely to cause greater environmental problems than can be achieved by the recycling of the aluminum, while a complete mechanical separation according to JP 52112673, which is also a prerequisite for the method according to JP 51020159, is difficult to achieve due to of the adhesion between the different layers.

In connection with the increasingly stringent legislation with higher requirements for material recycling of e.g. used packaging that is now being introduced in different countries, the need for new technology has been accentuated.

The object of the present invention is to provide a method which enables aluminum and plastic to be separated in a simple manner so that an aluminum-free plastic fraction and an aluminum fraction with a low plastic content are obtained. This is achieved by means of a method and a device which have obtained the features stated in the claims.

The method involves heating the appropriately sized fragmented plastic / aluminum laminate in an inert atmosphere to a temperature which is substantially below the melting point of the aluminum but at which the plastic is readily flowable. At the same time, the molecular structure of the plastic must be largely maintained. This can be done by appropriate choice of time, temperature and atmosphere. Stabilizers can also be used to reduce the degradation of polymer molecules, such as oxidation and cleavage of molecular chains. From the mixture of molten plastic and aluminum flakes, aluminum is separated by centrifugation. The density of aluminum is about 3 times that of plastic material at the current temperature.

Further details are given in the examples given with reference to completed tests.

Some examples will now be described with reference to the accompanying drawings in which Figures 1 and 2 show in diagrammatic form the molecular weight distribution of the samples given in the examples, while Figure 3 schematically shows a device intended for use in the method according to the invention.

Example 1 A packaging laminate of the cardboard / aluminum foil / polyethylene type with the weight proportions of about 75/5/20% had previously been treated in a process where the cardboard part was taken care of for material recycling in a wet process. The residual material aluminum foil / polyethylene was the starting material for the experiment. The thickness of the aluminum foil was 6-7 μm. The material was previously fragmented into about 0.5 cm: large flakes. After drying, the weight fraction of aluminum was determined to be 23%. The remainder was assumed to be polyethylene. A total of 58 g of this material was heated in a glass test tube with a diameter of 40 mm. Due to the voluminous nature of the material, this had to be done in four batches of about 15 g at a time. During heating, the lower part of the test tube was immersed in a molten tin bath with a temperature of 360 ° C. The polyethylene part of the laminate melts.

Nitrogen gas was added simultaneously in the test tube to obtain an environment that was less oxidizing than air. Between meltings, the hot tube test tube was transferred to a laboratory centrifuge and centrifuged for 5 minutes at 3000 rpm. During the movement of the sample and during the centrifugation, the test tube was thermally insulated so that the temperature could be maintained as much as possible. The test tube was also kept closed to reduce contact with atmospheric oxygen. After centrifugation, the test tube was crushed and the cooled sample was examined. The upper part of the sample consisted of plastic without any remnants of aluminum. However, the plastic was brown. It was not further investigated. The lower part of the sample was enriched in aluminum; the closer to the bottom of the test tube to an increasing degree. Of the most enriched part, 25 g were melted together with a slag former (Montanal salt) in a graphite crucible at 700 ° C.

A total of 6.8 g of aluminum was recovered.

Example 2 An experiment similar to Example 1 was made with a type of 502 884 aluminum / plastic laminate used for vacuum packaging of coffee. This laminate consists of a polyester film / aluminum foil / polyethylene film with parts by weight of about 10/20/70%. The thickness of the aluminum foil was 7 .mu.m. Under the same conditions as stated above, a total of 82 g of laminate was melted in three batches. In this case, too, plastic and aluminum were separated well.

Example 3 Materials of the same type as in Example 1 were treated in basically the same way as there. Of a total of about 300 g of material which was enriched in batches, about 35 g of the aluminum-rich part was melted and about 14 g of aluminum was extracted therefrom. On analysis, this was found to have a composition that complies with the requirements for unalloyed aluminum 99.0% (SS 4010, AA 1200) except for the Sn content, 0.4%, which was judged to be contamination from the tin melt.

About 50 g of the aluminum-free, solidifying plastic material in the upper part of the test tube was divided into pieces about 1 cm3 in size.

The color of the material was light brown, reminiscent of beeswax. It was quite soft and easy to carve. The material was designated "Sample 'R". In SEC analysis (SEC == Size-exclusion Liquid Chromatography) it was found that the molecular weight Mn (number average) was about 4700, while a good polyethylene material should have Mn = 10,000 - 15,000. The factors that most strongly contributed to the degradation of the polymer has been judged to be high temperature, long time and relatively high oxygen content in the atmosphere.

In the experiments described above, it has been shown that the principle works. It is thus possible to separate plastic and aluminum by centrifugation at high temperature. However, the experimental technique needed to be improved so that the polymer was more effectively separated from degradation. Experiments were therefore made with a more effective shielding of ambient air oxygen, lowering the temperature and the use of oxidation stabilizers.

IMPROVED EXPERIMENTAL TECHNIQUE In an approximately 140 mm long, thick-walled test tube with a diameter of 502 884 Dy / di 22/18 mm, test material of the same type as in previous examples was heated to 200 ° C in a thermostated heating block. A significant difference from the previous one was that in most experiments the sample material was provided with about 0.2% by weight of the oxidation stabilizer Irganox B561 (Ciba-Geigy) in order to reduce the degradation of the polymer.

In this case, carbon dioxide was used as shielding gas instead of nitrogen gas. The reason is that carbon dioxide, in contrast to nitrogen, has a higher density than air and is therefore judged to provide a better protective effect in the test in question.

Test tubes with test material were purged during the 11 minute heating with shielding gas. The hot (sticky) sample could be easily compacted to about one third of its previous volume using a 17 mm diameter round rod and then purged for an additional 4 minutes with shielding gas. Then the open end of the test tube was sealed. The test tube was then picked up and allowed to cool in a sealed condition.

The sealed test tube was then moved to an electrically heated crucible furnace for final heating prior to centrifugation. The furnace space around the test tube had been pre-filled with carbon dioxide as a shielding gas. In the oven compartment, the test tube was placed in a similar heating block as before. In a number of experiments, both the time and temperature of the sample in the oven were varied.

The time was chosen to be 10 or 20 minutes. The temperature was varied between 300 ° C and 400 ° C.

In order to be able to carry out centrifugation at a high temperature and to avoid rapid cooling of the sample, special measures had to be taken. The stainless steel holder of the centrifuge was filled with gypsum mass which was allowed to solidify. A 30 mm cylindrical hole was drilled in the plaster body. The hole was lined with ceramic fiber insulating felt to the appropriate diameter for the test tube. Prior to centrifugation, the gypsum body was preheated. In this way, the test tubes could be kept warmer than otherwise during the 5 minute spinning time. The speed was increased to 4,000 rpm.

The average radius from the sample to the center of rotation was 23 cm, giving the G ~ number about 4,100.

Example 4 Attempts were made to find the optimum temperature for the process. In Examples 1-3, the temperature of 360 ° C had been applied and it was considered desirable to be able to use a lower process temperature. In experiments with the improved technique at varying temperatures from 300 ° C and upwards, it was found that separation by centrifugation was not obtained at 300, 330 or 360 ° C but only at 385 ° C. The reason for this is probably higher viscosity (at a certain temperature) of the plastic fraction due to reduced degradation due to the improved process technology. For the further experiments, therefore, the temperature of 385 ° C has been used.

Example 5 Sample materials of the same type as in Example 1 (and 3) were treated according to the improved technique at 385 ° C and with 0.2% by weight of B561, the oven time being 20 or 10 minutes (Sample 14 and V31, respectively). In both cases, the separated plastic fraction had a significantly lighter color than from Sample R in Example 3. The average molecular weight Mn was 8,300 resp. 9 900. This example shows that the material in samples 14 and 31 has decomposed to a much lesser extent than in sample R, and that the shorter time in the furnace has resulted in less decomposition.

Treatment Average molecular weight Sample ° C / min / staff. number average sss / zo / sssi a zoo 14 sss / io / Bssi 9 900 31 Example 6 The purpose of this experiment was to determine how much the thermal treatment actually affected the material. PE granules of the type used for the product in question were used as sample material. The granules were processed according to the improved technique and in the same way as the laminates.

The average molecular weight of granules processed at 385 ° C / min and 385 ° C / 10 minutes partly without, partly with the addition of 0.2% by weight of B561 was compared with that of unprocessed granules.

The following results were obtained: 502 884 7 Treatment, Mean molecular weight, Sample ° C / min / staff. number average 385/20 / ---- 9 200 ll 385 / l0 / ---- 12 500 26 385/10 / B56l 13 600 29 none 18 650 0 The molecular weight distribution for the above samples is shown in diagram form in Figures 1 and 2, The results show what effect both short process time and the addition of stabilizer have on the current application.

Example 7 In order to get an idea of the extent to which the PE material has changed during use as a package, a comparison was made of the molecular weight of the current type of granulate resp. used laminates after being subjected to the same treatment (385/10 / B561) according to the above improved technique. Then the comparison is this: Starting material Average molecular weight, Sample number average granules 13 600 29 used laminate 9 900 31 The result indicates that an aging that led to a significant reduction in the molecular weight of the laminate material occurred between the manufacture and recycling of the packaging material. The results in Example 6 show that the molecular weight of granules in the process was reduced by 27%. If the corresponding ratio is assumed to apply to the laminate used, its molecular weight before the process in sample 31 would have been 13,560.

It can also be mentioned here that when processing used laminate, the remelted plastic obtained a significantly darker color than in the corresponding experiments with granules. This is judged to be mainly due to pollutants of e.g. ink from the packages used. 502 884 8 Summary of the experiments performed - The experiments have thus shown that it is possible to extensively enrich aluminum from composite materials, for example packaging laminates consisting of thin aluminum foil and various types of thermoplastic polymeric films by heating in an inert atmosphere followed by centrifugation at elevated temperature. The proportion of aluminum has been increased in simple laboratory experiments from about 20% to over 60%, which considerably facilitates material recycling of the aluminum.

- Experiments with material recovery by melting the aluminum in enriched fraction as above have shown that remelted aluminum of high quality can be obtained.

Although an undesired degradation of the thermoplastics is obtained with the applied technique, recycled plastic material with the obtained average molecular weight can be considered to have such an acceptable quality that it can be used as raw material for certain types of plastic products.

Industrialization of the process Industrialization of the described process can take place using a custom decanter centrifuge. The use of decanter centrifuges is a proven technique to separate e.g. a solid phase from a liquid. Industrial decanter centrifuges operate with the volume fraction fixed from less than 1% up to over 60% and with operating temperatures up to 360 ° C and G-figures of up to 10,000.

Of several possible devices for carrying out the above-mentioned method, one is schematically shown in Fig. 3. The starting material should be dry. Otherwise a special drying must take place.

The material is fed from a filling device 10, for example by means of a screw conveyor 11 into a chamber 12 or the like. having a heating zone 13 and further to a decanter centrifuge 14.

The chamber 12 has an inlet 15 for shielding gas and is separated from the surroundings by means of a lock 16, which is arranged in connection with the filling device 10.

The heating in the shielding gas atmosphere must take place in such a way that the material quickly reaches the process temperature. Electromagnetic (inductive) heating may be a suitable such technique. After heating, the mixture is fed by means of the screw conveyor 11 into the decanter centrifuge 14, the construction of which is adapted to the required working temperature and to operation with shielding gas.

The aluminum-rich phase departs via a first outlet 17 and is collected for pre-treatment in a later process before remelting and material recycling of the aluminum.

The polymer fraction in the aluminum fraction is judged to be best utilized by energy recovery in connection with the said pretreatment.

The liquid polymer fraction is allowed to cool to a suitable temperature for granulation and can in the form of granules constitute a raw material for new plastic products. The proportion of plastic that should be recyclable is shown in the following theoretical calculation with typical weight percentages for Al and plastic in laminate. If the aluminum fraction is enriched to 60% Al (and 40% plastic), then 92% of the plastic content in a 90 / 10- laminate (with 90% plastic and 10% Al) separated. For an 80/20 laminate, the corresponding degree of separation is 83% if the aluminum fraction is enriched to 60% Al. It is thus a significant part of the total plastic content that can in this way be made available for material recycling. For aluminum, high-yield material recycling is possible even before enrichment, but is easier to implement the lower the plastic content.

Claims (13)

502 884 10 Patent claims A method of recovering at least a part of the metal and / or plastic contained in the material on the basis of composite materials containing at least plastic and metal, characterized in that the material ev. after fragmentation, it is heated so that at least a part of the plastic contained in the material melts and that the melt is centrifuged, whereby the metal and plastic are enriched in the melt and that the metal and / or plastic in further treatment steps is recovered from the enriched and possibly solidified the melt 2. A method according to claim 1, characterized in that the composite material consists of a laminate and the metal consists of aluminum. 3. A method according to claim 1 or 2, characterized in that the plastic consists of at least one or more thermoplastics. Method according to one of the preceding claims, characterized in that the material is heated in connection with the centrifugation to a temperature between 200-500 ° C, preferably between 300-400 ° C. 5. A method according to any one of the preceding claims, characterized in that the heating takes place in a non-oxidizing environment. 6. A method according to claim 5, characterized in that the non-oxidizing environment consists of a shielding gas e.g. carbon dioxide or by vacuum. Method according to one of the preceding claims, characterized in that an oxidation stabilizer is added to the material and / or the melt. Method according to one of the preceding claims, characterized in that the material is successively fed to the centrifuge during heating. Method according to one of the preceding claims, characterized in that the plastic phase obtained by centrifugation is separated and disposed of for recycling. 10. A method according to any one of the preceding claims, characterized in that the aluminum-rich fraction obtained by the centrifugation is separated and disposed of for further treatment. 11. ll. A method according to claim 10, characterized in that the aluminum-rich fraction is thermally treated so that organic and 502,884 μl volatile material are evaporated at a temperature lower than the melting temperature of aluminum. 12. A method according to claim 11, characterized in that impurities in the aluminum-rich fraction are separated mechanically, magnetically or electromagnetically from the base material. Device for recovering, on the basis of composite materials containing plastic and metal, at least a part of the metal and / or plastic contained in the material according to the method specified in claim 1, characterized in that the device comprises a centrifuge (14), preferably a decanter centrifuge, with a chamber (12) separated from the environment in which a non-oxidizing environment prevails, the material from a filling device (10) being introduced into the chamber (12), that the chamber comprises a heating zone (13) intended to heat the material before it is introduced into the centrifuge (14) and that the centrifuge is so equipped that the material is kept at the desired operating temperature, the centrifuge being provided. with at least two outlets where during the centrifugation process enriched aluminum exits through the first outlet (17) and enriched plastic exits through the second outlet (18).