WO1994009064A1

WO1994009064A1 - Way to regain polythene and polypropylene and other polyolefines from return material, especially such of composite type

Info

Publication number: WO1994009064A1
Application number: PCT/SE1993/000836
Authority: WO
Inventors: Sven Ljungbo
Original assignee: Sven Ljungbo
Priority date: 1992-10-15
Filing date: 1993-10-13
Publication date: 1994-04-28

Abstract

There are methods known to regain polythene and polypropene and other polyolefines from return materials through extraction with different solvents at higher temperatures and precipitation of the polyolefines out of the solution by sinking the temperature. The cooling of the solution is, however, difficult to accomplish as the precipitated polyolefine is smeary and produces discharges and stoppages in an ordinary heat exchanger. The present invention solves this problem by using water insoluble solvents for the extraction and by injecting the warm solution into cold water. As the density of the solution differs considerably from that of the water, the solution either comes up to the water surface or sinks to the bottom of the water tank. There the polyolefine dispersion, formed at cooling, is separated from the water and then broken up into solvents and a filter cake. The filter cake is dried through evaporation either to a powder or to a sintered cake of pure polyolefine. Alternatively the filter cake can also be warmed up again so as to make a new solution, but considerably higher concentrated than the original one. The new solution is then spread or spurted out on a line of heated cardboard or paper, after which the rest of the solvent is vaporized in a closed space, with recovery of the vaporized solvent. As a result a polyolefine-paper-laminate is obtained, that can be used for packages etc. In the same way you can make a polyolefine-film if the line - for example made by steel wire or band - is coated by Teflon TM. In that case the film, formed after the evaporation of the solution can be pulled away from the line and rolled up.

Description

Way to regain polythene and polypropylene and other polyolefines from return material - especially such of composite type

The present invention is a method to regain polythene, polyprophylene and other polyolefines from return material such as production waste, assorted refuse, household garbage etc., in order to re-use them to the same or just as qualified products as by their first use. The invention is founded upon the following qualities in polyolefines: PE and PP and many other polyolefines and some copolymers of olefines mutually combined or combined with other monomers are, at higher temperatures, soluble in several solvents, first hydro-carbons and chlorinated hydro-carbons. At rising percentage of the comonomer the temperature, required for disolving the polymer sinks and drops to room temperature or lower at higher comonomer proportions. The temperature, at which a certain solvent dissolves a certain one of these polymeres, is thus different for different polymeres. This temperature is below called the dissolving temperature. Several of the above mentioned polyolefines are characterized by their precipita- ting from the solvent as powder if the temperature of the solution is lowered under the dissolving temperature. Through pressfiltering this powder can be separated from the bulk of the solvent in the form of a powder cake, that can be rid of remaining solvents through drying. These properties of the polyolefines are accounted for, in the German Auslege- schrif 26 39 864, in the German patent DE 2 801 522 and in the international application WO 91/03515. The method proposed here is composed of the follo- wing elements: The return material is if needed removed from other materials than paper and plastic products. Then it is mixed with solvent and heated to at least dissolving temperature so as to dissolve the polyolefine in the material. The solution and the remaining not dissolved material are separated whereupon the restmaterial is washed a couple of times with a new solvent at the same temperature, alternatively washed once with counter flow. If the return material has such qualities that already the first dissolution of the polymer can be made by solvent flowing through without the bulk getting sticky and corking up the apparatures the whole dissolving- and washing - process is carried through in one step by the counterflow principle. The polyolefine solution, segregated from the restmaterial, is then separated in polyolefine and solvent through chilling the solution to a temperature below dissolving temperature. Then the solution congeals into a powder bulk, rather jelly- like in the beginning. The main part of the solvent can be removed through filtering i.e. through suction, centrifugalizing or pressfiltering. The last part of the solvent is removed by evaporation. This is best done at temperatures so far below the dissolving temperature as possible; thus the dry polyolefine is produced in the form of a free- flowing powder. If the drying is done only a few dozen degrees below dissolving temperature the powder will sinter into a compact body, from which it may even be difficult to get out the last remains of the solvent. The cooling of the warm polyolefine solution for precipitation of the polyolefine involves certain problems. The precipitated polyolefine strives to form deposits on the tube walls in an ordinary heat exchanger and thus impairs the heat conduction. In the worst case the heat exchanges gets blocked up. In the German patent DE 2 801 522 this problem is solved by leading the separated warm solution to a tank, where it is vacuum-destilled, the outgoing stream is chilled and condensed and the cold condensate returned to the tank. The vacuum evapori- sation as well as the return of the cold condensate chills the solution, remaining in the tank, so the polyolefine is precipitated. This process is, however, both apparatus- energy-intensive, and, more over, difficult to make continuous. According to the present invention the problem is solved in the following way: The warm polyolefine solution is injected into a tank with cold water through a heat- insulated jet. Since the polyolefine as well as the solvent are insoluble in water the solution rises to the water surface, if the solvent is a hydrocarbon or sinks to the bottom, if the solvent is a chlorinated hydro carbon. When passing through the water the solution is chilled to about the same temperature as the water has. From the tank the solution is transported to the filter works, where the polyolefine is separated from the main part of the solvent, which is brought back to the start of the process to dissolve new return material. The water in the tank is chilled in a heat-exchanger or through jacket-cooling. Alternatively to this process the cold water can be injected or dropped into the polyolefine solution and the two liquids separated as described above. 2

3 As solvents alifatic hydrocarbons (paraffins) are best due to the following reasons: except polyolefines they do not dissolve any of the most common plastics for example

5 polystyrene, polyvinylchloride, acrylonitrile - butadienestyren plastics. Many of them

6 have a low boiling point, which is advantageous to the drying of the filtered poly- olefine powder.

8

9 They allow squeezing of the powder cake up to a somewhat higher percentage 0 than the xylene, recommended in the German patent documents mentioned above. 1 2 If the return material contains other polyolefines with different dissolving 3 temperatures the treatment of the residue from the separation of the first poly- 4 olefine is repeated at the next higher dissolving temperature etc. 5 6 If the contents of additives in the polyolefines for example stabilizers stay 7 in the solvent at the precipitation of the polyolefine or have not been dissolved but 8 have stayed in the rest material, a new additive ought to be added to the reclaimed 9 polyolefine before this is used again. If the return material has contained oils, 0 fats, soluble paints or other substances, soluble in the used solvent, the concentration 1 of these in the solvent regained at filtering, must be kept below the level, that can give 2 unwished effects on the polyolefine, regained in the next set. This is best achieved 3 through continuous purification of a part of a solvent regained at the filtering from 4 these substances before it is returned to the process. The purification can be made 5 through distilling, membranefiltering or other methods. 6 7 When the return material partly or largely consists of polyolefine laminate with paper, 8 cardboard or other products of woodfibre, the polyolefine can of course be extracted 9 from these ones in the same way as mentioned above. But then you had better 0 disperse the material in water before or during the soaking with a warm solvent. As 1 the power of the water to wet and penetrate into wooden or cellulose fibres is 2 considerably greater than those of the used solvents, it will be easier to separate the 3 polyolefine solution from the fibres. Further a considerably smaller volume of solvent 4 for treating a certain quantity of returnmaterial is required. 5 6 The necessary volume of solvent can also be reduced by mechanically separating 7 as far as possible the cardboard or the paper from the covering plastic layer . 8 Thus only the fibre layer directly fastened to the plastic film needs to be separated 9 from the latter through extraction with solvents. i An advisable method to make the mechanic separation is to defibrate the paper- 2 plastic laminate in some kind of refiner. The best separation is here acquired by a 3 turbo-refiner, construction Asplund. 5 The following example shows without limiting the method, some ways to carry it out. Example 1 Waste of production of a foil-laminate of PE and PP glued together with fuse glue, is decomposed into small pieces with a hammer-mill or a screwmill. Stirring them these pieces are leached with fivefold the amount of toluene so as to dissolve the fuse glue. Then the solution is separated from the foil residue. This residue is washed with pure toluene, separated from it and dried from remaining toluene. This drying can be made by blowing steam at 1 ata through the residue and then condensing the water and toluene steams or through vacuum evaporation of the toluene, followed by its condensation. Instead of toluene the fuse glue can be dissolved by benzene, methylethylpentone, chloroform, dichloromethane and other solvents, which are easier to evaporate from the foil residue, due to their low boiling point. The residue is mixed with its sevenfold amount of heptane and is heated and stirred in autoclave up to 110° c temperature and a pressure of 130-150 k Pa. Then the PE foil turns into solution which is separated from the undissolved PP foil. The foil is washed at the same temperature with pure heptane, which , after separation, is used for dissolving the next lot. The PE solution is chilled to 20° c temperature so as to precipitate the polythene. The heptane is, as far as possible, centrifugalized away, whereupon the PE powdermass with the last heptane residue is spread out on a warm roll, which then boils away the heptane at 95 - 99° c. The heptane steam is condensed in a cooler and brought back to the process. The polythene appears as a porous sintered cake. If PE is wanted as powder, the drying ought to be carried out under vacuum at a temperature of below 30° c. Alternatively the heptane can be exchanged for hexane or pentane or iso-pentane (their boiling points at 1 ata is 68, 36 respectively 28° c). In return the pressure at the dissolving process must be raised to about 400 k Pa for hexane and still higher for pentane and iso-pentane. An alternative to the process described above is to treat the decomposed PE PP laminate with 105° c warm toluene, which then dissolves both the polythene and the fuse glue. After the separation of the solution from the PP foil pieces, the former is chilled to 20° c temperature, allowing PE to precipitate and be separated from the solution. Thereafter it is washed with pure toluene and dried. The separated toluene and the fuse glue in it are then separated from each other through destination. The PE powder as well as the cleaned purified PP foil pieces are used to produce new PE respectively PP foils. To begin with the stabilizers and other additives, which have been washed out at the separation ought to be replaced by new ones. Example 2 Assorted milkpacks of twofold PE laminated cardboard are decomposed in a screwmill, then cleaned from possible scraps of glas, china, metal etc. and dispersed in water, 80 - 90° c temperature. To the water sodium hydroxide has been added in quantities of 1-2 % of the weight of the cardboard laminate. The 3% paper- plastic-dispersion is strongly stirred during 5 minutes, after which the water is sucked out on a filterdrum, where the pulp also is cleaned from remaining lyewater, containing fat and casein rests dispersed by the lye. The so washed pulp is dehydrated to a 10%-dryness and taken over to an autoclave. There it is mixed, strongly stirring it, with heptane in a quantity corresponding to 8 - 10 times the weight of the PE in the cardboard pulp. At the same time the temperature is raised to 110° c. After 10 minutes' treatment at this temperature the stirring is stopped and the so formed heptane-solution separated the suspension through sedimentation, that is accelerated by vibration. An additional acceleration of the sedimentation can be obtained by a small reduction of the pressure in the autoclave. Then small heptanebubbles are formed. They raise against the oversurface of the pulp and thus bring the small drops of PE-heptane- solution with them. Alternatively the process is continually driven. The 10% pulp is then warmed to 1 10° c. Stirring it all the time the pulp is introduced at the top of the autoclave and taken out at ^"the bottom. From there the pulp, while diluting it with 1 10° c water, is transferred to another autoclave. Due to the dilution the PE heptane-solution rises to the surface so quickly that the separation becomes complete in spite of the fact that the pulp all the time moves against the bottom of the autoclave, where the cleaned pulp is taken out to be dehydrated and dried. The 1 10° c water is brought back to the process. In both the cases the PE heptane solution is taken out of the layer, lying on top of the fibre pulp and is separated to PE and heptane in the manner described in example 1. The need of autoclave volume can with retained production capacity be reduced in the following way: The above described dispersion of plastic-cardboard-laminate pieces in water is treated in a refiner with a wide slit between the milling organs. The best result is accquired by the turbo refiner, constructed by Asplund. Through sieving, the plastic foil pieces mounted with a thin fibrelayer are separated from the other fibres. Then only the first fraction is extracted with solvent, while the filtered fibre fraction can be used directly for the production of cardboard. 2

3 In the same way, as described above, also polyolefines and cardboard or paper can be separated out of domestic refuse, i.e. from the paper-plastic fraction, which is

5 obtained from the refuse after crushing, magnetic separation, windsieving etc.

6 If the fraction contains several different polyolefines and one wants to separate them,

7 the extraction with solution must be made gradually, at different temperatures. If the

8 difference in dissolving temperature is considerable, as for example between PE 105 -

9 1 10° c and PP 125-130° c it may be favourable to change the kind of solvent

10 between the two extractions to avoid using a considerably higher pressure in the i i autoclave at the second extraction. If the plastic-paper-fraction from the domestic

12 refuse containes a relatively small amount of paper, it can be most favourable to make

13 the extraction with solvent directly without disperging the fraction in water.

14 15

16 Example 3

17

18 The process described in example 2 is made with xylene instead of heptane as solvent

19 up to the point, where a 1 10° c warm solution of PE in xylene is reached. This 0 solution is chilled to precipitate the PE, after which the bulk of the xylene is separated 1 through filtering or through centrifugalizing. The PE-xylene-mass thus obtained is 2 then heated to dissolve the PE in the remaining xylene. If necessary stabilizers and 3 possibly other additives are added, after which the solution by an injection moulding 4 machine with a straight slit jet is spurted out as a thin film, which is put on to a 5 cardboard or paper line previously heated to 140-150° c. 6 7 The latter stands, as the slit jet, in a closed heated room, where the line runs, until all 8 the xylene has been dried from the PE film. Then the line is taken out between two 9 cylinders to be rolled up or turned over a cylinder to make the underside upside. 0 The cardboard or paper is also on this side coated with a polythene film, which is 1 dried after which the laminate is taken out of the heating room to be rolled up. 2 The xylene steam, set free, is drawn off the heated room to a condenser and 3 reclaimed. 4 5 To prevent danger of explosion at the start and breaking off the process the oven 6 room, during these occasions, is filled with an incombustible gas, for example 7 nitrogen, carbon dioxide or overheated water steam of atmospheric pressure. 8 For the same reason the pressure in the oven room is carefully controlled during the 9 process so as to allow only a slight amount of air to enter the oven room at the outlet 0 of the laminate. 1 2 If a lower temperature is wanted, more lenient to the cardboard and its possible text, 3 octane or methylheptane or toluene or other alifatic or alicyclic hydrocarbons with 4 boiling points at atmospheric pressure in the range of 1 10 - 130° ^{c can} be used. 5 2 Example 4

3 In example 1, corresponding to the way described in example 3, you can first dissolve

5 the PE foils in 105 degrees warm toluene, separate the PP foil and other solid

6 contaminates, cool the solution to precipitate the polythene and separate as much

7 toluene as possible from the PE powder. Then the powder-toluenemixture is warmed

8 so as to dissolve the polythene. As shown in example 3 this solution is spurted out

9 through a straight slit nozzle. The so formed foil is taken up and dried on a warm 10 conveyor belt of for example steel band or woven wire, coated by teflon or silicone π rubber or another polymer with good releasing power against PE. The PE foil,

12 formed after drying, which is pulled off the conveyor belt and collected in a roll

13 can be used to produce a PE-PP-foil-laminate of the same kind as the starting

14 material or other PE foil products.

15

16 Instead of sprouting the solution through a straight slit nozzle it can be sprouted

17 through a circular slit nozzle and blown up to a flexible tube. The latter is pulled up

18 through a vertical tunnel or tube in counter-current hot air or overheated water steam

19 so it is dried from the solvent, after which it is cut up to foil. 0 1 The coating of the cardboard, paper or conveyor belt can also be made by spreading 2 the solution with a knife or a guardboard. Usually it is then necessary to work with a 3 more diluted solution than coating made by injection-moulding and slit nozzle. 4 5 The process in example 3 and 4 means that the last stage in the recovery of the 6 polythene at the same time is the first, respectively one of the first, stages of process 7 in the recycling of the same PE. This gives a saving of one of the process steps, 8 compared to the methods in example 1 and 2 to reclaim PE, including the following 9 preparations of products made from it. 0 1 Example 5 2 3 If the return material contains printing ink or other matter, which at dissolving 4 temperatures for polythene is soluble in the solvent used for PE recycling for 5 example heptane it is made in the following way: 6 7 The washed paper plastic dispersion, described in example 2, with a dry content of 8 2-3 % and a temperature below the dissolving temperature of the polythene, best 9 done at 70-80° ^c, is mixed, stirring it all the time, with an amount of heptane, 0 corresponding to 1-3% of the weight of the dispersion. After 3-5 minutes i stirring the solvent is separated through sedimentation or centrifugalizing. The 2 solvent has now dissolved or gelatined and turned absorbed in the printing ink film 3 on the inside of the external PE film of the cardboard laminate. Through destination 4 the heptane is separated from the colour remains and restored to the process. 5 The dispersion, filtered from colour is drained to 10% dry content and further treated as in ex 2 or 3 or 4. In addition to the return material mentioned above and their likes one can also use such materials from which some other components than polyolefines have been extracted through chemical treatment. Such an example is the remains after sugar- rizing the cellulose and hemicellulose from household and building refuse - through for example highly concentrated hydrocloric acid - and the separation of the sugar for ethanol fermentation. These remains - mostly plastics and lignine powder - are treated in the same way as the one in the examples above.

Claims

y

C l a i m s 1. The method of claim 1 comprising: Way to recover from return material one or more polyolefines for example polythene and polypropylene by treating, at minimum dissolving temperature for the intended polyolefine, the return material with a solvent, difficult to dissolve or indissoluble in water, separate the polyolefine-solution from the residue material, chill the solution so as to precipitate , filter off and dry the polyolefine, comprising the steps of the polyolefine solution being chilled by mixing it with cold water, when, the polyolefine- solvent-dispersion formed through refrigeration on account of its from water different density rises to the water surface or sinks to the bottom, after which it is separated from the water then to be separated to polyolefine and solvent. 2. The method of claim 1, comprising: As much as possible of the solvent is separated from the polyolefine powder, preci- pitated through refrigeration, by mechanical separation such as filtering or centrifugalizing, after which the last solvent residues are separated from the polyolefines through evaporation. 3. The method of claims 1 and 2 comprising: The final drying of the polyolefine powder is made at temperatures below 50° c. 4. The method of claim 1 and 2 comprising the polyolefine powder allusion, concentrated by filtering or centrifugalizing, is heated to solution, which is spurted through a slit nozzle to form a foil, which by evaporation gets rid of the remaining solvent. 5. The method of claims 1, 2 and 4 comprising: The foil directly after the slit nozzle is put on cardboard or paper after which it gets rid of the solvent by evaporation, forming a laminate with the cardboard or paper. 6. The method of claim 1 comprising: The return material is first washed with the solvent at temperatures below the dissol- ving temperature to get rid of colouring matters and other disturbing substances, which are soluble in the solvent at these temperatures. 7. The method of claim 1 comprising: The return material, if containing paper fibres, is first saturated with water, before it is treated with solvent. 8. The method of claim 1 comprising: The return material, if containing laminate of polyolefines with cardboard and paper, is first dispersed in water and treated in a refiner to rip off the bulk of the paper fibre from the cling-films and separate the fibres through straining them off from the cling- films before the latter with their fixed, thin fibre-layer are treated with solvents to extract the pure polyolefine from it. 9. The method of claim 1 comprising: The solvent used belongs to the section alifatic hydrocarbons.