DE2900666A1 - Separating different thermoplastic polymers from mixed waste - reducing particles size dry and treating suspension in successive hydrocyclones - Google Patents

Abstract

Mixed thermoplastic waste materials of different density are sepd. for recovery by reducing the material to max. 20mm. particle (pref. 5mm. long), washing and sterilising if necessary, and suspending in a liquid. Successive hydrocyclones are appropriate are arranged in stages, with upper cylindrical parts through which the suspended materials are dropped; the ratio of the dias. of the overflow/underflow outlets is 1-4 (pref. 1-2.5), the ratio of the length/dia. of the top cylindrical part is 1-10 but increases with decrease in difference in density between the polymers and liquid. If the polymer's density exceeds that of the liquid, and if they are mainly film materials, the angle of the cyclone cone is 120-180 degrees; if the density of the polymers is only partly above that of the liquid this angle is 5-40 degrees. Continuous operation with high throughput is obtd.

Description

"Process for separating mixtures of different art

waste material "The invention relates to a method for separating Mixing different plastic waste of different densities into their components for their recovery, in which the plastic waste in particles with a maximum of 20 mm, preferably smaller than 5 mm edge length or diameter, and if necessary

washed and sanitized suspended in a carrier liquid are5 whose density differs from the density of the plastic to be separated or this is the same.

For separating mixtures of different plastic waste after Their density has so far only been static floating-sink separators in practice applied. Sword beets or fluids are used in these separators a separation of the plastics is carried out according to their density, the slurry in their density is adjusted so that they are separated from the density of each Plastics differs.

Attempts have also been made to separate them by flotation to undertake (Shimoiizaka, Junzo; Akira Konosu and Yuzo Hayashi: Studies on Separation of plastic waste. Nippon kogyo kai shi 90, (1974), H. 1042, pp.775 (17) - (779), (21), (Journal of the Mining and Netallurgical Institute of Japan).

With the well-known swim-sink separators, for example in the form from cone or box separators, plastics with density can differ up to to 0.02 g / cm3, if the natural hydrophobicity of the plastics through Addition of wetting agents is canceled, so that sufficient wetting of the plastics occurs with the carrier liquid. The residence time of plastics in separators is a function of the plastic fractions to be separated. Accordingly, the generally relatively small differences in density between the various types of plastic long dwell times in the swim-sink separators are required. The separation process in these separators is also unfavorable due to currents in the separating liquid influenced, in particular by the discharge devices for the sinking and floating material as well as for the solids feed inevitably generated. This is the reason why In the case of the known method1, the need for a turbulence-free as far as possible To achieve flow guidance, both structural and procedural Problems. The application of the known method leads in terms of purity the separation products to satisfactory results, with a selective separation A mix of teaching components is possible via a correspondingly multi-level static Density separation, where the carrier liquid, in the individual stages adapted to the plastic components still present in the carrier liquid must become.

The known separation systems are structurally relatively complex and lead in relation to the structural effort only to a relatively low throughput rate, which increase with a reduction in the density differences of the plastic components to be separated reduced.

The object of the present invention is to provide a method of the introductory called type so that a continuous separation of the plastic components from the suspension in the flow by influencing this flow is achieved at high throughput.

The aforementioned method is used to solve the above problem through the use of, if necessary, multi-stage fluidically arranged one behind the other Hydrocyclones with a cylindrical upper part through which each suspended Plastics are conveyed through, the ratio of the diameter of the Overflow to underflow nozzle between 1 and 4, preferably between 1 and 2.5, the Ratio of the length of the cylindrical upper part to its diameter between 1 and 10 lie, increasingly with decreasing density difference between the to be separated plastics and the carrier liquid, and that at a density plastics to be separated greater than the density of the Carrier liquid and in the case of plastics which - predominantly or exclusively consist of foils, the cone angle between 120 and 1800 and with a density of the to be separated Plastics partly larger, partly smaller than the density of the carrier liquid Cone angle is between 5 and 400.

The separation of solids from a suspension according to density with the help of hydrocyclones is for special cases in the processing of ores, Coals and salts are known (DE-OS 26 12 874) .1 There are also processes for fractionation of suspended solids by means of hydrocyclones, in which the fraction nation through a height-controllable sludge filling in the area of the underflow nozzle is influenced (DE-OS 26 22 880). An application of this separation process for plastic mixtures However, it has so far been considered impossible by the professional world and therefore not examined. The small differences in density between the types of plastic and the great difference in the shape of the particles to be separated were considered insurmountable Considered obstacles, a separation of such a plastic mixture in the individual components in the highly turbulent centrifugal field of a hydrocyclone the previous practical experience as well as the theoretical ideas via the separation process taking place in the cyclone. For the separation of plastic particles with such small differences in density as they are in practice occur, was only used by the experts Swim-sink separation considered the only possible solution because it was believed that turbulent flows with the small differences in density of the plastics to be separated would only have an unfavorable effect on the separation process, while with the sink-float separators a laminar flow of the carrier liquid could be ensured.

Deviating from the above considerations, the experts could determine be made that with an appropriate design of the hydrocyclone as a function of the density difference between the plastics to be separated and / or the Carrier liquid surprisingly good results could be achieved, although for the separation of the different fractions of hydrocyclones of different forms according to the above are necessary.

The throughput achieved in the hydrocyclone can be related on the interface, compared to a static float-sink separator around the Factor 100 can be increased, with this result in a suitable for practice Pilot plant was identified.

The zydrocyclone (s) can thereby with a high throughput, 1 i.e. operated at a relatively high inlet speed, with a high Infeed speed has a beneficial effect on the separation of the film components of the plastic mixture affects.

The volume ratio of plastic in the suspensions is expedient set less than 1:20 to the carrier liquid.

Experience has shown that a higher concentration of the plastic lead to a deterioration in the separation results in the carrier liquid.

As with the well-known swim-sink separation, it is recommended also, when using hydrocyclones to reduce the carrier liquid to add a wetting agent to the interfacial tension when plastics are separated, which are difficult to wet by the carrier liquid.

When separating several plastic components from a carrier liquid one has the choice, either in the first stage of the separation the plastic with the lowest density or those with the highest density of the other plastic components to separate. Depending on the intended separation process, a carrier liquid must be used corresponding density can be selected in comparison to the plastic to be separated.

It is useful when separating several plastic components in series-connected hydrocyclones first the plastic of greater density, if it forms the larger proportion, it is separated and in the subsequent cyclones the plastics are deposited with decreasing density or the plastic first with the smaller density, if this is the largest Proportion forms, separates and in the subsequent cyclones the plastics with increasing Density are deposited. For example, if in the first stage polyvinyl chloride (in the following.

PVC called) as the largest proportion of a mixture of polyethylene (PE), polystyrene (PS) and PVC are to be separated, water can be used5 because PVC has a density of about 1.37 g / cm3 and thus has a higher density than water. The separation of the PVC from the other plastic components from the Suspension takes place according to the above explanations with the help of a hydrocyclone leaner Execution, i.e. a hydrocyclone, the cylindrical upper part of which is of great length compared to its diameter and has a cone angle between 120 to 1800. In comparison to the carrier liquid, it becomes more dense PVC discharged from the underflow nozzle, while the other plastic components be discharged with the carrier liquid through the overflow nozzle.

It is useful to separate plastic with a density above 1 g / cm3 as the carrier liquid water with an additive to increase the density, such as CaCl or NaCl, to be used and for the separation of plastics of a density smaller than 1 g / cm3 organic liquids or mixtures of water and organic To use liquids whose density is between the density of the plastics to be separated lies. The liquid liquids to be used must correspond to the respective densities of the separating plastics are adapted accordingly, the density difference between the plastics and / or the carrier liquid represents a measure of the separation effect and also determines which plastic is through the overflow or through the underflow the hydrocyclone is discharged.

In order to keep the need for carrier liquid as low as possible in the case of multi-stage separation, it is advisable to use the plastic particles discharged with the liquids, which are fed to the next stage, previously separated from the liquid, sprayed off and suspended with the carrier liquid of the next stage. The carrier liquid thus separated from the plastic particles can be recycled as well as the carrier liquid from the separated component of the Of course, plastics are recycled and used for the production of new suspensions is used.

The application of the method provided according to the invention has after to the experience. led to a separation of the various plastic components up to degrees of purity in the order of magnitude between 95 and gg, when separating of PVC can, if necessary, separate the individual PVC types through flotation as for other plastic components, post-cleaning is carried out by a Flotation is possible to further the purity of the separated plastics to increase and in this way to increase the range of edge uses.

The drawing gives an embodiment of the process scheme for the present invention as well as the schematic representation of the used Embodiments of the hydrocyclones in a separate representation again.

They show: FIG. 1 the process scheme, FIGS. 2 and 3 embodiments the hydrocyclones, which are denoted by 4 and 9 in the process diagram.

Refer to the process scheme and reproduced hydrocyclones on a system for separating a plastic mixture consisting of granules following composition: fraction 1: PVC 54.0% density = 1.38 g / cm3 fraction 2: PS 22.7 density = 1.03 g / cm3 Fraction 3: PE 23.3% density = 0.95 g / cm3.

The plastic mixture from the aforementioned three fractions is initially fed to a cutting mill 1 and there in plastic particles smaller than 4 mm maximum Chopped up diameter and possibly according to one not shown in the scheme Washing and sanitizing are supplied to a mixing container 2 in which a separating liquid with a density of 1.05 g / cm3 is introduced simultaneously, in one such an amount that to 1 part by volume of the plastic about 60 parts of the carrier liquid omitted. Water with an additive is used as the separating liquid for the above-mentioned fractions, because the density of the carrier liquid is noticeably greater than the density of the fraction 2 should be in order in the first separation stage that in the largest amount of the mixture to be able to separate the PVC contained with the required degree of purity. It is hence the water by adding salt to the aforementioned value of density 1.05 g / cm3, the density of the separating liquid being monitored and readjusted must become. Unless a particularly high degree of purity of the PVC to be separated is required However, it is also possible to use water without an additive to change the Use density of the carrier liquid.

The suspension created in the stirred tank 2 is pumped via the vortex pump 3 fed to the hydrocyclone 4, the dimensions and proportions of which from the Fig. 2 emerge.

It can be seen that the first stage hydrocyclone used is designed to separate the PVC slim conical, the cone angle only 8e and the ratio of the length of the cylindrical upper part to the diameter is 4.

In the hydrocyclone 4 there is a separation in such a way that by the overflow a part of the carrier liquid with the Frakticnen 2 and 3 and through The other part of the carrier liquid with fraction 1 is discharged into the underflow will.

The overflow fraction A reaching the dewatering screen 5, which is subsequently fed to the stirred tank 7 has the following composition: Fraction 2: PS 49.5% fraction 3: PE 50.5%.

The liquid draining from the dewatering screen is passed through the Line 15 together with the drain from the dewatering screen 6 for the underflow fraction returned to the stirred tank 2.

In the dewatering screen 5, the fractions 2 and 3 are sprayed to remove the residual salt from these fractions.

The end product is made from the dewatering screen 6 for the underflow fraction B obtained with the following composition: Fraction 1: PVC> 99.9% yield > 99.9.

Fraction 1 is also sprayed off in the dewatering screen 6 to to remove the salt residue.

The fractions 2 and 3 from the drainage screen 5 get into the Stirred container 7, in which they are filled with a carrier liquid with a density of 0.97 g / cm3, e.g. mixture of water and alcohol, can be suspended for the separation step. Here, too, has to be an ongoing one Leakage control and regulation take place. The suspension is fed to the hydrocyclone 9 via a free-flow centrifugal pump 8, which has the design and dimensions shown in FIG. 3. It deals This is a hydrocyclone with a flat bottom, in which the cone angle M is about 1700 amounts to. The ratio of the length of the cylindrical top of the hydrocyclone to its diameter is 8 in this example.

The overflow fraction passes from the hydrocyclone 9 into the dewatering screen 10. Fraction 3 falls as end product C in this dewatering screen the following composition: Fraction 3: PE 90.8% yield 94.4%.

The underflow fraction falls in the dewatering screen 11 with the end product D of the following composition: Fraction 2: PS 94.4% yield 90.3%.

To remove the separating liquid from fractions 2 and 3 you can these are also rinsed off in the drainage sieves 10 and 11. From the The carrier liquid separated there passes over dewatering screens 10 and 11 the line 16 back into the stirred tank 7.

The test data and flow rates are given in the table below shown.

Products C and D can, if necessary, be further processed in post-cleaning stages. mm g / cm³ bar m³ / h fraction 1 kg / h fraction 2 kg / h fraction 3 kg / h Zyklon- do du pF #P Vo Vu mo mu mo mu mo mu Type Level 1 17.5 10 1.05 1.9 4.1 0.6 - 30.48 12.84 - 13.12 - AK 1 Level 2 26 18 0.97 0.5 2.9 2.8 - - 1.25 11.59 12.39 0.74 BK 4 do = diameter of the cyclone overflow product B: PVC content 99.9% output: 99.9% du = diameter of the cyclone overflow product C: PE content 90.8% output: 94.4% vu, mo = volume resp. Mass flows in the upper reaches Product D: PS content 94.0% Yield: 90.3% Vu, mu = volume or mass flows in the lower reaches. Below, some more practical examples of experiments are given, which are listed again in a summary below.

1. Separation of the PVC component from a PE + PS and PVC mixture Task: 5 g / l each PE, PS and PVC granulate (grain size small 4 mm) Mixing ratio of the plastics: 1: 1 separation medium density: 1.05 g / cm3 cyclone: 50 mm; Length of the cylindrical part: 200 mm; Cone angle: 80; Overflow nozzle diameter: 17.3 mm; Underflow nozzle diameter: 10 mm.

A PVC product is obtained with a throughput of 5 m3 / h with a purity of greater than 99.9% in the lower reaches.

2. Separation of the PVC component from a PS-PVC mixture Task: 6 g / l each PS and PVC granulate (grain size small 4 mm) Separation medium density: 1.0 g / cm3 Cyclone: 50 mm; Length of the cylindrical part: 200 mm; Cone angle: 1700; overflow nozzle diameter: 1753 mm; Underflow nozzle diameter: 10 mm.

With a throughput of 2.3 m3 / h, the result is a PVC output of 98.8 with a grade of 97.3% and a PS yield of 96.8% with a grade of 98.6%.

3. Separation of a PE-PS mixture Task: each 5g / l PE and PS granulate (Grain size small 4 mm) separation medium density: 0.97 g / cm3 cyclone: 100 mm d; Length of cylindrical part: 800 mm; Cone angle: 1700; Overflow nozzle diameter: 26 mm; Underflow nozzle diameter: 18 mm; With a throughput of 5.7 m3 / h, the PS product has a content of 93.4% with an output of 90.2% and the PE product a content of 94.4 with a yield of 92.6%.

4. Separation of a PVC fraction from a mixture of PE (granules / foils), PS (granulate) and PVC (soft PVC granulate films) Task: 4 g / l each PE, PS soft PVC granulate (Particle size small 4 mm) per 2 g / l PE-PVC film (particle size small 4 mm) Separation medium density: 1.06 g / cm3 cyclone: 100 mm; Length of the cylindrical part: 600 mm; Cone angle: 140; Overflow nozzle diameter: 26 mm; Underflow nozzle diameter: 18.2 mm; At a Throughput of 9 m3 / h, a PVC product was obtained with a content of 99.9% with an output of 98.2%. The PVC content in the overflow is only 0.6.

Compilation of Examples 1 - 4 Plastic material ground to <4 mm When- underflow- overflow- volume- density Dmr. Cylinder Slim cone nozzle dia. Nozzle underflow overflow play faction faction m. thin. des length heit- angle overlap. Lower mated Product product Medium grade ant.heavy build U: UDL Lz / D do you do / you mm mm mm mm 1 PVC PE + PS 1: 1 1:66 1.05 50 200 4 8 ° 17.5 10 1.75 99.9 - - - granulated granulated 2 PVC PS 1: 1 1:82 1 50 200 4 170 ° 17.5 10 1.75 97.3 98.8 98.0 96.8 granulated granulated 3 PS PE 1: 1 1:99 0.97 100 800 8 170 ° 26 18 1.44 93.4 90.2 94.4 92.0 granulated granulated 4 PVC PS granul. 1: 1.67 1:74 1.06 100 600 6 14 ° 0 26 18 1.44 99.9 98.2 99.4 99.9 granulated + PE + Granulated foils + Foils

Claims (6)

Claims Process for separating mixtures of different plastic waste different density in their components for their recovery, in which the plastic waste in particles with a maximum of 20 mm, preferably less than 5 mm edge length or diameter crushed and, if necessary, washed and sanitized suspended in a carrier liquid are5 whose density differs from the density of the plastic to be separated or this is the same, g e k e n n -z e i c h n e t d u r c h the use of if necessary, with hydrocyclones arranged one behind the other in terms of flow technology cylindrical upper part through which the suspended plastics are conveyed be5 where the ratio of the diameter of the overflow nozzle to the underflow nozzle is between 1 and 4, preferably between 1 and 2.5, the ratio of the length of the cylindrical Upper part to its diameter between 1 and 10, and increasingly with decreasing density difference between the plastics to be separated and the carrier liquid, and that at a density of plastics to be separated greater than the density of the Carrier liquid and in the case of plastics, which predominantly or exclusively consist of Foils consist of a cone angle between 120 and 1800 and a density of Plastics to be separated partly larger, partly smaller than the Density of the carrier liquid the cone angle is between 5 and 40 °. 2. The method according to claim 1, d a d u r c h g e k e n n -z e i c h n e t that in the suspensions the volume ratio of plastic to the carrier liquid less than 1:20 is set. 3. Veffahren according to claim 1 or 2, d a d u r c h gek e n n z e I ne t that the carrier liquid to reduce the interfacial tension a wetting agent is added. 4. The method according to any one of the preceding claims, d a d u r c h e k e n n n n z e i n e t that in several hydrocyclones connected in series First of all, the plastic of greater density, if it forms the greater proportion of the amount5 separates and in the subsequent cyclones the plastics with decreasing density be deposited or the plastic with the lower density first, if this forms the largest proportion5 and is separated in the subsequent cyclones the plastics are deposited with increasing density. 5. The method according to claim 4, d a d u r c h g e k e n n -z e i c h n e t that for the separation of plastics with a density above 1 g / cm3 as Carrier liquid water, possibly with an addition to increase the Density like NaCl used, and for the separation of plastics of a density lower than 1 g / cm3 organic liquids or mixtures of water with organic Liquids are used. 6. The method according to any one of the preceding claims, d a d u r c h e k e n n n z e i c h n e t5 that in the case of multi-stage separation, those with the liquids discharged plastic particles, which are fed to the next stage 5 previously separated from the liquid, sprayed off and with the carrier liquid of the be suspended in the next stage.