DE4329434C2 - Process for the processing of waste plastics or mixtures of waste plastics for raw material recycling - Google Patents

Description

Plastics are among the intelligent materials that stand out because of their flexibility and adaptability and not lastly due to their price-performance ratio on many Areas.

The so-called industrial waste that occurs during production batches, approach and bypass products, samples from continuous Process and analysis devices etc.) or processing (faulty batches, sprues, etc.) have been around for 20 years processed and used as a material.

Waste plastics from commercial use can usually be used if single or similar, and depending on the contact Return the degree of minimization to material recycling.

Waste plastics from household waste pose a problem fluctuating composition, different degrees of pollution and different levels of contamination and damage.

Some of these plastics can be made by different constructions horseback riding (swimming, sinking separation technique, Hydrocyclone, centrifuges etc.) separated according to their density and processed and used again in a manner typical of plastics. In usually this goes with a loss of properties in the Quality cascade and the use of such recyclates limited in quantity and property and only limited buildable.  

The mixed old plastics, which are due to their composition and their Withdrawing the degree of damage from material reuse is becoming increasingly scarce becoming landfill poses a serious problem, so that a material use of the damaged old plastics must take place. It is known that plastics due to their Structure (mainly carbon and hydrogen) have a high calorific value and as petroleum-based finishing products apply.

For this reason, it has already been proposed several times, preferably old substances Polyolefins, analogous to petroleum, for the production of hydrocarbons (e.g. DD- PS 2 00 891). The old plastics are dissolved in liquid hydrocarbons and the pumpable solutions obtained in this way into existing mineral oil-like solutions Petroleum processing systems fed in or used directly as heating oil. The disadvantage is that to get rid of impurities (dirt, metals, other inert substances), but in The molar mass of unchanged old plastics can only be added in very small quantities because otherwise the viscosity increases inadmissibly. If you want to improve the economy, you have to Increase the proportion of old plastics added.

Methods to reduce the molecular weight have been proposed to solve this problem (e.g. H. Hammer and G. Rauser, Hydrating Liquefaction of Plastic Waste, Lecture to the German Industry Forum for Technologists, 03. and 04.12.92 - conference volume DIF 21/28/03 or G. Menges et al. a. DE 40 17 089 A1).

It is also known that the chain degradation of plastics by adding catalysts (Oxygen, air, water, water vapor, peroxides, inorganic additives such as metals etc.) can accelerate.

Here, too, the temperature plays a crucial role because these radical reactions are strong are temperature dependent.

Such studies have been carried out by Menges and Lackner (Kunststoffe 82, 1992/2, 106- 109) on various new plastic materials and on model mixtures in one Twin screw extruder carried out by at a temperature of 400 ° C in about In the middle of the extruder barrel via an injection block oxygen or compressed air into the Melt were injected.

The 100% use of waste plastics according to DE 40 17 089 A1 analogous to the known ones Processes of petroleum processing (hydrogenation, gasification, etc.) fail at the Profitability and logistics, because such systems due to the extensive Peripheral systems (gas cleaning etc.) only at very high levels  location capacities work economically. They also have to reactive gases (O₂, H₂, water vapor) due to the fluctuations the input plastics are constantly readjusted, which the Process makes uneconomical or no syn thesegas supplies.

DE 40 19 880 A1 describes a method for gasifying art substances for the production of fuel gases have been described in which Appropriate plastics by treatment at elevated temperature Neten devices are liquefied so far that they burn rooms or reactor rooms can be injected. In the case, that with certain plastics, gasification after the extruder is not yet sufficient, the still fluid art substances according to DE 40 38 897 A1 not in one Combustion chamber or reactor injected, but in an upstream Gasification chamber, which is heated and in which the gasification follows.

However, it has been shown that ancient art treated in this way mixtures of substances due to their strongly fluctuating molecular weight weight distributions when adding to petroleum intermediates only insufficiently dissolved and mixed and it during the delivery and injection into the reactors are too irregular keiten is coming.

The task was therefore to develop a process for breaking down the moles mass of waste plastics or mixtures of waste plastics winding, in which products are obtained which are mixed lead to stable mixtures in petroleum intermediates.  

The task is carried out by a process for the recycling of waste plastics or Used plastic mixtures for raw material recycling using an extruder, without additives reactive gases, in which the waste plastics or mixtures of waste plastics move into the Extruder liquefied under shear and at temperatures in the range of 400 to 475 ° C are broken down, solved by according to the first 2/3 of the extruder length progressive temperature profile up to max. 475 ° C and on the remaining 1/3 extruder length degressive temperature profile from 475 to max. 380 ° C is set, and then the Used plastic melt passes through at least two static mixers, one down graduated temperature profile with levels from 10 to 50 K per static mixer is set. When using two static mixers, the temperature levels are 20 to 50 K, preferably at 20 to 30 K, per static mixer.

It has been shown that, depending on the number of static mixers, the gradation of the Temperature ranges in smaller areas, which should be at least 10 K, is advantageous. It has also proven to be particularly advantageous if the number of Deflections of the polymer melt in each static mixer is 4 or more.

The processing of the old plastics or old plastic mixtures according to the invention is either integrated into a refinery, the one leaving the static mixer Product stream is mixed as a bypass in the main stream of the crude oil treatment, or installed externally, the product obtained in a suitable form, preferably in the form of granules, assembled and incorporated into the refining stream as a bypass via a melting unit becomes.  

It is also possible after the preparation according to the invention of the old plastics or mixtures of old plastics the ones obtained Melt in a known manner directly or after a calming stretch filter to fine powdery mineral additives, pigments or discard unmelted shares. As waste plastics or plastic mixtures in the sense of the invention can after one or more uses in the commercial sector resulting products, such as B. Agricultural films, trans use port packaging, canisters, hollow bodies, bottles etc., or the household waste products, preferably the Floating fraction (products with a density <1 g / cm³). It is but also possible to manufacture products (batches, Approach and bypass products in the event of a change of type, samples from process and analyzers etc.) or processing (faulty batches, Injection molding sprue etc.). It is advisable the input products initially to a grain size of 3 to 8 mm bring to. Both single and double are used as extruders screw extruder, preferably co-rotating twin screws extruder, can be used, bring the appropriate shear forces and enable the degradation temperatures according to the invention.

The invention is illustrated by the following examples explained in more detail.

example 1

In a co-rotating twin screw extruder with one Screw diameter of 53 mm and an effective screw length L of 42D was removed from impurities and old polyethylene brought to a size of 3 to 8 mm siert.  

The temperature profile was set progressively and showed at 28D effective process length a value of 420 ° C, then a degressive temperature profile was set so that on A value of 380 ° C was present at the end of the extruder.

Two static mixers were attached to the extruder. In each static mixer the product was diverted four times. The tem temperature at the end of the first mixer was 330 ° C and at the end of the second mixer 300 ° C. The product was sold under a sub water granulation ready-made. Using gel permeation chro Matography (GPC) showed a molar inconsistency U = 5.1 determined.

The degraded polyethylene became 20% hydro gap paraffin mixed in the liquid state. The mix was stable, it came no settlements within the trial period. The Mixture was converted to ethylene, propylene and in a steam cracker Butadiene implemented.

Example 2

The procedure was analogous to Example 1. One was used Floating fraction (i.e. density <1 g / cm³) from the household waste container riding.

At 28D a temperature of 450 ° C was set and at the end of the extruder 380 ° C. 3 static mixers were used. The number of redirections per mixer was 4.

The temperatures were raised to 340 ° C at the respective mixer end, 320 ° C and 290 ° C set. The granules obtained had one Inconsistency of U = 3.0.  

A vacuum residue was added to 35% and at 450 ° C and 24 MPa hydrogenated in the presence of hydrogen. The Liquid product yields were 82 mol%.

Example 3

The procedure was analogous to Example 1 and 2. A polyolefin fraction from commercial plastic waste was ex truder dismantled. The product to be dismantled reached 28D a temperature of 475 ° C and was then at a Temperature of 380 ° C cooled.

There were three static mixers at the head of the extruder together with 12 mixing elements installed. The temperatures along the Mixer distances were 330 ° C, 290 ° C and 280 ° C.

The degraded plastic fraction had a very low Un uniformity of 2.5. The extrudate thus obtained was mixed with 5% by mass directly into the vacuum visbreaker residue of a shell gasification driven and there with oxygen and water to syn thesegas implemented.

Claims (4)

1.Process for the processing of waste plastics or mixtures of waste plastics for raw material recycling by means of an extruder, without the addition of reactive gases, in which the waste plastics or mixtures of waste plastics liquefy after being drawn into the extruder under shear and degraded at temperatures in the range from 400 to 475 ° C are characterized in that on the first 2/3 of the extruder length a progressive temperature profile up to max. 475 ° C and on the remaining 1/3 of the extruder length a degressive temperature profile from 475 to max. 380 ° C is set and then the waste plastic melt passes through at least two static mixers, in which a temperature profile stepped down is set with levels of 10 to 50 K per static mixer. 2. The method according to claim 1, characterized in that the Use of two static mixers grading the tem temperatures 20 to 50 K, preferably 20 to 30 K, depending on the stati the mixer. 3. The method according to claim 1, characterized in that with increasing number of static mixers the temperature levels per mixer are reduced to a minimum of 10 K. 4. The method according to any one of claims 1 to 3, characterized in that the number of deflections in each static mixer 4 or is more.