DE4329434A1 - Process for reprocessing plastics waste or plastics waste mixtures for raw-material recycling - Google Patents

Abstract

Previous processes for reprocessing produce plastics waste products which, owing to their extremely varied molecular weight distribution, can be separated and mixed only inadequately during admixing with petroleum intermediates and cause disturbances and irregularities in further processing. The object was therefore to develop a process for reducing the molecular weight of plastics waste or plastics waste mixtures in which products are produced which result in stable mixtures during admixing with petroleum intermediates. According to the invention, the reprocessing of the plastics waste or plastics waste mixtures is performed by means of extruders having a progressive temperature profile over 2/3 and a degressive temperature profile over 1/3 of the effective screw length of the extruder. The melt itself and the molecular weight are made more uniform by means of downstream static mixers having a graduated temperature profile. The process unit for reprocessing may be integrated in the refinery units (cracking, hydrogenation, gassification, visbreaking), or be installed externally, the plastics waste to be treated then being incorporated in the refinery flow by means of a bypass device.

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 due to their together setting and their degree of damage a material Withdrawing re-use, make it increasingly scarce Landfill opportunities pose a serious problem, so a substance Liche use of the damaged plastics must be done. It it is known that plastics (mainly Carbon and hydrogen) have a high calorific value and are considered petroleum-based finishing products.

For this reason, Alt has been proposed several times substances, preferably polyolefins, analogous to petroleum to Ge use of hydrocarbons (e.g. DD-PS 2 00 891). The old plastics are used in liquid hydrocarbons dissolved and the resulting mineral oil-like pump capable solutions in existing oil processing plants feeds or used directly as heating oil. The disadvantage is that one which are contaminated (dirt, metals, other inert substances ten) exempt, but the molar mass unchanged old plastics can only add in very small quantities, otherwise the viscos activity increases inadmissibly. If you want to improve the economy, you have to to significantly increase the proportion of used plastics added.

To solve this problem, methods for reducing the Molar mass proposed (e.g. H. Hammer and G. Rauser, Hydrie Rende liquefaction of plastic waste, lecture on German Industry forum for technologists, 03. and 04.12.92 - conference proceedings DIF 21/28/03 or G. Menges et al. a. DE-OS 40 17 089).

The 100% use of waste plastics according to DE-OS 40 17 089 analogous to the known processes of petroleum processing (Hydrie gassing, gasification etc.) fails due to economy and the 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-OS 40 19 880 describes a process 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 the additional patent DE-OS 40 38 897 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 was accomplished through a process for reprocessing old plastics or plastic mixtures with the introduction of Shear and elevated temperatures using an extruder where when no reactive gases are added, solved by inventing according to the waste plastics or mixtures of waste plastics Feeding into the extruder at the beginning liquefied under shear and then be dismantled, taking 2/3 of the extruder length a progressive temperature profile up to max. 475 ° C and on the remaining 1/3 extruder length a degressive temperature profile from 475 to max. 380 ° C is set, and then the old art melt passes through at least two static mixers, in which have a downgraded temperature profile with steps of 10 to 50 K is set for each static mixer. When used The use of two static mixers is the temperature level at 20 to 50 K, preferably at 20 to 30 K, each static Mixer.

It has been shown that, depending on the number n, the sta tables mixers the gradation of the temperature ranges into small ren areas, but which should be at least 10 K, advantageous is imprisoned. It has also proven to be particularly advantageous sen if the number m of deflections of the polymer melt per sta table mixer is 4.

The processing of the old plastics or old according to the invention plastic mixtures are either integrated into a refinery, the product stream leaving the static mixers as Bypass is mixed into the main stream of petroleum treatment, or installed externally, the product obtained in approved Neter form, preferably as granules, packaged and over a melting unit as a bypass in the refining stream will work.  

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. A process for the preparation of old plastics or mixtures of old plastics for the raw material recycling with introduction of shear and elevated temperatures by means of an extruder, whereby no reactive gases are added, as characterized in that the old plastics or mixtures of old plastics after being drawn into the extruder at the beginning liquefied under shear and then degraded by a progressive temperature profile up to max. 475 ° C and on the remaining 1/3 of the extruder a degressive temperature profile from 475 to max. 380 ° C is set, and then the plastic melt passes through at least two static mixers, in which a temperature profile graded downwards 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 n of static mixers the temperature levels per mixer are reduced to a minimum of 10 K. 4. The method according to claims 1 to 3, characterized in that the number m of deflections per static mixer  4 lies.