EP1077747B1 - Method for the material decomposition of composites containing artificial resin - Google Patents

Abstract

The invention relates to a method for the material decomposition of composites containing artificial resin, characterized in that the high-molecular structure of the artificial resin component is broken down by a chemical reaction with hydroxides of the alkali metals at temperatures above 250 DEG C and possibly partly or fully reprocessed.

Description

INTRODUCTION

Around 1.5 million tonnes are currently falling in Germany every year Electronic waste, which is about 200,000 tons Printed circuit board scrap are included. PCBs belong due to their complex structure and the ones they contain Pollutants among the most problematic in terms of recycling technology Components of the electronic scrap, and the contained in them Recyclable materials are a scarcely developed resource. The common disposal methods such as landfill or Burns are extremely problematic because they are either toxic Heavy metals such as copper, tin or lead occur in the leachate or when burning because of the content of bromine Flame retardants both aggressive acids as well aromatic dioxins and furans can arise. For the Recovery of the metals from the PCB scrap according to the previously used methods, some of which are complex and environmentally problematic procedures necessary.

STATE OF THE ART

A circuit board is usually made up of numerous components equipped, of which particularly problematic such as batteries, Capacitors, rectifiers and mercury switches be removed before processing. This also happens with particularly valuable components such as gold-plated connector strips. The partial denaturation is environmentally friendly Utilization or disposal absolutely necessary, since All processes that have been carried out so far have at least a rough crushing is connected upstream. Otherwise it would become one Distribution of pollutants and recyclables, which come recovery is difficult as well as possible Pollutant release leads. The risk of one Pollutant emissions could only be reduced by: all process stages in hermetically sealed devices be carried out, which is of course expensive.

In terms of weight, the proportions of components and detached circuit board are approximately the same size (45%: 55%). It is advisable to separate all components from the circuit board beforehand, since the components contain about 95% of chromium and 85% of nickel and iron, while around 80% of tin, copper and lead can be found in the circuit board. As a rule, such complete dismantling is not yet carried out in practice, although the necessary methods are known (DE-PS 42 05 405,
DE-OS 41 31 620). Component-free printed circuit boards are therefore usually production waste.

A printed circuit board is mainly made of metal (30% by weight), glass fiber (50% by weight) and polymer resin (20% by weight), so far only the metals are considered as valuable materials. To regain them, they first need to be enriched and separated from the residues as much as possible become. There are several procedures for this, which also work together can be combined.

• Beim Standard-Mahlverfahren kann es durch thermische Belastungen zur Bildung von polybromierten aromatischen Dibenzodioxinen (PBDD) und polybromierten Dibenzofuranen (PBDF) aus dem Flammschutzmittel kommen.
• Beim Kryo-Mahlverfahren wird bei so tiefen Temperaturen gemahlen, daß das Material versprödet. Dabei wird die Bildung thermischer Abbauprodukte vermieden. Diesen Vorteilen stehen jedoch höhere Energiekosten gegenüber, wobei unerheblich ist, ob die Kühlung direkt, z.B. mit flüssigem Stickstoff, oder indirekt über eine Kältekaskade erfolgt.
• Durch teilweise Kühlung wird der Bereich zwischen Normal- und Kryoverfahren abgedeckt.
• Beim Ultraschall-Verfahren wird das Verbundmaterial mittels Ultraschall zertrümmert, wobei materialspezifische Korngrößenverteilungen auftreten. Dieses Verfahren ist sehr teuer, erlaubt jedoch die Isolierung von bis zu vier verschiedenen Metallfraktionen.

According to one mode of operation, the circuit board is mechanically roughly shredded (shredded) for better handling and freed from ferromagnetic parts by means of a magnetic separator. This is followed by fine grinding, which can be carried out in various ways:

• In the standard grinding process, thermal stress can lead to the formation of polybrominated aromatic dibenzodioxins (PBDD) and polybrominated dibenzofurans (PBDF) from the flame retardant.
• The cryogenic grinding process involves grinding at temperatures so low that the material becomes brittle. The formation of thermal degradation products is avoided. However, these advantages are offset by higher energy costs, it being irrelevant whether the cooling takes place directly, for example with liquid nitrogen, or indirectly via a cooling cascade.
• The area between normal and cryogenic processes is covered by partial cooling.
• In the ultrasound process, the composite material is broken up using ultrasound, with material-specific grain size distributions occurring. This method is very expensive, but allows the isolation of up to four different metal fractions.

• Nach einer anderen Arbeitsweise, dem Naßzerkleinerungs-Verfahren werden feuchte Leiterplatten gemahlen, wodurch sowohl das Mahlgut vor thermischer Belastung geschützt als auch eine Staubentwicklung vermieden wird. Die anschlies-sende Wertstofftrennung erfolgt gewöhnlich über ein flotationsähnliches Verfahren mit anschließender Trocknung.

After crushing, the components are separated according to density, grain size or magnetic or electrical properties. For this purpose screening and classifying systems as well as magnetic separators, eddy current separators and electrostatic separators are used. Loss of valuable materials cannot be prevented because the fine metal particles are distributed over all fractions. The heavy metal-containing dusts, which accumulate in considerable quantities, are particularly problematic, since they sometimes reach the lungs and cause health damage.

• According to a different method of working, the wet comminution process, moist printed circuit boards are ground, as a result of which both the ground material is protected from thermal stress and dust formation is avoided. The subsequent recycling is usually carried out using a flotation-like process followed by drying.

• Liegt der Edelmetallgehalt über 0,02 %, so lohnt sich die Aufarbeitung für Edelmetallscheideanstalten. Hierbei werden die Edelmetalle entweder mit einer schwach alkalischen Cyanidlösung ausgelaugt und anschließend reduktiv zurückgewonnen oder thermometallurgisch bei 1000-1200 °C im Schachtofen mit Blei extrahiert. Im Anschluß hieran wird das Blei im Treibofen als Bleiglätte wieder entfernt. Die Aufarbeitung erfolgt in beiden Fällen elektrolytisch, und die edelmetallfreien Rückstände werden an Kupferhütten weitergegeben.
• Liegt der Edelmetallgehalt unter 0,02 Gew.%, so wird das Material in die zweite Stufe des Kupferherstellungsprozesses eingeschleust. Hierbei wird das Rohkupfer in einem Drehrohrofen (Peirce Smith Konverter) unter Silikatzusatz vom Eisen befreit, wobei sich eine Eisensilikatschlacke bildet, welche andere Schwermetalle dauerhaft einschließt und als Baumaterial Verwendung findet (Kopfsteinpflaster) . Das Kupfer wird anschließend elektrolyrisch gereinigt, wobei sich die Edelmetalle im Anodenschlamm wiederfinden.

The metal-rich fraction is further processed by chemical or thermal means.

• If the precious metal content is above 0.02%, it is worthwhile to refurbish it for precious metal refineries. Here, the precious metals are either leached out with a weakly alkaline cyanide solution and then reductively recovered, or extracted with lead thermometallurgically at 1000-1200 ° C in a shaft furnace. Following this, the lead is removed again in the blowing furnace as a lead smoothness. In both cases, they are processed electrolytically and the residues free of precious metals are passed on to copper smelters.
• If the precious metal content is below 0.02% by weight, the material is introduced into the second stage of the copper production process. Here, the raw copper is freed of iron in a rotary tube furnace (Peirce Smith converter) with the addition of silicate, forming an iron silicate slag which permanently encloses other heavy metals and is used as a building material (cobblestones). The copper is then cleaned electrolytically, whereby the precious metals are found in the anode sludge.

Chemical processing by solvolysis of the polymer has so far failed due to the long response times and the high response times Cost of the procedure, however, is both more concentrated Nitric acid at room temperature as well as with suitable ones Solvents are possible at higher temperatures in the autoclave.

All the physical methods mentioned have the same general conflicting goals. For one thing, the material has to be very be finely crushed to the individual components to be able to separate from each other; but the finer the powder its separation becomes more difficult because of surface effects level the material differences. On the other hand the purity of a fraction is inevitably at the expense of Yield. Another problem is that the metal arms Group disposed of together with the dust fraction must be included and comprise more than 2/3 of the total. this happens usually by dumping in a normal landfill, though their powder form and the remaining heavy metal pollution actually a disposal in a hazardous waste landfill or required by a special waste incineration plant do.

In all of the processing procedures mentioned, the Contamination of the metal fraction with polymer and glass This represents a problem. This leads to a complex digestion of the material necessary before the metal is electrolytically cleaned can be. The metal content also prevents the residual fraction their further use or their disposal difficult.

US Pat. No. 5,580,905 describes a method for hydrolytic Cleavage of polyesters, namely polyalkylene terephthalates using caustic solutions of alkali hydroxides, in which the mixture is heated and the polyester to underlying salt and polyol is broken down. The reaction always takes place at temperatures up to the boiling point of the Polyols, so up to about 200 ° C to evaporate and cut off. The use described in column 6 / 30-32 of powdery or melted hydroxides is related to see with the overall disclosure of the aforementioned U.S. PS namely that the required directly from this in the reaction mixture Solutions of the alkali metal hydroxides are formed and that in such Working at temperatures at which the polyol will not decompose can be evaporated and distilled off. This in Columns 4 / 7-11 also described later heating up clearly higher temperatures clearly do not apply more on the pulping of the polyester, but thermal decomposition of contaminants under conditions where the alkali terephthalate is still stable.

Furthermore, DE-OS 4 001 897 describes a method for Dissolution of circuit boards (printed circuit boards) known, in which this with the exclusion of oxygen at temperatures above 400 ° C introduced into a melt of alkali hydroxide and alkali oxide become. By giving up oxygen, the alkali oxide converted into peroxide, which is then converted into the Melt diffuses and oxidizable components such as carbon or hydrogen-containing compounds from the boards breaks down. The melt of alkali hydroxide and alkali oxide used as a matrix for the oxidation in this mode of operation (Column 1 / 25-32) and prevents the occurrence of toxic gases, how they would be created by combustion. As in column 1 / 29-34 is a raw material recovery and Can not be used for the synthetic resin or for the glass fibers.

INVENTION

The object of the invention is now to develop a method that the material bond between metal, glass and Polymer dissolves. By isolating largely pure Metal, glass and polymer fractions are said to be further processed and thus a substantial reduction or one largely avoidance of residual fractions to be disposed of become.

The invention now relates to a method for material Digestion of composite materials containing synthetic resin, in which the high molecular structure of the synthetic resin chemical reaction in melts of alkali metal hydroxides is broken down at temperatures of 250 ° to 370 ° C.

The hydroxides of the alkali metals are preferred NaOH or KOH and particularly preferably mixtures of NaOH and KOH. In such mixtures the proportion is: Potassium hydroxide for example 3 to 60% by weight, preferably 5 up to 20% by weight - the relatively small amount of potassium hydroxide is also due to the higher price Substance-related.

The reaction temperatures are generally in the range between 260 ° and 370 ° C, preferably in the range between 280 ° and 370 ° C and particularly preferably in the range between 300 and 350 ° C. The choice of the most suitable temperature depends naturally on the type and composition of the starting materials from, it should be borne in mind that at higher temperatures both the speed of reaction and the danger the thermal formation of unwanted degradation products increased becomes. In general, can also within the above Temperature ranges when using potassium hydroxide work at a lower temperature than at of sodium hydroxide, and when using mixtures of Sodium and potassium hydroxide at even lower temperatures.

The reaction can be carried out using reaction aids are supported, which the wettability of the Improve the composite material with alkali metal hydroxides, lower or lower the melting point of the alkali metal hydroxides the reaction conditions a solvent or swelling power for the Have synthetic resin or its degradation products.

As a reaction aid, the wettability of the composite improve, come for example with the Reaction temperatures resistant surfactants into consideration. Such, which lower the melting point of the alkali metal hydroxides e.g. B. inorganic salts of alkali, alkaline earth or earth metals or of metals of the fourth group of the periodic Systems or of metals of subgroups with strong or weak inorganic acids. The use of salts from Metals already contained in the raw materials can also support the reaction. This also has the advantage that no foreign elements in the system be introduced. As a reaction aid, the one Dissolving or swelling capacity for the synthetic resin or its degradation products own, come z. B. oligomeric fragments or Base body of the synthetic resin into consideration under the reaction conditions are stable. In the event of digestion come from starting materials containing epoxy resin, for example the phenolic bases bisphenol A and F (4,4 ' Diphenylol-2,2-propane or -methane) into consideration.

The synthetic resins are networked or uncrosslinked Polymers that are chemically cleavable in the main chain contain functional groups, such as polyesters, polyamides, Polyethers, polyurethanes, but preferably polyimides such as Polyphthalimides and poly-bimalinimides, polyaramides and polycyanate esters, but especially epoxy resins. These consist of usually from condensation products of bisphenols, such as Bisphenol A and bisphenol F, and epichlorohydrin. This list is to be understood as exemplary and not restrictive. Restrictions result from the type of chemical Disclosure and are obvious to the expert.

The amount of alkali metal hydroxide used for digestion can be varied within wide limits. Of course, the in the amount applied in practice must be at least sufficient to to ensure that the procedure is carried out. For example but 50% by weight, based on the synthetic resin content, is sufficient out. But is useful for easier handling a significantly larger amount of alkali metal hydroxide is used.

Since the procedure is very simple, it can be easily applied to others Composites are transferred. Particularly advantageous is the application of the process to metallic components containing composite materials common in electrical engineering, such as, for example, but not exclusively in printed circuit boards, Components or production waste during manufacture of printed circuit boards and components. Under Components are understood to mean in particular all components, that are used or used on printed circuit boards can, such as processors, memory chips, resistors and capacitors. This list is exemplary and not restrictive to understand. It makes sense here, but not necessary that the printed circuit boards and those on them Components separated before the reaction and possibly completely or partially worked up separately, which according to usual Procedure can happen. The separation can e.g. B. after chemical (tin / lead stripping), thermal (desoldering) and mechanical ("planing") processes take place.

For shredding composite materials such as printed circuit boards commercially available shredder systems can be used. There No fine grinding is necessary on these Sub-process made no high demands. The maximum tolerable For the person skilled in the art, the piece size results from the Procedural requirements of the subsequent stages.

In the dry shredding of the composite materials according to As is known, the prior art also produces dust-like ones Shares that are separated and disposed of as filter dust. The method according to the invention now has the advantage that such dusts by themselves or in combination with the comminuted reaction material to be subjected to the digestion can. It is a particular advantage of the invention that it is also suitable for processing such dusts, which contain flame retardants and / or metals as they do especially when shredding in electrical engineering usual composite materials.

For the chemical degradation of the synthetic resin, commercially available Reactors are used. This is in essential to stirred tanks and stirred tank cascades discontinuous, or around extruders and extruder cascades, e.g. a twin-screw extruder with continuous operation. The main advantage of the extruder lies in the short and defined response time. The danger of education thermal degradation products (dioxins and charring) therefore much less than when using a stirred tank. On the other hand there are long dwell times with an extruder not or only through complex extruder cascades realize. Experiments gave reaction times (Examples 1 to 3), which can be achieved with an extruder. There the cleaning of the reaction chamber in the extruder is also easier and no longer necessary with continuous operation is, the extrusion process is preferred, due to the better mixing of the twin-screw extruders in particular suitable is.

To recycle the components of the composite materials , they must be separated from each other after the digestion has taken place be what can be done in a conventional manner, e.g. B. after dry (windsifting / electrostatics) or wet (Flotation) process. In both cases, the use is more commercially available Investments possible. The advantage of dry processes consists mainly in lower water and energy consumption, while in the wet process the emission of Dusting is easier to avoid. For the separation of the Degradation products of synthetic resin and the recovery of excess Reagent are extraction processes with organic and aqueous solvents are preferred. Here, too, commercially available Attachments are used. Choosing suitable ones Extraction method and extractant is for the expert possible without difficulty.

EXAMPLES 1 TO 3

A bare, i.e. i. free of components FR-4 class epoxy-based circuit board laminate, i.e. i. a flame retardant product, was roughly crushed, the resulting fragments being a size of 20x20 mm with a thickness of 1.6 mm. The crushed Laminate was made with the same weight percentage Added alkali hydroxide and in a tempered metal bath implemented. According to Example 1 was with NaOH at 340 ° C, according to Example 2 with KOH at 320 ° C and according to Example 3 with a Mixture of equal parts by weight of NaOH and KOH at 300 ° C implemented. The reaction was in less than 5 minutes each finished with gas evolution. The resulting gas could be used as Water to be condensed. After the reaction was over Cooled reaction mixture and washed with cold water, until the wash water was about neutral. After separating the dismantled Polymers and subsequent drying made metal and glass fraction are simply separated from one another.

Claims (10)

1. A method of material decomposition of composites containing synthetic resin, characterised in that the high-molecular structure of the synthetic-resin fraction is broken down by chemical reaction with hydroxides of the alkali metals at temperatures of 250 ° to 370 °C, advantageously at temperatures between 260 ° and 370 °C, preferably in the range between 280 ° and 370 °C, especially preferably in the range between 300 ° and 350 °C.
2. A method according to Claim 1,
   characterised in that NaOH or KOH, but preferably mixtures of NaOH and KOH, are used as an alkali hydroxide.
3. A method according to Claim 1 or 2,
   characterised in that reaction promoters are used which improve the wettability of the composite by alkali hydroxides, lower the melting point of alkali hydroxides, or under the reaction conditions possess an ability to dissolve the synthetic resin or its breakdown products.
4. A method according to one or more of Claims 1-3, characterised in that the synthetic resins are cross-linked or non-cross-linked polymers containing chemically cleavable functional groups in the main chain, such as polyesters, polyamides, polyethers, polyurethanes, preferably polyimides, polyaramides and polycyanate esters, and in particular epoxy resins.
5. A method according to one or more of Claims 1 to 4, characterised in that the composite contains metallic components.
6. A method according to one or more of Claims 1 to 5, characterised in that the starting material is a composite commonly used in electrical engineering and consists in particular of printed circuit boards, components or production waste from the manufacture of printed circuit boards or components, the printed circuit boards and the components located thereon preferably being separated prior to the reaction.
7. A method according to Claim 6,
   characterised in that the starting material consists of or contains dusts resulting from break-up, in particular ones containing flameproofing agents and/or metals.
8. A method according to one or more of Claims 1 to 7, characterised in that the reaction is performed discontinuously in a stirred-tank reactor, preferably in a series of stirred-tank reactors, or continuously in an extruder or a series of extruders, preferably in a twinscrew extruder.
9. A method according to one or more of Claims 1 to 8, characterised in that the alkali hydroxide amounts to at least 50% by weight, relative to the proportion of synthetic resin.
10. Another embodiment of the method according to one or more of Claims 1 to 9, characterised in that the constituents of the composites are separated from on another after the reaction and, if necessary, partially or wholly worked up.