WO2000003764A1

WO2000003764A1 - Method for the material decomposition of composites containing artificial resin

Info

Publication number: WO2000003764A1
Application number: PCT/EP1998/004467
Authority: WO
Inventors: Frank Detlef
Original assignee: Frank Detlef
Priority date: 1998-07-17
Filing date: 1998-07-17
Publication date: 2000-01-27
Also published as: JP2002520196A; DE59802480D1; AU8976798A; ATE210482T1; EP1077747A1; EP1077747B1

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 °C and possibly partly or fully reprocessed.

Description

Process for the material digestion of composite materials containing synthetic resin

Description

INTRODUCTION

Around 1.5 million tons of electronic waste are currently generated in Germany every year, which includes around 200,000 tons of printed circuit board scrap. Due to their complex structure and the pollutants they contain, printed circuit boards are among the most problematic components of electronic waste in terms of recycling technology, and the valuable materials they contain form a resource that has hardly been developed yet. The common disposal methods such as landfilling or incineration are extremely problematic, since either toxic heavy metals such as copper, tin or lead occur in the leachate or because of the content of bromine-containing flame retardants, both aggressive acids and aromatic dioxins and furans can be generated during incineration. For the recovery of the metals from the printed circuit board scrap, the previously used methods sometimes require complex and environmentally problematic processes.

STATE OF THE ART

A printed circuit board is usually equipped with numerous components, from which particularly problematic ones such as batteries, capacitors, rectifiers and mercury switches are removed before refurbishment. This also happens with particularly valuable components such as gold-plated connector strips. The partial denitrification is absolutely necessary for an environmentally compatible recycling or disposal, since at least one coarse shredder is connected upstream in all processes that have been carried out to date. Otherwise it would ner distribution of pollutants and recyclables, which both makes recovery difficult and possible. Chen pollutant release leads. The risk of pollutant emissions could only be reduced by carrying out all process stages in hermetically sealed devices, which is of course expensive.

In terms of weight, the proportions of components and dismantled circuit board are roughly 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 denatured printed circuit board mainly consists of metal (30% by weight), glass fiber (50% by weight) and polymer resin (20% by weight), so far only the metals have been considered as valuable materials. To recover them, they first have to be enriched and separated from the residues as much as possible. There are several methods for this, which can also be combined with one another.

According to one method 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 loads 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, and it is 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 by means of ultrasound, whereby material-specific grain size distributions occur. This method is very expensive, but allows the isolation of up to four different metal fractions.

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

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 because they sometimes reach the lungs and cause health damage.

According to another method of working, the wet comminution process, moist printed circuit boards are ground, which both protects the regrind from thermal stress and avoids dust formation. The subsequent recycling is usually carried out using a flotation-like process followed by drying.

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. Hιerb.eι the precious metals are either leached out with a weakly alkaline cyanide solution and then recovered reductively or thermometallurgically at 1000-

1200 ° C extracted in the shaft furnace with lead. Following this, the lead is removed again in the blowing furnace as a lead smooth. The processing takes place electrolytically in both cases, and the residues free of precious metals are passed on to copper smelters.

If the precious metal content is less than 0.02% by weight, the material is introduced into the second stage of the copper production process. Here, the raw copper is removed from the 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 (headstemoflaster). The copper is then cleaned electrolytically, the precious metals being found in the anode sludge.

The chemical workup by solvolysis of the polymer has so far failed due to the long reaction times and the high costs of the process, but is possible both with concentrated nitric acid at room temperature and with suitable solvents at higher temperatures in the autoclave.

All of the physical processes mentioned have the same general conflicting objectives. On the one hand, the material must be crushed very finely in order to be able to separate the individual components; however, the finer the powder becomes, the more difficult it becomes to separate, since surface effects level out the material differences. On the other hand, the purity of a fraction inevitably affects the yield. Another problem is that the low metal fraction has to be disposed of together with the dust fraction and comprises more than 2/3 of the total. This is usually done by depositing in a normal depot never, although their powder form and the remaining heavy metal contamination actually make disposal at a special, waste landfill or through a special waste incineration plant necessary.

Contamination of the metal fraction with polymer and glass poses a problem in all of the workup processes mentioned. As a result, a complex digestion of the material is necessary before the metal can be cleaned electrolytically. In addition, the metal content of the residual fraction prevents its further use or complicates its disposal.

US Pat. No. 5,580,905 describes a process for the hydrolytic cleavage of polyesters, specifically polyalkylene terephthalates by means of caustic solutions of alkali metal hydroxides, in which the mixture is heated and the polyester is broken down into the underlying salt and polyol. The reaction basically takes place at temperatures up to the boiling point of the polyol, ie up to approx. 200 ° C, in order to evaporate and separate it. The use of powdery or molten hydroxides described in column 6 / 30-32 is to be seen in connection with the overall disclosure of the US patent mentioned, namely that the required solutions of the alkali metal hydroxides are formed therefrom directly in the reaction mixture and that it is necessary to work at such temperatures , in which the polyol can be evaporated without being decomposed and distilled off. The subsequent heating to significantly higher temperatures also described in column 4 / 7-11 clearly no longer relates to the material pulping of the polyester, but to the thermal decomposition of impurities under conditions in which the alkali terephthalate is still stable.

Furthermore, DE-OS 4 001 897 discloses a process for dissolving printed circuit boards (printed circuit boards), in which these are introduced into a melt of alkali hydroxide and alkali oxide with the exclusion of oxygen at temperatures above 400 ° C. By adding oxygen, the alkali oxide is converted into peroxide, which is then converted into the Melt diffused and degrades oxidizable components such as carbon fabric or hydrogen-containing compounds from the boards ^{^.} The melt of alkali hydroxide and alkali oxide is used as a matrix for the oxidation in this working method (column 1 / 25-32) and prevents the occurrence of toxic gases, which would be generated by combustion. As disclosed in column 1 / 29-34, raw material recovery and use is neither possible for the synthetic resin nor for the glass fibers.

INVENTION

The object of the invention is now to develop a method that dissolves the material bond between metal, glass and polymer. By isolating largely pure

Metal, glass and polymer fractions to processing their further on ^¬ and thus a significant reduction or substantial avoidance be allowed to be disposed of residual fractions.

The invention now relates to a process for the material digestion of composite materials containing synthetic resin, in which the high molecular structure of the synthetic resin is broken down by chemical reaction in melts of alkali metal hydroxides at temperatures above 250.degree.

The hydroxides of the alkali metals are preferably NaOH or KOH and particularly preferably mixtures of NaOH and KOH. In such mixtures, the proportion of potassium hydroxide is, for example, 3 to 60% by weight, preferably 5 to 20% by weight. The relatively small amount of potassium hydroxide is partly due to the higher price of this substance.

The reaction temperatures are generally in the range between 260 and 400 ° 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, whereby it should be borne in mind that at higher temperatures both the reaction rate and the risk of thermal formation of undesired degradation products are increased. In general, it is also possible to work at a lower temperature when using potassium hydroxide than when using sodium hydroxide, and when using mixtures of sodium and potassium hydroxide at even lower temperatures.

The reaction can be supported by the use of reaction auxiliaries which improve the wettability of the composite material by alkali metal hydroxides, lower the melting point of the alkali metal hydroxides or, under the reaction conditions, have a solvent or swelling capacity for the synthetic resin or its degradation products.

Reaction aids that improve the wettability of the composite material include, for example, the

Reaction temperatures resistant surfactants into consideration. Those that lower the melting point of the alkali metal hydroxides are e.g. B. inorganic salts of alkali, alkaline earth or earth metals or of metals of the fourth group of the periodic table or of metals of the subgroups with strong or weak inorganic acids. The use of salts of metals that are already contained in the starting materials can also support the reaction. This also has the advantage that no foreign elements are introduced into the system. As a reaction aid, the one

Solvent or swelling capacity for the synthetic resin or its degradation products come, for. B. oligomeric fragments or base of the synthetic resin into consideration, which are stable under the reaction conditions. For the digestion of epoxy resin-containing starting materials, for example, the phenolic bases bisphenol A and F (4,4 'diphenylol-2, 2-propane or -methane) come into consideration. The synthetic resins are crosslinked or uncrosslinked polymers which contain chemically cleavable functional groups in the main chain, such as polyesters, polyamides, polyethers, polyurethanes, but preferably polyimides such as polyphthalimides and polybimalinimides, polyaramides and polycyanate esters, in particular but epoxy resins. These usually consist of condensation products of bisphenols, such as bisphenol A and bisphenol F, and epichlorohydrin. This list is exemplary and should not be understood as restrictive. Restrictions result from the type of chemical digestion and are obvious to the person skilled in the art.

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

Because the process is very simple, it can easily be transferred to other composites. It is particularly advantageous to apply the method to composite materials containing metallic components that are common in electrical engineering, such as, for example, but not exclusively, in printed circuit boards, components or production waste in the production of printed circuit boards and components. Components are understood to mean in particular all components that are or can be used on printed circuit boards, such as processors, memory chips, resistors and capacitors. This list is to be understood as an example and not as restrictive. It is useful, but not necessary, that the printed circuit boards and the components thereon are separated before the reaction and, if necessary, completely or partially worked up separately, which can be done by customary methods. The separation can e.g. B. by chemical (tin / lead stripping), thermal (desoldering) and mechanical ("planing") procedures. Standard shredder systems can be used to shred composite materials such as printed circuit boards. Since no fine comminution is necessary, no high demands are placed on this sub-process. For the person skilled in the art, the maximum tolerable piece size results from the process requirements of the subsequent stages.

As is known, the dry comminution of the composite materials according to the prior art also produces dust-like fractions which are separated off and disposed of as filter dusts. The process according to the invention now has the advantage that such dusts can be subjected to digestion by themselves or in combination with the comminuted reaction material. It is a particular advantage of the invention that it is also suitable for working up such dusts which contain flame retardants and / or metals such as are obtained in particular in the comminution of composite materials customary in electrical engineering.

Commercially available reactors can be used for the chemical degradation of the synthetic resin. These are essentially stirred tanks and stirred tank cascades in the case of discontinuous operation, or extruders and extruder cascades, for example a twin-screw extruder in the case of continuous operation. The main advantage of the extruder is the short and defined reaction time. The risk of the formation of thermal degradation products (dioxins and charring) is therefore significantly lower than when using a stirred tank. On the other hand, long dwell times with an extruder cannot be achieved or only with complex extruder cascades. Experiments have shown reaction times (Examples 1 to 3) which can be achieved with an extruder. Since the cleaning of the reaction chamber in the extruder is also simpler and is no longer necessary in the case of continuous operation, the extrusion process is preferred, the twin-screw extruder being particularly suitable on account of the better mixing. In order to be able to recycle the constituents of the composite materials, they have to be "separated" from one another after the digestion has taken place, which can be done in the usual way, for example by dry (air sifting / electrostatics) or wet (flotation) methods. In both cases The advantage of the dry process is above all the lower water and energy consumption, while the wet process makes it easier to avoid the emission of dusts. Extraction processes are used to separate the degradation products of the synthetic resin and to recover excess reagent with organic and aqueous solvents. Commercial systems can also be used here. The selection of suitable extraction methods and extraction agents is possible without difficulty for the person skilled in the art.

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 having a size of 20x20 mm and a thickness of 1.6 mm. The shredded laminate was mixed with the same proportion by weight of alkali hydroxide and reacted in a tempered metal bath. According to Example 1, the reaction was carried out 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. The reaction was complete in less than 5 minutes with evolution of gas. The resulting gas could be condensed as water. After the reaction was complete, the reaction mixture was cooled and washed with cold water until the wash water was approximately neutral. After separating the degraded polymer and then drying it, the metal and glass fraction could easily be separated from one another.

Claims

P a t e n t a n s r u c h e

Process for the material digestion of composite materials containing synthetic resin, characterized in that the high molecular structure of the synthetic resin portion by chemical reaction with hydroxides of the alkali metals at temperatures above 250 ° C, advantageously at temperatures between 260 and 400 ° C, preferably in the range between 280 and 370 ° C, particularly preferably in the range between 300 and 350 ° C.

The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that NaOH or KOH, but preferably mixtures of NaOH and KOH are used as the hydroxide of the alkali metals.

3. The method according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that reaction aids are used which improve the wettability of the composite material by alkali metal hydroxides, the melting point of

Lower alkali metal hydroxides or, under the reaction conditions, have a solvency for the synthetic resin or its degradation products.

4. The method according to one or more of claims 1-3, characterized in that the synthetic resins are crosslinked or uncrosslinked polymers which contain chemically cleavable functional groups in the main chain, such as polyesters, polyamides, polyethers, polyurethanes, preferably polyimides, polyaramides and polycyanate esters and especially epoxy resins.

5. The method according to one or more of claims 1-4, d a d u r c h g e k e n n z e i c h n e t that the composite material contains metallic components.

6. The method according to one or more of claims 1-5, characterized in that the starting material is a composite material customary in electrical engineering and in particular consists of printed circuit boards, components or production waste in the manufacture of printed circuit boards or components, preferably the printed circuit boards and those located thereon Components are separated before the reaction.

7. The method according to claim 6, d a d u r c h g e k e n n z e i c h n e t that the starting material consists of dusts resulting from the comminution or contains such, especially those containing flame retardants and / or metals.

8. The method according to one or more of claims 1-7, that the reaction is carried out batchwise in a stirred tank, preferably in a stirred tank cascade, or continuously in an extruder or an extruder cascade, preferably in a twin-screw extruder.

9. The method according to one or more of claims 1-8, d a d u r c h g e k e n n z e i c h n e t that the amount of alkali metal hydroxide is at least 50 wt.%, Based on the synthetic resin content.

10. A further embodiment of the method according to one or more of claims 1 to 9, that the components of the composite materials are separated from one another after the reaction and, if appropriate, are partially or completely worked up.