EP0302313A1 - Process and apparatus for treating objects with solvents in a closed vessel - Google Patents

Abstract

PCT No. PCT/EP88/00671 Sec. 371 Date Mar. 9, 1989 Sec. 102(e) Date Mar. 9, 1989 PCT Filed Jul. 21, 1988 PCT Pub. No. WO89/01057 PCT Pub. Date Feb. 9, 1989.In a method, especially for stripping enamel and removing coatings from objects, the advantages of a solvent treatment are to be retained, without having to put up with the disadvantages of contaminating the environment. This is accomplished essentially by using in a closed treating vessel a treating mixture with at least a preponderance of a solvent with a proportion of water in excess of that required for an azeotropic mixture and carrying out the treatment while boiling the treating mixture. After the treating mixture is removed from the vessel, any solvent components still present are distilled off azeotropically from the system with water and removed before the vessel is opened.

Description

The invention relates to a method and a device for treating objects in a closed container with solvent, the objects to be treated being treated at least temporarily by immersion in solvent and then sprayed off in a solvent-free area of the container.

DE-A-33 00 666 discloses a washing process for small parts, in which the small parts are passed through solvents in treatment baskets in a closed container and are sprayed off above the solvent level. This process is used as a washing process and has some advantages, but it is not suitable for stripping or stripping objects.

For stripping or stripping of objects to be treated, so-called cold stripping processes in large open tubs are known, which have the major disadvantage that they are harmful to health as a result of vapors occurring above and in the vicinity of plunge pools. In addition, adhering solvents can be released during removal. The solvents dripping and draining from the parts can enter the ground or groundwater long. In addition, methylene chloride evaporates very quickly and therefore also pollutes the air.

Otherwise, the solvent may carry over through the treated parts. The paint residues contain chlorine-containing solvents, which means expensive destruction. Only a limited use of additives, such as phenols, cresols or the like, is also possible for health and environmental reasons. With a degree of silting of the immersion baths of about 50%, the entire system must be destroyed or replaced. Due to the higher requirements for environmental compatibility, this known technology has been replaced by other processes.

For example, it is known to carry out pyrolysis by means of higher temperatures. For such pyrolysis, which can take place at temperatures around 400 ° C., natural restrictions on the objects to be treated, as far as their material is concerned, are self-evident. For example, no temperature-sensitive parts such as wood, plastic, hardened metals, thin sheets, light and non-ferrous metals, soldered parts, magnetized metals, etc. may be treated. In addition, halogen compounds can occur in the hot exhaust gases if, for example, polyvenyl chloride or chlorinated rubber is carbonized. These acidic gases can be neutralized in so-called afterwashers the. However, the combustion produces highly toxic dioxins (Seveso), which can then be found in the wash water or can be released into the environment via the fireplace.

Another technology is the cyrostatic paint stripping at extremely low temperatures of around -196 ° C in liquid nitrogen, which, however, involves a great deal of technical effort. The area of application is also restricted, particularly in the case of elastic and thin layers of lacquer. Unwanted tensions can also occur, particularly in the area of welding and soldering points.

Paint stripping by burning is no longer possible today for environmental reasons, otherwise it can only be used to a limited extent, if at all.

In addition to the treatments described above, so-called hot stripping in hot alkali solutions or acids, for example hot sulfuric acid, is also known. This treatment is dangerous, the baths are enriched with heavy metals, complexing agents, surfactants, so that there can ultimately be a pollution of the environment, especially of the waste water. But extremely aggressive, corrosive vapors also have a negative impact on the environment and personnel and must be recorded and neutralized in a complex manner. Furthermore, used pickling liquids have to be destroyed in a cost-intensive manner. The amount of waste thus increases considerably and puts a strain on the sewage treatment plants due to large amounts of salt.

The object of the invention is to provide a solution with which the disadvantages described above are avoided not only when stripping paint, but also during other stripping treatment of surfaces, in particular also solvents in the coating materials can be completely removed and kept in the treatment process, and materials can be easily disposed of and can be treated in an environmentally friendly manner.

• a) als Lösungsmittel wird nach Schließen des Behandlungs­behälters ein Behandlungsmittelgemisch mit wenigstens einem Hauptanteil an Lösungsmittel, wie Methylenchlo­rid, mit einem Überschußanteil an Wasser zum azeotropen Gemisch eingesetzt,
• b) das Behandlungsmittelgemisch wird auf Siedetemperatur des Gemisches erwärmt,
• c) nach Beendigung der Behandlungszeit wird das sich ab­setzende und sich ggf. kondensierende Lösungsmittel aus dem Behandlungsbehälter entfernt,
• d) Wasser wird im Behandlungsbehälter erhitzt und ver­dampft, wobei
• e) das an oder in den Beschichtungs- bzw. Lackrückständen und den zu behandelnden Gegenständen befindliche Lö­sungsmittel wird vor dem Öffnen des Behälters aus dem System mit Wasser azeotrop abdestilliert und entfernt.

This object is achieved according to the invention in that the process for stripping and stripping the objects is used and in this case additionally comprises at least the following process steps:

• a) after closing the treatment container, a treatment agent mixture with at least a major proportion of solvent, such as methylene chloride, with an excess proportion of water is used as solvent to form the azeotropic mixture,
• b) the treatment agent mixture is heated to the boiling point of the mixture,
• c) after the end of the treatment time, the settling and possibly condensing solvent becomes removed from the treatment tank,
• d) water is heated and evaporated in the treatment tank, whereby
• e) the solvent on or in the coating or lacquer residues and the objects to be treated is azeotropically distilled off and removed from the system with water before opening the container.

The process has considerable advantages over known processes. By using a treatment agent mixture of solvent and an excess proportion of water (azeotropic methylene chloride / water 98.5 to 1.5%, here for example 80 to 20%), the advantages of azeotropic distillation can be exploited, which are particularly important in the recovery of the solvent Meaning.

The closed circuit avoids polluting emissions such as pollution of air, soil and water. There is also no need for thermal removal of halogen coating materials, as a result of which there is no formation of dioxides, for example in the pyrolysis of PVC. The treatment in the boiling treatment agent mixture, which in the example of methylene chloride boils with water at 38.1 ° C., shortens the treatment times many times over, so that the throughput of such a treatment is also reduced System increased or the size can be reduced accordingly, the amount of substances to be used can be kept correspondingly low.

Another advantage is that the materials that have to be removed from the surface of the objects to be treated can be removed in comparatively large pieces, which are then e.g. are recyclable. A load on the treatment liquids by foreign substances, such as resins or the like, is thereby avoided or reduced over a long period of time, so that rare regeneration phases can be maintained.

In an embodiment, the invention provides that circulated water is used to remove the solvent from the system and from the coating or lacquer residues, at least some of this water having previously been used as part of the treatment agent mixture.

The water in the system can therefore be reused very often, which also leads to a very economical procedure.

One embodiment of the invention is that after complete removal of the solvent from the system by boiling and recondensing, the parts in the treatment be hosed and removed from the container and / or that the solvent-free residues are collected and recycled.

It is advantageous if only part of the treatment container is filled with solvent and the filling level of the solvent is kept at a distance from the cooling and condensing coils provided in the region of the container cover. This allows a gas space to be created which is also suitable for the treatment of objects whose treatment is to be carried out only by treatment agent vapors. The cooling and condensing coils in the area of the container lid can also prevent treatment vapors from escaping unintentionally when the container lid is open.

The invention also provides that the vapor phase of the solvent condenses in the upper region of the immersion tank and the condensate can be used as a spray. This has the advantage that the entire process, as far as the solvent is concerned, can be recycled, i.e. the risk of polluting the environment is avoided.

It has proven to be particularly expedient if additives are added to the spraying agent. These additives can be of very different types, they can be corrosives, chemicals for passivation, if with an acidic medium, for example in a medium containing formic acid, has been stripped, it can be oily and / or aqueous additives and the like. More.

In addition to the procedure described here, the invention can also be used in the same way, e.g. for degreasing surfaces with other solvents or treatment mixtures in the liquid or vapor phase. The expulsion of such solvents or treatment mixtures can then again be azeotropic, e.g. by boiling with water, for example: trichlorethylene with water (ratio 93.4% tri to 6.6% H₂O) or tetrachloroethene with water in a ratio of 87.1% tetrachloroethene to 15.9% water, here the principle the system displacement by the higher boiling substance is exploited in a completely closed procedure.

Basically, the environmentally harmful azeotrope component should be driven out in the system by the less or not at all polluting substance (here essentially H₂O).

In addition to the advantages described, the procedure according to the invention has additional advantages. For example the following:

Low operating costs, since only the low heating costs, in order to work with warm stripping agents and later to distill extractively, require energy. Thermal treatments require temperatures of approx. 400 ° C compared to 38.1 ° C or 100 °.

Since the stripping agents are only present in the system as an intermediate stage, as in most extractive processes, and are removed from them after the stripping process, they do not cause any additional waste problems. (Cold paint removers with a content of approx. 50% paint are often destroyed due to silting up, i.e. doubling and additional pollution of the waste with environmentally harmful additives).

The residues can often be reused in the recycling process for secondary coating processes because they have only been physically removed and have hardly changed chemically. (According to the law on waste prevention and reuse of raw materials.)

Due to the relatively low processing temperatures (long time at approx. 40 ° C during the stripping process and briefly up to a maximum of 100 ° C during the extractive phase (steam distillation)), hardly any Changes to the basic material. The thermal processes, such as high temperature, pyrolysis and molten salt, require temperatures of 400 ° C and above, treatment times of up to 15 hours and more, such as the discontinuous chamber process. This leads to structural changes in the base material, such as softening of hardened materials, e.g. spring steel, forged parts, such as transport and lifting chains, twisting and loss of stability of alloyed materials, such as light metals, deformation and deformation of thin, stamped, drawn or cast parts. No application is possible with organic materials. At low temperatures, for example when immersed in liquid nitrogen at -196 ° C, the crystal structures of the parts to be treated become brittle and change. The result is cracking until the solder or weld seams break off and material fatigue. A complex mechanical post-treatment by blasting with steel grit etc. is necessary if the surface is damaged.

The dampened aggressiveness enables small surface changes compared to many raw materials by using inhibitors in the acidic as well as in the alkaline range. Strongly caustic processes are often used to remove extremely resistant layers from sensitive base materials. (Hot concentrated sulfuric acid, hot caustic soda, etc.). This doesn't just mean Surface changes, but also complex neutralization in the aftertreatment (over-salting of the waste water).

The mechanical load on the parts is insignificant. High-pressure processes with a water jet of 800 bar only allow decoating of coarse parts, such as gratings or the like.

The gentle stripping does not affect the health of the staff, since the chemicals only come into contact with the parts to be stripped in the closed system. When opening, only stripped parts and water-wet residue are removed.

To achieve the object formulated above, the invention also provides a system with an immersion tank that can be at least partially filled with a solvent mixture, this system being characterized in that the immersion tank with a heating device in its lower region and with a cooling device in the region of the above Lid is equipped.

With the heating device, it becomes possible to keep the super-azeotropic solvent / water mixture at the boiling point of this mixture during the treatment process. The treatment process is complete and the solvent has been pumped out of the container. So ent neither water remaining in the container nor separately introduced water are heated, the solvent being expelled from the mixture and the coating materials first at the appropriate temperature of the azeotrope.

The cooling device in the area of the upper edge is able to condense the solvent vapors, so the solvent can be removed from the container. A further heating of the water via the heating device then ensures the evaporation of the water. The condensate or. Cooling device in the head region of the container can be used to return the water to other parts of the system, which means that all vaporizable components can be removed from the container before opening the lid.

The cooling device in the head area of the immersion tank also has the task of forming a type of vapor barrier when the tank is open, but if solvent residues, for whatever reason, should remain in the open tank, their vapors can then be condensed without causing it to environmental pollution.

In an embodiment, the invention provides that the immersion container, at least in its gas space, has a spray device for objects to be treated there de is equipped. This spraying device can be installed in a stationary manner, but it can also be a spraying lance or the like which can be operated by hand, of course both options can also be provided at the same time. The gas space is to be understood as both the space above a liquid level and the total space of the container when the treatment agent mixture has been pumped out.

As mentioned, the invention has the particular advantage of the completely closed mode of operation. For this purpose, it is provided in an embodiment that at least one collecting container for solvents, one collecting container for water and one collecting container for a further treatment agent, such as a neutralizing agent or the like, are assigned to the immersion container. It should be mentioned that of course several such containers can be provided for the corresponding substances. At least one of the collection containers for solvents can also be used as a collection container for the treatment agent mixture, i.e. e.g. for the mixture of methylene chloride with an excess of water based on the azeotropic mixture.

In order to prevent the danger of polluting the environment with even the smallest amounts of solvent vapors, it is provided in a further embodiment that the immersion tank has an activated carbon filter and / or a pressure compensation is provided. These system elements have the task of providing gas volume compensation when the container is closed and after flooding with the treatment agent mixture when the heating device begins to heat. The portion of the gas volume expanding over the treatment agent mixture is released into the environment via the activated carbon filter by increasing the volume compared to the gas space volume of the immersion tank, or it acts on the pressure compensation tank.

A simple further embodiment of the invention consists in that the cooling device is assigned a condensate collection channel with drain lines. The drain lines can be feed lines to the corresponding collecting containers for the treatment agent mixture and / or for the solvent and / or for water, but it can also be a bypass line which returns the condensate directly to the treatment room.

Further details, features and advantages of the invention result from the following description and from the drawing. In the single figure, this shows a schematic diagram of a system according to the invention in a simplified representation.

The system generally designated 1 for the treatment, for example for stripping or stripping, of objects 2 consists essentially of a dip tank 3, which can be closed by a removable cover 4 on the top. Through the opening released by the lid 4, the immersion container 3 is loaded with the objects 2 to be treated, which are arranged, for example, in an immersed basket 5.

The immersion tank 3 is provided in the lower area with a heating device 6, in the upper area near the cover 4 with cooling coils 7, which are equipped with a condensate channel 8 underneath.

Storage tanks are provided for receiving treatment liquid and / or neutralizing agent and / or water or the like, such as the treating agent tank 9, the condensate / water tank 10 and the neutralizing agent tank 11, each of which is shown in the figure by additional tanks 9a, 9b or 10a and 11a are added to show that the type and size of the tanks are not important.

In the head region of the immersion tank 3, a relief line 12 is provided, which leads to an activated carbon plant 13 and to a pressure compensation tank 14. Via the activated carbon system 13, a gas volume can be released to the environment via the valve 15, which gas volume is formed by thermal expansion when heated.

In the figure it is also shown that the immersion container 3 is approximately half filled with liquid so that the container is divided into a liquid region 16 and a gas space 17. In the area of the gas space 17, spray devices are provided, e.g. a permanently installed spraying system 18 and a manual spraying system 19, the specific design of which is not important.

The system works as follows:

If the container is empty, it can be filled with the latter for the treatment of the objects 2. First, the cover 4 is removed and the cooling runs over the cooling device 7. After equipping the immersion container 5, which can be provided with an additional perforated plate 5 a on one of its undersides, the latter is introduced into the immersion container 3 from above. Now the lid is closed and, for example, a mixture of methylene chloride and alcohols and other solvents, acids or alkali, such as, for example, armines or surfactants or the like, and water is introduced in an over-azeotropic ratio from the tank or tanks 9 or 9a, 9b. The tanks 9, 9a, 9b can be arranged higher in the direction of gravity than the highest filling level of the container 3, so that an additional pumping is unnecessary when filling, but a complete pumping out of the mixture can be ensured when emptying.

After flooding, the heating device is turned on and the treatment agent mixture is heated, a mixture of methylene chloride / water azeotrope boiling at 38.1 ° C. in a ratio of 89.5 to 1.5%. Boiling or bubbling the liquid accelerates the reaction, the treatment time of the parts 2 to be treated can thus e.g. compared to a cold stripping process can be shortened by a multiple, approximately 10 to 20 times, which means a 10 to 20 times higher throughput of the system.

When heated, the gas mixture expanding in the gas space 17 is fed via the line 12, for example to the activated carbon filter system 13, and can be released into the environment via the valve 15. A vapor of solvent and water which then forms in the gas space 17 is condensed on the cooling coils 6 and collected via the condensate collecting channel 8 and, for example via a bypass line 20, is fed directly back to the immersion container 3. When the treatment is finished, the heating is switched off. In the case of methylene chloride as solvent, it settles down below after a short time, while the water floats up as a lighter medium. The methylene chloride can now be pumped back into or into one of the containers 9 to 9b, and a water fraction is left in the immersion container 3.

Now the extraction phase begins, i.e. the heating is switched on again. At the beginning, the methylene / water mixture boils again azeotropically at 38.1 ° C. As long as the system contains methylene chloride, this boiling point remains constant. The gas phase is condensed again on the cooling coils and is now fed to the storage tank 9 via line 21. If the temperature rises above 38.1 ° C, the operator finds that all methylene chloride has been distilled out. Between this temperature and the boiling point of water there are further azeotropes of the other additives, such as alcohols, formic or acetic acids, esters and the like. Like. These can then be distilled out accordingly. At the boiling point of the water, all volatile, low boilers are distilled into the storage tank. The heating can now be switched off and the residual water is fed into the water storage tank, e.g. the tank 10, pumped, if necessary, additional water and neutralizing agent can be added to the immersion tank 3 in order to render acids, alkalis or other additives chemically harmless.

At the end of this treatment stage, the lid can be removed. Solvents are now completely removed from the immersion container 3, there are only parts of lacquer or paint or plastics or other detached coating materials and possibly water in the container. When slowly extending the diving basket 5 NEN the parts are now hosed by the stationary or the hand-operated spraying systems 18 and 19, in such a way that the coatings, which generally peel off over a large area, collect in the lower perforated plate 5a. As with the treatment liquid, additives may also be added to the water to be treated, such as anti-corrosion agents or the like. This also saves an external spraying place by spraying in the immersion tank. The water-wet residues on the perforated plate can be dewatered via filter presses or the like and can be reused. With the appropriate procedure, the hosed and removed parts are still comparatively warm, so that they dry very quickly, which additionally reduces corrosion.

With the system according to the invention, regeneration of the liquids or liquid mixtures used can also be achieved in a simple manner. If the liquids are contaminated by the finest varnish parts, pigments or the like, such as resins that have dissolved, a complete regeneration of the decoating agent can be made possible. In this case, the entire treatment liquid can be distilled over in one treatment stage, ie in this case there is no, if only partial, pumping off of the liquids, but rather they are corresponding to the boiling temperatures via line 21 the tank 9 as a solvent or the line 22 to the water tank 10.

Depending on the size or fill level of the container or reactor 3, in addition to the immersion treatment in the area 16, a solvent vapor treatment in the steam space 17 can also be carried out simultaneously, e.g. of objects that are not suitable for immersion treatment, e.g. Light metals and their alloys, non-ferrous metals, wood, plastics u. This procedure can e.g. also used for incorrectly painted parts from electronics, from aircraft construction, from automobile production, for example for light alloy high-speed rims. Like. more. In principle, the system can work completely closed, a certain volume of gas is discharged in the upward process via the activated carbon filter system 13, it is the only emission to the environment, but this volume can also be collected in a pressure expansion tank 14, then the system is pressurized to a certain extent operated towards the environment.

As already mentioned, degreasing processes or other treatment processes can also be carried out in the system, depending entirely on the liquid mixtures used or their over-azeotropic compositions.

Claims (12)

1. A method for treating objects with a closed container with solvent, the objects to be treated being treated at least temporarily by immersion in solvent and then sprayed off in a solvent-free area of the container,
characterized,
that the process for stripping and stripping the objects is used and additionally includes at least the following process steps: a) a solvent mixture is used after closing the treatment container with at least a major proportion of solvent, such as methylene chloride, with an excess proportion of water to the azeotropic mixture. b) the treatment agent mixture is heated to the boiling point of the mixture, c) after the end of the treatment time, the settling and possibly condensing solvent is removed from the treatment container, d) water is heated and evaporated in the treatment tank, whereby e) the solvent on or in the coating or lacquer residues and the objects to be treated is azeotropically distilled off and removed from the system with water before opening the container. 2. The method according to claim 1,
characterized,
that circulated water is used to remove the solvent from the system and from the coating or lacquer residues, at least some of this water having previously been used as part of the treatment agent mixture. 3. The method according to claim 1 or 2,
characterized,
that after complete removal of the solvent from the system by boiling and recondensing, the parts in the treatment tank are sprayed and removed from the tank. 4. The method according to any one of the preceding claims,
characterized,
that the solvent-free residues are collected and in particular recycled. 5. The method according to any one of the preceding claims,
characterized,
that only part of the treatment container is filled with solvent and the filling level of the solvent is kept at a distance from the cooling and condensation coils provided in the region of the container cover. 6. The method according to any one of the preceding claims,
characterized,
that the solvent mixture is also used as a spray in the gas space of the treatment tank. 7. The method according to any one of the preceding claims,
characterized,
that additives for passivation or corrosion protection are added to the solvent as treatment liquid and / or spray liquid. 8. Plant for carrying out the method according to one of the preceding claims with an immersion container which can be at least partially filled with a solvent mixture,
characterized,
that the immersion container (3) is equipped with a heating device (6) in its lower area and with a cooling device (7) in the area of the lid (4) provided above. 9. Plant according to claim 8,
characterized,
that the immersion tank (3) is equipped, at least in its gas space (17), with a spray device (18, 19) for objects (2) to be treated there. 10. Plant according to claim 8 or 9,
characterized,
that at least one collecting container (9) for solvent, one collecting container (10) for water and one collecting container (11) for a further treatment agent, such as a neutralizing agent or the like, is assigned to the immersion container. 11. Plant according to one of the preceding claims,
characterized,
that the immersion tank (3) is provided with an activated carbon filter (13) and / or a pressure compensation tank (14). 12. Plant according to one of the preceding claims,
characterized,
that the cooling device (7) is assigned a condensate collecting channel (8) with drain lines (20-22).

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