DE2945523A1 - METHOD FOR CLEANING EXHAUST AIR FROM PAINT SPRAYING CABINS - Google Patents

Description

The invention relates to a method for cleaning the exhaust air from paint spray booths by washing out the paint mist with water,

In paint spray booths, the «paint mist, the does not get to the part to be painted, sucked out of the spray booth with the booth air. From this air For reasons of environmental hygiene, the paint mist must be removed before the air can get outside. That happens in generally by washing out with water. The air is mixed intensively with the wash water, with the paint particles remain in the washing water. The wash water contains a coagulant that prevents the confluence (the coagulation) of the paint particles causes them to form larger units, which reduces the stickiness of the paint particles lowers in order to avoid sticking and contamination in the washing system and that in the settling basin Makes paint particles float or sink.

However, as the development of paint progresses, it always will

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more difficult to coagulate the paint particles sufficiently, resulting in severe sticking and contamination in the Car wash leads. These adhesions and impurities must, in order to ensure the safe functioning of the system, through laborious and costly cleaning removed by hand.

The object of the present invention is therefore to provide a cleaning method for the exhaust air from paint spray booths by washing out the paint mist with water, which prevents contamination and sticking Paint separation can take place within the washing system.

This object is achieved by the method described in the patent claims.

In contrast to the previously common procedure, the Paint particles no longer coagulate in the wash water, i.e. brought to flow together and detackify, but emulsified by means of an emulsifier, i.e. the coalescence of the dispersed paint particles is deliberately prevented The stability of the dispersion is increased and creaming and phase separation are avoided. The resulting emulsion is filtered in an ultrafiltration system, the ultrafiltrate (Permeate) goes back into the washing system and the paint concentrate (retentate) is either deposited as before or it is worked up to paint that is suitable for Make the body, such as internal parts, cavities, etc. can be reused.

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The emulsifiers customary in industry are used as emulsifiers. Anionic emulsifiers are suitable Type, e.g. salts of higher molecular weight fatty acids (Cg - C o), Salts of sulfuric acid esters such as Na lauryl sulfate, Na salts of sulfosuccinic acid dialkyl esters or sulfuric acid esters of ethoxylated fatty alcohols and alkylphenols, also salts of sulfonic acids, such as alkylbenzenesulfonates, Xylene and naphthalene sulfonates, alkyl naphthalene sulfonates, Paraffin or olefin sulfonates or fatty acid addition products various hydrophilic groups such as protein condensation products or phosphates.

Furthermore, cation-active emulsifiers, e.g. fatty amines, quaternary ammonium compounds and the like and ampholytic compounds such as long chain substituted ones Amino acids, e.g., N-alkyl-di- (aminoethyl) -glycine or N-alkyl-2-aminopropionate, or betaines, e.g., (3-acylaminopropyl) -dimethylglycine or alkyl imidazolium betaines are used will.

Another known group of emulsifiers that are used consists of non-ionic compounds, e.g. partial esters of polyalcohols such as glycerol mono- or distearate and oleate, sorbitol monostearate and oleate Ethylene oxide or propylene oxide adducts with fatty acids, fatty alcohols, partial fatty acids of polyhydric alcohols, Alkyl phenols or from polyalkylene glycols. Other known emulsifiers such as cellulose derivatives (cellulose ethers and the like) or synthetic high polymers such as polyvinylal-

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alcohols can be used. In many cases it is also advantageous to use mixtures of different emulsifiers, provided they are are chemically compatible with each other.

It is also advantageous to use solubilizers such as polyhydric alcohols, e.g. glycols. These connections are used together with other emulsifiers, but they are advantageously used on their own because they have more have a good emulsifying effect and remain in the permeate during filtration. Sometimes it can also be an advantage as an emulsifier in addition to other emulsifiers or on their own high polymer types, such as polyvinyl alcohols (PVA) or Use carboxivinyl polymers because they are less foaming. To excessive foaming of the wash water and thus a Impairment of the performance of the washing system avoid, it may be necessary to add suitable amounts of conventional foam inhibitors to the wash water, e.g. long-chain alcohols, high polymer glycols, fatty acid polyglycol esters, etc. If the paint is recovered from the retentate should be, silicone-containing foam inhibitors should not be used, as they have a disadvantageous Have an influence on the paint quality. Instead of water, other suitable liquids can also be used in which the paint can be dispersed, can be used.

The amount of emulsifier required for emulsification, i. the amount that causes sufficient stabilization of the paint particles in the washing water and contamination of the washing system prevented depends on the type of paint and the

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Deten emulsifier and can by a few preliminary tests by everyone Easily determined by those of ordinary skill in the art. Pure the currently commonly used in the automotive industry Polybutadiene styrene type varnishes are sufficient when using Diethylglycol emulsifiers have an emulsifier concentration of about 1 to 5 wt .- ^ in the wash water. This value can but only serve as a guide. As already mentioned, exact values must be individual for each lacquer / emulsifier system be determined.

Since the washing water in the washing system is usually circulated, the paint concentration in the washing water (emulsion) would increase over the course of the operating time. In order to keep the paint concentration in the emulsion at a desired low level of about 1 to 5 wt ^ ^1, is withdrawn from the circulated washing water (emulsion), a partial stream and subjected to ultrafiltration. Filtration of a partial flow is generally sufficient to maintain a certain paint concentration in the emulsion and is usually cheaper than if the entire wash water were filtered with each cycle, which, however, can sometimes be necessary. The amount of the partial flow is such that as much paint has to be removed with the partial flow per unit of time as paint is added to the wash water with the booth exhaust air.

The ultrafiltration gives a filtrate (permeate),

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which consists of pure washing water and into the washing water circuit is returned as well as a highly concentrated paint emulsion (retentate). The paint concentration in the retentate is 20 to 30 wt .- ^ and can in multi-stage ultrafiltration systems up to ^ O wt .- ^ increase. The ultrafiltration can take place in the numerous commercially available ultrafiltration systems. As a membrane material the commercially available modern anisotropic plastic membranes are preferred, which have a high filtering speed at low pressure (up to approx. 12 at). The pore size of the membrane depends on the size of the paint particles in the washing water and can be determined without difficulty by any person skilled in the art. In general, find membranes with pore sizes below 0.1 / in use.

The advantages that can be achieved with the invention are, above all, that the emulsifying effect causes soiling of the Washing system and associated costly cleaning operations be avoided. Furthermore, the addition of emulsifiers in the washing water promotes the washing out of the paint particles from the cabin air, so that less expensive washing systems can be used with the same degree of separation, or with the same Apparatus expenditure a considerably more effective exhaust air purification can be achieved. Furthermore, the process is characterized by great environmental friendliness and economy because the ultrafiltrate is reused and water or chemicals only need to be replaced in the same amount as they are discharged from the washing system with the retentate.

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Claims (3)

Daimler-Benz Aktiengesellschaft Daim Stuttgart November 7, 1979 EPT Dr.Am/pfa patent claims 1. Procedure for cleaning exhaust air from paint spray booths by washing out the paint mist with water, characterized in that the paint particles with the addition of an emulsifier in Wash water emulsified, at least part of the emulsion subjected to an ultrafiltration and the ultrafiltrate again used as washing water. 2. The method according to claim 1,
characterized in that paraffin, olefin or alkylbenzenesulfonates are added to the wash water as emulsifiers. 3. The method according to claim 1,
characterized in that polyhydric alcohols are added as an emulsifier. h . Method according to claim 3 » characterized in that diethylene glycol is added as an emulsifier. 130021/032 0 ORIGINAL INSPECTED