JPH03143525A - Method for controlling discharge of solvent into atmosphere - Google Patents

Abstract

PURPOSE:To control the discharge of solvent into the atmosphere with high efficiency at a low cost by bubbling a water-insoluble gaseous solvent in an org. liq. completely miscible with the solvent at low vapor pressure or in the mixture of the liq. and water to absorb the solvent. CONSTITUTION:The gaseous solvent and coating mist generated in spray coating in a booth 10 are passes through a water curtain 11 to remove most of the coating mist, and then introduced into a scrubber 2 from its lower part. The gas is brought into contact with the water sprayed from a shower 21 to remove the coating mist almost completely, and the collected water is mixed with the water from the water curtain at the lower part of the booth 10. The mixture is sent to a solid separation vessel 12, and the water freed of solid is sent to a water storage tank 13 and supplied therefrom to the water curtain 11 and shower 20.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for suppressing atmospheric emissions of water-insoluble solvents. More specifically, the present invention particularly relates to a method for suppressing atmospheric emissions of solvents mainly consisting of aromatic solvents and/or ester compound solvents.

[Prior Art] Although there are many sources of solvent gas, a large amount of solvent gas is generated, for example, in the spray painting process, baking drying process, etc. of vehicles.

Conventionally, various methods have been adopted as pollution countermeasures to suppress atmospheric emissions of solvent gases generated during painting processes and the like. One method is to collect the generated solvent gas by some means, but most of these methods involve improving the paint in order to improve the collection efficiency.

For example, by using a water-soluble paint, that is, a paint whose solvent is water-soluble, the generated solvent gas is led to a scrubber device and absorbed into circulating water, and the solvent in the paint mist is absorbed into the water in the wash booth, thereby releasing it into the air. Efforts are being made to prevent pollution.

[Problems to be solved by the invention] However, water-soluble paints have special solvents;
It has the disadvantage of high cost.

On the other hand, paints whose main component is water-insoluble solvents such as intershell aromatic solvents and ester compound solvents (hereinafter referred to as water-insoluble solvent paints) are low-cost, but they generate water-insoluble solvent gas. At present, there is no practical method to remove them with high efficiency and low cost.

In view of the above points, the present invention provides a highly efficient and low-cost way to reduce atmospheric emissions of the solvent generated in the case of water-soluble paints when using water-insoluble solvent paints, which are cheaper than water-soluble paints. The aim is to provide a method that can suppress this problem.

[Means for Solving the Problems] The present invention converts a solvent gas mainly consisting of one or more kinds of water-insoluble solvents into an organic liquid having a relatively low vapor pressure and which is completely miscible with the solvent. The present invention relates to a method for suppressing atmospheric emissions of a solvent, which is characterized by bubbling and absorbing a solvent into an absorption liquid consisting of a mixture of an organic liquid and water.

[Function and Examples] The present invention uses aromatic solvents such as toluene, xylene, high-boiling alkylbenzenes, and alkyl fused polycyclic compounds;
The target gases are aliphatic solvents such as heptane, and ester compound solvents such as butyl acetate, ethyl acetate, and carpitol acetate, either alone or as a mixture of two or more. Here, the concept of gas includes solvent mist and even paint mist.

Paint mist refers to the atomized state of paint, which consists of solvent, pigment, and resin.

The aromatic solvent is Swasol (manufactured by Cosmo Oil).
, Tsurpets ■ (manufactured by Esso Kagaku ■) (both are mixtures of high-boiling point alkylbenzenes and alkyl condensed polycyclic compounds).

In addition, the target solvent may contain a water-soluble solvent of several vol% to about 20 vol%, as long as it is mainly composed of the above-mentioned water-insoluble solvent. Examples of water-soluble solvents include propyl alcohol and butyl alcohol.

Examples of paints using solvents mainly composed of water-insoluble solvents include baking paints for vehicles, electrical appliances, and the like.

These paints are mainly made of aromatic solvents such as xylene, toluene, Swazol, and Tsurpetz, and also contain butyl acetate, ethyl acetate, carpitol acetate,
Alternatively, it contains a small amount of a water-soluble solvent such as n-butyl alcohol or butyl cellosolve.

1. The liquid that absorbs the gas of the water-insoluble solvent has a relatively low vapor pressure and is completely compatible with the water-insoluble solvent in order to prevent air pollution due to its own vaporization and to improve absorption of the solvent gas. Miscible organic liquids are used.

Such organic liquids include liquid paraffin (which mainly consists of naphthenic hydrocarbons), carbon number lX
Examples include aliphatic hydrocarbons having about 10 to 3×10 2 carbon atoms, and alkyl condensed polycyclic compounds such as high-boiling point alkylbenzenes and alkylnaphthalenes alone or in mixtures. These organic liquids are appropriately selected in consideration of the composition of the solvent to be absorbed, and depending on the composition of the solvent, it may be preferable to use a mixture of two or more in terms of collection efficiency.

Liquid paraffin has a high boiling point of 300-400'C.
Its vapor pressure is almost zero at room temperature.

The vapor pressure of aliphatic hydrocarbons having about 1X10 to 3X102 carbon atoms is almost zero at room temperature, and about 5 to 20 maHg at 250°C. Specific examples include engine oil and paraffin engine oil additives. Examples of paraffin-based engine oil additives include copolymerized oligomers of ethylene and α-olefin, polybutene, and poly-α-olefin. is an alkyl group having about 1 to 5 carbon atoms, X, )'
, , I) are integers, respectively), and the number average molecular fA is 700 to 3,800.

As the high boiling point alkylbenzene and alkyl condensed polycyclic compound (hereinafter referred to as high boiling point alkyl aromatic compound), those having a boiling point of about 150 to 270°C are used. Some high-boiling point substances are solid at room temperature when used alone;
In that case, it is used after being dissolved in another solvent. Specific examples of high boiling point alkyl aromatic compounds include the above-mentioned Swazol and Tsurpetz.

If liquid paraffin having a high viscosity (for example, 10 cSt or more) is used without being mixed with water, bubbling may not be carried out well due to the high viscosity in the initial stage when the solvent is not absorbed. In this case, it is preferable to use it in combination with a high boiling point alkyl aromatic compound. In this case, the mixing ratio of liquid paraffin and high-boiling alkyl aromatic compound is preferably in the range of 100:3 to 20 (volume ratio). If the proportion of the high boiling point alkyl aromatic compound is less than the above range, the viscosity will be high and bubbling will be difficult. When using low viscosity liquid paraffin, there is no particular need to add a high boiling point alkyl aromatic compound to lower the viscosity.

The organic liquid for absorption may be used alone, or may be used in combination with water. Mixing with water reduces the risk of ignition.

Furthermore, in the case of bubbling the solvent gas into the absorbent organic liquid, if existing equipment is used, the amount of the absorbent organic liquid must exceed a certain level from the equipment point of view, and the absorbent organic liquid is expensive. Therefore, water is sometimes used as a bulking agent. Furthermore, in the case of a water-insoluble solvent paint, since the solvent also contains a water-soluble solvent, the collection efficiency is improved when water is used in combination.

When water is used in combination, the amount of water used relative to the organic liquid is not so limited. When the proportion of organic liquid is small, the frequency of distillation to remove the collected solvent increases, but from the viewpoint of collection efficiency it is sufficient to increase the number of stages of the absorption device. In addition, when the proportion of organic liquid is large, the frequency of distillation is reduced, and the number of stages of the absorption device can be reduced. When water is used together, 80 to 20 parts of water per 100 parts by volume of organic liquid.
A ratio of 0.00 parts by volume is commonly used.

Bubbling the solvent gas into the absorption liquid does not require any special equipment; for example, store the absorption liquid in an arbitrary tank, insert a blowing pipe into it, and blow the solvent gas into the absorption liquid through the blowing pipe. Just let it bubble inside. The blowing tube may be provided with a large number of pores, or may have a mesh or the like attached to the opening at its tip. The absorption tanks may be connected in series or in parallel. No special equipment is required when a mixture of organic liquid and water is used as the absorption liquid. By bubbling the solvent gas, the organic liquid and water are mixed and converted into an emulsion state, which remains in the reemulzidine state unless left standing. The mixture in emulsion state can absorb gaseous solvents well. The emulsion state can be further stabilized by using an emulsion stabilizing surfactant.

Although various methods are employed for post-treatment of the absorbent that has absorbed the solvent, the following method is usually used.

When using an organic liquid alone, there are two methods. A method is also used in which evaporation is also distilled off. The distilled off solvent can be purified and reused if desired.

When a mixture of organic liquid and water is used as the absorption liquid, it is introduced into a separation tank, and if necessary, a surfactant for breaking the emulsion is added for separation to separate the organic liquid layer and the water layer. The organic liquid layer may be subjected to distillation in the same manner as described above. Alternatively, the organic liquid may be subjected to distillation together with water without being separated from the water, and after distillation, the water and the organic liquid may be separated.

When an organic liquid is used alone, it may be mixed with water for the purpose of cleaning, etc., and treated in the same manner as when the organic liquid and water are used together.

In order to continuously recover the solvent and recycle the organic liquid in the above process, if only the organic liquid is used, for example, a part of the organic liquid that has absorbed the solvent is continuously led to a distillation apparatus, and the extracted organic liquid is An appropriate method may be adopted, such as replenishing fresh organic liquid (from the distillation apparatus) in an amount equal to the amount of the liquid and returning it to the absorption tank. When mixing an organic liquid with water, for example, a part of the organic liquid separated in a separation tank is continuously extracted and introduced into a distillation device, and a fresh organic liquid corresponding to the amount of the extracted organic liquid is produced. Methods such as replenishing the water layer, mixing it with the water layer, and returning it to the absorption tank may be adopted as appropriate.

The vaporized solvent generated during painting generally accompanies a mist containing paint resin components.

If the solvent gas accompanied by such mist is directly introduced into the absorption tank, paint resin components will accumulate and recovery operations will become more frequent. Therefore, in the present invention, it is preferable to remove as much paint mist as possible in advance before introducing it into the absorption tank. In order to remove the paint mist in advance, a method of bringing it into gas-liquid contact with water using a water curtain, a scrubber device, etc. can be appropriately employed.

Note that even if the paint mist is removed in advance, paint resin components will gradually accumulate during long-term operation.

In this case, if the absorbing organic liquid is liquid paraffin or aliphatic hydrocarbons, these will not dissolve the paint resin components, so the resin components will form floc-like precipitates and disperse together with foam. Eventually, the fluidity of the organic liquid phase disappears and bubbling becomes impossible.

In addition, if the absorbing organic liquid is a high boiling point alkyl aromatic compound, it will dissolve the paint resin component, but although the phenomenon has not yet been elucidated, as the amount of treatment increases, the liquid becomes yogurt-like. There will be no liquidity, and it will either bubble or become impossible.

In the present invention, it has been found that when a surfactant is added in such a state, the floc-like or yoghurt-like paint resin aggregates, the organic liquid phase becomes fluid, and bubbling becomes possible. Served.

The type of surfactant to be used is best determined by trial and error since the system is complex, but a household liquid detergent (for example, Mama Lemon ■ (manufactured by Lion ■), etc.) can be used to achieve sufficient effects.

Next, the present invention will be explained with reference to Examples.

In the following example, an experiment was conducted to collect the solvent generated during spray painting of a water-insoluble solvent paint using an experimental device equipped with a small painting booth, a small scrubber device, and a small absorption tank shown in FIG.

In Figure 1, the Foundation has a small painting booth (width 350m).
+ex length 650mm x height 70mm, volume 0.01
8m'), (2) is a scrubber device attached to the booth, (40) is an absorption tank, and (50> is an exhaust pipe).

A water curtain 01) (water supply amount: 18.9 N/min) is provided between the booth □ and the scrubber device (4).

In the spraying at booth □□□, most of the paint mist is removed through the solvent gas generated during painting and the water curtain 01), and then introduced into the scrubber device -〇 from the bottom, and then into the shower equipment ff1 (21). The paint mist is almost safely extracted by contact with the water sprayed from the paint. The water that collected the paint mist is collected by Booth (foundation)
The water is collected at the bottom of the water curtain and mixed with water.

The mixture is sent to the solid content separation tank 02), and the water layer from which the solid content has been separated is sent to the water storage tank, from where it is supplied to the water curtain (II) and the shower device (21).

The scrubber device ■ is connected to an exhaust duct ■ equipped with a fan (31), and the duct is connected to a blowing pipe (32), and the opening at the tip of the blowing pipe (32) is connected to a mesh (33).
) is installed. The solvent gas from which the paint mist has been almost safely removed by the scrubber device is passed through the duct by the fan (31) and from the blowing pipe (32) to the absorption tank (40).
It is bubbled into the absorption liquid <41> contained therein. The exhaust gas from which the solvent gas has been removed is discharged into the atmosphere from the exhaust pipe (50). A drum can (inner diameter 570 mm, height 880 am) is used as the absorption tank (40), and the blow pipe (32) is a pipe with an inner diameter of 70 cm, the same diameter as the exhaust duct, with an opening at the end of the pipe having an opening of 0.5 to 0.5 mm. 1. One with an On+m mesh attached was used.

The solvent concentration is determined by measuring the inlet concentration in the center of the painting booth ('IO) in Figure 1, and measuring the outlet concentration at the outlet (81) of the exhaust pipe (50). From these values, the solvent collection efficiency can be calculated. I asked for it.

In the following examples, percentages are percentages by weight. Further, the proportion of each solvent in the solvent composition is the proportion (%) to the entire paint (the same applies hereinafter).

Examples 1 to 3 Using the experimental apparatus shown in FIG. 1, the collection efficiency of the solvent generated during spray painting of the following paints was measured.

Paint: White painted solid paint Paint resin Niamino alkyd resin Solid content: 57% Solvent composition: xylene 20%, Swasol 15%, 3-methoxybutyl acetate 3%, n-butyl alcohol 5% Paint discharge mffi: 10ml /min or 40
m1/min scrubber device ■ Number of shower stages: 26 Wind speed (air volume) in the blowing pipe (32): 19 m/5 ec (44 yd/min) Absorbing liquid: Mixture of water 27411 and the following organic liquid 9 g Example 1: Shiraishi Solvent No. 6 (manufactured by Nippon Oil Corporation, carbon number 1)
Mixture of 6 to 21 aliphatic hydrocarbons and high-boiling aromatic compounds): Cosmo P-Go (liquid paraffin manufactured by Cosmo Oil ■) Example 3: Solvesso 200 (mixture of high-boiling alkylbenzene and alkyl condensation manufactured by Esso Chemical ■) mixture of polycyclic compounds) shown in the table.

[Leaving space] Example 2 Results are shown in the first example Examples 4 to 6 9 g of the solvent obtained by removing the solid content from the solid paint used in Examples 1 to 3 was added in advance to each absorption liquid used in Examples 1 to 3. The collection efficiency was measured in the same manner as in Examples 1 to 3 except for the blending.

The reason why the paint solvent was mixed into the absorption liquid was to conduct a practical test to check whether the collection efficiency decreases as the paint is sprayed. That is, this was carried out to examine the collection efficiency in a state where the paint solvent was mixed in due to running and was far removed from the fresh absorption liquid, rather than the fresh absorption liquid.

The results are shown in Table 2.

[Margin below] Examples 7 to 9 The collection efficiency was determined in the same manner as in Examples 11 to 3, except that in Examples 1 to 3, each absorption organic liquid was used alone without being mixed with water. Note that 31 J of each organic liquid was used.

The results are shown in Table 3.

[Blank below] [Effects of the invention] When spraying paints containing aromatic or ester compound-based solvents, especially those based on these solvents, the solvent gas generated during painting can be mixed with the solvent at low vapor pressure. By bubbling it into a liquid, it can be collected efficiently and air pollution can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing a solvent collection efficiency measuring device used in Examples. (Main symbols in the drawing) 00), Paint booth ■ Varnish scrubber device (32): Blowing pipe (40): Absorption tank (41): Absorption liquid

Claims (1)

[Scope of Claims] 1. An organic liquid or a mixture of the liquid and water that has a relatively low vapor pressure and is completely miscible with the solvent gas, which is mainly composed of one or more types of water-insoluble solvents. A method for suppressing atmospheric emissions of a solvent, which comprises bubbling and absorbing a solvent into an absorption liquid consisting of: 2. The absorbing treatment is performed after most of the paint mist has been removed in advance from the exhaust gas generated when spray painting a paint mainly composed of an aromatic solvent and/or an ester compound solvent. the method of. 3 The organic liquid is liquid paraffin, carbon number 1 x 10
3. The method according to claim 1, wherein the hydrocarbon is one or a mixture of two or more selected from the group consisting of ~3x10^2 aliphatic hydrocarbons, and high-boiling alkylbenzenes or alkyl fused polycyclic compounds. 4. The method according to claim 1, 2 or 3, wherein the organic liquid that has absorbed the solvent is subjected to distillation to recover the solvent and recycle the organic liquid to suppress the concentration of the solvent at the outlet to the atmosphere.