Volatile organic compounds (VOC) contribute substantially to the formation of ground level ozone. High ozone concentrations in the air are detrimental to human health and stunt plant growth. To fulfil the environmental goal of making sure that ground ozone does not exceed 110µg/m3, it will be necessary to reduce VOC emissions by 70 to 80 percent compared to 1990 levels. The main source of VOC emissions in Germany is the use of solvents; this includes surface cleaning with halogen-free organic solvents.

This research report gives up-to-date statistical data on the consumption, emission and disposal of halogen-free organic solvents used in surface cleaning (the actual situation) and also determines the potential for VOC emissions reduction on an operational level (the situation as it should be). The report covers every major sector where surface cleaning is done. The primary results are based on direct local research with users and on interviews with experts in the solvent trade, in facility construction, associations, trade publications and science.

The political context of the study is the Council Directive 1999/13/EC of 11 March 1999 on the limitation of emissions of volatile organic compounds due to the use of organic solvents in certain activities and installations (VOC directive). It will be transposed into German law within the next two years.

Altogether, about 63,700 tonnes (t) of fresh solvents made of inflammable hydrocarbons (HC) are supplied to facilities every year for surface cleaning purposes. In 1998, halogen-free organic solvents for surface cleaning were used and emitted as shown in Table I.

About 49 percent, or 31,150 t, were emitted into open air during use. The other 51 percent became waste and were disposed of in different ways. Of the 32,550 t of used cleaning solvent, about 6300 t were recovered for reuse and were a part (10 percent) of the annual supply. About 2300 t were processed for other purposes (all purpose diluents, antifreezes, etc.). Slightly more than 1000 t (oxygenous HC derivates) were rinsed into the sewage system and did not decompose until they reached water purification plants. Most of the used solvents, about 23,000 t (70 percent) were burned for energy consumption.

Halogen-free solvent use is proportionately different in each of the six major sectors where solvents are applied for cleaning.

1. Services outside the industry

Particularly in automobile service, cleaning is done intermittently and manually, not on a serial basis. For this purpose, 6000 t of HC cleaning agents are supplied to simple cleaning table installations by retailers who afterwards collect the contaminated solvents for processing. (These HC cleaning agents belong to the Class A-III type as defined in the German statutory order on flammable liquids.) Therefore the proportion of reuse of initial input is relatively high (46 percent). Fugitive emissions are about 20 percent of the input volume. In addition, 5000 t of solvents (Class A-I and B types) in spray cans are used to clean vehicles and equipment - these evaporate completely (100 percent).

2. Car dewaxing

About 6600 t HC (Class A-III) are used in a mixture with 95 percent hot water to dewax new cars. On a large scale (where consumption per plant is more than 2 t/a), this process takes place in 29 automatic installations at haulage companies and manually at about 250 car dealerships. Altogether, emissions are 1225 t, some of them in waste gases and some fugitive.

3. General industrial metal degreasing

The major application of halogen-free HC surface cleaners is in the general degreasing of metal in industry, with an input of more than 27,000 t. Operations have been standardised and use de-aromatised HCs which belong to the Class A-II and A-III types - this means their flash point is above 21°C, or respectively, 55°C. In part, they replace the earlier use of chlorinated hydrocarbons. About 90 percent of HCs are used for discontinuous manual cleaning with brushes and cloths at room temperature in industrial workshops and production facilities. They are also used to clean products that don't fit into washing machines, such as large-sized parts produced in small numbers, small leftover parts, and measuring and monitoring parts that need cleaning in between. Ten percent of HC input goes into cleaning plants that work on a serial basis. There are 250 facilities that clean at room temperature and use heat only for drying. There are already more than 300 closed HC plants that attain very high degrees of purity due to vacuum technology - they use hot solvent and vapour for degreasing. Their waste gas emissions are low due to refrigerator condensation.

4. Special industrial applications

About 12,000 t of organic cleaners with concentrated solvent ability (esters, ketones, aromatics, special benzine, alcohols, glycol ethers) are used for cleaning where simple HCs don't work. Typically, this concerns not grease and oil but rather polymers such as adhesives, sealants, resins, paints, and so forth. These materials must be cleaned off production equipment more often than from the products themselves. Cleaning is done manually and in open conditions for the most part, and always at room temperature. The ready flammability of Class A-I and A-II types of HC requires that cleaning is done in this way. Since these HCs are highly volatile, emissions are very high (72 percent).

5. Precision cleaning

In the fields of electronics, optics and fine mechanics, CFCs have often been replaced by mild solvents that guarantee a high degree of surface purity and dry quickly: cyclohexane, isopropanol and acetone. However, they are all readily flammable and must be used in explosion protection installations that operate with continuous suction for safety reasons. This raises already high emissions to more than two-thirds of input. This rate applies to the field of fine optics as well, where, on a wide scale, cleaning is manually done with alcohol. Emissions would be much higher if many highly volatile solvents hadn't recently been replaced by less volatile ones such as glycol ethers or N-methylpyrrolidone (NMP). The total solvent input is 4400 tonnes.

6. Lacquer removal

Organic solvents such as glycol ethers and NMP are used to remove lacquer from aluminium or zinc coated metal parts. These solvents can swell up and dissolve lacquer at 50-60°C. Fugitive emissions are about 15 percent (370 t) of 2500 t of solvent input. More than 700 t are rinsed off with water and are not decomposed until they reach water purification plants. More than 1100 t are recovered from the paint sludge for reuse as fresh lacquer removal agents.

Much of halogen-free HC surface cleaning is done by hand. Of the 63,700 t of annual organic solvent input, nearly 50,000 t are used manually and less than 14,000 t primarily by hand and at room temperature.

There are about 100,000 facilities that do HC surface cleaning. (This does not include the 120,000 industrial pad printers that each annually use only 30-35 kg, altogether 4000 t, to manually clean clichés.) However, only a few more than 3000 facilities consume more than 2 tonnes of solvent per year. Most of them, about 2100, are in the metal degreasing industry. But these users, making up three percent of all users of HC solvents for surface cleaning, need more than 60 percent of all domestic solvent input and are the source of more than 45 percent of all VOC solvent emissions (excluding pad printers).

The goal of the EU VOC solvent directive is to significantly reduce VOC emissions. In this context, the study will look into the potential for reducing emissions. It will be asked what effect the VOC directive will have if the specific limits it defines for emissions are completely met by the users in each sector in Germany where surface cleaning occurs. The directive defines a limit value for fugitive emissions of 20 percent of the input volume, and a limit for emissions in waste gas of 75 mg C per cubic meter. Both of these values apply when solvent consumption is above the threshold given by the directive of 2 t/a per installation.

Apart from the emission reductions required by the VOC directive, it can be asked how large the reduction potential for VOC emissions from surface cleaning is in general, based on the present standard of technology. The usefulness of the directive can be measured by how far it utilises reduction potential that is financially reasonable. Table II shows not only the volume of emission reductions occurring if the VOC directive is completely realised by the installations concerned, but also the volume of reduction that exceeds the directive's prescribed limit values if state of the art technology is fully exploited.

1. In three areas, the VOC directive has practically no effect on reducing emissions. In services outside the industry and the lacquer removal sector, the 20 percent limit for fugitive emissions is complied with anyway. In car dewaxing, the low HC content of the cleaning fluid exempts it in a special clause from compliance with the limits set by the VOC directive.

However, fully exploiting technological potential clearly reduces emissions beyond what is demanded by the VOC directive. In the service sector, this amounts to 2900 t if plants with more than 20 employees generally use hot water for cleaning. In car dewaxing, it amounts to 1125 t if new cars are not waxed, or otherwise, if HC cleaning takes place in plants where waste gas is effectively treated. And finally, 70 tonnes are saved in the lacquer removal sector if organic solvents are used only where the material (aluminium) requires it.

2. General industrial metal degreasing and precision cleaning are the areas where full realisation of the VOC directive has the greatest effect. Total emissions of 14,755 t (12,000 t and 2755 t respectively) are more than halved if the 2340 plants consuming more than two tonnes of solvent per year comply with the limits set by the directive. Reduction occurs mainly when the 20 percent limit for fugitive emissions is observed in all manual and mechanical cleaning processes. The second largest reduction occurs when plants using a technology with high emissions convert to HC systems that clean within a closed vacuum or use less volatile solvents in open air operations.

Additional technologically feasible reductions not required by the VOC directive amount to 1180 t (1080 t and 100 t, respectively). They occur mainly when installations consuming more than two tonnes of HC solvent per year not only observe the directive's limits for HC cleaning but also replace this technology with water cleaning processes. Reductions also occur if HC emissions are reduced to a technical minimum in installations that already consume less than two tonnes.

3. In special industrial applications, the emissions reducing effect of the VOC directive is limited in two ways. First, surface cleaning which is not an independent operational activity, such as cleaning tools for adhesives, is legislatively seen as a subordinate process in another solvent use regulated by the VOC directive (adhesive coating) and does not fall under surface cleaning in that sense. Only about half of cleaning done with special solvents in these cases falls under the VOC directive as it applies to surface cleaning. Second, although there are a multitude of uses for special solvents, each use is generally quite small. Only rarely are more than two tonnes (threshold) consumed per unit. Thus, the VOC directive applies to only about 250 installations in this case and has the effect of moderately reducing emissions here by only 300 tonnes.

Independent technological measures not required by the VOC directive reduce emissions by more than seven times as much. This is a result of using less volatile solvents to clean tools in pad printing and by making constructional changes to reduce the amount of solvent cleansing in moulding plants for two component resins. Yet the additional reduction potential is relatively low at 2200 tonnes because the containment of fugitive emissions in this sector is very difficult.

The full realisation of the VOC directive's limit values leads to a reduction of 8310 tonnes of VOC emissions from surface cleaning. This is almost 27 percent of the present total emissions of 31,150 tonnes. This figure becomes about 32 percent when it is adjusted to exclude the organic special industrial applications that do not fall under the VOC directive's surface cleaning category, and car dewaxing. Adjusted additional technologically feasible reductions not required by the VOC directive amount to 5250 tonnes, or almost 17 percent. Thus, the potential to reduce VOC emissions in surface cleaning amounts to nearly 50 percent.

In view of the environmental necessity to substantially reduce VOC emissions and of the limited effectiveness of the VOC directive, it should be examined how far the directive can be strengthened.