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Effective, economical and environmentally friendly cleaning

Du Pont Engineering Polymers : 01 February, 2003  (Company News)
PPG Industries Lacke GmbH, Wuppertal (Germany) has developed a new cleaning process for the 50 transportation containers in which they make their daily deliveries of coatings for the automotive industry.
These containers, with a capacity of 250 to 1000 litres, are cleaned with the environmentally friendly and easily biodegradable solvent DBE (Dibasic Esters) from DuPont.

High solvency power, effective cleaning and a safer working environment are the main advantages of this new process. Additionally, emissions associated with the use of DBE are significantly lower than those currently requested by government regulations, giving PPG long term process security.

The transport containers used by PPG for the transportation of aqueous based paints are for multiple usage, hence they must be effectively cleaned and the old paint residues removed before refilling. In the past PPG had used a standard solvent mixture comprising mainly Xylene and butylacetate for this cleaning operation. The use of these solvents had significant operational disadvantages in that their high volatility led to both high emission levels and the need for workers to wear masks when dry wiping the containers in the final step. In the face of increasing pressure from the German Environmental Protection Authorities to reduce emissions, PPG decided against the typical solution of installing additional air filters and incineration equipment.

PPG chose a different path: the original cleaning solvents were replaced by DBE from DuPont. This solvent, which comprises a mixture of the methyl esters of naturally occurring adipic, glutaric and succinic acids, has high solvency power, a high flash point and low vapour pressure. Consequently, the emissions associated with working with DBE are well below those limits required by law.

The only “disadvantage” is that DBE remains as a “film” on the container surface and needs to be washed away with warm water after the cleaning process. Owing to the easily biodegradable nature of DBE, the waste rinse water can then be treated by standard waste water technology.

After the switch to DBE, PPG continued to use all of their original existing equipment without modification and added a wash water re-circulation loop. After a testing phase of approximately 2 years, PPG is now cleaning all their paint transportation containers in the following three steps:

1) Cleaning: Cleaning step is done with pre-used / recycled DBE.
2) DBE Rinse: The rinse uses virgin DBE which is afterwards collected in a tank and re-used in step1 in the next cycle.
3) Water Rinse: The remaining DBE film on the surface is rinsed away with water at 60oC. Because DBE is not readily soluble in water, the rinse liquid can be pumped down to a separator and the aqueous phase extracted and sent to storage for subsequent recycling.

Within the PPG group, the Wuppertal facility has the reputation for being a 'green' plant, and the experience of converting to DBE has been very positive. In addition to giving regulatory security, the workers can operate today without masks, which in the past were obligatory. PPG have also found that DBE dissolves more residues than the former solvent formulation because it has a higher solvency power. When the DBE / organic layer from the separator eventually becomes saturated with paint it is dispatched for recovery by distillation. Typically, 30 per cent of the volume sent for recovery is lost as residue and ultimately incinerated. This loss represents virtually the total make-up volume to the overall cleaning process, as other more usual sources of loss, for example evaporation from vessels or lines, are not significant for DBE. After PPGs positive experiences of using DBE, it is now planned that other cleaning processes in Wuppertal will also be converted to DBE.

DBE is a clear, colourless liquid with high boiling and flash points, and a mild odour. DBE is classified as “non hazardous” according to all E.U. criteria, which allows easier handling. DBE is produced from dibasic acids manufactured at DuPont’s adipic acid plants. These refined dimethylesters of adipic, glutaric and succinic acid function as solvents for coatings, cleaning formulations, paint strippers, foundry core binders and agro chemicals.
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