VOCs: a market improvement
The key EU legislation buoying the European market for Volatile Organic Compounds (VOC) control equipment is Council Directive 1999/13/EC, "on the limitation of emissions of volatile organic compounds due to the use of organic solvents in certain activities and installations". It specifies that EU Member States are required to adopt necessary measures to ensure that existing installations are in compliance with the Directive's stipulations by October 2007. By April 2001, EU Members are instructed to have implemented mandatory laws, regulations and administrative provisions to act in accordance with the procedures laid down in the Directive. (Fear not, with the exception of dry cleaning processes, all sectors included in the Directive are already covered to some extent by UK environmental legislation.)
Paint your wagonDr Neil Carter, R&D manager for Industrial Copolymers Ltd, winner of the SME Industrial category at the recent Green Chemistry Awards, proffers a solvent solution.
One major contributor to world-wide solvent emission to atmosphere is the automotive paint market. According to the most recent figures (European Chemical News in 1992), in Europe alone 160,000 tonnes of solvent were emitted after use in automotive refinish, which consists in the main of two-component solvent based polyurethane coatings. In April 1999, EC legislation to curb emissions to 70% of 1990 levels came into force, which will affect 400,000 firms accounting for an estimated 10 million jobs.
Two possible routes exist to reducing solvent. Firstly, replacement with water-based alternatives. These are restricted by the need to dispose of aqueous waste generated, poor performance (particularly chemical resistance) compared to solvented products, and an unwillingness to change to water-based alternatives due to the investment required in new equipment and staff training. A March 1998 survey by Akzo Nobel of 300 European refinishers found that as much as 95% wish to continue with solvent-based coatings.
The second option is high solids coatings. Limitations exist with viscosity for spray application. Another difficulty with two-component solvent-based polyurethane coatings is the unwanted side reaction of the isocyanate component with water, which is present in parts per million in the polyol, solvent, pigment and in the atmosphere after application. One of the products of this reaction is carbon dioxide gas that produces pinholes in the coating leading to film defects and down glossing.
Incozol LV, a bisoxazolidine reactive diluent, has been developed to overcome both problems. The incorporation of Incozol LV into the polyol component replacing solvent will lead to a significant reduction in the VOC of the coating, and help prevent the carbon dioxide generation by preferentially reacting with water and using it as the driving force for incorporation into the coating. Incorporation of Incozol LV at levels up to 30% replacement of polyol will not alter the cure and dry coating properties of two-part polyurethanes. Thus, there exists considerable scope for reducing VOC beyond the present regulations.
Emission expansionA unique system installed by Anguil Environmental has enabled a company to increase its VOC emission treatment capacity by more than a factor of seven. The customer, a spray painting plant in Italy, planned to install new spray booths and ovens resulting in a five-fold increase in the air volume exhausted to atmosphere.
Originally, the VOC emissions were treated by a regenerative thermal oxidiser, but this unit had little additional capacity and could certainly not treat the projected increase in exhaust air volume. The customer was therefore faced with the purchase of a much larger regenerative thermal oxidiser at a very high capital cost - plus no space was readily available to site such a large unit. The solution was to install a rotary concentrator prior to the existing oxidiser. The concentrator operates by converting a high volume/low VOC concentration stream into a correspondingly lower volume/higher VOC concentration stream. Concentration factors can be up to 20 times, but in this case a design factor of ten was utilised. Not only was the capital cost four times lower than a new larger oxidiser, but the support fuel costs of the combined oxidiser and concentrator system are virtually eliminated as the oxidiser runs in an autothermal mode.