VOCs: a market improvement

A recent study by Frost & Sullivan, the international market consulting company, points out: “The VOC control equipment market, amassing sales worth $373.6m in 1999, faces major difficulties and lacks a new technology that will resolve them readily. Mitigation at source is likely to diminish the potential for VOC control equipment and half the total market is mature, raising the possibility that a significant proportion of 50% of the total market will become stagnant. R&D has been focused on cost reduction in the face of price resistance and falling prices across all markets and there is a prevailing lack of technological innovation, other than performance enhancement of existing technologies.”

Paint your wagon

Dr 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 expansion

A 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.

Concentration

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.

New method of VOC capture and recovery

Researchers at the University of Illinois have developed a new method for capturing and recovering dilute VOCs and other hazardous air pollutants. The method uses an electrically conductive activated carbon fibre cloth with almost twice the adsorptive capacity of activated carbon granules. The electrothermal desorption method, devised by Mark Rood, professor of civil and environmental engineering, first uses the cloth to remove the contaminants from the air before an electrical current is passed through the fabric, allowing for rapid heating. This releases the solvent, which is then condensed on the inside of the chamber and drained.