Low Temperature Oxidation Catalyst:

Dilute stream pollution control is becoming recognized as a major environmental control issue for the United States industrial community at large. Air stripping of VOC contaminated groundwater produces dilute air emissions for which current technology provides no satisfactory solution. High temperature catalytic oxidizers are available, but require processing tremendous volumes of air at temperatures of 300oC and higher, resulting in uneconomic performance at these dilute concentrations. Thermal incinerators also require excessive supplemental fuel for such dilute mixtures of VOCs arising from air strippers. Gas membrane processes are only now emerging for gas separation, and are ill suited for dilute mixtures. Pressure swing adsorption using zeolites or resins is not applicable to dilute mixtures, and rotating wheel adsorbers are uneconomic for such dilute concentrations. Packed bed activated carbon adsorption is inefficient for many VOCs such as MTBE, and simply transfers the MTBE problems of odor and carcinogenicity to the hazardous solid waste, which is increasingly difficult to manage. Carbon regeneration by steam is costly, and is generally economic only for very large-scale operations. Landfill options for spent carbon will become more limited, as it involves transportation and disposal of hazardous wastes.

To meet these control objectives, VOC oxidation catalysts with dramatically higher activity are required, compared to traditional commercial catalysts. KSE has developed such catalysts, allowing operation at temperatures near ambient. Patent applications are pending on composition of matter.

Catalytic MTBE Oxidation Performance
Air stripping is a conventional method for removing organics from water, and could be considered for remediation of groundwater contaminated by MTBE. The Henry’s law constant is a measure of the tendency of an organic compound to be removed from water by air stripping. The Henry’s law constant of MTBE is several times lower than that of other organics commonly treated by air stripping (e.g., trichloroethylene and benzene). Hence air stripping of MTBE will prove more difficult than in historical applications of air stripping to remove organics from ground water. However, air stripping of groundwater contaminated by MTBE has been accomplished commercially, for drinking water treatment in La Crosse, Kansas and Rockaway Township, New Jersey. It simply requires more air in the stripping column. Hence, larger volumes of air are released from the air stripper with more dilute MTBE concentrations, compared to conventional air stripper applications. Nevertheless, air stripping is the one method proven commercially to reduce aqueous phase MTBE concentrations successfully and inexpensively. To utilize such a technology, it is imperative that MTBE emissions from air strippers be controlled, both for environmental safety reasons and in recognition of odor issues arising from MTBE emissions in densely urban areas.

Typical comparative results for the KSE low temperature oxidation catalysts are presented in Table 1. Note that MTBE can be destroyed at temperatures below 60oC, because its activity is shown to be over 100 times that of a conventional commercial VOC oxidation catalyst, platinum on alumina.

Table 1. Activity of KSE Catalysts

For a process flow rate of 500 SCFM, the KSE catalyst can achieve 95% destruction efficiency for MTBE using a catalyst volume of only 0.5 ft3 of catalyst at 60oC. By contrast, the conventional platinum on alumina catalyst would require 100 times the catalyst volume, or 50 ft3. As a result, economics requires that the conventional platinum on alumina catalyst be operated at elevated temperature, often over 400oC. Hence, the high activity KSE catalyst not only requires less catalyst, but also can be used without heat exchangers and high temperature metallurgy for the reactors.

Formaldehyde Catalytic Oxidation
Another important application is the low temperature oxidation of formaldehyde. As shown in Figure 1, KSE catalyst formulations provide literally an order of magnitude higher catalyst activity at 25oC than available from traditional commercial catalysts. The measure of activity used in Figure 1 is proportional to turnover number, and inversely proportional to required reactor size.

Figure 1. KSE Catalyst Activity for Ambient Temperature Formaldehyde Oxidation

In addition, it is well known that commercial applications of catalysts for oxidation of emissions of formaldehyde in air become deactivated, due to the formation of oligomers of formaldehyde on the catalyst surface. As shown in Figure 2, no deactivation of the KSE catalyst was observed over a 2,500 hour test period. By contrast, Figure 2 illustrates that the commercial platinum alumina catalyst undergoes severe deactivation within only 500 hours.

Figure 2. Excellent Stability against Deactivation of KSE Catalyst

Although not shown in the figures, the selectivity of the KSE catalysts was also excellent. Carbon balances were performed to demonstrate that the measured carbon dioxide product fully accounted for the disappearance of all the formaldehyde, showing no other byproducts could have been produced. Also, detailed analytical studies of the reactor effluent found no byproducts of the catalytic reaction by the KSE catalysts.

Economics Benefits of KSE Catalysts
Comparative economic analyses for the KSE technology and vendor quotes from alternative technologies are shown in Figure 3. Here, the annual emissions control cost shown in Figure 3 includes both the annual operating cost and an annual recovery of capital investment (25%). Note that several of the vendor quotes excluded items which will add significantly to the cost of their competitive technologies. Nevertheless, the KSE catalyst achieves pollution control at only 10% to 20% of the cost of competitive technologies. This is achieved due to the low temperature operating system, allowing use of inexpensive Fiber Reinforced Plastic (FRP) construction materials, and eliminating the furnaces, heat exchangers, exotic metallurgy, and extensive control systems associated with high temperature emissions control systems. It also avoids the high cost of consumables and the disposal of hazardous materials associated with Granular Activated Carbon or permanganate alternatives.

Generally, if a new technology is an order of magnitude less expensive than the traditional technology, it is viewed as a “break-through” technology. Not only will the new technology displace the traditional technology in the traditional markets, but also the break-through technology can enter entirely new markets due to its improved cost-effectiveness. The new class of catalysts offers this potential.

Figure 3. Comparative Annual Emissions Control Cost for KSE Catalyst

The commercial potential of the KSE catalyst technology is excellent, driven by the dramatic cost advantages shown in Figure 3. Emissions control systems for formaldehyde producers represent a significant market, with over 3 billion pounds of formaldehyde being produced annually. In addition, the ability of the KSE catalyst to function at room temperature opens possibilities for catalytic indoor air quality control, a market not currently served by catalysis. The advantage is being captured of low temperature VOC oxidation, allowing use of inexpensive FRP construction materials, and eliminating the furnaces, heat exchangers, exotic metallurgy, and extensive control systems associated with high temperature emissions control systems, as described above.

The new catalyst technology may also find applicability to such fields as Fischer-Tropsch catalysis, carbonylation catalysis, alcohol synthesis, electrochemical processes, and photochemical applications..