Final Report: Advanced Low Temperature Emissions Control Technology for MTBE DestructionEPA Contract Number: 68D03045
Title: Advanced Low Temperature Emissions Control Technology for MTBE Destruction
Investigators: Kittrell, J. R.
Small Business: KSE Inc.
EPA Contact: Manager, SBIR Program
Project Period: May 1, 2003 through April 30, 2005
Project Amount: $225,000
RFA: Small Business Innovation Research (SBIR) - Phase II (2002) Recipients Lists
Research Category: Hazardous Waste/Remediation , SBIR - Waste , Small Business Innovation Research (SBIR)
Cost-effective technologies are needed to clean up groundwater and soils contaminated by oxygenates that were used in reformulated gasoline and oxygenated winter transportation fuels. Methyl tertiary butyl ether (MTBE) is a widely used oxygenate compound that historically was added to gasoline. It provided a low-cost means to achieve high gasoline octane ratings and was credited with reducing air emissions from automobiles.
In past decades, gasoline containing MTBE was released into the environment through leaking fuel storage tanks, leaking product pipelines, accidental releases at gasoline dispensing areas, and via spillage and emissions from passenger vehicles and watercraft. These leaks often occurred in densely urban areas. MTBE has been found in lakes, underground aquifers, and urban wells in 49 states. The U.S. Environmental Protection Agency tentatively classified MTBE as a possible human carcinogen. Furthermore, MTBE has an objectionable odor and taste at very low concentrations. One television news magazine, 60 Minutes, called MTBE “the biggest environmental crisis of the next decade.”
Some gasoline fractions are reasonably biodegradable and naturally can decompose underground. Unfortunately, MTBE is not readily biodegradable. In underground plumes, MTBE has been found long after other gasoline hydrocarbons have been biodegraded naturally. MTBE is an unusually long-lived environmental contaminant. The combination of slow biodegradation, odor, taste, and possible carcinogenicity has led to regulatory prohibitions against continuing use of MTBE in gasoline.
Air stripping is considered a well-demonstrated and inexpensive method for removing organics from water. Due to the physical and chemical properties of MTBE, however, it is difficult and costly to remediate MTBE and treat the resulting MTBE off-gas emissions. KSE, Inc., developed a novel technology to treat these MTBE emissions by oxidation of the stripper off-gas at low temperature. This new technology destroys the MTBE emissions while avoiding the alternative costs of high temperature oxidation or carbon adsorption.
The price of energy is reaching new highs month after month. Because pollution control activities often involve relatively dilute concentrations of contaminants in large amounts of air, heating and cooling costs are becoming larger. The cost of energy is becoming a more important contribution to overall pollution control costs. Indeed, plant owners may be tempted to shortcut their pollution control activities in an effort to reduce overall fuel costs. The low temperature catalytic oxidation technology of this research project is inherently of low energy consumption, directly due to the utility of low operating temperatures that require little heating or cooling. The emergence of the new low temperature emissions control device from this Phase II project is timely.
The purpose of Phase II was to complete the research and development of a novel low temperature oxidation technology for MTBE destruction that utilizes a new class of catalysts developed specifically for this low temperature application. This technology is highly effective for destruction of dilute concentrations of MTBE arising from use of air strippers to remediate MTBE-contaminated groundwater or from soil remediation using vapor extraction of MTBE. Approximately 100 catalysts were synthesized and characterized for the new low temperature application. The project also included experimental studies of catalytic reactor system performance and engineering evaluations of design, cost, and system performance. The technology was demonstrated to be highly effective for complete oxidation of MTBE.
This technology was designed to be highly effective for the destruction of either dilute concentrations of MTBE in high flow rate air strippers, or more concentrated emissions of MTBE from soil vapor extraction facilities. Phase II research provided a new class of catalysts that are active enough to destroy MTBE in air at very low temperatures, exhibit high reaction selectivity and stability, and are useful in low pressure drop catalyst formulations. The new catalysts utilize a reducible oxide in combination with low amounts of noble metal to achieve high activity at low temperatures of use, termed a noble metal reducible oxide (NMRO) catalyst. The reducible oxide in the catalyst changes its oxidation state and serves to pump oxygen atoms to the noble metal component, thereby circumventing certain limiting steps in catalytic oxidation reaction mechanism. The resulting catalysts utilize this oxygen pump to destroy MTBE at temperatures below 100°C, depending on the space velocity used. By contrast, conventional volatile organic compound (VOC) oxidation catalysts are ineffective for low temperature oxidation of MTBE, instead requiring temperatures of 300°C to 500°C.
The new KSE NMRO catalyst is orders of magnitude more active than the traditional
commercial platinum on alumina catalyst. The catalyst composition was successfully
produced in a monolith form, offering low pressure drop and low energy consumption
for air blowers. The new catalyst provides extremely high activity for MTBE
destruction to carbon dioxide at low temperatures. If carbon dioxide is not
desired (e.g., due to global warming arguments), the catalyst can be operated
to produce more readily biodegradable oxygenated compounds that can be absorbed
into water and reinjected into the ground. Because of its high inherent activity,
the catalyst also can be formulated with 20-50 percent of the cost of traditional
platinum-coated monolith catalysts.
The catalyst selectivity was excellent. The selectivity was demonstrated through more than 100 carbon balances, showing that the carbon dioxide product accounted for all of the carbon in the MTBE and/or other contaminants fed to the reactor (i.e., no other significant byproducts were produced). In addition, trace byproduct analyses were conducted by chromatography and other analytical studies. During tests of more than 1,000 hours duration, there was no evidence of catalyst deactivation at these low operating temperatures.
The recent escalation of the global price of energy has affected the economy in general, and is making pollution control more expensive. With the high price of fuel, site owners may be tempted to reduce operating temperatures to conserve fuel, at the expense of destruction efficiency and the environment. Therefore, the emergence of the low temperature oxidation process of this Phase II research project is particularly timely. Furthermore, the new KSE NMRO catalyst can be used in existing high temperature catalytic oxidation units, allowing reduced operating temperatures and conserving fuel. With current energy prices, the advantages in operating costs of the new low temperature KSE NMRO oxidation technology are dramatic, as shown in Figure 1.
Figure 1. Dramatic savings in pollution control costs in high energy price environment using low temperature catalytic oxidation technology.
Design and cost estimates were developed for an MTBE remediation case study and compared to vendor quotes obtained for granular activated carbon (GAC) adsorption and high temperature catalytic oxidation. One metric used in the comparison was the life cycle cost of pollution control, which included both the operating costs and an annual charge on capital. The new technology provided annualized costs of only 10-20 percent of those of presently available technologies—GAC or high temperature catalytic oxidation. Savings in both capital investment and energy costs accounted for the major overall cost advantages of the new technology.
The new low temperature technology offers many competitive features, advantages, and benefits. For example, low temperature operation greatly reduces material construction requirements. Fiberglass-reinforced plastic construction materials can be used in place of stainless steel, with both cost savings and corrosion benefits. The use of low temperatures reduces energy consumption, for both fuel and electricity. In addition, it avoids the requirement of stainless steel gas-to-gas heat exchangers, which exhibit low heat transfer coefficients in air service and are inherently costly. Because of the high cost of such heat exchangers, savings usually are accrued by selecting exchangers with low overall energy recovery (about 50%). Therefore, even with heat exchange, an opportunity remains for substantial energy savings from use of a low temperature catalyst technology. For applications with high concentrations of MTBE, such as soil vapor extraction, the lower ignition temperature of the new catalyst allows the reaction exotherm to occur from 100-600°C, instead of between the traditional limits of 300-600°C. This, in turn, allows more concentrated feeds and less dilution air, providing smaller and less costly units even for the rich concentration case. For GAC, MTBE adsorbs poorly. This characteristic requires large and costly GAC beds, along with frequent, troublesome, and high-maintenance GAC replacement costs. Also, MTBE-contaminated GAC may be considered a hazardous material, increasing disposal costs. All such costs are avoided with the low temperature NMRO catalytic oxidation technology.
The research and development necessary for commercialization of the new class of MTBE oxidation catalysts has been completed. Commercial success of the new technology is highly likely. Phase II studies completed the development of this new class of catalysts, optimized their performance, finalized commercial catalyst performance requirements, and extended their application to other types of VOCs.
The new air pollution control catalyst will find applications in lowering the cost of remediation activities involving MTBE-contaminated gasoline, including contamination of both soils and water. Other industrial plants exhibiting oxygenate emissions also could benefit from the technology. The ability of the technology to operate at low temperatures should save capital investment and operating costs of pollution control, particularly in an environment of upwardly spiraling energy prices.