Final Report: Advanced Low-Temperature Emissions Control Technology for MTBE DestructionEPA Contract Number: 68D02029
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: April 1, 2002 through September 1, 2002
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2002) RFA Text | Recipients Lists
Research Category: SBIR - Waste , Hazardous Waste/Remediation , Small Business Innovation Research (SBIR)
Description:Cost-effective technologies are needed to clean up ground water 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 also is credited with reducing air emissions from automobiles. In past decades, gasoline containing MTBE has been released into the environment through leaking fuel storage tanks, leaking product pipelines, accidental releases at gasoline dispensing areas, and spillage and emissions from passenger vehicles and watercraft. These leaks often occur in densely urban areas, and MTBE has been found in lakes, underground aquifers, and urban wells in 49 states. The U.S. Environmental Protection Agency has tentatively classified MTBE as a possible human carcinogen, and MTBE has an objectionable odor and taste. One television news program, 60 Minutes, has called MTBE "the biggest environmental crisis of the next decade."
Air stripping is considered to be a well-demonstrated and inexpensive method for removing organics from water. However, due to the physical and chemical properties of MTBE, it is difficult and costly to treat the resulting MTBE off-gas emissions. In this Phase I research project, a novel technology was investigated to treat these MTBE emissions by oxidation of the stripper off-gas at near-ambient temperature. This new technology destroys the MTBE emissions while avoiding the alternative costs of high-temperature oxidation or carbon adsorption.
The purpose of the Phase I project was to establish the technical and economic feasibility 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 the destruction of dilute concentrations of MTBE and other contaminants arising from the use of air strippers to remediate MTBE-contaminated groundwater or from soil vapor extraction to remediate MTBE-contaminated soils. The technology was demonstrated to be technically and economically feasible.
The overall goal of the Phase I research project was to establish the technical and economic feasibility of a novel, low-temperature catalytic oxidation technology for MTBE and benzene, toluene, ethylbenzene, and xylene (BTEX) destruction that utilizes a new class of catalyst compositions developed for low-temperature application. This technology was designed to be highly effective for the destruction of dilute concentrations of MTBE, toluene, and t-butyl alcohol (TBA) in high flow rate air streams arising from the use of air strippers to remediate MTBE-contaminated groundwater or for soil vapor extraction to remediate MTBE-contaminated soils. Toluene was used as a model compound to represent the class of BTEX compounds found in MTBE-contaminated soils, whereas TBA was used as a model compound for biological degradation by-products of MTBE in the soil. Phase I research has demonstrated the technical feasibility of developing new catalysts that are active enough to economically destroy MTBE, toluene, and TBA in air at flow rates needed for MTBE remediation, which exhibit high reaction selectivity, and which are capable of use in low pressure drop catalyst formulations. In the Phase I feasibility study, the project required synthesis and characterization of approximately 30 catalysts (Task 1); evaluations of the catalytic reactor system performance (Task 2); and evaluations of design, cost, and system performance considerations (Task 3).
The new catalysts utilized a reducible oxide in combination with low amounts of noble metal to enable use at near-ambient temperature. The reducible oxide in the catalyst changes its oxidation state and serves to pump oxygen atoms to the noble metal component, producing a reverse spillover of oxygen atoms to circumvent certain limiting steps in the Mars-van Krevelen reaction mechanism. The resulting catalyst was shown to convert MTBE and TBA at temperatures near 30°C and to completely destroy t-butyl alcohol and butenes at temperatures below 60°C. Toluene was fully oxidized at temperatures below 80°C. In contrast, conventional volatile organic compound (VOC) oxidation catalysts require temperatures of 300-600°C for such applications.
The catalyst is 275 times more active than commercially available platinum on alumina catalyst, when tested in pellet form. The catalyst composition was successfully produced in monolith form, providing extremely high activity for MTBE destruction to carbon dioxide at temperatures of 50-80°C. Although the catalyst was not optimized, it was 10-50 percent of the cost of traditional platinum coated monolith catalysts due to its low noble metal content, and was orders of magnitude more active.
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 other contaminants fed to the reactor. That is, no other by-products could exist. In addition, trace by-products were determined by chromatography and other analytical studies to be absent, confirming the carbon balances and showing carbon dioxide to be the sole reaction product. During tests of up to 40 days in duration, there was no evidence of catalyst deactivation at these low operating temperatures.
Design and cost estimates were developed for an MTBE remediation case study, and were compared to vendor quotes obtained for granular activated carbon (GAC) adsorption and high-temperature catalytic oxidation. One metric used in the comparison was the annualized project cost, which included both the operating costs and an annual charge on capital. The new technology provided annualized costs of only 5-15 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 Phase I technology.
The new low-temperature technology offers many advantages. For example, low-temperature operation greatly reduces materials of construction requirements. Fiberglass reinforced plastic construction materials can be used in place of stainless steel, with both a cost savings and corrosion benefits. The use of low temperatures obviously reduces energy consumption, for both fuel and electricity. Also, it avoids the requirement of stainless steel gas-to-gas heat exchangers, which exhibit low heat transfer coefficients and are inherently costly. Indeed, because of the high cost of such heat exchanges, savings usually are accrued by selecting exchangers with low overall energy recovery of about 50 percent. 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°C to 600°C, instead of between the traditional limits of 300°C and 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 Phase I technology.
Conclusions:KSE, Inc., concludes that commercial development of the new class of MTBE oxidation catalysts is technically feasible, and their commercial application is economically feasible. Commercial success of the new technology is highly likely. Phase II studies will complete the development of this new class of catalysts, optimize their performance, finalize commercial catalyst performance requirements, and extend their application to other types of VOCs.
The catalyst will find application in lowering the cost of remediation activities involving MTBE-contaminated gasoline, including contamination of both soils and water. It also is effective for air emissions control of other oxygenates, such as air emissions from ethanol plants, including ethanol and acrolein. Other industrial plants exhibiting oxygenate emissions also would benefit from the technology. The ability of the technology to operate at near-ambient temperatures could save capital investment and operating costs of pollution control by nearly an order of magnitude.