Final Report: Photocatalytic AIR Cleaner for Indoor Air Pollution ControlEPA Contract Number: 68D00275
Title: Photocatalytic AIR Cleaner for Indoor Air Pollution Control
Investigators: Kittrell, J. R.
Small Business: KSE Inc.
EPA Contact: Manager, SBIR Program
Project Period: September 1, 2000 through September 1, 2002
Project Amount: $225,000
RFA: Small Business Innovation Research (SBIR) - Phase II (2000) Recipients Lists
Research Category: Air Quality and Air Toxics , SBIR - Air Pollution , Small Business Innovation Research (SBIR)
The Phase II research project was focused on catalyst and system development for a novel photocatalytic system for IAQ control. The air contaminants emphasized were carbon monoxide, formaldehyde, ethylene, and toluene. Carbon monoxide can arise from malfunctioning furnaces in buildings or from process plant operations, and causes carbon monoxide poisoning. Formaldehyde can be emitted from building insulation, carpets, and furniture, and is a known carcinogen. Toluene is a contaminant generally originating from the outdoor air, and is brought into the building through air intake systems. The levels of these contaminants used to simulate indoor air pollution were selected from U.S. Occupational Safety and Health Administration (OSHA) workplace considerations. The photocatalytic system can provide a highly effective control of microorganisms that can contribute to allergic reactions of building occupants, such as in Sick Building Syndrome.
The Phase II research project consisted of five tasks. Task 1 was designed to synthesize and characterize the photocatalysts. Task 2 was to evaluate these catalysts in reactive tests simulating IAQ control applications for each of the compounds identified above. Task 3 focused on scale-up and systems development. Task 4 provided evaluations of design, cost, and system performance of the novel AIR pollution control technology for IAQ applications, including comparisons to other IAQ control alternatives. These alternatives were carbon adsorption and permanganate oxidation technologies, which are widely recognized for IAQ applications. Task 5 provided technical management to assure meeting all milestones on a timely basis, steward the program budget, and implement all required quality assurance/quality control (QA/QC) activities.
The photocatalysts developed for this project were significantly improved compared to the conventional titania photocatalyst historically used for photocatalytic applications. When destroying formaldehyde and carbon monoxide, back-to-back comparison tests were performed for these new catalysts relative to titania. These catalysts were orders of magnitude more active than titania. As an example, for formaldehyde the Phase II photocatalyst was shown to be 150 times more active than titania. For carbon monoxide, the same Phase II photocatalyst was shown to be 420 times more active than titania at the same operating conditions. A previous-generation KSE photocatalyst has been in service for the control of ethylene concentrations in certain indoor air purification applications in the International Space Station. The current Phase II photocatalysts are several-fold more active for ethylene destruction than that catalyst. This extremely high photocatalytic activity of the Phase II catalysts is important to successful IAQ application, because the size of the system, number of ultraviolet light bulbs, and cost of the system are reduced proportionately by this high photocatalytic activity.
Tests also were conducted to demonstrate that the performance of the Phase II photocatalysts does not deteriorate during extended use. Photocatalysts were used to destroy formaldehyde for more than 40 days of continuous operation, operating 24 hours per day and 7 days per week during this period. Photocatalyst performance was unchanged during this entire test period. Because formaldehyde is known to easily deactivate oxidation catalysts, the absence of deactivation is an important milestone in the development of this technology.
Extremely high reaction selectivity also is important to successful application of photocatalysis in IAQ control. That is, the catalyst must not produce any by-products of the oxidation reaction. Otherwise, these by-products may themselves act as indoor air pollutants, negating the advantages of this indoor air purification method. The absence of by-products was confirmed by several methods, including gas chromatography, compound-specific detector tubes, and individual gas sensors. In addition, carbon balances were used successfully to show that no unknown or undetected by-products could have been produced from oxidation of the contaminants.
As a capstone of the successful completion of the Phase II research project, design and cost estimates were performed for the IAQ control technology. In the evaluation of pollution control processes, classical rate of return methods for economic analysis of profitability are not sufficient guides to the evaluation of a new technology. Instead, a competitive technology assessment must be made, wherein the new technology is compared to existing technologies on a common design basis. This competitive technology assessment requires consideration of a number of criteria, such as investment, operating cost, lifecycle cost, reliability, service factor, ranges of applicability, amounts and types of effluent treatment, and so on.
A competitive technology assessment was completed using comparison criteria applicable to IAQ applications. For selected design cases, a complete capital and operating cost was developed for the AIR technology for IAQ control, based on the results of Tasks 1, 2, and 3. Capital and operating costs also were estimated for alternative technologies, carbon adsorption, and permanganate on alumina for a commercial building as a part of the competitive technology assessment conducted in Task 4.
Foresight Science and Technology, Inc., under contract to the U.S. Environmental Protection Agency, independently surveyed the IAQ market for technologies that could control VOCs. This independent survey also confirmed that the primary competition to photocatalysis for indoor air purification is carbon adsorption and permanganate oxidation. Hence, the competitive analysis would appear to be on a sound basis, confirmed by independent analysis.
The design and cost estimation required completion of the following: process operating plan, process design basis, process flow diagram, process equipment specifications, purchased equipment cost estimate, fixed capital investment estimate, and operating cost estimate. Vendor quotes were obtained for all major items of equipment. Allowances were developed from KSE's experience and vendor guidance for such items as electrical components and control requirements. Estimates were included for the costs of design, engineering, and manufacturing, based on the specific nature of the equipment. Operating cost estimates were developed from individual cost estimates for materials, labor and overhead, utilities, maintenance, investment-related costs, and energy consumption.
The results of these Task 4 studies consisted of evaluating a number of criteria, reflecting comparison of the performance characteristics of the photocatalytic technology to the competitive technologies. As an example of one case, a 10,000 ft3/min at standard conditions unit was considered for purifying air containing 10 ppm(v) of formaldehyde. For this case, the competitive permanganate oxidation technology was determined to be superior to carbon adsorption. Even the least cost case of permanganate oxidation would cost approximately $3 million per year for replacement of the permanganate media. For the Phase II photocatalytic technology, the annual operating cost is estimated to be less than $2,000 per year. Clearly, this photocatalytic technology offers the opportunity to be a revolutionary technology for indoor air pollution control.
The research and development of a novel photocatalytic technology has been completed for IAQ control. The effectiveness of the new technology is dependent on the extremely high photocatalytic activity of the photocatalyst. This photocatalyst is orders of magnitude more active than the conventional titania photocatalyst for the IAQ contaminants tested (carbon monoxide, formaldehyde, ethylene, and toluene). The Phase II photocatalyst also is highly resistant to deactivation with use and is highly selective. The cost of the system is estimated to be a small fraction of the cost of competitive IAQ control technologies, and could revolutionize the methods for purification of indoor air.