Final Report: Photocatalytic AIR Cleaner for Indoor Air Pollution Control

EPA Contract Number: 68D99053
Title: Photocatalytic AIR Cleaner for Indoor Air Pollution Control
Investigators: Kittrell, J. R.
Small Business: KSE Inc.
EPA Contact:
Phase: I
Project Period: September 1, 1999 through March 1, 2000
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (1999) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , SBIR - Air Pollution , Small Business Innovation Research (SBIR)

Description:

Health effects of indoor air pollution are particularly important because individuals spend large fractions of their time in indoor environments, and frequently have little control over the exposure time or atmosphere in the workplace. Some indoor air contaminants arise from indoor sources, such as emissions from building insulation, carpets, or furniture. Factories can also have indoor emissions sources, from tanks, pumps, dryers, and other process equipment. Other contaminants originate outside the building, and are drawn into the ventilation air intake systems to circulate in the indoor air. Such outdoor air may be polluted from nearby loading docks and other sources. Among the important indoor air contaminants are carbon monoxide, formaldehyde, toluene, bacteria and mold spores, which can be found in building ventilation systems. Carbon monoxide is poisonous, formaldehyde is a carcinogen, and allergic reactions can arise from microorganisms.

Ventilating the building with outdoor air can sometimes reduce indoor air pollution, if the outdoor air itself is of acceptable quality. However, ventilation with outdoor air is not always possible with new, sealed building designs. Also, ventilation of the indoor environment by increased input of outdoor air can create significant energy penalties, and can bring outdoor air pollution inside the building. New, cost-effective technologies for cleaning indoor air of carbon monoxide and volatile organic compounds (VOCs) are urgently needed. However, indoor air purification is technically challenging, requiring compact, reliable, and inexpensive technology.

The purpose of the Phase I SBIR research program was to establish the technical feasibility of application of an novel photocatalytic technology for cleansing indoor air at ambient temperature. The technology integrates a highly effective adsorption system with a highly effective reaction system to destroy indoor air contaminants. The Adsorption-Integrated-Reaction (AIR) technology should be selective, energy-efficient, and economic for indoor air quality (IAQ) control. The technology utilizes a unique photocatalyst which, when illuminated by ultraviolet light bulbs, destroys VOCs and microorganisms. The Phase I program efforts consisted of synthesis of photocatalysts of new compositions, testing of the photocatalysts in simulated IAQ service, and design and economic studies comparing their performance to other techniques for indoor air purification.

Summary/Accomplishments (Outputs/Outcomes):

The Phase I research program was focused on demonstrating the technical feasibility of developing a novel photocatalytic system for IAQ control. The air contaminants utilized in the Phase I research were carbon monoxide, formaldehyde, and toluene. Carbon monoxide can arise from malfunctioning furnaces in buildings or from process plant operations, and causes carbon monoxide poisoning well known to the public. 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 generally selected from OSHA workplace considerations. Although the photocatalytic system is also expected to be highly effective in control of microorganisms which can contribute to allergic reactions of building occupants, specific studies of these allergens were deferred until the Phase II program.

The Phase I research program consisted the three tasks. The first task was designed to synthesize and characterize the photocatalysts to be used in the experimental program. The second task was designed to evaluate these catalysts in reactive tests simulating IAQ control applications, for each of the three compounds identified above. The third task 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.

The photocatalysts developed for this program were significantly improved compared to the conventional titania photocatalyst used historically for photocatalytic applications. When destroying formaldehyde and carbon monoxide, back to back comparison tests were performed for these new catalysts relative to titania. It was found that the catalysts of this Phase I program were orders of magnitude more active than titania. For formaldehyde, for example, the Phase I photocatalyst was shown to be 48 times more active than titania. For carbon monoxide, the same Phase I photocatalyst was shown to be 257 times more active than titania, at the same operating conditions. This extremely high photocatalytic activity of the Phase I catalysts is very important to successful IAQ application, as the size of the system, the number of ultraviolet light bulbs, and the cost of the system are reduced proportionately by this high photocatalytic activity.

Tests were also conducted to demonstrate that the performance of the Phase I photocatalysts do not deteriorate during extended use. The photocatalyst was used to destroy formaldehyde for over 40 days of continuous operation, operating 24 hours per day and 7 days per week over this period. The photocatalyst performance was unchanged over this entire test period. The absence of deactivation is an important characteristic in the demonstration of technical feasibility of the Phase I technology.

Extremely high reaction selectivity is also important to successful application of photocatalysis in IAQ control. That is, the catalyst must not produce any byproducts of the oxidation reaction. Otherwise, these byproducts may themselves be indoor air pollutants, negating the advantages of this method of purification of indoor air. The absence of byproducts was confirmed by several methods, including gas chromatography, compound specific detector tubes, and individual gas sensors. In addition, carbon balances were successfully used to show that no byproducts could have been produced from oxidation of the contaminants used in the Phase I program.

For successful completion of the Phase I technical and economic feasibility assessment, design and cost estimates were performed for the indoor air quality control technology, reflecting the demonstrated performance of the Phase I experimental program. Indeed, to guide the effective conduct of the Phase II experimental program, the design and cost analysis provide specific insights into issues requiring emphasis in the future laboratory program. Such analyses were performed in Task 3 of the research program.

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, etc.

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 indoor air quality control, based on the results of Tasks 1 and 2. Capital and operating cost were also 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 3.

Foresight Science and Technology, Inc., under contract to the U.S. EPA, independently surveyed the IAQ market for technologies which could control VOCs. The analysis by Foresight Science and Technology was conducted in support of the EPA Phase I SBIR Program. 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 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 estimate were developed from individual cost estimates for materials costs, labor and overhead costs, utilities costs, maintenance costs, investment related costs, and energy consumption.

The results of these Task 3 studies consist of evaluation of a number of criteria, reflecting comparison of the performance characteristics of the Phase I photocatalytic technology to the competitive technologies. As an example of one case, a 10,000 SCFM unit was considered, to purify 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 about $3 million per year, for replacement of the permanganate media. For the Phase I photocatalytic technology, the annual operating cost is forecast to be slightly more than $5,000 per year. Clearly, the photocatalytic technology of the Phase I program offers the opportunity to be a revolutionary technology for indoor air pollution control.

Conclusions:

The technical and economic feasibility of the novel photocatalytic technology has been demonstrated for indoor air quality (IAQ) control, in the Phase I research program. The effectiveness of the new technology is dependent on the extremely high photocatalytic activity of the Phase I photocatalyst. This photocatalyst is orders of magnitude more active than the conventional titania photocatalyst for these IAQ contaminants tested, carbon monoxide, formaldehyde, and toluene. The Phase I photocatalyst is also highly resistant to deactivation with use, and is highly selective. The cost of the system is forecast to be a small fraction of the cost of competitive IAQ control technologies, and, when development is completed in the Phase II research program, could revolutionize the methods for purification of indoor air.

Supplemental Keywords:

Indoor, air, pollution, quality, purification, photocatalyst, experimental, ultraviolet, microorganism, carbon monoxide, formaldehyde, toluene, design, economics, cost, reactor., Economic, Social, & Behavioral Science Research Program, Scientific Discipline, Air, Toxics, air toxics, Chemistry, VOCs, indoor air, Engineering, Engineering, Chemistry, & Physics, Market mechanisms, air pollutants, indoor VOC compounds, ambient air, photocatalytic Adsorption-Integrated-Reaction (AIR) technology, air pollution, cost effective, indoor air quality, Volatile Organic Compounds (VOCs), air quality

SBIR Phase II:

Photocatalytic AIR Cleaner for Indoor Air Pollution Control  | Final Report