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The proposed research is to address the EPA new air quality standards by developing a new generation of more efficient and low cost electrostatic precipitators (ESPs) for which a permanent U.S. patent is pending. This is a novel concept based on the replacement of the particle collection plates in all ESPs by membranes made from inexpensive advanced materials. Instead of conventional rapping, in which heavy plates are pushed (buckled) to dislodge collected dust, the membranes will be either pulled to induce shear for dislodging the collected particles or cleaned by other novel means. This should result in decreased re-entrainment of particles and reduced complexity of the ESP. The preliminary experiments conducted at Ohio University with different membrane materials in a small-scale ESP show that membranes woven from carbon fibers can be used to collect dust particles as efficiently as conventional steel plates. However, ESPs operating in more severe thermal environment would require the use of a ceramic fabric, which must be coated to provide the electrical conductivity. The success of this concept depends on two key issues that will be studied in detail. The first is the induced vibration in the membranes. Relationship between the dust collection/removal efficiencies and vibration parameters such as gas flow speed, membrane tension, etc., need to be better understood. There are strong indications that the membrane vibration can be controlled by a proper design and by adjusting its tension. Another key factor is development of a coated membrane by integration of the required properties such as corrosion and fatigue resistance, electrical conductivity, fabric weave density etc. A significant advantage of this design is the drastic reduction in weight of collector plates, about one order of magnitude. The resulting reduction in cost of production, installation, transportation and repair of the collection surfaces should also have a significant economic effect. Another advantage of the new ESPs is that they can be fabricated from corrosion- resistant materials. Such fabrics will be suitable for implementation of new technologies for controlling gaseous, providing the next generation of ESPs with vast new capabilities to control pollution. It is also anticipated that the membrane can be coated with catalytic materials to promote removal of gaseous pollutants and heavy metals. The proposed research has elements of risk since the substitution of plates by membranes is a new concept that has not been fully tested yet.

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EPA Grant Number: R828206
Title: Development of a Heterogeneous Catalyst for Hydroformylation in Supercritical CO2
Investigators: Martin A. Abraham, Julian A. Davies, Mark R. Mason
Institution: Department of Chemical and Environmental Engineering and Department of Chemistry, University of Toledo, Toledo, OH
EPA Project Officer: Barbara Karn
Project Period: July 1, 2000 – June 30, 2003
Project Amount: $315,000
Research Category: Technology for a Sustainable Environment
Description:  

Many industrially important chemical syntheses are carried out commercially in liquid phase, organic solvents and through the use of homogeneous catalysts. The large-scale use of liquid organic solvents has substantial environmental implications, providing the current impetus for the development of alternative, environmentally benign, reaction solvents. Recovery of homogeneous catalysts also may involve the use of organic solvents and those may be eliminated completely if heterogeneous catalysts are used.

This proposal seeks to eliminate potentially hazardous organic solvents through two novel developments:

1. Perform the target reaction in the benign reaction solvent supercritical CO2, and

2. Develop a heterogeneous catalyst for the target reaction.

The use of CO2 as a reaction solvent offers optimal environmental performance because CO2 does not deplete the ozone layer, does not contribute to ground-level smog, and will not contribute to global warming. The use of CO2 by-product from existing commercial and natural sources will ensure that no net increase in global CO2 results from the use of this technology. One limitation of heterogeneous catalysis has been the inability to control selectivity. We believe, however, that modification of the catalyst and the support for optimization with scCO2 can allow the development of active and selective catalysts for the hydroformylation reaction. Use of supported metal-phosphine ligands will allow control of selectivity, similar to that seen in liquid-phase catalysis. Modification of the catalyst support, and the use of shape-selective catalysts with uniform molecular-size pores, provides further opportunity to achieve selectivity control. The work completed through this research will demonstrate the production of commercially important chemical intermediates without the use of organic solvents. The proposed process considers an environmentally benign synthesis that can be adapted for the production of many important chemicals. These process modifications decrease the potential for volatile organic compounds (VOCs) emission in large-scale production processes, providing one means for the chemical industry to be responsive to pollution prevention requirements.

Impending strict regulations of all combustion and thermal sources under the CAAA, RCRA, and EPA's Combustion Strategy will be based on calculated risk and the ability of the source to minimize emissions of harmful air pollutants. Research indicates that emissions of a potentially complex array of planar, chlorinated polynuclear aromatic hydrocarbons (ClPAHs) are major carcinogenic and/or endocrine disrupting products formed from thermal processing of chlorine containing materials. However there is insufficient information on the nature and origin of pollutant emissions with which to make scientifically defensible regulatory decisions. It is the origin and pathways of formation of these chemicals that we propose to study.
We have identified three research objectives for our proposed study: 1) determine the types of ClPAHs that can be formed, 2) determine their mechanism and rate of formation, and 3) develop reaction kinetic models of their formation. Previous research on molecular growth of chlorinated hydrocarbons (CHCs) indicates that C2 olefinic and acetylenic radical-molecule Cl-displacement reactions may proceed more rapidly than the corresponding H-displacement reactions. This finding, along with the resistance of CHCs to oxidation, suggests that PAH formation may be more facile in chlorine containing systems than purely hydrocarbon systems. Thus the central hypothesis that we will test is that CHCs are more prone to formation of PAH than hydrocarbon species.

 Combustion and thermal processes are generally recognized as the major source of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) in the environment. The US-EPA has targeted their emissions for stringent new regulation that generally involve the installation of costly new control devices that only transfer the PCDD/F to different media. The goal of this project is to prevent the formation of PCDD/F through modification of conditions in the source. Since it is now well-established that PCDD/F are formed in the post-combustion region, our strategies focus on techniques that apply to "cool-zone" chemistry.
We have developed a unified pathway of formation that incorporates most of the known observations and theories of PCDD/F formation. This pathways suggests the following hypothesized control strategies that we will test in this project:

1. Control through prevention of de novo formation of small-molecule, PCDD/F precursors that are formed from gas-solid reactions of combustion-generated radicals with combustion generated soot and char.

2. Control of chemisorption of large-molecule precursors (formed from gas-phase molecular growth involving the de novo precursors) on fly-ash surfaces.

3. Control of surface catalyzed chlorination by transition metal chlorides.

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