Chemistry: electrical and wave energy – Processes and products – Processes of treating materials by wave energy
Reexamination Certificate
2001-02-12
2003-03-11
Wong, Edna (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Processes of treating materials by wave energy
C204S157300, C204S158200, C588S253000
Reexamination Certificate
active
06531035
ABSTRACT:
FIELD OF THE INVENTION
Examples of treatable streams include, among others, ventilation makeup air, ambient air, air from stripping and off-gassing operations, soil vapor extraction (SVE), airborne matter (e.g. organic particulate, biogenic and microbial matter) and process vent gas, wastewater treatment off-gas, liquid effluents (e.g. wastewater, industrial and agricultural runoff) containing at least one undesirable or otherwise unwanted compound. Moreover, this application presents a holistic approach to the design of the high performance photo and thermocatalytic systems that possess:
i—Rapid species mass transfer to and from the active sites of the catalyst.
ii—Uniform transport of thermal and radiant energy to the active sites of the catalyst.
iii—Decoupling of the conversion efficiency from process intrinsic energy efficiency.
iv—Minimal pressure drop.
BACKGROUND OF THE INVENTION
As environmental regulations become progressively more stringent, new techniques and approaches are needed for dealing with difficult contaminants. For example, the required destruction and removal efficiencies (DREs) for some environmental pollutants, such as toluene diisocyanate (TDI), dioxin, dibenzofurans and polychlorinated biphenyls (PCBs) are extremely high. Conventional methods such as carbon adsorption or liquid scrubbing are not a complete remediation solution due to the fact that they simply transfer contaminants from one medium (i.e. water or air) to another (i.e. solid carbon or scrubbing liquid). On the other hand, incineration and catalytic thermal oxidation present their own limitations. For example, the widespread production and use of chlorinated compounds in the industrially developed countries has resulted in large amounts of halogenated organic contaminants to seep into the soil, water and air. Incineration and even thermocatalytic oxidation of wastestreams containing halogenated compounds in many cases produce emission of products of incomplete combustion (PIC) such as dibenzofurans, dioxin and other pollutants that are known or suspected carcinogens. It is to be understood that in the terminology of this application “target species/compounds” denote those entities contained within the contaminated stream that are targeted for complete destruction and removal.
The past two decades has seen rapid growth and promulgation of new remediation technologies. In particular, a class of pollution control technologies known as the advanced oxidation processes (AOPs) has been the focus of much research and development. Among AOPs, those that employ ultraviolet (UV) radiation in conjunction with active oxidants (i.e. ozone, hydrogen peroxide, hydroxyl radical, superoxide ion radical, etc.) to accomplish mineralization of the target organic contaminants are of special interest. Generally, UV/AOPs are characterized with respect to the type of either the catalyst and chemical reactions involved (i.e. homogeneous vs. heterogeneous) or light source employed (i.e. solar vs. artificial).
In general, UV/AOPs for treatment of the hazardous organic contaminants (HOCs) in fluids (both gas- and liquid-phase) comprise the following steps:
In the first step, an organic contaminant (hereafter-called “primary reactant” or “target compound”) that is adsorbed on the catalyst surface or resides within the fluid reacts to form products (hereafter termed “intermediate” or “secondary” products).
In the next step, the secondary products react to form other products (hereafter called “tertiary products” or “final products”) that can be regarded as more benign, safer, or less detrimental to health and environment. The tertiary products are formed through a sequence or stepwise reaction scheme and an effective way to obtain tertiary or final products is to use specially engineered catalytic reactors disclosed in this document.
DESCRIPTION OF THE PRIOR ART
It is generally recognized that the UV-based AOPs do not universally enjoy high process energy efficiencies. This realization has motivated many researchers to test the concept of integrated or hybrid processes. In this approach, several processes are combined to produce a hybrid system that is capable of treating contaminants in the waste stream at much higher overall process energy efficiency and reduced life-cycle costs than each of individual processes, alone. This is especially true in applications where the initial concentration of the target compound may vary wildly in the course of the treatment process.
A good example is ethanol emission (in air) from some pharmaceutical product dryers. Ethanol concentration in the product dryer varies during a typical cycle by two orders of magnitude. Also, hybrid processes can be used in certain applications where valuable chemicals (e.g. acrylonitrile monomer, solvents, etc.) are emitted in the effluent that can be recovered. Yet another example involves treatment of the energetic materials. It is known that the photocatalytic treatment and mineralization of 2,4,6-trinitrotoluene (TNT) in aqueous media is difficult. However, once partially oxidized, many microorganisms can readily metabolize the partial oxidation products. Here, a UV/AOP is combined with another treatment process (i.e. biological) to achieve a much higher process efficiency. Examples of surrogate processes employed in the prior art include bioremediation, electron beam, thermocatalytic oxidation, activated carbon or synthetic adsorbents, UV/H
2
O
2
and UV/O
3
, to name just few. Alternatively, performance improvement can be made at the catalyst/support level, using multifunctional catalytic media, i.e. capable of acting as both photocatalyst and thermocatalyst.
It is to be understood that, in the terminology of this application, “media” or “catalytic media” denotes the combination of photocatalyst(s) and its/their supporting base material(s). Most base material(s) of the prior art simply provide(s) a structural support for the active catalyst(s) used and do not normally partake in the reactions or provide other known functions. Examples include, but not limited to, U.S. Pat. Nos. 4,892,712, 4,966,759 and 5,032,241 to Robertson et al.; U.S. Pat. No. 5,126,111 to Al-Ekabi et al.; and U.S. Pat. No. 5,035,784 to Anderson et al. However, it is possible to have a multifunctional media that is both photocatalytically and thermocatalytically active. The rationale for using a multifaceted media will now be described.
Consider a UV/AOP that employs a high power light source such as a medium-pressure mercury lamp (MPML). MPMLs generate large amounts of thermal radiation, at relatively high temperatures. Even when a low-pressure mercury lamp (LPML) is used as the source of UV light, considerable amount of low-level waste heat is given off. For example, according to vendor specifications, a standard 65 W Voltarc
R
lamp (G64T5VH), converts less than 40% of the input electrical power to emitted light in the form of 254-nm radiation. The electric to UV energy conversion efficiency is lower yet for fluorescent black light (less than 25%) and medium pressure mercury lamps (less than 15%).
It is generally recognized that only a very thin layer on the photocatalyst surface can actually be excited to enter photocatalytic reactions. For most active photocatalysts, the physical thickness of this layer or skin does not exceed few microns. This is due to the fact that UV radiation is completely absorbed within a skin only few microns thick on the exposed photocatalyst surface. On the other hand, thermal radiation can penetrate deep into the supported catalyst and base material. The fact that most target species can also be adsorbed into the deep layers of the photocatalytic media (inaccessible to UV but affected by thermal radiation and heat) encourages the use of multifunctional catalysts capable of utilizing both heat and light emitted by medium and high pressure UV lamps. Thus, a multipurpose catalyst can comprise a base material that acts as both a thermocatalyst as well as support structure for the photocatalyst. Alternatively, a dual catalyst may be used that can
Martin Eric
Muradov Nazim Z.
Tabatabaie-Raissi Ali
Law Offices of Brian S. Steinberger , P.A.
Steinberger Brian S.
University of Central Florida
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