Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment – Gas – vapor – or critical fluid
Reexamination Certificate
1999-09-09
2001-06-12
Phasge, Arun S. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
Gas, vapor, or critical fluid
C205S763000
Reexamination Certificate
active
06245214
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to carbon monoxide removal from a hydrocarbon reformate fuel. More specifically, it relates to apparatus and methods that use a catalytic material to adsorb carbon monoxide and an electrical current to initiate a chemical reaction between an oxidizing agent and carbon monoxide that has been adsorbed by the catalytic material, thereby regenerating the material.
The internal combustion engine found in most cars and trucks burns a hydrocarbon fuel such as diesel or gasoline to drive pistons or rotary mechanisms by the force of the expanding gas. Many electrical power plants burn fossil fuel to produce electrical energy through combustion turbines. These processes suffer from a number of limitations. They are inefficient because of the intrinsic limit of the thermodynamic principles involved. Burning of fossil fuel is oftentimes incomplete and produces harmful byproducts such as carbon monoxide, nitrogen oxides and various hydrocarbons in the emissions, which have resulted in environmental pollution. In addition, there is a growing awareness that we are rapidly depleting the non-renewable energy resources on this planet. This, in turn, has led to concerns about the reduction of energy consumption by increasing efficiency and utilizing renewable energy resources.
Fuel cells convert the chemical energy in the fuel directly into electrical energy through an electrochemical reaction. Because they do not operate on the principle of gas expansion through combustion, they do not suffer the same limitations of thermodynamic efficiency commonly found in automobile engines and steam turbines. Accordingly, it is possible for fuel cells to achieve a level of efficiency far greater than that seen in most traditional industrial processes. Additionally, fuel cells make it possible for fuel processors to use renewable forms of energy such as methanol and ethanol, thereby conserving the limited fossil fuel resources of the planet. Moreover, because of the operating environment of a fuel processor and fuel cell, hydrocarbon, nitrogen oxide and carbon monoxide emissions are negligible, approaching a zero emission state.
While there are several types of fuel cells existing in practice, this invention is targeted mainly for applications in polymer electrolyte fuel cells (PEFCs) which are also known as proton exchange membrane fuel cells (PEMFCs). A very efficient PEFC uses pure hydrogen for fuel and oxygen for an oxidant. Pure hydrogen, however, has traditionally been difficult to handle and relatively expensive to store and distribute. Consequently, attempts have been made to use hydrogen rich gas mixtures obtained from reforming of various hydrocarbon fuels. To obtain a convenient and safe source of hydrogen for the fuel cells, on-board reforming of hydrocarbon based fuels, such as gasoline and methanol, is expected to be utilized. However, these fuels usually contain nitrogen, carbon dioxide, and low levels of carbon monoxide in the range from 100's of ppm to a few percent. While the presence of carbon dioxide generally has little effect on the efficient operation of a fuel cell, even relatively low concentrations of carbon monoxide can degrade fuel cell performance. The degradation results from the carbon monoxide chemically adsorbing over the active sites in the electrode of the fuel cell. Thus, the removal of carbon monoxide from fuel has become a major concern in the advancement of PEFC technology.
Prior attempts to remove carbon monoxide from a gas mixture include a pressure swing adsorption method disclosed in Nishida et al., U.S. Pat. No. 4,743,276. They disclose a method for selectively absorbing carbon monoxide by means of Cu(l) disposed on a zeolite support, including the step of adiabatically compressing a gas mixture in the pressure range of 0.5 kg/cm
2
to 7 kg/cm
2
. Golden et al., U.S. Pat. No. 5,531,809 disclose a vacuum swing method as a variation of the pressure swing method disclosed in Nishida. A solid absorbent is selected which physically absorbs carbon monoxide under pressure. When the pressure is reduced to the range of approximately 20 to 100 torr, the carbon monoxide is released from the solid absorbent. By cyclically repeating this process, carbon monoxide may be removed from a gas.
There are, however, multiple limitations to applying the pressure swing adsorption method to fuel cell applications. Firstly, bulky and expensive pressure resistant tanks, as well as pressure and vacuum pump apparatus, are required to carry out the process. The parasitic weight and volume of these devices make it extremely difficult to apply the pressure swing adsorption method for transportation applications such as a fuel cell power plant for an automobile. A second disadvantage of this approach is the significant power expenditure necessary to cycle the pressurization and depressurization steps. This additional power consumption will result in the reduction of overall efficiency of the fuel cell system. Yet another disadvantage of this process is that the toxic carbon monoxide released from desorption has to be converted to carbon dioxide with additional process steps and equipment.
Another prior art process has been referred to as preferential catalytic oxidation (PROX) of carbon monoxide which was documented in U.S. Pat. No. 5,271,916 by Vanderborgh et. al. In the PROX process, a small amount of pure oxygen or air is mixed into the reformate fuel before it enters a one—or multiple stage catalytic reactor. The catalyst in the reactor, which usually contains dispersed precious metals such as platinum, ruthenium, iridium, etc., preferentially reacts with carbon monoxide and oxygen to convert them to carbon dioxide. Due to the limited selectivity, however, more than a stoichiometric amount of oxygen is needed to reduce carbon monoxide to an acceptable level. Also, the excess oxygen will oxidize the hydrogen in the reformate fuel. Even with the PROX process, the concentration of CO in the reformate stream is often still significantly higher than the desirable level for sustainable PEFC operation. Furthermore, the carbon dioxide in the reformate may be converted to carbon monoxide through a reversed water-gas shift reaction inside of the fuel cell.
To further eliminate residual carbon monoxide that escapes from the pretreatment or forms from the reversed water-gas-shift reaction inside of the fuel cell, a direct oxygen injection to fuel cell method was developed. For example, Gottesfeld, U.S. Pat. No. 4,910,099 discloses a method of injecting a stream of oxygen or air into the hydrogen fuel so as to oxidize the carbon monoxide. Pow et al., U.S. Pat. No. 5,316,747 disclose a similar means of eliminating carbon monoxide directly by introducing pure oxygen or an oxygen containing gas along the latter portion of a reaction chamber in an isothermal reactor in the presence of a catalyst that enhances the oxidation of the carbon monoxide. Wilkinson et al., U.S. Pat. No. 5,482,680 disclose the removal of carbon monoxide from a hydrogen fuel for a fuel cell by means of introducing a hydrogen rich reactant stream into a passageway having an inlet, an outlet and a catalyst that enhances the oxidation of carbon monoxide; introducing a first oxygen containing gas stream into the hydrogen rich reactant stream through a first port along the passage way, thereby oxidizing some of the carbon monoxide within the reactant stream; and introducing a second oxygen containing gas at a subsequent point, further oxidizing the remaining carbon monoxide. Wilkinson et al., U.S. Pat. No. 5,432,021 similarly oxidize carbon monoxide to carbon dioxide by means of an oxygen containing gas introduced into a hydrogen rich reactant stream in the presence of an unspecified catalyst.
There are several significant limitations for the PROX process and oxygen injection process. One of these limitations is the parasitic consumption of hydrogen. Due to the limited selectivity, the oxidant injected into a hydrogen rich fuel is always higher than the stoichiometric amount necessary
Kaiser Mark
Liu Di-Jia
Rehg Timothy J.
Williams James C.
Allied-Signal Inc.
Phasge Arun S,.
Zak, Jr. Esq. William J.
LandOfFree
Electro-catalytic oxidation (ECO) device to remove CO from... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electro-catalytic oxidation (ECO) device to remove CO from..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electro-catalytic oxidation (ECO) device to remove CO from... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2453719