Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis
Reexamination Certificate
2000-01-26
2001-12-25
Valentine, Donald R. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
C205S343000, C205S765000, C205S770000
Reexamination Certificate
active
06332968
ABSTRACT:
TECHNICAL FIELD
This invention relates to the field of electrochemical reactors which facilitate the transfer of oxygen. In particular, this invention relates to oxygen semipermeable membranes, components for electrochemical reactors comprising the oxygen semipermeable membrane, electrochemical reactors and reactor components comprising the oxygen semipermeable membranes and optional catalyst, and electrochemical processes which use the oxygen semipermeable membrane and optional catalyst to facilitate electrochemical processes which utilize oxygen transport from an oxygen-containing gas to a gas that consumes oxygen.
BACKGROUND OF THE INVENTION
Synthesis gas is composed primarily of hydrogen and carbon monoxide. Generally, the H
2
/CO molar ratio is from about 0.6 to 6. The production of synthesis gas from light hydrocarbons such as methane and natural gas by partial oxidation is known. The present invention describes an electrochemical reactor having a solid multi-component membrane, which facilitates the electrocatalytic conversion of light hydrocarbons to synthesis gas.
Numerous publications describe conventional fuel cells which completely oxidize methane to carbon dioxide and water. These fuel cells are not designed to conduct chemical processes, but rather-to generate electricity from fuel gas and air (or oxygen). The processes conducted in fuel cells are selected for complete combustion rather than partial combustion and require completion of an external electric circuit for oxidation of fuel gas to proceed.
Other uses for the electrochemical reactor of the present invention include the partial oxidation of hydrocarbons to form olefins, the partial oxidation of ethane, substitution of aromatic compounds, extraction of oxygen from one or more oxygen-containing gases such as SO
2
, SO
3
, N
2
O, NO, NO
2
, steam, CO
2
, ammoxidation of methane, etc.
Dehydrogenation processes for the conversion of saturated organic compounds to unsaturated compounds are well known. Continued efforts have been made in recent years to improve such processes in order to improve the conversion rate and selectivity to desired products. The present invention describes a continuous process for dehydrogenation of saturated hydrocarbons such as ethane to ethylene and acetylene, and propane to propene and propyne. In this process of the present invention, water is a by-product, and electricity may be generated.
The commercial ethane dehydrogenation process, which is an equilibrium limited thermal reaction, must rely on the use of high reaction temperatures to obtain reasonable per pass yields of ethylene. As a result of the high temperatures required, rates of competing cracking and coking reactions are high enough to adversely affect product selectivities.
Convent onal oxydehydrogenation processes, which are not inherently equilibrium limited, also suffer from poor product selectivities at high ethane conversions.
The present invention overcomes the disadvantages inherent in the prior art processes in order to achieve high conversion to unsaturated hydrocarbons combined with low rates of competing cracking and coking reactions.
Processes for the substitution of aromatic compounds are well known. Continued efforts have been made in recent years to improve such processes in order to improve the conversion rate and selectivity to desired products. The present invention describes a continuous process for the substitution of aromatic compounds such as benzene, with a second hydrogen-containing compound. In this process of the present invention, water is a by-product, and electricity can be generated.
Sulfur and nitrogen oxides, for example, are well known noxious pollutants in gas streams emanating from stationary and mobile sources such as power plants, automobiles, ships, trains, etc. Sulfur oxides are known to combine with water vapor to form a highly corrosive vapor causing irritation to eyes and mucous membrane, damage to metal-containing structures, and environmental harm to vegetation due to acid rain. Nitrogen oxides are toxic irritants and are also damaging to the environment. Carbonyl sulfide (COS) is another toxic pollutant formed as a product of a reaction between a sulfur-containing compound and carbon monoxide in a gas stream effluent. Regulations on the discharge of these pollutants into the atmosphere have become increasingly stringent. The present invention describes an electrocatalytic process and electrochemical cell for removing sulfur and nitrogen oxides from gas streams which utilize the chemical driving force of a fuel gas.
SUMMARY OF THE INVENTION
A solid multi-component membrane is described for use in the processes of the present invention. The solid multi-component membrane generally comprises intimate, gas-impervious, multi-phase mixtures of an electronically-conductive phase and an oxygen ion-conductive phase and/or gas impervious “single phase” mixed metal oxides having a perovskite structure and having both electron-conductive and oxygen ion-conductive properties. Solid multi-component membranes are also described for use in electrochemical reactors comprising the aforementioned multi-phase mixtures and/or the aforementioned mixed metal oxides, provided that the mixed metal oxides are represented by the formula:
A
s
A′
t
B
u
B′
v
B″
w
O
x
wherein A represents a lanthanide or Y, or a mixture thereof; A′ represents an alkaline earth metal or a mixture thereof; B represents Fe; B′ represents Cr or Ti, or a mixture thereof; and B″ represents Mn, Co, V, Ni or Cu, or a mixture thereof and s, t, u, v, w, and x each represent a number such that:
s/t equals from about 0.01 to about 100;
u equals from about 0.01 to about 1;
v equals from 0.01 to about 1;
w equals from zero to about 1;
x equals a number that satisfies the valences of the A, A′, B, B′and B″ in the formula; and
0.9<(s+t)/(u+v+w)<1.1.
An element is described for use in the processes of the present invention having a first surface capable of reducing oxygen to oxygen ions, a second surface capable of reacting oxygen ions with an oxygen-consuming gas, an electron-conductive path between the first and second surfaces and an oxygen ion-conductive path between the first and second surfaces. The element may also comprise (1) a porous substrate, (2) an electron-conductive metal, metal oxide or mixture thereof and/or (3) a catalyst. The porous substrate (1); conductive coating (2); and/or (3) catalyst may be applied as separate materials or the functions of the porous substrate (1); conductive coating (2); and/or catalyst (3) may be combined in one or two materials. Elements are described for use in an electrochemical reactor as defined above wherein the element comprises (1) a catalyst, such an a sulfur reducing catalyst at a surface thereof, or (2) (A) a solid multi-component membrane characterized by (1) an intimate, gas-impervious, multi-phase mixture of an electronically-conductive phase and an oxygen ion-conductive phase or (2) a mixed metal oxide material having a perovskite structure and (B) a conductive coating, a catalyst, or a conductive coating comprising a catalyst.
An electrochemical reactor cell for transporting oxygen from any oxygen containing gas to any gas that consumes oxygen is also described which generally comprises the aforementioned elements having an entrance end, an exit end and a passage therebetween for the movement of one or more gases from the entrance end to the exit end. In one embodiment, the passage between the entrance end and exit end may optionally comprise a catalyst, such as a discrete particle or fiber catalyst packed in the passage between the entrance end and the exit end of the reacter cell. This electrochemical reactor cell is placed in an environment containing an oxygen-containing gas on one side and an oxygen-consuming gas on the other side under reaction conditions of appropriate temperature and percentage of respective gases.
An electrochemical reactor for reacting an oxygen-consuming gas with an oxygen-
Cable Thomas L.
Frye, Jr. John G.
Kliewer Wayne R.
Mazanec Terry J.
The Standard Oil Company
Valentine Donald R.
Yassen Thomas A.
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