Chemistry of inorganic compounds – Hydrogen or compound thereof – Elemental hydrogen
Reexamination Certificate
1999-05-13
2002-10-15
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Hydrogen or compound thereof
Elemental hydrogen
C423S650000, C252S373000
Reexamination Certificate
active
06464955
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the partial oxidation of hydrocarbons, and more particularly to the production of hydrogen and carbon monoxide by the oxidation of hydrocarbons. Specifically, the invention relates to a process comprising contacting ceramic oxygen-selective mixed conductors with steam and/or carbon dioxide at high temperatures, thereby causing oxygen to be adsorbed by the mixed conductor, and subsequently producing hydrogen and carbon monoxide by contacting the oxygen-containing mixed conductor with hydrocarbons.
BACKGROUND OF THE INVENTION
Syngas and its components, hydrogen and carbon monoxide, are conventionally produced by the high temperature partial oxidation of hydrocarbons with controlled amounts of air or oxygen. Although air is less expensive and more convenient to use in partial oxidation reactions, it is less attractive than oxygen for such reactions because the large quantities of nitrogen that are produced when air is used as the oxidant must be subsequently separated from the product gas prior to its use. The cost of separation, purification and heat exchange equipment for product gas purification and recovery of heat energy from the nitrogen adds considerably to the cost of syngas production using air.
Although oxygen is more desirable than air as an oxidant for partial oxidation reactions, its use is not without disadvantage, in that oxygen must be imported into the system, or it must be generated on site, for example, by means of a cryogenic air separation plant or an adsorption system. In either alternative, using oxygen as the oxidant likewise adds considerably to the cost of the process.
On site production of oxygen using ceramic-based materials for applications such as hydrocarbon partial oxidation reactions has been recently reported. U.S. Pat. No. 5,714,091 discloses an oxygen-based hydrocarbon partial oxidation process in which the oxygen is produced on site by subjecting air to membrane separation using a membrane constructed of perovskite-type ceramic material. Oxygen, which is permeable to the membrane, passes through the membrane and is made to react with hydrocarbons on the downstream side of the membrane unit. The disadvantages of this method of oxygen production are the high cost of production of the membrane and the difficulty of producing membrane structures that are leak-proof.
The partial oxidation of hydrocarbons with oxygen retained in ceramic-based oxygen-selective mixed conducting substances, such as perovskite-type ceramics, is disclosed in copending U.S. patent application Ser. No. 09/175,175, filed Oct. 20, 1998, and Ser. No. 09/290,768, filed Apr. 13, 1999, the specifications of which are incorporated herein by reference.
In the above-described hydrocarbon partial oxidation processes, up to one-half mole of hydrogen and up to one mole of carbon monoxide, respectively, are produced for each hydrogen atom and each carbon atom contained in the hydrocarbon feed to the process. For instance, when methane is partially oxidized by the above-described processes, a maximum of two moles of hydrogen and one mole of carbon monoxide can be obtained for each molecule of methane. The equation for this reaction is:
CH
4
+1/20
2
→CO+2H
2
The present invention provides a hydrocarbon partial oxidation process which uses an oxygen-selective mixed conductor, but which has the advantage over the above-described processes of producing more hydrogen and/or more carbon monoxide for each mole of hydrocarbon feed to the process.
SUMMARY OF THE INVENTION
According to a broad embodiment, the invention comprises a process comprising the steps:
(a) contacting at least one oxygen ion-conducting ceramic with a feed gas comprising a component selected from the group consisting of steam, carbon dioxide, sulfur oxides, nitrogen oxides and mixtures thereof in an adsorption zone at a temperature in the range of about 300 to about 1400° C. and at an absolute pressure in the range of about 0.5 to about 50 bara, thereby at least partially saturating the at least one oxygen ion-conducting ceramic with oxygen and producing hydrogen, carbon monoxide, sulfur, nitrogen or mixtures thereof; and
(b) removing oxygen from the at least partially oxygen saturated oxygen ion-conducting ceramic.
In a preferred embodiment, the at least one oxygen ion-conducting ceramic comprises an oxygen-selective mixed conductor. In a more preferred embodiment, the oxygen ion-conducting ceramic comprises a perovskite-type ceramic having the structural formula A
1-x
M
x
BO
3-&dgr;
, where A is an ion of a metal of Groups 3a and 3b of the periodic table of elements or mixtures thereof; M is an ion of a metal of Groups 1a and 2a of the periodic table or mixtures thereof; B is an ion of a d-block transition metal of the periodic table or mixtures thereof; x varies from >0 to 1; and &dgr; is the deviation from stoichiometric composition resulting from the substitution of ions of metals of M for ions of metals of A.
In another preferred embodiment, the oxygen is removed from the at least partially saturated mixed conductor by increasing the temperature in the adsorption zone, by decreasing the pressure in the adsorption zone, by contacting the at least partially oxygen saturated mixed conductor with a reducing agent or by combinations thereof
In another preferred embodiment, the feed gas of step (a) is steam, carbon dioxide or mixtures thereof. In this preferred embodiment, step (b) of the process preferably comprises contacting the at least partially oxygen-saturated oxygen ion-conducting ceramic mixed conductor with a reducing agent comprising at least one organic compound selected from the group consisting of hydrocarbons, oxygen-containing hydrocarbons and mixtures thereof in a reaction zone at a temperature in the range of about 300 to about 1,400° C., thereby partially oxidizing the at least one organic compound and producing product gas comprising hydrogen, carbon monoxide or mixtures of these, and at least partially depleting the mixed conductor of oxygen.
In another preferred embodiment, the process is carried out by repeatedly performing steps (a) and (b) in sequence. In one preferred aspect, the process is carried out in a fixed bed comprising the at least one oxygen-selective mixed conductor, and the fixed bed serves as the adsorption zone during step (a) and as the reaction zone during step (b). In another preferred aspect, the process is carried out in a moving bed system, and it further comprises recycling the at least partially oxygen-depleted mixed conductor to the adsorption zone. Preferably, the moving bed system is a fluidized bed system and the at least partially oxygen-saturated mixed conductor is fluidized and carried into the reaction zone by the at least one organic compound, steam, carbon dioxide or mixtures thereof.
In a more preferred embodiment, the at least one oxygen ion-conducting ceramic is a perovskite-type ceramic and x varies from about 0.1 to 1.
In another more preferred embodiment, the at least one oxygen ion-conducting ceramic is a perovskite-type ceramic and A is one or more f-block lanthanides. In a more preferred embodiment, A is La, Y, Sm or mixtures thereof.
In another more preferred embodiment, the at least one oxygen ion-conducting ceramic is a perovskite-type ceramic and M is at least one metal of Group 2a of the periodic table of elements. In a more preferred embodiment M is Sr, Ca, Ba or mixtures thereof.
In another more preferred embodiment, the at least one oxygen ion-conducting ceramic is a perovskite-type ceramic and B is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn or mixtures thereof. In a more preferred embodiment, B is V, Fe, Ni, Cu or mixtures thereof.
In another more preferred embodiment, the at least one oxygen ion-conducting ceramic is a perovskite-type ceramic and x is about 0.2 to 1.
In another more preferred embodiment, the at least one oxygen ion-conducting ceramic is a perovskite-type ceramic and A is La, Y, Sm or mixtures thereof, M is Sr, Ca or mixtures thereof, and B is V, Fe, Ni, Cu or mixtures there
Fitch Frank R.
Limbach Kirk Walton
MacLean Donald L.
Ramprasad Narayanan
Tamhankar Satish S.
Cheung Wan Yee
Johnson Edward M.
Neida Philip H. Von
Pace Salvatore P.
Silverman Stanley S.
LandOfFree
Production of hydrogen and carbon monoxide does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Production of hydrogen and carbon monoxide, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Production of hydrogen and carbon monoxide will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2993554