Mixed conducting membranes for syngas production

Details Mixed conducting membranes for syngas production Mixed conducting membranes for syngas production

2000-08-22

2002-12-10

Kopec, Mark (Department: 1751)

Catalyst, solid sorbent, or support therefor: product or process

In form of a membrane

C502S300000, C502S325000, C502S344000, C502S353000, C096S011000, C252S519100

Reexamination Certificate

active

06492290

ABSTRACT:

BACKGROUND OF THE INVENTION
Synthesis gas (syngas) containing hydrogen and carbon oxides is an important feedstock for the production of a wide range of chemical products. Syngas mixtures having controlled ratios of hydrogen and carbon monoxide are catalytically reacted to produce liquid hydrocarbons and oxygenated organic compounds including methanol, acetic acid, dimethylether, oxoalcohols and isocyanates. The syngas product can be further processed and separated to yield high purity hydrogen and carbon monoxide. The cost of generating the syngas is frequently the largest part of the total cost of preparing these products.
Two major reaction routes are commonly used by industry for syngas production, namely steam reforming of light hydrocarbons, primarily natural gas, naphtha and refinery offgases, and the partial oxidation of carbon-containing feed stocks ranging from natural gas to high molecular weight liquid or solid carbonaceous materials. Autothermal reforming is an alternate process which uses a light hydrocarbon feed which combines features of partial oxidation and steam reforming reactions in a single reactor. A concise review of such processes is described in U.S. Pat. No. 6,077,323. Such processes typically require oxygen in purities of greater than 95 vol %, which is available from cryogenic air separation in large tonnage volumes or pressure swing absorption for smaller volumes.
Alternative processes have been developed for syngas production wherein oxygen necessary to conduct the partial oxidation reaction is provided in situ by the separation of air at high temperatures using solid-state membranes which conduct oxygen ions and electrons under operating conditions. Solid-state membranes which conduct oxygen ions and electrons are also known as mixed conducting membranes. Such mixed conducting membranes can be used in combination with appropriate catalysts to produce syngas in a membrane reactor eliminating the need for a separate oxygen production step. A membrane reactor typically has one or more reaction zones, wherein each reaction zone comprises a mixed conducting membrane which separates each reaction zone into an oxidant side and a reactant side.
Multicomponent metallic oxides are represented in the art by formulae which present one or more “A-site” metals and one or more “B-site” metals. By way of example, U.S. Pat. No. 5,306,411 discloses certain multicomponent metallic oxides having the perovskite structure represented by the formula A
s
A′
t
B
u
B′
v
B″
w
O
x
, wherein A represents a lanthanide, Y or a mixture thereof; A′ represents an alkaline earth metal or mixture thereof; B represents Fe; B′ represents Cr, Ti or a mixture thereof; and B″ represents Mn, Co, V, Ni, 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 about 0.01 to 1; w equals from 0 to about 1; x equals a number that satisfies the valences of A, A′, B, B′ and B″ in the formula; provided that 0.9<(s+t)/(u+v+w)<1.1. In a preferred embodiment A′ is calcium or strontium and B″ represents Mn or Co or a mixture thereof. These multicomponent metallic oxides require chromium or titanium as a B-site element.
Multicomponent metallic oxides depicted by formulae presenting A-site metals and B-site metals may be stoichiometric compositions, A-site rich compositions or B-site rich compositions. Stoichiometric compositions are defined as materials wherein the sum of the A-site metal stoichiometric coefficients equals the sum of the B-site metal stoichiometric coefficients. A-site rich compositions are defined as materials wherein the sum of the A-site metal stoichiometric coefficients is greater than the sum of the B-site metal stoichiometric coefficients. B-site rich compositions are defined as materials wherein the sum of the B-site metal stoichiometric coefficients is greater than the sum of the A-site metal stoichiometric coefficients.
U.S. Pat No. 6,033,632 discloses a solid-state membrane for use in a catalytic membrane reactor which utilizes a membrane fabricated from a multicomponent metallic oxide having the stoichiometry A
2−x
A′
x
B
2−y
B′
y
O
5+z
, wherein A is an alkaline earth metal ion or mixture of alkaline earth metal ions; A′ is a metal ion or mixture of metal ions where the metal is selected from the group consisting of metals of the lanthanide series and yttrium; B is a metal ion or mixture of metal ions, wherein the metal is selected from the group consisting of 3d transition metals and the group 13 metals; B′ is a metal ion or mixture of metal ions where the metal is selected from the group of the 3d transition metals, the group 13 metals, the lanthanides and yttrium; x and y are independently of each other numbers equal to or greater than zero and less than 2; and z is a number that renders the compound charge neutral. In a preferred embodiment the 3d transition metal is Fe and the group 13 metal is Ga, whereas A′ preferably is La and A is Sr and Ba.
U.S. Pat. Nos. 5,356,728 and 5,580,497 disclose cross-flow electrochemical reactor cells formed from multicomponent metallic oxides which demonstrate electron conductivity and oxygen ion conductivity at elevated temperatures. According to both documents, suitable multicomponent metallic oxides are represented by (Sr
1−y
M
y
)
&agr;
(Fe
1−x
Co
x
)
&agr;+&bgr;
)
&dgr;
, wherein M is a metal selected from the group consisting of elements having atomic number in a range from 56 to 71, calcium and yttrium, x is a number in a range from about 0.01 to about 0.95, y is a number in a range from about 0.01 to about 0.95, &agr; is a number in a range from about 1 to about 4, &bgr; is a number in a range upward from 0 to about 20, such that 1.1<(&agr;+&bgr;)/&agr;≦6, and &dgr; is a number which renders the compound charge neutral.
U.S. Pat. No. 6,056,807 teaches a fluid separation device capable of separating oxygen from an oxygen-containing gaseous mixture which utilizes at least one solid-state membrane comprising a dense mixed conducting multicomponent metallic oxide layer formed from a composition of matter represented by the formula:
Ln
x
A′
x″
A′
x″
B
y
B′
y′
O
3−z
,
wherein Ln is an element selected from the f block lanthanides, A′ is selected from group 2, A″ is selected from groups 1, 2 and 3 and the f block lanthanides and B and B′ are independently selected from the d block transition metals, excluding titanium and chromium, wherein 0≦x<1, 0<x′≦1, 0≦x″<1, 0<y<1.1, 0≦y′<1.1., x+x′+x″=1.0, 1.1>y+y′>1.0 and z is a number which renders the compound charge neutral. This reference discloses B-site rich non-stoichiometric compositions because the sum of the x indices is 1.0 and the sum of the y indices is greater than 1.0.
U.S. Pat. No. 5,712,220 presents a class of multicomponent metallic oxides which are well suited toward use in fabricating components used in solid-state oxygen separation devices. While the reference relates primarily to B-site rich compositions, the reference discloses A-site rich non-stoichiometric compositions represented by the formula Ln
x
A′
x′
A″
x′
B
y
B
y′
B″
y″
O
3−z
wherein Ln is an element selected from the f block lanthanides, A′ is selected from Group 2, A″ is selected from Groups 1, 2 and 3 and the f block lanthanides and B, B′ and B″ are independently selected from the d block transition metals, excluding titanium and chromium, wherein 0≦x<1, 0<x′<1, 0≦x″<1, 0<y<1.1, 0<y′<1.1, 0<y″<1.1, x+x′+x″=1.0 0.9<y+y″<1.0 and z is a number which renders the compound charge neutral wherein such elements are

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