Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2001-01-04
2003-08-05
Silverman, Stanley S. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S303000, C502S304000, C502S305000, C502S313000, C502S317000, C502S319000, C502S325000, C502S330000, C502S344000, C502S506000, C502S514000
Reexamination Certificate
active
06602819
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for reducing carbon monoxide (CO) and carbonyl sulfide (COS) emissions.
BACKGROUND
A process for chlorinating titanium-containing materials in a fluidized bed reactor is known. Suitable processes are disclosed in patents U.S. Pat. Nos. 2,446,181; 2,701,179; 3,591,333; and 3,883,636. In such processes, chlorine, particulate coke, particulate titanium-bearing materials, chlorine and optionally oxygen or air, wherein at least one of these contains sulfur, are fed into a fluidized bed reactor under conditions which chlorinate the titanium and many of the other metallic impurities. Gaseous titanium tetrachloride, other metallic chlorides, carbon monoxide (CO), carbonyl sulfide (COS), carbon dioxide (CO
2
) and other gaseous products exit the fluidized bed reactor. The gaseous titanium tetrachloride produced can then be separated from the other metal chlorides and impurities and oxidized to titanium dioxide, a white pigment, or further processed to produce titanium metal.
Details of fluidized bed processes for chlorinating titanium containing materials are disclosed in U.S. Pat. No. 5,585,078 ('078). The '078 patent also discloses and claims a process for reducing the emissions of CO and COS from the fluidized bed reactor effluent. The emission reduction process involves introducing an oxygen containing gas into at least one location which is downstream of the surface of the fluidized bed, as measured in its static condition, with the oxygen containing gas being introduced in an amount to convert at least some of the COS and CO to CO
2
and SO
2
which reduces CO and COS emissions. In the example given in the '078 patent, the CO emitted from the fluidized bed chlorinator was reduced by 36.7%, and the COS was reduced by 92.5%.
In the titanium chlorination process, it is desirable to convert COS to SO
x
, where x is 2 or 3, and CO to CO
2
, because environmental requirements often require low levels of emissions for CO and COS. However, as stated in U.S. Pat. No. 4,961,911, while means are known to reduce the amount of carbon monoxide emitted, they involve addition of compounds which can be undesirable in the titanium dioxide pigment or in the process to make such pigment.
Carbonyl sulfide (COS) is known to be a fairly inert chemical compound. Furthermore, carbonyl sulfide is a known poison for many supported metal oxidation catalysts. Because of the above, catalytic oxidation of CO in the presence COS is a difficult problem.
There is a need for an efficient catalytic process for the oxidation of carbon monoxide to carbon dioxide in the presence of carbonyl sulfide and also to simultaneously oxidize-carbonyl sulfide to sulfur oxides.
SUMMARY OF THE INVENTION
This invention provides a process for reducing carbon monoxide and carbonyl sulfide emissions which are produced in a process for chlorinating titanium containing material in a fluidized bed reactor which evolves gaseous material including CO, COS and TiCl
4
. The process comprises contacting a gaseous material comprising CO, COS or TiCl
4
and a gas comprising oxygen with a catalyst selected from the group consisting of (a) metal oxides comprising oxides of the formula, (Bi
a
Co
b
Ni
c
)
y
Mo
1−y
O
z
, where a, b and c are from 0 to 1, y is from 0.01 to 0.75 and z is from 1.125 to 4.875; (b) a xerogel or aerogel, comprising Au, Rh, Ru and Co in aluminum oxide/oxyhydroxide matrices, of the formula [(Au
1−(w+d)
Rh
w
Ru
d
)
e
Co
f
AlO
1.5−u
(OH)
2u
]
1−(e+f)
, where w and d are from 0 to 1, e is from 0.001 to 0.2, f is from 0 to 0.2 and u is from 0 to 1.5; (c) composites comprising Au, Rh, Ru and Cr, and cerium oxide and lanthanum oxide of the formula (Au
1−(w+d)
Rh
w
Ru
d
)
e
Cr
f
(Ce
g
La
1−g
)
1−(e+f)
O
v
, where w and d are from 0 to 1, e is from 0.001 to 0.2, f is from 0 to 0.2, g is from 0 to 1 and v is from 1.1 to 2.4; and (d) a supported metal comprising at least one metal selected from the group consisting of Pd, Rh, Ru and Cu, wherein said support is selected from the group consisting of alumina and carbon, wherein said metal is present from about 0.01 to 20 weight percent of the catalyst weight; at a temperature of from about 250° C. to about 500° C. to produce CO
2
and SO
x
, where x is 2 or 3.
The present invention also discloses a composition of matter, comprising Au, Rh, Ru and Cr, and cerium oxide and lanthanum oxide of the formula (Au
1−(w+d)
Rh
w
Ru
d
)
e
Cr
f
(Ce
g
La
1−g
)
1−(e+f)
O
v
, where w and d are from 0 to 1, e is from 0.001 to 0.2, f is from 0 to 0.2, g is from 0 to 1 and v is from 1.1 to 2.4.
A further disclosure of the present invention is a product made by the process comprising the steps of: (i) dissolving precursor salts selected from the group consisting of Au, Rh, Ru, Ce, Cr and La in a solvent to form a solution or fine colloid; (ii) rapidly freezing the solution by immersing into a suitable medium to form a frozen solid; (iii) transferring the frozen solid to a freeze drying chamber maintained at a temperature ranging from about 0° C. to about −40° C. with a vacuum of from about 0.3 Pa to about 1.3 Pa until freeze-drying is complete; and optionally; (iv) heating the solid in air at a temperature ranging from about 250° C. to about 600° C. for a time sufficient to decompose the precursors.
DETAILED DESCRIPTION
In a typical titanium tetrachloride manufacturing process, titanium-containing material, carbonaceous material, chlorine, and optionally oxygen or air, wherein at least one of these reactants contains sulfur, are fed into a fluidized bed reactor. The titanium containing material can be any suitable titanium containing source material, such as titanium containing ores including rutile, ilmentite or anatase ore; beneficiates thereof; titanium containing by-products or slags; and mixtures thereof. Any carbonaceous material which has been subjected to a coking process or is substantially free of hydrogen is suitable for use in the titanium manufacturing process.
Gaseous reaction products from the fluidized bed reactor are cooled in stages to first condense and remove metal chlorides other than titanium tetrachloride, such as iron chloride. The remaining product from the reactor is then cooled to condense titanium tetrachloride leaving a non-condensable exhaust gas stream comprising COS and CO.
Since the catalysts of this invention are reactive to CO and COS, catalysts are useful for emissions derived from any process for the reaction or abatement of CO, COS, and mixtures thereof.
In the present process, the exhaust gas stream comprising COS and CO is oxidized to CO
2
and SO
x
with an oxygen containing gas, where x is 2 or 3, in the presence of a heterogeneous catalyst in a fixed bed reactor.
The catalysts useful in the process of the present invention can be prepared by a variety of known art methods such as impregnation, including variants such as ion-exchange, deposition and grafting; xerogel or aerogel formation; and freeze-drying. Other synthetic methods such as spray roasting or co-precipitation can also be employed. The catalysts of the present invention can be used in the form of granules, powder or pellets.
The impregnation technique typically comprises contacting the support with a solution of a compound of the catalytically active material or a solution of compounds of the catalytically active materials. The contacting is followed by drying and calcining the supported materials.
The xerogels or aerogels used in this invention typically comprise a matrix material which is derived from a solution of the matrix component(s) and which incorporates the active catalyst component(s) which is obtained from a dissolved component(s). A matrix is a skeletal framework of oxides and oxyhydroxides prepared by the hydrolysis and condensation of alkoxides and other reagents. The framework typically comprises 30% or more, by weight, of the total catalyst composition. The matrix material typically comprises aluminum, oxid
Coulson Dale R
Kourtakis Kostantinos
E. I. du Pont de Nemours and Company
Silverman Stanley S.
Vanoy Timothy
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