Compositions – Gaseous compositions – Carbon-oxide and hydrogen containing
Reexamination Certificate
2000-07-10
2003-06-03
Silverman, Stanley S. (Department: 1754)
Compositions
Gaseous compositions
Carbon-oxide and hydrogen containing
C423S648100
Reexamination Certificate
active
06572787
ABSTRACT:
The present invention relates to a catalyst suitable for the preparation of carbon monoxide and/or hydrogen from a gaseous or liquid hydrocarbonaceous feedstock, a process for the preparation of such a catalyst, and a catalytic partial oxidation process using such a catalyst.
The partial oxidation of hydrocarbons, for example methane or natural gas, in the presence of a catalyst is an attractive route for the preparation of synthesis gas. The partial oxidation of a hydrocarbon is an exothermic reaction and, in the case in which methane is the hydrocarbon, proceeds by the following reaction:
2CH
4
+O
2
→2CO+4H
2
The optimum catalytic partial oxidation process for application on a commercial scale would give high yields of carbon monoxide and hydrogen at elevated pressures, for example about 30 bar, and high space velocities, for example of the order of 1,000,000 Nl/kg/h or more. For thermodynamic reasons, in order to obtain high yields of carbon monoxide and hydrogen under these process conditions, it is necessary to operate the partial oxidation process at high temperatures.
The literature contains a number of documents disclosing details of experiments conducted into the catalytic oxidation of hydrocarbons, in particular methane, employing a wide range of catalysts. Reference is made for instance to U.S. Pat. No. 5,149,464, WO 92/11199, and WO 93/01130. The majority of these experiments, however, have been conducted under relatively mild conditions or under conditions unsuited to the operation of a large, commercial catalytic partial oxidation process.
The literature, moreover, contains a number of documents disclosing details of experiments conducted into the catalytic partial oxidation of hydrocarbons under conditions required for commercial operation to produce mixtures of carbon monoxide and/or hydrogen.
In EP-A-640561 is disclosed that the catalytic partial oxidation process may be operated under conditions demanded of commercial processes, in high yield and with low deactivation by employing a catalyst comprising a Group VIII catalytically active metal supported on a refractory oxide having at least two cations selected from Groups IA, IIA, IIIA and IVA of the Periodic Table or the transition metals.
Moreover, in EP-A-737164 is disclosed that, when operated under the conditions of elevated pressure and at high temperature as demanded by a commercial process, the catalytic partial oxidation of hydrocarbons can, in the presence of nitrogen, yield a synthesis gas product containing a number of by-products, in particular ammonia (NH
3
) and hydrogen cyanide (HCN), in low but significant amounts. It has been found that such by-products can adversely affect downstream processes to convert the carbon monoxide and/or hydrogen produced by the catalytic partial oxidation process, e.g. in the case of Fischer-Tropsch synthesis or of the synthesis of methanol. The presence of by-products, in particular ammonia or hydrogen cyanide, in the products of the catalytic partial oxidation process is thus undesirable. In EP-A-737164 is disclosed that the generation of such by-products is significantly lower in a process employing a catalyst comprising rhodium, iridium or platinum as catalytically active metal. At such levels it is possible to remove any undesired by-products, using known solvent, absorption processes and the like. Alpha-alumina is employed as the catalyst support.
In WO 96/04200 is disclosed a catalytic partial oxidation process which employs a Group VIII catalytically active metal supported on a zirconia-based carrier, which is found to have a high thermal-shock resistance.
In EP 548 679 is disclosed a catalytic partial oxidation process wherein a catalyst containing ruthenium and/or rhodium as an active ingredient and cobalt and/or manganese as a promoter is used.
Accordingly, it will be apparent that there are a number of conditions and circumstances which affect the performance of a catalytic partial oxidation reaction, and that whilst it is possible to optimize in terms of individual performance parameters, there is some conflict between individual optimizations, each directed specifically to one of the above performance parameters, whereby it is not possible to operate a process with simultaneous optimization of all conditions. Specifically, nitrogen is present in many natural gas feedstocks, and the preparation of pure, nitrogen-free oxygen on a commercial scale is both very expensive and technically difficult. Therefore the process must produce acceptably low levels of N-containing by-product. Moreover, the choice of catalytically active metal, refractory oxide and the like in the catalyst to be effective on a commercial scale must be made bearing in mind factors including high temperature and pressure resistance and thermal-shock resistane under the extreme conditions to be employed in terms of the factors hereinbefore mentioned. Finally, the process must produce optimum yields and selectivity to desired products and optimum lifetime under such extreme conditions, and indeed under varying conditions which may prevail in the event of fluctuations in operation.
Accordingly, there is a need for a process for the catalytic partial oxidation of hydrocarbons in which nitrogen may be present during the partial oxidation reactions, which may be applied on a commercial scale to produce a product of carbon monoxide and/or hydrogen in high yield and selectivity, containing a minimum of components such as ammonia and hydrogen cyanide, and at low or negligible catalyst deactivation rates.
Surprisingly, it has been found that, by employing in the catalytic partial oxidation process a catalyst comprising the catalytically active metal associated with a performance modifying cation selected.from Al, Mg, Zr, Ti, La, Hf, and Si, the above objects may be achieved in admirable manner, for a wide range of operating conditions. Moreover, selection of cation employed may be made for optimization of specific performance factors, including feedstock conversion and product yield, catalyst stability, coke formation, top temperature control and the like.
Accordingly, the present invention provides a catalyst comprising a catalytically active metal, selected from Ru, Rh, Os and Ir, associated with a metal cation selected from Al, Mg, Zr, Ti, La, Hf, and Si supported on a carrier, obtainable by a process comprising providing the metal cation and the catalytically active metal in solutions adapted for impregnation or co-impregnation on the carrier, drying, and optionally calcining.
The inorganic metal cation is selected from Al, Mg, Zr, Ti, La, Hf, and Si, of which Zr is preferred. The cation is preferably in the form of its oxide.
The catalyst is supported on a carrier, for example comprising a refractory oxide having at least one cation, or comprising a metal or other attrition resistant, high temperature resistant substrate.
Preferably, the catalyst comprises cation to metal in an atomic ratio in excess of or equal to 1.0 at its surface, more preferably in excess of or equal to 2.0, even more preferably in excess of or equal to 3.0 up to a maximum only limited by the constraints of the method for constructing the catalyst, e.g. impregnation.
It is a particular advantage of the catalyst of the present invention that the nature of association of the catalytically active metal and the metal cation would seem to be at least partially self-regulating or directing. Without being limited to this theory it would seem that a form of feedstock conditioning by the metal cation serves to optimize catalytic activity and thereby generate enhancement in the performance parameters of yield, selectivity, deactivation resistance and low by-product formation simultaneously.
The catalytically active metal is selected from ruthenium, rhodium, osmium and iridium, preferably from rhodium and iridium. As has been discussed hereinbefore, these metals offer the significant advantage that substantially lower amounts of ammonia and hydrogen cyanide are produced during the catalytic partial oxidation react
Huisman Hans Michiel
Mercera Patrick Dennis Lawrence
Pieterse Coen Willem Johannes
Schaddenhorst David
Schoonebeek Ronald Jan
Johnson Edward M.
Shell Oil Company
Silverman Stanley S.
LandOfFree
Evacuation of hydrogen and carbon monoxide from a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Evacuation of hydrogen and carbon monoxide from a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Evacuation of hydrogen and carbon monoxide from a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3117695