Surface supported cobalt catalysts, process utilizing these catalysts for the preparation of hydrocarbons from synthesis gas and process for the preparation of said catalysts

Abstract

A supported particulate cobalt catalyst is formed by dispersing cobalt, alone or with a metal promoter, particularly rhenium, as a thin catalytically active film upon a particulate support, especially a silica or titania support. This catalyst can be used to convert an admixture of carbon monoxide and hydrogen to a distillate fuel constituted principally of an admixture of linear paraffins and olefins, particularly a C10+ distillate, at high productivity, with low methane selectivity. A process is also disclosed for the preparation of these catalysts.

Description

BACKGROUND AND PROBLEMS1. Field of the InventionThis invention relates to catalyst compositions, process wherein these compositions are used for the preparation of liquid hydrocarbons from synthesis gas, and process for the preparation of said catalysts. In particular, it relates to catalysts, and process wherein C.sub.10+ distillate fuels, and other valuable products, are prepared by reaction of carbon monoxide and hydrogen over cobalt catalysts wherein the metal is dispersed as a thin film on the outside surface of a particulate carrier, or support, especially a titania carrier, or support.2. The Prior ArtParticulate catalysts, as is well known, are normally formed by dispersing catalytically active metals, or the compounds thereof upon carriers, or supports. Generally, in making catalysts the objective is to disperse the catalytically active material as uniformly as possible throughout a particulate porous support, this providing a uniformity of catalytically active sites from th...

AI Technical Summary

Benefits of technology

A further object is to provide a process utilizing such catalyst compositions for the production from synthesis gas to C.sub.10+ linear paraffins and olefins, at high productivity with decreased methane selectivity.

In accordance with this invention the catalytically active cobalt component is dispersed and supported upon a particulate refractory inorganic oxide carrier, or support as a thin catalytically active surface layer, ranging in thickness from less than about 200 microns, preferably about 5-200 microns, with the loading of the cobalt, expressed as the weight metallic cobalt per packed bulk volume of catalyst, being sufficient to achieve the productivity required for viable commercial operations, e.g., a productivity in excess of about 150 hr.sup.-1 at 200.degree. C. The cobalt loading that achieves this result is at least about 0.04 grams (g) per cubic centimeter (cc), preferably at least about 0.05 g / cc in the rim also referred to as the thin catalytically active surface layer or film. Higher levels of cobalt tend to increase the productivity further and an upper limit of cobalt loading is a function of cobalt cost, diminishing increases in productivity with increases in cobalt, and ease of depositing cobalt. A suitable range may be from about 0.04 g / cc to about 0.7 g / cc, preferably 0.05 g / cc to about 0.7 g / cc in the rim, and more preferably 0.05 g / cc to 0.09 g / cc. Suitable supports are, e.g., silica, silica-alumina and alumina; and silica or titania or titania-containing support is preferred, especially a titania wherein the rutile:anatase ratio is at least about 3:2. The support makes up the predominant portion of the catalyst and is at least about 50 wt % thereof, preferably at least about 75 wt % thereof. The feature of a high cobalt metal loading in a thin catalytically active layer located at the surface of the particles, while cobalt is substantially excluded from the inner surface of the particles (the catalyst core should have <0.04 g / cc of active cobalt), is essential in optimizing the activity, selectivity and productivity of the catalyst in producing liquid hydrocarbons from synthesis gas, while minimizing methane formation.

Problems solved by technology

Ceramic or metal cores have been selected to provide better heat transfer characteristics, albeit generally the impervious dense cores of the catalyst particles overconcentrates the catalytically active sites within a reduced reactor space and lessens the effectiveness of the catalyst.

Sometimes, even in forming catalysts from porous support particles greater amounts of the catalytic materials are concentrated near the surface of the particles simply because of the inherent difficulty of obtaining more uniform dispersions of the catalytic materials throughout the porous support particles.

For example, a catalytic component may have such strong affinity for the support surface that it tends to attach to the most immediately accessible surface and cannot be easily displaced and transported to a more central location within the particle.

These early cobalt catalysts, however, are of generally low activity necessitating a multiple staged process, as well as low synthesis gas throughput.

The iron catalysts, on the other hand, are not really suitable for natural gas conversion due to the high degree of water gas shift activity possessed by iron catalysts.

Higher temperature operation, however, leads to a corresponding increase in the methane selectivity and a decrease in the production of the more valuable liquid hydrocarbons.

However, it is also essential the high productivity be achieved without high methane formation, for methane production results in lower production of liquid hydrocarbons.

Higher levels of cobalt tend to increase the productivity further and an upper limit of cobalt loading is a function of cobalt cost, diminishing increases in productivity with increases in cobalt, and ease of depositing cobalt.

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