Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2000-02-18
2003-12-02
Silverman, Stanley S. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S341000, C502S415000, C502S527140, C502S527150, C502S527160
Reexamination Certificate
active
06656875
ABSTRACT:
The present invention relates to novel alumina-based extrudates. It also relates to processes for preparing these extrudates and to their use as catalyst supports, in particular for hydrotreatment.
Hydrotreatment of petroleum cuts is a purification operation carried out in hydrogen which encompasses several types of treatment, in particular: hydrodesulphurisation, hydrodemetallisation, hydrodenitrogenation, Conradson Carbon number hydroreduction (HDCC), asphaltene hydrogenation (HDAS) and aromatic hydrogenation (HDAr).
Hydrodemetallisation can eliminate metals, in particular nickel and vanadium, contained in the heavy petroleum fractions from vacuum distillation of the first refinery stages.
Hydrodesulphurisation can eliminate sulphur-containing compounds such as RSH or R
2
S, R being an alkyl radical. It is primarily used on light petroleum fractions or those with a low metals (Ni and V) content.
When hydrotreating heavy petroleum cuts, it is important for the catalyst used to be equilibrated for hydrodemetallisation and hydrodesulphurisation, i.e., that it has the same efficacy for the two activities.
Further, the catalyst must have a good retention capacity for hydrodemetallisation. In contrast to hydrodesulphurisation where the reaction products remain in the reaction medium, the products resulting from hydrodemetallisation remain absorbed on the catalyst. It is thus important that the catalyst can absorb as much as possible of the metallic derivatives from hydrodemetallisation as once saturated with metallic derivatives, it has to be replaced.
During catalytic hydrodemetallisation, metal elimination encounters a certain number of catalytic problems, in particular as regards the catalytic support.
A first problem arises from the fact that the metallic compounds are high molecular weight compounds, such as asphaltenes and resins, with a high degree of steric hindrance resulting in diffusional limitations in the catalyst's pore network.
A second problem arises since the metals, of more exactly the metal sulphides, from the decomposition of the metallic compounds accumulate during the operation, gradually reducing the pore diameter.
A third problem arises because the metallic compounds of the asphaltene type tend to dehydrogenate then to polycondense under the operating conditions to give rise to products which are insoluble in the hydrocarbon medium and to coke which remains fixed on the catalyst thus gradually reducing its activity.
A heavy cut hydrotreatment catalyst must thus be composed of a catalytic support with a porosity profile which is particularly adapted for the specific diffusional constraints encountered in hydrotreatment, in particular hydrodemetallisation.
The catalysts are normally composed of a support on which metallic oxides, such as cobalt, nickel or molybdenum oxides are deposited. The support is generally alumina-based, its role being to disperse the active phase and to provide a texture which is suitable for good capture of the metallic impurities, avoiding the problems defined above.
Prior art alumina-based supports fall into two categories.
The first category consists of alumina extrudates prepared from alumina gel. Such alumina gel extrudates represent the majority of catalyst supports for hydrotreatment, but they suffer from a number of disadvantages.
Firstly, their porosity is particularly adapted for hydrodesulphurising and hydrotreating light hydrocarbon-containing cuts, but not for other types of treatment.
Then, although such extrudates are equilibrated as regards their hydrodemetallisation/hydrodesulphurisation ratio, their hydrodemetallisation retention capacity is low, in general at most 30%, so they are rapidly saturated and have to be replaced.
Further, alumina gel is expensive, meaning that the supports which are produced are expensive.
Finally, the process for preparing the alumina gel is particularly polluting in contrast to that of the alumina produced by rapid dehydration of hydrargillite, known as flash alumina.
Alumina beads prepared from alumina from the rapid dehydration of hydrargillite are also used for hydrotreatment, at a lower cost. Such beads, however, suffer from a disadvantage: the bead diameter has to be more than 2 mm for a satisfactory cost price, meaning that the metals cannot be introduced to the core of the beads. The catalytic phase with which the bead core is impregnated is thus not used.
Smaller flash alumina extrudates would not have this disadvantage, but currently there is no preparation process which would produce such flash alumina extrudates with a porosity suitable for hydrotreatment.
One aim of the present invention is to provide cheap alumina-based supports for hydrotreatment.
Another aim of the present invention is to provide alumina extrudates produced by rapid dehydration of hydrargillite with characteristics which are adapted for their use as supports for hydrotreatment catalysts.
A still further aim of the present invention is to provide processes for preparing these alumina extrudates.
With these aims in mind, in a first aspect, the invention provides alumina extrudates produced by a preparation process starting from an alumina produced by the rapid dehydration of hydrargillite with a total pore volume of at least 0.6 cm
3
/g, an average mesoporous diameter in the range 140 to 360 Å, and an alumina content produced by boehmite decomposition in the range 5% to 70% by weight.
The invention also concerns a first process for forming an alumina from a starting alumina produced by the rapid dehydration of hydrargillite, comprising the following steps:
a
1
starting with an alumina produced by rapid dehydration of hydrargillite;
b
1
rehydrating the starting alumina;
c
1
mixing the rehydrated alumina in the presence of an emulsion of at least one hydrocarbon in water;
d
1
extruding the alumina-based paste obtained from step c
1
;
e
1
drying and calcining the extrudates;
f
1
carrying out a hydrothermal acid treatment in a confined atmosphere on the extrudates from step e
1
;
g
1
optionally drying, then calcining the extrudates from step f
1
.
The invention also concerns a second process for forming an alumina from a starting alumina produced by the rapid dehydration of hydrargillite, comprising the following steps:
a
2
starting from a starting alumina produced by rapid dehydration of hydrargillite;
b
2
forming the alumina into beads in the presence of a pore-forming agent;
c
2
ageing the alumina beads obtained;
d
2
mixing the beads from step c
2
to obtain a paste which is extruded;
e
2
drying and calcining the extrudates obtained;
f
2
carrying out a hydrothermal acid treatment in a confined atmosphere on the extrudates obtained from step e
2
;
g
2
optionally drying, then calcining the extrudates from step f
2
.
The invention also concerns a third process for forming an alumina from a starting alumina produced by the rapid dehydration of hydrargillite, comprising the following steps:
a
3
starting from an alumina produced by rapid dehydration of hydrargillite;
b
3
rehydrating the starting alumina;
c
3
mixing the rehydrated alumina with a pseudo-boehmite gel, the gel being present in an amount in the range 1% to 30% by weight with respect to the rehydrated alumina and the gel;
d
3
extruding the alumina-based paste obtained from step c
3
;
e
3
drying and calcining the extrudates obtained;
f
3
carrying out a hydrothermal acid treatment in a confined atmosphere on the extrudates obtained from step e
3
;
g
3
optionally drying, then calcining the extrudates from step f
3
.
Finally, the invention concerns the use of this alumina as a catalyst or catalyst support.
FIGS. 1 and 2
are photographs of sections of an extrudate of the invention produced by transmission electron microscopy.
In hydrotreatment, the extrudates of the invention have the advantage of being equilibrated in hydrodemetallisation and hydrodesulphurisation and of having a good retention capacity for hydrodemetallisation.
Other advantages of the invention will become apparent from the following more detailed descripti
Bortzmeyer Denis
Le Loarer Jean-Luc
Nussbaum Hubert
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Silverman Stanley S.
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