Irregularly shaped non-spherical supported catalyst, and a process for hydroconverting heavy oil fractions

Abstract: The invention also concerns the use of said catalyst alone or as a mixture in a fixed bed or ebullated bed reactor. The present invention concerns a catalyst for hydrotreating and/or hydroconverting heavy metal-containing hydrocarbon feeds, said catalyst comprising a support in the form of mainly irregular and non-spherical alumina-based agglomerates the specific shape of which results from a crushing step, and containing at least one catalytic metal or a compound of a catalytic metal from group VIB and/or group VIII (groups 8, 9 and 10 of the new periodic table notation), optionally at least one doping element selected from the group constituted by phosphorus, boron and silicon (or silica which does not form part of that which may be contained in the selected support) and halogens, said catalyst essentially being constituted by a plurality of juxtaposed agglomerates each formed by a plurality of acicular platelets, the platelets of each agglomerate generally being oriented radially with respect to each other and with respect to the centre of the agglomerate. The specific shape of the catalyst improves its performance when using it for hydroconverting/hydrotreating heavy metal-containing hydrocarbon feeds. (end of abstract)

Irregularly shaped non-spherical supported catalyst, and a process for hydroconverting heavy oil fractions description/claims

Brief Patent Description

Full Patent Description

Patent Application Claims

FIELD OF THE INVENTION

The present invention concerns a catalyst for hydrotreating and/or hydroconverting heavy metal-containing hydrocarbon feeds, said catalyst comprising a support in the form of mainly irregular and non-spherical alumina-based agglomerates the specific shape of which results from a crushing step, and comprising at least one catalytic metal or a compound of a catalytic metal from group VIB (group 6 in the new periodic table notation) and/or group VIII (groups 8, 9 and 10 of the new periodic table notation), optionally at least one doping element selected from the group constituted by phosphorus, boron and silicon (or silica which does not form part of that which may be contained in the selected support) and halogens, said catalyst essentially being constituted by a plurality of juxtaposed agglomerates each formed by a plurality of acicular platelets, the platelets of each agglomerate generally being oriented radially with respect to each other and with respect to the centre of the agglomerate. The specific shape of the catalyst improves its performance when using it for hydroconverting/hydrotreating heavy metal-containing hydrocarbon feeds.

PRIOR ART

The skilled person will be aware that during hydrorefining and/or hydroconverting oil fractions containing organometallic complexes, the majority of those complexes are destroyed in the presence of hydrogen, hydrogen sulphide and a hydrotreatment catalyst. The constituent metal of those complexes then precipitates in the form of a solid sulphide which will become bound to the inner surface of the pores. This is particularly the case with complexes of vanadium, nickel, iron, sodium, titanium, silicon and copper which are naturally present in crude oils to a greater or lesser extend depending on the origin of the oil and which, during distillation operations, tend to become concentrated in the high boiling point fractions and in particular in residues. This is also the case with coal liquids which comprises metals, in particular iron and titanium. The general term “hydrodemetallization” is used to denote destruction or deaggregation of organometallic complexes in hydrocarbons.

The accumulation of solid deposits in the pores of a catalyst may continue until some of the pores controlling access of reagents to a fraction of the interconnected pore network is plugged so that that fraction becomes inactive even though the pores of that fraction are only slightly obscured or even intact. That phenomenon may thus cause premature and major deactivation of the catalyst. This is particularly the case with hydrodemetallization reactions carried out in the presence of a supported heterogeneous catalyst. The term “heterogeneous” means not soluble in the hydrocarbon feed. In this case, it can be shown that the pores of the periphery become blocked more quickly that the central pores. Similarly, the pore mouths become blocked more quickly than their other parts. Pore obstruction goes hand in hand with a gradual reduction in their diameter, which increasingly limits diffusion of molecules and accentuates the concentration gradient and thus the heterogeneity of the deposit from the periphery to the interior of the porous particles, to the point that total obstruction of the pores mouth to the exterior occurs very rapidly: access to the almost intact internal porosity of the particles is thus impossible for the reagents and the catalyst is prematurely deactivated.

The phenomenon which has just been described is well known as pore mouth plugging. Proof of its existence and an analysis of its causes have been widely published in the international scientific literature.

A catalyst for hydrotreating heavy metal-containing hydrocarbon cuts must thus be composed of a support having a pore profile, a pore structure and a shape (geometry) which is particularly suited to the intragranular diffusional constraints specific to hydrotreatments to avoid problems with plugging mentioned above.

Usually, the catalysts are in the form of beads or extrudates and are composed of an alumina-based support having a particular porosity and an active phase based on mixed sulphides constituted both by a sulphide of a group VIB metal (preferably molybdenum) and a sulphide of a group VIII metal (preferably Ni or Co). The metals are deposited in the oxide state and are sulphided to be active for hydrotreatment. The atomic ratio between the group VIII element and the group VIB element which is usually considered to be optimal, group VIII atom/group VIB atom, is in the range 0.4 to 0.6. Recently, it has been shown in European document EP-A1-1 364 707 (FR-A-2 839 902) that independently of the pore texture, a ratio of less than 0.4 can limit catalyst deactivation and thus prolong the service life of the catalysts.

The skilled person will be aware that two types of alumina-based support for catalysts for hydrorefining and/or hydroconverting heavy metal-containing hydrocarbon feeds. These supports are broadly distinguished by their pore distribution profiles.

Catalysts with a bimodal porosity profile are highly active, but have a poorer retention capacity than catalysts with a polymodal porosity profile.

The polymodal porosity profile corresponds to a graph of the cumulative distribution of the pore volume as a function of the pore diameter obtained by the mercury intrusion method which is neither monomodal nor bimodal, in the sense that distinct categories of pores appear with pore diameters which are centred on well defined mean values do not appear, but a relatively continuous pore distribution is seen between two extreme diameter values. Between those extreme values, there is no horizontal stage in the pore distribution curve. Said polymodal distribution is linked to a “thorny chestnut husk” or “sea-urchins” pore structure obtained with alumina agglomerates prepared by the rapid dehydration of hydrargillite then agglomerating the flash alumina powder obtained in accordance with one of the Applicant\'s patents (U.S. Pat. No. 4,552,650-IFP). The prepared alumina agglomerates may be in the form of beads or in the form of extrudates, as shown in FR-A-2 764 213 and U.S. Pat. No. 6,043,187.

The thorny chestnut husk or sea-urchins structure is constituted by a plurality of juxtaposed agglomerates each formed by a plurality of acicular platelets, the platelets of each agglomerate generally being radially orientated with respect to each other and with respect to the centre of the agglomerate. At least 50% of the acicular platelets have a dimension along their longer axis of between 0.05 and 5 micrometers and preferably between 0.1 and 2 micrometers, a ratio of this dimension to their average width of between 2 and 20, preferably between 5 and 15, and a ratio of this dimension to their average thickness of between 1 and 5000, preferably between 10 and 200. At least 50% of the agglomerates of acicular platelets constitutes a collection of pseudo-spherical particles with a mean size of between 1 and 20 micrometers, preferably between 2 and 10 micrometers. A highly suitable image which can be used to help to represent such a structure is a pile of thorny chestnut-husks or of a pile of sea-urchins, hence the pore structure denominations “thorny chestnut husk” or “sea-urchins” which is used by the skilled person.

The majority of the pores is constituted by the free spaces located between the radiating acicular platelets. These pores, which are by nature “wedge-shaped”, have a continuously variable diameter of between 100 and 1000 Å. The network of interconnected macropores results from the space which is left free between the juxtaposed agglomerates.

These catalysts with a polymodal pore profile have a pore distribution (determined by mercury porosimetry) which is preferably characterized as follows:

- total pore volume: 0.7 to 2.0 cm³/g;
- % of total pore volume as pores with a mean diameter of less than 100 Å: between 0 and 10
- % of total pore volume as pores with a mean diameter between 100 and 1000 Å: between 40 and 90
- % of total pore volume as pores with a mean diameter between 1000 and 5000 Å: between 5 and 60
- % of total pore volume as pores with a mean diameter between 5000 and 10000 Å: between 5 and 50
- % of total pore volume as pores with a mean diameter of more than 10000 Å: between 5 and 20.