Homogeneous catalyst bed and process of transforming...

Details Homogeneous catalyst bed and process of transforming... Homogeneous catalyst bed and process of transforming...

2000-02-08

2002-09-17

Griffin, Walter D. (Department: 1764)

Mineral oils: processes and products

Chemical conversion of hydrocarbons

Reforming

C208S134000, C208S135000, C208S136000, C208S137000, C208S138000, C585S407000, C502S305000, C502S308000, C502S310000, C502S319000, C502S321000, C502S322000, C502S323000, C502S325000, C502S326000, C502S327000, C502S334000, C502S339000, C502S349000, C502S355000

Reexamination Certificate

active

06451199

ABSTRACT:

The present invention relates to a homogeneous catalyst bed with improved trimetallic and bifunctional effects, the catalyst particles having reduced local fluctuations in composition, resulting in greatly improved catalytic performances in particular, and in improved activities and gasoline yields. Such a bed is termed “homogeneous on the micronic scale”. The invention also relates to a process for transforming hydrocarbons to aromatic compounds using the catalyst, such as the gasoline reforming process and the aromatic compound production process.
Catalysts for gasoline reforming and/or aromatic compound production are well known. They generally contain a matrix, at least one noble metal from the platinum family, at least one halogen and at least one promoter metal, also known as an additional metal.
Promoter metals particularly include tin for regenerative processes and rhenium for fixed bed processes. Frequently, a second promoter is used, for example tungsten for regenerative processes (Pt, Sn, W) and indium for fixed bed processes (Pt, Re, In).
Catalysts for gasoline reforming and/or for aromatic compound production are bifunctional catalysts with two functions which are essential for producing the correct performances: a hydrodehydrogenating function which dehydrogenates naphthenes and hydrogenates coke precursors, and an acid function which ensures isomerisation of naphthenes and paraffins and ring closure of long chain paraffins. The hydrodehydrogenating function can be provided by an oxide such as molybdenum oxide MoO
3
, chromium oxide Cr
2
O
3
or gallium oxide Ga
2
O
3
, or by a metal from column 10 (Ni, Pd, Pt). It is known that metals, in particular platinum, are much more active than oxide phases for hydrodehydrogenation reactions, and for this reason metallic catalysts have replaced supported oxide catalysts for reforming gasoline and/or for aromatic compound production. However, metals such as Ni, and to a lesser extent palladium and platinum, also have a hydrogenolysing activity to the detriment of the desired gasoline yield for gasoline reforming and/or for aromatic compound production. This hydrogenolysing activity can be substantially reduced, and thus the catalyst selectivity can be increased, by adding a second metal such as tin. Further, adding a second metal such as iridium or rhenium increases the hydrogenating properties of platinum, which encourages hydrogenation of coke precursors and thus enhances the stability of the catalyst. These various reasons have encouraged the success of bimetallic catalysts over first generation monometallic catalysts. More recently, trimetallic catalysts have been introduced, which retain the improved stability of bimetallic catalysts by increasing the gasoline selectivities of these catalysts.
An increase in selectivity can thus be achieved by various means. Prior art document U.S. Pat. No. 5,128,300 recommends, for catalyst extrudates, a homogeneous distribution of tin with a local composition which does not fluctuate by more than 25% about the average tin content, this being 0.1-2% by weight of catalyst.
We have discovered, and this constitutes the subject matter of the present invention, that the performance of the catalyst can be substantially improved not only by limiting the variation in a single element, but by controlling the relative fluctuations of the ratio of the compositions of the different promoters. Thus homogeneity of the trimetallic (noble—promoter metals) effect is attained in the particle bed, which improves the overall performances of the process for which the catalyst is used.
More precisely, the invention concerns a homogeneous bed of catalyst particles, said catalyst comprising at least one amorphous matrix, at least one noble metal from the platinum family, at least two additional metals M1 and M2 and at least one halogen, and in which, for a catalyst particle, C
pt
is the local concentration of platinum, C
M1
is the local concentration of additional metal M1, C
M2
is the local concentration of additional metal M2, in which catalyst particle bed the standard deviation of the distribution of ratios C
M1
/C
M2
. measured along the particle diameter, is better than 25% relative.
The amorphous catalyst matrix is generally a refractory oxide such as magnesium, titanium or zirconium oxides, alumina or silica, used alone or as a mixture. The preferred support contains alumina or is constituted by alumina.
For gasoline reforming and/or aromatic compound production reactions, the preferred matrix is alumina, and advantageously its specific surface area is 50-600 m
2
/g, preferably 150-400 M
2
/g.
The catalyst also contains at least one noble metal from the platinum family (Pt, Pd, Rh. Ir), preferably platinum. Advantageously, the catalyst can contain a noble metal (such as Pt).
Additional metals M1 and M2 are selected from the group formed by tin, germanium, lead, gallium, indium, thallium, rhenium, iridium, manganese, chromium, molybdenum and tungsten. With gasoline reforming and/or regenerative aromatic compound production processes carried out in a moving bed, the preferred metal is tin, and very advantageously it is combined with platinum (catalysts containing Pt, Sn) and still more advantageously, the catalyst also contains tungsten or iridium (catalysts containing Pt, Sn, W or containing Pt, Sn, Ir or containing Pt, Sn, W, Ir or containing Pt, Sn, In or containing Pt, Ir, In).
In fixed bed processes, the preferred metal is rhenium; highly advantageously it is combined with platinum (catalysts containing Pt, Re) and more advantageously the catalyst contains indium (catalysts containing Pt, Re, In), further, tungsten or iridium can be present (catalysts containing Pt, Re, W or Pt, Re, In, W or Pt, Re, Ir or Pt, Re, In, Ir). These catalysts are usually and preferably sulphurised before or after loading up.
The halogen is selected from the group formed by fluorine, chlorine, bromine and iodine, preferably chlorine.
The catalyst generally contains 0.02% to 2% by weight, preferably 0.04% to 2% by weight of a noble metal, 0.1% to 15% of halogen and 0.02% to 10%, preferably 0.04% to 10%, of additional metal M1 and 0.02%10% to 10%, preferably 0.04% to 10% of additional metal M2. Preferably, the catalyst of the invention contains at most 2% of additional metal M1 and at most 2% of additional metal M2. Under these preferred conditions, the catalyst has the best performances due to an optimised trimetallic effect.
The catalyst is in the bed in the form of particles which can be beads, extrudates, trilobes or any of the forms usually employed.
C
pt
is the local concentration of noble metal, expressed in atoms/unit of measurement (the noble metal is not necessarily platinum), C
M1
is the local atomic concentration of additional metal M1, C
M2
is the local atomic concentration of additional metal M2 and C
x
is the local atomic concentration of halogen.
The overall catalyst composition can be determined by X ray fluorescence using the catalyst in the powdered state, or by atomic absorption of the catalyst after acid attack.
The local composition measured on the micronic scale as opposed to the overall composition of the catalyst can be measured using an electron microprobe and can be completely evaluated by STEM (Scanning Transmission Electron Microscopy). This measurement can be made by determining the platinum and additional metal contents in zones of a few cubic microns along the diameter of a catalyst particle which are termed the measurement units. This measurement enables the macroscopic distribution of the metals to be determined inside the particles, more exactly, it constitutes an elemental analysis on the micronic scale.
The analyses were carried out using a JEOL JXA 8800 electron microprobe or using a Microbeam type CAMEBAX, equipped with wavelength-dispersive spectrometers. The particles were coated in resin then polished to their diameter. The acquisition parameters were as follows: acceleration voltage 20 kV, current 30 nA, Pt L&agr;, Sn L&agr;, Cl K&agr; lines and count time 20 s.
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