Chemistry of inorganic compounds – Zeolite – With change of synthesized zeolite morphology
Reexamination Certificate
2001-02-21
2004-02-17
Sample, David (Department: 1755)
Chemistry of inorganic compounds
Zeolite
With change of synthesized zeolite morphology
C423S708000, C423S709000, C423S717000, C423SDIG003, C502S066000, C502S074000, C585S739000, C585S750000
Reexamination Certificate
active
06692723
ABSTRACT:
The present invention relates to a zeolite with structure type MTT in the form of crystals and crystal aggregates with a specific ganulometry and to a catalyst comprising such a zeolite. The present invention also relates to the use of said catalyst in the principal transformation processes used in refining, in particular in straight chain paraffin isomerisation processes intended to improve the quality of such paraffin fractions for upgrading them, in particular into vehicle fuels. To this end, the isomerisation reaction can transform straight chain paraffinic hydrocarbons (normal paraffins, nP) with low octane numbers into branched hydrocarbons from the same family (isoparaffins, iP) with much higher octane numbers.
The isomerisation reaction leads to secondary reactions, coking and cracking, and conventional catalysts used to carry out such a reaction, namely bifunctional catalysts generally comprising an acid function and a hydrodehydrogenating function, lack selectivity for isoparaffins to the advantage of the secondary reactions cited above that constitute substantial losses for the desired reaction.
Further, in order to minimize secondary reactions, the Applicant has studied the synthesis of novel bifunctional zeolitic catalysts that are more active and more selective for converting straight chain parafffins than known catalysts.
In particular, the physical characteristics inherent in the catalyst have been studied and it has been discovered that the crystal size, and more precisely the size of the aggregates formed by the crystals of the zeolite comprised in said catalyst, have a major influence on paraffin hydrocarbon transformation catalytic performance in terms of activity and selectivity.
Zeolites with a specific granulometry have already been described in the prior art. As an example, European patent application EP-A2-0 323 893 describes an L zeolite that can be used to convert hydrocarbon feeds, which possesses aggregates of crystals with a length in the range 0.50 to 1.50 &mgr;m and with a diameter in the range 0.2 to 0.6 &mgr;m. That patent discloses that the aggregate size depends on the alkalinity of the reaction mixture during preparation of the zeolite. In their International patent application WO-A-93/25476, Verduijn et al. describe a ZSM-5 zeolite comprising aggregates in the form of needles with a maximum average length of 10 &mgr;m, obtained by controlling parameters such as the crystallization temperature or alkalinity of the reaction mixture. Other authors (WO-A-93/08125) also suggest controlling the crystal and aggregate size of a molecular sieve formed from an MFI, MEL or &bgr; type zeolite by means of the crystallisation temperature. It should be noted that these prior art patent application never mention the specific size of the crystals and aggregates in combination with particular catalytic properties.
The Applicant has made significant progress by developing a catalyst containing a zeolite with structure type MTT, in particular ZSM-23 zeolite, having well defined crystal and crystal aggregate sizes, so as t reduce by a maximum the formation of undesirable cracking products and coke during isomerisation reactions.
ZSM-23 zeolite with structure type MTT, which has already been described in the prior art, has a unidimensional microporous framework, with a pore diameter of 4.5×5.2 Å (1 Å×1 Angstrom=1×10
−10
m) (“Atlas of Zeolite Structure Types”, W. M. Meier and D. H. Olson, 4
th
edition, 1996) Further, A. C. Rohmann et al (Zeolite, 5, 352, 1985).J. L. Schenker et al (private communication, 1992) and B. Marler et al (J. Appl. Cryst. 26, 636, 1993) have stated that the crystalline lattice has orthorhombic symmetry (Pmn2
1
, a=21.5 Å, b=11.1 Å, c=5.0 Å)with channels parallel to axis c, delimited by rings of 10 tetrahedra. The synthesis mode and physico-chemical characteristics of ZSM-23 zeolite have been described in a variety of patents which differ in the nature of the organic template used. That zeolite can be synthesised using pyrrolidine U.S. Pat. No. 4,076,842), diisopropanolamine (British patent GB-A-2 190 910), quaternary ammonium compounds such as heptamethonium bromide (U.S. Pat. No. 5 405 596) octamethonium bromide (GB-A-2 202 838) dodecamethonium bromide (U.S. Pat. No. 5 405 596) and quaternary triammonium compounds (U.S. Pat. No. 5,332,566) The mode of synthesis compries mixing an oxide, generally a silicon oxide, and an oxide, generally an aluminium oxide, in the presence of the template.
Other zeolite structure type MTT and differ from ZSM-23 zeolite in the mode of preparation, in particular in the organic template used. These are EU-13 zeolite (European patent EP-A-0 108 486), using a quaternary methylated ammomium or phosphonium salt, ISI-4 zeolite (EP-A- 0 102 497) using ethylene glycol or a monoethanolamine, SSZ-32 zeolite (U.S. Pat. No. 4 483 835) using imidazole derivatives or KZ-1 zeolite using a variety of amines (L. M. Parker et al, Zeolite, 3,8, 1988)
SUMMARY OF THE INVENTION
The present invention concerns a zeolite with structure type MTT comprising MTT zeolite crystals with a size of less than 5 &mgr;m, at least a portion of the MTT zeolite crystals being in the form of MTT zeolite crystal aggregates, said aggregates having a granulometry such that the dimension Dv,90 is in the range 40 nm to 100 &mgr;m. More particularly, the invention concerns ZSM-23 zeolite with structure type MTT, and its use as an acidic solid in the composition of a catalyst for isomerising light straight chain paraffins.
IMPORTANCE OF THE INVENTION
MTT zeolite, for example ZSM-23 zeolite as defined in the present invention, used as a catalyst in association with at least one binder, at least one metal selected from elements from group VIII of the periodic table, has improved catalytic performances for hydrocarbon transformations in terms of activity and selectivity, such as isomerising light paraffinic hydrocarbons containing 5 to 10 carbon atoms per molecule.
DESCRIPTION OF THE INVENTION
The zeolite with structure type MTT of the invention comprises crystals of MTT zeolite wherein at least a portion is in the form of aggregates of MTT zeolite. The zeolite with structure type MTT of the invention can be ZSM-23 zeolite, EU-13 zeolite, ISI-14 zeolite or KZ-1 zeolite.
Throughout the remaining text, the term “aggregate” as used in the present invention means an ensemble formed from at least two zeolite crystals having at least one mutual point of contact. The granulometry of the crystal aggregates is represented by the dimension Dv,X, defined as the diameter of the equivalent sphere such that the size of X% by volume of aggregates is less than said diameter.
The zeolite with structure type MTT of the invention is characterized in that the size of the MTT zeolite crystals is less than 5 &mgr;m, limits included, at least a portion of the zeolite crystals being collected into aggregates, said crystal aggregates being characterized in that their granulometry is such that the dimension Dv,90 is in the range 40 nm to 100 &mgr;m.
The zeolite with structure type MTT of the present invention generally has the following formula in its anhydrous form 0 to 20R
2
O; 0-10 T
2
O
3
: 100 XO
2
, where R represents a cation with valency n, X represents silica and/or germanium, T represents at least one element selected from aluminium, iron, gallium, boron, titanium, vanadium, zirconium, molybdenum, arsenic, antimony, chromium and manganese, the overall atomic ratio X/T being 5 or more and preferably more than 10.
The crystal size is determined by X ray diffraction and/or using an electron microscope. The aggregate size is determined by laser diffraction granulometry and/or by electron microscopy. The granulometry is measured by laser diffraction using the zeolite suspended in water. The size distribution of the aggregates, defined by volume, is calculated from light signals collected by detectors and applying the Fraunhofer theory. The granulometric characteristics of the zeolite with s
Benazzi Eric
Kolenda Frederic
Rouleau Loïc
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Sample David
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