Chemistry of hydrocarbon compounds – Saturated compound synthesis – By isomerization
Reexamination Certificate
1998-11-24
2001-02-20
Dunn, Tom (Department: 1754)
Chemistry of hydrocarbon compounds
Saturated compound synthesis
By isomerization
C502S063000, C502S080000, C502S084000, C502S085000
Reexamination Certificate
active
06191333
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to a process for isomerization, in the presence of hydrogen (also called a hydro-isomerization process), of normal C5-C10 paraffins using a long-reticulate-distance dioctahedral phyllosilicate 2:1 (sometimes also referred to as bridged clay).
The isomerization of normal paraffins that contains between 5 and 10 carbon atoms per molecule is currently of considerable importance in the petroleum industry, mainly in connection with the elimination of lead alkyls from gasolines.
At the present time, moreover, the specifications for gasoline fractions are becoming more stringent as regards their contents of aromatics. Reducing the amount of aromatics present in gasolines, taking into account the availability of the various gasoline fractions would mean reducing the octane rating, which would have to be offset. One possible way of limiting the octane loss would consist in isomerizing the linear paraffins having seven or eight carbon atoms, without aromatizing them. This transformation would allow a significant improvement in octane rating: n-heptane has an octane rating of 0, while that of methylhexanes is approximately 47, and that of dimethylpentanes is approximately 87.
Based on the number of carbon atoms that are present in the linear paraffins that are to be isomerized, different types of catalyst have been developed:
In the case of the isomerization (also called hydro-isomerization) of short linear paraffins that contain 4 to 6 carbon atoms per molecule, catalysts of the Friedel and Crafts types, such as aluminum chloride, are used at low temperatures (approximately 80-130° C.), as well as catalysts that contain at least one metal from group VIII supported on a halogenated, preferably chlorinated, base, which are used at moderate temperatures (approximately 150° C.). Nonetheless, the selectivity of these catalysts in terms of isomerized products turns out to be inadequate in the case of the isomerization of longer C6+ paraffins (paraffins having more than six carbon atoms per molecule).
Many patents have as their objects zeolitic catalysts or molecular sieves that contain at least one metal from group VIII deposited on a zeolite; said catalysts are used at high temperatures (220° C. or more) and in the presence of hydrogen. In the case of linear paraffins with 5 and 6 carbon atoms per molecule, said catalysts lead to smaller improvements in octane in the products that are produced than the two kinds of catalysts described above, but they have the advantage of being easier to use and more resistant to poisons. By way of example of the hydro-isomerization of paraffins on zeolites, the catalysts based on mordenite and a hydro-dehydrogenating element are described in patents U.S. Pat. No. 3,432,568 and U.S. Pat. No. 3,673,267. Or, more recently, patents EP-398416 and WO 96/18705, which claim the use of catalysts based on Beta zeolites (BEA) and at least one hydro-dehydrogenating metal, in the presence of hydrogen, in order to carry out the hydro-isomerization of short paraffins.
The isomerization (hydro-isomerization) of linear paraffins having 4 to 8 carbon atoms per molecule can also be carried out with bifunctional catalysts that combine an acid function with a hydro-dehydrogenating function. With this kind of catalyst, the main parasitic reactions are cracking, hydrogenolysis, aromatization, and coking.
The catalysts that are described above for the isomerization (hydro-isomerization) of short linear paraffins (having 4 to 6 carbon atoms per molecule) have also been used in the hydro-isomerization of C7 and C8 paraffins, but these catalysts provide isomerized-product yields that are still inadequate.
Non-zeolitic molecular sieves (SAPO, silico-aluminophosphates) with shape selectivity have also been claimed, patents U.S. Pat. No. 5,114,563 and U.S. Pat. No. 4,710,485, for the purpose of ensuring the selective hydro-isomerization of C7 to C20 linear paraffins. These molecular sieves, which have acidity levels that are much sweeter than zeolites, lead to higher yields of isomerized products. As a matter of fact, it has been noted that cracking reactions, secondary reactions, are of less significance when these solids are used as isomerization catalysts. Nevertheless, these solids have activity levels that are lower; this makes it necessary to work with them at higher temperatures than with zeolite-based catalysts. However, thermodynamics teaches us that any increase in the reaction temperature leads to a reduction in the percentage of multi-branched products in the reaction products, and hence to a smaller gain in octane rating.
SUMMARY OF THE INVENTION
The work that has been done has led us to show that, surprisingly, a catalyst that contains at least one dioctahedral phyllosilicate 2:1, which is preferably synthesized in a fluoride medium in the presence of HF acid and/or another source of fluoride anions, whose reticulate distance is equal to at least 20×10
−10
m (or 2 nanometers or 2 nm) and which includes pillars based on at least one oxide from the elements of groups IVB, VB, VIB, VIII, IB, IIB, IIA, IVA, or any combination of these oxides, and preferably selected from the group composed of SiO
2
, Al
2
O
3
, TiO
2
, ZrO
2
and V
2
O
5
, or any combination of said oxides, makes it possible to achieve an isomerized-product (hydro-isomerized product) selectivity that is better than that of the catalysts known in the prior art and even, in certain cases, with a higher level of activity.
This invention therefore pertains to the use of a catalyst that contains at least one dioctahedral phyllosilicate 2:1, which is preferably synthesized in a fluoride medium in the presence of HF acid and/or another source of fluoride anions, whose reticulate distance is equal to at least 20×10
−10
m (2 nm) and which includes pillars based on at least one oxide from the elements of groups IVB, VB, VIB, VIII, IB, IIB, IIA, IVA, or any combination of these oxides, and preferably selected from the group composed of SiO
2
, Al
2
O
3
, TiO
2
, ZrO
2
, and V
2
O
5
, or any combination of the latter and at least one element from group VIII, in a conventional process for isomerization of a feedstock that contains mainly normal paraffins that carry 5 to 10 carbon atoms per molecule and preferably 5 to 8 carbon atoms per molecule, whose normal operating conditions are presented below.
More accurately, the catalyst contains at least one dioctahedral phyllosilicate 2:1 whose reticulate distance is equal to at least 20×10
−10
m (2 nm) and which includes pillars based on at least one oxide from the elements of groups IVB, VB, VIB, VIII, IB, IIB, IIA, IVA, or any combination of these oxides, and preferably selected from the group composed of SiO
2
, Al
2
O
3
, TiO
2
, ZrO
2
, and V
2
O
5
, or any combination of the latter, at least one matrix, and at least one hydro-dehydrogenating element from group VIII that is selected from the group composed of: Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt. The dioctahedral phyllosilicates 2:1 (which are preferably prepared in advance in a fluoride medium in the presence of HF acid and/or another source of fluoride anions) which are preferably bridged by the process described below, have a reticulate distance d
001
that is equal to least 20×10
−10
m (2 nm), preferably equal to least 26.5×10
−10
m, and even more preferably equal to least 28×10
−10
m, and most preferably equal to least 30×10
−10
m. Said reticulate distance is generally less than or equal to 60×10
−10
m, and preferably less than or equal to 50×10
−10
m. Said reticulate distance, which is represented by d
001
, represents the sum of the thickness of a sheet and the inter-sheet space. This value is directly accessible by the method that is familiar to one skilled in the art of x-ray fraction on oriented powder.
Dioctahedral phyllosilicates 2:1 are minerals that are produced by the stacking of elementary sheets. Even though the chemical bonds between th
Baron Jacques
Benazzi Eric
Brendle Jocelyne
Le Dred Ronan
Saehr Daniel
Dunn Tom
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
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