Mineral oils: processes and products – Chemical conversion of hydrocarbons – Cracking
Reexamination Certificate
2000-12-26
2003-03-18
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Cracking
C208S109000, C208S111250, C208S111350, C423S324000, C423S326000, C423S327100, C423S331000, C502S063000, C502S080000
Reexamination Certificate
active
06533923
ABSTRACT:
The present invention relates to trioctahedral phyllosilicates 2:1 of the stevensite or kerolite type containing fluoride, fluorinated in synthesis in an acid medium and modified post-synthesis to bring about the Si/Al and/or Mg/Al substitutions which impart acid properties to the solid.
These phyllosilicates may be incorporated in the composition of catalysts used to convert hydrocarbons, in particular for hydrocracking.
Phyllosilicates have a micro- or even meso-pore structure, attributable amongst other things to the nature, number and size of the compensation cations. The variation in the thickness of the space between sheets due to the exchange of compensation cations for other cations causes changes in properties. Phyllosilicates are used for adsorption and catalysis either as an active phase or as a means of assisting the active phase.
Due to the nature of the elements present in the tetrahedral and octahedral cavities and the nature of the compensation cations, the chemical composition of phyllosilicates is also an important factor affecting the selectivity of the exchange of cations, the adsorption selectivity and in particular the catalytic activity. This is explained by the nature and intensity of interactions between their internal and external surfaces on the one hand and with the adsorbed molecules on the other.
Numerous applications, particularly acid catalysis, require proton forms from which compensation cations introduced during synthesis have been completely removed. These forms may be obtained by one or more exchanges of these cations for NH
4
+
ions followed by calcination in order to generate the proton form.
Although the chemical bonds between the elements in the structure of phyllosilicates are ion-covalent, they will be assumed to be ionic here in order to simplify the description. Starting from a presentation in which the O
2−
ions are in one plane, in contact with one another, in the most compact manner, it is possible to obtain a plane having hexagonal cavities, referred to as a hexagonal plane, by removing one O
2−
ion in two from one of every two rows of O
2−
ions. The structure of a phyllite may be simply represented using arrangements of hexagonal planes of O
2−
ions and compact planes of O
2−
and OH
−
ions. The OH
−
ions fill the cavities in hexagonal planes of O
2−
ions. Placing two compact planes one on top of the other bounded on either side by a hexagonal plane enables an octahedral layer (O) to be defined between 2 tetrahedral (T) layers, hence the name TOT sheet. Such an arrangement, also referred to as 2:1, enables a layer of octahedral cavities to be defined, located between two layers of tetrahedral cavities. Each tetrahedron has one O
2−
ion in common with the octahedral layer and each of the other three O
2−
ions is shared with another tetrahedron in the same tetrahedral layer.
The crystal lattice is therefore made up of six octahedral cavities having four tetrahedral cavities on either side. If the octahedral sites are occupied by divalent cations, this will be referred to as a trioctahedral phyllosilicate 2:1. In the case of a phyllosilicate made up of the elements Si, Mg, O and the OH group, such an arrangement corresponds to the formula Si
8
Mg
6
O
20
(OH)
4
. The tetrahedral cavities contain the silicon element and the octahedral cavities the magnesium element. Such a formula corresponds to the natural product known as talc.
If a very small fraction of octahedral cavities are unoccupied, a lack of positive charge appears within the structure. This lack of charge will be compensated by the presence of exchangeable compensation cations located in the interlayer space. In the case of a phyllosilicate made up of the elements Si, Mg, O and the OH group, the formula of such a compound may be written as follows for a lattice
C
2/zm
m+
Si
8
(Mg
6−z
□
z
)O
20
(OH)
4
where □ represents an unoccupied octahedral cavity, i.e.
Mg
z
Si
8
(Mg
6−z
□
z
)O
20
(OH)
4
or Na
2z
Si
8
(Mg
6−z
□
z
)O
20
(OH)
4
if the exchangeable cation C corresponds to the magnesium or sodium element respectively.
The structural group [Si
8
(Mg
6−z
□
z
)O
20
(OH)
4
]
2z−
for a lattice or [Si
4
(Mg
3−z
□
z
)O
20
(OH)
2
]
2z−
for a half lattice corresponds to a natural smectite known as kerolite if z is very close to zero and stevensite if z if higher. Generally speaking, it is not uncommon in the natural product for Mn(II) and Fe(II) ions to be present alongside the magnesium cation in the octahedral cavity.
It is not easy to understand why trioctahedral phyllosilicate 2:1 should be lacking in positive charges in the octahedral layer, currently known under the name of stevensite, as distinct from the products cited in background literature. Its occurrence in nature has been the subject of controversy, because some regard phyllosilicate as a variety of talc. The fact that its chemical composition is close to that of talc goes a long way towards explaining this. Natural stevensite occurs in veins or pockets, mixed to a greater or lesser degree with other phases, which may explain the difficulties encountered when attempting to characterise or sample it. However, progress in the systematic classification of natural phyllosilicates and improved analysis of samples has improved what we know about their characteristics.
Until now, the Si/Al or Mg/Al combination has been produced by synthesis or, in the case of minerals of the smectite type, by a cationic exchange with aluminium in order to adjust the Si/Al and Mg/Al ratios to improve the stability of materials, these exchanges being effected in the absence of any fluoride ion (patent JP 94-191549).
The present invention relates to stevensite or kerolite trioctahedral phyllosilicates 2:1 containing fluorine and having inter-sheet Mg
2+
cations, fluorinated in synthesis in an acid medium and modified post-synthesis in the presence of fluorine, said post-synthesis fluorination consisting in incorporating aluminium in the structure of the stevensite or kerolite (Mg), i.e. producing a substitution of the silicon and/or magnesium elements by the aluminium. The advantage of this method is that it enables the acidity of the phyllosilicate proposed by the invention to be increased in a controlled manner.
Another objective of the present invention is to propose a method of preparing said phyllosilicates and their use for converting hydrocarbons.
The phyllosilicates proposed by the invention are obtained by processing, post-synthesis, stevensite or kerolite type trioctahedral phyllosilicates 2:1 immediately after synthesis, and these are synthesised in a fluoride medium (for example in the presence of HF acid or any other acid source of fluoride ions and/or any other source of fluoride ions).
The general chemical formula (for a half lattice) of the initial phyllosilicates is as follows:
C
2z/m
m+
Si
4
(Mg
3−z
□
z
)O
10
(OH)
2−u
F
u
,n
H
2
O
where
C is the compensation cation from the reaction medium constituted at least partially by the Mg
2+
cation or a cation introduced by at least one process of post-synthesis ion exchange, selected from the group consisting of the cations of elements from groups IA, IIA and VIII of the periodic table, the cations of rare earths (cations of elements having an atomic number 57 to 71 inclusive), the ammonium cation, organic cations containing nitrogen (among which are alkylammonium and arylammonium),
m is the valence of the cation C,
z is a number greater than 0 and less than or equal to 1, preferably ranging between 0.01 and 1,
u is a number greater than 0 and less than or equal to 1, preferably ranging between 0.01 and 2,
n is a real positive number and not zero,
and □ stands for an octahedral cavity.
The magnesium element may be partially substituted by at least one of the elements from the group consisting of nickel, cobalt and zinc, these elements being taken from th
Baron Jacques
Lacombe Sylvie
Le Dred Ronan
Schlussel Véronique
Griffin Walter D.
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
LandOfFree
Trioctahedral phyllosilicates 2:1 of a stevensite or... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Trioctahedral phyllosilicates 2:1 of a stevensite or..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Trioctahedral phyllosilicates 2:1 of a stevensite or... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3035778