Mineral oils: processes and products – Chemical conversion of hydrocarbons – Cracking
Reexamination Certificate
1999-05-20
2001-05-29
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Cracking
C208S109000, C208S111350, C208S111300, C208S111150, C208S114000
Reexamination Certificate
active
06238550
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to silicoaluninophosphates (SAPOs) having unique silicon distributions, a method for their preparation and their use as catalysts for the hydroprocessing of hydrocarbon feedstocks. More particularly, the new SAPOs, designated ECR-42 herein, have a high silica:alumina ratio and a beneficial silicon atom distribution.
BACKGROUND OF THE INVENTION
The preparation of crystalline silicoaluminophosphates is well known. U.S. Pat. No. 4,480,871 describes the preparation of crystalline, microporous silicoaluminophosphates by hydrothermal crystallization of silicoaluminophosphate gels containing a molecular structure-forming template. SAPOs are members of a class known as non-zeolitic molecular sieves. The SAPO molecular sieve has a framework of AlO
4
, SiO
4
and PO
4
tetrahedra linked by oxygen atoms. The negative change in the network is balanced by the inclusion of exchangeable protons or cations such as alkali or alkaline earth metal ions. The interstitial spaces of channels formed by the crystalline network enables SAPOs to be used as molecular sieves in a manner similar to crystalline aluminosilicates, such as zeolites.
Accordingly, numerous microporous framework structures analogous to the aluminosilicate zeolites can be synthesized having an AlPO
4
composition and have been called ALPOs. A modified family of materials has been made by the substitution of Si
4+
for Al
3+
and P
5+
(SAPOs). Although the ALPO structures are neutral frameworks, the substitution of Si
4+
for P
5+
imparts a negative charge on the framework. By suitable choice of a cation, this can be translated into catalytic activity. However, alternate substitutions may be possible that may result in a disproportionately low exchange capacity. The exact nature of Si substitution into ALPO structures is complex and highly variable and may depend on both the topology of the ALPO/SAPO and the method of preparation. The result is that preferred catalysts may be made by a suitable choice of synthesis method. For example, SAPO-5 and SAPO-11 may be conventionally prepared in an aqueous solution or from microemulsions. The latter processes use hexanol and a cationic or neutral surfactant to a two-phase gel leading to the formation of a microemulsion.
The microemulsion process is a two-phase approach to preparing SAPOs attempts to reduce the amount of undesirable silica island formation by supplying the silicon from an organic phase to the aqueous phase at a low concentration during crystallization. The organic phase contains the organic solvent and organic silicon source, tetraethylorthosilicate, which is only slightly soluble in the aqueous phase. The aqueous phase is where crystallization occurs and contains the phosphorus and aluminum. It has been theorized that as the silicon is depleted from the aqueous phases by the growing SAPO crystals, it will be replenished from the organic phase, thereby forming a silicoaluminophosphate product having a more uniform distribution of silicon in the framework.
Conventional SAPO molecular sieves have application for a wide variety of uses, for example as catalysts. In this regard, conventional SAPOs may be used as catalysts in petroleum processing. For example, SAPO catalysts may be used in lubricating oil hydroconversion procedures, hydrocracking, dewaxing, and combinations thereof. In this regard, it is known that increasing Si concentration at first results in an increase in catalytic activity. However, increasing Si content beyond about 0.04 mole fraction in the framework, based on the total amount of silicon, aluminum, and phosphorus in the framework, provides no increase in activity, and may even lead to a decrease, depending on the specific distribution and clustering of the Si
4+
substituent.
In that the distribution of Si in the SAPO framework affects catalytic activity, the catalytic activity of SAPOs therefore depends on both the global composition and the Si distribution. Accordingly, SAPOs are defined not only by chemical composition and X-Ray Diffraction pattern, but also by
29
Si MAS NMR spectra which define the Si distributions.
On the basis of this last technique, it has been shown that when the SAPOs contain low amounts of Si, the silicon atoms are mostly isolated. However, when the Si content increases, Si islands start to appear, i.e., Si sites having silicon atoms and no aluminum atoms in neighboring lattice positions.
There remains a need, though, for improved silicoaluminophosphates for use in hydrocarbon processing, and in particular silicoaluminophosphates having an improved silicon distribution.
SUMMARY OF THE INVENTION
In one embodiment, the invention is a method for catalytically dewaxing a hydrocarbon, comprising contacting the hydrocarbon with a catalytically effective amount of a SAPO catalyst under catalytic conversion conditions, the SAPO catalyst being a molecular sieve with a framework tetrahedra of silicon, aluminum, and phosphorus, and having a total silicon amount ranging from above about 4 molar percent to about 20 molar percent, a total aluminum amount ranging from about 40 molar percent to about 55 molar percent, and a total phosphorus amount ranging from about 30 molar percent to about 50 molar percent, the molar percents being based on the total amount of aluminum, phosphorus, and silicon present in the composition, and the molecular sieve having the topology AEL and being isostructural with conventional SAPO-11, wherein
(a) the silicon present in the molecular sieve and the conventional SAPO-11 is distributed among silicon sites in the framework tetrahedra, each site having a first, a second, a third, and a fourth next nearest neighbor position, and each next nearest neighbor position being independently occupied by one atom selected from silicon, and aluminum, and
(b) the molecular sieve has a substantially smaller number of silicon sites having silicon atoms among all four next nearest neighbor positions than the conventional SAPO-11 having the same total silicon amount.
In another embodiment, the invention is a method for catalytically dewaxing a hydrocarbon comprising contacting the hydrocarbon with a catalytically effective amount of a SAPO catalyst under catalytic conversion conditions, the SAPO catalyst being a molecular sieve framework tetrahedra of silicon, aluminum, and phosphorus, the composition having a total silicon amount ranging from above about 4 molar percent to about 20 molar percent, a total aluminum amount ranging from about 40 molar percent to about 55 molar percent, and a total phosphorus amount ranging from about 30 molar percent to about 50 molar percent, the molar percents being based on the total amount of aluminum, phosphorus, and silicon present in the composition, and the molecular sieve having the topology AEL and being isostructural with conventional SAPO-11, wherein
(a) the molecular sieve has a first number of Si atoms coordinated as Si(4Si),
(b) the conventional SAPO-11 with the Si amount has a second number of Si atoms coordinated as Si(4Si), and
(c) the first number of Si atoms is substantially less than the second number of Si atoms.
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paten
Cody Ian A.
Linek Sandra J.
Murphy William J.
Strohmaier Karl G.
Vaughan David E. W.
Cromwell Michael A.
Exxon Research and Engineering Company
Griffin Walter D.
Hughes Gerard J.
Preisch Nadine
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