PATENT
Pub. No.: WO/2012/005981 International Application No.: PCT/US2011/041810
Publication Date: 12.01.2012
Applicants: CHEVRON U.S.A. INC. [US/US]; 6001 Bollinger Canyon Road San Ramon, California 94583 (US)
Abstract:
BACKGROUND OF THE FNVENTION
High quality lubricating oils are critical for the operation of modern machinery and motor vehicles. However, current crude oil supplies are inadequate to meet present demands for such lubricants. Therefore, it is necessary to upgrade crude oil fractions otherwise unsuitable for lubricant manufacture. As an example, high-quality lubricating oils must often be produced from waxy feeds. Numerous processes have been proposed for producing lubricating base oils by upgrading ordinary and low quality feedstocks.
Hydrocarbon feedstocks may be catalytically dewaxed by hydrocracking or hydroisomerization. Hydrocracking generally leads to a loss in yield due to the production of lower molecular weight hydrocarbons, such as middle distillates and even lighter C4- products, whereas hydroisomerization generally provides higher yields by minimizing cracking.
U.S. Patent No. 7,384,538 discloses hydroisomerization of waxy feed for base oil production in an isomerization zone comprising a catalyst bed having at least two isomerization catalysts, wherein a first catalyst has a channel diameter of at least 6.2 A, and a second catalyst has a channel diameter not more than 5.8 A. U.S. Patent Application
Publication No. 2008/0083657 discloses dewaxing a hydrocarbon feed with a metal-modified small crystallite MTT framework molecular sieve. U.S. Patent Application Publication No. 2009/0166252 discloses lube basestock production using two isomerization catalysts, wherein a first catalyst has a Constraint Index (CI) of not more than 2, and a second catalyst has a CI greater than 2.
Apart from product yield, another important factor in the catalytic production of base oil is the minimization of catalyst aging. In this regard, U.S. Patent No. 5,951,848 discloses the use of a two catalyst system comprising a hydrotreating catalyst and a dewaxing catalyst. The aging of the dewaxing catalyst may be slowed by the presence of the hydrotreating catalyst layer.
U.S. Patent Nos. 6,468,417 and 6,468,418 disclose the production of lube oil having a reduced tendency to form a haze by a process including contacting a dewaxed lube stock or base oil feed with a solid sorbent to produce a dehazed base oil having a reduced cloud point relative to that of the dewaxed lube stock or base oil feed.
There is a continuing need for improved dewaxing processes and catalyst systems showing increased isomerization selectivity and conversion of waxy hydrocarbon feedstocks for the production of valuable Group II and Group III base oils.
SUMMARY OF THE INVENTION
This invention relates to processes for efficiently converting wax-containing hydrocarbon feedstocks into high-grade products, including lubricant base oils having a low pour point, a low cloud point, a low pour-cloud spread, and a high viscosity index (VI). Such processes employ a layered catalyst system comprising a plurality of hydroisomerization dewaxing catalysts. Hydroisomerization converts aliphatic, unbranched paraffinic hydrocarbons (n-paraffins) to isoparaffms and cyclic species, thereby decreasing the pour point and cloud point of the base oil product as compared with the feedstock. In an embodiment, a layered catalyst system of the present invention may further comprise a hydrotreating catalyst as a guard layer, whereby "aging" of the hydroisomerization catalysts is decelerated, and base oil product yield can be maintained for longer periods of time, as compared with conventional processes, at a temperature in the range from about 450°F to about 725°F (232°C to 385°C).
According to one aspect of the present invention there is provided a process for catalytically dewaxing a waxy hydrocarbon feedstock comprising contacting the hydrocarbon feedstock in a first hydroisomerization zone under first hydroisomerization dewaxing conditions with a first hydroisomerization catalyst to provide a first isomerization stream, and contacting at least a portion of the first isomerization stream in a second hydroisomerization zone under second hydroisomerization dewaxing conditions with a second hydroisomerization catalyst to provide a second isomerization stream. Each of the first and second hydroisomerization catalysts may comprise a molecular sieve and a Group VIII metal. The molecular sieve of at least one of the first hydroisomerization catalyst and the second hydroisomerization catalyst may comprise zeolite SSZ-32x having, after calcination, an X-ray diffraction pattern substantially as in Table 1, infra.
In an embodiment, the present invention provides a process for catalytically dewaxing a waxy hydrocarbon feedstock comprising contacting the hydrocarbon feedstock in a first hydroisomerization zone under first hydroisomerization dewaxing conditions with a first hydroisomerization catalyst to provide a first isomerization stream, and contacting at least a portion of the first isomerization stream in a second hydroisomerization zone under second hydroisomerization dewaxing conditions with a second hydroisomerization catalyst to provide a second isomerization stream. Each of the first hydroisomerization catalyst and the second hydroisomerization catalyst may comprise a 1-D, 10-ring zeolite and a Group VIII metal. At least one of the first hydroisomerization catalyst and the second hydroisomerization catalyst may be doped with a metal modifier selected from the group consisting of Mg, Ca, Sr, Ba, K, La, Pr, Nd, Cr, and combinations thereof. The first and second hydroisomerization catalysts may be disposed in the same reactor. The zeolite of the first hydroisomerization catalyst may comprise SSZ-32x having, after calcination, an X-ray diffraction pattern substantially as in Table 1, infra.
In another embodiment, the present invention provides a layered catalyst system comprising a first hydroisomerization zone comprising a first hydroisomerization catalyst, and a second hydroisomerization zone comprising a second hydroisomerization catalyst. Each of the first and second hydroisomerization catalysts may comprise a molecular sieve and a Group VIII metal. The molecular sieve of at least one of the first hydroisomerization catalyst and the second hydroisomerization catalyst may be doped with a metal modifier selected from the group consisting of Mg, Ca, Sr, Ba, K, La, Pr, Nd, Cr, and combinations thereof. The molecular sieve of at least one of the first hydroisomerization catalyst and the second hydroisomerization catalyst may comprises zeolite SSZ-32x having, after calcination, an X-ray diffraction pattern substantially as in Table 1, infra.
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