Mineral oils: processes and products – Paraffin wax; treatment or recovery – Chemical treatment
Reexamination Certificate
2001-04-26
2003-11-25
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Paraffin wax; treatment or recovery
Chemical treatment
C208S111010, C208S111350, C585S734000, C585S736000, C585S739000
Reexamination Certificate
active
06652735
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates to the hydroisomerization and dewaxing of hydrocarbon streams. In particular, the present invention relates to a catalyst combination that provides a high distillate yield with improved fluidity, viz., a reduced pour point and cloud point.
Most lubricating oil feedstocks must be dewaxed in order to manufacture finished products which will remain fluid down to the lowest temperature of use. Dewaxing is the process of separating or converting hydrocarbons which solidify readily (e.g., waxes) in petroleum fractions. Processes for dewaxing petroleum distillates have been known for a long time. As used herein, dewaxing means a reduction in at least some of the normal paraffin content of the feed. The reduction may be accomplished by isomerization of n-paraffins and/or cracking, or hydrocracking.
Dewaxing is required when highly paraffinic oils are to be used in products which need to flow at low temperatures, i.e., lubricating oils, heating oil, diesel fuel, and jet fuel. These oils contain high molecular weight straight chain and slightly branched paraffins which cause the oils to have high pour points and cloud points and, for jet fuels, high freeze points. In order to obtain adequately low pour points, these waxes must be wholly or partly removed or converted. In the past, various solvent removal techniques were used, such as MEK (methyl ethyl ketone-toluene solvent) dewaxing, which utilizes solvent dilution, followed by chilling to crystallize the wax, and filtration.
The decrease in demand for petroleum waxes as such, together with the increased demand for gasoline and distillate fuels, has made it desirable to find processes which not only remove the waxy components but which also convert these components into other materials of higher value. Catalytic dewaxing processes achieve this end by either of two methods or a combination thereof. The first method requires the selective cracking of the longer chain n-paraffins, to produce lower molecular weight products which may be removed by distillation. Processes of this kind are described, for example, in
The Oil and Gas Journal
, Jan. 6, 1975, pages 69 to 73 and U.S. Pat. No. 3,668,113. The second method requires the isomerization of straight chain paraffins and substantially straight chain paraffins to more branched species. Processes of this kind are described in U.S. Pat. No. 4,419,220 and U.S. Pat. No. 4,501,926.
To date, there have been a number of methods developed for dewaxing hydrocarbon feeds. Many dewaxing processes that are presently being used reduce the pour and cloud point of a hydrocarbon stream to acceptable levels at the price of producing more than a desirable amount of naphtha and light gas. An ideal economic fuel dewaxing process would reduce the pour point of the feed to acceptable levels while maximizing the yields of diesel fuel and heating oil and minimizing the yields of naphtha and light gas. Previous dewaxing processes have utilized zeolite hydrodewaxing catalysts including ZSM-5, ZSM-11, ZSM-12, ZSM-20, ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-38, ZSM-48, ZSM-50, mordenite, SAPO-11, and zeolite beta.
In order to obtain the desired selectivity, many previously known processes have used a zeolite catalyst having a pore size which admits the straight chain n-paraffins, either alone or with only slightly branched chain paraffins, but which excludes more highly branched materials, cycloaliphatics and aromatics. Zeolites such as ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35 and ZSM-38 have been proposed for this purpose in dewaxing processes and their use is described in U.S. Pat. Nos. 3,894,938; 4,176,050; 4,181,598; 4,222,855; 4,229,282; and 4,247,388. A dewaxing process employing synthetic offretite is described in U.S. Pat. No. 4,259,174. A hydrocracking process employing zeolite beta as the acidic component is described in U.S. Pat. No. 3,923,641.
Isomerization Dewaxing (“IDW”) technology is currently employed to lower the pour and cloud points of distillate fuel oils and gas oils to acceptable levels while minimizing the amount of naphtha and light gas. This goal is obtained through a series of mechanisms. The ideal end result is that the zeolite catalyst selectively isomerizes paraffins in the presence of aromatics. However, zeolite-based IDW also involves some conversion reactions, thereby resulting in significant yields of naphtha and C
4
-gases.
An improved dewaxing process is disclosed in U.S. Pat. No. 4,419,220 to La Pierre et al., the entire contents of which is incorporated herein by reference. This patent discloses that hydrocarbons such as distillate fuel oils and gas oils may be dewaxed primarily by isomerization of the waxy components over a zeolite beta catalyst. The process may be carried out in the presence or absence of added hydrogen, although operation with hydrogen is preferred. This process can be used for a variety of feedstocks including light gas oils, both raw and hydrotreated, vacuum gas oils and distillate fuel oils obtained by fluid catalytic cracking (FCC).
Although catalytic dewaxing (whether shape selective dewaxing or isomerization dewaxing) is an effective process, it has some limitations. A catalytic dewaxing process removes wax, but it does not change the end point of the product to a great extent. The problem is most severe when using a shape selective zeolite catalyst, such as ZSM-5, which selectively cracks the normal and slightly branched chain paraffins, but leaves most other components untouched. Thus, the feeds to most shape selective catalytic dewaxing processes are selected based on the desired product because the end point of the product usually sets the end point of the feed. This limits the available feedstocks, since these dewaxing processes can be used to dewax heavier feedstocks, but the heavier feedstocks cannot produce light products.
U.S. Pat. No. 4,446,007 to Smith, which is incorporated herein by reference, discloses a process for producing a relatively high octane gasoline by-product from the cracking of normal paraffins by increasing the hydrodewaxing temperature to at least 360° C. within about seven days of start-up. This approach improves the economics of the dewaxing process by making the light by-products (the gasoline fraction) more valuable, but does not address the end-point problem. As a consequence, Smith does not take full advantage of the ability of the process to tolerate heavier feeds.
Other dewaxing processes reduce the pour point and cloud point of waxy feeds through the use of catalysts which isomerize paraffins in the presence of aromatics. These processes typically operate at relatively high temperatures and pressures, which results in extensive cracking and thereby degrades useful products to less valuable light gasses.
In light of the disadvantages of the conventional processes for improving distillate yield, there is a need for a new process that provides a high distillate yield with a reduced pour point and cloud point.
SUMMARY OF THE INVENTION
The present invention is a process for the isomerization dewaxing of a hydrocarbon feed. The process includes contacting the hydrocarbon feed with a catalyst containing a large pore crystalline molecular sieve having a Constraint Index of less than 2, an alpha value of less than 100 and an ultimate crystal size of less than 1 micron and a catalyst containing an intermediate pore crystalline molecular sieve having a Constraint Index greater than 2, an alpha value less than 100, an ultimate crystal size of less than 1 micron and an unidimensional or a non-intersecting two dimensional pore structure; under hydroprocessing conditions to produce a dewaxed product having improved fluidity. It is preferred that the process be carried out at superatmospheric hydrogen partial pressure.
The hydrocarbon feed preferably contains waxy components having a cloud point greater than about 0° C., an ASTM D2887 end boiling point exceeding 275° C., and a pour point greater than 5° C. Preferably, the pour point of the feedstock is reduced by at least 5° C.
The la
Angevine Philip J.
Degnan Thomas F.
ExxonMobil Research and Engineering Company
Griffin Walter D.
Keen Malcolm D.
Kliebert Jeremy J.
LandOfFree
Process for isomerization dewaxing of hydrocarbon streams does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for isomerization dewaxing of hydrocarbon streams, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for isomerization dewaxing of hydrocarbon streams will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3118991