Mineral oils: processes and products – Chemical conversion of hydrocarbons – Reforming
Reexamination Certificate
1998-12-30
2001-04-03
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Reforming
C208S134000, C208S135000, C208S137000, C208S111010, C208S111350, C208S015000, C208S016000, C208S143000, C208S144000, C208S145000, C585S266000, C585S269000
Reexamination Certificate
active
06210563
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a hydrocracking process. More particularly, the invention relates to a hydrocracking process which yields diesel fuels with increased cetane levels.
Due to upcoming global environmental and governmental mandates, petroleum refiners are seeking the most cost-effective means of improving the quality of their diesel fuel products. The new European Union (EU) diesel cetane number specification of 58 in the year 2005 will require existing processes to be upgraded or the development of new processes.
Aromatic saturation has been commonly utilized to upgrade the cetane level of diesel fuels. However, even with complete aromatic saturation, the cetane level of diesel fuels is only marginally improved; especially those fuels derived from thermal cracking processes such as light cycle oil and coker gas oil. This limited improvement in cetane levels is due to the fact that aromatic saturation can only make low cetane naphthenic species, not the high cetane components such as normal paraffins and iso-paraffins.
A process that increases diesel cetanes through selective ring-opening of naphthenic species, while avoiding cracking the beneficial diesel fuel range paraffins to naphtha and gaseous by-products is therefore desirable. Prior attempts to further increase product cetane levels through selective ring opening of the hydrogenated naphthenic intermediates have not been very successful for a number of reasons.
First, the conventional hydrocracking catalysts are not very selective and cannot be limited to opening naphthene rings, without concurrently cracking some of the paraffinic components. Thus, they frequently result in high diesel yield loss and high yield of gaseous by-product.
Secondly, commercial hydrocracking catalysts which rely on acidity as the active ring opening site will also catalyze increased branching of the resulting naphthenes and paraffins. This branching or isomerization results in cetane loss. Consequently, the more hydroisomerization a given catalyst exhibits, the more cetane loss the diesel products suffer. Typically, as a result of hydroisomerization activity, a cumulative loss of 18-20 cetane numbers is observed for each methyl branching increase.
Thirdly, regardless of the cracking mechanism, molecular weight reduction results in cetane loss when similar molecular structure types are preserved. Normally, a decrease of 3-4 cetane numbers per carbon loss is observed. Thus, endpoint cracking frequently results in cetane loss.
In light of the disadvantages of the conventional processes, there remains a need for a hydrocracking process that produces an increased cetane number without the corresponding diesel yield loss.
SUMMARY OF THE INVENTION
In accordance with the present invention, a hydrocracking process is provided which increases the cetane number in the diesel yield through the use of novel low acidic catalysts. The process minimizes diesel yield loss, the production of iso-paraffins, and gaseous by-product.
In the process, a feedstock is contacted under superatmospheric hydrogen conditions with a catalyst having a crystalline molecular sieve material component and a Group VIII noble metal component. The crystalline molecular sieve material component is a large pore faujasite structure having an alpha acidity of less than 1, preferably less than 0.3. Zeolite USY is the preferred crystalline molecular sieve material component.
The Group VIII noble metal component can be platinum, palladium, iridium, rhodium, or a combination thereof Platinum is preferred. The content of the Group VIII noble metal component can vary between about 0.01 and about 5% by weight of the catalyst.
The Group VIII noble metal component is located within the catalyst in dispersed clusters. In the preferred embodiment, the particle size of the Group VIII metal on the catalyst is less than about 10 Å. Dispersion of the metal can also be measured by hydrogen chemisorption technique in terms of the H/metal ratio. In the preferred embodiment, when platinum is used as the Group VIII noble metal component, the H/Pt ratio is between about 1I.1 and 1.5.
The hydrocracking conditions can be a pressure from about 400 to about 1000 psi H
2
, a temperature from about 550° F. to about 700° F., a space velocity of about 0.1 to about 10 LHSV, and a hydrogen circulation rate of about 1400 to about 5600 SCF/bbl. It is preferred that the catalyst utilized in the process of the invention be formed by self and/or silica binding.
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Angevine Philip J.
Huang Tracy J.
Tsao Ying-Yen P.
Griffin Walter D.
Hughes Gerard J.
Mobil Oil Corporation
Preisch Nadine
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