Patent Grant
7776207
Not applicable.
The invention relates to a process for the production of middle distillates from synthetic naphtha.
Iso-paraffinic synthetic fuels (or “synfuels” for short) generally lack one or more desirable fuel attributes. For gasoline, this includes low octane values. In the case of jet fuel, these include lower density and lack of seal-swelling properties. Lack of seal-swelling properties means that a fuel tank equipped with nitrile rubber closure gasket used for conventional petroleum fuels (“petro-fuels”) will leak if filled with an iso-paraffinic synfuel. These differences with petro-fuels can limit use of iso-paraffinic synfuels. One solution has been to blend these synfuels with petro-fuels. However, blending with petro-fuels generally downgrades the synfuel's low emission qualities. Particulate emissions are attributed to naphthalene-type molecules in crude oil.
Since aromatic hydrocarbons have higher density and can impart seal swelling properties, alkyl benzenes of jet fuel boiling range may be used as blend stocks for corresponding iso-paraffinic synfuels to solve the seal-swell and density issues without affecting their desirable low particulate emission qualities. In the case of gasoline, the alkyl-benzenes are known to increase synfuel octane value.
Synthesis of alkyl aromatics via olefins and benzene has industrially important applications, such as manufacture of cumene and detergent-range linear alkyl benzenes. Alkyl benzenes having alkyl groups with from about 4 to about 9 carbon atoms may also be used as chemical intermediates or as fuel blend stocks.
Traditional processes for manufacturing alkyl aromatic components employ different catalysts and reactors for the benzene and olefin components used to make the alkyl benzene products. For example catalytic reforming may be used to convert paraffinic feedstock to benzene by dehydrocyclization. Olefin production is typically achieved by dehydrogenation of the paraffins. Thus, the combination of two processes to make these components is capital-intensive.
Consequently, a simpler process for the preparation of alkyl benzenes and synthetic fuels would be useful.
A process for producing one or more middle distillate fuels is described. An embodiment of the described process includes (a) dehydrogenating/aromatizing a paraffinic naphtha stream into a composition containing olefins and aromatic hydrocarbons (b) subjecting the olefins and aromatic components to aromatic alkylation, and (c) separating the alkyl aromatics of middle distillate range.
In some embodiments the synthetic naphtha is a product of the Fischer-Tropsch process. Selected Fischer-Tropsch processes employ synthesis gas derived from coal, petroleum coke, natural gas, petroleum residue and biomass. In other embodiments, the synthetic naphtha may be the co-product of hydroprocessing glycerides (mono-, di-, and tri-), and fatty acids present in vegetable oils, animal fats, and restaurant greases.
Embodiments of the invention also include products produced by one or more of the methods described herein, particularly wherein the products include chemical intermediates, gasoline, kerosene, jet fuel and diesel fuel. Products further comprising petroleum- or bio-based fuels in any desirable amount are also contemplated.
The terms “middle distillate product(s)” and “middle distillate” refer to hydrocarbon mixtures with a boiling point range that corresponds substantially with that of kerosene and gas oil fractions obtained in a conventional atmospheric distillation of crude oil material. The middle distillate boiling point range may include temperatures between about 150° C. and about 600° C., with a fraction boiling point between about 200° C. and about 360° C.
The term “middle distillate fuel” means jet fuel, kerosene, diesel fuel, gasoline, and combinations thereof.
The term “BTX” means Benzene, Toluene, Xylene, or a mixture of any of Benzene, Toluene, and Xylene.
The term “Cx”, where x is a number greater than zero, refers to a hydrocarbon compound having predominantly a carbon number of x. As used herein, the term Cx may be modified by reference to a particular species of hydrocarbons, such as, for example, C5 olefins. In such instance, the term means an olefin stream comprised predominantly of pentenes but which may have impurity amounts, i.e. less than about 10%, of olefins having other carbon numbers such as hexene, heptene, propene, or butene.
The term “light fraction” generally indicates a hydrocarbon comprised primarily of C2 to C24 hydrocarbons; preferably C2-C9 in some cases.
The term “heavy fraction” generally indicates a hydrocarbon comprised primarily of hydrocarbons having a carbon number greater than about C24, but in some cases the heavy fraction contains C1+fractions.
Naphtha fractions described herein generally have a boiling range of 30 to 250 degrees F. and contains alkanes in the C5 to C9 range.
LPG fractions generally refer to hydrocarbons having from 2 to 5 carbon atoms, but in most cases 3 and 4.
It has surprisingly been found that using certain noble metal catalyst systems naphtha range paraffins that do not cyclize to an aromatic will dehydrogenate to form olefins which will react in the alkylation step to form alkylated aromatics in the middle distillate boiling range. In particular, commercially available tin/platinum-on-alumina catalysts convert n-hexane to benzene and convert C7 paraffins to linear internal olefins with high selectivity. Thus, the conversion of naptha-range n-paraffin feed to a composition suitable for aromatic alkylation.
One such process is schematically represented in
When the paraffinic naphtha is the byproduct of a middle distillate synfuel process, this method can be employed to maximize C10+ product yield and modify the product properties such as density and seal swell.
Commercial Sn/Pt-on-alumina dehydrogenation catalyst from Englehard Corporation comprising 0.65-0.85 wt. percent Sn, 0.40-0.58 wt. percent Li, 0.30-0.45 wt. percent Pt is used. The catalyst has a particle size of 1.58-2.54 mm and a surface area of 140-180 m2/g according to BET-N2 surface area measurements. Tube-in-tube glassware is used in a reactor with about 0.1 g of catalyst in the inside tube. Slits in the bottom tube allow for bottom-up feed flow. The reactor is placed in a furnace and heated to about 450° C. under a flow of hydrogen suitable for catalyst activation. After 30 minutes of activation, hydrocarbon recirculation is started. Results from n-hexane, n-heptane, and n-octane are presented in Tables I-III respectively.
Variations, modifications and additions to this invention will be readily apparent to one skilled in the art and such modifications and additions would be fully within the scope of the invention, which is not limited by the claims.
This Application claims priority to U.S. Provisional Application No. 60/828,373, filed on Oct. 5, 2006.
Research for the development of the present invention was partially funded by the U.S. Department of Defense-contract no. W56HZV05-6-0435.
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| Number | Date | Country | |
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| Number | Date | Country | |
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| 60828373 | Oct 2006 | US |
