Chemistry of hydrocarbon compounds – Saturated compound synthesis – By isomerization
Reexamination Certificate
2001-01-22
2004-04-20
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Saturated compound synthesis
By isomerization
C585S740000, C585S750000, C585S751000, C208S027000, C208S950000
Reexamination Certificate
active
06723889
ABSTRACT:
This application is related to two other applications filed concurrently with this application. Those applications are “A Diesel Fuel Having A Very High Iso-Paraffin To Normal Paraffin Mole Ratio” (by Stephen Miller, Arthur Dahlberg, Kamala Krishna, and Russell Krug) and “A Diesel Fuel With Reduced Potential For Causing Epidermal Hyperplasia” (by Stephen Miller, Arthur Dahlberg, Kamala Krishna, and Russell Krug and Russell White).
The present invention relates to a process for producing a highly paraffinic (at least 70% C
10+
paraffins) diesel fuel having a high iso-paraffin to normal paraffin mole ratio.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,594,468 teaches that it is desirable to have a low iso
ormal ratio of paraffins in gas oils made from Fischer Tropsch catalysts. The examples show normal/iso ratios of from 2.7:1 to 7.5:1 (iso
ormal ratios of from 0.13:1 to 0.37:1) in conventional processes and from 9.2 to 10.5:1 (iso
ormal ratios of from 0.095:1 to 0.11:1) for examples of its invention.
U.S. Pat. No. 5,135,638 discloses isomerizing a waxy feed over a catalyst comprising a molecular sieve having generally oval 1-D pores having a minor axis between 4.2 Å and 4.8 Å and a major axis between 5.4 Å and 7.0 Å, with at least one group VIII metal. SAPO-11, SAPO-31, SAPO-41, ZSM-22, ZSM-23 and ZSM-35 are disclosed as examples of useful catalysts.
U.S. Pat. No. 5,689,031 teaches a clean distillate useful as a diesel fuel, produced from Fischer-Tropsch wax. The isoparaffin
ormal paraffin ratio is given as being from 0.3:1 to 3.0:1, preferably from 0.7:1 to 2.0:1.
U.S. Pat. No. 5,866,748 teaches a solvent (not a diesel fuel) produced by hydroisomerization of a predominantly C
8
-C
20
n-paraffinic feed. The isoparaffin
ormal paraffin ratio is given as being from 0.5:1 to 9.0:1, preferably from 1:1 to 4:1.
Two papers, “Studies on Wax Isomerization for Lubes and Fuels”
Zeolites and Related Microporous Materials: State of the Art
1994 Studies in Surface Science and Catalysis, Vol. 84, Page 2319 (1994), and “New molecular sieve process for lube dewaxing by wax isomerization” Microporous Materials 2 (1994) 439-449, disclose dewaxing by a catalytic (Pt-SAPO-11) wax isomerization process. These papers disclose isomerization selectivity for n-hexadecane of from 93% to 84% at 89% to 96% conversion, respectively, for iso
ormal ratios of from 7.4:1 to 20.7:1. A third paper, “Wax Isomerization for Improved Lube Oil Quality,” Proceedings, First International Conference of Refinery Processing, AlChE Natl. Mtg, New Orleans, 1998 discloses isomerization selectivity for n-C
24
lube oil of from 94% to 80% at 95% to 99.5% conversion, respectively, for iso
ormal ratios of from 17.8:1 to 159:1.
SUMMARY OF THE INVENTION
The present invention provides a highly paraffinic (at least 70% C
10+
paraffins) diesel fuel having a very high iso-paraffin to normal paraffin mole ratio. The diesel fuel must have an iso-paraffin to normal paraffin mole ratio of at least 5:1, preferably at least 13:1, more preferably at least 21:1, most preferably at least about 30:1
Preferably the diesel fuel has a total paraffin content of at least 90%. The term “total paraffin content” refers to the percentage of the diesel fuel that is any type of paraffin (iso-paraffin or normal paraffin). Preferably, the diesel fuel is derived from a Fischer-Tropsch catalytic process.
The diesel fuel can be produced by contacting a highly paraffinic feed in an isomerization/cracking reaction zone with a catalyst comprising at least one Group VIII metal and a molecular sieve having generally oval 1-D pores having a minor axis between 3.9 Å and 4.8 Å and a major axis between 5.4 Å and 7.0 Å. The molecular sieve can be selected from the group consisting of SAPO-11, SAPO-31, SAPO-41, ZSM-22, ZSM-23, ZSM-35, and mixtures thereof. More preferably, it is selected from the group consisting of SAPO-11, SAPO-31, SAPO41, and mixtures thereof. Most preferably, it is SAPO-11. Preferably, the Group VIII metal is selected from the group consisting of platinum, palladium, and mixtures thereof. More preferably, it is platinum.
At least 40% of the paraffinic feed are C
10+
normal paraffins and at least 20% of the feed are C
26+
paraffins. Preferably at least 40% of the feed are C
26+
paraffins.
Preferably, the process is carried out at a temperature of from 200° C. to 475° C., a pressure of from 15 psig to 3000 psig, and a liquid hourly space velocity of from 0.1 hr
−1
to 20 hr
−1
. More preferably, it is carried out at a temperature of from 250° C. to 450° C., a pressure of from 50 to 1000 psig, and a liquid hourly space velocity of from 0.1 hr
−1
to 5 hr
−1
. Most preferably, it is carried out at a temperature of from 340° C. to 420° C., a pressure of from 100 psig to 600 psig, and a liquid hourly space velocity of from 0.1 hr
−1
to 1.0 hr
−1
. These process conditions are sufficient to both isomerize the C
10
to C
20
paraffins and crack the higher paraffins.
Preferably, the process is carried out in the presence of hydrogen. Preferably, the ratio of hydrogen to feed is from 500 to 30,000 standard cubic feet per barrel, more preferably from 1,000 to 10,000 standard cubic feet per barrel.
The feed has at least 40% C
10+
normal paraffins, preferably at least 50% C
10+
normal paraffins, more preferably at least 70% C
10+
normal paraffins. Preferably, the feed is derived from a Fischer-Tropsch catalytic process.
DETAILED DESCRIPTION OF THE INVENTION
In its broadest aspect, the present invention involves a highly paraffinic (at least 70% C
10+
paraffins) diesel fuel having a very high iso-paraffin to normal paraffin mole ratio (at least 5:1). In one embodiment, the diesel fuel has an iso-paraffin to normal paraffin mole ratio of at least 21:1, preferably at least about 30:1.
One possible benefit of such a diesel fuel is reduced toxicity. Other benefits of such a diesel fuel could include improved cold filter plugging performance, when distillation end point is kept the same. The necessity to meet cold filter plugging specification limits distillation end point and, therefore limits yield, which in turn limits project economics. Where distillation end point is increased (such as to the cold filter plugging limit) other possible improvements include cetane number, lubricity, and energy density.
Definitions
As used herein the following terms have the following meanings unless expressly stated to the contrary:
The term “total paraffin content” refers to the percentage of the diesel fuel that is either iso-paraffin or normal paraffin.
The term “diesel fuel” refers to hydrocarbons having boiling points in the range of from 350° to 700° F. (177° to 371° C.).
The term “C
10+
paraffins” refers to paraffins having at least ten carbon atoms per molecule, as determined by having a boiling point of at least 350° F. (177° C.).
The term “C
26+
paraffins” refers to paraffins having at least twenty six carbon atoms per molecule, as determined by having a boiling point of at least 775° F. (413° C.).
Unless otherwise specified, all percentages are in weight percent.
The Highly Paraffinic Feed
The feed is highly paraffinic, having at least 40% C
10+
normal paraffins and at least 20% C
26+
paraffins. Preferably, the feed has at least 40% C
26+
paraffins. Preferably, the feed has at least 50% C
10+
normal paraffins, more preferably at least 70% C
10+
normal paraffins.
Preferably, the feed is derived from a Fischer-Tropsch catalytic process. Fischer-Tropsch conditions are well known to those skilled in the art. Preferably, the temperature is in the range of from 150° C. to 350° C., especially 180° C. to 240° C., and the pressure is in the range of from 100 to 10,000 kPa, especially 1000 to 5000 kPa. Any suitable Fischer-Tropsch catalyst maybe used, for example one based on cobalt or iron, and, if the catalyst comprises cobalt or iron on a support, very many different supports may be used, for
Dahlberg Arthur John
Krishna Kamala R.
Krug Russell R.
Miller Stephen J.
Burns Doane Swecker & Mathis L.L.P.
Chevron U.S.A. Inc.
Griffin Walter D.
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