Stable, moderately unsaturated distillate fuel blend stocks prepared by low pressure hydroprocessing of Fischer-Tropsch products

Abstract

The invention relates to a distillate fuel comprising a stable, low sulfur, highly paraffinic, moderately unsaturated distillate fuel blend stock. The highly paraffinic, moderately unsaturated distillate fuel blend stock exhibits excellent combustion properties in diesel and jet engines as a result of the high paraffin content. The blend stock is preferably prepared from a Fischer-Tropsch derived product that is hydroprocessed under conditions during which a moderate amount of unsaturates are formed or retained.

Description

RELATED APPLICATIONS [0001] The present application is a continuation-in-part of U.S. application Ser. No. 09 / 999,667, “Distillate Fuel Blends from Fischer Tropsch Products with Improved Seal Swell Properties,” filed Oct. 19, 2001, the contents of which are hereby incorporated by reference. The present application is also related to U.S. patent application Ser. No. ______(Docket No. 005950-779) entitled “Highly Paraffinic, Moderately Aromatic Distillate Fuel Blend Stocks Prepared by Low Pressure Hydroprocessing of Fischer Tropsch Products,” filed herewith.FIELD OF THE INVENTION [0002] The invention is directed to a low sulfur distillate fuels comprising a Fischer-Tropsch distillate fuel blend stock, which have excellent stability and moderate content of unsaturates. BACKGROUND OF THE INVENTION [0003] Distillate fuel derived from the Fischer-Tropsch process is highly paraffinic and has excellent burning properties and very low sulfur. This makes Fischer-Tropsch products ideally suite...

AI Technical Summary

Benefits of technology

[0015] In another embodiment, the present invention relates to a Fischer-Tropsch diesel fuel blend stock. The Fischer Tropsch diesel fuel blend stock comprises unsaturates in an amount between 2 and 20 weight %, paraffins in an amount 90 weight % or greater, sulfur in an amount less than 1 ppm and peroxide precursors in an amount such that less than 5 ppm peroxides are formed after storage at 60° C. for four weeks. The unsaturates comprise less than 20 weight % polynuclear aromatics, preferably less than 10 weight % polynuclear aromatics, and even more preferably less than 5 weight % polynuclear aromatics. Preferably the unsaturates comprise both olefins and aromatics, and most preferably the olefins are present in amounts greater than or equal to 1 wt %. Characteristics of the diesel fuel blend stock include a cetane index greater than 60, a percent reflectance according to ASTM D6468 at 150° C. in excess of 65% when measured at 90 minutes.

[0016] In yet another embodiment, the present invention relates to a Fischer-Tropsch jet fuel blend stock. The Fischer Tropsch jet fuel blend stock comprises unsaturates in an amount between 2 and 10 weight %, paraffins in an amount 90 weight % or greater, sulfur in an amount less than 1 ppm, and peroxide precursors in an amount such that less than 5 ppm peroxides are formed after storage at 60° C. for four weeks. The unsaturates comprise less than 20 weight % polynuclear aromatics, preferably less than 5 weight % polynuclear aromatics, and even more preferably less than 5 weight % polynuclear aromatics. Characteristics of the jet fuel blend stock include a smoke point of 30 mm or greater, and a passing rating in ASTM D3241 (JFTOT Procedure) at 260° C. for 2.5 hours.

[0017] In a further embodiment, the present invention relates to a process for preparing a highly paraffinic, moderately unsaturated distillate fuel blend stock. The process comprises converting syngas to a Fischer Tropsch derived feedstock by a Fischer Tropsch process and hydroprocessing the Fischer-Tropsch derived feedstock. A highly paraffinic, moderately unsaturated distillate fuel blend stock is recovered. The highly paraffinic, moderately unsaturated distillate fuel blend stock contains between 2 and 20 weight % unsaturates less than 1 ppm sulfur, and peroxide precursors in an amount such that less than 5 ppm peroxides are formed after storage at 60° C. for four weeks. The hydroprocessing conditions include a temperature of 600-750° F., a pressure of less than 1000 psig, and a liquid hourly space velocity of greater than 0.25 hr−1.

[0018] In yet a further embodiment the present invention relates to

Problems solved by technology

However, conventional hydrotreating and hydrocracking processes require the use of expensive hydrogen to saturate olefins and convert oxygenates into paraffins.

While they are highly paraffinic, Fischer-Tropsch products also contain olefins, alcohols, and traces of other compounds that can cause problems with stability.

However, hydroprocessing requires the use of expensive hydrogen gas and expensive facilities designed to operate at high pressure.

As described by Vardi et al, fuels can become unstable with respect to peroxide formation when their sulfur content is reduced to low levels by hydroprocessing.

However, since sulfur compounds increase sulfur emissions, this approach is not desirable.

The patent shows that Fischer Tropsch products having a peroxide number of 24.06 after 4 weeks have unacceptable stability.

However, this solution requires the use of expensive hydrogen gas.

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