US20080155889A1

US20080155889A1 - Fischer-tropsch derived diesel fuel and process for making same

Info

Publication number: US20080155889A1
Application number: US11/950,175
Authority: US
Inventors: Dennis J. O'Rear
Original assignee: Chevron USA Inc
Current assignee: Chevron USA Inc
Priority date: 2006-12-04
Filing date: 2007-12-04
Publication date: 2008-07-03
Also published as: ZA200903686B; AU2007329380A1; JP2010522249A; WO2008070677A1; CN101679883A; GB2457190A; GB0909228D0

Abstract

The present invention is directed to a Fischer-Tropsch derived distillate suitable for use as a distillate fuel having a flash point 38° C. minimum measured by ASTM D 93 and a cloud point of +14° C. or less and further containing not less than 0.01 wt,% oxygen in each of 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol and not more than 0.01 wt.% oxygen in C₁₁₊linear alcohols. Preferably, the Fischer-Tropsch derived distillate will have a cloud point at or below 0° C., and more preferably the cloud point of the Fischer-Tropsch derived distillate, will be at or below −15° C.

Description

FIELD OF THE INVENTION

The invention relates to a Fischer-Tropsch diesel fuel, distillate fuel, or blend component, which also meets the specifications for diesel fuel but with a lighter density than conventional diesel fuel and a process for preparing the fuel.

BACKGROUND OF THE INVENTION

A distillate fuel refers to a fuel containing components boiling above the typical end point of gasoline (approximately 400° F. or 204° C.), but excludes non-distillable components (material boiling above 1100° F. or 593° C.). Distillate fuels can be burned in stationary engines, such as those used to generate electricity. A diesel fuel refers to a distillate which may be burned in a diesel engine to provide power for various human activities. The specifications for diesel fuel are more stringent than distillate fuels. For example in the United States, the end point specification for diesel fuels are 640° F. (338° C.) for No. 2-D and 550° F. (288° C.) for No. 1-D.
Various grades of diesel fuel have specifications which place limits on the cloud point. These frequently vary by geographical region and time of year. For example, ASTM D975-00 defines the specifications for No. 1-D and No. 2-D diesel fuels in the United States. It includes the statement in footnote j of Table 1, “Tenth percentile minimum air temperatures for U.S. locations are provided in Appendix X4 as a means of estimating expected regional temperatures. This guidance is general. Some equipment designs or operations may allow higher or require lower cloud point fuels.” The temperatures in Appendix X4 range from a low of −49° C. for the northern region of Alaska in January, to +14° C. for southern Florida in October. Likewise the World Wide Fuel Charter (2002) includes the statement that the cloud point “maximum must be equal to or lower than the lowest expected ambient temperature.” Thus acceptable diesel fuels should have cloud points at or below +14° C., for example, at or below 0° C., or at or below −15° C., or at or below −25° C., or at or below −49° C. Because their composition will be highly paraffinic, their densities may be below specifications. Where the specification density of conventional diesel fuel needs to be maintained, these compositions of the invention are best used as blend stocks.
The Fischer-Tropsch process provides a way to convert a variety of hydrocarbonaceous resources into products usually provided by petroleum. These include diesel fuel. In preparing hydrocarbons via the Fischer-Tropsch process, a hydrocarbonaceous resource, such as, for example, natural gas, coal, refinery fuel gas, tar sands, oil shale, municipal waste, agricultural waste, forestry waste, wood, shale oil, bitumen, crude oil, and fractions from crude oil, is first converted into synthesis gas which is a mixture comprising carbon monoxide and hydrogen.
Synthesis gas generation process is one that converts a hydrocarbonaceous asset into synthesis gas by use of a gaseous oxidant. The gaseous oxidant can be purified O₂, enriched air, air, steam, carbon dioxide and combinations. The process can either be above ground or in-situ. Examples of above ground synthesis gas generation processes that use gaseous hydrocarbons having carbons numbers less than 20 (for example methane) as feedstocks for the reactor are AutoThermal Reformer (ATR), Partial Oxidation (POX), Gas Heater Reformer (GHR), and steam reforming. When these feedstocks contain more than 2 mol % C₂and heavier hydrocarbons, a pre-converter (pre-reformer) is often used to convert the C₂+ hydrocarbons into methane. The pre-reformer uses a catalyst containing a Group VIII metal catalyst (for example Ni) with hydrogen at super-atmospheric pressures. An example of synthesis gas production is described in Kirk Othmer On-Line Edition “Fuels, Synthetic, Liquid Fuels” especially section 1, pages 2 to 14 online Edition incorporated herein by reference.
And in the same on-line reference “Methanol 4. Manufacture and Processing” at pages 299 to 311, incorporated herein by reference.
Synthesis gas can also be generated by reacting underground hydrocarbonaceous assets with a gaseous oxidant. An example of this in-situ process is described in
U.S. Pat. No. 6,698,515, issued Mar. 2, 2004 to Karanikas et al. Examples of underground hydrocarbonaceous assets are coal, oil shale, heavy oil, tar sands, petroleum deposits and bitumen. An example of a petroleum deposit suitable for in-situ conversion is a petroleum deposit from which the easily-extractable petroleum has been extracted by conventional methods such as pumping, steam flooding, and water flooding.
The synthesis gas, in turn, is converted into synthetic hydrocarbonaceous compounds that have a predominantly linear structure, primarily n-paraffins, 1-alcohols, 1-olefins, and traces of other species. These hydrocarbonaceous species may be refined into various products, including distillate fuels.
European Patent Nos. 0861311, 0885275; U.S. Pat. Nos. 5,689,031, 6,274,029, 6,296,757, 6,607,568, 6,822,131 describe the preparation of a Fischer-Tropsch derived product containing C₅-C₂₄primary linear alcohols and preferably primary linear alcohols C₁₂-C₂₄or C₁₂₊primary linear alcohols. Exactly what primary linear alcohols are supposed to encompass is unclear. However, these middle distillates have a density less than diesel fuel specification. The presence of alcohols are claimed to improve the lubricity of the middle distillate fuel. Unfortunately, the compositions taught in these documents employing the range of alcohols specified, particularly with C₁₁plus alcohols, would fail to meet the cloud point specifications for diesel fuel, and, consequently, they would not be suitable as commercial diesel fuel. The present invention comes from the realization that the alcohols must be C₁₀and lower and is particularly directed to Fischer-Tropsch derived diesel fuel compositions which are able to meet the cloud point, preferably, enhancing yields in the process.
Cloud point represents the temperature below which solid hydrocarbons may form in diesel fuels. Cloud point is determined by ASTM D 2500 which measures the fuel temperature at which solid hydrocarbon crystals formed on cooling.
As used in this disclosure the phrase “Fischer-Tropsch derived” refers to a hydrocarbon stream in which a substantial portion, except for added hydrogen, is derived from a Fischer-Tropsch process regardless of subsequent processing steps, and regardless of the methods of making the synthesis gas. The feed for the creation of the “Fischer Tropsch derived” refers to products derived from any carbon source, for example natural gas, coal, refinery fuel gas, tar sands, oil shale, municipal waste, agricultural waste, forestry waste, wood, shale oil, bitumen, crude oil, and fractions from crude oil.
As used in this disclosure the word “comprises” or “comprising” is intended as an open-ended transition meaning the inclusion of the named elements, but not necessarily excluding other unnamed elements. The phrase “consists essentially of” or “consisting essentially of” is intended to mean the exclusion of other elements of any essential significance to the composition. The phrase “consisting of” or “consists of” are intended as a transition meaning the exclusion of all but the recited elements with the exception of only minor traces of impurities.

SUMMARY OF THE INVENTION

The present invention is directed to a Fischer-Tropsch derived distillate suitable for use as a diesel fuel having a flash point of 38° C. minimum measured by ASTM D 93 and a cloud point of +14° C. or less and further containing not less than 0.01 wt. % oxygen in at least two 1-alcohols of 1-pentanol, 1-hexanol. 1-heptanol, 1-octanol, 1-nonanol, and 1-decanol and not more than 0.01 wt. % oxygen in C₁₁₊linear alcohols. Mixtures of all the C₅-C₁₀alcohols are within the scope of the invention. The upper wt. % oxygen limit of the alcohols is less than an amount which has the fuel failing the appropriate cloud point and/or other fuel specifications. Optionally two of the three alcohols can be used in a concentration not less than 0.03 wt. % oxygen for the two species, i.e., C₅and C₇or C₅and C₆or C₆and C₇. The Fischer-Tropsch derived distillate fuel will have a cloud point of +14° C. or less, for example, at or below 0° C., or at or below −15° C., or at or below −25° C., or at or below −49° C. All the wt. % oxygen amounts are on a water free basis. Where density forms part of the diesel fuel specification, Fischer-Tropsche diesels will contain supplements to reach the appropriate density specification.
It is useful to summarize the boiling points of various paraffins and alcohols:


	Boiling	Boiling	Melting	Melting
	Point of	Point of	Point of	Point of
	the n-	the 1-	the n-	the 1-
Carbon	Paraffin	Alcohol	Paraffin	Alcohol
Number	(° F., ° C.)	(° F., ° C.)	(° F., ° C.)	(° F., ° C.)

5	97, 36	281, 138	−201, −130	−110, −79
8	258, 125	381, 193	−71, −56	+2, −17
10	346, 174	441, 227	−23, −30	+45, +7
11	384, 195	469, 242	−14, −25	+61, +16
12	422, 216	495, 257	+14, −10	+79, +26
14	489, 254	545, 285	+42, +6	+103, 39

To achieve a flash point by ASTM D 93 of 38° C. requires that the boiling point be 250° F. (121° C.) or higher. Because of the different boiling points of the paraffins and alcohols, this corresponds to n-C₈and 1-pentanol. Likewise if C₁₁₊alcohols are to be excluded, by use of distillation, and they boil at or above 495° F. (257° C.), then this corresponds to paraffins boiling at above n-C₁₄eg, C₁₅₊products. The 640° F. (338° C.) end point of No. 2-D diesel fuel is met when the paraffins are less than or equal to C₂₀. Some branched paraffins up to C₂₄can be included. The 550° F. (288° C.) end point of No. 1-D diesel fuel is met when the paraffins are less than or equal to C₁₆, although some branched paraffins up to C₁₈can be included. When alcohols are added from a source other than the FT reation stream products, the cut point can be higher because the deleterious higher alcohols are not present.
The present invention is also directed to a process for preparing a Fischer-Tropsch derived distillate fuel preferably maximizing yield by permitting the C₁₅₊products to be upgraded and retaining the C₁₄₋products with alcohols in the lighter fraction. The process comprises (a) separating a Fischer-Tropsch condensate into a first and second fraction, wherein (i) said first fraction comprises not less than 0.01 wt. % oxygen from at least two of 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, and 1-decanol and not more than 0.01 wt. % oxygen in C₁₁₊linear alcohols and (ii) said second fraction comprises C₁₁₊linear alcohols; (b) removing the C₁₁₊linear alcohols from at least a portion of said heavy third fraction and recovering a treated heavy fraction substantially free of C₁₁₊linear alcohols; and (c) blending at least a portion of the first fraction of step a(i) and a portion of the treated heavy fraction of step (b) in the proper proportion to prepare a Fischer-Tropsch derived distillate fuel wherein the sum of the oxygenate content of the C₅-C₁₀alcohols present are within the range of from 0.01 wt. % oxygen and 1 wt. % oxygen, the cloud point is not more than +14° C. and the flash point of 38° C. minimum measured by ASTM D 93. This flash point can generally be met where 121° C. (250° F.) is the minimum 5% point measured by ASTM D 2887. In carrying out the process of the invention a third fraction may be separated from the Fischer-Tropsch condensate in step (a) which contains C₄₋linear alcohols.
The present invention resides in the discovery that the presence of more than 0.01 wt. % oxygen in C₁₁₊linear alcohols will significantly increase the cloud point of the composition rendering it unsuitable for use as a diesel fuel. Further processing the C₁₅₊fraction also can increase the yields since C₁₄₋paraffins are suitable for use in diesel fuel. As used in this disclosure, the term “C₄₋linear alcohols” refers to linear alcohols containing 4 or less carbon atoms in the molecule, such as methanol, ethanol. 1-butanol, and 1-propanol. The term “C₁₁₊linear alcohols” refers to linear alcohols having 11 or more carbon atoms in the molecule, such as 1-undecanol, 1-dodecanol. 1-tridecanol, 1-tetradecanol, 1-pentadecanol, 1-hexadecanol, etc. Linear C₅-C₁₀alcohols referred to in this disclosure are 1-pentanol, 1-hexanol. 1-heptanol, 1-octanol, 1-nonanol, and 1-decanol, and mixtures of these.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is based upon the discovery that the presence of as little as 0.01 wt. % oxygen in C₁₁₊linear alcohols in a Fischer-Tropsch derived distillate fuel will raise the cloud point to an unacceptable temperature. Surprisingly, the presence of C₅-C₁₀linear 1-alcohols, more specifically 1-pentanol, 1-hexanol, 1-heptanol. 1-octanol, 1-nonanol, and l-decanol in the same fuel has a negligible effect on cloud point. Minor other alcohols species and higher carbon number alcohols can be included so long as the diesel fuel cloud point specifications are met. This generally means other alcohol species would be present only as impurities. Additionally the problem to be solved was to reduce the cost of preparation of diesel fuel by reducing the severity of the hydrotreating operation which increases yield while meeting the cloud point requirements for diesel fuel.
In the process of the invention the Fischer-Tropsch product (condensate, wax or blends) is separated into at least two fractions, a first fraction comprising C₁₀and lower alcohols and a heavier fraction. Preferably the lighter fraction has not less than 0.01 wt. % oxygen of at least two of 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, and 1-decanol and not more than 0.01 wt. % oxygen in C₁₁₊linear alcohols and a second heavier fraction comprising C₁₁₊linear alcohols. A portion of the heavier second fraction which is intended to be blended back into the first fraction is treated to remove substantially all of the C₁₁₊linear alcohols present. Finally, the treated heavy second fraction is blended with at least a portion of the first fraction in a proportion calculated to yield a Fischer-Tropsch derived distillate fuel having a cloud point of not less than +14° C. In general, the sum of the oxygenate content of the C₅-C₁₀alcohols present the Fischer-Tropsch derived distillate fuel will fall within the range of from 0.01 wt. % oxygen and 1 wt. % oxygen. Combinations of any two alcohols, i.e. C₅and C₆or C₅and C₇or C₆and C₇can be present in an amount from 0.01 wt. % oxygen, preferably 0.03 wt. % oxygen up to 1.0 wt. % oxygen. The fuel preferably should also have a flash point 38° C. minimum measured by ASTM D 93. Unless blended with conventional petroleum feedstocks, the density will be less than the standards but still function effectively as a distillate and diesel fuel.
The products recovered from the Fischer-Tropsch operation (condensate, wax and blends) will contain varying amounts of oxygenates. The majority of the oxygenates present are in the form of alcohols; however, lesser amounts of ketones, aldehydes, carboxylic acids, and anhydrides may also be present. In order to prepare the heavy fraction which is substantially free of C₁₁₊linear alcohols, it is necessary to either remove the C₁₁₊linear alcohols or convert them into other hydrocarbons. There are a number of processes known to those skilled in the art which may be used to accomplish this step. These processes include, but are not necessarily limited to, hydrotreating, hydrocracking, hydroisomerization, dehydration, adsorption, absorption, or various combinations of these processes. As used in this disclosure, “substantially free of C₁₁₊linear alcohols” means that the distillate fraction contains C₁₁₊alcohols in an amount less than a concentration which increases the cloud point to values warmer than the diesel fuels specification.
Hydrocracking and hydrotreating are similar processes which differ primarily in the degree of severity. They may be referred to collectively in this disclosure as “hydroprocessing”. In the process of the present invention hydrocracking and hydrotreating are intended primarily for the purpose of removing alcohols that are present in the Fischer-Tropsch distillate. “Hydrotreating” refers to a catalytic process, usually carried out in the presence of free hydrogen, in which the primary purpose when used to process conventional petroleum derived feed stocks is the removal of various metal contaminants, such as arsenic; heteroatoms, such as sulfur and nitrogen; and aromatics from the feed stock. In the present process, the primary purpose is to remove the alcohols and secondarily to saturate the olefins present. Generally, in hydrotreating operations cracking of the hydrocarbon molecules, i.e., breaking the larger hydrocarbon molecules into smaller hydrocarbon molecules is minimized. For the purpose of this discussion the term hydrotreating refers to a hydroprocessing operation in which the conversion is 20% or less. Conversion can be defined on the basis of the increase in the amount of material in the product relative to the feed, boiling below the 5% point of the feed as measured by ASTM D 2887. “Hydrocracking” refers to a catalytic process, usually earned out in the presence of free hydrogen, in which the cracking of the larger hydrocarbon molecules is a primary purpose of the operation. In contrast to hydrotreating, the conversion rate for hydrocracking, for the purpose of this disclosure shall be more than 20%. In the present invention, hydrocracking is used to remove the alcohols and to hydrogenate the olefin.
Catalysts used in carrying out hydrotreating and hydrocracking operations are well known in the art. See for example U.S. Pat. Nos. 4,347,121 and 4,810,357, the contents of which are hereby incorporated by reference in their entirety, for general descriptions of hydrotreating, hydrocracking, and of typical catalysts used in each of the processes. Suitable catalysts include noble metals from Group VIIIA (according to the 1975 rules of the International Union of Pure and Applied Chemistry), such as platinum or palladium on an alumina or siliceous matrix, and unsulfided Group VIIIA and Group VIB, such as nickel-molybdenum or nickel-tin on an alumina or siliceous matrix. U.S. Pat. No. 3,852,207 describes a suitable noble metal catalyst and mild conditions. Other suitable catalysts are described, for example, in U.S. Pat. Nos. 4,157,294 and 3,904,513. The non-noble hydrogenation metals, such as nickel-molybdenum, are usually present in the final catalyst composition as oxides, or more preferably or possibly, as sulfides when such compounds are readily formed from the particular metal involved. Preferred non-noble metal catalyst compositions contain in excess of 5 wt. % oxygen, preferably 5 to 40 wt. % oxygen molybdenum and/or tungsten, and at least 0.5, and generally 1 to 15 wt. % oxygen of nickel and/or cobalt determined as the corresponding oxides. Catalysts containing noble metals, such as platinum, contain in excess of 0.01% metal, preferably between 0.1 and 1.0% metal. Combinations of noble metals may also be used, such as mixtures of platinum and palladium.
The hydrogenation components can be incorporated into the overall catalyst composition by any one of numerous procedures. The hydrogenation components can be added to matrix component by co-mulling, impregnation, or ion exchange and the Group VI components, i.e.; molybdenum and tungsten can be combined with the refractory oxide by impregnation, co-mulling or co-precipitation. Although these components can be combined with the catalyst matrix as the sulfides, that is generally not preferred, as the sulfur compounds can interfere with the Fischer-Tropsch catalysts.
The matrix component can be of many types including some that have acidic catalytic activity. Ones that have activity include amorphous silica-alumina or may be a zeolitic or non-zeolitic crystalline molecular sieve. Examples of suitable matrix molecular sieves include zeolite Y, zeolite X and the so called ultra stable zeolite Y and high structural silica:alumina ratio zeolite Y such as that described in U.S. Pat. Nos. 4,401,556; 4,820,402; and 5,059,567. Small crystal size zeolite Y, such as that described in U.S. Pat. No. 5,073,530 can also be used. Non-zeolitic molecular sieves which can be used include, for example, silicoaluminophosphates (SAPO), ferroaluminophosphate, titanium aluminophosphate and the various ELAPO molecular sieves described in U.S. Pat. No. 4,913,799 and the references cited therein. Details regarding the preparation of various non-zeolite molecular sieves can be found in U.S. Pat. Nos. 5,114,563 (SAPO) and 4,913,799 and the various references cited in U.S. Pat. No. 4,913,799. Mesoporous molecular sieves can also be used, for example the M41S family of materials as described in J. Am. Chem. Soc. 114:10834-10843(1992)), MCM-41; U.S. Pat. Nos. 5,246,689: 5,198,203; and 5,334,368; and MCM-48 (Kresge et al., Nature 359:710 (1992)). Suitable matrix materials may also include synthetic or natural substances as well as inorganic materials such as clay, silica and/or metal oxides such as silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-berylia, silica-titania as well as ternary compositions, such as silica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesia, and silica-magnesia zirconia. The latter may be either naturally occurring or in the form of gelatinous precipitates or gels including mixtures of silica and metal oxides. Naturally occurring clays which can be composited with the catalyst include those of the montmorillonite and kaolin families. These clays can be used in the raw state as originally mined or initially subjected to calumniation, acid treatment or chemical modification.
In performing the hydrocracking and/or hydrotreating operation, more than one catalyst type may be used in the reactor. The different catalyst types can be separated into layers or mixed.
Hydrocracking conditions have been well documented in the literature. In general, the overall LHSV is 0.1 hr-1 to 15.0 hr-1 (v/v), preferably from 0.25 hr-1 to 2.5 hr-1. The reaction pressure generally ranges from 500 psig to 3500 psig (10.4 MPa to 24.2 MPa, preferably from 1500 psig to 5000 psig (3.5 MPa to 34.5 MPa). Hydrogen consumption is typically from 500 to 2500 SCF per barrel of feed (89.1 to 445 m3 H2/m3 feed). Temperatures in the reactor will range from 400° F. to 950° F. (205° C. to 510° C.), preferably ranging from 650° F. to 850° F. (340° C. to 455° C.).
Typical hydrotreating conditions vary over a wide range. In general, the overall LHSV is 0.5 to 5.0. The total pressure ranging from 200 psig to 2000 psig. Hydrogen recirculation rates are typically greater than 50 SCF/Rbl, and are preferably between 1000 and 5000 SCF/Bbl. Temperatures in the reactor will range from 400° F. to 800° F. (205° C. to 425° C.).
“Hydroisomerization”, also called simply “isomerization”, is intended to improve the cold flow properties of the Fischer-Tropsch derived product by the selective addition of branching into the molecular structure. In the present invention, it may also be used to remove the alcohols. Isomerization ideally will achieve high conversion levels of the normal paraffins to iso-paraffins while at the same time minimizing the conversion by cracking. Isomerization operations suitable for use with the present invention typically uses a catalyst comprising an acidic component and may optionally contain an active metal component having hydrogenation activity. The acidic component of the catalysts preferably includes an intermediate pore SAPO, such as SAPO-11, SAPO-31, and SAPO-41, with SAPO-11 being particularly preferred. Intermediate pore zeolites, such as ZSM-22, ZSM-23, SSZ-32, ZSM-35, and ZSM-48, also may be used in carrying out the isomerization. Typical active metals include molybdenum, nickel, vanadium, cobalt, tungsten, zinc, platinum, and palladium. The metals platinum and palladium are especially preferred as the active metals, with platinum most commonly used.
The phrase “intermediate pore size”, when used herein, refers to an effective pore aperture in the range of from 4.0 to 7.1 Angstrom when the porous inorganic oxide is in the calcined form. Molecular sieves having pore apertures in this range tend to have unique molecular sieving characteristics. Unlike small pore zeolites such as erionite and chabazite, they will allow hydrocarbons having some branching into the molecular sieve void spaces. Unlike larger pore zeolites such as faujasites and mordenites, they are able to differentiate between n-alkanes and slightly branched alkenes, and larger alkanes having, for example, quaternary carbon atoms. See U.S. Pat. No. 5,413,695. The term “SAPO” refers to a silicoaluminophosphate molecular sieve such as described in U.S. Pat. Nos. 4,440,871 and 5,208.005.
In preparing those catalysts containing a non-zeolitic molecular sieve and having an hydrogenation component, it is usually preferred thai the metal be deposited on the catalyst using a non-aqueous method. Non-zeolitic molecular sieves include tetrahedrally-coordinated [AlO2 and PO2] oxide units which may optionally include silica. See U.S. Pat. No. 5,514,362. Catalysts containing non-zeolitic molecular sieves, particularly catalysts containing SAPO's, on which the metal has been deposited using a non-aqueous method have shown greater selectivity and activity than those catalysts which have used an aqueous method to deposit the active metal. The non-aqueous deposition of active metals on non-zeolitic molecular sieves is taught in U.S. Pat. No. 5,939,349. In general, the process involves dissolving a compound of the active metal in anon-aqueous, non-reactive solvent and depositing it on the molecular sieve by ion exchange or impregnation.
The dehydration of alcohols may be accomplished by processing the feedstock over a catalyst, such as gamma alumina. During dehydration the alcohols are converted into olefins. The dehydration of alcohols to olefins is discussed in Chapter 5, “Dehydration” in Catalytic Processes and Proven Catalysis by Charles L. Thomas, Academic Press, 1970. Another process is disclosed and completely incorporated herein by reference in U.S. Pat. No. 6,933,323.
Another method, also described in examples of U.S. Pat. No. 6,933,323, for removing the alcohols involves passing the condensate through an adsorption bed containing an adsorbent capable of adsorbing the alcohols. A satisfactory adsorbent may include a molecular sieve having low silica to alumina ratio. Large pore molecular sieves having a low silica to alumina ratio, particularly those molecular sieves characterized as having an FAU type of framework, are generally suitable for use as an adsorbent for alcohols and other oxygenates. Preferred FAU molecular sieves are X zeolites, with 13X zeolite being particularly preferred. As used herein, the term “FAU molecular sieve” refers to the IZA Structure Commission standard which includes both X and Y zeolites.
The synthesis of X-type zeolites is described in U.S. Pat. Nos. 2,882,244; 3,685,963; 5,370,879; 3,789,107 and 4,007,253 which are hereby incorporated herein by reference in their entirely. 13X Zeolite are a faujasite (FAU) type X zeolite. It has a low silica/alumina ratio and is comprised of silicon, aluminum and oxygen. The oxygen ring provides a cavity opening of 7.4 angstroms, but can adsorb molecules up to 10 angstroms. 13X zeolite have a Chemical Abstracts (CAS) number of [63231-69-6]. 13X zeolite are commercially available from several sources, including Aldrich Chemical Company and the Davison Division of W. R. Grace. Additionally the process as described in U.S. Pat. No. 6,933,323 can be used herein as noted above.
Flash point is the temperature to which the fuel must be heated to create sufficient fuel vapor above the surface of the liquid fuel for ignition to occur when exposed to an open flame. Flash point determined by ASTM D 93 and preferably is a minimum of 38° C.
The following examples highlight the problem to be solved by the realization of the effect of including C₁₁₊alcohols in distillate fuel and not being able to meet diesel cloud point specifications.

EXAMPLE 1

In this example, a 600° F. (315° F.) end point (by ASTM D2887) Fischer Tropsch diesel fuel with a high i/n ratio was prepared and tested.
A commercial sample of Fischer Tropsch C₈₀wax was obtained from Moore and Munger Co. It has an initial boiling point as determined by ASTM D 2887 of 790° F. and a boiling point at 5 wt. % of 856° F. It was hydrocracked in a single stage pilot plant at 669° F., 1.0 LHSV, 1000 psig, 10000 SCF/Bbl Hydrogen at 90% conversion in a once-through operation (without recycle). A commercial sulfided hydrocracking catalyst was used. A 260-600° F. product with the following properties was recovered by distillation. This product contains over 2 wt. % n-C₁₄₊n-paraffins yet has a cloud point of −51° C.


	Density at 15° C., g/ml	0.7626
	Sulfur, ppm	0
	Viscosity at −20° C., cSt	6.382
	Freeze Point, ° C.	−47.7
	Cloud Point, ° C.	−51.
	Flash Point, ° C.	54.
	Smoke Point, mm	>45

Hydrocarbon types, wt. % by Mass Spec. (ASTM D2789)


	Paraffins	93.1
	Mono-cycloparaffins	5.2
	Di-cycloparaffins	1.5
	Alkylbenzenes	0.1
	Benzonaphthalenes	0.0
	Naphthalenes	0.1

N-paraffin Analysis by GC

CARBON	DISTRIBUTION	NORMAL	NON
NUMBER	(Wt. Percent)	PARAFFIN	N-PARAFFIN

6	0.00	0.00	0.00
7	0.00	0.00	0.00
8	0.12	0.10	0.02
9	8.75	1.83	6.92
10	10.95	1.56	9.39
11	11.25	1.22	10.03
12	11.24	1.19	10.05
13	11.26	0.68	10.58
14	10.66	0.77	9.90
15	10.21	0.58	9.62
16	9.70	0.41	9.29
17	9.37	0.30	9.07
18	6.36	0.03	6.33
19	0.12	0.00	0.12
20	0.02	0.00	0.02
21	0.00	0.00	0.00
22-52	0.00	0.00	0.00
TOTAL	100.00	8.67	91.33

Average Carbon Number: 13.28
Average Molecular Weight: 187.93

Simulated Distillation, ° F. by wt. %, ASTM D 2887


0.5%	267
5%	287
10%	310
20%	342
30%	378
40%	405
50%	439
60%	472
70%	504
80%	535
90%	564
95%	579
99%	595
99.5%	598

This sample was mixed with n-dodecanol in varying amounts and the cloud point was determined. The original sample had a cloud point of −51° C. which meets the most stringent cloud point specification in ASTM D975, but adding as little as 0.1 wt. % oxygen as dodecanol significantly increased the cloud point.
Blending of Diesel Fuel with 1-Dodecanol for Cloud Point Measurements

Fischer-Tropsch Diesel Fuel

								Pour
Test	Wt	Wt Diesel Fuel,	Total Wt in,	Actual Wt %	Target Wt %	Wt %	Cloud Point,	Point,
No	1-Docecanol, g	g	g	1-Dodecanol	1-Dodecanol	Oxygen	° C.	° C.

1				0	0	0.00	−51	<−59
2	0.1309	10.8550	10.9859	1.19	1.18	0.10	−8
3	0.5910	49.4220	50.0130	1.18	1.18	0.10	−9	−38
4	0.5878	9.5348	10.1226	5.81	5.79	0.50	1
5	3.0133	49.0511	52.0644	5.79	5.79	0.50	3	−1

EXAMPLE 2

An additional diesel fuel sample was prepared with a 675° F. (357° C.) and 450° F. (232° C.) end points and a moderate i/n ratio and tested as shown below. This sample meets the end point and flash point requirements of ASTM D975 for No. 2-D fuel.
Samples of Fischer Tropsch condensate and wax from a cobalt catalyst were obtained. The condensate was hydrotreated at 3.36 LHSV, 1000 psig total pressure, 5000 SCFR recycle gas rate over a sulfided commercial whole extrudate non-acidic NiMo/Al₂O₃catalyst. The wax was hydrocracked at 1.2 LHSV, 66% per pass conversion below 675° F. (357° C.), 1000 psig total pressure, 5000 SCFB recycle gas rate over a sulfided commercial whole extrudate acidic NiW/Al₂O₃—SiO₂catalyst. The products from the two units were continuously blended and distilled. The material boiling above the diesel cut point (roughly 675° F.-357° C.) was recycled to extinction in the hydrocracker.
Properties of the 250-675° F. (121-357° C.) diesel fuel are shown below:


	Gravity, °API	52.7
	Nitrogen, ppm	0.24
	Sulfur, ppm	<1
	Water, ppm by Karl Fisher, ppm	21.5
	Pour Point/Cloud Point/CFPP,	−23/−18/−21/−14
	° C./Freeze Point, ° C.
	Flash Point, ° C.	58
	Viscosity at 25° C. × 40° C., cSt	2.564/1.981
	Cetane Number	74
	Aromatics by Supercritical	<1
	Fluid Chromatography, wt %
	Neutralization No.	0
	Ash Oxide, Wt %	<0.001
	Ramsbottom Carbon Residue, wt %	0.02
	Cu Strip Corrosion	1A
	Color, ASTM D1500	0
	GC-MS Analysis
	Paraffins, Wt %	100
	Paraffin i/n ratio	2.1
	Oxygen as oxygenates, ppm	<6
	Olefins, Wt %	0
	Average Carbon Number	15.15

Distillation by D-2887 by Wt %,
° F. and D-86 by Vol %, ° F.	D-2887	D-86

0.5/5	255/300	329/356
10/20	326/368	366/393
30/40	406/449	419/449
50	487	480
60/70	523/562	510/539
80/90	600/637	567/597
95/99.5	659/705	615/630

Detailed GC-MS Analysis.


	N-alkane	Branched	Total	i/n by
Formula	area %	alkane area %	alkanes	Carbon No.

C9H20	2.96	0.00	2.96	—
C10H22	3.59	4.24	7.83	1.18
C11H24	3.80	4.65	8.45	1.22
C12H26	3.65	4.77	8.42	1.31
C13H28	3.41	5.34	8.75	1.57
C14H30	3.00	5.34	8.34	1.78
C15H32	2.61	5.56	8.17	2.13
C16H34	2.33	8.65	10.98	3.71
C17H36	1.99	5.74	7.72	2.89
C18H38	1.51	6.11	7.62	4.04
C19H40	1.60	5.98	7.58	3.73
C20H42	1.18	5.35	6.53	4.52
C21H44	0.58	3.82	4.41	6.54
C22H46	0.22	2.00	2.23	8.94

This diesel fuel was mixed with various primary linear alcohols and the cloud point determined. Adding 1-heptanol makes no significant change in the cloud point, but adding C₁₁₊alcohols does increase the cloud point. These results show that a +14° C. cloud point cannot be achieved when the C₁₆₊alcohol content is in excess of 0.3 wt % oxygen as oxygenates. Adding 1-hexanol does not make a significant increase in the cloud point, but adding 1-dodecanol does. When C₁₁₊alcohols were present in blends with 1-hexanol, significant increase in the cloud point was still observed in most cases. High levels of 1-hexadecanol and 1-eicosanol were not soluble at ambient conditions (and even 50° C.). Thus cloud points could not be measured. They were well in excess of +14° C.


Experi-		Actual
ment		Oxygen	Cloud
No	Alcohol	Wt %	Point	Comments

1	None	0	−18, −19;
			−20; −20
2	1-Hexanol	0.0010	−19
3	1-Hexanol	0.0101	−19
4	1-Hexanol	0.3000	−20	Soluble at ambient
5	1-Dodecanol	0.0010	−17
6	1-Dodecanol	0.0101	−14
7	1-Dodecanol	0.2996	−3	Soluble at ambient
8	1-Hexadecanol	0.0010	−19
9	1-Hexadecanol	0.0101	−10
10	1-Hexadecanol	0.3000	unable to	Not soluble at
			detect	ambient
11	1-Eicosanol	0.0010	−12
12	1-Eicosanol	0.0100	13	Soluble at ambient
13	1-Eicosanol	0.2999	solid	Not soluble at
				ambient, turned
				solid, did not
				determine cloud
				point
14	Mixed Alcohols	0.0010	−18
15	Mixed Alcohols	0.0101	−10
16	Mixed Alcohols	0.3000	17	Not soluble at
				ambient

Mixed alcohols were an equal weight percent mixture of 1-hexanol, 1-dodecanol 1-hexadecanol and 1-eicosanol.

EXAMPLE 3

The diesel product from example 2 was further distilled to obtain a 250-400° F. (121-204° C.) diesel fuel fraction which simulated a No. 1-D fuel with these properties.


Property	Value	Units

Density @ 20° C.	0.7269	g cm⁻¹
Refractive Index @ 20° C.	1.4096
Molecular Weight	142	Daltons
n-d-M Analysis
% Paraffinic Carbon	98.42	Wt %
% Naphthenic Carbon	1.52	Wt %
% Aromatic Carbon	0.00	Wt %
Naphthenic Rings per molecule	0.03
Aromalic Rings per molecule	0.00
Cloud Point	−60	° C.
Sulfur	2.3	ppm weight
Nitrogen	0.178	ppm weight
Bromine Index	228
Aromatics by SFC
Monoaromatics	<0.5	Wt %
Polyaromatics	<0.5	Wt %
Total Aromatics	<0.5	Wt %
FIAM (D1319)
Aromatics	1	Vol %
Olefins	0	Vol %
Paraffins/Naphthenes	99	Vol %
n-Paraffin Analysis by Carbon Number
n-C₅	0.01	Wt %
n-C₆	0.01	Wt %
n-C₇	0.50	Wt %
n-C₈	11.13	Wt %
n-C₉	16.42	Wt %
n-C₁₀	16.97	Wt %
n-C₁₁	13.59	Wt %
n-C₁₂	0.46	Wt %
n-C₁₃and heavier	0.00	Wt %
Total Normal Paraffins	59.09	Wt %
Distilliation by D-2887, Wt % by ° F.
St/5 wt %	196/256
10/30 wt %	260/304
50 wt %	330
70/90 wt %	350/388
95/99 wt %	389/406

These studies show that addition of small amounts of dodecanol has a significant detrimental impact on the cloud point. Adding as little as 0.01 wt. % oxygen as 1-dodecanol resulted in cloud points (as measured by ASTM D2500, ° C.) well in excess of the lowest cloud limit, −49° C. Adding C₅to C₁₀alcohols did not result in a notable increase in the cloud point. As noted above all wt. % oxygen concentrations are on a water free basis.
Preferred FT diesel alcohol compositions with 1-C₅to 1-C₁₀are exemplified below.
FT Diesel with 1-Heptanol


Test	Wt	Wt Diesel Fuel,	Total wt in,	Actual wt % 1-	Target Wt % 1-	Wt %	Cloud Point,
No	1-Heptanol, g	g	g	Heptanol	Heptanol	Oxygen	° C.

6

0

No added alcohol

0

−−63

7	0.00597	8.49875	8.50472	0.07	0.0725	0.01	−61.6
8	0.03208	4.38771	4.41979	0.73	0.725	0.10	−58.8

FT Diesel with 1-Pentanol


Test	Wt	Wt Diesel Fuel,	Total wt in,	Actual wt % 1-	Target Wt % 1-	Wt %	Cloud Point,
No	1-Pentanol g	g	g	Pentanol	Pentanol	Oxygen	° C.

9	0.00315	6.00633	6.00948	0.05	0.055	0.01	−61.6
10	0.03231	6.02061	6.05292	0.53	0.55	0.10	−55.8

FT Diesel with 1-Dodecanol


Test	Wt	Wt Diesel Fuel,	Total wt in,	Actual wt % 1-	Target Wt % 1-	Wt %	Cloud Point,
No	1-Docecanol, g	g	g	Dodecanol	Dodecanol	Oxygen	° C.

11	0.01050	9.00597	9.01647	0.116	0.11625	0.01	−37
12	0.06792	6.00194	6.06986	1.119	1.1625	0.10	−11

FT Diesel with 1-Decanol


Test	Wt	Wt Diesel Fuel,	Total wt in,	Actual wt % 1-	Target Wt % 1-	Wt %	Cloud Point,
No	1-Decanol, g	g	g	Decanol	Decanol	Oxygen	° C.

13	0.0233	23.9778	24.0011	0.10	0.09875	0.01	−52

FT Diesel with 1-Octanol


Test	Wt	Wt Diesel Fuel,	Total wt in,	Actual wt % 1-	Target Wt % 1-	Wt %	Cloud Point,
No	1-Decanol, g	g	g	Decanol	Decanol	Oxygen	° C.

14	0.00331	4.00237	4.00568	0.083	0.08125	0.01	−60.7
15	0.08838	10.93777	11.02615	0.802	0.8125	0.10	−61

This examples illustrate the inability to get low cloud points with normal alcohols such as 1-dodecanol while C₅to C₁₀normal alcohols can be employed and obtain a low cloud point, especially when the distilled fraction has a lower end point than the prior example and a moderate i/n ratio.

Claims

1. A Fischer-Tropsch derived distillate suitable for use as a diesel fuel having a flash point 38° C. minimum measured by ASTM D 93 a cloud point of +14° C. or less and further containing not less than 0.01 wt. % oxygen in at least two alcohols selected from the group consisting of 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol; and mixtures of more than two alcohols, and not more than 0.01 wt. % oxygen in C₁₁₊linear alcohols.

2. The Fischer-Tropsch derived distillate of claim 1 wherein the cloud point is 0° C.

3. The Fischer-Tropsch derived distillate of claim 2 wherein the cloud point is −15° C. or less.

4. The Fischer-Tropsch derived distillate of claim 3 wherein the cloud point is −25° C. or less.

5. The Fischer-Tropsch derived distillate of claim 4 wherein the cloud point is −49° C. or less.

6. The Fischer-Tropsch derived distillate of claim 1 wherein the sum of the oxygenate content of the C₅-C₁₀linear alcohols present are within the range of from 0.01 wt. % oxygen and 1 wt. % oxygen.

7. A process for preparing a Fischer-Tropsch derived distillate fuel which comprises;

(a) separating a Fischer-Tropsch condensate into a first and second fraction, wherein:

(i) said first fraction comprises not less than 0.01 wt. % oxygen of alcohols selected from the group consisting of 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, and mixtures thereof, and not more than 0.01 wt. % oxygen in C₁₁₊linear alcohols and

(ii) said second fraction comprises C₁₁₊linear alcohols;

(b) removing the C₁₁₊linear alcohols from at least a portion of said second fraction and recovering a treated heavy fraction substantially free of C₁₁₊linear alcohols; and

(c) blending at least a portion of the first fraction of step a(i) and a portion of the treated heavy fraction of step (b) in the proper proportion to prepare a Fischer-Tropsch derived distillate fuel wherein the sum of the oxygenate content of the C₅-C₁₀alcohols present are within the range of from 0.01 wt. % oxygen and to 1 wt. % oxygen, the cloud point is not more than +14° C., and the flash point 38° C. minimum measured by ASTM D 93.

8. The process of claim 7 wherein the first fraction and the second fraction are blended in step (c) with the proper proportion to prepare a Fischer-Tropsch derived distillate fuel having a cloud point of not more than 0° C.

9. The process of claim 8 wherein the first fraction and the second fraction are blended in step (c) with the proper proportion to prepare a Fischer-Tropsch derived distillate fuel having a cloud point of not more than −15° C.

10. The process of claim 7 wherein the Fischer-Tropsch condensate is separated into first, second, and third fractions wherein said first and second fractions are as described and said third fraction comprises C₄₋linear alcohols.

11. The process of claim 7 wherein the second fraction is treated by a process selected from hydrotreating, hydrocracking, hydroisomerization, dehydration, adsorption, absorption, or a combination thereof to obtain the treated heavy fraction substantially free of C₁₁₊linear alcohols.

12. In a distillate fuel having a cloud point of +14° C. or less, the improvement comprising not less than 0.01 wt. % oxygen in at least two alcohols selected from the group consisting of 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, and mixtures of more than two alcohols; and not more than 0.01 wt. % oxygen in C11₊linear alcohols.

13. The distillate fuel of claim 12 wherein the cloud point is 0° C. or less.

14. The distillate fuel of claim 13 wherein the cloud point is −15° C. or less.

15. The distillate fuel of claim 12 wherein the sum of the oxygenate content of the C₅-C₁₀linear alcohols present are within the range of from 0.01 wt. % oxygen and 1 wt. % oxygen.

16. The diesel fuel of claim 12 wherein the alcohol is any two of the C₅-C₁₀linear alcohols in a total concentration less than 1 wt. % oxygen.

17. The Fischer-Tropsch derived distillate of claim 1 wherein the alcohol is any two of the C₅-C₁₀linear alcohols in a total concentration less than 1 wt. % oxygen.

18. The Fischer-Tropsch derived distillate of claim 7 wherein the alcohol is any two of the C₅-C₁₀linear alcohols in a total concentration less than 1 wt. % oxygen.

20. The Fischer-Tropsch derived distillate according to claim 19 with 1-alcohols selected from the groups consisting of C₅and C₆; C₅and C₇; or C₆and C₇.

21. The process of claim 7 wherein the first fraction further includes 1-alcohols C₈, C₉and C₁₀and step b removes the C₁₁₊linear alcohols from at least a portion of said second fraction and recovering a treated heavy fraction substantially free of C₁₁₊linear alcohols and step (c) blends at least a portion of the first fraction of step a(i) and a portion of the treated heavy fraction of step (b).

22. The diesel fuel of claim 12 further comprising 1-alcohols selected from the group consisting of C₈, C₉and C₁₀and mixtures thereof alcohols and wherein the paraffins are at least 90% i-paraffins.

23. The diesel fuel of claim 1 further comprising 1-alcohols selected from the group consisting of C₈, C₉and C₁₀and mixtures thereof alcohols and wherein the paraffins are at least 90% i-paraffins.