AU765274B2

AU765274B2 - Process for producing middle distillates and middle distillates produced by that process

Info

Publication number: AU765274B2
Application number: AU63001/99A
Authority: AU
Inventors: Luis Pablo Dancuart; Robert De Haan; Ewald Watermeyer De Wet; Mark Jan Prins
Original assignee: Sasol Technology Pty Ltd
Current assignee: Sasol Technology Pty Ltd
Priority date: 1998-10-05
Filing date: 1999-09-17
Publication date: 2003-09-11
Anticipated expiration: 2019-09-17
Also published as: JP3824490B2; EP1129155A1; WO2000020535A1; MY125273A; JP2002526637A; JP2006161056A; JP4261552B2; AU6300199A

Description

PROCESS FOR PRODUCING MIDDLE DISTILLATES AND MIDDLE DISTILLATES PRODUCED BY THAT PROCESS Field of the Invention This invention relates to middle distillates having good cold flow properties, such as the Cold Filter Plugging Point (CFPP) measured in accordance with the IP method 309, and a high Cetane number, as well as to a process for production of such disti-llates. More particularly, this invention relates to middle distillates produced from a mainly paraffinic synthetic crude which is produced by the reaction of CO and H 2 typically by the Fischer-Tropsch (FT) process.

Background to the invention Waxy products of a FT hydrocarbon synthesis process, particularly the products of a cobalt and/or iron based catalytic process, contain a high proportion of normal paraffins. Primary FT products provide notoriously poor cold flow properties, making such products difficult to use where cold flow properties are vital, e.g. diesel fuels, lube oil bases and jet fuel. It is known in the art that cold flow properties of a middle distillate, such as jet fuel, can be improved by 20 increasing the branching of the paraffins of distillates within the proper boiling range, as well as by hydrocracking and hydroisomerising heavier components. Hydrocracking, however, produces smaller amounts of gases and light products, which reduce the yield of valuable distillates. There remains an incentive for a process to maximize middle distillates obtained from FT waxes having good cold flow properties and a high Cetane number.

The middle distillate fuel described in this invention is produced from a highly paraffinic synthetic crude (syncrude) obtained from synthesis gas (syngas) through a reaction like the FT S reaction. The FT primary products cover a broad range of hydrocarbons from methane to species with molecular masses above 1400; including mainly paraffinic hydrocarbons and 30 much smaller quantities of other species such as olefins, and oxygenates.

The prior art teaches in US 5,378,348 that by hydrotreating and isomerizing the products from a Fisher-Tropsch reactor one can obtain a jet fuel with freezing point of -34°C or lower due to the iso-paraffinic nature of this fuel. This increased product branching relative to the waxy paraffin feed corresponds with a Cetane rating (combustion) value less than that for normal (linear) paraffins, depicting that an increase in branching reduces the Cetane value of paraffinic hydrocarbon fuels.

Further, WO 97/14769 discloses diesel fuels having excellent lubricity, oxidative stability and high cetane number produced from the non-shifting Fischer-Tropsch processes and having wt% paraffins with an iso to normal ratio of from 0.3 to 3.0 No mention is made regarding the effect of branching on the cold flow properties or the cetane number.

Still further, WO 98/34998 discloses a process for producing additve compositions, especially via a Fischer-Tropsch reaction, useful for improving the cetane number or lubricity of a middle distillate diesel fuel. The additive is prepared by fractionating the products of a Fischer-Tropsch reation into a low boiling 371 degC fraction and a high boiling fraction, and hydroisomerising the high boiling fraction into a low boiling fraction and blending the low boiling fraction and the hydroisomerised high boiling fraction to produce the additive having wt% C 1 6 to C 20 paraffins of which >50 wt% are isoparaffins. This disclosure does not disclose that a diesel fuel having good cold flow properties and high cetane number can be produced, only an additive, also the disclosure requires hydroisomerisation of a high boiling fraction which leads to a loss of material from the diesel boiling range into lighter material 20 and to the formation of branched isomers, which leads to Cetane ratings less than the corresponding n-paraffins. The disclosure also does not address the issue of cold flow properties simulataneously with high a Cetane number.

Surprisingly, it has now been found by the applicant, that a hydroprocessed middle distillate, such as diesel, may be produced having a high Cetane number as well as good cold flow properties. The middle distillates of the present invention could be used on their own or in blends to improve the quality of other diesel fuels not meeting the current and/or proposed, more stringent fuel quality specifications.

**o 30 Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a *stated integer or group of integers but not the exclusion of any other integer or group of integers.

The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia as at the priority date of the application.

Summary of the invention Thus, according to a first aspect of the invention, there is provided a process for the production of a middle distillate or distillate blend, such as diesel, having a high Cetane number as well as good cold flow properties.

The synthetic middle distillate cut may comprise more than 50% paraffins lighter than C 16 in which more than 50 mass% of all paraffins of the synthetic middle distillate cut are isoparaffins, the isoparaffins being predominantly methyl and/or ethyl and/or propyl branched, wherein a Clo to C 18 fraction of the synthetic middle distillate cut has a mass ratio range of isoparaffins to n-paraffins of between 1:1 and 9:1; a C 8 to C 9 fraction of the synthetic middle distillate cut has a mass ratio range of isoparaffins to n-paraffins lower than that of the C 1 o to Cs 1 20 fraction; and a C 19 to C 24 fraction of the synthetic middle distillate cut has a mass ratio range of isoparaffins to n-paraffins of from 3.3:1 to 5:1.

The isoparaffins to n-paraffins mass ratio may be 8.54:1 for a C 1 5 fraction of the synthetic middle distillate cut.

The mass ratio of isoparaffins to n-paraffins may be adjusted by controlling the blend ratio of hydrocracked to straight run components of the synthetic middle distillate cut. Thus, the 3 isoparaffins to n-paraffins mass ratio of the Clo to C 18 fraction having 30% straight run component may be between 1:1 and 2:5:1.

The synthetic middle distillate cut may comprise 20 mass% of a straight run component thereby selecting the isoparaffins to n-paraffins mass ratio of the Clo to Ci 8 fraction to be between 2:1 and 2.5:1.

The synthetic middle distillate may comprise 20 mass% of a straight run component thereby selecting the isoparaffins to n-paraffins mass ratio of the Clo to C 1 8 fraction to between 1.5:1 and 3.5:1.

The synthetic middle distillate cut may comprise 10 mass% of a straight run component thereby selecting the isoparaffins to n-paraffins mass ratio of the Clo to C 18 fraction to between 2.3:1 and 4.3:1 The isoparaffins to n-paraffins mass ratio of the Clo to C 18 fraction having substantially only a hydrocracked component may be between 4:1 and 9:1.

At least some of the isoparaffins may be methyl branched. At least some of the isoparaffins may be di-methyl branched. At least 30% (mass) of the isoparaffins are typically monomethyl branched.

Some of the isoparaffins may however be ethyl branched.

Table A: Comparison of the Branching Characteristics of Blends of SR ,HX and SPD Diesels SR Diesel HX Diesel SPD-Diesel In-Paraff I-Paraff Total n-Paraff I-Paraff Total n-Paraff I-Paraff Total C8 1.07 1.07 0.38 0.38 0.58 0.58 C9 22.64 1.57 24.21 1.86 5.37 7.23 6.01 3.60 9.61 CIO 14.73 1.74 16.47 1.90 8.43 10.33 6.48 6.12 12.60 C11 5.43 0.32 5.75 1.60 8.75 10.35 6.13 6.31 12.44 C12 11.79 0.67 12.46 1.41 8.88 .10.29 6.57 5.94 12.51 C13 11.16 0.65 11.81 1.32 8.46 9.78 6.31 6.03 12.34 C14 11.66 0.70 12.36 1.27 8.95 10.22 6.41 5.82 12.23 9.19 0.46 9.65 1.03 8.80 9.83 4.98 4.97 9.95 C16 4.94 0.31 5.25 0.96 6.38 7.34 2.58 3.53 6.11 C17 0.88 0.88 0.88 3.92 4.80 0.76 2.33 3.09 C18 0.08 0.08 0.90 2.73 3.63 0.66 1.93 2.59 C19 0.60 2.69 3.29 0.38 1.47 1.85 0.54 2.38 2.92 0.32 0.78 1.10 C21 0.56 2.73 3.29 0.29 0.72 1.01 C22 0.60 2.12 2.72 0.29 0.53 0.82 C23 0.41 1.93 2.34 0.25 0.40 0.65 C24 0.23 0.92 1.15 0.16 0.38 0.54 0.14 10.14 Total J93.57 6.42 j99.99 16.45 83.58 1100.031 49.16 50.86 J100.02 In the table: SPD Sasol Slurry Phase Distillate SR Straight Run HX Hydrocracked Table B: Branching Characteristics of Blends of SR HX Diesels isomnormal Paraffins Ratio (mass) SR Diesel 0% 10% 20% (mass) C8 0.0 0.0 0.0 0.0 C9 2.9 1.3 0.8 4.4 2.4 1.6 1.1 Cil 5.5 4.0 3.0 2.3 C12 6.3 3.3 2.1 1.4 C13 6.4 3.3 2.1 1.4 C14 7.0 3.5 2.2 8.5 4.3 2.7 1.8 C16 6.6 4.3 2.9 2.1 St Branching Characteristics of FT Diesel oo*

E

0 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 SR e9-10% SR 20% SR -e30% SR According to a further aspect of the invention, there is provided a synthetic middle distillate cut having a Cetane number above 70 and a CFPP, in accordance with IP 309, of below said distillate having an isoparaffinic content substantially as described above.

In one embodiment, the synthetic middle distillate cut is a FT product.

The invention extends to a diesel fuel composition including from 10% to 100% of a middle distillate cut as described above.

Typically, the diesel fuel composition may include from 0 to 90% of one or more other diesel fuel.

The diesel fuel composition may include at least 20% of the middle distillate cut, the composition having a Cetane number greater than 47 and a CFPP, in accordance with IP 309, below -22°C.

The diesel fuel composition may include at least 30% of the middle distillate cut, the composition having a Cetane number greater than 50 and a CFPP, in accordance with IP 309, below -22°C.

The diesel fuel composition may inlcude at least 50% of the middle distillate cut, the composition having a Cetane number greater than 52 and a CFPP, in accordance with IP 309, below The diesel fuel composition may include at least 70% of the middle distillate cut, the composition having a Cetane number greater than 60 and a cold flow plug point, in accordance with IP 309, below S S The diesel fuel composition may further include from 0 to 10% additives.

5 The additives may include a lubricity improver.

The lubricity improver may comprise from 0 to 0.5% of the composition, typically from .00001% to 0.05% of the composition. In some embodiments, the lubricity improver comprises from 0.008% to 0.02% of the composition.

The diesel fuel composition may include, as the other diesel, a crude oil derived diesel, such as US 2-D grade (low sulphur No. 2-D grade for diesel fuel oil as specified in ASTM D 975- 94) and/or CARB (California Air Resources Board 1993 specification) diesel fuel.

According to yet another aspect of the invention, there is provided a process for producing a synthetic middle distillate having a Cetane number higher than 70, the process including: separating the products obtained from synthesis gas via the FT synthesis reaction into one or more heavier fraction and one or more lighter fraction, wherein the one or more heavier fraction has an isoparaffins to n-paraffins mass ratio of between 2:1 and 9:2 and the one or more lighter fraction has an isoparaffins to n-paraffins mass ratio of between 1:1 and 11:2; hydroprocessing the heavier fraction under conditions which yield mainly middle distillates; separating the middle distillate product of step from a light product fraction and a heavier product fraction which are also produced in step and blending the middle distillate fraction obtained in step with at least a portion of the 0.00 one or more lighter fraction of step or products thereof.

The hydroprocessing of step may be a hydrocracking step.

The process for producing a synthetic middle distillate may include one or more additional step of fractionating at least some of the one or more lighter fraction of step or products 0 thereof, prior to step *oo *00..

to. The process for producing a synthetic middle distillate may include the additional step of 30 hydrotreating at least some of the one or more light fraction of step or products thereof, prior to step The one or more heavier fraction of step may have a boiling point above about 270°C, however, it may be above 300°C.

The one or more lighter fraction may have a boiling point in the range C 5 to the boiling point of the heavier fraction, typically in the range 160 0 C to 270C.

The product of step may boil in the range 100°C to 400 0 C. The product of step may boil in the range 160 0 C to 370 0

C.

The product of step may be a diesel fuel.

The product of step may have a CFPP below -20 0 C, typically below -30°C, and even below -35 0

C.

The product of step may be obtained by mixing the middle distillate fraction obtained in step with at least a portion of the one or more lighter fraction of step or products thereof, in a volume ratio of between 1:1 and 9:1, typically 2:1 and 6:1, and in one embodiment, in a volume ratio of 84:16.

oo The invention extends further to a process for the production of middle distillate fuels from FT primary products, comprising predominantly long chain linear paraffins.

In this process, the waxy product from the FT process is separated into at least two fractions, a heavier and at least one lighter fraction. The lighter fraction may be subjected to mild catalytic hydrogenation to remove hetero-atomic compounds such as oxygen and to saturate olefins, thereby producing material useful as naphtha, solvents, diesel and/or blending components therefor. The heavier fraction may be catalytically hydroprocessed without prior hydrotreating •to produce products with good cold flow characteristics. This hydroprocessed heavier fraction could be blended with all or part of the hydrogenated and/or unhydrogenated light fraction to ••obtain, after fractionation, naphtha and a diesel fuel characterised by a high Cetane number.

The catalysts suitable for the hydroprocessing steps are commercially available and can be selected towards an improved quality of the desired final product.

Detailed Description This invention describes the conversion of primary FT products into naphtha and middle distillates, for example, diesel having a high Cetane number in excess of 70, while also having good cold flow properties, as described above.

The FT process is used industrially to convert synthesis gas, derived from coal, natural gas, biomass or heavy oil streams, into hydrocarbons ranging from methane to species with molecular masses above 1400.

While the main products are linear paraffinic materials, other species such as branched paraffins, olefins and oxygenated components form part of the product slate. The exact product slate depends on reactor configuration, operating conditions and the catalyst that is employed, as is evident from e.g. Catal.Rev.-Sci. Eng., 23(1&2), 265-278 (1981).

Preferred reactors for the production of heavier hydrocarbons are slurry bed or tubular fixed bed reactors, while operating conditions are preferably in the range of 160'C 280'C, in some oo oo 20 cases 210-260 0 C, and 18 50 Bar, in some cases 20-30 bar.

•Preferred active metals in the catalyst comprise iron, ruthenium or cobalt. While each catalyst will give its own unique product slate, in all cases the product slate contains some waxy, highly paraffinic material which needs to be further upgraded into usable products. The FT products can be converted into a range of final products, such as middle distillates, gasoline, solvents, lube oil bases, etc. Such conversion, which usually consists of a range of processes such as hydrocracking, hydrotreatment and distillation, can be termed a FT work-up process.

9* °99 The FT work-up process of this invention uses a feed stream consisting of C 5 and higher 30 hydrocarbons derived from a FT process. This feed is separated into at least two individual fractions, a heavier and at least one lighter fraction. The cut point between the two fractions is preferably less than 300'C and typically around 270C.

The table elow gives a typical composition of the two fractions, with a 10% accuracy: The table b~elow gives a typical composition of the two fractions, with a ±10% accuracy: Table 1: Typical Fischer-Tropsch product after separation into two fractions (vol% distilled) Condensate Wax 270'C fraction) 270°C fraction)

C

5 -160 0 C 160-270 0 C 51 3 270-370 C 4 370-500 0 C 42 500°C The >270 0 C fraction, also referred to as wax, contains a considerable amount of hydrocarbon material, which boils higher than the normal diesel range. If we consider a typical diesel boiling range of 160-370°C, it means that all material heavier than 370°C needs to be converted into lighter materials by means of a catalytic process often referred to as hydroprocessing, for example, hydrocracking.

Catalysts for this step are of the bifunctional type; i.e. they contain sites active for cracking and for hydrogenation. Catalytic metals active for hydrogenation include group VIII noble metals, such as platinum or palladium, or a sulphided Group VIII base metals, e.g. nickel, 15 cobalt, which may or may not include a sulphided Group VI metal, e.g. molybdenum. The support for the metals can be any refractory oxide, such as silica, alumina, titania, zirconia, vanadia and other Group III, IV, VA and VI oxides, alone or in combination with other refractory oxides. Alternatively, the support can partly or totally consist of zeolite. However, for this invention the preferred support is amorphous silica-alumina.

Process conditions for hydrocracking can be varied over a wide range and are usually laboriously chosen after extensive experimentation to optimize the yield of middle distillates.

In this regard, it is important to note that, as in many chemical reactions, there is a trade-off between conversion and selectivity. A very high conversion will result in a high yield of gases 25 and low yield of distillate fuels. It is therefore important to painstakingly tune the process conditions in order to limit the conversion of >370 0 C hydrocarbons. Table 2 gives a list of the preferred conditions.

Table 2: Process conditions for hydrocracking CONDITION BROAD PREFERRED RANGE RANGE Temperature, °C 150-450 340-400 Pressure, barg 10-200 30-80 Hydrogen Flow Rate, 100-2000 800-1600 m 3 ,/m 3 feed Conversion of>370°C material, 30-80 50-70 mass Nevertheless, it is possible to convert all the >370 0 C material in the feedstock by recycling the part that is not converted during the hydrocracking process.

As is evident from table 1, most of the fraction boiling below 270 0 C is already in the typical boiling range for diesel, i.e. 160-370 0 C. This fraction may or may not be subjected to hydrotreating. By hydrotreating, hetero-atoms are removed and unsaturated compounds are hydrogenated. Hydrotreating. is a well-known industrial process, catalyzed by any catalyst having a hydrogenation function, e.g. Group VIII noble metal or sulphided base metal or Group VI metals, or combinations thereof. Preferred supports are alumina and silica.

Table 3 gives typical operating conditions for the hydrotreating process.

S

0

**SS

S

*55S SS SO 00 0

S

*(b

S

*SSS

S. SO 0 S 0 0

**SS*

*0 Sd

OS

0 0 Table 3: Operating conditions for the hydrotreating process.

CONDITION BROAD PREFERRED RANGE RANGE Temperature, °C 150-450 200-400 Pressure, bar(g) 10-200 30-80 Hydrogen Flow Rate, 100-2000 400-1600 m 3 n/m 3 feed 12- While the hydrotreated fraction may be fractionated into paraffinic materials useful as solvents, the applicant has now surprisingly found that the hydrotreated fraction may be directly blended with the products obtained from hydrocracking the wax. Although it is possible to hydroisomerise the material contained in the condensate stream, the applicant has found that this leads to a small, but significant loss of material in the diesel boiling range to lighter material. Furthermore, isomerisation leads to the formation of branched isomers, which leads to Cetane ratings less than that of the corresponding normal paraffins.

The combination of highly linear paraffins derived from the <270°C fraction and mainly branched paraffins derived from the >270°C fraction results in a superb diesel.

Important parameters for a FT work-up process are maximization of product yield, product quality and cost. While the proposed process scheme is simple and therefore cost-effective, it produces High Performance Diesel, having a Cetane number >70, and naphtha in good yield.

In fact, the process of this invention is able to produce a diesel of hitherto unmatched quality, which is characterized by a unique combination of both high Cetane number and excellent cold flow properties. This is believed to be related to a low degree of isomerisation in the 160- 20 270C fraction of the diesel and contrary to this, a high degree of isomerisation in the 270- 370°C fraction of the diesel.

The total amount of isomers in the light boiling range of the diesel (160-270°C fraction) and the heavier range of the diesel (270°C-370°C) are shown in the following table 4.

Table 4: Isoparaffins: n-Paraffins of Middle Distillate Fractions Boiling Corresponding Average Iso:Normal Paraffins Ratio Range Carbon Range Range Typical value 160-270 0 C C 10

-C

1 7 0.5-4.0 2.2 270-370°C C 17

-C

23 4.0 14.0 10.5 The relatively high percentage of normal paraffins in the light boiling range contributes to the high Cetane number of the diesel fuel, without affecting the cold flow properties. On the other hand, in the heavier range of the diesel, branching is of utmost importance because the linear hydrocarbons in this range provide very poor cold flow properties and in some cases, may even crystallize. Therefore, the amount of iso-paraffins in this range is maximised during hydroprocessing under the process conditions described herein.

It is this unique composition of the synthetic fuel, which is directly caused by the way in which the FT work-up process of this invention is operated, that leads to the unique characteristics of said fuel.

The applicant has also found, that from the perspective of fuel quality, it is not necessary to hydrotreat the <270°C fraction, adding said fraction directly to the products from hydrocracking the wax. While this results in the inclusion of oxygenates and unsaturates in the final diesel, fuel specifications usually allow for this. Circumventing the need for hydrotreatment of the condensate results in considerable savings of capital and operating costs.

The described FT work-up process of Figure 1 may be combined in a number of configurations. The applicant considers these an exercise in what is known in the art as S* Process Synthesis Optimisation.

S: However, the specific process conditions for the Work-up of FT primary products the possible process configurations of which are outlined in Table 5, were obtained after extensive and laborious experimentation and design.

Table 5 Possible Fischer-Tropsch Product Work-up Process Configurations Process Configuration Process Step A B C D E F 2 Light FT Product Fractionator X X 3 Light FT Product Hydrotreater X X X X 4 Hydrotreater Products Fractionator X X X Waxy FT Product Hydrocracker X X X X X X 6 Hydrocracked Products Fractionator X X X X X X Numbers reference numerals of Figure 1 FT Fischer-Tropsch The basic process is outlined in the attached Figure 1. The synthesis gas (syngas), a mixture of Hydrogen and Carbon monoxide, enters the FT reactor 1 where the synthesis gas is converted to hydrocarbons by the FT reaction.

A lighter FT fraction is recovered in line 7, and may or may not pass through fractionator 2 and hydrotreater 3. The product 9 from the hydrotreater may be separated in fractionator 4 or, alternatively, mixed with hydrocracker products 16 sent to a common fractionator 6.

A waxy FT fraction is recovered in line 13 and sent to hydrocracker 5. If fractionation 2 is considered the bottoms cut 12 are be sent to hydrocracker 5. The products 16, on their own or 15 mixed with the lighter fraction 9a, are separated in fractionator 6 Depending on the process scheme, a light product fraction, naphtha 19, is obtained from fractionator 6 or by blending equivalent fractions 10 and 17. This is a C 5 -160°C fraction useful as naphtha.

A somewhat heavier cut, synthetic diesel 20, is obtainable in a similar way from fractionator 6 or by blending equivalent fractions 11 and 18. This cut is recovered as a 160-370 0 C fraction useful as diesel.

0 The heavy unconverted material 21 from fractionator 6 is recycled to extinction to S 25 hydrocracker 5. Alternatively, the residue may be used for production of synthetic lube oil bases. A small amount of CI-C 4 gases are also separated in fractionator 6.

The following examples will serve to illustrate further this invention.

Examples EXAMPLE 1 A commercially available hydrocracking catalyst was used for hydrocracking of a nonhydrotreated FT hydrocarbon fraction with an initial boiling point of about 280C. The active metals on the catalyst comprised cobalt and molybdenum, while the support was amorphous silica-alumina. Operating conditions were temperatures between 375 and 385°C, pressure of bar and hydrogen flow rate of 1500 m 3 /m 3 feed. The experiment was carried out in a pilot plant reactor. The conversion of >370'C material to lighter material ranged between 65 and Diesel component A is obtained after fractionation of the reactor products. The properties of this diesel component are given in table 1.

EXAMPLE 2 ooooo A non-hydrotreated FT hydrocarbon fraction with a final boiling point of ca 285°C and alcohol content of ca. 4.3 mass%, expressed as n-hexanol, was rigorously hydrotreated using a 20 commercially available catalyst. The active metals on the catalyst comprised molybdenum and cobalt, while the support was alumina. The process conditions were temperatures around 250'C, pressure of 68 bar and hydrogen flow rate of 1070 m3/m 3 feed. The test was carried in a commercial scale fixed bed reactor. Diesel components B and C were obtained after fractionation of respectively the reactor feed and reactor product. The properties of these 25 diesel components are given in table 6.

S.gee .ooo.

Table 6: Diesel Blending Components EXAMPLE 3 r r r r

D

r The diesel fraction obtained from hydrocracking a heavy FT material (component A) was blended with a hydrogenated lighter FT material (component B) in a volume ratio of 84:16.

The properties of the final blend, called Blend I, are given in table 7.

10 Those skilled in the art will realize that Blend I may be used on its own, but also as a blending feedstock. The combination of a high Cetane numbers, above 70, and excellent cold flow properties, with CFPP substantially better than -20C, make Blend I an ideal blending feedstock to upgrade crude oil derived diesels.

EXAMPLE 4 The diesel fraction obtained from hydrocracking a heavy FT material (component A) was directly blended with a lighter non-hydrogenated FT material (component C) in a volume ratio of 84:16. The properties of the final blend, called Blend II, are given in table 7.

-17- Similar to example 3, Blend II may be used on its own, but also as a blending feedstock. In addition to a high Cetane numbers, above 70, and excellent cold flow properties, with CFPP substantially better than -20 0 C, Blend II contains alcohols and smaller quantities of other oxygenates, the level of which depend on the blending ratio used to prepare the blend.

Table 7: Diesel Blends Blend I Blend II ASTM D86 distillation IBP, C 189 185 °C 209 208 °C 256 257 °C 331 332 FBP, °C 356 358 Density, kg/dm 3 15 0 C 0.7769 0.7779 Viscosity, cSt 40 0 C 2.43 2.42 Flash Point, °C 73 67 Cold Filter Plugging Point, oC -37 -34 Cetane Number >73.7 73.3 .r

S

a S EXAMPLE The diesel Blend I of Example 3 was blended with US 2-D grade diesel having desired Cetane number and CFPP properties, as shown in Table 8 and charts 1 and 2 below, were obtained.

S

Table: 8 Performance properties of Sasol SPD diesel, 2D diesel and blends PROPERTY TEST SASOL 80:20 50:50 30:70 US 2-D METHOD SPD SPD:2D SPD:2D SPD:2D GRADE DIESEL DIESEL Cetane number ASTM D 270 73.7 62.2 55.2 50.9 47 (min) CFPP C) IP 309 -37 -37 -34 -31 -21 Thermal Stability Octel F21-61 99.1 90 81.2 70.4 66.5 reflectance) test (180 minutes, 150'Q) Lubricity: SL ASTMD 6078/ 2700 /567 2700 /491 3050 /473 3650 /491 3950 /485 BOCLE HFRR CEC F-06-A- (WSD in urn) 96 a Cold flow properties of SPD diesel, 2D diesel and blends a.

P.

(C 0L

L-

U.

SPD Diesel Volume, Cetane number of SPD diesel, 2D diesel and blends

C

0% 10% 20% 30% 40% 50% 60% SPD Diesel Volume 70% 80% 90% 100% C

C

Chart 2: Cetane Number of Applicants Diesel and Blends Thereof.

Claims

1. A synthetic middle distillate cut comprising more than 50 mass% paraffins lighter than C 1 6 in which more than 50 mass% of all paraffins of the synthetic middle distillate cut are isoparaffins, the isoparaffins being predominantly methyl and/or ethyl and/or propyl branched, wherein a C 1 o to C 18 fraction of the synthetic middle distillate cut has a mass ratio range of isoparaffins to n-paraffins of between 1:1 and 9:1; a C 8 to C 9 fraction of the synthetic middle distillate cut has a mass ratio range of isoparaffins to n-paraffins lower than that of the Clo to C 18 fraction; and a C 1 9 to C 24 fraction of the synthetic middle distillate cut has a mass ratio range of isoparaffins to n-paraffins of from 3.3:1 to 5:1.

2. A synthetic middle distillate cut as claimed in claim 1, wherein the gradient of an isoparaffins to n-paraffins mass ratio profile of the synthetic middle distillate cut increases from about 1:1 for C 8 to 8.54:1 for C 1 5 and decreases again to about 3:1 for C 18

3. A synthetic middle distillate cut as claimed in claim 1 or claim 2, wherein the C 19 to C 24 fraction of the middle distillate cut has a mass ratio range of isoparaffins to n- paraffins of between 4:1 and 4.9:1.

4. A synthetic middle distillate cut as claimed in claim 1, which comprises 30 mass% of a straight run component thereby selecting the isoparaffins to n-paraffins mass ratio of the Clo to C 18 fraction to between 1:1 and 2.5:1.

5. A synthetic middle distillate cut as claimed in claim 1, which comprises 20 mass% of a straight run component thereby selecting the isoparaffins to n-paraffins mass ratio of the C 1 o to C 1 8 fraction to between 1.5:1 and 3.5:1.

6. A synthetic middle distillate cut as claimed in claim 1, which comprises 10 mass% of a straight run component thereby selecting the isoparaffins to n-paraffins mass ratio of the Clo to C 18 fraction to between 2.3:1 and 4.3:1.

7. A synthetic middle distillate cut as claimed in claim 1, wherein the isoparaffins to n- 30 paraffins mass ratio of the C 1 o to C 1 8 fraction having substantially only a hydrocracked component is between 4:1 and 9:1.

8. A middle distillate cut as claimed in any one of the preceding claims, wherein at least some of the isoparaffins are di-methyl branched.

9. A middle distillate cut as claimed in any one of the preceding claims, wherein at least mass% of the isoparaffins are mono-methyl branched. A middle distillate cut as claimed in any one of claims 1 to 9, wherein at least some of the isoparaffins are ethyl branched.

11. A middle distillate cut as claimed in any one of the preceding claims, wherein the ratio of isoparaffins to n-paraffins of the middle distillate cut is from about 0.5:1 to about 81:19.

12. A synthetic middle distillate cut as claimed in claim 11, wherein the isoparaffins to n- paraffins mass ratio is between about 2:1 to about 4:1.

13. A synthetic middle distillate cut as claimed in any one of the preceding claims, having a light fraction in the boiling range 160°C to 270 0 C wherein the isoparaffins to n- paraffins mass ratio of the light fraction is from 1:1 to 11:2.

14. A synthetic middle distillate cut as claimed in any one of the preceding claims, having a heavy fraction in the boiling range 270°C to 370 0 C wherein the isoparaffins to n- paraffins mass ratio of the heavy fraction is from 2:1 to 9:2. A synthetic middle distillate cut as claimed in any one of claims 1 to 14, wherein the synthetic distillate is derived from one or more FT primary product.

16. A diesel fuel composition including from 10% to 100% of a middle distillate cut as e: claimed in any one of the preceding claims. 20 17. A diesel fuel composition as claimed in claim 16, including from 0 to 90% of one or more other diesel fuel.

18. A diesel fuel composition as claimed in claim 16, including from 20 to 80% of one or more other diesel fuel.

19. A diesel fuel composition as claimed in any one of claims 16 to 18, including at least 20% of the middle distillate cut, the composition having a Cetane number greater than 47 and a CFPP, in accordance with IP 309, below -22°C. A diesel fuel composition as claimed in claim 16, including at least 30% of the middle distillate cut, the composition having a Cetane number greater than 50 and a CFPP, in accordance with IP 309, below -22°C. 30 21. A diesel fuel composition as claimed in claim 16, including at least 50% of the middle o* distillate cut, the composition having a Cetane number greater than 52 and a CFPP, in "accordance with IP 309, below -22-

22. A diesel fuel composition as claimed in claim 16, including at least 70% of the middle distillate cut, the composition having a Cetane number greater than 60 and a CFPP, in accordance with IP 309, below

23. A diesel fuel composition as claimed in any one of claims 16 to claim 22, including from 0 to 10% additives.

24. A diesel fuel composition as claimed in claim 23, wherein the additives include a lubricity improver. A diesel fuel composition as claimed in any one of claims 18 to 24 wherein one of the other diesel fuels is US 2-D grade diesel fuel.

26. A diesel fuel composition as claimed in any one of claims 18 to 24, wherein one of the other diesel fuels is CARB grade diesel fuel.

27. A process for producing a synthetic middle distillate having a Cetane number higher than 70, the process including: separating the products obtained from synthesis gas via a FT synthesis reaction into one or more heavier fraction and one or more lighter fraction, wherein the one or more heavier fraction has an isoparaffins to n- paraffins mass ratio of between 2:1 and 9:2 and the one or more lighter fraction has an isoparaffins to n- paraffins mass ratio of between 1:1 and 11:2; hydroprocessing the one or more heavier fraction under conditions which 20 yield mainly middle distillates; separating the middle distillate product of step from a light product O fraction and a heavier product fraction which are also produced in step and blending the middle distillate fraction obtained in step with at least a portion of the one or more lighter fraction of step or products thereof.

28. A process for producing a synthetic middle distillate as claimed in claim 27, wherein the hydroprocessing step of step is a hydrocracking step. •29. A process for producing a synthetic middle distillate as claimed in claim 27 or claim 28, including one or more additional step of fractionating at least some of the one or i 30 more lighter fraction of step or products thereof, prior to step

30. A process for producing a synthetic middle distillate as claimed in any one of claims "27 to 29, including the additional step of hydrotreating at least some of the one or more light fraction of step or products thereof, prior to step -23-

31. A process for producing a synthetic middle distillate as claimed in any one of claims 27 to 30, wherein the one or more heavier fraction of step boils above about 270 0 C.

32. A process for producing a synthetic middle distillate as claimed in any one of claims 27 to 31, wherein the one or more heavier fraction of step boils above about 300 0 C.

33. A process for producing a synthetic middle distillate as claimed in any one of claims 27 to 32, wherein the one or more lighter fraction boils in the range C 5 to the boiling point of the heavier fraction.

34. A process for producing a synthetic middle distillate as claimed in any one of claims 27 to 33, wherein the one or more lighter fraction boils in the range 160'C to 270 0 C. A process for producing a synthetic middle distillate as claimed in any one of claims 27 to 34, wherein the product of step boils in the range 100 0 C to 400'C.

36. A process for producing a synthetic middle distillate as claimed in any one of claims 27 to 35, wherein the product of step boils in the range 160 0 C to 370 0 C.

37. A process for producing a synthetic middle distillate as claimed in any one of claims 27 to 36, wherein the product of step is a diesel fuel which has a CFPP below 0 C.

38. A process for producing a synthetic middle distillate as claimed in any one of claims oooof 27 to 37, wherein the product of step is obtained by mixing the middle distillate fraction obtained in step with at least a portion of the one or more lighter fraction of step or products thereof, in a volume ratio selected to provide a diesel fuel having a required specification.

39. A process for producing a synthetic middle distillate as claimed in any one of claims 27 to 38, wherein the product of step is obtained by mixing the middle distillate fraction obtained in step with at least a portion of the one or more lighter fraction of step or products thereof, in a volume ratio of between 1:1 and 9:1.

40. A process for producing a synthetic middle distillate as claimed in claim 39, wherein "m "the product of step is obtained by mixing the middle distillate fraction obtained in i 30 step with at least a portion of the one or more lighter fraction of step or products thereof, in a volume ratio of between 2:1 and 6:1. S. 41. A process for producing a synthetic middle distillate as claimed in any one of claims 38 to 40, wherein the product of step is obtained by mixing the middle distillate -24- fraction obtained in step with at least a portion of the one or more lighter fraction of step or products thereof, in a volume ratio of 84:16.

42. A synthetic middle distillate cut, substantially as herein described and illustrated.

43. A diesel fuel composition, substantially as herein described and illustrated.

44. A process for producing a synthetic middle distillate having a Cetane number higher than 70, substantially as herein described and illustrated. A new synthetic middle distillate cut, a diesel fuel composition, or a new process for producing a synthetic middle distillate having a Cetane number higher than substantially as herein described. Dated this Eighteenth day of July 2003. Sasol Technology (Pty) Limited Applicant Wray Associates Perth, Western Australia Patent Attorneys for the Applicant *oo o a* S S