WO2008144782A2

WO2008144782A2 - Fischer-tropsch gasoline process

Info

Publication number: WO2008144782A2
Application number: PCT/ZA2008/000040
Authority: WO
Inventors: Arno De Klerk
Original assignee: Sasol Technology (Pty) Ltd
Priority date: 2007-05-21
Filing date: 2008-05-20
Publication date: 2008-11-27
Also published as: WO2008144782A3

Abstract

The invention provides a Fischer-Tropsch motor-gasoline refining process which has a motor-gasoline selectivity in excess of 65% by mass based on the total motor-gasoline, jet fuel, and distillate production and a yield of motor-gasoline, jet fuel and distillate in excess of 65% of the total C2 and heavier Fischer-Tropsch syncrude product, said process including at least three of the following six conversion processes: a. cracking FT kerosene and heavier material fraction or fractions from an FT syncrude; b. oligomerising one or more of an FT syncrude fraction including hydrocarbons in the range C2 to C8, and a product from process a.; c. hydrotreating one or more of an FT syncrude fraction, a product from process b.,and an alkylated FT syncrude fraction; d. aromatizing one or more of an FT syncrude fraction, including hydrocarbons in the range C2 to C8, a product from process a., a product from process b., a product from process c., and an product from an aromatic alkylation process; e. alkylating one or more of an FT syncrude fraction including hydrocarbons in the C2 to C6 range, a product from process b., and a product from process d; and f. skeletally isomerising one or more of an FT syncrude fraction including hydrocarbons in the C4 to C6 range, a product from process a., a product from process b., a product from process c., a product from process d., and a product from process e.

Description

FISCHER-TROPSCH GASOLINE PROCESS

Field of the invention

The invention relates to a process for the production of motor-gasoline from synthetic crude produced by a Fischer-Tropsch process.

BACKGROUND OF THE INVENTION

Refineries for the production of transportation fuels, irrespective of whether they refine crude oil, Fischer-Tropsch derived synthetic crude, coal liquids, oil shales or tar sands, produce a product slate that may include a naphtha cut. Some refining processes may also result in the production of material boiling in the naphtha range (typically 20-180⁰C). The composition of the naphtha cut is dependent on the feed source and requires further refining to meet fuel specifications.

Although motor-gasoline specifications tend to be country specific, generically there is commonality between the specifications. In this respect the main challenge is to produce a motor-gasoline with high enough octane number, while not exceeding the limits imposed on specific compound classes in the composition of the fuel. Typically a motor-gasoline should have a research octane number (RON) of 95 or higher as determined by the ASTM D 2699 method and a motor octane number (MON) of 85 or higher as determined by the ASTM D2700 method. These properties need to be achieved by a naphtha range mixture that is constrained in terms of composition by a limit on the total aromatics (typically less than 35% by volume) and the benzene content specifically (typically less than 1% by volume), as well as total olefins (typically less than 18% by volume) and oxygenates (typically less than 2.7% oxygen by mass). However, on inspection of the fuel properties of compounds typically found in fuel (for example the ASTM DS 4B tables), it is clear that the compounds restricted by fuel specifications are those compounds that also happen to in general have the highest octane numbers. The only compound class that is not restricted by motor-gasoline specifications is paraffins. Yet, for a Cβ and heavier paraffin to have a better than 90 RON, it generally requires a branching ratio of 0.3 or better, where the branching ratio is defined as number of branches divided by number of carbon atoms in the molecule.

Since the paraffins in straight run naphtha from crude oil and Fischer-Tropsch derived synthetic crude on average have a branching ratio of less than 0.3, much refining effort is expended to produce motor-gasoline. This can be seen in the complex configurations of crude oil refineries that are generally required to upgrade naphtha to meet motor-gasoline specifications. A typical 1990's crude oil refinery in is of the topping-reforming-cracking-visbreaking-alkylation-isomerisation (TRCVAI) type. Furthermore, such refineries always include hydrotreating and often include etherification units too. (See for example: Wauquier, J. -P. ed., Petroleum refining Volume 1. Crude oil. Petroleum Products. Process Flowsheets. Editions Technip: Paris, 1995, p.410, 412; Jones, D.S.J. , Pujadό, P.R. eds., Handbook of petroleum processing. Springer: 2006, p.107-108; Speight, J. G., The chemistry and technology of petroleum. CRC Press: Boca Raton, 2006, p.396; Totten, G. E. ed., Fuels and lubricants handbook: Technology, properties, performance, and testing. ASTM: West Conshohocken, 2003, p.4; Bartholomew, C. H., Farrauto, R.J. Industrial catalytic processes. Wiley: Hoboken, 2006, p.637).

The refining units found in Fischer-Tropsch refineries are somewhat different to that found in crude oil refineries, since Fischer-Tropsch synthetic crude is quite different to crude oil (Prepr. Am. Chem. Soc. Div. Fuel Chem., 51 :2, 2006, 704; Proc. World Pet. Congr, 18, 2005, Johannesburg, South Africa, cdO185; Stud. Surf. Sci. Catal., 152, 2004, 482). Yet, if we have to judge by current commercial Fischer-Tropsch refinery designs used for the production of motor-gasoline, it is as complex as crude oil refineries. In addition to the already named units, olefin oligomerisation is added to the list, while visbreaking can be omitted from the list. It can further be noted that only high temperature Fischer-Tropsch technology is presently applied for the production of motor-gasoline on account of its carbon number distribution and suitability for such production (Prepr. Am. Chem. Soc. Div. Fuel Chem., 51 :2, 2006, 704). In principle synthetic crude from low temperature Fischer-Tropsch synthesis can also be refined to motor-gasoline, but this is not presently done.

In some markets, motor-gasoline is the preferred product and the need for a refinery design that maximises motor-gasoline production is beneficial. Although a "motor- gasoline only" refinery may be conceptually devised, there are limits to the yield of naphtha range material that can be obtained in practise.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a Fischer-Tropsch motor-gasoline refining process which has a motor-gasoline selectivity in excess of 65% by mass based on the total motor-gasoline, jet fuel, and distillate production and a yield of motor-gasoline, jet fuel and distillate in excess of 65% of the total C₂ and heavier Fischer-Tropsch syncrude product, said process including at least three of the following six conversion processes: a. cracking FT kerosene and heavier material fraction or fractions from an FT syncrude; b. oligomerising one or more of an FT syncrude fraction including hydrocarbons in the range C₂ to Ce, and a product from process a.; c. hydrotreating one or more of an FT syncrude fraction, a product from process b.,and an alkylated FT syncrude fraction; d. aromatizing one or more of an FT syncrude fraction, including hydrocarbons in the range C₂ to Ce, a product from process a., a product from process b., a product from process c, and an product from an aromatic alkylation process; e. alkylating one or more of an FT syncrude fraction including hydrocarbons in the C₂ to C₆ range, a product from process b., and a product from process d; and f. skeletally isomerising one or more of an FT syncrude fraction including hydrocarbons in the C₄ to C₆ range, a product from process a., a product from process b., a product from process c, a product from process d., and a product from process e. The process may include at least 4 of the 6 conversion processes.

The process may have a motor-gasoline selectivity in excess of 70% by mass based on the total motor-gasoline, jet fuel, and distillate production and a yield of motor- gasoline, jet fuel and distillate in excess of 70% of the total C₂ and heavier Fischer- Tropsch syncrude product.

Depending of the carbon number distribution of the Fischer-Tropsch syncrude and desired yield structure, conversion process a. may be omitted.

The conversion processes b. and e. may be combined where process b. is carried out using SPA catalyst.

The cracking conversion process a. may be selected to increase naphtha and kerosene yield.

The cracking conversion process a. may be selected to be a hydrocracking process.

The cracking conversion process a. may be selected to be a thermal cracking process.

The cracking conversion process a. may be selected to be an acid catalysed cracking process.

The oligomersation process b. may be selected to oligomerise the FT syncrude to naphtha range hydrocarbons in such a way that both the unhydrogenated and hydrogenated naphtha has high octane numbers.

The hydrotreating process c. is selected to remove olefins and oxygenates to produce fuel that complies with the limitations imposed on those two compound classes by the fuel specifications and/or to serve as pretreatment for conversion processes that may be adversely affected by such compounds in the feed. The aromatization process d. may be selected to produce aromatics, including benzene, to improve the octane number of the motor-gasoline and/or can be used as feed for alkylation to produce more desirably aromatic compounds.

The aromatization process d. may be selected to avoid co-production of binuclear and polynuclear aromatics that may adversely affect the fuel quality.

The alkylation process e. may be selected to increase multiple alkylation of aromatics with ethylene to produce mainly dialkylated aromatics that can be used in motor-gasoline and jet fuel, while reducing the ethylene in the product.

The alkylation process e. may be selected to reduce multiple alkylation of aromatics with olefins to maximise production of alkylaromatics in the naphtha and/or kerosene boiling range that can be used in motor-gasoline and jet fuel.

The skeletal isomerisation process f. may be selected to convert linear hydrocarbons to branched hydrocarbons with the same carbon number in high yield.

The skeletal isomerisation process f. may be selected in such a way that it is capable of isomerising a hydrocarbon feed containing olefins.

The skeletal isomerisation process f. may be selected in such a way that it is can hydroisomerise a hydrocarbon feed containing olefins.

The skeletal isomerisation process f. may be selected in such a way that it is tolerant of oxygenates in the hydrocarbon feed.

It is believed that the above may result in a refinery of reduced complexity that can produce a motor-gasoline in high yield that meets most international motor-gasoline specifications, while co-producing chemicals and/or other transportation fuels that may also meet fuel specifications such as Jet A-1 and Euro-4 fuels. Such a refinery may overcome some of the limitations imposed by straight run distillation yield and high linearity (low octane).

Depending on the selection of technology types and the ordering of the conversion units, the quantity of on specification jet fuel and quality of other products may be improved. This in itself is a further benefit of the invention, since it is flexible, it allows tailoring of the secondary products and it can accommodate different refining technology preferences. It is especially flexible with respect to additional jet fuel production.

Figure 1 shows a process for producing a high yield of motor-gasoline from Fischer- Tropsch syncrude.

The process of Figure 1 makes use of a combination of at least four of the following conversion processes: cracking (unit [a]), oligomerisation (unit [b]), hydrotreating (unit [c]), aromatisation (unit [d]), alkylation (unit [e]) and isomerisation (unit [f]).

Cracking. The first conversion unit (Figure 1 , unit [a]) is where cracking takes place to give a product that has a lower average molecular weight than the feed material. The feed may consist of material in the kerosene (stream 6), distillate (stream 7) and residue (stream 8) boiling ranges, or any combination of these feed streams that typically contain C₉ and heavier material.

No feed pre-treatment is required and the feed consists of hydrocarbons and oxygenates typical of Fischer-Tropsch syncrude. This process can be selected to be a hydrocracking process, a thermal cracking process or an acid catalysed cracking process, such as a fluid catalytic cracking process.

If a hydrocracking process is used, which is known mainly for the conversion of residue (>360°C boiling material) to distillate, the hydrocracking takes place partly under hydroisomerisation and partly under hydrocracking conditions. The catalyst used for this conversion is bifunctional, containing acid and metal sites, as is well- known in the art. Its application within the present invention operates the unit in such a way that kerosene and naphtha production is favoured, rather than distillate. For most benefit this may require operation in a way that is different from that known in the art insofar as feed composition and unit configuration is concerned.

If a thermal cracking process is used, it should preferably be operated at such a temperature that is high enough to reduce thermal oligomerisation to products heavier boiling than kerosene (typically >400°C). Such a process requires no catalyst and has some advantages in removal of metal carboxylate species as is known in the art. A further benefit from a thermal cracking process is the production of olefins that can be combined with the straight run Fischer-Tropsch cuts of similar boiling range and may be separated in the same separation units.

If a catalytic cracking process is used, it should be selected and operated in such a way that naphtha and kerosene production is maximised. Such a conversion can be performed in a process such as fluid catalytic cracking. Acid catalysts and additives can be selected to achieve this goal as is known in the art. A benefit of acid catalysed cracking is that the product may be rich in olefins and aromatics that may be co-processed along similar pathways as the Fischer-Tropsch straight run feed.

Oligomerisation. Olefin oligomerisation is the second conversion unit (Figure 1 , unit [b]) and is known in the art for the conversion of olefinic material to products that are heavier than the feed. The olefin may be selected from a straight run Fischer- Tropsch product, the preferred being in the C₃-C₄ range (streams 2-3), or olefins produced by a conversion process, such as cracking (stream 15a). The choice of oligomerisation catalyst has a significant impact on the product distribution and properties. In this invention the preferred embodiment is an olefin oligomerisation process based on solid phosphoric acid (SPA) catalysis, due to the quality of the hydrogenated product from butene oligomerisation, the quality of the olefinic motor- gasoline in general and product distribution that is limited to naphtha and kerosene range material. Other acid catalysts may also be used and the invention is not limited or restricted to SPA, although it is known in the art that the other acid catalyst types yield poorer quality motor-gasoline. Feed pre-treatment is not necessarily required, although the inherent limitations of the selected catalyst should be borne in mind. The conversion step has three main products, namely light hydrocarbons, typically liquid petroleum gas range hydrocarbons (stream 10a), motor-gasoline range products, typically rich in olefin oligomers (stream 10b) and kerosene / distillate range products (stream 10c). In the case of SPA stream 10c typically consists of only kerosene range material. Other aspects of this conversion process as taught in the art, such as heat management by paraffin recycle, are implied.

Hydrotreating. The third conversion unit (Figure 1 , unit [c]) is a hydrotreater that is used to increase the storage stability of the products and to meet olefin and oxygenate related specifications such as the bromine and acid number. It is also used to provide some feed pre-treatment for processes such as aromatisation (Figure 1, unit [d]) if it is required by the aromatisation technology that has been selected. The catalyst used is a metal promoted hydrotreating catalyst as known in the art. Its use in the present invention is not different from that described in the art. The feed may be straight run Fischer-Tropsch material in the range C₆-C₂₂ (streams 5-7) or products from conversion processes, such as olefin oligomerisation (stream 10c). The products are the saturated analogues of the feed and the process is preferably operated in such a way that little hydrodearomatisation takes place. Other aspects of this conversion process as taught in the art, such as hydrogen co-feeding, are implied. The kerosene product from hydrotreating the products from olefin oligomerisation (stream 14b) is also known as iso-paraffinic kerosene (IPK), which is known in the art as an excellent component for jet fuel.

Aromatisation. The fourth conversion unit is aromatisation (Figure 1 , unit [d]). This process produces the aromatics needed to meet octane specifications for motor- gasoline, the aromatics needed to meet aromatics and density specification of jet fuel and to provide hydrogen to the hydrogen consuming processes detailed in this invention. The latter use is less important, since hydrogen is also available from the Fischer-Tropsch gas loop. The composition of feed to this unit is determined by the technology selection, with two main types of technology being distinguished. The first type of aromatisation process is naphtha aromatisation, which requires a feed in the naphtha range (Cβ and heavier). A preferred embodiment of this invention uses a non-acidic Pt/L zeolite based aromatisation process, which is a type of naphtha aromatisation excellently suited to the conversion of Fischer-Tropsch material. It is also possible to use standard catalytic reforming process, which is based on platinum promoted chlorided alumina catalysts, but it is less efficient in the present application. This can be understood in terms of the feed properties, with a non-acidic Pt/L-zeolite process preferring linear hydrocarbons (Fischer-Tropsch syncrude is rich in linear hydrocarbons), while a Pt-alumina process prefers naphthenic (cyclo-paraffin) rich feed. In both instances the feed has to be pretreated to remove heteroatoms, which can be done by hydrotreating (Figure 1 , unit [c]).

The second type of aromatisation process is light hydrocarbon aromatisation, which can convert a feed consisting of C₃ and heavier hydrocarbons. This type of aromatisation process is based on metal promoted H-ZSM-5 zeolite catalysts, with the metals Ga and Zn being most often used. This conversion can also be achieved with an unpromoted H-ZSM-5 catalyst, but it is not a preferred embodiment, since the metal is required for hydrogen desorption as molecular hydrogen. The ZSM-5 based processes are more tolerant to heteroatom compounds in the feed, such as oxygenates and the feed can be used without prior hydrotreating. However, it is known in the art that oxygenates are detrimental to catalyst lifetime.

The type of aromatisation process not only determines the feed requirements, but also the yield structure, which is different for the difference processes. In a naphtha aromatisation process any C5 and lighter hydrocarbons formed during the process can be considered fatal conversion to such products, since it cannot be converted to aromatics by recycling. Conversely, in a light hydrocarbon aromatisation process the

C₃ and heavier hydrocarbons can be recycled to improve aromatics yield. Despite differences such as these, three main product fractions are produced during aromatisation, namely light gas, typically hydrogen and C₁-C₂ hydrocarbons ( stream

13b), gas and light naphtha, typically C3-C6 hydrocarbons (stream 13c) and aromatics rich naphtha, typically C₆ and heavier aromatics and C₇ and heavier hydrocarbons (streams 13a and 13d). Other feed and product streams as known from the art are implied.

The light gas (stream 13b) is a hydrogen rich product. This is an excellent source of hydrogen and the hydrogen can be recovered by processes known in the art, such as pressure swing absorption. Depending on the process and yield structure, this may provide sufficient hydrogen for hydrotreating (Figure 1, unit [c]) and cracking, if hydrocracking is selected as process (Figure 1, unit [a]). Excess hydrogen can be exported to the Fischer-Tropsch gas loop to increase syncrude yield. The hydrogen lean gas can be used as fuel gas, or used as feed to synthesis gas production, depending on the nature of the Fischer-Tropsch technology.

Alkylation. The fifth conversion unit is an aromatic alkylation process (Figure 1 , unit [e]). This unit is mainly used to convert benzene and ethylene to useful products in the motor-gasoline and kerosene boiling range. By doing so, two shortcomings are overcome, namely the refining of ethylene to good quality fuel, which is generally difficult to accomplish and the reduction of the benzene content in the motor- gasoline, which is limited by fuel specifications. The preferred feed to this unit is therefore Fischer-Tropsch derived C2's (stream 1) and benzene from aromatisation (stream 13a). However, the present invention is not limited to this preferred embodiment. The composition of the olefinic and aromatic feed components, as well as the type and operation of the alkylation process may be selected to suite the refining requirements and to maximise the production of kerosene range aromatics. In one possible embodiment of this invention, the olefin oligomerisation (Figure 1 , unit [b]) and aromatic alkylation (Figure 1 , unit [e]) processes may be combined as a single process. The catalyst may be that taught in the art.

Isomeήsation. The sixth conversion unit is a skeletal isomerisation process (Figure 1 , unit [f]). This conversion is used mainly to improve the octane number of the C₅-

C₆ paraffinic motor-gasoline fraction. Various processes employing different catalysts, separation and recycling strategies are known in the art. The preferred embodiment for the present invention is a process based on a platinum promoted mordenite catalyst with complete recycle of the linear paraffins. The catalyst is less sensitive to oxygenates in the feed than most other catalyst types used for this process and does not require feed pre-treatment with oxygenate containing Fischer- Tropsch feed. Depending on the overall quality of the motor-gasoline produced by the other conversion processes, this unit may not be necessary and it is not considered critical to the present invention.

The detailed description which follows forms an integral part of the disclosure of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described, by way of non-limiting examples only, with reference to the accompanying representations. In the representations,

EXAMPLES

The following examples illustrate the present invention, although it should not be construed as limiting the invention in any way. The upgrading of the Fischer-

Tropsch syncrude is considered in terms of different boiling ranges or syncrude fractions. For the example given, the fractions considered are streams containing: mainly C₂ hydrocarbons (stream 1), mainly C₃ hydrocarbons (stream 2), mainly C₄ hydrocarbons (stream 3), mainly C₅ hydrocarbons (stream 4), a 40-130⁰C boiling range cut that contains mainly Cε-Cβ hydrocarbons (stream 5), a 130-180⁰C boiling range cut that contains mainly C₉-Ci₀ hydrocarbons (stream 6), a 180-360°C boiling range cut that contains mainly C₁₁-C₂₂ hydrocarbons (stream 7) and a residue cut containing material boiling above 360⁰C containing mainly heavier than C₂₂ hydrocarbons (stream 8). The separation of the syncrude in these fractions can be done by ways known in the art. It will also be noted that not all examples require pre-fractionation of the syncrude to produce all of these fractions. Example 1.

A process is shown in Figure 2 for the conversion of high temperature Fischer- Tropsch syncrude with properties similar to that of the syncrude from the commercial Sasol and PetroSA operations in South Africa. The aim of this example is to show how much unleaded 95 RON / 85 MON motor-gasoline can be produced without residue conversion.

The process in this example does not include a cracker (unit [a]).

The oligomerisation process of unit [b] is based on a process using a solid phosphoric acid (SPA) catalyst. The C₃ hydrocarbons (stream 2) and C₄ hydrocarbons (stream 3) are not mixed, but converted separately. This is a requirement, since it is known in the art that butene rich feed and especially Fischer- Tropsch derived 1 -butene rich feed can be converted on SPA to oligomers with high hydrogenated octane numbers. It is also known in the art that propene rich feed can be converted on SPA to oligomers that have high unhydrogenated octane numbers. The naphtha range product from C₃ oligomerisation is used as olefinic motor- gasoline component (stream 10b), while the unconverted propane rich gas is used as liquid petroleum gas (stream 10a). The kerosene range material from C₃ oligomerisation is combined with the total product from C₄ oligomerisation to be hydrogenated (stream 10c).

In the hydrogenation process of unit [c] the product from oligomerisation (stream 10c) is hydrotreated separately from the straight run Fischer-Tropsch C₆-C₂₂ feed

(streams 5-7). In this example it is not necessary to pre-fractionate the C6-C22 feed, since the combined feed is hydrotreated before fractionation. The hydrogenated product from olefin oligomerisation is fractionated in motor-gasoline (stream 14a) and jet fuel (stream 14bj), while the hydrogenated product from Fischer-Tropsch syncrude is fractionated in C₆-C₈ material (stream 12), jet fuel (stream 14bπ) and distillate (stream 14c). The aromatisation process of unit [d] is based on a non-acidic platinum promoted L- zeolite and takes a C₆-C₈ feed from the hydrotreater (stream 12). The product from aromatisation is rich in aromatics and hydrogen. A benzene-rich fraction (stream 13a) serves as feed to the alkylation unit [e]. The light gas (stream 13b) is used as source of hydrogen for the refinery, which can be recovered by processes known in the art. The light paraffins, mainly C3-C₄ (stream 13c) can be used as liquid petroleum gas, but may also be blended into the motor-gasoline up to the vapour pressure limit. The naphtha range product (stream 13d) is rich in aromatics and is used as high octane motor-gasoline component.

The alkylation process of unit [e] alkylates the benzene (stream 13a) with ethylene (stream 1). It is used not only to produce high-octane aromatics and kerosene range aromatics for jet fuel, but also serves as refinery benzene reduction strategy. The process uses a zeolite catalyst, such as H-ZSM-22, but differs from standard commercial practice for the production of ethyl benzene in that the mono-alkylated benzene is recycled with the benzene to increase the yield of diethyl benzene. The product containing mainly diethylbenzene can be used as either a high-octane motor-gasoline component (stream 9b) or a jet fuel component (stream 9c) depending on blending requirements. The light gas, which is ethane-rich (stream 9a) can be used as fuel gas.

The skeletal isomerisation unit [f] is preferably based on a process using water- tolerant platinum promoted mordenite catalyst. Since the conversion of the C₅ hydrocarbon feed (stream 4) is equilibrium limited, it is operated with a separation step to recycle the linear C₅ hydrocarbons to extinction. The product, which is rich in iso-pentane (stream 11), is used as motor-gasoline component.

This refinery design yielded a naphtha: kerosene:distillate split of 73:17:10, with the naphtha cut meeting specifications for unleaded 95 RON / 85 MON motor-gasoline and the kerosene cut meeting specifications for fully synthetic Jet A1 (Table 1). A summary of the streams considered are given (Table 2) and are reported on a total Fischer-Tropsch syncrude basis of 500 000 kg/h (excluding water gas shift gases). The yield of naphtha, kerosene and distillate on C₂ and heavier hydrocarbon and oxygenated hydrocarbon products entering the refinery, is 75% by mass. The refinery design presented in this example does not show processing of the Fischer- Tropsch C₂₂+ hydrocarbons or oxygenates dissolved in the aqueous product from Fischer-Tropsch synthesis. The C₂₂+ hydrocarbons can be used as fuel oil, while chemicals such as ethanol, acetone, isopropanol, n-propanol and methyl ethyl ketone can be recovered from the aqueous product by processes known in the art. The C₂ and heavier oxygenates can also be converted to olefins and processed with the other FT C₂-C₅ feed materials to increased the yield of naphtha on the same Fischer-Tropsch feed basis.

Table 1. Calculated motor-gasoline and jet fuel properties for example 1 , as shown in figure 2.

Property Example 1 Specifications

Motor-gasoline Euro-4

RON 96 95 minimum

MON 89 85 minimum

Vapour pressure 49 60 maximum

(kPa)

Density (kg/m3) 741 720-775 range

Olefins (vol%) 18 18 maximum

Aromatics (vol%) 31 35 maximum

Oxygenates (vol%) 0 15 maximum

Benzene (vol%) 0.3 1 maximum

Jet fuel Jet A-1

Density (kg/m3) 775 775-840 range

Aromatics (vol%) 15 8-25 range

Naphthalene (vol %) <1 3 maximum

Sulphur (mass %) <0.001 0.3 maximum

Table 2. Summary of streams shown in figure 2 of example 1.

Stream Description From To Flow (kg/h)

(#c1) H2 H2 [C] 3704 (#c2) Waste/H2O [C] Waste 1738 (#f1) H2 H2 [f] 1151

(1) FT C2's HTFT [e] 50348 (2) FT C3's HTFT [b] 65462 (3) FT C4"s HTFT [b] 55603 (4) FT C5's HTFT [f] 46277 (5) FT C6-C8's HTFT [C] 94916 (6) FT C9-C10's HTFT [C] 22345 (7) FT C11-C22's HTFT [C] 35297

(8) FT C22+ HTFT Fuel oil 14681

(9a) Fuel gas [e] Fuel gas 24641

(9b) Naphtha [e] Tank 52984

(9c) Kero [e] Tank 9743

(10a) LPG [b] Tank 9102

(10b) Olefinic petrol [b] Tank 39910

(10c) SPA oligomers [b] [C] 72053

(11) iso-C5 [f\ Tank 47428

(12) Hydr. C6-C8 [C] [d] 95620

(13a) Benzene [d] [e] 37020

(13b) H2-rich gas [d] H2 recovery 10834

(13c) LPG [d] Tank 5527

(13d) Aromatic-rich [d] Tank 42239

(14a) Naphtha [C] Tank 47581

(14bi) SPA kero [C] Tank 25544

(14bϋ) FT kero [C] Tank 22453

(14c) FT distillate [C] Tank 35379

Example 2.

The process of Figure 3 in this example is similar in feed composition to that of Example 1 , but additionally includes olefins derived from the oxygenates dissolved in the Fischer-Tropsch aqueous product. These olefins are produced from the oxygenates by methods know in the art, such as partial hydrogenation followed by dehydration. The ethanol in this stream is similarly recovered for use as fuel ethanol. The inclusion of the products from the Fischer-Tropsch aqueous product improves the overall refinery efficiency, but should not be seen as an integral part of the present invention. The aim of this example is to show that it is possible to make final products that meet fuel specifications, and specifically produce motor-gasoline in high yield, with the configuration proposed in this invention.

The cracking process of unit [a] is a hydrocracking process and takes its feed from the FT Cg and heavier material (streams 6-8). The feed is hydroisomerised and hydrocracked to produce products separated into different boiling fractions and consisting mainly of propane (stream 15a), C₄-C5 hydrocarbons (stream 15bj), Cδ-Cβ hydrocarbons (stream 15bπ), kerosene (stream 15c) and heavier material that is recycled to extinction. The C₄-C₅ hydrocarbons are directly blended into the motor- gasoline, while the C₆-C₈ hydrocarbons are used as feed to the aromatisation unit [d]. The kerosene range material is used as a jet fuel component.

The oligomerisation process of unit [b] uses a solid phosphoric acid (SPA) catalyst and is configured similarly to that of Example 1. The C₃ hydrocarbons (stream 2) are co-processes with the C₃ and heavier olefins from the Fischer-Tropsch aqueous product work-up (stream 16), while the C₄ hydrocarbons (stream 3) is converted separately. The unconverted propane rich gas is used as liquid petroleum gas (stream 10a). The naphtha range product from C₃ oligomerisation is mainly used as olefinic motor-gasoline component (stream 10b), although not all material can be included in the motor-gasoline due to the specification limit on olefins in motor- gasoline. The remainder of the naphtha and kerosene range material from C₃ oligomerisation is combined with the total product from C₄ oligomerisation to be hydrogenated (stream 10c).

In hydrogenation process of unit [c], the product from oligomerisation (stream 10c) is hydrotreated separately from the straight run Fischer-Tropsch C₆-C₈ feed (streams 5). The hydrotreater is therefore only a feed pre-treatment step for the latter ( stream 12), which can also be done in the hydrocracker, albeit with some yield loss. The hydrogenated product from olefin oligomerisation is fractionated in motor-gasoline ( stream 14a) and jet fuel (stream 14b).

The aromatisation process of unit [d] is similar to that of Example 1, but in this example the hydrocracker derived C₆-C₈ material (stream 15bϋ) is combined with the hydrotreated C₆-C₈ Fischer-Tropsch feed (stream 12). The product from aromatisation is rich in aromatics and hydrogen. A benzene-rich fraction (stream

13a) serves as feed to the alkylation unit [e]. The light gas (stream 13b) is used as source of hydrogen for the refinery, which can be recovered by processes known in the art. The light paraffins, mainly C₃-C₄ (stream 13c) can be used as liquid petroleum gas, but may also be blended into the motor-gasoline up to the vapour pressure limit. The naphtha range product (stream 13d) is rich in aromatics and is used as high-octane motor-gasoline component.

The feeds to and products from the aromatic alkylation unit [e] and skeletal isomerisation unit [f] are the same as in Example 1.

The refinery design in this example produced naphtha and kerosene in a ratio of 71 :29. The naphtha cut meets specifications for unleaded 95 RON / 85 MON motor- gasoline and the kerosene cut meets specifications for fully synthetic Jet A1 (Table 3). A summary of the streams considered are given (Table 4) and are reported on a total Fischer-Tropsch syncrude basis of 500 000 kg/h (excluding water gas shift gases). The yield of naphtha, kerosene and distillate on C₂ and heavier hydrocarbon and oxygenated hydrocarbon products entering the refinery, is 85% by mass.

Table 3. Calculated motor-gasoline and jet fuel properties for products from example 2, as shown in figure 3.

Property Example 1 Specifications

Motor-gasoline Euro-4

RON 96 95 minimum

MON 89 85 minimum

Vapour pressure 58 60 maximum

(kPa)

Density (kg/m3) 737 720-775 range

Olefins (vol%) 18 18 maximum

Aromatics (vol%) 26 35 maximum

Oxygenates (vol%) 6 15 maximum

Benzene (vol%) 0.3 1 maximum

Jet fuel Jet A-1

Density (kg/m3) 775 775-840 range

Aromatics (vol%) 22 8-25 range

Naphthalene (vol %) <1 3 maximum

Sulphur (mass %) <0.001 0.3 maximum

Table 4. Summary of streams shown in figure 3 of example 2.

Stream Description From To Flow (kg/h)

(#a1) H2 H2 [a] 1116

(#a2) Waste/H2O [a] Waste 1821

(#c1) H2 H2 [C] 3288

(#c2) Waste/H2O [C] Waste 1337

(#f1) H2 H2 [f] 1151 (1) FT C2's HTFT [e] 50349

(2) FT C3's HTFT [b] 65462

(3) FT C4's HTFT [b] 55604

(4) FT C5's HTFT [f] 46277

(5) FT C6-C8"s HTFT [C] 94916

(6) FT C9-C10's HTFT [C] 25586

(7) FT C11-C22's HTFT [C] 35297

(8) FT C22+ HTFT [a] 14681

(9a) Fuel gas [e] Fuel gas 22784

(9b) Naphtha [e] Tank 46366

(9c) Kero [e] Tank 20894

(10a) LPG [b] Tank 9260

(10b) Olefinic petrol [b] Tank 44740

(10c) SPA oligomers [b] [C] 82814

(11) iso-C5 [f] Tank 47428

(12) Hydr. C6-C8 [C] [d] 95619

(13a) Benzene [d] [e] 39695

(13b) H2-rich gas [d] H2 recovery 11521

(13c) LPG [d] Tank 5743

(13d) Aromatic-rich [d] Tank 46065

(14a) Naphtha [C] Tank 53791

(14b) SPA kero [C] Tank 30271

(15a) LPG [a] Tank 1234

(15b,) C4/5 naphtha [a] Tank 4936

(15bϋ) C6-C8 [a] [d] 7405

(15c) Kero [a] Tank 61284

(16) FT aq. workup HTFT [b] 15748

Example 3

A refinery design to convert syncrude from a low temperature Fischer-Tropsch process into mainly motor-gasoline and jet fuel is presented in Figure 4. The light alcohols are recovered from the Fischer-Tropsch aqueous product and used as oxygenated fuel for motor-gasoline. Contrary to commercial LTFT based refineries, this design does not include a hydrocracker, but a catalytic cracker. The aim of this example is to show how the same basic refinery design can be used to convert LTFT syncrude to motor-gasoline that meets fuel specifications, unlike present commercial refinery designs that rely of the sale of the naphtha fraction as naphtha.

The cracking process (Figure 4, unit [a]) is a fluid catalytic cracking process that converts all the Cg and heavier syncrude to gas and liquids boiling mainly in the naphtha and kerosene ranges. Typical products and yields have been described in the open literature, for example lnd Eng Chem Prod Res Dev 24 (1985) 501 and Appl. Catal. B 63 (2006) 277. The C₂ and lighter gas is used as fuel gas, while the C₃-C₄ olefin rich fractions are fractionated into their respective carbon number cuts. The C₃ cut (Figure 4 stream 15aj) is used for benzene alkylation (Figure 4, unit [e]) and the C₄ cut (Figure 4 stream 15aπ) is used for oligomerisation (Figure 3, unit [b]). The C₅-C₆ naphtha (Figure 4, stream 15bj) is hydroisomerised (Figure 4, unit [f]) and the C₆-C₈ naphtha (Figure 4, stream 15bϋ) is used as feed to the aromatisation unit (Figure 4, unit [d]). The cut-point between the latter two streams is determined by the propylene availability in the refinery to alkylate the benzene from C₆ naphtha aromatisation. The Cg and heavier kerosene range material (Figure 4, stream 15c) is hydrogenated (Figure 4, unit [c]) and used as jet fuel.

The oligomerisation process (Figure 4, unit [b]) is based on a SPA catalyst and is used to convert the C₄-rich FCC derived cracker gas (Figure 4, stream 15aπ) and a

C₄-HCh LTFT stream into a naphtha and kerosene range product. The negative impact that propylene has on the octane number of the product (Figure 4, stream

10b) after hydrogenation (Figure 4, unit [c]) is offset by the high isobutene content in the FCC derived feed. The butane-rich LPG product is partly used as LPG and partly blended into the motor-gasoline up to the vapour pressure limit.

The LTFT C₆-Cs naphtha (Figure 4, stream 5), oligomerisation product (Figure 4, stream 10b) and C₆ and heavier FCC product (Figure 4, streams 15bϋ and 15c) are hydrogenated (Figure 4, unit [c]) as feed pre-treatment for aromatisation (Figure 4, stream 12) and to produce motor-gasoline (Figure 4, stream 14a) and jet fuel (Figure 4, stream 14b) as final products.

The aromatisation unit (Figure 4, unit [d]) is based on platinum promoted non-acidic L-zeolite technology. The process takes its feed from the hydrogenated C₆-Ce LTFT syncrude and FCC cuts (Figure 4, stream 12). This is converted to an aromatics and hydrogen rich product. The benzene-rich fraction (Figure 4, stream 13a) serves as feed to the alkylation unit (Figure 4, unit [e]). The hydrogen-rich gas (Figure 4, stream 13b) is used as source of refinery hydrogen after hydrogen recovery in an appropriate separation step, such as pressure swing absorption. The LPG (Figure 4, stream 13c) is a final product and the aromatic-rich naphtha (Figure 4, stream 13d) is used as motor-gasoline component.

The benzene-rich product from aromatisation (Figure 4, stream 13a) is alkylated with the combined C₃ cuts from LTFT (Figure 4, stream 2) and FCC (Figure 4, stream 15a,) in an aromatic alkylation process (Figure 4, unit [e]). This process uses a SPA catalyst to produce mainly cumene. The products from the process are LPG (Figure 4, stream 9a), motor-gasoline (Figure 4, stream 9b) and jet fuel (Figure 4, stream 9c).

A hydroisomerisation process (Figure 4, unit [f]) is used to hydrotreat and isomerise the LTFT C₅ naphtha (Figure 4, stream 4) and FCC C₅-C₆ naphtha fraction (Figure 4, stream 15bj) to improve its octane number. This is an optional unit in the present refinery design, since the motor-gasoline is long in octane and olefins. The isomerate (Figure 4, stream 11) is blended into the motor-gasoline.

The design in this example produces motor-gasoline and jet fuel in a 75:25 ratio. Both the motor-gasoline and jet fuel meets fuel specifications (Table 5). The motor- gasoline properties were calculated for the mixture after splash blending with the methanol/ethanol recovered from the Fischer-Tropsch aqueous product. The streams considered are given (Table 6) and are reported on a total Fischer-Tropsch syncrude basis of 500 000 kg/h (excluding water gas shift gases). The yield of naphtha, kerosene and distillate on C₂ and heavier hydrocarbon and oxygenated hydrocarbon products entering the refinery, is 85% by mass.

Table 5. Calculated motor-gasoline and jet fuel properties for products from example 3, as shown in figure 4.

Property Example 3 Specifications

Motor-gasoline Euro-4

RON 99 95 minimum

MON 91 85 minimum

Vapour pressure 60 60 maximum

(kPa)

Density (kg/m3) 744 720-775 range

Olefins (vol%) 1 18 maximum

Aromatics (vol%) 34 35 maximum

Oxygenates (vol%) 4 15 maximum

Benzene (vol%) 0.2 1 maximum

Jet fuel Jet A-1

Density (kg/m3) 776 775-840 range

Aromatics (vol%) 21 8-25 range

Naphthalene (vol %) <1 3 maximum

Sulphur (mass %) <0.001 0.3 maximum

Table 6. Summary of streams shown in figure 4 of example 3.

Stream Description From To Flow (kg/h)

(#a2ι) Fuel gas [a] Fuel gas 3424

(#a2_H) Coke [a] Energy 1454 '

(#c1) H2 H2 [C] 4798

(#c2) Waste/H2O [C] Waste 1127

(#e1) Heavies [e] Waste 280

(#f1) H2 H2 [f\ 2352

(2) FT C3's LTFT [e] 11090

(3) FT C3-C4's LTFT [b] 27981

(4) FT C5"s LTFT [f] 12532

(5) FT C6-C8's LTFT [C] 32206

(6) FT C9-C10's LTFT [C] 16958

(7) FT C11-C22's LTFT [C] 97386

(8) FT C22+ LTFT [a] 249160

(9a) LPG [e] Tank 4925

(9b) Naphtha [e] Tank 60273

(9c) Kero [e] Tank 20379

(10a) LPG [b] Tank 7568

(10b) SPA oligomers [b] [C] 50089

(11) lsomerate [f\ Tank 108459

(12) Hydr. C6-C8 [C] [d] 166154

(13a) Benzene [d] [e] 50797

(13b) H2-rich gas [d] H2 recovery 17071

(13c) LPG [d] Tank 7157

(13d) Aromatic-rich [d] Tank 91129

(14a) Naphtha [C] Tank 42500

(14b) SPA kero [C] Tank 88717

(15aj) C3-rich [a] [e] 23970

(15aϋ) C4-rich [a] [b] 29676

(15bO C5/6 naphtha [a] [f\ 93575

(15bϋ) C6-C8 [a] [C] 132028

(15c) Kero [a] [C] 79377

Claims

1. A Fischer-Tropsch motor-gasoline refining process which has a motor- gasoline selectivity in excess of 65% by mass based on the total motor-gasoline, jet fuel, and distillate production and a yield of motor-gasoline, jet fuel and distillate in excess of 65% of the total C₂ and heavier Fischer-Tropsch syncrude product, said process including at least three of the following six conversion processes: a. cracking FT kerosene and heavier material fraction or fractions from an FT syncrude; b. oligomerising one or more of an FT syncrude fraction including hydrocarbons in the range C₂ to Ce, and a product from process a.; c. hydrotreating one or more of an FT syncrude fraction, a product from process b.,and an alkylated FT syncrude fraction; d. aromatizing one or more of an FT syncrude fraction, including hydrocarbons in the range C₂ to Cs, a product from process a., a product from process b., a product from process c, and a product from an aromatic alkylation process; e. alkylating one or more of an FT syncrude fraction including hydrocarbons in the C₂ to CQ range, a product from process b., and a product from process d; and f. skeletally isomerising one or more of an FT syncrude fraction including hydrocarbons in the C₄ to Ce range, a product from process a., a product from process b., a product from process c, a product from process d., and a product from process e.

2. A process as claimed in claim 1 , which includes at least 4 of the 6 conversion processes.

3. A process as claimed in claim 1 or claim 2, which has a motor-gasoline selectivity in excess of 70% by mass based on the total motor-gasoline, jet fuel, and distillate production and a yield of motor-gasoline, jet fuel and distillate in excess of 70% of the total C₂ and heavier Fischer-Tropsch syncrude product.

4. A process as claimed in any one of the preceding claims, wherein depending on the carbon number distribution of the Fischer-Tropsch syncrude and desired yield structure, conversion process a. is omitted.

5. A process as claimed in any one of the preceding claims, wherein the conversion processes b. and e. are combined when process b. is carried out using solid phosphoric acid (SPA) catalyst.

6. A process as claimed in any one of claims 1 to 3, wherein the cracking conversion process a. is selected from a hydrocracking process, a thermal cracking process, and an acid catalysed cracking process.

7. A process as claimed in any one of the preceding claims, wherein the oligomersation process b. is selected to oligomerise the FT syncrude to naphtha range hydrocarbons so that both the unhydrogenated and hydrogenated naphtha has high octane numbers.

8. A process as claimed in any one of the preceding claims, wherein the hydrotreating process c. is selected to remove olefins and oxygenates to produce fuel that complies with the limitations imposed on those two compound classes by the fuel specifications and/or to serve as pretreatment for conversion processes that are adversely affected by such compounds in the feed.

9. A process as claimed in any one of the preceding claims, wherein the aromatization process d. is selected to produce aromatics, including benzene, to improve the octane number of the motor-gasoline and/or is used as feed for alkylation to produce more desirable aromatic compounds and/or to avoid co- production of binuclear and polynuclear aromatics that may adversely affect the fuel quality.

10. A process as claimed in any one of the preceding claims, wherein the alkylation process e. is selected to increase multiple alkylation of aromatics with ethylene to produce mainly dialkylated aromatics that are used in motor-gasoline and jet fuel, while reducing the ethylene in the product or is selected to reduce multiple alkylation of aromatics with olefins to maximise production of alkylaromatics in the naphtha and/or kerosene boiling range that is used in motor-gasoline and jet fuel.

11. A process as claimed in any one of the preceding claims, wherein the skeletal isomerisation process f. is selected to convert linear hydrocarbons to branched hydrocarbons with the same carbon number in high yield, to be capable of isomerising a hydrocarbon feed containing olefins, to be capable of hydroisomerising a hydrocarbon feed containing olefins, and/or to be tolerant of oxygenates in the hydrocarbon feed.