Production of oilfield hydrocarbons

Abstract

A process (20) to produce olefinic products suitable for use as or conversion to oilfield hydrocarbons includes separating (42) an olefins-containing Fischer-Tropsch condensate (64) into a light fraction (68), an intermediate fraction (82) and a heavy fraction (94), oligomerizing (44) at least a portion of the light fraction (68) to produce a first olefinic product (72) which includes branched internal olefins, and carrying out either one or both of the steps of (i) dehydrogenating (50) at least a portion of the intermediate fraction (82) to produce an intermediate product (84) which includes internal olefins and alpha-olefins, and synthesizing (52) higher olefins from the intermediate product which includes internal olefins and alpha-olefins to produce a second olefinic product (86), and (ii) dimerizing (52) at least a portion of the intermediate fraction to produce a second olefinic product (86). At least a portion of the heavy fraction (94) is dehydrogenated (58) to produce a third olefinic product (96) which includes internal olefins. Also provided is a process (30) to produce paraffinic products suitable for use as or conversion to oilfield hydrocarbons which includes separating (110) a Fischer-Tropsch wax (124) into at least a lighter fraction (126, 128) and a heavier fraction (130), hydrocracking (120) the heavier fraction (130) to provide a cracked intermediate (144), and separating (122) the cracked intermediate (144) into at least a naphtha fraction (148), a heavier than naphtha paraffinic distillate fraction (150) suitable for use as or conversion to oilfield hydrocarbons, and a bottoms fraction (152) which is heavier than the paraffinic distillate fraction (150).

Claims

1. A process to produce olefinic products in the carbon range C.sub.16-C.sub.30 suitable for use as or conversion to oilfield hydrocarbons, the process comprising: separating an olefins-containing Fischer-Tropsch condensate into a light fraction which is a C.sub.5-C.sub.7 fraction, an intermediate fraction which is a C.sub.8-C.sub.15 fraction which includes paraffins and alpha-olefins and a heavy fraction which is a C.sub.16-C.sub.22 fraction which includes paraffins and alpha-olefins; oligomerising at least a portion of the light fraction using a zeolitic catalyst to produce a first olefinic product which includes branched internal olefins; carrying out either one or both of the steps of: (i) dehydrogenating at least a portion of the intermediate fraction to convert the paraffins to internal olefins thereby to produce an intermediate product which includes internal olefins and alpha-olefins, and synthesising higher olefins, by means of dimerisation or olefin metathesis, from the intermediate product which includes internal olefins and alpha-olefins to produce a second olefinic product; and (ii) dimerising at least a portion of the intermediate fraction to produce a second olefinic product; and dehydrogenating at least a portion of the heavy fraction to convert the paraffins to internal olefins thereby to produce a third olefinic product which includes internal olefins, the first olefinic product and the second olefinic product being such that a combination of the first olefinic product and the second olefinic product provides an olefinic product with at least 50% by mass of hydrocarbons having carbon chain lengths of between 15 and 30 carbon atoms per molecule.

2. The process according to claim 1, in which the olefins-containing Fischer-Tropsch condensate is a C.sub.5-C.sub.22 Fischer-Tropsch condensate product or stream.

3. The process according to claim 1, in which at least 95% by mass of molecules making up the light fraction boils between ?30? C. and 100? C.

4. The process according to claim 1, in which at least 95% by mass of molecules making up the intermediate fraction boils between 110? C. and 270? C.

5. The process according to claim 1, in which at least 95% by mass of molecules making up the heavy fraction boils between 280? C. and 370? C.

6. The process according to claim 1, which includes combining a C.sub.3 and/or C.sub.4 fraction which is gaseous under ambient conditions with the light fraction prior to oligomerising the light fraction.

7. The process according to claim 1, in which said first olefinic product obtained from the oligomerisation of at least a portion of the light fraction includes branched internal olefins in the range of C.sub.9-C.sub.22, the process further comprising fractionating the first olefinic product into a C.sub.9-C.sub.15 fraction and a C.sub.15.sup.+ fraction.

8. The process according to claim 7, in which the C.sub.9-C.sub.15 fraction is converted in an aromatic alkylation unit to produce branched di-alkylates, or when the intermediate fraction is subjected to the dehydrogenation and higher olefin synthesis step (i), the C.sub.9-C.sub.15 fraction is combined with the intermediate product which includes internal and alpha-olefins resulting from the dehydrogenation of the intermediate fraction, and is synthesised into higher olefins as part of the intermediate product thereby to form part of the second olefinic product.

9. The process according to claim 7, in which, when the intermediate fraction is subjected to the dimerisation step (ii), the C.sub.9-C.sub.15 fraction is combined with the intermediate fraction so that it is also subjected to dimerisation and hence forms part of the second olefinic product.

10. The process according to claim 1, in which the second olefinic product is a C.sub.16-C.sub.30 mixture of vinylidenes and/or internal olefins.

11. The process according to claim 1, in which a combination of the first olefinic product and the second olefinic product provides an olefinic product with at least 90% by mass of hydrocarbons having carbon chain lengths of between 15 and 30 carbon atoms per molecule and having at least 0.5 branches per molecule on average.

12. The process according to claim 1, which comprises using the second olefinic product to alkylate aromatics, or which comprises hydroformylating and alkoxylating the second olefinic product to produce linear and branched oilfield hydrocarbon pre-cursor molecules.

13. The process according to claim 1, which comprises using the third olefinic product to alkylate aromatics, or which comprises hydroformylating and alkoxylating the third olefinic product to produce linear and branched oilfield hydrocarbon pre-cursor molecules.

14. The process according to claim 7, which comprises using the C.sub.15.sup.+ fraction from the first olefinic product to alkylate aromatics, or which comprises hydroformylating and alkoxylating the C.sub.15.sup.+ fraction from the first olefinic product to produce linear and branched oilfield hydrocarbon pre-cursor molecules.

15. The process according to claim 1, which comprises dehydrating the olefins-containing Fischer-Tropsch condensate to convert any oxygenated hydrocarbons to alpha-olefins.

16. The process according to claim 1, in which the olefins-containing Fischer-Tropsch condensate includes at least 50% by mass olefins and is obtained from a Fe-based catalytic Fischer-Tropsch process.

17. A process to produce olefinic products suitable for use as or conversion to oilfield hydrocarbons and to produce paraffinic products suitable for use as or conversion to oilfield hydrocarbons, the process including a process according to claim 1.

Description

(1) The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings. In the drawings,

(2) FIG. 1 shows a process in accordance with a first embodiment of the invention to produce olefinic products suitable for use as or conversion to oilfield hydrocarbons and to produce paraffinic products suitable for use as or conversion to oilfield hydrocarbons, together with base oils; and

(3) FIG. 2 shows a portion of a process in accordance with a second embodiment of the invention, to produce olefinic products suitable for use as or conversion to oilfield hydrocarbons and to produce paraffinic products suitable for use as or conversion to oilfield hydrocarbons, together with base oils.

(4) Referring to FIG. 1, reference numeral 10 generally shows a process in accordance with a first embodiment of the invention to produce olefinic products suitable for use as or conversion to oilfield hydrocarbons and to produce paraffinic products suitable for use as or conversion to oilfield hydrocarbons, as well as base oils. The process 10 is a combination of a process 20 in accordance with the invention to produce olefinic products from a Fischer-Tropsch condensate, and a process 30 in accordance with the invention to produce paraffinic products (and base oils) from a Fischer-Tropsch wax.

(5) The process 20 includes a dehydration stage 40, a distillation column 42, an oligomerisation stage 44, a distillation column 46, an aromatic alkylation unit 48, a dehydrogenation stage 50, a dimerisation stage 52, an aromatic alkylation stage 54 or an optional hydroformylation and alkoxylation stage 56, a dehydrogenation stage 58, an aromatic alkylation stage 60 and an optional hydroformylation and alkoxylation stage 62.

(6) In the process 20, an olefins-containing Fischer-Tropsch condensate is fed by means of a line 64 to the dehydration stage 40. The olefins-containing Fischer-Tropsch condensate is obtained from a Fischer-Tropsch synthesis stage in which synthesis gas is subjected to Fischer-Tropsch synthesis in the presence of a Fischer-Tropsch catalyst to produce a slate of hydrocarbons and by-products such as oxygenates. The Fischer-Tropsch catalyst can be either a cobalt-based catalyst or an iron-based catalyst, although an iron-based catalyst is preferred. U.S. Pat. No. 7,524,787 and U.S. Pat. No. 8,513,312 teach preparation of Co and Fe catalysts that can be used in said Fischer-Tropsch synthesis stage. Table 1 shows suitable or even preferred operating conditions for such a Fischer-Tropsch synthesis stage for both cobalt-based catalysts and iron-based catalysts.

(7) TABLE-US-00001 TABLE 1 Operating conditions Catalyst Co/Pt/Al.sub.2O.sub.3 Precipitated Fe Temperature 230? C. 245? C. Pressure 25 bar 21 bar Syngas molar 2:1 1.55:1 H.sub.2:CO ratio Wax alpha value 0.91 0.945

(8) Table 2 shows typical product slates for such a Fischer-Tropsch synthesis stage using cobalt-based catalysts or iron-based catalysts. As will be appreciated by those skilled in the art, depending on the type of Fischer-Tropsch catalyst used, the temperature and H.sub.2:CO syngas molar ratio, the hydrocarbon species of a syncrude produced by Fischer-Tropsch synthesis could be varied between predominantly paraffins or fairly substantial quantities of olefins, the bulk of these olefins typically appearing in the liquid condensate fraction (>30% by mass). When Fischer-Tropsch syncrude is derived from a low to medium temperature Fe-based Fischer-Tropsch catalytic process (200? C.-300? C. with the bulk of the syncrude being in the liquid phase under reaction conditions) the resulting olefin content in condensate syncrude typically exceeds more than 15% by mass of total syncrude.

(9) Most of the C.sub.3-C.sub.22 hydrocarbons shown in Table 2 form part of the olefins-containing Fischer-Tropsch condensate, although some of the C.sub.3 and C.sub.4 hydrocarbons will be produced by the Fischer-Tropsch synthesis stage in the form of a gas which can be liquefied to form liquefied petroleum gas (LPG). The olefins-containing Fischer-Tropsch condensate thus typically is made up of C.sub.5-C.sub.22 hydrocarbons and some oxygenates (2-10% by mass)

(10) TABLE-US-00002 TABLE 2 Fischer-Tropsch Syncrude Composition (based on total mass %) Fischer-Tropsch Co Low Temperature Fe Low Temperature Process Fischer-Tropsch Catalyst Fischer-Tropsch Catalyst C.sub.3-C.sub.7 Olefins (incl. 7 10 LPG) C.sub.8-C.sub.15 Olefins 5 10 C.sub.8-C.sub.15 Paraffins 24 10 C.sub.16-C.sub.22 Paraffins 8 6 Condensate 5-10 5-10 Oxygenates C.sub.22-C.sub.50 waxy 35 35 paraffins C.sub.50+ waxy paraffins 9 15

(11) The olefins-containing Fischer-Tropsch condensate is thus recovered from the top of a Fischer-Tropsch slurry reactor operating at a temperature in the range of 200? C. to 300? C. in conventional fashion and is a liquid under ambient conditions. As can be seen from Table 2, the olefins-containing Fischer-Tropsch condensate includes some unwanted oxygenates that may potentially deactivate catalysts used in downstream process units. The olefins-containing Fischer-Tropsch condensate is thus dehydrated in the dehydration stage 40 to convert the oxygenated hydrocarbons, comprising mostly of primary alcohols, to alpha olefins, typically using an alumina catalyst. Alternatively, these oxygenates can be recovered from the olefins-containing Fischer-Tropsch condensate by means of a methanol liquid extraction unit (not shown). This will however be at the expense of the production of olefins.

(12) Once dehydrated, the olefins-containing Fischer-Tropsch condensate, which also includes a significant proportion of paraffins as can be seen in Table 2, is fed to the distillation column 42 by means of a flow line 66.

(13) In the distillation column 42, the olefins-containing Fischer-Tropsch condensate is separated into a light C.sub.5-C.sub.7 fraction, an intermediate C.sub.8-C.sub.15 fraction and a heavy C.sub.16-C.sub.22 fraction. The C.sub.5-C.sub.7 light fraction is withdrawn by means of a flow line 68 and combined with liquefied petroleum gas from the Fischer-Tropsch synthesis stage which is fed by means of a flow line 70. The light C.sub.5-C.sub.7 fraction, together with the liquefied petroleum gas, is oligomerised in the oligomerisation stage 44, using a zeolitic catalyst, producing a first olefinic product which includes branched internal olefins in the distillate boiling range C.sub.9-C.sub.22. Examples of preferred zeolitic catalysts can be found in U.S. Pat. No. 8,318,003 and EP 38280461. The first olefinic product is withdrawn by means of the flow line 72 and fractionated in the distillation column 46 into a C.sub.9-C.sub.15 olefin stream and a C.sub.15.sup.+ olefin stream. The C.sub.9-C.sub.15 olefin stream is withdrawn from the distillation column 46 by means of a flow line 74 and is used in the aromatic alkylation stage 48 to alkylate aromatics from a flow line 76 to produce branched di-alkylates, which is withdrawn by means of a flow line 78. The C.sub.15.sup.+ olefin stream is withdrawn from the distillation column 46 along a flow line 75. Alternatively, the C.sub.9-C.sub.15 olefins from the distillation column 46 or a portion thereof can be dimerised in the dimerisation stage 52, as shown by the optional flow line 80, to produce C.sub.18-C.sub.30 branched olefins.

(14) The C.sub.8-C.sub.15 intermediate fraction from the distillation column 42 is fed by means of a flow line 82 to the dehydrogenation stage 50 where the C.sub.8-C.sub.15 intermediate fraction is dehydrogenated using commercially available technology, such as UOP's PACOL? technology, to produce internal olefins. Optionally, i.e. if required, the alpha olefins can be separated (not shown) from the paraffins, e.g. in a UOP OLEX? unit, with only the resultant paraffin fraction then passing to the dehydrogenation stage 50. A mixture of internal and alpha olefins is fed via a flow line 84 and is dimerised in the dimerisation stage 52 using a suitable dimerisation catalyst, e.g. as described in WO 99/55646 and/or EP 1618081B1. A second olefinic product, which is typically a mixture of C.sub.16-C.sub.30 vinylidenes and internal olefins, is withdrawn from the dimerisation stage 52 by means of a flow line 86. The second olefinic product can either be used to alkylate aromatics from a flow line 88 in the aromatic alkylation stage 54 to produce branched mono-alkylates which are withdrawn by means of a flow line 90, or can more preferably be hydroformylated and alkoxylated as shown by the optional hydroformylation and alkoxylation stage 56 to produce various linear and branched oilfield pre-cursor molecules withdrawn by means of a flow line 92.

(15) The heavy C.sub.16-C.sub.22 fraction from the distillation column 42 is withdrawn by means of a flow line 94 and dehydrogenated in the dehydrogenation stage 58, for example again using UOP's PACOL? technology, to produce a third olefinic product which includes internal olefins. The third olefinic product is withdrawn from the dehydrogenation stage 58 by means of a flow line 96. The third olefinic product can also be used to alkylate aromatics provided by means of a flow line 98 to the aromatic alkylation unit 60 thereby to produce branched mono-alkylates which are withdrawn by means of a flow line 100, or be hydroformylated and alkoxylated in the hydroformylation and alkoxylation stage 62 to produce linear and branched oilfield pre-cursor molecules withdrawn by means of a flow line 102.

(16) As will be appreciated, in the process 20, olefins from a Fischer-Tropsch condensate have through various chemical transformation steps been upgraded to higher molecular weight olefins of high value. These higher molecular weight olefins can be used as EOR surfactant feedstock or drilling fluids in the C.sub.16-C.sub.30 carbon range.

(17) The process 30 includes a vacuum distillation column 110, a hydro-treating stage 112, a hydro-isomerisation stage 114, a vacuum distillation column 116, a hydro-treating stage 118, which may be optional, a hydro-cracking stage 120 and an atmospheric distillation column 122.

(18) Fischer-Tropsch wax from the Fischer-Tropsch synthesis stage (not shown), mainly made up of linear paraffins in the C.sub.15 to C.sub.105, or as high as C.sub.120 carbon range depending on the Fischer-Tropsch catalyst used and the subsequent alpha value obtained, and thus including C.sub.22-C.sub.50 waxy paraffins and C.sub.50.sup.+ waxy paraffins as shown in Table 2, is fed by means of a flow line 124 to the vacuum distillation column 110. If the Fischer-Tropsch synthesis stage employs a cobalt-based catalyst, the waxy paraffins may range from about up C.sub.15 to about C.sub.80 and may have an alpha value of about 0.91. If the Fischer-Tropsch synthesis stage however employs an iron-based catalyst, the waxy paraffins can include up to about C.sub.120 hydrocarbons. Traditionally Low Temperature Fischer-Tropsch Co waxes were hydrocracked to maximise fuel type products e.g. diesel, kerosene and naphtha with lubricant base oils being a potential by-product from the heavier bottoms of the hydrocracker. However, shifting to higher alpha value (0.945) waxes e.g. Fe wax in a slurry reactor one also shifts the wax to condensate mass ratio higher (62:38) producing more wax having higher average carbon numbers (peaking around C.sub.30), with a longer tail (up to C.sub.120) on the Schultz-Flory distribution, in comparison to traditional Co slurry processes with wax to condensate mass ratio roughly 50:50 over the lifetime of the catalyst and the wax peaking at around C.sub.21.

(19) The Fischer-Tropsch wax is typically recovered from a side of a Fischer-Tropsch slurry reactor and is thus preferably produced using an iron-based Fischer-Tropsch catalyst under the conditions shown in Table 1, producing wax with an alpha value of about 0.945 and ranging up to about C.sub.120. The Fischer-Tropsch wax contains mostly linear paraffins in said range of about C.sub.15-C.sub.120.

(20) In the vacuum distillation column 110, the Fischer-Tropsch wax is separated into a light C.sub.15-C.sub.22 fraction, an intermediate C.sub.23-C.sub.50 fraction withdrawn by means of a flow line 128 and a C.sub.50.sup.+ heavier fraction withdrawn by means of a flow line 130.

(21) The C.sub.15-C.sub.22 light fraction is mainly paraffinic and is combined with the C.sub.16-C.sub.22 heavy fraction in flow line 94 of the process 20 for dehydrogenation in the dehydrogenation stage 58 of the process 20 to produce more internal olefins.

(22) The C.sub.23-C.sub.50 intermediate fraction is in the lubricant base oil range and is passed to the optional hydro-treating stage 112 to remove any small amounts of oxygenates or olefins that may be present in the intermediate fraction. The hydro-treating stage 112 may employ a hydro-treating catalyst which can be any mono-functional commercial catalyst, e.g. Ni on alumina.

(23) The hydro-treated intermediate fraction is withdrawn from the hydro-treating stage 112 by means of a flow line 132 and fed to the hydro-isomerisation stage 114 where the C.sub.23-C.sub.50 intermediate fraction is reacted over preferably a noble metal catalyst on SAPO-11, ZSM-22, ZSM-48, ZBM-30 or MCM-type support, to provide a hydro-isomerised intermediate product. The hydro-isomerised intermediate product is withdrawn by means of a flow line 134 and separated in the vacuum distillation column 116 into three lubricant base oil grades or fractions, namely a light grade base oil fraction withdrawn by means of a flow line 136, a medium grade base oil fraction withdrawn by means of a flow line 138 and a heavy base oil fraction withdrawn by means of a flow line 140.

(24) The C.sub.50.sup.+ heavier fraction from the vacuum distillation column 110 is subjected to hydro-treatment in the optional hydro-treating stage 118, if necessary, to remove any small amounts of oxygenates or olefins that may be present in the C.sub.50.sup.+ heavier fraction, before being passed by means of a flow line 142 to the hydro-cracking stage 120. The hydro-cracking stage 120 employs a hydro-cracking catalyst which is preferably a noble metal-based catalyst on either an amorphous SiO.sub.2/Al.sub.2O.sub.3 support or a Y-zeolite. The hydro-cracking stage is preferably run under conditions of high severity such that at least 80% by mass of components of the C.sub.50.sup.+ heavier fraction boiling above 590? C. are converted or cracked to form components boiling at less than 590? C. Care must however be taken to avoid over-cracking to provide a distillate selectivity of C.sub.12-C.sub.22 hydrocarbons that is still above 75% with the pour point for such a distillate being less than ?15? C. EP 1421157 gives a good description of what could be achieved under high severity noble metal hydrocracking conditions.

(25) A cracked intermediate is thus withdrawn from the hydro-cracking stage 120 by means of a flow line 144 and passed to the atmospheric distillation column 122.

(26) The hydro-isomerised intermediate product from the hydro-isomerisation stage 114 may include naphtha and other components lighter than C.sub.22, depending on the severity of the hydro-isomerisation process. The distillation column 116 may thus produce a distillate lighter than C.sub.22 which may be combined with the cracked intermediate in flow line 144.

(27) In the atmospheric distillation column 122, the cracked intermediate is separated into a light fraction for producing liquefied petroleum gas (LPG), as shown by flow line 146, a naphtha fraction withdrawn by means of a flow line 148, a heavier than naphtha paraffinic distillate fraction withdrawn by means of a flow line 150, and a bottoms fraction which is heavier than the paraffinic distillate fraction and which is withdrawn by means of a flow line 152.

(28) The light LPG fraction withdrawn by means of the flow line 146 can be used in the process 20 in the form of liquefied petroleum gas as represented by flow line 70.

(29) The naphtha fraction, which is typically a C.sub.5-C.sub.11 fraction, has relatively little value. The naphtha fraction in flow line 148 can be used as diluent, e.g. to improve pumpability of any high viscosity material produced in the process 10, or as feedstock to a steam cracker. Alternatively, the naphtha fraction can be combined with the intermediate fraction in flow line 82 from the distillation column 42 of the process 20.

(30) The heavier than naphtha paraffinic distillate fraction from the atmospheric distillation column 122 can be used as a synthetic paraffinic drilling fluid component having better profit-contributing margins than diesel. In order to ensure that the distillate fraction has a flash point above 60? C., a bottom cut point of the heavier than naphtha paraffinic distillate fraction is set around C.sub.12 or higher in the atmospheric distillation column 122, rather than the traditional C.sub.9 as is the norm for diesel. The pour point of the paraffinic distillate fraction is at a good value for drilling fluids (less than ?15? C.) with a high percentage of branched paraffinic molecules (greater than 30% by mass i:n paraffin ratio) due to the use of the noble metal hydro-cracking catalyst run at high severity in the hydro-cracking stage 120. If the desired pour point for certain applications needs to be below ?25? C. the C.sub.12-C.sub.22 paraffinic distillate fraction or drilling fluid could be further hydro-isomerised with a similar noble metal catalyst as was mentioned for the hydro-isomerisation stage 114, producing a highly branched product which would then typically have an i:n paraffin mass ratio greater than 2:1. The C.sub.12-C.sub.22 paraffinic distillate fraction has less than 1% by mass aromatics, which is of importance from an eco-toxicity and biodegradability perspective.

(31) The bottoms fraction, typically C.sub.22+ can be recycled by means of the flow line 152 to the hydro-cracking stage 120. Alternatively, and preferably, the bottoms fraction is however fed to the hydro-isomerisation stage 114 to produce more high valuable base oils with profit margins considerably higher than those of drilling fluids.

(32) Referring to FIG. 2, reference numeral 200 generally indicates a portion of a process in accordance with a second embodiment of the invention to produce olefinic products suitable for use as or conversion to oilfield hydrocarbons and to produce paraffinic products suitable for use as or conversion to oilfield hydrocarbons, as well as base oils.

(33) Parts of the process 200 which are the same or similar to those of the process 10 of FIG. 1, are indicated with the same reference numerals.

(34) The process 200 differs from the process 10 of FIG. 1 as regards its process 20, and more particularly as regards the workup of its intermediate C.sub.8-C.sub.15 fraction and its heavy C.sub.16-C.sub.22 fraction emanating from the distillation column 42.

(35) In the process 200, the C.sub.8-C.sub.15 intermediate fraction passes, by means of the flow line 82, directly to the dimerisation stage 52, that is, the dehydrogenation stage 50 of the process 10 is dispensed with. In the dimerisation stage 52, alpha olefins in the intermediate fraction are dimerised. The product from the dimerisation stage 52 passes along the flow line 86 into a fractionation column 202. The fractionation column 202 separates the product from the stage 52 into a C.sub.8-C.sub.15 paraffin fraction, which is withdrawn along a flow line 204, and a C.sub.16-C.sub.22 olefin stream that passes, along a flow line 206, into the hydroformylation and alkoxylation stage 56. Optionally, but less preferably, the C.sub.16-C.sub.22 olefin stream from the fractionation column 202 can be routed to the aromatic alkylation stage 54.

(36) The C.sub.8-C.sub.15 paraffin stream from the fractionation column 202 passes, by means of the flow line 204, to the flow line 94 so that this fraction is also subjected to dehydrogenation in the dehydrogenation stage 58. The product from the dehydrogenation stage 58 passes, by means of the flow line 96, into a fractionation column 208, where it is separated out into a C.sub.8-C.sub.15 internal olefin fraction and a C.sub.16-C.sub.22 internal olefin fraction. The C.sub.8-C.sub.15 internal olefin fraction is withdrawn from the column 208 along a flow line 210 and passes into the aromatic alkylation stage 60. The C.sub.16-C.sub.22 internal olefin fraction passes from the column 208, along a flow line 212, into the hydroformylation and alkoxylation stage 62, where alkoxylated alcohols are produced.

(37) When the process 200 is compared with the process 10 of FIG. 1, it will be noted that the dehydrogenation stage 50 and the optional intermediate fraction separation stage of the process 10, are, in effect, replaced by the two fractionation columns 202, 208.

(38) It will be appreciated that the flow lines 75, 206 and 212 can all feed into a single hydroformylation and alkoxylation stage, say the hydroformylation and alkoxylation stage 56, which will result in a substantial reduction in capital and operating costs. Similarly, the flow lines 74 and 210 can lead into a single aromatic alkylation stage, say the aromatic alkylation stage 48, which will also result in savings in capital and operating costs.

(39) The products obtained from the single hydroformylation/alkoxylation unit would be a mixture of linear and branched alkoxylated alcohols, while the product from the single aromatic alkylation unit would be a mixture of linear and branched di-alkylates. More specifically, the C.sub.15.sup.+ olefin stream withdrawn from the distillation column 46 along the flow line 75 would produce branched oligomerised alcohols, while the C.sub.16-C.sub.22 olefin stream withdrawn from the fractionation column 202 along the flow line 206, and comprising mainly vinylidene olefins, would also produce branched alcohols. The C.sub.16-C.sub.22 internal olefin fraction withdrawn from the fractionation column 208 along the flow line 212 would produce linear alcohols. The C.sub.9-C.sub.15 olefin stream withdrawn from the distillation column 46 along the flow line 74, and comprising mainly branched oligomerised olefins, produces branched di-alkylates, while the C.sub.8-C.sub.15 internal olefin fraction withdrawn from the fractionation column 208 along the flow line 210, and comprising mainly internal olefins, produce linear di-alkylates.

(40) However, if it is desired to produce mono-alkylates in preference to d alkylates, then one could retain stages 54 and/or 60 as separate stages.

(41) As will be appreciated, by means of the process 30, a Fischer-Tropsch wax has through various hydro-processing steps been upgraded to higher value paraffins that can be used in oilfield hydrocarbons, for example as surfactants or solvents or drilling fluids, for on-shore or off-shore drilling operations, in the C.sub.12-C.sub.22 carbon range, and to produce various valuable base oil fractions boiling in the C.sub.22-C.sub.50 carbon range.

(42) Advantageously, the processes 10, 200 provide a total yield of olefins in the C.sub.16-C.sub.30 carbon range exceeding 25% by mass, possibly even 30% by mass. The yield of total paraffins exceeds 25% by mass with the lubricant base oil fractions exceeding 15% by mass and the yield of paraffinic drilling fluid exceeding 10% by mass, producing more than 50% by mass valuable oilfield and base oil hydrocarbons from a single Fischer-Tropsch synthesis facility. The balance of the syncrude not mentioned in Table 2 and not converted to valuable oilfield hydrocarbons or base oils could be a small percentage of lower paraffins (C.sub.3-C.sub.7) and Fischer-Tropsch reactor tail gas, e.g. CH.sub.4, C.sub.2H.sub.4, C.sub.2H.sub.6 as well as a C.sub.1-C.sub.5 aqueous product.

(43) Whereas refining of hydrocarbon streams, e.g. from a Fischer-Tropsch synthesis process, conventionally targeted a C.sub.5-C.sub.9 naphtha fraction, a C.sub.9-C.sub.15 jet fuel fraction, a C.sub.9-C.sub.22 diesel fraction and a C.sub.22-C.sub.40 base oil fraction, the present invention, as illustrated, attempts to maximise olefin production and targets a C.sub.16-C.sub.30 olefins fraction and various other olefinic and paraffinic fractions and base oil grades, different from the conventional fractions, with a view to improving profit margins and to supply the demand for oilfield hydrocarbons and lubricant base oils cost-effectively.