WO2009083714A2

WO2009083714A2 - A method for producing a lube oil from a fischer-tropsch wax

Info

Publication number: WO2009083714A2
Application number: PCT/GB2008/004270
Authority: WO
Inventors: Knut Vebjorn Grande; Solvi Storsaeter Bjorgum
Original assignee: Statoilhydro Asa; Rees, David, Christopher
Priority date: 2007-12-27
Filing date: 2008-12-23
Publication date: 2009-07-09
Also published as: GB0725271D0; GB2455995B; WO2009083714A3; GB2455995A

Abstract

A method of upgrading wax feedstock product from a Fischer-Tropsch synthesis reaction comprising C5+ hydrocarbons, which comprises treating the wax feedstock by subjecting the wax feedstock and a source of hydrogen to a temperature in the range 200 to 400° C and a pressure in the range 20 to 100 bar (2 MPa to 10 MPa) at a hydrogen to hydrocarbon liquid volumetric flow rate of 100 to 1000 N1 H2 per 1 liquid hydrocarbon feed, over at least one bifunctional hydrogenation active catalyst, and subsequently fractionating the treated product to produce a base oil fraction. The feedstock comprises the entire C 5+ fraction from an FT synthesis containing at least 0.2 wt% oxygen as oxygenates and having a C5 - C9/C10+ weight ratio of at least 0.05.

Description

A method for producing a lube oil from a Fischer-Tropsch wax

It is known that waxes produced by Fischer-Tropsch processes may be hydroisomerised and dewaxed in order to obtain desirable and useful products. The products may include bases for formulations of lubricating oil ("base oil"), and other hydrocarbon fractions such as diesel fractions, kerosene fractions, gas fractions, naphtha fractions, and so on.

A waxy hydrocarbon feed may be subjected to a hydroisomerisation step and a subsequent dewaxing step, under different reaction conditions. It has been suggested that this process can be carried out in one step, in which the feed is hydroisomerised and also sufficiently dewaxed so that a base oil having desirable properties can be separated from the product.

Standard conditions for carrying out a hydroisomerisation step are a pressure of from 5 to 7 MPa, a temparature T from 300 ⁰C to 400 ⁰C and a liquid

-i hourly space velocity (LHSV) of 1 to 2 h . The process stream may then be subjected to a dewaxing step, for example, catalytic dewaxing or solvent dewaxing. The process stream is fractionated and hydrocarbon fractions, for example, naphtha, kerosene, diesel and base oil fractions, may be obtained.

The yield and properties of each fraction vary depending on factors such as the nature of the feed wax which is processed and the conditions at which each process step is carried out. It is desirable to maximise the yield of base oil, since this is a high value product. The characteristics of the base oil should also be tailored to be as favourable as possible.

Base oil can be characterised by various properties like viscosity index (VI), viscosity at 100 ⁰C or pour point. A hydrocarbon fraction boiling over 360 ⁰C, and/or comprising mainly C25 - C40 molecules can be utilised as a base oil, which can be combined with various additives before use as a lubricating oil. The pour point of a base oil should be < -10 ⁰C. The viscosity index of a base oil can be calculated by standard methods using the viscosity of the base oil at 40 ⁰C and 100 °C, and should be > 80. It is desirable for a base oil to have a pour point as low as possible, for example -20 ⁰C, and a high viscosity index, for example 130. A base oil with a low pour point and a high viscosity index can be used in the formulation of a lube oil which can operate well over a large temperature range.

US Patent 5,362,378 discloses production of a base oil from a Fischer-Tropsch wax using hydroisomerisation without a separate dewaxing step. The method is catalyzed by beta zeolites having a high silica to alumina ratio, in combination with a hydrogenation/dehydrogenation component (for example a "Group VIIIA" metal, for example Pt). The patent discloses in column 2, lines 40 - 53 that a base oil with acceptable characteristics can be produced by subjecting a Fischer-Tropsch wax to a severe hydroisomerisation step, with no dewaxing step necessary.

European patent EP 1114127 discloses the production of a base oil from a Fischer-Tropsch wax without a separate dewaxing step. The catalyst disclosed comprises a catalytic metal and acidic oxide components. Olefins and oxygenates are hydrogenated during the hydroisomerisation step (page 3 line 47;

The aim of the present invention is to provide a method for processing hydrocarbons which reduces the complexity and cost of obtaining a base oil having a low pour point, preferably below -10⁰C and a high VI, preferably above 120, more preferably above 130. The method provides a high yield of base oil. The preferred feedstock is hydrocarbon wax obtained by the Fischer-Tropsch process.

According to one aspect of the invention, there is provided a method of upgrading wax feedstock product from a Fischer-Tropsch synthesis reaction comprising C5+ hydrocarbons, which comprises treating the wax feedstock by subjecting the wax feedstock and a source of hydrogen to a temperature in the range 200 to 400⁰C and a pressure in the range 20 to 100 bar (2 MPa to 10 MPa) at a hydrogen to hydrocarbon liquid volumetric flow rate of 100 to 1000 Nl H₂ per 1 liquid hydrocarbon feed, over at least one bifunctional hydrogenation active catalyst, and subsequently fractionating the treated product to produce a base oil fraction; and in which the feedstock comprises the entire C5+ fraction from an FT synthesis containing at least 0.2 wt% oxygen as oxygenates and having a C5 - C9/C10+ weight ratio of at least 0.05.

Conveniently, the hydroisomerisation step and the dewaxing step are carried out with a LHSV of 0.1 - 10 hr - 1, a pressure of 15 - 75 barg, a hydrogen feed of 50 - 1000 N litres of hydrogen to 1 litre of wax and a temperature of 210 - 400^°C.

The preferred reaction conditions may be: Pressure 40 -70 barg, LHSV = 0.5 - 2

-1 h , reaction temperature: 230 - 400 ⁰C, H2/oil ratio 200 - 800 Nl/1. Preferably, the diesel fraction produced has: pour point < -15⁰C, cetane number > 65. Preferably, the feed is an FT wax with high content of C20+, and a low content of olefins and oxygenates. In a preferred regime, the hydroisomerisation step is carried out at a temperature in the range 300 - 360^°C and the dewaxing step is carried out at a temperature in the range 210 - 400° C. Thus, the reactor configuration may be according to any of the following three cases. Preferably there is one reactor containing one catalyst (preferably Pt/S APO-11), which effectively converts the FT product into good quality diesel and base oil using no separate dewaxing. The second case is one reactor containing two beds of catalyst, a first bed consisting of a catalyst effective for hydroisomerisation, and a second bed containing a catalyst effective for dewaxing. The third case is two reactors in series, with or without separation between, the first reactor containing a hydroisomerisation catalyst and the second reactor containing a dewaxing catalyst. In the first two cases, there is only one fractionation step, which separates the effluent from the reactor into good quality naphtha, kerosene, diesel and base oil.

In the third case there may be a fractionation step between the hydroisomerisation reactor and the dewaxing reactor, which separates into naphtha, kerosene, diesel and a base oil precursor fraction (360+). The base oil precursor fraction is then dewaxed in the dewaxing reactor, and the effluent from the dewaxing reactor is fractionated into naphtha, kerosene, diesel and base oil.

In addition, for all three cases, the base oil fraction may be fractionated into different viscosity ranges of base oil. Optionally there could be a fractionation step in front of the hydroisomerisation, only subjecting a certain fraction of the Fischer-Tropsch product to hydroisomerisation and dewaxing. In addition there may be one or more fractionation steps between the hydroisomerisation and dewaxing, either subjecting only the 360+ fraction to dewaxing, or also to separate the 360+ fraction into two or more base oil precursor fractions to be individually dewaxed. Fractionation before a separate dewaxing step has the advantage that the size of the dewaxing reactor can be reduced, since only the base oil precursor fraction, and not the whole process stream, will be dewaxed. The invention therefore extends to a method of optimising the production of base oil which comprises subjecting an F-T wax feed to a hydroisomerisation reaction and dewaxing reaction, using a common catalyst in a common reactor, and adjusting the reaction parameters of the two reactions in different zones of the reactor, the reaction parameters including temperature, pressure, LHSV.

Any waxy feed having a suitable certain content of paraffinic hydrocarbon can be used, though it should be essentially sulphur and nitrogen free. The waxy feed can be a synthetic wax as from the FT process, a slack wax or a deoiled wax.

The feedstock is a Fischer-Tropsch wax. A Fischer-Tropsch feedstock contains mainly pure paraffins, which have a high viscosity index, thus it is possible to obtain base oils having high viscosity index. In addition the feedstock contains no sulphur, nitrogen or aromatics, which is highly beneficial for the production of synthetic base oils, and allows the use of a noble metal catalyst having very high hydrogenation activity. It is desirable that the feedstock containes high amounts of C20+ paraffins, in order to maximize the yield of base oil.

Preferably, the feedstock has an initial boiling point below 343 ⁰C, taking the entire C5+ fraction produced by the Fischer-Tropsch reaction. Existing processes for the production of base oil use a narrower fraction. This process is therefore novel in that the feedstock has a lower initial boiling point and wider carbon distribution than previously known. When the IBP of the feedstock is lowered, the amount of olefins and oxygenates will also be higher, since most of the olefins are contained in the lower boiling fractions.

The feed may be subjected to hydrotreating to saturate olefins and remove oxygenates, and removal of water before hydroisomerisation. Preferably, the entire C5+ fraction enters the hydroisomerisation reactor without hydrotreating first. It has been found that the presence of alcohols and olefins increases the hydrogen consumption of the hydroisomerisation process. In addition, the catalyst activity is decreased, so that a higher reactor temperature is required. However, it has been realised by the present inventors that the catalyst stability is not unduly affected, and consequently it is not necessary to remove the olefins and oxygenates before the process stream goes through hydroisomerisation.

Several dewaxing catalysts are known in the art. In principle any bifunctional catalyst consisting of an acidic support and a hydrogenation metal function can be used. The pores of the support should be selective with respect to iso-paraffins and n-paraffins. The hydrogenation metal may be at least one of a Group VIB metal and/or a Group VIII metal. If present, Group VIB metal components include tungsten, molybdenum and/or chromium as sulphide, oxide or in its elemental form, and typically in the range 5-30 wt%. More preferably only a Group VIII metal component is present, both noble and non-noble metals, especially palladium, platinum, nickel and/or cobalt in sulphidic, oxidic and/or elemental form. Typically less than 10 wt% of a Group VIII metal is present, more preferably from 0.2 - 5 wt%. The support may be a molecular sieve, and more suitably intermediate pore size zeolites. Preferably the intermediate pore size zeolites have a pore diameter of between 0.35 and 0.8 ran. Suitable zeolites are mordenite, ferrierite, zeolite Beta, zeolite X, zeolite Y, ZSM5, ZSM-11, ZSM-12, ZSM-20, ZSM-22, ZSM-23, ZSM-25, ZSM-34, ZSM-35, ZSM-38, ZSM-48, ZSM-50, ZSM-57, SSZ-32 and SSZ-48. Another preferred group of molecular sieves are the silicaaluminaphosphate (SAPO) materials, such as SAPO-I l, SAPO-31 and SAPO-41. Hydroisomerisation catalysts are also known and may be based on the same metals and supports as those listed above. In addition amorphous alumina, silica-alumina, zirconia, titania etc. may be used as supports.

The invention also extends to products, particularly the base oil, produced in accordance with the method of the invention.

The following examples illustrate the method as carried out on a hydrocarbon wax derived from the Fischer-Tropsch process. Three examples are disclosed for a combined hydroisomerisation and catalytic dewaxing process using a paraffinic C20+ wax feed. A further example is disclosed using the entire C5+ feed from the FT synthesis as feed to the hydroisomerisation reactor.

In Examples 1 to 3, a refined Fischer-Tropsch wax was hydroisomerised in a first trickle-bed reactor over a commercial Pt/Silica-alumina catalyst. Properties for the paraffinic wax feed are given in Table 1. The total effluent from the first reactor was passed over a dewaxing catalyst in a second trickle-bed reactor. Run conditions for both reactors in all examples were, LHSV = 1 h^"1, 50 barg reactor pressure, and a once through hydrogen rate of 600 Nl H2/1 wax. The total liquid effluent from the second reactor was distilled using the ASTM D-2892 method, into naphtha (IBP < 15O⁰C), gas oil (IBP between 15O⁰C and 36O⁰C) and baseoil (IBP >360°C). Example 1 used a Pt/zeolite catalyst in the second reactor, Example 2 used a Ni/zeolite catalyst in the second reactor and Example 3 used a Pt/S APO-11 catalyst in the second reactor.

In Example I₅ a 0.35 wt% Pt/ZSM-5 catalyst was used in the dewaxing step. The Pt/ZSM-5 catalyst is a modification of the commercially available Ni/HYDEX-L catalysts, where the Ni metal is replaced with Pt. The process was carried out at a range of temperatures, between 234 ⁰C and 251 ⁰C. The results are shown in Table II, which lists the yield of yield in the total product (after hydroisomerisation followed by catalytic dewaxing) in terms of the wt percentage of four hydrocarbon fractions, the pour point, viscosity, viscosity index and density of the fraction having a boiling point equal or greater than 360 ⁰C, referred to as "360+". The 360+ fraction can be used as a base oil.

In Comparative Example 2, a Ni/ZSM- 5 catalyst was used in the dewaxing step. A commercially available catalyst known as Ni/HYDEX-L was used. The process was carried out at a range of temperatures, between 229 ⁰C and 246 ⁰C. The results are shown in Table III, which lists the yield in the total product (after hydroisomerisation followed by catalytic dewaxing) in terms of the wt percentage of four hydrocarbon fractions, the pour point, viscosity, viscosity index and density of the fraction having a boiling point equal or greater than 360 ⁰C, referred to as "360+". The 360+ fraction can be used as a base oil.

In the example according to the invention, Example 3, a 0.35 wt% Pt/SAPO-11 catalyst was used in the dewaxing step. The process was carried out at a range of temperatures, between 328 ⁰C and 403 ⁰C. The results are shown in Table IV, which lists the yield in the total product (after hydroisomerisation followed by catalytic dewaxing) in terms of the wt percentage of four hydrocarbon fractions, the pour point, viscosity, viscosity index and density of the fraction having a boiling point equal or greater than 360 ⁰C, referred to as "360+". The 360+ fraction can be used as a base oil.

Conversion and yields, as well as the properties of the obtained base oils are given in Table II - Table IV. The conversion is calculated as the conversion of components boiling above 360 °C into components boiling below 360 ⁰C.

Table 1 : Properties for the wax feed

Table II

Pt/ZSM-5

R1 temperature [°C]

325 325 321 321 316 316 (hydroisomerisation) 316 311 311 306 R2 temperature [°C]

Reactor 238 243 243 249 249 254 260 260 254 (dewaxing) 254 conditions

360+ conversion R1 [%] 65,6 66,5 43,6 44,6 22,1 21 ,5 19,6 10,0 10,0 5,7

360+ conversion R1 + R2

69,7 75,8 52,4 56,9 46,6 48,8 56,4 47,5 57,5 52,0 [%]

Gas (C1-C4) 6,7 7,5 6,7 10,0 9,7 15,6 20,5 15,8 22,4 17,6

Yields in total C5-150 ⁰C 21,4 25,7 19,2 21 ,3 19,4 21 ,1 24,8 24,4 30,8 27,9 effluent from R2 (after dewaxing) 150 °C - 360°C 44,3 45,3 29,5 28,0 19,8 15,0 14,1 10,5 8,3 10,5

360°C + (base oil) 30,3 24,2 47,6 43,1 53,4 51,2 43,6 52,5 42,5 48,0

Pour point [°C] -30 <-39 -21 <-39 -18 -30 <-39 -12 -33 -3

Viscosity at 40 °C [cSt] 18,8 18,8 21,2 20,8 22,8 21,7 22,6 22,4 21,6 22,3

Properties of 360 Viscosity at 100 °C [cSt] 4,2 4,1 4,6 4,5 4,9 4,7 4,7 4,9 4,7 4,9 °C + fraction

Viscosity Index 126 125 134 133 141 136 130 145 137 153

Density at 15 °C 817 817 819 819 820 819 820 819 819 819

Table III

Ni/HYDEX-L

R1 temperature [^°C]

330 330 330 327 327 327 (hydroisomerisation)

R2 temperature [°C]

230 235 240 235 240 245

Reactor conditions (dewaxing)

360+ conversion R1 [%] 65,3 65,9 67,0 46,7 44,6 43,4

360+ conversion R1 + R2 [%] 69,5 73,6 78,0 57,4 59,3 64,9

Gas (C1-C4) 6,5 9,0 15,2 7,5 11 ,8 18,3

Yields in total C5-150 "C 21,3 24,9 29,9 18,6 22,0 26,7 effluent from R2

(after dewaxing) 150 °C - 360°C 43,9 38,5 33,1 33,7 28,3 24,7

360°C + (base oil) 30,5 26,4 22,0 42,6 40,7 35,1

Pour point [°C] -24 -30 <-39 -21 -27 <-39

Viscosity at 40 ⁰C [cSt] 19,2 18,9 19,1 20,1 20,1 21,3

Properties of 360

Viscosity at 100 °C [cSt] 4,3 4,2 4,2 4,5 4,5 4,5 °C + fraction

Viscosity Index 133 129 128 139 140 127

Density at 15 °C 778 778 111 792 794 795

Table IV

Pt/SAPO-11

R1 temperature [^*C] 330 330 326 326 326 326 321 321 321 321 316 316 316 197 197

R2 temperature [°C]

Reactor 328 333 338 348 358 368 368 373 378 385 385 390 395 398 403 conditions 360+ conversion R1 [%1 61 63 45 40 44 44 24 23 24 21 8 8 8 0 0

360+ conversion R1

+ R2 [%] 70 75 51 54 63 68 44 48 51 57 47 56 59 46 53

Gas (C1-C4) 3,5 3,8 2,5 2,9 3,6 4,1 2,9 3,3 3,5 4,3 4,2 4,9 4,9 5,5 5,5

Yields in total C5-150 °C 17,3 19,3 11,2 11,6 14,5 16,5 10,1 10,6 12,0 13,7 11,1 13,2 14,9 11,4 13,5

150 °C - 360^°C 50,7 52,6 37,1 40,4 44,7 47,0 32,8 33,9 36,5 41 ,1 35,2 37,9 40,8 31,5 34,8

360^°C + (base oil) 28,5 24,5 48,6 45,1 36,4 32,2 55,8 52,5 48,0 41,7 50,2 44,4 39,8 52,3 47,2

Pour point [°C] -18 -27 _* -18 -30 -30 -18 -24 -24 -33 -24 -30 -33 -21 -21

Viscosity at 40 °C _* 18,1 _* 20,2 19,8 19,4 _* * 21,4 19,5 19,1 20,7 20,0

Properties [cSt] of 360 ^°C + Viscosity at 10O ⁰C _* 4,1 _* 4,5 4,4 4,3 4,7 4,6 4,5 4,4 4,8 4,3 4,4 4,7 4,5 fraction [cSt]

Viscosity Index 133 _* 145 138 133 _* _* _* * 148 141 137 153 144

Density at 15 °C _*

In Example 4, a raw Fischer-Tropsch wax, containing the entire C5+ fraction from the Fischer-Tropsch reactor including olefins, alcohols and other trace components besides paraffins, is hydroisomerised in a trickle-bed reactor over a commercial Pt/Silica-alumina catalyst. Run conditions for for the hydroisomerisation reactor were, 1.0 LHSV, 50 barg reactor pressure, and a once through hydrogen rate of 600 Nl H2/1 wax. The raw Fischer-Tropsch wax was produced in a slurry reactor, and contained less than lwppm sulphur and less than 1 wppm nitrogen. The boiling point distribution of the wax feed as determined according to the method IP/PM 98 is given in Table V.

Table V

In Example 4, the synthesized waxy feed was formed from a synthesis gas feed comprising H₂ and CO having a mole ratio of about 2.0:1 or less. The synthesis gas feed was reacted in a slurry reactor containing a dispersed catalyst in hydrocarbon liquid slurry (hydrocarbon products from the synthesis reaction), the catalyst comprising cobalt supported on alumina. The liquid product from the Fischer-Tropsch synthesis was collected as light oil, heavy oil and wax, and the three fractions were mixed in order to obtain a C5+ Fischer-Tropsch product having the boiling point distribution given in Table V. This C5+ fraction, containing raw Fischer-Tropsch products including olefins, alcohols and other trace components from the synthesis, was hydroisomerised over a commercial available Pt/SiAl catalyst without prior prefractionation. The 360 °C+ content in the feed was 44 wt%. Prior to the introduction of waxy C5+ Fischer-Tropsch feed to the hydroisomerisation catalyst, the catalyst was stabilized with a refined Fischer-Tropsch wax having the composition as set forth in Table I. The catalyst deactivation during the period with waxy C5+ Fischer-Tropsch feed was checked in the end by introducing to the hydroisomerisation catalyst the same refined Fischer-Tropsch wax as in the beginning. The conditions during the hydroisomerisation reaction were, 1.0 LHSV, 50 barg reactor pressure, and a once through hydrogen rate of 600 Nl H2/1 wax. The reactor bed temperature was selected in order to obtain conversion of 360°C+ from 35% to 96%. The conversion is defined as:

360^C^Conv = ^{Wt%mθ C}"^feed - ^Wt%360°^C+P^rθduCt , l00% wt%360° C⁺feed

The results are given in Table VI, showing the 360°C+ conversion and the reactor temperature at increasing time on stream and with change in feed composition. Table VI

After 8 days on stream with the refined Fischer-Tropsch wax, stable activity was obtained at a temperature of 322.5°C and a 360°C+ conversion slightly above 80%. Then introducing the raw Fischer-Tropsch wax at day 9, the reactor bed temperature had to be increased in order to sustain a high conversion level. About 12 days after introducing the C5+ Fischer-Tropsch wax, the activity started to stabilize again, and the catalyst activity, expressed as the required temperature increase needed to achieve the same level of yield, was about 18.5 °C less than that for the refined Fischer-Tropsch wax.

However, a slow deactivation was observed for some days, and first 5 days later the catalyst activity seemed to be stable at a reactor temperature of 336°C and 47 % 360°C+ conversion. The reactor bed temperature was than adjusted to collect information about the yields and product qualities obtainable at six different conversion levels over a period of about 30 days (day 26 to day 55). The yields at different 360°C+ conversion levels are given in Table VII along with the cold flow properties of the 150-360 fractions.

Then the same reactor conditions as at day 36 were repeated, in order to check the deactivation during a period of almost four weeks. A decrease in 360°C+ conversion of about 3% was observed, corresponding to about 0.9 ⁰C. At day 64, after 55 days on stream with raw Fischer-Tropsch wax, the feed was changed back to refined Fischer-Tropsch wax. The immediate catalyst activity was then approximately the same for the two feeds. After a few days on stream with the refined Fischer-Tropsch wax, some reactivation of the catalyst activity was observed, but the catalyst reactivation was rather slow.

After 20 days on stream, the 360°C+ conversion increased by 14 %, corresponding to about 2.3 ⁰C. The next 10 days the catalyst activity was stable, and a 360°C+ conversion of 92% was reached at about 344 ⁰C. The total irreversible deactivation during the period with C5+ raw Fischer-Tropsch wax was 19 °C, occurring all in the first three weeks of operation with this raw wax feed.

These results indicate that the total liquid product from the Fischer-Tropsch reactor can be hydroisomerised in one reactor, without removal of oxygenates, olefins and other trace components in the feed in a hydrotreating step prior to the hydroisomerisation unit. No measurable levels of oxygenates were found in the product, thus, oxygenates in the feed are hydrogenated over the hydroisomerisation catalyst. The only catalytic effect of hydroisomerisation of the total C5+ Fischer-Tropsch product without hydrotreating the feed first, is a reactor bed temperature of about 20 ⁰C above that for refined Fischer-Tropsch wax.

The results in Example 1 - 3 show that the selectivity of the ZSM-5 based catalysts and the S APO-11 catalyst are quite different. The SAPO-11 catalyst has much higher isomerisation selectivity and a lower cracking selectivity than the ZSM-5 based catalysts. The SAPO- 11 catalyst gives significantly higher yields of diesel and lower yields of gas and naphtha than the ZSM-5 based catalyst, which is beneficial. The yields of base oil, the pour point of the base oils and the viscosity index of the base oils are comparable for the three catalysts. For the two ZSM-5 based catalyst, Pt as the hydrogenation component is beneficial over Ni as the hydrogenation metal, due to lower gas make, and also lower naphtha make.

- The yield of lighter fractions is lower in Example 3 than in the two comparative examples, which is beneficial. The hydroisomerisation and dewaxing the SAPO-11 catalyst is quite different. The SAPO-11 catalyst has much higher isomerisation selectivity and a lower cracking selectivity than the ZSM-5 based catalysts. The SAPO-11 catalyst give significantly higher yields of diesel and lower yields of base oil, the pour point of the base oils and the viscosity index of the base oils are comparable for the three catalysts. For the two ZSM-5 based catalyst, Pt as the hydrogenation component is beneficial over Ni as the hydrogenation metal, due to lower gas make, and also lower naptha make.

- The yield of lighter fractions is lower in Example 3 than in the two comparative examples, where is beneficial to overall value of the products of the process.

- The hydroisomerisation and dewaxing temperatures can be very similar with the dewaxing catalyst of Example 3, which is an advantage when using two catalysts in one reactor, because additional cooling or heating between the different catalyst layers is not required.

- The low cracking selectivity in combination with high isomerisation selectivity makes the SAPO-11 catalyst suitable for a one step process, with one reactor and one catalyst (Figure 1), for combined hydroisomerisation and catalytic dewaxing. As shown in Example 3, high yields of base oil with good cold flow properties and a high viscosity index can be produced by a one step process using the SAPO-11 catalyst. The high cracking selectivity for ZSM-5 based dewaxing catalysts makes them no good candidates for such a one step process. These catalysts are most suitable for two step processes (Figure 3), or alternatively, a one reactor process (Figure 2) with two different catalyst layers, with interstage cooling between the catalyst layers. Table VII

Reactor R1 temperature [°C] 334.4 336.0 338.4 341.9 345.8 347.7 conditions 360+ conversion R1 [%] 36% 47% 52% 62% 86% 95%

Gas (C1-C4) 0,3% 0,6% 0,5% 0,8% 1,2% 1,5%

C5-15CTC 9,3% 11,5% 12,1% 13,6% 18,5% 22,0%

Yields in total effluent from R2 150-360⁰C 62,6% 64,9% 67,1% 69,7% 75,3% 75,0%

Unconverted wax

28,0% 23,2% 20,8% 16,1% 5,1% 2,0% (360°C+)

The three preferred reactor configurations will now be described by way of example in the reference to the accompanying drawings, in which the three Figures are schematic representations of the three configurations.

In Figure 1, a wax feed 11 and a hydrogen feed 12 are mixed and fed to the top of hydroisomerisation reactor 13. The reactor includes a bed 14 of a hydroisomerisation catalyst. The hydroisomerised wax product leaves the bottom of the reactor 13 via an outlet line 15 and this is fed to a fractionation column 16. In the fractionation column 16, the product is split into gas fraction 17, a naptha fraction 18, a kerosene fraction 19, a diesel fraction 21 and a base oil 22.

The arrangement in Figure 2 is similar to that in Figure 1 in that a mixed feed of wax 11 and hydrogen 12 is fed to the top of a reactor 23. However, the reactor 23 is a combined hydroisomerisation and dewaxing reactor, and to this end, it includes a bed 24 of a hydroisomerisation catalyst and beneath this, a bed 25 of a dewaxing catalyst.

The mixed feed passes through the two catalyst beds 24, 25 sequentially and the hydroisomerised and dewaxed product 26 is fed to a fractionation column 16, as before. Similar product fractions 17 to 22 are removed.

In order to be able to control the temperature in catalyst bed 24 and 25 individually a part of the fresh hydrogen 12 is added in between the two catalyst layers 24 and 25 in a separate line 27. The hydrogen added in between the catalyst beds 24 and 25 is either superheated to increase the bed 25 temperature compared to the bed 24 temperature or quenched to decrease the bed 25 temperature compared to the bed 24 temperature.

In the arrangement shown in Figure 3, there is a hydroisomerisation reactor 13 and a separate dewaxing reactor 31. In this case, the mixed feed of wax 11 and hydrogen 12 is fed to the hydroisomerisation reactor 13, in the same way as in the arrangement of Figure 1, and the hydroisomerised wax product leaves the bottom of the reactor via the outlet line 15 and is fed to the fractionation column 16. Again as in Figure 1, the product from the reactor is split into the five fractions 17 to 22.

However, the base oil fraction 22 is mixed with hydrogen, or at least make-up hydrogen 32, and the mixture is fed to the top of the dewaxing reactor 31. It then passes through a dewaxing catalyst bed 34. The dewaxed product 35 is fed to a second fractionation column 36 where it is split into a gas fraction 37, a naphtha fraction 38, a kerosene fraction 39, a diesel fraction 41 and a gas oil fraction 42.

In a possible variant, the first fractionation column 16 is dispensed with and the base oil fraction 15 from the hydroisomerisation reactor 13 is fed directly to the dewaxing reactor 31, after mixing with the make-up hydrogen 32.

Claims

1. A method of upgrading wax feedstock product from a Fischer-Tropsch synthesis reaction comprising C5+ hydrocarbons, which comprises treating the wax feedstock by subjecting the wax feedstock and a source of hydrogen to a temperature in the range 200 to 400° C and a pressure in the range 20 to 100 bar (2 MPa to 10 MPa) at a hydrogen to hydrocarbon liquid volumetric flow rate of 100 to 1000 Nl H₂ per 1 liquid hydrocarbon feed, over at least one bifunctional hydrogenation active catalyst, and subsequently fractionating the treated product to produce a base oil fraction; and in which the feedstock comprises the entire C5+ fraction from an FT synthesis containing at least 0.2 wt% oxygen as oxygenates and having a C5 - C9/C10+ weight ratio of at least 0.05.

2. A method as claimed in Claim 1, in which the proportion of the feedstock having a melting point <20°C is at least 10 wt%.

3. A method as claimed in any preceding claim, in which the treatment of the wax feedstock comprises hydroisomerisation and dewaxing.

4. A method as claimed in Claim 3, in which the hydroisomerisation and dewaxing are carried out simultaneously over a common bifunctional catalyst.

5. A method as claimed in Claim 4, in which the catalyst comprises a Group VIII metal on a SAPO support.

6. A method as claimed in Claim 5, in which the catalyst comprises platinum on a SAPO-11 molecular sieve support.

7. A method as claimed in Claim 3, in which the feedstock is first subjected to hydroisomerisation and then dewaxing.

8. A method as claimed in Claim 7, in which the hydroisomerisation is catalysed by a catalyst comprising a Group VIII metal and optionally a promoter on a silica-alumina support.

9. A method as claimed in Claim 7 or Claim 8, in which the dewaxing is catalysed by a catalyst comprising a Group VIII metal on a silicoaluminophosphate molecular sieve support.

10. A method as claimed in Claim 7 or Claim 8, in which the dewaxing is catalysed by a catalyst comprising platinum on a support comprising SAPO 11 and/or ZSM-5.

11. A method as claimed in any of Claims 3 to 10, in which the hydroisomerisation step and the dewaxing step are carried out with a LHSV of 0.1 - 10 hr - l₅ a pressure of 15 - 75 barg, a hydrogen feed of 50 - 1000 N litres of hydrogen to 1 litre of wax and a temperature of 210-400°C.

12. A method as claimed in Claim any of Claims 3 to 10, in which the hydroisomerisation step is carried out at temperature in the range 300 - 360^°C and the dewaxing step is carried out at a temperature in the range 210 - 400°C.

13. A method as claimed in any of Claims 7 to 12, in which the hydroisomerisation step is carried out in a hydroisomerisation zone and the dewaxing step is then carried out in a dewaxing zone, in one single reactor.

14. A method as claimed in any of Claims 7 to 12, in which first the hydroisomerisation and then the dewaxing steps are carried out sequentially in separate reactors, prior to fractionation.

15. A method as calimed in any of Claims 7 to 12, in which the feedstock is first subjected to hydroisomerisation, then to a first fractionation, then a base oil fraction from the first fractionation is subjected to dewaxing and the dewaxed product is subjected to a second fractionation.

16. A method as claimed in any preceding claim, in which the fractionation products comprise a gas fraction, a naphthe fraction, a kerosene fraction, a diesel fraction and a base oil fraction.

17. A method as claimed in any preceding claim, in which the wax feedstock is not subjected to a hydrotreating step prior to the hydroisomerisation step.