ZA200506511B - Process for producing premium Fischer-Tropsch diesel and lube base oils - Google Patents

Description

i WO 2004/0774406 PCT/US2004/004306 1 PROCESS FOR PRODUCING PREEVIUM 2 FISCHER-TROPSCH DIESEL AND LUBE BASE OILS 3 ‘ 4 FIELD «OF THE INVENTION

6 The- present invention relates to the production of a pre=mium Fischer-Tropsch 7 derived diesel product produced by the blending of a Fischer-Tropsch derive=d 8 diessel fraction and a heavier isormerized Fischer-Tropsech derived base oil 9 fraction to meet at least one pre—selected target property for the diesel product. 11 12 BACKGROUND OF THE INVENT! ON 13 14 Trarsportation fuels intended for use in diesel engines must conform to the current version of at least one of the following specificamtions: 16 17 AST M D 975 — “Standard Specification for Diesel Fuel Oils” 18 19 Eurcopean Grade CEN 90

21 Jap=anese Fuel Standards JIS K 2204 22 23 The United States National Conf erence on Weights anad Measures (NCWM) : 24 199 7 guidelines for premium die =sef fuel

26 The= United States Engine Manu®acturers Association rescommended guidelin e 27 for premium diesel fuel (FQP-1AL) 28 ‘ 29 The-se specifications set a numb er of minimum technical requirements for diessel, so establishing a minimurm quality level below wwhich the diesel fuel is 31 not considered technically fit for -the purpose.

1 Fischer-Tropsch derived trammsportation fuels meeting the specifications for 2 «diesel fuels have certain advaantageous properties which rake it possible to 3 prepare a premium diesel fuesl having very low sulfur content and an excellent ’ 4 | cetane number. However, due to the unique characteristics of

Fischer-Tropsch derived syn crude additional processing Operations must be ) 6 carried out to produce a suitzable diesel fuel. Since Fischer-Tropsch derived 7 products generally contain a significant proportion of olefi ns, in order to 8 improve the oxidation stability a hydroprocessing operation, such as mild 9 hydrotreating, is usually necessary to saturate the doubler bonds. In addition, in order to improve the cold #low properties of the fuel, thes isoparaffin content 11 usually must be increased bry a dewaxing step. Unfortunaately, in the large 12 volumes characteristic of tra nsportation fuels, the cost of the dewaxing step 13 may make the Fischer-Tropssch derived diesel fuel uncompetitive with 14 conventional petroleum derived diesel fuels. 16 Premium lubricating base oi Is may also be prepared from Fischer-Tropsch 17 derived hydrocarbons, but d ue to the high proportion of li near paraffins in the 18 product a dewaxing step als-o is required to improve the cold flow properties 19 prior to sale. However, lubricating base oils generally are» produced in smaller quantities than transportatio n fuels and have a higher coammercial value, so 21 the dewaxing operation is neot commercially impractical. 22 23 The present invention is direacted to an integrated proces s which is able to 24 produce a premium Fischer—Tropsch derived diesel fuel i n combination with a premium Fischer-Tropsch d erived lubricating base oil. In the process of the 26 invention, the properties of he base oil fraction recovere d from the syncrude 27 are carefully controlled to produce a product which after further processing 28 may be blended back into tthe diesel fraction to produce a diesel fuel having : 29 the desired properties. The process of the invention is advantageous because it is possible to produce a p remium diesel fuel without hy droisomerizing the 31 entire diesel product. This decrease in feed results in significant savings in 32 capital costs due to the smaller vessel size required for the isomerization 33 reactor. By significantly low ering the cost of processing the Fischer-Tropsch

1 derived diesel fuel, itis possible to produce a premium product which is 2 competitive in cost with conventional petroleeum derived diesel fuel. 3 ’ 4 The Fischer-Tmopsch syncrude fraction whieh is processed into diessel fuels usually will hawve a boiling range between a bout 150 degrees F (about ) 6 65 degrees C)» and about 750 degrees F (a bout 400 degrees C), typically 7 between about 400 degrees F ( about 205 «degrees C) and about 8 600 degrees = (about 315 degrees C). The= majority of the hydrocambons 9 boiling in the r-ange of diesel will contain be=tween about 9 and about 19 carbon atomms in the molecule. Lubricatimg base oils are general ly prepared 11 from that porti- on of the Fischer-Tropsch sy ncrude boiling above ab~out 12 600 degrees FF (about 315 degrees C) and containing at least 13 20 carbon ato:ms in the molecule. However, the initial boiling point -of the 14 base oil fraction may be higher, for exampl e about 750 degrees F about 400 degrees CC). One skilled in the art will recognize that there is considerable 16 overlap betwe=en the upper boiling point of diesel and the initial boiling point of 17 the base oil fractions. The precise cut point selected will depend ugoon the 18 properties dessired in the final products. By carefully controlling the separation 19 point betweern diesel and base oil, it is pos sible to tailor the properties of the two products, so that when a portion of thes hydroisomerized base «oil is 21 blended back into the diesel, the diesel product will meet the criter ia of a 22 premium dies el fuel without the necessity ©f isomerizing the entire diesel 23 stream. 24

Naphtha whiczh is also produced by the process of present invention has a 26 boiling range below that of diesel but abov-e that of the normally g=aseous 27 hydrocarbonss, such as butane and proparme. Accordingly, naphtha. generally 28 has a boiling range between ambient temperature and about 150 cdegrees F ’ 29 (about 65 degrees C), and the molecules boiling within this range ~will contain between abowit 5 and about 8 carbon atoms. The naphtha producezd by this 31 process will Lmsually have a low octane rati ng due to the highly paraffinic 32 nature of Fischer-Tropsch materials. Conssequently, the naphtha p=roduced by 33 this process generally is not suitable for usse as a transportation fu el without n WO 2004/074406 PCT./US2004/004306 1 further processsing. However, the naphtha p-roduced may be used as feed to 2 an ethylene cracker without additional processing. Hydrocarbons having less 3 than 5 carbon atoms in the molecule are nasrmally gaseous at ambient : 4 temperature amd are included among the owerhead gases and may be recycled upstresam in the Fischer-Tropsch processing train before or after } 6 optionally reco-vering the LPG (C3 and C4) fraction. 7 8 Processing schemes similar to the process of the present inve=ntion have been 9 proposed and been commercially practiced for conventional peetroleum derived products. See, for example, U.S. Patent Nos. 5,976,354; 5,980,729; 11 6,337,010 B1; and 6,432,297 B1. However none of these processing 12 schemes were= intended for the processing of Fischer-Tropsch derived 13 materials and their purpose is quite differert. In addition, for most of these 14 process schermes the primary product of concern is the lubricating base oil fraction. In the= present process, while a lubsricating base oil may be one of the 16 products recowered, the primary product of interest is the dies el fuel product. 17 Accordingly, the temperature conditions un der which the sepamration between 18 the diesel frac=tion and the base oil fraction is made is carefully controlled to 19 assure that thes portion of the isomerized base oil fraction which is blended back into the Cliesel fraction will produce a «diesel product havi ng the desired 21 properiies. In addition, since most of these processes are con. cerned with 22 processing pe=troleum derived feeds, the hwdroprocessing operations to which 23 the feed is subjected prior to separation of the diesel and basee oil fractions is 24 for a different purpose, typically involving a hydrotreating opetr—ation to remove : 25 sulfur and nitr-ogen (see U.S. Patent No. 5, 976,354) or a hydreocracking 26 operation to readuce the average molecular weight of the feed (see U.S. Patent 27 No. 6,337,010 B1). In the present process, the hydroprocessi ng operation is 28 primarily interded to saturate the olefins ard to remove the oxxygenates. ) 29 :

As used in thi s disclosure the words "comporises" or "comprisimng"” are intended 31 as an open-erded transition meaning the i nclusion of the named elements, 32 but not neces sarily excluding other unnam ed elements. The phrases "consists 33 essentially of” or "consisting essentially of™ are intended to me=an the

1 exclusion of other elements of any essential significance to the ccomposition. 2 The phrasess "consisting of" or "consists Of" are intended as a transition 3 meaning the exclusion of all but the reciteed elements with the e><ception of “ 4 only minor traces of impurities. i 6 SUMMARY OF THEE INVENTION 7 8 The present invention is directed to a pro cess for producing a premium 9 Fischer-Tropsch diesel fuel which compri ses (a) treating a waxy~

Fischer-Tropsch feed recovered from a Fischer-Tropsch synthesis in a 11 hydroproces-sing zone under hydroprocesssing conditions in the gpresence of a 12 hydroproces-sing catalyst intended to saturate the olefins and to remove the 13 oxygenates that are present in the feed, whereby a first Fischer—Tropsch 14 intermediate= product is produced with recduced olefins and oxygeenates relative to the Fischer-Tropsch feed; (b) separatirg the first Fischer-Tropsch 16 intermediate- product in a separation zone into a heavy Fischer-Tropsch 17 fraction and alight Fischer-Tropsch fracti on under controlled separation 18 conditions wherein the light Fischer-Trops=sch fraction is characte=rized by an 19 end boiling point falling within the boiling range of diesel, and thee heavy

Fischer-Tropsch fraction being characteri zed by a boiling range above that of 21 the light Fisczher-Tropsch fraction; (c) con facting the heavy Fischer-Tropsch 22 fraction with a hydroisomerization catalysst in a hydroisomerizaticon zone under 23 hydroisomerization conditions selected to improve the cold flow properties of 24 the heavy Fi scher-Tropsch fraction and recovering an isomerize=d heavy

Fischer-Tropsch fraction; (d) mixing the isomerized heavy Fisch er-Tropsch 26 fraction with at least a portion of the light Fischer-Tropsch fraction of (b); and 27 (e) recoverirmg from the blend a Fischer-Tropsch derived diesel poroduct 28 meeting a ta_rget value for at least one pres-selected specificatior for diesel ) 29 fuel. The hezavy Fischer-Tropsch fraction will generally have an mnitial boiling point within tthe lower end of the boiling range for lubricating basse oil and the 31 upper end of the boiling range for diesel, i.e., the initial boiling paint will 32 usually be beetween about 550 degrees F (about 285 degrees C7) and about © 33 750 degreess F (about 400 degrees C). However, in order to meest the target

1 val ue for the selected specification or specifications for the die=sel product, it : 2 may under certain circumstances be desirable to produce moree of the heavy 3 fra«ction by lowering the initial boiling point of the heavy fractior below : 4 606 degrees F, perhaps as low as 450 degrees F (about 230 cdegrees C). In thiss instance, the amount of the heavy fraction that will be isonerized and ) 6 ble=nded back into the diesel will be significantly increased. 7 8 The hydroprocessing conditions in the first step of the process used to 9 saturate the olefins and remove the oxygenates present in the

Fischer-Tropsch feed are preferably mild and usually are selected to minimize 11 the cracking of the molecules. However, by varying the conversion rate of the 12 hyadroprocessing operation, the amount of diesel or of lubricatimng base oil may 13 be maximized. For example, by operating at a higher conversieon, typically 14 greater than about 20 percent conversion, the amount of dieses! produced by the process may be increased, since a portion of the Cg plus mmolecules 16 pre=sent in the feed will be cracked into products within the boil ing range of 17 tra nsportation fuels. Similarly, by minimizing the amount of corversion in this 18 step, generally less than 20 percent conversion, the amount off base oil 19 produced will be maximized due ta the very low cracking rate. 21 As. used in this disclosure “conversion” of a hydrocarbon feedstock refers to 22 the percent of the hydrocarbons recovered from the hydroproczessing zone 23 which have an initial boiling point above a given reference temperature 24 fol lowing the conversion of the Fischer-Tropsch feed into prod ucts boiling be low the reference temperature. See U.S. Patent No. 6,224,747. For the 26 pu rposes of this disclosure the reference temperature selected is usually 27 ab out 650 degrees F (340 degrees C). 28 ) 29 A portion of the isomerized heavy Fischer-Tropsch fraction produced is bleended back with the diesel in order to meet the target value or one or more 31 pre-selected specifications for diesel. One skilled in the art will recognize that 32 the specification or specifications selected will depend on the mature of the 33 opeeration and the market into which the diesel product is to be= sold.

1 Generally, the diesel speci fication or specifications selected will include orme or 2 more of the cold filter plugging point, the cloud point , or the pour point. Each 3 of these specifications may be readily controlled in thhe diesel product by the : 4 blending back a portion of the isomerized heavy Fisacher-Tropsch fraction. 6 in most embodiments of the invention, the separatiosn zone will include at | east 7 two separation zones, refexrred to herein as a first ard a second separatior 8 zone. The first separation zone, which in most embodiments will comprise a 9 hot high pressure separator, is used to separate the= heavy Fischer-Tropsch fraction from the naphtha, diesel and gaseous hydrogen rich fraction and 11 usually will be operated at a temperature which is about 50 degrees F 122 (28 degrees C) below the temperature of the hydroprocessing zone. The 13% second separation zone, wvhich in most embodiments will comprise a cold 14- high pressure separator, iss used to separate the ovesrhead gases from the 1& remaining hydrocarbons bxoiling in the range of transportation fuels. The iG operation of the separation zone is critical to the invention, since the 17 separation between the hesavy and light Fischer-Tro=psch fractions will 18 determine how much of thwose hydrocarbons boiling in the diesel range wil 1 be 19 isomerized along with the heavy fraction which is willl be blended back as part of the final diesel product. 21% 22 |n order to facilitate the sezparation in the high press=ure separator if is 23 preferable that a stripping gas be used. Stripping gases, such as, for exarmple, 224 steam or hydrogen may b e employed in the hot highh pressure separator.

Generally hydrogen is prexferred as the stripping gass in the present scheme. 26 2d BRIEF DESCRIPTION OF THE D2RAWING 28 ) 29 The drawing is a diagram illustrating a process scheeme which represents one embodiment of the invent ion.

a

1 DETAILED DESCRIPTION OF THE | NVENTION 2 3 The present invention may oe more clearly understood by reference to the : 4 drawing which represents ome embodiment of the process scheme.

In the drawing the Fischer-Tropsch condensate feed 2 and the Fischer-Tropsch ’ 6 waxy feed 4 are shown separately prior to entering tthe hydrotreating reacteor 6 7 via a common conduit 8 wheere the feeds are also mezixed with hydrogen fromm 8 line 11 which is provided by make-up hydrogen entering by lines 9 and 10 and 9 by recycle hydrogen from lire 28. In the hydrotreatirg reactor 6 the olefins present in the feed are satu rated and the oxygenatess, mostly consisting of™ 11 alcohols, are removed.

The effluent from the hydrotmreating reactor referred to 12 in this disclosure as the firsk Fischer-Tropsch intermu ediate is carried via 13 line 12 to the first separatiomn zone 14 comprising a Enot high pressure 14 separator where the heavy Fischer-Tropsch fractiorm comprising primarily waxy material boiling in the base oil range, but also including at least some 16 hydrocarbons boiling in the diesel range, are separated from a lower boilirmg 17 Fischer-Tropsch fraction which includes hydrocarbomns boiling both in the 18 range of naphtha and diese=l as well as overhead gaseous comprising 19 hydrogen and C4 minus hycdrocarbons.

The hot higlm pressure separator is usually operated at a temperature that is at least 50» degrees F (28 degree=s C) 21 below the operating temperature of the hydrotreatin g reactor 6. The heavy 22 Fischer-Tropsch fraction is collected in conduit 16 amnd carried to the 23 hydroisomerization unit 18. Hydrogen for the isomerization step is added From 24 make-up hydrogen via lines 9 and 19. Returning to the hot high pressure separator 14, the lower boil ing hydrocarbons and owerhead gaseous are 26 collected by conduit 20 andi carried to the second separation zone which 27 comprises a cold high pres=sure separator 22. In the= cold high pressure 28 separator the hydrogen ricin overhead gaseous are separated from those ) 29 hydrocarbons boiling in the range of transportation —fuels.

The hydrogen rich overhead gases pass via lime 24 to an optional recycle gas scrubber 26 in 31 order to remove any hydrogen sulfide or ammonia poresent prior to being ssent 32 via line 28 to the recycle geas compressor 30 to be recycled by line 11 bac kto 33 the hydrotreating reactor 6. The hydrocarbons com prising primarily those

. WO 2004/074406 PCH/US2004/004306 1 boiling within the range of naphtha and diesel are recovered Edy line 32 from 2 the cold high pressure separator and sent to a low pressure sseparator 34. 3 - 4 Returning to the hydroisomerization unit 18, the heavy Fischear-Tropsch fraction which contains most of thie Fischer-Tropsch wax is isomerized to ’ 6 increase the isoparaffin content of the fraction and improve its cold flow 7 properties, such as the cold filter plugging point, the pour poirt, and the Vi, as 8 well as the cloud point.

The isomerized heavy Fischer-Tropsch fraction is 9 collected in line 36 and passed to the hydrofinishing reactor 38 where the oxidation stability is further improved.

The isomerized and hycdrofinished 11 heavy fraction is carried by line 40 to a high pressure separat or 42 where the 12 hydrogen rich overhead gases are collected and carried by lire 44 back to the 13 cold high pressure separator 22 to be recycled to the hydrotreating unit.

The 14 effluent from cold high pressure separator containing the hea-vy fraction is carried by line 46 to the low pressure separator 34 where the isomerized and 16 hydrofinished heavy fraction are mixed with the light fraction coming from the 17 cold high pressure separator 22. The overhead gases compri-sing primarily C, 18 minus hydrocarbons are collected from the top of the low pressure separator 19 by line 47 and carried {o the top of a product stripper 48. The mixture of heavy and light Fischer-Tropsch fractions are collected in line 49 fro:am the bottom of 21 the low pressure separator and passed to the lower section of the product 22 stripper 48 where additional C; minus hydrocarbons are sepa rated from the 23 Cs plus hydrocarbons.

The C4 minus hydrocarbons are colleczted from stripper 24 by conduit 50. The product stream comprising Cs plus hydroc-arbons are collected in line 52 and passed to the atmospheric distillation unit 54 where 26 the naphtha 56 and diesel 58 are collected separately from ary remaining Cy 27 minus hydrocarbons in line 60. The heavy bottoms fraction is collected and 28 sent via line 62 to the vacuum distillation unit 64 where the lig ht base oil ) 29 fraction 66, medium base oil fraction 68, and heavy base oil fr—action 70 are shown being separately collected. 31 32 By controlling the operation of the hot high pressure separatomr 14, the non- 33 waxy molecules are removed from the feed to the hydroisome=rization unit 18 -g-

1 and prevented ~from contacting the isomerization catalyst.

The li ght 2 Fischer-Tropsc=h fraction comprising the maj ority of the diesel amd 3 substantially al | of the naphtha fraction thus bypass the isomeri=zation : 4 operation maki ng the isomerization step mu ch more efficient, slince it handles a smaller volurme of hydrocarbons than it ma ght otherwise.

Only~ that fraction ’ 6 containing the majority of the Fischer-Trops ch wax will enter thee 7 hydroisomerizaation zone.

This separation step also is used to rmeet the 8 specifications —for the diesel fuel that is prod uced by the integra“ted process.

By 9 blending a portion of the isomerized and hy-drofinished heavy Fischer-Tropsch fraction with the diesel, the overall cold flows properties and clomid point of the 11 diesel products is improved without the necessity of hydroisome=rizing and 12 hydrofinishing the entire diesel product.

Masst of the heavy fraction which is 13 recovered withh the diesel product from the atmospheric distilla—tion column 54 14 will comprise -a lighter base oil fraction, i.e. , the base oil fractio n which has an upper boiling point of less than 750 degree=s F (400 degrees C=). Thus by 16 controlling thea cut points in the hot high pressure separator amd in the 17 fractionation cooperation the amount of isomerized and hydrofinmshed base oil 18 blended into ®&he diesel product may be coxtrolled.

In addition, the operation of 19 the hydroisormnerization unit may be controWled to optimize the conversion of the heavy fra ction which also will contribute to the properties of the final diesel 21 product recovered from the operation. 22 23 As already neoted, the operation of the hydlroprocessing unit, sshown in the 24 drawing as the hydrotreating unit 6, may toe varied to make nmore hydrocarbon s boiling in the range of trans- portation fuels.

By operating under 26 more sever conditions to increase the corversion, the larger mmolecules may 27 be cracked t 0 yield more diesel. 28 ) 29 As an integr ated process, the process of the present inventicon also allows for the efficient recycling of the hydrogen rich C4 minus overheasd gases fo the 31 hydroprocesssing zone, the catalytic dewaxing zone, and the hydrofinishing 32 zone. lt is geenerally advantageous to opearate the hydroprocesssing reactor, 33 catalytic dexwaxing reactor, and hydrofinishing reactor at sub stantially the

1 same pmessure, since such operation reduces the capital c=ost by saving on 2 the nee d for additional pumps and compressors.

However, hydroisomerizatiorn 3 general ly has an optimal reaction presssure below that for Imydrocracking, : 4 hydrotreating, and hydrofinishing.

Therefore, it may be adwantageous under certain circumstances to operate the catalytic dewaxing uit at a lower 6 pressure than the hydroprocessing unit and the hydrofinisiming unit.

See for 7 exampl e, U.S.

Patent No. 6,337,010 B 1. 8 9 Fischer-Tropsch Synthesis

11 In the Fischer-Tropsch synthesis proc ess, liquid and gase=ous hydrocarbons 12 are forrmed by contacting a synthesis gas (syngas) comprising a mixture of 13 hydrog-en and carbon monoxide with am Fischer-Tropsch c. atalyst under 14 suitables temperature and pressure reactive conditions.

Th. e Fischer—Tropsch reactio nis typically conducted at tempmeratures of from abseout 300 degrees F to 16 about #00 degrees F (about 150 degrees C to about 370 edegrees C) 17 prefersably from about 400 degrees F { 0 about 550 degree=s F (about 18 205 de=grees C to about 230 degrees CC); pressures of frorm about 10 psia to 19 about E00 psia (0.7 bars to 41 bars), preferably 30 psia tom 300 psia (2 bars to 21 bars), and catalyst space velocities of from about 100 cc/g/hr. fo about 21 10,000 cc/g/hr., preferably 300 cc/g/hr. to 3,000 cc/g/hr. 22 23 The products may range from C4 to Coq plus hydrocarboms with a majority, by 24 weights, in the Cs-Cqgo plus range.

The reaction can be comnducted in a variety of reactor types, for example, fixed be=d reactors containirag one or more 26 catalysst beds, slurry reactors, fluidized bed reactors, ora combination of 27 differe nt type reactors.

Such reaction processes and reacztors are well known 28 and documented in the literature.

Slurry Fischer—Tropscha processes, which is ) 29 a prefearred process for producing the feed stocks used for carrying out the invent ion, utilize superior heat (and mmass) transfer characteristics for the 31 strongly exothermic synthesis reactiom and are able to pr-oduce relatively higin 32 molec ular weight, paraffinic hydrocartoons when using a cobalt catalyst.

In a 33 slurry process, a syngas comprising & mixture of hydrogen and carbon

1 monoxide is bubbled up in the reactor as a third phase through a slurry “which 2 comprises a particu late Fischer-Tropsch type hydrocarbon synthesis catalyst 3 dispersed and susp ended in a slurry liquid compmrising hydrocarbon products : 4 of the synthesis rea ction which are liquid at the resaction conditions.

The= mole ratio of the hydroge mn to the carbon monoxide ma y broadly range from a bout 6 0.5 to about 4, but iss more typically within the rarmge of from about 0.7 to about 7 2.75 and preferably from about 0.7 to about 2.5. _A particularly preferred 8 Fischer-Tropsch process is taught in EP 0609079, also completely 9 incorporated herein by reference for all purposes=.

11 Suitable Fischer-Tropsch catalysts comprise one or more Group Vil catalytic 12 metals such as Fe, Ni, Co, Ru and Re, with cobamlt generally being one 13 preferred embodiment.

Additionally, a suitable catalyst may contain a 14 promoter.

Thus, in one embodiment, the Fischer—Tropsch catalyst will comprise effective amounts of cobalt and one or more of Re, Ru, Pt, Fe=, Ni, 16 Th, Zr, Hf, U, Mg amd La on a suitable inorganic ssupport material, prefemrably 17 one which comprises one or more refractory met al oxides.

In general, the 18 amount of cobalt present in the catalyst is betwee=n about 1 and about 19 50 weight percent of the total catalyst compositiosn.

The catalysts can al so contain basic oxide promoters such as ThO;, La=03, MgO, IK20 and Ti(O,, 21 promoters such as ZrO,, noble metals (Pt, Pd, R u, Rh, Os, Ir), coinage metals 22 (Cu, Ag, Au), and o ther transition metals such ass Fe, Mn, Ni, and Re.

Suitable 23 support materials include alumina, silica, magnessia and titania or mixtures 24 thereof.

Preferred supports for cobalt containing catalysts comprise alumina or titania.

Useful ca falysts and their preparation &are known and illustrated in 26 U.S.

Patent No. 4,568,663, which is intended to be illustrative but non-lamiting 27 relative to catalyst selection. 28 ) 29 The products from the Fischer-Tropsch process -usually are collected separately as a waxy fraction which contains the majority of the 31 Fischer-Tropsch wax, a condensate fraction which contains the hydrocarbons 32 boiling in the range of transportation fuels, and a gaseous fraction containing 33 unreacted hydrogem and carbon monoxide and C4 minus hydrocarbons . The

1 waxy fraction is normally & solid at ambient temperature and represeents the 2 fraction which makes up t he majority of the material that will be ison—erized in 3 the present process.

The condensate fraction, in a«ddition to containiing most : 4 of the hydrocarbons boilirag in the range of naphthaa and diesel, also contains oxygenates, mostly in forrm of alcohols, which mus® be removed pricor to 6 further processing.

All of t he fractions contain a sig nificant amount cof olefins 7 which must be saturated i nthe hydroprocessing steep. 8 9 Hydroprocessing

11 Hydroprocessing in the present invention refers to the step intended primarily 12 for the purpose of removirg any residual nitrogen, saturating the ole=fins, and 13 removing oxygenates that: may be present in the Fischer-Tropsch fe=ed stock. 14 By increasing the severity of the hydroprocessing step, the amount eof diesel recovered in the final procduct slate may be increas ed.

For the purpomses of this 16 discussion, the term hydrcoprocessing is intended to refer to either 17 hydrotreating or hydrocracking.

Hydroisomerizatior and hydrofinishing, while 18 also a type of hydroprocesssing, will be treated separately because oof their 19 different functions in the p rocess scheme.

21 Hydrotreating refers to a c=atalytic process, usually carried out inthe presence 22 of free hydrogen, in which the primary purpose when used to processs 23 conventional petroleum derived feed stocks is the removal of variouss metal 24 contaminants, such as arssenic; heteroatoms, such as sulfur and nitreogen; and aromatics from the feed sEock.

In the present processs, the primary purpose is 26 to saturate the olefins and remove the oxygenates in the feed stock prior to 27 the catalytic dewaxing operation.

Generally, in hydrotreating operaticons 28 cracking of the hydrocarbon molecules, i.e., breakirmg the larger hydr—ocarbon ’ 29 molecules into smaller hycdrocarbon molecules is minimized.

For the purpose of this discussion the term hydrotreating refers to a hydroprocessing operation 31 in which the conversion is 20 percent or less.

. WO 2004/074406 PCT/US2004/004306 1 Hydraocracking refers to a c atalytic process, usually carried out in the 2 presence of free hydrogen, in which the cracking of the | arger hydrocarbon 3 molecules is the primary purpose of the operation. In comtrast to : 4 hydrotreating, the conversieon rate for hydrocracking, for the purpose of this disclosure. shall be more than 20 percent. Hydrogenatio-n of the olefins and 6 removal of the oxygenates as well as denitrification of th e feedstock also will 7 occur. In the present invention, cracking of the hydrocarbon molecules may 8 be desirable in order to incaease the yield of diesel and rminimize the amount 9 of heavy Fischer-Tropsch fraction passing through the c atalytic dewaxing operation. 11 12 Catalysts used in carrying «out hydrotreating and hydrocracking operations are 13 well known in the art. See ¥or example U.S. Patent Nos. 4,347,121 and 14 4,810,357, the contents of which are hereby incorporate=d by reference in their entirety, for general descriptions of hydrotreating, hydroscracking, and of 16 typical catalysts used in each of the processes. Suitable» catalysts include 17 noble metals from Group \WIIA (according to the 1975 rules of the 18 International Union of Pures and Applied Chemistry), suc=h as platinum or 19 palladium on an alumina o r siliceous matrix, and unsulfided Group VIIA and

Group VIB, such as nickel—molybdenum or nickel-tin on an alumina or 21 siliceous matrix. U.S. Pate nt No. 3,852,207 describes a suifable noble metal 22 catalyst and mild conditiore s. Other suitable catalysts are described, for 23 example, in U.S. Patent Nos. 4,157,294 and 3,904,513. The non-noble 24 hydrogenation metals, suc=h as nickel-molybdenum, are usually present in the final catalyst composition &s oxides, or more preferably or possibly, as 26 sulfides when such compounds are readily formed from the particular metal 27 involved. Preferred non-ncable metal catalyst compositiomns contain in excess 28 of about 5 weight percent, preferably about 5 to about 4-0 weight percent ’ 29 molybdenum and/or tungsten, and at least about 0.5, ard generally about 1 to about 15 weight percent of nickel and/or cobalt determiried as the 31 corresponding oxides. Catalysts containing noble metal s, such as platinum, 32 contain in excess of 0.01 percent metal, preferably between 0.1 and

1 1.0 percent metal. Combinations of noEole metals may also be used, such as 2 mixtures of platinum and palladium. 3 : 4 The hydrogenation components can be incorporated into t_he overall catalyst composition by any one of numerous procedures. The hydlirogenation 6 compone=nts can be added to matrix component by co-muBling, impregnation, 7 orion exchange and the Group VI conmponents, i.e.; molylodenum and 8 tungsten can be combined with the refaractory oxide by imgoregnation, 9 co-mullin gor co-precipitation. Although these componentss can be combined with the catalyst matrix as the sulfides, that is generally nost preferred, as the 11 sulfur cormpounds can interfere with thes Fischer-Tropsch c=atalysts. 12 13 The matr-ix component can be of many types including sorme that have acidic 14 catalytic activity. Ones that have activity include amorphous silica-alumina or may be em zeolitic or non-zealitic crystal line molecular sieve. Examples of 16 suitable rmatrix molecular sieves includ e zeolite Y, zeolite = and the so called 17 ultra stai>le zeolite Y and high structural silica:alumina ratio zeolite Y such as 18 that desc=ribed in U.S. Patent Nos. 4,401,556; 4,820,402; ==nd 5,059,567. 19 Small crystal size zeolite Y, such as thaat described in U.S. Patent

No. 5,073,530 can also be used. Non-=eolitic molecular sieaves which can be 21 used incl ude, for example, silicoalumin ophosphates (SAP), 22 ferroalunminophosphate, titanium alumimnophosphate and thme various ELAPO 23 molecula r sieves described in U.S. Pat-ent No. 4,913,799 &and the references 24 cited therein. Details regarding the pregparation of various ron-zeolite molecula rsieves can be found in U.S. Patent Nos. 5,114,563 (SAPO) and 26 4,913,79%9 and the various references cited in U.S. Patent No. 4,913,799. 27 Mesoporeous molecular sieves can also be used, for exampple the M418 family 28 of materials as described in J. Am. Chem. Soc., 114:1083=4-10843(1992)), ] 29 MCM-41z U.S. Patent Nos. 5,246,689; 5,198,203; and 5,334,368; and

MCM-48 (Kresge et al., Nature 359:71€ (1992)). Suitable rmatrix materials 31 may also- include synthetic or natural swibstances as well a s inorganic 32 materialss such as clay, silica and/or meatal oxides such as silica-alumina, 33 silica-ma-gnesia, silica-zirconia, silica-tioria, silica-berylia, silica-titania as well -E5-

1 as ternary compositions, such as silica-almumina-thoria, silica-alLamina-zirconia, 2 silica-alumin a-magnesia, and silica-magn esia zirconia. The latter may be 3 either naturally occurring or in the form of gelatinous precipitate s or gels : 4 including mix<tures of silica and metal oxic es. Naturally occurring clays which can be composited with the catalyst include those of the montmorillonite and 6 kaolin families. These clays can be used i nthe raw state as originally mined 7 orinitially sulbjected to calumniation, acid treatment or chemical modification. 8 9 In performing the hydrocracking and/or hy=drotreating operation, more than one catalyst type may be used in the reacztor. The different catalyst types can 11 be separated into layers or mixed. 12 13 Hydrocrackirg conditions have been well «documented in the lite=rature. In 14 general, the woverall LHSV is about 0.1 hr-—1 to about 15.0 hr-1 (v-/v), preferably from about O .25 hr-1 to about 2.5 hr-1. Thee reaction pressure generally 16 ranges from about 500 psig to about 35008 psig (about 10.4 MPzm to about 17 24.2 MPa, preferably from about 1500 psisg to about 5000 psig (=about 3.5 MPa 18 to about 34.5 MPa). Hydrogen consumption is typically from about 500 to 19 about 2500 SCF per barrel of feed (89.1 to 445 m3 H2/m3 feed) .

Temperature sin the reactor will range frorm about 400 degrees = fo about 21 950 degrees F (about 205 degrees C to atoout 510 degrees C), preferably 22 ranging from about 650 degrees F to about 850 degrees F (about 23 340 degrees C to about 455 degrees C). 24

Typical hydrotreating conditions vary over a wide range. In gene ral, the 26 overall LHSV is about 0.5 to 5.0. The total pressure ranging fron about 27 200 psig to about 2000 psig. Hydrogen recirculation rates are typically greater 28 than 50 SCF/Bbl, and are preferably between 1000 and 5000 SCCF/Bbi. ’ 29 Temperatures in the reactor will range frormn about 400 degrees F to about 800 degrees F (about 205 degrees C to aloout 425 degrees C).

1 Separation Zosne

3 Inthe processa of the present invention, tlhe separation zone &s used to : 4 separate thosee hydrocarbons boiling in tie range of transportation fuels, i.e., inrange of na phtha and diesel (referred ®&o as the light Fischesr-Tropsch 6 fraction) from - those hydrocarbons boiling in the base oil rangme (referred to as 7 the heavy Fischer-Tropsch fraction) fromm the first Fischer-Tropsch 8 intermediate product collected from the haydroprocessing ope=ration.

Generally, 9 the cut-point feor the separation between —the heavy Fischer-T ropsch fraction and the light Fischer-Tropsch fraction wil | be within the temperature range of 11 between aboumt 550 degrees F and about= 750 degrees F (about 12 285 degrees CC to about 400 degrees C). Usually the cut-poirit will be about 13 600 degrees = (315 degrees C). Howeve=r, due to the unique properties of 14 Fischer-Trops ch derived products the cu=t-point may be as low as 16 450 degrees = (about 230 degrees C). Thhe precise cut-point selected will 16 depend upon Ehow much of the base oil p resent in the first Fischer-Tropsch 17 intermediate product is selected for isom-erization.

The selec®ion of how much 18 base oil to serd to the catalytic dewaxingg zone will depend u pon the target 19 value selectecH for the property or properizies of the final diese=| product.

In : general, the lomwer the cut-point between the heavy and light —fractions, the 21 more Fischer-Tropsch wax will be sent tc the catalytic dewaxzing zona.

More 22 wax isomerizamtion will result in improved cold-flow properties in the diesel 23 product.

However, most of the Fischer-Tr-opsch wax is conce ntrated in the 24 higher boiling —fractions.

Thus dropping th e cut-point below a =certain temperature yields decreasing benefits ir the properties of th e diesel product. 26 In addition, the more heavy Fischer-Trop:sch fraction sent to &he catalytic 27 dewaxing zones, the larger the reaction veessel must be to harmdle the increased 28 volume of matzerial which results in highe r capital costs.

Thus= one skilled in ’ 29 the art will recaognize that a balance mustz be achieved betwesen the size of the catalytic dewa xing reactor and the propemties of the final dies el product.

The 31 diesel product must meet the target valuess for the selected specification while 32 atthe same tirme minimizing the amount of material sent to thae catalytic 33 dewaxing unit.

- VO 2004/074406 PCT/US2004/004306 1 The separation in the separation zone will usually take pmlace at a temperature 2 thatis at least 50 degrees F (30 degrees C) below the o perating temperature 3 of the hydroprocessing reactor.

This is necessary in the present scheme due : 4 to the nature of the Fischer-Tropsch feed.

This aspect differs from the operation of similar schemes described in the prior art w=hich are directed to 6 the processing of conventional petroleum derived feed s-tocks.

See U.S. 7 Patent Nos. 5,976,354 and 6,432,297. Although the configuration of the 8 equipment used in the prior art schemes is similar to tha_t used for the scheme 9 described herein, the actual operation is quite different.

Bn processing 1 0 conventional petroleum feeds, the separator is operated at substantially the 1 1 same temperature as the hydroprocessing operation.

Simnce petroleum derived 1 2 fractions which include diesel are not waxy, substantiallyw all of the diesel is 1 3 recovered along with the naphtha and overhead gases imn the prior art 14 processes.

Virtually none of the final diesel product has passed through the 1 5 catalytic dewaxing unit in these schemes.

In the present process, due to the 16 waxy nature of the Fischer-Tropsch diesel, a significant mount of the 1 7 material that will be included in the final diesel product is: isomerized. 18 Typically, between about 25 and about 75 volume perce nt of the final diesel 19 product will have passed through the catalytic dewaxing unit.

The actual amount of the final diesel product which has passed through the catalytic 21 dewaxing unit will depend on the target value selected for the diesel 22 specification. 23 24 Usually the separation zone will comprise at least two separation vessels.

In the drawing, the separation zone comprises a hot high peressure separator 2.6 and a cold high pressure separator.

In this scheme the tot high pressure 27 separator makes the initial separation between the heav-y Fischer-Tropsch 2 8 fraction and the light Fischer-Tropsch fraction.

While this separation will take ’ 2.9 place at a relatively high temperature, it usually will still toe at a temperature 3.0 thatis at least 50 degrees F (30 degrees C) lower than t he temperature in the 3 1 hydroprocessing reactor.

In the cold high pressure sepawrator, the overhead 3 2 gases are separated from the hydrocarbons boiling in th-€ range of those 3-3 transportation fuels which will not pass through the catal ytic dewaxing zone.

1 Catalytic.

Dewaxing and Hydroisomerization

3 Catalytic dewaxing consists of three main classes, conventiomal ) 4 hydrodewwvaxing, complete hydroisomerization dewaxing, and partial hydroisommerization dewaxing.

All three classes involve passimng a mixture of a ] 6 waxy hycdrocarbon stream and hydroge n over a catalyst that econtains an 7 acidic co mponent to reduce the normal and slightly branched: iso-paraffins in 8 thefeed and increase the proportion of other non-waxy speci es.

The method 9 selected for dewaxing a feed typically d epends on the produczt quality, and the wax content of the feed, with conventiomal hydrodewaxing oft-en preferred for 11 low wax «content feeds.

The method for dewaxing can be effe cted by the 12 choice of the catalyst.

The general subj ect is reviewed by Avi lino Sequeira, in 13 Lubrican® Base Stock and Wax Processsing, Marcel Dekker, Irc., 14 pages 194-223. The determination betvween conventional hyc83rodewaxing, complete= hydroisomerization dewaxing, and partial hydroisonaierization 16 dewaxing can be made by using the n-Mexadecane isomerizamtion test as 17 described in U.S.

Patent No. 5,282,958 _. When measured at £6 percent, 18 n-hexade=cane conversion using conventional hydrodewaxing catalysts will 19 exhibit a selectivity to isomerized hexadlecanes of less than 1 0 percent, partial hydroisormerization dewaxing catalysts will exhibit a selectivity to isomerized 21 hexadeczanes of greater than 10 percent to less than 40 percent, and 22 complete= hydroisomerization dewaxing catalysts will exhibit a selectivity to 23 isomerize=d hexadecanes of greater thar or equal to 40 perce nt, preferably 24 greater tian 60 percent, and most preferrably greater than 80 percent.

26 In convertional hydrodewaxing, the pour point is lowered by selectively 27 cracking “the wax molecules mostly to srnaller paraffins using =a conventional 28 hydrodewwaxing catalyst, such as, for example ZSM-5. Metals may be added ’ 29 to the catzalyst, primarily to reduce fouling.

In the present invertion conventional hydrodewaxing may be us ed to increase the yield of diesel in the 31 final prod uct slate by cracking the Fischer-Tropsch wax molecules.

In the 32 present perocess, the isomerization of the paraffins also is use«d to improve the 33 cold flow properties and cloud point of the diesel fraction.

Typical conditions

1 for hydroisomerization as used in the present process invo-Ive temperatures 2 from about 400 degrees F to about 800 degrees F (about 2200 degrees C to 3 about 425 degrees C), pressures from about 100 psig to 2€000 psig, and 4 space velocities from about 0.2 to 5 hr-1. 5 . 6 Complete hydroisomerization d ewaxing typically achieves Bhigh conversion 7 levels of wax by isomerization to non-waxy iso-paraffins while at the same 8 time minimizing the conversion by cracking.

Since wax conaversion can be 9 complete, or at least very high, this process typically does mot need to be combined with additional dewaxing processes to produce aa lubricating oil 11 base stock with an acceptable pour point.

Complete hydroi-somerization 12 dewaxing uses a dual-functional catalyst consisting of an a cidic component 13 and an active metal component having hydrogenation activ=ity.

Both 14 components are required to conduct the isomerization reac=tion.

The acidic component of the catalysts used in complete hydroisomeriz=ation preferably 16 include an intermediate pore SAPO, such as SAPO-11, SA_P0O-31, and 17 SAPO-41, with SAPO-11 being particularly preferred.

Interr mediate pore 18 zeolites, such as ZSM-22, ZSM-23, SSZ-32, ZSM-35, and =ZSM-48, also may 19 be used in carrying out complete hydroisomerization dewas=ing.

Typical active metals include molybdenum, nickel, vanadium, cobalt, tung sten, zinc, 21 platinum, and palladium.

The metals platinum and palladiurm are especially 22 preferred as the active metals, with platinum most common ly used. : 23 24 In partial hydroisomerization dewaxing, a portion of the wayc is isomerized to iso-paraffins using catalysts that can isomerize paraffins seBectively, but only if 26 the conversion of wax is kept to relatively low values (typicaally below 27 50 percent). At higher conversions, wax conversion by crac king becomes 28 significant, and yield losses of lubricating base stock beconmes uneconomical. ’ 29 Like complete hydroisomerization dewaxing, the catalysts u sed in partial hydroisomerization dewaxing include both an acidic comporent and a 31 hydrogenation component.

The acidic catalyst components useful for partial 32 hydroisomerization dewaxing include amorphous silica aluninas, fluorided 33 alumina, and 12-ring zeolites (such as Beta, Y zeolite, L zeolite). The

1 hydrogenation component of the catalyst is the same ass already discussed 2 with complete hydroisomerization dewaxing.

Because tie wax conversion is 3 incomplete, partial hydroisomerization dewaxing must bee supplemented with : 4 an additional dewaxing technique, typically solvent dewsaxing, complete hydliroisomerization dewaxing, o r conventional hydrodeveaxing in order to 6 pro-duce a lubricating base stock with an acceptable pour point (below about 7 +10 degrees F or -12 degrees C). 8 9 In preparing those catalysts containing a non-zeolitic molecular sieve and having a hydrogenation component for use in the presemt invention, it is 11 usumally preferred that the metal be deposited on the catalyst using a 12 nom-aqueous method.

Catalysts, particularly catalysts containing SAPQ's, on 13 whi-ch the metal has been deposited using the non-aqueous method, have 14 shoewn greater selectivity and activity than those catalysts which have used an 156 aqumeous method to deposit the active metal.

The non-acyueous deposition of 16 active metals on non-zeolitic molecular sieves is taught in U.S.

Patent 17 No. 5,939,349. In general, the p rocess involves dissolvirg a compound of the 18 acti-ve metal in a non-aqueous, Mon-reactive solvent and depositing it on the 19 mol ecular sieve by ion exchange or impregnation.

21 Hyd&rofinishing 22 23 Hyd®rofinishing operations are intended to improve the U V stability and color of 24 the products. lis believed this is accomplished by satur-ating the double bon ds present in the hydrocarbosn molecules, including t hose found in 26 arormatics, especially polycyclic aromatics.

As shown in #the drawing, only the 27 hea vy Fischer-Tropsch fraction which has passed through the catalytic 28 dewwaxer is sent to a hydrofinisher.

A general description of the hydrofinishing 29 proccess may be found in U.S.

Patent Nos. 3,852,207 anad 4,673,487. As used in this disclosure the term UV stability refers to the stabil ity of the lubricating 31 base oil or other products when exposed to ultraviolet ligght and oxygen. 32 Instability is indicated when a visible precipitate forms or darker color 33 deve=lops upon exposure to ultraviolet light and air which results in a

1 cloudiness or floc in the= product. It may also be desi rable that the diesel 2 product prepared by thes process of the present inve ntion be UV stabilize d 3 prior to marketing in which case this fraction may alsso be hydrofinished. ’ 4

Typically, the total pres=sure in the hydrofinishing zore will be between aloout 6 200 psig and about 300®0 psig, with pressures in the range of about 500 gosig 7 and about 2000 psig be=ing preferred. Temperature ranges in the 8 hydrofinishing zone are usually in the range of from about 400 degrees — 9 (about 205 degrees C) to about 650 degrees F (abo ut 345 degrees C). T he LHSV is usually within the range of from about 0.3 to about 5.0. Hydroge=n is 11 usually supplied to the hydrofinishing zone at a rate of from about 1000 to 12 about 10,000 SCF per barrel of feed. Typically the hmydrogen is fed at a rate of 13 about 3000 SCF per barrel of feed. 14 16 Suitable hydrofinishing catalysts typically contain a Group VIII metal 16 component together wit-h an oxide support. Metals o=r compounds of the 17 following metals are useful in hydrofinishing catalysi=s include nickel, 18 ruthenium, rhodium, iricdium, palladium, platinum, armd osmium. Preferably the 19 metal or metals will be molatinum, palladium or mixtur-es of platinum and palladium. The refractomy oxide support usually consists of alumina, silica, 21 silica-alumina, silica-alLumina-zirconia, and the like. "The catalyst may 22 optionally contain a zeolite component. Typical hydrofinishing catalysts are 23 disclosed in U.S. Paten t Nos. 3,852,207; 4,157,294= and 4,673,487. 24 :

Diesel Product 26 27 In the present inventiorm the final diesel product is pr epared by blending = 28 lower boiling fraction of the isomerized heavy fractiosn back into the diese=l ’ 29 fraction recovered from the separation zone. As illustrated in the drawingg the isomerized heavy fractison and the light fraction are blended together in the 31 low pressure separator. The diesel product, includin g part of the isomeri=ed 32 heavy fraction, is showr in the drawing as being separated from the lighter 33 naphtha, C4; minus fraction, and base oil in the atmoespheric fractionation unit.

1 The various lube fractions may be —further separated, if desired in a vacuurm 2 fractio nation column. 3 4 Inthe presentinvention, the propemrties of diesel product ray be controlled at several points in the process.

The Hirst control point and tlhe most importarit 6 are in “the separation zone.

As alreaady noted, the separat ion zone controlss 7 how rmmauch of the waxy material which will be included in the diesel product will 8 pass though the hydroisomerizatiomn operation.

The secord point of contro 9 resides in the hydroisomerization ue nit.

By controlling the \wax conversion, #&he cold flow properties of the diesel al so may be adjusted.

Finally, the proper-ties 11 of the «diesel product may be controlled in the fractionatior step.

How muchh of 12 the isommerized base oil fraction rermnains as part of the die=sel product also =will 13 help determine what the final propesrties of the diesel product will be.

One 14 skilled in the art will recognize that there are other schem-es than the one shown in the drawing to accomplistn the overall process without departing 16 from the spirit of the invention. : 17 18 In the goresent invention the diesel fraction and isomerized base oil fraction are 19 blende=d to achieve a target value for at least one diesel s pecification.

The diesel specifications will usually be selected from one or rmore of the cold filter 21 plugging point, the cloud point, and the pour point.

In the acase of the cold Filter 22 pluggimg point, the target value will usually be a temperatuure of -10 degree=s C 23 orless , preferably -20 degrees C om less.

The target value for cloud point vevill 24 usually be a temperature of -8 degr-ees C or less, preferaloly -18 degrees C or less.

T he target value for pour point will typically be -15 degrees C or less, 26 preferably -25 degrees C or less. 27 28 The cold filter plugging point (“CFPIF") is a standard test ursed to determine= ) 29 the easse with which fuel moves under suction through a fi Iter grade representative of field equipment.

T he determination is repoeated periodical ly 31 during steady cooling of the fuel sarmple, the lowest temperature at which tlhe 32 minimum acceptable level of filteraloility is still achieved bezing recorded as ~the

1 "CFPP" tem perature of the sample.

The deetails of the CFPP te st and cooling 2 regime are sspecified in ASTM D-6371. 3 ’ 4 Pour point iss the temperature at which a saample of the diesel fuel will begin to flow under c=arefully controlled conditions.

In this disclosure, po-ur point, unless 6 stated otherwise, is determined by the stamndard analytical metiod 7 ASTM D-59250. 8 9 Fischer-Tropsch Derived Lubricating Base= Oil

11 In addition, to producing a premium diesel product, the present- invention may 12 also be used to produce a premium Fischer-Tropsch derived lu bricating base 13 oil.

Fischer-Tropsch derived base oils recomvered from the process of this 14 invention typically will contain very low sulfur and aromatics, hamve excellent 16 oxidation stability, and excellent cold flow oroperties.

Generally-, the lubricating 168 base oils recovered from the process will have a kinematic visc=osity of at least 17 3 cStat 100 degrees C, preferably at least: 4 ¢St.; a pour point Below 18 20 degrees €C, preferably below -12 degrees C; and a Vi that is usually greater 19 than 90, preferably greater than 100. The | ower boiling base oil s usually will be included mn the final diesel blend, therefore, there is very littl= of the low 21 viscosity material recovered from the vacumum distillation column.

Claims (1)

1. oo So A\

   2 WHAT WE CLAIM IS: 3 : 4 1. A proczess for producing a premium Fischer-Tropsch diesel fuel which comprises: . 6 : 7 (a) treating a waxy Fischer-Tropsch feed recovered from a 8 Fischer-Tropsch synthesis in a hwydroprocessing zone under 9 hydroprocessing conditions in th e presence of a hydroprocessing catalyst intended to saturate the olefins amd to 11 remove the oxygenates that are present in the feed, where=by a 12 first Fischer-Tropsch intermediate product is produced witim 13 reduced olefins and oxygenates relative to the Fischer-Tro psch 14 feed;

   16 (b) separating the first Fischer-Trop sch intermediate product ir a 17 separation zone into a heavy Fischer-Tropsch fraction and a 18 light Fischer-Tropsch fraction urader controlled separation 19 conditions wherein the light Fischer-Tropsch fraction is characterized by an end boiling point falling within the beili ng 21 range of diesel, and the heavy Fischer-Tropsch fraction be=ing 22 characterized by a boiling range> above that of the light 23 Fischer-Tropsch fraction; 24 (c) contacting the heavy Fischer-Tropsch fraction with an 26 hydroisomerization catalyst in a hydroisomerization zone Lander 27 hydroisomerization conditions selected to improve the colcd flow 28 properties of the heavy Fischer-Tropsch fraction and recowwering 29 an isomerized heavy Fischer-Tropsch fraction;

   31 (d) mixing the isomerized heavy Fischer-Tropsch fraction with: at 32 least a portion of the light Fischer-Tropsch fraction of (b); and

   . N 1 (e) recovering from the bleend a Fischer-Tropsch derived diesel 2 product meeting a targ et value for at least ones pre-selected 3 specification for diesel fuel. : 4

   2. The process of claim 1 where=in the conversion of thes Fischer-Tropsch } 6 feed in the hydroprocessing zone is 20 percent or le=ss. 7 g§ 3. The process of claim 2 where=in the hydroprocessingg conditions include 9 a hydrogen partial pressure of between about 200 p=sig to about 2000 psig, a temperature in the range of from about 400 degrees F to 11 about 800 degrees F, a LHS of between about 0.5 and about 5.0. 12 13 4. The process of claim 2 wherein the hydroprocessingg catalyst 14 comprises at least one actives metal selected from G-roup VIIA of the Periodic Table of the Elemerwts and at least one acti—ve metal selected 16 from Group VIB of the Periodic Table of the Elemen 1s, said active 17 metals being present on a refractory support. 18 19 5. The process of claim 2 further including the intermeediate step of hydrofinishing the isomerized heavy Fischer-Tropsc=h fraction of 21 step (c) in a hydrofinishing zone under hydrofinishineg conditions prior to 22 blending the first portion of the isomerized heavy Fisscher-Tropsch 23 fraction with the light Fischer-Tropsch fraction. 24

   6. The process of claim 5 wher=ein a second portion of the hydrofinished 26 and isomerized heavy Fischear-Tropsch fraction is a Iso recovered 27 separately as a lubricating b=ase oil. 28 : 29 7. The process of claim 5 wherein the pressure in the hydroprocessing zone and in the hydrofinishirmg zone are substantially the same. 31

   1 8. The process of claim 7 wherein the hydois©merization zone is operated 2 at a lower pressure than the hydroprocess ing zone and the 3 hydrofinishing zone. : 4

   Oo. The process of claim 1 wherein the light Fischer-Tropsch fraction ha=s 6 an end point. falling within the range betwe=en about 450 degrees F aand 7 about 750 desgrees F. 8 9 10. The processs of claim 1 wherein the isome rization catalyst in the catalytic dev-vaxing zone is a hydroisomeri zation catalyst. 11 12 11. The processs of claim 10 wherein the hydroprocessing catalyst contains 13 a molecular sieve selected from the group consisting essentially of 14 ZSM-22, ZSSM-23, SSZ-32, ZSM-35, ZSME-48, SAPO-11, SAPO-31, and SAPO-<41. 16 17 12. The proces=s of claim 11 wherein the hydr-oisomerization catalyst 18 contains arm active metal selected from pl atinum, palladium, or a 19 combinatiorn of platinum and palladium. 21 13. The processs of claim 1 wherein the pre-selected specification for diesel 22 fuel to which the Fischer-Tropsch diesel product is blended is the cold 23 filter pluggi ng point. 24

   14. The processs of claim 1 wherein the pre-selected specification for d iesel 26 fuel to which the Fischer-Tropsch diesel product is blended is cloued 27 point. 28 ’ 290 15. The processs of claim 1 wherein the pre-selected specification for diesel fuel to whisch the Fischer-Tropsch diesel product is blended is pour 31 point. 32 ”

   1 16. The process of claim 1 in which the separation zone= of step (b) is 2 divided into at least a first intermediate separation zone and a second 3 intermediate separation zeone and wherein the separation of step (b) : 4 includes the additional steps of (i) separately recove=ring from the first intermediate separation zeone the heavy Fischer-Tro psch fraction and &2 6 mixture containing the light Fischer-Tropsch fraction and a 7 hydrogen-rich C4 minus fraction; (ii) feeding the mixture containing the 8 light Fischer-Tropsch fraction and the hydrogen- ricta C4 minus fraction 9 to the second intermediate separation zone; and (iii recovering separately from the secord intermediate separation zone the light 11 Fischer-Tropsch fraction &and the hydrogen- rich C4 rminus fraction. 12 13 17. The process of claim 16 vevherein the hydrogen-rich €4 minus fraction is 14 recycled to the hydroproc=essing zone.

   16 18. The process of claim 16 v=vherein the hydrogen-rich €, minus fraction is 17 sent to the hydroisomerization zone. 18 19 19. The process of claim 16 v—vherein the hydrogen-rich «4 minus fraction is sent to a hydrofinishing zone. 21 22 20. The process of claim 16 v-vherein a stripping gas is uased in the first 23 intermediate separation z one to assist in recovering the mixture 24 containing the light Fischeer-Tropsch fraction and thes hydrogen- rich C4 minus fraction.