EP1627028B1

EP1627028B1 - Process to upgrade kerosenes and a gasoils from naphthenic and aromatic crude petroleum sources

Info

Publication number: EP1627028B1
Application number: EP04741581A
Authority: EP
Inventors: Willem Bosch
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2003-05-22
Filing date: 2004-05-17
Publication date: 2007-12-12
Anticipated expiration: 2024-05-17
Also published as: US20070021636A1; DE602004010648T2; WO2004104142A1; JP5478806B2; CN100362085C; DE602004010648D1; ATE380855T1; JP2007502899A; CN1795258A; EP1627028A1; DK1627028T3

Abstract

A process to prepare a kerosene and a gasoil product from a crude petroleum source having a Watson characterization factor K value of equal or below 12.0 by (a) isolation of a petroleum derived kerosene fraction and a petroleum derived gasoil fraction from said crude petroleum source, wherein the petroleum derived kerosene fraction has a smoke point of below 25 mm or below 19 mm if naphthalenes content of the kerosene fraction is below 3% vol and the petroleum derived gas oil has a cetane number of below 50 or a density higher than 845 kg/m<SUP>3</SUP>, ( ) adding a Fischer-Tropsch derived kerosene fraction to the petroleum derived kerosene fraction in an amount sufficient to obtain a mixture having a smoke point value of above 25 mm or above 19 mm if the naphthalenes content of the mixture is below 3% vol and (c) adding a Fischer-Tropsch derived gas oil fraction to the petroleum derived gasoil fraction such that the resultant mixture has a cetane number value of above 51.

Description

Field of invention

Process to upgrade low quality kerosenes and gasoils from Naphthenic and Aromatic crude petroleum sources, featuring a value for the Watson characterisation factor K of equal of below 12.

Background of invention

Crude petroleum sources featuring a value for the Watson characterisation factor K of in between 11 and 12 are also referred to as "naphthenic" crude. If the K factor below 11 the crude is also referred to as "aromatic" crude. The Watson characterisation factor K for hydrocarbons has been defined in the API technical data book (Section 2 Characterisation).
Virgin naphtha fractions as distilled from Napthenic or Aromatic crudes are very suitable to prepare high octane motor gasoline components as they are easy convertable via Catalytic Reforming to high octane value reformates. However virgin kerosenes and virgin gasoils produced from Naphthenic and/or Aromatic crudes are being characterised by certain quality properties which makes them unsuitable to meet certain environmentally driven fuels specifications as required by an increasing number of legislators in various Regions and Markets.
Aviation kerosenes produced from naphthenic and/or aromatic crudes by distillation and treating will typically have a smoke point far below the required international specification (min. 25 mm) set for Aviation Turbine Fuels (Avtur) in Checklist No. 19 of Aviation Fuel Quality Requirements for Jointly Operated Systems (AFQRJOS), or does not meet the alternative specification of maximum smokepoint (min. 19 mm) if naphthalenes content of the kerosene is below 3 %vol. Sometimes naphthalenes levels are too high in kerosenes produced from these crudes in case of high final boiling points of the kerosenes. Also other specification requirements set for Aviation kerosenes like a minimum Total Acid Number of 0.015 mg KOH/g, a maximum specified aromatics level 25 %vol and Thermal stability requirements (JFTOT) are difficult to be met with kerosenes directly distilled from Naphthenic and/or Aromatic crude sources.
Diesel quality gasoils produced from such naphthenic or aromatic crudes will typically feature a low cetane number (CN). Typically the cetane number will be between 35-50 below the required international Cetane number specifications set for Diesel grades. Internationally there is a clear drive to increase Cetane number of Diesel fuels to reduce vehicle emissions. For example the minimum Cetane Number requirement in the European Diesel specification (EN 590) has been increased to minimum of 51 from year 2000 onwards to meet the European Diesel fuel and emissions requirements set in the EU Fuels Directive 98/70 for Euro III fuels. Global car manufacturers want to increase Diesel fuel Cetane Number requirements even further to minimum 55 as published in their World Wide Fuel Charter in year 2002.
Gas oils produced from naphthenic or aromatic crudes also feature high densities. Maximum density limits of international Diesel qualities are currently being reduced to meet Dieselcar emissions requirements. Again in EU the maximum specification for Diesel fuels in EU 590 has been reduced in 2000 to a maximum of 845 kg/m³ as set in the EU Fuels Directive 98/70.
The consequence of these emission driven fuel requirements is that middle distillate fuels produced from naphthenic or aromatic crudes may not be suitable to meet the severe environmental driven fuels specification requirements being set for Avtur and Diesel. This will result in "off-spec" Diesel or Kerosene qualities if these crudes are being processed in so-called Hydroskimming refineries. Hydroskimming refineries are relatively simple refineries consisting of crude distilling and hydrotreating processes.
To improve the quality of the distillates produced from these crudes to meet the specified Product Qualities these refineries have two options:

1) As a first option, further improvement of the inferior distillate qualities can be achieved by more applying more severe hydroprocessing or hydrocracking. This option may need however expensive investment for those refineries not equipped with these processing units.
In these processes by catalytic ring opening of the naphthenic components in the kerosene fraction as described in US-A-3607729 , the smoke point of the kerosene fraction can be improved. Also the cetane values of gasoils can be improved in these processes due to hydrogenation and ringopening reactions.
US-A-3775297 describes a process wherein the gas oil fraction as isolated from a naphthenic crude is converted into a lubricating base oil and a motor gasoline.
More recent developments as illustrated in US-A-5107056 , involve processes wherein the undesired naphthenic compounds are removed by membrane separation from the oil.
2) A second option to improve the kerosene and gas oil properties is to blend and co-process these inferior quality types of naphthenic and aromatic crudes with more paraffinic type of crudes. The final distillate yields of this crude blend can be calculated from the crude blend ratio multiplied by the distillate yields obtainable for each crude.

A disadvantage of blending with paraffinic crudes is that such crudes are not always available at the refinery location or only at a much higher price. Another disadvantage is, that it is not always possible to find a paraffinic crude to blend which will meet both kerosene and gas oil properties and volume demands of distillates to the qualities respectively quantities as specified.
Normally crude blending will result in quality give-away for example it is either the kerosene blend or the gas oil blend which will meet the smoke point respectively the cetane number specification after blending such crudes. The other blend will have a property value exceeding the specification while the property value of said blend will be the same or near a blend having a property closer to the specification. This so-called quality give away is preferably to be avoided for obvious reasons. Nevertheless, as explained above, when optimizing both kerosene and gas oil products in a refinery blending environment such quality give-away cannot always be avoided. Co-processing of a paraffinic crude will also result in more crude storage and handling, blending, crude distilling and processing requirements.
In Cookson David J et al., "Observed and predicted properties of jet and diesel fuel formulated from coal liquefaction and Fischer-Tropsch feedstocks", Energy Fuels 1992, 6, pages 581-585, it is described how the kerosene and gas oil fraction as obtained from a non-crude source, namely a coal liquefaction process are blended with respective Fischer-Tropsch derived kerosene and gas oil.
The object of the present invention is to obtain a process to prepare kerosene and gas oil from a naphthenic or aromatic crude wherein the product quality give away is being reduced and wherein special measures to reduce the naphthenic or aromatic hydrocarbon contents is not required.

Summary of invention

This object is achieved with the following process. Process to prepare a kerosene and a gasoil product from a crude petroleum source having a Watson characterisation factor K value of equal or below 12.0 by (a) isolation of a petroleum derived kerosene fraction and a petroleum derived gasoil fraction from said crude petroleum source, wherein the petroleum derived kerosene fraction has a smoke point of below 25 mm or below 19 mm if naphthalenes content of the kerosene fraction is below 3 %vol and the petroleum derived gas oil has a cetane number of below 50 or a density higher than 845 kg/m³, (b) adding a Fischer-Tropsch derived kerosene fraction to the petroleum derived kerosene fraction in an amount sufficient to obtain a mixture having a smoke point value of above 25 mm or above 19 mm if the naphthalenes content of the mixture is below 3 %vol and (c) adding a Fischer-Tropsch derived gas oil fraction to the petroleum derived gasoil fraction such that the resultant mixture has a cetane number value of above 51, wherein the weight ratio of iso-paraffins to normal paraffins in the Fischer-Tropsch derived kerosene and gasoil is greater than 0.3.

Detailed description of the invention

The process according to the invention provides a simple method to obtain kerosene and gas oil products having desired properties while avoiding the need to co-processing a paraffinic crude. The use of Fischer-Tropsch products as blending components also facilitates the use of virgin kerosene and gas oil distilled from a naphthenic or aromatic crude type. This will thus reduce the need or even avoid hydroprocessing steps, which are normally applied to reduce the naphthenic or aromatics contents in these fractions.
Additional advantages are that also other product characteristics of the kerosene will be improved. E.g. the Hydrogen content will be increased due to a higher heating value of the kerosene. The thermal stability will also be improved.
Similarly also other gas oil properties apart from Cetane Number will be improved after blending virgin napthenic gasoils with Fischer-Tropsch derived Gasoils. E.g. Thermal Stability will be increased, density will be reduced, as well as Sulphur and Aromatics contents will be reduced as required by Motor manufacturers in their World Wide Fuels Charter (Revised in 2002) for Category 4 Diesel grades
The petroleum crude source feature a value of the Watson characterisation factor K of equal or below 12.0. These K-values are being calculated according to formulae and nomograms described in the API Technical Data Book (section 2 characterisation). Examples of crude petroleum sources having such a low K value are West African crudes, for example Forcados and Nigerian Light, Far East crudes, for example Champion Export, Labuan and Miri Light, North Sea crudes for example Danish (DUC), Troll, Gryphon and Alba crudes and South American crudes, for example Tia Juana Pesado, Bachequero and Maya. Preferably the petroleum derived fraction of the gas oil and kerosene products as obtained from the process according to the invention are for more than 50 wt%, more preferably more than 70 wt% and most preferably more than 90 wt% based on a crude having a K value equal or below 12.0.
From the petroleum crude source a petroleum derived kerosene and gas oil is isolated, preferably by distillation. Such distillation is preferably carried out in an atmospheric distillation column by well known processes for the person skilled in refinery operations. The fractions isolated by distillation and which have not been subjected to another conversion process are referred to as virgin distillate fractions.
The petroleum derived kerosene fraction will preferably have an ASTM D 86 distillation IBP of between 140 and 200 °C and a final boiling point of between 200 and max 300 °C.
The petroleum derived gas oil fraction should preferably have an ASTM D 86 IBP of between 250 and 300 °C and a FBP of between 340 and 380 °C.
The Fischer-Tropsch derived kerosene and gas oil fractions are suitably obtained from the (hydrocracked) Fischer-Tropsch synthesis product. Examples of Fischer-Tropsch derived kerosene and gas oils are described in EP-A-583836 , WO-A-9714768 , WO-A-9714769 , WO-A-011116 , WO-A-011117 , WO-A-0183406 , WO-A-0183648 , WO-A-0183647 , WO-A-0183641 , WO-A-0020535 , WO-A-0020534 , EP-A-1101813 , US-A-5766274 , US-A-5378348 , US-A-5888376 and US-A-6204426 .
Suitably the Fischer-Tropsch derived kerosene will consist of at least 90 wt%, more preferably at least 95 wt% of iso and linear paraffins. The weight ratio of iso-paraffins to normal paraffins will suitably be greater than 0.3. This ratio may be up to 12. Suitably this ratio is between 2 and 6. The actual value for this ratio will be determined, in part, by the hydroconversion process used to prepare the Fischer-Tropsch derived kerosene or gas oil from the Fischer-Tropsch synthesis product. Some cyclic-paraffins may be present.
The Fischer-Tropsch derived kerosene will suitably have a smoke point of higher than 25 mm and preferably above 50 mm and the ASTM D 86 distillation curve which will for its majority be within the typical kerosene range: between about 150 and 200 °C, a density of about 740 kg/m³ at 15 °C, and zero sulphur and aromatics levels (below detection limits).
Suitably the Fischer-Tropsch derived gas oil will consist of at least 90 wt%, more preferably at least 95 wt% of iso and linear paraffins. The weight ratio of iso-paraffins to normal paraffins will suitably be greater than 0.3. This ratio may be up to 12. Suitably this ratio is between 2 and 6. The actual value for this ratio will be determined, in part, by the hydroconversion process used to prepare the Fischer-Tropsch derived kerosene or gas oil from the Fischer-Tropsch synthesis product. Some cyclic-paraffins may be present.
The Fischer-Tropsch derived gas oil will suitably have a cetane number of higher than 60 and preferably above 70 and an ASTM D 86 distillation curve which will for its majority be within the typical gas oil range: between about 200 and 400 °C. The Fischer-Tropsch gas oil will suitably have a T90 %vol of between 300-400 °C, a density of between about 0.76 and 0.79 g/cm³ at 15 °C, and a viscosity between about 2.5 and 4.0 centistokes at 40 °C.
Blending can either be performed by so-called in-line blending, on-line blending or batch blending. This depends on the level of automation. In batch blending the petroleum derived fraction and the Fischer-Tropsch derived fraction are first mixed and subsequently supplied to a storage vessel and than supplied to a ship, rail or road car or other means of transport of the final blend. The desired product quality, i.e. smoke point or cetane number, of the feed to the storage vessel is measured and the quantity of the blending components is adjusted such that the property value is maintained within a pre-determined range in order to minimise quality give-away.
When in line blending is being applied no intermediate storage vessel is being applied but the blending ratio/volumes are adjusted automatically in line by Quality Measuring Instruments(QMI) and blends are directly discharged into the ship, rail or roadcar. The measurement and control of the quality or property of the blend in line can be performed by well known techniques, for example near infrared (NIR). Examples of a suitable method is describe in WO-A-0206905 .
The invention will be illustrated with the following non-limiting examples. The Examples are based on calculations using known blending rules.

Example 1

A naphthenic crude having a UOPK value of 11.5 is distilled into a naphtha fraction, a kerosene fraction and a gas oil fraction. The properties of the different fractions are listed in Table 1.

Table 1 Distillates properties of a typical Naphthenic crude

	Kerosene	Gas oil
Yield on naphthenic crude (%woc)	12.2	36.9
Initial boiling point (°C)	165	235
Final boiling point (°C)	235	350
Density (spec <845 kg/m³ Diesel EN 590)	840	887
Smoke point (spec >25 mm)	18	-
Aromatics (%vol)	21	43
Sulphur (%wt)	0.02	0.07
Cetane number (spec >51	33	38.5

Example 2

Example 1 is repeated. In addition an paraffinic crude having a Watson K characterisation factor value of 12.3 was distilled to obtain blending components to improve the kerosene and gas oil properties of the fractions listed in Table 1. The amount of paraffinic crude that was used was enough to obtain a kerosene and gas oil mixture to adjust the respective fraction of Table 1 to meet the desired specification. The properties of the blends are reported in Table 2.

Table 2 Distillates properties of Paraffinic and Naphthenic crudes and blend

	Naphthenic crude		Paraffinic crude		Crude Blend (31/69 %w/w N/P)
	Kero	Gasoil	Kero	Gasoil	Kero	Gasoil
Yield on paraffinic crude (%woc)	12.2	36.9	17.1	28.6	15.5	31.3
Initial boiling point (°C)	165	235	165	235	165	235
Final boiling point (°C)	235	350	235	350	235	350
Density (kg/m³) (spec <845 kg/m³ Diesel EN 590)	840	887	790	826	0.806	0.845
Smoke point (spec >19 mm)	18	-	26	-	24
Aromatics (%vol)	21	43	16	14	17	24
Sulphur (%wt)	0.02	0.07	0.01	0.04	0.01	0.05
Cetane number (spec >51	33	38.5	52	62.8	47	55

As can be seen from Table 2 a quality give away is observed for Smokepoint of the Kero produced from the blend and some of the Gasoil qualities like Cetane and Density.

Example 3

Example 1 is repeated. To the kerosene and gas oil fractions of Table 1 an amount of Fischer-Tropsch kerosene and gas oil (having the properties as listed in Table 3) respectively is added in an amount sufficient to meet the smoke point and cetane number specifications. The resulting properties are listed in Table 4.

Table 3 FT Distillates properties

	Fischer-Tropsch derived kerosene	Fischer-Tropsch derived Gas oil
Initial boiling point (°C)	150	200
Final boiling point (°C)	200	345
Density (kg/m³)	738	775
Smoke point (mm)	>50	-
Cetane number	60	76
Sulphur (ppmwt)	<1 (below detection limits)	<1 (below detection limits)
Aromatics (%vol)	<0.1	<0.1

Table 4 Blends of FT distillates with Naphthenic crude distillates

	Kerosene from Naphthenic crude	Kerosene Blend with FT kerosene	Gasoil from Napthenic crude	Gasoil Blend with FT Gas oil
Fraction of Fischer-Tropsch derived components in blend (%wt)	0	5	0	34
Initial boiling point (°C)	165	162	235	220
Final boiling point (°C)	235	230	350	348
Density kg/m³ (spec <845 kg/m³ EU 590 Diesel)	840	834	887	845
Smoke point mm (spec >19 mm)	18	19.6	-	-
Cetane number (spec >51 EU 590)	33	35	38.5	52
Sulphur (%wt)	0.02	0.019	0.07	0.046
Aromatics (%vol)	21	20	43	27

Claims

Process to prepare a kerosene and a gasoil product from a crude petroleum source having a Watson characterisation factor K value of equal or below 12.0 by
(a) isolation of a petroleum derived kerosene fraction and a petroleum derived gasoil fraction from said crude petroleum source, wherein the petroleum derived kerosene fraction has a smoke point of below 25 mm or below 19 mm if naphthalenes content of the kerosene fraction is below 3 %vol and the petroleum derived gas oil has a cetane number of below 50 or a density higher than 845 kg/m³,

(b) adding a Fischer-Tropsch derived kerosene fraction to the petroleum derived kerosene fraction in an amount sufficient to obtain a mixture having a smoke point value of above 25 mm or above 19 mm if the naphthalenes content of the mixture is below 3 %vol and (c) adding a Fischer-Tropsch derived gas oil fraction to the petroleum derived gasoil fraction such that the resultant mixture has a cetane number value of above 51, wherein the weight ratio of iso-paraffins to normal paraffins in the Fischer-Tropsch derived kerosene and gasoil is greater than 0.3
Process according to claim 1, wherein the kerosene and the gas oil is isolated from the crude petroleum source in a hydroskimming refinery.
Process according to any one of claims 1-2, wherein the petroleum gas oil and kerosene are for more than 50 wt% based on a crude having a Watson K value equal or below 12.0.
process according to any one of claims 1-3, wherein the petroleum derived kerosene fraction has a ASTM D86 distillation initial boiling point of between 140 to 200 °CC and a final boiling point of between 200 to 300 °C.
Process according to any one of claims 1-4 wherein the petroleum derived gas'oil fraction has a ASTM D86 distillation initial boiling point of between 250 to 300°C and a final boiling point of between 340 and 380°C.
Process according to any one of claims 1-5, wherein the Fischer-Tropsch derived kerosene has a iso-paraffin to normal paraffin weight ratio of between 2 and 6.