WO2006069407A2

WO2006069407A2 - Production of diesel

Info

Publication number: WO2006069407A2
Application number: PCT/ZA2005/000185
Authority: WO
Inventors: Cyril David Knottenbelt; Carl Dunlop; Kholekile Zono; Maxwell Thomas
Original assignee: The Petroleum Oil And Gas Corporation Of South Africa (Pty) Ltd
Priority date: 2004-12-23
Filing date: 2005-12-20
Publication date: 2006-06-29
Also published as: US20080250699A1; WO2006069407A3; EP1836282A2

Abstract

The invention provides a process for the production of synthetically derived diesel and diesel produced by the process. The process includes the steps of catalytic conversion of Fisher-Tropsch derived light olefins to distillates (COD) over a zeolite type catalyst at pressures of more than 50barg, one step hydrotreating the COD product to simultaneously hydrogenate both olefins and aromatics, and collecting a hydrotreated fraction boiling between about 180°C to 360°C.

Description

Title: Production of Near Zero Aromatics Containing Diesels

Technical field of the invention

This invention relates to a process for the production of synthetically derived near zero aromatic content diesel.

Background to the invention

It is well known that aromatics are carcinogenic and undesired in diesels. Ever evolving vehicle emission control regulations require low aromatic content diesel fuels.

Crude derived diesels are not popular due to their high sulphur content.

While High Temperature Synthetically derived Fischer-Tropsch (FT) diesel fuels have a low or near zero sulphur content, they are associated with relatively high aromatic levels some of which are multiple ring aromatic compounds which are considered undesirable.

It is an object of this invention to provide a one step process for the production of a synthetically derived diesel having typically less than 0.1% of mono cyclic (single ring) aromatics and no hazardous multiple ring aromatics (polycyclics). It is also an object of this invention to provide near zero aromatic diesel with good cold flow properties and low emission qualities.

Normally catalytical conversion of Fisher-Tropsch derived olefins with shape selective zeolites to distillates (COD) produce distillates having more than about 10% aromatics.

In this specification, references to percentage proportions refer to volume percentage proportions unless otherwise specified. Traditionally hydrogenation of synthetically derived distillates is performed in two steps i.e. olefin hydrogenation followed by aromatic hydrogenation using a second more active catalyst. Catalysts used for the first step normally include cobalt and/ or other metals. These catalysts normally need to be sulphided with sulphur containing compounds such as DMDS to ensure that the catalyst remains in the sulphided form. The sulphur containing compounds also quench the activity of the catalyst preventing runaway reactions emanating from highly reactive olefinnic feeds.

General description of the invention

According to a first aspect of the invention, there is provided a process for the production of synthetically derived diesel, which process includes the steps of: catalytic conversion of Fisher-Tropsch derived light olefins to distillates

(COD) over a zeolite type catalyst at pressures of more than 50barg; one step hydrotreating the COD product to simultaneously hydrogenate both olefins and aromatics; and collecting a hydrotreated fraction boiling between about 180⁰C to 360^°C.

The Fisher-Tropsch derived olefins are converted to distillates over a shape selective zeolite type catalyst, a COD-9 or similar catalyst as defined by the International Zeolite Association (IZA). More specifically the Fisher- Tropsch derived light olefins comprising of carbon numbers 3 to 6 are oligomerised and isomerised to produce an intermediate highly branched olefinnic distillate.

The catalytic conversion reactor temperature may be maintained below 280^° C.

The one step deep hydrotreating step may include hydrogenation over a Group 10 metal catalyst. The Group 10 metal catalyst may include a high nickel content.

Alternatively, the Group 10 catalyst may include a noble metal catalyst such as supported platinum catalysts. These catalysts may also be bimetallic.

The support for the metal may be neutral. The applicant is aware that an acidic support causes unwanted cracking during hydrogenation.

The catalyst may be Nickel supported on alumina or platinum supported on allumina. (Sud Chemie G134 or Axens LD 402).

The one step hydrotreating step may include hydrogenation over a high nickel content hydrotreating catalyst or hydrotreating with a noble metal catalyst. Reactor pressures for such reactions would typically range from 5000 kPa to about 8000 kPa but not excluding higher pressures. Reaction temperatures vary from about 200⁰ C to 260 ^"C while the LHSV range from 0.3 to 2 depending on the feed.

The olefin content measured as Bromine Number determines the reactivity of a particular feed, highly reactive feeds may require a portion of the hydrogenated product to be recycled to quench the hydrogenation reaction. The LHSV may also be altered to below 0.5 to control excessive exothermic reactions.

The catalyst may be loaded into the reactor bed in an increased graded approach to limit an excessive exothermic reaction developing at the top of the reactor. The catalyst bed may have multiple zones with increased grades. Typically, a 4-zone graded catalyst bed. The concentration of the active catalyst in each of the 4 zones may be diluted with an inert ceramic in the following typical ratios of catalyst to ceramics, 0.2; 0.5; 170.0 and 650.

The Fisher-Tropsch derived olefins are converted to distillates over a shape selective zeolite catalyst. The conversion includes oligomerising and isomerising of the Fisher-Tropsch derived olefins to produce an intermediate olefinic COD product.

The catalytic conversion at pressures of more than 50barg and/ or a reactor temperature maintained below 280⁰ C produces a product stream with low aromatics and it will be appreciated that the relative low aromatics from the COD step allows moderate hydrogenation reactor conditions.

The process may include the step of blending the intermediate COD product or the hydrotreated fraction with crude derived diesels to enhance performance and/ or emission properties of crude derived diesels.

The process may include' the step of blending the intermediate COD product or the hydrotreated fraction with biodiesel derived from vegetable oils to improve the cold flow properties and motoring performance of the biodiesel.

The process may include the step of blending the intermediate COD product or the hydrotreated fraction with alcohols to reduce particulate matter emissions from fuels derived from intermediate COD product or the hydrotreated fraction. The alcohols may range from 1 to 5 carbon alcohols, preferably 2 to 5 carbon alcohols.

According to a second aspect of the invention there is provided a synthetically derived diesel produced by a catalytic conversion of Fisher- Tropsch derived olefins to distillates (COD) and deep hydrotreating thereof, the diesel boiling in the range of about 180 to 360^° C, and including: less than 10% n-paraffins; more than 60% iso-paraffins; and less than 1 % aromatics.

The iso-paraffins may be predominantly methyl branched.

The methyl branched iso-paraffins may range between 50 and 80%, preferably between 60 and 70%, of the iso-paraffins. The diesel may include about 20% naphtenes.

The naphtenes may be predominantly monocyclics.

The applicant has found that a relatively high cetane number can be maintained by replacing n-paraffins with predominantly methyl branched iso- paraffins and monocyclic naphtenes instead of more branched iso-paraffins and bicyclic naphtenes.

The boiling range may be between 180 and 360⁰ C, however preferably between 210 and 345^° C.

The flash point of the diesel as measured by ASTM D93 may be higher than 6O⁰C but preferably as high as 100^° C significantly improving the safety of product during handling.

The diesel fuels kinematic viscosity at 40^° C as measured by ASTM D445 may be below about 5.0 cSt but not lower than 2.0 cSt as measured at 40^° C. The kinematic viscosity plays a role in the diesel fuel pump ability as well as the fuel injectors ability to efficiently inject fuel. High viscosity fuels negatively influence the fuel atomisation process limiting the formation fine droplets that lead to poor air fuel mixing within the combustion chamber (cylinder) resulting in turn in incomplete combustion accompanied by loss of power and economy. Excessively low viscosities lead to fuel pump leakage, incorrect metering and the inability for the fine atomised spray to penetrate the length of the combustion chamber and will result in poor combustion and in turn, result in loss of power and economy. A viscosity between 2.2 and 2.8 cSt as tested by ASTM D445 at 40^° C is preferred.

The cold flow properties are excellent due to the over 800 isoparaffinic hydrocarbon molecules that the diesel fuel comprises of. Low temperature operability is measured by Cold Filter Plugging Point (CFPP) as tested by IP 85

309 and is as low as minus 45^° C enabling these fuels to be used even in extreme low temperature conditions.

The total sulphur content of the diesel may be below 2 ppm (m/m) as measured by ASTM 3120. Sulphur in diesels creates a distinctive odour and contributes to the emission of particulate matter during combustion. Fuels with such low sulphurs enable modern vehicle exhaust emission treatment technologies.

The olefins content may be respectively reflected by a Bromine

Number of well below 1 mg/100g as measured by IP 129 and a peroxide number of less than 1 mg/100g as measured by ASTM D3703.

The diesel may include blends with crude derived diesels in 10 to 90%v/v, preferably 30 to 70%v/v ratios.

The diesel may include blends with biodiesel derived from vegetable oils.

The diesel may include blends with 1 to 5 carbon alcohols in 0.5 to

10%v/v,

The compositions of the fuels are such that once combusted they offer excellent environmental benefits over crude derived diesel fuels. Exhaust emission qualities as tested on heavy-duty vehicles and compared against a standard US pump crude derived diesel fuel offered reductions in the following regulated emissions; particulate matter, oxides of nitrogen, carbon monoxide, carbon dioxide and hydrocarbons.

These fuels offer a relatively high Cetane Number of greater than 50 as tested by ASTM D613. Detailed description of the invention

The invention is now further described by non limiting examples.

EXAMPLE 1

Light olefins in the carbon range C₃ to C₆ originating from a the High Temperature Fischer Tropsch plant located in Mossel Bay were oligomerised over a proprietary zeolyte catalyst (COD 9) as supplied by Sud Chemie. The oligomerisation reaction was performed at moderate temperatures below 280^° C and relatively high pressures of 55 bar process were used for the oligomerisation reaction to produce an intermediate olefinic distillate with a Bromine Number of over 90 g Br/10Og sample and containing 5.8% aromatics. Normally the intermediate distillate would contain more than 10% aromatics. This distillate was hydrotreated in one step using a high Nickel content commercial catalyst as supplied by Sud Chemie (Sud Chemie G134). The catalysts (about 270 cc) were loaded into a pilot plant reactor in a graded bed format and diluted with inert ceramics in the ratios of catalyst to ceramics of, 0.2; 0.5; 170.0 and 650. The reactor pressure was maintained at 58 bar, the WABT did not exceed 220^° C₁ the LHSV was maintained at 0.9 and a third of the product was recycled back to the feed.

The one step hydrotreated distillate was fractioned by means of a true boiling point distillation apparatus to yield a diesel fraction in the boiling range 220^° C to 340^° C. This fuel was found to contain less than 0.1 % v/v aromatics and no detectable polyaromatic hydrocarbons.

The fuel typical quality is depicted below:

PROPERTY MEASURE TEST METHOD TYPICAL

UNIT ANALYSI!

Colour ASTM ASTM D 156 +30

Density @ 20⁰C kg/I ASTM D 1298 0.796

Aromatic Content % (m/m) IP391 < 1

Distillation: ASTM D86 90% (v/v) Recovery ⁰C 320

FBP ⁰C 340

Flash Point ( P.M.cc.) ⁰C ASTM D93 93

Kinematic Viscosity @ 40⁰C CSt ASTM D445 2.7

Cold Filter Plugging Point ⁰C IP309 < minus 45

Ash Content % (m/m) ASTM D482 < 0.01

Sediment by Extraction % (m/m) ASTM D473 < 0.01

Water Content % (v/v) ASTM D1744 (Mod) < 0.01

Carbon Residue, Ramsbottom % (m/m) ASTM D524 0.15

(on 10% residue)

Total Sulphur % (m/m) ASTM D2622 or 0.0004

ASTM D5453

Copper Corrosion (3hrs @ 100⁰C) Rating ASTM D 130

Cetane Number - ASTM D613 - IP41 54

Oxidation Stability mg/100 ml ASTM D2274 < 0.1

The above fuel combined with it's low aromatics content, favourable emission qualities and excellent cold flow properties make it an excellent fuel for use in polluted cities (City Diesel) especially those with cold climates.

EXAMPLE 2

Light olefins in the carbon range C3 to C6 originating from a the High Temperature Fischer Tropsch plant located in Mossel Bay were oligomerised over a proprietary zeolyte catalyst (COD 9) as supplied by Sud Chemie. The oligomerisation reaction took place at moderate temperatures below 280^° C and relatively high pressures of 55 bar process were used for the oligomerisation reaction to produce an oleffinic distillate with a Bromine Number of over 12O g Br/10Og sample. This distillate was hydrotreated in one step using a supported Platinum commercial catalyst (Axens LD402). The catalyst (270 cc) was loaded into a pliot plant a graded bed format and diluted with inert ceramics. The reactor pressure was maintained at 60 bar, the

WABT did not exceed 230^° C, the LHSV was maintained at 0.9 and a portion of the product was recycled.

The one step hydrotreated distillate was fractioned by means of a true boiling point distillation apparatus to yield a diesel fraction in the boiling range 220^°C to 340^° C. This fuel was found to contain less than 0.1 % v/v aromatics.

8 Emission testing performed on a similar fuel made from the process was found to offer substantial vehicle regulated reductions over commercial low sulphur diesel fuels. Reductions were noted for all regulated emissions, these included hydrocarbons, carbon monoxide, carbon dioxide, nitrous oxides and particulate matter.

The fuel was dosed with a commercial lubricity additive (OLI 5000) as supplied by Ethyl at a dose rate of 150 ppm v/v. This was found to be an ideal additive for sulphur free synthetically derived fuels as produce by the above process.

The absence of sulphur from these fuels enables modern vehicle exhaust aftertreatment technologies. In cases were these fuels are used in a bus equipped with a catalytic device the exhaust emissions were further reduced.

The fuel typical quality is depicted below:

PIONA composition as tested by GC-FIMS:

Parafins-lso 65,3 % mass

Parafins- n 2,7 % mass

Monocycloparaffin's24,3 % mass

Dicycloparaffin's 7,6 % mass Aromatics <0.1 % mass

The % branching of iso-paraffins; methyl 60 to 70; ethyl 2 to 10; propyl 0.2 to 5; butyl 0.1 to 5; hexyl θ.1 to 2. The NMR branching index is 0.165, 0 indicating absence of branching and 1 indicating full branching.

Claims

1. A process for the production of synthetically derived diesel, which process includes the steps of: catalytic conversion of Fisher-Tropsch derived light olefins to distillates

(COD) over a zeolite type catalyst at pressures of more than 50barg; one step hydrotreating the COD product to simultaneously hydrogenate both olefins and aromatics; and collecting a hydrotreated fraction boiling between about 180⁰ C to 36O⁰ C.

2. A process as claimed in Claim 1 , wherein the Fisher-Tropsch derived olefins are converted to distillates over a shape selective zeolite type catalyst selected from a COD-9 or similar catalyst.

3. A process as claimed in Claim 1 or Claim 2, wherein the catalytic conversion reactor temperature is maintained below 280^° C.

4. A process as claimed in any one of the previous claims, wherein the one step hydrotreating step includes hydrogenation over a Group 10 metal catalyst.

5. A process as claimed in Claim 4, wherein the Group 10 metal catalyst includes a high nickel content.

6. A process as claimed in Claim 4, wherein the Group 10 catalyst includes a noble metal such as platinum supported on a carrier.

7. A process as claimed in any one of Claim 4 to Claim 6, wherein the hydrotreating catalyst is bimetallic.

8. A process as claimed in any one of the previous claims, wherein the reactor pressures for the hydrotreating step reactions range from 5000 kPa to about 8000 kPa with reaction temperatures ranging from about 200^° C to 26O⁰ C while the LHSV range from 0.3 to 2.

9. A process as claimed in any one of claims 4 to 8, wherein the hydrotreating catalyst is loaded into the reactor bed in an increased graded approach to limit an excessive exothermic reaction developing at the top of the reactor.

10. A process as claimed in any one of the previous claims, which includes the step of blending the COD product or the hydrotreated fraction with crude derived diesel, biodiesel or alcohols.

11. A synthetically derived diesel produced by a catalytic conversion of Fisher-Tropsch derived olefins to distillates (COD) and one step hydrotreating thereof, the diesel boiling in the range of about 180 to 360^° C, and including: less than 10% n-paraffins; more than 60% iso-paraffins; and less than 1 % aromatics.

12. A synthetically derived diesel wherein the iso-paraffins are predominantly methyl branched.

13. A synthetically derived diesel as claimed in Claim 12, wherein the methyl branched iso-paraffins range between 50 and 80%.

14. A synthetically derived diesel as claimed in Claim 12, wherein the methyl branched iso-paraffins range between 60 and 70%, of the iso- paraffins.

15. A synthetically derived diesel as claimed in any one of the previous claims, which includes about 20% naphtenes.

16. A synthetically derived diesel as claimed in Claim 15, wherein the naphtenes includes predominantly monocyclics.

17. A synthetically derived diesel as claimed in any one of the previous claims having a boiling range between about 210 and 345^° C.

18. A synthetically derived diesel as claimed in any one of the previous claims having a flash point at least as high as high as 100^° C.

19. A synthetically derived diesel as claimed in any one of the previous claims having a kinematic viscosity between 2.2 and 2.8 cSt as tested by ASTM D445 at 40^° C.

20. A synthetically derived diesel as claimed in any one of the previous claims having a total sulphur content of the diesel below 2 ppm

(m/m) as measured by ASTM 3120.

21. A synthetically derived diesel as claimed in any one of the previous claims having a Bromine Number of below 1 mg/100g as measured by IP 129 and a peroxide number of less than 1 mg/100g as measured by ASTM D3703.

22. A synthetically derived diesel as claimed in any one of the previous claims, which includes blends with crude derived diesels, biodiesel or alcohols.

23. A process for the production of synthetically derived diesel, substantially as herein described.

24. A synthetically derived diesel, substantially as herein described.