WO2009116989A1

WO2009116989A1 - Process for the preparation of a middle distillate fuel

Info

Publication number: WO2009116989A1
Application number: PCT/US2008/057243
Authority: WO
Inventors: Joanna Margaret Bauldreay; Vijay Nair; Augustinus Wilhelmus Maria Roes; James Timothy Talbert
Original assignee: Shell Oil Company; Shell Internationale Research Maatschappij B.V.
Priority date: 2008-03-17
Filing date: 2008-03-17
Publication date: 2009-09-24

Abstract

The present invention relates to a process for the preparation of a middle distillate fuel from a kerogen pyrolysis product, comprising (a) hydrotreating the middle distillate fraction of a kerogen pyrolysis product, and (b) isolating a kerosene or diesel base fuel from the product of step (a) by means of distillation.

Description

PROCESS FOR THE PREPARATION OF A MIDDLE DISTILLATE FUEL

The present invention relates to a process for the preparation of middle distillate fuels from kerogen materials from oil shale, the base fuels thus obtained, blends thereof, and their use in compression ignition (diesel) engines or aviation engines.

Oil shale is a fine-grained sedimentary rock containing kerogen. The latter is a solid mixture of hydrocarbons . The kerogen in oil shale can be converted to a synthetic crude, through mining and subsequent surface retorting of the mined product, as described for example in Ullman' s Encyclopedia of Industrial Chemistry, Fifth Edition, Volume 18A, VCH Publishers, 1991, 101-126. When heated to a sufficiently high temperature, a full range liquid shale oil product and a combustible shale gas is yielded. A work-up procedure of a full range shale oil to obtain lubricating base oils is described for instance in US-A-4 , 744 , 884. This document discloses a process comprising hydrotreating of a full range shale oil, followed by hydrodewaxing the fraction boiling above 343⁰C derived from the hydrotreating step. The full range shale oil is most likely obtained from a mined and subsequently retorted full range shale oil. The product from the hydrodewaxing step has subsequently to be hydrogenated. After hydrogenating, the product from the hydrogenation stage is fractionated into one or more lubricating oil fractions. This process is rather complex. Furthermore, it contains a number of distillations which are energy consuming. The products disclosed in US-A-4, 744 , 884 comprise high concentrations of polynaphthenic compounds as well as of unsaturated compounds, including polyaromatic compounds, which are highly undesirable when a product is desired with a high thermal stability.

Applicants have now found that a middle distillate fuel product with high thermal stability and good cetane index can be obtained from oil shale by subjecting the oil shale to if the oil shale is converted in an in-situ conversion, and if the thus obtained in-situ kerogen pyrolysis product is hydrotreated .

Accordingly, the present invention relates to a process for the preparation of a middle distillate fuel from a kerogen pyrolysis product, comprising

(a) hydrotreating the middle distillate fraction of a kerogen pyrolysis product, and

(b) isolating a kerosene or diesel base fuel from the product of step (a) by means of distillation.

Applicants have found that the pyrolysis product of kerogen in oil shale may be converted to a middle distillate base fuel or a fuel blending component having a high energy content, relatively low density, and high thermal stability, and a high cetane number, and good low temperature performance through a relatively simple process, and under mild conditions.

As feed for step (a) , preferably a synthetic crude is produced from the kerogen in the oil shale formation utilizing downhole heaters, producing a hydrocarbon fluid from the formation by pyrolysing hydrocarbons present in the formation. This process has been described for instance in US-A-2634961, US-A-2732195, US-A-2780450, US- A-2789805, US-A-2923535, US-A-4886118, US-A-2914309, US- A-4344483, US-A-4067390 , US-A-4662439, US-A-4384613, US- A-2923535, US-A-4886118 and EP-A-1276959. This process treats a hydrocarbon containing formation or reservoir in situ and produces a hydrocarbon fluid from the formation by pyrolysing hydrocarbons present in the formation. The term "pyrolysis product" generally refers to a fluid produced substantially during pyrolysis of hydrocarbons. As used herein, a "pyrolysis zone" generally refers to a volume of hydrocarbon containing formation that is reacted or reacting to form a pyrolysis product. The pyrolysis product may be obtained either from an in-situ process, wherein the heat is generate in a kerogen containing formation to produce a pyrolysis product, or a to a surface retorting of kerogenic material. Preferably, the pyrolysis product is obtained in the in-situ process, since the pyrolysis products having a low olefin content (e.g.<10% by weight) and low average carbon number (e.g.<35) . The absence of larger amounts of components having more than 35 carbon atoms is particularly beneficial for the manufacture of fuel products, since the need for conversion of these compounds through suitable conversion processes such as thermal or catalytic cracking into the fuel carbon range to obtain a product in the Diesel boiling range is only strongly reduced. An example of such a process is that disclosed in EP-A-1276959, wherein a system of heat injection and hydrocarbon fluid production wells for use in the method according to the invention and pyrolysis products having a low olefin content (e.g.<10% by weight) and low average carbon number (e.g.<35) which are obtainable by the in- situ pyrolysis method and system is described in some detail.

Preferably, the middle distillate fraction of a kerogen pyrolysis product is derived from an in-situ conversion of oil shale set out above. Such feeds were further found to contain only a limited amount of metals, generally present in concentrations below 1.0 ppmw, with most of the metals present in much lower concentrations. However, preferably a guard bed of appropriate demetalization catalyst is employed to efficiently remove any metal ions considered to interfere with the catalysts of steps (a) and/or (c) .

The term "middle distillate fraction" herein refers to the hydrocarbonaceous product boiling in the range of from 18O⁰C to 400⁰C (ASTM D86) . This middle distillate range comprises a kerosene fraction (usually boiling of from 180 to about 23O⁰C) and a Diesel fraction (usually boiling of from about 230 to 400°C) . Although full range shale oil, or middle distillate fractions of shale oil derived from conventional surface retorting may be employed, these products are generally less suitable for the subject process due to the high content of metals, heteroatom containing compounds, and olefins. This may require a pre-treatment, e.g. to remove arsenic, copper iron and/or zinc ions present in the feed. Furthermore, in order to achieve products of sufficiently high stability and cetane numbers, rather stringent treatment conditions have to be employed in step (a), and the yields are lower.

The hydrotreating reaction of step (a) is preferably performed in the presence of hydrogen and a catalyst, which catalyst can be chosen from those known to one skilled in the art as being suitable for this reaction. Catalysts for use in step (a) typically comprise an acidic functionality and a hydrogenation- dehydrogenation functionality. Preferred acidic functionalities are refractory metal oxide carriers. Suitable carrier materials include silica, alumina, silica-alumina, zirconia, titania and mixtures thereof.

Preferred carrier materials for inclusion in the catalyst for use in the process of this invention are silica, alumina and silica-alumina.

Preferred hydrogenation-dehydrogenation functionalities are Group VIII non-noble metals, for example iron, nickel and cobalt which non-noble metals may or may not be combined with a Group IVB metal, for example W or Mo, oxide promoters. The catalyst may comprise the hydrogenation/dehydrogenation metal active component in an amount of from 0.005 to 5 parts by weight, preferably from 0.02 to 2 parts by weight, per 100 parts by weight of carrier material.

A particularly preferred catalyst comprises an alloy of Nickel and Molybdenum and/or Cobalt and molybdenum on an alumina carrier. If desired, applying a halogen moiety, in particular fluorine, or a phosphorous moiety to the carrier, may enhance the acidity of the catalyst carrier. Examples of suitable hydrocracking/hydroisomerisation processes and suitable catalysts are described in WO-A-0014179, EP-A-532118, EP- A-666894 and EP-A-776959.

Preferably, the catalyst bed is protected by a guard bed against potential fouling due to particulates, asphaltenes, and/or metals present in the feed. Preferably any compounds having 4 or less carbon atoms and any compounds having a boiling point in that range are separated from the synthetic crude product before being used in step (a) . The synthetic crude product preferably has not been subjected to any hydroconversion step on the surface apart from the, above referred to, optional mild hydrotreating step.

In addition to the synthetic crude also other feeds may be additionally processed in step (a) . Possible other fractions may suitably be a higher boiling fraction obtained in step (b) .

In step (a) the feed is contacted with hydrogen in the presence of the catalyst at elevated temperature and pressure. The temperatures typically will be in the range of from 175 to 380 ⁰C, preferably higher than 250 ⁰C and more preferably from 300 to 370 ⁰C, and yet more preferably from at a reactor temperature from 343 to to 370 ⁰C (650 to 700° F) .

Preferably, step (a) is performed at a pressure reactor pressure between at 500 and 5000 psig reactor pressure, preferably at 750 to 2500, more preferably at 1000 to 1800 psig. Liquid hourly space velocities (LHSV) are preferably in the range of from of 0.5 - 1.0 1/hr, and hydrogen treat rates preferably in the range of from 4,000 - 5,000 SCF/bbl.

In step (b) the product of step (a) is preferably separated into one or more lower boiling fuel fractions, and a kerosene and/or Diesel fraction.

The term "gas oil" or "gas oil (blending component) "herein refers to middle distillate fractions, such as the kerosene or Diesel fractions defined herein below. The term "middle distillate fraction" herein refers to the hydrocarbonaceous product boiling in the range of from 18O⁰C to 400⁰C (ASTM D86) . This middle distillate range may comprise a kerosene fraction

(boiling in the typical kerosene range of from about 180 to about 26O⁰C) and a Diesel fraction (usually boiling of from about 26O⁰C to 400°C) .

The product fractions obtained may be employed as kerosene for primary use as jet fuel, and a higher boiling Diesel for primary use in compression ignition engines .

The kerosene fraction obtainable by the process may be employed as a kerosene base fuel. As a kerosene base fuel, it preferably has an initial boiling point in the range 130 to 16O⁰C and a final boiling point in the range 250 to 300°C as determined according to ASTM method D86. It preferably comprises less than 15% by weight of aromatic compounds, and at least of 80 % by weight of aliphatic hydrocarbons, of which at least 20% by volume are n-paraffins and at least 25% by volume are cycloparaffins, as determined by according to ASTM method D2425. Within the context of this application, the term

"aliphatic hydrocarbons" includes paraffins (n- and iso- paraffins) as well as cycloparaffins, otherwise also known as naphthenic compounds. The term "naphthenic aromatic compounds" herein describes alkyl benzenes and higher annulated aromatic ring systems with alkyl side chains . Monoaromatic compounds are compounds having one aromatic ring structure, while diaromatic compounds have two aromatic ring structures, while triaromatic compounds have three aromatic ring structures. The term "base fuel" as used herein determines a fuel component that can be used either neat, additized, or as blending component.

The kerosene base fuel thus obtained was surprisingly found to have a very high thermal stability when compared to mineral crude derived hydrotreated kerosene compositions. This stability was particularly high at elevated temperatures, i.e. at temperatures above 34O⁰C, as illustrated by the Jet Fuel Thermal Oxidation Test (JFTOT, as determined according to ASTM method D3241) . This test method covers the procedure for rating the tendencies of gas turbine fuels to deposit decomposition products within the fuel system.

A Diesel fraction may be employed as Diesel base fuel. Such Diesel base fuels usually preferably have a TlO wt% (as determined by ASTM method D86) boiling point of between 200 and 450 ⁰C. The T90 wt% boiling point of the gas oil precursor fraction is preferably between 300, and preferably between 400 and 550 ⁰C. If the feed to step (a) contains higher boiling compounds, a separate higher boiling fraction may be removed from the gas oil precursor fraction in order to meet these T90 wt% boiling points. Diesel fuel compositions usually contain one or more base fuels which may typically comprise liquid hydrocarbon middle distillate gas oil(s). Such fuel compositions will typically have boiling points within the usual middle distillate range of 150 to 400⁰C, depending on grade and use. They will typically have a density from 750 to 1000 kg/m³, preferably for automotive uses from 780 to 860 kg/m³, at 15⁰C (e.g. ASTM D4502 or IP 365) and a cetane number (ASTM D613) of from 35 to 120, more preferably from 40 to 85. They will typically have an initial boiling point in the range 150 to 23O⁰C and a final boiling point in the range 290 to 400⁰C. Their kinematic viscosity at 4O⁰C (ASTM D445) might suitably be from 1.5 to 6 cSt. Industrial gas oils will contain a base fuel which may comprise fuel fractions such as the kerosene or gas oil fractions obtained in traditional refinery processes, which upgrade crude petroleum feedstock to useful products. Preferably such fractions contain components having carbon numbers in the range 5 to 40, more preferably 5 to 31, yet more preferably 6 to 25, most preferably 9 to 25, and such fractions have a density at 15⁰C of 650 to 1000 kg/m³, a kinematic viscosity at 2O⁰C of 1 to 80 cSt, and a boiling range of 150 to 400°C.

The fuels of the present invention preferably contain low levels of olefins. The fuels of the present invention preferably contain <5.0 weight% olefins, more preferably <2.0 weight % olefins, and even more preferably <1.0 weight % olefins. The weight % olefins can be calculated from the bromine number and the average molecular weight by use of the following formula: Wt % Olefins= (Bromine No.) (Average Molecular Weight) /159.8. The Diesel base fuel that was directly obtainable by the subject process could also serve as a Diesel fuel for compression ignition engines. However, it was found that the cold flow properties of the Diesel base fuel could be significantly improved by addition of a kerosene base fuel obtained by the same process. The resultant blend had a high thermal stability.

Accordingly, the present invention further relates to a fuel composition comprising a blend of a kerogen derived Diesel base fuel and a kerogen derived kerosene base fuel, and to a process for its preparation. In this blend, preferably, the kerosene base fuel is present in an amount of 0.1 to 99.9%v, more preferably 0.1 to 40%v, and most preferably 10 to 25% volume. The amount of kerosene present in the blend depends on the desired properties such as pour point and cloud point, as well as volatility and cetane number of the fuel.

The blend may be prepared simply by adding the two fractions under suitable conditions. However, the process for its preparation preferably comprises the steps of

(a) hydrotreating subsequently or in parallel a kerosene precursor fraction and a Diesel precursor fraction of a kerogen pyrolysis product, and

(b) isolating a diesel base fuel and a kerosene base fuel from the product of step (a) by means of distillation, and

(c) blending the diesel base fuel and a kerosene base fuel to obtain a Diesel fuel composition.

The blend preferably has a density at 15 ⁰C of between 0,775 and 0,820 kg/m3. It further preferably has a flash point of 140 to 180 ⁰F as determined according to ASTM method D93. It further preferably also has a total nitrogen content of less than 3 ppm as determined according to ASTM method D4629, and a total sulphur content of less than 15 ppm as determined according to ASTM method D5453. Yet further, the blend preferably comprising less than 15 % volume of aromatic compounds, as determined according to ASTM method D1319.

According to the present invention there is yet further provided a method of operating a jet engine or a diesel engine and/or an aircraft which is powered by one of more of said engines, which method involves introducing into said engine a Diesel fuel composition according to the present invention. The present invention may be used to formulate fuel blends which are expected to be of particular use in modern commercially available internal compression ignition engines as alternatives to the standard engine base fuels, for instance as commercial and legislative pressures favour the use of increasing quantities of synthetically derived fuels.

In the context of the present invention, "use" of a fuel component in a fuel composition means incorporating the component into the composition, typically as a blend (i.e. a physical mixture) with one or more other fuel components, conveniently before the composition is introduced into an engine.

The fuel compositions to which the present invention relates have use in aviation engines, such as jet engines or aero diesel engines, but also in any other suitable power source. Each base fuel may itself comprise a mixture of two or more different fuel components, and/or be additivated as described below. It may be desirable for the composition to contain 5%v or greater, preferably 10%v or greater, or more preferably 25%v or greater, of the fuel component according to the invention. The fuel blend according to the invention may itself be additivated (additive-containing) or unadditivated (additive-free). If additivated, e.g. at the refinery or in later stages of fuel distribution, it will contain minor amounts of one or more additives selected for example from anti-static agents (e.g. STADIS™ 450 (ex. Octel) ) , antioxidants (e.g. substituted tertiary butyl phenols), metal deactivator additives (e.g. N, N'- disalicylidene 1, 2-propanediamine) , fuel system ice improver additives (e.g. diethylene glycol monomethyl ether) , corrosion inhibitor/lubricity improver additives (e.g. APOLLO™ PRI 19 (ex. Apollo), DCI 4A (ex. Octel), NALCO™ 5403 (ex. Nalco) ) , or thermal stability improving additives (e.g. APA 101™, (ex. Shell)) that are approved in international civil and/or military jet fuel specifications .

Unless otherwise stated, the (active matter) concentration of each such additional component in the additivated fuel composition is at levels required or allowed in international jet fuel specifications.

In this specification, amounts (concentrations, %v, ppmw, wt%) of components are of active matter, i.e. exclusive of volatile solvents/diluent materials. The present invention is particularly applicable where the fuel composition is used or intended to be used in a jet engine, a direct injection diesel engine, for example of the rotary pump, in-line pump, unit pump, electronic unit injector or common rail type, or in an indirect injection diesel engine. It may be of particular value for rotary pump engines, and in other diesel engines which rely on mechanical actuation of the fuel injectors and/or a low pressure pilot injection system. The fuel composition may be suitable for use in heavy and/or light duty diesel engines . The present invention may lead to any of a number of advantageous effects, including good engine low temperature performance . Examples

The present invention will now be described by way of example:

Example 1

A diesel range hydrocarbon material originating from kerogen converted in-situ in a pilot production field was employed as feed for the preparation of the Diesel base fuel. This material was fractioned from a full range shale oil pyrolysis product.

The properties of the feed are listed in Table 1.

Table 1 Feedstock ex PARC Properties

The feed was subjected to a hydrotreatment in a hydrotreating microreactor pilot plant unit, by bringing the feed into contact with a catalyst in the presence of hydrogen and at elevated temperatures and pressure. The catalyst bed was an 80/20 stacked bed of (a) a commercially available Ni-Mo on alumina hydrotreating catalyst that is usually employed for nitrogen removal, followed by (b) commercial high performance Co-Mo catalyst on alumina employed for sulphur removal . The catalysts were diluted in a 2:1 volume ratio with 120 mesh (125 micrometer) silicon carbide, i.e., 2.0 volumes of silicon carbide to 1.0 volume of catalyst. The catalyst bed was protected by a guard bed of against potential fouling due to particulates, asphaltenes, and/or metals present in the feed.

This stacked bed configuration and the catalyst combination was employed to reduce both nitrogen and sulphur level of the diesel product to below specification of 15 ppmw for an Ultra Low Sulfur Diesel (ULSD) commercial product.

The catalyst beds were activated by flowing a commercial vacuum as oil feedstock over the catalyst for 3 days at 650 deg. F. The unit feed was then switched to the pyrolysis product diesel feed of Table 1, and the operating conditions adjusted to the values set out below.

The product from the hydrotreating reactor was transported into a high pressure separator, where it was separated into a gaseous and a liquid stream. The liquid stream was subsequently sent to a stripper vessel, where nitrogen gas was bubbled through the liquid to remove any dissolved hydrogen sulfide and ammonia from the liquid. The stripped liquid was then collected in the unit product accumulator. The gas stream from the high pressure separator was combined with the gas stream from the stripper vessel. The flow rate of the combined gas stream was measured using a wet test meter, and the gas was analysed via chromatography. Hydrogen was added (treat rates expressed as standard cubic feet per barrel of feed (SCFbbl) , whereby 1 normal cu.m. per barrel (Nm3/b) equals 37.33 standard cu . ft . per barrel (SCFbbl) ) .

Initial operations with the Diesel feed were conducted at 1,200 psig reactor pressure (15 psig = 103 kpa gauge) . Other operating conditions were reactor temperatures of 650 - 700 deg. F, liquid hourly space velocities (LHSV) of 0.5 - 1.0 1/hr, and hydrogen treat rates of 4,000 - 5,000 SCF/bbl (500 SCF/bbl = 99.8 standard m3/m3) .

The reactor pressure was then increased to 1,500 psig, where performance data was obtained at the conditions of 675 deg. F reactor temperature, 0.5 1/hr LHSV, and 5,000 SCF/bbl.

Table 2 depicts the results of the hydrotreatment :

Table 2 Properties of Hydrotreated components

The above data show that the Diesel fraction, although meeting the requirements for ultra low sulphur Diesel, was not suitable as winter diesel, with a pour point of -2O⁰C. Accordingly, blends were prepared from the two components. A 60:40 blend of Diesel: Kero fulfilled the necessary requirements (Table 3 and 4) :

Table 3

Table 4 : Composition of the blend

The belnd was subjected to a further test programme, as set out in Tables 5 and 6. In Table 5, its properties are compared with those of a mineral derived No. 1 and No. 2 Diesel fuels, while Table 6 list further properties . Table 5. ASTM fuel property test results

n.d. = not determined

Table 6 - Test Results for the 40/60 Blend

Table 2 (continued)

O

Claims

C L A I M S

1. A process for the preparation of a middle distillate fuel from a kerogen pyrolysis product, comprising

(a) hydrotreating the middle distillate fraction of a kerogen pyrolysis product; and (b) isolating a kerosene or diesel base fuel from the product of step (a) by means of distillation.

2. A process according to claim 1, wherein the middle distillate fraction of step (a) is derived from the in- situ conversion of an oil shale reservoir.

3. A process according to claim 1 or 2, comprising

(a) hydrotreating subsequently or in parallel a kerosene precursor fraction and a Diesel precursor fraction of a kerogen pyrolysis product;

(b) isolating a diesel base fuel and a kerosene base fuel from the product of step (a) by means of distillation; and

4. A kerosene or diesel base fuel, or blend obtainable according to any one of claims 1 to 3.

5. A Diesel base fuel according to claim 4 having an initial boiling point in the range 230 to 26O⁰C and a final boiling point in the range 380 to 400⁰C, as determined according to ASTM method D6730.

6. A blend according to claim 4, having a density at 15 ⁰C of between 0,775 and 0,820 kg/m³, a flash point of 140 to 180 ⁰F as determined according to ASTM method D93.

7. A blend according to claim 6, having a total nitrogen content of less than 3 ppm as determined according to ASTM method D4629, and a total sulphur content of less than 15 ppm as determined according to ASTM method D5453.

8. A blend according to any one of claims 6 or 7, comprising less than 15 % volume of aromatic compounds, as determined according to ASTM method D1319.

9. A fuel composition comprising a middle distillate fuel component or blend according to any one of claims 1 to 8 present in the fuel composition in the amount of 0.1 to 99.9%v, and further at least one additive.

10. A method of operating a compression ignition (diesel) engine and/or an aircraft which is powered by one of more of said engines, which method involves introducing into said engine a fuel composition according to claim 9.