WO2009156713A1

WO2009156713A1 - Purification method

Info

Publication number: WO2009156713A1
Application number: PCT/GB2009/001546
Authority: WO
Inventors: Simon Christopher; Alisdair Quentin Clark; Robert Stuart Grace
Original assignee: Bp Oil International Limited
Priority date: 2008-06-23
Filing date: 2009-06-19
Publication date: 2009-12-30
Also published as: GB0811505D0

Abstract

A method for the purification of a middle distillate fuel composition, for example jet fuel composition, contaminated with at least one fatty acid alkyl ester which process comprises contacting the fuel composition with a silica adsorbent to adsorb at least a portion of the fatty acid alkyl ester on the silica adsorbent and thereby to reduce the total concentration of fatty acid alkyl esters in the middle distillate fuel composition.

Description

PURIFICATION METHOD

This invention relates to a purification method. In particular, this invention relates to a method of removing fatty acid alkyl esters from middle distillate fuel compositions for example, from jet fuel compositions.

Middle distillate fuel compositions, for example jet fuel compositions must meet many criteria before they are considered acceptable for use. Thus, jet fuel compositions must comprise hydrocarbons, which may be derived from mineral sources, for example from crude oil, shale oil, or tar sands, or from non-mineral sources, for example from Fischer Tropsch derived synthetic kerosine or biological sources, for example severely hydrotreated vegetable oils. Jet fuel compositions may comprise only specified additives within defined concentration limits and 'trace' contaminates, for example sulphur and nitrogen, which may be linked to the method of manufacture. Chemical compounds outside these criteria are strictly not allowed in jet fuel compositions. ' Middle distillate fuel compositions, for example jet fuel compositions, which comprise hydrocarbons derived from the severe hydrotreatment of vegetable oils may contain unacceptable traces of fatty acid alkyl esters contaminants for example, resulting from their method of manufacture.

Also, middle distillate fuel compositions other than jet fuel compositions, may not be permitted to contain unacceptable concentrations of fatty acids alkyl esters. For example, marine fuel required to meet ISO 8217.

It may be desirable to reduce the amount of fatty acid alkyl ester contaminants in middle distillate fuel compositions to reduce the risk of microbiological growths and/or contamination. Middle distillate fuels including for example, jet fuel compositions, are transported to airport and storage facilities in various ways through distribution systems. Commercially, it is highly advantageous to distribute such middle distillate fuel compositions, including jet fuel compositions, to airports and/or storage facilities using pipe-lines. These may be short, for example vessel to terminal, or cover some considerable distance from example, across many regions or counties. Such middle distillate fuel compositions, including jet fuel compositions, are not the only compositions using such pipe-lines. Typically, gasoline, diesel and other hydrocarbon compositions may be transported through such pipelines. When transporting different fuel compositions through the same distribution system it is important to mitigate the risks of cross-contamination for example, by interfacing fuel compositions which are compatible with each other. Thus, it is common to transport diesel fuel compositions and jet fuel compositions using the same distribution system e.g. pipe-line, vessels and the like, because these fuel compositions have compatible flash points.

There has been considerable interest in using 'bio' components in fuel compositions. For example, bio-derived methyl esters in diesel fuel ('FAME' - fatty acid methyl esters). Due to their oxygenated nature, such bio-components may become attracted to surfaces in the distribution system for example to the walls of pipe-lines, vessels and the like, when compositions comprising such bio-components are transported through the distribution system. In particular, there is a risk that diesel or other fuel compositions comprising bio- components such as fatty acid alkyl esters, may leave trace amounts of such bio- components in the distribution system (for example, on surfaces) which can subsequently contaminate middle distillate fuel compositions, for example, jet fuel compositions, subsequently transported through the system, and where the presence of more than trace amounts of such components is not permitted or is undesirable. This is particularly the case because as mentioned above, it is common to interface jet fuel compositions and diesel fuel compositions in the same distribution system. Thus, there is a need for a method of purification of middle distillate fuel compositions including for example, jet fuel compositions, contaminated with fatty acid alkyl esters, which addresses or at least mitigates these problems.

Thus, according to the present invention there is provided a method for the purification of a middle distillate fuel composition, contaminated with at least one fatty acid alkyl ester which process comprises contacting the middle distillate fuel composition with a silica adsorbent to adsorb at least a portion of the fatty acid alkyl ester on the silica adsorbent and thereby to reduce the total concentration of fatty acid alkyl esters in the middle distillate fuel composition.

The present invention solves the technical problem identified above by the use of a silica adsorbent. More than one silica adsorbent may be used.

Preferably, the middle distillate fuel composition is a jet fuel composition.

The method of the present invention may further comprise adding one or more jet fuel additives to the jet fuel composition after it has been contacted with the silica adsorbent. Suitable additives which may be added include anti-oxidant additives (for example hindered phenols), anti static additives, fuel system icing inhibitors (for example, diethylene glycol monomethyl ether), corrosion inhibitor/lubricity additives (for example, fatty acids/dimer acids with carbon chain length of up to 36 carbon atoms) and metal deactivators (i.e. N,N-disalicylidene 1,2-propanediamine). Anti-oxidant additives may typically be added at up to a maximum treat rate of 24 mg/1. Anti-static additives my typically be added at up to a maximum treat rate of 5 mg/1. Fuel system icing inhibitors may typically be added at up to a maximum treat rate of 0.15 % by volume. Corrosion inhibitor/lubricity additives may typically be added at up to a maximum treat rate of 23 mg/1. Metal deactivators may typically be added at up to a maximum treat rate of 5.7 mg/1.

The method of the present invention may further comprise analysing and/or testing the middle distillate fuel composition, for example jet fuel composition, after it has been contacted with the silica adsorbent to determine whether the total concentration of fatty acid alkyl ester has been reduced to a predetermined concentration, for example to less than 1000 parts per million by weight, preferably to less than 100 parts per million, more preferably to less than 30 parts per million or less than 20 parts per million and yet more preferably to less than or equal to 5 parts per million by weight. The testing may be performed using gas chromatography, for example by GC/MS (gas chromatography/mass spectroscopy).

Suitably, the silica adsorbent comprises one or more high surface area silicas, for example, silicas each having a specific surface area of greater than 400m²/g. The silica adsorbent may comprise one or more acid washed silicas. Preferably, the silica adsorbent comprises one or more acid washed, high surface area silicas, for example, one or more acid washed, high surface area silicas each having a specific surface area of greater than 400m²/g.

The silica adsorbent may comprise one or more silica gels, for example each having a granule diameter in the range 0.05 to 5.0mm, preferably 0.1 to 1.0mm. The silica gels may have granule diameters of less than or equal to 0.5 mm, for example, 0.2 to 0.5mm. The silica may be supported. One or more silica adsorbents may be used in combination with one or more further adsorbents other than silica adsorbents. The middle distillate fuel composition may be contacted with one or more further adsorbents other than silica adsorbents.

For example, in one embodiment one or more silica adsorbents and one or more further adsorbents may be used in series. For example, the middle distillate fuel composition (for example, jet fuel composition) may be contacted with one or more silica adsorbents to adsorb a large proportion of the fatty acid alkyl ester from the middle distillate fuel composition and then contacted with one or more further adsorbents to adsorb some or all of the remaining fatty acid alkyl ester from the middle distillate fuel composition and/or to adsorb other contaminants, for example surface active components, from the middle distillate fuel composition. In this embodiment, the further adsorbents may be or comprise one or more clays.

Alternatively, or additionally, the middle distillate fuel composition (for example jet fuel composition) may be contacted with one or more further adsorbents upstream of one or more silica adsorbents to remove contaminants other than fatty acid alkyl esters present in the middle distillate fuel composition for example, contaminants which may be detrimental to the performance of the silica adsorbent in removing fatty acid alkyl ester. In this embodiment, the one or more further adsorbents may be or comprise for example, one or more super adsorbent polymers, e.g. sodium polyacrylate.

Advantageously, water may be removed from the middle distillate fuel composition (for example, jet fuel composition) by contacting the middle distillate fuel composition with one or more super adsorbent polymers and/or one or more water coalescers, upstream of one or more silica adsorbents, which may protect the silica adsorbents from water contamination and consequent deactivation.

In a preferred embodiment, one or more silica adsorbents may be used in series with at least two further adsorbents. For example, the middle distillate fuel composition (for example, jet fuel composition) contaminated with at least one fatty acid methyl ester may be contacted with more or more super adsorbent polymers and/or one or more water coalescers, then contacted with one or more silica adsorbents, and then contacted with one or more clay adsorbents.

The middle distillate fuel composition (for example, jet fuel composition) contaminated with at least one fatty acid alkyl ester may be contacted with the silica adsorbents by passing it through one or more beds of silica adsorbent. The one or more beds of silica adsorbent may be packed beds of silica. Suitable beds of silica adsorbent may have a length to diameter ratio to provide plug flow of the contaminated middle distillate fuel composition (for example, jet fuel composition) through the bed. A suitable ratio to provide plug flow is at least 2: 1. A ratio of about 1 :8 to about 2: 1 may be used. The middle distillate fuel composition (for example, jet fuel composition) contaminated with at least one fatty acid alkyl ester may be contacted with the silica adsorbent by passing it through a bed of silica adsorbent at a high liquid hourly space velocity of about 50 to about 190, preferably about 100 to about 140, for example about 120. Alternatively, in some applications, capacity of the silica adsorbents may be increased by passing the jet fuel composition through the one or more silica adsorbents at a low liquid hourly space velocity of about 0.5 to about 20, or about 20 to about 50.

The middle distillate fuel composition (for example, jet fuel composition) may comprise hydrocarbons derived from at least one of crude oil, shale oil, tar sands, Fischer Tropsch synthetic kerosine and severely hydrotreated vegetable oils, (for example, rape seed, palm oil, jatropha oil and/or coconut oil). The middle distillate fuel composition (for example, jet fuel composition) may be made by processes known in the art. The middle distillate fuel composition (for example, jet fuel composition) may be made by processes comprising one or more refining processes, for example hydrotreating, desulphurisation, cracking, fluid catalytic cracking or reforming.

Suitably, the middle distillate fuel composition has a density of 750 kg/m³ to 920 kg/m³, preferably 750 kg/m³ to 880 kg/m³, more preferably 775 kg/m³ to 880 kg/m³, and most preferably 77 kg/m³ to 840 kg/m³.

When the middle distillate fuel composition is jet fuel or diesel fuel it may have a boiling point (for example, as measured according to ASTM D 86 - 09) of 130 to 400 ⁰C. When the middle distillate fuel composition is jet fuel it may have a boiling point (for example, as measured according to ASTM D 86 - 09) of 130 to 300 ⁰C.

The jet fuel composition may be Jet-A, Jet-Al, Jet-B, TS-I, RT, AVCAT, AVTAG, or NATO grade F-34, F-35, F-37, F-40, F44 or F-76 or US grade JP-4, JP-5, JP-7 JP-8, JP-8 + 100 or JP-TS jet fuel. The middle distillate fuel composition may be a turbine fuel. The middle distillate fuel composition may be a marine fuel, for example intended to meet ISO 8217. The middle distillate fuel may be a heating kerosine.

The middle distillate fuel composition (for example, jet fuel composition) may be contaminated with at least one fatty acid alkyl ester to a total concentration of fatty acid alkyl esters of greater than 5 parts per million by weight, for example greater than 20 ppm by weight, greater than 100 ppm by weight or greater than 1000 parts per million by weight and preferably, up to 5000 ppm by weight. The middle distillate fuel composition (for example, jet fuel composition) may be contaminated with at least one fatty acid alkyl ester to a total concentration of fatty acid alkyl esters of up to 5000 parts per million by weight, or up to 1000 ppm by weight, or up to 200 ppm by weight or up to 20 parts per million by weight. Suitably, the method of the present invention reduces the total concentration of fatty acid alkyl esters in the middle distillate fuel composition (for example, jet fuel composition) from less than 5000 ppm but greater than 1000 ppm by weight, to less than 1000 parts per million by weight. The method of the present invention may reduce the total concentration of fatty acid alkyl esters in the middle distillate fuel composition (for example, jet fuel composition) from greater than 5 parts per million by weight (and optionally, less than 5000 ppm, or less than 1000 ppm, or less than 200 ppm or less than 20 ppm by weight) to less than or equal to 5 parts per million by weight. The method of the present invention may reduce the total concentration of the fatty acid alkyl esters to an intermediate value, for example from greater than 400 ppm by weight to less than or equal to 400 parts per million by weight, from greater than 80 ppm by weight to less than or equal to 80 parts per million by weight, from greater than 50 ppm by weight to less than or equal to 50 parts per million or from greater than 20 ppm by weight to less than or equal to 20 parts per million by weight. The method of the preset invention may reduce the total concentration of fatty acid alkyl esters in the middle distillate fuel composition from greater than 20 parts per million by weight (and optionally, less than 5000 ppm, or less than 1000 ppm, or less than 200 ppm by weight) to less than or equal to 5 parts per million by weight. Each fatty acid alkyl ester may be a methyl, ethyl, propyl and/or butyl ester. Usually, the fatty acid alkyl ester is a fatty acid methyl ester. The fatty acid of each fatty acid alkyl ester may have 10 to 25 carbon atoms. Preferably, the fatty acid alkyl ester has 12 to 25 carbon atoms. More preferably the fatty acid alkyl ester has 16 to 18 carbon atoms. The fatty acid may be saturated or unsaturated. Preferably, the fatty acid alkyl ester is acyclic. The fatty acid alkyl esters may be prepared by esterification of one or more fatty acids. The fatty acid alkyl esters may be made by transesterification of one or more triglycerides of fatty acids. The triglycerides may be obtained from vegetable oils, for example, castor oil, soyabean oil, cottonseed oil, sunflower oil, rapeseed oil (which is sometime called canola oil), Jatropha oil or palm oil, or obtained from tallow (for example sheep and/or beef tallow), fish oil or used cooking oil.

The at least one fatty acid alkyl ester may be rapeseed oil methyl ester (RME), soya methyl ester or combinations thereof.

The invention will now be illustrated by way of example only. Example 1

A batch of Jet A-I fuel composition was doped with 1000 ppm fatty acid methyl ester (Rape seed methyl ester : Soya methyl ester 50:50 volume mixture). One litre of contaminated jet fuel composition was passed through a bed of high surface area silica solid adsorbent in a Buchner funnel at a flow rate of (180-200 ml/min) by applying a laboratory vacuum system to the outlet of the funnel. Four further 1 litre aliquots of the jet A-I fuel composition doped with 1000 ppm fatty acid methyl ester were passed through the adsorbent bed. The aliquots of treated jet fuel composition collected from the outlet of the funnel were analysed by GC/MS to determine their fatty acid methyl ester concentration (FAME) and the results are given in Table 1.

The silica-containing Buchner funnel is commercially available, for example Supelco Pre-packed Buchner funnels. The silica was a high surface area silica with the following properties :

Specific surface area 486 m²/g N₂ BET method

Average pore diameter 71 Angstrom

Total pore volume 0.86 cm³/g

Average particle diameter 54 micrometres

Experiment A

Example 1 was repeated using charcoal solid adsorbent.

Experiment B Example 1 was repeated using commercial grade Attapulgus clay adsorbent.

The results of Examples 1 to 3 are presented in Table 1 below : Table 1

This shows that the method of the present invention using silica adsorbent, can reduce the concentration of fatty acid alkyl ester in the contaminated jet fuel composition to less than 100 parts per million by weight. The reduction was significant for the first aliquot but was about 20% for subsequent aliquots. Further, Experiments A and B demonstrate that the level of adsorption of FAME which is achieved by the present invention using silica adsorbent cannot be achieved by the use of charcoal or attapulgus clay adsorbents.

It is expected that one or more jet fuel additives could be added to the jet fuel composition after it has been contacted with the silica adsorbent.

Experiment C

Five 1 litre aliquots of jet fuel containing approximately 1000 ppm fatty acid methyl ester (50/50 rape seed and soy methyl esters) were passed through a 50g packed bed of Attapulgus clay at a liquid hourly space velocity of approximately 120. The capacity of the clay for the fatty acid methyl esters was determined to be approximately 0.55 % by weight. Examples 2 and 3 and Experiments D-G

Further tests were performed using Attapulgus clay, the same type of high surface area silica as used in Example 1 and Kaolin with apparatus similar to that used in Example

1 , except that in Experiments F and G and Example 3 a cylindrical separating funnel with glass wool plugs was used as the vessel for the adsorbent. Details are shown in Table 3 below.

In each test, 1 litre of contaminated jet fuel containing 20 ppm by weight fatty acid methyl ester was passed through the adsorbent and the collected treated composition analysed. The treated fuel compositions were analysed by GC/MS for their fatty acid methyl ester concentration and the results are shown in Table 2 below. In Experiment E, 100ml aliquots of the treated jet fuel composition were analysed.

In Experiment G, using Kaolin adsorbent, the test was abandoned after 3 hours because the flow rate was very slow - 100ml in 3 hours. Examples 2 and 3 show that the high surface area silica adsorbent was able to remove almost all the fatty acid methyl ester from the contaminated jet fuel composition for the bulk 1 litre volume of jet fuel passed through. Experiment E demonstrates that whilst the clay adsorbent initially reduced the fatty acid methyl ester content to around 4ppm, as more jet fuel was passed through the adsorbent its ability to reduce the concentration of FAME in the j et fuel declines

Table 2.

Table 3.

Experiment H

4475ml of Jet A-I jet fuel was doped with approximately lOOppm of a mixture of fatty acid methyl esters having the carbon chain lengths and numbers of double bonds given in Table 4 below.

Table 4

The contaminated jet fuel was passed through a bed of three layers of super adsorbent polymer arranged to form a cone in a glass funnel having a volume of approximately 20cm³. Five 20ml aliquots of the treated jet fuel were collected at various time intervals and were analysed by GC/MS. The fatty acid methyl ester concentration in parts per million by weight was calculated on a linear basis from the peak area of the GC-MS results, normalising for carbon number and using the untreated contaminated fuel as reference.

The results of Experiment H are shown in Table 5 below.

Table 5

The results shown in Table 5 demonstrate that super adsorbent polymer does not significantly reduce the concentration of fatty acid methyl ester in the jet fuel.

Example 4

0.5 litres of jet fuel composition containing approximately lOOppm of a mixture of rape seed methyl ester, palm oil methyl ester, soy methyl ester and tallow methyl ester was passed through a 1 g bed of silica gel (supplied by Sigma Aldrich as silica gel 60 for column chromatography) having a granule diameter of 0.2 to 0.5mm at a flow rate of 150cm³ per hour. 20cm³ aliqouts of fuel were collected after 20, 80, 180, 280, 380 and 480cm³ of the contaminated jet fuel had passed through the silica and were analysed by GC/MS and the concentration of fatty acid alkyl ester was determined in a similar manner to Experiment H. The concentration of fatty acid methyl esters in the first 20 cm³ aliquot was 43 ppm. The concentration of fatty acid methyl esters in subsequent aliquots was the same as in the untreated jet fuel composition.

Example 5

0.5 litres of jet fuel containing approximately lOOppm of a mixture of rape seed methyl ester, palm oil methyl ester, soy methyl ester and tallow methyl ester was passed through a Ig bed of silica gel (supplied by Sigma Aldrich) having a granule diameter of 1 to 3mm at a flow rate of 150cm³ per hour. 20cm³ aliqouts of fuel were collected after 20, 80, 180, 280, 380 and 480cm³ of the contaminated jet fuel had passed through the silica and were analysed by GC/MS and the concentration of fatty acid alkyl ester was determined in a similar manner to Experiment H. The concentration of fatty acid methyl esters in each of the aliquots was the same as in the untreated jet fuel composition.

Examples 4 and 5 demonstrate that the silica gel having a granule diameter of 0.2 to 0.5 mm is more effective under the conditions employed, than the silica gel having a granule diameter of 1 to 3 mm diameter, the latter not reducing the concentration of fatty acid methyl esters under the conditions employed.

Claims

Claims :

1. A method for the purification of a middle distillate fuel composition contaminated with at least one fatty acid alkyl ester which process comprises contacting the middle distillate fuel composition with a silica adsorbent to adsorb at least a portion of the fatty acid alkyl ester on the silica adsorbent and thereby to reduce the total concentration of fatty acid alkyl esters in the middle distillate fuel composition.

2 A method as claimed in claim 1 in which the middle distillate fuel composition is a jet fuel composition.

3 A method as claimed in claim 1 or claim 2 in which the middle distillate composition is contaminated with at least one fatty acid alkyl ester to a total concentration of fatty acid alkyl esters of greater than 1000 parts per million by weight.

4 A method as claimed in claim 3 in which the middle distillate fuel composition is contaminated with at least one fatty acid alkyl ester to a total concentration of fatty acid alkyl esters of up to 5000 ppm.

5 A method as claimed in any one of the preceding claims in which the total concentration of fatty acid alkyl esters in the middle distillate fuel composition is reduced from greater than 20 parts per million by weight to less than or equal to 20 parts per million by weight.

6. A method as claimed in any one of the preceding claims in which the total concentration of fatty acid alkyl esters in the middle distillate fuel composition is reduced from greater than 5 parts per million by weight to less than or equal to 5 parts per million by weight.

7. A method as claimed in claim 5 in which the total concentration of fatty acid alkyl esters in the middle distillate fuel composition is reduced from greater than 20 parts per million by weight (and optionally, less than 5000 ppm, or less than 1000 ppm, or less than 200 ppm by weight) to less than or equal to 5 parts per million by weight.

8. A method as claimed in any one of the preceding claims in which the silica adsorbent comprises one or more high surface area silicas.

9. A method as claimed in any one of the preceding claims in which the silica adsorbent comprises one or more acid washed silicas.

10. A method as claimed in any preceding claim in which the silica adsorbent comprises one or more silica gels having a granule diameter in the range 0.05 to 5.0mm

11. A method as claimed in any one of claims 1 to 9 in which the silica adsorbent comprises one or more silica gels having a granule diameter of less than or equal to 0.5 mm.

12. A method as claimed in any preceding claim in which the middle distillate fuel composition is contacted with the silica adsorbent by passing it through one or more beds of silica adsorbent.

13. A method as claimed in claim 12 in which the middle distillate fuel composition is passed through one or more beds of silica adsorbent at a liquid hourly space velocity of 50 to 190 or 0.5 to 20.

14. A method as claimed in any one of the preceding claims in which the middle distillate fuel composition has a density of 750 kg/m³ to 920 kg/m³.

15. A method as claimed in any one of the preceding claims in which the middle distillate fuel composition is jet fuel or diesel fuel and has a boiling point of 130 to 400 ⁰C.

16. A method as claimed in any one of claims 1 to 14 in which the middle distillate fuel composition is jet fuel and has a boiling point of 130 to 300 ⁰C.

17. A method as claimed in any one of the preceding claims in which the middle distillate fuel is a jet fuel and which method further comprise adding one or more jet fuel additives to the jet fuel composition after it has been contacted with the silica adsorbent.

18 A method as claimed in any one of the preceding claims which further comprises analysing and/or testing the middle distillate fuel composition after it has been contacted with the silica adsorbent to determine whether the total concentration of fatty acid alkyl ester has been reduced to a predetermined concentration.

19 A method as claimed in claim 18 in which the predetermined concentration is less than or equal to 5 parts per million by weight.

20. A method as claimed in any one of the preceding claims in which the middle distillate fuel composition is contacted with one or more further adsorbents other than silica adsorbents.

21. A method as claimed in claim 20 in which the middle distillate fuel composition is contacted with one or more silica adsorbents to adsorb a large proportion of the fatty acid alkyl ester from the middle distillate fuel composition and then contacted with one or more further adsorbents to adsorb some or all of the remaining fatty acid alkyl ester from the middle distillate fuel composition and/or to adsorb other contaminants.

22 A method as claimed in claim 21 in which the further adsorbents are or comprise one or more clays.

23. A method as claimed in claim 20 which, the middle distillate fuel composition is contacted with one or more further adsorbents upstream of one or more silica adsorbents to remove contaminants other than fatty acid alkyl esters present in the middle distillate fuel composition.

24 A method as claimed in claim 21 or claim 22 in which additionally, the middle distillate fuel composition is contacted with one or more further adsorbents upstream of one or more silica adsorbents to remove contaminants other than fatty acid alkyl esters present in the middle distillate fuel composition.

25. A method as claimed in claim 23 or claim 24 in which the contaminants other than fatty acid alkyl esters are contaminants which are detrimental to the performance of the silica adsorbent in removing fatty acid alkyl ester.

26 A method as claimed in any one of claims 23 to 25 in which the one or more further adsorbents are or comprise, one or more super adsorbent polymers.

27 A method as claimed in claim 26 in which water is removed from the middle distillate fuel composition by contacting the middle distillate fuel composition with one or more super adsorbent polymers and/or one or more water coalescers, upstream of one or more silica adsorbents.

28. A method as claimed in any one of claims 20 to 27 in which, one or more silica adsorbents are used in series with at least two further adsorbents.

29 A method as claimed in claim 28 in which, the middle distillate fuel composition contaminated with at least one fatty acid methyl ester is contacted with more or more super adsorbent polymers and/or one or more water coalescers, then contacted with one or more silica adsorbents, and then contacted with one or more clay adsorbents.