WO2002018519A1

WO2002018519A1 - Process for the deacidification of crude oil

Info

Publication number: WO2002018519A1
Application number: PCT/GB2001/003746
Authority: WO
Inventors: Simon Neil Duncum; Christopher George Osborne
Original assignee: Bp Exploration Operating Company Limited
Priority date: 2000-09-01
Filing date: 2001-08-21
Publication date: 2002-03-07
Also published as: GB0021488D0; AU2001282295A1

Abstract

A process for deacidifying a crude oil and/or crude oil distallate containing organic acids, said process comprising: (a) contacting the crude oil and/or crude oil distillate with (i) a Group IA metal salt selected from the group containing of Group IA metal oxides, hydroxides and alkoxides and (ii) a polar solvent, in the presence of less than 5 % volume of water based on the volume of the crude oil and/or crude oil distillate such that at least a portion of the organic acids are converted into Group IA metal neutralisation salts thereof and at least a portion of the neutralisation salts are extracted into the polar solvent as an extract phase; and separating a crude oil and/or crude oil distillate phase which is reduced in acidity from the polar solvent extract phase.

Description

Process for the Deacidification of Crude Oil This invention relates to a process for deacidification of crude oil and/or a crude oil distillate.

Crude oil and distilled fractions thereof may contain organic acid impurities such as naphthenic acid. Typical Total Acid Number (TAN) values, as measured by ASTM Method D0664, for acidic crude oils are in the range of 0.5 to 4 mg KOH/g while acidic distilled fractions such as kerosene may have TAN values of, for example, 0.5 to 8 mg KOH/g. These organic acid impurities can cause corrosion problems, particularly in refinery operations where temperatures of 200°C and above are encountered. For this reason, it is desirable to reduce the acidity of crude oils, for example, by reducing the amount of organic acids, such as naphthenic acid present in the crude oil.

Various methods for deacidifying crude oil and/or crude oil distillates (hereinafter "oil") are known. In a conventional de-acidification process, an alkali such as aqueous sodium hydroxide or aqueous potassium hydroxide is contacted with the oil to neutralise any acid present. The reaction produces an aqueous phase comprising water, and alkali metal naphthenate. This aqueous phase has to be removed from the deacidified oil, before the oil can be used or sold.

According to US 4 199440, alkali metal naphthenates are chemically similar to soap, and tend to emulsify hydrocarbon and aqueous phases. This emulsion interferes with the efficient separation of the deacidified oil and aqueous phase. The solubility of alkali metal naphthenates in the aqueous phase, however, increases as the concentration of alkali in the aqueous phase decreases. Thus, by using a dilute solution of sodium or potassium hydroxide, the tendency of alkali naphthenate to emulsify hydrocarbon phases is reduced. Accordingly, the problem of emulsion formation may be alleviated by using a dilute solution of the aqueous base.

EP 0 881 274 endeavours to improve the process of US 4 199 440 by avoiding the formation of a stable emulsion. According to EP 0 881 274, stable emulsions are formed when bases are added to oil at an oil to base ratio of 1 : 1 or less. Thus, in the process of EP 0 881 274, oil is added to aqueous base at an oil to base ratio of 1 :3 to 1:15. By treating the oil in this manner, an unstable dispersion of oil in a continuous aqueous base phase is produced. This unstable emulsion is easily broken, allowing the alkali metal naphthenates and aqueous base to be conveniently removed from the oil phase.

A problem with EP 0 881 274 is that it requires large volumes of aqueous base to be used. This makes the process relatively uneconomic, particularly when very large volumes of oil require treatment.

WO 97/08270 describes a process in which the volume of aqueous base employed is relatively small. Specifically, the reference describes a deacidification process in which a Group IA or Group UA metal oxide, hydroxide or hydroxide hydrate is contacted with crude oil in the presence of from zero to 7 wt % water. When a Group IA compound is employed, the process does not require the addition of water. When a Group UA metal compound is employed, a small amount of water must be present to render the base effective for neutralising acid. The treatment produces a treated crude having a reduced acidity. Any solid suspended in the oil after treatment is separated by centrifugation.

Whilst this process may be effective for treating oil on a small-scale, it cannot be used to treat large quantities of oil in an efficient manner. This is because the rate of deacidification is limited by the constraints of having to centrifuge the entire volume of oil treated.

A further example of a crude oil deacidification process is described in PCT patent application GB9904387. In this application, a crude oil is contacted with a polar solvent (for example, methanol), such that at least part of the organic acid present in the oil is extracted into the solvent as an extract phase. The extract phase is then separated from the oil. However, a problem with this process is that certain of the acid impurities are not extractable into the solvent. A further problem is that the organic acid partitions between the oil and the extract phase such that high amounts of polar solvent and repeated extractions are required to reduce the acid content of the oil to an acceptable level. This has a further disadvantage that large volumes of polar solvent need to be regenerated for recycling to the extraction stage. 5 It has now found that when a Group IA metal oxide, hydroxide or alkoxide is contacted with oil in the presence of a polar solvent that the neutralisation product, for example, Group IA metal naphthenate, preferentially partitions into the polar solvent. It has also been found that the formation of stable emulsions can be avoided by controlling the amount of water that is present during the neutralisation reaction. 10 According to the present invention, there is provided a process for deacidifying a crude oil and/or crude oil distillate containing organic acids, said process comprising:

(a) contacting the crude oil and/or crude oil distillate with (i) a Group IA metal salt selected from the group consisting of Group IA metal oxides, hydroxides and alkoxides and (ii) a polar solvent, in the presence of less than 5 % volume of water based on the volume of

15 the crude oil and/or crude oil distillate such that at least a portion of the organic acids are converted into Group IA metal neutralisation salts thereof and at least a portion of the neutralisation salts are extracted into the polar solvent as an extract phase; and

(b) separating a crude oil and/or crude oil distillate phase which is reduced in acidity from the polar solvent extract phase. 0 Without wishing to be bound by any theory it is believed that the Group IA metal neutralisation salts of the organic acids (such as sodium naphthenate) have substantially higher affinities for the polar solvent than for the crude oil and/or crude oil distillate and, accordingly, are selectively extracted into the polar solvent phase.

Examples of organic acids that maybe present in the crude oil and/or crude oil 5 distillate (hereinafter "oil") include phenolic acids, sulphur-containing acids, and most commonly, naphthenic acid. By neutralising the organic acids with a Group IA metal oxide, hydroxide or alkoxide the TAN of the oil may be reduced to 0.9 and below, preferably, 0.5 and below, and most preferably, 0.3 and below.

Examples of suitable crude oil distillates which may be deacidified using the 0 process of the present invention include gasoline, gas oil, diesel and kerosene.

In step (a), oil is contacted with a Group IA metal oxide, hydroxide or alkoxide. Suitably, the Group IA metal oxide may be selected from lithium oxide, sodium oxide or potassium oxide. Suitably, the Group IA metal hydroxide may be selected from lithium hydroxide, sodium hydroxide, and potassium hydroxide, preferably, sodium hydroxide. Suitably, the Group IA metal alkoxide may be selected from lithium methoxide, lithium ethoxide, sodium methoxide, sodium ethoxide, potassium methoxide, and potassium ethoxide, preferably, sodium methoxide and sodium ethoxide. It is envisaged that mixtures of Group LA metal oxides and/or hydroxides and/or alkoxides may be employed.

Step (a) may be carried out by adding solid Group IA metal oxide, hydroxide, or alkoxide to the oil, and subsequently extracting the Group IA metal neutralisation salts (and any unconverted Group IA metal oxide, hydroxide or alkoxide) from the oil by washing the oil with a polar solvent. The amount of solid Group IA metal oxide, hydroxide or alkoxide which is added to the oil is dependent upon the TAN value of the oil. For example, the amount of Group IA metal oxide, hydroxide or alkoxide which is added to the oil may be determined by converting the TAN value of the oil from mg KOH/g of oil to moles KOH/g oil. Preferably, the ratio of the amount of Group IA metal oxide, hydroxide or alkoxide which is added to the oil (moles/g of oil) to the TAN value of the oil (moles KOH/g of oil) is in the range 0.7:1 to 1:1, more preferably, 0.8:1 to 0.9:1, for example 0.85:1. Suitably, the volume ratio of polar solvent to oil in the washing step is from 1:1 to 1:40, preferably, 1:4 to 1:20, more preferably, 1:7 to 1:13, for example 1:10. The washing step may be repeated several times, preferably 2 to 6 times, for example 2 to 4 times, until the concentration of Group IA metal neutralisation salt (and of any unreacted Group IA metal oxide, hydroxide or alkoxide) in the oil is reduced to an acceptable value. Suitably, the concentration of Group IA metal in the treated oil is less than 30 ppm, preferably, less than 15 ppm. The washing step(s) may be carried out in a counter current extraction column.

Alternatively, the oil may be contacted with a solution of the Group IA metal oxide, hydroxide or alkoxide in a polar solvent. Without wishing to be bound by any theory, it is believed that the Group IA metal oxide, hydroxide or alkoxide will at least in part partition into the oil to neutralise any organic acid impurities present therein. It is envisaged that the oil may be contacted with a dilute solution of the Group IA metal oxide, hydroxide or alkoxide in a polar solvent (hereinafter "dilute solution"). An advantage of using a dilute solution is that this may avoid having to wash the oil with polar solvent to reduce the level of Group IA metal in the oil to an acceptable value. By "dilute solution" is meant that the concentration of Group IA metal oxide, hydroxide or alkoxide is less than 0.025 moles per litre, preferably, less than 0.0125 moles per litre. Suitably, the volume ratio of the dilute solution to the oil may be from 1:1 to 1:40, preferably, 1 :4 to 1 :20, more preferably, 1 :7 to 1 : 13, for example 1 :10. Steps (a) and (b) may be repeated several times, preferably 2 to 6, for example 2 to 4 times, until the level of organic acids in the oil is reduced to an acceptable value. Step (a) may be carried out in a counter current extraction column.

Alternatively, the oil may be contacted with a relatively concentrated solution of Group IA metal oxide, hydroxide or alkoxide in a polar solvent (hereinafter

"concentrated solution"). By concentrated solution is meant that the concentration of Group IA metal oxide, hydroxide or alkoxide is greater than 0.25 moles/litre, preferably, greater than 0.4 moles/litre, for example, greater than 0.525 moles/litre. Suitably, the volume ratio of the concentrated solution to the oil maybe from 1:1 to 1:40, preferably, 1:4 to 1 : 20, more preferably, 1:7 to 1: 13, for example, 1:10. After separation of the polar solvent phase, the treated oil phase is preferably extracted (washed) with polar solvent. Suitably, the volume ratio of polar solvent to the treated oil phase may be from 1:1 to 1:40, preferably, 1:4 to 1:20, more preferably, 1:7 to 1:13, for example, 1:10. The washing step may be repeated several times, preferably, 2 to 6 times, for example 2 to 4 times, until the level of Group IA metal neutralisation salts (and any unconverted Group IA metal oxide, hydroxide or alkoxide) in the oil is reduced to an acceptable value. The contacting of the oil with the "concentrated solution" and the washing step(s) may be carried out in counter current extraction columns.

Any suitable polar solvent maybe employed in the process of the present invention. Such solvents include alcohols, alcohol derivatives and ethers. Suitable alcohols include methanol, ethanol, n-propanol, and iso-propanol with methanol and ethanol being preferred. Glycols such as ethylene glycol and polyethylene glycols may also be suitable. Suitable ethers include glycol ethers such as alkyltriglycol ethers. The alkyl group of the alkyltriglycol ether may be straight or branched chain and suitably has 3-6 carbon atoms, preferably 3-5 carbon atoms. The alkyl group in the alkyltrigycol ether more preferably has 4 carbon atoms and is especially n-butyltriglycol ether (also known as triethylene glycol mono-n-butyl ether). Other suitable glycol ethers include ethylene glycol mono butyl ether and butyl diglycol ether. Alcohol derivatives such as alcohol polyalkoxylates may also be employed. Mixtures of polar solvents maybe used. The polar solvent has a large capacity to solubilise, or dissolve, ionic species and thus can extract the Group IA metal neutralisation salts (and any unreacted Group IA metal oxide, hydroxide or alkoxide) from the oil.

Preferably, the polar solvent employed in step a) is substantially anhydrous, by which is meant that the polar solvent contains less than 2% wt water, preferably, less than 1% water, more preferably, less than 0.5 % wt water, most preferably, less than 0.25% wt water. The use of a substantially anhydrous polar solvent mitigates the risk of a stable emulsion being produced in step (a). However, where the oil which is to be treated using the process of the present invention has a high water content, it may be necessary to at least partially dehydrate the oil prior to carrying out the process of the present invention. At least a portion of the water may be separated from the oil in, for example, a separator or coalescer. Preferably, the concentration of water in step a) is maintained at less than 4% volume of oil, more preferably less than 3 % volume of oil, still preferably less than 2 % volume of oil, most preferably less than 1% volume of oil, in particular, less than 0.5 % volume of oil, for example, less than 0.25 % volume of oil.

Step (a) may be carried out using a mechanical stirrer, an ultrasonic stirrer or by bubbling an inert gas through the reaction mixture. The mixing step may last 2 to 30 minutes, preferably, 5 to 20 minutes and most preferably, 8 to 15 minutes. The mixing step may be carried out at a temperature of up to 60°C, preferably 10 to 60°C, most preferably, 10 to 25°C. Preferably, the mixing is carried out without heating the oil. After mixing, the reaction mixture may be allowed to settle, for example, in a settling unit. This causes the reaction mixture to separate into an oil phase and a polar solvent extract phase. Any water present in the reaction mixture (arising from the oil, polar solvent or as a by-product of the neutralisation reaction) will preferentially partition into the polar solvent extract phase. Depending on the density of the polar solvent, the polar solvent extract phase may be either the upper of lower phase in the settling unit. Where methanol is used as the polar solvent, the methanol extract phase will be the upper layer.

The two phases may also be separated using, for example, a decanter, a hydrocyclone, electrostatic coalescer and/or centrifuge.

The separated oil phase may be used directly, or may be further processed, for example, by fractional distillation.

The polar solvent phase which is isolated from step b) comprises polar solvent, water and Group IA metal neutralisation salts (and any unconverted Group IA metal oxide, hydroxide or alkoxide). In order for the polar solvent to be recovered for re-use, the level of the Group LA metal and of water in the polar solvent phase has to be reduced.

In the present invention, the Group IA metal neutralisation salts may be removed by contacting the polar solvent extract phase with a Bronsted acid which is capable of reacting with the Group IA metal neutralisation salts to regenerate the organic acids and to form water and the Group IA metal salt of the Bronsted acid (step (c)). Preferably, an aqueous solution of hydrochloric, hydrobromic orhydroiodic acid (hereinafter "hydrohalic acid") is employed as the Bronsted acid (with the generation of the corresponding Group IA metal halide). Preferably, the hydrohalic acid is present in the aqueous solution at a concentration of from 10% to 40% wt, for example 30 to 40% wt. Suitably, sufficient Bronsted acid is employed to convert substantially all of the neutralisation salts to the corresponding organic acids. The use of excess Bronsted acid is not preferred since this will render the polar solvent acidic. The contacting temperature for step (c) may be up to 60°C, preferably, 10 to 60°C, most preferably, 10 to 25°C.

Alternatively, the polar solvent phase may be contacted in step (c) with an acid ion exchange resin, for example, Amberlyst 15 wet resin. Thus, the Group IA metal ions will exchange with acid sites (H⁺) on the ion exchange resin thereby regenerating the organic acids and removing the Group IA metal from the polar solvent. Preferably, the polar solvent phase is contacted with an acid ion exchange resin at a temperature of above 50°C, more preferably, above 60°C, and most preferably, between 60 and 80°C.

It has been found that in the presence of the acid ion exchange resin, at least a portion of the regenerated organic acids may react with a portion of the polar solvent to form an organic phase. This organic phase can be conveniently removed from the remainder of the polar solvent without the need for distillation, for example, by decantation or centrifugation. For example, where the polar solvent is an alcohol such as methanol, the organic acids can react with the alcohol to form esters, such as methyl esters. Such esters tend to be insoluble/immiscible, and thus, separable from the as a separate organic phase. The remainder of the polar solvent stream may still contain some organic acids. Where the concentration of organic acids is insufficiently low for the polar solvent to be reused in the process of the present invention, the polar solvent may be treated with a neutralising agent (eg an Amberlyst 21 ion exchange column). The organic acid phase may also be separated from the polar solvent phase using, for example, a decanter, a hydrocyclone, electrostatic coalescer and/or centrifuge.

The organic acid stream may be used in a number of applications, for example, in the production of detergents, or as a solvent for metal ions. The direct production of organic acids makes the process of the present invention particularly efficient, both economically and in terms of the amount of waste generated.

Where the organic acids were regenerated using a hydrohalic acid it is preferred to reduce the level of the Group IA metal halide salt in the polar solvent stream prior to recycling the polar solvent stream to step (a).

The level of Group IA metal halide may be reduced by contacting the separated polar solvent phase with a basic ion exchange resin which exchanges hydroxide ions for the halide anion of the Group IA metal salt thereby generating the corresponding Group

IA metal hydroxide. Ion exchange resins which are capable of exchanging hydroxide for chloride anions include:

Amberlite® TRA-400(OH) and Amberlite® IRA-420C(OH) (strongly basic gel-type resins);

DOWEX® G-55 OH, DOWEX® 550A OH (examples of Dowex-1 -hydroxide, strongly basic anion exchange resins); and DOWEX® 66, DOWEX® MARATHON® WBA, DOWEX® WGR-2 (examples of

Dowex hydroxide, weakly basic anion, macroporous resins).

In order to prevent the build-up of water in the process of the present invention it is preferred to dehydrate at least some of the polar solvent before recycling the polar solvent stream to step (a). At least some of the polar solvent may be dehydrated, for example, by distillation, by contacting the wet solvent with a drying agent such as a molecular sieve, or by feeding the wet solvent to a deliquescent drier or to a pervaporation unit. It is envisaged that the polar solvent may be separated from both the Group IA metal halide and from the water by distillation. However, distillative separation is high in energy and is therefore not preferred.

The process of the invention may be carried out on a crude oil pipeline. Thus, part or all of the oil flowing through the pipeline may be delivered into a mixing chamber where it is contacted with (i) the Group IA metal oxide, hydroxide or alkoxide and (ii) the polar solvent: typically a counter-current extraction column may be used, with oil entering at a one end and a solution of the Group IA metal oxide, hydroxide or alkoxide in the polar solvent at the other end. After mixing, the two phases are separated, and the oil is either returned to the pipeline or subjected to further treatment (eg water washing to remove polar solvent), whilst the solvent is recycled (after removal of the neutralisation salts and water, as described above). Preferably, the oil flowing though the pipeline is at least partially dehydrated prior to being fed to the mixing chamber. The process of the present invention may also be carried out on a refinery, or whilst the oil is being transported, for example, in a tanker at sea.

The present invention will now be described with reference to the following Examples. Example 1

In this Example, known volumes of methanol (having a water content of less than 0.05 % wt) and crude oil together with a known mass of sodium hydroxide were added to a separating funnel. The funnel was stoppered, shaken for between 2 to 4 minutes and the contents of the separating funnel were allowed to separate into an oil rich bottom phase and a methanol rich upper phase. The phases were separated, weighed, and a sample of the separated oil phase was taken and analysed for Total Acid Number (TAN).

The treated crude oil was then returned to the separating funnel, together with a known volume of clean methanol and a known weight of sodium hydroxide. The funnel was stoppered, shaken for 2 minutes and the phases were separated, weighed and analysed for TAN as above. This washing procedure was repeated a further two times. The methanol phases from the treatment and washing steps were combined.

Hydrochloric acid (35% wt in water) was added to the combined methanol phase in order to regenerate the organic acids. After addition of 2-3 ml of aqueous hydrochloric acid solution the methanol rich phase appeared cloudy. After addition of 10-11 mis of aqueous hydrochloric acid solution, oily brown droplets comprising organic acids were observed floating on the top of the methanol phase.

The conditions employed in this Example are summarised in Table 1 below: The crude oil (a mixture of crude oils from the North Sea) had an initial TAN of

1.1 mg KOH/g.

Table 1

The results above show that the TAN levels of the crude oil can be reduced to an acceptable level by treatment with a methanol solution of sodium hydroxide. Example 2

In this example, crude oil (150g, TAN = 1.1), sodium hydroxide (7.5 g) and methanol (7.5 g; water content of less than 0.05% wt) were introduced into a separating funnel. The funnel was stoppered and the contents were shaken for between 2 and 4 minutes (Treatment step; Wash 0) before being allowed to separate into an upper methanol extract phase and a lower oil phase. The oil phase was found to have a sodium content of 358 ppm. The oil phase was separated from the methanol extract phase and was introduced to a separating funnel together with fresh methanol (15 g). The funnel was stoppered, shaken for between 2 and 4 minutes (Wash 1) and the phases were separated, weighed and the oil phase analysed for TAN as above. The oil phase was found to have a sodium content of 138 ppm. This washing procedure was repeated (Wash 2). The oil phase was found to have a sodium content of 64 ppm.

The conditions employed in this Example are summarised in Table 2 below:

Table 2

Example 3

Sodium hydroxide (2.023 g) was dispersed in methanol (98 g; water content = 0.05% wt; initial sodium content = 66 ppm) by means of a stirrer. The final sodium content of the resulting dispersion was 9990 ppm. Dry Harding crude oil (lOOOg; TAN = 2.78 mg KOH/g oil; Na content 17 ppm) and the dispersion of sodium hydroxide in methanol were introduced into a separating funnel. The funnel was stoppered and the contents were shaken for between 2 and 4 minutes (Treatment Step; Wash 0) before being separated into an upper methanol extract phase and a lower oil phase by means of a centrifuge. The oil phase was recovered from the methanol extract phase and was found to have a sodium content of 255 ppm and a TAN value of 0.40 mg KOH/g of oil. The sodium content of the methanol extract phase was 7230 ppm. 701.2 g of the recovered oil phase were introduced to a separating funnel together with fresh methanol (70.1 g; water content of less than 0.05% wt; sodium content of 66 ppm). The funnel was stoppered, shaken for between 2 and 4 minutes (Wash 1) and the resulting mixture was separated into an upper methanol extract phase and a lower oil phase by means of a centrifuge. The oil phase was recovered from the methanol extract phase and was found to have a sodium content of 111 ppm while the methanol extract phase had a sodium content of 1490 ppm. 550.0g of the separated oil phase were washed with 55.0 g of fresh methanol (Wash 2) and the separation procedure was repeated. The recovered oil phase was found to have a sodium content of 58 ppm while the methanol extract phase had a sodium content of 654 ppm. 425.0 g of the recovered oil phase were contacted with 43.0 g of fresh methanol (Wash 3) and the separation procedure was repeated. The recovered oil phase and the methanol extract phase were found to have a sodium content of 26 and 315 ppm respectively. 330.2 g of the recovered oil phase were then contacted with 33.0 g of fresh methanol (Wash 4) and the separation procedure was again repeated. The separated oil phase was found to have a sodium content of 13 ppm and a TAN value of 0.35 mg KOH/g of oil while the methanol extract phase had a sodium content of 173 ppm. It was found that for Washes 0 to 2 centrifugation was required to achieve separation of the oil and methanol extract phases. In Washes 3 and 4 the oil and methanol extract phases separated in the separating funnel. Nethertheless, centrifugation was used to achieve a more complete separation of the two phases.

The conditions employed in this Example and the results of the analyses of the recovered oil phases and methanol extract phases are summarised in Table 3 below:

* dry Harding crude oil

** contains 2.023 g of NaOH. Process efficiency after 1 treatment step and 4 wash steps = 87%.

The sodium content of the recovered oil phase was reduced to below 30 ppm after 3 wash steps. Example 4

Example 3 was repeated using wet Harding crude oil (2% volume of water; TAN 2.78 mg/KOH/g of oil; Na content = 17 ppm). A dispersion of sodium hydroxide in methanol was prepared as described in Example 3 except that 2.026 g of sodium hydroxide were used to prepared the dispersion.

The conditions employed in this Example and the results of the analyses of the recovered oil phases and methanol extract phases are summarised in Table 4 below:

* wet Harding crude oil (2 % volume of water); ** contains 2.026 g of NaOH.

Process efficiency after 1 treatment step and 4 wash steps = 89%. The sodium content of the recovered oil phase was reduced to below 30 ppm after 4 wash steps.

Claims

1. A process for deacidifying a crude oil and/or crude oil distillate containing organic acids, said process comprising:

(a) contacting the crude oil and/or crude oil distillate with (i) a Group IA metal salt selected from the group consisting of Group IA metal oxides, hydroxides and alkoxides and (ii) a

5 polar solvent, in the presence of less than 5 % volume of water based on the volume of the crude oil and/or crude oil distillate such that at least a portion of the organic acids are converted into Group IA metal neutralisation salts thereof and at least a portion of the neutralisation salts are extracted into the polar solvent as an extract phase; and

(b) separating a crude oil and/or crude oil distillate phase which is reduced in acidity from 10 the polar solvent extract phase.

2. A process as claimed in claim 1, wherein step (a) is carried out by adding solid Group IA metal oxide, hydroxide, or alkoxide to the oil, and subsequently extracting the Group IA metal neutralisation salts (and any unconverted Group IA metal oxide, hydroxide or alkoxide) from the oil by washing the oil with a polar solvent.

15 3. A process as claimed in claim 2, wherein the ratio of the amount of Group IA metal oxide, hydroxide or alkoxide which is added to the oil (moles/g of oil) to the TAN value of the oil (moles KOH/g of oil) is in the range 0.7:1 to 1:1.

4. A process as claimed in claim 2 or 3, wherein the volume ratio of polar solvent to oil in the washing step is from 1:1 to 1 :40. 20

5. A process as claimed in claim 1, wherein step a) is carried out by contacting the oil with a solution of the Group IA metal oxide, hydroxide or alkoxide in a polar solvent.

6. A process as claimed in claim 5, wherein the concentration of Group IA metal oxide, hydroxide or alkoxide in the polar solvent is less than 0.025 moles per litre.

7. A process as claimed in claim 5, wherein the concentration of Group IA metal oxide, hydroxide or alkoxide is greater than 0.25 moles/litre.

8. A process as claimed in any preceding claim, wherein the polar solvent employed is at least one solvent selected from the group consisting of alcohols, alcohol derivatives and ethers.

9. A process as claimed in any preceding claim, which further comprises: i) recovering the polar solvent phase separated in step b), ii) treating the separated polar solvent phase to reduce its Group IA metal neutralisation salt content, and iii) re-using the treated polar solvent phase from step ii) in Step a).

10. A process as claimed in claim 9, wherein step ii) is carried out by contacting the polar solvent extract phase with a Bronsted acid which is capable of reacting with the Group IA metal neutralisation salts to produce the corresponding organic acid, and separating said organic acid from the remainder of the polar solvent phase, preferably, without distillation.

11. A process as claimed in claim 9, wherein step ii) is carried out by contacting the polar solvent extract phase with an acid ion exchange resin.

12. A process as claimed in any one of claims 9 to 11, wherein the polar solvent is dehydrated at least in part prior to step iii).

13. A process as claimed in any preceding claim, which is carried out on a crude oil pipeline, on board a ship, or in a storage tank.

14. A process as claimed in claim 11, wherein the polar solvent extract phase is contacted with an acid ion exchange resin at a temperature of greater than 50°C.