Process for desalting crude oil

Abstract

The present invention relates to a process of desalting crudeoil, in particular a process for desalting a crude oil which comprises an ionic liquid, an organic acid and any resulting organic salt.

Claims

1. A process of separating an ionic liquid from a crude oil and an organic acid from the crude oil in a desalter, the process comprising the steps of: (i) introducing into the desalter a mixture comprising crude oil, an ionic liquid, and an organic acid, together with water in an amount of greater than 30% by volume relative to the mixture; and (ii) separating a crude oil phase from one or more liquid phases comprising the ionic liquid, organic acid, and water.

2. The process of claim 1, wherein the water is introduced into the desalter in an amount of less than 70% by volume relative to the mixture.

3. The process of claim 1, wherein the mixture and the water are subjected to mixing.

4. The process of claim 3, wherein the mixture and the water are passed through a mixing valve.

5. The process of claim 4, wherein the pressure differential across the mixing valve is from 1 psi to 20 psi.

6. The process of claim 1, wherein an electrostatic field is applied to the desalter.

7. The process of claim 6, wherein the electrostatic field is from 1 kV AC to 25 kV AC.

8. The process of claim 1, wherein the desalter is maintained at a temperature of from 60 C. to 120 C.

9. The process of claim 1, wherein a demulsifier is introduced into the desalter.

10. The process of claim 1, wherein the one or more liquid phases include a water extract phase comprising the organic acid and the ionic liquid and the process further comprises the step of separating the ionic liquid and the organic acid.

11. The process of claim 10, wherein at least one of the ionic liquid and the organic acid are regenerated.

12. The process of claim 1, wherein the organic acid is naphthenic acid.

13. The process of claim 1, wherein the process is a continuous process.

14. The process of claim 1, wherein the ionic liquid is a basic ionic liquid.

15. The process of claim 14, wherein the ionic liquid comprises a basic anion selected from at least one member of a group consisting of: serinate, prolinate, histidinate, threoninate, valinate, asparaginate, taurinate, lysinate, alkylcarbonate and hydrogen carbonate.

16. The process of claim 15, wherein the basic anion is an alkylcarbonate.

17. The process of claim 14, wherein the basic ionic liquid comprises a cation selected or derived from the group consisting of: ammonium, azaannulenium, azathiazolium, benzimidazolium, benzofuranium, benzothiophenium, benzotriazolium, borolium, cinnolinium, diazabicyclodecenium, diazabicyclononenium, diazabicycloundecenium, dibenzofuranium, dibenzothiophenium, dithiazolium, furanium, guanidinium, imidazolium, indazolium, indolinium, indolium, morpholinium, oxaborolium, oxaphospholium, oxathiazolium, oxazinium, oxazolium, iso-oxazolium, oxazolinium, pentazolium, phospholium, phosphonium, phthalazinium, piperazinium, piperidinium, pyranium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, pyrrolidinium, pyrrolium, quinazolinium, quinolinium, iso-quinolinium, quinoxalinium, selenazolium, sulfonium, tetrazolium, thiadiazolium, iso-thiadiazolium, thiazinium, thiazolium, iso-thiazolium, thiophenium, thiuronium, triazadecenium, triazinium, triazolium, iso-triazolium, and uronium.

18. The process of claim 17, wherein the cation is selected from the group consisting of: ##STR00007## wherein: R.sup.a, R.sup.b, R.sup.c, R.sup.d, R.sup.e, R.sup.f and R.sup.g are each independently selected from hydrogen, a C.sub.1 to C.sub.30, straight chain or branched alkyl group, a C.sub.3 to C.sub.8 cycloalkyl group, or a C.sub.6 to C.sub.10 aryl group, wherein said alkyl, cycloalkyl or aryl groups are unsubstituted or may be substituted by one to three groups selected from: C.sub.1 to C.sub.6 alkoxy, C.sub.2 to C.sub.12 alkoxyalkoxy, C.sub.3 to C.sub.8 cycloalkyl, C.sub.6 to C.sub.10 aryl, CN, OH, SH, NO.sub.2, C.sub.6 to C.sub.10 aryl and C.sub.7 to C.sub.10 alkaryl, CO.sub.2(C.sub.1 to C.sub.6)alkyl, OC(O)(C.sub.1 to C.sub.6)alkyl, or any two of R.sup.b, R.sup.c, R.sup.d, R.sup.e and R.sup.f attached to adjacent carbon atoms form a methylene chain (CH.sub.2).sub.q wherein q is from 3 to 6.

19. The process of claim 17, wherein the cation is selected from:
[N(R.sup.a)(R.sup.b)(R.sup.c)(R.sup.d)].sup.+, [P(R.sup.a)(R.sup.b)(R.sup.c)(R.sup.d)].sup.+, and [S(R.sup.a)(R.sup.b)(R.sup.c)].sup.+, wherein: R.sup.a, R.sup.b, R.sup.c and R.sup.d are as defined in claim 18.

20. The process of claim 19, wherein the cation is selected from:
[N(R.sup.a)(R.sup.b)(R.sup.c)(R.sup.d)].sup.+, wherein: R.sup.a, R.sup.b, R.sup.c and R.sup.d are each independently selected from C.sub.1 to C.sub.8 alkyl, including C.sub.2, C.sub.4 and C.sub.6 alkyl.

21. The process of claim 20, wherein the cation is tributyl(methyl)ammonium or triethyl(methyl)ammonium.

22. The process of claim 14, wherein the basic ionic liquid comprises a cation represented by the formula:
Cat.sup.+-(Z-Bas).sub.n wherein: Cat.sup.+ is a positively charged moiety; Bas is a basic moiety; Z is a covalent bond joining Cat.sup.+ and Bas, or is a divalent linking group; and n is an integer of from 1 to 3.

23. The process of claim 22, wherein [Cat.sup.+-Z-Bas] is selected from the group consisting of: ##STR00008##

24. A process according to claim 1, wherein the acid containing crude oil is pre-treated in a de-salter to remove inorganic salts.

Description

(1) The present invention will now be described, by way of example only, with reference to the accompanying Figures, in which:

(2) FIG. 1 shows a process flow diagram of a process in accordance with the present invention;

(3) FIG. 2 is a graph comparing the quantity of naphthenate salt extracted from a process which utilises water in an amount of 10% and of 30% by volume of the mixture, as a function of process operating time;

(4) FIG. 3 is a graph showing the quantity of naphthenate salt extracted (diamonds) from, and the quantity of naphthenate salt in the feed (squares) to, a process which utilises water in an amount of 10% by volume of the mixture, as a function of process operating time.

(5) FIG. 4 is a graph showing the quantity of naphthenate salt extracted (diamonds) from, and the quantity of naphthenate salt in the feed (squares) to, a process which utilises water in an amount of 30% by volume of the mixture, as a function of process operating time.

(6) FIG. 5 is a graph showing the ratio of product water to product crude oil from a process in which water is used in an amount of 30% by volume of the mixture, as a function of process operating time;

(7) FIG. 6 is a graph showing crude oil mass balance from a process in which water is used in an amount of 30% by volume of the mixture, as a function of process operating 30 time;

(8) FIG. 7 is a graph showing water mass balance from a process in which water is used in an amount of 30% by volume of the mixture, as a function of process operating time;

(9) FIG. 8 is a graph showing the amount of total feed to a process in which water is used in an amount of 30% by volume of the mixture, as well as the amounts of crude oil product and water product from the process, as a function of process operating time; and

(10) FIG. 9 is a graph showing the amounts of feed mixture and feed water to a process in which water is used in an amount of 30% by volume of the mixture, as well as the amounts of crude oil product and water product from the process, as a function of process operating time.

(11) Looking at FIG. 1, there is shown a desalter 100 which has been adapted for carrying out the process of the present invention. In the desalter 100, a stream 2 comprising of crude oil and organic acid is contacted with an ionic liquid feed stream 4 to form a mixture comprising crude oil, organic acid and ionic liquid. This mixture is passed through a first mixing valve 1 and then through a first heat exchanger 5. The mixture is heated in the first heat exchanger 5 (preferably to a temperature in the range of 80 to 100 C.) in heat exchange with a first hot oil stream 8.

(12) A water feed stream 6 is heated by way of a second heat exchanger 7. The water feed stream 6 is heated in the second heat exchanger 7 (preferably to a temperature of 70 to 90 C.) in heat exchange with the first hot oil stream 8.

(13) In the embodiment shown in FIG. 1, it can be seen that the first hot oil stream 8 passes in heat exchange contact with the mixture comprising crude oil, organic acid and ionic liquid, and subsequently with the water feed stream 6. Accordingly, the heating imparted to the feed water stream 6 is less than that imparted to the mixture stream.

(14) The heated water feed stream exiting the second heat exchanger 7 is contacted with the heated mixture comprising crude oil, organic acid and ionic liquid. Once contacted, the resulting combination is passed through a further mixing valve 3 and into a separating vessel 9.

(15) The temperature in the separator vessel 9 is maintained at 90 C. by means of heat exchange with a second hot oil stream 10. An electrostatic field is applied to increase the rate of separation.

(16) A deacidified crude oil phase is formed in the separating vessel 9 and extracted as a product stream 12, with an aqueous phase comprising organic acid and ionic liquid being formed as a by-product and extracted as stream 16.

(17) The deacidified crude oil phase 12, being less dense than the aqueous phase 16, is extracted near the top of the separator vessel.

(18) The present inventions will now be described further by way of example.

EXAMPLES

(19) The examples were carried out using a vertical desalter manufactured by Howe Baker Engineers (Serial No.: 1498; Year built: 1980). The separating vessel of the desalter was maintained at a temperature of about 90 C.

(20) The crude oil used in the examples is from an Australian field and is called Pyrenees. The crude oil has a TAN of 1.5 mg KOH g.sup.1. The crude oil was subjected to constant circulation before use so as to prevent stratification.

(21) The ionic liquid used in the examples is tributyl(methyl)ammonium methyl carbonate. The ionic liquid was added in 0.7 wt % concentration with respect to the crude.

(22) As the naphthenate anion forms an association with the tributyl(methyl)ammonium cation, the quantity of naphthenate salt which is extracted from the crude oil is based upon the quantity of tributyl(methyl)ammonium cation which is extracted, as measured using NMR. Unlike naphthenate anions which vary in structure, tributyl(methyl)ammonium cations give a clear set of peaks on an NMR spectrum.

Example 1

Use of Water in an Amount of 10% by Volume of Mixture

(23) Acidic crude oil was mixed with ionic liquid in an amount of 0.7% by weight of acidic crude oil until the TAN of the crude oil was measured to be <0.3 mg KOH g.sup.1 of oil. Mixing was achieved by passing the stream through a mixing valve and was complete within 4 hours.

(24) The salt containing crude oil was then combined with an aqueous stream in a continuous mode of operation to form a mixture containing approximately 10% water by volume. Further mixing was achieved by passing the combined streams through a second mixing valve.

(25) The stream was then fed into a separating vessel containing an electrostatic field of 6 kV alternating current which increased the rate of phase separation.

(26) The process was analyzed to determine the amount of naphthenate salt that was recovered from the process. The quantity of naphthenate salt that was recovered increased as the process approaches steady state conditions. It can be seen from FIG. 3 that, once the process had reached steady state conditions, the recovery of the naphthenate salt was greater than 30 mol %.

Example 2

Use of Water in an Amount of 30% by Volume of Mixture

(27) By utilizing an identical set-up as in Example 1, but increasing the water feed to an amount of 30% water by volume of mixture, the total quantity of recoverable naphthenate salt can be increased to greater than 70 mol % (see FIG. 2).

(28) It can be seen from FIG. 4 that, once the process had reached steady state conditions, the recovery of the naphthenate salt was greater than 30 mol %.

(29) This demonstrates that by increasing the amount of water added to the process, the recovery of the naphthenate salt from the mixture is improved.

(30) FIGS. 5 to 9 also show mass balance data from a process in which water is used in an amount of 30% by volume of the mixture.