Effective novel polymeric additive for inhibiting napthenic acid corrosion and method of using the same

Abstract

The present invention relates to the field of inhibition of metal corrosion in hot acidic hydrocarbons, wherein acidity is derived from presence of naphthenic acid. More particularly, it relates to a polymeric additive for inhibiting high temperature napthenic acid corrosion, wherein said polymeric additive is polymeric phosphate ester of polyisobutylene succinate ester or oxide derivative of polymeric phosphate ester of polyisobutylene succinate ester. A polymeric phosphate ester of polyisobutylene succinate ester which is capable of acting as naphthenic acid corrosion inhibitor by inhibiting naphthenic acid corrosion in crude oil/feedstock/hydrocarbon streams containing naphthenic acid, and demonstrating higher thermal stability at elevated temperature varying from about 200 C. to about 400 C. [about 400 F. to about 750 F.] is disclosed.

Claims

1. A naphthenic acid corrosion inhibitor consisting of polymeric phosphate ester of polyisobutylene succinate ester to inhibit naphthenic acid corrosion in crude oil, feedstock, or hydrocarbon streams containing naphthenic acid; and wherein said inhibitor has thermal stability of about 50% weight loss as determined by thermogravimetric analysis in a temperature range varying from 350 C. to 400 C.; and wherein said polymeric phosphate ester of polyisobutylene succinate ester is a reaction product of: (a) reacting, in first step, a mixture consisting of polyisobutylene succinic anhydride [PIBSA] and a glycol while bubbling with nitrogen gas to produce hydroxy terminated polyisobutylene succinate ester having acid value of about 5 mg KOH/gm or less; (b) reacting, in second step, the hydroxy terminated polyisobutylene succinate ester of the first step with phosphorus pentoxide (P.sub.2O.sub.5) while maintaining nitrogen gas blanket to produce said polymeric phosphate ester of polyisobutylene succinate ester.

2. A naphthenic corrosion inhibitor as claimed in claim 1, wherein said ester is selected from polymeric phosphate esters having one of the following structures I, II or III: ##STR00010## wherein the R.sup.1, R.sup.2 and R.sup.3 are hydroxy terminated polyisobutylene succinate ester having molecular weight varying from 800-10,000 Daltons.

3. A naphthenic corrosion inhibitor as claimed in claim 1, wherein said inhibitor has phosphorus contents varying from 2% to 5% of the inhibitor.

4. A naphthenic corrosion inhibitor as claimed in claim 1, wherein said glycol comprises mono-glycols, aliphatic glycols, aryl glycols, di-glycols, aliphatic di-glycols, or aryl di-glycols.

5. A naphthenic corrosion inhibitor as claimed in claim 1, wherein said glycol and PIBSA are taken in a mole ratio varying from 1:0.4 to 1:1 mole.

6. A naphthenic corrosion inhibitor as claimed in claim 1, wherein said phosphorus pentoxide and said hydroxy terminated polyisobutylene succinate ester are taken in a ratio of P.sub.2O.sub.5 to hydroxy terminated polyisobutylene succinate ester as 0.01 to 4 mole of P.sub.2O.sub.5 to 1 mole of hydroxy terminated polyisobutylene succinate ester.

7. A naphthenic corrosion inhibitor as claimed in claim 1, wherein said PIBSA is prepared by reacting high reactive polyisobutylene [HRPIB] with maleic anhydride.

8. A naphthenic corrosion inhibitor as claimed in claim 7, wherein said high reactive polyisobutylene is reacted with maleic anhydride in a mole ratio varying from 1:0.5 to 1:1.

9. A method for inhibiting naphthenic acid corrosion on metallic surfaces of the processing units processing the stream containing naphthenic acid in a reactor comprises following steps: a) heating the stream containing naphthenic acid to vaporize a portion thereof; b) allowing the stream vapors to rise in a distillation column; c) condensing a portion of the stream vapours passing through the distillation column to produce a distillate; d) adding to the distillate a sufficient amount of naphthenic acid corrosion inhibitor so as to achieve inhibition of naphthenic acid corrosion; e) allowing the distillate containing naphthenic acid corrosion inhibitor additive to substantially contact entire metallic surfaces of the distillation unit so as to form protective film thereon, whereby said surface is inhibited against corrosion; wherein the process is characterized by adding corrosion inhibition amount of said naphthenic acid corrosion inhibitor which is selected from polymeric phosphate ester of polyisobutylene succinate ester as claimed in claim 1 and its oxide derivative.

10. A method as claimed in claim 9, wherein said corrosion inhibition amount of said naphthenic acid corrosion inhibitor varies from 1 to 2000 ppm.

11. A method as claimed in claim 9, wherein said polymeric phosphate ester of polyisobutylene succinate ester is selected from compounds having one of the following structures I, II or III: ##STR00011## wherein the R.sup.1, R.sup.2 and R.sup.3 are hydroxy terminated polyisobutylene succinate ester having molecular weight varying from 800-10,000 Daltons.

12. A method as claimed in claim 9, wherein said stream includes crude oil, feedstock, and hydrocarbon streams and/or fractions thereof.

13. A method as claimed in claim 9, wherein said inhibitor is added to distillate that is later returned to the reactor, or which contact the metallic interior surfaces of the reactor so that metallic surfaces are substantially protected from naphthenic acid corrosion.

14. A method comprising using naphthenic acid corrosion inhibitor consisting of polymeric phosphate ester of polyisobutylene succinate ester as claimed in claim 1 to inhibit naphthenic acid corrosion in crude oils, feedstocks, or hydrocarbon streams.

15. A naphthenic corrosion inhibitor as claimed in claim 1, wherein said glycol is ethylene glycol.

16. A method comprising using naphthenic acid corrosion inhibitor consisting of polymeric phosphate ester of polyisobutylene succinate ester as claimed in claim 2 to inhibit naphthenic acid corrosion in crude oils, feedstocks, or hydrocarbon streams.

17. A naphthenic acid corrosion inhibitor consisting of oxide derivative of polymeric phosphate ester of polyisobutylene succinate ester to inhibit naphthenic acid corrosion in crude oil, feedstock, hydrocarbon streams containing naphthenic acid; and wherein said inhibitor has thermal stability of about 50% weight loss as determined by thermogravimetric analysis in a temperature range varying from 350 C. to 400 C.; wherein said inhibitor has acidity varying from 1 mg KOH/gm to 20 mg KOH/gm as determined by titration of samples against normal alcoholic KOH samples; and wherein said oxide derivative of polymeric phosphate esters of polyisobutylene succinate ester is a reaction product of: (a) reacting, in first step, a mixture consisting of polyisobutylene succinic anhydride [PIBSA] and a glycol while bubbling with nitrogen gas to produce hydroxy terminated polyisobutylene succinate ester having acid value of about 5 mg KOH/gm or less; (b) reacting, in second step, the hydroxy terminated polyisobutylene succinate ester of the first step with phosphorus pentoxide (P.sub.2O.sub.5) while maintaining nitrogen gas blanket to produce said polymeric phosphate ester of polyisobutylene succinate ester; (c) reacting, in third step, the polymeric phosphate esters of polyisobutylene succinate ester of the second step with oxirane compound to result in the oxide derivatives of polymeric phosphate ester of polyisobutylene succinate ester.

18. A naphthenic corrosion inhibitor as claimed in claim 17, wherein said oxirane compound is selected from ethylene oxide, propylene oxide and butylene oxide.

19. A method comprising using naphthenic acid corrosion inhibitor consisting of oxide derivative of polymeric phosphate ester of polyisobutylene succinate ester as claimed in claim 17 to inhibit naphthenic acid corrosion in crude oils, feedstocks, or hydrocarbon streams.

20. A naphthenic corrosion inhibitor as claimed in claim 17, wherein said inhibitor has phosphorus contents varying from 2% to 5% of the inhibitor.

21. A naphthenic corrosion inhibitor as claimed in claim 17, wherein said oxirane compound is selected from group consisting of ethylene oxide, propylene oxide and butylene oxide.

22. A naphthenic corrosion inhibitor as claimed in claim 17, wherein said oxirane compound is butylene oxide.

23. A naphthenic corrosion inhibitor as claimed in claim 17, wherein said oxirane compound is 1,2 butylene oxide.

24. A naphthenic corrosion inhibitor as claimed in claim 17, wherein said inhibitor has phosphorus contents varying from 1% to 5% of the inhibitor.

Description

DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION

(1) With aim to overcome one or more of above-described problems of the prior art, the inventor of present invention has found that when a polymeric additive selected from polymeric phosphate ester of polyisobutylene succinate ester and oxide derivative of polymeric phosphate ester of polyisobutylene succinate ester is employed as naphthenic acid corrosion inhibitor, the corrosive activity of crude oil/feedstock/hydrocarbon stream containing naphthenic acid is surprisingly reduced, inhibited and eliminated, and level of protection [corrosion inhibition efficiency] afforded by employing polymeric corrosion inhibitor of present invention has been found to be about 99% at elevated temperature and that's too with lower amounts of about 300 ppm, which surprisingly has also been found to have substantially higher thermal stability and lower acidity and lower phosphorus contents, and therefore, has been found to avoid disadvantages associated with lower thermal stability, higher acidity and higher phosphorus contents. Further, the polymeric corrosion inhibitor of present invention surprisingly does not decompose, and therefore, does not producing the deposits.

(2) Accordingly, in one embodiment, the present invention relates to a polymeric additive which is polymeric phosphate ester of polyisobutylene succinate ester capable of inhibiting naphthenic acid corrosion and demonstrating higher thermal stability at elevated temperature varying from about 200 C. to about 400 C. [about 400 F. to about 750 F.], by reducing, inhibiting the corrosive activity of crude oil/feedstock/hydrocarbon stream containing naphthenic acid.

(3) In accordance with present invention, the polymeric phosphate esters of polyisobutylene succinate ester is selected from polymeric phosphate esters having one of the following structures I, II or III:

(4) ##STR00002##
wherein R.sup.1, R.sup.2 and R.sup.3 are hydroxy terminated polyisobutylene succinate ester having molecular weight varying from about 800-10,000 deltons.

(5) Accordingly, in one embodiment, the present invention relates to a polymeric additive which is oxide derivative of polymeric phosphate ester of polyisobutylene succinate ester capable of inhibiting naphthenic acid corrosion and demonstrating higher thermal stability at elevated temperature varying from about 200 C. to about 400 C. [about 400 F. to about 750 F.], by reducing, inhibiting and eliminating the corrosive activity of crude oil/feedstock/hydrocarbon stream containing naphthenic acid.

(6) In accordance with present invention, the oxide derivatives of polymeric phosphate esters of polyisobutylene succinate ester is selected from polymeric phosphate esters having one of the following structures A or B:

(7) ##STR00003##
wherein R.sup.1 and R.sup.2 are hydroxy terminated polyisobutylene succinate ester having molecular weight varying from about 800-10,000 delton;
X is H, CH.sub.3 or C.sub.2H.sub.5; and
n may vary from 1 to 20.

(8) It has been found that polymeric additives of present invention are capable of demonstrating substantially higher thermal stability of about 50% weight loss as determined by thermogravimetric analysis in a temperature range varying from about 350 C. to about 400 C., and have lower acidity varying from about 1 mg KOH/gm to about 80 mg KOH/gm as determined by titration of samples against normal alcoholic KOH samples and lower phosphorus contents varying from about 2% to about 5% of the additive, and therefore, are capable of avoiding disadvantages associated with lower thermal stability, higher acidity and higher phosphorus contents.

(9) Further, it has been found that polymeric corrosion inhibitors of present invention surprisingly do not decompose, and therefore, do not produce the deposits in the stream and on the walls of the column.

(10) The polymeric additives of present have been found to have substantially higher thermal stability, therefore, these do not get decomposed and deposited at metallic surfaces of the reactor/distillation unit, meaning thereby do not cause fouling and other associated problems.

(11) In accordance with one embodiment of the present invention, the polymeric phosphate ester of polyisobutylene succinate ester of present invention is prepared by reacting polyisobutylene succinic anhydride [PIBSA] with a glycol to form hydroxy terminated polyisobutylene succinate ester, which is reacted with phosphorus pentoxide to result in polymeric phosphate ester of polyisobutylene succinate esters.

(12) In accordance with present invention, the glycol is selected from mono-glycols, aliphatic glycols, aryl glycols, di-glycols, and aliphatic di-glycols, aryl di-glycols, particularly mono-glycols, aliphatic glycols, aryl glycols, more particularly ethylene glycol.

(13) In accordance with present invention, the glycol and PIBSA are preferably taken in a mole ratio varying from about 1:04 to about 1:1 mole.

(14) In accordance with present invention, the ratio of P.sub.2O.sub.5 to hydroxy-terminated PIB is preferably 0.01 to 4 mole of P.sub.2O.sub.5 to 1 mole of hydroxy-terminated PIB.

(15) In accordance with present invention, the polyisobutylene succinic anhydride [PIBSA] may be prepared by reacting high reactive polyisobutylene with maleic anhydride by employing conventional process.

(16) In accordance with present invention, the high reactive polyisobutylene is reacted with maleic anhydride after taking in a mole ratio varying from about 1:0.5 to about 1:1.

(17) In accordance with one embodiment of the present invention, the oxide derivative of polymeric phosphate esters of polyisobutylene succinate ester of present invention is prepared by reacting polymeric phosphate esters of polyisobutylene succinate ester with oxirane compound to result in oxide derivatives of polymeric phosphate ester of polyisobutylene succinate ester.

(18) In accordance with present invention, the oxirane compound is selected from ethylene oxide, propylene oxide and butylene oxide, preferably the oxirane compound is butylene oxide, more preferably 1,2 butylene oxide.

(19) It has been found that oxide derivative of polymeric phosphate esters of polyisobutylene succinate ester prepared by reacting polymeric phosphate esters of polyisobutylene succinate ester with butylene oxide demonstrates better thermal stability of about 50% weight loss as determined by thermogravimetric analysis in a temperature range varying from about 350 C. to about 400 C., and has very low acidity varying from about 1 mg KOH/gm to about 20 mg KOH/gm as determined by titration of samples against normal alcoholic KOH samples and very low phosphorus contents varying from about 1% to about 5% of the additive.

(20) In accordance with one of the preferred embodiments of the present invention, conventional PIBs and so-called high-reactivity PIBs (see for example EP-B-0565285) are suitable for use in present invention. High reactive PIB in this context is defined as a PIB wherein at least 50%, preferably 70% or more, of the terminal olefinic double bonds are of the vinylidene type, for example the GLISSOPAL compounds available from BASF.

(21) It has been surprisingly discovered by the inventor of the present invention, that a polymer based phosphate ester, having low phosphorus content, low acidity and high thermal stability, and non-fouling nature gives very effective control of napthenic acid corrosion.

(22) The level of protection [corrosion inhibition efficiency] afforded by employing polymeric corrosion inhibitors, particularly oxide derivative of polymeric phosphate esters of polyisobutylene succinate ester of present invention has been found to be about 99% at elevated temperature and that's too with very lower amounts of about 300 ppm. As stated herein above, this additive surprisingly has also been found to have substantially higher thermal stability, and lower acidity and lower phosphorus contents.

(23) Therefore, the additives of present invention, particularly oxide derivative of polymeric phosphate esters of polyisobutylene succinate ester of present invention has been found to be capable of avoiding disadvantages associated with lower thermal stability, higher acidity and higher phosphorus contents.

(24) Further, it has been observed that polymeric corrosion inhibitors of present invention surprisingly do not decompose, and therefore, do not produce deposits, and thereby avoid fouling problem.

(25) In one embodiment, the present invention also relates to method for inhibiting naphthenic acid corrosion on metallic surfaces of the processing units which processes crude oils/feedstocks/hydrocarbon streams and/or their fractions containing naphthenic acid.

(26) In one embodiment of the present invention, method for inhibiting naphthenic acid corrosion on metallic surfaces of the processing units processing the stream in a reactor containing naphthenic acid comprises following steps: a) heating the stream containing naphthenic acid to vaporize a portion thereof; b) allowing the stream vapors to rise in a distillation column; c) condensing a portion of the stream vapours passing through the distillation column to produce a distillate; d) adding to the distillate a sufficient amount of naphthenic acid corrosion inhibitor additive so as to achieve inhibition of naphthenic acid corrosion; e) allowing the distillate containing naphthenic acid corrosion inhibitor additive to substantially contact entire metallic surfaces of the distillation unit so as to form protective film thereon, whereby said surface is inhibited against corrosion; wherein the process is characterized by adding corrosion inhibition amount of naphthenic acid corrosion inhibitor additive selected from polymeric phosphate ester of polyisobutylene succinate ester and oxide derivative of polymeric phosphate ester of polyisobutylene succinate ester.

(27) In accordance with one of the embodiments of the present invention, the corrosion inhibition amount of naphthenic acid corrosion inhibitor additive varies from about 1 to about 2000 ppm.

(28) In accordance with one of the embodiments of the present invention, the polymeric phosphate ester of polyisobutylene succinate ester is selected from compounds having one of the following structures I, II or III:

(29) ##STR00004##
wherein R.sup.1, R.sup.2 and R.sup.3 are hydroxy terminated polyisobutylene succinate ester having molecular weight varying from about 800-10,000 deltons.

(30) In accordance with one of the embodiments of the present invention, the oxide derivatives of polymeric phosphate esters of polyisobutylene succinate ester is selected from compounds having one of the following structures A or B:

(31) ##STR00005##
wherein R.sup.1 and R.sup.2 are hydroxy terminated polyisobutylene succinate ester having molecular weight varying from about 800-10,000 delton;
X is H, CH.sub.3 or C.sub.2H.sub.5; and
n may vary from 1 to 20.

(32) In accordance with one of the preferred embodiments of the present invention, the stream includes crude oil, feedstock, and hydrocarbon streams and/or fractions thereof.

(33) It is advantageous to treat distillation column, trays, pumparound piping and related equipment to prevent naphthenic acid corrosion, when condensed vapours from distilled hydrocarbon fluids contact metallic equipment at temperatures varying from about 200 C. to about 400 C. so that severe conditions of naphthenic acid corrosion are substantially avoided.

(34) In accordance with preferred embodiment of present invention, the additive is generally added to the condensed distillate and the condensed distillate is allowed to contact the metallic surfaces of the distillation column, packing, trays, pump around piping and related equipment as the condensed distillate passes down the column and into the distillation vessel. The distillate may also be collected as product. The unreacted corrosion inhibitors of the instant invention remain in the resultant collected product.

(35) In commercial practice, the additives of present invention may be added to a distillate return to control corrosion in a draw tray and in the column packing while a second injection may be added to a spray oil return immediately below the draw trays to protect the tower packing and trays below the distillate draw tray.

(36) It may be noted that it is not so critical where the additive of the invention is added as long as it is added to distillate that is later returned to the distillation vessel, or which contact the metallic interior surfaces of the distillation column, trays, pump around piping and related equipments so that these surfaces are substantially protected from naphthenic acid corrosion.

(37) In one embodiment, the present invention relates to use of additives selected from polymeric phosphate ester of polyisobutylene succinate ester and oxide derivative of polymeric phosphate ester of polyisobutylene succinate ester as naphthenic acid corrosion inhibitors to inhibit naphthenic acid corrosion in crude oils/feedstocks/hydrocarbon streams.

(38) In another embodiment, the present invention also relates to use of additives selected from polymeric phosphate ester of polyisobutylene succinate ester and oxide derivative of polymeric phosphate ester of polyisobutylene succinate ester as naphthenic acid corrosion inhibitors to inhibit naphthenic acid corrosion in crude oils/feedstocks/hydrocarbon streams by employing the method of inhibition of present invention.

(39) The present invention is now explained with the help of following examples, which have been incorporated for explaining its best mode and are not intended to limit its scope.

EXAMPLES OF THE INVENTION

Example 1

Step 1: Preparation of Polyisobutenyl succinic anhydride

(40) About 89.48% by wt of high reactive polyisobutylene is reacted with about 10.52% by wt of maleic anhydride by employing following process steps: 1. Charging high reactive polyisobutylene into a clean and dry four necked flask equipped with nitrogen inlet, stirrer and thermometer; 2. Raising the temperature to about 125 C.; 3. Starting N.sub.2 gas bubbling and continuing it for about 10 minutes; 4. Stopping or reducing rate of N.sub.2 gas bubbling and a sample for moisture content is taken out; 5. Adding maleic anhydride at a temperature of about 125 C.; 6. After addition of maleic anhydride raising the temperature to about 170 C. and maintaining this temperature for about 2 hours with nitrogen bubbling; 7. After completion of said period of step 6, raising the temperature to about 205 C., and heating at a rate that it reaches in a range of temperature varying from about 170 C. to about 205 C. in about 3 hours, and such rate is about 5 C. per 25 min; 8. maintaining the reaction mass at about 205 C. for about 6 hours; 9. After completion of said period of about 6 hours at a temperature of about 205 C., the reaction mixture is cooled to a temperature of about 170 C.; 10. raising the temperature of the reaction mixture to about 205 C. while applying slow vacuum, which is continued for about 2 hrs at vacuum of about 10 mm; After 2 hours sample onlineI for Acid value and free maleic acid and after 3 hours sample onlineII for Acid value and free maleic acid were drawn.

(41) The polyisobutenyl succinic anhydride prepared was found to have acid value of about 110 mg KOH/gm. Typically the range is between 70 to 120 mg KOH/gm.

Step II: Preparation of hydroxy terminated polyisobutylene succinate ester [HRPIB]

(42) About 79.89% by wt of polyisobutylene succinic anhydride [PIBSA] prepared in stepI is reacted with about 20.11% by wt of mono ethylene glycol to form hydroxy terminated polyisobutylene succinate ester [HRPIB], wherein PIBSA is diluted on toluene to about 85% strength, in this example it is of 85.714% strength] by employing following process steps: 1. Charging diluted PIBSA and mono ethylene glycol in a dean stark vessel; 2. Raising the temperature of reaction mixture to about 190 C. while removing toluene and water from dean stark to reach the desired temperature and while bubbling with nitrogen gas; 3. The temperature of about 190 C. is maintained to achieve desired acid value of about 5 mg KOH/gm or less.

Example 2

Preparation of polymeric phosphate ester of polyisobutylene succinate ester

(43) The polymeric phosphate ester of polyisobutylene succinate ester of present invention is prepared by reacting hydroxy terminated polyisobutylene succinate ester [HRPIB] prepared in step 2 of example 1 with phosphorus pentoxide in following manner:

Example 2a

(44) About 94.23% by wt of hydroxy terminated polyisobutylene succinate ester [HRPIB] prepared in step 2 of example 1 is reacted with about 5.77% by wt of phosphorus pentoxide to prepare polymeric phosphate ester of polyisobutylene succinate ester having phosphorus content of about 2.5% of the additive by employing following steps: 1. Charging HRPIB with nitrogen gas blanket while raising temperature to about 90 C.; 2. Adding phosphorus pentaoxide (P.sub.2O.sub.5) in two equal lots at about 15 minutes interval, wherein the exotherm is observed; 3. After addition of phosphorus pentoxide, the reaction mixture is continuously stirred for about 15 minutes and the temperature is raised to about 140 C. along with nitrogen gas blanket; 4. Maintaining said temperature for about 1 hour followed by cooling to about 70 C. and diluting to about 50% strength [about 1:1] with toluene solvent; 5. filtering by bed made by Hiflow or clay to remove impurities and to result in polymeric phosphate ester of polyisobutylene succinate ester.

(45) The oven dried sample of polymeric phosphate ester of polyisobutylene succinate ester prepared as above has been found to have acid value of about 55.3 mg KOH/gm.

Example 2b

(46) About 93.09% by wt of hydroxy terminated polyisobutylene succinate ester [HRPIB] prepared in step 2 of example 1 is reacted with about 6.91% by wt of phosphorus pentoxide in same manner as above to prepare polymeric phosphate ester of polyisobutylene succinate ester having phosphorus content of about 3.0% of the additive.

(47) The oven dried sample of polymeric phosphate ester of polyisobutylene succinate ester prepared in Example 2b as above has been found to have acid value of about 62.51 mg KOH/gm.

Example 3

Preparation of oxide derivative of polymeric phosphate esters of polyisobutylene succinate ester

Example 3a

(48) About 91.74% by wt of polymeric phosphate esters of polyisobutylene succinate ester prepared in above Example 2a is reacted with about 8.26% by wt of 1,2 butylene oxide to result in oxide derivatives of polymeric phosphate ester of polyisobutylene succinate ester having phosphorus content of about 2.30% of the additive by employing following steps:

(49) It was observed acid value was 55.3 mg KOH/gm for the example 2a, which surprisingly drastically reduced to about 3 mg KOH/gm for example 3a which is for oxide derivative. 1. Charge polymeric phosphate esters of polyisobutylene succinate ester prepared in above Example 2 with 1,2 butylene oxide in two lots at an interval of about 15 minutes, wherein the exotherm is observed at about 10 to 15 C.; 2. Raising the temperature of reaction mixture to about 60 C.; 3. Maintaining the said temperature for about 2 hours when a sample is drawn after about 1 hr, which should have acid value in the range of about 0 to about 5 mg KOH/gm for Example 2 products.

(50) The sample of oxide derivative of polymeric phosphate ester of polyisobutylene succinate ester prepared as above has been found to have acid value of about 3.0 mg/KOH/gm.

Example 3b

(51) About 90.90% by wt of polymeric phosphate esters of polyisobutylene succinate ester prepared in above Example 2b is reacted with about 9.10% by wt of 1,2 butylene oxide to result in oxide derivatives of polymeric phosphate ester of polyisobutylene succinate ester having phosphorus content of about 3.0% of the additive by employing process steps as for example 3a.

(52) The sample of oxide derivative of polymeric phosphate ester of polyisobutylene succinate ester prepared as above in Example 3b has been found to have acid value of about 2.5 mg KOH/gm.

(53) It is observed that acid value of the oxide derivative [example 3b] is dramatically reduced to about 2.5 mg KOH/gm when compared to acid value of its corresponding ester of Example 2b, which was found to have acid value of about 62.5 mg KOH/gm.

(54) It may be noted that oxide derivative of polymeric phosphate ester of polyisobutylene succinate ester surprisingly has substantially reduced acid value as compared to polymeric phosphate ester of polyisobutylene succinate ester.

(55) Therefore, oxide derivative of polymeric phosphate ester of polyisobutylene succinate ester additive is most preferred choice of present invention.

Example 4

High Temperature Naphthenic Acid Corrosion Test

(56) In this example, various amounts of a 50% additives prepared in accordance with Examples 2 and 3, were tested for corrosion inhibition efficiency on carbon steel coupons in hot oil containing naphthenic acid. A weight loss coupon immersion test was used to evaluate the invention compound for its effectiveness in inhibition of naphthenic acid corrosion at 290 C. temperature. Different dosage such as 300, 400 and 600 ppm of invention compound were used as 50% active solution.

(57) A static test on steel coupon was also conducted without using any additive of present invention. This test provided a blank test reading.

(58) The reaction apparatus consisted of a onelitre four necked round bottom flask equipped with water condenser, N.sub.2 purger tube, thermometer pocket with thermometer and stirrer rod. 600 gm (about 750 ml) paraffin hydrocarbon oil (D-130) was taken in the flask. The N.sub.2 gas purging was started with flow rate of about 100 cc per minute and the temperature was raised to about 100 C., which temperature was maintained for about 30 minutes.

(59) Additive compounds of examples 2 and 3 were added in separate batch tests. The reaction mixture was stirred for about 15 minutes at about 100 C. temperature. After removing the stirrer, the temperature of the reaction mixture was raised to about 290 C. A pre-weighed weight-loss carbon steel coupon CS 1010 with dimensions 76 mm . . . times 13 mm . . . times 1.6 mm was immersed. After maintaining this condition for about 1 hour to about 1.5 hours, about 31 gm of naphthenic acid (commercial grade with acid value of about 230 mg KOH/gm) was added to the reaction mixture. A sample of one gm weight of reaction mixture was collected for determination of acid value, which was found to be approximately 11.7 mg KOH/gm. This condition was maintained for four hours. After this procedure, the metal coupon was removed, excess oil was rinsed away, the excess corrosion product was removed from the metal surface. Then the metal coupon was weighed and the corrosion rate was calculated in mils per year.

(60) Calculation of Corrosion Inhibition Efficiency:

(61) The method used in calculating Corrosion Inhibition Efficiency as given below. In this calculation, corrosion inhibition efficiency provided by additive compound is calculated by comparing weight loss due to additive with weight loss of blank coupon (without any additive).

(62) $\mathrm{Corrosion}\mathrm{Inhibition}\mathrm{Efficiency}=\frac{\begin{array}{c}\left(\mathrm{Weight}\mathrm{loss}\mathrm{for}\mathrm{blank}\mathrm{without}\mathrm{additive}\right)-\\ \left(\mathrm{weight}\mathrm{loss}\mathrm{with}\mathrm{additive}\right)\end{array}}{\left(\mathrm{weight}\mathrm{loss}\mathrm{for}\mathrm{blank}\mathrm{without}\mathrm{additive}\right)}100$

(63) The corrosion rate in MPY (mils per year) is calculated by the formula,

(64) $MPY=\frac{534\mathrm{Weight}\mathrm{loss}\mathrm{in}\mathrm{mg}}{\left(\mathrm{Density}\mathrm{in}\mathrm{gm}\text{/}\mathrm{cc}\right)\left(\mathrm{Area}\mathrm{in}{\mathrm{in}}^2\right)\left(\mathrm{Time}\mathrm{of}\mathrm{test}\mathrm{in}\mathrm{hours}\right)}$

(65) The calculated magnitudes are entered in the Tables in appropriate columns.

(66) The results of the experiments are presented in Table I and II.

(67) TABLE-US-00001 TABLE I [with 2.5% Phosphorous for non-butylene oxide treated and 2.3% Phosphorous for Butylene oxide treated] Corrosion Experiment Dosage Effective Weight Loss Corrosion Inhibition No. Compound in Ppm Dosage in ppm in mg Rate MPY efficiency 1 Blank 89 445 2 EXAMPLE 600 300 18.4 92 79 2a 400 200 20.7 103 77 3 EXAMPLE 600 300 1 5 99 3a 400 200 5.4 27 94 200 100 23.5 117 74

(68) In the table above example 2a refers to polymeric phosphate ester of polyisobutylene succinate ester prepared in accordance with example 2a and example 3a refers to oxide derivative of polymeric phosphate ester of polyisobutylene succinate ester prepared in accordance with Example 3a.

(69) It can be observed from the table above that additive of Example 2a gives corrosion protection of about 79% with effective dosage of 300 ppm. However, with additive of Example 3a, the level of protection surprisingly dramatically improves. The maximum efficiency observed for additive of Example 2a is only 79% at a active dosage of 300 ppm, and whereas for the additive of Example 3a the corrosion inhibition efficiency is about 99% at the same dosage and about 94% at effective dosage of about 200 ppm.

(70) The above data clearly establishes that oxide derivatives of polymeric phosphate ester of polyisobutylene succinate ester surprisingly have substantially high corrosion inhibition efficiency even at very low dosages as compared to corresponding polymeric phosphate ester of polyisobutylene succinate ester.

(71) Therefore, oxide derivatives of polymeric phosphate ester of polyisobutylene succinate ester additive are most preferred choice of present invention.

(72) It may be noted that above experiments have been performed only with effective amount upto 300 ppm of the inhibitors of present invention and corrosion inhibition efficiency has been found to be 99% in case of oxide derivatives of polymeric phosphate ester of polyisobutylene succinate ester additive. It is possible to achieve even higher efficiency by employing higher amounts of the inhibitors of present invention.

(73) TABLE-US-00002 TABLE II [with 3.0% Phosphorous for NON butylene oxide treated and 2.7% Phosphorous for Butylene oxide treated] Corrosion Experiment Dosage Effective Weight Loss Corrosion Inhibition No. Compound in ppm Dosage in ppm in mg Rate MPY efficiency 1 Blank 89 445 2 EXAMPLE 600 300 16.1 80 82 2b 3 EXAMPLE 600 300 3.1 16 96 3b 400 200 6.8 34 92 300 150 10.4 52 88

(74) In the table above example 2b refers to polymeric phosphate ester of polyisobutylene succinate ester prepared in accordance with example 2b and example 3b refers to oxide derivative of polymeric phosphate ester of polyisobutylene succinate ester prepared in accordance with Example 3b.

(75) It can be observed from the table above that additive of Example 2b gives corrosion protection of about 82% with effective dosage of 300 ppm. However, with additive of Example 3b, the level of protection surprisingly dramatically improves. The maximum efficiency observed for additive of Example 2b is only 82% at a active dosage of 300 ppm, and whereas for the additive of Example 3b the corrosion inhibition efficiency is about 96% at the same dosage and about 92% at effective dosage of about 200 ppm, and about 88% at effective dosage of about 150 ppm.

(76) The corrosion inhibition tests as per example above were also conducted for prior art additive Step 2 of example 1. The results are tabulated in table III. The additive of step 2 of example 1 is hydroxyl terminated polyisobutylene succinate ester. and prior art additive 1, 2 are 2 ethyl hexyl phosphate, (please refer to thermal analysis section for details of prior art additive).

(77) TABLE-US-00003 TABLE III Corrosion Inhibition Test of Prior Art Additive and Hydroxy Terminated Polymer. Active ppm Mg loss MPY after % Efficiency Details (100%) after test test after test Prior art 1 100 12.1 60.6 86.4 (11.7% Phosphorous) Prior art 2 (15.4% 100 7.87 39.04 91.2 Phosphorous) Example 1 step 2, 500 70.0 350 21.3 Hydroxy terminated Polyisobutylene ester (No phosphorous)

(78) In the table above the corrosion inhibition values of the prior art additives 2-ethyl hexyl phosphate having various Phosphorous content are given. It is observed that at 100 ppm the prior art additives gives a maximum protection of 91.2%. The prior art additive 1 has a phosphorous content of 11.7% and the prior art additive 2 has a phosphorous content 15.4%. If the dosage multiplied by the percent phosphorous content will give the P used for the corrosion protection. Thus for the prior art additive 1, the P used for the corrosion protection is 11.7 ppm and that for the prior art additive it is 15.4 ppm.

(79) If the above values are compared with the data of the invention additives as shown in above Tables 1, and 2, it can be concluded that in the case of Example 3a and Example 3b, the P content used for the corrosion protection is only about 4.8 ppm for 94% efficiency and 5.4 ppm for 92% efficiency. It is well known to those skilled in the prior art that P is an strong poison for the catalyst used for hydrocracking operations. It is desirable to use additive with least phosphorous content. Therefore, the additives, particularly the oxide additive of present invention is most preferred choice.

Example 5

High Temperature Naphthenic Acid Corrosion Dynamic Test

(80) The dynamic testing was carried out by using rotating means provided in the temperature-controlled autoclave and was carried out by using passivated steel coupons. A dynamic test on steel coupon was conducted without using any additive. This test provided a blank test reading. The passivation procedure is explained below:

(81) Passivation Procedure:

(82) About 600 gm of paraffin hydrocarbon oil (D-130) was taken in a reaction vessel comprising a four necked round bottom flask equipped with water condenser, N.sub.2 purger tube, thermometer pocket with thermometer and stirrer rod. The N.sub.2 gas was purged. For passivation of the steel coupon, various amounts of compound of Example 3a 200 400 ppm, (each of which included 50% active additive compound), were added to this reaction mixture. The reaction mixture was stirred for about 15 minutes at about 100 C. temperature. After removing the stirrer, the temperature of the reaction mixture was raised to about 290 C. A pre-weighed weight-loss coupon CS 1010 with dimensions 76 mm . . . times 13 mm . . . times 1.6 mm was immersed. After maintaining this condition for about 4 hours, the steel coupon was removed, excess oil was rinsed away, and the coupon was dried. The metal coupon was weighed. This formed the pre-passivated coupon.

(83) In this example, various amounts of a about 50% of additive prepared in accordance with Examples 3a were tested dynamically for corrosion inhibition efficiency on steel coupons in a hot oil containing naphthenic acid. A weight-loss coupon immersion dynamic test was used to evaluate the invention compound for its effectiveness in inhibition of naphthenic acid corrosion at 290 C. temperature in dynamic condition.

(84) The following test equipment and materials were used in the Dynamic Corrosion Test: 1. Temperature controlled autoclave 2. Preweighed weight-loss carbon steel coupons CS 1010 with dimensions 76 mm . . . times 13 mm . . . times 1.6 mm. 3. Means to rotate the coupon, to provide a peripheral velocity in excess of 3 m/second. Material: 1. Paraffin hydrocarbon oil (D-130) with naphthenic acid added to provide an acid neutralization number of approximately 2 mg/KOH. 2. Nitrogen gas in the vapour space.

(85) Two pre-weighed and pre-passivated weight-loss carbon steel coupons, were clamped to the rotating means of the autoclave. The dynamic test was conducted at about 290 C. for about 4 hours. In one test only passivated coupons were used and in another test passivated and 30 ppm of product was additionally added. After the test, the coupons were removed, excess oil was rinsed away, excess corrosion product was removed from the surface of coupons. The coupons were then weighed and the corrosion rate was calculated as mils/year. The results of this dynamic test are presented in Table IV

(86) In Table IV, Experiment no 2 only the passivated coupons were used in Expt no. 3 passivated coupons were used and additional product of 30 ppm was added. It can be seen from the table that only additives of present invention give excellent protection with mere passivation also.

(87) TABLE-US-00004 TABLE IV dynamic test data Corrosion Expt. Dosage in Effective Weight Loss Corrosion Inhibition Passivation No. Compound Ppm (100%) Dosage in ppm in mg Rate MPY efficiency Dose in ppm 1 Blank 7.5 37.5 2 Example 0 0 100 200 3a 0.2 1 97 100 3 Example 30 15 0 0 100 200 3a 0 0 100 100

(88) Fouling Tendency of the Additives of the Invention:

(89) The fouling tendency of additives of the present invention was determined by heating a 1% solution of the additives in the oil at about 290 C. for about 2 hours. It has been found that additives of Examples 3a and 3b did not give any haze or precipitate confirming that no fouling takes place. Neglible precipitate was seen for example 2a and 2b. The prior art additive 1 and 2 (please refer thermal analysis section for details of prior art additive) showed heavy precipitate. Tributyl Phosphate another commonly used additive for naphthenic acid corrosion inhibition also showed high amount of haziness.

(90) The above results demonstrates the advantages of polymeric phosphate esters.

(91) Thermal Stability Analysis:

(92) The Thermal Stability studies were compared with prior art additives named 2 ethyl hexyl phosphate ester, which were prepared by reacting 73.34% by wt of 2-Ethyl Hexanol with 26.66% by wt of Phosphorous Pentoxide, which in below table is identified as Prior Art 1, and was found to have phosphorus contents of about 11.5% by wt; and by reacting 64.72% by wt of 2-Ethyl Hexanol with 35.28% by wt of Phosphorous Pentoxide, which in below table is identified as Prior Art 2, and was found to have phosphorus contents of about 15.4% by wt, and thermal stability results are given in Table V below.

(93) TABLE-US-00005 TABLE V Thermogravimetric Analysis Temp. Deg C. at Residue @ 600 Product Phosphorous, % 50% loss deg C. PRIOR ART 1 11.5 220 28.5632 PRIOR ART 2 15.4 192 36.9247 Example 2a 2.50 393 9.0379 Example 3a 2.28 384 5.9965 Example 2b 3.0 390 7.3786

(94) The thermal analysis test of the additives of present invention and the additives of prior art were carried out in the Mettler Toledo Thermo Gravimetric Analyzer. A known weight of the sample was heated in the analyzer from 30 C. to 600 C. at a rate of 10 C./minute under nitrogen atmosphere. The temperature at which 50% loss in weight of sample occurs is taken as the representative of thermal stability. The weight of the residue obtained at 600 C., and the temperature at 50% weight loss are presented in Table V. The weight of the residue is indicative of the tendency of the additive, to deposit at high temperature zones of equipments like furnaces, which may cause fouling of the equipment in due course.

(95) Discussion about Thermal Stability:

(96) It can be seen from the above table that the invention compounds (example 2a to example 3b, example 2b) the temperature of 50% weight loss varies from (393 C., 384 C. to 393 C.) respectively. These values are much higher when compared with the prior additives which have a value of only 220 C. and 192 C. These findings clearly indicate the higher thermal stability of the invention compounds when compared with the prior art compounds.

(97) It is known to the person skilled in the art that it is desirable to have additives with higher thermal stability since these will not decompose to volatile products leading to fouling and contamination of other streams. The other advantage of thermally stable compound is they retain their corrosion inhibition efficiency at higher temperatures.

(98) The above data clearly establishes that oxide derivatives of polymeric phosphate ester of polyisobutylene succinate ester surprisingly have substantially high thermal stability at elevated temperature as compared to corresponding polymeric phosphate ester of polyisobutylene succinate ester.

(99) It is also observed that treatment of polymeric phosphate ester of polyisobutylene succinate ester with butylene oxide in accordance with present invention results in reduction of phosphorous contents and also the residue at 600 C.

(100) It is also seen from the above table that the invention compounds leave much lower residues at 600 C. The residue obtained for the invention compounds (experiment 2a, 2b, 3b in the above table) is much lower than the prior additives [Prior art 1 and Prior Art 2] which is 28.5632 and 38.9247% (in the table). The above data clearly indicates that the invention compounds will have least deposition tendency in the areas of furnace.

(101) In view of above findings, the oxide derivatives of polymeric phosphate ester of polyisobutylene succinate ester are the most preferred choice of present invention.

(102) Accordingly, it is well understood that the naphthenic acid corrosion inhibitors, particularly the oxide derivatives of the present invention, and prepared in accordance with present invention, which have been found to be polymeric in nature are capable of overcoming above-described drawbacks and problems of the prior art.

(103) As also established with the help of forgoing examples, the naphthenic acid corrosion inhibitors of present invention have been found to be effective and thermal stability at elevated temperatures. These inhibitors have not been found to get decomposed and deposited at metallic surfaces of the reactor/distillation unit. These inhibitors have not been found to cause fouling and other associated problems, and therefore, are capable of effectively treating Indian crude oil, and crude oil from countries like China, Africa and Europe without causing corrosion due to presence of naphthenic acid.

(104) Further, the corrosion inhibitors of present invention have also been found to be effective for possible concentrations of naphthenic acid in the stream that's too without causing associated disadvantages.

(105) Further, the above experiments also confirm that inhibitors, particularly the oxide derivatives of the present invention have lower acidity and have not been found to contribute to acidity of the stream being treated, and have been found to have lower and effective amounts of phosphorus.

(106) It may be noted that effectiveness of present inhibitors has been checked for crude oil containing naphthenic acid, but these are suitable for crude oil containing naphthenic acid and sulfur compounds.

(107) It will be apparent from the foregoing discussion that the present invention comprises the following items: 1. A polymeric phosphate ester of polyisobutylene succinate ester which is capable of acting as naphthenic acid corrosion inhibitor by inhibiting naphthenic acid corrosion in crude oil/feedstock/hydrocarbon streams containing naphthenic acid, and demonstrating higher thermal stability at elevated temperature varying from about 200 C. to about 400 C. [about 400 F. to about 750 F.]. 2. A corrosion inhibitor as described in item 1, wherein said ester is selected from polymeric phosphate esters having one of the following structures I, II or III:

(108) ##STR00006## wherein R.sup.2 and R.sup.3 are hydroxy terminated polyisobutylene succinate ester having molecular weight varying from about 800-10,000 deltons. 3. An oxide derivative of polymeric phosphate ester of polyisobutylene succinate ester which is capable of acting as naphthenic acid corrosion inhibitor by inhibiting naphthenic acid corrosion in crude oil/feedstock/hydrocarbon streams containing naphthenic acid, and demonstrating higher thermal stability at elevated temperature varying from about 200 C. to about 400 C. [about 400 F. to about 750 F.]. 4. A corrosion inhibitor as described in item 3, wherein said oxide derivative is selected from polymeric phosphate esters having one of the following structures A or B:

(109) ##STR00007## wherein R.sup.1 and R.sup.2 are hydroxy terminated polyisobutylene succinate ester having molecular weight varying from about 800-10,000 delton; X is H, CH.sub.3 or C.sub.2H.sub.5; and n may vary from 1 to 20. 5. A corrosion inhibitor as described in any one of the preceding items, wherein said inhibitor has thermal stability of about 50% weight loss as determined by thermogravimetric analysis in a temperature range varying from about 350 C. to about 400 C. 6. A corrosion inhibitor as described in any one of the preceding items, wherein said inhibitor has acidity varying from about 1 mg KOH/gm to about 80 mg KOH/gm as determined by titration of samples against normal alcoholic KOH. 7. A corrosion inhibitor as described in any one of the preceding items, wherein said inhibitor has phosphorus contents varying from about 2% to about 5% of the inhibitor. 8. A corrosion inhibitor as described in items 1 or 2, wherein said inhibitor is prepared by reacting polyisobutylene succinic anhydride [PIBSA] with a glycol to form hydroxy terminated polyisobutylene succinate ester, which is reacted with phosphorus pentoxide to result in polymeric phosphate ester of polyisobutylene succinate esters. 9. A corrosion inhibitor as described in item 8, wherein said glycol is selected from mono-glycols, aliphatic glycols, aryl glycols, di-glycols, and aliphatic di-glycols, aryl di-glycols, particularly mono-glycols, aliphatic glycols, aryl glycols, more particularly ethylene glycol. 10. A corrosion inhibitor as described in items 8 or 9, wherein said glycol and PIBSA are taken in a mole ratio varying from about 1:04 to about 1:1 mole. 11. A corrosion inhibitor as described in item 8, wherein said phosphorus pentoxide and said hydroxy terminated polyisobutylene succinate ester are taken in a ratio of P.sub.2O.sub.5 to hydroxy terminated polyisobutylene succinate ester as 0.01 to 4 mole of P.sub.2O.sub.5 to 1 mole of hydroxy terminated polyisobutylene succinate ester. 12. A corrosion inhibitor as described in item 8, wherein said PIBSA is prepared by reacting high reactive polyisobutylene with maleic anhydride. 13. A corrosion inhibitor as described in item 12, wherein said high reactive polyisobutylene is reacted with maleic anhydride after taking in a mole ratio varying from about 1:0.5 to about 1:1. 14. A corrosion inhibitor as described in items 3 or 4, wherein said oxide derivative of polymeric phosphate esters of polyisobutylene succinate ester is prepared by reacting polymeric phosphate esters of polyisobutylene succinate ester of item 1 or 2 with oxirane compound to result in oxide derivatives of polymeric phosphate ester of polyisobutylene succinate ester. 15. A corrosion inhibitor as described in item 14, wherein said oxirane compound is selected from ethylene oxide, propylene oxide and butylene oxide, preferably the oxirane compound is butylene oxide, more preferably 1,2 butylene oxide. 16. A corrosion inhibitor as described in items 14 or 15, wherein said inhibitor has thermal stability of about 50% weight loss as determined by thermogravimetric analysis in a temperature range varying from about 350 C. to about 400 C., and acidity varying from about 1 mg KOH/gm to about 20 mg KOH/gm as determined by titration of samples against normal alcoholic KOH samples and phosphorus contents varying from about 1% to about 5% of the inhibitor. 17. A method for inhibiting naphthenic acid corrosion on metallic surfaces of the processing units processing the stream containing naphthenic acid in a reactor comprises following steps: a) heating the stream containing naphthenic acid to vaporize a portion thereof; b) allowing the stream vapors to rise in a distillation column; c) condensing a portion of the stream vapours passing through the distillation column to produce a distillate; d) adding to the distillate a sufficient amount of naphthenic acid corrosion inhibitor so as to achieve inhibition of naphthenic acid corrosion; e) allowing the distillate containing naphthenic acid corrosion inhibitor additive to substantially contact entire metallic surfaces of the distillation unit so as to form protective film thereon, whereby said surface is inhibited against corrosion; wherein the process is characterized by adding corrosion inhibition amount of said naphthenic acid corrosion inhibitor which is selected from polymeric phosphate ester of polyisobutylene succinate ester and oxide derivative of polymeric phosphate ester of polyisobutylene succinate ester. 18. A method as described in item 17, wherein said corrosion inhibition amount of said naphthenic acid corrosion inhibitor varies from about 1 to about 2000 ppm. 19. A method as described in item 17, wherein said polymeric phosphate ester of polyisobutylene succinate ester is selected from compounds having one of the following structures I, II or III:

(110) ##STR00008## wherein R.sup.1, R.sup.2 and R.sup.3 are hydroxy terminated polyisobutylene succinate ester having molecular weight varying from about 800-10,000 deltons. 20. A method as described in item 17, wherein said oxide derivatives of polymeric phosphate esters of polyisobutylene succinate ester is selected from compounds having one of the following structures A or B:

(111) ##STR00009## wherein R.sup.1 and R.sup.2 are hydroxy terminated polyisobutylene succinate ester having molecular weight varying from about 800-10,000 delton; X is H, CH.sub.3 or C.sub.2H.sub.5; and n may vary from 1 to 20. 21. A method as described in any one of the items 17 to 20, wherein said stream includes crude oil, feedstock, and hydrocarbon streams and/or fractions thereof 22. A method as described in any one of the items 17 to 21, wherein said inhibitor is added to distillate that is later returned to the reactor, or which contact the metallic interior surfaces of the reactor so that metallic surfaces are substantially protected from naphthenic acid corrosion. 23. Use of additive polymeric phosphate ester of polyisobutylene succinate ester as described in items 1 or 2 as naphthenic acid corrosion inhibitor to inhibit naphthenic acid corrosion in crude oils/feedstocks/hydrocarbon streams. 24. Use of additive oxide derivative of polymeric phosphate ester of polyisobutylene succinate ester as described in item 3 or 4 as naphthenic acid corrosion inhibitors to inhibit naphthenic acid corrosion in crude oils/feedstocks/hydrocarbon streams. 25. A corrosion inhibitor substantially as herein described with reference to the foregoing examples. 26. A method for inhibiting naphthenic acid corrosion substantially as herein described with reference to the foregoing examples. 27. Use of corrosion inhibitor substantially as herein described with reference to the foregoing examples.