Effective novel non-polymeric and non-fouling additive for inhibiting high-temperature naphthenic acid corrosion and method of using the same

Abstract

The present invention relates to inhibition of high temperature naphthenic acid corrosion occurring in hydrocarbon processing units. The invention provides an effective novel non-polymeric and non-fouling additive for inhibiting high-temperature naphthenic acid corrosion, comprising an effective corrosion-inhibiting amount of a second phosphate ester wherein said second phosphate ester is obtained by reacting a first phosphate ester with an oxirane compound selected from the group consisting of butylene oxide, ethylene oxide, propylene oxide or any other oxirane compound or a combination thereof, preferably with butylene oxide, capably yielding said second phosphate ester, having a structure A or B, ##STR00001##
wherein R.sup.1 and R.sup.2 are each independently selected from the group consisting of moieties having 1 to 20 carbon atoms and R.sup.1 and R.sup.2 may be identical or different, X is H, CH.sub.3 or C.sub.2H.sub.5; and n may vary from 1 to 20,
wherein said first phosphate ester is having a structure I or II, ##STR00002##
wherein R.sup.1 and R.sup.2 are each independently selected from the group consisting of moieties having 1 to 20 carbon atoms and R.sup.1 and R.sup.2 may be identical or different, said first phosphate ester being obtained as a reaction product of reaction of an alcohol with a phosphorous pentaoxide.

Claims

1. A process for inhibiting high temperature naphthenic acid corrosion of a metallic surface of a hydrocarbon processing unit of a petrochemical plant, used for processing a stream containing naphthenic acid, with said processing units comprising distillation columns, strippers, trays, pump around piping and related equipments, and wherein the process comprises the steps of: (a) heating said hydrocarbon containing naphthenic acid to vapourize a portion of said hydrocarbon; (b) condensing a portion of the hydrocarbon vapors, passing through said hydrocarbon processing unit, to produce a condensed distillate; (c) adding to said condensed distillate, before said condensed distillate is returned to said hydrocarbon processing unit or collected as a product, from 1 to 2000 ppm of a non-polymeric and non-fouling additive for inhibiting high-temperature naphthenic acid corrosion in a corrosion-inhibition-effective-amount to form a reaction mixture; (d) allowing said reaction mixture to contact said metallic surface of said hydrocarbon processing unit to form a protective film on said metallic surface whereby said metallic surface is inhibited against corrosion; and (e) allowing said condensed distillate to return to said hydrocarbon processing unit, or to be collected as said product, wherein said non-polymeric and non-fouling additive comprises oxide treated phosphate ester, wherein the oxide treated phosphate ester is a reaction product of a phosphate ester and an oxirane compound selected from the group consisting of butylene oxide, ethylene oxide, propylene oxide or any other oxirane compound or a combination thereof, and comprises a mixture of compounds having structural formulae A and B: ##STR00010## wherein R.sup.1 and R.sup.2 are each independently selected from the group consisting of moieties having 1 to 20 carbon atoms, and R.sup.1 and R.sup.2 may be identical to or different from each other, X is H, CH.sub.3 or C.sub.2H.sub.5; and n may vary from 1 to 20, wherein said phosphate ester at least comprises a mixture of compounds of structural formulae I and II: ##STR00011## wherein R.sup.1 and R.sup.2 are each independently selected from the group consisting of moieties having 1 to 20 carbon atoms, and R.sup.1 and R.sup.2 may be identical to or different from each other, wherein said phosphate ester is a reaction mixture of reacting an alcohol with a phosphorous pentaoxide.

2. The process as claimed in claim 1, wherein said stream includes crude oil, feedstock, and hydrocarbon stream and/or fractions thereof.

3. The process as claimed in claim 1, wherein the additive has acidity varying from about 1 mg KOH/gm to about 20 mg KOH/gm.

4. The process as claimed in claim 1, wherein the additive has phosphorus contents varying from about 0.5% to about 9% of said additive.

5. The process as claimed in claim 1, wherein mole ratios of said phosphorus pentoxide and said alcohol are used, such that the mole ratio of said phosphorus pentoxide to said alcohol is 1 mole of said phosphorus pentoxide to 1 to 10 mole of said alcohol and 1 mole of said phosphorus pentoxide to 1 to 7 mole of said alcohol.

6. A method comprising: using a non-polymeric and non-fouling additive for inhibiting high temperature naphthenic acid corrosion of metallic surface of a hydrocarbon processing unit of a petrochemical plant, used for processing a stream containing naphthenic acid, with said processing units comprising distillation columns, strippers, trays, pump around piping and related equipments, wherein the non-polymeric and non-fouling additive is added to said processing units and comprises oxide treated phosphate ester, wherein the oxide treated phosphate ester is a reaction product of a phosphate ester and an oxirane compound selected from the group consisting of butylene oxide, ethylene oxide, propylene oxide or any other oxirane compound or a combination thereof, and comprises a mixture of compounds having structural formulae A and B: ##STR00012## wherein R.sup.1 and R.sup.2 are each independently selected from the group consisting of moieties having 1 to 20 carbon atoms, and R.sup.1 and R.sup.2 may be identical to or different from each other, X is H, CH.sub.3 or C.sub.2H.sub.5; and n may vary from 1 to 20, wherein said phosphate ester at least comprises a mixture of compounds of structural formulae I and II: ##STR00013## wherein R.sup.1 and R.sup.2 are each independently selected from the group consisting of moieties having 1 to 20 carbon atoms, and R.sup.1 and R.sup.2 may be identical to or different from each other, wherein said phosphate ester is a reaction mixture of reacting an alcohol with a phosphorous pentaoxide.

7. The method as claimed in claim 6, wherein the additive has acidity varying from about 1 mg KOH/gm to about 20 mg KOH/gm.

8. The method as claimed in claim 6, wherein the additive has phosphorus contents varying from about 0.5% to about 9% of said additive.

9. The method as claimed in claim 6, wherein mole ratios of said phosphorus pentoxide and said alcohol are used, such that the mole ratio of said phosphorus pentoxide to said alcohol is 1 mole of said phosphorus pentoxide to 1 to 10 mole of said alcohol and 1 mole of said phosphorus pentoxide to 1 to 7 mole of said alcohol.

Description

DESCRIPTION OF THE INVENTION

(1) The present invention uses the following reacted compound to be used as corrosion inhibitor for inhibiting high temperature naphthenic acid corrosion. This reacted compound is obtained by reaction of alcohol with phosphorous pentoxide followed by reaction with oxirane compounds selected from the group consisting of butylene oxides ethylene oxides and propylene oxides and other such compounds.

(2) The mole ratio of P.sub.2O.sub.5 to alcohol is preferably 1 mole of P.sub.2O.sub.5 to 1 to 10 mole of alcohol and preferably 1 mole of P.sub.2O.sub.5 to 1 to 7 mole of alcohol.

(3) It has been surprisingly discovered by the inventor of the present invention, that a phosphate ester, reacted by oxirane compounds such as butylene oxide are having lower phosphorus content, low acidity and, and non-fouling nature and gives very effective and improved control of naphthenic acid corrosion, as compared with use of only non-treated phosphate ester.

(4) The novel additive is made in two basic steps. 1. Alcohol is reacted with phosphorus pentoxide. (The resulting reaction compound is a commercially used prior art additive used in inhibition of naphthenic acid corrosion). The reaction can be carried out by using various mole ratios of alcohol and phosphorus pentoxide. The resultant reaction compound is a phosphate ester. This reaction compound is highly acidic in nature. 2. The resultant reaction-compound, of step 1 is further reacted with oxirane compounds like butylene oxide. Alternatively, the other common oxides like ethylene oxide or propylene oxide or any other oxirane compound also can be used. The resultant reaction compound obtained after this step no. 2 is butylene-oxide-treated phosphate ester.

(5) It should be noted that during synthesis of phosphate esters, wherein alcohol and phosphorous pentaoxide are used, the resulting compound contains a mixture of mono-, di-, and tri-phosphate and many other phosphorous compounds are formed. Typical structures I & II, respectively, of mono- and di-phosphate ester are shown below.

(6) ##STR00006##
wherein R.sup.1 and R.sup.2 are each independently selected from the group consisting of moieties having 1 to 20 carbon atoms and R.sup.1 and R.sup.2 may be identical to or different from each other.

(7) This mixture predominantly contains mono- and di-phosphates and other phosphorous compounds which are acidic in nature and expected to take part in reaction with the oxirane compounds like butylene oxide, ethylene oxide and propylene oxide capably yielding phosphate ester. Typical structures A or B, respectively, of mono- and di-phosphate ester reacted with oxides are shown below

(8) ##STR00007##
wherein R.sup.1 and R.sup.2 are each independently selected from the group consisting of moieties having 1 to 20 carbon atoms and R.sup.1 and R.sup.2 may be identical to or different from each other, X is H, CH.sub.3 or C.sub.2H.sub.5; and n may vary from 1 to 20.

(9) It should be noted that the above mentioned steps can be understood better by referring to the corresponding examples.

(10) The present invention is directed to a method for inhibiting corrosion on the metal surfaces of the processing units which process hydrocarbons such as crude oil and its fractions containing naphthenic acid. The invention is explained in details in its simplest form wherein the following method steps are carried out, when it is used to process crude oil in process units such as distillation unit. Similar steps can be used in different processing units such as, pump-around piping, heat exchangers and such other processing units.

(11) These method steps are explained below: a) heating the hydrocarbon containing naphthenic acid to vaporize a portion of the hydrocarbon: b) allowing the hydrocarbon vapors to rise in a distillation column; c) condensing a portion of the hydrocarbon vapours passing through the distillation column to produce a distillate; d) adding to the distillate, from 1 to 2000 ppm of, for example, butylene-oxide-treated phosphate ester, which is the required additive of present invention; e) allowing the distillate containing additive compound of step (d) to contact substantially the entire metal surfaces of the distillation unit to form protective film on such surface, whereby such surface is inhibited against corrosion.

(12) It is advantageous to treat distillation column, trays, pump-around piping and related equipment to prevent naphthenic acid corrosion, when condensed vapours from distilled hydrocarbon fluids contact metallic equipment at temperatures greater than 200° C., and preferably 400° C. 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 corrosion inhibitors of the instant invention remain in the resultant collected product.

(13) In commercial practice, the additives of this 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. 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 metal interior surfaces of the distillation column, trays, pump around piping and related equipments.

EXAMPLES

(14) The method of using the additive of the present invention for achieving inhibition of high temperature naphthenic acid corrosion is explained below with the help of examples and tables.

Example 1

(15) Into a clean four-necked round bottom flask, kept in an oil bath at 30° C., 733.4 gm of 2-ethyl-hexanol was charged, and nitrogen gas purging was started. Total amount of 266.5 gm of phosphorous pentoxide was added to the flask in six installments. Exotherm was observed after addition of phosphorous pentoxide to the flask. After addition of phosphorous pentoxide was completed, the temperature of reaction mixture was raised to 99° C. and this temperature was maintained for four hours.

(16) The reaction mixture was cooled to 30° C.-35° C., filtered and analyzed for acid value and phosphorous content by method of Inductive Coupled Plasma (ICP).

(17) The acid value was found to be in the range of 280 to 330 mg KOH/gm. Typical acid value was 308 mg KOH/gm. The phosphorous content was in the range of 10 to 12%. Typical value of phosphorous content was 11.65%. The resulting reaction mixture of Example 1 is prior art's additive for Naphthenic Acid Corrosion Inhibition. The results of experiments of Example 1 are given in Table 1.

Example 2

(18) Into a clean four-necked round bottom flask, kept in an oil bath at 30° C., 200 gm of reaction mixture of Example 1 was charged. Into this reaction mixture 150 gm of butylene oxide was slowly added. The exotherm was observed and the temperature was maintained below 40° C. till the addition of entire quantity of 150 gm of butylene oxide was completed. The samples of resulting chemical mixture were taken intermittently and were analyzed for acid value. The reaction was continued till the acid value was 10 mg KOH/gm.

(19) The resulting reaction mixture was then heated to 60° C. temperature, and was maintained at this temperature for two hours.

(20) The resulting reaction mixture was cooled to 30° C.-35° C., filtered and analyzed for acid value and phosphorous content, by method of ICP.

(21) The acid value was found to be less than 10 mg KOH/gm. Typical acid value was 1 mg KOH/gm. The phosphorous content was in the range of 5 to 7%. Typical phosphorous content value was 6.53%. The resulting reaction mixture of Example 2 is used as Invention-Additive for Naphthenic Acid Corrosion Inhibition. The results of experiments of Example 2 are given in Table 1.

Example 3

(22) Into a clean four-necked round bottom flask, kept in a water bath at 30° C., 486 gm of 2-ethyl-hexanol was charged, and nitrogen gas purging was started. Total amount of 265 gm of phosphorous pentoxide was added to the flask in six installments. Exotherm was observed after addition of phosphorous pentoxide to the flask. After addition of phosphorous pentoxide was completed, the temperature of reaction mixture was raised to 99° C. and this temperature was maintained for four hours.

(23) The reaction mixture was cooled to room temperature of 30° C., filtered and analyzed for acid value and phosphorous content by method of ICP.

(24) The acid value was found to be in the range of 320 to 350 mg KOH/gm. Typical acid value was 331 mg KOH/gm. The phosphorous content was in the range of 14 to 16%. Typical value of phosphorous content was 15.408%. The resulting reaction mixture of Example 3 is prior art's additive for Naphthenic Acid Corrosion Inhibition. The results of experiments of Example 3 are given in Table 1.

Example 4

(25) Into a clean four-necked round bottom flask, kept in a water bath at 30° C., 100 gm of reaction mixture of Example 3 was charged. Into this reaction mixture 88 gm of butylene oxide was slowly added. The exotherm was observed and the temperature was maintained below 40° C. till the addition of entire quantity of 88 gm of butylene oxide was completed. The samples of resulting chemical mixture were taken intermittently and were analyzed for acid value. The reaction was continued till the acid value was 10 mg KOH/gm.

(26) The resulting reaction mixture was then heated to 60° C. temperature, and was maintained at this temperature for two hours.

(27) The resulting reaction mixture was cooled to room temperature of 30° C., filtered and analyzed for acid value and phosphorous content, by ICP.

(28) The acid value was found to be less than 10 mg KOH/gm. Typical acid value was 6.8 mg KOH/gm. The phosphorous content was in the range of 7 to 9%. Typical phosphorous content value was 8.19%. The resulting reaction mixture of Example 4 is used as Invention-Additive for Naphthenic Acid Corrosion Inhibition. The results of experiments of Example 4 are given in Table 1.

Example 5

(29) High Temperature Naphthenic Acid Corrosion Test

(30) In this example, various amounts of additives prepared in accordance, with Examples 1 to 4, were tested for corrosion inhibition efficiency on steel coupons in a 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 dosages of invention additive compounds are used as shown in Table 1.

(31) A static test on steel coupon was conducted without using any additive. This test provided a blank test reading.

(32) The reaction apparatus consisted of a one-litre 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) with fractions boiling above 290° C., was taken in the flask. N.sub.2 gas purging was started with flow rate of 100 cc/minute and the temperature was raised to 100° C., which temperature was maintained for 30 minutes.

(33) In different experiments, additive compounds of Examples 1 to 4 were used for testing their effectiveness in Naphthenic Acid Corrosion Inhibition. The reaction mixture after addition of additive compound was stirred for 15 minutes at 100° C. temperature. After removing the stirrer, the temperature of the reaction mixture was raised to 290° C. A pre-weighed weight-loss carbon steel coupon CS 1010 with dimensions 76 mm×13 mm×1.6 mm was immersed. After maintaining this condition for 1 hour to 1.5 hours, 31 gm of naphthenic acid (commercial grade with acid value of 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. This condition was maintained for four hours. After this procedure, the metal coupon was removed, excess oil was rinsed away, and 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.

(34) Calculation of Corrosion Inhibition Efficiency

(35) The method used in calculating Corrosion Inhibition Efficiency is 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).

(36) $\mathrm{Corrosion}\mathrm{Inhibition}\mathrm{Efficiency}=\frac{\begin{array}{c}\left(\mathrm{Weight}\mathrm{loss}\mathrm{for}\mathrm{blank}\mathrm{without}\mathrm{additive}\right)-\\ \left(\mathrm{weight}\mathrm{loss}\mathrm{with}\mathrm{additive}\right)\end{array}}{\left(\mathrm{weight}\mathrm{loss}\mathrm{for}\mathrm{blank}\mathrm{without}\mathrm{additive}\right)}\times 100$
The calculated magnitudes are entered in the Table 1 in appropriate columns.

Example 6

(37) High Temperature Naphthenic Acid Corrosion Dynamic Test

(38) The dynamic testing was carried out by using rotating means provided in the temperature-controlled autoclave and was carried out by using steel coupons. A weight-loss coupon immersion dynamic test was used to evaluate the invention compound for its effectiveness in inhibition of naphthenic acid corrosion at 260° C. temperature under dynamic condition. In this example, various amounts of an about 50% or neat additive prepared in accordance with Examples 1 to 4 were tested. A dynamic test on steel coupon was conducted without using any additive. This test provided a blank test reading.

(39) The following test equipment and materials were used in the Dynamic Corrosion Test: 1. Temperature controlled autoclave 2. Pre-weighed weight-loss carbon steel coupons CS 1010 with dimensions 76 mm×13 mm×1.6 mm. 3. Means to rotate the coupon.
Material: 1. Naphthenic acid was externally added to provide an acid neutralization number of approximately 12 mg/KOH/gm. 2. Nitrogen gas in the vapour space.

(40) Two pre-weighed carbon steel coupons, were clamped to the rotating means of the autoclave. The dynamic test was conducted at about 260° C. for about 6 hours. 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 2.

(41) TABLE-US-00001 TABLE 1 Resulting Typical Reaction Phospho- Additive Additive Product rous Total Active Weight % from Content Dosage Dosage Loss in Effi- Example % (ppm) (ppm) mg MPY ciency Example 1 11.65 100 100 10.9 55 86.4 (Prior art) 50 50 42.3 212 47.4 Example 2 6.53 75 75 3.4 17 95.8 (Invention 50 50 13.8 69 82.8 Additive) Example 3 15.408 100 100 7.1 36 91.2 (Prior Art) 50 50 39.9 200 50.4 Example 4 8.19 50 50 5.9 30 92.7 (Invention 25 25 25.2 126 68.7 Additive) Blank 0 0 0 80.4 402 NA

(42) TABLE-US-00002 TABLE 2 AUTOCLAVE TEST (Example 6) Typical % Additive Additive Phospho- Active Mg effi- Total Active rous Phospho- loss MPY ciency Dosage Dosage content rous, after after after Product (ppm) ppm (%) ppm* test test test Blank — — — 43.1 143.8 — Example 1 500 500 11.65 58.25 9.3 31.0 76.1 Example 2 500 500 6.53 32.65 3.1 10.34 92.8 Example 3 500 500 15.40 77.04 7.25 24.2 83.2 Example 4 500 500 8.19 40.95 1.4 4.7 96.7 Example 4 250 250 8.19 20.48 3.67 12.24 91.5 Tributyl 500 500 11.6 58.0 38.05 127 11.7 Phosphate Tris 2 Ethyl 500 500 7.0 35 40.89 136.4 5.10 Hexyl Phosphate *The column indicates active phosphorous in the system

Example 7

(43) Fouling Tendency Of Corrosion Inhibiting Additives

(44) The fouling tendency of each of invention additives and prior art additives was determined by heating 1% solution of each additive in the oil at 290° C. for two hours. The observations with respect to precipitate-formation are given in Table 3.

(45) TABLE-US-00003 TABLE 3 Additive Observation with respect to precipitate - formation Example 1 Heavy precipitation Example 2 Slight solids - formation Example 3 Heavy precipitation Example 4 Slight solids - formation Tributyl Phosphate Completely hazy solution
Detailed Discussion about Experimental Results

(46) The detailed discussion given below, with respect to the experimental results, presented in Tables 1 to 3, for different experiments described in Examples 1 to 6, explains the high effectiveness of the invention additive compound of present invention, in high temperature naphthenic acid corrosion inhibition. The inventor of the present invention has surprisingly found that, even with reduction in amount of dosages used of the active components of invention additive compound as compared with the amount of dosages of prior art additive compounds, high effectiveness in corrosion inhibition is obtained.

(47) Detailed Discussion of Experimental Results Given in Table 1

(48) It is seen that in Examples 1 and 3, wherein prior art additive compounds were used, with active dosage amounts of 100 ppm of additive compound, in each case, having typical phosphorous content percentage of 11.65 and 15.408, respectively and the percent efficiency of corrosion-inhibition was respectively 86.4 and 91.2. In the same examples, by reducing the active dosage amounts to 50 ppm of additive compound in each case with same percentages of phosphorous contents mentioned above, the corresponding percentage efficiency of corrosion inhibition, dropped down respectively to 47.4 and 50.4.

(49) While comparing the above mentioned results about effectiveness of prior art additives, it is seen in Examples 2 and 4, wherein invention additive compounds are used for naphthenic acid corrosion inhibition, that higher corrosion inhibition efficiencies are obtained by using lower dosage amounts, also providing lesser percentages of phosphorous contents, as shown below.

(50) In Example 2, along with providing lesser percent phosphorous content of 6.53, in each case, use of active dosage amounts of invention additive compound of 75 ppm and 50 ppm, the corresponding percentage efficiencies of common inhibition were respectively 95.8 and 85.8.

(51) In Example 4, along with providing a little higher percent phosphorous content of 8.19, in each case, with use of even reduced active dosage amounts of invention additive compound of 50 ppm and 25 ppm, the corresponding percent efficiencies of corrosion inhibition were respectively 92.7 and 68.7 respectively.

(52) Detailed Discussion of Experimental Results Given in Table 2

(53) It is seen that by using procedures of Examples 1 and 3, wherein prior art additive compounds were used with active dosage amounts of 500 ppm of additive compound, in each case, the typical phosphorous content percentage was respectively 11.65 and 15.408, and the percent efficiency of corrosion-inhibition was respectively 76.1 and 83.2.

(54) It is also seen that, by using prior art additive compound of tributyl phosphate, with active dosage amount of 500 ppm, with typical phosphorous content of 11.6%, the percent efficiency of corrosion inhibition was only 11.7%.

(55) Similarly, it is seen that, by using prior art additive compound of Tris 2 ethyl hexyl phosphate, with active dosage amount of 500 ppm with typical phosphorous content of 7%, the percent efficiency of common inhibition was only 5.1%.

(56) While comparing the above mentioned results about effectiveness of prior art additives it is seen by using procedures of Examples 2 and 4, wherein invention additive compounds were used for naphthenic acid corrosion inhibition, that higher corrosion inhibition efficiencies of 92.8% and 96.7% respectively were obtained by using same active dosage amounts of 500 ppm in each case, along with percentages of typical phosphorous contents, of 6.53% and 8.19% respectively.

(57) By using procedure of Example 4 along with providing a percent of typical phosphorous content of 8.19, with use of even reduced active dosage amount of 250 ppm of invention additive compound, the corresponding percent efficiency of corrosion inhibition was 91.5%.

(58) Detailed Discussion of Experimental Results Given in Table 3

(59) Referring to Table 3, it is clearly seen from results of Examples 2 and 4, that use of invention additive compounds led to very slight solid-formation, whereas in case of Examples 1 and 3, use of prior art additive compounds additive compounds led to heavy precipitation, which could lead to heavy fouling of equipments. Similarly use of prior art additive of tributyl phosphate also led to completely hazy solution.

(60) All of these details discussed above clearly point out to the fact that, as compared to additive compounds of prior art, the invention additive compound of the present invention provides better efficiency of corrosion inhibition along with lower percent phosphorous content (and hence lower acidic value) and lower dosages of active invention additive compound (thereby making it more economical). The invention additive compound is also non-fouling as it leads to very slight solids-formation.

Discussion of Distinguishing Features of Present Invention

(61) Thus, it is seen that the additive compound of present invention used for corrosion-inhibition has the following important distinguishing features, as compared to the prior art. 1) The inventor of the present invention, after extensive experimentation, has surprisingly found that the additive compound used by the inventor, is highly effective in high temperature corrosion inhibition, as shown by the experimental results given in Tables 1 and 2. 2) Another distinguishing feature of the additive compound of present invention is that, it has very low acidity as compared to the additive compounds of prior art, for example, the phosphate esters of prior art has very high acidity. The phosphate esters of prior art are known to have a tendency to decompose, even at lower temperatures, to form phosphoric acids, which travel further along the hydrocarbon stream and react with metal surfaces of equipments such as packing of distillation column, to form solid iron phosphate. These solids plug the holes of equipments and thereby lead to fouling of distillation column (refer to Table 3).

(62) The additive compound of the present invention does not have this deficiency. 3) The invention compound is very effective in corrosion-inhibition, even when used in much lower dosage amounts, as compared to the prior art compounds. 4) The corrosion-inhibition-efficiency is achieved by present invention-additive, at low-phosphorous-concentrations (as compared to prior art additives). This is very advantageous because the phosphorous is poisonous for the performance of catalysts used in further downstream units. 5) The invention compound has extremely low potential for fouling as explained in the Table 3. 6) The invention-additive is shown to perform much better by giving higher efficiencies as compared to other prior art additives like trialkyl phosphates such as tributyl phosphate, tris 2 ethyl hexyl phosphate. 7) The invention compound is a low-cost corrosion-inhibiting-additive, as compared to prior art additive.

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

(64) In view of the above, it is understood that, the present invention comprises of the following items: Item 1: An effective novel non-polymeric and non-fouling additive for inhibiting high-temperature naphthenic acid corrosion, comprising an effective corrosion-inhibiting amount of a second phosphate ester wherein said second phosphate ester is obtained by reacting a first phosphate ester with an oxirane compound selected from the group consisting of butylene oxide, ethylene oxide, propylene oxide or any other oxirane compound or a combination thereof, preferably with butylene oxide, capably yielding said second phosphate ester, having a structure A or B,

(65) ##STR00008##
wherein R.sup.1 and R.sup.2 are each independently selected from the group consisting of moieties having 1 to 20 carbon atoms and R.sup.1 and R.sup.2 may be identical to or different from each other, X is H, CH.sub.3 or C.sub.2H.sub.5; and n may vary from 1 to 20,
wherein said first phosphate ester is having a structure I or II,

(66) ##STR00009##
wherein R.sup.1 and R.sup.2 are each independently selected from the group consisting of moieties having 1 to 20 carbon atoms and R.sup.1 and R.sup.2 may be identical to or different from each other, said first phosphate ester being obtained as a reaction product of reaction of an alcohol with a phosphorous pentaoxide. Item 2: An effective additive, as described in item 1, wherein said effective additive has acidity varying from about 1 mg KOH/gm to about 20 mg KOH/gm as determined by titration of samples against normal alcoholic KOH. Item 3: An effective additive, as described in item 1, wherein said effective additive has phosphorus contents varying from about 0.5% to about 9% of said effective additive. Item 4: An effective additive, as described in item 1, wherein mole ratios of said phosphorus pentoxide and said alcohol are used, such that the mole ratio of said phosphorus pentoxide to said alcohol is preferably 1 mole of said phosphorus pentoxide to 1 to 10 mole of said alcohol and preferably 1 mole of said phosphorus pentoxide to 1 to 7 mole of said alcohol. Item 5: An effective additive as described in item 1, wherein active dosage of said additive is 1 to 2000 ppm. Item 6: A process of high temperature naphthenic acid corrosion inhibition of metallic surfaces of any of the hydrocarbon processing units of a petrochemical plant, used for processing a stream containing naphthenic acid, with said processing units comprising distillation columns, strippers, trays, pump around piping and related equipments, and said process using said second phosphate ester of item 1, comprising the steps of: a. heating said hydrocarbon containing naphthenic acid to vapourize a portion of said hydrocarbon; b. condensing a portion of the hydrocarbon vapors, passing through said hydrocarbon processing unit, to produce a condensed distillate; c. adding to said distillate, before said condensed distillate is returned to said hydrocarbon processing unit or collected as a product, from 1 to 2000 ppm of said second phosphate ester of item 1 in corrosion-inhibition-effective-amount, capably forming a reaction mixture; d. allowing said reaction mixture to contact said metallic surfaces of said hydrocarbon processing unit to form a protective film on said surfaces whereby each of said surfaces is inhibited against corrosion; and e. allowing said condensed distillate to return to said hydrocarbon processing unit, or to be collected as said product. Item 7: A process as described in item 1, wherein said stream includes crude oil, feedstock, and hydrocarbon stream and/or fractions thereof.

(67) The present invention has been described with reference to foregoing examples. It is obvious for the person skilled in the art to modify these without deviating from its scope, which are intended to be included within its scope.