PENNER JOSEPH (IL)
GROYSMAN ALEC (IL)
PENNER JOSEPH (IL)
| WO1998033869A1 | 1998-08-06 |
| US4975219A | 1990-12-04 | |||
| US20060091044A1 | 2006-05-04 | |||
| US5556451A | 1996-09-17 | |||
| US5552085A | 1996-09-03 |
S. NASRAZADANI AND S. CARROLL: "Effects of Phosphoric-Tannic Acids On Rusting Kinetics of Clean and Rusted Low Carbon Steels", CORROSION 2002 - PAPER N. 02367, 2002, XP002517278, Retrieved from the Internet
GROYSMAN ET AL.: "Naphthenic Acids Combat Naphthenic Acid Corrosion", THE PRELIMINARY PROGRAM FOR 17TH INTERNATIONAL CORROSION CONGRESS: EG-2: CORROSION IN REFINERY/GAS PROCESSING, 10 October 2008 (2008-10-10), XP002517279, Retrieved from the Internet
CLAIMS
1. A process for inhibiting naphthenic acid corrosion of the inner metallic surfaces of a refining apparatus induced during distillation of an acidic and corrosive crude oil or kerosene, said process comprising adding an effective corrosion inhibiting amount of a corrosion inhibitor to a non-acidic non-corrosive crude oil or kerosene treated in said refining apparatus for a sufficient time period prior to distillation of said acidic and corrosive crude oil or kerosene so as to form a protective film on the inner metallic surfaces of said refining apparatus, wherein said corrosion inhibitor is selected from (i) tannic acid;
(ii) a high-density alcohol having a density of 0.95-1.3 g/ml and a boiling point in a range of 180-300°C;
(iii) a heavy vacuum gas oil (HVGO) fraction distilled at 370-520 0 C from an acidic high sulfur content crude oil, characterized in that it is viscous at ambient temperature, has a density of 0.93-0.96 g/ml, contains 3.0-4.2% sulfur and has a total acid number (TAN) of 0.9-1.2 mg KOH/g; or (iv) a high molecular weight residue remaining after distillation of a naphthenic acid mixture at 1 atm and a final boiling point of above 300 0 C, characterized in that it has a density of 0.92-0.995 g/ml, contains 0.03-0.4% sulfur and has a TAN of 4-60 mg KOH/g.
2. The process of claim 1, wherein said corrosion inhibitor is tannic acid.
3. The process of claim 2, wherein the tannic acid is in powder form.
4. The process of claim 3, wherein said effective corrosion inhibiting amount is calculated so as a concentration of the tannic acid in said non-acidic non-corrosive crude oil or kerosene is in a range of 10-200 ppm, preferably 100- 150 ppm, more preferably about 150 ppm.
5. The process of claim 2, wherein the tannic acid is dissolved in at least one organic solvent.
6. The process of claim 5, wherein said organic solvent is a high-density alcohol having a density of 0.95-1.3 g/ml and a boiling point in a range of 180-300 0 C, a low-density alcohol having a density of 0.78-0.81 g/ml and boiling point in a range of 60- 100°C, or a mixture thereof.
7. The process of claim 6, wherein said high-density alcohol is selected from 1,2-propanediol, 1,3-propanediol, glycerol, ethylene glycol, diethylene glycol (DEG) or propylene glycol, and said low-density alcohol is selected from isopropyl alcohol (IPA), 2-methyl-2-propanol, propan-1-ol (propanol) or methanol.
8. The process of claim 7, wherein the tannic acid is dissolved in 1,2- propanediol in a ratio (v. v) of 1 :4 (tannic acid: 1,2-propanediol) and said effective corrosion inhibiting amount is calculated so as a concentration of the tannic acid in said non-acidic non-corrosive crude oil or kerosene is in a range of 10-100 ppm, preferably about 10 ppm.
9. The process of claim 7, wherein: (i) the tannic acid is dissolved in 1,2-propanediol and IPA in a ratio (v. v. v) of 1 :4: 1 (tannic acid: l,2-propanediol:IPA) and said effective corrosion inhibiting amount is calculated so as a concentration of the tannic acid in said non-acidic non-corrosive crude oil or kerosene is in a range of 5- 50 ppm, preferably about 8 ppm; (ii) the tannic acid is dissolved in DEG and IPA in a ratio (v. v. v) of 1 :2:2
(tannic acid:DEG:IPA) and said effective corrosion inhibiting amount is calculated so as a concentration of the tannic acid in said non-acidic non-corrosive crude oil or kerosene is in a range of 10-20 ppm, preferably about 20 ppm; (iii) the tannic acid is dissolved in glycerol and methanol in a ratio (v. v. v) of
1 : 1 :3 (tannic acid:glycerol:methanol) and said effective corrosion inhibiting amount is calculated so as a concentration of the tannic acid in said non-acidic non-corrosive crude oil or kerosene is in a range of 5- 10 ppm, preferably about 5 ppm; or
(iv) the tannic acid is dissolved in glycerol and methanol in a ratio (v. v. v) of
1 :2:3 (tannic acid:glycerol:methanol) and said effective corrosion inhibiting amount is calculated so as a concentration of the tannic acid in said non- acidic non-corrosive crude oil or kerosene is in a range of 5-
20 ppm, preferably about 8-10 ppm.
10. The process of claim 1, wherein said corrosion inhibitor is the high-density alcohol of (ii).
11. The process of claim 10, wherein said high-density alcohol is selected from 1,2-propanediol, 1,3 -propanediol, glycerol, ethylene glycol, diethylene glycol (DEG) or propylene glycol.
12. The process of claim 11, wherein said high-density alcohol is 1,2- propanediol and said effective corrosion inhibiting amount is calculated so as a concentration of the 1 ,2-propanediol in said non-acidic non-corrosive crude oil or kerosene is in a range of 10-400 ppm, preferably 25-200 ppm, more preferably about 50 ppm, or said high-density alcohol is glycerol and said effective corrosion inhibiting amount is calculated so as a concentration of the glycerol in said non- acidic non-corrosive crude oil or kerosene is about 50 ppm.
13. The process of claim 1, wherein said corrosion inhibitor is the HVGO fraction of (iii).
14. The process of claim 13, wherein said HVGO fraction is distilled from the "Altamira" crude oil and characterized in that it is viscous at ambient temperature, has a density of about 0.95 g/ml, contains about 4.08% sulfur and has a TAN of about 0.946 mg KOH/g.
15. The process of claim 14, wherein said effective corrosion inhibiting amount is calculated so as a concentration of the HVGO fraction in said non-acidic non- corrosive crude oil or kerosene is in a range of 25-100 ppm, preferably 50-100 ppm, more preferably about 50 ppm.
16. The process of claim 1, wherein said corrosion inhibitor is the high molecular weight residue of (iv).
17. The process of claim 16, wherein said high molecular weight residue remains after distillation of a naphthenic acid mixture at a final boiling point in a range of 300-35O 0 C, preferably 305-330 0 C, more preferably 325-33O 0 C.
18. The process of claim 17, wherein said high molecular weight residue is selected from the fractions herein designated "fraction F", "fraction A", "fraction M" or "fraction K".
19. The process of claim 18, wherein said high molecular weight residue is the fraction herein designated "fraction F" and said effective corrosion inhibiting amount is calculated so as a concentration of said fraction in said non-acidic non- corrosive crude oil or kerosene is in a range of 50-500 ppm, preferably 200-500 ppm, more preferably about 300 ppm.
20. The process of claim 18 wherein said high molecular weight residue is the fraction herein designated "fraction A" and said effective corrosion inhibiting amount is calculated so as a concentration of said fraction in said non-acidic non- corrosive crude oil or kerosene is in a range of 100-300 ppm, preferably about 300 ppm.
21. The process of claim 18, wherein said high molecular weight residue is the fraction herein designated "fraction M" and said effective corrosion inhibiting amount is calculated so as a concentration of said fraction in said non-acidic non- corrosive crude oil or kerosene is in a range of 50-200 ppm, preferably about 200 ppm.
22. The process of claim 18, wherein said high molecular weight residue is the fraction herein designated "fraction K" and said effective corrosion inhibiting amount is calculated so as a concentration of said fraction in said non-acidic non- corrosive crude oil or kerosene is in a range of 50-100 ppm, preferably about 50 ppm.
23. The process of any one of claims 1 to 22, further comprising continuously adding said corrosion inhibitor to said acidic and corrosive crude oil or kerosene, in an amount sufficient to maintain a constant level of naphthenic acid corrosion inhibition.
24. The process of claim 23, wherein said amount is calculated so as a concentration of said corrosion inhibitor in said acidic and corrosive crude oil or kerosene is in a range of 5-10 ppm.
25. A process for inhibiting naphthenic acid corrosion of the inner metallic surfaces of a refining apparatus induced during distillation of an acidic and corrosive crude oil or kerosene, said process comprising adding an effective corrosion inhibiting amount of a corrosion inhibitor to a non-acidic non-corrosive crude oil or kerosene treated in said refining apparatus for a sufficient time period prior to distillation of said acidic and corrosive crude oil or kerosene so as to form a protective film on the inner metallic surfaces of said refining apparatus, and continuously adding said corrosion inhibitor to said acidic and corrosive crude oil or kerosene, in an amount sufficient to maintain a constant level of naphthenic acid corrosion inhibition, wherein said corrosion inhibitor is selected from
(i) tannic acid;
(ii) a high-density alcohol having a density of 0.95-1.3 g/ml and a boiling point in a range of 180-300 0 C;
(iii) a HVGO fraction distilled at 370-520 0 C from an acidic high sulfur content crude oil, characterized in that it is viscous at ambient temperature, has a density of 0.93-0.96 g/ml, contains 3.0-4.2% sulfur and has a TAN of 0.9-1.2 mg KOH/g; or
(iv) a high molecular weight residue remaining after distillation of a naphthenic acid mixture at 1 atm and a final boiling point of above 300 0 C, characterized in that it has a density of 0.92-0.995 g/ml, contains 0.03-0.4% sulfur and has a TAN of 4-60 mg KOH/g. |
PROCESS FOR INHIBITING NAPHTHENIC ACID CORROSION
FIELD OF THE INVENTION
The present invention relates to a process for inhibiting corrosion in refinery operations, in particular, for inhibiting naphthenic acid corrosion induced during distillation of acidic and corrosive crude oils.
BACKGROUND OF THE INVENTION
Since the early 1990s, the oil refining industry has seen a trend toward refining more highly acidic oils which may extend the economic life of some existing refineries; however, increases potential corrosion problems. Crude oils contain varying amounts of naphthenic acids possessing high corrosiveness towards metals and alloys under certain conditions, and therefore, are very dangerous to the oil refining industry. Naphthenic acid corrosion has been known for a long time and continues to be a major problem in high temperature refinery corrosion (Derungs, 1956; Heller et al, 1963; Gutzeit, 1977; Piehl, 1988; Craig, 1995; Craig, 1996; Babaian-Kibala et al, 1993), and is localized particularly in areas of high velocity or where condensation of concentrated acid vapors occurs.
Distillation towers, pipelines and other equipments operating at temperatures above 200 0 C and containing crude oil, light and heavy diesel oil, atmospheric residue, light and heavy vacuum gas oil or vacuum residue are potential areas for naphthenic acids attack. In particular, kerosene fractions distilled at 190 to 21O 0 C are highly corrosive (Groysman et al, 2005a-b).
The name naphthenic acids is a generic name used for all of the organic acids present in crude oils. Most naphthenic acids are believed to have the chemical formula R(CH 2 ) n COOH where R is a cycloalkane, particularly cyclopentane, ring and n>0, typically greater than 12. In other words, naphthenic acids form/constitute a large group of high molecular weight organic acids containing saturated rings. Their corrosiveness is a function of their molecular weight and boiling point, as
well as the temperature of their use. When hydrocarbons containing such naphthenic acids contact iron alloys at elevated temperatures ( 190 to 400 0 C), severe corrosion problems can occur, and as a result, iron can accumulate in the hydrocarbon up to 10 ppm and impair catalyst. Naphthenic acid corrosion control can be attained by various mitigation measures including (i) predistillation and removal of naphthenic acids from the crude oil being processed (WO/1999/050375); (ii) blending of acidic with non-acidic crude oils or distilled fractions (Groysman et al, 2005b); (iii) neutralization by injection of soda or other neutralizers; (iv) use of corrosion inhibitors; and (v) coatings, and limiting of fluid flow (Jayaraman et al, 1986). In addition, corrosion resistant materials may be selected, such as stainless steel containing above 2% weight molybdenum, or aluminized carbon steel that showed good resistance to naphthenic acid corrosion and naphthenic acid erosion-corrosion at total acid number (TAN)=6 mg KOH/g at 25O 0 C (Wu et al, 2004a-b). Furthermore, higher sulfur concentrations are generally considered to be beneficial for the inhibition of naphthenic acid corrosion (Turnbull et al, 1998; Babaian-Kibala et al, 1993).
Various agents were disclosed as effective inhibitors of high temperature (175-400 0 C) naphthenic acid corrosion. Most of these agents are phosphorous based agents such as phosphorous acid (US 6,706,669); phosphate/phosphate esters (Babaian-Kibala, 1994; Jackson et al, 2004; Jackson et al, 2005; Winslow, 2005; Vanhove, 2006); phosphate ester containing organic polysulfide (US 5,630,964); thio-phosphate or thio-phosphite esters (US 5,552,085); di- or tri-alkylphosphites (US 4,941,994, US 5,500,107); thiophosphorus compounds including alkyl dithiophosphoric acid and thiophosphonic acid derivative (US 5,863,415); aryl containing phosphate compounds (US 5,611,911); and trialklylphosphate and an alkaline earth metal phosphonate-phenate sulfide (US 5,314,643); however, it is known that phosphorus based inhibitors can poison catalysts (Johnson et al, 2002; Groysman et al , 2005a).
Additional agents disclosed as inhibitors of high temperature naphthenic acid corrosion are sulfonated alkylphenol (US 5,252,254) and 4-sulfophthalic acid (US
6,583,091), as well as 5-aminoisophthalic acid, 3,5-dinitrophenol and 3,5- dintrioaniline (US 6,593,278). BJ Chemical Services offers a naphthenic acid corrosion inhibitor called RNB 40218, claimed to show 91% efficiency for carbon steel at 30 ppm in an accelerated bomb test at 313°C and 250 psi (TAN=7.5 mg KOH/g). As stated in the firm's website (www.bjservices.com), this inhibitor rapidly passivates metal surfaces and can be applied in atmospheric gas oil pump- around, heavy vacuum gas oil pump-around and cat cracker feed.
US 6,559,104 discloses a process for inhibiting the high temperature corrosivity at a temperature of from 200 to 420°C of an organic acid containing petroleum stream in contact with a corrosion prone metal-containing surface, by adding a corrosion inhibiting effective amount of a tri-substituted aromatic compound selected from 5-hydroxyisophthalic acid, 1,3,5-benzenetricarboxylic acid, 1,2,3-benzenetricarboxylic acid, or mixtures thereof to said organic acid containing petroleum stream. US Publication No. 20060157387 discloses a process for combating the corrosion by naphthenic acids of the metal walls of a refining plant, characterized in that it comprises the addition to the hydrocarbon stream to be treated by the refining plant, of an effective amount of a compound of formula: HS-B-COOR in which: B represents a saturated divalent hydrocarbon radical which can either be acyclic, in the linear or branched form, or cyclic and which comprises from 1 to 18 carbon atoms; and R represents a hydrogen atom, an alkali or alkaline earth metal, an ammonium group, or an alkyl (linear or branched), cycloalkyl, aryl, alkylaryl or arylalkyl radical, said radical comprising from 1 to 18 carbon atoms and optionally one or more heteroatoms. US Publication No. 20060009663 discloses a process for reducing the metal corrosion of a hydrocarbonaceous liquid which causes corrosion as measured by NACE Standard TMO 172-2001, namely at 38 0 C, said process comprising blending with the hydrocarbonaceous liquid at least 0.1 weight percent of an acidic Fischer- Tropsch product in sufficient proportion to produce a hydrocarbonaceous blend displaying reduced metal corrosion as measured by NACE Standard TMO 172-2001
when compared to the hydrocarbonaceous liquid. As defined in this publication, the "hydrocarbonaceous liquid" is typically a fuel, such as, e.g., motor gasoline, kerosene, naphtha, diesel, fuel oil, aviation kerosene, military DFM, etc.; however, it may also be crude oil; base oil; a hydrocarbon feedstock or blending component, such as, e.g., FCC gasoline, iso-octane, reformate, hydrotreated straight run naphtha, hydrotreated mid-distillates; etc.
International Publication No. WO 2005/040313 teaches that the corrosivity of naphthenic acids in Athabasca oilsand bitumen crudes is a function of its molecular weight, molecular structure, true boiling point, reactive sulfidic species and local environment; and introduces the concept of α and β naphthenic acids, wherein the α naphthenic acids are corrosive, with low molecular weights, and the β as non-corrosive and inhibitive, with high molecular weights. According to this publication, hot extraction wash of the raw oil sand mixture appears to preferentially remove the higher water-soluble α fraction leaving the less corrosive, less water-soluble, β fraction, and naphthenic acid surviving after thermal hydroprocessing tends to be of the inhibitive β type. In particular, WO 2005/040313 discloses a combination of a first refinery feedstock and a second refinery feedstock, wherein the fraction of the second refinery feedstock in the combination is at least in part a function of respective quantities of an α fraction and a β fraction of total naphthenic acids in the first refinery feedstock, preferably effective to reduce naphthenic acid corrosivity of the first refinery feedstock; and a combination of a refinery crude and a composition enriched in a β fraction of naphthenic acids, wherein an amount of the composition in the combination is an amount effective to reduce naphthenic acid corrosivity of the first refinery crude.
SUMMARY OF THE INVENTION
It has been found, in accordance with the present invention, that pretreatment with (i) tannic acid; (ii) the high-density alcohol 1,2-propanediol or glycerol; (iii) the heavy vacuum gas oil fraction distilled from the acidic Mexican crude oil
"Altamira" at 370-520 0 C; or (iv) high molecular weight residues remaining after distillation of various commercially available naphthenic acid mixtures at 1
atmosphere (atm) and a final boiling point of above 300 0 C, significantly inhibited the naphthenic acid corrosion of pure iron and of carbon steels ClOlO and A516Gr70 in acidic and corrosive kerosene.
The present invention thus relates to a process for inhibiting naphthenic acid corrosion of the inner metallic surfaces of a refining apparatus induced during distillation of an acidic and corrosive crude oil or kerosene, said process comprising adding an effective corrosion inhibiting amount of a corrosion inhibitor to a non- acidic non-corrosive crude oil or kerosene treated in said refining apparatus for a sufficient time period prior to distillation of said acidic and corrosive crude oil or kerosene so as to form a protective film on the inner metallic surfaces of said refining apparatus, wherein said corrosion inhibitor is selected from (i) tannic acid; (ii) a high-density alcohol having a density of 0.95-1.3 g/ml and a boiling point in a range of 180-300 0 C; (iii) a heavy vacuum gas oil (HVGO) fraction distilled at 370-520 0 C from an acidic high sulfur content crude oil, characterized in that it is viscous at ambient temperature, has a density of 0.93-0.96 g/ml, contains 3.0-4.2% sulfur and has a total acid number (TAN) of 0.9-1.2 mg KOH/g; or (iv) a high molecular weight residue remaining after distillation of a naphthenic acid mixture at 1 atm and a final boiling point of above
300 0 C, characterized in that it has a density of 0.92-0.995 g/ml, contains 0.03-0.4% sulfur and has a TAN of 4-60 mg KOH/g.
DETAILED DESCRIPTION OF THE INVENTION
The term "effective corrosion inhibiting amount", as used herein, refers to an amount of corrosion inhibitor added to the non-acidic non-corrosive crude oil or kerosene treated in the refining apparatus, which is sufficient to form, after a sufficient time period, a protective film on the inner metallic surfaces of the refining apparatus, and gives rise to a corrosion rate of carbon steels that is less than the allowable value of 0.1 1 mm/year. This effective amount varies between the various
corrosion inhibitors, and is calculated so as to obtain a certain concentration of the corrosion inhibitor in the non-acidic non-corrosive crude oil or kerosene treated.
As described in the Examples section hereinafter, in order to evaluate the naphthenic acid corrosion inhibition efficiency of each one of the various corrosion inhibitors of the present invention, steel surfaces were pretreated at 195°C for 24 hours in a non-acidic non-corrosive kerosene containing different concentrations of the various corrosion inhibitors. Subsequently, the pretreated steel surfaces were immersed for 72 hrs during boiling at 195°C in the most acidic and aggressive kerosene fraction distilled from the acidic crude oil "Azeri Light" from Azerbaijan at a temperature range of 190-210 0 C, without the corrosion inhibitor.
Tannic acid is a high molecular weight polymer of gallic acid (3,4,5- trihydroxybenzoic acid) and glucose, termed penta-m-digalloyl-glucose and defined as a polyphenol that is a yellow to light brown amorphous powder, highly soluble in water, alcohol and acetone. Tannic acid is known as a corrosion inhibitor by itself or in the form of a salt, usually in a mixture with other corrosion inhibitors, but apparently not as an inhibitor of naphthenic acid corrosion in refinery operations. In particular, (i) US 4,975,219 discloses a corrosion inhibitor comprising tannic acid and/or a salt thereof, a sugar for boiler water system, and at least one member selected from aldonic acids of hexoses or salts thereof, or aldonic acids of heptoses or salts thereof; and (ii) US Publication No. 20060116313 provides a composition comprising an organic amine, optionally an organic solvent, and at least about 0.5% by weight of tannic acid or salt thereof or both, for selectively removing residue such as photoresist and processing residue from a substrate without causing any undesired extent corrosion of metal that might also be exposed to the composition.
As shown in Example 1, pretreatment of pure iron and carbon steels ClOlO and A516Gr70 surfaces with various concentrations of tannic acid, as a powder, inhibited the corrosion induced by the acidic and corrosive kerosene fraction by up to about 99%. Alcoholic solutions of tannic acid were found to inhibit naphthenic acid corrosion as well, and in particular, a solution of tannic acid in 1,2-propanediol
inhibited the corrosion induced by the acidic and corrosive kerosene fraction by up to about 99%; and a solution of tannic acid in 1 ,2-propanediol and isopropyl alcohol inhibited the corrosion of carbon steel ClOlO induced by the acidic and corrosive kerosene fraction by about 98%. Thus, in one aspect, the corrosion inhibitor according to the present invention is tannic acid.
In one embodiment, the tannic acid is in powder form. In a more preferrred embodiment, the concentration of the powdered tannic acid in the non-acidic non- corrosive crude oil or kerosene is in a range of 10-200 ppm, preferably 100-150 ppm, more preferably about 150 ppm.
In another embodiment, the tannic acid is dissolved in at least one organic solvent. The organic solvent as defined herein may be a high-density alcohol having a density of 0.95-1.3 g/ml and a boiling point (T b ) in a range of 180-300°C, which is insoluble in petroleum distillates at ambient temperature but soluble at boiling point; a low-density alcohol having a density of 0.78-0.81 g/ml and boiling point in a range of 60-100 0 C, which is well dissolved in petroleum distillates; or a mixture thereof.
The high-density alcohol according to the present invention may be any alcohol that is non-volatile at ambient temperature, having the physico-chemical properties mentioned hereinabove. Such high-density alcohols includes, without being limited to, 1,2-propanediol, 1,3 -propanediol, glycerol, ethylene glycol, diethylene glycol (DEG) and propylene glycol.
The low-density alcohol according to the present invention may be any alcohol that is volatile at ambient temperature, having the physico-chemical properties mentioned hereinabove. Such low-density alcohols include, without being limited to, isopropyl alcohol (IPA, isopropanol, propane-2-ol), 2-methyl-2- propanol, propan-1-ol (propanol) and methanol.
In one preferred embodiment, the tannic acid is dissolved in a high-density alcohol. In a more preferred embodiment, the high-density alcohol is 1,2- propanediol, the tannic acid is dissolved in the 1,2-propanediol in a ratio (v. v) of 1 :4
(tannic acid: l,2-propanediol) and the concentration of the tannic acid in the non- acidic non-corrosive crude oil or kerosene is in a range of 10-100 ppm, preferably about 10 ppm.
When high-density alcohols are mixed with low-density volatile alcohols, they become compatible with petroleum distillates at ambient temperature.
Thus, in another preferred embodiment, the tannic acid is dissolved in a mixture of a high-density alcohol and a low-density alcohol. In one more preferred embodiment, the mixture of high-density alcohol and low-density alcohol consists of 1,2-propanediol and IPA, the tannic acid is dissolved in that mixture in a ratio (v. v. v) of 1 :4: 1 (tannic acid: l,2-propanediol:IPA) and the concentration of the tannic acid in the non-acidic non-corrosive crude oil or kerosene is in a range of 5- 50 ppm, more preferably about 8 ppm. In another more preferred embodiment, the mixture of high-density alcohol and low-density alcohol consists of DEG and IPA, the tannic acid is dissolved in that mixture in a ratio (v. v. v) of 1 :2:2 (tannic acid:DEG:IPA) and the concentration of the tannic acid in the non-acidic non- corrosive crude oil or kerosene is in a range of 10-20 ppm, more preferably about 20 ppm. In a further more preferred embodiment, the mixture of high-density alcohol and low-density alcohol consists of glycerol and methanol, the tannic acid is dissolved in that mixture in a ratio (v. v. v) of 1 : 1 :3 (tannic acid:glycerol:methanol) and the concentration of the tannic acid in the non-acidic non-corrosive crude oil or kerosene is in a range of 5-10 ppm, more preferably about 5 ppm. In still a further more preferred embodiment, the mixture of high-density alcohol and low-density alcohol consists of glycerol and methanol, the tannic acid is dissolved in that mixture in a ratio (v. v. v) of 1 :2:3 (tannic acid:glycerol methanol) and the concentration of the tannic acid in the non-acidic non-corrosive crude oil or kerosene is in a range of 5-20 ppm, more preferably about 8-10 ppm.
As further shown in Example 1, a significant inhibition of the corrosion of pure iron and of carbon steels ClOlO and A516Gr70, induced by the acidic and corrosive kerosene fraction, was further attained by using different concentrations of a high-density alcohol alone. In particular, 1,2-propanediol inhibited the
corrosion induced by the acidic and corrosive kerosene fraction by up to about 92- 94%, and glycerol inhibited the corrosion induced by the acidic and corrosive kerosene fraction by about 99%.
Thus, in another aspect, the corrosion inhibitor according to the present invention is a high-density alcohol as defined above.
In one embodiment, the high-density alcohol is 1 ,2-propanediol (T b =188°C), which is insoluble in petroleum distillates at ambient temperature but soluble at boiling point, and the concentration of the 1 ,2-propanediol in the non-acidic non- corrosive crude oil or kerosene is in a range of 10-400 ppm, preferably 25-200 ppm, more preferably about 50 ppm.
In another embodiment, the high-density alcohol is glycerol (T b =290°C), which is insoluble in petroleum distillates at ambient temperature but soluble at boiling point, and the concentration of the glycerol in said non-acidic non-corrosive crude oil or kerosene is about 50 ppm. A significant inhibition of the corrosion of pure iron and of carbon steels
ClOlO and A516Gr70, induced by the acidic and corrosive kerosene fraction, was further attained by using the HVGO fraction distilled at 370-520 0 C from the Mexican crude oil "Altamira". In particular, the corrosion inhibition efficiency attained by that fraction was up to about 96%. As described in Example 2, the aforesaid HVGO fraction encompassed about 18% of the total crude oil volume, had a density of 0.95 g/ml, contained 4.08% sulfur and had a TAN of 0.946 mg KOH/g.
Thus, in a further aspect, the corrosion inhibitor according to the present invention is a HVGO fraction distilled at 370-520 0 C from an acidic high sulfur content crude oil, characterized in that it is viscous at ambient temperature, has a density of 0.93-0.96 g/ml, contains 3.0-4.2% sulfur and has a TAN of 0.9-1.2 mg KOH/g.
In one embodiment, the HVGO fraction according to the present invention is distilled from the Mexican crude oil "Altamira", which has a density of about 0.95 g/ml, contains about 4.08% sulfur and has a TAN of about 0.946 mg KOH/g. In a
more preferred embodiment, the concentration of this HVGO fraction in the non- acidic non-corrosive crude oil or kerosene is in a range of 25-100 ppm, preferably 50-100 ppm, more preferably about 50 ppm.
As shown in Example 3, pretreatment of pure iron and of carbon steels ClOlO and A516Gr70 with different concentrations of high molecular residues remaining after distillation of commercially available naphthenic acid mixtures, at 1 atm and a final boiling point of above 300 0 C, significantly inhibited the corrosion induced by the acidic and corrosive kerosene fraction.
Thus, in still another aspect, the corrosion inhibitor according to the present invention is a high molecular weight residue remaining after distillation of a naphthenic acid mixture at 1 atm and a final boiling point of above 300 0 C, characterized in that it has a density of 0.92-0.995 g/ml, contains 0.03-0.4% sulfur and has a TAN of 4-60 mg KOH/g.
In preferred embodiments, the distillation of the naphthenic acid mixture is carried out according to ASTM 96 (Standard Test Method for Distillation of Petroleum Products at Atmospheric Pressure) and ASTM E 1405 (Standard Specification for Laboratory Glass Distillation Flasks).
In one embodiment, the high molecular weight residue remains after distillation of a naphthenic acid mixture at a final boiling point in a range of 300- 350 0 C, preferably 305-330 0 C, more preferably 325-330 0 C.
Examples of naphthenic acid mixtures from which the high molecular weight residue can be obtained include, without being limited to, the naphthenic acid mixtures provided by Fluka Chemie AG (Switzerland), Acros Organics (Belgium) and Karvan-L (Azerbaijan), as well as the crude naphthenic acid mixture provided by Merichem Chemicals and Refinery Services LLC (Texas, USA).
In one preferred embodiment, the high molecular weight residue is the fraction remains after distillation at a final boiling point of 328 0 C of the naphthenic acid mixture marketed by Fluka Chemie, herein designated "fraction F". In a more preferred embodiment, the concentration of fraction F in the non-acidic non-
corrosive crude oil or kerosene is in a range of 50-500 ppm, preferably 200-500 ppm, more preferably about 300 ppm.
In another preferred embodiment, the high molecular weight residue is the fraction remains after distillation at a final boiling point of 325°C of the naphthenic acid mixture marketed by Acros Organics, herein designated "fraction A". In a more preferred embodiment, the concentration of fraction A in the non-acidic non- corrosive crude oil or kerosene is in a range of 100-300 ppm, preferably about 300 ppm.
In a further embodiment, the high molecular weight residue is the fraction remains after distillation at a final boiling point of 305 0 C of the crude naphthenic acid mixture marketed by Meridiem Chemicals and Refinery Services LLC, herein designated "fraction M". In a more preferred embodiment, the concentration of fraction M in the non-acidic non-corrosive crude oil or kerosene is in a range of 50- 200 ppm, preferably about 200 ppm. In still another embodiment, the high molecular weight residue is the fraction remains after distillation at a final boiling point of 33O 0 C of the naphthenic acid mixture marketed by Karvan-L (Azerbaijan), herein designated "fraction K". In a more preferred embodiment, the concentration of fraction K in the non-acidic non- corrosive crude oil or kerosene is in a range of 50-100 ppm, preferably about 50 ppm.
According to the present invention, an effective corrosion inhibiting amount of a corrosion inhibitor, as defined above, should be injected into the pump-around pipeline of the refining apparatus, namely, added to a non-acidic non-corrosive crude oil or kerosene treated by the refining apparatus, for a sufficient time period prior to the distillation of the acidic and corrosive crude oil or kerosene, so as to form a protective film on the inner metallic surfaces of the refining apparatus.
In one embodiment, the time period sufficient to form such a protective film on the inner metallic surfaces of the refining apparatus is about 24 hours.
After formation of a protective film on the inner metallic surfaces of the refining apparatus, an acidic and corrosive crude oil or kerosene may be distilled
without further injection of the corrosion inhibitor during at least about 72 hours, depending on the corrosivity level of the specific crude oil or kerosene treated. However, in case distillation of the acidic and corrosive crude oil or kerosene continues beyond that period of time, the corrosion inhibitor should then be continuously added to the acidic and corrosive crude oil or kerosene in an amount sufficient to maintain a constant level of naphthenic acid corrosion inhibition. This amount of corrosion inhibitor is calculated such as to preserve a constant required concentration of said inhibitor in the acidic and corrosive crude oil or kerosene during all the distillation period. In one embodiment, the concentration sufficient to maintain a constant level of naphthenic acid corrosion inhibition is in a range of 5-10 ppm.
Thus, the present invention further provides a process for inhibiting naphthenic acid corrosion of the inner metallic surfaces of a refining apparatus induced during distillation of an acidic and corrosive crude oil or kerosene, said process comprising adding an effective corrosion inhibiting amount of a corrosion inhibitor to a non-acidic non-corrosive crude oil or kerosene treated in said refining apparatus for a sufficient time period prior to distillation of said acidic and corrosive crude oil or kerosene so as to form a protective film on the inner metallic surfaces of said refining apparatus, and continuously adding said corrosion inhibitor to said acidic and corrosive crude oil or kerosene, in an amount sufficient to maintain a constant level of naphthenic acid corrosion inhibition, wherein said corrosion inhibitor is selected from
(i) tannic acid;
(ii) a high-density alcohol having a density of 0.95-1.3 g/ml and a boiling point in a range of 180-300 0 C;
(iii) a heavy vacuum gas oil (HVGO) fraction distilled at 370-520 0 C from an acidic high sulfur content crude oil, characterized in that it is viscous at ambient temperature, has a density of 0.93-0.96 g/ml, contains 3.0-4.2% sulfur and has a total acid number (TAN) of 0.9-1.2 mg KOH/g; or
(iv) a high molecular weight residue remaining after distillation of a naphthenic acid mixture at 1 atm and a final boiling point of above 300 0 C, characterized in that it has a density of 0.92-0.995 g/ml, contains 0.03-0.4% sulfur and has a TAN of 4-60 mg KOH/g. Unlike high temperature naphthenic acid corrosion inhibitors currently used, as described in the background chapter hereinabove, the naphthenic acid corrosion inhibitors of the present invention do not influence the quality, i.e., properties, of the fuels treated by them. Furthermore, tannic acid works as antioxidant of fuels, namely, it is capable of slowing or preventing the oxidation of the fuel treated, thus providing additional benefit in particular during storing of said fuel.
The invention will now be illustrated by the following non-limiting Examples.
EXAMPLES
Experimental Methods (i) Determining the corrosion rate of pure iron and carbon steels ClOlO andλ516Gr70 in acidic and corrosive kerosene
In order to determine the naphthenic acid corrosion rates of pure iron (Fe) and of carbon steels (C lOlO and A516Gr70) in an acidic and corrosive kerosene, as controls for the various experiments described hereinafter, the most acidic and aggressive kerosene fraction distilled from the acidic crude oil "Azeri Light" from Azerbaijan at a temperature range of 190-210 0 C was used. In particular, pure iron and carbon steel surfaces (steel coupons) were immersed in the aforesaid acidic and aggressive kerosene fraction, during boiling at 195 0 C for 72 hours, and their corrosion rates were measured and found to be 0.968 mm/year for iron; and 0.968 and 0.990 mm/year for ClOlO and A516Gr70 carbon steels, respectively.
In particular, corrosion tests were carried out according to the ASTM G31- 72(2004) "Standard Practice for Laboratory Immersion Corrosion Testing of Metals" by the weight loss method. The procedure included introduction of three round coupons of total area of 36 cm 2 into a flask of 1 L, containing 0.3 L of the
aforesaid acidic and aggressive kerosene fraction, and immersion at boiling temperature 195 0 C for 72 hrs. Then coupons were removed and chemically cleaned with 5% HCl inhibited with 0.2% proprietary blend of a chemical known as Rodine 213. After cleaning, the coupons were placed in a dessicator for 24 hours and weighed. Corrosion rate was calculated according to the formula:
M -M
Corrosion Rate, mm I year = — L - 3650 d - A - t wherein M 0 and M 1 are the coupon weights (grams) before and after the corrosion test, respectively; d is the density of the metal/alloy (gram/cm J ); A is the area of the coupon (cm 2 ); t is the period of the test (days); and 3650 is a coefficient for the calculation of the corrosion rate in mm/year.
(H) Determining the naphthenic acid corrosion inhibition efficiency of the various corrosion inhibitors of the present invention
Pure iron and/or carbon steels ClOlO and A516Gr70 surfaces (steel coupons) were pretreated in a non-acidic non-corrosive kerosene containing different concentrations of the corrosion inhibitor at 195 0 C for 24 hours, and were then removed and placed into another vessel with the acidic and corrosive kerosene fraction, distilled from the acidic crude oil "Azeri Light" from Azerbaijan at a temperature range of 190-210 0 C, without the corrosion inhibitor, and were immersed during boiling at 195 0 C for 72 hours. Then, coupons were removed and chemically cleaned with 5% HCl inhibited with 0.2% proprietary blend of a chemical known as Rodine 213. After cleaning, the coupons were placed in a dessicator for 24 hours and weighed.
The corrosion rates (mm/year) were calculated as described above, and the corrosion inhibition efficiency of the corrosion inhibitor in each case, namely, the percent of reduction in the corrosion rate of the iron and/or the carbon steels in the aforesaid acidic and aggressive kerosene in the presence of the corrosion inhibitor, was determined according to the formula:
Efficiency, % = CR " ~ CR ' ■ 100 CR 1 ,
wherein CR 0 and CR, are the corrosion rates of the iron or the carbon steel in the acidic and aggressive kerosene without, and in the presence of, the corrosion inhibitor, respectively.
Example 1. Tannic acid and/or high-density alcohols as naphthenic acid corrosion inhibitors
In these experiments, the corrosion inhibition efficiencies of tannic acid (TA), high-density alcohols such as 1 ,2-propanediol, glycerol and ethylene glycol (EG), as well as a solution of the high-density alcohol diethylene glycol (DEG) in the low-density alcohol isopropyl alcohol (IPA) were examined. In addition, the corrosion inhibition efficiencies of TA solutions in (i) the high density alcohol 1,2,- propanediol; (ii) the low-density alcohol IPA or methanol; and (iii) mixtures of 1,2- propanediol and IPA, DEG and IPA, or glycerol and methanol, were determined.
Pure iron as well as carbon steels ClOlO and A516Gr70 surfaces were pretreated in a non- acidic non-corrosive kerosene containing different concentrations of tannic acid and/or the various alcohols mentioned above, as described in Experimental Methods. The corrosion rates and the corrosion inhibition efficiencies are summarized in Table 1 hereinafter.
As shown, (i) pretreatment of both iron and carbon steel surfaces in the non- acidic kerosene containing 10 ppm TA (powder) resulted in an inhibition efficiency of about 71-88%, wherein further increase of TA concentration up to 150 ppm increased the inhibition efficiency to about 98-99%; (ii) pretreatment of both iron and carbon steel surfaces in the non-acidic kerosene containing 10 ppm 1,2- propanediol resulted in an inhibition efficiency of about 70-85%, wherein a further increase of 1,2-propanediol concentration up to 200 ppm increased the inhibition efficiency to about 91-93%; (iii) pretreatment of both iron and carbon steel surfaces in the non-acidic kerosene containing 50 ppm glycerol resulted in an inhibition efficiency of about 99%; (iv) pretreatment of both iron and carbon steel surfaces in the non-acidic kerosene containing 50 ppm solution of TA in 1 ,2-propanediol (1 :4 v. v), in particular, 10 ppm TA in 40 ppm 1,2-propanediol, resulted in an inhibition efficiency of about 99%, whereas increasing the solution concentration to 125 ppm
(25 ppm TA and 100 ppm 1,2-propanediol) decreases the inhibition efficiency to about 91-96% that increased again to about 98-99% with a further increase of the solution concentration to 500 ppm; (v) pretreatment of both iron and carbon steel surfaces in the non-acidic kerosene containing 25 ppm solution of TA in IPA (1 :5 v:v), in particular, -4.16 ppm TA in -20.83 ppm IPA, resulted in an inhibition efficiency of about 96%; (vi) pretreatment of both iron and carbon steel surfaces in the non-acidic kerosene containing 25 ppm solution of TA in methanol (1 :5 v:v), in particular, -4.16 ppm TA in -20.83 ppm methanol, resulted in an inhibition efficiency of about 85-89%; (vii) pretreatment of carbon steel C lOlO surface in the non-acidic kerosene containing 48 ppm solution of TA in 1,2-propanediol and IPA (1 :4: 1 v. v. v), in particular, 8 ppm TA in 32 ppm 1,2-propanediol and 8 ppm IPA, resulted in an inhibition efficiency of about 97%; (viii) pretreatment of carbon steel surfaces in the non-acidic kerosene containing 25 ppm solution of TA in DEG and IPA (1 :2:2 v. v. v), in particular, 5 ppm TA in 10 ppm DEG and 10 ppm IPA, resulted in an inhibition efficiency of about 25-38%, whereas increasing the solution concentration to 100 ppm (20 ppm TA, 40 ppm DEG and 40 ppm IPA) increased the inhibition efficiency to about 99-100%; (ix) pretreatment of carbon steel surfaces in the non-acidic kerosene containing 25 ppm solution of TA in glycerol and methanol (1 : 1 :3 v. v. v), in particular, 5 ppm TA in 5 ppm glycerol and 15 ppm methanol, resulted in an inhibition efficiency of about 95-97%, whereas increasing the solution concentration to 50 ppm (10 ppm TA, 10 ppm glycerol and 30 ppm methanol) slightly decreased the inhibition efficiency to about 93-96%; and (x) pretreatment of carbon steel surfaces in the non-acidic kerosene containing 50 ppm solution of TA in glycerol and methanol (1 :2:3 v. v. v), in particular, -8.33 ppm TA in -16.66 ppm glycerol and -25 ppm methanol, resulted in an inhibition efficiency of about 99%, whereas increasing the solution concentration to 100 ppm (-16.66 ppm TA, -33.33 ppm glycerol and -50 ppm methanol) did not change significantly the inhibition efficiency that was about 97-99%.
Since all alcohols have hydroxyl groups, a question was raised whether any natural substance containing hydroxyl groups may be used as a naphthenic acid
corrosion inhibitor. In order to address this issue, the corrosion inhibition efficiency of glucose (T m =146°C; Density=1.54 g/cm 3 ; powder) was examined as well, using the experimental procedure described above and the inhibition efficiencies determined are summarized in Table 2 hereinafter. As shown, with all the glucose concentrations tested, the corrosion rate calculated was higher than the allowable value of 0.11 mm/year.
Table 1: Corrosion rate of pure iron and carbon steels, pretreated with tannic acid and/or high-density alcohols after immersion in acidic and corrosive kerosene
Table 2: Corrosion rate of pure iron and carbon steels, pretreated with glucose (powder) after immersion in acidic and corrosive kerosene
Example 2. Heavy vacuum gas oil fraction of the crude oil "Altamira" as a naphthenic acid corrosion inhibitor
In this experiment, the corrosion inhibition efficiency of the heavy vacuum gas oil (HVGO) fraction, distilled at 370-520 0 C from the Mexican crude oil "Altamira", was examined. The HVGO fraction, containing 18.1% of the total crude oil volume, was viscous at ambient temperature, had a density of 0.95 g/ml, contained 4.08% sulfur and had a total acid number (TAN) of 0.946 mg KOH/g.
Pure iron as well as carbon steel ClOlO and A516Gr70 surfaces were pretreated in a non-acidic non-corrosive kerosene containing different concentrations of the aforesaid HVGO fraction as described in Experimental Methods. The corrosion rates and the corrosion inhibition efficiencies are summarized in Table 3 hereinafter. As shown, pretreatment of both iron and carbon steel surfaces in the non-acidic non-corrosive kerosene containing 50 ppm of the
HVGO fraction resulted in a corrosion inhibition efficiency of about 96%; however, both lower and higher concentrations of this fraction resulted in a relatively decreased corrosion inhibition efficiency.
Table 3: Corrosion rate of iron and carbon steels, pretreated with a HVGO fraction of the crude oil "Altamira" after immersion in acidic and corrosive kerosene
Example 3. High molecular weight residues remaining after distillation of naphthenic acid mixtures as naphthenic acid corrosion inhibitors
In these experiments, the corrosion inhibition efficiencies of various high molecular weight residues remaining after distillation, at 1 atm and a final boiling point of above 300 0 C, of commercially available naphthenic acid mixtures, were examined. In particular, the high molecular weight residues used were (i) the residue remaining after distillation at a final boiling point of 328°C of the naphthenic acid mixture provided by Fluka Chemie AG (Switzerland), herein designated "fraction F"; (ii) the residue remaining after distillation at a final boiling point of 325 0 C of the naphthenic acid mixture provided by Acros Organics (Belgium), herein designated "fraction A"; (iii) the residue remaining after distillation at a final boiling point of 305 0 C of the crude naphthenic acid mixture provided by Merichem Chemicals and Refinery Services LLC (Texas, USA), herein designated "fraction M"; and (iv) the residue remaining after distillation at a final boiling point of 33O 0 C of the naphthenic acid mixture provided by Karvan-L (Azerbaijan), herein designated "fraction K". All the distillation processes were
carried out according to ASTM 96 (Standard Test Method for Distillation of Petroleum Products at Atmospheric Pressure) and ASTM E 1405 (Standard Specification for Laboratory Glass Distillation Flasks), and the physico-chemical properties of these fractions are presented in Table 4 below.
Table 4: Physico-chemical properties of fractions F, A, M and K
Inhibitor fiDensity, 5 ! 1 v TAN, 7 fSulfufl
| teήβ£ure, 0 C Ig/ml at20° * C * it
Fraction F >328 0 9225 17 461
Fraction A >325 0 9401 4 6 330
Fraction M >305 0 9250 50 1000
Fraction K >330 0.9720 13 1676
In the first experiment, carbon steel ClOlO surfaces were pretreated in a non- acidic non-corrosive kerosene containing different concentrations of fractions F, A or M, as described in Experimental Methods. The corrosion rates and the corrosion inhibition efficiencies are summarized in Table 5 hereinafter. As shown, increasing the concentration of both fractions F and fraction A from 50 to 300 ppm during pretreatment resulted in an increase in inhibition efficiency up to about 89-93%. Further increase of the fraction F concentration from 300 to 500 ppm caused a slight increase in the inhibition efficiency from about 93% to about 96%. As further shown, increasing the concentration of fraction M from 50 to 200 ppm during pretreatment resulted in an increase in the inhibition efficiency from about 74% to about 92%; however, further increasing the concentration of this fraction to 300 ppm resulted in a decrease in the inhibition efficiency to about 56%.
In the second experiment, pure iron and carbon steel ClOlO and A516Gr70 surfaces were pretreated in a non-acidic non-corrosive kerosene containing different concentrations of fractions M, as described in Experimental Methods. The corrosion rates and the corrosion inhibition efficiencies, summarized in Table 6 hereinafter, supported the findings of the first experiment and indicated that with respect to both pure iron and the aforesaid carbon steels, increasing the concentration of fraction M lrom 50 to 200 ppm during pretreatment resulted in an increase in the inhibition efficiency from about 73-74% to about 89-96%; however, further increasing the
concentration of fraction M to 300 ppm resulted in a decrease in the inhibition efficiency to about 50-56%
Table 5: Corrosion rate of carbon steel ClOlO pretreated with fractions F, A and M after immersion in acidic and corrosive kerosene
Table 6 Corrosion rate of iron and carbon steels pretreated with fraction M after immersion in acidic and corrosive kerosene
In the third experiment, pure iron and carbon steel ClOlO and A516Gr70 surfaces were pretreated in a non-acidic non-corrosive kerosene containing different concentrations of fraction K, as described in Experimental Methods. The corrosion rates and the corrosion inhibition efficiencies, summarized in Table 7 hereinafter,
indicated that with respect to both pure iron and the aforesaid carbon steels, increasing the concentration of fraction K from 25 to 50 ppm during pretreatment resulted in an increase in the inhibition efficiency from about 70-80% to about 94%; however, further increasing the concentration of fraction K up to 200 ppm resulted in a decrease in the inhibition efficiency to about 61-84%.
Table 7: Corrosion rate of iron and carbon steels pretreated with fraction K after immersion in acidic and corrosive kerosene
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