EP1654338A1 - Method for prevention of corrosion by naphthenic acids in refineries - Google Patents

Method for prevention of corrosion by naphthenic acids in refineries

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Publication number
EP1654338A1
EP1654338A1 EP04767456A EP04767456A EP1654338A1 EP 1654338 A1 EP1654338 A1 EP 1654338A1 EP 04767456 A EP04767456 A EP 04767456A EP 04767456 A EP04767456 A EP 04767456A EP 1654338 A1 EP1654338 A1 EP 1654338A1
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EP
European Patent Office
Prior art keywords
corrosion
formula
hydrocarbon
compound
treated
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP04767456A
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German (de)
French (fr)
Inventor
Francis Humblot
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Arkema France SA
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Arkema SA
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Publication date
Application filed by Arkema SA filed Critical Arkema SA
Publication of EP1654338A1 publication Critical patent/EP1654338A1/en
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G7/00—Distillation of hydrocarbon oils
    • C10G7/10—Inhibiting corrosion during distillation
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G75/00—Inhibiting corrosion or fouling in apparatus for treatment or conversion of hydrocarbon oils, in general
    • C10G75/02—Inhibiting corrosion or fouling in apparatus for treatment or conversion of hydrocarbon oils, in general by addition of corrosion inhibitors
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G9/00—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils
    • C10G9/14—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils in pipes or coils with or without auxiliary means, e.g. digesters, soaking drums, expansion means
    • C10G9/16—Preventing or removing incrustation

Definitions

  • the present invention relates to the field of the treatment of acidic crude oils in refineries. More specifically, it relates to a process for combating corrosion of refining units which process acid crudes, comprising the use of specific sulfur compounds. Petroleum refineries can face a serious corrosion problem when they have to process certain so-called acid crudes. These crude acids essentially contain naphthenic acids which are at the origin of this very particular corrosion phenomenon, since it occurs in a liquid medium which does not conduct electric current. These naphthenic acids correspond to saturated cyclic hydrocarbons carrying one or more carboxylic groups. The acidity of a crude oil is described by a standardized measurement according to standard ASTM D 664-01.
  • TAN Total Acid Number
  • patent EP 742277 describes the inhibitory action of a combination of a trialkyl phosphate and an organic polysulfide.
  • US patent 5552085 recommends the use of thiophosphorus compounds such as organo thiophosphates or thiophosphites.
  • the patent AU 693975 discloses as an inhibitor a mixture of trialkyl phosphate and phosphoric esters of sulfurized phenol neutralized with lime.
  • organophospores are very delicate to handle, due to their high toxicity. They are also poisons for hydrotreatment catalysts installed to purify hydrocarbon fractions from atmospheric and vacuum distillations. For these two reasons at least, their use in the refining field is not desirable.
  • the subject of the invention is therefore a process for combating corrosion by naphthenic acids of the metal walls of a refining unit, characterized in that it comprises the addition to the hydrocarbon stream to be treated by the unit d '' an effective amount of a compound of formula:
  • HS-B-COOR (I) in which: - B represents a bivalent saturated hydrocarbon radical which can be either acyclic, in linear or branched form, or cyclic, and which contains from 1 to 18 carbon atoms, preferably from 1 to 4; and - R represents a hydrogen atom, or an alkali or alkaline earth metal, or an ammonium group, or an alkyl radical (linear or branched), cycloalkyl, aryl, alkylaryl or arylalkyl, said radical containing from 1 to 18 atoms carbon, preferably 1 to 10, and optionally one or more heteroatoms.
  • thioglycolic acid of formula HS-CH 2 -COOH, or one of its esters, preferably an aliphatic ester, is used as compound of formula (I).
  • 2-ethyl hexyl thioglycolate, isooctyl thioglycolate or methyl thioglycolate are used.
  • the quantity of compound of formula (I) to be added to the hydrocarbon stream to be treated by the refining unit generally corresponds to a concentration (expressed in equivalent weight of sulfur) of said compound relative to the weight of the hydrocarbon stream, which can range from 10 to 5000 ppm, preferably from 50 to 500 ppm.
  • the method according to the invention advantageously makes it possible to treat hydrocarbon streams, in particular crude oils, whose TAN is greater than 0.2, and preferably greater than 2.
  • the process implementation temperature corresponds to that at which the corrosion reactions with naphthenic acids occur, and is generally between 200 and 450 ° C, and more particularly between 250 and 350 ° C.
  • the addition of the compound of formula (I) in the hydrocarbon stream can be carried out either at the very entrance of the unit (simultaneously with the hydrocarbon stream to be treated), for an overall treatment of corrosion, or in the part of the unit where the corrosion reaction takes place, for localized treatment.
  • metal walls of the refining unit means all the walls capable of being in contact with the stream of acidic hydrocarbon to be treated.
  • This test uses an iron powder simulating a metal surface, and a mineral oil in which is dissolved a mixture of naphthenic acids, simulating a stream of acid crude.
  • the characteristics of these reagents are as follows: - white mineral oil having a density of 0.838 - powder of spherical iron particles, with a particle size of -40 + 70 mesh (i.e. approximately 212 to 425 ⁇ m) - mixture of naphthenic acids having from 10 to 18 carbon atoms, a boiling point between 270 and 324 ° C and an average molar mass of 244 g / mol.
  • the following are introduced into a 150 ml glass reactor, equipped with a dropping funnel and a water cooler, and provided with a stirring and temperature measurement system: - 70 ml (i.e. 58.8 g) mineral oil, - 2 g of iron powder, - 2.8 g of the mixture of naphthenic acid.
  • the initial TAN of the reaction mixture is equal to 10.
  • These reagents are kept in contact for 2 hours at a temperature of 250 ° C., under an atmosphere of dry nitrogen to avoid oxidation reactions.
  • the concentration of dissolved iron in the medium is determined by a conventional method implementing a mineralization of a sample, taking up the residue in acidified water and dosing by a plasma torch. . This concentration of dissolved iron (expressed in ppm) is directly proportional to the rate of corrosion of the iron powder generated by the mixture of naphthenic acids present in the mineral oil.
  • Example 2 Tests in the Presence of Thioglycolic Acid Derivatives Example 1 is repeated by adding to the mineral oil compounds of formula (I) derived from thioglycolic acid when the reactor is charged. The content of these derivatives is calculated so as to obtain a corresponding concentration of 500 ppm by mass of sulfur in the mineral oil present in the reactor. The results obtained in Table II below are obtained. The table also shows the rate of inhibition of corrosion caused by the mixture of naphthenic acid.
  • Example 2 is repeated, replacing the thioglycolic acid derivatives with methyl mercaptopropionate at a content also corresponding to 500 ppm of sulfur in the medium.
  • An iron concentration equal to 118 ppm is measured at the end of the test, ie an inhibition rate of 42%.

Abstract

The invention relates to a method for prevention of corrosion by naphthenic acids in a refinery, comprising the use of a compound of formula: HS-B-COOR (I), where B = a saturated bivalent 1-18 C hydrocarbon and R = H, alkaline or alkaline earth metal, ammonium, straight or branched alkyl, cycloalkyl, aryl, alkylaryl or arylalkyl with 1 to 18 C atoms.

Description

PROCEDE DE LUTTE CONTRE LA CORROSION PAR LES ACIDES NAPHTHENIQUES DANS LES RAFFINERIES PROCESS FOR THE FIGHT AGAINST CORROSION BY NAPHTHENIC ACIDS IN REFINERIES
La présente invention concerne le domaine du traitement des pétroles bruts acides dans les raffineries. Elle a plus spécialement pour objet un procédé de lutte contre la corrosion des unités de raffinage qui traitent des bruts acides, comprenant la mise en œuvre de composés soufrés spécifiques. Les raffineries de pétrole peuvent être confrontées à un problème grave de corrosion lorsque qu'elles sont amenées à traiter certains bruts dits acides. Ces bruts acides contiennent pour l'essentiel des acides naphthéniques qui sont à l'origine de ce phénomène de corrosion très particulier, puisqu'il se produit dans un milieu liquide non- conducteur de courant électrique. Ces acides naphthéniques correspondent à des hydrocarbures cycliques saturés porteurs d'un ou plusieurs groupes carboxyliques. L'acidité d'un brut pétrolier est décrite par une mesure normalisée selon la norme ASTM D 664-01. Elle est exprimée en mg de potasse nécessaire pour neutraliser 1 g de pétrole et est appelée TAN (Total Acid Number). Il est connu dans ce domaine technique qu'un pétrole brut ayant un TAN supérieur à 0,2 est qualifié d'acide, et peut conduire à des dommages dans les unités d'une raffinerie. Cette réaction de corrosion dépend fortement des conditions locales telles que, par exemple, la température et la nature métallique de la paroi dans l'unité concernée, la vitesse spatiale de l'hydrocarbure, et la présence d'une interface gaz- liquide. Ainsi, même après d'importants travaux sur le sujet, les raffmeurs rencontrent de grandes difficultés pour prévoir l'importance des réactions de corrosion et leur localisation. L'une des solutions industrielles à ce problème de corrosion consiste à utiliser des équipements en aciers inoxydables, soit des alliages de fer avec notamment du chrome et du molybdène. Cependant, cette solution reste peu employée en raison de du coût d'investissement élevé. Ce choix, de plus, doit de préférence s'envisager lors de la conception de la raffinerie car les aciers inoxydables présentent des propriétés mécaniques inférieures à celles des aciers au carbone qui sont normalement utilisés et nécessitent une infrastructure adaptée. L'existence de ces difficultés techniques pour traiter les bruts acides a ainsi pour conséquence que ces bruts sont en général vendus aux raffineurs à un niveau de prix inférieur à celui des bruts standards. Une autre solution au problème du traitement d'un pétrole brut acide, utilisée par les raffineurs dans la pratique, consiste à le diluer par un autre brut pétrolier non acide, de façon à obtenir une acidité moyenne faible, par exemple inférieure au seuil de 0,2 de TAN. Dans ce cas, la concentration en acide naphthénique devient suffisamment faible pour générer des vitesses de corrosion acceptables. Cette solution reste cependant d'une portée limitée. En effet certains bruts acides présentent des TAN supérieurs à 2, ce qui plafonne leur utilisation à au plus 10% du volume total de bruts entrant dans la raffinerie. D'autre part, certains de ces mélanges de bruts avec brut acide conduisent parfois à l'effet inverse recherché, c'est-à-dire à une accélération des réactions de corrosion par les acides naphthéniques. Une autre approche pour lutter contre ce problème de corrosion est l'introduction dans le pétrole brut acide à traiter d'additifs chimiques inhibant ou prévenant l'attaque de la paroi métallique de l'unité concernée. Cette voie est souvent très économique par comparaison à celle consistant à utiliser les aciers ou alliages spéciaux indiquée précédemment. Des travaux de laboratoire, comme celui de Turnbull (Corrosion-November 1998 dans Corrosion, volume 54, N°ll, page 922) ont envisagé d'ajouter des petites quantités (de l'ordre de 0,1 %) d'hydrogène sulfuré dans le pétrole brut, pour réduire la corrosion par les acides naphthéniques. Cette solution n'est, cependant, pas applicable en raffinerie car l'hydrogène sulfuré, gazeux à température ambiante, est très toxique ce qui rend les conséquences d'une fuite extrêmement graves et en limite l'emploi. De plus, à plus haute température, l'hydrogène sulfuré devient lui-même très corrosif et conduira, dans d'autres parties de la raffinerie, à une aggravation de la corrosion généralisée. Le brevet US 5182013 décrit pour résoudre ce même problème de corrosion l'utilisation d'autres composés soufrés, à savoir des polysulfures de radicaux alkyle de 6 à 30 atomes de carbone. Plus récemment, l'utilisation d'inhibiteurs de corrosion à base de soufre et de phosphore a été également décrite. Ainsi, le brevet EP 742277 décrit l'action inhibitrice d'une combinaison d'un phosphate de trialkyle et d'un polysulfure organique. Le brevet US 5552085 recommande l'emploi de composés thiophosphorés comme des organo thiophosphates ou thiophosphites. Le brevet AU 693975 divulgue comme inhibiteur un mélange de phosphate de trialkyle et d'esters phosphoriques de phénol sulfurisé neutralisé à la chaux. Toutefois les organophosporés sont d'une manipulation très délicate, en raison de leur haute toxicité. Ce sont de plus des poisons pour les catalyseurs d'hydrotraitements installés pour purifier les coupes d'hydrocarbures issues des distillations atmosphériques et sous vide. Pour ces deux raisons au moins, leur utilisation dans le domaine du raffinage n'est pas souhaitable. De manière surprenante, il a à présent été trouvé que la mise en œuvre d'un composé soufré spécifique, ayant à la fois une fonction carboxylique et une fonction mercaptan, permet d' inhiber la corrosion par les acides naphthéniques, d'une façon plus efficace que les polysulfures organiques, et sans qu'il soit nécessaire d'introduire en outre des inhibiteurs phosphores. L'invention a donc pour objet un procédé de lutte contre la corrosion par les acides naphthéniques des parois métalliques d'une unité de raffinage, caractérisé en ce qu'il comprend l'addition au courant d'hydrocarbure à traiter par l'unité d'une quantité efficace d'un composé de formule :The present invention relates to the field of the treatment of acidic crude oils in refineries. More specifically, it relates to a process for combating corrosion of refining units which process acid crudes, comprising the use of specific sulfur compounds. Petroleum refineries can face a serious corrosion problem when they have to process certain so-called acid crudes. These crude acids essentially contain naphthenic acids which are at the origin of this very particular corrosion phenomenon, since it occurs in a liquid medium which does not conduct electric current. These naphthenic acids correspond to saturated cyclic hydrocarbons carrying one or more carboxylic groups. The acidity of a crude oil is described by a standardized measurement according to standard ASTM D 664-01. It is expressed in mg of potash necessary to neutralize 1 g of oil and is called TAN (Total Acid Number). It is known in this technical field that crude oil having a TAN greater than 0.2 is qualified as acid, and can lead to damage in the units of a refinery. This corrosion reaction is highly dependent on local conditions such as, for example, the temperature and metallic nature of the wall in the unit concerned, the space velocity of the hydrocarbon, and the presence of a gas-liquid interface. Thus, even after significant work on the subject, refiners encounter great difficulties in predicting the extent of corrosion reactions and their location. One of the industrial solutions to this corrosion problem consists in using equipment made of stainless steels, that is to say alloys of iron with in particular chromium and molybdenum. However, this solution remains little used due to the high investment cost. This choice, moreover, should preferably be considered during the design of the refinery because stainless steels have lower mechanical properties than carbon steels which are normally used and require a suitable infrastructure. The existence of these technical difficulties in treating acid crudes thus has the consequence that these crudes are generally sold to refiners at a price level lower than that of standard crudes. Another solution to the problem of treating an acidic crude oil, used by refiners in practice, consists in diluting it with another non-acidic crude oil, so as to obtain a low average acidity, for example below the threshold of 0 , 2 of TAN. In this case, the naphthenic acid concentration becomes low enough to generate acceptable corrosion rates. This solution remains however of limited scope. Indeed, some acid crudes have TAN higher than 2, which limits their use to at most 10% of the total volume of crude entering the refinery. On the other hand, some of these crude mixtures with crude acid sometimes lead to the desired reverse effect, that is to say an acceleration of the corrosion reactions by naphthenic acids. Another approach to combat this corrosion problem is the introduction into the acid crude oil to be treated of chemical additives which inhibit or prevent attack on the metal wall of the unit concerned. This route is often very economical compared to that of using the special steels or alloys indicated above. Laboratory work, such as that of Turnbull (Corrosion-November 1998 in Corrosion, volume 54, No. ll, page 922) has considered adding small quantities (of the order of 0.1%) of hydrogen sulfide in crude oil, to reduce corrosion by naphthenic acids. This solution is not, however, applicable in a refinery because hydrogen sulphide, gaseous at room temperature, is very toxic which makes the consequences of a leak extremely serious and limits its use. In addition, at higher temperatures, hydrogen sulfide itself becomes very corrosive and will lead, in other parts of the refinery, to an aggravation of generalized corrosion. US Patent 5182013 describes to solve this same corrosion problem the use of other sulfur compounds, namely polysulphides of alkyl radicals of 6 to 30 carbon atoms. More recently, the use of corrosion inhibitors based on sulfur and phosphorus has also been described. Thus, patent EP 742277 describes the inhibitory action of a combination of a trialkyl phosphate and an organic polysulfide. US patent 5552085 recommends the use of thiophosphorus compounds such as organo thiophosphates or thiophosphites. The patent AU 693975 discloses as an inhibitor a mixture of trialkyl phosphate and phosphoric esters of sulfurized phenol neutralized with lime. However, organophospores are very delicate to handle, due to their high toxicity. They are also poisons for hydrotreatment catalysts installed to purify hydrocarbon fractions from atmospheric and vacuum distillations. For these two reasons at least, their use in the refining field is not desirable. Surprisingly, it has now been found that the use of a specific sulfur compound, having both a carboxylic function and a mercaptan function, makes it possible to inhibit corrosion by naphthenic acids, in a more effective than organic polysulfides, and without the need to additionally introduce phosphorus inhibitors. The subject of the invention is therefore a process for combating corrosion by naphthenic acids of the metal walls of a refining unit, characterized in that it comprises the addition to the hydrocarbon stream to be treated by the unit d '' an effective amount of a compound of formula:
HS-B-COOR (I) dans laquelle : - B représente un radical hydrocarboné saturé bivalent qui peut être soit acyclique, sous forme linéaire ou ramifiée, soit cyclique, et qui contient de 1 à 18 atomes de carbone, de préférence de 1 à 4 ; et - R représente un atome d'hydrogène, ou un métal alcalin ou alcalino-terreux, ou un groupe ammonium, ou un radical alkyle (linéaire ou ramifié), cycloalkyle, aryle, alkylaryle ou arylalkyle, ledit radical contenant de 1 à 18 atomes de carbone, de préférence 1 à 10, et éventuellement un ou plusieurs hétéroatomes. Selon une variante préférée, on utilise comme composé de formule (I) l'acide thioglycolique, de formule HS-CH2-COOH, ou l'un de ses esters, de préférence un ester aliphatique. Selon un mode de réalisation particulièrement avantageux, on utilise le thioglycolate de 2-ethyl hexyl, le thioglycolate d'isooctyle ou le thioglycolate de méthyle. La quantité de composé de formule (I) à ajouter au courant d'hydrocarbure à traiter par l'unité de raffinage correspond généralement à une concentration (exprimée en poids équivalent de soufre) dudit composé par rapport au poids du courant d'hydrocarbure, pouvant aller de 10 à 5000 ppm, de préférence de 50 à 500 ppm. On pourra tout en restant dans ce domaine de concentration, fixer une teneur élevée au démarrage du procédé selon l'invention, puis réduire ensuite cette teneur à une dose de maintien. Le procédé selon l'invention permet avantageusement de traiter des courants d'hydrocarbures, notamment des pétroles bruts, dont le TAN est supérieur à 0,2, et de préférence supérieur à 2. La température de mise en œuvre du procédé correspond à celle à laquelle se produisent les réactions de corrosion par les acides naphthéniques, et est généralement comprise entre 200 et 450°C, et plus particulièrement entre 250 et 350°C. L'addition du composé de formule (I) dans le courant d'hydrocarbure peut être réalisée soit à l'entrée même de l'unité (simultanément au courant d'hydrocarbure à traiter), pour un traitement global de la corrosion, soit dans la partie de l'unité où a lieu la réaction de corrosion, pour un traitement localisé. Cette addition peut être réalisée par tout moyen connu de l'homme du métier, assurant un contrôle du débit d'injection et une bonne dispersion de l'additif dans l'hydrocarbure, par exemple au moyen d'une buse ou d'un mélangeur. On entend par parois métalliques de l'unité de raffinage dont la corrosion peut être prévenue par le procédé selon l'invention, toutes les parois susceptibles d'être en contact avec le courant d'hydrocarbure acide à traiter. Il peut donc s'agir aussi bien de à paroi interne proprement dite d' unités telles que les tours de distillation atmosphérique et sous vide, que de la surface des éléments internes à celles-ci comme leurs plateaux ou garnissages, ou encore des éléments périphériques à celles-ci, comme leurs lignes de soutirage et d'entrée, les pompes, fours de préchauffage, ou échangeurs de chaleur, dès lors que ces éléments sont portés à une température locale comprise entre 200 et 450°C. Comme exemple non limitatif de courant d'hydrocarbure à traiter conformément au procédé selon l'invention, on peut citer le brut pétrolier, le résidu de distillation atmosphérique, les coupes gazole issues des distillations atmosphérique et sous vide, ainsi que le distillât et le résidu sous vide issus de la distillation sous vide. Les exemples suivants sont donnés à titre purement illustratif de l'invention et ne sauraient être interprétés dans un but limitatif de sa portée. Dans ces exemples, on met en œuvre un test de corrosion dont les conditions sont données ci-après.HS-B-COOR (I) in which: - B represents a bivalent saturated hydrocarbon radical which can be either acyclic, in linear or branched form, or cyclic, and which contains from 1 to 18 carbon atoms, preferably from 1 to 4; and - R represents a hydrogen atom, or an alkali or alkaline earth metal, or an ammonium group, or an alkyl radical (linear or branched), cycloalkyl, aryl, alkylaryl or arylalkyl, said radical containing from 1 to 18 atoms carbon, preferably 1 to 10, and optionally one or more heteroatoms. According to a preferred variant, thioglycolic acid, of formula HS-CH 2 -COOH, or one of its esters, preferably an aliphatic ester, is used as compound of formula (I). According to a particularly advantageous embodiment, 2-ethyl hexyl thioglycolate, isooctyl thioglycolate or methyl thioglycolate are used. The quantity of compound of formula (I) to be added to the hydrocarbon stream to be treated by the refining unit generally corresponds to a concentration (expressed in equivalent weight of sulfur) of said compound relative to the weight of the hydrocarbon stream, which can range from 10 to 5000 ppm, preferably from 50 to 500 ppm. We can, while remaining in this concentration range, set a high content at the start of the process according to the invention, then reduce this content to a maintenance dose. The method according to the invention advantageously makes it possible to treat hydrocarbon streams, in particular crude oils, whose TAN is greater than 0.2, and preferably greater than 2. The process implementation temperature corresponds to that at which the corrosion reactions with naphthenic acids occur, and is generally between 200 and 450 ° C, and more particularly between 250 and 350 ° C. The addition of the compound of formula (I) in the hydrocarbon stream can be carried out either at the very entrance of the unit (simultaneously with the hydrocarbon stream to be treated), for an overall treatment of corrosion, or in the part of the unit where the corrosion reaction takes place, for localized treatment. This addition can be carried out by any means known to a person skilled in the art, ensuring control of the injection rate and good dispersion of the additive in the hydrocarbon, for example by means of a nozzle or a mixer. . The term “metal walls of the refining unit”, the corrosion of which can be prevented by the process according to the invention, means all the walls capable of being in contact with the stream of acidic hydrocarbon to be treated. It can therefore be both of the internal wall proper of units such as atmospheric and vacuum distillation towers, as of the surface of the internal elements thereof such as their plates or linings, or even peripheral elements to these, like their withdrawal and inlet lines, pumps, preheating furnaces, or heat exchangers, as soon as these elements are brought to a local temperature of between 200 and 450 ° C. As a nonlimiting example of a hydrocarbon stream to be treated in accordance with the process according to the invention, mention may be made of crude oil, atmospheric distillation residue, diesel fractions from atmospheric and vacuum distillation, as well as the distillate and the residue vacuum from vacuum distillation. The following examples are given purely by way of illustration of the invention and should not be interpreted with the aim of limiting its scope. In these examples, a corrosion test is carried out, the conditions of which are given below.
Description du test de corrosion : Ce test met en oeuvre une poudre de fer simulant une surface métallique, et une huile minérale dans laquelle est dissous un mélange d'acides naphthéniques, simulant un courant de brut acide. Les caractéristiques de ces réactifs sont les suivantes : - huile minérale blanche ayant pour densité 0,838 - poudre de particules de fer sphériques, ayant une granulométrie de -40+70 mesh (soit d'environ 212 à 425 μm) - mélange d'acides naphthéniques ayant de 10 à 18 atomes de carbone, un point d'ébullition compris entre 270 et 324 °C et une masse molaire moyenne de 244 g/mol. On introduit dans un réacteur en verre de 150 ml, équipé d'une ampoule de coulée et d'un réfrigérant à eau, et muni d'un système d'agitation et de mesure de la température : - 70 ml (soit 58,8 g) de l'huile minérale, - 2 g de la poudre de fer, - 2,8 g du mélange d'acide naphthénique. Le TAN initial du mélange réactionnel est égal à 10. Ces réactifs sont maintenus en contact durant 2 heures à une température de 250°C, sous atmosphère d'azote sec pour éviter des réactions d'oxydation. A la fin de l' essai, la concentration en fer dissous dans le milieu est déterminée par une méthode classique mettant en œuvre une minéralisation d'un échantillon, une reprise du résidu dans de l'eau acidifiée et le dosage par une torche à plasma. Cette concentration en fer dissous (exprimée en ppm) est directement proportionnelle à la vitesse de la corrosion de la poudre de fer générée par le mélange d' acides naphthéniques présent dans l'huile minérale.Description of the corrosion test: This test uses an iron powder simulating a metal surface, and a mineral oil in which is dissolved a mixture of naphthenic acids, simulating a stream of acid crude. The characteristics of these reagents are as follows: - white mineral oil having a density of 0.838 - powder of spherical iron particles, with a particle size of -40 + 70 mesh (i.e. approximately 212 to 425 μm) - mixture of naphthenic acids having from 10 to 18 carbon atoms, a boiling point between 270 and 324 ° C and an average molar mass of 244 g / mol. The following are introduced into a 150 ml glass reactor, equipped with a dropping funnel and a water cooler, and provided with a stirring and temperature measurement system: - 70 ml (i.e. 58.8 g) mineral oil, - 2 g of iron powder, - 2.8 g of the mixture of naphthenic acid. The initial TAN of the reaction mixture is equal to 10. These reagents are kept in contact for 2 hours at a temperature of 250 ° C., under an atmosphere of dry nitrogen to avoid oxidation reactions. At the end of the test, the concentration of dissolved iron in the medium is determined by a conventional method implementing a mineralization of a sample, taking up the residue in acidified water and dosing by a plasma torch. . This concentration of dissolved iron (expressed in ppm) is directly proportional to the rate of corrosion of the iron powder generated by the mixture of naphthenic acids present in the mineral oil.
EXEMPLE 1 (Comparatif) : Essai de référence en l'absence d'inhibiteurEXAMPLE 1 (Comparative): Reference test in the absence of an inhibitor
Le test précédent est mis en œuvre sans addition de composé de formule (I), avec 2 répétitions. Les résultats sont indiqués dans le tableau (I) ci- dessous. Tableau IThe previous test is carried out without addition of compound of formula (I), with 2 repetitions. The results are shown in Table (I) below. Table I
EXEMPLE 2 : Essais en présence de dérivés de l'acide thioglycolique On répète l'exemple 1 en ajoutant à l'huile minérale des composés de formule (I) dérivés de l'acide thioglycolique, lors de la charge du réacteur. La teneur de ces dérivés est calculée de façon à obtenir une concentration correspondante de 500 ppm massique en soufre dans l'huile minérale présente dans le réacteur. On obtient les résultats rassemblés dans le tableau II suivant. Dans ce tableau a été également indiqué le taux d'inhibition de la corrosion entraînée par le mélange d'acide naphthénique. Ce taux est exprimé en % et est défini par la formule : [Fer]avec inhibiteur inhibition (%) 1 ' X 100 [Eer] sans inhibiteur dans laquelle [Fer] est la concentration en fer dissous mesurée avec ou sans inhibiteur, la concentration en fer sans inhibiteur étant égale à 203,5 ppm conformément à l'exemple 1.EXAMPLE 2 Tests in the Presence of Thioglycolic Acid Derivatives Example 1 is repeated by adding to the mineral oil compounds of formula (I) derived from thioglycolic acid when the reactor is charged. The content of these derivatives is calculated so as to obtain a corresponding concentration of 500 ppm by mass of sulfur in the mineral oil present in the reactor. The results obtained in Table II below are obtained. The table also shows the rate of inhibition of corrosion caused by the mixture of naphthenic acid. This rate is expressed in% and is defined by the formula: [Iron] with inhibition inhibition (%) 1 'X 100 [Eer] without inhibitor in which [Iron] is the concentration of dissolved iron measured with or without inhibitor, the concentration of iron without inhibitor being equal to 203.5 ppm in accordance with Example 1.
Tableau IITable II
EXEMPLE 3 : Essai en présence de mercaptopropionate de méthyle de formule HS-CH2-CH2-COOMeEXAMPLE 3 Test in the presence of methyl mercaptopropionate of formula HS-CH 2 -CH 2 -COOMe
On répète l'exemple 2 en remplaçant les dérivés de l'acide thioglycolique par le mercaptopropionate de méthyle à une teneur correspondant également à 500 ppm de soufre dans le milieu. On mesure à la fin de l'essai une concentration fer égale à 118 ppm, soit un taux d' inhibition de 42 %. Example 2 is repeated, replacing the thioglycolic acid derivatives with methyl mercaptopropionate at a content also corresponding to 500 ppm of sulfur in the medium. An iron concentration equal to 118 ppm is measured at the end of the test, ie an inhibition rate of 42%.

Claims

REVENDICATIONS
1. Procédé de lutte contre la corrosion par les acides naphthéniques des parois métalliques d'une unité de raffinage, caractérisé en ce qu'il comprend l'addition au courant d'hydrocarbure à traiter par l'unité d'une quantité efficace d'un composé de formule :1. Method for combating corrosion by naphthenic acids of the metal walls of a refining unit, characterized in that it comprises the addition to the stream of hydrocarbon to be treated by the unit of an effective amount of a compound of formula:
HS-B-COOR (I) dans laquelle : - B représente un radical hydrocarboné saturé bivalent qui peut être soit acyclique, sous forme linéaire ou ramifiée, soit cyclique, et qui contient de 1 à 18 atomes de carbone, de préférence de 1 à 4 ; et - R représente un atome d'hydrogène, ou un métal alcalin ou alcalino-terreux, ou un groupe ammonium, ou un radical alkyle (linéaire ou ramifié), cycloalkyle, aryle, alkylaryle ou arylalkyle, ledit radical contenant de 1 à 18 atomes de carbone, de préférence 1 à 10, et éventuellement un ou plusieurs hétéroatomes.HS-B-COOR (I) in which: - B represents a bivalent saturated hydrocarbon radical which can be either acyclic, in linear or branched form, or cyclic, and which contains from 1 to 18 carbon atoms, preferably from 1 to 4; and - R represents a hydrogen atom, or an alkali or alkaline earth metal, or an ammonium group, or an alkyl radical (linear or branched), cycloalkyl, aryl, alkylaryl or arylalkyl, said radical containing from 1 to 18 atoms carbon, preferably 1 to 10, and optionally one or more heteroatoms.
2. Procédé selon la revendication 1, caractérisé en ce que l' on utilise comme composé de formule (I) l'acide thioglycolique ou l'un de ses esters, de préférence un ester aliphatique.2. Method according to claim 1, characterized in that one uses as compound of formula (I) thioglycolic acid or one of its esters, preferably an aliphatic ester.
3. Procédé selon l'une des revendications 1 ou 2, caractérisé en ce que on utilise le thioglycolate de 2-ethyl hexyl, le thioglycolate d'isooctyle ou le thioglycolate de méthyle.3. Method according to one of claims 1 or 2, characterized in that one uses 2-ethyl hexyl thioglycolate, isooctyl thioglycolate or methyl thioglycolate.
4. Procédé selon l'une des revendications 1 à 3, caractérisé en ce que la quantité de composé de formule (I) correspond à une concentration, exprimée en poids équivalent de soufre par rapport au poids du courant d'hydrocarbure, allant de 10 à 5000 ppm, de préférence de 50 à 500 ppm.4. Method according to one of claims 1 to 3, characterized in that the amount of compound of formula (I) corresponds to a concentration, expressed in equivalent weight of sulfur relative to the weight of the hydrocarbon stream, ranging from 10 at 5000 ppm, preferably from 50 to 500 ppm.
5. Procédé selon l'une des revendications 1 à 4, caractérisé en ce que le courant d'hydrocarbure à traiter a un TAN supérieur à 0,2, et de préférence supérieur à 2. 5. Method according to one of claims 1 to 4, characterized in that the hydrocarbon stream to be treated has a TAN greater than 0.2, and preferably greater than 2.
6. Procédé selon l'une des revendications 1 à 5, caractérisé en ce qu'il est mis en œuvre à une température comprise entre 200 et 450°C, et plus particulièrement entre 250 et 350°C. 6. Method according to one of claims 1 to 5, characterized in that it is implemented at a temperature between 200 and 450 ° C, and more particularly between 250 and 350 ° C.
7. Procédé selon l'une des revendications 1 à 6, caractérisé en ce que le courant d'hydrocarbure à traiter est choisi parmi un brut pétrolier, un résidu de distillation atmosphérique, des coupes gazole issues des distillations atmosphérique et sous vide, ainsi que un distillât et un résidu sous vide issus de la distillation sous vide. 7. Method according to one of claims 1 to 6, characterized in that the hydrocarbon stream to be treated is chosen from petroleum crude, an atmospheric distillation residue, diesel fractions from atmospheric and vacuum distillation, as well as a distillate and a vacuum residue from vacuum distillation.
EP04767456A 2003-07-07 2004-06-25 Method for prevention of corrosion by naphthenic acids in refineries Withdrawn EP1654338A1 (en)

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