Compositions – Preservative agents – Anti-corrosion
Reexamination Certificate
1998-10-06
2001-06-26
Brouillette, Gabrielle (Department: 1721)
Compositions
Preservative agents
Anti-corrosion
C252S388000, C208S047000, C208S04800Q, C208S0480AA, C208S263000
Reexamination Certificate
active
06251305
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for reducing the acidity and corrosivity of petroleum oils.
BACKGROUND OF THE INVENTION
Whole crudes and crude fractions with high organic acid content such as those containing carboxylic acids, specifically naphthenic acids are corrosive to the equipment used to extract, transport and process the crudes.
Efforts to minimize organic acid corrosion have included a number of approaches by neutralizing and removing the acids from the oil. For example, U.S. Pat. No. 2,302,281 and Kalichevsky and Kobe in Petroleum Refining with Chemicals (1956), Chapter 4, disclose various base treatments of oils and crude fractions, e.g., using bases such as ammonia (page 170). U.S. Pat. No. 4,199,440 discloses treatment of a liquid hydrocarbon with a dilute aqueous alkaline solution, specifically dilute aqueous NaOH or KOH. U.S. Pat. No. 5,683,626 teaches treatments of acidic crudes with tetraalkylammonium hydroxide and U.S. Pat. No. 5,643,439 uses trialkylsilanolates. PCT US96/13688, US/13689 and US/13690 (Publication WO 97/08270, 97/08271 and 97/08275 dated Mar. 6, 1997) teach the use of Group IA and Group IIA oxides and hydroxides to treat whole crudes and crude fractions to decrease naphthenic acid content. U.S. Pat. No. 4,300,995 discloses the treatment of carbonaceous material particularly coal and its products, heavy oils, vacuum gas oil, petroleum resids having acidic functionalities with a dilute quaternary base, such as tetramethylammonium hydroxide in a liquid (alcohol or water). This patent was aimed at improving yields and physical characteristics of the products and did not address the question of acidity reduction.
While these processes have achieved varying degrees of success there is a continuing need to develop more efficient methods for treating acidic crudes.
SUMMARY OF THE INVENTION
The present invention relates to a process for reducing the acidity of a petroleum oil containing organic acids comprising treating said petroleum oil containing organic acids with an effective amount of an alcohol at a temperature and under conditions sufficient to form the corresponding ester of said alcohol.
The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed.
DETAILED DESCRIPTION OF THE INVENTION
Some petroleum oils contain organic acids that contribute to corrosion or fouling of refinery equipment and that are difficult to separate from the processed oil. The organic acids generally fall within the category of naphthenic and other organic acids. Naphthenic acid is a generic term used to identify a mixture of organic acids present in petroleum stocks. Naphthenic acids may be present either alone or in combination with other organic acids, such as phenols. Naphthenic acids alone or in combination with other organic acids can cause corrosion at temperatures ranging from about 65° C. (150° F.) to 420° C. (790° F.). Reduction of the naphthenic acid content of such petroleum oils is a goal of the refiner.
The petroleum oils that may be treated in accordance with the instant invention are any organic acid-containing petroleum oils including whole crude oils and crude oil fractions that are liquid, liquifiable or vaporizable at the temperatures at which the present invention is carried out. As used herein the term whole crudes means unrefined, non-distilled crudes. The petroleum oils are preferably whole crudes.
Unexpectedly, Applicants have discovered that petroleum oils containing organic, specifically naphthenic acids, may have their naphthenic acid content reduced simply by treatment with an effective amount of alcohol. The treatment is conducted under conditions capable of converting the alcohol and acid to the corresponding ester. For example, if methanol is used, the methanol will be converted to methyl ester. Hence treatment temperatures will preferably range from about 250° C. and higher, preferably about 350° C. and higher and most preferably, about 250° C. to about 350° C. The temperature utilized should not exceed the cracking temperature of the petroleum oil. Pressures of from about 100 to 300 kPa are typical and generally result from the system itself. The molar ratio of petroleum acids to alcohol, typically ranges from about 1:0.5 to about 1:20, more preferably from about 1:1 to 1:10.
Optionally, any excess of methanol may be recovered and reused in either a batch or continuous process to contact additional untreated petroleum oil. Such recovery is readily accomplished by the skilled artisan.
Beneficially, the treatment with alcohol produces a treated crude that will not produce ash when burned unlike petroleum oils treated with inorganic oxides and hydroxides. Indeed, the esters produced from reaction of the acids and alcohols may be left in the petroleum oil without any detrimental effect.
The alcohols usable herein are commercially available. The alcohols may be selected from alkanols and alkane diols. The alkanols are preferably those having C
1
to C
6
carbons and the alkane diols are preferably those having C
2
to C
6
carbons. Preferably, the alcohol will be methanol or ethanol, most preferably methanol. The alcohols usable need only be capable of forming a thermally and hydrolytically stable ester with the acids contained in the petroleum oil being treated. Choice of alcohols meeting the above criteria is easily accomplished by the skilled artisan.
Treatment of the petroleum oils includes contacting the petroleum oil with an alcohol as described herein. Contacting times depend on the nature of the petroleum oil being treated and its acid content. Typically, contacting will be carried out from minutes to several hours. As noted previously, the contact time is that necessary to form an ester of the alcohol and acid. Applicants have also discovered that a slowly esterified crude may have its esterification rate increased by topping the crude and separating the lower boiling fraction, e.g., by separating the crude into its 650° F.
+
fraction and lower boiling fraction. The 650° F.
+
boiling fraction can then be esterified more rapidly, as compared to the whole crude, by treatment in accordance with the instant invention.
The concentration of acid in the crude oil is typically expressed as an acid neutralization number or acid number, which is the number of milligrams of KOH required to neutralize the acidity of one gram of oil. It may be determined according to ASTM D-664. Any acidic petroleum oil may be treated according to the present invention, for example, oils having an acid neutralization number of from 0.5 to 10 mg KOH/g acid. Typically, the decrease in acid content may be determined by a decrease in the neutralization number or in the intensity of the carboxyl band in the infrared spectrum at about 1708 cm
−1
. Petroleum oils with acid numbers of about 1.0 and lower are considered to be of moderate to low corrosivity. Petroleum oils with acid numbers greater than 1.5 are considered corrosive. Acidic petroleum oils having free carboxyl groups may be effectively treated using the process of the present invention.
Petroleum oils are very complex mixtures containing a wide range of contaminants and in which a large number of competing reactions may occur. Thus, the reactivity of particular compounds to produce the desired neutralization is not predictable. Unexpectedly, in the current process the acidity of the oil is effectively reduced by the simple addition of alcohol. The simplicity of the process makes it highly desirable. Indeed, not only is the acidity of the petroleum oil reduced, but the oil is concurrently rendered less corrosive.
Indeed, an additional benefit of the present invention is that no acidic catalyst nor water removal is necessary to carry out the invention.
The present invention may be used in applications in which a reduction in the acidity of an acidic petroleum oil would be beneficial.
REFERENCES:
patent: 2160632 (1939-05-01), Yabroff et al.
patent: 2302
Ballinger Bruce H.
Blum Saul C.
Dalrymple David C.
Sartori Guido
Savage David W.
Bakun Estelle C.
Brouillette Gabrielle
Cross LaToya
Exxon Research and Engineering Company
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