Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF THE INVENTION
The present invention relates to a process for decreasing the acidity
and corrosivity of crudes and crude fractions containing petroleum acids.
BACKGROUND OF THE INVENTION
Many petroleum crudes with high organic acid content, such as
whole crude oils containing naphthenic acids, are corrosive to the equipment
used to extract, transport and process the crude, such as pipestills and
transfer
lines.
Efforts to minimize naphthenic acid corrosion have included a
number of approaches. Examples of such technologies include use of oil soluble
reaction products of an alkynediol and a polyalkene polyamine (U.S. Patent
4,647,366), and treatment of a liquid hydrocarbon with a dilute aqueous
alkaline
solution, specifically, dilute aqueous NaOH or KOH (U.S. Patent 4,199,440).
U.S. Patent 4,199,440 notes, however, that the use of aqueous NaOH or KOH
solutions that contain higher concentrations of the base form emulsions with
the
oil, necessitating use of only dilute aqueous base solutions. U.S. Patent
4,300,995 discloses the treatment of carbonous materials particularly coal and
its
products such as heavy oils, vacuum gas oil, and petroleum residua, having
acidic functionalities, with a quaternary base such as tetramethylammonium
hydroxide in a liquid (alcohol or water). Additional processes using bases
such
aqueous alkali hydroxide solutions include those disclosed in Kalichevsky and
Kobe, Petroleum Refining With Chemicals, (1956) Ch. 4, and U.S. Patent
3,806,437; 3,847,774; 4,033,860; 4,199,440 and 5,011,579; German Patents
2,001,054 and 2,511,182; Canadian Patent 1,067,096; Japanese Patent
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59-179588; Romanian Patent 104,758 and Chinese Patent 1,071,189. Publica-
tions WO 97/08270, WO 97/08271 and WO 97/08275 published March 6, 1997,
collectively disclose treatment with overbased detergents and Group IA and IIA
oxides and hydroxides to decrease acidity and/or corrosion. Certain treatments
have been practiced on mineral oil distillates and hydrocarbon oils (e.g.,
with
lime, molten NaOH or KOH, certain highly porous calcined salts of carboxylic
acids suspended on carrier media). Whole crude oils were not treated.
U.S. Patents 2,795,532 and 2,770,580 (Honeycutt) disclose
processes in which "heavy mineral oil fractions" and "petroleum vapors",
respectively are treated, by contacting "flashed vapors" with "liquid alkaline
material" containing, inter alia, alkali metal hydroxides and "liquid oil"
using
mixture of molten NaOH and KOH as the preferred treating agent, with "other
alkaline materials, e.g., lime, also employed in minor amounts." The treatment
of whole crudes or fractions boiling at 1050 plus °F (565+°C) is
not disclosed;
only vapors and condensed vapors of the 1050 minus °F (565-°C)
fractions, that
is, fractions that are vaporizable at the conditions disclosed in '532 are
treated.
Since naphthenic acids are distributed through all crude fractions (many of
which are not vaporizable) and since crudes differ widely in naphthenic acid
content the '532 patent does not provide an expectation that one would be able
to
successfully treat a broad slate of crudes of a variety of boiling points or
to use
bases other than NaOH and KOH.
U.S. 2,068,979 discloses a method for preventing corrosion in a
petroleum still by adding calcium naphthenate to petroleum to react with and
scavenge strong free acids such as hydrochloric and sulfuric acids to prevent
corrosion in distillation units. The patent makes no claims with respect to
naphthenic acids, which would have been formed when the strong acids were
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converted to salts. Patents have disclosed, inter alia, the addition or
formation of
calcium carbonate (Cheng et al, U.S. 4,164,472) or magnesium oxide (Cheng
et al, US 4,163,728 and 4,179,383, and 4,226,739) dispersions as corrosion
inhibitors in fuel products and lubricating oil products, but not in whole or
topped crude oil. Similarly, Mustafaev et al (Sb. Tr., Azerb. Inst. Neft.
Khim.
(1971) 64-6) reported on the improved detergency and anticorrosive properties
of calcium, barium, and zinc hydroxide additives in lubricating oils. Calcium
hydroxide (Kessick, Canadian Patent 1,249,760) has been used to aid in
separation of water from heavy crude oil wastes.
Finally, acetone is synthesized commercially by heating calcium
acetate at appropriate conditions (see, e.g., Kirk-Othmer, Encyclopedia of
Chemical Technology, First Edition, Vol. I, page 89).
There is a continuing need to develop methods for reducing the
acidity and corrosivity of whole crudes and fractions thereof, particularly
residua
and other 650+°F (343+°C) fractions. Applicants' invention
addresses these
needs.
SUMMARY OF THE INVENTION
The present invention provides for a method for decreasing the
acidity and corl-osivity of an acid-containing, corrosive crude by contacting
a
starting acid-containing, corrosive crude oil with an effective amount of at
least
one oxide of manganese to produce a treated crude oil having a decreased
acidity
and corrosivity. The treated crude contains naphthenate and ketone derivatives
of the naphthenic acids. Water may be present in the crude or added or may be
absent.
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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 whole crude oils contain organic acids such as carboxylic
acids that contribute to corrosion or fouling of refinery equipment. These
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 can cause corrosion at
temperatures ranging from about 65°C ( 150°F) to 420°C
(790°F). Naphthenic
acids are distributed through a wide range of boiling points (i.e., fractions)
in
acid containing crudes. The present invention provides a method for broadly
treating such acids, and most desirably from heavier (higher boiling point)
and
liquid fractions in which these acids are often concentrated. The naphthenic
acids to be removed may be present either alone or in combination with other
organic acids, such as phenols.
Whole crude oils are very complex mixtures in which a large
number of competing reactions may occur. Thus, the potential for successful
application of a particular treatment or process is not necessarily
predictable
from the success of other treatments or processes. Unexpectedly, the acid
neutralization reactions described in the present invention occur although the
acid is dilute in comparison to the large excess of crude and other reactive
species typically present.
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The process of the present invention has utility in processes in
which inhibiting or controlling liquid phase corrosion, e.g., of metal
surfaces, is
desired. More generally, the present invention may be used in applications in
which a reduction in the acidity, typically, as evidenced by a decrease in the
neutralization number of the acidic crude or a decrease in intensity of the
carboxyl band in the infrared spectrum at about 1708 cm-1 of the treated
(neutralized) crude, would be beneficial and in which oil-aqueous emulsion
formation and large solvent volumes are not desirable. Appearance of a band at
1600 cm 1 indicates the formation of carboxylate groups and at 1715 cm 1 of
keto
groups from the carboxylic acid groups. Thus, the treated crude contains
naphthenate and, preferably ketone derivatives of the organic acids. The
present
invention also provides a method for controlling emulsion formation in acid
crudes, by treating a major contributing component of such emulsions,
naphthenic and similar organic acids, and by reducing the attendant handling
and
processing problems.
The concentration of acid in the crude oil is typically expressed as
an acid neutl-alization number or total acid number (TAN), which is the number
of milligrams of KOH required to neuh~alize the acidity of one gram of oil. It
may be determined according to ASTM D-664. 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.
Appearance of a band at 1600 cm ~ indicates the formation of a carboxylate
salt
and at 1715 cm-~ indicates formation of a keto group from the carboxylic acid
groups. Ctvde oils with total acid numbers of about 1.0 mg KOH/g and lower
are considered to be of moderate to low corrosivity (crudes with a total acid
number of 0.2 or less generally are considered to be of low corrosivity).
Crudes
with total acid numbers greater than 1.5 are considered corrosive. The IR
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analysis is particularly useful in cases in which a decrease in neutralization
number is not evident upon treatment with the base as has been found to occur
upon treatment with bases weaker than KOH.
The crudes that may be used are any naphthenic acid-containing
crude oils that are liquid or liquefiable at the temperatures at which the
present
invention is carried out. Typically the crudes have TAN of 0.2 to 10 mg KOH/g.
As used herein the term whole crudes means unrefined, undistilled crudes.
The contacting is typically carried out at a temperature between
100°C and 350°C. Typically, this range is from 120 to
300°C, with narrower
ranges suitably from about 150°C to 300°C, preferably
200°C to 300°C.
Corrosive, acidic crudes, i.e., those containing naphthenic acids
alone or in combination with other organic acids such as phenols may be
treated
according to the present invention.
The acidic crudes are preferably whole crudes. However, acidic
fractions of whole crudes such as topped crudes and other high boiling point
fractions also may be treated. Thus, for example, 500°F (260°C)
fractions,
650+°F (343+°C) fractions, vacuum gas oils, and most desirably
1050+°F
(565+°C) fractions and topped crudes may be treated.
In the present invention the crude is contacted with an effective
amount of at least one oxide of manganese at a temperature sufficient to
produce
a treated crude having a decreased acidity. The oxides include MnO, Mn203
and Mn304. The treatment may be carned out in the presence or absence of
water as effective. When present water may be added or naturally occurring.
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Reaction times depend on the temperature and nature of the crude
to be treated, its acid content, but typically may be carried out for from
less than
about 1 hour to about 20 hours to produce a product having a decrease in
corrosivity and acid content. The treated crude contains naphthenate salts of
the
corresponding oxide used in the treatment and more desirably contains ketone
derivatives of the naphthenic acids.
The material is added as a solid, which also may include a solid-in-
liquid slurry, solid-in-water or solid-in-organic liquid slurry or aqueous
suspension. The material is added to the acid containing crude in a molar
ratio
effective to produce a neutralized or partially neutralized (i.e., non-
corrosive)
crude oil; neutralization may be in whole or pal-tial as desired. Typically
ratios
of oxide to total acid of from 0.01:1 moles up to 5:1, preferably 0.25:1 to
2:1
may be used.
The formation of a crude oil-aqueous (i.e., either water-in-oil or
oil-in-water) emulsion tends to interfere with the efficient separation of the
crude oil and water phases and thus with recovery of the treated cl-ude oil.
Emulsion formation is undesirable and a particular problem that is encountered
during treatment of naphthenic acid-containing crudes with aqueous bases. The
processes of the present invention can be carried out in the essential absence
of
emulsion formation. Thus, an additional benefit of the treatment is the
absence
or substantial absence of emulsion formation.
The oxides may be purchased commercially or synthesized using
known procedures. In solid form, they may be in the form of a powder or a
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composite, sized particle or supported on a refractory (ceramic) matrix.
Certain
of the solids typically occur as crystals of the hydrate.
The present invention may be demonstrated with reference to the
following non-limiting exampres.
Example 1
The reaction apparatus was an autoclave with a capacity of 250 ml.
100 g of Bolobo 2/4 crude, having a total acid number of 7.4 mg
KOH/g, determined by infrared spectroscopy, were put into the autoclave.
0.53 g of manganous oxide were added, then the autoclave was closed, heated to
300°C and held with stirring for 24 hours. After cooling, the oil was
examined
by infrared spectroscopy. A band at about 1600 cm l, partly superimposed on a
band already present in untreated Bolobo 2/4, indicated formation of a
carboxylate, presumably manganous naphthenate. An intense band at 1708 cm 1
present in untreated Bolobo 2/4 and attributed to carboxyl groups, was not
present in the treated sample. A weak band at about 1715 cm ~, present in the
treated sample, did not change when the sample was treated with triethylamine,
indicating presence of a keto group rather than a carboxyl group.
Example 2
Experiment 1 was repeated without manganous oxide.
Examination of the reaction product by infrared spectroscopy
showed that the band at 1708 cm l, attributed to carboxyl groups, was slightly
lower than in untreated Bolobo 2/4. Addition of triethylamine completely
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eliminated the band at 1708 cm ~, showing that it was due to unchanged
carboxyl
groups.
Example 3
Experiment 1 was repeated, reducing the reaction time at 300°C
from 24 to 6 hours. The infrared spectrum of the product was similar to that
of
Example 1. The intense band at 1708 cm ~ present in untreated Bolobo had
nearly disappeared. A much smaller band present in the treated sample at about
1715 cm's did not change after addition of triethylamine, indicating presence
of
keto groups rather than carboxyl groups.
A band at about 1600 cm-~, pal-tly superimposed on a band present
in untreated Bolobo 2/4, indicated formation of a carboxylate, presumably
manganous naphthenate.
Example 4
The treated oil from Example 1 was distilled to 1050°F. The
distillate was found to have less than 0.08 ppm of manganese. The remaining
36 gms of resid, containing all the manganese oxide, was used to treat another
100 g batch of Bolobo 2/4 crude. As in Example 1, the reaction was carned out
in a closed 300 ml autoclave for 24 hours at 300°C. After cooling, the
oil was
examined by infrared spectroscopy. A band at about 1600 cm 1, partly super-
imposed on a band that was already present in the spectrum of untreated Bolobo
2/4, indicated the formation of carboxylate, presumably manganous naphthenate.
A band at 1715 cm ~, due to carboxyl groups, was considerably
less intense than in untreated Bolobo 2/4. Treatment of the sample with
triethyl-
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amine eliminated the peak at 171 S cm-~ only in part, indicating presence of
keto
groups.
Example 5
The reaction apparatus was the same autoclave described in
Example 1. 100 g of Gryphon crude, having an acid number of 4.2 mg KOH/g,
and 296 mg of Mn20~ were put into the autoclave and heated at 300°C for
24
hours. After cooling, a sample was centrifuged to separate the solids, then
the
oil was examined by infrared. A peak at 1715 cm ~ was about 20% as intense as
the 1708 cm'1 peak present in untreated Gryphon and due to carboxyl groups.
Treatment of the sample with triethylamine did not cause any change in the
1715 cm 1 peak, indicating that it was due to keto groups rather than to
residual
carboxyl groups.
Example 6
The reaction apparatus was as described in Example 1, except that
a non-chilled condenser was attached to the autoclave thus allowing air to
enter
the reactor and some light ends of the oil to escape. 100 g of Gryphon crude,
having an acid number of 4.2 mg KOH/g, and 296 mg of Mn203 were put into
the autoclave and heated at 300°C for 24 hours. After cooling, a sample
was
centrifuged to separate the solids, then the oil was examined by infrared
spectro-
scopy. A peak at 1715 cm' was about 20% as intense as the starting oil
carboxyl groups at 1708 cm ~. The peak at 1715 cm ~ is attributed to keto
groups.
