Note: Descriptions are shown in the official language in which they were submitted.
CA 02252033 1998-11-20
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 cl-udes 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 cnudes 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 foamed 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 cuude oil wastes.
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 corrosivity of an acid-containing, corrosive crude by contacting a
starting acid-containing, corrosive crude oil with an effective amount of
alkaline
earth carbonate selected from calcium and magnesium carbonates, preferably
magnesium carbonate to produce a treated crude oil having a decreased acidity
and corrosivity. Typically, the contacting is cal-ried out in the presence of
a
corresponding effective amount of water, which may be present in the crude or
added.
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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
removing such acids, and most desirably from heavier (higher boiling point)
and
liquid fractions in which these acids are often concenh~ated. The naphthenic
acids 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 occur although the acid is dilute in comparison to
the
large excess of crude and other reactive species typically present. And
desirably
the resulting salts remain oil soluble and tend to concentrate in the residua
rather
than distributing in lower boiling point side streams.
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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. The present invention
also provides a method for controlling emulsion formation in acidic 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 neutralization number or total acid number (TAN), 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. 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.
Crude oils with total acid numbers of about I .0 mg KOH/g and lower are
considered to be of moderate to low comosivity. 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 analysis is
particularly useful in cases in which a decrease in neutralization number is
not
evident upon treatment with base as has been found to occur upon treatment
with
bases weaker than KOH.
The cl-udes that may be used are any naphthenic acid-containing
crude oils that are liquid or liquefiable at the temperatures at which the
present
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invention is calTied 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
ambient temperature and 350°C, with narrower ranges suitably from about
20°C
to 300°C, preferably 30°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 cmdes 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 an alkaline earth metal cal-bonate of which magnesium carbonate is
the most preferred although calcium carbonate may also be used. 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. The carbonate is added to the acid
containing
crude in a molar ratio effective to produce a neutralized or partially
neutralized
crude oil; neutralization may be in whole or pautial as desired. Typically
ratios
of Group IIA metal carbonate to total acid of from 0.05:1 to 10:1, preferably
0.05:1 to S:1, more preferably 0.25:1 to 1:1 may be used.
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Some crudes themselves contain a sufficient amount of water,
others require water addition to the ranges specified herein. The total amount
of
water is an effective amount of from zero to 7 wt% of the crude, preferably 1
to
wt% of the crude.
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 crude 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 can-ied 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 cal-bonates may be purchased commercially or synthesized
using known procedures. In solid form, they may be in the form of a powder or
a composite, sized panicle or supported on a refractory (ceramic) matrix.
Certain of the solids may occur as crystals of the hydrate.
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 I hour to about 20 hours to produce a product having a decrease in acid
content. The treated crude may contain naphthenate salts of the corresponding
carbonate used in the treatment.
The present invention may be demonstrated with reference to the
following non-limiting examples.
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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, deter-
mined by infrared, were put into the autoclave. 0.62 g of magnesium carbonate
was added, then the autoclave was closed and heated at 300°C for 7
hours. After
cooling, the cmde was analyzed by infrared and found to have an acidity
corresponding to 1.8 mg KOH/g, i.e., 24% of the original.
Example 2
An experiment, as in Example 1 was carried out in which MgC03
was replaced by twice an equivalent amount of CaC03. Analysis of the treated
crude showed residual acidity of 6.2 mg KOH/g, corresponding to 84% of the
original. Thus MgC03 neutralizes 76% of the acid present while CaC03 only
neutralizes 16%.
Example 3
The reaction apparatus was a glass vessel, equipped with stirrer
and reflux condenser, immersed in an oil bath. 100 g of Bolobo 2/4 crude and
0.62 g of MgC03 were put into the reactor, which was then brought to
180°C and
held for 8 hours. After cooling, the crude was examined by infrared and found
to have a residual acidity of 4.7 mg KOH/g, cowesponding to 63% of the
original.
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Example 4
An experiment as in Example 3 was carried out in which MgC03
was replaced by an equivalent amount of CaCO~. Analysis of the treated crude
showed an acidity of 7.1 mg KOH/g, con-esponding to 96% of the original.
Example 5
The reaction apparatus was a glass jar with a magnetic bar.
50 g of Gryphon crude, with a total acid number of 4.2 mg KOH/g,
determined by infrared specn-oscopy, were put into the jar and 3.75 g of
calcium
carbonate added. The mixture was stiwed at room temperature for about 36
hours.
A small sample was centrifuged and submitted to infrared
examination. The peak at 1708 cm-~, due to carboxyl groups, was only
marginally smaller than in untl-eated Gryphon.
Example 6
2.5 g of water were added and the treated crude of Example 5 was
stirred at room temperature for about 36 hours. A small sample was centrifuged
and submitted to infrared examination. The peak at 1708 cm-~, due to carboxyl
groups, was about 50% as intense as in untreated Gryphon.
