Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROCESS FOR TREATMENT OF PETROLEUM ACIDS WITH AMMONIA
FIELD OF THE INVENTION
The present invention relates to a process for neutralizing petroleum
acids.
BACKGROUND OF THE INVENTION
Whole crudes and crude fractions with high petroleum acid content
such as those containing naphthenic acids are corrosive to the equipment used
to
extract, transport and process the crude.
Efforts to minimize naphthenic acid corrosion have included a
number of approaches for neutralizing and removing the acids from the oil. For
example, U.S. Patent 2,302,281 and Kalichevsky and Kobe in Petroleum Refin-
ing 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. Patent
4,199,440 discloses treatment of a liquid hydrocarbon with a dilute aqueous
alkaline solution, specifically dilute aqueous NaOH or KOH. U.S. Patent
5,683,626 teaches treatments of acidic crudes with tetraalkylammonium
hydroxide and U.S. Patent 5,643,439 uses triallrylsilanolates. PCT US96/13688,
US/13689 and US/13690 (Publ. WO 97/08270, 97/08271 and 97/08275 dated
March 6, 1997) teach the use of Group IA and IIA oxides and hydroxides to
treat
whole crudes and crude fractions to decrease naphthenic acid content. U.S.
Patent 4,300,995 discloses the treatment of carbonous material particularly
coal
and its products, heavy oils, vacuum gas oil and 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
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yields and physical characteristics of the products and did not address the
question of acidity reduction.
U.S. Patent 4,457,837 to Farnham teaches a process for treating
corrosive aqueous condensate acid released from petroleum following distilla-
tion, i.e., acidic materials such as HCl and HZS, not organic condensate. In
the
process the concentration of water is very high as evidenced by the
requirement
of a separate aqueous ammonia phase and a hydrocarbon phase. Farnham is
silent on the need to foam amides in the treatment process and, indeed the
presence of large quantities of water disfavors such a reaction.
U.S. Patent 4,634,519 to Danzik teaches a neutralization reaction of
naphthenic acids upon extraction into the aqueous methanolic phase to produce
ammonium salts of the naphthenic acids and requires the presence in critical
ratios of alkanols, water and ammonia. Danzik indicates that about 20% water
is
required which is consistent with Danzik's teaching of an aqueous ammonia
phase. The reference is selective and specifically states that it cannot be
success-
fully applied to treatment of crude oils in general.
While these processes have achieved varying degrees of success
there is a continuing need to develop more efficient methods for treating
acidic
crudes.
SLJIyIMARY OF THE INVENTION
The present invention relates to a process for decreasing the acidity
of an acidic crude oil by contacting the acidic crude oil with an effective
excess
of ammonia in the presence of water in an amount not to exceed the solubility
limit of the water in the crude (i.e., essentially anhydrous) at a temperature
and
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under conditions sufficient to foam the corresponding amide of the naphthenic
acids. Additionally, the process may be carried out in two steps by
pretreating
an acidic crude oil with an effective excess of ammonia in the presence of
water
in an amount not to exceed the solubility limit of the water in the crude
(i.e.,
essentially anhydrous) at a temperature and under conditions sufficient to
form
the corresponding ammonium salts of the naphthenic acids, and then treating
the
resulting crude containing ammonium salts of the naphthenic acid at a tempera-
ture and under conditions su~cient to form the corresponding amides of the
naphthenic acid.
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 crude 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).
Applicants have discovered that if a crude is treated with ammonia at
conditions at which an excess of ammonia is not present the resulting ammonium
salt of the naphthenic acid is formed, and on subsequent heating in the
absence
of additional (or a sufficient excess of) ammonia or at insufficient
temperature as
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can occur, for example, in further refining of a crude oil, this salt
decomposes to
give ammonia and the naphthenic acid. Thus, a critical step of Applicants'
invention is to ensure that the corresponding amide is produced. This is
accomplished by heating the crude oils under conditions such that any
ammonium salt of the naphthenic acid is converted into the corresponding
amide.
This requires the presence of ammonia and in sufficient excess concentration
in
the presence of only trace amounts of water, i.e., in the presence of water in
an
amount not to exceed the solubility limit of the water in the crude, at a
tempera-
ture to produce the corresponding amide. Prior art processes using higher
levels
of water (i.e., aqueous ammonia or predominately water containing systems)
produce naphthenic acid salts rather than amides. The resulting amide is heat
stable in that it does not decompose to ammonia and the naphthenic acid.
The crudes that may be used are any naphthenic acid-containing
whole crude oils that are liquid, liquifiable or vaparizable at the
temperatures at
which the present invention is carried out As used herein the term whole
crudes
means unrefined, non-distilled crudes. The acidic cruder are preferably whole
crudes. However, fractions of whole crudes also may be treated. An additional
benefit of the treatment process is the minimization of ash formation in the
event
that resulting crude or fraction is to be subsequently burned.
Crudes typically contain amounts of water but also may be
anhydrous or essentially anhydrous. Suitable crudes may be anhydrous or may
contain traces of water (i.e., water in an amount not greater than the
solubility
limit of the water in the crude and thus is insufficient to form a separate
aqueous
phase). Dewatering/desalting of water-containing crude to the required level
for
use in Applicants' process may be carried out by methods laiown to those
skilled
in the art.
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Applicants' treatment can be carried out using a staged or sequential
treatment of the acidic crude with a suffcient excess of ammonia. The tempera-
ture in any given stage should not exceed the cracking temperature of the oil.
When a one step treatment is used the conditions must be sufficient to form
the
amide of the naphthenic acid. Typically, treatment at temperatures above about
150-350°C, preferably above about 180-350°C and in the presence
of an
effective excess of ammonia are used. Typically, for the two stage treatment
in
the first stage the temperature is from about 10°C to 100°C
preferably 20°C to
50°C and in the second stage the temperature is greater than the
temperature in
the first stage and sufficient to produce amidation, typically above about
150-350°C, preferably above about 180-350°C. Pressures are
autogenous
pressures, typically from 100 to 300 kPa and may be the same or different in
the
two steps. In the two step process, the ratio of crude to ammonia is su~cient
to
produce the corresponding ammonium salt in the first step, and sufficient to
produce the corresponding amide in the second step. Typically, a large molar
excess of ammonia to the naphthenic acid (or of ammonia to ammonium salt) is
used, typically at least a threefold (3:1) molar excess of ammonia, more
desirably at least a five fold molar excess in a given stage.
The ammonia is dissolved in the crude oil to form an ammonia-in-
oil-phase. Thus suitable crudes are those that are anhydrous or essentially
anhydrous, i.e., in which the amount of water is less than that which results
in a
separate water phase.
Optionally, the excess, unreacted ammonia may be recovered and
reused in either a batch or continuous process to contact additional untreated
crude.
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The ammonia may be in a suitable solution preferably in a solvent
which is inert to naphthenic acids or non-aqueous and is available from
commercial sources.
Contacting times in each step depend on the nature of the crude to be
treated, its acid content, but typically may be carried out from a few minutes
to
8 hours.
The first and second steps may be carried out sequentially either in
batch (in one vessel with addition of one charge or separate stepwise
additions of
multiple charges of excess ammonia) or in multiple vessels (typically two).
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 deter-
mined according to ASTM D-664. Any acidic crude may be treated according to
the present invention, for example, crudes 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. Whole crude
oils with acid numbers of about 1.0 and lower are considered to be of moderate
to low corrosivity. Crudes with acid numbers greater than about 1.5 are
considered corrosive. Acidic crudes having free carboxyl groups may be
effectively treated using the process of the present invention.
Whole crude 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 neutraliza-
tion is not predictable. Unexpectedly, in the current two step process the
acidity
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of the crude is effectively decreased by a greater amount in comparison to a
one
step treatment process carried out at the same conditions using the same total
amount of ammonia as is evidenced by a comparison of Example 2 (two steps)
and Example 4 (one step). Additionally, use of an excess of ammonia su~cient
to ensure the formation of the corresponding amide of the naphthenic acid
either
in the one step or a two step process of the present invention produces a
greater
decrease in acidity than use of a lower ratio (sub-excess) of ammonia to
naphthenic acid groups under conditions that do not result in amide formation.
Beneficially, the treatment produces a treated crude (or distillation
residue derived therefrom) that will not produce ash when burned, unlike
crudes
treated with inorganic oxides and hydroxides. The amide remains dissolved in
the crude.
The present invention may be used in applications in which a
reduction in the acidity of an acidic whole crude would be beneficial.
The present invention may be demonstrated with reference to the
following non-limiting examples.
GENERAL CONDITIONS
Titration of the carboxyl groups with KOH was carried out accord-
ing to ASTM D-664. In addition, the extent of conversion of the naphthenic
acids to the corresponding amides can be established by infrared spectroscopy.
The reactions were calTied out in a 300 ml autoclave, unless otherwise noted.
Pressure during the amidation step was 300 kPa.
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Example 1
The reactions were carried out in an autoclave with a 300 ml
capacity.
100 g of Gryphon crude, having a total acid number of 4.2 mg
KOH/g of oil, determined by infrared spectroscopy, was put into the autoclave.
The autoclave was then pressurized to 300 kPa with anhydrous ammonia without
prior air removal. The oil was stirred at room temperature at 450 rpm for 24
hours. Examination of the reaction product by infrared spectroscopy showed
that the band at 1708 cm-1, attributed to carboxyl groups, had been reduced by
92%. A broad band at 1560 cm-1 that was not present in the untreated Gryphon
crude showed the formation of ammonium salts.
In the second step the treated Gryphon crude was heated is the same
autoclave to 190°C and stirred at 450 rpm while anhydrous ammonia was
passed
through the oil at a rate of 2 ml/minute. After 7'/z hours the autoclave was
allowed to cool to room temperature while the flow of 2 mls/minute of ammonia
was continued through the stirred oil. Examination of the reaction product by
infrared spectroscopy showed a large decrease in the band at 1560 cm-1
attributed to ammonium salts. The presence of a broad band with its maximum
at 1680 cm 1 was attributed to the formation of corresponding amides. Further
examination by use of KOH titration showed a total acid number (TAN) of 2.7
mg KOH/g of oil for the reaction product. This was a 36% reduction in total
acid number from the untreated Gryphon crude.
Example 2
Example 1 was repeated, increasing the reaction temperature of the
second step to 220°C. Examination by KOH titration showed a total acid
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number (TAN) of 1.5 mg KOH/g of oil. This was a 64% reduction in total acid
number from the untreated Gryphon crude. The infrared spectrum of the product
was similar to that in Example 1, and showed a 76% reduction in carboxyl
groups.
The product was heated to 350°C for 3 hours in an autoclave to see
if a higher temperature would reverse the amidation reaction. The heated
product had a resulting total acid number (TAN) of 1.4 mg KOH/g of oil.
Examination by infrared spectroscopy showed complete disappearance of the
band at 1680 cm-1, attributed to the amide groups. The band at 1708 cm-1,
attributed to carboxyl groups was unchanged in intensity. A weak band at
2246 cm-1 showed formation of nitrite groups.
Examute 3
Example 1 was repeated, increasing the reaction temperature of the
second step to 270°C. Examination by KOH titration showed a total acid
number (TAN) of 1.8 mg KOH/g of oil. This was a 57% reduction in total acid
number from the untreated Gryphon crude. Infrared spectroscopy showed a 92%
reduction of intensity of the band at 1708 cm-1, attributed to carboxyl
groups. A
band at 1680 cm-1 showed formation of amide groups.
The product was heated to 300°C for 3 hours in an autoclave. The
resulting product had a total acid number (TAN) of 2.2 mg KOH/g of oil.
Example 4
In this experiment there was no pre-neutralization of the Crryphon
crude. The first step of Example 2 was eliminated. The Gryphon crude was
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directly reacted with flowing ammonia gas at 220°C. The ammonia flow
rate
was 2 mls/minute and the reactants were mixed at 450 rpm for 7'/z hours.
Examination of the reaction product by infrared spectroscopy showed a similar
spectrum as Example 1 except the amide peak with its maximum at 1680 cm-1
was smaller and the ammonium salt peak at 1560 cm-1 was larger. Titration by
KOH showed a total acid number (TAN) of 2.9 mg KOH/g of oil.
Example 5
Example 2 was repeated but the flow rate of ammonia gas was
increased to 4 mls/minute. The infrared spectrum was similar to that in
Example
2. The KOH titration showed a total acid number (TAN) of 1.7 mg KOH/g of
oil. This was a 60% reduction in total acid number from untreated Gryphon
crude.
Example 6
The reaction apparatus was the 300 ml autoclave described in
Example 1. 100 g of Gryphon crude were placed in the autoclave. Some
gaseous ammonia was passed through the autoclave to remove air. Then the
autoclave was pressurized to 300 kPa with ammonia gas and stirred at 450 rpm
at room temperature for 24 hours. Then the autoclave was heated at
220°C with
stirring for 7 hours without NH3 flow.
After cooling, titration according to ASTM D-664 showed a total
acid number of 1.3 mg KOH/g of oil corresponding to a 69% reduction in acidity
compared to untreated Gryphon. Infrared spectroscopy showed a band at
1680 cm-', indicating formation of amide groups. The band at 1708 cm-1,
attributed to carboxyl groups was a small shoulder, partly superimposed on the
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amide peak. Based on its intensity, 83% of the original carboxyl groups had
been converted to amides.
Example 7
The reaction apparatus was the 300 mI autoclave described in
Example 1. 100 g of Gryphon crude were put into the autoclave, which was then
closed and swept with ammonia gas to displace air. Then the autoclave was
pressurized to 300 kPa with ammonia gas and stirred at room temperature for
24 hours. Then the autoclave was brought to 280°C and stirred at 450
rpm for
7 hours without NH3 flow.
After cooling, the oil was titrated with KOH according to ASTM
D-664. The total acid number was 0.6 mg KOH/g of oil, corresponding to an
86% reduction of the original acidity.
