AGENTS ANTI-CORROSION A BASE D'AMIDINE CYCLIQUE QUI EMPECHENT LA CORROSION PAR CO.SUB.2 ET H.SUB.2S

CYCLIC AMIDINE BASED CORROSION INHIBITORS WHICH INHIBIT CORROSION CAUSED BY CO.SUB.2 AND H.SUB.2S

Abrégé anglais

Abstract of the Disclosure
The invention relates to corrosion inhibitors
which are amides of cyclic amidines. The inhibitors are
particularly useful for preventing the corrosion of metals
caused by H2S and CO2 in water-in-oil, particularly in
saltwater-in-oil emulsions.

Revendications

The embodiments of the invention in which
an exclusive property or privilege is claimed are defined as
follows:

1. A compound having the following
structural formula:

Image

in which R represents a C7- to C25- alkyl or alkenyl radical
and in which n represents the numbers 1 or 2.


2. A composition comprising the product
prepared by mixing the compound of claim 1 with elementary
sulfur such that from 0.5 to 100 percent by weight of sulfur
is present relative to the compound of claim 1.


3. The composition of claim 2 wherein the
sulfur and compound of claim 1 are heated to 100°C to 200°C
within a period of 1 to 3 hours.


4. A process for inhibiting the corrosion
of metals caused by H2S and CO2 in water-in-oil emulsions
comprising adding, as corrosion inhibitor, a compound
of claim 1, to a water-in oil emulsion.


5. A process for inhibiting the corrosion
of metals caused by H2S and CO2 in water-in-oil emulsions
comprising adding, as corrosion inhibitor, a compound of claim 1,
to a water-in-oil emulsion and wherein from 50 ppm to 1000 ppm
of said corrosion inhibitor are used relative to the weight or
emulsion.



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6. A process for inhibiting the corrosion
of metals caused by H2S and CO2 in water-in-oil emulsions
comprising adding, as corrosion inhibitor, a composition
of claim 2, to a water-in-oil emulsion.


7. A process for inhibiting the corrosion
of metals caused by H2S and CO2 in water-in-oil emulsions
comprising adding, as corrosion inhibitor, a composition of
claim 2, to a water-in-oil emulsion and wherein from 50 ppm
to 1000 ppm of said corrosion inhibitor are used relative to
the weight of emulsion.


8. A process for inhibiting the corrosion
of metals caused by H2S and CO2 in water-in-oil emulsions
comprising adding, as corrosion inhibitor, a composition
of claim 3, to a water-in-oil emulsion.


9. A process for inhibiting the corrosion
of metals caused by H2S and CO2 in water-in-oil emulsions
comprising adding, as corrosion inhibitor, a composition of
claim 3, to a water-in-oil emulsion and wherein from 50 ppm
to 1000 ppm of said corrosion inhibitor are used relative
to the weight of emulsion.


10. The compound of claim 1 wherein n is
1 and R is selected from the group consisting of -C8H17,
-C17H33, C11H23 and C7H15.



11. The composition of claim 2 wherein n
is 1 and R is selected from the group consisting of -C8H17,
-C17H33, C11H23 and C7H15.


12. The composition of claim 3 wherein n
is 1 and R is selected from the group consisting of -C8H17,
-C17H33, C11H23 and C7H15.



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13. The process of any one of claims 4, 5
and 6, wherein n is 1 and R is selected from the group con-
sisting of -C8H17, -C17H33, C11H23 and C7H15.
14. The process of any one of claims 7, 8
and 9, wherein n is 1 and R is selected from the group
consisting of -C8H17, -C17H33, C11H23 and C7H15.



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Description

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CYCLIC AMIDINE BASED CORROSION INHIBITORS
WHICH INHIBIT CORROSION CAUSED BY C2 A~lD H2S


Background of the Invention
1. Field of the Invention
The invention relates to corrosion inhibitors
which are amides of cyclic amidines. The inhibitors are
particularly useful for preventing the corrosion of metals
caused by H2S and CO2 ("acid gas") in water-in-oil,
particularly in saltwater-in-oil emulsions.
2. Description of the Prior Art
It is known to inject a solution or dispersion of
corrosion inhibitors in the crude oil during oil recovery,
and in the transport or storage of the crude oil so that a
protective layer forms on the surface of the metal parts
coming in contact with the oil. The crude oil emulsions
usually contain saltwater and in many cases, depending upon
the origin of the oil, contain H2S and CO2 which have a pro-
nounced corrosive effect. The corrosion inhibitors to be
used for this purpose should be soluble in oil and should at
least be dispersible in saltwater so that they can have an
optimum effect.
Such systems are known from German published
application 2,846,977. These are imidazolinium salts which
are used dissolved in an oil soluble organic solvent in the
presence of a hydrocarbon oil. The problems with such




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systems are the relatively complicated metering form
l3 components) and the fact that the corrosion protection is
not satisfactory in all cases. We have noted, for instance,
that the imidazoline having the formula
~ N - CH2

17 33
N CH2
CH2CH20H
(as chloride) described in the referenced publication does
not develop sufficient effectiveness against the corrosive
erosion caused by the effects of H2S when used alone.
Summary of the Invention
The subject invention relates to compounds
having the following structural formula:
~ N-(CH2)n
HC

N -CH O
2 ll
CH2--~CH2 ~ NH-C-R



in which R denotes C7- to C25-, preferably C8- to C17-
alkyl or alkenyl radical and n represents the numbers 1
or 2 .
The present invention also provides a
composition comprising a mixture of the above compounds and
from 0.5 to 100 percent by weight of elementary sulfur relative
to the above compounds.
In accordance with the present invention,
n may be 1 and R may be selected from the group consisting of


C8H17 ; C17H33, CllH23 and C7H15.




~ - 2 -




The subject ccmpounds and compositions are p~ticularly
useful as corrosion inhibitors in pre~entin~ the corrosion of metal caused
by H2S and C02 in water-in-oil emulsions such as crude oil.
The compounds and cc~positions can be uni~o ~ y distributed in oil-
in-water emulsions without the aid of additional solvents.
~escription of the Preferred Embodiments

-
The subject compounds are amides of cyclic
amidines which are based upon an imidazoline- or 3,5-
tetrahydro-pyrimidine system. The compounds can be obtained
in a simple manner by traditional reactions.
Initially a carboxylic acid R-COOH, with R
representing a C7- to C25-, preferahly C8- to C17- alkyl or
alkenyl radical is reacted with diethylene triamine or di-n-
propylene triamine at 120C to 1~0C within 5 to 10 hours in
a mole ratio of 1:1 to 1:1O2 and the resultant acid amide is
reacted with formamide at 120C to 150C within 0.5 to 2
hours. Following this process the product is condensed at
200C to 300C preferably under vacuum (1.5 mbars to 80
mbars) within a period of 5 to 10 hours. The resultant
imidazoline and/or tetrahydro-pyrimidine derivatives may be
isolated in their pure form.
All of the above defined carboxylic acids are
suitable as starting carhoxylic acids. Preferably chosen
are, for instance, n-octanic acid, iso-octanic acid (2-
ethylhexanoic acid), iso-nonanoic acid (3,5,5-






trimethylhexanic acid), lauric acid, stearic acid, oleicacid, behenic acid and mixtures thereof. Mixtures of
natural fatty acids such as tallow fatty acid, coconut fatty
acid, colza oil fatty acid and palm kernel fatty acid are
also suitable.
The compounds alone have a very satisfac~ory
effect as inhibitors against H2S and CO2 corrosion. Testing
indicates that corrosion is less than a fourth of the value
obtained when the compounds are not used.
The inhibition effect can be increased, however,
if 0.5 to 100 percent by weight preferably 1 to 30 percent
by weight of colloidal sulfur is present relative to amides
of the cyclic amidine. The sulfur can be incorporated in
this system by a mere admixing of "colloidal" sulfur but is
preferahly incorporated by heating the mixture to 100C to
200C within a period of 1 to 3 hours. Inhibitors obtained
in this manner are capable of reducing the corrosion to less
than one-fifth of the value obtained when the inhibitors are
not used.
The subject corrosion inhibitors are added to the
water-in-oil emulsions in quantities of 50 ppm to 1000 ppm
relative to the weight of the emulsion. They disperse
without difficulties in the aqueous as well as in the oil
phase.



The following examples will illustrate in detail
the invention, but are not intended to limit the scope of
its application.
Examples
Examples 1 and 2 illustrate how the corrosion
inhibitors of the subject invention are prepared.
Example 1
In a reaction vessel, 423.7 grams of oleic acid
are heated to a temperature of 70C to 80C and at this
temperature are added dropwise into 170.3 grams of
diethylenetriamine. E'ollowing this, reaction water is
removed by distillation at 150C to 160C for 7 to 8
hours. Then 67.6 grams of formamide are added dropwise into
the resultant acid amide at 120C to 150C within a period
of 1 hour. Subsequently the mixture is condensed at 200C
to 250C under a vacuum of approximately 20 Torr for

8 hours. The compound had a structure of

/~N- CE32
HC
N--CH2 o ( ?
2 2


wherein R = C17 H33 . The yield was 565 grams of a brown
viscous oil.



Examp_e 2_
In a reaction vessel, 316.~ grams of isononamic
acid (3,5,5-trimethylhexanic acid) are heated to a tempera-
ture of 70C to 80C and are added dropwise into 288.7 grams
of ~ipropylenetriamine at this temperature. Following this
process, reaction water is removed by distillation at 150C
to 160C for 7 to 8 hours. Then 90 grams of formamide are
added dropwise into the resultant acid amide at 120C to
150C within a period of 30 minutes. Followiny this, the
product is condensed at 200C to 250C and under vacuum of
approximately 20 Torrs separating ammonium. The compound
had a structure of

N--C H2
IIC ~ ` CH2
N -CH2

2 2 2


wherein R = C8H17 . The yield was 560 grams of brown
viscous oil.
The corrosion inhihitors and several variations
thereof were tested according to the so-called dynamic or
"wheel" test. This is a method commonly employed in the
crude oil recovery to test inhibitors.
The test samples are iron sheet metal having the
dimensions of 130 mm x 10 mm x 1 mm. These are sanded,

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degreased with toluene, and are weighed. Test gasoline was
used as the test medium which contained 50 percent by weight
of saltwater wit}l 3 percent ~aCi in emulsified form. In
order to simulate field conditions, the test medium was
saturated with H2S and CO2 and was poured into test bot-
tles. Following this the inhibitors to be tested were added
in ~uantities of 250 ppm. The test samples of sheet metals
were fastened to the bottle covers and were immersed in the
test medium.
The test bottles were then fastened to a rotating
axis (wheel) which turned in a water bath maintained at 80C
at a speed of 40 rpm. The test duration was 16 hours.
Thereafter, the test strips were cleaned with an
inhibiting acid~ were degreased, dried and were weighed in
order to determine the weight losses. The results were
evaluated and compared with a blank value (test without
added inhibitor).
The specific corrosion inhibitors used and the
results are shown in the following table.




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TABLE

Compound Corrosion
of Formula R (m~/sample)

17 33 22.9
17 35 22.5
II C17H33 22.4
II C17H35 21.1
I + 1/5/10 ~ S C17H33 21.9/21.2/17.4
I + 1/5/10 % S C17H35 22.4/22.7/26.9
II + 1/5/10 % S C17H33 28.6/26.9/23.3
7 17 35.5
8 17 33.8
11 23 28.2
17 33 22.9
17 35 22.5
I Tallow fatty acid radical 26.4
I Coconut fatty acid radi Ql 24.9
I Crude oil fatty acid radical20.2
I Etalm kernel fatty acid radical 23.4
II 7 15 34.8
II 8 17 29.3
II CllH33 27.1
II C17H33 21.1
II C17H33 22.4
II Tallow fatty acid radical 24.2
II Coconut fatty acid radical 26.1
II Colza oil fatty acid radical21.3
II Palm kernel fatty acid radical 22.7

Blank value (without sulfur) 98.3

" " (with 10 percent sulfur) 114.9




Comparison*

¦ N CH~ ~

N - CH ~ [ ~ 52.8

L CH2CH2-0~

* In accordance with Germany pu~lished application
2,846,977.