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Description  |
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This invention relates to corrosion inhibitors, particularly but not
exclusively to corrosion inhibitors for use in pipelines used for the
transportation of hydrocarbon fluids such as crude petroleum or refined
petroleum fractions such as kerosene, aviation fuel or fuel oils, e.g. for
domestic heating purposes.
In the commercial transportation by pipeline of crude petroleum and/or
refined products thereof it is common practice to employ a corrosion
inhibitor. This is commonly injected into the liquid being transported in
the pipeline and is carried along by the liquid and evenly distributed
throughout the pipeline downstream of the point of injection.
Phosphorous containing inhibitors often used in pipelines have recently
become unacceptable to pipeline operations and the development of improved
inhibitors has therefore become desirable. For instance in U.S. Pat. No.
2,334,153 combinations of polycarboxylic acids having at least 16 carbon
atoms in a mutual solvent such as an alkylene glycol mono alkyl ether have
been proposed as corrosion inhibitors for flushing oils but these
additives have been found to be ineffective at the low concentrations
necessarily used in fuels. Furthermore in U.S. Pat. No. 3,696,048 it has
been suggested to use as corrosion inhibitors combinations of aliphatic
amine salts of C.sub.10.sub.-50 dimer acids and particular alkoxylated
alkyl phenols but when tested for water separability characteristics in
kerosene these additives have been found to provide unacceptably low WSIM
numbers (as hereinafter defined) falling below 50 and in some cases below
30.
We have now found a mixture of substances which exhibit particularly
desirable corrosion inhibiting properties whilst combining excellent water
separability characteristics.
Accordingly the present invention provides a mixture suitable for use as a
corrosion inhibitor, which mixture comprises (a) from 1.8 to 25 parts by
weight dimerised unsaturated fatty acid, and (b) 1 part by weight of an
alkoxylated alkyl phenol, and provides a WSIM number as hereinafter
defined of at least 60.
The WSIM (Water Separation Index, Modified) number is a numerical rating
indicating the ease of separating water from a hydrocarbon liquid by
coalescence. As used herein the term WSIM number means that rating as
determined at a concentration of 24 p.p.m. inhibitor by the method as
defined in the ASTM Specification D-2550 except in that kerosene is used
as the Reference Fluid Base. It is to be understood that the disclosure of
ASTM Specification D-2550 is accordingly imported herein by reference.
The dimerised unsaturated fatty acid component is preferably a dimer of a
comparatively long chain fatty acid, e.g. containing from 8 to 20 carbon
atoms, and may be pure, or substantially pure, dimer. Alternatively, and
preferably, the material sold commercially and known as "dimer acid" may
be used. This latter material is prepared by dimerising unsaturated fatty
acid and consists of a mixture of monomer, dimer and trimer of the acid. A
particularly preferred dimer acid is the dimer of linoleic acid available
commercially under such trade names as Empol 1022.
The second component of the inhibitor of the present invention is an
alkoxylated alkyl phenol which in conjunction with the dimerised
unsaturated fatty acid, and at the relative molar ratio of the components
used, provides an inhibitor of WSIM number of at least 60, and preferably
at least 70, more preferably at least 80. Alkoxylated alkyl phenols which
have been found to be particularly useful in this respect are alkoxylated,
especially ethoxylated, alkyl phenols having an average of from 1 to 8,
preferably 3 or 4, alkylene oxide residues per molecule. The most
preferred examples of such materials are alkoxylated p-alkyl phenols in
which the alkyl group contains from 4 to 16 carbon atoms, for example
alkoxylated p-octyl, p-nonyl or p-dodecyl phenol, or alkoxylated phenols
containing more than one alkyl group in which the alkyl groups contain a
total of from 4 to 16 carbon atoms. Such materials are available under
such trade names as Sterox NA, Sterox NB, Sterox NC and Sterox ND.
The inhibitors of the present invention preferably contain from 2 to 15
parts by weight, more preferably 2 to 9, and most preferably 2 to 5,
particularly about 3, parts by weight of the dimerised unsaturated fatty
acid component per 1 part by weight of the alkoxylated alkyl phenol. The
inhibitor may be used, for example, in a concentration of up to 12 lbs per
1,000 barrels of hydrocarbon fluid, preferably from about 1 to 31/2 lbs
per 1,000 barrels, more preferably from about 11/2 to 3 lbs per 1,000
barrels. (Note: 3 lbs per 1,000 barrels is equivalent to 10 p.p.m.). It is
often convenient however to utilise the inhibitors in the form of a
concentrate solution in a diluent process oil. Such concentrates may
contain, for example, from 50 to 70% by weight of the inhibitor, based on
the total weight of the concentrate.
Accordingly the present invention also includes as a further aspect a
solution of the inhibitor in a hydrocarbon solvent, the inhibitor being
present in an at least corrosion-inhibiting amount, i.e. at least 1 lb per
1,000 barrels solvent. In yet another aspect of the present invention
there is provided a method of inhibiting corrosion in pipelines used for
the transportation of hydrocarbon fluids which method comprises injecting
into the liquid being transported a corrosion inhibiting amount of a
corrosion inhibitor in accordance with the invention.
The present invention will now be illustrated with reference to the
following Examples:
EXAMPLE 1
A concentrate was formed from the following ingredients in the stated
proportions by weight:
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Dimer Acid (Empol 1022)
45%
Sterox ND 15%
Process Oil 10%
Kerosene 30%
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The process oil used in the above concentrate was a 100 solvent Neutral
high V.I. (about 92) mineral oil having viscosities of about 22 and 4 cSt
at 100.degree. F. and 210.degree. F. respectively. The kerosene was a
distillate of final boiling point 257.degree. C. and Specific Gravity at
60.degree. F. of about 0.78.
The concentrate was subjected to duplicate Rust Tests according to the
MIL-I-25017c specification at a concentration of 3 lb/thousand barrels and
passed in each case.
The concentrate was also tested for water separability characteristics in
various commercially available fuels at a concentration of 12 lbs per
1,000 barrels (i.e. 40 p.p.m. of concentrate, equivalent to 24 p.p.m. of
inhibitor), with the following results:
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Fuel WSIM No
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85% Bayol R-34 86/76/82*
Clay percolated Jet A
96/91*
Chevron Jet A50 83
Shell Odorless Kerosene
(Distillate boiling range:
205-259.degree. C. 80
Specific Gravity at
60.degree. F. : 0.818)
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*Results obtained in duplicate tests.
To demonstrate the effect of varying the alkoxylated alkyl phenol and ratio
of dimer acid to alkoxylated alkyl phenol, further concentrates were
prepared and subjected to rust and water separability tests in a similar
manner to Example 1, salient details of the concentrates tested and of the
results obtained being summarised in Table 1. In Table 1, it should be
noted that example numbers have been allocated only to concentrates in
accordance with the claimed invention, concentrates not allocated a number
having been included for comparison purposes only.
TABLE 1
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Mil-I-25017c Rust-Test and WSIM Results
Ethoxylated Alkyl Phenol Rust Test.sup.(B)
Concentra-
Ratio DA.sup.(A) to
tion of
Example
Alkyl sub-
No. of ethoxy
ethoxylated
Concentration
ethoxylated WSIM.sup.(C)
No. stituent
groups alkyl phenol
of DA.sup.(A) (ppm)
alkyl phenol
Result
No.
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-- -- -- nil nil 1 Fail
100.sup.(D)
-- -- -- 4.5 nil 2 Fails
-- -- -- 6.0 nil 3 Fails
81
nonyl 4 -- nil 20 1 Fail
2 nonyl 4 23:1 5.75 0.25 1 Pass
3 nonyl 4 11:1 5.5 0.5 3 Passes
89
1 Fail
4 nonyl 4 3:1 4.5 1.5 7 Passes
85
1 Fail
5 nonyl 4 2:1 4.0 2.0 3 Passes
2 Fails
nonyl 4 1.45:1 5.8 4.0 1 Fail
nonyl 4 1:1 5.0 5.0 1 Fail
nonyl 4 0.5:1 4.7 9.4 1 Fail
6 tributyl
4 3:1 4.5 1.5 1 Pass
75
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.sup.(A) Dimer acid Empol 1022
.sup.(B) Kerosene of final boiling point 257.degree. C. and Specific
Gravity at 60.degree. F. of 0.78 used as solvent.
.sup.(C) At concentration of 24ppm inhibitor in Shell Odorless Kerosene o
distillate range 205-259.degree. C. and specific gravity at 60.degree. F.
of 0.818, as Reference Base Fluid.
.sup.(D) Pure Reference Base Fluid.
From the rust test results in Table 1, it is observed that dimer acid alone
and alkoxylated alkyl phenol alone were ineffective and that a ratio of
dimer acid to alkoxylated alkyl phenol of less than 1.8:1 was also
ineffective.
To allow further comparison with previously known corrosion inhibitors in
respect of water separability characteristics, WSIM values were also
determined (at a concentration of 24 p.p.m. inhibitor) for concentrates
containing various corrosion inhibitor combinations described in U.S. Pat.
No. 3,696,048, the following results being obtained:
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1:1 salt of Duomeen T*
Empol 1022 45 parts
and Sterox ND 15 parts WSIM
kerosene+ 40 parts No 22
Monododecylamine salt of
Empol 1022 45 parts
Sterox ND 15 parts WSIM
kerosene+ 40 parts No 46
Basic Duomeen O* salt of
Empol 1022 45 parts
Sterox ND 15 parts WSIM
kerosene+ 40 parts No 16
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*Duomeens are a commercially available range of diamines.
+Shell Odorless Kerosene of distillate range 205-259.degree. C. and
specific gravity at 60.degree. F. of 0.818.
It is observed that the corrosion inhibitors of the present invention
provide significantly improved WSIM numbers as compared with the materials
described in U.S. Pat. No. 3,696,048.
* * * * *
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