U.S. patent application number 13/059375 was filed with the patent office on 2011-06-30 for fatty ester compositions with improved oxidative stability.
This patent application is currently assigned to TAMINCO. Invention is credited to Daniel Alford, Conor M. Dowling, Michael D. Gernon, Nicholas M. Martyak.
Application Number | 20110154724 13/059375 |
Document ID | / |
Family ID | 41319631 |
Filed Date | 2011-06-30 |
United States Patent
Application |
20110154724 |
Kind Code |
A1 |
Martyak; Nicholas M. ; et
al. |
June 30, 2011 |
FATTY ESTER COMPOSITIONS WITH IMPROVED OXIDATIVE STABILITY
Abstract
Compositions containing unsaturated fatty esters may be
stabilized against atmospheric oxidation by the addition of an
antioxidant package containing at least one nitroxide free-radical
scavenger and at least one alkylalkanolamine. Compositions treated
in this manner show good resistance to atmospheric oxidation and
resultant viscosity increase. An advantage of the nitroxide
free-radical scavenger is that it stops the oxidation of the
unsaturated fatty esters already during the initiation stage.
Moreover, it is much less volatile than for example the known
alkylhydroxylamine oxygen scavengers. By the use of a nitroxide
free-radical scavenger, the composition can thus be stabilized for
a longer period of time. The stability period is moreover less
affected by the supply of oxygen to the composition. The solubility
problem of the nitroxide in the fatty ester component can be solved
by dissolving the nitroxide first in the alkylalkanolamine.
Inventors: |
Martyak; Nicholas M.;
(Doylestown, PA) ; Alford; Daniel; (King of
Prussia, PA) ; Dowling; Conor M.; (Ambler, PA)
; Gernon; Michael D.; (Phoenixville, PA) |
Assignee: |
TAMINCO
Gent
BE
|
Family ID: |
41319631 |
Appl. No.: |
13/059375 |
Filed: |
August 28, 2009 |
PCT Filed: |
August 28, 2009 |
PCT NO: |
PCT/EP2009/061136 |
371 Date: |
March 17, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61092617 |
Aug 28, 2008 |
|
|
|
Current U.S.
Class: |
44/307 ; 44/349;
44/350; 44/384; 44/388 |
Current CPC
Class: |
C10L 1/19 20130101; C10L
1/23 20130101; C10L 1/232 20130101; C10L 1/14 20130101; C10L 1/22
20130101; C10L 1/2425 20130101; C10L 1/2412 20130101; C11B 5/005
20130101; C10L 1/2225 20130101 |
Class at
Publication: |
44/307 ; 44/349;
44/350; 44/384; 44/388 |
International
Class: |
C10L 1/00 20060101
C10L001/00; C10L 1/232 20060101 C10L001/232; C10L 1/22 20060101
C10L001/22; C10L 1/18 20060101 C10L001/18 |
Claims
1. A composition comprising: a fatty ester component constituting
at least 50 wt % of the composition and comprising unsaturated
fatty esters; and at least one alkylalkanolamine, characterised in
that the composition further comprises at least one nitroxide
free-radical scavenger or a precursor thereof.
2. The composition as claimed in claim 1, which comprises at least
one alkylalkanolamine selected from the group consisting of
N-alkylalkanolamines, N-alkyldialkanolamines and
N-dialkylalkanolamines.
3. The composition as claimed in claim 2, wherein said
alkylalkanolamine has the formula (II):
R.sup.1R.sup.2NCH.sub.2CH.sub.2OH wherein R.sup.1 is an alkyl group
or an isoalkyl group of 3 to 24 carbon atoms and R.sup.2 is --H,
--CH.sub.2, --CH.sub.2CH.sub.2OH or --R.sup.1.
4. The composition as claimed in claim 2, wherein said
alkylalkanolamine is selected from the group comprising
butyldiethanolamine (BDEA), butylaminoethanol (BAE),
dibutylaminoethanol (DBAE), diisopropylaminoethanol (DIPAE),
octylaminoethanol (OAE) and octyldiethanolamine (ODEA).
5. The composition as claimed in claim 1, wherein the nitroxide
free-radical scavenger has the formula (I): ##STR00004## wherein
each of R.sub.1, R.sub.2 and R.sub.3 and R.sub.4 is an alkyl group
or heteroatom substituted alkyl group having 1 to 15 carbon atoms,
and wherein R.sub.5 and R.sub.6 (a) each being an alkyl group
having 1 to 15 carbon atoms, or a substituted alkyl group having 1
to 15 carbon atoms wherein the substituent is halogen, cyano,
--CONH.sub.2, --SC.sub.6H.sub.5, --S--COCH.sub.3, --OCOCH.sub.3,
--OCOC.sub.2H.sub.5, carbonyl, alkenyl wherein the double bond is
not conjugated with the nitroxide moiety, or --COOR wherein R of
the --COOR group is alkyl or aryl, or (b) together forming part of
a ring that contains 4 or 5 carbon atoms and up to two heteratoms
of O, N or S.
6. The composition as claimed in claim 5, wherein the R.sub.1,
R.sub.2, R.sub.3 and R.sub.4 groups in formula (I) are each methyl,
ethyl or propyl groups.
7. The composition as claimed in claim 5, wherein R.sub.5 and
R.sub.6 in formula (I) are each methyl, ethyl or propyl groups.
8. The composition as claimed in claim 1, wherein the nitroxide is
a piperidino-1-oxyl, a pyrrolidino-1-oxyl or a pyrrolin-1-oxyl.
9. The composition as claimed in claim 8, wherein the nitroxide is
selected from the group consisting of
4-hydroxy-2,2,6,6-tetramethylpiperidino-1-oxy (4-hydroxy TEMPO),
4-oxo-2,2,6,6-tetramethylpiperidino-1-oxy and
2,2,6,6-tetramethylpiperidino-1-oxy (TEMPO), the nitroxide
comprising preferably
4-hydroxy-2,2,6,6-tetramethylpiperidino-1-oxy.
10. The composition as claimed in claim 1, wherein the nitroxide is
di-tert-butyl-nitroxide.
11. The composition as claimed in claim 1, which contains at least
1 ppm, preferably at least 5 ppm and more preferably at least 10
ppm of said nitroxide.
12. The composition as claimed in claim 1, which contains less than
200 ppm, preferably less than 100 ppm and more preferably less than
50 ppm of said nitroxide.
13. The composition as claimed in claim 1, which contains at least
50 ppm, preferably at least 100 ppm and more preferably at least
200 ppm of said alkylalkanolamine, but preferably less than 10 000
ppm thereof.
14. The composition as claimed in claim 1, wherein the fatty ester
component comprises a biodiesel.
15. The composition as claimed in 4, wherein the fatty ester
component contains at least 10 wt %, preferably at least 25 wt %
and more preferably at least 40 wt % of said unsaturated fatty
esters.
16. A method of making a stabilized composition as claimed in claim
1, comprising blending together: a fatty ester component comprising
an unsaturated fatty ester; at least one alkylalkanolamine; and a
nitroxide free-radical scavenger or precursor thereof.
17. The method as claimed in claim 16, wherein said nitroxide
free-radical scavenger is dissolved in said alkylalkanolamine
before being blended with said fatty ester component.
18. The method as claimed in claim 16, wherein said nitroxide
free-radical scavenger is dissolved in a hydroxylamine, or in a
mixture of a hydroxylamine and said alkylalkanolamine, before being
blended with said fatty ester component.
Description
[0001] The invention relates to fatty ester compositions. More
particularly, it relates to fatty ester compositions that contain
at least 50 wt % of a fatty ester component which comprises an
unsaturated fatty ester and that contain moreover additives,
including at least one alkylalkanolamine, that reduce their
oxidative degradation.
BACKGROUND OF THE INVENTION
[0002] Fatty esters are widely used commercially in a variety of
applications. Commonly used esters include natural fats and oils,
especially triglyceride oils. Well known examples include soybean
oil, rapeseed oil, jathropa oil, palm oil, canola oil, olive oil,
linseed oil, and tung oil.
[0003] Another important type of fatty ester is biodiesel, a
clean-burning alternative fuel produced from domestic, renewable
resources. Biodiesel contains no petroleum, but it can be blended
at any level with petroleum diesel to create a fuel blend. It can
be used in compression-ignition (diesel) engines with little or no
modification. Biodiesel is biodegradable, essentially nontoxic, and
essentially free of sulfur and aromatic compounds, and thus can
provide certain environmental advantages. Biodiesel is more
particularly an alkyl ester fuel that meets the specifications of
ASTM D 6751, which is incorporated herein by reference.
[0004] Biodiesel is essentially a mixture of methyl, ethyl, and/or
isopropyl esters of fatty acids, made through transesterification
of fatty acid triglycerides (oils) with the respective alcohols.
The most commonly used raw material oils are seed oils such as
soybean oil, palm oil, and rapeseed oil.
[0005] These and many naturally occurring fats and oils contain a
component, sometimes a major one, of unsaturated fatty acids
(mainly in the form of esters). These include such acids as oleic,
linoleic, linolenic, and others bearing one or more olefinic
moieties. Accordingly, biodiesel fuels made from these oils also
typically contain unsaturated acids and/or esters thereof. In both
natural oils and biodiesel, the unsaturation makes the materials
susceptible to oxidation by atmospheric oxygen and perhaps other
oxidants. Such oxidation, for example during processing or storage,
may result in an increase in rancidity, viscosity and/or pour point
temperature, which in many cases is undesirable. Therefore, ways of
reducing or eliminating oxidative degradation of fatty esters are
sought in the various industries in which these materials are
used.
[0006] WO 2007/146567 discloses an alkyl ester fuel, in particular
a biodiesel, the oxidative stability of which is improved by adding
a combination of an alkylalkanolamine and an alkylhydroxylamine.
Both additives, and the combination thereof, were found to increase
the oxidative stability. In the examples relatively high amounts of
both additives were used, namely 500 ppm of DEHA
(diethylhydroxylamine) and 1000 ppm of ODEA
(octydiethanolamine).
[0007] In the fatty ester compositions disclosed in US
2007/0137098, use is also made of an alkylhydroxylamine (in
particular DEHA) to improve the oxidative stability thereof. The
alkylhydroxylamine is more particularly used in combination with a
phenolic antioxidant. This combination appeared to have synergetic
effects on the oxidative stability of the fatty ester composition.
The phenolic antioxidant is in particular a hydroquinone which is
commonly used in biodiesel compositions. In the examples, the
hydroquinone (phenolic antioxidant), which is a quite expensive
additive, was used in relatively small amounts of 5 to 100 ppm.
Notwithstanding the observed synergetic effects, the DEHA
(alkylhydroxylamine) was however still to be used in quite high
amounts of 10 000 to 40 000 ppm.
[0008] The oxidative stability of biodiesel is an important
property thereof and is subjected to criteria which may differ from
country to country. In the US, oxidative testing of biodiesel is
done according to ASTM 6751-08 whereby the B100 (100% biodiesel)
must pass a minimum of three hours oxidative stability as done by
the Rancimat test. The European oxidation criteria is a minimum of
six hours as per EN 14112. Some commercial biodiesel manufacturers
and blenders require even eight hours oxidative stability to ensure
that B100 biodiesel stored for prolonged periods of time will be
suitable for commerce.
[0009] A problem with the biodiesel compositions disclosed in WO
2007/146567 and in US 2007/0137098 is that their long term
oxidative stability depends to a large extent on the conditions
wherein the biodiesel is handled and stored. The antioxidants used
therein are indeed oxygen scavengers which decompose or are
converted to their oxidized form by reaction with oxygen. They
react with the oxygen dissolved in the biodiesel and, when they are
rather volatile like DEHA, they may even react with the oxygen
present in the headspace above the biodiesel. When the storage tank
is kept closed, the biodiesel can be stored for a long period of
time. However, with continued ingress of oxygen into the biodiesel
(from opening and closing the storage tank), the antioxidants can
be quickly consumed.
[0010] An object of the present invention is therefore to provide a
new fatty ester composition, which comprises at least one
alkylalkanolamine and the oxidative stability of which is less
dependent on the amount of oxygen which comes into contact with the
composition.
SUMMARY OF THE INVENTION
[0011] To this end, the composition according to the invention
further comprises at least one nitroxide free-radical scavenger or
a precursor thereof.
[0012] Oxidation of the fatty ester component follows three steps:
initiation, propagation and termination. During the initiation
step, free radicals are produced by reaction with initiator
molecules. These free radicals can then react with dissolved oxygen
producing peroxide molecules and subsequently new free radicals.
Continuation of this propagation stage is a chain reaction
resulting in numerous hydroperoxides and fatty ester radicals
leading to accelerated oxidative instability until the dissolved
oxygen is consumed. The advantage of the nitroxide free-radical
scavenger used in the composition of the present invention is that
it stops the oxidation process already during the initiation stage
so that smaller amounts thereof are required and so that the
consumption of this free radical scavenger is not, or at least much
less, affected by the amount of oxygen which is supplied to the
fatty ester composition.
[0013] During the oxidation of hydroxylamines as used in US
2007/0137098 and in WO 2007/146567, reactive free radicals may also
be formed, as an intermediary product, but these free radicals are
only formed during the propagation stage and are not stable and
react quickly away. The nitroxide free-radical scavengers used in
accordance with the present invention, are on the contrary stable
compounds which remain in the composition until they react with any
free radical produced during the initiation stage. An important
advantage of the nitroxide free-radical scavengers is further that,
in contrast to the alkylhydroxylamines used in the prior art, they
are also much less volatile so that they remain in the
composition.
[0014] In the composition according to the present invention, the
nitroxide free-radical scavenger is combined with an alkanolamine.
A first advantage of this combination is that the nitroxide can
easily be dissolved into the alkylalkanolamine whereas it is
difficult to be dissolved in the fatty ester component itself. A
further advantage of this combination is that the antioxidant
effects of the nitroxide are improved by the presence of the
alkylalkanolamine, i.e. this combination has a synergetic effect on
the oxidative stability of the composition.
[0015] The nitroxide free-radical scavenger has preferably the
formula (I):
##STR00001##
wherein each of R.sub.1, R.sub.2 and R.sub.3 and R.sub.4 is an
alkyl group or heteroatom substituted alkyl group having 1 to 15
carbon atoms, and wherein R.sub.5 and R.sub.6 (a) each being an
alkyl group having 1 to 15 carbon atoms, or a substituted alkyl
group having 1 to 15 carbon atoms wherein the substituent is
halogen, cyano, --CONH.sub.2, --SC.sub.6H.sub.5, --S--COCH.sub.3,
-OCOCH.sub.3, --OCOC.sub.2H.sub.5, carbonyl, alkenyl wherein the
double bond is not conjugated with the nitroxide moiety, or --COOR
wherein R of the --COOR group is alkyl or aryl, or (b) together
forming part of a ring that contains 4 or 5 carbon atoms and up to
two heteratoms of O, N or S.
[0016] In an advantageous embodiment of the composition according
to the invention, the nitroxide is selected from the group
consisting of 4-hydroxy-2,2,6,6-tetramethylpiperidino-1-oxy
(4-hydroxy TEMPO), 4-oxo-2,2,6,6-tetramethylpiperidino-1-oxy and
2,2,6,6-tetramethylpiperidino-1-oxy (TEMPO), the nitroxide
comprising preferably
4-hydroxy-2,2,6,6-tetramethylpiperidino-1-oxy.
[0017] In a further advantageous embodiment of the composition
according to the invention, it comprises at least one
alkylalkanolamine selected from the group consisting of
N-alkylalkanolamines, N-alkyldialkanolamines and
N-dialkylalkanolamines, the alkylalkanolamine having preferably the
formula (II):
R.sup.1R.sup.2NCH.sub.2CH.sub.2OH
wherein R.sup.1 is an alkyl group or an isoalkyl group of 3 to 24
carbon atoms and R.sup.2 is --H, --CH.sub.2, --CH.sub.2CH.sub.2OH
or --R.sup.1.
[0018] In still a further advantageous embodiment of the
composition according to the invention, it comprises at least one
hydroxylamine which has the formula (III):
R.sup.1R.sup.2NOH
wherein R.sup.1 and R.sup.2 are each independently hydrogen, a
linear or branched, saturated or unsaturated C1-C20 aliphatic
moiety, or a C6-C12 aryl moiety, a C7-C14 araliphatic moiety or a
C5-C7 cycloaliphatic moiety.
[0019] The composition according to the invention may comprises
other additives, in particular:
[0020] a) a nonphenolic oxygen scavenger or precursor thereof;
wherein the non-phenolic oxygen scavenger or precursor thereof
includes a hydroxylamine, an amine N-oxide, an oxime, a nitrone, or
a mixture of any of these,
[0021] b) a primary, secondary or tertiary un-substituted or
substituted amine, and
[0022] c) a phenolic oxygen scavenger or precursor thereof,
comprising for example an oxidized or reduced quinone, which
quinone may be substituted.
[0023] The present invention also relates to a method of making a
stabilized composition comprising blending together a fatty ester
component comprising an unsaturated fatty ester, at least one
nitroxide free-radical scavenger or a precursor thereof and at
least one alkylalkanolamine.
[0024] Advantageously, said nitroxide free-radical scavenger is
dissolved in said alkylalkanolamine or in a hydroxylamine or in a
mixture of a hydroxylamine with the alkylalkanolamine before being
blended with said fatty ester component.
[0025] The nitroxide free-radical scavengers described hereabove
dissolve only slowly in the fatty ester composition so that this
composition should be heated. It has been found that the nitroxide
free-radical scavenger can however be dissolved easily in the
alkylalkanolamine or in a hydroxylamine (or in a mixture thereof)
so that heating and subsequently cooling of the fatty ester
composition can be avoided.
DETAILED DESCRIPTION OF THE INVENTION
[0026] According to the invention, compositions comprising fatty
esters may be treated by the addition of an antioxidant package
that slows or prevents oxidative instability such as an increase in
rancidity as reflected in an increase in viscosity of the
composition and/or increases in the pour point temperature. The
composition includes at least the following:
[0027] a) a fatty ester component constituting at least 50 wt % of
the composition and comprising an unsaturated fatty ester;
[0028] b) at least one nitroxide free-radical scavenger or
precursor thereof; and
[0029] c) at least one alkylalkanolamine.
[0030] In other to further increase the oxidative stability of the
composition, it may additionally comprise:
[0031] d) a nonphenolic oxygen scavenger or precursor thereof;
wherein the non-phenolic oxygen scavenger or precursor thereof
includes a hydroxylamine, an amine N-oxide, an oxime, a nitrone, or
a mixture of any of these,
[0032] e) a phenolic oxygen scavenger or precursor thereof; wherein
the phenolic oxygen scavenger or precursor thereof includes a
reduced or oxidized quinone that may be substituted, and
[0033] f) a primary, secondary or tertiary un-substituted or
substituted amine.
[0034] Compositions to be treated with the antioxidant package
include those containing at least 50 wt % of a fatty ester
component comprising unsaturated fatty esters. Typically the fatty
ester component will constitute at least 80 wt % of the
composition, more typically at least 90 wt % and most typically at
least 95 wt %. The fatty ester may be natural or synthetic. Usually
the fatty ester component contains at least 10 wt %, in particular
at least 25 wt % and more particularly at least 40 wt % of
unsaturated fatty esters. Nonlimiting examples of natural esters
include soybean oil, japtropha oil, canola oil, corn oil, olive
oil, linseed oil, palm oil, rapeseed oil, safflower oil, sunflower
oil, algae and tung oil. In certain embodiments, the ester may be a
biodiesel, by which is meant a natural oil that has been
transesterified with a lower alcohol, typically methanol, ethanol,
and/or isopropanol. Biodiesel derived from any natural or synthetic
fat or oil is suitable for treatment according to the invention,
for example algae. The composition may also contain a petroleum
distillate, or it may be essentially free of distillates.
[0035] Petroleum distillates suitable for admixture with biodiesel
fuels for use according to the invention include any of a variety
of petroleum-based fuels, including but not limited to those
normally referred to as "diesel." Exemplary distillates may also
include gasoline, gas-oil, and bunker fuel. Petroleum middle
distillates will be used in many applications, and such middle
distillates include mineral oils boiling in a range from 120 to
450.degree. C. obtained by distillation of crude oil, for example
standard kerosene, low-sulfur kerosene, jet fuel, diesel and
heating oil such as No. 2 fuel oil. Exemplary distillates that may
be blended with biodiesel for treatment with an antioxidant package
of this invention are those which contain not more than 500 ppm, in
particular less than 200 ppm, of sulfur and in specific cases less
than 50 ppm of sulfur or even less than 5 ppm. Useful distillates,
especially middle distillates, are generally those which were
subjected to refinement under hydrogenating conditions and which
therefore contain only small amounts of polyaromatic and polar
compounds that impart natural lubricating activity to them.
Distillates that have 95% distillation points of less than
370.degree. C., in particular less than 350.degree. C., and in
special cases less than 330.degree. C., may also be used.
[0036] Biodiesel is susceptible to oxidative instability due to
unsaturation within the methyl esters. Oxidation of B100 follows
three steps: initiation, propagation and termination. During the
initiation or induction stage, a hydrogen atom is extracted from
the methyl ester backbone (by an initiator molecule, .I) producing
a free radical, R.. In the presence of oxygen, a diradical itself,
a radical peroxide molecule forms, ROO.. It is possible to form a
hydroperoxide molecule, ROOH, if another hydrogen atom is extracted
from an adjacent methyl ester again forming and additional methyl
ester radical. Continuation of this propagation stage results in
numerous hydroperoxides and methyl ester radicals leading to
accelerated oxidative instability. This will continue until the
dissolved oxygen is consumed. Termination follows with the
formation of a simple hydrocarbon, R--R:
[0037] 1. Initiation: RH+.I.fwdarw.R.+HI
[0038] 2. Propagation:
R.+O.sub.2.fwdarw.ROO.ROO.+RH.fwdarw.ROOH+R.
[0039] 3. Termination: R.+R..fwdarw.R--R
[0040] There are two types of technology that may be used to
increase oxidative stability of methyl esters, one focusing on Step
2 (use of antioxidants) and the other stopping Step 1 from
progressing to Step 2. The use of antioxidants, as disclosed for
example in US 2007/0137098 and WO 2007/146567, removes or lowers
the concentration of dissolved oxygen in the methyl esters thus
limiting propagation of hydroperoxide formation. With regard to US
2007/0137098 and WO 2007/146567, there are two issues to be
concerned with: a) the use of a volatile antioxidant such as
diethylhydroxylamine (DEHA) and b) the initiation step is allowed
to progress uncontrollably. A typical oxygen scavenger such as DEHA
will consume dissolved oxygen (DO). DEHA is oxidized in the process
going through a series of sequential steps and in the process DO is
reduced to water. The driving force for the decomposition of the
hydroxylamine to the nitrone is the reduction of dissolved oxygen
to water. The nitrone can then hydrolyze forming ethyhydroxylamine
and acetaldehyde. With continued ingress of oxygen into the
biodiesel (from opening and closing the storage tank), the DEHA and
any phenolic antioxidant is quickly consumed leading to accelerated
biodiesel instability. Even with the use of an oxygen scavenger,
Step 1, initiation, is allowed to progress resulting in a large
number of free methyl ester radicals, R.
[0041] As discussed in US 2007/0137098, it may be possible to use a
precursor molecule to an oxygen scavenger such as DEHA. For
example, triethylamine N-oxide (TEAO) decomposes slowly under
typical ambient conditions to form ethylene and
diethylhydroxylamine. This is viewed as an unwanted technology for
two reasons. Since diethylhydroxylamine is volatile and may
partition into the headspace of the storage vessel, it may be lost
from continued opening and closing of the storage vessel.
Replenishment of lost DEHA may come from excess TEAO. At some point
in time with continued opening and closing of the storage
container, all the TEAO will be converted to DEHA and eventually
the DEHA itself will be oxidized as discussed above. Also, as
mentioned, ethylene is a by-product of TEAO decomposition and as
such, its concentration may build is a closed storage container
possible leading to an unwanted, hazardous and explosive
condition.
[0042] To obviate these drawbacks, the compositions according to
the invention comprise at least one nitroxide free-radical
scavenger or precursor thereof. Moreover, they comprise at least
one alkylalkanolamine.
Nitroxide Free-Radical Scavenger
[0043] With the use of a stable nitroxide free-radical scavenger,
oxidative instability is slowed or halted in Step 1 vs. Step 2. A
nitroxide is already a free radical, R--O., and as soon as the
methyl ester radicals form in Step 1, they are capped or stabilized
by the nitroxide. The difference between using a hydroxylamine
which produces an intermediate nitroxide and a molecule such as
TEMPO is that the TEMPO is a stable nitroxide whereas the nitroxide
produced from DEHA decomposition is unstable. Also, DEHA may be too
volatile being rapidly lost from continued opening and closing of
the storage vessel. TEMPO or other nitroxides are not nearly as
volatile and therefore are not lost leading to a more stabilized
fuel.
[0044] The use of stable nitroxide such as TEMPO (or its
derivatives) thus results in a more stable biodiesel. It stops the
oxidative instability after Step 1 (initiation) rather than slowing
Step 2. By stopping decomposition at Step 1 using a stable
nitroxide, the biodiesel is more tolerant to oxygen (and light) so
the storage container may be opened and closed numerous times as
opposed to keeping it air tight.
[0045] The nitroxide free-radical scavenger is a stable free
radical having preferably the formula (I):
##STR00002##
wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are alkyl groups or
heteroatom substituted alkyl groups and no hydrogen is bound to the
remaining valences on the carbon atoms bound to the nitrogen.
[0046] The alkyl (or heteroatom substituted) groups R.sub.1-R.sub.4
may be the same or different, and preferably contain 1 to 15 carbon
atoms. Preferably R.sub.1-R.sub.4 are methyl, ethyl, or propyl
groups. In addition to hydrogen the heteroatom substituents may
include, halogen, oxygen, sulfur, nitrogen and the like.
[0047] The remaining valences (R.sub.5 and R.sub.6) in the formula
above may be satisfied by any atom or group except hydrogen which
can bond covalently to carbon, although some groups may reduce the
stabilizing power of the nitroxide structure and are undesirable.
Preferably R.sub.5 and R.sub.6 are halogen, cyano, --COOR wherein R
is alkyl or aryl, --CONH.sub.2, --S--C.sub.6H.sub.5,
--S--COCH.sub.3, --OCOC.sub.2H.sub.5, carbonyl, alkenyl where the
double bond is not conjugated with the nitroxide moiety or alkyl of
1 to 15 carbon atoms, R.sub.5 and R.sub.6 may also form a ring of 4
or 5 carbon atoms and up to two heteroatoms, such as O, N or S by
R.sub.5 and R.sub.6 together. Examples of suitable compounds having
the structure above and in which R.sub.5 and R.sub.6 form part of
the ring are pyrrolidin-1-oxys, piperidinyl-1-oxys, the morpholines
and piperazines. Particular examples wherein the R.sub.5 and
R.sub.6 above form part of a ring are
4-hydroxy-2,2,6,6-tetramethyl-piperidino-1-oxy (4-hydroxy TEMPO),
2,2,6,6-tetramethyl-piperidino-1-oxy (TEMPO),
4-oxo-2,2,6,6-tetramethyl-piperidino-1-oxy and pyrrolin-1-oxyl.
Suitable R.sub.5 and R.sub.6 groups are methyl, ethyl, and propyl
groups. A specific example of a suitable compound where
R.sub.1-R.sub.6 are alkyl groups is di-tert-butylnitroxide. The
preferred carbonyl containing nitroxides are those wherein the
R.sub.5 and R.sub.6 form a ring structure with the nitrogen,
preferably a six number ring, for example,
4-hydroxy-2,2,6,6-tetramethylpiperidino-1-oxy, which is the
preferred nitroxide for use in the present invention.
[0048] The composition contains preferably at least 1 ppm, more
preferably at least 5 ppm and most preferably at least 10 ppm of
said nitroxide or nitroxides. Advantageously, it contains less than
200 ppm, preferably less than 100 ppm and more preferably less than
50 ppm of said nitroxide or nitroxides.
Alkylalkanolamine
[0049] The fatty ester compositions of the present invention
contain at least one alkylalkanolamine. This alkylalkanolamine may
comprise at least one alkylalkanolamine selected from the group
consisting of N-alkylalkanolamines, N-alkyldialkanolamines and
N-dialkylalkanolamines. The alkylalkanolamine may thus have the
formula (II):
R.sup.1R.sup.2NCH.sub.2CH.sub.2OH
wherein R.sup.1 is an alkyl group or an isoalkyl group of 3 to 24
carbon atoms and R.sup.2 is --H, --CH.sub.2, --CH.sub.2CH.sub.2OH
or --R.sup.1.
[0050] The alkylalkanolamine is preferably selected from the group
comprising butyldiethanolamine (BDEA), butylaminoethanol (BAE),
dibutylaminoethanol (DBAE), diisopropylaminoethanol (DIPAE),
octylaminoethanol (OAE) and octyldiethanolamine (ODEA).
[0051] The composition contains preferably at least 50 ppm, more
preferably at least 100 ppm and most preferably at least 200 ppm of
said alkylalkanolamine or alkylalkanolamines. The total
alkylalkanolamine content is however preferably less than 10 000
ppm.
[0052] An important advantage of the use of an alkylalkanolamine is
that it cannot only be used to improve the oxidative stability of
the composition, but also to assist in dissolving the nitroxide
free-radical scavenger. This nitroxide is soluble in the fatty
ester composition but doesn't dissolve easily therein. It takes
indeed a long time to dissolve the nitroxide therein or the fatty
ester composition has first to be heated. It has however now been
found that the nitroxide dissolves easily in the alkylalkanolamine
so that it can first dissolved therein and the obtained solution
can then be added easily to the fatty ester component. The
nitroxide remains dissolved therein and no heating of the fatty
ester component is required.
[0053] The composition may, aside from the nitroxide and the
alkylalkanolamine, consist essentially of the biodiesel (and
optionally the petroleum distillates), or it may also contain other
optional additives such as those detailed below. It should be noted
that certain additives, when included in the compositions of this
invention, may have a substantial effect on important properties of
the treated composition. The effects of such changes may or may not
be desirable in a given situation, and therefore some embodiments
of the invention preclude the use of certain additives in an amount
that materially affects one or more of these properties. Examples
of such additives whose presence (in high enough amounts) may be
precluded include compounds known to accelerate atmospheric
oxidation of unsaturated fatty acids and their esters, including
for example cobalt and manganese driers such as are used for curing
alkyds and drying oils. Generally, oxidizing agents should be
avoided. Such materials might include hydrogen peroxide or organic
peroxides.
[0054] As distinct from the foregoing list of additives, certain
other additives may typically be included in the treated
composition in an amount sufficient to achieve certain performance
advantages. In the case where the composition comprises a
biodiesel, conventional diesel additives may be included. For
example, surfactants may be included to help reduce the build-up of
deposits. Other ingredients might also include octane boosters,
cetane enhancers, pour point or cloud point depressants, and
explosion suppressors (e.g., tetraethyllead), and fatty acids for
use as friction modifiers. Water may also be present in the treated
fuel. If present, water may in some embodiments be included in only
small amounts, i.e., at less than 2 wt % or even less than 0.5 wt
%, most typically less than 500 ppm, as measured by ASTM 6751. It
may however be present in larger amounts, for example from 2 to 25
wt % based on the total weight of the resulting mixture, more
commonly 10 to 15 wt %, in the form of a solution, stabilized
emulsion, or other dispersion.
[0055] The following optional additives may be used to further
enhance the oxidative stability of the composition:
Nonphenolic Oxygen Scavenger
[0056] The nonphenolic oxygen scavenger may be a hydroxylamine. As
explained hereabove, hydroxylamines are oxygen scavengers which can
assist in improving the oxidative stability of the fatty ester
composition.
[0057] Nonlimiting examples of suitable hydroxylamines are
according to the formula R.sup.1R.sup.2NOH, wherein R.sup.1 and
R.sup.2 are each independently hydrogen, a linear or branched,
saturated or unsaturated C1-C20 aliphatic moiety, which can
optionally be mono- or polysubstituted, or a C6-C12 aryl moiety, a
C7-C14 araliphatic moiety or a C5-C7 cycloaliphatic moiety.
Representative hydroxylamines include but are not limited to:
hydroxylamine, methylhydroxylamine, dimethylhydroxylamine,
methylethylhydroxylamine, ethylhydroxylamine, diethylhydroxylamine
(DEHA), dibutylhydroxylamine, dibenzylhydroxylamine,
monoisopropylhydroxylamine and mixtures thereof.
[0058] The composition contains preferably at least 50 ppm, more
preferably at least 100 ppm and most preferably at least 200 ppm of
said hydroxylamine or hydroxylamines. The total hydroxylamine
content is however preferably less than 10 000 ppm.
[0059] In the same way as the alkylalkanolamine, the hydroxylamine
can also be used to dissolve the nitroxide free-radical scavenger
into the fatty ester component. It has indeed been found that the
nitroxide dissolves easily in the hydroxylamine so that it can
first be dissolved therein and the obtained solution can then be
added easily to the fatty ester component. The nitroxide remains
dissolved therein and no heating of the fatty ester component is
required. Instead of dissolving the nitroxide into the
alkylalkanolamine or into the hydroxylamine, it can also be
dissolved in a mixture thereof.
[0060] Another class of suitable nonphenolic oxygen scavengers
comprises oximes derived from aldehydes or ketones. Examples
include 2-butanone oxime, acetone oxime, cyclohexanone oxime,
benzoin oxime, propanal oxime, butanal oxime, and isobutanal
oxime.
[0061] Nitrones are also suitable for use as nonphenolic oxygen
scavengers. Any nitrone may be used. Suitable classes of nitrones
may be described according to the formula
##STR00003##
wherein R.sub.1 and R.sub.2 may be the same or different and are
each selected from the group consisting of hydrogen and hydrocarbon
radicals having between one and ten carbon atoms. R.sub.3 is a
hydrocarbon radical having between one and ten carbon atoms.
R.sub.1, R.sub.2, and R.sub.3 may all be selected from alkyl groups
(saturated or unsaturated), cycloalkyl groups, aryl groups, or
aralkyl groups. Examples of suitable alkyl groups include methyl,
ethyl, n-propyl, isopropyl, n-butyl, n-pentyl, n-hexyl, n-heptyl,
n-octyl, n-nonyl, n-decyl, and the various n-hexenyl, n-heptenyl,
n-octenyl, n-nonenyl and n-decenyl radicals. Examples of
cycloalkyl, aryl, and aralkyl groups, respectively, include
cyclohexyl, phenyl, and tolyl radicals. Typically the hydrocarbon
radicals are groups having from one to seven carbons. Specific
examples of suitable nitrones include formaldehyde
isopropylnitrone; formaldehyde ethylnitrone, formaldehyde
methylnitrone, acetaldehyde isopropylnitrone, acetaldehyde
propylnitrone, acetaldehyde ethylnitrone, acetaldehyde
methylnitrone, acetone isopropylnitrone, acetone propylnitrone,
acetone ethylnitrone, acetone methylnitrone, acetone
n-butylnitrone, acetone benzylnitrone, formaldehyde n-hexylnitrone,
methyl ethyl ketone ethylnitrone, formaldehyde cyclohexylnitrone,
isobutyraldehyde isopropylnitrone, isobutyraldehyde ethylnitrone,
n-butyraldehyde isoproylnitrone, n-butyraldehyde ethylnitrone, and
n-butyraldehyde propylnitrone.
[0062] In some embodiments, the oxygen scavenger comprises a
compound having a vapor pressure greater than 10 Torr at 25.degree.
C., preferably greater than 20 Torr, and more preferably greater
than 30 Torr. Diethylhydroxylamine is an example of such a
compound, having a vapor pressure of 32 Torr. The use of a
sufficiently volatile scavenger may improve the efficacy of the
antioxidant package by capturing oxygen in the headspace above the
composition, thereby preventing at least some of the oxygen from
reacting with unsaturated fatty esters. A drawback of such
antioxidants is however that they may be more quickly lost. The
nonphenolic oxygen scavenger (and/or precursor thereof) may be
incorporated in the treated composition in any amount. Typically,
it will be present in an amount equal to from 0.001 to 5 wt %
relative to the fatty ester component, more typically from 0.01 to
2 wt %, and most typically from 0.01 to 1 wt %.
[0063] Precursors To Non-Phenolic Oxygen Scavengers
[0064] Precursors to certain non-phenolic oxygen scavengers, for
example precursors to hydroxylamines, may be used in place of or in
addition to the non-phenolic oxygen scavengers themselves. As used
herein, the term "precursor" means a compound that liberates, or is
converted to, the desired compound in the composition in an amount
sufficient to provide resistance to oxidative degradation. In the
case of hydroxylamine, one type of precursor is a salt thereof with
an organic or inorganic acid. Such acids may include as nonlimiting
examples hydrochloric acid, sulfuric acid, sulfonic acids,
phosphonic acids, and carboxylic acids.
[0065] Another type of precursor for hydroxylamines is amine
N-oxides. For example, triethylamine N-oxide decomposes slowly
under typical ambient conditions to form ethylene and
diethylhydroxylamine. Any N-oxide is suitable for use. In some
applications, it is preferable that the N-oxide not act as a
surfactant, for example in cases where another surfactant package
is used or when no surfactant at all is desired. Some examples of
amine N-oxide types that show little surfactancy include those of
the formula R.sup.3R.sup.4R.sup.5N.fwdarw.O, in which R.sup.3,
R.sup.4, and R.sup.5 are each individually selected from C1-C8
linear or branched alkyl groups, provided that at least one of
R.sup.3, R.sup.4, and R.sup.5 has a primary, secondary, or tertiary
carbon atom at the 2 position relative to N, so that the group may
split out to form an olefin and thereby produce a
hydroxylamine.
Phenolic Antioxidant or Precursor
[0066] Suitable phenolic antioxidants may be selected from a wide
variety of materials known in the art. For example they may be
substituted or unsubstituted hydroquinones. Nonlimiting examples
include hydroquinones substituted in the ortho or meta positions
(or both) with moieties including but not limited to C-1 to C-6
alkyl or aryl moieties. Two suitable examples are
methylhydroquinone and tert-butylhydroquinone. In general, suitable
phenolic antioxidants include any known dihydroxybenzene or
aminohydroxybenzene compound or a lower alkyl, e.g., 1 to 8 carbon
atoms, substituted derivative thereof. Specific suitable compounds
include 2,4-diaminophenol; 5-methyl-o-aminophenol; o-aminophenol;
p-aminophenol; 3-methyl-p-aminophenol; 4,6-diamino-2-methylphenol;
p-methylaminophenol; m-aminophenol; p-(N-methylamino)phenol;
o-(N-butylamino)phenol; 3,4-dihydroxybenzaldehyde; and
2,5-dihydroxybenzaldehyde. Other examples include catechols and
substituted catechols, especially tertiary alkyl substituted ones.
Some specific examples are p-(tert-butyl)catechol,
p-(1,1-dimethylethyl)catechol, p-(1-ethyl-1-methyl hexyl)catechol,
p-(1,1-diethylpropyl)catechol, p-tributylmethylcatechol,
p-trihexylmethylcatechol, and p-(1,1-diethylethyl)catechol, etc.
Precursors of phenolic antioxidants include benzoquinone and
naphthoquinone, which may be converted to the corresponding
phenolic compounds by contact with a reducing agent such as the
nonphenolic oxygen scavenger. The phenolic antioxidant (and/or
precursor thereof) may be incorporated in the treated composition
in any amount. The effective amount of phenolic antioxidant may in
some cases be as low as 0.01 ppm by weight, relative to the fatty
ester component. Typically, it will be present in an amount equal
to from 1 to 500 ppm, more typically from 2 to 200 ppm, and most
typically from 4 to 100 ppm.
[0067] Treated compositions according to the invention generally
provide low rates of oxidative degradation, making them suitable
for use in a number of applications. They may for example be
particularly suitable as biodiesel fuels for use in cold climates,
where the negative effects of oxidative degradation are may be
particularly troublesome due to the resulting increase in pour
point temperature.
EXAMPLES
Example 1
Solubility Tests
[0068] a) An antioxidant package was prepared by dissolving 0.5
grams of 4-hydroxy TEMPO (4-HT) into 10 grams of octylaminoethanol
(OAE). The nitroxide was completely soluble in the
alkanolamine.
[0069] b) An antioxidant package was prepared by dissolving 0.5
grams of 4-HT along with 1 gram propyl gallate into 15 grams OAE.
The nitroxide and ester of gallic acid were completely soluble in
the alkanolamine.
[0070] c) An antioxidant package was prepared by dissolving 0.5
grams of 4-HT into 7.5 grams anhydrous diethylhydroxylamine (DEHA).
The nitroxide was completely soluble in the hydroxylamine.
[0071] d) An antioxidant package was prepared by dissolving 0.5
grams of 4-HT into 7.5 grams anhydrous DEHA. Additionally, 2 grams
of octyldiethanolamine (ODEA) was added to the additive mixture.
The nitroxide and amine was completely soluble in the
hydroxylamine.
Example 2
Combination of ODEA or BDEA and 4-Hydroxy TEMPO
[0072] Use was made in this example of a pure soy-biodiesel (methyl
ester of soy oil) from a commercial source having a Rancimat
oxidative stability (tested in accordance with EN 14112) of 5.1
hours.
[0073] a) Addition of 50 ppm 4-HT increased the oxidative stability
of this B100 biodiesel to 5.5 hours.
[0074] b) Addition of 450 ppm ODEA increased the oxidative
stability of this B100 biodiesel to 8.3 hours.
[0075] c) Addition of 450 ppm ODEA plus 50 ppm 4-HT increased the
oxidative stability test to 9.8 hours. Comparing Example 2a and
Example 2b to this Example, it is easy to see the synergy that
develops between ODEA and 4-HT.
[0076] d) Addition of 450 ppm BDEA to the soy methyl ester in
Example 2a increased the oxidative stability test to 6.1 hours.
[0077] e) Addition of 475 ppm BDEA plus 25 ppm 4-HT to the soy
methyl ester in Example 2a increased the oxidative stability test
to 9.4 hours. Comparing Example 2a and Example 2d to this Example,
it is easy to see the synergy that develops between BDEA and
4-HT.
[0078] f) Using a different sample of soy methyl ester, addition of
250 ppm BDEA resulted in an oxidation stability of only 3.5 hours.
Addition of 250 ppm BDEA+12.5 ppm 4-HT increased the oxidative
stability test to 6.0 hours
[0079] g) Using a different commercial sample of soy methyl ester,
the oxidative stability was only about 5.3 hours. Addition of 95
ppm ODEA+5 ppm 4-HT increased the oxidative stability test to 9.8
hours.
* * * * *