Note: Descriptions are shown in the official language in which they were submitted.
048906
MICROEMULSION DIESEL FUEL COMPOSITIONS AND METHOD OF
USE
FIELD OF THE INVENTION
The present invention relates to novel
microemulsion compositions which are transparent and
thermodynamically stable fluids useful in reducing
diesel exhaust emissions.
There is a wide variety of micro emulsion
fuel compositions known in the art. A disadvantage of
these has been a lack of stability under conditions to
which the fuels have been exposed. Prior compositions,
for example, have been unstable and have tended to
de-emulsify at high and at low temperatures; high
temperature de-emulsification has been a special
problem. Further, the addition of even very small
amounts of salt as by exposure to salt-containing air
or water has caused severe de-emulsification problems
in prior formulations that did not contain alcohols.
Another disadvantage of prior microemulsion fuel
compositions has been the high concentrations of
surfactants required to form the microemulsions. Prior
inventions, generally, employed one or more parts of
surfactant per part of solubilized water.
The microemulsions of the instant invention
seek to overcome the foregoing deficiencies by
providing improved temperature and salt stability and
employing lower concentrations of surfactants.
The present invention provides a translucent
and thermodynamically stable diesel fuel compositions
having improved combustion efficiency and reduced
smoke, particulate, CO, and NOx emissions. The diesel
fuel compositions comprise a diesel fuel, water or an
~o~89os
- 2 -
aqueous solution of a low molecular weight alcohol
and/or a water-soluble reagent, and a surfactant system
which comprises a balanced blend of one or more
hydrophilic surfactants and one or more lipophilic
surfactants, wherein the diesel fuel composition can
contain as high as 30 weight percent of aqueous phase
with an aqueous phase/surfactant ratio at least 2/1.
The present translucent and thermodynamically
stable microemulsion compositions of this invention
comprise a hydrocarbon fuel such as gasoline, jet fuel,
or preferably diesel fuel: about 1 to about 30 weight
percent, more preferably about 2 to about 20 weight
percent, and most preferably about 2 to about 15 weight
percent of an aqueous composition comprising water,
from 0 to 30 weight percent based on the amount of
water of a 1 to 3 carbon alkanol and less than 20
weight percent based on the amount of water of one or
more additives selected from the group consisting of
ashless inorganic oxidizing agents, low molecular
weight polar organic oxidizing agents, and nitrogen
oxide-containing compounds wherein the additive is
selected from the group consisting of: ammonium
nitrate, ammonium nitrite, hydrogen peroxide, ammonium
hypochlorite, ammonium chlorite, ammonium perchlorate,
ammonium chlorate, perchloric acid, chlorous acid,
hypochlorous acid, ammonium hypobromite, ammonium
bromate, hypobromous acid, bromic acid, ammonium
hypoiodite, ammonium periodate, hypoiodous acid, iodic
acid, periodic acid, 2,4 dinitrophenyl hydrazine, 2,5
dinitrophenol, 2,6 dinitrophenol, 2,4
dinitroresorcinol, nitroguanidine, 3 vitro-1,2,4-
triazole, 2 vitro imidazole, 4 vitro imidazole, pricric
acid, cumene hydroperoxide, cyanuric acid,
nitroglycerin, nitrobenzene, trinitrotoluene, and
mixtures thereof; and, about 0.5 to about 15 weight
percent, more preferably about 1 to about 10 weight
- 3 - X048900
percent and most preferably about 1 to about 5 weight
percent of a surfactant system which comprises a
balanced blend of one or more hydrophilic surfactants
and one or more lipophilic surfactants wherein the
ratio of aqueous composition/surfactant system is at
least 2/1.
It is well-known in the art that dispersions
of water and/or one or two carbon alkanols in diesel
fuel reduce harmful diesel emissions such as smoke,
soot, particulates, and NOx. It is also well-known
that debits associated with water and alkanols in
diesel fuels entail a severe reduction in cetane number
and a marked ignition delay often requiring engine
and/or operating parameter modification such as
advanced ignition timing or the installation of glow
plugs. The novel compositions of the instant invention,
by the incorporation into the aqueous composition of an
oxidizing and/or nitrogenous reagent, offset these
debits while still retaining the advantages in
emissions reduction.
In the practice of the present invention, at
least one hydrophilic surfactant and at least one
lipophilic surfactant are selected and their ratio
adjusted with respect to their combined hydrophilic and
lipophilic properties such that they form with the fuel
and the aqueous composition a single phase, translucent
microemulsion. The hydrophilic surfactants) is defined
by a set of operations wherein a blend of equal volumes
of fuel and aqueous composition with 2 grams of said
surfactant per deciliter of liquids forms a lower phase
microemulsion at 20°C such that the volume ratio of
fuel (oil) to surfactant (Vo/Vs) in the microemulsion
phase is at least 0.5, preferably greater than 1 and
more preferably greater than 2. The term "lower phase"
microemulsion is descriptive in context since it means
- 4 -
204906
that the aforementioned system consisting of the
hydrophilic surfactant and equal volumes of fuel and
aqueous composition separates into an aqueous lower
phase containing most of the surfactant in equilibrium
with an excess fuel (oil) phase which is essentially
surfactant-free.
The hydrophilic surfactant which is defined
by the above properties includes, but is not limited
to, the alkyl carboxylic and alkylaryl sulfonic acid
salts wherein the alkyl group is a Cg to C1g linear,
branched or bilinear structure, the aryl group is
selected from benzene, toluene, orthoxylene, and
naphthalene, and the salt is a salt of an alkali metal,
ammonia, or alkanol amine. Also included, and
preferred are the ethoxylated alkylphenols. Most
preferred are the ethoxylated. C12-C1g alkyl ammonium
salts of Cg-C24 alkyl carboxylic and alkylaryl sulfonic
acids containing 6 or more ethylene oxide (hereinafter
EO) groups, wherein the alkyl and aryl groups are as
previously defined above.
Representative examples of hydrophilic alkyl
carboxylic and alkylaryl sulfonic acid salts include
monoethanol ammonium laurate, ammonium palmitate,
diethanol ammonium stearate, monoethanol ammonium nonyl
o-xylene sulfonate, sodium dodecyl benzene sulfonate,
ammonium tetradecyl benzene sulfonate, diethanol
ammonium hexadecyl benzene sulfonate, and sodium
dodecyl naphthalene sulfonate. Preferred hydrophilic
carboxylic acid salts include monoethanol ammonium
oleate, penta-, deca-, and hexadeca-ethoxy octadecyl
ammonium oleate. Preferred hydrophilic sulfonic acid
salts include penta- and deca-ethoxy octadecyl ammonium
benzene sulfonate (designated C12BS-E18-5 and
C12BS-E18-10, respectively), heptaethoxy octadecyl
ammonium dodecyl o-xylene sulfonate (designated
~U~~9d~fp
C12XS-E18-7) and decaethoxy octadecyl ammonium dodecyl
ortho xylene sulfonate (designated C12XS-E18-10). The
ethoxylated alkyl amines used in preparing the
ethoxylated alkyl ammonium salts of alkyl aryl sulfonic
acids can be obtained from Exxon Chemical, Performance
Products, Tomah Products.
Representative hydrophilic ethoxylated alkyl
phenols include Igepal~ DM 710, Igepal~ DM 730, and
Igepal~ DM 880 available from GAF which are chemically
dinonyl phenols ethoxylated with 15, 24, and 49 moles
of EO, respectively. Preferred is Igepal~ DM 530 which
is dinonyl phenol ethoxylated with 9 moles of ethylene
oxide. Other suitable ethoxylated alkyl phenols
include Tritons~ X100, X102, and X114 available from
Rohm and Haas of Philadelphia, Pa., and Igepals CO 610,
630, 660, 710, 720, 730, 850, and 880 which are
chemically mono-octyl or nonyl phenols ethoxylated with
from 8 to 30 EO.
The lipophilic surfactant for purposes of
this invention is a surfactant having the properties of
providing at 2 g/dl concentration in equal volumes of
fuel and aqueous composition an upper phase
microemulsion at 20°C such that the volume ratio of
water to surfactant (Vw/Vs) in the microemulsion phase
is at least 0.5, preferably greater than 1 and most
preferably greater than 2. The term "upper phase"
microemulsion as used in defining the lipophilic
surfactant ingredient means that the system consisting
of the surfactant in equal volumes of fuel and aqueous
composition separates into a surfactant containing oil
upper phase in equilibrium with an excess aqueous phase
which is essentially surfactant free.
The lipophile having been defined by the
above properties includes, but is not limited to, the
- 6 - ~~4~~U6
ethoxylated alkyl phenols. Also included and preferred
are the alkyl and alkylaryl sulfonic acid salts wherein
the alkyl group is a C12 to C24 linear, branched, or
bilinear structure, the aryl group is selected from
benzene, toluene, orthoxylene, and naphthalene; and the
salt is a salt of an alkali metal, ammonia or alkanol
amine. More preferred are the ethoxylated C12-C18
alkyl ammonium salts of Cg-C24 alkyl carboxylic and
alkylaryl sulfonic acids containing less than six EO
groups, wherein the alkyl and aryl groups are as
previously defined above.
Representative examples of lipophilic alkyl
aryl sulfonates include monoethanol ammonium dodecyl
o-xylene sulfonate, sodium tetradecyl o-xylene
sulfonate, sodium hexadecyl o-xylene sulfonate,
diethanol ammonium pentadecyl o-xylene sulfonate,
triethanol ammonium octadecyl o-xylene sulfonate
(prepared from penta and hexa propylene), sodium
octapropylene benzene sulfonate, sodium tetracosyl
toluene sulfonate, and various high molecular weight
petroleum sulfonates. Preferred are the sodium and
monoethanol ammonium salts of dodecyl o-xylene sulfonic
acid. Most preferred are di-ethoxy octadecyl ammonium
oleate, di- and penta-ethoxy octadecyl ammonium dodecyl
o-xylene sulfonate (designated E18-2 oleate,
C12XS-E18-2 and C12XS-E18-5, respectively).
Representative lipophilic ethoxylated alkyl
phenols include Igepals CO 210 and CO 430 which are
nonyl phenols containing 1.5 and 4 moles of EO,
respectively, and Tritons~ X15 and X35 which are octyl
phenols containing 1 and 3 moles of EO, respectively.
The present invention is not confined to the
use of the aforementioned ethoxylated alkyl phenols but
_ ~ _ 2~489~06
includes other ethoxylated surfactants of the generic
formula:
R1X(CH2CH20)nY
wherein R1 is an alkyl or mono or di-alkyl aryl group
containing 8 to 30 carbon atoms,
H Rp RZ 0 0 0
X is -0-.-S-, -N-,-N-,[-N-]+C1-, -C-0-,-C-OR40-,-C-NH- or -S02NH-,
R3
and Y is -H-,-S03-M+ or-(P03H)-M+ wherein M+ is an
inorganic or ammonium cation including alkyl
substituted ammonium cations; R2 is an alkyl group
containing 1 to 20 carbon atoms or a polyethoxy ether
group containing from 1 to 30 (CH2CH20) groups; R3 is H
or an alkyl group containing 1 to 3 carbon atoms; R4 is
a polyhydroxy group derived from glycerol, glycols,
sorbitol, or various sugars; and n is an integer of
from 1 to 30.
The above ethoxylated alkyl phenols may be
blended with an alkali metal, ammonium, alkyl ammonium,
alkanol ammonium, or ethoxylated alkyl ammonium salt of
an alkyl or alkyl aryl sulfonic acid of the generic
formula:
R-S03H
wherein R is an alkyl or alkyl benzene group containing
8 to 30 carbon atoms in the giilkyl chain and the benzene
ring may be additionally substituted with one or two
alkyl groups containing 1 to 3 carbon atoms each to
provide the balanced blend of surfactants. Preferred
- 8 - ~U~48~~G
blends of ethoxylated alkyl phenols with alkyl aryl
sulfonates include combinations of Igepal~ CM 530 or
Igepal~ DM 710 with the sodium or monoethanol amine
salt of C12 o-xylene sulfonic acid.
Alternatively, ethoxylated alkyl ammonium
salts of the above alkylaryl sulfonic acids containing
varying degrees of ethoxylated are blended to provide
the balanced blend of surfactants. Preferred blends of
ethoxylated alkyl ammonium salts of alkylaryl sulfonic
acids include penta-ethoxy octadecyl ammonium dodecyl
benzene sulfonate combined with hepta-ethoxy octadecyl
ammonium dodecyl benzene sulfonate and di-ethoxy cocoa
ammonium dodecyl o-xylene sulfonate with deco-ethoxy
octadecyl ammonium dodecyl oxylene sulfonate. Most
preferred is the blend of penta-ethoxy octadecyl
ammonium dodecyl o-xylene sulfonate with hepta or
deco-ethoxy octadecyl ammonium dodecyl o-xylene
sulfonate, i.e., a blend of C12XS-E18-5 with C12XS-
E18-10.
Alternatively, alkali metal, ammonium, alkyl
ammonium, alkanol ammonium or ethoxylated alkyl
ammonium salts of alkyl carboxylic acids of the generic
formula:
R'-COOH
wherein R' is an alkyl group of 12 to 20 carbon atoms
may be substituted for the sulfonic acid salts
described above. These salts may be blended with
ethoxylated alkyl phenols. Alternatively, ethoxylated
alkyl ammonium salts of the above alkyl carboxylic
acids containing varying degrees of ethoxylation are
blended together to provide the balanced blend of
surfactants. Most preferred is a blend of
penta-ethoxy octadecyl ammonium oleate with deco-ethoxy
- 9 _ ~0~~906
octadecyl ammonium oleate, i.e. a blend of E18-5 oleate
with E18-10 oleate.
Under certain circumstances, up to 20,
generally 2 to 10, weight percent of a cosurfactant is
included in the surfactant blend to improve the
solubility of the surfactant in the fuel and reduce the
viscosity of the microemulsion diesel fuel composition.
The cosurfactants are of the class of alkylene glycol
monoalkyl ethers, C4 to C6 alkanols and mixtures
thereof. Representative cosurfactants include ethers
such as ethylene glycol monopropyl ether, methylene
glycol monoethyl ether, ethylene glycol monomethyl
ether, ethylene glycol monobutyl ether, diethyl glycol
monomethyl ether, diethylene glycol monoethyl ether,
diethylene glycol n-butyl ether, propylene glycol
monomethyl ether, dipropylene glycol monomethyl ether
and tripropylene glycol monomethyl ether, and alkanols
which include straight and branched chain members such
as butanol and pentanol. Of the alkanols, tertiary
amyl alcohol (TAA) is preferred. Of the ethers,
ethylene glycol monobutyl ether is preferred.
It is understood that when using a
cosurfactant, the ratio of the surfactants may have to
be readjusted for changes in phase behavior brought
about by the addition of cosurfactant. It is also
understood that the weight ratio of hydrophilic to
lipophilic surfactants may have to be readjusted for
changes in phase behavior brought about by different
aqueous reagents and variations in their concentration.
For example, an increase in the concentration of the
aqueous reagent ammonium nitrate, requires an increase
in the ratio of hydrophilic to lipophilic surfactants.
Likewise changes in the composition of the fuel
necessitate readjustment of the surfactant ratio. For
example, a higher concentration of aromatics in the
- 1~ - ~~4806
fuel requires an increase in the ratio of hydrophilic
to lipophilic surfactants. It is also understood that
when a change in surfactant ratio is inadequate to
compensate for a given change in the fuel or aqueous
composition, choice of a more (or less) hydrophilic
surfactant pair (e.g. more (or less) ethoxylation) may
be required. These points will be made clear by the
examples cited below. The preferred surfactant blends
of the instant invention provide a marked improvement
over the art by solubilizing much more aqueous phase
per unit of surfactant than disclosed in the art. The
art discloses diesel fuel microemulsions containing
less than 2 volumes of water per volume of surfactant.
The examples cited below disclose compositions with
greater than 2 up to 4 volumes of aqueous phase per
volume of surfactant.
The most preferred surfactants for the
instant invention are selected from Group 1, having the
generic formula:
R1 (CH2CH20)mH
R3_R2_X_ +N
H
(CH2CH20)nH
where R1 and R3 are alkyl groups which may be
paraffinic or olefinic and may contain 8 to 24 carbon
atoms, R2 is a methyl group or a benzene, toluene, or
xylene ring, m + n = 2 to 20 and X- is -COO- or S03-.
Non-limiting representative examples of Group 1
surfactants are ethoxylated octadecyl ammonium dodecyl
benzene sulfonate (C12BS-E18-(n+m) where R1 = Ci8H3~,
R3 = C12H25. R2 = C6H4. and X- - S03-); ethoxylated
octadecyl ammonium dodecyl xylene sulfonate
- 11 - 2~~89~6
(C12XS-E18-(n+m) where Rl = C1gH37, R3 = C12H25. R2 -
(CH3)2CgH2, and X- - S03-) and ethoxylated octadecyl
ammonium oleate (E18-(n+m) oleate where R1 - C1gH37. R3
- R2 - CH3(CH2)7CH=CH(CH2)7- and X- - COO-).
Other most preferred surfactants are selected
from Group 2, having the generic formula:
R3-R2-X' +N(CH2CH20H)x
H(4-x)
where R3 and R2 are defined as in Group 1 and x = 3.
Non-limiting representative examples of Group 2
surfactants are monoethanol ammonium dodecyl benzene
sulfonate (C12BS-MEA), monoethanol ammonium dodecyl
xylene sulfonate (C12XS-MEA), diethanol ammonium
pentadecyl benzene sulfonate (C15XSDEA), ammonium
oleate and monoethanol ammonium oleate.
We have discovered that it is often
advantageous to blend a surfactants) from Group 1 with
a surfactants) from Group 2 to form the balanced blend
of hydrophilic and lipophilic surfactant(s). We have
discovered that surfactants from Group 1 become more
lipophilic with increasing temperature while those from
Group 2 become more hydrophilic with increasing
temperature. We have also discovered that blends of
surfactants from Group 1 with those from Group 2 form
microemulsions which are more stable to phase
separation over a broad temperature range than
microemulsions hitherto found in the art. This
reduction in temperature sensitivity is a highly
desirable feature of our most preferred diesel fuel
microemulsions. Diesel fuel, when stored over a period
of time, may be subjected to wide temperature
fluctuations. Conventional microemulsified diesel fuel
X048906
- 12 -
phase separates under these conditions while our most
preferred fuel microemulsion compositions remain
stable.
Example I
Preparation of Anionic-Ethoxy Cationic Complexes
One hundred grams of the alkyl carboxylic or
alkyl aryl sulfonic acid is weighed into a wide mouth
jar. An appropriate weight of the ethoxylated alkyl
amine, as listed in Table I, is added and stirred
vigorously while warm from the heat of neutralization.
Properties, neutralization weights, and chemical
suppliers are listed in Table I.
~o~~~oos
- 13 -
TABLE I
Preparation of Anionic-Ethoxy Cationic Complexes
Average wt.%
Component Mol. wt. Actives E a 100
Oleic acid 282 100 0.354
C128SH (Vista SA 326 -98 0.3361
597)
C12XSH (ESSAF SA 354 -81 0.2261
149)
C18N(EO)2 (Tomah 357 -98 0.275
E18-2)a
C18N(EO)5 (Tomah 489 -98 0.200
E18-5)b
C18N(EO)10 (Tomah 709 -98 0.138
E18-10)c
C18N(EO)15 (Tomah 929 -98 0.105
E18-15)d
MEA (mono ethanol 61 100 1.639
amine)
iJeiaht(al of Amine/100 a Acid
min CIyXSH Cy,~BSH Oleic Acid
MEA 13.8 20.5 21.6
E18-2 82.3 122.4 128.0
E18-5 112.8 167.7 176.6
E18-10 163.5 243.1 256.1
E18-15 214.2 318.5 335.6
1 By titration
2 Direct replacements:a) Akzo Ethomeen
18/12
b) Ethomeen 18/15
c) Ethomeen 18/20
d) Ethomeen 18/25
Example II
Microemulsion Preparation
Microemulsions were prepared as follows. The
surfactants were weighed into a 16 x 125 mm flat bottom
tube fitted with a teflon-lined cap. A total of 15 ml
- 14 -
~~4~~a6
of diesel fuel and water were added. The tubes were
shaken and heated -30 minutes to 1 hour at 60-70°C.
They were then tumbled overnight to 2 days on an
automated tumbler. Most systems, particularly those
made with the alkyl benzene sulfonates, did not clear
at room temperature after 2 days of tumbling. They
could be made to clear in most cases by temperature
cycling 2 or 3 times from 70°C to 0°C. On storage at
room temperature, clarity improved with age for the
systems containing the MEA soaps. Systems based solely
on the C12XS E18-n surfactants were found to be
extremely temperature sensitive and to deteriorate with
age. Often systems which were initially single phase
and clear, phase separated on storage at room
temperature. The assumed cause was laboratory
temperature fluctuations coupled with the extreme
temperature sensitivity of these systems. Because of
poor storage stability, blends of only C12XS E18-n
surfactants were eliminated early on from further
study. However, work with these surfactants did
demonstrate that clear microemulsions could be prepared
with 3 vol.% water and as little as 1 g/dl ('1%)
surfactant. Clear single phase systems containing 5%
water stabilized by 2 g/dl of the C12XS E18-n
surfactants were also prepared. Blends of these C12XS
E18-n surfactants with surfactants based on MEA (e. g.
C12BS-MEA or C12XS-MEA) gave good stability and are
described below.
Example III
Selecting and Balancing the
Hydrophilic and Lipophilic Surfactant Blend
A 2 gm/dl mixture of monoethanol ammonium
dodecyl benzene sulfonate (hereafter C12BS-MEA) with
equal volumes of Maraven diesel fuel (oil) and water
forms a lower phase microemulsion at 20°C. The volume
- 15 - ~U~8~~6
of oil solubilized per gm of surfactant (oil uptake) is
greater than the most preferred design criterion for a
hydrophilic surfactant of 2 ml oil/gm surfactant. A 2
gm/dl mixture of di-ethoxy octadecyl ammonium dodecyl
benzene sulfonate (hereafter C12BS E18-2) with equal
volumes of Maraven diesel fuel and water forms an upper
phase microemulsion at 20°C. The volume of water
solubilized per gm of surfactant (water uptake) is
greater than the most preferred design criterion for a
lipophilic surfactant of 2 ml water/gm surfactant.
The combination C12BS-MEA/C12BS E18-2
represents a hydrophile-lipophile surfactant couple and
their combined hydrophilic and lipophilic properties
are varied by adjusting the weight ratio of
C12BS-MEA/C12BS E18-2. Table II presents phase data
for the C12BS-MEA/C12BS E18-2 surfactant couple at
various water to Maraven oil ratios and total
surfactant concentrations. The data were generated as
follows. The surfactant concentration was fixed at,
for example, 2 g per deciliter of oil and water at a
water/oil ratio of 5/95. The weight fraction of
C12BS-MEA, the hydrophile in the surfactant couple was
then varied in the range between 0.45 and 0.60. The
type of microemulsion at each weight fraction of
C12BS-MEA was noted after equilibrium was reached. A
change in microemulsion type indicated the approximate
phase transition boundary between upper and single or
single and lower phase microemulsions. These
transition boundaries are noted in Table II. The
procedure was repeated at 1.5 and 1.0 g/dl surfactant
concentration and the approximate transition boundaries
determined. Note that the data was developed on a
series of individual equilibrated tubes, each
containing the specific ratio of surfactants at the
listed total surfactant concentration in water and oil
at a 5/95 volume ratio. The single phase region lies
- 16 - 20489~fi
between the upper and lower phase transition
boundaries. The point where these phase boundaries
coincide indicates the minimum surfactant concentration
which will solubilize 5% water in Maraven diesel fuel
in this case, it takes somewhat more than 1 g/dl of
surfactant to form a stable microemulsion. However,
the proximity to the phase transition boundaries
indicates that this will not be a clear system. In
general, the clearest systems are found farthest from
the transition boundaries, that is, in the center of
the single phase region. The closer the transition
boundaries, the hazier the systems located between
them. Thus, maximum clarity at a given water
concentration is attained at higher surfactant
concentrations.
Table II presents similar phase data for the
C12BS-MEA/C12BS E18-2 surfactants holding the water/oil
volume ratio fixed at 4/96. The single phase region
has broadened and at 2 g/dl surfactant extends between
0.47 and 0 59 wt. fraction of C12BS-MEA compared with a
range of 0.48 to 0.56 for the 5/95 water/oil system.
Again the clearest systems are found in the center of
the single phase region and since the 4/96 systems are
farther from the phase transition boundaries than are
the 5/95 systems, they are also clearer in comparison.
The 4/96 water/oil systems form single phase
microemulsions at surfactant concentrations somewhat
below 1 g/dl. Again, these microemulsions are turbid
because of their proximity to the phase transition
boundaries.
The data in Table II reinforce the conclusion
that higher surfactant/water ratios provide clearer
microemulsions. The single phase region at a surfactant
concentration of 2 g/dl for the 3/97 water/oil system
extends between 0.46 and 0.60 wt. fraction C12BS-MEA.
i7 - ~Q~~9~~~
Thus microemulsions in the center of this range are
even farther from the transition boundaries and,
therefore, clearer than those found with 5/95 or 4/96
water/oil systems. The 3/97 system forms single phase
microemulsions at surfactant concentrations above 0.75
g/dl. Comparison with the 5/95 and 4/96 water/oil
systems shows that for all these water/oil ratios, the
minimum surfactant concentration for single phase
microemulsions corresponds to a water/surfactant ratio
of -4/1.
The data in Table II illustrate the critical
nature of selecting and balancing the
hydrophile/lipophile surfactant blend for a given
amount of water and surfactant. The data indicate that
stable microemulsions can be prepared with up to 5%
water with less than 1.5% surfactant. An increase in
surfactant concentration permits a proportionate
increase in the amount of water solubilized. These
surfactants are more efficient than those found in the
previous art.
204906
TABLE II
C,~BS-MEA/C12BS E18-2 Combositions for Single Phase
W/O Vol. Surfactant Wt Fraction C12BS-MEA1 at the
Ratio Concn q/dl Upper Phase TB2 Lower Phase TB3
5/95 1.0 0.52 0.52
1.5 0.50 0.54
2.0 0.48 0.56
4/96 1.0 0.53 0.53
1.5 0.50 0.56
2.0 0.47 0.59
3/97 0.75 0.52 0.52
1.0 0.50 0.54
1.5 0.48 0.57
2.0 0.46 0.60
1) At the indicated total surfactant concentration
2) Upper phase transition boundary U -~ S
3) Lower phase transition boundary S i L
The C12XS-MEA/C12XS E18-5 system, though not
as extensively investigated as the C12BS-MEA/C12BS
E18-2 system described above, provides a similar phase
behavior pattern. In this case, the C12XS-MEA is the
hydrophile: its increasing weight fraction leads to
lower phase microemulsions. Phase data obtained for
three water/oil ratios at a surfactant concentration
fixed at 1.5 g/dl are given in the following table.
- 1g - x.048906
C,~XS-MEA/C12XS E18-5 Compositions for Single Phase
Wt. Fraction C~ ~XS-MEA1
W/O Vol. Ratio UTB2 LTB3
5.0/95.0 0.49 0.55
4.5/95.5 0.47 (estim.) 0.57
4.0/96.0 0.44 (estim.) 0.60
1 At a total surfactant concentration of 1.5 g/dl.
2 Upper phase transition boundary: a -~ s
3 Lower phase transition boundary: s -~ 1
As discussed previously, the single phase
region, which lies between the upper phase transition
(UTB) and the lower phase transition boundary (LTB),
broadens and clarity improves with decreased water/oil
ratio. The clarity of microemulsions in the center of
the single phase region is somewhat better than
observed with the C12BS-MEA/C12BS E18-2 system. In
addition, the rate of equilibration is faster with the
C12XS-MEA/C12XS E18-5 system; less temperature cycling
is required and clarity is obtained sooner on ambient
storage after temperature cycling.
Example IV
~i~croemulsion Preparation From Concentrates
In order to check whether other compositional
paths to the final microemulsion might speed
equilibration, we explored the use of concentrates as
intermediate compositions. These concentrates were
prepared by backing out oil and in some cases part of
the water from the final composition. For example, the
following concentrate was prepared:
X048906
- 20 -
Concentrate NB 14483-75A
C12XS-MEA 3.0
C12 E18-5 12.0 wt.%
Ck #90537 D.O. 25.0
Water 50.0
The surfactants were dissolved in diesel oil
at room temperature and the Water mixed in last. The
system forms a thin, clear gel at room temperature
which melts into a clear fluid on gentle warming. If
1.2 g of this concentrate is added to 14.1 ml of diesel
fuel, the resulting mixture is turbid and clears slowly
over a period of several hours to form a bright
microemulsion. If the diesel fuel is mixed in stages
with the concentrate over a period of several minutes,
the final system is a clear microemulsion. This shows
that equilibration rate depends on composition path as
well as temperature path. It also suggests that it
would be advantageous to predilute the above
concentrate with some added diesel oil. With this in
mind we prepared the following concentrate:
Concentrate NB 14483-76A
C12XS-MEA 10.4
C12XS E18-5 9.6 wt.%
Ck #90537 D.O. 40.0
Water 40.0
The surfactants were dissolved in the diesel
oil at room temperature and the water added last. The
mixture was turbid initially but slowly cleared with
mild warming (-40°C) and stirring over a period of
several hours to finally form a clear amber "solution."
This fluid concentrate when diluted by a factor of 10
instantly forms with little mixing a bright
- 21 - ~~48996
microemulsion containing 2 wt.% surfactant and 4%
water. This microemulsion remains clear over the
temperature range of -10°C (lower cloud point) to >70°C
(upper cloud point) and is indefinitely stable at room
temperature. It is not known at this time whether the
turbidity below -10°C is due to phase separation in the
microemulsion or wax precipitation from the diesel
fuel.
The above concentrates have a water/
surfactant volume ratio of 2/1. In an attempt to raise
the water/surfactant ratio, the following concentrate
was prepared:
Concentrate NB 14483-78B ,
G12XS-MEA 5. 78 wt. %
G12XS E18-5 5.33
Ck X90537 D.O. 55.56
Water 33.33
The water/surfactant ratio in this package is 3/1. No
attempt was made to optimize the surfactant H/L ratio
for the added water. Clarity was achieved by adjusting
the oil/water ratio in the package. A quantity, 1.89 g
of this concentrate when diluted with 8.2 g of diesel
oil instantly forms a clear microemulsion containing 2%
surfactant and 6% water. This microemulsion is not
quite as bright as the microemulsion prepared with
concentrate NB 1448376A due to the higher water
content. Brightness may be improved with optimization
of surfactant H/L ratio. This essay holds promise of
achieving even higher water/surfactant ratios.
Example V
Ammonium Nitrate Diesel Fuel Microemulsions
In order to determine whether the loss in
cetane number due to microemulsified water could be
eliminated by the addition of potential cetane
improvers, we initiated experiments designed to
incorporate NH4N03 into the microemulsified aqueous
phase. Table III describes the results of our studies
to incorporate up to 10 wt.% NH4N03 based on water.
Since the microemulsions contain 10% aqueous phase, 10%
NH4N03 based on water translates into a 1% NH4N03
concentration overall. Based on previous results with
oil-soluble cetane improvers such as octyl nitrate,
O.1% or 1000 ppm NH4N03 was thought to be an effective
level for cetane improvement.
Table III describes microemulsion phase
behavior with varying surfactant hydrophile/lipophile
(H/L) ratio and salinity. H/L ratio depends on the
average degree of ethoxylation in the surfactant
mixture and is varied by changing the weight ratio of
ethoxylated surfactants. Listed under the column
heading microemulsion (ME) type is the phase separation
characteristic of a given composition. An upper phase
microemulsion (U) forms at low H/L ratio and high
salinity as a phase-separated system where an
oil-continuous microemulsion is in equilibrium with
excess settled water. A lower phase microemulsion (L)
forms at high H/L ratio and low salinity as a system
where water-continuous microemulsion is in equilibrium
with excess floating oil. A single phase microemulsion
(S) forms over a relatively narrow range of H/L ratios
and salinity and is a relatively clear,
thermodynamically stable dispersion containing all the
components. The last column lists the nephelometer
turbidity units (NTUj, which are a measure of single
- 23 - 2o~~sos
phase microemulsion clarity. Below -50 NTU the system
looks quite bright. From "50 to 100 NTU the system is
clear but with very slight haze developing. From 100
to 200 NTU haze visibly increases but the microemulsion
remains transparent. Above 200 NTU the system becomes
more and more cloudy though it remains translucent.
Readings below 150 NTU are considered satisfactory.
Table III shows that in order to prepare
single phase microemulsions at higher salinity, the
proportion of more highly ethoxylated surfactant must
be increased. Thus the ratio of C12XS E18-10/C12XS
E18-5 increases from 1/1 to 2.3/1 as we go from 5% to
10% NH4N03. This ratio lies in the middle of the
single phase region and has the lowest haze. The
haziest systems occur near the U -~ S and S -~ L phase
transition boundaries.
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Example VI
Hvdrocten Peroxide Diesel Fuel Microemulsions
Another approach to raising the cetane number
of microemulsified fuels is the incorporation of
aqueous hydrogen peroxide. The following table shows
that direct replacement of water with 3% H202 in the
salt-free microemulsion results in a clear, stable
microemulsion without rebalancing.
Microemulsions in DF2 Containing Cetane Improvers
Surfactant, g/dl Aqueous ME
C1ZXS-MEA C12XS-E5 phase Type N~LT
2.00 2.00 Water S 68
2.00 2.00 3% H202 S 55
All Systems Contain 10 Vol. % aqueous + 90 Vol. % DF2.
Example VII
o?eate Surfactants for Diesel Fuel Microemulsions
The advantage for carboxylate surfactants is
that they do not add sulfur to the diesel fuel
microemulsion composition. Sulfur-containing compounds
in diesel fuel are environmentally undesirable since
they may lead to sulfur oxides in the diesel exhaust.
Some localities have~established maximum sulfur levels
in diesel fuels; California, for example, specifies no
more than 500 ppm. The examples in Table IV show that
oleate surfactants are effective in preparing single
phase microemulsions of water and aqueous NH4N03 in
diesel fuel. The aqueous phase to surfactant ratio is
2.5:1 indicating that the instant ethoxylated alkyl
ammonium oleate surfactants are efficient micro-
emulsifiers when properly balanced. As in the case
- as - 20~8~06
with the ethoxylated alkyl ammonium alkyl aryl
sulfonates, increasing ethoxylation is required to
balance the surfactants when using higher NH4NOg
concentrations. This shows the criticality of
surfactant balancing which depends strongly on aqueous
phase composition. Temperature sensitivity is again
minimized by blending two or more surfactants with
opposing temperature dependencies; MEA-oleate becomes
more hydrophilic while the ethoxylated alkyl ammonium
oleate become more lipophilic with increasing
temperature. Blends of these surfactants give
temperature insensitive microemulsions.
- 27 -
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