Note: Descriptions are shown in the official language in which they were submitted.
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LOW EMISSIONS FUEL EMULSION COMPRISING FISCHER-TROPSCH
DERIVED HYDROCARBON
This application is a divisional application of co-pending application
2,482,339,
filed August 24, 2004
FIELD OF INVENTION
[0001] The present invention relates to an improved fuel which has reduced
particulate matter emission characteristics. More particularly the invention
is directed to
fuels that are in the form of hydrocarbon-in-water emulsions.
BACKGROUND OF THE INVENTION
[0002] Hydrocarbon-in-water emulsions have many potential uses, such as in
internal combustion engines and as a fuel for heating purposes. Indeed,
various studies
have suggested that burning hydrocarbon-in-water emulsions has the advantage
of
lowering the nitrogen oxide emissions nonnally associated with burning
hydrocarbons.
Emulsions are believed to reduce nitrogen oxide (NOx) emissions by lowering
the peak
flame teniperature during their combustion. A lower flame temperature,
however, often is
associated with an increase in the emission of particulate matter (Pm). This
pllenomenon,
known as the Pm-NOX trade off, is believed to limit the improvements one can
make to
diesel emissions.
[0003] h1 recent years there has been a tendency for more stringent emission
regulations, including particulate emissions. Therefore, an object of the
present invention
is to develop a method of more effectively controlling particulate emissions
without
adversely impacting presently achievable reduced nitrogen oxide emission
levels
demonstrated for eniulsified fuels.
100041 In the instance of diesel fueled engines, the reduction of particulate
emissions is particularly important. Consequently, another object of the
invention is to
provide an improved diesel fuel having reduced particulate matter emission
characteristics.
SUMMARY OF INVENTION
[0005] In accordance with the invention, a method for forming a fuel in water
emulsion, which when combusted has reduced particulate matter emissions
compared with
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Swedish Class 1 Diesel Fuel, comprises shearing a Fischcr-Tropsch derived
hydrocarbon
boiling in the diesel fuel range and water in the volume ratio of hydrocarbon
to water of
95:5 to 40:60 and about 0.05 to about 5.0 wt% based on the weight of
hydrocarbon and
water with a non-ionic surfactant or mixtures thereof having a HLB of about 5
to about 30
under shearing conditions sufficient to produce a liquid emulsion in which a
major portion
of the hydrocarbon has particle sizes of 1 micron or less.
[0006] These and other embodiments will become apparent upon a reading of the
detailed description of the invention which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Figure 1 is a diagrammatic illustration of one arrangement of multiple
static
mixers used to prepare an emulsion according to the invention.
[0008] Figures 2 and 3 graphically compare the performance of an emulsion of
the
invention with two non-emulsified fuels in a diesel engine without timing
adjustments.
[0009] Figures 4 and 5 graphically compare the performance of the fuels of
Figures 2 and 3 with timing adjustment.
DETAILED DESCRIPTION OF THE INVENTION
[0010] The emulsions of the present invention contain as the hydrocarbon, a
Fischer-Tropsch derived hydrocarbon fuel or a mixture of a FT fuel and a
conventional
liydrocarbon fuel. Preferably, the hydrocarbon is a FT derived fuel.
[0011] As is well known in the art the Fischer-Tropsch process involves the
reaction of a hydrogen and carbon monoxide containing feed in the presence of
a suitable
catalyst to produce a largely normal paraffin synthetic cra.ide. The process
is described, for
example, in U. S. Patents 5,348,982 and 5,545,674, and suitable catalysts in
U. S. Patent
4,568,663.
[0012] The hydrocarbon fuels produced in the Fischer-Tropsch process may be
separated from the product crude by standard distillation teeliniques.
Additionally,
however, the waxy component of the crude may be converted into filels by known
techniques such as hydrotreating, hydroisomerization and hydrocracking. An
example of
one such process can be found in U. S. 5,378,348.
[0013] In the context of the embodiments of the present invention the Fischer-
Tropsch derived hydrocarbon fuel may comprise either the direct liquid product
(C5+)
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f:rom the Fischer-Tropsch process, a converted Fischer-Tropsch product, or a
blend of the
foregoing. Thus, Fischer-Tropsch products boiling in the range of from about
25 C to
about 450 C are suitable. Such fuels include that disclosed in U. S.
5,807,413. Also
included are more convention Fischer-Tropsch products such as those boiling,
in the range
of about 140 C to about 370 C, and preferably in the range of about 160 C to
about 350 C.
[00141 The water of the emulsion of the invention may be that typically used
in
forining fuel emulsions such as tap water, distilled or deionized water. In
one embodiment,
water from the Fischer-Tropsch process constitutes the continuous phase of the
emulsion.
Fischer-Tropsch process water typically contains about < 2 wt% of oxygenates.
A typical
composition is shown in Table I below:
TABLE 1
Oxygenates Amount
C1-C2 alcohols 0.05 - 2 wt%
C--)-Ce acids 0 - 50 wppm
Cz-C6 ketones, aldehydes, acetates 0 - 50 wppm
other 0 - 500 wppm
100151 The amount of water used in forining the emulsion may be varied over a
wide range. For example, the volume ratio of Fischel Tropsch hydrocarbon fuel
to water
may range froin about 95:5 to about 60:40.
[00161 The einulsions of the present invention also include a nonionic
surfactant or
mixture of nonionic surfactants. The type of nonionic surfactants suitable
include
ethoxylated alcohols, ethoxylated alkyl phenols, ethoxylated carboxylic
esters, glycerol
esters, sorbital esters and the like. In general, the nonionic surfactant will
have an HLB in
the range of 5 to 30 and preferably 8 to 15. Among suitable surfactants
ethoxylated alkyl
phenols having from about 5 to about 30 and preferably 10 to 15 mole of
ethylene oxide
groups deserve special mention.
[0017] The amount of surfactant or mixtures thereof in the emulsion will range
from about 0.05 wt io to about 5.0 wt% based on the total weight of
hydrocarbons and
water with 0.05 wt% to about 2 wt% being typical.
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[0018] The emulsion compositions of the invention may include minor but
effective amounts of conventional additives such as emulsions stabilizers,
antioxidants and
the like. In the case where the fuel is diesel fuel the filel may also contain
conventional
quantities of diesel fi.iel additives such as cetane iniprovers, detergents,
heat stabilizers and
the like.
[00191 As is known in the art emulsions can be forrned by any number of
procedures. Central to all of these is providing sufficient shearing of the
components to
cause emulsification. In the practice of the present invention the fuel is
added to a mixture
of water and surfactant and sheared under conditions sufficient to produce
hydrocarbon
particles of predominantly 1 micron in size or less. Stated differently, the
particles are
substantially uniform in size, i. e., greater than 50% are in the range of
about (1.1. to about
1.0 microns in size. Experience has shown that extensive shearing results in
the fonnation
of a "gel" and consequently the shearing will be less than that which would
produce a gel.
[0020] To achieve the requisite shearing it is particularly preferred to
employ one
or more static mixtures such as those described in U. S. Patents 5,405,439;
5,236,624; and
4,832,747. In general more than one mixer will be used and the mixers will not
be of the
same size (length, diameter, number of internal elements). Rather the number,
size and
elements are selected to adjust mixing efficiency and emulsion particle size.
Ii1 the practice
of the present invention a combination of static mixtures is selected to
provide sufficient
shearing of the hydrocarbon and water to produce an emulsion having particle
sizes
predominantly 1 micron or less and less shearing than that which would produce
a "gel".
100211 A diagrammatic illustration of one arrangement of static mixers
suitable for
carrying out the emulsification of this invention is shown in the accompanying
Figure. As
shown, each of the six mixers have different dimensions. Obviously, different
members
and sizes of mixers may be used so long as the requisite shearing is achieved.
The
dimensions of the illustrated mixers are given in Table 2 below.
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TABLE 2
Mixer Length, inches Diameter, inches
1 12 1/2
2 6 1/2
3 4 1/4
4 4 1/4
6 3/16
6 4 3/16
100221 In the arrangement shown in the Figure, a water and surfactant solution
is
fed to the mixer 1 via line 7 and the Fischer-Tropsch derived hydrocarbon fuel
via line 8.
The product of each mixer is sequentially fed to the next mixer in the series,
e. g. , the
product of mixer 1 is fed to mixer 2; the product of mixer 2 is fed to mixer 3
and so on.
The emulsion exiting mixer 6 via line 9 has a particle size predominailtly
less than 1
micron. The einulsion in the instance where the Fisher-Tropsch fuel is a
diesel fuel, has a
viscosity in the range of about 50 to 200 mm2/sec at 20 C.
EXAMPLES
COMPARATIVE EXAMPLE 1
100231 3000 gms of a non-ionic surfactant (an ethoxylated nonyl phenol having
10
mols of ethylene oxide groups) was added to 9700 gms of water and fed through
mixers I
to 4 shown in the Figure. A Fischer-Tropsch diesel fuel (boiling range -40 C
to 300 C)
comprising 90'% of C6 to C16 linear paraffins was also fed with the water and
surfactant
through the four mixers. The volume ratio of fuel to water was 70:30. The
hydrocarbon
flow rate was 2650 ml/min and the water surfactant solution flow rate was 1380
ml/min.
The temperature was 24 C. The product of inixer 4 was not a hydrocarbon-in-
water
emulsion.
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EXAMPLE 1
100241 The sanie ingredients and amounts described in Comparative Example 1
were fed through mixers 1 to 6 shown in the Figure. The flow rate and
temperature was
the same as in Comparative Example 1. In this instance the product of mixer 6
was
liydrocarbon-in-water emulsion having a density of 0.82 gm/cc and a viscosity
of 150
mm2 /sec at 20 C. The hydrocarbon particles averaged 0.7 microns with 95%
below I
micron in size. This emulsion was shelf stable for more than 6 months.
EXAIVIPLE 2
(0025] The perforinance of the emulsified Fischer-Tropsch fuel of Example I
was
compared to the saine but not emulsified Fischer-Tropsch diesel fuel and to
Swedish Class
I Diesel fuel using a Catapillar I Y 540 single cylinder heavy duty Research
engine. Two
conditions were measured, low load (1500 rpm, 60 Nn torque and 3.0 bar BMEP
and
medium load (1500 rpm, 110 Nm torques and 5.5 bar BMEP.
100261 As is known Swedish Class 1 Diesel filel (also called Urban Diesel ECI)
is
a standard low emissions reference diesel fuel that produces about 10% to 20%
lower NOx
and 40% to 50% lower particulate matter (Pm) than conventional diesel fuel.
The
specification for Swedish Class I diesel fuel are given in Table 3.
TABLE 3
Cetane > 50
Cloud Point
Summer 0 C
Winter -16 C
Density, kglm3 800-820
IBP, C 180
T95, C 285 maximum
Viscosity at 40 C, mm'/second 1.2 to 4.0
Sulfur, ppm 10 maximum
Aromatics, vol% 5 maximum
Poly aromatics not detectable
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100271 The unemulsified Fischer-Tropsch fuel (FTF) has been shown to have
excellent emissions perforniance (see U.S. 5,807,413) with NOx reductions of
10-25% and
Pm reductions of 40-60% compared with conventional diesel fuels. Figures 2 and
3 show
the relative emissions performance of the Fischer-Tropsch fuel and an emulsion
of the
invention (Example 1) vs. Swedish Class 1 Diesel fuel at low and medium load.
[0028] As can be seen in Figure 2, the FTF exhibits similar behavior to
Swedish
Class 1 Diesel Fuel whereas the fuel emulsion of the invention shows NOx
emissions 22%
below Swedish Class 1 and Pm 53% below.
[0029] In Figure 3 a fuel emulsion of the invention shows even larger PM
reduction (91. 5%) than Swedish Class I fuel.
[0030] In Figures 4 and 5 the Pm/NOx perfonnance of the fuels is plotted
against
change in spark timing. As can be seen in the case of the FTF and Swedish
Class 1 fiiels
one can retard the timing to lower the NOx emissions.
