Water emulsions of Fischer-Tropsch liquids (LAW516)

Details Water emulsions of Fischer-Tropsch liquids (LAW516) Water emulsions of Fischer-Tropsch liquids (LAW516)

1999-01-25

2001-09-25

Lovering, Richard D. (Department: 1712)

Colloid systems and wetting agents; subcombinations thereof; pro

Continuous liquid or supercritical phase: colloid systems;...

Aqueous continuous liquid phase and discontinuous phase...

C044S301000, C044S302000, C137S013000

Reexamination Certificate

active

06294587

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to stable, macro emulsions comprising Fischer-Tropsch liquids and water.
BACKGROUND OF THE INVENTION
Hydrocarbon-water emulsions are well known and have a variety of uses, e.g., as hydrocarbon transport mechanisms, such as through pipelines, or as fuels, e.g., for power plants or internal combustion engines. These emulsions are generally described as macro emulsions, that is, the emulsion is cloudy or opaque as compared to micro emulsions that are clear, translucent, and thermodynamically stable because of the higher level of surfactant used in preparing micro-emulsions.
While aqueous fuel emulsions are known to reduce pollutants when burned as fuels, the methods for making these emulsions and the materials used in preparing the emulsions, such as surfactants and co-solvents, e.g., alcohols, can be expensive. Further, the stability of known emulsions is usually rather weak, particularly when low levels of surfactants are used in preparing the emulsions.
Consequently, there is a need for stable macro emulsions that use less surfactants or co-solvents, or less costly materials in the preparation of the emulsions. For purposes of this invention, stability of macro emulsions is generally defined as the degree of separation occurring during a twenty-four hour period, usually the first twenty-four hour period after forming the emulsion.
SUMMARY OF THE INVENTION
In accordance with this invention a stable, macro emulsion wherein water is the continuous phase is provided and comprises a Fischer-Tropsch derived hydrocarbon liquid, water and a surfactant. Preferably, the emulsion is prepared in the substantial absence, e.g., ≦2.0 wt % and preferably less than 1.0 wt %, or absence of the addition of a co-solvent, e.g., alcohols, and preferably in the substantial absence of co-solvent, that is, Fischer-Tropsch liquids may contain trace amounts of oxygenates, including alcohols; these oxygenates make up less oxygenates than would be present if a co-solvent was included in the emulsion. Generally, the alcohol content of the Fischer-Tropsch derived liquids is nil in the sense of not being measurable, and is generally less than about 2 wt % based on the liquids, more preferably less than about 1 wt % based on the liquids.
The macro-emulsions that are subject of this invention are generally easier to prepare and more stable than the corresponding emulsion with petroleum derived hydrocarbons. For instance, at a given surfactant concentration the degree of separation of the emulsions is significantly lower than the degree of separation of emulsions containing petroleum derived hydrocarbons. Furthermore, the emulsions require less surfactant than required for emulsions of petroleum derived hydrocarbon liquids, and does not require the use of co-solvents, such as alcohols, even though small amounts of alcohols may be present in the emulsions by virtue of the use of Fischer-Tropsch process water.
PREFERRED EMBODIMENTS
The Fischer-Tropsch derived liquids used in this invention are those hydrocarbons containing materials that are liquid at room temperature. Thus, these materials may be the raw liquids from the Fischer-Tropsch hydrocarbon synthesis reactor, such as C
4
+ liquids, preferably C
5
+ liquids, more preferably C
5
-C
17
hydrocarbon containing liquids, or hydroisomerized Fischer-Tropsch liquids such as C
5
+liquids. These materials generally contain at least about 90% paraffins, normal or iso-paraffins, preferably at least about 95% paraffins, and more preferably at least about 98% paraffins.
These liquids may be further characterized as fuels: for example, naphthas, e.g., boiling in the range C
4
to about 320° F., preferably C
5
-320° F., water emulsions of which may be used as power plant fuels; transportation fuels, jet fuels, e.g., boiling in the range of about 250-575° F., preferably 300 to 550° F., and diesel fuels, e.g., boiling in the range of about 320 to 700° F. Other liquids derived from Fischer-Tropsch materials and having higher boiling points are also included in the materials useful in this invention.
Generally, the emulsions contain 10 to 90 wt % Fischer-Tropsch derived hydrocarbon liquids, preferably 30 to 80 wt %, more preferably 50 to 70 wt % Fischer-Tropsch derived liquids. Any water may be used; however, the water obtained from the Fischer-Tropsch process is particularly preferred.
Fischer-Tropsch derived materials usually contain few unsaturates, e.g., ≦1 wt %, olefms & aromatics, preferably less than about 0.5 wt % total aromatics, and nil-sulfur and nitrogen, i.e., less than about 50 ppm by weight sulfur or nitrogen. Hydrotreated Fischer-Tropsch liquids may also be used which contain virtually zero or only trace amounts of oxygenates, olefins, aromatics, sulfur, and nitrogen.
The non-ionic surfactant is usually employed in relatively low concentrations vis-a-vis petroleum derived liquid emulsions. Thus, the surfactant concentration is sufficient to allow the formation of the macro, relatively stable emulsion. Preferably, the amount of surfactant employed is at least about 0.001 wt % of the total emulsion, more preferably about 0.001 to about 3 wt %, and most preferably 0.01 to less than 2 wt %.
Typically, surfactants useful in preparing the emulsions of this invention are non-ionic and are those used in preparing emulsions of petroleum derived or bitumen derived materials, and are well known to those skilled in the art. These surfactants usually have a HLB of about 7-25, preferably 9-15. Useful surfactants for this invention include alkyl ethoxylates, linear alcohol ethoxylates, and alkyl glucosides, preferably ethoxylated alkyl phenols, and more preferably ethoxylated alkyl, e.g., nonyl, phenols with about 8-15 ethylene oxide units per molecule. A preferred emulsifier is an alkyl phenoxy polyalcohol, e.g., nonyl phenoxy poly (ethyleneoxy ethanol), commercially available under the trade name Igepol.
The use of water-fuel emulsions significantly improves emission characteristics of the fuels and particularly so in respect of the materials of this emission invention where Fischer-Tropsch water emulsions have better emission characteristics than petroleum derived emulsions, i.e., in regard to particulate emissions.
The emulsions of this invention are formed by conventional emulsion technology, that is, subjecting a mixture of the hydrocarbon, water and surfactant to sufficient shearing, as in a commercial blender or its equivalent for a period of time sufficiently forming the emulsion, e.g., generally a few seconds. For emulsion formative, see generally, “Colloidal Systems and Interfaces”, S. Ross and I. D. Morrison, J. W. Wiley, NY, 1988.
The Fischer-Tropsch process is well known in these skilled in the art, see for example, U.S. Pat. Nos. 5,348,982 and 5,545,674 incorporated herein by reference and typically involves the reaction of hydrogen and carbon monoxide in a molar ratio of about 0.5/1 to 4/1, preferably 1.5/1 to 2.5/1, at temperatures of about 175-400° C., preferably about 180°-240°, at pressures of 1-100 bar, preferably about 10-40 bar, in the presence of a Fischer-Tropsch catalyst, generally a supported or unsupported Group VIII, non-noble metal, e.g., Fe, Ni, Ru, Co and with or without a promoter, e.g. ruthenium, rhenium, hafnium, zirconium, titanium. Supports, when used, can be refractory metal oxides such as Group IVB, i.e., titania, zirconia, or silica, alumina, or silica-alumina. A preferred catalyst comprises a non-shifting catalyst, e.g., cobalt or ruthenium, preferably cobalt, with rhenium or zirconium as a promoter, preferably cobalt and rhenium supported on silica or titania, preferably titania. The Fischer-Tropsch liquids, i.e., C
5
+, preferably C
10
+, are recovered and light gases, e.g., unreacted hydrogen and CO, C
1
to C
3
or C
4
and water are separated from the hydrocarbons.
The non-shifting Fischer-Tropsch process, also known as hydrocarbon synthesis may be shown by the reaction:
2nH
2
+nCO→CnH
2n+2
+nH
2
O
A preferred source of water for pr

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