Water emulsions of Fischer-Tropsch waxes

Details Water emulsions of Fischer-Tropsch waxes Water emulsions of Fischer-Tropsch waxes

1997-09-12

2001-09-04

Metzmaier, Daniel S. (Department: 1712)

Colloid systems and wetting agents; subcombinations thereof; pro

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

Aqueous continuous liquid phase and discontinuous phase...

C516S924000, C516S928000, C044S280000, C044S302000, C137S013000

Reexamination Certificate

active

06284806

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to stable, macro emulsions comprising Fischer-Tropsch waxes 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 pipelines. These emulsions are generally described as macro emulsions, that is, where 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.
The methods of making, e.g., wax emulsions, from petroleum derived materials are well known, but the material surfactants and co-solvents are usually expensive. Moreover, waxes produced from the Fischer-Tropsch process may be harder waxes, have higher melting points, are essentially odor free and free of sulfur and nitrogen, with low residual oils. These high melting point solids are, therefore, difficult to transport through pipelines.
Consequently, there is a need for a method of preparing low cost, stable emulsions of Fischer-Tropsch wax so the wax can be readily transported, e.g., through pipelines.
SUMMARY OF THE INVENTION
In accordance with this invention a stable, macro emulsion wherein water is the continuous phase is provided and comprises Fischer-Tropsch derived hydrocarbon waxes, water, and a first non-ionic surfactant and a second non-ionic surfactant. Preferably, the emulsion is prepared in the substantial absence, e.g., ≦2 wt %, and preferably less than 1 wt %, absence of the addition of a co-solvent, e.g., alcohols, or in the substantial absence of co-solvent, that is, Fischer-Tropsch waxes 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 wax is less than about 2 wt % based on the wax, more preferably less throughout 1 wt % based on the wax.
The macro-emulsions that are the subject of this invention are generally easier to prepare and are more stable than the corresponding emulsion with petroleum derived hydrocarbons. For example, 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 the use of less surfactant than required for emulsions of petroleum derived hydrocarbon liquids, and do-not require the use of co-solvents, such as alcohols, even though small amounts of alcohols may be present in the emulsions.
PREFERRED EMBODIMENTS
The Fischer-Tropsch derived waxes used in this invention are those hydrocarbons containing materials that are solid at room temperature. Thus, these materials may be the raw wax from the Fischer-Tropsch hydrocarbon synthesis reactor, such as C
4
+ wax, preferably C
5
+ wax. 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.
Generally, the emulsions contain up to about 90 wt % Fischer-Tropsch derived wax, preferably 20 to 90 wt % wax, more preferably 60 to 90 wt % Fischer-Tropsch derived wax. 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 % olefins & 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.
The non-ionic surfactant is usually employed in relatively low concentrations. Thus, the total surfactant concentration, that is, just surfactant plus second surfactant is that sufficient to allow the formation of the macro, relatively stable emulsion. Preferably, the total amount of surfactant employed is at least about 0.005 wt % of the total emulsion, more preferably about 1-10 wt % and most preferably 1 to about 7 wt %. The first surfactant is typically a non-ionic surfactant having an HLB (hydrophilic-lipophilic balance) of at least 11, preferably about 11-15 and the second surfactant is a non-ionic surfactant having an HLB of less than 11, preferably 8 to less than 11.
Typically, non-ionic surfactants useful in preparing the emulsions of this invention are those used in preparing emulsions of petroleum derived or bitumen derived materials, and are well known to those skilled in the art. Useful surfactants for this invention include alkyl ethoxylates, linear alcohol ethoxylates, and alkyl glucosides, and mono and di-alkyl substituted ethoxylated, phenols wherein the number of ethenoxy (EO) groups in the first surfactant are about 8 to 20, and in the second surfactant are 3 to 7. A preferred surfactant is an alkyl phenoxy poly alcohol.
The emulsions of this invention are prepared by a two step process: (1) forming a thick mixture of wax, water, and the first surfactant, i.e. a “pre-emulsion”, and (2) mixing the product of step 1 with the second surfactant to form the stable emulsion.
Step 1 is effectively carried out by melting the wax, usually by heating in excess of about 80° C., mixing the wax with water and the first surfactant, and providing sufficient shear to produce a pre-emulsion or a thick emulsion. Preferably, the water and surfactant are also heated to about the same temperature as the wax. It is also preferred to mix the water and surfactant prior to mixing either with the wax. The resulting mixture is usually cooled to ambient temperature, although not always necessarily, before carfying out Step 2. Upon mixing the pre-emulsion with the second suifactant, the mixture is again subjected to sufficient shear for a time period sufficient to form a stable, macro emulsion. The degree of shear for each step as well as shear time for each step may be readily determined with minimal experimentation.
While any suitable mixing or shearing device may be used, static mixers as described in U.S. Pat. Nos. 5,405,439, 5,236,624, and 4,832,747 and incorporated herein by reference are preferred for forming the wax emulsions of this invention.


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