Wax transport composition

Details Wax transport composition Wax transport composition

2001-07-20

2004-01-13

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

06677388

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a wax composition capable of being transported through pipelines.
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 having a water continuous phase, wherein the emulsion comprises Fischer-Tropsch derived hydrocarbon waxes, Fischer-Tropsch process water, 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 an addition of a co-solvent (e.g., alcohols).
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. The water obtained from the Fischer-Tropsch process is particularly preferred and results in improved emulsions when compared to distilled water.
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, based on the weight of wax and Fischer-Tropsch process water, 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 ethoxy (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, Fischer-Tropsch process 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 Fischer-Tropsch process water and the first surfactant, and providing sufficient shear to produce a pre-emulsion or a thick emulsion. Preferably, the Fischer-Tropsch process water and surfactant are also heated to about the same temperature as the wax. It is also preferred to mix the Fischer-Tropsch process water and surfactant prior to mixing either with the wax. The resulting mixture is usually cooled to ambient temperature, although not always necessarily, before carrying out Step 2. Upon mixing the pre-emulsion with the second surfactant, 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.
To more completely describe this invention, a series of examples, including comparison tests, are described and present in outline form in Table 4 herein below.
The Fischer-Tropsch process is well known to those 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 measures 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 ruthenium, rhenium or zirconium as a promoter, preferably 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.
A preferred source of water for preparing the emulsions of this invention is the process water produced in the Fischer-Tropsch process, preferably a non-shifting process. A generic composition of this Fischer-Tropsch process water is shown below and in which oxygenates are preferably <2 wt %, more preferably less than 1 wt %:12
C
1
-C
12
alcohols
0.05-2 wt %, preferably 0.05-1.5 wt %
C
2
-C
6
acids
 0-50 wppm
C
2
-C
6
ketones, aldehydes,
 0-50 wppm
acetates
other oxygenates
0-500 wppm


REFERENCES:
patent: 3551169 (1970-12-01), Cangdon
patent: 3553130 (1971-01-01), Stratton
pate

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