Winterized paraffin crystal modifiers

Details Winterized paraffin crystal modifiers Winterized paraffin crystal modifiers

1999-12-03

2001-10-30

Medley, Margaret (Department: 1714)

Fuel and related compositions

Liquid fuels

Containing organic -c

C044S397000, C044S445000, C044S447000, C044S448000, C044S451000

Reexamination Certificate

active

06309431

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to winterized wax crystal modifiers and their use in inhibiting or retarding the formation of wax crystal precipitates in petroleum fuel and crude oil at cold temperatures.
BACKGROUND OF THE INVENTION
Petroleum fuels and crude oils contain normal paraffin hydrocarbon waxes which tend to precipitate and crystallize at low temperatures, causing oil to lose its fluidity. Over a range of temperatures, these paraffin wax crystals continue to aggregate and can solidify the oil. This creates difficulties in transporting the petroleum fuel or crude oil through flow lines, valves, and pumps. Paraffin wax crystals are particularly problematic at lower temperatures and in colder climates where, as the temperature drops and approaches the crude oil's pour point, the transportation of crude oil becomes more difficult. Pour point is defined by the ASTM method D-97 as “the lowest temperature at which the crude oil will still flow when it is held in a pour point tube at ninety degrees to the upright for five seconds.” Paraffin wax crystals that have come out of solution also tend to plug flow lines, production tubing, flow lines, screens and filters.
This problem is well recognized, and various additives known as pour point depressants and wax crystal modifiers have been used to change the nature of the crystals that precipitate from the petroleum fuel or crude oil, thereby reducing the tendency of the wax crystals to set into a gel. Generally, wax crystal modifiers possess long segments of repeating saturated carbon chain groups (C
20
H
41
—C
50
H
101
) that are contained in or attached to a polymer backbone. These compositions, which are slightly soluble in highly aromatic solvents such as toluene, xylene and heavy aromatic naphtha at moderate temperature (i.e., 68° F.), are added to the petroleum fuel or crude oil to be treated. Typically, these crystal modifiers slowly co-crystallize with the paraffin waxes already present in the petroleum fuel or crude oil and effect morphological changes that retard further crystal growth. However, many of the standard crystal modifiers that are known in the art solidify at temperatures ranging from 30° F. to 140° F. Thus many of the crystal modifiers that are presently available are not particularly useful in the field at cold temperatures or under winter conditions.
SUMMARY OF THE INVENTION
The present invention is directed to wax crystal modifiers which remain fluid and pumpable at temperatures ranging from about −40° F. to 160° F. and their use in inhibiting or retarding the formation of wax crystal precipitates in petroleum fuels and crude oils at cold temperatures. The invention is particularly useful for treating petroleum fuels in cold climates and under winter conditions where standard wax crystal modifiers known in the art solidify at temperatures ranging from 30° F. to 140° F. Polymeric wax crystal modifiers useful in the present invention generally include acrylates and methacrylates with pendant groups of C10 to C50, as well as polymers with long repeating saturated carbon chain segments such as ethylene vinyl acetate copolymers. The wax crystal modifiers are added to and dissolved in a bipolar solvent or solvent mixture at elevated temperatures, then cooled with vigorous mixing to form a suspension of finely divided wax crystal modifier polymer particles. Alternatively, a high polarity solvent (or solvents) may also be added to help develop the polymeric suspension. When the wax crystal modifier suspension is added to petroleum fuel or crude oil by pumping or other mechanical means, the formation of paraffin wax crystals is disrupted, thereby retarding the formation of wax crystal precipitates that often impede the flow and transportation of crude oil through tubing, flow lines and pumps.
DETAILED DESCRIPTION
This application claims the benefit of U.S. Provisional Application Ser. No. 60/111,034 filed Dec. 4, 1998.
The present invention provides wax crystal modifiers suspended in bipolar solvate systems that are effective in retarding the formation of paraffin crystal precipitates, while remaining fluid over a range of temperatures from −40° F. to 160° F. Also provided are methods of winterizing or freeze protecting wax crystal modifiers and methods of inhibiting the formation of paraffin wax crystal precipitates in petroleum fuel or crude oil. In general, polymeric wax crystal modifiers are added to and dissolved in bipolar solvents or solvent mixtures that comprise a range of solubility parameters, hydrogen bonded characteristics, and densities that are necessary for the formation of highly dispersed and finely divided polymer particles that are stable as suspensions at the desired temperatures. The wax crystal modifiers of the present invention are highly advantageous in that they remain pumpable at temperatures well below freezing, unlike wax crystal modifiers known in the art which become solid at temperatures of about 30° to 140° F.
Polymeric wax crystal modifiers that are useful for practicing the present invention include acrylates and methacrylates with pendant groups of C10 to C50, as well as polymers with long repeating saturated carbon chain segments such as ethylene vinyl acetate (EVA) copolymers. These include but are not limited to acrylate or methacrylate esters of long chain alcohols, long chain alcohol esters of maleic acid, long chain fatty acid esters of acrylate and methacrylate polymers, maleic olefin alkyl esters, and ethylene vinyl acetate polymers of varying molecular weights. Copolymers, terpolymers and tetrapolymers are also contemplated. Preferred wax crystal modifiers include ethylene vinyl acetate copolymers, maleic olefin alkyl esters, acrylate esters, methacrylic esters, and mixtures thereof.
In general, polymeric wax crystal modifiers are solvated in a bipolar solvent or solvent mixture at elevated temperatures ranging from 150° to 350° F. The polymer/solvent mixture is then allowed to cool to ambient temperature with vigorous mixing. In a preferred embodiment, a high polarity solvent is added to the polymer/solvent mixture, generally during the cooling phase, to form a suspension. Alternatively, the high polarity solvent may be added to the polymer/solvent mixture before or during the heating phase. The use of a high polarity solvent is not always required. Surfactants and suspending agents may also be added but are not critical to the invention. The resulting suspension of finely divided wax crystal modifier particles remains fluid and pumpable at temperatures ranging from −40° F. to 160° F. When the wax crystal modifier suspension is added to petroleum fuel or crude oil by pumping or other mechanical means, the formation of paraffin wax crystals is disrupted. In effect, the wax crystal modifiers of the present invention change the morphology of the paraffin crystals that are already present in the petroleum fuel or crude oil and retard further crystal growth, altering the crystallization point of the petroleum fuel or crude oil that is being treated.
Alternatively, polymeric wax crystal modifiers are first solvated in a nonpolar aliphatic solvent or solvent mixture with mixing and heating to form a solution. Aliphatic solvents useful for practicing the invention include kerosene, KERMAC 600 (petroleum hydrocarbon distillate, commercially available from Calumet Lubricants Co.), and other low aromatic paraffinic solvents. Generally, the polymer/aliphatic solvent mixture is heated to a temperature above the melting point of the polymers. The solvent is then extracted by the addition of a bipolar solvent such as isopropyl alcohol with vigorous mixing to disperse the polymer particles.
It is believed that when the polymeric wax crystal modifiers are mixed with the bipolar solvent or solvent mixture, the polar segments of the crystal modifier(s) associate with the polar ends of the bipolar solvent, while the non-polar segments of the crystal modifier(s) associate with the non-polar segments of the bipolar solvent. This assoc

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