The present invention relates to low temperature flow improvers for wax-containing liquids.
Low temperature properties of wax-containing liquids, especially hydro-carbon-based liquids are important. When diesel fuels, home heating oils, various oils of lubricating viscosity, automatic transmission fluids, hydraulic fluids, crude oils, and other paraffinic liquids are cooled, solidification occurs progressively, normally over a range spanning some 10 to 15.degree. C. This solidification is generally undesirable for materials which are normally handled in the liquid state, and efforts to measure and ameliorate this phenomenon have been pursued. Cloud point is the measurement of the temperature at which paraffin crystals first appear when such a material is cooled. This value is determined by standardized methods such as ASTM D 2500. At temperatures below the cloud point, the material becomes increasingly solid, until the pour point (ASTM D 97) is reached, that is, the temperature at which the material has essentially solidified. Another test by which the low temperature properties is evaluated is the cold filter plugging point (CFPP) test, IP 309/80. Another test, commonly used in refineries, is the low temperature flow test (LTFT), ASTM D 4539-91, which simulates the slow cooling and filtration of diesel fuel through a fuel system at low temperatures.
Such wax-containing hydrocarbon materials often require the use of pour point depressant additives in order to allow them to flow freely at lower temperatures. Often kerosene is included in such oils as a solvent for the wax, particularly that present in distillate fuel oils. However, demands for kerosene for use in jet fuel has caused the amount of kerosene present in distillate fuel oils to be decreased over the years. This, in turn, has required the addition of wax crystal modifiers to make up for the lack of kerosene. Moreover, the requirement for pour point depressant additives in crude oils can be even more important, since addition of kerosene is not considered to be economically desirable. The use of kerosene as an additive for fuels, moreover, can be undesirable since it can lead to a higher flash point.
There have been many approached to modifying the low temperature properties of hydrocarbon fluids. U.S. Pat. No. 2,936,300, Tutwiler et al., May 10, 1960, discloses copolymers of vinyl acetate and dialkyl fumarate, useful for improving the pour point and viscosity index of oils.
U.S. Pat. No. 4,234,435, Meinhardt et al., Nov. 18, 1980, discloses carboxylic acid acylating agents derived from polyalkenes and a dibasic carboxylic reactant such as maleic or fumaric acid. The acylating agents can be reacted with a further reactant subject to being acylated, such as polyethylene polyamines.
U.S. Pat. No. 4,661,121, Lewtas, Apr. 28, 1987, discloses middle distillate compositions with improved low temperature properties, by addition of a polymer or copolymer of a n-alkyl vinyl or fumarate ester with n-alkyl groups of 14-18 carbon atoms. Copolymers of di-n-alkyl fumarates and vinyl acetate are preferred. Coadditives which may be present include polar nitrogen containing compounds; these are generally the C.sub.30 -C.sub.300 amine salts and/or amides formed by reaction of hydrocarbyl substituted amines with hydrocarbyl acids having 1-4 carboxylic groups. In an example, such a compound is the reaction product of phthalic anhydride with di-hydrogenated tallow amine.
U.S. Pat. No. 5,725,610, Vassilakis et al., Mar. 10, 1998, discloses an additive composition which comprises a combination of (i) the reaction product of an aliphatic compound of e.g. alkyl (10-32 C) maleic anhydride and a polyamine and (ii) the reaction product of (A) esterification of a saturated linear alcohol of 6 to 24 carbon atoms with acrylic acid or halide and (B) polymerization of the ester of (A) with itself or maleic, alkylmaleic, or alkenylsuccinic anhydride, acrylic acid, or fumaric acid, or esters thereof. The polyamine of (i) is of the general formula ##STR1## where R is a saturated aliphatic radical and R' is hydrogen or a saturated aliphatic radical (each of 1-32 carbon atoms). n is 2 to 4 and m is 1 to 4.