Wax appearance point

The wax appearance point is the temperature at which wax begins to precipitate (hence it is also called the wax precipitation point) from an oil under specified cooling conditions. Although more applicable to distillate fuel oil, the wax appearance point can also have implications for mineral oil use. In 

Austin, G.T. 1984. Shreve s Chemical Process Industries. 5th Edition. McGraw-HiU, New York. Chapter 37. 

Ballard, W.P. Cottington, G.I., and Cooper, T.A. 1992. Petroleum Processing Handbook. J.J. McKetta (Editor). Marcel Dekker, New York. p. 309. 

Banaszewski, A., and Blythe, J. 2000. In Modern Petroleum Technology. Volume 2 Downstream. A.G. Eneas (Editor). John Wiley Sons, New York. Chapter 30. Biske, V. 1973. In Criteria for Quality of Petroleum Products. J.P. Allinson (Editor). 

and Davidson, R.L. 1967. Petroleum Processing Handbook. McGraw-Hill, New York. 

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On the other hand, the wax appearance point (ASTM D-3117) may be determined by cooling of a sample under prescribed conditions with stirring. The temperature at which the wax first appears is the wax appearance point. 

Alternatively, the wax appearance point (ASTM D-3117) may also be determined as a means of estimating the composition of kerosene in terms of the wax (n-paraffins) content. The wax appearance point is the temperature at which wax crystals begin to precipitate from a fuel. In this test (ASTM D-3117), a sample is cooled under prescribed conditions with stirring. The temperature at which wax first appears is the wax appearance point. 

Wax appearance point the temperature at which wax crystals begin to precipitate from a fuel. 

The temperature at which a cloud or haze of wax crystals appears at the bottom of a sample of lubricating oil in a test jar, when cooled under conditions prescribed by test method ASTM D 2500. Cloud point is an indicator of the tendency of the oil to plug filters or small orifices at cold operating temperatures. It is very similar to wax appearance point. 

In most cases, the additive depresses the pour point, which delays agglomeration of the wax crystals, but usually has no significant effect on diesel engine performance. A preferred means of improving cold flow is to blend kerosene with the diesel fuel, which lowers the wax appearance point by about 10° C for each 10% increment of kerosene added. 

D 3117 Test Method for Wax Appearance Point of Distillate Fuels ... 

Note 10—Because the gases released by the coolant can obscure vision, the sample tube can be removed to o rve the iqipeaianoe of the wax crystals. The tube can be removed for periods no tonger than 10 s. If crystals have already formed, the temperature should be noted and the sample allowed to be reheated to 3 C atwve the point vdiere the crystals disappear. The sample should then be reimmers and allowed to cod. Remove the sample slightly above the noted temperature and observe the wax appearance point. 

Pour point Wax content Wax appearance temperature Pour point... 

The cloud point (ASTM D-2500, ASTM D-5771, ASTM D-5772, ASTM D-5773, IP 219) is the temperature at which wax appears in an oil. This information is significant for oils to be used at low temperatures, where precipitation of wax might affect the performance of the oil. 

Rheology experiments also give information in the determination of wax appearance temperatures of crude oils. In this research, WATs of crude oils were determined by viscometry from the point where the experimental curve deviates from the extrapolated Arrhenius curve (Figure 4). It was observed that all crude oils, except highly asphaltenic samples, are Newtonian fluids above their wax appearance temperatures. The flow behaviour of crude oils is considerably modified by the crystallization of paraffins corresponding to the variation of the apparent viscosity with temperature. Below the WAT, flow becomes non-Newtonian and approaches that of the Bingham and Casson plastic model [17,18]. 

Pour-Point Depressants. The pour point of alow viscosity paraffinic oil may be lowered by as much as 30—40°C by adding 1.0% or less of polymethacrylates, polymers formed by Eriedel-Crafts condensation of wax with alkylnaphthalene or phenols, or styrene esters (22). As wax crystallizes out of solution from the Hquid oil as it cools below its normal pour point, the additive molecules appear to adsorb on crystal faces so as to prevent growth of an interlocking wax network which would otherwise immobilize the oil. Pour-point depressants become less effective with nonparaffinic and higher viscosity petroleum oils where high viscosity plays a dominant role in immobilizing the oil in a pour-point test. 

The increase in fuel viscosity with temperature decrease is shown for several fuels in Figure 9. The departure from linearity as temperatures approach the pour point illustrates the non-Newtonian behavior created by wax matrices. The freezing point appears before the curves depart from linearity. It is apparent that the low temperature properties of fuel are closely related to its distillation range as well as to hydrocarbon composition. Wide-cut fuels have lower viscosities and freezing points than kerosenes, whereas heavier fuels used in ground turbines exhibit much higher viscosities and freezing points. 

Petroleum becomes more or less a plastic solid when cooled to sufficiently low temperatures. This is due to the congealing of the various hydrocarbons that constitute the oil. The cloud point of petroleum (or a product) is the temperature at which paraffin wax or other solidifiable compounds present in the oil appear as a haze when the oil is chilled under definitely prescribed conditions (ASTM D2500, D3117). As cooling is continued, petroleum becomes more solid, and the pour point is the lowest temperature at which the oil pours or flows under definitely prescribed conditions when it is chilled without disturbance at a standard rate (ASTM D97). 

Cloud point the temperature at which paraffin wax or other solid substances begin to crystallize or separate from the solution, imparting a cloudy appearance to the oil when the oil is chilled under prescribed conditions. 

Certain cloud point improvers function by effectively inhibiting the nucleation of wax crystals. This can be accomplished by dispersion of the wax, thus interfering with nucleation. By functioning as an effective dispersant, certain cloud point improvers can help to solubilize water into fuel to give the fuel a cloudy, hazy appearance. As little as 200 ppm of a cloud point improver can create an opaque, relatively stable haze in treated distillate fuel. 

Cloud Point This is the temperature at which a cloud or haze of wax crystals appears when a fuel or lubricant is cooled under standard test conditions. 

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