Wax appearance temperature

Overall, DSC is an excellent method to measure the wax appearance and crystallization temperatures of vegetable oils. Due to the complexity of the vegetable oil composition with respect to their FA distribution, the situation is not as simple as pure triacylglycerol molecules. Moreover, there is significant influence of the nature, relative abundance, and orientation of C=C bonds on the wax appearance temperatures. Further, presence of other saturated short-chain-length FAs in vegetable oil structure is found to affect the crystallization process. Statistical analysis of NMR-derived vegetable oil structure support the influence of several predictor variables associated with FA unsaturation on the crystalhzation process. 

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

The crystallization temperature (Tc) commonly called the wax appearance temperature (WAT) is determined from the intersection of the baseline mid the extrapolation of the peak in cooling experiments. Routine use of DSC apparatus shows a thermal noise of 7 pw. Therefore, the crystallization temperature is defined as the temperature at which tiie thermal power developed by the heat of crystallization of paraffins is 15 pw. In order to have a reasonable sensitivity, a smaller cooling rate ( l-2 C/min) must be used. This rate of cooling allows a better approach to file solid-liquid equilibrium temperature. Determination of... 

In DSC experiments, wax appearance temperatures (WAT) were determined manually by intersection of the baseline and extrapolation of the peak. Repeatability of the WAT determinations depends on the shape of the DSC profile of the crude oil and the accuracy can be estimated to be in the order of 2 °C. Typical DSC curves of different crude oils are given in Figure 2. 

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]. 

Figure 5. Determination of wax appearance temperatures of Crude oil 5 using DSC, viscometry and thermomicroscopy [4,5]...

The results indicate that, for crude oil samples with different contents of wax, differential scanning calorimetry (DSC), thermomicroscopy and rheometry provide excellent methods of measuring the wax appearance temperatures (WATs). Because of the diversity of the results, it is not possible to affirm which technique is most suitable for determining the onset of wax appearance. It is suggested that DSC and thermomicroscopy should be used together for a better understanding of the determination of WATs of crude oils. Viscometry should be used to study the flow properties of crude oils below the WAT, in particular when flow improvers are added. 

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. 

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. 

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... 

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

The material which crystallises out of solution from lubricant distillates or raffinates is known as wax. Wax content is a function of temperature. As the temperature is reduced, more wax appears. Sufficient wax must be removed from each base oil fraction to give the required low-temperature properties for each base oil grade. Naphthenic feedstocks, of course, are relatively free of wax and do not normally require de-waxing. 

Wax-coating temperature. Wax-coating temperatures do not appear to be so critical in the hydraulic process. Good results are obtained when the wax-coating temperature is 155-180°F. 

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. 

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. 

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. 

In appearance and on handling the material is somewhat intermediate between a wax and a rubber. It is also semi-tacky. Like isotactic polypropylene it is attacked by oxygen but unlike the isotactic material it swells extensively in aliphatic and aromatic hydrocarbons at room temperature. It is also compatible with mineral fillers, bitumens and many resins. 

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. 

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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