Wax pour point

What is the difference between Wax pour point and Viscosity pour point ... 

For oils containing wax, pour point is the temperature at which crystallization of wax has gone to such an extent that the oil will stop flowing if cooled furllier. This temperature is known as Wax pour point . For oils free from wax, xnir point is Ihe temperature at which the viscosity is so iiigh dial the. oil will slop (lowing, if cooled further, due to further iiKicase in viscosity. This temperature is known as Viscosity pour point . 

Pour point depressants are materials which, when added to oils containing wax, get adsorbed on Ihe surface of wax crystals during the initial stages of crystal formation. They thus reduce the size of the wax crystals. They also alter the, crystal structure in such a way that the amount of oil held by the crystals by adsorption or by entrainment is reduced. Both these effects enhance the. oil flow at lower temperature and thus reduce the Wax pour point of the oil. 

Paraflow is an important pour point dcpre.ssant which, when present in concentrations of 1 to 2 per cent, may reduce the Wax pour point of an oil by 50°F or more. Paraflow is a poly-alkyl naphthalene and is prepared by condensing chlorinated wax with naphthalene in the presence of anhydrous aluminium chloride which acts as a catalyst... 

During the production of mineral oils from vacuum distillates, one of the process steps, dewaxing , removes the high melting point materials in order to improve the oil s pour point. Dewaixing produces paraffins and waxes, the first coming from light distillates, and the second from medium or heavy distillates. 

Low temperature filtration (qv) is a common final refining step to remove paraffin wax in order to lower the pour point of the oil (14). As an alternative to traditional filtration aided by a propane or methyl ethyl ketone solvent, catalytic hydrodewaxing cracks the wax molecules which are then removed as lower boiling products. Finished lubricating oils are then made by blending these refined stocks to the desired viscosity, followed by introducing additives needed to provide the required performance. Table 3 Usts properties of typical commercial petroleum oils. Methods for measuring these properties are available from the ASTM (10). 

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. 

The pour point represents the lowest temperature at which the liquid fuel will pour. This is a useful consideration in the transport of fuels through pipelines. To determine the pour point, an oil sample contained in a test tube is heated up to 115°F (46°C) until the paraffin waxes have melted. The tube is then cooled in a bath kept at about 20°F (11°C) below the estimated pour point. The temperature at which the oil does not flow when the tube is horizontally positioned is termed the pour point. 

The pour point of a crude oil or product is the lowest temperature at which an oil is observed to flow under the conditions of the test. Pour point data indicates the amount of long-chain paraffins (petroleum wax) found in a crude oil. Paraffinic crudes usually have higher wax content than other crude types. Handling and transporting crude oils and heavy fuels is difficult at temperatures helow their pour points Often, chemical additives known as pour point depressants are used to improve the flow properties of the fuel. Long-chain n-paraffins ranging from 16-60 carhon atoms in particular, are responsible for near-ambient temperature precipitation. In middle distillates, less than 1% wax can be sufficient to cause solidification of the fuel. ... 

Paraffin crystalline waxes Apart from asphaltenes, a number of differing molecular weight paraffinic waxes are also present. These progressively crystallize at lowering temperatures (their respective pour points). These waxes increase friction and resistance to flow, so that the viscosity of the fuel is raised. This type of problem is controlled by the use of pour-point depressants (viscosity improvers), which limit the growth of the crystals at their nucleation sites within the fuel. They also have a dispersing effect. 

Cold flow improvers (pour point depressants) These viscosity improvers are often specified in cold climates for unheated gas oil or where existing residual oil heaters are inadequate. The use of these paraffin crystal modifiers permits fuel to continue to flow at temperatures of 30 to 40 °F lower than the point at which wax crystallization would normally occur. 

The crystallization of waxes at lower temperatures causes reduced liquidity of waxy crude oils, which considerably hampers the transportation of crude oils through long distance pipelines. Taking into consideration all of the economic aspects, additive treatment, which depresses the pour point and improves the... 

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). 

Some petroleum products, especially those containing higher-molecular-weight compounds such as waxes, do not crystallize rapidly when cooled. Instead, they form a gel-like network throughout the fuel matrix. This network can begin forming at temperatures well above the pour point of a fuel and may render the product unpumpable. 

Further cooling of the fuel leads to wax crystal formation throughout the fuel matrix. The growing wax crystals develop into a larger latticelike network encompassing the bulk fuel volume. This latticelike network eventually causes the fuel to become highly viscous and to eventually gel into a semisolid mass. The lowest temperature at which fuel remains in the liquid state just prior to gellation is called the pour point. 

The most common type of wax crystal modifier used to reduce the pour point and filtration temperature of distillate fuel is based on ethylene vinylacetate (EVA) copolymer chemistry. These compounds are quite common throughout the fuel additive industry. The differences, however, are found in the variation in the molecular weight and the acetate ratio of the copolymer. 

Problems associated with the use of wax crystal modifiers do not pertain so much to the ability of the modifier to perform, but to the proper application technique. These copolymers are quite viscous in nature and must be diluted in solvent in order to be handleable. Even after dilution, they are still quite viscous and have relatively high pour points. 

Fuel which does not contain a wax crystal modifier will have temperature differences between the cloud and pour points typically from 15°F to 20°F (8.3°C to 11.1°C). If the difference between the cloud and pour point values is greater than 25°F (13.9°C), it is quite reasonable to believe that the fuel contains a wax crystal modifier. 

When pour point testing is performed on crude oil, little to no shear is applied to the oil in the pour point tube. Under these conditions, the wax crystal lattice matrix which forms in the crude oil normally remains intact and the oil gels at the pour point. 

However, when disturbed by pumping, mixing, or agitation, the loosely formed wax crystal lattice can sometimes be broken with applied shear. If this occurs, some crude oils may again begin to pour and continue to flow at temperatures below the initial reported pour point. 

If shearing has destroyed the loosely formed wax lattice network of gelled crude oil so that the oil flows below its natural pour point, heating can restore the oil to its original pour point. By heating the crude oil to temperatures 20°F to 30°F (11.1 °C to 16.7°C) above the cloud point, waxes can be melted, solubilized and redistributed into the oil. When the pour point is then determined for this heated oil, the result obtained may be higher than the result obtained for the same oil which was not heated prior to pour point testing. All wax must be melted and solubilized into... 

It is believed that asphaltic compounds within these heavy oils may be better distributed by high-temperature preheating. Distribution of these compounds may interfere with the formation of an organized wax lattice throughout the oil matrix as the oil cools. The result would be a pour point which is lower than that for an unheated or mildly heated oil. 

Since highly aromatic fuels have little wax, they possess better natural low-temperature handling properties than paraffinic fuels. Also, the cloud point, pour point and low-temperature filtration of aromatic diesel fuel will typically be much lower than a paraffinic diesel fuel. 

In addition to refining techniques, compounds identified as wax crystal modifiers are available for use in contending with the effects of wax in fuels. Wax crystal modifiers, also called pour point depressants or cold flow improvers, are typically polymeric compounds which have the ability to crystallize with fuel wax as it forms. By co-crystallizing with wax, the modifiers typically effect a change in the size, shape, and conformation of wax crystals. Other wax crystal modifiers function by dispersing or inhibiting the nucleation or growth of wax crystals within a fuel or oil. 

The pour point and low-temperature viscosity of a residual fuel or heavy fuel oil can be reduced by using a heavy fuel wax crystal modifier. Often, pour point reversion can be prevented by using the correct wax crystal modifier. 

Pour Point Improvers—Wax Crystal Modifiers (WCM)—Cloud Point Improvers... 

In order to achieve very low pour points and filtration temperatures in some fuels, high levels of wax crystal modifiers must be used. On occasion, high concentrations of a WCM can cause the pour point or filtration temperature to reverse. This is due to the influence of the high viscosity of these inhibitors at the low test temperatures. 

Fuels treated with a cloud point improver (CPI) may require additional CPI treatment whenever a wax crystal modifier is used to reduce the pour point of the fuel. Often, the cloud point of a CPI-treated fuel will increase whenever a pour point improver is used. To compensate for this phenomenon, additional CPI must be added to recover the lost performance. 

When distillate fuel is cooled, wax crystals begin to form in the fuel. The temperature at which these crystals are first observed is identified as the cloud point of the fuel. Upon further cooling, these crystals begin to coalesce into a latticelike network to form a semisolid gel. The temperature at which this gelation occurs is termed the pour point. 

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