Crude oil pour point

The pour point of crude oils is measured to give an approximate indication as to their pumpability . In fact, the agitation of the fluid brought on by pumping can stop, slow down or destroy the formation of crystals, conferring on the crude additional fluidity beyond that of the measured pour point temperature. 

The measurement of this temperature is defined by the standard NF T 60-105 and by the standard ASTM D 97. 

Both test stipulate moreover, preheating the sample to 45 to 48°C. 

Crude oil pour points usually are between -60°C and -(-30°C (Table 8.2). 

Crude oil name Country of origin Pour point, C 

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Wang, Sophia L. 1994. (Internal report) Crude oil pour point reversion. 94/720. Sugar Land, Tex. Nalco/Exxon Energy Chemicals, L.P. 

The use of this test method is limited to use for crude oils. Pour point temperatures of other petroleum products can be determined by Test Method D 97. 

XI.2.1 Crude oils stored at temperatures below their cloud point will show wax deposition on the walls of the (sample) containers. The wax coming out of the solution will be preferentially the high melting wax. It is this type of wax that has the most pronounced influence on the crude oil pour point and, at the same time, is the most difficult to redissolve or disperse in the crude oil. Proper treatment of the samples before subsampling for pour point, therefore, is crucial for obtaining reliable crude oil pour point results. 

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. ... 

The most relevant parameters in pipeline transportation of heavy crude oil are velocity, viscosity, temperature, density, and pour point [691]. Heavy crude... 

Some crude oils are so waxy that their transportation by cold pipelines is very difficult, especially in winter. This is because of the high pour points of such crudes, which adversely affect the transportation process. 

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... 

Alternatively, the pour point is reduced by modifying the crude oil itself, for example, by cracking [655]. 

J. Balzer, M. Feustel, M. Krull, and W. Reimann. Graft polymers, their preparation and use as pour point depressants and flow improvers for crude oils, residual oils and middle distillates. Patent US 5439981, 1995. 

G. Meyer, D. Kessel, and I. Rahimian. The effect of pour point depressants of the polyacrylate-type on crude oil (Wirkung von Stockpunk-temiedrigem des Polyacrylat-Typs auf Rohole). Erdol Kohle-Erdgas-Petrochem, 48(3) 135-137, March 1995. 

M. N. Sunil Kumar. Review on polymeric and copolymeric pour point depressants for waxy crude oils and studies on bombay high crude oil. Quart J Tech Pap (Inst Petrol), pages 47-71, October-December 1989. 

Problems with Reproducing the Pour Point of Crude Oil and Heavy Residual Products... 

Testing of the pour point of crude oil and certain residual fuel products requires an understanding of how these oils can behave under certain conditions of heating and shearing. 

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... 

Crude oil and high-boiling-point, high-viscosity petroleum fractions such as 6 fuel oil, atmospheric tower bottoms, and vacuum gas oil can contain wax which crystallizes at temperatures often above room temperature. It is not unusual for these oils to have base pour points of 100°F (37.8°C) or greater. In order to utilize these heavy oils, the pour point and viscosity of these oils must be reduced. One method which is used to accomplish this is to dilute the heavy oil with lower-viscosity components such as diesel fuel or kerosene. The oil then becomes pumpable at lower temperatures. 

Another common method which is used to improve the handling characteristics of heavy oils is to treat the oils with a wax crystal modifier. The process is similar to that used in diesel fuel treatment. Wax crystal modifiers for use in heavy oils are typically higher in molecular weight than those used in diesel fuel applications. The pour point method ASTM D-97 is also used to evaluate crude oil and heavy oils. 

This procedure can be utilized to determine whether heavy fuel wax crystal modifiers will lose their performance properties after long-term storage at fluctuating temperatures. Daily heating and overnight cooling may interfere with the ability of some wax crystal modifiers to maintain their performance properties in some residual oils and crude oils. This loss of performance is frequently termed pour point reversion. The British Admiralty Pour Point Test can be utilized to help predict these reversion tendencies. 

PROBLEM INCREASE IN POUR POINT OF RESIDUAL FUEL OIL OR CRUDE OIL AFTER HEATING OR SHEARING... 

An unusual behavior can be seen in some crude oils and residual fuel oils after they have been heated or have been sheared through a high-rpm pump. When sampled at the pump outlet, some oils can experience an increase in pour point above that of the same oil prior to heating or shearing by pumping. 

PROBLEM REVERSION AND ACTUAL INCREASE IN THE POUR POINT OF A CRUDE OIL OR RESIDUAL FUEL OIL... 

This problem differs from the problem of pour point increase after shearing and heating. In the case of pour point reversion, an increase in the pour point of a crude oil or heavy fuel oil occurs upon long-term storage. 

Shale oils are dark-brown, viscous, waxy liquids that usually contain higher concentrations of nitrogen and oxygen heteroatoms than coal liquids or crude oil. Oils can often have high pour point temperatures and may have trace concentrations of arsenic. Nitrogen levels of 2% and oxygen concentrations of 1.5% are typical. The sulfur content averages about 1%. 

Because the paraffin and mixed-base crudes yield lubricating oil fractions of high quality, means had to be devised in the early days of the petroleum industry to separate the wax from the oil. The removal of wax from petroleum fractions is one of the most important phases in the production of lubricating oils and fuel oils of low pour point, and has received the attention of many investigators. 

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