Pour point of crude oil

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. 

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. 

A later test method (ASTM D-5853) covers two procedures for the determination of the pour point of crude oils down to -36°C. One method provides a measure of the maximum (upper) pour point temperature. The second method measures the minimum (lower) pour point temperature. In these methods, the test specimen is cooled (after preliminary heating) at a specifled rate and examined at intervals of 3°C (5.4°F) for flow character-... 

Pour point — The lowest temperature at which an oil will flow under specified conditions. The pour point of crude oils generally varies from -57° to 32°C. Lighter oils with low viscosities have lower pour points. 

Although the pour point test is still included in many specifications, it is not designated for high-boiling fuel oil (ASTM D 396). In fact, although the failure to flow at the pour point normally is attributed to the separation of wax from the fuel oil (in the case of waxy crude oil precursors), it also can be due to the effect of the viscosity of the fuel oil (in the case of naphthenic crude oil precursors). In addition, the pour point of fuel oil may be influenced by the previous thermal history of the fuel oil. Thus the usefulness of the pour point test in relation to fuel oil, especially residual fuel oil, may be open to question. 

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. ... 

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... 

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. 

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

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. 

The pour point of a crude oil product is the lowest temperature at which the oil will pour or flow under prescribed conditions. It is an approximate indicator of the relative paraffinic character and aromatic character of the material. For heavy oils and residua pour points are usually high (above 0°C 32°F) and are more an indication of the temperatures (or conditions) required to move the material from one point in the refinery to another. 

There are, however, some general relationships of crude oil composition that can be derived from pour point and viscosity data. Commonly, the lower the pour point of a crude oil the more aromatic it is, and the higher the pour point the more paraffinic it is. 

The pour point of petroleum is an index of the lowest temperature at which the crude oil will flow under specified conditions. The maximum and minimum pour point temperatures provide a temperature window where petroleum, depending on its thermal history, might appear in the liquid as well as the solid state. The pour point data can be used to supplement other measurements of cold flow behavior, and the data are particularly useful for the screening of the effect of wax interaction modifiers on the flow behavior of petroleum. 

Naphthenics are made from a more limited range of crude oils than paraffinics, and in smaller quantities, at a restricted number of refineries. Important characteristics of naphthenic base oils are their naturally low pour points, because they are wax-free, and excellent solvency powers. Their viscosity/temperature characteristics are inferior to paraffinics, i.e. they have low/medium VI, but they are used in a wide range of applications where this is not a problem. Since naphthenic crudes are free of wax, no de-waxing step is needed but solvent extraction or hydrotreatment is often used now to reduce aromatic content and especially to remove polycyclic aromatics which may present a health hazard in untreated oils. The main producers of naphthenics are in North and South America because most of the world s supply of naphthenic lubricant crudes are found there. 

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