Paraffin viscosity number

Figure 29.2. Viscosity-temperature curves for four commercial dimethylpolysiloxane fluids and for liquid paraffin. The numbers 1000, 300, 100 and 40 indicate the viscosities in centistokes at 38°C.

The pour point of residual fuel is not the best measure of the low-temperature handling properties of the fuel. Viscosity measurements are considered more reliable. Nevertheless, residual fuels are classed as high pour and low pour fuels. Low-pour-point fuels have a maximum pour point of 60°F (15.5°C). There is no maximum pour point specified for high-pour-point residual fuels. A residual oil paraffin carbon number analysis is provided in FIGURE 3-1. 

FIG. 7 Dependence of zero shear rate viscosity for mixture of polyethylene and paraffin on number of C atoms in backbone. (Data from Ref. 21.)... 

The products manufactured are predominantiy paraffinic, free from sulfur, nitrogen, and other impurities, and have excellent combustion properties. The very high cetane number and smoke point indicate clean-burning hydrocarbon Hquids having reduced harmful exhaust emissions. SMDS has also been proposed to produce chemical intermediates, paraffinic solvents, and extra high viscosity index (XHVI) lubeoils (see Lubrication and lubricants) (44). 

When simple Hquids like naphtha are cracked, it may be possible to determine the feed components by gas chromatography combined with mass spectrometry (gc/ms) (30). However, when gas oil is cracked, complete analysis of the feed may not be possible. Therefore, some simple definitions are used to characterize the feed. When available, paraffins, olefins, naphthenes, and aromatics (PONA) content serves as a key property. When PONA is not available, the Bureau of Mines Correlation Index (BMCI) is used. Other properties like specific gravity, ASTM distillation, viscosity, refractive index. Conradson Carbon, and Bromine Number are also used to characterize the feed. In recent years even nuclear magnetic resonance spectroscopy has been... 

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. 

Fisher Scientific Company Paraffin Oil, N.F., Saybolt Viscosity 125/135 and Mobil Oil Corp. S/V Industrial White Oil Number 320, Saybolt Viscosity 200/210 gave comparable results. 

Since the viscosity-temperature coefficient of lubricating oil is an important expression of its suitability, a convenient number to express this property is very useful, and hence, a viscosity index (ASTM D-2270) was derived. It is established that naphthenic oils have higher viscosity-temperature coefficients than do paraffinic oils at equal viscosity and temperatures. The Dean and Davis scale was based on the assignment of a zero value to a typical naphthenic crude oil and that of 100 to a typical paraffinic crude oil intermediate oils were rated by the formula ... 

One method (ASTM D-2501) describes the calculation of the viscosity-gravity coefficient (VGC)—a parameter derived from kinematic viscosity and density that has been found to relate to the saturate/aromatic composition. Correlations between the viscosity-gravity coefficient (or molecular weight and density) and refractive index to calculate carbon type composition in percentage of aromatic, naphthenic, and paraffinic carbon atoms are used to estimate of the number of aromatic and naphthenic rings present (ASTM D-2140, ASTM D-3238). 

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. 

The viscosity-gravity constant is of particular value in indicating petroleum of a predominantly paraffinic or cyclic composition. The lower the index number, the more paraffinic the stock for example, naphthenic lubricating oil distillates... 

Cracking all or part of the straight-chain paraffins improves cold-flow characteristics of the hydrocarbon cut processed, but on the other hand, it has the disadvantage of reducing its yield and of slightly deteriorating some important properties of the cut—the jet fuel smoke point, gas oil cetane number, and lube oil viscosity index. The dewaxing operation should therefore offer the best possible compromise between the desired cold-flow characteristics. the yield requirements, and the combustion or viscosity characteristics. 

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