Viscosity petroleum products

R. E. Hersch, E. K. Fisher, and M. R. Fenske, Viscosity of Petroleum Products. Viscosity-Temperature Characteristics of Pennsylvania Lubricating Oils, Industrial and Engineering Chemistry 27 1442-1446 (1935). 

Properties provided by the branched hydrocarbon chain stmcture of these PAO fluids include high viscosity index in the 130—150 range, pour points of —50 to —60° C for ISO 32 to 68 viscosity range (SAE lOW and SAE 20W, respectively), and high temperature stabifity superior to commercial petroleum products. In their use in automotive oils such as Mobil 1, some ester synthetic fluid is normally included in the formulation to provide sufficient solubihty for the approximately 20% additives now employed in many automotive oils. 

In many instances, two or more miscible liquids must be mixed to give a product of a desired specification, such as, for example, in the blending of petroleum products of different viscosities. This is the simplest type of mixing as it involves neither heat nor mass transfer, nor indeed a chemical reaction. Even such simple operations can however pose problems when the two liquids have vastly different viscosities. Another example is the use of mechanical agitation to enhance the rates of heat and mass transfer between the wall of a vessel, or a coil, and the liquid. Additional complications arise in the case of highly viscous Newtonian and non-Newtonian liquids. 

In the SI system, the theoretical unit of v is m2/s or the commonly used Stoke (St) where 1 St = 0.0001 m2/s = 100 cSt = 100 centiStoke. Similarly, 1 centiStoke = 1 cSt = 0.000001 m2/s = 0.01 Stoke = 0.01 st. The specific gravity of water at 20.2°C (68.4°F) is almost 1. The kinematic viscosity of water at 20.2°C (68.4°F) is for all practical purposes equal to 1 cSt. For a liquid, the kinematic viscosity will decrease with higher temperature. For a gas, the kinematic viscosity will increase with higher temperature. Another commonly used kinematic viscosity unit is Saybolt universal seconds (SUS), which is the efflux time required for 60 mL of petroleum product to flow through the calibrated orifice of a Saybolt universal viscometer, as described by ASTM-D88. Therefore, the relationship between dynamic viscosity and kinematic viscosity can be expressed as... 

Saybolt Universal Seconds (SUS) are used to measure viscosity. The efflux time is the SUS required for 60 mL of a petroleum product to flow through the calibrated orifice of a Saybolt Universal viscometer, under carefully controlled temperature and as prescribed by test method ASTM D 88. This method has largely been replaced by the kinematic viscosity method. SUS is also called the SSU number (Seconds Saybolt Universal) or SSF number (Saybolt Seconds Furol). 

Result The recovery of different fractions of petroleum distillate under atmospheric pressure was more than under reduced pressure because at lower pressure the vapour pressure of lighter molecule of crude oil increased so that they were siphoned out from the system without being condensed. Whereas a combination of distillation of lighter fraction under normal atmospheric pressure followed by the distillation of heavier contents under reduced pressure showed an improvement in the recovery of petroleum products. Recovery of distillates was still more when crude oil was first sonicated and then distilled under normal and reduced pressures. The viscosity of distillate increased with sonication whereas there was a decrease in value of density. 

Figure A-3 Viscosity of water and liquid petroleum products. From Crane.

The Cannon-Fenske viscometer is used for measuring the kinematic viscosity of transparent Newtonian liquids, especially petroleum products and lubricants. The Ubbelohde viscometer is also used for the measurement of kinematic viscosity of transparent Newtonian liquids, but by the suspended level principle. 

For practical purposes, saturated flow of a single fluid such as gasoline, kerosene, or another particular petroleum product can be predicted by the use of these equations. Standard units of linear measurement (feet, meters, etc.) and discharge are accommodated for by the corrections for viscosity and density. Field-testing procedures can be conducted using standard water well testing procedures. 

Viscosity and Specific Gravity of Common Petroleum Products... 

Petroleum is typically described in terms of its physical properties (such as density and pour point) and chemical composition (such as percent composition of various petroleum hydrocarbons, asphaltenes, and sulfur). Although very complex in makeup, crude can be broken down into four basic classes of petroleum hydrocarbons. Each class is distinguished on the basis of molecular composition. In addition, properties important for characterizing the behavior of petroleum and petroleum products when spilled into waterways or onto land and/or released into the air include flash point, density (read specific gravity and/or API gravity), viscosity, emulsion formation in waterways, and adhesion to soil. 

Suitable conversion tables are available (ASTM D341), and each table or chart is constructed such that for any given petroleum or petroleum product, the viscosity-temperature points result in a straight line over the applicable temperature range. Thus, only two viscosity measurements need be made at temperatures far enough apart to determine a line on the appropriate chart from which the approximate viscosity at any other temperature can be read. 

Changes in the chemical composition of the kerosene during volatilization also affect the physical properties of this petroleum product. Table 16.8 summarizes the effect of volatilization on kerosene viscosity, surface tension, and density when 20%, 40%, and 60% of the initial amount has been removed by the partial transfer of light hydrocarbon fractions to the atmosphere. Only the liquid viscosity is affected, with volatilization having a negligible effect on the density and surface tension of the kerosene. 

Wax-related problems are common throughout the petroleum product industry. Fuels and lubricants contain wax at varying concentrations. Filter plugging, line blockage, viscosity increase, and product haziness are all symptoms of wax formation within a fuel or oil. 

Petroleum product physical and chemical properties such as viscosity, aromatic content and distillation profile can provide a wealth of information about product quality and performance. The information provided in this chapter can be used to help identify how specific physical and chemical property measurements can be used to identify and solve fuel problems. 

The fundamental phases of petroleum production include (1) the initial exploration required to find heretofore undiscovered oil and gas reservoirs (2) primary and secondary recovery methods, which make use of both naturally occurring (or primary) reservoir energy and the application of secondary energy sources, such as the injection of gas or water and (3) enhanced oil recovery used to increase ultimate oil production beyond that achievable with primary and secondary methods. Enhanced oil recovery (EOR) methods increase the proportion of the reservoir by improving the sweep efficiency, reducing the amount of residual oil in the swept zones (increasing the displacement efficiency), and reducing the viscosity of thick oils. 

Fuel Oils Any liquid or liquifiable petroleum product burned for the generation of heat in a furnace or firebox or for the generation of power in an engine, Typical fuels include clean distillate fuel for home heating and higher-viscosity residual fuels for industrial furnaces. 

Redwood viscosity—method for determining the viscosity of petroleum products it is widely used in Europe, but has limited use in the U.S. The method is similar to Saybolt Universal viscosity viscosity values are reported as "Redwood seconds."... 

Saybolt Furol viscosity—the efflux time in seconds required for 60 milliliters of a petroleum product to flow through the calibrated... 

Viscosity is the most important single fluid characteristic governing the motion of petroleum and petroleum products and is actually a measure of the internal resistance to motion of a fluid by reason of the forces of cohesion between molecules or molecular groupings. 

Various studies have also been made on the effect of temperature on viscosity since the viscosity of petroleum, or a petroleum product, decreases as the temperature increases. The rate of change appears to depend primarily on the nature or composition of the petroleum, but other factors, such as volatility, may also have a minor effect. The effect of temperature on viscosity is generally represented by the equation... 

The EPA approved many of the methods published in the Annual Book of ASTM Standards for compliance monitoring under the CWA. ASTM methods used in environmental remediation projects determine soil properties, such as organic content, porosity, permeability, soil grain size, or the properties of free petroleum product contained in the subsurface, such as viscosity, density, and specific gravity. 

You can interpolate linearly for any API oil value between these equations and with extrapolation outside to 90°API. Temperature coverage is good from 50 to 300°F. If outside of this range, use the American Society for Testing and Materials (ASTM) Standard Viscosity-Temperature Charts for Liquid Petroleum Products (ASTM D-341 [6]). The values derived by Eqs. (1.1) to (1.4) are found to be within a small percentage of error by the ASTM D-341 method. 

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