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3E. Approximate Correlation Between MW and Relative Density for Hydrocarbon Liquids.

This page is used to determine the density of Hydrocarbon Liquids using the approximate correlation between molecular weight and relative density. There is no specific correlation between these two for liquids. However, an approximate correlation is useful for preliminary correlations on systems where detailed data are not available. The graph of Correlation between Molecular Weight and Relative Density for Hydrocarbon Liquids (Figure 3.9) is an approximate correlation.

Hydrocarbon is any compound composed solely of carbon and hydrogen atoms.

Example: Ethane

|  | H |  | H |  |
H | - | C | - | C | - | H
|  | H |  | H |  |

To calculate the density of hydrocarbon liquids, the method of calculation must be decided. If the Molecular Weight is known but the Relative Density is not, select "Molecular Weight known" by clicking on and shading the circle provided for that selection. This will yield an answer for Relative Density. If the Relative Density is known but the Molecular Weight is not, select "Relative Density known" by clicking on and shading the circle provided for that selection. This will yield an answer for Molecular Weight.

If the mixture is paraffinic select paraffinic mixture by clicking on and shading the Paraffinic Mixture box.

Paraffins are hydrocarbons that end in –ane, and in each case the number of hydrogen atoms are two times the number of carbon atoms plus two more for the ends of the chain.

Example: Methane

|  | H |  |
H | - | C | - | H
|  | H |  |

Once the method of calculation has been chosen the Average Molecular Weight or the Relative Density of the liquid must be entered into their entry spaces. To do so use the mouse to click the curser in the entry spaces and input the data. Once this has been done, select Run to execute the solution.

Average Molecular Weight:

Where: MW i = Molecular Weight of a component

yi = is the mole fraction of that component in the mixture

Relative Density is the density of a liquid divided by the density of pure water. At 15ºC [60ºF] the density for pure water is 1.0 g/cm³.

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