Question

1) One thousand barrels of a 40°API crude are blended with one thousand barrels

of a 20°API crude. Estimate the °API of the resulting blend. Clearly state your

assumptions and comment on your result. (Hint: Would °API blend linearly?)

2) Calculate Watson K factors for n-pentane, n-hexane, 2,2,4 trimethylpentane,

cyclohexane, methylcyclohexane, benzene, and xylene to consider the effects of

hydrocarbon type and methyl substitution on the characterization factor. Present

your results in a table and comment on the trends you observe. (You need to find

the necessary data yourself to calculate the characterization factor.

Watch the units used in the characterization factor correlation.

Answer 1

Ans 1

Assumption

Volume change of mixing is negligible.

SG can be taken on average basis but API not.

The API gravity equation

°API = (141.5 / SG_{15.6°C/15.6°C} ) - 131.5

For 1000 barrels of a 40°API crude

40 = (141.5 / SG1 ) - 131.5

SG1 = 141.5 / (40 + 131.5)

SG1 = 0.825

For 1000 barrels of a 20°API crude

20 = (141.5 / SG2 ) - 131.5

SG2 = 141.5 / (20 + 131.5)

SG2 = 0.934

Average SG = (SG1 + SG2) / 2

= (0.825 + 0.934) / 2

= 0.8795

°API of blend = (141.5 / SG) - 131.5

= (141.5 / 0.8795) - 131.5

= 29.39

API is not the average of the blend.