$47.$ The principle behind fractional distillation is the difference in $\_\_\_\_$ points among crude oil components, facilitating the production of $\_\_\_\_$ and $\_\_\_\_$ from the crude feed.

$48.$ ASTM distillation tests are essential for characterizing the $\_\_\_\_$ characteristics of petroleum products, guiding $\_\_\_\_$ practices and meeting industry $\_\_\_\_.$

$49.$ EFV distillation techniques simulate a single$-$stage $\_\_\_\_$ process, providing data critical for the design and optimization of $\_\_\_\_$ units.

$50.$ The separation efficiency of atmospheric and vacuum distillation units is enhanced by understanding the $5-95$ gap and t$50,$ which influence the $\_\_\_\_$ of distillation columns and the quality of $\_\_\_\_$ products.