$47.$ 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.