In petroleum refining, the heavy residue left at the bottom of the atmospheric distillation column is further separated using vacuum distillation rather than heating it to higher temperatures under normal atmospheric pressure. What is the primary technical reason for lowering the pressure during this industrial process?
- To lower the boiling points of high-molecular-mass components and prevent thermal crackingAnswer
- BTo increase the boiling points of the heavy residue fractions so they condense more rapidly
- CTo convert saturated alkanes into light gaseous alkenes before fraction collection
- DTo selectively solidify paraffin wax while keeping lubricating oils in the vapor phase
Answer
Vacuum distillation lowers atmospheric pressure inside the column, thereby decreasing the boiling points of heavy hydrocarbon fractions so they can be separated at lower temperatures without undergoing thermal cracking.
A liquid boils when its vapor pressure equals external pressure. In vacuum distillation, lowering the surrounding pressure decreases the boiling points of heavy hydrocarbons, allowing them to vaporize and separate at lower temperatures before thermal decomposition (cracking) occurs.
Step-by-Step Solution
Key Concept
Effect of pressure on boiling point in industrial vacuum distillation