What is retrograde condensation and how does it affect gas processing?

Retrograde condensation occurs when a gas mixture forms liquid when pressure decreases (opposite of normal behavior). It happens in the retrograde region between cricondentherm and critical point on the phase envelope. Mechanism: at constant temperature, reducing pressure from single-phase gas crosses dew point curve, forming liquid that increases to a maximum then decreases. Impact on gas processing: liquid dropout in pipelines during pressure reduction, condensate accumulation in separators not designed for liquids, two-phase flow in unexpectedly designed single-phase systems, and composition variation through processing. Design considerations: avoid retrograde region or design for two-phase handling.