Structured packing in azeotropic distillation must be selected around the complete entrainer recycle system, not only the main feed. Overhead condensation, decanter phase separation, reflux composition, water balance and entrainer circulation can substantially change liquid loading and wetting in the packed column. Hydraulic checks should therefore use section-specific vapor and liquid loads, while retrofit projects should evaluate the condenser, decanter and recycle loop before assuming that packing is the capacity bottleneck.

Structured packing can perform well in high-pressure distillation, but elevated pressure changes vapor density, actual vapor volume, vapor-liquid equilibrium and internal liquid traffic. Low pressure drop may become less dominant than in vacuum service, while separation efficiency, liquid load, hydraulic capacity, distribution and fouling become more important. Structured packing and trays should therefore be compared using the actual pressurized operating conditions rather than assuming that one technology is universally superior.

Large-diameter structured-packing columns are particularly sensitive to liquid and vapor maldistribution, wall flow, segment gaps, distributor coverage and installation tolerances. As tower diameter increases, average liquid flow becomes less useful as a performance indicator because large regions of the bed can be locally over- or under-irrigated. Packing segmentation, wall fit, distributor design, vapor entry, redistributors and field measurements should therefore be treated as part of the complete structured-packing system.

Structured packing in extractive distillation must be selected around the additional selective-solvent stream, which can substantially increase liquid loading below the solvent feed. Packing geometry, solvent distribution, solvent-to-feed ratio, viscosity, hydraulic capacity and required separation efficiency should be evaluated together. Poor solvent distribution can reduce product purity and encourage operators to increase solvent circulation, potentially worsening hydraulic loading rather than solving the underlying problem.

Structured packing is widely relevant to cryogenic air separation because oxygen, nitrogen, and argon distillation requires high mass-transfer efficiency while keeping column pressure drop very low. Packing selection should balance separation efficiency, vapor capacity, liquid distribution, packed height, cryogenic material selection, mechanical contraction, and oxygen-service cleanliness rather than simply maximizing specific surface area.