N-formylmorpholine extractive distillation recovers benzene and other aromatics by changing their relative volatility rather than relying on normal boiling-point differences alone. Lean NFM enters above the hydrocarbon feed, flows downward through the packed section and selectively retains aromatics, while non-aromatics leave overhead as raffinate. Structured packing must therefore handle substantial solvent circulation, provide uniform NFM distribution and support a separate upper washing zone that limits solvent carryover. Solvent/feed ratio, NFM composition, water content and phase behavior are as important as packing HETP. A higher-efficiency packing cannot correct poor solvent chemistry or maldistribution, so NFM circulation, feed elevations, distributor performance and column hydraulics should be reviewed together before a retrofit.

MTBE reactive distillation combines the reaction of isobutene and methanol with distillative separation inside one column. The catalytic reaction zone therefore requires a specialist structured internal that both contains acidic ion-exchange resin and allows vapor-liquid mass transfer; ordinary 250Y or 350Y structured packing cannot simply replace it. Published catalytic packing systems balance catalyst volume fraction against separation efficiency and hydraulic openness, while industrial scale-up studies show that incomplete catalyst wetting and liquid maldistribution can reduce the effective reaction rate even when the correct catalyst inventory is installed. Conventional structured packing can still be used in non-reactive rectification or stripping sections, so every MTBE retrofit RFQ should clearly separate catalytic and non-catalytic tower zones before packing is specified.

PGMEA production requires continuous removal of esterification water, but PGME and PGMEA can also leave with water through azeotropic behavior. Acetate entrainers such as isopropyl acetate, ethyl acetate or n-propyl acetate can improve water removal, yet may undergo unwanted transesterification with PGME when they contact it in the presence of acid catalyst. Structured packing can provide the separation stages needed to maintain a composition barrier between the entrainer-rich upper zone and catalyst-containing reaction liquid. Packing height, feed elevation, entrainer inlet, pressure drop, reflux distribution and condenser/decanter operation must therefore be designed together. For semiconductor-grade PGMEA, additional cleanliness, ion and particle-control requirements go beyond ordinary distillation purity.

Phosgene–hydrogen chloride separation in isocyanate production can use structured packing as part of a pressure-coupled recovery system. Modern BASF technology compresses the HCl-rich column overhead, partially condenses it at higher pressure, then depressurizes the liquid to create cold reflux at the distillation-column pressure. Structured packing helps provide the required rectification with relatively low pressure drop, but the packing, compressor, condenser and reflux inlet must be considered as one thermodynamic system. Startup can create a different hydraulic condition because an absorbing solvent may temporarily be introduced to control ascending phosgene before normal HCl reflux is established. Packing selection therefore requires process-stream composition, pressure profile, reflux phase condition and the surrounding overhead-system arrangement—not only tower diameter and packed height.

Maleic anhydride recovery absorbers can require different internals in different tower sections. A published organic-solvent recovery process uses structured packing or metal grids in two recirculating gas-cooling sections, where high liquid flow, heat removal, low pressure drop and short liquid residence time are important. The main and final absorption sections instead favor specially designed trays because local liquid loading becomes much lower. Temperature control is critical: excessive temperature reduces absorption and promotes maleic-to-fumaric-acid conversion, while excessive cooling can contribute to water condensation and fumaric-acid solid deposits. Structured packing should therefore be selected by local tower duty rather than specified across the entire absorber.