Process intensification of tubular reactors: Considerations on catalyst hold-up of structured packings

•Comparing structured packings on catalyst hold-up, heat transfer and pressure drop.•Proposal of a hybrid (particle packed) structure with 50, v% catalyst hold-up.•The hybrid structure has excellent heat transfer and pressure drop characteristics.•A Fischer–Tropsch model demonstrates 25% production increase.

Several structured packing elements for multiphase tubular fixed bed reactors are compared with regard to catalyst hold-up, heat transfer performance and pressure drop. Structured packings with catalyst coating typically exhibit low pressure drop compared to the conventional randomly dumped packed bed, as well as excellent heat transfer characteristics, but also have considerably less catalyst inventory per reactor volume. A particle-packed structured alternative (packed cross flow structure) exploits the advantages of structured flow, while not sacrificing much in catalyst hold-up (50 v%) compared to a randomly packed bed (65 v%). This alternative retains favorable pressure drop characteristics, which allows the use of reduced catalyst particle size. A numerical analysis of a 1-dimensional reactor model of a fixed bed Fischer–Tropsch process demonstrates that the packed cross flow structure, despite a lower catalyst hold-up than the randomly packed bed, can have a 25% higher C5+ productivity per tube volume than the RPB. The increased productivity results from an increased catalyst effectiveness combined with better temperature control, necessary to keep the catalyst sufficiently selective.

Graphical abstract(A) Cross sectional view of a single catalyst particle packed triangular channel in a network of channels that is proposed as a structured packing alternative to randomly dumped packings for tubular reactors. (B) Schematic 3-dimensional representation of a single triangular packed channel (50, v% catalyst hold-up). (C) Snapshot of a pseudo-2D (5.0 cm wide, 2.0 cm deep, 80.0 cm high) particle packed (2 mm particles) CCFS perspex model set-up during multiphase co-current downflow operation. The liquid flowpath is traced with a blue color, indicating the structured liquid flowpaths. (D) (P vs. superficial gas velocity for the particle packed CCFS and other packings at 15 mm/s superficial liquid velocity.Figure optionsDownload full-size imageDownload high-quality image (231 K)Download as PowerPoint slide