(241c) Development of a Novel Compact 3-Phase Hydrogenation Reactor

Selective catalytic three-phase hydrogenations are widely used for the manufacturing of fine chemicals, vitamins and pharmaceuticals. The reactor performance and catalyst selectivity and activity of these systems are considerably influenced by mass transfer. To minimize mass transfer limitations, production is often based on slurry reactors in batch or semi-batch mode using catalyst particle sizes of a few micrometers. The subsequent filtration of the product is a costly and time consuming additional process step. Another aspect of reactor design concerns the evacuation of reaction heat, since hydrogenations are highly exothermic (e.g. HR ≈ -170kJ/mol for acetylenic alcohols). To increase heat transfer capacity and maximize viable catalyst loadings, many applications resort to recycle reactors with external heat exchangers. This, however, entails a large increase in reactor volume as well as complete backmixing of reactants and products, leading to limited reactor performance and losses in process selectivity.

Continuous catalytic multiphase processes based on structured catalysts are a promising alternative to slurry batch technology in terms of productivity, energy consumption, catalyst handling and process safety. Various structured catalyst systems have been reported for different multiphase reactions, often yielding performances comparable or superior to industrial slurry catalysts. However, to tap the full potential of these catalysts, product recycle and the resulting backmixing have to be avoided, making the removal of reaction heat a far more demanding task.

Herein we report the use of sintered metal filters (SMF) as micro-structured catalyst support for multi-phase hydrogenations. The material consists of metal fibers (d ≈ 20µm) forming highly porous sheets of ~ 0.3mm thickness. The SMF-sheets are self-supporting and can easily be shaped into a structured staged bubble column. The open structure with porosities >80% ensures a low pressure drop and acts as a static mixture for enhanced bubble redistribution.

The SMF catalyst layers are integrated into a micro-structured cross-flow heat exchanger and used as stages in a bubble column reactor. Due to the high heat transfer performance of the micro-heat exchanger element in combination with the high activity of the SMF-based catalyst, the system can be operated as a compact 3-phase reactor cascade with minimum hold-up on each stage. This results in the reduction of total reactor volume by several orders of magnitude as well as largely increased reactor performance and process safety as compared to conventional batch or recycle reactors.

The reactor is tested in the selective hydrogenation of 2-methy-3-butyn-2-ol over a Pd/ZnO catalyst supported on SMF.