Mini-trickle bed

The oxidation of benzyl alcohol to benzaldehyde is carried out for elucidating mass transfer effects in a mini trickle-bed reactor [58]. 

Especially the favorable mass transfer of micro reactors is seen to be advantageous for the oxidation of benzyl alcohol [58]. As one key to this property, the setting and knowledge on flow patterns are mentioned. Owing to the special type of microreactor used, mixing in a mini trickle bed (gas/liquid flows over a packed particle bed) and creation of large specific interfaces are special aspects of the reactor concept. In addition, temperature can be controlled easily and heat transfer is large, as the whole micro-reactor construction acts as a heat sink. 

GL 23] [R 12] [P 16] Conversions near 70% were determined for a mini trickle-bed reactor (flow rate 20 mg min ) [36]. The corresponding reaction rate was 10 times larger than in typical batch operation on a laboratory-scale, which is restricted to milder conditions. 

UOP then carried out pilot-scale tests at still higher pressures in a fully automated explosion cell to reproduce vendor work and to study conditions and kinetics. Design was based on direct hydrogen peroxide synthesis using a mini-trickle bed reactor with a micro mixer. 

Process development was performed at laboratory scale using a slit-type interdigital micromixer-reactor, which was later replaced by a special high-pressure interdigital micromixer [12]. The mixers are followed by a cartridge filled with catalyst, which acts as mini-trickle bed. Many further plant details have been developed for the safe operation of the hazardous process gas mixture, but remain undisclosed. 

Speed-up of mixing is known not only for mixing of miscible liquids, but also for multi-phase systems the mass-transfer efficiency can be improved. As an example, for a gas/liquid micro reactor, a mini packed-bed, values of the mass-transfer coefficient K a were determined to be 5-15 s [2]. This is two orders of magnitude larger than for typical conventional reactors having K a of 0.01-0.08 s . Using the same reactor filled with 50 pm catalyst particles for gas/Hquid/solid reactions, a 100-fold increase in the surface-to-volume ratio compared with the dimensions of laboratory trickle-bed catalyst particles (4-8 mm) is foimd. 

These filled tubes or capillaries hence are mini fixed beds with internal micro flow regions. Such approach is a link between real micro structured units and conventional equipment. The type of processing may be analogous to conventional processing, e.g. fixed-bed or trickle-bed operation. 

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