Fixed-Bed Reactors and Trickle-Bed Mode

Fixed-bed reactors operating in the trickle-bed mode are typically used in conventional oil refineries. In a trickle-bed reactor liquid feed and gas are fed co-currently in downflow over a packed bed of catalyst particles in a vertically–positioned reactor.

The following processes are used to remove sulfur, nitrogen, and oxygen compounds in feedstocks:

• Hydrodesulfurization - the conversion of sulfur compounds to hydrogen sulfide.
• Hydrodenitrification - the conversion of nitrogen compounds to ammonia.
• Hydrodeoxygenation - the conversion of oxygen compounds to water.
• Hydrotreating - the simultaneous conversion of sulfur, nitrogen and oxygen compounds.

Furthermore, olefins and aromatics in the feedstocks are converted by:

• Hydrogenation - the saturation of olefins and/ or aromatics.
• Hydrocracking - the simultaneous cracking and hydrogenation, leading to boiling point reduction and olefins and/or aromatics saturation, respectively.

Trickle-bed reactors operate with low pressure drops and at relatively high temperatures and absolute pressures. The high temperatures are required due to the low activities of the catalysts for processing crude oil-sourced feedstocks which can contain very refractory compounds. High pressures are required to increase hydrogen solubility in the liquid which is reduced by high temperature operation. One disadvantage of the trickle-bed reactor is that liquid flow and chemical kinetics can be interconnected, making scale-up difficult. One way to decouple fluid mechanics from chemical kinetics is by packing laboratory reactors with diluent particles to ensure good liquid-catalyst contacting [1].

Intertek PARC has provided fixed-bed testing services to the global oil & refining industry since 1986. Fixed-bed pilot plants with a range of reactor sizes are available for isothermal as well as adiabatic operations. Furthermore, once-through and recycle operation options for gas and liquid are available. For more information about Intertek PARC’s capabilities, please visit: http://www.intertek.com/testing/pilot-plant/a-to-z/.

Reference 2 classifies catalytic reactors according to size, methods of charging and discharging, motion of catalyst particles relative to each other and fluid flow. Upon further consideration, catalytic reactors can also be categorized according to the motion of catalyst particles relative to each other and to the motion of the catalyst particles relative to the stationary reactor wall. We can classify ideal catalytic reactors with the following table:

References:
1. Al-Dahhan, et al., Ind. Eng. Chem. Res., 1997, 36, 3292-3314.
2. www.et.byu.edu/~bartc/presentations/Catalytic%20Reactors.