Hydrogenation of 1,5,9‐cyclododecatriene in fixed‐bed reactors: Down‐ vs. upflow modes

Abstract

Performance of trickle-bed and up-flow reactors was studied experimentally and theo-( ) retically for an exothermic multistep hydrogenation of 1,5,9-cyclododecatriene CDT in n-decane as sol®ent o®er 0.5% Pdralumina catalyst. Intrinsic kinetics was studied in a batch stirred slurry reactor using the powdered catalyst, and a Langmuir-Hinshelwoodtype rate model is proposed. Using this rate equation, a trickle-bed-reactor model was de®eloped that incorporates contributions of partial wetting and stagnant liquid holdup, in addition to the external and intraparticle mass transfer for the gas-phase reactant ( ) hydrogen . It was also modified to describe the beha®ior of the upflow reactor. Experi-( ) mental data were obtained in both upflow trickle-bed and down-flow modes at different liquid ®elocities, pressures, and inlet feed concentrations at 373 ᎐ 413 K. Reactor performance of the two modes was compared in terms of global hydrogenation rate, CDT con®ersion, selecti®ity to cyclododecene and the maximum temperature rise ob-ser®ed in the catalyst bed. The con®ersions and global hydrogenation rate were significantly higher in a trickle-bed reactor than in the upflow reactor. Similarly, a significant temperature rise in the catalyst bed was obser®ed for the downflow operation compared to the upflow mode, which is explained from wetting characteristics of the catalyst bed. Model predictions for both reactors agreed well with experimental data.

Parallel hydrogenation for the quantification of wetting efficiency and liquid–solid mass transfer in a trickle‐bed reactor

“…The hydrodynamics of trickle flow are rather complex and upflow operation has been advocated for pilot‐scale studies 5. Existing studies on the comparison of upflow with trickle flow operation were summarized by Chaudari et al,6 who advocated systematic studies comparing these two operating modes; especially because several studies show possible advantages of upflow operation above trickle flow operation.…”

Vanadium substituted SBA‐15 supported bimetallic Pt, Pd catalysts for hydrogenation of toluene to methylcyclohexane

“…Toluene conversion was found to decrease with an increase in feed WHSV of toluene that can be explained by two different ways. With an increase in the liquid feed rate, the wetted fraction of the catalyst as well as the gas–liquid and liquid–solid mass transfer coefficients also increase . At a lower liquid feed rate, catalyst particles are partially wetted, and under these conditions, conversion increases due to the direct transfer of the gas‐phase reactant to the catalyst surface, already wetted internally due to the capillary forces.…”

“…With an increase in the liquid feed rate, the wetted fraction of the catalyst as well as the gas-liquid and liquid-solid mass transfer coefficients also increase. [23] At a lower liquid feed rate, catalyst particles are partially wetted, and under these conditions, conversion increases due to the direct transfer of the gas-phase reactant to the catalyst surface, already wetted internally due to the capillary forces. Therefore, with an increase in the liquid feed rate an increase in the wetted fraction is expected to retard the conversion, while an increase in the external mass transfer coefficients will enhance the conversion.…”

Recent Trends in the Cleaning of Diesel Fuels via Desulfurization Processes

“…Industrial reactor configuration for deep HDS of gas oils in terms of reaction order and effect of H 2 S has been discussed (78,(81)(82)(83)(84)(85)(86)(87) . The reactor design and configuration involve one-stage and two-stage desulfurization as shown in Fig.…”