Mass transfer and selectivity in liquid-phase hydrogenation of nitro compounds in a monolithic catalyst reactor with segmented gas-liquid flow

Abstract

Hydrogenation of nitrobenzene and m-nltrotoluene in mixture was performed in a monolithic Pd catalyst reactor and with ground catalyst in a slurry reactor. The gas-liquid flow in the narrow channels of the monolithic catalyst was a segmented two-phase flow. The mass transfer of hydrogen directly from the gas plugs to the channel wall was found to be the dominating transport step. Tiis direct transport corresponded to more than 70% of the total transport of hydrogen to the channel wall In a typical run. The decreased selectivity of aniline formation found in the hydrogenations In the monolithic catalyst was explained by the influence of the film transport resistance near the channel wall. Hydrogenation of m-nltrotoluene was strongly delayed in the presence of nitrobenzene. Fitting different rate equations to the experimental data indicated that the reaction mechanism is complicated.A novel type of catalytic reactor for liquid-phase hydrogenations was recently presented by Hatziantoniou and Andersson (1984). The catalyst was a monolith of a type similar to the catalyst often used for cleaning exhaust gas from cars. The catalyst consisted of a great number of thin parallel porous plane plates, separated by interstitial corrugated plates, thus forming parallel channels in which gas and liquid flow cocurrently.Besides a very low pressure drop of the flow of the monolithic catalyst of this type (Satterfield and Ózel, 1977), the mass transfer to the channel wall from the liquid was found to be much greater for a segmented gas-liquid flow than for a continuous liquid flow (Hatziantoniou and Andersson, 1982). This effect was explained by an in-

Advanced Catalytic Hydrogenation Retrofit Reactor

“…The performance of the lab-scale monolith-testing unit was compared to a published hydrogenation rate. Under similar reaction conditions and catalyst loading (-5% Pd), the labscale monolith-testing unit gave a hydrogenation rate approximately twice (23.6 moles H2/m3 catalystlsec) that of the published rate by Hatziantoniou, et a1 [7], (15.4 moles H2/m3 catalystlsec). …”

Membrane reactor microstructured by filamentous catalyst

“…The porosity of the ÿlamentous packed bed is ∼ = 0:8. The speciÿc surface per volume is in the order of 108 m 2 m −3 and thus, about 50 times higher compared to washcoated tubes of the same inner diameter (Hatzlantonlou, Andersson, & Sch o on, 1986). …”

Microchannel Reactor System for Catalytic Hydrogenation

“…A literature review of the intrinsic kinetics of nitro group hydrogenation presents a confusing description of the overall process kinetics, with the investigators reporting reaction orders for nitro compound and hydrogen between zero and one depending upon reaction conditions (Chaudhari et al 1983;Hatziantoniou et al 1986;Tong et al 1978;Acres and Cooper 1972;Hernandez and Nord 1947;Hernandez and Nord 1948;Smith and Bedoit 1951;Smith and Bedoit 1955). Most kinetic studies are based on global kinetic rate models based on hydrogen consumption and overall conversion.…”

“…The regression analysis on the experimental data was performed purely on the mathematical basis and therefore did not account for the thermodynamic significance of the kinetic constants. Several models based on different mechanisms and different rate limiting steps were used for regression analysis (Chaudhari et al 1983;Hatziantoniou 1986;Winterbottom 1981). However, some of these models involve complex rate equations which are based on complex mechanisms and hence often fail to fit the experimental data (Hatziantoniou 1986 Based on all of the above criteria, the rate equations (from table 1.2) that best fitted the experimental data for reactions I and II are the following: For reaction I (desorption of the product controlling) r 1 = k I (C H2 C N )/((1+(K N C N ))(1+(K H2I C H2 ))) (1.11) For reaction II (surface reaction controlling) r 2 =k II (K H2II C H2 )(K I C I )/((1+(K I C I ))(1+(K H2II C H2 ))) (1.12) where, k I and k II are the rate constants for reactions I and II respectively, K N , K H2I , K I and K H2II are equilibrium constants of nitroanisole in the presence of hydrogen, hydrogen (for reaction I) in the presence of o-nitroanisole, 2-nitrosomethoxybenzene in the presence of hydrogen and hydrogen (for reaction II) in the presence of 2-nitrosomethoxybenzene respectively.…”