Experimental study of the peridoic operation of a trickle ‐bed reactor

Abstract

Trickle-bed reactors are a commonly used type of threephase catalytic reactors in which liquid and gas phases flow concurrently through a bed of catalyst particles. They are usually operated in the trickling regime. A common feature of most trickle-bed reactors is the complexity of the gas-liquid flow and that, in most cases, the overall reaction rate is governed by mass-transfer resistances. Gaseous species must dissolve into and then pass through the liquid phase to reach the catalyst particles. Mass-transfer resistances between the phases affect the conversion and the overall reaction rate. However, the liquid phase is essential to the system and cannot be completely eliminated.According to the recent literature, many attempts have been made to overcome this drawback by means of reducing the mass-transfer resistances. This can be accomplished using other reactor configurations (segregated flow reactors) or by means of cycling of the liquid phase. Segregated flow reactors basically consist of a tubular supported catalytic membrane. The liquid and gas streams are separated as they flow through the membrane (Hatziantoniou and Anderson, 1984;De Vos et al., 1986; Cini and Harold, 1991; Young and Cussler, 1987;Hatziantoniou et al., 1986;Carlsson et al., 1983). In all the cases the solution to overcome the mass-transfer resistance limitations is suggested by means of using another reactor, not a trickle-bed reactor.In the case of cycling, an inlet variable (that is, the liquidflow rate) is periodically changed between two given levels. When the liquid flow is cut off, the bed partially drains. This thins out or eliminates the liquid film surrounding the particles with a decrease in the transport resistance for the gaseous species. This mode of operation could be viewed as a way of segregating, at least partially, liquid and gas phases.Periodic operation of a trickle-bed reactor was studied by Haure et al. (1989). The reaction system under consideration was the sulfur dioxide oxidation over carbon catalyst. In this case, the reactants were present in the gas phase only. The sulfur trioxide formed was removed by the liquid flow (water). The liquid flow was turned on and off and an increase in the oxidation rate of about 30 to 40% was found within a range Correspondence concerning this article should be addressed to P. M. Haure of cycle periods from 2 to 80 min. Under this condition, wetting plays an important role in the behavior of the reactor. The influence of cycling results from the interplay of masstransfer and heat effects.Multiphase reaction-transport interactions at the single catalytic pellet level were studied by Funk et al. (1991) and Harold (1993, 1994). Their approach provides valuable information about local unsteady behavior within the fixed-bed multiphase reactor and gives insight into catalyst performance during periodic operation.The objective of this article is to compare the performance of a laboratory trickle-bed reactor operated in the cycling and conventional modes for a reaction system which is...

Carbon materials and catalytic wet air oxidation of organic pollutants in wastewater

“…Forced periodic operation of liquid flow must be considered as a new promising operation concept. Silveston and Hanika [199] lately reviewed periodic operation of TBRs pointing out the good results obtained for reactions including the wet oxidation of SO 2 over activated carbon [200] and the catalytic hydrogenation of a-methylstyrene [201,202] or crotonaldehyde [203]. Essentially, periodic operation consists in controlled ON-OFF liquid feed flow modulation to induce forced pulsing flow regime in the reactor.…”

Hydrogenation of 2‐Ethylanthraquinones in a Periodically Operated Trickle‐Bed Reactor

“…Lange et al [6,7], Castellari and Haure [8], Gabarain et al [9] and Banchero et al [10] investigated the hydrogenation of a-methyl styrene (AMS) in the presence of a palladium/alumina catalyst under ON-OFF mode operation and observed a 45~400 % improvement in conversion over the corresponding steady-state performance. Khadilkar et al [11] and Turco et al [12] also studied the AMS hydrogenation under a wide range of pressure and time-average liquid flow rate with both ON-OFF and PEAK-BASE mode operation.…”

An NMR Imaging Study of Steady-State and Periodic Operation Modes of a Trickle Bed Reactor

“…In this mode of operation, the catalyst bed is periodically flushed with the liquid phase while the gaseous phase is fed continuously. Several possible reasons for the intensification of the reaction progress in the periodic mode of the trickle bed reactor operation have been suggested: an increase of the catalyst temperature [1,2,4], reduction of mass transfer resistance, development of more channels in the catalyst bed, periodic changes in the liquid holdup and internal and external wetting efficiency [6], etc. In order to advance our knowledge about the periodic operation of trickle bed reactors, a deeper insight into the reactor performance is necessary.…”

“…Trickle bed reactors are usually operated under steady-state conditions. However, recently a periodic operation of trickle bed reactors has been intensively studied showing a significant improvement of reactor performance [1][2][3][4][5]. In this mode of operation, the catalyst bed is periodically flushed with the liquid phase while the gaseous phase is fed continuously.…”