Enhancing performance of three‐phase catalytic packed‐bed reactors

Abstract

Our pre®ious theoretical work predicted the possibility of enhancing three-phase packed-bed reactor performance by operating in the pulsing-flow regime. This article deals with the experimental study of the beneficial effect of pulsing flow on reaction outcome. Hydrogenation of phenylacetylene, dissol®ed in n-tetradecane o®er Ptralumina catalyst, was chosen as the experimental reaction system. This is a triangular reaction, with styrene and ethylbenzene as the desired intermediate and final products, respecti®ely. With properly designed experiments, the reaction performance in pulsing flow and trickling-flow regimes was compared directly. The effects of process ®ariables such as temperature, feed flow rates, and reactant concentration on reaction beha®ior were studied. A simplified model to describe the qualitati®e trends was also de®eloped. Both experiments and calculations show that the yield of styrene is higher in pulsing flow than in trickling flow, which confirms the ad®antages of pulsing-flow operation predicted by the theoretical work. IntroductionMultiphase reactions, in which gas and liquid reactants are selectively converted into desired products using solid catalysts, provide the basis for a large number of chemical, petro-Ž chemical, biochemical, and polymer processes Mills et al., . 1992;Dudukovic et al., 1999 . A common configuration for carrying out such reactions is a three-phase packed bed reactor, involving a stationary packed-bed of catalyst over which gaseous and liquid reactants flow in either a cocurrent or countercurrent manner. Due to complexity of this type of operation, many factors influence reactor behavior. These include liquid distribution, contacting efficiency and partial wetting, which have received prior attention in the literature ŽJiang et al. 1999;Al-Dahhan and Dudukovic, 1995; Watson . and Harold, 1994 . In cocurrent three-phase packed-bed reactors, four major flow regimes have been identified: trickling flow, pulsing flow, Ž . spray flow, and bubble flow Ng and Chu, 1987 , depending on factors such as gas and liquid flow rates, physical properties, and the nature of the reactor packing. These flow regimes Ž . result in different behavior such as holdup and transport Correspondence concerning this article should be addressed to A. Varma. Current address of R. Wu: Novartis Pharma, 59 Route 10, East Hanover, NJ 07936. around the catalyst, which could affect the overall reaction outcome. Specifically, when the reactor is operated in puls-Ž . ing-flow regime, liquid-rich slug pulse and gas-rich slug Ž . base regions are formed, and they move down the column alternatingly. The strong interactions between the phases within the pulses result in significant enhancement in overall Ž mass and heat transfer rates Blok and Drinkenburg, 1982; . Chou et al., 1979 , and be enhanced by operating the reactor in pulsing-flow regime and that optimization is possible by ''tuning'' the pulsing frequency prudently.In the present work, an experimental demonstration of the beneficial effe...

Kinetics of Phenylacetylene Hydrogenation over Pt/γ-Al2O3 Catalyst

“…4,8,9 However, attempts to correlate experimental data with reactor models are limited by the absence of accurate kinetics. By determining the intrinsic kinetics of the system, a valuable tool for analyzing reactor design and evaluating catalyst performance would be provided.…”

Solvent-free semihydrogenation of acetylene alcohols in a capillary reactor coated with a Pd–Bi/TiO 2 catalyst

“…In addition, liquid tends to form preferential pathways between the catalyst particles leading to poor radial dispersion and wide residence time distribution, which in the case of semihydrogenation results in low alkene yield [42][43][44]. Magnetically-recoverable catalysts offer a convenient way of catalyst introduction and good reusability, but the price of the catalysts and complexity of reactor operation seem to be a disadvantage for industrial semihydrogenation at the current stage.…”

Periodic Operation of Three — Phase Catalytic Reactors

“…Sims et al (1994) compared the catalytic decomposition of H 2 O 2 under trickle fl ow and natural pulsing fl ow under the same operating conditions and observed appreciably higher conversion in the latter regime at identical space times. Experiments reported by Wu et al (1998) and in further detail by Wilhite et al (2001) on the catalytic hydrogenation of phenylacetylene to styrene and further to ethylbenzene over a supported Pt catalyst demonstrated improvements in phenylacetylene conversion and on selectivity to styrene arising from operating in a pulsing fl ow regime. The reaction system is triangular, that is, there is a direct path from phenylacetylene to the fi nal product ethylbenzene and it is H 2 mass transfer controlled.…”