The term trickle bed is used here to mean a reactor in which a liquid phase and a gas phase flow concurrently downward through a fixed bed of catalyst particles while reaction takes place. The earliest antecedent probably was the so-called “trickling filter” which has long been used for removal of organic matter from wastewater streams by aerobic bacterial action. Biological growths are allowed to attach themselves to a bed of stone or other support over which the wastewater is allowed to trickle in contact with air. Another antecedent appeared in the 1930s when Duftschmid and co-workers at the I.G. Farbenindustrie used evaporative cooling of an inert oil which flowed upwards through a catalyst bed to remove the heat of reaction in a version of the FischerTropsch process for synthesis of liquid fuels from H2 and CO and a later version at the U.S. Bureau of Mines operated with concurrent upflow but without evaporative cooling. This was superceded by an ebulliating bed reactor because of difficulties with cementation of the catalyst in the fixed bed, but commercial scale operations of this process in Germany and elsewhere have all utilized completely vapor-phase reaction (Storch et al., 1951; Crowell et al., 1950; Benson et al., 1954; Kastens et al., 1952). Trickle-bed reactors have been used to a moderate extent in chemical processing, but most of the published information about their industrial applications concerns the processing with hydrogen of various petroleum fractions, in particular the hydrodesulfurization or hydrocracking of heavy or residual oil stocks and the hydrofinishing or hydrotreating of lubricating oils. Their commercial development during the 1950s by the Shell Companies and by the British Petroleum Company has been described by van Deemter (1964), Le Nobel and Choufoer ( 1959), and Lister (1964). The development of hydrocracking and hydrodesulfurization processes by Chevron, Esso (Exxon), Gulf, Union Oil, and others has been described in the proceedings of the various World Petroleum Congresses. Information is fragmentary on uses in chemical processing. A process for synthesis of butynediol (HOCH2C = CCH20H) from aqueous formaldehyde and acetylene uses trickle-bed flow over a copper acetylide catalyst and recycle of the product stream for heat removal (Brusie et al., 1963). Other trickle-bed studies of this reaction are given in a thesis by W. Bill, as reported by Bondi (1971), who also cites trickle-bed studies by H. Hofmann on the hydrogenation of glucose to sorbitol. Kronig (1963) describes a trickle-bed process used in one or more commercial plants for selective hydrogenation of acetylene to remove it in the presence of butadiene in Cq hydrocarbon streams. Operation at 10” to 20°C and 1.9 to 5.8 atm pressure allows liquid-phase processing which reportedly gives long catalyst life, unlike gas-phase processing in which polymers rapidly build up on the catalyst. The standard commercial process for manufacture of hydrogen peroxide utilizes a working solution of an alkyl

Trickle-bed reactors

Publisher Summary At the heart of the liquid-phase processes, gas scrubbing process, manufacturing of pure products, and biological systems, there exists the absorber or the reactor of a particular configuration best suited to the chemical absorption or reaction being carried out. Its selection, design, sizing, and performance depend on the hydrodynamics and axial dispersion, mass and heat transfer, and reaction kinetics. This chapter focuses on the subject of mass transfer with chemical reaction. It presents the techniques, results, and opinions on mass-transfer coefficients and interfacial areas in most types of absorbers and reactors. To study gas–liquid mass-transfer phenomena, it is convenient to consider steady-state situations in which the composition of the gas and the liquid are statistically constant when averaged over time in a specified region, such as a short, vertical slice of a tubular column or the entire volume of a single-compartment agitated vessel. Useful predictions have been developed for describing the behavior of complicated systems, using highly simplified models that simulate the situation for practical purposes without introducing a large number of parameters. The procedure differs depending on whether physical or chemical absorption is involved.

Mass-Transfer Rates in Gas-Liquid Absorbers and Reactors

Treatment of oil-in-water emulsions by coagulation and dissolved-air flotation

Destabilisation of oil-water emulsions and separation by dissolved air flotation.

Separation of oil from water by dissolved air flotation

Flow pattern and pulsation properties of cocurrent gas-liquid downflow in packed beds

Paying attention to the discrepancy between available data, probably due to the uncertainty in void fraction, the entrance end effect and characteristics of the experimental method, newexperimental results were obtained for air-water flow in 65.8 and 122 mmφ. columns packed with glass spheres of six different sizes between 2.59 and 24.3 mm0.The two-phase pressure loss based on an energy (not momentum) balance was correlated in terms of Lockhart-Martinelli parameters as follows : φl=1.30+1.85χ-0.85, 0.1<χ<20The total liquid holdup Ri was determined by weighing the excess weight of bed in operation over the dry column. The result was dependent on the specific surface area of the bed as and correlated by Rl=0.40 as1/3χ0.22 (as in mm-1)The present result on total holdup was higher than available results obtained by quickclosing valve, which measured probably the operating holdup. Data of void fraction for spherical packings are appended and the differences in void fraction and its reproducibility due to packing procedure are noted.

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Pressure loss and liquid holdup in packed bed reactor with cocurrent gas-liquid down flow

Mass transfer coefficient kls was measured over a range of flow rates of gas Ug= 0-100 cm.s-1 and liquid Ul=0.05-25 cm.s-1 in a column packed with spheres of three different diameters d=2.8-12.7 mm. The systems used were the dissolution of benzoic acid in water and diffusionlimited oxidation of brass with dichromate ion in sulfuric acid solution. The effect of Ug on kls is not found at all in gas continuous flow, is the greatest in pulse flow and becomes less significant again in dispersed bubble flow. The value of kls increases rapidly around the transition from gas continuous to pulse flow. The enhancement factor β (=kls in two-phase flow/kls in single-phase flow) increases from 1.2 to 2 with increasing d in gas continuous flow while it equals the reciprocal of liquid holdup in pulse and dispersed bubble flows. A liquid-film analogy in gas continuous flow and a single-phase analogy in pulse and dispersed bubble flows are proposed and the experimental results are examined in the light of them.

https://www.jstage.jst.go.jp/article/jcej1968/9/3/9_3_220/_pdf

Liquid-to-particle mass transfer in fixed bed reactor with cocurrent gas-liquid downflow

Volumetric absorption coefficient (ka)lg, specific interfacial area alg and mass transfer coefficient klg were measured for two-phase cocurrent flow of O2-water and CO2-NaOH systems in a column packed with glass spheres of 3 different sizes (2.59-12.2 mm). Values of (ka)lg observed were so high as to be that can be hardly attainable in conventional gas-liquid contactors. This is due to large alg of small bubbles dispersed in liquid where alg very often exceeds the geometrical surface area of packing. Values of klg range from 2 to 8×10-4m/sec, which are comparable to that of circulating bubbles in the usual systems. The effect of superficial gas velocity on (ka)lg and alg is much greater than that in a countercurrent packed column, while the effect of liquid velocity is approximately same. A liquid-phase energy loss El per unit volume of liquid contained in a bed was newly defined as a measure of microscopic flow intensity and was used for discussion and correlation of mass transfer properties. It was found that the bubble diameter is proportional to El-2/5.

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Liqusd phase mass transfer in packed bed reactor with cocurrent gas-liquid downflow

A loop reactor is regarded as a new type of reactor for bulk polymerization of olefins. Several approaches to evaluate its performance are made herein. A simple model of discharge flow is proposed and related with the results obtained by measurement of average circulation velocity. The average circulation velocity is proportional to impeller speed and the sine of the impeller blade angle. It depends upon Reynolds number and dimensions of the impeller. Flow pattern was measured and the influence of baffles and impeller geometry is discussed qualitatively. In the case of unbaffled conditions, fluid flows in a helical motion. Intensity of this motion increases with impeller speed and pitched angle. In the case of baffled conditions, tangential velocity component is suppressed and normalized distribution of axial velocity is independent of impeller geometry. Pressure distribution was measured and pressure loss was obtained. Total pressure loss shows good agreement with the value calculated by superposition of frictional loss in straight parts and bend loss in bends obtained from established correlations.

Tsutomu Hirose

Papers

Flow pattern and pulsation properties of cocurrent gas-liquid downflow in packed beds

Pressure loss and liquid holdup in packed bed reactor with cocurrent gas-liquid down flow

Liquid-to-particle mass transfer in fixed bed reactor with cocurrent gas-liquid downflow

Liqusd phase mass transfer in packed bed reactor with cocurrent gas-liquid downflow

Flow pattern, circulation velocity and pressure loss in loop reactor.