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Trickle-bed reactors (TBR) are often applied in chemical and petrochemical industry. The performance of these reactors can be improved substantially by periodic operation of the liquid feed and/or operation in the natural pulsing flow regime. The aim of this pilot plant study is to present a flow map for the cumene–hydrogen system at elevated pressures, and to evaluate the reactor performance improvement obtained by periodic operation of a trickle-bed reactor. The experiments presented in this work are performed in a pilot plant reactor of 0.051 m diameter and 1.2 m length.The transition from trickle to pulsing flow depends on fluid physical properties, operating conditions, and geometrical parameters. Although many industrial trickle-bed reactors using organic liquids are operated at high pressure, the transition map for these systems is scarcely reported in literature. In this study, the effect of operating pressure on transition from trickle to pulse flow has been investigated in the pressure range of 0.14–2.0 MPa. The boundary between trickle and pulse flow shifts towards higher superficial liquid velocity when the operating pressure increases.The hydrogenation of α-methyl styrene (AMS) over 2 wt.% Pd/C catalyst was selected as test reaction. The reaction is performed at a liquid inlet temperature of 40 °C and at an operating pressure of 0.2 MPa. The cyclic operation mode is compared with the trickle operation mode. It is found that periodic operation results in a significant improvement in reaction rate. [Copyright &y& Elsevier]

Monolith reactors are being studied as a replacement for conventional multiphase reactors such as trickle-bed reactors, slurry reactors, and slurry bubble column reactors for gas-liquid-solid reactions. Reactors with monolith catalyst packing have been found to be hydrodynamically superior to existing industrial reactors. This review covers multiphase reactions carried out in monolith reactors by various researchers. It first defines the monolith reactor and looks into the geometrical aspects of monolith. The section dealing with hydrodynamics reviews pressure drop, phase holdup, flow distribution, and dispersion characteristics. This study also considers the tools used to characterize the hydrodynamic parameters and their typical values. Although the available literature is scarce, monoliths are considered to have superior mass transfer characteristics. This review lists the mass transfer correlations for each category (gas-liquid, gas-solid, liquid-solid). The last section discusses the reaction aspects of monolith reactors. The ultimate goal is to implement such reactors for multiphase reactions. This section also compares the performance of monolith reactors with conventional multiphase reactors and lists the various reactor models reported to predict the overall performance of monolith reactors. [ABSTRACT FROM AUTHOR]

Catalytic liquid phase oxidation of aqueous phenol was studied in a pilot plant trickle bed reactor using a copper oxide catalyst supported on alumina. Catalysts were prepared by impregnating CuO on alumina extrudates and on computer designed shape (CDS) alumina pellets. Phenol oxidation was carried out in a 2.54cm diameter reactor with a catalyst bed length of 60cm and in the pressure range of 1–15atm and temperature range of 373–403K Compared to alumina extrudates higher phenol conversion was achieved over CDS pellets under identical conditions. Phenol oxidation reaction was strongly affected by the temperature and pressure, however, pressure had less effect. Hydrodynamics of the reactor had strong influence on phenol oxidation reaction. A one dimensional axial dispersion model was proposed to simulate the experimental results. The model satisfactorily explains the experimental results with a deviation of ±15%. [Copyright &y& Elsevier]

Excessive biomass formation in two-phase flow trickle-bed bioreactors induces clogging and leads to the progressive obstruction of the bed that is accompanied with a buildup in pressure drop and flow channeling. Currently, physical models linking the two-phase flow to the space-time evolution of biological clogging are virtually nonexistent. An attempt has been made with this contribution to fill in this gap by developing a unidirectional dynamic multiphase flow model based on the volume-average mass, momentum, and species balance equations. Phenol biodegradation by Pseudomonas putida as the predominant species immobilized on activated carbon was chosen as a case study to illustrate the consequences of formation of excessive amounts of biomass. Furthermore, in developing the transient model, the following basic processes were assumed to occur and have been accounted for in the mathematical model: oxygen transport from gas into liquid bulks, phenol, and oxygen transport from the liquid phase to the biofilm surface, simultaneous diffusion and reaction of phenol and oxygen within biofilm, as well as their simultaneous diffusion and adsorption within the porous supporting particles. [ABSTRACT FROM AUTHOR]

In this work, a comparative study on the combined effects of hydrodynamics and kinetics on the hydrodesulfurization (HDS) of a straight-run gas oil (SRGO) using a trickle-bed reactor with and without diluent (SiC) and different catalyst volume (0.1, 0.07, and 0.050 × 10−3 m3, respectively) was carried out. The tests were conducted in a pilot plant under conditions close to those used in industrial-scale units (5492 kPa, 445.4 m3(STP)/m3 H2/oil ratio, 623–643K, 0.9 and 2.5 h−1 LHSV values). The catalyst used was a commercial CoMoP/Al2O3 formulation shaped as tri-lobed extrudates (1/20 in, nominal size) or as crushed particles (dp = 1.2 × 10−3 m). Contrarily to that usually claimed, the undiluted systems showed better performance than those comprising small diluent (SiC) particles (dp ˜ 5 × 10−5 m). Calculations to evaluate hydrodynamic variables (plug-flow behavior, wall effects, wetting, and back-mixing) were carried out in order to explain the observed facts. The possible influences of the size of the diluent particles used are discussed. [ABSTRACT FROM AUTHOR]

Trickle bed reactors are widely used in many process industries. The catalyst particles are often incompletely wetted especially in the trickling flow regime and hence to design these reactors, the effectiveness factor of partially wetted catalyst needs to be calculated accurately. Numerical solutions by traditional methods are time consuming and not very accurate, especially for some commonly used complex catalyst shapes such as trilobes, quadrilobes etc. The paper presents a novel numerical solution for these problems based on the method of fundamental solutions. The advantage of the method is that it involves only boundary collocation and can be applied to catalysts of any shape. Further the method provides an accurate estimate of the gradient of the concentration profiles and this information can be related directly to the effectiveness factor. This accuracy of the method is demonstrated for two dimensional (2-D) and axisymmetric problems for a linear kinetics. Illustrative results are presented for some complex shapes under partial wetting conditions. [Copyright &y& Elsevier]

A systematic experimental analysis of the parameters affecting the behaviour of a Trickle Bed Reactor (TBR) was performed. Lignin peroxidases (LiPs) were produced in the reactor by Phanerochaete chrysosporium entrapped in a Ca-alginate film covering ceramic supports (Berl saddles). Gas and liquid velocity, liquid flow regime, and thickness of encapsulating matrix were experimentally investigated. Reactor productivity and biological activity were considered as representative of reactor performance and evaluated by six probe parameters to take into account different process system configurations, i.e. single LiP extraction, multiple LiP extraction every 24 h and in vivo applications. Liquid fluid dynamics were the critical phenomena affecting LiPs production; the ranges of gas and liquid superficial velocity influencing the reactor performance were also identified. Alginate film thickness was shown to influence specific biomass activity but a limited impact on reactor productivity was verified. [Copyright &y& Elsevier]

A kinetic study into the styrene hydrogenation over a palladium on alumina catalyst has been made. Styrene was used as a model component for pyrolysis gasoline. A kinetic rate expression has been derived and the inhibiting effect of sulfur components has been included. Using this kinetics and mass-transfer models compiled from literature, the performance of two types of reactors for the styrene (pyrolysis gasoline) hydrogenation has been evaluated. A structured reactor such as a monolith has large advantages over a conventional trickle-bed reactor. For the monolithic reactor a more than 3 times higher volumetric productivity is obtained with much less catalyst. The modeling results indicate that deactivation by gum formation should be significantly less due to much better hydrogen mass transfer in the reactor. [Copyright &y& Elsevier]

Catalytic wet oxidation of phenol was studied in a batch and a trickle bed reactor using 4.45% Pt/TiO2 catalyst in the temperature range 150–205°C. Kinetic data were obtained from batch reactor studies and used to model the reaction kinetics for phenol disappearance and for total organic carbon disappearance. Trickle bed experiments were then performed to generate data from a heterogeneous flow reactor. Catalyst deactivation was observed in the trickle bed reactor, although the exact cause was not determined. Deactivation was observed to linearly increase with the cumulative amount of phenol that had passed over the catalyst bed. Trickle bed reactor modeling was performed using a three-phase heterogeneous model. Model parameters were determined from literature correlations, batch derived kinetic data, and trickle bed derived catalyst deactivation data. The model equations were solved using orthogonal collocations on finite elements. Trickle bed performance was successfully predicted using the batch derived kinetic model and the three-phase reactor model. Thus, using the kinetics determined from limited data in the batch mode, it is possible to predict continuous flow multiphase reactor performance. [Copyright &y& Elsevier]

Traditionally the intermediate scale and fine chemicals industries have relied on stirred tank reactors, operated continuously or more commonly batchwise, as the work horse of their manufacturing plant to the almost total exclusion of any other type of liquid reactor. The switch to continuous processing has generally been resisted on the basis that this compromises plant flexibility and thus, reduces capital productivity. While the stirred tank and the associated slurry catalyst are of course reliable and flexible to the demands of multi-product plant, it is not always easy to scale up the chemistry from the laboratory and variability in product arises from imperfections in the mixing. This problem is exacerbated for multiphase reactions where the non-uniformity in mixing and mass transfer can lead to significant variance in reaction rate and selectivity, resulting in loss of product quality and productivity. The problem is that while the stirred tank is convenient, it is not in fact a particularly effective mixing device. While historically the stirred tank was one of few options, times are changing. There are many reactor designs now available for multiphase contacting and reaction. Some of these are a proprietary improvement on the simple stirred pot while others are significantly different, such as trickle beds, bubble columns and the use eductors and loop reactors for intense gas/liquid mixing. Interest is increasing into applying process and reactor intensification techniques to batch production through use of small flow channels and structured catalysts, of which monoliths are the best known example. This is however, but one example of work on structured catalysts and reactors that is expected to have an impact on the intermediate scale and fine chemicals manufacturing in the near future. [Copyright &y& Elsevier]

The stability of the hydrodynamic states corresponding to the operation on two branches of the hysteresis loop of pressure drop was examined for a trickle bed. The effect of nonsteady operation on the pressure drop and the gas-liquid mass transfer rate was investigated with several types of periodical perturbation on gas flow rate. It is found that the pressure drop and mass transfer coefficient obtained during operation under the conditions of the lower branch can be increased up to or even beyond those obtained by following the upper branch of the loop without necessarily traversing along the loop to pass through the pulsing point. These results shed light on the mechanism of performance enhancement by periodical operation of trickle beds and might provide a possible way to improve the operation of trickle bed reactors. [ABSTRACT FROM AUTHOR]

A fully predictive one-dimensional mechanistic model was developed for describing the hydrodynamics of power-law fluids in trickle-bed reactors. The model is a generalization of the slit approach to the case of non-Newtonian fluids obeying Ostwald–deWaele rheological behavior. Without recourse to adjustable parameters, the proposed model enabled prediction of the experimental values of (i) total two-phase total pressure drop and total liquid holdup in the trickle flow regime, (ii) frictional pressure drop in single-phase flows through packed beds, and (iii) total liquid holdup in gravity driven liquid downflow and stagnant gas through packed beds. Parametric simulations guided by knowledge of the behavior of highly viscous Newtonian liquids in trickle beds highlighted the capability of the model in the simulation and design of trickle flow operation using power-law fluids. [Copyright &y& Elsevier]

Effects of pH, moisture and flow pattern on the performance of a trickle-bed air biofilter (TBAB) treating benzene, toluene, ethylbenzene and o-xylene (BTEX) waste gas were investigated to establish the optimum operating conditions and design criteria. In the pH range of 7.5–8 and NFR range of 6.02–8.6 l/m3/h, removal efficiencies of each compound were greater than 80% with a loading of 143 g BTEX/m3/h. The TBAB appears to be an effective process for controlling BTEX emission with a high loading. Counter-current flow TBAB has the advantages of more uniform BTEX removal and biomass growth in each section than co-current flow TBAB, but suffers from a higher pressure drop across the bed. [Copyright &y& Elsevier]

A three phase heterogeneous model was used to analyse the performance of a pilot plant trickle bed reactor employed for hydrodesulphurisation of atmospheric gas oil fraction. have presented a three phase heterogeneous model for hydrodesulphurisation of vacuum gas oil in a trickle bed reactor and showed that it can be used to include the inhibiting effect of hydrogen sulphide on sulphur conversion. This model was based on two film theory and incorporated mass transfer phenomena at the gas–liquid and liquid–solid interface. The chemical reaction rates were described using Langmuir-Hinshelwood mechanism. Though heterogeneous models are assumed to be more rigorous than the pseudo homogeneous models, the validation data using different reactors and reaction systems is scarce. The present study aims to validate the model with particular attention to show the influence of hydrodynamic parameters and intrinsic rates of reaction on reactor performance. The model predictions were compared with experimental observation under wide range of operating conditions. The data generated on hydrodesulphurisation of an atmospheric gas oil fraction over commercially available CoO–MoO3/A12O3 catalyst was used to test the model. The simulation showed good agreement with the experiments carried out in a wide range of operating conditions. [ABSTRACT FROM AUTHOR]

Attempts to employ a trickle-bed air biofilter for treating acetone (AT) and methylacetate (MA) mixtures under different influent carbon loadings. Description of the biofilter process; Higher removal efficiencies of MA than those of AT; Efficiency of TBAB for treating ATMA emission with low to medium carbon loadings.

Evaluates a trickle-bed air biofilter performance for treating mixtures of ethylacetate (EA), toluene (T) and xylene (X) volatile organic compounds. Analysis of carbon balance; Elimination capacities of EA, T and X; Rate of leachate production.

Analyzes the effect of water content on the removal of volatile organic compounds in gas phase trickle bed biofilters. Use of periodic backwash to remove excess biomass; Mass transfer limitations due to water retained in the reactor; Biofilter removal with respect to ether removal.

• Pressure drop, liquid holdup measurements. • Transition flow regime identification. • Commercial catalyst shapes effects on the flow regimes, pressure drop, and liquid holdup. • Phenomenological and empirical models to investigate effect of catalyst shape on hydrodynamics. An atmospheric experimental study was carried out to measure hydrodynamics (pressure drop and liquid holdup) in TBR. The current work aimed to investigate the influence of catalyst shape, gas flow rate, and liquid flow rate on hydrodynamics through different industrial catalyst beds that comprised spherical, cylindrical, trilobe, and quadrilobe. Air was used as a gas phase with an extensive range from 0.03 to 0.27 m/s, while water was used with a range from 0.004 to 0.016 m/s, within 0.14 m inside diameter of a cylindrical column and 2 m bed length through various packing beds. The measured data were compared with two model approaches (phenomenological and empirical approaches) to investigate the effect of catalyst shape, gas flow rate, and liquid flow rate on the pressure drop and liquid holdup. The phenomenological model developed based on a physical picture with no two-phase fitted parameters. Ergun coefficients for a single-phase fluid flow were implemented to represent the bed characteristics in the bed. Modified Ergun coefficients were determined for each bed and compared with universal Ergun coefficients (E* 1 = 150 and E* 2 = 1.75) and non-spherical universal coefficients (E* 1 = 180 and E* 2 = 1.8). The comparison for total data regardless the bed indicated a maximum deviation of ±56% with Ergun and non-spherical coefficients, while decreased to a negligible value of 7% with modified coefficients. The results revealed a significant impact for catalyst shape, gas flow rate, and liquid flow rate on the hydrodynamics. Furthermore, the comparison between the data and models showed the phenomenological model exhibited a better agreement than the empirical model with a mean relative error for the pressure drop of 31.81% and the liquid holdup of 10.36%. [ABSTRACT FROM AUTHOR]

• Convection and mass transfer of H 2 into a film on a single 1% Pd/C pellet were decoupled. • Hydrogen uptake was significantly affected by dissolved hydrogen in the feed. • A new two stage mass transfer model was developed and fitted to the uptake data. • The model accounts for H 2 transfer over inert and catalytically active surfaces. • Catalyst productivity in mol/kg Pd increases if the G-L surface area in m2/kg Pd is increased. Heterogenous hydrogenations of high value chemicals are a widely used class of reaction that potentially benefit from the advantages continuous processing possesses. Trickle bed reactors offer a viable alternative to batch manufacture, however further understanding of the interplay between hydrogen mass transfer and catalytic reaction is required to facilitate the uptake of such technologies. To isolate the transport processes, the hydrogenation of styrene was conducted with a single 1% palladium on carbon pellet immobilized within glass beads with a liquid feed either hydrogen saturated or hydrogen free and the liquid flow rate was varied. The transfer rate of hydrogen was found to be significantly affected by the hydrogen content in the feed. The observations are well described by a new model in which the pellet film is treated as a plug flow reactor, with mass transfer from the gas phase to the film modelled as diffusion through a stagnant film, and mass transfer from the film to the catalyst surface and the subsequent reaction modelled as resistances in series. Our findings indicate that the provision of inert mass transfer area to saturate the fluid with hydrogen can significantly increase the productivity per unit mass of catalyst. In addition, by controlling the ratio of catalytic and inert surface the hydrogen concentration close to the catalyst surface can be tuned. This could be utilised to adjust both the activity and selectivity of the system and therefore, give trickle bed reactors an advantage in chemical manufacturing processes. [ABSTRACT FROM AUTHOR]

Intensified trickle bed reactors were developed for catalytic wet air oxidation (CWAO) of phenol, by generating microbubbles before gas/liquid fluid flows along catalyst packed‐beds. By coupling gas‐liquid microdispersion module, phenol disappearance rate significantly increases under the same operating conditions and phenol conversion reaches 92% in 22 seconds at 160°C and 1000 kPa. Effects of operating conditions were studied systematically and results demonstrated characteristics of high‐interaction regime at low Reynolds number. Comparison of effects among mass transfer and reaction steps shows CWAO reaction is controlled by resistance to liquid‐solid mass transfer of phenol in most cases, while gas‐liquid mass‐transfer‐resistance is ignorable. A dimensionless correlation, Sh = 2.29φ−0.91(ReL + ReG)0.04, was established, by considering influences of liquid film thickness and fluid flow situations on liquid‐solid mass transfer coefficient in microbubble‐in‐liquid/catalyst‐particle system. The study would provide an effective method for intensifying CWAO and other liquid‐solid‐mass‐transfer‐resistance‐controlled gas/liquid/solid catalytic reactions and help understand mass transfer mechanism in new gas/liquid/solid system. [ABSTRACT FROM AUTHOR]

To improve the reactor efficiency, this study investigated the influence of temperature on the biological hydrogen methanation (BHM) in trickle-bed reactors (TBR). Rising temperatures increase the metabolic activity of methanogenic microorganisms, thus leading to higher reactor specific methane formation rates (MFR). In order to quantify the potential for improved performance, experiments with four different operating temperatures ranging from 40 to 55 °C were carried out. Methane content increased from 88.29 ± 2.12 vol % at 40 °C to 94.99 ± 0.81 vol % at 55 °C with a stable biological process. Furthermore, a reactor specific methane formation rate (MFR) of up to 8.85 ± 0.45 m3 m−3 d−1 was achieved. It could be shown that the microorganisms were able to adapt to higher temperatures within hours. The tests showed that TBR performance with regard to BHM can be significantly increased by increasing the operating temperature. [ABSTRACT FROM AUTHOR]

This work describes the development of a new technique to measure local liquid velocity (VLL) for multiphase flows in trickle bed reactors (TBRs) (gas–liquid–solid system). In the studied TBR, the liquid phase is represented by water, gas by air and 3 mm expanded polystyrene beads as the solid packing. Three different superficial liquid velocities (VSL) and a constant superficial gas velocity (VSG) were used in the packed bed with an internal diameter of 4.25 cm. While the liquid is moving into the packed bed, tracking particles of 106–125 μm diameter (16.45% difference) are injected. The movement of the tracking particles is monitored and digitally recorded by a complementary metal–oxide–semiconductor detector. In this experiment, x-rays were used as the radiation source. Four replications were made with fresh packing. Comparable observations can be found from other published techniques (i.e. magnetic resonance imaging). Results from this study indicate that, at VSL = 0.13 cm s−1, the measured VLL can reach up to 51 times that of its VSL, while for VSL = 0.27 cm s−1, the measured VLL reached up to 35 times higher than the VSL and for VSL = 0.39 cm s−1, the VLL reached up to 39.8 times higher than its VSL. Through statistical analysis, the implementation of such a method is found to be reproducible throughout the experiments. The mean per cent difference in the measured VLL was 10% and 5% for lower implemented VSL of 0.13 and 0.27 cm s−1, respectively. At higher VSL (0.39 cm s−1), the particle tracer was greatly distributed and carried away by the high liquid flow rate. The variance or the range of the measured VLL does not vary for all replications in every VSL, which confirms the reproducibility of the experimental measurements, regardless of the VSL. [ABSTRACT FROM AUTHOR]

This study consisted of the preparation of iron carbides, structure determinations of these iron carbides, determination of reactions of the iron carbides during Fischer-Tropsch synthesis (in situ XRD) and the stability of Hägg carbide (x-Fe5C2) during FTS under commercial fixed bed reactor conditions. Time-temperature-transformation graphs were determined for iron catalysts with and without potassium promoter. [ABSTRACT FROM AUTHOR]