Conventional Trickle-bed Reactor Research Articles

Effect of phase maldistribution on performance of two‐phase catalytic monolith reactor and its comparison with trickle bed reactor

AbstractMonolith reactors are widely considered as an alternative to the conventional trickle bed reactor. For the commercial deployment of monolith reactors, comparative performance studies are required. Reliable comparative and performance studies require a detailed understanding of the effect of phase distribution/maldistribution on the performance studies. In this work, performance and comparative studies were carried out in a relatively large column that was 4.8 cm in diameter. Experiments were performed in the same conditions that were used in studies for which phase distribution data were available. Since the properties of the catalyst used were different in both the reactors, the apparent kinetics were studied to facilitate the comparison. The hydrogenation of alpha‐methyl styrene (AMS) was used as a test reaction. From the performance studies, it was found that the effect of maldistribution on the performance was stronger than the catalyst availability. From the comparative studies, it was found that the monolith reactor with maldistributed flow conditions provides higher productivity than the trickle bed reactor.

Effect of reactor configuration on performance of vacuum gas oil (VGO) hydrotreater: Modelling studies

While kinetics is independent of either scale or configuration of hydrotreating reactor, hydrodynamics of reactor depend on both. The hydrodynamics of reactor which comprise of phase mass-transfer, catalyst wetting and pressure drop affect its performance significantly and should be addressed adequately while deciding on configuration or scale up issues. This study evaluates and compares the performance of different configurations of commercial VGO hydrotreater by employing mathematical model encompassing kinetics and hydrodynamics. Two configurations have been studied:•Conventional trickle-bed reactor, subdivided into (a) beds in parallel and (b) beds in series.•Pre-saturated one liquid flow (POLF) reactor, subdivided into (a) reactor with single pre-saturator (POLF-SP) and (b) multiple reactors in series with intermittent pre-saturators (POLF-MP).The performance of conventional reactor in series/parallel is found to be superior to POLF configurations. The inferior performance of POLF configurations is attributed to mixed flow behaviour due to recycle as against plug flow behaviour in conventional trickle-bed reactors.

Liquid backmixing in an inclined rotating tubular fixed bed reactor – Augmenting liquid residence time via flow regime adjustment

The liquid residence time and the backmixing in an inclined rotating tubular fixed bed reactor operated with gas–liquid co-current downflow are studied experimentally. This novel reactor concept is introduced to extent the process intensification strategies of chemical multiphase reactors. The intermittent catalyst immersion due to rotation induces a continuous refreshment of the liquid at the catalyst surface and enhances the access of the gas phase to the catalyst in the drained section of the fixed bed. Depending on inclination angle and rotational velocity, different flow regimes are observed. In particular, the flow regimes with stratified gas–liquid flow can be utilized to enhance the performance of the reactor for heterogeneous catalytic reactions.The backmixing study is based on the method of the imperfect tracer pulse and the propagation of the tracer is measured by low-intrusive wire-mesh sensors. Compared to conventional trickle bed reactors, liquid residence time and axial dispersion are increased by the inclination and rotation. The effects of reactor inclination angle and rotational velocity as well as of particle size and liquid superficial velocity on the liquid backmixing in the inclined rotating tubular fixed bed reactor are shown in detail.

Process Intensification for Hydroprocessing of Vegetable Oils: Experimental Study

Process intensification for hydroprocessing of vegetable oils was achieved using microchannel and monolithic reactors with lower diffusion lengths, a thin layer of catalyst coating, high surface-to-volume ratios, and better heat/mass transfer. Use of such reactors results in improved reaction selectivities and throughput, with reliable utilization of catalysts. Laboratory scale microchannel and monolithic reactors were washcoated with sol–gel prepared Ni–Mo/γ-Al2O3 catalyst. The catalyst was thoroughly characterized by various techniques. Activity tests were performed on the sulfided catalyst for the hydroprocessing of vegetable oil, a mass and heat transfer limited reaction. Both reactors gave up to 20 times higher kerosene selectivities, up to 30 times higher isomer selectivities, and at least 20 times higher throughput than the conventional trickle-bed reactor. Undesirable oligomeric product yield was 3 times lower in the case of the monolithic reactor than in the case of the microchannel reactor.

Transesterification of rapeseed oil for biodiesel production in trickle-bed reactors packed with heterogeneous Ca/Al composite oxide-based alkaline catalyst

A conventional trickle bed reactor and its modified type both packed with Ca/Al composite oxide-based alkaline catalysts were studied for biodiesel production by transesterification of rapeseed oil and methanol. The effects of the methanol usage and oil flow rate on the FAME yield were investigated under the normal pressure and methanol boiling state. The oil flow rate had a significant effect on the FAME yield for the both reactors. The modified trickle bed reactor kept over 94.5% FAME yield under 0.6mL/min oil flow rate and 91mL catalyst bed volume, showing a much higher conversion and operational stability than the conventional type. With the modified trickle bed reactor, both transesterification and methanol separation could be performed simultaneously, and glycerin and methyl esters were separated additionally by gravity separation.

Mathematical modeling of a biofiltration process in a trickle-bed reactor

A conventional trickle bed reactor and its modified type both packed with Ca/Al composite oxide-based alkaline catalysts were studied for biodiesel production by transesterification of rapeseed oil and methanol. The effects of the methanol usage and oil flow rate on the FAME yield were investigated under the normal pressure and methanol boiling state. The oil flow rate had a significant effect on the FAME yield for the both reactors. The modified trickle bed reactor kept over 94.5% FAME yield under 0.6 mL/min oil flow rate and 91 mL catalyst bed volume, showing a much higher conversion and operational stability than the conventional type. With the modified trickle bed reactor, both transesterification and methanol separation could be performed simultaneously, and glycerin and methyl esters were separated additionally by gravity separation.

Diesel upgrading into a low emissions fuel

The revamp of existing diesel hydrotreating units using SHP technology was studied to improve the emission of the diesel engine. Gas and liquid-phase reactors were sequentially added to the actual trickle bed reactor. A special catalyst was employed. Micro-plant kinetic studies were performed and the results compared with those obtained with conventional trickle bed reactor operation. It was shown that using the gas and liquid-phase reactor, the hydrogenation, hydrogenolysis, and ring-opening reactions can be enhanced, so can be the sulfur and cetane number properties. The new scheme decreased the mono-aromatic content in the lighter part of the diesel that improve the NO x and particulate emissions in exhaust gases of a diesel engine. A simplified kinetic model for gas and liquid-phase reactors was developed to optimize SHP reactors and to minimize investment.

Liquid axial dispersion and holdup in column leaching

The liquid phase hydrodynamics in column and heap leaching is a key design aspect that has attracted some attention, but was not yet completely elucidated. On the other hand, conventional trickle bed catalytic reactors have received enormous attention for many decades; however, the operational variables range in this case is generally far from the column and heap leaching processes. This paper presents a hydrodynamic study performed in a bench scale column, where the axial dispersion and the liquid holdup, as a function of the liquid flow rate, are estimated using residence time distribution experiments. The normalized tracer concentrations are fitted using a non-linear least square method and the piston-dispersion-exchange model that is solved numerically using the finite differences method. The trends of axial dispersion, dynamic and static saturation, and exchange coefficient for mass exchange between mobile and stagnant phases, showed excellent agreement with previous results for low Reynolds number in conventional trickle bed reactors. In this study, these experimental results and empirical correlations are presented. The dynamic saturation of the bed increases with the flow rate while the static saturation decreases slightly. The axial dispersion is weak dependent of the liquid flow rate, but is non-negligible and should be accounted for in the mathematical modeling of heap and column leaching process.

Flow Regime Transitions in Trickle‐bed Reactors with Structured Packings

AbstractThe flow pattern in a trickle‐bed reactor (TBR) filled with structured packings (SPs) is inspected within a wide range of gas and liquid velocities using air and water, or CMC solutions of different viscosities, as model fluids. Flow regime transitions are identified from the analysis of time series of the current intensity measured with a polarized electrode that is part of the packing. Results are compared with a reported general correlation for determining flow regime transitions in conventional TBR.

A Novel Countercurrent Fixed Bed Reactor

AbstractA new three‐phase reactor configuration having countercurrent flow of gas and liquid is proposed. The reactor had an internal diameter of 0.04 m and a catalyst bed height of 1 m. A spiral coil made out of wire gauge was inserted inside the fixed bed of catalyst. The gas preferentially passed through the void spaces created due to the presence of the coil. Hydrodynamic studies were conducted using water as liquid and air as gas. The effect of various parameters such as the configuration of the spiral coil, flow rate of gas and liquid on the pressure drop and liquid hold up of the catalyst bed were studied and were also compared with that of a conventional trickle bed reactor.

Modeling of monolithic and trickle-bed reactors for the hydrogenation of styrene

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.

A numerical comparison of alternative three-phase reactors with a conventional trickle-bed reactor. The advantages of countercurrent flow for hydrodesulfurization

A computer model was developed to compare a conventional cocurrent trickle-bed reactor with two novel countercurrent three-phase reactors: the three-levels-of-porosity reactor and the internally finned monolith reactor. The hydrodesulfurization of a vacuum gas oil was taken as a case study. It was found that the application of countercurrent flow in the novel reactors results in significant increase of conversion. Sensitivity for mass transfer and H 2S inhibition were investigated. Reduced mass transfer compared to a conventional trickle-bed does not limit the reaction.

Liquid holdup in the three-levels-of-porosity reactor

Liquid holdup was measured as function of gas and liquid mass flow in the three-levels-of-porosity (TLP) reactor. Packing material and bed height were varied. Because a TLP reactor contains layers of catalyst there is an additional bed holdup compared to conventional trickle-bed reactors. Liquid bed holdup is composed of two parts: below the capillary fill height the interparticle pores are completely filled with liquid, above this height the liquid holdup is well described by literature relations for single-phase trickle-flow. Using residence time measurements it was shown that no stagnant zones for liquid flow existed in the tested TLP packings.

A comparative analysis of the trickle-bed and the monolithic reactor for three-phase hydrogenations

Based on numerical simulations, a quantitative comparison is made between the performance of a conventional trickle-bed reactor (TBR) and a monolithic reactor (MR). The model reaction considered is a consecutive, three-phase hydrogenation for which the kinetics can be described using a rate equation of the Langmuir—Hinselwood—Hougen—Watson (LHHW) type. A mathematical model is formulated for both the TBR and the MR based on literature correlations. The volumetric space-time yield ( STY υ), the selectivity towards the intermediate product and the pressure drop are taken as the main performance criteria. For the model system considered here, the selectivity of the intermediate product was found to be higher for the MR over almost the whole range of variables studied. STY υ is higher for TBR with particles of less than 2 mm diameter, but the pressure drop for such small particles is high. For larger spherical particles it is possible to reach comparable or higher STY υ using MR. The use of a shell catalyst in the TBR was also considered and it was found that by using large particles with a thin shell of active material, the selectivity as well as the catalyst load were comparable to those of the MR. The pressure drop in the MR is always low and sufficient flow rates can be obtained from the hydrostatic pressure alone. This implies that it is possible to operate at zero net pressure drop, which makes internal recirculation of gas very simple.