Operation Of Trickle-bed Reactor Research Articles

Epoxidation of Light Olefin Mixtures with Hydrogen Peroxide on TS-1 Catalyst

The direct epoxidation of mixed ethene and propene feedstocks using hydrogen peroxide over a titanium silicalite (TS-1) catalyst was investigated within a continuous trickle bed reactor operating in laboratory scale. Methanol was employed as the reaction solvent. This study aimed to streamline the epoxidation process by obviating the need for prior separation of alkenes, thereby enhancing process efficiency. An extensive array of operational parameters was explored in a trickle bed reactor, encompassing experimental parameters such as temperature, total pressure, hydrogen peroxide concentration, liquid flow rate, and gas composition. In contrast to prior investigations involving separate ethene and propene epoxidation, this study revealed a reduction in epoxide selectivity. The principal by-products observed were methoxy species, formed through the interaction between the epoxide and methanol, resulting in a ring-opening reaction. The influence of water on this ring-opening process was negligible. Notably, the tunability of the system was demonstrated, highlighting low temperature and elevated partial ethene pressure as pivotal factors for augmentingthe epoxide selectivity. The findings suggest that binary olefin mixtures exhibit diminished selectivity but improved stability. This behavior is potentially linked to the olefin solubility in methanol, or alterations in the surface species concentrations, typically associated with catalyst activity variations. These insights offer a valuable foundation for understanding and optimizing the direct epoxidation of mixed ethene and propene feedstock.Graphical

Computational Investigation of Liquid Holdup and Wetting Efficiency Inside Trickle Bed Reactors with Different Catalyst Particle Shapes

Liquid holdup and wetting efficiency are essential parameters for design of trickle bed reactors. Both parameters play an important role in reactor performance including pressure drop, conversion, and heat transfer. Empirical formulas are usually employed to calculate liquid holdup and wetting efficiency. However, factors such as particle shape and the wetting ability of liquid on the particle surface are not described clearly in traditional formulas. In this paper, actual random packing was built by DEM and CFD simulations were performed to investigate the factors affecting liquid holdup and wetting efficiency in trickle bed reactors, including particle shape, surface tension, contact angle, liquid viscosity, liquid density, liquid, and gas superficial velocity. Detailed fluid flow and liquid-solid interaction were described by VOF model. Four different particle shapes were investigated. It showed the particle shape has great effect and the 4-hole cylinder packing gained both highest liquid holdup and wetting efficiency. The overall simulations gave a detailed description of phase interactions and fluid flow in the voids between catalyst particles and these results could give further guidance for the design and operation of trickle bed reactors.

Performance enhancement of trickle bed reactor for the removal of organic compounds from petroleum industrial wastewater

Catalyst Wet Air Oxidation of phenol Promoted with Hydrogen Peroxide (PP-CWAO) was studied experimentally in this work using a trickle bed reactor operating in both steady state and periodic operation (liquid flow modulation). The effect of cyclic parameters (cycle period and split) are investigated under the same conditions chosen on the basis of the steady state results for PP-CWAO. The results showed that the PP-CWAO of phenol are kinetically controlled for steady state operation. For periodic operation, the time average conversion enhancement is indeed quite considerable in liquid flow modulation as split is lowered from steady state cycle split (σ = 1) to a value of (σ = 0.5) and reached as much as 6.66 % over the steady state at cycle period (τp) = 15 sec.

Hydrodynamics of Trickle Bed Reactors with Catalyst Support Particle Size Distributions

Characterization of the hydrodynamics enables operation of trickle bed reactors within the desired flow regime and under conditions for uniform distribution of gas and liquid, resulting in an essentially plug flow contacting pattern. Studies reported in the literature are typically restricted to systems of beds packed with catalyst supports of a uniform size. This work addresses the impact of supports with particle size distributions on reactor hydrodynamics. An experimental database of pressure drop and liquid holdup was developed and, by careful definition of the particle diameter, literature models were adapted to account for the particle size distribution. The resulting models give improved predictions for packing media with a particle size distribution while maintaining applicability to uniform systems.

Cyclic operation of trickle bed reactors: A review

Familiarized with the steady state behavior and advantages of the trickle bed reactors (TBR), for the past two decades, researchers and process engineers are continuously exploring the unsteady state hydrodynamics of periodically (or cyclic) operated trickle bed reactors to extract even more from its efficiency and performance. Despite its complicated nonlinear behavior that attributes to the process control safety at the commercial scale, cyclic operation of TBR is a promising process intensification technology that has immense potential for implementation on industrial TBR. In this paper, we have summarized and reviewed the research and progresses made in recent years on cyclic operation of TBR and potential applications of various mode of its operation. Several issues associated with its hydrodynamics scale-up and designs have been discussed with an emphasis on shock wave attenuation that arises during flow modulation.

Selective Hydrogenation of 1-Heptyne in a Mini Trickle Bed Reactor

The selective hydrogenation of 1-heptyne over a 2 wt % Pd/Al2O3 catalyst was studied in a trickle bed reactor operating in both batch recycle and continuous modes. The reaction was studied in a range of different solvents, including isopropanol, hexane, mixtures of these two solvents, and also isopropanol with small quantities of water and base (NaOH) added. It was found that the rate of reaction was fastest in hexane, owing to the higher hydrogen solubility in this solvent. However, the selectivity toward 1-heptene was higher in isopropanol, with over 95% selectivity being maintained for 120 min of the total 240 min reaction time. The addition of water or base led to an increase in reaction rate, possibly through modification of the adsorption equilibria at the catalyst surface or direct involvement in the reaction. The hydrodynamics of trickle flow upon the reaction were investigated, showing that increasing liquid flow rate led to enhancement of reaction rate, although a plateau was eventually reached ...

Modelling of unsteady-state hydrodynamics in periodically operated trickle-bed reactors:Influence of the liquid-phase physical properties

Process intensification using periodic operation of trickle bed reactors (TBRs) is still a long way from replacing conventional steady-state operation in industrial use, despite the numerous benefits described in the literature. Complex interactions between hydrodynamics, mass transfer and reaction phenomena make the design of periodically operated TBRs an almost insurmountable challenge. The development of hydrodynamic models able to provide reliable quantitative predictions of flow behaviour and possessing a sound physical basis, is an essential prerequisite for obtaining the necessary insights into this complexity. In this work, the two-phase pressure drop and dynamic liquid hold-up during max/min and on/off periodical operation were predicted using a model based on the relative permeability concept. In order to demonstrate the utility of this approach, a systematic investigation of the quantitative influence of the liquid-phase physical properties was carried out. The results obtained show that the modelling of the hydrodynamics in periodically operated TBRs using the relative permeability concept is feasible. By selecting suitable permeability parameters, unsteady-state hydrodynamics for different periodic operating modes can be predicted successfully.

Trickle bed reactor operation under forced liquid feed rate modulation

Paper deals with study of behavior of trickle-bed reactor under periodic feed rate modulation conditions. Unsaturated hydrocarbons hydrogenation (typical for pyrolysis gasoline hydrotreatment) was investigated. As model reactions hydrogenation of cyclohexene and styrene on egg-shell type palladium catalyst was studied. Numerical solution of theoretical model predicting strong effect of period split on a reactor performance is discussed. Periodic operation can enhance trickle-bed productivity due to decrease of flowing liquid film thickness and by increase of mean reactor temperature. Brief data about experimental pilot plant unit for investigation of dynamic operation of trickle bed reactor are presented.

Periodic Operation of Trickle Bed Reactors: An Approach To Catalyst Design through Modeling at the Particle Scale

The behavior of an isothermal catalytic particle in a TBR with ON-OFF liquid flow modulation has been modeled considering isothermal conditions. The impact of catalytic properties has been investigated considering uniform and egg shell distributions. Furthermore, the effect of varying inert core porosity for egg shell catalysts has also been addressed. The model represents experimental trends observed for slow and intermediate cycling. In most cases, egg shell catalysts presented a better performance in comparison with uniform catalysts. However, during cycling, performance depends on working conditions and catalytic properties. Therefore, catalyst design and mode of operation are related issues that need to be defined jointly. The relevance of internal processes (reaction, diffusion, and accumulation) and external transport on overall performance has been addressed. Therefore, the model would serve as a basis, coupled with the development at reactor scale, for the integral reactor design.

Periodically operated trickle-bed reactor for EAQs hydrogenation: Experiments and modeling

The influence of periodic operation on a consecutive reaction, the hydrogenation of 2-ethylanthraquinones (EAQs) over Pd / Al 2 O 3 , on a laboratory-scale trickle-bed reactor (TBR) was studied. The effects of operating parameters including cycle period, split, pressure, temperature, and time-average flow rate on the performance were experimentally examined in comparison with the steady-state operation. The results showed that under the interested operating conditions the conversion and the selectivity improved by 3–21% and 1–12%, respectively. A dynamic model consisting of a set of partial differential equations (PDEs) was developed to simulate the periodic operation of TBR for EAQs hydrogenation. The PDEs were converted into a set of ordinary differential equations (ODEs) using the method of lines (MOL) and then numerically solved by the semi-implicit Runge–Kutta method. The developed model was verified by simulating the effect of cycle period and split on the conversion and the selectivity enhancement and compared with the experimental results. It was found that the model was reliable and satisfactory when the cycle period was less than 200 s.

Elevation of performance of gas–liquid reactors on solid catalyst

Different kinds of initial conditions for the gas–liquid process on a solid catalyst are discussed in the paper. The advantages of process with preliminary saturation of liquid with gas are considered. For the liquid batch reactor it is theoretically shown that preliminary saturation of the initial solution with gas prior to reaction profits more in comparison with “usual” mode. The experiments on hydrogenation of ethyl ether of p-nitrobenzoic acid to anesthesyne on suspended 5% Pd/C catalyst in a batch reactor were carried out for verification of the main results from the proposed model ( P H 2 =40 bar, T=20–120 °C). As an example of a reactor, where the preliminary saturation effect can be used, the trickle-bed reactor operating without pumping was considered. Mathematical simulation of such type reactor is presented.

Effect of Forced Periodical Perturbation on Stability of Hydrodynamic States and Gas-Liquid Mass Transfer in a Trickle Bed

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.

How to Prevent Runaways in Trickle-Bed Reactors for Pygas Hydrogenation

In the past, several runaways have occurred in Trickle-Bed Reactors (TBR) used for the hydrogenation of pyrolysis gasoline as produced in ethylene cracking installations. This phenomenon has been studied in the framework of a special program in the Netherlands, which is administered by the National Science Foundation and which aims to keep scientific groups in the former Soviet Union working in their current difficult times. To this end a working party was set up at the Boreskov Institute of Catalysis (BIC) in Novosibirsk, Siberia in Russia. The day-to-day management of the working party was conducted locally by Professor Kirillov and the authors Westerterp and Kronberg scientifically and administratively managed the project. This paper reports the results of the study that took place in the years from 1997-2000. The study has led to certain recommendations for the design and operation of TBR's for the hydrogenation of pygas, which will be elucidated and explained here. To this end the phenomenon of particle runaway will first be discussed, and then the major results of the study at the BIC will be described, and eventually conclusions will be reached for the running of pygas hydrogenation TBR's. Later, in depth reports will be published on all work done, but now only the most important results are discussed, without going into detail.

Energetic Analysis of the Liquid-to-Wall Mass Transfer in a Trickle Bed Reactor

This paper presents an experimental study of the liquid/solid mass transfer at the wall of a trickle bed reactor operating in the high interaction regimes (pulsing and dispersed flow). The influence of Schmidt number was mainly investigated. The experimental results were interpreted using energy dissipation in terms of Kolmogoroff numbers. It was shown that the wall-to-liquid mass transfer coefficient can be correctly predicted by the following correlations: (i) in pulsing flow: ShØSc −1/3 m = 0.25( Ko ) 0.25 (ii) in dispersed flow: ShØSc −1/3 = 0.41( Ko ) 0.23

Unsteady state operation of catalytic particles with constant and periodically changing degree of external wetting

A dynamic model is developed to describe two parallel reactions between one gaseous and two non-volatile components on partially wetted catalysts with a time-dependent wetting efficiency. This simulates the performance of catalytic particles in a trickle-bed reactor operating in the pulsing-flow regime. The periodically varying external surface coverage results in periodically varying mass transfer rates to the surface of the particle. No a priori assumption is made about a rate limiting reactant. The results show the effect of interface and intraparticle mass transfer resistances as well as of the wetting efficiency and the frequency with which it varies on catalyst performance. It is shown that the wetting efficiency, the location of the wetted zones and the frequency need to be specified in order to determine the time-averaged effectiveness factors. For the same time-averaged wetting efficiency, pulse-flow can significantly enhance catalyst performance. Conditions are determined under which the effectiveness factors are maximized. The model is applied to a typical HDS process of heavy gas oil.

Periodic Operation of Trickle Bed Reactor for Hydrogenolysis in Gas-Liquid-Liquid-Solid Four Phases.

Trickle bed reactors are the most common gas-liquid-solid three-phase reactors involving a solid catalyst, and gaseous and liquid reactants. If solvents in the liquid phase are indissoluble in each other, gas-liquid-liquid-solid four phases exist in the reactor. Deprotection of amino acid was studied in a trickle bed reactor as a typical example of a four-phase system. A reactant (carbobenzoxy phenylalamine) could be dissolved in an organic phase and hydrogenated to a product (phenylalanine) using a Pd/C solid catalyst. Phenylalanine had hydrophilic properties and transferred from the organic phase to the aqueous phase. When two liquids were continuously introduced into the four-phase reactor, the product (phenylalanine) was deposited on the surface of the catalyst and the catalytic activity gradually decreased. Periodic operation was adopted to solve this problem. Only distilled water was periodically introduced into the reactor to wash the catalyst, which could be completely regenerated after this washing period. The optimal reaction period was determined by simulation to obtain a high concentration of the product.

Criteria for axial dispersion effects in adiabatic trickle bed hydroprocessing reactors

This paper first outlines an approximate solution to the governing equations for an adiabatic hydroprocessing trickle bed reactor operating in the presence of axial dispersion. The approximate solution agrees very well with the rigorous numerical solution for Peclet numbers greater than approximately three. Using the approximate solution, criteria for significant axial dispersion effect are obtained. These criteria indicate that at high conversions, an adiabatic operation produces a larger axial dispersion effect than the isothermal operation. At low conversions, opposite results are obtained. The derived criteria are used to evaluate the orders of magnitude of Peclet number required to avoid axial dispersion effect in pilot scale adiabatic reactors for (a) residual hydrodesulfurization (b) hydrocracking of gas oils and (c) denitrogenation of shale oils. The calculations indicate that the axial dispersion effect is of less importance in case (c) than in cases (a) and (b). Finally, the role of heat effects on the axial dispersion in a vapor phase fixed bed adiabatic reactor is evaluated.