Trickle Bed Research Articles

Effect of Binders on the Physicochemical and Catalytic Properties of Extrudate-Shaped Beta Zeolite Catalysts for Cyclization of Citronellal

Citronellal cyclization was carried out in a continuous mode over H-beta-25 zeolite-based extrudates in a trickle-bed reactor at 35 °C and 10 bar of Ar. The physicochemical properties of zeolitic c...

Tracer dispersion in trickle beds under tilts and roll motions – CFD study and experimental validation

A wire-mesh sensor was used to measure the liquid residence time distribution (RTD) and tracer dispersion in trickle beds subjected to stationary tilts and roll motions. The measured tracer characteristics were confronted to three-dimensional transient Euler-Euler CFD simulations to expose the role of inclined and oscillating porous media. The simulation results satisfactorily reproduced the widening tracer signals with increased bed inclination reflecting in asymmetric RTDs prompted by permanent gravity-driven stratified flow zone through the packing. Similarly, tracer dispersion was predicted to increase for rolling beds by increasing tilt angle and motion period. While an increase of tilt angle shortened RTD breakthrough time due to the faster tracer stream evolving in the liquid-rich lower-most zones, tracer elution tended to slow-down with increasing the rolling period. In addition, it was revealed that with altering the column angular position during roll motions the fluid flow structures inevitably varied inside the packing leading to different mixing behaviors and residence time distributions.

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.

Influence of input conditions on the flow distribution in trickle bed reactors

The pattern of distribution of the two-phase gas-liquid flow in the inlet pipeline and the effect of the input conditions on the distribution of the flow in the upper part on the trickle bed reactor was investigated by CFD. The multiphase Euler-Euler VOF (Volume Of Fluid) model was used.The analysis of the distribution of the two-phase flow in a trickle bed reactor was carried out using the inlet diffuser and the tray with chimney distributors. Two different cases of input diffusers, which are used in industry, were investigated. The first type is designed to eliminate the influence of the dynamic pressure of a two-phase jet from the inlet pipeline by placing several grids under the reactor inlet. The second type completely mixes the two-phase flow from the inlet pipeline, but does not eliminate the intense axial two-phase flow.Studies have shown that the choice of design of the inlet diffuser affects the distribution of the liquid phase in the distribution tray, distorting the curvature of the surface of the liquid layer to a different extent and drying various chimneys. This leads to a decrease in the quality of the distribution of the liquid phase to the underlying catalyst bed for both the studied types of the inlet diffuser. Consequently, the selection of the inlet diffuser is an important part of the design and creation of trickle bed reactors for hydrotreating processes.

Enhanced stability of Pd/SPS catalyst over the one-pot liquid-phase synthesis of methyl isobutyl ketone by adding GO

The low thermal-conductivity and poor thermal stability of resin limit the service life of commercial Pd/sulfonated polystyrene (SPS) catalyst for the industrial synthesis of methyl isobutyl ketone from acetone and H2. In this paper, a novel catalyst Pd/S(PS-GO) was fabricated via in situ microemulsion polymerization, followed by sulfonating and Pd loading. Both the long-term catalytic performance of Pd/S(PS-GO) and Pd/SPS catalysts were tested in a trickle-bed reactor. Results showed that Pd/S(PS-GO) catalyst exhibited obvious enhanced stability than Pd/SPS catalyst at 150 ℃ for 1000 h run. The characterizations of FT-IR, TGA, XPS, TEM and UV–vis revealed that the addition of GO significantly improved the thermal-conductivity and thermal stability of PS through noncovalent π–π stacking and covalent link between PS and GO sheets. As a consequence, the loss of –SO3H groups from resin matrix was efficiently depressed and led to the obvious enhanced stability of Pd/S(PS-GO) catalyst.

CFD Studies on Efficacy of Flow Modulation in a Hydrotreating Trickle-Bed Reactor

Hydrodesulfurization (HDS), a pivotal process for sulfur removal that is essential in deep processing of crude oil, is typically carried out in steady-state trickle-bed reactors (TBRs). Being famil...

Synthesis and Physicochemical Characterization of Shaped Catalysts of β and Y Zeolites for Cyclization of Citronellal

Continuous cyclization of citronellal over zeolite-based extrudates was performed in a trickle-bed reactor at 35–70 °C and 10 bar of argon. Catalytic results were correlated with the physicochemical properties of the shaped catalyst prepared by extrusion of β or Y zeolites with binders. Rheological tests were used to elucidate the flow properties of a catalytic slurry and relate them with the extrusion performance. This study revealed that application of methylcellulose and bentonite binder modified the textural and acidic properties of the final extrudates. The main product was (−)-isopulegol at all temperatures with selectivity remaining quite constant with time-on-stream. The results illustrated that a binder such as bentonite cannot be considered inert. The mass-transfer limitations observed in extrudates did not significantly influence selectivity to the desired pulegols. This study also showed that a direct transfer of the batch reactor data to industrial continuous operation in citronellal cyclizat...

Process intensification in catalytic wet air oxidation of phenol via coupling gas‐liquid microdispersion with trickle bed reactors

AbstractIntensified 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.

Analyzing the impact of implementing different approaches of the approximation of the catalyst effectiveness factor on the prediction of the performance of trickle bed reactors

Abstract A steady-state diffusion model comprising of diffusion and reaction in a catalyst pellet was used to study and understand the effect of the approximation of the catalyst effectiveness factor in the modeling of trickle bed reactors. The hydrogenation of alpha-methylstyrene was chosen as the case study reaction from literature for liquid-limited reaction conditions. The effectiveness factor values in this study were sensitive to reactor scale equations during the prediction of reactor performance. The approximation of accounting for the overall catalyst effectiveness factor in the reactor scale model equations from different models and solving the reactor scale model equations by different modeling approaches was assessed. It was observed that evaluating the overall effectiveness factor from pellet scale model equations and integrating the parameter in the reactor scale axial dispersion model at every local axial collocation point to simulate the reactor performance showed better agreement to the experimental data. This approach evaluates the effectiveness factor locally with the variation of the reactant concentration at different axial points across the reactor rather than using one value for the entire reactor. The approach of using a single effectiveness factor for the whole bed and using the effectiveness factor approximated as a fitted polynomial to the reactant concentrations did not properly predict the reactor performance.

Produce Low Aromatic Contents with Enhanced Cold Properties of Hydrotreated Renewable Diesel Using Pt/Alumina-Beta-Zeolite: Reaction Path Studied via Monoaromatic Model Compound

In this present work, Hydro-dearomatisation of toluene and hydro-isomerisation of n-hexadecane (n-C16) in ultralow sulphur diesel (ULSD) using Pt-Cl/H-Beta and Pt/H-Beta catalyst was investigated in a continuous down-flow trickle-bed reactor (DFTBR), and the physicochemical properties of products were studied. The catalytic effect on 40:60 wt% of H-beta-zeolite (H-β) and binder–aluminahydrochlorite extruded was characterized in scanning electron microscopy, nitrogen adsorption and coke testing. The study showed that 80 to 95 wt% of middle distillates recovered in ULSD on elevated temperature between 230 and 270 °C at 5 MPa. With a higher residence time of feed, the middle distillate recovered with 2.2 v/v% of aromatics and −32 °C of cloud point. In the model compound investigation of toluene and n-C16, it was observed that absorption of aromatic ring inhibits the rate of isomerisation; particularly it reduces the yield of branching and rearrangement of n-C16. Also, Cl-incorporated H-β extrudate enhanced the ring saturation and suppressed the reaction path in oligomerisation and cyclisation of paraffin. This methodology achieved asingle-stage upgrading technique involved in the delivery of commercial diesel in the market with low cloud point and aromatic content.

Slurry loop tubular membrane reactor for the catalysed aerobic oxidation of benzyl alcohol

A novel reactor that combines a catalyst slurry flowing inside a loop configuration, incorporating a tubular membrane (Teflon AF-2400) for controlled oxygen delivery was designed and employed for the aerobic oxidation of benzyl alcohol using a 1 wt% Au-Pd/TiO2 powdered catalyst. This reactor keeps the liquid phase saturated with oxygen, while avoiding the creation of bubbles in it, thus enhancing operation safety. Experimental results in batch mode compared with those of a conventional autoclave demonstrated that the slurry loop membrane reactor reached a similar oxidation turnover frequency (20,000–25,000 h−1) with comparable values of benzaldehyde selectivity (∼70%). Continuous operation was achieved by using a crossflow filter connected to the loop to keep the catalyst from exiting the reactor. Using a 60 cm long tubular membrane, with the slurry flow circulating at 10 mL/min, continuous reaction was performed at 100–120 °C, 0–5 bar oxygen pressure and 1.2–5.0 g/L catalyst loading. Selectivity to benzaldehyde increased by either decreasing the reaction temperature or increasing the external oxygen pressure. The oxygen consumption rate decreased linearly with the catalyst loading, suggesting negligible gas-liquid mass transfer resistance. This was further evidenced by doubling the length of the tubular membrane, which had no effect on the oxidation turnover frequency. The slurry loop membrane reactor showed significantly better performance than packed-bed membrane microchannel reactors, and similar performance as that of a trickle-bed capillary reactor. This reactor can be implemented for a wide range of applications, which rely on the use of powder catalyst, are limited by gaseous reactant availability and require safe operation.

Continuous conversion of CO2/H2 with Clostridium aceticum in biofilm reactors

A lab-scale stirred-tank bioreactor was reversibly retrofitted to a packed-bed and a trickle-bed biofilm reactor to study and compare the conversion of CO2/H2 with immobilised Clostridiumaceticum. The biofilm reactors were characterised and their functionality confirmed. Up to 8.6 g of C. aceticum were immobilised onto 300 g sintered ceramic carrier material, proving biofilm formation to be a robust means for cell retention of C. aceticum. Continuous CO2/H2-fermentation studies were performed with both biofilm reactor configurations as function of dilution rates, partial gas pressures and gas flow rates. The experiments showed that in the packed-bed biofilm reactor, the acetate space-time yield was independent of the dilution rate, because of low H2 gas-liquid mass transfer rates (≤17 mmol H2 L−1 h−1). The continuous operation of the trickle-bed biofilm reactor increased the gas-liquid mass transfer rates to up to 56 mmol H2 L−1 h−1. Consequently, the acetate space-time yield of up to 14 mmol acetate L−1 h−1 was improved 3-fold at hydrogen conversions of up to 96%.

Load change capability of an anaerobic thermophilic trickle bed reactor for dynamic H2/CO2 biomethanation

Increasing shares of energy production originating from fluctuating renewable sources require measures that are able to balance power production for a stable electricity grid. H2/CO2 biomethanation is a suitable approach to convert fluctuating excess renewable energy into the storable substitute natural gas. This study investigated the rapid load change capability of an anaerobic thermophilic trickle bed reactor while maintaining a high methane content. The return to full load (62.1 m3H2/m3trickle bed/d) after a 30-min operational off-cycle was possible almost immediately, while 24-h interruptions required a 60-min stepwise load increase. To accelerate this delayed microbial conversion activity, non-steady state substrate gas conversion can be controlled via substrate and product gas flow rates, allowing to reactivate the entire microbial community and produce high quality product gas. Reactor design might be further improved to avoid short-circuiting and use the entire trickle bed gas phase as high quality gas buffer during initial load increases.

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.

Modeling and evaluation of hydrodesulfurization and deactivation rates for partially wetted Trilobe catalyst using finite element method

Hydrodesulfurization of heavy oil is usually operated in a trickle bed reactor. Analysis and design of this reactor require modeling both at the macro-reactor scale and micro-catalyst scale. The paper is focused on the catalyst-level modeling and takes into consideration complex catalyst shapes, wettability, and spatial variation in diffusivity due to catalyst pore plugging. Furthermore, the effects of mass transfer from dry and wet zones around the partially wetted catalyst surface are included. Finite element method is used for two-dimensional analysis as it is versatile and can handle complex shapes. The catalyst-level model includes an updating of effective diffusivity with time, and hence the lifetime of a complex shaped catalyst can be predicted. Long-time operation shows that thickness of plugged pore is large and also non-uniform across the two-dimensional catalyst particle with more plugging near the catalyst surface. In addition, the reaction regime changes with time, the fresh catalyst initially being in a diffusion-resistance-free regime and changing to a strong-diffusion-resistance regime at longer operating times. The computational method can be used for optimization of the operating protocol and to design optimum pore size and shape of the catalyst, although these details are not addressed in this paper.

CFD Simulation of Porosity and Particle Diameter Influence on Wall-to-Bed Heat Transfer in Trickle Bed Reactors

Wall-to-bed (or wall-to-fluid) heat transfer issues in trickle bed reactors (TBR) has an important impact on operation and efficiency in this category of reactors. In this study, the hydrodynamic and thermal behavior of trickle bed reactors was simulated by means of computational fluid dynamics (CFD) technique. The multiphase behavior of trickle bed reactor was studied by the implementation of the Eulerian-Eulerian multiphase approach. Also, bed porosity effect was modeled by porosity function method. In order to study the effect of operating parameters on wall-to-bed heat transfer, the influence of catalyst particle diameter and catalytic bed porosity was investigated on wall-to-bed Nu number. The results showed that the enhancement of catalytic bed porosity from 0.36 to 0.5 decreases the Nu number about 15% due to a reduction of liquid velocity adjacent to the reactor wall. Also, the increase of particle diameter from 4 to 6 millimeter decreases wall-to-bed Nu number about 15% owing to a reduction in liquid phase volume fraction.

Optimal Kinetic Parameters of Trickle bed Reactor for Oxidation of 2-Proplymercaptan in Naphtha

The best kinetic of the reaction are estimated based on experimental data obtained from the literature using parameter estimation technique. The best mathematical model for oxidative 2-proplymercaption via oxygen is taking into account the apparent intrinsic kinetics considering internal diffusion and TBR hydrodynamic effect on the reaction process mainly , catalyst wetting efficiency, catalyst effectiveness factor, Thiele model and the effective diffusivity. The optimal operating condition for oxidative process is carried out utilizing. The optimization technique based upon the minimization of the sum squared error between experimental and predicted composition of naphtha oxidative process to determine the best parameters of kinetics models. The predicted product compositions for oxidation process found to be a good agreement with the experimental data for wide range of operating conditions (2.5-10 hr-1, 75-300 ppm and 293-353K) with minimum error 5% among all results

Fifty Years of Moment Technique for Dynamic Analysis of Chemical Reactor Parameters

Abstract Moment technique has been extensively used for the evaluation of the rate and equilibrium parameters in chemical reactors and also in adsorption vessels, for about five decades. Adsorption and reaction rate parameters, as well as axial dispersion constants, effective diffusivities within porous catalysts and heat and mass transfer coefficients were shown to be effectively evaluated by analyzing the moments of the response peaks, which could be obtained from pulse-response experiments performed in a reaction/adsorption vessel. A detailed review of chromatographic processes, involving moment analysis of adsorption equilibrium and rate constants in fixed beds, dynamic analysis of batch adsorbers, moment analysis of fluidized bed, slurry and trickle bed reactors are reported in this manuscript. Applications of the single-pellet moment technique, which was developed for the effective investigation of intrapellet rate and equilibrium processes, by eliminating the contributions of axial dispersion and external transport parameters, are comprehensively discussed. Recent studies for the analysis of reaction rate parameters using the TAP reactor approach, use of single pellet system for the investigation of catalytic and non-catalytic solid-gas reactions and extension of the moment technique to non-linear systems opened new pathways in reaction engineering research.

Developing a high-performance methane stage for biomass with high nitrogen loads

Biomass like poultry manure and sewage sludge have high nitrogen and chemical oxygen demand (COD) concentrations. This can cause disturbances in the anaerobic digestion process, by ammonia as well as accumulation of volatile fatty acids (VFA). Therefore, the target is to develope a high-performance methane stage for mesophilic monofermentation of these substrates. Hence a stepwise increase of the reactors, trickle bed reactor (RB), upflow anaerobic sludge bed reactor (UASB), and anaerobic filter reactor (AF) was done. To adapte the microorganizmen to nitrogen and organic loads plastic pellets have been adapted in RB and AF. The UASB enriches biomass by forming natural pellets through accumulation of the microorganism and the subsequent sedimentation. Altogether, to find out the weakness in the acetogenesis/methanogenesis the feeding process was done with a model substrate, which presents a hydrolyzate. With this one a stable process was determined for organic loads of 15.04 [kgCOD/m³*d] in RB and AF. So far, the UASB haven't reached a stable performance. Allover, there wasn't a significant linear correlation between ammonia and the biogas production detectable. The adaption of biomass through the stepwise increase of the organic loads, the immobilization of biomass as well as the reactor type influenced the process stability.

Hydrogen production from sucrose via aqueous-phase reforming

Commercial sucrose was used to produce hydrogen in a combined approach of hydrogenation and aqueous phase reforming (APR). First a mixture of technical sorbitol/mannitol was produced by hydrogenating an aqueous solution of sucrose in a trickle bed reactor over 5 wt % Ru/C. The produced polyols were treated in a continuous reactor at 498 K and elevated pressure deploying a 2.5 wt % Pt/C catalyst to yield hydrogen. The highest hydrogen selectivity was 62%. No large differences were found when comparing a commercial available sorbitol to the technical sorbitol/mannitol mixture in terms of conversion levels and selectivity to the gas-phase products. This was accompanied by a similar distribution of products retained in the liquid phase. The efficiency of APR when utilizing Pt/C was found to be still insufficient for industrial implementation in terms of hydrogen production. Thus, additional efforts should be made to increase the obtained amounts of hydrogen per mole of converted sugar alcohols.