Trickle Bed Research Articles

Kinetic parameter estimation with nonlinear mixed-effects models

Applications of fixed-effects models for kinetic parameter estimation using multiple batch experiments assume that all batches are independent. Multiple longitudinal batch experiments with time series data often exhibit biased residuals, violating this assumption. Nonlinear mixed-effects models offer an alternative approach to account for the two types of random experimental variation resulting from longitudinal experiments: the measurement error for each data point and the random batch-to-batch variation between experiments. Our case study models a single response hydrogenation reaction of acetophenone to 1-phenylethanol over a copper catalyst in a trickle-bed batch reactor system. Implementation of a mixed-effects model using nonlinear programming to model the batch reactor system results in parameter estimates with less bias compared to a fixed-effects model. We then apply the Bayesian notion of probability shares as a methodology for model discrimination between several candidate mixed-effects models, and demonstrate the ability to elucidate additional model information through the application of mixed-effects models when the use of fixed-effects models is inappropriate.

Combined Two-Model CFD Simulation of Trickle Bed Reactors with Head-Sump Extension: Case Study on Hydrodynamics and Biological Methanation

Trickle bed reactors are one of the world’s most employed technologies for multiphase processing, and they have been scrutinized for decades. However, accurate prediction and scale-up of trickle bed reactors are still challenging owing to complex interactions of multiphase flow, interfacial mass transfer, and reaction kinetics. The present computational model provides an insight into process phenomena on the basis of Eulerian–Eulerian methodology. It captures all parts of a trickle bed reactor─packing, head, and sump─which enables simulation of co- and countercurrent flow, gas or liquid recycle, and arbitrary retention time. Applying this model, hydrodynamic simulations reveal an improved prediction of liquid holdup, liquid dispersion, and pressure drop compared to CFD models of only the trickle bed. Furthermore, the interfacial surface area is analyzed and validated on account of a literature correlation. Exemplifying the entire approach with chemical absorption and reaction, the simulation of biological methanation presents methane concentration and productivity which are of the same order of magnitude as experimental data for an operating pressure of pop = 0.1–1 MPaabs.

Bed structure and its impact on liquid distribution in a trickle bed reactor

AbstractTrickle bed reactors, which has been a workhorse for the process and refining industry for many decades, are progressively being challenged to provide solutions to deep processing of feedstocks. It is known that the structure of the packed bed which is formed with a certain arrangement of catalyst particles in the three‐dimensional space within the reactor modulates in an unknown fashion the flow of fluids in the trickle bed, and in turn affects the conversion and selectivity in the trickle bed. Under deep processing conditions, the impact of the bed structure in modulating the overall reactor performance in a trickle bed is not as yet established. The question begets three sequential studies: estimating and quantifying the bed structure, measuring the liquid distribution, and estimating transport parameters (that are dependent on the bed structure and liquid distribution) so that the overall performance metrics as a reactor may be quantified. This contribution relates to the second of these questions, the first being already addressed to some extent by our earlier work. The current investigation aims at quantifying the effect of structure of the packed bed on hydrodynamics of the reactor. The impact of various packing techniques is discussed along with the development of correlations for two‐phase pressure drop and dynamic liquid holdup. Liquid distribution is studied in depth for various operating parameters such as gas and liquid superficial velocities and column aspect ratio for uniform and non‐uniform packing methods. The packing devices consist of various inserts attached to a hopper which can generate packing structures having void fraction in the range of 37.2%–46.4%. The maldistribution factor and flow maps for various aspect ratio of column suggest that maldistribution rises along with the increased channeling effect along the height of the column. Uniformly packed bed were measurably less prone to maldistribution along the length than the non‐uniformly packed beds.

Ex-situ biogas upgrading in thermophilic trickle bed reactors packed with micro-porous packing materials

Two thermophilic trickle bed reactors (TBRs) were packed with different packing densities with polyurethane foam (PUF) and their performance under different retention times were evaluated during ex-situ biogas upgrading process. The results showed that the TBR more tightly packed i.e. containing more layers of PUF achieved higher H2 utilization efficiency (>99%) and thus, higher methane content (>95%) in the output gas. The tightly packed micro-porous PUF enhanced biofilm immobilization, gas-liquid mass transfer and biomethanation efficiency. Moreover, applying a continuous high-rate nutrient trickling could lead to liquid overflow resulting in formation of non-homogenous biofilm and severe deduction of biomethanation efficiency. High-throughput 16S rRNA gene sequencing revealed that the liquid media were predominated by hydrogenotrophic methanogens. Moreover, members of Peptococcaceae family and uncultured members of Clostridia class were identified as the most abundant species in the biofilm. The proliferation of hydrogenotrophic methanogens together with syntrophic bacteria showed that H2 addition resulted in altering the microbial community in biogas upgrading process.

Aqueous phase reforming of birch and pine hemicellulose hydrolysates

The current work focuses on studying the aqueous phase reforming (APR) of pine and birch hydrolysate obtained from waste wood by using organic acids available from biorefineries. Processing of representative synthetic mixtures was utilized in the work in order to support data interpretation related to the influence of different chemical compound and processing parameters on the APR of the actual hydrolysates. It was shown, that hydrogenation of the hydrolysates prior to APR was not feasible in the presence of formic acid, which ruled out one potential processing route. However, it was successfully demonstrated that birch and pine hydrolysates could be directly processed obtaining close to full conversion. The best results were obtained with tailored bimetallic Pd-Pt/sibunit catalyst in a trickle bed reactor system in the temperature range 175 °C–225 °C.

Hydrotreating and oxidative desulfurization of heavy fuel oil into low sulfur marine fuel over dual function NiMo/γ–Al2O3 catalyst

The recent 0.5 wt% global sulfur cap on marine fuels increases the demand for low-sulfur marine fuels. Currently, marine fuels on the market contain up to 4.5 wt% of sulfur. The existing standalone desulfurization processes including hydrotreatment are not cost-effective for reducing the sulfur level of marine fuel to the mandated level. This study explored a new combination of desulfurization methods for marine fuels, first hydrotreatment under moderate process conditions, followed by oxidative desulfurization (ODS) to reduce the sulfur content to a desirable level of ≤ 0.5 wt%. The heavy fuel oil (HFO) feedstock of this study contains 3.4 wt% of S. Hydrotreating of HFO was performed in a trickle bed reactor using a commercial NiMo/γ–Al2O3 sulfide catalyst. Hydrotreating reduced the sulfur content of HFO to 1.14 wt%. It was further desulfurized by ODS using cumene hydroperoxide as an oxidant over the oxide form of NiMo/γ–Al2O3 catalyst. The FTIR analysis of the ODS product validated oxidation of sulfur compounds into sulfones and sulfoxides. The Box-Behnken design was applied to optimize ODS reaction variables such as temperature, oxidant concentration, and time. NiMo/γ–Al2O3 contains surface oxomolybdenum sites, which are expected to catalyze ODS by transferring oxygen from cumene hydroperoxide to sulfur compounds. The NiMo/γ–Al2O3 catalyst was found to be suitable for both hydrotreating and ODS. The upgraded heavy fuel oil of this two-step desulfurization process meets the IMO 2020 sulfur regulations.

Random trilobe packing using rigid body approach and local Gas-Liquid hydrodynamics simulation through CFD with experimental validation

It is quite difficult to measure the local information of the gas/liquid flow inside random packed extrudate catalyst beds in a large scale. Obtaining the local information through computational fluid dynamic (CFD) simulations in such system is also difficult due to the complexity of random particle packing and two-phase flow simulation. An efficient packing scheme was implemented to randomly pack 2917 trilobe particles (10 cm in height) in a 2-inch column to represent the trickle bed reactor (TBR) based on the rigid body approach. The generated geometry was used to define the computational domain for the two-phase hydrodynamics simulation based on the volume of fluids (VOF) approach. This hydrodynamics modelling study is paired with an experimental study using our in-house developed advanced measurement techniques based on optical fiber probes, which allowed to determine local liquid velocity and saturation profiles. The experimental measurements were used for local validation of the implemented model.

External Wetting Efficiency in a Three-Phase Fixed Bed Loaded with Porous and Non-Porous Packings

Films and rivulets are the two basic forms of dynamic liquid in a three-phase fixed bed (trickle bed), which determines the wetting efficiency of the catalyst. This paper is devoted to the conflicting wetting performance observed between non-porous glass beads and less wettable porous alumina, and a parallel zone model is applied to resolve the complex liquid flow texture. It shows in both cases of glass beads and aluminium pellets, the pressure drop, film flow and rivulet flow fractions all display pronounced multiplicities along with the liquid flow rates in increasing and decreasing branches, although the rivulet flow fraction is reduced to 0 in the liquid decreasing branch started from pulsing flow in both cases. Different from the glass beads, there is almost no wetting efficiency difference for the alumina pellets with respect to liquid flow rate increasing or decreasing, which is in agreement with the dynamic liquid holdup measurements. The liquid is significantly more uniformly distributed over the crosssection in the Al2O3 bed since rivulet flow is much reduced than in the case of glass beads.

Development of a new continuous process for the production of 3,5-dimethylpiperidine

The trickle bed reactor (TBR) is more efficiency than the kettle reactor (KR) in the hydrogenation of 3,5-dimethylpyridine (DPY) to 3,5-dimethylpiperidine (DPI) using the same Ru/C catalyst, which has the advantages of higher conversion, stable catalyst performance, milder reaction conditions and large-scale DPY hydrogenation capacity. So the TBR has a good industrial application prospect. This paper developed a new clean continuous process for the hydrogenation of 3,5-dimethylpyridine (DPY) to 3,5-dimethylpiperidine (DPI) without solvent. A series of Ru/C catalysts were prepared by impregnation method, which were characterized by the BET, ICP, CO chemisorptions, XRD, SEM, EDS, TEM and TG. The effect of active species, loading, catalyst support, reaction temperature and pressure on the catalytic performance was investigated. The influence of internal and external diffusion in the trickle-bed reactor (TBR) was basically eliminated by adjusting the particle size and dosage of the Ru/C catalyst. The reaction performance of the hydrogenation of DPY to DPI in the TBR and kettle reactor (KR) was compared, and the superiority of the TBR process was analyzed. The results show that this new continuous process developed in this study is an efficient way to realize the hydrogenation of DPY to DPI, and has a good industrial application prospect.

The Enhanced Biological Methanation Performance in Trickle-Bed Reactor by Different Continuous Hydrogen Supply from Nano-Zero Valent Iron Corrosion

The Enhanced Biological Methanation Performance in Trickle-Bed Reactor by Different Continuous Hydrogen Supply from Nano-Zero Valent Iron Corrosion

Effect of Hydraulic and Organic Load, in the Removal of Biochemical Oxygen Demand in Wastewater using Biofilter with Vegetable Carbon, in High Andean Climate

Generating new sustainable alternatives in the design of trickling filters for rural populations is necessary to improve the quality of discharges and optimize the design of secondary treatment units. The study determined the impact of hydraulic and organic charge on the removal of BOD in the environment charcoal biofilter. Biofilters prototypes were implemented at scale with charcoal filter medium on different surfaces that vary from 0.12 to 0.25 m2, carried out at an elevation of 2100 meters above sea level, the final concentration most effective in removing BOD obtained hydraulic load of 2.34 to 4.76 m3m−2d−1 and the organic load between 0.27 to 0.56 kg DBO m−3. The results of the Biofilter experiments determined that the hydraulic load generated a better distribution and mixing of the residual water throughout the trickling bed, achieving a good reaction and effective combination between the water that entered and the amount of air required to complete the aerobic process. and to achieve the removal of BOD, the organic load obtained in the measurements concentrates enough biomass that helps in the formation of the biofilm, for which it is concluded that this criterion has a determining effect on the reduction of organic matter in domestic wastewater, it is confirmed that the charcoal biofilter is efficient and can be used in small systems of wastewater treatment plants.

Investigation the impact of using the recess air bio-filter (TBAB) with integrated system of a cyclic 2-recess adsorption/desorption unit for treatment of squander gas streams

In the chemical industry, fluctuations in influent concentrations and shifts in the composition of waste air make biofiltration a challenging technique. As a possible solution to the constraints of biofiltration technology, this research designs and implements an integrated system that includes a cyclic 2-bed adsorption/desorption unit and a trickling bed air biofilter (TBAB). The study's major goal was to keep the TBAB volatile organic compound (VOC) degradation performance stable and consistent over time. The studies were conducted on different TBABs with a single VOC exchange and a biomass control of periodic backwashing. Solvents that are routinely used in paint booths were examined as VOCs. Two aromatic chemicals (styrene and toluene) were investigated, as well as two aliphatic chemicals (methyl ethyl ketone (MEK) and methyl isobutyl ketone) (MIBK). While the production process rotated, our study duplicated VOC emission rotation in certain chemical sectors. When VOCs were switched to aromatics, the biofilter required an apparent re-acclimation period, according to the results. The second phase looked at two different combinations of these VOCs in two separate TBAB trains with a step change in influent concentration. In the third phase, the buffering performance of a cyclic 2-bed adsorption unit was tested for a feeding composition based on an EPA industrial emission report under a square wave of fluctuating conditions. The VOC mixture was treated in the fourth step with an integrated system that includes two cyclic adsorption/desorption beds as well as TBAB. When compared to the control unit, the integrated system was able to achieve high steady performance, according to the studies' findings. Lastly, researchers looked at the microbial communities of the biofilters employed in the VOC interchange and VOC mixing studies. The interchange of VOCs demonstrated a steady transition in microbial diversity. The community structure of VOC mixes demonstrated a significant degree of independence from the component content.

Modelling of Jatropha Oil Hydrocracking in a Trickle-Bed Reactor to Produce Green Fuel

Trickle-bed reactor (TBR) modelling to produce green fuel via hydrocracking of jatropha oil using silica-alumina-supported Ni-W catalysts was performed in this research. The objectives of this study are to obtain a TBR with good heat transfer and the optimum condition for high purities of products. A two-dimensional axisymmetric model with a diameter of 0.1 m and a length of 10 m was used as a representative of the actual TBR system. Heterogeneous phenomenological models were developed considering mass, energy, and momentum transfers. The optimisation was conducted to obtain the highest green fuel purity by varying catalyst particle diameter, inlet gas velocity, feed molar ratio, and inlet temperature. The simulation shows that a TBR with an aspect ratio of 100 has achieved a good heat transfer. The diesel purity reaches 44.22% at 420°C, kerosene purity reaches 21.39% at 500°C, and naphtha purity reaches 25.30% at 500°C. The optimum condition is reached at the catalyst diameter of 1 mm, the inlet gas velocity of 1 cm/s, the feed molar ratio of 105.5, and the inlet temperature at 500°C with the green fuel purity of 69.4%.

Combining a robust thermophilic methanogen and packing material with high liquid hold-up to optimize biological methanation in trickle-bed reactors

The hydrogen gas-to-liquid mass transfer is the limiting factor in biological methanation. In trickle-bed reactors, mass transfer can be increased by high flow velocities in the liquid phase, by adding a packing material with high liquid hold-up or by using methanogenic archaea with a high methane productivity.This study developed a polyphasic approach to address all methods at once. Various methanogenic strains and packings were investigated from a microbial and hydrodynamic perspective. Analyzing the ability to produce high-quality methane and to form biofilms, pure cultures of Methanothermobacter performed better than those of the genus Methanothermococcus. Liquid and static hold-up of a packing material and its capability to facilitate attachment was not attributable to a single property. Consequently, it is recommended to carefully match organism and packing for optimized performance of trickle-bed reactors. The ideal combination for the ORBIT-system was identified as Methanothermobacter thermoautotrophicus IM5 and DuraTop®.

Use of CFD for pressure drop, liquid saturation and wetting predictions in trickle bed reactors for different catalyst particle shapes

The characterization of hydrodynamics in Trickle-Bed-Reactors is a complex task due to the opacity of the medium. In particular, the determination of pressure drop, liquid saturation , wetting of the catalyst surface and catalyst shape effect on these parameters is very important for optimal catalyst use and reactor operation. Measurements under industrial conditions are limited to indirect estimations, and direct measurement methods are limited to near-ambient conditions. In this context, the objective of the present article is to use Computational-Fluid-Dynamics to investigate pressure drop, liquid saturation and wetting efficiency in Trickle-Bed-Reactors and to improve existing correlations, with a special focus on the catalyst shape effect and wetting prediction.The Volume-Of-Fluid approach was used to simulate two-phase flow through particle loadings of spherical, trilobe and quadrilobe-shaped particles. The numerical model was validated against literature correlations in terms of pressure drop, liquid holdup and wetting efficiency. The CFD model was then employed to explore two effects that does not reach out a consensus in existing literature, i.e effects of particle shape and gas-phase velocity on wetting efficiency. As a result, it was shown that CFD provides good predictions of pressure drop and liquid saturation for different catalyst particle shapes, the achieved deviations between CFD results and correlation estimations are below 20%. A new wetting efficiency correlation is also proposed. This new correlation is able to predict wetting efficiency with a precision of 6.99% for a wide range of liquid velocities (from 0.2 to 0.8 cm/s) and gas velocities (from 5 to 20 cm/s) and three particle shapes.

The physicochemical and catalytic properties of clay extrudates in cyclization of citronellal

Four clay materials, namely, bentonite, bleaching earth, attapulgite and sepiolite, were shaped into the cylindrical body by extrusion. Clays were characterized in depth by TEM, SEM-EDX, N2 physisorption, pyridine FTIR, pH measurements, contact angle measurements, 27Al MAS NMR, and the crush test. Catalytic properties were investigated in the citronellal cyclization as a model reaction. The reaction was performed in the trickle-bed reactor at 70 °C, 10 bar of Ar with 0.086 M initial citronellal concentration in cyclohexane. The best results were obtained over attapulgite with isopulegols yield of 24% and stereoselectivity to the desired isopulegol isomer of 61%. Attapulgite had the highest meso-to-micropore volume ratio, the highest basicity, a low Brønsted-to-Lewis acid sites ratio, and the lowest amount of Brønsted acid sites compared to other extrudates. In addition, same clay exhibited the highest mechanical strength of extrudates.

Effect of minimizing carrier irrigation on H2 conversion in trickle bed reactors during ex situ biomethanation

Biological methanation of renewable H2 and CO2 has been projected to have considerable potential in future energy systems by coupling power and gas energy infrastructures. A suitable technology to facilitate the biological methanation is the ex-situ trickle bed reactor in which a methanogenic biofilm produces CH4 from H2 and CO2. Biofilm irrigation constitutes a critical element for reactor control and has previously been shown to both enhance and decrease reactor performances. In this study, an improvement in the H2 conversion rate of 53% was demonstrated when increasing the interval between sprinklings from 1 to 7 days. The results demonstrate a minimal requirement for nutrient supply to support biological activity and underline that carrier irrigation not only impairs H2 conversion at short-term due to increases in the mass transfer resistance, but also induces longer-term effects on process performance. Three potential mechanisms underlying the physicochemical and biological effects imposed by carrier irrigation are discussed.

Effects of stagnant zone on the effectiveness factor in a trickle bed

Industrial trickle-bed reactors are normally operated under complete wetting conditions, almost 20–30% of the particle external surface is covered by stagnant liquid. To investigate the influence of stagnant zone on the effectiveness factor, a multi-particle string model is studied by CFD simulation, with a high-speed video camera verifying the validity of simulation. It shows that stagnant liquid in liquid pendulum and liquid pocket would cause obvious external mass transfer limitation at high Thiele moduli, yet the effects of liquid pocket are more serious than liquid pendulum. The effects of liquid velocity, particle diameter, and particle number on effectiveness factor are evaluated. The effectiveness factor belonging to single particle due to absence of liquid pocket is higher than that of a multi-particle string, while the three-particle string model is similar to the four-particle approach, which indicates simulation of effectiveness factor in a trickle bed can be approximated by a three-particle string.

Modelling of transient kinetics in trickle bed reactors: Ethylene oxide production via hydrogen peroxide

Stationary kinetic methods are not sufficient for studying chemical processes in which solid heterogeneous catalysts and several phases (gas-liquid-solid) are involved, therefore transient experimental techniques are applied to reveal the molecular processes on the catalyst surfaces. Dynamic methods were used to study the kinetics of a heterogeneously catalyzed reaction i.e. the epoxidation of ethylene with hydrogen peroxide as the oxidizing agent and titanium silicalite (TS-1) as the heterogeneous catalyst. No detailed reaction mechanism and kinetic model has ever been proposed for this process. For the kinetic investigation, step response experiments were carried out in a laboratory-scale trickle bed reactor (TBR).A dynamic isothermal model for the TBR was presented together with a dynamic kinetic model based on a proposed surface reaction mechanism, where the key step is the reaction between adsorbed hydrogen peroxide and dissolved ethylene from the liquid phase. The TBR model consisted of dynamic mass balance equations for the components present in the gas and liquid bulk phases as well as adsorbed species on the catalyst surface. The model formed a coupled system of parabolic partial differential equations (gas and liquid phases) and ordinary differential equations (catalyst surface phase). The coupled system of differential equations, describing the concentration profiles from the step response experiments were solved numerically by the method of lines by discretizing the reactor length coordinate with finite differences and solving the large system of ordinary differential equations by a backward difference algorithm suitable for stiff ordinary differential equations. The parameters for surface kinetics, mass transfer and fluid dynamics were determined by non-linear regression analysis using the maximum likelihood approach. The model was able to predict the transient and stationary behavior of the system.

Tracking the heavy metal contaminants entrained with the flow into a Trickle bed hydrotreating Reactor packed with different catalyst shapes using newly developed noninvasive Dynamic radioactive particle Tracking

A newly developed modified Dynamic Radioactive Particle Tracking system (DRPT) was used to investigate the heavy metal contaminants deposition locations in different catalyst beds, sphere, cylinder, trilobe, and quadrilobed in Trickle Bed Reactors. In the present paper, Kernel Density Estimator (KDE) was used to estimate the probability density distributions of heavy metal contaminants depositions in terms of bed radius height. The result shows that the four cases have similar probability density distribution in terms of radius, while the spherical catalyst has the larger distribution range in terms of bed height. The heavy metal deposition is directly related to the pressure drops along the bed height which indicate the bed porosity and intricate bed structure in catalyst packed beds. Heavy metals have more chance to deposit at higher levels of packed beds with higher pressure drops.