Trickle Bed Research Articles

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.

Kinetic parameter estimation and reactor simulation of full-range low temperature coal tar during hydrodeasphaltenization over Ni–Mo/γ-Al2O3

In this study, the whole fraction low temperature coal tar (LTCT) was used as raw material, a series of hydrodeasphaltenization (HDAs) experiments were conducted in an isothermal trickle bed reactor, then the kinetic equation of the reaction was established in gPROMS software and the parameters were estimated. The trickle bed reactor model was established and the effects of operating conditions on HDAs reaction and catalyst effective factors were analyzed. The reactor temperature was varied from 623 to 683 K, the hydrogen pressure from 6 to 12 MPa, keeping constant hydrogen-to-oil volume ratio at 1000:1, liquid hourly space velocity at 0.5 h−1. The results showed that the relative error between the experimental and the simulated results were less than ± 5%, which proved that the model had good applicability; the activation energy was 149.8 kJ mol−1, the pre-exponential factor was 633,832, the reaction order was 1.347, and the order of hydrogen was 2.33. The higher activation energy indicated that the HDAs was difficult to occur compared with the reaction in crude oil. And the high hydrogen order indicated that the pressure had a significant influence on the reaction rate. However, the high temperature and low pressure would reduce the effective factor of the catalyst. The reason may be that the large diffusion limitation and reaction heat of asphaltenes lead to a large difference in reaction rates between the catalyst surface and the tunnel of pores under high temperature. This study could contribute to a more in-depth understanding of the features and rules of LTCT HDAs, and also provide a useful model for reactor design, operation and control.

Decoupling the relative rate of hydrogen uptake via convection and mass transfer by a single catalytic pellet in a scaled down trickle bed reactor

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.

An Efficient and Practical System for the Synthesis of N,N-Dimethylformamide by CO2 Hydrogenation using a Heterogeneous Ru Catalyst: From Batch to Continuous Flow.

In the context of CO2 utilization, a number of CO2 conversion methods have been identified in laboratory-scale research; however, only a very few transformations have been successfully scaled up and implemented industrially. The main bottleneck in realizing industrial application of these CO2 conversions is the lack of industrially viable catalytic systems and the need for practically implementable process developments. In this study, a simple, highly efficient and recyclable ruthenium-grafted bisphosphine-based porous organic polymer (Ru@PP-POP) catalyst has been developed for the hydrogenation of CO2 to N,N-dimethylformamide, which affords a highest ever turnover number of 160 000 and an initial turnover frequency of 29 000 h-1 in a batch process. The catalyst is successfully applied in a trickle-bed reactor and utilized in an industrially feasible continuous-flow process with an excellent durability and productivity of 915 mmol h-1 gRu -1 .

Effectiveness factors for a partially wetted catalyst based on the rivulet flow model

Partial wetting is a common phenomenon in a trickle bed reactor, which causes nonuniform mass transfer flux at the external surface of the catalyst. Previous work on effectiveness factor for a partially wetted catalyst are mainly based on the assumption that the spherical catalyst is wetted by a liquid film. In fact, it is only true when the liquid-solid contact angle is very small. In most situations, rivulet flow prevails. The purpose of the article is to calculate effectiveness factors for both gas-limited and liquid-limited reactions under the two wetting modes by using finite element method (FEM). The effects of wetting efficiency, Biot number, and Thiele modulus on effectiveness factors are investigated. On the basis of the FEM results, the intrinsic reason for the variation of effectiveness factors with respect to wetting efficiency is revealed, and good agreements are observed between this work and the conventional models.

Evaluation of Sponge Metal Catalysts in a Trickle Bed Reactor for the Continuous Hydrogenation of an Aliphatic Nitro Intermediate

Nine sponge nickel catalysts were assessed for the reduction of an aliphatic nitro group in a trickle bed reactor. Focused beam reflectance measurement (FBRM) was used to assess the mechanical stre...

Nanoparticle catalyzed hydrodesulfurization of diesel fuel in a trickle bed reactor: experimental and optimization study.

This work focuses on the preparation, simulation, and optimization of the hydrodesulfurization (HDS) of dibenzothiophene (DBT) using a nanocatalyst. A homemade nanocatalyst (3 percent Co, 10 percent Mo/γ-Al2O3 nanoparticles) was used in a trickle bed reactor (TBR). The HDS kinetic model was estimated based on experimental observations over ranges of operating conditions to evaluate kinetic parameters of the HDS process and apply the key parameters. Based on these parameters, the performance of the TBR catalyzed by the nanocatalyst was evaluated and scaled up to a commercial scale. Also, the selectivity of HDS reactions was also modeled to achieve the highest yield of the desired hydrogenation product based on the desirable route of HDS. A comprehensive modeling and simulation of the HDS process in a TBR was developed and the output results were compared with experimental results. The comparison showed that the simulated and experimental data of the HDS process match well with a standard error of up to 5%. The best reaction kinetic variables obtained from the HDS pilot-plant (specific reaction rate expression, rate law, and selectivity) TBR have been utilized to develop an industrial scale HDS of DBT. The hydrodynamic key factors (effect of radial and axial dispersion) were employed to obtain the ratio of the optimal working reactor residence time to reactor diameter.

Design Parameters for Diesel Hydro Desulfurization (DHDS)

Apart from all gaseous contaminants in air, sulfur dioxide is considered to be the principal pollutant. The emission of sulfur dioxide is generally caused by combustion of sulfur bearing fuels. This further gets converted into sulfuric acid in atmosphere as a result of its reaction with oxygen and moisture. This air borne acid is responsible to damage steel buildings, bridges and machinery. Hence there is a major need to decrease sulfur percentage in the environment in order to lead a better and healthy living. As we can see the world runs on energy, for which fossil fuels are the main constituents. As these all are the complex network of hydrocarbons, when they are combusted or utilized, the products or effluents are somewhat harmful to the atmosphere. Sulfur is one such effluent, which seriously harms the environmental conditions. So this has to be recovered up to appreciable levels. In India diesel is mostly utilized as fuel and it is up to 70%. So in order to reduce the sulfur content diesel is chosen as fuel oil. The reduction of sulfur is done by hydro desulfurization and the process is termed as diesel hydro desulfurization (DHDS). This is achieved by converting the mercaptane state sulfur to hydrogen sulfide (H2S) by reacting it with hydrogen alone on a cobalt molybdenum catalyst. By this the sulfur content is reduced from 1 wt% to 0.25 wt%. This is further reduced to 0.05 wt% using trickle bed reactors.

CO2 hydrogenation to formic acid over heterogenized ruthenium catalysts using a fixed bed reactor with separation units

An integrated continuous CO2 hydrogenation to formic acid process with trickle-bed reactor is developed using a heterogeneous Ru molecular catalyst.

Enhancement of HDO Activity of MoP/SiO2 Catalyst in Physical Mixture with Alumina or Zeolites

Catalytic properties of physical mixture of MoP/SiO2 catalyst with SiC, γ-Al2O3, SAPO-11 and zeolite β have been compared in hydrodeoxygenation of methyl palmitate (MP). MoP/SiO2 catalyst (11.5 wt% of Mo, Mo/P = 1) was synthesized using TPR method and characterized with N2 physisorption, elemental analysis, H2-TPR, XRD and TEM. Trickle-bed reactor was used for catalytic properties investigation at hydrogen pressure of 3 MPa, and 290 °C. The conversions of MP and overall oxygen-containing compounds have been increased significantly (from 59 to about 100%) when γ-Al2O3 or zeolite materials were used instead of inert SiC. MP can be converted to palmitic acid through acid-catalyzed hydrolysis along with metal-catalyzed hydrogenolysis, and as a consequence the addition of material possessing acid sites to MoP/SiO2 catalyst could lead to acceleration of MP hydrodeoxygenation through acid-catalyzed reactions. Isomerization and cracking of alkane were observed over the physical mixture of MoP/SiO2 with zeolites, but the selectivity of MP conversion trough the HDO reaction route is remained on the high level exceeding 90%.

Farm‐scale bio‐power‐to‐methane: Comparative analyses of economic and environmental feasibility

Power-to-gas technologies are considered to be part of the future energy sys- tem, but their viability and applicability need to be assessed. Therefore, models for the viability of farm-scale bio-power-to-methane supply chains to produce green gas were analysed in terms of levelised cost of energy, energy efficiency and saving of greenhouse gas emission. In bio-power-to-methane, hydrogen from electrolysis driven by surplus renewable electricity and carbon dioxide from biogas are converted to methane by microbes in an ex situ trickle-bed reactor. Such bio-methanation could replace the current upgrading of biogas to green gas with membrane technology. Four scenarios were compared: a refer- ence scenario without bio-methanation (A), bio-methanation (B), bio-methanation combined with membrane upgrading (C) and the latter with use of renewable energy only (all-green; D). The reference scenario (A) has the lowest costs for green gas production, but the bio-methanation scenarios (B-D) have higher energy efficiencies and environmental benefits. The higher costs of the bio-methanation scenarios are largely due to electrolysis, whereas the environmental benefits are due to the use of renewable electricity. Only the all- green scenario (D) meets the 2026 EU goal of 80% reduction of greenhouse gas emissions, but it would require a CO2 price of 200 € t−1 to achieve the levelised cost of energy of 65 €ct Nm−3 of the reference scenario. Inclusion of the intermittency of renewable energy in the scenarios substantially increases the costs. Further greening of the bio-methanation supply chain and how intermittency is best taken into account need further investigation.

P.181 Machine learning for classification of cognitive impairment according to antipsychotic dopamine receptor occupancy and illness severity in late-life schizophrenia

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.

Assessment of the Resilience against Liquid Maldistribution of Monolith Packings under Offshore Floating Conditions

The study provides insights for adapting commercially available packings to work on floating vessels in the marine context aiming at preserving performances similar to land-based packed-bed reactors. Specifically, liquid distribution for cocurrent gas-liquid downflow (Ug = 0.0065-0.131 m/s and Ul = 0.001-0.0078 m/s) inside monolith packings embarked on a hexapod emulator was compared against glass-bead containing trickle bed and open-cell foam packings using wire-mesh sensors under vertical, inclined and rolling column conditions. Sensitivity of the tested internals with regard to liquid maldistribution was diagnosed and analyzed in terms of a maldistribution factor for the vertical/inclined and rolling columns. Liquid maldistribution was found to prevail at high gas and low liquid superficial velocities for the tested three packings regardless of column conditions. Monolith packed beds demonstrated superior robustness to counteract liquid maldistribution induced by bed static inclinations and roll motion...

Defining nickel phosphides supported on sodium mordenite for hydrodeoxygenation of palm oil

Palm oil is largely produced in Thailand and sufficient to utilize as a biofuel feedstock through hydrodeoxygenation (HDO). In this work a new bifunctional catalyst consisting of nickel phosphide supported on zeolite mordenite in sodium form (Ni-P/NaMOR) was prepared by sequential impregnation and characterized extensively by several techniques to understand the reduction behavior, phases and distribution of nickel phosphides on the support. Nickel and phosphate precursors were transformed to Ni2P2O7 species by calcination and to a mixed phase between Ni12P5 and Ni2P by reduction. The phosphide species distributed in the zeolite cavities and external surface. The HDO of palm oil was tested in a down-flow stainless steel trickle bed reactor and the atmosphere was hydrogen. The mixed phase of nickel phosphides enhanced the HDO reaction. When tested by various temperatures and pressures, the optimum condition in this work was at 425 °C and 50 bar in which a complete of palm oil conversion, the largest HDO yield and selectivity toward C15-C18 alkanes were obtained. The green diesel and HDO yields from reduced Ni-P/NaMOR were larger than those from pure Ni2P and mixed Ni2P-Ni12P5. Interestingly, a small amount of isoparaffins was also observed likely due to the contribution of NaMOR support.

Modeling of a bench-scale fixed-bed reactor for catalytic hydrotreating of vegetable oil

A dynamic trickle-bed reactor model was developed to predict the behavior of reactive species and products during the catalytic hydrotreating of vegetable oil. The prediction capability of the model was verified with experimental information obtained during the hydrotreating of a jatropha oil at temperature of 420 °C, hydrogen pressure of 80 bar, 1500 Nl/l of H2/oil ratio and WHSV of 1–12 h−1 using a NiW/SiO2–Al2O3 catalyst. The proposed model allows to predict the partial pressure and concentration profiles along the catalytic bed as a function of the time-on-stream. The dynamic simulation results agree with experimental data reported at steady-state conditions. A comparison of experimental data and calculated results provides a correlation coefficient of 0.988.

On flow regime transition in trickle bed: Development of a novel deep‐learning‐assisted image analysis method

AbstractAn image analysis method was developed based on deep‐learning algorithms to extract phase fractions quantitatively in a rectangular trickle bed, and the average identification error was lower than 5%. Furthermore, the flow regime transition in the trickle bed was studied. In trickle‐to‐pulse flow transition, the trickle flow could be further classified into the stable trickle flow and accelerated one. The SD of liquid fractions and the peak width at half‐height of the probability density curve of liquid fractions were close to zero in stable trickle flow, increased rapidly in accelerated trickle flow, and remained approximately constant in pulse flow. In bubble‐to‐pulse flow transition, dispersed bubbles in bubble flow induced the outliers outside the upper boundary of the boxplot of gas fraction, while alternative appearance of gas‐rich zone and liquid‐rich zone in pulse flow induced outliers outside both the upper and lower boundaries of the boxplot of gas fraction.

Catalytic Wet Air Oxidation Using Supported Pt and Ru Catalysts for Treatment of Distillery Wastewater (Cognac and Sugarcane Vinasses)

The production of brandy from wine and bioethanol from sugarcane in distilleries generates vinasses, which are effluents that are rich in organic matter. Since they have a high pollution load characterized by high chemical and biological oxygen demands and a dark color, the depollution of these effluents is inevitable. Pt and Ru catalysts supported on titania and zirconia were explored in the catalytic wet air oxidation (CWAO) processing of cognac and sugarcane wastewaters, in batch mode and in a trickle-bed reactor, at a temperature condition of 190 °C and a pressure condition of 70 bar air. The addition of a catalyst promoted total organic carbon (TOC) abatement and the oxidation of ammonium ions formed from organic nitrogen in the effluents to dinitrogen or nitrates. The best results in terms of selectivity to N2 were obtained by using Pt catalysts; a selectivity of 92% to N2 and a TOC removal of 90% were observed in continuous oxidation of the sugarcane vinasse.

Numerical investigation of surface wettability on gas – Liquid flow hydrodynamics in microchannel: Application to trickle bed reactors

Two-phase gas-liquid flows are very important in trickle bed catalytic reactors. To investigate the effect of catalyst wettability on the two-phase flow hydrodynamics in the bed, microchannels are considered in order to simulate the pore scale phenomena. Since the surface area to volume ratio is a key factor at the microscale, the role of surface interaction becomes dominant. In this work, the channel hydrophobicity is varied in order to study the effect of the wetting properties of a rectangular horizontal micro-channel on the gas-liquid two-phase flow behavior. Air and water are injected through a Y junction microchannel where water is injected in the middle and air from side inlets, to investigate the air/water two-phase flow behavior in the straight section. The surface wettability of two types of catalysts is experimentally measured and used as input to the numerical computational model. The microchannel is of 300 μm, 100 μm and 1 cm in width, height and length, respectively. The CFD simulation is done on COMSOL Multiphysics, using the Level Set method. The level-set technique is used to represent a discrete fluid interface between the two phases. Navier Stokes equations and conservation of mass, coupled to the level set method keep track of the interface between the air and water in the flow field, including the interfacial interactions with the microchannel walls. The developed numerical model is used to characterize the hydrodynamics of cocurrent gas—liquid flow through the microchannel. The model was validated against published experimental data and good agreements are obtained. The prediction results demonstrate that the wetting properties of the microchannel affect drastically the two-phase flow hydrodynamic behaviors. We identified eight different flow patterns in the hydrophobic microchannel, whereas, in the case of hydrophilic microchannel, only two flow patterns were observed. All of these results were in good agreement with published experimental ones. The developed numerical model was thus used to predict trickle bed flow hydrodynamics at the microscale.

Effect of column inclination and oscillation on liquid spreading in a trickle bed

Gas–liquid–solid flow in a trickle bed installed on a floating production unit is affected by oscillations imparted by sea waves. The oscillations may affect the spreading of liquid, and in turn, the performance of a reactor. The present work investigates the effect of bed inclination and two types of oscillations (roll and roll+pitch) on the spreading of liquid in a cylindrical trickle bed with a single point liquid injection by using computational fluid dynamics. In the simulations, column tilt varied in a range of 0–15° and three oscillation frequencies (0.1, 0.2 and 0.5Hz) were considered. Initially, a three-phase Eulerian model was validated using the published experimental data for a stationary column. The effect of closure models such as capillary pressure model and Ergun drag model constants on predictions was analyzed for the selection of these closures. In a tilted column, liquid was pushed to flow in the direction of tilt. Increase in tilt angle from 0 to 15° resulted in increase in the flow segregation and ∼20% reduction in pressure drop. Oscillations (both roll and roll+pitch) resulted in more uniform liquid spreading and higher liquid holdup compared to a vertical column. With decrease in oscillation frequency, the index of uniformity in the radial liquid distribution further increased. The higher uniformity and liquid holdup caused by oscillations can be attributed to higher radial velocity of liquid due to the effect of gravity in the radial direction. Compared to the roll type oscillations, the roll+pitch type resulted in higher radial velocity and radial distribution of liquid.

Kinetic study of phenol oxidation in a trickle bed reactor over Al/Zr-pillared clay catalyst

Catalytic wet air oxidation of phenol was studied in a trickle bed reactor operated at 10 bar and temperatures between 120-160 °C over pillared clay wash-coated monolith catalyst. Different variables were studied including reaction temperature and liquid flow rate. The obtained results indicated that phenol conversion increase with an increase in temperature, whereas an increase in liquid flow rate has a negative effect on phenol conversion. Simple power law was used to model the kinetics of the process. When a simple power law model was used experimental results were predicted successfully with R2 = 0.9988 at 160 °C and the activation energy was 42.289 kJ/mol.