Statistical Characterization of Macroscale Multiphase Flow Textures in Trickle Beds

Experimental Studies (Lutran Et Al., Ind. Engng Chem. Res. 30 (1991) 1270; Ravindra Et Al., Ind. Engng Chem. Res. 36 (1997) 5133) and Numerical Simulation (Jiang Et Al., Chem. Engng Sci. 54 (1999) 2409-2419) Lead to the Conclusion that Fluid Flow Distribution in Trickle Beds is a Function of Bed Structure (I.e. Porosity Distribution), Particle External Wetting and Inlet Superficial Velocities of the Two Fluids. in This Study, Quantitative Relationships among the above Parameters Are Developed in a Statistical Manner through a Series of Computational Fluid Dynamics Simulations. the Contribution of Capillary Forces to Liquid Maldistribution is Significant in the Case of Partial Particle External Wetting; However, It is Shown that the Effect of Porosity Non-Uniformity in Packed Beds Can Be Reduced If the Particles Are Prewetted Well. © 2001 Elsevier Science Ltd. All Rights Reserved

Parametric Study of Unsteady-State Flow Modulation in Trickle-Bed Reactors

Unsteady-State Liquid Flow Modulation (Periodic Operation) Was Investigated for Hydrogenation of Alpha-Methylstyrene to Cumene in a Hexane Solvent over 0.5% Pd on Alumina Spheres. This Test Reaction Was Run under Both Gas and Liquid Reactant-Limited Conditions. It is Shown that Periodic Liquid Flow Modulation Can Alter the Supply of Liquid and Gaseous Reactants to the Catalyst and Result in Reactor Performance Different from that Obtained under Steady-State Conditions. the Effect of Key Parameters Such as Extent of Gas/liquid Limitation, Total Cycle Period, Cycle Split, and Liquid Mass Velocity Were Investigated Experimentally to Demonstrate the Cause-Effect Relationships in Periodic Operation. Performance Enhancement Was Observed for a Wide Range of Operating Conditions under Gas Reactant Limitation. It Was Strongly Dependent Upon the Extent of Catalyst Wetting under Liquid-Limited Conditions. the Feasibility of Achieving Improved Reactor Performance is Shown to Depend on the Extent of Reactant Limitation, the Cycle Period and Split, Mean Liquid Mass Velocity, and the Improvement of Liquid Maldistribution by Periodic Operation. Moreover, Performance Enhancement is Dependent Upon the Induced Flow Modulation Frequency and This is Discussed in Relation to the Natural Frequency of the Governing Process

Multicomponent Flow-Transport-Reaction Modeling of Trickle Bed Reactors: Application to Unsteady State Liquid Flow Modulation

A One-Dimensional Reactor and Catalyst Pellet Scale Flow-Transport-Reaction Model Utilizing the Multicomponent Stefan-Maxwell Formulation for Inter- and Intraphase Transport is Developed to Simulate Unsteady State Operation in Trickle Bed Reactors. the Governing Equations and Method of Solution Are Discussed. Results Are Presented for a Model Reaction System (Hydrogenation of A-Methylstyrene) under Gas Reactant Limiting Conditions, for Liquid Flow Modulation as a Test Case of Unsteady State Operation. Model Simulations Predict that Periodic Liquid Flow Modulation Can Alter the Supply of Liquid and Gaseous Reactants to the Catalyst and Result in Reactor Performance Enhancement above that Achieved in Steady State Operation. the Effects of Key Modulation Parameters Such as the Total Cycle Period, Cycle Split, and Liquid Mass Velocity Are Simulated, and Model Predictions Are Found to Be in Agreement with Experimentally Observed Trends in the Literature. © 2005 American Chemical Society

Prediction of Pressure Drop and Liquid Holdup in High-Pressure Trickle-Bed Reactors

The Holub Et Al. (1992, 1993) Phenomenological Model for Pressure Drop and Liquid Holdup in Trickle Flow Regime at Atmospheric Pressure Was Noted by Al-Dahhan and Duduković (1994) to Systematically Underpredict Pressure Drop at High Pressure and High Gas Flow Rates. in This Study, the Holub Et Al. (1992, 1993) Model Has Been Extended to Account for the Interaction between the Gas and Liquid Phases by Incorporating the Velocity and the Shear Slip Factors between the Phases. as a Result, the Prediction of Pressure Drop at the Operating Conditions of Industrial Interest (High Pressure) Has Been Improved Noticeably Without Any Significant Loss in Predictability of Liquid Holdup. the Extended Model and the Comparison between its Prediction and Experimental High Pressure and High Gas Flow Rate Data Are Presented and Discussed

Computed Tomographic Investigation of the Influence of Gas Sparger Design on Gas Holdup Distribution in a Bubble Column

The Effect of Gas Sparger Design on the Gas Holdup Radial Profile in a Bubble Column (With a Diameter of 0.162 M) Has Been Studied using Γ-Ray Computed Tomography (CT). Six Different Configurations of Gas Spargers Were Examined, using an Air-Water System for Selected Superficial Gas Velocities from 2 Cm/s to 30 Cm/s, Covering the Homogeneous and Heterogeneous (Churn-Turbulent) Flow Regimes. Two Operating Pressures Were Used: 1 and 4 Atm. Differences Were Found between the Gas Holdup Distributions Produced by Different Spargers at Dimensionless Radii of R/R \u3c 0.8 in the Central Region of the Column. the Cross and Single Nozzle Spargers Produced Closely Similar Gas Holdup Distributions, While the Perforated Plate Sparger Produced a Higher Gas Holdup When Compared to Other Spargers with the Same Percentage Open Area (POA). at 4 Atm, the Sparger Design Did Not Have a Significant Effect on the Gas Holdup Profiles, Compared to Atmospheric Pressure, Except for the Case of the Single-Hole Sparger, Which Was Found to Yield a Higher Gas Holdup. © 2009 American Chemical Society

Tomographic and Particle Tracking Studies in a Liquid-Solid Riser

A Liquid-Solid Circulating Fluidized Bed is a Potential Reactor of Interest in a Variety of Industrial Processes, Such as Petroleum Refining, and in the Synthesis of Fine Chemicals, Petrochemicals, and Foodstuffs. Rapid Deactivation of the Solid Catalyst in These Processes Necessitates Regeneration and Regulation of the Solids into the Riser Section in Which the Principal Reaction is Accomplished. in This Study We Show that Computer-Automated Radioactive Particle Tracking (CARPT) Can Be Used to Obtain Solids Velocity Patterns in the Riser and that Backflow of Solids Exists at the Tested Liquid Velocities. Γ-Ray Computed Tomography (CT) Reveals Slightly Higher Solids Concentrations in the Center of the Column. This is in Contrast to Gas-Solid Riser Reactors in Which the Concentration of Solids is Higher at the Walls

Investigation of a Complex Reaction Network: I. Experiments in a High-Pressure Trickle-Bed Reactor

A High-Pressure Trickle-Bed Reactor Was Used to Achieve High Productivity and Selectivity for the Manufacture of a Key Herbicide Intermediate (Α-Aminomethyl-2-Furanmethanol (Amino Alcohol, AA) from Α-Nitromethyl-2-Furanmethanol (Nitro Alcohol, NA). Raney Nickel Catalysts of Varying Activity Were Prescreened for Suitability in Trickle-Bed Operation. the Effect of Operating Parameters Such as Reactant Feed Concentration, Liquid Mass Velocity, and Temperature on the Yield of Amino Alcohol (AA) for RNi-A Are Discussed. the Superiority of Trickle-Bed Reactors over Others Such as Semibatch and Batch Slurry Systems is Demonstrated. the AA Yield Increases with Decrease in Feed Reactant Concentration and Liquid Mass Velocity, as Well as with Lowering of the Operating Temperature. a Maximum Product Yield of 90.1% Was Obtained at 8.3 Wt. % Feed Concentration of Nitroalcohol (NA), While at the Highest Feed Concentration of 40 Wt. % NA, the Maximum Product Yield Was 58%. the Volumetric Productivity of AA Was Significantly Higher at Higher Reactant Feed Concentrations, Even Though the Yield Was Lower under These Conditions. the Operating Temperature Was Also an Important Parameter, with a Lower Temperature Being Preferable for Trickle-Bed Experiments. Bed Dilution with Inert Fines Improved Catalyst Utilization and Increased the AA Yield and Productivity in the Laboratory-Scale Trickle-Bed Reactor

Investigation of a Complex Reaction Network: II. Kinetics, Mechanism and Parameter Estimation

Conventional Strategies for Discrimination of Intrinsic and Apparent Kinetics from Crushed- and Whole-Catalyst-Pellet Experimental Data, Respectively, Do Not Yield Satisfactory Results for the Reaction Network in the Manufacture of Α-Aminomethyl-2-Furanmethanol (Aminoalcohol) from Α-Nitromethyl-2-Furanmethanol (Nitroalcohol). Laboratory Trickle-Bed Reactor Tests in the Range of Concentration and Product Yield of Commercial Interest Are Utilized to Yield a Reasonable Set of Kinetic Parameters, Which Are Otherwise Unobtainable. This is Accomplished by Proposing a Reaction Network, a Plausible Mechanism, and Optimizing the Kinetic Parameters based on the Reactor-Model-Generated Performance Data to Fit Experimental Output Concentrations of All Species for the Entire Set of Experiments. a Complex Reaction Network for the Key Reactions in the System is Developed based on the Reaction Scheme in Part I. Fitting of Trickle-Bed Reactor Data to This Model is Attempted to Yield an Insight into the Actual Kinetics. the Results Show Promise of Obtaining an overall Network Kinetic Model, Even with the Limited Data Available