Multiphase reactors are very common in chemical industry, and numerous review articles exist that are focused on types of reactors, such as bubble columns, trickle beds, fluid catalytic beds, etc. Currently, there is a high degree of empiricism in the design process of such reactors owing to the complexity of coupled flow and reaction mechanisms. Hence, we focus on synthesizing recent advances in computational and experimental techniques that will enable future designs of such reactors in a more rational manner by exploring a large design space with high-fidelity models (computational fluid dynamics and computational chemistry models) that are validated with high-fidelity measurements (tomography and other detailed spatial measurements) to provide a high degree of rigor. Understanding the spatial distributions of dispersed phases and their interaction during scale up are key challenges that were traditionally addressed through pilot scale experiments, but now can be addressed through advanced modeling.

Computational Modeling of Multiphase Reactors

Methyl iodide, a common methylation intermediate used in the production of pesticides and pharmaceuticals, is characterized by both acute and chronic toxicity. In the nuclear industry, some of the radio-iodine release occurs in the form of methyl iodide, exacerbating the hazard posed by the chemical. Sorbents containing silver, particularly silver mordenites, have been preferentially investigated for capturing radio-iodine emissions including those of methyl iodide. Literature reports suggest that methyl iodide is catalytically decomposed by silver mordenite into diatomic iodine and hydrocarbons/hydrocarbon derivatives. Continuous column studies utilizing silver mordenite pellets have experienced difficulties obtaining consistent results within a reasonable time when dealing with air streams containing organoiodides at low (∼100 ppb) concentrations. An alternate approach based on utilizing a thin coating of reduced silver mordenite on an inert honeycomb cordierite matrix is described in the present study. This dynamic sorption study was conducted at 170°C with air streams containing methyl iodide at 110-140 ppb concentrations in absence of moisture. The reduction in the silver mordenite mass needed to conduct the investigations resulted in reduced runtimes and successful quantification of the catalytic decomposition of methyl iodide. Kinetics of this decomposition was determined by varying gas residence time and monitoring the methyl iodide conversion. Data analysis using the integral method revealed the reaction rate had a likely first order dependence on methyl iodide concentration with a rate constant of 0.1202 L/g sorbent/s at the operating temperature. Control experiments revealed that sodium mordenite did not exhibit a similar catalytic decomposition behavior. 

Treatment of Off-Gas Emissions: Kinetics of Silver Mordenite Catalyzed Methyl Iodide Decomposition

Applications of the Liquid–Solid flows are widespread across various disciplines and this chapter is aimed to provide coherent information to facilitate design and scale-up process in these fields. Solid size particles ranging from macroscale to nanoscale and its concentration in the liquid phase are the key factors that are helpful in broader classification of liquid–solid flows. Smaller solid sizes are beneficial in terms of better processing characteristics and high heat and mass transfer rates. Hence, colloidal and surface science interaction brings complex rheology inevitable in design system. With increase in particle size and concentration, settling behavior and interaction among solid particles also play a crucial role in hydrodynamics of system. To cover various aspects of Liquid–Solid flow complexities across Chemical Engineering discipline, four major applications are chosen i.e. i) Slurry transportation ii) Liquid–Solid Flows in Stirred Tank iii) Liquid–Solid flows in Fluidized Bed Reactors and iv) Hydro-cyclones. Slurry transport system for settling and non-settling solids were discussed along their hydrodynamic characteristics for transportation, mixing and suspension application. Influence of solids on rheological properties and slurry flow characteristics, its applications in in designing the slurry transportation and stirred tank have been demonstrated. For Liquid–Solid fluidized systems, solids behavior under fluidized to transport regime along with the different modelling methodologies has been discussed. With the versatility of such system, the applications ranging from reactive systems to classifier units have been reported. Finally, the intricacies of hydrocyclones have been deliberated with cut-size variation with various design and operating parameters. Solution to achieving a high separation efficiency or resolving issues with small liquid–solids density differences have been discussed with the application of multiple hydrocyclone configurations. Thus, this Chapter gives overview of recent advances in Liquid–Solid Flows by demonstrating its applications. It also touches upon key designing parameters and modeling approaches for Liquid–Solid flows which readers can extend in their respective field of operations. 

Liquid–Solid Processes

Abstract Carbon nanotubes can be produced at high quality through hydrocarbon catalytic decomposition. In addition, hydrogen can be produced as a valuable byproduct at a competitive price. In this article, the loading of the active phase in the decomposition catalyst is optimized using natural gas as a widely available hydrocarbon. Natural gas decomposition was investigated using different nickel loadings. Natural gas decomposition, as a widely available hydrocarbon, is investigated by manipulating nickel loading to optimize the loading of the active phase in the decomposition catalyst. Optimizing the catalyst loading can achieve higher quality and yield of carbon nanotube. In addition, a higher carbon nanotube yield will maximize hydrogen production. Increasing the quality of produced carbon and the amount of hydrogen will improve the overall process economics. Nickel is a highly active catalyst for natural gas decomposition and has a higher carbon affinity compared to other metallic catalysts. Different nickel loadings were tested for natural gas decomposition. Optimization was used to calculate the optimum nickel loading based on the experimental results. The optimum nickel loading over alumina was 12.5%. The economic analysis of the process indicated that the optimum nickel loading is 30%. 

https://link.springer.com/content/pdf/10.1007/s11696-023-02737-z.pdf

Optimization of nickel catalyst loading in Ni/γAl2O3 for producing carbon nanotubes through natural gas decomposition

The depectinization kinetics of bael (Aegle marmelos) juice using the enzyme pectinase was evaluated and it was observed to follow the Michaelis–Menten model. The suitable reaction time and enzyme concentration were estimated to be 60 min and 0.25% w/w, respectively. The conditions to obtain a unique steady state for such a reaction in a continuous stirred tank reactor were determined using the fixed point theorem and contraction mapping. The phase space plot was generated using parameters and , involving the operating conditions and kinetic constants (V is the reactor volume, vmax and KM are the kinetic parameters of the Michaelis–Menten model, v0 is the volumetric flow rate and CA0 is the feed concentration of the substrate), and the envelope of a unique steady state was developed. From the iso-conversion curves, the values of α and β were identified so that the reactor can operate at a unique steady state. It was found that β > 4 results in a feasible steady state. The range of α was reduced at a higher β in order to get a unique steady state. The critical residence time of the reactor decreased with the enzyme concentration and became invariant beyond 0.20% w/w. Deviation of the CSTR from ideal behavior led to an increase in the critical residence time. The present analysis is extendable to other reaction kinetic models as well, for appropriate design and scale up of commercial reactors so as to prevent the occurrence of multiple steady states leading to inaccurate product specifications.

Deniz Uner

Papers

Chemical Reaction Engineering