What is mass transfer limitations in catalysis?
13.2. Internal mass transfer limitation: refers to the catalyst structure and characterization that affects two factors [30]: • The diffusion of reactants and products in and out of the interior of the photocatalyst particle. • The light penetration inside the photocatalyst volume.
How do you define mass transfer?
Mass transfer is the net movement of mass from one location, usually meaning stream, phase, fraction or component, to another. Mass transfer occurs in many processes, such as absorption, evaporation, drying, precipitation, membrane filtration, and distillation.
When external mass transfer effects are negligible?
Therefore, the effect of external mass transfer is influenced by the reaction kinetics. When the saturation coefficient KA is larger, the external Thiele modulus is larger for the external mass transfer effects to be negligible. when Kβ = 0, Eq.
What is a diffusion limited reaction?
A diffusion limited reaction rate is one which depends solely on the rate at which solute molecules diffuse to the site of reaction such as the surface of a reactant particle.
What is mass transfer resistance?
Mass Transfer Resistance. Mass Transfer Resistance. The resistance to mass transfer is defined as the reciprocal of the mass transfer coefficient: represents the resistance to mass transfer in the liquid phase. represents the resistance to mass transfer in the gas phase.
What are the two factors that affect the rate of mass transfer?
Some important factors affecting the mass transfer rate, such as surfactant and its content, stirring speed, ratio of reagents, treating ratio and volume ratio of membrane phase to internal phase, have been studied.
What is mass transfer kinetics?
Mass-transfer kinetics First, the analyte is transferred out of the bulk solution towards the sensor chip surface. Second, the binding of the analyte to the ligand takes place. The first step is also known as mass transfer and is carried out by convection and diffusion (1). Both events have their own rate constants.
What is perfusion limited and diffusion limited?
Diffusion-limited gas exchange (left) is characterized by incomplete equilibration. In this scenario, the rate of gas diffusion across the alveolar membrane limits its transport away from the lung. In contrast, perfusion-limited gas exchange (right) is characterized by complete equilibration.
What causes mass transfer?
Mass transfer is mass in transit due to a species concentration gradient in a mixture. By concentration gradient, we mean a spatial difference in the abundance of the chemical species.
What does mass transfer mean in chemistry?
Mass transfer. Mass transfer is mass in transit due to a species concentration gradient in a mixture. By concentration gradient, we mean a spatial difference in the abundance of the chemical species.
What is mass transport in electrochemistry?
Mass transfer is defined as the movement of material in a solution from one location to another. There are three modes of mass transport in an electrochemical system. They are diffusion, convection, and migration.
What is diffusion mass transfer?
Diffusion is a mass transfer phenomenon that causes the distribution of a chemical species to become more uniform in space as time passes. In this case, species is a chemical dissolved in a solvent or a component in a gas mixture, such as the oxygen in air.
How do you know if a reaction is diffusion limited?
One classical test for diffusion control is to observe whether the rate of reaction is affected by stirring or agitation; if so then the reaction is almost certainly diffusion controlled under those conditions.
How do mass transfer and kinetics affect reaction rate?
Mass transfer and kinetics can compete and contribute to the overall reaction rate. Process scale-up and optimization require that the impact of mixing on the reaction rate be quantified. Laboratory reactors must be operated under conditions that will allow meaningful process characterization and scale-up.
What is the difference between diffusion and mass transfer?
Diffusion is the macroscopic result of random molecular motion on a microscopic scale. Mass transfer by convection involves the transport of material between a boundary surface (such as solid or liquid surface) and a moving fluid or between two relatively immiscible, moving fluids.
What is mass transfer by convection?
Mass transfer by convection involves the transport of material between a boundary surface (such as solid or liquid surface) and a moving fluid or between two relatively immiscible, moving fluids. Don’t confuse this phenomenon with the movement of mass caused by a chemical species simply being carried along in a fluid stream (advection).
Which rate process must be characterized when conducting a gas-liquid reaction?
The primary and most fundamental rate process that must be characterized when conducting any gas-liquid reaction is the mass transfer of gas into the liquid reaction phase.