In addition, we can make measurement of surface area, pore size, and pore size distribution. Changes in the intraparticle diffusion are evaluated by measuring the changes in effective diffusivity of the particle using a pulse-chromatagraphic method. GAS-SOLID REACTIONS
Overview:
A common feature of all gas-solid reactions is that the overall process involves several steps:
1. Transport of reactants from the bulk to the fluid-solid interface;
2. Intraparticle transport of reactants into the porous particle;
3. Adsorption of reactants at interior sites of the particle;
4. Chemical reaction of adsorbed reactants to adsorbed products (surface reaction);
5. Desorption of products;
6. Transport of products from the interior sites to the outer surface of the particle;
7. Transport of products from the fluid-solid interface into the bulk-fluid stream;
In studying gas-solid reactions we are concerned with these phenomena and other phenomena which affect the overall rate of reaction and performance of industrial equipment in which these gas-solid reactions are carried out. These other phenomena include: heat transfer, flow of gases and solids through reactors, and changes in the solid structure, all of which affect the rate of diffusion and surface area available for reaction.
Changes in the structural parameters such as surface area available for reaction, porosity, and pore size distribution will markedly affect the rate of gas-solid reactions. Accompanying these changes in structural parameters are changes in the resistance to diffusion of gaseous products and reactants through the pores of the solid. Porous structures can be present initially in the solid or evolve during reaction. By measuring the changes of the solid structure and effective diffusivity with conversion of the solid, and including their effect in an overall rate expression, a clear understanding of the nature of gas-solid reactions can be attained. In our lab we have the capability to study gas-solid reactions with several different techniques which include reaction rate measurements in a thermal gravimetric analyzer (TGA) and other reactor configurations including pulse reactors, differential reactors and fixed bed reactors.
In addition, we can make measurement of surface area, pore size, and pore size distribution. Changes in the intraparticle diffusion are evaluated by measuring the changes in effective diffusivity of the particle using a pulse-chromatagraphic method.
Applications. We have made measurements of changes in surface area and effective diffusivity as a function of conversion for coal char undergoing reaction with CO2(5). We have made measurement of the changes in catalyst undergoing deactivation as a result of carbon deposition. Other applications include the catalytic and non catalytic hydrogen reduction of ilmenite ( FeTiO3).
References.
Debelak, K. A. and Theis, J.R. "Effects of Internal Surface Area and Micropore Diffusion Upon the Rate of Reaction Between Illinois #6 Coal Char and Carbon Dioxide" Paper 19b, AIChE Annual Meeting, Nov., (1987).