Adsorption for gas separation

One of my objectives with writing these short essays is to provide high-quality technical information on designing and simulating adsorption processes. To that end, I thought I should write a short introduction on the topic and provide some foundations to build upon for those readers from different backgrounds.

Adsorption (notice the ‘d’ as opposed to ‘b’), is the process used to describe the concentration of molecules on solid surfaces. Specifically, physical adsorption is a reversible process, governed by van der Waals and electrostatic interaction. Porous solids, such as zeolites and metal-organic frameworks (MOFs), with stronger surface forces lead to a greater uptake of gas.

The equilibrium concentration of gas adsorbed (units of mol/kg) depends upon the pressure and temperature. This relationship can be described by isotherm models such as the famous Langmuir isotherm:

$$q_i = q_{max} \frac{b\exp({\frac{Q}{RT}})P_i}{1 + b\exp({\frac{Q}{RT}})P_i}$$

The varying degrees of affinity towards certain molecules enables equilibrium gas separation. After the adsorbent is saturated, no further separation of the feed gas can be achieved, and the adsorbent must be regenerated by swinging the pressure or temperature. These processes are known as pressure swing adsorption (PSA) and temperature swing adsorption (TSA), respectively.

My interests lie in the design of these separations. Simulation tools allow engineers to design these systems by solving the mass, energy and momentum conservation equations, coupled with the equilibrium and kinetic models.

I’m building an adsorption process simulation tool AdSim, and if that interests you, let’s talk.