Vacuum swing adsorption processes

Kumar, R., Vacuum Swing Adsorption Process for Oxygen Production— A Historical Perspective, Separ. Sci. TechnoL, 31, 877-893 (1996). 

This process (called Fractionated Vacuum Swing Adsorption Process) is also patented by Air Products and Chemicals [23]. The concept of operation of this process is illustrated by Figure 4. It shows that the N2 concentration... 

Impedance measurements also can be used to monitor industrial adsorption processes consisting of multi-step cycles like pressure swing adsorption processes (PSA) or vacuum swing adsorption processes (VSA), [3.37, 3.48, 3.42, 3.43]. 

Figure 5.16 Two-bed vacuum swing adsorption process for the production of nitrogen with a carbon molecular sieve (redrawn from Knoblauch 1978).

Figure 7.6 Three-bed vacuum swing adsorption process for O2 production (by kind permission of Air Products pic).

This fractional vacuum swing process is similar in many respects to the established vacuum swing adsorption process described in Section 7.3.4 but utilizes a CaX zeolite as the adsorbent and uses part of the oxygen-enriched gas produced from the first step of the process. 

Alternatives to the cryogenic separation process include the membrane separation process and adsorption processes. The adsorption processes include pressure swing adsorption (PSA)10 and vacuum swing adsorption (VSA). These methods are noncryogenic and produce a vapor product only. This reduces the cost of production considerably when the local use of gas-phase product is the primary objective. 

These differences become more pronounced with increasing deviations of the adsorption isotherm from a hnear relationship. As a rule the decision on the separation process as temperature swing adsorption (TSA), pressure swing adsorption (PSA), or vacuum swing adsorption (VSA) is a compromise between the steps of adsorption and desorption. Applying the PSA technique on approximately linear adsorption isotherms is advantageous. 

In this article we report i) the measurement of sorption equilibrium data of nC,-, and nCy in 5A zeolite pellets on a flow microbalance ii) The measurement of intraparticle diffusivity of nCs and nCc on 5A zeolite pellets with crystals of different size by ZLC and gravimetry and iii) The development of a mathematical model in order to predict the behavior of fixed bed and cyclic adsorption processes, iv) The prediction of breakthrough curves of propane/propylene and n/iso-paraffins mixtures in a fixed-bed adsorber based on a model including parameters independently measured, iv) Study of cyclic adsorption processes as Pressure Swing Adsorption (PSA) / Vacuum Swing Adsorption (VSA) and Temperature Swing Adsorption (TSA) for the separation of propane /propylene mixtures and n/iso-paraffins mixtures. 

The adsorption literature often classifies the adsorptive processes in terms of (a) Pressure Swing Adsorption (PSA) when the adsorption step is carried out at a super-atmospheric pressure level and the lowest desorption pressure is ambient (Processes A, D, E, F, G), (b) Vacuum Swing Adsorption (VSA) when the adsorption step is carried out at near-ambient pressure level and the lowest desorption pressure is sub-ambient (Processes H, I) and (c) Pressure Vacuum Swing Adsorption (PVSA) when the adsorption step is carried out at a super-atmospheric pressure level and the lowest desorption pressure is sub-atmospheric (Processes B, C). 

Pressure range. The process performance is often enhanced for a PSA cycle with desorption at sub-atmospheric pressures, usually called vacuum swing adsorption (VPSA). 

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