Potential-swing adsorption

Sometimes, the amount of species adsorbed from a solution onto an adsorbent, e.g. activated carbon, depends on the eiectrical potential applied to the adsorbent the amount adsorbed at equilibrium depends on the potential applied. This equilibrium phenomenon of potential dependent adsorption could provide a basis for potentialswing adsorption. Bisinger and Keiier (1990) have utilized such a phenomenon (see Zabasajja and Savinell (1989) for electrosorption of alcohols on graphite surfaces and references to earlier smdies) to develop a potential-swing adsorption process. They have experimentally studied 

A very high degree of separation can be achieved after multiple cycles, limited only by axial dispersion and finite mass-transfer rate between the mobile and fixed phases. 

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The objectives of the present study were to decrease the basic complexity of PSA and to increase its productivity - the amount of product produced per unit time per unit weight of adsorbent. Success in both of these areas should further enhance process economics and increase the potential application for pressure-swing-adsorption-based processes. 

The vast majority of possible applications of reactive adsorption aim at the improvement of the product yield by shifting the equilibrium in the required direction. In contrast to the nonreactive adsorption techniques, such as simulated moving beds and pressure-swing adsorption, and despite its great potential [for example, a 12-fold higher conversion per pass in oxidative methane coupling (67)], the... 

These conclusions can only be tentative with the limited data here. However the potential scope for future studies of the kinetics of adsorption and partitioning of mixed sorbates is evident. This is of particular interest with microporous sorbents, such as carbons, especially where molecular size effects may be predominant. Such an aspect is indeed particularly relevant in gas separation processes which may involve membranes and pressure swing adsorption. 

A zeolite and carbon molecular sieves (CMS) have been examined for N2/CH4 separation. A process using 4A zeolite for this separation was developed by Habgood (1958), but this process was limited to low temperatures (—79 to 0°C) and a high-methane feed content (>90%). Ackley and Yang (1990) have demonstrated the use of carbon molecular sieve (CMS) for separation of N2/CH4 mixtures in pressure swing adsorption (PSA) processes but have also shown that the potential for CMS to achieve the desired pipeline quality (90% methane) is doubtful. The only two promising sorbents are clinoptilolites and titanosilicates, as discussed below. 

The potential of adsorption as a basis of separation processes was greatly enhanced by the advent of the Pressure Swing Adsorption (PSA) process, and the development of new Carbon Molecular Sieve (CMS) adsorbents. The CMS are a... 

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