Use of the linear driving force approximation to guide the design of monolithic adsorbents

The objective of this paper is to provide the basic tools necessary to guide the optimal design of monolithic adsorbents. Previous work has concentrated on optimizing monolith manufacturing processes and experimental studies have suggested that the mass transfer performance of the monolithic form might be inferior to that of the more traditional packed bed form. In this paper, the classical linear driving force approximation, along with the parabolic concentration gradient assumption, is applied to a number of simple geometries. Transformation of square, rectangular, triangular and hexagonal geometries to an equivalent hollow cylinder on the basis of equal volume and equal internal surface area, facilitates use of the linear driving force analytical solution for a cylinder in order to guide the design of the more complex monolith geometries. Taking channel mass transfer performance and pressure gradients into consideration as well, the analyses indicate that regular hexagonal channels offer the best compromise on overall performance, with minimization of the wall thickness being the key design objective. Use of the algebraic design equations for the circular channel provides an excellent approximation for the regular hexagon and thus design work can be carried out with the former and simpler geometry. The engineering challenge now becomes one of manufacturing monoliths with appropriately thin walls. A challenge for the future is to obtain the full numerical solutions for the square, rectangular, triangular and hexagonal geometries.