Mark William Ackley

Application of natural zeolites in the purification and separation of gases

Abstract There are many natural zeolites of which a small number including clinoptilolite, chabazite, mordenite, erionite, ferrierite and phillipsite offer the greatest promise for gas separation. Patents and other literature have been surveyed to identify the bulk separation and purification processes for which these zeolites have potential. The abundance and low raw material cost of natural zeolites have rarely offset such disadvantages as variable composition, low purity and often poorer separation performance compared to the more-favored synthetic zeolites. The results of the present study indicate that these natural zeolites are particularly well suited for trace-gas removal. In contrast, they are less likely to provide competitive performance in bulk separations. Clinoptilolite and chabazite are judged the most versatile, while also offering unique adsorption characteristics. Effective and efficient methods for screening all types of adsorbents are presented for various gas separations. Natural zeolites must demonstrate unique or superior performance to be serious contenders in commercial separations. Use of these methods should enhance such opportunities. The importance of including relevant process considerations in the analyses is demonstrated through application to processes for a bulk separation (O2 production from air) and purification (removal of trace levels of N2O from air). The results are not encouraging for the use of natural zeolites in air separation. Conversely, clinoptilolite and chabazite outperform commercially available synthetics in N2O removal from air.

Discrete element simulation of the dynamics of adsorbents in a radial flow reactor used for gas prepurification

Radial flow reactors (RFR) are used in thermal swing adsorption (TSA) processes for gas prepurification. The aim of this work is to show the validity of the discrete element method (DEM) to simulate the effect of thermal expansion and contraction cycles occurring in such processes on the packed bed of RFR reactors. Both mono-layered and bi-layered packed beds of adsorbents are investigated. A DEM-based model of a full-scale size unit was developed, the parameters of which were calibrated by means of particle-scale experimental measurements and simple auxiliary DEM simulations. The DEM-based model used is isothermal and the thermal expansion and contraction phenomena are modelled through the displacement of the inner and outer walls of the computational domain. First, the accuracy of this model is assessed using analytical values of the static wall pressure (i.e. with no wall motion) as well as experimental measurements of the dynamic wall pressure (i.e. with wall motion) of a bi-layered bed. Next, simulation results for a few process cycles in the case of a bi-layered packed bed indicates that little mixing occurs at the interface between the two types of adsorbents. To our knowledge, this is the first time that simulation is used to investigate the behavior of the packed bed of a RFR in a TSA process. The results obtained with the proposed model show that the DEM is a valuable tool for the investigation of such slow dynamical processes, provided a careful calibration is done.

Frederick Wells Leavitt: a pioneer in adsorption technology

Fred was born in Elizabeth, New Jersey in 1928. He attended Union Junior College from 1946 to 1948 and Newark College of Engineering from 1948 to 1950 (both in New Jersey) where he obtained his B.S. Ch.E. He then served in the US Army from 1950 to 1952, with subsequent employment with the US Army Chemical Corps. Fred was admitted to the Chemical Engineering Graduate Study Program at Rensselaer Polytechnic Institute (RPI) in 1954 and completed a M.S. Ch. E. in 1955 and his Ph.D. in June 1957 (Leavitt 1957). On his application for admission to graduate study at RPI, Fred indicated interests in ‘‘heterogeneous systems, especially those containing dispersions of small particles .... study of solid–liquid–vapor equilibria, heat and mass transfer mechanisms, reaction kinetics, and the motion of small particles in resisting media.’’ In the career that followed, Fred made significant contributions in all of these areas. Fred joined the Molecular Sieve Group at Linde Air Products Company (Division of Union Carbide Corporation) in 1957. This timing is particularly significant to the field of adsorption due to the following events of the 1950s:

Elasticity of adsorbent beds

The practical application of adsorbents with the desired separation properties depends not only upon the adsorption characteristics of the material but also upon the mechanical properties of the packed bed. The packed bed, the vessel surrounding the bed and any internal structure that supports the bed are subjected to both static and cyclic loads during an adsorption process. In order to properly design the vessel and its internal structure, the bulk mechanical properties (most particularly the elastic properties) of the adsorbent bed must be known. The primary focus of this study was to determine the elastic properties of adsorbent beds packed with activated alumina, synthetic molecular sieve 13X or natural zeolite clinoptilolite. The bulk modulus of elasticity was found to be a linear function of applied stress for each of these materials in a range of stresses lower than the bulk crush strength. The Poisson’s ratio for the packed bed was also deduced from these results.