Sieve adsorption columns

Theoretical Prediction of Breakthrough Curves for Molecular Sieve Adsorption Columns... 

Prediction of the breakthrough performance of molecular sieve adsorption columns requires solution of the appropriate mass-transfer rate equation with boundary conditions imposed by the differential fluid phase mass balance. For systems which obey a Langmuir isotherm and for which the controlling resistance to mass transfer is macropore or zeolitic diffusion, the set of nonlinear equations must be solved numerically. Solutions have been obtained for saturation and regeneration of molecular sieve adsorption columns. Predicted breakthrough curves are compared with experimental data for sorption of ethane and ethylene on type A zeolite, and the model satisfactorily describes column performance. Under comparable conditions, column regeneration is slower than saturation. This is a consequence of non-linearities of the system and does not imply any difference in intrinsic rate constants. 

The usual solids for Gsc are charcoal, silica gel, alumina and molecular sieves. Adsorption columns are very efficient for the analysis of gases. The gases that can be separated on these solids (unpoisoned) are ... 

D. R. Garg and D. M. Ruthven, The Pnfomiance of Molecular Sieve Adsorption Columns ... 

Garg, D.R., and Ruthven, D.M., Theoretical prediction of breakthrough curves for molecular sieve adsorption columns, Chem. Eng. Sci., 28(3), 791-806 (1973). 

Particle Size and Shape. The polymerization process for producing macroporous synthetic polymers (539) leads to the formation of spherical particles whose size can be controlled within certain limits. The popular XAD polymers are usually sold with approximately 90 of the total weight encompassing smooth beads with 20-50-mesh sizes. Most users incorporate a suspension step to remove the fines in their purification of the polymer, but they do not remove the small number of particles larger than 20 mesh. The particle size and distribution vary with different polymer batches, and it is advisable to mechanically sieve polymer beads and choose only those within the 20-50-mesh size for preparation of the adsorption columns. 

Tphe breakthrough curve for a fixed-bed adsorption column may be pre-dieted theoretically from the solution of the appropriate mass-transfer rate equation subject to the boundary conditions imposed by the differential fluid phase mass balance for an element of the column. For molecular sieve adsorbents this problem is complicated by the nonlinearity of the equilibrium isotherm which leads to nonlinearities both in the differential equations and in the boundary conditions. This paper summarizes the principal conclusions reached from a recent numerical solution of this problem (1). The approximations involved in the analysis are realistic for many practical systems, and the validity of the theory is confirmed by comparison with experiment. 

Carbon molecular sieve adsorption desorption at 350°C into a cryogenically cooled troop flash evaporated onto a capillary column GC/MS system recommended sample volume 10 L flow rate 100 mL/min. 

The experimental system consisted of an adsorption column fitted with a thermal conductivity detector. The adsorbate gas mixture was passed through the column packed with Linde 5A molecular sieve. The details of the packed column are given in Table II. The carrier gas mixture was dried prior to introduction to the column. The gas flow rates were adjusted and measured until a desired carrier gas composition was achieved. A six-port valve with interchangeable loops was used for introducing a pulse in the carrier gas. The pressure drop across the column was measured with a manometer and was found to be negligible. The dead volume in the system between the points where the pulse was introduced and the response was measured was minimized. 

Adsorption is an effective technique to break an azeotrope. The separation makes use of molecular sieve adsorption, and can take place either in vapour or in liquid phase. Unlikely a process using a MSA that could contaminate the final product, here absolute purity product is obtained. Figure 9.33 depicts a process for pharmaceutical-grade ethanol (Stichlmair and Fair, 1999). After pre-concentration in the column C-1 operating at a pressure slightly above normal, the vapour distillate with the azeotropic composition is fed to the adsorption device. Here the water is retained, producing a vapour that consists of pure ethanol. This may be used to heat the second distillation... 

The importance of heat effects in adsorption column dynamics appears first to have been recognized by Leavitt in the early 1960s but detailed analysis came only some years later. The equilibrium theory of an adiabatic adsorption column, which is closely related to the equilibrium theory of multicomponent adsorption, was first developed by Amundson, Aris, and Swanson and the analysis was extended by Pan and Basmadjian ° who also verified some aspects of the theory in an experimental study of the adsorption of COj and 5A molecular sieve. These initial developments were expanded into a more complete treatment by Rhee, Amundson, and Heerdt as well as in later... 

In the last decade interesting studies have been performed, and further applications of open capillary gas adsorption columns have been suggested by de Nijs and de Zeeuw [35 - 37]. Chrompack (The Netherlands) has embarked upon the commercial production of some types of these columns, using alumina, molecular sieves, and polymer adsorbents [38 - 41],... 

Figure 12. Combined pressure (p) and dielectric (er) measurements of a periodic ad- and desorption process of nitrogen (N2) on molecular sieve MSNalBX (UOP) at 293 K taken inside an industrial sized adsorption column (PSA).

Adsorption Column—This column must completely separate oxygen, nitrogen, and methane. A 13X molecular sieve 80/100 mesh is recommended for direct injection. A 5A column can be used if a pre-cut column is present to remove interfering hydrocarbons. If a recorder is used, the recorder pen must return to the baseline between each successive peak. The resolution (R) must be 1.5 or greater as calculated in the following equation ... 

A bench-scale unit was assembled and tested for H2 purification from a 90/10 wt% H2/N2 mixture at 2.17 MPa. The apparatus comprised a membrane module with 341 fibers totaling 778 cm surface area, and two adsorption columns, each packed with 5 g of 5 A molecular sieve with 350-500 pm particle size. The cyclic operation was synchronized by means of a set of controlled switching valves. 

When adsorbents are used to dry gases or liquids, often in a flow system, the adsorbents may need pre- or post-treatment to avoid hazards. Thus, when ethylene was contacted with molecular sieve not previously treated with dilute ethylene, the adsorption exotherm heated the bed to red heat and ruptured the drier. When peroxide-containing ethers are simultaneously dried and purified by chromatography (passage through an alumina column), the peroxides are concentrated on the alumina, which must be treated before disposal. 

Garg, D. R. and Ruthven, D. M. A.I.Ch.E. Jl 21 (1975) 200. Linear driving force approximation for diffusion controlled adsorption in molecular sieve columns. 

---