Packed columns development

Gas-liquid chromatography invented by Martin and James Packed columns developed... 

Historically, GC was first performed using packed columns. Such columns were usually made of coiled metal or glass tubes, with length of 1 to 5 m and internal diameter of a few millimeters. These were packed with small particles of sohd support coated with nonvolatile liquid stationary phases. The solid particles themselves played the role of the stationary phase in GSC. Packed columns were characterized by poor efficiencies related to multiple flow paths among the packing particles (the A term in the van Deemter equation), as well as uneven distribution of the hquid phase within the particles and at the contact points between the particles. The number of theoretical plates in packed columns was several thousand at the most, therefore improvements in resolution were usually achieved by the use of more selective stationary phases. Consequently, hundreds of different stationary phases were available at the peak of packed column development. 

Experimental Mass Transfer Coefficients. Hundreds of papers have been pubHshed reporting mass transfer coefficients in packed columns. For some simple systems which have been studied quite extensively, mass transfer data may be obtained directiy from the Hterature (6). The situation with respect to the prediction of mass transfer coefficients for new systems is stiU poor. Despite the wealth of experimental and theoretical studies, no comprehensive theory has been developed, and most generalizations are based on empirical or semiempitical equations. 

Nonisothermal Gas Absorption. The computation of nonisothermal gas absorption processes is difficult because of all the interactions involved as described for packed columns. A computer is normally required for the enormous number of plate calculations necessary to estabUsh the correct concentration and temperature profiles through the tower. Suitable algorithms have been developed (46,105) and nonisothermal gas absorption in plate columns has been studied experimentally and the measured profiles compared to the calculated results (47,106). Figure 27 shows a typical Hquid temperature profile observed in an adiabatic bubble plate absorber (107). The close agreement between the calculated and observed profiles was obtained without adjusting parameters. The plate efficiencies required for the calculations were measured independendy on a single exact copy of the bubble cap plates installed in the five-tray absorber. 

Flooding and Loading Since flooding or phase inversion normally represents the maximum capacity condition for a packed column, it is desirable to predict its value for new designs. The first generalized correlation of packed-column flood points was developed by Sherwood, Shipley, and Holloway [Ind. Eng. Chem., 30, 768 (1938)] on the basis of laboratory measurements primarily on the air-water system. 

F = Factor for fractionation allowable velocity or packed column packing factor or pump developed head, ft. 

The development of the function describing (tm) for a capillary column is similar to that for the packed column but (r), the column radius, replaces (dp), the particle diameter. 

Due to the varying physical nature of the different packings, it appears that no one has developed a specific function for (com) for a packed column, but it was suggested... 

In the previous two chapters, equations were developed to provide the optimum column dimensions and operating conditions to achieve a particular separation in the minimum time for both packed columns and open tubular columns. In practice, the vast majority of LC separations are carried out on packed columns, whereas in GC, the greater part of all analyses are performed with open tubular columns. As a consequence, in this chapter the equations for packed LC columns will first be examined and the factors that have the major impact of each optimized parameter discussed. Subsequently open tubular GC columns will be considered in a similar manner. 

One question of chief interest concerns the number of runs that can be run with one individual SEC column. The lifetime of the sorbent itself must be tested as well as the maximum run number for the packed column. Because column packing procedures for SEC columns are rather time-consuming and all SEC columns have to be checked very carefully with respect to performance, very frequent repacking of the column is unreasonable. Therefore, CIP protocols are generally necessary. The CIP protocol should be developed as part of the process validation program. 

Chen [133] highlights the long-term growth of the technically popular use of bubble cap trays, valve and sieve trays, followed by the increased popularity of packed columns accompanied by the development of random and structured packings. There are some applications in chemical/ petrochemical/petroleum/gas treating processes where one type of contacting device performs better and is more economical than others. Chen [133] points out ... 

Few laboratories have developed their own facilities for packing conventional and small bore columns, preferring to rely on commercial manufacturers for their needs. This is understandable since packed columns containing any common phase can be obtained at an acceptable cost and with a guarantee of acceptable performance and stability. Column packing generally requires access to equipment not readily available in all laboratories and... 

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