Drying of solids

Crystalline and amorphous substances that are stable in the air and do not decompose when heated in the temperature interval from 100 to 130 °C are dried in a drying cabinet. The same substances can be dried in the air and in a desiccator over phosphorus anhydride, anhydrous calcium chloride, or concentrated sulphuric acid. 

Dry substances containing water of crystallization in desiccators over a drying agent and see that the water vapour pressure over it (Table 2) corresponds to the water vapour pressure over the crystal-lohydrate being dried. 

W ATER VAPOUR PRESSURE OVER DRYING AGENTS 

Substance Water vapour pressure, mmHg (20 C) Substance Water vapour pressure, mmHg (20 C) 

Dry hygroscopic solids containing no water of crystallization in a desiccator over a drying agent. Dry solids that are easily hydrolyzed by the moisture of the air, and also substances oxidized by the oxygen of the air in a vacuum desiccator or in a special vacuum drying cabinet. The vacuum in such cabinets is produced by an oil pump. 

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This subsection presents the theoiy and fundamental concepts of the drying of solids. 

Gas absorption, sembbing desorption, stripping Humidifieation and water eooling Dehumidifieation and air eonditioning Drying of solids, solutions/slumes... 

Nonhebel, G. and Moss, A.A.H., 1971. Drying of solids in the chemical industry. London Butterworths. 

F. Brochard, J. Daillant. Drying of solids wetted by thin films. Can J Phys 62 1084-1088, 1990. 

A desiccator is frequently also employed for the thorough drying of solids for analysis and for other purposes. Its efficient operation depends upon the condition of the desiccant the latter should therefore be renewed at frequent intervals, particularly if its drying capacity is low. For dealing with large quantities of solid a vacuum desiccator is advisable. 

Kishan B. Mathur and Norman Epstein, Dynamics of Spouted Beds W. C. Reynolds, Recent Advances in the Computation of Turbulent Flows R. E. Peck and D. T. Wasan, Drying of Solid Particles and Sheets... 

Gas absorption, scrubbing desorption, stripping Humidification and water cooling Dehumidification and air conditioning Drying of solids, solutions/slurries... 

Drying of Solid Particles and Sheets R. E. Peck and D. T. Wasan Author Index—Subject Index... 

The drying of solids may involve the removal of volatile solvents. When these are flammable, ignition sources must be excluded to minimise risk of fire or explosion. 

NONHEBEL, G. and MOSS, A. A. H. Drying of Solids in the Chemical Industry (Butterworth, London, 1971). THIJSSEN, H. A. C. and RULKENS, W. H. Recent Developments in Freeze Drying (Int. Inst. Refrigeration, Lausanne, 1969). 

Pearse, J. F., Oliver, T. R., and Newitt, D. M. Trans. Inst. Chem. Eng. 27 (1949) 1. The mechanism of the drying of solids. Part I. The forces giving rise to movement of water in granular beds, during drying. 

Corben, R. W. University of London, Ph.D. Thesis (1955). The mechanism of drying of solids. Part IV. A study of the effect of granulation on the rate of drying of a porous solid. 

As previously indicated, the drying of solid substances brings about a series of further problems. It no longer suffices that one simply pumps out a vessel and then waits until the water vapor diffuses from the solid substance. This method is indeed technically possible, but it would intolerably increase the drying time. 

In connection with multiphase diffusion another poorly understood topic should be mentioned—namely, the diffusion through porous media. This topic is of importance in connection with the drying of solids, the diffusion in catalyst pellets, and the recovery of petroleum. It is quite common to use Fick s laws to describe diffusion through porous media fJ14). However, the mass transfer is possibly taking place partly by gaseous diffusion and partially by liquid-phase diffusion along the surface of the capillary tubes if the pores are sufficiently small, Knudsen gas flow may prevail (W7, Bl). 

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