Filters, pressure commercial sizes

Figure 11.12 represents the main kinds of rotary drum filters. Commercial sizes are listed in Table 11.14. The fiowsketch of Figure 11.12(a) identifies the main auxiliaries required for this kind of filtration process. Feed to the drum may be dip-type as in Figure 11.12(b), but top feed designs also are widely used. The unit with internal filtering surface of Figure 11.12(c) is suited particularly to rapidly settling solids and has been adapted to pressure operation. 

Representative commercial sizes of some types of pressure filters for operation in batch modes are reported in Table 11.11. Some of these data are quite old, and not all of the equipment is currently popular thus manufacturers should be consulted for the latest information. Commercially available size ranges of continuous belt, rotary drum, rotary disk, and horizontal rotary filters are listed in Table 11.12. For the most part these devices operate with vacua of 500 Torr or less. 

Many different types of filters are available commercially. They can be broadly classified into two types with, however, some overlap. Fibrous filters are composed of mats of fi bets that may be ntade of cellulose, quartz, glass, polymeric materials, or metals. Porous membrane filters are usually composed of thin films of polymeric materials 0.05 to 0.2 mm thick sufficiently porous for air to How through under pressure. Pore size is controlled in the manufacturing process and ranges from 0.02 to 10 /rm, A significant fraction of the panicles may be caught on the upstream surface of the filter, but some particles may also penetrate and be caught inside the pores of the medium as well. 

Freeing a solution from extremely small particles [e.g. for optical rotatory dispersion (ORD) or circular dichroism (CD) measurements] requires filters with very small pore size. Commercially available (Millipore, Gelman, Nucleopore) filters other than cellulose or glass include nylon, Teflon, and polyvinyl chloride, and the pore diameter may be as small as 0.01 micron (see Table 6). Special containers are used to hold the filters, through which the solution is pressed by applying pressure, e.g. from a syringe. Some of these filters can be used to clear strong sulfuric acid solutions. 

A. Purification of phenanthrene. 1. By azeotropic distillation.2 A mixture of 300 g. of commercial phenanthrene (Note 1), 90 g. of maleic anhydride, and 600 ml. of xylene, contained in a 2-1. round-bottomed flask, is heated under reflux for 20 hours (Note 2). The initially yellow solution rapidly turns to a dark brown on heating. This solution is cooled to room temperature and filtered by suction to remove any insoluble adduct. The filtrate is then extracted with two 100-ml. portions of dilute sodium hydroxide, and the basic extracts are discarded. The organic phase is next washed with water and saturated sodium chloride solution, and finally is filtered through a layer of anhydrous magnesium sulfate. The excess xylene is removed by distillation, first at atmospheric pressure then the final portions are removed at reduced pressure. The residue, while still hot, is poured into a large mortar and, after solidification, is powdered to a convenient size. The yield of crude phenanthrene is 230-240 g. 

TABLE 11,10. Application of Cartridge Filters in Industry and TABLE 11.11. Sizes of Commercial Discontinuous Pressure Typical Particle Size Ranges Removed Filters... 

Commercially, separation is mostly performed by vacuum filtration on belt or drum filters or by pressure in membrane filters (Illingworth, 2002). Evenly-sized well-developed spherical crystals, such as those obtained in a well-executed Tirtiaux process, can be easily recovered using vacuum filters. For optimal filtration, the air on top of the filter may be cooled or heated to the filtration temperature to avoid melting or crystallization on the filter and clogging of the filter cake. This results in increasing entrainment and reducing filter speed. A considerable amount of oil is entrained in the filter cake, which can be as much as 60-70% for milk fat. 

TABLE 11, 11, Sizes of Commercial Discontinuous Pressure Filters... 

---