Vacuum filtration choice

Vacuum filtration is definitely the method of choice for filtration, and it is the most common method. Vacuum filtration is superior in that suction is used to force the liquid through the filter paper allowing for rapid filtration. Precipitates can be recovered quickly and easily. After the precipitate has been recovered, it can then be vacuum dried. Vacuum drying is simply allowing suction to continue after the liquid has been removed. The suction creates an excellent airflow, which dries the collected precipitate as it flows. Ten to twenty minutes is adequate time to dry any product. 

The choice of filtration (batch, continuous vacuum, cross flow, etc.)... 

Continuous filters are most attractive when the process application is a steady-state continuous one, but the rate at which cake forms and the magnitude of production rate are sometimes overriding factors. A rotary vacuum filter, for example, is a dubious choice if a 3-mm (0.12-in) cake will not form under normal vacuum in less than 5 min and if less than 1.4 m /h (50 ft /h) of wet cake is produced. Upper production-rate limits to the practicality of batch units are harder to establish, but any operation above 5.7 m /h (200 ft /h) of wet cake should be considered for continuous filtration if it is at all feasible. Again, however, other factors such as the desire for flexibility or the need for high pressure may dictate batch equipment. 

With the exception of the precoat applications, RVF s do not usually yield absolutely clear filtrate. Although still widely used, rotary vacuum filters are, in some cases, being replaced by membrane separation technology as the method of choice for clarification of fermentation broths and concentrating cell mass. Membranes can yield more complete filtration clarification, but often a wetter cell paste. 

Addition of L-malic acid to the reaction mixture containing free base 2 followed by concentration by vacuum distillation led to precipitation of sunitinib malate (1), which was isolated by filtration. The filtration of the L-malate salt took only about 30 min on a 50-kg scale (compared to 8 h for 13 kg of the free base), thereby vindicating the choice of the L-malate salt as the API. 

The air-water separating device is dqticted in Figure 11.18. Further care must be given to the alignment of the connecting ports in the vacuum box and the belt. Belt velocity is not a firee choice in a given application [Schwalbach,1990]. It is conditioned by the filtration characteristics of the material being separated. This point is demonstrated in Example 11.2. 

Various types of filtration equipment or hardware employ one of four main classes of driving force gravity, vacuum, pressure or centrifugal force. The choice of which type of equipment to use in a specific application depends upon many widely differing factors, which will not be detailed in this chapter. 

Leaf and plate filters are mostly relatively simple pressure-driven filters made up of fiat filtration elements, although they can also be vacuum driven. The overall configuration of the filter may be horizontal or vertical, and the basic choice between them is often made according to the space available in the factory. They are mainly used for batch-operated solids recovery, although in combination with precoat they can also be employed for clarification and decontamination duties. 

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