Process filters fine chemicals

Such vacuum filter dryers are used for processing pharmaceuticals, fine chemicals and toxic products, and can use a variety of filter media including sintered metal plates, woven wire mesh and a wide range of fabric cloths. Most processing steps can be carried out either under vacuum, or an inert gas such as nitrogen, or under normal atmospheric conditions. Dissolved solids can then be crystallized by application of cooling in the jacket. 

FILTER AIDS are fine, chemically inert powders applied in both process and waste rnicrofidtrations to tnaintain high flowrates while giving brilliant clarity. For difficult separations this long-established technology is the economical way to produce high quality fluids and manageable solid residues. Examples of filter aids are ... 

In fine chemicals manufacture, batch filtration prevails. This operation is the subject of R D in various steps of process development. The aim of R D on filtration is (1) to establish an effective procedure of filtration and washing providing a filter cake and/or filtrate of desired quality, and (2) to select the most appropriate filter or centrifuge for full-scale operation and determine its productivity. The productivity is defined as ... 

Safety. The MR is much safer than the MASR. (1) The reaction zone contains a much smaller amount of the reaction mixture (hazardous material), which always enhances process safety. (2) In case of pump failure, the reaction automatically stops since the liquid falls down from the reaction zone. (3) There is no need to filter the monolithic catalyst after the reaction has been completed. Filtration of the fine catalysts particles used in slurry reactors is a troublesome and time-consuming operation. Moreover, metallic catalysts used in fine chemicals manufacture are pyrophoric, which makes this operation risky. In a slurry reactor there is a risk of thermal runaways. (4) If the cooling capacity is insufficient (e.g. by a mechanical failure) a temperature increase can lead to an increase in reaction, and thus heat generation rate. 

Filter drying is especially appropriate for sterile batch processes in which solids have to be separated from the mother liquor mechanically and thermally in an enclosed system. It is particularly suitable for process plants in which frequent product changes are made (e.g., for the manufacture of pharmaceutical intermediate and final products, dyes and pigments, fine chemicals, agrochemicals, foodstuffs, etc.). 

The evolution of chemical processes and process equipment is closely related to the methods and apparatus used in the chemistry laboratory. At the early stage of evolution of chemical industries, process steps in the manufacture of a chemical mimicked the steps used in the chemistry lab in its preparation. Most of these processes were batch processes. Some of these evolved into continuous processes as the production volumes increased. Batch processes occupy the preeminent position, even today, in the pharmaceutical and fine-chemical industries. Some of the process equipment - stirred vessels, packed towers, filters, and so on - are the up-sealed versions of the apparatus used in the chemistry laboratory of yesteryear. Process intensification (PI), which represents a paradigm shift in equipment as well as in process design, takes advantage of advances in reaction engineering and transport phenomena in the design of equipment and processes (as opposed to the mere scale-up of the apparatus of the chemistry lab and mimicking the step in the laboratory preparation). 

Exemplarily, for a typical fine chemical manufacturing process, the simplified process scheme of the aspirin production is presented in Figure 7.14. Acetylsali-cylic acid as produced by reaction of salicylic acid and acetic anhydride in a batch reactor is subjected to a cooling crystallization. The resulting suspension is transferred to a filter to remove the solvent and acetic acid formed as by-product. 

The insoluble residue of diphenylurea from the original filtration is chemically almost pure. It may be recrystallised from hot rectified spirit or ethanol, a process which will be necessary if the material contains fragments of porcelain. When using either of these solvents, however, the hot solution should be filtered at the pump using a small Buchner funnel and flask which again have been preheated by the filtration of some of the hot solvent, as the solution when cooled rapidly deposits the diphenylurea. iSym-Diphenylurea (or carbanilide) is thus obtained as fine colourless crystals, m.p. 237° yield, 1-1 5 S ... 

---