Process for solvent recovery

Solvent extraction in batch or continuous systems is used to recover most of the residual oil from the presscake. Heptane, hexane, or a mixture of these solvents is used to recover the oil. The solvent-extracted presscake is steam stripped to recover solvent and a residual meal known as castor pomace, containing 1% residual oil. The solvent extracted oil is also processed for solvent recovery (qv). The oil from the extraction procedure is darker than the mechanically pressed oil and has a higher free fatty acid content. It is sometimes referred to as a No. 3 castor oil and is used for blending with higher quaUty oils that are well above No. 1 specifications. 

The medicinal chemistry synthesis produced 1300 L of waste per kilo of product, the majority of which was methylene chloride. After 4 year of chemical development, this had been reduced to 100 L/kg including a snbstantial reduction in methylene chloride use. However, a major step forward in implementing an environmentally friendly process was the introduction of a commercial route, which not only dramatically improved the yield but also set up the process for solvent recovery. In the mannfactnre of pharmaceuticals, diligent solvent recovery is very often required to fully optimize the environmental performance of a synthesis. The recovery of ethyl acetate and toluene was introdnced in 1998, the year Viagra was launched, and this was followed by the recovery of... 

During extraction the feed is polluted with traces of the solvent since there always exists some mutual solubihty of the two phases (i.e., rafifinate and extract). This fact requires a further separation process for solvent recovery, making extraction processes more complex than, for instance, distillation processes. 

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