Physical conversion extraction, solvent

Where larger quantities (upwards of Ig) are required, most of the impurities should be removed by preliminary treatments, such as solvent extraction, liquid-liquid partition, or conversion to a derivative (vide supra) which can be purified by crystallisation or fractional distillation before being reconverted to the starting material. The substance is then crystallised or distilled. If the final amounts must be in excess of 25g, preparation of a derivative is sometimes omitted because of the cost involved. In all of the above cases, purification is likely to be more laborious if the impurity is an isomer or a derivative with closely similar physical properties. 

The P(3HB-co-3HV) polymer has been a primary focus, because compared to P(3HB), the copolymer has physical and mechanical properties more conducive to melt-processing and subsequent commercial application. Investigators (Keenan et al, 2005 Nakas et al, 2004) have demonstrated the conversion of steam-exploded (aqueous) and organic solvent-extracted ( organosolv ) hemicellulosic hydrolysates (National Renewable Energy Laboratory, NREL, Golden, CO) to P(3HB-co-3HV) copolymers using levulinic acid as a cosubstrate (see Table 9.3). 

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