Chemicals, biomass solvent extraction

Primary recovery of the active ingredient from the solid or liquid phase to remove large quantities of unwanted waste materials, which may themselves be processed further. Suitable techniques include solvent extraction, precipitation by chemical or physical changes to the product-containing solution, and ultrafiltration or microfiltration to separate products above a particular size. Work done on combined biomass separation-primary product recovery processes such as expanded-bed adsorption are now being commercialized in the pharmaceutical industry. 

Metabolix has patented a solvent extraction process that might be appropriate for processing PHAs from plant biomass on a large scale (19), Two methods are described in the patent, each with an option to recover PHA as the polymer or as a chemically transformed derivative ... 

Figure 3 illustrates the first method whereby plant biomass is extracted with a solvent in which the oil is soluble and the PHA and meal are not highly soluble. This produces an oil fraction essentially free of PHA (less than 10 wt%). The PHA/meal mixture is then extracted with a second solvent in which the PHA is soluble. Alternatively, the PHA/meal mixture can be treated chemically or enzymatically to produce PHA derivatives which are then isolated from the meal. 

Figure 4 illustrates the second method whereby plant biomass is extracted with a solvent in which both the oil and PHA are soluble and the meal is not highly soluble. Less than 10 wt% of oil and PHA remain in the meal. PHA and oil are separated by a physical separation such as distillation. Alternatively, the PHA/oil product may be modified by chemical or biological treatment to provide a PHA derivative that is subsequently purified. 

The mechanism of product release by membrane permeabilization with organic solvents, on the other hand, is clear. Positive results with this method have been reported by Brodelius and Nilsson (184). Recently, however, Brodelius (111) concluded that regrowth of the biomass after different permeabilization procedures has not yet been possible. Reuse of biomass has been an important objective in this kind of research. It is not always clear which mechanism is responsible for product release stimulated by a certain chemical compound. Meijer (69) showed product release through the addition of polyethylene glycol. It is difficult to distinguish between the various mechanisms, such as osmotic stress, permeabilization, or extraction. 

Cost effectiveness of PHA isolation does not only depend on equipment and chemicals needed, but, most of all, on the yields for product recovery and the possibility to reutilize the compounds needed for the isolation. For direct extraction of PHA from biomass extraction solvents that can easily be recycled will be of interest [69]. Solubility of PHAs, especially pure crystalline PHB, is a complex topic. Unlike most low molecular mass compounds and noncrystaUizing amorphous polymers, the solubility of crystalline polymers such as PHB cannot be predicted... 

The isolation of these polymers from the biomass proceeds through the destruction of the cell membrane mechanically, chemically or eznymatically [42, 83], followed by the dissolution of the polyma- in a suitable solvent, for example chloroform, methylene chloride, 1,2-dichloro ethane or pyridine. The remnants of the cell walls are removed by filtration and/or centrifugation. Extraction, using mixed solvents, for example wate/organic solvent, is the last step applied for the final purification. 

Alonso et have eliminated pre-treatment steps to fractionate biomass. They made use of certain composition in biomass to obtain fuels and chemicals, and the rest of fraction was separated. The work used gamma-valerolactone (GVL) as solvent, and the cellulosic fraction of lignocellulosic biomass can be converted into levulinic acid (LA), while at the same conditions the hemicellulose fraction can be converted into furfural. The furfural can be separated by distillation during the reaction or can be kept in the reactor and subsequently processed to produce furfutyl alcohol and LA. The lignin was solubilized in the GVL and separated. This process not only obtains the production of fuels and chemicals by utilization of hemicellulose and cellulose, but also it benefits from the elimination of pre-treatment and extraction/separation steps. 

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