Solvent extraction, biomass products

Figure 2.5 Possible technological solutions to bioprocess problems a) Fed-batch culture b) Continuous product removal (eg dialysis, vacuum fermentation, solvent extraction, ion exchange etc) c) Two-phase system combined with extractive fermentation (liquid-impelled loop reactor) d) Continuous culture, internal multi-stage reactor e) Continuous culture, dual-stream multi-stage reactor f) Continuous culture with biomass feedback (cell recycling). (See text for further details).

Extraction into capsules with a solvent, for example, recovery of phenylethanol (a product of phenylalanine bioconversion by yeast) [67] or lactic acid from fermentation broth [68], has attracted interest recently. The polymeric core of the capsule prevents direct contact of the solvent with biomass. This process could be regarded as a batch MBSE. 

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. 

Lipopholic products are usually separated by extraction of the filtered broth, or the whole culture including the biomass, with water immiscible organic solvents, followed by separation of the solvent extracts and concentration in a vacuum evaporator. Chloroform, dichloromethane and ethyl acetate have been widely used as extraction solvents, however, 4-methyl-2-pentanone (methyl isobutyl ketone) appears to be the solvent of choice in the case of steroid substrates. Hydrophilic products, which cannot be extracted by organic solvents, can be isolated by ion exchange or by selective adsorption to polymeric resins (e.g., Amberlite XAD-resins). Resins of a wide range of polarity are available and lipophilic compounds can also be separated by this method. Final purification is accomplished in the usual way by crystallization, distillation or column chromatography. Preparative HPLC is a powerful tool for purification of small product quantities. 

Solvent extraction is widely used during early purification of fermentation-derived products and, indeed, of all natural product matrices for initial and intermediate purification prior to final purification by chromatography, crystallization, or precipitation. Solvent extraction provides the ease of liquid handling, the potential for high-throughput operation, and the potential for adaptation to continuous operation. Both water-miscible and immiscible solvents are used for extracting compoimds from the biomass. Frequently, multiple approaches can be employed to purify a fermentation-derived product. Wildfeuer (11) describes many possible approaches for purification of the antibiotic cephalosporin C. 

The second limitation of Py-GC-MS is that the complex pyrolysate was not just pyrolysis products it consisted of evaporation and combustion products of HS. ° It was reported that free compounds, e.g., alkanes, and fatty acids in HS macromolecules evaporated quickly under pyrolysis, and stmctural units split off through burning in the presence of oxygen and can be further incorporated into HS. For example, lipids, e.g., alkanes, fatty acids, dicarboxylic acids, and ketones were often found as free or solvent-extractable compounds in soils and soil HS. These compounds can be synthesized by microorganisms and plants, and can occur upon combustion of fossil fuels and biomasses. Alkylfurans and methoxylated phenols were considered pyrolysis products of... 

HS and combustion products of biomasses, and alkylbenzenes and thiophenes can be both evaporation/pyrolysis products from humic substances. At present, solvent extraction and low temperature desorption followed by TMAH Py-GC-MS have been proposed to distinguish combustion, evaporation and pyrolysis products in the pyrolysis. ... 

Extraction of natural materials in order to produce extracts with useful flavor, fragrance, nutritional and other pharmacological properties is a centuries old practice. Traditionally, such extracts are isolated from the relevant biomass (flowers, roots, peel, leaves etc.) using a variety of processes ranging from steam distillation through solvent extraction to simple mechanical expression. Many of these initial materials have been subjected to further refinement steps in order to produce a finished product of acceptable quality. 

The ideal HMF production process would use raw biomass as its feedstock, without the necessity for extensive drying or pretreatment (apart fi om mechanical reduction to particle sizes which do not suffer mass transfer limitations). Reactions would proceed in high yield over short time scales under mild conditimis in inexpensive media and use simple, non-foulable catalysts. The HMF product would be isolated without recourse to distillation or protracted solvent extraction, and all materials would be easily recyclable. Except for product yield, none of these objectives has currently been met in such a way as to be reducible to practice on an industrial scale. In the end, it is a matter of economics. When the dust settles, only the most competitive, industrially viable processes will be left standing, and the rest will be consigned to history. 

Garves reported formation of insoluble humic residue at the higher temperatures (P). In our work, the acid-catalyzed reactions of ethanol with seed hulls and with chaff or straw waste at 200 C produced a charcoal product with modest surface areas (//). A significant part (20%-30%) of the cellulose is carbonized to charcoal, which is easily removed by filtration. Flash distillation of the excess alcohol and solvent extraction of the levulinate ester leaves a resinous product consisting mainly of the lignin component of the biomass. Thus multiple marketable products are available from processing waste biomass with the acidic alcohols. 

The recovery system may affect the amount of product recovered, the convenience of the subsequent purification steps and the quality of the final product. Cell separation from the fermentation broth is the preliminary step of the recovery method. In order to recover the PHA granules, it is necessary to rupture the bacterial cell and remove the protein layer that coats the PHA granules. Alternatively, the PHA has to be selectively dissolved in a suitable solvent. Generally, two methods are usually utilized for the recoveiy and purification of PHAs from cell biomass, which include PHA solubilization or non-polymer cellular material (NPCM) dissolution. The majority of the PHA recovery method is performed using a solvent extraction process mainly by chloroform and methanol. Modifying the cell wall s permeability and then PHA dissolution in the solvent are the mechanisms for PHA extraction. 

More than a dozen organizations have recently patented technology relating to production of PHA in plants. Most of these patents describe bioengineering the metabolic pathways of plants to enable synthesis of PHAs. Of the approximately 50 recent patents in this field, ten describe separation processes for PHA recovery from plant biomass. About half of the separation patents rely on solvent extraction for PHA recovery. Currently, patents and other scientific literature on the purification of PHAs from plants is essentially limited to small laboratory scale experiments. 

Algae have a tough exterior to protect internal lipids. Therefore, oil extraction is of great importance to biodiesel production. In most cases, oil extraction from dried biomass can be performed in two steps mechanical rupture followed by organic solvent extraction. This process allows the solvent to significantly penetrate the biomass and to make the best physical contact with the lipid materials. As a result, more than 95% of the total oil present in algae can be successfully extracted. 

In the case of natural product materials, a suitable extract must be prepared. Ordinarily that means to grind or homogenize the biomass and then to carry out a series of selective solvent extractions to remove from the biomass the small molecule natural products which will be subsequently evaluated for their potential application as pharmaceuticals or agrochemicals. 

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