Separation, biomass extraction, solvent

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. 

After biosynthesis of the polyester and separation of the bacterial biomass from the supernatant, the required recovery process (typically a solid-liquid extractiOTi procedure) can constitute another not negligible cost factor, especially in large-scale production. Here extraction solvents that can easily be recycled will be of interest [53]. In order not to leave the patterns of sustainability in biopolymer production, it will be indispensable to concentrate the development of new extraction processes on such recyclable solvents that are also of environmentally sound nature [54], Typical harmful chlorinated solvents like chloroform must be avoided. A PHB production process embedded in an ethanol production plant has the advantage to utilise the medium chain length alcohol fraction (fusel alcohols) from the distillery step, consisting mainly of iso-pentanol. The application of the fusel alcohols as extracting solvents unites two important points On the one hand, this liquid normally constitutes a surplus product that has little market value. When used as an extraction solvent the costs for alternative solvents are saved. Furthermore, this extraction solvent is less harmful to handle than the classical extraction solvent chloroform [27],... 

Figure 8 illustrates one of the processing schemes used for separating various components in a hydrocarbon-containing plant. Acetone extraction removes the polyphenols, glycerides, and sterols, and benzene extraction removes the hydrocarbons. If the biomass species in question contain low concentrations of the nonhydrocarbon components, exclusive of the carbohydrate and protein fractions, direct extraction of the hydrocarbons with benzene or a similar solvent might be preferred. 

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. 

By removing biomass by centrifugation and selectively extracting the acid from the organic solvent with a saturated solution of NaHCOs, recovery of the unreacted flurbiprofen and its separation from the ester were easily accomplished. 

FIGURE 10.1 Example of solvent extraction scheme for separating various components in hydrocarbon-containing biomass. 

The USDA characterized a large number of biomass species for their traditional composition fractions of ash, crude protein, polyphenols, oils and hydrocarbons among others. These fiactions were defined operationally by the USDA botanochemical screening project their sample analysis and fraction partitioning scheme is summarized in Fig. 1. Of interest were extractives, components that can he separated/paititioned from the plant by solvents. The major extractives included various oils, terpenes, fatty acids, unsaponiflables, aromatic compounds, tannins, and quinones. In exceptional cases extractives composed over 15% of the biomass (especially ash) but generally they did not exceed S-10%. 

Smoke from forest fires may be collected by various means for subsequent laboratory analysis. The most applicable approach is to trap emissions from biomass burning on absorbent material. The absorbent material is then either solvent-extracted for GC analysis or directly desorbed onto a GC. For example, smoke is pulled with an air pump at a rate of 10-50mLmin through triple-layer glass cartridges with separate... 

The recovery of the ionic liquid l-ethyl-3-methylimidazolium acetate (abbreviated as [C2mim][OAc]) with a solvent mixture containing acetone, 2-propanol, and a small amount of water was demonstrated. This formed a phase switchable solvent system, which could concentrate and separate oleophilic solutes, short chain carbohydrates, and lignin fragments from used ionic liquid in a two-stage extraction procedure. Figure 7.5 shows the whole process of ionic liquid recovery and biomass separation. The research was conducted by pre-treating 100 g of corn stover with 10 wt.% of ionic liquid. After the separation process, the recovered ionic liquid contained few residual solutes, so it could be reused for biomass dissolution and... 

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. 

Bio-oil, a kind of biofuel, could be obtained by flash pyrolysis of biomass. Because bio-oil is a type of complex mixture, some researches about bio-oil separation have been conducted in the recent years. Xianwei Zheng et al. have successfully separated flash pyrolysis oil into four kinds of substances by united extraction and distillation. Garcia-Perez et al. have provided an efficient separation method by using five kinds of solvent extraction, and bio-oil was separated into six kinds of substances. 

Vanlautem and Gilain used liquid halogenated solvents like chloroethanes and chlo-ropropanes for the extraction of PHB. This method was found to be superior when compared to extraction using other solvents like tetrahydrofuran methyl cyanide, tetra-hydrofuran ethyl cyanide, and acetic anhydride. Noda developed a method with a mixture of PHB solvent and nonsolvent, the insoluble biomass is separated leaving behind a suspension of precipitated PHB in the nonsolvent. 

Solvent Extraction of PHAs. The majority of the patented separation processes describe the extraction of PHB from microbial biomass using organic solvents such as chlorinated hydrocarbons (eg chloroform or 1,2-dichloroethane), azeotropic mixtures [eg 1,1,2-trichloroethane with water (65)] chloroform with methanol, ethanol, acetone, or hexane (66), and cyclic carbonates [eg hot (120-150°C) ethylene carbonate or 1,2-propylene carbonate (67)] in which the polymer is soluble. With the wider variety of PHAs which can be produced today, the choice of solvents should be carefully considered. In general, solvents which are suitable for PHB should be equally good for any SCL and MCL PHA. The reverse may not be true. For example, while semicrystalline PHB is insoluble in acetone, MCL PHA will dissolve in it. 

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. 

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