Separation, biomass

Biomass separation of insoluble from soluble material, with either phase being retained depending on the location of the product as intracellular or extracellular material. Examples of unit operations commonly used include centrifugation, filtration, and sedimentation. 

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. 

The final system, shown in Figure 30.4D, is the continuous system with a partial (PRF) or complete (RF) cell recycle. It is similar to the continuous system, but cells are returned to the fermentor by means of a biomass separation device. Cross-filtration units, centrifuges, and settling tanks have all been used for biomass separation.22 In the partial cell recycle fermentor, a steady state is achieved as in the continuous system. This process is typically used to increase the productivity of the system and is used commonly in wastewater treatment and ethanol production type applications. 

Biomass feedstocks usually contain a wide variety of chemical functional pes within the biopolymer structure. Since thetmocbemical conversion has typically focused on the use of the "whole" biomass, separating the chemical function types has been of less interest. Using the "whole" has been viewed as the most cost-effective approach while the thermocliemical processes were considered robust enough to handle the range of chemical functional types. As a result, the products were a complex mixture of chemical entities useful primarily for fuel applications. The costs of collecting individual chemical products could not be justified in most cases. 

The application of ionic liquid to biomass separation recently started to attract a great deal of attention. Cellulose is poorly soluble in conventional solvents due to its many intermolecular hydrogen bonds. Ionic liquid was believed to be capable of disrupting such hydrogen bonds between different polysaccharide chains, thus decreasing the compactness of cellulose and... 

Figure 7.2 Examples of commonly used ionic liquid for cellulose dissolution and biomass separation.

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