Biomass component

The measurements of the labeled metabolites may be performed with GC- or LC-MS, or by NMR. Because it is the most commonly used method, we will only consider GC-MS based approaches here. Obviously and unfortunately, it is not possible to directly measure the isotopomer enrichments by GC-MS, because the apparatus only yields total masses of molecules or fractions thereof, but not directly the position of a label. Each MS peak is produced by all isotopomers with the same molecular weight that is, the same number of labeled carbon positions. Sometimes this concept is also called mass isotopomers [264]. In a so-called retrobiosynthetic approach, it has been shown that the labeling state of many intracellular pools can be determined indirectly by measuring the labels in macromolecular biomass components at steady state for example, the labeling state of alanine from hydrolyzed protein reflects the label of pyruvate [265]. Using this approach, it is possible to quantify fluxes into storage components. 

The fermentation products can be the cells themselves (biomass), components within the fermentation broth (extracellular), or those trapped in cells (intracellular), examples of which are listed in Table 10.1. As shown in Figure 10.1, if the product of our interest is the cell, cells are separated from the fermentation broth and then washed and dried. In the case of extracellular products, after the cells are separated, products in the dilute aqueous medium need to be recovered and purified. The intracellular products can be released by rupturing the cells and then they can be recovered and purified. The downstream processing for enzyme reactions will be similar to the process for extracellular products. 

Although ASPEN-Plus is widely used to simulate petrochemical processes, its uses for modeling biomass processes are limited owing to the limited availability of physical properties that best describe biomass components such as cellulose, xylan, and lignin. For example, Lynd et al. (1) used conventional methods to calculate the economic viability of a biom-ass-to-ethanol process. However, with the development by the National Renewable Energy Laboratory (NREL) of an ASPEN-Plus physical property database for biofuels components, modified versions of ASPEN-Plus software can now be used to model biomass processes (2). Wooley et al. (3) used ASPEN-Plus simulation software to calculate equipment and energy costs for an entire biomass-to-ethanol process that made use of dilute-H2S04 acid pretreatment. 

Table 1.4 General chemical compositions of selected biomass components and petroleum (Pun et ah, 2007)...

Biomass Component Chemical Composition Petroleum Component Chemical Composition... 

In this chapter, major routes for the production of bulk chemicals from biomass components including carbohydrates, oils, proteins and minor constituents will be identified. These major production pathways rely on microbial fermentation, enzymatic transformation and green chemical extraction or synthesis. 

The direct use of biomass components may be subject to specialty and fine chemicals or pharmaceuticals. Processes are well established and mainly comprise extraction and simple transformation of biomass components. Examples are monoterpenes or fatty alcohols. They can be summarized as products with a very similar molecular structure compared to the deployed biomass. 

When the structure of biomass components has to be quite drastically rearranged compared to the building blocks needed, synthesis gas or different sugars can serve as platform chemicals. The latter can be converted, for example, to sugar-derived building blocks (Figure 2.2.3) - that is, to glycerol, sorbitol, levulinic acid, and furfural. 

A-1) with respect to time results in the following first-order differential equation that can be simplified by integrating the biomass component over the soil depth z, so that By is in more conventional values of mass/area, and assuming that fy is not a function of time ... 

TABLE 3.6 Typical Carbon Content and Heating Value of Selected Biomass Components"... 

FIGURE 3.6 Chemical structures of some biomass components. 

Selected thermochemical syntheses are discussed here to show how the structural characteristics of biomass components can affect the methods chosen to manufacture a few specific commodity chemicals. The main components of biomass, the pentoses and hexoses from the polysaccharides and the lignins, lipids, and proteins, are examined as potential feedstocks. 

TABLE 13.7 Examples of Organic Chemicals Produced by Fermentation or Enzyme-Catalyzed Conversion of a Biomass Component, Primary or Secondary Biomass Derivative, or Other Organic Chemical ... 

Samples from beech wood as well as from biomass components have been investigated using the same crucibles as for the temperature calibration. Microciystallinc cellulose (Avicel, Merck) lignin (Oiganosolv, Aldrich), and xylan... 

There is no big difference in distribution of organic potassium between three main biomass components of cellulose, hemicellulose and lignin. 

---