Ethanol volumetric productivity

Ethanol volumetric production rate did not differ significantly between nonsupplemented and supplemented media, but ethanol was no longer... 

Fig. 2. Ethanol productivity for untreated hydrolysate (black bar), fractions from strong anion-exchange resins (dark gray bars), fractions from weak anion-exchange resins (light gray bars), and reference fermentation (glucose added but no hydrolysate) (white bar). The maximum mean volumetric productivity of ethanol (Qe,0h) in g/ (L-h) is indicated above each bar.

The maximum mean volumetric productivity of ethanol was obtained after 4 h in the reference fermentations. Therefore, the fermentability was evaluated by comparing the volumetric productivity, QEt0H (g/ [L-h]), of the different fermentations. QEt0H was calculated as the produced ethanol within the first 4 h of the fermentations divided by 4. 

The reactor volumetric productivities and product yields at pH 4.3 and various dilution rates were estimated based on the time course data in the pseudo steady state and are shown in Fig. 3. In general, production rates for butanol and acetate increased with an increase in the dilution rate from 0.1 to 1.2 h 1, whereas acetone and ethanol remained relatively unaffected by the dilution rate except at 0.1 h A maximum butanol productivity of 4.6 g/(L-h) at a dilution rate of 0.9 h 1 was obtained with reactor R at the beginning of the solventogenic fermentation, whereas a lower productivity of... 

Maximal Volumetric Production Rates and Yields for Cell Biomass, Ethanol, Arabitol, and Xylitol Obtained with D. hansenii CCMI941 Yeast for Different Tested Conditions... 

Pyruvate decarboxylase of Z. mobilis was transferred into E coli [103]. The transformant was able to produce 39.2 g/1 ethanol from 80 g/1 xylose with an indicated yield of 96% of the theoretical value. The maximal volumetric productivity was 0.7 g/1 ethanol per hour in batch fermentation [104]. 

The xylitol production rate is highest at very high xylose concentrations (80 g/1) [8, 10]. However, concentrating the hemicellulose hydrolysates using vacuum evaporation to achieve high xylose concentrations also concentrates the non-volatile inhibitors [11]. At these inhibitor concentrations, volumetric productivity actually declines [12-14]. Many studies have demonstrated the inhibitory effect of these hydrolysis-derived compounds on growth and production of products, such as ethanol and xylitol [15-16]. Concentrated hydrolysate requires detoxification for optimum xylitol production. 

The current state of strain development for ethanol production via C. thermocellum and T. saccharolyticum is summarized in Table 10.3 with reference to key performance metrics. It may be noted that solubilization data and fermentation of high substrate concentrations have been summarized in Table 10.1. Volumetric productivities (g ethanol 1 h ) calculated from the data in Table 10.3 include 0.78gl h for T. saccharolyticum fermentation of mixed cellodextrins and 0.20 gl h for C. thermocellum fermentation of Avicel. Similarly to the wild type, C. thermocellum mutant strains still secrete amino acids into the culture medium, providing a target for further increasing ethanol yields and titers. 

The advantageous use of membranes in the removal of toxic compoimds produced during fermentation has been demonstrated in several fermentation systems. Increased (2.5 fold) volumetric productivities and product concentration yields (fourfold) were reported by Christen et al. [209] in ethanolic fermentations assisted by supported hquid membranes. Increased final product concentrations and yield were also reported by Xavier et al. [134] when comparing membrane-assisted extractive fermentation of lactic acid with conventional fermentations. 

Capacity Limitations and Biofuels Markets. Large biofuels markets exist (130—133), eg, production of fermentation ethanol for use as a gasoline extender (see Alcohol fuels). Even with existing (1987) and planned additions to ethanol plant capacities, less than 10% of gasoline sales could be satisfied with ethanol—gasoline blends of 10 vol % ethanol the maximum volumetric displacement of gasoline possible is about 1%. The same condition apphes to methanol and alcohol derivatives, ie, methyl-/-butyl ether [1634-04-4] and ethyl-/-butyl ether. 

At the start-up of aerobic fermentation, ethanol vapour and carbon dioxide production begins almost immediately glucose is applied to the bed (Rottenbacher et al., 1987), climbing to peak volumetric levels in the off-gas wifhin abouf 15 minutes of applying the feed solufion. The levels fhen decline slighfly and stabilise at about 30 minutes run... 

---