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Xylose concentrations

The performance of the F-MF-ED system was also assessed in the case of lactate fermentation from xylose (Nomura et al., 1988). Starting with 50 kg of xylose per m3, the conventional or combined system allowed full exhaustion of the carbon source after 60 or 32 hours, respectively. By further increasing the initial xylose concentration to 80 kg/m3, both systems resulted in less (50 kg/m3) or more (75 kg/m3) consumption of xylose, respectively. Moreover, the simultaneous removal of microbial metabolites (lactate and acetate) via ED increased both lactate production and xylose consumption rates. [Pg.335]

Zadivar et al. (12) reported fermentation of a pure glucose/xylose mixture using their xylose-fermenting S. cerevisiae, but xylose mainly converted to xylitol with ethanol only as a minor product (12). Furthermore, the time needed for completion of the fermentation exceeded 100 h with an initial xylose concentration of 50 g/L. [Pg.415]

Fig. 5. Glucose and xylose concentration vs hydrolysis time at enzyme loading of 60 FPU/g of glucan. Fig. 5. Glucose and xylose concentration vs hydrolysis time at enzyme loading of 60 FPU/g of glucan.
Xylose concentration Ethanol yield (g/L) (g/g)c Ethanol productivity (g/[g cellsh])d Ethanol yield (g/g) Ethanol productivity (g/[g cells h])d... [Pg.1208]

Tanaka, K., Komiyama, A., Sonomoto, K., Ishizaki, A., Hall, S. J., and Stanbury, P. F. 2002. Two different pathways for D-xylose metabolism and the effect of xylose concentration on the yield coefficient of L-lactate in mixed-acid fermentation by... [Pg.263]

Although [fNT] can be taken to be proportional to the xylose concentration, there is no known experimental way to determine ka and kb explicitly. What is possible is to measure the actual yield as a function of time, xylose concentration, acidity, and temperature, for the experimental setup chosen, and to use these yield curves, together with the known pentose disappearance rate and the known furfural reslnification rate, as a graphical interpolation basis for determining the losses by the condensation reactions. Such a procedure, reported by Root, Saeman, Harris, and Neill [18], is given in an appendix chapter, but it is usually considered too complicated and too unreliable to be used for yield prognoses. [Pg.21]

In view of this situation, it may seem surprising that in the ampoule process , without any removal of furfural, the losses are hardly greater than in the industrial processes with their huge expense for steam stripping. The explanation lies in the simple facts that at any time the loss reactions are slower than the furfural formation, and that the principal loss, which is furfural condensation, diminishes as the xylose concentration diminishes, so that it comes to a halt when all of the xylose is consumed. [Pg.26]

Figure 110. Dependence of the Furfural Yield on Temperature and Time as obtained by a Sealed Ampoule Process with an Initial Xylose Concentration of 0.666 mole/liter (100 g/liter). Figure 110. Dependence of the Furfural Yield on Temperature and Time as obtained by a Sealed Ampoule Process with an Initial Xylose Concentration of 0.666 mole/liter (100 g/liter).
For 200 C as example, the procedure is shown in Figure 132. Curve A, representing the yield of the hypothetical process with resinification as the only loss, is obtained from equation (7) of the preceding chapter, and curve B is an experimental yield curve given in the literature [126] for 200 °C and for an initial xylose concentration of 0.666 mole/liter (100 g/liter). Experimental yield curves for other temperatures and other initial xylose concentrations are amply available in the same reference. The hatched area between the two curves A and B represents the condensation loss. To round the overall picture, the theoretical yield for the temperature considered is shown by the dashed curve C. [Pg.323]

Thus, although the new rate constants ka and kb can not be determined, it is readily seen that the condensation loss increases with an increasing initial xylose concentration, so that the actual yield decreases when the initial xylose concentration increases. This is bom out by the experimental yield curves shown in Figure 133, taken from the literature [126]. Hence, a fiir-fural reactor run at a high moisture content gives a better yield than a furfural reactor run at a... [Pg.323]

Figure 133. Experimentally Determined Yield Curves for 240 C and Various Initial Xylose Concentrations as Parameter [126]. Figure 133. Experimentally Determined Yield Curves for 240 C and Various Initial Xylose Concentrations as Parameter [126].
By contrast, the initial xylose concentration has absolutely no effect on the resini-fication loss as the xylose plays no part in the respective reaction. [Pg.326]

Fumaric acid can also be produced from xylose. The rate of xylose fermentation is much slower than with glucose with a specific productivity of only about 0.075 g fumaric acid/h/g biomass. Kautola and Linko [73] used immobilized R. arrhizus with polyurethane foam to ferment xylose. A specific productivity of 0.087 g/l/h was obtained when the initial xylose concentration was 100 g/1 and the resident time was 10.25 days. [Pg.268]

The reactor was loaded with 75 ml granular carrier material [14], and finally, the entire reactor system, including tubing and recirculation reservoir, was autoclaved at 120°C for 30 min. Before use, the reactor system was gassed for 15 min with N2/CO2 (4 1) to ensure anaerobic conditions and filled with BA medium with an initial xylose concentration of 10 g/1. The reactor was started up in batch mode by inoculation with 80 ml of cell suspension with an optical density (OD578) of 0.9-1. The batch mode of operation was maintained for 24 h to allow cells to attach and to immobilize on the carrier matrix. After the batch run, the system was switched to continuous mode, applying a hydraulic retention time (HRT the volume of the reactor divided by the influent flowrate) of 8 h and up-flow velocity of 1 m/h. To achieve operational stability, the reactor was run for 7 days under... [Pg.114]

Conversion efficiency is calculated by dividing the ethanol yield based on the glucose and xylose concentrations present in the influent by theoretical possible yield of 0.51 g/g CR carbon recovery... [Pg.119]

Initial rate kinetic assays were conducted at 37 C in 50 mM citrate buffer at pH 4.8 in 96-well microtiter plates using /)-nitrophenol P-D-xylopyranoside. For all assays, the XlnD was loaded at 1.5 p.g/ml of reaction, and initial substrate concentrations were varied from 0.1 to 3.2 mM. The release of pNP was monitored every 15 s for the initial 10 min of each reaction by measming the absorbance at 405 nm on a SpectraMax 190 UV/VIS microplate scanner from the Molecular Devices (Sunnyvale, CA). End product inhibition by D-xylose was confirmed by ranning identical assays to those described above with initial D-xylose concentrations ranging from 3.33 to 40 mM. Triplicate analyses of all assays were run at all conditions. All parameters estimated in this study were calculated using standard Michaelis-Menten kinetics as described previously [11]. [Pg.187]

Fig. 2 Assays with the purified XlnD on pNP-x, ran at 37 °C in 50 mM citrate buifer at pH 4.8 a reaction rate vs substrate concentration and b Michaelis-Menten plots of data from assays with varying initial D-xylose concentrations... Fig. 2 Assays with the purified XlnD on pNP-x, ran at 37 °C in 50 mM citrate buifer at pH 4.8 a reaction rate vs substrate concentration and b Michaelis-Menten plots of data from assays with varying initial D-xylose concentrations...
Although our co-immobilized enzyme approach is able to sustain the necessary pH difference between isomerization and fermentation steps in SIF [35], the overall production rate of ethanol in SIF will still be limited by the total concentration of xylulose available to the yeast [9]. Under normal equilibrium conditions, the xylulose concentration is usually at best one fifth of the xylose concentration. Hence, other avenues of shifting the equilibrium towards higher xylulose formation will further increase the rate of ethanol production. [Pg.230]

Unaltered Pellets As an initial control experiment, the isomerization of xylose to xylulose was studied using Sweetzyme pellets, as received, before co-immobilization with urease. The time course of xylose consumption and xylulose formation was monitored for an initial xylose concentration of 60 g/1 with 0.13 g pellets at 34 °C. The isomerization mixture was buffered at pH 7.5, which is the optimal pH for XI activity. As seen in Fig. 2, curve A, the concentration of xylulose steadily increased and reached an equilibrium value of about 9 g/1, suggesting an equilibrium xylose/xylulose ratio of nearly 6 1 under these conditions. When the same experiment was repeated at a reduced pH of 4.5, no xylulose was detected in the reaction mixture, even after 40 h (data not shown). At a pH of 4.5, XI is 3 pH units below its optimum and displays essentially no activity. [Pg.232]

In Fig. 5, transient xylulose production is shown as a function of total co-immobilized pellet mass. All pellets used were from the same co-immobilization batch and have the same urease and XI loadings. Experiments were conducted at 34 °C and pH 4.5 with 0.01 M urea, 0.05 M sodium tetraborate, and an initial xylose concentration of 60 g/1. Experiments shown in curves B and C have 3.3 (18 g/1) and 6.6 (36 g/1) times more of each enzyme compared to curve A (5.2 g/1). At time zero in all experiments, the interior pH increases rapidly to values closer to the optimum for XI activity as ammonia is produced. In experiments B and C, the increased mass of urease and XI will cause a more rapid decrease in the bulk urea and xylose concentrations than in A. As the bulk urea concentration decreases, the ammonia production per pellet decreases and the interior pH also starts to decrease. This drop in pH occurs earlier in cases where the total urease mass (activity) is higher, leading to an accompanying loss in specific XI activity. From the data shown in Fig. 5, the average specific XI activity was... [Pg.236]

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. [Pg.607]


See other pages where Xylose concentrations is mentioned: [Pg.507]    [Pg.528]    [Pg.545]    [Pg.549]    [Pg.982]    [Pg.1055]    [Pg.322]    [Pg.73]    [Pg.524]    [Pg.16]    [Pg.16]    [Pg.16]    [Pg.36]    [Pg.206]    [Pg.206]    [Pg.319]    [Pg.323]    [Pg.326]    [Pg.120]    [Pg.235]    [Pg.607]    [Pg.613]    [Pg.704]    [Pg.20]    [Pg.303]    [Pg.305]    [Pg.305]    [Pg.307]   
See also in sourсe #XX -- [ Pg.104 ]




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