| 1. |
- Adlercreutz, Patrick
(författare)
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Oxygen supply to immobilized cells : 5. Theoretical calculations and experimental data for the oxidation of glycerol by immobilized Gluconobacter oxydans cells with oxygen or p‐benzoquinone as electron acceptor
- 1986
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 28:2, s. 223-232
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical calculations of reaction kinetics were done for one‐step reactions catalyzed by cells immobilized in spherical beads. The reactions catalyzed by free cells were assumed to obey Michaelis–Menten kinetics for a one‐substrate reaction. Both external (outside the beads) and internal (inside the beads) mass transfer of the substrate were considered for the immobilized preparations. The theoretical calculations were compared with experimental data for the oxidation of glycerol to dihydroxyacetone by Gluconobacter oxydans cells immobilized in calcium alginate gel. Glycerol was present in excess so that the reaction rate was limited by oxygen. The correlation between experimental data and theoretical calculations was quite good. The calculations showed how the overall effectiveness factor was influenced by, for example, the particle size and the cell density in the beads. In most cases the reaction rate was mainly limited by internal mass transfer of the substrate (oxygen). As shown previously, p‐benzoquinone can replace oxygen as the electron acceptor in this reaction. The same equations for reaction kinetics and mass transfer were used with p‐benzoquinone as the rate‐limiting substrate. Parameters such as diffusivity, maximal reaction rate, and K were, of course, different. In this case also, the correlation between the model and the experimental results was quite good. Much higher production rates were obtained with p‐benzoquinone as the electron acceptor compared to when oxygen was used. The reasons for this fact were that p‐benzoquinone gave a higher maximal reaction rate for free cells and the solubility of p‐benzoquinone was higher than for oxygen. Different methods of increasing the rate of microbial oxidation reactions are discussed.
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| 2. |
- Kaul, Rajni, et al.
(författare)
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Coimmobilization of substrate and biocatalyst : A method for bioconversion of poorly soluble substances in water milieu
- 1986
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 28:9, s. 1432-1437
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Tidskriftsartikel (refereegranskat)abstract
- Coimmobilization of biocatalyst and substrate was studied as a method to increase the conversion rate in systems with substrates of extremely low solubility in water. The system studied was the conversion of hydrocortisone to prednisolone by Arthrobacter simplex. As a matrix for coimmobilization, alginate turned out to be superior to agar and agarose. After the reaction was complete, the beads were solubilized, andthe cells recovered for reuse, by centrifugation, whereas the prednisolone was extracted from the supernatant.
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| 3. |
- Zacchi, Guido, et al.
(författare)
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Economic evaluation of enzymatic hydrolysis of phenol-pretreated wheat straw
- 1988
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 1097-0290 .- 0006-3592. ; 32:4, s. 460-466
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Tidskriftsartikel (refereegranskat)abstract
- Experimental data from the enzymatic hydrolysis of phenol-pretreated Swedish wheat straw have been used to evaluate the cost fractions of capital and utility, enzyme, and raw material. Two different raw material prices and varying enzyme prices have been used. The evaluation is based on an empirical model for the enzymatic hydrolysis and a computer program where utility and equipment, enzyme, and raw material prices can be varied. The optimal residence time for the enzymatic hydrolysis is in the range of 70–110 h. A fed-batch procedure with substrate concentrations higher than 10% oven-dried material (ODM) and enzyme concentrations in the range (6–10) · 106 FPU/ton ODM should be used.
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| 4. |
- Zacchi, Guido, et al.
(författare)
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Economic evaluation of preconcentration in production of ethanol from dilute sugar solutions
- 1989
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 1097-0290 .- 0006-3592. ; 34:2, s. 223-233
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Tidskriftsartikel (refereegranskat)abstract
- The economic feasibility of preconcentrating dilute sugar solutions prior to fermentation is investigated. Two methods, evaporation and reverse osmosis, are compared. A computer program to determine the optimal preconcentration conditions for glucose solutions of 1.5–16 wt% has been developed. It was used to compute the fractional cost for labor and maintenance, preconcentration, fermentation, and distillation. Preconcentration with evaporation resulted in a higher total cost, compared with no preconcentration, for all cases studied, although a six-effect unit was used. Reverse osmosis was found to be economically feasible for preconcentration to about 5–10 wt % depending on the concentration of the feed.
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| 5. |
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