Bioconversion of D‐Xylose and Pretreated Oak Sawdust to Ethanol Using Clostridium Thermosacchrolyticum by Batch and Continuous Up‐Flow Reactors

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Abstract
Bioconversions of lignocellulosic biomass, in particular sawdusts, into ethanol were investigated, first, acid hydrolyses by dilute sulfuric acids using 0.5, 1.0, and 2.0 weight percent were performed. The optimum hydrolysis condition was found to be 1% acid at 124°C and hydrolysis time 50 min. The total yields of sacchrification, primarily xylose, is 23.7 g which is obtained from 100 grams of sawdusts with a liter of dilute at the optimum condition.Second, fermentations of xylose into ethanol were investigated using Clostridium thermosacchrolyticum (ATCC 31925) by a batch reactor and by a continuous up‐flow cylindrical reactor. In a continuous up‐flow reactor, two modes of operation are studied; namely, cells immobilized on polystyrene chips (size 2.79 × 3.78 × 2.64 mm) and cells freely suspended in the flowing substrate stream. The flow rates investigated were 17.5, 29.5, and 51.2 ml/hr for immobilized case and 27.3, 42.2, 66.1, and 109 ml/hr for free suspension case. The maximum concentration of ethanol yield obtained from the initial concentration of 6 g/l xylose was 1.8 g/l by a batch reactor, which is equivalent 60% of the theoretical conversion of xylose by weight. If the dilution rate is less than 0.3 hr−1, the concentration of ethanol by the continuous up‐flow reactor for both cases approach the maximum of that by a batch reactor.Modellings of bioconversion kinetic parameters in Monod and Luedeking‐Piret formulas were also obtained. The specific growth rate for the microorganism in CM‐4 medium is found to be 0.43 hr−1.