The hydrolytic hydrogenation of xylan to xylitol by a one-pot process was studied in detail in a batch reactor. The reaction was catalyzed by a combination of diluted sulfuric acid and precious metal Ru on carbon powder. Process parameters were varied between 120–150°C, while maintaining constant hydrogen pressure at 20 bar and an acid concentration equivalent to pH 2. The xylan solution consisted of 1 wt% beechwood powder (Carl Roth, >90%) in deionized water. Sulfuric acid was added to the solution until pH two was reached, then the 0.3 wt% catalyst powder (5% Ru on Act. C) was added and the solution was put into the batch reactor. The first approach of kinetic modeling began with conventional first-order kinetics and compared this to a more complex model based on Langmuir–Hinshelwood kinetics. The xylan and xylitol data reached a good fit. However, the modeling results also showed that the rate-limiting step of xylose-formation was still not represented in a satisfactory manner. Therefore, the model was adapted and developed further. The advanced model finally showed a good fit with the intermediate product xylose and the target product xylitol. The overall modeling methods and results are presented and discussed.
Für eine Messung von blechmassivumgeformten Bauteilen möglichst nahe am Fertigungsprozess spielen systematische Abweichungen durch den darauf noch verbliebenen Schmierstoff eine signifikante Rolle. Die erwartete Schichtdicke dieses Schmierstoffs liegt bei den betrachteten Bauteilen in einem Bereich von unter 35 µm. Für die Bestimmung des Brechungsindex des Schmiermittels und somit die Auswirkungen des Schmierstoffs auf die interferometrische Messung, wird ein Dünnschichtnormal vorgestellt, welches in einem Bereich von 6 bis 100 µm einen kontinuierlichen Messbereich abbildet. Mit dem eingesetzten Messverfahren, einer koaxialen interferometrischen Schichtdickenmessung, können so in verschiedenen Abständen die optische Dicke bestimmt werden. Daraus lässt sich im Anschluss der Brechungsindex näherungsweise bestimmen. Zudem können die Abweichungen der angezeigten Schichtdicke bei bekanntem Brechungsindex nun bewertet werden.
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