UBC Theses and Dissertations
Cerium mediated electrosynthesis of p-anisaldehyde Roussel, Robin
The objective of this project was to study the synthesis of p-anisaldehyde (PMA, C₈H₈0₂) via an indirect (mediated) in-cell electro-oxidation of p-methoxytoluene (PMT, C₈H₁₀O). The electro-oxidation was carried out in a batch recycle system without cosolvents and with an acid aqueous cerium (mediator) methanesulfonate solution. The batch recycle system is mainly made up of an electrochemical reactor (a laboratory FM01-LC cell from ICI) connected to a thermochemical reactor (CSTR) in a closed loop. The main advantage to studying the electro-oxidation of PMA via an in-cell versus an excell method is the potential for reduction in the capital cost of the electrochemical process. Two important reactions are involved in the indirect in-cell electrosynthesis of PMA: the chemical oxidation of PMT and the electrochemical regeneration of cerics ions (Ce(IV)). Before investigating the mediated in-cell electro-oxidation of PMT in the batch recycle system, the chemical and electrochemical steps were separately investigated in order to have a better understanding of the kinetics of these two reactions. A factorial design was performed to study the chemical oxidation of PMT in a conventional thermochemical batch reactor (batch reaction). Acidity, temperature, molar ratio Ce(IV)/ PMT, and residence time were studied in the range of 0.5-1.5 M, 20-60°C, 2-6, and 1-10 minutes, respectively. Over the range of the variables studied, acidity and the interaction acidity-temperature had the greatest influence on the yield of PMA. The highest yield of PMA (78%) was obtained at high temperature (60°C) and low acidity (0.5 M). An undivided cell with a Pt/ Ti mesh anode and a three dimensional porous graphite cathode was deemed effective (without fouling problems) to accomplish the electrooxidation of PMT. A second factorial design was conducted to investigate the performance of the electrochemical reactor for the oxidation of cerous methanesulfonate solutions (generation of Ce(IV) ions) in the batch recycle system. Acidity, temperature, and current applied were studied in the range of 0.2-0.8 M, 20-60°C, and 10-20 A (superficial current densities, 1563-3125 A/ m²), respectively. The current efficiency (78%) for Ce(IV) was not much influenced by these variables. Finally a third factorial design was performed to study the indirect in-cell electrooxidation of PMT in the batch recycle system in which both reactions (chemical and electrochemical) occur simultaneously. Acidity, temperature, volume ratio Org./ Aq., and conversion of PMT were studied in the range of 0.2-0.8 M, 20-60°C, 0.03-0.06, and 10- 30 %, respectively. Over the range of the variables studied, three important effects influence the yield of PMA, namely temperature, acidity and conversion of PMT. The interaction acidity-temperature was also significant. From an empirical model, it was concluded that the highest yield of PMA (28%) was obtained at low temperature (30°C), low acidity (0.2 M) and low conversion of PMT (10%). A rough economic estimation of the cost of electro synthesis of PMA via indirect ex-cell and in-cell methods was also done in this work. Comparisons of the two methods showed that the cost of energy and raw material was three times higher for in-cell than the ex-cell process. This economic study was done without optimisation of the electrochemical processes.
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