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UBC Theses and Dissertations

Electro synthesis of propylene oxide in a bipolar trickle bed reactor Manji, Aminmohamed


The synthesis of propylene oxide by electrolysis of dilute sodium bromide solution with propylene gas was investigated in an electrochemical bipolar reactor consisting of six parallel fixed beds of graphite particles separated by polypropylene felt diaphragms. One reactor was operated in single pass and recycle mode with two phase co-current flow of propylene and sodium bromide solution through the beds of graphite particles. The maximum pressure in the system was 2.22 atmospheres absolute. The effects of superficial current density* (413 - 2687 A/m²), electrolyte (sodium bromide solution) concentration (0.2 M and 0.5 M), electrolyte flow rate (100 and 300 cm³ /min), propylene gas flow rate (100/1000/1500/2000 cm³/min at STP), reactor outlet temperature (30° and 60°C), bed thickness (six beds - 8.57/4.29/3.07 cm) and different carbon types (Union Carbide and Ultra Carbon) on the space time yield and selectivity for propylene oxide were measured. Depending on the condition for single pass runs, the space-time yield for propylene oxide was between 5.5 kg/hr m³ and 97.2 kg/hr m³, and the selectivity was between 54.5% and 87.3%. The current efficiency and the specific energy consumption varied from 14.0 to 58.2 percent and 5.7 to 59.9 Kwh/kg of propylene oxide. The space-time yield for propylene oxide increased with decreasing bed thickness. For the recycle mode the space-time yield decreases with time. The highest space time yield obtained after one hour of operation was 127.8 kg/hr m³ with a selectivity of 95.9%. The current efficiency for hydrogen, oxygen and dibromopropane was also determined. *Superficial current density = applied current/electrode area.

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