Electrochemical prodn. of propylene oxide from propylene

The prodn. of propylene oxide (PO) from propylene comprises oxidising the propylene on the anode side of a gas diffusion cell. Other hydrocarbons with double or triple bonds may also be oxidised to their oxides or ethers by the same process. In an example, sulphuric acid soln. was electrolysed at 59 deg C in a test cell contg. a lead plate cathode with a PVC gas inlet/outlet tube, bonded onto a PVC sheet (12.20 cm ) and covered with a graphite cloth (8.8 cm ) and a catalyst fabric of the same size, with a 2-cm frame to prevent slippage. The assembly was covered with a sheet of asbestos felt (12.2 cm x 2.7 mm), fixed in a PVC frame and immersed in the electrolyte, and the anode compartment was maintained at reduced pressure with the aid of a water pump. The test was run with an applied voltage of 2.3 V d.c., after starting with nitrogen (1.5-1.6 V with no external voltage). Replacing nitrogen with hydrogen produced an increase in the cell current from 0.04 A to 3.68 A after 5 mins., at approx. constant voltage. On reverting to nitrogen, the current decreased to 0.36 A within 2 mins. and was then restored immediately to 3.56 A after changing back to hydrogen. After a further 80 mins., nitrogen was again admitted causing the current to fall to 0.76 A after 1 min. At this point nitrogen was replaced by propylene, resulting in a current of 3.80, 3.28, 3.44 and 3.64 A after 0, 10, 15 and 31 mins. respectively. Finally the propylene was replaced by nitrogen, resulting in a current of 3.52, 2.88, 1.84 and 0.28 A after 0, 10 mins., 2 hrs. 44 mins. and 3 hrs. 50 mins. respectively. A very strong smell of PO was evident during the propylene phase. The results showed that, unlike propane and butane, propylene reacts at the anode in the same way as hydrogen.