Patent GB-643687-A (GB)
Title: Improvement in production of propylene oxide
Filed: 1948-01-24
Abstract: Propylene oxide is obtained by reacting propane, propylene or mixtures thereof with a gas containing free molecular oxygen in a confined reaction zone in a bath at 275 DEG  to 700 DEG  C., preferably below 550 DEG  C., e.g. 325 DEG  to 425 DEG  C., the molar ratio of hydrocarbons to oxygen being 2-20, the reaction zone having an area of gas contacting surface to volume of free space exceeding 1.6, preferably 5-15, sq. cms. per c.c., and the sum of the partial pressures of the hydrocarbons and oxygen being maintained at 20-200 lbs., preferably 20-60 lbs., per sq. inch absolute. Propylene oxide is removed from the products by scrubbing with an aqueous alkali, e.g. sodium bicarbonate solution of pH 7 to 8, thus minimizing hydrolysis to the glycol.  After scrubbing excess hydrocarbons may be vented or returned to the oxidation stage and the oxide recovered from the scrubbing liquid by normal methods, e.g. flashing off under partial vacuum.  In continuous operations the preferred molar ratio of hydrocarbons to oxygen is in the range 3-8.  Inert gases, e.g. nitrogen, may be present and provide a form of temperature control. The surface of the reaction vessel is composed of inert materials such as ceramic material, stainless steel and aluminium although the use of copper and silver which catalyze the formation of carbon dioxide should be avoided.  In examples (1) to (4) the reactor consists of 14 connected steel tubes each 8 feet long and of inside diameter 1 1/8 inches, interiorly lined with a refractory cement and filled with non-porous Raschig rings to provide a ratio of surface to free space of 7.9 sq. cms. per c.c., fitted in a shell containing molten salt and in (1) propane, oxygen and recycle gas; (2) propane, air and recycle gas; (3) and (4) a mixture of about 85 per cent propane and 15 per cent propylene with oxygen and recycle gas with hydrocarbon to oxygen molar ratios of (1) 3.7, (2) 3, (3) 4.9 and (4) 4.6 is passed through the reaction zone with bath temperatures of 400 DEG , 365 DEG , 385 DEG  and 365 DEG  C., pressures of 57, 165, 60 and 165 lbs. per sq. inch absolute and rates of 630, 910, 600 and 945 cu. ft. per hr. respectively, propylene oxide is scrubbed with 0.2 per cent aqueous sodium bicarbonate from the products and after a small portion of the excess hydrocarbons have been purged, the remainder are recycled to the oxidation stage with fresh make-up gas, in (5) the reactor consists of a 1 inch diameter steel tube welded concentrically through two discs to a pipe 6.5 feet long and 3.5 inches wide, the 1 inch pipe is packed with porcelain Raschig rings to give a reaction space having a ratio of surface to free space of about 8, molten salt at about 350 DEG  C. is contained in the space between the two pipes and a mixture of propylene and oxygen in a molar ratio of 5.2 is passed at 45 lbs. per sq. inch absolute so that each molecule of gas is heated for 16 secs. and propylene oxide obtained from the products in conventional fashion.  In the Specification as open to inspection under Sect. 91 reference is also made to the use of steam as an inert diluent. This subject-matter does not appear in the Specification as accepted.