Abstract: In a reduced-pressure process for distilling crude maleic anhydride recovered by separation from an organic absorbent wherein reduced pressure is obtained using a liquid ring-seal vacuum pump, the improvement which comprises sealing the liquid ring-seal vacuum pump by circulating a maleic anhydride absorbent from a regenerating zone through the vacuum pump chamber.

Abstract: A process for producing maleic anhydride from a C.sub.4 hydrocarbon selected from n-butane and n-butene feed which comprises: (a) feeding the C.sub.4 hydrocarbon and air to a reactor; (b) contacting the C.sub.4 hydrocarbon and air in the reactor with a catalyst comprising vanadium and phosphorus oxides at reaction conditions including a temperature between 550.degree. and 1000.degree. F. so as to obtain a reactor effluent containing maleic anhydride, unreacted butane, nitrogen, oxygen, and acrylic, acetic or maleic acid or mixtures of the foregoing acids; (c) removing maleic anhydride from the reactor effluent to obtain maleic anhydride-lean effluent; (d) removing said acids from at least a portion of the maleic anhydride-lean effluent to obtain a purified recycle stream containing less than 100 ppm of the acids; and (e) recycling the purified stream to the reactor. Preferably the acids are removed in step (d) by water and/or caustic scrubbing the maleic anhydride-lean effluent.

Abstract: A process for producing maleic anhydride from n-butane which comprises:(a) feeding n-butane and air to a reactor;(b) contacting the butane and air with a catalyst comprising vanadium and phosphorus oxides at reaction conditions including a temperature between 550.degree. F. and 1000.degree. F. so as to convert 15 to 28% of the butane per pass and obtain a reactor effluent containing maleic anhydride, unreacted butane, nitrogen, and oxygen;(c) removing maleic anhydride from the reactor effluent to obtain maleic anhydride-lean effluent;(d) recycling a portion of the maleic anhydride-lean effluent to the reactor;(e) removing butane from the other portion of the maleic anhydride-lean effluent; and(f) recycling the removed butane to the reactor.Preferably the temperature in, and/or space velocity through, the reactor is adjusted to obtain a weight percent selectivity to maleic anhydride of at least 90% of the butane converted.

Abstract: In a process for separating maleic anhydride or phthalic anhydride from a gaseous mixture by absorption into an organic absorbent flowing downwardly and countercurrently to the gaseous mixture in an absorption column having at least 4 stages, the improvement is made which comprises removing heat from a zone of the absorption column above the gaseous mixture feed point and below the top 2 stages of the column in a sufficient amount so that more than half of the temperature gradient for the absorbent liquid in the column is across at least 2 stages above the gaseous mixture feed point and below the top 2 stages of the column. Preferably said heat is removed from the absorber column by withdrawing a stream of absorbent from the lower part of the column, cooling the stream and then recycling the resulting cooled absorbent to the column.