Patent GB-659786-A (GB)
Title: Improvements in or relating to the production of maleic acid
IPC: C07C51/25
Filed: 1949-03-01
Abstract: In a process of the type in which a hydrocarbon feedstock is oxidized in vapour phase and at elevated temperatures in the presence of a solid oxidation catalyst such as vanadium oxide, to give aliphatic dibasic acids and their anhydrides, principally maleic acid and anhydride, the feedstock comprises a hydrocarbon fraction boiling between 60 DEG  and 120 DEG  C. and containing substantial amounts of C6 diolefines, for example branched chain hexadienes or methyl pentadienes.  The hydrocarbon fraction may be obtained by steam cracking volatile petroleum stocks such as naphtha cuts and gasolines especially at temperatures of 1000 DEG  to 1600 DEG  F. and at 1 to 10 atmospheres pressure.  The charging stock is preferably diluted with steam in the cracking zone.  The hot cracked products are quenched and the higher boiling liquid products separated and fractionally distilled.  The 60-120 DEG  C. fraction contains conjugated C6 dienes, benzene, toluene and other hydrocarbons whilst a fraction of closer boiling range (75-85 DEG  C.) contains larger amounts of conjugated dienes mostly of the methyl pentadiene type together with benzene and other hydrocarbons.  It is preferred to use a cut of boiling range 80-100 DEG  C.  The catalyst may be employed in a fixed bed or it may be of the moving bed or fluid flow type, e.g. the technique described in Specifications 583,032, [Group III], 633,128, [Group XII], and 634,102, [Group III], may be used.  The transfer-line reactor described in Specification 634,102 [Group III], is specially suitable.  Specified oxidation catalysts are vanadium oxide, mixtures of vanadium oxide and other oxides such as molybdenum oxide.  Alkali metal salts such as sodium or potassium sulphate may be added as promoters.  The catalyst may be in the form of microspheres.  The oxidation can be effected either with or without the presence of an oxidizing gas.  The latter may be any oxygen containing gas, e.g. pure oxygen with or without a diluent such as steam.  Air or mixtures of oxygen with an inert gas such as nitrogen may also be used.  The oxidizing gas should be present in substantial excess over the hydrocarbons.  When no oxidizing gas is used, catalysts such as vanadium oxides may be used as oxygen carriers which can be enriched with oxygen in a separate zone.  The oxidation temperature may be 300 DEG  to 700 DEG  C. In examples maleic acid is obtained by (1) contacting a mixture of methyl pentadienes containing 2-methyl-1,3-pentadiene and 4-methyl-1,3-pentadiene and air with a catalyst containing V2O5 and M0O3 suspended on corundum and promoted with sodium sulphate; (2) contacting a mixture of 3-methyl-1,3-pentadiene with a catalyst as in (1); (3) contacting a mixture of air and a steam cracked petroleum fraction boiling at 80-100 DEG  C. and containing substantial amounts of C6 diolefins with a mixture of vanadium pentoxide and molybdenium oxide; (4) contacting a mixture of air and a steam cracked petroleum fraction of boiling range 65-80 DEG  C. containing methyl pentadienes with a mixture of V2O5 and M0O3 on corundum.  In this example a fused mixture of V2O5 and M0O3 which has been shape into microspheres may also be used as catalyst.