Methacrolein and Methacrylic Acid from Isobutene

Methacrylic acid is produced by a number of different processes, one of which is based on the oxidation of isobutene (or of t-butyl alcohol) via the intermediate formation of methacrolein (Equation 32). The general features and the catalyst for the first-stage process are not dissimilar to those for acrolein production, whereas the oxidation of methacrolein to MMA differs in that it is catalyzed by 

The competitiveness of the oxidation of isobutene compared to the conventional acetone cyanohydrin route (Equation 33) is not only related to its performance and better environmental standards but has to contend with the demands of other users for isobutene, particularly for MTBE and ETBE production. In fact the predominant methacrylic acid process is still the hydrolysis of acetone cyanohydrin however, the change of mood on the use of MTBE in gasoline blends in the USA, could signal a future shift of isobutene availability making it a more attractive feedstock for methacrylic acid production. 

Other routes to MMA start from ethylene, propylene or propyne and involve metal catalysis at some stage of multi-step transformations for example by the hydroformylation of ethylene to intermediate propionaldehyde, oxidation to propionic acid, followed by condensation with formaldehyde. The Pd-catalyzed carbonylation of propyne to MMA is a further method. However only the ethylene route has found some industrial application (see Chapter 4, Section 4.3.1). 

The initial drive for acrylonitrile (AN) production (6.2 Mt/a in 2004 worldwide) was the discovery, in the late 1930s, of the synthetic rubber Buna N. Today nitrile rubbers represent only a minor outlet for AN which is utilized primarily for polymerization to give textile fibres (50%) and ABS resins (24%), and for dimerization to adiponitrile (10%). Early industrial processes depended on the addition of hydrogen cyanide to acetylene or to ethylene oxide, followed by the dehydration of intermediate ethylene cyanohydrin. Both processes are obsolete and are now supplanted by the ammoxidation of propylene (Equation 34) introduced in 1960 by Standard Oil of Indiana (Sohio). The reason for the success stems from the effectiveness of the catalyst and because propylene, 

The early catalyst for AN production was a multicomponent metal oxide, mainly consisting of bismuth and molybdenum oxides. Its composition has evolved over the past 40 years, constantly improved by continuous development work for increasingly better performances. Other catalytic materials that have been used in commercial processes include in their compositions, iron-antimony oxides, uranium-antimony oxides and tellurium-molybdenum oxides. 

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