A new catalyst for skeletal isomerization

319 A New Catalyst for Skeletal Tsomensatlon Methyl tertiary butyl ether (MTBE) is rapidly becoming an important industrial chemical due to the fact that it can be substituted (in quantities up to ~7%) for lead alkyls to.improve the octane number of wtroleum (T. Floris, G. Pecci and G. Oriani, paper AM-79-69, National Petroleum Refiners Association Annual Meeting, March, 1979). It may be manufactured by the reaction of methanol with isobutene: CY3 ,CH3 CH30H + CHE = C, ->CH3-0-$-CH3 CH3 CH3 using,for example,the Snamprogetti/ANIC process, and almost twenty plants, with a total capacity of one million metric tons Per year, have been commissioned, all but one in the last two years (B. Notari, V. Fattore and G. Manara, paper AM-80-44, National Petroleum Refiner's Association Annual Meeting, March 1980). The methanol for this process can be made from coal, thus allowing part of a gasoline component to be produced from raw materials other than oil. The isobutane may be derived from a number of sources: (a) directly from C4 cuts in a refinery; (b) from dehydrogenationof isobutane; (c) by isomerisation of the n-butenes produced by catalytic cracking or steam reforming. Present technology is based on (a). Catalysts which bring about skeletal isomerisation are generally acidic in nature, and the second paper referred to above sunmarises a number of catalysts which have been used for the process, eg phosphates or supported phosphoric acid, alumina and modified aluminas, and silica aluminas. Each of these materials suffers a progressive deactivation during use due to coke deposition and therefore requires frequent regeneration by combustion in Os/H70 mixtures at high temperatures. rhoiphate catalysts are progressively destroyed during reactivation; silica-aluminas,although stable

to regeneration,give cracking of the raw materials; the aluminas, whether modified or not, sinter with consequent loss of activity and mechanical strength. Notari and his coworkers describe a new catalyst, Datented by Snamprogetti (US Patent4;038,337),which combines high activity and selectivity for the isomerisation reaction with outstanding resistance to sintering during the hydrothermal regeneration process. This material is-an active alumina modified at the surface with silica and is obtained by treating (for example) y- or n-Alp03 with an organic silicon compound, typically tetraethyl silicate, when surface compounds are formed of the following type: RR

R

R

R >Si, 0

,A’\ /Al, ,A1\ ,A\ 0

0

0 41\ 0

0'

P

i_l ii 0'1'0

‘p\,

Al' 0 \o/ \ o,.l,o

0

‘Al' Thermal decomposition causes elimination of the organic fragments leaving an imperfect monolayer of SiO2 on the surface of the alumina. The resultant catalyst has many of the properties of the original alumina, particularly with respect to isomerisationactivity, but, whereas the transition alusinas loose surface area after thermal treatment at 700°C, the silicated material does not than e itsarea appreciably until 10008C. A number of tests of the new material reported in the paper show that it has very suitable properties for an isomerisation process.