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 | environmental protection (no leaching of strong acids) |
| technological improvements (no aggressive, highly corrosive liquids |
| energy efficiency (increasing acidity of solid acids allowed low temperature isomerization) |
New regulation concerning the elimination of benzoid compounds from petrol in USA and Europe initiated correspondent changing in Ukrainian standards for petrol products also. Under NAFTOKHIM (main user of current project) supervision new standard for petrol products is currently developing. Ukrainian standard will be based on the European and USA ones and so will demand elimination of benzoid compounds from petrol products. It is known that in common technological petrol-cracking processes the main petrol fraction has low-octane number. Benzoid compounds were introduced to petrol for increasing of octane number instead on led compounds. But their toxicity and possible thermal destruction to carcinogenic polyaromatic products initiated research in development of new generation of petrol. This petrol should contain no led and benzoid components and posses high octane number. To solve this problem petrol should contain minimum of n-alkanes and maximum of iso-alkanes. Catalytic isomerization is used for this. Many disadvantages related to the use of liquid catalysts, namely H2SO4 or HF, mainly employed for catalytic alkylation have led to intensive research on solid catalysts. Fundamental expectations are connected with strong solid acids immobilised on inorganic carriers [1–4] in general and with sulphated zirconia, in particular [5]. According to proposed mechanism of short-chain alkan transformation [6] the catalytic process is bifunctional and requires co-operation among neighbouring acidic groups in transfer of a hydron [7]. Such co-operation is essential feature in the manifestation of superacidity.
Resent research [8] demonstrated that solids are much weaker acids then their liquid structural analogous because of rigidity. The rigidity prevents the immobilised acid groups from co-operation in proton transfer and so the postulation of superacidity for a number of solid acids appears to have no basis in fact. This results in higher temperature that should be applied to initiate catalytic isomerization of short parafins. From other hand it was shown [9] that deactivation rate is drastically increased if temperature of catalytic process raises from 45 to 55°C and so increasing of temperature is not desirable. Additionally, even in optimal conditions for all known solid catalysts their rapid deactivation takes place after short active period. So, in addition to common disadvantages of physically supported catalysts connected with:
| leaching of acid |
above-mentioned can be the main reason for:
| quick inactivation of sulfated solids especially by water [10], |
| increasing temperature for catalysis (lower acidity requires higher temperature of alkylation) |
It is crucial to develop technology for low temperature the isomerization of short alkanes to enable production of more environmentally friendly petrol. From chemical point of view the main problem for such technology is elaboration of the catalysts that enable such isomerization.
1
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3 Cheung T.K., Gates B.C. Chemtech, 1997, 27(9), 28-35.
4 Johansson M., Klier K. Topics In Catalysis, 1997, 4(1-2), 99-108.
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329-412.
6 Guisnet M., Gnep N.S. Applied Catalysis A-General, 1996, 146(1), 33-64 (Review).
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119(49), 11826-11831.
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124(1), 67-78.
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33(1-3), 303-312
