Reactions catalysed by inorganic catalysts

The reactants and inorganic catalysts used in kinetic studies of heterogeneous catalytic esterifications (transesterifications) are summarised in Table 20. As can be seen, no systematic comparative study with more than one catalyst (with the exception of paper [406]) has been performed by any one worker. The greatest attention was paid to silica gel [407— 411]. The reactants were usually low molecular weight acids and alcohols a typical pair of reactants is acetic acid—ethanol. Only in one study [126] was the structure of the reactants systematically varied in order to establish the effect on the reactivity. 

For a formal kinetic description of vapour phase esterifications on inorganic catalysts (Table 21), Langmuir—Hinshelwood-type rate equations were applied in the majority of cases [405—408,410—412,414,415]. In some work, purely empirical equations [413] or second-order power law-type equations [401,409] were used. In the latter cases, the authors found that transport phenomena were important either pore diffusion [401] or diffusion of reactants through the gaseous film, as well as through the condensed liquid on the surface [409], were rate-controlling. 

Equations reported as best fitting esterification (transesterification) data on inorganic catalysts 

Si02-Al203 r /ZsKaKbLOaPb -(PrPs/ )] Bauxite (1 + A + KrPb + KrPr + sPs)2 SR between molecularly adsorbed reactants 405,414 

Si02—A120 j A1203-B203 ai2o3 ) r = fes A BPAPB/(1 + kaPa + bPb)2 SR between molecularly adsorbed reactants 406 

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