Subshate concentration

Keeping the factors such as pH, temperature and enzyme concentration at optimum levels, if the substrate concentration is increased, the velocity of the reaction recorded a rectangular hyperbola. At very low substrate concentration the initial reaction velocity (v) is nearly proportional to the substrate concentration (first order kinetics). However, if the substrate concentration is increased the rate of increase slows down (mixed order kinetics). With a further increase in the subshate concentration the reaction rate approaches a constant (zero order-reaction where velocity is independent of substrate concentration). 

Considerable scientific argument has arisen around the question of whether supercritical hydrogenation reactions proceed faster and more efficiently in either a single or multiple phases indeed conflicting reports have been published [44— 47]. Much of this debate has revolved around the LHSV of a reaction, but this parameter only addresses part of the issue from an industrial perspective. Other important factors which have to be taken into account include catalyst lifetime, overall conversion, and product selectivity, as well as the solvent compression costs need. The situation has been at least partly resolved by a key paper by Nunes da Ponte and co-workers [10]. They have shown that biphasic reactions can sometimes be faster than monophasic ones, because the concentration of subshate (as opposed to H2) is lower under monophasic conditions. 

Techniques 3 and 4 cannot usually be applied to electroneutral ion carrier micropipettes that have large electrode resistance. For systems under steady-state conditions, the change in concentration profile with tip-substrate distance can be used to determine the tip-subshate separation. A theory to that effect is available (58). 

For high substrate concentrations, [S] and the reaction rate is zero order with respect to the subshate... 

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