“…There are resulting uncertainties, which cannot be investigated completely, and there is nearly always a risk of constructing an industrial unit that cannot be operated appropriately. Really, mass transfer correlations give about 10-fold difference in mass transfer coefficients even in the simplest systems where only inert compounds, both gas and liquid are studied, let alone the problems related to the uneven wetting, "hot spots", change of physical properties along the catalyst bed, and the possible influence of the chemical reaction on mass transfer [26,27,30].…”