Dynamic Experimental Methods Using in situ Measurements of the Surface Intermediates Applied to the Fine Chemistry

Unsteady-state kinetics can be used for the determination of the reaction mechanism of a heterogeneous catalytic reaction, and the characteristic shape of the time evolution curves of the concentrations at the outlet of the reactor can be associated with rate-limiting steps. To complete the information, in situ measurements of surface intermediates can be correlated with those response curves to get a physical meaning to the determined kinetic parameters. It is shown, how such an experimental setup can be realized. That the knowledge of the reaction mechanism and the identification of the active sites on the catalyst are of great use for reaction engineering is shown with the example of the methylation of catechol, an intermediate in fine chemistry, where the catalyst has been selectively modified to increase the yield of the desired 3-methylated product from 25 to nearly 70%

Kinetics and deactivation of the NO reduction by CO on Pt-supported catalysts

Reaction kinetics and catalyst deactivation during the redn. of NO with CO on a 0.5%Pt-3.4%MoO3/a-Al2O3 catalyst were investigated. The reaction shows an ignition/quenching behavior. After ignition, the reaction kinetics (formation of N2 and N2O) obey the bimol. Langmuir-Hinshelwood equations, in accordance with a dissociative mechanism. A slow catalyst deactivation is obsd. under reductive conditions (pCO >> pNO). The proposed mechanism comprises the formation of electron-withdrawing isocyanates on the Pt surface which slow down the Pt-CO bond formation, which is typical for the quenched state. It is pointed out that the isocyanates delay the formation of the quenched state but that the low activity in the quenched state is due to adsorbed CO

Forced concentration oscillations for catalytic reactions with stop-effect

The effect of forced concn. oscillations on a catalytic reaction with stop-effect was studied based on 2 different adsorption-desorption models. Both models predict mean reaction rates which can be more than twice as high as the max. rate under optimum steady-state conditions. An anal. soln. is presented to describe the mean performance as a function of concn., length of period, and cycle split. [on SciFinder (R)

Heavy metal adsorption to a chelating resin in a binary solid fluidized bed

The addn. of inert particles of lighter d. and smaller diam. increases considerably the mass transfer coeff. in comparison to that of mono-component active particles at the same liq. velocity. This effect was applied to elimination of Cu ions by adsorption on a chelating resin. The intensification of the film mass transfer coeff. in binary system leads to a 15% increase of the usable adsorbent efficiency. [on SciFinder (R)

A generalized correlation for equilibrium of forces in liquid-solid fluidized beds

A review of publication on the expansion of fluidized bed with the fluid velocity. The well-known Richardson-Zaki equation is applied to develop a more accurate relation linking the apparent drag force Fd, the effective gravitational force Fg, and the voidage of fluidized beds under intermediate regime. A correcting const. a in the relation is a function of Archimedes no. which may provide a degree of flexibility for different systems covering a wide range of variables. With addn. of the correlation developed in this work, equivalence correlations between equil. forces and the Richardson-Zaki equation can be found for a whole regime. [on SciFinder (R)

Multi-injection microstructured reactor for intensification of fast exothermic reactions: proof of concept

Quasi-instantaneous exothermic reactions lead to the formation of unwanted hot spots even when carried out in conventional microstructured reactors (MSR) with tube diameter of 100-1000 μm. For this reason, alternative MSR designs are warranted to enable process intensification of fast reactions with characteristic reaction times 0.98 reaching a 500-fold process intensification as compared to the conventional semi-batch process. The temperature profiles monitored by quantitative infrared thermal imaging confirmed an 8-fold reduced temperature rise compared to adiabatic temperature rise, which was achieved by injecting the reactants at three different injection point