J.G.M. Winkelman

Experimental comparison of three reactor designs for photocatalytic water purification

The photocatalytic degradation of formic acid was compared for a suspended system, an immobilized system with a coated wall and an immobilized system packed with coated glass beads. The quantum yields found for the three systems are comparable. Mass transfer limitations only occurred in the tubular reactor with the catalyst coated on the wall. The addition of air directly in this reactor increased the degradation rate by decreasing the mass transfer limitation. In the packed-bed reactor, two bead diameters were compared. The activity of these packed-bed reactors appeared to be comparable for low amounts of titanium dioxide, whereas the packed-bed reactor with the large beads shows a higher activity for high amount of catalyst.

Modeling the photocatalytic degradation of formic acid in a reactor with immobilized catalyst

A kinetic model for the photocatalytic degradation of formic acid in an immobilized system is presented, including the dependency of the reaction rate on the concentration of formic acid and oxygen, the catalyst layer thickness and the light flux. In the system some external mass transfer limitation occurs which is included in the modeling with experimentally determined values for the mass transfer coefficient of both formic acid and oxygen. The model describes the measurements well. The degradation rate appears to depend linearly on the light intensity. The adsorption of formic acid and oxygen on the catalyst layer appears to play an important role in the degradation rate.

Comparison of the efficiency of immobilized and suspended systems in photocatalytic degradation

The photocatalytic degradation of formic acid in suspended and immobilized systems, with and without oxygen addition, are compared. In the immobilized system, oxygen addition to the reactor appeared to increase the efficiency, not only because oxygen acts as an efficient electron scavenger, but also due to increased mass transfer in this two-phase reactor. This immobilized system had an efficiency comparable to that of the suspended system. The addition of oxygen to the immobilized system appeared to increase the quantum yield with a factor 4, whereas the addition of oxygen to the suspended system hardly had any effect.

Kinetics and chemical equilibrium of the hydration of formaldehyde

Abstract The reaction rate of the hydration of formaldehyde is obtained from the measured, chemically enhanced absorption rate of formaldehyde gas into water in a stirred cell with a plane gas–liquid interface, and mathematically modelling of the transfer processes. Experiments were performed at the conditions prevailing in industrial formaldehyde absorbers, i.e. at temperatures of 293– 333 K and at pH values between 5 and 7. The observed rate constants could be correlated as k h =2.04×10 5 × e −2936/T s −1 . Using the results, and the dehydration reaction rate constant, obtained previously at similar conditions, the chemical equilibrium constant for the hydration is obtained as K h =e 3769/ T −5.494 .

Proof of concept for continuous enantioselective liquid–liquid extraction in capillary microreactors using 1-octanol as a sustainable solvent

The use of capillary microreactors for enantioselective liquid–liquid extraction (ELLE) was successfully demonstrated using a model system consisting of a buffered aqueous amino acid derivative (3,5-dinitrobenzoyl-(R,S)-leucine) solution (phosphate buffer, pH 6.58) and a chiral cinchona alkaloid (CA) host in an organic solvent. It was shown that 1-octanol is a suitable replacement for the commonly used chlorinated solvents like 1,2-dichloroethane. Experiments were conducted in a capillary microreactor set-up (0.8 mm internal diameter) operated in the slug flow regime at 294 K (residence times between 12 and 900 s, 1 : 1 flow ratio of the aqueous to organic phases, 1 mM of host and 1 mM of amino acid derivative). The enantiomeric excess (ee) was shown to be a function of the solvent and residence time and varied between 37% and 49% in 1,2-DCE and 28 and 46% in 1-octanol in the organic phase. The ee values in the organic phase at shorter residence times were higher than the independently determined equilibrium ee values (41% in 1,2-DCE and 31% in 1-octanol at a host concentration of 1 mM). This is an unprecedented observation with large implications for ELLE, as it implies that operation in the kinetic regime may lead to improved enantioseparation performance.

Process Intensification of Enzymatic Fatty Acid Butyl Ester Synthesis Using a Continuous Centrifugal Contactor Separator

Fatty acid butyl esters were synthesized from sunflower oil with 1-butanol using a homogeneous Rhizomucor miehei lipase in a biphasic organic (triglyceride, 1-butanol, hexane)– water (with enzyme) system in a continuous setup consisting of a cascade of a stirred tank reactor and a continuous centrifugal contactor separator (CCCS), the latter being used for integrated reaction and liquid–liquid separation. A fatty acid butyl ester yield up to 93% was obtained in the cascade when operated in a once-through mode. The cascade was run for 8 h without operational issues. Enzyme recycling was studied by reintroduction of the water phase from the CCCS outlet to the stirred tank reactor. Product yield decreased over time to an average of 50% of the initial value, likely due to accumulation of 1-butanol in water phase, loss of enzyme due to agglomeration, and the formation of a separate enzyme layer.