Hydrogel coated monoliths for enzymatic hydrolysis of penicillin G.

The objective of this work was to develop a hydrogel-coated monolith for the entrapment of penicillin G acylase (E. coli, PGA). After screening of different hydrogels, chitosan was chosen as the carrier material for the preparation of monolithic biocatalysts. This protocol leads to active immobilized biocatalysts for the enzymatic hydrolysis of penicillin G (PenG). The monolithic biocatalyst was tested in a monolith loop reactor (MLR) and compared with conventional reactor systems using free PGA, and a commercially available immobilized PGA. The optimal immobilization protocol was found to be 5 g l(-1) PGA, 1% chitosan, 1.1% glutaraldehyde and pH 7. Final PGA loading on glass plates was 29 mg ml(-1) gel. For 400 cpsi monoliths, the final PGA loading on functionalized monoliths was 36 mg ml(-1) gel. The observed volumetric reaction rate in the MLR was 0.79 mol s(-1) m(-3) (monolith). Apart from an initial drop in activity due to wash out of PGA at higher ionic strength, no decrease in activity was observed after five subsequent activity test runs. The storage stability of the biocatalysts is at least a month without loss of activity. Although the monolithic biocatalyst as used in the MLR is still outperformed by the current industrial catalyst (immobilized preparation of PGA, 4.5 mol s(-1) m(-3) (catalyst)), the rate per gel volume is slightly higher for monolithic catalysts. Good activity and improved mechanical strength make the monolithic bioreactor an interesting alternative that deserves further investigation for this application. Although moderate internal diffusion limitations have been observed inside the gel beads and in the gel layer on the monolith channel, this is not the main reason for the large differences in reactor performance that were observed. The pH drop over the reactor as a result of the chosen method for pH control results in a decreased performance of both the MLR and the packed bed reactor compared to the batch system. A different reactor configuration including an optimal pH profile is required to increase the reactor performance. The monolithic stirrer reactor would be an interesting alternative to improve the performance of the monolith-PGA combination.

Potential application of monolith packed columns as bioreactors, control of biofilm formation.

Monolith reactors combine good mass transfer characteristics with low-pressure drop, the principle factors affecting the cost effectiveness of industrial processes. Recently, these specific features of the monolith reactors have drawn the attention toward the application of the monolith reactor in multiphase reaction systems. In this study, we explore the potential application of monolith reactors as bioreactor requiring gas-liquid mass transfer for substrate supply. It is demonstrated on theoretical grounds that the monolith reactor is a competitive alternative to conventional gas-liquid bioreactors such as stirred tanks, packed beds, and airlift bioreactors because it allows for a significant reduction of the energy dissipation that is normally required for gas-liquid contacting. A potential problem of monolith reactors for biological processes is clogging due to biofilm formation. This paper presents experimental results of a study into the formation and possible removal of biofilms during operation of a monolith reactor as suspended cells bioreactor. The results indicate that biofilm formation may be minimized and postponed by a proper choice of operating conditions. Periodic biofilm removal could straightforwardly be achieved by rinsing with water at moderate pressures and allows for stable operation for prolonged periods of time.

One-pot catalyst preparation: combined detemplating and Fe ion-exchange of BEA through Fenton's chemistry.

BEA zeolite has been simultaneously detemplated and Fe-exchanged by treating the parent zeolite with a Fenton's-type reagent (Fe3+-H2O2) at low temperature. This one-pot process simplifies and speeds up considerably the preparation route. The catalyst shows excellent performance on N2O decomposition compared to conventionally prepared Fe-BEA.

Ion exchanged Fe-FER through H2O2-assisted decomplexation of organic salts.

Decomplexation of organic ligands through redox titration has been applied to catalyst synthesis, developing an improved preparation method for Fe-ferrierite (Fe-FER), the catalyst showing excellent performance and durability for N2O decomposition under realistic conditions for nitric acid plants.

Breakthrough of shallow activated carbon beds under constant and pulsating flow.

During actual use of a gas mask canister the flow through the activated carbon bed is pulsating. Pulsating flows were found to be less favorable for the breakthrough behavior compared to a constant flow pattern. The present article demonstrates this difference and clarifies how and why the breakthrough time depends on the airflow pattern. Furthermore, it shows the importance of good estimates of both diffusion parameters and mass transfer coefficients to obtain accurate predictions of the initial part of the breakthrough curve. Breakthrough measurements applying continuous and pulsating flows were performed using toluene on shallow activated carbon beds; toluene is a good representative for the type of vapors for which activated carbon forms a suitable adsorbent. Pulsating flow was studied by using the positive halves of a sinusoidal flow pattern, which closely resembles the actual breathing pattern. A two-dimensional mathematical model was used to describe the dynamic behavior. The agreement between measured and simulated breakthrough curves was good for both the constant and pulsating flow experiments. The difference in time between simulation and experiment was 10% at most. The influence of pulsating flow on the breakthrough behavior is well accounted for by the model. The influence of flow rate on the mass transfer from the bulk gas phase to the surface of the adsorbent particles is ultimately responsible for the difference in breakthrough times. Testing under pulsating flow allows for a more realistic assessment of the performance of cartridges and canisters.