Absorption of toluene in silicone oil: effect of the solvent viscosity on hydrodynamics and mass transfer

International audienceThe purpose of this study was to compare toluene absorption performances using two PDMS of different viscosities (η = 5 and 50 mPas respectively) in terms of hydrodynamics and mass transfer. Three types of packing were tested in a counter-current packed gas-liquid contactor, Raschig rings, IMTP®, and Flexipac®. Hydrodynamic results showed that the viscosity of PDMS 50 is not a hurdle to be used with IMTP® or Flexipac®; the pressure drop being around 288 Pa m−1 for Flexipac® at the flooding point (FG = 0.99 Pa1/2; L’ = 4.95 kg m−2 s−1), which corresponds to an acceptable value for an industrial application. The determination of the loading zones showed that Raschig rings were not suitable for solvents having a high viscosity, such as PDMS 50; they resulted in high pressure drops if compared to IMTP® and Flexipac®. The mass transfer study showed that 100% removal efficiency can be reached for both PDMS using Flexipac®. For IMTP®, the removal efficiency is limited to 88% in the presence of PDMS 50. As a result, PDMS 50 should be a relevant absorbing liquid for the removal of toluene in the absorption–biodegradation process, and Flexipac® packing should be preferred to IMTP

Method for improving nucleation of crystals from solution

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Toluene degradation by a water/silicone oil mixture for the design of two phase partitioning bioreactors

International audienceToluene degradation performances were studied in a 10 L Two-Phase Partitioning Bioreactor (TPPB). The liquid phase consisted of a mixture of water and PDMS 50 (Poly DiMethylSiloxane, i.e. silicone oil, viscosity of 46 mPa.s) in the volume ratio of 75%/25%. Two series of experiments were carried out: in the first, the reactor was sequentially supplied with toluene whereas in the second, toluene was continuously supplied. Activated sludge from the wastewater treatment plant of Beaurade (Rennes, France) was used at an initial concentration of 0.5 dry mass g.(mixture L)(-1). The elimination capacity (EC) was investigated as well as the change in biomass concentration over time. Toluene biodegradation was very efficient (removal efficiency, RE = 100%) for toluene flows ranging from 0.2 to 1.2 ml.h(-1), corresponding to elimination capacities of up to 104 g.m(-3).h(-1). For a toluene flow of 1.2 ml.h(-1), the biomass concentration measured at the end of the experiment was 4.7 dry mass g.(mixture L)(-1). The oxygen concentration in the liquid phase was clearly not a limiting factor in these operating conditions. Based on these results, an extrapolation leading to the design of a large-scale pilot TPPB can now be considered to study toluene degradation performances in industrial conditions

Absorption of toluene in silicone oil: effect of the solvent viscosity on hydrodynamics and mass transfer

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Determination of the toluene removal capacity of a semi-continuous two-phase partitioning bioreactor

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Characterization and selection of PDMS solvents for the absorption and biodegradation of hydrophobic VOCs

International audienceBACKGROUND : Four silicone oils (PolyDiMethylSiloxane, PDMS) of different viscosities, namely 5, 20, 50, and 100 mPa s were characterized to select the most suitable polymer for the biol. treatment of toluene. The PDMS volatilities and the partition coeffs. of toluene between air and PDMS were investigated. Toluene biodegrdn. tests were also carried out to assess the absence of toxicity of the considered PDMS vis-a-vis the microorganisms. RESULTS : PDMS 20, 50 and 100 had negligible volatilities at 25 °C and 35 °C, whereas PDMS 5 was volatile even at 25 °C. The results indicate that the amt. of VOCs emitted by PDMS increased with the temp. according to a logarithmic law. The partition coeff. of toluene between air and the four PDMS were similar (H = 2.9 Pa m3 mol-1) indicating that the affinity between toluene and PDMS was identical whatever their viscosity. Moreover, biodegrdn. tests allowed the conclusion that the four PDMS tested are not toxic for microorganisms. CONCLUSION : PDMS 20, 50 and 100 were suitable at 25 °C for the biol. treatment of toluene. Since all these PDMS were satisfactory at 25 °C, it could make sense to select the least viscous oil for use in the process, i.e. PDMS 20. © 2015 Society of Chem. Industry

Continuous-Flow Tubular Crystallization to Discriminate between Two Competing Crystal Polymorphs. Part I: cooling crystallization

A laminar-flow tubular crystallizer was used for seedless continuous flow crystallization of an active pharmaceutical ingredient, namely, Brivaracetam, which has a polymorphic behavior: rod-shaped crystals and a pseudo-polymorphic solvated, needle-like crystal. The combination of fast cooling at 20 °C/s and high supersaturation values between 4 and 11 resulted in the discrimination of nucleation and growth of only the desired crystalline form even though its solubility curve is very close to the one of the undesired needle shape. Crystal nucleation and the start of crystal growth occur inside the tubular crystallizer; high flow rates prevent clogging of the crystallizer. Further crystal growth may be, if desired, stopped via immediate filtration. In this way, an industrially applicable continuous crystallizer is proposed. It is also demonstrated that the presence of restrictions in the tubing drastically increases the nucleation rate. A literature survey points out that induced turbulence can occur under current flow conditions using said restrictions.info:eu-repo/semantics/publishe

Continuous-Flow Tubular Crystallization to Discriminate between Two Competing Crystal Polymorphs. Part II: antisolvent crystallization

The development of a continuous flow antisolvent crystallization protocol for a commercial active pharmaceutical ingredient, Brivaracetam, is described. To obtain increased nucleation kinetics of the desired crystalline form, solutions of Brivaracetam/isopropyl acetate are injected into micrometric tubing and mixed with a refrigerated antisolvent hexane. In this way very high supersaturation conditions are induced shortly after mixing. Residence times below 1 s after mixing in short tubular crystallizers are necessary for the desired, but thermodynamically unstable, crystals to grow. Arresting all crystal growth by immediate removal of the antisolvent containing mother liquors by continuous filtration or by casting the product onto filter paper prevents the formation of the thermodynamically stable pseudopolymorph - undesired due to its needle shape and solvated nature. Sufficient solid material output can be generated in order to be implemented in actual processing conditions if combined with suited continuous filtration units.info:eu-repo/semantics/publishe

Role of Cosolutes in the Aggregation Kinetics of Monoclonal Antibodies

We propose a general strategy based on kinetic analysis to investigate how cosolutes affect the aggregation behavior of therapeutic proteins. We apply this approach to study the impact of NaCl and sorbitol on the aggregation kinetics of two monoclonal antibodies, an IgG1 and an IgG2. By using a combination of size exclusion chromatography and light scattering techniques, we study the impact of the cosolutes on the monomer depletion, as well as on the formation of dimers, trimers, and larger aggregates. We analyze these macroscopic effects in the frame of a kinetic model based on Smoluchowski’s population balance equations modified to account for nucleation events. By comparing experimental data with model simulations, we discriminate the effect of cosolutes on the elementary steps which contribute to the global aggregation process. In the case of the IgG1, it is found that NaCl accelerates the kinetics of aggregation by promoting specifically aggregation events, while sorbitol delays the kinetics of aggregation by specifically inhibiting protein unfolding. In the case of the IgG2, whose monomer depletion kinetics is limited by dimer formation, NaCl and sorbitol are found respectively to accelerate and inhibit conformational changes and aggregation events to the same extent

Kinetic Analysis of the Multistep Aggregation Mechanism of Monoclonal Antibodies

We investigate by kinetic analysis the aggregation mechanism of two monoclonal antibodies belonging to the IgG1 and IgG2 subclass under thermal stress. For each IgG, we apply a combination of size exclusion chromatography and light scattering techniques to resolve the time evolution of the monomer, dimer, and trimer concentrations, as well as the average molecular weight and the average hydrodynamic radius of the aggregate distribution. By combining the detailed experimental characterization with a theoretical kinetic model based on population balance equations, we extract relevant information on the contribution of the individual elementary steps on the global aggregation process. The analysis shows that the two molecules follow different aggregation pathways under the same operating conditions. In particular, while the monomer depletion of the IgG1 is found to be rate-limited by monomeric conformational changes, bimolecular collision is identified as the rate-limiting step in the IgG2 aggregation process. The measurement of the microscopic rate constants by kinetic analysis allows the quantification of the protein–protein interaction potentials expressed in terms of the Fuchs stability ratio (<i>W</i>). It is found that the antibody solutions exhibit large <i>W</i> values, which are several orders of magnitude larger than the values computed in the frame of the DLVO theory. This indicates that, besides net electrostatic repulsion, additional effects delay the aggregation kinetics of the antibody solutions with respect to diffusion-limited conditions. These effects likely include the limited efficiency of the collision events due to the presence of a limited number of specific aggregation-prone patches on the heterogeneous protein surface, and the contribution of additional repulsive non-DLVO forces to the protein–protein interaction potential, such as hydration forces