Flow experiments

Single pass flow techniques have been used for studies of vapor-liquid equilibria of reacting systems by various authors. Maurer and coworkers describe a special 

The problem of high amounts of substance needed in flow cells in a single pass mode can be circumvented using recirculation techniques. However, the recirculation can cause problems in studies of chemically reactive systems if an ongoing chemical reaction in the recirculating stream leads to shifting compositions of the evaporator feed, so that no steady state is reached. 

This brief survey shows that there are many options for measuring phase equilibria in reacting systems, which allow to carry out such studies for a wide range of systems and conditions. The main limitation for experimental investigations of reactive vapor-liquid equilibria is related to the velocity of the reaction itself if phase equilibrium measurements of solutions are needed, which are not in chemical equilibrium, the reaction must be considerably slower than the characteristic time constant of the phase equilibrium experiment. Apparatus are available, where that time constant is distinctly below one minute. For systems with reactions too fast to be studied in such apparatuses, it should in many cases be possible to treat the reaction as an equilibrium reaction, so that the information on the phase equilibrium in mixtures, which are not chemically equilibrated is not needed. 

Thermodynamics plays a key role in understanding, modeling, and designing reactive separation processes. The basic concepts of thermodynamic modeling of simultaneous chemical and phase equilibrium are summarized here with emphasis on the different options provided by classical thermodynamics. Several types of 

RD process models are compared with each other and with experimental data on the backgroimd of the model complexity and the amount of information needed to parameterize the models. 

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Although the Rouse theory is the source of numerous additional relationships, Eq. (3.98) is a highpoint for us, because it demonstrates that the viscosity we are dealing with in the Rouse theory for viscoelasticity is the same quantity that we would obtain in a flow experiment. Several aspects of this statement deserve amplification ... 

Fig ure 12-27. Temperature versus time plot from a semi-batoh heat flow experiment. (Source Hazard Evaluation Laboratory Ltd.)... 

Such effects principally cannot be observed in multi band detectors such as a UV diode array detector or a Fourier transform infrared (FTIR) detector because all wavelengths are measured under the same geometry. For all other types of detectors, in principle, it is not possible to totally remove these effects of the laminar flow. Experiments and theoretical calculations show (8) that these disturbances can only be diminished by lowering the concentration gradient per volume unit in the effluent, which means that larger column diameters are essential for multiple detection or that narrow-bore columns are unsuitable for detector combinations. Disregarding these limitations can lead to serious misinterpretations of GPC results of multiple detector measurements. Such effects are a justification for thick columns of 8-10 mm diameter. 

Fig. 12. Sketch of the conical-channel flow experiment of James and Saringer. The pressure drop was measured between ports 1 and 2 (redrawn according to Ref. [59])...

Basically the kinetic results are consistent with the first (rapid) reaction being the addition of a hydroxide ion to the diazonium ion followed by the very fast deprotonation of the (Z)-diazohydroxide to give the (Z)-diazoate (steps 1 and 2 in Scheme 5-14). In addition, however, the stopped-flow experiments showed that the diazonium ion also reacts with the water molecule, initially forming the conjugate acid of the (Z)-diazohydroxide (ArN2OH2), which is then very rapidly deprotonated (reaction 1 in Scheme 5-14). The rate of the relatively slow (Z/E)-isomerization (reaction 5 in Scheme 5-14) can in general be measured by conventional spectrophotometry. 

Dudukovic, M.P. (2001) Opaque multiphase flows experiments and modeling. 4th International Congress on Multiphase Flow, 2001, New Orleans. 

In some microfluidic applications liquid is transported with a comparatively low velocity. In such cases, a liquid volume co-moving with the flow experiences inertial forces which are small compared with the viscous forces acting on it. The terms appearing on the left-hand side of Eq. (16) can then be neglected and the creeping flow approximation is valid... 

In continuous flow experiments, catalyst was packed into a downflow trickle-bed reactor of 30 cc bed volume. Hydrogen was passed slowly over the catalyst at atmospheric pressme and the temperature was slowly raised to the desired reduction/activation temperature and held for at least four hours. After activation, the reactor was cooled to the desired reaction temperature, the pressure was raised, and flow of an aqueous feed of glycerol and sodium hydroxide initiated along with a corresponding amonnt of hydrogen. A large set of reaction conditions was tested. 

Hydrolytic Kinetic Resolution (HKR) of epichlorohydrin. The HKR reaction was performed by the standard procedure as reported by us earlier (17, 22). After the completion of the HKR reaction, all of the reaction products were removed by evacuation (epoxide was removed at room temperature ( 300 K) and diol was removed at a temperature of 323-329 K). The recovered catalyst was then recycled up to three times in the HKR reaction. For flow experiments, a mixture of racemic epichlorohydrin (600 mmol), water (0.7 eq., 7.56 ml) and chlorobenzene (7.2 ml) in isopropyl alcohol (600 mmol) as the co-solvent was pumped across a 12 cm long stainless steel fixed bed reactor containing SBA-15 Co-OAc salen catalyst (B) bed ( 297 mg) via syringe pump at a flow rate of 35 p,l/min. Approximately 10 cm of the reactor inlet was filled with glass beads and a 2 pm stainless steel frit was installed at the outlet of the reactor. Reaction products were analyzed by gas chromatography using ChiralDex GTA capillary column and an FID detector. 

Taking into account the relevance of the range of semi-dilute solutions (in which intermolecular interactions and entanglements are of increasing importance) for industrial applications, a more detailed picture of the interrelationships between the solution structure and the rheological properties of these solutions was needed. The nature of entanglements at concentrations above the critical value c leads to the viscoelastic properties observable in shear flow experiments. The viscous part of the flow behaviour of a polymer in solution is usually represented by the zero-shear viscosity, rj0, which depends on the con-... 

J. Gotz, K. Zick 2003, (Local velocity and concentration of the single components in water/oil mixtures monitored by means of MRI flow experiments in steady tube flow), Chem. Eng. Technol. 26 (1), 59-68. 

J. Gotz, K. Zick, W. Kreibich 2003, (Possible optimisation of pastes and the according apparatus in process engineering by MRI flow experiments), Chem. Eng. Process. 42 (7), 515-534. 

J. Gotz, K. Zick, V. Lehmann, D. Grog, M. Peciar, (Analysis of the mixing and flow behaviour of beer mashes in a stirring vessel by means of NMR flow experiments), in preparation. 

A flow experiment should be set up in a way that the largest detectable velocity present in the sample is covered by the corresponding velocity field of view. This avoids distortions by back-folding of velocities into the experimental velocity scale. 

Fig. 4.1.7 Superficial average velocity data for the flow experiment with the thin Bentheimer sandstone sample. Each arrow represents the direction and relative magnitude of the superficial average velocity at the corresponding voxel. The velocities are measured for 58 x 20 voxels.

In an NMR/MRI flow experiment, we would like to measure parameters such as velocity without regard to the starting position of the particle. Thus, mo is always set to zero. The moments m, are under the control of the experimenter in that they are manipulated by the choice of the time dependence of the gradient G. Thus, it is easy to see that m0 can be set to zero by simply making sure that the time integral of the gradient is zero. The easiest way to accomplish this is to have a bipolar gradient of equal absolute amplitude and duration. 

Filaments in chaotic flows experience complex time-varying stretching histories. Computational studies indicate that within chaotic regions, the distribution of stretches, A, becomes self-similar, achieving a scaling limit. 

Fig. 15. Affine stretching of a filament in the journal bearing flow. Experiments (top) agree well with computations (bottom) carried out assuming that the filament deforms as the suspending fluid (i.e., affine deformation) (Tjahjadi and Ottino, 1991).

Figure 51. Conductivity convergence (CUSUM graph) curves for the reference (no groundwater) and ground water flow experiment...

An on-flow experiment is now carried out. 50 pi of a solution of the product mixture (5 mg in 5 mL solvent) are injected and the NMR proton signal accumulation started simultaneously. The time taken for the chromatogram is 17 min. During this time a total of 128 proton NMR spectra are recorded, each with eight scans, i.e. an FID is accumulated approximately every 7 sec. After the Fourier transformation we obtain a two-dimensional representation (Fig. 33) of the on-flow experiment. 

Fig. 33 On-flow experiment carried out on the product mixture. Horizontal axis proton chemical shift. Vertical axis retention time...

Fig. 34a-c Proton NMR spectra from the on-flow experiment. FIDs recorded after a 1 min, b 3 min, c 7.5 min... 

Spectra which are better resolved (useful for example for the exact determination of coupling constants) can be obtained by carrying out stopped-flow experiments. Here we stop the chromatographic separation after 3 and 7.5 min, optimize the homogeneity (by shimming the magnet) and carry out the desired NMR experiments. 

Figure 35 shows the proton spectra which we obtain you can see that they are of much better quality than those we got from the on-flow experiment. The signals for acetonitrile and residual HDO have been cleanly removed using the WET sequence referred to above, and resolution and signal-noise are much better, so we can obtain coupling constants exactly. 

Fig. 35 Proton spectra obtained from the stopped-flow experiment. Above acetal 4. Below acetal 5. In each case 16 scans, relaxation delay 1 sec...

Fig. 36 COSY spectrum of acetal 5 obtained in a stopped-flow experiment. Measurement time 11 min...

The present study investigates the adsorption and trapping of polymer molecules in flow experiments through unconsolidated oil field sands. Static tests on both oil sand and Ottawa sand indicates that mineralogy plays a major role in the observed behavior. Effect of a surfactant slug on polymer-rock interaction is also reported. Corroborative studies have also been conducted to study the anomalous pressure behavior and high tertiary oil recovery in surfactant dilute-polymer systems(ll,12). 

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