High-pressure view cell

The last ATR cell described here in detail was designed for the study of catalytic reactions at high pressures and in particular in supercritical fluids. A schematic representation of the design is shown in Fig. 17 (76). An important issue in this type of reaction is the phase behavior of the system, which can have a large influence on the catalytic reaction 77,IS). The cell consists of a horizontal stainless-steel cylinder. It is designed to allow monitoring of the phase behavior via a video camera. For this purpose, one end of the cylinder is sealed with a sapphire window, behind 

A powerful characteristic of the cell described above is the opportunities it affords for the determination of the compositions of both the lower (denser) and upper (lighter) phases. In particular, the combination of ATR and transmission IR spectroscopy shows the distribution of the catalyst between the two phases. For example, in the homogeneously catalyzed formylation of morpholine with carbon dioxide and hydrogen by a ruthenium catalyst, a two-phase system was found at a 

The equipment depicted in Fig. 17 also allows monitoring of species adsorbed on a solid catalyst. For this application, the ZnSe IRE is coated with a layer of the catalyst before assembly of the cell and the start of the reaction. This approach was chosen for investigation, for example, of the interaction of the reactant with the catalyst during the asymmetric hydrogenation of ethyl pyruvate catalyzed by cinc-honidine (CD)-modified Pt/Al2O3 in the presence of supercritical ethane (79). 

Cross-section of the view cell at the spectroscopic level. The IR beam is directed either through the ATR crystal (bottom, solid hues) or through the transmission windows (upper part, dashed lines). The four mirrors are mounted on a motor-driven mobile attachment (76). 

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Figure 10.8 The monomers are polymerized inside a high-pressure view cell (a). After reaction, the scC02 is vented and the monolith removed from the cell (b)...

The phase equilibrium of the binary system stearyl alcohol/C02 was measured in a high pressure view cell (own design) according to the synthetic method by Teipel et al. [6] and presented in Fig. 2. The curves represent the border between the homogeneous and two phase region above the curve a homogeneous solution is present, below two phases exist. The measurements were carried out for different concentrations of stearyl alcohol in CO2 represented by the different curves. It is seen that 2.1 wt.% of stearyl alcohol are complete soluble in SC-CO2 at 333 K and 20 MPa. 

Tubing connects the chamber and a high-pressure view cell, which is thermostated to the same temperature as the chamber. In order to observe swelling behavior, some of the solid material is also placed into the view cell. It thus is in contact with the gas at the same pressure and temperature as the material in the suspended vial. The interior of the view cell may be observed through a video camera. The video images are scanned into a PC and analyzed for changes in size. 

Figure 13.1 Phase diagram showing supercritical region (a) and series of photographs showing the phase transition from biphasic to monophasic upon transition into the supercritical regime in a high-pressure view cell.

The supercritical fluid of interest is charged at ambient temperature to a suitable gas/liquid compressor, where it is compressed and delivered to a high-pressure equilibrium view cell. The constant-volume high-pressure view cell is immersed in a water bath, which can easily be controlled to within 0.rC. The pressure of the system is measured with an appropriate Bourdon tube Heise gage. The cell contents are mixed when the cell is rocked approximately 180°, causing a small stirring bar previously inserted into the cell to move through the cell contents. 

Figure 2.1-12 Scheme of a high pressure view cell (Robinson Cell, D.B. Robinson and Associates) [47]. 

During high pressure view-cell experiments of a solution of 4 wt% polymer in MMA at 0.7 MPa CO2 and 20°C, a second phase (polymer phase) has clearly been observed. This illustrates the strong antisolvent effect of CO2. Before the polymer actually precipitates, the antisolvent already causes a lower viscosity in the CO2-expanded system as compared to the bulk system. Because CO2 is a poor solvent for most polymers, the gyration radius of the polsrmer will be lower. This means fewer entanglements between polymer molecules, and subsequently a lower viscosity. Although the viscosity does not increase, so far only relatively low... 

Figure 10 A high-pressure system for evaluating stability of water-in-C02 microemulsions in supercritical CO2 used in the author s laboratory. (1) High-pressure view cell (2) video camera (3) temperature controller (4) stirrer (5) hand-operated syringe pump (6) pressure transducer (7) high pressure valve (8) ISCO syringe pump (9) collection vessel.

High-pressure view cells are used for the investigations of phase behavior and the phase equilibria of binary mixtures. The phase behavior shows whether two or more substances are completely miscible at certain temperatures and pressures or if they form separated phases. From the phase equilibria data, one gets information about the composition of the phases for example the amount of CO2, which is soluble in a polymer at elevated temperature and pressure. A sketch of a high-pressure view cell is shown in Fig. 7.5. The cell is made of a cylindrical steel body which provides access for a thermocouple and a pressure transducer. The inner volume of the cell amounts 3 x 10 m. Via two pipes the cell can be filled with the liquids that are to be analyzed as well as with CO2. 

Experiments Using a High-Pressure View Cell... 

The phase behavior as well as the phase composition of aqueous PVP solutimis (liquid phase) and CO2 (gas phase) were measured. Figure 7.6 shows the view into a high-pressure view cell. The cell is filled with an aqueous soiution of PVP K30 with a PVP concentration of 30 wt.%. The liquid is saturated with CO2 at a saturation pressure of 8 MPa. Afterwards the pressure is increased up to a vaiue of 15 MPa by adding N2. Therefore, the solution in this state is undersaturated. The series of pictures in Fig. 7.6 shows how the phase behavior changes during the pressure release from 15 MPa to ambient conditions (0.1 MPa). 

The stainless steel high-pressure view cell (D-2) is equipped with two sapphire windows, placed in the front and rear of the cell s body. This allows visualisation of the cell s interior and therefore also qualitative investigation of phase behaviour. The rear sapphire is connected to a pneumatic hydraulic piston (C-1). During sampling the piston moves forward, minimising the cell s volume and thereby ensuring a constant pressure. The view cell has a volume of 54 cm, which can... 

Fig. 15.1 Schematic flow chart of the high-pressure view cell used for the phase equilibria measurements...

A combination of two view cells and a DSA 100 measuring apparatus from Kruess GmbH, Germany was used as presented in Fig. 15.3. Since the Drop Shape Analyser instrument is designed by the manufacmrer for measurements at atmospheric pressure only, a high-pressure view cell (D-3) was placed between the camera (K-1) and light source (L-1) of the DSA 100, so that measurements under high pressure would also be possible. This cube-shaped stainless steel view cell is... 

At the beginning of the experiments, the cells were thoroughly cleaned. The procedure described previously for the solubility measurements was followed to saturate the triglycerides with CO2 in the high-pressure view cell. Before the mixing period was started the valves between the two cells were opened, so that some triglyceride could flow through the capillary into the second cell. This was done to ensure that the CO2 atmosphere in the second cell was saturated with the... 

The solubility of solutes in systems consisting of C02/solvent and C02/solvent mixtures was measured using the vanishing cloud point method. Wubbolts et al. developed this widely used technique for the quantification of the solubility of solutes at elevated pressures in terms of solute saturation mole fractions [16,17]. The solubilities of the solutes PCM and PVP were measured in the systems C02/ethanol, C02/acetone, and in mixtures of C02/ethanol/acetone. The measurements were carried out in a variable volume high-pressure view cell like shown in Fig. 24.5 left. The cell is equipped with a magnetic stirrer and a heating jacket and can be tempered using a thermostat. To monitor the conditions inside the vessel, a PtlOO-resistant thermometer and a pressure indicator are mounted at the appropriate... 

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