High-pressure setup

High-pressure oxygen reactions were performed in an externally heated Rene alloy vessel. An illustration of the high-pressure setup is shown in Fig. I. The reaction chamber was pressurized at or below room temperature with high-purity oxygen. Reaction temperatures were measured at a shallow recess in the reactor wall at the sample position, and pressure measured with an uncalibrated gauge. High-purity deionized water was used in all procedures. 

Figure 7.6 schematically shows the setup of gas introduction for the high-pressure reactor. For gas introduction, the male part of a Swagelok fitting (4 in Figure 7.6) is welded on a 1/8 in. tube of the cell lid (3 in Figure 7.6). A 1/32 in. PEEK tube...

The products were extracted with the mobile SCCO2 phase and isolated by controlled expansion after leaving the high-pressure reactor. A stable performance was achieved over more than 40 h time on stream with this simple setup. 

In the last decade methods of combinatorial catalysis and high throughput experimentation has obtained great interest [1-4]. In the field of heterogeneous catalysis most of the efforts are devoted to the investigation of gas phase reactions, where several hundreds catalysts can simultaneously be tested [5,6]. Contrary to that, in high-pressure liquid phase catalytic reactions in a single reactor module only 8-16 parallel experiments can be performed. There are reports to use up to six modules as a parallel setup [7]. 

Fig. I Experimental setup for UV-VIS spectroscopy under high pressures...

Injecting ions into a drift tube becomes increasingly more difficult with increasing drift tube pressure. However, high drift tube pressure is desirable for high ion mobility resolution. For these reasons omitting MSI is a common simplification of the basic setup in Fig. 1 and is typically found in analytical IMS-MS [35] and other high pressure drift tube applications (see Sect. 3.3) [36]. 

An experiment with a dilute ceramic suspension was made as follows A very small quantity of silicon carbide particles (d 6 /xm) was dissolved in silicon oil ( 350mPas). The suspension was pumped at high pressure through a glass capillary (d = 0.6 mm). The experimental setup is shown in Fig. 3. The velocities of the silicon carbide particles in the capillary are detected by an optical sensor. From these data, the statistics of the particles velocities is calculated. Due to the optical properties of the sensor, the particles are only detected in a wedge-like sector of the cross-section of the capillary. The measured velocity distribution of the particles (Fig. 4) depends on the shape of this sector and, additionally, on the measuring tolerances of the sensor. 

Today a stopped-flow instrument consists of oifly the unit itself combined with a diode array detector and a computer allowing fast kinetic measurements of time-resolved UV-vis spectra under anaerobic, high pressure and/or low temperature conditions. Improvements have been made as well, for example, syringes are installed vertically instead of horizontally (to avoid problems with gas bubbles) and polyetheretherketone (PEEK) is used instead of Teflon for valves and flow tubes to improve the anaerobic capabilities of the instrument. Further, the syringe drives setup was optimized. Application of rapid-scan devices (usually, but not exclusively, diode arrays) allows complete spectra to be collected at very short time intervals during a reaction. 

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