Open or Closed Vessels

One major benefit of performing microwave-assisted reactions at atmospheric pressure is the possibility of using standard laboratory glassware (round-bottomed flasks, reflux condensers) in the microwave cavity to carry out syntheses on a larger scale. In contrast, pressurized reactions require special vessels and scale-up to more 

---

Paint and varnish manufacturing Resin manufacturing closed reaction vessel Varnish cooldng-open or closed vessels Solvent thinning Acrolein, other aldehydes and fatty acids (odors), phthalic anhydride (sublimed) Ketones, fatty acids, formic acids, acetic acid, glycerine, acrolein, other aldehydes, phenols and terpenes from tall oils, hydrogen sulfide, alkyl sulfide, butyl mercaptan, and thiofen (odors) Olefins, branched-chain aromatics and ketones (odors), solvents Exhaust systems with scrubbers and fume burners Exhaust system with scrubbers and fume burners close-fitting hoods required for open kettles Exhaust system with fume burners... 

A case study on the influence of microwave-assisted reactions carried out in open or closed vessel has been described by Kappe and co-workers [ 158]. One of the examples deals with the cyclocondensation of tetrahydroquinohne and malonic esters. The reaction gave tricyclic hydroxyquinolones with loss of two molecules of ethanol, similar to the reaction described in Scheme 79. The results showed clearly that this reaction carried out in an open vessel gave more reproducible results. 

The caramelization process can be conducted in open or closed vessels. The mixture obtained is cooled and filtered, and then the pH and specific gravity are adjusted by the addition of acids, alkalis, or water. The chemical composition and properties of caramel colors depend on reactants used and technical conditions such as time, temperature, moisture content, and pressure. During the caramelization... 

Evaporation by steam-heat in open or closed vessels. 

General advantages of microwave heating for chemistry with either open or closed vessels, with or without solvents, now are well recognized [17,18]. In the main ... 

Varnish cooking-open or closed vessels Ketones, fatty acids, formic acids, Exhaust system with scrubbers and... 

Large Deviation from Plug Flow (Bo < 80) For Bo < 80, the tracer response curve is broad and passes the measuring point slowly, which leads to nonsymmetrical distribution curves (Figure 4.10.56a). Then the solutions of Eqs. (4.10.98) and (4.10.99) depend on the choice of the boundary conditions (open or closed vessel, closed-open, or open-dosed vessel), which do not necessarily satisfy actual experimental conditions. A dosed boundary condition at the inlet or outlet impUes that the vessel is isolated in the sense of communication with the connecting pipe. An open boundary condition presumes that the same flow distribution occurs in the vessel and in the connecting pipe. It also implies that any tracer injected at the inlet can appear upstream of the inlet. 

In burn-out experiments, a test section is part of a loop which may be open or closed, and the question arises as to whether or not any of the loop equipment, such as condensers, heaters, pumps, or pipe fittings, have any significant effect on the burn-out flux. This issue came to prominence at the Boulder Heat Transfer Conference in 1961 with a Russian paper by Aladyev (A4) describing burn-out experiments in which a branch pipe, connecting to a small vessel, was fitted close to the test section inlet. The test section itself was a uniformly heated tube 8 mm in diameter and 16 cm long. The results are reproduced in Fig. 9, and show burn-out flux plotted against exit steam quality. Curve (A) was obtained with the branch vessel filled with cold water,... 

In principle any of the equations 11.1.40, 11.1.44,11.1.45,11.1.47, or 11.1.48 could be used to determine the dispersion parameter. However, both equations 11.1.40 and 11.1.44 require that one accurately determine a small difference in large numbers to evaluate QjJuL. Hence equations 11.1.45 and 11.1.47 are preferred for evaluation of SiJuL for open and closed vessels, respectively. For small Q)JuL, equation 11.1.48 is appropriate. 

The pressure control system can equilibrate pressure change rates up to 20 bar/s. The outside guard heater can cope with temperature changes up to 100°C/min. A heat loss rate of less than 0.1°C/min can usually be achieved below 350°C and 25 bar [194]. The tests are run with either open or closed test cells in a closed outer bomb, which can be vented under specified conditions. The containment vessel can withstand pressures up to 100 bar. The use of a closed test cell results in the most severe pressure and temperature changes. 

The solution to this equation (unlike the partial differential equation 2.14) has been shown not to depend on the precise formulation of the inlet and outlet conditions, i.e. whether they are open or closed 051. In the following derivation, however, the reaction vessel is considered to be closed , i.e. it is connected at the inlet and outlet by piping in which plug flow occurs and, in general, there is a flow discontinuity at both inlet and outlet. The boundary conditions to be used will be those which properly apply to a closed vessel. (See Section 2.3.5 regarding the significance of the boundary conditions for open and closed systems.)... 

What if vessel oil outlet control loop fails open or closed ... 

In a disorete approach, the analytical system is confined in a vessel or container through the walls of which US energy is transmitted if an ultrasonic bath is used. The use of a US probe in this case can involve either to dip it into the vessel or into the transmitting liquid where the vessel is located. The complexity of the analytical system determines the type of vessel or container to be used, namely an open or closed, atmospheric pressure or pressurized device, a jacket-tailored device for maintaining the optimum temperature, etc. 

Laboratory-scale pyrolysers can be used for producing oils for analytical purposes. Many scientific and technical publications report on the pyrolysis of well-characterized polymers in open or closed reaction vessels, furnace-heated tubes, fixed-bed and fluidized-bed reactors. The pyrolysis products are generally analysed off-line, being condensed in cooled traps. 

Simple factors such as stirring or vessel shape may influence experimental results. Certainly whether or not the system was open or closed could have a profound effect. In addition, in the case of polyamides, there is the additional possibility of catalysis. 

---