Equipment Supercritical reactors

In order to study the catalyst deactivation phenomenon under supercritical conditions and the difference between the liquid phase (LP) and supercritical fluid phase (SCFP) reactions, experiments were carried out in an isothermal tubular reactor (D=I2 mm, L=600 mm) packed with grounded Y-type zeolite pellets of 60 mesh. The experimental equipment for the LP and SCF reaction processes is illustrated in Figure 1. 

The experimental unit consists of an Autoclave Engineers Supercritical Extraction Screening System (SCESS) equipped with a 300 cc packless autoclave reactor in place of the standard extractor vessel. The schematic of the experimental unit is shown in Figure 7. The unit is composed of three sections the feed preparation section, the autoclave reactor section and the sampling section. 

Basic research efforts with respect to supercritical water and SCWO have been directed within a number of areas that are critical for design and optimization of a SCWO reactor and ancillary equipment. These areas include physical property measurement and correlations, kinetics and reaction mechanisms, salt equilibrium and transport behavior, and corrosion. 

All experiments were conducted in a 0.5 L batch-type reactor (Taiatsu Techno MA22) that was equipped with an automatic temperature controller and had a maximum pressure of 30 MPa and a maximum temperature of 400°C (Fig. 1) (Mursito et al., 2010). The raw peat samples were introduced to the reactor without any pretreatment except for milling. The amount of the raw peat added to the reactor was 300 g, which corresponded to 40 g of moisture-free peat. The reactor was pressurized with N2 to 2.0 MPa at ambient temperature, after which the raw peat was agitated at 200 rpm wliile the reaction temperature was automatically adjusted from 150°C to 380°C at an average heating rate of 6.6°C/min. Under supercritical conditions (380°C), the charge was 230 g and the initial pressure was 0.1 MPa. After the desired reaction time of 30 min, the reactor was cooled immediately. 

Supercritical carbon dioxide represents an inexpensive, environmentally benign alternative to conventional solvents for chemical synthesis. In this chapter, we delineate the range of reactions for which supercritical CO2 represents a potentially viable replacement solvent based on solubility considerations and describe the reactors and associated equipment used to explore catalytic and other synthetic reactions in this medium. Three examples of homogeneous catalytic reactions in supercritical CC are presented the copolymerization of CO2 with epoxides, ruthenium>mediated phase transfer oxidation of olefins in a supercritical COa/aqueous system, and the catalyic asymmetric hydrogenation of enamides. The first two classes of reactions proceed in supercritical CO2, but no improvement in reactivity over conventional solvents was observed. Hythogenation reactions, however, exhibit enantioselectivities superior to conventional solvents for several substrates. 

The discussion above suggests an approximate minimum value of 5 = 7 for most reactions. For neat supercritical CO2,5 falls below 7 at a temperature of 83 C at 6000 psi and at 130 C at 10,000 psi using equation 6. The lower temperature limit is set by the critical temperature of CO2 31. TC. Thus, for most workers, the useful range for synthesis in supercritical CO2 is likely to be 31 < T < 83 C, P < 6000 psi. The outer Imiit, without die use of fairly specialized and expensive equipment is 31 < T < 130 C, P < 10,000 psi. If higher pressures are required, they may be most easily achieved using flow reactors, (which also scale more easily). How reactor methods for synthesis in supercritical carbon dioxide have been pioneered by Poliakoff and coworkers. 74) In practice, such reactors closely resemble those ady used for hydrothermal processing. 

Another very useful solvent for polymerization of (semi)fluorinated monomers in homogeneous solution is supercritical carbon dioxide (SCCO2) due to its high ability to dissolve fluorinated compounds. CO2 reaches the critical point at = 31°C and= 73.75 bar. Thus, high pressure cells are needed and special equipment, such as tubular reactors described by Beuermann et al. [69], has to be used. This type of reactor was also applied for the (controlled) radical polymerization of sf... 

Rosen, M.A., Naterer, G.F., Chukwu, C.C., Sadhankar, R., Suppiah, S., 2012. Nuclear-based hydrogen production with a thermochemical copper—chlorine cycle and supercritical water reactor equipment scale-up and process simulation. International Journal of Energy Research 36 (4), 456—465. 

The derived correlation can be used for supercritical fluid heat transfer calculations, in circular and other flow geometries, for heat exchangers, steam generators, nuclear reactors and other heat transfer equipment, for future comparison with other datasets, and for verification of computer codes and scaling parameters between water and modeling fluids. This correlation can be also used for supercritical carbon dioxide and other fluids. However, its accuracy might be less in these cases. Some specifics of pressure-drop calculations were also listed in the paper. 

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