Supercritical heating rate

The technique was implemented as follows. With solid naphthalene in our solubility cell we brought the system to a desired temperature and C02 pressure such that solid-supercritical gas equilibrium existed. The temperature was then slowly increased (heating rate approximately 1°C/hour) at constant pressure, while the NMR signal was monitored. When the S-L-G line was intersected, the solid naphthalene in the cell would melt with the formation of the naphthalene-rich liquid phase, and this resulted in a large and rapid increase in our NMR signal. The temperature at which we saw this discontinuous jump in our NMR signal gave the location of the phase line at that pressure. 

Drying to remove solvent from a gel drying method (e.g. evaporative vs. supercritical vs. freeze drying) temperature and heating rate pressure and pressurization rate time... 

Figure 6 Pressure effect on the temperature-induced and gas-assisted melting of tetracosane and PVDF (for more details and explanations, see refs. 26 and 29) (al) and (a2) heat rate evolution during fusion in the presence of supercritical CH and C 2 2 (VF), respectively (bl) fluid phase equilibria in the tetracosane/methane system and (b2) partial p—T phase diagram for the PVDF-VF and PVDF-N2 systems. Note the depression in the melting/crystallization temperatures in the pressure range up to 30 MPa for the tetracosane/CH and PVDF/VF systems...

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. 

Figure 6-16. Relative density versus temperature for the YAG powder compacts formed from (o) the supercritically dried gel and ( ) the conventionally dried gel during constant heating rate sintering at 5°C/min in air (Reproduced with permission from Manalert and Rahaman (1996) J. Mater. ScL, 31 3453—3458 Copyright 1996 Kluwer Acadentic Publishers.).

Process intensification can be considered to be the use of measures to increase the volume-specific rates of reaction, heat transfer, and mass transfer and thus to enable the chemical system or catalyst to realize its full potential (2). Catalysis itself is an example of process intensification in its broadest sense. The use of special reaction media, such as ionic liquids or supercritical fluids, high-density energy sources, such as microwaves or ultrasonics, the exploitation of centrifugal fields, the use of microstructured reactors with very high specific surface areas, and the periodic reactor operation all fall under this definition of process intensification, and the list given is by no means exhaustive. 

A power plant operating on heat recovered from the exhaust gases of internal-combustion < uses isobutane as the working medium in a modified Rankine cycle in which the upper pressure I is above the critical pressure of isobutane. Thus the isobutane does not undergo a change of p" as it absorbs heat prior to its entry into the turbine. Isobutane vapor is heated at 4,800 kPa to 2 and enters the turbine as a supercritical fluid at these conditions. Isentropic expansion in the turh produces superheated vapor at 450 kPa, which is cooled and condensed at constant pressure, resulting saturated liquid enters the pump for return to the heater. If the power output of the modi Rankine cycle is 1,000 kW, what is the isobutane flow rate, the heat-transfer rates in the heater condenser, and the thermal efficiency of the cycle ... 

When carbon dioxide is heated beyond its critical point, with a critical temperature of tc = 31.0 °C, a critical pressure of pc = 7.38 MPa, and a critical density of Pc = 0.47 g cm , the gaseous and the liquid phase merge into a single supercritical phase (SC-CO2) with particular new physical properties very low surface tension, low viscosity, high diffusion rates, pressure-dependent adjustable density and solvation capability ( solvation power ), and miscibility with many reaction gases (H2, O2, etc.). It can dissolve solids and liquids. The relative permittivity of an sc-fluid varies linearly with density, e.g. for SC-CO2 at 40 °C, r = 1.4 1.6 on going from 108 to 300 bar. This... 

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