In supercritical propane

Han S.J., Lohse D.J., Radosz M., and Sperling L.H. Thermoplastic vulcanizates from isotactic olypro-pylene and ethylene-propylene-diene terpolymer in supercritical propane Synthesis and morphology. Macromolecules, 31, 5407, 1998. 

Crystallisation of isotactic PP from homogeneous solution in supercritical propane yielded open-cell foams of high surface area. Their morphology usually consisted of microspheres with a dense core and a porous periphery... 

Propane or propane/C02 mixtures as liquid, near-critical, or supercritical fluids enhance the solubility of fats and oils (Harrod et al., 2000 Weidner and Richter, 1999). The decrease in viscosity and increase in diffusivity results in a higher hydrogenation rate (Figure 14.4). Harrod et al. (2000) have also demonstrated activity increases by reducing mass-transfer limitations in supercritical propane. 

The nonstatistical population is the group of molecules that directly cross the diradical and produce 32x. Carpenter hypothesized that with increasing pressure, collisions will become more common such that energy will be redistributed away from the modes that lead to direct crossing of the diradical, yielding a more statistical product distribution. In other words, collisions provide the barrier so that the momentum can be redirected. The reaction of 2>l-d2 was carried out in supercritical propane in order to control the pressure. The ratio of 32x to 32n did... 

Reverse micelle and microemulsion solutions are mixtures of a surfactant, a nonpolar fluid and a polar solvent (typically water) which contain organized surfactant assemblies. The properties of a micelle phase in supercritical propane and ethane have been characterized by conductivity, density, and solubility measurements. The phase behavior of surfactant-supercritical fluid solutions is shown to be dependent on pressure, in contrast to liquid systems where pressure has little or no effect. Potential applications of this new class of solvents are discussed. 

Figure 7. Conductivity of reverse micelle phases in supercritical propane and liquid iso-octane at various pressures, W = 1.

The size of w/c microemulsion droplets has been measured by neutron scattering for a di-chain hybrid surfactant (C7Hi5)-(C7Fi5)CHS04 Na [32], 667 g/mol PFPE-C00"NH4 [33], and for a partially fluorinated di-chain sodium sulfo-succinate surfactant [34]. For the PFPE-COO NH4 surfactant, the droplet radius increases from 20 A to 36 A for W o values of 14 and 35, respectively. For the di-chain sodium sulfosuccinate surfactant, droplet radius varied linearly from 12 to 36 A as Wo increased from 5 to 30. This linear relationship has also been shown for AOT reverse micelles in organic solvents [7]. In each of these studies for a one-phase microemulsion, droplet size and Wq were found to be only a weak function of pressure, unless the pressure is reduced to the phase boundary where droplets aggregate. This trend was calculated theoretically [6,23] and has been measured in AOT w/o microemulsions in supercritical propane [35,36]. 

Supercritical fluids exhibit quite different extraction capacities if their molecular weights are different. Fig. 4.8-11 shows the durability of alkylation reaction activity where 2-methyl-butane, 2-methyl-propane and propane in the supercritical state were utilized as the reaction medium. It should he mentioned that 2-methyl-butane and 2-methyl-propane were reactants as well. For the 2-methyl-butane case, hardly any deactivation was observed, but the initial yield was low (20 %). In contrast, a high initial yield of about 60 % was reached in the reaction in supercritical propane while deactivation was the most pronounced in this SCF. The reaction conducted in 2-methyl-propane showed intermediate results, compared to the reactions in 2-methyl-hutane or propane. 

The reason for the low alkylate yield in the reaction in 2-methyl-butane was most likely the high reaction temperature. High reaction temperatures favored side reactions, reducing the selectivity of alkylate. Indeed, C5-C7 hydrocarbon products formed in high selectivity in the high temperature reaction conducted in supercritical 2-methyl-butane. It is possible that hydrocracking occurred as a side reaction at the same site where the alkylation reaction proceeded. The temperature of the reaction with propane was low and the side reactions were effectively suppressed. The deactivation of this reaction is probably due to the poor extraction capacity of the propane medium, especially at the low reaction temperature used here. The low solubilities of catalyst poisons in supercritical propane at these reaction conditions deactivated the catalyst. 

The plant is multipurpose. The catalysts within the reactor can be changed to alter the chemistry. A view of the actual reactors may be seen in Figure 4. The plant, which is designed to work only with CO2 as the SCF, went on stream in June 2002 (a rather smaller plant for reactions in supercritical propane has recently been built in Goteborg [46]). 

PRA Pradhan, D. and Ehrlich, P., Morphologies of microporous polyethylene and polypropylene crystallized from solution in supercritical propane, J. Polym. Sci. Part B Polym. Phys., 33, 1053, 1995. 

The Borstar process involves the use of two cascaded reactors. In the first stage, ethylene is polymerized in supercritical propane by the addition of a transition metal catalyst in a loop reactor, which leads to low-molecular-weight polyethylene. The reaction mixture is then transferred into a gas-phase reactor in which high-molecular-weight polymers are formed. The direct result of this two-stage process is an intimate mixing of the two polymer fractions, which differ in their molar masses. 

In Table 1.1, the critical properties of some compounds which are commonly used as supercritical fluids are shown. Of these, carbon dioxide and water are the most frequently used in a wide range of applications. The production of polyethylene in supercritical propane is described in a loop reactor [13]. Supercritical ethylene and propylene are also apphed, where they usually act both as a solvent and as the reacting monomer. In the field of polymer processing, the Dow Chemical Company has developed a process in which carbon dioxide is used to replace chlorofluorocarbon as the blowing agent in the manufacture of polystyrene foam sheet [14, 15]. 

In our opinion, the process concept for the catalytic polymerization of olefins in SCCO2 should include a loop reactor type of apparatus (Fig. 8.16), as described by Ahvenainen et al. for the polymerization of ethylene in supercritical propane [45]. In this type of reactor, the residence time can be adjusted to sufficiently long values to obtain a reasonable conversion. Extending the concept to... 

Phase Behaviour Palmitic Acid and Its Derivatives in Supercritical Propane... 

Unfortunately, the use of reverse micelles in supercritical propane was somewhat disappointing. Phenol, naphthol and resorcinol were separated using a 0.05 M AOT-0.25 M water reverse micellar phase in supercritical propane. However the efficiencies obtained were average, in the 5000 plate range (h = 10 dp) for a 250x 1 mm 5pm column [9]. Neither the FID universal detector nor the mass spectrometer could be used due to the AOT molecules. The adjustment of the AOT/water ratio required a complex pumping arrangement. SFC as a separation technique is used less frequently. Micellar SFC would need more work to fully understand the physical and chemical processes involved in the separation of polar and apolar solutes. At the moment, this path seems to be set aside. 

As a consequence of the very low viscosity, reaction rates can be very high in supercritical media. This was recently demonstrated for hydrogenation of TGs in supercritical propane (Harrod and Moller, 1996). The reaction took place in a small cell, and reaction rates up to 1000 times higher than those obtained with traditional techniques were reported. 

Lang X, Akgerman A, Bukur DB. Steady state Fischer-Tropsch synthesis in supercritical propane. Ind. Eng. Chem. Res. 1995 34 72-77. 

A dual reactor process consisting of a loop operated in supercritical propane followed by a fluidised bed gas phase reactor has been developed especially for the production of bimodal polyethylene. This reactor combination gives the flexibility to both broaden the molecular weight distribution and to produce low density PE thus expanding the feasible operating window in terms of density of the final bimodal product to cover the whole range from LLDPE to HOPE. 

BL Knutson, AK DUlow, CL Liotta, CA Eckert. Kinetics of a Diels-Alder reaction in supercritical propane. In KW Hutchenson, NR Foster, eds. Innovations in Supercritical Fluids Science and Technology. ACS Symposinm Series No. 608. Washington, D.C. American Chemical Society, 1995, pp 166-178. 

One of the first reactions carried out in a SCF micelle system was the formation of A1(0H)3 from A1(N03)3 and ammonia (76). This mlcroemulsion system consisting of A1(N03)3 dissolved in water, supercritical propane, and surfactant was contacted with dry ammonia to form Al(OH)3. The ammonia, which is soluble in supercritical propane, diffused into the micelles and reacted with the A1(N03)3 in the aqueous phase. Particle size was shown to be a function of concentration. 

Microemulsions in SCFs have been used for the preparation of nanoparticles from several classes of materials (56,245-248). In an early publication (56), Matson et al. reported the production of nanometer- to micrometer-sized A1(0H)3 particles through the use of AOT-based reverse micelles in supercritical propane. The experiment involved a simple precipitation reaction of aqueous... 

---