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Supercritical fluid cleaning - McHardy J.

McHardy J., Sawan P.S. Supercritical fluid cleaning - Noyes publications, 1998. - 304 p.
Download (direct link): spercrificalfluidcleaning1998.pdf
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Polyoxyethylene 4-nonyl phenol 44 388 --- (47)
Polyoxyethylene 6-nonyl phenol 388 --- (47)
2-Tert-dodecylmercaptoethanol 169-377 --- (47)
Glyceryl monostearate u 388 --- (47)
Morpholinium perfluorooctanate 44 133 1-6 (47)
Bis(2-ethylhexyl) amine 44 213-278 --- (47)
n-Hexadecyl morpholine 44 202 --- (47)
F(CF2)75S02N(C2H5) (C2H4OH) 44 169 --- (47)
c8f17 S02N(C2H5)H u 109 --- (47)
Ami nopolyfluorosulfonate 136-160 --- (47)
CSF, 7S02N(C2Hs)(CH2C00K) a 300-500 6-8 (47)
Trimethyl fluoroalkyl
ammonium iodide a 160-500 12 (47)
Silicone based surfactants 40 300 --- (48)
Bis(poly(hexafluoropropylene
oxide))hydroxy aluminum (( 120 --- (48)
Sodium poly(hexafluoropropylene
oxide) carboxylate 160 --- (48)
Ammonium poly(hexafluoropropylene
oxide) carboxylate 120 --- (48)
Ammonium poly(hexafluoropropylene
oxide) carboxylic acid 120 --- (48)
Bis(dodecafluoroheptyl) sodium
sulphofumarate it 84-140 --- (48)
C7F15CH(0S03 Na+) C7H15 25-60 74-300 Up to 32 (46)
Ci2E03 40 200-400 --- (28)
C12E08 (t (( --- (28)
C8Ej 60 Up to 400 5 (63)
CE 50 10-100 --- (64)
65 300-500 0.32 % (w/w) (38)

Microemulsions in supercritical fluids generally have a limited capacity for the dissolution of water. As the W value increases, the size of the droplets increases to the point where the increased interdroplet attractive interactions lead to coalescence and phase separation. Figure 2 demonstrates this phenomenon for an AOT microemulsion formed in supercritical propane. In Fig. 2, the regions to the right of the solid lines represent one-phase clear microemulsions whereas the regions to the left of the solid lines are two-phase regions. At 103C and 100 bar, the maximum Wvalue is about 4 and this increases substantially at higher pressures up to a W of 13 at 300 bar. Thus the phase behavior and maximum W value can be manipulated using the pressure or density of the fluid in contrast to microemulsions formed in liquid alkanes where pressure has little or no effect. For cleaning operations, this type of behavior is important to understand in order to effectively implement these systems. The highly pressure-dependent phase behavior may also be exploited in a cleaning process to obtain a more effective cleaning cycle and may play a role in the recycle/recovery of the surfactant phase.
Water
Figure 2. Phase diagram of an .407/water/supercritical propane system in the oil-rich corner of the ternary phase diagram. The regions to the right of the solid lines are the one-phase, clear microemulsions. The various W value lines ([HzO]/ [AOT]) are also indicated. The temperature of the system is 103C. (Compositions are given in weight percent.)
The properties of the supercritical alkane microemulsions given in Table 1 can be summarized as follows.1231 For methane and ethane, the droplet size is relatively small corresponding to a Wno larger than about 10 for pressures up to 500 bar. At these W values, the solvent polarity of the microemulsion is just at the threshold for that of bulk water. For near-critical and supercritical propane, the W values can be as high as 20 to 30, with the highest amount of water being obtained in the lower-temperature near-critical fluid region. A near-critical propane microemulsion (T = 25C) is capable of dissolving appreciable amounts of almost all species that are soluble in bulk water including high molecular weight proteins.
Nonionic, cationic and zwitterionic surfactant systems have also been identified for supercritical and near-critical fluids. Many of the nonionic surfactants of the class of polyethylene glycol dodecyl ethers (QEOj) have been investigated as has the cationic surfactant, didodecyldimethyl ammonium bromide or DDAB. These surfactants also form spherical structures, although the nonionic surfactant aggregates are generally much smaller than ionic surfactant aggregates. The zwitterionic surfactant, L-a-phosphatidylcholine (lecithin) forms giant rodlike structures leading to large increases in the viscosity of the microemulsion up to the point of gelation.
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