Supercritical carbon dioxide atoms

Conventional nitrocellulose lacquer finishing leads to the emission of large quantities of solvents into the atmosphere. An ingeneous approach to reducing VOC emissions is the use of supercritical carbon dioxide as a component of the solvent mixture (172). The critical temperature and pressure of CO2 are 31.3°C and 7.4 MPa (72.9 atm), respectively. Below that temperature and above that pressure, CO2 is a supercritical fluid. It has been found that under these conditions, the solvency properties of CO2 ate similar to aromatic hydrocarbons (see Supercritical fluids). The coating is shipped in a concentrated form, then metered with supercritical CO2 into a proportioning airless spray gun system in such a ratio as to reduce the viscosity to the level needed for proper atomization. VOC emission reductions of 50% or more are projected. 

Supercritical atomization in spray coating, 7 70 Supercritical carbon dioxide, 9 456,24 2, 15 applications of, 24 20 as a medium for chemical reactions, 12 808-809... 

Amorphous fluoropolymers have many applications in the areas of advanced materials where they are used in applications requiring thermal and chemical resistance. Their manufacture is hindered by their low solubility in many solvents. Many fluoropolymerizations cannot be carried out in hydrocarbon solvents because the radical abstraction of hydrogen atoms leads to detrimental side reactions. Chlorofluorocarbons (CFCs) were thus commonly used, but their use is now strictly controlled due to their ozone depleting and greenhouse gas properties. Supercritical carbon dioxide is a very attractive alternative to CFCs and it has been shown that amorphous fluoropolymers can be synthesized by... 

Class 5 Liquids with no hydrogen-bond forming capability and no donor atoms, e.g., hydrocarbons, carbon disulfide, carbon tetrachloride, supercritical carbon dioxide, etc. 

The mole fraction solubilities of ten copper(II) and five chromium(III) P-diketo-nates were measured in SCCO2 with a spectroscopic technique and found to vary over four orders of magnitude. Observed trends indicate that the solubility in supercritical carbon dioxide is strongly dictated by the character of the hydrocarbon or fluorocarbon shell surrounding the central metal atom. A regular solutions approach was used for Cr(acac)°3 to quantitatively attempt to predict the solubility in SCCO2. Solubility... 

In what follows, we present new fluorescence spectra for pyrene in supercritical carbon dioxide. This is followed by molecular dynamics results on density augmentation in a mixture of Lennard-Jones atoms whose potential parameters were chosen so as to simulate pyrene and carbon dioxide. Finally, we compare the experimental and computational results, thereby obtaining information on the magnitude and extension of the density enhancements suggested by the experiments. 

Fletcher, B. Suleman, N. K. Tanko, J. M. Free Radical Chlorination of Alkanes in Supercritical Carbon Dioxide The Chlorine Atom Cage Effect as a Probe for Enhanced Cage Effects in Supercritical Fluid Solvents. J. Am. Chem. Soc. 1998, 120, 11839-11844. 

Xia, J. H. Johnson, T. Gaynor, S. G. Matyjaszewski, K. DeSimone, J. Atom Transfer Radical Polymerization in Supercritical Carbon Dioxide. Macromolecules 1999, 32, 4802-4805. 

The use of supercritical carbon dioxide (CO2) as a component in a solvent mixture is another ingenious technique to reduce VOC emission by 50 percent or more. This technique takes the advantage of the fact that CO2 is a supercritical fluid below its critical temperature (31.3°C) and critical pressure (7.4 MPa). Sohd coating and supercritical CO2 are metered into a proportioning spray gun in such a ratio so as to reduce the viscosity to the level needed for proper atomization. Airless spray guns are used. 

Figure 2 shows an example of separating organomercury using supercritical CO2. A 10-m X 50- tm-in-ner diameter SB-Methyl 100 column was used for the separation. Due to their poor solubility in supercritical carbon dioxide, monoorganomercury compounds were derivatized by diethyldithiocarbamate. An interface for a system consisting of SFC and atomic fluorescence spectrometry was developed for the detection of organomercurials. 

An important property of supercritical fluids and one that is related to their high densities (0.2 to 0.5 g/cm ) is their ability to dissolve large nonvolatile molecules. For example, supercritical carbon dioxide readily dissolves /t-alkanes containing 5 to 22 carbon atoms, di-n-alkylphthalates in which the alkyl groups contain 4 to 16 carbon atoms, and various polycyclic aromatic hydrocarbons consisting of several rings. ... 

Supercritical carbon dioxide, ethane, and propane have been examined for the fractionation of paraffin wax. The original feed contained wax molecules with 10-35 carbon atoms. A narrower carbon distribution is needed in the printing ink, cosmetics, and pharmaceutical applications. Based on the cost analyses, vacuum distillation was proposed to be a cheaper option for light paraffin wax, whereas supercritical fractionation... 

The environmentally benign nature of carbon dioxide comes from its very stable molecular bonds, which in turn do not provide high polarity. In fact, a carbon dioxide molecule has only a weak quadrupole moment, due to minor charge separation on oxygen and carbon atoms. Hence, the molecular interaction with most polar and heavy substances of interest is minor, providing only a weak solvent power. If needed, a small amount of cosolvent (also termed as entrainer or modifier) is added to enhance polarity and affinity with solutes. In many applications, however, the design limitation is the solubility of the substance in supercritical carbon dioxide. Therefore, the solubility data are essential both for the initial feasibihty study and final process design. 

S.R. Bysouth, J.F. Tyson, Supercritical carbon dioxide as a carrier for sample introduction in atomic absorption spectrometry, Anal. Chim. Acta 258 (1992) 55. 

Various alternative precursor delivery processes have been designed specifically to circumvent the low volatility and low thermal stability problems associated with (Ba(dpm)2 (see Sect. 2.4.1.2). The first method involves the dissolution of Y(dpm)j, Ba(dpm)2 and Cu(dpm)2 precursors in solvents such as butylacetate [188], THF [153, 156], toluene [189], decane [190] and supercritical carbon dioxide [191]. According to this process, termed aerosol-assisted CVD (AACVD), the multicomponent precursor solution is atomized or vaporized into a carrier gas stream or directly into the reaction chamber, with deposition occurring on a heated substrate. Some attractive features of AACVD include deposition at atmospheric pressure, the ability to use thermally sensitive precursors, and a high precursor transport rate [189]. Figure 2-30 shows a sum-... 

One would expect that basic free amino groups in enzymes could react with acidic supercritical carbon dioxide to form carbamates. Free amino groups exist in lysine, histidine, and arginine. Kamat et al. [20] obtained direct evidence that carbon dioxide forms carbamates with subtilisin, which is a protease with nine lysine groups. They used laser desorption mass spectrometry (LD-MS) to accurately measure the molecular weight increase when subtilisin was placed in dry ice . Subtilisin s molecular weight increased by 176 atomic mass units the weight of four CO2 molecules. The formation of carbamates was reversible. As the dry ice sublimed under vacuum. 

Heise, Palmans, de Geus, Villarroya and their collaborators (17,41,42) have been working on a chemoenzymatic cascade synthesis to prepare block copolymers. They combine enzymatic ring-opening polymerization (eROP) and atom transfer radical polymerization (ATRP). The synthesis of block copolymers was successful in two consecutive steps, i.e., eROP followed by ATRP. In the one-pot approach, block copolymers could be obtained by sequential addition of the ATRP catalyst, but side reactions were observed when all components were present from at the onset of reactions. A successful one-pot synthesis was achieved by conducting the reaction in supercritical carbon dioxide. 

SAA, supercritical assisted atomization This process is based on the solubilization of a fixed amount of supercritical carbon dioxide in the liquid solution then the ternary mixture is sprayed through a nozzle, and as a consequence of atomization, solid particles are formed ]. 

Here c and are the concentrations of the substance under test in the stationary and mobile phase respectively, F" and F are the volumes of the stationary and mobile phase in the column, and is the retention time of an inert substance. From measurements of and f the capacity ratio k, and from this the partition coefficient K, can be calculated. In Figure 37 experimentally determined log k values are plotted against the density p and the pressure p of supercritical carbon dioxide at 40 C as a mobile phase for SFC experiments with alkanes having between 10 and 30 carbon atoms a chemically bonded stationary phase (Carbowax 400 on Porasil C) was used and further details are given in the caption of Figure 37. > The curves show that with increasing density the retention time f and the capacity ratio k decrease and consequently the... 

Unlike liquid solvents, supercritical carbon dioxide does much more than dilute the coating to a low spray viscosity - it changes the nature of the atomization mechanism. Thus, low spray viscosity is less important than with conventional spray methods, and many new factors contribute to the spray-ability of the coating. 

Unlike previously developed, low-pollution spray systems, the coatings produced by the supercritical carbon dioxide spray are of high quality and thus are highly marketable. Due to the unique decompressive atomization mechanism caused by choked flow, the new spray has a feathered pattern with a narrow droplet-size distribution which produces coatings of more uniform thickness than those of conventional sprays. 

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