Carbon dioxide expanded liquids

A detailed analytical study of fhe acfivity of some solid acid catalysts, including mesoporous silica-supported Nation, in the acylation of anisole with AAN allows the conclusion that catalyst deactivation is caused by the primary ketone product and/or multiple acetylated products in the micropores of Nation catalyst aggregates. i Experiments were performed with a commercially available silica-supported Nation catalyst in a continuous-mode slurry operation by using carbon-dioxide-expanded liquids (nitromethane or nitrobenzene) as solvents. At 90°C, 80% AAN conversion is observed with a TOS of 2 h, but the catalyst rapidly deactivates, and 27% conversion is evaluated after 6 h TOS with a TON value of about 400. The catalyst can, however, be completely regenerated upon nitric acid treatment. These results confirm that silica-supported Nation catalysts are promising alternatives for the traditional aluminum chloride homogeneous Lewis acid catalyst. 

As has already been described in Table 9.1, transport properties are enhanced in CXLs compared with conventional solvents. For example, diffusivities of solutes are enhanced up to 7-fold in carbon dioxide expanded methanol, with little effect being seen on the nature of the solute (benzene pyrazine). Therefore, it is thought that physical rather than chemical interactions are causing this phenomenon, including reduced viscosity and surface tension upon carbon dioxide addition. The solubility of solids, liquids and gases in CXLs will... 

Once the liquid phase is separated from the gas, it is diverted to impinge on the wall of a glass vessel like a simple test tube or collection bottle. The liquid runs down the wall while the gas exits the top. The carbon dioxide expands 500 times. Under typical operating conditions, 25-30 L/min of gas exits out the top of the test tube or bottle. The waste gas is diverted through a waste collection container and then vented outside. A small amount of the modifier, like methanol, is present in this waste stream (due to the vapor pressure of the compound). As with the cyclone separator, the user is never exposed to the effluent of the chromatograph. 

Repeat step 1 using ethanol for both copper and phenylenediamine solutions. This time, when you vent the system after 45 min, place a carbon TEM grid at the base of the collector vessel (the instmctor will point this out). This technique, known as RESS (rapid expansion of the supercritical solution), is a unique benefit of performing reactions in supercritical fluids. When the system is vented, the gas/liquid carbon dioxide expands, being rapidly converted from its original... 

SoIldifica.tlon. Liquid carbon dioxide from a cylinder may be converted to "snow" by allowiag the Hquid to expand to atmospheric pressure. This simple process is used only where very small amounts of soHd carbon dioxide are required because less than one-half of the Hquid is recovered as soHd. 

The HC1 dissolved the dolomite, forming carbon dioxide (COj) gas. Under normal circumstances this gas remains in solution, but if the temperature of the acid or the acid concentration exceed certain limits, C02 evolves as a gas and accumulates in the upper portion of the cavity. The escape of even small amounts of C02 into the injection pipe can serve as a driving force to reverse the flow of the injected liquids, because as the C02 rises, pressure decreases and the gas expands. 

Cryo-cleaning, which is a blasting process that uses dry ice. Similar in size to rice corns, the granules are created by expanded liquid carbon dioxide. By impact, they clean and sublime directly into the gas phase ... 

The gaseous phase of any material occupies significantly more volume than either its solid or liquid phase, (a) Solid carbon dioxide (dry ice) is broken up into powder form, (b) The powder is funneled into a balloon, (c) The balloon expands as the contained carbon dioxide becomes a gas as the powder warms up. 

Carbon dioxide, either as an expanded liquid or as a supercritical fluid, may be a viable replacement for a variety of conventional organic solvents in reaction systems. Numerous studies have shown that many reactions can be conducted in liquid or supercritical C02 (sc C02) and, in some cases, rates and selectivities can be achieved that are greater than those possible in normal liquid- or gas-phase reactions (other chapters in this book Noyori, 1999 Savage et al., 1995). Nonetheless, commercial exploitation of this technology has been limited. 

The triple-point crystallization of carbon dioxide is illustrated in Figure 7, which shows a schematic carbon dioxide phase diagram expanded about the triple-point and a closed-cycle triple-point crystallizer operating with pure carbon dioxide. The operation of this closed-cycle unit is identical to that of a unit in the stripping section of a continous crystallizer cascade, except that in the cascade vapor would pass to the unit above, and liquid would pass to the unit below. 

Deposition of carbon dioxide gas occurs only with some help from humans. Carbon dioxide gas is compressed with pressure into a liquid and cooled. Then the liquid is allowed to expand at normal pressures. This expansion happens so quickly that much energy, or... 

Crosslinked Polystyrene. Polystyrene lightly crosslinked during polymerization by 0.01-0.25% divinylbenzene provides foams, expanded by carbon dioxide or other gases, with greater expandability and resistance to collapse at elevated temperatures (102, 103). Other divinylbenzene copolymers are reported, employing as blowing agent saturated aliphatic or fluoroaliphatic volatile liquids, tetramethylsilane, and azobis-isobutyronitrile (99,106, 108). 

Foaming methods vary widely. One is to whip air into suspension or a solution of the plastic, which is then hardened by heat curing. A second is to dissolve a gas in a mix, then expand it when the pressure is reduced. Another is to heat a mixture until one of its liquid components volatilizes. Similarly, water produced in an exothermic chemical reaction can be volatilized within the mass by the heat of reaction. A different technique uses a chemical reaction to produce carbon dioxide gas within solid mass. A related way is for a gas such as nitrogen to be... 

Liquid carbon dioxide (purity 99, 95 Vol %) was undercooled (W2) to avoid cavitation in the membran pump (P). After the compression to pre-expansion pressure, the fluid is heated to the extraction temperature (W3). The supercritical fluid loaded with anthracene leaves the extractor (V = 0,6 1). With a additional heat exchanger (W4), the solution is heated to pre-expansion temperature. In the separation vessel, the supercritical solution is expanded through a nozzle. The expanded gas will be condensed (Wl) and recompressed or let off. After the experiment, the separation vessel is opened and the particles were collected. The particle size is measured by laser diffraction spectroscopy (Malvern Master Sizer X). 

The linear dimerisation of butadiene with palladium(II) catalyst precursors has been investigated in [C4Ciim]+ with a variety of different anions.[24] Observed turnover frequencies, which range from 37-49 mol mol h, are affected only slightly by the nature of the ionic liquid or catalyst precursor. Best activities were obtained with four equivalents of triphenylphosphine per palladium at a reaction temperature of 70°C. Contrary to the reaction in THF, no formation of metallic palladium was observed and reuse of the catalyst solution was possible. Pressurising the reaction mixture with 5-10 bar of carbon dioxide led to a decrease in reaction rates, which was explained by decreased substrate solubility in the C02-expanded ionic liquid. 

Often the gas pressure is sufficient to use a turbo-expander which cools the gas to below 0 C and causes further condensation of hydrocarbon liquids. Because the gas stream also contains water, gas hydrate and ice formation can be a problem. This is prevented by the addition of an additive such as methanol. Following the removal of condensate, the gas stream is dried and if necessary treated further to remove acid gases such as hydrogen sulphide and carbon dioxide. 

Enhanced oil recovery (EOR) using carbon dioxide expansion is the largest scale application of gas expanded liquids. EOR using carbon dioxide aids in the flushing out of oil reservoirs carbon dioxide is injected into the well and displaces the remaining oil. It has several advantages over water, which can also be used in this process. For example, it lowers the viscosity of the crude oil, it... 

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