Carbon dioxide, as solvent

Description of extraction of grape seed oil by means of liquid and supercritical carbon dioxide as solvent (Gomez et al., 1996). 

Esterification between oleic acid and oleyl alcohol, catalyzed by the Mucor miehei immobihzed hpase in a batch-stirred tank reactor with supercritical carbon dioxide as solvent produced higher reaction rates at supercritical conditions than in the solvent-free system (Knez et al., 1995). 

Practicality has been an issue since many of the solvents referred to prior to 1994 have been quite expensive and the few others available have not had sufficient thermal stability to make them useful commercially. This chapter reviews our recent discovery of several commercially available cyclic perfluorocarbons as well as other halogenated fluids (and even carbon dioxide) as solvents for tetrafluoroethylene-containing polymers. We will describe solvation at atmospheric pressure, under autogenous conditions and under superautogenous... 

In addition, the polymerization itself can be performed in subcrit-ical carbon dioxide as solvent. Not that the critical point of carbon dioxide is at 37°C and 73 bar. 

Dense Carbon Dioxide as Solvent Medium for Chemical Processes... 

Fluorous Phases and Compressed Carbon Dioxide as Solvents 83... 

Micro emulsions can be formulated with carbon dioxide in supercritical state instead of a hydrocarbon as nonaqueous solvent. Fluorinated surfactants are commonly used to prepare such microemulsions. Water-in-carbon dioxide microemulsions can be made and the droplet size has been found to be similar to the size of the droplets of water-in-hydrocarbon micro emulsions with similar composition [21]. Such a microemulsion was used for conversion of benzyl chloride to benzyl bromide using KBr as hydrophilic nucleophile. The yield was an order of magnitude higher in the carbon dioxide microemulsion than in a conventional microemulsion at similar conditions, a fact that has been ascribed to low interfacial viscosity [22]. The big advantage with these micro emulsions is the environmental friendliness and the ease of work-up associated with carbon dioxide as solvent. 

All the methods of extracting caffeine take place before the beans are roasted. Caffeine and the other organic compounds that give coffee its taste are mainly non-polar. (Caffeine does contain some polar bonds, however, which allows it to dissolve in hot water.) Non-polar solvents, such as benzene and trichloroethene, were once used to dissolve and remove caffeine from the beans. These chemicals are now considered to be too hazardous. Today most coffee manufacturers use water or carbon dioxide as solvents. 

The ultimate in sustainable catalytic processes is the integration of chemocat-alytic and/or biocatalytic steps into catalytic cascade processes that emulate the metabolic pathways of the cell factory. It is an esthetically pleasing thought that, in the future, fuels, chemicals and polymers could be obtained from carbon dioxide and water as the basic raw materials via biomass, using sunlight as the external source of energy and water and supercritical carbon dioxide as solvents. The important difference between this bio-based scenario and the current oil-based one is the time required for renewal of the feedstocks. 

Wittmann K, Wisniewski W, Mynott R, Leitner W, Kranemann CL, Rische T, Eilbracht P, Kluwer S, Emsting JM, Elsevier CL. Supercritical carbon dioxide as solvent and temporary protecting group for rhodium-catalyzed hydro-aminomethylation. Chem Eur J 2001 7 4584-4589. 

The advantages of carbon dioxide as solvent have been well publicized it is, in fact, classified as GRAS - generally regarded as safe, it has low toxicity (threshold limit value - TLV = 5000 ppm), it is supercritical just above ambient temperature (critical temperature 31 C) and it is cheap. Also, like other supercritical fluids, it has advantageous gas-like transport properties, such as low viscosity and high diffusivity. 

The main drawback of spray-drying is the high temperatures needed. New technologies using compressed carbon dioxide as solvent do not need the utilization of relative high temperatures with the advantages to be nontoxic, environmentally friendly, and eliminated completely from the final product by depressurization (Varona et al., 2013). Particles from gas-saturated solutions... 

It was also reported that PPy could be polymerized using nontoxic supercritical fluids as solvents. In conventional chemical polymerization, incorporation of the oxidant into the polymerization process and/or washing to remove unwanted byproducts generates a large amount of environmentally hazardous solvent. In the process using supercritical fluid, which is nontoxic, nonflammable, and environmentally acceptable, PPy was polymerized within preformed polyurethane (PU) foam using supercritical carbon dioxide as solvent [41]. 

Darensbourg, D. J., Stafford, N. W. andKatsurao, T. (1995) Supercritical carbon dioxide as solvent for copolymerization of carbon dioxide and propylene oxide using a heterogeneous zinccarboxylate catalyst, J. Molecular Catalysis A Chemical 104, L1-L4. 

The BINAPHOS system has also been modified by using the perfiuoroalkyl-substituted derivative of (R,S)-B1NAPH0S (see Chapter 10) in the rhodium catalyzed hydroformylation of vinyl arenes in liquid or supercritical carbon dioxide as solvent This system leads to similar catalytic activity and the same level of enantiocontrol as the rhodium-(R,S)-BINAPHOS system in organic solvents [48]. 

Figure 12.7 Particles of benzoic acid precipitated using the RESS process with supercritical carbon dioxide as solvent. CourtoesyofA. Konig, Erlangen.

Walther D, Ruben M, Rau S (1999) Carbon dioxide and metal centres from reactions inspired by nature to reactions in compressed carbon dioxide as solvent. Coord Chem Rev 182 67-100... 

Figure 7.11 Extraction of a natural oil from roasted whole nuts using compressed carbon dioxide as solvent comparison between shrinking core model and experiment. p = 25l bar, T=308K,...

The selective acylation of hydroxyl functionalities of compounds bearing two stereogenic centers can lead to the formation of single diastereomers in enanti-omerically pure form, as occurs in the acylahon of different cyclic alcohols such as czs-and frans-l-(ferf-butoxycarbonyl)-4-hydroxypiperidine-3-carboxylate [69], trans-2-benzylindan-l-ol [70], frans-2-nitrocyclohexanol [71], frans-2-hydroxycyclohexane-carbonitriles, and ciS-5 -hydroxythalidomide (Figure 9.7), in the latter case using supercritical carbon dioxide as solvent [72]. 

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