Environmental issues carbon dioxide

As halogenated solvents are widely banned, either for health- or environmental reasons, the degreasing and cleaning of mechanical and electronic parts becomes a worldwide issue. Carbon dioxide, mainly in the liquid state, is becoming one of the most attractive substitutes for chlorinated solvents [25,26],... 

Rayon is unique among the mass produced man-made fibers because it is the only one to use a natural polymer (cellulose) directly. Polyesters, nylons, polyolefins, and acryflcs all come indirectly from vegetation they come from the polymerization of monomers obtained from reserves of fossil fuels, which in turn were formed by the incomplete biodegradation of vegetation that grew millions of years ago. The extraction of these nonrenewable reserves and the resulting return to the atmosphere of the carbon dioxide from which they were made is one of the most important environmental issues of current times. CeUulosic fibers therefore have much to recommend them provided that the processes used to make them have minimal environmental impact. 

Gas purification processes fall into three categories the removal of gaseous impurities, the removal of particulate impurities, and ultrafine cleaning. The extra expense of the last process is only justified by the nature of the subsequent operations or the need to produce a pure gas stream. Because there are many variables in gas treating, several factors must be considered (/) the types and concentrations of contaminants in the gas (2) the degree of contaminant removal desired (J) the selectivity of acid gas removal required (4) the temperature, pressure, volume, and composition of the gas to be processed (5) the carbon dioxide-to-hydrogen sulfide ratio in the gas and (6) the desirabiUty of sulfur recovery on account of process economics or environmental issues. 

Paul, J., and Pradier, C. (1994) Carbon Dioxide Chemistry Environmental Issues, Royal Society of Chemistry, London. 

A number of environmental issues have received widespread publicity (Table 7.1), from major accidents at plants (e.g., Seveso and Bhopal) to the global and regional impacts associated with energy utilization (e.g., carbon dioxide, acid rain, and photochemical oxidants), the improper disposal of chemical waste (e.g., Love Canal and Times Beach), and chemicals that have dispersed and bioaccumulated affecting wildlife (e.g., PCBs and DDT) and human health (e.g., cadmium, mercury, and asbestos). 

K. Seshan and J.A Lercher, in J. Paul and C. Pradier, (Eds.) Carbon dioxide. Environmental issues . The Royal Soc. Chem., Cambridge, 1994, pl6. 

Poor solubility in most common organic solvents represents an inherent problem in the synthesis and processing of many high molar mass fluoropolymers. In fact, CFCs and carbon dioxide are the best solvents for amorphous varieties of fluoropolymers. Due to the environmental problems associated with CFCs, the international community is seeking to replace them with more benign compounds such as hydrochlorofluorocarbons and hydrofluorocarbons. However, the environmental problems which will be created by the use of these replacement compounds such as the accumulation of trifluoroacetic acid in the atmosphere clouds this issue [71], Carbon dioxide presents an ideal inert solvent to effect the polymerization of these types of highly fluorinated monomers and obviates the use of solvents that are being phased out because of environmental concerns. 

Another environmental issue is the use of organic solvents. The use of chlorinated hydrocarbons, for example, has been severely curtailed. In fact, so many of the solvents favored by organic chemists are now on the black list that the whole question of solvents requires rethinking. The best solvent is no solvent, and if a solvent (diluent) is needed, then water has a lot to recommend it. This provides a golden opportunity for biocatalysis, since the replacement of classic chemical methods in organic solvents by enzymatic procedures in water at ambient temperature and pressure can provide substantial environmental and economic benefits. Similarly, there is a marked trend toward the application of organometal-lic catalysis in aqueous biphasic systems and other nonconventional media, such as fluorous biphasic, supercritical carbon dioxide and ionic liquids. ... 

Chemistry of the Environment focuses on the role of chemistry in environmental issues, including air and water pollution, solid wastes, and the relatively new field of green chemistry. The term pollution refers to the release of harmful or ohjectionahle substances into the environment, most commonly as the result of human activities. Some of the most obvious examples of pollution are smoke produced by industrial operations, carbon dioxide and other gases released into the atmosphere as a by-product of burning fuels, silt and sediment washed off land by rainwater, and garbage dumped on land. 

L. Rees and J. Hampson, C02-ZeoIite Reaction for Gas Separation, ed. C. Pradier and J. Paul, Carbon Dioxide Chemistry Environmental Issues, Proceedings of the International Symposium on C02 Chemistry, The Royal Society of Chemistry, Cambridge (1994) 250. 

Perry. R.H., D.W. Green, and I.O. Maloney Perry s Chemical Engineers Handbook, 7ih Edition. The McGraw-Hill Companies, Inc.. New York. NY. 1997. Pradlcr, Jan Paul, and Claire-Mane. Pradier Carbon Dioxide Chemistry. Environmental Issues. Lewis Publishing. Cherry Hill. NJ, 1994. 

Obviously, acute or chronic toxicity is not an issue with the use of C02. Similarly, the ecological impact of carbon dioxide is negligible when used as a solvent, and C02 is—by definition—not regulated as a VOC. The application of C02 as a solvent in chemical synthesis would not generate any additional carbon dioxide and therefore would not contribute to greenhouse gas emission. Even for large-scale applications, no toxic or environmental risk would arise in case of any accidental contamination of the immediate environment with the solvent C02 if sufficient ventilation is provided. 

The use of C02 circumvents the environmental concerns and the worker and consumer health issues associated with perc use. Carbon dioxide is nonflammable and thus does not have the site restrictions often encountered with petroleum. The controlled level of moisture in a C02 system does not damage hydrophilic fibers. And best of all, C02 cleaning leads to a high-quality finished product that is safer for clothes, workers, consumers, and the environment. 

Steinberg, M., Yuang, D., and Borgwardt, R.H., in Carbon Dioxide Chemistry Environmental Issues, Paul, J. and Pradier, C.H., Eds., Royal Society of Chemistry, Cambridge, UK, 1994, 189. 

In this special volume on polymer particles, recent trends and developments in the synthesis of nano- to micron-sized polymer particles by radical polymerization of vinyl monomers in environmentally friendly heterogeneous aqueous and supercritical carbon dioxide fluid media are reviewed by prominent worldwide researchers. Polymer particles are prepared extensively as synthetic emulsions and latexes, which are applied as binders in the industrial fields of paint, paper and inks, and films such as adhesives and coating materials. Considerable attention has recently been directed towards aqueous dispersed systems due to the increased awareness of environmental issues. Moreover, such polymer particles have already been applied to more advanced fields such as bio-, information, and electronic technologies. In addition to the obvious commercial importance of these techniques, it is of fundamental scientific interest to completely elucidate the mechanistic details of macromolecule synthesis in the microreactors that the polymer particles in these heterogeneous systems constitute. 

Polymerisation in supercritical carbon dioxide has generated great interest in recent years for a number of reasons, including its environmentally benign nature as a solvent and the ease of removing it from products at the end of a reaction, as well as more subtle issues such as the tuneability of its density and solvation... 

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