Carbon dioxide/water beneficiation

SAPIENZA ET AL. Carbon Dioxide Water for Coal Beneficiation... 

The environmental problem of sulfur dioxide emission, as has been pointed out, is very much associated with sulfidic sources of metals, among which a peer example is copper production. In this context, it would be beneficial to describe the past and present approaches to copper smelting. In the past, copper metallurgy was dominated by reverberatory furnaces for smelting sulfidic copper concentrate to matte, followed by the use of Pierce-Smith converters to convert the matte into blister copper. The sulfur dioxide stream from the reverberatory furnaces is continuous but not rich in sulfur dioxide (about 1%) because it contains carbon dioxide and water vapor (products of fuel combustion), nitrogen from the air (used in the combustion of that fuel), and excess air. The gas is quite dilute and unworthy of economical conversion of its sulfur content into sulfuric acid. In the past, the course chosen was to construct stacks to disperse the gas into the atmosphere in order to minimize its adverse effects on the immediate surroundings. However, this is not an en-... 

This reaction is accompanied by complete combustion into water and carbon dioxide. The only selective catalyst known is based on silver. This catalyst was known as early as the 1930s and has been continuously improved since then in a rather empirical way. It has been discovered that the catalyst may be promoted by the addition of alkali metal ions. Moreover, the presence of chlorine has a beneficial effect (cf. Fig. 5.11) [94]. Chlorine has to be added continuously because it disappears from the surface by reacting to give chlorinated ethane. It is sufficient to mix 10-40 ppm chlorine with the feed. The feed consists of a mixture of... 

The effects of prolonging catalyst use were all beneficial. Hydrogen consumption decreased and carbon dioxide production increased from run 1 to run 3. The organic product was an oil which contained 13 per cent oxygen and was 95 per cent benzene soluble. Approximately 55g of water was formed in each run. Thus the molar ratio of carbon dioxide product to water product was about 1 6 compared to an ideal ratio of close to 2 1. The oil yield appeared to be 38 per cent but subsequent distillation showed that the product contained about 9 per cent by weight of water. 

The reviews by Spivey [3] and by Jennings et al. [156] are excellent sources for further details on catalytic incineration of volatile organics emissions. Spivey [3] describes two types of techniques for removal of VOC from off-gases, namely one without preheater and one with a direct flame preheater. From an economically point of view it is more beneficial to carry out the catalytic oxidation at lower temperatures. In a catalytic incinerator, sometimes called an afterburner, VOCs are oxidized into carbon dioxide and water. The efficiency is about 70-90%. The incinerator has a preheat burner, a mixing chamber, a catalyst bed, and a heat recovery equipment. Temperatures of about 590 K are sirfficient for the destruction of VOCs. Various catalyst geometries have been used metal ribbons, spherical pellets, ceramic rods, ceramic honeycombs, and metal honeycombs. Precious metals such as platinum and palladium are often used in catalytic incinerators. 

The extraction techniques described in this book fulfill many of Anastas and Warner s principles. For example, the use of supercritical carbon dioxide (SC-CO2) as the sole extraction solvent results in a nonpolluting process (prevention of waste and safer solvents and auxiliaries). Other beneficial properties of supercritical CO2 include fast diffusivity and nearly zero surface tension, which lead to extremely efficient extractions. In Chapters 2-4, applications of SC-CO2 as an extraction solvent are described. Ethanol and water are also environmentally friendly solvents that can be used as extraction media in many applications (see Chapters 5-7). Pressurized hot water ( 100-200 °C) in particular is a safe and nonpolluting solvent that has a similar dielectric constant to polar organic solvents, such as ethanol or acetone. Hence, pressurized hot water is a viable green alternative to many current extraction processes that use toxic organic solvents. Similarly, pressurized hot ethanol is an excellent solvent for the extraction of most medium polar to nonpolar organic molecules. Some of the techniques, such as membrane-assisted solvent extraction, described in Chapter 10, use organic solvents but in much smaller amounts compared to classical extraction techniques. Other techniques, for instance solid-phase microextraction and stir-bar sorptive extraction, described in Chapter 11, use no solvents. 

Chemical oxidation shows several potential benefits compared to other treatment options. The main advantage is the possible minerahzation of organic substances to carbon dioxide and water. The substance can be completely de-structed and is not only simply enriched or shifted into another phase [33]. Furthermore, there is also a disinfecting effect if ozone is used. Ozonation is the oxidative treatment process most widely spread in drinking water treatment—though it is mainly implemented for disinfection and the oxidation is only considered a beneficial side effect [28]. 

Also, during the retorting operation, there is significant loss of oxygen. About two-thirds is lost as carbon dioxide and about one-third as water. Because of the loss of carbon dioxide, the C/H ratio has beneficially decreased from 7.8 in kerogen to 7.3 in shale oil. 

Essentiality and Toxicity for Plants It is generally accepted that various plant species, especially marine and shore plants and those adapted to saline soils (Australian Atriplex vesicaria), require small amounts of sodium for normal development. Sodium is important for plants, though definite beneficial effects on growth and development have been observed in only a few species. Na enhances the growth of some species if potassium is deficient. Sodium cannot generally perform the specific function of potassium in plants. It does so to a limited extent only, even in plants that respond to sodium fertilization (Saalbach 1973). Na is assumed to influence osmotic pressures in the vacuoles, and the water content of colloids in the plasma. In many species of plants it is reported to be involved in carbon dioxide assimilation. Salt fertilization always increases sodium yields of sugar beet, carrot and chard, even if potassium fertiliza-... 

Heterogeneous catalysis is also utilized in the catalytic converters in automobile exhaust systems. The exhaust gases, containing compounds such as nitric oxide, carbon monoxide, and unburned hydrocarbons, are passed through a converter containing beads of solid catalyst (see Fig. 12.16). The catalyst promotes the conversion of carbon monoxide to carbon dioxide, hydrocarbons to carbon dioxide and water, and nitric oxide to nitrogen gas to lessen the environmental impact of the exhaust gases. However, this beneficial catalysis can, unfortunately, be accompanied by the unwanted catalysis of the oxidation of SO2 to SO3, which reacts with the moisture present to form sulfuric acid. 

This chemical and physico-chemical behavior of the binary H2O-CO2 mixture [38] suggests that water is an attractive liquid to be combined with supercritical carbon dioxide in multiphase catalysis. CO2/H2O systems have adequate mass-transfer properties, especially if emulsions or micro-emulsions can be formed ([39] and refs, therein). The low pH of aqueous phases in the presence of compressed CO2 (pH ca. 3-3.5 [40]) must be considered and the use of buffered solutions can be beneficial in the design of suitable catalytic systems, as demonstrated for colloid-catalyzed arene hydrogenation in water-scC02 [41]. 

---