Carbon dioxide, 1.9

Carbon dioxide decomposes behind a shock front in accordance with the kinetics expected of a unimolecular reaction in its low-pressure region31-37. The second-order rate coefficients obtained by a number of experimentalists in the temperature range 2500-11000 °K are in reasonable agreement, but there is a considerable spread in the values derived for the Arrhenius activation energy (Table 3). Furthermore, even the highest of these values31 is much smaller than the endothermicity (D = 125.8 kcal.mole-1) of 

In an attempt to explain the discrepancy in terms of a participation of internal degrees of freedom of the C02-M complex in the process of collisional activation, some authors have invoked the classical rrk expression for the rate of energization 

Carbon dioxide commences to absorb light in the region of 1750 A. Photochemical studies have been confined to the wavelength region 1200-1700 A where 

The fate of an 0(1X 2) atom in a mixture of C02, CO and 02 has been the subject of considerable controversy46-48,50 52,54,56-60. There is, however, agreement on one point61 62, that the reaction 

0(1Z ) undergoes rapid reactions with C02, CO and 0254,56,61,64(a), reactions which we firmly believe result in deactivation of the excited atom to the ground state (at least in the gas phase at conventional pressures), e.g. 

Carbon dioxide is non-polar ( = 1.6 at 20°C) and is a poor solvent for inorganic salts. 

Its use as a reaction has been reviewed very recently [42]. Just a few examples will be mentioned here. Diels-Alder reactions occur normally and show no significant discontinuities in rate of going from sub- to super-critical [43]. A recent publication [44] describes the application of C02/water as a combined acid and solvent for the diazotisation and coupling of a weakly basic amine (equation 12.19). 

The process is remarkable in that no mineral acid is required, as is normally the case for diazotisation. It is unclear whether this process has been commercialised. 

Dissolution of carbon dioxide from the soil air into the soil solution affects the pH of the soil solution and the solubility of soil carbonates. Carbon dioxide dissolves 

Here H2CO3 refers to the sum of CO2, H2CO3, and C02aq dissolved in the aqueous solution. The H2CO3 dissociates successively to bicarbonate and carbonate ions as the pH increases  

The resulting distribution of aqueous CO2 species with pH is shown in Fig. 7.4. The concentrations of the various ions can be calculated from these equations by assuming equilibrium with a specific Pc02 Rainwater is in equilibrium with the Pco2 of 0.00035 in the atmosphere. In the absence of substances such as SO2, NO, and NH3, the acidity of rainwater is fixed at pH 5.7, as calculated from Eqs. 7.15 and 7.16. 

The solubility product of CaC03 in equilibrium with water and gaseous CO2 yields an acidity of 

The pH of a solution in equilibrium with CaC03 and atmospheric CO2 is 8.3. Equation 7.18 yields a value of pH 8.5 because activity coefficient corrections are ignored and because of rounding-off errors in the exponents of the equilibrium constants. 

Over 90% of all carbon dioxide is made by steam-reforming of hydrocarbons, and much of the time natural gas is the feedstock. It is an important by-product of hydrogen and ammonia manufacture. 

A small amount (1%) of carbon dioxide is still made from fermentation of grain. Ethyl alcohol is the main product. 

Another 1% is recovered as a by-product of ethylene oxide manufacture from ethylene and oxygen. When the oxidation goes too far some carbon dioxide is formed. 

Other small amounts are obtained from coke burning, the calcination of lime, and in the manufacture of sodium phosphates from soda ash and phosphoric acid. 

Carbon dioxide is a gas at room temperature. Below -78°C it is a solid and is commonly referred to as dry ice. At that temperature it sublimes and changes directly from a solid to a vapor. Because of this unique property, as well as its non-combustible nature, it is a common refrigerant and inert blanket. Table 3.4 shows the uses of carbon dioxide in all its forms liquid, solid, and gas. Refrigeration using dry ice is especially important in the food industry. Beverage carbonation for soft drinks is a very big application. In oil and gas recovery carbon dioxide competes with nitrogen as an inert atmosphere for oil wells. 

The phase diagram for carbon dioxide is shown in Fig. 5. The features to notice include the positive slope of the solid-liquid boundary (the direction of this line is characteristic of most substances), which indicates that the melting temperature of solid carbon dioxide rises as the pressure is increased. Note also that, as the triple point 

Water is also included in the table to make one point— the solvent that we are all most familiar with is a poor candidate from both engineering and safety standpoint. The critical temperature and pressure are among the highest for common solvents. Ammonia is very unpleasant to work with since a fume hood or other venting precautions are needed to keep it out of the laboratory atmosphere. One of the alternative fluids of potential interest is nitrous oxide. It is attractive since it has molecular weight and critical parameters similar to carbon dioxide, yet has a permanent dipole moment and is a better solvent than carbon dioxide for many solutes. There are evidences of violent explosive reactions of nitrous oxide in contact with oils and fats. For this reason, nitrous oxide should be used with great care and is not suitable as a general purpose extraction fluid. 

Fluid Molecular weight. My, (gm/mol) Density of Liquid (gm/mol) Temp, of liquid ( K) Dipole moment (debyes) Critical Temp. Factor, (TA) ( K/ C) Critical Pressure (P,) (bar) (atm) (psi) Critical Volume, (cmVmol) Critical Compress.  

In some petroleum refineries or chemical plants, an on-site fire brigade equipped with an apparatus capable of dispensing large volumes of dry chemical or a vehicle with a large-capacity carbon dioxide (CO ) cylinder is common practice. 

Carbon Dioxide (CO ) is used in fighting electrical fires. It is non-conductive and, therefore, the safest to use in terms of electrical safety. It also offers the least likelihood of damaging equipment. However, if the discharge horn of a CO extinguisher is allowed to accidentally touch an energized circuit, the horn may transmit a shock to the person handling the extinguisher. 

The very qualities that cause CO to be a valuable extinguishing agent also make it dangerous to life. When it replaces oxygen in the air to the extent that combustion cannot be sustained, respiration also cannot be sustained. Exposure of a person to an atmosphere of high concentration of COj will cause suffocation. 

Dry abrasive blasting will not disappear in the foreseeable future. However, other blasting techniques are currently of interest. Some are briefly described in this section dry blasting with solid carbon dioxide, dry blasting with an ice abrasive, and wet blasting with soda as an abrasive. 

Rice-sized pellets of carbon dioxide (dry ice) are flung with compressed air against a surface to be cleaned. The abrasive sublimes from solid to gas phase, leaving only paint debris for disposal. This method reportedly produces lower amounts of dust, and thus containment requirements are reduced. Workers are still exposed to any heavy metals that exist in the paint and must be protected against them. 

This method can be nsed to remove paint but is ineffective on mill scale and heavy rust. If the original surface was blast cleaned, the profile is often restored 

The decomposition of the excited state, C02 — -COOX + 0(3P, 1D, and 3S) is generally assumed simple. The state 0(3P) has apparently not been seen, which is consistent with Wigner s (1927) rule. In any case, the reported quantum yield of unity for the production of CO is often used in far-UV chemical actinometry. 

The increasing C02-content of the atmosphere is a problem of world-wide concern. By measuring both the concentration and isotope composition of CO2 on the same 

Long-term measurements of atmospheric CO2 are available for a few clean-air locations on an almost continuous basis since 1978 (Keeling et al. 1979,1984,1989, 1995 Ciais et al. 1995 Mook et al. 1983). These measurements clearly demonstrate that on average atmospheric CO2 increases by about 1.5 ppm per year while the isotope ratio shifts toward lower ratios. The annual combustion of 10 g of 

There is increasing awareness that the CO2 content of the Earth s atmosphere has varied considerably over the last 500 Ma. The clearest evidence comes from mea-snrements of CO2 from ice cores, which have yielded an impressive record of CO2 variations over the past 420,000 years (Petit et al. 1999). 

In a mnch broader context, Berner (1990) has modeled how long-term changes in CO2 concentrations can result from the shifting balance of processes that deliver CO2 to the atmosphere (such as volcanic activity) and processes that extract 

The boron isotope approach to pC02 estimation relies on the fact that a rise in the atmospheric CO2 concentration will increase pC02 of the surface ocean which in turn causes a reduction of its pH. By measuring the boron isotope composition of planktonic foraminifera Pahner et al. (1998) and Pearson and Palmer (2000) have reconstructed the pH-profile of Eocene sea water and estimated past atmospheric CO2 concentrations. However, Lemarchand et al. (2000) argued that 5 B records of planktonic foraminifera partly reflect changes in the marine boron isotope budget rather than changes in ocean pH. 

C02 affects microbial growth in various ways according to its appearance in catabolism as well as in anabolism. Morphological changes (e.g. [97]) and variations in growth and metabolic rates [195, 310] in response to pC02 have 

At 25°C and 101.325 kPa (latm) the distribution of the various species in the aqueous solution can be calculated from the solubility and the equilibrium ratios. The distribution is  

The units of concentration used here are molality or moles of species per kg of solvent (water). 

Carbon dioxide is also a weak diprotic acid, but the reactions for C02 are slightly different. The first reaction is a hydrolysis (a reaction with water)  

these reactions take place in the aqueous phase. The carbon dioxide exists in three species in the aqueous phase - the molecular form C02, and two ionic forms the bicarbonate ion, also call the hydrogen carbonate ion (HC03 ), and the carbonate ion (CQ,2). 

pH = -log[H ] and usually the concentration, [H ] is expressed in moles of solute per kg of water (molality), but for aqueous solutions at low concentration mol/kg of water is approximately equal to moles per litre of solution (molarity). 

As in the 1960s the demand for (3-pinene far exceeded its availability owing to its versatile applications, a large part of the more commonly occurring a-pinene was isomerized to (3-pinene using, for example, basic catalysts such as calcium amide and alkaline earth metal oxides. A major amount of (3-pincnc is converted to resins with adhesive properties and by pyrolysis to the acyclic monoterpene myrcene. 

Due to the enormous supplies of carbon dioxide in the atmosphere (1091), in the hydrosphere (1014t), and in the lithosphere (10lst), the question arises of whether they could be used economically in chemistry. Several industrial reactions have already been realized the synthesis of urea from C02 and ammonia, the addition of 

C02 in methanol synthesis, the synthesis of cyclic carbonates from C02 and epoxides, and the production of salicylic acid according to the Kolbe-Schmitt process. 

We have no information on past changes in the interhemi-spheric gradient of atmospheric CO2 because accurate determination of past COi concentrations from Northern-Hemisphere ice is still impossibile. 

in the light, and in particular when stomata are closed, CO2 stored as malic acid is reutilized in photosynthetic reactions effectively conserving the dark assimilation of CO2. 

The Metabolic Pathway of CAM Table 3.2. Proiiucts of dark and light CO2 fixation by Opuntia (data of Ting and Dugger, 1968)  

COa insertion into the M—N bonds of transition-metal dimethylamido-com-plexes [M(NMe2 ] (M=Ti, Zr, or V, /i=4 M=Nb or Ta, =5 M = W, =6) gives mixed dimethylamido-dimethylcarbamato-complexes which undergo easy CO2 exchange reactions, equations (5) and Originally the mechanism pro- 

Our estimates of the amount of hiomass exposed to fire worldwide (2.7-6.8 Pg of C per year Table 7.1) and the resulting prompt CO2 release to the atmosphere (1.8-4.7 Pg of C per year) are larger than earlier estimates [10, 13]. They are 30-80 % of the fossil fuel burning rate of 5.7 Pg of C per year [16]. 

Our estimates show very large emissions of CO, between 120 and 510 Tg of C per year. The estimated global source of CO is close to 1000 Tg of C per year [32] biomass burning is thus one of the main sources of atmospheric CO. Because about 70 % of the OH radicals in background air react with CO, biomass burning can substantially lower the oxidative efficiency of the atmosphere (which is mostly determined by the concentrations of OH), and thus can cause the concentrations of many trace gases to increase. 

For H2, biomass combustion may contribute 5-16 Tg per year. Its global sources and sinks have been estimated to be about 36 Tg per year, mostly due to fossil fuel burning [35]. Biomass burning may thus make a significant contribution to the global source of H2, which plays a role in stratospheric photochemistiy. 

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CARBON DIOXIDE 216-253 6 3208E4-00 -2 6423E-f03 -3.9322E-02 2 7347E700 2 67186-05... 

CARBON DIOXIDE -1.0919E402 2.4663E 03 -9.7531E 03 2. 4740E401... 

As an example of the application of a fixed-bed tubular reactor, consider the production of methanol. Synthesis gas (a mixture of hydrogen, carbon monoxide, and carbon dioxide) is reacted over a copper-based cat dyst. The main reactions are... 

For example, hydrogen sulfide and carbon dioxide can be removed from natural gas by reaction with monoethanolamine in an absorber according to the following reactions ... 

These reactions can be reversed in a distillation column. This releases the hydrogen sulfide and carbon dioxide for further processing. The monoethanolamine can then be recycled. 

Utility systems as sources of waste. The principal sources of utility waste are associated with hot utilities (including cogeneration systems) and cold utilities. Furnaces, steam boilers, gas turbines, and diesel engines all produce waste from products of combustion. The principal problem here is the emission of carbon dioxide, oxides of sulfur and nitrogen, and particulates (metal oxides, unbumt... 

Fuel switch. The choice of fuel used in furnaces and steam boilers has a major effect on the gaseous utility waste from products of combustion. For example, a switch from coal to natural gas in a steam boiler can lead to a reduction in carbon dioxide emissions of typically 40 percent for the same heat released. This results from the lower carbon content of natural gas. In addition, it is likely that a switch from coal to natural gas also will lead to a considerable reduction in both SO, and NO, emissions, as we shall discuss later. 

Benfield process Removal of carbon dioxide from fuel gases, such as those obtained by gasifying coal in the Lurgi process, by countercurrent scrubbing of the gases by hot potassium carbonate solution. 

Carbon dioxide, COj. Sublimes — 78 5 C. A colourless gas at room temperature, occurs naturally and plays an important part in animal and plant respiration. Produced by the complete combustion of carbon-containing materials (industrially from flue gases and from synthesis gas used in ammonia production) and by heating metal carbonates or by... 

Catacarb process An extraction process used to remove carbon dioxide from process gases by scrubbing the hot gases with potassium carbonate solution containing additives which increase the hydration rate of the gas in the solution. The Vetrocoke process is similar. See Benfield process. 

Trichloroethanoic acid, CCI3COOH. A crystalline solid which rapidly absorbs water vapour m.p. 58°C, b.p. 196-5" C. Manufactured by the action of chlorine on ethanoic acid at 160°C in the presence of red phosphorus, sulphur or iodine. It is decomposed into chloroform and carbon dioxide by boiling water. It is a much stronger acid than either the mono- or the dichloro-acids and has been used to extract alkaloids and ascorbic acid from plant and animal tissues. It is a precipitant for proteins and may be used to test for the presence of albumin in urine. The sodium salt is used as a selective weedkiller. 

Chlorophyll is present in all green plants, and is essential to the life of the plant, as it acts as a catalyst in the photosynthesis of carbohydrates from carbon dioxide and water. 

C2H3N. Colourless liquid with strong ammoniacal smell b.p. 56 C. Miscible with water and strongly basic. Prepared commercially from 2-aminoelhanol. Pure dry aziridine is comparatively stable but it polymerizes explosively in the presence of traces of water. Carbon dioxide is sufficiently acidic to promote polymerization. 

Changes in thermal conductivity, e.g. carbon dioxide in flue gas. 

Cj jH,2N202. Used as its sodium salt, which is a white hygroscopic powder. Unstable, readily absorbing carbon dioxide and liberating phenytoin. Made by treating a-bromodi-phenylacetylurea with alcoholic ammonia. It has a mild hypnotic and strong anticonvulsant action, and is used in the treatment of grand-mal and focal epilepsy. 

Many condensable vapours have been used as refrigerants, but the main ones are the chlorofluorocarbons (Freons ), ammonia and carbon dioxide. 

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