Henry high-pressure conditions

The chemical yield of the classical Henry reaction is not always good and depends on steric factors thus, highest yields are obtained when nitromethane is used. Performing the reaction under high pressure (9 kbar, 30 °C) with tetrabutylammonium fluoride catalysis19 enlarges the scope of the reaction dramatically. Thus, addition of nitropropane to 2-methylcyclohexanone, which is not reactive under the classical conditions, was achieved in 40 % yield. Improved yields... 

The adsorption of nitrogen on silicalite, DAY and NaX at 310 K was carried out up to a pressure of 15 bars. Combined manometric and microcalorimetric measurements were carried out under high-resolution conditions. The isotherms show a marked deviation from Henry s law behaviour. 

The solubilities of H2 [181] and CO [182] in many different ionic hquids have been measured in this context by Dyson and coworkers using high-pressure H- or C-NMR spectroscopy. CO solubility at ambient conditions (Henry s law constants) were found to be in the range of 8.05-0.67 x 10 MPa which were in the same range than those measured for H2 in the same ionic hquids (about 6.6-0.7 X 10 MPa). In order to establish the effect of the CO solubihty on the rate of hydroformylation reactions, the same authors studied the [RhH(CO)(PPhj)3] catalyzed hydroformylation of 5-hexen-2-one comparing catalyst activities in the different ionic liquids with the determined gas solubilities. 

The partial pressure of H2S on a volumetric basis in the atmosphere in equilibrium with a water phase of sulfide (H2S + HS ) is at a pH of 7, approximately equal to 100 ppm (gS m-3)-1 (Figure 4.2). It is clear that under equilibrium conditions, much lower concentrations than those corresponding to the values shown in Table 4.6 may result in odor and human health problems. This is also seen from the fact that Henry s constant for H2S is rather high, //H2S =563 atm (mole fraction)-1 at 25°C (Table 4.1). However, under real conditions in sewer networks, conditions close to equilibrium rarely exist because of, for example, ventilation and adsorption followed by oxidation on the sewer walls. Typically, the gas concentration found in the sewer atmosphere ranges from 2-20% and is normally found to be less than 10% of the theoretical equilibrium value (Melbourne and Metropolitan Board of Works, 1989). 

Henry s Law is obeyed with organic pollutants of low solubility provided the pressures are not high or temperatures too low - conditions under which one might expect deviations from ideal behavior. Experimental values for Henry s Law constant may be obtained by equilibrating a pollutant between the solvent and vapor phase and measuring its concentration in those two phases. Providing the solubility is low (PA< 0.1) Henry s Law constant can be calculated from the equilibrium vapor pressure (PA) and solubility (S) ... 

A realistic boundary condition must account for the solubility of the gas in the mucus layer. Because ambient and most experimental concentrations of pollutant gases are very low, Henry s law (y Hx) can be used to relate the gas- and liquid-phase concentrations of the pollutant gas at equilibrium. Here y is the partial pressure of the pollutant in the gas phase expressed as a mole fraction at a total pressure of 1 atm x is the mole fraction of absorbed gas in the liquid and H is the Henry s law constant. Gases with high solubilities have low H value. When experimental data for solubility in lung fluid are unavailable, the Henry s law constant for the gas in water at 37 C can be used (see Table 7-1). Gas-absorption experiments in airway models lined with water-saturated filter paper gave results for the general sites of uptake of sulfur dioxide... 

Dissolved pollutants can be transferred from a condensed (liquid or solid) phase into the vapor phase under the action of steam or air streams. As a mass transfer phenomenon, it is driven by a concentration gradient between the condensed and gas phases. It applies fundamentally to pollutants that show sufficiently high vapor pressures under the operating conditions. If the source phase is a liquid, Henry s law regulates the corresponding equilibrium (see Chapter 6). Steam can remove pollutants that may be difficult to remove with air. Obviously, the resulting (contaminated) gas stream or condensate must be treated before its release into the atmosphere. 

A practical demonstration of Henry s law is the effervescence of a soft drink when the cap of the bottle is removed. Before the beverage bottle is sealed, it is pressurized with a mixture of air and CO2 saturated with water vapor. Because of the high partial pressure of CO2 in the pressurizing gas mixture, the amount dissolved in the soft drink is many times the amount that would dissolve under normal atmospheric conditions. When the cap is removed, the pressurized gases escape, eventually the pressure in the bottle falls to atmospheric pressure, and the amount of CO2 remaining in the beverage is determined only by the normal atmospheric partial pressure of CO2, 0.0003 atm. The excess dissolved CO2 comes out of solution, causing the effervescence. 

---