Phosphoric acid vapour pressure

Liquid absorbents. If the partial pressure of the water in the gas is greater than the equilibrium partial pressure at the surface of a liquid, condensation will take place as a result of contact between the gas and liquid. Thus, water vapour is frequently removed from a gas by bringing it into contact with concentrated sulphuric acid, phosphoric acid, or glycerol. Concentrated solutions of salts, such as calcium chloride, are also effective. The process may be carried out either in a packed column or in a spray chamber. Regeneration of the liquid is an essential part of the process, and this is usually effected by evaporation. 

Fio. 46.—Vapour Pressures of Pyro- and Meta-phosphoric Acids. 

The 65 per cent peroxide, previously stabilized by adding a small amount of phosphoric acid, is introduced at the rate of 9001 per hr. into a second distillation unit, similar to the first, for re-distillation. Here the process is continuous a4 no solid substances accumulate in the retort. A temperature of 75 °C is njaintained at an absolute pressure of 40 mni Hg. When equilibrium has been reached, the concentration of the liquid in the retort will be about 80 per cent b.w. H2O2 and in the vapour phase will be about 44 per cent b.w. H202. The distilled vapour enters the rectifying column, from where a condensate containing 56 per cent b.w. H202 is continually returned into the retort. Uncondensed water vapour is liquefied in a tubular aluminium condenser connected to a vacuum pump. 

Vapour pressures of water at 100° C. were lowered in a high ratio by phosphoric acid, as appears from the following data —3... 

Orthophosphorio Acid —Preparation—Physical Properties of Solid Hydrates of P2Os—Solubilities, Melting-points and Eutectics of the System HjP04-Ha0—Densities of Aqueous Solutions—Vapour Pressures—Conductivities of Concentrated and Dilute Solutions—Viscosities—Refractive Index—Basicity and Neutralisation of the Phosphoric Acids—Constitution... 

Figure 14. Effect of water vapour pressure on the corrosion rate of Shawinigan acetylene black as a function of phosphoric acid concentration.

Hot phosphoric acid has been successfully used to digest ion-based alloys when HCl would have volatilized specific trace constituents. Phosphoric acid can also digest a wide range of aluminium slags, iron ores, chromium and alkali metals. The temperature and pressure profiles for H,POj indicate that temperatures of 240°C can be attained with just 3 atm. Because of its low vapour pressure, relatively high temperatures can be reached without disrupting the digestion. 

Chemical Shifts and Shielding ElSects.—Phosphorus-31. In this section, positive P chemical shifts (dp) are upheld from 85% phosphoric acid. A linear relationship between dp and vapour pressure for elemental phosphorus in the gas phase has been reported. Solvent effects have also been examined. dp compounds. The n.m.r. parameters of various protic and deuteriated... 

At elevated temperatures and pressures, water vapour will react with white phosphorus to form various products. Above 200°C in a sealed tube, phosphine and phosphorous acid are the main products (4.20) but above 1000°C, steam will oxidise phosphorus vapour to give the pentoxide (4.21). 

Polymerization efficiencies for the initiator systems hexamethylene di-isocyanate and 7V-acetyl caprolactam have been evaluated and the di-isocyanate found to be the more active. Studies on -caprolactam in closed systems have been made and the main polymerization processes for the system, caprolactam, water, and a viscosity stabilizer (acetic acid or butylamine), were evaluated. These are ring-opening polymerizations by hydrolysis, polycondensation of amine and carboxyl ends, and polyaddition of caprolactam to amino end-groups. Apparent activation energies were determined for these main reactions and it was suggested that addition occurred in preference to polycondensation. Post-polymerization of E-caprolactam under reduced pressure in the presence of water vapour and phosphoric acid has been kinetically analysed and the rate of increase of the degree of polymerization was derived theoretically as a function of reaction variables. 

The performance of a HT-PEMFC depends mainly on the amount of phosphoric acid in the polymer membrane and in the porous catalyst layer as well as on the temperature. Furthermore, it is well known that phosphoric acid dehydrates at low water vapour partial pressure and rehydrates with increasing partial pressure, effects which can be observed in HT-PEMFCs under operating conditions [1, 2]. The composition change of phosphoric acid results in a variation of the ionic conductivity as well as of the viscosity. 

In this chapter we will firstly present a literature survey on vapour pressure, viscosity and conductivity properties of phosphoric acid with an emphasis on the temperature and composition range relevant for fuel cell applications. In a second part we want to elucidate the physico-chemical interactions of a protic electrolyte like phosphoric acid as a doping agent with polybenzimidazole-type polymer membranes. Literature data on m-PBI and AB-PBI as well as own measurements on Fumapem AM-55, a commercial PBI derivative, will be cOTisidered. On the basis of the observed doping behaviour a model describing the thermodynamics of the adsorption process is presented. 

Data on the water vapour pressure of aqueous phosphoric acid can be found by Fontana [24], Brown and Whitt [25], Kablukov and Zagwosdkin [26], McDonald and Boyack [27]... 

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