Phosphoric acid system

One consequence of reducing the rate of corrosion of steel in an acid is to decrease the formation of hydrogen, which has been reported as the cause of explosions in phosphoric acid systems . Hydrogen may also form... 

Worldwide over 150 demonstration plants have been installed. These represent around 40 to 50 MW of electrical generating capacity. Nearly 75% is installed in Japan, over 15% in North America, and 9% in Europe. The U.S.-based International Fuel Cells (IFC) and its partner Toshiba are responsible for producing over 70%, Fuji over 25%, and Mitsubishi about 2% (WFCC analysis). These phosphoric acid systems are operating in real world commercial situations and have clearly demonstrated their suitability for on-site cogeneration. 

Inorganic phosphate ligands are important with respect to the behavior of actinides in the environment and as potential waste forms. There have been a number of experimental studies to determine the equilibrium constants in the actinide-phosphoric acid system, but they have been complicated by the formation of relatively insoluble solid phases and the formation of ternary actinide complexes in solution. 

Raghuraman BJ, Tirmizi NP, Kim BS, and Wiencek JM. Emulsion Uquid membranes for wastewater treatment Equilibrium models for lead- and cadmium-di-2-ethylhexyl phosphoric acid systems. Environ Sci Technol 1995 29 979-984. 

The base-neutralizing capacity of the phosphoric acid system with reference to the equivalence point, / = 2 (solution of Na2HP04 with the proton condition 2[H3P04] -h [H2P04 ] -h [H ] = [POj ] -h [OH" ]), is given by... 

Lin, S. H., Pan, C. L., Leu, H. G. (1999). Liquid membrane extraction of 2-chlorophenol from aqueous solution. Journal of Hazardous Materials 65 289-304. Raghuraman, B.J., Tirmizi, N.P., Kim, B.-S., Wiencek, J. M. (1995). Emulsion Liquid Membranes for Wastewater Treatment Equihbrium Models for Lead- and Cadmium-di-2-ethylheyl Phosphoric Acid Systems. Environmental Science and Technology 29 979-984. Liu, H. J., Wu, Q. S., Ding, Y. P., Liu, L. (2004). Biomimetic synthesis of metastable PbCrO4 nanoparticles by emulsion liquid membrane system with carrier and coupled treatment of Pb(II) and Cr(VI) wastewaters. Hrtij Chimica Sinica 62 946-950. 

It should be remarked here, that the tetrad effect is really not a new one" (our italics), and can be traced back to Endres (48) who divided the whole of the lanthanide series into four subdivisions, very much similar to those in the modern tetrad series. The paper of Fidelis and Siekierski (46) prompted Rowlands (49) to review the regularities . He plotted some 21 plots for 15 ligands and observed that the regularity proposed was based on insufficient data and this leaves doubt as to its general validity . Although the phosphoric acid systems exhibit the regularity, the same correlation could not be obtained for several other ligands. 

A variety of catalysts have been examined, comprising protonated acids inciuding phosphoric acid on Fuller s earth, sulphuric acid on the same support, and cation exchange materials. Lewis acids such as aluminium chloride, boron trifiuoride and its etherates, zinc chioride, siiica/aiumina, toluene-4-sulphonic acid and montmorillonite clays have found some application in numerous studies although generally the phosphoric acid system appears to be most favoured. 

Wachter, E. A. J. M. Hayes, 1985. Exchange of oxygen isotopes in carbon-dioxide-phosphoric acid systems. Chem. Geol. (Isot. Geosci. Sect.) 52 365-374. 

While studying the Ce(IV)/phosphoric acid system, a fibrous material of composition Ce(HP04)2.2H2O was obtained . Similar results were obtained with thorium . The structure of these compounds is unknown. The fibrous materials are of interest for electrochemical devices because they can be used to obtain very thin, autoconsistent membranes. The conductivity of anhydrous and trihydrated cerium phosphate is reported in Table 16.2. The conductivity of the hydrated compound was investigated as a function of temperature at different relative humidities and parametrized on the basis of the Arrhenius equation. The dependence of both activation energy and pre-exponential factor on relative humidity was similar to that of ZrP. This suggests that in cerium phosphate also the proton conduction is due, for the most part, to the hydrated surface of the particles. 

One of the frequently advertised advantages of the phosphoric acid imbibed polybenzimidazole systems is their zero water drag coefficient and their possibihty to operate with dry hydrogen and oxygen. However, a vast literature has been devoted to the study of the proton conduction and the effect of relative humidity on the conductivity of the PBl-phosphoric acid system. The promoting effect and the physicochemical interactions of water vapors with the polymer electrolyte and on the fuel cell performance have been explicitly shown for the PBl/PPy(50)coPSF 50/50 polymer blend imbibed with phosphoric acid under fuel cell conditions. ... 

Within the sensitivity limits (< 2x10" mol cm cm" s" Pa" ) of the instrument used in the study of Ref.94, the reacting gases permeability of the acid doped PBI/PPy(50)coPSF 50/50 membrane was not detectable, even for H2, in the temperature range of 130-170°C. It is also well known that org gen solubility is very low in phosphoric acid systems (0.5xl0""mol cm" Pa" ) and below the detection limits of the present technique. 

In all cases, the values of hydration enthalpy of the acid doped polymers reported in Table 4 are maity times higher than those reported for phosphoric acid in other references. This fact strongly suggests the positive effect of the polymer matnx on the ability of the membrane/ phosphoric acid system to absorb and retain water. 

It is likely that JB s fundamentally new results were in 1930 looked upon with scepticism, if not suspicion, because they had been obtained by such an intangible, mathematical analysis of data. Of course, the mathematics is the same as that involved in obtaining the acidity constants of the tetraprotonic pyrophosphoric acid, H4P2O7, whose step constants are much more different, making the relation between experiment and theo 7 more direct and transparent. Moreover, this system resembles the phosphoric acid system where die steps in the complexation (protonation) of the phosphate ion take place in quite distinct parts of the pH scale. 

Chemical Model Search Phosphoric Acid System... 

Plots of the logarithms of a values for the citric and phosphoric acid systems above are shown in Figures 5-7 and 5-8. Since, by definition, a C = [H A], we can write... 

A vast literature has been devoted to the study of the proton conduction and the effect of relative humidity on the conductivity of the polymer/ phosphoric acid systems [39, 43-48]. The conduction mechanism is substantiated through the proton transfer between a proton donor and a proton acceptor in combination to the ability of the proton carrier (positive ion) to rotate and move so that it will transfer the proton. Proton conductivity increases with relative humidity at a given temperature because the higher water content in the electrolyte lowers the viscosity within the membrane leading to higher mobility and rendering it more conductive [43], while it can play the role of proton carrier itself and provide more pathways (Hydrogen bonds) for protons to... 

Hydrophilic polymers such as poly (vinyl alcohol) or polyoxyethylene can be impregnated with a mineral acid and behave as solid proton conductors [119]. Several researchers [120] showed that polyethylenimine-sulfuric acid and phosphoric acid systems were well-behaved solid proton conductors under anhydrous conditions. Further information regarding these membranes is available in the literature [120]. Finally, Cakmak and Bicaksi [121] satisfactorily elaborated PEEK/PEI blend films. 

In this chapter, the early work on PBI-phosphoric acid systems that demonstrates the general appUcability of this polymer-acid membrane to high-temperature PEM operation will be reviewed. Two different PBI poly-... 

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