Pressure jump method

A modification of the Nelson and Eggertsen method was made by Haley who also used helium and nitrogen in a continuous flow system. Haley s apparatus differs from that described in the previous chapter in that the sample cell can be pressurized while the effluent flows from a pressure regulator through the cell to a flow controller and then to the detector maintained at ambient pressure. 

Starting with a 10% nitrogen-in-helium mixture, the sample, held slightly above ambient pressure, is immersed in the coolant. When the adsorption signal is complete, the pressure is raised to 2 atm, which increases the partial pressure of nitrogen to 0.2 atm or the equivalent of a 20 % mixture at 1.0 atm. After the completion of each adsorption signal, the pressure is incrementally increased until, at ISOpsia saturation is reached. 

Desorption is accomplished by incrementally decreasing the pressure and monitoring the nitrogen-rich desorption signals. 

The entire apparatus must be very tight to prevent leakage at high pressures. The sample cell should be metal or heavy wall glass and is wrenched into position. A further difficulty is that at high pressures the 

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Strehlow H and Beoker M 1959 The pressure-jump method for the measurement of rates of ionio reaotions Z. Eiektrochem. 63 457-61... 

In the pressure-jump method, the solution is pressurized, usually to several thousand atmospheres. At the desired moment a diaphragm is mechanically ruptured. The... 

Pressure filters, 76 658-659 horizontal belt, 77 379 thickening, 77 382-388 Pressure gauge, 20 645 Pressure gradients, flow caused by, 9 110 Pressure infiltration, of metal-matrix composites, 76 167-169 Pressure injection, moldings, 10 11 Pressure-jump method, 73 427-428... 

The principle of the pressure-jump method is based on the pressure dependence of the equilibrium constant, i.e.,... 

Due to the fast kinetics of adsorption/desorption reactions of inorganic ions at the oxide/aqueous interface, few mechanistic studies have been completed that allow a description of the elementary processes occurring (half lives < 1 sec). Over the past five years, relaxation techniques have been utilized in studying fast reactions taking place at electrified interfaces (1-7). In this paper we illustrate the type of information that can be obtained by the pressure-jump method, using as an example a study of Pb2+ adsorption/desorption at the goethite/water interface. 

Figure 1. Typical relaxation curve in the aqueous y-A1203 -Cu(N03)2 suspension observed by using the pressure-jump method. [P] = 30 g/dm3, and I = 7.5 x10-3 at 25 °C sweep 20 ms/div.

Table III suggests some of the proton transfer kinetic studies one is likely to hear most about in the near future. The very first entry, colloidal suspensions, is one that Professor Langford mentioned earlier in these proceedings. In the relaxation field, one of the comparatively new developments has been the measurement of kinetics of ion transfer to and from colloidal suspensions. Yasunaga at Hiroshima University is a pioneer in this type of study (20, 21, 22). His students take materials such as iron oxides that form colloidal suspensions that do not precipitate rapidly and measure the kinetics of proton transfer to the colloidal particles using relaxation techniques such as the pressure-jump method.

PRESSURE-JUMP METHOD CHEMICAL KINETICS PRE-STEADY STATE PHASE Prigogine,... 

Astumian, R.D. Sasaki, M. Yasunga,T. Schelly, Z.A. (1981) Proton adsorption-desorption kinetics on iron oxides in aqueous suspensions, using the pressure jump method. J. Phys. Chem. 85 3832—3835 Atkins, P.W. (1990) Physical chemistry. 4 Ed. 

Figure 4.12. Typical relaxation curves in aqueous y-ATOj-PbfNO, suspension observed by the pressure-jump method with (a) electric conductivity and (b) turbidity detection. Concentration of A1203, Cp, is 15 g dm 3 at 293 K sweep, 2 ms/division wavelength in (b), 525 nm, [From Hachiya et al., 1979), with permission.]...

Gruenewald, B., and Knoche, W. (1979). Recent developments and applications of pressure jump methods. In Techniques and Applications of Fast Reactions in Solutions (W. J. Gettins and E. Wyn-Jones, eds.), pp. 87-94. Reidel Publ., Dordrecht, The Netherlands. 

The conversion of a wide variety of P, S, and N organic compounds over H-mordenite and HZSM-5 catalysts has been described. The reaction of nitric oxide and chlorine near to equilibrium over H-mordenite was studied by use of a pressure-jump method. The preparation of aliphatic amines from the reaction of Ci—C3 alcohols and ethers with ammonia over HZSM-5, HZSM-11, and HZSM-21 has been described. The proportion of secondary and tertiary amines decreased as the size of alcohol or ether reactant increased. Chang and Silvestri showed that methanethiol is converted over HZSM-5 to hydrocarbons in a broadly similar way to methanol. However, a higher temperature (755 K) is required and even so 27.2 % total carbon remains unconverted as (CH3)2S. Propane is the major paraffin and the aromatics are largely C9. 

Knoche, W. 1974. Pressure-jump methods. 1974. p, 187-210. In G.G. Hammes (ed.) Techniques of chemistry, Vol. 6, Investigations of rates and mechanisms of reactions. 3rd ed. Wiley, New York. 

Hachiya, K., Takeda, K., and Yasunaga, T, Pressure-jump method to adsorption-desorption kinetics. Adsorption Sci. Technol.. 4. 25, 1987. 

Of the relaxation methods only the temperature-jump and pressure-jump methods have been adapted for high pressure application, and of these two only the former (hptj) has been used in many systems for volume of activation determinations. Despite the flurry of activity in developing hptj,84 88 the method has not found application in organometallic chemistry, although in principle it could be employed if the system properties and solvent were suitable. 

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