The aqueous-phase oxidation of m-xylene and phenol has been studied in a batch autoclave reactor. Both reactions were characterized by an induction period during which little of the organic was oxidized, followed by a rapid reaction phase during which most of the organic was destroyed. The distribution of organic between vapor and liquid and interphase transfer caused by liquid-phase reaction and sampling were considered in the analysis of the data. Over the range of concentrations studied, the length of the induction period is independent of the organic concentration and inversely proportional to the dissolved oxygen concentration. During the rapid reaction phase, the oxidation kinetics are first order in organic and half order in dissolved oxygen. Activation energies for m-xylene and phenol were found to be 103 and 94 kJ/g-mol during the induction period and 89.5 and 112 kJ/g-mol during the rapid reaction phase.

No abstract

High temperature protonic-conducting oxides based on the perovskite structure have been studied extensively since their discovery in 1981. 1 The hydrogen and deuterium isotope conductivities in these oxides have been evaluated 2,3 recently, and their potential application as hydrogen separation membranes has been discussed. 4 However, there are no reported studies on the tritium ion-conduction in these perovskites. In this paper, we report the hydrogen (H), deuterium (D), and tritium (T) conductivities of three protonic conducting perovskites, viz. SrZr 0.9 Yb 0.1 O 2.95 , BaCe 0.9 Yb 0.1 O 2.95 , and SrCe 0.95 Yb 0.05 O 2.975 . The conductivity of tritium ions through these perovskites not only gives fundamental information regarding the hydrogen transport in these perovskites, but also allows for the exciting possibility of tritium separation using these oxides as an electrochemical membrane.The proton-conducting compounds that were investigated in this study were selected for the following reasons. (1) The strontium zirconates are known to have the best chemical stability in CO 2 containing atmospheres (stable in 20 vol % CO 2 at 700ЊC). 5 (2) The barium cerates have one of the highest magnitudes of protonic conductivity. 6 (3) The strontium cerates, having a high protonic transference number, are the most extensively studied proton-conducting perovskites. [7][8][9] Although a H/D isotope effect has been shown in proton-conducting perovskites, the data in the literature is neither extensive nor consistent enough to clearly establish a model for protonic conduction in these perovskites. 2 The measured difference in activation energies for the H-and D-ion conduction has eliminated the possibility of proton hopping governed by a classical theory and has given support to a semiclassical approach. This approach takes into consideration the difference in zero point energies between the ground state of H and D, given by Eq. 1 10where E H and E D are the activation energies for the H-and D-ion conduction, respectively, and H and D are the OH and OD stretching frequencies. However the pre-exponential factors presented in the literature do not obey the predictions of the semiclassical theory given by Eq. 2, c eff -concentration of mobile protons, and v ϭ unit cell volume.In this paper, we present the H-, D-, and T-ion conductivities of SrZr 0.9 Yb 0.1 O 2.95 and BaCe 0.9 Yb 0.1 O 2.95 , and attempt to explain the various factors that need to be addressed in order to unambiguously determine the conduction mechanism in these perovskites. ExperimentalSingle-phase perovskite samples of SrZr 0.9 Yb 0.1 O 2.95 , BaCe 0.9 Yb 0.1 O 2.95 , and SrCe 0.95 Yb 0.05 O 2.975 were prepared using standard solid-state methods by heating appropriate stoichiometric mixtures of BaCO 3 , SrCO 3 , CeO 2 , ZrO 2 , and Yb 2 O 3 at 1773 K for 20 h with two intermediate ballmilling steps. The formation of a single-phase orthorhombic perovskite was confirmed by powder X-ray diffraction using a Siemens D 5000 diffractometer. Dense ceramic samples (...

In an effort to discover techniques for increasing intrinsic aqueous-phase oxidation rates, the rate of m-xylene oxidation has been studied at 400-473 K and 13.8 MPa in the presence of hydrogen peroxide and phenol. At these conditions, hydrogen peroxide decomposes instantaneously to produce free radicals necessary to initiate the m-xylene oxidation, thereby greatly reducing or even eliminating the induction period normally associated with m-xylene oxidation. Once the peroxide radicals are consumed, however, the m-xylene oxidation rate in the rapid reaction phase returns to the values expected in the absence of peroxide. Addition of more easily oxidized phenol to m-xylene produces a synergizing effect in which cross-initiation greatly enhances the m-xylene oxidation rate. The length of the m-xylene induction phase is greatly reduced, approaching the intrinsic phenol induction time, and the rapid reaction-phase rate constant for m-xylene can be increased by almost 2 orders of magnitude compared to the rate constant for m-xylene reacting alone.

No abstract