Gui-Bing Zhao

University of Wyoming, Laramie, WY, United States

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Publications (16)6.15 Total impact

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    ABSTRACT: Charge transfer reactions are commonly used to explain NOx conversion in nonthermal plasma. An analysis of optical emission spectra induced by pulsed corona discharge in NOx-containing argon suggests that, in fact, the contribution of charge transfer reactions to NOx conversion in nonthermal plasma is negligible. During electrical discharge in such gas mixtures, NO(B), an electronic excited state of NO formed due to the dissociative recombination reactions of NO2+ and N2O+ and the optical emission of NO(B) could be a proof that cations are responsible for NOx conversion. However, the optical emission of NO(B) is not observed, leading to the conclusion that cations are not involved to any measurable degree. Therefore, charge transfer reactions cannot play a significant role in nonthermal plasma largely because the cations are neutralized with electrons before any charge transfer reactions can occur and concentrations of radicals are far higher than those of cations, which inhibits charged particle reactions. Instead, neutral active species, such as atoms, molecular fragments, and excited molecules, are the major active species contributing to nonthermal plasma reactions.
    Journal of Applied Physics 02/2007; 101(3):033303-033303-14. · 2.21 Impact Factor
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    ABSTRACT: Laboratory studies of the effect of oxygen content in CO2 on the minimum miscibility pressure (MMP) are conducted on the n-C5H12/n-C16H34 model oil and Cottonwood Creek crude oil with three injection gases of different oxygen contents. The results indicate that the MMPs for these oils increase unfavorably with increasing O2 concentration in the CO2 stream. The experimental results are also supported by our modeling work using a multiple-mixing-cell model, which is found to capture the effects of compositions and temperature, and is found to be a robust and predictive method for determining the MMP. Our experiments and calculations indicate that the effect of O2 contamination on the MMP is larger for heavier oil and the effect of N2 impurity on the MMP is larger than that of O2 impurity.
    Industrial & Engineering Chemistry Research - IND ENG CHEM RES. 01/2007; 46(4).
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    ABSTRACT: Hydrogen sulfide (H2S) dissociation into hydrogen and sulfur has been studied in a pulsed corona discharge reactor (PCDR). Due to the high dielectric strength of pure H2S (∼2.9 times higher than air), a nonthermal plasma could not be sustained in pure H2S at discharge voltages up to 30kV with our reactor geometry. Therefore, H2S was diluted with another gas with lower dielectric strength to reduce the breakdown voltage. Breakdown voltages of H2S in four balance gases (Ar, He, N2, and H2) have been measured at different H2S concentrations and pressures. Breakdown voltages are proportional to the partial pressure of H2S and the balance gas. With increasing H2S concentrations, H2S conversion initially increases, reaches a maximum, and then decreases. H2S conversion and the reaction energy efficiency depend on the balance gas and H2S inlet concentrations. H2S conversion in atomic balance gases, such as Ar and He, is more efficient than that in diatomic balance gases, such as N2 and H2. These observations can be explained by proposed reaction mechanisms of H2S dissociation in different balance gases. The results show that nonthermal plasmas are effective for dissociating H2S into hydrogen and sulfur.
    Chemical Engineering Science - CHEM ENG SCI. 01/2007; 62(8):2216-2227.
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    ABSTRACT: In this work, we demonstrate that our simulation approach, referred to as the multiple-mixing-cell model, gives the same results as the analytical method for two-phase gas flooding. For a gas−oil system with nc components, the gas injection process leads to nc + 1 constant-composition zones, and the compositional path of the process, i.e., the path in composition space representing the total composition, is controlled by nc − 1 key thermodynamic equilibrium tie lines:  the initial tie line, the injection tie line, and nc − 3 crossover tie lines. In addition, our approach clearly demonstrates that both the gas/oil ratio and fluid mobility do not affect tie-line compositional paths, i.e., compositional paths that lie on the thermodynamic equilibrium tie lines, but they do affect nc − 2 non-tie-line compositional paths. Therefore, neither the gas/oil ratio nor the fluid mobility affects the minimum miscibility pressure (MMP). In the context of the multiple-mixing-cell model, this fact has never been explicitly clarified before.
    Industrial & Engineering Chemistry Research - IND ENG CHEM RES. 10/2006; 45(23).
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    ABSTRACT: 200–600 ppm of CO inhibit NO conversion in nonthermal Ar plasma, but do not produce N <sub>2</sub> O . However, 1.01% of CO has no effect on NO conversion, but produces N <sub>2</sub> O . In general, N <sub>2</sub> O conversion in Ar plasma decreases with increasing CO concentration. These experimental results cannot be explained by charge transfer reactions of Ar <sup>+</sup> . Selectivity analysis of all excited states of Ar possibly contributing to N O <sub>x</sub> conversion without and with CO suggests that only Ar (<sup>3</sup>P<sub>2</sub>) contributes to N O <sub>x</sub> conversion and CO dissociation. A kinetic model of 43 reactions is required to model NO conversion or N <sub>2</sub> O conversion in Ar without CO, whereas 81 reactions are required to model NO conversion and N <sub>2</sub> O conversion in Ar with CO. At constant gas pressure, a single set of model parameters can predict NO conversion or N <sub>2</sub> O conversion without and with CO. All experimental results can be explained using a reaction mechanism in which excited neutral states of Ar are the only active species, which supports the conclusion that cations have a negligible impact on these nonthermal plasma reactions.
    Journal of Applied Physics 07/2006; · 2.21 Impact Factor
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    ABSTRACT: This work reports the effect of capacitance, cathode material, gas flow rate and specific energy input on methane conversion, energy efficiency and product selectivity in a co-axial cylinder pulsed corona discharge reactor. Ethane and acetylene appear to be formed from dimerization of CH3 radicals and CH radicals, respectively, while ethylene is formed mainly from the dehydrogenation of ethane. At a given power input, low capacitance with high pulse frequency results in higher methane conversion and energy efficiency than operation at high capacitance with low pulse frequency. Platinum coated stainless steel cathodes slightly enhance methane conversion relative to stainless steel cathodes, perhaps due to a weak catalytic effect. As specific energy input increases, energy efficiency for methane conversion goes through a minimum, while the selectivity of acetylene has a maximum value. Comparison of methane conversion for different types of plasma reactors shows that the pulsed corona discharge is a potential alternative method for low temperature methane conversion.
    Chemical Engineering Journal. 01/2006;
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    ABSTRACT: Laser-induced fluorescence (LIF) is an effective in-situ probe for NO concentrations below 300ppm in a non-thermal plasma reactor. A new method has been developed to measure in-situ NO concentration in the reactor discharge region using a long-time—on the order of seconds—averaged fluorescence detection. This method, for quantifying NO concentration in a nonthermal plasma reactor, is simpler than a short-time—on the order of nanoseconds—fluorescence detection. For accurate measurement based on the new method, the LIF intensity must be close to the corona-induced fluorescence (CIF) intensity; the CIF intensity serves as a guide in selecting the LIF intensity. We find that a kinetic model proposed earlier works for two-tube reactors and represents the NO concentration in the middle of the reactor, which verifies the assumption of gas plug flow.
    Plasma Chemistry and Plasma Processing 07/2005; 25(4):351-370. · 1.73 Impact Factor
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    ABSTRACT: PPM-level concentrations of CO 2 are added to NO/N 2 mixtures to determine the effect of CO 2 on plasma generation and to investigate the mechanism of CO 2 reactions. Addition of 599.9 ppm CO 2 does not affect the electric discharge in NO x in N 2 nonthermal plasma. However, CO 2 slightly dissociates, with CO 2 conversion reaching a maximum of about 5.5% at the power input at which NO conversion ceases. NO(A), the first-excited electronic state of NO, is detected by corona-induced optical emission and is found to contribute to CO 2 dissociation. A kinetic model including 38 reactions is required to adequately model decomposition of NO x and CO 2 in the presence of CO 2 . About 18% of the NO(A) that is formed reacts with CO 2 to form NO, CO, and O.
    Industrial & Engineering Chemistry Research - IND ENG CHEM RES. 01/2005; 44(11).
  • Environmental Engineering Science - ENVIRON ENG SCI. 01/2005; 22(6):854-869.
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    ABSTRACT: This work explores the effect of gas pressure on the rate of electron collision reactions and energy consumption for NO conversion in N2 in a pulsed corona discharge reactor. A previous study showed that the rate constant of electron collision reactions, multiplied by the electron concentration, can be expressed as . The model parameter α remains constant with increasing gas pressure, which verifies the previous assumption that the electron temperature is inversely proportional to gas pressure. However, the model parameter β decreases with increasing gas pressure, which indicates that the rate constant of electron collision reactions decreases with increasing gas pressure. The new expression for the rate constant of electron collision reactions, , is more general because it explicitly accounts for the effect of gas pressure that was previously contained in the parameter β. The electron mean energy decreases with increasing gas pressure, which results in thermal dissipation of a larger fraction of the energy input to the reactor that heats the gas instead of producing plasma chemical reactions. Therefore, energy efficiency for NO conversion in N2 decreases with increasing gas pressure.
    Chemical Engineering Science. 01/2005;
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    ABSTRACT: Both NO x conversion and CO 2 conversion decrease with increasing percent-level CO 2 concentra-tion in nonthermal nitrogen plasma. The rate constants of electron collision reactions of both N 2 and CO 2 decrease with increasing CO 2 concentration because electronegative CO 2 reduces electron concentrations in the reactor due to the electron attachment process. The rate constant of CO 2 dissociation through electron collision is 1-2 orders of magnitude higher than that of N 2 dissociation because of low dissociation energy of CO 2 . Model data for reactor outlet NO x and CO x concentrations agree well with experimental data. The effect of CO 2 on NO, NO 2 , N 2 O, and CO concentrations can be explained on the basis of the proposed reaction mechanism and kinetic modeling.
    Industrial & Engineering Chemistry Research - IND ENG CHEM RES. 01/2005; 44(11).
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    ABSTRACT: The analysis of experimental data, chemical reaction mechanisms, and kinetic modeling data is used to determine the power input and pulsed-corona-discharge reactor configuration that minimizes energy consumption for converting N2O in nitrogen and N2O in argon, which are model binaries reminiscent of more complex NOx in flue gas systems. Specifically, it is found that in-series reactors are much more energy efficient than a single reactor and more energy efficient than parallel reactors. For example, 12 reactors in series are needed to remove 90% of N2O if its initial concentration in nitrogen is about 200 ppm.
    08/2004;
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    Industrial & Engineering Chemistry Research - IND ENG CHEM RES. 01/2004; 43(10):2315-2323.
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    ABSTRACT: Analysis of conversion mechanisms for NO and N2O in Ar plasma suggests that NO is converted through the reaction Ar+ + NO + e- → Ar + N + O, whereas N2O is converted through the reaction Ar+ + N2O + e- → Ar + N2 + O. A time-averaged lumped model developed on the basis of this analysis matches the experimental data. CO inhibits N2O conversion but not NO conversion. However, parts-per-million levels of CO affect neither N2O nor NO conversion. Compared to N2 plasma, which produces a weak streamer glow discharge and a small temperature increase along the reactor, Ar plasma produces a strong streamer discharge and a small temperature decrease along the reactor.
    Industrial & Engineering Chemistry Research - IND ENG CHEM RES. 01/2004; 43(23):7456-7464.
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    ABSTRACT: The goal of this experimental project was to design and fabricate a reactor and membrane test cell to dissociate hydrogen sulfide (HS) in a nonthermal plasma and to recover hydrogen (H) through a superpermeable multi-layer membrane. Superpermeability of hydrogen atoms (H) has been reported by some researchers using membranes made of Group V transition metals (niobium, tantalum, vanadium, and their alloys), but it was not achieved at the moderate pressure conditions used in this study. However, HS was successfully decomposed at energy efficiencies higher than any other reports for the high HS concentration and moderate pressures (corresponding to high reactor throughputs) used in this study.
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    ABSTRACT: All species that are likely to be responsible for nitrogen oxides (N 2 O, NO, and NO 2) conversion in nitrogen plasma are analyzed in detail through carefully designed systematic experiments and theoretical analysis. The effect of ppm-level CO 2 , CO, and 1% CO on N 2 O conversion reveals that the N 2 O conversion occurs mainly by interaction with N 2 (A 3 ∑ u +) excited species. The effect of 1% CO on the NO conversion suggests that only N atom radicals are predominantly involved in NO conversion. NO 2 conversion, on the other hand, occurs by interaction with both N 2 (A 3 ∑ u +) and N atom radicals. Therefore, only two active species, N 2 (A 3 ∑ u +) and N atom radicals, are found to be responsible for nitrogen oxides conversion in nitrogen plasma.