Xudong Hu

University of Wyoming, Laramie, WY, United States

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Publications (19)24.55 Total impact

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    ABSTRACT: A low-pressure Carbon Filter Process (patent pending) is proposed to capture carbon dioxide (CO 2) from flue gas. This filter is filled with a low-cost carbonaceous sorbent, such as activated carbon or charcoal, which has a high affinity (and, hence, high capacity) to CO 2 but not to nitrogen (N 2). This, in turn, leads to a high CO 2 /N 2 selectivity, especially at low pressures. The Carbon Filter Process proposed in this work can recover at least 90% of flue-gas CO 2 of 90%+ purity at a fraction of the cost normally associated with the conventional amine absorption process. The Carbon Filter Process requires neither expensive materials nor flue-gas compression or refrigeration, and it is easy to heat integrate with an existing or grassroots power plant without affecting the cost of the produced electricity too much. An abundant supply of low-cost CO 2 from electricity producers is good news for enhanced oil recovery (EOR) and enhanced coal-bed methane recovery (ECBMR) operators, because it will lead to higher oil and gas recovery rates in an environmentally sensitive manner. A CO 2 -rich mixture that contains some nitrogen is much less expensive to separate from flue-gas than pure CO 2 ; therefore, mixed CO 2 /N 2 -EOR and CO 2 /N 2 -ECBMR methods are proposed to maximize the overall carbon capture and utilization efficiency.
    Industrial & Engineering Chemistry Research 05/2008; 47(10). · 2.24 Impact Factor
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    ABSTRACT: Based on sorption experiments up to 180 bar and 75 °C, the CO2 solubility in an ammonium-type ionic polymer, such as poly(p-vinylbenzyltrimethyl ammonium tetrafluoroborate), is found to be much higher than that in an imidazolium-type ionic polymer, such as poly(1-(p-vinylbenzyl)-3-methyl-imidazolium tetrafluoroborate), which points to a cation-type effect on the CO2 sorption in polymerized ionic liquids. These two polymers remain glassy in the temperature and pressure ranges studied in this work. The CO2 solubility increases with decreasing temperature and with increasing pressure, but it reaches a limiting value, beyond which it is insensitive to pressure.
    Industrial & Engineering Chemistry Research - IND ENG CHEM RES. 07/2007; 46(17).
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    ABSTRACT: Brominated poly(2,6-diphenyl-1,4-phenylene oxide) (BPPOdp) is synthesized as a new membrane material for gas separation. BPPOdp forms flexible membranes with higher CO2 permeability (PCO2 = 78 Barrer) and selectivity (αCO2/N2 = 30) than poly(2,6-dimethyl-1,4-phenylene oxide) (PPOdm) membranes. BPPOdp also forms nanocomposite membranes with silica nanoparticles. The nanocomposite membranes have a greatly enhanced CO2 permeability while maintaining the CO2/N2 and CO2/CH4 selectivities of the pure BPPOdp membranes. The CO2 permeability increases as the silica content increases in the membrane. The 10-nm silica nanoparticles are more effective at increasing the CO2 permeability than the 30-nm silica nanoparticles. Mechanism studies show that the enhanced permeability results from the nanogaps between the silica nanoparticles and the polymer chains due to their incompatibility.
    Industrial & Engineering Chemistry Research - IND ENG CHEM RES. 03/2007; 46(8).
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    ABSTRACT: Silica-impregnated, brominated PPO [poly(phenylene oxide)] (BPPO) membranes exhibit enhanced CO2 permeability relative to pure BPPO membranes due to higher gas solubility and especially higher gas diffusivity. Among the three silica sizes (2, 10, and 30 nm) characterized in this work, the 10 nm silica is found to result in the highest gas permeability, about 5 times higher than that of the pure BPPO membranes. These permeability enhancements do not cause an appreciable loss of selectivity, which remains essentially unchanged, for example, about 21 for the CO2/N2 separation and about 15 for the CO2/CH4 separation. The permeability increases with increasing silica content, which, however, cannot exceed about 0.35 silica/BPPO weight ratio due to a substantial increase in brittleness.
    Industrial & Engineering Chemistry Research - IND ENG CHEM RES. 02/2007; 46(5).
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    ABSTRACT: The CO2 solubility in two ammonium-based polymerized ionic liquids, poly(p-vinylbenzyltrimethyl ammonium tetrafluoroborate), P[VBTMA][BF4], and poly([2-(methacryloyloxy)ethyl] trimethyl ammonium tetrafluoroborate), P[MATMA][BF4], up to 75°C and 15bar, is found to be higher than that in bisphenol-A polysulfone. The CO2 solubility in P[VBTMA][BF4] is found to be higher than that in P[MATMA][BF4] at the same temperature and pressure.
    Fluid Phase Equilibria 01/2007; 256(1):75-80. · 2.38 Impact Factor
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    ABSTRACT: Polyethylene glycol (PEG) is grafted onto ionic polymers poly[p-vinylbenzyltrimethylammonium tetrafluoroborate] (P[VBTMA][BF4]) and poly[2-(methylacryloyloxy)ethyl-trimethylammoniumtetrafluoroborate] (P[MATMA][BF4]). Membranes made of P[VBTMA][BF4]-g-PEG and P[MATMA][BF4]-g-PEG are found to be CO2 selective for CO2/CH4 and CO2/N2 separations, and less brittle than those made of pure P[VBTMA][BF4] and P[MATMA][BF4]. At the same permeability, the P[MATMA][BF4]-g-PEG membranes are demonstrated to have a higher CO2 selectivity than the previous polymeric membranes. The selectivity of both P[VBTMA][BF4]-g-PEG and P[MATMA][BF4]-g-PEG is primarily due to the solubility differences, not the diffusivity differences.
    Journal of Membrane Science 01/2006; 281:130-138. · 4.09 Impact Factor
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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: The configuration of a nonthermal plasma reactor strongly affects the rate of electron collision reactions. Experiments involving the decomposition of NO in N2 were performed in a reactor in which the number of parallel reactor tubes varied from 1 to 10 at a constant pressure of 147.6 kPa and ambient temperature. A previously developed lumped model of the reactions accurately predicted the effects of varying the initial concentrations of NO (from 240 ppm to 593 ppm) and gas residence time (from 1.93 to 7.42 s). With an increasing number of parallel reactor tubes, the rate of electron collision reactions decreases because the energy input per unit reactor volume at unit time decreases, while the energy consumption per molecule of NO converted to N2 and O2 decreases due to electrical and geometric effects associated with the decreasing peak width of the discharge voltage pulses and increasing reactor capacitance. Therefore, increasing the number of parallel reactor tubes provides a viable scale-up method for constructing more efficient pulsed corona discharge reactors. © 2005 American Institute of Chemical Engineers AIChE J, 2005
    AIChE Journal 05/2005; 51(6):1813 - 1821. · 2.58 Impact Factor
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    ABSTRACT: NO is mainly converted to NO2 by chemical oxidation in the presence of oxygen. Initial selectivity analysis shows that three electron collision reactions are important for NOx evolution in O2/N2. The rate constants of these reactions decrease with increasing oxygen concentration. This is because oxygen is electronegative and thus reduces electron concentration. The rate constant of O2 dissociation by electron collision reaction is almost two orders of magnitude higher than that of N2 dissociation. NO formation occurs predominantly through N(2D) + O2 → NO + O. The critical oxygen concentration, defined as the concentration at which the NOx formation rate counterbalances the NOx decomposition rate, increases with increasing initial NO concentration. © 2005 American Institute of Chemical Engineers AIChE J, 2005
    AIChE Journal 05/2005; 51(6):1800 - 1812. · 2.58 Impact Factor
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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: 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: 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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    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.
    Industrial & Engineering Chemistry Research 08/2004; 43(17). · 2.24 Impact Factor
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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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    Industrial & Engineering Chemistry Research - IND ENG CHEM RES. 01/2004; 43(10):2315-2323.
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    ABSTRACT: There has been an increasing recent research interest in the removal of NOx from combustion gases using electrical discharges, especially pulsed corona discharge reactors. The major issues in development of this technology are (a) the energy consumption required to achieve the desired pollutant reduction; and (b) the formation of undesirable byproducts. In this study, the transformations and destruction of nitrogen oxides—NO, NO2 and N2O—were investigated in a pulsed corona discharge reactor. Gas mixtures—NO in N2, N2O in N2, NO2 in N2 and NO–N2O–NO2 in N2—were allowed to flow through the reactor with initial concentrations, flow rates and energy input as operating variables. The reactor effluent gas stream was analyzed for N2O, NO, NO2, by means of an FTIR spectrometer. In some experiments, oxygen was measured using a gas chromatograph.Reaction mechanisms were proposed for the transformations and destruction of the different nitrogen oxides within a unified model structure. The corresponding reaction rates were integrated into a simple reactor model for the pulsed corona discharge reactor. The reactor model brings forth the coupling between reaction rates, electrical discharge parameters, and fluid flow within the reactor. It was recognized that the electron-impact dissociation of the background gas N2 leads to both ionic and radical product species. In fact, ionic reactions were found responsible for N2O destruction. Radical reactions were dominant in the transformation and destruction of NO and NO2. However, decomposition of N2+ ions also leads to indirect production of N radicals; this appears to be a less-power intensive route for NO destruction though longer residence times may be necessary. In addition, the decomposition of N2+ ions limits the N2O destruction that can be achieved. Comparison with our experimental data, as well as data in the literature, was very encouraging.
    Fuel 01/2003; · 3.36 Impact Factor
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    ABSTRACT: The removal of N2O by a pulsed corona reactor (PCR) was investigated. Gas mixtures containing N2O were allowed to flow in the reactor at various levels of energy input, and for different background gases, flow rates, and initial pollutant concentrations. The reactor effluent gas stream was analyzed for N2O, NO, NO2, by means of an FTIR spectrometer. It was found that destruction of N2O was facilitated with argon as the background gas; the conversion dropped and power requirements increased when nitrogen was used as the background gas.Reaction mechanisms are proposed for the destruction of N2O in dry argon and nitrogen. Application of the pseudo-steady state hypothesis permits development of expressions for the overall reaction rate in these systems. These reaction rates are integrated into a simple reactor model for the pulsed corona discharge reactor. The reactor model brings forth the coupling between reaction rates, electrical discharge parameters, and fluid flow within the reactor. Comparison with experiment is encouraging, though the needs for additional research are clearly identified.
    Fuel 01/2002; · 3.36 Impact Factor