William H. Green

Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

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Publications (197)480.24 Total impact

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    ABSTRACT: Methane (CH4) reforming was carried out in an internal combustion engine (an “engine reformer”). We successfully produced syngas from the partial oxidation of natural gas in the cylinder of a diesel engine that was reconfigured to perform spark ignition. Performing the reaction in an engine cylinder allows some of the exothermicity to be captured as useful work. Intake conditions of 110 kPa and up to 480 °C allowed low cycle-to-cycle variability (COVnimep < 20 %) at methane-air equivalence ratios (ΦM) of 2.0, producing syngas with an H2-to-CO ratio of 1.4. Spark ignition timing was varied between 45–30° before top-dead-center (BTDC) piston position, showing significant improvement with delayed timing. Hydrogen (H2) and ethane (C2H6) were added to simulate recycle from a downstream synthesis reactor and realistic natural gas compositions, respectively. Adding these gases yielded a stable combustion up to hydrocarbon-air equivalence ratios (ΦHC) of 2.8 with COVnimep < 5 %. Ethane concentrations (with respect to methane) of up to 0.2 L/L (20 vol%) (with and without H2) produced robust and stable combustions, demonstrating that the engine can be operated across a range of natural gas compositions. Engine exhaust soot concentrations demonstrated elevated values at ΦHC > 2.4, but < 1 mg/L below these equivalence ratios. These results demonstrate that the engine reformer could be a key component of a compact gas-to-liquids synthesis plant by highlighting the operating conditions under which high gas conversion, high H2-to-CO ratios close to 2.0, and low soot production are possible. This article is protected by copyright. All rights reserved
    No preview · Article · Jan 2016 · The Canadian Journal of Chemical Engineering
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    ABSTRACT: The vapor-phase hydrodeoxygenation (HDO) of m-cresol is investigated at 593 K and H2 pressures ≤1 bar for supported catalysts comprised of 10 wt% MoO3 dispersed over SiO2, γAl2O3, TiO2, ZrO2, and CeO2. Reactivity data show that all catalysts selectively cleave C-O bonds without saturating the aromatic ring, thus effectively transforming m-cresol into toluene at moderate to high conversions. MoO3/ZrO2 and MoO3/TiO2 feature the highest initial site time yields (23.4 and 13.9 h-1, respectively) and lowest first-order deactivation rate constants (0.013 and 0.006 h-1, respectively) of all catalysts tested after ca. 100 h on stream. Characterization studies demonstrate that the supports play an important role in stabilizing partially reduced, coordinatively unsaturated (CU) sites in surface oligomeric Mo moieties. Post-reaction X-ray photoelectron spectroscopy shows that the catalysts with higher activity feature larger proportions of intermediate oxidation species (Mo5+ and Mo3+). In contrast, the catalysts with lower reactivity show different oxidation states: bulk MoO3 features mostly Mo4+ and metallic Mo species, while MoO3/CeO2 features a high proportion of Mo6+ species. An inverse correlation is established between the catalyst activity and both the maximum hydrogen consumption temperature obtained during temperature programmed reduction, and the support cation electronegativity (with the exception of MoO3/CeO2).
    No preview · Article · Nov 2015 · Journal of Catalysis
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    ABSTRACT: The use of a rule-based automated kinetic model builder Genesys is illustrated for the thermal decomposition of diethyl sulfide and ethyl methyl sulfide. Rule-based automatic kinetic model generation builds-upon the users’ expert knowledge to define constraints per reaction family to limit the model size and exclude species and reactions that are considered irrelevant. In the case of alkyl sulfide pyrolysis intermolecular hydrogen abstractions, intermolecular additions/β-scissions and intermolecular homolytic substitutions are used to iteratively expand the model not considering species with more than 5 heavy atoms. Furthermore, the formation of biradical species and cyclic structures was avoided. Rate coefficients of elementary reactions and thermochemical properties of molecules were estimated through group additive methods, with parameters solely derived from high level ab initio calculations. 39 reactions were added to the model after the automatic generation out of which 37 got rate constants assigned from ab initio calculations. The generated model, consisting of 444 reactions between 28 molecules and 38 radical species, was validated using experimental data for the thermal decomposition of diethyl sulfide and ethyl methyl sulfide and showed that measured and predicted species mole fractions are in good agreement. However, there is a clear need for more accurate and more detailed experimental data for the pyrolysis of sulfur containing compounds.
    Full-text · Article · Oct 2015 · The Chemical Engineering Journal
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    ABSTRACT: The low-temperature auto-ignition of fuels is a complex process, occurring in multiple stages with distinct chemical processes governing each stage. The conversion from alkyl radical to chain branching products, which occurs through successive O-2 additions followed by thermal decomposition of the products, is at the core of the auto-ignition process. Our detailed understanding of this central process continues to evolve, with recent theoretical kinetics studies providing a particularly comprehensive description of the radical oxidation process for propane. In this study, we employ this improved description in a detailed numerical and analytical exploration of the first-stage ignition delay for low-temperature auto-ignition of propane, which may be considered as a prototype for larger alkane fuels. The traditional first-stage of ignition can be divided into two stages (stage-1A and stage-1B). During stage-1A, the concentration of radicals grows exponentially, and both OH and HO2 are important in the consumption of the fuel and generation of alkyl radicals. Stage-1A ends when the concentration of HO2 is sufficiently high that the chain-terminating bimolecular reaction HO2 + HO2 becomes competitive with other HO2 reactions including HO2 + fuel, thus slowing the HO2 concentration rise such that it is no longer a key contributor to fuel consumption. During stage-1B, increasing temperature and growing side reactions with secondary chemistry reduce the positive feedback and the concentrations of ketohydroperoxide species stop growing exponentially. The end of this stage is associated with the maximum in ketohydroperoxide, after which it is depleted. We present simple analytical approximations for the time it takes to complete these two sub-stages. These expressions clarify which rate constants control first-stage ignition, and they quantify how the ignition is influenced by mixture composition, temperature and pressure. The analysis is also extended to longer alkane fuels and is shown to provide fairly reliable predictions of the first-stage ignition delay.
    No preview · Article · Aug 2015 · Combustion and Flame
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    ABSTRACT: High concentrations of fuel-range hydrocarbons may be recovered from heavier alkyl-aromatic compounds in crude oil after supercritical water (SCW) treatment. Arabian Heavy (AH) crude oil was treated in SCW and analyzed using two-dimensional gas chromatography (GC × GC-FID). Cracking mechanisms were investigated using the model compound hexylbenzene under similar SCW treatment conditions. The results of the model compound experiments were compared to predictions of a kinetic model built by the Reaction Mechanism Generator (RMG). AH crude cracked significantly during SCW treatment. The GC-observable mass fraction increased by 90%. We conducted studies on the distilled samples of crude oil and found that significant changes in the composition of the SCW-treated heavy fraction occurred. Significant formation of aliphatic hydrocarbons and small-chain BTX-type compounds were found in the SCW-processed samples. Hexylbenzene conversions differed between the crude oil studies and the model compound studies. The mechanistic model for the cracking of hydrocarbons during SCW treatment of the model compound hexylbenzene predicted the observed major liquid products toluene, styrene, and ethylbenzene. The selectivity of ethylbenzene and styrene changed over time. The apparent conversion of styrene into ethylbenzene was possibly via a reverse disproportionation reaction. Ultimately, a mechanism was built that serves as a basis for understanding the kinetics of hydrocarbon cracking in SCW.
    No preview · Article · Jul 2015 · Energy & Fuels
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    ABSTRACT: Natural gas has the potential to increase the biofuel production output by combining Gas- and Biomass-to-Liquids (GBTL) processes followed by naphtha and diesel fuel synthesis via Fischer-Tropsch (FT). This study reflects on the use of commercial-ready configurations of GBTL technologies and the environmental impact of enhancing biofuels with natural gas. The autothermal and steam-methane reforming processes for natural gas conversion and the gasification of biomass for FT fuel synthesis are modeled to estimate system well-to-wheel emissions and compare them to limits established by U.S. renewable fuel mandates. We show that natural gas can enhance FT biofuel production by reducing the need for water gas shift (WGS) of biomass-derived syngas to achieve appropriate H2:CO ratios. Specifically, fuel yields are increased from less than 60 gallons per ton to over 100 gallons per ton with increasing natural gas input. However, GBTL facilities would need to limit natural gas use to less than 19.1% on a LHV energy basis (7.83 wt. %) to avoid exceeding the emissions limits established by the Renewable Fuels Standard (RFS2) for clean, advanced biofuels. This effectively constitutes a blending limit that constrains the use of natural gas for enhancing the Biomass-To-Liquids (BTL) process.
    Full-text · Article · Jun 2015 · Environmental Science and Technology
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    ABSTRACT: This work presents shock tube experiments and kinetic modeling efforts on the pyrolysis and combustion of JP-10. The experiments were performed at 6–8 atm using 2000 ppm of JP-10 over a temperature range of 1000–1600 K for pyrolysis and oxidation equivalence ratios from 0.14 to 1.0. This work distinguishes itself from previous studies as GC/MS was used to identify and quantify the products within the shocked samples, enabling the tracking of product yield dependence on equivalence ratio as well as identifying several new intermediates that form during JP-10’s decomposition. A detailed, comprehensive model of JP-10’s combustion and pyrolysis kinetics was constructed with the help of RMG, an open-source reaction mechanism generation software package. The resulting model, which includes 691 species reacting in 15,518 reactions, was extensively validated against the shock tube experimental dataset as well as newly published flow tube pyrolysis data from Ghent. Most of the important rate coefficients were computed using quantum chemistry. The model succeeds in identifying all major pyrolysis and combustion products and captures key trends in the product distribution. Simulated ignition delays agree within a factor of 4 with most experimental ignition delay data gathered from literature. The presented experimental work and modeling efforts yield new insights on JP-10’s complex decomposition and oxidation chemistry and identify key pathways towards aromatics formation.
    No preview · Article · May 2015 · Combustion and Flame
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    Yury V. Suleimanov · William H. Green
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    ABSTRACT: We present a simple protocol which allows fully automated discovery of elementary chemical reaction steps using in cooperation double- and single-ended transition-state optimization algorithms - the freezing string and Berny optimization methods, respectively. To demonstrate the utility of the proposed approach, the reactivity of several systems of combustion and atmospheric chemistry importance is investigated. The proposed algorithm allowed us to detect without any human intervention not only "known" reaction pathways, manually detected in the previous studies, but also new, previously "unknown", reaction pathways which involve significant atom rearrangements. We believe that applying such a systematic approach to elementary reaction path finding will greatly accelerate the possibility of discovery of new chemistry and will lead to more accurate computer simulations of various chemical processes.
    Full-text · Article · May 2015 · Journal of Chemical Theory and Computation
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    R Mével · K Chatelain · L Catoire · W H Green · J E Shepherd
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    ABSTRACT: Despite the beneficial impact of biofuels on most regulated pollutants and carbon dioxide emission, their combustion results in an increased production of aldehydes which are highly toxic. The oxidation of ac-etaldehyde by oxygen behind reflected shock waves has been investigated by simultaneously recording the emission profiles of excited OH*, CO 2 * and CH*. Experiments were performed at T 5 =1295-1580 K and P 5 =306-404 kPa. Equivalence ratios were Φ=0.5, 1 and 1.5. The argon dilution was held constant at 97%. Five detailed reaction mechanisms were tested with respect to the presently obtained data and those from the literature. The JetSurf model and one obtained using the RMG software overestimate the present ignition delay-times but reproduce fairly well the data from Yasunaga et al., Wang et al. and Kern et al.. The models from Konnov and Dagaut are in good agreement with the present measurements and reproduce some of the results of Yasunaga et al., Wang et al., Kern et al. and Bentz et al.. Overall, the model of Mével predicts a too high reactivity. Analyses have demonstrated the importance of the following reactions: R 1 : CH 3 CHO=CH 3 + HCO; R 2 : CH 3 CHO+CH 3 =CH 3 CO+CH 4 ; R 3 : CH 3 CHO+H=CH 3 CO+H 2 ; and R 4 : CH 3 CHO+CH 3 =CH 2 HCO+CH 4 .
    Full-text · Conference Paper · May 2015
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    ABSTRACT: The reaction between vinyl radical, C_2 H_3, and 1,3-butadiene, 1,3-C_4 H_6, has long been recognized as a potential route to benzene, particularly in 1,3-butadiene flames, but the lack of reliable rate coefficients has hindered assessments of its true contribution. Using laser flash photolysis and visible laser absorbance (λ=423.2 nm) we measured the overall rate coefficient for C_2 H_3+1,3-C_4 H_6, k_1, at 297 K≤T≤494 K and 4≤P≤100 Torr. k_1 is well-described in this range by the high-pressure-limit modified Arrhenius expression below. k_1=6.5×〖10〗^(-20) cm^3 molecule^(-1) s^(-1)×T^2.40 exp(-(1.76 kJ mol^(-1))/RT) Using photoionization time-of-flight mass spectrometry (PI TOF-MS) we also investigated the products formed. At T≤494 K and P=25 Torr we found only C_6 H_9 adduct species, while at 494 K≤T≤700 K and P=4 Torr, we observed ≤~10% branching to cyclohexadiene in addition to C_6 H_9. Quantum chemistry master-equation calculations indicate that n-C_6 H_9 is the dominant product at low T, consistent with our experimental results, and predict the rate and branching ratios at higher T where chemically activated channels become important.
    No preview · Article · Apr 2015 · The Journal of Physical Chemistry A
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    ABSTRACT: Potential energy surfaces and reaction kinetics were calculated for 40 reactions involving sulfur and oxygen. This includes 11 H2O addition, 8 H2S addition, 11 hydrogen abstraction, 7 beta scission, and 3 elementary tautomerization reactions, which are potentially relevant in the combustion and desulfurization of sulfur compounds found in various fuel sources. Geometry optimizations and frequencies were calculated for reactants and transition states using B3LYP/CBSB7, and potential energies were calculated using CBS-QB3 and CCSD(T)-F12a/VTZ-F12. Rate coefficients were calculated using conventional transition state theory, with corrections for internal rotations and tunneling. Additionally, thermochemical parameters were calculated for each of the compounds involved in these reactions. With few exceptions, rate parameters calculated using the two potential energy methods agreed reasonably, with calculated activation energies differing by less than 5 kJ/mol. The computed rate coefficients and thermochemical parameters are expected to be useful for kinetic modeling
    Preview · Article · Apr 2015 · Physical Chemistry Chemical Physics
  • Michael T. Timko · Ahmed F. Ghoniem · William H. Green
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    ABSTRACT: Supercritical water upgrading (SCWU) of heavy oils reduces sulfur content and decreases average molecular weight, without rejecting carbon as coke products. Despite many years of industrial and academic scrutiny, many fundamental questions remain in the field: intrinsic reaction rates and mechanisms; the role of water; the need for catalysts; the importance of phase behavior and mixing. In 2009, MIT initiated a SCWU research program aimed at improving the understanding of the relevant physical, chemical, and catalytic phenomena. This overview summarizes the work performed at MIT within the historical context of SCWU with a particular focus on new kinetic rate measurements and modeling, reaction mechanism analysis, catalyst investigation, and combined mass/heat transport modeling of hydrocarbon/water mixtures. Kinetic rate measurements showed that sulfide decomposition during SCWU is consistent with a radical chain reaction pathway. Mechanistic studies and product distribution analysis identified that sulfide decomposition likely occurs via thioaldehyde and aldehyde intermediates and that water plays important roles in thioaldehyde hydrolysis (as a reactant) and aldehyde decarbonylation (as a catalyst). Catalytic investigation found that ZnO has potential to improve sulfur removal during SCWU, without addition of molecular hydrogen. Mixing studies revealed the complex dynamic processes that occur when hydrocarbons are injected into near or supercritical water. The article concludes with a summary of research needs and thoughts on the future of SCWU.
    No preview · Article · Jan 2015 · Journal of Supercritical Fluids The
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    ABSTRACT: A detailed kinetic model for the thermal decomposition of the advanced fuel Jet-Propellant 10 (JP-10) was constructed using a combination of automated mechanism generation techniques and ab initio calculations. Rate coefficients for important unimolecular initiation routes of exo-TCD were calculated using the multireference method CAS-PT2, while rate coefficients for the various primary decompositions of the exo-TCD-derived monoradicals were obtained using CBS-QB3. Rate-of-production analysis showed the importance of four dominating JP-10 decomposition channels. The model predictions agree well with five independent experimental data sets for JP-10 pyrolysis that cover a wide range of operating conditions (T = 300-1500 K, P = 300 Pa-1.7 × 105 Pa, dilution = 0.7-100 mol% JP-10, conversion = 0-100%) without any adjustment of the model parameters. A significant part of the model comprises secondary conversion routes to aromatic and polyaromatic hydrocarbons and could thus be used to assess the tendency for deposit formation in fuel-rich zones of endothermic fuel applications.
    No preview · Article · Jan 2015 · Energy & Fuels
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    Yury V Suleimanov · Wendi J Kong · Hua Guo · William H Green
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    ABSTRACT: Following our previous study of prototypical insertion reactions of energetically asymmetric type with the RPMD (Ring-Polymer Molecular Dynamics) method [Y. Li, Y. Suleimanov, and H. Guo, J. Phys. Chem. Lett. 5, 700 (2014)], we extend it to two other prototypical insertion reactions with much less exothermicity (near thermoneutral), namely, X + H2 → HX + H where X = C(1 D), S(1 D), in order to assess the accuracy of this method for calculating thermal rate coefficients for this class of reactions. For both chemical reactions, RPMD displays remarkable accuracy and agreement with the previous quantum dynamic results that make it encouraging for the future application of the RPMD to other barrier-less, complex-forming reactions involving polyatomic reactants with any exothermicity.
    Full-text · Article · Dec 2014 · The Journal of Chemical Physics
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    ABSTRACT: Quantum effects play a crucial role in chemical reactions involving light atoms at low temperatures, especially when a light particle is exchanged between two heavier partners. Different theoretical methodologies have been developed in the last decades attempting to describe zero-point energy and tunneling effects without abandoning a classical or semiclassical framework. In this work, we have chosen the D + HMu -> DMu + H reaction as a stress test system for three well-established methods: two representative versions of transition state theory (TST), canonical variational theory and semiclassical instanton, and ring polymer molecular dynamics (RPMD). These calculations will be compared with accurate quantum mechanical results. Despite its apparent simplicity, the exchange of the extremely light muonium atom (0.114 u) becomes a most challenging reaction for conventional methods. The main result of this work is that RPMD provides an overall better performance than TST-based methods for such a demanding reaction. RPMD might well turn out to be a useful tool beyond TST applicability.
    Full-text · Article · Dec 2014 · Journal of Physical Chemistry Letters
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    ABSTRACT: Chirped-pulse (CP) Fourier transform rotational spectroscopy is uniquely suited for near-universal quantitative detection and structural characterization of mixtures that contain multiple molecular and radical species. In this work, we employ CP spectroscopy to measure product branching and extract information about the reaction mechanism, guided by kinetic modeling. Pyrolysis of ethyl nitrite, CH3CH2ONO, is studied in a Chen type flash pyrolysis reactor at temperatures of 1000-1800 K. The branching between HNO, CH2O, and CH3CHO products is measured and compared to the kinetic models generated by the Reaction Mechanism Generator software. We find that roaming CH3CH2ONO CH3CHO + HNO plays an important role in the thermal decomposition of ethyl nitrite, with its rate, at 1000 K, comparable to that of the radical elimination channel CH3CH2ONO CH3CH2O + NO. HNO is a signature of roaming in this system. [GRAPHICS]
    No preview · Article · Nov 2014 · Journal of Physical Chemistry Letters
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    Yu.V. Suleimanov · Joshua W. Allen · William H. Green · Yu. V. Suleimanov
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    ABSTRACT: We present RPMDrate, a computer program for the calculation of gas phase bimolecular reaction rate coefficients using the ring polymer molecular dynamics (RPMD) method. The RPMD rate coefficient is calculated using the Bennett–Chandler method as a product of a static (centroid density quantum transition state theory (QTST) rate) and a dynamic (ring polymer transmission coefficient) factor. The computational procedure is general and can be used to treat bimolecular polyatomic reactions of any complexity in their full dimensionality. The program has been tested for the H+H2, H+CH4, OH+CH4 and H+C2H6 reactions.
    Preview · Article · Oct 2014
  • Yuko Kida · Adam G. Carr · William H. Green
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    ABSTRACT: Two-dimensional gas chromatography with sulfur chemiluminescence detection (GC x GC-SCD) is applied to understand the changes in alkylated thiophenes, benzothiophenes (BTs), and dibenzothiophenes (DBTs) during supercritical water (SCW) upgrading of Arabian Heavy crude oil. It is shown that SCW treatment of heavy crude oil has several important effects: (1) The amount of BTs and DBTs in the distillate range increase, primarily due to cracking of heavier compounds. (2) Most of the long side chains on the thiophenes, BTs, and DBTs crack to form the corresponding thiophenic compounds with shorter side chains. (3) A small amount of the alkylated thiophenes undergo ring closure to form BTs during SCW treatment, and a small amount of the alkylated BTs appear to form DBTs in a similar way. As reported earlier, SCW treatment removes some of the sulfur from the oil phase, presumably as hydrogen sulfide (H2S). Distilling the heavy crude oil into light and heavy fractions and treating these fractions individually with SCW showed these effects more clearly. Model compound studies on hexylthiophenes confirm that SCW cleaves alkyl chains bound to thiophenes.
    No preview · Article · Oct 2014 · Energy & Fuels
  • Enoch E. Dames · Shamel Merchant · William H. Green

    No preview · Conference Paper · Aug 2014
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    ABSTRACT: Jet Propellant-10 (JP-10) pyrolysis is performed in a continuous flow tubular reactor near atmospheric pressure in the temperature range of 930-1080 K, a conversion range of 4-94%, and two dilution levels of 7 and 10 mol % JP-10 in nitrogen. Identification and quantification of the pyrolysis products of JP-10 are based on online two-dimensional gas chromatography with a time-of-flight mass spectrometer and a flame ionization detector. JP-10 starts to react at 930 K and is fully converted at 1080 K Among the more than 70 species up to C14H10 that were identified and quantified, tricyclo[5.2.1.0(2,6)]dec-4-ene was identified for the first time, indicating the importance of bimolecular H-abstraction reactions in the consumption of JP-10. Critical assessment of the experimental data with the JP-10 combustion model by Magoon et al. [Magoon, G. R.; Aguilera-Iparraguirre, J.; Green, W. H.; Lutz, J. J.; Piecuch, P.; Wong, H. W.; Oluwole, O. O. Detailed chemical kinetic modeling of JP-10 (exo-tetrahydrodicydopentadiene) high-temperature oxidation: Exploring the role of biradical species in initial decomposition steps. Int. J. Chem. Kinet. 2012, 44 (3), 179-193] showed that the model predictions of JP-10 agree reasonably well. The newly acquired and highly detailed experimental data help in understanding the thermal decomposition chemistry of JP-10 and can be used to validate future kinetic models of JP-10 pyrolysis.
    No preview · Article · Aug 2014 · Energy & Fuels

Publication Stats

4k Citations
480.24 Total Impact Points

Institutions

  • 1998-2015
    • Massachusetts Institute of Technology
      • • Department of Chemical Engineering
      • • Department of Civil and Environmental Engineering
      Cambridge, Massachusetts, United States
  • 1997
    • Northwestern University
      • Department of Chemical and Biological Engineering
      Evanston, Illinois, United States
  • 1990-1993
    • University of Cambridge
      • Department of Chemistry
      Cambridge, England, United Kingdom
  • 1987-1991
    • University of California, Berkeley
      • Department of Chemistry
      Berkeley, CA, United States