SEARCH · Engineering Papers

Results for “COMBUSTION”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,531 records · Page 85

All sources NASA NTRS DOE OSTI

DOE OSTI2020

Combustion of Silane-Hydrogen-Nitrous oxide Mixtures: Analysis of Laminar Flame Propagation and Condensed Products

The laminar burning rate, the explosion pressure, and the pressure rise coefficient have been measured for silane-nitrous oxide-argon mixtures using the spherically expanding flame technique in a constant volume combustion chamber. For these three parameters, the values obtained were higher than for hydrogen-nitrous oxide-argon and typical hydrocarbon-based mixtures. As an example, a maximum burning rate of 1800 g/m 2 s was measured at 101 kPa, whereas under similar conditions, a maximum burning rate around 950 g/m 2 s has been reported for hydrogen-nitrous oxide-argon mixtures. Here, the condensed combustion products formed in the silane-nitrous oxide-argon flames were sampled and characterized using electron micrograph, electronic diffraction, energy-dispersive spectroscopy, and X-ray powder diffraction. For all equivalence ratios, silica spherical particles with a mean diameter in the range 200-300 nm were observed. In addition, for mixtures with Φ ≥2.2, silicon nanowires were formed. X-ray diffraction experiments showed that the silicon nanowires are composed of a material referred to as “metal silicon” characterized by a cubic structure (lattice parameter: a = 5.425 Å) with the Fm-3m space group.

42 ENGINEERING↗

DOE OSTI2022

Experimental and kinetic modeling study of the low- temperature and high-pressure combustion chemistry of straight chain pentanol isomers: 1-, 2- and 3-Pentanol

Pentanols have received significant attention as a potential alternative fuel or fuel additive owing to their high energy densities and low vapor pressure. The development of robust chemical kinetic models for alternative fuels which can provide accurate and efficient predictions of combustion performance across a wide range of engine relevant conditions is important in developing cleaner, more efficient combustors. Although the high temperature oxidation kinetics of pentanol isomers has been researched considerably, their low temperature combustion chemistry needs further investigation. While previously proposed low temperature mechanisms for 1-pentanol based on analogy and rate rules need further refinement, the low temperature oxidation kinetics of 2-pentanol and 3-pentanol has not been studied previously by any means, experimentally or theoretically. A newly developed kinetic mechanism is presented in this work for the three straight chain pentanol isomers: 1-, 2- and 3-pentanol. Low temperature kinetics is based on a recent study by Lockwood et al., 2022 [20] involving theoretical calculations at the CCSD(T)/cc-pV∞Z level of theory for the oxidation pathways involving alcohol peroxy radicals. Rate of production analyses performed in this study highlight the importance of the newly added pressure-dependent reactions of the α-alcohol peroxy radical forming an RO 2 adduct. While the α-alcohol fuel radical reacts with O 2 to directly decompose via a chemically activated pathway at low pressures, the formation of the RO 2 adduct is favored at high pressures. Furthermore, the detailed model is comprehensively validated against new ignition experiments at low temperature and high pressure, together with the wide range of data available in the literature. Both qualitative and quantitative predictions of the experimental data using the proposed kinetic model are satisfactory for all three pentanol isomers studied here.

1-pentanol↗

DOE OSTI2019

The impact of tribology on energy use and CO 2 emission globally and in combustion engine and electric cars

Growing concerns over energy and environmental sustainability have lately sparked worldwide interest in more efficient and cleaner transportation systems and industrial activities. Friction roughly consumes one-fifth of all energy used worldwide. One-third of all energy used in transportation goes to overcome friction. At the same time, the fruits of decades of dedicated research on all-electric vehicles powered by advanced batteries are paving the way toward a much cleaner and sustainable transportation future. In this article, we provide a short overview of what are the energy efficiency and environmental impacts of current transportation, industrial, and residential systems and how much of that efficiency is adversely affected by friction and wear losses in moving mechanical parts and components. We also touch upon recent advances in new materials, lubricants, and design changes that could reduce energy losses by 18–40%, mainly resulting from friction and wear. The savings would be up to 8.7% of the total global energy use and 1.4% of the gross national products (GNP). Finally, we calculate the energy consumption and friction losses in battery-powered electric passenger cars and show the benefit of electric cars where the total energy use is in average 3.4 times lower compared to combustion engine powered cars. The CO 2 emissions are 4.5 times higher for a combustion engine car compared to an electric car when the electricity comes from renewable energy sources. Moving from fossil to renewable energy sources may cut down the energy losses due to friction in energy production by more than 60%.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2020

Stability, Combustion, and Compatibility of High-Viscosity Heavy Fuel Oil Blends with a Fast Pyrolysis Bio-Oil

Properties related to the combustion, stability, and compatibility of blends composed of high-viscosity heavy fuel oil (HFO) and highly acidic pyrolysis bio-oil were determined to assess the utility of bio-oil as a marine fuel. The addition of bio-oil was shown to be fully stable with HFO at blend levels up to 50 mass % for up to 2 weeks. Bio-oil concentrations as low as 5 mass % significantly reduced the viscosity of HFO at 25 and 50 °C. Aging studies at 50 and 90 °C showed that the HFO inhibited the polymerization of bio-oil. The heating value and lubricity showed a linear dependency with bio-oil content, and combustion quality was acceptable for blends containing up to 15% bio-oil. The highly acidic bio-oil was found to be corrosive to carbon steel, 2.25Cr-1Mo steel, and 409 stainless steels, but not 304L and 316L. When blended into HFO at levels less than 19 mass %, no measurable corrosion was observed on any of the steel materials, but a 50 mass % concentration produced low-to-moderate corrosion in the carbon steel, 2.25Cr-1Mo steel, and 409 stainless steel grades. The combination of good blend stability, polymerization inhibition, reduced viscosity, and acceptable compatibility for low blend levels suggests that bio-oils may be suitable for use as a marine fuel.

09 BIOMASS FUELS↗

DOE OSTI2018

Catalytic Steam and Partial Oxidation Reforming of Liquid Fuels for Application in Improving the Efficiency of Internal Combustion Engines

Here, this study investigated the potential for catalytically reforming liquid fuels in a simulated exhaust gas recirculation (EGR) mixture loop for the purpose of generating reformate that could be used to increase stoichiometric combustion engine efficiency. The experiments were performed on a simulated exhaust flow reactor using a Rh/Al 2 O 3 reformer catalyst, and the fuels evaluated included iso-octane, ethanol, and gasoline. Both steam reforming and partial oxidation reforming were examined as routes for the production of reformate. Steam reforming was determined to be an ineffective option for reforming in an EGR loop, because of the high exhaust temperatures (in excess of 700 °C) required to produce adequate concentrations of reformate, regardless of fuel. However, partial oxidation reforming is capable of producing hydrogen concentrations as high as 10%–16%, depending on fuel and operating conditions in the simulated EGR gas mixture. Meanwhile, measurements of total fuel enthalpy retention were shown to have favorable energetics under a range of conditions, although a tradeoff between fuel enthalpy retention and reformate production was observed. Of the three fuels evaluated, iso-octane exhibited the best overall performance, followed by ethanol and then gasoline. Overall, it was found that partial oxidation reforming of liquid fuels in a simulated EGR mixture over the Rh/Al 2 O 3 catalyst demonstrated sufficiently high reformate yields and favorable energetics to warrant further evaluation in the EGR system of a stoichiometric combustion engine.

33 ADVANCED PROPULSION SYSTEMS↗

DOE OSTI2015

Reaction Kinetics of Mixed CuO–Fe 2 O 3 with Methane as Oxygen Carriers for Chemical Looping Combustion

Reduction kinetics of alumina supported mixed Cu–ferrite oxide by methane was investigated for chemical looping combustion by the thermogravimetric analyzer (TGA) in the temperature range of 750–900 °C using continuous streams of 10%, 20%, and 30% CH 4 concentrations balanced by helium. The rate of reduction was determined by weight change. The variations of activation energies and n values (JMA exponent) during the reduction conversion indicate that the methane combustion with CuO and Fe 2 O 3 proceeds via a multistage reaction process. A kinetic model based on three parallel reactions was applied to the reduction data. In conclusion, the analysis of reduction showed that three reduction steps proceed simultaneously with the activation energies of 55.32 ± 3.11, 70.0 ± 2.0, and 165.0 ± 5.4 kJ/mol, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Use of Carbon Steel for Construction of Post-combustion CO 2 Capture Facilities: A Pilot-Scale Corrosion Study

Corrosion studies were carried out on metal coated and noncoated carbon steel as well as stainless steel in a pilot-scale post-combustion CO 2 capture process. Aqueous 30 wt % monoethanolamine (MEA) solvent was used without any chemical additive for antioxidation to examine a worst-case scenario where corrosion is not mitigated. The corrosion rate of all carbon steels was almost zero in the absorber column and CO 2 lean amine piping except for Ni-coated carbon steel (<1.8 mm/yr). Ni 2 Al 3 /Al 2 O 3 precoated carbon steels showed initial protection but lost their integrity in the stripping column and CO 2 rich amine piping, and severe corrosion was eventually observed for all carbon steels at these two locations. Stainless steel was found to be stable and corrosion resistant in all of the sampling locations throughout the experiment. This study provides an initial framework for the use of carbon steel as a potential construction material for process units with relatively mild operating conditions (temperature less than 80 °C), such as the absorber and CO 2 lean amine piping of a post-combustion CO 2 capture process. As a result, it also warrants further investigation of using carbon steel with more effective corrosion mitigation strategies for process units where harsh environments are expected (such as temperatures greater than 100 °C).

36 MATERIALS SCIENCE↗

DOE OSTI2026

Mechanism, Thermochemistry, and Kinetics for the CH + N 2 Reaction Leading to Prompt NO Formation in Combustion

Here, the reaction of CH + N 2 forming H + NCN is a remarkable example of activation of the nitrogen triple bond and is an important source of prompt NO in combustion. The reaction pathway is complex and proceeds through two competing mechanisms: a cyclic addition channel initiated by c-HC(NN) and a chain-addition channel initiated by HCNN, both of which eventually form HNCN prior to dissociation to H + NCN. This work reinvestigates this reaction with composite coupled cluster protocols, including a novel spin-flip equation of motion coupled cluster scheme, combined with pragmatic two-dimensional master equation simulations of the resulting rate coefficients. These improved calculations predict the CH + N 2 rate coefficient between the two more recent previous theoretical results and reduce the uncertainties of the best theoretical models of this reaction to less than a factor of 1.3. Additionally, we provide a closer theoretical investigation of the simultaneous dependence of the CH + N 2 rate coefficient on pressure and temperature, and affirm that collisionally stabilized HNCN, another potential source of prompt NO, emerges as an appreciable product of this reaction under conditions relevant to automotive internal combustion engines and aircraft gas turbine engines.

Nguyen, Thanh Lam [Univ. of Florida, Gainesville, ↗

DOE OSTI2017

Quantum Chemical Study of CH 3 + O 2 Combustion Reaction System: Catalytic Effects of Additional CO 2 Molecule

The supercritical carbon dioxide diluent is used to control the temperature and to increase the efficiency in oxycombustion fossil fuel energy technology. It may affect the rates of combustion by altering mechanisms of chemical reactions, compared to the ones at low CO 2 concentrations. In this work, we explore potential energy surfaces of the four elementary reactions in the CH 3 + O 2 reactive system in the presence of one CO 2 molecule. In the case of reaction CH 3 + O 2 → CH 2 O + OH (R1 channel), van der Waals (vdW) complex formation stabilizes the transition state and reduces the activation barrier by ~2.2 kcal/mol. Alternatively, covalently bonded CO 2 may form a six-membered ring transition state and reduce the activation barrier by ~0.6 kcal/mol. In case of reaction CH 3 + O 2 → CH 3 O + O (R2 channel), covalent participation of CO 2 lowers the barrier for the rate limiting step by 3.9 kcal/mol. This is expected to accelerate the R2 process, important for the branching step of the radical chain reaction mechanism. For the reaction CH 3 + O 2 → CHO + H 2 O (R3 channel) with covalent participation of CO 2 , the activation barrier is lowered by 0.5 kcal/mol. The reaction CH 2 O + OH → CHO + H 2 O (R4 channel) involves hydrogen abstraction from formaldehyde by OH radical. Its barrier is reduced from 7.1 to 0.8 kcal/mol by formation of vdW complex with spectator CO 2 . These new findings are expected to improve the kinetic reaction mechanism describing combustion processes in supercritical CO 2 medium.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Molecular Dynamics of Combustion Reactions in Supercritical Carbon Dioxide. Part 5: Computational Study of Ethane Dissociation and Recombination Reactions C 2 H 6 ⇌ CH 3 + CH 3

Fossil fuel oxy-combustion is an emerging technology where the habitual nitrogen diluent is replaced by high-pressure supercritical CO 2 (sCO 2 ), which increases the efficiency of energy conversion. In this study, the chemical kinetics of the combustion reaction C 2 H 6 ⇌ CH 3 + CH 3 in the sCO 2 environment is predicted at 30–1000 atm and 1000–2000 K. We adopt a multiscale approach, where the reactive complex is treated quantum mechanically in rigid rotor/harmonic oscillator approximation, while environment effects at different densities are taken into account by the potential of mean force, produced with classical molecular dynamics (MD). Here, we used boxed MD, where enhanced sampling of infrequent events of barrier crossing is accomplished without application of the bias potential. The multistate empirical valence bond model is applied to describe free radical formation accurately at the cost of the classical force field. Predicted rates at low densities agree well with the literature data. In conclusion, rate constants at 300 atm are 2.41 × 10 14 T –0.20 exp(–77.03 kcal/mol/RT) 1/s for ethane dissociation and 8.44 × 10 –19 T 1.42 exp(19.89 kcal/mol/RT) cm 3 /molecule/s for methyl–methyl recombination.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Optimal Size of a Cylindrical Pore for Post-Combustion CO 2 Capture

Pore size is an essential factor in controlling gas sorption in porous separation media. The overlap of the potential energy surface (PES) of CO 2 interacting with a cylindrical pore wall can be used to tune gas sorption inside a porous material, but how such overlap can benefit post-combustion CO 2 capture has not been fully addressed from a computational perspective. Here we use van der Waals density functional (vdW-DF) theory to assess the overlap of PES of CO 2 inside cylindrical pores as represented by carbon nanotubes (CNTs) of different diameters. Then we employ grand-canonical Monte Carlo simulations to obtain the adsorption capacity and selectivity of a CO 2 /N 2 mixture with a CO 2 partial pressure of 0.15 bar at room temperature. We find that the maximum PES overlap and maximum amount of CO 2 adsorbed are both achieved at a CNT diameter or cylindrical pore size of 7.8 Å, which corresponds to an accessible pore size of 4.4 Å. A further investigation of N2 adsorption corroborates the idea of PES overlap. GCMC simulations reveal that a maximum CO 2 /N 2 selectivity of ~33 is reached at a CNT diameter of 7.05 Å for the gas mixture. Here, this work suggests that a cylindrical pore size between 7 and 8 Å would be most beneficial for post-combustion CO 2 capture from overlap of PES.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Highly Selective Methane to Methanol Conversion on Inverse SnO 2 /Cu 2 O/Cu(111) Catalysts: Unique Properties of SnO 2 Nanostructures and the Inhibition of the Direct Oxidative Combustion of Methane

Direct methane to methanol (CH 4 → CH 3 OH) conversion in heterogeneous catalysis has been a long-standing challenge due to the difficulties in equalizing the activation of methane and protection of the methanol product at the same reaction conditions. Here, we report an inverse catalyst, consisting of small structures of SnO 2 (0.5-1 nm in size) dispersed on Cu 2 O/Cu(111), for highly selective CH 3 OH production from CH 4 . This system was investigated by combining theoretical [density functional theory calculations (DFT), kinetic Monte Carlo simulations (KMC)] and experimental methods [scanning tunneling microscopy (STM), ambient-pressure X-ray photoelectron spectroscopy (AP-XPS)]. The DFT and AP-XPS studies showed that on SnO 2 /Cu 2 O/Cu(111) the conversion of CH 4 by oxygen (O 2 ) preferred complete combustion to carbon dioxide (CO 2 ). The addition of water (H 2 O) enhanced the production of CH 3 OH to nearly 100% selectivity in KMC simulations. This trend was consistent with results of AP-XPS. The presence of water in the reaction environment rendered an extremely high amount of methoxy species (*CH 3 O), a precursor for CH 3 OH production. Further, the high CH 3 OH selectivity of SnO 2 /Cu 2 O/Cu(111) reflected the unique atomic and electronic structure of the supported SnO 2 nanoparticles. As a result, the O 2 adsorption and dissociation, and thus the full combustion of CH 4 to CO 2 , was completely suppressed; while the H 2 O dissociative adsorption was still feasible, providing active hydroxyl species for a truly selective CH 4 to CH 3 OH conversion.

03 NATURAL GAS↗

DOE OSTI2013

Mechanism of Methane Chemical Looping Combustion with Hematite Promoted with CeO 2

Chemical looping combustion (CLC) is a promising technology for fossil fuel combustion that produces sequestration-ready CO{sub 2} stream, reducing the energy penalty of CO{sub 2} separation from flue gases. An effective oxygen carrier for CLC will readily react with the fuel gas and will be reoxidized upon contact with oxygen. This study investigated the development of a CeO{sub 2}-promoted Fe{sub 2}O{sub 3}-hematite oxygen carrier suitable for the methane CLC process. Composition of CeO{sub 2} is between 5 and 25 wt % and is lower than what is generally used for supports in Fe{sub 2}O{sub 3} carrier preparations. The incorporation of CeO{sub 2} to the natural ore hematite strongly modifies the reduction behavior in comparison to that of CeO{sub 2} and hematite alone. Temperature-programmed reaction studies revealed that the addition of even 5 wt % CeO{sub 2} enhances the reaction capacity of the Fe{sub 2}O{sub 3} oxygen carrier by promoting the decomposition and partial oxidation of methane. Fixed-bed reactor data showed that the 5 wt % cerium oxides with 95 wt % iron oxide produce 2 times as much carbon dioxide in comparison to the sum of carbon dioxide produced when the oxides were tested separately. This effect is likely due to the reaction of CeO{sub 2} with methane forming intermediates, which are reactive for extracting oxygen from Fe{sub 2}O{sub 3} at a considerably faster rate than the rate of the direct reaction of Fe{sub 2}O{sub 3} with methane. These studies reveal that 5 wt % CeO{sub 2}/Fe{sub 2}O{sub 3} gives stable conversions over 15 reduction/oxidation cycles. Lab-scale reactor studies (pulsed mode) suggest the methane reacts initially with CeO{sub 2} lattice oxygen to form partial oxidation products (CO + H{sub 2}), which continue to react with oxygen from neighboring Fe{sub 2}O{sub 3}, leading to its complete oxidation to form CO{sub 2}. The reduced cerium oxide promotes the methane decomposition reaction to form C + H{sub 2}, which continue to react with Fe{sub 2}O{sub 3}/Fe{sub 3}O{sub 4} to form CO/CO{sub 2} and H{sub 2}O. This mechanism is supported by the characterization studies, which also suggest that the formation of carbonaceous intermediates may affect the reaction rate and selectivity of the oxygen carrier.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2013

Experimental Investigation of Spark-Ignited Combustion with High-Octane Biofuels and EGR. 2. Fuel and EGR Effects on Knock-Limited Load and Speed

The present study experimentally investigates spark-ignited combustion with 87 AKI E0 gasoline in its neat form and in midlevel alcohol–gasoline blends with 24% vol/vol isobutanol–gasoline (IB24) and 30% vol/vol ethanol–gasoline (E30). A single-cylinder research engine is used with an 11.85:1 compression ratio, hydraulically actuated valves, laboratory intake air, and was capable of external exhaust gas recirculation (EGR). Experiments were conducted with all fuels to full-load conditions with λ = 1, using both 0% and 15% external-cooled EGR. Higher octane number biofuel blends exhibited increased stoichiometric torque capability at this compression ratio, where the unique properties of ethanol enabled a doubling of the stoichiometric torque capability with E30 as compared to that of 87AKI, up to 20 bar IMEPg (indicating mean effective pressure gross) at λ = 1. The results demonstrate that for all fuels, EGR is a key enabler for increasing engine efficiency but is less useful for knock mitigation with E30 than for 87AKI gasoline or IB24. Under knocking conditions, 15% EGR is found to offer 1°CA of CA50 timing advance with E30, whereas up to 5°CA of CA50 advance is possible with knock-limited 87AKI gasoline. Compared to 87AKI, both E30 and IB24 are found to have reduced adiabatic flame temperature and shorter combustion durations, which reduce knocking propensity beyond that indicated by the octane number. However, E30+0% EGR is found to exhibit the better antiknock properties than either 87AKI+15% EGR or IB24+15% EGR, expanding the knock limited operating range and engine stoichiometric torque capability at high compression ratio. Furthermore, the fuel sensitivity (S) of E30 was attributed to reduced speed sensitivity of E30, expanding the low-speed stoichiometric torque capability at high compression ratio. The results illustrate that intermediate alcohol–gasoline blends exhibit exceptional antiknock properties and performance beyond that indicated by the octane number tests, particularly E30.

Splitter, Derek↗

DOE OSTI2013

Bimetallic Fe-Ni Oxygen Carriers for Chemical Looping Combustion

The relative abundance, low cost, and low toxicity of iron make Fe-based oxygen carriers of great interest for chemical looping combustion (CLC), an emerging technology for clean and efficient combustion of fossil and renewable fuels. However, Fe also shows much lower reactivity than other metals (such as Ni and Cu). Here, we demonstrate strong improvement of Fe-based carriers by alloying the metal phase with Ni. Through a combination of carrier synthesis and characterization with thermogravimetric and fixed-bed reactor studies, we demonstrate that the addition of Ni results in a significant enhancement in activity as well as an increase in selectivity for total oxidation. Furthermore, comparing alumina and ceria as support materials highlights the fact that reducible supports can result in a strong increase in oxygen carrier utilization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Influences of the molecular fuel structure on combustion reactions towards soot precursors in selected alkane and alkene flames

In this paper, we experimentally investigate the high-temperature oxidation kinetics of n-pentane, 1-pentene and 2-methyl-2-butene (2M2B) in a combustion environment using flame-sampling molecular beam mass spectrometry. The selected C 5 fuels are prototypes for linear and branched, saturated and unsaturated fuel components, featuring different C–C and C–H bond structures. It is shown that the formation tendency of species, such as polycyclic aromatic hydrocarbons (PAHs), yielded through mass growth reactions increases drastically in the sequence n-pentane < 1-pentene < 2M2B. This comparative study enables valuable insights into fuel-dependent reaction sequences of the gas-phase combustion mechanism that provide explanations for the observed difference in the PAH formation tendency. First, we investigate the fuel-structure-dependent formation of small hydrocarbon species that are yielded as intermediate species during the fuel decomposition, because these species are at the origin of the subsequent mass growth reaction pathways. Second, we review typical PAH formation reactions inspecting repetitive growth sequences in dependence of the molecular fuel structure. Third, we discuss how differences in the intermediate species pool influence the formation reactions of key aromatic ring species that are important for the PAH growth process underlying soot formation. Finally, as a main result it was found that for the fuels featuring a C=C double bond, the chemistry of their allylic fuel radicals and their decomposition products strongly influences the combination reactions to the initially formed aromatic ring species and as a consequence, the PAH formation tendency.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Kinetics of the benzyl + HO 2 and benzoxyl + OH barrierless association reactions: fate of the benzyl hydroperoxide adduct under combustion and atmospheric conditions

Radical–radical association reactions are challenging to address theoretically due to difficulties finding the bottleneck that variationally minimizes the reactive flux. For this purpose, the variable reaction coordinate (VRC) formulation of the variational transition state theory (VTST) represents an appropriate tool. Here, we revisited the kinetics of two radical–radical association reactions of importance in combustion modelling and poly-aromatic hydrocarbon (PAH) chemistry by performing VRC calculations: benzyl + HO 2 and benzoxyl + OH, both forming the adduct benzyl hydroperoxide. Our calculated rate constants are significantly lower than those previously reported based on VTST calculations, which results from a more efficient minimization of the reactive flux through the bottleneck achieved by the VRC formulation. Both reactions show different trends in the variation of their rate constants with temperature. We observed that if the pair of single occupied molecular orbitals (SOMOs) of the associating radicals show a similar nature, i.e. similar character, and thereby a small energy gap, a highly stabilized transition state structure is formed as the result of a very efficient SOMO–SOMO overlap, which may cancel out the free energy bottleneck for the formation of the adduct and result in large rate constants with a negative temperature dependence. This is the case of the benzoxyl and OH radical pair, whose SOMOs show O 2p nature with an energy gap of 20.2 kcal mol –1 . On the other hand, the benzyl and HO 2 radical pair shows lower rate constants with a positive temperature dependence due to the larger difference between both SOMOs (a 28.9 kcal mol –1 energy gap) as a consequence of the contribution of the multiple resonance structures of the benzyl radical. The reverse dissociation rate constants were also calculated using multi-structural torsional anharmonicity partition functions, which were not included in previous work, and the results show a much slower dissociation of benzyl hydroperoxide. Our work may help to improve kinetic models of interest in combustion and PAH formation, as well as to gain further understanding of radical–radical association reactions, which are ubiquitous in different environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

A single-component water-lean post-combustion CO 2 capture solvent with exceptionally low operational heat and total costs of capture – comprehensive experimental and theoretical evaluation

A comprehensive evaluation of a recently developed water-lean amine-based solvent, namely N-(2-ethoxyethyl)-3-morpholinopropan-1-amine (2-EEMPA), has been performed to analyze its post-combustion CO 2 capture performance. This evaluation comprises (1) fundamental characterization of the solvent–CO 2 interaction using vapor–liquid equilibria, kinetics and viscosity measurements; (2) process characterization of the CO 2 capture performance as measured in a laboratory scale continuous flow system and via Aspen Plus® simulation using a flue gas simulant; as well as (3) a full techno economic analysis of the capture process at industrial scale with corresponding projections of critical metrics. This paper summarizes the many parts of this comprehensive evaluation and shows how the various parts come together to empower validated conclusions about its process performance. Notably, it is projected that this solvent can operate at a regeneration heat rate of 2.0 GJ per tonne CO 2 for post-combustion capture, and at a total cost of capture of $50.6/tonne CO 2 . Overall, with further process optimization significant reductions in the capture cost are predicted.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗