Heat For Reaction Research Articles

Potential use of liquid metal oxides for chemical looping gasification: A thermodynamic assessment

A new concept for syngas production is proposed in which a liquid metal oxide (here copper oxide) is implemented as an oxygen carrier for chemical looping gasification. The proposed system consists of two interconnected bubble reactors as the fuel and air reactors, through which a liquid metal oxide is circulated to be successively reduced and oxidised providing the required heat and oxygen for the gasification reaction. The proposed system offers a potential process to avoid challenges such as agglomeration and sintering that are typically associated with the solid metal oxides that have previously been proposed for chemical looping gasification. Thermochemical equilibrium models are presented that show acceptable agreement with the available data. The model is then used to estimate that the carbon conversion of feedstock is up to 84.6% for gasification and 100% for combustion with the proposed concept. In addition, the mole fraction of gaseous copper oxide in the outlet stream from the air reactor is estimated to be 10−11, which implies that no further process is required to separate the evaporated copper oxide from the syngas.

Standard enthalpy of reaction for the reduction of Co3O4 to CoO

Two different high-temperature calorimetry methods were used to determine the enthalpy of reaction for the reduction of Co3O4 to CoO. This reaction is particularly interesting for assessing the thermodynamics of the first step of the electrochemical half-cell reaction for conversion anodes based on Co3O4 at very low discharge currents. The enthalpy of reaction for the reduction of Co3O4 to CoO was determined to be ΔrH°=205.14±2.48kJ/mol and ΔrH°=204.46±3.17kJ/mol from transposed temperature drop and high-temperature oxide melt drop solution calorimetry, respectively. Using this data, the enthalpy of reaction for the first step of the half-cell reaction for Co3O4 at very low discharge currents involving the formation of Li2O and CoO was calculated as ΔrH°=−393.60±3.67kJ/mol and ΔrH°=−394.28±4.16kJ/mol from the transposed temperature drop and the high-temperature oxide melt drop solution calorimetry, respectively.

Hydrogen Abstraction from Hydrocarbons by NH2.

This contribution investigates thermokinetic parameters of bimolecular gas-phase reactions involving the amine (NH2) radical and a large number of saturated and unsaturated hydrocarbons. These reactions play an important role in combustion and pyrolysis of nitrogen-rich fuels, most notably biomass. Computations performed at the CBS-QB3 level and based on the conventional transition-state theory yield potential-energy surfaces and reaction rate constants, accounting for tunnelling effects and the presence of hindered rotors. In an analogy to other H abstraction systems, we demonstrate only a small influence of variational effects on the rate constants for selected reaction. The studied reactions cover the abstraction of hydrogen atoms by the NH2 radical from the C-H bonds in C1-C4 species, and four C5 hydrocarbons of 2-methylbutane, 2-methyl-1-butene, 3-methyl-1-butene, 3-methyl-2-butene, and 3-methyl-1-butyne. For the abstraction of H from methane, in the temperature windows 300-500 and 1600-2000 K, the calculated reaction rate constants concur with the available experimental measurements, i.e., kcalculated/kexperimetal = 0.3-2.5 and 1.1-1.4, and the previous theoretical estimates. Abstraction of H atom from ethane attains the ratio of kcalculated/kexperimetal equal to 0.10-1.2 and 1.3-1.5 over the temperature windows of available experimental measurements, i.e., 300-900 K and 1500-2000 K, respectively. For the remaining alkanes (propane and n-butane), the average kexperimental/kcalculated ratio remains 2.6 and 1.3 over the temperature range of experimental data. Also, comparing the calculated standard enthalpy of reaction (ΔrH°298) with the available experimental measurements for alkanes, we found the mean unsigned error of computations as 3.7 kJ mol-1. This agreement provides an accuracy benchmark of our methodology, affording the estimation of the unreported kinetic parameters for H abstractions from alkenes and alkynes. On the basis of the Evans-Polanyi plots, calculated bond dissociation enthalpies (BDHs) correlate linearly with the standard enthalpy of activation (Δ⧧H°298), allowing estimation of the enthalpy barrier for reaction of NH2 with other hydrocarbons in future work. Finally, we develop six sets of the generalized Arrhenius rate parameters for H abstractions from different C-H bond types. These parameters extend the application of the present results to any noncyclic hydrocarbon interacting with the NH2 radical.

Modification of the AMX membrane surface by polyethyleneimine: Effect of ionic strength on the membrane ion exchange selectivity

AbstractIn order to improve the selectivity of the AMX membrane, a polyethyleneimine (PEI) layer was adsorbed on its surface by the immersion of the considered membrane in a solution of PEI. The adsorption process of PEI was studied and the results were well correlated with the Langmuir model and with Lagergren's pseudo‐first‐order kinetic model.Equilibrium ion exchange isotherms of , , and systems, using modified AMX membrane, were established at various ionic strengths from 0.1 to 0.5 mol/L and at constant temperature of 298 K.The results obtained with the modified membrane, in this range of ionic strengths, showed that the affinity order was: at I = 0.1 mol/L and I = 0.2 mol/L and it was for I = 0.3 mol/L and I = 0.5 mol/L. The ion exchange selectivity coefficients , thermodynamic ion exchange equilibrium constants , and the standard free enthalpies of the ion exchange reactions were determined for the three binary systems. These results were compared with those obtained with the unmodified membrane. It was observed that for the modified membrane the ion exchange selectivity towards sulphate ions decreased and increased towards monovalent anions.

HypCal, a general-purpose computer program for the determination of standard reaction enthalpy and binding constant values by means of calorimetry.

The program HypCal has been developed to provide a means for the simultaneous determination, from data obtained by isothermal titration calorimetry, of both standard enthalpy of reaction and binding constant values. The chemical system is defined in terms of species of given stoichiometry rather than in terms of binding models (e.g., independent or cooperative). The program does not impose any limits on the complexity of the chemical systems that can be treated, including competing ligand systems. Many titration curves may be treated simultaneously. HypCal can also be used as a simulation program when designing experiments. The use of the program is illustrated with data obtained with nicotinic acid (niacin, pyridine-3 carboxylic acid). Preliminary experiments were used to establish the rather different titration conditions for the two sets of titration curves that are needed to determine the parameters for protonation of the carboxylate and amine groups.

Benefits of microwave heating method in production of activated carbon

AbstractThis work investigates the chemical activation of a biochar sample using microwaves with KOH and NaOH. The activation of char samples was carried out in a microwave oven operating at 2.45 GHz with a power input of 1200 W. The specific surface area (SSA), yield (%), and pore size distribution were studied for microwave activation with KOH and NaOH. In microwave‐assisted activation, the activation yields for NaOH and KOH activation were in the ranges of 40–70 % and 60–80 %, respectively. The NaOH‐activation takes 1.5 h in a furnace to fabricate an activated carbon with a SSA of 2600 m2 · g−1. However, in microwave activation, a 5 min activation with a power of 1200 W results in activated carbon with a SSA of 1900 m2 g−1. The activation yield and SSA are mainly controlled by impregnation ratio in microwave‐assisted activation because KOH and NaOH were the sources of heat for the activation reaction. In this work, the microwave activation increased the reaction rate by 15 times compared to the furnace activation. Microwaves have a “non‐thermal effect” on the kinetic parameters of chemical activation reactions. This effect was more evident in the case of NaOH microwave activation, probably because it is a more reactive compound compared to KOH.

The Complexation of Cm(III) with Succinate Studied by Time-Resolved Laser Fluorescence Spectroscopy and Quantum Chemical Calculations.

The complexation of Cm(III) with succinate in an aqueous NaCl solution was studied as a function of ionic strength, ligand concentration, and temperature using time-resolved laser fluorescence spectroscopy (TRLFS). After the Cm(III) speciation was determined by peak deconvolution, the temperature-dependent thermodynamic stability constants (log Kn0(T)) were determined for the stepwise formation of [CmSucn]3–2n (n = 1–3) in the temperature range 20–80 °C (n = 3 only when T ≥ 50 °C) using the specific ion interaction theory (SIT). The first and second complexation steps show an endothermic behavior, as the respective standard reaction enthalpies (ΔrHm0) and entropies (ΔrSm0) derived from the integrated van’t Hoff equation are positive. These TRLFS results are complemented by quantum chemical calculations to resolve the molecular structure of the formed Cm(III) complexes. The results show that the formation of a seven-membered chelate ring is the favored conformation of [CmSucn]3−2n (n = 1−3).

Development of a stand-alone steam methane reformer for on-site hydrogen production

A small, stationary reformer designed as a stand-alone and self-sustaining type was developed for on-site hydrogen (H2) production. We created a compact reformer to produce H2 at a rate of 1 Nm3/h using the previously reported reaction kinetics of steam methane reforming (SMR). Both catalysts for the compact reformer - i.e., 15 wt% and 20 wt% Ni/γ-Al2O3 - showed good activity, with CH4 conversion exceeding 90% at 655 °C and a contact time of 3.0 gcath/mol, which were considered critical thresholds in the development of a small, compact stationary reformer. At an H2 production rate of 1 Nm3/h, the catalyst amount was calculated to be 167.8 g and the reformer length required to charge the catalyst was 613 mm, with a diameter of 1 inch. The CH4 conversion and H2 production rates achieved with the compact reformer using the 20 wt% Ni/γ-Al2O3 catalyst at 738 °C were 97.9% and 1.22 Nm3/h, respectively. Furthermore, a heat-exchanger type reformer was developed to efficiently carry out the highly endothermic SMR reaction for on-site H2 production. This reformer comprised a tube side (in which the catalysts were charged and the SMR reaction took place by feeding the reactants) and a shell side (in which the heat for the endothermic reaction was supplied by CH4 combustion). Reforming activities were evaluated using the active 20 wt% Ni/γ-Al2O3 catalyst, depending on the reactants' gas hourly space velocity (GHSV). The H2 production rate increased as the GHSV increased. Finally, the reformer produced a CH4 conversion of 98.0% and an H2 production rate of 1.97 Nm3/h at 745 °C, as well as a high reactants' GHSV of 10,000 h−1. Therefore, the heat-exchanger type reformer proved to be an effective system for conducting the highly endothermic SMR reaction with a high reactants' GHSV to yield a high rate of H2 production.

Thermodynamic Analysis of the Experimental Equilibria for the Liquid-Phase Etherification of Isobutene with C1 to C4 Linear Primary Alcohols

The chemical equilibrium of the liquid-phase syntheses of 2-methoxy-2-methylpropane (MTBE), 2-ethoxy-2-methylpropane (ETBE), 2-methyl-2-propoxypropane (PTBE), and 1-tert-butoxybutane (BTBE) by reaction of isobutene with methanol, ethanol, 1-propanol, and 1-butanol, respectively, has been studied. Four different ion exchange resins as the catalysts, and two different reactor systems, namely, a batch reactor and a setup of tubular reactors, were used. Temperature and pressure were in the range 313–383 K and 1.5–2.0 MPa, respectively. MTBE and ETBE synthesis reactions experiments were carried out mainly to validate the reliability of the reaction systems. Experiments in PTBE and BTBE etherifications allowed estimating thermodynamic properties for those reactions and involved species, namely, molar standard enthalpy and entropy changes of reaction and molar enthalpy change of formation of the four ethers. A comparison of estimated reaction thermodynamic values among the homologous series of linear alcohols, and with results quoted in the literature, when available, has been made.

Physico-chemical properties and fuel characteristics of oxymethylene dialkyl ethers

Oligomeric oxymethylene dimethyl ethers (OMDMEs, CH3O–(CH2O)n–CH3) are promising diesel fuel additives, which can reduce soot formation as well as NOx emissions. Due to the poor availability of high purity OMDMEs a comprehensive characterization of diesel standards was not feasible until now. Two types of oxymethylene dialkylethers (OMDMEs and oxymethylene diethyl ethers, OMDEEs) were synthesized, purified and characterized with respect to their physico-chemical and fuel properties. Density, melting point, flash point, auto ignition point as well as lubricity, kinematic viscosity and surface tension of OMDMEs and OMDEEs were measured and compared to the corresponding n-alkanes. Fuel requirements such as boiling points, flash points and surface tensions can be fulfilled by OMDMEs and OMDEEs. Furthermore, OMDMEs (n=3–5) and OMDEEs (n=2–4) are, due to their high cetane numbers of 124–180 and 64–103, particularly promising since cetane numbers in this range can lead to improved motor efficiency and smoother fuel combustion. Additionally, the heat of combustion as well as the standard enthalpy of formation and reaction were determined. Apart from somewhat lower heating values, OMDMEs exhibit fuel properties similar to conventional diesel complying the required fuel standards without the need of changing engines or fuel infrastructures.

Thermodynamics of a model biological reaction: A comprehensive combined experimental and theoretical study

In this work we applied experimental and theoretical thermodynamics to methyl ferulate hydrolysis, a model biological reaction, in order to calculate the equilibrium constant and reaction enthalpy. In the first step, reaction data was collected. Temperature-dependent equilibrium concentrations of methyl ferulate hydrolysis have been measured. These were combined with activity coefficients predicted with electrolyte PC-SAFT in order to derive thermodynamic equilibriums constants Ka as a function of temperature.In a second step, thermochemical properties of the highly pure reaction participants methyl ferulate and ferulic acid were measured by complementary thermochemical methods including combustion and differential scanning calorimetry. Vapor pressures and sublimation enthalpies of these compounds were measured by transpiration and TGA methods over a broad temperature range. Thermodynamic data on methyl ferulate and ferulic acid available in the literature were evaluated and combined with our own experimental results. Further, the standard molar enthalpy of methyl ferulate hydrolysis reaction calculated according to the Hess's Law applied to the reaction participants was found to be in agreement with the experimental reaction enthalpy from the equilibrium study.In a final step, the gas-phase equilibrium constant of methyl ferulate hydrolysis at 298.15 K was calculated with the G3MP2 method. This value was adjusted to the liquid phase using the experimental vapor pressures of the reaction participants. As a result, the liquid phase Ka value calculated by quantum chemistry with additional data on the pure reaction participants was in good agreement with the experimental Ka reported in the literature for the aqueous phase. The thermodynamic procedure based on the quantum-chemical calculations is found to be a valuable option for assessment of thermodynamic properties of biologically relevant chemical reactions.

On the exact results of a non-linear model arising in catalytic reaction in a flat particle with power kinetics reaction rate

The latest study of a model of heat and mass transfer for a catalytic reaction within a porous catalyst flat particle (Journal of the Taiwan Institute of Chemical Engineers 48 (2015) 49–55 [7]) shows that this model can be exactly solved when the reaction rate is taken linear term as f(y)=y, where y is heat within porous catalyst particle. In this paper, the mentioned model is revisited by considering the power kinetics nth order reaction rate instead of a linear reaction term. It is shown that the problem is still exactly tractable. Furthermore, it is revealed that previous results can be recovered from this exactly solvable generalization case. It is also proved that the problem might have multiple stationary solutions (unique, dual and triple solutions) depending on the values of the parameters of the model.

Size-Dependent Thermodynamic Properties of the Reaction of Nano-ZnO with Benzoic Acid

Studying the thermodynamic properties of the reaction of nanoparticle with organic substance is significant for the application of nanomaterial in organic fields. In this work, by using the reaction of nano- ZnO with different particle sizes with benzoic acid as a research system, the size-dependent standard equilibrium constant and reaction thermodynamic properties were analyzed theoretically, and the influence regularities of the particle size on the standard equilibrium constant and the reaction thermodynamic properties were studied. The excellent agreement between the experimental results and theoretical analysis shows that the particle size has remarkable influence on the standard equilibrium constant and the thermodynamic properties of the reaction; with the decrease of the particle size, the standard equilibrium constant increases, while the standard molar reaction Gibbs energy, the standard molar reaction enthalpy and the standard molar reaction entropy decrease. Furthermore, the logarithm of the standard equilibrium constant and the thermodynamic properties present linear relations with the reciprocal of the particle diameter, respectively. The theory and the influence regularities will provide useful tools to lead better and broader application of nanomaterial in organic fields.

Complex formation of Cm(III) with formate studied by time-resolved laser fluorescence spectroscopy

Pore waters of natural clays, which are investigated as potential host rock formations for high-level nuclear waste, are known to contain large amounts of low-molecular weight organic compounds. These small organic ligands might impact the aqueous geochemistry of the stored radionuclides and, thus, their migration behavior. In the present work, the complexation of Cm(III) with formate in aqueous NaCl solution is investigated by time-resolved laser fluorescence spectroscopy (TRLFS) as a function of the ionic strength (0.5–3.0mol/kg), the ligand concentration (0–0.2mol/kg) and the temperature (20–90°C). The Cm(III) speciation is determined by deconvolution of the emission spectra. The obtained distribution of Cm(III) species is used to calculate the conditional stability constants (logK′(T)) at a given temperature and ionic strength which are extrapolated to zero ionic strength by using the specific ion interaction theory (SIT). Thus, the thermodynamic logK0n(T) values for the formation of [Cm(Form)n](3−n)+ (n=1, 2) and the ion interaction coefficients (ε(i,k)) for [Cm(Form)n](3−n)+ (n=1, 2) with Cl− are obtained. The logK01(T) (2.11 (20°C)–2.49 (90°C)) and logK02(T) values (1.17 (30°C–2.01 (90°C)) increase continuously with increasing temperature. The logK0n(T) values are used to derive the standard reaction enthalpies and entropies (ΔrH0m, ΔrS0m) of the respective complexation reactions according to the Van’t Hoff equation. In all cases, positive ΔrH0m and ΔrS0m values are obtained. Thus, both complexation steps are endothermic and entropy-driven.

Theoretical study on the thermal decomposition and isomerization of 3-Me-1-heptyl radical

A detailed theoretical investigation on the thermal decomposition and isomerization of 3-Me-1-heptyl radical is performed at the ab initio CBS-QB3 level of theory. The calculation reveals that the detailed reaction mechanisms of 3-Me-1-heptyl radical mainly incorporate reversible intramolecular hydrogen atom transfer and the beta-site CC bond scission. The standard reaction enthalpies (ΔrH2980) and enthalpies of formation (ΔfH2980) are determined at the CBS-QB3 level of theory. All investigated decomposition reactions are generally endothermic, while most of the isomerization processes are exothermic. Among the hydrogen atom transfer processes, the 1,3- and 1,2-hydrogen atom migration (R5 and R6, respectively) are prohibited due to their high isomerization barriers, while the 1,6-(R2) and 1,5-hydrogen atom transfer (R3) are kinetically accessible (owing to their low ring strains in the cyclic transition states). Compared with the 1,5-hydrogen atom shift for the n-heptyl radical, the methyl-substitution increases the rate coefficient by a factor of about 3.0. The product distributions are predicted at different temperatures on the basis of the steady-state approximation (SSA). The ultimate and dominant products majorly include ethylene (C2H4), propylene (C3H6), 1-butylene (1-C4H8) and 2-hexene (2-C6H12) over the temperature range of 500–2500K.

The Complexation of Cm(III) with Oxalate in Aqueous Solution at T = 20–90 °C: A Combined TRLFS and Quantum Chemical Study

The complexation of Cm(III) with oxalate is studied in aqueous solution as a function of the ligand concentration, the ionic strength (NaCl), and the temperature (T = 20–90 °C) by time-resolved laser fluorescence spectroscopy (TRLFS) and quantum chemical calculations. Four complex species ([Cm(Ox)n](3–2n), n = 1, 2, 3, 4) are identified, and their molar fractions are determined by peak deconvolution of the emission spectra. The conditional log K′n(T) values of the first three complexes are calculated and extrapolated to zero ionic strength with the specific ion interaction theory approach. The [Cm(Ox)4](5–) complex forms only at high temperatures. Thus, the log K4(0)(T) value was determined at T > 60 °C. The log K1(0)(25 °C) = 6.86 ± 0.02 decreases by 0.1 logarithmic units in the studied temperature range. The log K2(0)(25 °C) = 4.68 ± 0.09 increases by 0.35, and log K3(0)(25 °C) = 2.11 ± 0.05 increases by 0.37 orders of magnitude. The log Kn(0)(T) (n = 1, 2, 3) values are linearly correlated with the reciprocal temperature. Thus, their temperature dependencies are fitted with the linear Van’t Hoff equation yielding the standard reaction enthalpy (ΔrHm(0)) and standard reaction entropy (ΔrSm(0)) of the stepwise formation of the [Cm(Ox)n](3–2n) species (n = 1, 2, 3). Furthermore, the binary ion–ion interaction coefficients of the four Cm(III) oxalate species with Cl(–)/Na(+) are determined. The binding energies, bond lengths, and bond angles of the different Cm(III) oxalate complexes are calculated in the gas phase as well as in a box containing 1000 H2O molecules by ab inito calculations and molecular dynamics simulations, respectively.

Multiplicity results and closed-form solution for catalytic reaction in a flat particle

Assume a flat geometry for the particle and that conductive heat transfer is negligible compared to convective heat transfer in the study of heat and mass transfer for a catalytic reaction within a porous catalyst flat particle. This article shows the governing differential equation, which is the direct result of a material and energy balance, is exactly solvable and furthermore, gives exact analytical solution in the implicit form for further physical interpretation. A full discussion is given and, it is also revealed that the problem may admit unique, dual or even more triple solutions depending on the values of Thiele modulus and other parameters of the model.

The exploration of hydrogen bonding properties of 2,6- and 3,5-diethynylpyridine by IR spectroscopy

Hydrogen bonding properties of 2,6- and 3,5-diethynylpyridine were analyzed by exploring of their interactions with trimethylphosphate, as hydrogen bond acceptor, or phenol, as hydrogen bond donor, in tetrachloroethene C2Cl4. The employment of IR spectroscopy enabled unravelling of their interaction pattern as well as the determination of their association constants (Kc) and standard reaction enthalpies (ΔrH⦵). The association of diethynylpyridines with trimethylphosphate in stoichiometry 1:1 is established through CH⋯O hydrogen bond, accompanied by the secondary interaction between CC moiety and CH3 group of trimethylphosphate. In the complexes with phenol, along with the expected OH⋯N interaction, CC⋯HO interaction is revealed. In contrast to 2,6-diethynylpyridine where the spatial arrangement of hydrogen bond accepting groups enables the simultaneous involvement of phenol OH group in both OH⋯N and OH⋯CC hydrogen bond, in the complex between phenol and 3,5-diethynylpyridine this is not possible. It is postulated that cooperativity effects, arisen from the certain type of resonance-assisted hydrogen bonds, contribute the stability gain of the latter. Associations of diethynylpyridines with trimethylphosphate are characterized as weak (Kc≈0.8–0.9mol−1dm3; -ΔrH⦵≈5–8kJmol−1), while their complexes with phenol as medium strong (Kc≈5mol−1dm3; -ΔrH⦵≈15–35kJmol−1). Experimental findings on the studied complexes are supported with the calculations conducted at B3LYP/6-311++G(d,p) level of theory in the gas phase. Two conformers of diethynylpyridine⋯trimethylphosphate dimers are formed via CH⋯O interaction, whereas dimers between phenol and diethynylpyridines are established through OH⋯N interaction.

Thermal decomposition and isomerization of 1-heptyl radical: a computational investigation

A detailed theoretical study on the thermal decomposition and isomerization of 1-heptyl radical at the CBS-QB3, BH&HLYP, B3PW91, BLYP, MPW1PW91, and M06-2X levels of theory is done. The result shows that the pyrolysis mechanism of 1-heptyl radical mainly includes the isomerization, the C–C, and C–H bond scission reactions. The standard reaction enthalpies for each elementary reaction involved in this system are estimated at several density functional theory methods together with cc-pVDZ basis set and the high-level ab initio CBS-QB3 approach. The theoretical rate coefficients of conventional transition state theory with Eckart tunneling correction (TST/Eckart) for individual elementary reaction involved in the above reaction system are evaluated over the temperature range of 500–2,500 K. The calculated values are in good agreement with available experimental measurements and previous theoretical reports. Furthermore, the isomerization and decomposition reactions are selected to compare their relative importance at different temperatures. It is found that the isomerization process is more pronounced when the temperature is below 1,200 K. Product distribution of 1-heptyl radical pyrolysis is predicted based on the steady-state approximation, and the eventual products are ethylene (C2H4), propylene (C3H6), 1-butylene (C4H8), 1-pentene (C5H10), and 1-butylethylene (C6H12).

Intramolecular interactions in polynorbornanes

The intramolecular interactions involving bridging groups in a series of hetero bridged fused [n]polynorbornanes (n=1–4) have been studied by using high-level ab initio method (G3-MP2B3) via the series of appropriate homodesmotic and protobranching compensated reactions. The calculated standard reaction enthalpies allowed us to obtain estimates of various nonbonding intramolecular interactions. The existence of rigid polynorbornane skeleton enabled us to “switch on” various interactions in a selective manner. The important intermolecular interactions comprise hydrogen bonding, hyperconjugation and non-bonding repulsive interactions (steric hindrance).