Non-equilibrium Products Research Articles

Mineralogical, crystal morphological, and isotopic characteristics of smooth slope travertine deposits at Reshuitang, Tengchong, China

Reshuitang is an important active hydrothermal area in the Tengchong geothermal field and is characterized by many hot springs and their associated deposits. Detailed mineralogical, crystal morphological, and stable isotopic investigations of the smooth slope fossil travertines at Reshuitang and hydrochemical studies of two active springs around the fossil travertines were conducted to study their genesis. The results show that 1) the modern springs discharge waters with high temperature (>70 °C), near-neutral pH (6.3–8.34), and high saturation indices of calcite and aragonite; 2) the fossil travertines contain calcite and small amounts of Mn-Fe oxides, halite, thenardite, and non‑carbonate debris; 3) the calcite include ray crystals, dendrite crystals, platy crystals, and spike crystals; and 4) δ13C and δ18O of the fossil travertines at Reshuitang range from −1.59‰ to −0.87‰ and 6.48‰ to 7.80‰, respectively. According to comparison between the travertines at Reshuitang and other travertines in Tengchong, all these travertines are thermogene travertines, with a large contribution of mantle degassing to their parent CO2, but are formed at different temperatures. The fossil travertines at Reshuitang, similar to those at Shuzhishi, are formed at high temperatures (near 100 °C), which results in weak microbial activities during the formation of the fossil travertines. Most of the calcite crystals at Reshuitang were non-equilibrium products precipitated directly from the spring waters during the deposition process, while the spike crystals originated from diagenetic dissolution of large calcite crystals. Comparison between the fossil travertines at Reshuitang and other smooth slope travertines from other areas shows these smooth slope travertines have different lithofacies and fabrics. In smooth slope environments, temperature may control the distribution and development of microbes and the intensity of CO2 degassing, and consequently cause the precipitation of contrasting fabrics and lithofacies.

Phase Change Transformations with Dynamically Addressable Aminal Metallogels.

Dynamic polymers assembled through hemiaminal and aminal functionalities reversibly fragment upon binding to trivalent metals. Gels produced with these dynamic polymers are broken down to liquids after the addition of metal salts. Nuclear magnetic resonance spectroscopy studies and density functional theory calculations of intermediates reveal that the presence of these metals causes shifts in the energetic landscape of the intermediates in the condensation pathway to render stable nonequilibrium products. These species remain stable in the liquid phase at room temperature but convert to gels upon heating. With thermal activation, the fragmented ligands transform catalytically into closed-ring hexahydrotriazine products, which are macroscopically observable as new gels with distinct physical properties. The interplay between equilibrium and nonequilibrium gels and liquids and the ligands responsible for these transformations has been observed rheologically, giving controlled gel times dictated by the thermodynamics and kinetics of the system. This constitutionally dynamic macromolecular system offers the possibility of harnessing an equilibrium/nonequilibrium system in tandem with its inherent self-healing properties and triggered release functionality.

A method of calculating of the thermodynamic properties and the composition of the explosion products of hydrocarbons and air under partial chemical equilibrium

We examined the approximate method to calculate composition and thermodynamic parameters of hydrocarbons-air nonequilibrium explosion products based on the assumption of the existence of a partial chemical equilibrium. With excellent accuracy of calculating thermodynamic properties and species mass fraction the respective stiff system of detailed kinetics differential equations can be replaced by the one differential equation or the two differential equations and a system of algebraic equations. This method is always consistent with the detailed kinetic mechanism. The constituent equations of the method were derived and the respective computer code written. We examine the applicability of the method by solving the test problem. The proposed method simulation results are in excellent agreement with the detailed kinetics model results corresponding the stiff ordinary differential equation solver including NO time histories.

An approximate method for calculating composition of the non-equilibrium explosion products of hydrocarbons and oxygen

We develop a method for calculating the changes in composition of the explosion products in the case where the complete chemical equilibrium is absent but the bimolecular reactions are in quasi-equilibrium with the exception bimolecular reactions with one of the components of the mixture. We investigate the possibility of using the method of "quasiequilibrium" for mixtures of hydrocarbons and oxygen. The method is based on the assumption of the existence of the partial chemical equilibrium in the explosion products. Without significant loss of accuracy to the solution of stiff differential equations detailed kinetic mechanism can be replaced by one or two differential equation and a system of algebraic equations. This method is always consistent with the detailed mechanism and can be used separately or in conjunction with the solution of a stiff system for chemically non-equilibrium mixtures replacing it when bimolecular reactions are near to equilibrium.

On the Role of Modified Post Weld Heat Treatment in Eliminating Incipient Melting of Non-equilibrium Product Resulting During Solid-State Welding of Astroloy

The formation of non-equilibrium phases as a result of segregation during solidification of castings or in the welds of nickel-based superalloys has been a major concern limiting the enhancement of the optimal heat treatment procedure that could have improved the performance of the superalloys to their full potential strength in service. Much consideration has not been given to the dissolution of the non-equilibrium products resulting from welding of nickel-based superalloys. The present work on astroloy shows how non-equilibrium welding products could be completely eliminated by a modified post weld heat treatment procedure.

Solution Transformation of the Products of AC Electrochemical Metal Oxidation

Electrochemical oxidation of copper and aluminium using alternating current of industrial frequency results in the formation of non-equilibrium products. Their transformations during the ageing in sodium chloride solutions of different concentrations have been considered. According to X-Ray diffraction confirmed by TG/DSC/DTG analysis, irrespective of solution concentration, the ageing products consist of aluminium oxyhydroxide (boehmite, AlOOH), copper-aluminium carbonate hydroxide hydrate (Cu–Al/LDH) and copper chloride hydroxide (Cu2(OH)3Cl). The increase of the solution concentration leads to Cu2(OH)3Cl formation and makes difficulties for metal oxide carbonization to Cu–Al/LDH. Ageing in highly diluted solution contributes not only to Cu–Al/LDH formation but also boehmite hydration that is verified by IR-spectra. The pore structure characteristics have been also discussed. They do not significantly depend on phase composition and vary in ranges of 161.2–172.6 m2/g (specific surface areas), 0.459–0.535 cm2/g (total pore volumes). Pore size distributions reveal that a pore structure is predominantly formed by pore with the sizes from 3 to 22nm; 3.6nm is the size of pores with the largest pore volume.

Autothermal Partial Oxidation of Glycerol to Syngas over Pt-, LaMnO3-, and Pt/LaMnO3-Coated Monoliths

Glycerol and glycerol/water solution were converted to syngas over Pt-, LaMnO3-, and Pt/LaMnO3-coated monoliths under autothermal partial oxidation. XRD and SEM were used to characterize the phase compositions and surface morphologies of freshly prepared and postreaction catalysts. A continuous fixed-bed design, without an upstream vaporizer or external heat supply, was operated at millisecond contact times. Among the catalysts used in this study, Pt was the least reactive, and its activity was found to be reduced by sintering. Pt also tended to produce nonequilibrium products such as ethylene and acetaldehyde in fuel-rich environments. In contrast, LaMnO3 was found to favor glycerol combustion, producing fewer minor products and generating sufficient heat to sustain autothermal operations in fuel- and steam-rich regimes. Pt supported on LaMnO3 showed a synergistic effect of Pt sintering suppression and a broad H2/CO distribution in the resulting syngas. This effect can be correlated to the interaction be...

Autothermal reforming of isobutanol

Catalytic partial oxidation (CPO) of isobutanol to produce synthesis gas with varying H2/CO ratios has been performed autothermally in a staged millisecond-contact-time reactor. A 1 wt% Rh-1 wt% Ce/α-alumina catalyst was used to carry out CPO of isobutanol over a range of fuel to oxygen ratios (C/O) in ∼20 ms residence times. Steam was added (S/C = 0 to S/C = 3) to promote the water gas shift (WGS) reaction and increase hydrogen production. Without steam addition, the maximum CO and H2 selectivities obtained were greater than 70%. Steam addition increased the maximum hydrogen selectivity to 103%, at C/O = 1 and S/C = 2. Conversion of isobutanol and oxygen was always > 99% at all C/O and S/C ratios after CPO where the autothermal temperatures were typically between 600 and 1000 °C . A 1 wt% Pt–1 wt% Ce catalyst was added downstream of the CPO stage to further reduce the CO and increase the H2 concentrations by the WGS reaction. Addition of the WGS stage resulted in a product stream containing 1.7 to 3 mol% CO at S/C of 2 and 3 which is comparable to the exit stream CO concentration of an industrial high temperature shift catalyst. With steam addition, selectivities to hydrogen greater than 100% were obtained at all C/O ratios, with a maximum of 122% at C/O = 0.9 and S/C = 3. At S/C = 3, the H2/CO ratio increased from ∼3 after the CPO stage to ∼12 after the WGS stage. Also, the WGS catalyst reduced the selectivities of non-equilibrium products like isobutylene and isobutyraldehyde by almost half compared to that after the CPO stage, which can reduce syngas cleanup costs after a reformer. Since the total residence time in the reactor is ∼100 ms and the product distribution can be tuned by addition of steam, this represents a compact and simple system for producing renewable syngas or hydrogen.

Interaction of powdery Al, Zr and Ti with atmospheric nitrogen and subsequent nitride formation under the metal powder combustion in air

The combustion process in air for aluminum nanopowders (nAl), micron-sized powders of aluminum (μAl), titanium (μTi) and zirconium (μZr) was accompanied by the predominant reaction of the metals with N 2 and the subsequent stabilization of the nitride phases (from 38 wt.% of ZrN for μZr combustion to 72 wt.% of AlN for nAl combustion) in the condensed combustion products (CCP). The combustion process, composition and structure of CCP of nAl, μAl, μTi, and μZr were studied. Scanning electronic microscopy (SEM), X-ray diffraction (XRD), energy dispersive (X-ray) spectroscopy (EDX), and chemical analysis were performed on both initial powders and CCP. The combustion mechanism for the studied metal powders was experimentally proved. The formation of a large amount of non-equilibrium products (AlN, ZrN, TiN) instead of oxides in air is the special feature of the above mentioned experimental conditions. Nitride formation in air was defined by high temperatures and high burning rates during combustion of powdery Al, Ti and Zr.

Modelling of fluidized bed biomass gasification in the quasi-equilibrium regime for preliminary performance studies of energy conversion plants

Thermodynamic equilibrium-based models of gasification process are relatively simple and widely used to predict producer gas characteristics in performance studies of energy conversion plants. However, if an unconstrained calculation of equilibrium is performed, the estimations of product gas yield and heating value are too optimistic. Therefore, reasonable assumptions have to be made in order to correct the results. This paper proposes a model of the process that can be used in case of deficiency of information and unavailability of experimental data. The model is based on free energy minimization, material and energy balances of a single zone reactor. The constraint quasiequilibrium calculations are made using approximated amounts of non-equilibrium products, i.e. solid char, tar, CH4 and C2H4. The yields of these products are attributed to fuel characteristics and estimated using experimental results published in the literature. A genetic algorithm optimization technique is applied to find unknown parameters of the model that lead to the best match between modelled and experimental characteristics of the product gas. Finally, generic correlations are proposed and quality of modelling results is assessed in the aspect of its usefulness for performance studies of power generation plants.

Autothermal Catalytic Partial Oxidation of Glycerol to Syngas and to Non‐Equilibrium Products

Glycerol, a commodity by-product of the biodiesel industry, has value as a fuel feedstock and chemical intermediate. It is also a simple prototype of sugars and carbohydrates. Through catalytic partial oxidation (CPOx), glycerol can be converted into syngas without the addition of process heat. We explored the CPOx of glycerol using a nebulizer to mix droplets with air at room temperature for reactive flash volatilization. Introducing this mixture over a noble-metal catalyst oxidizes the glycerol at temperatures over 600 degrees C in 30-90 ms. Rhodium catalysts produce equilibrium selectivity to syngas, while platinum catalysts produce mainly autothermal non-equilibrium products. The addition of water to the glycerol increases the selectivity to H(2) by the water gas shift reaction and reduces non-equilibrium products. However, water also quenches the reaction, resulting in a maximum in H(2) production at a steam/carbon ratio of 2:3 over a Rh-Ce catalyst. Glycerol without water produces a variety of chemicals over Pt, including methylglyoxal, hydroxyacetone, acetone, acrolein, acetaldehyde, and olefins.

Microstructural Evolvement of Al-1.5Si-1.1Mg-0.5Cu Alloy Ingot during Homogenization Treatment

The kinds, morphologies and distributions, enclosed the micro-structural evolvement of Al-1.5Si-1.1Mg-0.5Cu alloy during homogenization treatment were investigated by means of optical microscopy, XRD, SEM/EDS and TEM/EDS. The results show that there were mainly three kinds of morphologically distinct constituents in as-cast Al-1.5Si-1.1Mg-0.5Cu alloy for automotive panels, such as coarse Mg2Si and Al8(FeMn)2Si, and multiphase eutectic structure consisted of AlMgSiFeCu elements, except the α-Al matrix phase. The coarse Mg2Si and Al8(FeMn)2Si were distributed in the α-Al interdentritic regions or at grain boundaries, the former sometimes appears more obvious eutectic characteristics than the later one. The multiphase eutectic products distributed both inside grains with agglomerate aspects and along the α-Al interdentritic regions or at grain boundaries, which is contained with Si and Al2Cu. Coarse binary eutectic structure Mg2Si partly dissolved into matrix and the eutectic characteristics disappeared, whereas Al8(FeMn)2Si changed a little during homogenization. Agglomerate multi-eutectic structures were non-equilibrium products, some of them fully dissolved into matrix and the others partially dissolved and left the discrete blocky Si behind after homogenization.

Microstructural transformations and mechanical properties of cast NiAl bronze: Effects of fusion welding and friction stir processing

A plate of as-cast NiAl bronze (NAB) material was sectioned from a large casting. A six-pass fusion weld overlay was placed in a machined groove; a portion of the weld reinforcement was removed by milling and a single friction stir processing (FSP) pass was conducted in a direction transverse to the axis of and over the weld overlay. A procedure was developed for machining of miniature tensile samples and the distributions of strength and ductility were evaluated for the fusion weld metal; for the stir zone (SZ) produced by the friction stir processing; and for a region wherein friction stir processing had taken place over the fusion weld. A region of low ductility in the heat affected zone (HAZ) of the fusion weld and in the thermomechanically affected zone (TMAZ) of friction stir processed material was attributed to partial reversion of an equilibrium lamellar eutectoid constituent upon local heating above ∼800 °C and formation of non-equilibrium transformation products upon subsequent cooling. The adverse effect on ductility is worse in the heat affected zone of the fusion weld than in the thermomechanically affected zone of friction stir processing due to the lower heat input of the latter process. The implications of this work to engineering applications of friction stir processing are discussed.

The aqueous geochemistry of metals in the weathering environment: strengths and weaknesses in our understanding of speciation and process

Soil profiles developed in different climates and physical settings are highly variable in structure, in mineralogy, in the local biosphere and in the compositions of the soil gas and water phases. Discussion of metals in ‘the weathering environment’ needs to acknowledge and address this diversity.The thermochemical methods developed by Pourbaix (1949) and Garrels and Christ (1965) remain useful predictors of metal speciation and solubility but the approach is valid only for processes involving carbonates, sulphides, hydroxides and similar minerals in soils and sediments. Almost no primary silicates are thermodynamically stable: they spontaneously decompose to non-equilibrium solid products with metal release determined by kinetics.Hydrolysis constants for aquo-complexes are useful indicators of metal speciation, mobility and availability. Recent work on soluble soil organic matter confirms that the active ligands are overwhelmingly oxygen based: phenols, carboxylic acids, alcohols. Many of these molecules compete very effectively with aquo-complexes to form strong metal chelates and appear to be responsible for substantial Al and Fe mobilization within and translocation down soil profiles.It is important to note also that strong clay mineral/organic matter associations (clay-organic complex) will fix metals as a consequence of the same chelation reactions (in this case removing them from solution - retardation).

Tuning millisecond chemical reactors for the catalytic partial oxidation of cyclohexane

It is demonstrated that millisecond partial oxidation of cyclohexane can be tuned by varying the catalyst and operating conditions to generate product distributions that favor (1) oxygenates, (2) olefins, or (3) syngas (H 2 and CO). High selectivities to parent oxygenates require low conversions using low-temperature catalysts, such as Ag or Co. Olefins are favored by Pt or Pt-Sn and H 2 addition eliminates the production of CO and CO 2, thereby increasing olefin selectivities. For syngas, Rh is the catalyst of choice. Finally, a Pt-10% Rh single gauze gives high selectivities to both oxygenates and olefins. Conventional methods for the partial oxidation of cyclohexane are liquid-phase processes that are plagued by poor conversions, high recycle costs, long residence times (minutes to hours), and expensive catalysts. In contrast, with a cyclohexane–oxygen feed at C 6H 12/O 2=2, a Pt-10% Rh single gauze catalyst can give total selectivities exceeding 80% to oxygenates and olefins at 25% cyclohexane conversion and complete oxygen conversion. The products consist of nearly 60% selectivity to the C 6 products, cyclohexene and 5-hexenal. The temperature profile attained in the single-gauze reactor allows the preservation of these highly non-equilibrium products. Alternative catalysts for cyclohexane oxidation to oxygenates and olefins include α-alumina monoliths coated with Pt, Rh, Pt-Rh, Pt-Sn, Co, Mo or Ag. The Co, Mo and Ag catalysts give very high selectivities to C 6 oxygenates but are hindered by poor conversions (<5%) of both cyclohexane and oxygen at these millisecond contact times. H 2 addition to cyclohexane oxidation feed mixtures over Pt and Pt-Sn is shown to significantly increase the selectivities to C 6 olefins while reducing the formation of CO and CO 2. Cyclohexane oxidation in air over Rh monoliths enables the production of high yields (>95%) of syngas. This process could find applications in the automotive industry as the production of hydrogen from liquid fuels becomes important.

Influence of welding techniques on microstructure and pitting corrosion behaviour of 1441 grade Al–Li alloy gas tungsten arc welds

AbstractThe effects of changing the welding technique on the weld bead solidification structure and resistance to pitting corrosion of an aeronautical grade Al-Li based alloy have been studied. Russian alloy 1441, with a nominal composition Al-1.9Li-1.8Cu-1.0Mg-0.1Zr (wt-%) and in the form of sheet, was welded using constant current, pulsed current and arc oscillation gas tungsten arc welding techniques. Under the optimum conditions of welding, the solidification structure was coarse columnar in constant current welds, fine equiaxed in pulsed current welds and fine equiaxed intermixed with fine cellular grains in arc oscillation welds. The distribution of interdendritic (and intergranular) non-equilibrium solidification products became increasing discrete on changing from constant current to pulsed current and arc oscillation welding. Resitance to pitting corrosion was found to be greatest in welds having a discrete second phase distribution, i.e. those produced using the pulsed current and arc oscillatio...

ChemInform Abstract: Millisecond Chemical Reactions and Reactors

Short contact time chemical reactors have many features which are very different from conventional packed bed reactors in that temperatures are determined by inlet parameters only, performance is nearly unchanged over wide variations in flow rate, and highly nonequilibrium products can be obtained at high conversions. Chemical reactions occur in regions of large gradients in composition and temperature, so the kinetics of the processes cannot be simply extracted from experiments. We illustrate these systems with recent examples of oxidative dehydrogenation of ethane at 85% ethylene selectivity and cyclohexane partial oxidation to oxygenates and olefins at 80% selectivity. A major feature of both reaction systems is the probable existence of two zones in the monolith where oxidation reactions occur close to the entrance and successive reactions such as homogeneous pyrolysis occur after all O2 is consumed and the surface is passivated with carbon. For the single gauze reactor only homogeneous oxidation occurs after the gauze where the temperature decreases strongly and quenches further decomposition of olefins and oxygenates. Considerations of scaleup of these reactors for large-scale chemicals production are discussed.

Crystallization in a SHS wave

The crystallization of nonequilibrium amorphous SHS products increases the wave velocity. The regimes of such an acceleration are studied.

Turbulent combustion of a uniform mixture and the formation of toxic substances

Turbulent combustion of a uniform mixture and the formation of toxic substances is examined. A model is constructed on the basis of the hypothesis that the fundamental process of oxidation takes place in narrow zones, while complete combustion of the fuel and the formation of nitrogen oxides occurs throughout the entire volume of the weakly nonequilibrium combustion products. The first stage is described using the equation for the probability density of the temperature. Its solution is analyzed, and it is shown that the average propagation velocity of a plane flame is entirely determined by the conditions in its leading boundary (that bordering fresh mixture). The second stage of the process is described with the help of the equation for averaged concentrations. The averaged values for the reaction rates are computed on the basis of results for the probability density of the temperature.

An intergrown perovskite-wollastonite phase in some ferrous blast-furnace slags

During crystallization of silicate liquids, TiO2 tends to form its own mineral. Ferrous blast-furnace slags generally have perovskite as the titanium-rich phase. However, a rounded and fibrous phase, crystallizing instead of perovskite, has been observed in some slag samples: it has an apparently late position in the order of crystallization. Detailed electron microprobe analysis and X-ray diffraction have indicated that this unusual phase is composed of intergrown perovskite and wollastonite. However, wollastonite should not be an equilibrium phase in these slags. Therefore, a series of simple high-temperature furnace experiments were conducted to examine possible origins of this intergrowth. Solid solution, liquid immiscibility, and eutectic growth have all been discounted as possible explanations of the intergrowth. However, blast-furnace slags are non-equilibrium products, and their residual liquids crystallize independently. This intergrown perovskite—wollastonite phase has been accounted for as a product of fractional crystallization within the system CaO-MgO-Al2O3-TiO2-SiO2.