H2O CO2 Research Articles

Predicting the rapid devolatilization of mineral-free cellulose

This paper extends the validation of a reaction mechanism for the devolatilization of mineral-free cellulose called “cel-FC.” A single set of model parameters accurately interprets the partitioning of raw cellulose into oil, noncondensables, and solid residue and oil molecular weight distributions (MWDs) for temperatures to 600 °C, heating rates from 60 to 6000°C/s, contact times to 120 s, and pressures of vacuum and 0.1 MPa. The analysis incorporates depolymerization via random scission and unzipping from chain ends; charring via monomer decomposition, spontaneous charring, and thermal annealing; fragmentation statistics, and the flash distillation analogy. Random depolymerization is responsible for the induction of primary cellulose devolatilization and eventually generates chains short enough to vaporize. The accompanying surge in the relative concentrations of chain ends activates the unzipping process. The fastest oil production rates are driven by scission plus unzipping and mediated by flash distillation. Whenever vaporization of longer oil precursors is limited, unzipping delivers monomer derivatives into the oil. Whenever longer volatile chains can freely vaporize they are no longer subject to unzipping or scission, so there are necessarily fewer monomers in oil. This is why ultimate oil yields are essentially the same across broad ranges of heating rate, temperature (given sufficient contact time at low temperatures), and pressure, and why oil MWDs shift toward heavier molecular weights for progressively faster heating rates, hotter temperatures, and lower pressures. Cel-FC interprets the optimal primary products - 94 wt% oil plus a mixture of light oxygenates, CO2, and CO in H2O – as the limit of depolymerization via scission and unzipping without any charring reactions. Monomer decomposition and spontaneous charring produce hardly any bio-char from mineral-free cellulose but are major sources of noncondensable gases and responsible for greater gas yields for slower heating rates, hotter temperatures, and higher pressures.

Theoretical Thermodynamic Efficiency Limit of Isothermal Solar Fuel Generation from H2O/CO2 Splitting in Membrane Reactors

Solar fuel generation from thermochemical H2O or CO2 splitting is a promising and attractive approach for harvesting fuel without CO2 emissions. Yet, low conversion and high reaction temperature restrict its application. One method of increasing conversion at a lower temperature is to implement oxygen permeable membranes (OPM) into a membrane reactor configuration. This allows for the selective separation of generated oxygen and causes a forward shift in the equilibrium of H2O or CO2 splitting reactions. In this research, solar-driven fuel production via H2O or CO2 splitting with an OPM reactor is modeled in isothermal operation, with an emphasis on the calculation of the theoretical thermodynamic efficiency of the system. In addition to the energy required for the high temperature of the reaction, the energy required for maintaining low oxygen permeate pressure for oxygen removal has a large influence on the overall thermodynamic efficiency. The theoretical first-law thermodynamic efficiency is calculated using separation exergy, an electrochemical O2 pump, and a vacuum pump, which shows a maximum efficiency of 63.8%, 61.7%, and 8.00% for H2O splitting, respectively, and 63.6%, 61.5%, and 16.7% for CO2 splitting, respectively, in a temperature range of 800 °C to 2000 °C. The theoretical second-law thermodynamic efficiency is 55.7% and 65.7% for both H2O splitting and CO2 splitting at 2000 °C. An efficient O2 separation method is extremely crucial to achieve high thermodynamic efficiency, especially in the separation efficiency range of 0–20% and in relatively low reaction temperatures. This research is also applicable in other isothermal H2O or CO2 splitting systems (e.g., chemical cycling) due to similar thermodynamics.

Effects of atmosphere on mineral transformation of Zhundong coal during gasification in CO2/H2O conditions

Coal gasification has been regarded as a promising method for the thermochemical utilization of Zhundong (ZD) coals. However, ZD coals are characterized by the high content of alkali metal, which may cause a series of running problems such as ash accumulation, slag blocking and fouling on heating surface of the gasifier and waste heat boiler. To improve the efficiency of fuels utilization, the evolution behavior of minerals of ZD coals – Hongshaquan (HSQ) coal and Jiangjunmiao (JJM) coal was investigated by experiment and FactSage calculation in this work. The results gained by low temperature ashing method show that the minerals of both HSQ coal and JJM coal are basically similar mainly including quartz, kaolinite, calcite, halite and of pyrite. It was found that the minerals transformation of coal samples is greatly influenced by gasification atmosphere (CO2/H2O). For HSQ coal, the minerals of slag are mainly composed of quartz, nepheline, gehlenite and periclase under pure H2O or pure CO2 atmospheres, while the minerals of slag are mainly lime and periclase under the mixing CO2/H2O (CO2: H2O = 1:1) atmosphere. For JJM coal, the minerals of slag under the pure H2O atmosphere are obvious different from that under the pure CO2 atmosphere, and mainly include gehlenite, lime, magnesia, and nepheline in pure H2O atmosphere, and the pleonaste and merwinite minerals are detected under pure CO2 and CO2/H2O (CO2: H2O = 1:1) mixing atmosphere. Furthermore, the FTIR results for the two coal samples demonstrate that the more silicate minerals exist in coal slag, which might be caused by the factor that H2O promotes the melting and polycondensation of SiO2 and Al2O3 to increase the quantity of silicate. In addition, according to the calculation results of FactSage, iron is formed during the evolution of iron-containing minerals with water vapor in atmosphere which may be due to the promotion effect of water on the decomposition of pyrite in coal slag. Moreover, water vapor can promote the migration of the alkali metal sodium in the coal slag to the gas phase, reducing the sodium content in the slag, and thus results in a higher viscosity of the molten slag under the water vapor atmosphere than under the pure CO2 atmosphere. The order of slag viscosity is: η0(H2O) > η0(CO2/H2O) > η0(CO2). This work provides a theoretical information for the effect of CO2/H2O gasification conditions on the mineral’s evolution behavior of ZD coal and offers a guidance for the operation of gasifier.

CeO2‐TiO2 Hybid‐Nanotubes with Tunable Oxygen Vacancies as the Support to Confine Pt Nanoparticles for the Low‐Temperature Water‐Gas Shift Reaction

AbstractReducible oxides as supports have been demonstrated to improve the activity of Pt catalysts towards water‐gas shift (WGS) reaction. The Pt species anchored by the oxygen vacancies derived from these supports play as catalytic sites during low‐temperature WGS reaction. Herein, we introduced CeO2 to modify TiO2 nanotubes (TiO2NT) and prepared CeO2‐TiO2 hybid‐nanotubes ((CeO2)x(TiO2)1‐xNT, x=0.2, 0.4, 0.6) to confine Pt nanoparticles (NPs) as the efficient catalysts for the low‐temperature WGS reaction. Pt NPs confined in (CeO2)x(TiO2)1‐xNT catalysts exhibit higher WGS activity than that of the Pt NPs entrapped in pure TiO2NT (Pt‐in‐TiO2NT) and Pt/CeO2 catalysts throughout the entire reaction temperature range. Activity measurements coupled with the physicochemical characterization of catalysts suggest that the redox ability of PtOx species is positive correlated with WGS activity and oxygen vacancy adjacent to Pt (Pt‐Ov) serves as the active site for H2O dissociation and CO oxidation in WGS reaction.

Relative Contributions of Mg Hydration and Molecular Structural Restraints to the Barrier of Dolomite Crystallization: A Comparison of Aqueous and Non-Aqueous Crystallization in (BaMg)CO3 and (CaMg)CO3 Systems

Carbonate mineralization is reasonably well-understood in the Ca–CO2–H2O system but continuously poses difficulties to grasp when Mg is present. One of the outstanding questions is the lack of success in dolomite MgCa(CO3)2 crystallization at atmospheric conditions. The conventional view holds that hydration retards the reactivity of Mg2+ and is supported by solvation shell chemistry. This theory however is at odds with the easy formation of norsethite MgBa(CO3)2, a structural analogue of dolomite, leading to the premise that crystal or molecular structural constrains may also be at play. The present study represents our attempts to evaluate the separate contributions of the two barriers. Crystallization in the Mg–Ba–CO2 system was examined in a non-aqueous environment and in H2O to isolate the effect of hydration by determining the minimal relative abundance of Mg required for norsethite formation. The results, showing an increase from 1:5 to 6:4 in the solution Mg/Ba ratio, represented a ~88% reduction in Mg2+ reactivity, presumably due to the hydration effect. Further analyses in the context of transition state theory indicated that the decreased Mg2+ reactivity in aqueous solutions was equivalent to an approximately 5 kJ/mol energy penalty for the formation of the activated complex. Assuming the inability of dolomite to crystallizes in aqueous solutions originates from the ~40 kJ/mol higher (relative to norsethite) Gibbs energy of formation for the activated complex, a hydration effect was estimated to account for ~12% of the energy barrier. The analyses present here may be simplistic but nevertheless consistent with the available thermodynamic data that show the activated complex of dolomite crystallization reaction is entropically favored in comparison with that of norsethite formation but is significantly less stable due to the weak chemical bonding state.

Radiolytic Destruction of Uracil in Interstellar and Solar System Ices.

Uracil is one of the four RNA nucleobases and a component of meteoritic organics. If delivered to the early Earth, uracil could have been involved in the origins of the first RNA-based life, and so this molecule could be a biomarker on other worlds. Therefore, it is important to understand uracil's survival to ionizing radiation in extraterrestrial environments. Here we present a study of the radiolytic destruction kinetics of uracil and mixtures of uracil diluted in H2O or CO2 ice. All samples were irradiated by protons with an energy of 0.9 MeV, and experiments were performed at 20 and 150 K to determine destruction rate constants at temperatures relevant to interstellar and Solar System environments. We show that uracil is destroyed much faster when H2O ice or CO2 ice is present than when these two ices are absent. Moreover, destruction is faster for CO2-dominated ices than for H2O-dominated ones and, to a lesser extent, at 150 K compared with 20 K. Extrapolation of our laboratory results to astronomical timescales shows that uracil will be preserved in ices with half-lives of up to ∼107 years on cold planetary bodies such as comets or Pluto. An important implication of our results is that for extraterrestrial environments, the application of laboratory data measured for the radiation-induced destruction of pure (neat) uracil samples can greatly underestimate the molecule's rate of destruction and significantly overestimate its lifetime, which can lead to errors of over 1000%.

Corrosion Law of Metal Pipeline in Tahe Oilfield and Application of New Materials

Frequent corrosion perforation of metal pipes severely restricts oil and gas fields’ safety production and increases maintenance costs. Therefore, it is imminent to change the characteristics of metal materials fundamentally. In this paper, taking the metal pipe of Northwest Oil and Gas Field in China as an example, for the corrosion environment with high concentrations of H2S, CO2, H2O, Cl−, and O2, the main factors leading to corrosion are analyzed, the corrosion rules and optical materials of the pipe under different environmental and operating conditions are figured out, and the corrosion resistance of new pipes materials is evaluated. The main conclusions are as follows: (1) In the environment of the CO2–H2O–Cl− strong scouring system, electrochemical corrosion dominates, and the corrosion morphology is mainly groove-like corrosion and ulcer-like corrosion; (2) The H2S content affects the incubation period and development period of pipe corrosion; (3) Through the two optimization directions of 20# steel refining and material alloying, BX245-1Cr pipe material has been developed. At present, the application of this pipe material has relatively better results.

Determination of mass transfer coefficients in high-pressure CO2-H2O flows in microcapillaries using a colorimetric method

This study presents a method for the experimental determination of the local volumetric mass transfer coefficient kLaL in a high-pressure two-phase flow of water (H2O) and carbon dioxide (CO2) in a micro-capillary using a colorimetric method. H2O and CO2 are fed continuously and co-axially injected at high-pressure (10 MPa) and moderate temperature (303 K) into a microcapillary. Under the flow conditions studied, a segmented flow of CO2 in H2O is formed. The CO2 dissolves into the H2O-rich phase, thereby reducing the pH to about 3.3, depending on the pressure and temperature. The pH of the H2O-rich phase is determined over the entire length of the capillary using a pH sensitive indicator coupled with high-speed imaging and analysis. The concentration of CO2 in the water-rich phase is deduced from this pH value using literature experimental data. The CO2 concentration data and the unit-cell model, which has been modified to account for high pressure conditions, have then been used to determine the volumetric mass transfer coefficient, kLaL, of CO2 into the liquid phase along the entire length of the microreactor. The experimentally derived kLaL ​​ranges between 1 and 13 s−1.

Based on Atmospheric Physics and Ecological Principle to Assess the Accuracies of Field CO2/H2O Measurements From Infrared Gas Analyzers in Closed‐Path Eddy‐Covariance Systems

AbstractField CO2/H2O measurements from infrared gas analyzers in closed‐path eddy‐covariance systems have wide applications in earth sciences. Knowledge about exactness of these measurements is required to assess measurement applicability. Although the analyzers are specified with uncertainty components (zero drift, gain drift, cross‐sensitivities, and precision), exactness for individual measurements is unavailable due to an absence of methodology to comprehend the components as an overall uncertainty. Adopting an advanced definition of accuracy as a range of all measurement uncertainty sources, the specified components are composited into a model formulated for studying analyzers’ CO2/H2O accuracy equations. Based on atmospheric physics and environmental parameters, the analyzers are evaluated using the equations for CO2 accuracy (±0.78 µmolCO2 mol−1, relatively ±0.18%) and H2O accuracy (±0.15 mmolH2O mol−1). Evaluation shows that precision and cross‐sensitivity are minor uncertainties while zero and gain drifts are major uncertainties. Both drifts need adjusting through zero/span procedures during field maintenance. The equations provide rationales to guide and assess the procedures. H2O span needs more attentions under humid conditions. Under freezing conditions while H2O span is impractical, this span is fortunately unnecessary. Under the same conditions, H2O zero drift dominates H2O measurement uncertainty. Therefore, automatic zero becomes a more applicable and necessary tactic. In general cases of atmospheric CO2 background, automatic CO2 zero/span procedures can narrow CO2 accuracy by 36% (±0.74 to ± 0.47 µmolCO2 mol−1). Automatic/manual H2O zero/span procedures can narrow H2O accuracy by 27% (±0.15 to ±0.11 mmolH2O mol−1). While ensuring system specifications, the procedures guided by equations improve measurement accuracies.

Influence of rare-earth doping on the phase composition, sinterability, chemical stability and conductivity of BaHf0.8Ln0.2O3-δ (Ln = Yb, Y, Dy, Gd) proton conductors

BaHf0.8Ln0.2O3-δ doped with rare earth elements with different ionic radii (Ln = Yb, Y, Dy and Gd) as candidate materials for solid oxide fuel cells and H2 separation membrane have been prepared. Their phase composition, sinterability, chemical stability and conductivity were studied systematically. The rare earth elements are successfully incorporated into the main phase crystal lattice of barium hafnate to generate a single perovskite phase. The relative density of all samples sintered at 1600 °C reaches above 90%, and Y-doped BaHfO3 has the highest relative density (94.7%) and the biggest grain size (about 1 μm) among all samples. The conductivities of the samples firstly increase and then decrease with the increase of the doped ion radius. Among all samples the conductivity of BaHf0.8Y0.2O3-δ is the highest and reaches 6.02 × 10−3 S cm−1 in wet air at 700 °C, which is attributed to the good sinterability and suitable crystal structure (tolerance factor and free volume). All samples also show excellent chemical stability in the test atmospheres, including saturated H2O steam, pure H2 and CO2, 200 ppm H2S/Ar and boiling water. The Pt/BaHf0.8Y0.2O3-δ electrolyte/Pt single cell was fabricated with a 530 μm-thick disk and its electrochemical properties were tested. The peak power density reaches 10.21 mW cm−2 at 700 °C, which is comparable to similar fuel cells reported. These results suggest that BaHf0.8Y0.2O3-δ is a promising electrolyte candidate for proton-conducting fuel cells.

External electric field enhances CO2 geological Storage: A molecular dynamics simulation

The microscopic understanding of adsorption and storage of CO2 in minerals is of great significance for large-scale geological storage of CO2. The behaviors of the H2O − CO2 system absorbed on the kaolinite surfaces with oscillating and static electric fields were investigated by the non-equilibrium molecular dynamics simulation. The results show that the H2O molecules will adsorb onto clay surfaces and reduce the adsorption of CO2, which results in lower amounts of geological storage of CO2. However, the applied external static electric fields can break hydrogen bonds which formed between H2O molecules and clay surface, and thus promote the desorption of H2O and geological storage of CO2. The static electric fields are more pronounced in enhancing CO2 geological storage with an extra 15.58 % when the surface is vertical to the electric field direction. Meanwhile, the initial dipole orientation of H2O in the adsorption phase, which is parallel to the surface, decides that electric fields are more efficient on the surface vertical to the electric field direction. This research will be helpful to understand how electric fields promote CO2 geological storage on the molecular level.

Bio-FLASHCHAIN® theory for rapid devolatilization of biomass. 4. V.2.0 decomposition mechanism for mineral-free cellulose

According to cel-FC, the essential aspects of cellulose devolatilization are (1) Depolymerization reactions that disintegrate cellulose chains into a fragment distribution; (2) Probabilities that a given bond rupture produces a certain chain size; (3) A charring cascade that inhibits subsequent bond ruptures while bound glucose monomers decompose into progressively more refractory structures plus noncondensable gases; and (4) The Flash Distillation Analogy whereby volatile chains in the condensed phase vaporize into escaping noncondensable gases, depending on the molecular weight, temperature, and pressure. Predictions from cel-FC are evaluated with measured product distributions including bio-oil molecular weight distributions (MWDs) from mineral-free cellulose for temperatures to 900 °C, heating rates from 100 to 5000 °C/s, contact times to 30 s, and pressures from vacuum to 6.9 MPa. Cel-FC accurately depicts the impacts of temperature, heating rate, and pressure on the major products of primary cellulose devolatilization. Devolatilization during slow heating occurs at relatively cool temperatures where vaporization is limited for all but the lightest oil precursors. Unzipping circumvents this bottleneck by delivering a preponderance of monomer derivatives into the cumulative oil sample. Devolatilization at fast heating usually occurs at hotter temperatures where longer volatile chains can freely vaporize and produce an oil with relatively few monomers but abundant longer depolymerization fragments. As longer precursors vaporize, there are necessarily fewer monomers in a cumulative oil sample. This same observation explains why ultimate oil yields vary little across broad ranges of heating rate, temperature (given sufficient contact time at low temperatures), and pressure, and why oil MWDs shift toward heavier MWs for faster heating rates, hotter temperatures, and lower pressures. Cel-FC also interprets the optimal primary products - 94 wt% oil plus a mixture of light oxygenates, CO2, and CO in H2O – as the limit of depolymerization via scission and unzipping without any charring.

Thermodynamic modeling of iron and zinc reduction from B<sub>2</sub>O<sub>3</sub> ‒ CaO ‒ Fe<sub>2</sub>O<sub>3</sub> ‒ ZnО melt by СО ‒ CO<sub>2</sub> and H<sub>2</sub> ‒ Н<sub>2</sub>О mixtures

The paper presents the thermodynamic modeling results of zinc and iron reduction from B2O3 ‒ CaO ‒ Fe2O3 ‒ ZnО melts by CO ‒ CO2 and H2 ‒ H2O mixtures containing 0 – 60 % CO2 (H2O) at 1273 – 1673 K using a technique describing the reduction of metals from an oxide melt by gas in bubbling processes, under conditions that provide an approximation to real systems. Its originality is equilibrium determination for each individual portion of gas supplied into the working fluid. The reducible metals oxides content in each calculation cycle is taken from the previous data. During the calculations, changes in the content of zinc (СZnO ) and iron (СFe2O3 , СFe3O4 and СFeO ) oxides in the melt and the degree of their reduction were estimated. When using CO or H2 as a reducing agent, this process proceeds in three stages. In the first stage, Fe2O3 is reduced to Fe3O4 and FeO. CFe2O3 values decrease to almost zero, while CFe3O4 and CFeO increase simultaneously. By the end of the stage, СFe3O4 reaches its maximum value. At the second stage, the Fe3O4 → FeO transition occurs, when СFeO values reach its maximum. At these stages, there is a slight increase in the CZnO . At the third stage, the values CFeO and CZnO decrease, and iron and zinc are reduced. An increase in temperature dramatically reduces the gas consumption for zinc reduction by 2 – 3 times, and the replacement of CO with H2 reduces it by less than 20 %. In the presence of oxidizing agents (CO or H2O), only zinc is reduced. The process ends when the final content of zinc oxide in the melt corresponds to the equilibrium with the initial gas composition. The higher the temperature, the less CZnO is. The obtained data are useful for the development of technologies for the selective recovery of metals.

A comprehensive evaluation of the WSGG model for air- and oxy-fuel combustion conditions through three-dimensional calculations

This paper reports an assessment of the accuracy of most formulations of the weighted-sum-of-gray-gases (WSGG) model proposed in the last decade for the treatment of mixtures of water vapor and carbon dioxide. The analysis is based on non-coupled, three-dimensional radiative transfer calculations of cases representative of air- and oxy-fuel combustion at fixed or varying H2O–CO2 mole fraction ratios (MR). The reference solution is computed by line-by-line (LBL) integration. The WSGG model is shown as capable to provide accurate results for all cases under study, with existing correlations for the model displaying maximum errors below 4%. Formulations developed considering MR variations can in general be safely used even for cases where MR is constant; likewise, fixed-MR correlations can be applied for varying-MR scenarios, as long as the regions of most importance for the radiative transfer have a MR value close to the one for which the correlations were generated. The superposition WSGG model is tested as well, and it yields consistently accurate results for all test cases, although at a significantly larger processing cost than the standard WSGG model. An alternative approach for treating media with varying mole ratio, consisting of interpolating fixed-MR correlations, is also found to be promising.

Evonik presents its latest “Living polyurethanes” solutions for improving daily life at PU China 2021

This paper reports an assessment of the accuracy of most formulations of the weighted-sum-of-gray-gases (WSGG) model proposed in the last decade for the treatment of mixtures of water vapor and carbon dioxide. The analysis is based on non-coupled, three-dimensional radiative transfer calculations of cases representative of air- and oxy-fuel combustion at fixed or varying H2O–CO2 mole fraction ratios (MR). The reference solution is computed by line-by-line (LBL) integration. The WSGG model is shown as capable to provide accurate results for all cases under study, with existing correlations for the model displaying maximum errors below 4%. Formulations developed considering MR variations can in general be safely used even for cases where MR is constant; likewise, fixed-MR correlations can be applied for varying-MR scenarios, as long as the regions of most importance for the radiative transfer have a MR value close to the one for which the correlations were generated. The superposition WSGG model is tested as well, and it yields consistently accurate results for all test cases, although at a significantly larger processing cost than the standard WSGG model. An alternative approach for treating media with varying mole ratio, consisting of interpolating fixed-MR correlations, is also found to be promising.

Molecular dynamics investigation on supercritical water oxidation of a coal particle

The supercritical water oxidation (SCWO) is a technology with very low environmental impact and significant economic benefits. In present paper, the micro-scale dynamics and the kinetic reaction mechanism of the SCWO of a coal particle is investigated by the reactive force-field (ReaxFF) method for the first time. Comparisons between experimental and analytical results on the activation energy show the coal particle model and the ReaxFF MD can successfully reproduce the SCWO process. Results on the atomistic scale conversion ways of O2, CO2, H or H2 and H2O show the SCWO is not simply the gasification plus the combustion. In SCWO, the direct combustion of the coal is weakened apparently due to the existence of the water, the oxidation reaction between the water or H radicals and the oxygen to generate OH plays an important role in coal conversion. The oxidation between carbon structures and OH to generate CO2 and H2O has substituted for the direct combustion reaction with the oxygen to be the dominant way in coal conversion. This process contains the characteristics of both combustion and gasification process. The role of water molecules is something similar to the catalysis. It is converted to OH radicals first in a series of gasification and oxidation processes, then the OH radicals turn into H2O in the following oxidation reactions. After that, the effect of reaction conditions and the transition of N on the SCWO process are studied. Comparing to the single supercritical water gasification, N2 and NO are found to be the extra products in SCWO. CN, CHN and CHON are the dominant N-containing products before they are converted to N2 and NO. The results in present work give insight into the oxidation mechanism of the coal particle, and the SCWO can effectively reduce the pollution emission in a much cleaner way compared with the conventional coal-fired mode.

Evolution of ultrapotassic volcanism on the Kaapvaal craton: deepening the orangeite versus lamproite debate

Abstract Orangeites are a significant source of diamonds, yet ambiguity surrounds their status among groups of mantle-derived potassic rocks. This study reports mineralogical and geochemical data for a c. 140 Ma orangeite dyke swarm that intersects the Bushveld Complex on the Kaapvaal craton in South Africa. The dykes comprise distinctive petrographic varieties that are linked principally by olivine fractionation, with the most evolved members containing minor amounts of primary carbonate, sanidine and andradite garnet in the groundmass. Although abundant groundmass phlogopite and clinopyroxene have compositions that are similar to those of cratonic lamproites, these phases show notable Ti-depletion, which we consider a hallmark feature of type orangeites from the Kaapvaal craton. Ti-depletion is also characteristic of bulk rock compositions and is associated with strongly depleted Th–U–Nb–Ta contents at high Cs–Rb–Ba–K concentrations. The resultant high large ion lithophile element/high field strength element ratios of orangeites suggest that mantle source enrichment occurred by metasomatic processes in the proximity of ancient subduction zones. The Bushveld-intersecting orangeite dykes have strongly enriched Sr–Nd–Hf isotopic compositions (initial 87 Sr/ 86 Sr = 0.70701–0.70741; ε Nd = −10.6 to −5.8; ε Hf = −14.4 to −2.5), similar to those of other orangeites from across South Africa. Combined with the strong Ti–Nb–Ta depletion, this ubiquitous isotopic feature points to the involvement of ancient metasomatized mantle lithosphere in the origin of Kaapvaal craton orangeites, where K-rich metasomes imparted a ‘fossil’ subduction geochemical signature. Previous geochronology studies identified ancient K-enrichment events within the Kaapvaal cratonic mantle lithosphere, possibly associated with collisional tectonics during the 1.2–1.1 Ga Namaqua–Natal orogeny of the Rodinia supercontinent cycle. It therefore seems permissible that the cratonic mantle root was preconditioned for ultrapotassic magma production by tectonomagmatic events that occurred along convergent plate margins during the Proterozoic. However, reactivation of the K-rich metasomes had to await establishment of an extensional tectonic regime, such as that during the Mesozoic breakup of Gondwana, which was accompanied by widespread (1000 × 750 km) small-volume orangeite volcanism between 200 and 110 Ma. Although similarities exist between orangeites and lamproites, these and other potassic rocks are sufficiently distinct in their compositions such that different magma formation processes must be considered. In addition to new investigations of the geodynamic triggers of K-rich ultramafic magmatism, future research should more stringently evaluate the relative roles of redox effects and volatile components such as H 2 O–CO 2 –F in the petrogeneses of these potentially diamondiferous alkaline rocks.

Numerical Model of Co-Electrolysis in Solid Oxide Cells with Ni/Gd-Doped Ceria (CGO) Fuel Electrode

Solid oxide electrolysis cells (SOECs) are expected to play a crucial role in the conversion of electrical energy from sustainable sources into chemical compounds. The co-electrolysis of atmospheric carbon dioxide with steam is seen as a potential source of synthesis gas [1], which can be further processed with Fischer-Tropsch synthesis to renewable liquid fuels [2]. A key step during co-electrolysis is the energy conversion at the cermet fuel electrode through electro-reduction. This electro-reduction is commonly believed to take place at the triple phase boundary (TPB) between nickel, oxygen ion conducting ceramics and gas [3]. Recent studies show that, due to the high electro-catalytic activity and mixed ionic and electronic conductivity (MIEC) of the ceria phase, the electrochemically active electrode area on Ni/Gadolinium-doped ceria (CGO) electrodes further extends to the double phase boundary (DPB) between CGO surface and gas phase [4,5,6]. However, it is still unclear whether DPB or TPB pathways dominate the electrochemical reduction in industrially used porous electrodes [5], particularly after structural changes as a consequence of Ni degradation such as coarsening and migration [6].The proposed numerical model of a commercial electrolyser cell aims to reveal main kinetic mechanisms responsible for the electro-reduction at the Ni/CGO fuel electrode and to identify possibilities for the cell optimisation. The cell model includes: detailed gas and surface kinetics, detailed gas and ion transport. Cross-section images from scanning electron microscopy helped to identify 7 layers with different material properties. The model allows to differentiate the following aspects: charge transfer at the LSCF/CGO/air interface, charge transfer at CGO/fuel and Ni/CGO/fuel interfaces, charge transfer between CGO-surface and CGO-bulk, charge transfer between YSZ and CGO, as well as gas transport/conversion.For the model validation, electrochemical experiments were performed including current-voltage curves and electrochemical impedance spectroscopy with a full cell in the 3 operating modes H₂O electrolysis, CO₂ electrolysis and co-electrolysis. In order to avoid the overlap of electrochemical contributions and gas transport processes, a cell with a small active electrode area was operated with large fuel gas flow rates. Various operating temperatures (780 to 860 °C), fuel compositions (30 to 85% H₂O, 30 to 85% CO₂) and oxygen contents (1 to 100% O₂) were used to identify the electrochemical mechanisms. Possible reaction pathways are investigated and electro-reduction at DPB and TPB is compared.

Effect of Anode Side Purge Gas on the Degradation of Solid Oxide Electrolysis Cells

Solid oxide electrolysis cells (SOECs) has drawn great interest in recent years due to its high power to fuel efficiency. The technology is believed to be able to play an important role in the power-to-x (P2X) and carbon capture and utilization (CCU) applications due to its capability of CO2 electrolysis and H2O + CO2 co-electrolysis. The syngas produced from SOEC can be further catalytic converted into different higher value synthetic fuels, which is essential for the green transition of those hard-to-be-electrified sectors such as aviation and heavy transportation. Large-scale implementation of such a technology requires SOEC to be cost competitive with the current existing electrolysis technologies. High performance and long-term durability are keys to further bring down the SOEC fuel production costs. Understanding the degradation mechanisms and identifying limits for a “safe-operation-window” for which the degree of degradation is limited will help to further advance the SOEC technology to the market. In this work, the influence of operation parameters such as temperature, gas composition and reactant utilization on the SOECs’ degradation were examined with commercial solid oxide cells from Elcogen. The degradation mechanisms investigated by electrochemical impedance and post-test microstructure analysis will be presented and discussed.This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 838014 (C2FUEL).

Phase State and Thermodynamic Parameters of the Fluid System H2O–CO2–CH4 at P-T Conditions of the Crust and Lithosphere Mantle

Phase State and Thermodynamic Parameters of the Fluid System H2O–CO2–CH4 at P-T Conditions of the Crust and Lithosphere Mantle