In situ regeneration of ZSM-5 used in the ethylbenzene disproportionation under supercritical conditions

A study of the ethylbenzene disproportionation at a wide range of reaction pressures, from gas to supercritical conditions, was carried out in order to determine the influence of the reaction media properties, such as density, on the reaction parameters and especially on the deactivation by coke deposition.Pressure does not only favour the ethylbenzene disproportionation but also the formation of ethylene, a well-known coke precursor, by dealkylation reactions. However, coke extraction is also favoured by pressure, leading to an equilibrium between coke formation and extraction at high pressures, which is called in situ regeneration. So that, under certain supercritical conditions such as 400 °C and 91 bar, the reaction media properties make possible to obtain high ethylbenzene conversion and reduced deactivation by coking.     

干熄焦技术在清洁型热回收焦炉中的应用

对清洁型热回收焦炉熄焦方式进行了评价,指出干熄焦技术在节能、环保、改善焦炭质量以及经济效益上的积极意义。     

In situ compatibilization of starch-zein blends under shear flow

Starch-zein blends show poor adhesion between the two phases. Aldehyde starch was investigated as compatibilizer for these blends. Wheat starch was oxidized under mild conditions using sodium hypochlorite in the presence of the 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) and NaBr to prepare aldehyde starch. The oxidized starch was characterized by Nuclear Magnetic Resonance and Rapid Visco-Analyzer. Starch-zein blends plasticized with water and glycerol were prepared using simple shear flow in an in-house developed shearing device. Different zein ratios were tested to study the influence of aldehyde starch on the properties of the final material. The morphology of the blends was observed with confocal scanning laser microscopy and scanning electron microscopy. Tensile tests were used to evaluate the performance of the material. Both microscopy and tensile tests indicated that the blends had improved adhesion between the zein and starch phases, probably by reaction between the aldehyde groups in the starch molecules and zein. The aldehyde starch also influenced the properties of the starch matrix (higher viscosity, larger breakdown), which shows that physical or chemical crosslinks were formed inside the starch matrix.     

In situ co-adsorption of arsenic and iron/manganese ions on raw clays

The use of clays as effective arsenic sorbents has been strongly limited due to their low pH_ZPC and cation active behaviour in aqueous systems at pH > 3.5. A simple Fe/Al/Mn pre-treatment can significantly improve their sorption affinity to oxyanions, including arsenites and arsenates. The dynamics of arsenic adsorption from groundwater is also controlled by dissolved Fe/Mn ions, which behave as promoters of As adsorption, or competitors to adsorption sites. Low grade calcinated kaolin (MT) and bentonite (BT) were used as clay sorbents. Arsenic adsorption on raw clays without presence of Fe/Mn ions is very slow and limited. During co-adsorption the Fe/Mn ions and As oxyanions were adsorbed together onto a sorbent surface. Both Mn and Fe particles demonstrated a good sorption affinity to the clay surface, but only Fe particles supported As adsorption considerably (80% of As were removed in Fe/As system, while < 30% only in the Mn/As system). The kinetics of co-adsorption compared to the use of Fe/Mn pre-modified sorbents indicated a more dynamic process, while all mechanisms corresponded to the first order run (k ≈ 9.10^− 6- 1.10^− 4 s^− 1). Arsenic was strongly stabilized in pre-modified sorbents.     

In situ AFM investigation of crazing in polybutene spherulites under tensile drawing

This report deals with the study of the plastic deformation processes of semi-crystalline polymers at the micrometric and nanometric scales by atomic force microscopy. Capturing images from the same locus of the sample as a function of strain allows in situ observation of the processes. New experimental findings regarding initiation, growth and coalescence of crazes in poly(1-butene) are reported. The benefits of the technique are emphasized in comparison with previous studies carried out by transmission electron microscopy on ultra-thin films of various semi-crystalline polymers. The present situation is claimed to be closely representative of bulk deformation owing to the much greater sample thickness in comparison with the characteristic craze size. The occurrence of crazes oblique to the principal tensile stress is discussed in terms of triaxiality of the local stress field within the spherulites.     

In situ evaluation of structural changes in poly(ester-urethanes) during shape-memory cycles

The relationship between shape-memory behavior and structure was studied using three series of poly(ester-urethanes) with varying amounts of hard segment. The materials were designed to display a three-phase structure consisting of a disperse phase of crystallites and hard domains embedded in an amorphous matrix based on soft segment. Structure and thermal properties of the resultant materials were investigated using techniques such as modulated differential scanning calorimetry (MDSC), dynamic mechanical analysis (DMA) and small angle X-ray scattering (SAXS). The results revealed morphological changes in the materials during a low temperature shape-memory cycle. To study shape recovery, a deformed specimen was evaluated on a heating stage mounted at the SAXS beamline. Furthermore, to study the effect of temperature during recovery, the specimens were subjected to different thermo-cycles. Under each set of conditions, the phase morphology and composition were investigated. Temporary shape was stored by the metastable structure formed during deformation. The recovery was triggered by the melting of crystallites and hydrogen bonding between hard domains. The recovery process was divided into three stages. Bulk incompatibility and entropic recovery determined the final polyurethane morphology.     

In situ X-ray diffraction study of different graphites in a propylene carbonate based electrolyte at very positive potentials

Synchrotron based in situ X-ray powder diffraction was applied for the investigation of the PF₆⁻ intercalation behaviour into graphite of different particle size and various crystallinity at very positive potentials above 5 V vs. Li/Li⁺. In a propylene carbonate based electrolyte, small particles with low crystallinity show almost no anion intercalation and the particle structure remains intact. In graphite particles with increased particle size and/or higher crystallinity PF₆⁻ intercalation up to a stage 4 phase occurs but the reversibility is poor and exfoliation of graphene layers takes place as it was proven by post-mortem scanning electron microscopy. Thus, graphites with small particles and less crystallinity are preferred as conductive additive in positive “high voltage” cathodes in terms of structural integrity.     

In situ diagnostics of Victorian brown coal combustion in O2/N2 and O2/CO2 mixtures in drop-tube furnace

Experimental investigation of the combustion of an air-dried Victorian brown coal in O₂/N₂ and O₂/CO₂ mixtures was conducted in a lab-scale drop-tube furnace (DTF). In situ diagnostics of coal burning transient phenomena were carried out with the use of high-speed camera and two-colour pyrometer for photographic observation and particle temperature measurement, respectively. The results indicate that the use of CO₂ in place of N₂ affected brown coal combustion behaviour through both its physical influence and chemical interaction with char. Distinct changes in coal pyrolysis behaviour, ignition extent, and the temperatures of volatile flame and burning char particles were observed. The large specific heat capacity of CO₂ relative to N₂ is the principal factor affecting brown coal combustion, which greatly quenched the ignition of individual coal particles. As a result, a high O₂ fraction of at least 30% in CO₂ is required to match air. Moreover, due to the accumulation of unburnt volatiles in the coal particle vicinity, coal ignition in O₂/CO₂ occurred as a form of volatile cloud rather than individual particles that occurred in air. The temperatures of volatile flame and char particles were reduced by CO₂ quenching throughout coal oxidation. Nevertheless, this negative factor was greatly offset by char-CO₂ gasification reaction which even occurred rapidly during coal pyrolysis. Up to 25% of the nascent char may undergo gasification to yield extra CO to improve the reactivity of local fuel/O₂ mixture. The subsequent homogeneous oxidation of CO released extra heat for the oxidation of both volatiles and char. As a result, the optical intensity of volatile flame in ∼27% O₂ in CO₂ was raised to a level twice that in air at the furnace temperature of 1273 K. Similar temperatures were achieved for burning char particles in 27% O₂/73% CO₂ and air. As this O₂/CO₂ ratio is lower than that for bituminous coal, 30-35%, a low consumption of O₂ is desirable for the oxy-firing of Victorian brown coal. Nevertheless, the distinct emission of volatile cloud and formation of strong reducing gas environment on char surface may affect radiative heat transfer and ash formation, which should be cautioned during the oxy-fuel combustion of Victorian brown coal.     

In situ EC-STM studies of n-Si(1 1 1):H in 40% NH4F solution at pH 10

In situ electrochemical-scanning tunneling microcopy (EC-STM) was employed to investigate the etching dynamics of the moderately doped n-Si(1 1 1) electrode during cyclic voltammetric perturbation and at the seven different potentials including the open circuit potential (OCP) in 40% NH₄F solution at pH 10, which was prepared from 40% NH₄F and concentrated NH₄OH solution. The etching rate was significant at OCP and showed an exponential dependence on the potential applied to the silicon substrate electrode. Although some triangular pits were generated at the Si(1 1 1) surface, at the potentials more negative than OCP the site dependence in the removal of surface silicon atoms prevailed and led to the atomically flat Si(1 1 1):H surfaces with sharply defined steps of the step height 3.1 Å, where the interatomic distance of 3.8 Å was observed with a three-fold symmetry. At the potentials sufficiently more positive than OCP, macroporous hole was formed to limit further in situ EC-STM study. The results were compared with in situ EC-STM studies of the etching reaction of n-Si(1 1 1):H in the aqueous solution of dilute ammonium fluoride at pH 5, 40% NH₄F at pH 8, and 1 M NaOH reported in the literature.     

Creep strain recovery of an in situ spinel-forming refractory castable under loading/unloading compressive creep conditions

Creep strain recovery after unloading has been well studied for metals and certain ceramic composites; however, it has not yet been investigated for ordinary ceramic refractories applied in industrial furnaces. The present study explores the question whether creep strain recovery can be observed in ordinary ceramic refractories to justify its consideration in the design of such refractories and refractory linings. To this end, the dependence of creep strain recovery on different loading conditions was investigated for a high-alumina in situ spinel-forming castable, commonly used as refractory lining of steel ladles in secondary steel metallurgy. Several loading/unloading compressive creep tests were performed at 1300 °C for different loading histories. Creep strain recovery was observed to occur and it was significantly affected by the holding time and degree of unloading. A longer holding time for the loading period was found to increase the internal stress, which is the driving force for creep strain recovery. In addition, the findings indicate that a higher excess of internal stress over external stress after unloading induces higher strain recovery.