Effect Of Deactivation Research Articles

Survey of selective electrode deactivation attitudes and practices by cochlear implant audiologists

Objectives The purpose of this study was to explore clinician attitudes regarding selective electrode deactivation and to investigate the primary methodology used to identify poorly encoded electrodes, deactivate identified electrodes, and measure outcomes. Methods An online survey consisting of 32 questions was administered to certified clinical and research cochlear implant (CI) audiologists. Questions asked participants about their demographic information, device programming patterns, and attitudes regarding selective electrode deactivation. Results Fifty-four audiologists completed the survey. When asked whether they believed selectively deactivating poorly encoded electrodes could improve speech perception outcomes, 43% of respondents selected ‘Probably Yes,’ 39% selected ‘Definitely Yes,’ and 18% selected ‘Might or Might Not.’ Of those who reported deactivating electrodes as part of CI programming, various methodology was reported to identify and deactivate poorly encoding electrodes and evaluate effectiveness of deactivation. General reasons against deactivation were also reported. Discussion CI audiologists generally believed selective electrode deactivation could be used to improve speech perception outcomes for patients; however, few reported implementing selective electrode deactivation in practice. Among those who do perform selective electrode deactivation, the reported methodology was highly variable. Conclusion These findings support the need for clinical practice guidelines to assist audiologists in performing selective electrode deactivation.

Research Progress on Catalytic Combustion of Volatile Organic Compounds in Industrial Waste Gas

Volatile organic compounds (VOCs) emitted from industrial processes have high stability, low activity, and toxicity which cause continuous harm to human health and the atmospheric environment. Catalytic combustion has the advantages of low energy consumption and low cost and is expected to be one of the most effective methods to remove VOCs. At present, the selection of low cost, high activity, and durability catalysts are still a difficult problem. Industrial emissions of VOCs contain a certain amount of aromatic hydrocarbons; these substances are highly toxic substances, and, once inhaled by the human body, will cause serious harm to health. In this paper, the principle, advantages, and disadvantages of VOCs processing technology are analyzed in detail, and the catalytic combustion of aromatic hydrocarbons in VOCs is reviewed, including catalyst, reaction conditions, catalyst selection, inactivation reasons, and structure use. In addition, the deactivation effects of chlorine and sulfur on catalysts during the catalytic combustion of VOCs are discussed in detail. Finally, on the basis of literature research, the prospect of catalytic combustion of VOCs is presented, which provides influential information for further research on VOCs processing technology.

Effects of biochar on the transformation of cadmium fractions in alkaline soil

To investigate the chemical properties in the biochar-mediated transformation of soil cadmium (Cd) fractions, the effects of biochar applied at different pyrolysis temperatures on soil Cd-fractions, pH value, and soil organic matter (SOM) were studied through an in-lab incubation experiment on contaminated soil. The results showed that the dissolved organic carbon (DOC) of CsBC300 (biochar prepared at 300 °C) was significantly higher (up to 1.31 times) than that of CsBC600 (biochar prepared at 600 °C). However, CsBC600 was more aromatic. Due to the difference in pyrolysis temperatures, the Cd deactivation mechanism of CsBC300 and CsBC600 was mainly to provide a large amount of organic matter and aromatic functional groups to the soil, respectively. The addition of these two biochar types significantly reduced the acid-extracted Cd content, by 76.56–83.52% and 70.48–76.81%, respectively. Contrastingly, it increased the residual Cd content by 2.26–2.36 and 2.08–2.29 times, respectively, which promoted the Cd transformation from the unstable to the stable state. However, CsBC300 had slightly better deactivation effect than CsBC600 on the 120th day, which was due to the decrease of soil pH and the increased SOM content. These study results can provide a theoretical reference for the remediation of Cd-contaminated alkaline soil.

Site selective gold(i)-catalysed benzylic C-H amination via an intermolecular hydride transfer to triazolinediones.

Triazolinediones are known as highly reactive dienophiles that can also act as electrophilic amination reagents towards enolisable C-H bonds (ionic pathway) or weak C-H bonds (free radical pathway). Here, we report that this C-H amination reactivity can be significantly extended and enhanced via gold(i)-catalysis. Under mild conditions, several alkyl-substituted aryls successfully undergo benzylic C-H aminations at room temperature. The remarkable site selectivity that is observed points towards strong electronic activation and deactivation effects, that go beyond a simple weakening of the C-H bond. The observed catalytic C-H aminations do not follow the expected trends for a free radical-type C-H amination and show complementarity to existing methods. Density functional theory (DFT) calculations and distinct experimental trends provide a clear mechanistic rationale for observed selectivity patterns, postulating a novel pathway for triazolinedione-induced aminations via a carbon-to-nitrogen hydride transfer.

Advances in biomass derived low-cost carbon catalyst for biodiesel production: preparation methods, reaction conditions, and mechanisms.

Biodiesel is a less hazardous, environmentally friendly biofuel that has been extensively investigated in modern years to ensure that we lessen our dependency on fossil fuels and mitigate climate change. While fossil fuel substitutes like biodiesel may help transition to a less polluted world, industrial-scale manufacturing still relies highly on chemical catalysis. However, heterogeneous solid catalysts result in less activity for biodiesel production due to their deactivation effects, porosity, surface area, material stability, and lower reactivity under moderate conditions. The "sulfonated carbons" are metal-free solid protonic acids distinguished by their distinctive carbon structure and Brønsted acidity (H0 = 8-11). Heterogeneous sulfonated catalysts derived from waste biomass were a significant focus of the most advanced biodiesel processing techniques for simple and low-cost manufacturing processes. This study discusses the advantages and disadvantages of various catalysts, biomass sources and properties, synthesis of catalysts, and factors influencing the insertion of active sulfonic sites on biomass surfaces. Additionally, transesterification and esterification reaction mechanisms and kinetics are discussed. At last, future directions are provided for young, dynamic researchers.

New thermosphere neutral mass density and crosswind datasets from CHAMP, GRACE, and GRACE-FO

We present new neutral mass density and crosswind observations for the CHAMP, GRACE, and GRACE-FO missions, filling the last gaps in our database of accelerometer-derived thermosphere observations. For consistency, we processed the data over the entire lifetime of these missions, noting that the results for GRACE in 2011–2017 and GRACE-FO are entirely new. All accelerometer data are newly calibrated. We modeled the temperature-induced bias variations for the GRACE accelerometer data to counter the detrimental effects of the accelerometer thermal control deactivation in April 2011. Further, we developed a new radiation pressure model, which uses ray tracing to account for shadowing and multiple reflections and calculates the satellite’s thermal emissions based on the illumination history. The advances in calibration and radiation pressure modeling are essential when the radiation pressure acceleration is significant compared to the aerodynamic one above 450 km altitude during low solar activity, where the GRACE and GRACE-FO satellites spent a considerable fraction of their mission lifetime. The mean of the new density observations changes only marginally, but their standard deviation shows a substantial reduction compared to thermosphere models, up to 15% for GRACE in 2009. The mean and standard deviation of the new GRACE-FO density observations are in good agreement with the GRACE observations. The GRACE and CHAMP crosswind observations agree well with the physics-based TIE-GCM winds, particularly the polar wind patterns. The mean observed crosswind is a few tens of m·s−1larger than the model one, which we attribute primarily to the crosswind errors being positive by the definition of the retrieval algorithm. The correlation between observed and model crosswind is about 60%, except for GRACE in 2004–2011 when the signal was too small to retrieve crosswinds reliably.

Theoretical calculations of the relative additional fuel consumed when shutting down the cylinder

Cylinder deactivation is a technique used to improve the efficiency of an engine by shutting down a certain number of engine cylinders. Cylinder deactivation allows the remaining cylinders to operate more efficiently, increasing their load and improving efficiency. This technique has gained interest both domestically and internationally, particularly for automotive engines, as it helps improve fuel economy at idle and light loads. The process of calculating effective cylinder deactivation in a multi-cylinder engine and its effect on additional fuel consumption is discussed. The need to improve engine efficiency in various speed and load modes is driven by requirements for fuel economy, reduced exhaust toxicity, and the need to improve engine transients while maintaining other characteristics. In order to effectively utilize engine power and maintain performance, the fuel supply to operating cylinders must be increased. However, deactivating cylinders during engine operation results in a decrease in engine power, which in turn reduces crankshaft speed and torque. In summary, cylinder deactivation is a technique that has the potential to improve the economic performance of engines, particularly at idle and light loads. A method for effectively deactivating cylinders in multi-cylinder engines has been developed based on the dependence of indicator efficiency on load changes. The study examined the effect of cylinder deactivation on mechanical losses and efficiency when load is reduced from 100% to 30%. The results showed that it is possible to use only two cylinders of a four-cylinder engine at 30% load, resulting in reduced mechanical losses and improved efficiency. A proposed method for determining the relative additional fuel consumption when cylinders are deactivated is presented. Deactivated cylinders do not supply air to the exhaust manifold, which reduces pumping losses and creates less rolling resistance, resulting in up to a 25% reduction in fuel consumption. This reduction is especially noticeable in urban driving.

The synergistic effect of trap deactivation and hysteresis suppression at grain boundaries in perovskite interfaces via multifunctional groups.

In spite of the outstanding photoelectric properties of perovskite materials, numerous defects produced in the preparation process eventually result in decomposition of the perovskite layer. To date, the mechanism of defect passivation and hysteresis reduction via additive engineering has still been obscure for perovskite materials, which seriously restricts performance improvement of the devices. Herein, conductive atomic force microscopy (C-AFM) and Kelvin probe force microscopy (KPFM) measurements were applied to probe carbamic acid ethyl ester (EU)-based trap passivation and suppression of hysteresis in perovskite films. The results indicate that the internal interaction between multifunctional bonds ("CO" and "-NH2") of EU and Pb2+ ions of the perovskite may inactivate the trap state and inhibit ion migration within sub-grains and grain boundaries (GBs), resulting in improvement of the long-term stability of the cells. In consequence, the EU-modified champion device prepared in all-air achieved a power conversion efficiency (PCE) of 20.10%, one of the high performances for the devices fabricated in air to date. In short, this work will propose some interesting speculation about ion migration as well as its influence on hysteresis in perovskite materials.

Enhanced photocatalytic performance of NiFe2O4 nanoparticle spinel for hydrogen production

The spinel NiFe2O4, prepared from nitrates precursors, was characterized by thermal analyses, X-Ray Diffraction, UV-Vis diffuse reflectance, Scanning electron microscopy, X-Ray Fluorescence spectrometry, X-ray photoelectron spectroscopy and photo-electrochemistry measurements. The X-ray diffrcation analysis of the powder indicates a cubic phase with a lattice constant of 8.327(8) Å and crystallite size of 19 nm. The X-Ray Fluorescence spectrometry indicates a stoichiometry, very close to NiFe2O4 catalyst calcined at 900 °C The X-ray photoelectron spectroscopy analysis confirmed the valences and crystallographic sites of the transition elements. The direct optical gap of NiFe2O4 (1.78 eV), due to the crystal field splitting of the 3d orbital in the octahedral site, is well suited for the solar spectrum and attractive for photo-electrochemical H2 production. The flat band potential (Efb = 0.47 VSCE) was obtained from the capacitance-potential (C−2 - E) characteristic in NaOH (0.1 M) electrolyte. A conduction band of −1.11 VSCE, more cathodic than the H2 level (−0.8 VSCE), enabled the use of NiFe2O4 for the water reduction into hydrogen. The H2 evolution rate of 46.5 μmol g−1 min−1 was obtained under optimal conditions (1 mg of catalyst/mL, NaOH and 50 °C) in the presence of SO32− (10−3 M) as hole scavenger under visible light flux of 23 mW cm−2. A deactivation effect of only 1% was obtained.

Deactivation effects of Tb3+ on Ho3+ emission in fluoroindate glasses for 3.9 μm laser applications

A series of Ho3+/Tb3+ co-doped fluoroindate glasses with good thermal stability have been synthesized to study the deactivation effects of Tb3+ on the Ho3+: 3.9 μm emission. Efficient 3.9 μm emission enhancement is obtained under excitation by an 888 nm laser diode (LD). The Judd-Ofelt (J-O) intensity parameters and radiative properties are calculated to evaluate the spectroscopic properties. Possible energy transfer processes resulting in emission reinforcement are discussed. A higher spontaneous transition probability and larger peak emission cross section are achieved with the inclusion of Tb3+. This analysis supports the conclusion that Ho3+/Tb3+ co-doped fluoroindate glass is a potentially useful laser material for highly efficient 3.9 μm fiber lasers.

Repurposing FDA-approved drugs cetilistat, abiraterone, diiodohydroxyquinoline, bexarotene, and remdesivir as potential inhibitors against RNA dependent RNA polymerase of SARS-CoV-2: A comparative in silico perspective

Vaccines are undoubtedly the most effective means of combating viral diseases like COVID-19. However, there are risks associated with vaccination, such as incomplete viral deactivation or potential adverse effects in humans. However, designing and developing a panel of new drug molecules is always encouraged. In an emergency, drug repurposing research is one of the most potent and rapid options. RdRp (RNA-dependent RNA polymerase) has been discovered to play a pivotal role in viral replication. In this study, FDA-approved drugs bexarotene, diiodohydroxyquinoline, abiraterone, cetilistat, and remdesivir were repurposed against the RdRp by molecular modeling, docking, and dynamic simulation. Furthermore, to validate the potency of these drugs, we compared them to the antiviral remdesivir, which inhibits RdRp. Our finding indicated that the selected drugs have a high potential to be developed as RdRp inhibitors and, with further validation studies, could serve as potential drugs for the treatment of COVID-19.

Evolution of Coke Formation and Its Effect on β-Zeolite in Catalytic Cracking

Deactivation by coke formation is a very important feature in catalytic cracking. The evolution of coke and its effect on the catalyst need further clarification. This was studied by using a recycle electrobalance reactor with various hydrocarbon feeds over a β-zeolite catalyst. The coking rate was measured online. The effects of the deactivation on the physical properties of the catalysts and the cokes produced at different stages were characterized. It could be confirmed that light olefins were the key components in coke formation, leading to coke contents up to 9.68 wt %. Aromatics had strong synergistic effects on coking. The coke formation did not change the intrinsic structure of the catalysts, but mainly functioned by blocking the entrance to the pores of the catalysts. The large molecules could accelerate the pore blockage and lead to sharply decrease of the BET surface area. The nature of the coke in paraffin cracking mainly consisted of polyaromatics with 3–5 rings and an average molecular weight from 231.0 Da to 337.9 Da. The reaction routes of coke formation were depicted based on the experimental results. These data are the basis upon which the effects of deactivation on different types of elementary steps in catalytic cracking could be estimated.

Inactivation of Alicyclobacillus contaminans in apple juice by dielectric barrier discharge plasma

Cold plasma (CP) has the potential for inactivating microorganisms; however, the deactivation effect of CP for Alicyclobacillus contaminans in apple juice is still rarely reported. In this study, dielectric barrier discharge plasma (DBDP) was applied to inactivate Alicyclobacillus contaminans vegetative cells and investigate the impact on the physicochemical properties of apple juice. After 65 V treatment for 4 min, the total viable bacterial count in sterilized saline and apple juice decreased by 6.4 log10 and 4.5 log10, respectively. And the initial cell concentrations had an insignificant effect on the inactivation of treatment. Inactivation kinetics models (Biphasic shoulder and double Weibull) fit well with the bactericidal curve of DBDP treatment. DBDP treatment caused the apple juice to darken and turn greenish and yellowish. The chroma, browning index, and chromatic aberration increased slightly. The pH value of apple juice was decreased after treatment. There were negligible changes in the total soluble solids, clarity, and turbidity; however, the antioxidant activity decreased slightly. The reactive oxygen species concentration, cell membrane peroxidation degree, protein content in the sample, and scanning electron microscopy and transmission electron microscopy measurements indicated that the cell membrane was damaged after DBDP treated, leading to cell leakage and death. DBDP is a promising method to reduce Alicyclobacillus contaminans in apple juice. Industrial relevanceNonthermal plasma technology is an emerging technology that can be used to rapidly inactivate microorganisms in food, with minimal influence on the sensory properties and product quality. This research demonstrated the effectiveness of dielectric barrier discharge plasma (DBDP) for inactivating Alicyclobacillus contaminans in apple juice and indicating the feasibility of using DBDP. The minimal changes in the physicochemical properties of apple juice after processing demonstrated the applicability of DBDP treatment. This study provides initial support for using cold plasma in apple juice processing.

Intermediate temperature exposure regenerates performance and active site dispersion in sintered Pd–CeO2 catalysts

Methods that can impede or reverse the effects of high-temperature sintering and deactivation are necessary to improve the utilization of catalytic materials. This work demonstrates that exposure to intermediate temperatures (800 °C) can effectively regenerate catalytic performance in sintered Pd-CeO2 catalysts, through the disintegration and partial redispersion of agglomerated Pd, which increases the abundance of sites that interface strongly with the CeO2 support. Pretreating the catalyst at 800 °C before sintering forms highly dispersed Pd species that slow the sintering of small, polycrystalline CeO2 domains. This preserves the density of Ce3+ sites that trap mobile Pd, which improves the efficacy of regeneration. The regenerated catalyst is effective in the co-oxidation of CO and C3H8, two species which are known to competitively adsorb. The simplicity of this treatment makes it attractive for on-stream regeneration of catalyst performance.

Quantified Database for Methane Dehydroaromatization Reaction

AbstractDirect conversion of methane to aromatics, known as methane dehydroaromatization (MDA) is a very promising one‐step conversion route that could significantly reduce CO2 emissions and simplify the process. There is an increasing interest in this reaction evident by a large number of literature and patents published so far. Although this review examined 500 scientific articles studying the MDA reaction, the ones considered to be suitable to create a quantified database did not exceed 150 articles. This resulted in more than 300 experimental studies carried out at different combinations of catalyst compositions, and operating conditions for the reaction and the regeneration phases. This work provides a quantitative database in a unified manner, which sets it apart from other literature reviews in the field. A set of definitions are used to quantify the cyclic operation of this complex reaction that included deactivation and regeneration. Most of the studies in this work utilize the commonly used Mo/ZSM‐5 based catalyst. Other zeolites such as Mo/IM‐5, Mo/MCM‐22, and Mo/SiO2 are also included in this database with different metal compositions. This database is limited to experiments carried out using fixed‐bed reactors to allow a fair comparison. The quantified database generated many valuable results. The validity of different proposed research claims is tested against all collected experimental studies to verify the effect of Mo content, reaction temperature, reaction space velocity, and particle size. Most of the reported claims aligned with the reported data; however, they were only satisfied within a very narrow range of conditions which demonstrates how critical the correlation between the parameters is on the catalytic performance. This work proposed a simple decay model to quantify the rate of deactivation for the different studies. Additionally, figures of merit were generated from the quantified database to guide future experiments in this field, map out the performances achieved so far, as well as create a benchmark to identify best‐performing catalysts and operating conditions. A global yield is defined by taking into account the effect of deactivation and regeneration. This factor proved to be valuable as a benchmark of the enhancement in the catalyst stability and productivity. Some of the studies achieved high values for both the initial yield and the global yield. One study used a continuous feeding of CO2 in the feed and added Mg to the Mo/ZSM‐5 catalyst. Another study added minor amounts of C2H4 and C2H6 to the feed which help reduce regeneration and increase the yield. Studies that used periodic‐switch feeding with H2, showed promising results as they maintained the performance for a longer time on stream for the same initial yield; thus, maximizing the global yield. A correlation analysis was performed on the MDA database to further statistically investigate the existence of correlations between input operating conditions (reaction temperature, reaction space velocity, and Mo. content) and the outputs (methane conversion, benzene yield, and decay factor). The absolute values of the correlation coefficients were categorized as weak [0–0.3], moderate [0.3–0.7], and strong [0.7–1]. The main highlights from this analysis are: (i) the conversion and yield are strongly correlated; (ii) Mo content has a nonlinear relation to the CH4 conversion. It has a positive moderate correlation for Mo content within the range of 1 to 3 wt % while a negative moderate correlation within the range of 4 to 6 wt %; (iii) space velocity and yield are strongly and negatively correlated; and (iv) there is a weak correlation between temperature and decay rate. The correlation analysis is efficient to analyze available data and provided similar conclusions as that of the knowledge‐based approach. However, much more valuable as it quantifies the strength of the correlation. Besides, it imposes the need to study the operating conditions space more comprehensively. The correlation matrix, on its own, does not always provide decisive conclusions as shown by the effect of Mo content on CH4 conversion due to the nonlinear relationship between the variables. The real value is reached when the correlation matrix analysis is combined with the prior expert knowledge.

Compensation or Aggravation: Pb and SO2 Copoisoning Effects over Ceria-Based Catalysts for NOx Reduction.

Severe catalyst deactivation caused by multiple poisons, including heavy metals and SO2, remains an obstinate issue for the selective catalytic reduction (SCR) of NOx by NH3. The copoisoning effects of heavy metals and SO2 are still unclear and irreconcilable. Herein, the unanticipated differential compensated or aggravated Pb and SO2 copoisoning effects over ceria-based catalysts for NOx reduction was originally unraveled. It was demonstrated that Pb and SO2 exhibited a compensated copoisoning effect over the CeO2/TiO2 (CT) catalyst with sole active CeO2 sites but an aggravated copoisoning effect over the CeO2-WO3/TiO2 (CWT) catalyst with dual active CeO2 sites and acidic WO3 sites. Furthermore, it was uniquely revealed that Pb preferred bonding with CeO2 among CT while further being combined with SO2 to form PbSO4 after copoisoning, which released the poisoned active CeO2 sites and rendered the copoisoned CT catalyst a recovered reactivity. In comparison, Pb and SO2 would poison acidic WO3 sites and active CeO2 sites, respectively, resulting in a seriously degraded reactivity of the copoisoned CWT catalyst. Therefore, this work thoroughly illustrates the internal mechanism of differential compensated or aggravated deactivation effects for Pb and SO2 copoisoning over CT and CWT catalysts and provides effective solutions to design ceria-based SCR catalysts with remarkable copoisoning resistance for the coexistence of heavy metals and SO2.

Pd/BEA hydrocarbon traps: Effect of hydrothermal aging on trapping properties and Pd speciation

Interest in Pd/zeolites as automobile exhaust catalysts has driven research focused on understanding the chemical environment of Pd active centers. Here, we studied the effects of hydrothermal deactivation on a Pd/BEA hydrocarbon trap. Hydrothermal aging (HTA) led to decreased ethylene storage capacity and oxidation activity. Characterization by x-ray absorption spectroscopy (XAS) and NOx adsorption indicated that for lower Si/Al ratio samples, the amount of ion exchanged Pd increased after HTA. Temperature programmed desorption of NOx after NO exposure revealed two desorption peaks, with a high temperature peak that increased in area with increased aging temperature. Based on infrared spectroscopy, XAS and reactor results, the high temperature desorption peak is consistent with NO stored on Pd+. The Pd+ formed during NO adsorption, existing originally as [Pd(OH)]+. This species was less active in ethylene storage and oxidation than the original Pd2+ species. [Pd(OH)]+ stored NOx to a higher temperature than Pd2+.

Phosphodiesterase 10A deactivation induces long-term neurological recovery, Peri-infarct remodeling and pyramidal tract plasticity after transient focal cerebral ischemia in mice

The phosphodiesterase (PDE) superfamily comprises enzymes responsible for the cAMP and cGMP degradation to AMP and GMP. PDEs are abundant in the brain, where they are involved in several neuronal functions. High PDE10A abundance was previously observed in the striatum; however its consequences for stroke recovery were unknown. Herein, we evaluated the effects of PDE10A deactivation by TAK-063 (0.3 or 3 mg/kg, initiated 72 h post-stroke) in mice exposed to intraluminal middle cerebral artery occlusion. We found that PDE10A deactivation over up to eight weeks dose-dependently increased long-term neuronal survival, angiogenesis, and neurogenesis in the peri-infarct striatum, which represents the core of the middle cerebral artery territory, and reduced astroglial scar formation, whole brain atrophy and, more specifically, striatal atrophy. Functional motor-coordination recovery and the long-distance plasticity of pyramidal tract axons, which originate from the contralesional motor cortex and descend through the contralesional striatum to innervate the ipsilesional facial nucleus, were enhanced by PDE10A deactivation. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) revealed a set of dopamine receptor-related and neuronal plasticity-related PDE10A targets, which were elevated (e.g., protein phosphatase-1 regulatory subunit 1B) or reduced (e.g., serine/threonine protein phosphatase 1α, β-synuclein, proteasome subunit α2) by PDE10A deactivation. Our results identify PDE10A as a therapeutic target that critically controls post-ischemic brain tissue remodeling and plasticity.

The water assisted vinylene mechanism for cobalt Fischer-Tropsch synthesis assessed by multi-catalyst modelling of kinetics and deactivation

The paper describes development of a mechanism and a consistent rate expression for Fischer-Tropsch (FT) synthesis over cobalt-based catalysts. The developed mechanism relies on a two-step hydrogen assisted activation of CO. The carbon atom of CO is first hydrogenated by surface hydrogen to formyl; followed by the rate-limiting step whereby the oxygen atom is hydrogenated by adsorbed water. The produced CH* monomer is incorporated into the growing chain giving vinylene intermediate. The vinylene intermediate is either terminated to an olefin by adding hydrogen to the α-carbon atom or propagates by adding hydrogen to the β-carbon position. The resulting expression for CO consumption, the Fischer-Tropsch rate, can respond positively or negatively to the partial pressure of water, in agreement with experimental observations. A special feature is that the chain propagation probability does not depend on the partial pressure of hydrogen. The resulting kinetic model is tested on several cobalt catalysts supported on alumina; spanning from γ-alumina with average pore sizes ranging from 6.1 to 18.3 nm to α-alumina with a wide pore structure; and with cobalt particle sizes from 8 to 19 nm. Water was added sequentially to the syngas feed, causing enhanced deactivation, for testing the water response on activity and selectivity. A deactivation model comprising sintering and cobalt oxidation, and the FT-kinetics, describe the observed CO conversions with great precision for all catalysts. Selectivities are also well described, but with slight deviations at least partly due the effect of deactivation. Trends in some of the kinetic parameters are rationalized in terms of cobalt crystallite and pore sizes.

Dynamic coupling of reactor and heat exchanger network considering catalyst deactivation

Catalyst activity decreases with time. Identifying the variation of optimal system parameters along with the catalyst deactivation can alleviate the effects of catalyst deactivation and reduce energy consumption. A graphic method is established to integrate reactor and HEN, considering the catalyst deactivation. Based on the reaction kinetics, the catalyst deactivation kinetics, and the material and energy balances, the relations among running time, catalyst activity, reactor temperatures, and heat load are deduced for different reactors. Their influences on energy consumption are studied by pinch analysis and algebraic reasoning. The heat load variation of each heat exchanger in the path/loop is analyzed, and the load-shift laws are proposed. A Reactor-HEN coupling diagram is constructed to illustrate the variation of system parameters with running time and determine the catalyst's optimal replacement node. The proposed method can be applied to guide the operation of the practical process and evaluate the process through the catalyst replacement cycle in the design stage. An alkylation process of benzene to ethylbenzene is studied by the proposed method, and the optimal catalyst replacement node is identified to be 5.2 months.