Understanding the kinetic behavior of a Mo-V-Te-Nb mixed oxide in the oxydehydrogenation of ethane

Two kinetic models based on Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms were developed to describe the oxydehydrogenation of ethane to yield ethylene over a Mo-V-Te-Nb catalyst. Obtained in a lab-scale fixed-bed reactor, experimental data at the steady-state were used to estimate the kinetic models parameters via a nonisothermal regression. Experiments were performed using an ethane, oxygen and nitrogen mixture as feedstock, spanning temperatures from 673 to 753 K, inlet partial pressures of oxygen and ethane between 5.0 and 22.0 kPa, and space-time from 10 to 70 g(cat) h(molethane)- (1). Ethylene, CO and CO2 were the only detected products, the selectivity for ethylene ranged from 76% to 96% for an ethane conversion interval 4-85%. A series of tests feeding ethylene instead of ethane were also performed at 713 K, varying inlet partial pressures and space-time in the same ranges as was done for ethane. Ethylene conversion was relatively low, 3-14%, the dominant product being CO with CO/CO2 ratios from 0.73 to 0.79. The LH mechanism was found to represent better the experimental data. The oxydehydrogenation of ethane was the reaction with the lowest activation energy, 108-115 kJ mol (1). Except for the conversion of ethane into CO2, deep oxidations were detected as very energetically demanding steps, 156-193 kJ mol (1). Competitive adsorption between reagents and products occurred in the two mechanisms particularly at relatively high reaction severity, water re-adsorption being weaker in comparison with COx re-adsorption. (C) 2014 Elsevier Ltd. All rights reserved.This work was financially supported by the Instituto Mexicano del Petroleo.Quintana-Solorzano, R.; Barragan-Rodriguez, G.; Armendariz-Herrera, H.; López Nieto, JM.; Valente, JS. (2014). Understanding the kinetic behavior of a Mo-V-Te-Nb mixed oxide in the oxydehydrogenation of ethane. Fuel. 138:15-26. doi:10.1016/j.fuel.2014.07.051152613

Mechanism and Modelling of the Partial Oxidation of Methanol over Silver

This work involves an experimental and kinetic modelling study of the silver catalysed reaction of methanol to formaldehyde. The motivation for this was the desire to investigate the potential for Process Intensification in formaldehyde production. Formaldehyde production from methanol over silver catalyst is a fast, exothermic process where dilution is used to control heat release, and these properties are both indicators of Process Intensification potential. The process is run adiabatically and produces hydrogen (which is currently burnt). Oxygen is consumed during the reaction but is also required to activate the catalyst and is fed in understoichiometric quantities. The central overall reactions in the silver catalysed process for formaldehyde production are oxydehydrogenation CH3OH + ½ O2 -> CH2O + H2O (DH = -159kJ/mol) and dehydrogenation CH3OH CH2O + H2 (DH = 84kJ/mol). When sufficient oxygen is available, formaldehyde can be further oxidised to carbon dioxide CH2O + O2 -> CO2 + H2O (DH = -519kJ/mol). Formaldehyde can decompose to carbon monoxide and hydrogen CH2O CO + H2 (DH = 12.5kJ/mol). Oxidation of methanol and hydrogen also occurs and other minor products of the reaction are methyl formate, methane and formic acid. These overall reactions do not adequately describe the silver catalysed reaction mechanism. In particular, the overall dehydrogenation reaction does not include oxygen as a reactant, but it will not occur over silver that does not have active atomic oxygen species adsorbed on the surface, and these atomic oxygen species are formed from gas phase oxygen. In the absence of a complete mechanism for silver catalysed formaldehyde production, the intensification of the process was investigated using a thermodynamic model (based on the overall oxydehydrogenation and dehydrogenation reactions, not reaction kinetics). It was found that by using heat exchange (rather than heat generated from the exothermic oxydehydrogenation path) and a lower oxygen concentration in the feed stream, hydrogen selectivity could be increased while maintaining the required methanol conversion. Before this iv opportunity could be further investigated, a complete reaction mechanism that would allow the requirement of oxygen for catalyst activation to be included was required. There is agreement in the literature that two active atomic oxygen species react with methanol on silver. These are weakly bound atomic oxygen (Oa) and strongly bound atomic oxygen (Og). The location of Oa is on the surface of the silver, while the location of Og has been described as being in the silver surface (where it substitutes for silver atoms). Both species react with methanol to form formaldehyde. When the concentration of Oa is high enough, Oa will also react with formaldehyde forming carbon dioxide (while Og will not). The literature presents differing views on the extent of involvement of each atomic oxygen species in industrial formaldehyde production. There is also disagreement on the pathways for water and hydrogen formation. An extensive experimental investigation of the partial oxidation of methanol to formaldehyde was carried out using a flow reactor. The effect of temperature (250- 650°C), reactant concentration (7000-40000ppm methanol) and the feed ratio of methanol to oxygen (2.5-5.5) were studied. The extreme case of methanol reaction with Og in the absence of gas phase oxygen was also investigated. To isolate the effect of secondary reactions, the oxidation of formaldehyde, carbon monoxide and hydrogen were investigated, both in the presence and absence of silver catalyst. When methanol was exposed to silver catalyst that had been activated by being covered in Og (with this being the only source of oxygen) the catalytic nature of Og was demonstrated by the high selectivity to formaldehyde and hydrogen that was achieved (with very little carbon dioxide or water production). When gas phase oxygen was fed to the reactor along with methanol, hydrogen selectivity over silver increased up to about 40% as the concentration of reactants was increased. This result is consistent with the general rule of thumb from industrial practice that hydrogen selectivity is about 50%. When formaldehyde and oxygen were exposed to silver in the flow reactor, the only reaction products were carbon v dioxide and water and the combination of high temperature and excess oxygen was required for complete conversion of formaldehyde. A pseudo-microkinetic model (based on a Langmuir-Hinshelwood mechanism) for the partial oxidation of methanol to formaldehyde (over silver) was taken from the literature and investigated. This model predicts formaldehyde production using only Oa (no other active atomic oxygen species are included) but lacks pathways for reactions between Oa and adsorbed hydrogen or hydroxyl (so the only possible fate of adsorbed H atoms is to desorb as H2). The Oa model was combined with literature models for hydrogen desorption and the reactions involving adsorbed hydroxyl (desorption, self reaction, decomposition and reaction with adsorbed hydrogen). Comparison of this Hybrid model with experimental data showed that reactions involving Oa will predict formaldehyde formation and oxidation, but not hydrogen formation (because the rate of hydrogen desorption is too slow compared with the rate of water formation). It is concluded that any detailed model must include the reaction between methanol and Og (producing hydrogen). Although the reaction between two adsorbed OgH species has been suggested as the pathway for hydrogen formation from Og, this is not certain and so all possible reactions involving Og and hydrogen need be investigated and the appropriate pathways added to the Hybrid model. Once a complete microkinetic mechanism for the partial oxidation of methanol to formaldehyde over silver is available it can be used to further investigate the process intensification of this process. In particular, the use of staged addition of oxygen (to keep the catalyst active) combined with heat exchange (to replace the heat normally supplied by the oxydehydrogenation path) with the aim of simultaneously maximizing methanol conversion and selectivity to formaldehyde and hydrogen

Propane Dehydrogenation by Autothermal Reforming

The proposed design is for the the production of propene through propane dehydrogenation using Thyssen Krupp’s STAR technology and a hybrid membrane separation. The plant has a capacity of 700 kT/yr and will be located in the Middle East. At current propane/propene prices, the use of Thyssen Krupp’s STAR process and hybrid membrane separation is not economical and has a negative IRR. The NPV of this project at current market prices is -$865MM. However, economic feasibility depends on volatile market conditions. The process begins with the oxydehydrogenation section, consisting of four reformers connected to four oxyreactors that are cycled to allow for regeneration of the .2-.6%Pt- Sn/ZnAl2O5 catalyst. In order to produce polymer grade propene, a separation is needed following dehydrogenation. Separation operations include adsorption, MEA absorption system, distillation, and a hybrid distillation/membrane C3 splitter

Effect of Dopants and Mechanochemical Treatment on Vanadium Phosphate Catalysts For Partial Oxidation of N-Butane to Maleic Anhydride

Oxidation of n-butane to maleic anhydride catalyzed by vanadium phosphate catalyst is one of significant worldwide commercial interest since decades. Introductions of dopants and/or mechanochemical treatment are the most promising approach for the improvement of the catalytic performance of vanadium phosphate catalyst. Tellurium doped vanadium phosphate catalyst (VPDTe) was prepared via VOPO4·2H2O phase after calcinating the tellurium doped precursor, VOHPO4•0.5H2O at 733 K in a flowing of n-butane/air for 18 h. VPDTe catalyst gave very high for n-butane conversion, 80% compared to only 47% for the undoped catalytst. The crystallite size, morphology, surface reactivity and reducibility of the catalyst have been affected by the addition of tellurium. VPDTe catalyst has result a higher existence of V5+ phase in the catalyst bulk with having nearly the optimum amount of V5+/V4+ ratio, 0.23. The SEM micrographs showed that the tellurium altered the arrangement of the platelets from “rose-like” clusters to layer with irregular shape. The sizes of platelets are even thicker and bigger which led to lower surface area compared to undoped VPD catalyst. An addition of 1% tellurium has markedly lowered the reduction activation energies of the vanadium phosphate catalyst as revealed by TPR profiles. The amount of oxygen species removed from the peak associated with V4+ phase for VPDTe catalyst significantly higher. These phenomenon suggested that the O=V bond of the VPDTe catalyst are weaker with higher mobility and more reactive of the oxygen as compared to the undoped counter part. All mechanochemial treated VPD catalysts have shown an increased surface P/V ratio, reduced the crystallite size of the catalysts and displayed different degree of crystallinity. TPR results demonstrated that both reduction peaks for every mechanochemical treated catalyst shifted to lower temperature and improved the amount of oxygen removed from the catalysts. VPDM catalyst gave 57% of conversion, 10% higher from the untreated VPD catalyst. The presence of cobalt in mechanochemical treated vanadium phosphate catalyst has slightly lowered the n-butane conversion to 54%. Meanwhile, treating the tellurium doped catalyst through mechanochemical treatment i.e. milling in stainless steel (VPDTeM) or agate (VPDTeM-ag) with ethanol as solvent has reduced the conversion from 80% to 58% and 50%, respectively. The selectivity of all catalysts prepared was almost retained in all cases (~ 33%) except for VPDCoM catalyst (19%)

A simplified route to the synthesis of CMK-3 replica based on precipitation polycondensation of furfuryl alcohol in SBA-15 pore system

A novel method of synthesis of mesoporous, polymer-derived CMK-3 carbon replica was proposed. Instead of a multi-stage, time-consuming and toxic solvent involving procedure, the direct, acid-catalyzed precipitation polycondensation of furfuryl alcohol to poly(furfuryl alcohol) (PFA), as the carbon precursor, in the pore system of SBA-15 silica was used. The optimal PFA/SBA-15 mass ratio resulting in the complete pore filling was found. The final carbon material was obtained by carbonization of the formed composite and subsequent removal of silica by treatment with HF. Low-temperature sorption of nitrogen, powder X-ray diffraction and transmission electron microscopy confirmed the formation of well-ordered, hexagonal carbon mesostructure. The produced CMK-3 exhibited the presence of oxygen-containing surface groups, recognized as mainly carbonyl and carboxyl species by X-ray photoelectron spectroscopy and temperature-programmed desorption. The presence ofthese groups caused the mesoporous carbon to be catalytically active in the oxidative dehydrogenation of ethylbenzene to styrene.This work was supported by the National Science Centre under the Grant No. DEC–2011/01/N/ST5/05595. Rafał Janus wishes to thank the Foundation for Polish Science MPD Programme co-financed by the EU European Regional Development Fund for the financial support. The research was carried out with the equipment purchased thanks to the financial support of the European Regional Development Fund in the framework of the Polish Innovation Economy Operational Program (contract No. POIG.02.01.00-12-023/08)

Safety-oriented Resilience Evaluation in Chemical Processes

In the area of process safety, many efforts have focused on studying methods to prevent the transition of the state of the system from a normal state to an upset and/or catastrophic state, but many unexpected changes are unavoidable, and even under good risk management incidents still occur. The aim of this work is to propose the principles and factors that contribute to the resilience of the chemical process, and to develop a systematic approach to evaluate the resilience of chemical processes in design aspects. Based on the analysis of transition of the system states, the top-level factors that contribute to Resilience were developed, including Design, Detection Potential, Emergency Response Planning, Human, and Safety Management. The evaluation framework to identify the Resilience Design Index is developed by means of the multifactor model approach. The research was then focused on developing complete subfactors of the top-level Design factor. The sub-factors include Inherent Safety, Flexibility, and Controllability. The proposed framework to calculate the Inherent Safety index takes into account all the aspects of process safety design via many sub-indices. Indices of Flexibility and Controllability sub-factors were developed from implementations of well-known methodologies in process design and process control, respectively. Then, the top-level Design index was evaluated by combining the indices of the sub-factors with weight factors, which were derived from Analytical Hierarchical Process approach. A case study to compare the resilience levels of two ethylene production designs demonstrated the proposed approaches and gave insights on process resilience of the designs

Development of a Risk Based Inherent Safety Index Using an Integrated Approach

Copyright © 2018 by Mary Kay O’Connor Process Safety Center Prepared for Presentation at American Institute of Chemical Engineers 2018 Spring Meeting and 14th Global Congress on Process Safety Orlando, Florida April 22 – 25, 2018The growing demand for petrochemical products and the implementation of new process technologies have made the petrochemical plants more complex; therefore, it becomes more challenging to manage the risk. Traditionally, additional layers of protection were added to prevent incidents, which further adds complexity to the existing process. Inherently safer design aims at managing the risk from the design stage of petrochemical plants, which eliminates the hazard in the process rather than control the risk during operation. When designing a new plant or modifying an existing plant, a safety index system will be helpful to assess the risk level of various options effectively. This can be achieved by considering the inherently safer design principles, i.e., elimination, substitution, moderation, and simplification. In this work, a novel safety index system was developed to cover the life cycle of a process design, which includes the research stage, process development stage, and engineering design stage. This safety index will be used to evaluate the risk level of petrochemical facilities by comparing toxic, flammable, explosive, runaway reaction, dust and physical explosion risks and identify the areas where inherently safer design principles can be used to improve the process. A case study on ethanol synthesis process will be presented for the validation of the index system developed.Mary Kay O'Connor Process Safety Center; Texas A&M Engineering Experiment Station(TEES

Deshidrogenación oxidativa de propano con materiales a base de cobalto, tungsteno y molibdeno

RESUMEN: La deshidrogenación oxidativa de propano es una alternativa interesante para la obtención de olefinas. En este trabajo se presentan los resultados obtenidos en la deshidrogenación oxidativa de propano utilizando dos materiales a partir de cobalto, tungsteno y molibdeno. Los materiales fueron caracterizados utilizando Difracción de Rayos X (XRD), espectroscopia infrarroja con transformada de Fourier (FTIR), análisis termogravimétrico (TGA) y análisis térmico diferencial (DTA). El material CoMoϕy al ser calcinado a 623 K se transforma en la fase β-CoMoO4 (CoMoϕy623), la misma fase es obtenida cuando el material se calcina a 873 K (CoMoϕy873). CoMoϕy623 muestra un buen desempeño en la deshidrogenación oxidativa de propano, se obtuvo un rendimiento a propeno de 3,4% a una temperatura de 623 K y una velocidad espacial de 100 mL g-1 min-1. El material CoWsϕy fue calcinado a 673 K, obteniéndose una fase wolframita de baja cristalinidad. Este material presenta una alta selectividad a propeno y un bajo rendimiento. CoMoϕy873 presenta una buena actividad y selectividad, comparable con otros materiales reportados en la literatura, y su potencial como catalizador en la deshidrogenación oxidativa de propano se hace más evidente con la prueba que muestra ser estable durante 24 h de operación continua a 773 K. Palabras clave: Calidad del agua, análisis multivariado, emisarios submarinos, variación espacial, variación temporal.ABSTRACT: Oxidative dehydrogenation of propane is a reliable alternative for olefins production. This paper presents the results obtained on oxidative dehydrogenation of propane by using two materials based on cobalt, tungsten, and molybdenum. The materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), temperature programmed reduction (TPR), thermogravimetric analysis (TGA), and differential thermal analysis (DTA). The CoMoϕy material was calcined at 623 K, transforming itself to β-CoMoO4 phase (CoMoϕ623), the same phase is observed when the material is calcined at 873 K (CoMoϕy873). CoMoϕy623 showed the best performance in oxidative dehydrogenation of propane, a yield to propene of 3.4% was obtained at 623 K using a space velocity of 100 mLg-1min-1. CoWsϕy was calcined at 673 K, a low crystallinity wolframite was obtained. This material has a high selectivity to propene and low yield. CoMoϕy873 has a selectivity and conversion within the range of the results reported in the literature. This is a prospective catalyst for the oxidative dehydrogenation of propane; it was stable for 24 h of continuous operation at 773 K. Keywords: Water quality, Multivariate statistical techniques, submarine outfall, spatial variation, temporal variatio