Partial Oxidation Of Ethylene Research Articles

Extremely Low Temperatures for the Synthesis of Ethylene Oxide

The partial oxidation of ethylene in a methane atmosphere by pure oxygen is the most important industrial process for the synthesis of ethylene oxide. However, due to the high reactivity and exothermicity of the reaction system, the overall production is limited by kinetic and safety issues. The shift toward mild operative conditions can support the management of undesirable side reactions, enhancing the performance of the whole process. In the future, the direct use of liquefied ethylene and oxygen-enriched air, a low-cost waste in membrane-based nitrogen production, can provide convenient sources for heat removal as well as promote the use of innovative and more sustainable solutions. This work is focused on the experimental and numerical characterization of the oxidation of ethylene/methane/nitrogen/oxygen mixtures at different operative conditions, including extremely low temperatures, and oxidant compositions. To this aim, the laminar burning velocity and flammability limits were first measured utilizing the heat flux burner and compared with detailed kinetic mechanisms and experiments retrieved from the current literature. The reported data were adopted to identify the operational limits for innovative processes, paving the way to unlocking the potential of innovative chemistry at extreme conditions. Eventually, key performance indicators accounting for kinetic and safety aspects were defined to identify the most sustainable and convenient operative conditions.

Simulation of ethylene oxide production from ethylene cholorhydrin

This research has been performed in the Ethylene Oxide production process. It is a flammable and colorless gas at temperatures above 11 °C. It is an important commodity chemical for the production of solvents, antifreeze, textiles, detergents, adhesives, polyurethane foam, and pharmaceuticals. Small amounts of Ethylene Oxide [EO] are used in manufacturing fumigants and sterilants for spices and cosmetics, as well as hospital sterilization for surgical equipment. Modern Ethylene oxide [EO] productions employ either air or oxygen (O2)to oxidize ethylene (C2H4) with a silver catalyst on an alumina oxide carrier[Ag/Al2O3]catalyst packed in a fixed-bed reactor (plug-flow reactor)but the oxygen-base reaction process is more desirable here we used oxygen. Mainly two reactions occur, partial oxidation of ethylene to ethylene oxide and total oxidation of ethylene to carbon dioxide and water. The design models of the process in this research based on a three-part system. They are: the reaction system, absorption system and Ethylene Oxide [EO] purification system. The largest cost in production of ethylene oxide is ethylene therefore, it’s important to optimize the selectivity towards ethylene oxide and thus reduce the consumption of Ethylene. The aim of this work is to create a simulation model of the Ethylene Oxide production process from Ethylene using Aspen Hysys V9. Also to knowing the optimum operational conditions (temperature –pressure –flow rate) for the oxidation reactions of Ethylene. The simulation was running three times with various operational conditions to make a good result. The conclusion was that during operational time the activation energy increased for both reactions which have to be compensated with increasing reactor temperature. At the same time the selectivity for producing Ethylene Oxide decreases, i.e. more carbon dioxide and water are formed. The simulation models yield Ethylene Oxide with purity of 99.2%.

Ethylene–air mixtures under flowing conditions: a model-based approach to explosion conditions

Propylene oxide, ethylene oxide (EO), methanol, and phthalic anhydride are examples of versatile, widely applied chemical intermediates, produced at elevated temperature and pressure conditions, demanding rigorous safety considerations. Well-known industrial applications in which ethylene at the vapour phase is oxidized with oxygen are the manufactures of vinyl acetate and of EO. Partial oxidation of ethylene is usually performed at elevated temperature and pressure in multitubular cooled reactors where the application of explosive limits experimentally obtained under stagnant conditions could entail a not justified economical handicap. Bearing in mind these considerations, in this paper, we developed a novel physical–mathematical model to predict the ignition and flame-propagation phenomena in the presence of gaseous explosive mixtures. The explicit formulae for the ignition condition and the transition from local reaction to the fully developed explosion were obtained by exploring a broad range of operative conditions. A fairly good agreement was found between the predictions in this study of the oxygen critical concentration corresponding to the explosion point and the results of previous experimental studies performed by different researchers.

Microreactors as tools in kinetic investigations: Ethylene oxide formation on silver catalyst

The kinetics of ethylene oxide formation from ethylene and molecular oxygen in an isothermal microreactor was studied. A set of kinetic experiments was carried out by varying the concentrations of oxygen (from 2vol% to 30vol%) and ethylene (from 2vol% to 25vol%) in the feed. The total pressure was varied between 1 and 5bar. The reaction temperature was 250°C. Pure silver microplates were used as catalysts for the experiments. The reaction products were analysed with rapid micro gas chromatography.By increasing the ethylene concentration, the chemical system was more favourable towards the partial oxidation of ethylene. The oxygen concentration had a positive effect on the conversion and selectivity towards ethylene oxide. A clearly improved catalyst stability and activity were achieved by pretreating the silver microplates during 12h with ethylene. The reaction order was close to one with respect to oxygen, while the reaction order of ethylene was around 0.5. A new generalized kinetic model was proposed for ethylene oxide formation. The model is consistent with the experimental data, predicting correctly the observed reaction orders and selectivities. The work demonstrated that gas-phase microreactors combined to micro gas chromatography are strong tools in kinetic research.

In situ DRIFTS study during C 2H 4-SCR of NO over Co-ZSM-5

The formation of surface intermediates and their reactivities with some reactant gases during the selective catalytic reduction of NO with ethylene (C 2H 4-SCR) over Co-ZSM-5 was investigated systematically by in situ diffused reflectance infrared Fourier transformed spectroscopy. Some new IR bands relevant to the surface intermediates formed in the title reaction were identified. The results show that formate species, formed during the partial oxidation of ethylene over Co-ZSM-5, is reactive towards nitrates to yield formyl nitro compound, an intermediate critical for the formation of cyanide and isocyanate species by further reacting with nitrates. Kinetics analysis suggests that the cyanide and isocyanate at different sites vary in reactivity towards nitrates. The Co 2+–CN and Al 3+–NCO species subsequently react with nitrates for final production of N 2, CO 2 and H 2O, however, the –CN bound to Brønsted and Lewis acid sites show poor reactivity towards a flow of NO + O 2/He. On the basis of these investigations, a proposed reaction mechanism explains the formation and roles of all intermediates detected by IR spectroscopy in this study.

In situ DRIFTS study on the partial oxidation of ethylene over Co-ZSM-5 catalyst

The interaction of C2H4 and C2H4 + O2 with Co-ZSM-5 has been studied by in situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS). XRD, UV–vis and H2–TPR were used for characterizing the Co-ZSM-5 samples. DRIFTS results showed that a partial oxidation of ethylene over Co-ZSM-5 occurred at definite temperatures(⩾250 °C), leading to the formation of formate species in the presence or absence of gas phase oxygen. Investigation on active sites in Co-ZSM-5 by using NO as probe molecules revealed that a reduction of Co3+ to Co2+ occurred during reaction and Co3+ (presenting in Co3O4) were primarily responsible for the oxidation of ethylene.

Ethylene Epoxidation in Low-Temperature AC Dielectric Barrier Discharge: Effects of Oxygen-to-Ethylene Feed Molar Ratio and Operating Parameters

Ethylene oxide (EO), a valuable chemical feedstock in producing many industrial chemicals, which is industrially produced by the partial oxidation of ethylene, so-called ethylene epoxidation, has been of great interest in many global research studies. In this work, the epoxidation of ethylene under a low-temperature dielectric barrier discharge (DBD) was feasibly investigated to find the best operating conditions. It was experimentally found that the EO yield decreased with increasing O2/C2H4 feed molar ratio, feed flow rate, input frequency, and electrode gap distance, while it increased with increasing applied voltage up to 19 kV. The highest EO yield of 5.6% was obtained when an input frequency of 500 Hz and an applied voltage of 19 kV were used, with an O2/C2H4 feed molar ratio of 1:1, a feed flow rate of 50 cm3/min, and an electrode gap distance of 10 mm. Under these best conditions, the power consumption was found to be as low as 6.07 × 10−16 Ws/molecule of EO produced.

Ethylene oxidation over Ag supported on novel carbon nano-structured supports

The potential of graphite nanofiber (GNF) supported silver catalysts to function as a catalyst system for the partial oxidation of ethylene to ethylene oxide has been investigated at 220°C and atmospheric pressure. It was found that when the metal was dispersed on “platelet”GNF that had been modified by pretreatment in argon at 2300°C the performance of the catalyst was superior to that of the current commercial system Ag/a-alumina, when reacted under the same. It is suggested that the observed enhancement in both activity and selectivity is related to electronic perturbations in the metal particles when dispersed on a highly conductive support medium.

Partial oxidation of alkenes by a membrane catalyst utilizing fuel cell reactions

Partial oxidation of ethylene with a gas-cell system were studied at 353 K. The gas-cell structure was [ C 2 H 4, H 2 O|(Pd- black+ VGCF)- anode|H 3 PO 4 /silica– wool|cathode|O 2] (VGCF: vapor growing carbon fiber). Addition of NO to O 2 stream at the cathode dramatically enhanced the oxidation rate of ethylene to MeCHO more than 10 times with high selectivities >95%. The enhancement of the formation rate of MeCHO was due to the acceleration of the electrochemical oxidation rate of Pd 0 to Pd 2+ at the anode by a strong oxidant of NO 2 produced from O 2 and NO. NO 2 was electrochemically reduced to H 2O and NO that functioned as a mediator over the graphite-cathode. When a membrane of carbon matrix holding H 3PO 4 was chosen instead of H 3PO 4/silica–wool, both H + and e − could conduct from anode to cathode side through the H 3PO 4/carbon matrix, self-short circuiting condition. The oxidation of C 2H 4 could perform with the self-shorted cell reactor excluded electric parts. Several carbon matrices were tested for the oxidation by the self-shorted cell and the suitable one was a sheet of (VGCF+AC+PTFE) (AC: active carbon) prepared by the hot-press method. This self-shorted gas-cell was more active than the cell system. In the case of propene oxidation, acetone was selectively produced with the self-shorted cell. Kinetic studies were carried out to get information for reaction mechanism of the alkene oxidation. The self-shorted cell works as a new type of membrane catalytic system for the oxidation of alkene [alkene|oxidation catalyst|mixed conductor of H + and e −|reduction catalyst|oxidant]. This membrane catalyst also functioned as a hydrogen permeation membrane.

Partial Oxidation of Ethylene Over Silver Catalyst Supported on Mesoporous Materials

The partial oxidation of ethylene was investigated over silver catalysts supported on mesoporous materials. KIT-1 mesoporous materials with 30–50 wt.% silver exhibited a high conversion of ethylene and a relatively high selectivity for ethylene oxide. The selectivity of Ag/KIT-1 is enhanced by the modification of the silane.

IR study of the secondary reaction of ethylene oxide over silver catalyst supported on mesoporous material

The secondary reaction of ethylene oxide over silver catalyst supported on MCM-41 mesoporous material was investigated by thein-situ IR method. MCM-41 mesoporous material with a large content of hydroxyl group was very active in catalyzing the isomerization of ethylene oxide to acetaldehyde. The reduction of hydroxyl group by silane treatment or silver loading suppressed the isomerization of ethylene oxide. The selectivity for ethylene oxide in the partial oxidation of ethylene is enhanced by silane modification, revealing the acceleration of the consumption of ethylene oxide on the hydroxyl group.

Electron transfer and back-transfer in the partial oxidation of ethylene on an Ag surface: dipped adcluster model study

The crucial step in catalyst design to increase the overall selectivity of epoxidation of ethylene on a silver surface is the reaction of atomically adsorbed oxygen with ethylene to give ethylene oxide, as shown previously. The energy diagram is recalculated using the dipped adcluster model combined with MP2 geometry optimizations. The previous result is confirmed. At the key transition state (TS), one-electron is back-transferred from the admolecule to the bulk Ag surface. The energy barrier is calculated to be 41 kcal/mol, comparable with the energy barrier of 39 kcal/mol in the complete oxidation path. The energy barrier of this electron-transfer type TS must be lowered to obtain a higher overall selectivity of ethylene oxide.

ESR Studies of Well-Dispersed Ag Crystallites on SiO2

ESR was utilized to study Ag on SiO2 over a dispersion range of 0.04 to 0.32, which gave average Ag crystallites sizes between 4 and 31 nm. For all samples only a single sharp signal was observed at g = 2.0028 ± 0.0002 with a peak-to-peak linewidth of 1.5-6.0 G, whether after reduction at 773 K or after adsorption of O2, N2O or C2H5Cl. This signal was shown to be associated with conduction electrons existing only in small nanocrystallites (ca. 7 nn or smaller) in which quantum size effects occur to increase the spin relaxation time and provide a CESR signal. The use of 17O verified the peak was not due to any paramagnetic oxygen species. No correlation between line width or g shift acid average crystallite size (below 7 mn) was observed, although a model invoking quantum size effects has predicted one. Adsorption of O2 or N2O at either 300 or 443 K produced identical results-the peak intensity was decreased and no new peaks were detected. Exposure to H2 at 443 or 300 K provided almost complete or partial restoration of the signal, respectively. Adsorption of C2H5Cl at 300 K had no effect, but at 523 K adsorption on clean Ag markedly decreased intensity, and adsorption on an oxygen-covered Ag surface further decreased signal strength, thus indicating the strong interaction Cl atoms can achieve when such promoters are used in the partial oxidation of ethylene.

Infrared emission study of vibrationally excited molecules formed by catalytic oxidation of hydrocarbons

Vibrationally excited molecules produced by molecular-beam hydrocarbon oxidation reactions on a Pt surface have been studied by using infrared emission spectroscopy. The selective production of syngas (CO + H 2) was observed by the partial oxidation reaction of small alkanes (ethane, propane, butane) and ethylene at higher surface temperatures (above 1000 K). The infrared spectra of the product CO desorbed from the Pt surface were measured during the partial oxidation of ethylene (O 2/C 2H 4 = 3/1) on Pt at the surface temperature of 1500 K, and the spectral analyses showed that the desorbed CO molecules were vibrationally excited (vibrational temperature, T V = ca. 2500 K) but rotationally very cool (rotational temperature, T R = 380 K). The low T R value was due not to the rotational relaxation by the gas phase collision, but the product CO formed by the reaction between C ad and O ad was desorbed without being thermally accommodated to the surface. The vibrational and rotational states of the product CO 2 formed by the ethylene oxidation at the higher O 2/C 2H 4 ratio were also studied in comparison with those of CO 2 formed by the catalytic oxidation of CO, and implications of these results for the dynamics of the oxidation reactions are discussed.

Two oxygen states and the role of carbon in partial oxidation of ethylene over silver

The interaction of O 2 and a C 2H 4+ O 2 reaction mixture with the surface of polycrystalline silver at P = 10 −2−10 3 Pa and T = 420−620 K was studied by XPS, TDS and TPR. The formation of two states of O ads with E BO 1s = 528.4 and 530.5 eV is shown and the necessity of participation of both states in ethylene epoxidation is stated. It is assumed that an elementary carbon resulting from oxidative dehydrogenation of ethylene stabilizes defects of the silver surface and takes part in the formation of a mixed adsorption layer consisting of two states of O ads.

Influence of feed water vapour on the selective oxidation of ethylene over silver catalyst

The selective oxidation of ethylene over supported silver catalyst was studied in the presence of 0.2–16% feed water vapour. In addition to silver, alumina and silica, the catalyst also contains Li, Na, K, Mg, Ca, Ba, Mn and Fe additives in trace amounts. Steady-state kinetic measurements were carried out using a glass flow-circulation system at atmospheric pressure and in the temperature range 210–264°C, varying the oxygen-to-ethylene concentration ratio in the feed. The results show that the partial oxidation of ethylene is inhibited by the presence of feed water but the complete oxidation is promoted by it. This result contradicts the results of other workers. The reason for this contradiction is probably the presence of the additives in the studied catalyst. The effect of water is stronger at low feed concentrations (0.2–1.4%), at which the process is carried out in the industrial reactor. This fact could be of great importance for selecting the optimum conditions for the industrial process. The presence of feed water has an unfavourable effect on the selectivity for ethylene oxide, unlike the effect of carbon dioxide in the feed established in previous work over the same catalyst. An explanation of the effect of water vapour on the oxidation of ethylene is proposed on the basis of the assumed reaction mechanism.

ChemInform Abstract: Chemisorption and Industrial Catalytic Processes

Abstract In recent years workers in the field of surface science have established the utility of their experimental techniques by in-depth investigations of simple adsorption systems, particularly the interaction of carbon monoxide with transition metal surfaces. Lately, attention has begun to shift toward areas of more directly practical interest, especially chemical reactions catalysed by metal and oxide surfaces. In this paper two commercial catalytic processes will be discussed in detail. Firstly, the conversion of synthesis gas (in this case a mixture of CO, CO 2 and H 2 ) to methanol over Cu/ZnO/Al 2 O 3 catalysts and secondly the partial oxidation of ethylene to ethylene oxide using silver catalysts. In these processes, as in many heterogeneously catalysed reactions, the interaction between the gas phase species and the surface is important in determining the rate of product synthesis and the selectivity of the reaction. An understanding of the fundamental adsorption properties of such systems is clearly important for the elucidation of synthesis mechanisms and for the development of more efficient catalysts. The nature of the adsorption, desorption and surface reaction events involved in the two particular synthesis routes under consideration will be discussed and will be related to the global features of the commercial process.

Influence of γ irradiation upon catalytic selectivity. II: The role of Ca in the Ag catalyzed oxidation of ethylene

In the partial oxidation of ethylene, calcium, present within supported Ag apparently as distinct oxide phase inclusions, is shown to be a necessary ingredient to cause yield of ethylene oxide enhancement due to pre-irradiation of said catalyst with γ rays in the presence of air.

Chemically stimulated exo-electron emission from silver catalyst during partial oxidation of ethylene

Exo-electron emission from a silver catalyst during partial oxidation of ethylene has been studied by measuring simultaneously the exo-electron emission rate and the rate of ethylene oxide formation. The silver catalyst emits exo-electron continuously in a temperature range 150–210 °C and its emission rate is proportional to the rate of ethylene oxide formation. The temperature dependence of the exo-electron emission obeys the Richardson relation for thermo-electron emission from semiconductor, whereas the rate of ethylene oxide formation fits to the Arrhenius equation. This continuous exo-electron emission is discussed using a schematic diagram of electronic levels of the silver surface with conclusions that the exo-electron emission from the silver catalyst during partial oxidation of ethylene is regarded as a thermo-electron emission from a thin semiconducting oxide layer on silver, the work function of which is reduced by adsorption of ethylene in the form of ethylene oxide. No exo-electron emission and no ethylene oxide formation are shown to occur from metallic copper, nickel oxide and iron oxide, with which only complete oxidation of ethylene proceeds.