Hybrid modeling of ethylene to ethylene oxide heterogeneous reactor

In this research a dynamic grey box model (GBM) of ethylene oxide (EO) fixed bed reactor has been presented. In the first step of the study, kinetic model of the existing reactions was obtained using artificial neural network (ANN) approach. In order to build the ANN model industrial data of a typical EO reactor were employed. Time, C₂H₄, C₂H₄O, CO₂, H₂O and O₂ mole fractions were network inputs and the multiplication of reaction rate and catalyst deactivation (r * a)was ANN output. From 164 data, 109 data were employed to train ANN. After employing different training algorithms, it was found that, the radial basis function network (RBFN) training algorithm provides the best estimations of the data. This best obtained network was tested against fifty five unseen data. The network estimations were close to unseen data which confirmed generalization capability of the obtained network.In the next step of study, (r * a) was estimated with ANN and then the hybrid model of the reactor was solved. Simulation results were compared with EO mechanistic model and also with plant industrial data. It was found that GBM is 8.437 times more accurate than the mechanistic model.     

The influence of competitive interactions on multiple eutectic phase behavior in poly(ethylene oxide) molecular complexes

Binary mixtures of poly(ethylene oxide) and resorcinol exhibit two eutectic phase transitions at 40 and 80 °C, which are separated by a single-phase stoichiometric complex at ≈33 mol% resorcinol. These eutectic temperatures increase slightly at higher molecular weights of poly(ethylene oxide). The eutectics and the molecular complex are absent in ternary mixtures with either 25 or 40 wt% poly(2-vinylpyridine) because both polymers contain electron-pair donors which participate in hydrogen bonding interactions with the hydroxyl groups of the small-molecule aromatic. In contrast, 25 wt% polystyrene does not disrupt the bi-eutectic phase behavior of poly(ethylene oxide) and resorcinol because polystyrene is inert in these ternary mixtures. The lightest lanthanides with the largest ionic radii in the first-row of the f-block, like LaCl₃(H₂O)₆ and CeCl₃(H₂O)_x, are more effective than neodymium, terbium and ytterbium trichloride hexahydrates from the viewpoint of (i) competing with resorcinol, (ii) interacting with poly(ethylene oxide), (iii) eliminating eutectic melting, and (iv) disrupting the 2:1 stoichiometric complex between poly(ethylene oxide) and resorcinol. High-resolution ¹³C solid state NMR spectroscopy identifies resorcinol in several different molecular environments. Multiple resonances are observed for chemically equivalent, but morphologically and crystallographically inequivalent, ¹³C sites in the solid state. The isotropic chemical shift of the phenolic ¹³C site in this small-molecule aromatic is very sensitive to the strength of intermolecular interactions in various phases. For example, self-association of resorcinol in pure crystalline phase γ yields a phenolic carbon chemical shift at 155 ppm. The formation of a 2:1 stoichiometric complex between poly(ethylene oxide) and resorcinol in co-crystallized phase β is identified by a phenolic carbon chemical shift at 158 ppm. When resorcinol and poly(2-vinylpyridine) interact in a homogeneous amorphous phase, the phenolic carbon resonance appears at a chemical shift of 160 ppm. A resorcinol-rich disordered crystalline phase in ternary mixtures with poly(ethylene oxide) and poly(2-vinylpyridine) yields a phenolic carbon resonance at 159 ppm. Temperature-composition projections of the binary and ternary phase diagrams, constructed via differential scanning calorimetry, allow one to interpret ¹³C NMR spectra of these strongly interacting blends and complexes in the solid state.     

Improvement of ethylene epoxidation in low-temperature corona discharge by separate ethylene/oxygen feed

In this work, the ethylene epoxidation performance in a low-temperature corona discharge system was improved by initially producing oxygen free radicals prior to the reaction with unactivated ethylene molecules, in which the ethylene was separately fed into the system at various feed positions of the plasma zone. In addition, various operating parameters, including O₂/C₂H₄ feed molar ratio, applied voltage, input frequency, total feed flow rate, and gap distance between pin and plate electrodes, were optimized for the separate feed system. The highest ethylene oxide (EO) yield was achieved under the operating conditions of a C₂H₄ feed position of 0.2 cm, an O₂/C₂H₄ feed molar ratio of 1:2, an applied voltage of 18 kV, an input frequency of 500 Hz, a total feed flow rate of 100 cm³/min, and an electrode gap distance of 10 mm. In comparisons between the separate feed and the mixed feed of C₂H₄ and O₂ under their own optimum conditions, the separate feed provided higher EO selectivity and yield with lower undesired product selectivities and lower power consumption, as compared to the mixed feed. The results confirm that the separate feed with a suitable C₂H₄ feed position has sufficient reaction time with minimum ethylene molecules to be activated which, in turn, can reduce all undesired reactions including cracking, dehydrogenation, hydrogenation, combustion, and coupling reactions of ethylene, resulting in superior ethylene epoxidation performance.     

Synthesis of self-organized mixed oxide nanotubes by sonoelectrochemical anodization of Ti-8Mn alloy

Self ordered arrays of titanium manganese mixed oxide nanotubes were prepared by anodization of Ti8Mn alloy (UNS R56080) under ultrasonication in diluted ethylene glycol containing fluoride. The dimensions of the nanotubes (diameter: 20-100 nm and length: 0.5-2.0 μm) could be tuned by changing the synthesis parameters. The as-anodized nanotubes showed a stoichiometry of (Ti,Mn)O₂. Upon annealing at 500 °C in oxygen atmosphere, the nanotubes contained a mixture of anatase + rutile phases of TiO₂ and Mn₂O₃. The composition of the oxide nanotubes was influenced by the chemistry of the phases present in the alloy. More manganese content was observed in the oxide formed on the β-phase than in the oxide layer of α-phase. Anodization in the ultrasonic field increased the kinetics of nanotubular oxide formation and resulted in homogeneous ordering of the nanotubular arrays as compared to the anodization by conventional stirring in the fluoride containing ethylene glycol solution. Whereas, anodization in aqueous acidified fluoride solutions resulted in severe attack of the β-phase and did not show presence of nanotubular oxide structure.     

Effect of ethylene glycol on the mullite crystallization

Mullite is one of the most important aluminosilicate due to its unique thermal properties. In this work, mullite was obtained by sol-gel process at low temperature using sodium metasilicate, water, aluminum nitrate and ethylene glycol. The samples were prepared with a volume ratio of ethylene glycol/water equal to 0/1, 1/1, 2/1 and 3/1. The ethylene glycol effect on mullite crystallization was studied by X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), Scanning Electron Microscopy (SEM) and Differential Thermal Analysis (DTA). The sample prepared without ethylene glycol, the less homogeneous one, formed amorphous silica, spinel-phase and α-alumina at 1000 °C, and then crystallized mullite at 1200 °C, with an alumina molar fraction of 0.58. The other samples formed amorphous silica at 900 °C and crystallized mullite as the only crystalline phase at 1000 °C. However, the alumina content in mullite formula depends on the thermal treatment, reaching 0.58 at 1250 °C.     

Pervaporation dehydration of ethylene glycol by NaA zeolite membranes

Home-made NaA zeolite membranes were used for pervaporation dehydration of ethylene glycol (EG)/water mixtures. Hydrothermal stability of the membranes in pervaporation was investigated for industrial application purpose. The membranes exhibited good stability for water content of less than 20 wt.% at 100 °C. The reduction of operating temperature was effective to improve membrane stability for operating at high feed water content (e.g. 30 wt.%). The influence of feed water content and operating temperature on dehydration of EG was extensively investigated. A permeation flux of 4.03 kg m⁻² h⁻¹ with separation factor of >5000 was achieved at 120 °C for the separation of the solution with 20 wt.% water content. A pilot-scale pervaporation facility with membrane area of 3 m² was built up for dehydration of EG with the water content of 20 wt.%, which showed technical feasibility for industrial application.     

Interfacial tension and the behavior of microemulsions and macroemulsions of water and carbon dioxide with a branched hydrocarbon nonionic surfactant

Measurements of interfacial tensions for 2-ethyl-hexanol-(propylene oxide)∼_4.5-(ethylene oxide)∼₈ (2EH-PO_4.5-EO₈) at the planar water-CO₂ interface and the surfactant distribution coefficient are utilized to explain microemulsion and macroemulsion phase behavior from 24 to 60 °C and 6.9 to 27.6 MPa. A CO₂ captive bubble technique has been developed to measure the interfacial tension γ at a known surfactant concentration in the aqueous phase, with rapid equilibration at the water-CO₂ interface. The surface pressure (γ_o − γ) decreases modestly with density at constant temperature as CO₂ solvates the surfactant tails more effectively, but changes little with temperature at constant density. The area per surfactant at the CO₂-water interface determined from the Gibbs adsorption equation decreases from 250 A²/molecule at 24 °C and 6.9 MPa, to 200 A²/molecule at 27.6 MPa. It was approximately twofold larger than that at the water-air interface, given the much smaller γ_o driving force for surfactant adsorption. For systems with added NaCl, γ decreases with salinity at low CO₂ densities as the surfactant partitions from water towards the W-C interface. At high densities, salt drives the surfactant from the W-C interface to CO₂ and raises γ. Compared with most hydrocarbon surfactants, this dual tail surfactant is unusually CO₂-philic in that it partitions primarily into the CO₂ phase versus the water phase at CO₂ densities above 0.8 g/ml, and produces γ values below 1 mN/m. With this small γ, a middle phase microemulsion and a C/W microemulsion were formed at low temperatures and high CO₂ densities, whereas macroemulsions were formed at other conditions.     

Effect of processing method on physical properties of Nb2O5

Samples of Nb₂O₅ were prepared by laser floating zone (LFZ) technique and by solid-state reaction in order to study some of their physical properties as a function of synthesis conditions. Single crystals fibres were obtained by LFZ, while a structural orthorhombic to monoclinic phase transition was observed in samples sintered at temperature higher than 800 °C. Transmission optical spectroscopy and photoconductivity measurements allowed identifying a ∼3.2 eV bandgap energy for the H-Nb₂O₅ monoclinic crystalline phase. Band gap shrinkage of ∼100 meV was observed from 14 K to RT. For the orthorhombic phase (T-Nb₂O₅), the photoconductivity measurements evidence a higher energy bandgap. The sintered samples have shown a broad recombination luminescence band at the orange/red spectral region while no luminescence was detected from the LFZ grown fibres. A dielectric constant of ∼40 was found for the 800 °C and 1200 °C sintered pellets while that of 1000 °C reached four times that value.     

Carbon dioxide/ethane mixed-gas sorption and dilation in a cross-linked poly(ethylene oxide) copolymer

Mixed-gas CO₂/C₂H₆ sorption and dilation in a cross-linked poly(ethylene oxide) copolymer were studied at temperatures ranging from −20 to 35 °C. The polymer was prepared by photopolymerization of a solution containing 70 wt.% poly(ethylene glycol) methyl ether acrylate (PEGMEA) and 30 wt.% poly(ethylene glycol) diacrylate (PEGDA). Four different gas mixtures (10, 25, 50 and 70 mol% CO₂) were considered at operating pressures up to 21 atm. At a given temperature, polymer dilation increased with pressure and CO₂ content. Compared to pure-gas values, CO₂ solubility was higher in the presence of ethane, an effect whose extent increased with decreasing temperature. Ethane solubility in the polymer also increased in the presence of CO₂ compared to the pure-gas value at T ≥ 25 °C. However, at T ≤ 0 °C, the presence of carbon dioxide initially reduced ethane solubility. As the fugacity of CO₂ in the mixture increased and the polymer dilated, ethane solubility progressively increased, eventually surpassing the pure-gas value. The multicomponent Flory-Huggins model could describe the pure- and mixed-gas data simultaneously, provided that an empirical composition dependence was included in the interaction parameters for T < 25 °C.     

Synthesis of nitrogen-containing carbon nanofibers by catalytic decomposition of ethylene/ammonia mixture

The formation of carbon nanofibers (CNFs) doped with nitrogen was investigated during decomposition of C₂H₄/NH₃ mixtures at 450-675 °C over metal catalysts: 90Ni-Al₂O₃, 82Ni-8Cu-Al₂O₃, 65Ni-25Cu-Al₂O₃, 45Ni-45Cu-Al₂O₃, 90Fe-Al₂O₃, 85Fe-5Co-Al₂O₃, 62Fe-8Co-Al₂O₃, 62Fe-8Ni-Al₂O₃. It was found that the yield of CNFs, their structural and textural properties, as well as nitrogen content in CNFs are strongly dependent on the synthesis conditions such as: catalyst used, feed composition, temperature and duration. The 65Ni-25Cu-Al₂O₃ was proved to be the most efficient catalyst for the production of nitrogen-containing carbon nanofibers (N-CNFs) with nitrogen content up to 7 wt.%. Ammonia concentration in the feed equal 75 vol.%, temperature 550 °C and duration 1 h were found to be the optimum reaction parameters to reach the maximum nitrogen content in N-CNFs. TEM studies revealed that the nanofibers have a helical morphology and a “herringbone” structure composed of graphite sheets. According to the XPS data, the nitrogen incorporation in the N-CNF structure leads to the formation of two types of nitrogen coordination: pyridinic and quaternary, and their abundance depends on the reaction conditions.     

The partition coefficients of ethylene between hydrate and vapor for methane + ethylene + water and methane + ethylene + SDS + water systems

The hydrate formation of CH₄+C₂H₄ mixture was studied experimentally in two different cases, with and without the presence of sodium dodecyl sulfate (SDS) in water. The results manifested that the presence of SDS could not only accelerate the hydrate formation process, but also increase the partition coefficient of ethylene between hydrate and vapor drastically. The partition coefficients of ethylene between hydrate and vapor for methane + ethylene + water with the presence of 500 ppm SDS in water were then systematically measured. The experimental temperature ranged from 273.15 to 278.15 K, the pressure ranged from 2.5 to 5.5 MPa, the initial gas-liquid volume ratio ranged from 95 to 240 standard volumes of gas per volume of liquid, and the mole percentage of ethylene in feed gas mixture ranged from 5.28% to 79.36%. The results demonstrated that ethylene could be enriched in hydrate phase and partition coefficients were increased with the presence of SDS in water. This conclusion is of industrial significance; it implies that it is feasible to recover ethylene from gas mixture, e.g., various kinds of refinery gases or cracking gases in ethylene plant, by forming hydrate.     

Electrochemical characterization of a new binary oxide of Mo with Co for O2 evolution in alkaline solution

The α-CoMoO₄ oxide has been obtained by a precipitation method and investigated for the first time for electrocatalysis of the oxygen evolution reaction (oer) in alkaline medium. This method produced the pure crystalline CoMoO4 monoclinic phase with crystallite size ∼46 nm and lattice constants: a = 9.666 Å, b = 8.854 Å, c = 7.755 Å and β = 113.82°. The average particle size (based on area density) and the BET surface area of powders of the oxide were 11.58 μm and 9.4 m² g⁻¹, respectively. Results show that the new oxide is quite active for the oer. Values of the Tafel slope and the reaction order with respect to OH⁻ concentration are observed to be ∼60 mV and ∼1, respectively.     

Solubility of non-ionic poly(fluorooxetane)-block-(ethylene oxide)-block-(fluorooxetane) surfactants in carbon dioxide

The impact of side chain and midblock length on the solubility of ABA triblock copolymers of fluorooxetane-(ethylene oxide)-fluorooxetane in carbon dioxide is examined. The use of short fluorinated side chains instead of long fluorinated chains prevents issues with bioaccumulation of the degradation products of the surfactant. At 40 °C for the same degree of polymerization, increasing the number of perfluoro-units from one to four results in a non-monotonic change in the cloud point pressure; the cloud point pressure decreases as the side chain is increased from perfluoromethyl to perfluoroethyl. However, further increasing the fluorinated side chain to perfluorobutyl results in a significant increase in the cloud point. However when the temperature is increased to 60 °C, the cloud point pressure for the surfactants with perfluoroethyl and perfluorobutyl side chains is statistically similar, while the perfluoromethyloxetane based surfactant requires a substantially larger pressure to obtain comparable solubility. An increase in cloud point pressure is observed when increasing the hydrophilic ethylene oxide segment. These results illustrate that commercially available fluorooxetane-(ethylene oxide)-fluorooxetane surfactants are highly soluble in CO₂.     

Polymer electrolytes based on poly(ethylene glycol) dimethyl ether and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate: Preparation, physico-chemical characterization, and theoretical study

Polymer electrolytes based on poly(ethylene glycol) dimethyl ether (PEGdME) and the ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF₆) have been prepared and characterized by different techniques. Coordination of the IL by the polymer occurs mainly in the amorphous phase. This finding was correlated with previous theoretical investigations of a similar model for polymer electrolytes based on poly(ethylene oxide), PEO, and IL. It has been obtained ionic conductivity σ ∼ 10⁻³ S cm⁻¹ for the polymer electrolyte with 35 wt% of IL at 100 °C. The same order of magnitude for σ was obtained by molecular dynamics simulation of PEO/IL. This work demonstrates consistency between experimental and theoretical results for polymer electrolytes containing ionic liquids.     

Synthesis and characterization of poly (ethylene oxide) containing copolyimides for hydrogen purification

Reverse selective membranes comprising poly(ethylene oxide) (PEO) containing copolyimides (PEO-PI) with variations of acid dianhydrides and diamines have been synthesized for hydrogen purification. The reverse selectivity of the membranes decimate the energy required for hydrogen recompression process. Factors including PEO content, PEO molecular weight, and fractional free volume (FFV) that would affect the gas transport performance have been investigated and elucidated in terms of degree of crystallinity, phase separation in the PEO domain as well as inter-penetration between the hard and soft segments. In mixed gas tests of CO₂ and H₂ mixtures, a highly condensable CO₂ out compete H₂ for the sorption sites in hard segment and diminishes H₂ permeability. Thus the CO₂/H₂ selectivity in the mixed gas tests is much higher than that in pure gas tests. Mixed gas permeation tests at 35 °C and 2atm show that the best reverse selective membranes have a CO₂ permeability of 179.3 Barrers and a CO₂/H₂ permselectivity of 22.7. The physical properties of PEO-PIs have also been characterized by FTIR, DSC, GPC, WAXS, AFM and tensile strain tests.     

Enhancement of nitric oxide removal by ammonia on a low-rank coal based carbon by sulphuric acid treatment

This work presents a study of the effect of wet sulphuric acid treatment and gas-phase treatment with SO₂ + O₂ + H₂O on the catalytic activity of a low-rank coal-based carbon for the nitric oxide reduction with ammonia. Carbons were characterized by N₂ adsorption, TPD, and FTIR in order to assess how the surface chemistry and the texture of carbons change after the treatments. A great amount of oxygenated functional groups both CO₂ and CO evolving ones are produced by liquid-phase sulphuric acid treatment. However, the amount of those groups after gas-phase treatment with SO₂ + O₂ + H₂O is lower, in particular the CO₂ evolving groups. The catalytic activity of carbons was examined in a fixed bed reactor at 150 °C in a gas flow containing NO, O₂, N₂ and NH₃, the effluent concentration being monitored continuously during the reaction. The obtained results indicate that an appropriate balance between the type of oxygen functional groups and surface area available to the reactant gas are required to reach high levels of NO conversion.     

Correlation between interactions, miscibility, and spherulite growth in crystalline/crystalline blends of poly(ethylene oxide) and polyesters

Crystalline/crystalline blend systems of poly(ethylene oxide) (PEO) and a homologous series of polyesters, from poly(ethylene adipate) to poly(hexamethylene sebacate), of different CH₂/CO ratios (from 3.0 to 7.0) were examined. Correlation between interactions, miscibility, and spherulite growth rate was discussed. Owing to proximity of blend constituents' T_g's, the miscibility in the crystalline/crystalline blends was mainly justified by thermodynamic and kinetic evidence extracted from characterization of the PEO crystals grown from mixtures of PEO and polyesters at melt state. By overcoming experimental difficulty in assessing the phase behavior of two crystalline polymers with closely spaced T_g's, this work has further extended the range of polyesters that can be miscible with PEO. The interaction parameters (χ₁₂) for miscible blends of PEO with polyesters [poly(ethylene adipate), poly(propylene adipate), poly(butylene adipate), and poly(ethylene azelate) with CH₂/CO = 3.0-4.5] are all negative but the values vary with the polyester structures, with a maximum for the blend of PEO/poly(propylene adipate) (CH₂/CO = 3.5). The values of interactions are apparently dependent on the structures of the polyester constituent in the blends; interaction strength for the miscible PEO/polyester systems correlate in the same trend with the PEO crystal growth rates in the blends.     

Environmental durability of slurry based mullite-gadolinium silicate EBCs on silicon carbide

Water vapor oxidation and salt corrosion resistances of mullite-gadolinium silicate (Gd₂SiO₅) environmental barrier coatings (EBCs) dip coated on α-SiC substrates and sintered to 1430 °C/3 h in air were investigated. The EBC exhibited excellent adherence to the substrate during thermal cycling between 1350 °C and room temperature (RT) for 100 h in a simulated lean combustion environment (90% H₂O-balance O₂), ^{[11], [13] and [15]} forming ∼10 μm porous silica layer at coating-substrate interface, compared to ∼17 μm for uncoated α-SiC exposed under same conditions. The EBC did not spall after a 24 h 1200 °C exposure in Na₂SO₄ corrosion environment leading to further coat densification. However, after 48 h salt exposure, the EBC showed severe through-thickness cracks, and cavities and de-lamination at coating-substrate interface. The corrosion gaseous products such as CO₂, CO and SO₂ trapped under a low viscosity glassy (Na₂O·x(SiO₂)) liquid phase were formed due to salt vapor reaction with α-SiC substrate created these cavities.     

Development of new alumina-modified sorbents for CO2 sorption and regeneration at temperatures below 200 °C

A new regenerable alumina-modified sorbent was developed for CO₂ capture at temperatures below 200 °C. The CO₂ capture capacity of a potassium-based sorbent containing Al₂O₃ (KAlI) decreased during multiple CO₂ sorption (60 °C) and regeneration (200 °C) tests due to the formation of the KAl(CO₃)(OH)₂ phase, which could be converted into the original K₂CO₃ phase above 300 °C. However, the new regenerable potassium-based sorbent (Re-KAl(I)) maintained its CO₂ capture capacity during multiple tests even at a regeneration temperature of 130 °C. In particular, the CO₂ capture capacity of the Re-KAl(I)60 sorbent which was prepared by the impregnation of Al₂O₃ with 60 wt.% K₂CO₃ was about 128 mg CO₂/g sorbent. This excellent CO₂ capture capacity and regeneration property were due to the characteristics of the Re-KAl(I) sorbent producing only a KHCO₃ phase during CO₂ sorption, unlike the KAlI30 sorbent which formed the KHCO₃ and KAl(CO₃)(OH)₂ phases even at 60 °C. This result was explained through the structural effect of the support containing the KAl(CO₃)(OH)₂ phase which was prepared by impregnation of Al₂O₃ with K₂CO₃ in the presence of CO₂.     

A proton-conducting composite membrane: Sn0.95Al0.05P2O7 and polystyrene-b-poly(ethylene/propylene)-b-polystyrene

An anhydrous proton conductor, Sn_0.95Al_0.05P₂O₇ (SAPO), composed of polystyrene-b-poly(ethylene/propylene)-b-polystyrene (SEPS), was developed and characterized using morphological, structural, and electrochemical analyses. In the composite membrane with 20 wt% SEPS, a homogeneous distribution of SAPO particles in the matrix was obtained in the thickness range of 65-90 μm, yielding a proton conductivity of 3.4 × 10⁻³ S cm⁻¹ at 200 °C, tensile strength of 4.6 MPa and an elongation at break of 711.0% at room temperature. Fuel cell tests verified that the open-circuit voltage was maintained at a constant value of approximately 1 V between 100 and 250 °C. The peak power densities achieved with unhumidified H₂ and air were 77.0 mW cm⁻² at 100 °C, 121.0 mW cm⁻² at 150 °C, and 163.1 mW cm⁻² at 225 °C.