Insight into the topology effect on the diffusion of ethene and propene in zeolites: A molecular dynamics simulation study

Selectivity control is a difficult scientific and industrial challenge in methanol-to-olefins(MTO)conversion.It has been experimentally established that the topology of zeolite catalysts influenced the distribution of products.Besides the topology effect on reaction kinetics,the topology influences the diffusion of reactants and products in catalysts as well.In this work,by using COMPASS force-field molecular dynamics method,we investigated the intracrystalline diffusion of ethene and propene in four different zeolites,CHA,MFI,BEA and FAU,at different temperatures.The self-diffusion coefficients and diffusion activation barriers were calculated.A strong restriction on the diffusion of propene in CHA was observed because the self-diffusion coefficient ratio of ethene to propene is larger than 18 and the diffusion activation barrier of propene is more than 20 kJ/mol in CHA.This ratio decreases with the increase of temperature in the four investigated zeolites.The shape selectivity on products from diffusion perspective can provide some implications on the understanding of the selectivity difference between HSAPO-34 and HZSM-5 catalysts for the MTO conversion.

Self-metathesis of 1-butene to ethene and hexene over molybdenum-based heterogeneous catalysts

A novel route involving self‐metathesis of1‐butene under mild conditions that gave high yields ofethene and hexene was proposed.The results of thermodynamic analysis revealed that the Gibbsenergy of the target Metathesis I reaction(1‐butene?ethene+3‐hexene)was much higher thanthat of the main side Metathesis II(1‐butene+2‐butene?propene+2‐pentene).Suppression of1‐butene double‐bond isomerization was the key step to increase the selectivity for the target olefinin the reaction network.The relationship between the catalytic performance and support nature was investigated in detail.On basis of H2‐TPR,UV‐Vis spectra and HRTEM results,an alumina(Al2O3)support with large surface area was beneficial for the dispersion of molybdenum(Mo)species.Both suitable acidity and sufficient Mo dispersion were important to selectively promote the self‐metathesis reaction of1‐butene.On the optimal6Mo/Al2O3catalyst,1‐butene conversion reached47%and ethene selectivity was as high as42%on the premise of good catalytic stability(80°C,1.0MPa,3h?1).?2018,Dalian Institute of Chemical Physics,Chinese Academy of Sciences.Published by Elsevier B.V.All rights reserved.

Effect of Reaction Temperature and Pressure on the Metathesis Reaction between Ethene and 2-Butene to Propene on the WO_3/Al_2O_3-HY Catalyst

Effect of reaction temperature and pressure on the metathesis reaction between ethene and 2-butene to propene was studied on the WO3/γ-Al2O3-HY catalyst. The activity is found to increase with elevated temperature and reaches a plateau at 150-240 ℃. After that, the activity undergoes a remarkable decrement at too high temperature. The effect of temperature is elucidated by the oxidation state of tungsten species. The evaluation results also indicate that the stability is dependent on this reaction parameter. Medium pressure （0.5-0.8 MPa） is favorable for stability, while atmospheric pressure or too high pressure （〉1.0 MPa） deteriorates the stability. For explanation, UV Vis, FT-IR, O2-TPO, and TG techniques are used to characterize the spent catalysts.

Cross metathesis of butene-2 and ethene to propene overMo/MCM-22-Al_2O_3 catalysts with different Al_2O_3 contents

A series of 3.0Mo/MCM-22-Al2O3 catalysts with γ-Al2O3 contents in the range of 0-100 wt% were prepared and applied in the metathesis reaction of ethene and butene-2. Addition of γ-Al2O3did not affect the structure of MCM-22 zeolite as evidenced by XRD and N2 adsorption measurements. It was deduced from TPR experiments that γ-Al2O3 phase favored the formation of polymolybdate or multilayered Mo oxide, while more Al2（MoO4）3 species were generated over MCM-22 zeolites. Alumina content in the support was directly related to the metathesis activity of ethene and butene-2 to propene. Mo species with higher valence （Mo6＋or Mo5＋） contributed more to the excellent performance of catalyst than metallic Mo. The best catalyst activity and stability was obtained over 3.0Mo/（MCM-22-30%Al2O3） under the reaction condition of 1.0 MPa and 125℃ using N2 as the pretreatment gas.

Ethene／norbornene copolymerization by[Me2Si（3—^tertBuCp）（N^tertBu）]TiCl2／MAO—catalyst

?Ethene/norbornene copolymerization by the catalyst system [Me_2Si( 3- tertBuCp)(N tertBu)]TiCl_2/MAO was investigated in detail at 30 ℃, 60℃, and 90℃. A mass flow controller was used in this work to obtain kine tic data and investigate tempera ture's effects on activity, norbornene incorporation, copolymerization parameter , microstructure, glass transition temperature, and molar masses were described. H igh copolymerization values r_E and high alternation are determined. The n umber of isotactic alternating sequences is much higher than that of the syndiot actic alter nating sequences.

Oxidative dehydrogenation of ethane to ethene over a superbase supported LiCl system

LiCl-promoted superbase catalysts were found to be stable and highly selective to ethene for oxidative dehydrogenation of ethane,giving 84%ethane conversion and 74%ethene yield at 923 K.Results indicated that the stronger the basicity of LiC1-based catalysts,the better the catalytic performance.

Ethene and butene oligomerization over isostructural H-SAPO-5 and H-SSZ-24: Kinetics and mechanism

BrФnsted-acidic zeolite and zeotype materials are potential catalysts for the conversion of ethene to higher alkenes. In this study, two materials with AFI structure but different acid strength, H-SAPO-5 and H-SSZ-24, were subject to studies of ethene, cis-2-butene and ethene-butene mixture conversion under conditions where C3-C5 alkene formation is thermodynamically favoured over higher hydrocarbons(673-823 K, 1 atm). Ethene and cis-2-butene partial pressures were varied in the range 9-60 and 0.9-8.1 kPa, respectively, and contact times were varied in the range 3.78-756 and 0.573-76.4 s.μmol H+/cm^3 over H-SAPO-5 and H-SSZ-24, respectively. Less than 1% conversion of ethene and less than 10% conversion of butene was obtained in the range of conditions used for elucidation of rate parameters. The ethene conversion rates were more than an order of magnitude higher over the more acidic H-SSZ-24 than over H-SAPO-5(6.5 vs. 0.3 mmol/mol H+.s at 748 K, Pethene = 33 kP a), with corresponding lower reaction order in ethene(1.5 vs. 2.0 at 673 K) and lower apparent activation energy(52 vs. 80 kJ/mol at 698-823 K). Propene selectivity was substantially higher over H-SSZ-24 than over H-SAPO-5(68% vs. 36% at 0.5% ethene conversion). A similar difference in apparent reaction rates was observed for cis-2-butene conversion over the two catalysts, and for co-feeds of ethene and cis-2-butene. However, the cis-2-butene conversion to C3-C5 alkenes was found to be severely influenced by thermodynamic limitations, impeding a detailed kinetic analysis, and leading predominantly to isobutene formation at the highest temperatures.

Chemical Dynamics Simulations of the Hydroxyl Radical Reaction with Ethene

We present a theoretical study of the reaction of the hydroxyl radical with ethene using electronic structure calculations and direct-dynamics simulations. High-accuracy electronic structure calculations at the CCSD（T）/aug-cc-pVTZ//MP2/aug-ce-pVDZ level have been carried out to characterize the representative regions of the potential energy surface of various reaction pathways, including OH-addition and H-abstraction. These ab initio calculations have been employed to derive an improved set of parameters for the MSINDO semiempirieal Hamiltonian specific to the OH＋C2H4 reaction. The specific-reaction-parameter Hamilto- nian captures the ab initio data accurately, and has been used to perform direct quasiclassica] trajectory simulations of the OH＋C2H4 reaction at collision energies in the range of 2-10 kcal/mol. The calculated cross sections reveal that the OH-addition reaction domi- nates at all energies over H-abstraction. In addition, the excitation function of addition is reminiscent of a barrierless capture process, while that for abstraction corresponds to an activated one, and these trends can be connected to the transition-state energies of both reactions. We note that the development of an accurate semiempirical Hamiltonian for the OH＋C2H4 reaction in this work required the inclusion of empirical dispersion corrections, which will be important in future applications for which long-range intermoleeular attraction becomes significant.

ON NONEQUILIBRIUM OF PYROLYSIS PROCESS IN THE MANUFACTURE OF ETHENE

Nonequilibrium process for cracking ethane and n-buthane in the manufacture of ethene has been analytically and numerically investigated in a Heaviside function temperature field and through a normal shock wave. The results demonstrate that, while the reaction temperature increases, the maximum value of ethene yield is increased, and the optimal reaction duration is sharply shortened. For the identical initial reaction temperature, the maximum value of ethene yield through a stationary normal shock wave is less than that in a Heaviside function temperature field. However, the ethene consumption after the maximum value in the former case is less than that in the latter. Higher ethene yield will be obtained by using the gasdynamic heating method than by using the current methods. (Edited author abstract) 5 Refs.

The Influence of Temperature on Ethene Diffusion in HZSM-5 Studied by Molecular Dynamics

Molecular dynamics(MD) simulation of ethene diffusion in the lattice of HZSM 5 was performed at the temperature ranging from 300 K to 700 K. The calculated diffusion coefficients increase with the temperature from 2.60×10 -9 m 2/s at 300 K to 12.78×10 -9 m 2/s at 700 K. The Arrhenius plot gives an activation energy of 6.31 kJ/mol . The anisotropy of the diffusion process was examined.

Solid-Phase Stereoselective Synthesis of (E)-1, 2-Disubstituted Ethenes from Polymer-Sopported a-Selenoaldehydes

Reaction of polymer-supported a-selenoaldehydes with Grignard reagents afforded polymer-bound B-hydroxyalkyl selenides, which treated with thionyl chloride and triethylamine leading to (E)-1, 2-disubstituted ethenes in good yield.

Direct Oxidation of Ethene to Acetic Acid

Direct oxidation of ethene to acetic acid over Pd-SiW12/SiO2 catalysts prepared by several methods was studied. A better method for reducing palladium composition of the catalysts was found. Acetic acid was obtained with selectivity of 82.7% and once-through space time yield (STY) of 257.4 g/h .L.

Qilu Petrochem Ethene Installation Hits Target Ahead of Schedule

TheetheneinstallationofQiluPetrochemCorp.,akeyStateproject,hasproduced450,000tonsofethylenethisyear,achievingtheafter-transformationannualproductioncapacity30daysaheadofschedulewithallthemajortechnicalindicessettinghistoricalrecords.Thustheinstallati...

Experimental Investigation on Hydrothermal Reduction of Sulfates to H₂S and Organic Sulfides by Ethene

The kinetic characteristics of alkenes involved in thermochemical sulfate reduction (TSR) have been never reported in geological literature. In this study, TSR by ethene under hydrothermal conditions was performed in the constrained simulation experiments. Typical TSR products consisted of H2S, CO2, mercaptans, sulfides, thiophenes derivatives and benzothiophene. The apparent activation energy E and apparent frequency factor A for TSR by ethene were determined as 76.370 kJ/mol and 4.579 s-1, respectively. The lower activation energy for ethene involved in TSR relative to ethane suggested that the reactivity of ethene is much higher than that of ethane, in accordance with the thermodynamic analysis. Rate constants were determined experimentally using first-order kinetics extrapolate to MgSO4 half-lives of 67.329 years - 3.053 years in deep burial diagenetic settings (120°C - 180°C). These values demonstrate that the reaction rate for TSR by ethene is extraordinarily fast in high-temperature gas reservoirs (120°C - 180°C). Consequently, the newly formed ethene from thermal cracking and TSR alteration of natural gas and/or petroleum could not survive after TSR process and were rarely detected in natural TSR reservoirs.

Influences of Brnsted Acidic Sites in HZSM-5 on Polarization and Electronegativity of Ethene Studied by Molecular Dynamics

Molecular dynamics simulation has been performed for studying thepolarization and electronegativity of ethene molecules near Broensted acidic sites in H[Al] ZSM-5.The result shows that the molecules are polarized most at the edges of intersections and least atthe segments of channels. On the contrary, the highest global molecular electronegativity is foundat the centers of channel segments. Al substitution slightly increases the molecular dipole moment,but hardly affects the molecular electronegativity. Broensted acidic proton decreases the dipolemoment of guest molecule, but increases the molecular elec-tronegativity.

Molecular dynamics simulation of ethene adsorption,polarization and diffusion in three kinds of zeolites

Molecular dynamics （MD） simulation was performed to study ethene adsorption, polarization and diffusion in orthorhombic and monoclinic MFI and H[Al] ZSM-5 at 300 K. The resuits show that the interaction between ethene molecule and orthorhombic MFI is the strongest.Ethene molecules possess relatively low energy in the lattice of orthorhombic MFI. The existence of Al and Brnsted H atoms in the framework of H[AI]ZSM-5 can lower the energy of adsorbed ethene molecules. At the edges of intersections of channels, especially those near Al sites,ethene molecules are polarized most. Ethene molecules prefer the locations at the centers of channel intersections. The diffusion coefficients of ethene in the lattices of orthorhombic, monoclinic MFI and H[AI]ZSM-5 are 2.7 x 10-9, 2.1 x l0-9, 1.6 x 10-9 m2·s-1, respectively. The infrared spectrum of ethene in the framework of H[Al] ZSM-5 shows five vibration peaks (v10,v7, v12, v11 and V9), which is consistent with the experimental result.

Photochromism of cis(z)-1,2-bispyrryl-substituted ethene derivatives

Photochromism of two bispyrryl-substituted ethenes, 2, 3-bis-(1-p-methoxyphenyl-5-phenyl-2-methyl-3-pyrryl)-2-butene (BPE1) and 2,3-bis(1-p-bromophenyl-4-phenyl-2-methyl-3-pyrryl)-2-butene (BPE2), was studied by laser flash photolysis technique. The results indicate that photocyclization of these compounds proceeds mainly via the excited triplet state, and the cis-trans isomerization proceeds mainly via the excited singlet state. After UV laser pulse irradiation, both photocylization and cis-trans isomerization of BPEl occur, but photocydization is the main reaction. On the other hand, laser photolysis of BPE2 leads mainly to photocydization. The effects of the substituents on the photochromic mechanism are also discussed.

A Flow-Tube and PERCA Study of Radical Yields in the Ozonolysis of Ethene

The production of radicals in the ozonolysis of ethene in air in a flow tube was monitored directly by a chemical amplification instrument at room temperature （298±2） K and 1 × 10^5 Pa. The radical yield is 0.50± 0.08 （σ） and found to be independent of CO. The result shows that the indirectly measured radical yields for the ozonolysis of ethene may be underestimated by a factor of 2.

A pilot scale test of ozonization treatment of ethene wastewater for reuse

Apilot scale test of advanced treatment of ethene wastewater by ozonization was carried out for industrial water reuse.Effects of different operating conditions on COD degradation,such as wastewater flow rate,ozonized gas flow rate,operating voltage of ozonizer and two ozone generation means,using pure oxygen or air,was investigated.The results show that the increase of ozonizer operating voltage,the decrease of wastewater flow rate and the suitable ozonized gas flowrate improve the removal ofCOD inwastewater and thatozone generatedrespectively fromair and pure oxygen can effectively remove COD of ethene wastewater to meet the industrial water reuse criterion.

Plasma-catalytic Selective Reduction of NO with C_(2)H_(4)in the Presence of Excess Oxygen

This paper reports observations of significant synergistic effects between dielectric barrier discharge (DBD) plasmas and Cu-ZSM-5 catalysts for C2H4 selective reduction of NOx at 250 °C in the presence of excess oxygen by using a one-stage plasma-over-catalyst (POC) reactor. With the reactant gas mixture of 530 ppm NO, 650 ppm C2H4, 5.8% O2 in N2 and GHSV = 12000 h-1, the pure catalytic, pure plasma-induced (discharges over fused silica pellets) and plasma- catalytic (in the POC reactor) NOx conversion are 39%, 1.5% and 79%, respectively. The in-situ optical emission spectra of the reactive systems imply some short-lived active species formed from plasma-induced and plasma-catalytic processes may be responsible to the observed synergistic effects in this one-stage POC system.