Olefins from Natural Gas by Oxychlorination

Ethylene and propylene are the key building blocks of the chemical industry, but current processes are unable to close the growing gap between demand and manufacture. Reported herein is an exceptional europium oxychloride (EuOCl) catalyst for the selective (≥95 %) production of light olefins from ethane and propane by oxychlorination chemistry, thus achieving yields of ethylene (90 %) and propylene (40 %) unparalleled by any existing olefin production technology. Moreover, EuOCl is able to process mixtures of methane, ethane, and propane to produce the olefins, thereby reducing separation costs of the alkanes in natural gas. Finally, the EuOCl catalyst was supported on suitable carriers and evaluated in extrudate form, and preserves performance for >150 h under realistic process conditions.     

C2 and C3 hydrocarbon separations in poly(1,5-naphthalene-2,2′-bis(3,4-phthalic) hexafluoropropane) diimide (6FDA-1,5-NDA) dense membranes

The transport of olefin and paraffin namely ethane, ethylene, propane and propylene in aromatic poly(1,5-naphthalene-2,2′-bis(3,4-phthalic) hexafluoropropane) diimide (6FDA-1,5-NDA) dense membranes was investigated. The gas permeability coefficients were measured at pressures from 2.5 to 16 atm for the C₂ hydrocarbon gases and pressures up to 8.4 atm for C₃ systems at 35 °C. This membrane exhibits permeabilities of 0.15, 0.87, 0.023 and 0.24 Barrer with respect to pure ethane, ethylene, propane and propylene, and shows an ideal selectivity of 5.8 for the separation of ethylene/ethane, 10 for propylene/propane, 7.6 for nitrogen/ethane and 50 for nitrogen/propane. The olefins showed a preferred permeability to paraffins and discussion were drawn to the permeability, diffusivity and solubility coefficients. The activation energies of permeation, diffusion and solution were also reported and the effect of temperature on the permeation properties was discussed for the pure gas permeability data obtained from 30 to 50 °C. The plasticisation effect was also found for propane and propylene, respectively, although it was neither detected in the saturated nor unsaturated C₂ hydrocarbons at pressures up to 16 atm.     

Reactions of 12C+ with hydrocarbons at 296 K:carbon-carbon bond formation

Rate constants and product distributions have been determined for the ion-molecule reactions between ¹²C⁺ and methane, ethane, propane, ethylene, propylene, allene, acetylene, propyne and benzene. The measurements were carried out with the SIFT technique at a temperature of 296 ± 2K. The results provide insight into the build-up of carbon skeletons to form C⁺_n+1 ions and other competing modes of reaction at room temperature.     

Oxidative processing of light alkanes: State-of-the-art and prospects

Recent literature data on partial oxidation of light alkanes into syngas and oxidative coupling of methane into C₂ hydrocarbons are reviewed. The problems of these processes (high cost of pure oxygen; safety; activity, selectivity and stability of catalysts; temperature regime; coke formation and other by-products; insufficient level of methane transformation into ethane and ethylene) are considered. Possible solutions of these problems and prospects of practical use of light alkanes processing are discussed.     

CO2选择氧化低碳烷烃的研究进展

本文以低碳烷烃的选择催化氧化反应为对象，对几种CO₂选择氧化低碳烷烃的反应工艺进行了归纳总结，重点分析讨论了催化氧化反应中CO₂作为氧化剂的作用机制，并提出了研究展望。     

加拿大合成原油瓦斯油裂解反应规律与产物生成机理

利用小型固定流化床实验装置研究了加拿大合成原油重瓦斯油(HGO)和轻瓦斯油(LGO)的催化裂解性能和热裂解性能。HGO和LGO催化裂解总低碳烯烃(乙烯+丙烯+丁烯)产率在660℃附近达到最大值,分别为33.8%和35.6%。HGO和LGO热裂解反应程度很大,700℃的转化率分别为66.7%和76.3%。HGO热裂解总低碳烯烃的产率在680℃达到最大值27.9%。通过对比分析催化裂解与热裂解气体产物产率的比值发现,催化剂的加入促进了乙烯和液化气的生成,同时抑制了甲烷和乙烷的生成。研究结果揭示了小分子烃类的生成机理,甲烷和乙烷主要是自由基反应的产物,乙烯和液化气是自由基反应和正碳离子反应的共同产物。     

Zur Thermischen Zersetzung von Dimethylzink

On the Thermal Decomposition of Dimethyl Zinc The thermal decomposition of dimethyl zinc has been investigated in a static system between 588 and 673 K in the pressure range from 8 to 372 mbar. Gaseous products are methane, ethylene, ethane, propane, propylene and butane. The formation of a new solid product of the composition CH₃(ZnCH₂)_xZnCH₃ (x = 3,2…4,0) has been detected.     

静电纺丝法制备硼掺杂氧化硅纳米纤维用于低碳烷烃氧化脱氢制烯烃

乙烯和丙烯等低碳烯烃是重要的基础有机化工产品,广泛应用于化工生产的各个领域.相比于其他工艺,低碳烷烃氧化脱氢制烯烃工艺具有不受热力学平衡限制、无积炭等特点而被广泛研究.近年发现六方氮化硼(h-BN)、硼化硅(SiB6)和磷酸硼(BPO4)等非金属硼基催化剂能够高效催化烷烃氧化脱氢反应,并抑制产物烯烃的过度氧化,表现出高的催化活性和烯烃选择性.大量的研究表明,硼基催化剂活性起源于催化剂表面的"BO"物种(如B-O和B-OH等基团).氧化硼(B2O3)作为一种氧化气氛中化学性质稳定的含硼化合物,兼具丰富的"BO"位点,在反应条件下可形成多种结构以适用不同的化学环境,为制备高效的烷烃氧化脱氢催化剂提供了可能.在之前的研究中,多将B2O3浸渍在常规的TiO2,SiO2,A12O3等三维多孔载体上用于氧化脱氢反应.考虑到B2O3结构的灵活性和易于成键特性,需开发更为有效的合成策略,以提升B2O3催化剂在氧化脱氢反应中的活性和稳定性.本文采用静电纺丝技术合成了直径为100～150 nm的多孔掺硼二氧化硅纳米纤维(PBSN)用于低碳烷烃氧化脱氢反应.静电纺丝法合成的催化剂中硼物种在开放的氧化硅纤维骨架上均匀分散且稳定固载.一维纳米纤维结构不仅有利于扩散,且赋予催化剂在高重时空速(WHSV)条件下优异的烷烃氧化脱氢反应活性.在乙烷氧化脱氢反应中,当乙烷的转化率达到44.3％时,乙烯的选择性和产率分别为84％和44.2 μmol gcat-1 s-1.而在丙烷脱氢反应中,当丙烷转化率为19.2％时,总烯烃选择性及丙烯产率分别为90％和76.6 μmol gcat-1 s-1.在温度为545 ℃,丙烷WHSV高达84.6 h-1的条件下,催化剂保持长时间稳定.与其他负载型氧化硼催化剂相比,PBSN催化剂具有更高的烯烃选择性和稳定性.研究表明,在氧化硅负载B2O3催化剂催化丙烷氧化脱氢反应中,载体中Si-OH基团的存在可能会降低丙烯的选择性.瞬态分析和动力学实验表明,硼基催化剂催化烷烃氧化脱氢反应过程中O2的活化受到烷烃的影响.本文不仅为高效硼基催化剂的合成提供了新思路,也为深入理解该类催化剂上烷烃氧化脱氢反应过程提供了实验支撑.     

Production of gas mixtures with regulated ratios between ethylene and carbon monoxide by the gas-phase oxidative cracking of light alkanes

It was found that, in the gas-phase oxidative cracking of C₂-C₅ light alkanes, the ratio between ethylene and CO in the products depends on both the residence time in a reactor and the process temperature. This is due to a change in the contributions of product formation and/or consumption channels with increasing the conversion of the reactants. However, the hydrocarbon/oxygen ratio is the main parameter responsible for the limiting ratio between these products reached in the region of deep conversions of both of the reactants. The channels of formation and, correspondingly, the composition of the main products of oxidative cracking change on going from ethane to n-pentane. In this case, the ethylene: CO ratio increases due to an increase in the concentration of ethylene in the products as the number of carbon atoms in the initial alkane molecule is increased at a constant alkane: oxygen ratio. In the oxidative cracking of the C₂₊ alkane constituents of natural gases, it is necessary to consider the influence of methane, which inhibits the oxidative conversion of heavier alkanes in comparison with their oxidation in an inert gas atmosphere. This leads to a significant decrease in the conversion of oxygen and an increase in the ethylene: CO ratio in the reaction products.     

Vapor–liquid equilibrium of systems containing alcohols,water, carbon dioxide and hydrocarbons using SAFT

The statistical associating fluid theory (SAFT) equation of state is employed for the correlation and prediction of vapor–liquid equilibrium (VLE) of eighteen binary mixtures. These include water with methane, ethane, propane, butane, propylene, carbon dioxide, methanol, ethanol and ethylene glycol (EG), ethanol with ethane, propane, butane and propylene, methanol with methane, ethane and carbon dioxide and finally EG with methane and ethane. Moreover, vapor–liquid equilibrium for nine ternary systems was predicted. The systems are water/ethanol/alkane (ethane, propane, butane), water/ethanol/propylene, water/methanol/carbon dioxide, water/methanol/methane, water/methanol/ethane, water/EG/methane and water/EG/ethane. The results were found to be in satisfactory agreement with the experimental data except for the water/methanol/methane system for which the root mean square deviations for pressure were 60–68% when the methanol concentration in the liquid phase was 60 wt.%.     

Electron–proton and electron–methyl exchanges in pyrolysis of polyacetylene and polymethylacetylene

Pyrolysis of polyacetylene is marked by high yields of proton-enriched products methane, ethane, ethylene, propane, polypylene, butadiene, cyclopentadiene, 1,3-pentadiene, and toluene in total amounts exceeding benzene. The activation energies for their formation are low. Polyacetylene doped with AsF₅ and iodine produced these products in even higher yields of two to 17 times of undoped polymers. The dominant mechanism is thought to be random-chain scission followed by electron–proton exchange reactions. Polymethylacetylene is thermally less stable than polyacetylene. Pyrolysis gave mesitylene as the expected main product. However, as in the case of polyacetylene, large amounts of proton-enriched products were formed with moderate activation energies. (The yields of methane, propylene, and propane are nearly the same in the pyrolysis of polymethylacetylene as compared to that of polyacetylene at 923°K referenced to mesitylene and benzene, respectively.) By analogy, mechanisms involving both electron-proton and electron–methyl exchange reactions were proposed to account for the formation of all the pyrolyzates of polymethylacetylene. These reactions, not observed in the pyrolysis of polypropylene and polyisoprene, are attributable to the conjugated backbone permitting facile migrations of electrons, protons, and methyl groups.     

Gallium-containing catalysts for oxidative dehydrogenation of organic compounds

A method was developed for introducing gallium into Mg-Al hydrotalcites—precursors of oxide catalysts for oxidative dehydrogenation of alkanes. Samples of oxide catalysts were synthesized that contained gallium oxide and also oxides of magnesium, aluminum, chromium, vanadium, molybdenum, and niobium in various combinations. The catalytic properties of the produced catalysts were studied in the oxidative dehydrogenation of ethane, propane, isobutane, and hexane. It was established that the addition of gallium to catalysts increases the ethylene and propylene yields in the oxidative dehydrogenation of ethane and propane. New hydroxo salts with a layered structure of the hydrotalcite type were synthesized: ternary magnesium gallium aluminum hydroxonitrate of variable composition [Al_{1 ? n} Ga _n Mg _m (OH)_{3 + 2m ? 1}][NO₃ · nH₂O] and quaternary magnesium gallium chromium aluminum hydroxonitrate of the composition [AlGaCrMg_1.8(OH)_11.6][NO₃ · nH₂O]; these salts were found to be isostructural.     

低碳烷烃与二氧化碳催化转化研究进展

页岩气革命为低碳经济发展提供了重要契机.在低碳烷烃(甲烷和乙烷)催化转化过程中,以二氧化碳作为氧化剂参与反应,通过C-H键的选择性活化可将页岩气转化为优质化工原料——合成气和乙烯,是一种低碳烷烃转化与二氧化碳资源化利用的工艺路线.本文总结了近年来甲烷干重整与乙烷和二氧化碳反应中与C-H键活化相关的研究进展,分析了甲烷干...     

Regioselective alkane oxygenation with H2O2 catalyzed by titanosilicalite TS-1

Titanosilicalite TS-1 catalyses oxidation of light (methane, ethane, propane and n-butane) and normal higher (hexane, heptane, octane and nonane) alkanes to give the corresponding isomeric alcohols and ketones. The oxidation of higher alkanes proceeds in many cases with a unique regioselectivity. Thus, in the reaction with n-heptane the CH₂ groups in position 3 exhibited a reactivity 2.5 times higher than those of the other methylene groups. This selectivity can be enhanced if hexan-3-ol is added to the reaction mixture, the 3-CH₂/2-CH₂ ratio becoming 10. It is assumed that the unusual selectivity in the oxidation of n-heptane (and other higher alkanes) is due to steric hindrance in the catalyst cavity. As a result, the catalytically active species situated on the catalyst walls can only easily react with certain methylenes of the alkane, which is adsorbed in the cavity taking U-shape (hairpin) conformations.     

A density functional theory investigation on the mechanism and kinetics of dimethyl carbonate formation on Cu2O catalyst

A theoretical analysis about the mechanism and kinetics of dimethyl carbonate (DMC) formation via oxidative carbonylation of methanol on Cu₂O catalyst is explored using periodic density functional calculations, both in gas phase and in solvent. The effect of solvent is taken into account using the conductor‐like screening model. The calculated results show that CO insertion to methoxide species to produce monomethyl carbonate species is the rate‐determining step, the corresponding activation barrier is 161.9 kJ mol^?1. Then, monomethyl carbonate species reacts with additional methoxide to form DMC with an activation barrier of 98.8 kJ mol^?1, above reaction pathway mainly contributes to the formation of DMC. CO insertion to dimethoxide species to form DMC is also considered and analyzed, the corresponding activation barrier is 308.5 kJ mol^?1, suggesting that CO insertion to dimethoxide species is not competitive in dynamics in comparison with CO insertion to methoxide species. The solvent effects on CO insertion to methoxide species involving the activation barriers suggest that the rate‐determining step can be significantly affected by the solvent, 70.2 kJ mol^?1 in methanol and 63.9 kJ mol^?1 in water, which means that solvent effect can reduce the activation barrier of CO insertion to methoxide species and make the reaction of CO insertion to methoxide in solvents much easier than that in gas phase. Above calculated results can provide good theoretical guidance for the mechanism and kinetics of DMC formation and suggest that solvent effect can well improve the performance of DMC formation on Cu₂O catalyst in a liquid‐phase slurry. © 2012 Wiley Periodicals, Inc.     

Surface Chemistry and Catalytic Reactivity of Borocarbonitride in Oxidative Dehydrogenation of Propane

Borocarbonitride (BCN) materials are newly developed oxidative dehydrogenation catalysts that can efficiently convert alkanes to alkenes. However, BCN materials tend to form bulky B₂O₃ due to over-oxidation at the high reaction temperature, resulting in significant deactivation. Here, we report a series of super stable BCN nanosheets for the oxidative dehydrogenation of propane (ODHP) reaction. The catalytic performance of the BCN nanosheets can be easily regulated by changing the guanine dosage. The control experiment and structural characterization indicate that the introduction of a suitable amount of carbon could prevent the formation of excessive B₂O₃ from BCN materials and maintain the 2D skeleton at a high temperature of 520 °C. The best-performing catalyst BCN exhibits 81.9 % selectivity towards olefins with a stable propane conversion of 35.8 %, and the propene productivity reaches 16.2 mmol h⁻¹ g⁻¹, which is much better than hexagonal BN (h-BN) catalysts. Density functional theory calculation results show that the presence of dispersed rather than aggregated carbon atoms can significantly affect the electronic microenvironment of h-BN, thereby boosting the catalytic activity of BCN.     

Effect of methane co-feeding on the selectivity of ethylene produced from oxidative dehydrogenation of ethane with CO2 over a Ni-La/SiO2 catalyst

A Ni-La/SiO₂ catalyst was prepared through the incipient wetness impregnation method and tested in the oxidative dehydrogenation of ethane (ODHE) with CO₂. The fresh and used catalysts were characterized by XRD and SEM techniques. The Ni-La/SiO₂ catalyst exhibited catalytic activity for the oxidative dehydrogenation of ethane, but with low ethylene selectivity in the absence of methane. The selectivity to ethylene increased with increasing molar ratio of methane in the feed. The carbon deposited on the catalyst surface in the sole ODHE with CO₂ was mainly inert carbon, while much more filamentous carbon was formed in the presence of methane. The filamentous carbon was easy to be removed by CO₂, which might play a role in improving the conversion of ethane to ethylene. The introduction of methane might affect the equilibrium of the CO₂ reforming of ethane and the ODHE with CO₂. As a consequence, the synthesis gas produced from CO₂ reforming of methane partly inhibited the reaction of ethane and promoted the ODHE with CO₂, thus increasing the selectivity of ethylene.     

Laser-induced fluorescence monitoring of higher alkanes production from pure methane using non-oxidative processes

A novel method for the study of non-oxidative methane conversion process into higher value hydrocarbon and hydrogen has been invented. The method involves the multiphoton dissociation of methane under the influence of the high power pulsed ultraviolet laser radiation at 355 nm wavelength at room temperature (293 K) and standard pressure (1 atm). The products generated as a result of methane conversion like ethane, ethylene, propane, propylene and isobutane are analyzed using an online gas chromatograph while the other species such as CH, CH₂ and C₂H₂, atomic and molecular hydrogen are characterized by real-time laser-induced fluorescence technique for the first time. A typical 7% conversion of methane into ethane has been achieved using 80 mJ of laser irradiation at 355 nm. The important features of this method are that it is non-oxidative, does not require any catalyst, high temperatures or pressures, which is normally the case in conventional techniques for methane conversion.     

High pressure pyrolysis of n-heptane

Pyrolysis of n-heptane was investigated in a tubular reactor in the temperature range of 793–953 K and pressure range of 0.1–2.93 MPa. At all conditions, the main products were methane, ethylene, ethane, propylene, 1-butene, 1-pentene and 1-hexene. With an increase in pressure, the selectivities of hydrogen, methane, ethylene and propylene decreased and that of propane, n-butane and 1-butene increased. To explain the product distribution at high pressure, the Rice–Kossiakoff theory was modified by including the bimolecular reactions of alkyl radicals with the parent hydrocarbon. The initial product selectivities, calculated using the modified R–K mechanism, were in good agreement with the experimental selectivities. The overall kinetics of n-heptane pyrolysis was determined by non-linear analysis. The optimum values of the kinetic parameters at each pressure were determined by minimizing the difference between the calculated and experimental conversions. At each pressure, the reaction order was close to unity and the activation energy ranged between 209 and 219 kJ mol⁻¹.     

Mechanism and kinetics of the silane decomposition in the presence of acetylene and in the presence of olefins

Kinetic data and product studies are reported for the silane pyrolysis in the presence of olefins and acetylene. The kinetics of silane loss in the presence of acetylene was found to be identical to the initial gas phase silane decomposition step (SiH₄ + M → SiH₂ + H₂ + M) when corrected for pressure fall-off effects. This result and the absence of methane or ethane from the pyrolysis of SiH₄ in the presence of 1-butene or 1-pentene demonstrate that silyl radicals and H atoms are not involved in silane-olefin or silane-acetylene reactions. Qualitative aspects and kinetic data from the SiH₄ pyrolysis in the presence of propylene are in accord with propylsilane formation via propylsilylene formed by silylene addition to propylene.