C2 Hydrocarbons Research Articles

Binary alloys for electrocatalytic CO2 conversion to hydrocarbons and alcohols

Bimetallic alloys are expected to create superior catalytic performance that cannot be achieved on monometallic catalysts by regulations of both electronic and surface structures. In this work, the reaction mechanism and catalytic kinetics of electrochemical CO2 conversion on nine ⅠB group metal binary alloys are studied by using DFT computations. Various reduction products, from CO to CO-beyond products and from C1 to C2 hydrocarbons and alcohols, can be produced on different bimetallic catalysts by controlling their reaction kinetics of competing OH bond formation, CH bond formation, and CC coupling. Among all the studied binary alloys, Au-Ag alloys show enhanced CO production ability with respect to elemental Au and Ag. Cu1/4Au3/4 gives the best performance to catalyze CO2 conversion to methane and methanol as a result of simultaneously promoting CORR activity and suppressing HER side reaction. By adjusting the CORR pathway through COH* intermediate, the CC coupling barriers are lowered on Cu3/4Ag1/4 and Cu3/4Au1/4 catalysts, which deliver potential capacity to catalyze CO2 transformation to C2 products.

Single-step ethylene purification from ternary C2 hydrocarbon mixtures in a scalable metal–organic framework

Single-step purification of the ternary C2 hydrocarbon mixture to produce ethylene (C2H4) directly using adsorption-based technologies is desirable for reducing large energy consumption. However, it is challenging to develop an appropriate adsorbent, having preferential adsorption characteristics toward ethane (C2H6) and acetylene (C2H2) rather than C2H4 coupled with high adsorption capacity owing to their similar physicochemical properties. Herein, we present a highly stable, cheap, and scalable CAU-23 adsorbent, which enables single-step production of high-purity C2H4 (>99.9%) from the ternary C2 hydrocarbon mixture. CAU-23 exhibited higher uptake capacity of C2H6 (4.0 mmol g−1) and C2H2 (4.7 mmol g−1) compared to that of C2H4 (3.8 mmol g−1). Further, it showed the reasonable selectivity for both C2H6/C2H4 (1.54) and C2H2/C2H4 (1.5) with an equimolar binary mixture, indicating that the separation performance of CAU-23 is comparable to the benchmark porous materials for separating C2 ternary gas mixture. The breakthrough experiments demonstrated its capability to produce high-purity C2H4 (>99.9%) with various C2H6/C2H4/C2H2 compositions at 298 K and 1 bar with high recyclability. The origin of the separation performance was further explored by using computational simulations of the grand canonical Monte Carlo (GCMC) and density functional theory (DFT).

Mass transfer under distillation of positive, neutral, and negative system in the I.D. 0.3 m column packed with structured packing

The distillation of three binary test systems differing in the surface tension gradient along the column, namely: cyclohexane/n-heptane (negative), cyclohexane/toluene (neutral), n-hexane/cyclohexane (positive), has been performed under total reflux in the i.d. 0.3 m distillation column packed with MellapakPlus 452. Y structured packing. Although all constituents are C6 – C7 hydrocarbons with close physical properties in the gas phase, the resulting HETP differ by up to 20 %. Further analysis suggests that system negativity causes the approx. 30 % decrease of the effective interfacial area with respect to positive and neutral systems, which behave comparably. Indeed, observation of the distillation on the inclined plate in the IR spectra shows breakage of the negative system liquid films into rivulets, supporting the result.

Photocatalytic CO2 reduction to C1–C5 hydrocarbons using K2Fe2O4/g-C3N4 as coupling photocatalyst

A particularly interesting and difficult research topic is converting inexpensive and abundant single-carbon (C1) molecules to high-value multicarbon (C2+) molecules, especially to improve selectivity and conversion efficiency. Photocatalytic reduction offers a green technique for activating C1 molecules and controllable C–C coupling under mild and environmentally friendly conditions. This study synthesizes K2Fe2O4/g-C3N4 as a magnetic ferrite-containing photocatalyst for the C–C coupling of CO2 in the absence of a sacrificial agent. The findings significantly advance the photocatalytic conversion of CO2 into C2+ compounds, particularly CnH2n+2, CnH2n, and CnH2n−2 (n = 1–5), which are crucial in the chemical and energy industries. The photocatalyst, which has a remarkable selectivity to hydrocarbons (52% CH4, 48% C2+), was optimized to achieve the optimum progressive selective conversion from CO2 to CH4 and finally to C2+ hydrocarbons. The optimized K2Fe2O4/g-C3N4 shows an optimal CO2 to CH4 conversion rate of 130.96 μmol/g/h, which is 6.27 and 8.60 times the reaction rate constant of K2Fe2O4 and g-C3N4 as catalysts, respectively. It is speculated that this study will help understand the activation of CO2 in photocatalytic reduction and the highly selective production of hydrocarbons via the C–C coupling reaction.

Skeletal kinetic mechanism for predicting formation of non-fuel hydrocarbons and soot in ethylene flames – A CFD approach

Since existing reduced mechanisms of ethylene oxidation are either too large or lack of sufficient chemical reactions to describe aromatics formation, the study aims at developing a skeletal mechanism with extended predictive capability and lowered computational cost in computational fluid dynamics modeling of ethylene combustion. The newly assembled and refined kinetic mechanism composed of 664 species and 3582 reactions is minimized to 79 species and 538 reactions without empirically adjusting kinetic parameters. In the 1-D simulation for a premixed flame of ethylene, the ethylene-PAH mechanism generally well predicts experimental profiles of five hydrocarbons and nine aromatics. Integrated into a 2-D axisymmetric laminar finite-rate model, the ethylene-PAH mechanism reproduces experimental data of seven C2–C5 hydrocarbons, five aromatic hydrocarbons and soot in a diffusion flame of ethylene. In comparison with the 158-species (Narayanaswamy) mechanism, the newly proposed ethylene mechanism leads to a speedup of approximately 5.5 times in the 2-D laminar diffusion flame simulation and improved accuracy for predicting species formation in both premixed and nonpremixed flames. Moreover, we unveil the correlation between reaction pathways and intermediate formation from ethylene oxidation at the low temperature regime.

Degradation of trichloroethylene vapors by micrometric zero-valent Fe[sbnd]Cu and Fe[sbnd]Ni bimetals under partially saturated conditions

The degradation of trichloroethylene (TCE) vapors by zero-valent Iron-Copper (Fe–Cu) and Iron-Nickel (Fe–Ni) bimetals with 1%, 5% and 20% weight content (%wt) of Cu or Ni was tested in anaerobic batch vapor systems carried out at ambient room temperature (20 ± 2 °C) under partially saturated conditions. The concentrations of TCE and byproducts were determined at discrete reaction time intervals (4 h-7 days) by analyzing the headspace vapors. In all the experiments, up to 99.9% degradation of TCE in the gas phase was achieved after 2–4 days with zero-order TCE degradation kinetic constants in the range of 134–332 g mair−3d−1. Fe–Ni showed a higher reactivity towards TCE vapors compared to Fe–Cu, with up to 99.9% TCE dechlorination after 2 days of reaction, i.e., significantly higher than zero-valent iron alone that in previous studies was found to achieve comparable TCE degradation after minimum 2 weeks of reaction. The only detectable byproducts of the reactions were C3–C6 hydrocarbons. Neither vinyl chloride or dichloroethylene peaks were detected in the tested conditions above their method quantification limits that were in the order of 0.01 g mair−3. In view of using the tested bimetals in horizontal permeable reactive barriers (HPRBs) placed in the unsaturated zone to treat chlorinated solvent vapors emitted from contaminated groundwater, the experimental results obtained were integrated into a simple analytical model to simulate the reactive transport of vapors through the barrier. It was found that an HPRB of 20 cm could be potentially effective to ensure TCE vapors reduction.

Non-oxidative coupling of methane over Mo-doped CeO2 catalysts: Understanding surface and gas-phase processes

Direct catalytic non-oxidative coupling is a promising route for the valorization of abundant methane. Understanding the mechanism is difficult because reactions at the surface of the catalyst and in the gas phase via radicals are important at the high temperatures employed. Herein, a series of Mo-doped CeO2 samples with isolated Mo sites were prepared by flame spray pyrolysis method and screened for their performance in non-oxidative coupling of methane. The selectivity to value-added C2 hydrocarbons (ethane and ethylene) among gas-phase products could reach 98%. During the reaction, the isolated Mo-oxo species in the as-prepared catalyst are reduced and convert into Mo (oxy-)carbide species, which act as the active sites for methane activation. By varying the available catalyst-free gas volume along the length of the reactor, we studied the contribution of gas-phase reactions in the formation of different products. Ethane is the primary product of non-oxidative methane coupling and, at least, a part of ethylene and most of benzene is formed through gas-phase chemistry. This work provides insights into the design of efficient catalysts for non-oxidative coupling of methane and highlights the importance of reducing the free volume in the reactor to limit secondary gas-phase reactions.

Non-oxidative conversion of methane into various petrochemical grades over tunable tri-metallic Fe-W-Mo/HZSM-5 catalyst systems

Most mono-metallic catalysts applied in non-oxidative conversion of methane exhibit low catalyst activity and limited selectivity towards useful petrochemicals. In this study, a series of thermally stable and tunable 5.4 wt% metal/support Fe-W-Mo/HZSM-5 catalyst systems were synthesized, characterized, and applied in non-oxidative conversion of methane in a custom-made stainless-steel reactor at various process conditions. Analysis of products from the reactor was done using Shimadzu 2014 gas chromatograph. Varying the amount of Fe, W, and Mo on HZSM-5 greatly influenced catalyst activity in terms of methane conversion and product distribution. When the quantities of Fe and W were increased to 2.25 wt% each and the quantity of molybdenum reduced to 0.9 wt% in the overall 5.4 wt% metal/ HZSM-5 catalyst, the resultant catalyst system became most active in methane conversion (17.4%) at 800 °C. Reducing the quantity of Fe and W each to 1.35 wt% and increasing Mo to 2.7 wt% in the overall 5.4 wt% catalyst, the resultant catalyst system became less selective towards C2 hydrocarbons and coke, but highly selective towards xylene and benzene. Therefore, this study demonstrates that varying metal loading presents an opportunity to tune the 5.4 wt% binary Fe, W, and Mo on HZSM-5 to achieve desired methane conversion and product distribution.

Frontispiece: The Adsorptive Separation of Ethylene from C2 Hydrocarbons by Metal‐Organic Frameworks

Ethylene is a critical chemical raw material widely used in manufacturing and petrochemical fields. The adsorptive separation of ethylene from C2 hydrocarbon mixtures using metal-organic frameworks to replace traditional high-energy separation technologies is essential but challenging. This review highlights the C2hydrocarbon separation realized with MOF adsorbents. For more details, see the Review by W. Xie, L. Yang, J. Zhang, and Y. Zhao (DOI: 10.1002/chem.202300158).

Metal confined in metal‐organic framework‐based mixed matrix membranes for efficient butadiene recognition separation

AbstractThe efficient separation of butadiene (1,3‐C4H6) from C4 hydrocarbons is a critical step in petrochemical processes. However, the traditional cryogenic distillation suffers from energy‐intensity and serious environmental stress, necessitating the development of alternative technologies for efficient 1,3‐C4H6 separation. Herein, a 1,3‐C4H6 recognition mixed matrix membrane is reported via incorporating metal copper encapsulated a metal‐organic framework (CuBTC@Cu) into elastic poly(dimethylsiloxane) (PDMS). The resulting CuBTC@Cu/PDMS membrane can efficient separate 1,3‐C4H6 from various C4 hydrocarbons including 1,3‐C4H6/n‐C4H8, 1,3‐C4H6/iso‐C4H8, 1,3‐C4H6/n‐C4H10 and 1,3‐C4H6/iso‐C4H10, yielding superior selectivity of 5.11, 6.35, 4.78, and 10.30, respectively, with 1,3‐C4H6 permeability of 53240 Barrer. Notably, the appropriate π‐complexation interaction between butadiene molecules and CuBTC@Cu as well as suitable transmission channel size enable the membrane only permeable to 1,3‐C4H6 and block the permeation of other C4 hydrocarbons, showing a unique 1,3‐C4H6 recognition behavior in membrane separation. The concept of affinity‐relying separation combining molecular sieving would open a new direction for designing gas membranes for efficient light hydrocarbon separations.

Experimental study on n-hexane pyrolysis initiated by 1-nitropropane in a low-pressure flow reactor

In order to investigate the species pool and primary channels of initiated pyrolysis of n-hexane, the low-pressure (30 Torr, 4.0 kPa) flow reactor pyrolysis of n-hexane initiated by 5% 1-nitropropane (1-NP) was studied experimentally in a wide range of temperature from 623 K to 1223 K. Combined with synchrotron vacuum ultraviolet (SVUV) photoionization mass spectra scanned at photon energies ranging from 9.0 to 14.7 eV and near-threshold photoionization efficiency (PIE) spectra, 29 pyrolysis species, covering C1–C6 hydrocarbons and several pyrolysis species containing O or N atoms, were identified. Based on the ion signal intensities of the visible peaks in the mass spectra, the mole fraction profiles of all the experimental species were evaluated. The experimental results suggested that the initial pyrolysis temperature of n-hexane was reduced by approximately 275–325 K. On the basis of the mole fraction profiles and the initial formation temperatures reported in this work and rate coefficients proposed in previous studies, the 1-NP-initiated pyrolysis mechanisms of n-hexane were discussed. It was suggested that n-hexane was dominantly consumed by the H-abstraction reactions by the attack of OH radical in this work. The 1-NP-initiated pyrolysis of n-hexane mainly proceeded via reactions to produce C3H6 + C3H7, or 1-C4H8 + C2H5, or 1-C5H10 + CH3.

Solar Hydrocarbons: Single-Step, Atmospheric-Pressure Synthesis of C2 -C4 Alkanes and Alkenes from CO2.

Cobalt ferrite (CoFe2 O4 ) spinel has been found to produce C2 -C4 hydrocarbons in a single-step, ambient-pressure, photocatalytic hydrogenation of CO2 with a rate of 1.1 mmol g-1 h-1 , selectivity of 29.8 % and conversion yield of 12.9 %. On stream the CoFe2 O4 reconstructs to a CoFe-CoFe2 O4 alloy-spinel nanocomposite which facilitates the light-assisted transformation of CO2 to CO and hydrogenation of the CO to C2 -C4 hydrocarbons. Promising results obtained from a laboratory demonstrator bode well for the development of a solar hydrocarbon pilot refinery.

Solar Hydrocarbons: Single‐Step, Atmospheric‐Pressure Synthesis of C2−C4 Alkanes and Alkenes from CO2

AbstractCobalt ferrite (CoFe2O4) spinel has been found to produce C2−C4 hydrocarbons in a single‐step, ambient‐pressure, photocatalytic hydrogenation of CO2 with a rate of 1.1 mmol g−1 h−1, selectivity of 29.8 % and conversion yield of 12.9 %. On stream the CoFe2O4 reconstructs to a CoFe−CoFe2O4 alloy‐spinel nanocomposite which facilitates the light‐assisted transformation of CO2 to CO and hydrogenation of the CO to C2−C4 hydrocarbons. Promising results obtained from a laboratory demonstrator bode well for the development of a solar hydrocarbon pilot refinery.

La0.5Ce0.5O1.75-Catalytic Layer for Methane Conversion into C2 Products Using Solid Oxide Fuel Cell

Methane (CH4), the major constituent of natural gas and biogas, is an abundant source to obtain value-added hydrocarbons. The oxidative coupling of methane (OCM) is a direct catalytic route to convert CH4 towards C2 hydrocarbons, ethane (C2H6) and ethylene (C2H4). Using a solid oxide fuel cell (SOFC) is a strategy to overcome some challenges of fixed-bed catalytic reactors. In this context, we have studied the La0.5Ce0.5O1.75 (LCO) oxide as a catalytic layer in a SOFC for methane conversion to C2. The activity test was carried out at different O2-/CH4 ratios, varying the anode gas composition, and applied currents.

Fine-Tuning MOFs with Amino Group for One-Step Ethylene Purification from the C2 Hydrocarbon Mixture.

Due to the similar kinetic diameters of C2H2, C2H4, and C2H6, one-step purification of C2H4 from a ternary C2H2/C2H4/C2H6 mixture by adsorption separation is still a challenge. Based on a C2H6-trapping platform and crystal engineering strategy, the N atom and amino group were introduced into NTUniv-58 and NTUniv-59, respectively. Gas adsorption testing of NTUniv-58 showed that both the C2H2 and C2H4 uptake capacities and the C2H2/C2H4 separation ability were boosted compared with the original platform. However, the C2H4 uptake value exceeds the C2H6 adsorption data. For NTUniv-59, the C2H2 uptake at low pressure increased and the C2H4 uptake decreased; thus, the C2H2/C2H4 selectivity was enhanced and the one-step purification of C2H4 from a ternary C2H2/C2H4/C2H6 mixture was realized, which was supported by the enthalpy of adsorption (Qst) and breakthrough testing. Grand canonical monte carlo (GCMC) simulation indicated that the preference for C2H2 over C2H4 originates from multiple hydrogen-bonding interactions between amino groups and C2H2 molecules.

Vapor-liquid-liquid equilibria of binary and ternary aqueous systems containing C6-hydrocarbons

BackgroundTo develop process for separating water and C6-hydrocarbons, the vapor-liquid-liquid equilibrium (VLLE) data of the related mixtures are fundamentally important. MethodsThe isothermal vapor-liquid-liquid equilibrium (VLLE) data were measured for the binary and the ternary aqueous mixtures containing C6 hydrocarbons (benzene, n-hexane, and cyclohexane) at temperatures from 343 K to 383 K by using a modified static-type apparatus equipped with a visual cell. The VLLE data were correlated with the NRTL-HOC and the UNIQUAC-HOC models, respectively. Significant findingsIn addition to literature data, the experimental results of the binary systems reveal the temperature and molecular structure effects on the saturated compositions in three coexistent phases. The experimental ternary VLLE properties form a basis to verify the prediction by using the determined parameters of constituent binaries and also to modify the values of the binary parameters for improving the ternary VLLE calculations. The findings of this study offer new phase equilibria data for model development and process design for the related separation units.

Selective peroxidation of isobutane with molecular oxygen over molybdenum oxide catalyst for direct synthesis of di-tert-butyl peroxide

The direct conversion of isobutane to high value-added chemicals is important for utilization of C4 hydrocarbon resources. This work proposed a novel route of isobutane peroxidation with molecular oxygen for green synthesis of di-tert-butyl peroxide (DTBP), widely used as polymerization initiating/crosslinking agent and diesel additive. For the first time, MoO3 was demonstrated as selective catalyst for isobutane peroxidation to DTBP. The results indicated that, the reactivity depended on the oxygen adsorption capacity of MoO3 catalyst, and the selectivity to DTBP was determined by the amount of surface Mo = O sites. During the reaction, tert-butyl hydroperoxide (TBHP) was generated from isobutane peroxidation as intermediate product, and subsequently converted to DTBP on Mo = O active sites. Under the optimized conditions, a high oxygen conversion (>95%) and stable product selectivities (DTBP ∼ 20 wt%, TBHP ∼ 13 wt%) were obtained during continuous catalyst re-usage runs. This work provides an environmental route for both C4 hydrocarbon utilization and DTBP production.

The Effect of Support on Catalytic Performance of Ni-Doped Mo Carbide Catalysts in 2-Methylfuran Production

Ni-doped Mo carbide with Ni/Mo atomic ratio of 0.1 was supported on SiO2, Al2O3, and a porous carbon material (C), using a combination of gel combustion and impregnation methods. XRD, XPS, XANES, and EXAFS analyses indicated that the main active sites for the supported catalysts were metallic nickel and Mo carbides. The catalysts were evaluated in furfural hydrogenation to produce 2-methylfuran (2-MF) in a batch reactor at 150 °C under a hydrogen pressure of 6.0 MPa. The carbide materials supported on C showed the highest activity and selectivity towards 2-MF formation, with a yield of 61 mol.% after 3.5 h. Using furfuryl alcohol as the feedstock instead of furfural resulted in a high selectivity to 2-MF production. The carbon-supported sample was tested in a fixed-bed reactor at 160–260 °C with a pressure of 5.0 MPa in the hydrogenation of furfuryl alcohol, leading to the formation of up to 82 mol.% of 2-MF at 160–200 °C. The higher temperature (260 °C) resulted in the formation of C5 alcohols and hydrocarbons, while the hydrogenation of furfural at the same temperature led to 100 mol.% conversion, and up to an 86 mol.% yield of 2-MF.

Non-Thermal Plasma Pyrolysis of Fuel Oil in the Liquid Phase

A pulsed plasma pyrolysis reactor with an efficient control system was designed for fuel oil processing. Non-thermal plasma pyrolysis was carried out in the liquid phase at low temperatures (not higher than 100 °C) in a 300 cm3 reactor without additional reagents or catalysts. The main process parameters and characteristics of non-thermal plasma fuel oil products were investigated within the DC source voltage range of 300–700 V. An increase in the energy of pulsed discharges led to an increase in the productivity of the plasma pyrolysis process and the yield of hydrogen but reduced the yield of acetylene and ethylene. The resulting gas consisted predominantly of hydrogen (46.5–50.0 mol%), acetylene (28.8–34.3 mol%), ethylene (7.6–8.6 mol%), methane (4.2–6.2 mol%), and C3–C5 hydrocarbons. The solid-phase products were in the form of disordered graphite and multilayer nanotubes.

Ultramicroporous Metal-Organic Framework with Inert Pore Surfaces for Inversed Separation of Ethylene from C2 Hydrocarbons Mixtures.

The achievement of direct C2H4 separation from C2 hydrocarbons is very challenging in the petrochemical industry due to their similar molecular sizes, boiling points, and physicochemical properties. In this work, a nonpolar/inert ultramicroporous metal-organic framework (MOF), [Co3(μ3-OH)(tipa)(bpy)1.5]·3DMF·6H2O (1), with stand-alone one-dimensional square tubular channels was successfully constructed, its pore enriched with plenty of aromatic rings causing nonpolar/inert pore surfaces. The MOF shows preferential adsorption of C2H6 compared to C2H4 and C2H2 in the low-pressure region, which is further verified by adsorption heats and selectivities. The C2H4 separation potential in one step for binary C2H6/C2H4 (50/50 and 10/90) and ternary C2H4/C2H6/C2H2 (89/10/1) is also examined by transient breakthrough simulations. Moreover, grand canonical Monte Carlo simulations demonstrate that the unique reversed adsorption mechanism is due to the shortest and most number of C-H···π interactions between C2H6 and the framework.