Pure Acetylene Research Articles

Reverse Separation of Carbon Dioxide and Acetylene in Two Isostructural Copper Pyridine‐Carboxylate Frameworks

AbstractSeparating acetylene from carbon dioxide is important but highly challenging due to their similar molecular shapes and physical properties. Adsorptive separation of carbon dioxide from acetylene can directly produce pure acetylene but is hardly realized because of relatively polarizable acetylene binds more strongly. Here, we reverse the CO2 and C2H2 separation by adjusting the pore structures in two isoreticular ultramicroporous metal–organic frameworks (MOFs). Under ambient conditions, copper isonicotinate (Cu(ina)2), with relatively large pore channels shows C2H2‐selective adsorption with a C2H2/CO2 selectivity of 3.4, whereas its smaller‐pore analogue, copper quinoline‐5‐carboxylate (Cu(Qc)2) shows an inverse CO2/C2H2 selectivity of 5.6. Cu(Qc)2 shows compact pore space that well matches the optimal orientation of CO2 but is not compatible for C2H2. Neutron powder diffraction experiments confirmed that CO2 molecules adopt preferential orientation along the pore channels during adsorption binding, whereas C2H2 molecules bind in an opposite fashion with distorted configurations due to their opposite quadrupole moments. Dynamic breakthrough experiments have validated the separation performance of Cu(Qc)2 for CO2/C2H2 separation.

Effect of high aspect ratio additives on microstructural and mass transport properties of the microporous layer in a proton exchange membrane fuel cell

Tuning up transport properties of the microporous layer is an effective way to enhance mass transport in a proton exchange membrane fuel cell. The incorporation of non-spherical conductive additives in the conventional microporous layer can modify its pore structure. In this study, 5, 20, and 50 wt.% of two high aspect ratio additives, multiwall carbon nanotube and graphene nanoplatelet, are mixed with the acetylene-black carbon to systematically study their impact on ink and the final diffusion media properties. Using a bottom-up approach, the rheological properties of the ink are correlated to the mass transport resistance in the diffusion media. The ink with additives exhibits rheological properties of a less compact microstructure with large agglomerates. Whereas, a more compact agglomerated network is observed from the ink with pure acetylene black carbon nanoparticles. Graphene nanoplatelet has a dominating effect on the surface quality of the microporous layers due to its two-dimensional structure. The test results show that the microstructure formed by the synergy of acetylene black and additives can enhance ohmic and mass transport performance. 20 wt.% of the additive loading is found to be optimal and multiwall carbon nanotube shows the best fuel cell performance.

A Comparative Study of a:SiCN:H Thin Films Fabricated with Acetylene and Methane

In this paper we present a comparative study of the properties of amorphous hydrogenated silicon carbonitride (SiCN:H) thin films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD). The elemental composition, growth rate, density, and refractive index values of the SiCN:H thin films were analyzed as functions of flow rates of pure acetylene (C2H2) and methane (CH4) hydrocarbon precursors. The mechanical properties were studied with nanoindentation measurements to compare hardness and Young’s modulus of the SiCN:H thin films deposited with different carbon sources. Variable angle spectroscopic ellipsometry (VASE), elastic recoil detection (ERD), and Rutherford backscattering spectrometry (RBS) were used to determine thin film properties. Higher carbon content in the thin films was achieved by acetylene compared to methane at the same flow rate due to its lower ionization energy during the deposition. Infrared (IR) absorption spectra of the thin films deposited with acetylene precursor were analyzed to determine the correlation between the hydrocarbon flow rate and the intra-molecular bond intensities in the thin films. We found that the major contribution to the hardness comes from hydrogen (H) in the SiCN matrix which makes the films less dense. Carbon improves the hardness, however, H introduced by the hydrocarbon reduces the mechanical strength.

Two Solvent-Induced In(III)-Based Metal-Organic Frameworks with Controllable Topology Performing High-Efficiency Separation of C2H2/CH4 and CO2/CH4.

For pure acetylene manufacturing and natural gas purification, the development of porous materials displaying highly selective C2H2/CH4 and CO2/CH4 separation is greatly important but remains a major challenge. In this work, a plausible strategy involving solvent-induced effects and using the flexibility of the ligand conformation to make two In(III) metal-organic frameworks (MOFs) is developed, showing topological diversity and different stability. The X-shaped tetracarboxylic ligand H4TPTA ([1,1':3',1″-terphenyl]-4,4',4″,6'-tetracarboxylic acid) was selected to construct two new heteroid In MOFs, namely, {[CH3NH3][In(TPTA)]·2(NMF)} (MOF 1) and {[In2(TPTA)(OH)2]·2(H2O)·(DMF)} (MOF 2). MOF 1 is a (4, 4)-connected net showing a pts topology with a large channel that is not conducive to fine gas separation. By contrast, with the reduction of SBU from uninucleated In to an {In-OH-In}n chain, MOF 2 has a (4, 6)-connected net with the fsc topology with an ∼5 Å suitable micropore to confine matching small gas. The permanent porosity of MOF 2 leads to the preferential adsorption of C2H2 over CO2 with superior C2H2/CH4 (332.3) and CO2/CH4 (31.2) separation selectivities. Meanwhile, the cycling dynamic breakthrough experiments showed that the high-purity C2H2 (>99.8%) capture capacities of MOF 2 were >1.92 mmol g-1 from a binary C2H2/CH4 mixture, and its separation factor reached 10.

Tunable acetylene sorption by flexible catenated metal-organic frameworks.

The safe storage of flammable gases, such as acetylene, is essential for current industrial purposes. However, the narrow pressure (P) and temperature range required for the industrial use of pure acetylene (100 < P < 200 kPa at 298 K) and its explosive behaviour at higher pressures make its storage and release challenging. Flexible metal-organic frameworks that exhibit a gated adsorption/desorption behaviour-in which guest uptake and release occur above threshold pressures, usually accompanied by framework deformations-have shown promise as storage adsorbents. Herein, the pressures for gas uptake and release of a series of zinc-based mixed-ligand catenated metal-organic frameworks were controlled by decorating its ligands with two different functional groups and changing their ratio. This affects the deformation energy of the framework, which in turn controls the gated behaviour. The materials offer good performances for acetylene storage with a usable capacity of ~90 v/v (77% of the overall amount) at 298 K and under a practical pressure range (100-150 kPa).

Influence of Flow and Pressure of Carburising Mixture on Low-Pressure Carburising Process Efficiency

Low-pressure carburising (LPC) of steel is an industrially accepted method for improving the properties of a steel surface. LPC is environmentally friendly, does not cause intergranular oxidation and consumes less energy. Its effectiveness depends on the correct choice of process inputs. This paper aims to determine the effect of this type of carboniferous gas, pressure and flow rate on the efficiency of carbon transfer to the surface layer under low-pressure carburisation. A total of 40 disks of 16MnCr5 steel were carburised using pure acetylene or a mixture of acetylene, ethylene and hydrogen as a carboniferous gas, pressures of 2 or 6 hPa and two gas flow rates. The specimens were gravimetrically tested for the increase in the mass of carbon in the carburised layer. The results were analysed with U Mann–Whitney analysis and t-Student test. It was evidenced that carburising with pure acetylene resulted in a higher increase in carbon mass than carburising with the mixture (p &lt; 0.05). Pressure and gas flow rates are important for carburising efficiency (p &lt; 0.05).

Metal phthalocyanines as efficient electrocatalysts for acetylene semihydrogenation

• Cobalt phthalocyanine was developed as an electrocatalyst for acetylene semihydrogenation. • Cobalt phthalocyanine exhibited an ethylene current density of 150.8 mA cm −2 and a FE of ∼96%. • Co sites in cobalt phthalocyanine facilitate acetylene adsorption and ethylene desorption. • Under ethylene-rich flow, CoPc manifested a high conversion rate, TOF and space velocity. Compared to their booming thermocatalytic counterparts, electrocatalytic acetylene semihydrogenation still remain stagnant owing to its low activity and poor selectivity. Here, we first explore metal phthalocyanines (M(Pc)s) featuring a defined metal coordination environment as electrocatalysts for acetylene semihydrogenation. Consequently, CoPc exhibits an ethylene current density of 150.8 mA cm −2 and a ∼ 96% ethylene faradaic efficiency under a pure acetylene stream. In-situ electrochemical Raman and theoretical calculations demonstrate that CoPc favors acetylene absorption/hydrogenation processes. Even for crude ethylene containing 1 × 10 4 ppm acetylene, CoPc manifests a ∼ 99.5% acetylene conversion, a high turnover frequency of 4.86 × 10 –3 s −1 and a large space velocity of 2.4 × 10 5 ml·g cat –1 ·h −1 , outperforming those for reported thermocatalysts. This work facilitates the development of electrocatalytic acetylene semihydrogenation and promises alternatives to traditional thermocatalytic processes.

Functional Aqueous Zinc-Acetylene Batteries for Electricity Generation and Electrochemical Acetylene Reduction to Ethylene.

The available processes for removing acetylene impurities from crude ethylene are tremendously energy-intensive. Herein, we demonstrate a novel aqueous Zn-C2 H2 battery, which not only switches energy-consuming acetylene removal to electricity generation, but also reduces acetylene to ethylene through a unique discharge mechanism: C2 H2 +Zn+H2 O→C2 H4 +ZnO. Under a pure acetylene stream, this Zn-C2 H2 battery exhibits an open circuit potential of 1.14 V and a peak power density of 2.2 mW cm-2 , which exceed those of reported Zn-CO2 batteries. Even for simulated crude ethylene, the Zn-C2 H2 battery manifests an acetylene conversion of 99.97 % and continuously produces polymer-grade ethylene with only ≈3 ppm acetylene during a long-term discharge operation. Such a functional battery is universally appliable for reducing other alkynes and generating electricity. Therefore, this work provides an effective strategy for green ethylene purification and the design of functional batteries.

Functional Aqueous Zinc–Acetylene Batteries for Electricity Generation and Electrochemical Acetylene Reduction to Ethylene

AbstractThe available processes for removing acetylene impurities from crude ethylene are tremendously energy‐intensive. Herein, we demonstrate a novel aqueous Zn–C2H2 battery, which not only switches energy‐consuming acetylene removal to electricity generation, but also reduces acetylene to ethylene through a unique discharge mechanism: C2H2+Zn+H2O→C2H4+ZnO. Under a pure acetylene stream, this Zn–C2H2 battery exhibits an open circuit potential of 1.14 V and a peak power density of 2.2 mW cm−2, which exceed those of reported Zn–CO2 batteries. Even for simulated crude ethylene, the Zn–C2H2 battery manifests an acetylene conversion of 99.97 % and continuously produces polymer‐grade ethylene with only ≈3 ppm acetylene during a long‐term discharge operation. Such a functional battery is universally appliable for reducing other alkynes and generating electricity. Therefore, this work provides an effective strategy for green ethylene purification and the design of functional batteries.

Efficient electrocatalytic acetylene semihydrogenation by electron\u2013rich metal sites in N\u2013heterocyclic carbene metal complexes

Electrocatalytic acetylene semihydrogenation is a promising alternative to thermocatalytic acetylene hydrogenation due to its environmental benignity and economic efficiency, but its performance is far below that of the thermocatalytic reaction because of strong competition from side reactions, including hydrogen evolution, overhydrogenation and carbon–carbon coupling reactions. We develop N–heterocyclic carbene–metal complexes, with electron–rich metal centers owing to the strongly σ–donating N–heterocyclic carbene ligands, as electrocatalysts for selective acetylene semihydrogenation. Experimental and theoretical investigations reveal that the copper sites in N–heterocyclic carbene–copper facilitate the absorption of electrophilic acetylene and the desorption of nucleophilic ethylene, ultimately suppressing the side reactions during electrocatalytic acetylene semihydrogenation, and exhibit superior semihydrogenation performance, with faradaic efficiencies of ≥98 % under pure acetylene flow. Even in a crude ethylene feed containing 1 % acetylene (1 × 104 ppm), N–heterocyclic carbene–copper affords a specific selectivity of >99 % during a 100–h stability test, continuous ethylene production with only ~30 ppm acetylene, a large space velocity of up to 9.6 × 105 mL·gcat−1·h−1, and a turnover frequency of 2.1 × 10−2 s−1, dramatically outperforming currently reported thermocatalysts.

Highly Selective Adsorption of Carbon Dioxide over Acetylene in an Ultramicroporous Metal-Organic Framework.

Separating carbon dioxide from fuel gases like hydrocarbons by physical adsorbents is industrially important and more energy-efficient than traditional liquid extraction or cryogenic distillation methods. It is very important while very challenging to develop CO2 -selective adsorbents, considering CO2 is less polarizable than light hydrocarbon molecules, particularly those simultaneously with almost identical molecular dimensions and physical properties, such as acetylene. Herein, an ultramicroporous metal-organic framework constructed from copper(II) and 5-fluoropyrimidin-2-olate, termed Cu-F-pymo, is carefully studied under different activations for inverse separation of CO2 from C2 H2 . The partially desolvated Cu-F-pymo can exclusively capture CO2 over C2 H2 with very high selectivity exceeding 105 under ambient conditions, the highest ever reported. Sorption experiments and modeling studies reveal that such molecular sieving effect is attributed to the suppression of C2 H2 adsorption from the blockage of the preferential sites for C2 H2 by residual water molecules. The inverse separation is further confirmed by column breakthrough studies given that highly pure acetylene (>99.9%) can be directly harvested from the gas mixture. Cu-F-pymo also shows remarkable stability under harsh conditions.

Selective capture of carbon dioxide from hydrocarbons using a metal-organic framework

Efficient and sustainable methods for carbon dioxide capture are highly sought after. Mature technologies involve chemical reactions that absorb CO2, but they have many drawbacks. Energy-efficient alternatives may be realised by porous physisorbents with void spaces that are complementary in size and electrostatic potential to molecular CO2. Here, we present a robust, recyclable and inexpensive adsorbent termed MUF-16. This metal-organic framework captures CO2 with a high affinity in its one-dimensional channels, as determined by adsorption isotherms, X-ray crystallography and density-functional theory calculations. Its low affinity for other competing gases delivers high selectivity for the adsorption of CO2 over methane, acetylene, ethylene, ethane, propylene and propane. For equimolar mixtures of CO2/CH4 and CO2/C2H2, the selectivity is 6690 and 510, respectively. Breakthrough gas separations under dynamic conditions benefit from short time lags in the elution of the weakly-adsorbed component to deliver high-purity hydrocarbon products, including pure methane and acetylene.

Unraveling synergistic effects on pyrolysis reactivity and indene formation in co-pyrolysis of toluene and acetylene

Synergistic effect is one of the most important interactions between different fuel components and is very influential on combustion characteristics such as polycyclic aromatic hydrocarbon (PAH) and soot emissions, pyrolysis/oxidation reactivity and so on. In order to explore the potential synergistic effects between aromatics and open-chained fuels, pure toluene pyrolysis, pure acetylene pyrolysis and co-pyrolysis of toluene and acetylene were investigated in a flow reactor using synchrotron vacuum ultraviolet photoionization mass spectrometry at 1057–1340 K and 1 atm. Mole fractions of fuels and key products including both stable and reactive ones were evaluated. The experimental results indicate that in the co-pyrolysis of toluene and acetylene, the decomposition of both fuels is greatly stimulated and the formation of indene is significantly improved compared to the pyrolysis of pure toluene and pure acetylene. As a result, remarkable synergistic effects can be observed on pyrolysis reactivity and indene formation. A kinetic model for co-pyrolysis of toluene and acetylene was updated from our previous toluene model and was validated against the new data. The modeling analysis reveals that the unimolecular decomposition reaction of toluene producing benzyl radical and H atom is the chain-initiation reaction in both pure toluene pyrolysis and co-pyrolysis of toluene and acetylene. In the pure toluene pyrolysis, the self-combination reaction forming bibenzyl dominates the consumption of benzyl radical and results in strong chain termination. In the co-pyrolysis of toluene and acetylene, instead of the chain-termination reaction, a circulating reaction sequence initiating from the reaction between benzyl radical and acetylene continuously converts toluene and acetylene to indene and H2, which can explain the observed synergistic effects on pyrolysis reactivity and indene formation in the co-pyrolysis of toluene and acetylene.

Improving the synthetic efficiency of single-wall carbon nanotube forests using a gas-analysis-designed mixed carbon feedstock

A high efficiency, mixed gas carbon feedstock was designed by gas analysis of ethylene-based single-wall carbon nanotube (SWCNT) chemical vapor deposition. Gas analysis identified acetylene and 1,3-butadiene as the primary contributors to CNT growth based on the observed correlation between the decrease in respective concentrations and the CNT growth rate. In addition, a semi-empirical chemical kinetics growth model was developed which further verified that the experimentally observed decrease of acetylene and 1,3-butadiene were due to their contribution to the synthesis reaction. Using these results, we designed a mixed carbon feedstock of acetylene and 1,3-butadiene at a ratio of 2:5 which efficiently grew high purity and selectivity SWCNTs at a high growth efficiency, four-times that of pure ethylene and two-times that of pure acetylene. The combination of acetylene and 1,3-butadiene proved synergetic due to the inherent differences in reactivity and hydrogen content through “carbon scavenging” by the hydrogen byproducts. As a result, unlike single-source carbon feedstocks, the total carbon feedstock concentration could be increased, which resulted in increasing yields without saturating the catalysts. Our results demonstrate the complementary roles of carbon feedstocks in developing high efficiency synthesis, which is important for the advancement of the synthesis of long and clean CNTs.

Preparation of Aniline-Based Nitrogen-Containing Diamond-Like Carbon Films with Low Electrical Resistivity

The intrinsic high electrical resistivity of diamond-like carbon (DLC) films prevents their use in certain applications. The addition of metal or nitrogen during the preparation of the DLC films leads to a lower resistivity of the films, but it is usually accompanied by several disadvantages, such as a potential contamination risk for surfaces in contact with the film, a limited area that can be coated, deteriorated mechanical properties or low deposition rates of the films. To avoid these problems, DLC films have been prepared by plasma source ion implantation using aniline as a precursor gas, either in pure form or mixed with acetylene. The nitrogen from the precursor aniline is incorporated into the DLC films, leading to a reduced electrical resistivity. Film properties such as hardness, surface roughness and friction coefficient are nearly unchanged as compared to an additionally prepared reference sample, which was deposited using only pure acetylene as precursor gas.

Accelerated C2H2/CO2 Separation by a Se-Functionalized Porous Coordination Polymer with Low Binding Energy.

High-quality pure acetylene (C2H2) is a kind of crucial starting material for various value-added products. However, selective capture of C2H2 from the main impurity of CO2 via porous absorbents is a great challenge, as they possess extremely similar kinetic diameters and boiling points, as well as the explosive and reactive properties of C2H2. Herein, we report a porous coordination polymer (PCP), (NTU-55), which assembled from the coordination between a Cu dimer and a newly designed ligand with a nonmetal selenium (Se) site. Static single-component adsorption and dynamic breakthrough experiments reveal that desolvated NTU-55 can completely adsorb C2H2 from the C2H2/CO2 mixture (1/4, v/v) at 298 K, along with higher C2H2 capacity and much lower binding energy. The origin of this separation, as comprehensively revealed by density functional theory (DFT) calculations, is derived from the interaction discriminatory of C2H2 and CO2 toward accessible Se and Cu adsorption sites. To the best of our knowledge, this is the first time to find the positive effect of nonmetal Se sites for selective C2H2 capture.

Catalytic performance and deactivation of Ni/MCM-41 catalyst in the hydrogenation of pure acetylene to ethylene.

Ni/MCM-41 catalysts were prepared by an impregnation method for acetylene hydrogenation to ethylene based on the calcium carbide acetylene route. X-ray diffraction and transmission electron microscopy indicated that Ni was uniformly dispersed on the support. Temperature-programmed reduction and X-ray photoelectron spectroscopy demonstrated a strong interaction between Ni and MCM-41, and Ni(0) and Ni(ii) coexisted in the catalyst. We optimized the catalytic activity by optimizing the Ni loading and reaction conditions including temperature, space velocity, and hydrogen/acetylene ratio. The acetylene conversion reached 100%, the ethylene selectivity reached 47%. Additionally, we tested the catalyst stability; the acetylene conversion was maintained at 100% for 25.73 h and was then rapidly reduced. ICP, TEM, FT-IR, thermogravimetric analysis and BET were used to investigate the reasons for catalyst deactivation; it was found that green oil deposition on the catalyst surface was the main reason for the catalyst deactivation.

Charging and heating processes of dust particles in an electron cyclotron resonance plasma

Incandescent dust particles are observed with the naked eye in plasmas excited at the electron cyclotron resonance produced in pure acetylene. To investigate the heating mechanisms involved and their potential impact on the dust particle charge, as a first approach, a probe is used to measure the floating potential and to estimate the temperature reached by the material. Both highly depend on the position in the magnetic field and on the plasma conditions (pressure and gas, namely argon or helium). Numerical simulations based on the balance of the currents and of the heat fluxes on the probe emphasize a key role of primary electrons: they are responsible for the very negative floating potential as well as for the high probe temperature. Numerical simulations are also adapted to the case of a dust particle in a non-reactive plasma. However, even it can reach temperatures higher than 1600 K, the dust particle remains negatively charged.

Polycyclic aromatic hydrocarbon (PAH) formation during acetylene pyrolysis in tubular reactor under low pressure carburizing conditions

Low-pressure carburizing involves hydrocarbon pyrolysis, which leads to a fast gas-phase formation of polycyclic aromatic hydrocarbons (PAHs), some of which, such as benzo[a]pyrene, are carcinogenic. Workers can be exposed to these PAHs during maintenance and cleaning operations of carburizing furnaces. Experiments of acetylene pyrolysis were carried out in conditions close to low-pressure gas carburizing processes, at 1173 K and 8 kPa, in tubular reactors. At the outlet of the reaction zone, the reactant and the reaction products were analyzed by gas chromatography (TCD, FID and MS). Amongst other products, 16 PAHs classified as priority pollutants by the United States Environmental Protection Agency (US EPA) were observed and quantified. The study of the influence of residence time and of inlet reactant concentration shows that amounts of PAHs increase with residence time at low acetylene concentration but slightly decrease with pure acetylene due to the conversion of PAHs into soot. Results were compared to simulation results obtained with a detailed kinetic model of light hydrocarbon pyrolysis.

Temperature-dependent line parameter study of acetylene transitions near 3 µm

Knowledge of the acetylene spectrum is important for astrophysics, atmospheric, and combustion chemistry research. Twelve acetylene transitions across eleven bands have been studied between 3335.0 and 3336.5 cm−1 with a tunable interband cascade laser. Linestrengths and temperature-dependent lineshape parameters, including collisional broadening and narrowing, are reported through Voigt, Rautian, and Galatry lineshape fits to two strong cold band transitions. Measurements were made in pure acetylene, as well as with diluents argon, nitrogen, and methane, over a temperature range of 296–637 K and pressures of 5–90 Torr. Linestrengths and temperature-dependent self-broadening coefficients are also reported for ten weak hot band transitions through Voigt lineshape fits, measured between 296–513 K and 5–20 Torr. Line parameter measurements are found to be in good agreement with the literature and extend experimental lineshape studies of acetylene into new rovibrational bands, a sparsely-studied temperature regime, and a new perturber: methane.