High Acetylene Research Articles

High Volumetric and Gravimetric Acetylene Uptakes in a Cu-MOF with Tailored Cages.

NTUniv-80 exhibits record-high volumetric and gravimetric acetylene (C2H2) uptakes of 210 cm3 (STP) g-1 and 227 cm3 (STP) cm-3 at 295 K and 1 atm, respectively. Grand canonical Monte Carlo (GCMC) simulation indicates that those remarkable C2H2 uptakes are attributed to the open Cu2+ sites and tailored cages.

Hemilabile Binding of Acetylene in an Amide-Rich Ultramicroporous MOF Enables Strong Acetylene Selectivity.

Thanks to a hemilabile amide-based binding site, a previously unreported amide-functionalized metal-organic framework (MOF) exhibits high acetylene affinity over ethylene, methane, and carbon dioxide, three-in-one.

The Geometric and Electronic Effects of Ceria on Promoting PdZn catalyst for Enhanced Acetylene Semi‐Hydrogenation

AbstractPdZn intermetallic compounds (IMCs) have been extensively reported for acetylene semi‐hydrogenation due to unique geometric and electronic structure of isolated Pd sites. However, to achieve high ethylene selectivity at high conversion remains challenging. Here we show the promotional role of ceria in modifying the geometric and electronic structure of PdZn IMCs towards enhanced catalytic performance for acetylene semi‐hydrogenation. The Ce (0.1 wt%) promoted Pd−Zn‐Al catalyst shows by far the best catalytic performance among other Pd based catalysts in literature, maintaining high selectivity (>95 %) and excellent stability (~130 h) at high acetylene conversion (~90 %). Using in situ spectroscopic techniques, the geometric and electronic effects of CeOx promotor were clearly elucidated. At low Ce content, the presence of highly dispersed Ce3+ species in the periphery of PdZn alloys enhanced electronic metal‐oxide interaction, resulting in electron‐rich Pd sites that promote hydrogen dissociation and ethylene desorption, and account for the outstanding catalytic performance. At high Ce content, the formation of bulk‐phase CeO2 suppressed the PdHx formation during PdZn alloying and led to phase separation yielding highly dispersed Pd ensembles, consequently lowering ethylene selectivity. Our results provide a new route for the design of PdZn catalyst by applying rare earth promoters towards high‐performance acetylene semi‐hydrogenation.

Experimental study and modeling of the liquid phase hydrogenation of acetylene

Selective hydrogenation of acetylene is an important process for both ethylene purification and ethylene production from acetylene in the industry. Herein, we proposed liquid phase acetylene hydrogenation for high feed concentrations of C2H2 (8 %) and CO (20 %), which is used to produce ethylene as a subsequent process of partial oxidation of natural gas. The experiments were carried out in a stirred tank reactor using N-methylpyrrolidone (NMP) as solvent and PdAg/SiO2 as catalyst. The liquid phase process obtained a much higher selectivity to ethylene (92 %) with only 8 % selectivity to green oil (GO) and C4, compared to 71 % ethylene selectivity in gas phase hydrogenation. Furthermore, in the liquid phase ethylene selectivity increased with increasing acetylene conversion, especially in the conversion range of 80–100 %. We developed a model incorporating reaction kinetics, mass transfer and reactor model to predict the acetylene conversion and ethylene selectivity in liquid phase hydrogenation. The calculation results indicated that hydrogenation in the liquid phase operated at a lower acetylene concentration and a higher H2/C2H2 ratio, especially under high acetylene conversions. This explains why the liquid phase hydrogenation of acetylene has a much higher selectivity to ethylene than the gas phase process.

Selective hydrogenation of high concentration acetylene over the well-defined crystalline sites of Pd1Cu1 and Pd1Cu3

The Pd1Cu1 crystalline site inhibits excessive hydrogenation and oligomerization and exhibits superior ethylene selectivity and stability.

Nitrogen-rich porous organic cages with high acetylene storage and separation performance

Two nitrogen-rich porous organic cages (POCs) have been investigated for acetylene (C2H2) storage and separation applications, achieving a high C2H2 uptake value of up to 146 cm3 g−1 at 298 K and 1 atm and effective separation of C2H2/CO2 mixtures.

Lowering the Operating Temperature of Gold Acetylene Hydrochlorination Catalysts Using Oxidized Carbon Supports

The commercialization of gold for acetylene hydrochlorination represents a major scientific landmark. The development of second-generation gold catalysts continues with a focus on derivatives and drop-in replacements with higher activity and stability. Here, we show the influence that the support surface oxygen has on the activity of carbon supported gold catalysts. Variation in the surface oxygen content of carbon is achieved through careful modification of the Hummers chemical oxidation method prior to the deposition of gold. All oxidized carbon-based catalysts resulted in a marked increase in activity at 200 °C when compared to the standard nontreated carbon, with an optimum oxygen content of ca. 18 at % being observed. Increasing oxygen and relative concentration of C–O functionality yields catalysts with light-off temperatures 30–50 °C below the standard catalyst. This understanding opens a promising avenue to produce high activity acetylene hydrochlorination catalysts that can operate at lower temperatures.

Efficient Adsorption of Acetylene over CO2 in Bioinspired Covalent Organic Frameworks

Rational design of covalent organic frameworks (COFs) to broaden their diversity is highly desirable but challenging due to the limited, expensive, and complex building blocks, especially compared with other easily available porous materials. In this work, we fabricated two novel bioinspired COFs, namely, NUS-71 and NUS-72, using reticular chemistry with ellagic acid and triboronic acid-based building blocks. Both COFs with AB stacking mode exhibit high acetylene (C2H2) adsorption capacity and excellent separation performance for C2H2/CO2 mixtures, which is significant but rarely explored using COFs. The impressive affinities for C2H2 appear to be related to the sandwich structure formed by C2H2 and the host framework via multiple host-guest interactions. This work not only represents a new avenue for the construction of low-cost COFs but also expands the variety of the COF family using natural biochemicals as building blocks for broad application.

Time evolution of neutral and charged species in Ar/C2H2 capacitively-coupled RF discharges

The first stages of polymerization in plasmas of Ar/C2H2 have been studied both experimentally and using a kinetic model, by following the time evolution of the main neutral and ionic species in the discharge. The abundances of the different neutrals and ions have been measured by quadrupole mass spectrometry in conditions specifically chosen to avoid dust formation in the plasma. Maxima occurring at different times from the ignition of the discharge were detected for the density of the neutral species sampled, generally consistent with a stepwise polymerization mechanism. Ions were found to fundamentally follow the trend of their neutral counterparts, with the time evolution for negative ions stressing the difference in the chemical mechanisms responsible for the formation of the two primitive anions, C2H− and H2CC−. Positive and negative ion distributions were measured in the steady state of the discharge. Detection of anions with up to 22 carbon atoms was possible in mixtures with high acetylene content. A volume averaged kinetic model with a simple description of the Ar/C2H2 chemistry was used to identify the main reaction pathways and was able to satisfactory reproduce the experimental results.

π-Adsorption promoted electrocatalytic acetylene semihydrogenation on single-atom Ni dispersed N-doped carbon

As a novel electrocatalyst for acetylene semihydrogenation, single-atom nickel dispersed N-doped carbon exhibits a high acetylene conversion of 97.4%, which are attributed to weak π-adsorption of ethylene on individual Ni sites.

Photopolymerized and acetylene-functionlized polyacrylates for photoclickable elastomers

The acetylene functional groups on polymer chains provide a photochemical access to modulate or actuate the properties of the polymer. We report here a photochemical way to actuate a polyacrylate to elastomers. High molecular weight acetylene functionalized homo- and copolymers of are prepared with a novel monomer, 2-(dimethylpropargyloxy)ethyl methacrylate, DMPOEMA, by photo-initiated free-radical polymerization (FRP) in solution at room temperature. The acetylene groups are tolerant of the solution photo FRP at 50 wt% concentration, but not tolerant to thermal FRP and photo FRP at 80 wt% concentration. Copolymers P(DMPOEMA-co-EA) with‾Mn in 12,500–15,100 g/mol were prepared with conversion up to 90% at 50% concentration and three monomer feed ratios. The feed ratio of DMPOEMA had slight effects on the polymerization rate, but effects on PDI at higher monomer conversion with prolonged photo-irradiation. The acetylene functionalized polyacrylates become photo-sensitive and are photo cross-linkable or photo clickable after solvent is removed. Real-time FT-IR study reveals that the photo cross-linking with a tri-thiol compound follows the normal thiol-yne photochemistry, and the photo cross-linking catalyzed with only photoinitiator results in diene units in the cross-linked polymer networks. These photo-treated polyacrylate exhibited designable elastomer properties: with Tg in −24 to −11 °C, more than 10 times increase of relative cross-linking density and resistant to solvents, improved stress, strain and elongation properties. This work paves a way for the acetylene functionalized (meth)acrylates as advanced photo-reactive material.

Cyclotrimerization of Acetylene on Clusters Con+/Fen+/Nin+(n = 1-16).

Cyclotrimerization of acetylene to benzene has attracted significant interest, but the role of geometric and electronic effects on catalytic chemistry remains unclear. To fully elucidate the mechanism of catalytic acetylene-to-benzene conversion, we have performed a gas-phase reaction study of the Fen+, Con+, and Nin+ (n = 1-16) clusters with acetylene utilizing a customized mass spectrometer. It is found that their reactions with acetylene are initiated by C2H2 molecular adsorption and allow for dominant dehydrogenation with the relatively low partial pressure of the acetylene gas. However, at high acetylene concentrations, the cyclotrimerization in Mn+ + 3C2H2 (M = Fe, Co, Ni) becomes the dominant reaction channel. We demonstrate theoretically the favorable thermodynamics and reaction dynamics leading to the formation of the M+(C6H6) products. The results are discussed in terms of a cluster-catalyzed multimolecule synergistic effect and the cation-π interactions.

Breaking the inverse relationship between catalytic activity and selectivity in acetylene partial hydrogenation using dynamic metal–polymer interaction

The partial hydrogenation of acetylene impurities in ethylene is industrially important because acetylene acts as a catalyst poison in downstream ethylene polymerization processes. In this reaction, simultaneously achieving high acetylene conversion and partial hydrogenation selectivity is challenging, and most known catalyst systems exhibit an inverse activity–selectivity relationship. Here, an amorphous polyphenylene sulfide (Am-PPS) was synthesized as a promoter for 0.1 wt% Pd/α-Al2O3. The catalyst modification using a trace amount of Am-PPS (0.15 wt%) enabled a remarkable enhancement of ethylene selectivity without an appreciable loss in acetylene hydrogenation activity. This could be attributed to the dynamic change of the Am-PPS–Pd interface, which selectively allows the cooperative adsorption of acetylene and H2, but not ethylene. Besides, the modified catalyst exhibited excellent long-term stability because of the high thermochemical stability of the polymer. These results demonstrate the unique possibility of using dynamic metal–polymer interaction to design partial hydrogenation catalysts that simultaneously exhibit high activity, selectivity, and stability.

Iodide-Coordinated Single-Site Pd Catalysts for Alkyne Dialkoxycarbonylation

Heterogeneous single-metal-site catalysts (HSMSCs) have attracted considerable interest, but most studies have focused on the metal atoms in the active site while ignoring the key role of ligands. The unique coordination environment of a single-site catalyst is crucial for realizing its potential. Constructing this kind of catalyst via a feasible and practical fabrication method is challenging. Herein, a single-site Pd catalyst with iodide ligands supported on activated carbon (Pd1/AC) was successfully fabricated by atomic dispersion of large Pd nanoparticles (NPs). Intermediate I• radicals were detected during the atomic dispersion process of Pd NPs by in situ imaging photoelectron photoion coincidence spectroscopy (in situ iPEPICO) with vacuum ultraviolet synchrotron radiation. The molecular structure of single-site Pd was established as [Pd(CO)I4(O═AC)]2– through combined characterization. Alkyne dialkoxycarbonylation with high selectivity toward 1,4-dicarboxylic acid esters (>94%) and high acetylene conversion (>99%) was achieved. A sulfonic promoter on the Pd1/AC catalyst for alkyne dialkoxycarbonylation was avoided because of the iodide ligand. Good durability and a broad substrate scope were successfully achieved.

Long-term effects of acetylene on denitrifying N2O production: Biomass performance and microbial community

Maximizing production and use of N2O produced by the process of denitrification has emerged as a promising concept for energy recovery from nitrogen. Acetylene is well known as an inhibitor of N2O reductase activity, however, to date, few studies have utilized long-term cultivation with acetylene to achieve denitrifying N2O recovery. This work assessed the performance of N2O production and shifts in the denitrifying community in response to long-term exposure of acetylene during nitrite denitrification. Batch tests showed that long-term exposure to acetylene at high concentrations (volume fraction >40 %) resulted in high N2O accumulation, up to 98.6 %. High-throughput 16S rRNA gene analysis suggested that Saprospiraceae dominated the microbial community at the end of the cultivation period with its abundance increasing from the initial 3.2% to 42.2%. Metagenomic analysis revealed that after the long-term cultivation under high level acetylene, the relative abundance of nosZ in the community did not change significantly. Instead, the nosZⅡ-harboring bacteria became dominant. Batch tests in series demonstrated that N2O reduction could be restored rapidly upon removal of acetylene. This study describes an effective method for high yield production of N2O during nitrite denitrification that can be used to enhance energy recovery and improves our understanding of the long-term effect of acetylene on the denitrifying community.

Atomically Dispersed Pd Atoms on a Simple MgO Support with an Ultralow Loading for Selective Hydrogenation of Acetylene to Ethylene.

We report a simple and efficient Pd/MgO catalyst loaded with ppm level of Pd (7.8 ppm) for semi-hydrogenation of acetylene to ethylene. The catalyst showed excellent performance with high acetylene conversion (97%), high ethylene selectivity (89%) and good stability. Moreover, the atomically dispersed Pd atoms are inactive for ethylene hydrogenation. Isotopic and FTIR results suggest that H2 dissociates at isolated Pd atoms in a heterolytic manner forming O-H bond, which may account for the high selectivity.

Efficient Separation of Acetylene and Carbon Dioxide in a Decorated Zeolite

AbstractThe almost identical molecular sizes and volatilities of acetylene and carbon dioxide make their separation extremely challenging in industry. Reported here is the efficient separation of acetylene and carbon dioxide (v/v=2/1, which is relevant to that in the industrial cracking stream) in faujasite zeolites decorated with atomically‐dispersed copper(II) sites under ambient conditions. In situ neutron powder diffraction and inelastic neutron scattering confirm that the confined copper(II) site displays chemoselective yet reversible binding to acetylene, whereas adsorbed carbon dioxide molecules are stabilized by weak host–guest supramolecular interactions with the framework oxygen centers, thus resulting in the efficient separation of these two gases under flow conditions. A designed adsorption‐purging‐desorption system based upon Cu@FAU is established for the recovery of high purity acetylene (98–99 %) from the mixture of acetylene and carbon dioxide, offering an unprecedented separation factor of 22.2 with an effective dynamic uptake of acetylene of 1.51 mmol g−1 at 298 K.

Efficient Separation of Acetylene and Carbon Dioxide in a Decorated Zeolite.

The almost identical molecular sizes and volatilities of acetylene and carbon dioxide make their separation extremely challenging in industry. Reported here is the efficient separation of acetylene and carbon dioxide (v/v=2/1, which is relevant to that in the industrial cracking stream) in faujasite zeolites decorated with atomically-dispersed copper(II) sites under ambient conditions. In situ neutron powder diffraction and inelastic neutron scattering confirm that the confined copper(II) site displays chemoselective yet reversible binding to acetylene, whereas adsorbed carbon dioxide molecules are stabilized by weak host-guest supramolecular interactions with the framework oxygen centers, thus resulting in the efficient separation of these two gases under flow conditions. A designed adsorption-purging-desorption system based upon Cu@FAU is established for the recovery of high purity acetylene (98-99 %) from the mixture of acetylene and carbon dioxide, offering an unprecedented separation factor of 22.2 with an effective dynamic uptake of acetylene of 1.51 mmol g-1 at 298 K.

Optimization of oxy-acetylene flame hardening parameters to analysis the surface structure of low carbon steel

The oxy-acetylene flame hardening is one of the surface structure modification process is also known as heat treatment process. Using of high pressure oxy acetylene gas mixture expose to the top surface of the material with around 30,000 C, and the material comes to recrystalization temperature at that time the work samples is cooled by means of sudden water quenching. This action changes the micro structural and to increase the micro hardness of the material. The low carbon steel material is selected for this investigation to improve the micro hardness value by the application of oxy-acetylene flame hardening. The increasing of hardness with the effects of flame hardening parameters are flame temperature in o C, torch cap in mm, and quenching period in sec. Taguchi L27 OA is consider for this experiment to evaluate the maximum microhardness values of specimens effectively. The factors influencing for this study is estimated through Signal to Noise ratio efficiently.

Highly sensitive updatable green hologram recording polymer with photoisomerizable azobenzene with highly birefringent acetylene as the side chain

To develop highly sensitive updatable hologram materials, an azobenzene monomer was synthesized herein that supports effective photoisomerization under visible green beam irradiation. Furthermore, an acetylene group was introduced via Sonogashira coupling for higher birefringence. Polymerization was performed on the synthesized azobenzene monomer and on the methyl methacrylate (MMA) monomer, which serves as the skeleton of the film. The structures of all molecules were characterized by nuclear magnetic resonance (NMR) spectroscopy, and UV-Visible absorption spectroscopy was performed to analyze their optical properties. The holographic writing and rewriting capabilities of the newly synthesized azobenzene side-chain polymer were characterized by using a green laser as a writing beam, which showed that a high diffraction efficiency was reliably achievable under low-energy laser irradiation when evaluated with a four-wave-mixing optical scheme. In this study, high birefringent acetylene group containing azobenzene-based polymers were synthesized as materials for rewritable green-laser holograms, and their properties were evaluated. Birefringence change of polymer, which has an absorption wavelength suitable for green laser (532 nm), is 0.018. The diffraction efficiency of polymer was 72% under low-energy irradiation (7 J/cm2). These results show that the hologram recording material made in this study with high birefringent azobenzene are stable, without undergoing decomposition even when repeated recording and rewriting were performed.