Adsorption Of Ethylene Research Articles

In-situ silver-modification of Silicalite-1 for trace ethylene capture under humid conditions

The removal of trace C2H4 at high relative humidity has significant importance for the preservation of fruit; however, owing to the severe storage environment and competitive adsorption of high humidity water vapor and carbon dioxide, few suitable adsorbent materials are currently available for this application. Herein, silver-loaded silicalite-1 sorbent (S-1@Ag) was synthesized via an in-situ silver modification method to enhance its interaction with ethylene. By adjusting the amount of silver source to 0.94 wt%, the ethylene uptake of S-1@Ag at P/P0 of 0.01 was sixteen times greater than unmodified silicalite-1. S-1@Ag prepared using the in-situ method exhibits a uniform distribution of Ag+ that enhances the recognition of ethylene, resulting in an excellent ability to capture ethylene at low pressures. Crucially, S-1@Ag(0.94 %) was unaffected by the presence of water vapor and carbon dioxide in its application environment, and exhibits the best preferential adsorption of ethylene under low pressures. Dynamic breakthrough tests under humid conditions demonstrated that S-1@Ag(0.94 %) captures trace ethylene four times more effectively than S-1@Ag, even under different gas mixtures (C2H4/N2, 0.1/99.9, v/v; C2H4/CO2/N2, 0.1/0.1/99.8 and 0.1/1/98.9, v/v/v). Furthermore, banana storage experiments show that S-1@Ag(0.94 %) slows the decay time of the fruit and improves its storage life.

Synthesis, characterization, and gas adsorption performance of an efficient hierarchical ZIF-11@ZIF-8 core–shell metal–organic framework (MOF)

In this paper, the solvent-assisted linker exchange (SALE) technique was successfully applied for the synthesis of porous ZIF-11@ZIF-8 core–shell composite structure metal–organic framework (MOF). The RHO-type ZIF-11 owing to larger cavities along with higher freedom in linker rotation, acts as the core and contributes in adsorption capacity enhancement. On the other hand, the SOD-type ZIF-8 provides greater molecular sieving features due to its lower degree of linker flexibility and thereby results in an improvement of the adsorption selectivity. The morphology and structure of the fabricated MOFs were characterized by XRD, FTIR, FESEM, EDS, TEM, BET, and TGA analyses and formation of the core–shell structure was confirmed. The BET surface area and micropore volume of the synthesized ZIF-11@ZIF-8 MOF were obtained as high as 1023.4 m2/g and 0.435 cm3 g−1, respectively. Gas adsorption measurements were carried out for CO2, N2, CH4, C2H6, and C2H4 gases at 298 and 328 K and equilibrium pressures up to 4 bar. The results revealed a remarkable rise (∼100 %) in CO2 adsorption capacity of ZIF-11@ZIF-8 nanoparticles (8.21 mmol g−1), compared to the pristine ZIF-11 (4.35 mmol g−1) at 298 K. The CO2/N2 and CO2/CH4 adsorption selectivity values were also augmented by 131 % and 92 %, respectively. In addition, the fabricated core–shell MOF, exhibited greater ethane (C2H6) adsorption capacity by ∼ 65 %, along with ethane to ethylene (C2H4) adsorption selectivity enhancement by ∼ 50 %. The higher adsorption capacity values without sacrificing adsorption selectivity suggests that the controlled core–shell MOF structures would be promising candidates for effective separation of CO2 from CH4 and N2 as well as C2H6 from C2H4.

Evaluating the detection and trapping of small gas molecules on hydrogenated siligene

The use of new two-dimensional systems to detect and capture organic molecules remains a vital research area. In this work, we have investigated, by first-principles calculations, the feasibility of using a hydrogenated siligene (HSiGeH) monolayer to detect and capture small gas molecules through a self-propagating reaction mechanism. We have studied the adsorption of formaldehyde (CH2O), acetylene (C2H2), and ethylene (C2H4) on an HSiGeH monolayer with an H-vacancy (including two situations: an H-vacancy on a Si or a Ge atom). In each case, the molecule chemisorbs at the H-vacancy, increasing the C–O or C–C bond lengths, indicating that double and triple bonds of the molecule are partially broken, resulting in unpaired electrons in one C atom of each molecule. We have found that the hydrogenated chemisorbed molecule -with a new H-vacancy formed on the surface- is the most energetically favorable configuration for each reaction. The viability of the reactions was analyzed by describing the minimum energy path (MEP) computed by the climbing image nudged elastic band method (CI-NEB). Our results show that the self-propagating reaction is viable except for one case, where the C2H4 chemisorbs on the monolayer with the H-vacancy on Ge. These results point toward the application of the HSiGeH monolayer as a possible system for novel gas-removal systems.

Chain length effects of phenylene sulfide modifiers on selective acetylene partial hydrogenation over Pd catalysts

We recently reported that polymer chains with phenylene sulfide moieties can efficiently modify the Pd catalyst surface, enabling selective partial hydrogenation of acetylene under ethylene-rich conditions. In the present study, we synthesized oligomeric and polymeric phenylene sulfides with tailored molecular sizes to systematically investigate the catalytic effect of chain length of organic modifiers. The results showed that the increased chain length of the modifiers is beneficial for improving the acetylene partial hydrogenation selectivity by inhibiting adsorption and full hydrogenation of ethylene. This was attributed to the fact that modifiers with a greater number of sulfide groups per molecule can bind more efficiently to the Pd surface for entropic reasons (chelate effect) and thus better inhibit ethylene adsorption. In contrast, the adsorption of acetylene to Pd was nearly unaffected by the presence and size of the modifiers owing to its stronger binding ability and small kinetic diameter. Modifiers with larger chain lengths were also advantageous in improving long-term catalyst stability because of their higher thermochemical stability and greater ability to inhibit the formation of carbonaceous deposits. The present results showed that polymers can act as more efficient and long-lasting selectivity modifiers than commonly used small organic molecules.

Steam reforming of ethanol, acetaldehyde, acetone and acetic acid: Understanding the reaction intermediates and nature of coke

The small aliphatic organics like ethanol, acetaldehyde, acetone and acetic acid are frequently used as feedstocks for hydrogen production via steam reforming. These organics have distinct functionalities, which might result in formation of different reaction intermediates and coke. This was investigated in this study with Ni/KIT-6 as a catalyst under normalized conditions. The results indicated that dehydration to ketene but not cracking was major route for dissociative adsorption of acetic acid on Ni/KIT-6 from 100 °C. Thermally stable CH and CC in alkenes, formed via dehydration of ethanol and aromatization of acetone/intermediates via bimolecular Aldol-condensation, were important precursors of coke in ethanol and acetone reforming. Although acetone strongly adsorbed on Ni/KIT-6, it did not polymerize to heavy oxygen-containing organics that were difficult to be gasified with steam. In comparison, the similar strong adsorption of acetaldehyde led to rapid polymerization even at 100 °C, forming the polymeric coke of highly aliphatic nature. The coking tendency in reforming followed the order: acetone > acetic acid > ethanol > acetaldehyde. Nevertheless, the amorphous form of coke in acetaldehyde reforming led to the rapid deactivation of Ni/KIT-6. The coke in ethanol, acetone and acetic acid reforming were mainly the catalytic type with the highly aromatic nature, high carbon crystal crystallinity, high thermal stability, high resistivity towards oxidation and the carbon nanotube morphology. Nevertheless, the varied reaction intermediates involved in reforming of these varied feedstock also formed the coke of some unique features.

Control of pore structure by the solvent effect for efficient ethane/ethylene separation

The purification of ethylene (C2H4) by selective adsorption of small amounts of ethane (C2H6) is a crucial industrial process. However, most porous adsorbents prefer C2H4 over C2H6 due to the increase in kinetic diameter and decrease in quadrupole moment from C2H4 to C2H6. The construction of ethane-selective adsorbents for ethylene purification is therefore a very challenging task. In this study, we designed and synthesized a family of C2H6-selective metal–organic framework (MOF) adsorbents, named Co-1-ina, Co-5-ina and Co-9-ina, through the strategy of crystal engineering using the same metal salt (Co2+) and ligand (isonicotinic acid). Notably, the pore structures and topologies of these materials vary according to the reaction conditions. Among them, Co-9-ina has the highest C2H6 adsorption capacity and C2H6/C2H4 separation performance. The C2H6/C2H4 selectivity of Co-9-ina at 298 K and 1 bar is astoundingly 2.69, which is greater than most C2H6-selective MOFs reported to date. The pyridine rings bind more strongly to C2H6 via van der Waals interactions for ethane adsorption according to theoretical calculations and single crystal structures. The C2H6/C2H4 separation performance for Co-9-ina was further validated by breakthrough studies under dynamic conditions.

Development of a novel ethylene scavenger made up of pumice and potassium permanganate and its effect on preservation quality of avocados

The purpose of this research was to develop a novel ethylene scavenger by combining pumice and potassium permanganate (KMnO 4 ) to preserve fruit and vegetables. The study showed that pumice with smaller particle sizes and lower relative humidity (RH) were favorable to ethylene adsorption. The optimal ratio was 1 g of pumice (<5 μm) to 100 mg of KMnO 4 with approximately 620 μL/g of ethylene adsorption capacity within 24 h at lab room RH (30%). Further, this novel ethylene scavenger restricted the ethylene production rate of avocados to 0 μL/kg/h for nine days, and simultaneously, the carbon dioxide (CO 2 ) production rate remained below 25 mL/kg/h. In addition, the firmness of avocados preserved by the novel ethylene scavenger was 4.04 × 10 5 N/m 2 on the 9th d. The results confirmed that the shelf life of avocados was extended by one week at 25 °C under the preservation of the novel ethylene scavenger. • Smaller particle size and lower relative humidity favored ethylene removal. • Pumice physically adsorbed ethylene and KMnO 4 oxidized ethylene. • Ethylene and CO 2 production rate were restricted by the ethylene scavenger. • The ethylene scavenger could extend shelf life of avocados by one week.

Amino acid (histidine) modified Pd/SiO2 catalyst with high activity for selective hydrogenation of acetylene

Suppressing the excessive hydrogenation capacity of palladium has great significance for selective hydrogenation of acetylene. Herein, an amino acid (histidine or His in abbreviation) modified Pd/SiO2 catalyst (Pd-His/SiO2) for selective hydrogenation of acetylene was prepared by incipient wetness impregnation, followed by hydrogen reduction at 240 °C. The intense interaction between Pd and histidine greatly affects the structure and properties of Pd-His/SiO2. The Pd nanoparticles are highly dispersed on the support with an average diameter of 1.0 nm and positively charged. The use of histidine weakens the adsorption of acetylene and ethylene on the metal. Especially, the adsorption of di-σ-bonded ethylene is significantly impaired on the catalyst, which is beneficial to improve the ethylene selectivity. The conversion of acetylene is up to 100.0 % at 160 °C on Pd-His/SiO2 while the ethylene selectivity reaches 81.5 %. A 50-hour test at 160 °C confirms the good stability of Pd-His/SiO2.

Friedel–Crafts Synthesis of Carbazole-Based Hierarchical Nanoporous Organic Polymers for Adsorption of Ethane, Carbon Dioxide, and Methane

Friedel–Crafts Synthesis of Carbazole-Based Hierarchical Nanoporous Organic Polymers for Adsorption of Ethane, Carbon Dioxide, and Methane

Zero-energy-consumption temperature swing system for ethane adsorption and release

Temperature swing adsorption (TSA) technology plays an important role in industrial gas capture, but the temperature swing procedure consumes a huge amount of energy, which takes over 80% of the total energy consumed. In this work, we report a C2H6-selective temperature swing system completely driven by solar irradiation. For adsorption, the adsorbent is placed under a layer of poly(vinylidenefluoride-co-hexafluoropropene) [P(VdF-HFP)HP] which can reflect sunlight and radiate heat to outer space, thus efficiently decreasing adsorption temperature under light irradiation. While desorption, the adsorbent is placed above P(VdF-HFP)HP and directly heated by sunlight, leading to the liberation of C2H6 adsorbed. The whole temperature-swing process do not need any energy input other than solar energy. The metal–organic framework (MOF), Ni(bdc)(ted)0.5, is selected as the adsorbent because of its high working capacity and easy regeneration. This zero-energy-consumption temperature swing system shows stable performance in the repeated C2H6 adsorption–desorption tests for 5 months. The present work sheds light on the development of energy-efficient TSA technologies for the capture of light hydrocarbons.

Adsorption equilibria and kinetics of ethane and ethylene on zeolite 13X pellets

To establish a design basis of the cyclic adsorption process for ethylene purification, the adsorption equilibria and kinetics of ethane and ethylene on zeolite 13X pellets were measured by a volumetric method at 303–343 K under pressure up to 600 kPa. The Sips model showed better prediction of ethane in the full pressure range, but the dual-site Langmuir (DSL) model was more accurate for ethylene in the pressure range of <250 kPa. The strong cation-π interaction between ethylene and Na+ in zeolite 13X led to higher adsorption capacity and affinity than those of ethane. It resulted in a greater isosteric heat of adsorption (Qst) of ethylene at a low loading amount, while Qst variance in ethane was almost linearly increased with a dominant lateral interaction. At 303 K, the adsorption amount and affinity of ethylene at <5 kPa were slightly greater than those of propane but lower than those of propylene. However, the adsorption isotherms of ethane/ethylene became higher than those of propane/propylene above a certain pressure. The experimental uptake curves of ethane and ethylene were well predicted by a non-isothermal sorption model, considering the adsorption thermal effects. The difference in the apparent reciprocal diffusional time constant (Dapp/R2) between ethane and ethylene was mainly attributed to the thermal effects by the heat of adsorption. The comparison of Dapp/R2 values between zeolite 13X pellet and powder indicated that macropore diffusional resistance also contributed to the adsorption kinetics.

An anti-humidity palladium-containing MFI composite as a robust ethylene scavenger

The inhibition of ethylene exposure is necessary for preserving the quality of postharvest fruit and vegetables. In this study, we report a rational design of Pd-based MFI composite adsorbents consisting of Pd-ZSM-5 and S-1 zeolites with high ethylene adsorption capacity even in the humid environment. The effects of S-1 incorporation on the morphology, apparent surface area, Pd nanoparticles distribution, and the hydrophobicity of the MFI composite were investigated in relation to their ethylene adsorption performance in dry and humid environments. Our finding reveals a synergistic effect between the Si-rich layer and Pd nanoparticles on moisture protection and ethylene capture, respectively, leading to an exceptional ethylene adsorption ability of S-1/Pd-ZSM-5 under high relative humidity. Compared with the conventional ZSM-5-supported Pd adsorbent, S-1/Pd-ZSM-5 exhibited a two-fold enhancement in ethylene removal in the presence of moisture (0.195 mmol/g vs. 0.416 mmol/g). In particular, the secondary crystallization of S-1 achieved by 72 h of hydrothermal treatment gave an excellent confinement over the Pd-ZSM-5 structure. This novel design of S-1/Pd-ZSM-5 provides the valuable applicability of the composite zeolite for ethylene regulation in postharvest crops in the future.

Pore-Window Partitions in Metal-Organic Frameworks for Highly Efficient Reversed Ethylene/Ethane Separations.

The development of paraffin-selective adsorbents is desirable but extremely challenging because adsorbents usually prefer olefin over paraffin. Herein, a new pore-window-partition strategy is proposed for the rational design of highly efficient paraffin-preferred metal-organic framework (MOF) adsorbents. The power of this strategy is demonstrated by stepwise installations of linear bidentate N-donor linkers into a prototype MOF (SNNU-201) to produce a series of partitional MOF adsorbents (SNNU-202-204). With continuous pore-window partitions from SNNU-201 to SNNU-204, the isosteric heat of adsorption can be tuned from -34.4 to -19.4 kJ mol-1 for ethylene and from -25.5 to -20.7 kJ mol-1 for ethane. Accordingly, partitional MOFs exhibit much higher ethane adsorption capacities, especially for SNNU-204 (104.6 cm3 g-1), representing nearly 4 times as much ethane as the prototypical counterpart (SNNU-201; 27.5 cm3 g-1) under ambient conditions. The C2H6/C2H4 ideal adsorbed solution theory selectivity, dynamic breakthrough experiments, and theoretical simulations further indicate that pore-window partition is a promising and universal strategy for the exploration of highly efficient paraffin-selective MOF adsorbents.

Assembled Reduced Graphene Oxide/Tungsten Diselenide/Pd Heterojunction with Matching Energy Bands for Quick Banana Ripeness Detection.

The monitoring of ethylene is of great importance to fruit and vegetable quality, yet routine techniques rely on manual and complex operation. Herein, a chemiresistive ethylene sensor based on reduced graphene oxide (rGO)/tungsten diselenide (WSe2)/Pd heterojunctions was designed for room-temperature (RT) ethylene detection. The sensor exhibited high sensitivity and quick p-type response/recovery (33/13 s) to 10–100 ppm ethylene at RT, and full reversibility and excellent selectivity to ethylene were also achieved. Such excellent ethylene sensing behaviors could be attributed to the synergistic effects of ethylene adsorption abilities derived from the negative adsorption energy and the promoted electron transfer across the WSe2/Pd and rGO/WSe2 interfaces through band energy alignment. Furthermore, its application feasibility to banana ripeness detection was verified by comparison with routine technique through simulation experiments. This work provides a feasible methodology toward designing and fabricating RT ethylene sensors, and may greatly push forward the development of modernized intelligent agriculture.

Direct Visualization of Supramolecular Binding and Separation of Light Hydrocarbons in MFM-300(In).

The purification of light olefins is one of the most important chemical separations globally and consumes large amounts of energy. Porous materials have the capability to improve the efficiency of this process by acting as solid, regenerable adsorbents. However, to develop translational systems, the underlying mechanisms of adsorption in porous materials must be fully understood. Herein, we report the adsorption and dynamic separation of C2 and C3 hydrocarbons in the metal–organic framework MFM-300(In), which exhibits excellent performance in the separation of mixtures of ethane/ethylene and propyne/propylene. Unusually selective adsorption of ethane over ethylene at low pressure is observed, resulting in selective retention of ethane from a mixture of ethylene/ethane, thus demonstrating its potential for a one-step purification of ethylene (purity > 99.9%). In situ neutron powder diffraction and inelastic neutron scattering reveal the preferred adsorption domains and host–guest binding dynamics of adsorption of C2 and C3 hydrocarbons in MFM-300(In).

Machine-Learning-Assisted Catalytic Performance Predictions of Single-Atom Alloys for Acetylene Semihydrogenation.

Selective semihydrogenation of acetylene for the production of polymer-grade ethylene is a significant chemical industrial process. Facile activization of acetylene and weak adsorption of ethylene are critical requirements for high-performance catalysis. Single-atom alloys (SAAs) have strong binding effect on acetylene and weak effect on ethylene, which have been regarded as the superior catalysts for acetylene semihydrogenation. Herein, we established a pioneering machine learning (ML) assisted approach to investigate the reaction activity and selectivity of 70 SAA catalysts for acetylene semihydrogenation. As the most desirable ML model, the gradient boosting regression (GBR) algorithm has been extended to predict the energy barrier of *C2Hn (n = 2-4) hydrogenation with a root-mean-square error (RMSE) of only 0.02 eV. Notably, five candidate SAAs with excellent activity and selectivity for acetylene semihydrogenation are screened out via accessible descriptors. These data of ML prediction have been verified by DFT calculation with a high-accuracy (error less than 0.07 eV). This work demonstrates the potential of ML-assisted approach for predicting the energy barrier of transition state and simultaneously provides a convenient approach for the rational design of efficient catalysts.

Cooperative control of intralayer and interlayer space in MOFs enables selective capture of intermediate-sized molecules

Adsorptive separation of the smallest or largest molecules from a mixture can be realized by the sieving effect; however, it is still an arduous task to specifically discriminate between the intermediate-sized component from a complicated multicomponent mixture. Here, we report a strategy via cooperative control of intralayer and interlayer space for selective adsorption of ethane from methane and propane on a 2D-layered MOF termed Ni(4-DPDS)2CrO4. The intralayer channels work as main adsorption sites, while interlayer channels are designed to achieve optimal discrepancy of kinetic diffusion rates. The restricted diffusion of C3H8 in the interlayer channels results in a dramatic inversed, equilibrium-kinetic, combined selectivity for C2H6/C3H8. Mixture breakthrough experiments manifest an efficient capture of C2H6 owing to the equilibrium-kinetic synergetic effect. The mechanism for selective gas adsorption is well supported by kinetic results and crystallography studies, demonstrating that fabrication of MOFs with multiple distinct controllable micropores enables selective capture of intermediate-sized molecules.

Selective adsorption of ethane over ethylene through a metal–organic framework bearing dense alkyl groups

Metal-organic frameworks (MOFs) have been widely applied as adsorbents for the purification of C2H4. Selective adsorption of C2H6 from C2H6/C2H4 mixture can be expected to directly achieve high purity C2H4 in a single separation step, but it remains a daunting challenge. Here, we fabricated a MOF-based adsorbent with ethane-philic environment, Ni-MOF-BD, by incorporation of dense alkyl groups into its pores. Experimental results show that the adsorption capacity of C2H6 on such adsorbent can be reached up to 88.9 cm3·g−1 at 298 K and 1 bar, and offering a C2H6/C2H4 adsorption capacity ratio of 137%. Corresponding ideal adsorption solution theory (IAST) calculation revealed that the adsorption selectivity reaches 2.0. Molecular simulation study indicates that the alkyl groups inside the pores is poised to bind with C2H6 through strong van der Waals interactions, rendering Ni-MOF-BD an enhanced C2H6 selectivity. The present work successfully demonstrated another strategy of improving adsorption affinity for C2H6 by developing MOF-based adsorbent with dense alkyl groups, thereby providing a new C2H6-selective adsorbent for purifying C2H4.

A Scandium‐based Microporous Metal‐Organic Framework for Ethane‐Selective Separation

AbstractPurification of ethylene (C2H4) is one of the most important industrial separation practices. In this report, Sc‐abtc, a rare‐earth microporous metal‐organic framework was successfully constructed from 3,3’,5,5’‐azobenzenetetracarboxylic acid (H4abtc) and scandium through facile solvothermal method. Sc‐abtc have shown preferrential adsorption of ethane over ethylene with 4.28 mmol g−1 uptake of ethane at ambient conditions. The calculated isosteric heat of adsorption revealed Sc‐abtc has stronger binding affinity toward C2H6 (28.2 kJ mol−1) than C2H4 (11 kJ mol−1), which revealled the mechanism of the ethane‐selective property. Moreover, column breakthrough tests were conducted to further verified the practical C2H4/C2H6 separation with excellent cycling stability.

The Role of Nickel and Brønsted Sites on Ethylene Oligomerization with Ni-H-Beta Catalysts

The present work studies the adsorption of ethylene on Ni-H-Beta particles to unravel the roles of nickel and Brønsted sites in the catalytic oligomerization of ethylene. Three models (i.e., two based on the Cossee–Arlman mechanism and one based on the metallacycle mechanism) are examined in terms of the nature of the active sites and the adsorption mechanism involved in the ethylene coordination step. The results are consistent with the participation of two active sites in the formation of [Ni(II)-H]+ Cossee–Arlman centers and also suggest that ethylene dissociates upon adsorption on [Ni(II)-H]+ sites. Further characterization of Ni-H-Beta catalysts prepared at different nickel loadings and silica-to-alumina ratios reveals that highly dispersed Ni2+ exists on the catalyst surface and interacts with the catalyst’s lattice oxygen and free NiO crystals. At the same time, the kinetic results indicate that Brønsted sites may form isolated nickel-hydride ([Ni(II)-H]+) centers on the catalyst surface. In addition, the presence of residual, noncoordinated Ni2+ and Brønsted sites (not involved in the formation of [Ni(II)-H]+ sites) shows a reduced probability of the formation of nickel-hydride sites, hindering the conversion rate of ethylene. A mechanism for forming [Ni(II)-H]+ centers is proposed, involving ethylene adsorption over Ni2+ and a Brønsted site. This research has important implications for improving ethylene oligomerization processes over nickel-based heterogeneous catalysts.