Molecular Sieve Type Research Articles

Performance of exhaust detritiation system for a fusion test device in the initial phase of the operation

Abstract The exhaust detritiation system (EDS) has been operating for the deuterium plasma experiment in large fusion test device since 2016. The EDS consists of two systems: the molecular sieves (MS) type for plasma exhaust gas, the polymer membrane (PM) type for vacuum vessel purge gas during the maintenance activity. The tritium removal performance of the EDS was evaluated for four years. As the operation results, the maximum detritiation factor (DF) of the MS system was achieved to be more than 103 even though the average tritium concentration in the process gas was less than 104 Bq/m3. On the other hand, the DF of the PM system was less than 103, because the average tritium concentration during the vacuum vessel maintenance activity was at the order of less than 103 Bq/m3. Throughout the initial phase of the deuterium plasma experiment, the tritium concentration at the outlet of EDS was maintained to be less than the order of 102 Bq/m3. Also, a failure analysis was performed to evaluate the reliability of the EDS in the initial phase of the operation. Over the four years of operation, the overall failure rate of the MS system was on the order of 10−5 events/hour.

Synthesis of Aluminophosphate Molecular Sieves in Alkaline Media.

Unlike conventional aluminosilicate zeolites synthesized in alkaline media, aluminophosphate molecular sieves (AlPOs) have always been prepared under acidic conditions in the past three decades; this has been regarded as one of essential factors for synthesis, except for the case of silica-substituted analogues (SAPOs). For the first time, we demonstrate herein a simple and generalized route for synthesizing various types of aluminophosphate molecular sieves in alkaline media. A series of aluminophosphate sieves and their analogues have been prepared with different quaternary ammonium cations as structure-directing agents in this manner. The above successes have extended the systematic media from acidic or neutral to alkaline for the preparation of a series of aluminophosphate molecular sieves, which possibly open an alternative route for the synthesis of aluminophosphate molecular sieves.

Recycling waste plastics packaging to value-added products by two-step microwave cracking with different heating strategies

Waste plastics packaging (WPP) was converted into valuable products by two-step microwave cracking. The wax (38.47–72.53 wt%), gas (20.18–43.85 wt%) and solid (2.00–24.18 wt%) were produced in the first step, and the liquid (60.55–79.94 wt%), gas (18.44–38.45 wt%) and solid (1.00–5.56 wt%) were produced in the second step. Different heating strategies including the selection of absorbers and catalyst, the adjustment of heating power, the mass ratio of absorber to feedstock have been proposed to optimize the products in each step. Commercial spherical activated carbon, columnar activated carbon and molecular sieves type 4A have been used as absorbers and catalysts. The gas products (mainly H2, CH4, C2H4 and C3H6) can be used as combustion gas. The solid products (mainly CaO, TiO2 and SiO2) in the first step are suitable for absorbers because of their fast temperature rise (30–115 °C/min) in microwave field. The liquid products are distributed between C7 and C26, which are suitable for gasoline and diesel fractions. Absorbers have been used many times to reduce costs. Two-step method can effectively remove plastic additives, and other attachments in the first step, and the separation of ‘dirty’ process and ‘clean’ process can reduce the possibility of catalyst deactivation due to impurity coverage.

Separation of CO2/N2 mixture by vacuum pressure swing adsorption (VPSA) using zeolite 13X type and carbon molecular sieve adsorbents

Separation of carbon dioxide in flue gases from the combustion equipment is one of the most serious concerns for industries and especially for the power plants which are the main producers of this pollutant gas. From the various separation methods, vacuum pressure swing adsorption (VPSA) process is attracted interest due to its lower energy consumption and high efficiency. A VPSA process was studied for the separation of a mixture of CO2/N2 (80% N2 and 20% CO2). Experiments were performed in an eight-step, four-bed setup using zeolite 13X and carbon molecular sieve (CMS) as adsorbents. Experimental measurements by the bench-scale system have been obtained in a pressure range of 2.7–4.7 bar, cycle times of 360–600 s, the product flow rate of 1–3 (lit/min), and temperature 30 °C. The effects of pressure, cycle time, and product flow rate were investigated. With using 560 s for a cycle time at 3.7 bar, the maximum purity of 97.6% was obtained for zeolite 13X adsorbent.

KINETICS OF HYDROGEN SEPARATION FROM REFINERY OFF-GAS

Adsorption and desorption kinetic curves for equimolar hydrogen – methane mixture on molecular sieve type 5A were experimentally obtained for pressure range 0.122 – 3.546 MPa.The linear driving force rate expression model was used to simulate the dynamic of adsorption and desorption in adiabatic fixed bed adsorber. The model takes into account the interference effects for non-linear isotherms and non-isothermal system. The equations were solved by backward finite difference method with a fixed gridding technique. The individual mass transfer parameters were obtained by matching the theoretical with the experimental data and found to be equal to 8.510 s-1 and 0.783 s-1 for hydrogen and methane, respectively.The predicted effluent histories were shown to be in close agreement with the experimental data for the system. The lowest relative capacity of the bed for methane was almost approximately 95% of that predicted equilibrium capacity. The predicted temperature profiles tracked the experimental temperature data points, but with higher values. Furthermore, the maximum temperature increasing was observed for the adsorption of methane onto 5A molecular sieve at 35 atmospheres and was recorded as 44 K.

Adsorption of carbon dioxide, nitrogen and methane on modified titanosilicate type molecular sieves

Separation of N2 and CO2 from methane is a vital step in natural gas refining processes. The adsorption of carbon dioxide, nitrogen and methane was studied and compared on modified titanosilicate molecular sieves ETS-10 (cation exchanged forms of ETS-10 involving Na-ETS-10, Ag-ETS-10 and Ba-ETS-10) as a packed bed adsorbent. The synthesized ETS-10 was characterized by SEM for crystal structure, powder X-ray diffraction for the phase structure and BET for the pore textural properties. The adsorption equilibrium isotherms of CO2, N2 and CH4 on the adsorbents were measured at 277, 298, and 310 K and pressures up to 10 bar. The experimental adsorption equilibrium isotherms were well described by the UNILAN equation. Breakthrough curves were measured for the fixed bed. Na-ETS-10 is found to have selectivity 5.72 for CO2 over methane and 1.09 for N2 over methane at 277 K and 1000 kPa in Henry's law regime. For Ag-ETS-10 selectivity of CO2/CH4 is 4.86 and for N2/CH4 is 1.49. Finally, Ba-ETS-10 has been found to be a better adsorbent for the removal of impurity from methane with selectivity 8.37 for CO2/CH4 and 1.24 for N2/CH4. The selectivity increased with pressure in all cases studied, especially for Barium exchanged form. The packing efficiency of the bed was increased through granule size decrease from 4 mm to 2 mm.

Gas phase Catalytic Oxidation of VOCS using Hydrothermally Synthesized Nest-like K-OMS 2 Catalyst

Toluene and benzene are hazardous air pollutants commonly found in the atmosphere at relatively high concentrations. Due to this, a need to remove these pollutants became a necessity. In this study, octahedral molecular sieve type manganese oxide (K-OMS 2) prepared by hydrothermal method was utilized to decompose toluene and benzene. X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmet-Teller (BET), X-ray absorption near edge structure (XANES) analysis were used to investigate the crystallinity, morphology, surface area and oxidation state of K-OMS 2, respectively. It was confirmed that K-OMS 2 was successfully produced from hydrothermal method. Central composite design (CCD) was used to investigate the main and interaction effects of gas hourly space velocity (GHSV) and reaction temperature on the thermal catalytic oxidation of benzene and toluene. Both factors were found to have significant main and interaction effects on toluene oxidation. However, only the main effects of the factors were significant for benzene. This result was due to the difference in the stability of the structures of the two VOCs. The K-OMS 2 obtained has excellent efficiency on toluene and benzene removal. Toluene was completely decomposed at a temperature as low as 250°C while benzene decomposition reached around 98% at 292.4°C.

Equilibrium adsorption of ethyl mercaptan and thiophene using molecular sieve 13X

In the present study, adsorption of the sulfur compound onto two types of molecular sieve (HYD10B and LQ-MS-13X) in a batch system was investigated. It has been illustrated that HYD10B type has more adsorption capacity than LQ-MS-13X type to separate ethyl mercaptan from simulated liquid mixture. Selected as the better adsorbent, the isotherm equilibrium adsorptions of ethyl mercaptan and thiophene in liquid phase had been carried out by using this type of molecular sieve in the temperature range of 25–65 °C. HYD10B-MS-13X brought out the highest adsorption capacity for adsorption of ethyl mercaptan component. Diminution of adsorption capacity with temperature increment has been found and it was shown that adsorption of ethyl mercaptan is less affected by temperature changes. Using four more common isotherm models (Langmuir, Freundlich, Tempkin and Dubinin-Radushkevich), Freundlich isotherm was found to be the best representative model for describing ethyl mercaptan and thiophene equilibrium data.

An ultrasonic atomization assisted synthesis of self-assembled manganese oxide octahedral molecular sieve nanostructures and their application in catalysis and water treatment.

Manganese oxides of octahedral molecular sieve (OMS-2) type have important applications in oxidation catalysis, adsorption, and as battery materials. The synthesis methods employed determine their morphology and textural properties which markedly affect their catalytic activity. In this work, a room temperature ultrasonic atomization assisted synthesis of OMS-2 type materials is demonstrated. This synthesis differs from previously reported methods in that it is a simple, no-heat application that leads to a striking morphological characteristic of uniformly sized OMS-2 fibers and their self-assembly into dense as well as hollow spheres. Control of various parameters in the ultrasonic atomization assisted synthesis led to OMS-2 with high surface areas (between 136-160 m2 g-1) and mesoporosity. Catalytically these materials have higher activities in the oxidation of hydroxymethylfurfural (HMF), a bio-based chemical, (65% conversion of HMF vs. 14% with conventional OMS-2 catalyst) and a higher adsorption of lead from aqueous solutions (70% vs. 12% in conventional OMS-2 materials).

Self-Oxidation of Lignin to Aromatic Acids with High Selectivity Catalyzed by Designed Acidic Mesoporous Molecular Sieves Incorporating Heteroatoms

An economic method for the synthesis of crystalline mesoporous sieves and the self-oxidation of alkali lignin (INDULIN AT) to aromatic acids is reported herein. Crystalline mesoporous molecular sieves ILM-Al have been prepared in strongly acidic ionic liquid (IL) media and used as catalysts for the self-oxidation of alkali lignin to aromatic acids. In the preparation of the new type of mesoporous molecular sieves, the imidazolium-based acidic functional IL system served as both solvent and structure-directing agent. The ILM-Al exhibited higher catalytic performance and selectivity for aromatic acids in the self-oxidation of lignin than in that of fossil fuels, and the main products were homoveratric acid and homovanillic acid. The catalyst could be recycled and reused with negligible loss in activity over five cycles, and the IL could also be recycled for further use. Moreover, Zr and Sn were also successfully incorporated into the framework of ordered crystalline mesoporous materials by the same simple m...

A Novel Preparation of SAPO-18 Molecular Sieve with Enhanced Stability for Dimethyl Ether to Olefins

SAPO-18 molecular sieve is an important catalyst for dimethylether-to-olefins (DTO) reaction. Although the conventional synthesized SAPO-18 using N,N′-diisopropylethylamine (DIEA) alone exhibits nanoparticles and better catalytic performance due to the weaker diffusion resistance, its high cost of preparation and difficult separation of the powder limit the industrial process of this type of molecular sieve. Therefore, reducing the cost and increasing the particle size appropriately become the key issues for its practical application. In this study, SAPO-18 catalysts were synthesized hydrothermally using mixture of triethylamine (TEA) and a small amount of DIEA as templates. The results revealed that fairly pure SAPO-18 molecular sieve with particle size of approximately 1.0 μm could be synthesized under the initial gel composition as: xDIEA:(1.4−x)TEA: 1.0 Al2O3: 0.9 P2O5:0.6SiO2:50H2O, where x varies from 0.2 to 0.6. Furthermore, the catalytic performance for DTO reaction over the novel synthesized SAPO-18 catalysts showed higher selectivities to light olefins and much lower coke deposition than the conventional synthesized SAPO-18 using DIEA alone.

Relationship between the Catalytic Activities of Acidic Protons in Aluminosilicate and Silicoaluminophosphate Molecular Sieves for n-Butane Cracking and Their 1H Chemical Shifts Measured at the Reaction Temperature

Zeolite materials are used as solid acid catalysts in petrochemical reactions, which typically occur at Bronsted acid sites located at bridging hydroxyl groups (Si–OH–Al). These sites have been investigated spectroscopically, albeit at room temperature; a proper understanding requires that such data be acquired at actual reaction temperatures. The influence of temperature on the 1H chemical shifts and dynamic properties of Si–OH–Al sites in proton-type aluminosilicate and silicoaluminophosphate molecular sieves was examined by variable-temperature 1H magic-angle spinning nuclear magnetic resonance spectroscopy, from 298 to 673 K. The chemical shifts and line widths of the peaks due to Si–OH–Al protons were strongly dependent on the temperature, whereas those due to P–OH protons in the silicoaluminophosphate were slightly dependent. The relationship between the 1H chemical shifts of the Si–OH–Al groups in both types of molecular sieves, (δ1H) and their catalytic activities for n-butane cracking were examin...

High-performance carbon molecular sieve membranes for ethylene/ethane separation derived from an intrinsically microporous polyimide

An intrinsically microporous polymer with hydroxyl functionalities, PIM-6FDA-OH, was used as a precursor for various types of carbon molecular sieve (CMS) membranes for ethylene/ethane separation. The pristine polyimide films were heated under controlled N2 atmosphere at different stages from 500 to 800°C. All CMS samples carbonized above 600°C surpassed the polymeric ethylene/ethane upper bound. Pure-gas selectivity reached 17.5 for the CMS carbonized at 800°C with an ethylene permeability of about 10Barrer at 2bar and 35°C, becoming the most selective CMS for ethylene/ethane separation reported to date. As expected, gravimetric sorption experiments showed that all CMS membranes had ethylene/ethane solubility selectivities close to one. The permselectivity increased with increasing pyrolysis temperature due to densification of the micropores in the CMS membranes, leading to enhanced diffusivity selectivity. Mixed-gas tests with a binary 50:50 v/v ethylene/ethane feed showed a decrease in selectivity from 14 to 8.3 as the total feed pressure was increased from 4 to 20bar. The selectivity drop under mixed-gas conditions was attributed to non-ideal effects: (i) competitive sorption that reduced the permeability of ethylene and (ii) dilation of the CMS that resulted in an increase in the ethane permeability.

Cryogenic separation of an oxygen-argon mixture in natural air samples for the determination of isotope and molecular ratios.

The separation and purification of oxygen-argon mixtures are critical in the high-precision analysis of Δ(17) O and δ(O2 /Ar) for geochemical applications. At present, chromatographic methods are used for the separation and purification of oxygen-argon mixtures or pure oxygen, but these methods require the use of high-purity helium as a carrier gas. Considerable interest has been expressed in the development of a helium-free cryogenic separation of oxygen-argon mixtures in natural air samples. The precise and simplified cryogenic separation of oxygen-argon mixtures from natural air samples presented here was made possible using a single 5A (30/60 mesh) molecular sieve column. The method involves the trapping of eluted gases using molecular sieves at liquid nitrogen temperature, which is associated with isotopic fractionation. We tested the proposed method for the determination of isotopic fractionations during the gas exchange between water and atmospheric air at equilibrium. The dependency of fractionation was studied at different water temperatures and for different methods of equilibration (bubbling and stirring). Isotopic and molecular fractionations during gas desorption from molecular sieves were studied for different amounts and types of molecular sieves. Repeated measurements of atmospheric air yielded a reproducibility (±SD) of 0.021 ‰, 0.044 ‰, 15 per meg and 1.9 ‰ for δ(17) O, δ(18) O, Δ(17) O and δ(O2 /Ar) values, respectively. We applied the method to determine equilibrium isotope fractionation during gas exchange between air and water. Consistent δ(18) O and Δ(17) O results were obtained with the latest two studies, whereas there was a significant difference in δ(18) O values between seawater and deionized water. We have revised a helium-free, cryogenic separation of oxygen-argon mixtures in natural air samples for isotopic and molecular ratio analysis. The use of a single 13X (1/8" pellet) molecular sieve yielded the smallest isotopic and molecular fractionations, and this fractionation by molecular sieves can be corrected by the amount of molecular sieve used in the experiment. The reproducibility of the method was tested by the measurement of the oxygen isotope ratios of dissolved oxygen at equilibrium with atmospheric air. We confirmed that the choice of methods for making air-equilibrated water was not related to the magnitude of isotope fractionation, whereas there was a difference between seawater and deionized water.

Aminopropyl-modified mesoporous molecular sieves as efficient adsorbents for removal of auxins

In the present study, mesoporous siliceous materials grafted with 3-aminopropyltriethoxysilane (APTES) were examined as sorbents for removal of chosen plant growth factors (auxins) such as 1-naphthaleneacetic acid (NAA), indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA). Four different types of mesoporous molecular sieves including SBA-15, PHTS, SBA-16 and MCF have been prepared via non-ionic surfactant-assisted soft templating method. Silica molecular sieves were thoroughly characterized by nitrogen adsorption–desorption analysis, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FT-IR). The maximum adsorption capacity (Qmax) for NAA, IAA and IBA was in the range from 51.0 to 140.8mg/g and from 4.3 to 7.3mg/g for aminopropyl-modified adsorbents and pure silicas, respectively. The best adsorption performance was observed for IAA entrapment using both APTES-functionalized SBA-15 and MCF matrices (Qmax of 140.8 and 137.0mg/g, respectively) which can be ascribed to their larger pore volumes and pore diameters. Moreover, these silicas were characterized by the highest adsorption efficiency exceeding 90% at low pollutant concentration. The experimental points for adsorption of plant growth factors onto aminopropyl-modified mesoporous molecular sieves fitted well to the Langmuir equation.

Carbonylation of Methanol with CO in Presence Potassium Methoxide Catalyst

Catalysts prepared from potassium hydroxide and methanol were tested for methanol carbonylation with CO in the range of 70-90oC and 20-25kg/cm2(g). Methyl formate was produced selectively under the studied conditions. Lower temperatures and higher pressures enhanced the conversion of CO. Water in the catalyst solution did not completion removed by molecular sieve type 3A, thus the catalyst activity becomes decreased. The influence of inert gases in the gas mixture will cause the partial pressure of CO decreased and also conversion of CO. The reaction rate was first order with respect to the concentration of CO in the gas phase. The activation energy was found to be 14.95kJ/mol and frequency collision factor is 0.59 min-1.

N-methyldiethanolamine: A multifunctional structure-directing agent for the synthesis of SAPO and AlPO molecular sieves

In the present study, N-methyldiethanolamine (MDEA) is demonstrated to be a multifunctional structure-directing agent for the synthesis of aluminophosphate-based molecular sieves. Four types of molecular sieves, including SAPO-34, -35, AlPO-9 and -22, are for the first time acquired with MDEA as a novel template. The phase selectivity of the present synthesis is found to be condition-dependent. SAPO-34 (CHA) crystallizes from a conventional hydrothermal system with a higher MDEA concentration. When using MDEA as both the template and solvent, pure SAPO-35 (LEV) is obtained from the synthetic gel with a high P2O5/Al2O3 ratio of (2–3), in which the concentration of MDEA could be varied in a wide range. AlPO-9 and AlPO-22 (AWW) are synthesized under the similar conditions to SAPO-35, except without the addition of Si source. The physicochemical properties of the obtained samples are investigated by XRD, XRF, SEM, N2 physisorption, TG-DSC, and various NMR spectra (13C, 29Si, 27Al and 31P). Both SAPO-34 and SAPO-35 show good thermal stability, large surface area, and high pore volume. The catalytic performance of SAPO-34 is evaluated by the methanol-to-olefins (MTO) reaction and a good (C2H4+C3H6) selectivity of 82.7% has been achieved.

Synthesis of Gallosilicate Type Molecular Sieve with CDO Topology and Application to Solid Acid Catalyst

Synthesis of Gallosilicate Type Molecular Sieve with CDO Topology and Application to Solid Acid Catalyst

Verifying the mechanism of the ethene-to-propene conversion on zeolite H-SSZ-13

Several types of microporous molecular sieves with similar nSi/nAl ratios (except for SAPO-34) and different pore structures were prepared and applied as ethene-to-propene (ETP) catalysts. H-SSZ-13 zeolite consisting of chabazite cages connected via 8-ring windows possessed the highest adsorption capacity for ethene and exhibited the best activity in the ETP conversion. The decreasing amount of Brønsted acid sites after dealumination of H-SSZ-13 caused a prolonged lifetime of the catalyst in the ETP reaction. The reaction mechanism and deactivation behavior of H-SSZ-13 catalysts during the ETP process were investigated by in situ FT-IR, UV/Vis, GC–MS, TGA and 1H MAS NMR methods. Ethene was rapidly oligomerized and converted into naphthalene-based carbenium ions, playing a significant role in the ETP reaction. The accumulation of these species lead to the formation of polycyclic aromatics, which are responsible for a total blocking of H-SSZ-13 pores, and cause the deactivation of the catalyst.

Microwave radiation hydrothermal synthesis and characterization of micro- and mesoporous composite molecular sieve Y/SBA-15

A microwave radiation hydrothermal method to control synthesis of micro- and mesoporous Y/SBA-15 composite molecular sieves was reported. The synthesized SBA-15 and Y/SBA-15 were characterized by scanning electron microscopy (SEM) and N2 adsorption–desorption. The three kinds of different concentrations of hydrochloric acid (0.75M, 2M and 3.25M) were used to investigate the effect on Y/SBA-15. The analysis results of the composite products indicated that the optimization synthesis condition employed zeolite type Y and TEOS as silicon sources under 0.75M hydrochloric acid by the microwave radiation hydrothermal synthesis method. The N2 adsorption–desorption test results of micro–mesoporous composite molecular sieve type Y/SBA-15 in mesoporous extent indicated that SBET is 355.529m2/g, D‾BET is 4.050nm, and mesoporous aperture focuses on the distribution region of 5.3nm. It was found that the received composite product has an appropriate proportion of smaller size, larger size pore structure and the thicker pore wall. In addition, its internal channels have a high degree of order and smooth flow in long-range channels.