Medium Pore Research Articles

Mechanism of action of heat treatment on the adsorption of polymorphic gases from raw coal

ABSTRACT The adsorption properties of coal determine the economic benefits of coalbed methane (CBM) extraction. To investigate the gas adsorption behavior of raw coal after heating, gas adsorption tests and pore characterization tests were conducted. Meanwhile, the influence of high temperature on coal pore structure and polymorphic gas adsorption was analyzed. The results showed that the gas adsorption gradually increased with the increase of coal grade at the same temperature. For the same coal grade coals, the adsorbed gas content decreased 5.96%-21.53% and the non-adsorbed gas content increased 51.25%-95.47% with the increase of temperature. The high temperature has a dilating effect on coal pores, causing the proportion of tiny pores to decrease and the adsorbed gas storage capacity to become weaker, and the proportion of medium and large pores to increase and the non-adsorbed gas storage capacity to become stronger. This study can provide data support for coalbed methane heat injection extraction.

Changes in Soil Water Retention and Micromorphological Properties Induced by Wetting and Drying Cycles

Wetting and drying (W-D) cycles are responsible for significant changes in soil structure. Soil often undergoes irreversible changes affecting infiltration and solute retention through W-D cycles. Thus, it becomes essential to evaluate how soils under natural conditions are altered by W-D cycles. This study analyzed two non-cultivated (from grassland and secondary forest) Oxisols (Typic Hapludox and Rhodic Hapludox) of different textures under 0 and 6 W-D cycles. The main results obtained showed that soil water retention was mainly affected in the driest regions (smaller pore sizes). The contribution of residual pores to total porosity increased with 6 W-D and transmission pores decreased in both soils. The Rhodic Hapludox presented differences in water content at field capacity (increase), while the Typic Hapludox showed alterations at the permanent wilting point (increase), affecting the amount of free water (Rhodic Hapludox) and water available to plants (Typic Hapludox). Both soils showed increases in imaged porosity with 6 W-D. Variations in the contribution of small and medium rounded pores, mainly large and irregular (with an increase in both soils not significant in the Rhodic Hapludox), could explain the results observed. The micromorphological properties were mainly influenced by changes in the number of pores, in which smaller pores joined, forming larger ones, increasing the areas occupied by larger pores. Overall, this study showed that the investigated soils presented pore systems with adequate water infiltration and retention capacities before and after continuous W-D cycles.

Humin Formation on SBA-15-pr-SO3H Catalysts during the Alcoholysis of Furfuryl Alcohol to Ethyl Levulinate: Effect of Pore Size on Catalyst Stability, Transport, and Adsorption

Herein, the alcoholysis of furfuryl alcohol in a series of SBA-15-pr-SO3H catalysts with different pore sizes is reported. Elemental analysis and NMR relaxation/diffusion methods show that changes in pore size have a significant effect on catalyst activity and durability. In particular, the decrease in catalyst activity after catalyst reuse is mainly due to carbonaceous deposition, whereas leaching of sulfonic acid groups is not significant. This effect is more pronounced in the largest-pore-size catalyst C3, which rapidly deactivates after one reaction cycle, whereas catalysts with a relatively medium and small average pore size (named, respectively, C2 and C1) deactivate after two reaction cycles and to a lesser extent. CHNS elemental analysis showed that C1 and C3 experience a similar amount of carbonaceous deposition, suggesting that the increased reusability of the small-pore-size catalyst can be attributed to the presence of SO3H groups mostly present on the external surface, as corroborated by results on pore clogging obtained by NMR relaxation measurements. The increased reusability of the C2 catalyst is attributed to a lower amount of humin being formed and, at the same time, reduced pore clogging, which helps to maintain accessible the internal pore space.

Microscopic Production Characteristics of Pore Crude Oil and Influencing Factors during Enhanced Oil Recovery by Air Injection in Shale Oil Reservoirs.

High-pressure air injection (HPAI) is one of the effective methods to improve shale oil recovery after the primary depletion process. However, the seepage mechanisms and microscopic production characteristics between air and crude oil are complicated in porous media during the air flooding process. In this paper, an online nuclear magnetic resonance (NMR) dynamic physical simulation method for enhanced oil recovery (EOR) by air injection in shale oil was established by combining high-temperature and high-pressure physical simulation systems with NMR. The microscopic production characteristics of air flooding were investigated by quantifying fluid saturation, recovery, and residual oil distribution in different sizes of pores, and the air displacement mechanism of shale oil was discussed. On this basis, the effects of air oxygen concentration, permeability, injection pressure, and fracture on recovery were studied, and the migration mode of crude oil in fractures was explored. The results show that the shale oil is mainly found in <0.1 μm (small pores), followed by 0.1-1 μm (medium pores), and 1-10 μm (macropores); thus, it is critical to enhancing oil recovery in pores less than 0.1 and 0.1-1 μm. The low-temperature oxidation (LTO) reaction can occur by injecting air into depleted shale reservoirs, which has a certain effect on oil expansion, viscosity reduction, and thermal mixing phases, thereby greatly improving shale oil recovery. There is a positive relationship between air oxygen concentration and oil recovery; the recoveries of small pores and macropores can increase by 3.53 and 4.28%, respectively, and they contribute 45.87-53.68% of the produced oil. High permeability means good pore-throat connectivity and greater oil recovery, and the production degree of crude oil in three types of pores can be increased by 10.36-24.69%. Appropriate injection pressure is beneficial to increasing the oil-gas contact time and delaying gas breakthrough, but high injection pressure will result in early gas channeling, which causes the crude oil in small pores to be difficult to produce. Notably, the matrix can supply oil to fractures due to the mass exchange between matrix fractures and the increase of the oil drainage area, and the recoveries of medium pores and macropores in fractured cores increased by 9.01 and 18.39%, respectively; fractures can act as bridges for matrix crude oil migration, which means that proper fracturing before gas injection can make the EOR better. This study provides a new idea and a theoretical basis for improving shale oil recovery and clarifies the microscopic production characteristics of shale reservoirs.

Effect of foam stabilization on the properties of foamed concrete modified by expanded polystyrene

This paper aims to study the modified foamed concrete by mixing expanded polystyrene (EPS) particles. In order to analyze the influence of EPS particle dosage and particle size on the mechanical properties and thermal conductivity of the foamed concrete, the EPS modified foamed concrete was compared with the ordinary foamed concrete. The pore structures of the foamed concrete with and without EPS were characterized and compared by scanning electronic microscopy (SEM), mercury intrusion porosimetry (MIP), and image-pro plus (IPP). The results showed that when large and small size EPS replaced 60% foam, the water absorption of the EPS modified foamed concrete was approximately 38% and 55% lower than that of the ordinary foamed concrete, respectively, with a corresponding 0.13 and 0.5 MPa increase in compressive strength. In addition, the thermal conductivity of the EPS modified foamed concrete was similar to/even slightly lower than that of the ordinary foamed concrete. The addition of EPS in foamed concrete increased the proportion of small connected pores and reduced the proportion of medium and large pores. Overall, the addition of EPS in foamed concrete can effectively improve the stability.

Laboratory investigation and BP neural network modeling on heat-activated oil shale semi-coke attributable to the mechanical properties of concrete

Concrete construction requires the consumption of large quantities of raw materials. If oil shale semi-coke can be used in concrete projects in a reasonable way, not only will it ease the shortage of raw materials for concrete, but it will also consume oil shale semi-coke and reduce its ecological impact. This investigation aims to study the feasibility of using semi-coke in concrete construction based on its mechanical properties. The chemical components and microstructures of four thermal activation temperature oil shale semi-cokes were first analyzed by X-Ray Fluorescence (XRF) and scanning electron microscope (SEM). Then, by replacing the cement with equal mass of semi-coke, the effect of heat-activated calcination temperature and the amount of semi-coke admixture on the mechanical strength of mortars sand and concrete was tested. Finally, a BP neural network was used to establish a strength prediction model for semi-coke concrete and the evolution of internal pores of semi-coke concrete was analyzed by nuclear magnetic resonance (NMR). The results show that semi-coke is mainly composed of SiO2 and Al2O3, which can be used as a concrete mineral admixture for volcanic ash reaction. The oil shale semi-coke is flaky with a porous surface, resulting in the semi-coke contributing more to the flexural strength of the mortar than to the compressive strength. At the calcination temperature of 500 ℃ and a semi-coke content of 15%, the concrete has the lowest porosity and the best mechanical properties, and is therefore recommended. The developed BP neural network prediction model has a high prediction level and can provide guidance for practical engineering. The increase in the amount of coke admixture leads to a continuous increase in the number of pores in the medium and large pore sizes inside the concrete, which is the main reason for the change in concrete strength due to semi-coke.

Microstructure Study of High-Rank Coal in an Alkaline Solution at the Chengzhuang Mine.

To study the adsorption performance of coal bodies after alkaline solution erosion and the microscopic mechanism of alkali erosion on coal bodies, isothermal adsorption experiments at different pH values and with different numbers of soaking days were conducted on high-order coal bodies from the Chengzhuang mine. The results showed that the adsorption capacity of the coal bodies after alkali leaching was improved compared to that of the original coal, all of which was in accordance with the Langmuir equation. The unit adsorption capacity of coal samples increased gradually with an increase in the number of soaking days and solution pH, reaching the maximum at pH 13 and eight soaking days. The adsorption constant a of the coal sample was positively correlated with the pH, and the number of soaking days was a power exponential function; the adsorption constant b increased gradually with an increase in the pH of the solution and increased first and then decreased with an increase in the number of soaking days. The change in the adsorption of coal samples occurs because the alkaline solution reacts with the minerals in the coal as well as the mineral ions, and the resulting complex gels and precipitates block the pore channels of the coal body, which in turn inhibits the adsorption of gases. The presence of Na, Mg, Al, Si, Ca, Fe, and other elemental compounds detected in the generated sediments verified the mechanism of alkaline solution erosion. The changes in the microscopic pore structure of the coal body were quantified by low-temperature liquid nitrogen adsorption experiments. The small and medium pore volumes of the coal samples reached the maximum values at pH 13 and with eight soaking days, which is in agreement with the conclusion of optimal alkali modification.

Enhancing both strength and permeability of pervious concrete by optimizing pore structure: An experimental study

AbstractThe large porosity enables pervious concrete to obtain water permeability, but seriously decreases its strength. Hence, how to coordinate the contradiction between strength and permeability is a critical challenge for pervious concrete. This research was mainly aimed at mix design of pervious concrete for enhancing both strength and permeability by optimizing the pore structure. Six groups of pervious concrete with 15% target porosity were prepared by 10–15 mm coarse aggregate and different fine aggregate (natural sand, basalt aggregate, and steel slag). Moreover, a group of pervious concrete with 20% target porosity as control samples was prepared by 4.75–9.5 mm aggregate. The compressive strength and permeability coefficient of these samples were tested. Based on CT scanning and image analysis, the influence of pore structure optimization on permeability and compressive strength was analyzed. The results show that though the porosity is reduced by 5% after pore structure optimization, the porosity of large pores and medium pores changes little, the porosity of small pores decreased significantly, and finally the average pore size is still increased. This can explain why the experimental groups gain a similar/better permeability as the control group. The experimental groups of cement or steel slag have an increased compressive strength compared to the control group, which is due to the decrease of porosity and “small pores” content, as well as more abundant hydration products.

Experimental analysis of the pore structure, relative permeability, and water flooding characteristics of the Yan'an Formation sandstone, southwestern Ordos Basin

The oil and gas potential of the Yan'an Formation in the Ordos Basin has yet to be fully tapped. In this study, the pore structure, mobile fluid saturation, and water flooding micro-mechanism of the Yan'an Formation sandstone are systematically studied through the application of a series of rock physics and fluid experiments. The results show that there is a good positive correlation between porosity and permeability, and the reservoirs are divided into types Ⅰ, Ⅱ, and Ⅲ. Mercury injection tests show that the average pore throat radius of the oil-bearing reservoir ranges from 1 to 7 μm. The displacement pressure of the Yan'an Formation is also relatively low, and it decreases from 0.1 MPa to 0.01 MPa as the rock porosity increases from 11% to 18%. NMR tests show that small (diameter <0.5 μm) and medium pores (diameter ranging from 0.5 to 2.5 μm) are predominant in the reservoir. Different types of reservoirs have different characteristics of relative permeability curve. In addition, when the average oil recovery rate is less than 1 ml/min, the oil displacement efficiency increases faster. However, when the average oil recovery rate is between 1–3.5 ml/min, the oil displacement efficiency is maintained at around 27%–30%. Physical properties of the reservoir, pore-throat structure, experimental pressure difference, and pore volume injected — all have significant effects on oil displacement efficiency. For Type Ⅰ and Type Ⅱ reservoirs, the increase of the pore volume injected has a significant effect on oil displacement efficiency. However, for Type Ⅲ reservoirs, the change of pore volume injected has insignificant effect on oil displacement efficiency. This study provides a reference for the formulation of estimated ultimate recovery (EUR) measures for similar sandstone reservoirs.

Formation and dissociation of CO2 hydrates in porous media in the presence of clay suspensions

CO2 storage in marine sediments in the form of solid hydrates with high storage capacity and stability is a promising approach for the control of greenhouse gas pollution. Specifically, clay is much abundant in marine minerals, and multiple forces exist between fine clay particles suspended in seawater, significantly affecting the hydrate formation and dissociation behavior. This study investigates the phase transition performance of CO2 hydrates with or without montmorillonite and illite particles using low-field nuclear magnetic resonance. According to the DLVO theory, the total interaction potential between the montmorillonite particles reached 358 kbT, with that between illite particles being only 43 kbT. It was found that water in large pores was preferentially consumed during hydrate formation, with clay particles significantly promoting the conversion of water into hydrate. In seawater-montmorillonite and seawater-illite solutions, a higher number of water molecules was detected in the small and medium pores, respectively. Notably, the initial pore structure changed upon hydrate dissociation, with more medium pores formed. This effect was enhanced in the seawater-montmorillonite solutions and weakened in seawater-illite solutions. The findings could further clarify the formation and dissociation kinetics of CO2 hydrates in the presence of clay particles, as well as the geological structure evolution and safety of CO2 hydrate storage under the seafloor.

Analysis of the Influence of Micro-Pore Structure on Oil Occurrence Using Nano-CT Scanning and Nuclear Magnetic Resonance Technology: An Example from Chang 8 Tight Sandstone Reservoir, Jiyuan, Ordos Basin

The micro-pore structure of a tight sandstone reservoir remarkably impacts the occurrence characteristics of the tight oil. The micro-pore structure of the Jiyuan Chang 8 tight sandstone reservoir in the Ordos Basin was examined in this research using a core physical property test, an environmental scanning electron microscope, thin section identification, and high-pressure mercury intrusion. Using nano-CT scanning and nuclear magnetic resonance technologies, representative core samples were chosen for studies evaluating the tight oil occurrence statically and dynamically. The micro-pore structure effect of a tight sandstone reservoir on the occurrence of tight oil was investigated, and the occurrence of tight oil in the reservoir forming process was discussed. It was significant to the study of tight oil in the reservoir forming process in Ordos Basin. Findings indicated that the Chang 8 reservoir in Jiyuan, Ordos Basin has poor physical properties and exhibits a high degree of heterogeneity. In addition, the oil charging simulation experiment (oil charging) can be separated into the following three stages: fast growth, gradual growth, and stability. In the process of crude oil charging, oil always preferentially entered into medium pores and large pores. These pores were the primary areas of tight oil distribution. Furthermore, the occurrence of tight oil was affected by pore type, pore structure parameters, throat parameters, and combination mode of pore and throat. First, substantially large and medium pores lead to effective pore connectivity and generate a considerable amount of tight oil. The occurrence morphology includes oil film, cluster, porous, and isolated. Second, the greater the degree of intergranular pore growth and soluble feldspar pore development, the thicker the throat, the more developed the effective throat, and the greater the quantity of tight oil. Finally, oil saturation was negatively correlated with median pressure and displacement pressure and positively correlated with sorting factors, median radius, maximum pore throat radius, and efficiency of inverted mercury.

Pore shrinkage capacity of Shajiang black soils (Vertisols) on the North China Plain and its influencing factors

Different pore sizes present different pore shrinkage capacities in a nonrigid soil. However, the shrinkage capacities of different pore sizes and their influencing factors are not clear. We aimed to quantify the shrinkage capacities of different pore sizes (large pores, > 50 μm; medium pores, 0.2–50 μm; fine pores, < 0.2 μm) and determine how soil properties impact soil shrinkage capacity at the regional scale. Two sampling transects from west to east (360 km long, 35 samples) and from north to south (190 km long, 29 samples) were selected to investigate soil shrinkage capacity and physicochemical properties of at 0–20 cm depth in the Vertisol (locally known as Shajiang black soil) region of the North China Plain. The results showed that soil total shrinkage capacity, indicated by the coefficient of linear extensibility (COLE), had a mean value of 0.041–0.051 in the west-east and north-south transects. Large pores had higher pore shrinkage index (PSI) values (0.103–0.109) than medium (0.077–0.096) and fine (0.087–0.091) pores. The PSI of fine pores showed a fluctuating increasing trend from northwest to southeast, and the fine pore shrinkage capacity determined the COLE (r2 = 0.789, P < 0.001). The PSI of large pores had a significant relationship with soil bulk density (r = 0.281, P < 0.05) and organic carbon (r = -0.311, P < 0.05), whereas those of medium and fine pores were correlated with soil clay content (r = 0.381 and 0.687, respectively, P < 0.001). In addition, the PSI of fine pores was also correlated with montmorillonite content (r = 0.387, P < 0.01). It can be concluded that the PSI of large pores is related to anthropogenically influenced soil properties with low stability, whereas those of medium and fine pores are related to pedogenic properties. The high variability in anthropogenic and pedogenic factors explains the spatial pattern of Vertisol shrinkage capacity on the North China Plain.

Structural and dynamic characterization of two-component waterproof mortars by 1H NMR, FT-IR, mechanical and SEM investigations

Advanced 1H NMR relaxometry is an important tool used for the characterization of a large range of materials like mortars. CPMG pulse sequence and saturation recovery methods were used for the measurement of four samples (MF, C166, P288, AQSE) of two-component waterproof mortars at 1, 3, 7, and 28 days after preparation. In general, four dynamics components were observed for the T2 Laplace distributions can be associated with 1H from bound water and with those from small, medium, and large pores. Due to particular characteristics, such as high elasticity the flexural tensile strength and compressive strength could not be measured for all samples. SEM images were recorded, and the reported composition was correlated to NMR parameters and FT-IR spectra. The hydrating behaviour of the two-component waterproofing mortar dried under natural conditions was observed for 28 days and then the hydration process was characterized using 2D 1H NMR T1-T2 correlation map.

Preparation of three-dimensionally linked pore-like porous atomized ceramics with high oil and water absorption rates

Ceramic atomization cores are a new application of porous ceramics; however, the challenging regulation of the pore structures of porous ceramics has limited their application. To improve the low liquid absorption rates and low liquid storage capacity of porous ceramics in the field of atomization, this study used three substances, polymethyl methacrylate (PMMA), starch, and diatomaceous earth, to produce porous ceramics with a three-dimensional interconnected triple-porous structure by sacrificial templating. In the porous ceramics, large pores resulting from PMMA increase liquid storing capacity, medium pores resulting from the starch facilitate the transport of liquid, and small pores resulting from diatomaceous earth enhance capillary action, significantly increasing the rate of liquid absorption. By varying the PMMA contents and type of starch in the preform, water and oil storage capacities of up to 123% and 143%, respectively, can be achieved. We found that an optimized porous ceramic with dimensions of 15 mm × 15 mm × 15 mm absorbs water rapidly (reaching saturation in only 1.67 s), demonstrates good solid–liquid properties and shape stability, and is recyclable (requires drying before reuse). The proposed porous ceramics have promising atomization core and oil–water separation applications.

Pore-Throat Structure and Fractal Characteristics of Tight Sandstones: A Case Study from the Chang 63 Sublayer, Southeast Ordos Basin

The micropore-throat structure is a controlling factor on the capacity of storage and seepage for the tight sandstone reservoirs. Therefore, quantitatively analyzing the pore-throat structure is crucial for realizing the oil accumulated in the tight reservoirs. To study the micropore-throat, a battery of experiments such as casting thin sections, scanning electron microscopy, high-pressure mercury injection, and the petrophysical characteristics of reservoirs were conducted on ten samples gathered in the Late Triassic Chang 63 sublayer in the Southeast Ordos Basin, China. The main pore types of the samples are intergranular pores, feldspar dissolved pores, and intergranular dissolved pores. Meanwhile, the pore-throat structure of each sample was identified as large pores, medium pores, and small pores by combining the result of HPMI with fractal theory. The corresponding mean values of the fractal dimension D for large, medium, and small pores are 2.83, 2.69, and 2.31, respectively, indicating that the complex structure and strong heterogeneity were presented in the large pores according to the maximum fractal dimension. In addition, the fractal dimension of the medium pores ( D P − 2 ) has a negative correlation with porosity, permeability, median pore-throat radius, maximum mercury saturation, mercury withdrawal efficiency, displacement pressure, and content of quartz, while a positive correlation with feldspar content, sorting coefficient, and coefficient of variation. Thus, the reservoir space and seepage capacity of all samples in this study were determined by the size, complexity, and distribution of the medium pores. Furthermore, the content of quartz contributes to the storage of the reservoir and the homogeneity of the pore-throat structure, thereby the storage capacity improves with the increase of quartz content. Feldspar dissolution pores are developed widely in the study area, leading to various pores with diverse types, sizes, complex structures, and large fractal dimensions. Although the storage capacity of tight sandstone reservoirs was enhanced with increasing feldspar content, the pore-throat structure complexity was also stronger, resulting in the reduction seepage capacity of fluid.

Curing conditions effect on pore structure, compressive strength and elastic modulus of cementitious tailings backfills

As a widespread application in underground metal mines, cementitious tailings backfill (CTB) has a significant implication for recycling dangerous process tailings and enhancing the safety of mining voids. The pore structure of CTB that is liable on the features and proportions of tailings and binders is correlated to its mechanical characteristics (i.e., elastic modulus, uniaxial compressive strength). This study deals with the influence of curing conditions such as temperature (20–50 °C), stress (0–540 kPa), and time (3–28 days) on mechanical and pore structure characteristics of CTB. Fill samples were prepared in a stable solid dosage and cement/water ratio of 76% and 1/6, respectively, and put into cylindrical molds (D × H: 50 × 100 mm). A new lab instrument with adjustable curing conditions was adopted for fills. A PC-controlled mechanical press and Hg intrusion porosimetry were applied to assess CTB's strength and pore structure properties. Results suggest that, with advancing curing temperature/stress, the strength and elastic modulus of CTB show a rising trend, while its growth rates show a falling trend. CTB's porosity shows a declining trend, and it exists a good linear correlation between fill's strength and apparent porosity. CTB's strength essentially depends on the volume of medium (1–10 μm) and micro (0.01–1 μm) pores. As a result, several practical equations for CTB specimens are established, which consider types of tailings and admixtures.

Exploration of microstructure characteristics and mechanical behaviors of thermal-damaged argillaceous sandstone via LF-NMR and µ-CT technologies

The effect of high temperature on the microstructure and mechanical behavior of rocks is a fundamental issue relevant to the exploitation of underground oil and gas resources, underground disposal of highly radioactive nuclear waste, and the development of geothermal energy. In this study, samples of argillaceous sandstone are subjected to high-temperature treatments (i.e., 25 ºC, 300 ºC, 600 ºC, 900 ºC, 1000 ºC, and 1200 ºC) followed by a series of uniaxial compression tests. Qualitative and quantitative analyses of the microscopic structures of the samples are carried out using scanning electron microscopy (SEM), low-field nuclear magnetic resonance (LF-NMR) and micron-scale computed tomography (µ-CT). Thermal damage defined by porosity is established and used to describe the evolution of rock damage over the temperature increase. After the high-temperature treatments, LF-NMR results indicate that small and medium pores consistently dominate the structure, with pore volumes of up to 98.8% to 100%. µ-CT test results show that the distribution frequency of medium pores is 16.5–28.3% and that of large pores is 71.7–83.5%. The µ-CT porosity ranges from 11.1 to 15.2% and the LF-NMR porosity ranges from 18.9 to 26.3%. When subjected to the same temperature, the µ-CT porosity is generally smaller than the LF-NMR porosity. When the temperature is increased, the peak stress and elastic modulus increases first and then decreases, while the peak strain decreases first and then increases. Test results of three mechanical parameters all indicate that 300 ºC is probably the threshold temperature of the test rock type, and the SEM, LF-NMR and µ-CT test results confirm this temperature. The relationship between thermal damage and temperature suggests that the argillaceous sandstone evolves through strengthening, damage derivation, and damage development as applied temperature increases.

Kinetic and Spectroscopic Studies of Methyl Ester Promoted Methanol Dehydration to Dimethyl Ether on ZSM-5 Zeolite

Methyl carboxylate esters have been shown to be potent promoters of low-temperature methanol dehydration to dimethyl ether (DME) using various zeolite catalysts. In the present work, catalytic kinetic studies, in-situ Fourier-transform infrared spectroscopy (FT-IR) and solid-state nuclear magnetic resonance spectroscopy (NMR) techniques were used to elucidate the promotional mechanism of methyl carboxylate esters on methanol dehydration to DME, using the medium pore zeolite H-ZSM-5 (MFI) as the catalyst. Kinetic studies were performed using the very potent methyl n-hexanoate promoter. The DME yield was dependent on both the methanol and methyl n-hexanoate partial pressures across the temperature ranges used in this study (110 to 130 °C). This is consistent with the promoted reaction being a bimolecular reaction between methanol and ester species adsorbed at the catalyst active sites, via an SN2 type reaction, as previously postulated. The in-situ FT-IR studies reveal that the Brønsted acid (BA) sites on H-ZSM-5 were very rapidly titrated by ester carbonyl group adsorption and bonded more strongly with esters than with methanol. Upon methanol addition, an even lower DME formation temperature (30 °C) was observed with methyl n-hexanoate pretreated H-ZSM-5 samples in the in-situ NMR studies, further confirming the strong promotion of this methyl ester on methanol dehydration to DME. The adsorption and reactivity of different methyl esters on H-ZSM-5 indicates that while methyl formate more easily dissociates into a surface methoxy species, [Si(OMe)Al], and carboxylic acid, it is a less potent promoter than alkyl-chain-containing methyl esters in methanol dehydration to DME, which in turn did not show this dissociative behavior in the low-temperature NMR studies. This indicates that methyl alkyl carboxylates do not need to be dissociated to a surface methoxy species to promote the methanol dehydration reaction and that a bimolecular associative mechanism plays an important role in promoting DME formation.

Effect of Membrane Pore Size on Membrane Fouling of Corundum Ceramic Membrane in MBR.

Ceramic membrane has emerged as a promising material to address the membrane fouling issue in membrane bioreactors (MBR). In order to optimize the structural property of ceramic membrane, four corundum ceramic membranes with the mean pore size of 0.50, 0.63, 0.80, and 1.02 μm were prepared, which were designated as C5, C7, C13, and C20, respectively. Long-term MBR experiments showed that the C7 membrane with medium pore size experienced the lowest trans-membrane pressure development rate. Both the decrease and increase of membrane pore size would lead to more severe membrane fouling in the MBR. It was also interesting that with the increase of membrane pore size, the relative proportion of cake layer resistance in total fouling resistance was gradually increased. The content of dissolved organic foulants (i.e., protein, polysaccharide and DOC) on the surface of C7 was quantified as the lowest among the different ceramic membranes. Microbial community analysis also revealed the C7 had a lower relative abundance of membrane fouling associated bacteria in its cake layer. The results clearly demonstrated that ceramic membrane fouling in MBR could be effectively alleviated through optimizing the membrane pore size, which was a key structural factor for preparation of ceramic membrane.

ECNU-13: A High-Silica Zeolite with Three-Dimensional and High-Connectivity Multi-Pore Structures for Selective Alkene Cracking.

A high-silica zeolite ECNU-13 (Si/Al=23) with a new three-dimensional (3D) pore system and a nanosized morphology has been developed, consisting of multitudes of 10-membered ring (10-R) medium pores and one set of 8-R small pores. A phase-discrimination strategy was proposed to synthesize ECNU-13 by regulating the gel compositions and nucleation processes that were used for preparing 12-R large-pore germanosilicate IM-20 with the known UWY topology. The crystallization was directed towards forming one set of single four-ring (s4r) composite building units together with one set of double four-ring (d4r) rather than two different types of d4r units in IM-20. The electron crystallographic investigations elucidated that the ECNU-13 structure was composed of two kinds of polymorphs as a result of distinct atomic positionings in s4r units. In catalytic cracking of 1-butene, ECNU-13 exhibited high propene selectivity (55.6 %) and propene to ethylene molar ratio (>4.7) superior to well-studied conventional ZSM-5 zeolite catalyst.