Development of natural zeolites for their use in water-treatment systems

This paper gives an overview of research and patents concerning the use of natural zeolites in water-treatment systems in the last ten years. Furthermore, nanocomposite materials made of natural zeolites and organic and polymeric materials are also mentioned as an effective solution in water treatment. An additional emphasis is put on a variety of possibilities for further application of natural zeolite materials for environment protection and preservation.     

The development of gold catalysts for use in hydrogenation reactions

With increasing emphasis placed on cleaner chemical synthesis, energy efficiency and waste minimisation, the manufacture of pharmaceuticals and fine chemicals is undergoing a progressive shift from conventional stoichiometric organic processes to a harnessing of catalytic selectivity. In hydrogenation processes, gold catalysts have untapped potential in terms of selectivity in the reduction of a target functionality in multifunctional reactants. This Review provides a comprehensive evaluation of the catalytic applications of Au in hydrogenation, assessing the benefits relative to conventional transition metal (e.g. Pt, Pd and Ni) catalytic systems. Hydrogenation activity requires the formation of nanoscale Au particles that are (typically) anchored to oxide supports. The crucial catalyst structural and surface properties required to achieve enhanced hydrogenation performance in terms of rate, selectivity and stability are discussed. The synthesis procedures and characterisation methodologies directed at catalyst optimisation are evaluated. The practical application of Au catalysts is illustrated taking, as a case study, the hydrogenation of nitroaromatics, where critical features such as hydrogen adsorption/activation, structure sensitivity, metal–support interactions and active site characteristics are discussed. Commonality with the catalytic action of supported Ag is flagged with a consideration of the future outlook and direction for selective hydrogenation using Au catalysts.     

汽车尾气净化负载钯超微粒催化剂的研究

以复合稀土氧化物的γ-Al2O3为催化剂载体,将负载钯的超微粒子金属铁、钴、镍与γ-Fe2O3粉体混合成型焙烧制成催化刺.研究了复合稀土氧化物对γ-Al2O3表面积的影响,通过催化剂老化实验、丙烷化合物起燃温度检测和对模拟汽车尾气中丙烷、CO及NOx等物质的转化性能的研究,表明该型催化剂各性能较好.     

Milling as a pretreatment method for increasing the reactivity of natural zeolites for use as supplementary cementitious materials

This work examined the effects of milling using a gravity ball mill on the reactivity of natural zeolites used as supplementary cementitious materials (SCMs). Six different particle size distributions of zeolites, created by milling the as-received zeolite in a ball mill for a specified amount of time, were characterized using x-ray fluorescence, quantitative x-ray diffraction, particle size analysis, pore size distribution and surface area analysis. Following material characterization, the pozzolanic reactivity of the zeolites was determined by measuring the quantity of calcium hydroxide in paste after 28 or 90 days and by tracking the compressive strength of zeolite-cement mortars. Results showed that a critical milling time exists, corresponding to a d₅₀ of 7–9 μm, after which reductions in particle size can no longer be achieved and zeolite performance can no longer be improved through ball milling.     

Radon exposures from the use of natural gas in buildings

Low levels of natural radioactivity in the ground produce radon-222 and its decay products which can be entrained with gas streams and become distributed with gas supplies to commercial and domestic users. Levels of radon in blended gas received by most users are comparable with the levels that are present naturally in buildings as a result of ingress from the ground and this is further diluted during the combustion process. For typical rates of gas usage with an average radon level of about 200 Bq x m(-3), the estimated dose from the use of natural gas is estimated at 4 microSv, less than 1% of the dose from radon exposure at the average level in UK homes. Commercial users may receive somewhat higher doses, and the estimate for a critical group is a few tens of microsievert. The total radon emission to the environment is estimated at about 10(13) Bq x y(-1) which represents less than 10(-4) of the natural emission rate from the ground. There is some variability of radon levels in gas from different sources and it would be prudent to keep this source of exposure under review. A standard sampling and measurement protocol has been developed in conjunction with a technical group representing the industry.     

中国页岩气资源潜力及其在天然气 未来发展中的地位

中国页岩气勘探已在四川、鄂尔多斯等盆地及重庆、云南、贵州、湖南等地区获得发现,证实具有良好资源前景。依据最新资料,落实了稳定区面积、集中段厚度、可采资源丰度、含气量等资源评价关键参数,采用3种方法预测了我国页岩气可采资源量及分布。借鉴美国典型页岩气区发展经验,采用多种方法预测了我国页岩气未来达到的产量规模和发展路线图,明确提出了页岩气在我国未来天然气发展中的地位和作用。     

Derivative dilatometric study of natural zeolites

This study concerns the expansion-shrinkage behavior of the following zeolites: natrolite, thomsonite, scolecite, heulandite, clinoptilolite, and stilbite. The analytical method used was derivative dilatometry. The use of dilatometric measurement provides a clearer representation of metaphase formation during the thermal dehydration of a zeolite. The dehydration of the minerals in the natrolite group can be described as expansive, whereas the dehydration of heulandite, clinoptilolite, and stilbite is characterized by contracting reactions. This contrasting behavior seems to be consistent with the varying qualities of the water bonding in the zeolite lattice.     

反相微乳液法制备铈锰取代六铝酸盐甲烷燃烧催化剂

研究了组成及温度对水/环己烷/TX-100 正戊醇体系反相微乳液区的影响,选择合适组成的反相微乳液做为合成介质,制备了BaMnCeAl10O19-δ六铝酸盐催化剂,研究了制备条件对催化剂样品的比表面积、结构及甲烷燃烧催化活性的影响.结果表明,该体系反相微乳液区面积的变化受到组成和温度的影响,当n=3:2、温度为25℃时,体系的反相微乳液区最大.油相和硝酸盐加入量的不同对催化剂的活性、粒径以及比表面积有较大的影响,油相用量增加、硝酸盐混合溶液用量的减少有利于所制备活性的提高以及比表面积的增加.在油相用量较大(硝酸盐混合溶液用量较小)的条件下,制备出的催化剂活性最高,其T10%、T50%和T90%分别达到456、582和698℃.     

Removal of pyridine from liquid and gas phase by copper forms of natural and synthetic zeolites

Zeoadsorbents on the basis of copper forms of synthetic zeolite ZSM5 and natural zeolite of the clinoptilolite type (CT) have been studied taking into account their environmental application in removing harmful pyridine (py) from liquid and gas phase. Sorption of pyridine by copper forms of zeolites (Cu-ZSM5 and Cu-CT) has been studied by CHN, X-ray photoelectron spectroscopy, X-ray powder diffractometry, FTIR spectroscopy, thermal analysis (TG, DTA and DTG) and analysis of the surface areas and the pore volumes by low-temperature adsorption of nitrogen. The results of thermal analyses of Cu-ZSM5, Cu-(py)(x)ZSM5, Cu-CT and Cu-(py)(x)CT zeolitic products with different composition (x depends on the experimental conditions of sorption of pyridine) clearly confirmed their different thermal properties as well as the sorption of pyridine. In the zeolitic pyridine containing samples the main part of the pyridine release process occurs at considerably higher temperatures than is the boiling point of pyridine, which proves strong bond and irreversibility of py-zeolite interaction. FTIR spectra of Cu-(py)(x)zeolite samples showed well resolved bands of pyridine. The results of thermal analysis and FTIR spectroscopy are in a good agreement with the results of other used methods.     

Analysis and countermeasures of natural gas development in China

Natural gas has become a transitional bridge from fossil to green and clean energy worldwide. The importance of natural gas utilization in energy structure optimization and green development is no exception for China. However, the supply of China’s natural gas limits the country’s demand with three factors. (1) China’s natural gas resource is relatively rich, but its quality is poor with deep burial depth. Therefore, the annual plateau yield of natural gas cannot be high, with an estimated value of approximately 260–270 ×10⁹ m³. (2) The demand for natural gas in China’s economic development is growing rapidly. The peak demand is estimated to be approximately 550–650 ×10⁹ m³ per year or even higher. The import volume of natural gas will soon exceed that of domestic self-produced gas. (3) Natural gas is a necessity closely related to livelihood. Particularly, a shortage in natural gas supply affects social stability. Therefore, its external dependency should be under 50% and not exceed 60%. In this study, the future situation of China’s natural gas is forecasted, and relevant countermeasures and suggestions are proposed in accordance with research on China’s natural gas resource potential, production trend, supply-demand link, and gas supply safety factors.     

Kinetic study of trichloroethylene combustion on exchanged zeolites catalysts

In this paper is presented a kinetic study of the catalytic combustion of trichloroethylene (TCE) over Y-zeolites exchanged with several cations. The catalysts, based on zeolite, were prepared by ion exchange and characterized by means of physico-chemical techniques and then tested under kinetic conditions. The kinetic results obtained were interpreted using kinetic models of power-law type and Eley-Rideal. The results obtained indicate that catalyst Y-Cr is more active than Y-Co catalyst. The greater activity of catalyst exchanged with Cr can be attributed to the higher acidity that presented these catalysts.     

Effect of mechanical activation on the properties of natural zeolites

We have examined the effect of mechanical activation on the Sr²⁺ and Cu²⁺ ion exchange selectivity of Russian natural zeolites: clinoptilolite-containing tuffs and chabazite concentrates. We have studied their structural changes and thermal properties and determined the specific surface area and porosity of the mechanically activated zeolites. At specific milling energies below 0.5–0.7 kJ/g, the dominant process is disintegration of zeolite particles and changes in their bulk porosity. At higher milling energies, amorphization prevails. Our results demonstrate that, in the initial stage of activation, one can markedly raise the Sr²⁺ selectivity of some zeolites (e.g., by 16 times for Shivyrtuiskoe clinoptilolites and by 300 times for chabazite) and increase the Cu²⁺ selectivity (by 40 to 100 times), which will persist at high specific milling energies.     

Cationic surfactants-modified natural zeolites: improvement of the excipients functionality

Context: In this study an investigation of cationic surfactants-modified natural zeolites as drug formulation excipient was performed. Objective: The aim of this work was to carry out a study of the purified natural zeolitic tuff with high amount of clinoptilolite as a potential carrier for molecules of pharmaceutical interest. Materials and methods: Two cationic surfactants (benzalkonium chloride and hexadecyltrimethylammonium bromide) were used for modification of the zeolitic surface in two levels (equal to and twice as external cation-exchange capacity of the zeolitic tuff). Prepared samples were characterized by Fourier transform infrared spectroscopy, thermogravimetric, high-performance liquid chromatography analysis, and powder flow determination. Different surfactant/zeolite composites were used for additional investigation of three model drugs: diclofenac diethylamine, diclofenac sodium, and ibuprofen by means of adsorption isotherm measurements in aqueous solutions. Results: The modified zeolites with two levels of surfactant coverage within the short activation time were prepared. Determination of flow properties showed that modification of zeolitic surface reflected on powder flow characteristics. Investigation of the model drugs adsorption on the obtained composites revealed that a variation between adsorption levels was influenced by the surfactant type and the amount present at the surface of the composites. Discussion and conclusion: In vitro release profiles of the drugs from the zeolite-surfactant-drug composites revealed that sustained drug release could be attained over a period of 8 hours. The presented results for drug uptake by surfactant-zeolite composites and the afterward drug release demonstrated the potential use of investigated modified natural zeolite as excipients for advanced excipients in drug formulations.     

Microprobe analysis of noble gas encapsulates in zeolites

Electron microprobe analysis has been employed for the first time to investigate gases immobilized in zeolites. Two trapping procedures and two different molecular sieves were tested: on one hand Kr as well as one to one $\text{Xe}\text{Kr}$ and $\text{Xe}\text{Ar}$ mixtures were trapped hydrothermally in X-ray amorphous zeolite 5A, and on the other, Kr was immobilized in mordenites by a combination of physical sorption and chemical modification procedure. The results show that the noble gases Ar, Kr and Xe can be quickly and specifically identified in these inorganic matrices. Because in all samples the density of the noble gas follows exactly the density of the aluminosilicate framework it is concluded that the noble gas is homogeneously distributed in the zeolite material. Analysis of noble gas mixtures indicates that each of the noble gases Ar, Kr and Xe can be specifically monitored in the presence of the two others. In addition, an analysis of other elements present in the pellet can be simultaneously carried out. The variation of the concentration of these elements with structure can be followed with resolution of ≈ 1μm.     

Opportunities and challenges of natural gas development and utilization in China

Clean Technologies and Environmental Policy - In the background that the China government robustly advocates low carbon and green energy, China has turned to focus on natural gas, both production...