An FT-IR study of adsorption of sulfur dioxide on alpha- and gamma-alumina

In the Claus process hydrogen sulfide reacts to elemental sulfur. Because the Claus reaction is thermodynamically limited, sulfur compounds are still present in Claus tailgas. To avoid air pollution, the tailgas has to be treated.Alfa- and gamma-alumina are being used either as a catalyst or as a support for an active component in the Claus process and some tailgas treatment processes. In order to elucidate the mechanism of the Claus reaction, the adsorption of sulfur dioxide on both of the above aluminas was investigated using Fourier transform infrared spectroscopy.Different adsorbed species displaying a different heat of adsorption were detected. A broad band near 3500 cm^–1 is associated with the basic hydroxyl groups. This band is assigned to a hydrogen bond between the surface of alumina and a bisulfite species. As bisulfite species are reactive towards hydrogen sulfide, we assume that bisulfite species are active intermediates on alumina in the Claus reaction.     

Features of claus treatment of acid gases with low content of hydrogen sulfide

Changes in the activity of industrial alumina catalysts CR-31 and AO-MK-2, which occur under the real industrial conditions in the last catalytic stage of the Claus process in the coke-oven gas treatment shop of the Magnitogorsk Metallurgical Plant, are analyzed.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 8, 2004, pp. 1323–1326.Original Russian Text Copyright © 2004 by Platonov, Ryabko, Tsemekhman.     

Influence of final calcination temperature and calcium addition on the properties of titania-based sulfur recovery catalysts

Compared to traditional alumina Claus catalysts, titania based sulfur recovery catalysts demonstrate improved initial activity for the recovery of elemental sulfur from both hydrogen sulfide and sulfur dioxide and are less prone to aging by sulfation. The influence of the preparation mode on the properties of titania catalysts is studied in detail: With increasing calcination temperature, surface area drastically decreases, whereas mechanical strength goes through a minimum, with only minor modifications of total pore volume and catalytic activity. Addition of calcium during catalyst preparation hinders the loss of mechanical properties while allowing a higher calcination temperature. Hydrothermal aging of such catalysts is therefore limited during operation in the plant.     

Der Claus‐Prozess. Reich an Jahren und bedeutender denn je

Modern industrial societies are dependent on fossil feedstocks as source of fuels and base chemicals. Due to the sulphur content of mineral oil, natural gas and coal, desulphurisation technology in general and the Claus process in particular are crucial to protect the environment from sulphur emissions. Sulphur recovery from natural gases or process gases with high H₂S content is the domain of the Claus Process, also predominating as source of the base chemical sulphur. The process is still steadily growing in importance.     

Analysis of the activity of an aluminum oxide Claus catalyst in commercial operation

Activity dynamics of an AO-MK-2 aluminum oxide catalyst in conversion of hydrogen sulfide and carbonyl sulfide during four years of service in an industrial Claus reactor was analyzed. The rate constants of the Claus reaction were determined and changes in the active surface area of the catalyst were examined.     

ADVANCES IN CLAUS REACTION AND RELATED REACTIONS

Abstract

During the sweetening of sour natural gas H2S and other contaminants are separated from natural gas. The conversion of H,S and other sulfur conipounds to sulfur is accomplished by the well known Claus process in which H2S and SOz are allowed to react catalytically over an alumina-based catalyst at around 250°C. The Claus reaction is thermodynamically limited so that 2–4 catalytic stages, with intervening sulfur removal, are required to achieve total conversions of 95–98%. There is considerable research activity into all phases of sulfur recovery operations with the major emphasis on maximizing the overall sulfur recovery. This report summarizes the developments in Claus reaction and attempts to focus attention on potential areas for future research.     

Chemistry of alumina, reactions in aqueous solution and its application in water treatment

Due to the presence and significance of alumina in the natural aquatic environment and its increasing application in drinking and wastewater purification, the knowledge of the structure of alumina and its possible interactions with organic and inorganic compounds in water are of great importance. This is of particular importance in both the understanding of natural aquatic environment processes and efficient industrial applications. The chemistry of alumina reactions in water is complex. The adsorption ability of alumina towards organic and inorganic compounds might be influenced by several factors such as: surface characteristics of the adsorbent (surface area, density, pore volume, porosity, pore size distribution, pH(PZC) as well as mechanical strength and purity), pH of the solution, ionic strength, composition of water and the physicochemical properties of adsorbates. The aim of this paper is to give a brief review of the properties of alumina and its reactivity with organic and inorganic compounds present in aqueous solutions. It also summarises the usage of alumina and alumina supported phases in water treatment technology.     

块状石英纤维/Al_2O_3气凝胶复合材料的非超临界干燥法制备及表征

采用溶胶-凝胶法和常压干燥法以N,N′-二甲基甲酰胺(DMF)作为干燥控制化学添加剂制备了低密度石英纤维增强Al2O3气凝胶复合材料.通过氮气吸附-脱附实验比较研究了石英纤维对氧化铝气凝胶孔结构参数的影响;采用X射线衍射技术表征了在升温过程中石英纤维/Al2O3气凝胶复合材料的相结构变化;利用扫描电子显微镜和透射电子显微镜观察了Al2O3气凝胶基体及其石英纤维复合材料的微观形貌;初步探讨了DMF对Al2O3气凝胶形貌和密度的影响.研究结果表明石英纤维/Al2O3气凝胶复合材料成块性好,纤维与气凝胶基体结合紧密,石英纤维提高了Al2O3相转变温度,适量的DMF有利于形成均匀凝胶网络结构,减小干燥收缩压力.     

Field technology for desulfurization of associated petroleum gas

Applicability of gas desulfurization technologies for sulfur-containing gases under conditions of the limited choice is analyzed. Data on efficiency of a new process for catalytic desulfurization of sulfur-containing gases through H2S and RSH conversion in sulfur and disulfides, respectively, is demonstrated. The technology is approved in pilot projects of gas desulfurization at a flare line, on a gas-processing plant. The equipment is developed and certificated. Installations for catalytic desulfurization are intended to be equipped with a complete set of blocks for gas preparation and power-generating equipment directly at deposits. This solution substantially decreases both capital and operational expenditures compared to the traditional multi-stage absorption/desorption technologies such as expensive Claus process.

     

胶溶法制备镧-钡共稳定氧化铝的性能

以硝酸为胶溶剂, 两种拟薄水铝石为前驱体, 用胶溶法制备了镧-钡共稳定的氧化铝. 采用X 射线衍射(XRD)、表面分析仪(BET)、氨气程序升温脱附(NH3-TPD)和NO2程序升温脱附(NO2-TPD)技术对所制备的镧改性和镧钡共改性氧化铝的结构特性和表面性能进行了表征. XRD结果表明, 改性氧化铝在1273 K焙烧后均以γ-Al2O3相存在. 当BaO添加量达到14%(w)时, 有少量BaCO3生成. BET结果表明, 在1273 K下焙烧5 h后, 5%(w)La2O3稳定的氧化铝(Ba-0)和5%La2O3与8%BaO共同稳定的氧化铝(Ba-8)均具有较大的比表面积, 各种氧化铝的吸附等温线表明它们的孔形状均为狭缝型孔和瓶型孔, 孔径分布曲线表明, 仅有样品Ba-8的孔径分布较宽, 孔径为6-10 nm, 其它三种样品的孔径均集中在10 nm; NH3-TPD结果表明, 随着氧化钡添加量的逐渐增多, 氧化铝表面的酸量、酸强度逐步减少. NO2-TPD结果表明, 添加BaO后载体对NO2的吸附量增多, 随着BaO含量的增多, 体相Ba(NO3)2增多. 由于样品Ba-8同时具有很好的织构性质、适中的表面酸量和酸强度分布及NO2吸附脱附能力, 使得以它为载体的催化剂具有最好的催化性能,丙烷的起燃温度和完全转化温度分别为526 K和593 K.     

Encapsulation of proteins into tunable and giant mesocage alumina

Protein bioadsorption has rapidly attracted attention partially because of the promising advances in diagnostic assays, sensors, separations, and gene technology. Tunable and giant mesocage alumina cavities (5 nm to 20 nm) show capability in size-selective encapsulation and diffusivity of large proteins into interior pores.     

制备工艺条件对SO42-/TiO2-Al2O3-Al固体酸催化剂性能影响

采用铝阳极氧化法制备了Al2O3-Al-体型多孔氧化铝载体,再采用电沉积技术将TiO2沉积到氧化铝多孔的纳米孔道内,制备了催化精馏专用SO42-/TiO2-Al2O3-Al型固体酸催化剂,并以乙酸乙酯合成为模型反应,考察了水封条件,电沉积电压、电沉积时间等制备工艺条件对催化剂活性的影响.实验结果表明,适宜的制备条件为水封温度为50℃,水封时间为1 h,电沉积电压为6V,电沉积时间为30 min,在此制备条件下,醋酸转化率为31.34%.采用扫描电镜(SEM),X射线衍射分析(XRD)手段对所制备催化剂进行了表征.结果表明:阳极氧化铝膜的结构为无定型结构,TiO2在载体上呈高度分散状态.     

Acetylene from benzene: A novel and selective microwave assisted cracking synthesis

A novel and efficient process for the cracking of benzene to acetylene with over 90% selectivity is described. The reactions are induced by a pulsed microwave technology over alumina and silica supported Nickel catalysts.     

Synthesis and characterization of mesoporous ceria/alumina nanocomposite materials via mixing of the corresponding ceria and alumina gel precursors

Mesoporous ceria/alumina, CeO(2)/Al(2)O(3), composites containing 10, 20 and 30% (w/w) ceria were prepared by a novel gel mixing method. In the method, ceria gel (formed via hydrolysis of ammonium cerium(IV) nitrate by aqueous ammonium carbonate solution) and alumina gel (formed via controlled hydrolysis of aluminum tri-isopropoxide) were mixed together. The mixed gel was subjected to subsequent drying and calcination for 3 h at 400, 600, 800 and 1000 degrees C. The uncalcined (dried at 110 degrees C) and the calcined composites were investigated by different techniques including TGA, DSC, FTIR, XRD, SEM and nitrogen adsorption/desorption isotherms. Results indicated that composites calcined for 3 h at 800 degrees C mainly kept amorphous alumina structure and gamma-alumina formed only upon calcinations at 1000 degrees C. On the other hand, CeO(2) was found to crystallize in the common ceria, cerinite, phase and it kept this structure over the entire calcination range (400-1000 degrees C). Therefore, high surface areas, stable surface textures, and non-aggregated nano-sized ceria dispersions were obtained. A systematic texture change based on ceria ratio was observed, however in all cases mesoporous composite materials exposing thermally stable texture and structure were obtained. The presented method produces composite ceria/alumina materials that suit different applications in the field of catalysis and membranes technology, and throw some light on physicochemical factors that determine textural morphology and thermal stability of such important composite.     

Extraction and characterization of highly pure alumina (α, γ, and θ) polymorphs from waste beverage cans: A viable waste management approach

The recycling and recovery of important materials from inexpensive feedstock has now become an intriguing area and vital from commercial and environmental viewpoints. In the present work, extraction of different single phases of alumina (α, γ, θ-Al₂O₃) having high purity (>99.5 %) from locally available waste beverage cans (～95 % Al) through facile precipitation route calcined at distinct temperatures has been reported. The optimization of process technology was done by a variety of different synthesis parameters, and the production cost was estimated between 84.47-87.45 USD per kg of alumina powder. The as prepared alumina fine particles have been characterized using different sophisticated techniques viz. TG-DTA, WD-XRF, XRD, FT-IR, SEM, DLS-based particle size analysis (PSA) with zeta (ζ) potential measurement and UV–Visible Spectroscopy. X-ray diffractogram confirms the formation of γ-, θ-, and α-alumina at 500–700 °C, 900–1000 °C, and 1200 °C respectively and crystallite size, crystallinity, strain, dislocation density, and specific surface area were measured using major X-ray diffraction peaks which varies with temperature. The SEM studies showed that the as prepared alumina particles were agglomerated, irregular-shaped with particle size (0.23–0.38 µm), pore size, and porosity were calculated from SEM image. ζ-potentials at different pH values as well as isoelectric point (IEP) of α, γ, and θ alumina were calculated in an aqueous medium which changes with temperature. The direct band gap (E_g) energies were found between 4.09 and 5.19 eV of alumina obtained from different calcination temperatures. The synthesized materials can be used in sensors, ceramics, catalysis, and insulation applications.     

Effect of micropores on the effective diffusion coefficient

The effective diffusion coefficient for catalysts differing in their porous structure has been derived from experimental data on H₂S conversion in the Claus reaction. The effective diffusion coefficient increases under conditions of catalyst deactivation due to sulfur condensation in micropores. A mathematical model is suggested to describe the micropore effect on the effective diffusion coefficient.     

Fluoride wastewater treatment by adsorption onto metallurgical grade alumina

The adsorption of fluoride onto metallurgical grade alumina (to produce Al) was investigated under different conditions: pH, contact time and adsorbent concentration. Data were evaluated with the aim of developing an alternative treatment technology for washing wastewater arising from an Aluminum can production plant. Kinetics and adsorption isotherms data have been also produced Sorption is greatly affected by pH and the best condition for fluoride removal are obtained at pH 5-6 and alkalinity competes successfully with fluoride ions for the exchange sites. Experiments with fixed beds indicate that fluoride is removed from wastewater by metallurgical-grade alumina with a capacity of 12.21 mg of F per gram and adsorption increases of about 25% at appropriate pH. The Mass Transfer Zone at 5% of the breakthrough occupies 70.6% of the total column length. The optimization of aluminum precipitation by pH adjustment and with different precipitant agents has been done.     

Role of the direct reaction H2S + SO2 in the homogeneous Claus reaction

Quantum chemical methods at the Gaussian-2 and -3 levels of theory have been used to investigate the reactions between H(2)S, SO(2), and S(2)O such as might occur in the front-end furnace of the Claus process. The direct reaction between H(2)S and SO(2) occurs via a 5-centered transition state with an initial barrier of approximately 135 kJ mol(-1) and an overall barrier of approximately 153 kJ mol(-1) to produce S(2)O and H(2)O. We indicate approximate values here because there are a number of isomers in the reaction pathway that have barriers slightly different from those quoted. The presence of a water molecule lowers this by approximately 60 kJ mol(-1), but the van der Waals complex required for catalysis by water is thermodynamically unfavorable under the conditions in the Claus reactor. The direct reaction between H(2)S and S(2)O can occur via two possible pathways; the analogous reaction to H(2)S + SO(2) has an initial barrier of approximately 117 kJ mol(-1) and an overall barrier of approximately 126 kJ mol(-1) producing S(3) and H(2)O, and a pathway with a 6-centred transition state has a barrier of approximately 111 kJ mol(-1), producing HSSSOH. Rate constants, including a QRRK analysis of intermediate stabilization, are reported for the kinetic scheme proposed here.     

Interface modification and characterization of silicon carbide platelets coated with alumina particles

A colloidal-chemistry-based technique was developed for interface modification of silicon carbide platelets (SiCp) by coating with alumina particles. The coating process utilizes electrostatic and/or electrosteric interactions between the particles to promote heterocoagulation. Since an understanding of the chemical interface between the SiCp and alumina is important for improving the coating process, the powders were characterized by the measurement of the electrokinetic sonic amplitude (ESA). The major factors studied were particle size, type of alumina, presence of polyacrylate surfactant, and concentration of alumina in the coating slip. The surface coverage and morphology of the alumina coating on SiCp was determined quantitatively by scanning electron microscopy (SEM). The results indicate that around pH 5.8, the surface charge difference between SiCp and alumina was the largest and the coating of alumina on SiCp was feasible. The SEM data showed that surface coverage was uniform, and the highest surface coverage on SiCp was 66% when the surface area ratio of alumina to SiCp was 250% in the suspension. No significant improvement of the coating rate was observed by the addition of a polyacrylate for dispersion of SiCp. The concentration of alumina in the slip exhibited a strong influence on the amount of surface coverage on SiCp.     

高比表面积有序介孔氧化铝的制备与表征

采用溶胶-凝胶法以非离子表面活性剂PEO-PPO-PEO三嵌段共聚物F127为模板剂, 以异丙醇铝为铝源, 以异丙醇为溶剂, 成功地制备出比表面积为485 m2/g、孔径分布窄(2~20 nm)、孔容在1.2 cm3/g以上和孔道呈蠕虫状且具有一定有序性的介孔氧化铝. 采用BET, TEM, XRD和TG多种测试技术对产物性能进行了表征. 探讨了水铝比、醇水混合溶液的滴加速度、反应时间、水浴温度、陈化温度及陈化时间等条件对合成的有序介孔氧化铝结构的影响.