Carbon molecular sieves produced by the fixation of sulphur surface complexes

Summary A Saran carbon has been treated with carbon disulphide and sulphur in order to introduce sulphur surface complexes, a commercial activated carbon was also used. Samples obtained were characterized by their surface areas and porosities. The adsorption of n-hexane, benzene and cyclohexane has been measured out at high temperatures and under dynamic conditions using a gas chromatographic technique. Results were compared with those obtained when oxygen-surface complexes were introduced and it can be concluded that when CS₂ is used with a highly microporous carbon, such as Saran, a molecular sieve for cyclohexane (mean size 0.58 nm) is produced at determined amounts of sulphur fixed.     

Carbon dioxide adsorption over DIPA functionalized MCM-41 and SBA-15 molecular sieves

The capture of carbon dioxide was carried out using MCM-41 and SBA-15 as adsorbents. These mesoporous materials were synthesized by the hydrothermal method, and subsequently functionalized with the di-iso-propylamine (DIPA). Then, they were characterized by XRD, BET, and TG/DTG. The X-ray diffraction patterns of the synthesized samples showed the characteristic peaks of MCM-41 and SBA-15, indicating that the structures of these materials were obtained. The functionalized samples presented a decrease of the intensities of these peaks, suggesting a decreasing in the structural organization of the material; however, the mesoporous structure was preserved. For the adsorption capacity measurements, the materials were previously saturated with carbon dioxide at 75 °C, and then desorbed in a thermobalance in the temperature range of 25–900 °C, under helium atmosphere. Desorption tests showed that the functionalized MCM-41 presented a weight loss of 7.5 wt%, against 5.9 wt% for SBA-15. The obtained values indicate that these nanostructured materials can be used as adsorbent for carbon dioxide capture.     

Nanostructured zeolite 4A molecular sieving air separation membranes

A novel membrane forming strategy is reported to probe the intrinsic O2/N2 selectivity of zeolite 4A membrane and to fabricate highly selective nanocomposite membranes by using a nanocrystal-derived hierarchical porous zeolite 4A membrane whose non-zeolitic mesoporsity is filled with a nonpermeable polymer material (polyfurfuryl alcohol).     

A new TMA adsorptive expansion test for molecular sieves

Until recently, it has been believed that during adsorption and desorption cycles of molecular sieve pellets, the pellets have been passive participants in the process. It has lately been shown by others using X-ray diffraction technique that the molecular sieve structure undergoes expansion and contraction as a result of moisture content changes.A new thermomechanical analyzer (TMA) technique has been developed that allows the dimensional change to be measured continuously as a function of time and, concurrently, moisture content, thus creating an unique method for measuring adsorption rates.The instrument modifications (DuPont 990 and 943), collection and evaluation of data, and the sensitivity of the adsorption rate due to various parameters are discussed in the paper.

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Zusammenfassung Bis vor kurzem wurde angenommen, dass wÄhrend der Adsorptions- und Desorptionszyklen an Molekularsiebpellets, diese sich als passive Teilnehmer an dem Vorgang beteiligen. Durch andere Autoren wurde unter Anwendung der Röntgendiffraktionstechnik gezeigt, da\ die Molekularsiebstruktur infolge von Änderungen des Feuchtigkeitsgehalts Expansionen und Kontraktionen ausgesetzt ist.Eine neue thermomechanische Analysentechnik wurde entwickelt, welche die kontinuierliche Messung der DimensionsÄnderung als Funktion der Zeit unter gleichzeitiger Messung des Feuchtigkeitsgehalts gestattet und somit eine einzigartige Methode zur Ermittlung von Adsorptionsgeschwindigkeiten schafft.Die Varianten des Instrumentes (DuPont 990 und 943), die Datensammlung und -Verarbeitung, sowie die durch verschiedene Parameter bedingte Empfindlichkeit der Adsorptionsgeschwindigkeit werden in der Veröffentlichung erörtert.

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Résumé Jusqu'à tout récemment on pensait que lors des cycles d'adsorption et de désorption des tamis moléculaires, les particules des tamis étaient des participants passifs. Depuis peu de temps des auteurs ont montré, en se servant de la technique de diffraction des rayons X, que par suite à des variations de l'humidité, la structure des tamis moléculaires subit des dilatations et des contractions.On a développé une nouvelle technique d'analyse thermomécanique qui permet de mesurer, en continu, les variations de dimension en fonction du temps simultanément avec la teneur en humidité, créant ainsi une méthode unique de mesure des vitesses d'adsorption.Les modifications apportées à l'appareil (Du Pont 990 et 943), l'acquisition et l'évaluation des données, ainsi que la sensibilité de la vitesse d'adsorption due à divers paramètres sont discutées.

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介孔分子筛在生物酶固定化中的应用

综述了MCM-48和SBA-15等新型介孔分子筛用生物酶固定化载体研究的新进展。介孔分子筛由于拥有巨大的比表面积(~1000m2/g)、纳米尺寸孔道(2~50m)和较大的孔容(~1.0 cm3/g),因此以分子筛为载体利用物理吸附制备的固定化酶呈现出高的催化活性,但固定化酶操作稳定性较低,在使用过程中部分酶分子发生了脱落,其原因是分子筛表面自由的硅羟基通过物理吸附或氢键作用固定酶分子。借助介孔分子筛自身的自由硅羟基在表面嫁接-COOH、-NH2、-CH=CH2等有机官能团来构筑酶固定化的微环境,改善酶分子和载体的亲和作用,提高固定化酶的活性。目前,利用有机官能团功能化介孔分子筛固定化酶是研究发展的趋势。     

Spontaneous liquid-gas imbibition for characterization of carbon molecular sieves

Spontaneous liquid-gas imbibition at 293.2K and 0.1 MPa was conducted to assess the micropore size and size-exclusion property of carbon molecular sieves (CMS). The CMS were firstly saturated with N(2) and then immersed into water. The volume of gas recovered by the water imbibition was measured and applied to evaluate the density of the N(2) adsorbed in the CMS. The micropore size of the CMS was determined by comparing the N(2) density from the water-N(2) imbibition with that calculated by grand canonical simulation. The micropore size evaluated by the liquid-gas imbibition coincides with that obtained by N(2) adsorption at ambient temperature. The size-exclusion property of the CMS was estimated through comparing the N(2) recovery by imbibition of liquids with increasing molecular dimensions, that is, water, benzene, and cyclohexane. The amount of N(2) recovered from benzene imbibition is dramatically less than that from the water imbibition, showing that the dominated micropore size of the CMS is smaller than 0.37 nm. Furthermore, the effect of chemical vapor deposition treatment on the porous texture of the CMS was revealed by the liquid-gas imbibition.     

Adsorption of water vapour from humid air in carbon molecular sieves: carbosieve S-III and carboxens 569, 1000 and 1001

The adsorption of water vapour in carbon molecular sieves (CMS) used to determine volatile organic compounds (VOCs) in air was investigated. The CMS mass in the trap was found not to affect the mass of retained water under conditions of incomplete saturation of the adsorbent bed with water. Thus, the restrictions commonly imposed on the CMS mass are not necessary. The usefulness of four different CMSs to sample large volumes of humid air was estimated. Carboxen 1000 exhibited the best performance. To assess the magnitude of CMS mass in the trap in dependence on the volume, the relative humidity and the temperature of the sample, the use of a novel parameter, called the water vapour interference factor, was suggested.     

Evaluation of Carboxen carbon molecular sieves for trapping replacement chlorofluorocarbons

A method has been developed for trapping and preconcentrating the very volatile replacement chlorofluorocarbons (hydrofluorocarbons and hydrochlorofluorocarbons) using microtraps filled with Carboxen, a carbon molecular sieve type material, without the need for extensive cryotrapping using liquid nitrogen. We present here the adsorption characteristics of four Carboxen materials, Carboxen 569, 1000, 1001, and 1002, used to trap a range of replacement chlorofluorocarbons varying in boiling point from −48.4 to −9.8°C. The application of these traps for the automated analysis of trace gases in atmospheric and environmental chemistry could prove extremely useful.     

A heterogeneous model for gas transport in carbon molecular sieves

A dual resistance model with distribution of either barrier or pore diffusional activation energy is proposed in this work for gas transport in carbon molecular sieve (CMS) micropores. This is a novel approach in which the equilibrium is homogeneous, but the kinetics is heterogeneous. The model seems to provide a possible explanation for the concentration dependence of the thermodynamically corrected barrier and pore diffusion coefficients observed in previous studies from this laboratory on gas diffusion in CMS. The energy distribution is assumed to follow the gamma distribution function. It is shown that the energy distribution model can fully capture the behavior described by the empirical model established in earlier studies to account for the concentration dependence of thermodynamically corrected barrier and pore diffusion coefficients. A methodology is proposed for extracting energy distribution parameters, and it is further shown that the extracted energy distribution parameters can effectively predict integral uptake and column breakthrough profiles over a wide range of operating pressures.     

Application of natural zeolites for air separation

The application for air separation purposes of modified versins of clinoptilolite and mordenite containing tuffs, deposited in the Tokaj Mountains (Hungary), is demonstrated. The importance of adsorption kinetics in the design of any pressure swinging adsorption (PSA) operation is shown.

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Synthesis of Schiff's bases from furylacroleins and aminopyridines in the presence of molecular sieves

We have studied the reactions of (hetero)aromatic aldehydes with 2-aminopyridines. The results obtained suggest that molecular sieves play a role in these processes not only as a dehydrating agent but also as an acid catalyst. We have synthesized a series of novel heterocyclic azomethines.Dedicated to Professor M. A. Yurovskaya on her Jubilee.Latvian Institute of Organic Synthesis, Riga LV-1006 Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 324–335, March, 2000.     

Improved light olefin yield from methyl bromide coupling over modified SAPO-34 molecular sieves

As an alternative to the partial oxidation of methane to synthesis gas followed by methanol synthesis and the subsequent generation of olefins, we have studied the production of light olefins (ethylene and propylene) from the reaction of methyl bromide over various modified microporous silico-aluminophosphate molecular-sieve catalysts with an emphasis on SAPO-34. Some comparisons of methyl halides and methanol as reaction intermediates in their conversion to olefins are presented. Increasing the ratio of Si/Al and incorporation of Co into the catalyst framework improved the methyl bromide yield of light olefins over that obtained using standard SAPO-34.     

分子筛催化剂上甲醇与三聚甲醛缩合制聚甲醛二甲醚

对HY、HZSM-5、Hβ和HMCM-22分子筛催化剂上甲醇与三聚甲醛缩合制聚甲醛二甲醚（PODE_n或DMM_n）的反应性能进行了研究,考察了分子筛种类和酸性对产物分布的影响。结果显示,以酸性分子筛为催化剂,甲醇与三聚甲醛可缩合得到聚甲醛二甲醚。HY分子筛上反应产物主要为短链的甲缩醛（DMM）;HZSM-5和Hβ分子筛上产物以DMM₁~3为主,其柴油添加剂组分DMM₃~8的收率分别为6.40%和13.78%;HMCM-22分子筛为催化剂时,长链的聚合物收率明显增加,其柴油添加剂组分DMM₃~8的收率可以达到29.39%。NH₃-TPD表征结果表明催化剂表面的酸性对产物分布有着明显的影响：表面弱酸位有利于短链产物DMM的生成,而中等强度的表面酸性位则能促进柴油添加组分DMM₃~8的生成。     

Liquid-phase synthesis of isopulegol from citronellal using mesoporous molecular sieves mcm-41 and zeolites

Isopulegol (IPG) was synthesized from citronellal (CTN) at atmospheric pressure and 40~60°C in a batch reactor by using mesoporous molecular sieves MCM-41 as well as zeolites HZSM-5 and Hβ. The catalysts were characterized by the methods of XRD, N₂ adsorption, ²⁷Al and ²⁹Si MAS-NMR and TPD of ammonia. Under our reaction conditions, Al-MCM-41 was found to be the best catalyst; it exhibited much higher activity, despite slightly lower IPG selectivity. The catalytic results depend on a variety of factors, viz. the acidity, the pore size and the pore channel of catalysts. The reaction paths were proposed and the kinetic parameters for competitive first order reactions of CTN were estimated. This revised version was published online in June 2006 with corrections to the Cover Date.     

Thermal analysis applied for the removal of surfactant from mesoporous molecular sieves MCM-41 synthesized from gold mine tailings slurry

The aim of the current study is to obtain the thermal behavior and kinetic analyses of the removal of surfactant from MCM-41 synthesized from tailings slurry at different heating rates. X-ray diffraction and thermogravimetric analyses were carried out to determine the characterization of the synthesized samples. Kissinger–Akahira–Sunose and Friedman isoconversional kinetic methods were applied for the purpose of determining the kinetic analysis parameters of the decomposition of surfactant from the mesoporous molecular sieves MCM-41 under non-isothermal conditions. For the comparison of these results, MCM-41 was synthesized from a pure silica source. The thermal behaviors of MCM-41 synthesized from tailings slurry do not differ from samples synthesized from pure silica during the decomposition reactions. The kinetic analysis’ results indicate that the decomposition reactions of the synthesized MCM-41 samples had complex reaction mechanisms.     

Headspace gas chromatographic separation of toxic organic impurities from air

Summary To determine toxic organic compounds (methanol, ethanol, n-propanol, acetone, methyl ethyl ketone, methyl isobutyl ketone) in air a method was developed for their headspace gas chromatographic analysis with preconcentration in n-butanol (alcohols) and in n-pentanol (ketones). The distribution coefficients of analytes in the air-absorbent system have been measured: 1051 (MeOH), 5630 (EtOH), 6773 (n-PrOH), 307 (Me₂CO), 580 (MeCOEt), 1035 (MeCOBu-i). The minimum detectable level (mg m⁻³) was determined as low as 0.9 (MeOH), 4.0 (EtOH), 0.9 (n-PrOH), 0.2 (Me₂CO), 0.1 (MeCOEt), 0.4 (MeCOBu-i). The method was effectively used for gas effluent air control in the workplace and in the atmosphere. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996