The role of sulfur trapped in micropores in the catalytic partial oxidation of hydrogen sulfide with oxygen

The catalytic oxidation of hydrogen sulfide into sulfur with molecular oxygen has been studied in the temperature range 130–200 °C. Active carbon, molecular sieve 13X and liquid sulfur were used as catalysts. Sulfur is adsorbed in the micropores (3 < r < 40 Å) of the catalysts. Experiments with a surface of liquid sulfur demonstrated that sulfur is a catalyst for H2S oxidation.\ud \ud This catalytic function reflects itself in the fact that H2S oxidation rate showed a maximum as a function of the amount of sulfur present in the pores of active carbon and molecular sieve 13X. The kinetics of the reaction and the activation energy are equal on catalysts of different chemical composition.\ud \ud The mechanism of the catalysis by sulfur is discussed as well as the function of traces of iron oxide, present in most catalysts

The adsorption of sulfur by microporous materials

The sorption of sulfur by the zeolites NaX (= 13X) and CaA (= 5A) and an activated charcoal prepared from sugar was investigated at temperatures between 150 and 350°C and relative sulfur pressures between 10−4 and 10−1. The adsorbate-adsorbate interaction indicated by the S-shaped isotherm for the zeolite NaX points to physical or chemical interaction of sulfur molecules in neighboring supercages. In CaA adsorbate-adsorbate interaction between sulfur species in different supercages is negligible. Below 200°C the rate of sulfur uptake by the zeolite CaA is determined by the diffusion rate of a sulfur species through the zeolitic framework. In activated charcoal a strong adsorbate-adsorbent interaction is present and part of the sulfur is chemisorbed at 350°C. The differences in the density of the adsorbed sulfur determined with three different methods indicate that even at full saturation of the micropore volume with sulfur, there is still some residual adsorption volume

Kinetic research on heterogeneously catalysed processes: a questionnaire on the state-of-the-art in industry

On the initiative of the Working Party `Chemical Engineering in the Applications of Catalysis¿ of the European Federation of Chemical Engineering an assessment of the issues in the determination and application of kinetic data within the European industry was performed. The basis of the analysis consisted of a questionnaire put together by researchers from Dow, DSM, Shell and Eindhoven University of Technology. The 24 companies, which have responded to the questionnaire, can be classified into four groups: chemical, oil, engineering contractors and catalyst manufacturers. From the overall input it appears that there are three, equally important, utilisation areas for kinetic data: process development, process optimisation and catalyst development. There is a wide variety of kinetic data sources. Most of the respondents make use of test units which were primarily designed for development and optimisation. Avoiding transport limitation is, certainly in the case of short range projects or for complex feedstocks, not always taken care of. With respect to the modelling approaches, a common philosophy is `as simple as possible¿. Most of the respondents state that `in principle¿ one should strive for intrinsic kinetics, but the majority nevertheless does for various reasons not separate all transport phenomena from reaction kinetics. Kinetic models are mostly simple first or nth order or Langmuir-Hinshelwood type expressions. More complex kinetic models are scarcely used. Three areas were frequently identified to offer opportunities for improvement. Gathering of kinetic data is too costly and time consuming. There is no systematic approach at all for determination and application of kinetics in case of unstable catalytic performance. Furthermore, the software available for the regression of kinetic data to rate equations based on mechanistic schemes as well as software to model reactors are insufficiently user friendly. The majority of the respondents state that the problems indicated should be solved by cooperation, e.g., between companies, between industry and academia and between the catalysis and the chemical engineering community. A workshop on the above topics was held in December 1996 with 15 companies and 6 academics attending. More information can be obtained from the secretariat of the Working Party

Mercury chemisorption by sulfur adsorbed in porous materials

The sorption of mercury vapor by adsorbed sulfur in the zeolites CaA (= 5A) and NaX (=13X) and two types of active carbon has been measured at a temperature of 50°C. With increasing degree of micropore filling by sulfur the fraction of sulfur accessible to mercury atoms decreased for CaA and NaX. The sulfur chemisorbed on carbon (only less than 0.05 g sulfur per g) is not very active for mercury chemisorption. The mercury uptake shows a sharp maximum as a function of the amount of sorbed sulfur in the case of CaA, NaX and activated sugar charcoal. The oxidation rate of H2S with oxygen on NaX and activated sugar charcoal correlates with the capacity for mercury chemisorption, both as a function of the amount of sorbed sulfur. From the amount of sorbed mercury an estimate of the specific sulfur surface area may be given. When sulfur impregnated CaA, NaX or activated sugar charcoal are used as adsorbents for mercury traces out of gas streams, the mercury sorption capacity may be maximized by using materials with a micropore volume approximately half filled with sulfur

The mechanism of the catalytic oxidation of hydrogen sulfide *1: III. An electron spin resonance study of the sulfur catalyzed oxidation of hydrogen sulfide

ESR experiments on the oxidation of hydrogen sulfide were performed in the temperature range 20–150 °C. Alumina, active carbon and molecular sieve zeolite 13X were investigated as catalysts. For zeolite 13X it was demonstrated that the reaction is autocatalytic and that sulfur radicals are the active sites for oxygen chemisorption. The intensity of the sulfur radical ESR signal, which is related to the degree of conversion of these radicals, by oxygen, fits in with an oxidation-reduction mechanism.\ud \ud The sulfur-oxygen radical species, which appear when oxygen is admitted to sulfur radicals, are assigned to sulfur chains containing one or two oxygen atoms at the end of the chain. It is very likely that these sulfur-oxygen radicals are intermediates in the proposed mechanism. The formation of the byproduct SO2 from SxO2 · − at temperatures above 175 °C is also visible in the ESR spectrum.\ud \ud On the basis of the experiments it is concluded that in the mechanism of H2S oxidation on active carbons, carbon radicals do not play an important role

A heart for fibrillin : spatial arrangement in adult wild-type murine myocardial tissue

Fibrillins are major constituents of microfibrils, which are essential components of the extracellular matrix of connective tissues where they contribute to the tissue homeostasis. Although it is known that microfibrils are abundantly expressed in the left ventricle of the heart, limited data are available about the presence of microfibrils in the other parts of the myocardial tissue and whether there are age or sex-related differences in the spatial arrangement of the microfibrils. This basic knowledge is essential to better understand the impact of fibrillin-1 pathogenic variants on the myocardial tissue as seen in Marfan related cardiomyopathy. We performed histological analyses on wild-type male and female murine myocardial tissue collected at different time-points (1, 3 and 6 months). Fibrillin-1 and -2 immunofluorescence stainings were performed on cross-sections at the level of the apex, the mid-ventricles and the atria. In addition, other myocardial matrix components such as collagen and elastin were also investigated. Fibrillin-1 presented as long fibres in the apex, mid-ventricles and atria. The spatial arrangement differed between the investigated regions, but not between age groups or sexes. Collagen had a similar broad spatial arrangement to that of fibrillin-1, whereas elastic fibres were primarily present in the atria and the vessels. In contrast to fibrillin-1, limited amounts of fibrillin-2 were observed. Fibrillin-rich fibres contribute to the architecture of the myocardial tissue in a region-dependent manner in wild-type murine hearts. This knowledge is helpful for future experimental set-ups of studies evaluating the impact of fibrillin-1 pathogenic variants on the myocardial tissue