Thiophene sulfided sample

In sample 1, it is clear that the predominant form of sulfur in the residuum is thiophenic, while the sulfide forms seem to predominate in residua 2 and 3. In asphaltene samples 1 and 3, the thiophenic sulfur content increases relative to the respective residua, indicating that the molecules containing sulfide sulfur may be more soluble in heptane than those containing thiophenes. For sample 2, there appears to be no such discrimination within the 10% accuracy limits currently established for the XANES analysis. 

Table 1 shows the effect of the sulfidation time on the S/Mo ratio and the activity of the Mo(S)/MSA in simultaneous HDS of thiophene and HDN of pyridine. The sample sulfided for 1 h displayed a low S/Mo ratio, suggesting the incomplete sulfidation of the Mo phase. The prolongation of the sulfidation time resulted in the increase of the S/Mo ratio almost to the stoichiometric value of 2. Both samples differed in their activities, which were lower in the case of the shortly sulfided sample A. 

It is of interest to compare the Smob/Scat data with Sexc/Scat obtained in studies on the S-exchange of catalyst sulfide with H2S.I 1 The degree of MoOx sulfidation was 63% if sulfided with thiophene, [ 1 that by the H2S-sulfided sample — 48%.t l The fraction of exchangeable sulfur in the... 

A Sulfur K Edge X-ray Absorption Near Edge Structure (XANES) Spectroscopy method has been developed for the direct determination and quantification of the forms of organically bound sulfur in nonvolatile petroleum and coal samples. XANES spectra were taken of a number of model compounds, mixtures of model compounds, heavy petroleum and coal samples. Analysis of the third derivatives of these spectra allowed approximate quantification of the sulfidic and thiophenic components of the model mixtures and of heavy petroleum and coal samples. These results are compared with those obtained by X-ray Photoelectron Spectroscopy (XPS). 

XANES of Petroleum Residua. On the left side of Figure 1 the sulfur K edge spectra for three different petroleum residua and the asphaltene samples prepared from them are shown. While the absorption spectra all appear to be similar, differences are revealed by examining the third derivatives of the spectra, which are shown on the right side of the figure. All the residua samples appear to contain sulfur bound in sulfidic and thiophenic forms, the amount of sulfidic sulfur increasing from sample 1 to sample 3. The asphaltene samples prepared from residua 2 and 3 also appear to contain both forms. Assuming that the composition of the sulfur... 

This work has demonstrated that organically bound sulfur forms can be distinguished and in some manner quantified directly in model compound mixtures, and in petroleum and coal. The use of third derivatives of the XANES spectra was the critical factor in allowing this analysis. The tentative quantitative identifications of sulfur forms appear to be consistent with the chemical behavior of the petroleum and coal samples. XANES and XPS analyses of the same samples show the same trends in relative levels of sulfide and thiophenic forms, but with significant numerical differences. This reflects the fact that use of both XPS and XANES methods for quantitative determinations of sulfur forms are in an early development stage. Work is currently in progress to resolve issues of thickness effects for XANES spectra and to define the possible interferences from pyritic sulfur in both approaches. In addition these techniques are being extended to other nonvolatile and solid hydrocarbon materials. 

The utility of sulfur K-edge X-ray absorption spectroscopy for the determination and quantification of sulfur forms in nonvolatile hydrocarbons has been investigated. X-ray Absorption Near Edge Structure (XANES) spectra were obtained for a selected group of model compounds, for several petroleum asphaltene samples and for Rasa coal. For the model compounds the sulfur XANES was found to vary widely from compound to compound, and to provide a fingerprint for the form of sulfur involved. The use of third derivatives of the spectra enabled discrimination of mixtures of sulfide and thiophenic model compounds, and allowed approximate quantification of the amount of each component in the mixtures, in the asphaltene samples and the coal. These results represent the first demonstration that nonvolatile sulfide and thiophenic sulfur forms can be distinguished and approximately quantified by direct measurement. 

Several papers in this book and in the recent literature (3) discuss use of pyrolysis techniques coupled with gas chromatography and mass spectrometry to determine forms of organically bound sulfur, but these methods introduce an uncertainty due to the possible interconversion of these sulfur forms during the heating step. For example, it has been shown that when benzyl sulfide was heated to 290°C, tetraphenyl thiophene, hydrogen sulfide and stilbene were produced (4). Coupled with heat and mass transport limitation considerations, particularly for viscous liquids and solids, it is not unreasonable to question whether at least some of the thiophenic forms observed by these techniques were produced during the analysis and may not have been present in the original sample. 

Assuming that the composition of the sulfur forms in the asphaltene samples and the Rasa coal is approximated by the simple two component mixture of dibenzothiophene and dibenzylsulfide models, an estimate of the relative molar quantities of sulfide and thiophenic forms can be obtained as described above and from Figure 3. These approximate values are listed in Table II. 

This simple analysis indicates that sample 3 contains about 50% sulfide forms and 50% thiophenic forms (ie. about a 1 1 molar mixture), while sample 2 contains 43% sulfide and 37% thiophenic. In the latter case, the totals do not add to 100%. For X-ray fluorescence data this method of quantification is susceptible to errors resulting from distortion of the XANES spectra by thickness... 

The analysis indicates that 30% of the organic sulfur is sulfide and 70% is thiophenic in the Rasa coal sample. Some confirmation of these values comes from the work of Kavcic (20), who showed that about 75% of the sulfur in this coal was not reactive toward methyl iodide this lack of reactivity was attributed to the sulfur being bound in ring structures. 

Sample Depth (m) Asphaltene (%) Sulfides Thiophenes (% of maltene) Biodegraded... 

Two ways of pretreatment were used 1 the samples were pretreated in a flow of hydrogen sulfide for 30 min at the temperature of air calcination. The physically adsorbed hydrogen sulfide was removed by purging with argon up to room temperature (2h). Before catalytic test the catalysts were heated in argon flow to the temperature of reaction (350°C) 2) the sample calcined at 350°C prior to the introduction of thiophene was heated 1,5 h in hydrogen flow (40ml/min). The sample was sulfided with H2S evolved upon thiophene... 

The catalytic activity of the samples was measured in a flow system at atmospheric pressure, temperature 350°C and space velocity of 0,6 h 1 with gas chromatographic analysis of products, The activity was evaluated by means of conversion of thiophene into hydrocarbons (a, %) and hydrogen sulfide (0, %),... 

The electron spin resonance (ESR) spectra were acquired on a Bruker 200 D spectrometer at room temperature. Prior to recording the samples were treated in a quartz reactor with flow of air, hydrogen sulfide or hydrogen-thiophene mixture. 

At the same time a decrease of the thiophene conversion can be related with blockage of some active species by hydrogen sulfide released during reaction and thiophene adsorbed too. The activity restoration when adsorbed components of reaction mixture are flowed by H2 or Ar is related to the reformation of the active species (Figure 2). The H2 S desorbtion (revealed in desorbed products along with butenes) leads to increase of the HDS activity and intensity of the Mos signals. The same result was also observed on the preliminarily reduced sample. 

The study of the HDS activity of HPMo/SiOa as a model catalyst has shown that the reversible deactivation effect is connected with increasing of sulfur iones in Mo5 surrounding, blockage Mos species by S-compounds and deeper reduction of molybdenum. The sample containing only molybdenum sulfide exhibits about two times lower initial and steady thiophene conversion in comparison with partially sulfided HPMo. 

Figure 24. Hydrodesulfurization activity of catalysts (Procata-lyse HR 306) activated according to different procedures at different temperatures (RS) simultaneous reduction sulfidation (15% H2S in H2) - except for the experiment at 573 K, the samples were first reacted for 4 h at 673 K, then progressively heated to the temperature indicated in the figure and maintained at this temperature for 4h (R + RS) successive reduction in H2 (4h) and reduction-sulfidation, as above (4h), both at the temperature indicated (R + RS ) reduction at the temperature indicated (4 h) followed by reduction-sulfidation at 673 K (4 h) as above (S + RS) sulfidation by pure H2S (4 h) followed by reduction sulfidation as above (4 h), both steps at the temperature indicated. The reaction with hydrogen with a feed containing 0.5% thiophene and 30% cyclohexene in cyclohexane was made under a total pressure of 3 MPa [138, 152],...

Thiophene HDS was performed at 673 K in a microflow reactor with on-line gas chromatography (GC) analysis. The catalyst samples (200 mg) were pre-sulfided in situ using conditions described in the preparation section. The reaction mixture consisting of 4.0 mol% thiophene in H2 was fed through the reactor and was analyzed every 35 min (flow rate 50 ml min , 673 K, 1 bar). First order rate constants for thiophene conversion to hydrocarbons (Khds) and the consecutive hydrogenation of butene (knyo) were calculated as described elsewhere [8]. 

Fig. 2 a-c shows the activities of the Ir-Mo/alumina sulfide catalysts in HDS of thiophene, HY of pyridine and HDN of piperidine during the parallel HDN/HDS, plotted against Ir amount in the catalysts. It is seen that addition of Ir to the Mo catalyst led to a substantial increase of activity. This increase was about 2 in HDS and about 3 in both steps of pyridine HDN. The data show that an optimum Ir amount in modified catalysts was found between 0.3-0.5 %. Above this Ir content, the activities in HDS and pyridine HY remained almost unaffected while activity in piperidine HDN clearly diminished. This decrease was explained by a diminution of the Ir dispersion, as evaluated from TEM measurements. The mean diameter of the majority of the Ir particles in reduced Ir-Mo sample with 0.53 % Ir was below 0.8 nm and some particles approached 1 nm. On the other hand, when the Ir amount increased to 0.79 %, the mean size of the majority of the particles approached 0.8-1.5 nm and the mean size of some smaller fractions (=>10 %) increased up to 1.5-2.5 nm [11]. 

Phenol-formaldehyde (PF) resins have been used as model compounds for the study of pyrolysis and combustion reactions that occur in solid fuels [10]. Utilising these resins it is possible to incorporate a wide range of heteroatomic and hydrocarbon moieties to simulate compounds that arise naturally in the solid fuels. A series of phenol resins crosslinked with thiophene, dibenzo-thiophene, diphenylsulfide, benzyl phenyl sulfide, thioanisole, 8-hydroxyquin-oline and 2-hydroxycarbazole were synthesised. These samples were then cured at 200°C (Fig. 15.2.1) and the resulting resins examined by solid-state NMR spectroscopy. The C CP/MAS spectra of a standard PF resin is shown... 

Thiophenes from alkynes 48 The alkyne is dissolved in methanol, ethanol, or acetone and the solution is adjusted to pH 9-10 by adding N-sodium hydroxide solution in the proportion 9 1. Hydrogen sulfide is then led in at 20-80° until a sample of the mixture no longer shows acetylene bands in its UV spectrum (4-20 h). The mixture is then treated with water, and the product is taken up in ether, dried over sodium sulfate, freed from solvent, and distilled or recrystallized. Thus were prepared 2,5-dimethylthiophene, b.p. 134-136° (70%), 2,5-dlethyl-thiophene, b.p. 180-181° (65%), and 2,5-diphenylthiophene, m.p. 152-153° (85%). 

This detector is well adapted for sulfur, phosphoms, or tin determination. Two flames are often used to separate the region of sample decomposition to sample emission. Response is dependent on the environment of the sulfur atoms (thiols, sulfides, disulfides, thiophenes). The FPD can also detect iron. 

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