Sulfur distribution

As with HjS, the distribution of sulfur among the other FCC products depends on several factors, which include feed, catalyst type, conversion, and operating conditions. Feed type and residence time are the most significant variables. Sulfur distribution in FCC products of several feedstocks is shown in Table 2-4. Figure 2-9 illustrates the sulfur distribution as a function of the unit conversion. 

Sulfur Distribution of the FCC Products as a Fuction of Unit Conversion... 

Figure 2-9. Sulfur distribution of the FCC products as a function of unit conversion.

The sulfur distribution from the coal conversion plant is shown in Figure 4. The wt% of sulfur remaining in the ash depends on several factors among which are the relative distribution of organic and inorganic sulfur in the coal and the chemical composition of the ash. High alkaline ashes will capture sulfur as sulphide or sulfate. 

To study the effect of chemical composition on sulfur distribution during pyrolysis, it appeared desirable to study the pyrolysis of sulfur-containing model compounds of well-defined structure. The correlation of chemical composition and sulfur distribution during pyrolysis is the subject of this paper. 

A series of 10 polycyclic compounds and blends with starch, Bakelite, and hydrogenated creosote were employed as model substances to examine the effect of carbon, hydrogen, and oxygen on sulfur distribution during pyrolysis at a temperature of about 625°C. 

Experimental data were obtained on the carbonaceous residue (char), and sulfur distribution was calculated for the solid and gaseous products from the pyrolysis of model compounds. Sharp differences were observed in the quantity of char and the sulfur distribution for the different substances studied. The quantity of volatile matter varied from 21 to 43%. The sulfur retained by the char varied from 21 to 74% of the total present in the compound pyrolyzed (see Table I). The raw data show a possible relationship between the volatile matter and sulfur retention which indicates that as volatile matter decreases, sulfur retention generally increases (Table I). Neither structural features nor the molecular size of the various model compounds appear to have a significant relationship to sulfur distribution. 

In an attempt to correlate sulfur distribution with elemental composition, the mechanism of sulfur elimination was assumed to involve two processes ... 

Fig. 8. Radial lead and sulfur distribution in poisoned catalyst pellet. [From Klimisch et al. (42).] (Reprinted with permission from Advances in Chemistry Series. Copyright by the American Chemical Society.)...

Characterization of DOM according to molecular size, polarity, or other structure-based properties include often the demand for element specific information. Questions to be answered might concentrate, for example, on the phosphorous, nitrogen, or sulfur distribution in the different molecular size ranges. From the point of view of transport processes, the heavy metal content in the different fractions might be important for the interactions between inorganic or geogenic colloids and DOM. 

Direct Characterization Techniques. The in situ analysis of elemental composition of coals by ion microprobe was first demonstrated by Dutcher t al. (85). Raymond (86) has applied this technique to examine the variation in composition of coal macerals which has been especially effective for looking at sulfur distribution. An example of the organic sulfur distribution for two bituminous coals is shown in Table II which is taken from reference (86). Note that the liptinites contain the... 

Table II Organic Sulfur Distribution in Various Coals(I)...

Solid solutions in metallic alloys are normally compositionally very uniform random variations of 5% would be unusual. Also, a two phase layer normally is found between two solid solutions. The sulfur distribution in coal seems not to behave this way. Apparently, the distribution pattern established at some early stage of coal formation is frozen-in and the organic sulfur is bound so tightly to its hydrocarbon sites that it cannot diffuse until the temperature of the coal is raised to 400°C or above (18). 

Product Weight Total Sulfur Total Sulfur Distribution Remarks... 

Analysis. The heating value, ash content, and sulfur distribution of the raw and treated coals were determined according to ASTM procedures (7). Iron in the extracts of the raw and treated coals was determined by titration with a cerium (IV) solution. Iron in the residues from the acid extractions of the raw and treated coals was determined spectrophotometrically using ferrozine (20). The liquid extracts were analyzed for total sulfur (as sulfate) by ion chromatography after separation of the sulfate from nitrate on an alumina column (21). Nitrogen was determined in the raw and treated coal and in their nitric acid-extracted residues by a modified Kjeldahl method. 

Radioactive L-cystathionine (10) (765 mg.) containing 6.85 x 106 counts per minute of S35 was fed to the human cystinuric patient who had served previously as the subject in an experiment demonstrating the formation of cystine from sulfur-labeled methionine (11). The same precautions were followed with regard to human experimentation involving radioactive material as in the latter experiment. After the feeding of the cystathionine, 24-hour urine specimens were collected for 3 days and sulfur distributions were determined by the titrimetric method of Fiske (6). Cystine determinations were carried out by the procedure of Sullivan, Hess, and Howard (12). 

Radioactivity measurements were made upon benzidine sulfate recovered from the sulfur distribution determinations, as well as on benzidine sulfate from the sulfur analysis of the cystine samples. The results of these measurements are given in Table I. 

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