Sulfur analysis general problems

Some general problems associated with the determination of sulfur in coal are nonuniform distribution of pyrite particles, failure to convert all the sulfur to sulfate, and loss of sulfur as sulfur dioxide during the analysis. The nonuniform distribution of pyrite necessitates the collection of many sample increments to ensure that the gross sample is representative of the lot of coal in question. Pyrite particles are both hard and heavy and have a tendency to segregate during the preparation and handling of samples. Because the particles are harder, they are more difficult to crush and pulverize and tend to concentrate in the last portion of material that remains from these processes. 

Their kinetic and product analysis is consistent with the working hypothesis indicated previously for insertions the singlet process is stereospecific, while the triplet process is at best only selective. Here, as in the reaction of sulfur atoms with alkenes, (217), some progress has been made in separating the problem of the reacting species and their reaction rates from the observed SS in the product (Gunning and Strausz, 1966). In general, however, interconversion rates of triplet cisoid and transoid diradicals are uncertain, and deductions from overall stereoselectivity are also uncertain. 

To put these problems into perspective based on conventional approaches for HDS of diesel fuels, for reducing the sulfur level from current 500 ppmw to 15 ppmw (the regulation in 2006) by conventional HDS processing, the volume of catalyst bed will need to be increased by 3.2 times as that of the current HDS catalyst bed. This is consistent in general with the analysis on a t3 ical Co-Mo catalyst by Haldor Topsoe regarding the required increase in catalyst activity and bed temperature for further reduction of sulfur from 500... 

Several methods including spectrophotometric or chromatographic techniques have been proposed for the determination of furans such as HMF or furfural, or developed to determine both furan compounds simultaneously. The spectrophotometric methods do not differentiate between HMF and furfural without the need of a previous separation procedure. The commonly employed colorimetric method for HMF is Winkler s 38), which is based on the use of barbituric acid and p-toluidine. Toxicity of p-toluidine, instability of the color complex formed, and interference of sulfurous acid and possibly other compounds present in the fruit juice 40) are known to be problems. Unlike HMF, the colorimetric method for furfural was based on a previous distillation of juice and the colorimetric analysis of distillate for furfural based on colorimetric reaction with aniline acetic acid in juices 41). However, distillation procedure with poor recovery (about 34%) and long reaction time for color development (approximately 1 h), and requirement of hazardous chemical aniline 20) are known to be the drawbacks of the colorimetric method for furfural. Also, colorimetric method generally requires strict control of reaction time and temperature to achieve stable and reproducible color development. 

The ability of copper salts to dissolve carbon monoxide was first discovered by Leblanc (1850). Early interest in the phenomenon centered around its use in gas analysis for the determination of carbon monoxide. The first aqueous solutions were generally acid and unsuited for use in conventional equipment because they caused severe corrosion. This problem was mitigated by the use of salts of weak acids, such as carbonic and formic, rather than previously used salts of hydrochloric or sulfuric acids. 

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