Pyrolysis sulfur reduction

Another method for the determination of oxygen in coal involves reduction of the coal by pyrolysis in the presence of hydrogen, whereupon the oxygen is converted catalytically to water. However, the procedure is relatively complex and the catalyst may be poisoned by sulfur and by chlorine. 

The reductive process is the more traditional process for tire pyrolysis. This process excludes all sources of oxygen and relies on the reactor heat alone to decompose the tires. Some processors pressurize the reactor with an inert gas such as nitrogen to prevent air from leaking into the reactor, while some inject hydrogen to react with the sulfur present in the rubber in the tires to form hydrogen sulfide. Hydrogen sulfide can be recovered and sold as a by-product. 

Apart from the pyrolysis of 2-tert-butylsulfonylpyrazine to afford pyrazine (1) [in 49% yield with loss of sulfur dioxide and unsaturated ( ) hydrocarbon]239 and the reduction of pyrazine to piperazine (2) (in 76% yield by treatment of an alkaline solution with Ni—A1 alloy),479 no new or improved routes to pyrazine or piperazine appear to have been reported in recent years nor has any di- or tetrahy-dropyrazine been prepared. Both pyrazine and piperazine are now available commercially at modest cost. 

Following pyrolysis of column effluent, unwanted species are removed and the relevent products mixed with a liquid (alcohol/water) and differential conductivity subsequently measured. Depending upon the reaction gas used and whether the process is reductive or oxidative, speciflcity for nitrogen, sulfur or halogen compounds can be obtained l... 

Burchfield and his associates (12, 13, 14) reported a procedure involving reductive pyrolysis of the effluent gases whereby compounds containing chlorine, sulfur, or phosphorus form HCl, H2S, or PH3, respectively. By using an aluminum oxide scrubber following the pyrolysis stage, the system was specific for phosphorus. However, the detection system appears to be inferior to other available detectors for phosphorus and will probably have little or no use for this purpose. 

Synthetic applications of dithietane 35 are not limited to its use as a source of hexafluorothioacetone. This compound is also a valuable precursor for the synthesis of a variety of fluorinated sulfur-containing derivatives. For example, the pyrolysis of 35 at 325 C results in the high-yield formation of (CF3)2C=C(CF3)2. The reaction of 35 with PhaP was found to be a convenient route to (Ph)3P=C(CF3)2, which was used for the preparation of l,l-bis(trifluoromethyl) alkenes and CF2=C(CF3)P(0)(0R)2. Recently reported transformation of fluorinated thietanes involves reductive ring expansion to substituted dihydrothiophenes. For example, the treatment of compound 47 with aluminum powder in the presence of a catalytic amount of PbCl2 resulted in an interesting ring expansion process leading to the formation of compound 48 in excellent yield (Scheme 2.23). Readily available fluorinated cycloadducts 49... 

Herrmann I, Kramm UI, Radnik J, Fiechter S, Bogdanoff P (2009) Influence of sulfur on the pyrolysis of CoTMPP as eiectrocataiyst for the oxygen reduction reaction. J Electrochem Soc 156(10) B1283-B1292... 

Scheme 13.24. The demonstration of the location of oxygen substituents in thebaine (and hence morphine and codeine) and the presence of a phenanthrene (barring rearrangement) system. The degradative work is from Vongerichten, E. Dittmer, O. Chem. Ber., 1906,39,1718. The synthesis, using the sodium salt of the 4-methoxyphenylacetic acid reacting with the nitrobenzaldehyde derivative (in acetic acid for 3 days at 100°C) followed by reduction [rron(II) sulfate], diazotization (sodium nitrite in methanolic sulfuric acid), cychzation, and pyrolysis (loss of carbon dioxide) was effected by Pschorr, H. Liebigs Ann. Chem., 1912, 391,40.

J. Langmaier, F. Opekar, and V. Pacakova. Application of a metallized membrane electrode for the determination of gaseous sulfur compoimds after reductive pyrolysis. Talanta 34 453-459,1987. 

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