Sulfur compounds, pyrolysis

Peter H. Given J. R. Jones and I have studied the pyrolysis of some aromatic sulfur compounds, including dibenzothiophene and thioxanthone (dibenzothiopyrone). Much of the sulfur is lost from the thioxanthone as volatile products, whereas much of the sulfur in dibenzothiophene is retained in the char. The difference in behavior no doubt arises from some difference in aromatic stability between the two sulfur heterocycles hence, aromaticity or aromatic character may well be a general factor determining how much sulfur is retained in the char on pyrolysis. 

Figure 10. Py-GC-FPD traces showing the effect of maturation on the distribution of sulfur compounds released by flash pyrolysis at 600 C.

N, S and 0 heterocyclic compounds, along with noncyclic sulfur compounds and hydrocarbons, are predominant in "meaty" flavor volatiles. The mechanisms of heterocyclic formation by Maillard and pyrolysis reactions have been reviewed by Vemin and Parkanyi (57) and the Maillard reaction itself is a recurring subject of review (58). Since other speakers contributing to this volume will discuss these aspects of meat flavor, they will not be repeated in this presentation. 

Processes are of two types, catalytic and tbcnnaL However, apart from the operadng condidons, their flow sheets are identicaL Depending on the feedstock, a simplihed version is available with dealkylation alone, and another more-elaborate version, which includes pretreatment of the pyrolysis cut intended to convert the diolehns, stable sulfur compounds, nitrogen and oxygen compounds, etc. by selective hydrogenadon. 

Tobacco leaf has a complicated chemical composition including a variety of polymers and small molecules. The small molecules from tobacco belong to numerous classes of compounds such as hydrocarbons, terpenes, alcohols, phenols, acids, aldehydes, ketones, quinones, esters, nitriles, sulfur compounds, carbohydrates, amino acids, alkaloids, sterols, isoprenoids [48], Amadori compounds, etc. Some of these compounds were studied by pyrolysis techniques. One example of pyrolytic study is that of cuticular wax of tobacco leaf (green and aged), which was studied by Py-GC/MS [49]. By pyrolysis, some portion of cuticular wax may remain undecomposed. The undecomposed waxes consist of eicosyl tetradecanoate, docosyl octadecanoate, etc. The molecules detected in the wax pyrolysates include hydrocarbons (Cz to C34 with a maximum of occurrence of iso-Czi, normal C31 and anti-iso-C32), alcohols (docosanol, eicosanol), acids (hexadecanoic, hexadecenoic, octadecanoic, etc ). The cuticular wax also contains terpenoids such as a- and p-8,13-duvatriene-1,3-diols. By pyrolysis, some of these compounds are not decomposed and others generate closely related products such as seco-cembranoids (5-isopropyl-8,12-dimethyl-3E,8E,12E,14-pentadecatrien-2-one, 3,7,13-trimethyl-10-isopropyl-2,6,11,13-tetradecatrien-1al) and manols. By pyrolysis, c/s-abienol, (12-Z)- -12,14-dien-8a-ol, generates mainly frans-neo-abienol. 

Kraft). It was found that pyrolysis at 600° C and 1350° C indicates little difference in the levels of sulfur in any sample. However, combustion at 1350° C increases this level significantly, probably due to the participation of some inorganic sulfur in generating volatile sulfur compounds. The presence of specific ions such as H , Na and Ca was also shown to have some effect on the measurement. The detected level of sulfur in the pulp is shown in Figure 16.4.1. 

The first js the pyrolysis of acetone in a tubular reactor. As for the cracking of acetic arid, it is preferable to use chromium steel (25 per cent) tubes. The use of conventional alloys may be feasible after passivation of the inner walls by a mixture of H2 and CO. or by prior treatment with steam, or by the injection of small amounts of sulfur compounds (H,S, CS etc.). The effluents leaving the furnace are quenched in two stages ... 

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