Mariko Ishiwatari

Pyrolysis of chlorophyll a after preliminary heating at a moderate temperature: Implications for the origin of prist-1-ene on kerogen pyrolysis

Abstract Pyroprobe pyrolyses of chlorophyll a were performed to investigate the possible precursors and formation mechanisms of prist-1-ene often observed in the products of kerogen pyrolysis. Thermal maturation was simulated by preheating chlorophyll a for different times at 250°C. Phytadienes dominated the pyrolyzates from unheated or briefly preheated samples. Little prist-1-ene was produced from unheated chloropyll a during pyrolysis at 400°C for 1 s, whereas a considerable yield was obtained after preheating. Pyrolysis at 470°C for 15 s produced prist-1-ene from both unheated and preheated chlorophyll a. The yield of prist-1-ene increased with the time of preheating, relative to the yield of phytadienes. Additional isoprenoid hydrocarbons (C 9 C 20 ) were formed from the fragmentation of chlorophyll a. Possible pyrolysis mechanisms to explain these results are presented.

Thermal reaction of β-carotene: Part 2. Pyrolysis in the presence of kaolinite

Abstract β-Carotene was heated with a clay mineral (kaolinite) under vacuum at temperatures ranging from 200 to 350°C for 24 h. Several polymethylbenzenes, naphthalenes and probably phenanthrenes were observed in the pyrolysate at 350°C. Furthermore, ionene, some polymethylbenzenes and a dimethylnaphthalene were detected at temperatures between 200 and 250°C. It was concluded that the clay mineral may act as an acidic catalyst.

Thermogravimetry and pyrolysis—GC of chlorophyll-a: with a special emphasis on thermal behavior of its phytyl chain

Abstract The thermal alteration of chlorophyll-a (Chl-a) was examined by means of thermogravimetry (TG) and pyrolysis—gas chromatography (Py-GC). Py-GC/mass spectroscopy, gas chromatography and infrared spectrometry were also used as complementary methods. When pyrolyzed at 340 °C for 15 s, Chl-a produced virtually only C20-isoprenoid hydrocarbons (C20-ISOPs). This result indicates that the major decomposition reaction below 340 °C is the release of a phytyl (3,7,11,15-tetramethyl-2-hexadecenyl) chain. When the 340 °C-pyrolysis residue was pyrolyzed again at 470 °C for 15 s, notable amounts of isoprenoid hydrocarbons with carbon numbers of 19 or less (S-ISOPs) were produced and amounts of C20-ISOPs became smaller. We assume that these S-ISOPs are produced from a phytanylaromatic structure which may have been formed during the 340 °C pyrolysis. On heating Chl-a at 150 °C for a long time (504 h) resulted in the formation of a material barely soluble in many organic solvents. S-ISOPs produced from the barely soluble material upon pyrolysis at 470 °C are similar in molecular distribution to those obtained by the pyrolysis at 470 °C of the 340 °C-pyrolysis residue of Chl-a. This suggests that a phytanyl-aromatic structure is formed also on long-term 150 °C heating. The Chl-a-derived S-ISOPs were almost identical to those obtained upon flash pyrolysis of kerogens (insoluble organic matter in sedimentary rocks) in terms of molecular composition. Thus, it is supposed that Chl-a changes into a polycondensed material having a phytanyl-aromatic structure in sediments/sedimentary rocks and is finally incorporated into a kerogen assemblage in nature.

Thermal decomposition behavior of oil shale kerogens observed by stepwise pyrolysis—gas chromatography

Abstract Thermal decomposition behavior was investigated by use of stepwise pyrolysis—gas chromatography for four oil shales (Colorado, Condor, Maoming and Timhadit oil shales from USA, Australia, China and Morocco, respectively) and their kerogen concentrates. It was revealed that product distribution was dependent on pyrolysis temperature for all the kerogens examined as well as for the oil shales. Isoprenoid hydrocarbons were mostly generated at 430°C from all samples examined, while the majority of 1-alkenes and n-alkanes were generated at 470°C and/or 520°C. Yields of benzene, toluene and xylenes did not significantly change through the stepwise pyrolysis. Based on the pyrolysis behavior, the carbon skeleton structure of kerogen is discussed.

Thermal reaction of β-carotene. Part 1

Abstract β-Carotene has ben heated under vacuum at temperatures ranging from 200 to 350°C for 24 h as a model of geothermal reaction of carotenoids in sediments and of a thermal reaction of highly conjugated polyene. Compounds with molecular weights of 138, 240, 346 and 444 and isomers of β-carotene were obtained in addition to toluene, xylene, ionene and 2,6-dimethylnaphthalene, which have been reported previously as pyrolysis products of β-carotene. Possible reaction mechanisms for the formation of the pyrolysis products are given.

Organic sulphur compounds produced by flash pyrolysis of Timhadit oil shale

Abstract The pyrolysis behaviour of a kerogen concentrate from Timhadit oil shale (Morocco) has been examined. The concentrate gave various alkylthiophenes and alkylbenzothiophenes, accounting for 38% of the total amount of the organic pyrolysis products, with carbon atom numbers lying in the range from 6 to 20. It has been shown that these organic sulphur compounds were mainly generated at lower temperatures than olefins and paraffins.

Application of pyrolysis-gas chromatography to the study of thermal alteration of chlorophyll-a — effect of clay minerals

Abstract The effect of clay minerals (montmorillonite and kaolinite) on the thermal alteration of chlorophyll-a (Ch-a) was examined by means of pyrolysis-gas chromatrography. When preliminarily heated at 150 °C for a period ranging from 2 h to 504 h in the presence of montmorillonite or kaolinite, Ch-a produced a considerable amount of material which was insoluble in a 9:1 mixture of iso-octane/ethanol (I/E) but soluble in 3:1 benzene/methanol (B/M). The yield of I/E insoluble-B/M soluble fraction (B/M extract) increased with increased preheating time. Upon pyrolysis, the B/M extract produced isoprenoid hydrocarbons (ISOPs) of carbon number 20 or less. With increased preheating time, the yields of ISOPs of carbon number 20 (C20-ISOPs) dramatically decreased, compared to those of ISOPs of smaller carbon numbers (S-ISOPs). The S-ISOPs were mostly identical to those produced upon pyrolysis of kerogens (insoluble organic matter in sedimentary rocks). The trend in the decrease in the yields of C20-ISOPs with preheating time is similar to that observed for Ch-a preheated in the absence of clay minerals. Clay minerals seem to promote the formation of a structure which preferentially produces 1-pristene (2,6,10,14-tetramethyl-1-pentadecene, Pr-1), the most predominant compound in the ISOPs from kerogens, upon pyrolysis.

Effects of maceral composition on pyrolytic behaviour of kerogens

Optical microscopy, thermogravimetry and stepwise pyrolysis-gas chromatography were applied to three oil shale kerogens. Colorado kerogen, consisting mostly of alginite, gave a sharp d.t.g. peak, whereas Condor and Maoming kerogens, composed of alginite and vitrinite (~ 9:1) gave slightly broader peaks. Step-py-g.c. of all the kerogens gave many peaks of 1-alkene and n-alkane homologues. Condor and Maoming kerogens also gave several moderate g.c. peaks of phenolic compounds, which were hardly seen in the pyrograms of Colorado kerogen. The yields of the phenolic compounds were not strongly dependent on pyrolysis temperature, compared with alkenes and alkanes. The phenolic compounds were thought to be derived from vitrinite. This was confirmed by examining Ozasa vitrinite, for which step-py-g.c. gave large peaks of phenolic compounds similar to those from kerogens in terms of molecular weight distribution and generation profile. These results indicate that maceral composition is an important factor in the pyrolytic behaviour of kerogen.

Insights on the origin of pristane and phytane in sediments and oils from laboratory heating experiments

We investigated a formation pathway of pristane (Pr) and phytane (Ph) in crude oils and ancient sediments from the phytyl side chain of chlorophyll and degradation of Pr and Ph during thermal maturation by laboratory heating experiments of pure dihydrophytol (DHP), Pr and Ph, followed by measurement of carbon isotopic compositions. In the first heating experiment, dihydrophytol (DHP) was pyrolyzed in a closed system at 320–350°C for 1-12 h. DHP yields large amounts of Pr and prist-1-ene with lesser amounts of Ph and phytenes. The Pr/Ph ratio which was obtained after hydrogenation of prist-1-ene and phytenes increases from 0.7 to 21 with increasing thermal degradation of DHP. We conclude that DHP originating from chlorophyll pigments can be an important precursor of Pr under geological conditions. Pr and Ph produced from DHP are slightly depleted in 13C compared to the original DHP and δ13C of Pr is similar to that of Ph. This result supports the idea of a common source for both Pr and Ph, primarily chlorophyll pigments. In the second heating experiment which was intended to evaluate the role of thermal stress on the fate of Pr and Ph in petroleum, Pr and Ph were heated at 380 or 420°C under vacuum for 5–800 h, and the shift in their carbon isotopic composition was studied as a function of thermal decomposition. The decomposition of Pr and Ph follows apparently first-order kinetics. Pr/Ph ratio does not change significantly during thermal decomposition of 90% of the initial amount of these isoprenoids. The fractionation factors for both Pr and Ph are practically identical: α = 0.9994 ± 0.0002 (n = 23). The effect of temperature on the fractionation factor is negligible. Although Pr and Ph are enriched in 13C with increasing thermal decomposition, the magnitude of the enrichment is small and 90% of Pr and Ph must be thermally decomposed to cause a 1.4 ± 0.4increase in δ13C values. The results also indicate that Pr/Ph ratio does not change significantly during thermal decomposition. Therefore, we conclude that small changes in Pr/Ph ratios and in δ13C of Pr and Ph with increasing thermal maturity may be a notable feature of occurrence of thermocracking of Pr and Ph in crude oils.

Thermal behavior of ternary Sm2Fe17Nx magnets

The Mössbauer spectra of Sm2Fe17Nx, prepared by the nitrogenation of Sm2Fe17 powders in an ammonia and hydrogen atmosphere, were observed at elevated temperatures to shed light on the thermal behavior of nitrogen in the compounds Sm2Fe17Nx. It was found that there were large differences in thermal behavior between the starting Sm2Fe17, crystalline Sm2Fe17Nx (x≈1.7) and amorphous Sm2Fe17Nx(x∼7).The thermal decomposition behavior of Sm2Fe17N3.2, developed as one of the most promising hard magnetic materials, was found to be different under different atmospheres.ZusammenfassungZur Klärung des thermischen Verhaltens von Stickstoff in Sm2Fe17Nx-Verbindungen wurde bei höheren Temperaturen das Mössbauer-Spektrum von Sm2Fe17Nx auf-genommen, wobei die Verbindung aus Sm2Fe17 durch Nitrierung in Wasserstoffatmosphäre hergestellt wurde. Man fand, daß erhebliche Differenzen zwischen dem thermischen Verhalten des Ausgangsstoffes Sm2Fe17, kristallinem Sm2Fe17Nx (x∼1.7) und amorphem Sm2Fe17Nx (x∼7) bestehen.Für unterschiedliche Atmosphären fand man unterschiedliches thermisches Zersetzungsverhalten von Sm2Fe17N3.2, entwickelt als eines der vielversprechendsten harten magnetischen Materialien.