Haru Sakashita

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.

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.

Effect of halogen anion on hexane aromatization activity of Pt/KL catalysts

Potassium salts were added to the catalyst prepared by ion exchange of KL with [Pt(NH3)4]Cl2 and the effect of their counter anion on the activity and selectivity for hexane aromatization was studied. The catalyst to which KF was added showed the highest activity and selectivity for benzene formation; methylcyclopentane and hydroisomerization products were negligible. Although the catalyst with KCl added also exhibited excellent performance, the catalysts with KBr or KI added gave rise to low hexane conversion and benzene yield. Infra-red spectra of adsorbed CO revealed that the presence of the low frequency C-O stretching band is closely related to catalytic performance of the Pt/KL series catalysts. The electron-rich Pt site formed through the interaction with KF or KCl may be responsible for the high activity and selectivity for hexane aromatization.

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.

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.

Selective macrolactonization using zeolite molecular sieves

‘In-pore’ reactions of 15-hydroxypentadecanoic acid on dealuminated HY zeolite effected intramolecular esterification exclusively to give the monomeric lactone, pentadecanolide.