Chemical structural units of macromolecular coal components

Chemical degradations of coal resins, coal asphaltenes and coal residues have been performed with selective, non-oxidative reagents. The coal comprise samples a rank interval 0.30–1.21 %R_m. Degraded low-molecular-weight compounds were analyzed by GC-MS. The distributions of pentacyclic terpanes, isoprenoids, n-alkanes, acids and alcohols obtained as degradation products illustrate a considerable variability between the macromolecular coal fractions. A structural study on the molecular level of the degraded compounds from coal resins and coal asphaltenes show their potential to generate hydrocarbons during coalification process.     

Biomarker distributions in asphaltenes and kerogens analysed by flash pyrolysis-gas chromatography-mass spectrometry

Biomarker distributions in a suite of asphaltenes and kerogens have been analysed by flash pyrolysis directly coupled to a GCMS system. Attention has been focussed on biomarkers of the sterane and triterpane types. The sample suite under investigation consists of sediments with different kerogen types and some crude oils. Biomarker distributions in the pyrolysates have been compared with the “free” biomarkers in the corresponding saturated hydrocarbon fractions.The analyses show significant differences between the distributions of the free biomarkers and those in the pyrolysates. The latter have lower amounts of steranes while diasteranes are absent or present at low concentrations only. In the triterpane traces a shift of maximum intensity from C₃₀ (free compounds) to C₂₇/C₂₉ is observed. Furthermore, the pyrolysates contain a set of triterpenes (not present among the free compounds), and there is a selective loss of “non-regular” triterpanes that are present in the saturated hydrocarbon fractions. The observed differences between pyrolysates and free hydrocarbons can be explained partly by the processes occurring during pyrolysis such as bond rupture and subsequent stabilisation of primary pyrolysis products. To a certain extent these differences also show that maturation processes occurring in sediments have effects on free biomarker molecules different from those on molecules that are enclosed in a macromolecular matrix (kerogen or asphaltenes).Differences between biomarker distributions of asphaltene and kerogen pyrolysates are relatively small. A comparison with the pyrolysates from extracted whole sediments suggests that these differences are mainly caused by interactions between the organic material and the mineral matrix during pyrolysis.Oil asphaltenes behave differently from sediment asphaltenes as their pyrolysates are more similar to the corresponding saturated hydrocarbon fractions, i.e. the differences described above are observed to a much smaller extent. This different behaviour appears to be the result of coprecipitation of a part of the maltene fraction with the oil asphaltenes.     

沥青质傅里叶变换红外光谱 (FT IR)分析及其在有机地球化学研究中的应用

沥青质傅里叶变换红外光谱（FT－IR）分析可以反映出其分子结构上的特征，红外吸收因子Z[I(1380cm^-1)/I(720cm^-1）]能指示不同来源沥青质的母质类型；吸收因子Y[I(1600cm^-1)/I(1450cm^-1)]可以较好地讨论沥青质的成熟度演化状况；沥青质的红外研究认为，所有的沥青质都具有较好的再生烃潜力，其中Ⅲ型母质来源的沥青质具有较好的再生气潜力。而Ⅰ和Ⅱ型母质来源的沥青质具有高的再生油潜力。     

辽河油田生物降解原油沥青质热解产物中单体化合物碳同位素组成

生物降解原同在我国分布广泛并且在重油资源中占有一定的比例。本文通过采用单体化合物碳同位素分析技术对取自辽河油田西部凹陷的重油以及它们沥青质组分的热解产物进行单体碳同位素测定,来研究原油沥青质热解产物中正构烷烃单体碳同位素的组成及其一物降解油的指示意义。研究结果表明,沥青质热解产物中正构烷烃组分的单体碳同位素组成可用于生物降解较严重的重油样品进行油／油相比,并且与原油中的正构烷烃单体碳同位素组成的对     

Structural investigations of sulphur-rich macromolecular oil fractions and a kerogen by sequential chemical degradation

Structural studies of a sulphur-rich kerogen and macromolecular oil fractions from the Monterey Formation were performed by selective sequential chemical degradation. The method provides low-molecular weight compounds as former building blocks of the network which allow detailed analyses on a molecular level. The degradation sequence is based on three subsequently performed reactions—a selective cleavage of sulphur bonds in the first step carried out with Ni(0)cene/LiAlD₄, an ether and ester bond cleavage (BCl₃), and an oxidation of aromatic entities by ruthenium tetroxide as a final step. Each step of this sequence afforded a considerable amount of low-molecular weight material which was separated chromatographically and studied by GC and GC/MS, while the high-molecular weight or insoluble fractions were subjected to the next reaction step.The chemical degradation products—hydrocarbons and carboxylic acids—are discussed in terms of incorporation into the macromolecular structure, distribution of heteroatomic bridges and the genetic relationships between the different macromolecular crude oil fractions and kerogen.Labelling experiments with deuterium provided evidence for a simultaneous linkage by oxygen and sulphur functionalities or by aromatic units and sulphur bonds of cross-linking macromolecular network constituents.The determination of sulphur positions in the macromolecule suggests early diagenetic sulphur incorporation into the biological precursor compounds and subsequent formation of a cross-linked network.     

Geochemical significance of hydrocarbons desorbed from asphaltenes

Saturate hydrocarbon fractions desorbed (cleaned) from asphaltenes extracted and separated from two core samples (a tar sand and a reservoir sandstone sample) were analyzed by gas chromatography-mass spectrometry (GC-MS). The results indicated thatn-alkanes adsorbed in asphaltenes were kept quite well during and after severe biodegradation over 360 Ma. Hydrocarbon desorption could be an alternative method of, or even better than the pyrolysis of asphaltenes to reconstruct the hydrocarbon fingerprints of primary oils and extend the understanding of the origins of hydrocarbon reservoirs. Project supported by the Chinese Academy of Sciences, State Key Laboratory of Organic Geochemistry and Research Center of Tarim Petroleum Exploration and Development.     

Characterisation of the non-asphaltene products of mild chemical degradation of asphaltenes

The major steranes of the non-asphaltene fraction of Nigerian tar sand bitumen (maltene) are the c₂₇-c₂₉ diasteranes [13β(H),17α(H); 20R + S] and C₂₈-C₂₉ regular steranes [14β (H),17β (H); 20S]. The reducing metal reaction products of the corresponding asphaltenes (maltene-I) contain mainly C₂₇-C₂₉ regular steranes with the 14β(H),17β(H); 20R + S and 14α(H),17α(H); 20R + S configurations as well as the corresponding diasteranes having the 13β(H),17α(H); 20R + S configuration. These sterane distributions suggest that maltene-I corresponds to an unaltered oil whilst the maltene is equivalent to the product of severe biodegradation of maltene-I. This is consistent with maltene-I being the remnant of “original oil” trapped within the asphaltene matrix and protected from the effect of in-reservior biodégradation.Degradation of Nigerian asphaltenes by refluxing with ferric chloride-acetic anhydride or methanolic potassium hydroxide also releases soluble reaction products having the characteristics of unaltered oil such as the presence of n-alkanes having an unbiased distribution. These methods appear to be milder and more suitable than reducing metal reactions for releasing hydrocarbons occluded by asphaltenes.     

A comparison of organosulphur compounds produced by pyrolysis of asphaltenes and those present in related crude oils and tar sands

Asphaltenes and NSO fractions from a variety of oils and tar sands have been characterized by pyrolysis-gas chromatography (Py---GC) using both flame ionization and flame photometric detectors. Organosulphur compounds were not always produced by pyrolysis of the asphaltenes isolated from the biodegraded tar sand extracts although pyrolysis of the NSO fractions produced a series of thiophenes from all of the samples examined. These observations suggest that under certain conditions, asphaltene fractions may be affected by biodegradation, leading to preferential removal of the sulphur containing compounds. In addition, it was observed that Py---GC of asphaltenes permitted oils to be differentiated on the basis of their source rock lithology. Oils derived from carbonate source rocks produced thiophene/benzothiopene ratios <1 whilst the same ratio was >1 for oils derived from shales. Thiophene/dibenzothiophene ratios could be used in a similar manner.     

Hydrous pyrolysis of Monterey asphaltenes

Hydrous pyrolysis of asphaltenes has been tested as a method to reconstruct the chemical composition of biodegraded oils and oil seeps. The asphaltenes of three oils (a nondegraded oil, a biodegraded oil, and a biodegraded oil seep) from the Monterey Formation were studied. Results show that the aliphatic fraction generated by hydrous pyrolysis is very similar in chemical composition to the non-degraded oil. This makes the method very useful in correlation studies of biodegraded and nondegraded oils. It also allows to roughly estimate the maturity of the source of the biodegraded oil or oil seep.     

9 and 34 GHz EPR study of the free radicals in various asphaltenes: Statistical correlation of the g-values with heteroatom content

The 9 and 34 GHz EPR spectra of eight asphaltenes from different locations have been studied at 294 K in an attempt to correlate the observed g-values with the heteroatom content. It is found that the EPR linewidths are larger and the g-values are smaller at 34 GHz than at 9 GHz. Quantitative statistical analysis of the g-values observed in those asphaltenes derived from tar sand bitumens and crude oils shows that they are uncorrelated with the heteroatom content, unlike those from coal. It is concluded that g-values may not be a good analytical tool for elucidating the structure of those asphaltenes not derived from coal.