This paper reports different concentration patterns of n-alkanes distribution in the sedi- ments from the Chukchi Sea, the Bering Sea in the Arctic. Factor statistical analysis method is used for studying the source o...This paper reports different concentration patterns of n-alkanes distribution in the sedi- ments from the Chukchi Sea, the Bering Sea in the Arctic. Factor statistical analysis method is used for studying the source of n-alkanes and paleoenvironment. The result shows that n-alkanes is in the range of nC15-nC33 and n-alkane distribution patterns are characterized by two modes. The first mode belongs to the higher molecular with MH being nC25-nC27, CPI > 1 and with remarkable odd-even dominance. They are of terrigenous plant origin. The second one belongs to lower carbon range with MH being nC17 -nC20, CPI > 1 and with indistinct odd-even dominance. Therefore they are contributed by marine bio- logicla inputs. The contribution of land origin is larger than that of marine source. Pr/Ph is lower than 1 in the investigated area, which indicates the depositional environment of reducing reaction with lower oxygen. The result of factor analysis has good agreement with composition characteristics of n-alkanes in the sediment.展开更多
n-Alkanes are widely used in paleoenvironmental reconstructions.However,our understanding of changes in the distribution of n-alkanes with climatic and environmental factors remains unclear in arid/semi-arid regions.W...n-Alkanes are widely used in paleoenvironmental reconstructions.However,our understanding of changes in the distribution of n-alkanes with climatic and environmental factors remains unclear in arid/semi-arid regions.We sampled 26 surface sediments from three climatic zones across the southwestern Tibetan Plateau to evaluate the sensitivity of chain length distributions of n-alkanes to climatic and environmental parameters.Our observations demonstrate that average chain length(ACL),proportion of aquatic macrophyte(Paq),carbon preference index(CPI)and ratio of the contents of nC_(27)and nC_(31)(nC_(27)/nC_(31))are all sensitive to hydroclimatic conditions.In contrast to commonly-adopted assumptions,the correlations between these indices and hydrological parameters are not always good,which indicates that the interpretation of n-alkane indices is special on the southwestern Tibetan Plateau.These might be related to the vegetation characteristics and seasonality of biological activity,and need to be considered in paleoclimatic reconstruction.The impact of seasonal precipitation on n-alkanes indices was also evaluated.展开更多
Basing on the DFT calculations we propose the new theoretical model which describes both the surface tension σ of the short chain n-alkanes at their normal boiling points and their reaction rate constants with hydrox...Basing on the DFT calculations we propose the new theoretical model which describes both the surface tension σ of the short chain n-alkanes at their normal boiling points and their reaction rate constants with hydroxyl radicals OH<span style="white-space:nowrap;">•</span> (at 297 ± 2 K) on the basis of their molecular orbital electronic characteristics. It has been shown that intermolecular dispersion attraction within the surface liquid monolayer of these compounds, as well as their reaction rate constants k with OH<span style="white-space:nowrap;">•</span> radicals are determined by the energies <em>E<sub>orb</sub></em> of the specific occupied molecular orbitals which are the same in the determination of both the above physico-chemical characteristics of the studied n-alkanes. The received regression equations confirm the theoretically found dependences between the quantities of σ and k and the module |<em>E<sub>orb</sub></em>|. For the compounds under study this fact indicates the key role of their electronic structure particularities in determination of both the physical (surface tension) and the chemical (reaction rate constants) properties.展开更多
Stable carbon isotopic compositions of n-alkanes in surface sediments of the Bohai and North Yellow Seas were investigated to elucidate sources of sedimentary organic matter in these seas. The long-chain n-alkanes in ...Stable carbon isotopic compositions of n-alkanes in surface sediments of the Bohai and North Yellow Seas were investigated to elucidate sources of sedimentary organic matter in these seas. The long-chain n-alkanes in surface sediments are predominantly long-chain C27, C29, and C31 types, with obvious odd carbon predominance. The δ13 C values of long-chain n-C27, n-C29, and n-C31 alkanes are-30.8% ± 0.5‰,-31.9% ± 0.6‰, and-32.1% ± 1.0‰, respectively, within the range of n-alkanes of C3 terrestrial higher plants. This suggests that sedimentary n-alkanes are derived mainly from terrestrial higher plants. Compound-specific carbon isotopic analysis of long-chain n-alkanes indicates that C3 terrestrial higher plants predominate(64%–79%), with angiosperms being the main contributors. The n-alkane δ13 C values indicate that mid-chain n-alkanes in sediments are derived mainly from aquatic emergent macrophytes, with significant petroleum pollution and bacterial degradation sources for short-chain n-alkanes.展开更多
Long-chain n-alkanols and n-alkanes in core sediments from the northern South China Sea(SCS)were measured to make a comparison during terrestrial vegetation reconstruction from~42 ka to~7 ka.The results showed that te...Long-chain n-alkanols and n-alkanes in core sediments from the northern South China Sea(SCS)were measured to make a comparison during terrestrial vegetation reconstruction from~42 ka to~7 ka.The results showed that terrestrial vegetation record from long-chain n-alkanes matched well with previous studies in nearby cores,showing that more C_(4)plants developed during the Last Glacial Maximum(LGM)and C_(3)plants dominated in the interglacial period.However,these scenarios were not revealed by terrestrial vegetation reconstruction using long-chain n-alkanols,which showed C_(3)plant expansion during the LGM.The discrepancy during the interglacial period could be attributed to the aerobic degradation of functionalized long-chain n-alkanols in the oxygen-rich bottom water,resulting in poor preservation of terrestrial vegetation signals.On the other hand,the different advantages of functionalized n-alkanols and non-functional n-alkanes to record local and distal vegetation signals,respectively,may offer a potential explanation for the contradiction during the LGM when the SCS was characterized by low-oxygen deep water.Nevertheless,large variations on n-alkyl lipid compositions in C_(3)/C_(4)plants could play a part in modulating sedimentary long-chain n-alkanols and n-alkanes toward different vegetation signals,thereby suggesting that caution must be taken in respect to the terrestrial vegetation reconstruction using long-chain n-alkanes and long-chain n-alkanols.展开更多
The new theoretical models describe both the solubility S of the shot chain n-alkanes in water at 298.15 K, and their reaction rate constants k with nitronium cation NO<sub>2</sub><sup>+ </sup>...The new theoretical models describe both the solubility S of the shot chain n-alkanes in water at 298.15 K, and their reaction rate constants k with nitronium cation NO<sub>2</sub><sup>+ </sup>at 293.15 K on the basis of their molecular orbital characteristics. It is shown that both the quantities S and k are determined by the energies E<sub>orb</sub> of the specific virtual (for S) and occupied (for k) molecular orbitals of these n-alkanes. The obtained regression equations confirm the theoretically found dependences of S and k on the absolute value of E<sub>orb</sub>. This fact demonstrates that the electronic structure particularities of the studied n-alkanes play a crucial role in both their above-mentioned physicochemical properties.展开更多
This study investigates the decomposition of a gas mixture of four n-alkanes(n-heptane,n-octane,n-nonane,and n-decane)using a dielectric barrier discharge reactor.We show that the conversion of n-alkanes increased fro...This study investigates the decomposition of a gas mixture of four n-alkanes(n-heptane,n-octane,n-nonane,and n-decane)using a dielectric barrier discharge reactor.We show that the conversion of n-alkanes increased from 7.2%(C7H(16)),9.7%(C8H(18)),8.4%(C9H(20)),and 10.5%(C(10)H(22))to 23.8%(C7H(16)),25.0%(C8H(18)),27.9%(C9H(20)),and 32.1%(C(10)H(22))when the energy density increased from 84 J l^-1 to 324 J l^-1.The conversion of n-alkanes when using the gas mixture is close to that found when using a single n-alkane.The influences of reaction temperature and O2 concentration are also investigated,and the activation energies for the decomposition of each alkane are given.展开更多
Both monsoons and westerlies have exerted influence on climate dynamics over the Tibetan Plateau(TP) since the last deglaciation, producing complex patterns of paleohydroclimatic conditions. Diverse proxy records are ...Both monsoons and westerlies have exerted influence on climate dynamics over the Tibetan Plateau(TP) since the last deglaciation, producing complex patterns of paleohydroclimatic conditions. Diverse proxy records are essential to forge a robust understanding of the climate system on the TP. Currently, there is a general lack of understanding of the response of inland lakes over the TP to climate change, especially glacier-fed lakes. Paleohydrological reconstructions of such lakes could deepen our understanding of the history of lake systems and their relationship to regional climate variability. Here we use records of n-alkanes and grain size from the sediments of Bangong Co in the western TP to reconstruct paleohydrological changes over the past 16,000 years. The Paq record(the ratio of non-emergent aquatic macrophytes versus emergent aquatic macrophytes and terrestrial plants) is generally consistent with the variations in summer temperature and precipitation isotopes. The changes in grain-size distributions show a similar trend to Paq but with less pronounced fluctuations in the early-middle Holocene. The new data combined with previous results from the site demonstrate that: 1) Bangong Co experienced relatively large water-level fluctuations during the last deglaciation, with a steadily high lake-level during the early-middle Holocene and a decreasing lake-level in the late Holocene;2) The lake level fluctuations were driven by both high summer temperatures via the melting water and monsoon precipitation. However, the dominant factor controlling lake level changed over time. The lake-level history at Bangong Co deduced from the n-alkanes and grain-size records reveals the past hydrological changes in the catchment area, and stimulates more discussion about the future of glacier-fed lakes under the conditions of unprecedented warming in the region.展开更多
Shale oil formations contain both inorganic and organic media.The organic matter holds both free oil in the pores and dissolved oil within the kerogen molecules.The free oil flow in organic pores and the dissolved oil...Shale oil formations contain both inorganic and organic media.The organic matter holds both free oil in the pores and dissolved oil within the kerogen molecules.The free oil flow in organic pores and the dissolved oil diffusion in kerogen molecules are coupled together.The molecular flow of free n-alkanes is an important process of shale oil accumulation and production.To study the dynamics of imbibition process of n-alkane molecules into kerogen slits,molecular dynamics(MD)simulations are conducted.Effects of slit width,temperature,and n-alkane types on the penetration speed,dynamic contact angle,and molecular conformations were analyzed.Results showed that molecular transportation of n-alkanes is dominated by molecular structure and molecular motion at this scale.The space-confinement conformational changes of molecules slow down the filling speeds in the narrow slits.The n-alkane molecules with long carbon chains require more time to undergo conformational changes.The high content of short-chain alkanes and high temperature facilitate the flow of alkane mixtures in kerogen slits.Results obtained from this study are useful for understanding the underlying nanoscale flow mechanism in shale formations.展开更多
Excess molar enthalpies,H^E,for the binary mixtures of 2-pentanol with n-alkanes(n-heptane,n-octane,and nnonane)have been determined at three different temperatures T=(293.15,298.15 and 303.15)K and normal atmospheric...Excess molar enthalpies,H^E,for the binary mixtures of 2-pentanol with n-alkanes(n-heptane,n-octane,and nnonane)have been determined at three different temperatures T=(293.15,298.15 and 303.15)K and normal atmospheric pressure over the entire composition range using a Calvet microcalorimeter.All mixtures show endothermic mixing with the maximum values of the excess enthalpies occurring in the n-alkane-rich region.The H^Edata are smoothed using Redlich–Kister equation.The applicability of the Treszczanowicz–Benson,ERAS,Renon–Prausnitz and Chen–Bagley models to correlate H^Eof studied mixtures is tested,and the agreement between experimental and theoretical results is satisfactory.Each model includes a self-association equilibrium constant that represents hydrogen bonding and an adjustable parameter that reflects physical interactions.展开更多
Long-chain n-alkanes are one of the most common organic compounds in terrestrial plants and they are well-preserved in various geological archives.n-alkanes are relatively resistant to degradation and thus they can pr...Long-chain n-alkanes are one of the most common organic compounds in terrestrial plants and they are well-preserved in various geological archives.n-alkanes are relatively resistant to degradation and thus they can provide high-fidelity records of past vegetation and climate changes.Nevertheless,previous studies have shown that the interpretation of n-alkane proxies,such as the average chain length(ACL),is often ambiguous since this proxy depends on more than one variable.Both vegetation and climate could exert controls on the n-alkane ACL,and hence its interpretation requires careful consideration,especially in regions like the Qinghai-Tibet Plateau(QTP)where topography,biome type and moisture source are highly variable.To further evaluate the influences of vegetation and climate on the ACL in high-elevation lakes,we examined the n-alkane distributions of the surface sediments of 55 lakes across the QTP.Our results show that the ACL across a climatic gradient is significantly affected by precipitation,rather than by temperature.The positive correlation between ACL and precipitation may be because of the effect of microbial degradation during deposition.Finally,we suggest that more caution is needed in the interpretation of ACL data in different regions.展开更多
We report on the concentration and compositional features of n-alkanes of natural and anthropogenic origins in the snow samples collected from the Qiyi glacier in the Qilian Mountains, the Yuzhufeng glacier in eastern...We report on the concentration and compositional features of n-alkanes of natural and anthropogenic origins in the snow samples collected from the Qiyi glacier in the Qilian Mountains, the Yuzhufeng glacier in eastern Kunlun Mountains, the Xiaodongkemadi glacier in the Tanggula Mountains, and the Gurenhekou glacier in the Nyainqêntanglha Range. The results indicate a decrease in the total n-alkane concentration (T-HCs) from the northeast to the south over the Tibetan Plateau. The T-HCs in these studied areas were close to those in the Belukha and Sofiyskiy glacier, Russian Alati Mountains and the Dasuopu glacier in the Himalaya but were much higher than those in the Greenland ice sheet, suggesting that the mountain glaciers in the Asian continent may receive a higher loading of n-alkanes than the Greenland ice core. Moreover, the compositional characteristics of n-alkanes indicated that the n-alkanes in the studied areas were probably originated from the plant waxes as well as the fossil-fuel combustion exhaust, whereas the contribution from the lower organisms was small. In addition, the plant wax (Cn(wax)) and anthropogenic (non-Cn(wax)) contributions revealed that fast industrialization may have significant effects on the organic pollutant composition in glacier over the Tibetan Plateau and its circumference environment. Particularly, except for the Yuzhufeng glacier, the ΣnC21-/ΣnC22+ and (nC15+nC17+nC19)/(nC27+nC29+nC31) ratio decreased from the Qiyi glacier to the Gurenhekou glacier over the Tibetan Plateau, while the carbon preference index (CPI) values increased. These results indicate a decrease in terrigenous input while an increase in marine input from the northeast to the south over the Tibetan Plateau. These two ratios can be used as the climatic and environmental change indicators.展开更多
In the late 1980s the introduction of a new isotopic analytical technique of GC-C-MS that can determine the carbon isotopic composition at the molecular level has led to the appearence of the stable carbon isotopic ge...In the late 1980s the introduction of a new isotopic analytical technique of GC-C-MS that can determine the carbon isotopic composition at the molecular level has led to the appearence of the stable carbon isotopic geochemistry of biomarker compounds as a new field of scientific research. The relationship between the carbon isotopic compositions of biomarker compounds and biological precursors and diagenetic evolution is one of the key problems in this research field. Some studies on this problem have been carried out abroad in terms of organisms and modern sediments as well as the experiments of thermal simulation. Studied results show that the carbon isotopic compositions of biomarker compounds in the sediments are closely related to those in biological precursors and diagenetic evolution. For example, Reiley et al. have examined the carbon展开更多
Isotopic compositions of carbon-bound hydrogen in individual n-alkanes from sev-eral typical crude oil samples from Lunnan Oilfield, Tarim Basin, NW China, were firstly measured using newly developed gas chromatograph...Isotopic compositions of carbon-bound hydrogen in individual n-alkanes from sev-eral typical crude oil samples from Lunnan Oilfield, Tarim Basin, NW China, were firstly measured using newly developed gas chromatography-thermal conversion-isotope ratio mass spectrometry. The similar range of δ D of individual n-alkanes of crude oils among reservoirs of different geo-logical times reflects that hydrocarbons are all derived from the same marine depositional envi-ronment. Compared to the theoretic value (?150‰) and the reported δ D values (nC13―nC27, ?160‰―?90‰) of individual n-alkanes for Ordovician-sourced crude oils in the Canadian Wil-liston Basin, the hydrogen isotopic composition of individual n-alkanes in crude oils from Lunnan Oilfield is characterized by heavy hydrogen isotopic values (nC12―nC27, ?120‰―?60‰). In terms of the factors that control the fractionation of hydrogen isotopes, relatively saline deposi-tional environment and higher thermal maturation were attributed to the heavy δ D values of in-dividual n-alkanes in crude oils from Lunnan Oilfield.展开更多
n-Alkanes and polycyclic aromatic hydrocarbons(PAHs) bound to atmospheric particulate matter(PM_1) were investigated in a traffic site located in an urban area of Venice Province(Eastern Po Valley, Italy) during the c...n-Alkanes and polycyclic aromatic hydrocarbons(PAHs) bound to atmospheric particulate matter(PM_1) were investigated in a traffic site located in an urban area of Venice Province(Eastern Po Valley, Italy) during the cold season. Considering the critical situation affecting the Veneto Region concerning the atmospheric pollution and the general lack of information on PM_1 composition and emission in this area, this experimental study aims at determining the source profile, their relative contributions and the dispersion of finer particles. Four sources were identified and quantified using the Positive Matrix Factorization receptor model:(1) mixed combustions related to the residential activities,(2)agricultural biomass burning in addition to the resuspension of anthropogenic and natural debris carried by the wind,(3)gasoline and (4)diesel traffic-related combustions. The role of local atmospheric circulation was also investigated to identify the pollutant sources.展开更多
Simulation experiment was carried out on all kinds of modern organisms significant to oil-gas generation and the C-isotopic values of n-alkanes in different organisms. The distribution characteristics of individual n-...Simulation experiment was carried out on all kinds of modern organisms significant to oil-gas generation and the C-isotopic values of n-alkanes in different organisms. The distribution characteristics of individual n-alkane isotopes are studied. The experimental results supply important clues in biological provenance of n-alkanes in sedimentary organisms.展开更多
n-Alkanes have been widely used as phase change materials(PCMs) for thermal energy storage applications because of their exceptional phase transition performance, high chemical stability, long term cyclic stability an...n-Alkanes have been widely used as phase change materials(PCMs) for thermal energy storage applications because of their exceptional phase transition performance, high chemical stability, long term cyclic stability and non-toxicity. However, the thermodynamic properties, especially heat capacity, of n-alkanes have rarely been comprehensively investigated in a wide temperature range, which would be insufficient for design and utilization of n-alkanes-based thermal energy storage techniques. In this study, the thermal properties of n-alkanes(C;H;-C;H;), such as thermal stability, thermal conductivity, phase transition temperature and enthalpy were systematically studied by different thermal analysis and calorimetry methods, and compared with previous results. Thermodynamic property of these n-alkanes was studied in a wide temperature range from 1.9 K to 370 K using a combined relaxation(Physical Property Measurement System, PPMS), differential scanning and adiabatic calorimetry method, and the corresponding thermodynamic functions, such as entropy and enthalpy, were calculated based on the heat capacity curve fitting. Most importantly, the heat capacities and related thermodynamic functions of n-heneicosane and n-docosane were reported for the first time in this work, as far as we know. This research work would provide accurate and reliable thermodynamic properties for further study of n-alkanes-based PCMs for thermal energy storage applications.展开更多
The high-waxy condensate in the Qianmiqiao Ordovician burial-hill zone, Bohai Gulf Basin, North China has been investigated by way of high temperature gas chromatography. As high-mature oil, its high molecular weight ...The high-waxy condensate in the Qianmiqiao Ordovician burial-hill zone, Bohai Gulf Basin, North China has been investigated by way of high temperature gas chromatography. As high-mature oil, its high molecular weight wax fraction is mainly composed of C35—C69 n-alkanes with CPI37—55 values of 0.94—1.10. On conditions that core-drilling of source rocks was limited and the exact location of source kitchen is still uncertain in the region, it is inferred that the ori-entation of main source kitchen for the condensate should be on the east of the burial-hill zone, i.e. from the direction of Qikou Sag, according to oil-oil correlation between the condensate and surrounding high-waxy oils as well as lateral distribution of the wax content of crude oils. In addi-tion, it is also further confirmed that the oil filling direction for this condensate reservoir is from NE to SW, i.e. from wells BS-4, through BS-7, to BS-8 based on the analyses of 9 maturity and 3 pyrrolic N-compound parameters.展开更多
Here we combine n-alkanes preserved in a shell bar section from Qarhan paleolake, Qaidam Basin with the other sedimentary proxies to elucidate the lake evolution process during the period 39.7 to 17.5 14C ka BP (calib...Here we combine n-alkanes preserved in a shell bar section from Qarhan paleolake, Qaidam Basin with the other sedimentary proxies to elucidate the lake evolution process during the period 39.7 to 17.5 14C ka BP (calibrated age ranges from 43.5 to 22.4 cal. ka BP). In different stages, the n-alkane homologues exhibited different distribution modes indicative of variations in the surrounding vegetation and the hydrologic condition of the lake. The n-alkanes proxies (CPIh, ACLh, Paq) have the same trends as the summer solar insolation variation, implying that the summer insolation is the most important climatic factor driving the environmental changes and also indirectly controls lake evolution on the Tibetan Plateau. CPIh and ACLh as well as the total pollen concentration appear to show a trend comparable with methane concentration record from the GRIP ice core that reflected the Dansgaard-Oeschger events. This demonstrates that the paleoclimate variations in Qarhan area generally agree with global climate change and show rapid oscillations in late MIS3. These findings provide the latest molecular fossil evidence from paleolake sediments to confirm that lake evolution on Tibetan Plateau in late MIS3 was closely associated with enhanced summer insolation.展开更多
基金This study was supported by The NKBRSF Project under contract No. G2000078500 and the First Chinese NationalScientific Expedit
文摘This paper reports different concentration patterns of n-alkanes distribution in the sedi- ments from the Chukchi Sea, the Bering Sea in the Arctic. Factor statistical analysis method is used for studying the source of n-alkanes and paleoenvironment. The result shows that n-alkanes is in the range of nC15-nC33 and n-alkane distribution patterns are characterized by two modes. The first mode belongs to the higher molecular with MH being nC25-nC27, CPI > 1 and with remarkable odd-even dominance. They are of terrigenous plant origin. The second one belongs to lower carbon range with MH being nC17 -nC20, CPI > 1 and with indistinct odd-even dominance. Therefore they are contributed by marine bio- logicla inputs. The contribution of land origin is larger than that of marine source. Pr/Ph is lower than 1 in the investigated area, which indicates the depositional environment of reducing reaction with lower oxygen. The result of factor analysis has good agreement with composition characteristics of n-alkanes in the sediment.
基金co-supported by the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(GML2019ZD0201)the Basic Scientific Research Fund of Institute of Geology,Chinese Academy of Geological Sciences(J2018),Geological Survey Project of China(DD20190370)+1 种基金National Natural Science Foundation of China(Grant 41877301)China Postdoctoral Science Foundation(2017M620852)。
文摘n-Alkanes are widely used in paleoenvironmental reconstructions.However,our understanding of changes in the distribution of n-alkanes with climatic and environmental factors remains unclear in arid/semi-arid regions.We sampled 26 surface sediments from three climatic zones across the southwestern Tibetan Plateau to evaluate the sensitivity of chain length distributions of n-alkanes to climatic and environmental parameters.Our observations demonstrate that average chain length(ACL),proportion of aquatic macrophyte(Paq),carbon preference index(CPI)and ratio of the contents of nC_(27)and nC_(31)(nC_(27)/nC_(31))are all sensitive to hydroclimatic conditions.In contrast to commonly-adopted assumptions,the correlations between these indices and hydrological parameters are not always good,which indicates that the interpretation of n-alkane indices is special on the southwestern Tibetan Plateau.These might be related to the vegetation characteristics and seasonality of biological activity,and need to be considered in paleoclimatic reconstruction.The impact of seasonal precipitation on n-alkanes indices was also evaluated.
文摘Basing on the DFT calculations we propose the new theoretical model which describes both the surface tension σ of the short chain n-alkanes at their normal boiling points and their reaction rate constants with hydroxyl radicals OH<span style="white-space:nowrap;">•</span> (at 297 ± 2 K) on the basis of their molecular orbital electronic characteristics. It has been shown that intermolecular dispersion attraction within the surface liquid monolayer of these compounds, as well as their reaction rate constants k with OH<span style="white-space:nowrap;">•</span> radicals are determined by the energies <em>E<sub>orb</sub></em> of the specific occupied molecular orbitals which are the same in the determination of both the above physico-chemical characteristics of the studied n-alkanes. The received regression equations confirm the theoretically found dependences between the quantities of σ and k and the module |<em>E<sub>orb</sub></em>|. For the compounds under study this fact indicates the key role of their electronic structure particularities in determination of both the physical (surface tension) and the chemical (reaction rate constants) properties.
基金financially supported by the Ministry of Science and Technology of People’s Republic of China (No. 2016YFA0600904)the National Natural Science Foundation of China (No. 41476058)。
文摘Stable carbon isotopic compositions of n-alkanes in surface sediments of the Bohai and North Yellow Seas were investigated to elucidate sources of sedimentary organic matter in these seas. The long-chain n-alkanes in surface sediments are predominantly long-chain C27, C29, and C31 types, with obvious odd carbon predominance. The δ13 C values of long-chain n-C27, n-C29, and n-C31 alkanes are-30.8% ± 0.5‰,-31.9% ± 0.6‰, and-32.1% ± 1.0‰, respectively, within the range of n-alkanes of C3 terrestrial higher plants. This suggests that sedimentary n-alkanes are derived mainly from terrestrial higher plants. Compound-specific carbon isotopic analysis of long-chain n-alkanes indicates that C3 terrestrial higher plants predominate(64%–79%), with angiosperms being the main contributors. The n-alkane δ13 C values indicate that mid-chain n-alkanes in sediments are derived mainly from aquatic emergent macrophytes, with significant petroleum pollution and bacterial degradation sources for short-chain n-alkanes.
基金The Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)under contract No.GML2019ZD0104the Science and Technology Program of Guangzhou,China under contract No.201804010264+3 种基金the Guangdong MEPP Fund under contract No.GDOE[2019]A41the National Natural Science Foundation of China under contract No.41706059the Fund of Institution of South China Sea Ecology and Environmental Engineering,Chinese Academy of Sciences under contract No.ISEE2020YB05the State Key R&D Project under contract No.2016YFA0601104。
文摘Long-chain n-alkanols and n-alkanes in core sediments from the northern South China Sea(SCS)were measured to make a comparison during terrestrial vegetation reconstruction from~42 ka to~7 ka.The results showed that terrestrial vegetation record from long-chain n-alkanes matched well with previous studies in nearby cores,showing that more C_(4)plants developed during the Last Glacial Maximum(LGM)and C_(3)plants dominated in the interglacial period.However,these scenarios were not revealed by terrestrial vegetation reconstruction using long-chain n-alkanols,which showed C_(3)plant expansion during the LGM.The discrepancy during the interglacial period could be attributed to the aerobic degradation of functionalized long-chain n-alkanols in the oxygen-rich bottom water,resulting in poor preservation of terrestrial vegetation signals.On the other hand,the different advantages of functionalized n-alkanols and non-functional n-alkanes to record local and distal vegetation signals,respectively,may offer a potential explanation for the contradiction during the LGM when the SCS was characterized by low-oxygen deep water.Nevertheless,large variations on n-alkyl lipid compositions in C_(3)/C_(4)plants could play a part in modulating sedimentary long-chain n-alkanols and n-alkanes toward different vegetation signals,thereby suggesting that caution must be taken in respect to the terrestrial vegetation reconstruction using long-chain n-alkanes and long-chain n-alkanols.
文摘The new theoretical models describe both the solubility S of the shot chain n-alkanes in water at 298.15 K, and their reaction rate constants k with nitronium cation NO<sub>2</sub><sup>+ </sup>at 293.15 K on the basis of their molecular orbital characteristics. It is shown that both the quantities S and k are determined by the energies E<sub>orb</sub> of the specific virtual (for S) and occupied (for k) molecular orbitals of these n-alkanes. The obtained regression equations confirm the theoretically found dependences of S and k on the absolute value of E<sub>orb</sub>. This fact demonstrates that the electronic structure particularities of the studied n-alkanes play a crucial role in both their above-mentioned physicochemical properties.
基金supported by the Zhejiang Basic Public Welfare Research Program(No.LGG19E080001)Natural Science Foundation of Zhejiang Province(No.LY19B070002)。
文摘This study investigates the decomposition of a gas mixture of four n-alkanes(n-heptane,n-octane,n-nonane,and n-decane)using a dielectric barrier discharge reactor.We show that the conversion of n-alkanes increased from 7.2%(C7H(16)),9.7%(C8H(18)),8.4%(C9H(20)),and 10.5%(C(10)H(22))to 23.8%(C7H(16)),25.0%(C8H(18)),27.9%(C9H(20)),and 32.1%(C(10)H(22))when the energy density increased from 84 J l^-1 to 324 J l^-1.The conversion of n-alkanes when using the gas mixture is close to that found when using a single n-alkane.The influences of reaction temperature and O2 concentration are also investigated,and the activation energies for the decomposition of each alkane are given.
基金financially supported by the Natural Science Foundation of China (41601205,41772178,41072120)
文摘Both monsoons and westerlies have exerted influence on climate dynamics over the Tibetan Plateau(TP) since the last deglaciation, producing complex patterns of paleohydroclimatic conditions. Diverse proxy records are essential to forge a robust understanding of the climate system on the TP. Currently, there is a general lack of understanding of the response of inland lakes over the TP to climate change, especially glacier-fed lakes. Paleohydrological reconstructions of such lakes could deepen our understanding of the history of lake systems and their relationship to regional climate variability. Here we use records of n-alkanes and grain size from the sediments of Bangong Co in the western TP to reconstruct paleohydrological changes over the past 16,000 years. The Paq record(the ratio of non-emergent aquatic macrophytes versus emergent aquatic macrophytes and terrestrial plants) is generally consistent with the variations in summer temperature and precipitation isotopes. The changes in grain-size distributions show a similar trend to Paq but with less pronounced fluctuations in the early-middle Holocene. The new data combined with previous results from the site demonstrate that: 1) Bangong Co experienced relatively large water-level fluctuations during the last deglaciation, with a steadily high lake-level during the early-middle Holocene and a decreasing lake-level in the late Holocene;2) The lake level fluctuations were driven by both high summer temperatures via the melting water and monsoon precipitation. However, the dominant factor controlling lake level changed over time. The lake-level history at Bangong Co deduced from the n-alkanes and grain-size records reveals the past hydrological changes in the catchment area, and stimulates more discussion about the future of glacier-fed lakes under the conditions of unprecedented warming in the region.
基金financially supported by the National Natural Science Foundation of China(Grant No.52004317,42090024)the Natural Science Foundation of Shandong Province of China(No.ZR2020ME091)+1 种基金the Fundamental Research Funds for the Central Universities(20CX06016A)the National Science and Technology Major Project(2017ZX05049-004)
文摘Shale oil formations contain both inorganic and organic media.The organic matter holds both free oil in the pores and dissolved oil within the kerogen molecules.The free oil flow in organic pores and the dissolved oil diffusion in kerogen molecules are coupled together.The molecular flow of free n-alkanes is an important process of shale oil accumulation and production.To study the dynamics of imbibition process of n-alkane molecules into kerogen slits,molecular dynamics(MD)simulations are conducted.Effects of slit width,temperature,and n-alkane types on the penetration speed,dynamic contact angle,and molecular conformations were analyzed.Results showed that molecular transportation of n-alkanes is dominated by molecular structure and molecular motion at this scale.The space-confinement conformational changes of molecules slow down the filling speeds in the narrow slits.The n-alkane molecules with long carbon chains require more time to undergo conformational changes.The high content of short-chain alkanes and high temperature facilitate the flow of alkane mixtures in kerogen slits.Results obtained from this study are useful for understanding the underlying nanoscale flow mechanism in shale formations.
文摘Excess molar enthalpies,H^E,for the binary mixtures of 2-pentanol with n-alkanes(n-heptane,n-octane,and nnonane)have been determined at three different temperatures T=(293.15,298.15 and 303.15)K and normal atmospheric pressure over the entire composition range using a Calvet microcalorimeter.All mixtures show endothermic mixing with the maximum values of the excess enthalpies occurring in the n-alkane-rich region.The H^Edata are smoothed using Redlich–Kister equation.The applicability of the Treszczanowicz–Benson,ERAS,Renon–Prausnitz and Chen–Bagley models to correlate H^Eof studied mixtures is tested,and the agreement between experimental and theoretical results is satisfactory.Each model includes a self-association equilibrium constant that represents hydrogen bonding and an adjustable parameter that reflects physical interactions.
基金financially supported by the National Natural Science Foundation of China(Grant No.42171159)the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(No.2019QZKK0601).
文摘Long-chain n-alkanes are one of the most common organic compounds in terrestrial plants and they are well-preserved in various geological archives.n-alkanes are relatively resistant to degradation and thus they can provide high-fidelity records of past vegetation and climate changes.Nevertheless,previous studies have shown that the interpretation of n-alkane proxies,such as the average chain length(ACL),is often ambiguous since this proxy depends on more than one variable.Both vegetation and climate could exert controls on the n-alkane ACL,and hence its interpretation requires careful consideration,especially in regions like the Qinghai-Tibet Plateau(QTP)where topography,biome type and moisture source are highly variable.To further evaluate the influences of vegetation and climate on the ACL in high-elevation lakes,we examined the n-alkane distributions of the surface sediments of 55 lakes across the QTP.Our results show that the ACL across a climatic gradient is significantly affected by precipitation,rather than by temperature.The positive correlation between ACL and precipitation may be because of the effect of microbial degradation during deposition.Finally,we suggest that more caution is needed in the interpretation of ACL data in different regions.
基金Supported by National Natural Science Foundation of China for Distinguished Young Scholars (Grant No. 40525001)National Basic Research Program of China (Grant No. 2005CB422003)+1 种基金CAS International Partnership Project (Grant No. CXTD-Z2005-2)National Natural Science Foundation of China (Grant Nos. 40801023, 40871038, 40771046 )
文摘We report on the concentration and compositional features of n-alkanes of natural and anthropogenic origins in the snow samples collected from the Qiyi glacier in the Qilian Mountains, the Yuzhufeng glacier in eastern Kunlun Mountains, the Xiaodongkemadi glacier in the Tanggula Mountains, and the Gurenhekou glacier in the Nyainqêntanglha Range. The results indicate a decrease in the total n-alkane concentration (T-HCs) from the northeast to the south over the Tibetan Plateau. The T-HCs in these studied areas were close to those in the Belukha and Sofiyskiy glacier, Russian Alati Mountains and the Dasuopu glacier in the Himalaya but were much higher than those in the Greenland ice sheet, suggesting that the mountain glaciers in the Asian continent may receive a higher loading of n-alkanes than the Greenland ice core. Moreover, the compositional characteristics of n-alkanes indicated that the n-alkanes in the studied areas were probably originated from the plant waxes as well as the fossil-fuel combustion exhaust, whereas the contribution from the lower organisms was small. In addition, the plant wax (Cn(wax)) and anthropogenic (non-Cn(wax)) contributions revealed that fast industrialization may have significant effects on the organic pollutant composition in glacier over the Tibetan Plateau and its circumference environment. Particularly, except for the Yuzhufeng glacier, the ΣnC21-/ΣnC22+ and (nC15+nC17+nC19)/(nC27+nC29+nC31) ratio decreased from the Qiyi glacier to the Gurenhekou glacier over the Tibetan Plateau, while the carbon preference index (CPI) values increased. These results indicate a decrease in terrigenous input while an increase in marine input from the northeast to the south over the Tibetan Plateau. These two ratios can be used as the climatic and environmental change indicators.
基金Project supported by the National Natural Science Foundation of China.
文摘In the late 1980s the introduction of a new isotopic analytical technique of GC-C-MS that can determine the carbon isotopic composition at the molecular level has led to the appearence of the stable carbon isotopic geochemistry of biomarker compounds as a new field of scientific research. The relationship between the carbon isotopic compositions of biomarker compounds and biological precursors and diagenetic evolution is one of the key problems in this research field. Some studies on this problem have been carried out abroad in terms of organisms and modern sediments as well as the experiments of thermal simulation. Studied results show that the carbon isotopic compositions of biomarker compounds in the sediments are closely related to those in biological precursors and diagenetic evolution. For example, Reiley et al. have examined the carbon
基金the Knowidedge Innovation Pioject of the Chinese Academy of sciences(Grant No.KZCX1-SW-18) the National Natural Science Foundation of China(Grant No.40402013).
文摘Isotopic compositions of carbon-bound hydrogen in individual n-alkanes from sev-eral typical crude oil samples from Lunnan Oilfield, Tarim Basin, NW China, were firstly measured using newly developed gas chromatography-thermal conversion-isotope ratio mass spectrometry. The similar range of δ D of individual n-alkanes of crude oils among reservoirs of different geo-logical times reflects that hydrocarbons are all derived from the same marine depositional envi-ronment. Compared to the theoretic value (?150‰) and the reported δ D values (nC13―nC27, ?160‰―?90‰) of individual n-alkanes for Ordovician-sourced crude oils in the Canadian Wil-liston Basin, the hydrogen isotopic composition of individual n-alkanes in crude oils from Lunnan Oilfield is characterized by heavy hydrogen isotopic values (nC12―nC27, ?120‰―?60‰). In terms of the factors that control the fractionation of hydrogen isotopes, relatively saline deposi-tional environment and higher thermal maturation were attributed to the heavy δ D values of in-dividual n-alkanes in crude oils from Lunnan Oilfield.
文摘n-Alkanes and polycyclic aromatic hydrocarbons(PAHs) bound to atmospheric particulate matter(PM_1) were investigated in a traffic site located in an urban area of Venice Province(Eastern Po Valley, Italy) during the cold season. Considering the critical situation affecting the Veneto Region concerning the atmospheric pollution and the general lack of information on PM_1 composition and emission in this area, this experimental study aims at determining the source profile, their relative contributions and the dispersion of finer particles. Four sources were identified and quantified using the Positive Matrix Factorization receptor model:(1) mixed combustions related to the residential activities,(2)agricultural biomass burning in addition to the resuspension of anthropogenic and natural debris carried by the wind,(3)gasoline and (4)diesel traffic-related combustions. The role of local atmospheric circulation was also investigated to identify the pollutant sources.
文摘Simulation experiment was carried out on all kinds of modern organisms significant to oil-gas generation and the C-isotopic values of n-alkanes in different organisms. The distribution characteristics of individual n-alkane isotopes are studied. The experimental results supply important clues in biological provenance of n-alkanes in sedimentary organisms.
基金the financial support from the National Nature Science Foundation of China (No. 22003065)Liaoning Provincial Natural Science Foundation of China (No. 2019-MS-318)+3 种基金Science and Technology Major Project of Liaoning Province (No. 2019JH1/10300002)the Scientific Instrument Developing Project of the Chinese Academy of Sciences (No. YJKYYQ20190046)Dalian Institute of Chemical Physics (No. DICP I202036)Dalian Outstanding Young Scientific Talent Program (No. 2019RJ10)。
文摘n-Alkanes have been widely used as phase change materials(PCMs) for thermal energy storage applications because of their exceptional phase transition performance, high chemical stability, long term cyclic stability and non-toxicity. However, the thermodynamic properties, especially heat capacity, of n-alkanes have rarely been comprehensively investigated in a wide temperature range, which would be insufficient for design and utilization of n-alkanes-based thermal energy storage techniques. In this study, the thermal properties of n-alkanes(C;H;-C;H;), such as thermal stability, thermal conductivity, phase transition temperature and enthalpy were systematically studied by different thermal analysis and calorimetry methods, and compared with previous results. Thermodynamic property of these n-alkanes was studied in a wide temperature range from 1.9 K to 370 K using a combined relaxation(Physical Property Measurement System, PPMS), differential scanning and adiabatic calorimetry method, and the corresponding thermodynamic functions, such as entropy and enthalpy, were calculated based on the heat capacity curve fitting. Most importantly, the heat capacities and related thermodynamic functions of n-heneicosane and n-docosane were reported for the first time in this work, as far as we know. This research work would provide accurate and reliable thermodynamic properties for further study of n-alkanes-based PCMs for thermal energy storage applications.
基金This study was supported by the National Natural Science Foundation of China (NSFC No. 40172056) the Research Found for the Doctoral Program of High Education (RFDP No. 2000042506).
文摘The high-waxy condensate in the Qianmiqiao Ordovician burial-hill zone, Bohai Gulf Basin, North China has been investigated by way of high temperature gas chromatography. As high-mature oil, its high molecular weight wax fraction is mainly composed of C35—C69 n-alkanes with CPI37—55 values of 0.94—1.10. On conditions that core-drilling of source rocks was limited and the exact location of source kitchen is still uncertain in the region, it is inferred that the ori-entation of main source kitchen for the condensate should be on the east of the burial-hill zone, i.e. from the direction of Qikou Sag, according to oil-oil correlation between the condensate and surrounding high-waxy oils as well as lateral distribution of the wax content of crude oils. In addi-tion, it is also further confirmed that the oil filling direction for this condensate reservoir is from NE to SW, i.e. from wells BS-4, through BS-7, to BS-8 based on the analyses of 9 maturity and 3 pyrrolic N-compound parameters.
基金supported by National Natural Science Foundation of China (Grant Nos. 40871096, 40371117)
文摘Here we combine n-alkanes preserved in a shell bar section from Qarhan paleolake, Qaidam Basin with the other sedimentary proxies to elucidate the lake evolution process during the period 39.7 to 17.5 14C ka BP (calibrated age ranges from 43.5 to 22.4 cal. ka BP). In different stages, the n-alkane homologues exhibited different distribution modes indicative of variations in the surrounding vegetation and the hydrologic condition of the lake. The n-alkanes proxies (CPIh, ACLh, Paq) have the same trends as the summer solar insolation variation, implying that the summer insolation is the most important climatic factor driving the environmental changes and also indirectly controls lake evolution on the Tibetan Plateau. CPIh and ACLh as well as the total pollen concentration appear to show a trend comparable with methane concentration record from the GRIP ice core that reflected the Dansgaard-Oeschger events. This demonstrates that the paleoclimate variations in Qarhan area generally agree with global climate change and show rapid oscillations in late MIS3. These findings provide the latest molecular fossil evidence from paleolake sediments to confirm that lake evolution on Tibetan Plateau in late MIS3 was closely associated with enhanced summer insolation.
