Structural Aspects of Crude Oil Derived Asphaltenes by NMR and XRD and Spectroscopic Techniques

Asphaltene samples obtained from crude processed at two Indian refineries were characterized for chemical composition and structure by nuclear magnetic resonance (NMR), X-ray diffractometry (XRD), fluorescence spectroscopic techniques, and chromatographic (column and GPC) techniques. Estimation of NMR average structural parameters were obtained by combined ¹H, NMR ¹³C, NMR DEPT-45, and QUAT pulse sequence spectral editing techniques. The macrostructure and crystalline parameters of these samples were obtained by XRD. The nature of the functional groups have been obtained by IR technique. A combined NMR and XRD parameters were used to estimate the size of average aromatic structural units. Asphaltenes from one of the crudes (ASP-A) was found to be highly pericondensed, highly substituted, and higher molecular size compared to ASP-B asphaltene molecules. The number of aromatic sheets per unit sheets are 3.7 and 2.5 in the sample ASP-A and ASP-B, respectively. Both the asphaltene molecules in the samples have periodically and systematic arrangement of aromatic sheets in the unit sheet. The number of aromatic rings per unit sheet in ASP-A and ASP-B are 6.0 and 5.0, respectively. The fluorescence spectral studies has also exhibited λ_max (the wavelength of maximum intensity) at 505 and 509 nm confirming to pericondensed higher polycondensed aromatic ring system in both the samples. The analysis of liquid chromatographic fractions of these samples show that each sample is composed of several polycondensed aromatic systems where unit sheet of ring sizes vary from 1.8 to 6.3 with varying molecular sizes. These structural parameters allowed a model structure of the asphaltenes to be constructed.     

Structural characterization of asphaltenes derived from nigerian bitumen using the x-ray diffraction technique

Petroleum asphaltenes consist of complex hydrocarbon molecules that pose a marked difficulty in the production of crude oils. They tend to flocculate and precipitate during oils refinery and this stimulates considerable interest in the elucidation of their molecular structure for improved processing. In this investigation, five bitumen samples obtained from oil sand outcrops at five localities in Nigeria were used. These were treated with n-pentane that necessitates the precipitation of asphaltene. The different asphaltene samples were analyzed by the x-ray diffraction technique to obtain their various structural parameters. The parameters were determined from the peaks of the gamma (γ) band, graphene (c = c) or (002) band and the (10) or (11) band in the diffraction spectra of the respective samples. Slight variations in the distance between the aliphatic chains and the distance between the aromatic sheets were observed for three of the samples, while the remaining two presented significant variations in the structural parameters. Variations in the average number of carbon atoms per aromatic units correspond to the variation in the size and number of aromatic units and aliphatic chains. The variations consequently determined the level of processing necessary to improve the heavy oil (bitumen).     

Investigation of the Molecular Structure of Turkish Asphaltenes

Abstract

Molecular structure of asphaltenes prepared from four Turkish crude oils with different origin were characterized by elemental analysis, proton nuclear magnetic resonance (¹H NMR), gel permeation chromatography (GPC) by X-ray diffraction (XRD) and by Fourier transform infrared spectroscopy (FTIR). The X-ray diffraction method was used to investigate the crystallite and aromaticity parameters of the asphaltenes. Average distance between the aromatic sheets, average distance between the aliphatic chains, average diameter of the cluster, and average number of aromatic sheets per stack parameters were calculated for the asphaltenes. The combined NMR, FTIR, molecular weight, elemental content, and XRD results have been used to calculate hypothetical structure of the Turkish asphaltenes.     

The study of the composition of oils and structure of their components during the preliminary refining of oil feedstock with metal powders

The results of elemental analysis, determination of molecular masses, IR and ¹H NMR studies of the resin—asphaltene components, and gas chromatographic—mass spectrometric analysis of lube oils from a blend of West Siberian crude oil and the liquid products of its treatment with powders of iron and copper modified with nickel and cobalt ions are presented. The structural—group analysis has been performed and the structural fragments of the average asphaltene and resin molecules have been described. The changes in the structural parameters of their molecules under the treatment conditions and in the composition of hydrocarbons and hetero compounds of lube oils have been revealed. It has been shown that the preliminary upgrading of the petroleum feedstock decreases the concentration of heteroatoms in the composition of the resin—asphaltene components and the concentration of heteroatoms and aromatic hydrocarbons the lube oils.     

The Structural Characterization of Saturate,Aromatic, Resin,and Asphaltene Fractions of Batiraman Crude Oil

Abstract

The structural characterization of fractions of Batiraman crude oil, which is the heavy crude oil from a field in the southeastern part of Turkey, was investigated. Batiraman crude oil and its saturate, aromatic, resin, and asphaltene (SARA) fractions were seperated. Treatment of crude oil with n-heptane provided the separation of asphaltene. Maltene was collected by evaporating the n-heptane from the filtrate. Then, maltene was separeted into saturates, aromatics, and resins by SARA technique. Maltene was separated into saturate, aromatic, and resin fractions using column chromatography. SARA fractions were quantified on a weight percent basis. Fractions of Batiraman crude oil were characterized by elemental analysis, proton nuclear magnetic resonance (¹H NMR) analysis, electrospray ionization mass spectrometry (ESI-MS), and Fourier transform infrared (FTIR) spectroscopy techniques.     

Change of asphaltene and resin properties after catalytic aquathermolysis

Resin and asphaltene were separated from Liaohe heavy oil. Catalytic aquathermolysis of asphaltene and resin was investigated by using water soluble catalysts （NiSO4 and FeSO4） and oil soluble catalysts （nickel naphthenate and iron naphthenate）. Before and after aquathermolysis, the properties of the resin and asphaltene was compared by means of ultimate analysis, vapor pressure osmometer （VPO） average molecular weight, X-ray diffraction （XRD）,^13C and ^1H nuclear magnetic resonance （NMR）. The conversion sequence was as follows： No-catalyst〈NiSO4〈FeSO4〈nickel naphthenate〈iron naphthenate. In the presence of catalysts, the amount of H2 and CO increased significantly, while H2S in the gas product decreased. The molecular weight of asphaltene and resin increased after reaction without catalyst. But the catalysts restrained this trend. The H/C ratio of asphaltene and resin decreased after reaction. From the results of average structural parameters and molecular weight, it was found that asphaltene and resin were partly aggregated after aquathermolysis.     

A study of structural transformations of asphaltene molecules during hydroconversion of vacuum residue at various temperatures in the presence of nanosized molybdenum disulfide particles

Elemental analysis, molecular mass, and ¹H NMR data are presented for vacuum residue asphaltenes and the products of vacuum residue hydroconversion in the presence of nanosized MoS₂ catalyst particles obtained “in situ” in the hydrocarbon medium. Structural group analysis of average asphaltene molecules has been performed and their structural units have been described. The main trends of change in the structural parameters of the molecules under the hydroconversion conditions and the effect of temperature on the character of these changes have been revealed.     

Spectroscopic Studies on Some Crude Oils from The North Western Desert,Egypt

Abstract

A direct method for crude oil evaluation based on spectral techniques is demonstrated in this article. This method is demonstrated for four crude oils from the El-Faras and Raml oil fields in the North Western Desert in Abu Gharadeg Basin, Egypt. The crude oils have been studied by ¹³C nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. Several parameters calculated from the ¹³C NMR and FTIR spectra provide useful information about the maturity of the organic matter in term of relative aliphatic, aromatic, and carbonyl/carboxyl concentrations; aliphatic chain length; and type and degree of substitution of aromatic structures. These spectra techniques may provide valuable information about the aromaticity and diverse functionalities that are important to the thermal history of the crude oil samples. Results showed that the composition of crude oil samples have higher aliphatic compounds than that of the aromatic compounds.     

Hydrotreating of Furrial Crude Oil Using NiMoS Supported on Alumina: Study of the Asphaltene and Their Fractions in Cyclohexane

Abstract

The Furrial crude oil originated in northern Monagas State. This shows problems such as the colloidal instability of the asphaltenes fraction present in them, causing its precipitation. This work is oriented to achieve an interpretation of the colloidal behavior of the asphaltenes through the study of the effect of the hydrotreating reactions (HDT) on the asphaltenes of the Furrial crude oil, using NiMoS/γ-Al₂O₃ as a catalyst. The results obtained after HDT reactions were analyzed to know the percentage of asphaltene and their fractions in cyclohexane, the measurement of flocculation thresholds and molecular weights by the VPO technique, and ¹³C NMR as well as the determination of the total sulfur content. Appreciable changes on the asphaltene of the Furrial crude oil and its fractions in cyclohexane after HDT, under conditions used, were observed. In general terms, the amount of asphaltene diminished and the percentage of distribution for insoluble fraction in cyclohexane (IFC) and for soluble fraction in cyclohexane (SFC) was affected causing an increase in the stability of the asphaltene. The asphaltene and IFC were observed to be a pronounced variation of the molecular weight average in number, in comparison with SFC. ¹³C NMR spectra indicate that the hydrotreated asphaltene shows structural change, and IFC presents a variation of the percentage of sulfur minor in comparison to SFC.     

固态13C-NMR法表征渣油沥青质的结构组成

以长庆常压渣油、胜利减压渣油和加拿大减压渣油为原料,研究了正庚烷沥青质的结构及组成,根据固态13C NMR分析结果,计算了沥青质分子的平均结构单元参数,并模拟出了沥青质的结构单元模型。结果表明,沥青质分子由4个左右的结构单元组成,每个结构单元包括5～7个缩合芳香环。沥青质中的饱和碳以环烷碳为主,并包含少量的短烷基侧链,沥青质的n(HS)/n(CS)在16左右。对于平均相对分子质量较大、具有较短烷基侧链和较少取代基的沥青质分子,由核磁共振氢谱计算其结构参数时,采用重油计算过程的假设--芳香环烷基侧链上α位及β位和β位以远的氢/碳比为2(x=y=2)是不合理的,可能会导致计算结果与沥青质的真实结构存在较大的误差。     

不同重油的正戊烷及正庚烷沥青质性质对比

以中东减压渣油（MEVR）、加拿大油砂沥青（VTB）、辽河稠油减压渣油（LHVR）、委内瑞拉常压渣油及减压渣油（VAR、VVR）等5种重油为原料，利用溶剂沉淀法制备正戊烷及正庚烷沥青质，采用元素组成、GPC、1H-NMR、13C-NMR、XRD、SEM等分析方法和手段进行沥青质性质评价以考察其差异性。结果表明，五种重油的C5沥青质、C7沥青质在含量、分子结构、平均结构单元数目、分子大小、微观结构形态等方面差异明显。沥青质芳碳率在0.47~0.54之间，VTB、LHVR沥青质中参与有序堆积结构的芳香碳较少，而MEVR，VAR，VVR沥青质中该部分芳香碳则相对较多。     

中低温煤焦油沥青质的分析表征

采用XPS、XRD、FT IR、13C NMR、元素分析等手段分析表征了中低温煤焦油正庚烷沥青质(CT C7沥青质),系统研究了CT C7沥青质表面元素的赋存状态、相对含量以及其晶体结构。结果表明,该沥青质的主要结构为多环稠合芳香烃并富含杂原子,其芳香度(fa)明显大于一般原油沥青质;烷基链间距和芳香片层直径值较小,其芳环上烷基侧链短而少且难以形成堆积结构;表面C主要以sp2和sp3碳的形式存在,二者摩尔分数之和达699%,以C=O和COO-基团存在的C较少。该沥青质表面的杂原子以O原子为主,N和S原子较少,其中含氧官能团主要是酚羟基和醚氧基,摩尔分数达619%。含氮官能团主要以吡啶氮(N 6)和吡咯氮(N 5)为主,二者摩尔分数之和为805%;含硫官能团中,噻吩硫、烷基硫比较多,摩尔分数之和达517%。该C7沥青质表面加氢难度较大的N 6、N 5和噻吩硫的摩尔分数低于石油沥青质,这可能是煤焦油加氢工艺中N、S脱除效率较高的原因之一。     

加氢反应温度对塔河沥青质结构组成的影响

以塔河常压渣油的正庚烷沥青质为原料,在高压釜内考察了加氢反应温度对沥青质结构组成的影响。结果表明,与原生沥青质相比,加氢后次生沥青质的H/C原子比、平均相对分子质量、单元薄片数目和芳香环系缩合度参数HAU/CA均减小,芳碳率fA增大;加氢后沥青质单元薄片的平均相对分子质量增大,Hα、Hβ和Hγ减小,HA增加,总环数RT和芳香环数RA也都明显增加,质子芳碳比例增加,取代芳碳比例减小,表明沥青质在加氢过程中发生了明显的烷基侧链和单元薄片的脱除反应及少量的脱氢缩合反应。随加氢反应温度升高,沥青质结构参数的变化更明显,且在653～673 K范围时各结构参数的变化幅度最大。     

悬浮床加氢裂化助剂对渣油中沥青质的作用

 通过红外光谱及紫外可见光谱分析了悬浮床加氢裂化助剂对辽河常压渣油沥青质的作用。结果表明,辽河常压渣油沥青质的单元芳香片主要含3～4个芳香环,共轭芳香环的排列形式主要为"线性排列",即渺位缩合。助剂可吸附在沥青质上,其头部磺酸基官能团与沥青质表面的羟基和氨基中的H形成分子间氢键可能是其中的一种作用方式;而尾部的疏水链则能形成稳定层,可将沥青质分子包裹起来,从而能使部分沥青质增溶在正庚烷中。     

Changes in Asphaltenes Properties Modified with Fe in Hydrotreating Reactions

Abstract

The properties of the Hamaca of asphaltenes extra-heavy crude oil (AsfH) of Petroliferous Orinoco Belt can be modified for evaluating the changes produced with hydrotreating (HDT). One characterized the solid modified by means of UV-visible spectroscopy and nuclear magnetic proton resonance (NMR ¹H). The samples were put under hydrotreating to 200°C to avoid thermal cracking, atmospheric pressure, and a flow of feeding of 10.5 mL/hr in a fixed-bed reactor in the presence of H₂S generated in situ. The reactivity was followed by gas chromatography (GC). All the samples were evaluated before and after being hydrotreated by ¹H NMR, total sulfur analysis, and determination of molecular weight average by vapor pressure osmometry (VPO). The obtained results suggest the iron possibly is inserted in the structure of the asphaltene forming a new active phase catalytically, presumably a mixed sulfide (pyrrotite type) of iron-metal of transition (V and Ni) present in the asphaltene.     

Determination of the functional groups and the melting point of iraqi asphaltenes

A qualitative analysis study of n-C5 asphaltene of Iraqi crude oil from (Al-Dura, Kirkuk and Basra) oil fields was done using Fourier transform infrared spectroscopy (FT-IR). The melting points of the three oil derived asphaltenes were determined using Hot stage polarizing microscope at 180?°C for Al-Dura, 125?°C for Kirkuk and 140?°C for Basra asphaltenes. The FTIR spectrum shows an aromatic behavior of the asphaltene samples at a wavelength of 3049?cm^?1 and aliphatic chains were found at wavelengths 2924?cm^?1.     

VARIATION IN THE CHEMICAL NATURE OF ASPHALTENES WITH THE PROCESS,THE COAL AND THE REACTION CONDITIONS

ABSTRACT

Average structure data for twelve asphaltenes are reported, based on ¹³C- and H- n.m.r. spectroscopy combined with elemental, molecular weight and functional group analyses. The asphaltenes were from supercritical gas extraction, flash pyrolysis and hydrogenation of a brown and a bituminous coal. The effect of the reaction temperature and, for hydrogenation, the catalyst and solvent on the nature of the asphaltene produced was studied. The asphaltene obtained from supercritical gas extraction of the brown coal at 350°C was the least aromatic (f_a = 0.44) with the highest H/C atomic ratio (1.16) and probably consists mainly of single ring aromatlcs with about half of the aromatic sites substituted. A significant proportion of the carbon in this asphaltene is in long alkyl chains and the hydroxyl content is high. Whereas, the asphaltenes produced by hydrogenatlon of the bituminous coal at 450°C were far more aromatic with more highly condensed but less substituted aromatic ring systems and few, if any, long alkyl chains, together with a lower hydroxyl content. The asphaltenes obtained from the brown coal are less aromatic with less condensed aromatic ring systems but a higher degree of aromatic substitution than those produced from the bituminous coal under the same conditions. The asphaltenes formed at 450°C had lower H/C atomic ratios, molecular weights and degree of aromatic substitution, but higher aromaticities Ohan those produced at 35O°C or 400°C under like processing conditions. The asphaltene produced in the presence of both stannous chloride catalyst and tetralin was less aromatic than when either of these species was absent.     

Study and Evaluation of Aging Performance of Petroleum Asphalts and Their Constituents During Oxygen Absorption. III. Average Molecular Structure Parameter Changes

Abstract

The changes of the structural parameters of the average molecules of Chinese Shanjiasi and Shengli petroleum asphalts and their constituents during oxygen absorption were studied based on the oxygen absorption behaviors and the chemical group composition and structure changes. The results show that all the structural parameters of the average molecules of asphalts and their constituents increase clearly after oxygen absorption with the exceptions of the naphthene carbon rates and the paraffin carbon rates. The parameters include the total carbon numbers, the aromatic carbon numbers, the naphthene carbon numbers, the paraffin carbon numbers, the total ring numbers, the aromatic ring numbers, the naphthene ring numbers, the total hydrogen numbers, the aromaticities, and the concentration indexes. The most obvious are the structural parameter changes of the average molecules of the asphalt resin and asphaltene constituents. The structural parameter changes of the average molecules of Shengli asphalt and its constituents are remarkably greater than those of Shanjiasi asphalt and its constituents. The clearer changes of all the average molecular structure parameters of SHL asphalt resin and asphaltene, especially resin could possibly be one of the key factors leading to the much clearer deterioration of the colloidal stability and the serviceability than SJS asphalt in oxygen absorption.     

Characterization of Asphalt Fractions by NMR Spectroscopy

Abstract

Petroleum asphalt was separated into saturates, naphthalene aromatics, polar aromatics, and asphaltenes using the Corbett method. These asphalt fractions were characterized by H-1 and C-13 nuclear magnetic resonance spectroscopy (NMR). The spectra of saturates illustrate only traceable quantities of aromatic hydrogen and aromatic carbon. Naphthalene aromatics, polar aromatics, and asphaltenes all have broad bands in the aromatic regions of both H-1 and C-13 NMR spectra. These broad bands demonstrate the presence of polycondensed aromatic rings present in the structure of naphthalene aromatics, polar aromatics, and asphaltenes. Based on available literature, numerous NMR resonance bands are identified. The quantitative estimations for various kinds of protons and carbons in the asphalt fractions are compared.     

Structural Changes of Sub-fractions in Residue Hydrotreating Products by Ruthenium Catalyzed Oxidation

Abstract

Structure of aromatics, resins, and asphaltenes in petroleum residue was undertaken by using ruthenium ion catalyzed oxidation. The distribution of alkyl side chains and bridges connected to aromatic rings was quantified, and the condensed type of aromatic rings was deduced. The structural changes of fractions in residue during hydrotreating were discussed. The results showed that fractions have abundant alkyl side chains (C₁–C₂₇), mainly n-alkyl side chains, attached to aromatic carbons, and polymethylene bridges connected to at least two aromatic ring systems are also present. The molar concentrations of these alkyl groups are declined as the increase of chain length. Cata-condensed, peri-condensed, and biphenyl-type aromatic unit structures coexist in fractions, while the proportion of biphenyl type structure is relatively small. The aromatic structure of aromatics is mostly cata-condensed, while for resins the proportion of cata-condensed and peri-condensed type aromatic structures is comparable, and structure of asphaltene is mostly peri-condensed. The chemical structure of fractions in residue changed due to the increase of hydrotreating degree. The enrichment of large aromatic units made asphaltene have more aromatic structures and higher condensed degree.