Isolation of nitrogen bases from coal-derived asphaltenes and preasphaltenes

High molecular-mass basic fractions considerably enriched in nitrogen compounds are obtained from coal-derived asphaltenes and pre-asphaltenes by means of a new acid/base fractionation procedure using acid-modified silica. Ultimate analysis, F.T.-i.r., and gas- and size-exclusion chromatography were used to characterise the basic fractions, and to show that the new method affords considerable advantages over adduction with gaseous hydrogen chloride.     

Liquid Chromatographic fractionation of oil-sand and crude oil asphaltenes

Asphaltenes extracted from Alberta oil sands (Athabasca, Cold Lake, and Peace River) and crude oils (Taber South and Fenn-Big Valley) were fractionated by sequential elution solvent chromatography (SESC) involving 10 organic solvents on a silica column. Athabasca asphaltenes and SESC fractions were further studied by elemental analysis, i.r., u.v., and n.m.r. spectroscopy. Incomplete extraction of maltenes from the oil-sand bitumens increased the yields of the first two SESC fractions, the saturates and aromatics, of oil-sand asphaltenes relative to the crude oil asphaltenes. About 55 wt% of the asphaltenes elute in fractions 3–5. Two distinct molecular types are present in the asphaltenes; namely, lower functionality species with lower heteroatom content and the higher functionality species with higher heteroatom content. Compounds eluting in fractions 3–10 are predominantly polynuclear aromatics with alkyl substituants and probably bridged by cycloalkanes. The extent of bridging as well as the location, number and type of heteroatoms determines the fraction in which each compound appears. Complexity of compounds eluting increases with time: earlier fractions are composed of smaller-size polynuclear aromatic centers and contain heteroatoms in predominantly ring locations, whereas later fractions contain a larger proportion of complex species and more functional heteroatom groups.     

Separation of coal-derived liquids by gel permeation chromatography

Coal-derived liquids, obtained from pilot plants and bench-scale reactors, have been separated by gel permeation chromatography into aromatic, phenolic, and asphaltenic fractions, where asphaltenes and long-chain hydrocarbons are in the same fraction. The Chromatographie system uses 10 nm μStyragel columns and solvents such as tetrahydrofuran (THF) and toluene. The separation is reasonably clean and almost devoid of overlapping. The saturated hydrocarbons are separated from the asphaltenes by vacuum distillation. Aromatic, phenolic and aliphatic fractions are characterized by high-resolution gas chromatography—mass spectrometry. The phenolic fraction contains alkylated phenols, indanols, and naphthols. The aromatic fraction is composed of alkylated benzenes, indans, naphthalenes and small amounts of multi-ring aromatics such as alkylated fluorenes and pyrenes. Most of the long-chain hydrocarbon fraction is of straight-chain alkanes ranging from tetradecane to tetratetracontane. Some branched alkanes, such as pristane and phytane, are also present. If olefins are present in the sample they also separate with the long-chain hydrocarbon fraction. Although various analytical data such as i.r., n.m.r., molecular size distribution and elemental composition of asphaltenes have been obtained, the chemical characterization is not complete. The gel permeation Chromatographie separation technique, as discussed in this paper, is very useful for fast analysis of any coal-derived liquid.     

Heterocompounds present in asphaltenes from various products of coal hydrogenation

The asphaltenes from hydrogenated coal extract (product A) as well as from hydrogenated low-temperature coal tars (products B and C) obtained from three bituminous coals were investigated. The asphaltenes were separated into basic (B) and acidic/neutral (A/N) fractions by precipitation of HCl adducts of nitrogen bases. The B and A/N fractions were investigated by means of thin-layer chromatography and i.r. spectroscopy to assist functional-group detection. Moreover, their high-resolution and field-ionization mass spectra were determined. The molecular weights of the asphaltene fractions are in the 80–600 amu range, and a few hundred molecular peaks were observed on the FIMS spectra. Part of the components were identified by HRMS — 27 nitrogen-compound types were found in the B fractions, while 38 compound types of O, N and S were detected in the A/N fractions. Although the asphaltenes were derived from two different liquefaction processes of three different coals, no significant differences in their composition have been found. They are hydrogenbonded complexes of basic and acidic components that are essentially the same heterocompounds in products A, B and C.     

Coal-derived asphaltenes: characterization by acid-base fractionation

Asphaltenes isolated from liquid products of the liquefaction of Pittsburgh seam bituminous coal under different process conditions were separated into basic, acid/neutral and, in one case, acid and neutral fractions. Molecular weights were obtained by boiling point elevation and molecular size distributions by gel-permeation chromatography. The basic fraction is mostly composed of larger molecules than the acid/neutral fraction. The relative amount of benzylic hydrogen, as determined by n.m.r., is reduced as the extent of conversion increases. Hydrogen bonding between the acid/neutral and basic fractions is shown to account for the pentane insolubility of only a minor amount of the total asphaltene.     

DIFFUSION-CONTROLLED ADSORPTIVE UPTAKE OF COAL AND PETROLEUM ASPHALTENES IN A NiMo/Al2O3 HYDROTREATING CATALYST

In this work, hindered diffusion of one coal and two petroleum asphaltenes was studied by adsorptive uptake in THF from a bath surrounding a NiMo/Al₂O₃ catalyst. A mathematical model for the adsorption-diffusion of asphaltenes was developed. The model parameters were obtained by simulating the experimental data with the model solution. Several asphaltene fractions were defined via SEC (Size Exclusion Chromatography), with the molecular weight of each fraction being determined by its elution characteristics. It was found that both the coal and petroleum asphaltenes have very broad molecular weight distributions; however, the molecular weights of the coal asphaltenes (50-2000) were much smaller than those of the petroleum asphaltenes (200-30000). The uptake rates for asphaltene fractions with different molecular weights varied, depending on their diffusion rates and adsorption constants. Simulation results showed that even though the properties of coal and petroleum asphaltenes were quite different, the values of model parameters for the fractions of the three asphaltenes had the same trend and could be estimated by same numerical expressions; with increasing molecular weight of the fraction, the adsorption constant monotonically increased, and the effective diffusivity decreased. The experimental uptake data for the three asphaltenes as a function of molecular weight were well represented by same mathematical model.     

Original preasphaltenes and asphaltenes in coals

The preasphaltene (PA) and asphaltene (A) fractions from untreated coal show a direct relationship of PA/A (w/w) to the carbon content of coal. Their thermal stability was investigated by in-situ pyrolysis FTIR, and the results show that PA has higher thermal stability than A. By means of a vacuum FTIR method, five types of hydrogen bonds formed by hydroxyl groups were clearly observed in PA and A, i.e., OH-π, self-associated OH, OH–ether oxygen, cyclic OH groups, and OH–N. The self-associated OH and OH–ether oxygen are the two main hydrogen bonds. The insolubility of PA in benzene and A in hexane is determined by the hydrogen bond strengths of the acid/base fraction but is not strongly related to their structural parameters and molecular weight. The acid/base associated strength of preasphaltenes and asphaltenes is estimated to be within the following ranges, asphaltenes, <5.15 kJ/mol; preasphaltenes, 5.15–30.9 kJ/mol.     

Chemical depolymerization of petroleum asphaltenes

The acid-catalysed phenol depolymerization of three petroleum asphaltenes has been investigated. Asphaltenes from Cold Lake, Arabian Heavy, and Tia Juana Medium residua were subjected to depolymerization conditions using phenol and para-toluenesulphonic acid, and the products were examined by a variety of instrumental and chemical methods. The treatment resulted in reduced average molecular weights, increased oxygen contents, formation of toluene-insoluble fractions, increased aromatic to aliphatic hydrogen ratios, and increased hydroxyl contents. These observations, when coupled with the finding that silylation resolubilized the toluene-insoluble material, have led to the conclusion that insolubility resulted from phenol incorporation into the asphaltene structure and a concomitant increase in polarity and hydrogen bonding. Since it has been shown in the literature that this treatment can depolymerize coal by breaking the alkyl-aromatic bonds which link aromatic units, the present observations are consistent with the presence in petroleum asphaltenes of condensedring systems linked by alkyl bridges. An additional implication is that the size of the individual condensed-ring systems is smaller than would be the case in the absence of bridging since the resulting molecules are composed of smaller condensed systems linked by aliphatic bridges as opposed to one large condensed unit.     

Investigations on Romashkino asphaltic bitumen. 3. Fractionation of asphaltenes using ion-exchange chromatography

The fractionation of asphaltenes originally separated¹ from Romashkino asphaltic bitumen has been achieved by means of stepwise anion- and cation-exchange chromatography through macroreticular resins. The fractionation procedure and yields of the fractions are given. A detailed structural analysis has been made of original asphaltenes and their acid- and base-free fraction using elemental and densimetric analyses, gel-permeation chromatography and proton magnetic resonance spectroscopy. Inverse gas-liquid chromatography has also been used to detect the chemical functionality of the asphaltene fractions. Results are presented to show the effect of ion-exchange resins treatment upon the composition of asphaltenes, noting that molecular weight as well as chemical structure changes appreciably.     

基于1H NMR测定和基团贡献法预测石油馏分的热化学性质

测定了两种原油 2 0个石油馏分的¹H NMR谱和氢、碳元素含量等结构参数 ,以及馏分的燃烧焓、蒸发焓等热化学性质 .假设每个石油馏分仅由CH₃ 、CH₂ 、CH、ACH和C这 5种简单基团构成 ,基于¹H NMR测定和元素分析结果解出石油馏分平均分子结构中的基团数目 ,再用纯有机物的基团贡献法预测石油馏分的燃烧焓、蒸发焓 ,预测值与实验数据吻合良好     

The significance of kinetic parameters and structural markers in source rock asphaltenes,reservoir asphaltenes and related source rock kerogens,the Duvernay Formation (WCSB)

Asphaltenes from reservoir oils, source rock bitumen and the kerogen of related source rocks of the Duvernay Formation (WCSB) have been studied in order to compare their petroleum generation characteristics. Open system bulk petroleum pyrolysis for bulk kinetic evaluation and geological extrapolation and pyrolysis GC experiments for petroleum compositional characterisation were applied in order to evaluate the reliability of petroleum asphaltenes in source rock evaluation studies in which a potential source rock sample is not available.Kinetic parameters and resulting geological extrapolations of petroleum formation calculated on immature source rock kerogens and asphaltenes fit exactly to corresponding parameters measured on asphaltenes precipitated on low mature oils. In contrast molecular characteristics such as aromaticity and the amount of alkylated thiophenes reveal highest values in source rock asphaltenes, while oil asphaltenes demonstrate lowest aromaticity. Source rock kerogens seem to represent an intermediate between both types of asphaltenes at low levels of maturity. Interestingly the molecular ratios observed in products formed from oil asphaltenes fit exactly to those observed in natural oils and support the application of petroleum asphaltenes to predict petroleum formation and especially petroleum compositional characteristics.     

基于1H NMR测定和基团贡献法预测石油馏分的热化学性质

测定了两种原油 2 0个石油馏分的¹H NMR谱和氢、碳元素含量等结构参数 ,以及馏分的燃烧焓、蒸发焓等热化学性质 .假设每个石油馏分仅由CH₃ 、CH₂ 、CH、ACH和C这 5种简单基团构成 ,基于¹H NMR测定和元素分析结果解出石油馏分平均分子结构中的基团数目 ,再用纯有机物的基团贡献法预测石油馏分的燃烧焓、蒸发焓 ,预测值与实验数据吻合良好     

Relationship between solvent-derived and compound-class fractions in coal-derived distillates and vacuum still bottoms

High-boiling SRC-1 process-derived distillable liquids and nondistillable vacuum still bottoms (VSB) from Wyodak and Kentucky 9/14 coals were separated into solvent-derived and compound-class fractions using Chromatographic techniques. The fractions were characterized using infrared spectrometry, proton nuclear magnetic resonance spectrometry, field ionization mass spectrometry, and elemental analysis. Emphasis was placed on the determination of the composition of oils and asphaltenes. Results showed that oils and asphaltenes consist of the same compound classes: hydrocarbons, nitrogen compounds, and hydroxyl aromatics. The main differences between the oil and asphaltene fractions are in concentrations of compound classes. It was found that oils are rich in hydrocarbons while asphaltenes are rich in hydroxyl aromatics. Also, oils and asphaltenes contain compounds of the same homologous series, and molecular weight is not a factor which differentiates oils and asphaltenes. Components in VSB oils have higher molecular weights than components in distillate asphaltenes. Molecular structure rather than molecular weight is a major parameter that determines solubility of coal-derived liquids.     

Oxidative degradation of carbon blacks with nitric acid: II. Formation of water-soluble polynuclear aromatic compounds

Furnace black and acetylene black were oxidized with concentrated nitric acid at 100 °C for prolonged periods. The oxidized carbon black was dissolved/dispersed into alkaline solution and was size-fractionated into six fractions by ultrafiltration. The yields of the fractions revealed that oxidized furnace black contains oxygenated polynuclear aromatic compounds with a variety of molecular sizes, but oxidized acetylene black consists of only a great quantity of the largest size fraction, probably carbon black particles, and a scarce amount of the smallest size fraction. With oxidized furnace black, elemental compositions of all fractions except the largest molecular-size fraction were independent of the period of oxidation, suggesting that each fraction possesses a similar molecular structure. Noncarbon constituents such as oxygen and hydrogen increased with decreasing molecular size. The mean molecular weights of fractions were estimated to be in a range from ca. 400 to 1200 and more on the basis of elemental and functional group analyses. ¹³C-NMR and IR analysis showed that the molecules of fractions comprise phenolic, carboxylic, nitro, perhaps quinonic carbonyl groups, and aromatic carbons, but no aliphatic carbons. Ultraviolet and visible spectra of fractions denoted that absorption at higher wavelengths increased with increasing the molecular weights, indicating extension in the conjugated aromatic ring system. On the basis of the experimental results molecular structure models for the fractions were proposed.     

Molecular size and weight of asphaltene and asphaltene solubility fractions from coals, crude oils and bitumen

The molecular weight of asphaltenes has been a controversy for several decades. In recent years, several techniques have converged on the size of the fused ring system; indicating that chromophores in virgin crude oil asphaltenes typically have 4-10 fused rings. Consequently, the molecular weight debate is equivalent to determining whether asphaltenes are monomeric (one fused-ring system per molecule) or whether they are polymeric. Time-resolved fluorescence depolarization (FD) is employed here to interrogate the absolute size of asphaltene molecules and to determine the relation of the size of the fused ring system to that of the corresponding molecule. Coal, petroleum and bitumen asphaltenes are compared. Molecular size of coal asphaltenes obtained here by FD-determined rotational diffusion match closely with Taylor-dispersion-derived translational diffusion measurements with UV absorption [1]. Coal asphaltenes are smaller than petroleum asphaltenes. N-methyl pyrrolidinone (NMP) soluble and insoluble fractions are examined. NMP soluble and insoluble fractions of asphaltenes are monomeric. It is suggested that the ‘giant’ asphaltene molecules reported from SEC studies using NMP as the eluting solvent may actually be the expected flocs of asphaltene which are not soluble in NMP. Data is presented that intramolecular electronic relaxation in asphaltenes does not perturb FD results.     

GPC characterization for assessing compatibility problems with heavy fuel oils

Precipitation of solids is one of the major problems associated with the shipping and handling of heavy residual oils especially No. 6 heating oil. ASTM specifications which currently include viscosity, flash point and pouring point are not adequate to predict the handling problems. The residual oils are becoming more complex in composition due to modern refinery techniques for cracking the heavier residues into distillable fractions. In this study, several heating oil samples, including a sample which partially solidified during transport, were analyzed using various techniques including separation by gel permeation chromatography (GPC), vacuum distillation, separation of petroleum asphaltenes by ASTM method, elemental analysis and proton and ¹³C NMR spectroscopy. The distillable species in the fraction separated by GPC were characterized by high resolution gas chromatography—mass spectroscopy (GC—MS). The study showed that the GPC can be used as a reliable technique for the analysis of heavy residual oils. The GPC separation of No. 6 heating oil gave three fractions enriched with chemically distinct species. The first fraction was composed of heavy molecular species generally known as asphaltenes. The second fraction was mostly straight chain paraffins. The third fraction was composed of low molecular weight aromatics. Although occasional verification of GPC data by GC—MS and by NMR spectroscopy is desirable, the GPC alone is an efficient analytical tool for evaluating the composition as well as predicting the handling problems associated with shipping and storage of various residual oils.     

Composition of petroleum heavy ends. 2. Characterization of compound types in petroleum >675 °C residues

The characterization of polar compound types in petroleum residues of b.p. >675 °C are described. The fractions of acids, bases, and neutral nitrogen compounds prepared by the method described in Part 1 (Fuel 1981, 60, 14) were further separated and analysed. Major compound types identified in the acid fraction are carboxylic acids, phenols, pyrrolic nitrogen compounds, and amides. Quantitative estimates of the compound types were made by two infrared methods. Major compound types identified in the bases were pyridine benzologs, amides, and pyrrolic nitrogen compounds; types found in the neutral nitrogen fraction were amides and pyrrolic nitrogen compounds. The average molecular weight of the >675 °C residues was estimated to be 900 after being determined by four different methods.     

Molecular size of asphaltene fractions obtained from residuum hydrotreatment

Previously, fluorescence depolarization techniques (FD) have been shown to measure asphaltene molecular size, thereby establishing the substantial difference between asphaltenes derived from crude oil vs from coal. Here, FD is used to track the changes of the asphaltenes from a petroleum atmospheric resid feedstock that has been subjected to increasing thermal severity of catalytic hydrothermal cracking. Changes in asphaltene properties with increasing cracking are readily observed and understood. In addition, asphaltene molecular size is measured for various asphaltene solubility fractions in binary solvent mixtures of toluene with either n-heptane or acetone; a strong dependence is found of asphaltene properties on the particular solvent mixtures in accord with recent publications.     

Carbonization of petroleum feedstocks II: Chemical constitution of feedstock asphaltenes and mesophase development

The characterization of the asphaltene fractions of a range of petroleum feedstocks by FT-IR, ¹H and ¹³C NMR spectroscopy indicated distinct differences in the molecular structure of the asphaltenes. Some of these differences could be related to the variations in the size of the principal optical texture of the semi-cokes produced by carbonization. The principal optical texture size was observed to increase steadily with the increasing hydrogen aromaticity of the asphaltenes over the whole range of the feedstocks used. There was no consistent correlation, however, between the carbon aromaticity of the asphaltenes and the optical texture size. The correlation between the hydrogen aromaticity and the principal optical texture size was attributed to structural differences among the asphaltenes that are critically important for the mesophase development.     

磷、柠檬酸改性对MoW/Ni/Al2O3催化剂性质及加氢脱氮性能的影响

采用等体积浸渍法制备了以γ-Al₂O₃为载体,Ni、Mo、W为活性金属组分的三金属催化剂,考察了磷改性、柠檬酸改性以及磷-柠檬酸组合改性对催化剂性质、加氢脱氮性能和脱氮选择性的影响。通过NH₃-TPD、Py-IR、H₂-TPR、XPS和HRTEM对催化剂进行表征,结果表明：磷改性不但提高了催化剂的表面弱酸量,而且提高了金属的硫化性能,促进碱性氮和非碱性氮的脱除,但磷改性导致金属活性相的堆垛层数偏高、分散度下降;柠檬酸改性降低了催化剂活性金属氧化物的硫化温度,提高了催化剂的加氢活性,但对氢解性能基本没有影响,表现为非碱性氮脱除性能的提高;而磷-柠檬酸组合改性,不但提高了催化剂的氢解性能,而且改善了其加氢活性,使催化剂对焦化蜡油中碱性氮和非碱性氮的脱除率均得到大幅提升,分别达到80.1%、54.9%。