沥青质分散剂的研究进展

分析了石油加工过程中的结构原因并比较了各种除垢方法的特点,综述了沥青质的组成、结构和沉积机理,阐述了沥青质分散剂的类别、作用机理以及沥青质分散剂在国内外的发展状况。最后对沥青质分散剂的发展方向进行了展望。     

渣油中沥青质的分子结构及反应性能的研究进展

沥青质在渣油的组成中占很大的一部分,在渣油加氢反应过程中,沥青质的转化是渣油加氢转化的难点。研究沥青质结构有助于更好地加工渣油。在前人的研究基础上概括了研究沥青质结构、组成的方法,并对于沥青质的反应性能作了分析,有助于对沥青质进行更深入的研究。     

石油沥青质分子结构模型研究进展

沥青质是石油中最重、结构最复杂的组分,对其分子结构的研究争议较大。目前对沥青质的分子结构认识主要有两种模型,即经典孤岛模型和群岛模型。经典孤岛模型主要由时间分辨荧光去极化、荧光相关谱法、质谱/串联质谱和直接分子成像等技术支持,从芳香核结构、分子量等角度进行了印证。而对于群岛模型,则是由薄膜热解法、稳态荧光发射技术和质谱联用技术等提供支持,从沥青质的整体性质和稠和芳香核的核数来证明。然而沥青质分子结构的复杂性决定了其难以用一种模型来概括,而且质谱技术的结果前后不一。近年来人们更倾向于支持孤岛模型与群岛模型共存。确定孤岛-群岛结构相对比例方法的提出则为这一观点提供了强有力的证明,但这种方法仍有缺陷,如何准确地测定出孤岛-群岛结构相对比例将是未来沥青质分子结构模型的关键和难点。     

渣油中沥青质的存在形态及其加氢转化反应

沥青质是渣油的重要组成部分,是渣油加氢反应过程中的转化难点。文章在叙述沥青质化学结构表征方法的基础上,讨论了沥青质的结构组成及其在渣油中的存在形态,并对渣油加氢转化反应过程中沥青质的转化行为和反应机理进行了论述。     

沥青质沉积化学防治技术研究

通过分析沥青质沉积的机理及危害,综述了国内外在防治沥青质沉积方面进行的研究。防治沥青质沉积主要通过添加化学抑制剂来实现。本文从作用机理、实验方法、性能评价等方面,介绍了沥青质防治技术的发展,并与目前石油行业的实际情况相结合,对沥青质沉积防治技术的发展和应用提出建议与展望。     

石油沥青质的微观结构分析和轻质化

通过总结和深化对石油沥青质微观结构及其轻质化工艺的认识,探索沥青质有效转化途径,为解决重质油加工过程中沥青质轻质化的难题提供思路。首先对沥青质微观结构的研究进展进行了总结,并通过分析沥青质基本单元片层结构和构成纳微缔合结构的相互作用力,推测构成沥青质纳微尺度结构的只有少数似晶缔合体,大部分为非晶缔合体。通过分析沥青质轻质化工艺发现热裂化和加氢转化工艺并未实现沥青质的轻质化,沥青质大多缩合生成了焦炭产物,虽然溶解作用使得沥青质在超临界水中有部分转化,但由于释放的活性氢数量有限,解决不了沥青质缩合问题,焦炭产率仍然很高。液相加氢转化利用活性氢自由基终止沥青质大分子自由基的链反应避免了生焦,实现了沥青质的有效轻质化。通过分析沥青质转化过程中胶体体系的稳定性,发现维持热裂化和加氢转化过程中重油胶体体系的稳定性较差,以沥青质为中心的胶束与分散介质之间的转化性能差异导致体系发生相分离而生成焦炭。液相加氢转化工艺中,由于新建立的胶体体系的分散介质保证了稳定的沥青质胶束的溶解能力,而为沥青质的有效转化提供了优良的反应环境。本文对沥青质的纳微缔合结构提出了新的观点,同时指出对非晶缔合体进行有效解构是沥青质液相加氢实现轻质化的关键。     

胶质和沥青质对渣油胶体稳定性的影响述评

胶质和沥青质在渣油的组成中占很大的比重,其分子结构以及单元结构间的相互作用影响着渣油胶体稳定性和加氢反应过程。同时渣油体系的不稳定性阻碍着加氢过程中转化率的提高。鉴于胶质和沥青质均为以溶解度和极性定义的复杂混合物,其组成和结构极为复杂。目前,只是对胶质和沥青质平均分子结构和沥青质模型分子结构的研究,还未有对胶质和沥青质的结构和配伍性的详尽文献。简述了胶质和沥青质互溶模型和C、CI、NCSI等参数公式来判断体系的稳定性。微观结构上分析了胶质和沥青质对胶体稳定性、兼容性和相关联参数公式的影响;以及研究沥青质重组分在加氢过程中含量和结构性质的变化。     

胶质和沥青质对渣油胶体稳定性的影响述评

胶质和沥青质在渣油的组成中占很大的比重,其分子结构以及单元结构间的相互作用影响着渣油胶体稳定性和加氢反应过程。同时渣油体系的不稳定性阻碍着加氢过程中转化率的提高。鉴于胶质和沥青质均为以溶解度和极性定义的复杂混合物,其组成和结构极为复杂。目前,只是对胶质和沥青质平均分子结构和沥青质模型分子结构的研究,还未有对胶质和沥青质的结构和配伍性的详尽文献。简述了胶质和沥青质互溶模型和C、CI、NCSI等参数公式来判断体系的稳定性。微观结构上分析了胶质和沥青质对胶体稳定性、兼容性和相关联参数公式的影响;以及研究沥青质重组分在加氢过程中含量和结构性质的变化。     

原油沥青质分子结构与乳化特性的关联研究

以核磁共振氢谱为基础,用改进的Brown-Ladner法计算六种原油沥青质的平均结构参数和平均分子式,关联原油水乳状液的表观黏度。结果表明:沥青质的芳香取代率在0.37～0.54之间,芳香环系周边碳的取代率在0.40～0.53之间,RA/RN均大于1。与穆尔班原油沥青质相比,胜利、文森特原油沥青质的芳香核结构较小,而支链烷烃数量较多;达里亚沥青质芳香核结构较少,支链数目较多;新文昌的支链比穆尔班沥青质的要长;巴林沙中沥青质的芳香结构较为致密。可以推测:沥青质分子结构中含硫官能团在原油水乳状液反相时起到交联作用,增大了沥青质界面膜强度;含氧官能团是亲水基团。     

基于固体13C核磁共振技术对油砂沥青质结构的研究

采用固体13C核磁共振(13C NMR)技术对油砂沥青质的化学结构特征进行详细的研究。通过对油砂沥青质的核磁谱图分析,获得了表征油砂沥青质结构特征的12个碳结构骨架参数。根据研究分析结果,油砂沥青质中的脂碳含量达60%左右,表明其化学结构主要以脂碳结构为主。在脂碳中,亚甲基含量最多,主要出现在脂肪链中,且其脂肪链平均长度小于8个碳原子,可推断为中等长度脂链;芳香碳含量小于40%,其中质子化芳香碳含量多于非质子化芳香碳。在非质子化芳香碳中芳香桥碳含量最多,可推断芳香碳呈多环模式;羰基碳在油砂沥青质结构中所占比例极小。虽然基于获得的油砂沥青质的元素组成,可以将油砂沥青质归类到Ⅰ型干酪根,但是两者在成烃潜量和结构特征都存在较大差异,由此判断油砂沥青质并非干酪根的降解产物。     

油砂沥青质分离纯化及其热裂解研究

为更好地开采并利用油砂,以新疆某油田油砂沥青质为研究对象,在分离纯化后进行热裂解实验研究,探寻油砂沥青质的转化规律。实验结果表明,超声震荡可以快速将沥青质包裹组分释放出来,缩短沥青质的分离纯化时间;沥青质中3种重要物质生烃、生气、生焦含量变化与温度和时间的关系非常密切;沥青质裂解具有明显的一级反应动力学特征,随着温度的升高,时间逐渐缩短,而其表观速率常数总体呈增加的趋势。     

稠油、超稠油热采技术研究进展

稠油或超稠油与常规的石油资源不同,具有胶质沥青质含量高,粘度和凝固点高等特点,因此利用传统的采油技术很难将其抽出来。目前普遍采用热采技术进行重油的开发利用。本文主要介绍几种热采技术及其发展状况。     

On-column precipitation and re-dissolution of asphaltenes in petroleum residua

A new automated separation technique was developed for measuring the distribution profiles of the most polar, or asphaltenic components of an oil, using a continuous flow system to precipitate and re-dissolve asphaltenes. Methods of analysis based on this new technique were explored. One method based on the new technique involves precipitation of a portion of residua sample in heptane on a polytetrafluoroethylene-packed (PTFE) column. The precipitated material is re-dissolved in three steps using solvents of increasing polarity: cyclohexane, toluene, and methylene chloride. The amount of asphaltenes that dissolve in cyclohexane is a useful diagnostic of the thermal history of an oil, and its proximity to coke formation. For example, about 40% (w/w) of the heptane asphaltenes from unpyrolyzed residua dissolves in cyclohexane. As pyrolysis progresses, this number decrease to below 15% as coke and toluene-insoluble pre-coke materials appear. Currently, the procedure for the isolation of heptane asphaltenes and the determination of the amount of asphaltenes soluble in cyclohexane spans three days. The automated procedure takes one hour. Another method uses a single solvent, methylene chloride, to re-dissolve the material that precipitates in heptane on the PTFE-packed column. The area of this second peak can be used to calculate a value which correlates with gravimetric asphaltene content. Currently the gravimetric procedure to determine asphaltenes takes about 24 h. The automated procedure takes 30 min. Results for four series of original and pyrolyzed residua were compared with data from the gravimetric methods. Methods based on the new on-column precipitation and re-dissolution technique provide significantly more detail about the polar constituents oils than the gravimetric determination of asphaltenes.     

Precipitation of asphaltenes from solvent-diluted heavy oil and thermodynamic properties of solvent-diluted heavy oil solutions

Ratios of n-heptane (hep) to toluene (tol) affect the solubility of the asphaltenes in heavy oil extraction processes. Consequently phase changes and time after mixing n-heptane and heavy oil in toluene are important for understanding produced emulsions. The kinetics of phase change when n-heptane is added to toluene-diluted heavy oils, and the thermodynamic properties of partially deasphalted heavy oils were studied. The methods used were monitoring precipitation in time using light microscopy, quantitative asphaltenes analysis by near infrared spectroscopy, refractive index and densities measurements, and calculated solubility parameters of mixtures. At critical mass ratios of hep/tol from 1.37 to 2.0 in diluted heavy oil the precipitated asphaltene particles were observed under the microscope after lag times from 2 h to instantly. Lag times were longer at low initial oil concentration. The floc growth time decreased as heavy oil concentration in toluene increased. The growth patterns in time appeared as dots to beads (strings) to clusters (fractal-like flocs). Final wt% precipitated asphaltenes vs. mass fraction (hep+tol)/heavy oil followed sigmoidal relationships. Curves showing wt% soluble asphaltenes vs. mass fraction hep/tol after 24 h initially followed the same shape as time zero curves and diverged at the onset ratios of hep/tol. Slope for precipitated asphaltenes vs. solubility parameters curve showed a break at 16.4 MPa^1/2. Linear correlations were established for concentrations of soluble asphaltenes in residual oils and density, for refractive index and density and for refractive index and solubility parameter. The latter correlation was in accordance with Lorenz-Lorentz theory. These equations provided a means by which oil density, refractive index and solubility parameter can be predicted when these measurements are difficult to measure practically.     

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.     

Investigation on the flocculation of asphaltenes and the colloidal stability of the crude oil fraction (> 210°C)

Several problems are encountered with asphaltenes during the exploitation, transportation, storage and treatment of crude oil. The purpose of the present work was to study the behaviour of the crude oil fraction (<210°C) by varying the temperature and doping with some hydrocarbons including solid paraffin and aromatic concentrate. The effect of flooding water was investigated. A preliminary characterization study on asphaltenes removed from the crude oil using two different solvents was performed. The state of the oil was determined by the stability factor which indicates the susceptibility of asphaltenes to agglomerate or to disperse in the continuous phase.     

Characterisation of aliphatic chains in vacuum residues (VRs) of asphaltenes and resins using molecular modelling and FTIR techniques

Asphaltenes are the main components of crude oil, and their chemical structures are very difficult to be analysed and characterised. Fourier Transform Infrared Spectroscopy (FT-IR) is one of the available analytical methods for interpreting the structure of asphaltenes and it has been used to characterise functional groups in these compounds. In the present work, FT-IR spectra of alkyl-benzenes, obtained both experimentally and theoretically (by quantum mechanic modelling), were studied using a semi-empirical software AM1. Based on these spectra, the linear relationship between the intensity ratios at 2927 and 2957 cm^− 1, and the ratios nCH₂ / mCH₃ from carbon chains of alkyl-benzenes, have been analysed to determine the terminal aliphatic chains of asphaltenes. This methodology was satisfactorily evaluated using molecular average structures found in the literature. Also, using both theoretical IR and experimental DRIFTS spectra, with deconvolution, the relationship between methylene and methyl groups, which are part of the aliphatic chains, were calculated for three types of Brazilian vacuum residue asphaltenes.     

油砂沥青质对油砂沥青中甲苯残留的影响

利用热重质谱联用仪（TG-MS）分析了三种油砂沥青（印尼油砂沥青、伊朗油砂沥青、加拿大油砂沥青）中的甲苯残留以及油砂沥青质含量对油砂沥青中甲苯残留的影响，并在此基础上，进一步研究了油砂沥青质中的甲苯残留。结果发现，不同油砂沥青中甲苯残留量存在一定差异，其中印尼油砂沥青中的甲苯残留量最多。进一步对沥青质质量分数分别为10%、19%、30%的油砂沥青样品进行热重质谱实验，发现随着油砂沥青中沥青质含量的增加，甲苯的残留量会成倍增加。以加拿大油砂沥青质为例，研究了油砂沥青质对溶剂残留的影响，发现油砂沥青质具有对甲苯分子的夹带能力，导致甲苯分子在超过自身沸点40℃以上才能从沥青质中分离出来。油砂沥青中其他组分的存在也会加剧沥青质对甲苯的夹带作用。此外，研究还发现，在350~650℃时，油砂沥青质可以热解产生甲苯，而且油砂沥青中的沥青质含量越高，热解生成的甲苯越多。     

On the formation and properties of asphaltene nanoaggregates and clusters by DC-conductivity and centrifugation

The hierarchical nanocolloidal structure of asphaltenes in solvent and even in crude oil has recently been delineated by a variety of techniques. It is highly desirable to compare results for the same samples from various techniques dependent on different physics. Here, the critical nanoaggregate concentration (CNAC) of specific asphaltenes is determined using both DC-conductivity and centrifugation; excellent agreement is found. In addition, the role of the lightest asphaltenes (or heaviest resins) in nanoaggregation is now amenable to direct measurement; inclusion of this weaker binding fraction does not materially impact the CNAC except by a trivial effect of dilution of the aggregating asphaltenes. DC-conductivity shows there is no observable change in CNAC over a moderate temperature range indicating that the enthalpy of formation of the nanoaggregate is zero. A simple analysis reveals that the entropy of nanoaggregate formation is positive, in agreement with previous work. Finally, the critical clustering concentration is observed at higher concentrations, and as always the clusters of nanoaggreates are found to have a small aggregation numbers. As with the CNAC, the heaviest resins do not affect the clustering concentration except by a trivial dilution effect.     

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.