Molecular size and weight of asphaltene and asphaltene solubility fractions from coals, crude oils and bitumen
Molecular size and weight of asphaltene and asphaltene solubility fractions from coals, crude oils and bitumen
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DOI：
10.1016/j.fuel.2005.05.021
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发表时间：
2006-01-01
期刊：
影响因子：
7.4
通讯作者：
Mullins, OC
中科院分区：
文献类型：
--
作者：
Badre, S;Goncalves, CC;Mullins, OC
沥青质的分子量是一个争论了几十年的问题。近年来，几种技术已经集中在稠环系统的尺寸上;表明在直馏原油沥青质中的发色团通常具有4-10个稠环。因此，分子量的争论相当于确定沥青质是单体的（每个分子有一个稠环系统）还是聚合的。时间分辨荧光去偏振（FD）在这里被用来询问沥青质分子的绝对大小，并确定稠环系统的大小与相应的分子的大小的关系。比较了煤、石油和沥青的沥青质。这里通过FD确定的旋转扩散获得的煤沥青质的分子尺寸与泰勒色散衍生的平移扩散测量与UV吸收密切匹配[1]。煤沥青质比石油沥青质小。检查N-甲基吡咯烷酮（NMP）可溶性和不溶性级分。沥青质的NMP可溶和不可溶部分是单体。这表明，从SEC研究报告使用NMP作为洗脱溶剂的“巨型”沥青质分子实际上可能是预期的沥青质絮凝物，其不溶于NMP。数据表明，沥青质分子内电子弛豫不干扰FD结果。(c)2005爱思唯尔有限公司保留所有权利。
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 floes of asphaltene which are not soluble in NMP. Data is presented that intramolecular electronic relaxation in asphaltenes does not perturb FD results. (c) 2005 Elsevier Ltd. All rights reserved.