脱沥青溶剂类型对煤焦油沥青质结构的影响

Effect of Deasphalting Solvent on Structure of Coal Tar Asphaltene

从中低温煤焦油中提取正戊烷沥青质(As-C_5)、正己烷沥青质(As-C_6)、正庚烷沥青质(As-C_7)。采用元素分析、凝胶渗透色谱法(GPC)、X射线衍射(XRD)、核磁共振氢谱法(~1H-NMR)、核磁共振碳谱法(^(13)C-NMR)、扫描电子显微镜(SEM)等表征手段对上述3种沥青质的组成、结构、表观形态等方面进行了表征和分析,并比较分析了中低温煤焦油沥青质与其他焦油沥青质。结果表明,随着正构烷烃溶剂的碳数依次增加,沥青质的收率、H/C原子比依次减少,芳香片层间距(dm)、烷基链的间距(dγ)、层直径(La)、晶胞高度(Lc)逐渐减小,芳碳率(f_A)逐渐增大,缩合度参数(HAU/CA)、芳香环系周边氢取代率(σ)逐渐减小。结果说明了As-C_5、As-C_6、As-C_7的烷基链及环烷环所占比例逐渐变小,芳环比例逐渐增大,芳香片层堆积程度逐渐增强,原料加氢利用过程中As-C_5、As-C_6、As-C_7的结焦潜质逐渐增大。从整体来看,中低温煤焦油沥青质的收率、芳碳率f_A均明显大于一般原油沥青质,其芳环上烷基侧链短而少、支链化程度低、难以形成堆积结构。因此,在中低温煤焦油加氢制取轻质油前,有必要对其进行预处理。

n-Pentane asphaltene(As-C_5),n-hexane asphaltene(As-C_6),n-heptane asphaltene(As-C_7)precipitated medium/low temperature coal tar.The properties such as structure parameters,crystal structure and micro-structure were charactered and analyzed by elemental analysis,gel permeation chromatography(GPC),X-ray diffraction(XRD),nuclear magnetic resonance spectroscopy(~1H-NMR and ^(13)C-NMR),scanning electron microscope(SEM)characteristic means,and comparative analysis of low temperature coal tar pitch and other tar asphaltene.The results show that with the carbon number of n-alkane solvents increases,the yield of asphaltene gradually decreased.It shows that the precipitation quantity of asphaltene decreased with the increase of molecular mass of precipitant.The H/C atomic ratio,aromatic layer spacing(dm),alkyl chain spacing(dγ),aromatic layer diameter(La),aromatic sheet height(Lc)of n-pentane,n-hexane,n-heptane asphaltene gradually decreased,the aromatic carbon rate(f_A)gradually increased,the aromatic ring condensation(HAU/CA)and aromatic ring around the hydrogen substitution rate(σ)gradually decreased.These conclusions confirmed that the proportion of alkyl chain and naphthenic ring gradually decreased,the proportion of the aromatic ring gradually increased,the accumulation degree of aromatic lamella gradually enhanced in As-C_5,As-C_6 and As-C_7,the coking potential of asphaltene increased gradually during the process of middle-low temperature coal tar hydrogenation.From the whole,the yield of As-C_5,As-C_6 and As-C_7 in the medium/low temperature coal tar asphaltene and the f_A was significantly larger than that of the crude oil asphaltene,the degree of branching is low and it is difficult to form the stacked structure.Consequently,it is necessary to pretreat the medium/low temperature coal tar before hydrogenation to produce light oil.