基于固相萃取法结合顶空GC-MS技术的沥青老化机理研究

沥青老化是影响沥青路面使用寿命的重要因素之一，探究沥青的老化机理对于老化沥青再生和沥青材料的循环利用至关重要。当前中国对于沥青老化机理的研究主要集中于化学组分变迁和物理性能变化的阐述方面，对于老化沥青化学成分变化的研究较少。开发了一种沥青四组分分离方法-固相萃取法，其中软沥青和沥青质的分离借助了超声、高速离心和氮吹浓缩的方法，软沥青中的三组分分离则使用商品化的固相萃取柱进行分离，利用不同极性的溶剂对饱和分、芳香分和胶质进行依次洗脱分离，分离后的组分溶液经浓缩干燥后进行含量变化分析。组分含量分析结果表明，老化沥青的饱和分和芳香分含量减少而胶质和沥青质含量升高。为证明该方法的可行性，将其与传统四组分分离方法进行比较，发现该方法可以将有毒溶剂的使用量减少1个数量级，方法重现性好，且非常适合用作质谱等分析技术中沥青样本的前处理方法。在建立了固相萃取方法后，将其与顶空气相色谱质谱联用(Gas Chromatography-Mass Spectrometry,GC-MS)技术结合，对固相萃取法分离得到的饱和分和芳香分中挥发性化合物进行了定性分析。结果表明：沥青老化前后饱和分中化合物类型变化并不明显，而芳香分中化合物类型变化较为显著，通过谱图比对共发现了14种差异化合物，其中萘、甲基萘、苯酚和甲基苯等化合物在老化沥青中未检测到，而含有羧基的化合物在老化沥青中明显增多。最后，借助红外色谱对质谱分析方法得到的试验结果进行了辅助验证，发现红外光谱得到的官能团总量变化结果与顶空气相色谱质谱得到的分析结果相一致。

Study on Asphalt Aging Mechanism Based on Solid Phase Extraction Combined with Headspace GC-MS

Asphalt ageing is an important factor affecting the service life of asphalt. Understanding the asphalt aging mechanism is very important for the regeneration and recycling of asphalt materials. In China, research on the asphalt aging mechanism has been confined to the elaboration of physical properties and changes in asphalt components, and there are few studies on the detailed analysis of the chemical composition changes of aging asphalt. The current study provides a new solid-phase extraction (SPE) method to separate four polarity-based fractions (saturates, aromatics, resins, and asphaltenes, SARA). For asphaltene-maltene separation, an ultrasonic cleaner, high-speed centrifuge, and nitrogen-blowing sample concentrator were used in the experiment. Saturates, aromatics, and resins in maltene were separated using commercially available pre-packed solid phase extraction (SPE) cartridges, and solvents with different polarities were used as eluting solvents, and the SARA was weighed after concentration and drying. The results show that the saturates and aromatics of aging asphalt decrease while the content of resins and asphaltene increases. Compared with the traditional SARA separation method, the proposed method has the advantages of good reproducibility and lower solvent consumption. Moreover, the proposed method is suitable as a sample pretreatment method for mass spectrometry. Headspace GC-MS was performed to analyze the compounds in the saturates and aromatics separated by the established SPE method. The results showed that there was no significant change in saturates, while the changes in aromatics were more significant before and after asphalt aging. Fourteen different compounds were identified by chromatographic comparison. Among them, naphthalene, methyl naphthalene, phenol, and methyl benzene were not detected in the aging asphalt, whereas the amount of compounds containing carboxyl groups increased significantly in the aging asphalt. Finally, the experimental results obtained were verified using infrared chromatography analysis, and it was found that the total amount change of functional groups obtained by the infrared spectrum was consistent with the analysis results obtained by headspace GC-MS.