Model Molecules for Evaluating Asphaltene Precipitation Onset of Crude Oils

Predicting the compatibility of crude oils from different streams can be done by applying models that use the solubility parameter of the oils. The approximate solubility parameter value of a given crude oil can be calculated by observing the asphaltene precipitation onset caused by titration with n-heptane. For oils whose precipitation onset is not well defined, a small quantity of another petroleum with easily detected onset can be added. It would be ideal to always use the same petroleum for this addition, but this is obviously not possible. The purpose of this study was to replace this petroleum by a synthetic molecule. Therefore, molecules were selected and synthesized to obtain structures containing aromatic ring, aliphatic chain and heteroatom. The molecules were characterized by infrared spectrometry, gas chromatography-mass spectrometry, elemental analysis and gel permeation chromatography. Nitrated cardanol, polycardanol obtained by addition polymerization (PCA) and nitrated PCA presented the desired behavior. However, the concentration of the molecule in toluene needs to be adjusted in function of the characteristics of the petroleum. For a particular crude oil, when model molecule present solubility in a wider solubility parameter range, lower concentration will require to identify the precipitation onset of that oil.

通过采用基于原油溶解度参数的模型，可实现不同物流原油的配伍性预测。针对目标原油，可通过观测正庚烷滴定引发的沥青质沉淀起始点，计算得到其近似溶解度参数值。对于沉淀起始点难以明确判定的原油，可添加少量另一款沉淀起始点易于检测的石油样品。若能始终使用同一款石油进行该添加操作将最为理想，但显然这并不现实。本研究的目标便是使用合成分子替代该石油样品。为此，我们筛选并合成了兼具芳香环、脂肪链与杂原子结构的分子，并通过红外光谱法、气相色谱-质谱联用法、元素分析及凝胶渗透色谱法对所合成的分子进行了结构表征。硝化腰果酚、经加聚反应制得的聚腰果酚（PCA）以及硝化PCA均表现出预期的性能。不过，甲苯中该分子的浓度需根据石油样品的特性进行调整。针对某一特定原油，若模型分子的溶解度参数范围更广，则仅需更低浓度即可判定该原油的沉淀起始点。