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.

不同来源原油的配伍性预测，可通过采用原油溶解度参数（solubility parameter）的模型实现。通过观测正庚烷（n-heptane）滴定引发的沥青质沉淀起始点（asphaltene precipitation onset），可计算得到给定原油的近似溶解度参数值。对于沉淀起始点不明确的原油，可加入少量另一种沉淀起始点易于检测的石油样品。理想情况下应始终使用同一种石油作为添加样，但这显然难以实现。本研究的目标即采用合成分子替代该类石油添加样。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。通过红外光谱法（infrared spectrometry）、气相色谱-质谱联用法（gas chromatography-mass spectrometry）、元素分析（elemental analysis）与凝胶渗透色谱法（gel permeation chromatography）对所合成分子进行了表征。硝化腰果酚、加聚型聚腰果酚（polycardanol obtained by addition polymerization，PCA）以及硝化PCA均表现出预期的性能。然而，甲苯（toluene）中模型分子的浓度需根据原油的特性进行调整。对于特定原油，当模型分子的溶解度覆盖更宽的溶解度参数范围时，仅需更低的浓度即可准确识别该原油的沉淀起始点。