Abstract:

Based on an in-house Couette wax deposition device, the effect of polyoctadecyl acrylate (POA) pour point depressant upon wax deposition formed by synthetic waxy oils was investigated. The macroscopic morphology, DSC test, HTGC and wax crystal microscopic observation of the outer deposit (away from the wax deposition barrel) and inner deposit (close to the wax deposition barrel) were analyzed. It was found that the addition of POA reduces the wax deposition rate, accelerates the aging rate of the wax deposit, and leads to the formation of heterogeneous wax deposition structure (wax content gradually increased from outer deposit to inner deposit) in a certain concentration range (50-200 μg·g^-1), while the structure of wax deposit became homogeneous when adding 400 μg·g^-1 of POA. The critical carbon number (CCN) of the wax deposit of pure waxy oil is C₂₄, but the CCN of the wax deposit formed by additive treated waxy oil rises to C₂₅. In comparison with the outer-layer wax deposit, the contents of the n-alkanes with carbon number ≤ C₂₄ in the inner-wax deposit are lower and the contents of the n-alkanes with carbon number ≥ C₂₅ are higher. With the increase of POA content, the waxy morphology of the wax deposit is gradually changed from small needle-like wax crystals to big sheet-like wax crystals, and the structure becomes more compact.

Key words: pour point depressant, waxy oil, wax deposition, aging, critical carbon number

摘要：

采用自主研发的Couette结蜡装置研究了聚丙烯酸十八酯（POA）降凝剂对合成蜡油体系结蜡特性的影响。通过对结蜡层表面样（远离结蜡筒）和底部样（靠近结蜡筒）的宏观观察、DSC放热、气相色谱及蜡晶微观结构的分析发现：POA的加入降低了蜡油体系的结蜡速率，加快了蜡油体系的老化速率，且在一定浓度范围内（50～200 μg·g^-1）导致了径向不均质蜡沉积结构的形成，从结蜡层表面到底部含蜡量逐渐升高，但在较高加剂浓度（400 μg·g^-1）时径向不均质蜡沉积结构消失；POA的加入使得结蜡层表面样和底部样的临界碳数（CCN）都由C₂₄升高到C₂₅，但结蜡层底部样与表面样相比低碳数正构烷烃（≤ C₂₅）有所减少，高碳数正构烷烃（≥ C₂₆）有所增加；随着油样中POA浓度的增大，结蜡层表面样与底部样的蜡晶形貌由针状蜡晶逐渐转变为片状蜡晶，且蜡晶尺寸逐渐变大，结构更为致密。

关键词: 降凝剂, 蜡油, 结蜡, 老化, 临界碳数