EVA加剂量对含沥青质蜡油流变性的改善效果

Effects of EVA Additive Dosage on Rheolegical Properties of Asphaltenic Waxy Oils

通过流变实验、差示扫描量热分析以及显微观察,探究了乙烯-醋酸乙烯酯共聚物(EVA)质量分数对含沥青质蜡油流变性改善效果的影响,并揭示了EVA与沥青质协同降凝降黏机理。结果表明,单独添加EVA或沥青质可在一定程度上改善纯蜡油的低温流变性,且随着EVA质量分数的增大,蜡油的凝点不断降低,低温流变性逐渐变好,在EVA质量分数为1000 mg/kg时,蜡油凝点由加剂前的35℃降为20℃,15℃时的表观黏度由870.2 mPa·s降到229.6 mPa·s。EVA和0.75%质量分数的沥青质能够产生良好的协同作用,进一步改善蜡油的低温流变性,且随着EVA质量分数的提高,协同效果呈现先变好后变差的规律,并在EVA质量分数为100 mg/kg时取得最佳的协同降凝降黏效果,此时析出的蜡晶可形成尺寸最大、结构最致密的蜡晶絮凝体,蜡油凝点降低至-20℃以下,黏弹性参数与表观黏度也大幅度降低;进一步增大EVA加剂量导致协同效果变差,凝点、黏弹性参数和表观黏度都略有回升。

To understand the mechanism of synergistic effect between ethylene-vinyl acetate copolymer(EVA)and asphaltenes and its effect on pour point and viscosity,effects of EVA mass fraction(0-1000 mg/kg)on the flowability of model waxy oils were investigated through rheological measurement,differential scanning calorimeter(DSC)analysis and microscopic observation.Experimental results show that addition of either EVA or asphaltenes can slightly improve low temperature rheological behaviors of waxy oils.It was found that pour point of the waxy oil continuously decreases with increasing EVA dosage,but the rheology improves slowly with increasing EVA dosage.The optimum EVA dosage was identified at 1000 mg/kg.At the optimum dosage,pour point of the waxy oil can decrease from 35℃to 20℃,and the apparent viscosity at 15℃can decrease from 870.2 to 229.6 mPa·s.Meanwhile,adding 0.75%mass fraction asphaltenes and EVA simultaneously can generate good synergistic effect and thus can further improve the low temperature rheological behaviors of waxy oils.However,it was observed that,with increasing EVA mass fraction,this synergistic effect is good at the beginning but become bad later.When EVA mass fraction is at 100 mg/kg,the optimum synergistic effect can be reached.At this optimum dosage,the largest size of wax crystals can be flocculated and the most dense structure can be formed;pour point can be dropped to less than-20℃;viscoelastic parameters and apparent viscosity are also can be significantly reduced.Further increasing EVA dosage can result in bad synergistic effect,i.e.,resulting in slightly higher pour point,larger viscoelastic parameters and increased apparent viscosity.