(425f) Study on Poly(styrene-co-alkyl maleimide) As a Flow Improver for the Model Crude Oil with Heavy Asphaltenes

Authors: 
Zhu, Q. J., Zhejiang University
Wei, X. X., Zhejiang University
Yao, Z., Zhejiang University
Cao, K., Zhejiang University

*Corresponding Author’s E-mail: kcao@che.zju.edu.cn

This study was supported by the National Natural Science Foundation of China through Project No. 21176217.

The waxes and asphaltenes in crude oils are detrimental to pipeline transportation and processing due to the significant solubility decrease of waxes and asphaltenes with the depression in temperature or variation of other conditions, causing formation and deposition of stable wax crystals and asphaltene particles. Polymeric flow improvers are often widely used to solve this problem by retarding the wax crystallization and inhibiting the asphaltene aggregation. In our previous work, model waxy crude oils without and with low content of asphaltenes (0.1 wt %) have already been investigated, which indicates that the various molecular structure of the flow improvers have significant influence on the effectiveness of flow improving.

In present work, a synthesized flow improver, poly (styrene-co-octadecyl maleimide) is studied intensively for the performance in improving flowability of the model waxy crude oil with much higher content of asphaltenes (3 wt %). The characteristics of model crude oil have been essentially altered by the great amount of asphaltenes present and are quite different with that of the aforementioned two kinds of model crude oils. As the asphaltenes have been found to be incompatible with the waxes, they can readily precipitat followed by further aggregation forming large asphaltene particles and finally sediment especially at such high concentration. Hence the model crude oil with high content of asphaltenes is a heterogeneous system other than a homogeneous system as the model crude oil without or with low content of asphaltenes is. Therefore, the flow improving performance and mechanism of flow improvers may be different.

Flow improvers with a variety of structures are derived from the precursor, poly (styrene-co-maleic anhydride). The influence of various molecular structure, including molecular weights, maleic anhydride content of precursor, imidization degree and block structure on the effectiveness of flow improvers is thoroughly explored herein. The influence is interpreted in aspects of the yield stress and viscosity of the model crude oil, the stability of asphaltene particles in matrix, morphology of asphaltenes and wax crystallization temperature by the methods of rheometer, particle stability analysis through Turbiscan Lab Expert, microscopy and differential scanning calorimetry, respectively. Compared to untreated model crude oil, the viscosity and yield stress of crude oils with flow improvers are decreased considerably. The asphaltene particles are stabilized, better dispersed and the sedimentation is retarded. The wax crystallization temperature is depressed as well. Hence, poly (styrene-co-octadecyl maleimide) with an optimal structure can potentially be a kind of efficient flow improver for heavy crude oil with high content of asphaltenes and waxes.