Study On Flow Improvers For The Waxy Oils With Asphaltenes

Crude oil is a complex mixture of hydrocarbons that contain groups such as waxes, asphaltenes, resins, aromatics and so on. On one hand, wax can easily crystallize at low temperature, resulting in an increase in oil viscosity and even causing pipelines dragging in crude oil production. On the other hand, asphaltenes precipitation due to solubility limit causes heavy losses to the oil transportation. Flow improvers are widely used to improve the low-temperature flowability of crude oil. Among them, Poly (styrene-co-N-octadecyl maleimide)(SNODMI) is studied intensively for its good performance in pour point depression and viscosity reduction. A series of well-defined poly (styrene-co-maleic anhydride) as precursor was synthesized through RAFT polymerization, and the products named SNODMI with different imidization degree obtaining from the imidization reaction with octadecyl amine were used as flow improvers in model waxy oils with asphaltenes, with an emphasis on the influence of polymer structures.Firstly, it had been viewed the effects of flow improvers with different imidization degree on crystallization temperature, crystalline morphology, yield stress etc. in model waxy oil with asphaltenes. Consist with the results in model waxy oils-the higher imidization degree, the lower crystallization temperature for model waxy oils with asphaltenes. But the flow improvers with medium imidization degree performed the best in the improvement of crystalline morphology and the reduction of complex viscosity and yield stress. In the meantime, with the maleic anhydride content in precursor polymer increasing, the imidization degree of the folw improvers with the best performance also grows. Moreover, with the increase of maleic anhydride content in the flow improver, that is the increase of octadecyl side chain, the the wax crystals became smaller and more disperse in oils, asphaltenes particles were dispersed better, the crystallization temperature and the yield stress could be reduced considerably.To evaluate the effect of molecular weight and molecular weight distribution of the SNODMIs in two model oils, the (alt) SNODMIs and (ran) SNODMIs with different molecular weight were synthesized through RAFT polymerization. It was found that both the (alt) SNODMI and (ran) SNODMI with medium molecular weight (Mn=5600,7000respectively) performed the best in the improvement of flowability of model waxy oils with asphaltenes. Similarly, in model waxy oils without asphaltenes, the (alt) SNODMI with the molecular weight3300was the. most beneficial to the reduction of the crystallization temperature, complex viscosity and yield stress. The (ran) SNODMI with medium molecular weight also had the best performance as flow improvers, and (ran) SNODMI with larger molecular weight had solubility problems. In model waxy oils with asphaltenes, the (alt) SNODMI with broad molecular weight distribution benefited the decrease of crystallization temperature, the size of asphaltenes particles, the complex viscosity and yield stress, that was to say, it benefited the effectiveness of flow improvers. In the meantime, the (alt) SNODMI with broad molecular weight distribution did adverse performance as flow improvers in model waxy oils.Finally, the effects of block structures of polystyrene-b-poly (styrene-ran-maleic anhydride)(PS-b-(ran) SNODMI) on the crystallization temperature, crystalline morphology and yield stress of the waxy oils with asphaltenes were evaluated. To our investigation extent, both the increase of block (ran) SNODMI and block PS facilitated the reduction of the crystallization temperature, complex viscosity and yield stress of the samples. Consist with the results mentioned, the increase of octadecyl side chain in block (ran) SNODMI improved the flowability of model systems.