Pressure Effect On The Performance Of Comb-like Copolymers To Improve The Flowability Of Waxy Crude Oil

Heavy hydrocarbons in crude oil start to precipitate as wax crystals when the surrounding temperature is lower than the wax appearance temperature (WAT). The formation of wax crystals may give rise to either a reduction of oil flow or a clogging of pipelines. One extensively researched and economically viable solution is the employment of polymeric additives to improve the flow behavior of crude oil at low temperatures. Polymeric additives, acting as pour-point depressants (PPDs), wax inhibitors, or flow improvers are capable of incorporating themselves into wax crystals. This integration disrupts the wax formation process by reducing the tendency of wax crystals to interconnect into large agglomerates. So far, many of researches regarding to the cold flow behavior of waxy oils and the efficacy of chemical additives has been confined to the rheological properties or the morphology of waxes at atmospheric pressure. However, crude oils are usually transported in pipelines at well-defined pressures, which influence considerably on the cold flowability of crude oil. In the case of deep oil spills, the surrounding pressure is of even greater concern. Therefore, a systematic approach to research the flow behavior of heavy crude oils and assess the efficacy of chemical additives at elevated pressure is urgently needed.In this work, two series of copolymers with and without aromatic functional groups were successfully synthesized through free radical polymerization. The as-synthesized copolymers are MAC-24-18/MAC-18-18 series and AMAC/NMAC/ANMAC series. The chemical structures of these copolymers were characterized by1H NMR. Rheological, morphological methods were conjunctively employed to investigate the effect of these copolymers on the flowing behavior of waxy oil. As a result, all of these copolymers can effectively reduce the yield stress of waxy oil. However, the microscopic images indicate that these copolymers may take effect by different interaction with the waxes. MAC with no aromatic component mainly take effects by co-crystallizing with the waxes while the copolymers with aromatic parts can disperse the waxes through an absorption mechanism.Rheological properties of Liaohe high wax crude oil in the absence and presence of polymeric flow improvers under various pressures were systematically investigated. The measurements were conducted from 1 bar to 100 bar using a high-pressure (HP) rheometer. High pressure DSC was also employed in this work to investigate the gelling process of the oils. Interaction between copolymers and wax at different pressures was explored and elucidated by fluorescence optical microscope. It is found that both of the two kinds of copolymers can effectively improve the cold flow ability of waxy oil under varying pressure. However, the MAC with no aromatic components can interact with the waxes through co-crystallization mechanism, and this interaction retains well at high pressure. AMAC with aromatic component prominently absorb on the surface of the waxes and take effects through a repulsive force between the waxes and their aromatic parts. This effective is weakened to some extent under elevated pressure. This work provides some thought for designing new generation of copolymers which are more effective under higher pressure.