Jain Ankita, Seth Jyoti R, Juvekar Vinay A, Verma Nidhi, Pandey Nandini
Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India.
Soft Matter. 2020 Dec 16;16(47):10657-10666. doi: 10.1039/d0sm01404d.
Uninterrupted transport of waxy crude oil through pipelines remains a pressing concern for the petroleum industry. When the ambient temperature falls below the pour point of the crude, deposition of wax particles may lead to complete blockage of the pipeline. We demonstrate that the application of a DC electric field to waxy crude below its pour point can effectively break the wax network and also reduce the viscosity by up to two orders of magnitude. We have studied the dynamics of the change in viscosity during and after application of an electric field. Three regimes are observed. First is the induction regime, where viscous stresses dominate and the viscosity remains unchanged. During the intermediate and final regimes, the decrease in viscosity follows first order kinetics with rate constants proportional to the strength of the electric field and to the square of the strength, respectively. Microscopic evidence shows that some network connections break during the intermediate regime, whereas in the final regime, further fragmentation of the pieces of the broken network occurs. This is accompanied by aggregation of fine wax fragments. After cessation of the field, the viscosity increases gradually. The rate and the extent of recovery of viscosity depend only on the value of viscosity at the point of cessation of the field. That the breakage of the network occurs, even in the absence of shear, has been demonstrated. Through measurement of the dielectric constants and conductivities of the crude oil and its component phases, we have shown that the wax network experiences compressive Maxwell stress, which is dominated by the electric field within the wax particles.
通过管道不间断地输送含蜡原油仍然是石油行业面临的紧迫问题。当环境温度降至原油的倾点以下时，蜡颗粒的沉积可能导致管道完全堵塞。我们证明，在倾点以下的含蜡原油中施加直流电场可以有效地破坏蜡网络，并且还能将粘度降低多达两个数量级。我们研究了施加电场期间及之后粘度变化的动力学。观察到三种状态。首先是诱导状态，此时粘性应力占主导，粘度保持不变。在中间状态和最终状态期间，粘度的降低遵循一级动力学，速率常数分别与电场强度和电场强度的平方成正比。微观证据表明，在中间状态期间一些网络连接会断裂，而在最终状态下，破碎网络的碎片会进一步破碎。这伴随着细蜡碎片的聚集。电场停止后，粘度逐渐增加。粘度恢复的速率和程度仅取决于电场停止时的粘度值。即使在没有剪切的情况下，网络的断裂也已得到证明。通过测量原油及其组分相的介电常数和电导率，我们表明蜡网络受到压缩麦克斯韦应力的作用，该应力由蜡颗粒内的电场主导。
