Studies in coking of Arabian mix vacuum residue

Abstract

Batch reaction experiments pertaining to the coking of Arabian mix vacuum residue (AMVR) were carried out in the temperature range of 430-475°C and at a pressure of 0.2 MPa in an autoclave bomb reactor. The reaction time was varied in the range of 5-90 min. An attempt has been made to understand the inception, growth and saturation of coke formation within the range of temperature and reaction time covered in this work. The study revealed that the coke formation starts near the wall and then propagates towards the centre of the reactor and the temperature difference between the reaction mass at the wall and at the centre of the reactor was found to be as low as 0-1°C and as high as 8-12°C depending upon the severity of the reaction and the rate of coke formation. The present investigation also revealed that the coke formation levels off after a certain reaction time and thereafter a slight fall in the coke yield occurs. The reaction mixture was also quantified in terms of gas, distillates and unconverted vacuum residue. A four lump, three rate parameter kinetic model comprising vacuum residue (VR), gas (G), distillates (D) and the coke (C) has been proposed. VR was found to undergo first order decomposition and the apparent activation energy for the reaction pathways involving the formation of gas, distillates and coke from VR was found to be 51, 39 and 63 kcal mol⁻¹, respectively.