PETROLEUM AND PETROLEUM/COAL BLENDS AS FEEDSTOCKS IN LABORATORY-SCALE AND PILOT-SCALE COKERS TO OBTAIN CARBONS OF POTENTIALLY HIGH VALUE

Open Access
Author:
Escallon, Maria Mercedes
Graduate Program:
Energy and Geo-Environmental Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
October 03, 2008
Committee Members:
  • Harold Harris Schobert, Committee Chair
  • Elizabeth C Dickey, Committee Member
  • Alan W Scaroni, Committee Member
Keywords:
  • solubility parameters
  • needle coke
  • petroleum
  • coal
  • co-coking
  • interactions
Abstract:
The main goal of this research is to understand how the chemical composition of the feedstock and reactor design affects the quality of the coke toward the formation of a needle (premium) coke. Although a lot of information has been published related to the production of the premium coke, via mesophase formation, some contradictory results have been reported because the conclusions are reached based on chemical composition of the feedstock alone or reactor design alone. A raw decant oil, EI-107, was hydrotreated to different levels giving origin to six derivatives. Based on greater differences in chemical composition between the hydrotreated decant oils and the raw decant oil, and the sample quantity, three out of six derivatives were selected to continue with the carbonization process. It was found that the quality of the coke obtained through the pyrolysis of the four decant oils using the reactor operated at atmospheric pressure and 465„aC (LSCopen) is related to the chemical composition of the decant oil. The coke that displays the lowest coke quality is EI-135, which is explained by the presence of five-membered rings and biphenyls in the decant oil that are detrimental to the mesophase formation due to the loss of planarity and free rotation. Even though this decant oil has alkylbenzenes which improve the mesophase formation, it appears that the amount of these compounds is not enough to compensate the negative effect that five-membered rings and biphenyls exert on the mesophase. The next best coke in quality is EI-107. While its feedstock (EI-107) has the lowest amount of alkylbenzenes and naphthenic compounds, the decant oil EI-107 displays little or no presence of five-membered rings and biphenyls making its quality higher than coke EI-135. The cokes EI-134 and EI-138 display, respectively, the highest coke quality among the four cokes tested. Their feedstocks have the highest amount of alkylbenzenes and naphthenic compounds but an intermediate content of biphenyls. Five-membered ring compounds were not detected in decant oils EI-134 and EI-138. The viscosity of the system has been reported to be crucial for the coke quality, via mesophase growth. This study was performed by using a laboratory-scale coker operated under autogenous pressure and 465„aC (LSCclose), which keeps the gases in the reactor so that the viscosity of the system is reduced. The hierarchy in coke quality was found to be completely different to when the LSCopen was used. The coke EI-107, which is derived from the highest polycondensed feedstock, displayed the highest quality. The cokes EI-134, EI-135 and EI-138, which are the cokes derived from the hydrotreated decant oils, displayed the lowest. In summary, there is an optimum viscosity to obtain a high coke quality. When viscosity is too low, mesophase spheres do not coalesce. Last but not least, this work also studied blends of coal and the four selected decant oils as a feedstock to produce coke; the blend was pyrolyzed using the reactors LSCopen, LSCclose and the pilot-scale coker (PSC). Miscibility and chemical interactions (hydrogen transferability) between coal and decant oil were calculated in order to study their influence on the co-coke quality. When the reactors operated under atmospheric and near-atmospheric pressure (LSCopen and PSC), no correlation was found between miscibility or chemical interactions with co-coke quality. However, chemical interaction appears to correlate when LSCclose is used. This is attributed to the higher contact time between coal and decant oil, which occurs at the operational conditions of the reactor LSCclose.