| Abstract
| - This study was instigated in view of the recent commercial exploitation of the Doba oil field inlandlocked Chad, which is a region from which crude oil is extracted and expected to be routedto the Atlantic shore through pipeline transportation. Thus, nonisothermal kinetic hydrovisbreaking tests of Doba crude oil were conducted in a mechanically stirred baffled autoclave reactorunder various conditions to alter the rheological properties of the treated crude. The crudehydrovisbreaking kinetics was modeled based on the four-parameter reaction severity concept(ω, γ, E, βo), as a function of the conversion in polyaromatics and polar maltenic subfractions.The hydrovisbreaking of Doba crude was observed to be a pseudo-first-order reaction (i.e., inexcess of H2), with respect to the polyaromatics and polar maltenic conversion. The followingassortment of kinetic parameters was identified under noncatalytic hydrovisbreaking conditions: heterogeneity coefficient, γ = 1; characteristic temperature, ω = 29.95 K; and activationenergy, E = 140.9 kJ/mol. Four viscosity mitigation scenarios involving catalytic (FeS, MoS2)and noncatalytic hydrovisbreaking of Doba heavy crude oil were investigated. It was found thatthe minor proportions of the fractions that distilled before 250 °C and the small asphaltene yieldsmarginally affected the crude viscosity. It was therefore determined that it is possible to meetthe viscosity specification for pipeline transportation via (noncatalytic) hydrovisbreaking, whichrequires neither predistillation (topping) nor post-deasphalting units. The treated crudes andthe syncrudes (mixtures of untreated and treated crudes) were observed to exhibit nonelasticviscous Newtonian behavior over the temperature range typical of crude transportation viapipeline. Treated crudes at 440 °C for 25 min and syncrudes that were the result of mixing 50 wt% of untreated crudes with crudes treated at 460 °C for 15 min yielded kinematic viscositieswithin the pumping specifications (i.e., ≤ 25cSt @ 50 °C). The use of catalysts led to even less-viscous maltenes subfractions; however, post-deasphalting was required, because the catalyst−coke mixture, as well as asphaltenes, inflated the viscosity above the norm. An iron sulfide catalystoutperformed a molybdenum sulfide catalyst, in terms of the deasphalted crude viscosity. Agingtests over two-month periods indicated that the higher the treatment severity, the more stablethe viscosity of the Doba treated crudes, which is potentially compatible with the residence timesof syncrudes within the 1050-km-long transportation pipeline between Chad and Cameroon.
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