Performance & Molecular Structure of Fuel Oils & Lube Base Oils ...
Performance & Molecular Structure of Fuel Oils & Lube Base Oils ...
Performance & Molecular Structure of Fuel Oils & Lube Base Oils ...
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16th Saudi Arabia-Japan Joint SymposiumDhahran, Saudi Arabia, November 5-6, 2006increased with the rising concern about environmental issues such as emissions <strong>of</strong>particulate materials and Nox [1, 2]. Many refining companies have been developingmethods <strong>of</strong> production <strong>of</strong> fuel oils containing less than 10wtppm sulfur from crude oil.Gas-to-liquid (GTL) technology is expected to provide another method <strong>of</strong> producingcleaner fuel oils [3, 4, 5, 6].<strong>Fuel</strong> oils, such as kerosene or gas oil, which are derived directly fromFischer-Tropsch (FT) synthesis and indirectly via hydrocracking/isomerization <strong>of</strong> FTwax consist almost exclusively <strong>of</strong> n- and iso- paraffins. Therefore, the properties <strong>of</strong>fuel oils derived from FT synthesis depend on the branching state <strong>of</strong> the paraffins aswell as the carbon number distribution.Diesel oil is an effective application <strong>of</strong> fuel oil production from FT synthesis, asdiesel oil derived from the FT process (FT diesel) consists mainly nocyclic paraffinsand has excellent combustion properties, whereas diesel oils derived from crude oilinclude substantial amounts <strong>of</strong> aromatic compounds [7], which increase particulatematerial emission from vehicles. Diesel oil properties largely depend on the molecularstructural characteristics such as the content <strong>of</strong> n-paraffins, so control <strong>of</strong> molecularstructure is crucial to optimize the performance <strong>of</strong> diesel oil derived from FT synthesis[8].A great deal <strong>of</strong> effort has been devoted to the effect <strong>of</strong> the composition <strong>of</strong> FT dieselon combustion properties [9, 10, 11, 12], but information on the molecular structure <strong>of</strong>FT diesel remains insufficient, especially the effect <strong>of</strong> hydrocracking/isomerization onthe molecular structure.The recent tendency <strong>of</strong> clean fuel oils has also required improvement in theproperties <strong>of</strong> lube oil cleaner and more efficient as well. According to a recent survey[13], the total demand for lube base oil has been almost constant during the past twodecades, but the demand for high grade base oil (i.e. Group II or III) has graduallyincreased. <strong>Base</strong> oils prepared from paraffinic and clean source, such as FT synthesizedparaffin, are becoming more attractive as these products mainly consist <strong>of</strong> noncyclicparaffins and have very high viscosity indexes [14]. However, viscosity indexes <strong>of</strong>prepared lube oils varied widely and were strongly influenced by severity <strong>of</strong>hydrocracking/isomerization reaction.Authors attempted to describe the average molecular structures <strong>of</strong> each fraction byseveral parameters and correlate with properties <strong>of</strong> fuels or lube oils.One <strong>of</strong> the most fundamental structural parameters <strong>of</strong> base oil is the carbon numberdistribution, but this parameter is too complicated to relate to the performance <strong>of</strong> fueloils or lube base oil, so the average carbon number was taken as the parameter thatrepresents the size <strong>of</strong> molecule.Another important structural parameter is the branching <strong>of</strong> the paraffin molecule.<strong>Oils</strong> heavier than kerosene fraction contain so many isomers that it is impossible toidentify all isomers, for example by chromatography. One effective way to measure the2