Performance & Molecular Structure of Fuel Oils & Lube Base Oils ...

16th Saudi Arabia-Japan Joint SymposiumDhahran, Saudi Arabia, November 5-6, 2006increased with the rising concern about environmental issues such as emissions ofparticulate materials and Nox [1, 2]. Many refining companies have been developingmethods of production of fuel oils containing less than 10wtppm sulfur from crude oil.Gas-to-liquid (GTL) technology is expected to provide another method of producingcleaner fuel oils [3, 4, 5, 6].Fuel oils, such as kerosene or gas oil, which are derived directly fromFischer-Tropsch (FT) synthesis and indirectly via hydrocracking/isomerization of FTwax consist almost exclusively of n- and iso- paraffins. Therefore, the properties offuel oils derived from FT synthesis depend on the branching state of the paraffins aswell as the carbon number distribution.Diesel oil is an effective application of 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 of aromatic compounds [7], which increase particulatematerial emission from vehicles. Diesel oil properties largely depend on the molecularstructural characteristics such as the content of n-paraffins, so control of molecularstructure is crucial to optimize the performance of diesel oil derived from FT synthesis[8].A great deal of effort has been devoted to the effect of the composition of FT dieselon combustion properties [9, 10, 11, 12], but information on the molecular structure ofFT diesel remains insufficient, especially the effect of hydrocracking/isomerization onthe molecular structure.The recent tendency of clean fuel oils has also required improvement in theproperties of 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. Base oils prepared from paraffinic and clean source, such as FT synthesizedparaffin, are becoming more attractive as these products mainly consist of noncyclicparaffins and have very high viscosity indexes [14]. However, viscosity indexes ofprepared lube oils varied widely and were strongly influenced by severity ofhydrocracking/isomerization reaction.Authors attempted to describe the average molecular structures of each fraction byseveral parameters and correlate with properties of fuels or lube oils.One of the most fundamental structural parameters of base oil is the carbon numberdistribution, but this parameter is too complicated to relate to the performance of fueloils or lube base oil, so the average carbon number was taken as the parameter thatrepresents the size of molecule.Another important structural parameter is the branching of the paraffin molecule.Oils 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