Upgrading Naphtha

Fjo. 10-10. Combination hydrojjKtreatiDg-hydrofwiniBg process for upgrading naphthas, using fixed-bed reactors. 

Upgrade lower-value materials such as heavy residues to more valuable products such as naphtha and LPG. Naphtha is mainly used to supplement the gasoline pool, while LPG is used as a fuel or as a petrochemical feedstock. 

SSPD [Sasol slurry phase distillate] A process for converting natural gas to diesel fuel, kerosene, and naphtha. Operated by Sasol in South Africa since 1993. Three stages are involved. In the first, natural gas is converted to synthesis gas by reforming. In the second, the synthesis gas is converted to waxy hydrocarbons in a slurry-phase reactor. In the third, the waxes are upgraded to middle distillates. See also Arge. 

Apart from FT synthesis for naphtha, the MtSynfuels process has the advantage of sufficiently high octane numbers (RON 92) of the naphtha fraction. Therefore, this naphtha can be used directly as a fuel (gasoline) for petrol engines without further upgrading (Liebner et al., 2004). 

Liquid products contain sulfur and nitrogen and must be hydroprocessed to improve quality. Separate hydroprocessing units for upgrading the naphtha, kerosene, and gas oil fractions can be used to optimize the overall process. Refined gas oil or diesel fuel is aromatic in character and contains more cycloparaffins than conventional crude oil. The resulting fuel is low in cetane number, high in density, and typically has very good low-temperature handling properties. 

Bitumen is recovered using a caustic assisted hot water flotation process and diluted with naphtha to facilitate the removal of residual solids and water. Diluent naphtha is removed by distillation prior to feeding bitumen to the Upgrading facilities. 

Catalytic reformers upgrade low octane naphthas into gasoline in the presence of hydrogen to retard deposition of carbon on the catalyst. Temperatures to 500°C and pressures to 35 atm are necessary. Representative reactors are shown in Figure 17.25. 

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