AM-00-51 Processing Of Fischer Tropsch Syncrude And Benefits Of Integrating Its Products With Conventional Fuels

Description:

There are several commercial options for the conversion of natural gas into liquid fuels. These are also known as Gas-to-Liquid (GTL) processes. The Fischer-Tropsch (F-T) synthesis is used in some of these GTL schemes. Its product is a mixture of hydrocarbons, mostly paraffinic, that can be described as a syncrude. One of the F-T based GTL processes is the Sasol Slurry Phase Distillate (SPD) process. This uses a Slurry Phase reactor to obtain a F-T syncrude, which is produced in two streams: condensate and wax. These streams are transformed into commercial products through hydroprocessing. The light stream, F-T condensate, contains hydrocarbons in the naphtha and distillate ranges. It is hydrogenated to convert olefins and other non-paraffin species to alkanes. The second stream, F-T wax, includes hydrocarbons from the heavy distillate range up to species heavier than hectane. These heavy paraffins are converted to lighter products using hydrocracking. The sulfur and aromatic content of F-T syncrude is intrinsically extremely low. When this is coupled with hydroprocessing the result is that GTL products are predominantly paraffinic. All these characteristics make them extremely attractive for blends with conventional fuels to meet stringent performance and environmental specifications. The Sasol SPD diesel has low sulfur and aromatic content and very high cetane number, all of these properties desirable in low emission fuels. The engine tests completed with the Sasol SPD diesel confirmed this fuel could meet strict environmental requirements. Moreover, it can also be used to upgrade lesser fuels to low emission standards. The highly paraffinic Sasol SPD Naphtha is an ideal feedstock for ethylene production. Recently Sasol has tested the performance of the several Sasol SPD naphthas in a standard diesel engine. These tests included for comparison purposes a South African diesel, on its own and in blends with a Sasol SPD Naphtha. The emissions and overall performance can be regarded as attractive and open a possibility for blends with lower quality distillates. This application could be of specific interest for winter grade diesels. The inclusion of the Sasol SPD products in blends with conventional fuels could be a viable alternative to the new refinery units required to meet stricter quality specifications. Moreover, these can be used advantageously to minimise the impact of seasonal changes in a fuels pool. Extensive engineering work for commercial SPD plants resulted in confirming $25 000 per daily barrel as the capital estimate for a Sasol SPD plant in a developed location. Sasol believes that there are several promising prospects for GTL ventures, even at oil prices as low as $15/bbl.