MolaKule
Staff member
The GTL Group III+ Base Oil Synthesis Process (A Summary derived from various Patents)
by MolaKule
by MolaKule
The Gas-to-Liquid process is executed primarily by using a Fisher-Tropsch process
10.2. Fischer-Tropsch Synthesis
Liquid transportation hydrocarbon fuels and various other chemical products can be produced from syngas via the well-known and established catalytic chemical process called Fischer-Tropsch (FT) synthesis, named after the original German inventors, Franz Fischer and Hans Tropsch in the 1920s...
www.netl.doe.gov
whereby a mixture of Carbon monoxide CO and Hydrogen H2 gases are catalytically converted into liquid hydrocarbons, in a mole ratio of approximately 0.7 to 2.5. (A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change).
The catalyst is in the form of a fluidized bed or a slurry of catalyst particles, usually cobalt, but may also use cobalt mixed with other metals. The synthesis gas mixture of CO and H2 is forced into the bottom of and bubbled up through the catalyst slurry and reacts in the presence of the F-T synthesis catalyst in conditions effective to form hydrocarbons, a portion of which are liquid, and a portion which passes out of the reaction vessel as vapors.
Depending on the final liquid characteristics desired, the reactor vessel may be operating under a temperature of from 320F to 850F, a pressure off from 80psi to 600psi, and varying volumetric flow rates.
Some of these vapors are further condensed to liquid and combined with the other liquid hydrocarbons to affect the final liquid hydrocarbon viscosity, pour point, Viscosity Index, etc.
Purification and clarification of the resulting liquid may be done by filtration, centrifuging, and further hydroprocessing. (See https://bobistheoilguy.com/ A Review of Mineral and Synthetic Base Oils, for definitions of the various Hydroprocessing techniques and other pertinent definitions).
The resulting synthetic GTL liquid base oil may have a viscosity range of from 2 cSt to 50 cSt, with the preferable range being 3.5 cSt to 30cSt. The viscosity index averages 130, for example, for a 4 cSt oil. The pour points average about -45C.
Hopefully, this short technical note removes some of the mystery surrounding GTL base oils.
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