Gas-to-liquid (GTL) projects form an important part of Qatar's energy industry due to the country's extensive natural gas reserves. At present, commercial GTL plants in Qatar account for 36% of the total worldwide GTL production, but suffer from high operational costs due to limitations in the existing Fischer-Tropsch synthesis (FTS) reactor technologies, which are at the heart of the GTL process. Of the two FTS reactor types currently in use commercially, fixed-bed reactors (i.e. gas-phase FTS) offer poor temperature control while slurry-bed reactors (i.e. liquid-phase FTS) suffer from difficult catalyst separation and other challenges. The utilization of supercritical fluids (SCF) as solvents in FTS (SCF-FTS) provide several advantages over the existing commercial technologies. SCF-FTS can improve the heat transfer properties relative to fixed-bed reactors, while also offering high diffusivity of the reactants relative to slurry-bed reactors. The results presented here summarize multidisciplinary research activities, led by our research team at Texas A&M University at Qatar, in collaboration with top scientists from institutions around the word and supported by an industrial advisory board. The work was funded by different agencies and combined several projects, which have been undertaken over the past four years. This work was unique in that it focused on understanding both the micro- and macro-scale behaviours of the FTS chemistry and reactor. The micro-scale studies enabled better understanding of the reaction mechanism and kinetics, FTS thermodynamics and phase behavior (via experimental and modeling studies), and intra-particle catalyst effectiveness factor. The macro-scale investigations covered: 1) identifying the overall (heat/mass/hydrodynamic) profile inside the reactor, 2) selecting an appropriate supercritical solvent, and 3) building a lab scale reactor unit. The outcome of these studies is that we were able to identify the most applicable solvent(s) while providing a detailed techno-economic and safety evaluation of this process. Furthermore, the overall structure of the separation process for solvent recovery and recycle has been completed based on energy optimization. Currently, we are at the stage of developing an upgraded design for this technology based on the data to be generated from our demo-scale FTS reactor unit.


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