Abstract
Comprehensive two-dimensional gas chromatography (GCxGC) analysis for 1-alcohols and gas chromatography–mass spectrometry (GC-MS) analysis for carboxylic acids, derivatised as their methyl esters, have been applied to liquid and wax Fischer-Tropsch (FT) hydrocarbon products. These methods in combination with conventional one-dimensional gas chromatography (GC) analysis of the aqueous, gaseous, liquid hydrocarbon and wax products plus conventional high-performance liquid chromatography (HPLC) analysis of the aqueous phase has allowed a quantitative distribution analysis of FT hydrocarbon and oxygenated products to be demonstrated for a Co/TiO2 catalyst operating in a fixed bed gas phase pilot plant utilising CANSTM catalyst carrier devices. The GC-MS method used is, to the best of our knowledge, the first application of this derivatisation route for the quantification of individual carboxylic acids in FT hydrocarbon product streams.Whilst the hydrocarbons and oxygenates that were identified are known compounds formed during the low temperature, Co catalysed, FT process the combination of the multiple analysis techniques used has allowed a level of detail to be gained on the product composition that is seldom reported.Additionally, 1H nuclear magnetic resonance spectroscopy (NMR) and 13C NMR analyses were used to quantify the average concentration of 1-olefin, cis- and trans-2-olefins, 1-alcohol and aldehyde as appropriate for the technique used. Comparison of GCxGC versus 1H NMR and GC-MS versus a KOH titration confirmed the applicability of the chromatographic methods for the quantitative analysis of FT oxygenated compounds. Long-chain 1-alcohols and carboxylic acids, ≥ C3, were found to be present at levels of 1/10th and 1/1000th that of hydrocarbons of equivalent carbon chain length respectively. The 1-olefin:n-paraffin ratio in the hydrocarbon liquid and wax products was found to decrease significantly with increasing carbon chain length and much more so than those of the 2-olefin or 1-alcohol.
Highlights
Fischer-Tropsch (FT) synthesis is a well-known and much studied catalytic process for converting synthesis gas to hydrocarbon and oxygenate products having linear carbon chains ranging from C1 to over C100 (Day 2002; Khodakov et al 2007)
We show the application of comprehensive two-dimensional gas chromatography (GCxGC) for the quantification of alcohols and gas chromatographymass spectrometry (GC-MS) for the quantification of carboxylic acids, derivatised as their methyl esters, in liquid and wax hydrocarbon FT products
Aqueous phase composition The main product in the aqueous phase were the 1alcohols from C1 to C10 with trace levels of methyl acetate, 2-methylpropan-1-ol and ethanoic acid being observed in the GC chromatogram (Additional file 1: Figure S2)
Summary
Fischer-Tropsch (FT) synthesis is a well-known and much studied catalytic process for converting synthesis gas to hydrocarbon and oxygenate products having linear carbon chains ranging from C1 to over C100 (Day 2002; Khodakov et al 2007). A tubular reactor demonstration plant was commissioned in Alaska in 2002 (Collins et al 2006) using a Co/ZnO catalyst. This facility is the largest FT plant built in the US, producing 300 bbl/day of synthetic crude product from pipeline natural gas feedstock. The original fixed bed tubular reactor technology was developed as a method of monetising stranded natural gas in remote locations but was typically only competitive at large scale (> 30,000 bbl/day) in areas with low natural gas prices and high oil prices
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