Study of extractants selectivity for extraction of organosulfur compounds from model solutions

Extraction of sulfur compounds from oil and petroleum products is a high priority task associated with tightening of the criteria of fuel quality control, negative impact of sulfur on the processing and storage of crude oil, environmental safety, as well as widespread use of organosulfur substances in different industries. The selectivity of several organic and inorganic extractants (methanol, N,N-dimethylformamide, acetonitrile, 15% NaOH, PEG 4000, PEG 200, diethylene glycol, monoethanolamine, dimethylacetamide, n-methylpyrrolidone) in relation to thiophene, dibenzothiophene, thiophenol, dodecanethiol and metilsulfide was studied for model solutions of organic sulfur compounds in n-heptane and n-octane. Extraction was carried out under static conditions. Sulfur content in the initial sample and in the sample after extraction was determined using an x-ray fluorescence analyzer SPECTROSCAN S. Chromatographic analysis of the samples was performed on an Agilent gas chromatograph with a mass-selective quadrupole detector. The selectivity of the studied extractants in relation to the studied groups of sulfur compounds was assessed through recovering (%) of a particular sulfur compound. It is shown that acetonitrile, N,N-dimethylformamide, dimethylacetamide and n-methylpyrrolidone are the most effective extractants for thiophene extraction. Methanol, N,N-dimethylformamide, acetonitrile, PEG200, diethylene glycol, monoethanolamine, dimethylacetamide and n-methylpyrrolidone are capable of extracting a wide range of organosulfur compounds from model solutions. Aqueous solutions of PEG 200 and PEG 4000 provide extraction less than 11% of organosulfur compounds, whereas 15% NaOH solution and a mixture of 50% NaOH:ethanol (1:2) are selective extractants for aliphatic mercaptans and provide up to 99% extraction of thiophenol and dodecanthiol, respectively. It was found that n-methylpyrrolidone, dimethylacetamide and N,N-dimethylformamide have the highest extraction capacity among the studied extractants. A series of studies gives ground to propose a possible extraction scheme for recovery of mercaptans from a mixture of organosulfur compounds.

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