Impact of TSR experimental simulation using two crude oils on the formation of sulfur compounds

Two representative crude oils were used in participating in thermochemical sulfate reduction (TSR) and thus to evaluate their pyrolysis behaviors, which is of great relevance to the formation of sulfur compounds. TSR was conducted in autoclave on the system of crude oils with and without magnesium sulfate under high temperature (350-450 °C) and pressure (5-14 Mpa) conditions. The gaseous products were analyzed by gas chromatography and microcoulometry. The yields of non-hydrocarbon and hydrocarbon gases were measured and compared in order to reveal the distribution of gaseous compounds at different temperatures. Higher total sulfur contents and ratio of methane in gases were obtained with increased temperature. The crystallographic phases of MgO and MgSO4 were detected to coexist in the results of FT-IR and XRD, respectively. The sulfur compounds in oil phase products were reacted by methylation to form methylsulfonium salts and then characterized by positive ion electrospray (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Elemental composition and distribution of sulfur compounds were characterized by their double bond equivalents (DBE) values and carbon numbers. The results showed that types of sulfur compounds from TSR were mainly S1, S2, N1S1, O1S1 and O2S1. Among the identified sulfur compounds, the S1 class species was dominant. The most abundant S1 class species increase associated with the DBE value and carbon number increasing which also indicated the evolution of organic sulfur compounds in TSR is from the labile one to the stable one. In pure blank pyrolysis experiments without TSR, different composition and distribution of organic sulfur compounds in oil phase products were determined using mass spectra in order to evaluate the pyrolysis behaviors of the crude oils.