Emulsification and corrosivity study of bio-oil and vacuum gas oil mixtures with a novel surfactant system

Abstract

Co-processing bio-oil (BO) with petroleum intermediates such as vacuum gas oil (VGO) in existing refining infrastructures provides a promising pathway to transform low-quality BO into value-added biofuels. Nevertheless, the immiscibility between BO and VGO is one of the major obstacles to BO co-processing, especially during the feeding stage of upgrading. To inject BO and VGO as a single-phase fluid and maximize their interactions, emulsification was applied to mix BO and VGO. In this study, a novel surfactant system, based on Span 80 (SP), Tween 80 (TW), and methanol (ME), was developed to suit the remedy to the immiscibility of BO and VGO. Thermogravimetric analysis (TGA), X-ray imaging, and optical microscopy were employed to examine the thermal behavior, phase stability, and microstructure of the as-developed emulsions. Immersion experiments were conducted with carbon steel (CS) strip coupons in BO/VGO emulsions at 50 °C for corrosivity assessment. Results showed that surfactant ST (a mixture of SP and TW) outranked SP and TW in stabilizing BO/VGO emulsions indicating that surfactants with a middle hydrophilic-lipophilic balance value (approximately 8) are more suitable for BO/VGO emulsions. Adding ME notably prolonged the stabilization time of BO/VGO emulsions. The addition of new mixed surfactant STM (e.g., BO:VGO:STM with a weight ratio of 1:4:0.1) resulted in the longest phase separation starting time (100 min, at 50 °C), one order of magnitude longer than that of BO:VGO as 1:4. The BO/VGO emulsion stayed single-phase for 80, 50, and 20 min when reduced the STM ratio to 0.05, 0.03, and 0.02, respectively. TGA results indicated that hydrogen transfers from VGO to BO reduced the coke formation of BO by 55 % at above 400 °C, highlighting the significance of mixing BO and VGO properly before co-processing. Immersion experiments concluded that the addition of studied surfactants did not show prominent effects on CS corrosion in BO/VGO emulsions.