Avaliação de aditivos baseados em óleo de mamona como desemulsificantes de emulsões tipo água em óleo

Abstract

The petroleum industry has encountered a number of difficulties associated with flow assurance, such as formation of stable water-in-oil emulsions. Emulsified systems represent problems in oil transportation, handling and processing, as there is an increase in fluid viscosity, an elevation of energy expenditure in processing and unwanted water coproduction. These problems could be mitigated by use of synthetic additives, interfacial active compounds and sometimes polymeric in nature, that favor phase separation by a chemical demulsification process. In this work, chemical modifications to castor oil were made in order to develop two classes of demulsifying surfactants, castor oil maleate (MACO) and castor oil maleate and styrene copolymers (MACO-St). All synthesized additives were characterized by Fourier transform infrared spectroscopy, gel permeation chromatography and thermal stability. Five MACO and three MACO-St were evaluated for their demulsifying capacity at concentrations of 100 to 5000 ppm. For this, two samples of national oils, named P1 and P2, were selected. For water-oil emulsions formulation in 30:70 ratio (% by volume), sodium chloride solutions were used at specific concentrations consistent with the nature of oils, from 60 g/L to P1 and 240 g/L to P2. Emulsions were formulated aiming at their stability for a period of 2 hours and average drop diameter set at 10 µm. Bottle test method evaluated the visual phase separability for 2 hours at 60 °C and atmospheric pressure. All samples were centrifuged for total free water separation. Interfacial tension analyzes were performed under the same bottle test conditions and their data were correlated to additive diffusivity by Ward and Tordai equation. The results show that the MACO class exhibited better demulsifying behavior, highlighting the best performing to MACO 5 additive for both oils (90% separability). Copolymers R2 and R3 showed an inversion process in the demulsification at high concentrations. All visual behavior was related to interfacial activity, where all additives reduced water-oil interfacial tension. Long-time asymptotic approximation to transport coefficients were calculated and corroborated the observed demulsifying behaviors.