Remoção de hidrocarbonetos da água produzida de petróleo por meio dos processos de coalescência e adsorção

Abstract

An important question to the oil production industry is the amount of water produced (PW) generated during the operation of its industrial processes, being considered the largest stream of effluents and of complex composition presenting high salinity, suspended solids, chemical additives, heavy metals, considerable oil and grease (O&G) content and other contaminants. The O&G is a parameter that deserves attention because the discharge of PW is supervised by regulatory agencies that take this mainly criterion. This work aimed to evaluate the potential of the coalescence and adsorption processes in the treatment of produced water supplied by Petrobras, Pilar-AL Unit, using an integrated system composed of a horizontal bed coalescer in combination with a fixed bed column. The parameters evaluated in the coalescer were the flow velocity and the bed type. The materials evaluated to compose the coalescedor bed were: coconut fiber (Cocos nucifera), considered a byproduct of the industry, and loofa sponge (Luffa cylindrica), an easy material to be found in the Northeast region of the Brazil. The fixed bed column (adsorption process) used biochar (produced by pyrolysis) and activated carbon (using chemical activation method) produced from ouricuri (Syagrus coronata), a regional raw material. The biomasses used (coconut fiber, loofa sponge and ouricuri, as well as biochar and activated carbon) were characterized by the following techniques: moisture, thermogravimetric analysis, energy dispersive X-ray (EDX), X-ray diffractometry and Fourier transform infrared spectroscopy (FTIR). Initially, the type of bed and the flow rate of the coalescing bed were evaluated: 40, 60 and 80 L/h, corresponding, respectively, to the superficial velocities 5.8; 8.7 and 11.5 m/h in relation to the diameter of the coalescer. The O&G at the coalescer inlet and outlet were evaluated, and the oil and grease removal efficiency was determined. Coconut fiber and 40 L/h flow rate showed higher efficiency, removing around 80% of O&G. Then, as aforementioned, activated carbon were produced from ouricuri, and the activation process used phosphoric acid, sulfuric acid and sodium hydroxide. The adsorptive capacity evaluation experiments were carried out in a finite bath system under the following conditions: Coil = 120 mg/L, temperature = 30ºC, Cbiomass = 2 g/L, rotation = 160 rpm and time = 2h. The results showed that the activated carbon with NaOH presented higher adsorptive capacity (q = 9,67 mg/g). Once the best bed type and coalescer feed rate were defined, in addition to the fixed bed activated carbon type; a set of experiments using an integrated system (coalescer and fixed bed column) was carried out. The experimental design consisted of a complete factorial system (23) for the experimental runs in the integrated system, where the evaluated variables were: type of carbon (biochar and activated carbon with NaOH), mean particle diameter (0.149 - 0.3 mm and 0.3 - 0.5 mm) and fixed bed column flow rate (2.2 and 4.4 L/h). The best result was obtained with the experiment that used the biochar, with particle diameter between 0.149 - 0.3 mm and flow rate of 4.4 L/h, obtaining an O&G removal of around 84% (confirming that the three variables studied influence the process efficiency (particle diameter and the combination of flow and coal type). The results showed that the integration of adsorption coalescence processes using biomass and biochar can be an alternative for the treatment of petroleum produced water, meeting the environmental requirements for disposal and reinjection.