62ª Reunião Anual da SBPC
B. Engenharias - 1. Engenharia - 12. Engenharia Química
ELECTROCHEMICAL TECHNOLOGY FOR REMOVING PETROLEUM HYDROCARBONS FROM PRODUCED WATER GENERATED BY BRAZILIAN PETROCHEMICAL INDUSTRY
Carlos Alberto Martínez-Huitle 1
Daniel Araújo Carvalho 1
Jéssica Horacina Bezerra Rocha 1
Gustavo Rodrigues de Oliveira 1
Aline Maria Sales Solano 1
Djalma Ribeiro da Silva 1
1. Departamento de Química - Universidade Federal do Rio Grande do Norte - UFRN
INTRODUÇÃO:
Produced water (PW) is considered to be one of the largest waste streams in the petroleum, oil and gas industry. The drilling and extraction operations that are aimed to maximize the production of oil may be counterbalanced by huge production of contaminated water (called PW) with pollutants, such as heavy metals, organic compounds (Benzene, toluene, xylene, phenol, halogenated aromatic compounds, chloroform and trichloroethylene), and dissolved/suspended solids. Therefore, considerable studies have been conducted to investigate new techniques in order to remove these compounds from PW. Electrochemical oxidation (EO) of refractory effluents has received a great deal of attention thanks to its attractive characteristics, such as versatility, energy efficiency, amenability of automation and environmental compatibility. Few studies have reported the results about the application of electrochemical technologies for removing contaminants from oil industry wastewaters, but no attempts to degrade organic pollutants from PW by EO have been reported yet. In this context, the present study aims to investigate the efficiency and energy requirements of a DSA anode (Ti/Ru0.23Ti0.66Sn0.11O2) by using EO process for removing hydrocarbons from PW produced by petrochemical industry.
METODOLOGIA:

PW samples were supplied by Petrobras plant in Rio Grande do Norte. Measurements of each organic pollutant in PW samples were carried out by gas chromatography (GC) technique and solid phase micro-extraction. GC results showed that PW samples contain approximately 25-30 mg dm-3 of benzene, toluene, ethyl benzene, xylene, and 5 mg dm-3 of phenol. The bulk electrolyses were performed in a one-compartment electrolytic flow cell with a Ti/Ru0,23Ti0,66Sn0,11O2 electrode as anode, while stainless steel bars as cathodes. Electrodes were fabricated in-house on circular Ti mesh plate by calcinations of IrCl4 and TiCl2 precursors in an O2-saturated atmosphere. EO experiments were performed applying a constant current density (8.9 mA cm-2) by using a power supply. PW sample (5 dm3) was passed through glass reservoir and circulated through the electrolytic cell by a centrifugal pump, in order to study the influence of recirculation flow rates (0,25; 0,5; 0,8 and 1,3 dm-3 h) in the removal efficiency. Key points for the development of clean methodologies are the energetic and economic aspects; for that, the energy consumption for the removal of one m3 of pollutants was calculated; whereas taking into consideration an electrical energy cost per kWh, the process expenditure was also estimated.

RESULTADOS:

The anodic oxidation of organic pollutants from produced water generated by petroleum exploration of the Petrobras plant-Brazil was studied using a Ti/Ru0.23Ti0.66Sn0.11O2 electrode. Under galvanostatic conditions (j=8.9 mA cm-2), it was observed that the performance of the electrode material is influenced by flow rate as it was shown by GC analysis. It was found that the organic pollutants degradation, using different flow rates (0.25, 0.5, 0.8 and 1.3 dm-3 h), achieved distinct removal efficiencies (98, 97, 95 and 84% were achieved, respectively). Importantly, under the same conditions, Ti/Ru0.23Ti0.66Sn0.11O2 showed poor degradation of phenol and ethyl-benzene: 20-47% (at 0.25, 0.8 and 1.3 dm-3 h) and 17-47% (at 0.25, 0.5, 0.8 dm-3 h), respectively. Results showed hat the pollutant concentrations contained on PW were rapidly dropped, forming a large number of reaction intermediates (phthalic and maleic acids). Complete elimination of pollutants was obtained after 0.5-2.5 h of electrochemical treatment. GC analysis did not reveal traces of organochlorinated compounds. Energy consumption (kWh m-3) decreases in an almost linear fashion with flow rate. Therefore, this technique could be economically suitable for waste pre-treatment aiming to remove organic pollutants from PW.

CONCLUSÃO:
Electrochemical process to remove organic pollutants from PW samples was investigated by using a DSA electrode. The present findings indicated that the oxidation rate was insignificantly affected by higher electrolyte flow rate, thus suggesting that direct oxidation of hydrocarbons on DSA anode is the main mechanism. Other strong electrogenerated oxidants, such as .OH and Cl- formed by supporting electrolyte (NaCl), can be also participating in the EO, therefore increasing the efficiency of oxidation process. Energy consumption measured depends largely on the applied current density, and a decrease of energy was observed when an increase in the flow rate was attained. These data showed the applicability of electrochemical technology for the treatment of organic petroleum wastewater, and they point to the DSA anode as an alternative for pollutants removal from PW generated in petrochemical industries. Further experiments are in progress in order to improve the current efficiency and reduce the charge required for complete oxidation. Other parameters such as pH, chemical oxygen demand, total organic carbon and oxidation intermediates during electrochemical process will be studied in a near future.
Instituição de Fomento: Universidade Federal do Rio Grande do Norte - UFRN and PETROBRAS.
Palavras-chave: Electrochemical technologies , Produced water, Environmental protection alternatives.