Projeto e construção de um ozonizador pela combinação de energia elétrica fotovoltaica com eletrólise alcalina aquosa

Abstract

Ozone is a substance with a high oxidation potential (2.07 V), and its instability with a short half-life of 20 minutes in distilled water gives it the characteristic of being non-residual and advantageous in many industrial applications. Alkaline aqueous electrolysis is a relatively simple process in the production of high-purity oxygen (98%), which serves as raw material for ozone production in corona reactors. Considering renewable energy sources like photovoltaic solar as the power supply for these two reactors (electrolytic and corona), ozone production becomes sustainable, advantageous, and can be carried out at ambient pressure and temperature. For this reason, this work aimed to study ozone production by electrolysis in a portable corona generator using renewable energy from photovoltaic solar under the meteorological conditions of the Triângulo Mineiro region (MG). An electrolytic cell was designed with a volume of 1.13 L, using 316 stainless steel electrodes separated by a Nafion® membrane, immersed in potassium hydroxide (KOH) solution at concentrations ranging from 1.0 to 8.0 mol.L-1 in 1.0 mol.L-1 intervals. The results revealed that the best conditions for volumetric oxygen generation (3.51 mL/J and 481.56 mL/min) occurred at a concentration of 7.0 mol.L-1 with three electrolytic cells in series, limiting the current below 20 A. The electrical energy used in the process was generated by a 365 Wp photovoltaic solar panel, connected through a 40 A charge controller to a 45 Ah automotive battery. Productions of oxygen (O2), hydrogen (H2), ozone (O3), relative humidity, internal and external temperatures, current, and electrical voltages in the reactors were monitored using electrochemical sensors. Sensor signals were sent to the cloud via WiFi using ESP32 programmable processors with the MATLAB ThingSpeak platform. The equipment and reactors were mounted on a steel mobile platform measuring 140x100 cm at the base and 124 cm in height, transportable by a medium-sized pickup truck. Ozone generation was evaluated using calibrated electrochemical sensors with volumetric iodometry. The ozone sensor showed low precision, indicating a need for studies to improve sensitivity and data analysis methods such as using Neural Networks. It was found that the cylindrical shape with two concentric hollow tubes facilitated gas connections compared to reactors with parallel flat plates. The gas volume produced was proportional to the reactor volume and the level of high electrical voltage applied, resulting in production consistent with literature values (25 g/h and 90 W of electrical energy consumption) according to the physical dimensions of the reactor (3" diameter and 30 cm length). Finally, it was concluded that the designed system produced ozone from oxygen extracted from the air at a proportion of 17% compared to oxygen generated in the electrolytic cell. The financial cost of the reactor ($ 27 as of June 2023) remained within expectations, demonstrating the economic feasibility of the constructed mobile prototype.