Catalytic oxidation of SO2 by novel Mn/copper slag nanocatalyst and optimization by Box-Behnken design

International Journal of Industrial Chemistry https://doi.org/10.1007/s40090-018-0141-8 RESEARCH Catalytic oxidation of SO2 by novel Mn/copper slag nanocatalyst and optimization by Box‑Behnken design Fattah Rabiee1 · Kazem Mahanpoor1 Received: 18 November 2016 / Accepted: 12 March 2018 © The Author(s) 2018 Abstract In this research, the oxidation of sulfur dioxide (SO2) gases is investigated by Mn/copper slag nanocatalyst (Mn/CS) as a novel catalyst at low temperatures. The removal of SO2 gas from industrial exhaust is important to reduce environmental pollution. The SO2 gas in aqueous solution was oxidized and converted to sulfuric acid as an energy source by Mn/CS in the semi-batch reactor (SBR). The characterization of the catalyst was studied using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FESEM), and Fourier transform infrared spectroscopy (FTIR), simultaneous thermal analysis (thermogravimetry/differential thermal analysis) STA (TG/DTA) techniques, X-ray fluorescence microscopy (XRF) and BET surface area. A Box-Behnken design (BBD) was used for the optimization of influencing factors such as the amount of nanocatalyst, the temperature and the reaction time in the oxidation of SO2. The graphical counter plots and response surface were used to determine the optimum conditions. The results showed that the nanocatalyst had the most significant effect on S O2 oxidation compared with the other two variables. Temperature = 283 K, Mn/CS amount = 6 g/L and Time = 60 min were determined as maximum efficiency for oxidation of SO2. Keywords SO2 oxidation · Mn/copper slag nanocatalyst · Box-Behnken design · Optimization Introduction Sulfur dioxide (SO2) and other gases emitted from specific resources are major pollutants of air. These gases create problems for humans, such as acid rain. There are many processes to reduce sulfur dioxide and other pollutants from the air. Among these methods, the process of removing S O2 at low temperatures is important. These methods require less energy and equipment [1]. Removal of sulfur dioxide from gas emissions using absorption is a common method to reduce air pollution and environmental risks [2]. Activated carbon and zeolite constitute an exciting group of catalysts, which have been presented recently as potential catalysts for the oxidation of SO2 to sulfuric acid [3, 4]. Some transition metal ions such * Kazem Mahanpoor k‑mahanpoor@iau‑arak.ac.ir Fattah Rabiee f‑rabiee@iau‑arak.ac.ir 1 Department of Chemistry, Arak Branch, Islamic Azad University, P.O. Box 38135‑567, Arak, Iran as Mn or Cu have been reported for the catalytic oxidation of SO2 [5]. Mn2+ has shown to be a very active catalyst for oxidation of S O2 in aqueous solution [6]. Copper slag has high mechanical strength and high resistance to temperature changes. It seems to be a suitable material to support Mn ions. In the metallurgical industry, copper slag is produced as a byproduct of the smelting process [7]. Mechanical stability and acidic solution resistance, suitable surface for supporting catalyst on it, non-coagulation and geometric shape and high temperature resistance are the most important properties of copper slag [8]. Optimizing processes reduce costs and increase productivity. Recently, response surface method (RSM) is a mathematical and statistical technique used for modeling and optimization of various processes such as removal of organic and many dyes from different wastewater by different process [9–12]. The Box-Behnken design (BBD) in RSM is an important design, implement used for optimization of processes. BBD prepares comprehensive results and detailed information even for a smaller number of experiments and positive influences of operating parameters on all responses [13]. The main goal of this study is to optimize the efficiency of S O2 catalytic oxidation in 13 Vol.:(0123456789) International Journal of Industrial Chemistry aqueous solution. In current research, a novel Mn/copper slags nanocatalyst prepared by impregnation method and characterized by XRD, FESEM, EDX and FTIR analysis. The conductometry method is a powerful tool for monitoring SO2 oxidation and used for determination of catalyst performance. A Box-Behnken design was selected to study the effects of operational parameter such as temperature, reaction time, and amount of nanocatalyst on the efficiency of the SO2 oxidation process. Experimental procedure Material and apparatuses Copper slag samples were purchased from Mesbareh Company, Kerman, Iran. The copper-slag-based standard is measured using a glass slide. Hardness of copper slag was much more than silica. Density of copper slag was (3.5 g/ cm3). All of the standard gases included N2, O2, SO2 with purity > 99.9% and were purchased from Gas Company, Iran. Other materials were provided by Merck Company. The characterizations of copper slag and Mn/CS were identified using XRD (STOE STADI MP model Germany), FTIR spectrophotometer (PerkinElmer, a spectrum American with the KBr pellet technique), FESEM, EDX (MIRA3-XMU, USA) and XRF (Model: JSX 3201Z). The differential thermal analysis/thermogravimetric analysis (DTA/TG) experiments were carried out in a Netzsch STA 409 C simultaneous thermal analysis (STA). The samples were kept at 100 °C for 30 min, the heating rates were 25 (°C/min) to a final temperature of 1200 °C. BET surface area of materials was determined by N2 adsorption–desorption method at 77 K, measured using a BELSORP-mini II instrument. The samples were degassed under vacuum at 473 K for 12 h before the BET measurement. The measurements of pH value were performed by a pH meter (Metrohm model 827, Switzerland with an electrode of glass). The pH meter was calibrated before use, with standard buffers (pH 4.0, pH 7.0 and pH 9.0). Input and output gas of the process was identified by a flue gas analyzer (KIGAZ 300, Kimo Company, France). The experimental setup is shown in Fig. 1. The pH and conductivity measurement (Metrohm Model 712) was used for checking the progress of oxidation reaction. The reactor temperature was controlled by external jackets and thermo-bath (RW-0525G). Preparation of nanocatalyst and oxidation procedure For activation of copper slag, 100 g of copper slag was added to 500 ml sulfuric acid solution (0.1 M). The sulfuric acid solution was heated to 60° C. The copper slag remained 13 Fig. 1  Schematic diagram of experimental system: (1–3) N2, O2, SO2 gas cylinder, (4) valve; (5) mass flow controller (MFC); (6) mixing chamber; (7) dryer; (8) thermo-bath; (9) thermal-jacket; (10) semibatch reactor; (11) mixer; (12) gas distributor; (13) conductometer; (14) pH meter; (15) gas analyzer; (16) tail gas absorber in the hot sulfuric acid solution to 5 h. Copper slags were isolated from acid solution. Copper slags were washed with distilled water several times and finally washed with ethanol. Then samples were dried at 110 °C (...truncated)