Microsoft Word - ETASR_V12_N5_pp9265-9269 Engineering, Technology & Applied Science Research Vol. 12, No. 5, 2022, 9265-9269 9265 www.etasr.com Kamal & Abbas: Langmuir-Hinshelwood-Hougen-Watson Heterogeneous Kinetics Model for the … Langmuir-Hinshelwood-Hougen-Watson Heterogeneous Kinetics Model for the Description of Fe (II) Ion Exchange on Na-X Zeolite Sanarya K. Kamal Chemical Engineering Department College of Engineering University of Baghdad Baghdad, Iraq sanarya.kamal1507d@coeng.uobaghdad.edu.iq Ammar S. Abbas Chemical Engineering Department College of Engineering University of Baghdad Baghdad, Iraq ammarabbas@coeng.uobaghdad.edu.iq Received: 26 June 2022 | Revised: 14 July 2022 | Accepted: 29 July 2022 Abstract-This study aimed to investigate the kinetics of the anion exchange step of ferrous ions with Na-X zeolite in a temperature range of 20 and 80°C for a period of up to 8 hours. A ferrous sulfate heptahydrate solution was used as a ferrous ion source to exchange with the sodium of the Na-X zeolite. The results showed a change in the physical appearance of the zeolite with the progress of the ion exchange process. The catalyst color was observed with the progress of the ion exchange time and changed from yellow to brown. The ferrous ion exchanged contents increased with temperature and reached 0.519 at 80°C after 8 hours. A kinetic model based on the Langmuir-Hinshelwood- Hougen-Watson model was suggested and developed to describe the ion-exchange process. The proposed model was solved numerically, and the results indicated its ability to describe the experimental results with high correlation coefficients. Finally, the activation energy for the forward reaction was 31590.7J/mole compared to 28105.5J/mole for the backward, and the frequency factors for the forward and backward reactions were investigated. Keywords-Fe exchanged; Na-X zeolite; ion exchange; anion capacity I. INTRODUCTION Zeolites are microporous, crystalline aluminosilicates with a unique mix of physical and chemical properties that make them excellent for a wide range of uses in industry [1-3], agriculture, medicine [4], and environmental pollution cleanup [5]. Na-X zeolites are synthetic zeolites that have been used and investigated in industrial chemicals as ion exchangers, sorbents [5, 6], and catalysts [7] due to their significant void volume of 50% of the frame structure, their ion exchange capacity, shape selectivity, and solid acid sites [8, 9]. The structure of Na-X zeolites is a Faujasite framework with a cage made up Na86[(AlO2)86(SiO2)106].H2O with a ratio of 1-1.5 joined together by bridging oxygen atoms resulting in a 12-ring pore opening and 3-dimensional channel system [10]. The negative charges of AlO4 units are balanced by sodium cations (Na + ) which are exchanged by other cations such as CO 2+ , Cu 2+ , Zn +2 , and Cr +3 ions in the solution [11, 12]. Because of the destruction of the zeolite framework, the exchange capacity of Na-X zeolites makes them particularly effective adsorbents or catalysts. Metal-containing zeolites are especially appealing [13]. Iron-containing zeolites can be used as heterogeneous Fenton or photo-Fenton catalysts [14] and utilized to remove organic pollutants in water treatment plants [15, 16]. Transition metal-containing zeolites are manufactured using a variety of methods including: (i) ion exchange from aqueous solution [11, 17, 18] or solid-state reaction [19], (ii) hydrothermal synthesis [20], and (iii) adsorption and decomposition of volatile organometallic compounds [21, 22]. Ion exchange from an aqueous solution is frequently used to introduce transition metal ions into Na-X zeolites. The mechanics and outcomes are not always straightforward. Transition metal ions may usually replace only a portion of the original cations, which are mainly sodium ions [23]. Ferrous ions (Fe (II)), which are frequently introduced into Na-X zeolites by ion exchange, can coordinate with oxygen atoms more selectively than filling the shell cations and have easy access to other oxidation states [24], so their introduction into zeolites leads to new mechanisms for their function as sorbents [14] and catalysts [25]. However, because ion exchange is reversible, once adsorbed nuclides in water are exchanged by other cations (Na + , Ca 2+ , Mg 2+ , etc.) [26]. This research aimed to study the effect of temperature and time on the Fe (II) exchange process with Na on the X zeolite. A heterogeneous kinetics model was developed to describe the exchange process based on the heterogeneous Langmuir- Hinshelwood-Hougen-Watson (LHHW) approach. II. EXPERIMENTAL PROCESS The zeolite used was the type Na-X zeolite (commercial grain, Si/Al ratio 1.75, pore volume 0.2733cm 3 /g, surface area 450m 2 /g, initial Na=14.719%), which was crushed and then sieved with 200 mesh strainers to homogenize its size. 40g of zeolite were weighed and then washed with distilled water. Afterward, they were washed with deionized water at various Corresponding author: Ammar S. Abbas Engineering, Technology & Applied Science Research Vol. 12, No. 5, 2022, 9265-9269 9266 www.etasr.com Kamal & Abbas: Langmuir-Hinshelwood-Hougen-Watson Heterogeneous Kinetics Model for the … times, the Na-X zeolite was filtered by filter paper (Chm F1002 filter paper,150mm, penetration range (7-8µ m)), went through a Buckner funnel, a vacuum pump, and then was dried at 60 o C overnight in an oven (Memmert, Sigma, England UK). Na-X was mashed by crushing until powder again. The activation process was carried out using a 0.1N chloride acid solution (36.5% HCl, USA) to clean the pore surface of zeolite and remove impurities. The cleaning HCl acid solution was mixed with Na-X zeolite in a 10:1 ratio (v/w ratio) and stirred with a hot plate magnetic stirrer (Thermo Fisher Scientific Inc, USA) for 1 hour at 250rpm at 25°C [27]. The HCl solution was separated from the Na-X zeolite using filter paper, washed with distilled water, and stopped until a neutral pH=7 was obtained. The activated Na-X zeolite was dried at 60°C overnight. The calcination of the cleaning Na-X zeolite samples was obtained at 550°C for 3 hours with a furnace (Carbonite, Sigma, England UK). After cooling, the samples were stored in a desiccator to prevent water absorption. Then, Na-X zeolite containing a high sodium weight percentage (14.719%) was exposed to an ion exchange procedure with ferrous sulfate heptahydrate (FeSO4∙7H2O, India) to replace the sodium from Na-X zeolite. This procedure was carried out in beakers with a volume of 0.5lt, under controlled temperatures (20, 40, 60, and 80°C) and were stirred again. 5g of dried Na-X zeolite were added to 100ml of a 0.319M solution and maintained at the required temperature with constant stirring at 300rpm for 8 hours. Subsequently, exchanged Na-X zeolite samples were taken from the ion-exchanged solution and filtered, washed several times with distilled water to remove the Fe (II) that was not exchanged, and taken to an oven to dry at 60°C overnight. The samples were calcined in a furnace at 550°C for 3 hours, and were left to cool inside desiccator until they reached room temperature. The concentration of Fe (II) in the exchange solution was measured using atomic absorption spectrophotometry (VarianAA240FS, Australia), and the amount of exchange Fe (II) was determined. The atomic absorption spectrophotometry was tested at North Gas Company (Ministry of Oil, Iraq). III. RESULTS AND DISCUSSION The ion exchange reaction was carried out between Na-X zeolite and ferrous sulfate solution with a stoichiometric amount of Fe/Na at different temperatures for a processing time up to 8 hours. At first, the color of the catalyst was observed with the progression of the ion exchange process. A darker yellowish-brown product was generally obtained with increasing ion-exchange time and processing temperature. Figure 1 depicts three zeolites: original Na-X zeolite, activated Na-X zeolite, and X zeolite after Fe (II) ions were exchanged for 8 hours at 80°C. The color change of the treated zeolite indicated that Fe-13X was formed. (a) (b) (c) Fig. 1. Color of (a) Na-X Zeolite, (b) Na-X activated, and (c) Modified Fe-13X for 8 hours at 80°C. The amount of Fe (II) conversion versus time and temperature by ion exchange reaction is shown in Figure 2. Figure 2 shows that the Fe (II) ion exchange (conversion) increased with the reaction time and temperature, and the results showed a rapid increase during the first 0.25h, after which the conversion increased slowly and reached a similar to the equilibrium state at the end of the studied time. The conversion accelerated with the reaction time as the temperature increased. The conversion was 0.179 after 0.25h of reaction at 20°C, whereas it was 0.415 after the same period at 80°C, while the higher required value of Fe (II) conversion was 0.519 obtained after 8h of ion exchange at 80°C. These results agree with the Cobalt exchange on Na-X zeolite previously found in [28]. Fig. 2. Fe (II) conversion on the Na-X zeolite versus time at different temperatures. Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetics model assumes that before the surface reaction, the Fe (II) is adsorbed onto the catalyst surface. The final stage of the mechanism involves the desorption of Na ions. 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