Basicity Optimization of KF/Ca-MgO Catalyst using Impregnation Method

This research aimed at determining the optimum value between calcination temperature (X1), calcination time (X2) and %wt KF (X3) toward optimum basicity of KF/Ca-MgO catalyst. Approximately 2-4%wt KF was added to the KF/Ca-MgO catalyst using the impregnation method to assist the CaMgO, at 450-550 oC and a calcination time of 2-4 hours. Furthermore, its basicity was analyzed using Tanabe's titration method. The use of Variance Analysis (ANOVA), indicated that calcination temperature (X1) factor achieved the highest basicity of KF/Ca-MgO catalyst, as indicated by its high F-value (16.46262) and low p-value (0.0067). The correlation between each operating variables and the responses were shown in a mathematical equation. The optimization value is estimated by limiting the calcination temperature from 415.9 to 584.1 oC, with a calcination time ranging from 1.32 to 4.68 hours, and %wt KF of 1.3182 to 4.6818 % that obtained 1.18 mmol/g for the optimal catalyst basicity. Copyright © 2019 BCREC Group. All rights reserved


Introduction
Potassium Fluoride (KF) is an alkaline halide molecule with an active and reactive F (fluorine) element, making it easier to rebound with metals. An increase in its effects leads to a higher catalyst activity [1][2][3][4][5]. However, when it is added in surplus, it decreases the catalyst activity. This has been proven by Wen et al. [6] during research by adding KF in CaO, where its addition above 25%, decreased the catalyst ac-tivity. When the amount is large, it covers the surface of the catalyst, thereby reducing its activity. Hu et al. [7] also conducted a study of the addition of KF in several catalysts, such as CaO-Fe3O4, SrO-Fe3O4, and MgO-Fe3O4 in which each had the optimum condition with the addition of KF. This was shown from the acquisition of biodiesel. According to Hu et al. [7], the obtained biodiesel was high assuming the addition of KF reaches 25% for CaO, 35% for MgO, and 10% for SrO.
The dispersion of active metals to the surface of the solid material is capable of expanding the catalyst surface and increasing the number of active sites. Furthermore, when the contact between the reactants and the catalyst increases, the reaction would be more comfortable and faster [8][9][10][11][12][13]. Another aim of using the carrier is to regulate the amount of metal required as well as to increase the catalyst activity and workability [14][15].
The classical method of optimization involves varying one parameter at a specific time while keeping the other constant. However, this method is inefficient as it fails to understand the relationships between variables (reaction time, temperature, molar ratio) and percentage yield [16][17]. Response Surface Methodology (RSM) is a valid statistical technique used to estimate complex processes. Its main advantage is in the reduction of experimental runs number required to provide adequate acceptable information statistically. It is an easy and cheap technique used to gather research results than the classical method [18]. RSM technique has been successfully applied in the field of quality experimental work [19][20][21][22].
The treatment processes/sol-gel used in this research is in three stages, namely impregnation, drying, and calcination. Furthermore, the study aims to analyze the optimum basicity of KF/Ca-MgO catalyst (Y) concerning calcination temperature (X1), calcination time (X2), and %wt KF (X3).

Materials and Methods
Magnesium acetate, calcium nitrate, and citric acid compounds were weighed according to the predetermined calculations and dissolved in 95% ethanol. All three solutions are stirred at 350 rpm with the temperature of sol at 80 ºC until the color became clear. The formed gel was then dried at 110 °C for 6 hours by using an oven. The catalyst obtained was mashed using a mortar and calcined for 3 hours at 550 °C using a furnace. Impregnation of Ca-MgO will be achieved by dissolving KF with %wt between the ranges of 2-4 % in deionized water, after which it was stirred for 1 hour. Furthermore, the absorbed water was extracted from the catalysts surface by exposing it to 140 ºC for 6 hours and calcined at 450-550 ºC with a time range of 2-4 hours. The basicity of KF/Ca-MgO catalyst was further analyzed using the Tanabe's titration method.

Results and Discussion
The experimental design matrix designed using the central composite design method and results of the basicity of KF/Ca-MgO catalyst values are shown in Table 1. The result consists of 16 sets of coded condition expressed in natural values. The design consists of eight factorial, six axial, and three central points. The sequence of the experiment was randomized to minimize the effects of uncontrolled factors.
The Analysis of Variance (ANOVA), used to analyze the basicity of KF/Ca-MgO catalyst was shown in Table 2. The significance between each factor stated in Table 2  The order of this equation is selected by correlating the coefficient of determination (R 2 ) for the mathematical equation is 92.37 %.This value indicates a match between the predicted value and experimental data shown in Figure  1. The linear line shown in Figure 1 is called a regression line, which indicated the best prediction between independent variables (X) against dependent variables (Y). However, it is not perfectly predictable, with a substantial reoccurring variation of the observed points around the fitted regression line (Figure 1). Residual value is defined as the deviation of a specific point from the regression line (the predicted value).
In Figure 2, the 3D surface graph shows the correlation between temperature and time of calcination, with a temperature range of 450 to 550 ºC. Furthermore, it reaches the optimum basicity level, due to the temperature range of 450 to 550 ºC with a change in the catalyst composition, which affects its basicity. This is by the research conducted by Xie and Huang [23] where the basicity value of the catalyst with the addition of KF on the KF/ZnO decreased after when the temperature exceeds 550 ºC. The 3D surface graph in Figure 3 shows that an increase in %wt KF leads to an increase in its basicity. Therefore, its addition affects its level [24]. Figure 4 shows the correlation between the calcination time and %wt KF, which failed to contribute to the increase   . Surface plot of correlation between calcination temperature and %KF on the basicity of catalysts generated at center point of catalyst basicity. The longer the calcination time, the higher the catalyst basicity value, however, it does not give a significant improvement. This shows that the addition of KF support to the CaO-MgO is the dominant factor which helps increase catalyst activity leading to higher basicity [6].

Conclusions
The optimized operating condition of the catalyst production is easily estimated by limiting the calcination temperature in ranges of 415.9 to 584.1 ºC, the time between 1.32 to 4.68 hours, and the %wt KF content ranging from 1.3182 to 4.6818 %. This obtained an optimal catalyst basicity value of 1.18 mmol/g. The correlation between calcination temperature (X1), calcination time (X2), %wt KF (X3) and the catalyst basicity (Y) is shown in Equation (1).