Calculation Values of potential Stickiness (S*) and Apparent Activation Energy (AAE) from Adsorption of Some Aromatic Carboxylic Acids on the Surface of a New Adsorbent Substance

Abstract

This study includes calculation of the potential stickiness (S) and apparent activation energy (AAE) by the adsorption process of some aromatic carboxylic acids using sand (clay) as a new adsorbent material. This clay was collected from dust storms coming to the city of Mosul. The obtained results showed that physical adsorption which is achieved by applying the modified Arrhenius equation through the values of (S *) and (AAE) which have low values and bear a negative charge is preferable. Adsorption process occurs in two-step mechanism. The effect of the concentration of the acidic solution, temperature and the substituted groups SO3, NO2, OH, NH2 on the aromatic ring) was studied to clarify the nature of the association between organic carboxylic acid anions and inorganic metal oxides to form a complex surface model. The study concluded that the values of (S *) for all acids were less than one and they were more than the value of zero. Also, the values of (AAE) gave an indication that the adsorption process is exothermic and spontaneous. The presence of water molecules and (H) ions in solution is very important to change the nature of the clay surface. Keyword: Potential stickiness, apparent activation energy, aromatic carboxylic acids, new adsorbent material. Introduction: Adsorption is an effective and important method to remove pollution. It is simple and low-cost [1][2]. The substituted benzoic acids (5SSA, ONBA, OABA) are used in chemical industry, these acids are considered harmful substances for humans [3] [4] [5]. As an adsorbent material, Clay, consists of poly metal oxides from a rocky source [6] and different inorganic materials [7]. Metal oxides on the clay surface contain negative polar charges [8] as active sites that attract positive ions by absorbing them through physical forces. This type of attraction is called physical adsorption, while the chemical absorption occurs when the surface contains unsaturated electrons. Knowledge of adsorption mechanism is important for designing physical type of adsorption systems, through which absorbent material can be recovered and the process accomplished in an easy and Ind Calculation Values of potential Stickiness (S*) and Apparent Activation..... 78 inexpensive way. The (AAE) values represent the desired degree of the optimum temperature to achieve the complete adsorption process. Whether it occurs spontaneously or not and whether the adsorption process is endothermic or exothermic, the positive or negative values of (AAE) give a good description of the thermodynamic condition for the adsorption process. Materials and Methods : 1The chemicals were used without further purification and they were supplied by Fluka and BDH companies. 2The new clay was used as an adsorbent material. This clay was collected (using clean and dry plastic containers) from dust storms that hit the city of Mosul. The clay has been sifted (filtered out) using a sieve (75) micrometer and the surface area was (3434) cm/gm. It was measured using the "plaine device" at the Technological Institute in Mosul. The clay components (listed in Table 1) were measured using X-rays Appearance-Type (pan analytical 7602 EA, Almelo) at Badush Cement Factory. Table 1. The components of clay 8.5 pH 37.36% CaO 19.71% SiO2 5.91% AL2O3 3.47% MgO 1.89% Fe2O3 0.48% SO3 3Preparation of solutions: aSolutions of three acids (5SSA, ONBA, OABA) at different concentrations using a mixture solvent (5% absolute ethanol and 95% distilled water) have been prepared. bStandard solution of (0.1), (0.01) M sodium hydroxide by titration with (potassium hydrogen phthalate) using (phenolphthalein) as indicator has been prepared. 4Study the adsorption process using batch method. 5A programmed water bath equipped with a vibrator at speed of 100 cycle/ min was used. 6An equal amount of adsorbent in the adsorption process for all concentrations was used. 7-The optimum conditions for adsorption were as follows: A-The weight of clay used =0.06 gm. B-Concentration of acids =5x10 molar C-The favorite pH = natural pH for each acid D-Contact time for each acid with percentage of adsorption is shown in table 2. Table (2). Contact time and percentage of adsorption for acids on clay surface at 25 C° Ind Calculation Values of potential Stickiness (S*) and Apparent Activation..... 79 % Adsorption Contact time (min) Acid 76 40 5SSA 92 30 ONBA 74 40 OABA EThe adsorption process was studied at temperature ranging from (20-60) C° to obtain values of (S). FThe concentration of acid remaining in solution after the adsorption was calculated using spectrophotometric method. GThe amount of ions covered on the surface of the sorbent material was calculated at each concentration using different temperatures (20-60) ° C. HThe modified Arrhenius equation [9] that was applied, can be written as follows: S* = (1 θ) e Ea RT (modified Arrhenius equation) Ln (1 – θ) = ln S* Ea RT When draw Ln (1-θ) at (x) axis and 1 T at (y) axis gives intercept (Ln S*) while slope equal −Ea R which gives (AAE). 8The instruments: aVibratory water path type (julabo sw23). bElectric oven type (memmert). cDouble-beam spectrophotometer (schimaduz) model UV-1800. dThe surface area of the clay was measured using ( a plain) device and the amount of surface area was ( 3434 ) cm / gm . Results and Discussion: The modified Arrhenius equation (MAE) [9] depends on the amount of ions covering the surface at any concentration by using different temperatures. When experimental adsorption results are applied to (MAE), we obtain a value of (S *) through which the type of chemical or physical adsorption prevails. In addition, the value of (AAE) provides a qualitative description of the thermodynamic state of the adsorption process. The value of (S *), which represents the potential stickiness to the surface, is the preferred (adsorbed / adsorbent) system function of the range (o 1, it means that the adsorbent substance is non-sticking on the adsorbed substance. If S* =1, it means that the liner relationship of stickiness between the adsorbed and adsorbent is predominated for a mixture of physical and chemical adsorption. S*=0 stickiness has occurred on adsorbed material and chemical absorption is predominant. If 0 < S , this represents the preferred stickiness of the adsorbent material on the clay, and the physical absorption is predominant. Ind Calculation Values of potential Stickiness (S*) and Apparent Activation..... 80 In this study, the positive and negative values of (AAE) do not represent the areal activation energy, but rather give a description of the thermodynamic state of the adsorption process, since the acid ions prefer adsorption at low temperatures and the adsorption process is exothermic by nature .The low negative values of (AAE) give the conclusion that the adsorption process is a controlled diffusion process. The best value for (S) is shown when it is less than one. This indicates that the physical adsorption of ions occurs on the surface. In this case the adsorbent substance can be retrieved and used again, and this is economically important. Tables (3 – 5) Values of (S*) and (AAE) for (5SSA),( ONBA), (OABA) at different concentrations on the clay surface Table3 (5SSA) R AAE KJ/mole S* Conc(M) 0.9698 -21.100 142×10 0.005 0.9739 -2.646 0.1474 0.007 0.9529 -1.472 0.1560 0.009 0.9824 -1.168 0.3109 0.011 0.9979 -1.085 0.9078 0.013 Table 4(ONBA) Table 5(OABA) The results in tables (3-5) which refer to acids (5SSA,ONBA,BABA) at different concentrations. The used temperatures were ranged from (20-60)C at each concentration. Depending on the obtained results, the following conclusions can be reached: 1. The predominance of the physical adsorption in the adsorption process and this is preferred for the ease of recovery of the absorbent material [9][10]. 2. The increase in the concentration of the acid solution increases the values of (S*). This means that the conversion of the physical adsorption into a mixture of physical and chemical adsorption is at the highest concentration when the value of (S*) is one. Diluting the acidic concentration makes the value of (S*) very low because the ions have free movement within the solution (they easy move to the surface of the absorbent R2 AAE(Kj/mole) S* Conc(M) 0.97 -29.488 611×10 0.005 0.93 -4.568 0.0480 0.007 0.98 -2.547 0.1590 0.009 0.99 -1.397 0.3078 0.011 0.99 -0.961 0.4043 0.013 R AAE(Kj/mole) S* Conc(M) 0.99 -7.423 0.0125 0.005 0.99 -2.749 0.1460 0.007 0.99 -1.654 0.2878 0.009 0.99 -1.192 0.3905 0.011 0.99 -0.835 0.4885 0.013 Ind Calculation Values of potential Stickiness (S*) and Apparent Activation..... 81 material (clay) as well as, the availability of the active sites on it which means that there is no competition between ions to adsorption on the surface. Thus the chemical adsorption becomes predominant. 3(AAE) values are negative and low, and they decrease as the concentration of the acid solution is increased by converting it from the highest negative values to the negative values that are close to the zero values. These results indicate that the adsorption process in the case of the acidic dilute solution (0.005) M prefers low temperature and ultimately it will be exothermic. This is because the ionic, molecular reaction and interferences are decreased in the case of the dilute acidic solution, then the adsorption process occurs spontaneously. Whereas in a concentrated acid solution (0.013) M , these interferences are increased, which leads to a decrease in the negative values of (AAE). This indicates the need for the adsorption system to have a low energy to complete the adsorption process, so that it turns from high spontaneously to low one. In addition, it converts from an exothermic to an endothermic process [9]