New Octyl-modified Aleppo Bentonite as Support in Gas Chromatographic Analysis

 

Abdul Aziz Ramadan¹*, Saad Aantakli², Ahmad Birouty

Department of Chemistry, Faculty of Sciences, University of Aleppo, Syria

 

ABSTRACT:

A new Octyl-modified Aleppo Bentonite support was developed. The method is based on the thermal treatment of Aleppo Bentonite which have diameter particles (150-250 mm) and washed by concentrated HCl (B_A). B_A was chlorinated by dimethyldichlorosilane, then, the resultant product was reacted with Griniard reagent as octylmagnesium bromide to obtain (B_AOctyl). The surface properties of B_A and B_AOctyl were characterized by nitrogen adsorption at 77K (BET) and differential thermal analysis (DTA). It was found that, the BET surface areas (S_BET) were 6.39 and 2.71 m²/g, the total pore volume v_p were 0.0161 and 0.0072 mL/g and the mean pores radii r_a were 50.39 and 53.14 Å, respectively. Twenty eight hydrocarbons components in gasoline were determined by using B_AOctyl as support in GC. The principle gasoline components groups (total C₅ to total C₁₀) percent were presented as follows: 20.265%, 20.691%, 24.383%, 17.110%, 11.595% and 1.611% (95.655%). The developed support is applied for the determination of some hydrocarbons compounds (as automobile gasoline). The column of B_AOctyl provided excellent symmetrical peaks and less retention time compared with B_APhenyl-modified support.

 

 

 

 

INTRODUCTION:

Aleppo Bentonite is rocky clay which consists of 47% SiO₂, 14.4% Al₂O₃ and some other oxides as Fe₂O₃, MgO, CaO, Na₂O and others[1,2]. The thermal treatment causes decreasing its specific surface area with increasing in the temperature[3,4]. Bentonite clays are used in many industrial processes[5,6], and it can be used as chromatographic supports in gas chromatography to separate many mixtures after grafting as: lidocaine hydrochloride, carbinoxamine maleate and chlorphenramine maleate in some pharmaceuticals on grafted Bentonite with silicon OV-1 as support[7]. Bentonite is used also as stationary phase in thin layer chromatography to separate some metal ions and vitamins B₁, B₆, B₁₂ [8].

 

The surface areas (S_BET), the mean pores radii (r_a) and the total pore volumes were determined[9,10]. Gas chromatographic analysis (GC) of automobile gasoline using phenyl-modified Aleppo Bentonite was studded. The particles of Aleppo Bentonite which have diameter particles (150-250 mm) were thermal treatment and washed by concentrated HCl (B_A). B_A was chlorinated by dimethyldichlorosilane, then, it was reacted with Grignard reagent as phenylmagnesium bromide to obtain (B_APhenyl)[11]. The surface properties of B_A and B_APhenyl were characterized by nitrogen adsorption at 77K and differential thermal analysis (DTA). B_APhenyl was applied to separate thirty four hydrocarbons components in automobile gasoline in (GC)[11].

 

This paper a new support from Octyl-modified Aleppo Bentonite was developed for determination of automobile gasoline using gas chromatographic analysis (GC).

 

MATERIALS AND METHODS:

Instrumentation:

The chromatograms were obtained by using a GC-9A gas chromatograph equipped with a flame ionization detector (FID) and chromatopac C-R3A printer (Shimadzu Co.), 1 μL syringe (Hamilton Co.). Surface area and pore size measurement (BET) were recorded using Micromeritics Gemini III 2375 under nitrogen atmosphere (USA). Differential thermal analysis (DTA), LINSEIS type STA PT-1600, Germany and pH meter from Radio meter company model Ion Check were used. Diluter pipette model DIP-1 (Shimadzu), having 100 μL sample syringe and five continuously adjustable pipettes covering a volume range from 20 to 5000 μL (model PIPTMAN P, GILSON), an ultrasonic processor model powersonic 405, electronic balance (Sartorius-2474; d=0.01 mg), ash furnace at 100-1200^oC type Nabertherm and oven at 50-350^oC for treatment Bentonite were used.

 

Reagents and materials:

Tetrahydrofuran, dichloromethane, dimethyldichlorosilane, 1-bromooctyl and magnesium metal were purchased from Merck, Germany.

 

RESULTS AND DISCUSSION:

Thermal treatment and Acidic washing Bentonite:

Bentonite was crushed to obtain small granules, which have diameter particles (150-250 mm), and was thermally treated by two steps at 600 ^oC then at 1000 ^oC, after each step was refluxed with 6N HCl at boiling point for 20 hours to remove soluble oxides especially iron oxide. Then it was washed several times with distilled water and dried at 120˚C for 3 hours (B_A).

 

Acid washed Bentonite chlorination:

30 g of washed Bentonite (B_A) is dispersed in 250 mL of dichloromethane and 10 mL of dimethyldichlorosilane. The mixture was left under reflux during 3 hours. The solvent was evaporated and the residue was dried at 280°C during 3 hours. The chlorinated product was kept under inert Nitrogen atmosphere (B_ACl), as the equation:

 

      B_A                   dimethyldichlorosilane                      B_ACl

 

Octyl-modified Aleppo Bentonite (B_AOctyl):

Grignard reagent was prepared from reaction 17.6 mL of 1- Bromooctyl with 2.4 g of clean and dry magnesium in 200 mL of anhydrous tetrahydrofuran (THF) as the equation:

 

 

The solution of Grignard reagent was added to chlorinated Bentonite (B_ACl) under inert atmosphere (N₂). The mixture was allowed to reflex for 3h. Then the contents were allowed to cool. The product was filtered and washed with methanol and dried at 105 °C for 2 hours (B_AOctyl), as the equation:

 

Surface Properties of B_A and B_AOctyl:

Specific Surface areas of B_A and B_AOctyl were determined by the nitrogen adsorption at 77K (BET) [12-15]. For the determination of textural properties, the adsorption was carried out until near saturation (p/p_o1.0), then the desorption was completed until closure of the hysteresis loop. Representative adsorption-desorption isotherms of nitrogen for B_A and B_AOctyl are shown in Figure 1. The isotherms are II and IV type of SING and BDDT classifications, which indicate the presence of mesoporous structure. Application of the linear BET equation to the nitrogen adsorption data was as the follows:

 

^y=^m.x+ⁱ;

 

where y is x/[v_s(1-x)], x is p/p_o , v_s is adsorbed volume of N₂, C_BET is BET constant and V_m is the monolayer capacity (cc/g STP). These equations were obtained within the range of relative pressures (0.02 – 0.25) as the follows: y=0.680x+0.0015 (R²=0.9993) and y=1.610x+0.0030 (R²=0.9995) for supports B_A and B_AOctyl, respectively.

 

BET specific surface areas (S_BET) were 6.41 and 2.71 m²/g. The total pores volume V_p (0.0161 and 0.0072 mL/g) was determined from the adsorbed volume at p/p_o = 0.95 in the liquid form and the mean pores radii r_a (50.23 and 53.14 Å) was determined from the equation: r_a = 2.10⁴.V_p/S_BET, for supports B_A and B_AOctyl, respectively. The variation of specific surface area (S_BET, m²/g), total pores volume (V_p , mL/g), mean pores radii (r_a, Å) and (C_BET) causing by grafting modification, as seen in Table 1.

 

Table 1: Surface properties of B_A and B_AOctyl.

Support	SBET, m2 /g	Vp , mL/g	ra, Å	CBET
BA	6.41	0.0161	50.23	454.3
BAOctyl	2.71	0.0072	53.14	537.7
BAPhenyl	4.21	0.0155	73.49	357.9

 

 

Fig. 1. Adsorption-desorption isotherm of nitrogen at 77K on B_A(a) and on B_AOctyl (b).

 

It was noticed that the specific surface area and the total pores volume for B_A and B_AOctyl decreased from (6.41 m²/g and 0.0161 mL/g) to (2.71 m²/g and 0.0072 mL/g) and the mean pores radii increased from 50.23 Å to 53.14 Å, respectively, (Table 1).

 

In comparison with B_APhenyl-modified column [11], the S_BET, V_p and r_a values of B_AOctyl-modified column decreased from 4.21 m²/g, 0.01547 mL/g and 73.49 Å to 2.71 m²/g, 0.0072 mL/g and 53.14 Å, and C_BET values increased from 53.14 Å to73.49 Å, (Table 1).

 

Differential Thermal Analysis (DTA):

A useful method for the characterization of B_A and B_AOctyl was measured by differential thermal analysis (DTA) technique [16-18] in air atmosphere using 40 mg Bentonite with α-Al₂O₃ as reference and heating rate 10^oC/min. Figure 2 shows that, the DTA trace of the B_A and B_AOctyl. It exhibited two endothermic peaks. The first appears at 145^oC, which is corresponding to the loss of water of hydration. The second, which occurred at about 600^oC, is related to the burning of hydrocarbon in B_AOctyl support.

 

Fig. 2. Differential thermal analysis curve for B_A (1) and B_AOctyl (2) (in air atmosphere using 40 mg bentonite with a-Al₂O₃ as reference and heating rate 10^oC/min).

 

Hydrophobicity:

Hydrophobicity estimation before and after modification, by comparing the dispersiblility of the B_A and B_AOctyl in water and n-hexane [19,20]. Figure 3 showed that the B_A dispersing was in water layer only. By opposition, the presence of hydrophobic alkyl group on the external surface of B_AOctyl, made the B_AOctyl deposited in organic phase at the n-hexane-water.

 

Fig 3 . B_A (right) and B_AOctyl (left) dispersed in water/ n-hexane (organic phase) system.

 

Variation of the logarithm of retention volume in function of the reverse of absolute temperature log v_s=f(1/T):

The modification superficial structure of Octyl-modified Aleppo Bentonite (B_AOctyl) compared to bare one B_A was studied by "inverse gas chromatographic method" in the range 50-110ºC and column dimension (100cm×4 mm) using dichloromethane (polar), benzene (moderate polarity) and n-pentane (non-polar) as auxiliary solutes. The plotted relationship log v_s=f(1/T) shown that, a decreasing of volume retention was noticed with grafted Bentonite by modification octyl group compared to bare B_A, see Fig. 4. Figure 4 shows that the modification by non-polarity material (as octyl) has led to greater retention times of non-polar materials as n-pentane (curves 2 and 4), whereas polar materials as dichloromethane have only slightly weakened retention times (curves 5 and 6). This figure also shows that the three auxiliary solutes approve the modification of the superficial structure of the Bentonite B_A support surface.

 

Fig. 4. Variation of log Vs = f(1/T) on (100 cm × 4 mm) packed columns using bare Bentonite B_A (1, 3, 5) and Octyl-modified Aleppo Bentonite B_AOctyl (2, 4, 6); benzene (1, 2); n-pentane (3, 4); dichloromethane (5, 6).

 

Identification of gasoline:

Select the gasoline to test for the validity of the B_AOctyl support and compare its results with the Phenyl-modified Aleppo Bentonite (B_APhenyl) support [11]. This method has been developed for the determination of gasoline components by gas chromatography with flame ionization detector (FID) using Octyl-modified Aleppo Bentonite (B_AOctyl) as support. The chromatographic conditions for analysis are as the following: analytical copper column (100 cm × 4 mm), packed with B_AOctyl, programmed column temperature between 35-215ºC, with increasing temperature rate 3ºC/min, FID, flow rate of N₂ carrier gas 35 mL/min, the injection volume 0.2 μL and injected port temperature 190ºC, the gasoline chromatogram was shown in Fig. 5. Comparing these results with a column filled by B_APhenyl [11]. It was found that the retention times have decreased clearly, especially for the aromatic components. The analytical results were characterized by high precision, accuracy and reproducibility. The components groups (C₅ –C₁₀) of gasoline was observed in Table 2.

 

Table 2: Carbon Number of components groups in gasoline by GC analysis using Octyl-modified Aleppo Bentonite (B_AOctyl).

 

Fig.5. Gas chromatographic analysis of gasoline components using grafted Aleppo bentonite B_AOctyl (Programmed column temperature between 35-215ºC, with increasing temperature rate 3ºC/min, FID, flow rate of N₂ carrier gas 35 mL/min, the injection volume 0.2 μL and injected port temperature 190ºC)

 

CONCLUSION:

Octyl-modified Aleppo Bentonite (B_AOctyl) as support for GC was developed. The BET surface areas (S_BET) for B_AOctyl was 2.71 m²/g , the total pores volume (V_p) was 0. 0072 mL/g and the mean pores radii (r_a) was 53.14 Å. Twenty eight hydrocarbons components in gasoline were determined by using B_AOctyl as support in GC. The principle gasoline components groups (total C₅ to C₁₀) percent were presented as follows: 20.265%, 20.691%, 24.383%, 17.110%, 11.595% and 1.611% (total C₅-C₁₀ =95.655%).

 

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Accepted on 31.05.2017        © RJPT All right reserved