CC BY
56
https://doi.org/10.29013/AJT-19-11.12-33-37
Mamadoliev Ikromjon Ilkhomidinovich, Tashkent research institute of Chemical Technology E-mail: [email protected]
STUDY OF THE SORPTION AND TEXTURAL PROPERTIES OF BENTONITE AND KAOLIN
Abstract. The sorption, textural, and physicochemical characteristics ofbentonite and kaolin are investigated. To determine the relative surface of the samples, the Brunauer-Emmett-Teller method (BET) was used, and the Barret-Joyner-Helend method (BLC) was used to determine the volume and size of pores. As a result of the research, a relationship was established between the volume of adsorbed gas and the relative pressure and pore radius. It has been established that at P/P0 = 0-0.05 in the mesopores monomolecular adsorption is observed, at P/P0 = 0.05 simultaneously mono- and multimolecular adsorption, at P/P0 = 0.05-0.4 there is a polymolecular adsorption.
Keywords: bentonite, kaolin, colloidality, swelling, adsorbed gas volume, adsorption capacity, meso and micropores.
Introduction
Adsorption methods for industrial hydrocarbon purification are one of the most common methods in the industry. Their use allows a number ofvaluable compounds to be returned to production in order to reuse. The most important requirements for adsorption materials are: high specific surface area, selective responsiveness and easy regeneration [1-4]. In addition, the adsorbent should be cheap and harmless, with no corrosive properties, should retain its adsorption feature for a long time, and be highly mechanically durable. One of the most common adsorbents is activated carbon and is produced by various brands. In recent years, natural and artificial zeolites have been widely used in the purification of hydrocarbons. One of the most important areas for now is the development of environmentally friendly sorbents, catalysts and catalysts based on local raw materials [5-7].
Experimental
To determine the chemical and physicochemical characteristics, we placed sample granules in 100 g of mass in a 250-cm glass tube and poured 150 cm3 of distilled water. The flask was stirred for 24 hours
on the AVU-6 unit at 120 rpm. After drying, the adsorbent was passed through a sieve with 0.5- and 0.25-mm diameter, and the mechanical and physico-chemical properties were studied. Before acid treatment, we grinded the soil samples until to reach particle size 0.08 mm. We added 40 ml H2SO4 heated to 10 g of grinded soil and stir in a water bath. After processing, the soil was filtered through a paper filter in the Buchner funnel and washed with distilled water at pH = 5.4-5.7. The soil was then dried with the filter paper in the dryer for 12 hours at 120 °C. Specific surface area and the distribution of pore sizes were found in the automatic adsorbometer ASAB2010 by the low-temperature nitrogen desorption method. Sediment analysis was performed on water and glycerol mixture in different dispersion environments using the Oden method.
X-ray diffraction analysis (Co-Ka-radiation) was performed on the DRON-4 diffractometer with a cobalt X-ray tube. The PDF-2 database of the International Center for Diffraction Data (JCPDS, 1999) was used for the analysis of diffractograms. The porosity of the samples was determined by Quantrome NOVA (USA) analyzer of low-temperature nitrogen
desorption. Each sample was dehydrated for 2 hours at 250 °C under vacuum prior to measurement.
The Brunauer-Emmett-Teller (BET) method was used to determine the relative surface of solid samples. This method is used by the following BET equations:
1
1
C -1 P
ip \ A n
W ■
W ■C + W ■C
^ -1
V P J
where W-P/P0 is the adsorbed mass at a relative pressure, W - the adsorbed mass on the surface coated a
' m
monolayer; S - is a BET constant, which shows the adsorption effect of adsorbents and represents the adsorption energy of the first adsorption layer.
The Barrett-Joyner-Halenda (BJH) method was used to determine the volume and the size distribution of pores. In the calculations, the desorption
Table 1. - Chemical content of
and adsorption areas of the isotherm with a pressure range of 0.967-0.4 P/P0 were used.
To determine the shear density, the sorbent weighed 500 g and was kept in the dryer for 600 h at 60 °C. 400 g of the dried sample was weighed and placed in a 500 ml cylinder, measured a volume V. We then densified th sorbent by light tapping under the cylinder and t and again measured a volume V2.
The bulk density of the sorbent was determined by the following formula:
Yi = V. Y = P. [g/cm3]
1 2
where P is the mass of the sorbent; Density of -sorbent and subsequent bulk density, g/cm3.
Results and discussion
The subject ofthe study was the Navbakhor ben-tonite and Pahtachi kaolin.
bentonite in Bavbakhor district
Name SiO2 TiO2 AlO. Fe O MgO CaO Na2O K2O PO5 SO3
Alkali bentonite soil 57.91 0.35 13.69 5.10 1.84 0.48 1.53 1.75 0.43 0.75
Alkali earth soil 56.23 0.61 13.56 6.50 3.76 0.69 0.98 2.20 0.92 0.49
Prior to acidification of bentonite or kaolin, the Si02-70.17, Al203-9.49, Fe203-1.39, Mg0-0.64, sample was heated at 150 °C for 30 min to remove Na20-0.17, K20-1.27, Ca0-0.20, Ti02-1.63, water. Mn0-0.01.
Mass% after acidic acid:
Table 2.- Dependence of the activation mode on the physicochemical properties of soil
Porperties of soil Activation time, seconds
0 10 20 40 60 80 100 120 180
Navbakhor bentonite
Swelling, mg/g 15 18 19.6 22 24 26 27 28 25
Colloid property,% 49 51.6 55 62.2 67.7 70.2 74.7 80 70.9
Water absorption, 2.5 2.46 2.42 2.38 2.36 2.34 2.32 2.3 2.45
Pakhtachi kaolin
Swelling, mg/g 25 28 29,6 30 33 36 38 42 44
Colloid property,% 89 90 92 94 96 96 99 100 100
Water absorption 10 12 14 16 18 20 22 28 30
Table 3.- Physical characteristics of natural soil
Pakhtachi kaolin Navbakhor bentonite
1 2 3
Specific surface are, m2/g 250-300 125-200
1 2 3
Bulk density, kg/m2 600-700 570-650
Pore volume, cm3/g 0.028-0.041 0.048
Pore size, nm 2.6-2.8 3.4-4.3
In the equilibrium mode, the adsorption test allows to determine the maximum adsorption rate and to calculate the thermodynamic parameters of adsorption at low temperature fluctuations.
Adjusting the adsorption equation by the experimental design of adsorption isotherms is accepted. The expression of adsorption by Langmuir and Freundlich models is widely used in the literature:
a Kl-Q
«oo 1 + KL C0
a
a = K,, ■ C — =
Kl C
a
C / C0
1
+ -
k -1
1 + KLC
a1
Q-X
C0
where k = eRT thus Q -h - adsorption heat
a
KR • C10
1 + a- C°p'
a, f - Redlich-Peterson equation parameters There is a relationship between the adsorption equation and the change in adsorption enthalpy and entropy:
AS„
AH„
K = e R
ads V
RT
The rate of adsorption process can be expressed in time units by changing the amount of adsorbed substance in the mass of the adsorbent as follows:
rads = -T [(mg/g)/s]
-t
Thus, the mass of adsorbed substance in a-1 g of adsorbent, - the time.
The following expression is important for the dynamic system in an open system, such as the flow adsorber:
W ■ -C W ■ -C
V = ■
S ■ dL dV
ads
where V - is the rate of the adsorption process, W - the volume rate of the current; C - reactor cross-section surface, l - adsorbent layer height; Vais - the volume of adsorbent.
Studies have shown that the adsorption process is subject to a 2-order reaction equation:
k2 •(«00-«T )2
-T
k2 •(a*,-aT )2
1 + k2 •(«00-«t)
Or its integrated form is as follows:
T
a
1
k2 'a2
- + -
a
700
600-
500-
g 400-1
13
> 300 c ^o
K 200
o
m
< 100
0-
-100
0,0 0,2 0,4 0,6 0,8 Relative pressure (P/P0)
1,0
600-
) 500
c 400
o 300
>
H 200
sO ■ß
< 100
0,0 0,2 0,4 0,6 0,8 Relative pressure (P/P0)
1,0
1,2
Figure 1. Adsorption-desorption isotherms of nitrogen in mesopores of synthesized sorbents
0
Diffusion model for the adsorption process:
1
aT = kdiff t2 + S
diffusion constant of the adsorption rate, S-constant number.
Dynamic capacity of the adsorbent is found using the formula:
Pm V 'IS]
ad =■
m„
Comparison of surface and microwave size was calculated by BET method for mesoporous sorbents and Dubinin method for mesoporous sorbents. To confirm the structure of the sorbents, we present the nitrogen adsorption desorption curves for mesoporous sorbents(Figure 1).
As shown in Figure 1, the adsorption-desorption isotherms presented are typical of type IV isotherms. We consider the distribution of pore size for the synthesized porous sorbents (calculated by the BJH method).
0,12 -, 0,10 -0,08-Ü 0,06-
o 0,04 -I
>
0,02-
0,00-
IS
10
20
30
40
50
60
70
0,06
0,05
0,04
A 0,03
Ô 0,02
>
0,01
0,00
10
20
30
40
50
60
70
Diameter (nm) Diameter (nm)
Figure 2. Pore volume distribution depending on diameters of mesoporous sorbents
As Figure 2 shows, the synthesized porous sor- Microporous sorbents provide characteristic iso-bents consist mainly of pore volume around 2 nm. therms of nitrogen adsorption.
2003 150
о 100
>
с
о
-О
<
50-
0-
140 ■ 120 ■
100 --
О
Г 80-
<
60-
40-
20-
0-
-20-
0,0
0,2
0,4
0,6
0,8
1,0
0,0
0,2
0,4
0,6
0,8
1,0
Relative pressure (P/P0)
Relative pressure (P/P0)
Figure 3. Nitrogen adsorption-dsorption isotherms in micropores of microporous sorbents
ds
0
0
As can be seen from Figure 3, the isotherms pres- method to determine the pore volume and size disent are of the first type of isotherms (horizontal planes tribution.
present). 3) The study investigated the relationship be-
Conclusions tween adsorption volume and relative pressure and
1) The sorption, texture and physicochemical pore radius.
characteristics of bentonite and kaolin were studied. 4) Monomolecular adsorption at the interval
2) The Brunauer-Emmett-Teller (BET) method P/P0 = 0-0.05, mono- and polymolecular adsorption was used to determine the specific surface areasof at the interval P/P0 = 0.05, and P/P0 = 0.05-0.4 poly-the samples, and the Barrett-Joyner-Halenda (BJH) mer molecular adsorption processes have been proven.
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