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Absorption of Aromatic Compounds From Solutions by Zeolite 13X
P.A. Jacobs and R.A. van Santen (Editors), Zeolites: Fncts, Figures, Funrre 0 1989 Elsevier Scicnce Publishcrs B.V., Amsterdam - Printed in The Netherlands
945
SORPTION OF AROMATIC COMPOUNDS FROM SOLUTIONS BY ZEOLITE 13X K. AL-ZAID1. F. OWAYSIl, S. AKASHAHl and Y.A. ELTEKOV2 lKuwait Institute for Scientific Research, Petroleum, Petrochemicals and Materials Division, P.O. Box 24885, 13109 - Safat Kuwait
-
21nstitute of Physical Chemistry of USSR Academy, Leninskii prospect, 31, Moscow, 117915, USSR ABSTRACT Measurements of the equilibrium extent, kinetic and dynamic of adsorption of individual aromatic hydrocarbons: n-dodecylbenzene, naphthalene, and dibenzothiophene from isooctane solutions by molecular sieves 13X were carried out at 343 K and at concentrations 30 kg/m3. The separation factor and numbers of adsorbate molecules occupied in the unit cell of the molecular sieves were calculated. The diffusion coefficients were determined using Barrer-Brook equation. The mass transfer zone has been determined using modified Shilov equation and dynamic system of adsorption. INTRODUCTION The development of process of refining of liquid paraffins and waxes is closely related to problem of improving their quality. The meaning of molecular sieves for dearomatization process of commercial liquid paraffins is growing at present time.
Technology of dearomatized liquid paraffins and waxes using mole-
cular sieves is developed on the theoretical and experimental investigations of adsorption of individual and mixtures hydrocarbons and related compounds. Molecular sieves have been applied industrially for many years. For example, processes have been developed for the separation of n-alkanes from crude oil fractions by means of selective adsorption on molecular sieves. However, there is only limited literature on the adsorption of high molecular weight aromatic
hydrocarbons from solution to be found. Mair and Shamiengar (ref. 1) developed a method for separating certain aromatic hydrocarbons according to their shape and size using molecular sieves 1OX and 13X in a packed column.
Satterfield and
Cheng (ref. 2) have found that the steric effect has a significant influence on the selectivity of the adsorption process, Many patents relevant to the separation of light aromatics from petroleum fractions for either improving the stability of the kerosene cuts or for purification purposes have been registered (refs. 3-8). Some publications have described the results of study of adsorption of sulfur, and oxygen organic compounds on zeolite NaX (refs. 9-10]. From the above survey it seems that there have been few investigations relevant to adsorption of aromatic hydrocarbons and some heterogenous compounds.
946 Therefore, this work presents a study of the adsorption of aromatic hydrocarbons and sulfur compounds in an attempt to find the relationship between the sizes and properties of the adsorbate molecules and the structure of zeolite using static and dynamic systems of adsorption. THEORY AND EXPERIMENTAL For the description of experimental results of study of equilibrium adsorption was applied the theory of multicomponent adsorption from solutionworkedout (refs. 11-12).
The equation of adsorption isotherm was derived under the
conditions of the equality of the chemical potentials of solution components of the bulk and surface phases.
This equation gives the possibility to calculate
the constants of adsorption equilibrium and the adsorption capacity A, for positively adsorbing component of binary solutions. The diffusion coefficients for aromatic compounds were calculated from kinetics experiments using BarrerBrook equation (1953).
The dynamic properties, particularly, the height of
mass transfer zone was calculated from dynamic experiment using modified Shilov equation (ref. 13). Molecular sieves 13X (Linde-Davisson, Union Carbide, USA) in form of extrudates and the fraction of 1-2 mm was taken for experiments. Before the adsorption experiments the specimens of zeolite were calcined at 723 K for 5 hours. The autoclaves with capacity 100 cm3 were used for the study of equilibrium and kinetics of adsorption. For studying the dynamic of adsorption, a glass column was used with length of 660 mm and 18 m i.d. packed with molecular sieves type 13X. Process temperature was maintained at 343 K.
As
a solvent isooctane was used.
Maximum
concentrations of aromatic compounds in solutions were 30 kg/m3 aromatic compounds and monoalkylbenzene with an average of 12 carbon atoms in an unbranched side chain were employed in the study (see Table 1). The change in concentration of a known amount of the binary mixture was measured by UV-spectrometer (Shimadzu UV-160 model) and the adsorption value G was expressed in the form of Gibb's excess energy equation:
-
xo x1 n G = ------m
(1)
where Xo and Xi are initial and equilibrium mole fraction of the solute (e.g., component 11, m is the mass of the molecular sieve in the experiment, and n is the total number of moles of components 1 and 2. RESULTS AND DISCUSSION Experimental adsorption isotherms have been calculated according to equation (ref. 9):
941
TABLE 1 The physical properties of the individual aromatic compounds Name
General formula
Structural formula
Mol. Wt. glmole
Density gIcm3 at 343 K 0.8215
Naphthalene
Dibenzothiophene
C12HgS
128.18
0.9928
184.26
1.0629
S
G
1
=
A
(f-1) (1-X1) X1 [ l
m
+
( f
-
1) X1 1-l
(2)
where G1 is adsorption value of component 1 at equilibrium mole fraction X1, f is the separation factor: -1
f = K K K a 1 2
(3)
where K is the constant of adsorption equilibrium K1 and K2 are the ratio of activity coefficients of components 1 and 2 in bulk and surface phases, respectively,
is the ratio of molecular volumes of components 1 and 2.
Due to the absence of molecules of the second component isooctane in the zeolite cavities, it is possible to assume by definition that f >>1.
A
m
=
f and often
and f can be calculated from a graphical solution of the equation in
the form:
x1
(1
- X1)
1
___-_-----= ---------G1
BAm (f-1)
+
x1
----
(4)
Am
This was done by plotting X1 (l-Xl)/Gl VS X1 and determining the slope of the straight line for each aromatic hydrocarbon-isooctane pair (see Fig. 1 ) . The initial sections of the adsorption isotherms for the aromatic hydrocarbons and sulfur compound are shown in Fig. 2.
Table 2 presents results of
application of equation 2. Actually the adsorption of the aromatic hydrocarbons occurred as a result of an interaction of the g-electron system of the benzene ring with the cation or hydroxyl group of the molecular sieves. The aromatic ring is attached on the
948
30
25 20
m
.-( D
.
15
G h
10
4
?
ri
v
a 4
5 0
5
15
10
20
xl. 103
Fig. 1. Slopes of the adsorbates on molecular s i e v e s 13X a t 343 K . (1) n-Dodecylbenzene, ( 2 ) Naphthalene, (3) Dibenzothiophene.
1.0 0.8
. ' 3 3
0.6
d
0
E,
L3
0.4 0.2
0
8
16
2 4 28
xl. I 03
Fig. 2 . Adsorption isotherms of n-Dodecylbenzene (1) Naphthalene, ( 2 ) Dibenzothiophene, (3) on z e o l i t e 13X a t 343 K .
949 TABLE 2 Constants of adsorption isotherms, kinetics and dynamic adsorption properties for n-dodecylbenzene, naphthalene and dibenzothiophene from solution using NaX at 343 K Hydrocarbon type
N
4,
mole/ kg
Log f
De* 10l2 Gt/G, = 0.5
hz m
m2/sec n-dodecylbenzene naphthalene dibenzothiophene
0.38 0.85 0.78
5.1 11.4 10.5
surface or within the zeolite cavity.
3.01 3.2
4.1
33.5 20 14.5
111 47 58
As shown in Table 2. it can be seen
that the value log f > 3 indicates a high selectivity of adsorption of these aromatic hydrocarbons from isooctane by molecular sieves type 13X.
The long
alkyl chain connected to the benzene ring (such as in dodecylbenzene) will weaken the nonspecific interaction. This explains why the separation coefficient of n-dodecylbenzene is less than other hydrocarbons.
The interactions
between heterogenous hydrocarbon and zeolite crystals have a specific character which means that separation coefficient for dibenzothiophene is higher than other compounds (log f = 4.1).
The number of adsorbate molecules of n-dodecyl-
benzene occupied in one unit cell of molecular sieves is less than the other
-
hydrocarbons. This is due to the steric factor of adsorption and close packing of aromatic molecules with ling aliphatic chain (N for n-dodecylbenzene
5.1).
The adsorption kinetics in terms of G as a function of T, where G is the amount of adsorption at time
'I
were presented in Fig. 3.
n-dodecylbenzene has
a larger critical molecular diameter and diffuses at 343 K slowly and equilibrium was approached within 3 hours, and equilibrium adsorption value was 0.52 mole/kg, while the equilibrium value of adsorption for naphthalene was 1.3 mole/kg and this can be attributed the small molecule size and dense packing molecules in cavities of zeolite crystal. It can be seen from Fig. 3 that, equilibrium adsorption value for dibenzothiophene was lower than for the other compounds (0.85 mole/kg).
This occurred because the presence of the sulfur
atom with two pairs of ion electrons increases the activity of the dibenzothiophene.
Thus the molecules penetrate through the pores of zeolite crystals more
easily (De = 14.5 x
m2/S), and interact more strongly with the cations
present on the surface of molecular sieve pores. Using dynamics of adsorption for three types of hydrocarbons from solution in isooctane, breakthrough curves were determined and were illustrated in Fig. 4.
The height of mass transfer zone h,, was calculated using modified
950
Fig. 3 . Kinetic curve f o r adsorption G,mole/kg for (1) n-Dodecylbenzene, ( 2 ) Naphthalene and (3) Dibenzothiophene on z e o l i t e 13X at 343 K .
0
0.2
0.4 t x 10-3
0.6
niin
n. a
.
F i g . 4 . Breakthrough curves of l i q u i d phase adsorpt i o n of d i f f e r e n t types of aromatic compounds from s o l u t i o n with isooctane. (1) n-Dodecylbenzene, ( 2 ) Dibenzothiophene, (3) Naphthalene.
951
Shilov equation (ref. 1 3 ) and are presented in Table 2. It is clear from Table 2 that at 343 K, naphthalene possessed the best dynamic adsorption properties, followed by dibenzothiophene with n-dodecylbenzene last.
Comparison of these data with data obtained on adsorption isotherms
(see Table Z),
indicates similar trends.
For example, the numbers of molecules
captured per unit cell of adsorbent were 5.1, 11.4 and 10.5 for n-dodecylbenzene, naphthalene, and dibenzothiophene, respectively at 3 4 3 K; the height of mass transfer zone shows the same trend, i.e., it was the lowest for naphthalene (hz
=
47 mm) and the highest for n-dodecylbenzene (hz
=
111 mm), as shown
in Table 2. CONCLUSIONS In conclusion, the isotherms, kinetics and dynamics of adsorption of aromatic hydrocarbons and heterogenous compounds from solution in isooctane by molecular sieves 13X are due to the energy distribution of the force field in the cavities of zeolite crystals and the capability for specific adsorption of adsorbate molecules on the cationized surface of the adsorbent, which is the characteristic of the chemical structure of aromatic compounds.
NOMENCLATURE
Am
B De f G1 hZ
Ka K1
K2 m n
N xO
x1
The adsorption capacity of aromatic compounds calculated by equation(2) Coefficient of mutual displacement, defined as the ratio of molar volumes of aromatic compound and the solvent (isooctane) Diffusivity, m2/sec Selective coefficient (constant of adsorption equilibrium) Value of adsorption at a certain concentration, m
3
kg
-1
Height of mass transfer zone, mm Constant of adsorption equilibrium Ratio of activity coefficient of solute Ratio of activity coefficient of solvent Mass of zeolite used in the adsorption, kg
Number of moles of solute and solvent in solution Number of adsorbate molecules occupied per one unit cell of molecular cell Mole fraction in solution before adsorption Mole fraction in solution after adsorption
952
REFERENCES 1 B.J. Mair and M. Shamalengar, Anal. Chem. 3 0 (1958) 276. 2 C.N. Satterfield, Chon S. Cheng, AIChE symposium, 67, No. 117 (1976) 43. 3 W.R. Epperly and F.S. Pramuk, U.S. Patent, No. 3, 278 (1966) 422. 4 H. Rosback and R.W. Nauzil, U.S. Patent, July, No. 3, 969 (1976) 223. 5 E.V. Zubareva, M.N. Frid, L.V. Borisova and O.A. Cherednichenko, Zh. Fiz. Khim. 55 (1981) 2134. 6 J. Armand de Rosset, U.S. Patent, June, No. 4, 337 (1982) 156. 7 G. Jean, P. Chantal, S. Ahmed and H. Sawatzk, Prepr. Pap. Am. Chem. SOC., Div. Fuel Chem., 3 1 (1986) 262. 8 F. Owaysi, E.A. Gureev, Yu.A. Eltekov and M.I. Falkovich, Khimiya Technologiya Topliv i masel, 2, 39 (1981) 742. 9 Yu.A. Eltekov and A.V. Kiselev, Molecular Sieves, Society of Chemical Industry, London (1967) 267-278. 10 A.V. Kiselev, E.A. Aripov and Yu.A. Eltekov, Kolloid Zh. 36 (1974) 742. 11 V.K. Semenchenko and Z.H. Kolloid, 9 (1947) 125. 12 A.V. Kiselev and A.A. Lopatkin, Molecular Sieves Series, 4th-6th April, University of Londong (1967) 252-266. 13 A.M. Stadnik and Yu.A. Eltekov, Russ. J. Phys. Chem., 59 228 (1977) 2697.
-
945
SORPTION OF AROMATIC COMPOUNDS FROM SOLUTIONS BY ZEOLITE 13X K. AL-ZAID1. F. OWAYSIl, S. AKASHAHl and Y.A. ELTEKOV2 lKuwait Institute for Scientific Research, Petroleum, Petrochemicals and Materials Division, P.O. Box 24885, 13109 - Safat Kuwait
-
21nstitute of Physical Chemistry of USSR Academy, Leninskii prospect, 31, Moscow, 117915, USSR ABSTRACT Measurements of the equilibrium extent, kinetic and dynamic of adsorption of individual aromatic hydrocarbons: n-dodecylbenzene, naphthalene, and dibenzothiophene from isooctane solutions by molecular sieves 13X were carried out at 343 K and at concentrations 30 kg/m3. The separation factor and numbers of adsorbate molecules occupied in the unit cell of the molecular sieves were calculated. The diffusion coefficients were determined using Barrer-Brook equation. The mass transfer zone has been determined using modified Shilov equation and dynamic system of adsorption. INTRODUCTION The development of process of refining of liquid paraffins and waxes is closely related to problem of improving their quality. The meaning of molecular sieves for dearomatization process of commercial liquid paraffins is growing at present time.
Technology of dearomatized liquid paraffins and waxes using mole-
cular sieves is developed on the theoretical and experimental investigations of adsorption of individual and mixtures hydrocarbons and related compounds. Molecular sieves have been applied industrially for many years. For example, processes have been developed for the separation of n-alkanes from crude oil fractions by means of selective adsorption on molecular sieves. However, there is only limited literature on the adsorption of high molecular weight aromatic
hydrocarbons from solution to be found. Mair and Shamiengar (ref. 1) developed a method for separating certain aromatic hydrocarbons according to their shape and size using molecular sieves 1OX and 13X in a packed column.
Satterfield and
Cheng (ref. 2) have found that the steric effect has a significant influence on the selectivity of the adsorption process, Many patents relevant to the separation of light aromatics from petroleum fractions for either improving the stability of the kerosene cuts or for purification purposes have been registered (refs. 3-8). Some publications have described the results of study of adsorption of sulfur, and oxygen organic compounds on zeolite NaX (refs. 9-10]. From the above survey it seems that there have been few investigations relevant to adsorption of aromatic hydrocarbons and some heterogenous compounds.
946 Therefore, this work presents a study of the adsorption of aromatic hydrocarbons and sulfur compounds in an attempt to find the relationship between the sizes and properties of the adsorbate molecules and the structure of zeolite using static and dynamic systems of adsorption. THEORY AND EXPERIMENTAL For the description of experimental results of study of equilibrium adsorption was applied the theory of multicomponent adsorption from solutionworkedout (refs. 11-12).
The equation of adsorption isotherm was derived under the
conditions of the equality of the chemical potentials of solution components of the bulk and surface phases.
This equation gives the possibility to calculate
the constants of adsorption equilibrium and the adsorption capacity A, for positively adsorbing component of binary solutions. The diffusion coefficients for aromatic compounds were calculated from kinetics experiments using BarrerBrook equation (1953).
The dynamic properties, particularly, the height of
mass transfer zone was calculated from dynamic experiment using modified Shilov equation (ref. 13). Molecular sieves 13X (Linde-Davisson, Union Carbide, USA) in form of extrudates and the fraction of 1-2 mm was taken for experiments. Before the adsorption experiments the specimens of zeolite were calcined at 723 K for 5 hours. The autoclaves with capacity 100 cm3 were used for the study of equilibrium and kinetics of adsorption. For studying the dynamic of adsorption, a glass column was used with length of 660 mm and 18 m i.d. packed with molecular sieves type 13X. Process temperature was maintained at 343 K.
As
a solvent isooctane was used.
Maximum
concentrations of aromatic compounds in solutions were 30 kg/m3 aromatic compounds and monoalkylbenzene with an average of 12 carbon atoms in an unbranched side chain were employed in the study (see Table 1). The change in concentration of a known amount of the binary mixture was measured by UV-spectrometer (Shimadzu UV-160 model) and the adsorption value G was expressed in the form of Gibb's excess energy equation:
-
xo x1 n G = ------m
(1)
where Xo and Xi are initial and equilibrium mole fraction of the solute (e.g., component 11, m is the mass of the molecular sieve in the experiment, and n is the total number of moles of components 1 and 2. RESULTS AND DISCUSSION Experimental adsorption isotherms have been calculated according to equation (ref. 9):
941
TABLE 1 The physical properties of the individual aromatic compounds Name
General formula
Structural formula
Mol. Wt. glmole
Density gIcm3 at 343 K 0.8215
Naphthalene
Dibenzothiophene
C12HgS
128.18
0.9928
184.26
1.0629
S
G
1
=
A
(f-1) (1-X1) X1 [ l
m
+
( f
-
1) X1 1-l
(2)
where G1 is adsorption value of component 1 at equilibrium mole fraction X1, f is the separation factor: -1
f = K K K a 1 2
(3)
where K is the constant of adsorption equilibrium K1 and K2 are the ratio of activity coefficients of components 1 and 2 in bulk and surface phases, respectively,
is the ratio of molecular volumes of components 1 and 2.
Due to the absence of molecules of the second component isooctane in the zeolite cavities, it is possible to assume by definition that f >>1.
A
m
=
f and often
and f can be calculated from a graphical solution of the equation in
the form:
x1
(1
- X1)
1
___-_-----= ---------G1
BAm (f-1)
+
x1
----
(4)
Am
This was done by plotting X1 (l-Xl)/Gl VS X1 and determining the slope of the straight line for each aromatic hydrocarbon-isooctane pair (see Fig. 1 ) . The initial sections of the adsorption isotherms for the aromatic hydrocarbons and sulfur compound are shown in Fig. 2.
Table 2 presents results of
application of equation 2. Actually the adsorption of the aromatic hydrocarbons occurred as a result of an interaction of the g-electron system of the benzene ring with the cation or hydroxyl group of the molecular sieves. The aromatic ring is attached on the
948
30
25 20
m
.-( D
.
15
G h
10
4
?
ri
v
a 4
5 0
5
15
10
20
xl. 103
Fig. 1. Slopes of the adsorbates on molecular s i e v e s 13X a t 343 K . (1) n-Dodecylbenzene, ( 2 ) Naphthalene, (3) Dibenzothiophene.
1.0 0.8
. ' 3 3
0.6
d
0
E,
L3
0.4 0.2
0
8
16
2 4 28
xl. I 03
Fig. 2 . Adsorption isotherms of n-Dodecylbenzene (1) Naphthalene, ( 2 ) Dibenzothiophene, (3) on z e o l i t e 13X a t 343 K .
949 TABLE 2 Constants of adsorption isotherms, kinetics and dynamic adsorption properties for n-dodecylbenzene, naphthalene and dibenzothiophene from solution using NaX at 343 K Hydrocarbon type
N
4,
mole/ kg
Log f
De* 10l2 Gt/G, = 0.5
hz m
m2/sec n-dodecylbenzene naphthalene dibenzothiophene
0.38 0.85 0.78
5.1 11.4 10.5
surface or within the zeolite cavity.
3.01 3.2
4.1
33.5 20 14.5
111 47 58
As shown in Table 2. it can be seen
that the value log f > 3 indicates a high selectivity of adsorption of these aromatic hydrocarbons from isooctane by molecular sieves type 13X.
The long
alkyl chain connected to the benzene ring (such as in dodecylbenzene) will weaken the nonspecific interaction. This explains why the separation coefficient of n-dodecylbenzene is less than other hydrocarbons.
The interactions
between heterogenous hydrocarbon and zeolite crystals have a specific character which means that separation coefficient for dibenzothiophene is higher than other compounds (log f = 4.1).
The number of adsorbate molecules of n-dodecyl-
benzene occupied in one unit cell of molecular sieves is less than the other
-
hydrocarbons. This is due to the steric factor of adsorption and close packing of aromatic molecules with ling aliphatic chain (N for n-dodecylbenzene
5.1).
The adsorption kinetics in terms of G as a function of T, where G is the amount of adsorption at time
'I
were presented in Fig. 3.
n-dodecylbenzene has
a larger critical molecular diameter and diffuses at 343 K slowly and equilibrium was approached within 3 hours, and equilibrium adsorption value was 0.52 mole/kg, while the equilibrium value of adsorption for naphthalene was 1.3 mole/kg and this can be attributed the small molecule size and dense packing molecules in cavities of zeolite crystal. It can be seen from Fig. 3 that, equilibrium adsorption value for dibenzothiophene was lower than for the other compounds (0.85 mole/kg).
This occurred because the presence of the sulfur
atom with two pairs of ion electrons increases the activity of the dibenzothiophene.
Thus the molecules penetrate through the pores of zeolite crystals more
easily (De = 14.5 x
m2/S), and interact more strongly with the cations
present on the surface of molecular sieve pores. Using dynamics of adsorption for three types of hydrocarbons from solution in isooctane, breakthrough curves were determined and were illustrated in Fig. 4.
The height of mass transfer zone h,, was calculated using modified
950
Fig. 3 . Kinetic curve f o r adsorption G,mole/kg for (1) n-Dodecylbenzene, ( 2 ) Naphthalene and (3) Dibenzothiophene on z e o l i t e 13X at 343 K .
0
0.2
0.4 t x 10-3
0.6
niin
n. a
.
F i g . 4 . Breakthrough curves of l i q u i d phase adsorpt i o n of d i f f e r e n t types of aromatic compounds from s o l u t i o n with isooctane. (1) n-Dodecylbenzene, ( 2 ) Dibenzothiophene, (3) Naphthalene.
951
Shilov equation (ref. 1 3 ) and are presented in Table 2. It is clear from Table 2 that at 343 K, naphthalene possessed the best dynamic adsorption properties, followed by dibenzothiophene with n-dodecylbenzene last.
Comparison of these data with data obtained on adsorption isotherms
(see Table Z),
indicates similar trends.
For example, the numbers of molecules
captured per unit cell of adsorbent were 5.1, 11.4 and 10.5 for n-dodecylbenzene, naphthalene, and dibenzothiophene, respectively at 3 4 3 K; the height of mass transfer zone shows the same trend, i.e., it was the lowest for naphthalene (hz
=
47 mm) and the highest for n-dodecylbenzene (hz
=
111 mm), as shown
in Table 2. CONCLUSIONS In conclusion, the isotherms, kinetics and dynamics of adsorption of aromatic hydrocarbons and heterogenous compounds from solution in isooctane by molecular sieves 13X are due to the energy distribution of the force field in the cavities of zeolite crystals and the capability for specific adsorption of adsorbate molecules on the cationized surface of the adsorbent, which is the characteristic of the chemical structure of aromatic compounds.
NOMENCLATURE
Am
B De f G1 hZ
Ka K1
K2 m n
N xO
x1
The adsorption capacity of aromatic compounds calculated by equation(2) Coefficient of mutual displacement, defined as the ratio of molar volumes of aromatic compound and the solvent (isooctane) Diffusivity, m2/sec Selective coefficient (constant of adsorption equilibrium) Value of adsorption at a certain concentration, m
3
kg
-1
Height of mass transfer zone, mm Constant of adsorption equilibrium Ratio of activity coefficient of solute Ratio of activity coefficient of solvent Mass of zeolite used in the adsorption, kg
Number of moles of solute and solvent in solution Number of adsorbate molecules occupied per one unit cell of molecular cell Mole fraction in solution before adsorption Mole fraction in solution after adsorption
952
REFERENCES 1 B.J. Mair and M. Shamalengar, Anal. Chem. 3 0 (1958) 276. 2 C.N. Satterfield, Chon S. Cheng, AIChE symposium, 67, No. 117 (1976) 43. 3 W.R. Epperly and F.S. Pramuk, U.S. Patent, No. 3, 278 (1966) 422. 4 H. Rosback and R.W. Nauzil, U.S. Patent, July, No. 3, 969 (1976) 223. 5 E.V. Zubareva, M.N. Frid, L.V. Borisova and O.A. Cherednichenko, Zh. Fiz. Khim. 55 (1981) 2134. 6 J. Armand de Rosset, U.S. Patent, June, No. 4, 337 (1982) 156. 7 G. Jean, P. Chantal, S. Ahmed and H. Sawatzk, Prepr. Pap. Am. Chem. SOC., Div. Fuel Chem., 3 1 (1986) 262. 8 F. Owaysi, E.A. Gureev, Yu.A. Eltekov and M.I. Falkovich, Khimiya Technologiya Topliv i masel, 2, 39 (1981) 742. 9 Yu.A. Eltekov and A.V. Kiselev, Molecular Sieves, Society of Chemical Industry, London (1967) 267-278. 10 A.V. Kiselev, E.A. Aripov and Yu.A. Eltekov, Kolloid Zh. 36 (1974) 742. 11 V.K. Semenchenko and Z.H. Kolloid, 9 (1947) 125. 12 A.V. Kiselev and A.A. Lopatkin, Molecular Sieves Series, 4th-6th April, University of Londong (1967) 252-266. 13 A.M. Stadnik and Yu.A. Eltekov, Russ. J. Phys. Chem., 59 228 (1977) 2697.
-