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KIMYA PROBLEMLERI № 3 2017 ISSN 2221-8688
341
UDC 541.128:547,593.211
THE KINETIC MODEL OF THE REACTION OF OXIDATIVE DEHYDROGENATION OF CYCLOHEXANOL OVER MODIFIED ZEOLITE CATALYST
A.M. Aliyev, Z.A. Shabanova, M.K. Aliyeva, G.A. Alizadeh
Acad. M.F.NagiyevInstitute of Catalysis and Inorganic Chemistry H.Javid ave., 113, Baku AZ1143, Azerbaijan Republic, e-mail: kqki@kqki.science.az
Based on experimental data, a probable-stage scheme of the mechanism of oxidative dehydrogenation of cyclohexanol reaction over modified zeolite catalyst suggested. Also, theoretically based kinetic model of the process has been developed and numerical values of the constants of a kinetic model calculated.
Keywords: cyclohexanol, cyclohexanone, oxidative dehydrogenation, kinetics
INTRODUCTION
It should be noted that cyclohexanone is used in the organic synthesis as intermediate in obtaining caprolactam which is manufactured from polymer polyamide fiber, and as a solvent for many substances. One of the major industrial methods for preparing cyclohexanone is the oxidation of cyclohexane by atmospheric oxygen under elevated pressure in the presence of substantially homogeneous catalysts, specifically soluble cobalt salts [1-2]. All of
these catalysts show high activity and selectivity at relatively higher temperatures. We have lately revealed that natural clinoptilolite modified with cations; Cu2+, Zn2+, Co2+ and Cr3+ by ion-exchange is the active catalyst for the reaction of oxidative dehydrogenation of cyclohexanol into cyclohexanone.
The purpose of the work is to analyze the kinetics and mechanism of the reaction.
EXPERIMENTAL PART
Results of the experimental analysisto select a catalyst for thereaction of oxidative dehydrogenation of cyclohexanol have shown that the most effective catalysts for this reaction
is Cu,Pd,Sn-clinoptilolite (0.5% Cu2+, 0.15%
Pd2+, 0.5% Sn2+) [3].
The examined
kinetics in the
of the reaction was following conditions:
temperature - 260-370oC; space velocity of the
reaction mixture (V) - 1036-3109 h- ; partial pressure (Palcohol) - 0.06-0.24 atm. and (PO2) -0.05-0.24 atm.
Proceeding from the analysis of literary materials [3-5] and experimental data, a mechanism of cyclohexanone formation has been suggested. A simplified diagram of the stage mechanism is as follows:
O2 + 2Z
^2ZO
ZO + C6 H11OH-^ zoc6 h11oh
zoc6 h11oh-
+ C6H10O + H2O 2
p2 + c6 h11oh = c6 h10o + h 2o
1
1
All these stages are practically corresponding stages; Pi and P2- partial
irreversible. Assuming their simplicity, we find pressure oxygen and alcohol.
the following expressions for the rates of In steady-state conditions:
stages: r4=r1=r2=r3 (2)
r1=k1P1012; r2=2k2P202;r3=2k303 (1) where, r4-general rate of cyclohexanone
formation.
ft, ft, ft- vacancy sections of the Based on these equations and constancy
modified ze°hte ^^ with ^^ oxygen; of total surface areas and formations ft overall
^d^x^d molecules and surface reaction rate as a function of concentration of
mtamedrnte with ki, k2, k3- rate constants reactants is as follows: corresponding index stages; r1, r2, r3-rate index
01 + 02+03=1 (3)
kiPi 02=2k2P^2;e2=(kiPi)/(2k2P2) kiPi e2=2k3e3; e3=[(kiPi)/2k3]ei
From the equations (i):
e2 = 2$; e?; e3 = ^ e?
( kiPi kiPi V 2
- o
v 2k2P2 2k3 J
- + -
By substituting expression 62, 63, in the equation (3) we get:
ef + ei - i = 0 (4) Solving the equation (4), we obtain the following expression for 01:
J-
Therefore, the rate of cyclohexanone equation can be represented as follows:
(5)
i + 4 kiPi kiPi
V 2k2P2 2k3
?i kiPi kiPi ^
+-
V 2k2P2 2k3 J
r = kiPi
1 + 4| -ML + ^ i 2k2Pi 2k:
2|Jk^ + kP
v 2k2Pi 2k:
Note that 2-cyclohexen-i-one is produced through the reaction of adsorbed molecules of cyclohexanone with dissociatively adsorbed oxygen molecules. Kinetic equation corresponding to this mechanism
dA2 kW K2 P2 • K3 P3
14 V K 2 P2 'K 3 P3
r2_CeHsO_i_on = T =
d
( Gk ^ (i + Ki Pi +VK2P2 + K3P: + K4PA + K5P5 + K6P6 + K9 P9 + KioP2 )2
n0 J
V C6HiiOH J
Total rate of cyclohexanone formation is as follows: dAi
Tcho = —,-r- = r4 _ r (6)
( Gk ^
d
n0
V C6HiiOH J
Note that cyclohexene is formed by dehydration adsorbed cyclohexanole molecules. This mechanism corresponds to the kinetic equation:
k 5 K1P
r6 =
1 + K1p1+V k 2 p2 + k3 p3 + k 4 P4 + K5 p5 + K6 p6 + k9 p9 + K10 p2
Methylcyclopentene is formed by isomerization of adsorbed cyclohexene molecules. Kinetic equation corresponding to this mechanism is as follows:
k 6 K 5 P5
r7 =
1+k1p1W k 2 p2 + k3 p3 + K 4 p4 + k5 p5 + k6 p6 + k9 p9 + k10 p2
Note that CO2 is formed by the interaction of adsorbed molecules of cyclohexene and oxygen. This mechanism corresponds to the kinetic equation:
k 7 k10 p2 • p5
r =-
1 + k1p1 w k 2 p2 + k3 p3 + K 4 p4 + K 5 p5 + k 6 p6 + k 9 p9 + k10 p2
where total rate of cyclohexene formation is as follows:
(7)
dÀ3
rC6H10 = —7-r- = r6 - r7 -
d
{^ n0
V C6H11OH y
Note that methylcyclopentene oxidation takes place through the reaction of adsorbed oxygen and methylcyclopentene molecules:
_ _k8 k10 p2 • p5_
9 ~ 1 + k1p1 w k 2 p2 + k 3 p3 + k4 p4 + k5 p5 + k 6 p6 + k9 p9 + k10 p2 Total rate of the of methylcyclopentene formation
dA4 iO\
rCH3C5H7 _ —p-r- _ r7 - r9 (8)
' gk
d
n 0
V C6H11OH y
Total rate of the formation of carbon dioxide is presented by the equation as follows: dA5
rcO2 -r- _ r8 + r9 (9)
' Gk ^
d 0 n
V C6H11OH y
It should be noted that A1, A2, A3, A4, The kinetic model of the reaction is
A5 generate cyclohexanone, 2-cyclohexen-1- subjected to statistical analysis in line with one, cyclohexene, methylcyclopentene and kinetic data. Numerical values of kinetic carbon dioxide respectively. Equations (5) - model constants are presented in the Table. (9) constitute the kinetic model of the process.
Table. Numerical values of kinetic model constants
ln k0 (ln K0 ) Et (Q ), kcal/mole
ln k0 7.49 E1 8.56
ln k 20 0.68 e2 3.0
ln k30 59.29 E3 9.45
ln k40 22.99 E4 16.73
ln k 50 34.43 E5 35.96
ln k60 2.73 E 6 16.73
ln k7 33.44 E 7 24.12
ln k80 8.86 E8 26.95
ln K0 -5.15 01 1.00
ln K2° -9.70 02 8.99
ln K 30 -7.93 03 9.00
ln k 4 -0.16 04 8.72
ln K 50 14.9 05 1.01
ln K 60 3.027 06 2.49
ln k 70 -0.59 07 1.50
ln k 8 -1.75 08 1.56
Calculations have shown that the mean square error of the experiments does not exceed 2%.
REFERENCES
1. Chaudhari S.M., Waghulde A.S., Samuel V., Bari M.L. and Chumbhale V.R. Characterization of ZnO and modified ZnO catalysts for anaerobic oxidation of cycloheksanol . Res. J. Chem.Sci. 2013, vol. 3(7), P. 38-44.
2. Vyawhare Y.K., Chumbhale V.R., Pardhy S.A., Samuel V., Aswar A.S. Gas - phase oxidant free oxidation of cyclohexanol over V2O5 -MoO3-M2O (M=Na, K,Cs). IJCT, 2010, vol.17, p. 43.
3. Aliyev A.M., Shabanova Z.A., Aliyeva M.K., Ali-zadeh G.A. Oxidative dehydration of aliphatic and alicyclic alcohols on modified zeolite catalysts. Proceedings of the Republican Scientific Conference in Commemoration of the 80-anniversary of the M.Nagiyev Institute of Catalysis and Inorganic Chemistry, Baku, 15-16 November, 2016, p.230-231. (In Azerbaijan).
4. Aliyev A.M., Majidova S.M., Saryjanov A.A. et al. Ion-exchanging method of modifying zeolites by metal cationsas maximum model of the catalyst. Azerb. Chem. Journ. 2011, no. 4, p.9-12. (In Azerbaijan).
5. Shahtakhtinskiy T.N., Aliyev A.M. et al. Selection of active catalyst and the kinetics of partial oxidation reaction of isoamyl alcohol. Kinetics and Catalysis. 1996, vol. 37, №2, p.286-290. (In Russian).
TSiKLOHEKSANOLUN MODiFiKASiYA OLUNMU§SEOLiTKATALiZATORLAR UZORiNDO OKSiDLd§DiRiCi DEHiDROGENLO^MOSi REAKSiYASININ KiNETiK MODELi
A.M. dliyev, Z.A. §abanova, M.Q.Oliyeva, G.A.Oli-zada
AMEA-nin akad. M.Nagiyev adina Kataliz vd Qeyri-uzvi Kimya institutu AZ1143, Baki, H.Cavidpr., 113; e-mail: e-mail: kqki@kqki.science.az
Received 22.06.2017.
Tdcrubi mticdbr dsasinda tsikloheksanolun oksidld§dirici dehidrogenld§mdsi reaksiyaninin ehtimal olunan getmd mexanizmi verilmi§dir. Prosesin ndzdri cdhdtddn dsaslandirilmi§ kinetic modeli i§ldnib hazirlanmi§ vd kinetic modelin parametrldrinin ddddi qiymdtldri hesablanmi§dir.
Agar sozlar: Tsikloheksanol, tsikloheksanon, oksidls§dirici dehidrogenhqms, kinetika
КИНЕТИЧЕСКАЯ МОДЕЛЬ РЕАКЦИИ ОКИСЛИТЕЛЬНОГО ДЕГИДРИРОВАНИЯ ЦИКЛОГЕКСАНОЛА НА МОДИФИЦИРОВАННЫХЦЕОЛИТНЫХКАТАЛИЗАТОРАХ
А.М. Алиев, З.А. Шабанова, М.К. Алиева, Г.А. Ализаде
Институт катализа и неорганической химии им. акад. М.Нагиева Национальной АН Азербайджана AZ1143 Баку, пр.Г.Джавида, 113; e-mail: kqki@,kqki. science.az
На основе экспериментальных данных была предложена вероятная схема механизма реакции окислительного дегидрирования циклогексанола. Разработана теоретически основанная кинетическая модель процесса и рассчитаны численные значения констант кинетической модели.
Ключевые слова: циклогексанол, циклогексанон, окислительное дегидрирование, кинетика
Redaksiyaya daxil olub 22.06.2017.
