Научная статья на тему 'Kinetic model of oxidative dehydrogenation of cyclohexanol reaction over modified zeolite catalyst'

Kinetic model of oxidative dehydrogenation of cyclohexanol reaction over modified zeolite catalyst Текст научной статьи по специальности «Химические науки»

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CYCLOHEXANOL / CYCLOHEXANONE / OXIDATIVE DEHYDROGENATION / KINETICS / ЦИКЛОГЕКСАНОЛ / ЦИКЛОГЕКСАНОН / ОКИСЛИТЕЛЬНОЕ ДЕГИДРИРОВАНИЕ / КИНЕТИКА

Аннотация научной статьи по химическим наукам, автор научной работы — Aliyev A.M., Shabanova Z.A., Aliyeva M.K., Alizadeh G.A.

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.

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Текст научной работы на тему «Kinetic model of oxidative dehydrogenation of cyclohexanol reaction over modified zeolite catalyst»

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: [email protected]

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

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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: [email protected]

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.

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