Kinetics of o-chlorotoluene hydrogenolysis in the presence of 3%, 5% and 10% Pd/C catalysts
Graphical abstract
The kinetics of o-chlorotoluene hydrogenolysis in the presence of 3%, 5% and 10% Pd/C catalysts was experimentally investigated in an alkaline – n-heptane – gaseous hydrogen system. The main product of hydrogenolysis was toluene. Kinetic characteristics for the reaction were obtained for all the catalysts at 20, 40 and 60 °C. The activation energies of o-chlorotoluene hydrogenolysis for these catalysts were calculated.
Introduction
Chloroaromatic compounds can be converted to parent hydrocarbons over Ru, Rh, Ni, Pd and Pt metal catalysts during hydrogenolysis with gaseous hydrogen [1], [2], [3], [4]. Palladium is the most active hydrodechlorination catalyst in such conditions [5]; rhodium is the most effective in transfer hydrogenolysis with propanol-2 as the hydrogen source [6].
Hydrodechlorination of chlorobenzene, chlorotoluenes, chlorobiphenyls and 1,1-bis (4-chlorophenyl)-2,2,2-trichloroethane in the presence of Pd catalyst has been carried out in the gaseous [7], [8], [9] and liquid [6], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33] phases. Hydrogenolysis has been done in the presence of Pd/Al2O3 [7], [8], [12], Pd/ZrO2 [9], Pd/AlPO4–SiO2 PM2 [17], [18], [19], Pd/zeolites [21], Pd/poly(dimethylsiloxane) [22] and Pd/C [6], [10], [11], [13], [14], [15], [16], [20], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33] using gaseous hydrogen [7], [8], [9], [11], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], propanol-2 [6], [10], [11], [12], potassium formate [11], formic acid [12], hydrazine [12] or hypophosphite [23] as the source of hydrogen. Liquid-phase hydrodechlorination has been investigated in one liquid medium with [13], [14], [15], [16], [17], [19] and without a base [18], [20], [21], [22], as well as in two liquids [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33]. In these two liquids – multiphase systems – hydrodechlorination proceeds effectively even under mild conditions, that is, at temperatures up to 50 °C and with hydrogen at atmospheric pressure. Experiments in these systems have been performed in the presence of a transfer phase catalyst (PT) [23], [24], [25], [26], [27], [28], [29] and in its absence [32], [33]. Our previous papers reported on the results of the hydrodechlorination of chlorobenzene, dichlorobenzenes and chlorotoluenes in a batch-type multiphase reactor. The process was carried out in the presence of a 10% Pd/C catalyst dispersed in an n-heptane or n-hexane solution of the chlorinated compound and an aqueous solution of NaOH. We studied the influence of in situ generated and gaseous hydrogen [32], the stirring rate, NaOH concentration, temperature, and the impact of preconditioning Pd/C on the effectiveness of the hydrogenolysis [33]. Little has been published on the kinetics of the hydrodechlorination of chloroaromatic compounds in multiphase systems [25], [29], [30], [31]. In this paper, the effect of the palladium content in the catalyst on the kinetics of o-chlorotoluene hydrogenolysis is explored. The investigations on the hydrogenolysis of this model system may be of utilitarian value in that it creates a framework for developing methods of treating organochlorine wastes.
Section snippets
Materials
The catalysts – 3% Pd/C, 5% Pd/C and 10% Pd/C, as well as o-chlorotoluene (99.9% purity), p-chlorotoluene (98% purity), 1,2-dichlorobenzene (99% purity) and n-dodecane (>99.9% purity) were purchased from Sigma–Aldrich; the n-heptane (99.5% purity) solvent was from Lab-Scan. 4-chlorobiphenyl was synthesised in our laboratory. Sodium hydroxide (p.a. purity) was supplied by POCH-Gliwice, the nitrogen and hydrogen (>99.5% purity) by Linde. The characteristics of the catalysts are as follows: 3%
Results and discussion
In a multiphase, heterogeneous catalytic system containing two immiscible liquids with different polarities, pre-conditioning of the catalyst influences the kinetics of the reaction. In our previous paper [33] we studied the kinetics of chlorobenzene hydrodechlorination over 10% Pd/C in an n-heptane – aqueous solution of NaOH. We found that when the catalyst was preconditioned by soaking and stirring it in an n-heptane solution of chlorobenzene and n-dodecane prior to hydrogenolysis, the time
Conclusions
The hydrogenolysis of o-chlorotoluene in the presence of Pd/C catalyst removes chlorine from it with a yield of up to 100%, which is a promising result if the intention is to dechlorinate this particular compound.
All three catalysts used exhibit a similar catalytic activity. The extent of dechlorination increases with time and temperature, and depends on the amount of catalyst in the system.
Kinetic analysis based on the Langmuir–Hinshelwood approach enabled the kinetic constants to be
Acknowledgements
The authors wish to thank Dr J. Okal from the Institute of Low Temperature and Structure Research of the Polish Academy of Sciences in Wroclaw for the dispersion measurements of the catalysts.
The financing of this work from the State Funds for Scientific Research (grant No. DS/8000-4-0026-7) is gratefully acknowledged.
References (41)
- et al.
J. Mol. Catal. A Chem.
(2001) - et al.
Appl. Catal. B Environ.
(1998) - et al.
J. Catal.
(1978) - et al.
J. Catal.
(1986) - et al.
J. Mol. Catal. A Chem.
(2004) - et al.
J. Mol. Catal. A Chem.
(1997) - et al.
C.R. Acad. Sci. Paris, Serie IIc, Chimie/Chemistry
(2000) - et al.
Appl. Catal. A Gen.
(2004) - et al.
J. Mol. Catal. A Chem.
(2000) - et al.
Tetrahedron Lett.
(2002)
Tetraedrom Lett.
J. Appl. Catal. B Environ.
Appl. Catal. B Environ.
J. Mol. Catal. A Chem.
J. Mol. Catal. A Chem.
Appl. Catal. B Environ.
Catal. Today
J. Mol. Catal. A Chem.
React. Funct. Polym.
A Gen.
Cited by (12)
Toluene and 4-chlorotoluene decomposition in air mixture in electron beam generated non-thermal plasma reactor and their by-products identification
2013, Surface and Coatings TechnologyCitation Excerpt :Concerning 4-chlorotoluene (4-CT), a few works have been reported for its removal in gas phase [23]. Dechlorination of 4-chlorotoluene in aqueous solution was studied, toluene [24] and benzene [25] were reported as dechlorination products. Radical species formed from AOTs can oxidatively destroy organic pollutants in gas phase.
Kinetic study of the hydrogenolysis of polychlorobenzenes over a Pd/C catalyst in an alkaline aqueous-n-hexane system
2010, Catalysis CommunicationsEffectiveness and stability of commercial Pd/C catalysts in the hydrodechlorination of meta-substituted chlorobenzenes
2009, Applied Catalysis B: EnvironmentalTunable Crystalline Organic Cage for Selective Sorting of Ortho-Monohalotoluene Isomers
2024, ACS Materials LettersDechlorination of chlorotoluene rectification residual liquid (CRRL) by using Williamson ether synthesis (WES) method
2020, Environmental Science and Pollution Research