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AZ9RBAYCAN KIMYA JURNALI № 4 2016
УДК 544.4;544.47:544.344
SELECTIVE OXIDATION OF CHLOROTOLUENES TO CHLOROMALEIC ANHYDRIDES OVER OXOVANADIUM CATALYSTS
E.M.Babayev, A.C.Efendi, I.G.Melikova, N.F.Aykan, B.A.Ismayilova
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
[email protected] Received 30.06.2016
Studies devoted to the eco-friendly disposal of hazardous chloro-substituted toluenes (CT) through oxidation in the presence of oxovanadium catalysts (OVC) are reviewed. The common feature of having one or more covalent bound chlorine atoms, these compounds show a complex diversity of behavior that is primarily characterized by their aromatic character and the presence of other functional groups. Nevertheless, the introduction of chlorine atom(s) into desired products significantly influences its physicochemical and biochemical properties. These properties have pushed the chloro-hydrocarbon chemistry into the focus of considerable debate and research topic. The oxidation rate and direction determined by the temperature (300-4000C), proportions between the reagents (1:1-1:15 mol/L), bond dissociation energies, the effects of active components of catalyst and contact time.
Keywords: oxidation reaction, chlorotoluene, catalysts, maleic anhydride, chloro-maleic anhydrides, oxovanadium catalyst, chlorobenzaldehyde.
Introduction
Catalytic systems based on salts and oxides of V, Mo, St, Bi, Cu, Cr, Co were prepared by co-precipitation, impregnation and mechanical-chemical shifting for carrying out heterogeneous oxidation reactions of alkylaro-matic chlorohydrocarbons, and the systems supported on carriers Al2O3, SiO2, TiO2, pumice, coal showed more higher performance among the received systems [1, 2]. Among several elements that are being tested and tried for catalysis, vanadium oxide and other compounds containing vanadium have attracted significant attention as catalyst for the reaction [3, 4]. Depending on the specific oxide support vanadium catalysts may show different catalytic activity and selectivity due to the nature and the surface area of the support as well as the vanadium content, which are all key factors in the formation of surface species [5-7]. Apart from this, vanadium oxide has also been explored for various other applications including pseudo-capacitors and cathode material in various conversion reactions. Notably, vanadium has displayed excellent catalytic activities in all forms, whether it has been employed as a supported active phase or in the form of mixed oxides prepared in combination with other ions; it displayed efficient catalytic properties as an oxidation catalyst.
In this respect, the present work is aimed at preparation and textural, structural and acid characterization as well as catalytic behaviour in the gas phase selective oxidation of mono-CT of vanadium systems with different V2O5 loading, supported Al2O3 and SiO2. Catalytic systems were prepared by co-precipitation and characterized by Scanning Electron Microscope (SEM), IRS, X-ray diffraction, N2 adsorption/desorption, thermal analyses. The effect of heat treatment and phase formation of the synthesized catalytic systems were studied on their activity in the oxidation reactions.
Experimental part
The systems were mainly received by the diluting vanadate, phosphate in the oxalate or hydrochloric acid. Solid solution was evaporated for the short time and permeated on the SiO2 or Al2O3. Then desiccated on air at 180-2300C for an hour, at further step it was calcined in the fume cupboard 270-3800C for two hours, and finally calcined for an hour at 5000C. Before the reaction the reagents were heated to above than 1000C, and then oxidation process was carried out. Kinetic regularities of heterogeneous catalytic oxidation of chlorinated alkyl aromatic hydrocarbons were studied. Probable mechanism scheme, kinetic and mathematical models of the oxidation processes were proposed. The
АЗЕРБАЙДЖАНСКИМ ХИМИЧЕСКИМ ЖУРНАЛ № 4 2016
influence of initial, intermediate products and reaction yields on the kinetics of oxidation reactions has been revealed.
Phase identification and qualification: phase properties (cell parameters, crystallite size, and lattice strain), are offered crystal structure of synthesized catalytic systems was determined by the Bruker manufactured (Germany) D2 Phase X-ray powder Diffraction analyzer. BET surface area was measured on a Gas Adsorption Porosymeter surface area and pore size analyzer (Thermo Scientific, Italy). Thermogravimetric analysis was carried out using NETZSCH STA 449F3 (Germany). SEM and elemental analysis were carried out. This was used to determine the morphology of the system and its elemental composition.
Selective oxidation mono-CT was carried out in a continuous flow fixed-bed reactor at an atmospheric pressure and in the temperature range of 370-4800C. Chlorotoluenes were fed by means of micro-feeder at 0.8 mL/h and the ratio CT/air (O2) =1:20. Catalyst was pre-treated at the reaction temperature for 1 h in a Fair = 25 cm3/min. An analysis of reagent and product composition was carried out using Agilent 7820A (Agilent Technologies, USA) Gas Chromatography equipped with a flame ionization detector (FID) and Hp5 column.
The values of CT oxidation rate, rCT were obtained from conversion (X) values, according to the equation, rCT=XF/W*100, where Wis catalyst weight, and F is a feed rate of CT (mol/h).
Results and discussion
Catalysts characterization. The morphology and particle size of the synthesized catalysts were characterized using SEM. The SEM micrographs of the pre-calcined (3000C) catalyst VPO/SiO2, where V:P=1:1-1:5, are shown in Figure 1. It was observed that the morphology of the synthesized catalysts is not well defined, and the surface appears to be rugged without any obvious phase separation. The stoichiometric amount of elements was confirmed from the EDX, analysis and found to be approximately in agreement with calculated value.
The result of elemental analysis is given in the Table. There is insignificant amount of
600MKm
Fig.1. SEM view of VPO/SiO2
calcium and sodium in the system which probably doesn't influence on catalytic behaviour in the system, as it is seen in the Table 1.
Elemental characterization of VPO/SiO2 (V:P=1:2)
Element Weight, % Atom, % Component, % Formula
Na,K 0.43 0.39 0.58 Na2Ü
Si, K 28.62 21.26 61.23 SiO2
P, K 9.59 6.46 21.97 P2O5
Ca, K 0.21 0.11 0.30 CaO
V, K 8.92 3.66 15.93 V2O5
O 52.23 68.12
Total 100.00
Figure 2 shows X-ray diffraction patterns of mixed oxides of phosphorous silica, with different ratio of vanadium oxide pre-calcined at 3 000C. Determined of both oxovanadium (33.3%) and divanadium pentoxide (28.3%) in the catalytic system vanadium includes on the monoclinic structure.
The thermal stability of the synthesized catalyst with different % loading of vanadium oxide systems were studied using TGA analysis. Temperature was programmed from 25 to 9000C at a heating rate of 10 C/min. It was observed that almost all synthesized catalysts are thermally stable, yielding maximum loss of weight of 31.97 % at 8950C the catalyst VPO/SiO2 (V:P=1:5) was the least stable while VPO/SiO2 (V:P=1:2) was the most thermally stable catalysts with a least weight loss % just 18.4 % at the same temperature among the synthesised systems. A graphical illustration is given in Figure 3.
Fig. 2. XRD patterns of VPO/SiO2 (V:P=1:2) calcined at 3000C.
100 50 0 -50 100 150 >00 250 »0
Dil/- 1 £ 1 RAP mr-UImn
DSC /(mcV/mg)
Gas flo'.v/l "i-V n)
t EXO
300 400
Temperature °C
Fig. 3. TGA curves of synthesized catalyst VPO/SiO2.
Catalytic test. There is defined chloro-toluenes (CT) form n- and o-complexes while adsorption on a surface of heterogeneous catalysts (VPO/SiO2 and etc.) which turning into maleate structures desorbs in the form of ma-
leic anhydride (MA) and its chloraderivatives. Oxidation process of CT takes place on the redox mechanism and a series of parallel pattern was revealed [3, 8].The reaction scheme for the p-chlorotoluene is shown below:
CHO
[O]
CH,
II Cat
Y
X=H, Y=Cl; X=Cl, Y=Cl
-H2O
O^C_-OH
X
[O]
Y
X
Y
X
[O]
-CO2 C Y
O // -C \
O _
-c' -H2O, HCl SO
[O]
_ H2O -HCl
CO2
[O]
C
The oxidation processes of chlorinated alkyl aromatic hydrocarbons were investigated bothon a fixed bed and fluid-bed layer of the catalyst. Although the process of heterogeneous catalytic oxidation of chlorotoluenes took place with a higher conversion in a fixed bed but it showed higher selectivity of fluid-bed layer of catalyst. It was determined that used vanadium/phosphorus/oxide system (VPO/SiO2 and etc.) deactivated both on a fixed bed and fluid-bed layer of catalyst, but deactivation rate and time was almost twice lower on the fluid-bed layer of catalyst.
An effect of active components of these catalysts on the oxidation reaction was also studied. CT performs 75-92% conversion at a V:P=V:Mo=1:2-1:3 ratios, the yields of chloromaleic anhydride (CMA) was 24-32%. Yield of chlorobenzaldehyde begins to increase at V:P=1:4-1:5 ratios. According to the obtained results usage of the catalytic systems
too
90 80 70 60 50 40 30 20 10 0
Conclusion
In conclusion, it has been determined that oxovanadium systems modified with molybdenum, phosphorous, and supported on SiO2 and Al2O3 (V-P-O/SiO2 and V-Mo-O/Al2O3) are the most active and selective catalytic systems in the gas phase selective partial oxidation of chlorotoluenes. The catalysts show excellent recyclability and reusability.The optimum reaction condition for the activity and selectivity for received catalysts was designated.
based on V: P=1:2-1:3 are considered purposeful for our further researches.
Temperature dependence of oxidation reaction of chlorotoluene on the oxovanadium systems was established (Figure 4). Although the oxidation reaction begins from the 350 C determined that the yields of main products are negligible. By increasing temperature both the conversion of the CT and yield of CMA begins to enhance, and at the 4200C temperature it shows the maximum (24-32%), and simultaneously, yields of maleic anhydride (MA), chlorobenzaldehyde and chlorobenzoic acid (CB acid) decreases. By the further rise of temperature CT conversion continues to increase, but also yields of the main products at its maximum begin to decrease and this happens by way of their exposing deep oxidation process that verified by increasing of CO2 yield as it is seen from the reaction scheme.
Fig. 4. Temperature dependence of the ^-chlorotoluene oxidation reaction yields on the synthesized V-P-O systems supported by SiO2.
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OKSOVANADIUM KATALiZATORLARININ i§TiRAKINDA XLORTOLUOLLARIN XLORMALEiN
ANHiDRlDiNO SELEKTiV OKSiDLO^MOSi
E.M.Babayev, A.C.Ofandi, i.H.Melikova, N.F.Aykan, B.A.ismayilova
Oksovanadium katalizatorlarinin i§tirakinda xloravazli toluollarin (XT) ekoloji-tamiz zararsizla§dirilmasi öyranilmiijdir. Bir va ya daha gox kovalent rabitali xlor atomlu bu birla§malarin kompleks müxtaliflik göstarmasi tarkibda aromatik halqanin, elaca da digar funksional qruplarin olmasi ila xarakteriza olunur. Bununla bela, xlor atomlarnin alinan maddalarin tarkibina daxil edilmasi onlarin fiziki-kimyavi va biokimyivi xassalarina ahamiyyatli daracada tasir edir. Bütün bu göstaricilar xlor-karbohidrogen kimyasini önamli müzakira va tadqiqat obyektina gevrilmiijdir Oksidla§manin süratina va istiqamatina temperaturun (300-4000C), reagentlarin bir-birina olan nisbati (1:1-1:15 mol/l), rabitalarin dissosasiya enerjilarinin, katalizatorlarin aktiv komponentlarinin va kontakt müddatinin tasiri müayyan edilmi§dir.
Agar sözlar: oksidh§m3 reaksiyasi, xlortoluol, katalizatorlar, malein anhidridi, xlor-malein anhidridi, oksovanadium katalizatoru, xlorbenzaldehidi.
СЕЛЕКТИВНОЕ ОКИСЛЕНИЕ ХЛОРТОЛУОЛОВ В ХЛОРМАЛЕИНОВЫЙ АНГИДРИД В ПРИСУТСТВИИ ОКСИВАНАДИЕВЫХ КАТАЛИЗАТОРОВ
Э.М.Бабаев, А.Д.Эфенди, И.Г.Меликова, Н.Ф.Айкан, Б.А.Исмаилова
Изучено обезвреживание хлорзамещенных толуолов в присутствии оксиванадиевых катализаторов. Показано, что наличие в молекуле полученных соединений ковалентно связанных атомов хлора существенно влияет на их химические и биологические свойства. Эти показатели наряду с решением экологических вопросов также являются интересными с точки науки превращения хлоруглеводородов. Выявлено влияние температуры (300-4000C), соотношения реагентов 1:1-1:15 моль/л. энергии диссоциации, соотношения активных компонентов и времени контакта на скорость и направление реакции окисления.
Ключевые слова: реакция окисления, хлортолуол, катализаторы, малеиновый ангидрид, хлормалеиновый ангидрид, оксиванадиевый катализатор, хлорбензальдегид.
