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72 AZERBAIJAN CHEMICAL JOURNAL No 4 2020 ISSN 2522-1841 (Online)
ISSN 0005-2531 (Print)
UDC 542.943:661.725.6 OXIDATIVE DEHYDROGENATION OF CYCLOHEXANOL TO CYCLOHEXANONE CATALYSED BY MODIFIED ZEOLITE CATALYST
Z.A.Shabanova
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
zumrud-042425-@mail. ru
Received 08.04.2020 Accepted 15.07.2020
Gas-phase oxidative dehydrogenation at atmospheric pressure and a temperature of 260-3700C in the presence of a modified zeolite catalyst clinoptilolite cyclohexanol with a conversion of 90-99 % was oxidized to cyclohexanone with the selectivity of 96-98 %. It has been studied kinetic laws of the reaction.
Keywords: oxidative dehydrogenation, cyclohexanol, cyclohexanone, modified clinoptilolite.
doi.org/10.32737/0005-2531-2020-4-72-75
Introduction
Cyclohexanone, a large-capacity product of organic and petrochemical syntheses, is widely used in the production of polyamide plastics, synthetic fibers and biologically active preparations [1]. In this regard, the scale of its production is increasing annually. On an industrial scale, cyclo-hexanone is mainly obtained by oxidation of cy-clohexane with atmospheric oxygen at elevated pressure, mainly in the presence of homogeneous catalysts - soluble cobalt salts [2, 3].
In previous works [3-8] we found that zeolites modified by metal cations by the ion exchange method exhibit relatively high catalytic activity and selectivity in the oxidative reactions of aliphatic alcohols at relatively low temperatures (250-3500C). The use of multifunctional metal-zeolite catalysts in these reactions leads to a reduction in the consumption of raw materials, lower operating costs for the isolation and purification of the resulting product, and environmental protection. The development of these processes requires a detailed study of the mechanism of these reactions proceeding.
The aim of this present work is to study the catalytic activity of the modified zeolite in the oxidative dehydrogenation of cyclohexanol and to investigate the kinetic laws of the reaction.
Experimental part
The test of the activity of the metal-zeolite catalysts and a study of the kinetic regularities of the reactions was carried out in a flow
device with the quarts tube reactor connected directly to the gas chromatograph at atmospheric pressure, in the temperature range 260-3700C, space velocities by the alcohol 0.91-7.0 h-1, molar ratios of reagents C6H11OH:air = (0.63-1.3): (5.57-8.1).
Chromatographic analysis of oxidation products was carried out on an "Agilent 7890" chromatograph with an "Agilent-5975" mass detector with HP-5 MS column, 30 m long, 0.32 mm in diameter, filled with 5% phenyl, 95% methylpolysiloxane. The carrier gas is helium, flow rate - 2 cm3/min. program control of the temperature from 70 to 1800C at a speed of 150C per minute.
To prepare a catalyst based on the natural clinoptilolite it was initially dealuminated. A fraction of the initial zeolite with a grain size of 0.25-0.63 mm in a sample of 50 g is taken and processed in a liter flask at stirring with 2 N HCl solution (three times for 2 hours) at T = 95-960C. Cations of transition elements are introduced into the zeolite by the method ion exchange. A specific sample of zeolite with a grain size of 0.25-0.63 mm is placed in a 1-liter round-bottom flask, into which 100 ml of distilled water is added (until the zeolite is coated) and heated at stirring to 95-980C. Then, in this flask, dropwise, chloride solutions of the corresponding transition element are added. This mixture was stirred for 8-16 hours until the ions were completely exchanged. To determine the
completeness of the exchange, qualitative reactions of the interaction of the introduced ions are used. At the end of the exchange, the catalyst is washed from the Cl- ions with distilled water and dried at T=1500C. Before the study, the powdery zeolite was pressed into tablets with a diameter of 10 mm, which were crushed with the release of a fraction of 0.25-0.63 mm. Then the catalyst was activated by air purging at a feed rate of 2400 h-1 for 2 hours at T = 350-4000C, then the temperature decreased to the reaction temperature and the system was purged with nitrogen within one hour. The experiments showed that after preliminary processing of the catalyst, the latter worked stably, that was systematically verified during the study by control experiments confirming the reproducibility of the results.
The amount of introduced elements into the clinoptilolite composition was determined by ion spectral analysis on an "Agilent 7700 ICP-MS". We used catalysts with a particle size of 0.25-0.63 mm.
Results and its discussion
Table 1 shows the experiments results of synthesized catalysts in the cyclohexanol oxidation reaction at a space velocity of 2363 h-1 and the molar ratio of cyclohexanol: air = 1.1: 6.7.
As can be seen from Table 1, the initial cli-noptilolite exhibits a relatively low catalytic activity in the studied reaction. Modification of zeolite leads to an increase the catalyst activity. The results of the studies allow us to conclude that the most highly efficient catalyst for this reaction among the studied catalytic systems at the studied process parameters is the catalyst CuPdSn-clinoptilolite (0.5% Cu2+, 0.15% Pd2+, 0.5% Sn2+).
A study of the kinetic laws of the reaction was carried out under the following conditions: temperature - 260-3700C;the space velocity of reaction mixture (V) is 1036-3109 h-1; partial pressure (PalcohoO - 0.06-0.24 atm and (Po2) -0.05-0.24 atm. Tables 2, 3 present the results of a study of the kinetic laws of the oxidative de-hydrogenation of cyclohexanol on the selected active catalyst (CuPdSn-clinoptilolite).
Data in Table 2 that show, at a space velocity of 2073 h-1, at a constant Palcohol (0.12 atm) and a variation of P o2 from 0.05 to 0.24 atm, the maximum ketone yield is reached at P o2 = 0.18 atm at all studied temperatures. A further increase in P o from 0.18 to 0.24 atm leads to a decrease in the yield of cyclohexa-none. In the entire range studied, with an increase in the partial pressure of oxygen, the yields of the reaction products - methylcyclo-pentene, 2-cyclohexen-1-one, carbon dioxide, and cyclohexane conversion increase, and the cyclohexene yield decreases.
From the Table 3 it can be seen that at constant P o2 (0.17 atm) and with an increasing of Palcohol from 0.06 to 0.12 atm, the yield of cy-clohexanone increases and reaches a maximum. A further increase in Palcohol leads to a decrease in the yield of cyclohexanone. A decrease in the yield of ketone is accompanied by an increase in the yield of cyclohexene and methylcyclo-pentene and a decrease in the conversion of alcohol and the yields of 2-cyclohexen-1-one and carbon dioxide. This is explained by the fact that at a given partial oxygen pressure, the relatively high partial pressures of cyclohexanol prevent the coordination of oxygen with the active sites of the metal zeolite catalyst.
Catalyst Concentration of cations, % T, 0C Conversion, % Selectivity, %
Sn Pd Cu
Clin. - - - 300 85.4 17.1
Clin. (treat. NH4OH) - - - 280 98.0 27.4
Clin. (treat. NH4OH) - - - 320 96.8 50.9
Clin. 0.1 0.5 330 77.1 75.8
Clin. 0.5 0.15 0.5 245 80.8 92.2
Clin. 0.5 0.15 0.5 335 99.5 96.6
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Z.A.SHABANOVA
Table 2. The influence of the partial pressure of oxygen on the oxidative dehydrogenation of cyclohexanol (V=2073 h-1; VO =0.55 l/h; n0 =0.04785 mole/h; P o =0.17 atm; Gcat=2.94 g)
T, 0C Partial pressure, atm. Conversion, % The yield of the reaction products, %
P o2 P N2 Cyclohexene Cyclohexanone Methyl cyclopenthene Cyclohexyl cyclohexanone-1 CO2
260 0.05 0.83 49.7 2.9 38.5 0.9 7.4 -
260 0.13 0.75 75.5 1.8 54.7 1.1 17.9 -
260 0.17 0.71 90.42 1.1 65.5 1.9 21.9 0.02
260 0.24 0.64 94.2 0.5 65.8 3.7 23.8 0.4
320 0.13 0.75 90.41 3.2 81.1 3.6 2.5 0.01
320 0.17 0.71 97.38 1.8 88.7 4 3.3 0.08
320 0.24 0.64 99.4 0.5 89.3 4.9 3.9 0.8
350 0.13 0.75 92.8 2.3 87.9 1.9 0.5 0.2
350 0.17 0.71 99.2 1 94.4 2.1 1.1 0.6
350 0.24 0.64 100 0.1 94.7 2.5 1.5 1.2
370 0.13 0.75 95.4 2 86.6 1.4 - 5.4
370 0.17 0.71 100 0.4 91.8 1.7 0.2 5.9
370 0.24 0.64 100 - 90.5 1.9 0.7 7.3
Table 2. The influence of the partial pressure of cyclohexanol to the oxidative dehydrogenation of cyclohexanol (V =2073 h"1, Vo2=0.55 l/h; n0 = 0.04785 mole/h; P ^ =0.17 atm; Gcat=2.94 g)
T, 0C Partial pressure of the reagents, atm Conversion, % The yield of the reaction products, %
P 1 C6H,,OH Cyclohexene Cyclohexanone Methyl cyclopenthene Cyclohexyl cyclohexanone-1 CO2
260 0.17 0,67 84.1 2.1 63.4 2.5 16.1 -
260 0.24 0.59 75.5 3.1 60.2 3.5 8.7 -
290 0.17 0,67 90.72 2.8 79.8 3.3 4.8 0.02
290 0.24 0.59 87.1 4.4 75.6 4.9 2.2 -
320 0.06 0.77 99.1 1.5 79.5 1.7 15.7 0.7
320 0.12 0.74 97.88 1.8 88.7 4 3.3 0.08
320 0.17 0,67 96.75 4.2 85.6 4.7 2.2 0.05
350 0.06 0.77 100 0.8 86.2 1.5 9.8 1.5
350 0.12 0.74 99.2 1 94.4 2.1 1.1 0.6
350 0.17 0,67 97.1 1.7 92.9 2.8 - 0.2
370 0.06 0.77 100 - 84.5 1.1 6.9 7.5
370 0.12 0.74 100 0.4 91.8 1.7 0.2 5.9
370 0.17 0,67 99.8 1.5 90.9 2.5 - 4.9
From the above stated results it follows that the optimal partial pressures of the reagents at which the highest yield of cyclohexanone is achieved, are: Palcohol=0.12 atm and POz=0.18 atm.
From the data Table 2 and 3 it follows that with increasing temperature from 260 to 3500C, the yield of cyclohexanone increases and reaches a maximum at 3500C, and a further increase in temperature to 3 700C leads to a decrease in yield. Alcohol conversion and CO2 yield continuously increase throughout the studied temperature range.
The high selectivity (75-97%) of the
formation of cyclohexanone and the conversion of cyclohexanol (77-99%) and moderate temperature suggest the proposed catalyst may be of interest for further practical use.
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MODIFIKASIYA OLUNMU§ SEOLIT KATALIZATORU ILO TSIKLOHEKSANOLUN TSIKLOHEKSANONA KATALITIK OKSIDLO§DIRICI DEHIDROGENLO§MOSI
Z.0.§abanova
Modifikasiya olunmu§ seolit katalizatoru i§tirakinda 260-3700С temperaturda qaz fazada oksidkbijdirici dehidrogen-bsdirilmakla tsikloheksanol 90-99% konversiya va 96-98% selektivlikla tsikloheksanona oksidta§dirilmi§dir. Reaksiyanin getmasinin kinetik qanunauygunluqlari oyranilmi^dir.
Agar sozlzr: oksidh^dirici dehidrogenh§m3, tsikloheksanol, tsikloheksanon, modifikasiya olunmu§ klonoptilolit.
ОКИСЛИТЕЛЬНОЕ ДЕГИДРИРОВАНИЕ ЦИКЛОГЕКСАНОЛА В ЦИКЛОГЕКСАНОН, КАТАЛИЗИРУЕМОЕ МОДИФИЦРОВАННЫМ ЦЕОЛИТОМ
З.А.Шабанова
Газофазным окислительным дегидрированием при атмосферном давлении и температуре 260-3700С в присутствии модифицированного цеолитного катализатора циклогексанол с конверсией 90-99 % был окислен в циклогексанон с селективностью 96-98 %. Изучены кинетические закономерности протекания реакции.
Ключевые слова: окислительное дегидрирование, циклогексанол, циклогексанон, модифицированный клиноптилолит.
