CC BY
88
AZ9RBAYCAN KIMYA JURNALI № 1 2018
23
UDC 544.4;544.47544.344
THE SYNTHESIS OF NEW MONOOXYGENASE BIOMIMETIC CATALYSTS AND OXIDATION IN THE THEIR PRESENCE OF HYDROCARBONS BY HYDROGEN PEROXIDE TO CHEMICALLY IMPORTANT COMPOUNDS
L.M.Gasanova
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS Azerbaijan
[email protected] Received 25.12.2017
Heterogeneous ironporphyrin-containing biomimetic catalysts were investigated for their selectivity in relation of determined compound in the cyclohexane gas-phase oxidation process and mixture of the latter with its derivatives by hydrogen peroxide. On the basis of experimental investigations of the cyclohexane monoox-idation process it was investigated that the complex reaction, consisting of parallel-consecutive monooxida-tion reactions and oxidative dehydrogenation, which are the coherent-synchronized reactions were proceed on the biomimetic catalyst. The probable mechanisms of cyclohexane biomimetic transformation to desired products, in which there is a unity of mechanisms of acid-base catalysis and the redox system by the principle of BRC (bonds redistribution chain) typical for enzymatic catalysis, were presented. The direct oxidation of methane to methanol by hydrogen peroxide also was investigated in the presence of biomimetic catalyst.
Keywords: cyclohexane, cyclohexanol, cyclohexanone, coherent-synchronized reactions, biomimetic catalysts, enzymatic catalysis, methane, methanol.
Monooxidation of cyclohexane by hydrogen peroxide on biomimetic catalyst
Heterogeneous biomimetic catalysts on the base of ironporphyrin complexes being an active part of enzyme cytochrome P-450 allow us to realize coherent-synchronized oxidation of a number of hydrocarbons by hydrogen peroxide in gas phase in the most mild conditions with high selectivity [1, 2].
One of the important processes of the oil chemistry is the oxidation of cyclohexane, which oxidation products have a wide application. Application of biomimetic catalyst in this process, investigation of its activity, selectivity, also study of its action mechanism is the one of priority directions of our investigation.
The wide experimental investigation of gas-phase monooxidation of cyclohexane by hydrogen peroxide was performed in the presence of biomimetic catalyst - perfluorinated iron(III)tet-raphenylporphyrin [3-12].
The first stage of the investigations was the investigation of the biomimetic catalytic system for the selective nature of their actions by using as a raw material the mixtures of cy-clohexane with some derivatives.
The results of investigations by using of raw material with the composition (%) 88.85 C6H12, 6.25 C6HnOH and 2.53 CH3C6H11 were showed that during the oxidation process, mainly cyclo-hexane undergoes transformation, but quantity of
methylcyclohexane presented in the composition of the raw material remains practically unchanged.
With the aim to establish selective action of used by us ironporphyrin-containing biomi-metic catalysts in the oxidation of complex mixtures, as a raw material there was taken artificially prepared mixture with a content, %: 45.4 C6H12, 38.64 CH3C6H11, 1.91 C6H11OH.
The investigation results of the oxidation process of this mixture by 20% hydrogen peroxide at various raw material supplying rates and different temperatures on the biomimetic PPFe(III)/Al2O3 were shown in Table 1. From the data of Table 1 an unambiguous conclusion follows about the selective action of the catalytic biomimetic in relation of cyclohexane oxidation in the mixture that have a significant quantity of methylcyclohexane (38.6%).
On the base of obtained results the mechanism of the coherent-synchronized biomimetic oxidation reaction of cyclohexane is presented. Kinetic regularities of the cyclohexane transformation on the biomimetic catalyst per-FTPhPFe(III)OH/Al2O3 in dependence of temperature (Figure 1) show that at temperature of 150-1800C with the greatest speed proceed the oxidation reaction of cyclohexane to cyclohexanone and cyclohexanol.
Table 1. The results of cyclohexane oxidation process in the mixture on the biomimetic, PPFe(III)/Al2O3 by hydrogen peroxide: Ch2q2 = 20%, Vh2o2 = 1.41 ml/h, Vc6h12 = 0.9 ml/h
Composition of raw material Reaction products rn
t, 0C C6H12 C6H11CH3 C6HuOH Dimethylcyclo-hexane C6H12 C6H11CH3 CeHnOH C6HuO C6H10 Dimethylcyclo-hexane ,n oi 'и Ö £ Ö ac ,n ■ s ■-§ la
Co ee о
150 45.439 38.638 1.913 5.479 37.1 38.928 0.641 3.445 6.256 6.771 8.34 91
180 45.439 38.638 1.913 5.479 33.19 39.31 1.848 4.239 8.073 7.078 12.2 88
200 45.439 38.638 1.913 5.479 29.34 36.579 2.793 5.715 9.5 7.165 16.0 84
220 45.439 38.638 1.913 5.479 24.85 38.63 2.5 7.5 12.5 6.7 20.5 79
By temperature increasing the yield of cyclohexene dramatically increases and discreetly cyclohexadiene, due to the increase in the reaction rate of oxidative dehydrogenation of cyclohexane in these conditions. The yield of cyclohexanol with temperature is decreased, but
the yield of cyclohexanone at 1800C passes through a maximum (10.34%).
The influence of the aqueous solution of hydrogen peroxide concentration on the process of monooxidation and oxidative dehydrogenation of cyclohexane is presented in Figure 2.
Yield, %
Yield, %
80
20
10
0
80
70
6
30
__---* i
-- 4 20
10
s^! —— 3
5
• 2 0
150 180 200 230 t, °C
Fig.1. Temperature dependence of products yields of cyclohexane oxidative transformation by hydrogen peroxide in the mixture with 6.25% C6H„OH and 2.53% CH3C6H11 on biomimetic per-FTPhPFe(III)/Al2O3: 1 - conversion of C6H12 , 2 - cyclohexanol, 3 - cyclohexanone, 4 - cyclohexene, 5 - cyclohexa-diene, 6 - 02; CH O = 25%, VH O = 1.41
6
i
3
4 2
5
25 30
35
~~'-С
40 °-ьЛн2О2
Fig.2. Dependence of products yields of cyclohexane oxidation reaction on biomimetic per-FTPhPFe(III)/Al2O3 on aqueous solution H202: 1 - conversion of C<;H12, 2- cyclohexanol, 3 - cyclohexanone, 4 - cyclohexene, 5 - cyclohexadi-
ene, 6 - 02; t = 2000C, VHO =1.41 ml/h,
= 0.9 ml/h.
ml/h, 1:1.7.
= 0.9 ml/h, C6H12:H2O2 =
L.M.GASANOVA
25
Increasing of Н2О2 concentration leads to marked decreasing of the speed of oxidative dehydrogenation of cyclohexane and considerable increasing of cyclohexanone yield. Kinetic curves of monooxidation products formation -cyclohexanone and cyclohexanol, show that the yield of cyclohexanone increases from 10% to 14%, while the cyclohexanol yield passes through a maximum (7.6 %).
The complex nature of these kinetic curves (Figures 1 and 2) does not give an unambiguous answer to the key question: whether cyclohexanone is formed from cyclohexanol. In this regard, the reaction of cyclohexanol oxidation (97.52% in original C6HnOH) was investigated under identical conditions.
From the kinetic curves of Figure 3 it follows that the peroxidase reaction of cyclohexa-nol, i.e., the formation of cyclohexanone is practically not observed, there basically goes on a dehydration of cyclohexanol to cyclohexene.
yield, %
of cyclohexanol increases to the side of cyclohexene formation.
The experimental data of Figure 3 unambiguously show that in the reaction system the reaction of cyclohexanol dehydration to cyclohexene occurs. Thus, the kinetic data of Figures 1 and 3 shed light on the mechanism of cyclohexanol and cyclohexene formation. Really, the kinetic data of Figure 1 show that at temperatures up to 150-1800C, mainly, the reaction of cyclohexane monooxidation proceeds, and above 1800C the reaction of oxidative dehydro-genation of cyclohexane to cyclohexene (curve 4, Figure 1) is accelerates, the yields of cyclo-hexanol and cyclohexanone decrease, respectively. Sharp increase in cyclohexene yield in parallel with decreasing of the cyclohexanol yield indicates that at 2300C and at lower concentrations of H2O2 in the reaction system cy-clohexanol converts into cyclohexene. Such conclusion unambiguously is confirmed by the experimental data of C6H11OH oxidation on bio-mimetic catalyst, at 200-2300C: cyclohexanol fully subjected to dehydration (Figure 3) with obtaining a high yield of cyclohexene (16-30%).
Thus, from the experimental data of Figures 1 -3 we can conclude that the process of cyclohexene formation proceeds via the consecutive-parallel mechanism, which can be represented in the following scheme:
^C^O+ffljO
C6Hn +H20: -^CfHnOH^C;Hls +H20 (1)
It should be noted that the temperature increasing from 1500C to 2300C the conversion
C6H1S + 2H:0
Comparing the kinetic curves of cyclo-hexene formation in Figures 1 -3 it can be concluded that at temperatures above 1800C and at the lowest concentration of H2O2, the main part of cyclohexene is formed by oxidative dehy-drogenation of cyclohexane by the reaction of 4 (scheme 1). Of course, this does not exclude the possibility of cyclohexene formation via the consecutive reactions 2 and 3. The formation of cyclohexanone takes place by direct conversion of cyclohexane (reaction 1). The coherent-synchronized reactions of cyclohexane mono-
oxidation by hydrogen peroxide is described by the following generalized scheme [1, 2]:
H;0
H;
* H;0 + O;
ImtOH —{ 1
(2)
yf^- reac.prod. (С^цОХ, ImtOOH -7 2 CsHmO; CsHio; CsHs)
CsHi;
From this scheme it follows that the primary reaction of H2O2 decomposition forms the
highly reactive hydroperoxide active center, which interacts in the system both with H2O2 molecules and molecules of cyclohexane. Scheme 3 illustrates the principle of construction of the complex ImtOOH/Al2O3 on the biomimetic per-FTPhPFe3+OH/Al2O3 by the theory of bonds redistribution chain (BRC) in catalase reaction, like the formation of the Chance complex (PPFe OOH) under the action of the enzyme catalase. As the matrix of the acidic-basic nature in our case, Al2O3 is used [13].
Primary (catalase) reaction
H202 + ImtOH/АЬОз Н202 + Imt0H/Al203-> Н20 + 02 + ImtOH
\
4 '"Vl H
о. PI " -'О,
/ > С> / v '
--о. \ ^ о \ ЬА1
+Н;0
where, ImtOH/Al2O3 - catalytic biomimic (imitator); ImtOOH/Al2O3 - intermediate; + and ••• - correspondingly breaking and formation of bonds, respectively.
High-active intermediate per-FTPhPFe(III)OOH/Al2O3 interacting with cy-
clohexane leads to the formation of desired products (secondary reactions).
Mechanisms of cyclohexane monooxida-tion to cyclohexanol and oxidative dehydro-genation of it to cyclohexene on the biomimetic catalyst, according to known representations [1], can be represented as follows:
Mechanism of cyclohexane monooxidation to cyclohexanol
where A and B are acid and base centers respectively.
In the schemes of the mechanism of cy-clohexane transformation to cyclohexene and cyclohexanol there is also traced the unity of the acid-base and oxidation-reduction mechanisms on the principle of BRC (scheme 4 and 5). Under
the action of acid-base centers of support takes place the transfer of two or more protons from the substrate and the acid center of the substrate with the formation of cyclohexanol or cyclohexene at different stages of cyclohexane oxidation.
Methane oxidation by hydrogen peroxide on the biomimetic catalyst
The chemical transformation of low al-kenes, the main products of natural and associated gases, has become one of the important trends of the modern petrochemical industry and a new industrial sector: the gas chemistry. The direct transformation of methane to methanol and other oxygen-containing compounds for many decades was the goal of the gas industry.
The main common industrial method of methanol producing from methane consists of two stages: 1) methane transformation to the synthesis-gas (2CH4+O2^2CO+4H2) by deep oxidation; 2) transformation of synthesis-gas to methanol. Despite numerous studies in the field of direct oxidation of methane to methanol with oxygen or air in the presence of various catalysts, these processes have not found industrial application due to low yields of methanol and low selectivity. It is known that methane is difficult to convert the hydrocarbon component, and its thermic transformation occurs only at temperatures above 9000C.
A few years ago, due to induction property of hydrogen peroxide the transformation of methane was achieved without using of any catalysts at atmosphere pressure at 460-5 800C by free-radical mechanism. In this process the yield
of methanol was only 5-6% with low selectivity, the main product of reaction was formaldehyde [14, 15]. Conducting this process under pressure at temperature 4000C it was possible to increase the yield of methanol to 17% [16]. Last time, by using synthesized biomimetic catalyst in the process of methane oxidation by hydrogen peroxide already at a temperature of 1800C methanol with high selectivity was form with the yield of 3040%. As a biomimetic catalyst we use the iron protoporphyrin (hemin), immobilized on various supports - PPFe(III)OH/Al2O3, PPFe(III)OH/AlMgSi, PPFe(III)OH/NaX. These catalysts quickly lose their activity. Even catalyst PPFe(III)OH/AlMgSi manifesting the highest activity worked only 6 hours [17].
The aim of the present work is to develop a new more resistant to temperature and oxidant biomimetic catalyst for direct, partial oxidation of methane. For the synthesis of new biomimetic catalyst we use fluorinated 5,10,15,20-tetra-kis(pentaflurofenil)-21H,23H-Fe(III)Cl, in which the hydrogen atoms of phenyl groups of ironpor-phyrin complex substituted by fluorine. Immobilization of this complex on Al2O3 was carried out from its solution in dimethylformamide by adsorption method. The catalysts with concen-
trations of active complex 2.92 and 1.92 mg/g were obtained.
Investigation of the process of methane oxidation by hydrogen peroxide in the presence of this biomimetic catalyst was carried out at temperature 200-300°C. At temperature 2400C 5.84% of methanol was obtained, at 2800C -8.6%, on missed methane, on the catalyst with concentration 2.92 mg/g. Further temperature increasing (over 2800C) led to decrease the yield of methanol to 4.7% at 3000C, that associated with production of 4.0% CH2O and 0.2% CO2 (Figure 4).
The next series of experiments is dedicated to studying H2O2 concentration influence and biomimetic catalyst on the reaction proceeding and it is established that the temperature increasing of these concentrations has a positive effect on the yield of methanol.
The investigation of the catalyst surface was conducted by scanning electron microscope, and were determined the micro- and na-nosizes of pores of Al2O3 support and active complexes adsorbed in those pores (Figure 5).
Yield, % 10
Fig.4. Dependence of reaction products yields on temperature: 1 - CH3OH, 2 - CH2O, 3 -
CO2; CHA = 30%, VH2c2 = 1.01 ml/h, VCH =
0.24 ml/h, CH4:H2O2 = 1.08:1.
220 230 240 250 260 270 2№ 290 '00 t, °C
L.M.GASANOVA
29
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YENi MONOOKSiDLO§DiRlCi BiOMiMETiK KATALiZATORLARIN SiNTEZi УЭ ONLARIN i§TiRAKINDA KARBOHiDROGENLORiN HiDROGEN PEROKSiDLO KiMYOVi OHOMiYYOTLi
MOHSULLARA OKSiDLO^MOSi
L.M.Hasanova
Tsikloheksan va onun töramalari ila qari§iginin hidrogen peroksidla oksidla§masi prosesinda damirporfirintarkibli heterogen biomimetik katalizatorlarin müayyan birla§maya qar§i segiciliyi tadqiq olunmu§dur. Tsikloheksanin monooksidla§masi prosesinin eksperimental tadqiqi asasinda müayyan edilmi§dir ki, biomimetik katalizator sathinda paralel-ardicil monooksidla§ma va oksidla§dirici dehidrogenla§ma reaksiyalarindan ibarat koherent-sinxronla§dirilmi§ mürakkab reaksiya ba§ verir. Tsikloheksanin reaksiya mahsullarina gevrilmasinin fermentativ kataliza xarakterik olan rabitalarin zancirvari paylanmasi prinsipi (RZP) ila tur§u-asasi kataliz va redoks sistemlarin birga mexanizmlarinin
daxil oldugu mexanizmbri tasvir edilmiíjdir. Hamginin metanin biomimetik katalizator i§tirakinda hidrogen peroksidla birba§a metanola oksidbíjmasi prosesinin tadqiqi apanlmi§dir.
Agar sozbr: tsikloheksan, tsikloheksanol, tsikloheksanon, koherent-sinxronla§dmlmi§ reaksiyalar, biomimetik katali-zatorlar, fermentativ kataliz, metan, metanol.
СИНТЕЗ НОВЫХ МОНООКСИДИРУЮЩИХ БИОМИМЕТИЧЕСКИХ КАТАЛИЗАТОРОВ И ОКИСЛЕНИЕ В ИХ ПРИСУТСТВИИ УГЛЕВОДОРОДОВ ПЕРОКСИДОМ ВОДОРОДА В ХИМИЧЕСКИ ВАЖНЫЕ СОЕДИНЕНИЯ
Л^Гасанова
Исследованы гетерогенные железопорфиринсодержащие биомиметические катализаторы на их избирательность в отношении определённого соединения в процессе газофазного окисления циклогексана и смеси последнего с его производными пероксидом водорода. На основе экспериментальных исследований процесса монооксидирования циклогексана было установлено, что на биомиметическом катализаторе происходит сложная реакция, состоящая из параллельно-последовательных реакций монооксидирования и окислительного дегидрирования, являющиеся когерентно-синхронизированными реакциями. Представлены вероятные механизмы биомиметического превращения циклогексана в целевые продукты, в котором прослеживается единство механизмов кислотно-основного катализа и редокс-системы по принципу цепи перераспределения связей (ЦПС), характерному для ферментативного катализа. Проведено также исследование прямого окисления метана в метанол пероксидом водорода в присутствии биомиметического катализатора.
Ключевые слова: циклогексан, циклогексанол, циклогексанон, когерентно-синхронизированные реакции, биомиметические катализаторы, ферментативный катализ, метан, метанол.
