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ISSN 2522-1841 (Online) AZERBAIJAN CHEMICAL JOURNAL № 1 2022 ISSN 0005-2531 (Print)
UDC 547.057; 547.21
EFFECT OF THE COMPOSITION OF A MANGANESE-CONTAINING POLYMER CATALYST ON THE KINETICS OF THE OXIDATION REACTION OF N-HEPTANE
WITH MOLECULAR OXYGEN
A.F.Isazade, U.A.Mammadova, M.M.Asadov, N.A.Zeynalov, D.B.Tagiev, S.A.Mammadova
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
aygunisazade. chemist@gmail. com
Received 07.10.2021 Accepted 17.11.2021
Catalysts with manganese nanoparticles (5 and 10 wt %) immobilized on poly-4-vinylpyridine were prepared. When interacting with molecular oxygen, the catalyst forms active oxygen, which is involved in the low-temperature oxidation of n-heptane. These catalyst compositions have been used to oxidize n-heptane with pure oxygen to give alcohols, aldehydes and ketones. Oxidation of n-heptane was carried out in the temperature range 303-383 K, molar ratios of heptane:oxygen = 1:3.38, and at atmospheric pressure. It has been found that the non-crosslinked (MnP4VP polymer poly-4-vinylpyridine) and N,N'-methylene-bis-acrylamide-crosslinked MnP4VP/MBAA metal-polymer catalyst containing 5 wt % Mn2+ exhibits the highest activity in n-heptane oxidation reactions. The kinetic parameters of the reaction of n-heptane oxidation with oxygen at low temperatures were studied using a kinetic model based on the heptane conversion data. The kinetic model was compiled on the basis of experimental data: heptane:oxygen = 1:3.38 at atmospheric pressure using Mn (wt. 5%) P4VP/MBAA in the temperature range 303-383 K. Within the framework of the chosen kinetic model effective rate constants of the oxidation reaction with the formation of alcohols was calculated.
Keywords: polymer catalysts, manganese immobilization, low-temperature oxidation of n-heptane with oxygen, n-heptane conversion, reaction rate constants.
doi.org/10.32737/0005-2531-2022-1-41-50
Introduction
The use of metal nanoparticles in catalysis is due to the following reasons. On the one hand, they have a developed specific surface area, which determines their effectiveness. On the other hand, they are characterized by a high proportion of metal atoms on the surface, which act as potential active centers. Therefore, the development of new catalytic systems that make it possible to increase the efficiency of reactions and ensure high selectivity is an urgent task. Metal nanoparticles encapsulated in polymers can apparently be considered as a boundary region between homogeneous and heterogeneous catalysis. Distinctive features of such catalytic systems are the possibility of their separation from the reaction mass and repeated use.
The use of such catalysts in important industrial processes makes it possible to increase the production of various products from organic raw materials. One such process is the oxidation of hydrocarbons due to the high demand for oxidized products [1]. Activation of the C-H bond of hydrocarbons is an effective approach to the molecular functionalization of a substance [2]. For
example, the plasma-activated reaction of partial oxidation of methane to chemicals on Fe, Mo, Pd, and zeolite catalysts was carried out in [3]. In a liquid product of 21.5% CH3OH, 20.4% CH2O, 0.3% HCOOH, and 2.4% CH3COOH using pure plasma, a maximum cumulative yield of 5.21 mol% organic oxygenates was achieved. The kinetics of periodate oxidation of carbohydrates in a polymer medium was studied in [4]. The rate constants were calculated from the responses of the calorimetric decay curves, which are proportional to the rate of periodate transformation. The dependence of kinetic rates on the molecular weight of dextran samples and substrate concentration was studied. The presence of two reactions with comparable reaction rates complicates the analysis of calorimetric curves even for the simple case of pseudo first order reactions. Therefore, the kinetic data of such reactions have been studied by phenomenological processing. In [5], a calorimetric approach to the analysis of the kinetics of peri-odate oxidation on a number of monosaccharide substrates is described. Rate constants at multiple temperatures were calculated from calorimetric
decay curves that are proportional to the rate of conversion of various carbohydrates. It is shown that the calorimetric method makes it possible to monitor the kinetics of slow reactions and control the course of the reaction.
There are few works related to the catalytic oxidation of n-heptane at low temperatures to obtain important products. In particular, the authors of [6] propose an improved kinetic model for the low-temperature oxidation of n-heptane (n-C7Hi6). An experimental study of the oxidation of n-heptane in a jet reactor with a stirrer from low to high temperatures and pressures up to 40 atm showed the following [7]. The products formed during the oxidation of n-heptane belong to the low-temperature (below 750 K) and high-temperature reaction mechanisms. The transition from low-temperature to high-temperature oxidation regime depends on a pressure of about 40 atm. The results are interpreted in terms of peroxy formation and isomerization of radicals and further reactions of hydroperoxyalkyl radicals. The stabilization of the excited intermediate is facilitated by an increase in the total pressure. In [8], low-temperature intermediate products of n-heptane oxidation (760 K, 4.9 atm) were studied by laser absorption and gas chromatography methods. The results obtained using combined diagnostics provide information on the kinetics of low-temperature oxidation of n-heptane. A decrease in the rate of the heptylperoxy isomeriza-tion reaction by an appropriate value makes it possible to estimate the yield of n-C7H16, C2H4, CO, H2, and C3H6.
The effect of metal particle size and carbon contamination on the rate of heptane oxidation was studied in [9]. Platinum catalysts used with dispersion from 10 to 81% in a 5% excess of oxygen and at temperatures from 90 to 1400C. The rate of reaction decreases exponentially with time as carbon fouls the surface of the metal. The rate of deactivation corresponds to the first order of the concentration of active centers. The rate of coke formation depends on the size of the metal particles, the composition of the support, and the density of the metal particles on the support. The rate of catalyst deactivation occurs in the opposite direction compared to coke formation. Small particles are deactivated slowly. On average,
large crystallites are 23 times more active than small ones. With a long reaction time for the oxidation of heptane, the reaction rate is insensitive to particle size.
Experimental and model studies of the low-temperature oxidation of n-heptane were carried out in [10]. The studies were carried out using a reactor with jet mixing and two methods of analysis: gas chromatography and synchrotron vacuum ultraviolet photoionization mass spectrometry with sampling through a molecular jet. Products, such as molecules with hydroperoxy functions, have been identified that are not sufficiently stable. The mole fractions of the reactants and reaction products were also determined as functions of temperature (500-1100 K) at a residence time of 2 s at a pressure of 1.06 bar and under stoichiometric conditions. The components involved in the low-temperature oxidation of n-heptane, such as olefins, cyclic ethers, aldehydes, ketones, compounds with two carbonyl groups (di-ones), and ketohydroperoxides, were analyzed. Diones and ketohydroperoxides are intermediate products of the low-temperature oxidation of n-alkanes, and their formation is difficult. At low temperatures, organic acids (acetic and propanoic) are also formed. An analysis of the catalytic reactions of alkane oxidation shows that these reactions have complex chemical kinetics, since several reactions often occur simultaneously. This limits the possibilities of kinetic studies and modeling [11].
In [12], the authors propose a simplified model of the n-heptane oxidation reaction. The model is based on the kinetics of low-temperature oxidation of C1 -C4 hydrocarbons. Initial reaction steps and complex low temperature oxidation processes are simplified through the use of linear chemical coupling reactions. Using this mechanism for high- and low-temperature oxidation (550-2500 K) of mixtures at pressures from 1 to 42 bar, reaction mechanisms for chemically more complex types of hydrocarbons (for example, isooctane, n-de-cane, etc.) have been proposed.
The review [13] considers methods for increasing the catalytic activity of transition metal complexes in reactions involving hydrocarbons. In particular, the reactions of oxidation of al-kylarenes with oxygen are discussed. Methods for controlling the catalytic activity of the complexes
MLxn [M = Ni(II), Fe(II, III); L = acac (acetil-acetonatami), enamac (C(O)MeCHC(Me)NH-chelate group); n = 2, 3] in alkylarene oxidation to hydroperoxides were carried out by introducing additional electron-donating modifying ligands. The activity of Ni and Fe catalysts in chain development in the radical chain oxidation of ethylbenzene is evaluated.
In [14], the reaction of selective oxidation of carbon monoxide (CO) was studied. Mono-and bimetallic Co, Cu, and Fe, as well as heterogeneous Cu-Co and Cu-Fe catalysts using carbon nanotubes as substrates have been studied. Catalytic conversion for the CO oxidation process was carried out in source gases containing hydrogen, water, and carbon dioxide in the temperature range of 120-2200C. It was shown that the addition of iron or cobalt to Cu/CNT (carboxyl nano-tubes) improved the activity of the oxidation catalyst compared to Cu/CNT. The temperatures at which 50% CO conversion is achieved were as follows: Cu-Fe/CNT(1200C)> Cu-Co/CNT( 1400C) « Cu/CNT (1400C).
There are also known catalytic systems with the participation of polymer substrates. So, for example, in work [15] polymer-supported O6-(benzotriazol-1-yl)inosine derivatives (Pol-I and Pol-dI) were synthesized by the reaction of phosphonium nucleoside salts with a polymer-bound support. The results of reactions with polymer-supported new modified nucleosides are proposed to be used for targeted synthesis.
There are also works related to the use of manganese-containing nanocatalysts. In particular, it was shown in [16] that silicate nanoparti-cles functionalized with manganese act as oxi-dative nanocatalysts. They can decompose 80% of the tested organic compound in 30 minutes at neutral pH and room temperature. The activity of the nanocatalyst can be related to the manganese framework, which decomposes H2O2 into reactive hydroxyls. Unlike manganese in Mn3O4 or Mn2O3 nanoparticles, bound Mn does not contribute to the simultaneous decomposition of hydrogen peroxide, which easily decomposes organic pollutants dissolved in water.
In work [17], a manganese-containing (MnOx) catalyst supported on a structured porous silicate was synthesized. The resulting catalyst contains homogeneously distributed and hydro-
3+
thermally stable MnOx nanoparticles with Mn ions and Mn2+ centers. Its textural porosity makes both types of Mn particles/sites accessible. Thus, due to its non-toxic nature and cost-effective synthesis, Mn-containing silicate is proposed as an environmentally friendly catalyst.
On the other hand, metal complex catalysts based on polymeric materials can increase the selectivity and yield of important chemical products. In [18], a review is presented in the field of obtaining polymer-immobilized clusters and metal nanoparticles. Their applications in the catalysis of organic reactions are also considered. An analysis of known data [19-21] shows that manganese in compounds can be in various oxidation states. Therefore, manganese compounds exhibit different reactivity in catalytic reactions.
Thus, improving the technology of manganese-containing catalysts for the oxidation of n-alkanes is an urgent task. This article presents the results of the influence of a manganese-containing polymer catalyst on the process of n-heptane oxidation.
Experimental part
We prepared a manganese-immobilized polymer catalyst [22, 23] for the oxidation of n-heptane. The catalytic activity and recyclability of Mn polymer complexes were determined taking into account the partial characteristics of the components of the n-heptane oxidation reaction according to the procedure described in [24, 25].
The study was divided in two stages. Firstly, poly(4-vinylpyridine) (P4VP) was qua-ternized with benzyl chloride. Secondly, for the formation of immobilized Mn containing polymer complexes, MnCl24H2O was added to polymer solution and studied in liquid phase. Additionally, herein we used quaternized non-cross-linked and cross-linked P4VP polymer.
The quartenization of poly(4-vinylpyridine)
To obtain Mn containing polymer catalyst, the polymer was quaternized [24, 25]. In this regard, solution of the P4VP (1 g of P4VP: 100 ml of C2H5OH) were heated to 333 K and at this temperature benzyl chloride in amounts of 10-60% of the dissolved polymer was added to the solution, and stirred for 6h, in a three-necked flask equipped with a stirrer. At the end of the process, P4VP samples quaternized to
various degrees. The quaternized polymer was precipitated with 0.1N NH4OH solution, washed with diethyl ether to remove the excess of benzyl chloride and dried in vacuum 10-2 Pa at 313 K to constant weight.
Poly(4-vinylpyridine) crosslinking
The polymer was crosslinked in the following way: quaternized samples of P4VP were crushed and dissolved in ethanol, and 8-10% solutions were prepared. The cross-linking agent N,N/methylene-bis-acrylamide (30% of the amount of P4VP) was added to the resulting mixture. The resulting mass was crushed and stirred for 1-3 min in a ball mill with a ball diameter of 0.8 cm. The particle size of the crushed mixture was in the range of 0.05-0.1 mm. Tablets were prepared from the resulting mixture. Tablets with a diameter of 8 mm and a thickness of 0.2-0.4 mm were pressed from a mixture of MnP4VP and MBAA. These tablets were heated for 2-3 hours in quartz ampoules evacuated to 10-2 Pa at 393-403 K.
Synthesis of P4VP-manganese complexes
P4VP-Mn catalysts were prepared by adding 0.36 g of MnCl2-4H2O to ethanol solutions of quaternized P4VP samples. The mixture was then transferred to a 500 ml three-necked flask equipped with a stirrer. The mixture was stirred for 3 hours and then the reducing agent NaBH4 was added to the solution. The precipitated MnP4VP complexes were washed with distilled water to remove excess Mn(II) cations and dried in vacuum until completely dry at 313 K.
Results and discussion
Characterization
The structure and phase composition of the prepared catalysts was determined by X-ray diffraction analysis (XRD; D2-Phaser Bruker diffractometer), FT-IR spectroscopic analysis (FT-IR spectroscopy Nicolefisio VSA), scanning electron microscopy (SEM and EDS on Sigma VP. Carl Zeiss Jena), The products of the catalytic testing were analyzed using a Agilent 7890B Gas Chromatograph (GC) with column HP-5 with a gas carrier velocity (H2 and N2) of 1.2 ml/min and a pressure of 5.41 psi (pound-force per square inch) [25].
Manganese-containing polymer-supported catalysts exhibit catalytic activity in the oxidation of n-alkanes. The study of reactions with
quaternized uncrosslinked and crosslinked manganese-containing polymeric (based on poly-4-vinylpyridine (P4VP) and N,N'-methylene-bis-acrylamide (MBAA)) complexes showed their activity. These catalytic systems showed different activities during the oxidation of n-heptane with oxygen. Oxidation yielded heptan-1-ol; heptan-2-ol; heptan-3-ol; heptan-4-ol, heptanal and heptanone in different yields.
Studies of the surface of manganese-containing complexes before and after the n-heptane oxidation reaction show that active manganese changes its chemical state. The oxidized form of manganese depends on the reaction conditions for the oxidation of n-heptane with the production of several products (Table 1).
Kinetics of complex reactions of n-hep-tane oxidation with molecular oxygen
The influence of the obtained samples of MnP4VP and MnP4VP/MBAA catalysts in the oxidation of n-heptane with oxygen was studied in a flow reactor. The reaction was carried out at molar ratios of heptane/oxygen=1:3.38. The temperature in different experiments was varied within 303-383 K at atmospheric pressure, respectively. The reactor was charged with n-hep-tane (5 ml) and MnP4VP or MnP4VP/MBAA catalyst (0.8 cc). The molar ratio of n-heptane to catalyst was 0.038:(0.0012-0.006). The reactor was placed on a heated MS-5 magnetic stirrer. Data identification was carried out on an Agilent 7890B GC with an HP-5 column at a carrier gas (H2 and N2) velocity of 1.2 ml/min and a pressure of 5.41 psi (pound force per square inch). Studies of the kinetics of the n-heptane oxidation reaction show stable catalytic activity and high selectivity with respect to manganese-immobilized poly-4-vinylpyridine.
Choosing a kinetic model and performing calculations
Within the framework of the principle of independence of chemical reactions, we consider the kinetics of complex reactions that include several elementary stages. Let us assume that several simple reactions take place in the system, and each of them obeys the basic postulate of chemical kinetics, independently of other reactions.
Table 1. The results of testing of non-crosslinked and cross-linked metal-polymer catalysts in the oxidation reaction of n-heptane at T = 313 K, molar ratio of reagents C6H14:O2:manganese =1:3.38:0.003 and t= 6 h_
f,% The conversion of heptane The yield of the reaction products, œ, wt.%
The composition of the catalyst, wt. % C7HJ6-4- heptanon
№ CvH^-1-ol CvH^-2-ol C7Hj6-3-ol heptanal 4. 3 2
1 Mn (2%) P4VP* 10.3 - 4.2 5.8 0.3 - - -
2 Mn (5%) P4VP* 13.2 - 5.8 6.6 0.8 - - -
3 Mn(2%)P4VP/MBAA* * 23.2 1.4 7.3 8.6 3.4 - 0.9 1.6
4 Mn (5%)P4VP/MBAA** 49.1 2.9 9.4 10.8 5.3 1.2 2.6 3.9
f,% - conversion of n-heptane, * - non-crosslinked catalyst; vinylpyridine, MBAA = N,N'-methylene-bis-acrylamide
When studying chemical reactions, in particular the oxidation of heptane, it is necessary to know which products (C, D, ...) are formed from the reactants (A, B, ...), as well as the stoichio-metric coefficients (a, b, c, d, ... ) in the chemical reaction equation aA + cO + ...The reaction we considered was complex, and to predict the dependence of its rate on the concentration of reagents, it is not enough to know the chemical equation. One should also have an idea of the elementary stages through which the transformation under study is carried out. According to the kinetic mechanism, we will take this complex chemical reaction in general terms as competing (sequential and/or parallel) reactions.
Consider a sequential reaction consisting
of two monomolecular stages: S ^ X ^ P. Here S is the initial substrate, P is the final products, and fc2 reaction rate constants
Consider the kinetics of this reaction based on the law of mass action. Then for the rate of simple reactions we can write a system of three differential equations dcs
—— = -kics dt 1 S
dcX= -kiCs-k2Cx
(1)
dcP "dt
= k2Cx
where
Cs, Cx, Cp are the concentrations of substances S, X, P, respectively.
Integration of the system of equations (1) makes it possible to determine the dependences of the concentrations cs, cX, cP on time (Figure 1). The kinetic curves reflect the features of these successive reactions. The concentration cs of
** - crosslinked metal-polymer catalysts, P4VP = poly-4-
the initial substrate S decreases monotonically with time. The concentration of intermediate X increases, reaches a maximum, and then decreases. The concentration of the final product P increases monotonically with time.
For the transformation indicated above, we assume that c = cS, x = cx, p = cP, initial conditions: c = c0, x = p = 0. With this in mind, for special cases we can write the following relations
c = c0e-
-M
ki / = kkki^O
-kit
P
= Co(l
k1
k2 - k1
-k.t
+
) (2)
k1
k2 - k1
An analysis of equation (2) shows that the rate of transformations of complex successive reactions is determined by the slowest stage. Equation (2) can serve as a mathematical model for the kinetics of heptane transformations.
However, due to the inconstancy of the value of fc, the criterion for the validity of the kinetic equation for the heptane oxidation reaction is violated.
Taking into account the above, the calculations of the rate constant of the heptane oxidation reaction were carried out within the framework of the kinetic model given in [25].
During the oxidation of n-heptane to various products, the yield, selectivity, and conversion were determined experimentally using known methods [25-32]. The kinetics of the catalytic oxidation of n-heptane to target products, in particular alcohols, was carried out in a flow reactor. For this, a reactor in the form of a tube of constant cross section with a constant volume was used.
x
k
e
e
Fig. 1. Dependences of the concentrations of the substance 1 - cs. 2 - cx,
3 - Cp. on time.
The mixture was fed into the reactor at a rate of 10 ml/min. The activity of the catalyst was evaluated by the conversion of n-heptane in the products at different temperatures. The temperature was raised stepwise with a step of 100C. Before the start of the process, catalysts were loaded into the reactor in an amount of 0.8 cm3. The conversion was determined under steady state conditions.
Conversions of C7H16 (f,%) and O2 (f,%) were determined from the ratios
^(CyHie) =
№) =
([C7H16] ini - [C7H16]ult) [C7H16] ini
([O2]ini - [O2]ult)
x 100%
[O2]
x 100%
2]ini
based on the initial and final concentrations of heptane and oxygen at the inlet and outlet of the reactor. In the entire volume of the reactor, the temperature was maintained constant. Such a condition was created in the reactor that the amount of heat released or absorbed was small, and there were no temperature gradients.
Taking into account the residence time of the mixture of initial components in the reactor, we studied the kinetics of n-heptane oxidation with oxygen. In this case, at the temperature of 313 K, the selectivity for the formation of alcohols is 57.8% and the Mn (wt. 5%) P4VP/MBAA catalyst was more active than other compositions due to
the large number of active sites of manganese oxide in it.
The kinetic model was chosen based on the experimental data as follows. When the process takes place in a tubular flow reactor, the system of kinetic equations retains its form if instead of the reaction time t we use the concept of "residence time", which is defined by the expression t = x/u (x is the current coordinate, u is the linear velocity of the gas).
Consider the following case. According to experimental data, the chemical reaction proceeds in a closed volume with a decrease in the number of moles according to the scheme A (n-heptane)+B (oxygen) ^ C (alcohols). The molar concentrations of the initial substances A (n-heptane)+B (oxygen) change due to chemical interaction, as well as due to a decrease in the density of the mixture. In this case, the simple kinetic model is inapplicable.
Due to competing reactions, the rate constants (fc) had a significant scatter. However, in the studied reactions, an inverse dependence of
the total reaction rate on temperature was obser-
k
ved. In this case, the formal scheme A + B ^ C does not allow finding the value of k in the form k = k0exp(-E/RT), where is a constant, E is the activation energy, R is the universal gas constant.
Taking into account the above and the multipath of the heptane oxidation reaction, the following model [25] was used to determine the reaction constant, taking into account the conversion of heptane.
The kinetic constant was determined from the conversion of the initial substances ^ according to the ratio
(3)
= Ao-Aft),^ [0,1]
A0
where is the initial concentration of the initial substance, ^(t) is the molar concentration of the corresponding substance at any values of t (time). The initial concentrations of the initial substances were assumed to be the same A0 = B0. Then for any values oft we have A(t) = B(t). Taking this into account, the kinetic equation of the initial substance can be written:
The results of calculating the rate constant of the reaction proceeding with the participation of a manganese-containing polymer catalyst are given in Table 2. Here t characterizes the residence time of the mixture (heptane + oxygen) after the establishment of stationarity in the reactor.
Note that, the time and temperature dependences of the properties of the ongoing hex-ane oxidation reactions with the production of various products are similar to each other.
The dependence of the conversion of n-heptane on the oxidation temperature for a Mn (5%) P4VP/MBAA sample is shown in Figure 2. The high activity of the manganese-containing systems Mn (wt. 5%) P4VP/MBAA at low temperatures indicates the occurrence of an interaction reaction with manganese cations.
Table 2. The total rate constants of the reaction of n-heptane oxidation with oxygen to alcohols (heptane:oxygen = 1:3.38) at atmospheric pressure, proceeding with the participation of a manganese-containing polymer catalyst_
T, K Q, mol/h t, min A0, mol/ m3 Ç,%(C7H16) kx105, m3/mol-min
303 0.0341 360 38 0.45 0.60
313 0.0327 370 34 0.49 0.76
323 0.0315 379 32 0.52 0.89
333 0.0304 387 28 0.58 1.27
343 0.0289 396 26 0.62 1.58
353 0.0277 407 24 0.65 1.90
363 0.0262 417 22 0.68 2.32
373 0.0251 430 20 0.70 2.71
383 0.0243 437 18 0.75 3.81
Q - is the volumetric flow rate of the initial mixture at the inlet to the reactor, t is the residence time of the mixture in the reactor
Fig. 2. The dependence of the conversion of n-heptane on the oxidation temperature for a Mn (5%) P4VP/MBAA sample.
T, K
dA = -kAB = kA2, A = A(t),A(0) = A0 = const. (4)
Integrating equation (4), we obtain
*« = *m=i+£E. (5)
From equation (5) we find f = (6)
Using equation (6), we determined the kinetic constant
300 320 3+0 360 380
The activation energy (£"a) of the reaction was estimated using the maximum likelihood method. That is, we used the method of estimating an unknown parameter by maximizing the likelihood function.
The value of £"a was taken as the "most plausible" value of the parameter. It was assumed that the parameter £"a maximizes the probability of obtaining a given sample x = (xi,...., xn) in n experiments. This value of the parameter £"a depends on the sample and is the desired estimate. The likelihood function was calculated according to the kinetic formula taking into account the conversion of the product, and the parameter £"a was estimated from the condition of maximizing the likelihood function at a certain temperature, pressure, and contact time. For example, the reaction activation energy calculated by this method at = 0.7 and 290 K was 47 kJ/mol.
Conclusions
Manganese nanoparticles (5-10 wt.%) immobilized on poly-4-vinylpyridine were prepared for the oxidation of n-heptane with oxygen to the corresponding alcohols, in smaller amounts, aldehydes and ketones. Studies carried out in the temperature range 303-383K, molar ratios of heptane:oxygen = 1:3.38 and at atmospheric pressure showed that the obtained catalyst can also be used in subsequent catalytic cycles. It has been shown that the direct conversion of n-heptane into target products using a manganese-containing polymer catalyst has an advantage over similar processes. Thus, for example, optimal results were obtained with n-heptane: oxygen mixtures (the ratio of the molar concentrations of the initial reagents is 1:3.38) at 383 K with significant conversion (£, = 0.75; £"a = 47 kJ/mol) at a reaction time of less than 7.2 hours. The constructed kinetic model of the general oxidation reaction of heptane with a manganese-containing polymer catalyst made it possible to calculate the kinetic parameters, the values of which are consistent with the data of experiments and similar reactions. By varying the concentration of the initial reagents, the ratios were also established between other independent pa-
rameters, which make it possible to obtain the maximum yield of the target product. Taking into account the kinetic model, the influence of the composition of the manganese-containing polymer catalyst, the ratio of the initial components, temperature, pressure, and contact time of the components on the reaction rate constants and conversion are determined. At a long contact time of the interacting components (2 h), the rate constants of the n-heptane oxidation reaction satisfactorily describe the experimental data. At short contact times (20 s), the rate constants of oxidation reactions are determined less accurately.
Acknowledgements
The authors acknowledge this work was supported by the Science Development Foundation Under the President of the Republic of Azerbaijan - Grant № EIF-ETL- 2020-2(36)-16/09/4-M-09
The authors declare that they have no conflict of interest.
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MANQAN TORKÍBLÍ POLÍMER KATALÍZATORUN TORKÍBÍNÍN N-HEPTANIN MOLEKULYAR OKSÍGENLO OKSÍDLO§MO REAKSÍYASININ KÍNETÍKASINA TOSÍRÍ
A.F.Ísazada, Ü.A.Mamm3dova, M.M.Osadov, N.A.Zeynalov, D.B.Tagiyev, S.A.Mammadov
Poli-4-vinilpiridin üzarina immobiliza olunmu§ manqan nanohissaciklari (5 va 10 agirliq %) asasinda katalizatorlar hazirlanmi§dir. Molekulyar oksigenla qar§iliqli alaqada olan katalizator n-heptanin a§agi temperaturda oksidla§masinda i§tirak edan aktiv oksigen amala gatirir. Bu katalitik kompozisiyalar n-heptani tamiz oksigenla oksidla§dirmakla spirtlarin, aldehidlarin va ketonlann alinmasi ügün istifada edilmi§dir. N-heptanin oksidla§masi 303-383 K temperatur intervalinda, heptan:oksigen = 1:3,38 molyar nisbatinda va atmosfer tazyiqinda apanlmi§dir. Müayyan edilmi§dir ki, tarkibinda 5 wt. % Mn2+ saxlayan tikilmami§ (poli-4-vinilpiridin polimer MnP4VP) va N,N'-metilen-bis-akrilamidla tikilmi§ - metal polimer katalizatoru MnP4VP/MBAA, n-heptanin oksidla§masinda an yüksak aktivlik nümayi§ etdirir. A§agi temperaturda n-heptanin oksigenla oksidla§ma reaksiyasinin kinetik parametrlari heptanin konversiya malu-matlanna asaslanan kinetik modeldan istifada etmakla tadqiq edilmi§dir. Segilmi§ kinetik model gargivasinda (hep-tan:oksigen = 1:3.38) atmosfer tazyiqinda Mn (kütla 5%) P4VP/MBAA katalizatorunu istifada etmakla 303-383 K temperatur diapazonunda oksidla§ma reaksiyasinin effektiv sürat sabitlari spirtlarin amala galmasi ila hesablanmi§dir.
Agar sözlzr: polimer katalizatorlari, manqanin immobilizasiyasi, n-heptanin oksigenla a§agi temperaturda oksidla§-masi, n-heptanin konversiyasi, reaksiya süratinin sabitlari.
ВЛИЯНИЕ СОСТАВА МАРГАНЕЦ-СОДЕРЖАЩЕГО ПОЛИМЕРНОГО КАТАЛИЗАТОРА НА КИНЕТИКУ РЕАКЦИИ ОКИСЛЕНИЯ Н-ГЕПТАНА МОЛЕКУЛЯРНЫМ КИСЛОРОДОМ
А.Ф.Исазаде, У.А.Мамедова, М.М.Асадов, Н.А.Зейналов, Д.Б.Тагиев, С.А.Мамедова
Были приготовлены катализаторы с наночастицами марганца (5 и 10 мас. %), иммобилизованными на поли-4-винилпиридине. При взаимодействии с молекулярным кислородом катализатор образует активный кислород, участвующий в низко температурном окислении н-гептана. Эти каталитические композиции использовались для окисления н-гептана чистым кислородом с получением спиртов, и альдегидов и кетонов. Окисление н-гептана проводили в интервале температур 303-383 K, мольном соотношении гептан:кислород = 1:3,38 и при атмосферном давлении. Установлено, что несшитый (поли-4-винилпиридиновый полимер MnP4VP) и сшитый М,№-метилен-бис-акриламид-металлополимерный катализатор MnP4VP/MBAA, содержащий 5 мас. % Mn2+, проявляет наибольшую активность в реакции окисления н-гептана. Кинетические параметры реакции окисления н-гептана кислородом при низких температурах были изучены с помощью кинетической модели, основанной на данных конверсии гептана. В рамках выбранной кинетической модели (гептан:кислород = 1:3,38) при атмосферном давлении с использованием Mn (мас. 5%) P4VP/MBAA в интервале температур 303383 K были рассчитаны эффективные константы скорости реакции окисления с образованием спиртов.
Ключевые слова: полимерные катализаторы, иммобилизация марганца, низкотемпературное окисление н-гептана кислородом, конверсия н-гептана, константы скорости реакции.
