CC BY
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AZ9RBAYCAN KIMYA JURNALI № 2 2018
ISSN 2522-1841 (Online) ISSN 0005-2531 (Print)
UDC 546.661.5
NITROGEN FIXATION AT CONJUGATED OXIDATION
12T.M.Nagiev, 1N.I.Ali-zadeh, 1L.M.Gasanova, 2I.T.Nagieva, 1Ch.A.Mustafaeva 1N.N.Malikova, 1A.A.Abdullaeva, 1E.S.Bakhramov
1Nagiev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
2Baku State University
Received 05.02.2018
Using the new principle of nitrogen oxidation by hydroperoxide has helped in discovering a new method of nitrogen fixation, mainly shaped as N2O, other oxides with low admixtures or nitrogen-containing acids under conditions, which are relatively soft for such reaction type. Gas-phase oxidation of nitrogen with hydrogen peroxide is rather complicated and consists of primary nitrous oxide formation. When nitrous oxide with the reaction mixture is yielded by the reaction (high-temperature) zone, it enters secondary reactions with other reagents in the mixture and, on rapid cooling, forms H2N2O2 and other nitrous acids.
Keywords: nitrogen, fixation, hydrogen peroxide, nitrous oxide, nitrous acid.
Introduction
The problem of nitrogen fixation is one of the most important scientific and technical tasks. The nitrogen and nitrogen-compound-making industry is one of the leading branches of the modern chemical industry. The state of the art of it is the main factor affecting the supply of nitrogenous fertilizers to agriculture and of various nitrogen-containing substances to industry.
Overview
D.I.Mendeleev was the first to bring up the question of nitrogen fixation from air: time will come, when nitrogen compounds will be produced from air nitrogen. This will be a great success for practiced life, because having nitrogen compounds and using them as fertilizers one can obtain high crops of cultivated plants. One of the tasks of applied chemistry is searching for technically advantageous method of obtaining nitrogen compounds containing assimilable nitrogen from the air nitrogen. The fortune of agriculture is mostly dependent on discovery of such a method.
It is common knowledge that both shapes of mineral bound nitrogen-ammonia and nitrateare directly accessible for plants. Therefore, at present, the question of nitrogen fixation in inorganic compounds is urgent. The problem is that human and animal organisms are unable to
use nitrogen from inorganic compounds for protein synthesis. As for nitrogen nutrition, its resources are limited by assimilating activity of plants and weed-eating animal proteins. Therefore, meeting human and animal demand for proteins depends on the level of meeting the demand of plants for mineral fixed nitrogen.
The following methods of nitrogen fixation are developed: ammonia, arc, cyan-amide, plasmatic, thermal and nitric oxides synthesis in a nuclear reactor. However, besides ammonia synthesis, no other methods have found wide industrial application. This method has many disadvantages, for example: multistage type and production awkwardness, the necessity for specific materials, equipment and machinery suitable for working under high pressure and temperature conditions, inexpensive raw material demand in the form of natural gas, coke oven gas or petroleum residues, high investments, etc. Therefore, research into new, simple and more economic methods of atmospheric nitrogen fixation are continuing. Direct air nitrogen oxidation can be implemented at high temperatures and under the influence of high velocity electrons and -y-radiation, in a nuclear reactor, etc.
Thermal oxidation of nitrogen was studied by Gabor Nemst, Zeldovich and others [1]. Various methods of atmospheric nitrogen ther-
6
mal fixation in regeneration ovens and reactors of various constructions and principles of operation were suggested. The essence of all methods consists in obtaining equilibrium values of nitric oxide concentrations at different temperature modes. In a plasma jet, bulk mean air temperature can simply be raised to 30004000 K and pressure boosted to several tens of atmospheres. This increases nitric oxide concentration in nitrous gas to 5%. Compared with the ammonia method, the advantage of the plasmatic method is the presence of almost inexhaustible resources of raw materials, simplicity of formation and an opportunity for plant construction in close proximity to the customer.
Among methods of nitrogen chemical fixation, direct nitrogen oxidation by air oxygen giving nitric oxide is of special attention for application purposes. The wide distribution of the initial products and their low cost are obvious. The problem is reduced to reaction implementation with the lowest costs. In the USA, the Bradley-Lovejoy [2] method of atmospheric nitrogen fixation by oxygen in a high-voltage discharge was applied in industry.
Stokes and Knipe obtained nitric oxides by mixing nitrogen plasma jet with gen. The average conversion of O2 in these experiments equaled 2%. La Roche [3] obtain higher yields in high-quality discharge plasma. Maximal concentration in a sample with low quenching rate just slightly exceeded 2%. The use of devices providing high quenching rate NO concentration above 4% which testifies to the importance of quenching for this process.
A possibility of NO synthesis from the air was studied [4]. Fromens used thermal reaction, the so-called Wisconsin process, which at maximal temperature 2500 K gave an NO yield equals 1.9% and at 1900 K - below 0.45%.
Thompson [4] described a thermal process in a flow oven with a temperature up 3000 K. Under favorable experimental conditions, NO concentration in nitrous gases reached 3.7%.
Analysis of the works in which NO formation is studied [5] in the nitrogen-oxygen system at high temperature shows NO concentrations ranging within 2-4%.
There were experiments [6] studying formation of nitric oxides in nitrogen plasma jet with injected oxygen, oxygen-nitrogen mixture and water. In this case, NO concentration in nitrous gases reached 8%.
According to data by Polak and Shipachev, the main object of expenditure in the production of nitrogen from air in plasma jets is electric power.
The works by Volpin and Shur [7] as well as by Shilov [8] on molecular nitrogen fixation via complexing with transition metals indicates nitrogen readily reacting with low-valence or-ganometallic compounds of titanium, chromium, molybdenum, wolfram andiron.
More investigations of nitrogen reactions with transition metal compounds confirmed the capability of nitrogen to readily enter reactions and reduction by many organometallic and inorganic coordination compounds of transition metals.
Shilov et al. [9] displayed the possibility of synthesizing stable ruthenium complex with molecular nitrogen.
Thus, at present, the task of atmospheric nitrogen fixation has mainly been developed in two directions: reduction and oxidation fixation. Chemical fixation of molecular nitrogen by the reduction mechanism on transition metals is a comprehensively studied branch of physical chemistry, displaying several discoveries made in this direction [10].
Meanwhile, another direction, that of oxidative fixation of nitrogen, has been poorly studied, because only several oxidation reactions are known; for example, the above-described reactions in electric arc, plasma or induced by ionizing radiation [11]. They are all endothermic oxidation reactions, consuming high energy and possessing low selectivity and yield.
The analytical analysis in methods of nitrogen fixation methods prompts the conclusion that all currently existing techniques possess specific disadvantages. Therefore, besides modernization of synthetic ammonia production process, new methods of molecular nitrogen fixation are also searched for. In this connection, of interest is the development of chemical-engineering processes in which conjugated reaction principles will be used and, therefore,
non-spontaneous oxidative fixation of nitrogen will be implemented with the help of chemical induction (similar to biological systems).
Experimental part and discussion
As shown below, the application of this principle to nitrogen oxidation by hydroperoxide has helped in discovering a new method of nitrogen fixation, mainly shaped as N2O, other oxides with low admixtures or nitrogen-containing acids under conditions, which are relatively soft for such reaction type. The method is also energy saving and ecologically friendly [12, 13].
For the sake of comparison, let us briefly consider the commonly known method of nitrous oxide synthesis by thermal decomposition of ammonia nitrate at 523-533 K by the following reaction:
NH4NO3 o N2O + 2H2O.
Admixtures are 1 -2% nitrogen and NO, which can be removed by passing bivalent iron sulfate through the solution. Moreover, N2O is also produced by nitrates and nitrites reduction under definite conditions or by hyponitrite decomposition.
It is shown [14] that besides N2O, an acid suggested to be hyponitrous acid (H2N2O2) is formed in the aqueous part of products of molecular nitrogen oxidative fixation with hydrogen peroxide. This acid then dissociates to N2O and H2O. Acid formation is also indicated by predominant presence of N2O in the aqueous phase in amounts significantly exceeding its solubility in water. The presence of soft acid (which is H2N2O2) may be judged by changes in the pH of the solution (3-4). Hence, direct detection of H2N2O2 was reduced to qualitative reaction of yellow-colored silver hyponitrite (Ag2N2O2) precipitation [15]. Taking into account the fact that silver cation also gives a yellow deposit with nitrite anion NO 3. As well as some technical difficulties associated with Ag2N2O2 (which is an extremely unstable salt) extraction from the solution, titration by lithium and potassium hydroxides was performed in one part of the reaction product. Hyponitrites of lithium and potassium hydroxides display high
thermal stability up to 2600C [16]. X-ray diffraction analysis of these salts, extracted by solvent evaporation, showed the presence of NO 3 and NO 3 anions in them shaped as KNO2,
KNO3 and LiNO32H2O. According to the analyses discussed below, the main part of these salts consists of alkaline metal hyponitrites.
In alkaline metal salts, hyponitrite-ion N2O2 was detected using IR-spectroscopy technique (by the presence of intensive absorption bands at 500 and 1000 cm-1) [16] and from qualitative reactions.
HJ and starch action. As HJ and starch are poured into a potassium hyponitrite solution, the latter is colored blue 2-3 min afterwards, which is a result [16] of insignificant amounts (traces) of NO2 anion presence, which were formed in the following reactions [16, 17]:
3K2N2O2 + 2H2O o 2KNO2 + 2KOH + 2N2, K2N2O2 + O2 = 2KNO2.
The action of concentrated H2SO4. Potassium hyponitrite decomposes completely under the effect of concentrated H2SO4. The reaction is outrage and releases nitrous oxide, which unambiguously indicates its origin, because interaction with H2SO4, KNO2 and KNO3 does not release N2O. The main reaction is described by the following equation:
K2N2O2 + H2SO4 = K2SO4 + H2O + N2O.
Oxidation with KMnO4. The solution used contained 0.2 g KM1O4 and 30 ml H2SO4. As K2N2O2 and KNO2 were poured into the solution, it became colorless. Then for the purpose of HNO3 detection, which may be formed in the reactions below [16], the aliquot part was extracted:
H2N2O2 °2 > HNO3,
HNO3 °2 > HNO2.
In the case, when only KMnO4 solution (0.2 g in 30 ml H2SO4) is poured to the mixture, outrage release of gases is observed. Chroma-tographic analysis of these gases indicated the presence of equal parts of N2O and N2. After pouring H2SO4 to the system this ratio shifts toward nitrous oxide.
Thus, the results of above analyses of aqueous reaction products and salts extracted by hydroxide titration indicate the presence of N2O 3, NO 3 and NO 3 anions in the reaction products.
The latter anion can also be obtained in another reaction [17]:
KNO2+K2N2O2+H2O=KNO3+2KHOH+N2.
It may be concluded from generalized results that the conjugated reaction of molecular nitrogen oxidative fixation with hydrogen peroxide mostly produces nitrous oxide (N2O) in concentrations below 19%. In the quenching zone, most of the nitrous oxide is converted to H2N2O2
due to the action of active sites (H0'2 and OH)
and H2O2. Small amounts of HNO2 and HNO3 (up to 0.1%) are also detected [18].
Figure shows the dependence of molecular nitrogen conversion on its volume rate in the temperature range of 773-873 K. It is clearly observed that the quantity of fixed nitrogen per injected molecular nitrogen increases to some extent with the amount of injected molecular nitrogen. A further increase of raw material rate does not change the level of nitrogen fixation. Despite shorter contact time, the increase of N2 volume rate from 1 to 4 //h intensifies the reaction.
0.3
o
2 0.2
0.1
0.4
0.6
0.8
x, s
Kinetics of nitrogen fixation with hydrogen peroxide: 1-3: at T = 773, 823 and 873 K respectively; 4-6 -theoretical curves at these temperatures. Molar ratio N2:30% H2O2= 1:1.6.
The aqueous hydroperoxide rate is constant for all nitrogen rates. However, at a nitrogen rate of 4-5 1/h the fixed nitrogen yield is altered.
Thus, chemical induction is the main factor promoting N2 fixation in a N2-H2O2-H2O system. It manifests itself owing to conjugation of H2O2 dissociation reactions, which generate the intermediate - HO'2 radical - to the system. This intermediate transfers the induction action of the primary reaction to the N2 oxidation process. In this case, H2O2 is injected in amounts much greater than demanded by N2 oxidation, because the main requirement for effective chemical
conjugation is the presence of HO'2 in high concentration.
To conclude the discussion, it should be noted that oxidative fixation of molecular nitrogen with hydrogen peroxide is fairly simple for process-engineering design, usually proceeds under homogeneous conditions without any catalyst under atmospheric pressure, and produces high yields of fixed nitrogen.
Among other aims, the author attempted in this chapter to give a simple phenomenological description of the kinetic regularities of conjugated oxidation with hydrogen peroxide in the gas phase with time, plotted as curves in the figures above. Thus, the quantitative data accumulated in kinetic investigations must be transformed to qualitatively absolutely different results, associated with the decoding of the chemical conjugation mechanism in reactions of oxidation with hydrogen peroxide and the basic principles of its operation.
This work was supported by the Science Development Foundation under the President of the Republic of Azerbaijan - Grant № EiF-KETPL-2-2015-1(25)-56/18/4.
References
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2. Curtis H.A. Fixed Nitrogen. No 4. The Chem. Cataloqueco. 1932. Chap. 4. 463 p.
3. La Roche N.G., Etude de la torche electronique, la chemie des hautes temperatures. Proc. CNRS, 1955. 212 p.
4. Thomson A.L., Formation and quen-ching of nitric oxide in a continuous flow furnace. Spring
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Meeting of Western States Combustion Institute. 1965. P. 243.
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6. Guliaev G.V., Kozlov G., Polak L.S. Kinetika i termodinamika himicheskikh reaktcii v nizkotem-peraturnoi plazme. M.: Nauka, 1965. S. 132-151.
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9. Shilov A.K., Shilov A.E., Brodko Yu.G. Obrazo-vanie kompleksov molekuliarnogo azota s soedi-neniiami ruteniia i osmiia //Docl. AN SSSR. 1967. T. 176. № 6. S. 1297-1299.
10. Hardy R., Bottomli F. Problemy fiksatcii azota. M.: Mir, 1982. 734 s.
11. Chatt Dzh., Kamara P., Richards R. Novoe v himicheskoi fiksatcii azogta. M.: Mir, 1983. 304 s.
12. Nagiev M.F., Nagiev T.M., Bairamov V.M., Isken-derov R.A. Sviazyvanie azota v vide ego zakisi // Docl. AN SSSR. 1973. T. 213. № 5. S. 1096-1098.
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AZOTUN OLAQOLÍ (QO§ULMU§) OKSÍDLO§MO ÍLO FÍKSASÍYASI
T.M.Nagiyev, N.Leli-zada, L.M.Hasanova, LT.Nagiyeva, C-^.Mustafayeva, N.N.Malikova,
A.0.Abdullayeva, E.S.Bahramov
Azotun hidrogen peroksidla oksidla§masinin prinsipinin tadqiqi tamamila yeni metodla nisbatan mülayim §araitda azotun fiksasiyasini hayata asas etiban ila azot-1 oksidin va az miqdarda digar oksidlarin, hamginin azot tur§ulannin alinmasina imkan verir. Azotun hidrogen peroksidla qaz fazali oksidla§masi mürakkab xarakter da§iyir va ilk anda azot-1 oksidin alinmasindan ibaratdir. Alinan bu qaz yüksak temperaturlu reaksiya zonasindan gixarkan qaz halinda reaksiya mahsullari qari§iginda ikinci gevrilmalara maruz qalir va kaskin soyudulma §araitinda H2N2O2 va digar azot tur§ulari alinir.
Agar sozlar: azot, fiksasiya, hidrogen peroksid, azot-1 oksid, nitrit tur§usu.
ФИКСАЦИЯ АЗОТА ПРИ СОПРЯЖЕННОМ ОКИСЛЕНИИ
Т.М.Нагиев, Н.И.Али-заде, Л.М.Гасанова, И.Т.Нагиева, Ч.А.Мустафаева, Н.Н.Меликова,
А.А.Абдуллаева, Э.С.Бахрамов
С использованием нового принципа окисления азота пероксидом водорода совершенно новым путем осуществлена фиксация азота в основном в виде N2O и других оксидов с незначительными примесями, а также азотсодержащих кислот в сравнительно мягких для подобного типа реакций условиях. Показано, что газофазное окисление азота пероксидом водорода носит сложный характер и состоит из первичной реакции образования закиси азота, которая при выходе из реакционной (высокотемпературной) зоны в составе газообразной реакционной смеси вступает во вторичные реакции с ее компонентами и в условиях резкого охлаждения образует кислоту H2N2O2 и другие азотные кислоты.
Ключевые слова: азот, фиксация, пероксид водорода, закись азота, азотистая кислота.
