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Section 12. Chemistry
Afandiyeva Lala Mahammad, PhD in chemistry Abbasov Vagif Maharram, academician Ismailov Etibar Hummat, professor Aliyeva Nushaba Musa, senior researcher Suleymanova Samira Abbas, chemist, Institute of Petrochemical Processes, Azerbaijan National Academy of Sciences, Baku, Azerbaijan E-mail: efendiyevalm7@gmail.com
Liquid-phase aerobic oxidation of petroleum hydrocarbons in the presence of Cr- and Co-complexes
Abstract: The liquid-phase aerobic oxidation of the hydrocarbons of naphthenic-paraffinic concentrate with boiling temperature 217-349 °C of diesel fraction ofAzerbaijan oil in the presence of Cr salt of natural petroleum acids and their mixtures with penta- nuclear complexes of Cr and Co was carried out. The increased yields of synthetic petroleum acids in the case of mixed Cr and Co complexes are observed. The yield of petroleum acids and activity of catalysts as a function of the composition of the catalyst are discussed.
Keywords: Cr complexes, catalytic oxidation, petroleum hydrocarbons.
Introduction
The oxidative conversion ofpetroleum hydrocarbons (PH) into the oxygenated products is one of the effective ways of rational processing of natural hydrocarbons. Among products of the oxidative conversion of the oil hydrocarbons the synthetic petroleum acids (including carbon oxy-acids) have a special place [1; 2]. Synthetic petroleum acids (SPA) instead of natural petroleum acids (NPA) are widely used in the preparation of corrosion inhibitors, desic-cants, catalysts, surface — active detergents, softeners, emulsifiers, bactericides, additives for fuels and many other beneficial products [3; 4]. Thus, the growing demand to oil acid and at the same time the limited of its natural resources, as well as the fact that they exist in
the form of complex mixtures, makes the production of SPA relevant and important.
In the present paper Cr salt of NPA (CrNPA) and pentanuclear Cr, Co-complexes are tested as catalyst in the aeroobic oxidation of PA into SPA.
Experimental/methodology
The used petroleum hydrocarbons are represented the dearoma-tized fraction ofAzerbaijan oils boiled in the range 217-349 °C. The diesel fraction is dearomatized by exstraction method. As an exstrac-tant n-methyl pyrrolidon (NMP) is used. Some physical-chemical parameters of the diesel fraction before and after the extraction are determined and presented in Table 1.
Table 1. - The values of physical-chemical parameters of the diesel fraction before and after the extraction
Parameters Diesel fraction
Before extraction After extraction
Molecular weight, M O ' w 225 200
Density, p 2°, kg/m 3 842 835.9
Refraction coefficient, nD° 1.4677 1.4638
Kinematic viscosity, at 2° °C, mm 2/s 5.71 5.52
Freezing temperature, °C minus 41.4 minus 51
Boiling temperature, °C 217-349 220-340
Acid number (A. n.), mgKOH/g 1.73 -
Iodine number, at1°° g fuel, gJ2 2.25 -
Amount of sulfur, % wt. 0.0936 0.03
Amount of the aromatic hydrocarbons, % wt ~17-18 1
As a catalyst for oxidation of petroleum hydrocarbons in liquid phase Cr salt of NPA (CrNPA), pentanuclear [Cr5 (tpda)4ClJ and [Co5 (tpda^ClJ (tpda = tripiridildiamin) complexes are studied. The Cr salt of NPA is obtained from sodium salt of NPA by exchange reaction [5]. Cr and Co- complexes of tpda are synthesized in the Tayvan National University and presented courtesy to investigate their catalytic properties [6]:
where Me is Cr or Co.
The oxidation process is carried out in the bubble type installation and the air flow rate was 300 Z/kg-hour during the 6 hours at 135-140 °C. The content of Cr, Co penthanuclear complexes in ratio to liquid phase were 0.1 mas. % and CrNPA — 0.2 mas. %. After the reaction the liquid products of oxidation process was separated and characterized by chromatography and infrared-spectroscopy. The atomic absorption spectrometer iCE 3000, Thermo Scientific, USA is used to determine the amount of the Cr and Co in the catalytic systems before and after the reaction. The particle size analyzer LB 550, Horiba is used to determine the size of the particles in catalytic systems before and after catalysis. Infrared spectra were obtained using the Bruker ALFA FTIR spectrometer.
Results and Discussion
The results of catalytic oxidation of the used petroleum hydrocarbons are given in the table 2.
Table 2. - The yield and composition of reaction products
№ Liquid phase without and in the presence of catalysts Conversion, % Yield of the carbon acids, % Reaction products, % Acid number, mgKOH/g
SPA SPOA SPA SPOA
1. Without catalyst 14.6 4.2 3.2 0.5 84.4 62.1
2. [Cr5 (tpda^Cy (0.1 mas. %) 67.2 24.7 15.0 7.1 130 122.5
3. [Cr5 (tpda^Cy (0.1 mas. %) 70.8 35.8 21.5 6.4 140.5 125.5
4. CrNPA (0.1 mas. %) 67.7 30.2 17.1 4.1 132 115.8
5. CoNPA(0.1 mas. %) 68.2 29.8 19.2 7.3 128.8 116.4
6. CrNPA + Co-comp. (0.15 mas. % = 0.1+0.05) 72.2 42.5 23.4 6.9 142.4 125
7. CrNPA + Cr-comp. (0.15 mas. % = 0.1 + 0.05) 68.4 31.5 22.8 6.8 134.8 122.6
As can be seen from the table 2 in the presence of catalyst the conversion of hydrocarbons and the yield of the petroleum acids are essentialy increased. A marked difference in the yield of acids is due to, of course, the nature of the catalyst. In these systems, the oxidation of hydrocarbons takes place, with the activation of molecular oxygen in the first stage of the reaction is most likely into the ion-radical state, which is the necessary in the formation of the hydroperoxides as the intermediates in the further oxidation of the hydrocarbon into the acid. The formation of hydroperoxides as the intermediates is the necessary for transformation of the hydrocarbons into acids. The cobalt complexes more easily than Cr complexes activate molecular oxygen into the ion-radical form O".
This fact can be the main in the primary higher activity of the cobalt complexes in comparison with the complexes of chromium in the oxidative conversion of hydrocarbons to acids.
The state of the catalyst in the liquid phase before and after oxidation process is characterized by dynamic light scattering method. For the all studied systems the values of "hydrodynamic diameter" and diffusion coefficient of particles are estimated and it was shown that the estimated values of particle size in PA dispersions are in the range 1 - 2 nm. and after the reaction the complex picture in DLS spectra is observed. DLS spectra and the values of DLS parameters for the catalytic system with Cr complex before and after the oxidation process are presented in the fig. 1, 2 (a, b) and table 3, accordingly.
a) b)
Fig. 1. DLS spectra for catalyst powder before (a) and after (b) the reaction in PH dispersion
6000 l.O 10.0 lOO.O lOOO
Diameter (nm)
a) b)
Fig. 2. a, b — sample with fig.1, b -diluted 2 and 8 times, respectively
Table 3. - The values of DLS parameters for PH dispersions with the isolated powder from catalytic system based on [Cr5 (tpda)4Cl2] complex after reaction
Samples* Parameters of Dynamic Light Scattering (DLS)
Diameter of particles in liquid, nm Span Diffusion coefficient, m2/sec
% of particles with diameter Median Mean Mode
10 50 90
1 1.0 1.1 1.4 1.1 1.2 1.1 0.3217 3.8123E-7
2 4864.3 5482.4 5892.7 5482.4 5180.9 5513.1 0.1876 7.8452 E-11
2, a 4524.9 5445.5 5884.8 5445.5 5021.8 5494.3 0.2497 7.9003 E-11
2, b 4818.7 5475.6 5891.2 5475.6 5212.9 5504.0 0.1959 7.8838 E-11
2, c 5143.2 5507.7 5898.1 5507.7 5284.9 5528.4 0.1371 7.8478 E-11
2, d 5129.2 5499.4 5894.4 5499.4 5217.9 5526.2 0.1395 7.8500 E-11
2, e 5177.0 5527.8 5902.4 5527.8 5405.5 5538.5 0.1312 7.8153 E-11
2, f 5173.8 5525.9 5902.0 5525.9 5379.1 5538.8 0.1318 7.8216 E-11
Note: * — Dispersions of catalyst powder before (1) and after reaction (2); 2, a, b- the next 2nd and the 3rd measurements of the sample 2; 2, c, d, e, f -initial dispersion 2 after dilution 2,4,8,16 times, respectively, with the same PA.
The synthesized catalysts before and isolated solid products of catalytic reactions after oxidation of petroleum hydrocarbons were characterized by atomic absorption spectroscopy and infrared spectroscopy. The content of chromium is determined by AAS (°.°22 and °.°19 mas. %, respectively). The difference in content of
chromium between the samples before and after reaction connected with the increase of the organic part of the sample after the reaction due to reaction products chemically bonded with the catalysts crystals. Infrared spectra of Cr-complex before and after oxidation of petroleum hydrocarbons are given in fig. 3.
Fig. 3. a) IR spectra of catalytic system with Cr-complex before oxidation
Fig. 3. b) IR spectra of catalytic system with Cr-complex after oxidation
The observed changes in FTIR spectra from isolated samples of catalyst after oxidation process also can be due to reaction products which chemically bonded to the surface of the catalyst.
Conclusion. Cr, Co complexes with different composition and structure was used as catalyst in the oxidation process of petroleum hydrocarbons into the petroleum acids. It was shown that in all cases the catalytic systems are the liquid systems with nano- and
micro-sized catalyst particles and it can be supposed that the oxidative conversion of petroleum hydrocarbons into the petroleum acids are catalyzed by these nano- and micro-sized particles based on Cr-, Co complexes. The formation of the oxygen ion-radical O2- more easily in the case of cobalt complexes than chromium complexes can be accepted as the main factor of higher activity of cobalt complexes than complexes of chromium.
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