MODIFICATION OF CATALYTIC SYSTEMS IN THE PROCESS OF OBTAINING SYNTHETIC HIGH FATTY ACIDS THROUGH OXIDATION OF PARAFFIN HYDROCARBONS

ABSTRACT

In the article, describes the selection of catalytic systems and their modification processes in the production of synthetic high fatty acids by oxidation of paraffin hydrocarbons. The effect of complex catalysts on the oxidation process and the yield of acids was studied on the example of paraffins from local oil fields.

АННОТАЦИЯ

В статье описаны выбор каталитических систем и процессы их модификации при производстве синтетических ВЖК окислением парафиновых углеводородов. Исследовано влияние комплексных катализаторов на процесс окисления и выход кислот на примере парафинов местных месторождений нефти.

Keywords: Paraffin, hydrocarbon, petroleum, mine, oxidation, catalyst, modification.

Ключевые слова: Парафин, углеводород, нефть, шахта, окисление, катализатор, модификация.

Today, the need for synthetic high fatty acids and products based on them is increasing. In order to meet the above demand and expand production networks, the issue of increasing production of carbonic acids by oxidizing paraffin hydrocarbons is considered urgent. A promising way in this direction is the improvement of industrial catalytic systems.

Research conducted by researchers shows that [1] salts of Mn, Co, Fe, Cu, Cr, Ni and other metals were always used in the process of catalysis during liquid phase oxidation of paraffins. Their synergistic effect was observed in the oxidation process.

The most common catalysts are cobalt salts and manganese compounds, which were observed to increase the activity of a mixture of MnSt2 and CoSt2, as well as during the oxidation of hydrocarbons using technical oxygen through MnSt2 and CuSt. The highest activity of the Mn-Co mixture was observed in the composition containing 1-5 mol % of manganese. The maximum activity for the Mn-Cu mixture is shown when the mixture contains about 20-50 mol% of copper, and the oxidation level increases by 1.5-2 times. A similar effect was found for Mn-Cu and Mn-Fe salts during the oxidation of paraffin with ozonated air [2].

The oxidation of paraffins in the presence of FeSt2 is significantly accelerated by small additions of MnSt2. Increased catalytic activity was noted for manganese and nickel stearates, as well as for chromium and nickel in the oxidation of hydrocarbons to hydroperoxides and ketones.

The synergistic effect is a common feature of variable valence metals in hydrocarbon oxidation processes. The observed regularity can be justified by two opposing points of view, which are the continuation or rejection of complexity in the accepted solution. The main reason for the independence of the catalytic effect of a mixture of salts is the specific activity of one of the transition metals.

However, this view cannot explain why synergism occurs within a very narrow range of metal concentrations. A number of researchers have expressed the beneficial aspects of synergistic effects based on the increased catalytic activity of complexes or mixed micelles of variable valence metals in hydrocarbon media [3].

During the oxidation of paraffin hydrocarbons with the help of a catalyst, it is possible to control the content of acids [4].

Catalytic systems used in liquid phase oxidation technologies of hydrocarbons have a clear disadvantage that they contain various salts of disordered metals such as cobalt and manganese. Acceleration of the oxidation reaction in the formation of the target product, as well as the formation of side compounds in them, including resinous substances. Despite these negative aspects of catalyzing liquid-phase oxidation reactions with salts of polyvalent metals, they cannot be replaced by more efficient and cheaper ones.

As catalysts for the oxidation of paraffins, synergistic systems containing a dominant amount of metal salts with constant valency from groups I and II of the periodic table can be shown. The addition of trace amounts of constant-valent metals, such as calcium, polyvalent metals to salts increases their catalytic activity.

According to the opinion supported by extensive research materials, industry has used a manganese-alkali catalyst for the oxidation of paraffins to synthetic fatty acids: replacement of manganese dramatically reduces the selectivity of the process to acids [7].

However, it is possible to increase the activity and selectivity of the industrial catalyst by modifying the third component.

The role of the modifying additive is to accelerate the individual stages of paraffin oxidation, stop side reactions and reduce the oxidation of multifunctional compounds.

A number of catalysts have been developed for the oxidation of paraffins to synthetic fatty acids, including conventional alkali manganese salts as well as cobalt, chromium, iron, titanium, nickel and vanadium salts.

These metals direct the oxidation of n-alkanes to the formation of acids, and the compositions containing them have a number of advantages over industrial catalysts. Thus, modification of Mn-Na(K) catalyst with cobalt compounds increases their activity and helps to increase the rate of paraffin oxidation compared to Mn-Na(K)-catalyst. As a result, the quality of the acids produced is also improved.

The synergistic effect of oxidation of alkanes with cobalt and manganese salts, as shown in binary systems of catalysts, is explained by the ability of these metals to form compounds in hydrocarbon solution with catalytic activity in oxidation reactions. However, the presence of certain alkali metal catalysts prevents the association of salts with transition metals, and obviously the loss of their catalytic effect leads to synergy.

The increase in the oxidation rate of n-alkanes in the presence of the Co-Mn-K catalyst can be explained by the ability to accelerate the oxidation of some alcohols by cobalt salts and the high activity of divalent cobalt in decomposition reactions of hydroperoxides.

The formed acids are produced in a catalytic system with a molar ratio of Co:Mn:K=0.5:0.5:1 components, with the presence of which more pure acids are synthesized at high speed. A promising way to activate the oxidation process of paraffinic hydrocarbons is to introduce chromium compounds into the industrial catalyst.

The composite Cr:Mn:K=1:1:1 catalyst with the ratio of components Cr-Mn-K accelerates the oxidation reaction of paraffins by 1.5-2 times in mixtures with unsaponifiables. The peculiarity of the action of the chromium component is that, unlike manganese, it does not react with peroxide radicals, but helps the decomposition of alkyl hydroperoxides mainly into ketones, which are quickly oxidized to acids in the next step. Decomposition of hydroperoxides with a preference for the formation of ketones in the presence of chromium compounds reduces the percentage of alcohols in the oxidation products. This situation is probably related to the good solubility of the catalyst in the oxide and brings the catalyst to a homogeneous state during the entire oxidation, which allows better control of the composition of oxidation products than the rapid precipitation of the Mn-K-catalyst [5].

In order to intensify the process and improve the quality of acids, the use of 0.1-0.4% of Cr:Mn-alkaline catalyst with an atomic ratio of Cr:Mn:alkali metal components equal to 0.2-1:1-3:1-3 is a good result. gives

Manganese compounds used as accelerators in paraffin oxidation and synthetic fatty acid production industries are expensive and scarce, so there is an opportunity to replace them with other non-rare metals. When accelerating the oxidation process, manganese can be replaced by 50-70% of iron compounds, in which case the optimal composition of the accelerator includes 0.1% by weight. Fe, 0.03 wt%. Mn and Na are 0.04% by weight.

A characteristic feature of the catalytic effect of the titanium-manganese-sodium catalyst is to increase the rate of initiation, increase the ratio of chain continuation and termination rate constants. Experimental industrial tests show that titanium-manganese-sodium oxidation catalysts can convert paraffinic hydrocarbons into acids and improve their quality and reduce paraffin consumption. Titanium catalysts with optimal content contain the following component concentrations: Mn=0.020%, Na=0.083%, Ti=0.015% or Mn=0.035, N=0.18, Ti=0.015% [6].

By oxidizing a mixture of solid paraffins with an average number of carbon atoms from 20 to 40, mainly carboxylic acids with a number of carbon atoms from 10 to 20 are obtained.

The composition of the resulting acids depends on the average molecular weight of the alkanes.

Table 1.

Results of the oxidation of paraffins from various domestic oil fields

A comparison of the results of the oxidation of paraffins of different composition (Table 1) shows that the total yield of fatty acids in the raw state increases with the increase in the boiling temperature and average molecular weight of the initial paraffin.

The average number of carbon atoms in the crude fatty acid molecule also increases, which is always 60% of the average number of carbon atoms in the initial hydrocarbon molecule. The amount of acids increases in C₂₀ and cubic residue. But the amount of acids of the C₅-C₉ fraction decreases [8].

The maximum yield of acids in the C₁₀-C₂₀ fraction corresponds to a mixture of hydrocarbons with an average molecular weight of 437 g/mol, that is, C_30.7. The proportion of individual components in the acids of the C₁₀-C₂₀ fraction used for soap making is different, which depends on the oxidation of the raw materials. Thus, the composition of C₁₀-C₁₆ acids in the C₁₀-C₂₀ fraction during oxidation is as follows (%):

Paraffin of the Khanqizi field…………………………………………….46.3

Paraffin of Varik field…………………………………………………...44 ,9

Southern Almalyk Paraffin……………………………………………….49.9

Paraffin in fraction 370-470 °C…………………………………………..43.6

Paraffin in the 400-500 °C fraction………………………………………35.8

Consequently, the higher the molecular mass of paraffin, the lower the yield of acids in the C₁₀-C₁₆ fraction.

The highest yield of acids in the C₁₀-C₁₆ fraction was obtained during the processing of paraffin boiling in the range of 260-350 °С. Thus, the molecular mass composition of the resulting synthetic fatty acid mixture is primarily determined by the composition of the initial mixture of hydrocarbons. Therefore, the choice of paraffin for oxidation should be based on the molecular weight of the main part of synthetic fatty acids. Until recently, large quantities of petroleum paraffins were separated from paraffinic distillates by crystallization and condensation under certain conditions, and paraffin was produced more or less continuously. With the development of a new technology for the production of paraffin by treating petroleum distillates with selective solvents, it became possible to obtain paraffin from petroleum distillates of any molecular weight. In 1958, 23% of paraffin produced was used for the production of synthetic fatty acids, in 1970 this amount increased to 53%, and by 2021 to 87.5% [9].

Therefore, the quality of the produced paraffin must first of all meet the requirements of the synthetic fatty acid industry. It is desirable to create the following types of paraffin for synthesis: liquid boiling in the range of 250-350 °C and containing normal C₁₆-C₂₀ hydrocarbons; A medium liquid should have a boiling range of 300-430 °C (C₁₇-C₂₈) and a solid should have a boiling range of 420-500 °C (C₂₇-C₃₅). When using liquid paraffin with a high yield, C₈-C₁₂ acids, medium-liquid C₁₀-C₁₆ acids and C₁₈-C₂₃ solid acids are obtained.

Currently, synthetic fatty acids of fractions C₁₀-C₁₆ and C₇-C₉ are of great importance for the national economy. Synthetic fatty acids, which are found in sufficient quantities in natural sources, have already been proven to be widely used in the production of detergents, plasticizers, etc. To achieve the maximum yield of these acids, it is desirable to use paraffins of lower molecular weight, which boil up to 430 °C. Depending on the need for acids of different molecular weight, it is desirable to process paraffin of the first two types separately. Paraffin boiling at a temperature higher than 430 °C is an unnecessary raw material for the production of synthetic fatty acids, because during its processing, a large amount of distillation residue (up to 40%) and acids above C₂₀, as well as isostructural acids, naphthenic and dicarboxylic acids are formed. Therefore, it is more acceptable to use such paraffin as a raw material for the production of olefins and other needs [10].

References:

1. Manakov Okislenie parafinov normalnogo stroeniya v prisutstvii soley metallov peremennoy valentnosti // M.N. Manakov, V.A. Kruchinin // Petrochemistry.- 1971 .-T. 11.- №2.- p.219-223. [in Russian]
2. Tyutyunnikov B.N. Spektrofotometricheskoe issledovanie troynogo uskoritelya okisleniya parafina do kislot // B.N. Tyutyunnikov, Z.M. Nikitina // Maslojir.prom-t.-1965.-V.5. -p.20-23.
3. Perchenko A.A. Okislenie parafinovыx uglevodorodov v prisutstvii Cr-Mn-K-katalizatora // А.А. Perchenko, V.V. Serov, G.F. Yanusik i dr. // Nefteximiya.-1978.- T.18.- №. 15.-p.744-748.
4. Synthesis and research of fatty acids based on local secondary petroleum products // K Khujakulov, B Mavlanov, S Fozilov, R Niyozova… - IOP Conference Series: Earth and Environmental …, 2021
5. Obtaining synthetic fatty acids based on n-alkanes // AA Madjidov, SF Fozilov, KR Khuzhakulov … - Science and Education, 2022
6. Аnaliz sostava razlichnыx neftey i vozmojnosti ispolьzovaniya tverdogo parafina v poluchenii sinteticheskix jirnыx karbonovыx kislot // АM Narzullaeva, KR Xujakulov, SF Fozilov… - Universum: texnicheskie nauki, 2020
7. Xujakulov K.R., Narzullaeva А.M. Fozilov C.F. Mavlanov B.А. Raxmonov B.O. Izuchenie optimalьnыx parametrov protsessa polucheniya vыsshix jirnix kislot iz vtorichnыx nefteproduktov // «Innovatsionnыe puti resheniya aktualnix problem razvitiya piщevoy i neftegazoximicheskoy promыshlennosti» mejdunarodnoy nauchno-prakticheskoy konferentsii. Bukhara, 2020. p. 305-307.
8. Khujakulov K.R., Mavlonov B.A., Fazilov S.F. The technology of obtaining synthetic high fatty acids based on secondary oil products and their industrial application // Monograph. - Tashkent, "VNESHINVESTPROM", 2021.-194 pp.
9. K.R.Khujakulov A.M Narzullaeva, Z.X Rayimov, R.N Niyozova, N.Q Jamilova, B.O Raxmonov. Analysis of Physical and Mechanical Properties of Skin Oil Based on Secondary Petroleum Products // International Journal of Advanced Research in Science,Engineering and Technology. – India, 2020. – p.15733-15738.
10. Khujakulov K.R. Mathematical modeling of the process of oxidation of petroleum paraffins // National Information Agency of Uzbekistan - electronic journal of the Department of Science of the Republic of Uzbekistan March 2022. - p. 231-240.