OBTAINING SYNTHETIC FATTY ACIDS BASED ON PARAFFIN AND STUDYING THE MECHANISM OF ITS FORMATION

ABSTRACT

Synthesis of higher fatty acids by oxidation of paraffin with potassium permanganate is a complex chemical process involving various reactions. The article presents the results of determining the technological parameters of the process of obtaining carbonic acids by oxidizing paraffin, a secondary product formed during pyrolysis of hydrocarbons. The chemical reaction mechanism of formation is presented. Synthesized synthetic fatty acids were analyzed by IR spectroscopy and gas chromatography methods of analysis. These analytical techniques give important information about the structural characteristics and degrees of purity of the produced fatty acids, enabling a thorough comprehension of their chemical makeup and possible uses in a range of industrial domains. During the reaction, the diagram of catalyst consumption and product yield was studied.

АННОТАЦИЯ

Синтез высших жирных кислот окислением парафина перманганатом калия — сложный химический процесс, включающий различные реакции.

В статье представлены результаты определения технологических параметров процесса получения углекислот путем окисления парафина – вторичного продукта, образующегося при пиролизе углеводородов. Представлен механизм химической реакции образования. Синтезированные синтетические жирные кислоты анализировали методами ИК-спектроскопии и газовой хроматографии. Эти аналитические методы дают важную информацию о структурных характеристиках и степени чистоты производимых жирных кислот, позволяя тщательно понять их химический состав и возможное использование в ряде промышленных областей. В ходе реакции изучали диаграмму расхода катализатора и выхода продукта.

Keywords: Potassium permanganate, paraffin, oxidation, synthetic fatty acid, saturated carboxylic acid, unsaturated fatty acid, gas chromatography, IR-spectroscopy, catalyst. gas chromatography.

Ключевые слова: Перманганат калия, парафин, окисление, синтетическая жирная кислота, насыщенная карбоновая кислота, ненасыщенная жирная кислота, газовая хроматография, ИК-спектроскопия, катализатор. газовая хроматография

Introduction. One of the urgent problems of the chemical industry is to obtain useful substances for the national economy from secondary products of refined oil. The synthesis of higher fatty acids by oxidation of paraffin with potassium permanganate has potential advantages.

Higher fatty acids play an important role in industry and pharmaceutics due to their long carbon chains and carboxyl functional group. Such compounds are used in the production of soaps and detergents, the main precursors for the production of lubricants, cosmetics and even biofuels. In the field of pharmaceuticals, higher fatty acids are used as raw materials and as solvents in the synthesis of various drugs.

Generally, higher fatty acids are produced by processes such as the hydrolysis of oils and fats. This method requires high energy and is rarely used because agricultural products are used. Alternative chemical synthesis methods, such as the Fischer-Tropsch process or oxidation of olefins, require the use of high pressure, high temperature, or expensive catalysts.

The oxidation of paraffin with potassium permanganate is convenient for the production of fatty acids. Paraffins are saturated hydrocarbons, abundant and relatively cheap raw materials, and the use of potassium permanganate as an oxidant has several advantages:

Economic efficiency: Compared to other catalysts and oxidizers used in the synthesis of fatty acids, KMnO₄ is a relatively cheap and widely used compound.

Literature analysis

Increasing the rate of chemical reaction by reducing the active net energy of the process with the help of a catalyst is important for the chemical industry. Catalysts not only help reduce costs associated with chemical processes, but they also play an important role in the environment. It should be noted that catalysis occupies an important place as one of the main principles of green chemistry, to which all chemical processes should be directed and studied; and the influence of the chemical structure of some lower paraffin molecules on the catalytic process in the presence of a platinum catalyst should be investigated [1]. Tallman and Nagvekar performed paraffin dehydrogenation using metal oxide catalysts to produce light olefins [2]. Research on the effect of stearates on the thermal oxidation process of paraffin shows that cobalt stearate has a positive effect on the oxidation process. However, the oxidation process is multi-step [3]. Liu et al proposed a paraffin oxidation device consisting of an oxidizer, an air compressor, and a condenser tube. In this device, it is possible to precisely control the amount of air supplied and the reaction temperature [4].

A special wax was obtained as a result of liquid phase oxidation of paraffin with air at atmospheric pressure at 150-170°C in the presence of a catalyst [5].

Research methodology

Fraction with a boiling range of 350-450°C and a liquefaction temperature of 40-60°C, consisting of C₂₅ -C₃₅ hydrocarbons, was used as a raw material for obtaining fatty acids.

Refined solid paraffin is obtained by deparaffinizing the oil fractions of paraffinic oils. The deparaffinization method involves the crystallization of paraffin at low temperatures in the presence of a solvent. In recent years, the method of separating oil fractions with liquid propane, which serves not only as a solvent, but also as a refrigerant, has become widespread. Paraffin obtained by such methods contains 95-99% solid n-paraffin hydrocarbons . Paraffin of the B brand (according to DS 23683-2021) produced at the Fergana oil refinery was used as a raw material for oxidation.

200 grams of paraffin was heated to 120℃ in a flask, and 0.6 grams of KMnO₄ dissolved in 2 grams of distilled water was added to it as a catalyst. Air was fed through a glass tube with a radius of 2 mm with a rheometer, 12 liters of air for 16 hours, while stirring for the oxidation process to proceed. Since the process is exothermic, the temperature was kept between 110-120℃. The acid number of the oxide was determined every two hours. Acid number is 70 mg KOH/g, and oxidation is stopped. The resulting oxide was placed in a separation funnel and washed 2-3 times by pouring distilled water at a temperature of 20-25℃. In this case, water-soluble low-molecular carboxylic acids and by-products formed during oxidation are removed with water. Based on the saponification reaction, synthetic fatty acids were isolated from the obtained oxide.

Analysis and results

According to fractionation, melting point and structure, paraffins are divided into liquid ( T_{melting point} ≤ 27 ℃), solid (T_{melting point} = 28-70 °C) and microcrystalline (T_{melting point} > 60-80 °C) - ceresins. Paraffins are inert to most chemicals . They are oxidized by nitric acid, atmospheric oxygen (at temperatures of 140°C and above) and other oxidizing agents to form various acids similar to fatty acids found in vegetable and animal fats. The oxidation of paraffin hydrocarbons is a complex heterogeneous catalytic process with heat release, which occurs on the basis of a radical mechanism. The limiting stage of the process is the formation (initiation) of free radicals. Nucleation of chains occurs under the influence of metal salts of variable valency (KMnO₄ in this reaction) as a catalyst.

A GC-MS chromatogram is presented for the qualitative and quantitative analysis of the paraffin fraction (Fig. 1) .

Figure 1 . GC-MS chromatogram of paraffin fraction

Based on the obtained data, the amount of hydrocarbons in the fraction is presented in Table 1.

Table 1

The composition of the paraffin fraction

When potassium permanganate is used as a catalyst in the oxidation of paraffins to obtain higher carboxylic acids, the process involves several main steps, each of which converts the relatively inert paraffin into an active state. The process is characterized by the strong oxidizing ability of KMnO₄, which facilitates the conversion of paraffins into carbonic acids, respectively.

1) The reaction begins with the oxidation of a hydrocarbon with KMnO₄, a hydrogen atom is separated and an alkyl radical is formed. The initial active center is formed in the reaction: [6,7]

RH + KMnO₄ → R• + MnO₂ + H₂O + KOH

Manganese divalent MnSt₂ forms salt

2) In the second step, the free radical (R•) reacts with the oxygen molecule and produces a peroxide radical:

R• + O₂ → ROO•

3) The peroxide radical, in turn, reacts with a hydrocarbon molecule, forming a hydroperoxide molecule and a free radical:

ROO• + R′-H → ROOH + R′•

4) Analyzing the decomposition kinetics of hydroperoxides in detail, Emanuel and his colleagues found that bimolecular decomposition is possible, came to the conclusion that high:

ROOH + R'H → R′ • + RO • + N ₂ O

Under the influence of a catalyst, hydroperoxide breaks down to form free radicals:

ROOH + MnSt₂ → RO• + Mn(OH)St₂

Here, manganese Mn²⁺ ion changes to Mn³⁺ ion

If the -OOH group is located on the primary carbon atom, the RO• radical combines with a hydrocarbon to form an alcohol:

RO• + R′′H → ROH + R′′

In the decomposition of secondary hydroperoxides, the main reaction products are secondary alcohols and ketones with the same number of carbon atoms. The formation of ketones from hydroperoxide occurs as follows:

The resulting free radicals of another structure (R′′• + OH•) react again, continuing the chain and leading to final products.

Acids are not formed directly from hydroperoxides, but are formed as a result of further oxidation of intermediate products.

The formation of acids with the same number of carbon atoms as the original hydrocarbon occurs as a result of the reaction of oxygen with the hydrocarbon by breaking the C-H bond on the primary carbon atom, but such a reaction is unlikely due to the high activation energy. Secondary carbon atoms are mainly oxidized and secondary alcohols and ketones are formed in the hydroperoxide phase. Then it turns into acids as a result of C-C bond breaking. Therefore, the number of carbon atoms in an acid is less than the number of carbon atoms in the original hydrocarbon. Oxidation of ketones to fatty acids passes through the stage of α-ketohydroperoxides and, like the oxidation of hydrocarbons, proceeds as a chain radical reaction. But since the C-H bond energy is reduced, this reaction occurs only on the C atom in the α-state relative to the carbonyl group. In the subsequent oxidation, the C-C bond is broken and a carboxyl group is formed at the location of the carbonyl group, and an aldehyde group is formed at the location of the hydroperoxyl group.

Here manganese is Mn^{3 +} ion Mn ^{2 +} will be returned to

At the same time, as a result of additional reactions, the final oxidation product (oxidate) is a complex mixture of fatty acids, hydroxy and ketoacids, lactones, esters, as well as non-oxidized hydrocarbons of different molecular weight containing oxygen.

The IR spectrum of the synthesized substance is shown in Fig. 2.

Figure 2. IR spectrum of synthesized fatty acid

The IR-spectrum of the synthesized substance revealed the absorption areas specific to the functional groups in the molecule. A broad absorption band at 3009 cm^-1 indicates valence vibrations characteristic of O-H. Broad absorption bands typically indicate hydrogen bonding in alcohols, phenols, and carboxylic acids. Absorption area at 2927 and 2854 cm^-1: - C-H bond in aliphatic compounds is characteristic of valence bonds. The region of 2927 cm^-1 corresponds to asymmetric vibration, and 2854 cm^-1 is associated with the symmetric vibration of methylene groups (CH₂). 1710 cm^-1 absorption region: - is characteristic for valence vibration of C=O bond, which is usually observed in ketones, aldehydes, carboxylic acids or ethers. Absorption region at 1651 cm^-1: - indicates C=C bond vibration in alkenes or gives a combined system associated with C=O vibration. Absorption area 1457 cm^-1: - Associated with bending vibrations of C-H in CH₂ and CH₃ groups. Absorption at 1409 cm^-1: - characteristic of -CH₃ group or -OH group connected to carboxyl group. 937 cm^-1 absorption area: - due to vibration of =CH and CH₂ groups in alkenes. And the 716 cm^-1 absorption region is typical for out-of-plane deformation vibrations of =CH in aromatic compounds or vibrations of -CH₂ groups in aliphatic chains. Absorption region at 1651 cm^-1 is characteristic of alkene. Based on the analysis of the IR-spectrum, it was determined that the formed substance is unsaturated higher carbonic acid. A chromatogram of the formed carboxylic acids obtained on an Agilent 7820A GC device is presented in Figure 3.

Figure 3. Chromatogram of synthetic fatty acids

Gas chromatography analysis shows that the composition of the fraction mainly consists of carbonic acids C₁₀ – C₂₂ (Table 2).