PRODUCTION OF POLYETHYLENE TEREPHTHALATE

ABSTRACT

The article analyzes the methods of obtaining polyethylene terephthalate from petroleum and coke chemical processing products, which play a leading role in the creation of a new generation of polymer materials in the polymer industry.

АННОТАЦИЯ

В статье проанализированы способы получения полиэтилентерефталата из продуктов переработки нефти и коксохимии, играющие ведущую роль в создании полимерных материалов нового поколения в полимерной промышленности.

Keywords: polyethylene terephthalate (PETP,PET), terephthalic acid (TPA), ethyleneglycol (EG), esterification, diethylene glycol (DEG), isophthalic acid (IPA), thixotrope, monoglycol ether, diglycol ether

Ключевые слова: полиэтилентерефталат (ПЭТФ, ПЭТФ), терефталаткислота (ТФК), этиленгликоль (ЭГ), этерификация, диэтиленгликоль (ДЭГ), изофталевая кислота (ИФК), тиксотроп, моногликольэфир, дигликольэфир

The chemistry and technology of polymeric materials is an important technology of modern development, and the possibility of obtaining new properties of materials based on a given combination of known polymers is very important.

Today, in the polymer industry, the creation of a new generation of polymer materials based on the achievements of innovative technologies in world practice is leading.

Polyethylene terephthalate (PETP, PET) is a saturated polyester based on ethylene glycol and terephthalic acid.

The production of polyethylene terephthalate is based on the direct esterification of TPA with ethylene glycol and the subsequent polycondensation of the resulting diglycol ether to form a high molecular weight polyester.

The scheme of obtaining PETP from petroleum and coke chemical refining products can be summarized as follows (Figure 1)

Figure 1. General connection scheme for PETP

PETP production raw materials

The main raw materials for the production of PETP are terephthalic acid and ethylene glycol. They are derived from petroleum and coke chemical products.

Terephthalic acid is a crystalline substance that is less soluble in water and organic liquids than dicarboxylic acids (phthalic acid and isophthalic acid), which are isomers to it.

Terphthalic acid is oxidized to p-xylene. P-xylene is obtained by catalytic reforming of the gasoline fraction. Oxidation of P-xylene is carried out in air in a solution of acetic acid at a pressure of 125–275⁰C and up to 40 atm in the presence of catalysts (cobalt and manganese acetates) and promoters (bromine, mainly sodium bromide-containing compounds). The solvent in this case is actively involved in the oxidation process. Acetic acid activates oxygen, shortens the induction period and increases the rate of formation and decomposition of hydroperoxides.

Changes in the oxidation of p-xylene occur in the following sequence (Figure 2): p-xylene 1 → p-toluene acid 2 → p-toluene acid 3 → p-carboxybenzaldehyde 4 → p-benzoldicarboxylic acid (TPA)

1                                   2                                      3                                4                            TPA

Figure 2 Sequence of changes in the oxidation of p-xylene

Ethylene glycol is a hygroscopic, odorless liquid with a clear colorless light oily consistency when purified. It mixes with water, various alcohols, acetone, glycerin in different proportions, is insoluble in aromatic hydrocarbons, chloroform, carbon sulfide.

Direct oxidation of ethylene glycol with air or pure oxygen in a silver catalyst to ethylene oxide, followed by hydration of ethylene oxide at 10 atm and in the presence of 0.1-0.5% sulfuric and orthophosphate acids is obtained by. (Figure 3)

Figure 3. Ethylene glycol extraction reactions from ethylene

Hydration is carried out with a large amount of excess water to minimize the formation of other glycols. When the reaction is carried out within 1 hour, the yield of ethylene glycol reaches ~ 90%.

Small amounts of diethylene glycol and isophthalic acid are used as modifiers in the esterification and pre-polycondensation stages of PETP to form specific properties [1].

Diethylene glycol (DEG) gives polyester its elasticity and clarity properties. Isophthalic acid (IPA) prevents premature crystallization when blowing products from preforms, which reduces the breakdown of items from cracking.

The general formula of the modified PETF is shown in figure 4

Figure 4. General formula of modified polyester:

 x- amount of IFK,% mass; y - amount of DEG,% mass; p- degree of polycondensation.

The process of obtaining PETP consists of two main stages:

1 - esterification stage; 2 -  polycondensation stage.

Etherification of terephthalic acid with ethylene glycol.

Etherification of terephthalic acid with ethylene glycol is carried out by the continuous method at a temperature of 280 - 285⁰C by delivering a pre-prepared suspension of TPA in ethylene glycol to the reactor-esterifier, adding to the TPA as a modifier in the amount of isophthalic acid (2.0 ± 0.1)%. swells.

Properties of preparation of TPA suspension in ethylene glycol.

In ethylene glycol, the TPA suspension is prepared in a molar ratio of EG: TFK 1: 1 to 2: 1. For convenience, we denote the ratio of goods by the Latin letter ƒ. For example, when ƒ = 2, 2 moles of ethylene glycol in suspension with a concentration of TFK of 57.23% (Table 1).

Table 1.

Characteristics of TPA suspensions in ethylene glycol

During preparation, the density of the suspension is calculated according to the formula:

Here

Cj is the density of the liquid, kg / m3;

Csp - suspension density, kg / m3;

Dc - space density difference, kg / m3;

Ct - solid phase density, kg / m3;

Cm is the percentage of solid phase in the suspension.

ƒ=2 The suspension retains its fluidity and can be driven by special pumps. Other ratios ƒ = 1.3–1.6 can also be used. Such suspensions, which retain a large amount of solid phase at low internal friction stresses, do not leak, only change their shape. When the internal friction force is higher than a certain value, the suspension starts to flow.

Suspensions that retain large amounts of solid phase are structured over time. The structuring process is caused by the presence of TPA microparticles in the chain, which in turn form spatial three-dimensional networks (networks). The higher the solid phase concentration, the smaller the network cell and the stronger the network as a whole. In the cells there is a liquid phase - ethylene glycol between the particles (network nodes). If such a suspension is constantly stirred, it will have the appearance of a viscous liquid. If mixing is stopped, the suspension will not flow for some time due to the internal structure of the solid phase particles. If this happens in a large-capacity device, it can still be mixed. In practice, the drive reducer often breaks when the agitator is started.

Heating this suspension reduces the likelihood of structuring and makes it easier to mix and blend and drive.

Suspensions are often thixotropic fluids.

These fluids are fluids whose shear stress decreases over time at constant rates of deformation. Thixotropic fluids are able to restore their structure after removing the external force that causes leakage.

In practice, the suspension is prepared by mixing TFK with ethylene glycol at 110–160⁰C and ƒ = 1.6–1.8. This creates a technological reserve of suspension for 4-5 hours. At the same time, the suspension is stirred continuously and heated to maintain the set temperature.

Heating the suspension initiates the esterification reaction. For example, at 140⁰C, the suspension begins to lose its fluidity after 3 hours. At 130℃, this process takes much longer, about 12 hours. Under these conditions, the esterification of TPA is shown in figure 5.

                                         TPA monoglycol ether

diglycol ether

Figure 5. Etherification of TPA

ƒ˂2 insufficiency of ethylene glycol relative to the stoichiometric amount leads to incomplete conversion of TPA, ie the formation of a mixture of mono- and diglocol esters.

From the above, the following conclusions can be drawn.

1) When preparing a mixture of TPA in EG, a suspension can be formed in the range of values ƒ = 1 ÷ 2, which exhibits thixotropic fluid properties of non-Newtonian viscous fluid with non-Newtonian viscous fluid properties.

2) At rest, the suspension can be structured and requires external force to disrupt its internal structure to create flexibility.

3) In the preparation of a suspension of TPA in EG, an esterification reaction is initiated at a temperature of 110 ℃ and above. This reaction is maintained until the hydrolysis reverse reaction with water is reached to a steady state.

4) When the suspension is kept in a stirred state for a long time, the solid phase does not break down as a result of mechanical action on the TPA particles. The reduction in particle size occurs due to the esterification reaction that occurs on the surface of TPA crystals, which results in a reduction in their size.

5) The processes that take place during the preparation of the suspension of TPA in EG do not lead to a defective product (waste) in the later stages of production.

Reference:

1. ОгрельЛ.Д. Оценка накопления, сбора и переработки отходов ПЭТФ в России // Экологический вестник России. – 2012. - №4 – с. 34.
2. O’G’Li, Rayimov Zuhriddin Khayriddin, and Jamilova Niginabonu Qobil Qizi. "ANALYSIS OF IMPORTANCE AND METHODS OF PRODUCTION OF BLOCK SOPOLYMERS BASED ON POLYETYLENTEREPHTALATE." International Journal of Advanced Technology and Natural Sciences 3.1 (2022): 51-55.
3. Жамилова, Н. К. К., Зарипов, М. Х. У., & Мирзаев, С. С. (2017). Изучение процесса регенерации цеолитовой очистки природного газа на УДП" Шуртаннефтгаз". Вопросы науки и образования, (2 (3)), 45-47.Жамилова, Н. К. К., Зарипов, М. Х. У., & Мирзаев, С. С. (2017). Изучение процесса регенерации цеолитовой очистки природного газа на УДП" Шуртаннефтгаз". Вопросы науки и образования, (2 (3)), 45-47.
4. Rayimov, Z. X. O. G. L. (2021). Ftal angidridning vinillanish jarayoni erituvchilari. Science and Education, 2(12), 266-269.
5. Ахмедов, Вохид Низомович, Бобир Баходир Угли Олимов, and Шомурод Комилович Назаров. "Электронная структура и квантово-химические расчёты виниловых эфиров фенолов." Universum: химия и биология 4 (70) (2020).