METHODS FOR DETERMINING THE DEPENDENCE OF COPPER CONTENT IN A CATALYST POSSESSING HIGH CATALYTIC ACTIVITY AND SELECTIVITY IN THE OXIDATIVE CHLORINATION OF ETHYLENE

АННОТАЦИЯ

В данной работе представлены результаты количественного определения массовой доли меди в сложном каталитическом комплексе, предназначенном для процесса получения винилхлорида из этилена. Актуальность исследования обусловлена необходимостью точного контроля состава катализаторов оксихлорирования, поскольку содержание активного металла напрямую влияет на их активность и селективность. Анализ проводили объемным титриметрическим методом, который отличается высокой воспроизводимостью и доступностью для рутинного лабораторного контроля. Расчет массовой доли иона меди осуществляли по формуле

где, V – объем титранта, K – поправочный коэффициент, G – масса навески.

Для реализации реакции оксихлорирования этилена был обоснованно выбран многокомпонентный катализатор состава KClZnCl2MnCl2*CuCl2. Данная композиция обеспечивает высокую каталитическую активность и избирательность в целевой реакции образования винилхлорида, минимизируя побочные продукты.

ABSTRACT

This paper presents the results of the quantitative determination of the copper mass fraction in a complex catalytic system designed for the production of vinyl chloride from ethylene. The relevance of this study is driven by the need for precise composition control of oxychlorination catalysts, as the content of the active metal directly influences their activity and selectivity. The analysis was performed using a volumetric titrimetric method, which offers high reproducibility and is suitable for routine laboratory monitoring. The mass fraction of the copper ion was calculated using the formula

Where V is the titrant volume, K is the correction factor, and G is the sample weight.

To carry out the oxychlorination reaction of ethylene, a multicomponent catalyst with the composition KClZnCl2MnCl2*CuCl2 was deliberately selected. This formulation provides high catalytic activity and selectivity towards the target vinyl chloride formation, while minimizing by-products.

Ключевые слова: этилен, водород хлорид, медь, селективность, симм-дихлорэтан, механизм.

Keywords: ethylene, hydrogen chloride, copper, selectivity, sym-dichloroethane, mechanism.

Introduction. Vinyl chloride is one of the largest-scale products of organic synthesis, and its global production is steadily increasing day by day. Up to 95% of the produced vinyl chloride is used for the production of polyvinyl chloride. The remaining portion of vinyl chloride is utilized in the manufacture of various vinyl copolymers [1].

The most widely applied industrial method is the production of vinyl chloride from ethylene in the gas phase using heterogeneous catalysts. These catalysts, selected for this reaction, possess high catalytic activity and selectivity [2, 3].

According to the mechanism, all reactions for producing vinyl chloride from ethylene can be divided into two main groups: 1) reactions proceeding through the intermediate oxidation of hydrogen chloride to chlorine, which then chlorinates the organic substrate in the presence of oxygen; and 2) reactions that do not require the preliminary oxidation of hydrogen chloride to chlorine. The reaction proceeds within the temperature range at which both the oxidation of hydrogen chloride and the production of vinyl chloride from ethylene, replacing alkanes, are carried out [4,5].

In general, the synthesis of substances important for the chemical industry from natural gas, which is the only alternative to oil, represents one of the pressing challenges.

Methods. Methods for Determining the Copper Content in a Catalyst Possessing High Catalytic Activity and Selectivity in the Oxidative Chlorination of Ethylene, Selected for the Production of Vinyl Chloride from Ethylene.

The mass fraction of copper in the catalyst, selected for the production of vinyl chloride from ethylene and exhibiting high catalytic activity and selectivity in the oxychlorination of ethylene, was determined by a volumetric method. This method is based on the titration with a sodium thiosulfate solution of the equivalent amount of free iodine liberated by the reaction of iodide ions with Cu²⁺ ions. A sample of the catalyst under study, weighing 2.0-2.5 g, is treated with 30 mL of hydrochloric acid. The resulting mixture is boiled for 10 minutes. The obtained suspension is cooled, distilled water is added, followed by an ammonia solution. Subsequently, 5 mL of acetic acid and 20 mL of potassium iodide solution are added. The liberated iodine is titrated with a sodium thiosulfate solution. The mass fraction of the copper ion is calculated using the following formula:

Where V is the volume of the 0.1 N sodium thiosulfate solution consumed for titration, mL; 0.006350 is the mass of copper equivalent to 1 mL of the 0.1 N sodium thiosulfate solution, g; K is the correction factor to adjust the concentration of the sodium thiosulfate solution to exactly 0.1 N; G is the weight of the sample, g.

Results, and Discussion. Figure 1 illustrates the dependence of the content of chlorine-containing organic products—namely sym-dichloroethane (1,2-dichloroethane) and sym-trichloroethane (1,1,2-trichloroethane)—on the concentration of CO₂ in the initial reaction mixture during the production of vinyl chloride from ethylene (referred to as "chlorine selectivity").

Figure 1. Dependence of the content of sym-dichloroethane (1,2-dichloroethane) and sym-trichloroethane (1,1,2-trichloroethane) in chlorine-containing organic products of the vinyl chloride production process from ethylene on the CO₂ content in the initial reaction mixture

As can be seen from Figure 1, an increase in the amount of carbon dioxide leads to an increase in the selectivity of sym-dichloroethane (1,2-dichloroethane) formation, which is associated with a decrease in the selectivity of sym-trichloroethane (1,1,2-trichloroethane) formation.

Table 1 shows the dependence of the reaction rates of sym-dichloroethane (1,2-dichloroethane) hydrochlorination at various temperatures.

Table 1.

Influence of the amount of sym-dichloroethane (1,2-dichloroethane) per unit mass or volume on the rate of its dehydrochlorination reaction at different temperatures. Catalyst: KClZnCl₂MnCl₂*CuCl₂

Analysis of the data presented in Table 1 indicates that at relatively low temperatures (200–215 °C), the reaction rate of vinyl chloride formation is described by a first-order equation:

When the temperature rises to 240 °C, a deviation from linear dependence is observed. In general form, the reaction rate equation can be expressed by the following formula (2):

During preliminary experiments, it was shown that within the studied temperature range, the pure support does not catalyze the dehydrochlorination reaction of sym-dichloroethane (1,2-dichloroethane). Therefore, the active sites containing copper on the surface of the catalyst, selected for the production of vinyl chloride from ethylene and possessing high catalytic activity and selectivity, play a decisive role in this reaction.

Сonclusion. In studies on the catalytic hydrochlorination of chlorohydrocarbons, it was determined based on the reaction rate of product formation that the copper content is of great importance in the process of vinyl chloride production from ethylene when using catalyst samples selected for this reaction, possessing high catalytic activity and selectivity with the composition KClZnCl₂MnCl₂*CuCl₂.

The condensing organic products were analyzed by gas-liquid chromatography, and their composition was recalculated using the internal normalization method of the chromatogram.

Reference:

1. Flid M. R. Vinyl chloride technology: Present and future //Catalysis in Industry. – 2009. – Т. – №. 4. – С. 285-293.
2. Д.С. Курбанова, С. Ю. Бобомуродова. Этиленни кислород иштирокида водород хлорид таъсирида оксихлорлаш жараёни // Ўзбeкистон миллий унивeрситeти хабарлари 2023, [3/2/1] ISSN 2181-7324(370-373-бет)
3.  Д.С.Курбанова, С.Ю.Бобомуродова Симм-дихлорэтан (1,2-дихлорэтан)дан водород хлорид ажралиш реакциясининг оптимал шароитларини аниқлаш. // Ўзбекистонда фанлараро инновациялар ва илмий тадқиқотлар журнали ISSN:2181-3302 SJIF(2024)  IMPACT FACTOR 6.618 30-сон 20.05.2024 (100-110-бетлар)
4. С.М. Котова, Л.В. Пучкова, Е.В. Чихун и др. Оценка некоторых показателей метаболизма меди при остеопорозе // Материалы Российского конгресса по остеопорозу. - Москва, 2003. С. 34.
5. Ю.Ю. Петрова, М.К. Беклемишев, А.Г. Гиновкер. методов разделения и определения а-аминокислот в различных объектах анализа является актуальной проблемой.