TEXTURAL CHARACTERISTICS OF ZINC ACETATE CATALYST FROM CERAMZITE PREPARED FOR THE SYNTHESIS OF VINYL ACETATE FROM ACETYLENE

ABSTRACT

Based on the BET (Brunoir, Emmet and Teller) method and on the idea of multilayer adsorption of water vapour. the equation of the adsorption isotherm was obtained in the work which is as follows: After treatment of activated expanded clay with hydrogen peroxide. the value of the Sud. measured by the adsorption of non-polar adsorbate. increases by 44. The adsorption of zinc acetate on modified expanded clay was studied under static and dynamic conditions at different temperatures ranging from 0 to 85 °C. In all experiments. the volume ratio of solution to activated expanded clay was 4:1. The total amount of salt absorbed by the support was determined by measuring the concentration of the solution at the time of reaching equilibrium. To sum up, hydrolysed forms of salt at pH>8 are neutralised with adsorbed acetic acid.

АННОТАЦИЯ

На основе метода БЭТ (Брюнуара, Эммета и Теллера) и на основе идеи многослойной адсорбции пара в работе получено уравнение изотермы адсорбции. которое выглядит следующим образом: После обработки активированного керамзита перекисью водорода значение измеренное по адсорбции неполярного адсорбата, увеличивается в 44. Окисление активированного керамзита перекисью водорода происходит по типу процесса декарбоксилирования. Адсорбцию ацетата цинка на модифицированном керамзите изучали в статических и динамических условиях при различных температурах от 0 до 85°С. Во всех экспериментах объемное соотношение раствора и активированного керамзита было равно 4:1. Общее содержание соли. поглощенной носителем. определяли путем измерения концентрации раствора до установления равновесия. Таким образом, гидролизованные формы соли при pH>8 нейтрализуются адсорбированной уксусной кислотой.

Keywords: acetylene. acetic acid. vinyl acetate. hydrogen peroxide. textural characteristics.

Ключевые слова: ацетилен. уксусная кислота. винилацетат. водород пероксид. текстур характеристика.

Introduction

This method is based on the vinylization reaction. which consists of adding acetic acid to acetylene:

The process of obtaining vinyl acetate from acetylene is carried out in both the vapour and liquid phases. Vinyl acetate was first obtained as a by-product of the liquid phase synthesis reaction of ethylidene diacetate. Later this method was implemented as the first industrial method to obtain vinyl acetate: the reaction was carried out in acetic acid at 40-100°С in the presence of mercury salts and strong acids such as oleum. etc. [1-4].

Currently, the optimisation of the process of obtaining vinyl acetate from acetylene and acetic acid is being carried out in several directions. including the design of synthesis reactors that can provide the highest removal of the target product with the least consumption of raw materials and energy resources. In order to develop a mathematical model of the reactor. it is necessary to build a kinetic model of this process[5-6].

The kinetics of the synthesis of vinyl acetate from acetylene and acetic acid has been studied on catalysts containing zinc and cadmium. Most of the studies were carried out in a differential reactor at a conversion below 8% in which case the results were treated as those obtained in a non-gradient reactor.

Today, the world's annual demand for vinyl acetate is 8 million tonnes. This requires research to create a system to optimise the technology for obtaining vinyl acetate and its derivatives with the participation of local catalysts. Therefore. it is important to conduct research on the development and improvement of technology for the production of vinyl acetate with the participation of local catalysts [7-10].

Experimental part

As mentioned above. traditional catalysts for the vapour phase synthesis of vinyl acetate from acetylene and acetic acid are catalysts consisting of carboxylic acid salts on supports such as zinc. cadmium and bismuth acetates. as well as mixtures of these acetates. The supports used are activated carbon and silica gel.

High silica zeolite and activated carbon were obtained from the natural mineral raw materials Navbahor bentonite and walnut shell by chemical. thermal and mechanical activation methods. Activated carbon with a particle size of 2-4 mm was first treated with water and 24% by mass with an aqueous solution of hydrogen peroxide (volume ratio between hydrogen peroxide solution and activated carbon was 3:1). The mixture was stirred intensively in a cylindrical reactor for 2 hours at a temperature of 70°С with a constant air flow through the reactor at a speed of 5-6 cm/s. The coal was then filtered and heated for 1 hour at a temperature of 340-350°С. The study showed that increasing and decreasing the oxidation temperature and changing the concentration of hydrogen peroxide gave poor results in terms of catalyst activity.

Method for modifying ceramsite with acetic acid. The expanded clay with a particle size of 2-4 mm dried at 280-300°С, was treated with a 10% by mass acetic acid solution in a volume ratio of 4:1 between the solution and the expanded clay. The solution is continuously transferred through the activated expanded clay layer in the reactor for 120 minutes using a circulation pump at a temperature of T=(70+5) °С at a speed of 8-9 cm/s. Then the expanded clay is passed through a filter and heated at a temperature of T=120-130°С for 1.5 hours.

Experimental results and their discussion

The morphological structure of activated expanded clay does not change after modification according to SEM data (20000 magnification). Keramsite particles have a corpuscular shape and an amorphous structure formed by irregular polyhedra.

The characteristics of the porous structure of the modified expanded clay were calculated according to the adsorption isotherms of water and citric acid vapours and are presented in Table and Figure 1.

Table 1.

Porous structure parameters of activated expanded clay before and after treatment with H₂O₂ and CH₃COOH

1- treated with H₂O₂;                             2- Treated with CH₃COOH

Figure 1. Differential curves of pore size distribution for expanded clay according to acetic acid vapor adsorption isotherms

After treatment of activated expanded clay with hydrogen peroxide. the value of Sud. measured by adsorption of non-polar adsorbate increases by 44. The content ratio of N/S elements after oxidation of expanded clay with hydrogen peroxide increases from 0.029 to 0.044 mass (Table 2). i.e. decarboxylation of expanded clay occurs with removal. In this case. the capacity of oxidised expanded clay is 0.5 mmol/g in terms of acetic acid vapours and 0.4 mmol/g in terms of water vapours. which allows us to speak of increased hydrophobicity of expanded clay. It can be assumed that the oxidation of activated carbon with hydrogen peroxide takes place as a decarboxylation process. In this case. the volume of micropores does not decrease but increases (Table 2).

Table 2.

Descriptions of ceramsite modified samples

In the study of the adsorption of zinc acetate on the surface of hydrogen peroxide and acetic acid under static and dynamic conditions. the rate of adsorption and the amount of adsorbed salt in the solution were measured. as previously investigated. FK treated with nitric acid. when passing through the support layer (Fig. 2-3) to the static conditions of lowering into the solution circulation mode increases significantly. In this case. the highest adsorption capacity and adsorption rate occur at a linear velocity of 15+2 cm/s through the maximum.

Figure 2. Dependence of the adsorption capacity of Zn(OAc)₂ in hydrogen peroxide on the circulation speed V (cm/s) at the discharge temperature T=50

Figure 3. Dependence of Zn(OAc)2 adsorption capacity on activated carbon in acetic acid on circulation speed V (cm/s) at discharge temperature T=50

Conclusion

At the drying temperature of the sorbent treated with acetic acid T=90-95°С, taking into account that most of the acetic acid is adsorbed on the surface of expanded clay, Zn(CH₃COO)₂ The extreme dependence of the maximum capacity on рH surface complexes H[Zn(OAc)₃] can be explained by the preferential adsorption of associates or neutral forms of salts. In this case, hydrolysed forms of salt at pH>8 are neutralised with adsorbed acetic acid.

References:

1. Gonzalez Caranton. AR; to Silva Pinto. JCC; Stavale. F .; Barreto. J .; Schmal. M. Statistical analysis of the catalytic synthesis of Vinyl acetate over Pd-Cu / ZrO ₂ nanostructured based catalysts. Catal. Today 2020. 344. 108–117. [CrossRef]
2. Han. YF; Kumar. D .; Goodman. DW Particle size effects in vinyl acetate synthesis over Pd / SiO2. J. Catal. 2005. 230. 353–358. [CrossRef]
3. Li. ZJ; Thuening. T .; Tysoe. WT The adsorption of ethylene on Au / Pd (100) alloy surfaces. Surf. Sci. 2016. 646. 65–71. [CrossRef]
4. Omanov B.Sh.. Fayzullayev NI. Khatamova MS Vinylacetate Production Out of Acetylene // International Journal of Advanced Research in Science. Engineering and Technology. ISSN: 2350-0328. Vol. 6. Issue 12. December 2019. rp.12011-12017
5. Omanov B.Sh.. Fayzullaev NI. Musulmonov N.Kh.. Xatamova MS. Asrorov DA Optimization of Vinyl Acetate Synthesis Process. // International Journal of Control and Automation. ISSN: 2005-4297. Vol. 13. No1. (2020). pp. 231 - 238.
6. Omanov B.Sh.. Fayzullaev NI. Xatamova MS Vinyl Acetate Production Technology. // International Journal of Advanced Science and Technology. ISSN: 2005-4238. Vol. 29. № 03. 2020.pp. 4923-4930.
7. Omanov B.Sh.. Fayzullaev NI. Khatamova MS Catalytic synthesis of acetylene ut of vynyl acetate and texture characteristics of catalysts. // «Asian journal of multidimensional research. ISSN: 2278-4853. Special Issue. March. 2020. pp. 234-241.
8. Omanov B.Sh.. Fayzullaev N.I. Parameters of technological mode of synthesis of vinyl acetate. // Universum: «Chemistry and Biology». Scientific journal. Moscow. 2020. Release: 4 (70). April. 45-48 p.
9. Bekhruzjon Omanov. Normurot Fayzullaev. Mukhabbat Khatamova. Almagul Xalibekova. Madina Avezova//Optimizing Vinyl Acetate Production Process and Selecting of Appropriate Reactor Type//AIP Conference Proceedings 2789. 020008 (2023) https://doi.org/10.1063/5.0145637
10. Bekhruzjon Omanov. Normurot Fayzullaev. Mukhabbat Khatamova. Nigina Ruziqulova. Sardor Rustamov//Energy and Resource Saving Technology of Vinylacetate Production from Acetylene// AIP Conference Proceedings 2789. 020009 (2023) https://doi.org/10.1063/5.0145636