STUDYING THE ACTIVITY OF THE CATALYST DURING THE PRODUCTION PROCESS OF SYNTHETIC LIQUID HYDROCARBONS

ABSTRACT

It was studied depending on the performance of promotion of 15% Co-15% Fe/HZS with group VIII and IV metals (Ni, Zr) in the synthesis of CO and H₂ hydrocarbons. The addition of Ni and Zr metals to the So and Fe storage catalyst resulted in an increase in the yield of liquid hydrocarbons from 118 to 124-139 g/m3. As a result of research, a 15%Co-15%Fe-5%Ni-1%ZrO2/HZS dispersed catalyst was selected. The catalytic activity of the selected catalyst is controlled by the time and method of initial treatment and the study of the catalytic action of diluting the catalytic system with quartz. it was found that the selectivity of production increases from 72 to 85%. A noticeable decrease in the total productivity of gaseous participants was observed (from 96 to 52 g/m³). Increasing the dilution of the catalyst with quartz also led to a decrease in the proportion of ethylene hydrocarbons and an increase in the content of saturated hydrocarbons from the liquid surfaces of the synthesis.

АННОТАЦИЯ

Изучена зависимость эффективности промотирования 15% Со-15% Fe/ЮКЦ металлами VIII и IV групп (Ni, Zr) в синтезе СO и H₂ углеводородов. Добавление в катализатор хранения Co и Fe металлов Ni и Zr привело к увеличению выхода жидких углеводородов со 118 до 124-139 г/м³. В результате исследований был выбран дисперсный катализатор 15%Co-15%Fe-5%Ni-1%ZrO2/ЮКЦ. Каталитическая активность выбранного катализатора контролируется временем и способом первичной обработки, а также исследованием каталитического действия разбавления каталитической системы кварцем установлено, что селективность производства увеличивается с 72 до 85%. Наблюдалось заметное снижение общей продуктивности газообразных участников (с 96 до 52 г/м³). Увеличение разбавления катализатора кварцем также привело к уменьшению доли этиленовых углеводородов и увеличению содержания предельных углеводородов с жидких поверхностей синтеза.

Keywords: catalyst, regeneration, carbon monoxide, hydrogen, liquid hydrocarbons, conversion, reaction yield, dilution.

Ключевые слова: катализатор, регенерация, оксид углерода, водород, жидкие углеводороды, конверсия, выход реакции, разбавление.

1. Introduction

GTL (Gas-to-Liquid) technologies are technologies for processing natural gas into motor fuel and other heavier hydrocarbon products. The synthesis of hydrocarbons from CO and H₂ is an exothermic reaction. The thermal effect reaches 600 kcal/Nm³ of synthesis gas or 41 kcal/mol. The activation energy of the process is about 24 kcal/mol. From carbon monoxide and hydrogen, the formation of hydrocarbons of any molecular weight, type and structure, except acetylene, is thermodynamically possible [1].Mixtures with a wide fractional composition (from C1 to C30 and even up to C100 and higher), including paraffin and olefinic hydrocarbons, have been synthesized. Thermodynamic calculations show that at a pressure of 1-100 atm and a temperature of 20-700 ° C, paraffinic hydrocarbons, especially methane, are most likely to be formed.The upper temperature limit for the formation of hydrocarbons at a pressure of 1atm is 400-500 ° C. With an increase in pressure to 100 atm, this temperature increases to about 150-200 ° C. A decrease in temperature contributes to an increase in the equilibrium level of carbon monoxide conversion. The lower the temperature, the more favorable the thermodynamic properties for the synthesis of all homologous series compounds from CO and H₂.In practice, the lower temperature limit is determined by the temperature at which the catalyst is active. In addition, secondary processes are possible in the entire temperature range used for the synthesis of hydrocarbons from CO and H₂: hydrogenation of alkenes, hydrocracking of the resulting alkanes, dehydrogenation of alkanols, isomerization processes, oligomerization, double bond migration, polymerization, cis -trans isomerization.methane - alkanes - alkenes - products containing oxygen. The probability of formation of normal alkanes decreases with increasing chain length; for simple alkenes, the order is reversed [2]. An increase in synthesis temperature favors the formation of alkenes and aldehydes. An increase in the total pressure in the system favors the formation of high molecular weight products, and an increase in the partial pressure of hydrogen in the synthesis gas leads to the predominant formation of alkanes [3].Thus, hydrogen-rich syngas is preferred for alkanes production, while carbon monoxide-enriched syngas helps to increase the yield of alkenes and aldehydes, if coke formation is not considered. For paraffins with the same number of carbon atoms in the molecule, the n-alkane/iso-alkane equilibrium ratio increases with product chain length and is, for example, 1.1 for butanes and 19.2 for nonanes [4]. However, the composition of the products of the catalytic synthesis of hydrocarbons from CO and H₂ is significantly different from the equilibrium. Fischer-Tropsch synthesis is a kinetically controlled process, and the nature of the catalyst and the synthesis conditions affect the distribution of products [5].The synthesis of hydrocarbons from CO and H₂ can legitimately be considered a polycondensation process, since the molecular weight distribution of the synthesis products, as a rule, obeys the formal kinetics of polymerization:

where M is a metal, C1, Cn-1, Cn, Cn+1 is a carbon fragment containing 1, 1-n, n, n+1 carbon atoms, respectively, k1 and k2 are chain growth rate constants and corresponding to finish

The simplest, but at the same time adequate model is based on the following assumptions [6]:

• after each introduction of C1 monomer molecule, the next step of chain elongation with rate constant k1 or chain termination with rate constant k2 can occur, which leads to the formation of the next observed product;
• chain growth and termination rate constants k1 and k2 are independent of chain length.

A large amount of products of secondary changes (cracking, isomerization) - isoparaffins and olefins - was found in all fractions of synthesized hydrocarbons. The most amount of isoparaffinswas recorded for the composite catalyst - the iso/n parameter is equal to 0.6, which indicates that it has increased activity compared to the catalysts absorbed in the hydroimprovement reactions. High concentrations of olefins were found for catalysts with low cobalt content, which is due to their low hydrogenation capacity compared to unsaturated hydrocarbons [7].

Figure .1. Molecular-mass distribution of C₅+ hydrocarbons obtained in the presence of catalysts: a-Co-Fe-Ni-ZrO2/HZS+ Fe₃O₄+d-FeOOH; β-absorbent, containing 6.5% iron

The use of zeolite in the composition of hybrid catalysts allows obtaining C₅+ hydrocarbons whose molecular-mass distribution does not obey the AShF equation. Maximum MMD corresponds to C5-C10 hydrocarbons. The products consist mainly of liquid hydrocarbons. The selectivity in the formation of C5-C18 hydrocarbons for absorbing catalysts is 46-49%, for the composition it is 62.6% (Fig. 1).Thus, it was found that the use of cobalt mixing and cobalt precipitation methods by impregnation into the formed carrier has a significant effect on the physicochemical and catalytic properties of hybrid catalysts.

The use of the absorption method for the preparation of hybrid catalysts creates a system that exhibits lower catalytic properties in the process of hydrocarbon synthesis than the composite catalyst. This is likely due to both diffusion factors, pore blocking by precipitated cobalt, and the formation of compounds of cobalt and aluminum oxides that are difficult to recover from oxide-oxide interactions.

2. Methods of research

Hydrocarbon synthesis centers and zeolitic acid sites in absorbent catalysts are in close contact with each other, which should contribute to the enhancement of secondary processes. At the same time, the amount of liquid hydrocarbons (C₅-C₁₈) in the composition of C₅+ hydrocarbons is about 83%, which is 12% less than that of the composite catalyst.For the composite catalyst prepared by mixing the components, no oxide-oxide interaction was found, the pores of the zeolite are not blocked by cobalt, which allows efficient delivery of reactants to the active part of hydrocarbon synthesis.

Such a catalyst has a high activity in the synthesis of hydrocarbons - the conversion rate of CO is 76.2%, the productivity and selectivity for C₅+ hydrocarbons is 93.8 kg/m3 cat h and 68.6%.

In the composite catalyst salted in silicon oxide, the acid center is not blocked by the cobalt located on the silicon oxide in the Co-Fe-Ni-ZrO2/HZS+Fe3O4+d-FeOH catalyst. There are both external and internal centers for hydrocarbons, as a result of which the composite catalyst increases the activity in hydrolysis reactions - the amount of liquid hydrocarbons reaches 95%. In this context, the preferred method for the preparation of hybrid catalysts is to mix the active components using a binder [8].

3. Results

The effect of CO pressure during the activation stage on the main parameters of the synthesis. In order to obtain more information about the effect of СO pressure on the activity of 15%Co-15%Fe-5%Ni-1%ZrO2/HZS FeOH nano-sized catalyst during the activation stage, we conducted detailed studies. .The main parameters of the synthesis of catalysts obtained by activation at different pressures of CO are presented in Table 1. It can be seen that the pressure of CO, as in the case of hydrogen, does not significantly affect the main parameters of the synthesis of hydrocarbons from CO and H2 in the nanoheterogeneous catalyst. In all studied ranges of pressures, CO conversion was ~78%, yield of liquid products of synthesis was ~120 g/m3, selectivity for C₅+ was 62%, productivity was 478.8 g/kg·cat·h [9].

Table 1.

Effect of regeneration conditions of 15%Co-15%Fe-5%Ni-1%ZrO2/HZS

Figure 2.2 shows the dependence of the output of the target products of synthesis - liquid hydrocarbons on CO conversion. As can be seen from the table, it can be concluded that the obtained dependences are almost independent of the CO pressure during the regeneration stage. All of them are almost linear, which indicates good heat dissipation [10].

Figure 2. Effect of CO pressure on the activation stage

The gas pressure during the regeneration stage has almost no effect on the fractional and group composition of the target products of the synthesis - liquid hydrocarbons (Table 2). However, when the pressure increases, it is observed that by-products oxygenates, especially ethanol, are formed more [11-12].

Table 2.

Effect of CO pressure on the liquid hydrocarbon composition during the 15%Co-15%Fe-5%Ni-1%ZrO2/HZS FeOH catalyst activation

4. Conclusions

Thus, nano-sized samples of the nanocatalyst with 15%Co-15%Fe-5%Ni-1%ZrO2/HZS FeOH composition were prepared by the method of thermolysis of appropriate salts of precursors or their solutions in a dispersion medium boiling at high temperature in a wide temperature range, and in the presence of this catalyst, the effect of catalyst concentration in the reaction zone, the effect of zirconium concentration in the reaction space, the effect of regenerator properties, the effect of regeneration conditions, the effect of CO pressure in the activation stage, and the effect of synthesis conditions studied.

References:

1. Kuybokarov O.E. research of the catalytic properties of a catalyst selectedfor the production of high-molecular weight liquidsynthetic hydrocarbons from synthesis gas//Universum: technical sciences. – 2023. – No. 10 (115). - pp. 28-32. 40).
2. Kuybokarov O.E. and others. Catalytic synthesis of high-molecular weight hydrocarbons from synthesis gas in apolyfunctional catalyst //Universum: technical sciences. – 2022. – No. 1-2 (94). - pp. 93-103. 351).
3. SalievA.N. Technology of a cobalt zeolite-containing catalyst for the selective synthesis of liquid hydrocarbons fromCO and H2: dissertation of candidateof technical sciences: 05.17.01 Novocherkassk 2018.
4. Cheng S., Shang N., Feng C., Gao S., Wang C., Wang Z. Efficient multicomponent synthesis of propargylaminescatalyzed by copper nanoparticles supported on metal-organic framework derived nanoporous carbon // CatalysisCommunications. 2017. Vol. 89. pp. 91-95.
5. Wang X., Meng F., Chen H., Gao F., Wang Y., Han X., Fan C., Sun C., Wang S., Wang L. Synthesis of a hierarchicalZSM-11/5 composite zeolite of high SiO2/Al2O3 ratio and catalytic performance in the methanol-to-olefins reaction // ComptesRendusChimie. 2017. Vol. 20, No. 11. pp. 1083-1092.
6. Kobrakov I.K. Synthesis of hydrocarbons from CO and H2 on promoted cobalt-containing catalysts, dissertationof candidateof technical sciences. - Kobrakov Ivan Konstantinovich - M., 2007.-126 p.
7. Huang H., Meng X., Chen C., Zhang M., Meng Z., Li C., Cui Q. Effect of Phosphorus Addition on the Performanceof Hierarchical ZSM-11 Catalysts in Methanol to Propene Reaction // Catalysis Letters. 2016. Vol. 146, No. 11. pp. 2357-2363.
8. Catizzone E., Cirelli Z., Aloise A., Lanzafame P., Migliori M., Giordano G. Methanol conversion over ZSM-12,ZSM-22 and EU-1 zeolites: from DME to hydrocarbons production // Catalysis Today. 2018. Vol. 304. pp. 39-50.
9. Zhao X., Wang L., Li J., Xu S., Zhang W., Wei Y., Guo X., Tian P., Liu Z. Investigation of methanol conversionover high-Si beta zeolites and the reaction mechanism of their high propene selectivity // Catalysis Science & Technology. 2017. Vol. 7, No. 24. pp. 5882-5892.
10. Terasaka K., Imai H., Li X. Control of Morphology and Acidity of SAPO-5 for the Methanol-To-Olefins (MTO)Reaction // J AdvChem Eng. 2015. Vol. 5, No. 4.11. Sanchez-Sanchez M., Romero A.A., Pinilla-Herrero I., Sastre E. Ionothermal preparation of triclinic SAPO-34 andits catalytic performance in the MTO process // Catalysis Today. 2017. T. 296. pp. 239-246.
11. Yakovenko R.E. Technology of cobalt catalyst and higher hydrocarbons from CO and H2: dissertation. - South-RussianState Polytechnic university named after M.I. Platov, 2017.
12. Han L., Zhao X., Yu H., Hu Y., Li D., Sun D., Liu M., Chang L., Bao W., Wang J. Preparation of SSZ-13 zeolitesand their NH3-selective catalytic reduction activity // Microporous and Mesoporous Materials. 2017. T. 261. pp. 126-136.
13. Bohstrom Z., Arstad B., Lillerud K.P. Preparation of high silica chabazite with controllable particle size // Microporousand Mesoporous Materials. 2016. T. 195. pp. 294-302.