CHEMICAL REACTOR MODELING IN ACETONE PRODUCTION PROCESS USING ASPEN PLUS SOFTWARE

ABSTRACT

The effect of various factors (temperature, volume velocity, acetylene:water ratio, catalyst composition, etc.) on the product yield and process selectivity in the catalytic hydration reaction of acetylene was studied. The surface area of the catalytic system was determined by the S_sol=BET method, and the volume of micro- and mesopores was determined by the BJH method.  The kinetic laws of the catalytic hydration reactions of acetylene were studied and the mechanisms of their progress were proposed, and the additive kinetic equations representing the progress of the reactions were proposed (the mean square deviation does not exceed 5%). The activation energy for the hydrogenation reaction of acetylene was determined by calculating E and E = 75000 J/mol. For the first time, an improved and low-waste compact computer model of acetone production by catalytic acetylene hydration has been developed.

АННОТАЦИЯ

Изучено влияние различных факторов (температуры, объемной скорости, соотношения ацетилен: вода, состава катализатора и др.) на выход продукта и селективность процесса в реакции каталитической гидратации ацетилена. Площадь поверхности каталитической системы определяли методом S_сол=БЭТ, а объем микро- и мезопор определяли методом БЖХ. Изучены кинетические законы реакций каталитической гидратации ацетилена и предложены механизмы их протекания, а также предложены аддитивные кинетические уравнения, отражающие протекание реакций (среднеквадратичное отклонение не превышает 5%). Энергию активации реакции гидрирования ацетилена определили путем расчета Е и Е = 75000 Дж/моль. Впервые разработана улучшенная и малоотходная компактная компьютерная модель получения ацетона каталитической гидратацией ацетилена.

Keywords: acetylene, water, acetone, catalyst, "wet" and suspension technology, Aspen Plus program, computer model.

Ключевые слова: ацетилен, вода, ацетон, катализатор, «мокрая» и суспензионная технология, программа Aspen Plus, компьютерная модель.

INTRODUCTION

Acetone is obtained in relatively small quantities by dry distillation of wood together with acetic acid. Obtained by fermentation of carbohydrates in the presence of special bacteria for a long time (acetone-butyl fermentation.) Fermentation products contain 30.5% acetone, 62% n-butyl alcohol, 7.5% ethyl alcohol and other substances. Currently, this method is rapidly being replaced by synthetic methods of acetone production. Oil, petroleum gases and coal processing products are used here as raw materials.

The process is carried out in a large-scale calcium-cadmium-phosphate catalyst placed on reactor shelves at a temperature of 330-410℃, atmospheric pressure, and the volume ratio of water vapor and acetylene is 7:11. The volumetric rate of acetylene is 200-300 l/l catalyst in 1 hour.

Adiabatic superheating is equal to 500℃, when H₂O:C₂H₂=7:1. The speed of the process is determined by the temperature difference in the catalyst layer and above it; this difference should not exceed 35℃. An increase in temperature in the catalyst layer increases the formation of side products, primarily croton aldehyde. This is due to the fact that the activation energy leading to the formation of croton aldehyde is higher than that of acetylene hydration. A decrease in volumetric velocity (increase in contact time) also produces the same result. A decrease in the ratio of steam: acetylene from 7:1 also increases the formation of side products; an increase in the ratio leads to the consumption of a large amount of steam and, therefore, to the consumption of energy for its condensation and rectification of the water-aldehyde mixture. The optimal ratio is 8-9:1. In this case, the rate of acetylene turnover in one pass is ≈ 30%.

EXPERIMENTAL PART

The morphology of the catalysts was studied using wave electron microscopy (ZEM) at Vegall LMU (Czech Republic). Also, the porous structure was established based on the analysis of adsorption curves obtained by the thermosorption method of nitrogen. The surface area of the catalytic system was determined by the S_sol=BET method, and the volume of micro- and mesopores was determined by the BJH method.

Table 1.

Composition and properties of synthesized zinc-iron-chromium-manganese-vanadium/HSZ catalysts (T=698-703 K)

As can be seen from Table 1, given catalysts provide high acetylene conversion. Their stability is 1-1.5 times lower than zinc-iron-chromium-manganese-vanadium/HSZ catalyst.

The catalyst promoted with up to 1.0% V₂O₅ has sufficient activity, mechanical strength and stability. The catalyst containing 5%ZnO·5%Fe₂O₃·5%Cr₂O₃·3%MnO₂ provides high acetone yield. When the reaction is carried out at 300-500℃, the yield of acetone is 96.2% in relation to the reacted acetylene. Acetaldehyde, 3-oxybutanal, croton aldehyde, butanal, ethyl acetate and paraldehyde are formed as by-products.

Nitrate salts with the following composition during the promotion of catalysts prepared by suspension method based on zinc-iron-chromium-manganese-vanadium/YUKS compounds: Zn(NO₃)₂·6H₂O, Fe(NO₃)₃·6H₂O, Cr(NO₃)₃·9H₂O, Mn(NO₃)₂·6H₂O va VO(NO₃)₃ by X-ray analysis and found that it leads to an increase in catalyst activity.

In the presence of this nanocatalyst, the conversion of acetylene is 90-97%, the yield of acetone is 96.2%, and the yield of acetaldehyde is 2.2%.

The effect of volume velocity on acetone yield and acetylene conversion was also studied, and the experimental results are presented in Table 2.

Table 2.

The effect of volume velocity on acetone yield and acetylene conversion (cat №9; T= 425-430℃)

As can be seen from the table, the total conversion of water increases with the increase in the volumetric rate of acetylene in the reaction mixture.

The volumetric rate of primary acetylene is 96.3% selectivity to acetone up to 180 h^-1. Volumetric velocity of initial acetylene

When it exceeds 180 h^-1, the selectivity of acetone formation decreases due to the formation of additional substances (acetaldehyde, 3-oxybutanal, croton aldehyde, butanal, ethylacetate and paraldehyde).

To keep the acetylene conversion constant at 96.5-97.2%, the temperature is increased by 5-10℃ for 20-22 hours. The effect of acetylene volumetric rate on acetone yield and acetylene conversion was studied in the range of 80-220 h^-1. The obtained results are presented in Figure 1.

1-rasm. Asetilen konversiyasiga asetilen hajmiy tezligining ta'siri

Figure 1. Effect of acetylene volumetric rate on acetylene conversion

As can be seen from Figure 1, the acetylene conversion and acetone yield increase when the volumetric rate of the mixture of acetylene and water vapor is increased from 80 h^-1 to 180 h^-1. When the volumetric rate of the mixture of acetylene and water vapor is increased from 180 to 220 h^-1, the acetylene conversion and acetone yield decrease due to the formation of additional substances (acetaldehyde, 3-oxybutanal, croton aldehyde, butanal, ethylacetate and paraldehyde). This leads to the conclusion that the process takes place in the external diffusion field.

The effect of temperature, catalyst size, reactor parameters, and catalyst layer heights on the technological parameters of the process was studied. The effect of the height of the catalyst layer on the conversion rate of acetylene is presented in Figure 2

Figure 2. The effect of the height of the catalyst layer on the conversion rate of acetylene

As can be seen from Figure 2, the acetylene conversion increases as the height of the catalyst layer increases to 400-750 mm, which indicates that the reaction proceeds in the internal diffusion zone.

The ratio of the height of the catalyst layer to the diameter of the reactor is 50-60, and the volume speed of acetylene is 180 h-1. Under these conditions, catalyst №9 (Table 3.2.6.1) works for 300 hours with constant activity, after 18-24 hours of regeneration, the catalyst fully restores its activity.

For the mathematical description, we used the material balance equation for the reactant for the plug reactor, the equation representing the catalyst deactivation process, the flow continuity equation, the stoichiometric equilibrium equation, and the equation obtained as a result of Avogadro's law for the isothermal process. Combining these equations, we get:

here,

Thus, the system of equations of the mathematical model of the process in the isometric state looks like this:

To solve this system, it is necessary to obtain numerical values ​​of the constants E, K¹, K_o.

The activation energy for the hydrogenation reaction of acetylene was determined by calculating E and E = 75000 J/mol.

To determine the constants K, K_o, the parameter averaged over the length of the reactor is used.

Here,

S- is the surface area of the catalyst.

Pressure drop can also be taken into account when modeling chemical reactors, but when the process is modeled by reaction conversion, pressure does not affect reaction rate or equilibrium.

The computer model of the considered process was made by selecting all the necessary devices available in the Aspen Plus program. Figure 3 shows the process of producing acetone from acetylene at steady state.

Figure 3. A computer model of the process of obtaining acetone from acetylene

Due to the insufficient kinetic data for the existing reactions in this process, the use of reactor conversion or stoichiometric reactors is useful when the conversion changes of the chemical reaction are known and when kinetic data are not available or are not considered important. It is also possible to calculate the amount of the mixture coming out and the amount of heat transferred through this reactor model. 

CONCLISIONS

The use of new high-performance nanocatalysts in industry leads to the improvement of the environmental characteristics of processes and technologies, the reduction of emissions into the atmosphere, the creation of environmentally friendly alternative energy resources, new products and materials. Catalytic hydration of acetylene was thermodynamically justified. For the first time, an improved and low-waste compact computer model of the catalytic acetylene hydration of acetone was developed.

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