AROMATIZATION OF PROPANE AND ITS BASIC LAWS

ABSTRACT

The article presents the results of studying some laws of the catalytic aromatization reaction of propane in the presence of a 2%Zr-2%Zn-7%Mo/MGS catalyst. Before the catalytic experiments, the samples were heated in a hydrogen stream (2500 h^-1) for 2 h. Then, the experiments were carried out according to the same procedure at a constant volumetric rate (V=500 h^-1). Also, the main parameters of the propane aromatization process in 2%Zr-2%Zn-7%Mo/MGS and 5%Zr-2%Zn-7%Mo/MGS catalyst, prepared by solid phase modification method with hydrogen pretreatment and The main parameters of the aromatization process of propane in the 2%Zr-2%Zn-7%Mo/MGS catalyst, propane production in the 5%Zr-2%Zn-7%Mo/MGS catalyst prepared by impregnation method without pretreatment with hydrogen and by soaking method the main parameters of the aromatization process were studied.

In this article of the work is to study the laws of the aromatization reaction of propane in 2%Zr-2%Zn-7%Mo/MGS and 5%Zr-2%Zn-7%Mo/MGS catalysts.

АННОТАЦИЯ

В статье представлены результаты исследования некоторых закономерностей каталитической реакции ароматизации пропана в присутствии катализатора 2%Zr-2%Zn-7%Mo/MGS. Перед каталитическими экспериментами образцы нагревали в токе водорода (2500 ч^-1) в течение 2 ч. Затем эксперименты проводили по той же методике с постоянной объемной скоростью (V=500 ч^-1). Также изучены основные параметры процесса ароматизации пропана на катализаторах 2%Zr-2%Zn-7%Mo/MGS и 5%Zr-2%Zn-7%Mo/MGS, приготовленных методом твердофазной модификации с предварительной обработкой водородом и Основные параметры процесса ароматизации пропана на катализаторе 2%Zr-2%Zn-7%Mo/MGS, получение пропана на катализаторе 5%Zr-2%Zn-7%Mo/MGS, приготовленном методом пропитки без предварительной обработки водородом и методом пропитки, основные параметры процесса ароматизации. В этой статье изучение закономерностей реакции ароматизации пропана на катализаторах 2%Zr-2%Zn-7%Mo/MGS и 5%Zr-2%Zn-7%Mo/MGS.

Keywords: propane, aromatization, temperature, reaction yield, selectivity, mesoporous sorbent.

Ключевые слова: пропан, ароматизация, температура, выход реакции, селективность, мезопористый сорбент.

INTRODUCTION

Aromatization of light alkanes (mainly propane and butane) has been widely studied for almost three decades due to its importance in economic and strategic fields. For propane aromatization process, ZSM-5 catalyst promoted by Zn, Pt and Ga was recognized as an effective bifunctional catalyst. Light alkane chain growth on a bifunctional catalyst involves dehydrogenation. The transformation of light hydrocarbons into aromatic compounds is one of the most important catalytic reactions both from a scientific point of view and from the point of view of industrial implementation. As a result of aromatization of lower alkanes, aromatic hydrocarbons (mainly benzene, toluene, and xylenes) are formed, which are valuable raw materials for the chemical and petrochemical industries. In addition, this reaction is of interest from the point of view of studying the mechanism of conversion of hydrocarbons. Aromatization of low molecular weight paraffinic hydrocarbons is a complex process, which includes not only reactions aimed at obtaining the target product, but also a number of side reactions. Therefore, selective conversion of lower alkanes to aromatic hydrocarbons is possible only in the presence of a highly selective catalyst. The published results of the study of the process of aromatization of  hydrocarbons confirm the effectiveness of the used bifunctional systems. They are characterized by the presence of acidic areas of the sorbent carrier and active metal-containing areas formed when dehydration promoters are introduced into the catalyst.

EXPERIMENTAL PART

Propane - 99.9%, hydrogen - 99.9%, helium - 99.9%, nitrogen - 98.8% purity gases were used in the work. Catalysts were prepared in two ways: solid-phase modification (by mixing mesoporous sorbent powder with zirconium oxide for 2 hours) and soaking (the calculated amount of  was dissolved in distilled water until the salt was completely dissolved). The resulting solution was added to a measured amount of sorbent and evaporated in a water bath with constant stirring, and then calcined in an oven at 200 °C for 3 h. A sample of zirconium aluminosilicate with a mesoporous sorbent (MGS) structure was obtained by hydrothermal synthesis at high pressure using a catalytic dehydroaromatization reaction mixture of aluminosilicate propane containing zirconium nitrate. Before the experiments, the catalyst powder was crushed and passed through a sieve with a size of 1-2 mm and pressed and made into tablets. To improve heat transfer, the catalyst was diluted 1:1 with quartz of the same particle size. All samples were treated at 550 °C in air or hydrogen flow for 2 h before catalytic experiments. Regeneration in hydrogen flow (1 l/h) was carried out according to the following scheme:

- maintaining the temperature from 25 to 350 °C at a heating rate of 4 °C/min and at a temperature of 350 °C for 1 hour;

- temperature rise from 350 to 550°C, heating rate 4°C/min and 550°C for 1 hour;

After activation, the catalyst was purged with helium for 15 min at experimental temperature to remove residual water. Catalytic experiments on the catalytic aromatization of propane were carried out in a bed-flow reactor with a stationary catalyst at atmospheric pressure. A schematic diagram of the laboratory device is shown in Figure 1.

Figure 1. Schematic diagram of the experimental device

1- quartz furnace, 2- quartz reactor, 3- relay RER-10, 4- thermocouple for temperature control, 6- gas cylinder, 7- reducer 8- valve, 9- rheometer, 10- collection of products of catalytic dehydroaromatization reaction of liquid propane holder for, 11- Liquid nitrogen container, 12 - thermocouple (temperature regulator), 13- Thermometer.

The laboratory equipment consists of a vertical quartz furnace (1) in the form of a hollow cylinder heated by nichrome wire with asbestos insulation. A quartz reactor (2) with an inner diameter of 21 mm is placed in the furnace. The heating rate and temperature were controlled by RES-10 (3) and TRM-1 (4) devices with an accuracy of ± 1 . The temperature in the catalytic dehydroaromatization reaction zone of propane was varied in the range of 350-650  and was measured by a chrome-aluminum thermocouple (5) in a 1 mm diameter quartz housing. Propane, helium or hydrogen was supplied from cylinders (6) through a reducer (7). The gas flow rate is regulated by a valve (8) and measured using a rheometer (9) pre-calibrated for this gas. The volumetric rate of propane delivery is 500 h^-1. The duration of experiments is usually 2.5 hours. The products of the liquid propane catalytic dehydroaromatization reaction were taken into a liquid nitrogen (11)-cooled holder (10) twice for 40 min, degassed for 15-20 min at room temperature, and weighed and analyzed. Gaseous propane catalytic dehydroaromatization reaction products and propane catalytic dehydroaromatization reaction starting materials were collected in a gasometer for chromatographic determination of component concentrations. After each experiment, the catalyst was purged with helium for 15 min to remove the adsorbed propane catalytic dehydroaromatization reaction products. Helium was supplied from the cylinder at a rate of 5 l/h using a reducer, which was adjusted using a rheometer fine-adjustment valve. The catalyst was then regenerated with air at 550 °C for two hours.

EXPERIMENTAL RESULTS AND THEIR DISCUSSION

The reaction temperature of catalytic dehydroaromatization of propane at a constant volumetric rate (V = 500 h^-1) in MGSsorbent was changed (500-650°C). The main indicators of the process are presented in Table 1. Figure 2 shows the temperature dependence of the conversion, yield, and selectivity in the catalytic dehydroaromatization of propane for aromatic products. Aromatic hydrocarbons (ArU) formed in the catalytic aromatization of propane in the presence of a 2% Zr-2%Zn-7%Mo/MGS catalyst was 17.8% at 500°C. With a further increase in temperature, the yield of aromatic hydrocarbons formed during catalytic aromatization of propane in the presence of a 2%Zr-2%Zn-7%Mo/MGS catalyst increases and is 38.6% at 600°C. The propane conversion process is faster; with increasing temperature from 500 to 650°C, this indicator increased from 65.4 to 95.9%. The yield of catalytic aromatization products of gaseous propane is highly dependent on the reaction temperature of catalytic dehydroaromatization of propane. However, as shown in table 1, as the temperature increased from 500 to 650°C, the yield of methane increased by almost 50% (from 20.5 to 30.8%), and the yield of C₂ hydrocarbons increased from 21.8 to 27.4%.

Table 1

The main parameters of the propane aromatization process in the MG'S catalyst

Figure 2. Temperature dependence of the main parameters of the process of propane aromatization in MGS catalyst Aromatization in 2%Zr-2%Zn-7%Mo/MGS catalyst.

CONCLUSION

Thus, the reaction temperature of catalytic dehydroaromatization of propane at a constant volume rate (V=500 h^-1) in MGSsorbent changed (500-650°C). The main indicators of the process are presented in Table 1. Figure 4 shows the temperature dependence of the conversion, efficiency and selectivity in the catalytic dehydroaromatization of propane for aromatic products. Aromatic hydrocarbons (ArU) formed during catalytic aromatization with propane 2%Zr-2%Zn-7%Mo/MGS catalyst was 17.8% at 500°C. With a further increase in temperature, the yield of aromatic hydrocarbons formed during catalytic aromatization of propane in the presence of a 2%Zr-2%Zn-7%Mo/MGS catalyst increases and is 38.6% at 600°C. The propane conversion process is faster; with increasing temperature from 500 to 650°C, this indicator increased from 65.4 to 95.9%.

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