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1CATALYTIC SYNTHESIS OF DIMETHYLPHYR FROM
CARBON MONOXIDE
1Faizullaev N.I., 2Rakhmatov Kh.B., 3Rakhmonkulov M.T., 4Safarov M.Dj., 5Matmuratov Sh.S.
1Samarkand State University 2,3,4Karshi Institute of Engineering and Economics 5Urgench State University https://doi.org/10.5281/zenodo.13878915
Abstract. Currently, it is relevant to obtain dimethyl ether from synthesis gas in one step. In the work, the influence of various factors on the process of direct synthesis of dimethyl ether from syngas in one step was studied in CmO*ZnO*ZrO2/YuKTs catalyst. As a result of studies conducted on the effect of various factors on the production of target products in the process of obtaining dimethyl ether from synthesis gas, it was found that increasing the ratio of moles of pressure, temperature, and the mole ratio of hydrogen to greenhouse gas leads to an increase in greenhouse gas conversion due to the fact that the direct synthesis reaction of dimethyl ether from synthesis gas prevails. An increase in the volume velocity reduces the conversion of the carbon monoxide, because the reaction between the reactants in the gas phase and the methanol catalyst surface does not have time to occur due to the low contact time. It has been proven that the increase in the ratio of gas to hydrogen moles leads to an increase in the yield of dimethyl ether and the conversion of gas. As a result of the research, the following optimal conditions for obtaining dimethyl ether from carbon dioxide and hydrogen in one step were determined: R=1 MPa, T=300°C, hydrogen:carbon gas=2, volume velocity 1000 hour1. In this case, the conversion of exhaust gas does not decrease for 220 hours. At the same time, the physico-chemical and textural characteristics of the Cu2O*ZnO*ZrO2/№KU, catalyst were studied. The acidity of the Cu2O*ZnO*ZrO2/№KU, catalyst surface was determined by the method of thermoprogrammed desorption of ammonia. Acidity value for Cu2O*ZnO*ZrO2/№KU, was 0.065 mmol NH3/gkat. The calculated value of acidity of YuKTs was 0.26 mmol NH3/gkat. When Lewis acid centers (Lewis acidity center) were determined in the presence of Cu2O*ZnO*ZrO2/№KU, primary catalyst by IR-spectroscopy method, it was found that the concentration of Lewis acidity center was 49 /umol/g. The amount ofBmnsted acidity centers is 56 ¡j.mol/g of the total concentration of acidity centers.
The purpose of the work is to study the kinetic laws of the synthesis reaction of dimethyl ether from synthesis gas in one step and the textural characteristics of the catalyst.
Keywords: thermoprogrammed desorption, ammonia, high-silica zeolites, acidic properties, molecular gels.
INTRODUCTION
Deep processing of natural gas, petroleum satellite gas, etc. into valuable petrochemical products is one of the most important processes of the chemical industry[1,2]. Conversion of natural and petroleum satellite gas into easily transportable products allows to transfer these sources to universal energy reserves[3-7].
In recent years, the process of processing synthesis gas into dimethyl ether in one step has attracted great interest among world scientists. The composition and characteristics of synthetic hydrocarbons obtained from dimethyl ether depend on the properties of the zeolite catalyst used
for this process, the conditions of the process, and the composition of synthesis gas. Controlling the acidic properties of high-silica zeolites and the composition of the initial synthesis gas allows obtaining light sulfur-free synthetic oil from methanol and dimethyl ether [8-10]. It is known that acidic properties of zeolites depend on the nature of exchangeable cations[11-25] and their introduction method[22-29].
Currently, ethylene and propylene from syngas with methanol are supported in industry as catalysts for ZSM-5 type zeolites [30] and SAPO-34 type molecular gels [31].
EXPERIMENTAL PART
In the work, a Cu2O*ZnO*ZrO2/TOKU, catalyst was used to obtain dimethyl ether from synthesis gas.
The catalytic activity of the catalysts was studied in a device with a fixed-bed catalyst in a flow reactor, by injecting a mixture of hot gas and hydrogen into the reactor at a pressure of 1-2 MPa and a temperature of 220-300°C.
Qualitative and quantitative analysis of the reaction products was carried out by the chromatographic method on the gas chromatograph "Crystal 5000.2".
The phase composition of Cu2O*ZnO*ZrO2/TOKU, catalysts was determined by X-ray phase analysis method using unfiltered CuKa-radiation (X=1,5418 A) before and after catalytic tests on a Shimadzu XRD-6000 diffractometer. Brunauer-Emmet-Teller and Barrett-Joyner-Haland methods were used to determine the textural characteristics of the catalysts. The relative surface area was calculated from the data of nitrogen adsorption isotherms at 77 K. The pore volume was determined at a relative pressure of P/P0=0,97. The acidity properties of the catalysts were determined by the IR-spectrometer "Nicolet IR200".
Figure 1. Scheme of a laboratory device for obtaining dimethyl ether from syngas 1- faucet-doser; Catalytic reactor in the 2nd thermostat; 3-saturator; 4- gas preparation block; 5-balloon with gas carrier; 6-chromatographic column; 7-amongal-ionizing detector; 8-hydrogen; 9-katorometer; 10-manometer; 11-rheometer.
EXPERIMENTAL RESULTS AND THEIR DISCUSSION
As a result of the study of the effect of different proportions of the mixture of initial gases on the yield of dimethyl ether, it was found that the yield of dimethyl ether has the highest value when the mixture of initial gases (Fig. 1) is in a ratio of 1:2. The participation of carbon dioxide also plays an important role in the synthesis of dimethyl ether. As a result of the experiments, it was proved that the yield of dimethyl ether increases with the concentration of carbon dioxide. A number of experimental studies were carried out to determine the optimal amount of carbon dioxide added to the mixture used for the synthesis of dimethyl ether, and it was found that the yield of dimethyl ether is the highest in the conditions where the molar ratio of gases is 2:1:2.
100-. 75' 50
25-
I) -| f_, r т r
2:3 1:1 2:1:2 1:1(смеа>) -■- Конверсия CO, % -•- Выход ДМЭ % Figure 2. Effect of initial gas ratios on gas conversion and dimethyl ether yield P=1 MPa, T=300°C, hydrogen: carbon monoxide=2, volume velocity 1000 h-1, catalyst volume
5 cm3.
In the synthesis of dimethyl ether from hydrogen gas and hydrogen, the volume decreases, so the process was carried out at high temperature, the effect of temperature on the yield of dimethyl ether is shown in Figure 2. It can be seen that the conversion of carbon dioxide increases with increasing pressure, with the dimethyl ether yield having the highest value at a pressure of 1 MPa.
0 -1---1---.-.---
0.1 0,5 1 1,5 2,0 Давление, MPa
Figure 3. Effect of pressure on CO gas conversion and dimethyl ether yield in the ratio of 2:1:2 mixture of initial gases: T=300°C, hydrogen:carbon monoxide=2, volume
velocity 1000 hour-1.
-Л- Концентрация CO, % об Концентрации CHj % об.
The decrease in the yield of dimethyl ether can be explained by its decomposition CH3OCH3 ~ CH4 + CO + H2.
Table 1 shows the results of the analysis of products in the gas and liquid phase at different pressures.
Table 1
Effect of pressure on CO gas conversion and dimethyl ether yield T=300°C, hydrogen:carbon monoxide=2, volume velocity 1000 hour1
P, MPa Kco, % Хдмэ, % Concentratio n volume %. Concentration, %
CO2 CH4 methan ol water ethano l propanol-1
1 39 16 6 0,08 45 54 0,80 0,18
2 57 37 9 0,16 16 83 2,42 0,01
3 69 44 12 0,22 11 84 1,26 0,01
4 41 41 11 0,17 42 56 0,784 0,12
For the copper-retaining catalyst, it is preferable to carry out the process under mild conditions, because at a temperature lower than 220°C, mostly methyl formate is formed in the copper and zinc-retaining catalyst, and at a temperature higher than 300°, the copper catalyst burns and sticks. As the temperature increases, soot gas conversion and dimethyl ether yield increase (Figure 3).
100-1
11-1-.-,---I---I-
240 260 280 300 TeMneparypa, °C
The initial gases are a 2:1:2 mixture of hydrogen:hot gas:carbon dioxide: temperature 300°C, hydrogen:hot gas=2, volume velocity 1000 h-1.
Figure 4. Effect of temperature on the conversion of carbon dioxide to dimethyl ether
and the yield of dimethyl ether
It can be seen from Figure 4 that increasing the volume velocity decreases the conversion of CO and the yield of dimethyl ether (Figure 4). The reason for this is that the contact time of the reagents with the catalyst surface decreases with the increase in the volumetric velocity, that is, the increase in the volumetric velocity reduces the gas conversion, because the reaction between the reagents and the catalyst surface does not take place in the gas phase due to the low contact
time. At the same time, an increase in the mole ratio of carbon dioxide and hydrogen leads to an increase in the yield of dimethyl ether and conversion of carbon dioxide (Fig. 5).
1600 2400 3200
Объемная скорость, ч
P=1 MPa, T=300°C, hydrogen:carbon monoxide, volume velocity 1000 h-1. Figure 5. Effect of volumetric rate on conversion of CO gas to dimethyl ether and yield of
dimethyl ether
11 'CO
T=300°C, P=1 MPa, volume velocity 1000 h1.
Figure 6. Effect of hydrogen: CO gas mole ratio on initial feedstock conversion and dimethyl
ether yield.
The analysis of the results of the textural characteristics of the catalysts shows that the specific surface area of the Cu2O*ZnO*ZrO2/TOKU, catalyst decreases from 138 to 82 m2/g and the average diameter of the pores increases from 13 to 21 nm as a result of treatment in a hydrogen flow.
Thus, with the help of physico-chemical research methods, the textural characteristics of the Cu2O*ZnO*ZrO2/TOKU, catalyst under the influence of an oxidizing-reducing environment
were proven: a decrease in the specific surface area and an increase in the average diameter of the mesopores. The structure and composition of MKU, will remain unchanged.
Table 2
Textural characteristics of catalysts for the production of dimethyl ether from gas and
hydrogen
Catalyst treatment CrnO*ZnO*ZrO2^KU,
conditions Sco^ m2/g Vfob, m2/g Pores dyp, nm
Initial 138 0,355 13
Treated with hydrogen 82 0,375 21
at 320°C for 4 hours
Used in synthesis for 70 71 0,355 18
hours
Used in N2 at 320°, 1 68 0,355 15
MPa for 10 hours
CONCLUSION
The influence of various factors on the process of direct synthesis of dimethyl ether from synthesis gas in one step was studied in the Cu2O*ZnO*ZrO2^KU, catalyst, and the increase in volume velocity decreased the conversion of carbon monoxide and the yield of dimethyl ether, the increase in the mole ratio of carbon monoxide and hydrogen led to the increase of the yield of dimethyl ether and the conversion of carbon monoxide proved to come.
As a result of studies conducted on the effect of various factors on the yield of target products in the process of obtaining dimethyl ether from synthesis gas, it was found that the increase in pressure, temperature, and the mole ratio of hydrogen to greenhouse gas leads to an increase in the conversion of greenhouse gas due to the fact that the reaction of synthesis of dimethyl ether directly from synthesis gas prevails.
An increase in volume velocity reduces the conversion of carbon monoxide, because the reaction between the reagents in the gas phase and the methanol catalyst surface does not have time to occur due to the short contact time. As a result of the research, the following optimal conditions for obtaining dimethylether from hydrogen gas in one step were determined: P=1 MPa, T=300°C, hydrogen: gas=2, volumetric speed 1000 hour-1.
The physical-chemical and textural characteristics of the Cu2O*ZnO*ZrO2/ ЮКЦ catalyst were studied. The acidity of the Cu2O*ZnO*ZrO2^KU, catalyst surface was determined by the method of thermoprogrammed desorption of ammonia.
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