CN103012075B - Method for preparing dimethyl ether through activating carbon dioxide by using plasmas - Google Patents

Abstract

The invention discloses a method for preparing dimethyl ether by plasma activation of carbon dioxide. The method uses carbon dioxide as a raw material, _CO2 passes through a dielectric barrier discharge plasma activation device with a voltage of 5-14kV and a frequency of 0.05-12kHz, and then Using Cu-Fe-Zr/HZSM-5 as a catalyst, the raw material gas is a mixed gas of CO ₂ /H ₂ (volume ratio)=1:2～1:5, and the reaction space velocity is 1000～5000h ^-1 , the reaction The pressure is 2-5MPa, the reaction temperature is 220-280°C, and the gas-solid phase catalytic reaction is carried out in a fixed-bed reactor with temperature control. The main product of the reaction is dimethyl ether, and by-products are methane and carbon monoxide. The invention has the advantages of simple process, simple operation, fast reaction rate, high conversion rate of _CO2 , green reaction process, and high selectivity and yield of dimethyl ether.

Description

A kind of method that plasma activates carbon dioxide to prepare dimethyl ether

technical field

The invention belongs to the field of comprehensive utilization of carbon dioxide. Specifically, it is a method for preparing dimethyl ether by plasma catalyzing carbon dioxide.

Background technique

In recent decades, with the acceleration of industrialization and urbanization and the continuous upgrading of consumption structure, my country's energy demand has shown a rigid growth. Due to the constraints of domestic resource guarantee capacity and environmental capacity, as well as global energy security and the impact of climate change, resource and environmental constraints have become increasingly constrained. Strengthening, the situation of energy conservation and emission reduction during the "Twelfth Five-Year Plan" period is still very severe, and the task is very arduous. The CO ₂ produced by the combustion of hydrocarbon fuels such as coal, oil, and natural gas has far exceeded the level in the past, increasing the CO ₂ content in the atmosphere year by year. The increase of CO ₂ content in the air has caused the earth's temperature to change, which has become a serious global environmental problem. How to effectively control the content of CO ₂ in the atmosphere has aroused the great interest of multidisciplinary researchers in the environment, materials, and chemistry. The solution is to effectively convert CO ₂ into hydrocarbon fuels. Since CO ₂ is a stable molecule, energy needs to be provided to convert it. At present, the conversion methods of CO ₂ mainly include: thermochemical conversion, electrochemical conversion and photocatalytic conversion. .

The synthesis of DME by hydrogenation of carbon dioxide is similar to the synthesis of DME by using synthesis gas as a raw material. There are two main methods, two-step method and one-step method. The two-step method, that is, the first step is to synthesize methanol from CO ₂ , and then dehydrate the methanol to obtain DME. There are many studies in this area. For example, as early as 1945, Ipatieff and Monroe reported that CO ₂ on Cu-Al catalyst Hydrogenation of Methanol. Catalysts that have been studied more for the hydrogenation of _CO2 to methanol include Raney copper catalysts, supported noble metal catalysts, and copper-based catalysts. Among them, copper-based catalysts have been studied the most and have the best effect. Another type of method is the one-step method, that is, DME is directly synthesized from CO ₂ , and methanol synthesis and dehydration are both completed in the same step. Mao Dongsen et al. (ZL200810202011.2) used CuO-TiO ₂ -ZrO ₂ /HZSM-5 as catalyst, Liu Zhijian et al. (Industrial Catalysis, 2002, 10(2): 46-49) used CuO-ZnO-Al ₂ O ₃ /HZSM -5. Bie Liangwei et al. (Progress in Chemical Industry, 2009, 28 (8): 1365-1370) used CuO-ZnO-Al ₂ O ₃ -ZrO ₂ /HZSM-5, Huang Youmei et al. (Molecular Catalysis, 1997, 11 (4) ): 297-300) using Cu-ZnO-ZrO ₂ /HZSM-5, Zeng Chongyu et al. (Journal of Nanjing University of Technology, 2004, 26 (3): 89-93) using C207 and HZSM-5 mixed bifunctional catalysts to synthesize two methyl ether. However, because carbon dioxide itself is very stable, its activation is always a bottleneck problem that is difficult to solve, and the commonly used high-temperature activation method will easily lead to the deactivation of the added catalyst; The conversion rate is only 25%-30%, and the selectivity of dimethyl ether is 40%-50%.

In the process of converting _CO2 into useful chemicals, the biggest challenge is the activation of _CO2 . Through the analysis of the catalytic system of carbon dioxide in different reactions, it can be seen that the activation of carbon dioxide requires empty orbitals or electrons that match its first ionization energy. A composite metal compound can be used to balance its orbital energy level, and an external electric field or composite alloy can be used to provide matching electrons. , thereby activating carbon dioxide to achieve the chemical utilization of carbon dioxide. There are many ways to activate CO ₂ . The simplest way is to activate CO ₂ at high temperature, but high temperature can easily lead to catalyst deactivation, which in turn affects the conversion rate of CO ₂ . Plasma is the fourth state of matter, mainly composed of highly chemically active particles such as atoms, molecules, ions, electrons and free radicals. The plasma usually refers to low-temperature plasma. In low-temperature plasma, the extranuclear electrons of atoms are fully activated, and the electron temperature is as high as 10 ⁴ K, while the temperature of the nucleus is very low, so the substance is still at room temperature macroscopically. , so that reactions that cannot be realized at room temperature can be realized through plasma.

A series of studies have shown that plasma has a better activation effect on CO ₂ (Liu Changjun et al., FuelProcess Technology, 1999, 58(2-3): 119-134). Venugopalan et al. (Topic in Current Chemistry, 1983, 1-58) believed that under the action of plasma, CO ₂ can be activated into CO ₂ *, CO, O and other active substances; Dai Bin et al. (China Environmental Science, 1999, 19 (5 ): 410-412) It is speculated that under the action of plasma, CO ₂ can be ionized by high-energy electrons, dissociation reaction, and produce active substances such as CO ₂ ⁺ ; Liu Changjun et al. (Journal of Tianjin University, 2002, 35 (1): 19 -22) It was discovered that methane and carbon dioxide were converted by silent discharge and corona discharge to obtain different products: the product of corona discharge reaction is mainly synthesis gas, while the product of silent discharge includes hydrocarbons and oxygenates in addition to synthesis gas . These studies on plasma activation of _CO2 are mainly used in the preparation of methanol, synthesis gas, etc., and have not been used in the synthesis of dimethyl ether.

Contents of the invention

The object of the present invention is to provide a method for preparing dimethyl ether by plasma activation of carbon dioxide with simple process, low energy consumption, low cost, high yield and environment friendliness. And determine the best CO ₂ plasma activation method and its application in CO ₂ catalytic hydrogenation to dimethyl ether process.

The technical scheme that the present invention solves the problems of the technologies described above is as follows:

A method for preparing dimethyl ether by plasma catalyzing carbon dioxide is to use _CO2 as raw material, after using plasma to activate _CO2 , carry out catalytic hydrogenation to synthesize dimethyl ether, the operation steps are as follows:

1) Plasma activation of CO ₂ :

_CO2 passes through a dielectric barrier discharge plasma activation device with a voltage of 5-14kV and a frequency of 1-12kHz. One electrode of the device is a needle electrode, and the other electrode is a flat plate electrode with holes. After _CO2 passes through the needle electrode, the The dielectric barrier discharge plasma region formed between the needle-plate electrodes is activated. Then enter the fixed bed reactor for reaction.

2) Catalytic hydrogenation of _CO2 to dimethyl ether

After the activated CO ₂ enters the fixed-bed reactor, Cu-Fe-Zr/HZSM-5 is used as the catalyst, and hydrogen gas is introduced at the ratio of CO ₂ /H ₂ (volume ratio)=1:2～1:5, and the The reaction space velocity is 1000～5000h ^-1 , the reaction pressure is 2～5MPa, and the reaction temperature is 220～280℃ to carry out the gas-solid phase catalytic reaction. The main product of the reaction is dimethyl ether, and by-products are methane and carbon monoxide.

The discharge voltage of the dielectric barrier discharge plasma in the above step 1 is preferably 14kV, and the frequency is preferably 12kHz.

Compared with the prior art, the present invention has the following advantages:

1. The present invention uses plasma to activate CO ₂ . Compared with directly passing CO ₂ into the reactor for reaction, under the same reaction conditions, the conversion rate of CO ₂ , the selectivity and yield of dimethyl ether are higher.

2. The process of the present invention is simple, easy to operate, and the reaction rate is fast.

Detailed ways

The present invention will be further described below in conjunction with the examples, but it should be noted that the scope of application of the present invention is not limited to these examples.

Example 1

1) Plasma activation of _CO2

The CO ₂ raw material gas passes through a dielectric barrier discharge plasma activation device. The voltage between the needle-plate electrodes is 7kV and the frequency is 6kHz. After CO ₂ passes through the needle electrodes, the dielectric barrier discharge plasma area formed between the needle-plate electrodes is activated. , and then enter the fixed bed reactor for reaction.

2) Catalytic hydrogenation of _CO2 to dimethyl ether

The Cu-Fe-Zr/HZSM-5 catalyst that weighs 1g is put into fixed-bed reactor, and this catalyst n(Cu)/n(Fe)=1.5: 1 and the content of Zr is 2%wt, and the content of HZSM-5 The ratio of silicon to aluminum is 300, and then the activated CO ₂ is passed into the fixed bed reactor, and hydrogen is passed into the ratio of CO ₂ /H ₂ (volume ratio) = 1:3, and the reaction space velocity is 2000h ^-1 , The reaction pressure is 3MPa, and the reaction temperature is 240°C to carry out the gas-solid phase catalytic reaction. The experimental results for the preparation of dimethyl ether by this method are shown in Table 1.

Example 2

1) Plasma activation of _CO2

The CO ₂ raw material gas passes through a dielectric barrier discharge plasma activation device. The voltage between the needle-plate electrodes is 7kV and the frequency is 6kHz. After CO ₂ passes through the needle electrodes, the dielectric barrier discharge plasma area formed between the needle-plate electrodes is activated. , and then enter the fixed bed reactor for reaction.

2) Catalytic hydrogenation of _CO2 to dimethyl ether

The Cu-Fe-Zr/HZSM-5 catalyst that weighs 1g is put into fixed-bed reactor, and this catalyst n(Cu)/n(Fe)=2:1 and the content of Zr is 0.5%wt, and the content of HZSM-5 The ratio of silicon to aluminum is 300, and then the activated CO ₂ is passed into the fixed bed reactor, and hydrogen gas is passed into the ratio of CO ₂ /H ₂ (volume ratio) = 1:2, and the reaction space velocity is 5000h ^-1 , The reaction pressure is 2MPa, and the reaction temperature is 220°C to carry out the gas-solid phase catalytic reaction. The experimental results for the preparation of dimethyl ether by this method are shown in Table 1.

Example 3

1) Plasma activation of _CO2

The CO ₂ raw material gas passes through a dielectric barrier discharge plasma activation device. The voltage between the needle-plate electrodes is 7kV and the frequency is 6kHz. After CO ₂ passes through the needle electrodes, the dielectric barrier discharge plasma area formed between the needle-plate electrodes is activated. , and then enter the fixed bed reactor for reaction.

2) Catalytic hydrogenation of _CO2 to dimethyl ether

The Cu-Fe-Zr/HZSM-5 catalyst that takes 1g is put into fixed-bed reactor, and this catalyst n(Cu)/n(Fe)=1.5:1 and the content of Zr is 2%wt, and the content of HZSM-5 The ratio of silicon to aluminum is 300, and then the activated CO ₂ is passed into the fixed bed reactor, and hydrogen gas is passed into the ratio of CO ₂ /H ₂ (volume ratio) = 1:3, and the reaction space velocity is 3000h ^-1 , The reaction pressure is 3MPa, and the reaction temperature is 260°C to carry out the gas-solid phase catalytic reaction. The experimental results for the preparation of dimethyl ether by this method are shown in Table 1.

Example 4

1) Plasma activation of _CO2

The CO ₂ raw material gas passes through a dielectric barrier discharge plasma activation device. The voltage between the needle-plate electrodes is 14kV and the frequency is 12kHz. After CO ₂ passes through the needle electrodes, the dielectric barrier discharge plasma area formed between the needle-plate electrodes is activated. , and then enter the fixed bed reactor for reaction.

2) Catalytic hydrogenation of _CO2 to dimethyl ether

The Cu-Fe-Zr/HZSM-5 catalyst that takes 1g is put into fixed-bed reactor, and this catalyst n(Cu)/n(Fe)=1.5:1 and the content of Zr is 2%wt, and the content of HZSM-5 The ratio of silicon to aluminum is 300, and then the activated CO ₂ is passed into the fixed bed reactor, and hydrogen is passed into the ratio of CO ₂ /H ₂ (volume ratio) = 1:3, and the reaction space velocity is 2000h ^-1 , The reaction pressure is 3MPa, and the reaction temperature is 240°C to carry out the gas-solid phase catalytic reaction. The experimental results for the preparation of dimethyl ether by this method are shown in Table 1.

Example 5

1) Plasma activation of _CO2

The CO ₂ raw material gas passes through a dielectric barrier discharge plasma activation device. The voltage between the needle-plate electrodes is 14kV and the frequency is 12kHz. After CO ₂ passes through the needle electrodes, the dielectric barrier discharge plasma area formed between the needle-plate electrodes is activated. , and then enter the fixed bed reactor for reaction.

2) Catalytic hydrogenation of _CO2 to dimethyl ether

The Cu-Fe-Zr/HZSM-5 catalyst that weighs 1g is put into fixed-bed reactor, and this catalyst n(Cu)/n(Fe)=2:1 and the content of Zr is 0.5%wt, and the content of HZSM-5 The ratio of silicon to aluminum is 300, and then the activated CO ₂ is passed into the fixed bed reactor, and hydrogen is passed into the ratio of CO ₂ /H ₂ (volume ratio) = 1:3, and the reaction space velocity is 2000h ^-1 , The reaction pressure is 3MPa, and the reaction temperature is 240°C to carry out the gas-solid phase catalytic reaction. The experimental results for the preparation of dimethyl ether by this method are shown in Table 1.

Example 6

1) Plasma activation of _CO2

The CO ₂ raw material gas passes through a dielectric barrier discharge plasma activation device. The voltage between the needle-plate electrodes is 14kV and the frequency is 12kHz. After CO ₂ passes through the needle electrodes, the dielectric barrier discharge plasma area formed between the needle-plate electrodes is activated. , and then enter the fixed bed reactor for reaction.

2) Catalytic hydrogenation of _CO2 to dimethyl ether

The Cu-Fe-Zr/HZSM-5 catalyst that takes 1g is put into fixed-bed reactor, and this catalyst n(Cu)/n(Fe)=1.5:1 and the content of Zr is 2%wt, and the content of HZSM-5 The ratio of silicon to aluminum is 300, and then the activated CO ₂ is passed into the fixed bed reactor, and hydrogen gas is passed into the ratio of CO ₂ /H ₂ (volume ratio) = 1:3, and the reaction space velocity is 3000h ^-1 , The reaction pressure is 3MPa, and the reaction temperature is 260°C to carry out the gas-solid phase catalytic reaction. The experimental results for the preparation of dimethyl ether by this method are shown in Table 1.

Example 7

1) Plasma activation of _CO2

The CO ₂ raw material gas passes through a dielectric barrier discharge plasma activation device. The voltage between the needle-plate electrodes is 5kV and the frequency is 1kHz. After CO ₂ passes through the needle electrodes, the dielectric barrier discharge plasma region formed between the needle-plate electrodes is activated. , and then enter the fixed bed reactor for reaction.

2) Catalytic hydrogenation of _CO2 to dimethyl ether

The Cu-Fe-Zr/HZSM-5 catalyst that takes 1g is put into fixed-bed reactor, and this catalyst n(Cu)/n(Fe)=1.5:1 and the content of Zr is 2%wt, and the content of HZSM-5 The ratio of silicon to aluminum is 300, and then the activated CO ₂ is passed into the fixed bed reactor, and hydrogen gas is passed into the ratio of CO ₂ /H ₂ (volume ratio) = 1:5, and the reaction space velocity is 1000h ^-1 , The reaction pressure is 5 MPa, and the reaction temperature is 280° C. to carry out the gas-solid phase catalytic reaction. The experimental results for the preparation of dimethyl ether by this method are shown in Table 1.

Table 1 Experimental results

Note: X(CO ₂ ): conversion rate of carbon dioxide, S(DME): selectivity of dimethyl ether, S(CO): selectivity of carbon monoxide, S(CH ₄ ): selectivity of methane, Y(DME) : The yield of dimethyl ether.

Claims (1)

1. plasma-activated carbonic acid gas is prepared a method for dme, it is characterized in that, with CO ₂for raw material, using plasma activation CO ₂after, carry out shortening dimethyl ether synthesis, operation steps is as follows:

1) plasma-activated CO ₂:

CO ₂unstripped gas is by a dielectric barrier discharge plasma activating apparatus, and the voltage between pin-plate electrode is 14kV, and frequency is 12kHz, CO ₂be activated by the dielectric barrier discharge plasma district forming between pin-plate electrode after pin electrode, then enter fixed-bed reactor and react;

2) CO ₂shortening is dme:

The Cu-Fe-Zr/HZSM-5 catalyzer that takes 1g is put into fixed-bed reactor, and the content of this catalyzer n (Cu)/n (Fe)=1.5: 1 and Zr is 2%wt, and the silica alumina ratio of HZSM-5 is 300, then by the CO being activated ₂pass into fixed-bed reactor, and press CO ₂/ H ₂the ratio of (volume ratio)=1: 3 passes into hydrogen, is 2000h at reaction velocity ^-1, reaction pressure is 3MPa, temperature of reaction is to carry out gas-solid catalysis under the condition of 240 ℃.