KR20220168404A - Method for producing methanol through direct conversion reaction of highly selective methane to methanol using a plasma-applied catalyst - Google Patents

Abstract

The present invention relates to a method of producing methanol through a high-selectivity direct methane conversion reaction using a plasma-applied catalyst, more specifically, a method of producing methanol from methane by performing a step of activating the catalyst by binding oxygen active species to the active metal in the catalyst under oxygen gas injection using low-temperature plasma in the pretreatment step of the methane direct conversion reaction using plasma. Additionally, according to the present invention, by using low-temperature plasma as an energy source for the catalyst activation step in the methane direct conversion reaction, the heating and cooling processes accompanying the catalyst activation and methane reaction steps in the conventional methane direct conversion reaction are not required. Accordingly, it significantly improves the efficiency of the methanol production process and is environmentally friendly.

Description

Method for producing methanol through direct conversion reaction of highly selective methane to methanol using a plasma-applied catalyst}

The present invention relates to a method for producing methanol through a high-selectivity direct conversion of methanol to methanol using a plasma-applied catalyst. It relates to a method for producing methanol from methane by performing a step of activating a catalyst by binding oxygen active species to an active metal.

Existing fossil fuels, including petroleum and coal, are of great importance as a source of energy and chemical raw materials. have been trying

Recently, the extraction of methane used as an energy source from abundant shale gas seemed to solve the problem of the existing fossil fuel reserves, but the extracted methane itself is not only a greenhouse gas that causes a strong greenhouse effect, but also It was a challenge to secure the use of methane from various angles in that it causes environmental problems due to the generation of carbon dioxide. As part of solving the above problems, a technology for converting methane into methanol is being developed.

The methanol itself can be used as a fuel for a methanol direct fuel cell (DMFC) and used as clean energy, and can be converted into dimethyl ether (DME) or dimethyl carbonate (DMC) by reaction, and is an important basic raw material for the chemical industry It can be converted to phosphorus acetic acid, formaldehyde, methyl tert-butyl ether (MTBE), etc., and at the same time, it can be used to produce clean gasoline through the methanol to gasoline (MTG) process.

However, the conventional methane-derived methanol production method requires a complex process involving synthesis gas production and synthesis gas ratio adjustment through steam reforming in a high-temperature environment followed by a reaction at high pressure, and a large amount of energy is consumed in the process there was a problem with

Accordingly, a technology for synthesizing methanol through direct conversion of methane has been reported, but methanol, which is a direct reaction product, has high reactivity to oxygen, and is further oxidized to produce carbon monoxide and carbon dioxide as by-products, and the selectivity of methanol is reduced There was a problem with Recently, studies on direct conversion of methanol involving several reaction steps have been attempted to avoid the problem of oxidation of methanol.

The direct conversion of methane involving the various reaction steps largely proceeds in the order of (1) catalyst activation step using oxygen gas, (2) methane adsorption step, and (3) methanol recovery step.

The (1) catalyst activation step is a step in which oxygen gas is supplied in the presence of a reaction catalyst to oxidize or combine the active metal in the catalyst with oxygen to form a μ-oxo bridge between the active metals. Reaction conditions for oxidation or oxygenation bonding of metals require heating to a high temperature of 400°C or higher.

In addition, the (2) methane adsorption step is a step of supplying methane gas to the active metal in the catalyst in which the mu-oxo bridge is formed to dissociate and adsorb to form a catalyst surface active species (CH ₃ O ^- ), In order to induce and suppress the peroxidation reaction to carbon dioxide, the temperature must be cooled again to below 200 °C.

Finally, (3) methanol recovery step is a step in which active species (CH ₃ O ^- ) formed in the catalyst are discharged as methanol under the supply of water or steam to recover it.

When methanol is produced by repeating steps (1) to (3) above, energy for activating the catalyst is removed in the cooling step for adsorbing methane, resulting in heat loss, and heating and cooling As a result, there is a problem in that the efficiency of the methanol production process is reduced due to the additional process time required. This is considered to be a major factor that makes it difficult to commercialize methane direct conversion process technology, and research and development is being attempted to solve this problem.

Patent Registration No. 10-2094881, a prior art related to the methane direct conversion process technology, relates to a method for producing methanol using a plasma-catalyst, and specifically, after treating a mixed gas containing methane introduced into a reactor with plasma However, it is disclosed that a methane conversion reaction step is performed in the presence of a catalyst, but methanol generated by plasma treatment of the mixed gas is further oxidized to CO and CO ₂ by oxygen contained in the mixed gas, so that the selectivity of methanol is increased. Decrease problems may arise.

Registered Patent Publication No. 10-2094881 (2020.03.30. Notice)

In the direct conversion of methane involving several reaction steps of the prior art, the present invention relates to the problem of reducing the efficiency of the methanol production process accompanying the creation of a high-temperature environment in the catalyst activation step and the direct conversion of methane. It is an object of the present invention to provide a method for producing methanol through a direct conversion of methanol to methanol with high selectivity using a plasma applied catalyst in order to solve the problem that the selectivity of methanol is reduced due to the high reactivity of methanol to oxygen.

In order to solve the above problem, in the method for producing methanol through a direct conversion of methanol to methanol with high selectivity using the plasma applied catalyst of the present invention, (a) while introducing oxygen gas into a reactor filled with a catalyst, plasma A catalyst activation step in which a mu-oxo bridge is formed through a reaction between oxygen and an active metal in the catalyst by conducting discharge; (b) after step (a), methane gas is introduced into the reactor to generate catalytically active species (CH ₃ O ^- ) on the surface of the catalyst; and (c) a methanol generating step in which a gas containing water is introduced and reacted with the catalytically active species to generate methanol and recovering the methanol in a gas phase.

In the present invention, in order to increase energy and process efficiency, the temperature may be kept constant during the steps (a) to (c).

As an embodiment of the present invention, the catalyst is a zeolite system in which a transition metal is ion-exchanged, and the transition metal is an active metal such as Cu, Fe, Ni, Co, Cr, Mn, Ga, Al, Mo, La, Na, At least one of Zn, Ce, Zr, Ru, Ag, In, Sn, Re, Ir, Pt, Pd, Au and Rh, wherein the zeolite is MOR, CHA, MAZ, FAU, FER, MFI, ERI, AEI, AFX , AFT, EAB, GME, KFI, LEV, LTL, MWW, OFF, SAS, SAT, SBS, SBT, SZR, BPH, MEI, BEA, EMT, LTA, ISV, IWW, IMF, TUN, EON It may be a rescue.

As another embodiment of the present invention, before introducing methane gas in step (b), a step of purging oxygen in the reactor with an inert gas may be performed.

As another embodiment of the present invention, a step of purging methane in the reactor with an inert gas may be performed before the introduction of water in step (c).

The plasma is characterized in that it is a dielectric barrier discharge (DBD) plasma.

The temperature in the steps (a) to (c) is 50 to 400 ° C, respectively, and the pressure is 0.5 to 100 bar.

On the other hand, in the present invention, a gas inlet and a gas outlet are formed on one side, a plasma reaction unit is formed inside, an electric furnace surrounds the outside of the plasma reaction unit, and the plasma reaction unit includes a dielectric material inside; a ground electrode covering the outside without being spaced apart from the dielectric material; and a high voltage electrode provided in the center of the dielectric material, wherein the gas injected through the gas inlet passes through the dielectric material filled with the catalyst under the condition that AC power is applied to the ground electrode; and a high voltage electrode; A plasma region in which plasma is formed is formed between, and a dielectric barrier discharge plasma reactor for producing methanol through a high selectivity methane direct conversion reaction, characterized in that a catalyst is filled in at least part or all of the inside of the plasma region. can provide

As an embodiment of the present invention, the dielectric material may include one or more metal oxides selected from among Al ₂ O ₃ , SiO ₂ , CeO ₂ and TiO ₂ .

According to the present invention, by using low-temperature plasma as an energy source for the catalyst activation step in the methane direct conversion reaction, the conventional heating and cooling processes involved in the catalyst activation and methane reaction steps of the direct methane conversion reaction are not required, thereby producing methanol. It significantly improves the efficiency and has an environmentally friendly effect.

In addition, in the catalyst activation step, a low-temperature plasma discharge is performed under the condition that oxygen gas is introduced in the presence of a catalyst, and methane and oxygen gases of the prior art are excluded by excluding methane gas unnecessary for the formation of mu-oxo bridges in the catalyst activation step. When is simultaneously present, methanol, which is a reaction product, is prevented from being oxidized by additional reaction with oxygen gas, thereby increasing selectivity and reducing energy consumption.

In addition, in the present invention, by directly applying plasma to the catalyst layer, oxygen atom (O) active species can be easily obtained by reducing the possibility of thermal decomposition of O ₃ generated when plasma is applied before the catalyst.

1 shows a schematic diagram of a low-temperature DBD plasma reactor according to an embodiment of the present invention.

Throughout the present specification, when a certain component is said to "include", it means that it may further include other components without excluding other components unless otherwise stated.

The present invention relates to a method for producing methanol through a direct methanol conversion reaction with high selectivity to methanol using a plasma-applied catalyst, wherein the direct methane conversion reaction is performed at 400 ° C. required in the catalyst activation step of the conventional methane direct conversion reaction. Instead of heating to create a higher temperature and cooling for the methane reaction step, the methanol generation process is performed through the catalyst activation step of discharging plasma after oxygen gas is introduced into the reactor filled with the catalyst. to be characterized

The prior art in the technical field to which the methane direct conversion reaction belongs uses a method of inputting energy generated through combustion or heating as an energy source for the reaction, but the temperature conditions required for each step in the reaction are different, so heating and cooling It was accompanied by a problem of reduction in process efficiency due to repeated execution of.

Also, as another prior art, there has been an attempt to use plasma discharge as a reaction energy source for generating methanol from methane. This is to discharge plasma in an environment in which a mixed gas containing methane and oxygen is simultaneously introduced into the methanol generation process to proceed with a methane partial oxidation reaction on the catalyst, and throughout the entire cycle of the partial oxidation reaction step Plasma discharge has been attempted to solve the energy efficiency problem of the conventional process, but in this case, methanol, a reaction product, may additionally react with oxygen and be oxidized.

Accordingly, the applicant has newly devised the methane conversion reaction of the present invention that can solve the above problems by applying low-temperature plasma to an environment in which oxygen gas is introduced in the presence of a catalyst in the catalyst activation step. In the catalytic reaction step multi-stage and activation step of the present invention, plasma treatment while separately introducing oxygen gas rather than a conventional mixed gas is a characteristic configuration that has never been attempted in the process field involving a direct methane conversion reaction. The above configuration excludes methane gas unnecessary for the formation of the mu-oxo bridge in the catalyst activation step during the multistaged catalytic reaction step, so that methanol, a reaction product, additionally reacts with oxygen gas when methane and oxygen gas of the prior art are present at the same time oxidation is prevented, and mu-oxo bridge formation is accelerated by plasma, thereby reducing process time and energy requirements.

Hereinafter, a method for producing methanol through direct conversion of methane in the presence of a catalyst and plasma applied with high selectivity according to an embodiment of the present invention will be described in detail.

In the method for producing methanol through the direct conversion of methanol to methanol with high selectivity using the plasma-applied catalyst of the present invention, (a) while introducing oxygen gas into a reactor filled with a catalyst, plasma discharge is performed to obtain oxygen and a catalyst A catalyst activation step in which a mu-oxo bridge is formed through a reaction between active metals in the inside; (b) after step (a), methane gas is introduced into the reactor to generate catalytically active species (CH ₃ O ^- ) on the surface of the catalyst; and (c) a methanol generating step in which a gas containing water is introduced and reacted with the catalytically active species to generate methanol and recovering the methanol in a gas phase.

In addition, steps (a) to (c) may be repeated one or more times.

In the (a) catalyst activation step, the temperature in the reactor filled with the catalyst is maintained at 50 to 400 ° C, in order to obtain the maximum reaction rate of the methane adsorption and methanol recovery reaction in the latter stage, and the temperature in the reactor is less than 50 ° C In the case of , there is a problem in that the water injected in the recovery step and the methanol produced are condensed.

Oxygen gas may be injected into the reactor in the form of a mixed gas containing oxygen and an inert gas, and the concentration of oxygen in the mixed gas may be 0.1% or more, and air may be used. The oxygen gas, that is, oxygen or a mixed gas of oxygen and an inert gas, improves the CH ₄ conversion rate per hour through a pressure condition of 0.5 to 100 bar, preferably 5 to 500 minutes, more preferably rapid step change under atmospheric pressure conditions. To do so, it may be introduced for 5 to 60 minutes under normal pressure conditions. The input amount of oxygen may be appropriately determined in consideration of factors such as the catalyst, the type of support and active metal constituting the catalyst, the amount of the catalyst, and the internal volume of the reactor.

The catalyst includes an active site that causes a change in physicochemical structure by reaction or combination of oxygen gas, and surface active species (CH ₃ O ^- ) can be used without limitation. As a preferred catalyst, a zeolite system in which a transition metal is ion-exchanged may be used, and the transition metal is an active metal such as Cu, Fe, Ni, Co, Cr, Mn, Ga, Al, Mo, La, Na, Zn, Ce, At least one of Zr, Ru, Ag, In, Sn, Re, Ir, Pt, Pd, Au and Rh, preferably Cu, and the support is all types of materials registered with the International Zeolite Association (IZA) Structures may be applied, which include MOR, CHA, MAZ, FAU, FER, MFI, ERI, AEI, AFX, AFT, EAB, GME, KFI, LEV, LTL, MWW, OFF, SAS, SAT, SBS, SBT, SZR , BPH, MEI, BEA, EMT, LTA, ISV, IWW, IMF, TUN, EON, but not limited thereto.

The reactor is a reactor in which a plasma discharge is generated, and any one of a thermal plasma discharge for heating and ionizing gas and a non-thermal plasma discharge for minimizing heating of gas and mainly heating and ionizing electrons can be used. However, in order to achieve the purpose of repeatedly performing the multi-staged methane conversion reaction of the present invention, any method capable of low-temperature plasma discharge capable of maintaining the temperature range of 50 to 400 ° C may be used without limitation. Preferably, among the low-temperature plasma discharge methods, any one of dielectric barrier discharge, pulsed corona discharge, and spark discharge may be used, and more preferably, it is operable under atmospheric pressure and room temperature conditions and non-equilibrium conditions, and high power discharge It is possible, and a low-temperature plasma using a dielectric barrier discharge (DBD) method that does not require a complicated pulse power supply can be used.

The plasma is not limited to AC or DC power, and the discharge initiation voltage and frequency may be determined according to the size of the reactor, and the reaction efficiency increases as the discharge voltage and frequency increase. Specifically, the plasma may use AC or DC power in a discharge voltage range of 1 to 100 kV, and a frequency in the case of AC power may be in a range of 0.1 to 100 kHz.

In step (b), methane is introduced into the catalyst activated in step (a) to form an active surface species (CH ₃ O ^- , hereinafter referred to as catalytically active species) adsorbed with methane. The catalytically active species is produced by the combination of oxygen and methane in the catalyst activated in step (a), and the reaction temperature at this time may be 50 ~ 400 ℃ and reaction pressure 0.5 ~ 100 bar, but preferably energy and process efficiency For this, the temperature in step (a) may be maintained the same.

In the step (b), a step of purging oxygen present in the reactor with an inert gas before introducing methane gas may be performed. At this time, the purpose of purging using an inert gas is to prevent the generation of by-products by direct reaction between oxygen and methane present in the reactor. At this time, the input time of methane gas may be 1 to 10 hours. The methane gas may be introduced in the form of methane alone or a mixed gas with any inert gas.

The step (c) is a step in which water is introduced into the reactor and the water and catalytically active species react to form methanol, and a step of purging methanol in the reactor using an inert gas may be performed before adding water. The water may be steam or a mixed gas of steam and inert gas, and preferably may be introduced in the form of a mixed gas in which water and steam are mixed in the range of 5:95 to 95:5.

The temperature range in the step may be 50 to 400 ^° C and the pressure may be 0.5 to 100 bar, but preferably, the temperature range is maintained the same as in step (a) for energy and process efficiency. Produced methanol is desorbed in the gas phase, and the desorbed methanol is recovered. As a method for recovering methanol, a conventional method may be used, and for example, a method of purging using an inert gas and cooling condensation may be used.

An example of a plasma reactor realizing the method of the present invention is shown in FIG. 1 . 1 is a schematic diagram of a low-temperature DBD plasma reactor 10 according to an embodiment of the present invention. Referring to FIG. 1, the dielectric barrier discharge plasma reactor has a gas inlet 110 on one side and a gas inlet 110 on the other side as a whole. A gas outlet 120 is formed, a plasma reaction unit 300 is formed inside, and an electric furnace 200 surrounds the outside of the plasma reaction unit. The structure of the plasma reactor is only an example of the present invention, and is not limited to the above description, and a structure of a known dielectric barrier discharge plasma reactor may also be adopted without limitation.

The gas inlet 110 is injected with oxygen gas introduced into the catalyst activation step and methane gas introduced into the methane adsorption step, the gas outlet 120 discharges the reaction product, and the gas outlet from the gas inlet 110 The gas line leading to 120 is heated by a separate heating means to prevent condensation of gas.

The electric furnace 200 continuously supplies energy using a heat source such as steam or electric energy from the outside so that the temperature of the plasma reaction unit can maintain the reaction temperature.

In addition, the plasma reaction unit, a dielectric material 310 forming a reactor tube; a ground electrode 320 covering the outside without being spaced apart from the dielectric material; and a high voltage electrode 330 provided at the center of the inside of the dielectric material, wherein the gas injected through the gas inlet passes through the dielectric material 310 under the condition that AC power is applied to the ground electrode 320. ; and a high voltage electrode 330; A plasma region 340 in which plasma is formed is formed therebetween, and the catalyst 311 is filled in at least part or all of the inside of the plasma region 340 .

The dielectric material 310 includes one or more metal oxides selected from among Al ₂ O ₃ , SiO ₂ , CeO ₂ and TiO ₂ , and preferably Al ₂ O ₃ may be used.

The plasma discharge in the reactor can use AC or DC power with a discharge voltage of 1 to 100 kV, and in the case of AC power, the frequency is applied by applying a frequency of 0.1 to 100 kHz. A mu-oxo bridge may be formed through the reaction.

The μ-oxobridge functions as an active site formed by combining oxygen active species (O) between two active metal elements in the catalyst. The active oxygen species is a decomposition product of ozone generated by discharging plasma to the injected oxygen gas, and can be easily bonded to an active metal located in an adjacent area by discharging the plasma to a region filled with a catalyst.

), Cu₂O₂ ²⁺(

), Cu₃O₃ ²⁺(

) 등 일 수 있으며, 상기 뮤-옥소 브릿지내 산소(O)는 후단의 메탄 해리흡착(반응) 단계에서 메탄이 결합될 수 있는 자리를 제공할 수 있다. As an example of the mu-oxo bridge, when the active metal in the catalyst is copper (Cu), Cu ₂ O ²⁺ (

), Cu ₂ O ₂ ²⁺ (

), Cu ₃ O ₃ ²⁺ (

), etc., and oxygen (O) in the mu-oxo bridge can provide a site where methane can be bonded in the subsequent methane dissociation adsorption (reaction) step.

The present invention will be explained through examples below.

<Example>

The conversion reaction of methane was performed using the dielectric barrier plasma-catalyzed reactor shown in FIG. 1 . Cu/MOR catalysts in the form of pellets selected to a size of 20/30 mesh were filled in the reactor, and O ₂ gas of 99.999% purity was injected under atmospheric pressure (1 bar) at a temperature of 200 ° C to activate the catalyst, and a voltage of 20 Discharge was performed for 30 minutes by applying kV and a frequency of 400 Hz. Then, the plasma discharge was terminated, and 99.999% N ₂ composition was purged for 10 minutes at the same temperature and pressure, and then 99.999% purity CH ₄ gas was flowed for 1 hour to adsorb and activate CH ₄ . Then, after purging with 99.999% N ₂ composition for 10 minutes, N ₂ gas containing 10% H ₂ O (steam) was flowed for 1 hour at the same temperature and pressure to generate methanol. The resulting product was analyzed using gas chromatography.

As a result of the reaction, it was confirmed that the selectivity of methanol produced by conversion of methane exceeded 90%.

As confirmed in the above examples, in the case of using the method of the present invention, by using plasma, the energy and time required for the heating / cooling process before / after the activation process of the catalyst are significantly reduced while maintaining high selectivity to methanol, As a result, it is possible to improve the energy inefficiency of the conventional process and shorten the process time.

The present invention has been described above with reference to the embodiments shown in the accompanying drawings, but these are only exemplary, and various modifications and other equivalent embodiments can be made by those skilled in the art in the art. will understand that Therefore, the technical protection scope of the present invention should be determined by the claims below.

Claims (9)

In the method for producing methanol through direct conversion of methanol to methanol with high selectivity using a plasma applied catalyst,
(a) a catalyst activation step in which a mu-oxo bridge is formed through a reaction between oxygen and an active metal in the catalyst by performing a plasma discharge while introducing oxygen gas into the reactor filled with the catalyst; (b) after step (a), methane gas is introduced into the reactor to generate catalytically active species (CH ₃ O ^- ) on the surface of the catalyst; And (c) a methanol generation step of introducing a gas containing water and reacting with the catalytically active species to generate methanol and recovering it in the gas phase; Method for producing methanol by conversion reaction.
According to claim 1,
A method for producing methanol by high selectivity direct conversion of methanol to methanol using a plasma applied catalyst, characterized in that the temperature is kept constant during the steps (a) to (c).
According to claim 1,
The catalyst is a zeolite system in which a transition metal is ion-exchanged,
The transition metal is an active metal such as Cu, Fe, Ni, Co, Cr, Mn, Ga, Al, Mo, La, Na, Zn, Ce, Zr, Ru, Ag, In, Sn, Re, Ir, Pt, Pd , at least one of Au and Rh,
The zeolite is MOR, CHA, MAZ, FAU, FER, MFI, ERI, AEI, AFX, AFT, EAB, GME, KFI, LEV, LTL, MWW, OFF, SAS, SAT, SBS, SBT, SZR, BPH, MEI , BEA, EMT, LTA, ISV, IWW, IMF, TUN, EON, characterized in that the structure of any one of the method for producing methanol by high selectivity direct conversion of methanol to methanol using a plasma-applied catalyst.
According to claim 1,
Before introducing methane gas in step (b), purging oxygen in the reactor with an inert gas is carried out, characterized in that, to produce methanol by direct conversion of methanol to methanol with high selectivity using a plasma-applied catalyst method.
According to claim 1,
Before the introduction of water in step (c), a step of purging methane in the reactor with an inert gas is performed, characterized in that, a method for producing methanol by direct conversion of methanol to methanol with high selectivity using a plasma applied catalyst.
According to claim 1,
The plasma is a method for producing methanol by high selectivity direct conversion of methanol to methanol using a plasma applied catalyst, characterized in that the dielectric barrier discharge (DBD) plasma.
According to claim 1,
In the steps (a) to (c), the temperature is 50 ~ 400 ℃, respectively, and the pressure is 0.5 ~ 100 bar. To produce methanol by high selectivity direct conversion of methanol to methanol using a plasma-applied catalyst, characterized in that method.
A gas inlet on one side and a gas outlet on the other side, a plasma reaction unit formed inside, an electric furnace surrounding the outside of the plasma reaction unit,
The plasma reaction unit may include an internal dielectric material; a ground electrode covering the outside without being spaced apart from the dielectric material; and a high voltage electrode provided at the center of the inside of the dielectric material,
the ground electrode while the gas injected through the gas inlet passes through the dielectric material filled with the catalyst under the condition that AC power is applied; and a high voltage electrode; A plasma region in which plasma is formed is formed between them,
A dielectric barrier discharge plasma reactor for producing methanol through a direct conversion of methanol to methanol, characterized in that the catalyst is filled in at least part or all of the inside of the plasma region.
According to claim 8,
The dielectric material comprises a metal oxide of at least one of Al ₂ O ₃ , SiO ₂ , CeO ₂ and TiO ₂ , Dielectric barrier discharge plasma for producing methanol through direct conversion of methanol to methanol with high selectivity. reactor.

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