CN112892588B

CN112892588B - Preparation method and application of atomic-scale monodisperse transition metal catalyst for preparing acetic acid by low-temperature catalytic oxidation of methane

Info

Publication number: CN112892588B
Application number: CN201911220250.5A
Authority: CN
Inventors: 丁云杰; 李彬; 宋宪根; 姜淼
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2019-12-03
Filing date: 2019-12-03
Publication date: 2022-03-29
Anticipated expiration: 2039-12-03
Also published as: CN112892588A

Abstract

The invention relates to a method for preparing acetic acid by using a single-atom catalyst loaded on a triphenylphosphine polymer carrier for low-temperature oxidation of methane, wherein the metal is one or two of Rh, Ir, Co, Pt, Pd and Cu, and mainly relates to a technology for oxidizing low-carbon methane hydrocarbon under a low-temperature condition to convert the low-carbon methane hydrocarbon into the acetic acid. The traditional low-carbon alkane oxidation technology has higher reaction temperature and large energy consumption, while the reaction temperature is lower than 300 ℃ in the invention, and TOF of generated acetic acid is close to 200h^‑1The selectivity of acetic acid is high, the carrier is triphenylphosphine polymer, and the specific surface area of the triphenylphosphine polymer is 400-1200 m²(ii)/g, the average pore diameter is 1-200 nm. The catalyst is used for preparing CH in a kettle reactor under certain temperature and pressure and under the action of the catalyst₄CO and O₂Can be converted into acetic acid, formic acid and methanol with high activity and high selectivity.

Description

Preparation method and application of atomic-scale monodisperse transition metal catalyst for preparing acetic acid by low-temperature catalytic oxidation of methane

Technical Field

The invention relates to a method for preparing acetic acid by low-temperature catalytic oxidation of methane by using an atomic-scale monodisperse transition metal catalyst loaded on a triphenylphosphine polymer.

Background

Methane, as is well known, is a plentiful, widely available fossil energy source with low electron and proton affinities, low polarity, high C-H bond energy 439kJ/mol, and high ionization energy, and is the most difficult species to convert to and utilize in C1 chemistry. Because of its chemical inertness, the activation of the first C-H bond appears to be an exceptionally difficult step, becoming the rate-determining step for methane activation, while its oxidation products are all characterized by being more reactive than methane. The methane activation for preparing high value-added chemicals, especially through a green low-energy consumption way, becomes a worldwide problem.

The methane conversion is divided into direct conversion and indirect conversion, wherein the indirect conversion is to prepare synthesis gas by reforming and oxidizing methane, and then synthesize other liquid fuels and chemical products by the synthesis gas. The synthesis gas prepared by reforming and oxidizing methane needs very high temperature (more than 800 ℃) and has higher energy consumption. Thus, the direct conversion of methane has great advantages in terms of both energy and process technology compared to the high energy consumption indirect route. Direct methane conversion, which includes primarily aerobic and anaerobic methane conversion, and methane halogenation.

Among catalysts for heterogeneous selective oxidation of methane, the most effective catalytic systems include iron-based and molybdenum-based catalysts; in the aspect of liquid-phase catalytic oxidation, the selective oxidation of methane is catalyzed by transition metal and rare earth metal catalysts under acidic conditions, but the catalysts are difficult to separate; in the aspect of enzyme catalytic oxidation, methane monooxygenase is an important catalyst for preparing methanol from methane, can realize the direct conversion of methane to methanol, and has good activity and selectivity. However, the biological enzymes are expensive and cannot be produced on a large scale.

The OCM route refers to the process that methane and oxygen generate ethane and ethylene under the action of a catalyst, generally, methane generates methyl free radicals on the surface of the catalyst, then the methyl free radicals diffuse into a gas phase to be coupled to generate ethane, and the ethane is dehydrogenated to generate ethylene. The anaerobic conversion of methane, 1993-Wanglinsheng research shows that methane can be directly converted into aromatic hydrocarbon on a Mo/HZSM-5 catalyst, the yield of the aromatic hydrocarbon can reach about 70-80% of thermodynamic equilibrium yield at 700 ℃, the main problems are poor stability and short service life of a few hours, and carbon deposition is generally considered to be a main cause of catalyst deactivation. The silicide lattice limited domain monatomic iron-center catalyst is covered and reported, and high-value-added chemicals such as ethylene, aromatic hydrocarbon, hydrogen and the like can be efficiently produced by methane in one step. At a temperature of 1090 ℃ and 21.4 L.g_cat ^-1·h^-1Under the conditions of (1), the conversion per pass of methane is 48.1%, the selectivity of ethylene is 48.4%, and the selectivity of all products (ethylene, benzene and naphthalene) is more than 99%, so that CO is realized₂The atomic utilization rate is close to 100 percent. The free energy of gibbs of methane halogenation and iodide is more than 0, the process is not spontaneous, the methane fluorination is strongly exothermic and is not easy to control, the explosion hazard exists, and compared with methane bromide, the chlorination reaction is easy to generate multi-substituted products. The catalyst is a super acid, and the existence of halogen causes certain corrosion to equipment.

Compared with the above paths, the low-temperature and low-pressure (100-200 ℃ and 0-3.5 MPa) oxidation of methane becomes the direction with the most competitive power and the most research value at present, and has important academic and industrial significance. Low temperature oxidation of methane, primarily methane in O₂Or H₂O₂In the presence of (2), the transition metal is activated into a methyl radical, and the methyl radical and CO undergo a migration insertion reaction at an active center to generate acetyl with high selectivity. Acetyl reacts with water to generate acetic acid, thereby realizing the new process for preparing the acetic acid by the low-temperature oxidation of methane with high selectivity.

For the supported nano metal catalyst, only atoms exposed on the surface of the metal catalyst have catalyst activity, so that the utilization efficiency of metal atoms is low, and particularly, the resource-limited precious metal causes resource waste. The monatomic dispersed metal catalyst, having the largest coordinatively unsaturated sites, is believed to be the active center for the catalytic reaction. Therefore, the metal catalyst dispersed at the atomic level may have high catalytic activity in addition to 100% of atomic utilization.

However, because the monatomic-level supported metal catalyst has high surface energy, mobility and easy agglomeration, the stability of the monatomic-level supported metal catalyst in the catalytic reaction process is a great challenge.

Along with the rapid development of global economy in recent years, the demand of human beings on resources is increasing day by day, and meanwhile, the problem of resource shortage is becoming more serious, the apparent consumption of acetic acid in China is rapidly increased, 100 ten thousand tons is broken through for the first time in 2001, the annual consumption reaches 105 ten thousand tons, nearly 200 ten thousand tons in 2007 is 198.9 ten thousand tons, and the development of a novel technology for preparing acetic acid is an epoch requirement.

Acetic acid is one of important organic acids, has wide application, and is mainly used for synthesizing vinyl acetate, cellulose acetate, acetic anhydride, acetate, metal acetate, PTA and the like; is also an important raw material for pharmacy, dye, pesticide and other organic synthesis. Acetic acid is industrially produced by, for example, a methanol oxo process, an acetaldehyde oxidation process, or a butane (light oil) liquid phase oxidation process. Acetaldehyde is used as a raw material, and oxidation reaction is carried out on a manganese acetate, cobalt acetate or copper acetate homogeneous catalyst to realize effective conversion of the acetaldehyde. The selection of acetic acid is generally higher than 95%, currently, the acetic acid in China mainly adopts a methanol carbonylation synthesis method, the activation energy of the carbonylation synthesis of the acetic acid is very high, and the carbonylation synthesis of the acetic acid can be realized only under the catalytic condition. As early as 1913, BASF discovered that methanol could be carbonylated to produce acetic acid, and did not build a first pilot-scale carbonylated acetic acid plant until the end of the last 50 th century when equipment for corrosion-resistant Mo/Ni alloy materials became available. Thereafter, BASF corporation employed iodination (CoI) by 1960₂) A first set of device for synthesizing acetic acid by methanol carbonylation is built for the catalyst. The methanol carbonylation process for rhodium/iodide catalyst was developed in 1970 by Monsanto corporation and improved the cobalt iodide catalyzed high pressure process pioneered by BASF corporation in 1960. The rhodium/iodide catalyzed methanol oxo process is highly selective and can be operated at lower pressures. Because noble metals are expensive, the recovery process is complex and uneconomical, and different supported catalyst systems such as polymer, activated carbon, inorganic oxides and molecular sieve supported catalyst systems have been studied in recent years.

In conclusion, the method for preparing acetic acid by directly oxidizing methane has the advantages of mild reaction conditions, cheap and easily-obtained raw materials and simple process flow, and can be used as an alternative way for producing acetic acid at present.

Disclosure of Invention

The key problem to be solved by the invention is to improve the selectivity of the target product acetic acid under mild reaction conditions, and simultaneously consider the economic problem of the catalyst, so that the method has the characteristics of low catalytic cost and high acetic acid yield.

In order to solve the problems, the technical scheme adopted by the invention is as follows:

an atomic-scale monodisperse transition metal catalyst used for loading triphenylphosphine polymer, a preparation method and an application thereof are characterized in that the catalyst consists of a main catalyst and a carrier. The transition metal as the active component in the catalyst is in an atomically monodisperse state. Can achieve the high-efficiency conversion of methane into acetic acid under the temperature condition which is obviously lower than that of the prior art.

The catalyst system is composed of a triphenylphosphine polymer self-supported transition metal single-atom heterogeneous catalyst, wherein the polymer with a multistage pore channel structure is obtained by triphenylphosphine monomer solvent thermal polymerization, and the metal is derived from one or more of chlorides of Rh, Ir, Co, Pt, Pd and Cu, acetylacetone metal salt or acetate.

The conditions of the monodisperse treatment of the atomic-scale monodisperse transition catalyst are as follows: the loading temperature is 0-120 ℃, preferably 100-100 ℃, the pressure is 0.01-1.0 MPa, and the treatment time is 0.01-48 h, preferably 0.5-24 h.

Introducing metal ions into the triphenylphosphine polymer catalyst by using a method of impregnating the carrier with a salt solution of the selected metal at normal pressure or reduced pressure in an equal volume or over volume; the impregnated catalyst is vacuum-dried by a Bush funnel at the temperature of 50-100 ℃ for 2-48 h.

The carrier is triphenylphosphine polymer, and the specific surface area of the triphenylphosphine polymer is 400-1200 m²The preferable specific surface area of the triphenylphosphine polymer is 680-1000 m²The average pore diameter of the triphenylphosphine polymer is 1-200 nm.

The transition metal monatomic catalyst prepared according to the scheme is subjected to a reaction activity evaluation experiment for preparing acetic acid by directly oxidizing methane in a 50ml reactor, and the reaction conditions are as follows: the system pressure is 0.1-5MPa, the reaction temperature is 100-400 ℃, and the reaction time is 0.1-12 h.

The invention will be further elucidated by means of some examples.

Detailed Description

[ example 1 ]

First, 0.1gRhCl was weighed₃Adding 10ml tetrahydrofuran solvent, stirring for dissolving, grinding triphenylphosphine polymer obtained by polymerization into powder, weighing 1g, placing in a flask, stirring for 8h, pumping to dry for 8h at normal temperature until completely dry to obtain catalyst 0.1 wt% Rh₃/PPh₃And then identified by HAADF-STEM characterization, and the catalyst is an atomic-scale monodisperse catalyst.

50mg of Rh were weighed₁/PPh₃Reaction temperature: 150 ℃, reaction pressure: CO 0.5MPa, CH₄:2.0MPa，O₂：0.2MPa，H₂O: 20g of the total weight of the mixture; 100ml kettle, magnetic stirring: 1200rpm, reaction time: and 4h, analyzing the liquid-phase product by using an Agilent 7890B gas chromatograph, and calculating the result by using an area normalization method. The results of the reaction are summarized in Table 1 below.

[ example 2 ]

Firstly, weighing 0.1g of copper acetylacetonate, adding 10ml of tetrahydrofuran solvent, stirring and dissolving, grinding triphenylphosphine polymer obtained by polymerization into powder, weighing 1g of the powder, placing the powder into a flask, stirring for 8 hours, pumping and drying at normal temperature for 8 hours until the powder is completely dried to obtain the catalyst, namely 0.1 wt% of Cu₂/PPh₃And then identified by HAADF-STEM characterization, and the catalyst is an atomic-scale monodisperse catalyst.

The oxidation performance evaluation experiment of the catalyst is equivalent to [ example 1 ], and details are not repeated herein.

[ example 3 ]

First, 0.1g of PtCl was weighed₄Adding 10ml of tetrahydrofuran solvent, stirring for dissolving, grinding the triphenylphosphine polymer obtained by polymerization into powder, weighing 1g of the triphenylphosphine polymer, putting the powder into a flask, stirring for 8 hours, pumping the solution at normal temperature for 8 hours until the solution is completely dried to obtain the catalyst of 0.1 wt% Pt₄/PPh₃And then identified by HAADF-STEM characterization, and the catalyst is an atomic-scale monodisperse catalyst.

[ example 4 ]

First, 0.1g of CoCl was weighed₂Adding 10ml of tetrahydrofuran solvent, stirring for dissolving, grinding the triphenylphosphine polymer obtained by polymerization into powder, weighing 1g of the triphenylphosphine polymer, putting the powder into a flask, stirring for 8 hours, pumping the solution at normal temperature for 8 hours until the solution is completely dried to obtain the catalyst, wherein the Co content is 0.1 wt% of the catalyst₂/PPh₃And then identified by HAADF-STEM characterization, and the catalyst is an atomic-scale monodisperse catalyst.

[ example 5 ]

First, 0.1g of PdCl was weighed₂Adding 10ml tetrahydrofuran solvent, stirring for dissolving, grinding triphenylphosphine polymer obtained by polymerization into powder, weighing 1g, placing in a flask, stirring for 8h, pumping to dry for 8h at normal temperature until completely dry to obtain catalyst 0.1 wt% Pd₂/PPh₃And then identified by HAADF-STEM characterization, and the catalyst is an atomic-scale monodisperse catalyst.

[ example 6 ]

First, 0.1g of IrCl was weighed₃Adding 10ml of tetrahydrofuran solvent, stirring for dissolving, grinding the triphenylphosphine polymer obtained by polymerization into powder, weighing 1g of the triphenylphosphine polymer, putting the powder into a flask, stirring for 8 hours, pumping the solution at normal temperature for 8 hours until the solution is completely dried, and obtaining the catalyst of 0.1 wt% Ir₃/PPh₃And then identified by HAADF-STEM characterization, and the catalyst is an atomic-scale monodisperse catalyst.

[ example 7 ]

Firstly, 0.1g of acetylacetonatodicarbonylrhodium is weighed, 10ml of tetrahydrofuran solvent is added for stirring and dissolving, the triphenylphosphine polymer obtained by polymerization is ground into powder, 1g of the triphenylphosphine polymer is weighed, the powder is placed in a flask for stirring for 8 hours, the mixture is pumped to dry for 8 hours at normal temperature until the mixture is completely dried, and then the catalyst of 0.1 wt% Rh is prepared₁/PPh₃And then identified by HAADF-STEM characterization, and the catalyst is an atomic-scale monodisperse catalyst.

[ example 8 ]

First, 0.1gRhCl was weighed₃Adding 10ml tetrahydrofuran solvent, stirring for dissolving, grinding triphenylphosphine polymer obtained by polymerization into powder, weighing 1g, weighing 0.1g copper acetylacetonate, placing in a flask, stirring for 8h, pumping to dry for 8h at normal temperature until completely drying to obtain catalyst 0.1 wt% Rh₃-0.1wt％Cu₂/PPh₃And then identified by HAADF-STEM characterization, and the catalyst is an atomic-scale monodisperse catalyst.

[ example 9 ]

Firstly, 0.1g of acetylacetonatodicarbonylrhodium is weighed, 10ml of tetrahydrofuran solvent is added for stirring and dissolving, triphenylphosphine polymer obtained by polymerization is ground into powder, 1g of acetylacetonatorhodium is weighed, 0.1g of acetylacetonatocopper is weighed, the powder is placed in a flask for stirring for 8 hours, the solution is dried for 8 hours at normal temperature until the solution is completely dried, and then the catalyst of 0.1 wt% Rh is prepared₁-0.1wt％Cu₂/PPh₃And then identified by HAADF-STEM characterization, and the catalyst is an atomic-scale monodisperse catalyst.

[ example 10 ]

Firstly, 0.1g of acetylacetonatodicarbonylrhodium is weighed, 10ml of tetrahydrofuran solvent is added for stirring and dissolving, triphenylphosphine polymer obtained by polymerization is ground into powder, 1g of the triphenylphosphine polymer is weighed, 0.1g of CuCl is weighed, the mixture is placed in a flask for stirring for 8 hours, the mixture is dried for 8 hours at normal temperature until the mixture is completely dried, and then the catalyst of 0.1 wt% Rh is prepared₁-0.1wt％Cu₁/PPh₃And then identified by HAADF-STEM characterization, and the catalyst is an atomic-scale monodisperse catalyst.

TABLE 1

Note: the products are mainly acetic acid and methanol, and trace methyl acetate, methyl formate and CO based on converted methane₂。

The results show that: the catalytic activity of the single metal supported transition metal catalyst, whether methane conversion or acetic acid selectivity, is weaker than that of the bimetallic supported catalyst; in the case of the double metal supported transition metal catalyst, the activity is the best when all the metal precursors used are metal organic complexes, and thus the activity of the transition metal catalyst using a metal organic complex as a metal precursor is the highest.

Claims

1. The application of transition metal catalyst loaded by triphenylphosphine polymer in the reaction of preparing acetic acid by methane oxidation is characterized in that: the reaction temperature is 100 ℃ and 250 ℃, and the reaction pressure is 0.1-8 MPa;

the catalyst consists of two parts of a transition metal active component and a carrier: the carrier is triphenylphosphine polymer; the transition metal is two metals of Rh, Ir, Co, Pt, Pd and Cu, the weight ratio of the supported metals ranges from 0.1 to 2 percent of the catalytic weight, and the lowest supported weight of each metal is 0.01 percent of the catalytic weight;

the transition metal as the active component in the catalyst is in an atomically monodisperse state.

2. Use according to claim 1, characterized in that: the specific surface area of the triphenylphosphine polymer is 400-1200 m²The pore size distribution of the triphenylphosphine polymer is 1-200 nm.

3. Use according to claim 1, characterized in that: the preparation process of the catalyst needs to be protected by Ar gas.

4. Use according to claim 1, characterized in that: the reaction uses water as a solvent.

5. Use according to claim 1, characterized in that: the reaction pressure is 0.8-4.5 MPa; the weight proportion range of the loaded metal in the catalyst is 0.5-1% of the catalytic weight; and wherein the minimum loading weight of each metal is 0.1% of the catalytic weight.

6. Use according to claim 2, characterized in that: the specific surface area of the triphenylphosphine polymer is 680-1000 m²/g。