CN114289040A

CN114289040A - Catalyst for gas phase synthesis of dimethyl carbonate and preparation method thereof

Info

Publication number: CN114289040A
Application number: CN202111653371.6A
Authority: CN
Inventors: 吕静; 曹新原; 侯强; 安继民; 翟瑞国
Original assignee: Ningbo Tianyan Jingkai Technology Co ltd; Zhejiang Research Institute Of Tianjin University
Current assignee: Ningbo Tianyan Jingkai Technology Co ltd; Zhejiang Research Institute Of Tianjin University
Priority date: 2021-12-30
Filing date: 2021-12-30
Publication date: 2022-04-08
Anticipated expiration: 2041-12-30
Also published as: CN114289040B

Abstract

The invention discloses a catalyst for gas-phase synthesis of dimethyl carbonate, wherein a carrier comprises titanium dioxide, pseudo-boehmite and an auxiliary agent, the mass ratio of the titanium dioxide to the pseudo-boehmite is 1 (1-10), and the auxiliary agent is 0.1-1% of the sum of the mass of the titanium dioxide and the pseudo-boehmite; the active components comprise soluble palladium salt, perchlorate and zirconium oxychloride, wherein the mass of the soluble palladium salt is 0.1-1% of the mass of the carrier, the molar ratio of the perchlorate to the soluble palladium salt is (1-20): 1, the mass of the zirconium oxychloride is 0.1-1% of the mass of the carrier, and the auxiliary agent is molybdate. The invention also discloses a preparation method of the catalyst for gas-phase synthesis of dimethyl carbonate, and the prepared catalyst has higher conversion rate and selectivity and longer service life.

Description

Catalyst for gas phase synthesis of dimethyl carbonate and preparation method thereof

Technical Field

The invention belongs to the technical field of chemical processes, and particularly relates to a catalyst for gas-phase synthesis of dimethyl carbonate and a preparation method thereof.

Background

Dimethyl carbonate (DMC) is an environment-friendly chemical raw material with low toxicity and environmental protection meeting the requirements of modern 'clean technology', has good DMC reaction activity, and is widely applied to the fields of pesticides, medicines, plastics, dyes, electronic chemicals, food additives, color development and the like. In recent years, with the rapid advance of lithium battery technology in China, the use level of DMC is greatly increased, and the supply of the electrolyte for lithium batteries is short.

The current production process routes mainly include a phosgene method, an ester exchange method, a urea alcoholysis method, a methanol oxidation carbonylation method and a methyl nitrite gas-phase carbonylation method. The phosgene process mainly uses highly toxic phosgene as a raw material, and belongs to a obsolete process for severe corrosion of equipment. The ester exchange method takes ethylene oxide or ethylene (propylene) carbonate as raw materials, has higher production cost and lacks market competitiveness. The DMC synthesis reaction by urea alcoholysis is carried out under high pressure and catalyst conditions, and the catalyst is expensive. The methanol oxidation carbonylation method has low cost of raw materials and high selectivity of products, but the catalyst is easy to inactivate. The methyl nitrite gas phase carbonylation method has the advantages of cyclic utilization of products, high atom utilization rate and low production cost, and is very suitable for industrialization.

Patent CN 110844918A provides a Y-type molecular sieve DMC catalyst, the Y-type molecular sieve is synthesized by a hydrothermal method and a microwave-assisted crystallization method, through the preparation of a guiding agent and the regulation and control of a titanium source and a phosphorus source on the composition of a mother solution, the Y-type molecular sieve is obtained through crystallization reaction after microwave pre-crystallization treatment, although the performance is better and chlorine is not generated, from the preparation perspective, the microwave crystallization process is very limited, the requirement on preparation equipment is high, the crystallization failure rate is difficult to control, and the large-scale production is difficult, so that the catalyst is high in price and the production cost and the production period are increased.

Patent CN 111018710A provides a synthetic method of novel strong basic ionic liquid and this novel ionic liquid inlays the solid-supported method of riveting formula, the homogeneous phase and heterogeneous catalyst that prepare are used for methyl carbonate catalytic synthesis, ionic liquid has better activity to ethylene carbonate and methyl alcohol ester exchange, be a homogeneous catalyst that hopefully replaces traditional catalyst, but ionic liquid's synthesis technology is complicated, need use organic solvent in the synthetic process, can produce waste water, increased ionic liquid's manufacturing cost on the one hand, on the other hand has also brought the pollution, the green characteristic of ionic liquid has been reduced. The ionic liquid has multiple purification steps and difficult purification, so the production cost is high.

Patent CN 111085220 a provides a spinel carrier, active components and auxiliaries; wherein the auxiliary agent is a chloride of a transition metal element, and the active component is PdCl₂The preparation method of the catalyst has the advantages that strong interaction is formed by the spinel carrier and the active component, so that the activity and the selectivity of the catalyst are improved to a certain extent, but the selectivity is still not high about 90%, HCl which is easy to prepare toxicity is used as a solvent in the preparation process of the catalyst, and the catalyst is roasted at 400 ℃ after being soaked, so that corrosive HCl is volatilized, the performance evaluation of the catalyst is only 6 hours, the performance of the catalyst does not reflect attenuation and reach a stable period, and therefore, whether the high performance can be maintained for a long time or not is questioned in the service life of the catalyst.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a catalyst for gas phase synthesis of dimethyl carbonate, which has higher conversion rate and selectivity and longer service life.

The invention is realized by the following technical scheme:

a catalyst for gas phase synthesis of dimethyl carbonate comprises a carrier and an active component, wherein;

the carrier comprises titanium dioxide, pseudo-boehmite and an auxiliary agent, the mass ratio of the titanium dioxide to the pseudo-boehmite is 1 (1-10), and the auxiliary agent is 0.1-1% of the sum of the mass of the titanium dioxide and the pseudo-boehmite;

the active components comprise soluble palladium salt, perchlorate and zirconium oxychloride, wherein the mass of the soluble palladium salt is 0.1-1% of the mass of the carrier, the molar ratio of the perchlorate to the soluble palladium salt is (1-20): 1, and the mass of the zirconium oxychloride is 0.1-1% of the mass of the carrier;

the auxiliary agent is molybdate.

In the technical scheme, the soluble palladium salt is one or more of palladium chloride, palladium nitrate, palladium acetate and palladium sulfate;

in the above technical scheme, the molybdate is one or more of ammonium molybdate, cobalt molybdate, iron molybdate, manganese molybdate, chromium molybdate, nickel molybdate and tungsten molybdate;

in the technical scheme, the perchlorate is one or more of copper perchlorate, magnesium perchlorate, cobalt perchlorate, chromium perchlorate, manganese perchlorate and nickel perchlorate.

Another object of the present invention is to provide a method for preparing a catalyst for gas phase synthesis of dimethyl carbonate.

A preparation method of a catalyst for gas-phase synthesis of dimethyl carbonate comprises the following steps:

step 1, uniformly mixing titanium dioxide, pseudo-boehmite, an auxiliary agent and first deionized water to obtain a first material, granulating the first material to obtain first particles, drying the first particles, and calcining at 300-700 ℃ to obtain a carrier;

in the first material, the mass ratio of titanium dioxide to pseudo-boehmite is 1 (1-10), and the mass of the auxiliary agent is 0.1-1% of the sum of the titanium dioxide and the pseudo-boehmite; the weight of the first deionized water accounts for 5% -15% of that of the first material;

step 2, dispersing soluble palladium salt, perchlorate and zirconium oxychloride in second deionized water to obtain a steeping liquor;

the mass of the soluble palladium salt is 0.1-1% of the mass of the carrier, the molar ratio of the perchlorate to the soluble palladium salt is (1-20): 1, and the mass of the zirconium oxychloride is 0.1-1% of the mass of the carrier;

the amount of the second deionized water is the maximum absorption mass of the carrier to the deionized water in the step 1;

step 3, dipping the carrier obtained in the step 1 into the dipping solution obtained in the step 2, and dipping for 2-24 hours to obtain a dipped carrier; and drying the impregnated carrier to constant weight to obtain the catalyst for gas-phase synthesis of dimethyl carbonate.

In the above technical scheme, the drying temperature of the first particles is 100 ℃.

In the technical scheme, the process of uniformly mixing the titanium dioxide, the pseudo-boehmite, the auxiliary agent and the first deionized water in the step 1 is completed by adopting a kneader; and the process of granulating the first material is finished by adopting a strip extruding machine.

In the technical scheme, in the step 2, soluble palladium salt, perchlorate and zirconium oxychloride are stirred and dispersed in first deionized water at the temperature of 20-60 ℃ to obtain a steeping liquor.

in the above technical scheme, the molybdate is one or more of ammonium molybdate, cobalt molybdate, iron molybdate, manganese molybdate, chromium molybdate, nickel molybdate, and tungsten molybdate.

In the technical scheme, in the step 3, the impregnated carrier is dried at the temperature of 60-120 ℃ to constant weight.

In the above technical scheme, the raw material used in step 2 may have crystal water, and if the raw material containing crystal water is used in step 2, the amount of the solvent is the mass of the carrier absorbed by the carrier in the maximum amount minus the total mass of the crystal water.

The invention also aims to provide a method for synthesizing the dimethyl carbonate.

A Methyl Nitrite (MN) and CO are used as raw materials in the synthesis method, and dimethyl carbonate is obtained through reaction synthesis under the action of the catalyst for gas-phase synthesis of dimethyl carbonate prepared in the technical scheme;

the synthesis temperature is 110-130 ℃, and the volume space velocity is 2000-2700 h^-1The molar ratio of methyl nitrite to CO is (1-2): 1.

In the technical scheme, the reaction synthesis process is completed in a fixed bed reactor, and the pressure of the catalytic bed is 0.2-0.7 MPa.

The invention has the advantages and beneficial effects that:

1. the doping effect of the transition metal element Mo in the catalytic carrier prepared by the technical scheme of the invention is due to Mo⁶⁺(r ═ 0.062nm) with Ti⁴⁺(r ═ 0.068nm) has a similar ionic radius, enabling it to enter the TiO₂Lattice of (2) in place of Ti⁴⁺In the position of (2), forming a new chemical bond and in the TiO₂The new energy level is introduced into the forbidden band, the activation energy required by the DMC reaction is reduced, and the DMC conversion rate can be improved.

2. The carbonylation of methanol to DMC produces H₂O，2CH₃OH+CO+1/2O₂→(CH₃O)₂CO+H₂O

Zirconium oxychloride in the catalyst belongs to a tetragonal crystal structure, and is very easy to combine with water to generate 8 crystal waters to become octahydrate, so that the forward production of DMC is accelerated, the effect of improving DMC conversion rate is achieved, and Zr in zirconium oxychloride molecules⁴⁺The 4d and 5s orbitals are all empty, can receive external lone pair electrons, have stronger electronegativity, have the properties similar to solid oxide, and have the synergistic action with the strong oxidizing property of perchlorate radicals to continuously enable the active center Pd²⁺The ions maintain the positive 2 valence state, and the service life of the catalyst is prolonged.

3. Perchlorate is a Lewis acid and has a strong electron-withdrawing ClO₄ ^－Anions and metal atoms with empty d-orbitals. In contrast to other anions, ClO₄ ^－The anion has the strongest electric absorption property, the electron cloud density around the metal ion can be reduced, so that the active center Pd ion is beneficial to being in favor of-ON-OCH in MN molecule₃Bridging occurs, and then-OCH of MN molecules are influenced₃The strength of the bond. In addition, the empty d orbit of the Pd atom is occupied by lone electron pairs in the oxygen atom of the MN, so that-OCH in MN molecules₃The bond strength is changed to make it easier to combine with CO to form-COOCH₃. Thus, the generation of dimethoxymethane and methyl formate as byproducts is avoided, the selectivity is improved, and the mechanism diagram can be shown in figure 13.

4. The catalyst has high CO conversion rate maintained stably over 30%, DMC selectivity over 95%, low reaction temperature, low reaction pressure and long catalyst life.

5. The preparation method of the catalyst provided by the invention does not use hydrochloric acid in the preparation process, because the hydrochloric acid belongs to a product easy to prepare poison. The method avoids equipment corrosion caused by volatilization of hydrochloric acid when the catalyst is dried, and almost no waste liquid is discharged due to the configuration of the impregnating solution according to the maximum water absorption capacity of the carrier. In addition, HCl gas does not need to be supplemented in the using process of the catalyst so as to ensure the activity and the service life of the catalyst and reduce the corrosion condition of Cl ions to equipment.

Drawings

FIG. 1 shows a catalyst evaluation apparatus;

FIG. 2 shows a gas chromatograph GC-2014C;

FIG. 3 shows a gas chromatograph GC-2014C with a vaporization chamber;

FIGS. 4-7 show SEM pictures of example 1;

FIG. 8 shows the EDS spectrum of example 1;

FIG. 9 shows the IR spectrum of example 1;

FIG. 10 is an XPS spectrum after 500h of evaluation of the catalyst of example 1;

FIG. 11 is an XPS spectrum of the comparative example 1c after 500h of catalyst evaluation;

fig. 12 is an XRD spectrum for evaluation of the catalyst in example 1: a. example 1 catalyst; b. example 1 after 500h of catalyst evaluation;

FIG. 13 is a schematic diagram showing the mechanism of the gas phase synthesis of dimethyl carbonate in the present invention.

For a person skilled in the art, other relevant figures can be obtained from the above figures without inventive effort.

Detailed Description

In order to make the technical solution of the present invention better understood, the technical solution of the present invention is further described below with reference to specific examples.

The materials used in the examples all contained no crystal water

Example 1

The preparation method of the catalyst for synthesizing the dimethyl carbonate comprises the following steps:

step 1: adding titanium dioxide, pseudo-boehmite, ammonium molybdate and deionized water 1 into a kneader for kneading, obtaining a first material after kneading, pouring the first material into a strip extruding machine for extruding strips, drying the extruded strips at 100 ℃, and calcining at 300 ℃ to obtain a carrier, wherein the mass ratio of the titanium dioxide to the pseudo-boehmite is 1:1, the adding amount of the ammonium molybdate is 0.1 percent of the sum of the mass of the titanium dioxide and the pseudo-boehmite, and the adding amount of the deionized water 1 is 5 percent of the total mass of the first material.

Step 2: stirring and dispersing palladium chloride, copper perchlorate and zirconium oxychloride in deionized water 2 at 20 ℃ to obtain impregnation liquid, wherein the addition amount of the palladium chloride is 0.1 percent of the mass of the carrier, the molar ratio of the addition amount of the copper perchlorate to the palladium chloride is 20:1, the addition amount of the zirconium oxychloride is 1 percent of the carrier, and determining the using amount of the deionized water 2 by adopting an isometric impregnation method;

and step 3: and (3) soaking the carrier in the step (1) into the soaking solution in the step (2), wherein the soaking process lasts for 2 hours, and after the soaking is finished, the material is placed into an oven and dried at 60 ℃ to constant weight to obtain the catalyst.

Comparative example 1

Compared with the example 1, the difference of the comparative example 1 is that no molybdate auxiliary agent is added in the step 1 in the comparative example 1, the proportion of other raw materials and reaction parameters are consistent with those of the example 1, and the catalyst No. 1a is prepared.

Comparative example 2

Compared with the example 1, the difference of the comparative example 2 is that no perchlorate auxiliary agent is added in the comparative example 2, and the proportion of other raw materials and reaction parameters are consistent with those of the example 1, so that the No. 1b catalyst is prepared.

Comparative example 3

Comparative example 3 compared to example 1, except that no zirconium oxychloride was added in comparative example 3, the other raw material ratios and reaction parameters were consistent with those of example 1, and catalyst No. 1c was prepared.

Example 2

step 1: adding titanium dioxide, pseudo-boehmite, ammonium molybdate and deionized water 1 into a kneader for kneading, obtaining a first material after kneading, pouring the first material into a strip extruding machine for extruding strips, drying the extruded strips at 100 ℃, and calcining at 500 ℃ to obtain a carrier, wherein the mass ratio of the titanium dioxide to the pseudo-boehmite is 1:5, the adding amount of the ammonium molybdate is 0.5 percent of the sum of the mass of the titanium dioxide and the pseudo-boehmite, and the adding amount of the deionized water 1 is 10 percent of the total mass of the first material.

Step 2: stirring and dispersing palladium chloride, copper perchlorate and zirconium oxychloride in deionized water 2 at 40 ℃ to obtain impregnation liquid, wherein the addition amount of the palladium chloride is 0.5 percent of the mass of the carrier, the molar ratio of the addition amount of the copper perchlorate to the palladium chloride is 10:1, the addition amount of the zirconium oxychloride is 0.5 percent of the mass of the carrier, and the dosage of the deionized water 2 is determined by adopting an isometric impregnation method;

and step 3: and (3) soaking the carrier in the step (1) into the soaking solution in the step (2), wherein the soaking process lasts for 12 hours, and after the soaking is finished, the material is placed into an oven and dried at 90 ℃ to constant weight to obtain the catalyst.

Example 3

step 1: adding titanium dioxide, pseudo-boehmite, cobalt molybdate and deionized water 1 into a kneader for kneading, obtaining a first material after kneading, pouring the first material into a strip extruding machine for extruding strips, drying the extruded strips at 100 ℃, and calcining at 700 ℃ to obtain a carrier, wherein the mass ratio of the titanium dioxide to the pseudo-boehmite is 1:10, the addition amount of the cobalt molybdate is 1% of the sum of the mass of the titanium dioxide and the pseudo-boehmite, and the addition amount of the deionized water 1 is 15% of the total mass of the first material.

Step 2: stirring and dispersing palladium acetate, magnesium perchlorate and zirconium oxychloride in deionized water 2 at 60 ℃ to obtain impregnation liquid, wherein the addition amount of the palladium acetate is 1% of the mass of the carrier, the molar ratio of the addition amount of the magnesium perchlorate to the palladium acetate is 1:1, the addition amount of the zirconium oxychloride is 0.1% of the mass of the carrier, and determining the using amount of the deionized water 2 by adopting an isometric impregnation method;

and step 3: and (3) soaking the carrier in the step (1) into the soaking solution in the step (2), wherein the soaking process lasts for 24 hours, and after the soaking is finished, the material is put into an oven and dried at 120 ℃ to constant weight to obtain the catalyst.

Example 4

step 1: adding titanium dioxide, pseudo-boehmite, iron molybdate and deionized water 1 into a kneader for kneading, obtaining a first material after kneading, pouring the first material into a strip extruding machine for extruding strips, drying the extruded strips at 100 ℃, and calcining at 300 ℃ to obtain a carrier, wherein the mass ratio of the titanium dioxide to the pseudo-boehmite is 1:1, the adding amount of the iron molybdate is 0.1 percent of the sum of the mass of the titanium dioxide and the pseudo-boehmite, and the adding amount of the deionized water 1 is 5 percent of the total mass of the first material.

Step 2: stirring and dispersing palladium nitrate, cobalt perchlorate and zirconium oxychloride in deionized water 2 at 20 ℃ to obtain impregnation liquid, wherein the addition amount of the palladium nitrate is 0.1 percent of the mass of the carrier, the molar ratio of the addition amount of the cobalt perchlorate to the palladium nitrate is 10:1, the addition amount of the zirconium oxychloride is 0.5 percent of the mass of the carrier, and the dosage of the deionized water 2 is determined by adopting an isometric impregnation method;

Example 5

step 1: adding titanium dioxide, pseudo-boehmite, manganese molybdate and deionized water 1 into a kneading machine for kneading, obtaining a first material after kneading, pouring the first material into a strip extruding machine for extruding strips, drying the extruded strips at 100 ℃, and calcining at 500 ℃ to obtain a carrier, wherein the mass ratio of the titanium dioxide to the pseudo-boehmite is 1:1, the adding amount of the manganese molybdate is 0.1 percent of the sum of the mass of the titanium dioxide and the pseudo-boehmite, and the adding amount of the deionized water 1 is 10 percent of the total mass of the first material.

Step 2: stirring and dispersing palladium sulfate, chromium perchlorate and zirconium oxychloride in deionized water 2 at 40 ℃ to obtain impregnation liquid, wherein the addition amount of the palladium sulfate is 0.5 percent of the mass of the carrier, the molar ratio of the addition amount of the chromium perchlorate to the addition amount of the palladium chloride is 1:1, the addition amount of the zirconium oxychloride is 0.1 percent of the mass of the carrier, and the dosage of the deionized water 2 is determined by adopting an isometric impregnation method;

Example 6

step 1: adding titanium dioxide, pseudo-boehmite, chromium molybdate and deionized water 1 into a kneader for kneading, obtaining a first material after kneading, pouring the first material into a strip extruding machine for extruding strips, drying the extruded strips at 100 ℃, and calcining at 700 ℃ to obtain the carrier, wherein the mass ratio of the titanium dioxide to the pseudo-boehmite is 1:1, the addition amount of the chromium molybdate is 0.1 percent of the sum of the mass of the titanium dioxide and the pseudo-boehmite, and the addition amount of the deionized water 1 is 15 percent of the total mass of the first material.

Step 2: stirring and dispersing palladium chloride, manganese perchlorate and zirconium oxychloride in deionized water 2 at 60 ℃ to obtain an impregnation solution, wherein the addition amount of the palladium chloride is 1 percent of the mass of the carrier, the molar ratio of the addition amount of the manganese perchlorate to the palladium chloride is 20:1, the addition amount of the zirconium oxychloride is 1 percent of the carrier, and the dosage of the deionized water 2 is determined by adopting an isometric impregnation method;

Example 7

step 1: adding titanium dioxide, pseudo-boehmite, tungsten molybdate and deionized water 1 into a kneader for kneading, obtaining a first material after kneading, pouring the first material into a strip extruding machine for extruding strips, drying the extruded strips at 100 ℃, and calcining at 300 ℃ to obtain a carrier, wherein the mass ratio of the titanium dioxide to the pseudo-boehmite is 1:1, the addition amount of the tungsten molybdate is 0.1 percent of the sum of the mass of the titanium dioxide and the pseudo-boehmite, and the addition amount of the deionized water 1 is 5 percent of the total mass of the first material.

Step 2: stirring and dispersing palladium acetate, nickel perchlorate and zirconium oxychloride in deionized water 2 at 20 ℃ to obtain a steeping fluid, wherein the addition amount of the palladium chloride is 0.1 percent of the mass of the carrier, the molar ratio of the addition amount of the nickel perchlorate to the palladium acetate is 10:1, the addition amount of the zirconium oxychloride is 0.5 percent of the mass of the carrier, and the dosage of the deionized water 2 is determined by adopting an isovolumetric dipping method;

Example 8

step 1: adding titanium dioxide, pseudo-boehmite, nickel molybdate and deionized water 1 into a kneader for kneading, obtaining a first material after kneading, pouring the first material into a strip extruding machine for extruding strips, drying the extruded strips at 100 ℃, and calcining at 500 ℃ to obtain a carrier, wherein the mass ratio of the titanium dioxide to the pseudo-boehmite is 1:1, the addition amount of the nickel molybdate is 0.1 percent of the sum of the mass of the titanium dioxide and the pseudo-boehmite, and the addition amount of the deionized water 1 is 15 percent of the total mass of the first material.

Step 2: stirring and dispersing palladium sulfate, cobalt perchlorate and zirconium oxychloride in deionized water 2 at 40 ℃ to obtain impregnation liquid, wherein the addition amount of palladium chloride is 0.5 percent of the mass of the carrier, the molar ratio of the addition amount of cobalt perchlorate to palladium sulfate is 1:1, the addition amount of zirconium oxychloride is 0.1 percent of the mass of the carrier, and the dosage of the deionized water 2 is determined by adopting an isometric impregnation method;

Example 9

step 1: adding titanium dioxide, pseudo-boehmite, iron molybdate and deionized water 1 into a kneader for kneading, obtaining a first material after kneading, pouring the first material into a strip extruding machine for extruding strips, drying the extruded strips at 100 ℃, and calcining at 700 ℃ to obtain a carrier, wherein the mass ratio of the titanium dioxide to the pseudo-boehmite is 1:1, the adding amount of the iron molybdate is 0.1 percent of the sum of the mass of the titanium dioxide and the pseudo-boehmite, and the adding amount of the deionized water 1 is 10 percent of the total mass of the first material.

Step 2: stirring and dispersing palladium nitrate, cobalt perchlorate and zirconium oxychloride in deionized water 2 at 60 ℃ to obtain impregnation liquid, wherein the addition of the palladium chloride is 1% of the mass of the carrier, the molar ratio of the addition of the cobalt perchlorate to the addition of the palladium chloride is 20:1, the addition of the zirconium oxychloride is 1% of the mass of the carrier, and the dosage of the deionized water 2 is determined by adopting an isometric impregnation method;

Example 10

This example is a performance evaluation of liquid phase chlorine-free catalysts No. 1-9 prepared in examples 1-9 and catalysts No. 1a, 1b and 1c prepared in comparative examples 1-3.

The synthesis reaction of the experimental case adopts a low-pressure fixed bed reactor and adopts gas phase CO coupling and regeneration. The prior process flow for synthesizing dimethyl carbonate specifically comprises the following steps:

(1) adding NO and O₂Respectively introducing anhydrous methanol into a packed tower for reaction to obtain a component CH₃ONO, NO and N₂Wherein the reaction pressure is 0.6MPa, the reaction temperature is 20 ℃, and the space velocity is 2800h^-1；NO。O₂The molar ratio of the anhydrous methanol to the anhydrous methanol is 5.9:1:5, nitrogen is used as balance gas, and the volume of the balance gas is CO and O₂1.5 times the total volume. Wherein, the NO is enough and the absolute methanol is excessive. The height of the packed tower is 1500mm, the diameter is 120 +/-5 mm, the flow rate of a liquid phase is 50ml/min, the materials are fed from the upper section of the packed tower and circulate from top to bottom, the gas phase is fed from the lower section of the packed tower, and the product is discharged from the middle part;

(2) mixing the first mixed gas and CO, introducing into a fixed bed reactor as raw material gas, wherein the pressure of a catalyst bed layer is 0.5Mpa, the temperature of a reaction bed layer is 125 ℃, and the volume space velocity is 3500h^-1And the retention time is 1.5s, and finally the dimethyl carbonate product is obtained, wherein the gas inlet quantity comprises the following components in percentage by volume: CO 11.12%, N₂ 57.68％、NO 11.56％、 CH₃19.64% of ONO, and the fixed bed reactor is a tubular reactor loaded with catalyst, the inner diameter of the tubular reactor is 50mm, the length of the tubular reactor is 500mm, and the catalyst loading is 10 ml.

(3) Gas phase composition analysis

(4) The gas phase component analysis was performed on-line using Shimadzu GC-2014C gas chromatograph.

(5) Analysis of liquid phase Components

(6) Liquid phase product analysis of the reaction was also analyzed using Shimadzu GC-2014C with a vaporization chamber.

(7) Coupling of CH to CO in the gas phase₃The calculations for the evaluation of the catalyst performance for the ONO synthesis of DMC show that:

(8) CO conversion (x) — (mol) CO converted/CO fed (mol) x 100%

(9) DMC selectivity(s) ═ amount of product DMC (mol)/amount of total product (mol). times.100%

(10) Mass space-time yield of DMC (sty) — weight of product DMC (g) × product DMC content%/[ catalyst volume (L) × time (h) ] × 100%

(11) The evaluation time of the implementation cases is 500h

The results of the performance evaluation are shown in the following table:

according to the results of Table 1, the initial CO conversion when DMC was synthesized by the methanol No. 1-9 gas phase catalysts prepared in examples 1-9 was 25.21% -37.66%; DMC selectivity was 89.34% -97.24%; the DMC space-time yield is 564.87-843.83g (g/Lcat h), and the CO conversion rate after 500h is evaluated to be 20.92% -35.93%; DMC selectivity is 83.39% -95.15%; the DMC space-time yield is 468.75-805.07g (g/Lcat h).

The patent TiO can be known from example 1 and comparative example 1a₂Is used as a carrier, and the doping effect of the transition metal element Mo is due to Mo⁶⁺(r ═ 0.062nm) with Ti⁴⁺(r ═ 0.068nm) has a similar ionic radius, enabling it to enter the TiO₂Lattice of (2) in place of Ti⁴⁺In the position of (2), forming a new chemical bond and in the TiO₂The new energy level is introduced into the forbidden band, the activation energy required by the DMC reaction is reduced, and the DMC conversion rate is improved. FIGS. 4 to 7 are SEM pictures of the catalyst of example 1 after evaluation for 500h, from which the catalyst has relatively uniform voids and intact crystal lattice, illustrating the good impregnation effect, FIG. 8 is an EDS spectrum of a cross section of the catalyst, from which EDS data it can be seen that Mo is present in the Ti lattice structure, FIG. 9 is an infrared spectrum, from which it can be seen that Mo is present at 650cm^-1Has a stronger Ti-O stretching vibration peak at 1600-1700cm^-1Is a strong stretching vibration peak of Ti-O-MoIt is clear that Mo has been successfully doped into TiO₂The lattice forms new chemical bonds, thereby validating the previous theory.

Compared with the catalyst in example 1, the catalyst No. 1b does not contain perchlorate, loses the characteristic of perchlorate Lewis acid, and does not have strong electricity-absorbing ClO₄ ^－Anions and metal atoms with empty d-orbitals, resulting in the bonding of CO to form-COOCH₃The tendency becomes weaker. The production of the by-products dimethoxymethane and methyl formate is increased, the CO conversion rate and DMC selectivity are obviously lower and very unstable, and the catalyst performance is greatly reduced after 500 hours.

The comparison of the catalysts of example 1 and comparative example 1c shows that the ratio of the CO conversion to the DMC selectivity is much higher after the zirconium oxychloride is added in the examples. The reason is that the oxidation generated by the synergism of the zirconium oxychloride and the perchlorate radical can continuously lead the active center Pd²⁺The ions maintain the positive 2 valence state, so that the service life of the catalyst is longer.

FIGS. 10 and 11 are XPS spectra of the catalysts of example 1 and comparative example 1c after 500h evaluation, respectively, and it can be seen from FIG. 10 that the catalyst of example 1 has a higher Pd strength at 342eV after 500h evaluation²⁺Peak, higher intensity Pd at 338ev⁴⁺And Pd at 335ev⁰The peak is very weak, and FIG. 11 comparative example 1c has a higher intensity Pd at 342ev²⁺Peak, and Pd at 335ev⁰The peak is also very strong, which indicates that the Pd in comparative example 1C has been mostly reduced to the 0 valence state, which is also the main reason for the low conversion selectivity of the comparative example, and the large reduction of Pd in the active center to the 0 valence state also indicates the low lifetime.

In fig. 12, a and b are XRD spectra before and after 500h of catalyst evaluation of example 1, respectively, and it can be seen from the spectra that the characteristic peak positions of XRD before and after the evaluation are not changed, but the peak intensities are reduced to some extent, which indicates that the evaluation process has an effect on the crystallinity of the catalyst, but has little effect, i.e. the catalyst has a long life.

Relational terms such as "first" and "second," and the like, may be used solely to distinguish one element from another element having the same name, without necessarily requiring or implying any actual such relationship or order between such elements.

The invention has been described in an illustrative manner, and it is to be understood that any simple variations, modifications or other equivalent changes which can be made by one skilled in the art without departing from the spirit of the invention fall within the scope of the invention.

Claims

1. A catalyst for gas phase synthesis of dimethyl carbonate is characterized in that the catalyst comprises a carrier and an active component, wherein;

the auxiliary agent is molybdate.

2. The catalyst of claim 1, wherein the soluble palladium salt is one or more of palladium chloride, palladium nitrate, palladium acetate, palladium sulfate; the molybdate is one or more of ammonium molybdate, cobalt molybdate, iron molybdate, manganese molybdate, chromium molybdate, nickel molybdate and tungsten molybdate; the perchlorate is one or more of copper perchlorate, magnesium perchlorate, cobalt perchlorate, chromium perchlorate, manganese perchlorate and nickel perchlorate.

3. A preparation method of a catalyst for gas phase synthesis of dimethyl carbonate is characterized by comprising the following steps:

the auxiliary agent is molybdate;

4. The method according to claim 3, wherein the drying temperature of the first granules is 100 ℃.

5. The preparation method according to claim 3, wherein the process of uniformly mixing the titanium dioxide, the pseudo-boehmite, the auxiliary agent and the first deionized water in the step 1 is completed by adopting a kneader; and the process of granulating the first material is finished by adopting a strip extruding machine.

6. The preparation method according to claim 3, wherein in the step 2, the soluble palladium salt, the perchlorate and the zirconium oxychloride are stirred and dispersed in the first deionized water at 20-60 ℃ to obtain the impregnation solution.

7. The preparation method according to claim 3, wherein the soluble palladium salt is one or more of palladium chloride, palladium nitrate, palladium acetate, palladium sulfate; the molybdate is one or more of ammonium molybdate, cobalt molybdate, iron molybdate, manganese molybdate, chromium molybdate, nickel molybdate and tungsten molybdate; the perchlorate is one or more of copper perchlorate, magnesium perchlorate, cobalt perchlorate, chromium perchlorate, manganese perchlorate and nickel perchlorate.

8. The preparation method according to claim 3, wherein in the step 3, the impregnated carrier is dried at 60-120 ℃ to a constant weight.

9. A dimethyl carbonate synthesis method is characterized in that methyl nitrite and CO are used as raw materials, and dimethyl carbonate is obtained through reaction synthesis under the action of the catalyst for gas-phase synthesis of dimethyl carbonate, which is obtained through the preparation method of any one of claims 3 to 8;

10. The dimethyl carbonate synthesis method according to claim 9, wherein the reaction synthesis process is completed in a fixed bed reactor, and the pressure of a catalytic bed layer is 0.2-0.7 MPa.