CN1141179C - Catalyst for gas-phase synthesis of oxalate and its preparing process - Google Patents

Abstract

The present invention discloses a catalyst for the gas phase synthesis of oxalic ester and a method for preparing the catalyst. The catalyst is prepared by that alpha-Al2O3 is used as a catalyst carrier, cerium metal and palladium metal are used as active constituents, and an immersion method is adopted. The catalyst has favorable effects in the reaction that carbon monoxide and nitrite ester are synthesized into dimethyl oxalate and diethyl oxalate. Experiments indicate that Pd-Ce/alpha-Al2O3 not only has high reaction activity and selectivity, but also has the advantages of long service life, stable reaction and easy control.

Description

Catalyst for vapor phase synthesis of oxalate and preparation method thereof

technical field

The invention relates to a catalyst and a preparation method thereof, in particular to a catalyst for gas-phase synthesis of oxalate and a preparation method thereof.

Background technique

Oxalate is an important chemical raw material, which can be used to prepare oxalic acid, ethylene glycol, oxamide and intermediates of some drugs and dyes.

At present, dialkyl oxalate is produced domestically by esterification and dehydration of oxalic acid and alkyl alcohol with toluene. One of its main raw materials, oxalic acid, is produced by the sodium formate method. Sodium formate is synthesized by carbon monoxide and sodium hydroxide at 160°C and 16-20kgf/ ^cm2 pressure, and then concentrated and dehydrogenated at 400 to form sodium oxalate, which is then reacted with lead sulfate Generate lead oxalate, further acidify with sulfuric acid to obtain crude oxalic acid, and finally coagulate and settle with barium carbonate and 1% polyacrylamide to generate high-quality oxalic acid. The production process is long and the cost is high, so it is urgent to find a new production method. The gas-phase catalytic synthesis of oxalate from carbon monoxide and nitrite has opened up a new and important way of carbon-chemical production of oxalate. Since the 1980s, new developments in the synthesis of oxalate esters have been reported at home and abroad. JP8242.656 Separate Patent Gazette first reported the process flow for the synthesis of dimethyl oxalate from carbon monoxide and methyl nitrite using a platinum group metal supported catalyst. The space-time yield of the catalyst was 432g/Lh. After 480 hours of continuous reaction, the yield was high. reduce. Subsequently, many patents have successively reported catalysts composed of additives such as Mo, Ni, Ti, Fe, Ga, Cu, _Na2O , and _SiO2 respectively added to the catalyst components, which are applied to the gas phase synthesis of carbon monoxide and nitrite In the process of dimethyl oxalate, diethyl oxalate and diisopropyl oxalate, the space-time yield is still low. For the Pd-Ti/Al ₂ O ₃ catalyst reported in US Patent No. 4,507,494, at a pressure of 2.5kg/cm ³ , 115-120°C and a space velocity of 3000h ^-1 , the initial feed gas composition: CH ₃ ONO: 10% CO: 20% CH ₃ OH: 4% NO: 3% N ₂ : 63% and other conditions, continuous reaction for 950 hours, the space-time yield of dimethyl oxalate is 429-462g/Lh, the selectivity of dimethyl oxalate from CO up to 95%.

Contents of the invention

The technical problem to be solved in the present invention is to develop a highly efficient catalyst for oxalate ester synthesis.

Technical solutions:

The active components of the catalyst in the invention are metal palladium (Pd) and metal cerium (Ce), and the carrier thereof is α-Al ₂ O ₃ . Wherein the metal palladium content is preferably 0.2-2.0% of the carrier weight, the best is 0.8-1.3%; the metal cerium content is preferably 0.05-1% of the carrier weight, the best is 0.1-0.6%; the carrier preferably has a porous structure The specific surface area of α-Al ₂ O ₃ is preferably 3-30m ² /g, most preferably 8-12m ² /g.

The method for preparing catalyst of the present invention comprises the steps:

(1) Prepare an aqueous solution with metal cerium (Ce) halides, nitrates, acetates or oxalates and water, the concentration of the aqueous solution is 0.003M-0.07M, and the carrier α-Al ₂ O ₃ in the aqueous solution After soaking in the medium for 4-15 hours, take it out and dry it, and then roast it for 3-8 hours to obtain a solid;

(2) Halides, nitrates, acetates or oxalates of metal palladium (Pd) and water are formulated into an aqueous solution, and the concentration of the aqueous solution is 0.03M-0.2M. After soaking in the medium for 4-15 hours, take it out and dry it, and then the catalyst of the present invention can be made.

In order to prevent the hydrolysis of metal cerium ions to form hydroxide or oxide precipitation, the same acid as the anion of the metal salt can be added to the aqueous solution of metal cerium halide, nitrate, acetate or oxalate to make the aqueous solution The pH value is 5-7.

The using method of catalyst of the present invention:

The catalyst needs to be reduced before use, the reducing gas is hydrogen or carbon dioxide, the flow rate is 30-70ml/min.g.cat, the reduction temperature is 250-350°C, the reduction time is 2-5 hours, until the outlet water until constant.

The reaction formula of carbon monoxide and nitrite gas-phase catalytic synthesis of oxalate is as follows:

Wherein: R is an alkane group.

The required nitrite for the reaction is generated by the reaction of sodium nitrite, sulfuric acid and alcohol or nitric oxide, oxygen and alcohol, wherein the alcohol can be selected from any saturated fatty alcohol containing 1-8 carbon atoms, methanol, ethanol and butane Alcohol is the best. In addition to generating the main product oxalate, the reaction also generates nitric oxide as a by-product. Nitric oxide can be recycled by reacting with oxygen and alcohol to generate nitrite. The reaction formula is as follows:

Two reaction cycles are carried out, and its total reaction formula is as follows:

Gas-phase synthesis of oxalate esters uses a fixed-bed reactor. The raw material gas carbon monoxide and nitrite are diluted with nitrogen gas. The contact time between the raw material gas and the catalyst is 0.2-4 seconds. The reaction temperature is controlled at 90-160 ° C. The CO and RONO content in the raw material gas It can be changed within a wide range, 10-60% for CO and 5-25% for RONO.

Specific implementation method:

The nitrate of metal cerium (Ce) and water are prepared into an aqueous solution, and the concentration of the aqueous solution is 0.003M-0.07M. In order to prevent the hydrolysis of metal ions to form hydroxide or oxide precipitation, nitric acid is added to the aqueous solution to make the pH of the aqueous solution Values are 5-7. Soak the carrier α-Al ₂ O ₃ with a porous structure and a specific surface area of 3-30m ² /g in the impregnation solution for 4-15 hours, dry it in a water bath to become a solid, and then dry the solid at 120°C for 10- For 15 hours, bake at 300-650°C for 3-8 hours, then soak the solid in an aqueous solution of metal palladium (Pd) halide with a concentration of 0.03M-0.2M for 4-15 hours, and then dry it at 120°C After 10-15 hours, the Pd-Ce/α-Al ₂ O ₃ catalyst can be made.

The catalyst of the present invention selects α-Al ₂ O ₃ as the catalyst carrier, and uses metal cerium and metal palladium as active components. The catalyst is prepared by an impregnation method. The catalyst synthesizes oxalic acid di Both methyl ester and diethyl oxalate have achieved good results. Experiments have proved that Pd-Ce/α-Al ₂ O ₃ not only has high reactivity and selectivity, but also has long life, stable reaction and easy control.

Below by embodiment the present invention will be further described:

Example 1,

Weigh 10g of α-Al ₂ O ₃ , prepare the catalyst according to the content of 1wt% Pd+0.3wt% Ce/α-Al ₂ O ₃ , the steps are as follows: choose Ce(NO ₃ ) ₃ , prepare the impregnation solution according to the Ce load, In order to prevent metal ions from being hydrolyzed to form hydroxides or oxides, a small amount of nitric acid is added to the impregnation solution to make the impregnation solution PH = 5, and then the carrier α-Al ₂ O ₃ with a specific surface area of 3m ² /g is added to the impregnation solution Soak in water for 12 hours, after fully absorbed, dry in water bath to become solid, then dry the solid at 120°C for 12 hours, roast at 300-650°C for 6 hours, and then prepare the solid in _PdCl2 according to the loading capacity of Pd Soak in the impregnation solution for 12 hours, and dry at 120°C for 12 hours to prepare the Pd-Ce/α-Al ₂ O ₃ catalyst.

Example 2,

Weigh 10g of α-Al ₂ O ₃ , and prepare the catalyst according to the content of 1wt% Pd+0.1wt% Ce/α-Al ₂ O ₃ , the steps are as follows: choose Ce(NO ₃ ) ₃ , prepare the impregnation solution according to the Ce load, In order to prevent metal ions from being hydrolyzed to form hydroxides or oxides, a small amount of nitric acid is added to the impregnating solution to make the impregnating solution PH = 7, and then the carrier α-Al ₂ O ₃ with a specific surface area of 30m ² /g is added to the impregnating solution Soak in water for 12 hours, after fully absorbed, dry in a water bath to become a solid, then dry the solid at 120°C for 12 hours, and then bake the solid at 300-650°C for 6 hours, then put the solid in Pd(NO ₃ ) ₂ is formulated to be immersed in the impregnating solution for 12 hours, and then dried at 120°C for 12 hours to prepare the Pd-Ce/α-Al ₂ O ₃ catalyst.

Example 3, the test of catalyst activity:

The catalyst is placed in a quartz glass reactor with an inner diameter of 20mm. The reactor is equipped with a thermocouple sleeve. The catalyst loading is 2ml. The raw material gas passes through the catalyst bed from top to bottom, and the product dimethyl oxalate is drawn out from the bottom of the reactor. . Before the catalyst participates in the reaction, it needs to undergo hydrogen reduction treatment. The reduction temperature is 350°C, the reduction time is 3 hours, and the hydrogen flow rate is 50ml/min. The optimal flow ratio of reaction gas carbon monoxide and nitrite is 1.3, the reaction is carried out under normal pressure, the reaction temperature is 140°C, the single-pass conversion rate of carbon monoxide reaches 78%, and the space-time yield of dimethyl oxalate is 821g/L.h, Dimethyl oxalate and formaldehyde were not detected in the product.

Claims (5)

1. The catalyst for synthesizing oxalate in gas phase is characterized in that active components of the catalyst are metal palladium and metal cerium, and a carrier of the catalyst is α -Al₂O₃Wherein: the active component contains 0.2-2.0% of metal palladium and 0.05-1% of metal cerium.

2. The catalyst of claim 1, wherein the support is α -Al having a porous structure₂O₃。

3. The catalyst of claim 2, wherein the support α -Al₂O₃The specific surface area is 3-30m²/g。

4. The method for preparing any one of the catalysts according to claims 1 to 3, comprising the steps of:

(1) preparing aqueous solution of halide, nitrate, acetate or oxalate of cerium metal and water with the concentration of 0.003-0.07M, and mixing the carrier α -Al₂O₃Soaking in the aqueous solution for 4-15 hours, taking out, drying at 120 ℃ for 10-15 hours, and roasting at 300-650 ℃ for 3-8 hours to obtain a solid;

(2) preparing an aqueous solution of halide, nitrate, acetate or oxalate of metallic palladium and water, wherein the concentration of the aqueous solution is 0.03-0.2M, soaking the solid obtained in the step (1) in the aqueous solution for 4-15 hours, taking out the solid, and drying the solid at 120 ℃ for 10-15 hours to obtain the catalyst.

5. The method according to claim 4, wherein the same acid as an anion of the metal salt is added to an aqueous solution of a halide, nitrate, acetate or oxalate of cerium metal to adjust the pH of theaqueous solution to 5 to 7.