Synthesis method of dimethyl oxalate

Abstract

The invention relates to a synthesis method of dimethyl oxalate, and mainly solves the technical problems of high reaction hot spot temperature, poor dimethyl oxalate selectivity and low space time yield in the prior art. According to the technical scheme, carbon monoxide, nitrogen and methyl nitrite (MN) are used as raw materials, and under the conditions that the inlet temperature is 70-100 DEG C, the volume space velocity is 1000-5000h <-1 >, the CO molar concentration is 10-40%, the CO / MN molar ratio is 1.0-3.0 and the reaction pressure is 0.05-2.0 Mpa, the raw materials pass through a Pd catalyst diluted by small balls with low specific surface area, large aperture and low acid content, the hot-spot temperature of a bed is lower than 125 DEG C, and the reaction is carried out for 1-2 hours, so that the methyl nitrite (MN) is obtained. According to the technical scheme, the problems are well solved, the selectivity of the dimethyl oxalate is larger than 98% in the long-time operation process, the space time yield of the dimethyl oxalate is larger than 750 g / (L.h), and the method can be used for industrial production of synthesizing the dimethyl oxalate through oxidative coupling of carbon monoxide.

Description

Technical Field

[0001] The present invention relates to a method for synthesizing dimethyl oxalate. Background Art

[0002] Oxalate esters are important chemical raw materials used in the preparation of oxalic acid, ethylene glycol, carbonates, pharmaceutical and dye intermediates, plastic accelerators, and solvents. The traditional synthesis of dimethyl oxalate involves the esterification of oxalic acid with methanol. Oxalic acid, one of its main raw materials, is produced using the sodium formate process. Carbon monoxide and sodium hydroxide are reacted at 160°C and 18-20 kg pressure to synthesize sodium formate. This is then concentrated and dehydrogenated at 400°C to form sodium oxalate, which then reacts with lead sulfate to form lead oxalate. This is further acidified with sulfuric acid to produce crude oxalic acid, which is then coagulated and precipitated with barium carbonate and 1% polyacrylamide to obtain refined oxalic acid. However, this production process is lengthy, energy-intensive, polluting, and costly, necessitating the development of new production processes. The synthesis of dimethyl oxalate by vapor-phase catalytic coupling of CO and methyl nitrite has opened up a new route for producing oxalic acid from carbon-one feedstocks. Since the 1980s, new advances in oxalic acid synthesis have been reported internationally.

[0003] Japanese Patent JP8242656 first disclosed a process for synthesizing dimethyl oxalate from CO and methyl nitrite using a platinum group metal-supported catalyst. The catalyst had a space-time yield of 432 g / (L·h), and the yield did not decrease after 480 hours of continuous reaction.

[0004] US Patent No. 4334433 discloses Pd-Mo / Al2O3 and Pd-Ni / Al2O3 catalysts at atmospheric pressure, 110°C and a space velocity of 2000h -1 Under the conditions of the initial raw gas composition of CH3ONO-15%, CO-20%, CH3OH-15%, NO-3%, and N2-47% (volume concentration, all gas concentrations below refer to volume concentrations), the space-time yield of dimethyl oxalate is 400 g / (L·h), and the selectivity of dimethyl oxalate from CO reaches 95%.

[0005] US Patent No. 4507494 discloses a Pd-Ti / Al2O3 catalyst which is heated at a pressure of 0.24 MPa, 115-120°C and a space velocity of 3000 h -1 Under the conditions of initial raw gas composition: CH3ONO-10%, CO-20%, CH3OH-4%, NO-3%, N2-63%, the reaction was continued for 950 hours, the space-time yield of dimethyl oxalate was 429-462g / (L·h), and the selectivity of dimethyl oxalate generated from CO reached 95%.

[0006] Chinese patent CN95116136.9 discloses a catalyst for oxalate synthesis. The catalyst, prepared using a Pd-Zr / Al2O3 impregnation method and using Zr as a catalyst promoter, was used in a fixed-bed reactor to synthesize oxalate from CO and nitrite. However, the catalyst in this invention exhibited low oxalate yields and high impurity requirements for the feed gas. While the selectivity for the product oxalate was 95%, the maximum single-pass conversion of nitrite was only 64%.

[0007] Since then, a large number of patents have reported catalysts composed of additives such as Mo, Ni, Ti, Fe, Ga, Cu, Na2O and SiO2 added to the catalyst components, which were used in the process of synthesizing oxalate from CO and methyl nitrite, but the space-time yields were relatively low.

[0008] Currently, domestic and international patents on the synthesis of dimethyl oxalate by the oxidative coupling of carbon monoxide mainly address technical issues such as low dimethyl oxalate space-time yield and poor selectivity from the perspectives of catalyst formulation, production process, and reactor design. However, there are no patent reports on related technical issues such as how to effectively control the hotspot temperature of the bed to improve catalyst activity and the space-time yield of dimethyl oxalate. Summary of the Invention

[0009] The present invention aims to solve the technical problems in the prior art of high reaction hotspot temperature, poor dimethyl oxalate selectivity and low space-time yield. The invention provides a new method for synthesizing dimethyl oxalate from CO, which controls the bed temperature within a relatively low temperature range, achieves high selectivity and high space-time yield of dimethyl oxalate, and is easy to control the reaction.

[0010] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0011] Carbon monoxide, nitrogen and methyl nitrite (MN) are used as raw materials. Under effective reaction conditions, the raw materials are brought into contact with the catalyst in a fixed bed reactor containing a Pd catalyst to generate dimethyl oxalate. The hot spot temperature of the reactor bed is lower than 125°C.

[0012] In the above technical solution, the molar concentration of CO in the raw material is 5-40%, and the molar ratio of CO / MN is 1.0-3.0;

[0013] In the above technical solution, preferably, the molar concentration of CO in the raw material is 10-30%, and the molar ratio of CO / MN is 1.2-2.5.

[0014] In the above technical solution, the effective reaction conditions are: the fixed bed reactor inlet temperature is 70-100 ° C, the volume space velocity is 1000-5000h -1 , the reaction pressure is 0.05-2.0Mpa.

[0015] In the above technical solution, preferably, the inlet temperature is 80-90°C, the volume space velocity is 1500-4000h -1 , the reaction pressure is 0.1-1.0Mpa.

[0016] In the above technical solution, the Pd-containing catalyst preferably uses alumina as a carrier; the Pd content in the catalyst is 0.1-5.0 wt% based on the weight of the carrier.

[0017] In the above technical solution, the Pd-containing catalyst comprises dilution beads, and the dilution beads are selected from at least one of aluminum oxide and silicon oxide.

[0018] In the above technical solution, the volume dilution ratio of the dilution beads and the catalyst is (0.25-5):1; preferably, the dilution ratio of the dilution beads and the catalyst is (0.5-4):1.

[0019] In the above technical solution, the specific surface area of ​​the dilution ball is 0.02-10m 2 / g, and the average pore size is 30-100nm.

[0020] In the above technical solution, the surface acid content of the diluted beads is 0.01-1 mmol / g.

[0021] As is well known, the reaction of CO and nitrite synthesizing oxalate is affected by the properties such as the dispersion of active component Pd on the carrier surface, the specific surface area and pore size, and surface acid amount of the carrier in the catalyst. In the prior art, the catalyst performance can be improved by catalyst optimization preparation to reach the purpose of improving dimethyl oxalate productive rate. But the reaction of CO and nitrite synthesizing oxalate belongs to strong exothermic reaction, and the surface acid amount on the catalyst simultaneously also can cause methyl nitrite to decompose, and the exothermic heat of this reaction is larger than the exothermic heat of CO and nitrite synthesizing oxalate reaction. The inventor has found after deliberation that the heat released by this reaction process can be quickly evacuated through diffusion and directly affect the selectivity and space-time yield of oxalate. Adopt the bead dilution and filling technology of low specific surface area, macropore, low surface acid amount of the present invention, the hotspot temperature of bed can be obviously reduced, thereby realize the high selectivity and high space-time yield of dimethyl oxalate, reaction is easy to control simultaneously, has solved the problem that puzzled technical personnel for a long time about product oxalate selectivity, space-time yield and reaction heat removal coupling well.

[0022] According to the technical solution of the present invention, the dilution pellets are selected from at least one of aluminum oxide and silicon oxide; the catalyst is Pd / Al2O3, the Pd content is 0.1-5.0% based on the weight of the carrier, and the balance is the carrier; the dilution ratio of the dilution pellets to the catalyst is (0.5-4):1 (volume ratio); the CO molar concentration is 10-30%, the CO / MN molar ratio is 1.2-2.5, and the balance is nitrogen raw material, at a reaction inlet temperature of 80-90°C and a volume space velocity of 1500-4000h -1 The reaction pressure is 0.1-1.0 MPa, the hot spot temperature of the reactor bed is lower than 125°C, the selectivity of the reaction product dimethyl oxalate is greater than 98%, and the space-time yield of dimethyl oxalate is greater than 750 g / (L·h), achieving good technical results.

[0023] Inlet temperature is a critical parameter in the reaction process. Controlling inlet temperature ensures that the catalyst can initiate the reaction. Hotspot temperature refers to the temperature corresponding to the highest point in the catalyst bed. Although this temperature only reflects the temperature at a specific point within the catalyst layer, it comprehensively reflects the temperature distribution and operating conditions of the catalyst layer. On the same catalyst, assuming other conditions remain unchanged, increasing the inlet temperature will lead to an increase in the hotspot temperature. In addition to being affected by inlet temperature, the hotspot temperature is also affected by factors such as catalyst performance, loading method, catalyst age, and process conditions. For certain highly exothermic reactions, controlling the hotspot temperature is an effective means of regulating reaction conversion and selectivity.

[0024] The present invention will be further described below by way of examples, which however do not limit the scope of the present invention in any way. DETAILED DESCRIPTION

[0025] The present invention will be further described below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention.

[0026] The surface acidity was tested by the Py-IR method: 10 mg of powder sample was pressed into 15-20 mg round pieces for later use, fixed in an infrared cell, and the sample was placed in the in-situ cell and programmed to rise to 400 degrees for 1 hour while evacuating the sample. The sample was then cooled to room temperature and then sampled. The sample was first vacuum-purified (350°C, 1×10 -3 Pa) for 2 hours, cooled to room temperature, and scanned the spectrum as background. After pyridine was adsorbed at room temperature, the temperature was raised to the measurement temperature (fixed point temperature was 200℃, 350℃) for vacuum desorption (1×10 -3 Pa) for half an hour, then cooled to room temperature, and recorded the 1700-1400 cm -1Infrared spectrum in the wavenumber region. The L acid and B acid amounts of the sample measured after desorption at 200℃ are the sum of acids of different strengths, and the L acid and B acid amounts of the sample measured after desorption at 350℃ are the sum of medium strength acid and strong acid. -1 The peak characterizing B acid is 1450 cm -1 The peak represents L acid.

[0027] Specific surface area and average pore size were determined using the low-temperature nitrogen physical adsorption-desorption (BET) method. The experiments were conducted on a Micromeritics TriStar 3000 and ASAP 2020M instrument. Samples were dried at 100°C for 1-2 hours and then degassed under vacuum at 300°C for 4 hours. The adsorption-desorption isotherm was measured at liquid nitrogen temperature using nitrogen as the adsorbent. The specific surface area of ​​the catalyst was calculated using the BET equation, and the pore size distribution was calculated using the BJH method using the desorption curves.

[0028] Calculation method of product selectivity and space-time yield:

[0029] (1) Dimethyl oxalate selectivity:

[0030]

[0031] (2) Space-time yield of dimethyl oxalate:

[0032]

[0033] [Example 1]

[0034] With a specific surface area of ​​5.0m 2 / g, an average pore size of 49nm, and a surface acidity of 0.33mmol / g of alumina as a dilution pellet; using alumina as a carrier, a catalyst with a Pd content of 0.5wt% was prepared by a loading method, the dilution ratio of the dilution pellet to the catalyst was 1:4, the total filling volume was 100ml, and the catalyst was required to be reduced with hydrogen at 180°C for 6 hours before use, with a CO molar concentration of 18%, a CO / MN molar ratio of 2.0, and the balance being nitrogen. The reaction was carried out at a reaction inlet temperature of 80°C and a volume space velocity of 1500h -1 Under the condition of a reaction pressure of 0.45 MPa, the raw materials contacted with the diluted catalyst in the fixed bed reactor to react. The reaction results after 120 hours were as follows: the bed hot spot temperature was 112°C, the selectivity of the reaction product dimethyl oxalate was 98.7%, and the space-time yield of dimethyl oxalate was 866 g / (L·h).

[0035] [Example 2]

[0036] With a specific surface area of ​​0.02m 2 / g, an average pore size of 87nm, and a surface acidity of 0.01mmol / g of silicon oxide as a dilution pellet; using aluminum oxide as a carrier, a catalyst with a Pd content of 1.5wt% was prepared by a loading method, the dilution ratio of the dilution pellet to the catalyst was 1:1, the total filling volume was 100ml, and the catalyst was required to be reduced with hydrogen at 180°C for 6 hours before use, with a CO molar concentration of 22%, a CO / MN molar ratio of 1.7, and the balance being nitrogen. The reaction was carried out at a reaction inlet temperature of 84°C and a volume space velocity of 2500h -1 Under the condition of a reaction pressure of 0.25 MPa, the raw materials contacted with the diluted catalyst in the fixed bed reactor to react. The reaction results after 120 hours were as follows: the bed hot spot temperature was 107°C, the selectivity of the reaction product dimethyl oxalate was 99.2%, and the space-time yield of dimethyl oxalate was 944 g / (L·h).

[0037] [Example 3]

[0038] With a specific surface area of ​​3.7m 2 / g, an average pore size of 55nm, and a surface acidity of 0.65mmol / g of alumina as a dilution pellet; using alumina as a carrier, a catalyst with a Pd content of 4.0wt% was prepared by a loading method, the dilution ratio of the dilution pellet to the catalyst was 4:1, the total loading volume was 100ml, and the catalyst was reduced with hydrogen at 180°C for 6 hours before use, with a CO molar concentration of 20%, a CO / MN molar ratio of 1.4, and the balance being nitrogen. The reaction was carried out at a reaction inlet temperature of 75°C and a volume space velocity of 3000h -1 Under the condition of a reaction pressure of 0.33 MPa, the raw materials contacted with the diluted catalyst in the fixed bed reactor to react. The reaction results after 120 hours were as follows: the bed hot spot temperature was 105°C, the selectivity of the reaction product dimethyl oxalate was 99.7%, and the space-time yield of dimethyl oxalate was 1015 g / (L·h).

[0039] [Example 4]

[0040] Taking the specific surface area as 10.0m 2 / g, an average pore size of 31nm, a surface acidity of 0.92mmol / g, and a specific surface area of ​​1.6m 2 / g, an average pore size of 76nm, and a surface acidity of 0.08mmol / g of silicon oxide as a dilution pellet; using aluminum oxide as a carrier, a catalyst with a Pd content of 1.0wt% was prepared by a loading method, the dilution ratio of the dilution pellet to the catalyst was 1:1:1, the total filling volume was 100ml, and the catalyst was required to be reduced with hydrogen at 180°C for 6 hours before use, with a CO molar concentration of 28%, a CO / MN molar ratio of 1.3, and the balance being nitrogen. The reaction was carried out at a reaction inlet temperature of 90°C and a volume space velocity of 3800h -1Under the condition of a reaction pressure of 0.60 MPa, the raw materials contacted with the diluted catalyst in the fixed bed reactor to react. The reaction results after 120 hours were: the bed hot spot temperature was 114°C, the selectivity of the reaction product dimethyl oxalate was 99.4%, and the space-time yield of dimethyl oxalate was 927 g / (L·h).

[0041] [Example 5]

[0042] With a specific surface area of ​​0.05m 2 / g, an average pore size of 63nm, a surface acidity of 0.07mmol / g, and a specific surface area of ​​9.4m 2 / g, an average pore size of 38nm, and a surface acidity of 0.12mmol / g of silicon oxide as a dilution pellet; using aluminum oxide as a carrier, a catalyst with a Pd content of 1.5wt% was prepared by a loading method, the dilution ratio of the dilution pellet to the catalyst was 1:1:2, the total filling volume was 100ml, and the catalyst was required to be reduced with hydrogen at 180°C for 6 hours before use, with a CO molar concentration of 16%, a CO / MN molar ratio of 2.0, and the balance being nitrogen. The reaction was carried out at a reaction inlet temperature of 80°C and a volume space velocity of 1800h -1 Under the condition of a reaction pressure of 0.12 MPa, the raw materials contacted with the diluted catalyst in the fixed bed reactor to react. The reaction results after 120 hours were as follows: the bed hot spot temperature was 117°C, the selectivity of the reaction product dimethyl oxalate was 98.1%, and the space-time yield of dimethyl oxalate was 976 g / (L·h).

[0043] [Example 6]

[0044] With a specific surface area of ​​0.53m 2 / g, an average pore size of 91nm, and a surface acidity of 0.03mmol / g of alumina as a dilution pellet; using alumina as a carrier, a catalyst with a Pd content of 3.5wt% was prepared by a loading method, the dilution ratio of the dilution pellet to the catalyst was 3:1, the total loading volume was 100ml, and the catalyst was reduced with hydrogen at 180°C for 6 hours before use, with a CO molar concentration of 15%, a CO / MN molar ratio of 2.0, and the balance being nitrogen. The reaction was carried out at a reaction inlet temperature of 84°C and a volume space velocity of 2000h -1 Under the condition of a reaction pressure of 0.20 MPa, the raw materials contacted with the diluted catalyst in the fixed bed reactor to react. The reaction results after 120 hours were as follows: the bed hot spot temperature was 108°C, the selectivity of the reaction product dimethyl oxalate was 99.4%, and the space-time yield of dimethyl oxalate was 1007 g / (L·h).

[0045] [Example 7]

[0046] With a specific surface area of ​​3.6m 2 / g, an average pore size of 60nm, and a surface acid amount of 0.47mmol / g of alumina and a specific surface area of ​​7.7m2 / g, an average pore size of 44nm, and a surface acid amount of 0.32mmol / g of silicon oxide were used as dilution beads; a catalyst with a Pd content of 2.5wt% was prepared by a loading method using alumina as a carrier, the dilution ratio of the dilution beads to the catalyst was 3:2:1, the total filling volume was 100ml, and the catalyst was reduced with hydrogen at 180°C for 6 hours before use, with a CO molar concentration of 19%, a CO / MN molar ratio of 1.6, and the balance being nitrogen. The reaction was carried out at a reaction inlet temperature of 90°C and a volume space velocity of 3300h -1 Under the condition of a reaction pressure of 0.40 MPa, the raw materials contacted with the diluted catalyst in the fixed bed reactor to react. The reaction results after 120 hours were as follows: the bed hot spot temperature was 110°C, the selectivity of the reaction product dimethyl oxalate was 99.0%, and the space-time yield of dimethyl oxalate was 895 g / (L·h).

[0047] [Comparative Example 1]

[0048] The steps and conditions of Example 1 were followed, except that the catalyst was loaded directly without dilution in a loading amount of 100 ml. Other conditions and raw materials were the same. The reaction results after 120 hours were: the bed hot spot temperature was 137° C., the selectivity of the reaction product, dimethyl oxalate, was 96.4%, and the space-time yield of dimethyl oxalate was 513 g / (L·h).

[0049] [Comparative Example 2]

[0050] The steps and conditions of Example 1 were followed except that the pellets were diluted to a specific surface area of ​​20.0 m 2 / g, an average pore size of 15nm, and a surface acid content of 39mmol / g alumina. Other conditions and raw materials were the same. The reaction results after 120 hours were: the bed hot spot temperature was 129°C, the selectivity of the reaction product dimethyl oxalate was 90.4%, and the space-time yield of dimethyl oxalate was 447g / (L·h).

[0051] [Comparative Example 3]

[0052] The steps and conditions of Example 2 were followed except that the pellets were diluted to a specific surface area of ​​120 m 2 / g, an average pore size of 8nm, and a surface acid content of 6.5mmol / g of silicon oxide. Other conditions and raw materials were the same. The reaction results after 120 hours were: the bed hot spot temperature was 131°C, the selectivity of the reaction product dimethyl oxalate was 93.4%, and the space-time yield of dimethyl oxalate was 496g / (L·h).

[0053] [Comparative Example 4]

[0054] The steps and conditions of Example 3 were followed, except that the catalyst was loaded directly without dilution in a loading amount of 100 ml. Other conditions and raw materials were the same. The reaction results after 120 hours were: the bed hotspot temperature was 150° C., the selectivity of the reaction product, dimethyl oxalate, was 95.2%, and the space-time yield of dimethyl oxalate was 665 g / (L·h).

[0055] [Comparative Example 5]

[0056] The steps and conditions of Example 2 were followed except that the pellets were diluted to a specific surface area of ​​5 m 2 / g, an average pore size of 102nm, and a surface acid content of 1.5mmol / g of silicon oxide. Other conditions and raw materials were the same. The reaction results after 120 hours were: the bed hot spot temperature was 128°C, the selectivity of the reaction product dimethyl oxalate was 91.4%, and the space-time yield of dimethyl oxalate was 405g / (L·h).

Claims

1. A method for synthesizing dimethyl oxalate, comprising: using carbon monoxide, nitrogen, and methyl nitrite (MN) as raw materials; under effective reaction conditions, the raw materials are contacted with the catalyst in a fixed-bed reactor containing a Pd catalyst to produce dimethyl oxalate; the hot spot temperature of the reactor bed is lower than 125°C.

2. The method for synthesizing dimethyl oxalate according to claim 1, wherein The CO molar concentration in the raw material is 5-40%, and the CO / MN molar ratio is 1.0-3.

0.

3. The method for synthesizing dimethyl oxalate according to claim 2, wherein The CO molar concentration in the raw material is 10-30%, and the CO / MN molar ratio is 1.2-2.

5.

4. The method for synthesizing dimethyl oxalate according to claim 1, wherein The effective reaction conditions are: fixed bed reactor inlet temperature of 70-100 ° C, volume space velocity of 1000-5000h -1 , the reaction pressure is 0.05-2.0Mpa.

5. The method for synthesizing dimethyl oxalate according to claim 4, wherein The inlet temperature is 80-90℃ and the volume space velocity is 1500-4000h -1 , the reaction pressure is 0.1-1.0Mpa.

6. The method for synthesizing dimethyl oxalate according to claim 1, wherein The catalyst is a Pd catalyst using aluminum oxide as a carrier; the Pd content in the catalyst is 0.1-5.0 wt% based on the weight of the carrier.

7. The method for synthesizing dimethyl oxalate according to claim 1, wherein The Pd-containing catalyst comprises dilution beads, which are selected from at least one of aluminum oxide and silicon oxide.

8. The method for synthesizing dimethyl oxalate according to claim 7, wherein The volume dilution ratio of the dilution beads and the catalyst is (0.25-5):1; preferably, the volume dilution ratio of the dilution beads and the catalyst is (0.5-4):

1.

9. The method for synthesizing dimethyl oxalate according to claim 7, wherein The specific surface area of ​​the dilution ball is 0.02-10m 2 / g, and the average pore size is 30-100nm.

10. The method for synthesizing dimethyl oxalate according to claim 7, wherein The surface acidity of the diluted beads is 0.01-1 mmol / g.

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