阅读说明：本技术 一种低温高效催化尿素和甲醇反应直接制备碳酸二甲酯的方法 (Method for directly preparing dimethyl carbonate by low-temperature high-efficiency catalysis of reaction of urea and methanol ) 是由 熊飞龙 于 2019-10-23 设计创作，主要内容包括：本发明涉及一种低温高效催化尿素和甲醇反应直接制备碳酸二甲酯的方法,采用高效固相催化剂Mg-Ga<Sub>2</Sub>O<Sub>3</Sub>/CeO<Sub>2</Sub>-Al<Sub>2</Sub>O<Sub>3</Sub>,能够进一步提高碳酸二甲酯的收率,具有较高的反应活性和选择性,且副产物较少,尿素的转化率可达100％,碳酸二甲酯的选择性在99.2％以上。(The invention relates to a method for directly preparing dimethyl carbonate by low-temperature high-efficiency catalysis of reaction of urea and methanol, which adopts a high-efficiency solid-phase catalyst Mg-Ga 2 O 3 /CeO 2 ‑Al 2 O 3 The method can further improve the yield of the dimethyl carbonate, has higher reaction activity and selectivity, and fewer byproducts, the conversion rate of the urea can reach 100%, and the selectivity of the dimethyl carbonate is over 99.2%.)

1. A method for directly preparing dimethyl carbonate by low-temperature high-efficiency catalysis of reaction of urea and methanol is characterized by comprising the following steps: adding a certain amount of urea and a certain amount of methanol into a reaction kettle, fully stirring and mixing to completely dissolve the urea in the methanol, adding a high-efficiency solid-phase catalyst, heating to a reaction temperature, reacting for a period of time, distilling after the reaction is finished to obtain dimethyl carbonate, absorbing ammonia gas with dilute sulfuric acid or dilute hydrochloric acid, and evaporating to obtain ammonium sulfate or ammonium hydrochloride solid used as a fertilizer raw material; the high-efficiency solid-phase catalyst Mg-Ga2O3/CeO2-Al2O 3.

2. The method for directly preparing the dimethyl carbonate by the reaction of the urea and the methanol under the high-efficiency catalysis at the low temperature according to claim 1, which is characterized in that: the mol ratio of the urea to the methanol is 1: 5-30; the adding amount of the high-efficiency solid phase catalyst is 0.1-2 wt% of the adding amount of the urea.

3. The method for directly preparing the dimethyl carbonate by the reaction of the urea and the methanol under the high-efficiency catalysis at the low temperature according to claim 1, which is characterized in that: the reaction temperature is between 100 ℃ and 180 ℃, preferably between 110 ℃ and 140 ℃.

4. The method for directly preparing the dimethyl carbonate by the reaction of the urea and the methanol under the high-efficiency catalysis at the low temperature according to claim 1, which is characterized in that: the reaction time is 3-12 hours.

5. The method for directly preparing the dimethyl carbonate by the reaction of the urea and the methanol under the high-efficiency catalysis at the low temperature according to claim 1, which is characterized in that: the preparation method of the high-efficiency solid-phase catalyst comprises the following steps:

s1, dissolving soluble gallium salt and soluble cerium salt in a certain amount of deionized water according to a certain proportion, fully stirring and uniformly mixing, adding an alumina carrier, adjusting pH, carrying out ultrasonic dispersion for 2-5 hours, carrying out dipping reaction for 2-3 hours, drying at 80-120 ℃ for 5-10 hours, and finally roasting at high temperature to obtain a catalyst precursor;

s2, adding the catalyst precursor and magnesium metal into a vacuum grinding reactor according to a certain proportion, and grinding and reacting for 3-5 hours to obtain the high-efficiency solid-phase catalyst Mg-Ga2O3/CeO2-Al2O 3.

6. The method for directly preparing dimethyl carbonate by the reaction of urea and methanol under the catalysis of low temperature and high efficiency according to claim 5, wherein in step S1, the soluble gallium salt is gallium nitrate or gallium chloride, and the soluble cerium salt is cerium nitrate, cerium chloride or cerium sulfate; the mol ratio of the soluble gallium salt to the soluble cerium salt is 1: 20-50.

7. The method for directly preparing the dimethyl carbonate by the reaction of the urea and the methanol under the high-efficiency catalysis at the low temperature according to claim 5, which is characterized in that: in step S1, the pH value is preferably 1-3.

8. The method for directly preparing the dimethyl carbonate by the reaction of the urea and the methanol under the high-efficiency catalysis at the low temperature according to claim 5, which is characterized in that: in the step S1, the high-temperature roasting temperature is 500-1200 ℃, and the roasting time is 2-12 hours.

9. The method for directly preparing the dimethyl carbonate by the reaction of the urea and the methanol under the high-efficiency catalysis at the low temperature according to claim 5, which is characterized in that: the amount of the metal added in step S2 is 1.5-10% by mass of the catalyst precursor.

10. The method for directly preparing the dimethyl carbonate by the reaction of the urea and the methanol under the high-efficiency catalysis at the low temperature according to claim 5, which is characterized in that: the temperature of the polishing reaction in step S2 is 200-300 ℃.

Technical Field

The invention belongs to the field of organic synthesis, and particularly relates to a method for directly preparing dimethyl carbonate by low-temperature high-efficiency catalysis of a reaction between urea and methanol.

Background

Dimethyl carbonate (DMC), a chemical raw material with low toxicity, excellent environmental protection performance and wide application, is an important organic synthesis intermediate, contains functional groups such as carbonyl, methyl, methoxy and the like in a molecular structure, has various reaction performances, and has the characteristics of safe and convenient use, less pollution, easy transportation and the like in production. Because the toxicity of the dimethyl carbonate is low, the dimethyl carbonate is a green chemical product with development prospect.

Dimethyl carbonate (DMC) is an important organic chemical intermediate, and because the molecular structure of the DMC contains carbonyl, methyl, methoxy and carbonylmethoxy, the DMC can be widely used in organic synthesis reactions such as carbonylation, methylation, methoxylation, carbonylmethylation and the like, and can be used for producing various chemical products such as polycarbonate, isocyanate, polyurethane, polycarbonate diol, allyl diglycol carbonate, methyl carbamate (carbaryl), anisole, tetramethylolammonium, long-chain alkyl carbonate, carbohydrazide, malonate, propylene glycol urethane, diethyl carbonate, triphosgene, furazolidone, methyl carbazate, methyl anilinecarboxylate and the like. Because DMC is non-toxic, DMC can replace virulent phosgene, methyl chloroformate, dimethyl sulfate and the like to be used as methylating agent or carbonylation agent, thereby improving the safety of production operation and reducing environmental pollution. As a solvent, DMC can replace Freon, trichloroethane, trichloroethylene, benzene, xylene, etc. and is used for paint, cleaning solvent, etc. As a gasoline additive, DMC can increase its octane number and oxygen content, and thus its antiknock properties. In addition, DMC can be used as an additive for detergents, surfactants and softeners. Because of its wide application, DMC is known as "new stone" of organic synthesis nowadays.

The initial method of DMC production was phosgene, which was successfully developed in 1918, but the toxicity and corrosiveness of phosgene have limited the use of this method, and particularly phosgene has been eliminated as environmental protection has become increasingly appreciated worldwide. Since the 80's of the 20 th century, research into DMC production processes began to receive widespread attention, and patents on DMC production processes exceeded 200 since 1980 and 1996, according to the statistics of michael.

In the beginning of the 20 th century, the EniChem company in italy realized the commercialization of a process for the oxidative carbonylation of methanol to DMC using CuCl as a catalyst, which was the first process to realize the industrial non-phosgene process for DMC synthesis and was the most widely used process. The disadvantage of this process is that the catalyst deactivation at high conversion is severe, so that the conversion per pass is only 20%.

In the 90 s of the 20 th century, research into DMC synthesis processes has rapidly progressed: japanese Ube improves the process of synthesizing DMC by methanol oxidative carbonylation of EniChem company, selects NO as a catalyst, thus avoiding the deactivation of the catalyst and leading the conversion rate to almost reach 100 percent, and the process realizes industrialization; texaco in the United states developed a process for producing DMC by reacting ethylene oxide with carbon dioxide to produce ethylene carbonate and then transesterifying it with methanol, which was now commercialized in 1992, and which was considered to be low in productivity and high in production cost, and its investment and cost could compete with other methods only when the annual production of DMC was higher than 55 kt.

In addition, an emerging process, namely urea methanolysis, is expected to be commercialized if the cost can be reduced by combining with urea production.

Disclosure of Invention

The invention aims to provide a preparation method for directly synthesizing dimethyl carbonate from urea and methanol with high yield and high selectivity.

The reaction for preparing dimethyl carbonate from urea and methanol is generally carried out in two steps:

1)NH₂-CO-NH₂+CH₃OH→NH₂-CO-OCH₃+NH₃

2)NH₂-CO-OCH₃+CH₃OH→OCH₃-CO-OCH₃+NH₃

both steps are endothermic, with the first step requiring reaction at 140-190 ℃ and the second step requiring reaction above 190 ℃. However, when reacting at the above temperature, at least a part of uric acid or urethane is decomposed into isocyanic acid, and isocyanic acid reacts with ammonia generated in the reaction or forms ammonium isocyanate, which is different from an alcohol solution and may be gradually converted into a less soluble substance such as ammonium cyanurate, which may cause clogging of the reactor and cooler pipes. The reaction temperature of the catalyst for catalyzing the reaction of urea and dimethyl carbonate in the prior art is required to be higher, and the problem caused by ammonium urate cannot be solved.

The invention provides a method for directly preparing dimethyl carbonate by catalyzing the reaction of urea and methanol at low temperature and high efficiency, which comprises the steps of adding a certain amount of urea and a certain amount of methanol into a reaction kettle, fully stirring and mixing to completely dissolve the urea into the methanol, adding a high-efficiency solid-phase catalyst, heating to the reaction temperature, reacting for a period of time, distilling after the reaction is finished to obtain dimethyl carbonate, absorbing ammonia gas by dilute sulfuric acid or dilute hydrochloric acid, and evaporating to obtain ammonium sulfate or ammonium hydrochloride solid for fertilizer raw materials; said high efficiencySolid phase catalyst Mg-Ga₂O₃/CeO₂-Al₂O₃。

Further, the molar ratio of the urea to the methanol is 1: 5-30; the adding amount of the high-efficiency solid phase catalyst is 0.1-2 wt% of the adding amount of the urea.

Further, the reaction temperature is between 100 ℃ and 180 ℃, preferably between 110 ℃ and 140 ℃.

Further, the reaction time is 3 to 12 hours.

Further, the preparation method of the high-efficiency solid-phase catalyst comprises the following steps:

s1, dissolving soluble gallium salt and soluble cerium salt in a certain amount of deionized water according to a certain proportion, fully stirring and uniformly mixing, adding an alumina carrier, adjusting pH, carrying out ultrasonic dispersion for 2-5 hours, carrying out dipping reaction for 2-3 hours, drying at 80-120 ℃ for 5-10 hours, and finally roasting at high temperature to obtain a catalyst precursor;

s2, adding the catalyst precursor and magnesium metal into a vacuum grinding reactor according to a certain proportion, and grinding and reacting for 3-5 hours to obtain the high-efficiency solid-phase catalyst Mg-Ga₂O₃/CeO₂-Al₂O₃。

Further, in step S1, the soluble gallium salt is gallium nitrate or gallium chloride, and the soluble cerium salt is cerium nitrate, cerium chloride or cerium sulfate; the mol ratio of the soluble gallium salt to the soluble cerium salt is 1: 20-50;

further, the pH value in step S1 is preferably between 1 and 3.

Further, the high-temperature calcination temperature in the step S1 is 500-1200 ℃, and the calcination time is 2-12 hours.

Further, the amount of the metal added in step S2 is 1.5-10% by mass of the catalyst precursor.

Further, the temperature of the milling reaction in step S2 is 200-300 ℃.

The catalyst of the invention adopts metal magnesium to activate gallium oxide and cerium oxide in the catalyst precursor, so that the activity of the catalyst is further improved.

Compared with the prior art, the invention has the following beneficial effects:

the novel composite catalyst prepared by the invention can further improve the yield of dimethyl carbonate, has higher reaction activity and selectivity, fewer byproducts, the conversion rate of urea can reach 100%, and the selectivity of dimethyl carbonate is more than 99.2%.

Detailed Description

The technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

[ example 1 ]

1) Preparing a high-efficiency solid-phase catalyst:

dissolving 0.1mol of gallium nitrate and 2mol of cerium nitrate in 300mL of deionized water, fully stirring and uniformly mixing, adding 30g of alumina carrier, adjusting the pH to 1 with 1mol/L of dilute hydrochloric acid, ultrasonically dispersing for 5 hours, performing immersion reaction for 3 hours, drying for 5 hours at 120 ℃, and finally calcining for 5 hours at 1000 ℃ to obtain a catalyst precursor; adding 10g of catalyst precursor and 0.8g of metal magnesium into a vacuum grinding reactor, and grinding and reacting for 5 hours at 300 ℃ to obtain the high-efficiency solid-phase catalyst Mg-Ga₂O₃/CeO₂-Al₂O₃。

2) Preparation of dimethyl carbonate:

1mol (60g) of urea and 6 mol of methanol were added to a reaction kettle, and the mixture was sufficiently stirred and mixed to dissolve all the urea in the methanol, 0.3g of the high-efficiency solid-phase catalyst prepared in step 1) was added, the temperature was raised to 110 ℃ to react for 5 hours, and after the reaction was completed, gas phase analysis was performed, and the results are shown in Table 1.

The reaction mixture was distilled to obtain dimethyl carbonate, and as shown in table 1, ammonia gas was absorbed by dilute sulfuric acid or dilute hydrochloric acid, and evaporated to obtain ammonium sulfate or ammonium hydrochloride solid for fertilizer raw materials.

[ example 2 ]

1) Preparing a high-efficiency solid-phase catalyst:

dissolving 0.1mol of gallium nitrate and 3mol of cerium nitrate in 350mL of deionized water, fully stirring and uniformly mixing, adding 40g of alumina carrier, adjusting the pH to 1 with 1mol/L of dilute hydrochloric acid, ultrasonically dispersing for 5 hours, performing immersion reaction for 3 hours, drying for 5 hours at 120 ℃, and finally calcining for 5 hours at 1000 ℃ to obtain a catalyst precursor; adding 10g of catalyst precursor and 0.8g of metal magnesium into a vacuum grinding reactor, and grinding and reacting for 5 hours at 300 ℃ to obtain the high-efficiency solid-phase catalyst Mg-Ga₂O₃/CeO₂-Al₂O₃。

2) Preparation of dimethyl carbonate:

1mol (60g) of urea and 10 mol of methanol were added to a reaction vessel, and the mixture was sufficiently stirred and mixed to dissolve all the urea in the methanol, 0.9g of the high-efficiency solid-phase catalyst prepared in step 1) was added, the temperature was raised to 110 ℃ to react for 5 hours, and after the reaction was completed, gas phase analysis was performed, and the results are shown in Table 1.

The reaction mixture was distilled to obtain dimethyl carbonate, and as shown in table 1, ammonia gas was absorbed by dilute sulfuric acid or dilute hydrochloric acid, and evaporated to obtain ammonium sulfate or ammonium hydrochloride solid for fertilizer raw materials.

[ example 3 ]

1) Preparing a high-efficiency solid-phase catalyst:

dissolving 0.1mol of gallium nitrate and 1.5mol of cerium nitrate in 250mL of deionized water, fully stirring and uniformly mixing, adding 30g of alumina carrier, adjusting the pH to 1 by 1mol/L of dilute hydrochloric acid, ultrasonically dispersing for 5 hours, performing immersion reaction for 4 hours, drying for 5 hours at 120 ℃, and finally roasting for 5 hours at 1000 ℃ to obtain a catalyst precursor; 10g of catalyst precursor and 0.8g of magnesium metal are added into a vacuum grinding reactor, and grinding reaction is carried out for 5 hours at 300 ℃ to obtain the high-efficiency solid-phase catalyst Mg-Ga2O3/CeO2-Al2O 3.

2) Preparation of dimethyl carbonate:

1mol (60g) of urea and 30 mol of methanol were added to a reaction kettle, and the mixture was sufficiently stirred and mixed to dissolve all the urea in the methanol, and 1.2g of the high-efficiency solid-phase catalyst prepared in step 1) was added thereto, and the temperature was raised to 110 ℃ to react for 5 hours, and after the reaction was completed, gas phase analysis was performed, and the results are shown in Table 1.

The reaction mixture was distilled to obtain dimethyl carbonate, and as shown in table 1, ammonia gas was absorbed by dilute sulfuric acid or dilute hydrochloric acid, and evaporated to obtain ammonium sulfate or ammonium hydrochloride solid for fertilizer raw materials.

Comparative example 1

1) Preparing a high-efficiency solid-phase catalyst:

dissolving 0.1mol of gallium nitrate and 2mol of cerium nitrate in 300mL of deionized water, fully stirring and uniformly mixing, adding 30g of alumina carrier, adjusting the pH value to 1 with 1mol/L of dilute hydrochloric acid, ultrasonically dispersing for 5 hours, dipping for 2-3 hours, drying for 5 hours at 120 ℃, and grinding for 5 hours at 300 ℃ to obtain the high-efficiency solid-phase catalyst Ga2O3/CeO2-Al2O 3.

2) Preparation of dimethyl carbonate:

1mol (60g) of urea and 6 mol of methanol were added to a reaction kettle, and the mixture was sufficiently stirred and mixed to dissolve all the urea in the methanol, 0.1g of the high-efficiency solid-phase catalyst prepared in step 1) was added, the temperature was raised to 110 ℃ to react for 5 hours, and after the reaction was completed, gas phase analysis was performed, and the results are shown in Table 1.

The reaction mixture was distilled to obtain dimethyl carbonate, and as shown in table 1, ammonia gas was absorbed by dilute sulfuric acid or dilute hydrochloric acid, and evaporated to obtain ammonium sulfate or ammonium hydrochloride solid for fertilizer raw materials.

TABLE 1

The foregoing description has disclosed fully preferred embodiments of the present invention. It should be noted that those skilled in the art can make modifications to the embodiments of the invention without departing from the scope of the claims. Accordingly, the scope of the appended claims is not to be limited to the specific embodiments described above.