阅读说明：本技术 一种低温连续合成碳酸二甲酯的工艺 (Process for continuously synthesizing dimethyl carbonate at low temperature ) 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连续合成碳酸二甲酯的工艺,通过在固定床反应其中装载高效固相催化剂Mg-Ga<Sub>2</Sub>O<Sub>3</Sub>/CeO<Sub>2</Sub>-Al<Sub>2</Sub>O<Sub>3</Sub>,不经实现了低温反应避免了副反应的发生,还提高了尿素的转化率和碳酸二甲酯的选择性,尿素的单程转化率可达95％以上,碳酸二甲酯的选择性在96.2％以上。(The invention relates to a process for continuously synthesizing dimethyl carbonate at low temperature, which comprises loading high-efficiency solid-phase catalyst Mg-Ga in a fixed bed reaction 2 O 3 /CeO 2 ‑Al 2 O 3 The method avoids side reaction without realizing low-temperature reaction, improves the conversion rate of urea and the selectivity of dimethyl carbonate, the conversion rate per pass of urea can reach more than 95%, and the selectivity of dimethyl carbonate is more than 96.2%.)

1. A process for continuously synthesizing dimethyl carbonate at low temperature is characterized in that urea and methanol are dissolved in a feeding tank to form a methanol solution, the urea methanol solution is introduced into a fixed bed reactor loaded with a high-efficiency solid-phase catalyst through a feeding pump to react the urea and the methanol to generate dimethyl carbonate and coproduce ammonia, an output material from the fixed bed reactor is firstly sent into a flash tank to separate a state mixture containing ammonia and a liquid material mainly comprising a dimethyl carbonate methanol solution, the ammonia-containing gas mixture is introduced into a tail gas absorption tower for producing an ammonia fertilizer, and the liquid material is sent into a rectifying tower to be separated to obtain a dimethyl carbonate product; the high-efficiency solid-phase catalyst Mg-Ga2O3/CeO2-Al2O 3.

2. The process for the low-temperature continuous synthesis of dimethyl carbonate according to claim 1, characterized in that: the concentration of urea in the urea methanol solution in the feed tank is 1-78 wt%.

3. The process for the low-temperature continuous synthesis of dimethyl carbonate according to claim 1, characterized in that: the feeding speed of the fixed bed reactor is 0.1-5ml/gcat min; the reaction temperature is 100 ℃ and 150 ℃, and the reaction pressure is 0.1-3 Mpa.

4. The process for the low-temperature continuous synthesis of dimethyl carbonate according to claim 1, characterized in that: the pressure of the flash tank is 0.6-0.9Mpa, and the temperature is 20-40 ℃; the temperature of the bottom of the rectifying tower is 100-200 ℃, the temperature of the top of the rectifying tower is 140-180 ℃, the reflux ratio is 3-8:1, and the number of theoretical plates is 2-10.

5. The process for the low-temperature continuous synthesis of dimethyl carbonate according to claim 1, 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 process for continuously synthesizing dimethyl carbonate at low temperature according to claim 5, wherein the soluble gallium salt in step S1 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 process for the low-temperature continuous synthesis of dimethyl carbonate according to claim 5, characterized in that: in step S1, the pH value is preferably 1-3.

8. The process for the low-temperature continuous synthesis of dimethyl carbonate according to claim 5, 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 process for the low-temperature continuous synthesis of dimethyl carbonate according to claim 5, characterized in that: the amount of the metal added in step S2 is 1.5-10% by mass of the catalyst precursor.

10. The process for the low-temperature continuous synthesis of dimethyl carbonate according to claim 5, 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 process for continuously synthesizing dimethyl carbonate at a low temperature.

Background

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.

At present, phosgene method is mostly adopted for industrial production of DMC. The method has the advantages of complex process, extremely toxic raw materials and elimination of the corrosion of the byproduct hydrochloric acid on equipment which does not meet the strategy of sustainable development. In the non-phosgene DMC synthesis process, ethylene carbonate and propylene carbonate which are raw materials of an ester exchange method in the process route are restricted by the petrochemical industry, and a large amount of ethylene glycol is byproduct. Propylene glycol methanol liquid phase oxidative carbonylation processes suffer from equipment corrosion due to the use of halide catalysts. The two-step method of methanol gas phase oxidation carbonylation has the problems of difficult product separation and catalyst recycling, and the like, needs to use poisonous methyl nitrite as a circulating agent by-product dimethyl oxalate to easily block pipelines, and has the one-step method of methanol gas phase oxidation carbonylation. Although the defects of the two-step method are overcome, the defects of low conversion per pass of raw materials, operation within the explosion limit and the like exist, and in addition, a methanol and carbon dioxide synthesis method and an electrochemical synthesis method exist. At present, methanol and urea are used for catalytically synthesizing DMC in a research stage, and the process route has the advantages of cheap and easily-obtained raw materials, particularly, anhydrous generation in the reaction avoids the problems that the non-phosgene routes need to treat methanol DMC, and the separation of a water complex system is attractive especially for developing downstream products in the existing fertilizer plants.

The fixed bed reactor is characterized in that a granular solid catalyst or a solid reactant is filled in the reactor to form a stacked bed layer with a certain height, and a gas or liquid material flows through a static fixed bed layer through a granular gap to realize a heterogeneous reaction process. The reactor is characterized in that solid particles filled in the reactor are fixed, and the reactor is different from a moving bed and a fluidized bed in which solid materials move in the reactor, and is also called a packed bed reactor. The fixed bed catalytic reactor has the advantages that: the catalyst is not easy to wear and can be used for a long time; when the ratio of height to diameter is large, the flow of the fluid in the bed layer is close to ideal displacement, so that the reaction rate is high, and a large yield can be obtained by using a small amount of catalyst and a small volume of a reactor; because the residence time can be strictly controlled and the temperature distribution can be properly adjusted, the selectivity is high and higher conversion rate can be achieved.

However, in the prior art, as for the alcoholysis method of urea and methanol, a continuous process using a fixed bed reactor as a main reactor has been rarely reported. Aiming at the defects of the prior art, the application provides a low-temperature continuous process for synthesizing dimethyl carbonate by adopting a fixed bed reactor.

Disclosure of Invention

The invention aims to provide a process for continuously synthesizing dimethyl carbonate at low temperature 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.

In order to solve the problems, the invention provides a process for continuously synthesizing dimethyl carbonate at low temperature, urea and methanol are dissolved in a feeding tank to form a methanol solution, the urea methanol solution is introduced into a fixed bed reactor loaded with a high-efficiency solid-phase catalyst through a feeding pump, and the urea and the methanol are reactedFirstly, conveying output materials of a fixed bed reactor into a flash tank to separate a gaseous mixture containing ammonia and a liquid material mainly comprising dimethyl carbonate methanol solution, introducing the gaseous mixture containing ammonia into a tail gas absorption tower for producing ammonia fertilizer, and conveying the liquid material into a rectifying tower to separate to obtain a dimethyl carbonate product; the high-efficiency solid-phase catalyst Mg-Ga₂O₃/CeO₂-Al₂O₃。

Further, the concentration of urea in the urea methanol solution in the feeding tank is 1-78 wt%;

further, the feeding speed of the fixed bed reactor is 0.1-5ml/gcat min; the reaction temperature is 100 ℃ and 150 ℃, and the reaction pressure is 0.1-3 Mpa.

Further, the pressure of the flash tank is 0.6-0.9Mpa, and the temperature is 20-40 ℃.

Further, the temperature of the bottom of the rectifying tower is 100-.

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 invention relates to a process for continuously synthesizing dimethyl carbonate at low temperature, which loads a high-efficiency solid-phase catalyst Mg-Ga in a solid bed reaction₂O₃/CeO₂-Al₂O₃The method avoids side reaction without realizing low-temperature reaction, improves the conversion rate of urea and the selectivity of dimethyl carbonate, the conversion rate per pass of urea can reach more than 95%, and the selectivity of dimethyl carbonate is more than 96.2%.

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 ]

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; 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 C1.

[ example 2 ]

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; 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 C2.

[ example 3 ]

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 C3.

[ example 4 ]

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, carrying out immersion reaction for 2-3 hours, drying for 5 hours at 120 ℃, and carrying out grinding reaction for 5 hours at 300 ℃ to obtain the high-efficiency solid-phase catalyst D1.

[ example 5 ]

Urea and methanol are dissolved in a feeding tank to form a urea methanol solution with the mass concentration of 35%, the urea methanol solution is introduced into a fixed bed reactor loaded with catalysts C1-C3 and D1 respectively at the speed of 1.2ml/gcat min through a feeding pump, the reaction temperature is 120 ℃, the urea and the methanol react to generate dimethyl carbonate and ammonia, the output material from the fixed bed reactor is firstly sent into a flash tank, the pressure of the flash tank is 0.8MPa, the temperature is 30 ℃, a liquid material containing ammonia and a liquid material mainly containing dimethyl carbonate methanol solution are separated, and the liquid material is analyzed, and the result is shown in table 1.

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.