A kind of production method of dimethyl carbonate

Abstract

The present invention relates to the technical field of fine chemical production, and in particular to a method for producing dimethyl carbonate. In order to solve the technical problem of low production efficiency in the method for preparing dimethyl carbonate by two-step alcoholysis, the present invention provides a method for producing dimethyl carbonate capable of realizing continuous production. The production method continuously adds urea, adds a methanol solution of sodium methoxide after adding a diol for a certain period of time, and continuously adds methanol after adding a methanol solution of sodium methoxide for a certain period of time. By controlling production factors such as the material addition flow rate and the amount of diol added, a continuous production mode of continuous feeding and continuous discharging is realized, and the production efficiency is high.

Description

Technical Field

[0001] The invention relates to the technical field of fine chemical production, and in particular to a method for producing dimethyl carbonate. Background Art

[0002] The molecular structure of dimethyl carbonate contains organic chemical functional groups such as methyl, methoxy, and carbonyl. It has active chemical properties and can undergo methylation, carbonylation, methylation, and transesterification with a variety of organic compounds. At the same time, it has low toxicity, is safe to use, meets the requirements of clean production and green environmental protection, and has become a new cornerstone of modern organic synthesis.

[0003] At the end of the last century, countries around the world began to realize the industrial application prospects and market of dimethyl carbonate, and carried out relevant research work. Among them, the United States and Japan took the lead and first carried out research on its synthesis route, developing the synthesis technology route of dimethyl carbonate in the direction of simplification, non-toxicity and pollution-free, and achieved great breakthroughs. At present, the synthesis process of dimethyl carbonate has become increasingly mature after several generations of replacement. The traditional phosgene synthesis method has been eliminated due to its pollution and danger, and the methanol oxidation carbonylation method has been gradually abandoned because it cannot keep up with the development of the market. The new synthesis technology-urea alcoholysis method has gradually been accepted by the market because of its own advantages such as non-toxicity, low pollution, and high safety factor of production conditions.

[0004] Urea alcoholysis is also a key research direction for the synthesis of dimethyl carbonate in various countries at this stage. Chinese patent CN1280254C discloses a method for synthesizing dimethyl carbonate by alcoholysis of methanol and urea, using methanol and urea as raw materials, amine salt type ionic liquid as catalyst, and adopting intermittent reaction to synthesize dimethyl carbonate. Chinese patent CN1903828A discloses a process for producing dimethyl carbonate using urea alcoholysis, further optimizing the reaction and separation conditions. Chinese patents CN100395019C and CN113385207A both propose supported catalysts for synthesizing dimethyl carbonate from urea and methanol, and achieve better catalytic performance through the combination of alkali metals, alkaline earth metals, additives and molecular sieves. Chinese patent CN103980124B optimizes the method of synthesizing dimethyl carbonate from propylene carbonate using ionic liquid catalysis. The above-mentioned methods for preparing dimethyl carbonate all adopt a one-step synthesis method, which mainly focuses on the renewal and preparation of the catalyst used in the reaction process. The production method is all intermittent production, which has technical problems such as low yield and low production efficiency, and has restricted the further expansion of production scale and efficiency.

[0005] Chinese patent CN106083585B discloses a method for preparing dimethyl carbonate by indirect alcoholysis; a two-step alcoholysis is adopted, and the intermediate product propylene carbonate is separated after the primary alcoholysis, and then the intermediate product and methanol are subjected to secondary alcoholysis. In this preparation method, the catalysts, reaction equipment and reaction conditions required for the two-step alcoholysis are different; and the primary alcoholysis needs to be carried out under vacuum conditions, the production conditions are harsh, the required production equipment is complex, continuous production cannot be achieved, and the production efficiency is low. Summary of the invention

[0006] In order to solve the technical problem of low production efficiency in the method for preparing dimethyl carbonate by two-step alcoholysis, the present invention provides a method for producing dimethyl carbonate capable of realizing continuous production; the production method uses the two-step alcoholysis method of urea in succession, produces dimethyl carbonate by continuous feeding and continuous discharging, and has high production efficiency. The production efficiency refers to the amount of the target product (dimethyl carbonate) produced per unit time.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A method for producing dimethyl carbonate comprises the following steps:

[0009] (1) In the presence of a catalyst, add to a reaction vessel:

[0010] Continuously add urea; the ratio of urea mass flow rate to reaction vessel capacity is: 200-300kg / h: 2m 3 ;

[0011] Add diol and stir to perform reflux reaction; the flow rate of diol is 1.4-1.6 times of the mass flow rate of urea, and the addition time of diol is 1 hour and 20 minutes to 1 hour and 40 minutes;

[0012] After the addition of diol is stopped, a methanol solution of sodium methoxide is added and stirred to perform a reflux reaction; when the mass of sodium methoxide in the reaction solution is 1-2% of the mass of urea, the addition of the methanol solution of sodium methoxide and the reflux reaction are stopped; the mass content of sodium methoxide in the methanol solution of sodium methoxide is 1-3%, and the flow rate of the methanol solution of sodium methoxide is 1-1.2 times the mass flow rate of urea;

[0013] After stopping the addition of the methanol solution of sodium methoxide, methanol is continuously added to stir and the steam is collected; the flow rate of methanol is 1-1.2 times the mass flow rate of urea;

[0014] During the entire process of step (1), the temperature of the reaction liquid in the reaction container is controlled to be 130-150°C;

[0015] (2) Ammonia and methanol are separated from the steam to obtain dimethyl carbonate.

[0016] The production method of the present invention adopts a two-step alcoholysis method, with urea and methanol as raw materials and diol as a reaction participant; the first step of alcoholysis: urea reacts with diol to generate cyclic carbonate, and the second step of alcoholysis: cyclic carbonate reacts with methanol to generate dimethyl carbonate and diol. The reaction formula, taking 1,2-propylene glycol as a reaction participant, is as follows:

[0017]

[0018] The catalyst used can be any catalyst disclosed in the prior art for preparing dimethyl carbonate by two-step alcoholysis; for example, a magnesium oxide supported catalyst, the support material is silicon dioxide, the mass content of magnesium oxide in the catalyst is 10%-15%; the amount of catalyst used is 0.1 times the mass of urea added per hour.

[0019] The urea mass flow rate, i.e., the mass of urea added per hour, is determined by the inventors through several laboratory experiments and production tests; a specific urea mass flow rate is a necessary condition for achieving continuous feeding, continuous production and high production efficiency. The urea mass flow rate provided by the present invention can achieve continuous feeding, continuous production and high production efficiency. 3 For example, urea mass flow rate is controlled at about 200-300kg / h, which can achieve high production efficiency.

[0020] The specific addition amount of the reaction participant diol is also a necessary condition for achieving continuous feeding, continuous production and high production efficiency. The present invention limits the addition amount of diol by limiting the continuous addition time of diol. Experimental studies have shown that too much or too little addition of diol will lead to the problem of inability to continuously feed (and thus inability to continuously produce) or / and decreased production efficiency. Possible reasons: The production method of the present invention requires the entire reaction system to be in dynamic equilibrium. Any change in the amount of raw materials (concentration in the reaction solution) will cause the dynamic equilibrium to change, causing the balance to continuously shift to the right or to the left, resulting in inability to continuously feed or continuously discharge, and thus inability to achieve continuous production, thereby affecting production efficiency. Preferably, the flow rate of diol is 1.5-1.52 times the mass flow rate of urea; the addition time of diol is 1.5h. Under this condition, the production efficiency is higher.

[0021] The diol can be ethylene glycol or 1,2-propylene glycol. Since ethylene glycol will produce the impurity 2-oxazolidinone in the actual production process, which is enriched in the reactor and does not utilize the recycling of diol, 1,2-propylene glycol is preferred.

[0022] Sodium methoxide acts as a catalyst for the second step of alcoholysis. Its dosage needs to be strictly limited. On the one hand, the amount must achieve catalytic activation; on the other hand, due to the activity and chemical hazard of sodium methoxide itself, too high a content will lead to local violent reactions and danger. Therefore, after repeated experimental studies, the amount of sodium methoxide in the reaction system is limited to 1-2% of the quality of urea.

[0023] In order to further improve the reaction rate and obtain high production efficiency, preferably, an auxiliary agent is used in combination with the catalyst. The auxiliary agent is dodecyl dimethyl tertiary amine, and the amount used is 0.1 times the amount of the catalyst.

[0024] The temperature of the reaction solution is preferably 130-134° C. Under this temperature condition, high production efficiency can be achieved without causing energy waste.

[0025] In step (2), the steam is a mixture of ammonia, gaseous methanol and gaseous dimethyl carbonate. The following separation method can be used: the steam is condensed to 0-5°C, and the gaseous substance and the liquid substance are collected separately; the liquid substance is washed with water to separate the organic phase and the aqueous phase, the organic phase is dried with anhydrous calcium chloride to obtain dimethyl carbonate, and the aqueous phase is distilled and dried with anhydrous calcium chloride to obtain methanol.

[0026] In addition, it should be noted that during the entire step (1) process, the reaction vessel should be kept free of water.

[0027] The beneficial effects of the present invention are:

[0028] The present invention provides a method for producing dimethyl carbonate, which uses a two-step alcoholysis of urea, uses urea and methanol as raw materials, and uses 1,2-propylene glycol as a reaction participant in the first step alcoholysis of urea, and produces dimethyl carbonate by continuous feeding and continuous discharging. The method of the present invention controls the material feeding speed, the feeding amount ratio, and the reaction time of the reaction participants and urea, so that the entire reaction system can maintain dynamic equilibrium under the condition of continuous feeding, thereby realizing continuous production with continuous feeding; on the other hand, this method promotes the right shift of the first step alcoholysis reaction equilibrium by continuously adding methanol to the reaction liquid after the first step alcoholysis and separating the second step alcoholysis product, and the next step reaction can be carried out without the first step alcoholysis being complete, thereby shortening the working hours, reducing costs, and greatly improving production efficiency. The present invention realizes continuous production, and compared with the traditional intermittent kettle production, the equipment utilization rate is high, the cost is reduced, and it is conducive to industrial promotion. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with embodiments.

[0030] The terms such as "upper", "lower", "left", "right", "middle" and "one" etc. used in this specification are only for the convenience of description and are not intended to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships shall be regarded as within the scope of implementation of the present invention without substantially changing the technical content.

[0031] The following examples and comparative examples are some of the raw material specifications used:

[0032] The reactor is a 2 cubic reactor (capacity 2m 3 ), all pipes and kettles were dried at 50℃ in advance;

[0033] The catalyst is a magnesium oxide-supported silica catalyst, with a magnesium oxide mass content of 15%, a spherical shape, and a diameter of about 3 cm;

[0034] The auxiliary agent is dodecyl dimethyl tertiary amine, analytical grade; the desiccant is anhydrous calcium chloride;

[0035] The raw materials are all industrial pure, and methanol and 1,2-propylene glycol are dried and dehydrated in advance.

[0036] The reaction operation of the embodiment is continuous feeding and discharging. For better comparison, 12 h is selected as a reaction cycle. The time for calculating the yield and efficiency is counted from the beginning of the dropwise addition of methanol, which is a total of 10.5 h.

[0037] Example 1

[0038] Step (1): add 20 kg of catalyst and 2 kg of auxiliary agent into the reactor, then continuously add urea and 1,2-propylene glycol into the reactor at a rate of 200 kg / h and 304 kg / h respectively for reflux reaction, start stirring after 30 minutes, raise the temperature of the reaction liquid in the reactor to 132±2°C by the heating jacket, maintain the temperature and continue to dropwise react for 1 hour.

[0039] Step (2): while maintaining the urea dosage (200 kg / h) unchanged and the temperature of the reaction liquid in the kettle at 132±2°C, perform the following operations: stop dripping 1,2-propylene glycol, start adding a methanol solution of sodium methoxide (the mass content of sodium methoxide in the methanol solution of sodium methoxide is 1%) at a rate of 220 kg / h below the liquid surface for reflux reaction, stop adding the methanol solution of sodium methoxide after 2 hours, and turn off the reflux; then continue adding methanol at a rate of 220 kg / h below the liquid surface, and collect steam.

[0040] Step (3): The steam is condensed to 0-5°C, and the gaseous substance is the by-product ammonia; the liquid substance is dimethyl carbonate and methanol. The by-product ammonia is dried and enters the ammonia temporary storage tank. The liquid substance is washed and separated to obtain an organic phase (dimethyl carbonate) and an aqueous phase (methanol aqueous solution). The organic phase is dried with anhydrous calcium chloride to obtain dimethyl carbonate, and the aqueous phase is distilled and dried with anhydrous calcium chloride to obtain methanol. Methanol can be recycled.

[0041] When step (2) is continued for 10.5 hours, the masses of the products obtained after treatment in step (3) are: 1244 kg ammonia, 3266 kg dimethyl carbonate, and 270 kg methanol.

[0042] The results of high performance gas chromatography showed that the purity of dimethyl carbonate was 99.54%, the yield of dimethyl carbonate was 91.13% (based on urea), and the production efficiency of dimethyl carbonate was 311 kg / h.

[0043] Example 2 (Compared with Example 1, the flow rate of urea is 300 kg / h, and the flow rates of other materials are adjusted accordingly)

[0044] Step (1): add 30 kg of catalyst and 3 kg of auxiliary agent into the reactor, then continuously add urea and 1,2-propylene glycol into the reactor at a rate of 300 kg / h and 456 kg / h respectively for reflux reaction, start stirring after 30 minutes, raise the temperature of the reaction liquid in the reactor to 138±2°C by the heating jacket, maintain the temperature and continue to add dropwise for 1 hour.

[0045] Step (2): while maintaining the urea dosage (300 kg / h) unchanged and the temperature of the reaction liquid in the kettle at 132±2°C, perform the following operations: stop adding 1,2-propylene glycol, start adding a methanol solution of sodium methoxide (the mass content of sodium methoxide in the methanol solution of sodium methoxide is 1%) at a rate of 330 kg / h below the liquid surface for reflux reaction, stop adding the methanol solution of sodium methoxide after 2 hours, and turn off the reflux; switch to adding methanol at a rate of 330 kg / h below the liquid surface, and collect steam.

[0046] Step (3): The steam is condensed to 0-5°C, and the gaseous substance is the by-product ammonia; the liquid substance is dimethyl carbonate and methanol. The by-product ammonia is dried and enters the ammonia temporary storage tank. The liquid substance is washed and separated to obtain an organic phase (dimethyl carbonate) and an aqueous phase (methanol aqueous solution). The organic phase is dried with anhydrous calcium chloride to obtain dimethyl carbonate, and the aqueous phase is distilled and dried with anhydrous calcium chloride to obtain methanol. Methanol can be recycled.

[0047] When step (2) lasts for 10.5 hours, the masses of the products obtained after treatment in step (3) are: 1865 kg ammonia, 4907 kg dimethyl carbonate, and 400 kg methanol.

[0048] The results of high performance gas chromatography showed that the purity of dimethyl carbonate was 99.55%, the yield of dimethyl carbonate (based on urea) was 91.28%, and the production efficiency of dimethyl carbonate was 467 kg / h.

[0049] Example 3 (Compared with Example 1, the addition time of 1,2-propylene glycol was shortened by 10 minutes)

[0050] Step (1): add 20 kg of catalyst and 2 kg of auxiliary agent into the reactor, then continuously add urea and 1,2-propylene glycol into the reactor at a rate of 200 kg / h and 304 kg / h respectively for reflux reaction, start stirring after 30 minutes, raise the temperature of the reaction liquid in the reactor to 132±2°C by the heating jacket, maintain the temperature and continue to dropwise react for 50 minutes.

[0051] Step (2): while maintaining the urea dosage (200 kg / h) unchanged and the temperature of the reaction liquid in the kettle at 132±2°C, perform the following operations: stop dripping 1,2-propylene glycol, start adding a methanol solution of sodium methoxide (the mass content of sodium methoxide in the methanol solution of sodium methoxide is 1%) at a rate of 220 kg / h below the liquid surface for reflux reaction, stop adding the methanol solution of sodium methoxide after 2 hours, and turn off the reflux; then continue adding methanol at a rate of 220 kg / h below the liquid surface, and collect steam.

[0052] Step (3): The steam is condensed to 0-5°C, and the gaseous substance is the by-product ammonia; the liquid substance is dimethyl carbonate and methanol. The by-product ammonia is dried and enters the ammonia temporary storage tank. The liquid substance is washed and separated to obtain an organic phase (dimethyl carbonate) and an aqueous phase (methanol aqueous solution). The organic phase is dried with anhydrous calcium chloride to obtain dimethyl carbonate, and the aqueous phase is distilled and dried with anhydrous calcium chloride to obtain methanol. Methanol can be recycled.

[0053] When step (2) lasts for 10.5 hours, the masses of the products obtained after treatment in step (3) are: 1240 kg ammonia, 3260 kg dimethyl carbonate, and 276 kg methanol.

[0054] The results of high performance gas chromatography showed that the purity of dimethyl carbonate was 99.52%, the yield of dimethyl carbonate (based on urea) was 90.96%, and the production efficiency of dimethyl carbonate was 310 kg / h.

[0055] Example 4 (Compared with Example 1, the addition time of 1,2-propylene glycol was extended by 10 minutes)

[0056] Step (1): add 20 kg of catalyst and 2 kg of auxiliary agent into the reactor, then continuously add urea and 1,2-propylene glycol into the reactor at a rate of 200 kg / h and 304 kg / h respectively for reflux reaction, start stirring after 30 minutes, raise the temperature of the reaction liquid in the reactor to 132±2°C by the heating jacket, maintain the temperature and continue to dropwise react for 50 minutes.

[0057] Step (2): while maintaining the urea dosage (200 kg / h) unchanged and the temperature of the reaction liquid in the kettle at 132±2°C, perform the following operations: stop dripping 1,2-propylene glycol, start adding a methanol solution of sodium methoxide (the mass content of sodium methoxide in the methanol solution of sodium methoxide is 1%) at a rate of 220 kg / h below the liquid surface for reflux reaction, stop adding the methanol solution of sodium methoxide after 2 hours, and turn off the reflux; then continue adding methanol at a rate of 220 kg / h below the liquid surface, and collect steam.

[0058] Step (3): The steam is condensed to 0-5°C, and the gaseous substance is the by-product ammonia; the liquid substance is dimethyl carbonate and methanol. The by-product ammonia is dried and enters the ammonia temporary storage tank. The liquid substance is washed and separated to obtain an organic phase (dimethyl carbonate) and an aqueous phase (methanol aqueous solution). The organic phase is dried with anhydrous calcium chloride to obtain dimethyl carbonate, and the aqueous phase is distilled and dried with anhydrous calcium chloride to obtain methanol. Methanol can be recycled.

[0059] When step (2) lasts for 10.5 hours, the masses of the products obtained after treatment in step (3) are: 1251 kg ammonia, 3264 kg dimethyl carbonate, and 273 kg methanol.

[0060] The results of high performance gas chromatography showed that the purity of dimethyl carbonate was 99.54%, the yield of dimethyl carbonate (based on urea) was 91.07%, and the production efficiency of dimethyl carbonate was 311 kg / h.

[0061] Example 5 (reaction temperature 150°C, other conditions are the same as in Example 1)

[0062] Step (1): add 20 kg of catalyst and 2 kg of auxiliary agent into the reactor, then continuously add urea and 1,2-propylene glycol into the reactor at a rate of 200 kg / h and 304 kg / h respectively for reflux reaction, start stirring after 30 minutes, raise the temperature of the reaction liquid in the reactor to 150±2°C by the heating jacket, maintain the temperature and continue to dropwise react for 1 hour.

[0063] Step (2): while maintaining the urea dosage (200 kg / h) unchanged and the temperature of the reaction liquid in the kettle at 150±2°C, perform the following operations: stop adding 1,2-propylene glycol, and start adding a methanol solution of sodium methoxide (the mass content of sodium methoxide in the methanol solution of sodium methoxide is 1%) at a rate of 220 kg / h below the liquid surface for reflux reaction. After 2 hours, stop adding the methanol solution of sodium methoxide and turn off the reflux; then continue adding methanol at a rate of 220 kg / h below the liquid surface and collect steam.

[0064] Step (3): The steam is condensed to 0-5°C, and the gaseous substance is the by-product ammonia; the liquid substance is dimethyl carbonate and methanol. The by-product ammonia is dried and enters the ammonia temporary storage tank. The liquid substance is washed and separated to obtain an organic phase (dimethyl carbonate) and an aqueous phase (methanol aqueous solution). The organic phase is dried with anhydrous calcium chloride to obtain dimethyl carbonate, and the aqueous phase is distilled and dried with anhydrous calcium chloride to obtain methanol. Methanol can be recycled.

[0065] When step (2) lasts for 10.5 hours, the masses of the products obtained after treatment in step (3) are: 1254 kg ammonia, 3263 kg dimethyl carbonate, and 274 kg methanol.

[0066] The results of high performance gas chromatography showed that the purity of dimethyl carbonate was 99.55%, the yield of dimethyl carbonate (based on urea) was 91.05%, and the production efficiency of dimethyl carbonate was 311 kg / h.

[0067] Comparative Example 1 (reaction temperature 120°C, other conditions are the same as in Example 1)

[0068] Step (1): add 20 kg of catalyst and 2 kg of auxiliary agent into the reactor, then continuously add urea and 1,2-propylene glycol into the reactor at a rate of 200 kg / h and 304 kg / h respectively for reflux reaction, start stirring after 30 minutes, raise the temperature of the reaction liquid in the reactor to 120±2°C by the heating jacket, maintain the temperature and continue to dropwise react for 1 hour.

[0069] Step (2): while maintaining the urea dosage (200 kg / h) unchanged and the temperature of the reaction liquid in the kettle at 120±2°C, perform the following operations: stop dripping 1,2-propylene glycol, start adding a methanol solution of sodium methoxide (the mass content of sodium methoxide in the methanol solution of sodium methoxide is 1%) at a rate of 220 kg / h below the liquid surface for reflux reaction, stop adding the methanol solution of sodium methoxide after 2 hours, and turn off the reflux; then continue adding methanol at a rate of 220 kg / h below the liquid surface, and collect steam.

[0070] Step (3): The steam is condensed to 0-5°C, and the gaseous substance is the by-product ammonia; the liquid substance is dimethyl carbonate and methanol. The by-product ammonia is dried and enters the ammonia temporary storage tank. The liquid substance is washed and separated to obtain an organic phase (dimethyl carbonate) and an aqueous phase (methanol aqueous solution). The organic phase is dried with anhydrous calcium chloride to obtain dimethyl carbonate, and the aqueous phase is distilled and dried with anhydrous calcium chloride to obtain methanol. Methanol can be recycled.

[0071] When step (2) lasts for 10.5 hours, the masses of the products obtained after treatment in step (3) are: 921 kg ammonia, 2718 kg dimethyl carbonate, and 612 kg methanol.

[0072] The results of high performance gas chromatography showed that the purity of dimethyl carbonate was 99.54%, the yield of dimethyl carbonate (based on urea) was 75.84%, and the production efficiency of dimethyl carbonate was 259 kg / h.

[0073] Comparative Example 2 (reaction temperature 160°C, other conditions are the same as in Example 1)

[0074] Step (1): add 20 kg of catalyst and 2 kg of auxiliary agent into the reactor, then continuously add urea and 1,2-propylene glycol into the reactor at a rate of 200 kg / h and 304 kg / h respectively for reflux reaction, start stirring after 30 minutes, raise the temperature of the reaction liquid in the reactor to 160±2°C by the heating jacket, maintain the temperature and continue to add dropwise for 1 hour.

[0075] Step (2): while maintaining the urea dosage (200 kg / h) unchanged and the temperature of the reaction liquid in the kettle at 160±2°C, perform the following operations: stop dripping 1,2-propylene glycol, start adding a methanol solution of sodium methoxide (the mass content of sodium methoxide in the methanol solution of sodium methoxide is 1%) at a rate of 220 kg / h below the liquid surface for reflux reaction, stop adding the methanol solution of sodium methoxide after 2 hours, and turn off the reflux; then continue adding methanol at a rate of 220 kg / h below the liquid surface, and collect steam.

[0076] Step (3): The steam is condensed to 0-5°C, and the gaseous substance is the by-product ammonia; the liquid substance is dimethyl carbonate and methanol. The by-product ammonia is dried and enters the ammonia temporary storage tank. The liquid substance is washed and separated to obtain an organic phase (dimethyl carbonate) and an aqueous phase (methanol aqueous solution). The organic phase is dried with anhydrous calcium chloride to obtain dimethyl carbonate, and the aqueous phase is distilled and dried with anhydrous calcium chloride to obtain methanol. Methanol can be recycled.

[0077] When step (2) lasts for 10.5 hours, the masses of the products obtained after treatment in step (3) are: 1252 kg ammonia, 3227 kg dimethyl carbonate, and 297 kg methanol.

[0078] The results of high performance gas chromatography showed that the purity of dimethyl carbonate was 99.55%, the yield of dimethyl carbonate (based on urea) was 90.04%, and the production efficiency of dimethyl carbonate was 307 kg / h.

[0079] Comparative Example 3 (Compared with Example 1, the urea flow rate is 400 kg / h, and the flow rates of other materials are adjusted accordingly)

[0080] Step (1): add 40 kg of catalyst and 4 kg of auxiliary agent into the reactor, then continuously add urea and 1,2-propylene glycol into the reactor at a rate of 400 kg / h and 608 kg / h respectively for reflux reaction, start stirring after 30 minutes, raise the temperature of the reaction liquid in the reactor to 138±2°C by the heating jacket, maintain the temperature and continue to add dropwise for 1 hour.

[0081] Step (2): while maintaining the urea dosage (400 kg / h) unchanged and the temperature of the reaction liquid in the kettle at 132±2°C, perform the following operations: stop adding 1,2-propylene glycol, start adding a methanol solution of sodium methoxide (the mass content of sodium methoxide in the methanol solution of sodium methoxide is 1%) at a rate of 440 kg / h to carry out a reflux reaction, stop adding the methanol solution of sodium methoxide after 2 hours, and turn off the reflux; switch to adding methanol at a rate of 440 kg / h to collect steam.

[0082] Step (3): The steam is condensed to 0-5°C, and the gaseous substance is the by-product ammonia; the liquid substance is dimethyl carbonate and methanol. The by-product ammonia is dried and enters the ammonia temporary storage tank. The liquid substance is washed and separated to obtain an organic phase (dimethyl carbonate) and an aqueous phase (methanol aqueous solution). The organic phase is dried with anhydrous calcium chloride to obtain dimethyl carbonate, and the aqueous phase is distilled and dried with anhydrous calcium chloride to obtain methanol. Methanol can be recycled.

[0083] When the statistical step (2) lasted for 5.5 hours, the reactor had been filled with 4 / 5 of the volume of the material, and the reaction could not proceed further, so the feeding was stopped.

[0084] Comparative Example 4 (using only catalyst, without auxiliary agent, other conditions are the same as Example 1)

[0085] Step (1): add 20 kg of catalyst to the reactor, then continuously add urea and 1,2-propylene glycol to the reactor at a rate of 200 kg / h and 304 kg / h respectively for reflux reaction, start stirring after 30 minutes, raise the temperature of the reaction liquid in the reactor to 132±2°C by the heating jacket, maintain the temperature and continue to dropwise react for 1 hour.

[0086] Step (2): while maintaining the urea dosage (200 kg / h) unchanged and the temperature of the reaction liquid in the kettle at 132±2°C, perform the following operations: stop dripping 1,2-propylene glycol, start adding a methanol solution of sodium methoxide (the mass content of sodium methoxide in the methanol solution of sodium methoxide is 1%) at a rate of 220 kg / h below the liquid surface for reflux reaction, stop adding the methanol solution of sodium methoxide after 2 hours, and turn off the reflux; then continue adding methanol at a rate of 220 kg / h below the liquid surface, and collect steam.

[0087] Step (3): The steam is condensed to 0-5°C, and the gaseous substance is the by-product ammonia; the liquid substance is dimethyl carbonate and methanol. The by-product ammonia is dried and enters the ammonia temporary storage tank. The liquid substance is washed and separated to obtain an organic phase (dimethyl carbonate) and an aqueous phase (methanol aqueous solution). The organic phase is dried with anhydrous calcium chloride to obtain dimethyl carbonate, and the aqueous phase is distilled and dried with anhydrous calcium chloride to obtain methanol. Methanol can be recycled.

[0088] When step (2) lasts for 10.5 hours, the masses of the products obtained after treatment in step (3) are: 1158 kg ammonia, 2965 kg dimethyl carbonate, and 456 kg methanol.

[0089] The results of high performance gas chromatography showed that the purity of dimethyl carbonate was 99.53%, the yield of dimethyl carbonate (based on urea) was 82.75%, and the production efficiency of dimethyl carbonate was 282 kg / h.

[0090] Comparative Example 5 (Batch Kettle Production)

[0091] Step (1): add 20 kg of catalyst and 2 kg of auxiliary agent into the reactor, then continue to add urea and 1,2-propylene glycol into the reactor at a rate of 200 kg / h and 304 kg / h respectively, start stirring after 30 minutes, raise the temperature of the reaction liquid in the reactor to 132±2°C by means of a heating jacket, maintain the temperature and continue to dropwise react for 2 hours, then stop dropping, continue to keep warm for 30 minutes, and the by-product ammonia is no longer produced.

[0092] Step (2): add sodium methoxide in methanol solution dropwise at a rate of 220 kg / h below the liquid surface for reflux reaction. Stop adding dropwise after 2 hours, turn off the reflux, start steam extraction, and simultaneously add methanol dropwise at a rate of 220 kg / h below the liquid surface at 132±2°C for 1 hour. Stop heating and adding dropwise.

[0093] Step (3): After condensation and drying, the by-product ammonia gas accumulates to 279 kg and enters a temporary ammonia storage tank. The steam methanol and dimethyl carbonate are cooled into liquids, washed and separated to obtain dimethyl carbonate and methanol aqueous solution. After drying with anhydrous calcium chloride, 778 kg of dimethyl carbonate is obtained. After distillation and drying with anhydrous calcium chloride, the methanol aqueous solution is 170 kg of methanol, which can be recycled.

[0094] The results of high performance gas chromatography showed that the content of dimethyl carbonate in the product was 99.55%, the yield of dimethyl carbonate was 91.14%, and the production efficiency was 141 kg / h.

[0095] Comparative Example 6 (the total time for adding 1,2-propylene glycol to the reactor is 1 h, and the other steps are the same as in Example 1) Step (1): Add 20 kg of catalyst and 2 kg of auxiliary agent to the reactor, and then continuously add urea and 1,2-propylene glycol to the reactor at a rate of 200 kg / h and 304 kg / h, respectively, for reflux reaction. Start stirring after 30 minutes, and heat the reaction liquid in the reactor to 132±2°C using the heating jacket. Maintain the temperature and continue the dropwise addition reaction for 0.5 h.

[0096] Step (2): while maintaining the urea dosage (200 kg / h) unchanged and the temperature of the reaction liquid in the kettle at 132±2°C, perform the following operations: stop dripping 1,2-propylene glycol, start adding a methanol solution of sodium methoxide (the mass content of sodium methoxide in the methanol solution of sodium methoxide is 1%) at a rate of 220 kg / h below the liquid surface for reflux reaction, stop adding the methanol solution of sodium methoxide after 2 hours, and turn off the reflux; then continue adding methanol at a rate of 220 kg / h below the liquid surface, and collect steam.

[0097] Step (3): The steam is condensed to 0-5°C, and the gaseous substance is the by-product ammonia; the liquid substance is dimethyl carbonate and methanol. The by-product ammonia is dried and enters the ammonia temporary storage tank. The liquid substance is washed and separated to obtain an organic phase (dimethyl carbonate) and an aqueous phase (methanol aqueous solution). The organic phase is dried with anhydrous calcium chloride to obtain dimethyl carbonate, and the aqueous phase is distilled and dried with anhydrous calcium chloride to obtain methanol. Methanol can be recycled.

[0098] After the reaction was carried out for 6 hours, the volume of the material in the reactor had increased from 0.5 times the initial volume to 0.7 times the volume of the reactor. As the material in the reactor continued to accumulate, the reaction could no longer proceed and the feeding reaction was stopped.

[0099] Comparative Example 7 (the total time for adding 1,2-propylene glycol to the reactor is 2 h, and the other steps are the same as in Example 1) Step (1): Add 20 kg of catalyst and 2 kg of auxiliary agent to the reactor, and then continuously add urea and 1,2-propylene glycol to the reactor at a rate of 200 kg / h and 304 kg / h, respectively, for reflux reaction. Start stirring after 30 minutes, and heat the reaction liquid in the reactor to 132±2°C using the heating jacket. Maintain the temperature and continue the dropwise addition for 1.5 hours.

[0100] Step (2): while maintaining the urea dosage (200 kg / h) unchanged and the temperature of the reaction liquid in the kettle at 132±2°C, perform the following operations: stop dripping 1,2-propylene glycol, start adding a methanol solution of sodium methoxide (the mass content of sodium methoxide in the methanol solution of sodium methoxide is 1%) at a rate of 220 kg / h below the liquid surface for reflux reaction, stop adding the methanol solution of sodium methoxide after 2 hours, and turn off the reflux; then continue adding methanol at a rate of 220 kg / h below the liquid surface, and collect steam.

[0101] Step (3): The steam is condensed to 0-5°C, and the gaseous substance is the by-product ammonia; the liquid substance is dimethyl carbonate and methanol. The by-product ammonia is dried and enters the ammonia temporary storage tank. The liquid substance is washed and separated to obtain an organic phase (dimethyl carbonate) and an aqueous phase (methanol aqueous solution). The organic phase is dried with anhydrous calcium chloride to obtain dimethyl carbonate, and the aqueous phase is distilled and dried with anhydrous calcium chloride to obtain methanol. Methanol can be recycled.

[0102] After the reaction was carried out for 10 hours, the volume of the material in the reactor had increased from 0.5 times the initial volume to 0.65 times the volume of the reactor. As the material in the reactor continued to accumulate, the reaction could no longer proceed and the feeding reaction was stopped.

[0103] Although the above describes the specific implementation methods of the present invention, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A method for producing dimethyl carbonate, characterized in that: The following steps are involved: (1) In the presence of a catalyst, add to a reaction vessel: Continuously add urea; the ratio of urea mass flow rate to reaction vessel capacity is: 200-300kg / h:2m 3 ; Add diol and stir to perform reflux reaction; the flow rate of diol is 1.4-1.6 times of the mass flow rate of urea, and the addition time of diol is 1 hour and 20 minutes to 1 hour and 40 minutes; After the addition of diol is stopped, a methanol solution of sodium methoxide is added and stirred to perform a reflux reaction; when the mass of sodium methoxide in the reaction solution is 1-2% of the mass of urea, the addition of the methanol solution of sodium methoxide and the reflux reaction are stopped; the mass content of sodium methoxide in the methanol solution of sodium methoxide is 1-3%, and the flow rate of the methanol solution of sodium methoxide is 1-1.2 times the mass flow rate of urea; After stopping the addition of the methanol solution of sodium methoxide, methanol is continuously added to stir and the steam is collected; the flow rate of methanol is 1-1.2 times the mass flow rate of urea; During the entire process of step (1), the temperature of the reaction liquid in the reaction container is controlled to be 130-150°C; (2) separating ammonia and methanol from the steam to obtain dimethyl carbonate; The auxiliary agent is used in combination with the catalyst, and the auxiliary agent is dodecyl dimethyl tertiary amine; The catalyst is a magnesium oxide supported silica catalyst; The diol is 1,2-propylene glycol.

2. The production method according to claim 1, characterized in that The flow rate of diol is 1.5-1.52 times of the mass flow rate of urea.

3. The production method according to claim 1, characterized in that The addition time of diol was 1.5 h.

4. The production method according to claim 1, characterized in that The temperature of the reaction liquid in the reaction container is 130-134°C.

5. The production method according to claim 1, characterized in that: The mass content of magnesium oxide in the catalyst is 10%-15%.

6. The production method according to claim 5, characterized in that The amount of catalyst used was 0.1 times the amount of urea added per hour.

7. The production method according to claim 5, characterized in that: The dosage of the additive is 0.1 times that of the catalyst.

8. The production method according to claim 1, characterized in that: The ammonia in the steam is separated by condensation, and the methanol is separated by water washing.

9. The production method according to claim 8, characterized in that: The steam is condensed to 0-5°C, and the gaseous substance and liquid substance are collected separately; the gaseous substance is ammonia; the liquid substance is washed and separated to obtain an organic phase and an aqueous phase, the organic phase is dried over anhydrous calcium chloride to obtain dimethyl carbonate, and the aqueous phase is distilled and dried over anhydrous calcium chloride to obtain methanol.

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