CN1241900C - Method for joint production of dialkyl carbonate and diatomic alcohol - Google Patents

Abstract

A low-energy-consumption method for the co-production of dialkyl carbonate and diols, comprising the synthesis of olefinic esters, the preparation of dialkyl carbonates and diols, and the recovery of catalysts. The present invention adopts the petrochemical route, optimizes the process flow and operating parameters on the basis of the original technology, takes the whole process of dialkyl carbonate synthesis as a large system of energy coupling and utilization, and utilizes the reaction heat of vinyl carbonate , and use heat pump technology to control the steam requirement for synthesizing dialkyl carbonate and co-producing glycol at a level of less than 1.0 tons per ton of product. The method of the present invention optimizes the production process of the co-production of dialkyl carbonate and dibasic alcohols, can greatly reduce energy consumption and cooling water consumption, and can reduce steam consumption by 50-90% compared with production devices of the same scale. Cooling water consumption is reduced by 40-60%.

Description

A kind of method of coproduction dialkyl carbonate and dibasic alcohol

technical field

The present invention relates to dialkyl carbonate (Dialkyl Carbonate, DAC), comprise the preparation method of dimethyl carbonate (Dimethyl Carbonate, DMC), diethyl carbonate (Diethyl Carbonate, DEC) etc., particularly relate to ) alkanes, monohydric alcohols, such as methanol and ethanol, and greenhouse gas carbon dioxide as basic raw materials, co-production of ethylene (propylene) glycol and dialkyl carbonate method.

Background technique

Dialkyl carbonate, such as dimethyl carbonate (DMC), is an "environmentally friendly" organic chemical with a wide range of uses, and its toxicity is very low, basically it can be called a non-toxic chemical. It can replace dimethyl sulfate (very toxic) as a methylating agent, and replace phosgene (very toxic) as a carbonylating agent, and can also be used as a gasoline additive to increase the octane number and oxygen content of gasoline (replacing Methyl tert-butyl ether, MTBE), can also be used as a paint solvent, such as replacing xylene and butyl or ethyl acetate, so it has high industrial application value.

There are many synthetic methods for dialkyl carbonate, but there are three main methods with industrial significance. The first is the petrochemical route, which is through the synthesis of ethylene (propylene) carbonate, and then transesterification with alkyl alcohol, while co-producing ethylene glycol or propylene glycol, also known as the transesterification method; the second is the coal chemical route, It is produced by carbonylation and oxidation of monohydric lower alcohols, such as methanol, oxygen and carbon monoxide, also known as carbonylation oxidation; the third is the fertilizer route, which uses urea and monohydric lower alcohols, such as methanol, for alcoholysis. Obtained, ammonia by-product simultaneously.

Problems with traditional technology:

Alkenyl carbonate, including the synthesis of propylene carbonate (PC) or ethylene carbonate (EC): the synthesis of alkenyl carbonate is a reversible reaction with a large heat release, and the catalyst is tetraethylammonium bromide (C ₂ H ₅ ) ₄ N ⁺ Br ^- or KI. Therefore, an effective measure to increase the conversion rate is to continuously reduce the reaction temperature as the reaction proceeds. Traditional method, such as in U.S. Patent No. 4,314,945, adopts product olefinic ester itself as solvent, or claims diluent, and wherein, ethylene carbonate accounts for 85-99.6% (wt), and reactor is a plurality of adiabatic reactions of interstage heat exchange devices in series. Because the reaction heat release of synthetic olefinic ester is relatively large, it is 23kcal/mol, therefore, a device with an annual output of 100,000 tons of DMC, this part of heat emitted per hour is equivalent to 5 tons of steam, and, due to the temperature range of the reaction Wider, between 100-200 °C, low-pressure steam can be produced by-product, but in traditional technology, the heat of reaction has not been well utilized.

Synthesis of dialkyl carbonate: The synthesis of dialkyl carbonate is based on the transesterification reaction of olefinic ester and monohydric alcohol. The catalyst is sodium alkoxide of a strong base dissolved in the reaction feed liquid, which belongs to a homogeneous catalytic reaction. There are catalysts and reaction materials The separation and recycling problem. Although there are many patents or documents that propose the use of insoluble solid bases to constitute a heterogeneous catalytic process, such as US Patent No. 4,661,609, and the document Applied Catalysis: A, 2001, 259-266, there is no problem of catalyst separation. However, the reaction rate of the heterogeneous process is much slower than that of the homogeneous process. In the case of homogeneity, the reaction can approach equilibrium in about 10 minutes, while in the case of heterogeneity, it usually takes several hours. Therefore, the heterogeneous process cannot meet the needs of large-scale production, and the homogeneous process can achieve large-scale production. However, one problem with homogeneous processes is catalyst separation and recycling.

The second problem is that ethylene carbonate and the corresponding diols, such as propylene carbonate + propylene glycol, form an azeotrope, and dialkyl carbonate and the corresponding monohydric alcohol also form an azeotrope, such as methanol and dimethyl carbonate Ester azeotropes have more complex product separation problems. In the applicant's existing Chinese invention patent ZL94112211.5, a reactive distillation technology using a plate column as a reactive distillation column is disclosed, which can make ethylene carbonate completely Conversion, at the bottom of the reactive distillation column, there can be no olefinic esters, PC/EC, eliminating the azeotrope of ethylene carbonates and corresponding diols. However, in the original patent, the reaction temperature in the tower reactor is too high, 185-190° C., which easily causes side reactions of the bottom product ethylene glycol or propylene glycol.

In the case of excessive monohydric alcohol raw materials, the top of the reactive distillation column can obtain monohydric alcohol and dialkyl carbonate, such as a mixture of dimethyl carbonate and methanol, and the two form an azeotrope, and there is a difficulty in their separation. For the dimethyl carbonate process, under normal pressure, the dimethyl carbonate content of the dimethyl carbonate+methanol azeotrope is 30%, methanol is 70% (wt), and the azeotropic point is 63.8°C. The prior art proposes various separation methods. In the applicant's existing Chinese invention patent ZL94112211.5, an extractive distillation technology using ethylene carbonate as an extraction solvent is disclosed. However, the published operating conditions have not been optimized, and the feed molar ratio of the extractant to the azeotrope is as high as 1-2; the reflux ratio of the extractive distillation column is too large, and the energy consumption is also high.

The 3rd problem that dimethyl carbonate is synthesized is, owing to adopted excessive monohydric alcohol, the mol ratio of alcohol and ethylene carbonate is about 10, therefore, a large amount of recycling of monohydric alcohol must bring higher energy consumption, therefore, Using coupled heat utilization technologies such as heat pumps to recycle energy is very meaningful for reducing production costs.

Contents of the invention

The technical problem to be solved in the present invention is to disclose a method for co-producing dialkyl carbonate and dihydric alcohol, so as to solve the defect of high energy consumption in the process by optimizing the process and process conditions.

Technical concept of the present invention is such:

The technology of the present invention belongs to the petrochemical route. On the basis of the original technology (such as the technology disclosed in the ZL94112211.5 patent), the optimization of the flow process and operating parameters has been carried out, and propylene oxide (Propylene Oxide, PO) or ethylene oxide (EO) and CO ₂ as raw materials, the whole process of dialkyl carbonate synthesis as a large system of energy coupling utilization, by utilizing the reaction heat of olefin carbonate, and using heat pump technology, the synthesis of dialkyl carbonate and The steam requirement for the co-production of glycol is controlled at a level of less than 1.0 ton per ton of product (total of dialkyl carbonate and glycol). Taking Propylene Oxide (PO) as an example, its basic reaction principle is as follows:

As a complete process, it is divided into two steps: (1) forming propylene carbonate (Propylene Carbonate, PC) by _CO2 and PO reaction; ) and DMC. These two reactions are actually exothermic reversible reactions limited by equilibrium. The equilibrium constant of reaction (1) is about 1000, and the heat of reaction is about 23kcal/mol. The reaction (2) is about 0.01, and the heat of reaction is very small, as 2-3kcal/mol.

Therefore, the total reaction is 1 molecule of CO ₂ , 1 molecule of propylene oxide and 2 molecules of methanol to generate 1 molecule of DMC and 1 molecule of PG. This process has the following two characteristics:

(1) The atomic utilization rate is 100%, which is a chemical reaction with zero emissions;

(2) Using greenhouse gas CO ₂ as raw material, turning waste into treasure;

Method of the present invention comprises the steps:

Synthesis of ethylene carbonate:

Reasonable use of reaction heat, by-product 0.4-0.6Mpa (temperature about 150 ℃) steam, can be used as a heat source for the reboiler of the dialkyl carbonate synthesis part.

Synthesis of Dialkyl Carbonate:

(1) The monohydric alcohol cycle is in vapor form, not in liquid form. The azeotrope of dialkyl carbonate and monohydric alcohol entering the bottom of the extractive distillation column from the top of the reactive distillation column is steam, that is, the reactive distillation column is partially condensed. The product and reflux at the top of the extractive distillation column are first withdrawn in the form of steam without using a condenser. The steam of the product unit alcohol is directly sent to the bottom of the reactive distillation tower after being pressurized, and is used as a recycled reaction raw material; the monohydric alcohol steam in the reflux part is compressed and heated and used as a heat source for the reboiler of the reactive distillation tower. All monohydric alcohol cycles use heat pumps to make full use of heat;

(2) Increase the molar ratio of monohydric alcohol and vinyl carbonate in the reactive distillation column, reduce the temperature of the tower bottom, and lower the temperature at 70°C-90°C. Since the top temperature of the reactive distillation tower and the extractive distillation tower is about 64°C, pressure can be used to increase the steam temperature at the top of the tower to 90-110°C as a heat source for the reheater of the tower still.

(3) Reduce the extractant/azeotrope molar ratio of the extractive distillation tower, thereby reduce the temperature of the extractive distillation tower still, provide guarantee for making full use of the reaction heat of olefinic ester synthesis part. The temperature of the extractive distillation column is controlled at about 120-140°C, and the low-pressure steam at about 140-160°C is by-produced by the reaction heat of vinyl carbonate.

The above three technical improvements can significantly reduce the steam energy consumption and cooling circulation water volume of the process.

The catalyst for transesterification between olefinic ester and monohydric alcohol generally uses sodium alkoxide, such as sodium methoxide or sodium ethoxide, which is soluble in both monohydric alcohol and dihydric alcohol. Therefore, as long as sodium alkoxide is not converted into sodium carbonate, the catalyst can be recycled for a long time use. However, in the presence of a trace amount of water as a catalyst, the olefinic carbonate reacts easily with sodium alkoxide and becomes sodium carbonate insoluble in the reaction material, resulting in deactivation. In the present invention, after the liquid in the reactor of the reactive distillation column is first evaporated and concentrated, the concentration of the catalyst in the solution is concentrated from 1-3% (wt) to 10-50%, and after being mixed with a monohydric alcohol, the concentration is reduced to 0.5-5%. The undissolved impurities, such as sodium carbonate, etc. are removed through the filter, and fresh catalyst is properly added to maintain the circulating catalyst concentration.

The method of the present invention optimizes the production process of the co-production of dialkyl carbonate and glycol, can greatly reduce energy consumption and cooling water consumption, and can reduce steam consumption by 60-90% compared with production devices of the same scale. Cooling water consumption is reduced by 40-70%.

Description of drawings

Fig. 1 is the synthetic flow chart of vinyl carbonate.

Fig. 2 is the flow chart of synthesizing dialkyl carbonate and dibasic alcohol by transesterification.

Figure 3 is a flow diagram of catalyst recovery and glycols.

Detailed ways

Referring to Fig. 1, Fig. 2 and Fig. 3, method of the present invention comprises the steps:

(1) Synthesis of ethylene carbonate:

Propylene oxide (abbreviated as PO, the same below) or ethylene oxide (abbreviated as EO, the _same below) reacts with CO at first in the first adiabatic reactor 101, and the reaction product enters the external heat exchanger 102, and utilizes the reaction heat by-product The low-pressure steam with a temperature of 145-160°C is used in the subsequent extractive distillation column reboiler, and then partly recirculates into the first adiabatic reactor 101, and partly enters the second first adiabatic reactor 103 for reaction. The flow rate of the heat exchanger 102 and the weight flow ratio entering the second reactor 103 are 5-30, preferably 10-20, preferably around 15, the inlet temperature of the first reactor 101 is 140-160° C., and the outlet temperature is 175-190°C, the temperature entering the second reactor is 130-145°C, preferably 135-140°C.

Other reaction conditions are:

The pressure P of the first reactor is 2-8Mpa, generally 3-6Mpa, preferably 4-4.5Mpa.

Raw material ratio CO ₂ /PO or EO=1.01-1.1, generally 1.03-1.05 (molar ratio).

The catalyst tetraethylammonium bromide/PO or EO=0.01-1.0%, generally 0.1%-0.5% (molar ratio).

After passing through the reaction system, the total conversion rate of PO or EO is greater than 99%, even greater than 99.5%.

The olefinic ester product from the second reactor 103, which contains unconverted CO ₂ and PO or EO, and catalyst tetraethylammonium bromide, is called crude olefinic ester. The crude enyl ester enters the decompression flash tank 104, the pressure of the flash tank 104 is 70-120kPa, the temperature is 130-180°C, preferably between 160-170°C, and the excess CO ₂ and PO are removed, and then enters the negative Press the refining tower 105, the top of the tower is ethylene carbonate, and the bottom of the tower is catalyst and ethylene carbonate (alkene carbonate is also used here as a solvent for dissolving the catalyst), which circulates into the first reactor 101. Since the by-products of high polymers may be produced, which may affect the activity of the catalyst to some extent, a small part can also be periodically drawn out to remove high polymers, that is, catalyst regeneration.

The pressure of the negative pressure refining tower 105 is 1-15kPa, generally 5-10kPa. The ratio of the reflux amount of ethylene carbonate to the amount of olefin carbonate produced is controlled between 0.1 and 0.5 (molar ratio), generally between 0.2 and 0.3. The temperature difference between the top of the negative pressure refining tower 105 and the bottom of the tower is not big, generally between 1-10°C, the temperature of the bottom of the tower is between 140-180°C, generally between 150-160°C, and the top of the tower is also between 150-100°C Between 160°C.

The product of the negative pressure refining tower 105 enters the top heat exchanger to produce low-pressure steam by-product. This part of the low-pressure steam can be directly used for the primary evaporation of the feed liquid in the subsequent reactive distillation column. Therefore, the steam heat at the top of the olefinic ester refining tower (also can be regarded as the heat consumed by the ethylene carbonate catalyst recovery) can be used for dialkyl carbonate catalyst recovery.

Like this, the heat of reaction of the reactor of the vinyl carbonate synthesis part and the secondary steam of the refining tower can be effectively utilized in the dialkyl carbonate synthesis part.

In addition, tetraethylammonium bromide is mainly used as the catalyst for ethylene carbonate synthesis, which is directly synthesized from triethylammonium and ethyl bromide in ethylene carbonate solution with a concentration of 10-20% (wt) and a temperature of 60-120°C.

(2) Preparation of dialkyl carbonate (abbreviated as DAC, hereinafter the same) and dibasic alcohol:

Alkenyl carbonate first enters the extractive distillation tower 202 as an extractant, and the monohydric alcohol and the DAC azeotrope steam separated from the top of the reactive distillation tower 201 are separated, and the monohydric alcohol is extracted from the top of the extractive distillation tower 202, and partly compressed by a compressor 204 After the pressure is increased and the temperature is raised, it is used as the heat source for the reboiler of the reactive distillation tower 201, and then refluxed after condensation. Part of the monohydric alcohol is pressurized and heated by the compressor 204 and then circulated into the reactive distillation tower 201 as a reaction raw material. The reactive distillation tower 201 The top of the tower is partially condensed, and the condensate is used as a reflux liquid. The uncondensed steam enters the extractive distillation tower 202, and the bottom of the extraction distillation tower 202 is crude DAC, which enters the diester tower 203, and high-purity DAC is obtained at the top of the tower, and the bottom of the tower is Ethylene carbonate, the material extracted from the tower kettle is divided into two stocks, one is recycled into the extractive distillation tower 202, and the other is used as the raw material of the reactive distillation tower 201. The mol ratio of the material entering the extractive distillation tower 202 and the material entering the reactive distillation tower 201 is 2～8;

The main feature of this step is that the azeotrope entering the extractive distillation column 202 from the reactive distillation column 201 is steam; The heat source of the tower kettle reboiler in tower 201 is condensed and then refluxed; the product monohydric alcohol is extracted in the form of steam, and then circulated into the reactive distillation tower 201 tower after being pressurized and heated as a reaction raw material;

The temperature of the reactor of the reactive distillation column 201 is 70-80°C. The purpose is to raise the latent heat of the steam in the reflux part of the extractive distillation column 202 to 90-100°C by pressurization, and use it as a heat source for the reboiler of the reactive distillation column 201. a part of.

The steam at the top of the reactive distillation tower is partially condensed, and the uncondensed steam is used as the raw material of the downstream extractive distillation tower 202, which is steam, which can reduce the steam consumption of the reactive distillation tower 201 and the consumption of cooling circulating water.

The reactive distillation column 201 adopts a tray column, and the total vapor phase resistance is between 10-30kPa, generally controlled between 12-16kPa. The operating pressure at the top of the extractive distillation column 202 is normal pressure, which is 101-105 kPa, generally between 101-102 kPa. The extractive distillation column 202 can also be a tray column, and the total vapor phase resistance is between 5-15kPa, generally between 8-10kPa. Thus, the total pressurized head of the circulating unit alcohol is 20-25 kPa.

The main operating parameters of the reactive distillation column 201 are as follows:

The total feed molar ratio of monohydric alcohol to vinyl carbonate is between 11 and 13.

The amount of catalyst circulation, converted to 100% sodium ions, has a content of 0.05-0.5% (wt) in the liquid phase in the reactive distillation column 201 .

The recycled catalyst is preferably mixed with all fresh monohydric alcohols, not recycled unit alcohols, into the reactive distillation column 201, and the molar ratio of the amount of fresh monohydric alcohols to dialkyl carbonate is 2-4.

The reflux ratio of the reactive distillation column 201 is 0.1-0.5;

Reactive distillation tower 201 tower bottom temperature is 65～90 ℃, preferably at 70～80 ℃;

The operating pressure at the top of the reactive distillation column 201 is 70-120 kPa, generally between 101-105 kPa.

In the reactive distillation column 201, the liquid phase flows through each tray, especially the tray where reaction and rectification exist simultaneously, and the average residence time of the liquid is controlled at 0.1-20 minutes, generally controlled at 1-5 minutes, the most Fortunately, 2-3 minutes. The control of residence time is not only to ensure that sufficient reaction residence time is provided for the transesterification reaction of synthesizing dialkyl carbonate, but also to limit the reaction speed of side reaction simultaneously. The side reaction is mainly the etherification reaction of dihydric alcohol and monohydric alcohol.

In the reactive distillation 201 column, olefinic carbonate can be completely converted. The dialkyl carbonate and monohydric alcohol of azeotrope are obtained at the top of the tower;

For the extractive distillation column 202 and the diester column 203, the main operating parameters are as follows:

Higher purity olefinic esters from the synthetic part of olefinic esters, the purity is greater than 99.9%.

The feed molar ratio of the extractant to the azeotrope is 0.2-1.0, preferably between 0.3-0.5, which can maintain the temperature of the bottom of the extractive distillation tower at 120-140°C, and facilitate the use of olefinic ester synthesis reactors By-product low-pressure steam.

The monohydric alcohol extracted from the top of the extractive distillation tower 201 is pressurized and then circulated to the reactive distillation tower 201 with a pressure head of 20-30kPa. The methanol returned to the top of the extractive distillation tower 202 is pressurized and heated to 90-100°C , the pressure is between 200 ~ 300kPa, as the heat source for the reboiler of the reactive distillation column 201;

The extractive distillation column 202 is operated under normal pressure, the diester column 203 is operated under negative pressure, and the pressure at the top of the column is between 1-20kPa, generally between 5-10kPa. The temperature of the tower kettle is between 150-170°C.

(3) Catalyst recovery and refining of dibasic alcohols:

The dibasic alcohol liquid product stream that comes from the reaction distillation tower 201 tower kettle contains monohydric alcohol, dibasic alcohol and catalyst, also contains a small amount of ether, enters evaporation flash tank 301, and the feed liquid of evaporation flash tank 301 is the catalyst of concentration The solution, in which the catalyst concentration is 5-30% (wt) in terms of sodium, is partially sent to the circulation heater 302 through the circulation pump 301, then returns to the evaporation flash tank 301, and the other part enters the circulation catalyst preparation tank 303. In the preparation tank 303, the raw material monohydric alcohol required by the reactive distillation column is used as a diluent, and the concentration of the catalyst is prepared between 0.2% and 2% (wt). The prepared catalyst circulates through the filter 304 to remove undissolved solids therein and then circulates into the reactive distillation column 201, and replenishes fresh monoalkoxide sodium catalyst to maintain the concentration of the catalyst.

The use of this arrangement and form of evaporation is particularly suitable for the process to which the present invention relates. Because the evaporated feed liquid contains metal sodium alkoxide and even undissolved sodium carbonate, this form can prevent or alleviate the scaling caused by the salting-out effect on the heating tube wall.

The dibasic alcohol and monohydric alcohol vapor at the top of the evaporating flash tank 301 enter the dibasic alcohol product tower 305, obtain the high-purity dibasic alcohol product in the tower still of the dibasic alcohol product tower 305, and also can draw out near the side line of the tower kettle, Can prevent the color of the product from appearing.

Glycol product tower 305 tower top adopts partial condensation, and the discharge is monohydric alcohol steam, wherein also contains glycol and ether, enters monohydric alcohol recovery tower 306, and in monohydric alcohol recovery tower 306, tower top obtains purity very high For high monohydric alcohols, ethers and dihydric alcohols are obtained from the tower reactor.

The output from the bottom of the monohydric alcohol recovery tower 306 enters the ether refining tower 307, and the ether refining tower 307 adopts batch rectification to obtain ether with high purity.

The main operating parameters are as follows:

The pressure of the evaporator 301 is 5-30kPa, and the temperature is 120-140°C;

The operating pressure at the top of the glycol product column 305 is between 5-30kPa, generally between 15-20kPa. The temperature of the tower kettle is controlled between 130-150°C, preferably between 135-140°C, so as to prevent the condensation side reaction of diols as much as possible.

The tower top operating pressure of monohydric alcohol recovery tower 306 is 5～30kPa, but in order to make the vapor of dihydric alcohol product tower 305 tower head directly flow to monohydric alcohol recovery tower 306, monohydric alcohol recovery tower 306 tower top pressure should be higher than dibasic alcohol The pressure at the top of the product tower 305 is 1-3kPa lower, and the pressure at the bottom of the monohydric alcohol recovery tower 306 is 50-65°C.

The ether refining tower 307 generally adopts batch rectification, and the operating pressure at the top of the tower is 5-30kPa. First, the monohydric alcohol with a low boiling point (generally containing a small amount of monohydric alcohol) is taken out, and then the ether is taken out. The remaining feed liquid in the tower kettle enters the evaporation tank 301 or Polyhydric alcohol product column 305, recovering dihydric alcohol.

Example 1

Take a device that co-produces 60,000 tons of dimethyl carbonate and 50,000 tons of propylene glycol as an example:

Raw materials: PO=87.5 kmol/h, CO ₂ =91.85 kmol/h, methanol=178.5 kmol/h.

The operating conditions for the olefinic ester moiety are:

The overall conversion of PO to the olefin carbonate moiety was 99.64%, and the yield of PC was 99.5%.

(1) the amount of circulating catalyst (calculated with 100% tetraethylammonium bromide) is 0.18kmol/h;

(2) The inlet temperature of the first reactor R101 is 153°C, the pressure is 4.2MPa, the outlet temperature is 178°C, the circulation ratio is 15.7, and the heat of by-product steam is 8.6×10 ⁶ kJ/h;

(3) The inlet temperature of the second reactor is 137°C;

(4) The pressure of the atmospheric pressure flash tank is 110kPa, and the temperature is 155°C;

(5) The top pressure of the refining tower T101 is 10kPa, the top temperature is 164°C, the reflux ratio is 0.3, the temperature of the tower bottom is 167°C, and the heat required by the bottom of the tower is 5.8×10 ⁶ kJ/h, which is provided by external steam. The available heat at the top of the tower is 6.1×10 ⁶ kJ/h.

The main operating conditions of the co-production part of dialkyl carbonate and dibasic alcohol are:

(1) total methanol/PC=11.8 in reactive distillation column;

(2) The reflux ratio is 0.4;

(3) The temperature of the tower kettle is 75°C;

(4) The total number of trays is 45, the feed plate of catalyst, fresh methanol and PC mixture is the fifth plate from the top of the tower downward, and the feed plate of methanol vapor recycled from the extractive distillation column is the fifth plate from the bottom of the tower. 10 pieces;

(5) Under normal operation, the reactive distillation tower does not need additional steam as the heat source of the reboiler, and its heat source is completely provided by the methanol vapor at the top of the extractive distillation tower;

(6) obtain the mixture of methyl alcohol and DMC at tower top, methanol content is 71% (wt), and DMC is 29% (wt), and total flow is 27.02 tons/h;

(7) obtain the mixture of methyl alcohol, propylene glycol, propylene glycol monomethyl ether and catalyst in tower still, the flow rate of each component is: methyl alcohol=8080kg/h, propylene glycol=6551.2kg/h, propylene glycol monomethyl ether=77.625kg/h, Catalyst sodium methoxide = 100kg/h;

(8) the total molar ratio of the PC/azeotrope of extractive distillation column is 0.5;

(9) the tower bottom temperature of extractive distillation tower is 138 ℃;

(10) The shaft power of the methanol compressor circulating from the top of the tower to the reactive distillation tower is 56kW, and the circulation capacity is 19.2 tons/h;

(11) The reflux vapor at the top of the tower is compressed to 200kPa, the temperature is 105.8°C, the shaft power required by the compressor is 78.5kW, and the amount of methanol compressed is 9.6 tons/h, which is equivalent to the reflux ratio of the extractive distillation column being 0.5;

(12) The reboiler of the extractive distillation column requires heat of 8.4×10 ⁶ kJ/h, while the temperature of the by-produced steam from the olefinic ester synthesis reactor is 150°C, and the heat is 8.6×10 ⁶ kJ/h , all of which are utilized here;

(13) The operating pressure at the top of the diester tower (that is, the extraction agent recovery tower) is 10kPa, the reflux ratio is 1.0, the temperature of the tower bottom is 161°C, and the heat required by the tower bottom is 5.9×10 ⁶ kJ/h, which is supplied from outside steam supply;

(14) Dimethyl carbonate with a purity of 99.8% (wt) was obtained in the diester tower reactor, and the mass flow rate was 7851 kg/h, which is equivalent to an annual output of dimethyl carbonate of 62810 tons/h.

The main operating conditions of catalyst recovery and PG refining part:

(1) The operating pressure of the evaporator is 15kPa, the temperature is 132°C, the required heat is 12.2×10 ⁶ kJ/h, and the by-product steam heat of the olefinic ester refining tower is 5.75×10 ⁶ kJ/h, and the remaining The heat of 6.45×10 ⁶ kJ/h is provided by external steam;

(2) The operating pressure of the PG refining tower is 14kPa, and the tower still temperature is 135 ° C, and the required heat is 2.8 × 10 ⁶ kJ/h, which is provided by external steam supply, and the tower still obtains propylene glycol with a purity of 99.9% (wt), The mass flow rate is 6538kg/h, which is equivalent to an annual output of propylene glycol of 52305 tons/h;

(3) The operating pressure at the top of the methanol recovery tower is 12kPa, the temperature at the bottom of the tower is 65°C, the heat to be provided is 2.5×10 ⁶ kJ/h, which is provided by external steam, and the purity obtained at the top of the tower is 99.5% (wt). Methanol, the mass flow rate is 8080kg/h;

(4) ether tower is batch rectification, can obtain the propylene glycol monomethyl ether of 77kg/h from tower top, and purity is 99.5% (wt).

Therefore, the total heat required to be provided by external steam is:

5.75+5.94+6.45+2.8+2.5＝23.44× ¹⁰⁶ kJ/h,

Equivalent to 11.2 tons of steam/h.

Since the total output per hour is 7851+6538=14389kg/h, the steam demand per ton of product is:

11.2/14.389=0.7785 tons, less than 1 ton/h.

Claims (6)

1. a method for co-producing dialkyl carbonate and glycols, comprising the synthesis of ethylene carbonate, the preparation and catalyst recovery of dialkyl carbonates and glycols, characterized in that the synthesis of olefin carbonates includes The reaction of propylene oxide or ethylene oxide with _CO2 and the refining of ethylene carbonate, propylene oxide or ethylene oxide and _CO2 first react in the first adiabatic reactor (101), and the reaction product enters the external heat exchange Device (102), by-product low-pressure steam, then through the second adiabatic reactor (103) reaction, the thick product of vinyl carbonate that reaction generates enters decompression flash tank (104), then enters negative pressure refining tower (105 ), the mol ratio of the vinyl carbonate reflux flow at the top of the tower and the extracted vinyl carbonate amount is 0.1～0.5, and the negative pressure refining tower (105) tower top and tower still temperature difference 1～10 ℃, the negative pressure refining tower (105 ) The tower top product enters the tower top heat exchanger, and by-product low-pressure steam; The preparation of dialkyl carbonate and dibasic alcohols includes reactive distillation in which monohydric alcohol reacts with olefinic esters, and extractive distillation in which ethylene carbonates are used as extractants; The monohydric alcohol is extracted from the top of the extractive distillation tower (202), and part of the monohydric alcohol is used as the heat source for the reboiler of the reactive distillation column (201) after being compressed and heated up, and then refluxed after condensation. Circulate into the reactive distillation column (201) as the reaction raw material, the top of the reactive distillation column (201) is partially condensed, the condensate is used as the reflux liquid, and the uncondensed steam enters the extractive distillation column (202); The mol ratio of the material entering the extractive distillation tower (202) and the material entering the reactive distillation tower (201) is 2 to 8; Catalyst recovery and the refining of dibasic alcohol comprise the following steps: the liquid product flow that comprises dibasic alcohol, monobasic alcohol and catalyzer from reactive distillation tower (201) tower bottom, enters evaporation flash tank (301), passes through circulation pump ( 301) part is sent into circulating heater (302), then returns to evaporation flash tank (301), and another part enters circulating catalyst preparation tank (303), enters reactive distillation tower (201) after being mixed with fresh monohydric alcohol ); The product dibasic alcohol is directly extracted from the bottom of the dibasic alcohol refining tower (305) or the lower side line, and the product at the top of the tower (305) is extracted as steam, which directly enters the monobasic alcohol recovery tower; The low-pressure steam by-produced by the heat exchanger (102), and the low-pressure steam by-produced by the overhead product of the negative pressure refining tower (105) are used as the heat source for the bottom reboiler of the extractive distillation tower and the evaporator for catalyst recovery. 2. method according to claim 1, it is characterized in that, the unit alcohol step-up range that the tower top of extractive distillation tower (201) is extracted is 20-30kPa, the methyl alcohol of extractive distillation tower (202) tower top reflux After pressurization, the temperature is raised to 90-100°C, and the pressure is 200-300kPa. 3. The method according to claim 1, characterized in that the reflux ratio of the reactive distillation column (201) is 0.1-0.5. 4. The method according to claim 3, characterized in that the temperature at the bottom of the reactive distillation column (201) is 65-90°C. 5. The method according to claim 1, characterized in that the feed molar ratio of the extractant to the azeotrope is 0.2 to 1.0. 6. The method according to claim 1, characterized in that the temperature of the bottom of the extractive distillation column (202) is 120-140°C.

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