CN1049212C - Improved synthetic method of dialkyl carbonate - Google Patents

Abstract

The invention discloses an improved synthesis method of dialkyl carbonate, which mainly includes three processes of reactive distillation, extractive distillation and diester separation. The reactive distillation process is mainly carried out in the reaction section of the reactive distillation tower. All olefinic carbonates can be converted into dialkyl carbonates, which has the advantages of high conversion rate (up to 99.8%), low energy consumption, and simple process.

Description

A kind of synthetic method of improved dialkyl carbonate

The invention belongs to the field of chemical reaction engineering, in particular to a synthesis method of alkyl carbonate.

As we all know, dialkyl carbonate (mainly referring to dimethyl carbonate and diethyl carbonate) is a useful intermediate cost in organic synthesis, not only can synthesize many organic chemical products, but also can replace dimethyl sulfate (very toxic product) as an alkylating agent, replacing phosgene (a highly toxic drug) as a carbonylating agent, but its greatest use is as a gasoline additive, which can increase the octane number and oxygen content of gasoline and make unleaded gasoline, so It has broad market prospects.

In 1972, U.S. Patent USP3642858 (hereinafter referred to as A patent) disclosed this "method for synthesizing dimethyl carbonate with acrylic acid and methyl alcohol", but there were three major problems in this method:

(1) The transesterification reaction of the material system is reversible, and the conversion rate of its reaction equilibrium is very low;

(2) reaction product dimethyl carbonate forms azeotrope with raw material methyl alcohol, causes separation difficulty;

(3) By-product propylene glycol and raw material propylene carbonate also form azeotropes, which also cause difficulties in separation.

For this reason, in 1974, U.S. Patent USP3803201 (hereinafter referred to as the B patent) improved the A patent and proposed:

(1) Distillation is adopted to evaporate the azeotrope of dimethyl carbonate and methanol in the reactant system to strengthen the reaction and improve the conversion rate of the transesterification reaction;

(2) Freeze the azeotrope of dimethyl carbonate and alcohol by adopting the frozen distillation method, (cryogenic cooling to -70°C), and then carry out rectification separation to extract dimethyl carbonate and recover methanol respectively .

Obviously, this method consumes a lot of energy, and the conversion rate of transesterification is less than 60%, so the production cost is also very high.

China's Zhang Shaogang and Luo Youshou (see "Natural Gas Chemical Industry", Vol. 16, No. 3, 1991) used propylene carbonate and methanol as raw materials to synthesize dimethyl carbonate, conducted verification research on B patent and technology, and found that:

(1) The transesterification reaction is mainly carried out in the tower kettle, and there are at least five components (two raw materials, two azeotropes, and a homogeneous catalyst) in the tower kettle, which not only brings great difficulties to the separation , And it affects the improvement of the conversion rate of the transesterification reaction.

(2) In order to improve the conversion rate, the azeotrope of dimethyl carbonate and methanol must be distilled out under the condition that the reflux ratio is as high as 8 to 10 (the conversion rate can be increased to 80%), so the energy consumption is very large, such as If the reflux ratio is reduced, the amount of azeotrope evaporated will be small, and the conversion rate will be less than 60%.

It can be seen that the above-mentioned prior art has not yet found a suitable method to further improve the conversion rate.

In 1987, the US patent USP4691041 (hereinafter referred to as C patent) improved the A patent and the B patent and proposed;

(1) Adopt strong basic ion exchange resin as the catalyst of esterification to solve the separation problem of catalyst;

(2) adopt pressurized rectification method, the dimethyl carbonate obtained by reaction separation and the azeotrope of methyl alcohol are separated and extracted respectively;

(3) By hydrolysis, the by-product ethylene (or propylene) glycol and ethylene carbonate in the azeotrope of ethylene carbonate is hydrolyzed into ethylene (or malonic) dioic acid and sodium carbonate for processing.

Apparently, the process of this method is more complicated, the operation is inconvenient, the utilization rate of the raw material is low (because the raw material vinyl carbonate is hydrolyzed), and the conversion rate has not been improved.

In 1988, Japanese Patent No. 63-205101 proposed a method for separating dimethyl carbonate and methanol azeotrope, using benzene and methanol to form a new azeotrope with a lower constant boiling point than methanol and dimethyl carbonate , thereby separating dimethyl carbonate, and the methanol in the new azeotrope is extracted with water and then recovered by distillation. Although this method has solved the separation problem of methyl alcohol and dimethyl carbonate preferably, because distillation must be used to reclaim methanol, it still needs more energy consumption, and the water-containing methanol returns to the system so that the product dimethyl carbonate also contains water. portion, affecting product quality, so this method is also unsatisfactory, and does not involve the improvement of conversion rate in patent A.

In summary, it can be seen that so far, the prior art has not properly resolved the three major problems involved in patent A, namely:

(1) How to take appropriate technical measures to make ethylene carbonate all be converted into dialkyl carbonate, that is, the conversion rate of ethylene carbonate reaches 100% during transesterification;

(2) How to take appropriate technical measures to separate and obtain methanol (or ethanol) and dialkyl carbonate azeotrope under low energy consumption, and then solve methanol (or ethanol) and carbonic acid in a complete manner under low energy consumption Separation of dialkyl esters;

(3) How to take appropriate technical measures to solve the problem of purification of the bottom product under low energy consumption. Obviously when the technical measures of (1) were fully resolved, then the separation of the bottom product became much easier.

The purpose of the present invention is to comprehensively overcome the three major problems of patent A, and propose an improved synthesis method of dialkyl carbonate, which can completely convert olefinic esters into dialkyl carbonate, and produce Separate and obtain dialkyl carbonate product and by-product ethylene (or propylene) glycol. Design of the present invention is such:

(1) According to the principle of reactive distillation, the transesterification reaction and separation are all carried out in the reaction section (rather than the reaction in the tower kettle as in the predecessors, and the separation is carried out in the tower section), so that the reaction product When it is generated, it is separated and removed, thereby constantly breaking the balance, increasing the driving force of the reaction, making the reaction develop in a direction that is conducive to the generation of products, and finally the raw material vinyl carbonate is completely converted into products.

(2) By increasing the feed ratio of the raw material "alcohol and vinyl carbonate", the upper part of the reactive distillation column is obtained as a mixture of dialkyl carbonate and alcohol, rather than azeotrope, so it can be used at a low reflux ratio The rectification and separation can be carried out under the lower conditions, thereby greatly reducing energy consumption.

(3) According to the principle of extractive distillation, the "steam" of the mixture of alcohol and dialkyl carbonate from the top of the reactive distillation tower is directly sent into the extractive distillation tower, and the corresponding ethylene carbonate is used as the extraction agent to remove the carbonic acid Dialkyl esters are extracted. The extract phase is obtained at the bottom of the tower—a mixture of dialkyl carbonate and carbon ester enester (referred to as the mixture of diesters, the same below), and the raffinate phase is obtained at the top of the tower—alcohol can be directly returned to the reactive distillation column for recycling. The diester mixture of gained enters in the diester separation tower, and through fractionation, the dialkyl carbonate product that purity reaches 99.8% (wt) above can be obtained at the top of the tower, and the olefinic ester of purity > 99% can be obtained at the bottom of the tower, which can be returned to It is recycled in the extractive distillation column. Separation is easy due to the large boiling point difference between the diesters.

(4) The by-product ethylene (or propylene) glycol of the reaction, because ethylene carbonate is almost all converted into dialkyl carbonate in the system, so only a trace amount of ethylene carbonate is contained in the by-product ethylene (or propylene) glycol Ester, and a small amount of catalyst (sodium alkoxide) and alcohol, its separation is relatively easy, it can be purified through the stripping section under the reactive distillation tower, and ethylene (or propylene) glycol with a purity of more than 99% is discharged . The present invention also realizes like this:

The method of the invention mainly includes three technological processes of reactive distillation, extractive distillation and diester separation.

(1) In a reactive distillation column mainly composed of a tower kettle, a stripping section, a reaction section and a rectification section, the reaction material vinyl carbonate and the catalyst sodium alkoxide dissolved with a small amount of alcohol enter the reactive distillation from the upper part of the reaction section tower, a large excess of raw material alcohol (methanol or ethanol) enters the reactive distillation tower from the lower part of the reaction section, and the two materials are in countercurrent contact in the reaction section, and are separated while performing transesterification, so that the product with a low boiling point of carbonic acid Alkyl esters are continuously vaporized and removed from the system. Said reactive distillation column is a tray column. Through the reaction section, the reaction material alkenyl carbonate is completely converted into dialkyl carbonate. The mixed steam of a large excess of alcohol (methanol or ethanol) and dialkyl carbonate goes up into the rectification section of the upper part of the reactive distillation column, and is further refined and recovered the entrained carbonic acid under the condition of reflux ratio of 0.6-1.0 The recovered olefinic carbonate descends to the reaction rectification section to continue to participate in the reaction, and the refined dialkyl carbonate and alcohol mixed steam (except the reflux part) directly enters the extractive distillation tower. The reaction by-product ethylene (or propylene) glycol, as well as a small amount of ethylene carbonate, a small amount of sodium alkoxide and alcohol enter the stripping section of the reactive distillation column, and the ethylene carbonate and sodium alkoxide are recovered through the stripping section. After mixing with alcohol, ethylene (or propylene) glycol with a purity of >99% enters the tower still, and is quantitatively discharged outside the tower still, and then can be sold as a product after being refined by further rectification. The operating pressure of the reactive distillation column is 90-110KPa, preferably under normal pressure. The molar ratio of alcohol/alkenyl carbonate can be selected within the range of 6-10. When methanol is used as raw material, the feeding molar ratio should be 8-10; when ethanol is used as raw material, the feeding molar ratio should be 6-8.

(2) In an extractive rectification tower mainly composed of tower kettle, stripping section, extraction section and rectification section, the mixed steam of dialkyl carbonate and alcohol (methanol or ethanol) from the reactive distillation tower Enter the lower part of the extraction section of the extractive distillation tower, and the extraction agent vinyl carbonate enters the tower from the upper part of the extraction section, and the two carry out countercurrent contact in the extraction section, so that all the dialkyl carbonate enters the extraction agent. The raffinate methanol goes up into the rectification section of the tower. Under the condition of reflux ratio of 0.6-1.2, after further refining to remove the entrained olefinic ester, methanol with a purity of more than 99% can be recovered, and the recovered methanol is returned to the reactive distillation recycled in the tower. The extraction phase is a mixture of ethylene carbonate and dialkyl carbonate (referred to as the diester mixture, the same below), which passes through the stripping section of the extractive distillation tower in a downward direction, removes the entrained methanol, then enters the tower kettle, and then quantifies It is discharged from the tower kettle and enters the diester separation tower. Said extractive distillation column is also a plate column. The amount of the extraction agent ethylene carbonate can be selected within the scope of the molar ratio of the extraction agent to the methanol in the mixed gas within 1-2. The top reflux ratio should be 0.8-1.0. The extractive distillation process should be carried out under normal pressure, but it can also be operated under negative pressure, for example, it can be operated under pressure of 70-101KPa.

(3) In a diester separation tower mainly composed of a tower bottom and a fractionation section, the diester mixture from the extractive distillation tower bottom enters the middle part of the fractionation section of the diester separation tower, and after fractionation, it is at the top of the tower Alkyl carbonate products with a purity greater than 99.8% (wt) can be obtained, and vinyl carbonate products with a purity greater than 99.9% (wt) can be recovered in the tower kettle, and the recovered vinyl carbonate can be returned to the extractive distillation tower for recycling. All the energy required for the fractionation process is provided by the external heat from the bottom of the tower. The reflux ratio at the top of the tower is 0.4-0.6, and the temperature of the tower kettle is 160-180°C. It should be operated under negative pressure, and the suitable operating pressure is 30-50KPa.

The content of the present invention will be further clarified below in conjunction with the drawings and examples, but these examples do not limit the protection scope of the present invention.

Accompanying drawing 1 is the technological process schematic diagram of production dialkyl carbonate of the present invention

in:

F—reactive distillation column

F ₁ —column, F ₂ —stripping section,

F ₃ —reaction section, F ₄ —rectification section,

1—the inlet of raw material alcohol, 2—the inlet of raw material ethylene carbonate,

3—Mixed gas outlet, 4—Return liquid inlet,

5—Ethylene (or propylene) glycol outlet.

T—extractive distillation column

T ₁ —column, T ₂ —stripping section,

T ₃ —extraction section, T ₄ —rectification section,

6—Mixed gas inlet, 7—Alcohol (gas) outlet,

8—reflux inlet, 9—extractant inlet,

10—the outlet of the diester mixture, 11—alcohol (liquid) delivery pipe.

D—diester separation tower

D ₁ —column, D ₂ —fractionation section,

12—inlet of diester mixture, 13—outlet of dialkyl carbonate

14—reflux inlet, 15—extractant outlet.

C ₁ , C ₂ , C ₃ — condenser

B ₁ , B ₂ , B ₃ — pumps

E—gas-liquid separator

16—dialkyl carbonate inlet,

17—Export of dialkyl carbonate products,

18—Exhaust gas outlet.

In the reactive distillation column F:

The alcohol from the storage tank is pumped into the lower part of the reaction section _F3 from inlet 1 after being metered, and the olefinic ester from the storage tank and the catalyst sodium alkoxide prepared by dissolving alcohol are respectively metered and then enter the reaction section _F3 from inlet 2 In the upper part, the two are subjected to transesterification and separation in the reaction section _F3 under the action of the catalyst sodium alkoxide. The mixed steam of the reaction product dialkyl carbonate and alcohol (referred to as the mixed gas, the same below) goes up through the rectification section _F4 to recover and remove the entrained olefinic ester material, and then it is discharged from the outlet 3, and part of the mixed gas is not condensed It is directly introduced into the lower T of the extractive distillation tower, and part of the mixed gas is condensed by the condenser C according to the reflux ratio required for tower operation, and then returned to the top of the reactive distillation tower through the reflux liquid inlet 4. The reaction by-product ethylene (or propylene) glycol and the entrained ethylene carbonate, alcohol and sodium alkoxide etc. then descend into the stripping section _F2 , and after stripping and refining, the ethylene (or propylene) diol with a purity greater than 99% is obtained. Alcohol enters the tower kettle _F1 , and is quantitatively discharged from the outlet 5 outside the kettle. In the extractive distillation column T:

The mixed gas from the top of the reactive distillation tower F enters the bottom of the extraction section _T3 through the inlet 6, and the extractant vinyl carbonate from the storage tank (or diester fractionation tower still) enters the extraction section _T3 through the inlet 9 In the upper part, the two are subjected to countercurrent extraction in the extraction section _T3 , and the dialkyl carbonate is extracted into the olefinic carbonate (referred to as the diester mixture, the same below). The diester mixture descends into the stripping section _T2 , removes the entrained alcohol, then enters the tower tank _T1 , and then quantitatively discharges out of the tank through the outlet 10, and is sent to the diester separation tower D by the pump _B2 . The raffinate phase (alcohol) goes up into the rectifying section _T4 , and after recovering and removing entrained olefinic esters, alcohol with a purity greater than 99% is obtained, which is discharged from the top of the tower through outlet 7, and then condensed by the condenser _C2 , and a part is obtained by The reflux ratio is required to return to the top of the extractive distillation column through the reflux liquid inlet 8, and another part of alcohol is sent to the reactive distillation column through the delivery pipe 11 for recycling. In the diester separation column D:

The diester mixture from the extractive distillation column is pumped into the middle part of the fractionation section _D2 through the inlet 12 by the pump _B2 , and undergoes fractionation at a pressure of 30-50KPa. The dialkyl carbonate obtained by fractional distillation goes up, and is discharged from the top of the tower through outlet 13. After being condensed by condenser _C3 , a part is returned to the top of the diester separation tower through inlet 14 according to the reflux ratio requirements during the operation of the diester splitter tower, and the other part is Then it enters the gas-liquid separator E through the inlet 16, and is discharged from the outlet 17 after the gas-liquid separation, and the tail gas after the gas-liquid separation enters the vacuum system through the outlet 18. The olefinic carbonate obtained by splitting descends into the tower _{still D1} , then quantitatively discharges out of the still through the outlet 15, and is pumped into the extractive distillation tower by the pump _B3 through the inlet 9 for recycling.

Example 1

In a process device mainly composed of a reactive distillation tower, an extractive distillation tower and a diester separation tower, propylene carbonate and methanol are input as raw materials, and dimethyl carbonate is produced under the action of catalyst sodium methoxide.

Said reactive distillation tower is a tray tower with a diameter of 1000 mm and a height of 18000 mm, with 36 trays inside, of which: 30 for the reaction section, 5 for the stripping section, and 1 for the rectifying section.

Said extractive distillation tower is a tray tower with a diameter of 1000 mm and a height of 15000 mm, with 23 trays inside, of which: 15 extraction sections, 7 stripping sections, and 1 rectification section.

Said diester separation tower is a tray tower with a diameter of 800 mm and a height of 2000 mm, with 3 trays inside, all in the fractionation section. The reactive distillation column operates under the following conditions:

Raw material methyl alcohol enters the bottom of reaction section with the speed of 1078.4kg per hour, and the speed of 382kg per hour of raw material propylene carbonate enters the top of reaction section, and the mol ratio of the two is 9, and catalyst sodium methylate (being first dissolved in methyl alcohol to form containing Sodium methylate 42% solution) enters the top of reaction zone with the rate of 4.55kg per hour, and the required whole energy of reaction rectification process is provided by external heat by tower kettle. The reflux ratio at the top of the tower is 0.75, the temperature of the tower bottom is 185-190°C, and the operating pressure is normal pressure. The mixed gas at the top of the tower (referring to the mixed gas of methanol and dimethyl carbonate, the same below) is discharged at a rate of 1175.7kg per hour, excluding the reflux flow, and it is directly introduced into the extractive distillation column without condensation. The composition ratio of the mixed gas is For: methanol content is 71.4% (wt), dimethyl carbonate content is 28.6% (wt). A propylene glycol by-product with a content of 99.2% (wt) was obtained in the tower kettle. [The rest is 0.12% (wt) of propylene carbonate, 0.01% (wt) of methanol, and 0.67% (wt) of sodium methoxide], after further refining and recovering sodium methoxide, propylene glycol can be used as a commercially available product, and the recovered sodium methoxide can be returned recycled in the system. The conversion rate based on propylene carbonate was 99.9%. The extractive distillation column operates under the following conditions:

The mixed gas enters the lower part of the extraction section at a rate of 1175.7 kg per hour. The extraction agent is propylene carbonate and enters the upper part of the extraction section at a rate of 4015 kg per hour. The molar ratio of the extraction agent to the methanol in the mixed gas is 1.5. The kettle provides all the energy required for the rectification operation through external heat, the reflux ratio at the top of the tower is 0.8, the temperature of the tower kettle is 160-180°C, and it operates under normal pressure. Methanol with a purity of 99.2% is recovered at the top of the tower and discharged at a rate of 834.4 kg per hour. The recovered methanol can be directly returned to the reactive distillation column for recycling. Obtain the mixture of propylene carbonate and dimethyl carbonate (being called for short diester mixture, the same below) at the bottom of the tower (in the tower still), its composition ratio is: propylene carbonate content is 92.25% (wt), dimethyl carbonate content It is 7.74% (wt), and there is a small amount of methanol, which is discharged at a rate of 4352.3 kg per hour and introduced into the diester separation column. The diester separation tower operates under the following conditions:

The diester mixture enters the middle part of the fractionation section at a rate of 4352.3kg per hour, and the energy required for the fractionation process is provided by the external heat from the tower tank _D1 . The reflux ratio at the top of the tower is 0.5, the temperature of the tower tank is 160-180°C, and the operating pressure is 30～50KPa. The top of the tower can obtain the dimethyl carbonate 337.5kg that purity is greater than 99.8% (wt) per hour, and the propylene carbonate 4014.8kg that purity is greater than 99.95% (wt) can be recovered per hour at the bottom of the tower (in the tower still), the carbonic acid that reclaims The propylene ester is returned to the extractive distillation column for recycling. The loss of extractant is less than 0.005%.

Example 2

In a process device mainly composed of a reactive distillation tower, an extractive distillation tower and a diester separation tower, ethylene carbonate and methanol are input as raw materials, and dimethyl carbonate is produced under the action of catalyst sodium methoxide.

Said reactive distillation column, extractive distillation column, and diester separation column are all described in Example 1. The reactive distillation column operates under the following conditions:

The raw material methanol enters the lower part of the reaction section at a rate of 1078.4kg per hour, and the raw material ethylene carbonate enters the upper part of the reaction section at a rate of 329.6kg per hour. The molar ratio of the two is 9. The catalyst is also sodium methylate. The rate of 4kg enters the upper part of the reaction section, and the tower kettle provides all the energy required for the reaction rectification process through external heat. The reflux ratio at the top of the tower is 0.75, the temperature of the tower kettle is 185-190°C, and the operating pressure is normal pressure. The mixed gas at the top of the tower (its composition ratio is the same as that of Example 1) is discharged at a rate of 1175.7 kg per hour (excluding the reflux flow), and is directly introduced into the extractive distillation column without condensation. Obtaining content in the tower still is 98.8% (wt) ethylene glycol by-product (all the other being ethylene carbonate 0.25%, methyl alcohol is 0.017%, sodium methylate is 0.93%), after further refining and reclaiming sodium methylate wherein, ethylene glycol Alcohol can be used as a commercial product, and the recovered sodium methoxide can be returned to the system for recycling. The conversion based on ethylene carbonate was 99.8%.

The operating conditions of the extractive distillation tower are all the same as in Example 1 except that the extractant is ethylene carbonate. Ethylene carbonate enters the upper part of the extraction section at a rate of 3464.3 kg per hour, and the molar ratio of the extraction agent to methanol in the mixed gas is also 1.5. Methanol with a purity of 99.3% is recovered at the top of the tower and discharged at a rate of 844.7 kg per hour. The recovered methanol is directly returned to the reactive distillation column for recycling. Obtain the mixture of ethylene carbonate and dimethyl carbonate (being called for short diester mixture, the same below) at the bottom of the tower (in the tower still), its composition ratio is: ethylene carbonate 91.28%, dimethyl carbonate 8.7% (wt), the rest It is a small amount of methanol, discharged at a rate of 3795kg per hour, and introduced into the diester separation tower.

The operating conditions of the diester separation tower are the same as in Example 1 except that the feed rate of the diester mixture is 3795kg/hr. Can obtain the dimethyl carbonate product 330.8kg that purity is greater than 99.8% per hour at the top of the tower, can reclaim and obtain the ethylene carbonate 3464.2kg that purity is 99.96% per hour at the bottom of the tower. The recovered ethylene carbonate is returned to the extractive distillation column for recycling. The loss of extractant is less than 0.005%.

Example 3

In a process device mainly composed of a reactive distillation tower, an extractive distillation tower and a diester separation tower, the raw materials propylene carbonate and ethanol are put in, and diethyl carbonate is produced under the action of the catalyst sodium ethoxide.

Said reactive distillation tower is a tray tower with a diameter of 600 millimeters and a height of 15000 millimeters, with 33 trays inside. Among them: the reaction section is 25 pieces, the stripping section is 7 pieces, and the rectification section is 1 piece.

Said extractive distillation tower is a plate tower with a diameter of 600 mm and a height of 12000 mm, with 20 trays inside, of which: 11 extraction sections, 8 stripping sections, and 1 rectification section.

Said diester separation tower is a packed tower with a diameter of 500 mm and a height of 2000 mm, and the packing layer height of the fractionating section is 1200 mm. The reactive distillation column operates under the following conditions:

Raw material ethanol enters the bottom of reaction section with the rate of 434kg per hour, and raw material propylene carbonate enters the top of reaction section with the rate of 137.5kg per hour, and the mol ratio of the two is 7, and catalyst sodium ethylate (being first dissolved in ethanol to form containing 37.5% solution of sodium ethylate) enters the upper part of the reaction section at a rate of 2.75kg per hour. All the energy required for the reactive distillation process is provided by the external heat from the bottom of the tower, the reflux ratio at the top of the tower is 0.8, the temperature of the bottom of the tower is 185-190°C, and it operates under normal pressure. The mixed gas at the top of the tower (referring to the mixed gas of ethanol and diethyl carbonate, the same below), is discharged at a rate of 470.1kg per hour (excluding the reflux), and is directly introduced into the extractive distillation tower without condensation. The composition ratio is as follows: the ethanol content is 66.2% (wt), and the content of diethyl carbonate is 33.8% (wt). The propylene glycol by-product that content is 99.1% is obtained in the tower still (all the other being 0.12% of propylene carbonate, sodium ethylate is 0.86% and a small amount of ethanol), after the sodium ethylate contained therein is recovered through further refining, propylene glycol can be used as commercially available product. The recovered sodium ethoxide can be returned to the system for recycling. The conversion based on propylene carbonate was 99.9%. The extractive distillation column operates under the following conditions:

The mixed gas enters the lower part of the extraction section at a rate of 470.1kg per hour. The extraction agent is propylene carbonate and enters the upper part of the extraction section at a rate of 1035kg per hour. The molar ratio of the extraction agent to the ethanol in the mixed gas is 1.5. The kettle provides all the energy required for the rectification operation through external heat, the top reflux ratio is 1.0, the temperature of the tower kettle is 160-180°C, and it operates under normal pressure. Ethanol with a purity of 99.4% is recovered at the top of the tower and discharged at a rate of 307.1 kg per hour. The recovered ethanol can be directly returned to the reactive distillation tower for recycling. Obtain the mixture of propylene carbonate and diethyl carbonate (being called for short diester mixture, the same below) in the tower still, its composition ratio is: propylene carbonate content is 86.4%, diethanol carbonate content is 13.5%, and a small amount of ethanol , which is discharged at a rate of 1198 kg per hour and introduced into the diester separation tower. The diester separation tower operates under the following conditions:

The diester mixture enters the middle part of the fractionation section at a rate of 1198kg per hour, and all the energy required for the fractionation process is provided by the external heat from the tower still _D1 . The temperature of the tower bottom is 160-180°C, and the operating pressure is 30-50KPa. The top of the tower can obtain the diethyl carbonate 162.9kg product that purity is greater than 99.8% (wt) per hour, and the tower kettle then reclaims and obtains the propylene carbonate 1035kg that purity is 99.95% (wt) per hour, and the propylene carbonate that reclaims returns to extraction again recycled in the distillation column. The loss of extractant is less than 0.005%.

Example 4

In a process device mainly composed of a reactive distillation tower, an extractive distillation tower and a diester separation tower, the raw materials ethylene carbonate and ethanol are put in, and diethyl carbonate is produced under the action of the catalyst sodium ethoxide.

Said reactive distillation tower is a tray tower with a diameter of 1600 mm and a height of 20000 mm, with 36 trays inside, of which 30 are in the reaction section, 5 are in the stripping section, and 1 is in the rectifying section.

Said extractive distillation tower is a tray tower with a diameter of 1600 mm and a height of 15000 mm, with 24 trays inside, of which: 15 extraction sections, 7 stripping sections, and 2 rectification sections.

Said diester separation tower is a plate tower with a diameter of 1000 mm and a height of 3000 mm, with 3 trays inside, all in the fractionation section. The reactive distillation column operates under the following conditions:

Raw material ethanol enters the bottom of reaction section with the speed of 3110.2kg per hour, raw material ethylene carbonate enters the top of reaction section with the speed of 850kg per hour, and the mol ratio of the two is 7, and catalyst sodium ethylate (its solution composition is the same as embodiment 3 ) enters the upper part of the reaction section at a rate of 20kg per hour, and the tower kettle provides all the energy required for the reaction and rectification process through external heat. The top reflux ratio is 1.0, and the tower kettle temperature is 185-190°C. operate. The mixed gas at the top of the tower (referring to the mixed gas of ethanol and diethyl carbonate, the same below) is discharged at a rate of 3368.7kg per hour (excluding the reflux flow), and is directly introduced into the extractive distillation column without condensation. The composition of the mixed gas The ratio is: ethanol content is 66.2% (wt), diethyl carbonate content is 33.8% (wt). Obtain the ethylene glycol by-product that content is 98.4% (all the other being ethylene carbonate 0.25%, sodium ethylate 1.4% and a small amount of ethanol) in the tower kettle, after further refining and reclaiming contained sodium ethylate wherein, ethylene glycol can be used as Commercially available products, the recovered sodium ethoxide can be returned to the system for recycling. The conversion based on ethylene carbonate was 99.8%. The extractive distillation column operates under the following conditions:

The mixed gas enters the lower part of the extraction section at a rate of 3368.7kg per hour. The extraction agent is ethylene carbonate and enters the upper part of the extraction section at a rate of 6400kg per hour. The molar ratio of the extraction agent to the ethanol in the mixed gas is 1.5. The kettle provides all the energy required for the rectification operation through external heat, the reflux ratio at the top of the tower is 1.0, the temperature of the tower kettle is 160-180°C, and it operates under normal pressure. Ethanol with a purity of 99.4% is recovered at the top of the tower and discharged at a rate of 2735.7 kg per hour. The recovered ethanol can be directly returned to the reactive distillation tower for recycling. A mixture of ethylene carbonate and diethyl carbonate (abbreviated as diester mixture, the same below) is obtained in the tower kettle, and its composition ratio is: the content of ethylene carbonate is 91.0% (wt). Diethyl carbonate 8.97% and a small amount of ethanol are discharged at a rate of 7033 kg per hour and introduced into the diester separation tower. The diester separation tower operates under the following conditions:

The diester mixture enters the middle part of the fractionation section at a rate of 7033kg per hour, and all the energy required for the fractionation process is provided by the external heat from the tower still _D1 . The temperature of the tower still is 160-180°C, and the whole tower operates at 30-50KPa. Can obtain the diethyl carbonate 632.1kg product that purity is greater than 99.8% (wt) per hour at the top of the tower, the tower kettle can reclaim per hour and obtain the ethylene carbonate 6400kg that purity is 99.95 (wt), the ethylene carbonate that reclaims returns to extraction again recycled in the distillation column. The loss rate of extractant is less than 0.005%.

As can be seen from the foregoing examples, according to the method of the present invention, dialkyl carbonate can be produced with high efficiency and low consumption, which will undoubtedly bring good development prospects and huge economic benefits to the production and chemical department of producing dialkyl carbonate.

Claims (3)

1. the synthetic method of an improved dialkyl carbonate, it is a raw material with ethylene (propylene) carbonate and alcohol, produce dialkyl carbonate under the effect of catalyzer sodium alkoxide, be characterised in that: said synthetic method is mainly separated three technological processs by reactive distillation, extracting rectifying and diester and is formed, wherein:

(1) reactive distillation processes is to carry out in a tray column, and the operating mode during its operation is:

1. reactive distillation processes mainly carries out on the column plate of the conversion zone of tower

2. the two mol ratio of the alcohol of charging and ethylene (propylene) carbonate is 6～10

3. the trim the top of column ratio is 0.6～1.0

4. working pressure is 90～110Kpa

5. tower still temperature is 185～190 ℃;

(2) the extracting rectifying process is to carry out in a tray column, and the operating mode during its operation is:

Used extraction agent is the ethylene (propylene) carbonate identical with reaction mass when 1. extracting

2. extraction agent is 1～2 with the mol ratio of going into the alcohol in the tower material

3. the trim the top of column ratio is 0.6～1.2

4. working pressure is 70～101Kpa

5. tower still temperature is 160～180 ℃;

(3) the operation operating mode of diester knockout tower is:

1. the trim the top of column ratio is 0.4～0.6

2. working pressure is 30～50Kpa

3. tower still temperature is 160～180 ℃;

(4) said dialkyl carbonate is a class carbonic acid two lower alkyl esters.

2. the method for claim 1, it is characterized in that reactive distillation operation and extracting rectifying operate under the normal pressure carries out.

3. as the described method of one of claim 1～2, the trim the top of column ratio when it is characterized in that the extracting rectifying operation is 0.8～1.0.