1. A semi-continuous reactive distillation process for the production of linear and cyclic carbonates by transesterification using a batch distillation unit, characterised in that one or more reactants are added to a reactor or column and one or more products are removed simultaneously during a batch reactive distillation, and by-products are removed from the reaction mixture by distillation as the reaction proceeds in the reactor and/or column, thereby driving the conversion of the one or more reactants towards completion.

2. The linear and cyclic carbonates of claim 1 including, but not limited to, dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), Glycerol Carbonate (GC), methylphenyl carbonate, diphenyl carbonate.

3. The reactive distillation apparatus of claim 1, wherein said reactive distillation apparatus comprises a distillation reactor and a reactive distillation column, both as reactor and distillation equipment, and said apparatus is operated under full vacuum and at a pressure of up to 500 psig.

4. The reactor/still and column of claim 3 may be a conventional batch distillation apparatus or the reactor and distillation column may be separate apparatus connected by piping means and the distillation column may be a conventional continuous distillation column or a batch distillation column.

5. The apparatus according to claims 3-4, characterized in that the reactor (still) is of any type, with or without stirrer, but preferably with stirrer, and the distillation column can be used with any type of packing or trays, as well as with partial packing and partial tray columns.

6. The reactive distillation apparatus of claim 5, wherein the reactive distillation apparatus is equipped with a circulation loop; the recycle loop may be taken from the bottom of the column (reactor) to any point, but the entry point of the recycle loop is preferably at an inlet along the distillation column.

7. The process of claim 1, wherein the point of entry of the feed reactants is anywhere along the circulation loop or anywhere in the reactor (still) during the reaction.

8. According to claims 1-7, after removal of one or more products or by-products and maximizing or complete conversion of at least one reactant, the final reactor mixture is transferred to a clean vessel or storage tank, or may be directly fed to another distillation unit operating batchwise, semi-continuously or continuously, to separate the mixture into high purity products, semi-continuous distillation being the preferred mode.

9. The process according to claim 8, characterized in that during the transfer of the reactor mixture to a holding tank or another distillation unit, the reactive distillation unit is still operated in batch distillation mode, so that lighter impurities and/or some unconverted reactants are kept in the column, minimizing impurities in the reactor (still).

10. The method according to claim 8, wherein instead of the distillation mode of claim 7, hot inert gas or vapour (e.g. N2) is blown into the column during the transfer of the reactor mixture to a holding tank or another distillation unit, the purpose of claims 8, 9 and 10 being to keep the impurities in the column from falling into the reactor (distillation tank), so that the next distillation of the reactor mixture contains no or only very little light impurities.

11. The reactor mixture according to claim 8, which is distilled and purified into separate individual products in one distillation unit, such distillation unit may be the same reactive distillation unit, or may be a different distillation unit operated in batch, semi-continuous or continuous mode, but preferably a semi-continuous distillation unit; such semi-continuous distillation is characterized by having a recycle loop from the distillation pot (or reactor) to the distillation column, the entry point of which can be anywhere along the distillation column, and thus such a column has both a rectifying section above the feed entry point and a stripping section below the entry point, such that a batch feed allows for a continuous distillation mode of operation.

12. Stripping section according to claim 11, characterized in that the stripping section can be of the packed type, but is preferably of the tray type, which is more suitable for catalytic reactions and possible mixtures containing solid particles, and the rectification section is preferably of the packed type, which can be any type of packing material, and when used alone as semi-continuous distillation, the column can be any kind of distillation column.

13. The semi-continuous distillation method of the semi-continuous reactive distillation apparatus described in claims 3 to 12, which is not limited to the production/purification process of linear/cyclic carbonates, but is also applicable to other conventional batch distillation production in which the raw materials for distillation are placed in a batch type in a batch distillation apparatus, but the distillation operation is carried out using the semi-continuous distillation method described in the present invention, such semi-continuous distillation can greatly improve the efficiency of the distillation operation.

Background

Organic carbonates, such as Ethylene Carbonate (EC), Propylene Carbonate (PC), dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), and the like, have been commercially produced for many years. Wherein, ethylene carbonate and propylene carbonate react with Ethylene Oxide (EO) to generate 1, 2 by CO2 in the presence of a catalyst.

Dialkyl carbonates, such as DMC, EMC and DEC, are usually prepared by transesterification of EC or PC with methanol or ethanol 3 or mixtures of methanol and ethanol, with Ethylene Glycol (EG) or Propylene Glycol (PG) as by-products. These dialkyl carbonates can also be prepared by transesterification of a carbonate with an alcohol. The following are some examples of transesterification reactions:

transesterification between linear carbonates also occurs as follows:

in those reactions, there are also side reactions that produce impurities that can be separated from the desired product by known separation techniques. These transesterification reactions are known to be reversible. The reaction rate, conversion and selectivity of these reactions depend on the catalyst and the reaction conditions. Many of the reactions and production methods described above have been well developed and industrially produced in the chemical industry. However, techniques to reduce equipment, energy, material costs and environmental impact are constantly being developed and making good progress.

As described above, linear carbonates can be produced from the starting materials EO/PO and methanol/ethanol by two steps (1-2, 3-4). At the same time, DMC or DEC can also be synthesized by the one-shot process by:

in addition to those well known reactions, there are other reversible transesterification reactions, even if molecules containing OH groups, such as alcohols, polyols, ethylene glycol, propylene glycol, glycerol, and the like, react with ester groups to form different ester molecules and different OH-containing molecules, as shown in the following equations:

these reactions typically require a catalyst to occur and are reversible. In order for the reaction to approach completion, at least one product, typically the lowest boiling molecule or the highest boiling molecule, must be removed. All these general transesterification reactions are covered by the present invention, although the focus is on several linear carbonates.

The most interesting and important group of transesterification reactions are those described by equations (3) - (12), where linear carbonates (DMC, EMC, DEC) are the target product. Linear carbonates are widely used as components of solvents for lithium ion battery electrolytes. Most dimethyl carbonate (and sometimes diethyl carbonate) is formed by a direct oxidative carbonylation reaction, i.e. carbon monoxide, methanol (ethanol in the case of DEC) and oxygen are reacted over a catalyst⁴. DMC prepared in this way is generally used by the manufacturer for the preparation of polycarbonates by internal digestion, as well as various customary solvents customary in industry, and oxygen-containing additives in pesticides, gasolines^4,9,12. This method is not included in the discussion of this patent. DMC, EMC and DEC in the lithium battery (LiB) market are mostly DMC, EMC and DECThe Propylene Carbonate (PC) or the Ethylene Carbonate (EC) and methanol (or ethanol) are subjected to ester exchange reaction^4-10And preparing EMC and DEC by reactions (9) to (13).

DMC, EMC and DEC are widely used in industrial production by the reaction of the formula (3-10). It is characterized by that it utilizes the continuous reaction distillation process. The process removes one product on the right side of the equation to increase the conversion, yield and selectivity of the target compound^4-8,10This technology has been well studied and documented. However, the existing continuous reactive distillation process suffers from problems in that it requires the use of a plurality of distillation columns, associated high investment costs, and difficulty in preparing products of high purity and low impurities (e.g., H2O and — OH groups) is large. High purity and low impurities are critical to the application of lithium ion batteries. On the other hand, the transesterification route has the advantage that the starting materials EC and/or PC are derived from natural gas feedstocks and that the CO2 is converted instead of being released into the air, which is of great benefit for environmental efforts to reduce CO 2.

The high capital and operating costs described above are primarily associated with the formation and separation of a series of azeotropes in the reaction mixture. Compared with pure components, the azeotrope has the following properties:

table 1: boiling point temperature of pure component and azeotrope

In reactions (3, 4) in which DMC is the target product, DMC has a lower boiling temperature than EG/PG and should be the easiest component to remove, but the presence of a DMC-methanol azeotrope with an even lower boiling temperature determines that it is also necessary to remove large amounts of the starting methanol in equation (3, 4), or DMC in equation (9, 10). It is difficult to efficiently separate and purify the reaction mixture by the continuous reactive distillation technique. To achieve higher conversions, longer reaction times or temperatures are required, and particular consideration is given to the design of the distillation column, which typically requires the use of multiple higher distillation columns to purify the product. This increases the formation of impurities and equipment costs, and the capital investment threshold is high, making it difficult for new entrants to enter the linear carbonate market.

Disclosure of Invention

It is an object of embodiments of the present invention to provide a semi-continuous reactive distillation process for producing carbonate esters, which addresses the technical problems identified in the background art in the prior art.

The present examples were accomplished by a semi-continuous reactive distillation process for producing linear and cyclic carbonates by transesterification using a batch distillation unit. Characterized in that one or more reactants are added to the reactor or column during the space reaction distillation and one or more products are removed simultaneously. When the reaction is carried out in a reactor and/or column, the by-products are removed from the reaction mixture by distillation, thus driving the conversion of one or more reactants to near completion.

As a still further scheme of the invention: the linear and cyclic carbonates include, but are not limited to, dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), Glycerol Carbonate (GC), methylphenyl carbonate, diphenyl carbonate.

As a still further scheme of the invention: the reactive distillation apparatus comprises a distillation reactor and a reactive distillation column which can be used as both a reactor and a distillation apparatus, and can be operated under full vacuum and at pressures up to 500 psig.

As a still further scheme of the invention: the reactor/still and column may be a conventional batch distillation apparatus or the reactor and distillation column may be separate apparatus connected by piping elements and the distillation column may be a conventional continuous distillation column or a batch distillation column.

As a still further scheme of the invention: the reactor (still) is of any type, with or without stirrer, but preferably with stirrer. The distillation column may use any type of packing or trays, and may use partial packing and partial tray distillation columns.

As a still further scheme of the invention: the reactive distillation apparatus is equipped with a circulation loop; the recycle loop may be taken from the bottom of the column (reactor) to any point, but the entry point of the recycle loop is preferably at an inlet along the distillation column.

As a still further scheme of the invention: the entry point for the feed reactants can be anywhere along the recycle loop during the course of the reaction, and can be anywhere in the reactor (still).

As a still further scheme of the invention: after removal of one or more products or byproducts and maximizing or complete conversion of at least one reactant, the final reactor mixture is transferred to a clean vessel or storage tank or may be directed to another distillation unit operating batchwise, semi-continuously or continuously to separate the mixture into high purity products. Semi-continuous distillation is the preferred mode.

As a still further scheme of the invention: during the transfer of the reactor mixture to a holding tank or another distillation unit, the reactive distillation unit is still operated in batch distillation mode, so that lighter impurities and/or some unconverted reactants are kept within the column. Minimizing impurities in the reactor (still).

As a still further scheme of the invention: instead of the distillation mode of claim 7, hot inert gas or vapor (e.g., N2) is blown into the column during the transfer of the reactor mixture to a holding tank or another distillation unit. The object of claims 8, 9 and 10 is to keep the impurities in the column from falling into the reactor (retort) so that the next distillation of the reactor mixture contains no or only very small amounts of light impurities.

As a still further scheme of the invention: which is distilled and purified in one distillation unit into individual products. Such distillation units may be the same reactive distillation unit or may be different distillation units operating in batch, semi-continuous or continuous mode, but semi-continuous distillation units are preferred. This semi-continuous distillation is characterized by having a recycle loop from the distillation pot (or reactor) to the distillation column. The entry point to the recycle loop may be at any location along the distillation column. Thus, such a column has both a rectifying section above the feed entry point and a stripping section below the entry point, so that a batch feed can be subjected to a continuous distillation mode of operation.

As a still further scheme of the invention: the stripping section may be of the packed type, but is preferably of the tray type, which is more suitable for catalytic reactions and possible mixtures containing solid particles. The rectifying section is preferably packed and may be any type of packing material. When used alone as a semi-continuous distillation, the column may be any type of distillation column.

As a still further scheme of the invention: the method is not limited to the production/purification process of linear/cyclic carbonates, but is also applicable to other conventional batch distillation production in which the raw materials for distillation are placed in a batch distillation apparatus in a batch manner, but the distillation operation is carried out using the semi-continuous distillation method described in the present invention. Such semi-continuous distillation can greatly improve the efficiency of the distillation operation.

Compared with the prior art, the invention has the beneficial effects that: using a batch distillation device or a modified continuous distillation device, adding one or more reactants into a reactor or a distillation tower in the reaction distillation process to completely convert the other reactant, then distilling, distilling out light impurities from the top of the tower, keeping the residual light impurities in the distillation tower above a reaction kettle, and simultaneously sending the reacted mixture with the light components removed from the distillation kettle (reactor) to another set of distillation unit for separation. Or the DMC can be sent into a storage tank firstly and then rectified and separated by the same set of reactive distillation equipment to produce DMC, EMC and DEC with high purity. The process maximizes the conversion of one or more reactants, thereby avoiding azeotrope formation. The invention also provides a novel semi-continuous distillation unit operation characterized by a conventional batch distillation unit having both a stripping section and a rectifying section. The semi-continuous distillation unit has higher efficiency than a conventional batch distillation unit, and thus can produce a linear carbonate with high purity. The present invention makes it possible to produce all linear carbonates of high purity using only one or two semi-continuous or reactive distillation units, thereby significantly reducing the equipment investment and operating costs. The invention enables investors to easily enter the lithium battery market under the condition of reducing the equipment investment cost.

Drawings

FIG. 1 is a schematic view of a structure of a conventional batch reactive distillation.

FIG. 2 is a schematic view of a conventional batch distillation column for purification of high purity linear carbonate.

FIG. 3 is a schematic diagram of a semi-continuous reactive distillation structure with a circulation loop (EMC as a main product).

FIG. 4 is a schematic diagram of a semi-continuous distillation column with a recycle loop.

FIG. 5 is a schematic diagram of the structure of a divided semi-continuous reactive distillation unit (DEC as the main product).

FIG. 6 is a schematic diagram of a semi-continuous reactive distillation unit for producing DMC.

FIG. 7 is a schematic diagram of a semi-continuous distillation unit for producing DMC.

Item	Description of the invention
		1	Stills, or reactors
2	Stripping section (optional)
		3	Rectifying section
4	Gas phase condenser
		5	Condenser
6	Condensation receiver
		7	Fraction (b) of
8	Refluxing
		9	Circulating pump
10	Cooling/heating circuit
		11	Heat exchanger
12	Pipeline for circulating back to tower
		13	Feed/bottom mixer
14	Liquid removal reactor of distillation tower
		15	Reactor gas phase distillation tower
16	Stirrer

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Specific implementations of the present invention are described in detail below with reference to specific embodiments.

The present invention uses a semi-continuous (or so-called semi-batch) reactive distillation technique to allow linear carbonate production and other types of transesterification reactions and related separations/purifications to be carried out in one or two batch distillation systems with near complete conversion of one (or several) of the reactants, thereby simplifying the separation and purification process. By this technique, new entrants can more easily enter the high demand linear carbonate market due to reduced equipment costs and simplified operation. The following examples illustrate the working principle of this technique in the preparation of linear carbonates.

Example 1: production of high purity EMC and DEC from DMC

As shown in FIG. 1, a conventional batch distillation system is characterized in that a distillation still is equipped with a stirrer and is used as a reactor. The reactor was charged with a molar ratio of 1: 1 DMC and ethanol. Sodium methoxide (dissolved in methanol) was used as catalyst. The operation steps are as follows:

(1) the reactor was heated to a reaction temperature of 65-85 ℃. The distillation column was operated at full reflux until the temperature at the top of the column reached 63.5 ℃ (DMC-methanol azeotrope temperature at atmospheric pressure). Then continuing to move with 3: 1, and the reactor temperature was adjusted so that the overhead temperature was controlled at about 63.5 ℃.

(2) As the reaction temperature began to rise and the flow at the top of the column began to decrease, fresh DMC feedstock began to be pumped into the reactor. The DMC flow was controlled at the same level as the distillate flow at the top of the column.

(3) The reaction is continued, so that the temperature of the reactor is controlled to be 65-75 ℃, and the temperature of the top of the tower is 63.5-65 ℃. When the overhead cut is stopped, it is lowered until the DMC feed is stopped.

(4) Continuing the reactive distillation under the above conditions; the reaction temperature is raised to about 80-85 ℃ at the appropriate time until the overhead temperature rises to 75 ℃, and samples are taken from the reactor at any time for analysis of the alcohol content.

(5) When the alcohol content is less than 10ppm (wt), the same reactor temperature and stirring is maintained while the reactor mixture is drained into a clean holding tank. The discharged mixture contained DMC, EMC, DEC and a catalyst containing <10ppm alcohol and <10ppm water.

The purpose of step (4-5) is to keep the alcohol and water impurities in the distillation column by the upward flow of vapor so that the bottoms contains very little alcohol and water. This method facilitates subsequent separation, significantly improves the yield of high purity product, and reduces production time and process costs.

(6) The above reactor mixture was pumped to the next batch distillation unit which was purged with nitrogen for further fractional distillation purification. And the original reactive distillation unit can start the reactive distillation operation of the next batch.

As shown in fig. 2. The reaction mixture can also be fed to a buffer vessel, the reactive distillation unit is then purged thoroughly with nitrogen and the reaction mixture in the buffer vessel is then fed back to the same reactive distillation unit for further purification by fractional distillation. Therefore, only one set of reaction distillation system is needed to complete the reaction and fractionation operation, and the equipment investment is greatly saved.

(7) The reactor mixture was distilled and cut into high purity DMC, high purity EMC, high purity DEC (purity > 99.99%, H2O <10ppm, alcohol <10 ppm). Between the fractions DMC and EMC, EMC and DEC, there are middle fractions containing DMC/EMC and EMC/DEC. These cut pieces are mixed into one receiver or tank and distilled in the next batch.

The distillation bottoms stream was a particulate liquid mixture containing DEC and NaCH 3O. This mixture was used as catalyst for the next batch of reactive distillation.

(8) The top of the tower in the step (3) is a mixture of DMC and methanol. This mixture is collected and sent to a distillation unit for distillation under pressure. This distillation unit may be a batch distillation unit for carrying out reactive distillation, or another batch or continuous distillation unit. This separation is a conventional distillation separation.

(9) The pressure of the distillation column of step (8) should be 3 atmospheres or more, preferably 8 to 10 atmospheres. At higher pressures, the azeotropic point of DMC-methanol shifts toward the highly DMC containing component, thereby making the DMC fraction easier to separate from methanol. The methanol-rich overhead fraction can be used as a feedstock to produce DMC or as a fuel or other use. This separation process is a conventional pressure distillation and is not described in detail in the present invention.

Although the DMC-methanol azeotrope can be distilled according to steps 7-9, the material can also be used as a starting material for the EC (or PC) + methanol reaction to DMC, as shown in equations (3, 4) and (7, 8).

Example 2, as shown in fig. 3, the conventional batch distillation apparatus used in example 1 was changed to a semi-continuous distillation apparatus. A circulation pump is added to pump the reaction mixture into the column or reactor vapor space to enhance the heat and mass transfer of the reactive distillation. Heat exchange may be added to the recycle loop to increase heating/cooling capacity, but this heat exchanger is optional depending on other design parameters of the plant and the nature of the reaction.

The recycle loop entry point may be any point of the distillation column. By introducing the reaction mixture into the column, which thus has stripping and rectifying sections, a column batch column can be used as the continuous distillation column 13, thereby increasing the efficiency of the column. In a typical batch distillation operation, the column has only a rectifying section and no stripping section. The recycle loop changes the distillation mode from batch mode to continuous distillation mode and is therefore referred to as a semi-continuous distillation unit because the starting feed is maintained in the still.

Feeding into a reactor a mixture of a 1: 1 technical grade DMC and ethanol, and adding a catalyst to accelerate the reaction. This ratio is to make EMC higher than DEC yield. An example of a catalyst is sodium methoxide (NaCH 3O). The operation steps are as follows:

(1) the reactor mixture was introduced into the column and the reactor was heated to a reaction temperature of 65-85 ℃. The circulation pump is started. The column was operated at full reflux until the temperature at the top of the column reached 63.5 ℃ (DMC-methanol azeotrope temperature at atmospheric pressure). The column was then operated at 3: a reflux ratio of 1 was run while the overhead temperature was controlled at 63.5 c by the reactor temperature.

(2) When the reactor temperature began to rise and the overhead flow rate decreased, please begin to flow fresh DMC into the reactor loop. The inlet for fresh DMC is preferably before the heat exchanger (if used), but may also be after the heat exchanger. Fresh DMC may also be injected directly into the reactor. The fresh DMC flow rate is the same as the overhead flow rate.

(3) The reaction is continued at 70-85 ℃. When the overhead flow stops and the temperature drops, the feed rate of fresh DMC is reduced until stopped.

(4) The reactive distillation was continued at the set temperature and samples were taken periodically from the reactor and analyzed for alcohol content.

(5) When the alcohol content was below 10ppm by weight, the reactor mixture was drained into a clean storage tank while continuing to maintain the same reactor temperature and agitation. The reactor mixture thus discharged contained DMC, EMC, DEC and contained <10ppm alcohol, <10ppm moisture.

The purpose of step (4-5) is to keep the alcohol impurities in the column by means of the upflowing vapor, so that the bottoms are free of excess alcohol and moisture. This method can significantly improve the yield of high purity products and reduce the production time and process cost.

(6) The reactor mixture was then introduced into a semi-continuous distillation apparatus as shown in figure 4. The semi-continuous distillation apparatus may be the above reactive distillation apparatus, but is thoroughly purged with N2 to completely remove water and alcohols. Or may be another distillation unit. The reaction mixture was cut by distillation to give high purity DMC, high purity EMC, high purity DEC (> 99.99%, H2O <10ppm, alcohol <15 ppm). Between the fractions DMC and EMC, EMC and DEC, there will be intermediate fractions containing DMC/EMC and EMC/DEC. These middle distillates were combined in one pot and then added to the next batch for distillation.

The bottom residue after distillation was a mixture containing DEC and the catalyst sodium methoxide particles, which was pumped only for the next batch to continue the reactive distillation.

In the two examples above, DMC: EMC: the proportion of DEC can be determined by DMC: the starting proportion of ethanol and subsequent use of fresh DMC (or ethanol) as well as other operating conditions are controlled. The above two examples are to maximize the EMC yield. Analysis showed that the EMC/DEC ratio thus obtained was about 85: 15. when DEC is preferred, the DMC: ethanol ratio should be low, and a continuous fresh ethanol feed may be used in place of the DMC feed in the above examples, as described in equations (9-12).

The above-described batch distillation unit may also be provided as a separate reactor (distillation tank) and distillation column; the reactor and the distillation column are connected by piping elements. The DEC preferred process using a split batch distillation unit but operating in a semi-continuous mode is depicted in fig. 5. Thus, the distillation column can be used as a continuous, semi-continuous and batch type.

It is worth noting that when two sets of distillation apparatus are used, the storage tank described in step (5) of the two examples above can be omitted and the reaction mixture can be pumped directly to the second set of distillation unit for rectification separation to obtain DMC/EMC/DEC product of high purity.

Thus, as described above, using one or two sets of distillation equipment to perform reactive distillation and mixture rectification can greatly save equipment investment, making it very easy to enter the very attractive lithium battery electrolyte solvent market.

EXAMPLE 3 preparation of dimethyl carbonate (DMC) from Ethylene Carbonate (EC)

As shown in fig. 6, a set of reactive distillation columns was used to react technical grade EC with technical grade methanol to produce DMC. The catalyst used was still sodium methoxide. The reactive distillation system adds a recycle loop which enters the column above the reaction section as shown in figure 6. The procedure for the operation of this system is similar to example 2.

(1) Feeding into a reactor a mixture of a 1: 2 EC and methanol. Sodium methoxide was added as a catalyst to accelerate the reaction. Heating to 65-80 deg.C to make the distillation tower in a complete reflux state. When the temperature of the tower top reaches 63.5 ℃, changing to 3: 1 operated with a reflux ratio, the overhead product (i.e., DMC/MeOH azeotrope) was removed.

(2) When the overhead flow drops and the temperature begins to drop, fresh methanol begins to be introduced into the reactor loop. The entry point for fresh methanol is preferably before the heat exchanger (if an external heat exchanger is used), but may also be after the heat exchanger. Fresh methanol may also be introduced directly into the reactor. The flow rate of fresh methanol was the same as the flow rate of the overhead product.

(3) The reactive distillation was continued under the conditions as above. Samples were taken periodically from the autoclave and analyzed for EC, methanol and DMC content.

(4) When the sample has an EC content of less than 0.5 to 1% (wt), the feed of fresh methanol is stopped and the distillation column overhead is switched to another receiving tank for receiving recovered methanol. Distillation was continued until the methanol content in the sample in the pan was below 50 ppm. The recovered methanol will be used in the next batch of reactive distillation.

(5) The circulation was stopped and the reactor mixture, which contained EG, DEG and catalyst containing <50ppm methanol, was pumped to a storage tank. While maintaining the same reactor temperature and agitation so that the light components in the column do not fall back into the reaction vessel.

(6) The mixed material of the reactor is sent to an EG distillation tower to carry out EG and DEG separation production. The same or different distillation units may be used for this purpose. Fractionation of EG/DEG is conventional and is not included within the scope of the present invention. The EG distillation bottoms stream is a slurry comprising EG/DEG and the catalyst sodium methoxide. This slurry was used as catalyst for the next batch of reactive distillation.

(7) The overhead DMC/MeOH azeotrope stream collected in step (1) is sent to a pressure distillation to produce high purity DMC. The operation steps were the same as those in example 1. However, DMC can be produced without pressure distillation by using methanol-rich DMC-MeOH azeotrope as feed to react with excess EC, which DMC can then be purified.

By combining the two processes of EC/methanol reactive distillation and DMC/ethanol reactive distillation, it is possible to consume EC, methanol and ethanol starting materials internally and convert them to the target products of high purity DMC, EMC and DEC, and by-products EG and DEG. Almost no waste liquid is produced during this process.

It is noted that in the examples, the conventional distillation unit (fig. 1) and the split distillation unit (fig. 5) are interchangeable. The separation type distillation device is more flexible and can be used for different application processes, such as batch type, continuous type and semi-continuous type. Also, in example 3, EC could be replaced with PC and EG with PG, while all other conditions and steps remain substantially unchanged.

In general, the concept of semi-continuous reactive distillation is more or less similar to conventional reactive distillation, but since all reactions and separations can be carried out in the same unit, it is also possible for two or more units to be more efficient. It saves a lot of equipment costs so that manufacturers can step-by-step from smaller to larger sizes as market demands. This greatly reduces the difficulty of new entry into the market. It saves material and simplifies operation and takes advantage of all the advantages of batch distillation and continuous distillation techniques. Compared with the conventional reactive distillation technology, the separation and purification efficiency is higher. These figures and examples are for illustration purposes and not design details.

Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of the disclosure following, in general, the principles of the disclosure and including such departures from the present disclosure as come within known or customary practice within the art to which the disclosure pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims.

It will be understood that the present disclosure is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.