阅读说明：本技术 一种含碳酸二甲酯的混合物流的精制方法及系统 (Refining method and system for mixed material flow containing dimethyl carbonate ) 是由 杨卫胜 施德 贺来宾 于 2019-10-18 设计创作，主要内容包括：本发明提供一种含碳酸二甲酯的混合物流的精制方法及系统,其中,将所述混合物流引入精制塔内,塔顶采出含碳酸二甲酯的循环物流,塔釜采出含重组分碳酸二甲酯外排,提馏段侧线采出精制的碳酸二甲酯产品。其中,所述混合物流为合成气制乙二醇过程偶联单元分离得到的含碳酸二甲酯的物流,本发明采用精馏的方式对含碳酸二甲酯的混合物流进行提质,进行脱轻,进一步提高碳酸二甲酯的纯度,同时采用提馏段侧线采出气相的方式,有效的进行了脱重脱色。(The invention provides a method and a system for refining a mixed material flow containing dimethyl carbonate, wherein the mixed material flow is introduced into a refining tower, a circulating material flow containing dimethyl carbonate is extracted from the top of the tower, dimethyl carbonate containing heavy components is extracted from the bottom of the tower and discharged outside, and a refined dimethyl carbonate product is extracted from the side line of a stripping section. The mixed material flow is a material flow containing dimethyl carbonate, which is obtained by separation of a coupling unit in the process of preparing ethylene glycol from synthesis gas, the mixed material flow containing dimethyl carbonate is upgraded by adopting a rectification mode, the light component is removed, the purity of dimethyl carbonate is further improved, and meanwhile, the heavy component removal and the decoloration are effectively carried out by adopting a mode of extracting a gas phase from a side line of a stripping section.)

1. A process for refining the mixture containing dimethyl carbonate includes introducing the mixture into refining tower, collecting the circulating stream containing dimethyl carbonate from tower top, collecting the dimethyl carbonate containing heavy components from tower bottom, discharging it out, and collecting the refined dimethyl carbonate from side of stripping segment.

2. The refining process of claim 1, wherein the mixed stream includes dimethyl carbonate, light components, and heavy components, or colored impurities therein;

preferably, the light components comprise methyl formate, methyl acetate, tetrahydrofuran, methanol and methylal, and the heavy components comprise nitrogen-containing compounds;

more preferably, the mixed stream is a dimethyl carbonate-containing stream separated from a coupling unit in a process of preparing ethylene glycol from synthesis gas.

3. Refining process according to claim 1, characterized in that a stripping section side draw or a stripping section side draw, preferably a stripping section side draw, is used in the process.

4. The refining method of claim 1, wherein the dimethyl carbonate containing heavy components is discharged from the bottom of the column, and the discharge proportion is 0.1-20%, preferably 1-10% of the dimethyl carbonate in the feed.

5. The refining method according to claim 2,

in the mixed material flow, the concentration of the dimethyl carbonate is 20-99.9%, preferably 25-98%; the content of the light component is 2-40%, and the content of the heavy component is 0-5000 ppm, wherein the content of the heavy component is calculated by the content of nitrogen element; and/or

The purity of the dimethyl carbonate product is more than 99.5%, the content of nitrogen-containing compounds is less than 500ppm, wherein the content of the nitrogen-containing compounds is calculated by the content of nitrogen elements, and the dimethyl carbonate product is colorless and transparent.

6. The refining method according to claim 1,

the number of theoretical plates of the refining tower is 10-50, and the feeding position is 5-35 theoretical plates; preferably, the number of theoretical plates of the refining tower is 20-40, and the feeding position is 10-30 theoretical plates.

7. The refining method according to any one of claims 1 to 6, wherein the operating pressure of the refining tower is-0.1 to 1MPaG, the tower top temperature is 40 to 140 ℃, and the tower kettle operating temperature is 50 to 190 ℃;

preferably, the operating pressure of the refining tower is 0-0.8 MPaG, the tower top temperature is 65-135 ℃, and the tower kettle operating temperature is 90-180 ℃.

8. The refining process according to claim 1, wherein two or more reboilers, preferably two reboilers, are provided in the column bottom of the refining column.

9. A dimethyl carbonate rectification system, preferably for carrying out the refining method according to any one of claims 1 to 8, wherein the rectification system comprises a refining column,

preferably, the number of theoretical plates of the refining tower is 10-50, and the feeding position is 5-35 theoretical plates;

more preferably, the number of theoretical plates of the refining tower is 20-40, and the feeding position is 10-30 theoretical plates.

10. Dimethyl carbonate rectification system according to claim 9, characterized in that,

a side-draw position is arranged at the stripping section of the refining tower and is used for side-draw of a dimethyl carbonate product; and/or

More than two, preferably two reboilers are arranged at the tower bottom of the refining tower.

Technical Field

The invention relates to the refining of dimethyl carbonate, in particular to a method and a system for refining a mixed material flow containing dimethyl carbonate, which are particularly used for refining dimethyl carbonate separated in the process of preparing ethylene glycol from synthesis gas.

Background

The oxalate is an important organic chemical raw material, can be used for producing various dyes, solvents, extracting agents and various intermediates, and is widely applied to fine chemical engineering. In addition, the oxalic ester can be used for preparing the ethylene glycol through hydrogenation reaction, and the method is a new large-scale industrialized ethylene glycol synthesis process route. Ethylene glycol has long been prepared mainly by petroleum routes, and is relatively high in cost.

The traditional oxalate synthesis process is prepared by heating and esterifying oxalic acid and alcohols in a toluene solvent, and the method has the advantages of high production cost, large energy consumption, large wastewater discharge and serious pollution. The d.f. fenton research of united states oil company in the last sixties of the century found that carbon monoxide, alcohol and oxygen can be directly synthesized into dialkyl oxalate through oxidative hydroxylation. After several generations of scientific research efforts, the most suitable route for preparing dimethyl carbonate by coupling carbon monoxide is that carbon monoxide and alkyl nitrite are coupled to react to generate dialkyl oxalate and generate nitrogen monoxide, and the nitrogen monoxide is then reacted with methanol and oxygen to regenerate alkyl nitrite, and the reaction equation is as follows:

coupling reaction: 2CO +2RONO → 2NO + (COOR)2 (1)

Esterification reaction: 2ROH +0.5O₂+2NO→2RONO+H₂O (2)

Wherein R represents an alkyl group. The nitric oxide and alkyl nitrite in the route are cyclically regenerated in the system.

The coupling reaction generates dimethyl oxalate and commonly produces dimethyl carbonate which is a byproduct with higher economic value, and the byproduct dimethyl carbonate is separated to obtain products above national standard first-class products, so that the economic benefit of the device can be effectively improved.

Because methanol and dimethyl carbonate have azeotropy, the existing method for separating the dimethyl carbonate mainly has two methods, one method is to adopt double-tower pressure swing separation and extract a dimethyl carbonate product from a tower kettle of a pressurized tower; the second method is to use dimethyl oxalate as an extracting agent to extract and separate methanol and dimethyl carbonate. Only crude dimethyl carbonate can be obtained usually, the problems of low purity, color and the like of the dimethyl carbonate exist, and the economic value of the byproduct dimethyl carbonate is greatly reduced.

Aiming at the problem of low purity of dimethyl carbonate, because the dimethyl carbonate mainly contains light components such as methanol, methylal and the like, light components can be removed through an additional rectifying tower, dimethyl carbonate with higher purity can be obtained at the tower bottom, and the purity reaches the requirement of national standard first-grade products.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention adopts a rectification mode to upgrade a dimethyl carbonate crude product, removes light and further improves the purity of dimethyl carbonate, and simultaneously adopts a mode of extracting a gas phase from a side line of a stripping section to effectively remove heavy and decolor, the indexes of the dimethyl carbonate product obtained by separation can reach the indexes of national first-grade products, the economic value of the dimethyl carbonate product is effectively improved, and the method can be well applied to the refining of the dimethyl carbonate product in the process of preparing ethylene glycol from synthesis gas.

The invention aims to provide a method for refining a mixed material flow containing dimethyl carbonate, wherein the mixed material flow is introduced into a refining tower, a circulating material flow containing dimethyl carbonate is extracted from the top of the tower, dimethyl carbonate containing heavy components is extracted from the bottom of the tower and discharged outside, and a refined dimethyl carbonate product is extracted from the side line of a stripping section.

The inventor finds that the colored impurities in the dimethyl carbonate have high boiling point, high relative volatility with the dimethyl carbonate and low content of the colored impurities in a gas phase, so that the dimethyl carbonate product skillfully extracted in the gas phase is colorless and transparent.

In a preferred embodiment, the mixed stream comprises dimethyl carbonate, light components and heavy components.

Wherein the light components comprise methyl formate, methyl acetate, tetrahydrofuran, methanol, methylal and the like, and the heavy components comprise nitrogen-containing compounds and the like.

In a further preferred embodiment, the mixed stream is a dimethyl carbonate-containing stream separated from a coupling unit in a process for preparing ethylene glycol from synthesis gas.

Wherein the recycle stream containing dimethyl carbonate taken out from the top of the tower can be further recycled to the coupling separation unit.

In the method of the invention, the dimethyl carbonate refining tower is divided into an upper section (a rectifying section) and a lower section (a stripping section), and because the mixed material flow containing dimethyl carbonate contains low-boiling point components (light components), the extraction position of the dimethyl carbonate product is required to be the stripping section, and the circulating material flow containing dimethyl carbonate is extracted from the top of the tower. Meanwhile, due to the problems of polymerization of nitrogen-containing compounds and dimethyl carbonate in coupling and the like, the dimethyl carbonate obtained at the tower bottom is easy to be colored, so that the dimethyl carbonate is extracted at the side line position of the stripping section.

In a preferred embodiment, a stripping section side-draw or a stripping section side-draw, preferably a stripping section side-draw, is used in the process.

Wherein, if the dimethyl carbonate stream to be treated comes from the autoclave and is colored, the dimethyl carbonate product must be extracted from the side line of the stripping section, and if the dimethyl carbonate stream to be treated comes from the top of the atmospheric tower and is colorless and transparent, the dimethyl carbonate product can be extracted from the side line of the stripping section. Therefore, in the present invention, the side-draw of the dimethyl carbonate product is performed in the stripping section below the feed inlet, and particularly when the mixture stream contains colored impurities or when the color of the dimethyl carbonate product is required, the gas phase is relatively pure.

Meanwhile, the methanol content in the material to be treated is high, so that the methanol must be recycled. Considering the problem of effective recovery of methanol, if the material to be treated contains tetrahydrofuran and other materials with boiling point higher than that of methanol and lower than that of dimethyl carbonate, the dimethyl carbonate material flow to be treated is more suitable to be sourced from the bottom of the pressurizing tower. At the moment, the dimethyl carbonate product is extracted from the side line of the stripping section, the side line gas phase extraction needs to pass through a gas-liquid separation tank, the carried liquid phase is separated, the liquid phase obtained by separation automatically flows back to the tower kettle, and the arrangement height of the gas-liquid separation tank is preferably more than 2m higher than the liquid level height of the tower kettle, so that the liquid phase automatically flows; and cooling the gas-phase product from the gas-liquid separation tank to obtain a colorless and transparent dimethyl carbonate product.

In a preferred embodiment, the dimethyl carbonate containing heavy components is extracted from the tower bottom and discharged outside, and the discharge proportion is 0.1-20%, preferably 1-10% of the dimethyl carbonate in the feed.

Wherein, the main purpose of discharging is to prevent the tower kettle from coking and remove trace heavy components.

In a preferred embodiment, the concentration of dimethyl carbonate in the mixture flow is 20 to 99.9%, preferably 25 to 98%; the content of the light component is 2-40%, and the content of the heavy component is 0-5000 ppm.

Wherein the content of the heavy component is calculated by the content of nitrogen element.

In a preferred embodiment, the purity of the dimethyl carbonate product is more than 99.5%, the content of nitrogen-containing compounds is less than 500ppm, and the product is colorless and transparent.

Wherein the content of the nitrogen-containing compound is calculated by the content of nitrogen element.

In a preferred embodiment, the number of theoretical plates of the refining tower is 10-50, the feeding position is 5-35 theoretical plates, and the number of the theoretical plates is increased from bottom to top.

In a further preferred embodiment, the number of theoretical plates of the refining tower is 20-40, and the feeding position is 10-30 theoretical plates.

In the invention, aiming at the dimethyl carbonate material flow to be treated, when the number of theoretical plates exceeds 40, the separation energy consumption is not reduced obviously any more, and when the number of theoretical plates is less than 20, the separation energy consumption is increased greatly.

In a preferred embodiment, the operation pressure of the refining tower is-0.1-1 MPag, the tower top temperature is 40-140 ℃, and the tower kettle operation temperature is 50-190 ℃.

In a further preferred embodiment, the operation pressure of the refining tower is 0-0.8 MPaG, the tower top temperature is 65-135 ℃, and the tower kettle operation temperature is 90-180 ℃.

In the invention, because methanol and dimethyl carbonate are subjected to azeotropic distillation, the higher the pressure is, the lower the content of dimethyl carbonate in the azeotropic point is, and the higher the separation efficiency is, but the higher the pressure causes the higher temperature of the tower bottom, and the dimethyl carbonate is easier to deposit carbon and coke. If the dimethyl carbonate content in the dimethyl carbonate material flow to be treated is higher (more than 60 percent), the lower operation pressure (less than 0.4PaG) is preferably adopted, the temperature of the tower bottom is reduced, and the coking of the tower bottom is reduced, and if the dimethyl carbonate content in the dimethyl carbonate material flow to be treated is lower (less than 30 percent), the higher operation pressure (more than 0.6PaG) is preferably adopted, so that the azeotropic concentration of the dimethyl carbonate in the methanol is reduced, and the separation efficiency is improved.

In a preferred embodiment, more than two, preferably two reboilers are arranged in the tower bottom of the refining tower, wherein one of the reboilers is in an operating state, the other reboilers are in standby, and the standby reboilers are used for switching the decoking process of the reboilers.

In the present invention, as shown in FIG. 1, a mixed stream 2 containing dimethyl carbonate enters the middle part of a refining tower 1, a recycle stream 3 containing dimethyl carbonate is taken out from the top part of the refining tower 1, a dimethyl carbonate product 4 is taken out from the middle part of the lower section (side line of a stripping section) of the refining tower 1, and dimethyl carbonate 5 containing heavy components is taken out from the bottom of the tower.

In the invention, preferably, the mixed stream containing dimethyl carbonate comes from a coupling unit for preparing ethylene glycol from synthesis gas, and the specific position can be, but not limited to, the atmospheric tower top of a process for separating dimethyl carbonate from methyl carbonate by a pressure swing separation method, or a pressurized tower kettle. Wherein the concentration of dimethyl carbonate of the stream extracted from the top of the atmospheric tower is about 30 percent, the rest is mainly methanol, and a small amount of methyl formate, methyl acetate, methylal and the like are also contained, so the stream is colored; the dimethyl carbonate concentration of the material flow extracted from the pressurizing tower kettle is more than 80 percent, and the material flow contains a small amount of methanol, tetrahydrofuran and the like.

In the present invention, the mixture stream containing dimethyl carbonate can also be a light overhead stream of dimethyl oxalate in an extraction separation process, such as a CN106518675B stream 30, and the stream 30 obtained to obtain a dimethyl carbonate product can also generally easily contain light components.

The second object of the present invention is to provide a rectification system for dimethyl carbonate, preferably for carrying out the purification method of the first object of the present invention.

In a preferred embodiment, the rectification system comprises a refining column 1.

In a further preferred embodiment, the number of theoretical plates of the refining tower is 10-50, and the feeding position is 5-35 theoretical plates; preferably, the number of theoretical plates of the refining tower is 20-40, and the feeding position is 10-30 theoretical plates.

In a preferred embodiment, a side draw position is arranged at the stripping section of the refining tower and is used for side drawing the dimethyl carbonate product.

As shown in figure 1, a mixed material flow 2 containing dimethyl carbonate enters the middle part of a refining tower 1, a circulating material flow 3 containing dimethyl carbonate is extracted from the top part of the refining tower 1, a dimethyl carbonate product 4 is extracted from the middle part of the lower section (side line of a stripping section) of the refining tower 1, and dimethyl carbonate 5 containing heavy components is extracted from the bottom of the refining tower.

In a preferred embodiment, more than two, preferably two reboilers are arranged in the tower bottom of the refining tower, wherein one of the reboilers is in an operating state, the other reboilers are in standby, and the standby reboilers are used for switching the decoking process of the reboilers.

The endpoints of the ranges and any values disclosed in the present application are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual values, and between the individual values may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein. In the above, the various technical solutions can in principle be combined with each other to obtain a new technical solution, which should also be considered as specifically disclosed in the present invention.

Compared with the prior art, the invention has the following beneficial effects:

(1) according to the invention, the mixed material flow containing dimethyl carbonate is upgraded by adopting a rectification mode, so that lightness removal is carried out, the purity of dimethyl carbonate is further improved, and meanwhile, the heavy-removal decoloration is effectively carried out by adopting a mode of extracting a gas phase from a side line of a stripping section;

(2) the method or the system solves the problems of complex flow and low quality of dimethyl carbonate products in the prior art, and has the characteristics of simple flow and high purity of dimethyl carbonate;

(3) the dimethyl carbonate product index obtained by separation can reach above the national standard first-grade product index, the economic value of the dimethyl carbonate product is effectively improved, and the method can be well applied to the refining of the dimethyl carbonate product in the process of preparing ethylene glycol from synthesis gas.

Drawings

FIG. 1 shows a schematic diagram of the method and system of the present invention.

In the figure 1, 1 is a refining tower, 2 is a mixed material flow, 3 is a circulating material flow containing dimethyl carbonate extracted from the top of the tower, 4 is a refined dimethyl carbonate product, and 5 is dimethyl carbonate extracted from the bottom of the tower.

Detailed Description

While the present invention will be described in detail with reference to the following examples, it should be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the present invention.

It is to be further understood that the various features described in the following detailed description may be combined in any suitable manner without departing from the scope of the invention. The invention is not described in detail in order to avoid unnecessary repetition.

In the examples, conventional components such as dimethyl carbonate and methanol were analyzed by gas chromatography, and the content of nitrogen was analyzed by ultraviolet spectrophotometry.

Example 1

The dimethyl carbonate purification method of this example is a scale-up apparatus for producing 20 ten thousand tons of ethylene glycol per year.

Dimethyl carbonate material flow to be treated is 1t/h and comes from a pressure tower kettle of a pressure swing separation process, and the weight components are as follows: 95% of dimethyl carbonate, 3% of methanol and 2% of tetrahydrofuran. The content of the nitrogen-containing compound was 1000ppm (in terms of nitrogen content), and the liquid was a dark brown liquid. Entering the middle section of a dimethyl carbonate refining tower.

The dimethyl carbonate refining tower is a packed tower, the diameter of the packed tower is 0.5m, the upper section of packing is divided into two layers, each layer is 3m, the lower section of packing is divided into three layers, the heights of the packing from top to bottom are respectively 3m, 3m and 1m, the position of a dimethyl carbonate product is above a packing layer of 1m, gas phase extraction is adopted, 25 theoretical plates corresponding to the whole tower are adopted, the feeding position is 12 theoretical plates, the extraction position is a theoretical plate of the 3 rd layer, and the gas phase extraction is carried out.

The operating pressure at the top of the column was 0.05MMPaG, the temperature at the top of the column was 74 ℃, the operating temperature at the bottom of the column was 104 ℃ and the reboiler duty was 0.23 MW.

The dimethyl carbonate product is colorless and transparent, the flow rate is 927kg/h, the purity is 99.9 percent, and the content of nitrogen-containing compounds is 100 ppm.

The dark brown material is extracted from the tower bottom at a rate of 10kg/h, and the discharge rate from the tower bottom is 1%.

63kg/h of a stream containing dimethyl carbonate were taken off at the top.

Example 2

The dimethyl carbonate production process of the embodiment is a device matched with the scale for producing 20 ten thousand tons of ethylene glycol annually.

The dimethyl carbonate material flow to be treated is 6t/h from the top of an atmospheric tower of a pressure swing separation process, and comprises the following components in parts by weight: 27% of dimethyl carbonate, 67% of methanol and 6% of methyl acetate. It is a colorless transparent liquid. Entering the middle section of a dimethyl carbonate refining tower.

The dimethyl carbonate refining tower is a float valve tower, the diameter of the tower is 1.2m, 30 layers of theoretical plates are arranged, the feeding position is 10 layers of theoretical plates, the extraction position of the dimethyl carbonate product is 2 layers of theoretical plates, and gas phase extraction is carried out.

The operating pressure at the top of the column was 0.6MPaG, the temperature at the top of the column was 123 ℃, the operating temperature at the bottom of the column was 167 ℃ and the reboiler duty was 2.99 MW.

The dimethyl carbonate product is colorless and transparent, the flow rate is 898kg/h, and the purity is 99.9 percent.

The dark brown material is extracted from the tower bottom at a ratio of 0.6 percent.

5092kg/h dimethyl carbonate-containing material flow is extracted from the tower top and recycled.

Example 3

The dimethyl carbonate stream to be treated in example 1 was treated by the same procedure, changing the operating pressure at the top of the column to 0.3MPaG, the temperature at the top of the column to 105 ℃, the operating temperature at the bottom of the column to 140 ℃, the reboiler duty to 0.30MW, and the reboiler at the bottom of the column was also prone to coking.

The dimethyl carbonate product is colorless and transparent, the flow rate is 942kg/h, the purity is 99.9 percent, and the content of nitrogen-containing compounds is 100 ppm. The dark brown material is extracted from the tower kettle at a rate of 95kg/h, and the discharge rate at the tower kettle is 10%. 63kg/h of a stream containing dimethyl carbonate were taken off at the top.

Example 4

The dimethyl carbonate stream to be treated in example 2 was treated in the same manner, with an operating pressure at the top of the column of 1.0MPaG, a temperature at the top of the column of 140 ℃ and a temperature at the bottom of the column of 190 ℃ with a reboiler duty of 1.93 MW. The reboiler heat duty is significantly reduced, but the increase in column temperature also causes the reboiler to coke more easily.

The dimethyl carbonate product is colorless and transparent, the flow rate is 813kg/h, and the purity is 99.9 percent. The dark brown material is extracted from the tower kettle at a rate of 95kg/h, and the discharge rate from the tower kettle is 5.8%. 5092kg/h dimethyl carbonate-containing material flow is extracted from the tower top and recycled.

Example 5

The dimethyl carbonate material flow to be treated in the example 1 is treated by adopting the same scheme, the number of theoretical plates is changed, the upper section of the dimethyl carbonate refining tower is divided into two layers, each layer is 2.5m, the lower section of the dimethyl carbonate refining tower is divided into three layers, the heights of the fillers from top to bottom are respectively 2.5m, 2.5m and 1m, the position of the dimethyl carbonate product is above a filler layer with the thickness of 1m, and gas phase extraction is adopted. The same separation was achieved with a heat load of 0.29 MW.

Wherein, the number of the theoretical plates of the whole tower is 20, the feeding position is 10 theoretical plates, the extraction position is 3 layers of theoretical plates, the gas phase extraction is carried out, and the discharge proportion of the tower kettle is 1%.

Example 6

The dimethyl carbonate stream of example 2 was treated using different theoretical plate numbers, feed plate numbers, take-off locations, column pressures, overhead column bottoms take-off ratios, with the results shown in example 6 in the table below.

Example 7

The dimethyl carbonate stream of example 1 was treated using different theoretical plate numbers, feed plate numbers, take-off locations, column pressures, overhead column bottoms take-off ratios, with the results shown in example 7 in the table below.

	Unit of	Example 6	Example 7
				Number of theoretical plates	Block	40	20
Number of feed plates	Block	30	10
				Production site	Block	5	3
Column pressure	MPaG	0.8	0.01
				Temperature at the top of the column	℃	135	65
Temperature of the column bottom	℃	180	93
				Flow at the top of the tower	kg/h	5152	63
Discharge ratio of tower still	％	3％	0.5％
				Dimethyl carbonate product color		Colorless and transparent	Colorless and transparent
Flow rate of dimethyl carbonate product	kg/h	800	932
				Purity of the product	％	99.9	99.9
Column bottom heat load	MW	2.27	0.26

Comparative example 1

The dimethyl carbonate material flow to be treated in the example 1 is treated by the same scheme, and the adopted form is changed into liquid phase extraction, so that the dimethyl carbonate product has color and cannot meet the requirements of first-class products of national standards.