阅读说明：本技术 一种含草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 oxalate ) 是由 施德 贺来宾 杨卫胜 于 2019-10-18 设计创作，主要内容包括：本发明提供一种含草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馏塔内,塔顶得到循环物流,塔釜得到含重组分的物流,侧线液相采出精制的草酸二甲酯产品。其中,所述混合物流优选为合成气制乙二醇过程偶联单元分离得到的含草酸二甲酯的物流,本发明所述方法和系统主要解决了现有技术中存在的流程复杂、草酸酯产品中杂质含量高的问题,具体地,利用本发明所述方法得到的草酸二甲酯产品的纯度为99.8～99.99％,优选大于99.9％。(The invention provides a method and a system for refining a mixed material flow containing dimethyl oxalate, wherein the mixed material flow is introduced into a rectifying tower, a circulating material flow is obtained at the top of the rectifying tower, a material flow containing heavy components is obtained at the bottom of the rectifying tower, and a refined dimethyl oxalate product is extracted from a side line liquid phase. The method and the system mainly solve the problems of complex flow and high impurity content in an oxalate product in the prior art, and particularly the purity of the dimethyl oxalate product obtained by the method is 99.8-99.99%, preferably more than 99.9%.)

1. A method for refining the mixed material flow containing dimethyl oxalate includes introducing the mixed material flow into a rectifying tower to obtain a circulating material flow at the top of the tower, obtaining a material flow containing heavy components at the bottom of the tower, and extracting the refined dimethyl oxalate product from a side line liquid phase.

2. The refining method of claim 1, wherein the mixed stream comprises dimethyl oxalate, dimethyl carbonate and heavy components, preferably the heavy components comprise nitrogen-containing compounds and heavy metals, and more preferably the mixed stream is a dimethyl oxalate-containing stream separated from a coupling unit in a process of preparing ethylene glycol from synthesis gas.

3. The refining method according to claim 2, wherein the content of the nitrogen-containing compound is 0 to 500ppm and the content of the heavy metal is 0 to 100ppm based on the total weight of the mixed stream, wherein the content of the nitrogen-containing compound is calculated by the content of nitrogen element therein.

4. The refining method according to claim 2, wherein the content of dimethyl oxalate is 99.0 to 99.99% and the content of dimethyl carbonate is 0 to 1% based on 100% of the mixture flow; preferably, the content of dimethyl oxalate is more than 99.8 percent, and the content of methyl carbonate is less than 0.2 percent.

5. The refining method according to claim 1, wherein the purity of the dimethyl oxalate product is 99.8 to 99.99%, and the content of dimethyl carbonate is 0 to 0.2%; preferably, the purity of the dimethyl oxalate product is more than 99.9%, and the content of dimethyl carbonate is less than 0.1%.

6. The refining process according to claim 1, wherein the recycle stream obtained at the top of the column contains 0 to 20%, preferably 1 to 10% of dimethyl carbonate.

7. The refining method according to any one of claims 1 to 6,

the position of the side line liquid phase extraction is a rectifying section at the upper section of the rectifying tower; and/or

The number of theoretical plates of the rectifying tower is 2-20, the feeding position is 0-18 theoretical plates, wherein 0 represents a tower kettle; preferably, the number of theoretical plates of the rectifying tower is 5-15, and the feeding position is 1-8; and/or

The operating pressure of the rectifying tower is-0.1-1 MPaG, and the temperature is 70-250 ℃; preferably, the operating pressure of the rectifying tower is-0.05-0.1 MPaG, and the temperature is 138-190 ℃.

8. The refining method of claim 7, wherein the stream containing heavy components is discharged from the bottom of the tower, wherein the discharge proportion is 0.1-10% based on 100% of the total feed of the rectifying tower, and the preferred discharge proportion is 0.5-2%.

9. A rectification system, preferably for carrying out the refining method according to any one of claims 1 to 8, wherein the rectification system comprises a rectification column, preferably, the rectification column has 2 to 20 theoretical plates and a feeding position of 0 to 18 theoretical plates, wherein 0 represents a column bottom; more preferably, the number of theoretical plates of the rectifying tower is 5-15, and the feeding position is 1-8.

10. The rectification system as claimed in claim 9, wherein a side draw position is provided at the rectification section of the rectification column for side liquid phase drawing of the dimethyl oxalate product.

Technical Field

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

Background

Dimethyl 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 dimethyl oxalate 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 dimethyl 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 oxalate 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 unit typically produces dimethyl oxalate by a process comprising: after dimethyl oxalate generated by the coupling reactor is absorbed by alcohol, dimethyl oxalate-containing material flow to be treated is extracted from a tower kettle through dealcoholization and carbonic ester. In the prior art, for example, in CN203960094U and CN106518675B, dimethyl oxalate products are usually obtained in a tower bottom, a dimethyl oxalate-containing material flow extracted from the tower bottom usually contains trace metals and catalyst element impurities, the trace metals mainly come from slow loss and metal corrosion of a catalyst, and in addition, a coupling-esterification system is a nitrogen oxide circulating system, so that a nitrogen-containing compound with a high boiling point cannot be avoided from being generated, and the dimethyl oxalate finally enters the tower bottom. Although the content of the impurities is low, the impurities are easy to cause coking and carbon deposition of a hydrogenation reaction system after entering the hydrogenation reaction system, and finally cause the increase of pressure drop, and simultaneously, the impurities which influence the quality of ethylene glycol products are generated after the nitrogen-containing compounds are hydrogenated and must be further removed.

Trace metals and high-boiling nitrogen-containing compounds can be removed by rectification, but dimethyl oxalate is easily decomposed at high temperature in the rectification process to generate light components such as dimethyl carbonate and CO, and the light components enter the dimethyl oxalate. Dimethyl carbonate is easy to generate ethylene carbonate with a boiling point close to that of ethylene glycol in the process of preparing the ethylene glycol by hydrogenating dimethyl oxalate, so that the purity of the ethylene glycol is reduced, and the product quality is influenced.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention adopts a rectification mode to remove the heavy components, effectively reduces the metal and nitrogen-containing compounds in the dimethyl oxalate product, and simultaneously adopts a mode of extracting a liquid phase from the lateral line of a rectification section to effectively separate light components which are possibly generated by decomposition in the process of removing the heavy components from the dimethyl oxalate. The produced high-quality dimethyl oxalate product is used for the process of preparing the ethylene glycol by hydrogenation, so that the stability of a hydrogenation reaction system is effectively improved, and the high-quality dimethyl oxalate product can be well applied to the process of preparing the ethylene glycol by synthesis gas. Solves the problems of complex flow and low purity of dimethyl oxalate in the prior art. Meanwhile, the method has the characteristics of simple process and high purity of dimethyl oxalate.

The invention aims to provide a method for refining a mixed material flow containing dimethyl oxalate, wherein the mixed material flow is introduced into a rectifying tower, a circulating material flow is obtained at the top of the rectifying tower, a material flow containing heavy components is obtained at the bottom of the rectifying tower, and a refined dimethyl oxalate product is extracted from a side line liquid phase.

The mixed material flow contains a very small amount of dimethyl carbonate, dimethyl oxalate is easy to decompose to generate dimethyl carbonate, CO and the like in the rectification process under the high-temperature condition, and the circulating material flow is led out from the top of the tower in the rectification process.

In a preferred embodiment, the mixed stream comprises dimethyl oxalate, dimethyl carbonate and heavies, preferably the heavies comprise nitrogen-containing compounds and heavy metals.

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

In a preferred embodiment, the nitrogen-containing compound is contained in an amount of 0 to 500ppm (in terms of nitrogen element) and the heavy metal is contained in an amount of 0 to 100ppm, based on the total weight of the mixed stream.

In a preferred embodiment, the content of dimethyl oxalate is 99.0-99.99% and the content of dimethyl carbonate is 0-1% based on 100% of the mixture flow.

In a further preferred embodiment, the content of dimethyl oxalate is more than 99.8% and the content of methyl carbonate is less than 0.2% based on 100% of the mixture flow.

In the invention, the feed purity is higher, but trace metal and catalyst element impurities, nitrogen compounds and other impurities are contained, and dimethyl oxalate may be decomposed to generate a small amount of light component dimethyl carbonate in the rectification, so that in the invention, a side-stream liquid phase extraction is skillfully adopted, the purity of dimethyl oxalate is further improved, and the stability of a hydrogenation reaction system in the process of preparing ethylene glycol by hydrogenation of refined dimethyl oxalate is effectively improved.

In a preferred embodiment, the purity of the dimethyl oxalate product is 99.8-99.99%, and the content of dimethyl carbonate is 0-0.2%.

In a further preferred embodiment, the purity of the dimethyl oxalate product is greater than 99.9% and the content of dimethyl carbonate is less than 0.1%.

Wherein, the research finds that the difference between the boiling point (90 ℃) of the methyl carbonate and the boiling point (163 ℃) of the dimethyl oxalate is large, the relative volatility is high, and in the invention, the difference between the contents of the dimethyl carbonate in the gas phase and the liquid phase in the tower is large. Even if the content of dimethyl carbonate generated by decomposition reaches 1%, the content of dimethyl carbonate in the dimethyl oxalate product can be reduced to be below 0.2% by taking out a liquid phase from a side line. The dimethyl oxalate product extracted by the method can be directly used for preparing ethylene glycol or methyl glycolate through hydrogenation.

In a preferred embodiment, the recycle stream obtained at the top of the column contains dimethyl carbonate in an amount of 0 to 20%.

In a further preferred embodiment, the recycle stream obtained at the top of the column has a dimethyl carbonate content of 1 to 10%.

Wherein, the non-condensable gas at the tower top is absorbed by methanol and then is discharged to a torch or is recycled to the system.

In a preferred embodiment, the number of theoretical plates of the rectifying tower is 2-20, the feeding position is 0-18 theoretical plates, wherein 0 represents a tower kettle.

In the invention, the rectifying tower can be a plate tower or a packed tower.

In a further preferred embodiment, the number of theoretical plates of the rectifying tower is 5-15, and the feeding position is 1-8.

The method can treat trace heavy components in raw materials (high-purity dimethyl oxalate), simultaneously solves light components generated by decomposition of dimethyl oxalate in the treatment process, has large difference between the boiling points of the trace heavy components and the dimethyl oxalate, needs a small number of theoretical plates, theoretically can realize separation by directly feeding and evaporating from a tower kettle, can feed materials at a position close to the tower kettle, and preferably adopts the theoretical plates above the tower kettle for further reducing entrainment.

In a preferred embodiment, the rectification column is operated at a pressure of-0.1 to 1MPaG and a temperature of 70 to 250 ℃.

In a further preferred embodiment, the rectification column is operated at a pressure of-0.05 to 0.1MPaG and a temperature of 138 to 190 ℃.

The rectifying tower has higher pressure, can back pressure the non-condensable gas at the top of the tower to a main device, has simple flow, and can cause the temperature of the tower kettle to be overhigh. Pure dimethyl oxalate has a stable structure, but impurities such as heavy metals in the tower bottom material of the invention can promote the decomposition of dimethyl oxalate after being concentrated, and the decomposition can be accelerated after the temperature is increased, so the tower bottom temperature is not too high, the tower top temperature is not too low, the tower top operating temperature is too low, the crystallization of dimethyl oxalate can be caused, a lower vacuum degree is also required, the preferred operating temperature is more than 138 ℃, and the tower top gas phase can be utilized to generate low-pressure steam to recover heat.

In a preferred embodiment, in the method, the stream containing the heavy components is discharged from the tower bottom, wherein the discharge proportion is 0.1-10% based on 100% of the total feeding of the rectifying tower, and the preferred discharge proportion is 0.5-2%.

The material consumption and the accumulation of heavy components in the tower kettle are comprehensively considered by the external discharge capacity of the tower kettle, the concentration of the heavy components in the tower kettle is too high due to too low discharge capacity, the decomposition of dimethyl oxalate is aggravated, and the loss of the dimethyl oxalate is increased due to too large discharge capacity.

In the present invention, as shown in fig. 1, a mixed material flow 2 containing dimethyl carbonate enters the middle part of a rectifying tower 1, a circulating material flow 3 containing dimethyl oxalate containing dimethyl carbonate is taken out from the top of the rectifying tower 1, a dimethyl oxalate product 4 is taken out from the middle part of the upper section (the side line of the rectifying tower) of the rectifying tower 1, and a material flow 5 containing heavy components is taken out from the bottom of the rectifying tower.

In the present invention, the dimethyl oxalate-containing stream to be treated separated by the coupling unit is preferably a stream from the bottom of the column, such as CN203960094U stream 12 or CN106518675B stream 31.

The liquid phase stream containing light components of dimethyl oxalate taken out from the top of the tower is recycled and can be recycled to the process of removing light components of dimethyl oxalate in the coupling unit, such as CN203960094U stream 6 or CN106518675B streams 26 and 29.

The non-condensable gas at the top of the tower can be discharged to a torch after absorbing dimethyl oxalate in the non-condensable gas by adding a methanol absorption tower, or can be recycled to a coupling system, such as a tower bottom gas phase space of C101 in CN203960094U or a tower bottom gas phase space of a tower 23 in CN 106518675B. The reason why the gas phase space is required to be circulated back to the tower kettle is that when the non-condensable gas flows back, the purity of the dimethyl oxalate in the gas phase space is high as well, and the product quality of the dimethyl oxalate cannot be influenced.

It is a second object of the present invention to provide a rectification system, preferably for carrying out the purification process according to the first object of the present invention.

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

In a further preferred embodiment, the number of theoretical plates of the rectifying tower is 2-20, the feeding position is 0-18 theoretical plates, wherein 0 represents a tower kettle.

In a further preferred embodiment, the number of theoretical plates of the rectifying tower is 5-15, and the feeding position is 1-10.

In a preferred embodiment, a side-draw position is arranged at the rectifying section of the rectifying tower and is used for side-draw liquid phase to draw out the dimethyl oxalate product.

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) the invention adopts a rectification mode to remove the weight, effectively reduces the metal and nitrogen-containing compounds in the oxalate product, and simultaneously adopts a mode of taking a liquid phase from the side of a rectification section to effectively separate light components possibly generated by decomposition in the oxalate weight removal process.

(2) The method solves the problems of complex flow and high impurity content in the oxalate product in the prior art, and particularly, the purity of the dimethyl oxalate product obtained by the method is 99.8-99.99%, preferably more than 99.9%;

(3) the produced high-quality oxalate product is used in the process of preparing ethylene glycol by hydrogenation, so that the stability of a hydrogenation reaction system is effectively improved, and the high-quality oxalate product can be well applied to the process of preparing ethylene glycol by 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 rectifying tower, 2 is a mixture flow, 3 is a circulating flow extracted from the top of the tower, 4 is a refined dimethyl oxalate product, and 5 is a flow containing heavy components obtained 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 oxalate and dimethyl carbonate were analyzed by gas chromatography, the content of nitrogen was analyzed by ultraviolet spectrophotometry, and the content of heavy metals was analyzed by inductively coupled plasma mass spectrometry (ICP-MS).

Example 1

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

The stream to be treated containing dimethyl oxalate had a weight composition of (composition excluding trace amounts of nitrides and heavy metals) of 52 t/h: 99.9 percent of dimethyl oxalate and 0.1 percent of dimethyl carbonate. The content of N-containing compound was 100ppm (in terms of nitrogen element) and the content of heavy metal was 2 ppm.

The oxalic ester rectifying tower adopts a float valve tower, the number of theoretical plates is 10, the feeding position is the 4 th theoretical plate, the extraction position of the dimethyl oxalate product is the 5 th theoretical plate, and liquid phase extraction is carried out.

The operating pressure of the oxalate rectifying tower is 0.05MpaG, the operating temperature of the top of the tower is 173 ℃, and the discharge proportion of the tower kettle is 0.96%.

The flow rate of a dimethyl oxalate product collected from the side line is 51t/h, and the weight composition is (the composition does not contain trace nitride and heavy metal): 0.04% of dimethyl carbonate and 99.96% of dimethyl oxalate. The content of N-containing compound (calculated as nitrogen element) was 10ppm, and the content of heavy metal was 0.5 ppm.

360kg/h of liquid phase is extracted from the tower top and is circulated back to the dimethyl oxalate lightness removing process of the coupling unit, and the weight composition (the composition does not include trace nitride and heavy metal): 9.5 percent of dimethyl carbonate and 90.5 percent of dimethyl oxalate. The flow rate of the non-condensable gas is 140kg/h, and the weight composition is as follows: 44.5 percent of dimethyl carbonate, 38.7 percent of dimethyl oxalate and 15.8 percent of CO, and the non-condensable gas is sent to a torch after being absorbed by methanol. 0.5t/h brown dimethyl oxalate containing heavy components is extracted from the tower bottom.

Comparative example 1

The procedure of example 1 was repeated except that: the product extraction position is changed into the tower top, the content of dimethyl oxalate in the obtained dimethyl oxalate product is reduced to 99.75 percent, and the content of dimethyl carbonate is 0.25 percent.

Comparative example 2

The procedure of example 1 was repeated except that: the phase state of the produced product is changed into gas phase production, and the content of dimethyl oxalate in the obtained gas phase dimethyl oxalate product is also reduced to 99.75 percent, the content of dimethyl carbonate is 0.21 percent, and the content of CO is 0.04 percent.

Examples 2 to 6

The dimethyl oxalate stream in example 1 was treated using different theoretical plate numbers, feed plate numbers, withdrawal positions, column pressures, and top column withdrawal ratios, with the following results:

example 7

The dimethyl oxalate stream of example 1 was treated and the oxalate rectification column was packed with structured plate corrugations, 2m height of packing below the feed position, 3m height of packing above the feed position, and the side draw was above the feed position and below 3m of packing. The number of the whole tower theoretical plates is 10.

The operating pressure of the oxalate rectifying tower is 0.05Mpag, the operating temperature of the top of the tower is 173 ℃, and the discharge proportion of the tower kettle is 0.96%.

Because of adopting the packed tower, the pressure drop of the tower is low, the temperature of the tower bottom is low, the decomposition rate of the dimethyl oxalate is reduced, the flow rate of the dimethyl oxalate product extracted from the side line is 51t/h, and the weight composition (the composition does not comprise trace nitride and heavy metal): dimethyl carbonate 0.03%, dimethyl oxalate 99.97%, N-containing compounds and heavy metals can be reduced to 10ppm and 0.5 ppm.