CN121405568A - A purification method for dimethyl oxalate - Google Patents
A purification method for dimethyl oxalateInfo
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- CN121405568A CN121405568A CN202511995402.4A CN202511995402A CN121405568A CN 121405568 A CN121405568 A CN 121405568A CN 202511995402 A CN202511995402 A CN 202511995402A CN 121405568 A CN121405568 A CN 121405568A
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- dimethyl oxalate
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Abstract
本发明公开了一种草酸二甲酯的纯化方法，所述方法包括如下步骤：1）将粗草酸二甲酯通入预分离塔，脱除其中的轻组分；2）将步骤1）所得塔釜物料以接近泡点的温度引入纯化‑汽化塔；所述纯化‑汽化塔包括塔体，所述塔体内部填充有塔板或填料，所述塔体的塔釜设置有再沸器（2），所述纯化‑汽化塔的进料端位于塔体的中部；3）调节塔内物料的汽化率为90%‑98%，从所述纯化‑汽化塔的塔顶获得高纯度的气相DMO产品；富含重组分的釜液从塔底排出。本发明将纯化与汽化功能集成于纯化‑汽化塔中，系统简洁，控制变量少，易于实现长周期稳定运行，避免了传统精馏塔在极小回流比下操作的不稳定性。
This invention discloses a purification method for dimethyl oxalate, comprising the following steps: 1) passing crude dimethyl oxalate into a pre-separation tower to remove light components; 2) introducing the bottom material obtained in step 1) into a purification-vaporization tower at a temperature close to the bubble point; the purification-vaporization tower includes a tower body, the interior of which is filled with trays or packing, and a reboiler (2) is provided at the bottom of the tower body, with the feed end of the purification-vaporization tower located in the middle of the tower body; 3) adjusting the vaporization rate of the material in the tower to 90%-98%, obtaining a high-purity gaseous DMO product from the top of the purification-vaporization tower; the bottom liquid rich in heavy components is discharged from the bottom of the tower. This invention integrates purification and vaporization functions into a purification-vaporization tower, resulting in a simple system with few control variables, easy long-term stable operation, and avoiding the instability of traditional distillation towers operating at extremely low reflux ratios.
Description
Technical Field
The invention belongs to the technical field of chemical separation technology and catalytic reaction raw material pretreatment, and particularly relates to a purification method of dimethyl oxalate (DMO).
Background
Dimethyl oxalate (DMO) is a key feedstock for many catalytic reactions such as hydrogenation, decarbonylation, oxidation, etc. However, whether commercial DMO or online synthesized DMO, trace amounts of moisture are readily adsorbed during storage and transportation, which can lead to partial hydrolysis of the DMO to acid impurities such as oxalic acid. For a plurality of downstream reaction sections adopting high-activity and high-selectivity catalysts, the trace but uncontrollable acidic impurities are strong catalyst poisons, can lead to rapid deactivation of the catalysts and reduction of the reaction selectivity, and become a key bottleneck for restricting the long-period stable operation of the device.
To cope with this problem, there are two main approaches in the prior art:
The traditional double-tower rectification process is that the raw material DMO is firstly passed through a dealcoholization tower or a light component removal tower to remove various light components (such as Methyl Formate (MF), methanol, water and the like) generated in the DMO preparation process, then passed through a main rectification tower to obtain a DMO product with higher purity from the top of the tower, and heavy components (such as oxalic acid and other impurities) are discharged from the tower bottom. The process is mainly used for the primary refining of products in the process of producing DMO by CO carbonylation coupling, although the requirements of DMO products with higher purity can be met by increasing the number of plates and the reflux ratio, the main rectifying tower needs to maintain the high reflux ratio to ensure the purity of the products, so that the energy consumption is extremely high, the total heat load of the main rectifying tower can be generally more than 1.5 to 2.0 times of the theoretical heat load (Q vap) required for completely vaporizing DMO raw materials, and the cost is obviously increased.
The vaporization tower technology adopts a vaporization tower, and the device utilizes a steam heating or thermal circulation hydrogen mode to realize the vaporization of DMO, but only can realize the phase change of DMO, has no purification function of deeply removing heavy components (such as oxalic acid and the like) and can not solve the problem of poisoning of a reaction catalyst of the subsequent DMO. Thus, there is a need for a purification process specific to the starting DMO.
Disclosure of Invention
In order to ensure long-period stable operation of downstream high-value catalytic reactions (such as hydrogenation and decarbonylation), the invention provides a purification method of DMO, which can prevent trace moisture from hydrolyzing DMO to generate new oxalic acid in the process, and can deeply remove acidic impurities (such as oxalic acid) existing in raw materials so as to eliminate instant and potential toxicity to sensitive catalysts. Furthermore, the method can synchronously realize the deep removal of moisture and acid impurities with the lowest energy consumption and equipment investment, and directly produce the ultra-high purity DMO raw material suitable for downstream gas-phase feeding catalytic reaction.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a method for purifying dimethyl oxalate (DMO), said method comprising the steps of:
1) Introducing the crude dimethyl oxalate into a pre-separation tower to remove light components in the crude dimethyl oxalate;
2) Introducing the tower kettle material obtained in the step 1) into a purification-vaporization tower at a temperature close to the bubble point, wherein the purification-vaporization tower comprises a tower body, tower plates or fillers are filled in the tower body, a reboiler is arranged at the tower kettle of the purification-vaporization tower body, and the feeding end of the purification-vaporization tower is positioned in the middle of the tower body;
3) And regulating the vaporization rate of the materials in the tower to 90-98%, obtaining a gas-phase DMO product from the top of the purification-vaporization tower, and discharging the kettle liquid rich in heavy components from the bottom of the purification-vaporization tower.
According to an embodiment of the invention, the process further comprises a step 4) of transferring the vapor phase DMO product obtained at the top of step 3) directly to a downstream reaction unit or condensing it into a liquid DMO product by means of a condenser for storage.
According to an embodiment of the present invention, the method further comprises step 5), and the heavy component-rich kettle liquid discharged in step 3) is sent to an acid removal recovery unit (such as molecular sieve adsorption treatment) to recover the crude dimethyl oxalate therein.
According to an embodiment of the invention, the method further comprises a step 6) of returning the crude dimethyl oxalate recovered in step 5) to the feed end of the pre-separation column or the feed end of the purification-vaporization column for reuse. The material closed loop is formed by recycling the crude dimethyl oxalate, so that the total recovery rate of DMO can be improved to more than 99.5%.
According to an embodiment of the invention, the pre-separation column (T1) is used for removing minor amounts of light components under suitable separation conditions. The operating pressure is preferably from atmospheric pressure to a slight positive pressure (e.g., 0-50 kPaG). Under normal pressure operation, the temperature of the tower top is about 50-75 ℃, and the temperature of the tower bottom is about 150-165 ℃.
According to the embodiment of the invention, a feed preheater is arranged between the tower kettle discharge end of the pre-separation tower (T1) and the feed end of the purification-vaporization tower (T2). The feed preheater is used for heating a tower bottom material (S3) of the pre-separation tower (T1) to the bubble point temperature (150-160 ℃) when entering the purification-vaporization tower (T2), and then sending the material into the purification-vaporization tower (T2) so as to realize the optimal utilization of energy.
In the present invention, the preseparation tower is arranged for deep removal of light components in crude dimethyl oxalate, including Methyl Formate (MF), methanol, water, etc., for example.
According to the embodiment of the invention, the light component content in the tower kettle material in the step 1) is below 100 ppm.
According to an embodiment of the invention, in step 1), the pre-separation column is further connected to a DMO feed storage tank.
According to an embodiment of the invention, in step 2), 1-2 theoretical plates or packing sections are arranged above the feed end of the purification-vaporization column (T2). The theoretical plate or the packing section is used for removing heavy components and light components in the ascending gas phase, so that the gas-phase DMO product at the top of the tower is ensured to have extremely high purity.
According to an embodiment of the present invention, in step 2), the reboiler is an external thermosiphon reboiler. The external thermosiphon reboiler is adopted, the reboiler can be isolated, cleaned and maintained independently, potential scaling and corrosion problems are effectively solved, and continuous and stable operation of the process is ensured.
According to an embodiment of the invention, in step 2), the reboiler employs a built-in heating coil. The built-in heating coil is suitable for the scene that the downstream reaction needs to mix the reaction gas or inert shielding gas, and has better regulation and control capability in gasification rate and tower top gas phase product composition.
According to an embodiment of the invention, in step 2), 5-10 trays or packing are provided in the purification-vaporization column below the feed end. The ascending steam and the descending liquid in the tower perform multistage gas-liquid exchange and stripping on tower plates or packing in the tower, so that heavy component impurities (especially oxalic acid) are effectively enriched in the tower bottom of the purification-vaporization tower.
According to an embodiment of the invention, in step 2), no internal or external reflux means are provided inside or outside the purification-vaporization column.
According to an embodiment of the present invention, in step 3), the withdrawal flow rate of the overhead vapor phase DMO product of the purification-vaporization column is controlled to be 90-98% of the feed flow rate of the purification-vaporization column.
According to an embodiment of the invention, in step 3), the heavy component-rich tank liquor comprises DMO and oxalic acid.
The invention has the beneficial effects that:
(1) The purification-vaporization tower is not provided with a reflux device, does not depend on tower top reflux liquid as a separation medium, but carries out stripping through vaporization rate control on internal reflux, specifically, rising steam is partially condensed in the tower to form internal reflux liquid from top to bottom, the internal reflux liquid and rising steam are in countercurrent contact in a packing section or a tower plate, and the high-efficiency stripping washing effect is generated on heavy components (particularly oxalic acid) by utilizing the volatility difference between the heavy components and DMO, so that the heavy components are continuously enriched and pressed in the tower kettle to realize the coupling of separation and vaporization functions, the energy consumption is obviously reduced (the heat load of the heavy components can be reduced to about 1.1-1.5 times Qvap and is far lower than that of the traditional rectification process), and the energy consumption is reduced by more than 50 percent compared with the traditional rectification process, and the operation cost is huge. Qvap, the theoretical vaporization heat, refers to the heat required for completely vaporizing a target product (DMO) in a unit mass of raw material under the adiabatic and lossless conditions, and the value of Qvap can be calculated from the vaporization latent heat of DMO and the raw material throughput, and is the theoretical lower limit for evaluating the energy consumption of the separation process.
(2) In the purification method of dimethyl oxalate (DMO), firstly, the light components in the raw materials are deeply removed through a pre-separation tower, so that the new generation path of oxalic acid is fundamentally cut off, then, the pretreated materials are introduced into a purification-vaporization tower, and internal reflux for efficient stripping is formed in the tower by precisely controlling the vaporization rate (90% -98%), so that heavy component impurities (especially oxalic acid) are efficiently pressed in the tower. Finally, a vapor phase DMO product with a purity of greater than 99.9% is obtained from the top of the column, with the acidic impurity content reduced to very low levels that do not affect downstream catalytic reactions.
(3) The method can deeply remove oxalic acid and other heavy components through efficient stripping action to obtain a gas-phase DMO product with ultra-high purity (more than 99.9 percent), and can effectively protect a downstream high-value catalyst and prolong the service life of the downstream high-value catalyst.
(4) The purification and vaporization functions are integrated in the purification-vaporization tower, the system is simple, the control variable is few (the heat load of a reboiler is mainly controlled), the long-period stable operation is easy to realize, and the instability of the operation of the traditional rectifying tower under the condition of extremely small reflux ratio is avoided.
(5) The invention can directly produce gas-phase DMO products and can also flexibly obtain liquid products. The acid removal recovery unit is combined, so that closed loop recovery of materials can be realized, and raw material consumption and three-waste discharge are obviously reduced.
Drawings
FIG. 1 is a schematic illustration of a process flow of the present invention;
In the figure, T1, a pre-separation tower, T2, a purification-vaporization tower, B1, a DMO raw material storage tank, B2, an acid removal recovery unit, S1, a crude DMO raw material, S2, a light component, S3, tower bottom liquid of the pre-separation tower T1, S4, a high-purity DMO product, S5, a purification-vaporization tower bottom liquid, S6, an acid waste liquid, S7 and recovery of DMO;
FIG. 2 is a schematic diagram of the structure of a purification-vaporization column;
In the figure, the product is 1-tower bottom, 2-reboiler, 3-filling section, 4-feeding and 5-tower top.
Detailed Description
The technical scheme of the invention will be further described in detail below with reference to specific embodiments. It is to be understood that the following examples are illustrative only and are not to be construed as limiting the scope of the invention. All techniques implemented based on the above description of the invention are intended to be included within the scope of the invention.
Unless otherwise indicated, the starting materials and reagents used in the following examples were either commercially available or may be prepared by known methods.
The purifying-vaporizing tower (T2) comprises a tower body, wherein the feeding end of the purifying-vaporizing tower is positioned in the middle of the tower body;
1-2 theoretical plates or fillers are arranged above the feeding end of the purification-vaporization tower (T2), and 8 plates or fillers are arranged below the feeding end of the purification-vaporization tower;
the tower kettle of the tower body is provided with a reboiler (2), and the reboiler adopts an internal heating coil or an external thermosiphon reboiler.
According to the raw material purification direction, a DMO raw material storage tank B1, a pre-separation tower (T1), a purification-vaporization tower (T2) and an acid removal recovery unit (B2) are sequentially connected.
In order to achieve the above purification process, particularly the core operation of stably controlling the vaporization rate, the basic control principle of the present invention is to utilize the "pressure-vaporization rate" self-balancing characteristic inherent in the purification-vaporization column (T2) system. By setting the extraction flow of the gas phase product at the top of the purifying-vaporizing tower (T2) and taking the gas phase product as a main regulating means, the system establishes dynamic balance between heat supply at the tower bottom and extraction at the top of the purifying-vaporizing tower (T2). When the vaporization quantity changes to cause the fluctuation of the pressure in the tower, the change of the phase balance of the system reversely adjusts the actual vaporization rate, so that the operation parameters automatically return to stability, and finally, the self-stability control of the vaporization rate within the range of 90% -98% is realized.
Example 1
1. Raw material and system configuration
Raw material of crude dimethyl oxalate raw material (S1) with a treatment amount of 5000 kg/H is taken from a DMO raw material storage tank (B1), comprises about 99.5% of dimethyl oxalate (DMO), and contains trace amount of water (H 2 O), methanol (MeOH), oxalic acid generated by side reaction and other impurities.
The tower kettle of the tower body is provided with a reboiler (2), and the reboiler adopts an external thermosiphon reboiler.
2. Process steps
The purification method comprises the following steps:
(1) The pre-separation and light removal, namely, the raw DMO material (S1) is fed into a pre-separation tower (T1), the operation condition (the tower top temperature is 50-60 ℃, the tower bottom temperature is 150-160 ℃ and the operation pressure is about-10 kPaG) of the pre-separation tower (T1) is controlled, so that light components (S2) (mainly water and methanol) are extracted from the tower top, and the total content of the light components in the tower bottom material (S3) is reduced to be less than 100 ppm.
(2) Stripping-vaporization coupling purification, namely introducing the tower bottom liquid (S3) of the pre-separation tower T1 into the purification-vaporization tower (T2) from a feeding hole in the middle of the tower body at a temperature (about 160 ℃) close to the bubble point of the tower bottom liquid. In order to achieve a vaporization rate of about 95% and maintain its stability, the present embodiment adopts a control scheme in which a theoretical heat load is determined based on a process simulation, and the operation heat load of the reboiler is set to 110% of the theoretical value. On the basis, the extraction flow rate of the overhead gas-phase DMO product is stabilized at about 95% of the feeding flow rate. The purification-vaporization column (T2) is operated without external reflux from the top of the column, and the vapor rising in the column is partially condensed on the packing surface or on the trays to form an internal reflux. The internal reflux has high-efficiency stripping action on the heavy components (especially oxalic acid) in the downward flowing process, and effectively presses the heavy components (especially oxalic acid) in the tower kettle.
(3) And (3) extracting the product and waste liquid, namely obtaining a high-purity gas-phase DMO product (S4) from the top of the purification-vaporization tower (T2), wherein the purity is higher than 99.9%, and the oxalic acid content is lower than 10 ppm. The bottom of the purification-vaporization tower T2 is discharged from the bottom of the kettle (S5) rich in heavy components (mainly oxalic acid).
(4) And (3) heavy component recovery and circulation, namely conveying the kettle liquid (S5) rich in the heavy component in the step (3) into an acid removal recovery unit (B2). In the embodiment, the acid removal recovery unit B2 adopts a fixed bed adsorption tower provided with a molecular sieve, and selectively adsorbs and removes oxalic acid in the kettle liquid. The purified recovered DMO (S7) is returned to the feeding end of the pre-separation tower (T1) and is mixed with the crude raw material (S1) for re-purification. The acid waste liquid (S6) is sent out for external treatment.
3. Results and effects
By the method of the embodiment, the system stably operates. The heat load of the purification-vaporization column (T2) was estimated to be about 1.15 times Qvap. The purity of the gas-phase DMO product (S4) is higher than 99.9 percent, and the requirement of downstream high-end catalytic reaction is completely met. Compared with the traditional double-tower rectification process (the heat load is about 1.5-2.0 times Qvap), the energy consumption is obviously reduced on the premise of ensuring the purity of the product. Through the cyclic utilization of the acid removal recovery unit (B2), the total recovery rate of the DMO is improved to more than 99.5 percent.
Example 2
1. Raw material and system configuration
The raw materials were the same as in example 1.
The system configuration is basically the same as that of the embodiment 1, except that a reboiler (2) is arranged at the tower bottom of the tower body, a set of superheated gas supply system is added, the superheated gas supply system comprises a compressor, a preheater and corresponding control valves, and preheated superheated gas (30-100 ℃ higher than the boiling point of DMO) is introduced from the tower bottom.
2. Process steps and operating parameters
(1) The pre-separation and light weight removal steps are the same as in example 1.
(2) And (3) gas stripping-vaporization coupling purification, namely introducing the tower bottom liquid (S3) of the pre-separation tower into a purification-vaporization tower T2. Meanwhile, the temperature of the superheated gas which is introduced into the tower kettle is 200-250 ℃, and the superheated gas is introduced into the purification-vaporization tower T2 from the tower kettle. The molar flow rate of the gas entering the tower is about 100% of the total molar flow rate of the gas produced from the tower top. In the rising process of the superheated gas in the tower, the superheated gas is used as a heat source to heat and vaporize DMO and is also used as a stripping medium (carrier gas) to be in countercurrent contact with downstream liquid to complete the stripping process. The vaporization rate of DMO in the tower is stably controlled to be about 96% by adjusting the flow rate and the temperature of hydrogen.
(3) The product is mixed gas of DMO and gas component (S4), and the pressure and temperature can directly meet the feeding requirement of a downstream reactor. And (5) sending out the kettle liquid rich in the heavy components for external treatment. The purity of the product is more than or equal to 99.9 percent.
Comparative example 1
Traditional rectification process
The raw materials are firstly subjected to light component removal by a pre-separation tower (T1) which is the same as that of the embodiment 1, and tower bottom liquid of the pre-separation tower T1 enters a traditional rectifying tower, wherein the rectifying tower is provided with a complete tower top system (a complete condenser, a reflux tank and a reflux pump) and a tower bottom reboiler. In order to obtain a high-purity DMO product from the top of the column and discharge oxalic acid, a heavy component, from the bottom of the column, the reflux ratio R of the rectifying column was 2.0 and the number of theoretical plates was 20, so as to ensure sufficient separation accuracy.
Results and analysis a large amount of energy was used to maintain internal circulation (reflux) between overhead condensation and bottoms reboiling, rather than directly for product purification and vaporization. Although the purity of the product can reach the standard, the purity of the product is more than or equal to 99.9%, the energy consumption is firstly 50% higher than that of the embodiment 1, and the manufacturing cost and the complexity of equipment are also obviously disadvantageous (an overhead condenser, a reflux control unit and the like).
Comparative example 2
Vaporization tower scheme
The feedstock (S1) of example 1 was directly fed to a vaporization column equipped with a heating coil or an external heater to provide heat to a vaporization rate of 100% for DMO in the column and the vapor phase product was all withdrawn from the top of the column. Oxalic acid will be carried in significant amounts into the overhead gas phase, well above the downstream catalyst safety threshold of 10 ppm. The purity of the product is less than or equal to 99 percent.
Compared with the traditional double-tower rectification process, the method provided by the invention realizes the remarkable reduction of energy consumption and the remarkable improvement of material recovery rate on the premise of ensuring the product purity, and shows great economical and environmental protection advantages
The embodiments of the present invention have been described above by way of example. The scope of the invention is not limited to the embodiments described above. Any modifications, equivalent substitutions, improvements, etc. made by those skilled in the art, which fall within the spirit and principles of the present invention, are intended to be included within the scope of the present invention.
Claims (10)
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| CN202511995402.4A CN121405568A (en) | 2025-12-26 | 2025-12-26 | A purification method for dimethyl oxalate |
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