System for recovering methyl nitrite gas and purifying dimethyl oxalate
By achieving reverse contact between methanol and dimethyl oxalate and CO and dimethyl oxalate in the absorption tower and gas extraction tower, a system for recycling methyl nitrite gas and purifying dimethyl oxalate is designed, and the synthesis gas production is solved The problem of MN failure to recycle in the ethylene glycol process improves the stability of the raw materials and the quality of dimethyl oxalate.
Patent Information
- Application Number
- CN202420249743.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-01-31
- Publication Date
- 2024-12-31
- Estimated Expiration
- 2034-01-31
AI Technical Summary
In the synthesis gas-making ethylene glycol process, methyl nitrite (MN) cannot be effectively recycled, resulting in the loss of some N elements. The existing recycling process is complex and water-consuming.
A system including an absorption tower, a gas lift tower and a tower kettle pump was designed to achieve MN recovery and oxalic acid through a reverse contact absorption tower of methanol and a gas lift tower of CO and dimethyl oxalate. The purification of dimethyl ester is produced without by-products through physical changes.
The MN in dimethyl oxalate was effectively recovered and purified, which improved the raw material stability and quality of the ethylene glycol process, reduced material costs, and solved the problem of the failure of intermediate products to be recycled and utilized.
Smart Images
Figure CN222266660U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of ethylene glycol preparation, in particular to a system for recovering methyl nitrite gas and purifying dimethyl oxalate. Background Art
[0002] The process of producing ethylene glycol from syngas is a process of producing ethylene glycol using syngas as raw material under the action of a catalyst; it includes direct process and indirect process. The indirect process is that syngas is converted into ethylene glycol via an intermediate compound. The main synthesis steps are dimethyl oxalate (DMO) synthesis and dimethyl oxalate hydrogenation. The equation is as follows:
[0003] (1)2NO+1 / 2O2+2CH3OH→2CH3ONO+H2O;
[0004] (2)2CO+2CH3ONO→(COOCH3)2+2NO;
[0005] (3)2CO+1 / 2O2+2CH3OH→(COOCH3)2+H2O;
[0006] (4)(COOCH3)2+4H2→HOCH2CH2OH+2CH3OH;
[0007] It can be seen from reaction equations (1)(2)(3) that methyl nitrite (MN) is an intermediate transition product in the whole process. Under ideal conditions, the total nitrogen in the recycling system is balanced. However, in actual production, some N elements will be lost and cannot be recycled. The main reasons are as follows: (1) loss of system relaxation gas; (2) by-product HNO3 is generated in the MN recovery tower and is not completely absorbed into the subsequent wastewater treatment section after nitric acid reduction bubbling; (3) MN and NO are lost due to dissolution in methanol, and MN has a certain loss. Under normal working conditions, the lost MN is supplemented by a nitric acid reduction process, while patent CN101993365A uses a water washing tower to recover MN, but the process requires a large amount of water, and MN needs to be dehydrated before use. The patent recovers MN by chemical methods, and the recovery process is relatively complicated. There is an urgent need for a new MN recovery system to solve the problem of MN recovery in the synthesis gas to ethylene glycol process. Utility Model Content
[0008] In view of the deficiencies in the prior art, the utility model provides a system for recovering methyl nitrite gas and purifying dimethyl oxalate, which solves the problem that part of the intermediate product MN cannot be recycled during the indirect process for preparing ethylene glycol.
[0009] According to an embodiment of the utility model, a system for recovering methyl nitrite gas and purifying dimethyl oxalate includes an absorption tower, a gas stripping tower and a first tower bottom pump; the gas phase inlet at the top of the absorption tower is connected to the gas phase outlet at the top of the gas stripping tower, the first tower bottom pump is connected to the liquid phase outlet at the bottom of the absorption tower, and the tail of the first tower bottom pump has a first branch and a second branch; the first branch is connected to the middle of the absorption tower, and the second branch is connected to the liquid phase inlet at the top of the gas stripping tower, methanol enters from the top of the absorption tower, dimethyl oxalate gas phase material enters from the bottom of the absorption tower, and CO gas enters from the bottom of the gas stripping tower.
[0010] Compared with the prior art, the utility model has the following beneficial effects: the dimethyl oxalate gas phase material enters the bottom of the dimethyl oxalate absorption tower and contacts with the methanol from the top in reverse direction, and the dimethyl oxalate and a small part of MN in the gas phase are absorbed by the methanol; a part of the absorption tower bottom liquid is pressurized by the first tower bottom pump and circulated to the middle section of the absorption tower through the first branch to participate in secondary absorption, and the other part is sent to the top of the stripping tower; fresh CO gas enters the bottom of the stripping tower, the gas phase CO contacts with the liquid phase dimethyl oxalate in reverse direction in the stripping tower, and the gas phase CO is used as the stripping raw material to strip most of the MN in the liquid phase dimethyl oxalate, and the MN is recycled, thereby improving the quality of the dimethyl oxalate; the problem that part of the intermediate product MN cannot be recycled in the process of preparing ethylene glycol by the indirect process is solved; the process belongs to physical change, no by-products are generated, and a stable and reliable raw material is provided for the production of ethylene glycol.
[0011] Preferably, it also includes a gas phase recovery device; the gas phase recovery device includes a condensing section, a reflux tank, an esterification tower and a reflux pump; the gas phase inlet of the condensing section is connected to the gas phase outlet at the top of the absorption tower, the gas phase outlet of the condensing section is connected to the gas phase inlet of the reflux tank, and the liquid phase outlet of the condensing section is connected to the liquid phase inlet of the reflux tank; the liquid phase outlet of the reflux tank is connected to the reflux pump inlet, the gas phase outlet of the reflux tank is connected to the esterification tower, and the reflux pump outlet is connected to the liquid phase inlet at the top of the absorption tower.
[0012] The above technical solution has the advantages that the gas phase in the stripping tower is sent to the absorption tower, the gas phase after washing in the absorption tower is cooled in the condensation part and then enters the reflux tank, the gas phase in the reflux tank is sent to the esterification tower for use in the synthesis of dimethyl oxalate, and the liquid phase in the reflux tank is sent to the top of the absorption tower; in this process, most of the MN in the gas phase material of dimethyl oxalate is recycled and utilized, thereby reducing the material cost.
[0013] Preferably, the condensation section includes a first condenser and a second condenser; the gas phase outlet of the first condenser is connected to the gas phase inlet of the second condenser, the gas phase inlet of the first condenser is connected to the gas phase outlet at the top of the absorption tower, the gas phase outlet of the second condenser is connected to the gas phase inlet of the reflux tank, and the liquid phase outlet of the first condenser and the liquid phase outlet of the second condenser are connected in parallel to the liquid phase inlet of the reflux tank.
[0014] The above technical solution has the advantage that two condensers can be provided to fully cool the gas phase at the first gas phase outlet at the top of the absorption tower, so that more liquid phase can flow back to the absorption tower.
[0015] Preferably, a heater is further included; the heater is connected to the gas inlet at the bottom of the stripping tower, and the CO gas enters the stripping tower through the heater.
[0016] The above technical solution has the advantages that the melting point of DMO is 50-54°C, and the heater increases the gas temperature to avoid DMO crystallization.
[0017] Preferably, it also includes an intermediate tank and a second tower bottom pump; the inlet of the second tower bottom pump is connected to the liquid phase outlet at the bottom of the gas stripping tower, and the outlet of the second tower bottom pump is connected to the intermediate tank.
[0018] The above technical solution has the advantage that the liquid dimethyl oxalate is pumped to the intermediate tank for storage via the second tower bottom pump and is used by the dimethyl oxalate distillation system.
[0019] Preferably, a packing layer is provided in the stripping tower.
[0020] The advantages of adopting the above technical scheme are: the packing layer increases the contact area between the liquid and the gas in the tower, improves the mass transfer and heat transfer efficiency, and the gas phase CO and the liquid phase dimethyl oxalate are fully in reverse contact under the action of the packing layer of the stripping tower. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1 The present invention is a schematic diagram of the structure of a system for recovering methyl nitrite gas and purifying dimethyl oxalate according to an embodiment of the present invention. DETAILED DESCRIPTION
[0022] The technical solution of the present utility model is further described below in conjunction with the accompanying drawings and embodiments.
[0023] The reference numerals in the drawings of the specification include: absorption tower 1, gas stripping tower 2, first tower bottom pump 3, reflux pump 4, second tower bottom pump 5, esterification tower 6, first condenser 7, second condenser 8, reflux tank 9, heater 10, intermediate tank 11.
[0024] Example
[0025] like Figure 1As shown, the embodiment of the utility model proposes a system for recovering methyl nitrite gas and purifying dimethyl oxalate, which includes an absorption tower 1, a gas stripping tower 2, a first tower bottom pump 3, a second tower bottom pump 5, an intermediate tank 11, a heater 10 and a gas phase recovery device; the gas phase recovery device includes a condensing part, a reflux tank 9, an esterification tower 6 and a reflux pump 4; the condensing part includes a first condenser 7 and a second condenser 8; the gas phase outlet of the first condenser 7 is connected to the gas phase inlet of the second condenser 8, the gas phase inlet of the first condenser 7 is connected to the gas phase outlet at the top of the absorption tower 1, the gas phase outlet of the second condenser 8 is connected to the gas phase inlet of the reflux tank 9, the liquid phase outlet of the first condenser 7 and the liquid phase outlet of the second condenser 8 are connected in parallel to the liquid phase inlet of the reflux tank 9; the liquid phase outlet of the reflux tank 9 is connected to the inlet of the reflux pump 4, the gas phase outlet of the reflux tank 9 is connected to the esterification tower 6, and the outlet of the reflux pump 4 is connected to the liquid phase inlet at the top of the absorption tower 1.
[0026] The gas phase inlet at the top of the absorption tower 1 is connected with the gas phase outlet at the top of the stripping tower 2, and the gas phase in the stripping tower is sent to the absorption tower; the first tower bottom pump 3 is connected to the liquid phase outlet at the bottom of the absorption tower 1, and the tail of the first tower bottom pump 3 has a first branch and a second branch; the first branch is connected to the middle of the absorption tower 1, the second branch is connected to the liquid phase inlet at the top of the stripping tower 2, and the heater 10 is connected to the gas inlet at the bottom of the stripping tower 2; the DMO content of the dimethyl oxalate gas phase material is 2-5mol%, and the MN content is 2-10mol%, and methanol enters from the top of the absorption tower 1, and the dimethyl oxalate gas phase material enters from the bottom of the absorption tower 1, and the dimethyl oxalate and a small part of MN in the gas phase are absorbed by methanol; after absorption by the absorption tower 1, the DMO content in the gas phase of the material is 0-0.5mol%, the MN content is 2-10mol%, the DMO content in the liquid phase is 85-95wt%, and the MN content is 0.5-1.5wt%, and the gas phase after washing in the absorption tower enters the first condenser, and the gas phase recovery device recycles most of the MN in the dimethyl oxalate gas phase material.
[0027] Fresh CO gas enters from the bottom of stripping tower 2 after preheating, where the purity of CO in the gas phase flow at the bottom of stripping tower 2 is 99% and the flow rate is 3000-6000Nm 3 / h; a packing layer is arranged in the stripping tower 2, and the packing layer increases the contact area between the liquid and the gas in the tower, improves the mass transfer and heat transfer efficiency, and the gas phase CO and the liquid phase dimethyl oxalate are fully reversely contacted under the action of the packing layer of the stripping tower 2, and the CO gas is used as a stripping raw material to strip most of the MN gas in the liquid phase dimethyl oxalate material in the stripping tower; after the tower bottom liquid is pressurized by the first tower bottom pump 3, a part of it is circulated to the middle section of the absorption tower 1 through the first branch to participate in secondary absorption, and the other part is sent to the top of the stripping tower 2; the inlet of the second tower bottom pump 5 is connected to the liquid phase outlet at the bottom of the stripping tower 2, and the outlet of the second tower bottom pump 5 is connected to the middle The intermediate tank 11 is connected; the liquid dimethyl oxalate is sent to the intermediate tank 11 for storage through the second tower bottom pump 5 for use in the dimethyl oxalate distillation system; the DMO content of the material in the tower bottom of the absorption tower 1 is 85-95wt%, and the MN content is 0.5-1.5wt%; the DMO content of the material in the tower bottom after the gas stripping tower 2 is 90-95wt%, and the MN content is 0.01-0.10wt%; the above process fully recycles MN, which significantly improves the quality of dimethyl oxalate; and solves the problem that the intermediate product MN is partially lost and cannot be recycled in the process of preparing ethylene glycol by the indirect process.
[0028] The above is only an embodiment of the utility model, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the utility model, several deformations and improvements can be made, which should also be regarded as the protection scope of the utility model, and these will not affect the effect of the implementation of the utility model and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.
Claims
1. A system for recovering methyl nitrite gas and purifying dimethyl oxalate, characterized in that: The invention comprises an absorption tower, a gas stripping tower and a first tower bottom pump; the gas phase inlet at the top of the absorption tower is connected with the gas phase outlet at the top of the gas stripping tower, the first tower bottom pump is connected with the liquid phase outlet at the bottom of the absorption tower, and the tail of the first tower bottom pump has a first branch and a second branch; the first branch is connected to the middle of the absorption tower, the second branch is connected to the liquid phase inlet at the top of the gas stripping tower, methanol enters from the top of the absorption tower, dimethyl oxalate gas phase material enters from the bottom of the absorption tower, and CO gas enters from the bottom of the gas stripping tower; gas phase CO and liquid phase dimethyl oxalate are in reverse contact in the gas stripping tower, and the gas phase CO is used as a gas stripping raw material to strip out most of the MN gas in the liquid phase dimethyl oxalate.
2. A system for recovering methyl nitrite gas and purifying dimethyl oxalate according to claim 1, characterized in that: It also includes a gas phase recovery device; the gas phase recovery device includes a condensing section, a reflux tank, an esterification tower and a reflux pump; the gas phase inlet of the condensing section is connected to the gas phase outlet at the top of the absorption tower, the gas phase outlet of the condensing section is connected to the gas phase inlet of the reflux tank, and the liquid phase outlet of the condensing section is connected to the liquid phase inlet of the reflux tank; the liquid phase outlet of the reflux tank is connected to the reflux pump inlet, the gas phase outlet of the reflux tank is connected to the esterification tower, and the reflux pump outlet is connected to the liquid phase inlet at the top of the absorption tower.
3. A system for recovering methyl nitrite gas and purifying dimethyl oxalate according to claim 2, characterized in that: The condensation part includes a first condenser and a second condenser; the gas phase outlet of the first condenser is connected to the gas phase inlet of the second condenser, the gas phase inlet of the first condenser is connected to the gas phase outlet at the top of the absorption tower, the gas phase outlet of the second condenser is connected to the gas phase inlet of the reflux tank, and the liquid phase outlet of the first condenser and the liquid phase outlet of the second condenser are connected in parallel to the liquid phase inlet of the reflux tank.
4. A system for recovering methyl nitrite gas and purifying dimethyl oxalate according to claim 3, characterized in that: It also includes a heater; the heater is connected to the gas inlet at the bottom of the gas stripping tower, and the CO gas enters the gas stripping tower through the heater.
5. A system for recovering methyl nitrite gas and purifying dimethyl oxalate according to claim 4, characterized in that: It also includes an intermediate tank and a second tower bottom pump; the second tower bottom pump inlet is connected to the liquid phase outlet at the bottom of the gas stripping tower, and the second tower bottom pump outlet is connected to the intermediate tank.
6. A system for recovering methyl nitrite gas and purifying dimethyl oxalate according to claim 2, characterized in that: A packing layer is arranged in the gas stripping tower.