Energy-saving device and method for producing potassium methoxide by thermal coupling alkali method

Abstract

This invention belongs to the fields of chemical engineering and energy conservation, and discloses an energy-saving device and method for producing potassium methoxide using a thermally coupled alkaline process. The energy-saving device for producing potassium methoxide using a thermally coupled alkaline process includes: a reaction system, a distillation system, and a recovery system; the reaction system includes a reaction tower; the distillation system includes a distillation tower, a dehydrator, a first compressor, a second compressor, a falling film reboiler, and a distillation condenser; the recovery system includes a primary feed preheater, a secondary feed preheater, a first recovery tower condenser, a first recovery tower, a first recovery tower falling film reboiler, a second recovery tower, a second recovery tower falling film reboiler, a third recovery tower, and a third recovery tower reboiler. This invention discloses a method for producing potassium methoxide using an alkaline process based on the aforementioned energy-saving device for producing potassium methoxide using a thermally coupled alkaline process. This invention utilizes the heat from the product in the reaction tower bottom and the heat from the recovery system to thermally couple with the feed stream, saving energy consumption of steam in the reaction tower bottom and the amount of circulating water used.

Description

Technical Field

[0001] This invention belongs to the fields of chemical engineering and energy conservation, and relates to an energy-saving device and method for producing potassium methoxide by thermal coupling alkaline process. Background Technology

[0002] Potassium methoxide is a strong organic base, readily soluble in organic solvents such as methanol and ethanol. Its main applications are in the chemical and pharmaceutical fields. It can be used as a catalyst in organic synthesis reactions (such as transesterification and condensation reactions); it can also be used as a strong base reagent to remove active hydrogen from organic compounds, or participate in the preparation of other organopotassium salts; additionally, potassium methoxide can be used as an intermediate raw material in the production of vitamins, sulfadiazine, and other pharmaceuticals.

[0003] Currently, common methods for producing potassium methoxide include the direct reaction of metallic potassium with methanol (metallic potassium method) and the reaction of potassium hydroxide with methanol solution (alkali method).

[0004] Potassium metal method: 2K + 2CH3OH → 2CH3OK + H2↑. This method utilizes the substitution reaction between an active metal and an alcohol to produce potassium methoxide. However, potassium metal is expensive, and its reaction with methanol is violent and difficult to control. The reaction releases a large amount of hydrogen gas, posing a significant safety hazard, and therefore it is rarely used in industry.

[0005] Alkaline process: KOH + CH3OH → CH3OK + H2O. This method has become the mainstream choice in industry due to its low cost and high safety. The alkaline process to produce potassium methoxide is a reversible process, requiring dehydration to shift the reaction towards potassium methoxide production. The traditional alkaline process for producing potassium methoxide includes a reaction tower, a distillation tower, and a recovery tower. The reaction tower is mainly used to synthesize potassium methoxide. Methanol and water at the top of the tower enter the distillation tower for separation. The methanol gas at the top of the distillation tower is pressurized and heated by two compressors. One route returns to the reaction tower as stripping steam, while the other route is heated, condensed, and refluxed back to the distillation tower. The methanol-water solution at the bottom of the distillation tower enters the recovery tower for further separation. The high-concentration methanol at the top of the recovery tower is returned to the distillation tower, and the wastewater from the bottom of the recovery tower is discharged. The traditional process has high energy consumption and low methanol recovery. Chinese invention patent CN103288593A provides a mechanical vapor recompression production method, which realizes the circulation of high-temperature methanol vapor. Although the energy consumption is lower than that of the traditional process, the overall energy consumption of the system is still high. Chinese invention patent application CN110551003A discloses a process for producing sodium methoxide by heat pump compression cycle. The process is simple, involving only one distillation column, one dehydration column and one compressor. However, it cannot fully recover methanol, and the wastewater in the bottom of the dehydration column still contains methanol, which is directly discharged and causes waste of raw materials. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing processes by providing an alkaline process for producing potassium methoxide with low energy consumption and high methanol recovery.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A thermally coupled alkaline process for potassium methoxide production energy-saving device includes: a reaction system for alkaline synthesis of potassium methoxide, a distillation system for recovering methanol from the gas phase generated by the reaction system, and a recovery system for coupling system heat energy to reduce steam energy consumption.

[0009] The reaction system includes a reaction tower 1; the distillation system includes a distillation tower 2, a dehydrator 6, a first compressor 3, a second compressor 7, a distillation falling film reboiler 8, a distillation condenser 9, and a distillation reflux tank 10; the recovery system includes a primary feed preheater 13, a secondary feed preheater 14, a first recovery tower condenser 15, a first recovery tower reflux tank 16, a first recovery tower 18, a first recovery tower falling film reboiler 20, a second recovery tower reflux tank 21, a second recovery tower 23, a second recovery tower falling film reboiler 25, a third recovery tower reflux tank 26, a third recovery tower 28, and a third recovery tower reboiler 29.

[0010] The liquid phase outlet of the bottom of the reaction tower 1 is connected to the shell-side inlet of the secondary raw material preheater 14, and the shell-side outlet of the secondary raw material preheater 14 is connected to the liquid potassium methoxide product outlet pipe; the gas phase outlet at the top of the reaction tower 1 is connected to the feed inlet of the distillation tower 2.

[0011] The vapor outlet at the top of the distillation column 2 is connected to the dehydrator 6 and the second compressor 7, respectively. The outlet of the dehydrator 6 is connected to the inlet of the first compressor 3, and the vapor outlet of the first compressor 3 is connected to the inlet of the reaction column 1. The outlet of the second compressor 7 is connected to the shell-side inlet of the distillation falling film reboiler 8, and the shell-side outlet of the distillation falling film reboiler 8 is connected in sequence to the distillation condenser 9 and the distillation reflux tank 10. The liquid outlet of the distillation reflux tank 10 is connected to the reflux port of the distillation column 2. The liquid outlet at the bottom of the distillation column 2 is connected to the feed inlet of the first recovery column 18.

[0012] The vapor outlet at the top of the first recovery tower 18 is connected to the shell-side inlet of the primary feed preheater 13, and the shell-side outlet of the primary feed preheater 13 is connected in sequence to the condenser 15 of the first recovery tower and the reflux tank 16 of the first recovery tower; the liquid outlet of the reflux tank 16 of the first recovery tower is connected to the reflux port at the top of the first recovery tower 18 and the liquid inlet at the middle of the distillation tower 2.

[0013] The liquid phase outlet of the first recovery tower 18 is connected to the feed inlet of the second recovery tower 23;

[0014] The top gas phase outlet of the second recovery tower 23 is connected to the shell-side inlet of the falling film reboiler 20 of the first recovery tower, the shell-side outlet of the falling film reboiler 20 of the first recovery tower is connected to the liquid inlet of the reflux tank 21 of the second recovery tower, and the liquid phase outlet of the reflux tank 21 of the second recovery tower is connected to the reflux port of the second recovery tower 23 and the liquid phase inlet in the middle of the distillation column, respectively.

[0015] The liquid phase outlet of the second recovery tower 23 is connected to the feed inlet of the third recovery tower 28;

[0016] The gas phase outlet at the top of the third recovery tower 28 is connected to the shell-side inlet of the falling film reboiler 25 of the second recovery tower. The shell-side outlet of the falling film reboiler 25 of the second recovery tower is connected to the liquid inlet of the reflux tank 26 of the third recovery tower. The liquid phase outlet of the reflux tank 26 of the third recovery tower is connected to the reflux port at the top of the third recovery tower 28 and the liquid phase inlet in the middle of the distillation tower 2, respectively.

[0017] As a preferred technical solution of the energy-saving device for the thermally coupled alkaline process of potassium methoxide production described in this invention, it further includes: a dryer 4 and a dryer compressor 5; the dryer 4 includes a drying chamber body, which is provided with a liquid inlet and an air outlet; two jackets are provided at the bottom of the drying chamber body, each jacket being provided with an air inlet and a liquid outlet, one jacket being circulated with water vapor as a heat source, and the other jacket being circulated with methanol vapor as a heat source; the feed inlet of the dryer 4 is connected to the shell-side outlet of the secondary preheater 14 of the raw material, the air outlet of the dryer 4 is connected to the inlet of the dryer compressor 5, and the outlet of the dryer compressor 5 is connected to the air inlet of one of the jackets of the dryer. The liquid product from the reactor bottom enters the dryer 4 through the liquid inlet, the methanol is heated and vaporized in the dryer, and the methanol vapor is discharged from the air outlet of the dryer 4, enters the dryer compressor 5, is pressurized, and then returns to the dryer to provide a heat source, thus saving some steam consumption.

[0018] Both the primary raw material preheater 13 and the secondary raw material preheater 14 are shell-and-tube heat exchangers.

[0019] The tube-side inlet of the primary raw material preheater 13 is connected to the raw material feed pipe, the tube-side outlet of the primary raw material preheater 13 is connected to the tube-side inlet of the secondary raw material preheater 14, and the shell-side outlet of the secondary raw material preheater 14 is connected to the feed inlet of the reaction tower 1. The potassium hydroxide methanol mixture enters the reaction tower by passing through the tube side of the primary raw material preheater 13 and the tube side of the secondary raw material preheater 14 in sequence.

[0020] The reaction tower 1 is a plate tower; the lower part of the reaction tower 1 is equipped with a steam coil for steam heating; the upper part of the reaction tower is equipped with a feed inlet for introducing potassium hydroxide methanol mixture (referred to as alcohol-alkali solution), and the lower part of the reaction tower is equipped with a gas inlet for introducing high-temperature and high-pressure methanol gas from the distillation system.

[0021] Specifically, the feed inlet of the reaction tower is located above the first tray.

[0022] The distillation column 2 is a packed column; the packing of the distillation column is BX, CY metal wire mesh packing, 500X, 500Y, 700X, 700Y, 750X or 750Y plate corrugated packing; the middle part of the distillation column is provided with a feed inlet and a liquid inlet, which are used to introduce the gas phase from the top of the reaction column and the aqueous methanol from the recovery system, respectively; the upper part of the distillation column 2 is provided with a reflux port.

[0023] Specifically, the feed inlet of the distillation column 2 is located between the second and third packing layers; the liquid inlet in the middle of the distillation column 2 is located between the second and third packing layers; and the reflux outlet of the distillation column 2 is located above the first packing layer.

[0024] The distillation falling film reboiler 8 is a shell-and-tube heat exchanger.

[0025] The distillation condenser 9 is a shell-and-tube heat exchanger.

[0026] The first recovery tower condenser 15 is a shell-and-tube heat exchanger.

[0027] The first recovery tower falling film reboiler 20 is a shell-and-tube heat exchanger.

[0028] The second recovery tower falling film reboiler 25 is a shell-and-tube heat exchanger.

[0029] The third recovery tower reboiler 29 is a coiled tube heat exchanger, and the third recovery tower reboiler 29 is heated by steam.

[0030] Specifically, the third recovery tower reboiler 29 adopts the heat exchange equipment of Example 1 in patent CN206304714U.

[0031] The water separator 6 is filled with molecular sieves.

[0032] Preferably, the shell-side outlet of the distillation falling film reboiler 8 is connected to the inlet of the distillation condenser 9, the outlet of the distillation condenser 9 is connected to the feed inlet of the distillation reflux tank 10, the liquid phase outlet of the distillation reflux tank 10 is connected to the inlet of the distillation column reflux pump 11, and the outlet of the distillation column reflux pump 11 is connected to the reflux port of the distillation column 2.

[0033] Preferably, the liquid phase outlet of the distillation column 2 is connected to the inlet of the distillation column bottom pump 12, and the outlet of the distillation column bottom pump 12 is connected to the tube side inlet of the distillation falling film reboiler 8 and the feed inlet of the first recovery column 18, respectively.

[0034] The first recovery tower is a packed tower; the packing material of the first recovery tower is BX, CY wire mesh packing, 500X, 500Y, 700X, 700Y, 750X, or 750Y corrugated plate packing. The feed inlet of the first recovery tower 18 is located between the second and third packing layers. The reflux outlet of the first recovery tower is located above the first packing layer.

[0035] Preferably, the shell-side outlet of the primary raw material preheater 13 is connected to the inlet of the first recovery tower condenser 15, the outlet of the first recovery tower condenser 15 is connected to the liquid inlet of the first recovery tower reflux tank 16, the liquid phase outlet of the first recovery tower reflux tank 16 is connected to the inlet of the first recovery tower reflux pump 17, and the outlet of the first recovery tower reflux pump 17 is connected to the reflux port at the top of the first recovery tower 18 and the liquid phase inlet in the middle of the distillation column 2, respectively.

[0036] Preferably, the liquid phase outlet of the first recovery tower 18 is connected to the inlet of the first recovery tower bottom pump 19, and the outlet of the first recovery tower bottom pump 19 is connected to the tube side inlet of the first recovery tower falling film reboiler 20 and the feed inlet of the second recovery tower 23, respectively.

[0037] The second recovery tower is a packed tower; the packing material of the second recovery tower is BX, CY wire mesh packing, 500X, 500Y, 700X, 700Y, 750X, or 750Y corrugated plate packing. The feed inlet of the second recovery tower 23 is located between the second and third packing layers. The reflux outlet of the second recovery tower is located above the first packing layer.

[0038] Preferably, the shell-side outlet of the first recovery tower falling film reboiler 20 is connected to the liquid inlet of the second recovery tower reflux tank 21, the liquid phase outlet of the second recovery tower reflux tank 21 is connected to the inlet of the second recovery tower reflux pump 22, and the outlet of the second recovery tower reflux pump 22 is connected to the upper reflux port of the second recovery tower 23 and the liquid phase inlet in the middle of the distillation column, respectively.

[0039] Preferably, the liquid phase outlet of the second recovery tower 23 is connected to the inlet of the second recovery tower bottom pump 24, and the outlet of the second recovery tower bottom pump 24 is connected to the tube side inlet of the second recovery tower falling film reboiler 25 and the feed inlet of the third recovery tower 28, respectively.

[0040] The third recovery tower is a packed tower; the packing material of the third recovery tower is BX, CY wire mesh packing, 500X, 500Y, 700X, 700Y, 750X, or 750Y corrugated plate packing. The feed inlet of the third recovery tower 28 is located between the second and third packing layers. The reflux outlet of the third recovery tower 28 is located above the first packing layer.

[0041] Preferably, the shell-side outlet of the second recovery tower falling film reboiler 25 is connected to the liquid inlet of the third recovery tower reflux tank 26; the liquid phase outlet of the third recovery tower reflux tank 26 is connected to the inlet of the third recovery tower reflux pump 27, and the outlet of the third recovery tower reflux pump 27 is connected to the reflux port at the top of the third recovery tower 28 and the liquid phase inlet in the middle of the distillation tower 2, respectively.

[0042] As a preferred technical solution of the energy-saving device for the thermally coupled alkaline process for potassium methoxide production described in this invention, it further includes: a wastewater reuse system for recovering methanol from the tail gas; the wastewater reuse system includes a wastewater cooler 30, a primary water washing tower 31, a secondary water washing tower 32, a tertiary water washing tower 33, and a tail gas cooler 37.

[0043] The air inlet of the primary water washing tower 31 of the wastewater reuse system is connected to the gas phase outlet of the distillation reflux tank 10, the gas phase outlet of the first recovery tower reflux tank 16, the gas phase outlet of the second recovery tower reflux tank 21, and the gas phase outlet of the third recovery tower reflux tank 26 via the tail gas cooler 37.

[0044] The tube-side inlet of the wastewater cooler 30 is connected to the liquid phase outlet of the bottom of the third recovery tower 28; the tube-side outlet of the wastewater cooler 30 is connected to the water inlet at the top of the tertiary water washing tower 33.

[0045] The gas phase outlet at the top of the primary water washing tower 31 is connected to the air inlet of the secondary water washing tower 32, and the gas phase outlet at the top of the secondary water washing tower 32 is connected to the air inlet of the tertiary water washing tower 33. The water inlet at the top of the tertiary water washing tower 33 is connected to the tube-side outlet of the wastewater cooler 30, the liquid phase outlet at the bottom of the tertiary water washing tower 33 is connected to the water inlet at the top of the secondary water washing tower 32, the liquid phase outlet at the bottom of the secondary water washing tower 32 is connected to the water inlet at the top of the primary water washing tower 31, the liquid phase outlet at the bottom of the primary water washing tower 31 is connected to the shell-side inlet of the wastewater cooler 30, and the shell-side outlet of the wastewater cooler 30 is connected to the feed inlet of the third recovery tower 28.

[0046] The primary water washing tower is a packed tower, with the packing material being 170X, 170Y, 250X, 250Y, 350X, or 350Y corrugated plate packing. The secondary water washing tower is a packed tower, with the packing material being 170X, 170Y, 250X, 250Y, 350X, or 350Y corrugated plate packing. The tertiary water washing tower is a packed tower, with the packing material being 170X, 170Y, 250X, 250Y, 350X, or 350Y corrugated plate packing.

[0047] Preferably, the air inlet of the primary water washing tower 31 is located below the second section of packing, and the water inlet of the primary water washing tower 31 is located above the first section of packing; the air inlet of the secondary water washing tower 32 is located below the second section of packing, and the water inlet of the secondary water washing tower 32 is located above the first section of packing; the air inlet of the tertiary water washing tower 33 is located below the second section of packing, and the water inlet of the tertiary water washing tower 33 is located above the first section of packing; the gas phase outlet at the top of the tertiary water washing tower 33 is open to the atmosphere.

[0048] Preferably, the liquid phase outlet of the bottom of the tertiary water washing tower 33 is connected to the inlet of the tertiary water washing pump 36, and the outlet of the tertiary water washing pump 36 is connected to the liquid phase inlet of the secondary water washing tower 32; the liquid phase outlet of the bottom of the secondary water washing tower 32 is connected to the inlet of the secondary water washing pump 35, and the outlet of the secondary water washing pump 35 is connected to the liquid phase inlet of the primary water washing tower 31; the liquid phase outlet of the bottom of the primary water washing tower 31 is connected to the inlet of the primary water washing pump 34, the outlet of the primary water washing pump 34 is connected to the shell-side inlet of the wastewater cooler 30, and the shell-side outlet of the wastewater cooler 30 is connected to the feed inlet of the third recovery tower 28.

[0049] The wastewater cooler 30 is a shell-and-tube heat exchanger.

[0050] The exhaust gas cooler 37 is a shell-and-tube heat exchanger.

[0051] For those skilled in the art, the connection method between the column and the associated reboiler is conventional. The liquid phase outlet of the distillation column 2 is connected to the tube-side inlet of the falling film reboiler 8, and the tube-side outlet of the falling film reboiler 8 is connected to the distillation column 2; the liquid phase outlet of the first recovery column 18 is connected to the tube-side inlet of the first recovery column falling film reboiler 20, and the tube-side outlet of the first recovery column falling film reboiler 20 is connected to the first recovery column 18; the liquid phase outlet of the second recovery column 23 is connected to the tube-side inlet of the second recovery column falling film reboiler 25, and the tube-side outlet of the second recovery column falling film reboiler 25 is connected to the second recovery column 23; the liquid phase outlet of the third recovery column 28 is connected to the tube-side inlet of the third recovery column reboiler 29, and the tube-side outlet of the third recovery column reboiler 29 is connected to the feed inlet of the third recovery column 28.

[0052] Another object of the present invention is to provide a method for producing potassium methoxide by alkaline process based on the aforementioned energy-saving device for thermally coupled alkaline process, comprising the following steps:

[0053] Step (1), Reaction: The potassium hydroxide-methanol mixture (referred to as alcohol-alkali solution) sequentially enters the primary feed preheater 13 and the secondary feed preheater 14, where it undergoes primary heat exchange with the overhead gas phase from the first recovery tower 18 and secondary heat exchange with the liquid product from the bottom of the reaction tower. Then, it enters the reaction tower from the top. High-temperature and high-pressure methanol gas from the distillation system enters the reaction tower from the bottom and undergoes countercurrent mass transfer with the potassium hydroxide-methanol mixture, mainly providing the rising gas phase and heat energy for the reaction tower. The water produced in the reaction is removed, and 27-30 wt% liquid potassium methoxide product is obtained in the bottom of the reaction tower. The overhead gas phase of the reaction tower enters the distillation tower 2 of the distillation system.

[0054] Step (2), distillation: The vapor phase from the top of the reaction tower enters the distillation tower 2 from the middle for distillation. Methanol is collected from the top of the distillation tower. A portion of the methanol is dehydrated by the dehydrator 6 and pressurized and heated by the first compressor 3 to obtain high-temperature and high-pressure methanol gas, which is returned from the bottom to the reaction tower 1 to provide heat and methanol gas for the reaction tower. The remaining methanol is pressurized and heated by the second compressor 7 and enters the distillation falling film reboiler 8 as a heat source to exchange heat with the liquid at the bottom of the distillation tower. The methanol after heat exchange is condensed by the distillation condenser 9 and returned to the distillation tower. The liquid at the bottom of the distillation tower is sent to the recovery system.

[0055] Step (3), Recovery: The bottom liquid of the distillation column enters the first recovery column 18 for distillation. The vapor phase from the top of the first recovery column enters the primary feed preheater as a heat source to exchange heat with the potassium hydroxide-methanol mixture (alcohol-alkali solution), and then enters the condenser 15 of the first recovery column for condensation. After condensation, it enters the reflux tank 16 of the first recovery column. Part of the liquid phase in the reflux tank 16 of the first recovery column is returned to the first recovery column 18, and the remainder is returned to the distillation column 2. The bottom liquid of the first recovery column enters the second recovery column 23. The vapor phase from the top of the second recovery column enters the falling film of the first recovery column for further distillation. The boiling reboiler 20 serves as a heat source to exchange heat with the bottom liquid of the first recovery tower, and then enters the reflux tank 21 of the second recovery tower. A portion of the liquid phase in the reflux tank 21 of the second recovery tower is refluxed back to the second recovery tower, and the remainder is returned to the distillation tower. The bottom liquid of the second recovery tower enters the third recovery tower 28. The vapor phase at the top of the third recovery tower enters the falling film reboiler 25 of the second recovery tower to exchange heat with the bottom liquid of the second recovery tower, and then enters the reflux tank 26 of the third recovery tower. A portion of the liquid phase in the reflux tank 26 of the third recovery tower is refluxed back to the third recovery tower, and the remainder is returned to the distillation tower.

[0056] In step (1), the mass ratio of potassium hydroxide to methanol in the potassium hydroxide-methanol mixture is 1:3 to 1:4.5, preferably 1:3.5 to 1:4.1.

[0057] The reaction tower 1 is a plate tower with a theoretical number of plates of 20 to 50, preferably 30 to 45.

[0058] The operating pressure at the top of the reaction tower 1 is 0-0.1 MPaG, preferably 0-50 kPaG, and the operating temperature at the bottom of the tower is 100-120℃, preferably 105-115℃.

[0059] As a preferred embodiment of the alkaline process for producing potassium methoxide according to the present invention, the method further includes: the liquid potassium methoxide product enters the dryer 4 and is dried using external steam and / or methanol vapor as a heat source to obtain solid potassium methoxide; during the drying process, the methanol in the liquid potassium methoxide product is heated and vaporized to form methanol vapor, and the methanol vapor is pressurized by the dryer compressor and returned to the jacket of the dryer to provide a heat source.

[0060] The dryer compressor 5 pressurizes the methanol vapor by 30-120 kPa, preferably 50-100 kPa.

[0061] In step (2), the distillation column is a packed column; the top operating pressure of the distillation column is 0-0.1 MPaG, preferably 0-50 kPaG, the bottom operating temperature is 60-90℃, preferably 70-80℃, and the reflux ratio is 0.7-1.2, preferably 0.8-1.

[0062] After being compressed by the first compressor, the methanol is pressurized by 30-120 kPa, preferably 40-80 kPa; after being compressed by the second compressor, the methanol is pressurized by 60-150 kPa, preferably 80-120 kPa.

[0063] The outlet temperature of the distillation condenser 9 is 40-60°C, preferably 45-55°C.

[0064] The bottom liquid of the distillation column is a mixture of alcohol and water.

[0065] Preferably, a portion of the distillate from the bottom of the distillation column is pumped by the bottom pump 12 into the falling film reboiler 8 to exchange heat with the pressurized and heated methanol, and then returned to the distillation column. The remaining bottom liquid from the distillation column is pumped by the bottom pump 12 into the recovery system.

[0066] In step (3), the top operating pressure of the first recovery tower is 0 to 0.1 MPaG, preferably 0 to 50 kPaG, the bottom operating temperature is 60 to 120°C, preferably 70 to 110°C, and the reflux ratio is 0.4 to 0.9, preferably 0.6 to 0.8.

[0067] The outlet temperature of the condenser in the first recovery tower is 40–70°C, preferably 45–65°C.

[0068] The operating pressure at the top of the second recovery tower is 0.2–0.5 MPaG, preferably 0.25–0.45 MPaG, the operating temperature at the bottom of the tower is 100–140°C, preferably 110–130°C, and the reflux ratio is 0.8–1.1, preferably 0.9–1.0.

[0069] The operating pressure at the top of the third recovery tower is 0.5–0.9 MPaG, preferably 0.6–0.8 MPaG; the operating temperature at the bottom of the tower is 150–190℃, preferably 160–180℃; and the reflux ratio is 1.2–3, preferably 1.5–2.5.

[0070] As a preferred embodiment of the alkaline process for producing potassium methoxide according to the present invention, the method further includes step (4): recovering methanol from the methanol tail gas of the distillation system and the recovery system using a three-stage countercurrent process: the bottom liquid of the third recovery tower enters the wastewater cooler 30 to exchange heat with the bottom liquid of the first-stage water washing tower, and the cooled bottom liquid of the third recovery tower enters the third-stage water washing tower from the top, and then enters the second-stage water washing tower and the first-stage water washing tower in sequence; the methanol tail gas from the distillation system and the recovery system is cooled by the tail gas cooler 37 and then enters the first-stage water washing tower from the bottom, and then enters the second-stage water washing tower and the third-stage water washing tower in sequence; in each water washing tower, the gas and liquid are in countercurrent contact, and qualified tail gas is discharged from the top of the third water washing tower; the bottom liquid of the first water washing tower enters the wastewater cooler 30 to exchange heat with the bottom liquid of the third recovery tower and then enters the third recovery tower.

[0071] In step (4), preferably, the methanol tail gas from the distillation system and the recovery system is cooled to 20-23°C by tail gas cooler 37.

[0072] Preferably, the bottom liquid of the first water washing tower enters the wastewater cooler 30 to exchange heat with the bottom liquid of the third recovery tower and is heated to 155-165°C.

[0073] The apparatus of the present invention can also be used to produce methanol salts of other metal elements in Group 1.

[0074] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0075] (1) Compared with traditional processes, the present invention utilizes the heat of the product and recovery system in the reaction tower to thermally couple with the feed stream, thereby saving the steam energy consumption and circulating water consumption of the reaction tower.

[0076] (2) Traditional shell-and-tube reboilers have large pressure drops and low heat recovery. The reboiler in the third recovery tower of this invention adopts the heat exchange equipment of Example 1 in patent CN206304714U, which has smaller pressure drops and improves heat transfer efficiency by 15%.

[0077] (3) The use of a three-stage recovery tower to separate alcohol and water saves 60% of the energy consumption of the recovery system compared with the single tower separation process;

[0078] (4) Molecular sieves are used to further dehydrate the methanol vapor phase, saving the power consumption of the compressor and the steam energy consumption of the reaction tower;

[0079] (5) The wastewater from the bottom of the recovery tower is used to absorb methanol tail gas from various units in the plant area, further increasing the methanol recovery rate, and without generating new wastewater.

[0080] (6) This invention can be used to produce liquid or solid potassium methoxide, using high-temperature methanol vapor from the compressor outlet to replace part of the steam used in the dryer, thus saving some energy consumption. Attached Figure Description

[0081] Figure 1 This is a schematic diagram of the energy-saving device for the thermally coupled alkaline process of potassium methoxide production according to the present invention.

[0082] Figure 1 In the middle: 1-Reaction tower, 2-Distillation tower, 3-First compressor, 4-Dryer, 5-Dryer compressor, 6-Dehydrator, 7-Second compressor, 8-Distillation falling film reboiler, 9-Distillation condenser, 10-Distillation reflux tank, 11-Distillation tower reflux pump, 12-Distillation tower bottom pump, 13-First feed preheater, 14-Second feed preheater, 15-First recovery tower condenser, 16-First recovery tower reflux tank, 17-First recovery tower reflux pump, 18-First recovery tower, 19-First recovery tower bottom pump, 20-First recovery tower bottom pump 21-Second recovery tower reflux tank, 22-Second recovery tower reflux pump, 23-Second recovery tower, 24-Second recovery tower kettle pump, 25-Second recovery tower falling film reboiler, 26-Third recovery tower reflux tank, 27-Third recovery tower reflux pump, 28-Third recovery tower, 29-Third recovery tower reboiler, 30-Wastewater cooler, 31-First stage water scrubbing tower, 32-Second stage water scrubbing tower, 33-Third stage water scrubbing tower, 34-First stage water scrubbing pump, 35-Second stage water scrubbing pump, 36-Third stage water scrubbing pump, 37-Tail gas cooler. Detailed Implementation

[0083] The technical solution of the present invention will be further described below with reference to the embodiments. The following embodiments are illustrative and not limiting, and should not be used to limit the scope of protection of the present invention.

[0084] Example 1

[0085] like Figure 1 As shown, an energy-saving device for the thermally coupled alkaline process of potassium methoxide production includes: a reaction system for the alkaline synthesis of potassium methoxide, a distillation system for recovering methanol from the gas phase generated by the reaction system, a recovery system for coupling system heat energy to reduce steam energy consumption, and a wastewater reuse system for recovering methanol from the tail gas.

[0086] The reaction system includes a reaction tower 1, which is a plate tower (theoretically with 30 plates). A steam coil is installed at the bottom of the reaction tower 1 for steam heating. The feed inlet of the reaction tower 1 is located above the first plate. The feed inlet of the reaction tower 1 is connected to the feed pipe sequentially through the tube side of the secondary raw material preheater 14 and the tube side of the primary raw material preheater 13, thus feeding the potassium hydroxide-methanol mixture into the reaction tower.

[0087] The liquid phase outlet of the reactor 1 is connected to the shell-side inlet of the secondary raw material preheater 14, and the shell-side outlet of the secondary raw material preheater 14 is connected to the feed inlet of the dryer 4. The dryer 4 includes a drying chamber body, which is provided with a liquid inlet and an air outlet. The air outlet of the dryer 4 is connected to the inlet of the dryer compressor 5. Two jackets are provided at the bottom of the drying chamber body. Each jacket is provided with an air inlet and a liquid outlet. Water vapor is introduced into one jacket as a heat source, and the air inlet of the other jacket is connected to the outlet of the dryer compressor 5. The liquid phase potassium methoxide product from the reactor bottom enters the dryer 4 through the liquid inlet. Methanol is heated and vaporized in the dryer. Methanol vapor is discharged from the air outlet of the dryer 4, enters the dryer compressor 5, is pressurized, and then returns to the jacket of the dryer to provide a heat source.

[0088] The gas phase outlet at the top of the reaction tower 1 is connected to the feed inlet of the distillation tower 2 of the distillation system.

[0089] The distillation system includes a distillation column 2, a dehydrator 6, a first compressor 3, a second compressor 7, a distillation falling film reboiler 8, a distillation condenser 9, and a distillation reflux tank 10.

[0090] The distillation column 2 is a packed column (BX packing). The feed inlet of the distillation column is located between the second and third packing layers; the liquid inlet in the middle of the distillation column is located between the second and third packing layers; and the reflux port of the distillation column 2 is located above the first packing layer.

[0091] The vapor outlet at the top of the distillation column 2 is connected to the dehydrator 6 (filled with 3A molecular sieve) and the second compressor 7, respectively. The outlet of the dehydrator 6 is connected to the inlet of the first compressor 3, and the vapor outlet of the first compressor 3 is connected to the inlet of the reaction column 1. The outlet of the second compressor 7 is connected to the shell-side inlet of the distillation falling film reboiler 8, the shell-side outlet of the distillation falling film reboiler 8 is connected to the inlet of the distillation condenser 9, and the outlet of the distillation condenser 9 is connected to the feed inlet of the distillation reflux tank 10. The liquid phase outlet of the distillation reflux tank 10 is connected to the inlet of the distillation column reflux pump 11, and the outlet of the distillation column reflux pump 11 is connected to the reflux port at the top of the distillation column 2; the gas phase outlet of the distillation reflux tank 10 is connected to the gas inlet of the wastewater reuse system; the liquid phase outlet of the bottom of the distillation column 2 is connected to the inlet of the bottom pump 12, and the outlet of the bottom pump 12 is connected to the tube side inlet of the falling film reboiler 8 and the feed inlet of the first recovery column 18, respectively; the tube side outlet of the falling film reboiler 8 is connected to the distillation column 2.

[0092] The recovery system includes a primary raw material preheater 13, a secondary raw material preheater 14, a first recovery tower condenser 15, a first recovery tower reflux tank 16, a first recovery tower 18 (CY packing, with the inlet located between the second and third packing layers and the reflux port located above the first packing layer), a first recovery tower falling film reboiler 20, a second recovery tower reflux tank 21, a second recovery tower 23 (CY packing, with the inlet located between the second and third packing layers and the reflux port located above the first packing layer), a second recovery tower falling film reboiler 25, a third recovery tower reflux tank 26, a third recovery tower 28 (CY packing, with the inlet located between the second and third packing layers and the reflux port located above the first packing layer), and a third recovery tower reboiler 29.

[0093] The vapor outlet at the top of the first recovery tower 18 is connected to the shell-side inlet of the primary feed preheater 13. The shell-side outlet of the primary feed preheater 13 is connected to the inlet of the first recovery tower condenser 15. The outlet of the first recovery tower condenser 15 is connected to the liquid inlet of the first recovery tower reflux tank 16. The liquid outlet of the first recovery tower reflux tank 16 is connected to the inlet of the first recovery tower reflux pump 17. The outlet of the first recovery tower reflux pump 17 is connected to the reflux port at the top of the first recovery tower 18 and the liquid inlet in the middle of the distillation column 2, respectively. The vapor outlet of the first recovery tower reflux tank 16 is connected to the gas inlet of the wastewater reuse system.

[0094] The liquid phase outlet of the first recovery tower 18 is connected to the inlet of the first recovery tower bottom pump 19, and the outlet of the first recovery tower bottom pump 19 is connected to the tube side inlet of the first recovery tower falling film reboiler 20 and the feed inlet of the second recovery tower 23, respectively; the tube side outlet of the first recovery tower falling film reboiler 20 is connected to the first recovery tower 18.

[0095] The gas phase outlet at the top of the second recovery tower 23 is connected to the shell-side inlet of the falling film reboiler 20 of the first recovery tower. The shell-side outlet of the falling film reboiler 20 of the first recovery tower is connected to the liquid inlet of the reflux tank 21 of the second recovery tower. The liquid phase outlet of the reflux tank 21 of the second recovery tower is connected to the inlet of the reflux pump 22 of the second recovery tower. The outlet of the reflux pump 22 of the second recovery tower is connected to the reflux port of the second recovery tower 23 and the liquid phase inlet in the middle of the distillation column, respectively. The gas phase outlet of the reflux tank 21 of the second recovery tower is connected to the gas inlet of the wastewater reuse system.

[0096] The liquid phase outlet of the bottom of the second recovery tower 23 is connected to the inlet of the bottom pump 24 of the second recovery tower. The outlet of the bottom pump 24 of the second recovery tower is connected to the tube side inlet of the falling film reboiler 25 of the second recovery tower and the feed inlet of the third recovery tower 28. The tube side outlet of the falling film reboiler 25 of the second recovery tower is connected to the second recovery tower 23.

[0097] The vapor phase outlet at the top of the third recovery tower 28 is connected to the shell-side inlet of the falling film reboiler 25 of the second recovery tower. The shell-side outlet of the falling film reboiler 25 of the second recovery tower is connected to the liquid inlet of the reflux tank 26 of the third recovery tower. The liquid phase outlet of the reflux tank 26 of the third recovery tower is connected to the inlet of the reflux pump 27 of the third recovery tower. The outlet of the reflux pump 27 of the third recovery tower is connected to the reflux port at the top of the third recovery tower 28 and the liquid phase inlet in the middle of the distillation tower 2. The vapor phase outlet of the reflux tank 26 of the third recovery tower is connected to the gas inlet of the wastewater reuse system.

[0098] The liquid phase outlet of the third recovery tower 28 is connected to the tube-side inlet of the reboiler 29 and the tube-side inlet of the wastewater cooler 30, respectively; the tube-side outlet of the reboiler 29 is connected to the feed inlet of the third recovery tower 28; and the tube-side outlet of the wastewater cooler 30 is connected to the inlet of the wastewater reuse system.

[0099] The wastewater reuse system includes a wastewater cooler 30, a primary scrubbing tower 31 (170X plate corrugated packing), a secondary scrubbing tower 32 (350X plate corrugated packing), a tertiary scrubbing tower 33 (350X plate corrugated packing), and a tail gas cooler 37. The air inlet of the primary scrubbing tower 31 is located below the second section of packing, and the water inlet of the primary scrubbing tower 31 is located above the first section of packing. The air inlet of the secondary scrubbing tower 32 is located below the second section of packing, and the water inlet of the secondary scrubbing tower 32 is located above the first section of packing. The air inlet of the tertiary scrubbing tower 33 is located below the second section of packing, and the water inlet of the tertiary scrubbing tower 33 is located above the first section of packing.

[0100] The vapor phase outlets of the distillation reflux tank 10, the first recovery tower reflux tank 16, the second recovery tower reflux tank 21, and the third recovery tower reflux tank 26 are connected to the inlet of the primary water scrubbing tower 31 of the wastewater reuse system via the tail gas cooler 37. The vapor phase outlet at the top of the primary water scrubbing tower 31 is connected to the inlet of the secondary water scrubbing tower 32. The vapor phase outlet at the top of the secondary water scrubbing tower 32 is connected to the inlet of the tertiary water scrubbing tower 33. The vapor phase outlet at the top of the tertiary water scrubbing tower 33 is open to the atmosphere. The inlet at the top of the tertiary water scrubbing tower 33 of the wastewater reuse system is connected to the wastewater cooling... The tube-side outlet of the apparatus 30 is connected to the bottom liquid phase outlet of the three-stage water washing tower 33, which is connected to the inlet of the three-stage water washing pump 36. The outlet of the three-stage water washing pump 36 is connected to the liquid phase inlet of the two-stage water washing tower 32. The bottom liquid phase outlet of the two-stage water washing tower 32 is connected to the inlet of the two-stage water washing pump 35, which is connected to the liquid phase inlet of the first-stage water washing tower 31. The bottom liquid phase outlet of the first-stage water washing tower 31 is connected to the inlet of the first-stage water washing pump 34, which is connected to the shell-side inlet of the wastewater cooler 30. The shell-side outlet of the wastewater cooler 30 is connected to the feed inlet of the third recovery tower 28.

[0101] The distillation falling film reboiler 8 is a shell-and-tube heat exchanger.

[0102] The distillation condenser 9 is a shell-and-tube heat exchanger.

[0103] Both the primary raw material preheater 13 and the secondary raw material preheater 14 are shell-and-tube heat exchangers.

[0104] The first recovery tower condenser 15 is a shell-and-tube heat exchanger.

[0105] The first recovery tower falling film reboiler 20 is a shell-and-tube heat exchanger.

[0106] The second recovery tower falling film reboiler 25 is a shell-and-tube heat exchanger.

[0107] The third recovery tower reboiler 29 adopts the heat exchange equipment of Embodiment 1 in patent CN206304714U, which is a coiled tube heat exchanger, and the third recovery tower reboiler 29 is heated by steam.

[0108] The wastewater cooler 30 is a shell-and-tube heat exchanger.

[0109] The exhaust gas cooler 37 is a shell-and-tube heat exchanger that uses low-temperature water or other refrigerants as the cooling medium.

[0110] Example 2

[0111] Based on the energy-saving device for producing potassium methoxide using the thermally coupled alkaline method in Example 1, taking a daily output of 120 tons of liquid potassium methoxide as an example, the method is as follows:

[0112] Step (1), Reaction: A mixture of 20 wt% potassium hydroxide and 80 wt% methanol in an alcohol-alkali solution (25℃) enters the primary feed preheater 13 from the tube side inlet. Methanol vapor (65℃) discharged from the top of the first recovery tower 18 enters the primary feed preheater 13 from the shell side inlet. The alcohol-alkali solution undergoes primary heat exchange with the methanol vapor, heating the alcohol-alkali solution to 60℃. The heated alcohol-alkali solution then enters the secondary feed preheater 14 from the tube side inlet. The bottom liquid of the reaction tower (100℃ qualified potassium methoxide product) enters the secondary feed preheater 14 from the shell side inlet. The alcohol-alkali solution reacts with the methanol vapor in the reaction tower... The bottom liquid (temperature 100℃) undergoes a two-stage heat exchange, heating the alcohol-alkali solution to 79℃. After heat exchange, the alcohol-alkali solution enters reaction tower 1 (top operating pressure 0.05 MPaG, bottom operating temperature 105℃, steam consumption 1.87 t / h) through the top inlet. It counter-currently reacts with methanol gas compressed by the first compressor 3 from distillation tower 2. Potassium hydroxide reacts with methanol to produce potassium methoxide, resulting in a 5000 kg / h liquid potassium methoxide product with a content of 30 wt%. This potassium methoxide product enters the secondary feed preheater 14 through the shell inlet, where it exchanges heat with the alcohol-alkali solution before entering reaction tower 1, and is then collected as the liquid potassium methoxide product. The top gas phase (98.3 wt% methanol, 1.7 wt% water vapor) enters distillation tower 2 from the middle.

[0113] If solid potassium methoxide is to be produced, 30 wt% potassium methoxide product enters dryer 4. Steam is introduced into a set of jackets at the bottom of the dryer. The evaporated pure methanol vapor is compressed by dryer compressor 5 (dryer compressor power is 350KW), and the methanol vapor pressurized to 30KPa and temperature of 84℃ enters another set of jackets at the bottom of dryer 5 to provide some heat for the evaporation of methanol. The methanol condensate obtained in the jackets can be used to prepare alcohol-alkali solution. The steam consumption of dryer 4 is reduced from 1.9t / h to 1.5t / h.

[0114] Step (2), Distillation: The vapor phase from the top of the reaction column enters the distillation column 2 from the middle (the operating pressure at the top of the column is 0.003 MPaG, the operating temperature at the bottom of the column is 75℃, and the reflux ratio is 1). High-purity methanol is collected from the top of the distillation column (pressure 0.003 MPaG, temperature 65℃, water content 350 ppm). The methanol is divided into two streams with a split ratio of 50%: one stream of methanol first enters the dehydrator 6 and is dehydrated by a molecular sieve (the water content is reduced to 10 ppm), and then passes through the first compressor 3 (the power of the first compressor 3 is 420 KW). Methanol gas, compressed to 50 kPa and heated to 95°C, enters reaction column 1 from the bottom and undergoes counter-current mass transfer with the alcohol-alkali solution. Another stream of methanol is compressed by a second compressor 7, reaching 90 kPa and a temperature of 112°C, and enters the falling film reboiler 8 from the shell side inlet. This reboiler serves as a heat source for heating the bottom material of the distillation column. The heated methanol then enters the distillation condenser 9 (outlet temperature 50°C) for condensation, and then enters the distillation reflux tank 10. Finally, it is pumped by the distillation column reflux pump 11 from the top into distillation column 2. The distillation system compressor has a power of 750 kW and requires no steam.

[0115] Step (3), Recycling:

[0116] The methanol-water solution (75 wt% methanol and 25 wt% water) from the bottom of distillation column 2 enters the first recovery column 18 (bottom operating temperature 72℃, top operating pressure 0.002 MPaG, reflux ratio 0.751) via the bottom pump 12. The vapor phase from the top of the first recovery column (99.6 wt% methanol, 0.4 wt% water, temperature 65℃) enters the primary feed preheater 13 from the shell inlet as a heat source for preheating the feed. The resulting aqueous methanol enters the first recovery column condenser 15 and is condensed to 63℃, then enters the first recovery column reflux tank 16. 42.9% aqueous methanol is refluxed from the top of the first recovery column to the first recovery column 18 via the first recovery column reflux pump 17, and 57.1% aqueous methanol is returned to distillation column 2 via the liquid phase inlet in the middle via the first recovery column reflux pump 17. The bottom liquid of the first recovery column 18 (64.9 wt% methanol, 35.1 wt% water)... The wt% (at a temperature of 75℃) enters the second recovery tower 23 (with a tower bottom operating temperature of 105℃, a tower top operating pressure of 0.15MPaG, and a reflux ratio of 0.949) from the middle via the first recovery tower bottom pump 19 for further separation.

[0117] The vapor phase from the top of the second recovery tower (99.6 wt% methanol, 0.4 wt% water, temperature 90°C) enters the falling film reboiler 20 of the first recovery tower from the shell side inlet to provide heat for heating the bottom liquid of the first recovery tower. The temperature of the aqueous methanol obtained by heat exchange is 85°C, and then it enters the reflux tank 21 of the second recovery tower. 48.7% aqueous methanol is refluxed from the top of the second recovery tower to the second recovery tower 23 via the reflux pump 22 of the second recovery tower, and 51.3% aqueous methanol is returned to the distillation tower 2 from the liquid phase inlet in the middle via the reflux pump 22 of the second recovery tower. The bottom liquid of the second recovery tower (43.1 wt% methanol, 56.9 wt% water, temperature 105°C) enters the third recovery tower 28 (bottom operating temperature 171°C, top operating pressure 0.7 MPaG, reflux ratio 2.175) from the middle via the bottom pump 24 of the second recovery tower for further separation.

[0118] The vapor phase from the top of the third recovery tower (99.6 wt% methanol, 0.4 wt% water, temperature 128°C) enters the falling film reboiler 25 of the second recovery tower from the shell side inlet to provide heat for heating the bottom liquid of the second recovery tower. The temperature of the aqueous methanol obtained after heat exchange is 122°C, and then it enters the reflux tank 26 of the third recovery tower. 68.5% aqueous methanol is refluxed from the top of the third recovery tower to the third recovery tower 28 via the reflux pump 27 of the third recovery tower, and 31.5% aqueous methanol enters the distillation column 2 from the middle liquid phase inlet via the reflux pump 27 of the third recovery tower. Wastewater (temperature 171°C) is obtained in the bottom of the third recovery tower. Steam is introduced into the reboiler 29 of the third recovery tower, and the steam consumption of the entire recovery system is only 1.3 t / h.

[0119] Step (4), Wastewater Treatment: A three-stage countercurrent process is adopted, using the wastewater from the bottom of the third recovery tower 28 to absorb methanol tail gas from various units in the plant area. Specifically, the wastewater from the bottom of the third recovery tower (temperature 171℃) enters the wastewater cooler 30 from the shell-side inlet, where it exchanges heat with the liquid from the bottom of the first-stage water washing tower (9.2wt% methanol, 90.8wt% water, temperature 11℃) to cool it down to 17℃. The wastewater after heat exchange is discharged from the top into the third-stage water washing tower 33 (operating pressure 0.005MPaG). The wastewater from the bottom of the third-stage water washing tower 33 enters the second-stage water washing tower 32 (operating pressure 0.005MPaG) from the top via the third-stage water washing tower pump 36. The wastewater from the bottom of the second-stage water washing tower 32 enters the first-stage water washing tower 31 (0.005MPaG) from the top via the second-stage water washing tower pump 35. The vapor outlet of the distillation reflux tank 10, The methanol-containing tail gas discharged from the gas phase outlets of the first recovery tower reflux tank 16, the second recovery tower reflux tank 21, and the third recovery tower reflux tank 26 is cooled to 20°C by the tail gas cooler 37 and enters the first-stage water washing tower 31 from the bottom. The top gas phase of the first-stage water washing tower 31 enters the second-stage water washing tower 32 from the bottom, and the top gas phase of the second-stage water washing tower 32 enters the third-stage water washing tower 33 from the bottom. In each water washing tower, the gas and liquid are in countercurrent contact. Qualified tail gas (with a methanol content of 50 ppm) is discharged from the top of the third-stage water washing tower 33. The bottom liquid of the first-stage water washing tower (9.2 wt% methanol, 90.8 wt% water, temperature 11°C) enters the wastewater cooler 30 from the tube side inlet to exchange heat with the high-temperature wastewater at the bottom of the third recovery tower. After being heated to 165°C, it enters the third recovery tower 28 from the middle for further separation.

[0120] Example 3

[0121] Based on the energy-saving device for producing potassium methoxide using the thermally coupled alkaline process in Example 1, taking a daily output of 90 tons of liquid potassium methoxide as an example, the method is as follows:

[0122] Step (1), Reaction: At room temperature (25℃), an alcohol-alkali solution (20.2 wt% potassium hydroxide and 79.8 wt% potassium hydroxide) was reacted. A mixture of wt% methanol enters the primary feed preheater 13 through the tube side inlet. Methanol vapor (65°C) discharged from the top of the first recovery tower 18 enters the primary feed preheater 13 through the shell side inlet. The alcohol-alkali solution undergoes primary heat exchange with the methanol vapor, heating the alcohol-alkali solution to 60°C. The heated alcohol-alkali solution then enters the secondary feed preheater 14 through the tube side inlet. The bottom liquid of the reaction tower (100°C qualified potassium methoxide product) enters the secondary feed preheater 14 through the shell side inlet. The alcohol-alkali solution undergoes secondary heat exchange with the bottom liquid of the reaction tower (100°C), heating the alcohol-alkali solution to 79°C. The heat-exchanged alcohol-alkali solution enters the reaction tower 1 (top operating pressure 0.03 MPaG, bottom operating temperature 103°C, reaction tower steam consumption 1.84 t / h) through the top feed inlet. It counter-currently reacts with methanol gas compressed by the first compressor 3 from the distillation tower 2. Potassium hydroxide reacts with methanol to produce potassium methoxide, yielding 3750 kg / h of 29.7 t / h potassium hydroxide in the bottom of the tower. The wt% potassium methoxide product enters the secondary preheater 14 of the raw material from the shell side inlet and exchanges heat with the alcohol-alkali liquid to be introduced into the reaction tower 1. It is then collected as liquid potassium methoxide product. The gas phase at the top of the reaction tower (methanol content 97.1wt%, water vapor content 2.9wt%) enters the distillation tower 2 from the middle.

[0123] If solid potassium methoxide is produced, 29.7 wt% potassium methoxide product enters dryer 4. Steam is introduced into a set of jackets at the bottom of the dryer. The evaporated pure methanol vapor is compressed by dryer compressor 5 (dryer compressor power is 370KW). The methanol vapor pressurized by 50KPa and temperature of 95℃ enters another set of jackets at the bottom of dryer 4 to provide some heat for the evaporation of methanol. The methanol condensate obtained in the jacket can be used to prepare alcohol-alkali solution. The steam consumption of the dryer is reduced from 1.43t / h to 0.98t / h.

[0124] Step (2), Distillation: The vapor phase from the top of the reaction column enters the distillation column 2 from the middle (the operating pressure at the top of the column is 0.003 MPaG, the operating temperature at the bottom of the column is 75℃, and the reflux ratio is 1). The high-purity methanol collected from the top of the distillation column (pressure 0.003 MPaG, temperature 65℃, water content 654 ppm) is divided into two streams with a split ratio of 50%: one stream of methanol first enters the dehydrator 6 and is dehydrated by molecular sieve (the water content is reduced to 15 ppm), and then is compressed by the first compressor 3 (the power of the first compressor is 320KW) and pressurized by 4. Methanol gas at 0 kPa and 90°C enters reaction tower 1 from the bottom and flows counter-currently with alcohol-alkali solution. Another stream of methanol is compressed by the second compressor 7, and the pressurized methanol gas at 80 kPa and 103°C enters the distillation falling film reboiler 8 from the shell side inlet as the heat source for the distillation falling film reboiler 8. After heat exchange, the methanol enters the distillation condenser 9 (outlet temperature 50°C) for condensation, and then enters the distillation reflux tank 10. It then enters the distillation column 2 from the top via the distillation column reflux pump 11. The compressor power of the distillation system is 650 kW, and no steam is required.

[0125] Step (3), Recycling:

[0126] The methanol-water solution (75 wt% methanol and 25 wt% water) from the bottom of distillation column 2 enters the first recovery column 18 (bottom operating temperature 72℃, top operating pressure 0.002 MPaG, reflux ratio 0.748) from the middle. The vapor phase from the top of the first recovery column (99.58 wt% methanol, 0.42 wt% water, temperature 65℃) enters the primary feed preheater 13 from the shell side inlet as a heat source for preheating the feed. The aqueous methanol obtained from the heat exchange enters the condenser 15 of the first recovery column and is condensed to 63℃, then enters the reflux tank 16 of the first recovery column. 42.8% aqueous methanol is refluxed from the top of the first recovery column to the first recovery column via the reflux pump 17, and 57.2% aqueous methanol is returned to distillation column 2 from the liquid phase inlet in the middle via the reflux pump 17. The bottom liquid of the first recovery column 18 (64.7 wt% methanol, 35.3 wt% water) (wt%, temperature 75℃) enters the second recovery tower 23 from the middle via the first recovery tower bottom pump 19 (tower bottom operating temperature 102℃, tower top operating pressure 0.13MPaG, reflux ratio 0.931) for further separation;

[0127] The vapor phase from the top of the second recovery tower (99.58 wt% methanol, 0.42 wt% water, temperature 87°C) enters the falling film reboiler 20 of the first recovery tower from the shell side inlet to provide heat. The water-containing methanol obtained from the heat exchange is at a temperature of 82°C, and then enters the reflux tank 21 of the second recovery tower. 48.2% water-containing methanol is refluxed from the top of the second recovery tower to the second recovery tower 23 via the reflux pump 22 of the second recovery tower. 51.8% water-containing methanol is returned to the distillation tower 2 from the liquid phase inlet in the middle via the reflux pump 22 of the second recovery tower. The bottom liquid of the second recovery tower (43.3 wt% methanol, 56.7 wt% water, temperature 102°C) enters the third recovery tower 28 from the middle via the bottom pump 24 of the second recovery tower (bottom operating temperature 168°C, top operating pressure 0.65 MPaG, reflux ratio 2.175) for further separation.

[0128] The vapor phase from the top of the third recovery tower (99.56 wt% methanol, 0.44 wt% water, temperature 125°C) enters the falling film reboiler 25 of the second recovery tower from the shell side inlet to provide heat. The temperature of the aqueous methanol obtained after heat exchange is 120°C, and then it enters the reflux tank 26 of the third recovery tower. 68.5% aqueous methanol is refluxed from the top of the third recovery tower to the third recovery tower 28 via the reflux pump 27 of the third recovery tower, and 31.5% aqueous methanol is returned to the distillation tower 2 from the liquid phase inlet in the middle via the reflux pump 27 of the third recovery tower. Wastewater (temperature 168°C) is obtained in the bottom of the third recovery tower. Steam is introduced into the reboiler 29 of the third recovery tower, and the steam consumption of the entire recovery system is only 0.98g / h.

[0129] Step (4), Wastewater Treatment: A three-stage countercurrent process is adopted, using the wastewater from the bottom of the third recovery tower to absorb methanol tail gas from various units in the plant area. Specifically: the high-temperature wastewater from the bottom of the third recovery tower enters the wastewater cooler 30 from the shell-side inlet, and exchanges heat with the liquid from the bottom of the first-stage water washing tower (methanol 9.3wt%, water 90.7wt%, temperature 11℃) to cool it down to 17℃. The wastewater after heat exchange is discharged from the top into the third-stage water washing tower 33 (0.005MPaG). The wastewater from the bottom of the third-stage water washing tower 33 enters the second-stage water washing tower 32 (operating pressure 0.005MPaG) from the top via the third-stage water washing tower pump 36. The wastewater from the bottom of the second-stage water washing tower 32 enters the first-stage water washing tower 31 (0.005MPaG) from the top via the second-stage water washing tower pump 35. The vapor outlet of the distillation reflux tank 10, The methanol-containing tail gas discharged from the gas phase outlets of the first recovery tower reflux tank 16, the second recovery tower reflux tank 21, and the third recovery tower reflux tank 26 is cooled to 20°C by the tail gas cooler 37 and enters the first-stage water washing tower 31 (0.005 MPaG) from the bottom. The top gas phase of the first-stage water washing tower 31 enters the second-stage water washing tower 32 from the bottom, and the top gas phase of the second-stage water washing tower 32 enters the third-stage water washing tower 33 from the bottom. In each water washing tower, the gas and liquid are in countercurrent contact. Qualified tail gas (with a methanol content of 50 ppm) is discharged from the top of the third-stage water washing tower 33. The bottom liquid of the first-stage water washing tower is heated to 155°C by the wastewater entering the wastewater cooler 30 from the tube side inlet and then enters the third recovery tower from the middle for further separation.

Claims

1. An energy-saving device for the thermally coupled alkaline process of potassium methoxide production, characterized in that: include: A reaction system for the alkaline synthesis of potassium methoxide, a distillation system for recovering methanol from the gas phase generated by the reaction system, a recovery system for coupling system heat energy to reduce steam energy consumption, and a wastewater reuse system for recovering methanol from tail gas. The reaction system includes a reaction tower; the distillation system includes a distillation tower, a dehydrator, a first compressor, a second compressor, a falling film reboiler, a distillation condenser, and a distillation reflux tank; the recovery system includes a primary feed preheater, a secondary feed preheater, a first recovery tower condenser, a first recovery tower reflux tank, a first recovery tower, a first recovery tower falling film reboiler, a second recovery tower, a second recovery tower, a second recovery tower falling film reboiler, a third recovery tower reflux tank, a third recovery tower, and a third recovery tower reboiler; the wastewater reuse system includes a wastewater cooler, a primary water scrubbing tower, a secondary water scrubbing tower, a tertiary water scrubbing tower, and a tail gas cooler. The liquid phase outlet of the reaction tower bottom is connected to the shell-side inlet of the secondary feed preheater, and the shell-side outlet of the secondary feed preheater is connected to the liquid potassium methoxide product outlet pipe; the gas phase outlet at the top of the reaction tower is connected to the feed inlet of the distillation tower. The vapor outlet at the top of the distillation column is connected to a dehydrator and a second compressor, respectively. The outlet of the dehydrator is connected to the inlet of the first compressor, and the vapor outlet of the first compressor is connected to the inlet of the reaction column. The outlet of the second compressor is connected to the shell-side inlet of the falling film reboiler. The shell-side outlet of the falling film reboiler is connected in sequence to the distillation condenser and the distillation reflux tank. The liquid-side outlet of the distillation reflux tank is connected to the reflux port of the distillation column. The liquid-side outlet of the distillation column bottom is connected to the tube-side inlet of the falling film reboiler. The tube-side outlet of the falling film reboiler is connected to the distillation column. The vapor outlet at the top of the first recovery tower is connected to the shell-side inlet of the primary feed preheater, and the shell-side outlet of the primary feed preheater is sequentially connected to the condenser of the first recovery tower and the reflux tank of the first recovery tower; the liquid outlet of the reflux tank of the first recovery tower is connected to the reflux port at the top of the first recovery tower and the liquid inlet at the middle of the distillation column, respectively; the liquid outlet at the bottom of the first recovery tower is connected to the feed inlet of the second recovery tower. The vapor outlet at the top of the second recovery tower is connected to the shell-side inlet of the falling film reboiler of the first recovery tower. The shell-side outlet of the falling film reboiler of the first recovery tower is connected to the liquid inlet of the reflux tank of the second recovery tower. The liquid outlet of the reflux tank of the second recovery tower is connected to the reflux port of the second recovery tower and the liquid inlet in the middle of the distillation column, respectively. The liquid outlet at the bottom of the second recovery tower is connected to the feed port of the third recovery tower. The vapor phase outlet at the top of the third recovery tower is connected to the shell-side inlet of the falling film reboiler of the second recovery tower. The shell-side outlet of the falling film reboiler of the second recovery tower is connected to the liquid inlet of the reflux tank of the third recovery tower. The liquid phase outlet of the reflux tank of the third recovery tower is connected to the reflux port at the top of the third recovery tower and the liquid phase inlet at the middle of the distillation tower, respectively. The air inlet of the primary water washing tower is connected to the gas phase outlet of the distillation reflux tank, the gas phase outlet of the first recovery tower reflux tank, the gas phase outlet of the second recovery tower reflux tank, and the gas phase outlet of the third recovery tower reflux tank via the tail gas cooler. The tube-side inlet of the wastewater cooler is connected to the liquid phase outlet of the bottom of the third recovery tower; the tube-side outlet of the wastewater cooler is connected to the water inlet at the top of the three-stage water washing tower. The vapor phase outlet at the top of the primary water washing tower is connected to the inlet of the secondary water washing tower, and the vapor phase outlet at the top of the secondary water washing tower is connected to the inlet of the tertiary water washing tower. The water inlet at the top of the tertiary water washing tower is connected to the tube-side outlet of the wastewater cooler, the liquid phase outlet at the bottom of the tertiary water washing tower is connected to the water inlet at the top of the secondary water washing tower, the liquid phase outlet at the bottom of the secondary water washing tower is connected to the water inlet at the top of the primary water washing tower, the liquid phase outlet at the bottom of the primary water washing tower is connected to the shell-side inlet of the wastewater cooler, and the shell-side outlet of the wastewater cooler is connected to the feed inlet of the third recovery tower.

2. The energy-saving device for producing potassium methoxide using a thermally coupled alkaline process according to claim 1, characterized in that: Also includes: The dryer includes a drying chamber body, which has a liquid inlet and an air outlet. Two jackets are located at the bottom of the drying chamber body, each with an air inlet and a liquid outlet. One jacket is supplied with steam as a heat source, and the other with methanol vapor as a heat source. The dryer's feed inlet is connected to the shell-side outlet of the secondary raw material preheater, the dryer's air outlet is connected to the inlet of the dryer compressor, and the dryer compressor's outlet is connected to the air inlet of one of the dryer's jackets.

3. The energy-saving device for producing potassium methoxide using a thermally coupled alkaline process according to claim 1, characterized in that: Both the primary and secondary raw material preheaters are shell-and-tube heat exchangers. The tube-side inlet of the primary raw material preheater is connected to the raw material feed pipe, the tube-side outlet of the primary raw material preheater is connected to the tube-side inlet of the secondary raw material preheater, and the shell-side outlet of the secondary raw material preheater is connected to the feed inlet of the reaction tower. The potassium hydroxide-methanol mixture enters the reaction tower by passing through the tube side of the primary raw material preheater and the tube side of the secondary raw material preheater in sequence.

4. The energy-saving device for producing potassium methoxide using a thermally coupled alkaline process according to claim 1, characterized in that: The reaction tower is a plate tower, and a steam coil is installed at the bottom of the reaction tower; the distillation tower is a packed tower; the first recovery tower is a packed tower; the second recovery tower is a packed tower; the third recovery tower is a packed tower; the dehydrator is filled with molecular sieves; the distillation falling film reboiler is a shell-and-tube heat exchanger; the distillation condenser is a shell-and-tube heat exchanger; the first recovery tower condenser is a shell-and-tube heat exchanger; the first recovery tower falling film reboiler is a shell-and-tube heat exchanger; the second recovery tower falling film reboiler is a shell-and-tube heat exchanger; the third recovery tower reboiler is a coiled tube heat exchanger, and the third recovery tower reboiler is heated by steam.

5. The energy-saving device for the thermally coupled alkaline process of potassium methoxide production according to claim 1, characterized in that: The shell-side outlet of the falling film reboiler is connected to the inlet of the distillation condenser, the outlet of the distillation condenser is connected to the feed inlet of the distillation reflux tank, the liquid-phase outlet of the distillation reflux tank is connected to the inlet of the distillation column reflux pump, and the outlet of the distillation column reflux pump is connected to the reflux port of the distillation column; the liquid-phase outlet of the distillation column bottom is connected to the inlet of the distillation column bottom pump, and the outlet of the distillation column bottom pump is connected to the tube-side inlet of the falling film reboiler and the feed inlet of the first recovery column, respectively. The shell-side outlet of the primary raw material preheater is connected to the inlet of the first recovery tower condenser, the outlet of the first recovery tower condenser is connected to the liquid inlet of the first recovery tower reflux tank, the liquid phase outlet of the first recovery tower reflux tank is connected to the inlet of the first recovery tower reflux pump, and the outlet of the first recovery tower reflux pump is connected to the reflux port of the first recovery tower and the liquid phase inlet in the middle of the distillation column, respectively. The liquid phase outlet of the first recovery tower bottom is connected to the inlet of the first recovery tower bottom pump, and the outlet of the first recovery tower bottom pump is connected to the tube side inlet of the first recovery tower falling film reboiler and the feed inlet of the second recovery tower, respectively. The shell-side outlet of the falling film reboiler of the first recovery tower is connected to the inlet of the reflux tank of the second recovery tower. The liquid phase outlet of the reflux tank of the second recovery tower is connected to the inlet of the reflux pump of the second recovery tower. The outlet of the reflux pump of the second recovery tower is connected to the reflux port of the second recovery tower and the liquid phase inlet in the middle of the distillation column, respectively. The liquid phase outlet of the second recovery tower bottom is connected to the inlet of the second recovery tower bottom pump, and the outlet of the second recovery tower bottom pump is connected to the tube side inlet of the falling film reboiler of the second recovery tower and the feed inlet of the third recovery tower, respectively. The shell-side outlet of the falling film reboiler of the second recovery tower is connected to the inlet of the reflux tank of the third recovery tower; the liquid phase outlet of the reflux tank of the third recovery tower is connected to the inlet of the reflux pump of the third recovery tower, and the outlet of the reflux pump of the third recovery tower is connected to the reflux port of the third recovery tower and the liquid phase inlet in the middle of the distillation column, respectively.

6. A method for producing potassium methoxide using the alkaline process based on the energy-saving device for thermally coupled alkaline potassium methoxide production according to claim 1, characterized in that: Includes the following steps: Step (1), Reaction: The potassium hydroxide-methanol mixture sequentially enters the primary feed preheater and the secondary feed preheater, where it undergoes primary heat exchange with the overhead gas phase from the first recovery tower and secondary heat exchange with the liquid product from the bottom of the reaction tower. It then enters the reaction tower from the top. High-temperature, high-pressure methanol gas from the distillation system enters the reaction tower from the bottom, where it undergoes counter-current mass transfer with the potassium hydroxide-methanol mixture, resulting in a 27-30 wt% liquid potassium methoxide product in the bottom of the reaction tower. The overhead gas phase from the reaction tower enters the distillation tower of the distillation system. Step (2), distillation: The vapor phase from the top of the reaction tower enters the distillation tower from the middle for distillation. Methanol is collected from the top of the distillation tower. A portion of the methanol is dehydrated by a dehydrator and pressurized by the first compressor to obtain high-temperature and high-pressure methanol gas, which is returned to the reaction tower from the bottom. The remaining methanol is pressurized and heated by the second compressor and enters the distillation falling film reboiler to exchange heat with the liquid at the bottom of the distillation tower. The methanol after heat exchange is condensed by the distillation condenser and returned to the distillation tower. The liquid at the bottom of the distillation tower is sent to the recovery system. Step (3), Recovery: The bottom liquid of the distillation column enters the first recovery column for distillation. The vapor phase from the top of the first recovery column enters the primary preheater of the feedstock as a heat source to exchange heat with the potassium hydroxide-methanol mixture, and then enters the condenser of the first recovery column for condensation. After condensation, it enters the reflux tank of the first recovery column. Part of the liquid phase in the reflux tank of the first recovery column is returned to the first recovery column, and the remainder is returned to the distillation column. The bottom liquid of the first recovery column enters the second recovery column. The vapor phase from the top of the second recovery column enters the falling film reboiler of the first recovery column as a heat source to exchange heat with the bottom liquid of the first recovery column, and then enters the reflux tank of the second recovery column. Part of the liquid phase in the reflux tank of the second recovery column is returned to the second recovery column, and the remainder is returned to the distillation column. The bottom liquid of the second recovery column enters the third recovery column. The vapor phase from the top of the third recovery column enters the falling film reboiler of the second recovery column as a heat source to exchange heat with the bottom liquid of the second recovery column, and then enters the reflux tank of the third recovery column. Part of the liquid phase in the reflux tank of the third recovery column is returned to the third recovery column, and the remainder is returned to the distillation column. Step (4): Methanol is recovered from the methanol tail gas of the distillation system and the recovery system using a three-stage countercurrent method: the bottom liquid of the third recovery tower enters the wastewater cooler to exchange heat with the bottom liquid of the first-stage water washing tower. The cooled bottom liquid of the third recovery tower enters the third-stage water washing tower from the top, and then enters the second-stage water washing tower and the first-stage water washing tower in sequence. Methanol tail gas from the distillation and recovery systems is cooled by a tail gas cooler and then enters the first-stage water washing tower from the bottom, followed by the second-stage and third-stage water washing towers. In each water washing tower, gas and liquid come into countercurrent contact. Qualified tail gas is discharged from the top of the third water washing tower. The bottom liquid of the first water washing tower enters the wastewater cooler and exchanges heat with the bottom liquid of the third recovery tower before entering the third recovery tower.

7. The method for producing potassium methoxide by alkaline process according to claim 6, characterized in that: In step (1), the mass ratio of potassium hydroxide to methanol in the potassium hydroxide-methanol mixture is 1:3 to 1:4.5; The theoretical plate number of the reaction tower is 20 to 50; the operating pressure at the top of the reaction tower is 0 to 0.1 MPaG, and the operating temperature at the bottom of the tower is 100 to 120°C. In step (2), the operating pressure at the top of the distillation column is 0 to 0.1 MPaG, the operating temperature at the bottom of the column is 60 to 90°C, and the reflux ratio is 0.7 to 1.

2. Methanol is compressed by the first compressor and pressurized by 30–120 kPa; methanol is compressed by the second compressor and pressurized by 60–150 kPa. The outlet temperature of the distillation condenser is 40–60°C; In step (3), the top operating pressure of the first recovery tower is 0-0.1 MPaG, the bottom operating temperature is 60-120℃, and the reflux ratio is 0.4-0.

9. The outlet temperature of the condenser in the first recovery tower is 40–70°C. The second recovery tower has a top operating pressure of 0.2–0.5 MPaG, a bottom operating temperature of 100–140°C, and a reflux ratio of 0.8–1.

1. The operating pressure at the top of the third recovery tower is 0.5–0.9 MPaG, the operating temperature at the bottom of the tower is 150–190℃, and the reflux ratio is 1.2–3.

8. The method for producing potassium methoxide by alkaline process according to claim 7, characterized in that: In step (1), the mass ratio of potassium hydroxide to methanol in the potassium hydroxide-methanol mixture is 1:3.5 to 1:4.1; The theoretical plate number of the reaction tower is 30-45; the operating pressure at the top of the reaction tower is 0-50 kPaG, and the operating temperature at the bottom of the tower is 105-115℃. In step (2), the operating pressure at the top of the distillation column is 0-50 kPaG, the operating temperature at the bottom of the column is 70-80°C, and the reflux ratio is 0.8-1. Methanol is compressed by the first compressor and pressurized by 40–80 kPa; methanol is compressed by the second compressor and pressurized by 80–120 kPa. The outlet temperature of the distillation condenser is 45–55°C; In step (3), the top operating pressure of the first recovery tower is 0-50 kPaG, the bottom operating temperature is 70-110°C, and the reflux ratio is 0.6-0.

8. The outlet temperature of the condenser in the first recovery tower is 45–65°C. The second recovery tower has a top operating pressure of 0.25–0.45 MPaG, a bottom operating temperature of 110–130°C, and a reflux ratio of 0.9–1.

0. The operating pressure at the top of the third recovery tower is 0.6–0.8 MPaG, the operating temperature at the bottom of the tower is 160–180℃, and the reflux ratio is 1.5–2.

5.

9. The method for producing potassium methoxide by alkaline process according to claim 6, characterized in that: Liquid potassium methoxide product enters a dryer and is dried using external steam and / or methanol vapor as a heat source to obtain solid potassium methoxide. During the drying process, the methanol in the liquid potassium methoxide product is heated and vaporized to form methanol vapor. The methanol vapor is pressurized by the dryer compressor and returned to the jacket of the dryer to provide a heat source. The dryer compressor pressurizes the methanol vapor by 30 to 120 kPa.

10. The method for producing potassium methoxide by alkaline process according to claim 9, characterized in that: The dryer compressor pressurizes the methanol vapor by 50-100 kPa.

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