Device and process for preparing ethanol by coupling pressurized hydrogenation with acetate esterification micro-negative pressure purification

Abstract

This invention discloses an apparatus and process for preparing ethanol by acetic acid esterification under micro-negative pressure purification coupled with pressurized hydrogenation, relating to the field of ethanol preparation technology. The process includes: S100, mixing and preheating acetic acid, ethanol, and recycled materials; S200, feeding the mixed materials into an esterification reactor and allowing the esterification product to enter a first micro-negative pressure purification tower to obtain ethyl acetate; S300, feeding ethyl acetate and hydrogen into a hydrogenation reactor to generate ethanol product, and performing gas-liquid separation to obtain a gaseous hydrogen-rich tail gas and a liquid crude ethanol; S400, dividing the liquid crude ethanol into two parts: one part is returned to the esterification reactor for recycling, and the second part is introduced into the ethanol distillation stage for purification to obtain high-purity ethanol. This invention constructs a "negative pressure front and positive pressure back" pressure system. The micro-negative pressure purification at the front end significantly reduces separation difficulty and energy consumption, while the pressurized hydrogenation at the back end improves reaction efficiency and provides stable pressure support for the front end, forming a synergistic energy-saving effect.

Description

Technical Field

[0001] This invention relates to the field of ethanol preparation technology, and in particular to an apparatus and process for preparing ethanol by acetic acid esterification under micro-negative pressure purification coupled with pressurized hydrogenation. Background Technology

[0002] Currently, the main industrial methods for producing ethanol include bio-fermentation, ethylene hydration, and acetic acid hydrogenation. Fermentation uses crops such as corn, sugarcane, and cassava as raw materials, converting starch into ethanol through microbial fermentation. However, this method consumes a large amount of grain resources and has high production costs. Ethylene hydration relies on the petrochemical system and is divided into indirect and direct hydration processes. However, with the continuous rise in the cost of ethylene feedstock, ethanol production facilities in my country using the ethylene route have largely ceased operation.

[0003] In recent years, significant breakthroughs have been achieved in methanol carbonylation to acetic acid technology, leading to a rapid increase in acetic acid production capacity. There are two main technical routes for preparing ethanol from acetic acid: one is the direct hydrogenation of acetic acid, which requires extremely high corrosion resistance of the reaction equipment and has high costs for precious metal catalysts; the other is the two-step acetic acid esterification-hydrogenation method, which alleviates the corrosion problem through the esterification process, but requires the establishment of an ethanol circulation system to participate in the esterification reaction, resulting in a larger equipment scale and the drawback of excessive energy consumption in the hydrogenation process.

[0004] To address these issues, this invention proposes an ethanol preparation apparatus and process for acetic acid esterification under micro-negative pressure purification coupled with pressurized hydrogenation. Summary of the Invention

[0005] The purpose of this invention is to provide an apparatus and process for ethanol preparation by acetic acid esterification under micro-negative pressure purification coupled with pressurized hydrogenation, so as to solve the technical problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a process for preparing ethanol by acetic acid esterification under micro-negative pressure purification coupled with pressurized hydrogenation, comprising the following steps:

[0007] S100: Mix and preheat acetic acid, ethanol and recycled materials;

[0008] S200. The preheated and mixed materials are fed into the esterification reactor to carry out the esterification reaction with the organic acid catalyst, and the generated gaseous product containing ethyl acetate is introduced into the first micro-negative pressure purification tower to obtain high-purity ethyl acetate.

[0009] S300. The high-purity ethyl acetate and fresh hydrogen are fed into a hydrogenation reactor and hydrogenated under catalyst and pressure conditions to produce ethanol product. After gas-liquid separation by a separator, gas-phase hydrogen-rich tail gas and liquid-phase crude ethanol are obtained.

[0010] S400, the gaseous hydrogen-rich tail gas is recycled back to the hydrogenation reactor, and the liquid crude ethanol is divided into two parts. The first part is returned to the esterification reactor as an ethanol feedstock for recycling, and the second part is sequentially introduced into the second micro-negative pressure purification tower and molecular sieve for purification treatment to obtain high-purity ethanol.

[0011] Preferably, a mixer is provided at the inlet of the hydrogenation reactor, and the gaseous hydrogen-rich tail gas is mixed with fresh hydrogen in the mixer before entering the hydrogenation reactor.

[0012] Preferably, in step S200, after the ethyl acetate gas enters the first micro-negative pressure purification tower, it is cooled by a condenser set at the top of the first micro-negative pressure purification tower to obtain high-purity ethyl acetate, while the liquid phase product at the bottom of the first micro-negative pressure purification tower is recycled back to the esterification reactor to continue the reaction.

[0013] An apparatus for the preparation of ethanol by acetic acid esterification under micro-negative pressure purification coupled with pressurized hydrogenation includes:

[0014] An esterification reactor, a first micro-negative pressure purification tower, and a hydrogenation kettle are connected in sequence.

[0015] A gas-liquid separator is connected to the outlet of the hydrogenation reactor;

[0016] The first circulation pipeline has its inlet connected to the gas phase outlet of the gas-liquid separator and its outlet connected to the gas inlet of the hydrogenation reactor for circulating hydrogen-rich tail gas.

[0017] The second circulation pipeline has its inlet end connected to the liquid phase outlet of the gas-liquid separator, and it has two outlet ends, one of which is connected to the feed inlet of the esterification reactor for circulating part of the crude ethanol.

[0018] The product refining unit has its inlet connected to the second outlet of the second circulation pipeline. It includes a second micro-negative pressure purification tower and a molecular sieve connected in sequence, which are used to receive and refine another part of crude ethanol.

[0019] The second circulation pipeline is equipped with a flow diversion and pressure-resistant component to release pressure fluctuations within the second circulation pipeline.

[0020] Preferably, the second circulation pipeline includes a main pipe connected to the liquid phase outlet of the gas-liquid separator, and a first electric valve is provided on the main pipe. The diversion and pressure-resistant assembly includes a buffer tank connected to the main pipe, and a three-way pipe is provided at the outlet end of the buffer tank. The two branches of the three-way pipe are a first branch connected to the feed inlet of the esterification reactor and a second branch connected to the feed inlet of the product refining unit. A first flow meter, a second flow meter, a second electric valve, and a third electric valve are respectively provided on the first branch and the second branch.

[0021] Preferably, the diversion and pressure-resistant assembly further includes two pressure relief pipes provided on the first branch and the second branch, one end of each of the two pressure relief pipes being connected to a buffer tank, and a one-way component located between the two pressure relief pipes being provided in the first branch and the second branch respectively, for guiding the liquid pressure fluctuations in the branch to the buffer tank.

[0022] Preferably, the one-way component includes a first annular plate and a second annular plate fixedly connected to the inner wall of the tee pipe, a one-way ball is disposed between the first annular plate and the second annular plate, and an elastic element is disposed between the one-way ball and the second annular plate.

[0023] Preferably, the bottom of the buffer tank is funnel-shaped, the end of the pressure relief pipe is fixedly connected to the inclined surface of the funnel-shaped bottom, and the interior of the buffer tank is provided with an inverted conical demister mesh.

[0024] Preferably, the top of the buffer tank is provided with an exhaust pipe, one end of which is connected to the circumferential side of the gas-liquid separator and adjacent to the exhaust port of the gas-liquid separator.

[0025] Preferably, a liquid level sensor and a pressure sensor are respectively installed inside the buffer tank and the gas-liquid separator.

[0026] The beneficial effects of this invention are:

[0027] 1. This invention organically integrates three stages: acetic acid esterification, micro-negative pressure purification, and pressurized hydrogenation. Micro-negative pressure purification effectively inhibits the volatilization of corrosive components while reducing operating temperature and thermal decomposition, significantly mitigating equipment corrosion. It also constructs a "negative pressure front, positive pressure back" pressure system. Front-end micro-negative pressure purification significantly reduces separation difficulty and energy consumption, while back-end pressurized hydrogenation improves reaction efficiency and provides stable pressure support to the front end, creating a synergistic energy-saving effect. Furthermore, the system incorporates multiple material recycling mechanisms: unreacted materials are returned to the esterification reactor; hydrogen-rich tail gas is recycled to reduce hydrogen consumption; and crude ethanol is directly returned as raw material to the esterification stage, replacing the external ethanol recycling system. This not only simplifies the process and equipment but also enables in-situ regeneration and efficient utilization of key reactants, improving atom economy.

[0028] 2. By using the diversion and pressure-resistant components, the system effectively isolates pressure fluctuations in the two branches and independently and precisely controls the flow rate, ensuring stable system operation. Furthermore, the pressure release process is transformed into a positive opportunity for process optimization. The buffer tank not only has a pressure buffering function, but also utilizes demister mesh and backflushing liquid flow to achieve deep gas-liquid separation of crude ethanol at more than two stages, effectively removing dissolved hydrogen. This not only improves the hydrogen circulation efficiency by guiding it back to the system for recycling through a closed-loop design, but also avoids potential safety hazards and equipment burdens caused by hydrogen entering subsequent processes. This achieves a functional upgrade from passive pressure relief to active process enhancement. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the process flow for the preparation of ethanol by acetic acid esterification under micro-negative pressure purification coupled with pressurized hydrogenation according to the present invention.

[0030] Figure 2 This is a schematic diagram showing the connection between the gas-liquid separator and the second circulation pipeline of the present invention.

[0031] Figure 3 This is a three-dimensional structural diagram of the gas-liquid separator and the second circulation pipeline of the present invention.

[0032] Figure 4 This is a cross-sectional view of the shunt and anti-pressure component of the present invention.

[0033] Figure 5 for Figure 4 A magnified view of the area along direction A.

[0034] The attached figures are labeled as follows:

[0035] 1. Gas-liquid separator;

[0036] 2. Second circulation pipeline; 21. Main pipe; 22. First electric valve; 23. T-joint; 231. First branch; 232. Second branch; 24. First flow meter; 25. Second flow meter;

[0037] 3. Diversion and pressure-resistant assembly; 31. Buffer tank; 32. Pressure relief pipe; 33. One-way component; 331. First annular plate; 332. Second annular plate; 333. One-way ball; 334. Elastic component; 34. Defoaming mesh; 35. Exhaust pipe. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0039] In the existing technology, there are two main technical routes for preparing ethanol from acetic acid: one is the direct hydrogenation of acetic acid, which requires extremely high corrosion resistance of the reaction equipment and the cost of precious metal catalysts remains high; the other is the two-step acetic acid esterification-hydrogenation method, which alleviates the corrosion problem through the esterification process, but requires the establishment of an ethanol circulation system to participate in the esterification reaction, resulting in an expansion of the equipment scale, and also suffers from the drawback of excessive energy consumption in the hydrogenation process.

[0040] This embodiment was invented to solve the above problems.

[0041] Please see Figures 1 to 4 As shown, an embodiment of the present invention provides a process for the preparation of ethanol by acetic acid esterification under micro-negative pressure coupled with pressurized hydrogenation, comprising the following steps:

[0042] S100: Mix and preheat acetic acid, ethanol and recycled materials.

[0043] S200. The preheated and mixed materials are fed into the esterification reactor to undergo esterification with the organic acid catalyst. The resulting gaseous product containing ethyl acetate is introduced into the first micro-negative pressure purification tower to obtain high-purity ethyl acetate.

[0044] The steps S100 and S200 above are acetic acid esterification stages, and the recycled materials are ethyl acetate or crude ethanol from the subsequent reaction process.

[0045] The preheating process is carried out in preheater A. The pressure in the esterification reactor is 0.5~3.0MPa, the temperature is 100℃~180℃, the alcohol-acid ratio is 1:1, and the conversion rate is 95%~98%.

[0046] The first micro-negative pressure purification tower adopts a structured packed distillation tower, which is equipped with a gas distributor, a liquid distributor, structured packing, a condenser, a reboiler, and a temperature and pressure sensor group, etc. The internal temperature is 30~80℃ and the internal pressure is -0.05~-0.01MPa. The internal structure of the packed distillation tower is existing technology and will not be described in detail here.

[0047] Specifically, during the reaction process in the esterification reactor, the liquid phase remains in the esterification reactor and continues to undergo esterification equilibrium reaction with the newly added materials, while the gaseous product containing ethyl acetate enters from the middle of the first micro-negative pressure purification tower. During the rising process, the gas undergoes heat and mass transfer with the falling reflux liquid. The full exchange of heat and mass occurs within the packing. The reason for using structured packing in this embodiment is that it has a smaller pressure drop and lower energy consumption.

[0048] The gaseous product containing ethyl acetate is cooled by a condenser located at the top of the first micro-negative pressure purification tower to obtain high-purity ethyl acetate liquid, while the liquid product at the bottom of the first micro-negative pressure purification tower is recycled back to the esterification reactor to continue the reaction.

[0049] S300. The high-purity ethyl acetate and fresh hydrogen are fed into a hydrogenation reactor and hydrogenated under catalyst and pressure conditions to produce ethanol product. After gas-liquid separation by a separator, gas-phase hydrogen-rich tail gas and liquid-phase crude ethanol are obtained.

[0050] Step S300 is the hydrogenation stage of ethyl acetate. The temperature inside the hydrogenation reactor is 260~350℃, the pressure is 0.5~4.0MPa, the hydrogen-aldehyde ratio is (20-40):1, and the ethanol selectivity is 95%~98%.

[0051] Specifically, high-purity ethyl acetate liquid and fresh hydrogen gas enter the hydrogenation reactor from the bottom of the reactor. Under the conditions of catalyst and positive pressure, a hydrogenation reaction is carried out to produce ethanol. After the ethanol is separated into gas and liquid phases by a separator, a gas phase hydrogen-rich tail gas and a liquid phase crude ethanol are obtained.

[0052] S400, the gaseous hydrogen-rich tail gas is recycled back to the hydrogenation reactor, and the liquid crude ethanol is divided into two parts. The first part is returned to the esterification reactor as an ethanol feedstock for recycling, and the second part is sequentially introduced into the second micro-negative pressure purification tower and molecular sieve for purification treatment to obtain high-purity ethanol.

[0053] This stage is the ethanol distillation stage. In this embodiment, a mixer is provided at the inlet of the hydrogenation kettle. The gaseous hydrogen-rich tail gas and fresh hydrogen are mixed in the mixer and then enter the hydrogenation kettle together, realizing the recycling of the hydrogen-rich tail gas and reducing hydrogen waste.

[0054] Furthermore, the internal structure and reaction conditions of the second micro-negative pressure purification tower are the same as those of the first micro-negative pressure purification tower, and will not be described again here.

[0055] Specifically, the crude liquid ethanol produced in the hydrogenation stage is divided into two parts. One part is returned to the esterification reactor as a raw material for ethanol recycling, and the other part enters the second micro-negative pressure purification tower and molecular sieve for distillation and purification, finally obtaining high-purity ethanol. In this process, the crude ethanol that is recycled does not need to be further purified.

[0056] In summary, the present invention divides the preparation of high-purity ethanol into three stages: acetic acid esterification, ethyl acetate hydrogenation, and ethanol distillation, and organically integrates these three stages. In particular, the product purification is carried out immediately after acetic acid esterification under a micro-negative pressure condition. This not only reduces the risk of thermal decomposition of ethyl acetate by lowering the operating temperature, but also effectively inhibits the volatilization and diffusion of corrosive components such as acetic acid under a negative pressure environment, thereby significantly reducing the corrosion of the purification system.

[0057] Furthermore, a "negative pressure before positive pressure" system was established in the acetic acid esterification and ethyl acetate hydrogenation stages. The purification of ethyl acetate adopted a micro-negative pressure operation, which significantly reduced the difficulty of separating ethyl acetate from azeotropes such as alcohols and water, resulting in a significant reduction in the heat load of the distillation process. Meanwhile, the hydrogenation stage adopted moderately pressurized conditions, which not only improved the reaction rate and ethanol selectivity, but also provided a stable pressure environment to support the micro-negative pressure operation at the front end.

[0058] In addition, recycled materials participate in the reaction in all three stages. The bottom material of the first micro-negative pressure purification tower is returned to the esterification reactor to continue the reaction. The hydrogen-rich tail gas generated by the hydrogenation kettle is mixed with fresh hydrogen and recycled, which greatly reduces hydrogen consumption. More importantly, a portion of the crude ethanol produced by hydrogenation is directly returned to the esterification reactor as raw material, replacing the ethanol raw material that needs to be prepared externally and recycled independently in the traditional method. This not only eliminates the need for an additional ethanol recycling system, simplifying equipment configuration and investment, but also realizes the in-situ regeneration and efficient utilization of key reactants within the system, improving atom economy and raw material utilization rate. Example 2

[0059] This embodiment provides an ethanol preparation apparatus for acetic acid esterification with micro-negative pressure purification coupled with pressurized hydrogenation, used to implement the process in Embodiment 1. In Embodiment 1 of this invention, the liquid product in the gas-liquid separator 1 is divided into two parts. One part is returned to the esterification reactor as a recycled ethanol feedstock, and the second part is sequentially introduced into a second micro-negative pressure purification tower and a molecular sieve for purification to obtain high-purity ethanol. However, in practical application, it was found that since the splitting occurs downstream of the separator, and the pressure inside the downstream distillation tower differs significantly from the pressure in the upstream esterification reactor, simply adjusting the valve opening cannot accurately control the flow ratio.

[0060] Furthermore, if the flow rate in one direction is adjusted for any reason, it will directly cause a change in the flow rate in the other direction. For example, if the esterification reactor is shut down due to catalyst bed blockage or equipment failure, the corresponding feed flow rate needs to be reduced or even stopped. At this time, the flow rate in the split pipeline will be reduced or stopped, resulting in a large pressure fluctuation, similar to the water hammer effect, which will affect the flow rate through the downstream distillation column and damage the purification efficiency inside the distillation column.

[0061] Therefore, this embodiment is a further improvement on the above embodiment.

[0062] Please see Figures 2 to 4 As shown, it includes an esterification reactor, a first micro-negative pressure purification tower and a hydrogenation kettle connected in sequence, and also includes a gas-liquid separator 1, a first circulation pipeline, a second circulation pipeline 2, a product refining unit and a diversion and pressure-resistant assembly 3.

[0063] The gas-liquid separator 1 is connected to the outlet of the hydrogenation reactor.

[0064] The inlet end of the first circulation pipeline is connected to the gas phase outlet of the gas-liquid separator 1, and its outlet end is connected to the gas inlet of the hydrogenation reactor for circulating hydrogen-rich tail gas.

[0065] The inlet end of the second circulation pipeline 2 is connected to the liquid phase outlet of the gas-liquid separator 1. It has two outlet ends, one of which is connected to the feed inlet of the esterification reactor for circulating part of the crude ethanol.

[0066] The inlet of the product refining unit is connected to the second outlet of the second circulation pipeline 2, which includes a second micro-negative pressure purification tower and a molecular sieve connected in sequence, for receiving and refining another portion of crude ethanol.

[0067] The diversion and pressure-resistant component 3 is installed on the second circulation pipeline 2 to release pressure fluctuations within the second circulation pipeline 2.

[0068] Further details regarding the structure of the second circulation pipeline 2 and the diversion and pressure-resistant assembly 3 are provided. The second circulation pipeline 2 includes a main pipe 21 connected to the liquid phase outlet of the gas-liquid separator 1. A first electric valve 22 is installed on the main pipe 21. The diversion and pressure-resistant assembly 3 includes a buffer tank 31 connected to the main pipe 21. A three-way pipe 23 is installed at the outlet end of the buffer tank 31. The two branches of the three-way pipe 23 are a first branch 231 connected to the inlet of the esterification reactor and a second branch 232 connected to the inlet of the product refining unit. A first flow meter 24, a second flow meter 25, a second electric valve, and a third electric valve are respectively installed on the first branch 231 and the second branch 232.

[0069] The diversion and pressure-resistant assembly 3 also includes two pressure relief pipes 32 installed on the first branch 231 and the second branch 232. One end of each of the two pressure relief pipes 32 is connected to the buffer tank 31. A one-way component 33 located between the two pressure relief pipes 32 is installed in the first branch 231 and the second branch 232 respectively to guide the liquid pressure fluctuation in the branch to the buffer tank 31.

[0070] The one-way component 33 includes a first annular plate 331 and a second annular plate 332 fixedly connected to the inner wall of the three-way pipe 23. A one-way ball 333 is provided between the first annular plate 331 and the second annular plate 332. An elastic element 334 is provided between the one-way ball 333 and the second annular plate 332.

[0071] The bottom of the buffer tank 31 is funnel-shaped, and the end of the pressure relief pipe 32 is fixedly connected to the inclined surface of the funnel-shaped bottom. An inverted conical demister mesh 34 is provided inside the buffer tank 31.

[0072] The top of the buffer tank 31 is provided with an exhaust pipe 35, one end of which is connected to the circumferential side of the gas-liquid separator 1 and adjacent to the exhaust port of the gas-liquid separator 1.

[0073] The buffer tank 31 and the gas-liquid separator 1 are respectively equipped with a liquid level sensor and a pressure sensor.

[0074] Based on the above embodiments, during use, after ethyl acetate and hydrogen react with the catalyst in the hydrogenation reactor, the generated ethanol liquid enters the gas-liquid separator 1. At this time, the hydrogen-rich tail gas is discharged from the top of the gas-liquid separator 1, and the crude ethanol solution passes through the bottom of the gas-liquid separator 1 through the main pipe 21 into the buffer tank 31.

[0075] The liquid inside the buffer tank 31 enters the first branch 231 and the second branch 232 through the three-way pipe 23. Under the individual control of the second electric valve and the third electric valve, the flow rate of crude ethanol entering the esterification reactor and the second micro-negative pressure purification tower is adjusted. The first flow meter 24 and the second flow meter 25 are used to assist in calculating the flow rate.

[0076] When the esterification reactor malfunctions or suddenly stops due to catalyst bed blockage or flooding inside the second micro-negative pressure purification tower, and the corresponding feed flow rate needs to be urgently reduced or even stopped, a large pressure fluctuation will occur in the first branch 231 or the second branch 232 due to the "water hammer effect". At this time, the liquid in the branch is backflowed into the buffer tank 31 under the guidance of the two one-way components 33 and the pressure relief pipe 32, so as to avoid the downstream equipment of one branch from affecting the flow rate of the other branch.

[0077] Furthermore, the top of the buffer tank 31 is also equipped with an exhaust pipe 35 connected to the gas-liquid separator 1. This is because although the crude ethanol solution entering the buffer tank 31 has been separated by the gas-liquid separator 1, a small amount of hydrogen gas remains in the crude ethanol solution. Therefore, there is also obvious gas-liquid stratification inside the buffer tank 31. Hydrogen gas is mainly located in the upper space of the buffer tank 31, while the crude ethanol solution is located in the lower space of the buffer tank 31. When the buffer tank 31 is backflushed by liquid from at least one branch, the backflushed liquid not only causes the pressure inside the buffer tank 31 to increase rapidly, but also improves the gas-liquid separation effect inside the buffer tank 31 after the original liquid in the buffer tank 31 collides with the backflushed liquid during the liquid backflushing process. At this time, the hydrogen gas above the buffer tank 31 is discharged back into the gas-liquid separator 1 through the exhaust pipe 35 and finally mixes with the hydrogen-rich tail gas and fresh hydrogen gas to participate in the hydrogenation reaction.

[0078] It should be noted that, in order to further improve the isolation effect of the buffer tank 31 on the two branches, one-way components 33 are also provided in the two pressure relief pipes 32. The one-way components 33 in the pressure relief pipes 32 have the same structure as the one-way components 33 on the two branches, but allow the liquid to move in the opposite direction, so as to prevent some liquid from flowing into the normal branches due to excessive internal pressure of the buffer tank 31.

[0079] In addition, the buffer tank 31 is equipped with a demister mesh 34. When the crude ethanol solution enters the buffer tank 31 through the main pipe 21, the demister mesh 34 performs secondary gas-liquid separation on the crude ethanol solution. When the backflushing liquid collides with the liquid in the buffer tank 31 and splashes, the demister mesh 34 can further improve the gas-liquid separation effect, forming a tertiary gas-liquid separation. This avoids the waste of hydrogen after it enters the esterification reactor or the second micro-negative pressure purification tower through two branches, and reduces the burden on the esterification reactor and the second micro-negative pressure purification tower.

[0080] In summary, this invention constructs a buffering and distribution system capable of dynamically absorbing and isolating pressure fluctuations by setting a diversion and pressure-resistant assembly 3, which includes a buffer tank 31, a specific one-way component 33, and a pressure relief pipe 32, on the second circulation pipeline 2. Through the pressure stabilizing effect of the buffer tank 31, in conjunction with the electric valves and flow meters on each branch, the flow rates of circulating ethanol flowing to the esterification reactor and crude ethanol flowing to the product refining unit can be independently, stably, and precisely adjusted, ensuring that the two core processes of esterification and distillation are always in the optimal feeding state, thereby improving the operational stability and product purity of the entire system.

[0081] Furthermore, the buffer tank 31 not only serves as a "pressure buffer," but its internal inverted conical demister mesh 34 and the utilization of backflushing liquid flow enable secondary or even tertiary gas-liquid separation of the crude ethanol solution, further removing trace amounts of dissolved hydrogen. This improves hydrogen recovery efficiency, allowing it to be guided back to the gas-liquid separator 1 for circulation via the top exhaust pipe 35. On the other hand, it also prevents hydrogen from entering the esterification or distillation system, avoiding potential safety hazards and reducing the processing burden on these devices. This transforms the passive process of pressure release into a positive opportunity for secondary process optimization.

[0082] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A process for the production of ethanol by coupling pressurized hydrogenation with acetic esterification micro-negative pressure purification, characterized in that, Includes the following steps: S100: Mix and preheat acetic acid, ethanol and recycled materials; S200. The preheated and mixed materials are fed into the esterification reactor to carry out the esterification reaction with the organic acid catalyst, and the generated gaseous product containing ethyl acetate is introduced into the first micro-negative pressure purification tower to obtain high-purity ethyl acetate. S300. The high-purity ethyl acetate and fresh hydrogen are fed into the hydrogenation reactor and hydrogenated under the conditions of catalyst and pressure to generate ethanol product. After gas-liquid separation by gas-liquid separator (1), gas phase hydrogen-rich tail gas and liquid phase crude ethanol are obtained. S400. The gaseous hydrogen-rich tail gas is recycled back to the hydrogenation kettle, and the liquid crude ethanol is divided into two parts. The first part is returned to the esterification reactor as an ethanol feedstock for recycling. The second part is sequentially introduced into the second micro-negative pressure purification tower and molecular sieve for purification treatment to obtain high-purity ethanol. The gas-liquid separator (1) is connected to the outlet of the hydrogenation reactor. The liquid phase outlet of the gas-liquid separator (1) is connected to a second circulation pipeline (2). A diversion and pressure-resistant assembly (3) is provided on the second circulation pipeline (2) to release pressure fluctuations within the second circulation pipeline (2). The second circulation pipeline (2) includes a main pipe (21) connected to the liquid phase outlet of the gas-liquid separator (1). The diversion and pressure-resistant assembly (3) includes a buffer tank (31) connected to the main pipe (21). A three-way pipe (23) is provided at the outlet of the buffer tank (31). The two branches are a first branch (231) connected to the feed inlet of the esterification reactor and a second branch (232) connected to the feed inlet of the product refining unit. The diversion and pressure-resistant assembly (3) also includes two pressure relief pipes (32) installed on the first branch (231) and the second branch (232). One end of the two pressure relief pipes (32) is connected to the buffer tank (31) respectively. The first branch (231) and the second branch (232) are respectively provided with a one-way component (33) located between the two pressure relief pipes (32) to guide the liquid pressure fluctuation in the branch to the buffer tank (31).

2. The process for preparing ethanol by coupling pressurized hydrogenation with acetate- ized micro-negative pressure purification according to claim 1, characterized in that, A mixer is installed at the inlet of the hydrogenation reactor. The gaseous hydrogen-rich tail gas is mixed with fresh hydrogen in the mixer and then enters the hydrogenation reactor.

3. The process for preparing ethanol by coupling pressurized hydrogenation with acetate- ized micro-negative pressure purification according to claim 1, characterized in that, In step S200, after the ethyl acetate gas enters the first micro-negative pressure purification tower, it is cooled by a condenser set at the top of the first micro-negative pressure purification tower to obtain high-purity ethyl acetate, while the liquid phase product at the bottom of the first micro-negative pressure purification tower is recycled back to the esterification reactor to continue the reaction.

4. An apparatus for acetic acid esterification micro-negative pressure purification coupled with pressurized hydrogenation to prepare ethanol, used to implement the process described in any one of claims 1-3, characterized in that, include: An esterification reactor, a first micro-negative pressure purification tower, and a hydrogenation kettle are connected in sequence. A gas-liquid separator (1) is connected to the outlet of the hydrogenation reactor; The first circulation pipeline has its inlet end connected to the gas phase outlet of the gas-liquid separator (1) and its outlet end connected to the gas inlet of the hydrogenation reactor for circulating hydrogen-rich tail gas. The second circulation pipeline (2) has its inlet end connected to the liquid phase outlet of the gas-liquid separator (1), and has two outlet ends, one of which is connected to the feed inlet of the esterification reactor for circulating part of the crude ethanol. The product refining unit has its inlet connected to the second outlet of the second circulation pipeline (2), and includes a second micro-negative pressure purification tower and a molecular sieve connected in sequence for receiving and refining another part of crude ethanol. The second circulation pipeline (2) is equipped with a diversion and pressure-resistant component (3) to release pressure fluctuations within the second circulation pipeline (2); The second circulation pipeline (2) includes a main pipe (21) connected to the liquid phase outlet of the gas-liquid separator (1). The diversion and pressure-resistant assembly (3) includes a buffer tank (31) connected to the main pipe (21). A three-way pipe (23) is provided at the outlet end of the buffer tank (31). The two branches of the three-way pipe (23) are a first branch (231) connected to the feed inlet of the esterification reactor and a second branch (232) connected to the feed inlet of the product refining unit. The diversion and pressure-resistant assembly (3) also includes two pressure relief pipes (32) provided on the first branch (231) and the second branch (232). One end of the two pressure relief pipes (32) is connected to the buffer tank (31) respectively. A one-way component (33) located between the two pressure relief pipes (32) is provided in the first branch (231) and the second branch (232) respectively to guide the liquid pressure fluctuation in the branch to the buffer tank (31).

5. The apparatus for ethanol preparation by acetate esterification under micro-negative pressure purification coupled with pressurized hydrogenation according to claim 4, characterized in that, The main pipe (21) is equipped with a first electric valve (22), and the first branch (231) and the second branch (232) are respectively equipped with a first flow meter (24), a second flow meter (25), a second electric valve and a third electric valve.

6. The apparatus for ethanol preparation by acetate esterification under micro-negative pressure purification coupled with pressurized hydrogenation according to claim 4, characterized in that, The one-way component (33) includes a first annular plate (331) and a second annular plate (332) fixedly connected to the inner wall of the three-way pipe (23). A one-way ball (333) is provided between the first annular plate (331) and the second annular plate (332), and an elastic element (334) is provided between the one-way ball (333) and the second annular plate (332).

7. The apparatus for ethanol preparation by acetate esterification under micro-negative pressure purification coupled with pressurized hydrogenation according to claim 4, characterized in that, The bottom of the buffer tank (31) is funnel-shaped, and the end of the pressure relief pipe (32) is fixedly connected to the inclined surface of the funnel-shaped bottom. The interior of the buffer tank (31) is provided with an inverted conical demister mesh (34).

8. The apparatus for ethanol preparation by acetate esterification under micro-negative pressure purification coupled with pressurized hydrogenation according to claim 7, characterized in that, The top of the buffer tank (31) is provided with an exhaust pipe (35), one end of which is connected to the circumferential side of the gas-liquid separator (1) and adjacent to the exhaust port of the gas-liquid separator (1).

9. The apparatus for ethanol preparation by acetate esterification under micro-negative pressure purification coupled with pressurized hydrogenation according to claim 4, characterized in that, The buffer tank (31) and the gas-liquid separator (1) are respectively equipped with a liquid level sensor and a pressure sensor.

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