Post-deacetylation product gas separation process for methanol-to-olefin

Abstract

The invention discloses an after-deacetylation product gas separation process for methanol-to-olefin, which belongs to the field of organic chemical industry and comprises the following steps: pre-treated and dehydrated product gas enters a C2 and C3 cutting tower, a tower top gas phase is condensed and then partially refluxed, and the rest enters the tail section of a product gas compressor; and the tower kettle material enters a depropanizing tower. And a liquid-phase material at the top of the depropanizing tower is selectively fed into the downstream demethanizing tower or deethanizing tower through a pump. The C2 and C3 cutting and fractionating system is adopted, the material flow direction is optimized, the suction load of the tail section of a product gas compressor and the propylene refrigerant consumption of a subsequent demethanizing tower are greatly reduced, and meanwhile, the material circulation amount and the washing liquid requirement in the system are reduced, so that the equipment investment and the device operation energy consumption are remarkably reduced; and the technological process is simplified.

Description

Technical Field

[0001] This invention belongs to the field of organic chemical engineering, and in particular relates to a post-deacetylation product gas separation process for methanol-to-olefins. Background Technology

[0002] China is currently the world's largest producer of methanol-to-olefins (MTO). MTO is a process technology that, apart from steam cracking, can produce both ethylene and propylene. Moreover, the yields of ethylene and propylene are very close, making it an important means of replacing petroleum products in the production of basic chemical raw materials.

[0003] There are three main domestic companies using methanol-to-olefins (MTO) technology already in production: the Dalian Institute of Chemical Physics' DMTO technology, Sinopec Shanghai Research Institute's SMTO technology, and UOP's MTO technology. MTO product gas separation technologies mainly include pre-propane removal followed by hydrogenation and pre-ethane removal followed by hydrogenation. Pre-propane removal technology is further divided into pre-propane removal + propane washing and pre-propane removal + mixed C3 + propane washing. Propane washing technology is mainly provided by Lummus Technology (USA) and Shanghai Wison Technology. Mixed C3 + propane washing technology is KBR Technology (USA), and the latest Lummus technology also uses mixed C3 + propane washing. Pre-ethane removal technology comes from two Sinopec engineering companies: Beijing Engineering Company and Guangzhou Engineering Company. Beijing Engineering Company's technology is pre-ethane removal + C4 washing, mainly used in Sinopec's internal MTO projects and the Jiangsu Sirbon project. Guangzhou Engineering Company's technology is pre-ethane removal + propane washing, with fewer industrial applications.

[0004] Both the pre-propane and pre-ethane removal processes utilize subcooled heavy hydrocarbon washing and absorption technology for methanol-to-olefins product gas separation. The washing liquid is pumped back from downstream to upstream, which creates a washing liquid circulation problem. Material circulation leads to larger equipment, pipelines, and valves, and increased energy consumption. The pre-ethane removal process not only involves washing liquid circulation but also the circulation of C2 between the ethane removal tower, the methanation tower, and the ethylene recovery tower. The circulating C2 accounts for more than 25% of the total C2 volume and is in the gas phase, which greatly increases the size of equipment, pipelines, and valves in the circulation loop. Summary of the Invention

[0005] In view of this, the present invention provides a post-deacetylation product gas separation process for methanol-to-olefins, to solve the above-mentioned problems.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A post-deacetylation product gas separation process for methanol-to-olefins includes the following steps: S1. The product gas from the top of the water washing tower and the alkali washing tower is cooled to 10~15℃ with propylene refrigerant under the conditions of pressure of 1.0~2.0MPa and temperature of 45℃; S2. The cooled product gas is sent into the dryer gas-liquid separator for gas-liquid separation. The gas phase at the top of the tank enters the gas phase dryer for dehydration, and the liquid phase at the bottom of the tank is pumped into the coalescer. S3. The liquid hydrocarbon material at the top of the coalescer is fed into the C3 stripper, and the material at the bottom of the stripper is combined with the material at the bottom of the propane stripper. S4. After exchanging heat with the feed at the top of the C3 stripper, the gaseous material enters a separation tank. The liquid phase in the separation tank is pumped back to the bottom of the C3 stripper, and the gaseous phase at the top of the separation tank is combined with the gaseous phase at the top of the gas-liquid separator of the dryer and enters the gaseous product dryer together. S5. The dehydrated product gas is sent to the C2 and C3 cutting towers. The gas phase at the top of the towers is cooled and condensed by propylene refrigerant and then enters the reflux tank. The liquid phase at the bottom of the reflux tank is pumped back to the top of the C2 and C3 cutting towers as reflux. The gas phase material at the top of the reflux tank enters the end of the product gas compressor for compression. S6. The product gas after the final compression is cooled in multiple stages until the temperature drops to -20℃ to -40℃, and then sent to the demethanizer; the methane tail gas at the top of the demethanizer is sent to the propylene recovery cold box, and the material at the bottom of the tower is sent to the deethaner. S7. The material at the bottom of the C2 and C3 cutting towers is fed into the propane stripper, and the material at the bottom of the propane stripper is then fed into the butane stripper. S8. The liquid material at the top of the propane stripper is pressurized by a pump and selectively fed into the downstream demethanizer or deethaner. S9. The material at the bottom of the de-ethanizer is divided into two parts: one part is sent to the propylene distillation column, and the other part is sent to the top of the de-methanizer after cooling, as a washing liquid to control the ethylene content in the methane tail gas. S10. The gaseous C2 material from the top of the deethaner column is directly fed into the ethylene distillation column, or it is first fed into the acetylene hydrogenation reactor under temperature control, and then processed by a dryer before entering the ethylene distillation column.

[0007] Furthermore, the pressure of the product gas at the outlet of the compressor section is controlled at the maximum pressure at which liquid hydrocarbons do not appear after the product gas is condensed by the circulating water, and the product gas enters the water washing tower in a saturated gas phase state.

[0008] Furthermore, the gas at the top of the water washing tower is superheated by 10~15°C before being sent to the alkali washing tower.

[0009] Furthermore, when the proportion of liquid phase in the gas-liquid separator of the dryer is too large, the C3 stripping tower is cancelled and a liquid phase dryer is used to treat the liquid phase at the bottom of the tank.

[0010] Furthermore, the top operation of the C2 and C3 cutting towers aims to control the C4 component, while the bottom operation aims to extract as much C3 component as possible while ensuring that the methane content is within acceptable limits, in order to reduce the intake load at the end of the product gas compressor.

[0011] Furthermore, the operating pressure of the depropanizer is higher than that of the C2 and C3 cut-off towers. The material at the bottom of the C2 and C3 cut-off towers is pumped up and then sent to the depropanizer.

[0012] Furthermore, the overhead condensers of the C2 and C3 cutting towers and the propane removal tower are cooled with propylene refrigerant, or with material from the ethylene distillation tower as refrigerant; wherein the condenser and the reboiler of the ethylene distillation tower are the same heat exchanger.

[0013] Furthermore, the top condenser of the propane removal tower is a total condenser, while the top condenser of the C2 and C3 cutting towers is a partial condenser.

[0014] Furthermore, the destination of the liquid material at the top of the propane stripper is determined by its C2 content. When the C2 content is low, it is subcooled and sent to the demethanizer as a washing liquid; when the C2 content is high, it is sent directly to the deethanizer after recovering some of the cold energy.

[0015] Furthermore, before feeding the top material of the propane stripper into the methan stripper, it needs to be subcooled to -20°C to -40°C using cold material or propylene refrigerant.

[0016] The beneficial effects of this invention are as follows: 1. This invention uses a C2 or C3 fractionation system to replace the traditional pre-propane or pre-ethane removal system, which significantly reduces the material circulation volume and equipment size; 2. This invention reduces the intake volume at the end of the product gas compressor and the amount of propylene refrigerant used, thereby reducing operating energy consumption; 3. The material from the top of the propane stripper can be flexibly fed into the demethanizer or deethaner, optimizing the process and improving separation efficiency. 4. This invention is applicable to large-scale methanol-to-olefins plants and has good prospects for industrial application. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0018] Figure 1 This is a flowchart of a post-deacetylation product gas separation process for methanol-to-olefins. Detailed Implementation

[0019] 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.

[0020] See attached document Figure 1 A post-deacetylation product gas separation process for methanol-to-olefins includes the following steps: S1. The product gas from the top of the water washing tower and the alkali washing tower is cooled to 10~15℃ with propylene refrigerant under the conditions of pressure of 1.0~2.0MPa and temperature of 45℃; S2. The cooled product gas is sent into the dryer gas-liquid separator for gas-liquid separation. The gas phase at the top of the tank enters the gas phase dryer for dehydration, and the liquid phase at the bottom of the tank is pumped into the coalescer. S3. The liquid hydrocarbon material at the top of the coalescer is fed into the C3 stripper, and the material at the bottom of the stripper is combined with the material at the bottom of the propane stripper. S4. After exchanging heat with the feed at the top of the C3 stripper, the gaseous material enters a separation tank. The liquid phase in the separation tank is pumped back to the bottom of the C3 stripper, and the gaseous phase at the top of the separation tank is combined with the gaseous phase at the top of the gas-liquid separator of the dryer and enters the gaseous product dryer together. S5. The dehydrated product gas is sent to the C2 and C3 cutting towers. The gas phase at the top of the towers is cooled and condensed by propylene refrigerant and then enters the reflux tank. The liquid phase at the bottom of the reflux tank is pumped back to the top of the C2 and C3 cutting towers as reflux. The gas phase material at the top of the reflux tank enters the end of the product gas compressor for compression. S6. The product gas after the final compression is cooled in multiple stages until the temperature drops to -20℃ to -40℃, and then sent to the demethanizer; the methane tail gas at the top of the demethanizer is sent to the propylene recovery cold box, and the material at the bottom of the tower is sent to the deethaner. S7. The material at the bottom of the C2 and C3 cutting towers is fed into the propane stripper, and the material at the bottom of the propane stripper is then fed into the butane stripper. S8. The liquid material at the top of the propane stripper is pressurized by a pump and selectively fed into the downstream demethanizer or deethaner. S9. The material at the bottom of the de-ethanizer is divided into two parts: one part is sent to the propylene distillation column, and the other part is sent to the top of the de-methanizer after cooling, as a washing liquid to control the ethylene content in the methane tail gas. S10. The gaseous C2 material from the top of the deethaner column is directly fed into the ethylene distillation column, or it is first fed into the acetylene hydrogenation reactor under temperature control, and then processed by a dryer before entering the ethylene distillation column.

[0021] In a preferred embodiment, the pressure of the product gas at the outlet of the compressor section is controlled at the maximum pressure at which no liquid hydrocarbons appear after the product gas is condensed by the circulating water, and the product gas enters the water washing tower in a saturated gas phase state.

[0022] In a preferred embodiment, the gas at the top of the water washing tower is superheated by 10-15°C before being sent to the alkali washing tower.

[0023] In a preferred embodiment, the liquid phase at the bottom of the dryer feed separator is pumped into the coalescer, and the material at the top of the coalescer enters the C3 stripping tower.

[0024] In a preferred embodiment, the feed to the C3 stripper is heat-exchanged with the gaseous material at the top of the tower, the condensed material is returned to the top of the stripper as reflux, and the propane content in the bottom of the stripper is controlled.

[0025] In a preferred embodiment, the uncondensed gaseous material at the top of the stripping tower is combined with the gaseous material at the top of the dryer feed separator.

[0026] In a preferred embodiment, when the proportion of liquid phase in the gas-liquid separator of the dryer is too large, the C3 stripping tower is removed and a liquid phase dryer is used to treat the liquid phase at the bottom of the tank.

[0027] In a preferred embodiment, the top operation of the C2 and C3 cutting tower aims to control the C4 component, while the bottom operation aims to extract as much C3 component as possible while ensuring that the methane content is qualified, so as to reduce the intake load of the product gas compressor at the end.

[0028] In a preferred embodiment, the operating pressure of the propane stripper is higher than that of the C2 and C3 cut-off towers, and the material at the bottom of the C2 and C3 cut-off towers is pumped into the propane stripper after being pressurized.

[0029] In a preferred embodiment, the overhead condensers of the C2 and C3 cutting towers and the propane removal tower are cooled with propylene refrigerant, or with material from the ethylene distillation tower as refrigerant; wherein the condenser and the reboiler of the ethylene distillation tower are the same heat exchanger.

[0030] In a preferred embodiment, the top condenser of the propane removal tower is a total condenser, and the top condenser of the C2 and C3 cutting towers is a partial condenser.

[0031] In a preferred embodiment, the destination of the liquid material at the top of the propane stripper is determined by its C2 content. When the C2 content is low, it is subcooled and sent to the demethanizer as a washing liquid; when the C2 content is high, it is sent directly to the deethanizer after recovering some of the cold energy.

[0032] In a preferred embodiment, the material from the top of the propane stripper is subcooled to -20°C to -40°C using a cold material or propylene refrigerant before being fed into the methan stripper.

[0033] This invention is neither a pure pre-propane removal process nor a pure pre-ethane removal technology, but a C2 / C3 cutting and separation technology. The bottom material of the cutting tower enters the propane removal tower, and the liquid phase material at the top of the propane removal tower is pumped into the downstream demethanizer or deethaner. This not only reduces the intake volume at the end of the product gas compressor, but also reduces the amount of propylene refrigerant used from the end of the product gas compressor to the demethanizer. When the C2 content of the top material of the propane removal tower is low, it is subcooled and enters the demethanizer as washing liquid, reducing the amount of washing liquid used. When the C2 content of the top material of the propane removal tower is high, it can be sent to the deethaner after recovering part of the cold energy. This material skips the demethanizer, reducing the feed flow rate of the demethanizer and the amount of washing liquid required. This process not only reduces the size of the olefin separation unit equipment, pipelines, and valves, but also reduces the operating cost of the olefin separation unit.

[0034] The above descriptions are merely specific embodiments of the present invention, and common knowledge regarding the specific structures and characteristics of the solutions is not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

[0035] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0036] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A post-deyne removal product gas separation process for methanol-to-olefins, characterized in that, Includes the following steps: S1. The product gas from the top of the water washing tower and the alkali washing tower is cooled to 10~15℃ with propylene refrigerant under the conditions of pressure of 1.0~2.0MPa and temperature of 45℃; S2. The cooled product gas is sent into the dryer gas-liquid separator for gas-liquid separation. The gas phase at the top of the tank enters the gas phase dryer for dehydration, and the liquid phase at the bottom of the tank is pumped into the coalescer. S3. The liquid hydrocarbon material at the top of the coalescer is fed into the C3 stripper, and the material at the bottom of the stripper is combined with the material at the bottom of the propane stripper. S4. After exchanging heat with the feed at the top of the C3 stripper, the gaseous material enters a separation tank. The liquid phase in the separation tank is pumped back to the bottom of the C3 stripper, and the gaseous phase at the top of the separation tank is combined with the gaseous phase at the top of the gas-liquid separator of the dryer and enters the gaseous product dryer together. S5. The dehydrated product gas is sent to the C2 and C3 cutting towers. The gas phase at the top of the towers is cooled and condensed by propylene refrigerant and then enters the reflux tank. The liquid phase at the bottom of the reflux tank is pumped back to the top of the C2 and C3 cutting towers as reflux. The gas phase material at the top of the reflux tank enters the end of the product gas compressor for compression. S6. The product gas after the final compression is cooled in multiple stages until the temperature drops to -20℃ to -40℃, and then sent to the demethanizer; the methane tail gas at the top of the demethanizer is sent to the propylene recovery cold box, and the material at the bottom of the tower is sent to the deethaner. S7. The material at the bottom of the C2 and C3 cutting towers is fed into the propane stripper, and the material at the bottom of the propane stripper is then fed into the butane stripper. S8. The liquid material at the top of the propane stripper is pressurized by a pump and selectively fed into the downstream demethanizer or deethaner. S9. The material at the bottom of the de-ethanizer is divided into two parts: one part is sent to the propylene distillation column, and the other part is sent to the top of the de-methanizer after cooling, as a washing liquid to control the ethylene content in the methane tail gas. S10. The gaseous C2 material from the top of the deethaner column is directly fed into the ethylene distillation column, or it is first fed into the acetylene hydrogenation reactor under temperature control, and then processed by a dryer before entering the ethylene distillation column.

2. The post-deyne removal product gas separation process for methanol-to-olefins according to claim 1, characterized in that, The pressure of the product gas at the outlet of the compressor section is controlled at the maximum pressure at which no liquid hydrocarbons appear after the product gas is condensed by the circulating water, and the product gas enters the water washing tower in a saturated gas phase state.

3. The post-deyne removal product gas separation process for methanol-to-olefins according to claim 1, characterized in that, The gas at the top of the water washing tower is superheated by 10~15℃ before being sent to the alkali washing tower.

4. The post-deyne removal product gas separation process for methanol-to-olefins according to claim 1, characterized in that, When the proportion of liquid phase in the gas-liquid separator of the dryer is too high, the C3 stripping tower is cancelled and a liquid phase dryer is used to treat the liquid phase at the bottom of the tank.

5. The post-deyne removal product gas separation process for methanol-to-olefins according to claim 1, characterized in that, The top operation of the C2 and C3 cutting towers aims to control the C4 component, while the bottom operation aims to extract as much C3 component as possible while ensuring that the methane content is within acceptable limits, so as to reduce the intake load of the product gas compressor at the end.

6. The post-deyne removal product gas separation process for methanol-to-olefins according to claim 1, characterized in that, The operating pressure of the depropanizer is higher than that of the C2 and C3 cut-off towers. The material at the bottom of the C2 and C3 cut-off towers is pumped into the depropanizer after being pressurized.

7. The post-deyne removal product gas separation process for methanol-to-olefins according to claim 1, characterized in that, The overhead condensers of the C2 and C3 cutting towers and the propane removal tower are refrigerated with propylene refrigerant, or with material from the ethylene distillation tower as refrigerant; the condenser and the reboiler of the ethylene distillation tower are the same heat exchanger.

8. A post-deyne removal product gas separation process for methanol-to-olefins according to claim 7, characterized in that, The top condenser of the propane stripper is a total condenser, while the top condenser of the C2 and C3 cutting towers is a partial condenser.

9. A post-deyne removal product gas separation process for methanol-to-olefins according to claim 1, characterized in that, The destination of the liquid material at the top of the propane stripper is determined by its C2 content. When the C2 content is low, it is subcooled and sent to the demethanizer as a washing liquid. When the C2 content is high, it is sent directly to the deethanizer after recovering some of the cold energy.

10. A post-deyne removal product gas separation process for methanol-to-olefins according to claim 9, characterized in that, Before feeding the overhead material from the propane stripper into the methan stripper, it must be subcooled to -20°C to -40°C using cold material or propylene refrigerant.

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