Methanol purge gas hydrogen carbon fractionation recovery process and system

Abstract

The application discloses a methanol purge gas hydrogen-carbon grading recovery process and system. The process first carries out dehydration and methanol removal treatment on the purge tail gas discharged from a methanol synthesis loop of a CO2 hydrogenation methanol device in sequence through a product separation condenser and a pretreatment unit, so that pretreated tail gas is obtained; then the pretreated tail gas is sent into a selective permeation membrane separation unit, and is separated by using a polyimide membrane, a polybenzimidazole membrane or a polyetherimide, so that hydrogen-rich permeation gas and CO2-rich non-permeation gas are obtained. The hydrogen-rich permeation gas is pressurized by a circulating compressor, and is returned to the inlet of a methanol synthesis loop compressor or a circulating gas pipeline; the CO2-rich non-permeation gas enters a CO2 pressure swing adsorption unit, and through a multi-bed adsorption, pressure equalization, desorption and regeneration cycle, CO2 product gas and hydrogen-containing tail gas are produced. The process realizes efficient grading recovery and resource utilization of hydrogen and carbon dioxide in the purge tail gas.

Description

Technical Field

[0001] This application relates to the field of resource utilization technology, and in particular to a process and system for the graded recovery of hydrogen and carbon from methanol off-gas. Background Technology

[0002] In the CO2 hydrogenation to methanol process, CO2 and H2 react with a catalyst to produce methanol and water. Due to factors such as the thermodynamic equilibrium of the reaction and the accumulation of inert components in the circulation loop, the methanol synthesis loop usually needs to release a certain amount of purge gas to maintain stable operation. This purge gas typically contains a high proportion of H2 and CO2, as well as CO, CH4, and small amounts of inert gases.

[0003] In related technologies, methanol off-gas can be directly burned as fuel gas, or some of its usable components can be recovered through membrane separation, pressure swing adsorption, etc. Direct combustion will result in the loss of H2 and CO2 resources and increase carbon emissions; when membrane separation is used alone, more emphasis is usually placed on H2 recovery, and the CO2 enriched in the non-permeable gas of the membrane is difficult to further utilize; when pressure swing adsorption is used alone, the high H2 content in the feed will affect the CO2 adsorption load and operational stability, and it is not conducive to simultaneously achieving H2 and CO2 recovery.

[0004] Furthermore, CO2 hydrogenation to methanol units are often integrated with units such as gasification to syngas, electrolysis to hydrogen, and Fischer-Tropsch synthesis. In these integrated processes, the methanol synthesis loop and downstream syngas system have stable H2 / CO2 or hydrogen-carbon ratio requirements. If only a single component is recovered from the tail gas, without adjusting the separation and reflux processes in conjunction with changes in the H2 / CO2 molar ratio in the methanol synthesis loop, it will be difficult to adapt to fluctuations in upstream feedstock composition and changes in downstream gas demand.

[0005] Therefore, it is necessary to provide a process that can stage and recover H2 and CO2 from methanol off-gas and can be controlled by combining the H2 / CO2 molar ratio changes in the methanol synthesis loop, so as to improve the recovery and utilization of usable components in the off-gas and improve the operational stability of the methanol synthesis loop. Summary of the Invention

[0006] One objective of this application is to provide a hydrogen-carbon staged recovery process and system for methanol off-gas, which at least solves the problems in related technologies such as the difficulty in simultaneously and efficiently recovering H2 and CO2 from the off-gas of methanol synthesis loop, insufficient utilization of CO2 resources, and insufficient stability of the H2 / CO2 molar ratio adjustment in methanol synthesis loop.

[0007] To achieve the above objectives, some embodiments of this application provide the following aspects:

[0008] In a first aspect, this application provides a methanol off-gas hydrogen-carbon staged recovery process, the process comprising:

[0009] (1) The off-gas discharged from the methanol synthesis loop of the CO2 hydrogenation methanol production unit is first sent to the product separation condenser, and then sent to the pretreatment unit for dehydration and methanol removal to obtain pretreated gas.

[0010] (2) The pretreated tail gas is passed into the H2 selective permeation membrane separation unit to separate hydrogen-rich permeate gas and CO2-rich non-permeate gas; the selective permeation membrane is a polyimide membrane, a polybenzimidazole membrane or a polyetherimide membrane.

[0011] (3) The hydrogen-rich permeate gas is pressurized by a circulating compressor and then transported to the inlet of the methanol synthesis loop compressor and / or the methanol circulating gas pipeline;

[0012] (4) The CO2-rich non-permeable gas is introduced into the CO2 pressure swing adsorption unit and subjected to multi-bed adsorption, pressure equalization, desorption, and regeneration cycle operation to obtain CO2 product gas and H2-containing tail gas.

[0013] (5) Monitor the molar ratio of H2 to CO2 in the methanol synthesis loop in real time, and adjust the operating parameters of the H2 selective permeation membrane separation unit, the CO2 pressure swing adsorption unit and the reflux flow rate of CO2 product gas in conjunction with the detection data to maintain the molar ratio of the methanol synthesis loop within the preset target range.

[0014] Secondly, this application also provides a methanol off-gas hydrogen and carbon staged recovery system, the system being used to implement the methanol off-gas hydrogen and carbon staged recovery process described in the first aspect, the system comprising a product separation condenser, a pretreatment unit, an H2 selective permeation membrane separation unit, and a CO2 pressure swing adsorption unit connected in sequence.

[0015] The H2 selective permeation membrane separation unit includes a polyimide membrane, a polybenzimidazole membrane, or a polyetherimide membrane, and its permeation side is connected to a circulating compressor. The outlet of the circulating compressor is connected to the inlet of the methanol synthesis loop compressor and / or the methanol circulating gas pipeline.

[0016] The CO2 pressure swing adsorption unit is filled with at least one adsorbent selected from 13X molecular sieve and activated carbon. Its product gas outlet is connected to the feed gas pipeline of the CO2 hydrogenation to methanol unit / or the integrated process synthesis gas main pipeline through a reflux pipeline. The tail gas outlet of the CO2 pressure swing adsorption unit is equipped with an H2 reflux pipeline, which is connected to the inlet of the selective permeation membrane separation unit to form a circulating reflux structure.

[0017] The system also includes an online gas analyzer and an adaptive control system. The online gas analyzer is installed on the methanol synthesis loop to detect the molar ratio of H2 to CO2 in real time. The adaptive control system is connected to the online gas analyzer, the H2 selective permeation membrane separation unit, the CO2 pressure swing adsorption unit, and the regulating valve on the reflux pipeline to achieve linkage adaptive control. The adaptive control system is a DCS control system or a PLC control system.

[0018] Compared with related technologies, the solution provided in this application involves first sending the methanol synthesis loop purge gas into an H2 selective permeation membrane separation unit to recover H2, then sending the CO2-rich non-permeable gas into a CO2 pressure swing adsorption unit to obtain CO2 product gas, and at least a portion of the CO2 product gas is returned to the feed gas pipeline and / or the synthesis gas main pipeline. Simultaneously, linkage adjustment is performed based on online monitoring data of the H2 / CO2 molar ratio. This can improve the resource utilization of H2 and CO2 in the purge gas, reduce the loss of usable components in the gas, and improve the stability of the H2 / CO2 molar ratio adjustment in the methanol synthesis loop. Attached Figure Description

[0019] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0020] Figure 1 A flowchart of a methanol off-gas hydrogen-carbon staged recovery process provided for an exemplary embodiment of this application. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] This embodiment provides a process for the graded recovery of hydrogen and carbon from methanol off-gas. This process is used to grade and recover H2 and CO2 from the off-gas discharged from the methanol synthesis loop of a CO2 hydrogenation methanol production unit, and to adjust the process in conjunction with the H2 / CO2 molar ratio in the methanol synthesis loop.

[0023] like Figure 1As shown, the off-gas from the methanol synthesis loop is sequentially treated by a product separation condenser and a pretreatment unit before entering the H2 selective permeation membrane separation unit. On the permeate side of the H2 selective permeation membrane separation unit, hydrogen-rich permeate gas is formed, which is then pressurized and returned to the compressor inlet and / or circulating gas pipeline of the methanol synthesis loop. On the non-permeate side of the H2 selective permeation membrane separation unit, CO2-rich non-permeate gas is formed, which enters the CO2 pressure swing adsorption unit. The CO2 pressure swing adsorption unit obtains CO2 product gas, at least a portion of which is recycled back to the feed gas pipeline of the CO2 hydrogenation to methanol unit and / or the main synthesis gas pipeline connected to the integrated process of the CO2 hydrogenation to methanol unit. Furthermore, based on online monitoring data of the H2 / CO2 molar ratio in the methanol synthesis loop, the reflux flow rates of the H2 selective permeation membrane separation unit, the CO2 pressure swing adsorption unit, and the CO2 product gas are adjusted in a coordinated manner. This process includes the following steps.

[0024] (1) The off-gas discharged from the methanol synthesis loop of the CO2 hydrogenation methanol production unit is first sent to the product separation condenser, and then sent to the pretreatment unit for dehydration and methanol removal to obtain pretreated gas.

[0025] Specifically, the off-gas from the methanol synthesis circuit contains unreacted H2, CO2, CO, CH4, and other components, and may also carry methanol, water, and other condensable components. The off-gas is first condensed and separated in a product separation condenser to remove liquid methanol, water, and other condensable substances. The gas after condensation and separation then enters a pretreatment unit for dehydration and methanol removal to obtain pretreated off-gas with reduced moisture and methanol content.

[0026] This step reduces the amount of moisture and methanol entering the subsequent H2 selective permeation membrane separation unit and CO2 pressure swing adsorption unit, thereby improving the operational stability of the subsequent separation process.

[0027] (2) The pretreated tail gas is passed into the H2 selective permeation membrane separation unit to separate hydrogen-rich permeate gas and CO2-rich non-permeate gas; the selective permeation membrane is a polyimide membrane, a polybenzimidazole membrane or a polyetherimide membrane.

[0028] Specifically, after the pretreated exhaust gas enters the H2 selective permeation membrane separation unit, under the effect of the selective permeability of the membrane material, H2 preferentially permeates through the membrane relative to components such as CO2, CO, and CH4, forming hydrogen-rich permeate gas on the permeate side; CO2 and other components that do not permeate through the membrane form CO2-rich non-permeate gas on the non-permeate side.

[0029] After being discharged from the permeate side of the H2 selective permeate membrane separation unit, the hydrogen-rich permeate gas is pressurized by a compressor to meet the reuse requirements of the methanol synthesis loop, and then returned to the compressor inlet and / or circulating gas pipeline of the methanol synthesis loop. Thus, the H2 in the off-gas can re-enter the methanol synthesis loop to participate in the cyclic reaction.

[0030] This step allows for the recovery of H2 from the off-gas and the relative enrichment of CO2 on the non-permeable side, providing feed for subsequent CO2 pressure swing adsorption treatment.

[0031] Specifically, the CO2-rich non-permeable gas discharged from the non-permeable side of the H2 selective permeation membrane separation unit enters the CO2 pressure swing adsorption unit. During the adsorption phase, the CO2 in the CO2-rich non-permeable gas is selectively adsorbed; during the desorption phase, the adsorbed CO2 is released, thereby obtaining CO2 product gas. The volume fraction of CO2 in the CO2 product gas is not less than 95%.

[0032] This step allows for the further recovery of CO2 from CO2-rich non-permeable gas, building upon the prior recovery of H2 by the upstream membrane separation process. This enables the hydrogen and carbon components in the off-gas to be utilized in a phased manner along different pathways.

[0033] (3) The hydrogen-rich permeate gas is pressurized by a circulating compressor and then transported to the inlet of the methanol synthesis loop compressor and / or the methanol circulating gas pipeline;

[0034] (4) The CO2-rich non-permeable gas is introduced into the CO2 pressure swing adsorption unit and subjected to multi-bed adsorption, pressure equalization, desorption, and regeneration cycle operation to obtain CO2 product gas and H2-containing tail gas.

[0035] Specifically, the CO2 product gas output from the CO2 pressure swing adsorption unit can be used entirely or partially as a usable CO2 source. At least a portion of the CO2 product gas is returned to the feed gas pipeline of the CO2 hydrogenation to methanol unit via a reflux pipeline for reuse as CO2 feedstock for the methanol synthesis reaction; or, at least a portion of the CO2 product gas enters the main syngas pipeline connected to the integrated process of the CO2 hydrogenation to methanol unit to adjust the syngas composition in the integrated process.

[0036] Specifically, when the CO2 product gas is returned to the feed gas pipeline of the CO2 hydrogenation to methanol unit, it is used to regulate the CO2 supply entering the methanol synthesis loop and works together with the hydrogen-rich permeate gas returning to the methanol synthesis loop to regulate the H2 / CO2 molar ratio in the methanol synthesis loop. When the CO2 product gas is incorporated into the main synthesis gas pipeline, it is used to regulate the synthesis gas composition in the integrated process or to regulate the hydrogen-carbon ratio required by the downstream synthesis gas utilization unit.

[0037] This step allows the carbon components in the off-gas to be converted from fuel gas or emission paths into feedstock reuse paths, thereby improving the utilization rate of CO2 resources.

[0038] (5) Monitor the molar ratio of H2 to CO2 in the methanol synthesis loop in real time, and adjust the operating parameters of the H2 selective permeation membrane separation unit, the CO2 pressure swing adsorption unit and the reflux flow rate of CO2 product gas in conjunction with the detection data to maintain the molar ratio of the methanol synthesis loop within the preset target range.

[0039] Specifically, online monitoring data of the H2 / CO2 molar ratio is acquired in the methanol synthesis loop, and this online monitoring data is compared with a preset target range. Based on the comparison results, the reflux flow rates of the H2 selective permeate membrane separation unit, the CO2 pressure swing adsorption unit, and the CO2 product gas are adjusted in a coordinated manner.

[0040] In one embodiment, when the H2 / CO2 molar ratio deviates from a preset target range, the operating state of the H2 selective permeate membrane separation unit can be adjusted to change the amount of hydrogen-rich permeate gas formed; the operating state of the CO2 pressure swing adsorption unit can be adjusted to change the amount of CO2 product gas obtained; and the CO2 product gas reflux flow rate can also be adjusted. Specifically, adjusting the CO2 product gas flow rate refluxed to the feed gas pipeline of the CO2 hydrogenation to methanol unit is used to change the CO2 supply entering the methanol synthesis loop, thereby coordinating with the reuse process of the hydrogen-rich permeate gas to adjust the H2 / CO2 molar ratio in the methanol synthesis loop; adjusting the CO2 product gas flow rate incorporated into the main syngas pipeline is used to change the syngas composition in the integrated process or the hydrogen-to-carbon ratio required by downstream units.

[0041] Through the above-mentioned linkage adjustment, H2 and CO2 in the off-gas are recovered in stages along the hydrogen-rich permeate gas reuse path and the CO2 product gas return path, respectively, and the H2 / CO2 molar ratio in the methanol synthesis loop is maintained within the preset target range.

[0042] In this embodiment, the off-gas sequentially undergoes condensation separation and dehydration, methanol removal pretreatment, H2 selective permeate membrane separation, and CO2 pressure swing adsorption treatment. The hydrogen-rich permeate gas is pressurized and returned to the methanol synthesis loop, while the CO2-rich non-permeate gas enters the CO2 pressure swing adsorption unit to obtain CO2 product gas with a CO2 volume fraction of not less than 95%. At least a portion of the CO2 product gas is recycled to the feed gas pipeline and / or the main synthesis gas pipeline, and is adjusted in conjunction with the H2 / CO2 molar ratio based on online monitoring data. This allows for the staged recovery of H2 and CO2 from the off-gas and improves the stability of the H2 / CO2 molar ratio adjustment in the methanol synthesis loop.

[0043] Furthermore, in this embodiment, different reflux paths for the CO2 product gas can correspond to different adjustment targets. The CO2 product gas refluxed to the feed gas pipeline of the CO2 hydrogenation to methanol unit is mainly used to adjust the CO2 supply entering the methanol synthesis loop; the CO2 product gas incorporated into the main syngas pipeline is mainly used to adjust the syngas composition in the integrated process or the hydrogen-to-carbon ratio requirements of downstream units. Thus, the reflux path of the CO2 product gas can be matched with the corresponding process adjustment target.

[0044] In one embodiment, the purge gas discharged from the methanol synthesis circuit has the following molar fractions: H2 50%~65%, CO2 20%~35%, CO 5%~12%, and CH4 5%~15%.

[0045] Specifically, the CO2 hydrogenation to methanol reaction is affected by factors such as reaction equilibrium, recycle gas composition, and accumulation of inert components. The methanol synthesis loop requires the release of a certain amount of purge gas. In this purge gas, H2 and CO2 mainly originate from unreacted feed gas, CO can originate from side reactions or entrainment in the feed gas, and CH4 can accumulate in the recycle loop as an inert or low-reactivity component. Due to the high H2 content, the purge gas is suitable for first passing through an H2 selective permeation membrane separation unit to recover H2. Since the CO2 content is also relatively high, after membrane separation, a CO2-rich non-permeable gas can be formed on the non-permeable side, suitable for further CO2 recovery in a CO2 pressure swing adsorption unit.

[0046] In one specific embodiment, the total flow rate of the off-gas can be 12000 Nm³ / h, and its composition can be: H2 molar fraction 55.0%, CO2 molar fraction 32.0%, CO molar fraction 8.0%, and CH4 molar fraction 5.0%. After condensation separation and dehydration and methanol removal pretreatment, the off-gas enters the H2 selective permeation membrane separation unit. H2 preferentially permeates through the membrane to form hydrogen-rich permeate gas, while CO2 is enriched on the non-permeate side to form CO2-rich non-permeate gas.

[0047] In this embodiment, by limiting the composition range of H2, CO2, CO, and CH4 in the off-gas, the process is made more suitable for treating off-gas from CO2 hydrogenation to methanol units that simultaneously contain high levels of both H2 and CO2. This composition range facilitates the preferential recovery of H2 by the upstream H2 selective permeate membrane separation unit and also facilitates the recovery of CO2 from CO2-rich non-permeable gas by the downstream CO2 pressure swing adsorption unit, thereby supporting the staged recovery of H2 and CO2 from the off-gas.

[0048] In one embodiment, the H2 selective permeation membrane separation unit in step (2) uses a hollow fiber membrane module or a spiral wound membrane module, wherein the H2 selective permeation membrane is a polyimide membrane, a polybenzimidazole membrane or a polyetherimide membrane, and the H2 selective permeation membrane has an H2 / CO2 selectivity of not less than 20.

[0049] Specifically, after the pretreated exhaust gas enters the H2 selective permeation membrane separation unit, the dissolution and diffusion rate of H2 in the membrane material is higher than that of components such as CO2, CO, and CH4. Therefore, H2 can preferentially permeate through the membrane and form hydrogen-rich permeate gas on the permeate side. The H2 selective permeation membrane can be set as a hollow fiber membrane module to increase the membrane area per unit volume; it can also be set as a spiral wound membrane module for easy modular installation and maintenance.

[0050] In one embodiment, the H2 selective permeation membrane can be a polyimide membrane. Polyimide membranes have good gas separation performance and mechanical strength, making them suitable for separating methanol off-gas containing H2, CO2, CO, and CH4. In another embodiment, the H2 selective permeation membrane can be a polybenzimidazole membrane or a polyetherimide membrane to improve the stability of the membrane material in a CO2-containing atmosphere.

[0051] exist Figure 1 In the embodiment shown, the hydrogen selective permeation membrane unit can be a polyimide membrane, a polybenzimidazole membrane, or a polyetherimide membrane, i.e., a PI membrane, a PBI membrane, or a PEI membrane, so that hydrogen in the pretreated tail gas preferentially enters the permeation side to form a hydrogen-rich permeation gas; at the same time, carbon dioxide is relatively enriched on the non-permeation side to form a carbon dioxide-rich non-permeation gas, which enters the subsequent PSA unit.

[0052] In this embodiment, by selecting an H2 selective permeation membrane with an H2 / CO2 selectivity of not less than 20, the separation effect between H2 and CO2 can be improved, making the hydrogen-rich permeate gas suitable for returning to the methanol synthesis loop, while making the non-permeate side gas more suitable for entering the CO2 pressure swing adsorption unit, thereby improving the matching of the hydrogen-carbon staged recovery process of the off-gas tail gas.

[0053] In one embodiment, the pressure difference across the membrane of the H2 selective permeation membrane separation unit in step (2) is 0.8 MPa to 2.0 MPa, the permeation pressure is 0.1 MPa to 1.0 MPa, the operating temperature is 40°C to 80°C, and the volume fraction of H2 in the hydrogen-rich permeate gas is not less than 90%.

[0054] Specifically, after the pretreated exhaust gas enters the H2 selective permeation membrane separation unit, the pressure difference across the membrane provides the driving force for H2 permeation. When the pressure difference across the membrane is within the range of 0.8 MPa to 2.0 MPa, H2 can achieve a good permeation rate, while avoiding insufficient H2 recovery due to an excessively low pressure difference, or an increased operating load on the membrane module due to an excessively high pressure difference. The permeate-side pressure can be controlled between 0.1 MPa and 1.0 MPa to create suitable gas permeation conditions in conjunction with the pressure difference across the membrane. The operating temperature can be controlled between 40℃ and 80℃ to maintain the separation performance and operational stability of the membrane material.

[0055] In one specific embodiment, the pretreated exhaust gas enters a polyimide hollow fiber membrane module with a feed pressure of 6.5 MPa, a pressure difference of 1.5 MPa across the membrane, a permeate-side pressure of 0.4 MPa, and an operating temperature of 60°C. Under these conditions, H2 preferentially permeates through the membrane and forms hydrogen-rich permeate gas on the permeate side. The volume fraction of H2 in the hydrogen-rich permeate gas can reach over 90%, for example, approximately 93%. The hydrogen-rich permeate gas is then pressurized and returned to the compressor inlet and / or recirculation gas line of the methanol synthesis loop.

[0056] In this embodiment, by limiting the pressure difference across the membrane, the permeate side pressure, and the operating temperature, a suitable driving force can be provided for preferential H2 permeation, and the volume fraction of H2 in the hydrogen-rich permeate gas can reach no less than 90%. Therefore, the hydrogen-rich permeate gas can serve as a reusable hydrogen source for the methanol synthesis loop, reducing H2 loss in the off-gas.

[0057] In one embodiment, the volume fraction of CO2 in the CO2-rich non-permeable gas in step (2) is higher than the volume fraction of CO2 in the pretreated tail gas.

[0058] Specifically, after the pretreated exhaust gas enters the H2 selective permeation membrane separation unit, H2 preferentially permeates through the membrane and is discharged from the permeate side, while CO2 is retained in greater quantities on the non-permeate side compared to H2. Therefore, the gas discharged from the non-permeate side has a higher CO2 volume fraction than the pretreated exhaust gas entering the membrane separation unit, forming a CO2-rich non-permeate gas.

[0059] In one specific embodiment, the volume fraction of CO2 in the pretreated tail gas can be 32.0%. After treatment by the H2 selective permeation membrane separation unit, the volume fraction of CO2 in the CO2-rich non-permeable gas can be increased to 63.5%. After this CO2-rich non-permeable gas enters the CO2 pressure swing adsorption unit, since the CO2 concentration has been increased, the CO2 pressure swing adsorption unit can perform adsorption and desorption at a higher CO2 feed concentration, thereby obtaining CO2 product gas with a CO2 volume fraction of not less than 95%.

[0060] In this embodiment, by ensuring that the CO2 volume fraction in the CO2-rich non-permeable gas is higher than that in the pretreated tail gas, the H2 selective permeation membrane separation unit can simultaneously perform H2 recovery and CO2 pre-enrichment functions. Therefore, the subsequent CO2 pressure swing adsorption unit does not need to directly treat the high-H2 content raw off-gas, which helps reduce the CO2 adsorption and separation load and improves the stability of CO2 product gas acquisition.

[0061] In one embodiment, the CO2 pressure swing adsorption unit in step (4) uses at least one of 13X molecular sieve and activated carbon as adsorbent, and operates in a cycle of multi-bed adsorption, pressure equalization, desorption and regeneration to make the volume fraction of CO2 in the CO2 product gas 95%~98%.

[0062] Specifically, after CO2-rich non-permeable gas enters the CO2 pressure swing adsorption (PSA) unit, the adsorbent in the unit selectively adsorbs CO2. The adsorbent can be 13X molecular sieve, activated carbon, or a composite adsorption bed formed by a combination of 13X molecular sieve and activated carbon. 13X molecular sieve has a pore structure suitable for CO2 adsorption, and activated carbon has a large specific surface area; both can be used alone or in combination for CO2 adsorption and separation.

[0063] In one embodiment, the CO2 pressure swing adsorption unit operates with a multi-bed structure. Different adsorption beds can sequentially undergo adsorption, pressure equalization, desorption, and regeneration stages, allowing CO2-rich non-permeable gas to continuously enter the CO2 pressure swing adsorption unit and continuously or quasi-continuously obtain CO2 product gas. During the adsorption stage, CO2 in the CO2-rich non-permeable gas is preferentially adsorbed by the adsorbent; during the pressure equalization stage, pressure is balanced between different adsorption beds to recover some of the gas pressure energy; during the desorption stage, the adsorbed CO2 is released by depressurization or vacuuming; and during the regeneration stage, the adsorbent regains its adsorption capacity and enters the next cycle.

[0064] In one specific embodiment, the CO2 pressure swing adsorption (PSA) unit can adopt a 6-bed PSA structure, with an adsorbent consisting of a combination of 13X molecular sieve and activated carbon. The adsorption pressure is 1.2 MPa, the desorption pressure is 0.05 MPa, and the cycle time is 8 to 12 minutes. After CO2-rich non-permeable gas enters the CO2 PSA unit, a CO2 product gas with a CO2 volume fraction of 96.5% can be obtained. This CO2 product gas can be at least partially refluxed to the feed gas pipeline and / or the syngas main pipeline of the CO2 hydrogenation to methanol unit.

[0065] In this embodiment, by using at least one of 13X molecular sieve and activated carbon as adsorbent, and by operating the CO2 pressure swing adsorption unit in a multi-bed adsorption, pressure equalization, desorption and regeneration cycle, the volume fraction of CO2 in the CO2 product gas can reach 95% to 98%, thereby meeting the requirements for resource utilization by returning it to the methanol feed gas pipeline or the synthesis gas main pipeline.

[0066] In one embodiment, in step (4), at least a portion of the H2-containing tail gas generated by the CO2 pressure swing adsorption unit is returned to the inlet of the H2 selective permeation membrane separation unit, mixed with the pretreated tail gas, and then separated by membrane again.

[0067] Specifically, during the adsorption and desorption of CO2-rich non-permeable gas by the CO2 pressure swing adsorption (PSA) unit, in addition to obtaining CO2 product gas, H2-containing tail gas is also generated. This H2-containing tail gas may include a portion of the H2-containing stream from the PSA desorption gas and / or the H2-containing tail gas discharged from the PSA unit. Since this H2-containing tail gas may still contain recoverable H2, at least a portion of it can be returned to the inlet of the H2 selective permeate membrane separation unit.

[0068] In one embodiment, the H2-containing tail gas is mixed with the pretreated tail gas obtained through condensation separation, dehydration, and methanol removal pretreatment, and then enters the H2 selective permeate membrane separation unit. The mixed gas undergoes further H2 selective separation in the membrane separation unit, with H2 preferentially permeating the membrane to form hydrogen-rich permeate gas. This hydrogen-rich permeate gas is pressurized and returned to the compressor inlet and / or circulating gas line of the methanol synthesis loop; the non-permeate side gas continues to form CO2-rich non-permeate gas and enters the CO2 pressure swing adsorption unit.

[0069] exist Figure 1 In the embodiment shown, the PSA desorbed gas can be partially returned to the membrane inlet, mixed with the pretreated tail gas, and then re-enter the hydrogen selective permeation membrane unit, thereby forming a cross-coupled recovery path between the H2 selective permeation membrane separation unit and the CO2 pressure swing adsorption unit.

[0070] In this embodiment, by returning at least a portion of the H2-containing tail gas generated by the CO2 pressure swing adsorption unit to the inlet of the H2 selective permeation membrane separation unit, the loss of H2 caused by the discharge of PSA tail gas can be reduced, and the overall recovery degree of H2 in the off-gas can be improved. At the same time, the return gas is mixed with the pretreated tail gas and then separated again, which helps to form a cyclic coupling between the membrane separation and CO2 pressure swing adsorption processes, thereby improving the overall utilization efficiency of hydrogen-carbon staged recovery.

[0071] In one embodiment, the online monitoring in step (5) is obtained by an online gas analyzer installed in the methanol synthesis loop. The online gas analyzer detects the molar content of H2 and CO2 in the methanol synthesis loop and determines the molar ratio of H2 to CO2 based on the molar content of H2 and CO2. The molar ratio of H2 to CO2 is associated with the linkage regulation.

[0072] Specifically, the online gas analyzer can be installed in the circulating gas pipeline of the methanol synthesis loop, the inlet pipeline of the methanol synthesis compressor, or other locations that can reflect the gas composition of the methanol synthesis loop. The online gas analyzer continuously or intermittently samples and analyzes the gas in the methanol synthesis loop to obtain the molar content of H2 and the molar content of CO2, and determines the H2 / CO2 molar ratio based on their ratio.

[0073] In one embodiment, the online gas analyzer can be an online gas chromatograph, an infrared gas analyzer, a thermal conductivity gas analyzer, or an online analysis system composed of multiple detection modules. The H2 / CO2 molar ratio obtained by the online gas analyzer is sent to the control system as input data for linkage adjustment. The control system adjusts the H2 selective permeate membrane separation unit, the CO2 pressure swing adsorption unit, and the reflux flow rate of the CO2 product gas based on the deviation between the H2 / CO2 molar ratio and the preset target range.

[0074] exist Figure 1 In the embodiment shown, the methanol synthesis loop is equipped with an online H2 / CO2 monitoring device, which is connected to an adaptive control system to provide gas composition data for closed-loop control.

[0075] In this embodiment, the H2 / CO2 molar ratio in the methanol synthesis loop is obtained in real time or near real time by an online gas analyzer. This provides a data basis for subsequent linkage regulation, enabling H2 selective permeate membrane separation, CO2 pressure swing adsorption, and CO2 product gas reflux to be adjusted according to changes in the gas composition of the methanol synthesis loop, thereby improving the timeliness and stability of H2 / CO2 molar ratio regulation.

[0076] In one embodiment, the linkage adjustment includes adjusting at least one of the pressure difference across the membrane, the permeate side pressure, or the membrane separation recovery rate of the H2 selective permeation membrane separation unit; adjusting at least one of the adsorption time, desorption time, or pressure equalization step of the CO2 pressure swing adsorption unit; and adjusting the reflux flow rate of the CO2 product gas; the preset target range is 2.8~3.2, and the linkage adjustment is executed by a DCS control system or a PLC control system.

[0077] Specifically, after obtaining the H2 / CO2 molar ratio in the methanol synthesis loop, the online gas analyzer sends this ratio to the DCS or PLC control system. The DCS or PLC control system compares the H2 / CO2 molar ratio with a preset target range of 2.8–3.2 and outputs control commands based on the comparison results. These control commands can be applied to the H2 selective permeate membrane separation unit, the CO2 pressure swing adsorption unit, and the regulating valves or related actuators on the CO2 product gas return line.

[0078] In one embodiment, when the H2 / CO2 molar ratio is less than 2.8, it indicates that H2 is relatively insufficient or CO2 is relatively high in the methanol synthesis loop. In this case, the DCS or PLC control system can increase at least one of the following: increase the pressure difference across the membrane of the H2 selective permeate membrane separation unit, decrease the permeate-side pressure, or increase the membrane separation recovery rate, to increase the recovery of hydrogen-rich permeate gas; it can also reduce the reflux flow rate of CO2 product gas to reduce the amount of CO2 entering the feed gas pipeline and / or the main synthesis gas pipeline.

[0079] In another embodiment, when the H2 / CO2 molar ratio is higher than 3.2, it indicates that there is a relative excess of H2 or a relative deficiency of CO2 in the methanol synthesis loop. In this case, the DCS control system or PLC control system can reduce at least one of the following: reduce the pressure difference across the membrane of the H2 selective permeate membrane separation unit, increase the permeate-side pressure, or decrease the membrane separation recovery rate, to reduce the recovery intensity of the hydrogen-rich permeate gas; it can also increase the reflux flow rate of the CO2 product gas to increase the amount of CO2 entering the feed gas pipeline and / or the main synthesis gas pipeline.

[0080] Furthermore, the DCS or PLC control system can adjust the adsorption time, desorption time, or pressure equalization step of the CO2 pressure swing adsorption unit according to the changing trend of the H2 / CO2 molar ratio. For example, when it is necessary to increase the supply of CO2 product gas, the adsorption and desorption switching time can be adjusted to increase the CO2 product gas output of the CO2 pressure swing adsorption unit while meeting the CO2 product gas integral requirements; when it is necessary to stabilize the purity of CO2 product gas or reduce fluctuations, the pressure equalization step can be adjusted to improve the pressure matching in the multi-bed circulation process.

[0081] exist Figure 1 In the embodiment shown, the adaptive control system can be a DCS / PLC, and control the hydrogen selective permeation membrane unit, the PSA unit, and the CO2 product gas return flow based on online H2 / CO2 monitoring data. Figure 1 The dashed arrows in the diagram represent detection and control signals, while the solid arrows represent the main process material.

[0082] In this embodiment, by using a DCS control system or a PLC control system to adjust the membrane separation parameters, PSA operating parameters, and CO2 product gas reflux flow rate in a coordinated manner, the amount of H2 recovered, the amount of CO2 product gas obtained, and the CO2 reflux flow rate can be matched with the changes in the H2 / CO2 molar ratio in the methanol synthesis loop, thereby maintaining the H2 / CO2 molar ratio within the preset target range of 2.8 to 3.2.

[0083] In one embodiment, this embodiment provides a methanol off-gas hydrogen-carbon staged recovery system. This system can be used to perform condensation separation, pretreatment, H2 selective membrane separation, and CO2 pressure swing adsorption treatment on the off-gas discharged from the methanol synthesis loop of a CO2 hydrogenation to methanol unit. It also allows for linkage adjustment based on the H2 / CO2 molar ratio in the methanol synthesis loop, thereby realizing the methanol off-gas hydrogen-carbon staged recovery process described in any of the above embodiments.

[0084] Specifically, the system includes a product separation condenser, a pretreatment unit, an H2 selective permeation membrane separation unit, and a CO2 pressure swing adsorption unit connected in sequence.

[0085] The H2 selective permeation membrane separation unit includes a polyimide membrane, a polybenzimidazole membrane, or a polyetherimide membrane, and its permeation side is connected to a circulating compressor. The outlet of the circulating compressor is connected to the inlet of the methanol synthesis loop compressor and / or the methanol circulating gas pipeline.

[0086] The CO2 pressure swing adsorption unit is filled with at least one adsorbent selected from 13X molecular sieve and activated carbon. Its product gas outlet is connected to the feed gas pipeline of the CO2 hydrogenation to methanol unit / or the integrated process synthesis gas main pipeline through a reflux pipeline. The tail gas outlet of the CO2 pressure swing adsorption unit is equipped with an H2 reflux pipeline, which is connected to the inlet of the selective permeation membrane separation unit to form a circulating reflux structure.

[0087] The system also includes an online gas analyzer and an adaptive control system. The online gas analyzer is installed on the methanol synthesis loop to detect the molar ratio of H2 to CO2 in real time. The adaptive control system is connected to the online gas analyzer, the H2 selective permeation membrane separation unit, the CO2 pressure swing adsorption unit, and the regulating valve on the reflux pipeline to achieve linkage adaptive control. The adaptive control system is a DCS control system or a PLC control system.

[0088] In specific implementations, the condensation separation unit can correspond to a product separation condenser, the pretreatment unit can be used for dehydration and methanol removal, the H2 selective permeation membrane separation unit can correspond to a hydrogen selective permeation membrane unit, the CO2 pressure swing adsorption unit can correspond to a PSA unit, and the control unit can correspond to an adaptive control system. Solid arrows indicate the main process flow directions, such as purge tail gas, pretreatment tail gas, hydrogen-rich permeate gas, CO2-rich non-permeate gas, and CO2 product gas, while dashed arrows indicate circulation or control signals.

[0089] In this embodiment, by sequentially connecting the condensation separation unit, the pretreatment unit, the H2 selective permeation membrane separation unit, and the CO2 pressure swing adsorption unit, and by reconnecting the permeation side of the H2 selective permeation membrane separation unit to the methanol synthesis loop, and reconnecting the CO2 product gas outlet of the CO2 pressure swing adsorption unit to the feed gas pipeline and / or the synthesis gas main pipeline, and by configuring a control unit for linkage adjustment based on online monitoring data of the H2 / CO2 molar ratio, the staged recovery of H2 and CO2 in the off-gas and the stable adjustment of the H2 / CO2 molar ratio in the methanol synthesis loop can be achieved at the system level.

[0090] The scope of this application is defined by the appended claims rather than the foregoing description, and is therefore intended to encompass all variations falling within the meaning and scope of equivalents of the claims. No reference numerals in the claims should be construed as limiting the scope of the claims. Furthermore, it is clear that the word "comprising" does not exclude other elements or steps, and the singular does not exclude the plural.

[0091] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims, and the above embodiments should be considered exemplary and non-limiting.

Claims

1. A methanol off-gas hydrogen-carbon staged recovery process, characterized in that, The process includes: (1) The off-gas discharged from the methanol synthesis loop of the CO2 hydrogenation methanol production unit is first sent to the product separation condenser, and then sent to the pretreatment unit for dehydration and methanol removal to obtain pretreated gas. (2) The pretreated tail gas is passed into the H2 selective permeation membrane separation unit to separate hydrogen-rich permeate gas and CO2-rich non-permeate gas; the selective permeation membrane is a polyimide membrane, a polybenzimidazole membrane or a polyetherimide membrane. (3) The hydrogen-rich permeate gas is pressurized by a circulating compressor and then transported to the inlet of the methanol synthesis loop compressor and / or the methanol circulating gas pipeline; (4) The CO2-rich non-permeable gas is introduced into the CO2 pressure swing adsorption unit, and after multi-bed adsorption, pressure equalization, desorption, and regeneration cycle operation, CO2 product gas and H2-containing tail gas are obtained. (5) Monitor the molar ratio of H2 to CO2 in the methanol synthesis loop in real time, and adjust the operating parameters of the H2 selective permeation membrane separation unit, the CO2 pressure swing adsorption unit and the reflux flow rate of CO2 product gas in conjunction with the detection data to maintain the molar ratio of the methanol synthesis loop within the preset target range.

2. The methanol off-gas hydrogen-carbon staged recovery process according to claim 1, characterized in that, In step (1), the molar fraction of H2 in the exhaust gas is 50%~65%, the molar fraction of CO2 is 20%~35%, the molar fraction of CO is 5%~12%, and the molar fraction of CH4 is 5%~15%.

3. The methanol off-gas hydrogen-carbon staged recovery process according to claim 1, characterized in that, In step (2), the H2 selective permeation membrane separation unit adopts a hollow fiber membrane module or a spiral wound membrane module. The H2 selective permeation membrane is a polyimide membrane, a polybenzimidazole membrane or a polyetherimide membrane, and the H2 selective permeation membrane has an H2 and CO2 selectivity of not less than 20.

4. The methanol off-gas hydrogen-carbon staged recovery process according to claim 1 or 3, characterized in that, In step (2), the pressure difference across the membrane of the H2 selective permeation membrane separation unit is 0.8 MPa to 2.0 MPa, the permeation pressure is 0.1 MPa to 1.0 MPa, the operating temperature is 40℃ to 80℃, and the volume fraction of H2 in the hydrogen-rich permeate gas is not less than 90%.

5. The methanol off-gas hydrogen-carbon staged recovery process according to claim 1, characterized in that, In step (2), the volume fraction of CO2 in the CO2-rich non-permeable gas is higher than the volume fraction of CO2 in the pretreated tail gas.

6. The methanol off-gas hydrogen-carbon staged recovery process according to claim 1, characterized in that, In step (4), the CO2 pressure swing adsorption unit uses at least one of 13X molecular sieve and activated carbon as adsorbent, and operates in a cycle of multi-bed adsorption, pressure equalization, desorption and regeneration to make the volume fraction of CO2 in the CO2 product gas 95%~98%.

7. The methanol off-gas hydrogen-carbon staged recovery process according to claim 1 or 6, characterized in that, Step (4) At least a portion of the H2-containing tail gas generated by the CO2 pressure swing adsorption unit is returned to the inlet of the H2 selective permeation membrane separation unit, mixed with the pretreated tail gas, and then separated by membrane again.

8. The methanol off-gas hydrogen-carbon staged recovery process according to claim 1, characterized in that, The online monitoring in step (5) is obtained by an online gas analyzer installed in the methanol synthesis loop. The online gas analyzer detects the molar content of H2 and CO2 in the methanol synthesis loop and determines the molar ratio of H2 to CO2 based on the molar content of H2 and CO2. The molar ratio of H2 to CO2 is associated with the linkage regulation.

9. The methanol off-gas hydrogen-carbon staged recovery process according to claim 8, characterized in that, The linkage adjustment includes adjusting at least one of the pressure difference across the membrane, the permeate side pressure, or the membrane separation recovery rate of the H2 selective permeation membrane separation unit; adjusting at least one of the adsorption time, desorption time, or the pressure equalization step of the CO2 pressure swing adsorption unit; and adjusting the reflux flow rate of the CO2 product gas. The preset target range is 2.8~3.

2. The linkage adjustment is executed by a DCS control system or a PLC control system.

10. A methanol off-gas hydrogen-carbon staged recovery system, characterized in that, The system is used to implement the methanol off-gas hydrogen-carbon graded recovery process according to any one of claims 1 to 9. The system includes a product separation condenser, a pretreatment unit, an H2 selective permeation membrane separation unit, and a CO2 pressure swing adsorption unit connected in sequence. The H2 selective permeation membrane separation unit includes a polyimide membrane, a polybenzimidazole membrane, or a polyetherimide membrane, and its permeation side is connected to a circulating compressor. The outlet of the circulating compressor is connected to the inlet of the methanol synthesis loop compressor and / or the methanol circulating gas pipeline. The CO2 pressure swing adsorption unit is filled with at least one adsorbent selected from 13X molecular sieve and activated carbon. Its product gas outlet is connected to the feed gas pipeline of the CO2 hydrogenation to methanol unit / or the integrated process synthesis gas main pipeline through a reflux pipeline. The tail gas outlet of the CO2 pressure swing adsorption unit is equipped with an H2 reflux pipeline, which is connected to the inlet of the selective permeation membrane separation unit to form a circulating reflux structure. The system also includes an online gas analyzer and an adaptive control system. The online gas analyzer is installed on the methanol synthesis loop to detect the molar ratio of H2 to CO2 in real time. The adaptive control system is connected to the online gas analyzer, the H2 selective permeation membrane separation unit, the CO2 pressure swing adsorption unit, and the regulating valve on the reflux pipeline to achieve linkage adaptive control. The adaptive control system is a DCS control system or a PLC control system.

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