Membrane separation process for recovering hydrogen from styrene dehydrogenation tail gas

Abstract

The invention discloses a membrane separation process for recovering hydrogen from styrene dehydrogenation tail gas, which belongs to the technical field of membrane separation, and is characterized in that the styrene dehydrogenation reaction tail gas is subjected to separation treatment under certain temperature and pressure conditions through a specially-made high-selectivity hydrogen separation membrane, and hydrogen in the tail gas is efficiently recovered and purified; according to the method, a multi-stage membrane separation device is designed, efficient separation of hydrogen and other tail gas components can be achieved, energy consumption is reduced, and the hydrogen recovery rate is increased. Compared with a traditional adsorption and condensation method, the membrane separation technology has the advantages of being compact in structure, easy and convenient to operate, environmentally friendly, low in cost and the like, and is suitable for large-scale industrial production. The patented technology is beneficial to energy conservation, emission reduction and resource recovery, and has good economic benefits and social benefits.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of membrane separation technology, in particular to a membrane separation process for recovering hydrogen from styrene dehydrogenation tail gas. BACKGROUND

[0002] In the production of styrene, ethylbenzene is usually dehydrogenated to produce styrene, while a large amount of hydrogen-containing tail gas is produced as a byproduct. Since the dehydrogenation reaction is an endothermic process with limited equilibrium, the reaction conditions are harsh and the composition of the tail gas is complex. Traditionally, the styrene dehydrogenation tail gas is treated by burning and other methods for emission, resulting in waste of hydrogen resources and pollution to the environment. In recent years, with the increasing demand for hydrogen in the energy and chemical industries, efficient recovery of hydrogen from tail gas has gradually attracted attention.

[0003] Existing hydrogen recovery technologies, such as low-temperature separation and pressure swing adsorption (PSA), can achieve some degree of separation and purification, but have the disadvantages of complex equipment, high energy consumption, and high cost. SUMMARY

[0004] To solve the technical problems mentioned in the background art, the present application provides a membrane separation process for recovering hydrogen from styrene dehydrogenation tail gas, which separates and purifies the dehydrogenation tail gas through a multi-stage membrane separation system, achieving efficient and low-cost hydrogen recovery. The system not only significantly improves the purity of hydrogen, but also reduces energy consumption, realizes the recycling of tail gas resources, reduces environmental pollution, and adopts the following technical solutions:

[0005] It comprises a filter, a compressor, a condenser, a multi-stage membrane separation unit, and a tail gas treatment and discharge system.

[0006] The styrene dehydrogenation tail gas pretreatment process first removes impurities such as carbon black by filtration, then pressurizes by a compressor, and removes impurities again by a condenser. Most of the aromatic hydrocarbons and water will be condensed into liquid, facilitating subsequent oil-water separation. The impurity-removed tail gas enters the multi-stage membrane separation unit, which is equipped with membrane separation materials with high selectivity for hydrogen, used for step-by-step separation of hydrogen and improvement of hydrogen purity. The separated high-purity hydrogen is sent to a hydrogen storage unit, and the residual gas such as CH4, CO2, etc. that does not pass through is sent to the tail gas discharge system for further treatment.

[0007] The filter is connected to the compressor via a pipeline, the compressor is connected to the pre-cooler via a pipeline, the pre-cooler is connected to the condenser and the membrane assembly via pipelines, the membrane assembly is connected to the multi-stage membrane separation unit via a pipeline, the condenser is connected to the heat exchanger and the storage tank via pipelines, and the heat exchanger is connected to the pump via a pipeline.

[0008] Preferably, the membrane separation material for recovering hydrogen from the styrene dehydrogenation tail gas can be one or more of organic polymer membranes such as polyamide membranes, polyimide membranes, polyvinyl alcohol membranes, etc.; inorganic membranes such as zeolite membranes, carbon molecular sieve membranes, silica membranes, etc.; composite membranes such as polyamide / polyimide composite membranes, polyimide / silicon oxide composite membranes, palladium-based composite membranes, etc., to ensure that the membrane material has high selectivity and high permeability for hydrogen, thereby improving the separation efficiency of hydrogen.

[0009] Preferably, the membrane separation module for recovering hydrogen from the styrene dehydrogenation tail gas comprises at least two or more, to improve the recovery rate and purity of hydrogen.

[0010] Preferably, the membrane separation system for recovering hydrogen from the styrene dehydrogenation tail gas should comprise an automatic control system, which can facilitate real-time monitoring of the concentration and content of hydrogen in the tail gas, and facilitate adjustment of various parameters in the membrane separation process, thereby improving the recovery rate and purity of hydrogen.

[0011] Preferably, in the membrane separation technology for recovering hydrogen from the styrene dehydrogenation tail gas, the compression and condensation unit of the pretreatment section can pretreat the styrene dehydrogenation tail gas to reduce the impurity content, thereby prolonging the service life of the membrane separation material and improving the separation efficiency.

[0012] The present application has the following advantages:

[0013] (1) Multi-stage membrane separation process: Each membrane unit module of the multi-stage membrane can further remove impurities, gradually increasing the purity of the target gas (hydrogen), thereby meeting higher purity requirements and achieving higher gas recovery rate. At the same time, the concentration and content of hydrogen in the tail gas are monitored in real time, making the multi-stage membrane technology more flexible, and allowing the number of separation stages to be increased or decreased as needed, facilitating process optimization and expansion to meet different yield and purity requirements.

[0014] (2) High selectivity membrane separation material: The use of membrane materials with high selectivity and high permeability for hydrogen not only enables efficient hydrogen recovery, but also reduces the pollution of the membrane material after pretreatment and impurity removal, thereby prolonging the service life of the membrane material and improving the stability of the separation performance.

[0015] (3) Compared with traditional separation processes, this technology has a simple process flow, high automation degree, easy operation and maintenance, and can be applied to large-scale industrial production and application. At the same time, this technology can avoid the high energy consumption caused by one-time pressurization or depressurization, has the characteristics of low energy consumption, and meets the current concept of low carbonization. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The present application is a membrane separation process for recovering hydrogen from the styrene dehydrogenation tail gas.

[0017] Fig. 1, filter, 2, compressor, 3, pre-cooler, 4, condenser, 5, pump, 6, heat exchanger, 7, storage tank, 8, membrane module, 9, multi-stage membrane separation unit. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0019] Embodiment 1

[0020] The present application provides a membrane separation process for recovering hydrogen from styrene dehydrogenation tail gas, which comprises a filter 1, a compressor 2, a condenser 3, a multi-stage membrane separation unit 9 and a tail gas treatment and discharge system.

[0021] The raw gas is styrene dehydrogenation tail gas (about 65% hydrogen, 13% methane, 7% ethane and ethylene, 5% toluene and other aromatic hydrocarbons, 3% carbon dioxide and other impurities such as nitrogen, water vapor and carbon black particles), and the solid impurities such as carbon black particles contained in the tail gas are removed in the pretreatment step of filtration;

[0022] The tail gas after preliminary removal of impurities is pressurized by the compressor 2, and in the condenser 4, most of the aromatic hydrocarbons and water vapor are liquefied into liquid and sent to the subsequent oil-water separation section;

[0023] The remaining tail gas is sent to the multi-stage membrane separation unit 9 for treatment, and the system contains two stages of membrane separation units, wherein the membrane separation material in the multi-stage membrane separation unit 9 is organic high molecular polyimide membrane with a thickness of about 4 μm. The first stage separation membrane uses a higher selective separation membrane to separate out part of the hydrogen-containing gas, at this time the hydrogen recovery rate is higher but the purity is lower. The gas on the permeation side of the first stage module reenters the second stage separation membrane unit, at this time a higher selective membrane is used to further purify the hydrogen, and the hydrogen-rich gas on the permeation side of the second stage membrane unit has a purity of about 95%;

[0024] The remaining tail gas after hydrogen recovery contains part of nitrogen, methane, carbon dioxide and other gases, which is sent to the tail gas treatment and discharge system for further treatment.

[0025] Embodiment 2

[0026] A membrane separation process for recovering hydrogen from styrene dehydrogenation tail gas, which comprises a filter 1, a compressor 2, a condenser 4, a multi-stage membrane separation unit 9 and a tail gas treatment and discharge system.

[0027] The raw material gas is styrene dehydrogenation tail gas (about 67% hydrogen, 12% methane, 8% ethane and ethylene, 4% toluene and other aromatic hydrocarbons, 4% carbon dioxide and other impurities such as nitrogen, water vapor and carbon black particles), and the solid impurities such as carbon black particles contained in the tail gas are removed in the pretreatment step of filtration;

[0028] The tail gas after preliminary impurity removal enters the compressor 2 for pressurization, and in the condenser 4, most of the aromatic hydrocarbons and water vapor are liquefied into liquid and sent to the subsequent oil-water separation section;

[0029] The remaining tail gas is sent to a multi-stage membrane unit system for treatment, which contains two stages of membrane separation units, and the membrane separation material in the multi-stage membrane unit is carbon molecular sieve membrane with a thickness of about 0.3 μm. The first stage of separation membrane uses a higher selective separation membrane to separate out a part of hydrogen-containing gas, at this time the hydrogen recovery rate is higher but the purity is lower; the gas on the permeation side of the first stage module reenters the second stage of separation membrane unit, at this time a higher selective membrane is used to further purify hydrogen, and the hydrogen-rich gas on the permeation side of the second stage membrane unit has a purity of about 93%;

[0030] The remaining tail gas after hydrogen recovery contains part of nitrogen, methane, carbon dioxide and other gases, which is sent to the tail gas treatment and discharge system for further treatment.

[0031] Example 3

[0032] A membrane separation process for recovering hydrogen from styrene dehydrogenation tail gas, comprising: a filter 1, a compressor 4, a condenser 4, a multi-stage membrane separation unit 9 and a tail gas treatment and discharge system.

[0033] The raw material gas is styrene dehydrogenation tail gas (about 65% hydrogen, 12% methane, 8% ethane and ethylene, 5% toluene and other aromatic hydrocarbons, 4% carbon dioxide and other impurities such as nitrogen, water vapor and carbon black particles), and the solid impurities such as carbon black particles contained in the tail gas are removed in the pretreatment step of filtration;

[0034] The tail gas after preliminary impurity removal enters the compressor 2 for pressurization, and in the condenser 4, most of the aromatic hydrocarbons and water vapor are liquefied into liquid and sent to the subsequent oil-water separation section;

[0035] The remaining tail gas is sent to a multi-stage membrane separation unit 9 for treatment, and the system comprises three-stage membrane separation units, wherein the membrane separation material in the multi-stage membrane unit is organic polymer polyimide membrane, the membrane thickness is about 5 μm, the first-stage separation membrane adopts a higher selective separation membrane, and a part of hydrogen-containing gas is separated, at this time, the hydrogen recovery rate is higher, but the purity is lower; the gas on the permeation side of the first-stage module reenters the second-stage separation membrane unit, at this time, a higher selective membrane is adopted to further purify hydrogen, the hydrogen-rich gas on the permeation side of the second-stage membrane unit is sent to the third-stage membrane unit for purification, and the hydrogen-rich gas on the permeation side of the third-stage membrane unit has a purity of about 98%;

[0036] The remaining tail gas after hydrogen recovery contains part of nitrogen, methane, carbon dioxide and other gases, which is sent to a tail gas treatment and discharge system for further treatment.

[0037] The present application is simple in operation, convenient to use, and suitable for comprehensive promotion and application. Although the embodiments of the present application have been shown and described, it can be understood by those skilled in the art that various changes, modifications, replacements and modifications can be made to the embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A membrane separation process for recovering hydrogen from a styrene dehydrogenation off-gas, comprising: The preliminary filter (1), the compressor (2), the condenser (4), the multi-stage membrane separation unit (9) and the tail gas treatment and discharge system are characterized in that: 1) The styrene dehydrogenation tail gas is first filtered to remove impurities such as carbon black particles, then pressurized by the compressor (2), and then impurities are removed again by the condenser (4), most of the aromatic hydrocarbons and water are condensed into liquid, which is convenient for subsequent oil-water separation; 2) The impurity-removed tail gas enters the multi-stage membrane separation unit (9), which is prepared with a membrane separation material with high selectivity for hydrogen, for step-by-step separation of hydrogen and improvement of hydrogen purity; 3) The high-purity hydrogen obtained by separation is sent to the hydrogen storage unit, and the residual gas such as CH4, CO2, etc. that does not penetrate is sent to the tail gas discharge system for further treatment; Wherein, the filter (2) is connected with the compressor (2) through a pipeline, the compressor (2) is connected with the pre-cooler (3) through a pipeline, the pre-cooler (3) is connected with the condenser (4) and the membrane assembly (8) respectively through a pipeline, the membrane assembly (8) is connected with the multi-stage membrane separation unit (9) through a pipeline, and the condenser (4) is connected with the heat exchanger (6) and the storage tank (7) respectively through a pipeline. The heat exchanger (6) is connected with the pump (5) through a pipeline.

2. The membrane separation process for recovering hydrogen from styrene dehydrogenation off-gas according to claim 1, characterized in that, The membrane separation material can be one or more of organic polymer membranes such as polyamide membranes, polyimide membranes, polyvinyl alcohol membranes, etc.; inorganic membranes such as zeolite membranes, carbon molecular sieve membranes, silica membranes, etc.; composite membranes such as polyamide / polyimide composite membranes, polyimide / silicon oxide composite membranes, palladium-based composite membranes, etc., to ensure that the membrane material has high selectivity and high permeability for hydrogen, thereby improving the separation efficiency of hydrogen.

3. The membrane separation process for recovering hydrogen from styrene dehydrogenation off-gas according to claim 1, characterized in that, The membrane separation module for recovering hydrogen from the styrene dehydrogenation tail gas contains at least two and more than two to meet different hydrogen recovery rate and purity requirements.

4. The membrane separation process for recovering hydrogen from a styrene dehydrogenation off-gas according to claim 1, characterized in that, The technology also includes a membrane separation system containing an automatic control system, which can facilitate real-time monitoring of the concentration and content of hydrogen in the tail gas, and facilitate adjustment of various parameters in the membrane separation process, thereby improving the recovery rate and purity of hydrogen.

5. The membrane separation process for recovering hydrogen from a dehydrogenation off-gas of styrene according to claim 1, characterized in that, The compressor (2) and the condenser (4) can pretreat the styrene dehydrogenation tail gas to reduce the content of impurities, thereby prolonging the service life of the membrane separation material and improving the separation efficiency.

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