CN107954819B - Separation method of propane dehydrogenation reaction gas - Google Patents
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- CN107954819B CN107954819B CN201610902605.9A CN201610902605A CN107954819B CN 107954819 B CN107954819 B CN 107954819B CN 201610902605 A CN201610902605 A CN 201610902605A CN 107954819 B CN107954819 B CN 107954819B
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Abstract
The invention relates to the field of separation of propane dehydrogenation reaction gas, and discloses a separation method of propane dehydrogenation reaction gas, which comprises the following steps: (1) cooling the propane dehydrogenation reaction gas; (2) carrying out membrane separation on the cooled gas to obtain a permeable gas containing methane and hydrogen and a hydrocarbon-rich non-permeable gas; (3) cooling the hydrocarbon-rich non-permeate gas; (4) contacting an absorbent containing a carbon four component or a carbon five component with the hydrocarbon-rich non-permeate gas after cooling in an absorption tower such that the absorbent absorbs the carbon three component and/or heavier components of the hydrocarbon-rich non-permeate gas; (5) desorbing the absorbent absorbing the carbon three-component and/or heavier component in a desorption tower to obtain carbon three-component gas and tower bottom liquid; (6) and (5) performing propylene rectification on the carbon three-component gas obtained in the step (5) in a propylene rectification tower to obtain propylene and propane. The method of the invention has low energy consumption and can obtain high-purity hydrogen and propylene.
Description
Technical Field
The invention relates to the field of separation of propane dehydrogenation reaction gas, in particular to a separation method of propane dehydrogenation reaction gas.
Background
Propylene is an important petrochemical basic raw material and is mainly used for producing dozens of petrochemical products and raw materials such as polypropylene, propylene oxide, acrylic acid, acrylonitrile, alkylate oil and high-octane blending materials. Due to the rapid development of downstream products of propylene, the rapid increase of the demand of propylene in China is greatly promoted. Since 2000, the demand for propylene has increased over that of ethylene.
The propylene supply mainly comes from the catalytic cracking process of ethylene preparation by naphtha steam cracking and petroleum refining, but the existing traditional device can not meet the market demand. Under the huge gap of propylene, the technology for producing propylene attracts people's sight, including a plurality of technologies specially used for producing propylene, such as the technology for producing propylene by Propane Dehydrogenation (PDH), the olefin cracking technology, the technology for producing olefin by methanol, the technology for producing propylene by methanol and the like. In the new technologies, the biggest characteristic of propylene preparation by propane dehydrogenation is that only one raw material propane is used for producing one product of propylene, and compared with other production technologies, the technology for obtaining the same-scale propylene yield by the propane dehydrogenation technology is simpler. Therefore, propane dehydrogenation technology is currently the most competitive propylene process. The relatively mature process for preparing propylene by propane dehydrogenation comprises the following steps: a catalytic dehydrogenation (Oleflex) continuous moving bed process by UOP, a Catofin circulating multi-reactor system process by CBI Lummus, a STAR process by Krupp Uhde, a PDH process by Linde-BASF, and the like. They differ primarily in catalyst, reactor design, and catalyst regeneration process. Most of the industrial applications are the Oleflex process and the Catofin process. The separation flow of the two processes is basically similar, the reactor outlet material enters a cold box after being cooled, compressed and dried, the mixture of propylene and unreacted propane is condensed in the cold box, and the propylene and the recycled propane are recovered in a downstream rectification unit.
Patent application CN102795956A discloses a method of combining membrane separation and cryogenic cooling to separate a reaction product for producing propylene by propane dehydrogenation, which recovers a large amount of hydrogen with high added value and ensures high recovery rate of propylene, but the gas-liquid separation technology adopted by the method separates a hydrogen-rich product from a carbon three-component phase, the separation effect is poor, and the cryogenic cooling technology is adopted, so that the energy consumption is high.
Patent application CN102040445A proposes a process flow for producing propylene by low-carbon dehydrogenation rich in propane. Straight-run naphtha and the like are used as absorbents to separate light components and three carbon components in the propane dehydrogenation product, an oil-gas separator is mainly used for primarily separating gas, liquid and water phases, and then propylene is separated out, but the propylene yield is only 85.7% when the separation effect is poor.
Patent application CN103420757A discloses a hydrogen separation method for propane dehydrogenation reaction gas, which uses C4-C18 hydrocarbons as absorbent, the absorbent can absorb the hydrocarbons in the propane dehydrogenation reaction gas, so as to separate the hydrocarbons from hydrogen, then the separation effect of the hydrocarbons from hydrogen is not good, and it does not separate propylene and propane, and the patent application only primarily separates the propane dehydrogenation reaction gas to remove hydrogen.
Therefore, the existing industrial PDH reaction gas separation process needs to be subjected to deep cooling to-100 to-160 ℃ through a cold box, the energy consumption and the equipment investment are quite high, and the hydrogen in the PDH reaction gas separated by using the reported oil absorption method needs very large circulation amount of the absorbent due to high hydrogen content.
There is an urgent need for a separation method that can improve the separation effect of propane dehydrogenation reaction gas and has low energy consumption and cost.
Disclosure of Invention
The invention aims to overcome the defects of poor separation effect, high energy consumption and the like of propane dehydrogenation reaction gas in the prior art, and provides a separation method of propane dehydrogenation reaction gas.
In order to achieve the above object, the present invention provides a method for separating a propane dehydrogenation reaction gas, comprising:
(1) cooling the propane dehydrogenation reaction gas;
(2) carrying out membrane separation on the cooled gas to obtain a permeable gas containing methane and hydrogen and a hydrocarbon-rich non-permeable gas;
(3) cooling the hydrocarbon-rich non-permeate gas;
(4) contacting an absorbent containing a carbon four component or a carbon five component with the hydrocarbon-rich non-permeate gas after cooling in an absorption tower such that the absorbent absorbs the carbon three component and/or heavier components of the hydrocarbon-rich non-permeate gas;
(5) desorbing the absorbent absorbing the carbon three-component and/or heavier component in a desorption tower to obtain carbon three-component gas and tower bottom liquid;
(6) and (5) performing propylene rectification on the carbon three-component gas obtained in the step (5) in a propylene rectification tower to obtain propylene and propane.
The invention solves the problems of large equipment investment and high energy consumption caused by high-pressure deep cooling condition required by PDH reaction gas separation in the prior art, overcomes the defect of large circulation amount of an absorbent required by the conventional oil absorption method for separating PDH reaction gas, and provides a method for efficiently separating PDH reaction gas by combining oil absorption and membrane separation technologies. The method adopts membrane separation to recover hydrogen and methane, uses a carbon four component and/or a carbon five component as an absorbent, absorbs a carbon three and/or heavier fraction in PDH reaction gas in an absorption tower, and then obtains propane and a high-purity propylene product through subsequent desorption and rectification processes. In addition, the method of the invention keeps the absorption temperature above 5 ℃, does not need an ethylene and propylene refrigerator and an expander, and reduces the investment and energy consumption.
Specifically, the PDH reaction gas separation process of the present invention has the following advantages:
(1) in the method, the light components such as ethane, ethylene, methane and the like in the hydrocarbon-rich non-permeable gas are removed by using the C-four or C-five fraction as an absorbent, and the absorbent is easy to obtain raw materials and low in cost;
(2) the carbon four and/or carbon five fractions are used for absorbing and separating hydrocarbon-rich non-permeable gas, an ethylene and propylene refrigeration compressor and an expander are not needed in the process flow, the investment is low, and the operation is simple;
(3) in the method, the absorption temperature is higher, a lithium bromide refrigerator can be selected to provide refrigerant for refrigeration, and the energy consumption is low;
(4) in the method of the invention, the lowest operation temperature of the system is not lower than 5 ℃, and the equipment and the pipeline can adopt common low-temperature steel, thereby saving a large amount of investment.
Additional features and advantages of the invention will be set forth in the detailed description which follows.
Drawings
FIG. 1 is a flow diagram of a process for the separation of propane dehydrogenation reaction gas in accordance with one embodiment of the present invention.
Description of the reference numerals
1 compressor 2 first cooler 3 membrane separation System 4 second cooler
5 absorption tower 6 desorber 7 propylene rectifying column 8 pressure swing adsorption hydrogen production system
9 third cooler
Detailed Description
The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The invention provides a separation method of propane dehydrogenation reaction gas, which comprises the following steps:
(1) cooling the propane dehydrogenation reaction gas;
(2) carrying out membrane separation on the cooled gas to obtain a permeable gas containing methane and hydrogen and a hydrocarbon-rich non-permeable gas;
(3) cooling the hydrocarbon-rich non-permeate gas;
(4) contacting an absorbent containing a carbon four component or a carbon five component with the hydrocarbon-rich non-permeate gas after cooling in an absorption tower such that the absorbent absorbs the carbon three component and/or heavier components of the hydrocarbon-rich non-permeate gas;
(5) desorbing the absorbent absorbing the carbon three-component and/or heavier component in a desorption tower to obtain carbon three-component gas and tower bottom liquid;
(6) and (5) performing propylene rectification on the carbon three-component gas obtained in the step (5) in a propylene rectification tower to obtain propylene and propane.
In the present invention, the Propane Dehydrogenation (PDH) reaction gas may be various PDH reaction gases conventional in the art, for example, it may contain at least one of hydrogen, methane, ethane, ethylene, propane and propylene, and preferably, the PDH reaction gas contains 3 to 10 wt% of hydrogen, 0.1 to 2 wt% of methane, 0.1 to 2 wt% of ethane, 0.1 to 2 wt% of ethylene, 40 to 60 wt% of propane and 30 to 50 wt% of propylene.
According to the method of the present invention, preferably, the method further comprises: compressing the propane dehydrogenation reaction gas before the step (1); more preferably, the propane dehydrogenation reaction gas is cooled after being compressed to 0.8 to 5.0 MPa. In the present invention, since the pressure of the gas from the outlet of the PDH reactor is low, it is generally necessary to increase the pressure step by step, and the number of stages of the compressor is not particularly limited, and three-stage compression is preferably employed.
According to the method of the present invention, preferably, in the step (1), the propane dehydrogenation reaction gas is cooled to 10 to 40 ℃, more preferably 15 to 30 ℃, so that the separation effect of the propane dehydrogenation reaction gas can be significantly improved and the energy consumption can be reduced. Wherein the cooling is achieved by heat exchange using a cooler.
According to the method of the present invention, in the step (2), the membrane separation can be performed by a membrane separation system provided by a known technology that has been industrially implemented. Preferably, the conditions of the membrane separation include: the operation pressure is 1.0-4.0MPa, and more preferably 1.5-3.0MPa, so that the separation effect of the propane dehydrogenation reaction gas can be obviously improved, and the energy consumption can be reduced. The membrane separation system utilizes the difference of the permeability of the membrane to methane, hydrogen and other components to separate the hydrogen and the methane from the PDH reaction gas and store the hydrogen and the methane in the buffer tank. Other reaction products which are not separated enter a subsequent working section. Typical hydrogen recovery rates are 90-99.9%.
The pressure in the present invention means gauge pressure.
According to the method of the present invention, preferably, the method further comprises: performing pressure swing adsorption on the permeation gas containing methane and hydrogen obtained in the step (2) to prepare hydrogen; the pressure swing adsorption hydrogen production is realized by a pressure swing adsorption system (PSA) which is provided by a well-known technology which realizes industrialization. Preferably, the pressure swing adsorption hydrogen production conditions include: the adsorption pressure is 1.0-4.0MPa, the desorption pressure is 0.1-2.0MPa, more preferably, the adsorption pressure is 1.5-3.0MPa, and the desorption pressure is 0.1-1.0MPa, so that the purity of the hydrogen and the methane can be obviously improved. Under the preferred pressure swing adsorption hydrogen production conditions, hydrogen with higher purity (for example, the purity is 99-99.9%) can be obtained, so that the production cost can be reduced, wherein the larger the yield is, the larger the investment of the PSA system is, and therefore, the scale of the PSA system can be comprehensively optimized according to actual conditions.
According to the method of the present invention, preferably, in the step (3), the hydrocarbon-rich non-permeate gas is cooled to 5 to 30 ℃, more preferably 10 to 20 ℃, so that the separation effect of the propane dehydrogenation reaction gas can be significantly improved and the energy consumption can be reduced. Wherein the cooling is achieved by heat exchange using a cooler.
According to the method, in the step (4), the absorbent is contacted with the hydrocarbon-rich non-permeable gas after being cooled in the absorption tower, so that the absorbent absorbs the carbon three components and/or heavier components in the hydrocarbon-rich non-permeable gas. In the invention, the hydrocarbon-rich non-permeable gas contains a carbon three component and optionally a component heavier than the carbon three component, the absorbent absorbs the carbon three component and the component heavier than the carbon three component in the hydrocarbon-rich non-permeable gas when the hydrocarbon-rich non-permeable gas contains the carbon three component and the component heavier than the carbon three component, and the absorbent absorbs the carbon three component in the hydrocarbon-rich non-permeable gas when the hydrocarbon-rich non-permeable gas does not contain the component heavier than the carbon three component. Wherein, the absorbent can be sprayed from the top of the absorption tower to absorb the carbon three components and/or heavier components in the hydrocarbon-rich non-permeable gas; absorbing the carbon three components and/or heavier components in the hydrocarbon-rich non-permeate gas to obtain tower bottoms, and sending the tower bottoms to a desorption tower for further treatment; the unabsorbed components at the top of the column are light components such as carbon dioxide and less, for example, light components such as ethane, ethylene, methane, etc., and the light components can be used as fuel gas.
According to the method of the present invention, preferably, the method further comprises: before the step (4), the absorbent is cooled to 5-20 ℃ and then is introduced into an absorption tower. The cooling can be realized by a cooler with a refrigerant, wherein the refrigerant can be cold water with the temperature of about 5 ℃ and can be provided by a lithium bromide absorption refrigerator. The lithium bromide absorption refrigerator adopts an absorption refrigeration process, uses waste heat steam or hot water of a factory as a heat source, and has the advantage of low energy consumption.
According to the process of the present invention, in a preferred embodiment, the absorbent in step (4) contains a four-carbon component which is at least one of n-butane, 1-butene, trans-2-butene and cis-2-butene. More preferably, the content of butane in the absorbent is 10-50 wt%, the content of 1-butene is 5-10 wt%, the content of trans-2-butene is 20-40 wt%, and the content of cis-2-butene is 10-40 wt%, based on the total weight of the absorbent, so that the separation effect of the propane dehydrogenation reaction gas can be remarkably improved and the energy consumption can be reduced. The butane may be isobutane or n-butane, and the ratio of isobutane to n-butane is not particularly limited, and does not affect the separation effect. In the present invention, when the absorbent contains a carbon four component, the absorbent may further contain dimethyl ether, which is an inevitable impurity. Wherein the content of dimethyl ether is 0.1 wt% or less.
In another preferred embodiment of the process according to the present invention, the absorbent in step (4) contains a carbon five component which is at least one of isopentane, n-pentane and cyclopentane. More preferably, the absorbent contains 5-35 wt% of isopentane, 40-60 wt% of n-pentane and 5-40 wt% of cyclopentane, based on the total weight of the absorbent, so that the separation effect of the propane dehydrogenation reaction gas can be further improved and the energy consumption can be reduced. In actual production, pentane oil, which typically contains isopentane, n-pentane, cyclopentane, 2-methylpentane and dimethylpentane, may be used as the absorbent because of its availability and low cost, wherein the 2-methylpentane content in the pentane oil may be from 10 to 30% by weight and the dimethylpentane content may be from 4 to 6% by weight.
In the present invention, the above-mentioned preferred absorbent composition is also referred to as fresh absorbent composition.
According to the method of the present invention, in the step (4), there is no particular requirement on the amount of the absorbent used in the absorption column, and those skilled in the art can determine the amount according to the difference of specific components in the propane dehydrogenation reaction gas. Preferably, the weight ratio of the absorbent to the hydrocarbon-rich non-permeate gas after cooling is 1 to 7:1, more preferably 2 to 5:1, so that the separation effect of the propane dehydrogenation reaction gas can be significantly improved and the energy consumption can be reduced, and herein, the amount of the absorbent refers to the amount of the total absorbent, including fresh absorbent and recycled absorbent.
According to the method of the present invention, in step (4), the contacting conditions may be various adsorption contacting conditions conventional in the art, and preferably, the contacting conditions include: the theoretical plate number of the absorption tower is 20-50, the operation pressure is 0.2-1.5MPa, the tower top temperature is 5-60 ℃, and the tower kettle temperature is 30-150 ℃.
More preferably, the conditions of the contacting include: the theoretical plate number of the absorption tower is 25-45, the operation pressure is 0.3-1.2MPa, the tower top temperature is 20-50 ℃, and the tower bottom temperature is 40-130 ℃, so that the separation effect of the propane dehydrogenation reaction gas can be obviously improved, and the energy consumption can be reduced.
According to the method of the present invention, in step (5), the desorption conditions may be various desorption conditions conventional in the art, and preferably, the desorption conditions include: the theoretical plate number of the desorption tower is 15-50, the operation pressure is 0.2-2.0MPa, the tower top temperature is 5-60 ℃, and the tower kettle temperature is 50-200 ℃.
More preferably, the conditions of desorption include: the theoretical plate number of the desorption tower is 20-45, the operation pressure is 0.5-1.8MPa, the tower top temperature is 10-50 ℃, and the tower bottom temperature is 60-150 ℃, so that the separation effect of the propane dehydrogenation reaction gas can be obviously improved, and the energy consumption can be reduced.
According to the method of the present invention, the method further preferably comprises: recycling the tower bottom liquid obtained in the step (5) as an absorbent; more preferably, the tower bottom liquid obtained in the step (5) is cooled to 5-20 ℃ and then is introduced into an absorption tower to be used as an absorbent for recycling, so that the cost can be reduced. Since a small part of the absorbent is discharged with the gas phase at the top of the absorption tower, in the method provided by the invention, a fresh absorbent is preferably introduced as a supplement to ensure the absorbent flow rate of the absorption tower in the system. Wherein the dosage ratio of the fresh absorbent to the circulating absorbent is 1: 50-10000.
According to the method of the present invention, in the step (6), the conditions for the rectification of propylene may be various conditions for the rectification of propylene, which are conventional in the art. Preferably, the conditions for the rectification of propylene include: the theoretical plate number of the propylene rectifying tower is 110-160, the operating pressure is 1.5-2.1MPa, the tower top temperature is 30-60 ℃, and the tower bottom temperature is 40-70 ℃, so that the purity and yield of propylene and propane can be improved.
The present invention will be described in detail below by way of examples.
Example 1
This example is intended to illustrate the process for the separation of propane dehydrogenation reaction gas according to the present invention.
(1) As depicted in fig. 1, PDH gas from the outlet of a PDH reactor (see table 1 below for specific composition) was compressed to 2MPa by a compressor 1 having three compression stages and then passed into a first cooler 2 to be cooled to 20 ℃;
(2) introducing the cooled gas into a membrane separation system 3 to carry out membrane separation under the operation pressure of 2MPa to obtain a permeation gas containing methane and hydrogen and a hydrocarbon-rich non-permeation gas;
(3) and (3) introducing the non-permeate gas rich in hydrocarbon into a second cooler 4 to be cooled to 15 ℃, and introducing the permeate gas containing methane and hydrogen into a pressure swing adsorption hydrogen production system 8 to carry out pressure swing adsorption hydrogen production, wherein the pressure swing adsorption hydrogen production conditions are as follows: the adsorption pressure is 2.0MPa, the desorption pressure is 1.0MPa, the purity of the obtained hydrogen is 99.8 percent, and the yield is 99 percent;
(4) introducing the hydrocarbon-rich non-permeate gas cooled in the step (3) into an absorption tower 5, and spraying a fresh absorbent (the specific composition is shown in the following table 1) cooled to 15 ℃ from the top of the absorption tower 5 (the mass ratio of the total absorbent to the hydrocarbon-rich non-permeate gas is 4:1), so that the absorbent is contacted with the cooled hydrocarbon-rich non-permeate gas, the absorbent absorbs the carbon three components and heavier components in the hydrocarbon-rich non-permeate gas, and discharges carbon two and the following light components at the top of the absorption tower 5, and the tower bottom liquid is the absorbent absorbing the carbon three components and heavier components, wherein the contact conditions are as follows: the theoretical plate number of the absorption tower is 40, the operation pressure is 0.8MPa, the tower top temperature is 25.5 ℃, and the tower kettle temperature is 48.4 ℃;
(5) desorbing the absorbent absorbing the carbon three components in a desorption tower 6 to obtain carbon three component gas at the top of the tower and tower bottom liquid at the bottom of the tower, mixing the tower bottom liquid with a fresh absorbent (the specific composition is shown in the following table 1), cooling the mixture to 15 ℃ by a third cooler 9, and returning the mixture as a circulating absorbent to the absorption tower, wherein the desorption conditions are as follows: the theoretical plate number of the desorption tower is 30, the operation pressure is 0.9MPa, the tower top temperature is 19.2 ℃, and the tower kettle temperature is 73.5 ℃;
(6) and (3) performing propylene rectification on the carbon three-component gas obtained in the step (5) in a propylene rectification tower 7 to obtain propylene and propane, wherein the conditions of the propylene rectification are as follows: the theoretical plate number of the propylene rectifying tower is 130, the operating pressure is 1.9MPa, the tower top temperature is 46.1 ℃, and the tower kettle temperature is 54.8 ℃;
(7) the purity and yield of hydrogen and propylene obtained in the separation process were measured, and the results are shown in Table 5.
TABLE 1
Example 2
This example is intended to illustrate the process for the separation of propane dehydrogenation reaction gas according to the present invention.
(1) As depicted in fig. 1, PDH gas from the outlet of the PDH reactor (see table 2 below for specific composition) was compressed to 3.0MPa by a compressor 1 having three compression stages, and then passed into a first cooler 2 to be cooled to 30 ℃;
(2) introducing the cooled gas into a membrane separation system 3 to carry out membrane separation under the operating pressure of 3.0MPa to obtain permeation gas containing methane and hydrogen and hydrocarbon-rich non-permeation gas;
(3) and (3) introducing the non-permeate gas rich in hydrocarbon into a second cooler 4 to be cooled to 13 ℃, and introducing the permeate gas containing methane and hydrogen into a pressure swing adsorption hydrogen production system 8 to carry out pressure swing adsorption hydrogen production, wherein the pressure swing adsorption hydrogen production conditions are as follows: the adsorption pressure is 3.0MPa, the desorption pressure is 0.8MPa, the purity of the obtained hydrogen is 99.9 percent, and the yield is 99.1 percent;
(4) introducing the hydrocarbon-rich non-permeate gas cooled in the step (3) into an absorption tower 5, and spraying a fresh absorbent (the specific composition is shown in the following table 2) cooled to 13 ℃ from the top of the absorption tower 5 (the mass ratio of the total absorbent to the hydrocarbon-rich non-permeate gas is 4.5:1), so that the absorbent is contacted with the cooled hydrocarbon-rich non-permeate gas, the absorbent absorbs the carbon three components and heavier components in the hydrocarbon-rich non-permeate gas, and discharges the carbon two and the following light components from the top of the absorption tower 5, and the tower bottom liquid is the absorbent absorbing the carbon three components and heavier components, wherein the contact conditions are as follows: the theoretical plate number of the absorption tower is 40, the operation pressure is 0.5MPa, the tower top temperature is 24.5 ℃, and the tower kettle temperature is 53.6 ℃;
(5) desorbing the absorbent absorbing the carbon three components in a desorption tower 6 to obtain carbon three component gas at the top of the tower and tower bottom liquid at the bottom of the tower, mixing the tower bottom liquid with a fresh absorbent (the specific composition is shown in the following table 2), cooling the mixture to 13 ℃ by a third cooler 9, and returning the mixture as a circulating absorbent to the absorption tower, wherein the desorption conditions are as follows: the theoretical plate number of the desorption tower is 35, the operation pressure is 1.0MPa, the tower top temperature is 14.8 ℃, and the tower kettle temperature is 116.9 ℃;
(6) and (3) performing propylene rectification on the carbon three-component gas obtained in the step (5) in a propylene rectification tower 7 to obtain propylene and propane, wherein the conditions of the propylene rectification are as follows: the theoretical plate number of the propylene rectifying tower is 110, the operating pressure is 1.8MPa, the tower top temperature is 46.1 ℃, and the tower kettle temperature is 54.6 ℃;
(7) the purity and yield of hydrogen and propylene obtained in the separation process were measured, and the results are shown in Table 5.
TABLE 2
Example 3
This example is intended to illustrate the process for the separation of propane dehydrogenation reaction gas according to the present invention.
(1) As depicted in fig. 1, PDH gas from the outlet of the PDH reactor (see table 3 below for specific composition) was compressed to 2MPa by a compressor 1 having three compression stages and then passed into a first cooler 2 to be cooled to 15 ℃;
(2) introducing the cooled gas into a membrane separation system 3 for membrane separation under the operating pressure of 1.5MPa to obtain a permeation gas containing methane and hydrogen and a hydrocarbon-rich non-permeation gas;
(3) and (3) introducing the non-permeate gas rich in hydrocarbon into a second cooler 4 to be cooled to 15 ℃, and introducing the permeate gas containing methane and hydrogen into a pressure swing adsorption hydrogen production system 8 to carry out pressure swing adsorption hydrogen production, wherein the pressure swing adsorption hydrogen production conditions are as follows: the adsorption pressure is 1.5MPa, the desorption pressure is 0.8MPa, the purity of the obtained hydrogen is 99.6 percent, and the yield is 99.1 percent;
(4) introducing the hydrocarbon-rich non-permeate gas cooled in the step (3) into an absorption tower 5, and spraying a fresh absorbent (the specific composition is shown in the following table 3) cooled to 15 ℃ from the top of the absorption tower 5 (the mass ratio of the total absorbent to the hydrocarbon-rich non-permeate gas is 4.5:1), so that the absorbent is contacted with the cooled hydrocarbon-rich non-permeate gas, the absorbent absorbs the carbon three components and heavier components in the hydrocarbon-rich non-permeate gas, and discharges the carbon two and the following light components from the top of the absorption tower 5, and the tower bottom liquid is the absorbent absorbing the carbon three components and heavier components, wherein the contact conditions are as follows: the theoretical plate number of the absorption tower is 40, the operation pressure is 1.0MPa, the tower top temperature is 20.7 ℃, and the tower kettle temperature is 60.8 ℃;
(5) desorbing the absorbent absorbing the carbon three components in a desorption tower 6 to obtain carbon three component gas at the top of the tower and tower bottom liquid at the bottom of the tower, mixing the tower bottom liquid with a fresh absorbent (the specific composition is shown in the following table 3), cooling the mixture to 15 ℃ by a third cooler 9, and returning the mixture as a circulating absorbent to the absorption tower, wherein the desorption conditions are as follows: the theoretical plate number of the desorption tower is 20, the operation pressure is 0.5MPa, the tower top temperature is 50 ℃, and the tower kettle temperature is 120 ℃;
(6) and (3) performing propylene rectification on the carbon three-component gas obtained in the step (5) in a propylene rectification tower 7 to obtain propylene and propane, wherein the conditions of the propylene rectification are as follows: the theoretical plate number of the propylene rectifying tower is 130, the operating pressure is 1.5MPa, the tower top temperature is 46.1 ℃, and the tower kettle temperature is 60.6 ℃;
(7) the purity and yield of hydrogen and propylene obtained in the separation process were measured, and the results are shown in Table 5.
TABLE 3
Example 4
This example is intended to illustrate the process for the separation of propane dehydrogenation reaction gas according to the present invention.
The propane dehydrogenation reaction gas was separated by the same method as in example 1 except that the content of trans-2-butene in the fresh absorbent was 45% by weight and the content of cis-2-butene was 3.68% by weight, and the contents of the remaining components were the same as in example 1, and the purity and yield of hydrogen and propylene obtained in the separation process were measured, and the results are shown in Table 5.
Comparative example 1
Propane dehydrogenation reaction gas was separated according to the method of example 1, except that the absorbent was a carbon decaaromatic hydrocarbon (purchased from Nanjing Juji petrochemical company), the specific composition of which is shown in Table 4 below, and the purity and yield of hydrogen and propylene obtained during the separation process were measured, and the results are shown in Table 5.
TABLE 4
TABLE 5
The method for separating the propane dehydrogenation reaction gas can obviously reduce energy consumption and improve the yield and purity of hydrogen and propylene. Specifically, the purity and the yield of the hydrogen can reach more than 99 percent, and the purity and the yield of the propylene can reach more than 98 percent.
The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.
It should be noted that the various technical features described in the above embodiments can be combined in any suitable manner without contradiction, and the invention is not described in any way for the possible combinations in order to avoid unnecessary repetition.
In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.
Claims (23)
1. A method for separating propane dehydrogenation reaction gas is characterized by comprising the following steps:
(1) cooling the propane dehydrogenation reaction gas;
(2) carrying out membrane separation on the cooled gas to obtain a permeable gas containing methane and hydrogen and a hydrocarbon-rich non-permeable gas;
(3) cooling the hydrocarbon-rich non-permeate gas;
(4) contacting an absorbent containing a carbon four component or a carbon five component with the hydrocarbon-rich non-permeate gas after cooling in an absorption tower such that the absorbent absorbs the carbon three component and/or heavier components of the hydrocarbon-rich non-permeate gas;
(5) desorbing the absorbent absorbing the carbon three-component and/or heavier component in a desorption tower to obtain carbon three-component gas and tower bottom liquid;
(6) and (5) performing propylene rectification on the carbon three-component gas obtained in the step (5) in a propylene rectification tower to obtain propylene and propane.
2. The method of claim 1, wherein the method further comprises: and (3) performing pressure swing adsorption on the permeation gas containing methane and hydrogen obtained in the step (2) to prepare hydrogen.
3. The method of claim 2, wherein the pressure swing adsorption hydrogen production conditions comprise: the adsorption pressure is 1.0-4.0MPa, and the desorption pressure is 0.1-2.0 MPa.
4. The method of claim 2, wherein the pressure swing adsorption hydrogen production conditions comprise: the adsorption pressure is 1.5-3.0MPa, and the desorption pressure is 0.1-1.0 MPa.
5. The method of claim 1, wherein the method further comprises: the propane dehydrogenation reaction gas is compressed before step (1).
6. The process according to claim 5, wherein the propane dehydrogenation reaction gas is cooled after being compressed to 0.8 to 5.0 MPa.
7. The process according to claim 1, wherein, in the step (1), the propane dehydrogenation reaction gas is cooled to 10-40 ℃.
8. The process according to claim 1, wherein, in the step (1), the propane dehydrogenation reaction gas is cooled to 15 to 30 ℃.
9. The method of claim 1, wherein in step (2), the membrane separation conditions comprise: the operating pressure is 1.0-4.0 MPa.
10. The method of claim 1, wherein in step (2), the membrane separation conditions comprise: the operating pressure is 1.5-3.0 MPa.
11. The method of claim 1, wherein in step (3), the hydrocarbon-rich non-permeate gas is cooled to 5-30 ℃.
12. The method of claim 1, wherein in step (3), the hydrocarbon-rich non-permeate gas is cooled to 10-20 ℃.
13. The method according to claim 1, wherein in the step (4), the absorbent contains four carbon components, the four carbon components are at least one of n-butane, 1-butene, trans-2-butene and cis-2-butene, and the content of butane in the absorbent is 10-50 wt%, the content of 1-butene is 5-10 wt%, the content of trans-2-butene is 20-40 wt% and the content of cis-2-butene is 10-40 wt% based on the total weight of the absorbent;
the absorbent contains a carbon five component, the carbon five component is at least one of isopentane, n-pentane and cyclopentane, and the content of the isopentane, the n-pentane and the cyclopentane in the absorbent is 5-35 wt%, 40-60 wt% and 5-40 wt%, respectively, based on the total weight of the absorbent.
14. The method according to claim 1 or 13, wherein in step (4), the weight ratio of the absorbent to the hydrocarbon-rich non-permeate gas after cooling is 1-7: 1.
15. The method according to claim 1 or 13, wherein in step (4), the weight ratio of the absorbent to the hydrocarbon-rich non-permeate gas after cooling is 2-5: 1.
16. The method of claim 1 or 13, wherein the method further comprises: before the step (4), the absorbent is cooled to 5-20 ℃ and then is introduced into an absorption tower.
17. The method of claim 1 or 13, wherein in step (4), the contacting conditions comprise: the theoretical plate number of the absorption tower is 20-50, the operation pressure is 0.2-1.5MPa, the tower top temperature is 5-60 ℃, and the tower kettle temperature is 30-150 ℃.
18. The method of claim 1 or 13, wherein in step (4), the contacting conditions comprise: the theoretical plate number of the absorption tower is 25-45, the operation pressure is 0.3-1.2MPa, the tower top temperature is 20-50 ℃, and the tower kettle temperature is 40-130 ℃.
19. The method of claim 1, wherein in step (5), the desorption conditions comprise: the theoretical plate number of the desorption tower is 15-50, the operation pressure is 0.2-2.0MPa, the tower top temperature is 5-60 ℃, and the tower kettle temperature is 50-200 ℃.
20. The method of claim 1, wherein in step (5), the desorption conditions comprise: the theoretical plate number of the desorption tower is 20-45, the operation pressure is 0.5-1.8MPa, the tower top temperature is 10-50 ℃, and the tower kettle temperature is 60-150 ℃.
21. The method according to claim 1, wherein in the step (6), the conditions for the propylene rectification comprise: the theoretical plate number of the propylene rectifying tower is 110-160, the operating pressure is 1.5-2.1MPa, the tower top temperature is 30-60 ℃, and the tower kettle temperature is 40-70 ℃.
22. The method of claim 1, wherein the method further comprises: and (5) recycling the tower bottoms obtained in the step (5) as an absorbent.
23. The method of claim 22, wherein the method further comprises: and (4) cooling the tower bottoms obtained in the step (5) to 5-20 ℃, and introducing the tower bottoms into an absorption tower to be used as an absorbent for recycling.
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| CN102795956B (en) * | 2012-08-30 | 2015-01-07 | 惠生工程（中国）有限公司 | Method for separating reaction products produced during preparation of propylene by dehydrogenating propane |
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| US9517981B2 (en) * | 2013-12-06 | 2016-12-13 | Membrane Technology And Research, Inc. | Membrane-based gas separation processes to separate dehydrogenation reaction products |
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