Propylene purification method

Abstract

To prepare an absorbent provided with high selectivity and high absorption capacity, by obtaining a high purity propylene.SOLUTION: A method for purifying propylene according to one embodiment includes the following steps S1 to S3: In S1, water is removed from the propylene to be purified using a molecular sieve, which is activated at 300 to 400°C for 12 to 24 hours before use. In S2, reformulated porous carbon fibers are used to adsorb the propylene obtained in step S1. In S3, the propylene obtained in step S2 is placed in a distillation column for distillation processing. In this embodiment, functionalized reformulated porous carbon fibers are first used to adsorb impurities in the propylene in advance, removing a large amount of C4 hydrocarbon impurities with relatively low energy consumption, thereby reducing the burden on the subsequent distillation process and obtaining propylene with relatively high purity. The subsequent distillation step divides the normal distillation column into two sections with relatively high theoretical stages.

Description

[Technical field]

[0001] The present invention relates to the technical field of propylene purification, in particular to a process for propylene purification. [Background technology]

[0002] Electronic grade propylene contains carbon-carbon double bonds, so it is prone to chemical reactions and produces other substances that are deposited on the substrate surface. It is mainly used as epitaxy, deposition gas, film formation gas, or for the growth of amorphous silicon carbon, and is an important gas for semiconductor manufacturing. At present, the domestic production level of electronic grade propylene is not high. With the rapid change of semiconductor technology, larger wafer size and more fine process technology are required, so the demand for electronic grade propylene is becoming greater and the requirement for purity is becoming higher. The purity of industrial-grade propylene is 99.5%, and the main impurities include nitrogen, oxygen, carbon dioxide, hydrocarbon impurities and water. At present, the purification methods commonly used for propylene purification include adsorption, rectification, catalysis, selective adsorption of metal-organic framework materials and other means. Under general conditions, the selectivity of the adsorption method is not high. The rectification method has high requirements for equipment and high energy consumption. The catalyst used in the catalytic method is difficult to prepare. Although the selectivity of metal-organic framework materials is good, most of the MOFs reported so far have good selectivity for propylene, poor stability, high cost, and difficult industrial application. Summary of the Invention

[0003] The main objective of the present invention is to provide a method for purifying propylene in order to improve the technical problems of the existing propylene purification methods, such as low selectivity, high difficulty in catalyst preparation, poor stability, high cost, and high equipment requirements.

[0004] In order to achieve the above object, the present invention proposes a method for purifying propylene, which includes the following steps S1 to S3. In S1, molecular sieves are employed to remove water from the propylene to be purified, and the molecular sieves are activated at 300-400°C for 12-24h before use. In step S2, the modified porous carbon fiber is used to adsorb the propylene obtained in step S1. In S3, the propylene obtained in step S2 is introduced into a rectification column and subjected to rectification treatment.

[0005] Propylene is mainly obtained from the steam cracking and catalytic cracking of naphtha, and the product gas is inevitably mixed with C4 hydrocarbon impurities. The C4 hydrocarbon impurities mainly include butane, butylene, butadiene, etc. All of these gas components have higher polarizability than propylene, so they can be further removed from the propylene product gas through the strong van der Waals and hydrogen bonding forces between the adsorbent and the C4 hydrocarbon gas. Conventional molecular sieves have a limited specific surface area (usually <400 m 2 / g), the adsorption capacity is relatively low, and the desorption temperature is relatively high (usually >250 °C), which not only results in additional regeneration energy consumption, but also the adsorbed C4 hydrocarbons are easily catalyzed by the metal sites of the molecular sieve under high temperature conditions and polymerize in the pores of the molecular sieve, thereby reducing its working capacity and service life.

[0006] In this solution, modified porous carbon fibers are first employed to adsorb propylene. In contrast, porous carbon fibers have a high pore volume (>1.3 cm 3 / g), excellent steam stability, and gentle regeneration performance. By adjusting the pore chemistry of the porous carbon fiber and increasing its nitrogen and oxygen functional group content, the adsorption power and selectivity for C4 hydrocarbons are improved while maintaining higher adsorption sites. Furthermore, before the propylene and propane rectification separation step, a large amount of C4 hydrocarbon impurities are removed with relatively low energy consumption to obtain relatively high purity propylene. The propylene can then be rectified through a rectification process to further improve the purity of the obtained propylene.

[0007] Preferably, the rectification tower includes a deheavy fraction tower and a deheavy fraction tower which are connected to each other, the deheavy fraction tower includes a deheavy fraction tower A and a deheavy fraction tower B which are connected to each other, a condenser is provided at the top of the deheavy fraction tower A, and a reboiler is provided at the bottom of the deheavy fraction tower and the deheavy fraction tower B. The rectification process includes the following steps S31 to S35. In S31, the light fraction column and the heavy fraction column are evacuated, propylene is fed from the upper middle part of the light fraction column, and when the feed liquid level reaches 50 to 80%, the reboiler of the light fraction column is turned on and the temperature is set to 25 to 45°C, light impurities are discharged from the top of the light fraction column at a rate of 1.5 to 2.5 kg / h, and the light components in the liquid phase are detected every hour. If they pass, they are injected into the heavy fraction column B at an injection rate of 15 to 18 kg / h. In S32, when the feed liquid level of the B deheavy fraction column reaches 50 to 80%, the reboiler of the B deheavy fraction column is turned on and the temperature is set to 25 to 30°C, the top pressure of the A deheavy fraction column is set to 0.3 to 0.6 MPa, and propylene flows from the top of the B deheavy fraction column into the kettle of the A deheavy fraction column. In S33, when the liquid level in the A deheavy fraction column reaches 25 to 40%, propylene is returned from the A deheavy fraction column to the top of the B deheavy fraction column, and the liquid level in the A deheavy fraction column is controlled to 25 to 30%. In S34, steps S32 to S33 are repeated to stably purify the heavy fraction column A and the heavy fraction column B for 2 to 3 hours, and then the diaphragm compressor is started to return the propylene from the packed manifold to the light fraction column, In S35, steps S31 to S32 are repeated to detect the gas phase discharged from the top of the A deheavy fraction column, and if it passes, it becomes purified propylene, and if it fails, steps S31 to S35 are continued to be repeated.

[0008] The above rectification step is different from the traditional rectification process. The solution divides the normal rectification tower into two sections with relatively high theoretical plates, and the C4 impurities can be completely removed in the adjusted rectification step, so that the purity of the obtained propylene is higher.

[0009] Preferably, the refining pressure in each of the light fractions removal column and the heavy fractions removal column is 0.3 to 0.6 MPa.

[0010] Preferably, the preparation steps of the modified porous carbon fiber include the following S21 to S23: S21. In the pretreatment of the carbon fiber, the carbon fiber is mixed with an aqueous solvent, and then ultrasonically or agitated for 10 to 30 minutes, and the resulting solid is filtered and dried at a constant temperature of 80 to 180°C. In the functionalization treatment in step S22, the carbon fibers obtained in step S21 are added to an aqueous solution of an oxidizing agent or a nitriding agent, and are stirred at 40 to 80° C. for modification treatment. In S23. functionalization heat treatment, the carbon fibers obtained in step S22 are washed with water, dried, and then heat-treated at 260 to 700° C. for 1 to 6 hours in an air or nitrogen gas atmosphere to obtain modified porous carbon fibers.

[0011] The carbon fiber is put into an aqueous solution or water of an oxidizing or nitriding agent to carry out the modification treatment, and after drying, it is followed by medium-high temperature heat treatment in air or nitrogen gas atmosphere. The prepared nitrogen-oxygen functionalized modified carbon fiber is a porous carbon material with a stable structure, which can adsorb and remove C4 hydrocarbon gas from the mixed gas of propylene product, and has very good industrial application prospects. In addition, the raw materials of the above preparation method are widely available and cheap, the preparation steps are simple, the modification conditions are mild, and the regeneration performance of the material is excellent.

[0012] In the above preparation method, the carbon fiber is first pretreated with an aqueous ethanol solution. The main purpose is to remove impurities on the surface and internal pores of the carbon fiber, such as ash and air pollutants, so as to make the subsequent modification process more satisfactory. In addition, this solution does not adopt a strong oxidizing agent in a severe acidic oxidation environment to oxidize the carbon fiber. This is mainly because such an oxidation method increases the oxygen-containing functional groups on the carbon surface, while destroying the pore structure of the carbon material, causing some pores to collapse or fuse into mesopores, sacrificing some adsorption sites, and weakening the pore-limiting effect on small molecule gases (such as C4 hydrocarbons). The carbon fiber of this solution is directly added to the aqueous solution of an oxidizing agent or nitriding agent, and the introduction of metal sites in the modification strategy is avoided, which reduces the polymerization of C4 hydrocarbon gas in the pores, ensures the working capacity and service life, and has the advantages of being environmentally friendly and easy to regenerate.

[0013] In step S2, when the carbon fibers are modified with an oxidizing agent, an air atmosphere is used, whereas in step S2, when the carbon fibers are modified with a nitriding agent, a nitrogen gas atmosphere is used.

[0014] Preferably, the oxidizing agent comprises one of potassium persulfate, ammonium persulfate, sodium persulfate, hydrogen peroxide, and sodium hypochlorite. The oxidation means adopted in this solution is relatively mild and does not require additional acidic conditions. The oxidizing agent adopted is persulfate, hydrogen peroxide, sodium hypochlorite, etc., which can better coordinate the adsorption sites of micropores and the adsorption power of oxygen-containing functional groups under mild oxidation conditions.

[0015] Preferably, the nitriding agent comprises one of urea, sodium amide, glutamic acid, and glycine. The purpose of nitriding and oxidizing is the same, both of which are to introduce heteroatoms and increase the polarity of the material. In contrast, carbon fibers modified with nitriding agents usually have better chemical stability, especially water vapor stability, than carbon fibers modified with oxidizing agents.

[0016] Preferably, the solvent comprises one of ethanol, acetone, methanol, chloroform, with the most preferred solvent being ethanol.

[0017] Preferably, in step S23, when an air atmosphere is adopted, the air flow rate is 40-80 ml / min, the heat treatment temperature is 260-350°C, and the heat treatment time is 4-6 h. When a nitrogen gas atmosphere is adopted, the nitrogen gas flow rate is 40-60 ml / min, the heat treatment temperature is 550-700°C, and the heat treatment time is 1.5-2 h. The corresponding heat treatment temperature and heat treatment time are different in the air atmosphere and the nitrogen gas atmosphere. This solution limits the corresponding heat treatment parameters and flow rate conditions under the two atmospheres respectively to obtain a modified porous carbon fiber with better performance.

[0018] Preferably, in step S21, the drying temperature is 80-180°C, and the drying time is 8-10h. The drying process is mainly for removing the moisture in the carbon fiber. When the drying parameters are limited to the above ranges, the obtained carbon fiber is more favorable for the subsequent modification process.

[0019] Preferably, in step S21, the mass ratio of the carbon fiber to the ethanol aqueous solution is 1:5-20, and the mass ratio of ethanol to water in the ethanol aqueous solution is 1:4-10. The ethanol aqueous solution can be used to remove impurities on the surface or in the internal pores of the carbon fiber. When the mass ratio of the carbon fiber to the ethanol aqueous solution is limited to 1:5-20, the effect of removing impurities in the carbon fiber is better, and the subsequent modification process is further improved.

[0020] Preferably, the carbon fibers include at least one of polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, cellulose-based carbon fibers, polyimide-based carbon fibers, and polyvinylidene fluoride-based carbon fibers.

[0021] Preferably, in step S22, the concentration of each of the oxidizing agent aqueous solution and the nitriding agent aqueous solution is 0.2 to 1.5 mol / L, the stirring temperature is 40 to 80° C., and the stirring time is 6 to 12 hours.

[0022] Compared with the prior art, the propylene purification method of the present invention has the following beneficial effects: 1. In this propylene purification method, functionalized porous carbon fiber is first used to pre-adsorb impurities in propylene, and a large amount of C4 hydrocarbon impurities is removed with relatively low energy consumption, reducing the burden of the subsequent distillation process and obtaining propylene with relatively high purity. In the subsequent rectification step, a normal rectification tower is divided into two sections with relatively high theoretical plates, so that the hydrocarbon impurities can be completely removed and the purity of the obtained propylene is higher.

[0023] 2. In the preparation of the above modified porous carbon fiber, the widely available and inexpensive porous carbon fiber is used as the raw material, and under the condition of the presence of an oxidizing agent or a nitriding agent, a mild modification method and subsequent further heat treatment activation process are used to prepare an adsorbent with high selectivity and high adsorption capacity, which has the characteristic of preferentially adsorbing C4 hydrocarbon gas. Nitrogen functional groups and oxygen functional groups are introduced without destroying the adsorption site, improving the adsorption ability for C4 hydrocarbon gas, and can adsorb and remove C4 hydrocarbon gas from the propylene product gas mixture. The modified porous carbon fiber can be used to purify the propylene product gas, has a C4 hydrocarbon gas adsorption capacity of more than 2.5 mmol / g, has a stronger adsorption ability than propylene, and can remove the C4 hydrocarbon gas in the outlet gas to a relatively low level. This adsorbent also has the advantages of stable structure and low cost, and is an adsorption separation material that is excellent in adsorbing and removing C4 hydrocarbon gas from the propylene product gas mixture. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The following clearly and completely describes the technical solutions according to the embodiments of the present invention. Of course, the embodiments described herein are only a part, not all, of the embodiments of the present invention. All other embodiments that a person skilled in the art can obtain based on the embodiments of the present invention without creative work should be included in the protection scope of the present invention.

[0025] In addition, the technical solutions in each embodiment can be combined with each other, but they should be based on what those skilled in the art can implement. If the combination of technical solutions appears to be contradictory or cannot be realized, such combination of technical solutions should be deemed not to exist and not within the protection scope claimed by the present invention.

[0026] The method for purifying propylene includes the following steps S1 to S3. In S1, molecular sieves are employed to remove water from the propylene to be purified, and the molecular sieves are activated at 300-400°C for 12-24h before use. Specifically, propylene from the raw material tank is fed in gas phase, and molecular sieves are adopted to remove water. The outlet water content is required to be lower than 0.5ppm. If it fails the outlet detection, it needs to be returned to the adsorber for secondary removal. The purification pressure is 0.3-0.6Mpa, and the adsorption temperature is less than 50℃.

[0027] In S2, the propylene obtained in step S1 is adsorbed by the modified porous carbon fiber. Specifically, a. the absorber is heated and evacuated, the temperature is controlled to 120-160°C, and then cooled to 25-35°C after controlling the temperature to 120-160°C and maintaining it for 0.5-1h. Here, the absorber is filled with modified carbon fiber. There are several specific filling methods, such as pressing the carbon fiber into a block and then stacking it, plugging the carbon fiber with a metal mesh screen, stacking the plugs one layer at a time and filling the tower body, and cutting and forming the carbon fiber felt, then wrapping and filling it. b. the raw material (propylene) is fed from the bottom of the absorber, the feed pressure is set to 0.3-0.5Mpa, and the light fraction product is discharged from the top of the absorber at a rate of 1.5-2.5kg / h. If it passes the online detection, it is introduced into the rectification device. c. absorber regeneration: repeat step a until the C4 component is no longer detected.

[0028] In S3, the propylene obtained in step S2 is put into a rectification column for rectification and impurity removal. Before rectification, most of the water and hydrocarbon impurities have already been removed, and the rectification pressure is reduced. Specifically, the rectification tower includes a light fraction tower and a heavy fraction tower that are connected to each other, and the heavy fraction tower includes a heavy fraction tower A and a heavy fraction tower B that are connected to each other, and a condenser is provided at the top of the heavy fraction tower A, and a reboiler is provided at the bottom of the light fraction tower and the heavy fraction tower B. The rectification process includes the following steps S31 to S35. In S31, the light fraction column and the heavy fraction column are evacuated, propylene is fed from the upper middle part of the light fraction column, and when the feed liquid level reaches 50 to 80%, the reboiler of the light fraction column is turned on and the temperature is set to 25 to 45°C. The refining pressure of both the light fraction column and the heavy fraction column is set to 0.3 to 0.6 MPa. Light impurities are discharged from the top of the light fraction column at a rate of 1.5 to 2.5 kg / h. The liquid phase light components are detected every hour. If they pass, they are injected into the heavy fraction column B, and the injection rate is 15 to 18 kg / h. Here, the indicators for which the liquid phase light fraction passes detection are O2≦1.0 ppm, N2≦2.0 ppm, CO2≦0.5 ppm, H2≦0.5 ppm, and CH4≦0.5 ppm.

[0029] In S32, when the feed liquid level of the B deheavy fraction column reaches 50 to 80%, the reboiler of the B deheavy fraction column is turned on and the temperature is set to 25 to 30°C, the top pressure (refining pressure) of the A deheavy fraction column is set to 0.3 to 0.6 MPa, and propylene flows from the top of the B deheavy fraction column into the kettle of the A deheavy fraction column.

[0030] In S33, when the liquid level in the A deheavy fraction column reaches 25 to 40%, propylene is returned from the A deheavy fraction column to the top of the B deheavy fraction column, and the liquid level in the A deheavy fraction column is controlled to 25 to 30%.

[0031] In S34, steps S32 to S33 are repeated to stably purify the A deheavy fraction tower and the B deheavy fraction tower for 2 to 3 hours, and then the diaphragm compressor is started to return propylene from the filling manifold to the light fraction tower. (The propylene from the A deheavy fraction tower is sent to the manifold by the diaphragm compressor, and the manifold has a pipeline that returns to the light fraction tower. The propylene returned from the manifold can be detected online, and if it passes the detection in the manifold, it can be filled, and if it fails, it is returned to the light fraction tower and re-rectified.)

[0032] In S35, steps S31 to S32 are repeated to detect the gas phase discharged from the top of the A deheavy fraction column, and if it passes, it becomes purified propylene, and if it fails, steps S31 to S35 are continued to be repeated.

[0033] Here, the indicators of propylene that pass detection after going through the above steps include: C3H6 purity ≥ 99.999%, O2 ≤ 1.0 ppm, N2 ≤ 2.0 ppm, CO2 ≤ 0.5 ppm, H2 ≤ 0.5 ppm, CH4 ≤ 0.5 ppm, C2H6 ≤ 0.5 ppm, C2H4 ≤ 0.5 ppm, C3H8 ≤ 5.0 ppm, OHC ≤ 1.0 ppm, H2O ≤ 0.2.0 ppm.

[0034] The above propylene rectification purification adopts a continuous rectification process of first removing light fractions and then removing heavy fractions, and includes a light fraction removal tower and a heavy fraction removal tower. Propylene (boiling point -47.7 ° C) and propane (boiling point -42.1 ° C) have close boiling points, very close relative volatility, difficult to separate, and very close molecular properties, and the selectivity of ordinary adsorbents is very poor. The present invention optimizes the rectification equipment and rectification operation, and focuses on removing propane impurities in the heavy fraction removal tower. Since the boiling point difference between propylene and propane is small and the separation requirements are high, and the heavy fraction removal tower is relatively expensive, the heavy fraction removal tower is divided into two towers, heavy fraction removal tower A and heavy fraction removal tower B, and a condenser is installed at the top of the heavy fraction removal tower A and a reboiler is installed at the bottom of the heavy fraction removal tower B. The top of the B deheavy fraction column enters the tank of the A deheavy fraction column, and the liquid phase propylene from the A deheavy fraction column is returned to the top of the B deheavy fraction column by a liquid pump.

[0035] In addition, the conventional rectification tower only includes a de-light fraction tower and a de-heavy fraction tower, and the de-heavy fraction tower is not divided into two sections, so the removal effect of impurities, especially propane, is ordinary. The initial propane content in the raw material is 2800 PPM, and the propane content in the gas phase obtained after circulation in the rectification tower is still several hundred PPM. Meanwhile, the above rectification process of this solution can maintain the propane content in the gas phase obtained after circulation in the rectification tower below 2 PPM. If the purification pressures of the de-light fraction tower, the A de-heavy fraction tower and the B de-heavy fraction tower are set to 0.5-0.6 MPa, 0.37-0.45 MPa and 0.3-0.4 MPa, respectively, and the liquid levels of the A de-heavy fraction tower and the B de-heavy fraction tower in step S33 are set to 35-38% and 25-26%, respectively, the propane content in the gas phase obtained after circulation in the rectification tower can be reduced to below 1 PPM.

[0036] The preparation of the modified porous carbon fiber includes the following steps S21 to S23. S21. In the pretreatment of the carbon fiber, the carbon fiber is mixed with an aqueous ethanol solution, and then ultrasonically or agitated for 10 to 30 minutes. After filtration, the obtained solid is dried at a constant temperature of 80 to 180°C to remove impurities, and the drying time is 8 to 10 hours. Here, the mass ratio of the carbon fibers to the ethanol aqueous solution is 1:5-20. The mass ratio of ethanol to water in the ethanol aqueous solution is 1:4-10.

[0037] In the functionalization treatment in step S22, the carbon fibers obtained in step S21 are added to an aqueous solution of an oxidizing agent or a nitriding agent, and are stirred at 40 to 80° C. for modification treatment. Here, the concentration of the oxidizing agent aqueous solution or the nitriding agent aqueous solution is 0.2 to 1.5 mol / L, the stirring temperature is 40 to 80° C., and the stirring time is 6 to 12 hours.

[0038] S23. In the functionalization heat treatment, the carbon fibers obtained in step S22 are washed with water, dried (at a temperature of 100 to 130°C for 6 to 10 hours), and then heat-treated in a tubular furnace at 260 to 700°C for 1 to 6 hours under an air or nitrogen gas atmosphere to obtain modified porous carbon fibers.

[0039] In this regard, the present solution is verified by providing the following example. <Example 1>

[0040] The preparation of the modified porous carbon fiber includes the following steps S21 to S23. S21. In the pretreatment of the carbon fiber, the carbon fiber (polyacrylonitrile carbon fiber) was mixed with an aqueous ethanol solution, and then ultrasonically treated for 10 min. After filtration, the obtained solid was dried at a constant temperature of 130 ° C., and the drying time was 8 h. Here, the mass ratio of the carbon fibers to the ethanol aqueous solution was 1:12, and the mass ratio of ethanol to water in the ethanol aqueous solution was 1:6.

[0041] In the functionalization process in step S22, the carbon fibers obtained in step S21 were added to an aqueous solution of an oxidizing agent (potassium persulfate) and stirred at 40°C for modification. Here, the concentration of the oxidant aqueous solution was 1.2 mol / L, the stirring temperature was 40° C., and the stirring time was 11.5 hours.

[0042] In the functionalization heat treatment step S23, the carbon fiber obtained in step S22 was washed with water, dried, and then heat-treated at 300°C for 6h in an air atmosphere to obtain a modified porous carbon fiber. Here, the air flow rate was 65ml / min. <Example 2>

[0043] The preparation of the modified porous carbon fiber includes the following steps S21 to S23. S21. In the pretreatment of the carbon fiber, the carbon fiber was mixed with an aqueous ethanol solution and then stirred for 20 minutes. After filtration, the obtained solid was dried at a constant temperature of 100°C for 9 hours. Here, the mass ratio of the carbon fibers (polyimide-based carbon fibers) to the aqueous ethanol solution was 1:8, and the mass ratio of ethanol to water in the aqueous ethanol solution was 1:4.

[0044] In the functionalization process, the carbon fibers obtained in step S21 were added to an aqueous solution of a nitriding agent (glutamic acid) and stirred at 67°C for modification, and the stirring time was 10 h. Here, the concentration of the aqueous nitriding agent solution was 0.8 mol / L.

[0045] In the functionalization heat treatment step S23, the carbon fiber obtained in step S22 was washed with water, dried, and then heat-treated at 680°C for 2h in a nitrogen gas atmosphere to obtain a modified porous carbon fiber. Here, the flow rate of the nitrogen gas was 60ml / min. <Example 3>

[0046] The preparation of the modified porous carbon fiber includes the following steps S21 to S23. S21. In the pretreatment of the carbon fiber, the carbon fiber (pitch-based carbon fiber) was mixed with an aqueous ethanol solution, and then ultrasonically treated for 30 min. After filtration, the obtained solid was dried at a constant temperature of 160 ° C., and the drying time was 10 h. Here, the mass ratio of the carbon fibers to the ethanol aqueous solution was 1:19, and the mass ratio of ethanol to water in the ethanol aqueous solution was 1:8.

[0047] In the functionalization process in step S22, the carbon fibers obtained in step S21 were added to an aqueous solution of an oxidizing agent (hydrogen peroxide) and stirred at 75°C for modification. Here, the concentration of the oxidizing agent aqueous solution was 1.5 mol / L, the stirring temperature was 60° C., and the stirring time was 7 hours.

[0048] In the functionalization heat treatment step S23, the carbon fiber obtained in step S22 was washed with water, dried, and then heat-treated at 270°C for 5h in an air atmosphere to obtain a modified porous carbon fiber. Here, the air flow rate was 45ml / min.

[0049] In Examples 1 to 3, the modified carbon fiber obtained by the above-mentioned modification step was used to adsorb impurities in propylene, and the C4 impurities contained in the obtained gas-phase propylene were 0.3 PPM, 0.4 PPM, and 0.6 PPM, respectively. In addition, after several experiments and changing the parameters, the modified carbon fiber obtained by the above-mentioned modification step adsorbed propylene, and the C4 impurities in the obtained gas phase could be reduced to 0.9 PPM or less, and the parameters were optimized, so that the C4 impurities in the gas phase could be reduced to 0.2 PPM.

[0050] Under the same parameters, steps and reforming conditions as in Example 1 above, when the pretreatment is not performed, that is, step S21 is canceled, the C4 impurities contained in the gas phase propylene obtained after adsorption by the modified carbon fiber is about 13 PPM. This shows that not pretreating the porous modified carbon fiber is disadvantageous to the reforming effect, and is likely to cause a relatively poor removal degree of C4 impurities when the subsequent modified carbon fiber is adsorbed.

[0051] With the same parameters, steps and modification conditions as in Example 1 above, simply replacing the ethanol aqueous solution in the pretreatment of step S21 with deionized water, the C4 impurities in the gaseous propylene obtained after adsorption by the modified carbon fiber were about 7.3 PPM. This shows that the use of deionized water for pretreatment before carbon fiber modification is not favorable to the complete removal of surface and pore impurities, and the modification effect is average.

[0052] The parameters, steps and modification conditions are the same as those of Example 1 above, but the atmosphere during the functionalization treatment in step S22 is adjusted to an acidic atmosphere, that is, the carbon fiber obtained in step S21 is added to an aqueous solution of an oxidizing agent in an acidic environment, first washed with dilute hydrochloric acid, and then washed with water in step S23. After adsorption by the modified carbon fiber, the C4 impurities contained in the gas phase propylene obtained is about 5.4 PPM. This shows that when the modification treatment is performed under acidic conditions, the removal effect of the modified carbon fiber on the C4 impurities is relatively poor.

[0053] The parameters, steps and modification conditions are the same as those of Example 1 above, but an acid washing step is simply added during the functionalization treatment in step S22, that is, the carbon fiber obtained in step S21 is added to an aqueous solution of an oxidizing agent, and first washed (acid washed) with dilute hydrochloric acid, and then washed with water in step S23. After adsorption by the modified carbon fiber, the C4 impurities contained in the gas phase propylene obtained is about 1.3 PPM. This shows that washing the modified carbon fiber with dilute hydrochloric acid destroys part of the nitrogen oxygen functional groups, which causes the modification effect of the carbon fiber to be relatively poor. When an air atmosphere was used, the air flow rate was 40-80 ml / min, the heat treatment temperature was 260-350°C, and the heat treatment time was 4-6 hours. When a nitrogen gas atmosphere was used, the nitrogen gas flow rate was 40-60 ml / min, the heat treatment temperature was 550-700°C, and the heat treatment time was 1.5-2 hours.

[0054] The heat treatment temperature of 300°C in Example 1 (which is a heat treatment in an air atmosphere, and an oxidizing agent is adopted to modify the carbon fiber) was changed, and the remaining steps and parameters are all consistent with Example 1. The specific temperatures were adjusted to 260°C, 280°C, and 350°C, respectively. After adsorption by the modified carbon fiber, the C4 impurities contained in the obtained gas-phase propylene were 0.8PPM, 0.2PPM, and 0.5PPM, respectively. This shows that in the oxidation modification process, with a suitable heat treatment temperature of 280-350°C, on the one hand, the stability of the carbon structure can be maintained in an air atmosphere, and on the other hand, the oxidation effect can be improved to optimize the C4 removal effect, and the C4 impurities contained in the gas-phase propylene can be reduced to 0.5PPM or less.

[0055] The heat treatment temperature of 680°C in Example 2 (which is a heat treatment in a nitrogen gas atmosphere, and a nitriding agent is used to modify the carbon fiber) was changed, and the remaining steps and parameters are all consistent with Example 2. The specific temperatures were adjusted to 550°C, 600°C, and 700°C, respectively. After adsorption by the modified carbon fiber, the C4 impurities contained in the obtained gas-phase propylene were 0.9PPM, 0.7PPM, and 0.4PPM, respectively. This shows that in the nitriding modification process, the appropriate heat treatment temperature of 680-700°C can optimize the C4 removal effect, and the C4 impurities contained in the gas-phase propylene can be reduced to 0.4PPM or less.

[0056] The oxidizing agent includes one of potassium persulfate, ammonium persulfate, sodium persulfate, hydrogen peroxide, and sodium hypochlorite. The nitriding agent includes one of urea, sodium amide, glutamic acid, and glycine. The carbon fiber includes at least one of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, cellulose-based carbon fiber, polyimide-based carbon fiber, and polyvinylidene fluoride-based carbon fiber.

[0057] As in Example 1, the carbon fiber was modified using potassium persulfate as an oxidizing agent to obtain a modified carbon fiber, which adsorbed impurities in propylene. The C4 impurities contained in the obtained gaseous propylene were about 0.3 ppm, and the capacity loss measured in a water vapor stability test was 9%.

[0058] Under the same steps and modification conditions as those of the carbon fiber of Example 1 above, when the oxidizing agent potassium persulfate was simply replaced with the nitriding agent urea and the nitriding agent sodium amide, respectively (heat treatment parameters were heat treatment time 2h, nitrogen gas flow rate 50ml / min), the C4 impurities contained in the gas phase propylene obtained after adsorbing the propylene impurities were 0.6PPM and 0.5PPM, respectively, and the volume loss measured in the steam stability test of the porous modified carbon fiber was 4% and 3%, respectively. This shows that when the porous carbon fiber is nitrided and modified using a nitriding agent, the resulting adsorbent modified carbon fiber has better steam stability.

[0059] The water vapor stability test process involves leaving the porous carbon fiber under humid conditions (80% RH) for 5 days and comparing the degree of loss in (static) adsorption amount before and after the humidification treatment.

[0060] The above is merely a preferred embodiment of the present invention, and does not limit the scope of protection of the present invention. Based on the idea of ​​the present invention, the equivalent structural modifications made by utilizing the contents of the specification of the present invention, or the direct / indirect application to other related technical fields should be included in the scope of protection of the present invention.

Claims

1. A method for purifying propylene, comprising the following steps S1 to S3: In S1, a molecular sieve is used to remove water from the propylene to be purified, and the molecular sieve is activated at 300-400°C for 12-24h before use; In step S2, the modified porous carbon fiber is used to adsorb the propylene obtained in step S1; In step S3, the propylene obtained in step S2 is introduced into a rectification column and subjected to rectification treatment.

2. the rectification tower includes a deheavy fraction tower and a deheavy fraction tower which are connected to each other, the deheavy fraction tower includes a deheavy fraction tower A and a deheavy fraction tower B which are connected to each other, a condenser is provided at the top of the deheavy fraction tower A, and a reboiler is provided at the bottom of both the deheavy fraction tower and the deheavy fraction tower B, The rectification process includes the following steps S31 to S35: In S31, the light fraction column and the heavy fraction column are evacuated, propylene is supplied from the upper middle part of the light fraction column, and when the supply liquid level reaches 50-80%, the reboiler of the light fraction column is turned on and the temperature is set to 25-45°C, light impurities are discharged from the top of the light fraction column at a rate of 1.5-2.5 kg / h, and the liquid phase light components are detected every hour. If they pass, they are injected into the heavy fraction column B at an injection rate of 15-18 kg / h. In S32, when the feed liquid level of the B deheavy fraction column reaches 50-80%, the reboiler of the B deheavy fraction column is turned on and the temperature is set to 25-30° C., and propylene flows from the top of the B deheavy fraction column into the kettle of the A deheavy fraction column, In S33, when the liquid level of the A deheavy fraction column reaches 25-40%, propylene is returned from the A deheavy fraction column to the top of the B deheavy fraction column, and the liquid level of the A deheavy fraction column is controlled to 25-30%, In S34, steps S32 to S33 are repeated to stably purify the heavy fraction column A and the heavy fraction column B for 2 to 3 hours, and then the diaphragm compressor is started to return the propylene from the packed manifold to the light fraction column, The method for purifying propylene according to claim 1, characterized in that in S35, steps S31 to S32 are repeated to detect the gas phase discharged from the top of the A deheavy fraction column, and if the gas phase passes the detection, it becomes purified propylene, and if the gas phase fails the detection, the repetition of steps S31 to S35 is continued.

3. The method for purifying propylene according to claim 2, wherein the refining pressures of the light fraction removing column and the heavy fraction removing column are both 0.3 to 0.6 MPa.

4. The preparation steps of the modified porous carbon fiber include the following steps S21 to S23: S21. In the pretreatment of carbon fibers, the carbon fibers are mixed with an aqueous solvent solution, and then subjected to ultrasonic or stirring treatment for 10 to 30 minutes. After filtration, the obtained solid is dried at a constant temperature of 80 to 180 ° C. S22. In the functionalization process, the carbon fibers obtained in step S21 are added to an aqueous solution of an oxidizing agent or a nitriding agent, and the mixture is stirred at 40 to 80° C. to perform a modification process; S23. In the functionalization heat treatment, the carbon fiber obtained in step S22 is washed with water, dried, and then heat-treated at 260 to 700°C for 1 to 6 hours in an air or nitrogen gas atmosphere to obtain a modified porous carbon fiber.

5. the oxidizing agent comprises one of potassium persulfate, ammonium persulfate, sodium persulfate, hydrogen peroxide, and sodium hypochlorite; 5. The method of claim 4, wherein the nitriding agent comprises one of urea, sodium amide, glutamic acid, and glycine.

6. 5. The method of claim 4, wherein the solvent comprises one of ethanol, acetone, methanol, and chloroform.

7. In step S23, when an air atmosphere is adopted, the air flow rate is 40 to 80 ml / min, the heat treatment temperature is 260 to 350° C., and the heat treatment time is 4 to 6 h; The method for purifying propylene according to any one of claims 4 to 6, characterized in that, when a nitrogen gas atmosphere is adopted, the flow rate of the nitrogen gas is 40 to 60 ml / min, the heat treatment temperature is 550 to 700 ° C, and the heat treatment time is 1.5 to 2 h.

8. In step S21, the drying temperature is 80 to 180° C., and the drying time is 8 to 10 hours. The method for purifying propylene according to any one of claims 4 to 6, characterized in that a mass ratio of the carbon fiber to the aqueous ethanol solution is 1:5 to 20, and a mass ratio of ethanol to water in the aqueous ethanol solution is 1:4 to 10.

9. 5. The method for purifying propylene according to claim 4, wherein the carbon fibers include at least one of polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, cellulose-based carbon fibers, polyimide-based carbon fibers, and polyvinylidene fluoride-based carbon fibers.

10. The method for purifying propylene according to claim 4, characterized in that in step S22, the concentration of the oxidizing agent aqueous solution or the nitriding agent aqueous solution is 0.2 to 1.5 mol / L, the stirring temperature is 40 to 80° C., and the stirring time is 6 to 12 h.