CN103254932A - Process for extracting C4-C6 normal paraffins and co-producing isopentane and isomeric hexane from light naphtha - Google Patents

Abstract

The invention relates to a chemical separation process, in particular to a process for extracting C4-C6 normal alkanes in light naphtha and co-producing isopentane and isohexane. The invention adopts multi-tower pressure swing adsorption and rectification separation coupling process. The gas phase C4~C6 normal isomeric hydrocarbon mixed raw material is passed into the adsorption tower for adsorption and separation. After the adsorption is completed, the gas phase C7~C9 normal alkanes are used as the desorbent to desorb the bed layer, and the desorbed material enters the rectification tower to separate the product C4~ C6 normal paraffins and desorbent C7～C9 normal paraffins, the desorbent is recycled, and then the unadsorbed C4～C6 isoparaffins are used to regenerate the adsorption tower that adsorbs C7～C9 normal paraffins, and the regenerated materials are passed through two Separation by rectification to obtain high-purity desorbent C7-C9 normal paraffins and high-purity isopentane and isohexane. The invention can effectively separate normal isoparaffins, and the adsorbent is easy to regenerate, the process flow is simple, the economic benefit is high, and the energy consumption is greatly reduced compared with other desorption processes.

Description

Extraction of C4-C6 normal paraffins in light naphtha and co-production of isopentane and isohexane

Technical field:

The invention relates to a chemical separation process, in particular to a process for extracting C4-C6 normal alkanes in light naphtha and co-producing isopentane and isohexane.

Background technique:

Light naphtha is one of the products of hydrocracking in the aromatics complex. Since most hydrogen production units use natural gas to produce hydrogen, light naphtha is mainly used as raw material for cracking ethylene production and gasoline blending material. Because the isoparaffins in the naphtha are too high, it is not suitable as a raw material for steam cracking to produce ethylene; as a gasoline blending material, because of its high content of n-paraffins, it affects the octane number of oil products. Therefore, the rational separation of n-isoparaffins in light naphtha is of great significance for improving the comprehensive utilization value of light naphtha, integrating optimized light naphtha resources, and increasing the economic benefits of petrochemical enterprises.

CN101148390A describes the process of extracting high-purity n-hexane by pressure swing adsorption. It adopts the four-tower heating and pressure swing adsorption process to realize the desorption of the adsorbent n-hexane under vacuum conditions, and obtain n-hexane with a purity greater than 99% after being separated by a rectification tower .

CN101134703A invented the process of extracting n-heptane and co-producing n-octane by pressure swing adsorption, adopting multi-tower heating and pressure swing adsorption process, adding inert gas for purging while vacuum desorption, so that the bed layer can be fully desorbed, and co-production can be obtained N-heptane and n-octane with a purity greater than 99%.

CN1634812A proposes a method for separating normal alkanes from C5～C6 alkane isomerization products, realizes the separation under liquid phase conditions, adopts rectification method to remove isopentane in the raw material, and then uses adsorption method to adsorb and separate normal isopentane For the mixture of paraffins, n-octane is used as the liquid phase desorbent to analyze the bed.

Both CN101148390A and CN101134703A are the inventions of our laboratory. Since the use of inert gas desorption requires the subsequent condensation temperature to be below zero, the condensation pressure is high, and the energy consumption and equipment investment are relatively large. However, the combined desorption process using high-carbon C4-C6 normal alkanes in the gas phase as a desorbent and isoparaffins as a regenerating agent has not been reported, and the process can co-produce high-purity isopentane and isohexane as required, reducing energy consumption. greatly reduced, so on the basis of laboratory research, the invention of the process.

Invention content:

The object of the present invention is to provide a process for extracting C4-C6 normal paraffins in light naphtha and co-producing isopentane and isohexane in order to improve the deficiencies of the prior art. The invention adopts multi-tower pressure swing adsorption and rectification separation coupling process.

The technical scheme of the present invention is: a process for extracting C4-C6 normal paraffins in light naphtha and co-producing isopentane and isohexane, starting from the first adsorption tower T1 adsorption, four towers are simultaneously adsorbed and desorbed continuously , the specific steps are as follows: (1) Adsorption, C4~C6 n-isoparaffin mixed raw material is output from the raw material storage tank V3, and enters the first adsorption tower T1 for adsorption after gasification, the n-paraffin in the raw material is adsorbed, and the unadsorbed group The first adsorption tower T1 is output from the top of the first adsorption tower T1, and the second adsorption tower T2 that has completed the pressure equalization rise is regenerated; (2) The equal pressure drop, the first adsorption tower T1 that has completed adsorption and the third adsorption tower T3 that has completed desorption (3) bed replacement, use inert gas to replace the material in the dead space in the first adsorption tower T1, and the material is condensed to obtain the middle distillate; (4) desorption, C7 ~ C9 n-paraffin single component or two or more After gasification, the mixed components enter the first adsorption tower T1 where the replacement is completed, and the adsorbed C4-C6 normal alkanes are desorbed, and the desorbed materials are input into the second rectification tower T6; (5) The average pressure rises, and the adsorption is completed at this time The pressure equalization between the third adsorption tower T3 and the first adsorption tower T1 that has completed the desorption; (6) Bed regeneration, using the unadsorbed isoparaffins at the top of the fourth adsorption tower T4 that is being adsorbed as a regeneration agent, desorbed The C7-C9 normal alkanes adsorbed in the first adsorption tower T1 realize the regeneration of the adsorbent in the first adsorption tower T1, and the obtained regenerated materials enter the first rectification tower T5; (7) Combined rectification, the first adsorption tower The desorption material obtained in T1 is input into the second rectification tower T6, and the product C4-C6 normal paraffins are obtained from the top of the tower, and the desorbent C7-C9 normal paraffins are obtained from the tower bottom, and the C7-C9 normal paraffins are recycled; the first adsorption tower T1 The obtained regenerated material enters the first rectification tower T5, C4-C6 isoparaffins are obtained at the top of the tower, and the desorbent C7-C9 normal paraffins are obtained from the tower bottom for recycling, and the C4-C6 isoparaffins at the top of the tower pass through the third rectification tower T7 is further rectified to obtain isopentane and isohexane products.

The more detailed steps are as follows: (1) Adsorption, the C4-C6 alkane raw material in the raw material storage tank V3 is gasified by the second flow pump P3 and the third heat exchanger E3, and then enters the first adsorption tower T1 from the first pipeline 1 for adsorption (During the adsorption process of T1, the second adsorption tower T2 performs pressure equalization and regeneration successively, the third adsorption tower is undergoing desorption, and the fourth adsorption tower performs pressure equalization and replacement successively), C4～C6 normal alkanes are adsorbed, C4 ~C6 isoparaffins enter the second adsorption tower T2 for regeneration; (2) equal pressure drop, the first adsorption tower T1 that has completed the adsorption and the third adsorption tower T3 that has completed the desorption pass through the fifth pipeline 5 to equalize the pressure drop; (3) Bed replacement, the inert gas in the replacement gas nitrogen storage tank V2 passes through the fourth pipeline 4 to replace the material in the dead space in the first adsorption tower T1, and the material passes through the third pipeline 3, the eighth pipeline 8 and the eleventh pipeline 11 Enter the intermediate product storage tank V5; (4) Desorption, desorbent C7 ~ C9 normal paraffin desorbent (single component or two or more mixed components) in the desorbent C7 ~ C9 normal paraffin storage tank V1 passes through the first advection The pump P1 passes through the first heat exchanger E1 for gasification and heat exchange, then enters the first adsorption tower T1 that has just completed the replacement through the sixth pipeline 6, and desorbs the adsorbed C4-C6 normal alkanes, and the obtained desorbed material passes through the second pipeline 2 and the ninth pipeline 9 enter the second rectification tower T6; (5) equal pressure rise, at this time, the third adsorption tower T3 that has completed the adsorption is equal to the pressure rise of the first adsorption tower T1 that has completed the desorption through the fifth pipeline 5; ( 6) Bed regeneration. At this time, the fourth adsorption tower T4 is adsorbing, and the unadsorbed C4-C6 isoparaffin is mixed with the regenerant in the gasified regenerant isoparaffin storage tank V4 through the fifth pipeline 5. In the first adsorption tower T1, mixed gaseous C4-C6 isoparaffins are used as a regeneration agent to regenerate the first adsorption tower T1 that has just completed pressure equalization, and the C7-C9 normal paraffins adsorbed in the first adsorption tower T1 are purged and desorbed , to realize the regeneration of the adsorbent in the first adsorption tower T1, and the obtained regenerated material enters the first rectification tower T5 through the third pipeline 3, the eighth pipeline 8 and the twelfth pipeline 12; (7) combined rectification, the first The desorbed material obtained during the desorption of the adsorption tower T1 enters the second rectification tower T6, and the C4-C6 normal paraffins with a product purity of 99.0% to 99.5% are obtained from the top of the second rectification tower T6 and enter the C4-C6 normal paraffin product storage tank V6, the C7-C9 normal paraffin desorbent with a purity of 99.0% to 99.5% is obtained from the bottom of the second rectification tower T6, and the C7-C9 normal paraffin is input into the desorbent C7-C9 normal paraffin storage tank through the seventh pipeline 7 V1 is for recycling; the regenerated material obtained when the bed layer of the first adsorption tower is regenerated is input into the first rectification tower T5, and the top of T5 can obtain C4~C6 isoparaffins with a purity of 99.0%~99.5%, and some C4~C6 isoparaffins The C4～C6 isoparaffins diverted to the C4～C6 isoparaffin product storage tank V7, and the C4～C6 isoparaffins in the C4～C6 isoparaffin product storage tank V7 are then input into the V4 storage tank as a regeneration agent, and the purity of the T5 tower kettle is 99.0%～99.5 % of C7～C9 normal alkanes, C The 7-C9 normal paraffins are input into V1 through the seventh pipeline 7 for recycling, and the C4-C6 iso-paraffins that are not diverted to the C4-C6 iso-paraffin product storage tank V7 enter the third rectification tower T7, and the purity is obtained at the top of T7. The 99.0%-99.8% isopentane product is input into the isopentane storage tank V9, and the T7 tower kettle obtains the iso-hexane product with a purity of 99.5%-99.8%, and the iso-hexane product is input into the iso-hexane storage tank V8. So far, a pressure swing adsorption cycle is completed, and the four adsorption towers are continuously carried out simultaneously.

In the present invention, the C4-C6 alkane raw material is preferably hydrocracked naphtha, reformed tops or catalytic cracked naphtha, petroleum distillate at 60°C-165°C.

In the adsorption process of the present invention, the adsorption temperature is preferably 150-450°C, the gas phase space velocity is 40-2000h ^-1 , and the adsorption pressure is 0-3Mpa (gauge pressure).

The inert gas for bed replacement in the present invention is preferably nitrogen, helium, carbon dioxide or hydrogen, and the space velocity is 15-500h ^-1 .

In the desorption process of the present invention, the desorption temperature is preferably 120-450°C, the pressure is 0-1Mpa (gauge pressure), the gas phase space velocity is 40-2000h ^-1 , the desorption method used is purging desorption, and the desorption agent used is C7～ C9 single component normal alkanes or two or more mixed components.

The regenerating agent for bed regeneration in the present invention is preferably inert gas _N2 , _H2 , He, _CO2 or C4-C6 isoparaffins, more preferably C4-C6 isoparaffins, and the regeneration method is purge regeneration, regeneration The temperature is preferably 120-450°C, the pressure is preferably 0-2Mpa (gauge pressure), and the gas phase space velocity is preferably 40-2000h ^-1 .

The present invention uses rectification tower T6 to rectify and separate C4-C6 normal paraffins and C7-C9 normal paraffins, the temperature of the tower bottom is preferably 80-200°C, the temperature of the tower top is preferably 50-200°C, and the number of theoretical plates is preferably 40 to 120 blocks, C4 to C6 normal alkanes with a product purity of 99.0% to 99.5% are obtained at the top of the tower, and C7 to C9 normal alkanes with a purity of 99.0% to 99.5% are obtained at the bottom of the tower. Input V1 through the seventh pipeline 7 to be recycled.

The present invention uses rectification tower T5 to rectify and separate C4-C6 isoparaffins and C7-C9 normal paraffins desorbent, the temperature of the tower bottom is 80-200°C, the temperature of the tower top is 60-200°C, and the number of theoretical plates is 35-120 C4-C6 isoparaffins with a purity of 99.0% to 99.5% are obtained from the top of the tower, and C7-C9 normal paraffins with a purity of 99.0% to 99.5% are obtained from the bottom of the tower, and the C7-C9 normal paraffins are input into V1 through pipeline 7 to be recycled .

The present invention uses rectification tower T7 to separate isopentane and isohexane, the temperature of the tower bottom is 50-200°C, the temperature of the tower top is 40-200°C, the number of theoretical plates is 40-150, and the purity of the tower top is obtained. 99.0% to 99.8% isopentane product, and the tower reactor can obtain isohexane product with a purity of 99.5% to 99.8%.

The process for separating C4-C6 normal isoparaffins by pressure swing adsorption is a combination of multi-tower pressure swing adsorption and rectification separation process. The multi-tower pressure swing adsorption process is preferably two to fourteen towers, and the best is the four towers pressure swing adsorption process.

Beneficial effect:

The invention is a combined desorption process in which high-carbon normal alkanes in the gas phase are used as desorption agents and isoparaffins are used as regeneration agents, and high-purity isopentane and isohexane are co-produced. Compared with traditional rectification separation, the energy consumption of adsorption separation is greatly reduced, and the separation degree of normal isoparaffins is high; compared with vacuum desorption, the safety of this process is remarkable; compared with inert gas purging desorption, the desorption rate of the present invention is obvious Accelerate and greatly reduce energy consumption. Therefore, this process has great industrialization advantages.

Description of drawings:

Fig. 1 is the process flow diagram of separation of normal isoparaffins of the present invention; Wherein T1 is the first adsorption tower, T2 is the second adsorption tower, T3 is the third adsorption tower, T4 is the fourth adsorption tower; T5 is the first rectification Tower, T6 is the second rectification tower, T7 is the third rectification tower; P1 is the first advection pump, P3 is the second advection pump, P4 is the third advection pump, P2 is the first mass flow meter; E1 is the first Heat exchanger, E2 is the second heat exchanger, E3 is the third heat exchanger, E4 is the fourth heat exchanger; V1 is the desorbent C7~C9 n-paraffin storage tank, V2 is the replacement gas nitrogen storage tank, V3 is the storage tank for raw materials, V4 is the isoparaffin storage tank for regeneration agent, V5 is the storage tank for intermediate products, V6 is the storage tank for C4~C6 normal paraffin products, V7 is the storage tank for C4~C6 isoparaffin products, and V8 is the storage tank for isoparaffins. Hexane storage tank, V9 is isopentane storage tank; 1 is the first pipeline, 2 is the second pipeline, 3 is the third pipeline, 4 is the fourth pipeline, 5 is the fifth pipeline, 6 is the sixth pipeline, 7 8 is the eighth pipeline, 9 is the ninth pipeline, 10 is the tenth pipeline, 11 is the eleventh pipeline, and 12 is the twelfth pipeline.

Fig. 2 is the variation curve of the mass fraction of the two components in the desorption material when n-heptane desorbs n-pentane.

Fig. 3 is the concentration change curve of n-heptane in the regenerated material when isoparaffin is regenerated to the bed.

Fig. 4 is the change curve of the mass fraction of C4-C6 normal alkanes in the desorption liquid when the liquid-phase n-heptane desorbs C4-C6 normal-alkanes and the gas-phase n-heptane desorbs C4-C6 normal-alkanes.

Detailed ways:

Implementation Case 1: A petrochemical enterprise hydrocracked light naphtha as raw material, and the main composition of light naphtha is shown in Table 1:

Table 1 Composition of Light Naphtha

Table 2 shows the time distribution of the PSA cycles in the four towers: one PSA cycle is 24 minutes, and the specific time distribution for each stage is shown in Table 2.

Table 2 Four-tower pressure swing adsorption cycle schedule

[Note]: A-adsorption, ED-average pressure drop, R-displacement, V-desorption, ER-average pressure rise, H-regeneration

According to the process flow diagram 1 of pressure swing adsorption separation of n-alkanes in light naphtha, adsorption: the light naphtha raw material in V3 storage tank is input into vaporization chamber E3 through advection pump P3, and the gas is vaporized under the conditions of 150°C and 0.4MPa (gauge pressure) Vaporization, gasified light naphtha enters T1 through pipeline 1; equal pressure drop, after the adsorption is completed, put the internal pressure of T1 into T2 through pipeline 5, the pressure of T1 tower drops to 0.18MPa, and the pressure of T2 tower rises to 0.2MPa ;Bed replacement, at this time, the nitrogen in the nitrogen storage tank V2 is measured by the flow meter P2 and then enters the preheater E2 at a space velocity of 30h ^-1 , preheated at 150°C and 0.4Mpa (gauge pressure), and replaced through the pipeline 4 The materials in the dead space of T1 are collected in storage tank 5 through pipelines 3, 8 and 11 to obtain the middle distillate; after the desorption and replacement are completed, the n-heptane in storage tank V1 is input into gasification chamber E1 through advection pump P1, at 150°C and Gasification under the condition of 0Mpa (gauge pressure), enter the adsorption column T1 through pipeline 6 at a space velocity of 40h ^-1 , desorb the C4~C6 normal alkanes that have been adsorbed, and the desorbed material enters the rectification tower T6 through pipelines 2 and 9 , the number of effective plates in the rectification tower T6 is 40, and C4-C6 normal alkanes with a purity of 99.5% and n-heptane with a purity of 99.4% are obtained. The n-heptane is transported to V1 for recycling through pipeline 7; The pressure of T3 is reduced to the T1 where the desorption is completed through the pipeline 5, and the pressure equalization of T1 is realized; the bed layer is regenerated, and the unadsorbed isoparaffins in the adsorbed T4 enter T1 through the pipeline 5, and are used for desorption and adsorption. Heptane realizes the regeneration of the bed, and the space velocity of the isoparaffin is 40h ^-1 . When the isoparaffin in T4 is insufficient, the isoparaffin in T4 is replenished through V4 to obtain fresh molecular sieves; combined rectification, the regeneration liquid passes through pipelines 3, 8 and 12 enters the rectifying tower T5, the number of effective plates of T5 is 35, and the isoparaffin with a purity of 99.3% is obtained from the top of the tower and the normal heptane with a purity of 99.3% is obtained from the bottom of the tower. The paraffins are then input into the rectification tower T7, the number of effective plates of T7 is 40, the purity of 99.3% isopentane is obtained at the top of the tower, and the purity of 99.7% isohexane is obtained at the bottom of the tower. So far, a pressure swing adsorption cycle is completed. In this order, the four adsorption towers are carried out continuously at the same time.

The concentration change curve of n-heptane desorbing n-pentane is shown in Figure 2, n-heptane can desorb n-pentane within the first 25 minutes, and n-heptane itself does not reach the breakthrough point.

When isoparaffins regenerate the bed, the change curve of the mass fraction of n-heptane in the regeneration material is shown in Figure 3. From Figure 3, it can be seen that the regeneration rate of isoparaffins to n-heptane is fast, and the bed regeneration rate reaches 90%. % above, to meet the requirements of the next cycle.

Table 3 is the purity of each product obtained after rectification.

Purity of each component after table 3 rectification

Implementation case 2: Separation of catalytic cracking naphtha in a petrochemical enterprise. Process flow is similar to example 1.

Adsorption temperature is 450°C, adsorption pressure is 3MPa (gauge pressure), desorption temperature is 450°C, desorption pressure is 1MPa (gauge pressure), desorption space velocity is 2000h ^-1 , regeneration temperature is 450°C, regeneration pressure is 2MPa (gauge pressure), regeneration space velocity 2000h-1, the desorbent is a mass mixed component of n-heptane and n-hexane, and after the desorption is completed, use C4-C6 isoparaffins to regenerate the bed. The number of effective plates of the rectification towers T5, T6 and T7 is 120, 120 and 150 respectively, and the final product purity is shown in Table 4.

The purity of each component after table 4 rectification

Implementation case 3: Using a factory reformed topping oil as raw material, the composition of the raw material is shown in Table 5.

Table 5 Composition of reformed top oil

The four-tower pressure swing adsorption separation process is still used, and the adsorption process is similar. During desorption, n-octane with stronger adsorption force is used as the desorption agent, and the desorption rate and desorption effect of the gas phase and the liquid phase are compared. Bed regeneration uses isopentane as regenerant.

When the desorbent with the same liquid phase flow rate desorbs, the gas phase desorption and the direct liquid phase desorption rate comparison after gasification are shown in Figure 4, as can be seen from Figure 4, the gas phase desorption rate is significantly greater than the liquid phase desorption rate, The maximum desorption rate was reached within 5 minutes, while the liquid phase desorption rate was small, and the maximum desorption rate had not been reached after 25 minutes.

Implementation case 4: Catalyzed hydrogenated naphtha from a petrochemical enterprise was used as raw material. Similar to Example 1, using n-octane as desorbent, desorb under the conditions of desorption temperature 300°C, pressure 0.2MPa (gauge pressure), gas phase space velocity 40h ^-1 , the number of effective plates of rectification towers T5, T6 and T7 Be respectively 102, 98 and 114 final product purity as shown in Table 6.

Purity of each component after table 6 rectification

Claims (7)

1. A process for extracting C4～C6 normal paraffins in light naphtha and co-producing isopentane and isohexane. Starting from the first adsorption tower T1 adsorption, the four towers are simultaneously and continuously adsorbed and desorbed for separation. The specific steps are as follows: (1) Adsorption, C4~C6 n-isoparaffin mixed raw material is output from the raw material storage tank V3, and enters the first adsorption tower T1 for adsorption after gasification, the n-alkanes in the raw material are adsorbed, and the unadsorbed components are absorbed by the first adsorption tower The output from the top of tower T1 is to regenerate the second adsorption tower T2 that has completed pressure equalization; (2) pressure equalization drop, the pressure equalization between the first adsorption tower T1 that has completed adsorption and the third adsorption tower T3 that has completed desorption; (3) Bed replacement, using inert gas to replace the material in the dead space of the first adsorption tower T1, and the material is condensed to obtain the middle distillate; (4) Desorption, C7 ~ C9 n-alkane single component or two or more mixed components through gas After desorption, it enters the first adsorption tower T1 where the replacement is completed, and the adsorbed C4-C6 normal alkanes are desorbed, and the desorbed material is input into the second rectification tower T6; Pressure equalization between T3 and the first adsorption tower T1 that has completed the desorption; (6) bed regeneration, use the unadsorbed isoparaffins at the top of the fourth adsorption tower T4 that is being adsorbed as a regeneration agent, and desorb the first adsorption tower T1 The internally adsorbed C7-C9 normal alkanes realize the regeneration of the adsorbent in the first adsorption tower T1, and the obtained regenerated material enters the first rectification tower T5; (7) Combined rectification, the desorption material obtained by the first adsorption tower T1 Enter the second rectification tower T6, the product C4 ~ C6 normal paraffins are obtained from the top of the tower, and the desorbent C7 ~ C9 normal paraffins are obtained from the tower bottom, and the C7 ~ C9 normal paraffins are recycled; the regeneration material obtained by the first adsorption tower T1 enters In the first rectification tower T5, the C4-C6 isoparaffins are obtained from the top of the tower, and the desorbent C7-C9 normal paraffins are obtained from the bottom of the tower for recycling. Isopentane and isohexane products are obtained. 2. The method according to claim 1, wherein the mixed component of C4～C6 n-isomeric alkanes is hydrocracked naphtha, reformed top oil or catalytically cracked naphtha, petroleum at 60°C-165°C fraction. 3. The method according to claim 1, characterized in that the adsorption temperature is 150-450°C; the gas phase space velocity is 40-2000h ^-1 ; the pressure is 0-3MPa (gauge pressure). 4. The method according to claim 1, characterized in that the inert gas used for replacement is nitrogen, helium, carbon dioxide or hydrogen; the space velocity is 15-500h ^-1 . 5. The method according to claim 1, characterized in that the desorption temperature is 120～450°C; the pressure is 0～1Mpa; the gas phase space velocity is 40～2000h ^-1 ; the desorption method adopted is purging desorption, and the desorption agent adopted is C7～C9 single-component normal alkanes or two or more mixed components. 6. The method according to claim 1, characterized in that the regeneration agent is inert gas N ₂ , H ₂ , He, CO ₂ or C4-C6 isoparaffins. 7. The method according to claim 6, characterized in that the regeneration method is purge regeneration; the regeneration temperature is 120-450°C; the pressure is 0-2Mpa (gauge pressure); and the gas phase space velocity is 40-2000h ^-1 .

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