A process for the production of cyclopentane from coking crude benzene non-aromatic components

Abstract

The application discloses a method for producing cyclopentane from non-aromatic components of coking crude benzene, and belongs to the technical field of fine chemical separation. The method comprises the following steps: taking a fraction containing cyclopentane, benzene, C6 and C7 non-aromatic components as raw materials, the fraction being by-produced in the hydrogenation refining of coking crude benzene; after pretreatment by dehydration and desulfurization, the fraction is sent to a light component removal tower to remove light C5 components; the material at the tower bottom is sent to a heavy component removal tower; crude cyclopentane is collected at the top of the tower, and heavy components containing benzene C6 and C7 are collected at the bottom of the tower; the heavy component removal tower is branched into a main product branch and a by-product branch; the crude cyclopentane is refined by adsorption of a combined adsorption medium of molecular sieve, activated alumina and modified adsorbent in the main product branch, so as to obtain foaming-grade cyclopentane; the heavy components containing benzene are subjected to extractive distillation by N-formyl morpholine in the by-product branch; low-benzene non-aromatic components are collected at the top of the tower; the material at the bottom of the tower is separated by a negative pressure solvent recovery tower to obtain benzene products and regenerate and reuse N-formyl morpholine. The method is beneficial to the production of foaming-grade cyclopentane and the by-production of recovered benzene without introducing high-boiling-point extractants into the main product branch.

Description

Technical Field

[0001] This invention relates to the field of fine chemical separation technology, specifically a method for producing cyclopentane from the non-aromatic components of coking crude benzene. Background Technology

[0002] After hydrorefining and extraction of crude benzene from coking plants, a non-aromatic fraction is produced as a byproduct. This fraction contains cyclopentane, benzene, and various C6 and C7 non-aromatic hydrocarbons such as n-hexane, methylcyclopentane, cyclohexane, methylcyclohexane, and n-heptane. The cyclopentane content is relatively high, making it a valuable chemical feedstock. Currently, this non-aromatic fraction is mostly sold directly as low-end fuel or blending component, or burned, without effective separation of the cyclopentane, thus its resource value is not fully utilized. The main difficulty in producing foamed cyclopentane (purity not less than 99.5%, benzene content not more than 0.05%) from this fraction and simultaneously recovering benzene lies in the fact that this fraction is a complex multi-component system of "cyclopentane-benzene-C6 / C7". The boiling points of cyclohexane (boiling point 80.7℃) and benzene (boiling point 80.1℃) are very close, and benzene forms near-boiling compounds with various C6 and C7 non-aromatic hydrocarbons. It is difficult to reduce the benzene to the level required for foamed cyclopentane using conventional ordinary distillation.

[0003] In existing technologies, a representative approach is to recover cyclopentane from benzene-related or partially hydrogenated fractions. US6264799B1 (corresponding to CN1183070C, published in 2001) discloses using partially hydrogenated pre-benzene fractions or C5 fractions as feedstocks, first removing light components through fractionation, and then recovering cyclopentane and / or cyclopentene through subsequent fractionation. This route provides a main separation chain that first removes light components and then separates cyclopentane, but it focuses on a general pre-benzene or C5 system and does not reconstruct the process for situations where cyclopentane, benzene, and near-boiling C6 / C7 components coexist in the non-aromatic byproduct stream of coking crude benzene hydrogenation. It also does not involve the co-production recovery of benzene, making it difficult to directly obtain foamed cyclopentane.

[0004] Another representative approach is to concentrate the high-purification of cyclopentane in the extractive distillation unit of the main product branch. CN102391063B (published in 2013) discloses the preparation of high-purity cyclopentane by setting up extractive distillation after the heavy removal tower and using dimethylformamide as the extractant. CN109912377B (published in 2022) uses mixed C5 as raw material and prepares cyclopentane refrigerant through light removal, heavy removal, and extractive distillation. This type of route usually introduces extractive distillation and high-boiling-point extractants along the main product branch. Although it can improve the purity of cyclopentane, it increases the burden of solvent carryover, solvent recovery, and product post-processing in the main product branch. Moreover, it mainly focuses on the separation of cyclopentane from near-boiling alkanes and does not simultaneously handle the co-production recovery of benzene and the output of low-benzene non-aromatic hydrocarbons.

[0005] Another approach involves extractive distillation and solvent recovery separately for benzene and non-aromatic hydrocarbon mixtures. CN103086823B (published in 2015) discloses an extractive distillation separation and solvent recovery method for n-hexane, isohexane, and benzene. This route demonstrates that benzene and non-aromatic hydrocarbons can be independently separated through extractive distillation and solvent recovery, but it typically targets the residual oil system containing hexane and benzene, and does not combine it with a process that first recovers cyclopentane and then recovers benzene from the remaining benzene-containing heavy components.

[0006] Therefore, existing technologies disclose separation modules for cyclopentane recovery, high-purification of cyclopentane, and separation of benzene from non-aromatic hydrocarbons. However, for the complex "cyclopentane-benzene-C6 / C7" system produced by the hydrogenation of non-aromatic hydrocarbons from coking crude benzene, a complete solution is still lacking for separating the cyclopentane main product from the benzene-containing heavy component at appropriate locations and matching separation methods to the two branches. In particular, existing routes do not provide a direct and feasible solution for simultaneously achieving foaming-grade cyclopentane preparation, benzene co-product recovery, and stable extraction solvent circulation without reintroducing high-boiling-point extractants into the main product branch. Furthermore, the water and sulfides in this fraction can cause subsequent extractant hydrolysis losses and equipment corrosion, and affect the sulfur content of the product. Current practices often treat dehydration and desulfurization as general pretreatment, without coupling it with subsequent solvent stable circulation and low-sulfur product indicators.

[0007] Therefore, there is an urgent need for a method to produce cyclopentane from the non-aromatic components of coking crude benzene, which can stably prepare foamed cyclopentane and recover benzene in the complex system described above without introducing high-boiling-point extractants into the main product branch, while ensuring stable recycling of the extractant and low sulfur content in the product. Summary of the Invention

[0008] To address the problem in existing technologies for producing cyclopentane from non-aromatic by-product fractions of coking crude benzene hydrogenation, which is difficult to achieve simultaneously obtaining foamed-grade cyclopentane, recovering benzene, and maintaining stable extractant circulation without reintroducing high-boiling-point extractants into the main product branch, this invention provides a method for producing cyclopentane from non-aromatic components of coking crude benzene. This method stably prepares foamed-grade cyclopentane and recovers benzene from a complex system where cyclopentane, benzene, and C6 and C7 non-aromatic hydrocarbons coexist, while also ensuring stable solvent circulation and low-sulfur products.

[0009] The overall concept of this invention lies in organizing the separation of complex systems into two steps: first, separating the cyclopentane main product from the benzene-containing heavy components at an appropriate location; and then matching the most suitable methods to the two types of separation targets. In the non-aromatic fraction of coking crude benzene hydrogenation, the boiling points of light components such as n-pentane are lower than those of cyclopentane, while the boiling points of benzene and C6 and C7 components such as cyclohexane, n-hexane, methylcyclopentane, and methylcyclohexane are higher than those of cyclopentane and are close to each other in boiling point. Therefore, the light components lighter than cyclopentane are first removed by a light component removal tower, making cyclopentane the lowest boiling point among the remaining materials. Subsequently, crude cyclopentane is collected at the top of the heavy component removal tower, and the benzene-containing heavy components are collected at the bottom of the tower, thereby fixing the split point at the heavy component removal tower.

[0010] After the diversion, the remaining task of the main product branch is reduced to the final purification of trace benzene and minor impurities in the crude cyclopentane. Therefore, adsorption purification, a solid-phase method, is used to achieve this, eliminating the need for liquid-phase extractants in the main product branch and avoiding solvent carryover and recovery burdens. In the benzene-containing heavy fraction, benzene and C6 and C7 non-aromatic hydrocarbons are near-boiling, making efficient benzene removal difficult with ordinary distillation. Therefore, this is handled separately in an extractive distillation column using N-formylmorpholine as the extractant. Utilizing the selective action of the extractant on aromatics, benzene recovery is separated from the main product branch and independently completed in the by-product branch. The benzene-solvent mixture in the column bottom is then subjected to negative pressure solvent recovery to obtain the benzene product, and the solvent is regenerated and recycled. In conjunction with this, dehydration and desulfurization pretreatment is placed before the main separation and is linked to the stable circulation of the subsequent extractant, equipment corrosion prevention, and low-sulfur requirements of the product. This approach inhibits extractant hydrolysis loss upon contact with water, reduces corrosion caused by sulfides, and ensures the product's sulfur content from the source. It is the combination of the location of the diversion point, the selection of the methods for each of the two branches, and the relationship between pretreatment and solvent conditions that enables this method to simultaneously produce foaming-grade cyclopentane, recover benzene, and maintain stable solvent circulation in a continuous process.

[0011] To achieve the above objectives, the present invention adopts the following technical solution. The raw material is a non-aromatic fraction containing cyclopentane, benzene, and C6 and C7 non-aromatic hydrocarbons, which is a byproduct of the coking crude benzene hydrogenation refining extraction and separation unit. This raw material is first pretreated with dehydration and desulfurization to control the moisture and sulfides to low limits. The pretreated raw material enters a light component removal tower to remove the light C5 component (lighter than cyclopentane). The bottom material of the light component removal tower enters a heavy component removal tower. The heavy component removal tower collects crude cyclopentane from the top and benzene-containing C6 and C7 heavy components from the bottom, and at this point, the materials are divided into a main product branch and a by-product branch. The main product branch sends the crude cyclopentane to a combined adsorption medium composed of molecular sieves, activated alumina, and modified adsorbent for adsorption purification to remove trace amounts of benzene and other impurities, yielding a foamed cyclopentane product. The by-product branch sends the benzene-containing C6 and C7 heavy components into an extractive distillation column using N-formylmorpholine as the extractant. A low-benzene non-aromatic hydrocarbon stream is collected from the top of the column, while a mixture of benzene and N-formylmorpholine is collected from the bottom. This mixture then enters a negative-pressure solvent recovery column to separate the benzene from the solvent, yielding the benzene product. The regenerated N-formylmorpholine is returned to the extractive distillation column for recycling. The aforementioned pretreatment, removal of light and heavy hydrocarbons, adsorption purification, extractive distillation, and solvent recovery are sequentially linked and mutually constrained. The main product branch handles the final purification of cyclopentane, while the by-product branch handles the selective recovery of benzene, together forming a closed-loop process for the preparation of foamed cyclopentane and the co-production and recovery of benzene.

[0012] Furthermore, the non-aromatic fraction used as raw material contains 20 to 45% cyclopentane and 10 to 35% benzene by mass, with the remaining components including one or more of n-hexane, methylcyclopentane, cyclohexane, methylcyclohexane, and n-heptane. The dehydration and desulfurization pretreatment adopts a combination of adsorption dehydration and desulfurization purification to control the moisture content below 50 ppm and the sulfur content below 1 ppm, so as to inhibit the subsequent hydrolysis and failure of N-formylmorpholine in water, reduce equipment corrosion, and ensure low sulfur content in the product.

[0013] Furthermore, in the implementation involving the separation of light and heavy hydrocarbons, the light hydrocarbon removal tower only removes the light C5 components lighter than cyclopentane. Its top temperature is controlled at 45 to 55 degrees Celsius, and its bottom temperature is controlled at 70 to 80 degrees Celsius. The content of light hydrocarbons lighter than cyclopentane in the bottom material is not higher than 0.3% by mass. The heavy hydrocarbon removal tower uses cyclopentane as the lowest boiling point among the remaining components after light hydrocarbon removal and collects it from the top of the tower. Its top temperature is controlled at 53 to 63 degrees Celsius, and its bottom temperature is controlled at 79 to 89 degrees Celsius. Thus, a main product branch and a by-product branch are stably formed at the heavy hydrocarbon removal tower.

[0014] Furthermore, in the implementation of the main product branch, adsorption purification involves two adsorption columns operating alternately, one in the adsorption state and the other in the regeneration state. Regeneration is achieved by a combination of hot nitrogen purging and vacuum regeneration. The adsorption operating temperature ranges from room temperature to 60 degrees Celsius, and the operating pressure ranges from atmospheric pressure to 0.3 MPa absolute pressure. The crude cyclopentane product passes through the combined adsorption medium from bottom to top in the liquid phase to remove trace amounts of benzene, olefins, sulfides, oxygen-containing compounds, as well as colloids and color substances.

[0015] Furthermore, in the implementation of the by-product branch, the mass ratio of N-formylmorpholine to the benzene-containing C6 and C7 heavy components is 4 to 6, preferably 5; the reflux ratio of the extractive distillation column is 1.5 to 3.5, preferably 2.2; the theoretical plate number is approximately 30; the top pressure is controlled between 0.12 and 0.20 MPa absolute pressure, approximately 0.15 MPa absolute pressure; the bottom temperature is lower than the decomposition temperature of N-formylmorpholine, controlled between 178 and 192 degrees Celsius; the benzene content in the low-benzene non-aromatic hydrocarbon stream collected from the top of the column is not higher than 5% by mass, preferably not higher than 3% by mass; the solvent recovery column operates under negative pressure; the water content of the regenerated N-formylmorpholine is controlled below 200 ppm; the solvent recovery rate reaches more than 95%; and the solvent loss is not higher than 0.30 kg per ton of raw material.

[0016] Furthermore, in the implementation method for controlling product quality and operating status, the purity of the foaming grade cyclopentane product is not less than 99.5% by mass, the benzene content is not more than 0.05% by mass, the moisture content is not more than 50 ppm, the sulfur content is not more than 1 ppm, and the cyclopentane recovery rate is not less than 80%. The purity of the co-produced benzene product is not less than 99.93% by mass, and the benzene recovery rate is not less than 90%. During operation, the benzene content of the low-benzene non-aromatic hydrocarbon stream at the top of the extractive distillation column is monitored by an online analyzer and the reflux ratio is adjusted in series. The moisture content of the circulating N-formylmorpholine is monitored by a moisture meter and linked to the dehydration unit. The purity of the cyclopentane product after adsorption purification is monitored by an online gas chromatograph, so as to achieve coordinated quality release of the two branches.

[0017] In an embodiment that further reduces energy consumption and solvent loss, the reboilers of the light component removal column, heavy component removal column, and extractive distillation column are thermosiphon reboilers heated by low-pressure steam. This integrates the heat of condensation at the top of each column and the heat of reboiling at the bottom, thereby reducing the consumption of externally supplied steam. When the moisture or sulfur content of the pretreated feed exceeds the aforementioned control limits, the batch of feed is returned to the pretreatment unit for reprocessing before entering the separation system. When the benzene content at the top of the extractive distillation column exceeds the control value, adjustments are made within a predetermined solvent ratio and reflux ratio range, thereby maintaining stable product quality and solvent status under fluctuating feed composition and continuous operation conditions.

[0018] The beneficial effects of this invention are: The process design, which uses a split flow at the heavy product removal tower to create a main product branch and a by-product branch, overcomes the limitation of existing routes for recovering cyclopentane from benzene-related or hydrogenated fractions, which typically concentrate subsequent separation tasks on the same main product purification chain. Since cyclopentane becomes the lowest boiling point component remaining in the tower after light product removal, the heavy product removal tower collects crude cyclopentane from the top and benzene-containing heavy components from the bottom, narrowing the main product purification target to cyclopentane and its trace impurities. The benzene-containing heavy components are then processed separately in the by-product branch. This method of splitting the flow at an appropriate location and then matching the two types of separation targets to separate units avoids a single unit simultaneously handling both high-purity cyclopentane purification and benzene recovery, thus providing more favorable conditions for the stable separation of complex systems.

[0019] The crude cyclopentane from the top of the de-heavy phase distillation column is purified by adsorption instead of using an extractive distillation column along the main product line. This addresses the shortcomings of existing high-purity cyclopentane routes, which typically introduce high-boiling-point extractants along the main product line. The remaining separation task of the crude cyclopentane from the top of the column is transformed into the final purification of trace benzene and other minor impurities. These trace components can be selectively retained using solid-phase adsorption, eliminating the need for further liquid-phase extractants. Consequently, the main product line is no longer burdened with the additional costs of solvent carryover, solvent recovery, and post-processing, which facilitates the stable purification of crude cyclopentane to the foaming grade and reduces the operational complexity of the main product line.

[0020] A combined adsorption medium consisting of molecular sieves, activated alumina, and modified adsorbents, along with dual adsorption columns operating on a one-use-one-regeneration basis and hot nitrogen purging and vacuum regeneration, overcomes the shortcomings of single adsorbents or the lack of regeneration methods in continuously and stably removing multiple trace impurities. Different adsorption components in the combined medium are responsible for removing residual moisture, polar impurities, trace amounts of benzene, and trace amounts of oxygen-containing compounds. The alternating operation of the dual adsorption columns ensures that the adsorption capacity is not depleted during continuous production. The combination of the medium combination and the regeneration method continuously and stably reduces trace amounts of benzene, sulfides, oxygen-containing compounds, and color substances in the product, improving the operational stability and maintainability of the main product branch.

[0021] The benzene C6 and C7 heavy components in the bottom of the heavy removal column are separately fed into an extractive distillation column using N-formylmorpholine as the extractant. This solves the problem of near-boiling benzene and C6 and C7 non-aromatic hydrocarbons such as cyclohexane and n-hexane being difficult to efficiently remove with conventional distillation. It also compensates for the deficiency in existing benzene-non-aromatic hydrocarbon separation routes that do not combine with the prior recovery of cyclopentane. N-formylmorpholine selectively reduces the relative volatility of benzene and increases the relative volatility of non-aromatic hydrocarbons, thus separating the selective recovery of benzene from the main product branch to be completed independently in the by-product branch. While producing the main product of cyclopentane, benzene is recovered and a low-benzene non-aromatic hydrocarbon stream is obtained, improving the utilization rate of all components of the feedstock.

[0022] The negative pressure operation of the solvent recovery tower, combined with the constraint that the bottom temperature of the extractive distillation column is below the decomposition temperature of N-formylmorpholine, addresses the problems of easy solvent decomposition at high temperatures and high energy consumption in extraction and separation. The negative pressure operation lowers the bottom temperature of the solvent recovery tower, and the bottom temperature constraint, constrained by the decomposition temperature, keeps N-formylmorpholine stable during extractive distillation. The regenerated solvent is then recycled in a closed loop. This long-term stable solvent circulation and reduced steam consumption provide more favorable conditions for the reliable and continuous operation of the by-product branch.

[0023] The dehydration and desulfurization pretreatment, located before the main separation and coupled with solvent stability and product low-sulfur indicators, changes the current practice where dehydration and desulfurization are often treated merely as general pretreatment. Lowering the moisture content at the feed end suppresses downstream N-formylmorpholine hydrolysis losses, while removing sulfides reduces equipment corrosion and provides a source guarantee for the low-sulfur requirements of foaming-grade cyclopentane. This pretreatment simultaneously affects solvent circulation stability, equipment protection, and product sulfur indicators. Its upstream placement and connection to subsequent branches improve the stability of the entire process and the consistency of product quality.

[0024] Online analyzers, moisture analyzers, and online gas chromatographs were used to monitor and coordinate the benzene content at the top of the extractive distillation column, the water content of the circulating N-formylmorpholine, and the purity of the cyclopentane product after adsorption purification. This system compensated for the lack of online feedback, which made it difficult to maintain stable release under fluctuating feedstock and continuous operation conditions. Feedback on the benzene content at the top of the column was used to adjust the reflux ratio in a cascade manner; feedback on the solvent water content was used to coordinate the dehydration unit; and feedback on product purity was used to coordinate the quality release of the two branches. Together, these three systems constituted a closed-loop control during operation. This configuration of online monitoring and coordination helps maintain stable product quality and solvent status when feedstock composition fluctuates, improving the timeliness of quality control and the reliability of product release. Attached Figure Description

[0025] Figure 1 The process of this invention Figure 1 ; Figure 2 The process of this invention Figure 2 ; Figure 3 The process of this invention Figure 3 . Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1 like Figure 1 As shown in this embodiment, a complete implementation of a method for producing cyclopentane from the non-aromatic components of coking crude benzene is provided. The raw material is the non-aromatic fraction by-product of the coking crude benzene hydrorefining extraction and separation unit, with a processing capacity of 1250 kg per hour. Its representative component composition is shown in Table 1. The cyclopentane content in this fraction is 40.88 wt%, and the benzene content is 14.00 wt%, both falling within the range of 20 wt% to 45 wt% for cyclopentane and 10 wt% to 35 wt% for benzene. The remaining components are n-pentane, n-hexane, methylcyclopentane, cyclohexane, methylcyclohexane, n-heptane, and trace amounts of toluene, belonging to a complex multi-component system in which cyclopentane, benzene, and C6 and C7 non-aromatic hydrocarbons coexist. The water content of this raw material is approximately 280 ppm, and the sulfur content is approximately 2.5 ppm. In this system, the boiling point of cyclohexane (80.7℃) is very close to that of benzene (80.1℃). Benzene also forms near-boiling compounds with various C6 and C7 non-aromatic hydrocarbons. Ordinary distillation alone cannot reduce the benzene content to below 0.05 wt% required for foaming grade cyclopentane. Therefore, it is necessary to split the flow at an appropriate location and match the separation methods to the two branches.

[0028] Table 1. Representative component composition of raw materials in Example 1 Before entering the separation system, the raw materials undergo dehydration and desulfurization in the pretreatment unit. A combination of adsorption dehydration and desulfurization purification is used to control the moisture content below 50 ppm and the sulfur content below 1 ppm. The values ​​of 50 ppm and 1 ppm are determined by the hydrolysis sensitivity of N-formylmorpholine used in the downstream by-product branch and the low-sulfur requirement for the foaming-grade cyclopentane product: N-formylmorpholine is easily hydrolyzed and degraded in water; reducing the feed moisture to below 50 ppm inhibits its hydrolysis at the source. Sulfides exacerbate equipment corrosion and introduce into the main product; reducing the sulfur content to below 1 ppm serves both equipment protection and the release requirement that the product sulfur content not exceed 1 ppm.

[0029] The pretreated raw material is pumped into the light hydrocarbon removal tower, a packed tower with a top temperature of approximately 50°C and a bottom temperature of approximately 75°C. Light C5 components, such as n-pentane, with boiling points lower than cyclopentane, are removed from the top. The light components at the top are condensed, with part refluxed and part collected. The bottom material, retaining cyclopentane and all heavier components, is sent to the heavy hydrocarbon removal tower. The content of light hydrocarbons lighter than cyclopentane in the bottom material is controlled to be no more than 0.3 wt% to avoid interference from residual light components in the subsequent top collection of crude cyclopentane. The light hydrocarbon removal tower only removes light components and does not remove benzene; benzene continues to flow with the heavier components into the next tower.

[0030] The material from the bottom of the light component removal tower enters the heavy component removal tower, which is also a packed tower. The top temperature is approximately 58°C, and the bottom temperature is approximately 84°C. After light component removal, cyclopentane becomes the lowest boiling point component among the remaining components in the tower. Based on this, the heavy component removal tower collects crude cyclopentane from the top and benzene, as well as C6 and C7 heavy components such as n-hexane, methylcyclopentane, cyclohexane, and methylcyclohexane, from the bottom. This splits the material into two post-processing branches at the heavy component removal tower: one is the main product branch focusing on crude cyclopentane, and the other is the by-product branch focusing on benzene-containing C6 and C7 heavy components. This split point is fixed at the heavy component removal tower, neither before nor after the main product refining process. This narrows the main product refining process to crude cyclopentane and its accompanying trace amounts of benzene and minor impurities, while the by-product branch focuses on the selective recovery of benzene.

[0031] The main product feeder sends the crude cyclopentane from the top of the de-removal tower to the adsorption purification unit. The adsorption medium in this unit is a combination of molecular sieves, activated alumina, and modified adsorbent. The molecular sieves and activated alumina remove residual moisture and some polar impurities, while the modified adsorbent is designed to remove trace amounts of benzene and oxygen-containing compounds, further removing trace amounts of benzene, olefins, sulfides, oxygen-containing compounds, as well as colloids and color substances from the crude cyclopentane to the foaming level. Adsorption purification is achieved through continuous operation with two adsorption columns running alternately; one column is in adsorption mode while the other is in regeneration mode. The adsorption operating temperature ranges from room temperature to 60°C, and the operating pressure ranges from atmospheric pressure to 0.3 MPa absolute pressure. The crude cyclopentane passes through the combined adsorption medium in liquid phase from bottom to top. When the benzene content of the cyclopentane product at the outlet of the adsorption column increases and approaches the release limit of 0.05 wt%, the system switches to a regenerated standby column. The adsorption capacity of the decommissioned column is then restored by hot nitrogen purging combined with vacuum regeneration. After purification in this unit, foamed cyclopentane product is obtained with a purity of not less than 99.5 wt%, a benzene content of not more than 0.05 wt%, a moisture content of not more than 50 ppm, a sulfur content of not more than 1 ppm, and a cyclopentane recovery rate of not less than 80%.

[0032] The by-product branch pumps the benzene C6 and C7 heavy components from the bottom of the de-heavy column into the extractive distillation column via a bottom pump. N-formylmorpholine is used as the extractant and added from the top of the column, where it comes into countercurrent contact with the material flowing from bottom to top. The separation of benzene and non-aromatic hydrocarbons is achieved by utilizing the selective effect of N-formylmorpholine to reduce the relative volatility of benzene and increase the relative volatility of non-aromatic hydrocarbons. The mass ratio of N-formylmorpholine to benzene-containing C6 and C7 heavy components in the extractive distillation column is 5, falling within the operating range of 4 to 6; the reflux ratio is 2.2, falling within the range of 1.5 to 3.5; the theoretical number of plates is approximately 30, and based on a plate efficiency of approximately 0.7, the actual number of plates is approximately 43, which can also be replaced by equivalent high-efficiency structured packing; the column top pressure is approximately 0.15 MPa absolute pressure, falling between 0.12 and 0.20 MPa absolute pressure, slightly higher than atmospheric pressure, so a vacuum system is not required; the column top temperature is 48℃ to 100℃, and the column bottom temperature is 178℃ to 192℃. The upper limit of the column bottom temperature is selected based on the decomposition temperature of N-formylmorpholine at 200℃, so that the column bottom temperature is always kept below this decomposition temperature to ensure that the solvent does not decompose. The low-benzene non-aromatic hydrocarbon stream collected from the top of the extractive distillation column has a benzene content of no more than 5 wt%, which can be further controlled to below 3 wt%. It is discharged as a low-benzene refined non-aromatic hydrocarbon mixture or sent to subsequent comprehensive utilization. The mixture of benzene and N-formylmorpholine collected from the bottom of the column is sent to solvent recovery.

[0033] A mixture of benzene and N-formylmorpholine flows into a solvent recovery tower operating under negative pressure. Under negative pressure, benzene and N-formylmorpholine are separated, and the solvent is regenerated. The top of the tower yields a benzene product with a purity of not less than 99.93 wt% and a benzene recovery rate of not less than 90%. The regenerated N-formylmorpholine is recycled back to the extractive distillation tower for reuse. After regeneration, the water content of N-formylmorpholine is controlled below 200 ppm, the solvent recovery rate reaches over 95%, and the solvent loss is not higher than 0.30 kg per ton of raw material. The solvent recovery tower operates under negative pressure, which reduces the bottom temperature, saves steam, and further prevents the decomposition of N-formylmorpholine due to high temperatures. To reduce overall energy consumption, the reboilers of the light component removal tower, heavy component removal tower, and extractive distillation tower are all thermosiphon reboilers heated by low-pressure steam at 0.6 MPa. The steam consumption of the extractive distillation tower reboiler is approximately 0.5 t per hour. Simultaneously, the condensation heat at the top of each tower and the reboiling heat at the bottom are integrated, reducing the need for external steam supply.

[0034] To ensure stable product purity and solvent status during continuous operation, this embodiment employs online monitoring and coordinated control. An online analyzer monitors the benzene content in the low-benzene non-aromatic hydrocarbon stream at the top of the extractive distillation column, and accordingly adjusts the reflux ratio of the extractive distillation column to maintain a stable benzene content at the top of the column, not exceeding 5 wt% and approaching 3 wt%. A moisture analyzer monitors the water content of the circulating N-formylmorpholine; when the water content approaches the upper limit of 200 ppm, a molecular sieve dryer is activated in conjunction with the dehydration unit to dehydrate the solvent and suppress hydrolysis losses. An online gas chromatograph monitors the purity of the cyclopentane product after adsorption purification, ensuring coordinated quality release between the main product stream and the by-product stream.

[0035] In this embodiment, the non-aromatic fraction first undergoes dehydration and desulfurization in the pretreatment unit to achieve a moisture content of 50 ppm and a sulfur content of 1 ppm. The feed at ppm is then introduced into the light component removal tower to remove the light C5 component. The bottom material enters the heavy component removal tower and is split there. The crude cyclopentane from the top of the tower is purified by alternating adsorption of a dual-column adsorption medium along the main product branch to obtain foamed cyclopentane product. The benzene-containing heavy component from the bottom of the tower is extracted and distilled by N-formylmorpholine along the by-product branch to obtain a low-benzene non-aromatic hydrocarbon stream from the top of the tower and a benzene solvent mixture from the bottom of the tower. The latter is then passed through a negative pressure solvent recovery tower to obtain high-purity benzene and regenerate N-formylmorpholine for reuse. During operation, the benzene content, solvent water content and product purity at the top of the tower are monitored by an online analyzer, a moisture meter and an online gas chromatograph, respectively. The reflux ratio is adjusted, the dehydration unit is activated and the co-release is performed, thereby forming a continuous operation in which the main product branch purifies cyclopentane, the by-product branch recovers benzene and the solvent is recycled in a closed loop. Under this operating condition, the cyclopentane recovery rate is not less than 80%, the benzene recovery rate is not less than 90%, and the benzene content in the low-benzene purified non-aromatic hydrocarbons is not higher than 5 wt%.

[0036] The effectiveness of this embodiment stems from the coordination of three factors: the location of the split point, the choice of methods for the two branches, and the coupling of pretreatment and solvent conditions. The split point is fixed at the heavy removal tower rather than earlier or later because after the removal of light components, cyclopentane becomes the lightest component among the remaining components. At this point, crude cyclopentane is collected from the top of the heavy removal tower, allowing the main product to be separated before benzene becomes intensely entangled with cyclopentane at near-boiling levels. This narrows the main product refining target to cyclopentane plus trace impurities. If the split point is moved before the removal of light components, cyclopentane will be mixed with the light and heavy components; if it is moved after the main product refining, the benzene recovery pressure will remain on the main product line, both of which increase the subsequent burden. The main product branch was changed to adsorption purification instead of extraction distillation for high purification because the remaining task of the crude cyclopentane at the top of the column is the final purification of trace benzene and trace impurities. The standard can be met by selectively retaining trace benzene, oxygen-containing substances, sulfur and color substances with a solid-phase combined medium, thus avoiding the reintroduction of high-boiling-point N-formylmorpholine into the main product branch and increasing the burden of solvent carryover, recovery and product post-processing. In the combined medium, molecular sieves, activated alumina and modified adsorbents are responsible for dehydration, removal of polar impurities and removal of trace benzene and oxygen-containing substances. The alternating use of dual columns with hot nitrogen purging and vacuum regeneration ensures that the adsorption capacity is not exhausted during continuous operation, so the benzene content of the product can be stably reduced to below 0.05 wt%. The by-product branch uses N-formylmorpholine extractive distillation separately because benzene in the bottom of the column forms a near-boiling complex system with cyclohexane, n-hexane, methylcyclopentane, methylcyclohexane, etc. Ordinary distillation is difficult to efficiently remove benzene. However, the selective dissolution of aromatics by N-formylmorpholine can widen the relative volatility of benzene and non-aromatics, separating benzene recovery from the main product line and completing it independently in the by-product line. The solvent ratio of 5 and the reflux ratio of 2.2 are values ​​that take into account the solvent circulation rate and column load while ensuring that the benzene content at the top of the column does not exceed 5 wt%. The bottom temperature of the column is set at 178°C to 192°C, which is below the 200°C decomposition temperature of N-formylmorpholine, to ensure long-term stability of the solvent. The reason why pretreatment for dehydration and desulfurization is prioritized and tied to product indicators is that it simultaneously determines the hydrolysis loss rate of N-formylmorpholine, the degree of equipment corrosion, and the sulfur content of the product. Only when the moisture and sulfur are reduced to below 50 ppm and 1 ppm at the feed end can the closed-loop solvent circulation of the by-product branch and the low-sulfur release of the main product be simultaneously achieved.

[0037] This embodiment establishes quantitative triggering criteria, threshold sources, priority order, and recovery conditions for operational anomalies. The thresholds used for each anomaly trigger are derived from product release indicators and the hydrolysis and decomposition constraints of N-formylmorpholine. Specifically, 50 ppm and 1 ppm are derived from pretreatment feed requirements and product sulfur content release indicators; 0.05 wt% is derived from the upper limit of cyclopentane benzene content release for foaming grade; 5 wt% is derived from the low-benzene non-aromatic benzene content control value; and 200 ppm is derived from the upper limit of permissible water content for N-formylmorpholine. Anomalies are handled according to the priority order of safety and product release. Handling non-compliant feedstock takes precedence over operational adjustments within the branch line. Anomalies in the main product branch and the by-product branch are handled separately without exceeding authority. When the moisture content of the pretreated feedstock exceeds 50 ppm or the sulfur content exceeds 1 ppm, the pretreatment is deemed unqualified. This batch of feedstock does not enter the light residue removal tower or subsequent branches but is returned to the pretreatment unit for reprocessing until the moisture and sulfur content return to below 50 ppm and 1 ppm, respectively, before being released for feeding. When the entrainment of heavy components in the crude cyclopentane at the top of the heavy removal tower increases, leading to a higher load at the adsorption purification inlet, the heavy component entrainment is pushed back down by adjusting the top temperature and reflux ratio of the heavy removal tower, without transferring this deviation to the adsorption unit. When the benzene content of the cyclopentane product at the outlet of the adsorption column increases and approaches the 0.05 wt% release limit, the adsorption capacity of the column is determined to be saturated. The column is switched to a regenerated standby column to continue production, and the withdrawn adsorption column is purged with hot nitrogen and regenerated under vacuum. If the capacity recovery after regeneration is insufficient as detected by online gas chromatography, the vacuum regeneration or hot nitrogen purging time is extended before re-injection, and the unrecovered adsorption column is not put into production. When the water content of the circulating N-formylmorpholine approaches the upper limit of 200 ppm as monitored by a moisture analyzer, the dehydration unit is activated to use a molecular sieve dryer to dehydrate the solvent, bringing the water content back below 200 ppm before continuing the cycle. When the content of low-benzene non-aromatic benzene at the top of the extractive distillation column exceeds 5 wt% as monitored by an online analyzer, the reflux ratio is preferentially increased within the range of 1.5 to 3.5, and the amount of N-formylmorpholine is increased within the range of 4 to 6 to bring the benzene content at the top of the column back to the control value, without changing the feed definition or process structure. All of the above anomaly handling falls within the existing steps and control window, without introducing new separation units.

[0038] Example 2 like Figure 1 and Figure 2As shown, this embodiment, based on the complete process chain of Example 1, uses the non-aromatic fraction of coking crude benzene with high benzene and low cyclopentane content as raw material to illustrate the implementation method when the raw material composition shifts towards the high benzene end. The raw material contains approximately 23.21 wt% cyclopentane, approximately 31.08 wt% benzene, and approximately 1.17 wt% toluene. The remaining approximately 44.44 wt% consists of C6 and C7 non-aromatic hydrocarbons such as n-hexane, methylcyclopentane, cyclohexane, methylcyclohexane, and n-heptane. The raw material contains approximately 310 ppm water and approximately 2.23 ppm sulfur. Both cyclopentane and benzene fall within the range of 20 wt% to 45 wt% cyclopentane and 10 wt% to 35 wt% benzene. The raw material source, pretreatment method, light component removal tower, heavy component removal tower, adsorption purification unit, extractive distillation tower, and solvent recovery tower settings and operating parameters of this embodiment are the same as in Embodiment 1. That is, the pretreatment moisture content is not higher than 50 ppm and the sulfur content is not higher than 1 ppm. The top temperature of the light component removal tower is about 50°C, the bottom temperature is about 75°C, and the light hydrocarbon content in the bottom is not higher than 0.3 wt%. The top temperature of the heavy component removal tower is about 58°C, and the bottom temperature is about 84°C. The adsorption purification operating temperature is room temperature to 60°C, the operating pressure is atmospheric pressure to 0.3 MPa absolute pressure, the dual adsorption columns are alternately purged with hot nitrogen and vacuum regeneration, and the mass ratio of N-formylmorpholine to benzene-containing heavy components in the extractive distillation tower is in the range of 4 to 6, the reflux ratio is in the range of 1.5 to 3.5, there are about 30 theoretical plates, the top pressure is about 0.15 MPa absolute pressure, and the bottom temperature is 178°C to 192°C. This embodiment only makes corresponding adjustments to the load difference between the two branches caused by the change in raw material composition.

[0039] The raw material has a sulfur content of approximately 2.23 ppm. The sulfur content is controlled to below 1 ppm and the moisture content to below 50 ppm using the same adsorption dehydration and desulfurization purification method as in Example 1. These moisture and sulfur indicators are used as feed release conditions to protect the N-formylmorpholine in the by-product branch and to ensure the low sulfur requirements of the foaming grade cyclopentane product.

[0040] Because the proportion of cyclopentane in the raw material decreased to approximately 23.21 wt%, the yield of crude cyclopentane at the top of the heavy removal tower decreased accordingly. Consequently, the throughput of the adsorption purification unit in the main product branch decreased, and the time required for the adsorption column to reach a benzene content close to the 0.05 wt% release limit in the outlet cyclopentane product was extended. The switching cycle between the two adsorption columns was also extended. The adsorption medium remained a combination of molecular sieve, activated alumina, and modified adsorbent. The modified adsorbent was still designed for trace amounts of benzene and oxygen-containing compounds. The operating temperature, operating pressure, bottom-up liquid flow direction, and hot nitrogen purging combined with vacuum regeneration were all the same as in Example 1. After adsorption purification, foamed cyclopentane product with a purity of not less than 99.5 wt%, a benzene content of not more than 0.05 wt%, a moisture content of not more than 50 ppm, and a sulfur content of not more than 1 ppm was still obtained, with a cyclopentane recovery rate of not less than 80%.

[0041] As the proportion of benzene in the feedstock increased to approximately 31.08 wt%, the flow rate of the benzene-containing C6 and C7 heavy components in the bottom of the de-heavyweight column increased, and the feed rate and benzene load of the extractive distillation column in the by-product branch increased accordingly. To maintain the benzene content of the low-benzene non-aromatic stream at the top of the column to no more than 5 wt% and close to 3 wt% under the condition of increased feed benzene load, the mass ratio of N-formylmorpholine to the benzene-containing heavy components was appropriately increased from 5 within the same mass ratio range of 4 to 6 as in Example 1, and the reflux ratio was appropriately increased within the range of 1.5 to 3.5. The bottom temperature was maintained at 178°C to 192°C, below the decomposition temperature of N-formylmorpholine at 200°C, and the top pressure remained approximately 0.15 MPa absolute. The benzene and N-formylmorpholine mixture collected from the bottom of the distillation column flows into a solvent recovery column operating under negative pressure. Due to the increased benzene output, the benzene product yield increases accordingly. Toluene, which is relatively high in this batch of raw materials, enters this branch as a heavier aromatic hydrocarbon along with benzene. Since the boiling point of toluene (110.4℃) differs from that of benzene (80.1℃) by about 30℃ and they do not form a near-boiling system, they can be separated from benzene by conventional distillation. Therefore, the benzene product still yields high-purity benzene with a purity of not less than 99.93 wt% and a benzene recovery rate of not less than 90%. The regenerated N-formylmorpholine has a water content controlled below 200 ppm, a solvent recovery rate of over 95%, and a solvent loss of not more than 0.30 kg per ton of raw material before being recycled back to the extractive distillation column.

[0042] The online monitoring and linkage control methods are the same as in Example 1. An online analyzer is used to monitor the benzene content at the top of the extractive distillation column and adjust the reflux ratio in cascade. A moisture meter is used to monitor the water content of the circulating N-formylmorpholine and, when it approaches the upper limit of 200 ppm, it is linked to the molecular sieve dryer for dehydration. An online gas chromatograph is used to monitor the purity of the cyclopentane product after adsorption purification. Under the high benzene load in this example, the online adjustment range of the reflux ratio and solvent ratio is generally shifted upward compared to Example 1, but does not exceed the mass ratio range of 4 to 6 and the reflux ratio range of 1.5 to 3.5.

[0043] The working process of this embodiment is as follows: The high-benzene, low-cyclopentane feedstock is first pretreated to achieve feed conditions of 50 ppm moisture and 1 ppm sulfur, with a higher desulfurization load than in Example 1. It then enters the light component removal tower to remove the light C5 component and is split by the heavy component removal tower. A small amount of crude cyclopentane from the top of the tower is purified along the main product branch through alternating adsorption in a dual-column system to obtain foamed cyclopentane product. The adsorption column switching cycle is longer than in Example 1. A larger amount of benzene-containing heavy component from the bottom of the tower is extracted and distilled along the by-product branch using N-formylmorpholine. Under the adjusted mass ratio and reflux ratio, a low-benzene non-aromatic hydrocarbon stream from the top of the tower and a benzene solvent mixture from the bottom are obtained. The latter is processed through a negative pressure solvent recovery tower to obtain high-purity benzene, and the N-formylmorpholine is regenerated and reused. The benzene content, solvent moisture content, and product purity at the top of the tower are monitored and adjusted in conjunction with an online analyzer, a moisture meter, and an online gas chromatograph, forming a continuous dual-branch operation consistent with Example 1. The cyclopentane and benzene products still achieve a purity of not less than 99.5%. The equipment operates stably within a load flexibility range of 60% to 120%, with a benzene content not exceeding 0.05 wt% and a purity not lower than 99.93 wt%.

[0044] This embodiment illustrates that the adaptability of the dual-branch process to fluctuations in feed composition stems from the decoupling of the split point and the branch methods. Since cyclopentane remains the lowest boiling point among the remaining components after light component removal, the split point of collecting crude cyclopentane at the top of the heavy component removal column does not change with the relative ratio of benzene to cyclopentane. Therefore, when the feed benzene level increases and the cyclopentane level decreases, only the flow rate and load of the two branches change, not the split point or separation method. The adsorption and purification target of the main product branch remains cyclopentane plus trace impurities. An increase in benzene does not push the benzene recovery pressure back to the main product line. The by-product branch selectively dissolves benzene using N-formylmorpholine. When the benzene load increases, simply adjusting the solvent dosage and reflux ratio within the predetermined mass ratio and reflux ratio range is sufficient to maintain the target benzene content at the top of the column. Meanwhile, the column bottom temperature remains constant due to the 200°C decomposition temperature of N-formylmorpholine, and the solvent stability does not decrease with increased load. Because the two branches independently match and separate the objects, the method can stably produce qualified products with the same process structure between the high-benzene, low-cyclopentane composition and the composition of Example 1. This is also why the raw material composition range of the independent scheme can be covered at both ends.

[0045] The abnormal triggering criteria, threshold sources, priority order, and recovery conditions in this embodiment are the same as in Embodiment 1, with the following additions for high benzene loads. Among the triggering thresholds, 50 ppm and 1 ppm originate from feed requirements and product sulfur content release indicators; 0.05 wt% originates from the upper limit of cyclopentane benzene content release for foaming grade; 5 wt% originates from the low-benzene non-aromatic benzene content control value; and 200 ppm originates from the upper limit of permissible water content for N-formylmorpholine. Abnormalities are handled according to the priority order of safety and product release, with non-compliant feed handling taking precedence over branch line adjustments. If the sulfur content of the raw material remains above 1 ppm after pretreatment, the pretreatment is deemed unqualified, and the batch of raw material is returned to the pretreatment unit for reprocessing until the sulfur content drops below 1 ppm before being released for feeding. When the benzene load in the by-product branch increases, causing the content of low-benzene non-aromatic benzene at the top of the extractive distillation column to exceed 5 wt%, the reflux ratio is preferentially increased within the range of 1.5 to 3.5, and the N-formylmorpholine mass ratio is increased within the range of 4 to 6 to bring the benzene content at the top of the column back to no more than 5 wt%. If the target is still not met even at the upper limit of the range, the feed rate of the by-product branch is reduced to restore separation, rather than forcibly removing benzene by increasing the column bottom temperature, thus avoiding approaching the decomposition temperature of N-formylmorpholine. When the benzene content of the cyclopentane product at the outlet of the adsorption column approaches the upper limit of 0.05 wt%, the column is switched to the regenerated standby column to continue production. The adsorption column that has been taken out of operation is purged with hot nitrogen and regenerated under vacuum. If the capacity recovery after regeneration is insufficient, the vacuum regeneration or hot nitrogen purging time is extended before reinjection. All of the above abnormal handling falls within the existing steps and control window, without introducing new separation units.

[0046] Example 3 like Figures 1 to 3As shown, this embodiment, based on the complete process chain of Example 1, uses a non-aromatic fraction of coking crude benzene with high cyclopentane and low benzene content as raw material. It illustrates the implementation method when the raw material composition shifts towards the high cyclopentane end, and provides a boundary variation for upgrading to electronic-grade cyclopentane in the main product branch. The raw material contains approximately 40.93 wt% cyclopentane, approximately 14.07 wt% benzene, and approximately 0.04 wt% toluene. The remaining approximately 44.96 wt% consists of C6 and C7 non-aromatic hydrocarbons such as n-hexane, methylcyclopentane, cyclohexane, methylcyclohexane, and n-heptane. The raw material contains approximately 290 ppm water and approximately 3 ppm sulfur. Both cyclopentane and benzene fall within the range of 20 wt% to 45 wt% cyclopentane and 10 wt% to 35 wt% benzene. The raw material source, pretreatment method, light component removal tower, heavy component removal tower, adsorption purification unit, extractive distillation tower, and solvent recovery tower settings and operating parameters of this embodiment are the same as in Embodiment 1. That is, the pretreatment moisture content is not higher than 50 ppm and the sulfur content is not higher than 1 ppm. The light component removal tower has a top temperature of about 50°C, a bottom temperature of about 75°C, and a light hydrocarbon content of not more than 0.3 wt%. The heavy component removal tower has a top temperature of about 58°C and a bottom temperature of about 84°C. The adsorption purification operation temperature is room temperature to 60°C and the operation pressure is atmospheric pressure to 0.3 MPa absolute pressure. The dual adsorption columns are alternately purged with hot nitrogen and regenerated under vacuum. The extractive distillation tower has a mass ratio of N-formylmorpholine to benzene-containing heavy components in the range of 4 to 6, a reflux ratio in the range of 1.5 to 3.5, about 30 theoretical plates, a top pressure of about 0.15 MPa absolute pressure, and a bottom temperature of 178°C to 192°C. This embodiment only makes corresponding adjustments to the load difference between the two branches caused by the change in raw material composition and the deepening of the purification at the end of the main product branch.

[0047] Since the sulfur content of the raw material is about 3 ppm, which is higher than that in Example 1, the desulfurization and purification load of the pretreatment unit is increased accordingly. The sulfur content is controlled to below 1 ppm and the moisture content is controlled to below 50 ppm using the same adsorption dehydration and desulfurization purification method as in Example 1. These moisture and sulfur indicators are used as feed release conditions to protect the N-formylmorpholine in the by-product branch and ensure the low sulfur requirements of the foaming grade cyclopentane product.

[0048] As the proportion of cyclopentane in the feedstock increased to approximately 40.93 wt%, the yield of crude cyclopentane at the top of the heavy removal tower increased accordingly, leading to a larger processing capacity in the main product branch adsorption purification unit. The adsorption task focused on the final purification of trace amounts of benzene, trace amounts of sulfides, and trace amounts of oxygen-containing compounds in the crude cyclopentane. The adsorption medium remained a combination of molecular sieves, activated alumina, and modified adsorbent. The modified adsorbent was still designed for trace amounts of benzene and trace amounts of oxygen-containing compounds. The operating temperature, operating pressure, bottom-up flow direction of the liquid phase, and hot nitrogen purging combined with vacuum regeneration were all the same as in Example 1. Due to the increased processing capacity of the main product branch, the switching between the two adsorption columns was more frequent than in Example 1. The purity of the cyclopentane product after adsorption purification was monitored using an online gas chromatograph to determine the switching point. When the benzene content of the cyclopentane product at the outlet of the adsorption column approached the upper limit of 0.05 wt%, the column was switched to the regenerated standby column. After adsorption purification, foaming grade cyclopentane product with a purity of not less than 99.5 wt%, benzene content not more than 0.05 wt%, moisture content not more than 50 ppm, and sulfur content not more than 1 ppm is still obtained, with a cyclopentane recovery rate of not less than 80%.

[0049] Under the high cyclopentane conditions of this embodiment, the main product branch can also reserve an interface for upgrading to electronic-grade cyclopentane. While maintaining the dual-branch process structure and by-product branch setup unchanged, the adsorption purification process of the main product branch is enhanced, for example, by increasing the number of adsorption stages or increasing the ratio of modified adsorbent in the combined adsorption medium, to further reduce trace amounts of benzene and oxygen-containing compounds in the cyclopentane product, thereby improving the purity of cyclopentane from the foaming stage to the electronic stage. This enhancement process only affects the final purification depth of the main product branch, without introducing high-boiling-point extractants such as N-formylmorpholine into the main product branch, nor changing the splitting position at the deweighting tower or the extractive distillation and solvent recovery process of the by-product branch.

[0050] As the proportion of benzene in the feedstock decreased to approximately 14.07 wt%, the flow rate of the benzene-containing C6 and C7 heavy components in the bottom of the de-heavy distillation column decreased, and the feed rate and benzene load of the by-product branch extractive distillation column decreased accordingly. Within the same mass ratio range of 4 to 6 as in Example 1, the mass ratio of N-formylmorpholine to the benzene-containing heavy components can be appropriately reduced from 5, and the reflux ratio can be appropriately reduced within the range of 1.5 to 3.5. The bottom temperature of the column is still maintained at 178°C to 192°C, which is lower than the decomposition temperature of N-formylmorpholine at 200°C. The top pressure of the column is still approximately 0.15 MPa absolute pressure, and the benzene content of the low-benzene non-aromatic stream at the top of the column is still controlled to be no higher than 5 wt% and close to 3 wt%. The benzene and N-formylmorpholine mixture collected from the bottom of the distillation column flows into a solvent recovery column operating under negative pressure. Due to the reduced benzene output, the benzene product yield decreases accordingly, but a benzene product with a purity of not less than 99.93 wt% and a benzene recovery rate of not less than 90% is still obtained. The water content of the regenerated N-formylmorpholine is controlled below 200 ppm, the solvent recovery rate reaches more than 95%, and the solvent loss is not higher than 0.30 kg per ton of raw material before being recycled back to the extractive distillation column.

[0051] The online monitoring and linkage control methods are the same as in Example 1. An online analyzer is used to monitor the benzene content at the top of the extractive distillation column and adjust the reflux ratio in cascade. A moisture meter is used to monitor the water content of the circulating N-formylmorpholine and, when it approaches the upper limit of 200 ppm, it is linked to the molecular sieve dryer for dehydration. An online gas chromatograph is used to monitor the purity of the cyclopentane product after adsorption purification. Under the low benzene load of this example, the online adjustment range of reflux ratio and mass ratio is generally lower than that of Example 1, but not lower than the lower limit of the reflux ratio range of 1.5 to 3.5 and the lower limit of the mass ratio range of 4 to 6. When the electronic-grade upgrade enhancement treatment is enabled, the online gas chromatography monitoring results are used as the release basis for whether the main product branch has reached the upgrade target purity.

[0052] The working process in this embodiment is as follows: the high-cyclopentane, low-benzene raw material is first pretreated to achieve a moisture content of 50 ppm and a sulfur content of 1 ppm. The feed conditions were adjusted to ppm, with a higher desulfurization load than in Example 1. The product then entered a light component removal tower to remove the light C5 component and was split by a heavy component removal tower. A larger quantity of crude cyclopentane from the top of the tower was purified along the main product branch using alternating adsorption in a dual-column system to obtain foamed cyclopentane. The adsorption column switching was more frequent than in Example 1, and the switching points were determined by online gas chromatography. If necessary, the main product branch was enhanced to upgrade to the electronic grade. A smaller quantity of benzene-containing heavy components from the bottom of the tower was extracted and distilled along the by-product branch using N-formylmorpholine. Under the adjusted mass ratio and reflux ratio, a low-benzene non-aromatic hydrocarbon stream from the top of the tower and a benzene solvent mixture from the bottom of the tower were obtained. The latter was processed through a negative pressure solvent recovery tower to obtain high-purity benzene, and the N-formylmorpholine was regenerated and reused. The benzene content, solvent water content, and product purity at the top of the tower were monitored and adjusted in conjunction with an online analyzer, a moisture analyzer, and an online gas chromatograph, forming a continuous dual-branch operation consistent with Example 1. The cyclopentane product and the benzene product still achieved a purity of not less than 99.5 wt% and a benzene content of not more than 0.05%, respectively. The equipment meets the specifications of wt% and purity of not less than 99.93 wt%, and operates stably within a load elasticity range of 60% to 120%.

[0053] This embodiment illustrates that the stability of the method under high cyclopentane and low benzene conditions also stems from the decoupling of the split point and branch means, as well as the potential for further refinement brought about by the adsorption purification of the main product branch. Since cyclopentane remains the lowest boiling point among the remaining components after light component removal, the diversion of crude cyclopentane from the top of the heavy component removal column does not change with the increase of cyclopentane content. The increase in cyclopentane only allows the main product branch to handle a larger cyclopentane throughput, and its separation task still converges to the final purification of trace benzene and trace impurities. Therefore, trace benzene and trace oxygen-containing compounds can be further reduced in the same branch by increasing the number of adsorption stages or increasing the ratio of modified adsorbent, thus advancing the purity from the foaming stage to the electronic stage without the need to introduce extractive distillation and high-boiling-point extractants. The main product branch is never burdened by solvent. When the benzene load decreases, the by-product branch only needs to adjust the solvent dosage and reflux ratio within the predetermined mass ratio and reflux ratio range to maintain the target benzene content at the top of the column. The column bottom temperature remains unchanged due to the constraint of the 200℃ decomposition temperature of N-formylmorpholine, and the stable solvent circulation is not affected by low load. It is precisely because the main product branch adsorption purification can continue to be purified through enhanced end purification under high cyclopentane flux, and the by-product branch can still stably recover benzene under low benzene load, that the method can cover the end of the raw material composition range where cyclopentane is high and benzene is low, and together with Examples 1 and 2, it supports both ends of the raw material composition range of the independent scheme.

[0054] The anomaly triggering criteria, threshold sources, priority order, and recovery conditions in this embodiment are the same as in Embodiment 1, with the following additions for high cyclopentane and low benzene loads. Among the triggering thresholds, 50 ppm and 1 ppm originate from feed requirements and product sulfur content release indicators; 0.05 wt% originates from the upper limit of cyclopentane benzene content release for foaming grade; 5 wt% originates from the low-benzene non-aromatic benzene content control value; and 200 ppm originates from the upper limit of permissible water content for N-formylmorpholine. Anomalies are handled according to the priority order of safety and product release, with non-compliant feed handling taking precedence over branch-level adjustments. If the sulfur content of the raw material remains above 1 ppm after pretreatment, the pretreatment is deemed unqualified, and the batch of raw material is returned to the pretreatment unit for reprocessing until the sulfur content drops below 1 ppm before being released for feeding. When the cyclopentane throughput of the main product branch increases to the point that the benzene content of the cyclopentane product at the outlet of the adsorption column approaches the 0.05 wt% release limit, it is determined that the adsorption capacity of the column is approaching saturation. The column is then switched to a regenerated standby column to continue production. The adsorption column that has been taken out of operation is subjected to hot nitrogen purging and vacuum regeneration. If the capacity recovery after regeneration is insufficient, the vacuum regeneration or hot nitrogen purging time is extended before reinjection. When electronic-grade upgrade enhancement is activated, if online gas chromatography monitoring shows that the product purity does not meet the upgrade target, the product is released according to the foaming grade index instead of being forcibly collected as electronic grade to avoid erroneous release. When the benzene load of the by-product branch is low, resulting in the low-benzene non-aromatic benzene content at the top of the column still exceeding 5 wt%, the reflux ratio is preferentially adjusted within the range of 1.5 to 3.5, and the N-formylmorpholine mass ratio is adjusted within the range of 4 to 6 to bring it back to no higher than 5 wt%, rather than forcibly removing benzene by increasing the column bottom temperature to avoid approaching the decomposition temperature of N-formylmorpholine. All of the above-mentioned exception handling falls within the existing steps and existing control window, without introducing new separation units.

[0055] Example 4 This embodiment is a control embodiment, using three sets of control versions to verify the necessity of the three steps—adsorption purification, N-formylmorpholine extractive distillation branch, and dehydration and desulfurization pretreatment—for achieving the desired results. The control was set as follows: using the same feedstock as Example 1 (coking crude benzene hydrogenation non-aromatic fraction containing 40.88 wt% cyclopentane and 14.00 wt% benzene, with a processing capacity of 1250 kg / hour, feedwater content approximately 280 ppm, and sulfur content approximately 2.5 ppm) and the same process parameters as Example 1 (light weight removal tower top temperature approximately 50°C / bottom temperature approximately 75°C, heavy weight removal tower top temperature approximately 58°C / bottom temperature approximately 84°C, N-formylmorpholine to benzene-containing C6 / C7 heavy component mass ratio of 5, reflux ratio 2.2, theoretical plate number approximately 30, and tower top pressure approximately 0.15). Under the common conditions of absolute pressure (MPa, negative pressure operation of solvent recovery tower, etc.), a complete scheme V0 and three control versions were set up. The only change in V1 was that the adsorption purification of the main product branch was omitted (the crude cyclopentane from the top of the heavy product removal tower was used directly as the product without the combined adsorption medium). The only change in V2 was that the N-formylmorpholine extractive distillation of the by-product branch was omitted and replaced with ordinary distillation to separate and recover benzene (without adding N-formylmorpholine extractant, only using ordinary distillation to cut the benzene-containing C6 / C7 heavy components in the bottom of the heavy product removal tower into benzene and non-aromatic hydrocarbons). The only change in V3 was that the dehydration and desulfurization pretreatment of the raw material was omitted. Except for their respective unique changes, the other conditions remained the same for each version. Samples were taken under continuous steady-state operation conditions for each version, and all indicators were calculated as the average of three parallel measurements. Table 2 shows the measured values ​​of the seven release indicators for each version.

[0056] Table 2 Measured values ​​and comparisons of release indicators for each version As shown in Table 2, all seven indicators of the complete V0 scheme are within the release criteria. The benzene content of the cyclopentane product is 0.047 wt%, which is close to the upper limit of 0.05 wt%. This indicates that the crude product at the top of the de-weighting tower can be reduced to the foaming level after purification at the end of the combined adsorption medium, but the margin is not generous. After omitting adsorption purification in V1, the benzene content of the cyclopentane product increased to 0.31 wt%, and the product purity decreased to 99.2 wt%, both exceeding their respective release criteria. The benzene content exceeded the criteria by approximately six times. This is because the heavy removal tower, relying solely on the boiling point difference between cyclopentane and benzene (approximately 30.9℃), cannot remove trace benzene to below 0.05 wt%. The selective retention of trace benzene by the combined adsorption medium composed of molecular sieves, activated alumina, and modified adsorbent is an irreplaceable final step in ensuring purity. Benzene, as the most abundant residual impurity in crude cyclopentane, directly lowers the overall product purity due to its excessive content. All other indicators in V1 met the criteria. The sulfur content of the cyclopentane product (0.9 ppm) was slightly higher than V0's 0.7 ppm. This is because the activated alumina and molecular sieve in the combined adsorption medium also have a certain adsorption capacity for residual sulfides; omitting this step resulted in trace sulfur penetrating with the crude product. The product moisture content (42 ppm) was higher than V0's 28 ppm. The ppm level is due to the fact that the molecular sieve in the adsorption and purification unit also acts as a final drying agent for residual moisture while removing benzene. This drying function is lost when the sieve is omitted, but 42 ppm is still within the 50 ppm release limit. After replacing N-formylmorpholine extractive distillation with ordinary distillation in V2, the benzene product purity was only 92.1 wt%, and the non-aromatic benzene content at the top of the ordinary distillation column was still 14.8 wt%, both exceeding the release criteria. This is because the benzene in the bottom stream of the heavy removal column forms a near-boiling system with cyclohexane (boiling point difference of only 0.6℃), n-hexane, methylcyclopentane, and methylcyclohexane. Ordinary distillation cannot effectively separate benzene from non-aromatic hydrocarbons. Only by using N-formylmorpholine to selectively dissolve aromatics and increase relative volatility can high-purity benzene and low-benzene non-aromatic hydrocarbons be obtained simultaneously. The main product branch of V2 was unaffected; the cyclopentane product had a benzene content of 0.034 wt%, a sulfur content of 0.6 ppm, a purity of 99.6 wt%, and a moisture content of 25%. All ppm values ​​met the criteria, with the benzene content slightly lower than V0's 0.047 wt%, which is a normal fluctuation in the composition of the top of the de-heavy tower and the temperature distribution of the adsorption bed between different operating batches. Since this version does not use N-formylmorpholine, the circulating solvent water content is not applicable. After omitting the dehydration and desulfurization pretreatment in V3, the sulfur content of the cyclopentane product increased to 6.4 ppm, the product moisture content increased to 83 ppm, and the circulating N-formylmorpholine water content increased to 490 ppm, all exceeding their respective release criteria. Regarding the product sulfur content, light sulfides with boiling points similar to cyclopentane in the feedstock were not purified by front-end desulfurization and were distilled off along with the crude cyclopentane from the top of the de-heavy tower and enriched in the main product branch. The adsorption and purification unit's combined medium primarily removes benzene and polar impurities, and has limited capacity to retain high-load sulfides; therefore, the product sulfur content exceeded the 1 ppm criterion.Regarding product moisture content, approximately 280 ppm of moisture from the feedstock was not dehydrated at the front end. Although most of it entered the bottom of the de-heavyweighting tower along with the heavy components, some still entered the crude cyclopentane at the top of the tower in dissolved or trace entrainment form. The molecular sieve in the adsorption and purification unit was designed for residual moisture after pretreatment, and its capacity was insufficient to suppress the moisture to below 50 ppm when faced with the high moisture content of the untreated crude product, resulting in a product moisture content exceeding the standard of 83 ppm. Regarding the water content of the circulating solvent, the moisture from the feedstock entered the bottom of the de-heavyweighting tower and then flowed into the extractive distillation tower and solvent recovery tower with the stream, accumulating continuously in the closed-loop circulation. At the same time, the high-sulfur environment accelerated the hydrolysis of N-formylmorpholine, jointly pushing up the circulating water content to 490 ppm and depleting the solvent. The benzene content of V3 cyclopentane product is 0.049 wt%, close to but not exceeding the criterion, and the product purity is 99.5 wt%, just reaching the lower limit of the criterion. This indicates that the removal of benzene by adsorption purification does not depend on pretreatment. However, trace oxygen-containing compounds, colloids and other impurities in the untreated crude product compete with benzene for adsorption sites in the adsorption medium, narrowing both the benzene removal residue and the overall end-of-pipe purification residue to the critical level. The benzene content of V3 low-benzene non-aromatic hydrocarbons is 4.2 wt%, which still meets the criterion but is significantly higher than V0's 3.6 wt%. This is because the moisture and sulfides brought in by the raw material slightly weaken the selective dissolution effect of N-formylmorpholine on aromatic hydrocarbons after entering the extractive distillation column, resulting in an increase in the benzene residue in the non-aromatic hydrocarbons at the top of the column.

[0057] Regarding the non-compliance indicators of each control version, the V1 non-compliance items were concentrated in the benzene content and product purity at the end of the main product branch (adsorption purification target point), the V2 non-compliance items were concentrated in the separation of benzene and non-aromatic hydrocarbons in the by-product branch (extractive distillation target point), and the V3 non-compliance items were concentrated in the product sulfur content, product moisture content, and solvent water content (pretreatment target point). The three control groups independently verified the indispensability of the corresponding links in their target indicators, and the influence range of the three did not overlap with each other. There was no situation where a single control caused the failure of all indicators in a chain reaction.

[0058] Accordingly, adsorption purification is a necessary step to ensure the benzene content and purity of cyclopentane products meet standards; the N-formylmorpholine extractive distillation branch is a necessary step to ensure the purity of benzene products and the content of low-benzene non-aromatic benzenes meet standards; and dehydration and desulfurization pretreatment is a necessary step to ensure the sulfur content, moisture content, and circulating solvent water content of cyclopentane products meet standards. Compared with the control versions V1, V2, and V3, the complete scheme V0 has improvements in the corresponding release criteria. Specifically, the benzene content of cyclopentane products is reduced from 0.31 wt% to 0.047 wt%, the product purity is increased from 99.2 wt% to 99.6 wt%, the product moisture content is reduced from 83 ppm to 28 ppm, the product sulfur content is reduced from 6.4 ppm to 0.7 ppm, the benzene product purity is increased from 92.1 wt% to 99.94 wt%, the content of low-benzene non-aromatic benzenes is reduced from 14.8 wt% to 3.6 wt%, and the circulating N-formylmorpholine water content is reduced from 490 ppm to 175 ppm. The data in this embodiment are measured values ​​under the above steady-state operating conditions, reflecting the comparison results under these operating conditions and raw material batches. They do not represent the statistical distribution of all operating conditions and raw material batches, nor do they indicate general superiority over all existing technologies.

[0059] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be modified within the scope of the concept described herein by means of the above teachings or the technology or knowledge in related fields.

Claims

1. A method for producing cyclopentane from non-aromatic components of coking crude benzene, characterized in that, Includes the following steps: S1: The non-aromatic fraction produced by the coking crude benzene hydrogenation refining extraction and separation unit is used as raw material, wherein the non-aromatic fraction contains 20 to 45 wt percent cyclopentane and 10 to 35 wt percent benzene. S2: The raw material is subjected to dehydration and desulfurization pretreatment to control the moisture content to below 50 ppm and the sulfur content to below 1 ppm, so as to protect the subsequent N-formylmorpholine extractant and ensure the low sulfur index of the product. S3: The pretreated raw material is sent to the light component removal tower to remove the light C5 component that is lighter than cyclopentane, and the bottom material is sent to the heavy component removal tower. S4: The bottom material of the light-light distillation tower is sent to the heavy distillation tower for heavy distillation. Cyclopentane is taken out from the top of the tower as the lightest component in the remaining components after light distillation, and the heavy components containing benzene C6 and C7 are taken out from the bottom of the tower. Thus, the main product branch and the by-product branch are split at the heavy distillation tower. S5: The main product branch feeds the crude cyclopentane into an adsorption purification unit using a combination adsorption medium composed of molecular sieves, activated alumina and modified adsorbents for purification, removing trace amounts of benzene and trace impurities, to obtain a foaming grade cyclopentane product with a purity of not less than 99.5 wt percent and a benzene content of not more than 0.05 wt percent. S6: The by-product branch feeds the benzene-containing C6 and C7 heavy components into an extractive distillation column using N-formylmorpholine as the extractant for separation. The mass ratio of N-formylmorpholine to the benzene-containing C6 and C7 heavy components is controlled to be 4 to 6, the reflux ratio is 1.5 to 3.5, and the column bottom temperature is below 200 deg°C. A low-benzene non-aromatic hydrocarbon stream is collected from the top of the column, and a mixture of benzene and N-formylmorpholine is collected from the bottom of the column. S7: The mixture of benzene and N-formylmorpholine is fed into a solvent recovery tower operating under negative pressure for separation to obtain benzene product, and the regenerated N-formylmorpholine is recycled back to the extractive distillation tower, wherein the water content of the regenerated N-formylmorpholine is controlled below 200 ppm and the recovery rate reaches above 95 percent.

2. The method according to claim 1, characterized in that, The remaining components in the non-aromatic fraction include one or more of n-hexane, methylcyclopentane, cyclohexane, methylcyclohexane, and n-heptane.

3. The method according to claim 1, characterized in that, The dehydration and desulfurization pretreatment described in step S2 is carried out by combining adsorption dehydration with desulfurization purification to prevent N-formylmorpholine in the subsequent extraction and distillation branch from hydrolyzing and becoming ineffective in water and to reduce the risk of equipment corrosion.

4. The method according to claim 1, characterized in that, In step S3, the top temperature of the light hydrocarbon removal tower is 45 to 55 degC and the bottom temperature is 70 to 80 degC, and the content of light hydrocarbons lighter than cyclopentane in the bottom material is not higher than 0.3 wt percent; in step S4, the top temperature of the heavy hydrocarbon removal tower is 53 to 63 degC and the bottom temperature is 79 to 89 degC.

5. The method according to claim 1, characterized in that, The adsorption purification unit in step S5 uses a dual-adsorption column alternating operation mode, with one adsorption column in the adsorption state and the other adsorption column in the regeneration state. The regeneration method is hot nitrogen purging and vacuum regeneration. The operating temperature is from room temperature to 60 deg°C and the operating pressure is from atmospheric pressure to 0.3 MPa absolute pressure. The crude cyclopentane product passes through the combined adsorption medium in liquid phase from bottom to top to remove trace amounts of benzene, trace amounts of olefins, trace amounts of sulfides, trace amounts of oxygen-containing compounds, colloids and color substances.

6. The method according to claim 1, characterized in that, In step S6, the top pressure of the extractive distillation column is controlled between 0.12 MPa and 0.20 MPa absolute pressure. The mass ratio of N-formylmorpholine to the benzene-containing C6 and C7 heavy components is 5, the reflux ratio is 2.2, the theoretical plate number is 30, the top temperature is 48 to 100 degC, and the bottom temperature is 178 to 192 degC.

7. The method according to claim 1, characterized in that, The benzene content in the low-benzene non-aromatic hydrocarbon stream described in step S6 is no higher than 5 wt percent, preferably no higher than 3 wt percent.

8. The method according to claim 1, characterized in that, The foamed cyclopentane product has a moisture content of no more than 50 ppm, a sulfur content of no more than 1 ppm, and a cyclopentane recovery rate of no less than 80 percent; the benzene product has a purity of no less than 99.93 wt percent and a benzene recovery rate of no less than 90 percent.

9. The method according to claim 1, characterized in that, The benzene content of the low-benzene non-aromatic hydrocarbon stream at the top of the extractive distillation column in step S6 is monitored online using an online analyzer, and the reflux ratio of the extractive distillation column is adjusted in cascade. The water content of the circulating N-formylmorpholine is monitored online using a moisture analyzer, and the dehydration unit is activated in conjunction with the moisture analyzer. The purity of the cyclopentane product after adsorption purification is monitored online using an online gas chromatograph.

10. The method according to claim 1, characterized in that, The reboilers of the light-weight removal tower, heavy-weight removal tower, and extractive distillation tower are thermosiphon reboilers heated by low-pressure steam, integrating the heat of condensation at the top of each tower and the heat of reboiling at the bottom of the tower for cold and heat utilization. Furthermore, the solvent loss of the solvent recovery tower is no higher than 0.30 kg per ton of raw material.

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