A method for adsorptive separation of high purity p-cymene from heavy aromatic feedstocks

Abstract

The application discloses a method for adsorbing and separating high-purity p-ethyltoluene from heavy aromatic hydrocarbons by using an adsorption separation method, selects cation exchange modified NaX molecular sieve with excellent p-ethyltoluene adsorption selectivity as an adsorbent, uses the adsorption separation method, feeds heavy aromatic hydrocarbon raw materials into the adsorbent, adsorbs p-ethyltoluene in the heavy aromatic hydrocarbon raw materials, obtains a raffinate, feeds a desorption agent, desorbs the adsorbed p-ethyltoluene, and obtains an extract. The method can solve the problem that high-purity p-ethyltoluene cannot be obtained from heavy components at a high yield at present, and can reduce the energy consumption of existing extraction, rectification and other processes through the adsorption separation method.

Description

Technical Field

[0001] This invention relates to a method for separating p-toluene, specifically, to obtaining high-purity p-toluene as a single component from heavy aromatic hydrocarbons using an adsorption separation method. Background Technology

[0002] Heavy aromatics feedstocks are mainly composed of C9 and above monocyclic and polycyclic aromatic hydrocarbons. They are important byproducts of oil refining units, aromatics units, ethylene units, ethylbenzene units, and coal chemical units, primarily originating from catalytic cracking, catalytic pyrolysis, catalytic reforming, disproportionation, isomerization, steam cracking, styrene-ethylene alkylation to ethylbenzene, and high-temperature coal coking side reactions. With the successive commissioning of large-scale petrochemical reforming units in my country in recent years, the trend towards larger production facilities and more reusable feedstocks, as well as the continuous increase in large-scale fiber plants, the development and utilization of heavy aromatics has become a priority. Therefore, rapidly improving the resource utilization level of heavy aromatics to provide sufficient industrial feedstock for downstream products has become an increasingly urgent need.

[0003] In my country, heavy aromatics are generally processed and utilized using comprehensive heavy aromatics production facilities. Although research and utilization of heavy aromatics began in the 1980s, due to slow technological development, outdated processes, and small scale, large-scale production has not yet been achieved. Consequently, utilization rates are low, product quality is poor, energy consumption is high, yields are low, and utilization pathways are limited. This results in high product costs and weak competitiveness for heavy aromatics, limiting their use to low-efficiency applications such as fuel and mixed solvent oils, leading to significant resource waste. Currently, domestic technology and equipment can only extract parabens, mesitylene, and aromatic solvent oil components (No. 100-120) from heavy aromatics. Other components such as ethylbenzene, trimethylbenzene, and mesitylene have not yet entered the industrial production stage, hindering the realization of comprehensive economic benefits from heavy aromatics utilization and resulting in low resource utilization rates, lagging behind advanced international levels.

[0004] Ethylbenzene constitutes a significant proportion of heavy aromatic hydrocarbons, ranging from 20% to 30% by mass. It has numerous applications and uses in fine chemicals. Separating it into single components and developing downstream derivatives to increase its added value could yield substantial economic benefits and meet the rapidly growing domestic and international demand. All three isomers of ethylbenzene can be dehydrogenated to produce the corresponding methylstyrene monomers. These monomers can be copolymerized with various other monomers for the production of adhesives, resins, inks, dry cleaning agents, plastic coatings, and anti-slip coatings. Among these three monomers, p-methylethylbenzene is the most widely used. Its dehydrogenation produces p-methylstyrene, which has a structure similar to styrene monomers and superior properties. It has the potential to replace polystyrene in the future, becoming an indispensable chemical raw material in manufacturing. However, due to the similar boiling points of the components in C9 aromatic hydrocarbons, it is difficult to separate each component individually using conventional distillation equipment. Therefore, currently only the extraction of mesitylene and pseudotrimethylbenzene has formed a mature industrial production system, while the production and utilization of ethylbenzene remains a weak link. Currently, most industrial equipment uses precision distillation and extractive distillation, or a combination of both, to separate p-toluene from other C9 aromatic components. However, the distillation column requires a large number of trays, a large reflux ratio, and very high energy consumption. Furthermore, since the boiling points of m-toluene and p-toluene differ by only 0.7°C, it is difficult to completely separate them in one go. Therefore, in industry, a mixture of the two is used.

[0005] CN102372576B discloses a method for separating a mixture of m- and p-methylethylbenzene from C9 aromatics. In this method, after adding a catalyst during distillation, the stream is passed through a light-removal tower and a first catalyst removal tower, or through a heavy-removal tower and a second catalyst removal tower, to obtain a mixture of m- and p-methylethylbenzene with a purity higher than 98% and a yield higher than 85%.

[0006] CN101723790B discloses a method for separating m- and p-methylethylbenzene from C9 aromatic streams with almost no changes to the initial process. This method only increases the operating pressure of the heavy hydrocarbon removal tower and decreases the operating pressure of the light hydrocarbon removal tower, which can not only save 44% of energy consumption, but also obtain products with a purity of over 95.4% and a yield of over 54.5%.

[0007] CN105503500B discloses a method for separating m- and p-methylethylbenzene from C9 aromatics using a combined extractant. This method utilizes the cross-flow contact between the C9 feed and the combined extractant in an extractive distillation column to obtain a mixture of m- and p-methylethylbenzene with a purity higher than 99.37% and a yield higher than 90.65%.

[0008] CN101513818A discloses a separation process that combines C9 aromatic distillation and extraction. The main target product of this process is mesitylene, with a concentration of up to 98.5% and a yield of 79%. This invention can only separate p-toluene in the absence of m-toluene, and the purity is only 89%.

[0009] CN101077849B describes using dibutyl phthalate as the extractive distillation solvent, and employing an extractive distillation apparatus and a vacuum distillation apparatus to separate m-toluene and p-toluene in two steps, obtaining m-toluene with a purity of ≥97% and p-toluene with a purity of ≥92%. However, the purity of p-toluene obtained by this method is still relatively low.

[0010] Therefore, if the single component of para-toluene can be extracted from heavy aromatics in a low-energy-consumption manner, and used as a raw material to develop and produce high-value-added products, gradually forming a product chain for the enterprise, it can bring very considerable economic benefits to the enterprise. Summary of the Invention

[0011] To address the problems existing in the prior art, this invention provides a method for adsorbing and separating p-toluene (p-ethylbenzene) from heavy aromatics. This method offers advantages such as low energy consumption, precise control, the ability to handle a wide variety of feed components with varying mass fractions, high product concentration, and high yield, significantly increasing the added value of heavy aromatics. The method of this invention can significantly improve the separation coefficient and separation degree between p-ethylbenzene and other components of heavy aromatics, obtaining high-purity p-ethylbenzene through a simple and convenient operating procedure.

[0012] This invention provides a method for adsorbing and separating high-purity p-toluene-ethylbenzene from heavy aromatic hydrocarbon feedstock. The method includes introducing the heavy aromatic hydrocarbon feedstock into an adsorbent, causing the p-toluene-ethylbenzene in the feedstock to be adsorbed by the adsorbent, and discharging the unadsorbed components as the raffinate from the adsorption separation; then introducing a desorbent into the adsorbent to desorb the adsorbed p-toluene-ethylbenzene, obtaining the raffinate from the adsorption separation. The method is characterized by...

[0013] The heavy aromatics feedstock is a heavy aromatics containing multiple C9+ aromatic components and having a wide distribution of p-toluene and ethylbenzene mass fraction;

[0014] The adsorbent is (1) a NaX molecular sieve modified by cation exchange of one or more group IA metals selected from Li, K, Rb, and Cs;

[0015] (2) A NaX molecular sieve modified by exchange between one or more Group IA metal cations selected from Li, K, Rb, and Cs and one or more metal cations selected from Group IIA metals and Group IB metals, wherein, based on metal oxides, the molar ratio of Group IA metal oxides to Group IIA and Group IB metal oxides is not less than 0.05; or

[0016] (3) NaX molecular sieve modified by cation exchange of one or more metals selected from Group IIA metals Ba and Group IB metals.

[0017] The method for adsorbing and separating p-toluene from heavy aromatics provided by this invention simplifies the operation process, effectively reduces equipment energy consumption and production costs, and yields p-toluene products with high purity and yield. After subsequent processing, it can bring substantial economic benefits to enterprises. Attached Figure Description

[0018] Figure 1 Pulse spectrum of Example 5

[0019] Figure 2 This is a schematic diagram of the small-scale simulated moving bed adsorption separation process of the present invention. Detailed Implementation

[0020] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. Through these descriptions, the features and advantages of the present application will become clearer and more apparent.

[0021] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0022] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0023] In this invention, the term "C9" refers to a hydrocarbon containing 9 carbon atoms, and the term "C9+aromatic hydrocarbon" refers to an aromatic hydrocarbon containing 9 or more carbon atoms, which has the same meaning as "heavy aromatic hydrocarbon".

[0024] This invention separates high-purity p-toluene-ethylbenzene from heavy aromatic hydrocarbon feedstock via adsorption separation. A feed containing a significant amount of heavy aromatic hydrocarbon components, with a wide range of p-toluene-ethylbenzene mass fractions, is introduced into the adsorbent. Upon contact with the adsorbent, the p-toluene-ethylbenzene in the feed is adsorbed. The unadsorbed components are discharged as raffinate. A desorbent, consisting of alkylbenzene or a mixture of alkylbenzene and alkanes, is then introduced into the adsorbent to desorb the adsorbed p-toluene-ethylbenzene, yielding an extract. High-purity p-toluene-ethylbenzene can be obtained from the extract after separation. Both the raffinate and the extract contain desorbent, which is separated and recycled through distillation.

[0025] According to an exemplary embodiment of the present invention, the active component of the adsorbent used in the present invention is a group of cation exchange modified NaX molecular sieves. Preferably, the molar ratio of silica to alumina in the NaX molecular sieve is not less than 2.2, and the particle size is 0.5-1.0 micrometers. It is believed, however, that the particle size of the molecular sieve affects the mass transfer and strength of the adsorbent. Larger particle sizes result in poorer mass transfer of heavy aromatic hydrocarbon feedstock and desorbent within the adsorbent, thus affecting the adsorption and separation efficiency. Conversely, excessively small particle sizes lead to reduced adsorbent strength, thereby affecting the adsorbent's lifespan. Similarly, it is believed, however, that the molar ratio of silica to alumina in the molecular sieve also significantly affects the adsorption capacity of the adsorbent. A high molar ratio leads to poorer selectivity, while a low molar ratio not only reduces the adsorption capacity but also alters the internal structure of the molecular sieve. Through long-term research and practice, this invention has obtained a suitable range of molecular sieve crystal sizes and a suitable range of molar ratios of silicon oxide to aluminum oxide for separating p-toluene.

[0026] According to an exemplary embodiment of the present invention, the metal used for cation exchange modification may be selected from one or more Group IA metals selected from Li, K, Rb, and Cs, or from one or more metals selected from Group IIA metals Ba and Group IB metals. According to an exemplary embodiment of the present invention, the metal used for cation exchange modification may be selected from a combination of one or more Group IA metals selected from Li, K, Rb, and Cs and one or more metals selected from Group IIA metals Ba and Group IB metals, wherein, based on metal oxides, the molar ratio of Group IA metal oxides to Group IIA and Group IB metal oxides is not less than 0.05. According to an exemplary embodiment of the present invention, the molar ratio of adsorbed water to alumina in the modified adsorbent is not greater than 1.00, preferably not greater than 0.80. It is believed that through cation exchange modification, the electric field in the adsorbent changes, thereby giving the adsorbent a specific selectivity for p-toluene. According to a preferred embodiment of the present invention, the Group IB metal is Cu and / or Ag. According to another preferred embodiment of the present invention, the metal cation used for NaX molecular sieve modification is a combination of K and Ba or a combination of Li and Ba.

[0027] According to an exemplary embodiment of the present invention, cation exchange modification of NaX molecular sieves can be carried out using a modified metal salt solution. In this invention, the molar concentration of the metal salt used for ion exchange is 0.08–0.58 mol / L, preferably 0.15–0.45 mol / L, and the reaction temperature is 80–100 °C, preferably 85–95 °C. Through cation exchange modification, the degree of exchange of Na ions in the NaX molecular sieve adsorbent is 80–99.8 mol%, preferably 85–99 mol%.

[0028] According to an exemplary embodiment of the present invention, in addition to NaX-type molecular sieves, the adsorbent of the present invention may also contain a binder to facilitate the formation of the adsorbent. The adsorbent of the present invention contains 90–99 wt% NaX-type molecular sieves and 1–10 wt% binder. Suitable binders include kaolin, bentonite, and / or attapulgite. According to another exemplary embodiment of the present invention, the loss on ignition of the adsorbent after calcination at 600°C is not greater than 6.0 wt%, preferably not greater than 5.5 wt%.

[0029] According to an exemplary embodiment of the present invention, the heavy aromatics feedstock that can be processed by the present invention comes from reforming products, cracked gasoline, naphtha, by-products of ethylbenzene units, and catalytic cracking gasoline, wherein the C9+ aromatics include components such as p-ethylbenzene, m-ethylbenzene, o-ethylbenzene, propylbenzene, isopropylbenzene, mesitylene, pseudotrimethylbenzene, methylpropylbenzene, diethylbenzene, ethylxylene, and / or indene. The mass fraction distribution of p-ethylbenzene in the heavy aromatics feedstock of the present invention is relatively wide, with p-ethylbenzene accounting for 5-90 wt% of the C9+ aromatics component, and m-ethylbenzene accounting for 5-90 wt% of the C9+ aromatics component.

[0030] According to an exemplary embodiment of the present invention, the desorbent used in the present invention is alkylbenzene, preferably toluene, or a mixture of alkylbenzene and alkanes, wherein the mass fraction of alkylbenzene in the desorbent is 20 wt%, preferably 30 wt%. According to an exemplary embodiment of the present invention, the desorbent used in the present invention is para-alkylbenzene, preferably para-xylene.

[0031] According to an exemplary embodiment of the present invention, the adsorption temperature for adsorption separation is 100–185°C, preferably 115–185°C, more preferably 135–165°C, and the adsorption pressure is 0.5 MPa–1.5 MPa, preferably 0.8 MPa–1.0 MPa. By optimizing the operating conditions of the adsorption separation process, the extract from the adsorption separation can be made to contain essentially only p-toluene, with very low levels of other components.

[0032] According to an exemplary embodiment of the present invention, the adsorption separation process of the present invention employs a simulated moving bed device, but the present invention is not limited thereto. Figure 2As shown, the simulated moving bed device of the present invention may contain one or more adsorption towers, each containing multiple adsorption beds filled with adsorbent. Each bed has its own material inlet and outlet pipelines. The material in the adsorption tower flows from top to bottom, and through the transportation of the circulating pump, the material flows through the adsorption beds of different adsorption towers to form a closed loop. The material entering and exiting the adsorption beds includes at least raw material (F), desorbent (D), extractant (E), and raffinate (R). The material entering and exiting the simulated moving bed divides the adsorption beds into desorption zones, purification zones, adsorption zones, and isolation zones. The adsorption bed between desorbent injection and extractant collection is the desorption zone; the adsorption bed between extractant collection and raw material injection is the purification zone; the adsorption bed between raw material injection and raffinate collection is the adsorption zone; and the adsorption bed between raffinate collection and desorbent injection is the isolation zone. The bed ratio for the adsorption zone, purification zone, desorption zone, and isolation zone is 29±10%:37±15%:21±5%:13±4%. In the simulated moving bed operation, the positions of each material stream entering and exiting the adsorption bed can be changed periodically. Multi-port rotary valves or programmable valve groups can be used to control the entry and exit of each material stream into different adsorption beds. At a certain moment, each material stream is connected to a specific bed; at regular intervals (one step time), the entry and exit position of each material stream moves down one adsorption bed layer. Figure 2 The step time from the solid arrow to the dashed arrow position shown is typically 50–200 seconds, preferably 60–170 seconds. The time required for a material to travel through all adsorption beds from its entry point (or exit point) back to its starting position is called a cycle. A cycle typically takes 15–50 minutes, preferably 20–35 minutes.

[0033] According to an exemplary embodiment of the present invention, the components in the heavy aromatic hydrocarbon feedstock exhibit different adsorption selectivity on the adsorbent, with the adsorbent showing higher adsorption selectivity for p-toluene. The extract is rich in p-toluene and also contains a portion of desorbent. The desorbent in the extract is removed by distillation, followed by the removal of light components such as toluene and xylene to obtain a high-purity p-toluene product. The raffinate contains a smaller amount of p-toluene; the lower the content, the higher the adsorption and separation efficiency. The main components of the raffinate are the desorbent and other components in the feedstock besides p-toluene. After removing the desorbent from the raffinate by distillation, the resulting raffinate oil undergoes further processing and separation.

[0034] According to an exemplary embodiment of the present invention, in the adsorption separation process of the present invention, the mass flow rate ratio of the desorbent to the heavy aromatic feedstock entering the simulated moving bed is not greater than 1.60, preferably not greater than 1.20; the heavy aromatic feedstock flow rate relative to unit mass of adsorbent is not less than 0.40 kg / (h·kg adsorbent), preferably not less than 0.50 kg / (h·kg adsorbent). It is believed that by selecting a suitable flow rate ratio and flow rate of desorbent to heavy aromatic feedstock, so that the desorbent and heavy aromatic feedstock can be in sufficient contact, and so that p-ethylbenzene can be fully adsorbed, the content of p-ethylbenzene in the extract can be significantly increased, and the content of other components can be reduced.

[0035] The present invention is further illustrated below by way of examples, but the present invention is not limited thereto.

[0036] Example 1

[0037] Adsorbent A used in the preparation of adsorption separation process

[0038] X-type molecular sieves with a silica / alumina molar ratio of 2.3 were mixed with kaolin minerals at a mass ratio of 92:8, spheroidized, dried, and then calcined at 540℃ for 6 hours. The calcined spheres were treated with a mixed solution of sodium hydroxide and water glass (Na₂O concentration of 56 g / L and SiO₂ concentration of 10 g / L, based on oxides) at 90℃ for 12 hours. The alkali-treated and dried spheres were then subjected to cation exchange with a solution containing 0.30 mol / L barium nitrate and 0.15 mol / L potassium chloride for 8 hours at 85℃, with a liquid-to-solid ratio of 45. The degree of exchange, calculated based on the residual sodium content after exchange, was 98.5 mol%. After exchange, the spheres were dried at 100℃ for 3 hours and activated at 300℃ for 2 hours. After activation, the molar ratio of potassium oxide to barium oxide in the adsorbent was 0.053, and the molar ratio of adsorbed water to alumina was 0.42. The metal ion exchange conditions, the degree of exchange of the adsorbent after exchange, and the water content are shown in Table 1.

[0039] Example 2

[0040] Adsorbent B used in the preparation of adsorption separation

[0041] X-type molecular sieves with a silica / alumina molar ratio of 2.3 were mixed with kaolin minerals at a mass ratio of 94:6, shaped into spheres, dried, and then calcined at 550℃ for 6 hours. The calcined spheres were treated with a mixed solution of sodium hydroxide and water glass (Na₂O concentration of 56 g / L and SiO₂ concentration of 10 g / L, calculated as oxides) at 94℃ for 7 hours. The alkali-treated and dried spheres were then subjected to cation exchange with a 0.40 mol / L potassium chloride solution for 7 hours at 95℃, with a liquid-to-solid ratio of 50. The degree of exchange, calculated based on the residual sodium content after exchange, was 98.7 mol%. The exchanged spheres were dried at 100℃ for 4 hours and activated at 300℃ for 2 hours. The activated water / alumina molar ratio was 0.38. The metal ion exchange conditions, the degree of exchange of the adsorbent after exchange, and the water / alumina molar ratio are shown in Table 1.

[0042] Example 3

[0043] The adsorbent C used in the preparation of adsorption separation

[0044] X-type molecular sieves with a silica / alumina molar ratio of 2.4 were mixed with kaolin minerals at a mass ratio of 95:5, shaped into spheres, dried, and then calcined at 540℃ for 6 hours. The calcined spheres were treated with a mixed solution of sodium hydroxide and water glass (Na₂O concentration of 56 g / L and SiO₂ concentration of 10 g / L, calculated as oxides) at 93℃ for 8 hours. The alkali-treated and dried spheres were then subjected to cation exchange with a 0.25 mol / L rubidium nitrate solution for 7 hours at 94℃, with a liquid-to-solid ratio of 50. The degree of exchange, calculated based on the residual sodium content after exchange, was 85.6 mol%. The exchanged spheres were then dried at 100℃ for 3 hours and activated at 300℃ for 2 hours. After activation, the water / alumina molar ratio was 0.20. The metal ion exchange conditions, the degree of exchange of the adsorbent after exchange, and the water content are shown in Table 1.

[0045] Example 4

[0046] The adsorbent D used in the preparation of adsorption separation

[0047] X-type molecular sieves with a silica / alumina molar ratio of 2.3 were mixed with kaolin minerals at a mass ratio of 91:9, shaped into spheres, dried, and then calcined at 530℃ for 8 hours. The calcined spheres were treated with a mixed solution of sodium hydroxide and water glass (Na₂O concentration of 56 g / L and SiO₂ concentration of 10 g / L, based on oxides) at 95℃ for 10 hours. The alkali-treated and dried spheres were then subjected to cation exchange with a solution containing 0.15 mol / L lithium chloride and 0.35 mol / L barium chloride for 6 hours at 93℃, with a liquid-to-solid ratio of 40. The degree of exchange, calculated based on the residual sodium content after exchange, was 97.9 mol%. After exchange, the spheres were dried at 100℃ for 4 hours and activated at 300℃ for 2 hours. After activation, the molar ratio of lithium oxide to barium oxide in the adsorbent was 0.065, and the molar ratio of adsorbed water to alumina was 0.11. The metal ion exchange conditions, the degree of exchange of the adsorbent after exchange, and the water content are shown in Table 1.

[0048] Table 1

[0049]

[0050] Example 5

[0051] To evaluate the adsorption selectivity of the adsorbent material, a dynamic pulsed experimental setup was used to determine its adsorption selectivity and the adsorption and desorption rates of the target product. The setup consists of a feed system, an adsorption column, a heating furnace, and a pressure control valve. The adsorption column is a Ф6×1800 mm stainless steel tube. The lower inlet of the adsorption column is connected to the feed and nitrogen systems, while the upper outlet is connected to the pressure control valve, which in turn connects to an effluent collector.

[0052] The adsorption selectivity of the adsorbent is determined as follows: Weigh out the adsorbent particles (500 μm–800 μm in diameter) and pack them into the adsorption column. Shake the column to remove any gas from the system under a nitrogen atmosphere. Increase the system pressure to 0.85 MPa and the temperature to 145 °C. Stop the flow of desorbent and allow the column to absorb the adsorbent for 1.0 h. -1 A pulsed feed solution containing a non-adsorbed tracer was introduced at a volume hourly space velocity (VHSV) of 5-10 mL. Then, a desorbent was introduced at the same VHSV. Three drops of the desorbate were collected every 2 mL and analyzed by gas chromatography. Desorption curves were plotted with the volume of the desorbent on the x-axis and the concentrations of each component in the pulsed feed solution on the y-axis, as shown below. Figure 1As shown. The unadsorbed tracer can be used to obtain the dead volume of the adsorption system. Taking the midpoint of the tracer's half-peak width as the zero point, the net retention volume from the midpoint of the half-peak width to the zero point is measured for each component. The net retention volume of any component is proportional to the partition coefficient at adsorption equilibrium, reflecting the interaction force between each component and the adsorbent material. The ratio of the net retention volumes of the two components is the separation coefficient β. For example, the ratio of the net retention volume of p-toluene to that of m-toluene is the ratio of the adsorption performance of the adsorbent material for both, and is the separation coefficient of p-toluene relative to m-toluene, denoted as β. p / m Resolution is often used as an indicator of adsorbent separation efficiency, especially for evaluating the adsorption and separation performance of different adsorbents under the same operating parameters. Resolution is equal to the ratio of the difference in net retention volume between adjacent pulse peaks to the average half-width at half-maximum (HWHM) of the two pulse peaks. For example, the ratio of the difference in net retention volume between p-toluene and m-toluene to the average HWHM of their respective pulse peaks is the resolution between the two peaks, denoted as R. p / m .

[0053] Sixty mL of adsorbent A prepared in Example 1 was used to conduct a liquid-phase pulse experiment to determine its adsorption selectivity, resolution, and adsorption and desorption rates for methyl ethyl benzene. The desorbent used in the experiment consisted of 50 wt% toluene and 50 wt% n-heptane. The pulse feed solution consisted of 3 wt% each of the three isomers of methyl ethyl benzene, propylbenzene, isopropylbenzene, and trimethylbenzene, indane, n-nonane (NC9), and 70 wt% desorbent, with n-nonane serving as a tracer. The resulting desorption curves are shown below. Figure 1 As shown, the separation coefficients and resolutions (β1 and β2) between p-toluene and m-toluene, o-toluene, mesitylene, terephthalene, and propylbenzene are respectively... p / m and R p / m β p / o and R p / o β p / 1,3,5 and R p / 1,3,5 β p / 1,2,3 and R p / 1,2,3 β p / pb and R p / pb The results are shown in Table 2.

[0054] Example 6

[0055] The method described in Example 5 was used to separate p-toluene from a mixture of C9 aromatics, except that the desorbents were 30 wt% p-xylene and 70 wt% n-heptane. Separation coefficient and resolution (β) were also discussed. p / m and R p / m β p / o and R p / o β p / 1,3,5 and R p / 1,3,5 β p / 1,2,3 and R p / 1,2,3 β p / pb and Rp / pb The results are shown in Table 2.

[0056] Example 7

[0057] The method described in Example 5 was used to separate p-toluene from a mixture of C9 aromatics, except that the desorbent was 30 wt% p-diethylbenzene and 70 wt% n-heptane. The temperature of the adsorbent entering the adsorption bed was controlled at 145°C. The adsorption performance of the selected adsorbent is shown in Table 2.

[0058] Example 8

[0059] The method described in Example 5 was used to separate p-toluene from a mixture of C9 aromatics, except that adsorbent B was used, and the desorbents were 40 wt% toluene and 60 wt% n-heptane. The temperature of the adsorbent feed entering the adsorption bed was controlled at 140°C. The adsorption performance of the selected adsorbent is shown in Table 2.

[0060] Example 9

[0061] The method described in Example 5 was used to separate p-toluene from a mixture of C9 aromatics, except that adsorbent C was used and the desorbents were 30 wt% toluene and 70 wt% n-heptane. The temperature of the adsorbent feed entering the adsorption bed was controlled at 155°C. The adsorption performance of the selected adsorbent is shown in Table 2.

[0062] Example 10

[0063] The method described in Example 5 was used to separate p-toluene from a mixture of C9 aromatics, except that adsorbent D was used and the desorbents were 20 wt% toluene and 80 wt% n-heptane. The temperature of the adsorbent feed entering the adsorption bed was controlled at 135°C. The adsorption performance of the selected adsorbent is shown in Table 2.

[0064] Table 2

[0065]

[0066] Example 11

[0067] A small-scale simulated moving bed apparatus was used for liquid-phase adsorption separation to separate p-toluene and ethylbenzene. The apparatus consisted of 24 columns connected in series. The internal chamber of each column, 200 mm high and 40 mm in diameter, contained 2700 g of adsorbent. The 24th column was connected to the first column via a pump, allowing fluid circulation within the column. Material could be introduced or extracted at the connection points between each column. There were 7 columns between the raffinate outlet and the feed inlet (adsorption zone); 9 columns between the feed inlet and the raffinate outlet (purification zone); 5 columns between the raffinate outlet and the desorbent inlet (desorption zone); and 3 columns between the desorbent inlet and the raffinate outlet (isolation zone). The inlet and outlet positions changed with each step time; every step time, the inlet / outlet advanced one column. Figure 2 As shown, the position moves from the solid arrow to the dashed arrow, and the next step advances in the predetermined direction. This process continues, changing the positions of the inlet and outlet until they return to their starting positions, constituting one cycle. One step time is 80 seconds, and one cycle is 32 minutes.

[0068] The adsorption feedstock was a heavy aromatic hydrocarbon, mainly C9+ aromatics, including 15.5 wt% p-ethylbenzene, 35.1 wt% m-ethylbenzene, 18.8 wt% o-ethylbenzene, 20.6 wt% propylbenzene, 5.0 wt% cumene, and 5.0 wt% mesitylene. The temperature of the adsorption feedstock entering the adsorption bed was controlled at 145℃, and the operating pressure was 0.88 MPa. Adsorbent A was used, and the desorbent was 99.9 wt% toluene. The feed rate was 1.28 kg / h, the desorbent injection rate was 1.54 kg / h, the evaporator rate was 0.95 kg / h, and the residual evaporator rate was 1.87 kg / h. The mass flow rate ratio of desorbent to heavy aromatic hydrocarbon feedstock entering the simulated moving bed was 1.2, and the heavy aromatic hydrocarbon feedstock flow rate per unit mass of adsorbent was 0.47 kg / (h·kg adsorbent). The yield of the target product, p-ethylbenzene, was 99.50 wt%, and the purity was 99.84 wt%.

[0069] After the simulated moving bed operation stabilized, a mixed sample of the extract and raffinate from one cycle was taken and its composition analyzed. Based on the analytical results, the purity and yield of ethylbenzene were calculated as follows:

[0070]

[0071] Where X is the mass fraction of each component in the extract;

[0072]

[0073] Where X 对甲乙苯，抽出液 Q represents the mass fraction of p-toluene in the extract. 抽出液 X is the mass flow rate of the extracted liquid. 对甲乙苯，抽余液Q represents the mass fraction of p-toluene in the residual liquid. 抽余液 This represents the mass flow rate of the residual liquid.

[0074] Example 12

[0075] The method for separating p-toluene from heavy aromatic feedstock is followed as in Example 11, except that the apparatus consists of 12 columns connected in series. The internal chamber of each column is 200 mm high and 80 mm in diameter, containing a total of 2750 g of adsorbent. The 12th column is connected to the 1st column via a pump. The adsorption zone has 4 columns, the purification zone has 4 columns, the desorption zone has 3 columns, and the isolation zone has 1 column. One step time is 150 seconds, and one cycle is 30 minutes. The temperature of the feedstock entering the adsorption bed is controlled at 140°C, and the operating pressure is 0.88 MPa. The feed rate was 1.39 kg / h, the desorbent injection rate was 2.07 kg / h, the extract rate was 1.08 kg / h, and the residual liquid rate was 2.38 kg / h. The mass flow rate ratio of desorbent to heavy aromatic feedstock entering the simulated moving bed was 1.49, and the heavy aromatic feedstock flow rate per unit mass of adsorbent was 0.51 kg / (h·kg adsorbent). The yield of the target product, p-ethylbenzene, was 99.44 wt%, and the purity was 99.68 wt%.

[0076] Example 13

[0077] The method described in Example 11 was used to separate p-toluene from a heavy aromatic feedstock, except that adsorbent B was used instead of adsorbent B, and the desorbent consisted of 99.1 wt% toluene and 0.9 wt% n-heptane. The temperature of the feedstock entering the adsorption bed was controlled at 135 °C, and the operating pressure was 0.88 MPa. The yield of the target product, p-toluene, was 99.40 wt%, and the purity was 99.60 wt%.

[0078] Example 14

[0079] The method described in Example 11 was used to separate p-toluene from a heavy aromatic hydrocarbon feedstock, except that adsorbent C was used instead of p-toluene. The temperature of the feedstock entering the adsorption bed was controlled at 155°C, and the operating pressure was 0.88 MPa. The feedstock consisted of heavy aromatic hydrocarbons, including 15.5 wt% p-toluene, 25.1 wt% m-toluene, 0.8 wt% o-toluene, 10.6 wt% propylbenzene, 10.2 wt% isopropylbenzene, 5.0 wt% mesitylene, 5.0 wt% metabenzene, and 2.8 wt% indene. The yield of the target product, p-toluene, was 99.30 wt%, with a purity of 99.25 wt%.

[0080] Example 15

[0081] The method described in Example 11 was used to separate p-toluene from a heavy aromatic feedstock, except that adsorbent D was used instead. The yield of the target product, p-toluene, was 99.55 wt%, and the purity was 99.54 wt%.

[0082] Example 16

[0083] The method described in Example 11 was used to separate p-toluene from a heavy aromatic hydrocarbon feedstock, except that the temperature of the feedstock entering the adsorption bed was controlled at 155°C and the operating pressure at 0.92 MPa. The feedstock was a heavy aromatic hydrocarbon feedstock, comprising 30.5 wt% p-toluene, 20.5 wt% m-toluene, 15.2 wt% o-toluene, 5.6 wt% propylbenzene, 5.2 wt% isopropylbenzene, 5.0 wt% mesitylene, 5.0 wt% metabenzene, and 8.0 wt% indene. The yield of the target product, p-toluene, was 99.30 wt%, with a purity of 99.54 wt%.

[0084] The present application has been described above with reference to preferred embodiments; however, these embodiments are merely exemplary and illustrative. Various substitutions and modifications can be made to the present application based on these embodiments, all of which fall within the protection scope of the present application.

Claims

1. A method for adsorbing and separating high-purity p-toluene-ethylbenzene from heavy aromatic hydrocarbon feedstock, comprising: introducing the heavy aromatic hydrocarbon feedstock into an adsorbent, causing the p-toluene-ethylbenzene in the feedstock to be adsorbed by the adsorbent; discharging the unadsorbed components as the raffinate from the adsorption separation; and introducing a desorbent into the adsorbent to desorb the adsorbed p-toluene-ethylbenzene, thereby obtaining the raffinate from the adsorption separation, characterized in that... The heavy aromatics feedstock is a heavy aromatics containing multiple C9+ aromatic components, with p-toluene accounting for 5-90 wt% of the C9+ aromatic components. The adsorbent is (1) a NaX molecular sieve modified by cation exchange of one or more group IA metals selected from Li, K, Rb, and Cs; (2) A NaX molecular sieve modified by exchange of one or more Group IA metal cations selected from Li, K, Rb, and Cs with one or more metal cations selected from Group IIA metals and Group IB metals, wherein, based on metal oxides, the molar ratio of Group IA metal oxides to Group IIA and Group IB metal oxides is not less than 0.05; or (3) NaX molecular sieve modified by cation exchange of one or more metals selected from Group IIA metals Ba and Group IB metals; The adsorption separation process employs a simulated moving bed device, which includes an adsorption zone, a purification zone, a desorption zone, and an isolation zone, with a bed layer ratio of 29±10% : 37±15% : 21±5% : 13±4%. The modified adsorbent has a water-to-alumina molar ratio of no more than 1.00, the Na ion exchange rate of the NaX molecular sieve adsorbent is 80-99.8 mol%, and the NaX molecular sieve crystals have a particle size of 0.5-1.0 micrometers.

2. The method according to claim 1, wherein the molar ratio of silicon oxide to aluminum oxide in the NaX molecular sieve is not less than 2.

2.

3. The method as described in claim 1, characterized in that, The molar ratio of adsorbed water to alumina in the modified adsorbent is no greater than 0.

80.

4. The method as described in claim 1, characterized in that, Heavy aromatics feedstocks come from reforming products, cracked gasoline, naphtha, byproducts from ethylbenzene plants, or catalytic cracking gasoline.

5. The method as described in claim 4, characterized in that, The C9+ aromatic components in the heavy aromatic feedstock include p-ethylbenzene, m-ethylbenzene, o-ethylbenzene, propylbenzene, isopropylbenzene, mesitylene, pseudotrimethylbenzene, thionylbenzene, methylpropylbenzene, diethylbenzene, ethylxylbenzene and / or indene.

6. The method as described in claim 5, characterized in that, The mass fraction of p-toluene in the C9+ aromatic hydrocarbon component is 5~90 ​​wt%, and the mass fraction of m-toluene in the C9+ aromatic hydrocarbon component is 5~90 ​​wt%.

7. The method according to any one of claims 1 to 5, characterized in that, The desorbent is alkylbenzene.

8. The method as described in claim 7, characterized in that, The desorbent is toluene.

9. The method according to any one of claims 1 to 6, characterized in that, The desorbent is a mixture of alkylbenzene and alkanes, wherein the mass fraction of alkylbenzene in the desorbent is not less than 20 wt%.

10. The method as described in claim 9, characterized in that, The mass fraction of alkylbenzene in the desorbent is not less than 30 wt%.

11. The method according to any one of claims 1 to 6, characterized in that, The desorbent is a para-alkylbenzene.

12. The method according to any one of claims 1 to 6, characterized in that, The desorbent is p-xylene.

13. The method as described in claim 1, characterized in that, The adsorption temperature is 100 ~ 185℃.

14. The method as described in claim 13, characterized in that, The adsorption temperature is 115 ~ 185℃.

15. The method as described in claim 14, characterized in that, The adsorption temperature is 135 ~ 165℃.

16. The method as described in claim 1, characterized in that, The adsorption pressure is 0.5 MPa ~ 1.5 MPa.

17. The method as described in claim 16, characterized in that, The adsorption pressure is 0.8 MPa ~ 1.0 MPa.

18. The method as described in claim 1, characterized in that, Group IB metals are Cu and / or Ag.

19. The method as described in claim 1, characterized in that, The metal cations used for NaX molecular sieve modification are a combination of K and Ba.

20. The method as described in claim 1, characterized in that, The metal cations used for NaX molecular sieve modification are a combination of Li and Ba.

21. The method as described in claim 1, characterized in that, The molar concentration of the metal salt modified by metal cation exchange is 0.08 ~ 0.58 mol / L.

22. The method as described in claim 21, characterized in that, The molar concentration of the metal salt modified by metal cation exchange is 0.15 ~ 0.45 mol / L.

23. The method as described in claim 1, characterized in that, The reaction temperature for metal cation exchange modification is 80~100 ℃.

24. The method as described in claim 23, characterized in that, The reaction temperature for metal cation exchange modification is 85~95℃.

25. The method as described in claim 1, characterized in that, The exchange degree of Na ions in NaX molecular sieve adsorbent is 85~99 mol%.

26. The method as described in claim 1, characterized in that, The adsorbent contains 90-99 wt% NaX type molecular sieve and 1-10 wt% binder, and the loss on ignition of the adsorbent after calcination at 600 ℃ is no more than 6.0 wt%.

27. The method as described in claim 26, characterized in that, The loss on ignition of the adsorbent after calcination at 600 ℃ is no more than 5.5 wt%.

28. The method as described in claim 26 or 27, characterized in that, The binder is kaolin, bentonite and / or attapulgite.

29. The method as described in claim 1, characterized in that, The simulated moving bed device includes multiple adsorption beds filled with adsorbent. Each bed has its own material inlet and outlet pipelines. The materials entering and exiting the simulated moving bed device divide the adsorption beds into desorption zones, purification zones, adsorption zones, and isolation zones. The adsorption bed between desorbent injection and extractant collection is the desorption zone, the adsorption bed between extractant collection and feed injection is the purification zone, the adsorption bed between feed injection and residual liquid collection is the adsorption zone, and the adsorption bed between residual liquid collection and desorbent injection is the isolation zone.

30. The method as described in claim 1, characterized in that, The mass flow rate ratio of the desorbent to the heavy aromatic feedstock entering the simulated moving bed device is not greater than 1.

60.

31. The method as described in claim 30, characterized in that, The mass flow rate ratio of the desorbent to the heavy aromatic feedstock entering the simulated moving bed device is not greater than 1.

20.

32. The method as described in claim 1, characterized in that, The flow rate of heavy aromatic feedstock relative to unit mass of adsorbent is not less than 0.40 kg / (h·kg adsorbent).

33. The method as described in claim 32, characterized in that, The flow rate of heavy aromatic feedstock relative to unit mass of adsorbent is not less than 0.50 kg / (h·kg adsorbent).

34. The method as described in claim 1, characterized in that, One cycle of the simulated moving bed device is 15 to 50 minutes.

35. The method as described in claim 34, characterized in that, One cycle of the simulated moving bed device is 20 to 35 minutes.

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