A desulfurization molecular sieve adsorbent, a preparation method and application thereof

Abstract

The application discloses a desulfurization molecular sieve adsorbent and a preparation method and application thereof, and aims to solve the problem of low selectivity of existing adsorbents to carbon disulfide under the condition of coexistence of carbon five double olefins. The scheme comprises the following steps: mixing ZSM-5 molecular sieve raw powder with a specific silicon-aluminum ratio, pseudo-boehmite and rice powder in an acid buffer to obtain a homogeneous slurry; introducing silver nitrate under light-proof conditions to perform liquid phase ion exchange, so that silver ions are anchored to ion sites of the molecular sieve; and performing solid-liquid separation and washing to obtain a modified molecular sieve colloid; after the colloid is extruded into a strip, the strip is calcined in an inert atmosphere through programmed temperature rising, so that the silver ions complete coordination reconstruction in the five-membered ring pore, active centers with sigma-pi coordination effect on carbon disulfide are formed, and finally the adsorbent is obtained. The adsorbent realizes high selective adsorption of carbon disulfide through the size screening effect of the molecular sieve pore and the chemical coordination anchoring of the silver ions in the pore, and significantly improves the recovery rate of carbon five double olefins, and simultaneously has excellent performance of complete regeneration under mild conditions.

Description

Technical Field

[0001] This invention belongs to the field of adsorption separation technology, specifically relating to a desulfurization molecular sieve adsorbent, its preparation method, and its application. Background Technology

[0002] With the continuous expansion of the ethylene industry, the output of its byproduct, C5 distillate oil, has been increasing year by year. How to achieve refined and high-value utilization of this resource has become a key issue in improving the economic efficiency and competitiveness of the petrochemical industry. C5 distillate oil is rich in conjugated dienes such as isoprene, isoprene, and cyclopentadiene, making it an important raw material for synthetic rubber, fine chemicals, and pharmaceutical intermediates. However, the trace amounts of sulfur-containing impurities, such as carbon disulfide, commonly found in C5 distillate oil pose a serious poisoning threat to downstream polymerization catalytic systems, while also corroding process equipment and significantly reducing the purity and color of target products. Therefore, efficient and selective removal of carbon disulfide from C5 distillate oil is a necessary technical prerequisite for ensuring the high-quality utilization of C5 diene resources.

[0003] Among them, adsorption desulfurization technology using molecular sieves as the core adsorbent material has shown significant advantages in the deep purification of C5 distillate oil due to its mild operating conditions, flexible process flow, and zero hydrogen consumption. The core of this technology lies in utilizing the regular micropores and tunable surface chemistry of molecular sieves to physically or chemically capture sulfides. Conventional physical adsorbents mainly rely on high specific surface area and broad pore size distribution to exert their capacity advantage, but their pore surface lacks precise recognition sites for specific sulfide molecules. In a complex liquid environment composed of a large number of C5 dienes with similar chemical properties and molecular sizes, this purely physical sieving and broad-spectrum adsorption mechanism cannot effectively distinguish carbon disulfide from target olefin molecules thermodynamically and kinetically, constituting a fundamental selective barrier.

[0004] In existing technologies, hydrodesulfurization catalysts supported by metal oxides or modified with transition metal phosphides have achieved breakthroughs in activity and stability, but their preparation costs are high, and they are difficult to achieve deep conversion and removal of trace amounts of carbon disulfide under non-hydrogenation conditions without an external hydrogen source. Traditional metal ion-exchange molecular sieve adsorbents suffer from uneven dispersion of active metals and low pore utilization due to the separation of the ion exchange process and the molding process, resulting in adsorption selectivity and capacity for carbon disulfide that are far from ideal. More importantly, neither physical adsorbents nor conventional chemical adsorbents have been able to simultaneously construct a synergistic mechanism of size sieving and chemical anchoring from the perspective of matching the pore topology of the molecular sieve with the dynamic diameter of the adsorbed molecules. This leads to a low actual effective adsorption capacity of the adsorbent for carbon disulfide in competitive adsorption scenarios where C5 dienes coexist, and poor purity of the desorption products, making it difficult to simultaneously meet the requirements of high olefin retention and deep removal of sulfides down to the trace level. This constitutes a technical problem that urgently needs to be solved, restricting the development of this field. Summary of the Invention

[0005] The purpose of this invention is to provide a desulfurization molecular sieve adsorbent, its preparation method, and its application, which can effectively solve the problems in the background art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] Firstly, a method for preparing a desulfurization molecular sieve adsorbent includes the following specific steps: Step 1: Constructing a homogeneous molecular sieve-binder slurry with a specific pore topology: ZSM-5 molecular sieve powder, boehmite, and guar gum powder with a silica-alumina molar ratio within a preset range are mechanically stirred and mixed in an acidic buffer solution to obtain a highly dispersed mixed slurry, wherein the micropore size of the ZSM-5 molecular sieve powder is within a preset pore size range; Step 2: Introducing active centers through liquid-phase ion exchange: The mixed slurry is subjected to liquid-phase ion exchange with silver nitrate under light-protected conditions. The reaction involves anchoring silver ions to the ion exchange sites of the molecular sieve through ion exchange. After the reaction is complete, solid-liquid separation and purification washing are performed to obtain a modified molecular sieve colloid loaded with silver ions. Step 3 involves molding and active site coordination reconstruction: the modified molecular sieve colloid is formed into strips of a specific shape through an extrusion molding process, and then activated by programmed temperature calcination in an inert atmosphere, so that silver ions complete dehydration and coordination reconstruction in the molecular sieve channels, forming active centers with σ-π coordination with carbon disulfide. Finally, after cooling, crushing and sieving, the ion exchange modified molecular sieve adsorbent is obtained.

[0008] Preferably, in step 1, the micropore size of the ZSM-5 molecular sieve powder is within a preset narrow pore size range, and the effective sieving size of the five-membered ring channel opening in its crystal framework structure is between the molecular dynamic diameter of carbon disulfide and the molecular dynamic diameter of C5 diene. This size sieving effect constructs the first selective barrier at the molecular scale, allowing only carbon disulfide molecules with a dynamic diameter smaller than the pore opening size to enter the pore, while physically repelling C5 diene molecules with a larger dynamic diameter from entering the pore.

[0009] Preferably, in step 1, the silica-alumina molar ratio of the ZSM-5 molecular sieve powder is within a preset intermediate range, the pectin index of the boehmite is in the high pectin index range, and the silver nitrate in step 2 has a predetermined high purity. By synergistically controlling the silica-alumina ratio of the molecular sieve and the pectin index of the binder, the rheological properties and ion exchange capacity of the mixing system can be precisely adjusted during the slurry preparation stage. The silica-alumina ratio directly determines the negative charge density available for ion exchange on the molecular sieve framework, thus affecting the subsequent loading and distribution uniformity of silver ions.

[0010] Preferably, the silica-alumina molar ratio of the ZSM-5 molecular sieve powder and the solubility index of the pseudoboehmite are selected as specific values ​​that balance the optimal ion exchange capacity and molding strength of the matrix.

[0011] Preferably, in step 1, the acidic buffer solution is an acetate-sodium acetate buffer solution with a pH value within a predetermined weakly acidic range. This weakly acidic buffer environment can maintain a stable proton concentration in the liquid phase system, effectively inhibit the occurrence of dealumination reaction of the molecular sieve framework, protect the integrity of the molecular sieve crystal structure, and provide a suitable charge environment for the subsequent liquid-phase ion exchange reaction of silver ions.

[0012] Preferably, in step 1, the solid content of the ZSM-5 molecular sieve powder in the mixed slurry is within a preset solid content range, and the solid content of the boehmite is within another preset solid content range. Precise control of the solid content is fundamental to the subsequent extrusion molding process, directly affecting the plasticity of the colloid, the extrusion pressure, and the mechanical strength and bulk density of the final strip adsorbent. Preferably, the solid content of the molecular sieve powder and the solid content of the boehmite are each selected to their optimal values.

[0013] Preferably, in step 1, the mass ratio of the ZSM-5 molecular sieve powder, boehmite, and guar gum powder is within a preset range. Guar gum powder, acting as a pore-forming agent, decomposes and escapes during calcination, forming auxiliary mesoporous or macroporous channels within the adsorbent, optimizing the diffusion and mass transfer pathway of the adsorbate within the adsorbent particles, and enhancing adsorption kinetics. Preferably, this mass ratio is selected to achieve the optimal diffusion performance of the adsorbent.

[0014] Preferably, in step 1, the mixing is carried out at a predetermined temperature and a predetermined stirring rate for a predetermined time, so as to promote the full and uniform dispersion of each component in the acidic buffer solution, forming a macroscopically uniform and microscopically highly dispersed slurry system, which ensures the uniformity of the ion exchange reaction in step 2.

[0015] Preferably, in step 2, the added mass of silver nitrate is based on the mass ratio of silver ions to the dry molecular sieve substrate being within a preset range, and more preferably a specific ratio. This ratio achieves sub-monolayer or sub-nanometer-scale dispersion and loading of silver ions, effectively preventing the migration and aggregation of silver species during calcination, ensuring that the active centers are highly dispersed in the form of isolated cations on the inner surface of the pores, and maximizing their chemical anchoring effect.

[0016] Preferably, in step 2, the temperature of the liquid-phase ion exchange reaction is within a preset temperature range, preferably a specific temperature, and the reaction is carried out under light-protected conditions with a preset stirring rate for a preset time. Silver nitrate is used as the silver source, and its anion is nitrate, which can be completely decomposed during the subsequent calcination process, without introducing competing anionic impurities into the product. The light-protected condition is to prevent photochemical reduction of silver ions. After the reaction, the resulting suspension is filtered, and the filter cake is repeatedly washed with deionized water until the conductivity of the filtrate is lower than a preset conductivity threshold, so as to completely remove free silver ions and other impurity ions that have not undergone ion exchange.

[0017] Preferably, in step 3, the modified molecular sieve colloid is extruded into strips with a diameter within a preset size range using a screw extruder, preferably cylindrical strips. This geometry balances lower bed pressure drop and a large geometrical surface area, which is beneficial for achieving uniform fluid distribution and efficient mass transfer in a fixed-bed adsorber.

[0018] Preferably, in step 3, the calcination activation heating procedure is as follows: heating from room temperature to a predetermined final temperature range at a preset heating rate, and calcining at this temperature for a preset time. Preferably, heating to a specific final temperature at a specific heating rate, and calcining at this temperature for a specific time, is carried out entirely in a nitrogen atmosphere. Under this temperature window and inert atmosphere, silver ions undergo an evolutionary path of "dehydration-denitration-coordination reconstruction," forming active centers with specific coordination structures in situ on the inner surface of the five-membered ring channels of the ZSM-5 molecular sieve. These centers have σ-π coordination effects on the carbon-sulfur double bonds in the carbon disulfide molecule, constituting a second chemical anchoring mechanism.

[0019] Preferably, in step 3, the roasted and activated material is naturally cooled to room temperature, then crushed and sieved to select particles within a preset mesh size range, thus obtaining the final ion exchange modified molecular sieve adsorbent.

[0020] Secondly, the present invention also provides a desulfurization molecular sieve adsorbent prepared by any of the above preparation methods.

[0021] Thirdly, the present invention also provides the application of the above-mentioned desulfurization molecular sieve adsorbent in the selective adsorption of carbon disulfide from a hydrocarbon mixture containing C5 dienes. Specifically, the hydrocarbon mixture containing C5 dienes is a C5 distillate oil, wherein the total mass percentage of isoprene, isoprene, and cyclopentadiene is not less than a preset proportion, and the mass concentration of carbon disulfide is within a preset concentration range.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. This invention successfully achieves a synergistic effect between physical size sieving and chemical coordination anchoring mechanisms at the molecular sieve pore scale, fundamentally solving the technical problem of low selectivity of conventional adsorbents for carbon disulfide in the context of competitive adsorption of C5 dienes. By selecting ZSM-5 molecular sieve with pore size precisely between the kinetic diameters of carbon disulfide and isoprene as the matrix, combined with highly dispersed silver ion active centers within the pores, the selective adsorption capacity of carbon disulfide is improved by orders of magnitude, maximizing the recovery rate of the target olefin.

[0024] 2. The "liquid-phase ion exchange-forming-calcination" technical path of this invention completely avoids the defects of gradient distribution of active components and pore blockage in the traditional method of first forming and then impregnating for exchange. Silver ions complete the exchange in the slurry state before forming, so that their distribution in the molecular sieve micropores reaches a thermodynamic equilibrium state, truly realizing sub-nanometer monodispersion of active centers, greatly improving the accessibility and utilization efficiency of each active center, and increasing the adsorption separation coefficient of the desulfurizing agent by an order of magnitude compared with conventional activated carbon physical adsorbents.

[0025] 3. The adsorbent prepared by this invention possesses excellent regeneration performance and a low-energy regeneration process. Based on the moderate chemisorption energy of the σ-π coordination bond, it ensures efficient capture of carbon disulfide while achieving complete regeneration of the active center under mild nitrogen atmosphere conditions. Furthermore, after multiple adsorption-desorption cycles, its dynamic adsorption capacity retention rate remains at a high level, far superior to traditional metal oxide adsorbents that rely on high-temperature calcination for regeneration, significantly reducing the operating energy consumption and costs of industrial plants. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0027] The core of the preparation method of the ion exchange modified molecular sieve adsorbent provided by this invention lies in the in-situ construction of sub-nanometer-scale dispersed Ag with σ-π coordination anchoring effect on carbon disulfide within the pores of ZSM-5 molecular sieves with specific size sieving capabilities through an integrated path of "liquid-phase ion exchange-forming-calcination". + Active center. The specific implementation process of this method follows three closely connected steps.

[0028] Step 1: Construct a homogeneous molecular sieve-binder slurry with a specific pore topology.

[0029] The core objective of this step is to prepare an aqueous slurry system in which the components are highly dispersed, the rheological properties are controllable, and the original pore structure of the molecular sieve is completely preserved. This system forms the material basis for subsequent ion exchange reactions and molding processes.

[0030] In specific operations, ZSM-5 molecular sieve powder with a silicon-to-aluminum molar ratio ranging from 35 to 65 was selected as the functional matrix of the adsorbent. The crystalline framework structure of this ZSM-5 molecular sieve powder has a narrow pore size range of 0.42-0.48 nm. This pore size parameter ensures that the effective sieving size of the five-membered ring channel openings of the molecular sieve lies precisely between the kinetic diameter of carbon disulfide molecules (0.38 nm) and the kinetic diameter of C5 dienes, represented by isoprene (0.55 nm). This channel topology constructs the first physical selectivity barrier at the molecular scale, allowing only carbon disulfide molecules with smaller kinetic diameters to enter the internal channels while repelling larger C5 diene molecules from the pore openings.

[0031] Simultaneously, boehmite with a colloidal index of 85%-96% was selected as a binder precursor. The colloidal index of boehmite reflects its ability to disperse and hydrate in acidic media to form boehmite sol. A high colloidal index ensures that boehmite can be fully dissolved during subsequent mixing, generating an alumina sol component with high binding activity, effectively binding the molecular sieve crystal particles. Guaranteed guar powder was weighed as a pore-forming agent. The introduction of guar powder is to allow organic matter to decompose and escape during the subsequent calcination stage, forming a well-connected mesoporous or macroporous auxiliary channel network inside the final adsorbent particles.

[0032] The three solid powders are mixed in a preset mass ratio. The mass ratio of the three is precisely controlled to be 1:0.30-0.50:0.03-0.06.

[0033] A pre-prepared acidic buffer solution with a pH of 3.5-5.0, consisting of acetic acid and sodium acetate dissolved in deionized water in a specific ratio, was used as the dispersion medium. This weakly acidic buffer system maintains a relatively constant proton concentration in the liquid phase, inhibits potential framework dealuminization of the molecular sieve during stirring, and protects the integrity of its crystal structure. Simultaneously, this weakly acidic environment facilitates the complete dissolution of boehmite and provides a stable charge environment for the subsequent liquid-phase ion exchange reaction of silver ions in step 2.

[0034] The solid mixture is slowly added to the acidic buffer solution while stirring, and stirring continues until a homogeneous slurry is formed. During this process, the solid content of each component in the final slurry is precisely controlled by adjusting the volume of the acidic buffer solution. The solid content of the ZSM-5 molecular sieve powder in the slurry is controlled within the range of 0.35-0.45 g / mL. The solid content of the boehmite is controlled within the range of 0.10-0.12 g / mL. Precise control of the solid content directly determines the rheological parameters of the slurry, such as viscosity and thixotropy, ensuring the plasticity of the colloid and the mechanical strength of the extruded strips in the subsequent extrusion molding process in step 3.

[0035] The mixing process was carried out under constant temperature conditions of 25-35℃. A mechanical stirrer was used to continuously stir at a constant rate of 200 rpm for 3 hours. During this process, boehmite gradually dissolved in the acidic buffer solution, and its surface hydroxyl groups reacted with water molecules to form a network-structured alumina sol. This alumina sol uniformly coated the ZSM-5 molecular sieve crystal particles, forming a binder precursor film. The fibrous particles of guar gum powder were also uniformly dispersed among the components of the slurry system during this process. The purpose of this long-term, constant-speed stirring operation was to break up all soft agglomerates between solid particles, achieving a macroscopically homogeneous and microscopically multiphase highly dispersed suspension state for the molecular sieve powder, boehmite, and guar gum powder in the liquid medium, resulting in a homogeneous mixed slurry.

[0036] Step 2: Implement liquid-phase ion exchange to introduce active centers.

[0037] The core purpose of this step is to complete the ion exchange reaction of silver ions in the liquid slurry system before molecular sieve formation, so as to accurately anchor the active components in ionic form to the negative charge sites of the ZSM-5 molecular sieve framework, thereby achieving pre-dispersion and highly uniform loading of the active centers.

[0038] In the specific operation, silver nitrate, as the silver source, is added to the mixed slurry obtained in the previous step. The selected silver nitrate has a purity of not less than 99.8%, and its anion is nitrate. This anion can be completely decomposed and escaped as nitrogen oxide gas during the subsequent calcination process in step 3, and will not introduce competing impurity anions into the final adsorbent product. The amount of silver nitrate added is precisely measured based on the mass ratio of silver ions to the dry molecular sieve, which ranges from 0.06 to 0.12:1.

[0039] After silver nitrate is added, the entire reaction system is immediately placed in a light-protected environment, such as by covering the reaction vessel with a light shield or operating in a dark room. This light-protection measure aims to inhibit the photochemical reduction reaction of silver ions under light, preventing them from being prematurely reduced to elemental silver particles, which would lead to the aggregation and inactivation of active species.

[0040] Under light-protected conditions, heating and stirring were initiated to conduct a liquid-phase ion exchange reaction. The reaction temperature was controlled within the range of 70-85℃. After reaching the target temperature, mechanical stirring was activated at a rate of 300 rpm. The reaction was carried out for 6 hours under these conditions. During this process, hydrated silver ions in the solution, driven by their high migration kinetic energy and concentration gradient, diffused to the surface of the ZSM-5 molecular sieve crystals. Through ion exchange, they replaced protons or sodium ions on the negatively charged sites of the aluminum-oxygen tetrahedra in the molecular sieve framework, anchoring them as isolated cations on the inner surface of the molecular sieve micropores through electrostatic attraction and coordination. Because the exchange occurred in a highly fluid slurry state, the steric hindrance and diffusion limitations caused by binder encapsulation during the exchange were avoided. This ensured that silver ions achieved a near-thermodynamically balanced, highly dispersed state within the molecular sieve micropores, realizing sub-nanometer-scale monodisperse loading.

[0041] After the reaction, the resulting suspension underwent solid-liquid separation. A Buchner funnel connected to a vacuum filtration system was used to filter the suspension, separating the filter cake. The retained filter cake was the crude modified molecular sieve colloid loaded with silver ions. Subsequently, the filter cake was repeatedly washed with deionized water at 60-80℃ to remove free silver ions, nitrate ions, and acetate-sodium acetate buffer salts that were trapped between colloidal particles or weakly adsorbed on the surface. The washing endpoint was determined by online monitoring of the conductivity of the washing filtrate. Washing continued until the conductivity of the filtrate at 25℃ was below 50 μS / cm. This conductivity threshold ensured that all non-ion-exchangeable soluble impurity ions were thoroughly washed away, resulting in pure modified molecular sieve colloid loaded with silver ions.

[0042] Step 3: Perform molding and active site coordination reconstruction.

[0043] The core objective of this step is to endow the adsorbent with macroscopic geometry and mechanical strength through the shaping and controlled heat treatment of the colloid, while activating the silver ions in the micropores at the molecular scale, causing them to undergo coordination environment reconstruction and form highly active centers with specific σ-π coordination with carbon disulfide.

[0044] In practice, the modified molecular sieve colloid obtained in step 2 is fed into a screw extruder for extrusion molding. The screw extruder's barrel and die head have a specific geometric design. Under the push and extrusion of the screw, the colloid passes through a perforated plate with a pre-set diameter circular hole. The diameter of this die hole determines the size of the extruded strip, which is set to 1.8-2.0 mm, thus extruding the colloid into continuous cylindrical strips with a diameter in the range of 1.5-2.5 mm. This cylindrical strip geometry, when applied to a fixed-bed adsorber, ensures an effective flow cross-sectional area between particles to reduce bed pressure drop while providing a high geometrical surface area, which facilitates uniform fluid distribution in the bed and rapid mass transfer of adsorbate into the strip particles.

[0045] The extruded wet strips are cut into appropriate lengths, such as 5-15 mm, and then fed into a programmable temperature-controlled roasting furnace for roasting and activation. The entire roasting process is carried out in an inert atmosphere of high-purity nitrogen with a purity of not less than 99.99% to prevent oxidation side reactions of organic matter and silver species at high temperatures.

[0046] The calcination activation temperature program was strictly set and precisely executed. The program started at room temperature and was slowly heated at a constant rate of 2°C per minute. This slow heating rate allowed sufficient time for the physical adsorbed and chemically bound water inside the colloid to vaporize and migrate, and allowed organic matter and easily decomposable salts such as guar gum powder, acetate, and nitrate to decompose and escape systematically within their respective decomposition temperature ranges, avoiding particle disintegration or cracking caused by a sudden increase in internal gas pressure due to rapid heating. The temperature was continuously raised to a final temperature of 480°C. After reaching this final temperature, the system automatically switched to a constant temperature mode, maintaining the calcination at this temperature for 4 hours.

[0047] During the heating and isothermal process from room temperature to 480℃, hydrated silver ions within the molecular sieve channels undergo a sequential evolutionary path of "dehydration-denitrification-coordination reconstruction" as the ambient temperature increases stepwise. First, in the low-temperature range (e.g., below 200℃), silver ions shed their outer layer of physically adsorbed water and coordinated water. Subsequently, in the intermediate-temperature range (e.g., 200℃ to 400℃), nitrate ions undergo thermal decomposition and are expelled as nitrogen oxides with the nitrogen gas flow. Finally, in the high-temperature activation phase (isothermal period at 480℃), completely dehydrated bare Ag... +Under the unique electrostatic field and spatial constraint of the five-membered ring channels of ZSM-5 molecular sieve, ions undergo in-situ coordination reconstruction, resulting in a rearrangement of their electron cloud distribution and the formation of active centers with specific coordination unsaturation. These active centers possess extremely strong σ-π coordination feedback capabilities to the carbon-sulfur double bonds in carbon disulfide molecules. This chemical interaction constitutes a second chemical anchoring mechanism for carbon disulfide molecules that have entered the channels.

[0048] After the isothermal calcination stage, heating is stopped, but nitrogen purging continues, allowing the calcined and activated material to cool naturally within the furnace to near room temperature (below 50°C). The cooled, molded adsorbent material is then removed, appearing as strip-shaped particles with a certain mechanical strength. Subsequently, the material undergoes crushing and sieving. A jaw crusher or double-roll crusher is used to gently crush the long strips into short, columnar particles, which are then sieved using a standard test sieve. Particles with a size range of 20-40 mesh are collected. This 20-40 mesh particle size distribution balances the relationship between mass transfer rate and bed pressure drop, representing an ideal fixed-bed packing size. Finally, particles within this size range are collected, yielding an ion-exchange modified molecular sieve adsorbent with preferential adsorption selectivity for carbon disulfide.

[0049] As a further specification of the above method steps, a specific embodiment 1 includes the following operations:

[0050] Weigh out 1000 g of ZSM-5 molecular sieve powder (silicon-to-aluminum molar ratio 50, micropore size 0.45 nm), 400 g of boehmite (colloidal solubility index 93%), and 40 g of guar gum powder. Add this solid mixture to 2.5 L of acetate-sodium acetate buffer solution (pH 4.0) preheated to 30 °C. This buffer solution is prepared by mixing 0.2 mol / L acetic acid solution and 0.2 mol / L sodium acetate solution at a volume ratio of 8:2. Turn on the top-mounted stirrer and stir continuously at 200 rpm for 3 hours to obtain a fine, emulsified slurry without particle agglomeration. The solid content of the molecular sieve powder in this slurry is 0.40 g / mL, and the solid content of boehmite is 0.16 g / mL.

[0051] Under a red light in a dark room, 110.2 g of silver nitrate crystals with a purity of 99.9% were added to the above slurry in one go. The reaction vessel was quickly sealed with double-layered light-shielding cloth. The heating was turned on, and the system was heated to 80°C and reacted at a constant temperature and in the dark for 6 hours with a stirring rate of 300 rpm. After the reaction was completed, the hot reaction suspension was poured into a Buchner funnel and filtered under a vacuum of -0.08 MPa. The filter cake was repeatedly washed and rinsed with 80°C deionized water, and dried after each wash, repeated 5 times. The conductivity of the filtrate after the 5th wash at 25°C was measured to be 23 μS / cm, which was below the threshold of 50 μS / cm. Washing was stopped, and a silvery-white, moist modified molecular sieve colloidal filter cake was obtained.

[0052] The filter cake was fed into a twin-screw extruder with a screw diameter of 50 mm and a porous die with a pore size of 2.0 mm. The extrusion speed was 15 mm / s, yielding continuous cylindrical wet strips with a diameter of approximately 2.0 mm. After the wet strips were allowed to air dry at room temperature for 12 hours, they were cut into strips with an average length of 8 mm. The strips were laid flat in a corundum crucible and placed in a tube furnace. Nitrogen gas was introduced at a flow rate of 2 L / min to purge the air from the furnace for 30 minutes. Then, the temperature was programmed to rise from 25 °C to 480 °C at a rate of 2 °C / min, and calcined at 480 °C for 4 hours. After calcination, the strips were allowed to cool naturally to 45 °C under a continuous nitrogen flow. The strip-shaped product, which has turned yellowish-brown, is taken out and crushed by a double-roll crusher. It is then sieved using 20-mesh and 40-mesh standard sieves. The particles between the two sieves are taken to obtain the final Ag / ZSM-5 ion exchange modified molecular sieve adsorbent with high selective adsorption capacity for carbon disulfide.

[0053] The adsorbent exhibited preferential adsorption selectivity for carbon disulfide in subsequent application tests. The application process involved packing the adsorbent into a fixed-bed adsorption column with an inner diameter of 10 mm, setting the adsorption temperature to 30°C, and passing C5 distillate oil containing C5 dienes such as isoprene, isoprene, and cyclopentadiene, as well as carbon disulfide at concentrations ranging from 5 ppm to 500 ppm, through the adsorption column at a set volume hourly space velocity. The effluent was collected at the outlet, and sulfur and olefin content were analyzed. The dynamic adsorption capacity and selectivity coefficient were calculated based on the difference in inlet and outlet concentrations. The selectivity coefficient S was defined using the following formula:

[0054] Among them, Q CS2 and Q C5 , representing the adsorption capacities of the adsorbent for carbon disulfide and C5 diene at equilibrium, respectively; Ce,cs2 and Ce,c5 represent the concentrations of carbon disulfide and C5 diene in the fluid phase at adsorption equilibrium, respectively. In simulated tests of isoprene and carbon disulfide, the calculated selectivity coefficient S reached 7.1.

[0055] The adsorbent, after adsorption saturation, is regenerated. During regeneration, the temperature of the fixed bed is increased to 160°C at a rate of 3°C per minute under nitrogen purging, and maintained at 160°C for 2 hours. Under these mild conditions, carbon disulfide molecules adsorbed by σ-π coordination bonds gain sufficient energy to desorb from the Ag⁺ active centers and are carried away by the nitrogen flow. After regeneration, the bed is cooled to the adsorption temperature for the next cycle. After 5 consecutive adsorption-regeneration cycles, its dynamic adsorption capacity for carbon disulfide remains at 93.5% of the initial capacity. In another example testing product performance, using a simulated oil containing 50 wt% isoprene and 100 ppm carbon disulfide, the resulting adsorbent had an initial breakthrough adsorption capacity of 4.3 mg / g, a selectivity coefficient of 7.3, and a capacity retention rate of 92.8% after 5 regenerations.

[0056] Example 2

[0057] This embodiment demonstrates a technical solution implemented with an alternative combination of parameters. This solution adjusts the silica-to-alumina ratio and the silver ion exchange capacity of the molecular sieve.

[0058] In step 1, ZSM-5 molecular sieve powder with a silica-alumina molar ratio of 65 and a micropore size of 0.44 nm was selected. The gel solubility index of boehmite was 96%. 1000 g of the molecular sieve powder, 350 g of boehmite, and 50 g of guar gum powder were mixed in an acidic buffer solution. The acidic buffer solution was an acetate-sodium acetate buffer solution with a pH of 3.5. By controlling the amount of buffer solution, the solid content of molecular sieve in the mixed slurry was 0.50 g / mL, and the solid content of boehmite was 0.175 g / mL. The mixing conditions were 35°C, stirring at 250 rpm for 2 hours.

[0059] In step 2, the added silver nitrate was measured at a dry weight ratio of silver ions to molecular sieves of 0.12:1. The liquid-phase ion exchange reaction was set at 90°C and carried out for 4 hours with stirring at 400 rpm in the dark. After the reaction, the suspension was filtered and washed, with the washing endpoint being a filtrate conductivity of less than 50 microsiemens per centimeter.

[0060] In step 3, extrusion molding is performed using a die plate with a diameter of 2.5 mm to extrude cylindrical strips. The calcination activation process is as follows: under a nitrogen atmosphere, the temperature is increased from room temperature to 550°C at a rate of 3°C per minute, and calcined at this constant temperature for 3 hours. After natural cooling, the strips are crushed and sieved to obtain 20-40 mesh particles, yielding the finished adsorbent product.

[0061] Application testing of this adsorbent was conducted using C5 distillate oil containing a total mass percentage of cyclopentadiene and isoprene of not less than 45% and a carbon disulfide concentration of 500 ppm. At an adsorption temperature of 40°C, its selectivity coefficient S reached 6.9, and after 5 adsorption-desorption cycles, the dynamic adsorption capacity retention rate of carbon disulfide was 92.1%. Regeneration was performed under a nitrogen atmosphere, heating to 180°C for 1.5 hours.

[0062] Example 3

[0063] This embodiment further demonstrates the technical solution under the extreme conditions of low silicon-to-aluminum ratio and low calcination temperature in molecular sieves.

[0064] In step 1, ZSM-5 molecular sieve powder with a silica-alumina molar ratio of 35 and a micropore size of 0.48 nm was selected. The gel solubility index of boehmite was 85%. 1000 g of the molecular sieve powder, 600 g of boehmite, and 80 g of guar gum powder were mixed. The acidic buffer solution was an acetate-sodium acetate buffer solution with a pH of 5.0. The solid content of molecular sieve in the mixed slurry was controlled at 0.25 g / mL, and the solid content of boehmite was controlled at 0.15 g / mL. The mixture was stirred at 400 rpm for 4 hours at 25°C.

[0065] In step 2, the mass of silver nitrate added was measured according to a silver ion to molecular sieve dry basis mass ratio of 0.03:1. The liquid-phase ion exchange reaction was carried out at 60°C for 8 hours with stirring at 250 rpm in the dark. The filter cake was washed until the conductivity of the filtrate was less than 50 μSiemens per centimeter.

[0066] In step 3, extrusion molding yields cylindrical strips with a diameter of 1.5 mm. The calcination activation process is as follows: calcination is carried out in a nitrogen atmosphere at a rate of 1°C per minute to 400°C, followed by constant-temperature calcination for 5 hours. After cooling, crushing, and sieving, 20-40 mesh particles are obtained to produce the finished product.

[0067] In application testing, for a C5 distillate feedstock with a carbon disulfide concentration of 5 ppm, the selectivity coefficient S was calculated to be 7.0 at an adsorption temperature of 20°C, and the dynamic adsorption capacity retention rate was 92.5% after 5 regenerations. The regeneration conditions were treatment at 150°C in nitrogen for 3 hours.

[0068] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a desulfurization molecular sieve adsorbent, characterized in that, Includes the following steps: Step 1: Construct a homogeneous molecular sieve-binder slurry with a specific pore topology: ZSM-5 molecular sieve powder, boehmite, and guar gum powder with a silicon-to-aluminum molar ratio within a preset range are mechanically mixed in an acidic buffer solution to obtain a highly dispersed slurry. The micropore size of the ZSM-5 molecular sieve powder is 0.42-0.48 nm, and the effective sieving size of the five-membered ring pore opening in its crystal framework structure is between the molecular dynamic diameter of carbon disulfide and the molecular dynamic diameter of C5 diene. Step 2, Introducing active centers through liquid-phase ion exchange: The mixed slurry and silver nitrate are subjected to a liquid-phase ion exchange reaction under light-protected conditions, so that silver ions are anchored to the ion exchange sites of the molecular sieve through ion exchange. After the reaction is completed, solid-liquid separation and purification washing are performed to obtain modified molecular sieve colloid loaded with silver ions. Step 3, performing molding and active site coordination reconstruction: The modified molecular sieve colloid is formed into strips of a specific shape through extrusion molding process, and then activated by programmed temperature rise calcination in an inert atmosphere, so that silver ions successively undergo dehydration, denitrification and coordination reconstruction stages in the molecular sieve channels. Active centers with specific coordination structures are formed in situ on the inner surface of the five-membered ring channels of ZSM-5 molecular sieve. These active centers have σ-π coordination effect on the carbon-sulfur double bond in carbon disulfide molecules. Finally, after cooling, crushing and sieving, ion exchange modified molecular sieve adsorbent is obtained.

2. The preparation method according to claim 1, characterized in that, In step 1, the silicon-aluminum molar ratio of the ZSM-5 molecular sieve raw powder is 35-65, the gel solubility index of the pseudoboehmite is 85%-96%, the acidic buffer solution is an acetate-sodium acetate buffer solution with a pH of 3.5-5.0, the solid content of the ZSM-5 molecular sieve raw powder in the mixed slurry is 0.35-0.45 g / mL, the solid content of the pseudoboehmite is 0.10-0.12 g / mL, and the mass ratio of the ZSM-5 molecular sieve raw powder, pseudoboehmite and guar gum powder is 1:0.30-0.50:0.03-0.

06.

3. The preparation method according to claim 2, characterized in that, In step 1, the mixing is carried out at a constant temperature of 25-35℃ and a predetermined stirring rate for a predetermined time, so as to promote the full and uniform dispersion of each component in the acidic buffer solution, forming a macroscopically uniform and microscopically highly dispersed slurry system.

4. The preparation method according to claim 1, characterized in that, In step 2, the added silver nitrate is added at a mass ratio of silver ions to dry molecular sieve basis of 0.06-0.12:1, the purity of the silver nitrate is not less than 99.8%, the constant temperature of the liquid phase ion exchange reaction is 70-85℃, and the reaction is carried out under light-protected conditions at a preset stirring rate for a preset reaction time.

5. The preparation method according to claim 4, characterized in that, In step 2, silver nitrate is used as the silver source, and its anion is nitrate, which can be completely decomposed and released during the subsequent roasting process. The solid-liquid separation is carried out by vacuum filtration. The purification and washing process uses deionized water to repeatedly wash the filter cake until the conductivity of the filtrate is lower than the preset conductivity threshold, so as to completely remove free silver ions and other impurity ions that have not undergone ion exchange.

6. The preparation method according to claim 1, characterized in that, In step 3, the modified molecular sieve colloid is extruded into strips with a diameter within a preset size range using a screw extruder. The strips are cylindrical and their geometry balances low bed pressure drop and high geometric surface area.

7. The preparation method according to claim 1, characterized in that, In step 3, the heating process for calcination activation is as follows: the temperature is slowly increased from room temperature to a predetermined final temperature range at a constant heating rate of 2°C per minute, and then calcined at this temperature for a preset time, all in a nitrogen atmosphere.

8. The preparation method according to claim 1, characterized in that, In step 3, the roasted and activated material is naturally cooled to room temperature, then crushed and sieved to select particles within a preset mesh size range, thus obtaining the final ion exchange modified molecular sieve adsorbent.

9. A desulfurization molecular sieve adsorbent, characterized in that, Prepared according to the preparation method of any one of claims 1 to 8.

10. The application of the desulfurization molecular sieve adsorbent as described in claim 9 in the selective adsorption of carbon disulfide from a hydrocarbon mixture containing C5 dienes, characterized in that, The desulfurization molecular sieve adsorbent is packed into a fixed-bed adsorber. At a set adsorption temperature, the hydrocarbon mixture containing C5 dienes is passed through the fixed-bed adsorber at a set space velocity. The hydrocarbon mixture containing C5 dienes is C5 distillate oil, wherein the total mass percentage of isoprene, isoprene, and cyclopentadiene is not less than a preset ratio, and the mass concentration of carbon disulfide is within a preset concentration range. The desulfurization molecular sieve adsorbent achieves selective adsorption of carbon disulfide by means of the synergistic mechanism of the sieve pore size sieving effect of its ZSM-5 molecular sieve and the σ-π coordination of the active centers of silver ions in the pores.

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