Benzene partial hydrogenation catalyst recovery process

Abstract

The invention discloses a process for recovering a catalyst for partial hydrogenation of benzene, which comprises the following steps of: sequentially carrying out flash evaporation, phase separation, dehydration, suspension separation and cross-flow membrane separation treatment on reaction feed liquid containing generated oil, water and the catalyst to realize concentration and recovery of the catalyst in the reaction feed liquid. According to the invention, the loss of the catalyst is avoided by adopting a membrane separation technology, and meanwhile, suspension separation and membrane separation are coupled, so that the operation conditions of suspension separation and membrane separation are improved, and the recovery efficiency of the catalyst is improved; in addition, the process has the advantages of small change on the existing production device, small occupied area of equipment, low investment, low operation cost and remarkable economic benefit.

Description

Technical Field

[0001] This invention relates to the filtration, concentration, and recovery of benzene partial hydrogenation catalysts, and more specifically, to a novel process for recovering benzene partial hydrogenation catalysts. By employing membrane separation technology, catalyst loss is avoided. Simultaneously, suspension separation and membrane separation are coupled, improving operating conditions for both processes and increasing catalyst recovery efficiency. Furthermore, this process requires minimal modifications to existing production equipment, requires minimal equipment footprint, and offers low investment, operating costs, and significant economic benefits. Background Art

[0002] Cyclohexene is an important organic compound with the chemical formula C6H10. It is mainly used in organic synthesis, oil extraction and as a solvent. It is one of the raw materials for the production of nylon 6 and nylon 66, and has broad application prospects in medicine, dyes and other fields.

[0003] Domestic cyclohexene production capacity is approaching 10 million tons. The primary production process involves the hydrogenation of benzene with hydrogen in the presence of a hydrogenation catalyst. The hydrogenation catalyst's main components include a Ru-Zn catalyst, a zirconium oxide dispersant, a zinc hydroxide co-catalyst, and an aqueous zinc sulfate solution as the mother liquor. During actual production, a significant amount of Ru-Zn catalyst is lost from the reaction system along with the product oil (primarily composed of benzene, cyclohexene, and cyclohexane) into the subsequent separation unit, resulting in catalyst loss. For example, a 200,000 tons / year cyclohexanol plant loses approximately 260 kg of Ru-Zn catalyst annually, of which 90-94% is ruthenium metal. This ruthenium loss results in direct economic losses of approximately 25 million yuan annually.

[0004] To address these issues, domestic and international institutions have conducted extensive research on catalyst recovery for benzene partial hydrogenation. In Chinese patent CN111056903B, a mixed solution of catalyst slurry and product oil from a hydrogenation reaction unit is sequentially subjected to sedimentation separation, degassing, oil-water separation, catalyst sedimentation separation, and membrane separation. Water and catalyst are recovered from the mixed solution and then reused in the original production process. A portion of the water is used as flushing water for the flash tank and its feed and tank bottom discharge lines, while the remaining portion is reused in the original production process. It's important to note that the mixed solution of catalyst slurry and product oil from the hydrogenation reaction unit contains not only the Ru-Zn catalyst but also a large amount of zirconium oxide. This Ru-Zn catalyst adheres to the surface of the zirconium oxide, resulting in a black solid. During sedimentation, the aqueous zirconium oxide solution tends to form a highly viscous precipitate at the bottom of the settling tank, resulting in poor fluidity and clogging equipment and pipelines. If dead-end filtration is used, the highly viscous zirconium oxide filter cake rapidly degrades the membrane's filtration capacity and is difficult to remove. Furthermore, the filtered liquid contains compounds such as zinc sulfate and zinc hydroxide. Directly reusing the filtered solution into the original production process can cause changes in the concentrations of the catalyst components in the hydrogenation reactor, impacting the hydrogenation reaction. Summary of the Invention

[0005] The present invention provides a benzene partial hydrogenation catalyst recovery process, which avoids catalyst loss by adopting membrane separation technology, and at the same time couples suspension separation with membrane separation, thereby improving the operating conditions of suspension separation and membrane separation and increasing the catalyst recovery efficiency. In addition, the process requires little modification to existing production equipment, occupies a small area of ​​equipment, has low investment and operating costs, and has significant economic benefits.

[0006] The specific implementation scheme of the present invention is as follows: Flash tank: The reaction liquid is washed and flashed, and flash gases such as hydrogen and nitrogen are discharged from the top of the flash tank. The generated liquids such as oil, water, and catalyst enter the reflux tank from the bottom of the flash tank. Reflux tank: Receives the generated oil, water, catalyst from the bottom of the flash tank and the condensate from the top of the degassing tower, and performs oil-water separation in the reflux tank. The oil phase is pumped to the dehydration tower, and the water and catalyst are pumped to the suspension separator. Dehydration tower: receives the oil phase product from the reflux tank and performs dehydration treatment. The removed water enters the reflux tank from the top of the tower. The oil generated after dehydration is pumped from the tower bottom to the subsequent device; Suspension separator: Receives the catalyst and water concentrated from the reflux tank and cross-flow membrane filter, and re-concentrates the catalyst through the suspension separation process. The concentrated phase catalyst slurry is discharged from the bottom of the suspension separator, and the dilute phase catalyst slurry enters the intermediate tank from the upper outlet of the suspension separator; The solid content of the dense phase catalyst slurry discharged from the bottom of the suspension separator is 1-30 wt.%, preferably, the solid content is 3-25 wt.%; Intermediate tank: receives the dilute phase catalyst slurry from the suspension separator, as well as part of the water and catalyst slurry concentrated by the membrane filter, and pumps the received catalyst and water to the cross-flow membrane filter; Membrane filter: The catalyst and water from the intermediate tank are subjected to cross-flow membrane filtration. Part of the water is removed as filtered supernatant under the action of membrane filtration. The intercepted catalyst and remaining water are returned to the intermediate tank or the suspension separator inlet after cooling; Among them, the membrane filter uses cross-flow filtration to separate solids and liquids, and the membrane filter includes multiple groups of filtering devices connected in series and or in parallel; Wherein, a metal filter element and / or a ceramic filter element is provided in the filtering device, and preferably, the filter element is a metal filter element; The transmembrane filtration pressure difference of the filter is 1-300 kPa, preferably, the transmembrane filtration pressure difference is 5-150 kPa; The metal filter element has a single-layer or multi-layer composite structure. Preferably, the filter element has a multi-layer composite structure. The filtration precision of the filter element is 0.05-1.00 μm, preferably, the filtration precision of the filter element is 0.05-0.5 μm; The outer diameter of the metal filter element is 8-36 mm, and the thickness of the filter element is 1-3 mm. Preferably, the outer diameter of the metal filter element is 12-30 mm, and the thickness is 1.5-2.5 mm. The catalyst slurry concentrated by the membrane filter is then cooled and sent to an intermediate tank or suspension separator; Backwash tank: Perform periodic physical backwashing on the membrane filter, and the backwash medium is make-up water; The backwash tank backwashes the membrane filter in a pressure-driven or pump-driven manner. Preferably, the backwashing method is pressure-driven. The object of a single backwash is a single filter or multiple filters, preferably a single filter; The online backwash pressure difference is 0.5-6.0 bar, preferably, the backwash pressure difference is 2.0-4.0 bar; The online backwashing time interval of a single filter is 5 to 360 minutes, preferably 10 to 60 minutes. The single backwash time is 0.5 to 30 seconds, preferably 1 to 8 seconds. The backwash liquid medium is one or more of high-purity water, filtered clear liquid, and desalted water. Preferably, the backwash medium is filtered clear liquid and / or desalted water. The temperature of the backwash medium is 5-90°C, preferably 35-80°C.

[0007] Beneficial effects of the present invention: 1). Ru-Zn catalyst is effectively recovered, with significant economic benefits; 2) Using high-precision metal membrane cross-flow filtration technology, the catalyst interception efficiency is improved; 3) The suspension separation technology is used to improve the concentration efficiency of the catalyst slurry; 4). Using filtered liquid as the backwash medium of the membrane filter reduces water consumption; 5). Small number of equipment, small floor space, low equipment investment and low operating costs. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 It is a schematic diagram of the process of the present invention. Specific embodiments The following examples are used to illustrate the present invention. It should be emphasized that these examples are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Example

[0009] The reaction liquid containing reaction oil, catalyst and water enters the flash tank. After washing and flash evaporation, flash gases such as hydrogen and nitrogen are discharged from the top of the flash tank, and the generated liquids such as oil, water and catalyst enter the reflux tank from the bottom of the flash tank. The oil, water and catalyst from the bottom of the flash tank are separated from the condensate from the top of the dehydration tower in the reflux tank. The water phase containing the catalyst enters the suspension separator, and the oil phase enters the dehydration tower for dehydration. The dehydrated oil is then sent to the subsequent device from the bottom of the tower. The catalyst and water from the reflux tank are mixed with part of the catalyst and water concentrated from the membrane filter and enter the suspension separator. The catalyst solids are concentrated under the action of suspension separation. The concentrated phase catalyst slurry is discharged from the bottom of the suspension separator, and the dilute phase catalyst slurry enters the intermediate tank from the upper outlet of the suspension separator. The dilute phase catalyst slurry from the suspension separator is pumped into the membrane separator for solid-liquid separation. The water at the separation point is removed as the filtered clear liquid, and the intercepted catalyst and remaining water enter the inlet of the suspension separator after cooling. The pressure in the backwash tank is higher than the pressure in the membrane filter. The backwash liquid is driven by pressure to perform periodic physical backwashing on the single membrane filter, realizing online physical cleaning and regeneration of the metal filter element in the filter.

[0010] In the specific embodiment, the operating parameters are as follows:

Claims

1. A benzene partial hydrogenation catalyst recovery process, characterized in that: include: Flash tank: The reaction liquid is washed and flashed, and flash gases such as hydrogen and nitrogen are discharged from the top of the flash tank. The generated liquids such as oil, water, and catalyst enter the reflux tank from the bottom of the flash tank. Reflux tank: Receives the generated oil, water, catalyst from the bottom of the flash tank and the condensate from the top of the degassing tower, and performs oil-water separation in the reflux tank. The oil phase is pumped to the dehydration tower, and the water and catalyst are pumped to the suspension separator. Dehydration tower: receives the oil phase product from the reflux tank and performs dehydration treatment. The removed water enters the reflux tank from the top of the tower. The oil generated after dehydration is pumped from the tower bottom to the subsequent device; Suspension separator: Receives the catalyst and water concentrated from the reflux tank and cross-flow membrane filter, and re-concentrates the catalyst through the suspension separation process. The concentrated phase catalyst slurry is discharged from the bottom of the suspension separator, and the dilute phase catalyst slurry enters the intermediate tank from the upper outlet of the suspension separator; Intermediate tank: receives the dilute phase catalyst slurry from the suspension separator, as well as part of the water and catalyst slurry concentrated by the membrane filter, and pumps the received catalyst and water to the cross-flow membrane filter; Membrane filter: The catalyst and water from the intermediate tank are subjected to cross-flow membrane filtration. Part of the water is removed as filtered supernatant under the action of membrane filtration. The intercepted catalyst and remaining water are returned to the intermediate tank or the suspension separator inlet after cooling; Backwash tank: Perform periodic physical backwashing on the membrane filter, and the backwashing medium is make-up water;.

2. The process according to claim 1, characterized in that The membrane filter uses cross-flow filtration to separate solids and liquids. The membrane filter includes multiple groups of filtration devices connected in series and / or in parallel. The filtration device is equipped with a metal filter element and / or a ceramic filter element. The transmembrane filtration pressure difference is 1~300 kPa, and the metal filter element structure is a single-layer and / or multi-layer composite structure.

3. The process according to claim 1 or 2, characterized in that: The filtration accuracy of the filter element is 0.05~1.00 μm, wherein the outer diameter of the metal filter element is 8~36 mm and the thickness of the filter element is 1~3 mm.

4. The process according to claim 1 or 2, characterized in that: The backwash tank backwashes the membrane filter by pressure drive or pump drive. The single backwash target is a single or multiple filter equipment. The backwash pressure difference is 0.5~6.0 bar. The backwash interval of a single filter equipment is 5~360 minutes. The single backwash time is 0.5~30 seconds. The backwash medium is one or more of high-purity water, filtered liquid, and desalted water. The backwash medium temperature is 5~90 ​​ºC.

5. The process according to claim 1, characterized in that The backwash tank backwashes the membrane filter by pressure drive or pump drive.

6. The process according to claim 1, characterized in that The catalyst slurry concentrated by the membrane filter is then cooled and sent to an intermediate tank and / or suspension separator.

7. The process according to claim 1, characterized in that The solid content of the dense phase catalyst slurry discharged from the bottom of the suspension separator is 1~30 wt.%.

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