A deep hydrogenation purification process for recycled methanol solvent in green propylene oxide production

Abstract

This invention discloses a deep hydrogenation purification process for circulating methanol solvent in green propylene oxide production, belonging to the field of chemical production technology. It includes a two-bed trickle-bed reactor, with a feed pipe fixedly installed at the top inlet. The feed pipe is used to flow methanol feed containing impurities, which then enters the gas-liquid separator inside the reactor and trickles to the upper and lower catalysts packed inside. These catalysts efficiently remove hydrogen peroxide and aldehyde impurities from methanol, reducing hydrogen peroxide content to below 1 ppm and total aldehyde content to below 5 ppm, significantly improving product quality and market competitiveness. Simultaneously, it significantly reduces the amount of distillation additives used for aldehyde removal, suppresses the side reaction of methanol dehydration to dimethyl ether, achieves a methanol recovery rate exceeding 99.9%, and reduces solvent loss. The integrated design of a single reactor with two beds simplifies the process flow, reduces equipment investment, and, combined with a precise temperature control and safety monitoring system, ensures safe and stable production.

Description

Technical Field

[0001] This invention relates to the field of chemical production technology, specifically a deep hydrogenation purification process for circulating methanol solvent in green propylene oxide production. Background Technology

[0002] Propylene oxide is an important organic chemical raw material. The hydrogen peroxide process has become the mainstream production process due to its green and environmentally friendly nature. In this process, methanol is used as a solvent and is recycled within the system. After the epoxidation reaction, methanol usually contains about 2000 ppm hydrogen peroxide and about 1000 ppm aldehyde impurities. Existing methanol purification processes mostly employ a single hydrogenation method, which can effectively remove hydrogen peroxide but has virtually no effect on removing aldehydes. Industrially, special additives are added to the propylene oxide distillation section to react with aldehydes and generate hydrazones for removal. However, this process suffers from incomplete reactions and aldehyde residues, leading to excessive aldehyde content in propylene oxide products, which reduces product grade and market competitiveness. At the same time, traditional processes have drawbacks such as complex flow, numerous byproducts, easy catalyst deactivation, and insufficient operational safety. Summary of the Invention

[0003] Therefore, in order to overcome the above-mentioned shortcomings, the present invention provides a deep hydrogenation purification process for circulating methanol solvent in green propylene oxide production.

[0004] This invention is achieved by constructing a green process for deep hydrogenation purification of circulating methanol solvent in propylene oxide production. The apparatus includes the following steps: Step 1, Raw Material Pretreatment and Hydrogen Mixing: The methanol containing impurities obtained from the epoxidation reaction equipment after propylene removal and propylene oxide removal processes is used as raw material. The raw methanol temperature is 80-100℃, and it contains 1500-2000ppm hydrogen peroxide and 800-1000ppm aldehyde impurities. The raw methanol is mixed with high-purity hydrogen gas with a purity ≥99.9%, and the hydrogen / aldehyde molar ratio in the upper section of the reactor is controlled at 10:1-15:1. The mixture is then fed into a two-stage insulated fixed-bed trickle-flow reactor. Step 2, Preliminary Hydrogenation and Purification in the Upper Stage: The mixture enters the upper catalyst bed in the trickle bed reactor, and is subjected to hydrogenation at a reaction temperature of 80-100℃, a system pressure of 1.8-2.5MPa, and a liquid hourly space velocity (LHSV) of 4-6h. -1 Under the specified conditions, complete decomposition of hydrogen peroxide and preliminary hydrogenation reaction of aldehydes are achieved; hydrogen peroxide conversion rate ≥99.99%, outlet hydrogen peroxide content <1ppm, aldehyde conversion rate 85%-90%, outlet aldehyde residue 80-150ppm, and dimethyl ether byproduct selectivity <0.05%; Step 3, Inter-stage temperature adjustment and hydrogen replenishment optimization: The reaction products of the upper stage are redistributed through the inter-stage liquid collection component of the trickle bed reactor, and high-purity hydrogen at 25-30℃ is added to adjust the hydrogen / aldehyde molar ratio of the lower stage to 20:1-25:1. At the same time, the material temperature is adjusted back to 82.5-88℃ to cut off the accumulation of reaction heat. Step 4, Lower-stage deep hydrogenation purification: The material after temperature adjustment and hydrogen supplementation enters the lower-stage catalyst bed, where it reacts at a temperature of 85-95℃, a system pressure of 1.8-2.5MPa, and a liquid hourly space velocity (LHSV) of 3-5h. -1 Under the specified conditions, the deep hydrogenation reaction of residual aldehydes was completed; the total aldehyde conversion rate was ≥96%, the total aldehyde content in the outlet methanol was ≤5ppm, the methanol recovery rate was ≥99.9%, and the dimethyl ether selectivity was <0.01%. Step 5, Product Separation and Recycling: The lower-stage reaction products in the trickle bed reactor are sent to an external gas-liquid separator. The excess hydrogen separated is returned to the reactor for reuse via a circulating compressor. The purified methanol obtained from the separation is sent to the methanol recovery system to achieve solvent recycling.

[0005] Preferably, the two-section insulated fixed-bed trickle-bed reactor is specifically a reactor, wherein a feed pipe is fixedly installed at the top inlet of the reactor for circulating methanol feedstock containing impurities; a hydrogen feed pipe is also fixedly installed at the top air inlet of the reactor, and the hydrogen feed pipe is connected to a nitrogen connecting pipe; and a hydrogen branch is also provided on the hydrogen feed pipe.

[0006] Preferably, a gas-liquid distributor is fixedly installed on the top side inside the reactor; an upper catalyst is fixedly installed on the lower side of the gas-liquid distributor, and a liquid collection assembly is fixedly installed below the upper catalyst; the liquid collection assembly specifically consists of a liquid collector and a redistributor, and a lower catalyst is also fixed below the redistributor.

[0007] Preferably, the end of the hydrogen branch is also connected to the side port of the liquid collection assembly; and both the upper and lower catalyst layers are formed by clover or four-leaf clover extrusion molding.

[0008] Preferably, a hydrogen outlet pipe is fixedly installed at the outlet on the lower side of the reactor, and a pressure relief pipe is provided on the hydrogen outlet pipe; the hydrogen outlet pipe is connected to an external circulating compressor, and the pressure relief pipe is specifically an emergency pressure relief valve; the outlet at the bottom of the reactor is fixedly connected to a methanol outlet pipe, and the methanol outlet pipe specifically consists of an outlet pipe and a chromatograph and an analyzer connected in series on the outlet pipe.

[0009] Preferably, the upper catalyst is a highly active hydrogen peroxide decomposition-dominant bifunctional catalyst, comprising an active component, a support, and an additive; the active component is 0.3-0.5 wt% Pd, 4-5 wt% Ni, or 5-6 wt% Cu; the support is modified γ-Al₂O₃ with a specific surface area of ​​180-250 m² / g. 2 / g, pore size 8-15nm; the additives are 2-3wt% CeO2 and 0.5-1wt% La2O3.

[0010] Preferably, the lower-stage catalyst is a selectively supported bifunctional catalyst for deep aldehyde hydrogenation, comprising an active component, a support, and an auxiliary agent; the active component is 0.6-0.8 wt% Pd, 2-3 wt% Ni, or 3-4 wt% Cu, preferably a Pd-Cu composite system; the support is modified γ-Al₂O₃ with a specific surface area of ​​180-250 m² / g. 2 / g, pore size 8-15nm; the additives are 1-2wt% CeO2 and 1.5-2wt% La2O3.

[0011] Preferably, the reactor adopts a gas-liquid co-flow downward trickle bed operation mode; the reactor is equipped with a multi-stage umbrella-shaped gas-liquid distributor, and the support structure of the upper and lower catalyst layers consists of Johnson screens and ceramic ball support layers.

[0012] Preferably, the reactor is equipped with multiple temperature measurement points and bed pressure drop monitoring components, with each bed section having one temperature measurement point; and the temperature measurement points and bed pressure drop monitoring components are specifically temperature sensors and pressure sensors.

[0013] Preferably, the reactor and methanol discharge pipe are integrated as independent purification units into the methanol circulation loop of the existing propylene oxide production unit.

[0014] This invention has the following advantages: This invention provides an improved deep hydrogenation purification process for circulating methanol solvent in green propylene oxide production, which, compared with similar equipment, has the following improvements: The present invention discloses a deep hydrogenation purification process for circulating methanol solvent in green propylene oxide production, which can simultaneously and efficiently remove hydrogen peroxide and aldehyde impurities from methanol, reducing the hydrogen peroxide content to below 1 ppm and the total aldehyde content to below 5 ppm, significantly improving product quality and market competitiveness. Simultaneously, it significantly reduces the amount of distillation additives for aldehyde removal, suppresses the side reaction of methanol dehydration to dimethyl ether, achieves a methanol recovery rate of over 99.9%, and reduces solvent loss. The single-reactor, two-stage bed integrated design simplifies the process flow, reduces equipment investment, and, combined with a precise temperature control and safety monitoring system, ensures safe and stable production, extends catalyst life, and is suitable for large-scale continuous production, bringing significant economic benefits. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the process of this invention; Figure 2 This is a schematic diagram of the reactor structure of the present invention.

[0016] The components are: reactor-1, feed pipe-2, hydrogen feed pipe-3, nitrogen connecting pipe-4, hydrogen branch-5, gas-liquid distributor-6, upper catalyst-7, liquid collection assembly-8, lower catalyst-9, hydrogen outlet pipe-10, pressure relief pipe-11, and methanol outlet pipe-12. Detailed Implementation

[0017] The following is in conjunction with the appendix Figures 1-2 The principles and features of the present invention are described below. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. The invention is described more specifically in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the drawings are in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the invention.

[0018] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0019] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. The embodiments of this invention will now be described according to its overall structure.

[0020] Example 1:

[0021] Please see Figures 1-2This invention discloses a deep hydrogenation purification process for circulating methanol solvent in green propylene oxide production. The process includes a reactor 1, which is a two-bed adiabatic fixed-bed trickle-bed reactor. A feed pipe 2 is installed at the top inlet of the reactor 1, through which circulating methanol feedstock containing organic impurities enters the reactor 1. Simultaneously, a hydrogen feed pipe 3 is connected to the top inlet of the reactor 1 to replenish the hydrogen required for the hydrogenation reaction. To ensure nitrogen replacement and protection during start-up, shutdown, or emergency situations, a nitrogen connecting pipe 4 is connected in series on the hydrogen feed pipe 3. Furthermore, a hydrogen branch 5 is connected in parallel or in series with the hydrogen feed pipe 3. This branch is used to replenish hydrogen in the middle of the reactor to adjust the hydrogen-to-oil ratio and reaction depth in different beds. A gas-liquid distributor 6 is fixedly installed on the top side inside reactor 1. A multi-stage umbrella-shaped gas-liquid distributor is preferred to achieve uniform distribution and downward parallel flow of the gas and liquid phases. Below the gas-liquid distributor 6, an upper catalyst 7 is fixedly installed. This catalyst is a supported noble metal such as Pd or Pt, or a non-noble metal such as Ni or Cu hydrogenation catalyst, preferably using a cloverleaf or four-leaf clover-shaped extrusion molding to reduce bed pressure drop and improve mass transfer efficiency. Below the upper catalyst 7, a liquid collection assembly 8 is fixedly installed. This assembly specifically consists of a liquid collector and a recirculating... The distributor consists of a liquid collector for collecting the liquid phase after the upper reaction, and a redistributor for redistributing it evenly to the top of the lower catalyst bed 9. The end of the hydrogen branch 5 is connected to the port on the side of the liquid collection assembly 8, which allows for the replenishment of cold hydrogen between the two bed sections, enabling precise control of the bed temperature and preventing the adiabatic temperature rise from causing the side reactions to intensify or the catalyst to deactivate. The lower catalyst 9 also uses a clover or tetraclover-shaped extruded hydrogenation catalyst, and its composition can be the same as that of the upper layer or optimized according to the impurity composition. A hydrogen outlet pipe 10 is fixedly installed at the outlet on the lower side of reactor 1. A pressure relief fitting 11, specifically an emergency pressure relief valve, is connected in series on this pipe to quickly release the reaction pressure under overpressure conditions and ensure system safety. The outlet of the hydrogen outlet pipe 10 is connected to an external circulating compressor to realize the recovery and recycling of unreacted hydrogen. The outlet at the bottom of reactor 1 is fixedly connected to a methanol outlet fitting 12. This fitting includes not only the outlet pipe but also an online chromatograph and analyzer connected in series to monitor the residual concentration of impurities in the purified methanol in real time, thereby providing feedback to adjust operating parameters such as hydrogen feed rate, reaction temperature, or space velocity. Reactor 1 adopts a gas-liquid co-flow downward trickle bed operation mode. The support structure of the upper catalyst 7 and the lower catalyst 9 adopts a Johnson screen combined with a ceramic ball support layer, which ensures mechanical strength and avoids catalyst powder blockage or excessive pressure drop. Inside reactor 1, there are also multiple temperature measurement points and bed pressure drop monitoring components. Each bed section has 8 temperature measurement points arranged radially and axially, specifically composed of temperature sensors and pressure sensors, which are used to monitor the bed temperature distribution and pressure drop changes in real time to ensure that the hydrogenation reaction operates stably under optimal conditions. Reactor 1 and the methanol discharge pipe 12 connected to it are integrated into the methanol circulation loop of the existing propylene oxide production unit as an independent purification unit.

[0022] Based on the thermodynamic differences between the strong exothermic reaction of hydrogen peroxide decomposition and the mild exothermic reaction of aldehyde hydrogenation, and combined with the segmented differentiated catalytic mechanism, a single-reactor two-stage adiabatic fixed-bed trickle bed structure is adopted. It is equipped with a three-stage temperature control system of "utilizing the heat of reaction in the upper stage, controlling the temperature by heat interception between stages, and maintaining a constant temperature for fine reaction in the lower stage". With the exclusive dual-function catalysts in the upper and lower beds, thermodynamic decoupling and staged synergistic removal of the two types of impurities are achieved, which simultaneously improves the purification accuracy and process stability from the perspectives of mechanism and equipment structure.

[0023] The core chemical reaction equations and thermodynamic calculation formulas of this invention are as follows: the main reaction of hydrogen peroxide hydrogenation decomposition is H2O2 + H2 → 2H2O; the hydrogenation reduction reaction of formaldehyde is HCHO + H2 → CH3OH; the hydrogenation reduction reaction of acetaldehyde is CH3CHO + H2 → C2H5OH; the hydrogenation reduction reaction of propionaldehyde is C2H5CHO + H2 → C3H7OH; the methanol dehydration side reaction, which is the key process to be suppressed, is 2CH3OH → CH3OCH3 + H2O; the core thermodynamic calculation basis for temperature control in this invention is: the specific heat capacity of methanol medium C = 2.55 kJ / (kg·) When the feed contains 2000ppm hydrogen peroxide (mass fraction 0.2%), the heat released by the complete decomposition of hydrogen peroxide per unit mass of methanol is Q=0.2%×98kJ / mol÷0.034kg / mol≈5.765kJ / kg. The corresponding theoretical adiabatic temperature rise ΔT=Q / C≈2.25℃. After adding the heat released by the partial hydrogenation of aldehydes, the actual axial temperature rise in the lower section is controlled at 2.5~3℃, which is in high agreement with the theoretical calculation. The aldehyde impurities in the lower section are only 100~150ppm, the heat released by the reaction is extremely low, the bed temperature rise is less than 0.1℃, and the reaction process is completely controlled by kinetics.

[0024] In this embodiment, a differentiated catalyst matching design is adopted between the upper and lower layers. The upper catalyst 7 is set as a hydrogen peroxide decomposition-dominant catalyst, with active components of 0.4wt% Pd and 4.5wt% Ni, and auxiliary agents of 2.5wt% CeO2 and 0.8wt% La2O3. This formulation is precisely optimized according to the thermodynamic characteristics of the strong exothermic reaction in the upper layer, appropriately reducing the strong hydrogenation activity of the precious metal Pd, relying on the high Ni content to adapt to the rapid decomposition reaction of hydrogen peroxide, and at the same time, using CeO2 to build abundant oxygen vacancies on the catalyst surface to effectively promote the rapid heterolytic decomposition of hydrogen peroxide, adapting to the high impurity and strong exothermic reaction system in the upper layer; the lower catalyst 9 is set as a deep aldehyde hydrogenation selective catalyst. This catalyst uses 0.7wt% Pd and 3.5wt% Cu as active components, and 1.5wt% CeO2 and 1.8wt% La2O3 as promoters. This formulation increases the loading of the Pd active component, enhances the low-temperature activation capability of low-concentration aldehyde groups, and utilizes a high content of La2O3 to construct alkaline sites on the catalyst surface, effectively neutralizing the acidity of the γ-Al2O3 support. This suppresses the side reaction of methanol dehydration to dimethyl ether from the reaction mechanism, making it suitable for the downstream fine hydrogenation purification of trace aldehydes. The specific process parameters for this operation are set as follows: initial methanol temperature 90℃, system stable pressure 2.2MPa, upper inlet temperature 90℃, and liquid hourly space velocity (LHSV) = 5h⁻¹. -1 The hydrogen / aldehyde molar ratio is 12:1. After the material passes through the upper stage reaction, it is uniformly distributed through the inter-stage collector and redistributor. High-purity hydrogen at 28°C is added to bring the material temperature back up to 85°C. At the same time, the hydrogen / aldehyde molar ratio in the lower stage is increased to 22:1. The lower stage inlet temperature is 85°C, and the liquid hourly space velocity (LHSV) is 4 h⁻¹. -1 The entire process involves constant temperature control of the bed, ensuring a bed temperature rise of ≤1℃. All heat released during the reaction is absorbed by the sensible heat of the methanol material, achieving autonomous heat regulation without the need for external heat exchange equipment. The high-concentration hydrogen peroxide in the upper section rapidly and completely decomposes under the catalysis of the Ni-CeO2 active system, resulting in a natural axial temperature rise of 2.8℃, which highly matches the theoretical temperature rise calculation results of the superposition of aldehyde hydrogenation temperature rise. The multi-stage umbrella-shaped distributor in the upper part of reactor 1 can completely eliminate fluid channeling and flow deviation, ensuring uniform radial temperature and minimal temperature difference in the bed, effectively avoiding side reactions caused by local overheating. At the same time, the rapid and complete decomposition of hydrogen peroxide completely eliminates its oxidative poisoning effect on Pd active sites, ensuring the long-term stable activity of the catalyst.

[0025] When the material flows through the inter-stage region of reactor 1, the liquid collector and redistributor of the liquid collection component 8 can completely eliminate the temperature and concentration gradients of the material in the upper stage. The added room-temperature high-purity hydrogen can accurately offset the heat accumulation of the upper stage reaction, and stably control the material temperature within the optimal kinetic reaction range of the lower stage. The lower stage material is free from interference from strong oxidizing impurities such as hydrogen peroxide. The high Pd active catalyst can achieve precise hydrogenation conversion of residual aldehyde components at the bed inlet level of 100ppm, reducing formaldehyde, acetaldehyde, and propionaldehyde in the system to methanol, ethanol, and propanol, respectively. Combined with the La2O3 alkaline additive, the side reaction of dimethyl ether is continuously suppressed. Relying on the extremely low reaction exothermic characteristics of the lower stage, a refined and deep purification effect with constant temperature, low side reaction, and high precision is achieved.

[0026] Long-term continuous operation results under this condition show that the hydrogen peroxide conversion rate in the upper stage can reach 99.99%, the hydrogen peroxide content at the reactor 1 outlet is less than 1 ppm, the initial hydrogenation conversion rate of aldehydes reaches 88%, the residual aldehyde content in the upper stage effluent is 120 ppm, the axial temperature rise of the bed is stable at 2.8℃, completely within the thermodynamically controllable range, the radial temperature difference of the bed is only 0.6℃, the overall temperature distribution is uniform and stable, the dimethyl ether selectivity is as low as 0.04%, and the side reactions are extremely well controlled. After the lower stage deep hydrogenation reaction, the deep conversion rate of residual aldehydes reaches 97.5%, the total aldehyde content of methanol after purification is only 3.0 ppm, and the overall methanol recovery rate can reach 99.92%. After the recycled methanol is reused in the HPPO main production system, the aldehyde content in the final propylene oxide product can be reduced to 2.9 ppm. This process can completely solve the shortcomings of traditional hydrogenation reactors: first, the hydrogen peroxide conversion rate after hydrogenation can only reach 99.0% to 99.5%; second, the aldehyde hydrogenation conversion rate is less than 40%. The aldehyde impurities that are not removed are carried into the propylene oxide refining system and need to be removed by adding special additives to react with the aldehydes to form hydrazones. However, the removal capacity of this purification method is limited, which can easily lead to excessive aldehyde residue in the finished propylene oxide product. The pressure drop of the bed in this unit remains stable throughout the process, the temperature is precisely controlled, and there are no fluctuations in operation. It is fully adaptable to the long-term continuous and stable operation of industrial equipment.

[0027] Example 2:

[0028] Please see Figures 1-2 This invention discloses a green propylene oxide production process involving deep hydrogenation purification of circulating methanol solvent. Compared to Example 1, the specific process parameters in this example are set as follows: initial methanol temperature 82°C, system stable pressure 2.0 MPa, upper inlet temperature 82°C, and liquid hourly space velocity (LHSV) = 5.5 h⁻¹. -1 The hydrogen / aldehyde molar ratio was 10:1. High-purity hydrogen at 25°C was added between stages to bring the post-reaction material temperature back up to 83°C. The hydrogen / aldehyde molar ratio in the next stage was adjusted to 20:1, with the inlet temperature at 83°C and the liquid hourly space velocity (LHSV) at 4.5 h⁻¹. -1 The bed maintains a constant and stable temperature throughout the entire process.

[0029] The upper catalyst 7 and the lower catalyst 9 have the same components as in Example 1.

[0030] This embodiment primarily addresses and optimizes the technical challenges commonly encountered in industrial plants during low-temperature start-up and low-load production processes, such as slow reaction kinetics, reduced hydrogen solubility, and the tendency for hydrogen peroxide to undergo non-catalytic homogeneous decomposition. Under low-temperature conditions, relying on the highly active Ni-CeO2 catalytic system in the upper stage, the main catalytic decomposition reaction of hydrogen peroxide is preferentially triggered. The heat released by the reaction itself slightly increases the material temperature, effectively compensating for the kinetic defects caused by the low-temperature environment. This ensures that hydrogen peroxide can still be completely decomposed under low-temperature conditions. Combined with the thermodynamic temperature rise formula, the overall reaction heat release is slightly reduced under low-temperature feeding conditions, and the actual axial temperature rise of the bed is stabilized at 2.5℃, which is within the theoretically safe and controllable range.

[0031] The inter-stage low-temperature hydrogen replenishment temperature control operation can precisely regulate the overall temperature of the material, while effectively increasing the hydrogen partial pressure of the system. This compensates for the low rate constant and insufficient reaction kinetics of aldehyde hydrogenation reactions under low-temperature conditions. The high content of La2O3 in the lower stage can significantly enhance the adsorption and enrichment capacity of polar aldehyde molecules under low-temperature conditions, effectively improving the low-temperature catalytic efficiency of Pd active sites. This ensures the continuous and efficient hydrogenation reduction reactions of formaldehyde, acetaldehyde, and propionaldehyde within the system, while continuously neutralizing the acidic sites of the support and suppressing the side reaction of methanol dehydration to dimethyl ether throughout the process. The results of the test operation under this condition show that... Under low temperature and low load operating conditions, the upper stage hydrogen peroxide can achieve 100% complete removal, with the hydrogen peroxide content at the reactor outlet being less than 1 ppm. The initial conversion rate of aldehydes reaches 85.2%, and the residual aldehydes in the upper stage discharge are 148 ppm. The bed temperature rise is stable without sudden changes or local overheating. The dimethyl ether selectivity is only 0.035%, and the side reaction suppression effect is better than that under conventional ambient temperature conditions. After the lower stage low temperature fine hydrogenation purification, the total aldehyde content of the purified methanol at the outlet is 4.2 ppm, which meets the deep purification standard of ≤5 ppm for total aldehydes in industrial production. The methanol recovery rate can reach 99.91%.

[0032] Example 3:

[0033] Please see Figures 1-2 This invention discloses a green propylene oxide production process involving deep hydrogenation purification of circulating methanol solvent. Compared to Example 1, the specific process parameters in this example are set as follows: initial methanol temperature of 98°C, system stable pressure of 2.4 MPa, upper inlet temperature of 98°C, and liquid hourly space velocity (LHSV) of 4.5 h⁻¹. -1 The hydrogen / aldehyde molar ratio is 15:1. High-purity hydrogen at 30°C is added between stages to precisely lower the temperature of the high-temperature reactants to 88°C. The hydrogen / aldehyde molar ratio in the next stage is increased to 25:1, with an inlet temperature of 88°C and a liquid hourly space velocity (LHSV) of 3.5 h⁻¹. -1The lower bed layer is kept at a constant temperature throughout the entire process.

[0034] The upper catalyst 7 and the lower catalyst 9 have the same components as in Example 1.

[0035] This embodiment precisely simulates the full-load, high-temperature extreme production conditions of an industrial plant. Addressing the multiple technical challenges posed by the significantly increased hydrogen peroxide decomposition kinetic rate and high impurity handling load under high-temperature environments, which can lead to high-temperature sintering of Pd active components, carrier phase change failure, a significant decrease in hydrogen solubility, and exacerbated methanol dehydration side reactions, this invention utilizes a three-stage temperature control system that strictly adheres to the thermodynamic temperature rise formula to precisely manage the accumulation of reaction heat. The upper stage employs a low-Pd, high-Ni formulation to effectively mitigate the excessive hydrogenation activity of the catalyst under high-temperature conditions, avoiding the problem of localized overheating of the bed caused by the superposition of heat release from hydrogen peroxide decomposition and aldehyde hydrogenation. The overall bed temperature rise remains stable at 3.0℃, not exceeding the equipment's safe operating threshold. The inter-stage liquid collection and temperature adjustment device is the core control unit for this operation, rapidly absorbing and offsetting the accumulated heat generated by the high-temperature reaction in the upper stage, precisely lowering the temperature of the high-temperature material to the optimal kinetic reaction range in the lower stage. This completely prevents catalyst sintering and carrier phase change caused by the direct entry of high-temperature material into the lower stage. This process avoids damage such as rapid activity decay, while the high hydrogen-to-aldehyde ratio effectively compensates for the decrease in hydrogen solubility under high temperature conditions, providing sufficient hydrogen source for the hydrogenation reduction reactions of formaldehyde, acetaldehyde, and propionaldehyde. This ensures the deep removal of trace aldehyde impurities under high load conditions. The alkaline microenvironment constructed by the lower catalyst can continuously suppress methanol dehydration side reactions, effectively overcoming the industry problems of high by-product generation and large solvent loss under high temperature conditions. The actual operating effect of this process is excellent. Under continuous operation at high temperature and high load, the upper hydrogen peroxide can achieve complete removal, the overall aldehyde conversion rate reaches 89.5%, the residual aldehyde in the upper discharge is only 105 ppm, the radial temperature difference of the bed is less than 1℃, the bed temperature uniformity is excellent, there are no local high temperature hot spots, the dimethyl ether selectivity is only 0.048%, and the high temperature side reactions are effectively controlled. After the lower constant temperature fine hydrogenation purification, the total aldehyde content of the methanol at the outlet is as low as 2.1 ppm, which is the best purification precision among the multiple working conditions of this invention, and the methanol recovery rate is as high as 99.94%.

[0036] This invention provides an improved, green process for deep hydrogenation purification of circulating methanol solvent in propylene oxide production. This process simultaneously and efficiently removes hydrogen peroxide and aldehyde impurities from methanol, reducing hydrogen peroxide content to below 1 ppm and total aldehyde content to below 5 ppm, significantly improving product quality and market competitiveness. Simultaneously, it significantly reduces the amount of distillation additives used for aldehyde removal, suppresses the side reaction of methanol dehydration to dimethyl ether, achieves a methanol recovery rate exceeding 99.9%, and reduces solvent loss. The single-reactor, two-stage bed integrated design simplifies the process flow, reduces equipment investment, and, combined with a precise temperature control and safety monitoring system, ensures safe and stable production, extends catalyst life, and is suitable for large-scale continuous production, resulting in significant economic benefits.

[0037] The above description shows and illustrates the basic principles, main features, and advantages of the present invention. Standard parts used in the present invention can be purchased from the market, and irregular parts can be customized according to the description and drawings. The specific connection methods of each part adopt conventional methods such as bolts, rivets, and welding that are mature in the prior art. The machinery, parts, and equipment adopt conventional models in the prior art, and the circuit connection adopts conventional connection methods in the prior art, which will not be described in detail here.

[0038] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A deep hydrogenation purification process for recycled methanol solvent in green propylene oxide production, comprising the following steps: Step 1, Raw Material Pretreatment and Hydrogen Mixing: The methanol containing impurities obtained from the epoxidation reaction equipment after propylene removal and propylene oxide removal processes is used as raw material. The raw methanol temperature is 80-100℃, and it contains 1500-2000ppm hydrogen peroxide and 800-1000ppm aldehyde impurities. The raw methanol is mixed with high-purity hydrogen gas with a purity ≥99.9%, and the hydrogen / aldehyde molar ratio in the upper section of the reactor is controlled at 10:1-15:

1. The mixture is then fed into a two-stage insulated fixed-bed trickle-flow reactor. Step 2, Preliminary Hydrogenation and Purification in the Upper Stage: The mixture enters the upper catalyst bed in the trickle bed reactor, and is subjected to hydrogenation at a reaction temperature of 80-100℃, a system pressure of 1.8-2.5MPa, and a liquid hourly space velocity (LHSV) of 4-6h. -1 Under these conditions, complete decomposition of hydrogen peroxide and preliminary hydrogenation reaction of aldehydes are achieved; Step 3, Inter-stage temperature adjustment and hydrogen replenishment optimization: The reaction products of the upper stage are redistributed through the inter-stage liquid collection component of the trickle bed reactor, and high-purity hydrogen at 25-30℃ is added to adjust the hydrogen / aldehyde molar ratio of the lower stage to 20:1-25:1, while the material temperature is adjusted back to 82.5-88℃. Step 4, Lower-stage deep hydrogenation purification: The material after temperature adjustment and hydrogen supplementation enters the lower-stage catalyst bed, where it reacts at a temperature of 85-95℃, a system pressure of 1.8-2.5MPa, and a liquid hourly space velocity (LHSV) of 3-5h. -1 Under these conditions, the deep hydrogenation reaction of residual aldehydes is completed; Step 5, Product Separation and Recycling: The lower-stage reaction products in the trickle bed reactor are sent to an external gas-liquid separator. The excess hydrogen separated is returned to the reactor for reuse via a circulating compressor. The purified methanol obtained from the separation is sent to the methanol recovery system to achieve solvent recycling.

2. The deep hydrogenation purification process for circulating methanol solvent in green propylene oxide production according to claim 1, characterized in that: The two-section adiabatic fixed bed trickle bed reactor is specifically a reactor (1). A feed pipe (2) is fixedly installed at the top inlet of the reactor (1). The feed pipe (2) is used to flow methanol raw material containing impurities. A hydrogen feed pipe (3) is also fixedly installed at the top air inlet of the reactor (1). The body of the hydrogen feed pipe (3) is connected to a nitrogen connecting pipe (4). A hydrogen branch (5) is also provided on the body of the hydrogen feed pipe (3).

3. The deep hydrogenation purification process for circulating methanol solvent in green propylene oxide production according to claim 2, characterized in that: A gas-liquid distributor (6) is fixedly installed on the top side inside the reactor (1); an upper catalyst (7) is fixedly installed on the lower side of the gas-liquid distributor (6), and a liquid collection assembly (8) is fixedly installed below the upper catalyst (7); the liquid collection assembly (8) is specifically composed of a liquid collector and a redistributor, and a lower catalyst (9) is also installed below the redistributor.

4. The deep hydrogenation purification process for circulating methanol solvent in green propylene oxide production according to claim 3, characterized in that: The end of the hydrogen branch (5) is also connected to the side port of the liquid collection component (8); and the upper catalyst (7) and the lower catalyst (9) are both made by clover or four-leaf clover extrusion molding.

5. The deep hydrogenation purification process for circulating methanol solvent in green propylene oxide production according to claim 4, characterized in that: A hydrogen outlet pipe (10) is fixedly installed at the outlet on the lower side of the reactor (1), and a pressure relief pipe (11) is provided on the hydrogen outlet pipe (10); the hydrogen outlet pipe (10) is connected to an external circulating compressor, and the pressure relief pipe (11) is specifically an emergency pressure relief valve; the bottom outlet of the reactor (1) is fixedly connected to a methanol outlet pipe (12), and the methanol outlet pipe (12) specifically consists of an outlet pipe and a chromatograph and an analyzer connected in series on the outlet pipe.

6. The deep hydrogenation purification process for circulating methanol solvent in green propylene oxide production according to claim 5, characterized in that: The upper catalyst is a hydrogen peroxide decomposition-dominant bifunctional catalyst, comprising an active component, a support, and an additive; the active component is 0.3-0.5 wt% Pd, 4-5 wt% Ni, or 5-6 wt% Cu; the support is modified γ-Al₂O₃ with a specific surface area of ​​180-250 m² / g. 2 / g, pore size 8-15nm; the additives are 2-3wt% CeO2 and 0.5-1wt% La2O3.

7. The deep hydrogenation purification process for circulating methanol solvent in green propylene oxide production according to claim 6, characterized in that: The lower-stage catalyst is a selectively supported bifunctional catalyst for deep aldehyde hydrogenation, comprising an active component, a support, and an auxiliary agent; the active component is 0.6-0.8 wt% Pd, 2-3 wt% Ni, or 3-4 wt% Cu, preferably a Pd-Cu composite system; the support is modified γ-Al₂O₃ with a specific surface area of ​​180-250 m² / g. 2 / g, pore size 8-15nm; the additives are 1-2wt% CeO2 and 1.5-2wt% La2O3.

8. The deep hydrogenation purification process for circulating methanol solvent in green propylene oxide production according to claim 7, characterized in that: The reactor (1) adopts a gas-liquid co-flow downward drip bed operation mode; the reactor (1) is equipped with a multi-stage umbrella-shaped gas-liquid distributor (6), and the upper catalyst (7) and lower catalyst (9) are supported by a Johnson screen and a ceramic ball support layer.

9. The deep hydrogenation purification process for circulating methanol solvent in green propylene oxide production according to claim 8, characterized in that: The reactor (1) is equipped with multiple temperature measurement points and bed pressure drop monitoring components. Each bed section is equipped with 8 temperature measurement points. The temperature measurement points and bed pressure drop monitoring components are specifically temperature sensors and pressure sensors.

10. The deep hydrogenation purification process for circulating methanol solvent in green propylene oxide production according to claim 9, characterized in that: The reactor (1) and methanol discharge pipe (12) are integrated into the methanol circulation loop of the existing propylene oxide production unit as independent purification units.

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