Full-temperature-range liquid phase temperature swing adsorption process for deep dehydration and impurity removal of dioxolame

Abstract

The invention discloses a full-temperature-range liquid phase temperature swing adsorption process for deep dehydration and impurity removal of dioxolane, which mainly comprises the steps of raw material flow, temperature swing adsorption purification, temperature swing adsorption desorption and rectification concentration. Dioxolame with the purity of 99.9%, the water content of 500-1000 ppm, 100-300 ppm of micromolecular impurity components such as formaldehyde / methanol and the like, and the content of macromolecular impurity components such as ethylene glycol, hemiacetal, paraformaldehyde and the like is greater than or equal to 100 ppm is purified into dioxolame with the purity of greater than or equal to 99.999%, the water content is less than or equal to 100 ppm, the water content is less than or equal to 100 ppm, the water content is less than or equal to 100 ppm, and the water content is less than or equal to 100 ppm. The content of micromolecular impurity components of formaldehyde and methanol is smaller than or equal to 100 ppm, the content of macromolecular impurity components of ethylene glycol, methylal and paraformaldehyde is smaller than 50 ppm, the problems that the purity of products obtained through existing methods such as special rectification, extractive rectification and membrane separation does not reach the standard, and energy consumption and cost are high are solved, the process is simple, import is replaced, and the method is suitable for industrial production. And the quality requirement of the polymer-grade dioxolame required by polyformaldehyde production is met.

Description

Technical Field

[0001] This invention belongs to the field of deep dehydration, drying and separation of azeotropic organic solvents and preparation of electronic-grade organic solvents, and more specifically, it relates to a full-temperature liquid-phase temperature-switching adsorption process for deep dehydration and impurity removal of dioxolane. Background Technology

[0002] Dioxolane and trioxymethylene are important monomer raw materials for synthesizing the engineering plastic (co)polyoxymethylene (POM). Imported POM is mainly used in mid-to-high-end electronics, electric vehicles, and machinery parts, while domestic POM products from major manufacturers are still used in low-to-mid-end industrial building materials and auto parts, and their production processes are relatively backward. Therefore, POM is protected by the state as a strategic material, thus avoiding the impact of imported products. However, the purity of dioxolane has a significant impact on the polymerization reaction in the POM production process, and can lead to the polymerization reaction being difficult to initiate, especially if dioxolane contains water and low-molecular-weight volatile organic impurities, including formaldehyde and formic acid, which directly affect the quality of POM products. The dehydration process of dioxolane is relatively outdated. The dioxolane refining process still uses the traditional distillation process. The dioxolane product flowing out of the bottom of the light-light removal tower has a maximum purity of 99.99%, but the content of impurities such as water, formaldehyde, and formic acid still exceeds the standard, which is greater than 200-500 ppm. This makes it difficult to meet the dioxolane purity requirements for polyoxymethylene synthesis.

[0003] The polyoxymethylene (POM) process mainly includes the dioxolane production stage, the formaldehyde concentration stage, the trioxymethylene synthesis stage, and the POM polymerization stage. Among these, the production of dioxolane is also an important part of the POM process, except for the trioxymethylene synthesis stage. This is because dioxolane is one of the two main raw materials for synthesizing POM, and its product quality determines the final purity of the POM product. It is mostly integrated into the POM production process. There are also independent dioxolane manufacturers, but their products are mostly used in scenarios other than POM production.

[0004] The dioxolane production process mainly consists of the imported and assimilated polyoxymethylene process, including the dioxolane process flow and the latest domestic and internationally developed reactive distillation (i.e., synthetic distillation).

[0005] Taking the Polish ZAT process as an example, the imported dioxolane synthesis and purification process is as follows: A 60% (w / w) formaldehyde aqueous solution and 99.88% ethylene glycol are first synthesized into a hemiacetal in a hemiacetal reactor, then fed into a dioxolane synthesis reactor for dehydration to generate dioxolane. The reaction product containing 61% dioxolane from the synthesis reactor is sent to a feed recovery distillation column for distillation. The bottom product mainly consists of unreacted formaldehyde aqueous solution and ethylene glycol, which is recycled back to the synthesis reactor. The stream collected from the top of the recovery distillation column contains 63% dioxolane, as well as water, formaldehyde, and other impurities, and is sent to a dioxolane distillation column for further concentration. The stream collected from the bottom of the distillation column is a dilute formaldehyde solution, while the stream collected from the top contains 91.7% dioxolane and 7% water, with a boiling point close to the azeotropic point of 71.2℃. The top stream from the distillation column is then sent to a dioxolane extraction column for extraction and purification. Impurities such as formaldehyde and formic acid, along with a large amount of water, in the feed stream of the extraction tower are extracted into the bottom of the tower. The dioxolane content in the top stream after extraction reaches 97%. The extractant can be an organic solvent such as dichloromethane / ethane or an inorganic alkaline solvent such as sodium hydroxide. The top stream of the extraction tower is then fed into a series of distillation columns consisting of a dioxolane heavy removal column and a dioxolane light removal column, both operating at atmospheric pressure. The dioxolane is purified to 99.99% using conventional distillation methods and collected in the bottom of the light removal column. The stream collected from the top of the distillation column has a composition close to the dioxolane-water binary azeotropic composition. By using conventional extraction methods to bypass the azeotropic composition, a stream with a dioxolane concentration of 97% is obtained. This stream then passes through the light and heavy removal distillation columns, and finally, a dioxolane product with a purity of 99.99% is obtained from the bottom of the light removal column.

[0006] The dioxolane process of Hong Kong-based Fu Yi Company is basically similar to that of the Polish chemical process, differing only in the synthesis section. The subsequent separation and purification processes, such as extraction, light-weight removal tower, and heavy-weight removal tower, are identical. Specifically, a 45% sodium hydroxide aqueous solution is used as the extractant in the extraction section.

[0007] Both processes share the following common problems:

[0008] First, the dioxolane refining processes of both methods are complex, involve numerous pieces of equipment, and consume a lot of energy. Their main purpose is dehydration and purification. In the extractive distillation, the introduction of alkaline extractants, such as 40% sodium hydroxide aqueous solution, introduces water into the system again, which further increases the load on the subsequent light and heavy removal towers. This includes acid and alkali wastewater treatment, distillation for light and heavy removal, and dehydration. The process is complex and lengthy, and the water content in the dioxolane product obtained is difficult to reach below 200-500 ppm.

[0009] Secondly, because the boiling point of dioxolane lies between that of heavy components such as ethylene glycol / water and light components such as formaldehyde and formic acid, and because there are azeotropic points between dioxolane and water, ethylene glycol and water, and formaldehyde and water, purifying dioxolane using traditional distillation and azeotropic distillation becomes quite difficult. In existing processes, dioxolane is obtained from the bottom of the light component removal column after extractive distillation, recovery distillation, light component removal distillation (light component removal column), and heavy component removal distillation (heavy component removal column). Generally, to obtain high-purity dioxolane from the bottom of the distillation column, heavier impurities such as water and ethylene glycol are inevitably carried along, especially water. This results in a dioxolane concentration reaching 99.99%, but the water content still significantly exceeds the standard, reaching 200–500 ppm or more, failing to meet the requirement of less than 100 ppm for water and other impurities in polyoxymethylene (POM) production.

[0010] Third, because the ethylene glycol-water azeotropic system still exists in the dioxolane-water binary azeotropic system, and the latter's azeotropic temperature is higher than the former's, it is quite difficult to obtain high-purity dioxolane through distillation. The energy consumption is high, and the extractant cannot remove small amounts of volatile organic compounds, which cannot be removed by traditional distillation columns such as light and heavy removal columns. As a result, the purity of the final dioxolane product is difficult to reach above 99.95%. Furthermore, the content of the most important impurities affecting polyoxymethylene polymerization, such as water and formaldehyde, is greater than 100-500 ppm, which is seriously excessive, making it impossible to obtain high-end polyoxymethylene products.

[0011] To address the problems of existing technologies, the inventors, through experiments and result analysis, discovered that for full-temperature-range adsorption processes primarily used for the purification of dioxolane, using full-temperature-range liquid-phase temperature-switching adsorption as the main method is more convenient, feasible, and effective than gas-phase pressure-switching or gas-phase temperature-switching adsorption. Therefore, this invention employs the following technical solution to address these issues:

[0012] A full-temperature liquid-phase temperature-switching adsorption process for deep dehydration and impurity removal of dioxolane is characterized by the following steps and operations:

[0013] ① Raw material logistics: The product liquid obtained after purification of dioxolane or purchased dioxolane has a purity of 99.9% dioxolane. The water content is 500-1000 ppm, and trace amounts of small molecule organic impurities, including formaldehyde and methanol, are 100-300 ppm. The content of large molecule organic impurities, including ethylene glycol, hemiacetal and paraformaldehyde, is less than 100 ppm. The raw material is heated to 70-100℃ at room temperature and pressure, and then pumped into the subsequent temperature-switched adsorption purification unit for deep dehydration of dioxolane.

[0014] ② Temperature-switched adsorption purification: This method consists of three fixed-bed adsorption towers loaded with composite adsorbents. Heated raw material gas enters one of the towers from the bottom for adsorption. The adsorption temperature is 70–100℃, the pressure is atmospheric pressure or 0.01–0.02 MPa, and the adsorption time is approximately 30–60 minutes. The non-adsorbed phase liquid flowing out from the top of the tower is dioxolane, with a purity greater than or equal to 99.999%. Among these components, the water content is less than or equal to 100 ppm, the content of formaldehyde and methanol (small molecule impurities) is less than or equal to 100 ppm, and the content of ethylene glycol, methyl acetal, and paraformaldehyde (large molecule organic impurities) is less than 50 ppm. The temperature is 70–100℃, the pressure is atmospheric pressure or 0.01–0.02 MPa, and the gas is then transferred to the product tank after heat exchange with the raw material stream.

[0015] ③ Temperature-switched adsorption and desorption: While the adsorption step is underway, the other two adsorption towers are in the desorption and regeneration step. One adsorption tower is purged with dioxolane product gas after adsorption. The purging gas is superheated and enters from the bottom of the adsorption tower. The operating temperature is 110-150℃ and the purging time is 10-30 minutes. The purging gas flowing out from the top of the adsorption tower is used as desorption gas. After heat exchange with the feed liquid, it is cooled to 60-70℃ to form a desorption liquid with a composition of 80-90% dioxolane, 10-20% water, and a trace amount. This desorption liquid is then introduced into the subsequent distillation and concentration process. Meanwhile, the other adsorption tower is in the cooling and pre-adsorption stage. The heat-exchanged feed liquid is used to cool the adsorption tower bed and perform pre-adsorption to ensure that the bed temperature in the adsorption tower reaches the operating temperature and pressure required for the adsorption step, thus entering the next adsorption cycle.

[0016] ④ Distillation and Concentration: The desorbed liquid from the temperature-switching adsorption and desorption process is pumped to the upper inlet of the packed distillation column for dehydration. The water flowing out from the top of the distillation column is discharged into the wastewater pool for treatment, or returned to the dioxolane recovery unit in the dioxolane production process for treatment. The 99.9% pure dioxolane concentrate flowing from the bottom of the distillation column is pumped and mixed with the feed liquid before entering the temperature-switched adsorption purification process again to further recover dioxolane from the desorbed liquid. As a result, the yield of dioxolane product exceeds 95%. In addition, a stream containing macromolecular organic impurities, including ethylene glycol, hemiacetal, and paraformaldehyde, is periodically extracted from the lower part (above the bottom) of the distillation column and sent to a de-heavy distillation column. A small amount of macromolecular organic impurity components flow out from the bottom of the de-heavy distillation column for recovery. The 99.9% pure dioxolane concentrate flowing out from the top of the de-heavy distillation column is either incorporated into the feed liquid or used as a coolant and pre-adsorbed material in the temperature-switched adsorption-desorption unit.

[0017] Furthermore, in the aforementioned full-temperature liquid-phase temperature-switching adsorption process for deep dehydration and impurity removal of dioxolane, the adsorption tower loaded with adsorbents in the temperature-switching adsorption concentration and desorption steps is loaded with composite adsorbents including conventional 3A, 4A, 5A, 13X molecular sieves, silica gel, as well as activated carbon, carbon molecular sieves, carbon fibers, carbon nanotubes, graphene, and carbon aerogels.

[0018] Furthermore, in the aforementioned full-temperature liquid-phase temperature-switching adsorption process for deep dehydration and impurity removal of dioxolane, hot nitrogen is used as the purge gas instead of the dioxolane product gas in the temperature-switching adsorption and desorption step. The purge temperature is 160-200℃, which makes the desorption more complete. After hot nitrogen purging, the desorbed gas undergoes heat exchange and condensation. The non-condensable nitrogen gas escapes and is recycled after heating. The condensate produced by condensation is the desorbed liquid, which then enters the distillation and concentration process. The product yield of dioxolane is greater than or equal to 97%.

[0019] Furthermore, in the aforementioned full-temperature liquid-phase temperature-switching adsorption process for deep dehydration and impurity removal of dioxolane, the operational adjustments of the temperature-switching adsorption purification and desorption steps, besides the selection of adsorbent, the operating temperatures of adsorption and desorption, the desorption and regeneration methods, the three towers, and the matching of heating and cooling times with the cycle operation time, also affect the effectiveness of the full-temperature liquid-phase temperature-switching adsorption process. These factors include the adsorption tower space velocity, the stream flow rate, the adsorbent packing density, the tower height-to-diameter ratio, the ambient temperature and heat compensation, and the system's operational flexibility. Given a fixed process equipment, adjustable process conditions are required to accommodate fluctuations in the moisture content and impurity concentration of the raw material stream. This is particularly important when the moisture content exceeds 1000 ppm and macromolecular organic impurities such as ethylene glycol, hemiacetal, and paraformaldehyde exceed 100 ppm. In such cases, when the ambient temperature outside the system is below 20–30°C, the desorption and regeneration operating temperature must be increased to ensure the adsorption bed reaches the required operating temperature, preventing incomplete desorption and regeneration that could lead to substandard dioxolane products. The system needs a 10–20% margin in terms of capacity and heat load, including adjustments to adsorbent loading, space velocity, circulation time, and heating / cooling time. Simultaneously, the system should have 80–90% self-sufficiency or an operational flexibility of 60–110%.

[0020] Furthermore, in the aforementioned full-temperature liquid-phase temperature-switching adsorption process for deep dehydration and impurity removal of dioxolane, a permeable membrane system can be used instead of a distillation column in the distillation and concentration step. The desorbate from the temperature-switching adsorption and desorption process is pumped to a membrane separation system composed of one or more permeable membranes via a liquid pump. The water flowing out from the permeate side enters the wastewater treatment unit, while the dioxolane concentrate flowing out from the non-permeate side is mixed with the raw material stream and returned to the temperature-switching adsorption and purification step for further recovery of dioxolane.

[0021] Furthermore, in the aforementioned full-temperature liquid-phase temperature-switching adsorption process for deep dehydration and impurity removal of dioxolane, when the water concentration in the desorbate exceeds 30% in the temperature-switching adsorption-desorption step, a side stream is drawn from the upper part of the distillation column in the distillation process. This side stream is composed of a binary azeotrope of dioxolane and water, requiring an additional gas-phase temperature-switching or pressure-switching adsorption process for treatment. The non-adsorbed phase stream flowing out from this stream serves as an intermediate gas / liquid and is then concentrated in the distillation concentration process. The adsorbed phase stream flowing out from this stream enters a newly added dehydration distillation column. The water escaping from the top of the dehydration distillation column is discharged into the wastewater treatment facility. The dioxolane concentrate flowing out from the bottom of the column can either be directly mixed with the raw material stream and entered into the temperature-switching adsorption purification process, or it can be further dehydrated in the distillation concentration process to achieve a purity of 99.9% for the dioxolane concentrate, which is then mixed with the raw material stream and entered into the temperature-switching adsorption purification process.

[0022] Compared with the prior art, the main beneficial effects of the present invention are:

[0023] (1) When the full-temperature liquid-phase temperature-switching adsorption process of the present invention is used for deep dehydration and impurity removal of dioxolane, it can obtain dioxolane products with a purity of more than 99.99% and a water content of less than 50-100 ppm and a total impurity component content of less than 50-100 ppm. Traditional azeotropic distillation, reactive distillation, membrane separation and other methods cannot obtain high-purity dioxolane products, thus replacing imports.

[0024] (2) Compared with existing technologies such as azeotropic distillation and membrane separation, the full-temperature liquid phase temperature-switching adsorption process of the present invention is simple to operate, has low energy consumption, large processing capacity, long adsorbent life, and is safe and stable. It can adapt to the fluctuation of water and high molecular weight organic matter such as ethylene glycol and paraformaldehyde in the dioxane feed liquid.

[0025] (3) The full-temperature liquid-phase temperature-switching adsorption of the present invention can recover the dioxolane in the desorbed stream by simple distillation or membrane separation and return it to the temperature-switching adsorption process, so that the yield of dioxolane product is greater than or equal to 95-98%, while avoiding the composition of the desorbed stream falling into the composition range of dioxolane-water binary azeotrope, further reducing costs.

[0026] (4) When the content of macromolecular organic impurities in the raw material stream, including ethylene glycol, hemiacetal, paraformaldehyde, etc., fluctuates, or when the water content in the raw material stream or desorption liquid exceeds 1000ppm or 20%, the present invention can extract the stream through a side stream of the distillation and concentration process, or add a distillation column or a gas phase pressure swing or temperature swing adsorption process, so as to obtain high-purity polymer-grade dioxolane product and achieve stable operation of the full-temperature liquid phase temperature swing adsorption process.

[0027] (5) The present invention can further improve the product yield of dioxolane by treating the desorbed gas stream generated in the temperature-changing adsorption and desorption step with a pervaporation membrane. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the process in Example 1.

[0029] Figure 2 This is a schematic diagram of the process in Example 2.

[0030] Figure 3 This is a schematic diagram of the process in Example 3.

[0031] Figure 4 This is a flowchart of Example 4. Detailed Implementation

[0032] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0033] Example 1

[0034] like Figure 1 As shown, a full-temperature liquid-phase temperature-switching adsorption process for deep dehydration and impurity removal of dioxolane includes the following steps and operations:

[0035] 1) Raw material logistics: The raw material comes from the purified product liquid of dioxolane or purchased dioxolane with a purity of 99.9% dioxolane. The water content is 600-800 ppm, and trace amounts of small molecule organic impurities including formaldehyde and methanol are 300 ppm. The content of large molecule organic impurities including ethylene glycol, hemiacetal and paraformaldehyde is less than 100 ppm. The raw material is heated to 80-90℃ and pressure of 0.01-0.02 MPa at room temperature and pressure, and then pumped into the subsequent temperature-switched adsorption purification unit for deep dehydration of dioxolane.

[0036] 2) Temperature-switched adsorption purification consists of three fixed-bed adsorption towers loaded with composite adsorbents. The lower part of each tower is filled with activated carbon or carbon molecular sieves and silica gel, while the remaining parts are filled with 4A and 5A / 13X adsorbents, forming a fixed bed of composite adsorbents. Heated feed gas enters one tower from the bottom for adsorption. The adsorption temperature is 80–90°C, the pressure is 0.01–0.02 MPa, and the adsorption time is approximately 50–60 minutes. The non-adsorbed phase liquid flowing out from the top of the tower is dioxolane, with a purity greater than or equal to 99.999%. The water content is less than or equal to 100 ppm, the formaldehyde and methanol small molecule impurities are less than or equal to 100 ppm, and the ethylene glycol, methyl acetal, and paraformaldehyde large molecule organic impurities are less than 50 ppm. The temperature is 80–90°C, and the pressure is atmospheric pressure or 0.01–0.02 MPa. After heat exchange with the feed gas, the product is fed into the product tank.

[0037] 3) Variable-temperature desorption: While the adsorption step is underway, the other two adsorption towers are in the desorption and regeneration step. One adsorption tower is purged with dioxolane product gas after adsorption. The purging gas is superheated and enters from the bottom of the adsorption tower at an operating temperature of 120-140℃ for 20-30 minutes. The purging gas flowing out from the top of the adsorption tower is used as desorption gas. After heat exchange with the feed liquid, it is cooled to 60-70℃ to form a desorption liquid with a composition of 80-90% dioxolane, 15-20% water, and a trace amount, which enters the subsequent distillation and concentration process. Meanwhile, the other adsorption tower is in the cooling and pre-adsorption stage. The heat-exchanged feed liquid is used to cool the adsorption tower bed to the operating temperature required for adsorption, and pre-adsorption is performed to ensure that the bed temperature in the adsorption tower reaches the operating temperature and pressure required for the adsorption step, thus entering the next adsorption cycle.

[0038] 4) Distillation and Concentration: The desorbed liquid from the temperature-switched adsorption-desorption process is pumped to the upper inlet of a distillation column packed with Raschig rings for dehydration. The water flowing from the top of the distillation column is discharged into a wastewater tank for treatment. A 99.9% pure dioxolane concentrate flows from the bottom of the distillation column and is pumped back to the temperature-switched adsorption purification process via a circulating pump to further recover dioxolane from the desorbed liquid. This results in a dioxolane product yield exceeding 95%. A stream containing macromolecular organic impurities, including ethylene glycol, hemiacetal, and paraformaldehyde, is periodically drawn from the lower part (above the bottom) of the distillation column and fed into a de-heavy distillation column. A small amount of macromolecular organic impurities flows from the bottom of the de-heavy distillation column for recovery. A 99.9% pure dioxolane concentrate flows from the top of the de-heavy distillation column and is either incorporated into the feed liquid or used as a coolant and pre-adsorbed material in the temperature-switched adsorption-desorption unit.

[0039] Example 2

[0040] Based on Example 1, such as Figure 2 As shown, in a full-temperature liquid-phase temperature-switching adsorption process for deep dehydration and impurity removal of dioxolane, the temperature-switching adsorption-desorption step uses hot nitrogen as the purge gas instead of the dioxolane product gas, with a purge temperature of 160–180°C, resulting in more complete desorption. The desorbed gas after hot nitrogen purging undergoes heat exchange and condensation. The non-condensable nitrogen gas escapes and is recycled after heating. The condensate produced is the desorbed liquid, which then enters the distillation and concentration process, achieving a dioxolane yield of ≥97%.

[0041] Example 3

[0042] Based on Example 1, such as Figure 3 As shown, in a full-temperature liquid-phase temperature-switching adsorption process for deep dehydration and impurity removal of dioxolane, in the distillation and concentration step, a NaA-type molecular sieve permeable membrane system is used to replace the distillation column. The desorbate from the temperature-switching adsorption and desorption process is pumped to a membrane separation system composed of a primary molecular sieve permeable membrane. The water flowing out from the permeate side enters the aerobic organic wastewater biochemical treatment unit, while the dioxolane concentrate flowing out from the non-permeate side is mixed with the raw material stream and returned to the temperature-switching adsorption and purification step for further recovery of dioxolane.

[0043] Example 4

[0044] Based on Example 1, such as Figure 4 As shown, in a full-temperature liquid-phase temperature-switching adsorption process for deep dehydration and impurity removal of dioxolane, when the water concentration in the desorbate exceeds 30% in the temperature-switching adsorption-desorption step, a side stream is drawn from the upper part of the distillation column in the distillation process. This side stream is composed of a binary azeotrope of dioxolane and water, requiring an additional gas-phase pressure-switching adsorption process for treatment. The non-adsorbed phase stream flowing out from this process is used as an intermediate gas / liquid and then enters the distillation concentration process for concentration. The adsorbed phase stream flowing out from this process enters a newly added dehydration distillation column. The water escaping from the top of the dehydration distillation column is discharged into the wastewater treatment facility. The dioxolane concentrate flowing out from the bottom of the column enters the distillation concentration process for further water removal, so that the purity of the obtained dioxolane concentrate reaches 99.9%. It is then mixed with the raw material liquid and entered into the temperature-switching adsorption purification process, with a dioxolane product yield of greater than or equal to 97%.

[0045] Obviously, the embodiments described above are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments described in this invention, all other embodiments obtained by those skilled in the art without creative effort, or structural changes made under the guidance of this invention, that have the same or similar technical solutions as this invention, all fall within the protection scope of this invention.

Claims

1. A full-temperature liquid-phase temperature-switching adsorption process for deep dehydration and impurity removal of dioxolane, characterized in that, The process and operation steps include the following: 1) Raw material logistics: The raw material comes from the purified product liquid of dioxolane or purchased dioxolane with a purity of 99.9% dioxolane. The water content is 500-1000 ppm, and trace amounts of small molecule organic impurities including formaldehyde and methanol are 100-300 ppm. The content of large molecule organic impurities including ethylene glycol, hemiacetal and paraformaldehyde is less than 100 ppm. The raw material is heated to 70-100℃ at room temperature and pressure, and the pressure is atmospheric pressure or 0.01-0.02 MPa. It is then pumped into the subsequent temperature-switched adsorption purification unit for deep dehydration of dioxolane. 2) Temperature-switched adsorption purification consists of three fixed-bed adsorption towers loaded with composite adsorbents. Heated raw material gas enters the adsorption tower from the bottom for adsorption. The adsorption temperature is 70–100℃, the pressure is atmospheric pressure or 0.01–0.02 MPa, and the adsorption time is about 30–60 minutes. The non-adsorbed phase liquid flowing out from the top of the adsorption tower is dioxolane product with a purity greater than or equal to 99.999%. Among them, the water content is less than or equal to 100 ppm, the content of formaldehyde and methanol small molecule impurities is less than or equal to 100 ppm, and the content of ethylene glycol, methyl acetal, and paraformaldehyde macromolecular organic impurities is less than 50 ppm. The temperature is 70–100℃, the pressure is atmospheric pressure or 0.01–0.02 MPa, and after heat exchange with the raw material stream, it is fed into the product tank. 3) Temperature-switched adsorption and desorption: While the adsorption step is underway, the other two adsorption towers are in the desorption and regeneration step. One adsorption tower is purged with dioxolane product gas after adsorption. The purging gas is superheated and enters from the bottom of the adsorption tower. The operating temperature is 110-150℃, and the purging time is 10-30 minutes. The purging gas flowing out from the top of the adsorption tower is used as desorption gas. After heat exchange with the feed liquid, it is cooled to 60-70℃ to form a desorption liquid with a composition of 80-90% dioxolane, 10-20% water, and a trace amount, which enters the subsequent distillation and concentration process. Meanwhile, the other adsorption tower is in the cooling and pre-adsorption stage. The heat-exchanged feed liquid is used to cool the adsorption tower bed and perform pre-adsorption to ensure that the bed temperature in the adsorption tower reaches the operating temperature and pressure required for the adsorption step, and then enters the next adsorption cycle. 4) Distillation and concentration: The desorbed liquid from the temperature-switching adsorption and desorption process is pumped by a liquid pump to the upper inlet of the packed distillation column for dehydration. The water flowing out from the top of the distillation column is discharged into the wastewater pool for treatment, or returned to the dioxolane recovery unit in the dioxolane production process for treatment. The 99.9% pure dioxolane concentrate flowing from the bottom of the distillation column is pumped and mixed with the feed liquid before entering the temperature-switched adsorption purification process again to further recover dioxolane from the desorbed liquid. As a result, the yield of dioxolane product exceeds 95%. In addition, a stream containing macromolecular organic impurities, including ethylene glycol, hemiacetal, and paraformaldehyde, is periodically extracted from the lower part (above the bottom) of the distillation column and sent to a de-heavy distillation column. A small amount of macromolecular organic impurity components flow out from the bottom of the de-heavy distillation column for recovery. The 99.9% pure dioxolane concentrate flowing out from the top of the de-heavy distillation column is either incorporated into the feed liquid or used as a coolant and pre-adsorbed material in the temperature-switched adsorption-desorption unit.

2. The full-range liquid-phase temperature-switching adsorption process for deep dehydration and impurity removal of dioxolane as described in claim 1, wherein, The adsorption tower loaded with adsorbents in the temperature-switching adsorption concentration and desorption steps contains composite adsorbents including conventional 3A, 4A, 5A, 13X molecular sieves, silica gel, as well as activated carbon, carbon molecular sieves, carbon fibers, carbon nanotubes, graphene, and carbon aerogels.

3. The full-temperature liquid-phase temperature-switching adsorption process for deep dehydration and impurity removal of dioxolane as described in claim 1, wherein, In the temperature-switching adsorption-desorption step, hot nitrogen is used as the purge gas instead of the dioxolane product gas. The purge temperature is 160-200℃, which makes the desorption more complete. After hot nitrogen purging, the desorbed gas undergoes heat exchange and condensation. The non-condensable nitrogen gas escapes and is recycled after heating. The condensate produced by condensation is the desorbed liquid, which then enters the distillation and concentration process. The product yield of dioxolane is greater than or equal to 97%.

4. The full-temperature liquid-phase temperature-switching adsorption process for deep dehydration and impurity removal of dioxolane as described in claim 1, wherein, The operational adjustments of the temperature-switched adsorption purification and desorption steps, besides the selection of adsorbent, the operating temperatures of adsorption and desorption, the desorption and regeneration methods, the three towers, and the matching of heating and cooling times with the cycle operation time, also affect the effectiveness of the full-range liquid-phase temperature-switched adsorption process. These factors include the adsorption tower space velocity, stream flow rate, adsorbent packing density, tower height-to-diameter ratio, ambient temperature and heat compensation, and system operational flexibility. Under relatively fixed process equipment, adjustable process conditions are necessary to adapt to fluctuations in the water content and impurity content of the raw material stream. Especially when the water content in the raw material stream exceeds 1000 ppm and macromolecular organic impurities such as ethylene glycol, hemiacetal, and paraformaldehyde exceed 100 ppm, the desorption and regeneration operating temperature must be increased when the ambient temperature outside the system is below 20-30°C. This ensures that the desorption and regeneration temperature of the adsorption bed reaches the required operating temperature, avoiding the problem of substandard dioxolane products caused by incomplete desorption and regeneration. The system requires a 10-20% margin to increase the device capacity and heat load, including matching the adsorbent loading, space velocity, circulation time, and heating / cooling time. Simultaneously, the system needs 80-90% self-sufficiency or 60-110% operational flexibility.

5. The full-range liquid-phase temperature-switching adsorption process for deep dehydration and impurity removal of dioxolane as described in claim 1, wherein, In the distillation and concentration step, a permeable membrane system can be used to replace the distillation column. The desorbent from the temperature-switching adsorption and desorption process is pumped to a membrane separation system composed of one or more permeable membranes. The water flowing out from the permeate side enters the wastewater treatment unit, while the dioxolane concentrate flowing out from the non-permeate side is mixed with the raw material stream and returned to the temperature-switching adsorption and purification step for further recovery of pentane.

6. The full-temperature liquid-phase temperature-switching adsorption process for deep dehydration and impurity removal of dioxolane as described in claim 1, wherein, In the aforementioned temperature-switched adsorption-desorption step, when the water concentration in the desorbed liquid exceeds 30%, a side stream liquid is drawn from the upper part of the distillation column in the distillation process. This side stream liquid is composed of a binary azeotrope of dioxolane and water, requiring an additional gas-phase temperature-switched or pressure-switched adsorption process for treatment. The non-adsorbed phase stream flowing out from this process is used as an intermediate gas / liquid and then enters the distillation concentration process for further concentration. The adsorbed phase stream flowing out from this process enters a newly added dehydration distillation column. The water escaping from the top of the dehydration distillation column is discharged into the wastewater treatment facility. The dioxolane concentrate flowing out from the bottom of the column can either be directly mixed with the raw material stream and entered into the temperature-switched adsorption purification process, or it can enter the distillation concentration process to further remove water, so that the purity of the obtained dioxolane concentrate reaches 99.9%, and then it is mixed with the raw material liquid and entered into the temperature-switched adsorption purification process.

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