Method for Separation of Close-Boiling Mixture of Polyols

Abstract

This invention discloses an approach for the separation of the close-boiling mixture of polyols. The raw material is ethylene glycol containing miscellaneous polyols (such as 1,2-propylene glycol and 1,2-butanediol). Over an acid catalyst, these miscellaneous polyols, through (1) a dehydration reaction, (2) pinacol rearrangement, and (3) acetalization or ketalization reaction, are converted into aldehydes (small amounts), acetals, and ketals (trace amount), which are simultaneously and readily separated via distillation. Meanwhile, after the reaction, the mixture is further separated to obtain an ethylene glycol product at a high purity. The invention provides a technique to remove the miscellaneous polyols from ethylene glycol via liquid-phase dehydration reactions under mild conditions, with low energy consumption. In particular, this approach is markedly effective for the removal of 1,2-butanediol that is difficult to be removed via conventional techniques. The purity of the resulting ethylene glycol product is high, and value-added acetals or ketals are co-produced.

Claims

1. A method for separating a close-boiling mixture of ethylene glycol and other one or more than two of miscellaneous polyols including 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, and glycerol, comprising: (a) mixing the close-boiling mixture with an acid catalyst at >150° C.; (b) performing a dehydration reaction in a reactor under heating; (c) converting the miscellaneous polyols into volatile products via dehydration, acetalization, and ketalization reactions; (d) removing the volatile products via vaporization or distillation; (e) hence removing the miscellaneous polyols.

2. The method of claim 1 wherein said acid catalyst includes liquid Brønsted acids, solid Brønsted acids, Lewis acids, acid-site-containing oxides, an acid-site-containing mineral, other Brønsted acids, or their combinations.

3. The method of claim 1 wherein the ethylene glycol product after the reaction is further purified to remove the residual miscellaneous polyols via distillation, extraction, crystallization, adsorption, chromatography, or their combinations.

4. The method of claim 1 wherein the unconverted material in the dehydration reactor contains ethylene glycol and acid catalysts; (a) when only solid acid catalysts are used, the catalysts are removed from ethylene glycol through solid-liquid separation, evaporation or distillation; the removed solid acid is regenerated via calcination or elution or drying for the recycling of solid catalysts; (b) when only liquid acid catalysts are used, the catalysts are removed from ethylene glycol through evaporation or distillation for the recycling of liquid catalysts; the liquid acid catalysts are neutralized with an alkali and then the product of the neutralization reaction is removed from ethylene glycol through evaporation or crystallization; (c) when both solid and liquid acid catalysts are used, the solid catalysts are firstly removed from ethylene glycol through solid-liquid separation; the liquid acid catalysts are removed from ethylene glycol through evaporation or distillation; or, ethylene glycol is directly separated from both solid and liquid acid catalysts via evaporation or distillation.

5. The method of claim 1 wherein a volatile products of miscellaneous polyols in the dehydration, acetalization, and ketalization reactions are vaporized, condensed, and collected; (b) the removed products include volatile oil-phase and aqueous products; (c) the oil-phase and aqueous products are then separated; (d) the oil-phase product can be further separated into acetals, ketals, dioxanes, aldehydes, and ketones; apart from the removal of miscellaneous polyols, by-products of acetals, ketals, cyclic ethers, acyclic ethers, aldehydes, and ketones are co-produced; (e) the dehydration reactor itself also functions as a simple reactive distillation apparatus to remove the by-products from ethylene glycol; or, these by-products can also be produced and removed via multi-stage reactive distillation; or, the reaction system can also be refluxed in the reactor, and then the mixture is separated through decantation, extraction, adsorption, or distillation.

6. The method of claim 1 wherein the feedstock contains 50 wt %-95 wt % ethylene glycol and 5 wt %-50 wt % one or more than two of miscellaneous polyols including 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, and glycerol.

7. The method of claim 1 wherein said acid catalyst includes H-form molecular sieves, sulfonated activated carbon, H-form resins, sulfuric acid, hydrochloric acid, and nitric acid; the catalyst accounts for 0.1 wt %-15 wt % of the system of the dehydration reaction.

8. The method of claim 1 wherein the dehydration reaction takes place at 150-198° C. if the pressure of the system is atmospheric pressure.

9. The process of claim 1 wherein the raw ethylene glycol containing miscellaneous polyols is synthesized from coal or biomass.

10. The method of claim 1 wherein the device for solid-liquid separation can be a pressure filter, vacuum filter, settler, or centrifuge.

11. The method of claim 2 wherein said acid catalyst includes H-form molecular sieves, sulfonated activated carbon, H-form resins, sulfuric acid, hydrochloric acid, and nitric acid; the catalyst accounts for 0.1 wt %-15 wt % of the system of the dehydration reaction.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0044] Schematic flow diagram of the process in the present invention is illustrated in the FIGURE, and the numbers in the FIGURE denote the materials or equipment as follows:

1. feedstock of polyols 2. catalyst 3. dehydration reactor 4. catalyst separator 5. catalyst regenerator 6. vapor-liquid separator 7. liquid phase 8. gas phase 9. vacuum distillation equipment 10. high-boiling-point diethylene glycol, triethylene glycol, glycerol, etc 11. vacuum distillation equipment 12. miscellaneous polyols (such as 1,2-propanediol) 13. main product (ethylene glycol) 14. condenser 15. decantor 16. aqueous product 17. oil-phase raw product 18. distillation equipment 19. water 20. aldehydes and ketones 21. distillation equipment 22. acetaldehyde 23. propanal 24. acetone 25. distillation equipment 26. low-boiling-point acetals 27. raw dioxane 28. high-boiling-point oxygenates 29. distillation or chromatography equipment 30. 2-ethyl-1,3-dioxolane 31. 2-ethyl-4-methyl-1,3-dioxolane 32. high-boiling-pointacetals 33. distillation or chromatography equipment 34. 2-isopropyl-4-methyl-1,3-dioxolane 35. 2-propyl-1,3-dioxolane.

EMBODIMENTS

[0045] The present invention is described in detail with the FIGURE and the following examples:

Example 1

[0046] (a) Dehydration reaction: 100 mL of crude ethylene glycol (73 wt % ethylene glycol, 17 wt % 1,2-propanediol, and 10 wt % 1,2-butanediol) was added in a dehydration reactor. After the mixture was heated to 180° C., 2 g of 300-mesh HZSM-5 zeolite with a SiO.sub.2/Al.sub.2O.sub.3ratio of 25 was added. With stirring, the volatile products generated from the dehydration of miscellaneous polyols were continuously evaporated for 4 h.

[0047] (b) Separation of the catalyst: After the dehydration reaction, the zeolite was separated from the liquid product with a centrifuge at a speed of 6000 rpm.

[0048] (c) Further purification via distillation: after the previous step, the liquid mixture in the reactor was separated via vacuum distillation at an overhead pressure of 10 kPa and bottom temperature of 135-150° C. ˜65 g of ethylene glycol product at a purity of >90 wt % was obtained via simple distillation, in which the content of 1,2-butanediol was <1 wt %. The residue at the bottom was used to produce antifreezes.

[0049] (d) Removal of miscellaneous polyols via distillation: after the reaction, a small amount of 1,2-propanediol and 1,2-butanediol was still not reacted. These impurities were removed via vacuum distillation at a bottom temperature of 115-130° C. and an overhead pressure of 10 kPa. After the distillation, the purified ethylene glycol product was at a purity of >98 wt %.

[0050] (e) Gas-liquid separation: the evaporated volatile products in step 1 contained acetals, ketals (trace amount), moisture, acetone, propanal, and other low-boiling-point substances. In addition, a small amount of vapor of polyols was also mixed into the volatile products. 20 g of volatile products were liquefied and obtained with a condenser at 10° C.

[0051] (f) Liquid-liquid separation: the liquefied volatile products in the previous step were transferred into a decanter to be separated into 12 g of oil-phase product and 8 g of aqueous product.

[0052] (g) Concentration of aldehydes and ketones in the aqueous product: the aqueous product obtained in the previous step was separated via atmospheric distillation. The overhead (condenser) temperature was 8° C. and the bottom (reboiler) temperature was ˜92° C. The distillate was a mixture of acetaldehyde, propanal, and acetone, and an aqueous solution of dioxane was also recovered in the bottom, which was then concentrated through steam stripping for further utilization.

[0053] (h) Preliminary separation of the oil-phase product: the oil-phase product obtained instep 5 was preliminarily separated via atmospheric distillation into five products: aldehydes/ketones (boiling point: 20-60° C.), low-boiling-point acetals (boiling point: 70-90° C.), raw dioxane (boiling point: 90-100° C.), high-boiling-point acetals (boiling point: 110-140° C.), and high-boiling-point oxygenates (boiling point: 140-190° C.). Among them, the mixture of aldehydes/ketones was mixed with those obtained in the step 7 for further separation via distillation.

[0054] (i) Separation of acetals and ketals: the raw acetals in the previous step, containing a small amount of ketals, were the most abundant substances in the crude oil-phase product (˜4 g). Wherein, low-boiling-point acetals (mainly 2-ethyl-1,3-dioxolane and 2-ethyl-4-methyl-1,3-dioxolane) accounted for ˜60 wt %. High-boiling-point acetals (mainly 2-propyl-1,3-dioxolane and 2-isopropyl-4-methyl-1,3-dioxolane) accounted for ˜40 wt %. The low- and high-boiling-point acetals were then separated with two distillation columns independently. Finally, four pure acetal products were obtained.

[0055] (j) Regeneration of the catalyst: the spent HZSM-5 zeolite was regenerated through calcination at 550-580° C.

Example 2

[0056] (a) Dehydration reaction: 100 mL of crude ethylene glycol (73 wt % ethylene glycol, 17 wt % 1,2-propanediol, and 10 wt % 1,2-butanediol) was added in a dehydration reactor. After the mixture was heated to 185° C., 5 g of 300-mesh Hβ zeolite with aSiO.sub.2/Al.sub.2O.sub.3ratio of 25 was added. With stirring, the volatile products generated from the dehydration of miscellaneous polyols were continuously evaporated for 4 h.

[0057] (b) Separation of the catalyst: After the dehydration reaction, the zeolite was separated from the liquid product with a vacuum filter.

[0058] (c) Purification via distillation: after the previous step, the liquid mixture in the reactor was separated via vacuum distillation at an overhead pressure of 10 kPa. ˜65 g of raw ethylene glycol product (b.p. <150° C.) at a purity of >97.5 wt % was obtained via the vacuum distillation. The content of 1,2-butanediol was <0.5 wt % and the content of 1,2-propanediol was <2 wt % in the product. The residue at the bottom was used to produce antifreezes.

[0059] (d) Removal of miscellaneous polyols via distillation: the unreacted 1,2-propanediol was removed via vacuum distillation at a bottom temperature of 115-130° C. and an overhead pressure of 10 kPa. After the distillation, the purified ethylene glycol product was at a purity of 99.5 wt %.

[0060] (e) Gas-liquid separation: the evaporated volatile products in step 1 contained acetals, ketals (trace amount), moisture, acetone, propanal, and other low-boiling-point substances. In addition, a small amount of vapor of polyols was also mixed into the volatile products. ˜34 g of volatile products were liquefied and obtained with a condenser at 10° C.

[0061] (f) Liquid-liquid separation: the liquefied volatile products in the previous step were transferred into a decanter to be separated into 24.9 g of oil-phase product and 9.1 g of aqueous product.

[0062] (g) Concentration of aldehydes and ketones in the aqueous product: the aqueous product obtained in the previous step was separated via atmospheric distillation. The overhead (condenser) temperature was 8° C. and the bottom (reboiler) temperature was ˜92° C. The distillate was a mixture of acetaldehyde, propanal, and acetone, and an aqueous solution of dioxane was also recovered in the bottom, which was then concentrated through air stripping for further utilization.

[0063] (h) Preliminary separation of the oil-phase product: the oil-phase product obtained in step 5 was preliminarily separated via atmospheric distillation into five products: aldehydes/ketones (boiling point: 20-60° C.), low-boiling-point acetals (boiling point: 70-90° C.), raw dioxane (boiling point: 90-100° C.), high-boiling-point acetals (boiling point: 110-140° C.), and high-boiling-point oxygenates (boiling point: 140-190° C.). Among them, the mixture of aldehydes/ketones was mixed with those obtained in the step 7 for further separation via distillation.

[0064] (i) Separation of acetals and ketals: the raw acetals in the previous step, containing a small amount of ketals, were the most abundant substances in the crude oil-phase product (˜20 g). Wherein, low-boiling-point acetals (mainly 2-ethyl-1,3-dioxolane and 2-ethyl-4-methyl-1,3-dioxolane) accounted for ˜60 wt %. High-boiling-point acetals (mainly 2-propyl-1,3-dioxolane and 2-isopropyl-4-methyl-1,3-dioxolane) accounted for ˜40 wt %. The low- and high-boiling-point acetals were then separated with two distillation columns independently. Finally, four pure acetal products were obtained.

[0065] (j) Regeneration of the catalyst: the spent HP zeolite was regenerated through calcination at 650-700° C.

Example 3

[0066] (a) Batch reactive distillation: 100 g of HZSM-5 zeolite with a SiO.sub.2/Al.sub.2O.sub.3ratio of 25 was loaded in the lower reaction zone of a batch reactive distillation column. 100 g of packing was loaded in the upper distillation zone. 100 mL of crude ethylene glycol (73 wt % ethylene glycol, 17 wt % 1,2-propanediol, and 10 wt % 1,4-butanediol) was added in the bottom of the distillation column. The mixture in the bottom was heated to 180-190° C. and the overhead temperature was 10° C. 22 g of distillate was obtained after 3 h.

[0067] (b) Further purification via distillation: after the previous step, the liquid mixture in the bottom was further separated via another vacuum distillation column at an overhead pressure of 10 kPa and bottom temperature of 135-150° C. ˜67 g of raw ethylene glycol product at a purity of >93 wt % was distilled. The residue at the bottom was used to produce antifreezes.

[0068] (c) Removal of miscellaneous polyols via distillation: the unreacted 1,2-propanediol was further removed via vacuum distillation at a bottom temperature of 115-130° C. and an overhead pressure of 10 kPa. After the distillation, the purified ethylene glycol product was at a purity of >99.3 wt %.

[0069] (d) Liquid-liquid separation: the distillate in step 1 was transferred into a decanter to be separated into 13 g of oil-phase product and 9 g of aqueous product.

[0070] (e) Concentration of aldehydes and ketones in the aqueous product: the aqueous product obtained in the previous step was separated via atmospheric distillation. The overhead (condenser) temperature was 8° C. and the bottom (reboiler) temperature was ˜92° C. The distillate was a mixture of acetaldehyde, propanal, and acetone, and an aqueous solution of dioxane was also recovered in the bottom, which was then concentrated through steam stripping for further utilization.

[0071] (f) Preliminary separation of the oil-phase product: the oil-phase product obtained was preliminarily separated via atmospheric distillation into five products: aldehydes/ketones (boiling point: 20-60° C.), low-boiling-point acetals (boiling point: 70-90° C.), raw dioxane (boiling point: 90-100° C.), high-boiling-point acetals (boiling point: 110-140° C.), and high-boiling-point oxygenates (boiling point: 140-190° C.). Among them, the mixture of aldehydes/ketones was further separated via distillation.

[0072] (g) Separation of acetals and ketals: the raw acetals in the previous step, containing a small amount of ketals, were the most abundant substances in the crude oil-phase product (˜4 g). Wherein, low-boiling-point acetals accounted for ˜60 wt % and high-boiling-point acetals accounted for ˜40 wt %. The low- and high-boiling-point acetals were then separated with two distillation columns independently. Finally, four pure acetal products were obtained.

[0073] (h) Catalyst regeneration: Regeneration of the catalyst: the spent HZSM-5 zeolite was regenerated through calcination at 650-750° C.

Example 4

[0074] (a) Dehydration reaction: 100 mL of crude ethylene glycol (85 wt % ethylene glycol, 10 wt % 1,2-propanediol, and 5 wt % 1,3-butanediol) was added in a dehydration reactor. After the mixture was heated to 185° C., 4 g of 98 wt % sulfuric acid was added. With stirring, the volatile products generated from the dehydration of miscellaneous polyols were continuously evaporated for 4 h.

[0075] (b) Separation of sulfuric acid and purification via distillation: After the dehydration reaction, the liquid in the reactor was separated via vacuum distillation at an overhead pressure of 10 kPa and bottom temperature of 135-150° C. 67 g of raw ethylene glycol at a purity of >96 wt % was distilled.

[0076] (c) Removal of miscellaneous polyols via distillation: the unreacted 1,2-propanediol was further removed via vacuum distillation at a bottom temperature of 115-130° C. and an overhead pressure of 10 kPa. After the distillation, the purified ethylene glycol product was at a purity of >99.2 wt %.

[0077] (d) Gas-liquid separation: the evaporated volatile products in step 1 contained acetals, ketals (trace amount), moisture, acetone, propanal, and other low-boiling-point substances. In addition, a small amount of vapor of polyols was also mixed into the volatile products. 13 g of volatile products were liquefied and obtained with a condenser at 10° C.

[0078] (e) Liquid-liquid separation: the liquefied volatile products in the previous step were transferred into a decanter to be separated into 9 g of oil-phase product and 4 g of aqueous product.

[0079] (f) Concentration of aldehydes and ketones in the aqueous product: the aqueous product obtained in the previous step was separated via atmospheric distillation. The overhead (condenser) temperature was 8° C. and the bottom (reboiler) temperature was ˜92° C. The distillate was a mixture of acetaldehyde, propanal, and acetone, and an aqueous solution of dioxane was also recovered in the bottom, which was then concentrated through air stripping for further utilization.

[0080] (g) Preliminary separation of the oil-phase product: the oil-phase product obtained in step 5 was preliminarily separated via atmospheric distillation into five products: aldehydes/ketones (boiling point: 20-60° C.), low-boiling-point acetals (boiling point: 70-90° C.), raw dioxane (boiling point: 90-100° C.), high-boiling-point acetals (boiling point: 110-140° C.), and high-boiling-point oxygenates (boiling point: 140-190° C.). Among them, the mixture of aldehydes/ketones was mixed with those obtained in step 6 for further separation via distillation.

[0081] (h) Separation of acetals and ketals: the raw acetals in the previous step, containing a small amount of ketals, were the most abundant substances in the crude oil-phase product (˜4 g). Wherein, low-boiling-point acetals accounted for ˜60 wt % and high-boiling-point acetals accounted for ˜40 wt %. The low- and high-boiling-point acetals were then separated with two distillation columns independently. Finally, four pure acetal products were obtained.

[0082] (i) Regeneration of the catalyst: the residue in the bottom in step 2 contained sulfuric acid and diethylene glycol. The sulfuric acid was separated and regenerated through vacuum distillation.

Example 5

[0083] (a) Dehydration reaction: 100 mL of crude ethylene glycol (60 wt % ethylene glycol, 25 wt % 1,2-propanediol, and 15 wt % 2,3-butanediol) was added in a dehydration reactor. After the mixture was heated to 185° C., 3 g of 300-mesh HZSM-5 zeolite with aSiO.sub.2/Al.sub.2O.sub.3ratio of 25 was added. With stirring, the volatile products generated from the dehydration of miscellaneous polyols were continuously evaporated for 4 h.

[0084] (b) Separation of the catalyst: After the dehydration reaction, the zeolite was separated from the liquid product with a centrifuge.

[0085] (c) Further purification via distillation: after the previous step, the liquid mixture in the reactor was separated via vacuum distillation at an overhead pressure of 10 kPa and bottom temperature of 135-150° C. ˜53 g of ethylene glycol product at a purity of >84 wt % was obtained via simple distillation, in which the content of 2,3-butanediol was <1 wt %. The residue at the bottom was used to produce antifreezes.

[0086] (d) Removal of miscellaneous polyols via distillation: the unreacted 1,2-propanediol was further removed via vacuum distillation at a bottom temperature of 115-130° C. and an overhead pressure of 10 kPa. After the distillation, the purified ethylene glycol product was at a purity of >99 wt %.

[0087] (e) Gas-liquid separation: the evaporated volatile products in step 1 contained acetals, ketals (trace amount), moisture, acetone, propanal, and other low-boiling-point substances. In addition, a small amount of vapor of polyols was also mixed into the volatile products. 34 g of volatile products were liquefied and obtained with a condenser at 10° C.

[0088] (f) Liquid-liquid separation: the liquefied volatile products in the previous step were transferred into a decanter to be separated into 20 g of oil-phase product and 14 g of aqueous product.

[0089] (g) Concentration of aldehydes and ketones in the aqueous product: the aqueous product obtained in the previous step was separated via atmospheric distillation. The overhead (condenser) temperature was 8° C. and the bottom (reboiler) temperature was ˜92° C. The distillate was a mixture of acetaldehyde, propanal, and acetone, and an aqueous solution of dioxane was also recovered in the bottom, which was then concentrated through steam stripping for further utilization.

[0090] (h) Preliminary separation of the oil-phase product: the oil-phase product obtained in step 5 was preliminarily separated via atmospheric distillation into five products: aldehydes/ketones (boiling point: 20-60° C.), low-boiling-point acetals (boiling point: 70-90° C.), raw dioxane (boiling point: 90-100° C.), high-boiling-point acetals (boiling point: 110-140° C.), and high-boiling-point oxygenates (boiling point: 140-190° C.). Among them, the mixture of aldehydes/ketones was mixed with those obtained in the step 7 for further separation via distillation.

[0091] (i) Separation of acetals and ketals: the raw acetals in the previous step, containing a small amount of ketals, were the most abundant substances in the crude oil-phase product (˜8.5 g). Wherein, low-boiling-point acetals accounted for ˜60 wt %. The low- and high-boiling-point acetals were then separated with two distillation columns independently. Finally, four pure acetal products were obtained.

[0092] (j) Regeneration of the catalyst: the spent HZ SM-5 zeolite was regenerated through calcination at 700-750° C.

Example 6

[0093] (a) Reactive Distillation: 1.2 t of Hβ zeolite with aSiO.sub.2/Al.sub.2O.sub.3ratio of 160 was loaded in the lower reaction zone of a reactive distillation column. 1 t of packing was loaded in the upper distillation zone. Crude ethylene glycol (73 wt % ethylene glycol, 17 wt % 1,2-propanediol, and 10 wt % 1,2-butanediol) was pumped into the middle of the distillation column at a flow rate of 1 t/h. The mixture in the bottom was heated to 185° C. and the overhead temperature was 10° C. The distillate was obtained at a rate of 200 kg/h.

[0094] (b) Further purification via distillation: after the previous step, the liquid mixture in the bottom was further separated via another vacuum distillation column at an overhead pressure of 10 kPa and bottom temperature of 140° C. Raw ethylene glycol product at a purity of >96 wt % was distilled at a rate of 630 kg/h, in which the content of 1,2-butanediol was <0.4 wt %. The residue at the bottom was used to produce antifreezes.

[0095] (c) Removal of miscellaneous polyols via distillation: the unreacted 1,2-propanediol was further removed via vacuum distillation at a bottom temperature of 115-130° C. and an overhead pressure of 10 kPa. After the distillation, the purified ethylene glycol product was at a purity of >99.7 wt % and a flow rate of 610 kg/h.

[0096] (d) Liquid-liquid separation: the distillate in step 1 was transferred into a decanter to be separated into oil-phase product at a rate of 230 kg/h and aqueous product at a rate of 110 kg/h.

[0097] (e) Concentration of aldehydes and ketones in the aqueous product: the aqueous product obtained in the previous step was separated via atmospheric distillation. The overhead (condenser) temperature was 8° C. and the bottom (reboiler) temperature was ˜92° C. The distillate was a mixture of acetaldehyde, propanal, and acetone, and an aqueous solution of dioxane was also recovered in the bottom, which was then concentrated through air stripping for further utilization.

[0098] (f) Preliminary separation of the oil-phase product: the oil-phase product obtained was preliminarily separated via atmospheric distillation into five products: aldehydes/ketones (boiling point: 20-60° C.), low-boiling-point acetals (boiling point: 70-90° C.), raw dioxane (boiling point: 90-100° C.), high-boiling-point acetals (boiling point: 110-140° C.), and high-boiling-point oxygenates (boiling point: 140-190° C.). Among them, these aldehydes/ketones were mixed with those aldehydes/ketones obtained in step 5, and the mixture was further separated via distillation.

[0099] (g) Separation of acetals and ketals: the raw acetals in the previous step, containing a small amount of ketals, were the most abundant substances in the crude oil-phase product. The flow rate of the raw acetals was 197 kg/h, in which low-boiling-point acetals (mainly 2-ethyl-1,3-dioxolane and 2-ethyl-4-methyl-1,3-dioxolane) accounted for ˜60 wt % and high-boiling-point acetals (mainly 2-propyl-1,3-dioxolane and 2-isopropyl-4-methyl-1,3-dioxolane) accounted for ˜40 wt %. The low- and high-boiling-point acetals were then separated with two distillation columns independently. Finally, four pure acetal products were obtained.

[0100] (h) Regeneration of the catalyst: the spent Hβ zeolite was regenerated at 550-600° C. through calcination in an industrial furnace.

[0101] These examples illustrate the invention but should not be interpreted as a limitation thereon.