Process for recovering prenol

Abstract

The present invention relates to a process for recovering prenyl alcohol substantially free of formaldehyde from a crude prenyl alcohol stream containing prenyl alcohol, water and formaldehyde, which process comprises subjecting said crude prenyl alcohol stream or a prenyl alcohol containing fraction thereof to distillation in a low-boiler separation column operating at a pressure of 2.5 bar or more to obtain a distillate stream containing water-containing formaldehyde and a bottoms stream containing prenyl alcohol. The process of the present invention allows obtaining prenyl alcohol substantially free of formaldehyde. The present invention also provides an apparatus for recovering prenyl alcohol substantially free of formaldehyde from a crude prenyl alcohol stream containing prenyl alcohol, water and formaldehyde, which apparatus comprises a first low-boiler separation column, a second low-boiler separation column and a work-up column.

Description

[0001] The present invention relates to a method for recovering substantially formaldehyde-free isopentenol from a crude isopentenol stream containing isopentenol, water and formaldehyde, and to an apparatus for recovering isopentenol.

[0002] Isopentenol, or 3-methyl-3-buten-1-ol (MBE), is an important intermediate used in aromatic compounds such as citral and vitamins, with global annual production reaching thousands of tons. Industrially, isopentenol is prepared by reacting formaldehyde with isobutylene (2-methylpropene). This method is illustrated, for example, in DE 100 64 751A1. This reaction is typically carried out in the absence of a solvent and under high pressure and temperature, as described in, for example, WO 2020 / 049111 A1. DE 1 279 014 B describes a method for preparing 3-en-1-ol under high pressure and temperature in the presence of a base. WO 2019 / 030386 A1 relates to a method for recovering isopentenol from a feed stream containing isopentenol, one or more solvents, water, and isobutylene through a series of distillation steps.

[0003] The reaction of formaldehyde with isobutylene is an equilibrium reaction, and therefore incomplete. Unreacted formaldehyde is primarily separated during downstream distillation steps and disposed of via accumulated wastewater. However, a drawback of known methods is the limited efficiency of formaldehyde separation, leading to a tendency for formaldehyde to be ubiquitous in the distillation sequence and the presence of significant amounts of formaldehyde in the separated isopentenol. Formaldehyde contamination can impair downstream processes and result in higher consumption rates, quality issues, and challenges to the operability of the production unit.

[0004] Therefore, the object of the present invention is to provide a method for recovering formaldehyde-free isopentenol from a crude isopentenol stream.

[0005] In a first aspect, the present invention provides a method for recovering substantially formaldehyde-free isopentenol from a crude isopentenol stream containing isopentenol, water, and formaldehyde. This method comprises distilling the crude isopentenol stream or its isopentenol-containing fraction in a low-boiling-point separation column operating at a pressure of 2.5 bar or higher to obtain a distillate stream containing aqueous formaldehyde and a bottom stream containing isopentenol.

[0006] In one embodiment, the isopentenol-containing fraction of crude isopentenol is crude isopentenol from which water and low-boiling substances have already been separated in a first low-boiling substance separation column. This operation, by distillation in a second low-boiling substance separation column, allows for the yield of concentrated aqueous formaldehyde, suitable for recycling into the isopentenol synthesis process. Furthermore, in a second aspect, this method includes:

[0007] (i) The crude isopentenol feed stream is fed to a first low-boiling-point separation column operating at a pressure of 1.5 bar or lower to obtain a first bottom stream containing isopentenol and formaldehyde and a first distillate stream containing water and low-boiling-point substances.

[0008] (ii) The first bottom stream is fed to a second low-boiling-point separation column operating at 2.5 bar or higher to obtain a second distillate stream containing aqueous formaldehyde and a second bottom stream containing isopentenyl alcohol; and

[0009] (iii) The second bottom stream is fed to a post-processing column to obtain pure isopentenol as distillate stream and bottom stream containing high-boiling-point substances.

[0010] The present invention also provides an apparatus for recovering substantially formaldehyde-free isopentenol from a crude isopentenol stream containing isopentenol, water, and formaldehyde, the apparatus comprising:

[0011] - The first low-boiling-point separation tower is suitable for receiving crude isopentenol feed stream and separating the crude isopentenol feed stream by distillation into a first bottom stream containing isopentenol and formaldehyde and a first distillate stream containing water and low-boiling-point substances.

[0012] - A second low-boiling-point separation column, adapted to receive the first bottom stream from the first low-boiling-point separation column and to separate the first bottom stream by distillation into a second distillate stream containing aqueous formaldehyde and a second bottom stream containing isopentenyl alcohol; and

[0013] - A post-treatment tower suitable for receiving a second bottom stream from a second low-boiling-point separation tower and separating the second bottom stream by distillation into a pure isopentenyl alcohol as a distillate stream and a bottom stream containing high-boiling-point substances.

[0014] Selectively recovering formaldehyde from solutions containing both water and alcohol is extremely difficult. This difficulty stems from the fact that monomeric formaldehyde (as well as polymerized formaldehyde) simultaneously forms hydrates with water and hemiacetals with alcohols such as isopentenol. The hydrates and hemiacetals, with varying degrees of formaldehyde polymerization, have miscible boiling points. The stability and equilibrium between the hydrates and hemiacetals are temperature-dependent. The formaldehydes formed in the upper region of the distillation column can decompose at the hotter bottom, adding further complexity to the separation task.

[0015] However, it was found that formaldehyde can be almost completely separated from isopentenol by distillation at the temperature at which hemiacetal breaks down into formaldehyde and isopentenol, thus formaldehyde can be easily separated from isopentenol.

[0016] In particular, it was found that formaldehyde can be separated substantially completely from isopentenol, and concentrated aqueous formaldehyde suitable for recycling to the isopentenol synthesis process can be obtained in a distillation sequence comprising a first distillation at a temperature at which the equilibrium shifts toward the formaldehyde and isopentenol hemiacetal, thereby retaining substantially all of the formaldehyde in the distillation column bottoms; and a second distillation at a temperature at which the hemiacetal breaks down into formaldehyde and isopentenol, thereby allowing for easy separation of formaldehyde from isopentenol.

[0017] These observations are illustrated in the attached ternary diagram.

[0018] The following discussion focuses on the second aspect of the invention. It should be understood that the operating parameters and descriptions of the embodiments and preferred embodiments of the "second low-boiling-point separation tower," the "second distillate stream containing aqueous formaldehyde," and the "second bottom stream containing isopentenol" according to the second aspect can also be applied to the "low-boiling-point separation tower," the "distillate stream containing aqueous formaldehyde," and the "bottom stream containing isopentenol" according to the first aspect of the invention.

[0019] To allow for a first distillation at a temperature below the dissociation temperature of isopentenol-formaldehyde and a second distillation at a temperature above the dissociation temperature of isopentenol-formaldehyde, the present invention considers two low-boiling-point separation columns operating at different pressures in the second aspect. Furthermore, at the lower pressure predominant in the first low-boiling-point separation column, a first distillate containing water and a low-boiling-point product substantially free of formaldehyde are obtained. At the higher pressure predominant in the second low-boiling-point separation column, substantially all of the formaldehyde is separated from the isopentenol. Therefore, the method of the present invention allows for the yield of isopentenol substantially free of formaldehyde.

[0020] The term "substantially formaldehyde-free" is understood to mean that there is no significant amount of formaldehyde in the obtained pure isopentenol. Therefore, the obtained pure isopentenol preferably contains less than 0.5% by weight, more preferably less than 0.1% by weight of formaldehyde.

[0021] The crude isopentenol stream comprises isopentenol, water, and formaldehyde. Preferably, the crude isopentenol stream comprises 50-75% by weight of isopentenol, more preferably 60-65% by weight. Preferably, the crude isopentenol stream comprises 15-40% by weight of water, more preferably 22-35% by weight. Preferably, the crude isopentenol stream comprises 1-5% by weight of formaldehyde, more preferably 2-3% by weight.

[0022] Preferably, the crude isopentenol feed stream is a liquid stream. The liquid stream can be a single-phase liquid stream or a two-phase liquid stream.

[0023] The crude isopentenyl alcohol stream is typically a product stream from an isopentenyl alcohol production process, from which unreacted isobutylene has been removed. In one embodiment, the method includes reacting formaldehyde with isobutylene to obtain a reaction mixture, and removing unreacted isobutylene from the reaction mixture in an isobutylene distillation column to obtain the crude isopentenyl alcohol stream.

[0024] Formaldehyde preferably reacts with isobutylene under supercritical conditions. Supercritical conditions exist when a material or mixture of materials is subjected to temperatures and pressures exceeding the thermodynamic critical point of the material or mixture. It has been found that under supercritical conditions, isobutylene is sufficiently reactive with formaldehyde to allow for high conversion rates with high selectivity.

[0025] To achieve supercritical conditions, formaldehyde and isobutylene preferably react at a temperature of at least 220°C, for example, 220-290°C, and an absolute pressure of at least 200 bar. Unless otherwise stated, all pressures mentioned herein are absolute pressures. Further details regarding the reaction of formaldehyde and isobutylene under supercritical conditions can be found in WO 2020 / 049111 A1.

[0026] In a further embodiment, formaldehyde reacts with isobutylene in the presence of a solvent and a heterogeneous catalyst.

[0027] The advantage of the method of the present invention is that the second distillate is suitable for recycling into the formaldehyde reaction.

[0028] Unreacted isobutylene is removed from the reaction mixture in an isobutylene distillation column to obtain a crude isopentenyl alcohol stream.

[0029] Isobutylene is obtained as an isobutylene distillate stream. The isobutylene distillate stream preferably contains at least 70% by weight of isobutylene, more preferably at least 85% by weight. Preferably, the isobutylene distillate stream is recycled to the reaction of formaldehyde and isobutylene.

[0030] Crude isopentenol was obtained as the bottom feed stream of an isobutylene distillation column.

[0031] To minimize the compression of the circulating isobutylene, the isobutylene distillation column is suitably operated at a pressure of 4-15 bar, preferably 7-13 bar. Unless otherwise stated, the total pressure of the column or column described herein is understood to refer to the absolute pressure at the top of the column or column. The isobutylene distillation column may have 5-40 theoretical plates, more preferably 15-25 theoretical plates.

[0032] The bottom temperature of the isobutylene distillation column is typically in the range of 140-200°C, more preferably 160-180°C. The top temperature of the isobutylene distillation column is preferably in the range of 50-90°C, more preferably 60-80°C.

[0033] In a particularly preferred embodiment, the isobutylene distillation column is operated at a pressure of 7-13 bar, a bottom temperature of 160-180°C, and a top temperature of 60-80°C.

[0034] Under the above conditions, the crude isopentenol stream obtained in the isobutylene distillation column is in a superheated state. Preferably, the crude isopentenol stream is sent to a depressurization vessel before being sent to the first low-boiling-point separation vessel. In the depressurization vessel, the crude isopentenol stream is depressurized, preferably to the pressure of the first low-boiling-point separation column. In the depressurization vessel, a gas phase and a liquid phase are obtained, which are preferably sent to the first low-boiling-point separation column via a separation line.

[0035] According to a second aspect of the invention, crude isopentenol is fed to a first low-boiling-point separation column operating at a pressure of 1.5 bar or lower. Any higher pressure in the crude isopentenol stream is preferably released before it is fed to the first low-boiling-point separation column. Preferably, the crude isopentenol stream is added as a side stream to the first low-boiling-point separation column, defining a rectification section above the feed position and a stripping section below the feed position.

[0036] In the first low-boiling-point separation column, a first bottom stream containing isopentenol and formaldehyde is obtained, along with a first distillate stream containing water and low-boiling-point compounds. The term "low-boiling-point compounds" is understood to refer to organic compounds with a lower boiling point than isopentenol (unlike formaldehyde), so their boiling point is below approximately 130°C at atmospheric pressure. The most common low-boiling-point compounds are methanol and / or isopentenyl formate, which are formed as byproducts during this process.

[0037] In a preferred embodiment, the first low-boiling-point substance separation column is operated at a pressure of 1.2 bar or lower, preferably 0.5 bar or lower. The bottom temperature of the first low-boiling-point substance separation column is preferably in the range of 80-135°C, more preferably 90-115°C, and most preferably 95-105°C. The top temperature of the first low-boiling-point substance separation column is preferably in the range of 45-105°C, more preferably 55-80°C.

[0038] In a particularly preferred embodiment, the first low-boiling-point separator is operated at a pressure of 0.2-0.5 bar, a bottom temperature of 90-115°C, and a top temperature of 55-80°C.

[0039] The first low-boiling-point substance separation column preferably has 15-65 theoretical plates, more preferably 25-40 theoretical plates. In particular, the stripping section of the first low-boiling-point substance separation column preferably has 10-25 theoretical plates. The rectifying section of the first low-boiling-point substance separation column preferably has 5-40 theoretical plates.

[0040] The first bottom feed stream preferably contains 75-95% by weight of isopentenol, more preferably 80-90% by weight.

[0041] The first distillate is typically taken out as a gas at the top of the first low-boiling-point separation column and condensed to obtain a liquid two-phase stream. The two-phase stream preferably allows phase separation in a separation vessel to obtain an aqueous phase and an organic phase. The aqueous phase is preferably fed into a wastewater stripping column, as described below. The organic phase is preferably partially returned as a reflux stream to the top of the first low-boiling-point separation column. A portion of the organic phase is preferably discarded from the process to avoid the accumulation of water-insoluble low-boiling-point substances in the first low-boiling-point separation column.

[0042] In a preferred embodiment, at least a portion of the first distillate stream is fed to a wastewater stripping tower to separate low-boiling-point compounds and entrained isopentenyl alcohol from the water. Preferably, the portion of the first distillate stream fed to the wastewater stripping tower is the aqueous phase obtained through condensation and phase separation of the first distillate stream, as described above.

[0043] In a wastewater stripping tower, low-boiling-point distillate streams yield low-boiling-point substances, and wastewater is obtained as the bottom stream. Both the low-boiling-point distillate stream and the wastewater bottom stream are removed from the process and can be sent to further processing.

[0044] Furthermore, isopentenol is preferably obtained as a side stream in a wastewater stripping tower. The isopentenol side stream is typically a two-phase stream and preferably contains 15-40% by weight, more preferably 25-35% by weight of isopentenol. The isopentenol side stream is preferably recycled to a first low-boiling-point separation tower.

[0045] The low-boiling-point distillate stream preferably contains 75-95% by weight of low-boiling-point substances, more preferably 80-85% by weight.

[0046] The wastewater tower bottom stream preferably contains less than 1.2% by weight of organic matter, more preferably less than 0.6% by weight. The wastewater tower bottom stream typically contains formaldehyde, wherein the formaldehyde concentration is 0.05-1.5% by weight, for example 0.3-0.9% by weight.

[0047] The wastewater stripping tower is preferably operated at a pressure of 1.5 bar or lower, more preferably 1.1 bar or lower. The bottom temperature of the wastewater stripping tower is preferably in the range of 95-110°C, more preferably 97-103°C. The top temperature of the wastewater stripping tower is preferably in the range of 65-100°C, more preferably 75-85°C.

[0048] In a particularly preferred embodiment, the wastewater stripping tower is operated at a pressure of 0.95-1.1 bar, a bottom temperature of 97-103°C, and a top temperature of 75-85°C.

[0049] The wastewater stripping tower preferably has 6-30 theoretical trays, more preferably 10-20 theoretical trays.

[0050] According to the second aspect, the first bottom stream obtained in the first low-boiling-point substance separation column is fed to a second low-boiling-point substance separation column operating at a pressure of 2 bar or higher, preferably 2.5 bar or higher. Preferably, the first bottom stream is added as a side stream to the second low-boiling-point substance separation column, defining a rectification section above the feed position and a stripping section below the feed position.

[0051] In the second low-boiling-point separation column, a second distillate stream containing aqueous formaldehyde or essentially composed of aqueous formaldehyde is obtained, along with a second bottom stream containing isopentenol. The second bottom stream also contains high-boiling-point compounds. The term "high-boiling-point compounds" is understood to refer to organic compounds having a boiling point higher than isopentenol, i.e., above approximately 130°C at atmospheric pressure. The most common high-boiling-point compounds are diols and / or oligomers formed as byproducts during this process.

[0052] In a preferred embodiment, the second low-boiling-point substance separation column is operated at a pressure of 2.5 bar or higher, preferably 2.8 bar or higher, and most preferably 2.9 bar or higher. The bottom temperature of the second low-boiling-point substance separation column is preferably in the range of 160-200°C, more preferably 170-185°C, and most preferably 175-180°C. The top temperature of the second low-boiling-point substance separation column is preferably in the range of 115-160°C, more preferably 125-145°C.

[0053] In a particularly preferred embodiment, the second low-boiling-point separator is operated at a pressure of 2.9-3.5 bar, a bottom temperature of 175-180°C, and a top temperature of 130-140°C.

[0054] The second low-boiling-point substance separation column preferably has 20-60, more preferably 35-60 theoretical plates. In particular, the stripping section of the first low-boiling-point substance separation column preferably has 25-45 theoretical plates. The rectifying section of the first low-boiling-point substance separation column preferably has 7-20 theoretical plates.

[0055] At the top of the second low-boiling-point separation tower, exhaust gas is typically obtained. The exhaust gas mainly contains nitrogen, and may contain trace amounts of isopentenol, formic acid, water, formaldehyde, and / or decomposition gases.

[0056] The second bottom feed preferably contains 82-96% by weight of isopentenol, more preferably 87-91% by weight. The higher pressure of the second low-boiling-point separation column allows for a high degree of separation between formaldehyde and isopentenol. Therefore, the second bottom feed preferably contains up to 0.5% by weight of formaldehyde, more preferably up to 0.1% by weight.

[0057] The second distillate stream is an aqueous stream, which preferably contains 25-60% by weight of formaldehyde, more preferably 40-50% by weight, and particularly 45-50% by weight. The second distillate stream preferably contains up to 15% by weight of isopentenol, more preferably up to 5% by weight.

[0058] Because the vapor appearing at the top of the second low-boiling-point separation column exhibits a broad condensation profile, it is advantageous to use a condenser with liquid circulation. Direct condensation in quenching with liquid circulation is particularly advantageous. Furthermore, in a preferred embodiment of this method, a quenching section is provided downstream of the rectification section of the second low-boiling-point separation column along the direction of vapor flow. The term "direction of vapor flow" refers to the flow direction of the gaseous component in the separation column, i.e., upward, towards the top of the column. Preferably, a quenching section is provided within the second low-boiling-point separation column above the rectification section.

[0059] Direct condensation during quenching also mitigates scaling caused by various condensation processes and formaldehyde polymerization mechanisms, which can occur at sites of high local formaldehyde concentrations. To avoid the risk of scaling in the second low-boiling-point separator and downstream processes, particularly in the exhaust gas from the second low-boiling-point separator, the formaldehyde concentration in the second distillate is preferably not higher than 60% by weight, more preferably not higher than 55% by weight, and especially not higher than 50% by weight.

[0060] At the lower end of the quench section, the aqueous liquid is collected. When a quench section is provided in a second low-boiling-point separation column, the aqueous liquid can be collected, for example, at a collection tray located above the rectification section and below the quench section.

[0061] The aqueous liquid is partially circulated through a circulation line to the quenching section and partially withdrawn as a second distillate. Suitably, the portion of the aqueous liquid circulated to the quenching section is circulated back to the top of the quenching section. The circulation of the aqueous liquid is typically carried out using a pump. As described above, the second distillate may optionally be at least partially recycled to the reaction of formaldehyde with isobutylene.

[0062] A portion of the aqueous liquid circulates to the quenching section, allowing the vapor rising through the quenching section to be cooled, and formaldehyde is absorbed from the vapor into the aqueous liquid. Therefore, formaldehyde is quenched from the vapor rising through the quenching section.

[0063] Additionally, the aqueous liquid is partially returned as reflux to the rectification section of the second low-boiling-point separator. This can be achieved via a reflux line, or the aqueous liquid can be partially returned to the rectification section as overflow from the collection tray located below the quench section.

[0064] The mass flow rate ratio between the reflux stream and the second distillate is preferably in the range of 2:1 to 10:1, and more preferably in the range of 3:1 to 7:1.

[0065] In a preferred embodiment, the aqueous liquid is cooled before being circulated into the quenching section. Preferably, the portion of the aqueous liquid taken out as the second distillate is a portion of the cooled aqueous liquid stream.

[0066] The temperature of the aqueous liquid collected at the lower end of the quenching section is preferably in the range of 80-140°C, more preferably 125-135°C. The temperature of the cooled aqueous liquid circulating into the quenching section is preferably 10-80°C lower than the temperature of the aqueous liquid collected at the lower end of the quenching section. This allows for a process that is advantageous in terms of energy saving.

[0067] The hot, aqueous liquid extracted from the lower end of the quenching section undergoes thermal integration. In a suitable embodiment, this liquid undergoes heat exchange with the crude isopentenyl alcohol stream flowing into the first low-boiling-point separation tower before being recycled into the quenching section.

[0068] In one embodiment, a washing section is provided downstream of the quenching section along the direction of vapor flow, and water is introduced at the top of the washing section. Preferably, the washing section is provided above the quenching section within a second low-boiling-point separation tower. The washing section allows the formaldehyde concentration in the second distillate to remain below the aforementioned critical concentration, thereby preventing the deposition of oligooxymethylene, for example, in exhaust gas lines.

[0069] The mass flow rate ratio between the water introduced at the top of the washing section and the first bottom feed stream obtained in the first low-boiling-point separation tower is typically in the range of 0.01:1 to 0.06:1, more preferably in the range of 0.015:1 to 0.03:1.

[0070] According to the second aspect, the bottom stream of the second column is sent to the post-treatment column, where pure isopentenol is obtained as the distillate stream. High-boiling-point substances are then removed via the bottom stream. Because the second bottom stream is essentially formaldehyde-free, the separation task in the post-treatment column is significantly less complex compared to the lower formaldehyde separation efficiency in the low-boiling-point separation section.

[0071] The distillate stream of pure isopentenol preferably contains at least 97.0% by weight of isopentenol, more preferably 98.0% by weight, for example 98.1-99.5% by weight. Preferably, the distillate stream of pure isopentenol contains less than 0.5% by weight of formaldehyde, for example less than 0.1% by weight or less than 0.01% by weight.

[0072] The high-boiling-point substance bottom stream preferably contains 90-99.9% by weight of the high-boiling-point substance, more preferably 99-99.8% by weight. Preferably, the high-boiling-point substance bottom stream contains less than 0.2% by weight of formaldehyde, for example less than 0.05% by weight of formaldehyde.

[0073] In a preferred embodiment, the post-treatment tower is operated at a pressure of 0.5 bar or lower, preferably 0.25 bar or lower. The bottom temperature of the first low-boiling-point substance separation tower is preferably in the range of 130-190°C, more preferably 150-170°C. The temperature at the top of the post-treatment tower is preferably in the range of 60-90°C, more preferably 65-85°C.

[0074] In a particularly preferred embodiment, the post-treatment tower is operated at a pressure of 0.05-0.2 bar, a bottom temperature of 150-170°C, and a top temperature of 65-85°C.

[0075] The post-processing column preferably has 6-40 theoretical plates, more preferably 10-20 theoretical plates.

[0076] The columns and towers used in the methods and apparatus of this invention can be conventional distillation columns. Suitable types of distillation columns include packed columns, such as columns equipped with random or structured packing materials, plate columns (i.e., tray columns), and mixed columns that contain both packing materials and trays.

[0077] A suitable plate column may contain internal components on which the liquid phase flows. Suitable internal components include sieve trays, bubble cap trays, valve trays, tunnel trays, and... Tower trays, especially bubble cap trays, valve trays, tunnel trays, and Tower tray.

[0078] Randomly packed towers can be filled with various shaped profiles. Heat and mass transfer are improved by increasing the surface area using shaped profiles, which typically have dimensions of 25-80 mm. Suitable shaped profiles include Raschig rings (hollow cylinders), Lysing rings, Pall rings, Hiflow rings, and Intalox saddle packing. The packing material can be provided in the tower in a rectangular or irregular manner (as a packing material, i.e., loose packing). Suitable materials include glass, ceramics, metals, and plastics.

[0079] Structured fillers are an advancement over regular fillers, featuring a structure with a regular shape. This allows for reduced pressure loss during gas flow. Suitable types of structured fillers include fabric and sheet metal fillers.

[0080] The term "top" or "head" used in tower construction refers to the area excluding internal components, located above the uppermost tray or the topmost packing material. It is typically formed by a dome-shaped base (head, e.g.) Heads (or Korbbogen heads) are typically the end elements of a distillation column.

[0081] The term "bottom" or "sedimentation pool" used in towers refers to the area without internal components, located below the lowest tray or below the lowest layer of packing.

[0082] The method of the present invention can be performed continuously or intermittently. Preferably, the method of the present invention is performed continuously.

[0083] The present invention also relates to an apparatus for recovering substantially formaldehyde-free isopentenol from a crude isopentenol stream containing isopentenol, water, and formaldehyde, the apparatus comprising:

[0084] - The first low-boiling-point separation tower is suitable for receiving crude isopentenol feed stream and separating the crude isopentenol feed stream by distillation into a first bottom stream containing isopentenol and formaldehyde and a first distillate stream containing water and low-boiling-point substances.

[0085] - A second low-boiling-point separation column, adapted to receive the first bottom stream from the first low-boiling-point separation column and to separate the first bottom stream by distillation into a second distillate stream containing aqueous formaldehyde and a second bottom stream containing isopentenyl alcohol; and

[0086] - A post-treatment tower suitable for receiving a second bottom stream from a second low-boiling-point separation tower and separating the second bottom stream by distillation into a pure isopentenyl alcohol as a distillate stream and a bottom stream containing high-boiling-point substances.

[0087] It should be understood that the embodiments described above regarding the method of the present invention also apply to the apparatus of the present invention where applicable.

[0088] In a preferred embodiment, the second low-boiling-point separation tower of the device comprises:

[0089] - A quenching section located above the rectification section of the second low-boiling-point separator, wherein the second low-boiling-point separator is designed to collect the second distillate located at the lower end of the quenching section and to partially recycle the second distillate back to the quenching section via a circulation line; and

[0090] - The washing section is located above the quenching section, and the water inlet is located at the top of the washing section.

[0091] In a preferred embodiment, the second low-boiling-point separation tower of the apparatus includes an indirect heat exchanger designed to exchange heat between the aqueous liquid and the coolant stream before the aqueous liquid is circulated into the quenching section. The coolant stream suitable for the method of the present invention is, for example, the crude isopentenyl alcohol stream fed to the first low-boiling-point separation tower.

[0092] Alternatively, the bottom liquid of the first low-boiling-point separation column can be circulated via an indirect heat exchanger. This reduces the heating load on the evaporator of the first low-boiling-point separation column.

[0093] In a preferred embodiment, the apparatus includes an isobutylene distillation column adapted to receive a fluid reaction mixture and adapted to feed a liquid stream of crude isopentenol to a first low-boiling-point separation column.

[0094] In a preferred embodiment, the apparatus includes a reactor adapted for a high-pressure reaction of formaldehyde with isobutylene to obtain a fluid reaction mixture, and adapted for feeding the fluid reaction mixture to an isobutylene distillation column.

[0095] In a preferred embodiment, the apparatus includes a wastewater stripping tower adapted to receive the first distillate stream from a first low-boiling-point separation tower.

[0096] Figure 1 The method of the present invention for recovering isopentenol from a crude isopentenol feed stream in an apparatus according to the present invention is illustrated schematically.

[0097] Figure 2 A preferred embodiment of a second low-boiling-point substance separation tower used in the method of the present invention and present in the apparatus of the present invention is schematically depicted.

[0098] Figure 3 A known method for recovering isopentenol from a crude isopentenol stream is schematically depicted.

[0099] Figures 4a to 4c Showing a ternary plot of a mixture of isopentenol, formaldehyde, and water under different pressures.

[0100] Figure 5 This shows the relative volatility of a mixture of isopentenol and formaldehyde at different temperatures.

[0101] according to Figure 1 A crude isopentenol feed stream (101) containing isopentenol, water, and formaldehyde is fed to a first low-boiling-point separation column (102) operating at a pressure of 1.5 bar or lower. A first bottom stream (103) containing isopentenol and formaldehyde is obtained, as well as a first distillate stream (104) containing water and low-boiling-point substances.

[0102] The first bottom stream (103) is fed to a second low-boiling-point separation column (105) operating at a pressure of 2 bar or higher. A second distillate stream (106) containing aqueous formaldehyde and a second bottom stream (107) containing isopentenol are obtained.

[0103] The second bottom stream (107) is fed to the post-processing column (108). Pure isopentenol is obtained as the distillate stream (109). In addition, a bottom stream (110) containing high-boiling-point substances is obtained.

[0104] according to Figure 2The bottom feed stream from the first column is fed via a pipeline (201) to a second low-boiling-point separator (202) operating at a pressure of 2 bar or higher. The feed location of the feed stream (201) defines the rectification section (203) above the feed location and the stripping section (204) below the feed location, as indicated by the dashed line.

[0105] A quenching section (205) is provided downstream of the rectification section of the second low-boiling-point separation column (202) along the direction of vapor flow, particularly above the rectification section within the second low-boiling-point separation column. Accessories (206), such as plates, are located between the rectification section (203) and the quenching section (205).

[0106] At the lower end of the quench section (205), the aqueous liquid is collected via line (207). A portion of the aqueous liquid is circulated back to the top of the quench section (205) via the circulation line (208), and a portion is withdrawn as a second distillate via line (209). The remaining portion of the aqueous liquid is returned to the rectification section as reflux feed via the reflux line (210).

[0107] The portion of the aqueous liquid circulating to the top of the quenching section (205) passes through a heat exchanger (211), preferably a heat exchanger, to allow the aqueous liquid to exchange heat with the crude isopentenyl alcohol stream flowing into the first low-boiling-point separation tower (in Figure 2 (Not shown in the image).

[0108] Additionally, a washing section (212) is provided downstream of the quenching section (205) along the direction of steam flow, and water is introduced at the top of the washing section via a water inlet (213).

[0109] At the top of the second low-boiling-point substance separation tower (202), waste gas is removed via gas line (214). At the bottom of the second low-boiling-point substance separation tower (202), the second tower bottom stream is taken out via line (215).

[0110] according to Figure 3 A crude isopentenol feed stream (301) containing isopentenol, water, and formaldehyde is fed to a low-boiling-point separation column (302) operating at a pressure of 1.5 bar or lower. A distillate stream (304) containing water and low-boiling-point substances is obtained, as well as a bottom stream (303) containing isopentenol and formaldehyde.

[0111] The bottom feed stream (304) is fed to a post-processing column (305). Isoprene alcohol is obtained as the distillate stream (306). In addition, a bottom feed stream (307) containing high-boiling-point substances is obtained.

[0112] exist Figures 4a to 4c The mixture of isopentenol, formaldehyde, and water is shown in 0.1 bar ( Figure 4a ), 1 bar ( Figure 4b ) and 3 bar ( Figure 4c The ternary plot below. Along the three sides, the ternary plot shows the molar ratios of isopentenol, formaldehyde, and water. For example, along the right side, it shows the molar ratio of formaldehyde relative to isopentenol.

[0113] These curves are residual curves. Each residual curve represents a different feed composition with varying amounts of isopentenol, formaldehyde, and water. The residual curves follow the liquid residual composition in the distillation column, i.e., from the bottom (high temperature) to the top (low temperature). In the ternary diagram shown, following the residual curve towards the higher temperature indicates the composition at the bottom of the column. Following the residual curve towards the lower temperature indicates the composition at the top of the column.

[0114] exist Figure 4a In the ternary diagram (pressure 0.1 bar), a mixed azeotrope of water and isopentenol (HA) appears, with a boiling point of 43.7 °C. A high-boiling azeotrope (SSA) containing isopentenol and all formaldehyde appears, with a boiling point of 77.1 °C.

[0115] exist Figure 4b In the ternary plot (pressure 1 bar), the water-isoprene alcohol azeotrope (HA) has a boiling point of 96.0 °C. Additionally, a low-boiling-point azeotrope of water-formaldehyde (LSA) (98.3 °C) is observed. No other azeotrope is observed. Figure 4a The high-boiling-point azeotrope (SSA) of isopentenol and formaldehyde was observed in the ternary plot (0.1 bar). In fact, isopentenol (130.3 °C) represents the high-boiling-point fraction.

[0116] exist Figure 4c In the ternary diagram (at 3 bar pressure), the water-isoprenol azeotrope (HA) has a boiling point of 129.2 °C. The water-formaldehyde low-boiling-point azeotrope (LSA) has a boiling point shift to 128.0 °C and a higher formaldehyde concentration. At the bottom of the column, isopentenol was found to be essentially formaldehyde-free (169.1 °C).

[0117] Figure 5 This shows the relative volatility of formaldehyde in a mixture of isopentenol and formaldehyde, fitted from experimental data. Terminology Indicates the molar proportion of formaldehyde in the gas phase. (Terminology) This indicates the molar proportion of formaldehyde (including formaldehyde bound as hemiacetal) in the liquid phase. Clearly, the relative volatility of formaldehyde increases with increasing temperature, which is due to… Compared to The ratio is expressed as .

[0118] In particular, it can be seen that at 120°C (393K), the relative volatility ranges from 0.95 to slightly above 1.2. The relative volatility decreases with decreasing temperature; see the curves at 293K, 313K, and 333K. The higher the relative volatility of formaldehyde, the greater the degree to which formaldehyde separates from isopentenol as a low-boiling fraction. Example

[0119] Example 1

[0120] This embodiment involves simulating the distillation removal of formaldehyde from a liquid containing 98 wt% isopentenol and 2 wt% formaldehyde (FA) in a low-boiling-point separator having 27 theoretical plates in a stripping section and 13 theoretical plates in a rectifying section. The liquid is fed into the column at a rate of 100 kg / h. At the top of the column, a distillate containing aqueous formaldehyde is obtained, which is returned to the top of the column as a reflux stream at a rate of 35 kg / h. Water is added to the top of the column to achieve a 1:1 weight ratio of formaldehyde to water in the distillate (47.5 wt% formaldehyde and 47.5 wt% water). The concentration of isopentenol in the distillate is 5 wt%.

[0121] This method is simulated using CHEMASIM (an open-source version available as OPEN CHEMASIM). TM Obtained; see H. Hasse, B. Bessling, R. OPEN CHEMASIM TM Breaking Paradigms in Process Simulation; Edited by W. Marquardt and C. Pantelides, Computer-Aided Chemical Engineering, Elsevier, Vol. 21, 2006, pp. 255-260. https: / / doi.org / 10.1016 / S1570-7946(06)80055-6) .

[0122] The tower operation was simulated under different pressures, thus varying the bottom temperature. The results are shown in the table below.

[0123]

[0124] *Comparative Example

[0125] 1 FA in the bottoms: The proportion of formaldehyde in the bottoms relative to the formaldehyde in the feed.

[0126] 2 Yield: The proportion of formaldehyde in the distillate, relative to the formaldehyde in the feed.

[0127] Clearly, distillation at pressures above 2 bar can almost completely remove FA and recover isopentenol with high purity.

[0128] Example 2 (Comparative)

[0129] exist Figure 3 In the method shown, a crude isopentenol feed stream (0.98 kg / h) containing isopentenol (66 wt%), water (22 wt%), and formaldehyde (1.7 wt%) is fed to a low-boiling-point separation tower. Additionally, a stream from a wastewater stripping tower (in...) Figure 3 The isopentenol circulating feed stream (0.02 kg / h) containing isopentenol, water and formaldehyde (not shown in the text) is sent to the low-boiling-point separation tower.

[0130] The low-boiling-point separation column operates at a pressure of 1 bar, a bottom temperature of 130°C, and a top temperature of 97°C. A distillate stream (0.28 kg / h) containing water (83 wt%), isopentenol (7 wt%), and low-boiling-point substances (10 wt%) is obtained, along with a bottom stream (0.72 kg / h) containing isopentenol (87 wt%), formaldehyde (2.4 wt%), and high-boiling-point substances (11 wt%). The distillate stream is then fed to a wastewater stripping column for further processing.

[0131] The bottom feed stream is fed into a post-treatment column operating at 0.1 bar, a bottom temperature of 154°C, and a top temperature of 72°C. A bottom feed stream (0.07 kg / h) containing more than 99.5% by weight of high-boiling-point compounds (diols and oligomers) is obtained.

[0132] The gaseous stream taken from the top of the reprocessing tower is condensed in a condenser to obtain a condensate stream (1.60 kg / h). A portion of the condensate (1.0 kg / h) is returned to the reprocessing tower as reflux. The remaining condensate (0.65 kg / h) is taken out as distillate. This distillate contains isopentenol and 2.7% by weight of formaldehyde.

[0133] In the wastewater stripping tower, isopentenol is obtained as a side stream and then recycled to the low-boiling-point separation tower.

[0134] Example 3

[0135] exist Figure 1 In the method shown, a crude isopentenol stream (1.07 kg / h) containing isopentenol (67 wt%), water (19 wt%), and formaldehyde (1.9 wt%) is fed to the first low-boiling-point separation tower. Additionally, the isopentenol recycle stream from the wastewater stripping tower (in...) Figure 1 (Not shown in the text) is sent to the low-boiling-point substance separation tower. This method was simulated using CHEMASIM, as described in Example 1.

[0136] The first low-boiling-point separation column was operated at a pressure of 0.3 bar, a bottom temperature of 103 °C, and a top temperature of 67 °C. A distillate stream (0.24 kg / h) containing water (86 wt%), isopentenol (12 wt%), and low-boiling-point substances (2 wt%) was obtained, along with a bottom stream (0.85 kg / h) containing isopentenol (83 wt%), formaldehyde (2.3 wt%), and high-boiling-point substances (14.4 wt%).

[0137] The first tower bottom material flow is sent to... Figure 2 The second low-boiling-point separation column shown operates at a pressure of 3 bar, a bottom temperature of 173°C, and a top temperature of 130°C. A quenching section is provided above the rectification section. A collection tray is located between the rectification section and the quenching section. Additionally, a washing section is provided above the quenching section, and water (0.02 kg / h) is added at the top of the washing section via a water inlet.

[0138] Aqueous liquid (15 kg / h) is collected at the lower end of the quench section via a collection tray. The aqueous liquid contains formaldehyde (48 wt%), water (approximately 45 wt%), and isopentenol (approximately 7 wt%). A portion of the aqueous liquid is circulated to the top of the quench section via a recirculation line (14.7 kg / h) and partially withdrawn as a second distillate (0.04 kg / h). Another portion of the aqueous liquid is returned to the rectification section as reflux feed (0.23 kg / h) via a reflux line.

[0139] The aqueous liquid circulating to the top of the quenching section passes through a heat exchanger. In the heat exchanger, the aqueous liquid exchanges heat with the feed stream destined for the evaporator of the first low-boiling-point distillation column. The aqueous liquid is cooled from 125°C to 111°C.

[0140] At the top of the second low-boiling-point separation tower, waste gas (<0.01 kg / h) is removed via a gas pipeline. At the bottom of the second low-boiling-point separation tower, the second tower bottom stream (0.83 kg / h) is taken out, which contains isopentenol (85.2 wt%), water (<0.1 wt%), high-boiling-point substances (14.7 wt%), and formaldehyde (<0.1 wt%).

[0141] The second bottom feed stream is fed into a post-treatment column operating at 0.1 bar, a bottom temperature of 154°C, and a top temperature of 72°C. A bottom feed stream (0.07 kg / h) containing high-boiling-point compounds (including less than 0.4% by weight of isopentenol) is obtained.

[0142] At the top of the post-treatment tower, the fluid stream (approximately 1.1 kg / h) is condensed in a condenser. The condensate contains isopentenyl alcohol and less than 0.1% by weight of formaldehyde. A portion of the condensate (approximately 0.4 kg / h) is returned to the post-treatment tower as reflux. The remaining condensate (0.72 kg / h) is taken out as a second distillate. No additional waste gas stream is required for formaldehyde removal, except for the non-condensable components.

[0143] As can be clearly seen from the comparison of Comparative Example 2 and Example 3, the method of the present invention is capable of recovering isopentenol from a feed stream containing isopentenol, water and formaldehyde.

Claims

1. A method for recovering substantially formaldehyde-free isopentenol from a crude isopentenol stream containing isopentenol, water, and formaldehyde, the method comprising distilling the crude isopentenol stream or its isopentenol-containing fraction in a low-boiling-point separation column operating at 2.5 bar or higher to obtain a distillate stream containing aqueous formaldehyde and a bottom stream containing isopentenol.

2. The method according to claim 1, the method comprising reacting formaldehyde with isobutylene to obtain a reaction mixture, and removing unreacted isobutylene from the reaction mixture in an isobutylene distillation column to obtain a crude isopentenyl alcohol stream.

3. The method of claim 2, wherein the second distillate is recycled at least partially to the reaction of formaldehyde with isobutylene.

4. The method according to claim 1, wherein the method comprises: (i) The crude isopentenol feed stream is fed to a first low-boiling-point separation column operating at a pressure of 1.5 bar or lower to obtain a first bottom stream containing isopentenol and formaldehyde and a first distillate stream containing water and low-boiling-point substances. (ii) The first bottom stream is fed to a second low-boiling-point separation column operating at a pressure of 2.5 bar or higher to obtain a second distillate stream containing aqueous formaldehyde and a second bottom stream containing isopentenol. and (iii) The second bottom stream is fed to a post-processing column to obtain pure isopentenol as distillate stream and bottom stream containing high-boiling-point substances.

5. The method according to claim 2, wherein the method comprises: (i) The crude isopentenol feed stream is fed to a first low-boiling-point separation column operating at a pressure of 1.5 bar or lower to obtain a first bottom stream containing isopentenol and formaldehyde and a first distillate stream containing water and low-boiling-point substances. (ii) The first bottom stream is fed to a second low-boiling-point separation column operating at a pressure of 2.5 bar or higher to obtain a second distillate stream containing aqueous formaldehyde and a second bottom stream containing isopentenol. and (iii) The second bottom stream is fed to a post-processing column to obtain pure isopentenol as distillate stream and bottom stream containing high-boiling-point substances.

6. The method according to claim 3, wherein the method comprises: (i) The crude isopentenol feed stream is fed to a first low-boiling-point separation column operating at a pressure of 1.5 bar or lower to obtain a first bottom stream containing isopentenol and formaldehyde and a first distillate stream containing water and low-boiling-point substances. (ii) The first bottom stream is fed to a second low-boiling-point separation column operating at a pressure of 2.5 bar or higher to obtain a second distillate stream containing aqueous formaldehyde and a second bottom stream containing isopentenol. and (iii) The second bottom stream is fed to a post-processing column to obtain pure isopentenol as distillate stream and bottom stream containing high-boiling-point substances.

7. The method of claim 4, wherein a quenching section is provided downstream of the rectification section of the second low-boiling-point separation column along the direction of vapor flow, and an aqueous liquid is collected at the lower end of the quenching section, wherein the aqueous liquid is partially circulated to the quenching section via a circulation line and partially removed as a second distillate.

8. The method of claim 5, wherein a quenching section is provided downstream of the rectification section of the second low-boiling-point separation column along the direction of vapor flow, and aqueous liquid is collected at the lower end of the quenching section, wherein the aqueous liquid is partially circulated to the quenching section via a circulation line and partially extracted as a second distillate.

9. The method of claim 6, wherein a quenching section is provided downstream of the rectification section of the second low-boiling-point separation column along the direction of vapor flow, and an aqueous liquid is collected at the lower end of the quenching section, wherein the aqueous liquid is partially circulated to the quenching section via a circulation line and partially extracted as a second distillate.

10. The method of claim 7, wherein the aqueous liquid is cooled before being circulated into the quenching section.

11. The method of claim 8, wherein the aqueous liquid is cooled before being circulated into the quenching section.

12. The method of claim 9, wherein the aqueous liquid is cooled before being circulated into the quenching section.

13. The method of claim 10, wherein the aqueous liquid is subjected to heat exchange with the crude isopentenol feed stream flowing into the first low-boiling-point separation tower before being circulated into the quenching section.

14. The method of claim 11, wherein the aqueous liquid is subjected to heat exchange with the crude isopentenol feed stream flowing into the first low-boiling-point separation tower before being circulated into the quenching section.

15. The method of claim 12, wherein the aqueous liquid is subjected to heat exchange with the crude isopentenol feed stream flowing into the first low-boiling-point separation tower before being circulated into the quenching section.

16. The method according to any one of claims 7-15, wherein the aqueous liquid is partially returned to the rectification section as a reflux stream.

17. The method of claim 16, wherein the mass flow ratio between the reflux stream and the second distillate is in the range of 2:1 to 10:

1.

18. The method of claim 17, wherein the mass flow ratio between the reflux stream and the second distillate is in the range of 3:1 to 7:

1.

19. The method according to any one of claims 7-15, wherein a washing section is provided downstream of the quenching section along the direction of vapor flow, and water is introduced at the top of the washing section.

20. The method according to any one of claims 4-15, wherein the second distillate contains 25-60% by weight of formaldehyde.

21. The method of claim 20, wherein the second distillate contains 40-50% by weight of formaldehyde.

22. The method according to any one of claims 4-15, wherein the resulting pure isopentenol contains less than 0.5% by weight of formaldehyde.

23. The method of claim 22, wherein the resulting pure isopentenol contains less than 0.1% by weight of formaldehyde.

24. The method according to any one of claims 4-15, wherein the first low-boiling-point separation column is operated at a pressure of 1.2 bar or lower, and / or wherein the second low-boiling-point separation column is operated at a pressure of 2.5 bar or higher.

25. The method of claim 24, wherein the first low-boiling-point separator is operated at a pressure of 0.5 bar or less, and / or wherein the second low-boiling-point separator is operated at a pressure of 2.8 bar or higher.

26. The method according to any one of claims 4-15, the method comprising feeding at least a portion of the first distillate to a wastewater stripping tower to separate low-boiling-point substances from water.

27. An apparatus for recovering substantially formaldehyde-free isopentenol from a crude isopentenol stream containing isopentenol, water, and formaldehyde, the apparatus comprising: - The first low-boiling-point separation tower is suitable for receiving crude isopentenol feed stream and separating the crude isopentenol feed stream by distillation into a first bottom stream containing isopentenol and formaldehyde and a first distillate stream containing water and low-boiling-point substances. - A second low-boiling-point separation column, adapted to receive the first bottom stream from the first low-boiling-point separation column and to separate the first bottom stream by distillation into a second distillate stream containing aqueous formaldehyde and a second bottom stream containing isopentenyl alcohol; and - A post-treatment tower suitable for receiving a second bottom stream from a second low-boiling-point separation tower and separating the second bottom stream by distillation into a pure isopentenyl alcohol as a distillate stream and a bottom stream containing high-boiling-point substances.

28. The apparatus of claim 27, wherein the second low-boiling-point substance separation tower comprises: - A quenching section located above the rectification section of the second low-boiling-point separator, wherein the second low-boiling-point separator is designed to collect the second distillate located at the lower end of the quenching section and to partially recycle the second distillate back to the quenching section via a circulation line; and - The washing section is located above the quenching section, and the water inlet is located at the top of the washing section.

Images