process for recovering isoprenol

Abstract

A process for recovering essentially formaldehyde-free isoprenol from a crude isoprenol stream comprising isoprenol, water and formaldehyde, comprising subjecting the crude isoprenol stream or an isoprenol-containing fraction thereof to distillation in a light-end column operated at a pressure of 2.5 bara or greater to obtain a distillate stream comprising aqueous formaldehyde and a bottoms stream comprising isoprenol. The process of the present invention makes it possible to obtain isoprenol essentially free of formaldehyde. Further provided is a plant for recovering essentially formaldehyde-free isoprenol from a crude isoprenol stream comprising isoprenol, water and formaldehyde, the plant comprising a first light-end column, a second light-end column and a finishing column.

Description

Technical Field

[0001] The present invention relates to a process for recovering isoprenol substantially free of formaldehyde from a stream of crude isoprenol containing isoprenol, water and formaldehyde, and to a plant for recovering isoprenol.

Background Art

[0002] Isoprenol, or 3-methyl-3-buten-1-ol (MBE), is an important intermediate for aromatic compounds such as citral and vitamins, and thousands of tons are produced annually worldwide. Isoprenol is commercially synthesized by reacting formaldehyde with isobutylene (2-methylpropene). This process is described, for example, in German Patent Application Publication No. 10064751 A1. This reaction is typically carried out at high pressure and high temperature in the absence of a solvent, as described in, for example, International Publication No. 2020 / 049111 A1 pamphlet. German Patent No. 1279014 B describes a process for producing alk-3-en-1-ol at high pressure and high temperature carried out in the presence of a base. International Publication No. 2019 / 030386 A1 pamphlet relates to a process for recovering isoprenol from a feed stream containing isoprenol, one or more solvents, water and isobutene via a series of distillation steps.

[0003] The reaction of formaldehyde and isobutylene is an equilibrium reaction and is therefore incomplete. Unreacted formaldehyde is mainly isolated and disposed of via the accumulated wastewater during downstream distillation steps. However, known processes tend to have formaldehyde ubiquitous in the distillation train due to limited separation efficiency of formaldehyde, and a significant amount is found in the isolated isoprenol. Contamination by formaldehyde can have an adverse effect on downstream processes, causing increased consumption rates, quality problems, and operational difficulties in the production plant.

Summary of the Invention

[0004] Therefore, an object of the present invention is to provide a process for recovering formaldehyde-free isoprenol from a stream of crude isoprenol. [Means for solving the problem]

[0005] In a first aspect, the present invention provides a process for recovering formaldehyde-free isoprenol from a crude isoprenol stream containing isoprenol, water, and formaldehyde, the process comprising subjecting the crude isoprenol stream or the isoprenol-containing fraction thereof to distillation in a low-boiling point separation column operated at a pressure of 2.5 bara or higher to obtain a distillation stream containing aqueous formaldehyde and a bottom stream containing isoprenol.

[0006] In one embodiment, the isoprenol-containing fraction of crude isoprenol is crude isoprenol from which a large amount of water and low-boiling substances have been separated in a first low-boiling substance separation column. By doing so, a concentrated aqueous formaldehyde solution suitable for recycling into isoprenol synthesis can be obtained by distillation in a second low-boiling substance separation column. Therefore, in the second embodiment, the process is (i) A step of sending a stream of crude isoprenol to a first low-boiling-point separation column operated at a pressure of 1.5 bara or less to obtain a first bottom stream containing isoprenol and formaldehyde, and a first distillation stream containing water and low-boiling-point substances, (ii) A step of sending the first bottom flow to a second low-boiling point separation column operated at a pressure of 2 bara or more to obtain a second distillation flow containing aqueous formaldehyde and a second bottom flow containing isoprenol, (iii) The process includes sending a second bottom stream to a finishing column to obtain a bottom stream containing pure isoprenol and high-boiling substances as a distillation stream.

[0007] Furthermore, a plant is provided for recovering formaldehyde-free isoprenol from a stream of crude isoprenol containing isoprenol, water, and formaldehyde, and this plant is, - A first low-boiling-point separation column is provided, which receives a stream of crude isoprenol and is adapted to distillate the stream of crude isoprenol into a first bottom stream containing isoprenol and formaldehyde, and a first distillation stream containing water and low-boiling-point substances. - A second low-boiling-point separation column is configured to receive a first bottom flow from a first low-boiling-point separation column and to distillate the first bottom flow into a second distillation flow containing aqueous formaldehyde and a second bottom flow containing isoprenol, - Includes a finishing column that receives a second bottom flow from a second low-boiling-point separation column and is adapted to distillate the second bottom flow into a distillation stream consisting of pure isoprenol and a bottom flow containing high-boiling-point substances.

[0008] Selectively recovering formaldehyde from an aqueous alcohol solution is extremely difficult. This difficulty arises because monomeric formaldehyde (and polymeric formaldehyde) forms both a hydrate with water and a hemiformal with alcohols such as isoprenol. Hydrates and hemiformals, which have different degrees of polymerization, have coexisting boiling points. The stability of the hydrate and hemiformal, and the equilibrium between them, is temperature-dependent. Formal formed in the upper region of the distillation column may decompose at the high temperature at the bottom of the column, further complicating the separation process.

[0009] However, it was found that by distilling at a temperature at which hemiformal cleaves into formaldehyde and isoprenol, formaldehyde can be virtually completely separated from isoprenol, and as a result, formaldehyde can be easily separated from isoprenol.

[0010] In particular, it was found that formaldehyde can be separated substantially completely from isoprenol, and that a concentrated formaldehyde aqueous solution suitable for recycling into isoprenol synthesis can be obtained in a distillation column involving a first distillation at a temperature at which essentially all formaldehyde remains at the bottom of the column, and a second distillation at a temperature at which hemiformal is cleaved into formaldehyde and isoprenol, resulting in formaldehyde being easily separated from isoprenol.

[0011] These observations are shown in the attached ternary plot.

[0012] The following description focuses on a second aspect of the present invention. The operating parameters, embodiments, and preferred embodiments of the "second low-boiling-point separation column," "second distillation stream containing aqueous formaldehyde," and "second bottom stream containing isoprenol" according to the second aspect will be understood to also apply to the "low-boiling-point separation column," "distillation stream containing aqueous formaldehyde," and "bottom stream containing isoprenol" according to the first aspect of the present invention.

[0013] To enable a first distillation at a temperature lower than the isoprenol-formaldehyde dissociation temperature and a second distillation at a temperature higher than the isoprenol-formaldehyde dissociation temperature, the present invention, in a second embodiment, envisions two low-boiling-point separation columns operating at different pressures. Thus, a first distillate containing water and a low-boiling-point substance essentially free of formaldehyde is obtained at a relatively low pressure spreading through the first low-boiling-point separation column. At a relatively high pressure spreading through the second low-boiling-point separation column, substantially all of the formaldehyde is separated from the isoprenol. Thus, the process of the present invention makes it possible to obtain isoprenol essentially free of formaldehyde.

[0014] The term "essentially formaldehyde-free" is understood to mean that the resulting pure isoprenol does not contain a significant amount of formaldehyde. Therefore, the resulting pure isoprenol preferably contains less than 0.5% by weight, more preferably less than 0.1% by weight, of formaldehyde.

[0015] The crude isoprenol stream contains isoprenol, water, and formaldehyde. Preferably, the crude isoprenol stream contains 50-75% by weight, more preferably 60-65% by weight of isoprenol. Preferably, the crude isoprenol stream contains 15-40% by weight, more preferably 22-35% by weight of water. Preferably, the crude isoprenol stream contains 1-5% by weight, more preferably 2-3% by weight of formaldehyde.

[0016] Preferably, the crude isoprenol stream is a liquid stream. The liquid stream may be a single-phase or two-phase liquid stream.

[0017] Crude isoprenol stream is generally the product stream of an isoprenol production process from which unreacted isobutylene has been removed. In one embodiment, this process includes the steps of 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 isoprenol stream.

[0018] Formaldehyde is preferably reacted with isobutylene under supercritical conditions. Such conditions exist when a substance or mixture of substances is exposed to temperatures and pressures exceeding the thermodynamic critical point of that substance or mixture. Under supercritical conditions, the reactivity of isobutylene to formaldehyde has been found to be sufficiently high, enabling highly selective and efficient conversion.

[0019] To achieve supercritical conditions, formaldehyde and isobutylene are preferably reacted at a temperature in the range of at least 220°C, for example 220 - 290°C, and an absolute pressure of at least 200 bar. Unless otherwise specified, all pressures cited in this specification are absolute pressures. Further details regarding the reaction of formaldehyde and isobutylene under supercritical conditions can be found in WO 2020 / 049111 A1 pamphlet.

[0020] In a further embodiment, formaldehyde is reacted with isobutylene in the presence of a solvent and a heterogeneous catalyst.

[0021] The process according to the invention has the advantage that the second distillate is suitable for recycling to the reaction of formaldehyde.

[0022] Unreacted isobutylene is removed from the reaction mixture in an isobutylene distillation column to obtain a stream of crude isoprenol.

[0023] Isobutylene is obtained as an isobutylene distillation stream. The isobutylene distillation stream preferably contains at least 70% by weight, more preferably at least 85% by weight of isobutylene. The isobutylene distillation stream is preferably recycled to the reaction of formaldehyde and isobutylene.

[0024] Crude isoprenol is obtained as the bottom stream from the isobutylene distillation column.

[0025] To minimize the compression load on the recycled isobutylene, the isobutylene distillation column is suitably operated at a pressure of 4 - 15 bara, preferably 7 - 13 bara. All pressures of the columns and pipes described herein are understood to relate to the absolute pressure at the top of the column or pipe, unless otherwise stated. The isobutylene distillation column can have 5 - 40 theoretical stages, more preferably 15 - 25 theoretical stages.

[0026] The bottom temperature of the isobutylene distillation column is generally in the range of 140 to 200°C, more preferably 160 to 180°C. The top temperature of the isobutylene distillation column is preferably in the range of 50 to 90°C, and more preferably in the range of 60 to 80°C.

[0027] In a particularly preferred embodiment, the isobutylene distillation column is operated at a pressure in the range of 7 to 13 bara, a bottom temperature in the range of 160 to 180°C, and an upper temperature in the range of 60 to 80°C.

[0028] Under the conditions described above, the crude isoprenol stream obtained in the isobutylene distillation column is in a superheated state. The crude isoprenol stream is preferably sent to a vacuum chamber before being sent to a first low-boiling-point separation chamber. In the vacuum chamber, the crude isoprenol stream is preferably reduced to the pressure of the first low-boiling-point separation column. In the vacuum chamber, a vapor phase and a liquid phase are obtained, which are preferably sent to the first low-boiling-point separation column via separate lines.

[0029] According to a second aspect of the present invention, crude isoprenol is sent to a first low-boiling-point separation column operated at a pressure of 1.5 bara or less. Any high-pressure crude isoprenol stream is preferably released before being sent to the first low-boiling-point separation column. The crude isoprenol stream is preferably supplied to the first low-boiling-point separation column as a side stream, defining a rectification section above the supply position and a removal section below the supply position.

[0030] The first low-boiling-point separation column yields a first bottom stream containing isoprenol and formaldehyde, and a first distillation stream containing water and low-boiling-point substances. The term "low-boiling-point substances" is understood to refer to organic compounds (other than formaldehyde) that have a boiling point lower than the boiling point of isoprenol at atmospheric pressure, and therefore below approximately 130°C. The most common low-boiling-point substances are methanol and / or isoprenyl formate, which are formed as by-products during the process.

[0031] In a preferred embodiment, the first low-boiling-point separation column is operated at a pressure of 1.2 bara or less, preferably 0.5 bara or less. The bottom temperature of the first low-boiling-point separation column is preferably in the range of 80 to 135°C, more preferably 90 to 115°C, and most preferably 95 to 105°C. The top temperature of the first low-boiling-point separation column is preferably in the range of 45 to 105°C, and more preferably in the range of 55 to 80°C.

[0032] In a particularly preferred embodiment, the first low-boiling point separation column is operated at a pressure in the range of 0.2 to 0.5 bara, a bottom temperature in the range of 90 to 115°C, and an upper temperature in the range of 55 to 80°C.

[0033] The first low-boiling-point separation column preferably has a theoretical number of 15 to 65, more preferably 25 to 40. In particular, the removal section of the first low-boiling-point separation column preferably has a theoretical number of 10 to 25. The rectification section of the first low-boiling-point separation column preferably has a theoretical number of 5 to 40.

[0034] The first bottom flow preferably contains 75-95% by weight, more preferably 80-90% by weight of isoprenol.

[0035] The first distillate is typically taken out in gaseous form at the top of the first low-boiling-point separation column and condensed to obtain a liquid two-phase flow. The liquid two-phase flow is preferably separated in a separation vessel to obtain an aqueous phase and an organic phase. The aqueous phase is preferably passed through a wastewater removal pipe, as described later. The organic phase is preferably partially returned as reflux to the top of the first low-boiling-point separation column. Another 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.

[0036] In a preferred embodiment, at least a portion of the first distillation stream is sent to a wastewater removal pipe to separate the low-boiling substances and the isoprenol carried along with them from the water. Preferably, the portion of the first distillation stream sent to the wastewater removal pipe is the aqueous phase obtained by condensation and phase separation of the first distillation stream, as discussed above.

[0037] In the wastewater removal pipe, low-boiling-point materials are obtained as a low-boiling-point distillation stream, and wastewater is obtained as a bottom stream. Both the low-boiling-point distillation stream and the wastewater bottom stream are removed from the process, and each stream can be sent for further treatment.

[0038] Furthermore, isoprenol is preferably obtained as a side flow in the wastewater removal pipe. The isoprenol side flow is typically a two-phase flow and preferably contains 15-40% by weight, more preferably 25-35% by weight of isoprenol. The isoprenol side flow is preferably recycled to a first low-boiling point separation column.

[0039] The low-boiling-point distillation stream preferably contains 75-95% by weight, more preferably 80-85% by weight, of the low-boiling-point substance.

[0040] The wastewater bottom flow preferably contains less than 1.2% by weight, more preferably less than 0.6% by weight, of organic matter. The wastewater bottom flow typically contains formaldehyde at a concentration of 0.05 to 1.5% by weight, for example, 0.3 to 0.9% by weight.

[0041] The wastewater removal pipe is preferably operated at a pressure of 1.5 bara or less, more preferably 1.1 bara or less. The bottom temperature of the wastewater removal pipe is preferably in the range of 95 to 110°C, more preferably in the range of 97 to 103°C. The top temperature of the wastewater removal pipe is preferably in the range of 65 to 100°C, more preferably in the range of 75 to 85°C.

[0042] In a particularly preferred embodiment, the wastewater removal pipe operates at a pressure in the range of 0.95 to 1.1 bara, a bottom temperature in the range of 97 to 103°C, and an upper temperature in the range of 75 to 85°C.

[0043] The wastewater removal pipe preferably has 6 to 30 theoretical stages, more preferably 10 to 20 theoretical stages.

[0044] According to a second embodiment, the first bottom flow obtained in the first low-boiling-point separation column is sent to a second low-boiling-point separation column operated at a pressure of 2 bar or more, preferably 2.5 bar or more. The first bottom flow is preferably supplied to the second low-boiling-point separation column as a side flow, defining a rectification section above the supply position and a removal section below the supply position.

[0045] In the second low-boiling-point separation column, a second distillation stream containing, or essentially derived from, aqueous formaldehyde, and a second bottom stream containing isoprenol are obtained. The second bottom stream further contains high-boiling-point substances. The term “high-boiling-point substances” is understood to refer to organic compounds having a boiling point higher than the boiling point of isoprenol at atmospheric pressure, i.e., higher than approximately 130°C. The most common high-boiling-point substances are diols and / or oligomers formed as by-products during the process.

[0046] In a preferred embodiment, the second low-boiling-point separation column is operated at a pressure of 2.5 bara or higher, preferably 2.8 bara or higher, and most preferably 2.9 bara or higher. The bottom temperature of the second low-boiling-point separation column is preferably in the range of 160 to 200°C, more preferably 170 to 185°C, and most preferably 175 to 180°C. The top temperature of the second low-boiling-point separation column is preferably in the range of 115 to 160°C, and more preferably in the range of 125 to 145°C.

[0047] In a particularly preferred embodiment, the second low-boiling point separation column is operated at a pressure in the range of 2.9 to 3.5 bara, a bottom temperature in the range of 175 to 180°C, and an upper temperature in the range of 130 to 140°C.

[0048] The second low-boiling-point separation column preferably has a theoretical number of 20 to 60, more preferably 35 to 60. In particular, the removal section of the first low-boiling-point separation column preferably has a theoretical number of 25 to 45. The rectification section of the first low-boiling-point separation column preferably has a theoretical number of 7 to 20.

[0049] At the top of the second low-boiling point separation column, an off-gas is typically obtained. The off-gas is mainly nitrogen-based and may contain trace amounts of isoprenol, formic acid, water, formaldehyde, and / or decomposition gases.

[0050] The second bottom flow preferably contains 82-96% by weight, more preferably 87-91% by weight, of isoprenol. The relatively high pressure of the second low-boiling point separation column allows for a high degree of separation of formaldehyde and isoprenol. Therefore, the second bottom flow preferably contains at most 0.5% by weight, more preferably at most 0.1% by weight, of formaldehyde.

[0051] The second distillation stream is an aqueous stream, preferably containing 25-60% by weight, more preferably 40-50% by weight, and particularly 45-50% by weight of formaldehyde. The second distillation stream preferably contains at most 15% by weight, more preferably at most 5% by weight of isoprenol.

[0052] Because the vapor condensation curve appearing at the top of the second low-boiling-point separation column is broad, it is advantageous to use a condenser that recycles the liquid. Direct condensation with rapid cooling accompanied by liquid circulation is particularly advantageous. Therefore, in a preferred embodiment of this process, a rapid cooling section is provided downstream of the rectification section of the second low-boiling-point separation column in the direction of vapor flow. The term "direction of vapor flow" refers to the direction of flow of the gaseous components within the separation column, i.e., upward toward the top of the column. The rapid cooling section is preferably provided within the second low-boiling-point separation column above the rectification section.

[0053] Furthermore, direct condensation by rapid cooling reduces fouling caused by various condensation and polymerization mechanisms of formaldehyde that may occur in areas with localized high formaldehyde concentrations. To avoid the risk of fouling in the second low-boiling-point separation column and downstream processes, particularly in the off-gas of the second low-boiling-point separation column, the formaldehyde concentration in the second distillate is preferably 60% by weight or less, more preferably 55% by weight or less, and especially 50% by weight or less.

[0054] At the lower end of the quenching section, the aqueous liquid is collected. If the quenching section is located within a second low-boiling point separation column, the aqueous liquid can be collected, for example, in collection trays above the rectification section and below the quenching section.

[0055] The aqueous liquid is partially circulated through a circulation line to the quenching section and partially withdrawn as a second distillate. Ideally, a portion of the aqueous liquid circulated to the quenching section is circulated to the upper part of the quenching section. Circulation of the aqueous liquid is typically achieved by the use of a pump. As mentioned above, the second distillate can optionally be at least partially recycled for the reaction of formaldehyde with isobutylene.

[0056] By circulating a portion of the aqueous liquid into the rapid cooling section, it becomes possible to cool the vapor rising through the rapid cooling section and to absorb formaldehyde from the vapor into the aqueous liquid. Therefore, formaldehyde is rapidly cooled from the vapor rising through the rapid cooling section.

[0057] Furthermore, the aqueous liquid is partially returned to the rectification section of the second low-boiling point separation column as reflux. This can be achieved by a reflux line, or the aqueous liquid can be partially returned to the rectification section as an overflow from a collection tray below the quenching section.

[0058] The mass flow rate ratio of reflux to the second distillate is preferably in the range of 2:1 to 10:1, more preferably in the range of 3:1 to 7:1.

[0059] In a preferred embodiment, the aqueous liquid is cooled before being circulated to the quenching section. Preferably, a portion of the aqueous liquid extracted as a second distillate is a partial stream of cooled aqueous liquid.

[0060] The temperature of the aqueous liquid collected at the lower end of the quenching section is preferably in the range of 80 to 140°C, more preferably 125 to 135°C. The temperature of the cooled aqueous liquid circulated through the quenching section is preferably 10 to 80°C lower than the temperature of the aqueous liquid collected at the lower end of the quenching section. This enables an energetically advantageous process.

[0061] The hot aqueous liquid removed at the lower end of the quenching section is useful for thermal integration. In a suitable embodiment, it is heat-exchanged with the flow of crude isoprenol flowing into the first low-boiling point separation column before being circulated back into the quenching section.

[0062] In one embodiment, a scrubbing section is provided downstream of the rapid cooling section in the direction of vapor flow, and water is introduced to the top of the scrubbing section. Preferably, the scrubbing section is provided in a second low-boiling point separation column above the rapid cooling section. The scrubbing section makes it possible to maintain the formaldehyde concentration in the second distillate below the critical concentration mentioned above, and thus avoid the accumulation of paraformaldehyde, for example, in an off-gas line.

[0063] The mass flow rate ratio between the water introduced at the top of the scrub section and the first bottom flow obtained in the first low-boiling point separation column is typically in the range of 0.01:1 to 0.06:1, and more preferably in the range of 0.015:1 to 0.03:1.

[0064] According to the second embodiment, the second bottom flow is sent to a finishing column, where pure isoprenol is obtained as a distillation stream. High-boiling substances are removed via the bottom flow. Since the second bottom flow is essentially formaldehyde-free, the separation operation in the finishing column is not significantly more complex than when the efficiency of formaldehyde separation in the low-boiling substance separation section is low.

[0065] The pure isoprenol distillation stream preferably contains at least 97.0% by weight, more preferably 98.0% by weight, for example, 98.1 to 99.5% by weight of isoprenol. Preferably, the pure isoprenol distillation stream contains less than 0.5% by weight, for example, less than 0.1% by weight or less than 0.01% by weight of formaldehyde.

[0066] The high-boiling-point material bottom stream preferably contains 90 to 99.9% by weight of high-boiling-point material, more preferably 99 to 99.8% by weight. Preferably, the high-boiling-point material bottom stream contains less than 0.2% by weight of formaldehyde, for example, less than 0.05% by weight of formaldehyde.

[0067] In a preferred embodiment, the finishing column is operated at a pressure of 0.5 bara or less, preferably 0.25 bara or less. The bottom temperature of the first low-boiling point separation column is preferably in the range of 130 to 190°C, and more preferably in the range of 150 to 170°C. The top temperature of the finishing column is preferably in the range of 60 to 90°C, and more preferably in the range of 65 to 85°C.

[0068] In a particularly preferred embodiment, the finishing tower is operated at a pressure in the range of 0.05 to 0.2 bara, a bottom temperature in the range of 150 to 170°C, and an upper temperature in the range of 65 to 85°C.

[0069] The finishing tower preferably has 6 to 40 theoretical stages, more preferably 10 to 20 theoretical stages.

[0070] The columns and tubes used in the process and plant of the present invention may be conventional distillation tubes. Suitable types of distillation tubes include plate columns (i.e., tray columns), packed tubes, such as tubes with random or structured packing, and mixed tubes containing both packing material and trays.

[0071] A suitable plate tube may include an internal structure through which the liquid phase flows. Suitable internal structures include sieve trays, bubble cap trays, valve trays, tunnel trays, and Thormann® trays, in particular bubble cap trays, valve trays, tunnel trays, and Thormann® trays.

[0072] Randomly filled tubes can be filled with various molded bodies. Heat and mass transfer is improved by increasing the surface area with molded bodies, which typically have a size in the range of 25-80 mm. Suitable molded bodies include Raschig rings (hollow cylinders), Lessing rings, Pall rings, Hiflow rings, and Intalox saddles. The filling material can be supplied into the tube in a regular or irregular manner (as bulk material, i.e., loosely filled). Suitable materials include glass, ceramics, metals, and plastics.

[0073] Structured fillers are an evolution of regular fillers, possessing a regular molded structure. This reduces pressure loss in the gas flow. Suitable types of structured fillers include fabric fillers and metal sheet fillers.

[0074] The term "upper part" or "head" of a tube refers to the area above the top tray or the top layer of packing material that does not contain internal material. This is generally formed by the dome-shaped base (head, e.g., Kloepper head or Korbbogen head) that forms the terminal element of the distillation tube.

[0075] The term "bottom" or "sump" of a pipe refers to the area below the bottom tray or below the bottom layer of packing material that does not contain internal material.

[0076] The process of the present invention can be carried out continuously or in batches. Preferably, the process of the present invention is carried out continuously.

[0077] The present invention further relates to a plant for recovering formaldehyde-free isoprenol from a stream of crude isoprenol containing isoprenol, water, and formaldehyde, wherein the plant - A first low-boiling-point separation column is provided, which receives a stream of crude isoprenol and is adapted to distillate the stream of crude isoprenol into a first bottom stream containing isoprenol and formaldehyde, and a first distillation stream containing water and low-boiling-point substances. - A second low-boiling-point separation column is configured to receive a first bottom flow from a first low-boiling-point separation column and to distillate the first bottom flow into a second distillation flow containing aqueous formaldehyde and a second bottom flow containing isoprenol, - Includes a finishing column that receives a second bottom flow from a second low-boiling-point separation column and is adapted to distillate the second bottom flow into a distillation stream consisting of pure isoprenol and a bottom flow containing high-boiling-point substances.

[0078] The embodiments of the process of the present invention described above are understood to also relate to the plant of the present invention, where applicable.

[0079] In a preferred embodiment, the second low-boiling point separation column of the plant is - A quenching section above the rectification section of a second low-boiling point separation column, the second low-boiling point separation column is designed to collect a second distillate at the lower end of the quenching section and to partially circulate the second distillate back into the quenching section through a circulation line, - Includes a scrubbing section above the rapid cooling section and a water inlet above the scrubbing section.

[0080] In a preferred embodiment, the plant's second low-boiling-point separation column includes an indirect heat exchanger designed to exchange heat between the aqueous liquid and a coolant flow before the aqueous liquid is circulated to the quenching section. A suitable coolant flow specific to the process is, for example, a flow of crude isoprenol sent to the first low-boiling-point separation column.

[0081] Alternatively, the bottom liquid of the first low-boiling-point separation column can be circulated through an indirect heat exchanger. This reduces the heating load on the evaporator of the first low-boiling-point separation column.

[0082] In a preferred embodiment, the plant includes an isobutylene distillation column adapted to receive a fluid reaction mixture and to guide a liquid stream of crude isoprenol to a first low-boiling point separation column.

[0083] In a preferred embodiment, the plant includes a reactor adapted for a high-pressure reaction of formaldehyde and isobutylene to obtain a fluid reaction mixture, and the fluid reaction mixture is adapted to be led to an isobutylene distillation column.

[0084] In a preferred embodiment, the plant includes a wastewater removal tower adapted to receive a first distillation stream from a first low-boiling-point separation tube. [Brief explanation of the drawing]

[0085] [Figure 1] The process for recovering isoprenol from a stream of crude isoprenol according to the present invention in a plant according to the present invention is schematically shown. [Figure 2] A preferred embodiment of a second low-boiling-point separation column used in the process according to the present invention and present in the plant according to the present invention is schematically shown. [Figure 3] A known process for recovering isoprenol from a stream of crude isoprenol is schematically shown. [Figure 4a] The ternary plots of isoprenol, formaldehyde, and water mixtures at different pressures are shown. [Figure 4b] The ternary plots of isoprenol, formaldehyde, and water mixtures at different pressures are shown. [Figure 4c] The ternary plots of isoprenol, formaldehyde, and water mixtures at different pressures are shown. [Figure 5] This shows the relative volatility of a mixture of isoprenol and formaldehyde at different temperatures. [Modes for carrying out the invention]

[0086] As shown in Figure 1, a crude isoprenol stream (101) containing isoprenol, water, and formaldehyde is sent to a first low-boiling point separation column (102) operated at a pressure of 1.5 bara or less. A first bottom stream (103) containing isoprenol and formaldehyde, and a first distillation stream (104) containing water and low-boiling point substances are obtained.

[0087] The first bottom flow (103) is sent to a second low-boiling point separation column (105) operated at a pressure of 2 bara or more. A second distillation flow (106) containing aqueous formaldehyde and a second bottom flow (107) containing isoprenol are obtained.

[0088] The second bottom stream (107) is sent to the finishing column (108). Pure isoprenol is obtained as a distillation stream (109). Furthermore, a bottom stream (110) containing high-boiling-point substances is obtained.

[0089] According to Figure 2, the first bottom flow is sent via line (201) to a second low-boiling point separation column (202) operated at a pressure of 2 bar or more. The supply position of the flow (201) is indicated by a dashed line, with the rectification section (203) defined above the supply position and the removal section (204) below the supply position.

[0090] The quenching section (205) is located downstream of the rectification section of the second low-boiling-point separation column (202), specifically within the second low-boiling-point separation column above the rectification section, in the direction of vapor flow. An attachment (206), such as a plate, is positioned between the rectification section (203) and the quenching section (205).

[0091] The aqueous liquid is collected at the lower end of the quenching section (205) via line (207). The aqueous liquid is partially circulated to the upper part of the quenching section (205) via circulation line (208) and partially withdrawn as a second distillate via line (209). Another portion of the aqueous liquid is returned to the rectification section as reflux via reflux line (210).

[0092] A portion of the aqueous liquid circulated above the rapid cooling section (205) passes through a heat exchanger (211), which is preferably adapted to exchange heat with the flow of crude isoprenol into a first low-boiling point separation column (not shown in Figure 2).

[0093] Furthermore, a scrub section (212) is provided downstream of the rapid cooling section (205) in the direction of steam flow, and water is introduced into the upper part of the scrub section through a water inlet (213).

[0094] At the top of the second low-boiling-point separation column (202), the off-gas is removed via the gas line (214). At the bottom of the second low-boiling-point separation column (202), the second bottom flow is extracted via the line (215).

[0095] As shown in Figure 3, a crude isoprenol stream (301) containing isoprenol, water, and formaldehyde is sent to a low-boiling-point separation column (302) operated at a pressure of 1.5 bara or less. A distillation stream (304) containing water and low-boiling-point substances, and a bottom stream (303) containing isoprenol and formaldehyde are obtained.

[0096] The bottom flow (304) is sent to the finishing column (305). Isoprenol is obtained as a distillation stream (306). Further, a bottom flow (307) containing high-boiling substances is obtained.

[0097] Figures 4a-4c show ternary plots of isoprenol, formaldehyde, and water mixtures at 0.1 bar (Figure 4a), 1 bar (Figure 4b), and 3 bar (Figure 4c). Along the three sides, the ternary plots show the molar ratios of isoprenol, formaldehyde, and water. For example, along the right-hand side, the molar ratio of formaldehyde to isoprenol (x FA ) is shown.

[0098] The curves are residue curves. Each residue curve represents a different feed composition with varying amounts of isoprenol, formaldehyde, and water. The plot of residue curves follows the composition of the liquid residue in the distillation tube, i.e., from the bottom (high temperature) to the top (low temperature) of the distillation tube. In the ternary plot shown, i.e., following the residue curve up to a higher temperature shows the composition at the bottom of the distillation tube. Following the residue curve down to a lower temperature shows the composition at the top of the distillation tube.

[0099] In the ternary plot in Figure 4a (pressure 0.1 bar), a water-isoprenol heteroazeotropic mixture (HA) with a boiling point of 43.7°C is generated. A high-boiling point azeotropic mixture (SSA) containing isoprenol and all formaldehydes with a boiling point of 77.1°C is also generated.

[0100] In the ternary plot in Figure 4b (pressure 1 bar), the water-isoprenol heteroazeotropic mixture (HA) has a boiling point of 96.0°C. Furthermore, a low-boiling point azeotropic mixture of water-formaldehyde (LSA) is formed (98.3°C). The high-boiling point azeotropic mixture of isoprenol and formaldehyde (SSA), as observed in the ternary plot in Figure 4a (0.1 bar), is not formed. Rather, isoprenol (130.3°C) represents the high-boiling fraction.

[0101] In the ternary plot (at a pressure of 3 bar) in Figure 4c, the water-isoprenol heteroazeotropic mixture (HA) has a boiling point of 129.2°C. The boiling point of the water-formaldehyde low-boiling point azeotropic mixture (LSA) shifts to 128.0°C, indicating a higher formaldehyde concentration. At the bottom of the distillation tube, it can be seen that isoprenol is essentially formaldehyde-free (169.1°C).

[0102] Figure 5 shows the relative volatility of formaldehyde in a mixture of isoprenol and formaldehyde, as fitted from experimental data. The term TIFF0007902191000001.tif9161 indicates the mole fraction of formaldehyde in the gas phase. FAThe term indicates the mole fraction of formaldehyde (including formaldehyde bound as hemiformal) in the liquid phase. FA against As shown by the ratio in TIFF0007902191000002.tif9161, it is clear that the relative volatility of formaldehyde increases with increasing temperature.

[0103] In particular, at 120°C (393K), the relative volatility is found to be slightly above 0.95–1.2. As the temperature decreases, the relative volatility decreases; please refer to the curves at 293K, 313K, and 333K. The higher the relative volatility of formaldehyde, the greater the degree of separation of formaldehyde as a low-boiling fraction from isoprenol. [Examples]

[0104] Example 1 This embodiment relates to a simulation of the removal of distilled formaldehyde from a liquid containing 98 wt% isoprenol and 2 wt% formaldehyde (FA) in a low-boiling-point separation column having 27 theoretical plates in the removal section and 13 theoretical plates in the rectification section. The liquid was supplied to the low-boiling-point separation column at 100 kg / hour. A distillate containing an aqueous formaldehyde solution was obtained at the top of the low-boiling-point separation column, and 35 kg / hour of this distillate was returned to the top of the low-boiling-point separation column as reflux. Water was added to the top of the low-boiling-point separation column so that the weight ratio of formaldehyde to water in the distillate was 1:1 (47.5 wt% formaldehyde and 47.5 wt% water). The isoprenol concentration in the distillate was 5 wt%.

[0105] This process was simulated via CHEMASIM (its open-source version is OPEN CHEMASIM). (商標) Available as: H. Hasse, B. Bessling, R. Boettcher, OPEN CHEMASIM (商標)Reference: Breaking Paradigms in Process Simulation; Editor(s): W. Marquardt, C. Pantelides, Computer Aided Chemical Engineering, Elsevier, Volume 21, 2006, Pages 255-260, https: / / doi.org / 10.1016 / S1570-7946(06)80055-6).

[0106] The tower's operation was simulated by varying the pressure, and the bottom temperature was changed accordingly. The results are shown in the following table.

[0107] [Table 1]

[0108] It is clear that distillation at pressures exceeding 2 bara enables virtually complete removal of FA and recovery of isoprenol in high purity.

[0109] Example 2 (Comparison) In the process shown in Figure 3, a stream of crude isoprenol (0.98 kg / hour) containing isoprenol (66 wt%), water (22 wt%), and formaldehyde (1.7 wt%) was sent to a low-boiling-point material separation tower. Furthermore, an isoprenol recycling stream (0.02 kg / hour) containing isoprenol, water, and formaldehyde from a wastewater removal pipe (not shown in Figure 3) was also sent to the low-boiling-point material separation tower.

[0110] The low-boiling-point separation column was operated at a pressure of 1 bara, a bottom temperature of 130°C, and an upper temperature of 97°C. A distillation stream (0.28 kg / hour) containing water (83 wt%), isoprenol (7 wt%), and low-boiling-point substances (10 wt%) was obtained, as well as a bottom stream (0.72 kg / hour) containing isoprenol (87 wt%), formaldehyde (2.4 wt%), and high-boiling-point substances (11 wt%). The distillation streams were sent to a wastewater removal pipe for further treatment.

[0111] The bottom flow was sent to a finishing tower operated at 0.1 bara, a bottom temperature of 154°C, and an upper temperature of 72°C. A bottom flow (0.07 kg / hour) containing over 99.5 wt% high-boiling-point substances (diols and oligomers) was obtained.

[0112] The gas stream taken from the top of the finishing column was condensed in a condenser to obtain a condensate stream (1.60 kg / hour). A portion of the condensate (1.0 kg / hour) was refluxed back into the finishing column. The remaining condensate (0.65 kg / hour) was taken as a distillate. The distillate contained isoprenol and 2.7% by weight of formaldehyde.

[0113] In the wastewater removal pipe, an isoprenol recycled flow was obtained as a side flow and recycled to the low-boiling point material separation tower.

[0114] Example 3 In the process shown in Figure 1, a stream of crude isoprenol (1.07 kg / hour) containing isoprenol (67 wt%), water (19 wt%), and formaldehyde (1.9 wt%) was sent to a first low-boiling-point separation tower. Furthermore, an isoprenol recycling stream from a wastewater removal tower (not shown in Figure 1) was sent to a low-boiling-point separation tube. As described in Example 1, the process was simulated via CHEMASIM.

[0115] The first low-boiling-point separation column was operated at a pressure of 0.3 bara, a bottom temperature of 103°C, and an upper temperature of 67°C. A distillation stream (0.24 kg / hour) containing water (86 wt%), isoprenol (12 wt%), and low-boiling-point substances (2 wt%) was obtained, as well as a bottom stream (0.85 kg / hour) containing isoprenol (83 wt%), formaldehyde (2.3 wt%), and high-boiling-point substances (14.4 wt%).

[0116] The first bottom flow was sent to the second low-boiling point separation column shown in Figure 2, which was operated at a pressure of 3 bara, a bottom temperature of 173°C, and an upper temperature of 130°C. A quenching section was provided above the rectification section. A recovery tray was placed between the rectification section and the quenching section. Furthermore, a scrubbing section was provided above the quenching section, and water (0.02 kg / hour) was introduced to the top of the scrubbing section through a water inlet.

[0117] The aqueous liquid (15 kg / hour) was collected at the bottom of the quenching section via a collection tray. The aqueous liquid contained formaldehyde (48 wt%), water (approximately 45 wt%), and isoprenol (approximately 7 wt%). The aqueous liquid was partially circulated to the upper part of the quenching section through a circulation line (14.7 kg / hour) and partially extracted as a second distillate (0.04 kg / hour). Another portion of the aqueous liquid was returned to the rectification section as a reflux flow (0.23 kg / hour) via a reflux line.

[0118] The aqueous liquid circulated to the upper part of the rapid cooling section passed through a heat exchanger. In the heat exchanger, the aqueous liquid exchanged heat with the feed flow to the evaporator of the first low-boiling point distillation column. The aqueous liquid was cooled from 125°C to 111°C.

[0119] At the top of the second low-boiling-point separation column, off-gas (<0.01 kg / hour) was removed via a gas line. At the bottom of the second low-boiling-point separation column, a second bottom flow (0.83 kg / hour) containing isoprenol (85.2 wt%), water (<0.1 wt%), high-boiling-point substances (14.7 wt%), and formaldehyde (<0.1 wt%) was extracted.

[0120] The second bottom flow was sent to a finishing tower operated at 0.1 bara, a bottom temperature of 154°C, and an upper temperature of 72°C. A bottom flow (0.07 kg / hour) containing high-boiling-point material (including less than 0.4 wt% isoprenol) was obtained.

[0121] At the top of the finishing column, the fluid flow (approximately 1.1 kg / hour) condensed in the condenser. The condensate contained isoprenol and less than 0.1% by weight of formaldehyde. A portion of the condensate (approximately 0.4 kg / hour) was refluxed back into the finishing column. The remainder of the condensate (0.72 kg / hour) was taken as a second distillate. Except for the non-condensable components, no further off-gas flow was required to purge the formaldehyde.

[0122] A comparison of Comparative Example 2 and Example 3 clearly shows that the process of the present invention allows for the recovery of isoprenol from a stream containing isoprenol, water, and formaldehyde. Several embodiments are shown below. Item 1 A method for recovering formaldehyde-free isoprenol from a stream of crude isoprenol containing isoprenol, water, and formaldehyde, comprising the step of subjecting the stream of crude isoprenol or the isoprenol-containing fraction thereof to distillation in a low-boiling point separation column operated at a pressure of 2.5 bara or more to obtain a distillation stream containing aqueous formaldehyde and a bottom stream containing isoprenol. Section 2 The method according to claim 1, comprising the steps of 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 stream of crude isoprenol. Section 3 The method according to claim 2, wherein the second distillate is at least partially recycled into the aforementioned reaction of formaldehyde and isobutylene. Section 4 (i) The process of sending the stream of crude isoprenol to a first low-boiling-point separation column operated at a pressure of 1.5 bara or less to obtain a first bottom stream containing isoprenol and formaldehyde, and a first distillation stream containing water and low-boiling-point substances, (ii) A step of sending the first bottom flow to a second low-boiling point separation column operated at a pressure of 2.5 bara or more to obtain a second distillation flow containing aqueous formaldehyde and a second bottom flow containing isoprenol, (iii) A step of sending the second bottom stream to a finishing column to obtain a bottom stream containing pure isoprenol and high-boiling point substances as a distillation stream. The method described in any one of items 1 to 3, including the method described in item 1 to 3. Section 5 The method according to claim 4, wherein the quenching section is provided in the vapor flow direction downstream of the rectification section of the second low-boiling point separation column, the aqueous liquid is collected at the lower end of the quenching section, the aqueous liquid is partially circulated to the quenching section through a circulation line and partially withdrawn as the second distillate. Section 6 The method according to item 5, wherein the aqueous liquid is cooled before being circulated to the quenching section. Section 7 The method according to claim 6, wherein the aqueous liquid is heat-exchanged with the flow of crude isoprenol flowing into the first low-boiling point separation column before being circulated to the quenching section. Section 8 The method according to any one of claims 5 to 7, wherein the aqueous liquid is partially returned to the rectification section as reflux. Section 9 The method according to item 8, wherein the mass flow rate ratio of the reflux flow to the second distillate is in the range of 2:1 to 10:1, preferably 3:1 to 7:1. Item 10 The method according to any one of claims 5 to 9, wherein the scrub section is provided downstream of the rapid cooling section in the direction of steam flow, and water is introduced at the top of the scrub section. Section 11 The method according to any one of claims 4 to 10, wherein the second distillate contains 25 to 60% by weight, preferably 40 to 50% by weight, of formaldehyde. Item 12 The method according to any one of claims 4 to 11, wherein the obtained pure isoprenol contains less than 0.5% by weight, preferably less than 0.1% by weight, of formaldehyde. Item 13 The method according to any one of claims 4 to 12, wherein the first low-boiling-point separation column is operated at a pressure of 1.2 bara or less, preferably 0.5 bara or less, and / or the second low-boiling-point separation column is operated at a pressure of 2.5 bara or more, preferably 2.8 bara or more. Item 14 The method according to any one of claims 4 to 13, further comprising the step of sending at least a portion of the first distillation stream to a wastewater removal pipe to separate low-boiling-point substances from the water. Item 15 A plant for recovering formaldehyde-free isoprenol from a stream of crude isoprenol containing isoprenol, water, and formaldehyde, - A first low-boiling-point separation column is provided to receive the stream of crude isoprenol and to distillate the stream of crude isoprenol into a first bottom stream containing isoprenol and formaldehyde and a first distillation stream containing water and low-boiling-point substances, - A second low-boiling-point separation column, which receives a first bottom flow from the first low-boiling-point separation column and is adapted to distillate the first bottom flow into a second distillation flow containing aqueous formaldehyde and a second bottom flow containing isoprenol, - A finishing column receiving a second bottom flow from the second low-boiling-point separation column, and configured to distillate the second bottom flow into a distillation stream consisting of pure isoprenol and a bottom flow containing high-boiling-point substances, A plant that includes this. Item 16 The second low-boiling point separation column is, - A quenching section above the rectification section of the second low-boiling-point separation column, wherein the second low-boiling-point separation column is designed to collect a second distillate at the lower end of the quenching section and to partially circulate the second distillate through a circulation line to the quenching section, - The scrub section above the rapid cooling section and the water inlet above the scrub section, The plants described in item 15, including the plants described in item 15.

Claims

1. A method for recovering formaldehyde-free isoprenol from a stream of crude isoprenol containing isoprenol, water, and formaldehyde, comprising the step of subjecting the stream of crude isoprenol or the isoprenol-containing fraction thereof to distillation in a low-boiling point separation column operated at a pressure of 2.5 bar or more to obtain a distillation stream containing aqueous formaldehyde and a bottom stream containing isoprenol.

2. The method according to claim 1, comprising the steps of 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 stream of crude isoprenol.

3. The method according to claim 2, wherein the distillation stream is at least partially recycled to the reaction of formaldehyde and isobutylene.

4. (i) The process of sending the flow of crude isoprenol to a first low-boiling-point separation column operated at a pressure of 1.5 bar or less to obtain a first bottom flow containing isoprenol and formaldehyde, and a first distillation flow containing water and low-boiling-point substances, (ii) A step of sending the first bottom flow to a second low-boiling point separation column operated at a pressure of 2.5 bar or more to obtain a second distillation flow containing aqueous formaldehyde and a second bottom flow containing isoprenol, (iii) A step of sending the second bottom flow to a finishing column to obtain a bottom flow containing pure isoprenol and high-boiling point substances as a distillation flow. The method according to any one of claims 1 to 3, including

5. The method according to claim 4, wherein the quenching section is provided downstream of the rectification section of the second low-boiling point separation column in the direction of vapor flow, the aqueous liquid is collected at the lower end of the quenching section, the aqueous liquid is partially circulated to the quenching section through a circulation line and partially withdrawn as the second distillation flow.

6. The method according to claim 5, wherein the aqueous liquid is cooled before being circulated to the rapid cooling section.

7. The method according to claim 6, wherein the aqueous liquid is heat-exchanged with the flow of crude isoprenol flowing into the first low-boiling point separation column before being circulated to the quenching section.

8. The method according to any one of claims 5 to 7, wherein the aqueous liquid is partially returned to the rectification section as reflux.

9. The method according to claim 8, wherein the mass flow rate ratio of the reflux flow to the second distillation flow is in the range of 2:1 to 10:

1.

10. The method according to any one of claims 5 to 9, wherein the scrub section is provided downstream of the rapid cooling section in the direction of steam flow, and water is introduced at the top of the scrub section.

11. The method according to any one of claims 4 to 10, wherein the second distillation stream contains 25 to 60% by weight of formaldehyde.

12. The method according to any one of claims 4 to 11, wherein the obtained pure isoprenol contains less than 0.5% by weight of formaldehyde.

13. The method according to any one of claims 4 to 12, wherein the first low-boiling-point separation column is operated at a pressure of 1.2 bar or less, and / or the second low-boiling-point separation column is operated at a pressure of 2.5 bar or more.

14. The method according to any one of claims 4 to 13, comprising the step of sending at least a portion of the first distillation stream to a wastewater removal pipe to separate low-boiling point substances from the water.

15. A plant for recovering formaldehyde-free isoprenol from a stream of crude isoprenol containing isoprenol, water, and formaldehyde, - A first low-boiling-point separation column adapted to operate at a pressure of 1.5 bar or less, and to receive the stream of crude isoprenol and to distillate the stream of crude isoprenol into a first bottom stream containing isoprenol and formaldehyde, and a first distillation stream containing water and low-boiling-point substances, - A second low-boiling-point separation column, adapted to operate at a pressure of 2.5 bar or higher, and to receive a first bottom flow from the first low-boiling-point separation column, and to distillate-separate the first bottom flow into a second distillation flow containing aqueous formaldehyde and a second bottom flow containing isoprenol, - A finishing column receiving a second bottom flow from the second low-boiling-point separation column, and configured to distillate the second bottom flow into a distillation flow consisting of pure isoprenol and a bottom flow containing high-boiling-point substances, A plant that includes this.

16. The second low-boiling point separation column is, - A quenching section above the rectification section of the second low-boiling-point separation column, wherein the second low-boiling-point separation column is designed to collect a second distillation flow at the lower end of the quenching section and to partially circulate the second distillation flow through a circulation line to the quenching section, - The scrub section above the rapid cooling section and the water inlet above the scrub section, The plant according to claim 15, including the plant described in claim 15.

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