Method for purifying isopropanol

Abstract

Provided herein are methods of purifying isopropanol comprising (a) providing a feed comprising at least 99.0% by weight of isopropanol; and (b) subjecting the feed to two or more distillation steps, including higher pressure distillation at a pressure of at least 6 bar; and a lower pressure distillation at a pressure of 5 bar or less; and thus, purified isopropanol is obtained.

Description

Technical Field

[0001] This invention relates to a method for purifying isopropanol. Background Technology

[0002] Isopropanol (also known as "isopropyl alcohol" or "2-propanol," and referred to herein as "IPA") is a fluid widely used for various purposes such as coatings, industrial processes, household uses, and personal care products. Its rapid evaporation, miscibility with water, and ability to dissolve a wide range of nonpolar compounds also make it particularly suitable for semiconductor manufacturing processes, especially for wafer cleaning to remove trace amounts of organic matter, water, and particles. Proper cleaning is crucial in the manufacture of complex semiconductor chips, as residues can lead to defects and pattern collapse. High-purity isopropanol is required to avoid such residues.

[0003] Conventional isopropanol purification processes remove impurities through a combination of purification methods, such as distillation, ion exchange, and membrane filtration. International Patent Application Publication WO 01 / 94284 describes a method for producing ultra-high purity isopropanol via a separation column (e.g., a distillation column). US Patent 10,647,648 describes a method for purifying organic solvents (e.g., isopropanol) using a monolithic organic porous cation exchanger.

[0004] As semiconductor chips become increasingly advanced and miniaturized, contaminant removal becomes even more critical, necessitating the use of high-purity isopropanol for substrate cleaning. Methods for manufacturing ultra-pure isopropanol suitable for use in the semiconductor industry remain needed. Summary of the Invention

[0005] The purpose of this application is to provide a method for purifying isopropanol. Specifically, this document provides a method for purifying isopropanol, comprising:

[0006] (a) Providing a feed comprising at least 99.0% by weight of isopropanol; and

[0007] (b) subjecting the feed to one or more distillation steps, including higher pressure distillation at a pressure of at least 6 bar; preferably followed by lower pressure distillation at a pressure of less than 5 bar;

[0008] This yields purified isopropanol.

[0009] The inventors of this application have surprisingly discovered that distillation at higher pressures can effectively remove impurities such as tert-butanol (also known as "2-methylprop-2-ol" or "tert-butyl alcohol" and referred to herein as "TBA"), which is difficult to separate from IPA given that IPA and TBA have almost the same boiling point and similar chemical properties.

[0010] The independent and dependent claims set forth the particular and preferred features of the invention. Features from the dependent claims may be combined, as appropriate, with features from the independent or other dependent claims and / or with the features described above and / or below in the specification.

[0011] The above and other characteristics, features, and advantages of the present invention will become apparent from the following detailed description, which illustrates the principles of the invention by way of example. This description is given for illustrative purposes only and does not limit the scope of the invention. Attached Figure Description

[0012] The figures below are included to illustrate certain aspects of this disclosure, and should not be considered as exclusive embodiments. The disclosed subject matter is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to those skilled in the art who benefit from this disclosure.

[0013] Figure 1 This document describes a method for purifying isopropanol according to a specific embodiment of the method described herein.

[0014] Figure 2 This document describes an alternative embodiment of the method for isopropanol purification. Detailed Implementation

[0015] The invention will be described with respect to specific embodiments.

[0016] It should be noted that the term "comprising" as used in the claims should not be construed as limited to the means listed thereafter; it does not exclude other elements or steps. Therefore, it should be interpreted as indicating the presence of the claimed features, steps, or components, but not excluding the presence or addition of one or more other features, steps, or components, or groups thereof. Thus, the scope of the statement "an apparatus comprising means A and B" should not be limited to an apparatus consisting solely of components A and B. This means that, with respect to the invention, the only relevant components of the apparatus are A and B.

[0017] Throughout this specification, references to "one embodiment" or "implementation" are used. Such references indicate that a particular feature described with respect to an embodiment is included in at least one embodiment of the invention. Therefore, the phrases "in one embodiment" or "in an embodiment" appearing throughout this specification do not necessarily refer to the same embodiment, although they may. Furthermore, in one or more embodiments, a particular feature or characteristic may be combined in any suitable manner, as will be apparent to those skilled in the art.

[0018] All numerical values ​​described in detail herein are modified with “approximate” indicators and take into account experimental errors and variations that would be expected by one of ordinary skill in the art.

[0019] The following terminology is provided only to aid in understanding the invention.

[0020] Unless otherwise stated, "isopropanol with x% purity" means a composition containing x weight percentage (wt%) of isopropanol based on the total weight of the composition excluding water. The purity of isopropanol can be measured by gas chromatography with flame ionization detection (GC-FID). The water content in isopropanol can be determined by coulombic Karl Fischer titration according to ASTM E1064-16.

[0021] Unless otherwise stated, the term "ppm" means parts per million on a weight basis and is equivalent to mg / kg. Similarly, the term "ppb" means parts per billion on a weight basis and is equivalent to μg / kg; and the term "ppt" means parts per trillion on a weight basis and is equivalent to ng / kg.

[0022] Unless otherwise stated, the term "organic impurity" refers to organic molecules other than isopropanol, such as TBA, 1-propanol, etc. For the avoidance of confusion, water is not an organic molecule.

[0023] Unless otherwise stated, all pressures expressed in "bar" are absolute pressures. Only pressures expressed in "barg" are gauge pressures.

[0024] This document provides a method for purifying isopropanol, comprising (a) providing an isopropanol feed having a purity of at least 99.0%; and (b) subjecting the feed to one or more distillation steps, including higher pressure distillation at a pressure of at least 6 bar and lower pressure distillation at a pressure below 5 bar; thereby obtaining purified isopropanol. Further details regarding this method and its implementation will be discussed separately below.

[0025] In the first step of the method, an isopropanol feed is provided having an isopropanol purity of at least 99.0%, i.e., the isopropanol feed contains at least 99.0% by weight of isopropanol based on the total feed weight excluding water. In a preferred embodiment, the isopropanol feed has a purity of at least 99.5%, at least 99.8%, or at least 99.9%.

[0026] As described above, the purity of isopropanol is based on the total feed excluding water. In a preferred embodiment, the isopropanol feed contains 0.2% by weight or less water, preferably 0.1% by weight or less, for example, about 0.025% by weight.

[0027] In a preferred embodiment, the isopropanol feed contains less than 0.1% by weight of metal (metal ions), preferably less than 0.01% by weight, more preferably less than 1 ppm, for example, 1-10 ppb. The metal content can be determined using inductively coupled plasma mass spectrometry (ICP-MS).

[0028] The feedstock, isopropanol with a purity of at least 99.0%, is widely available from various manufacturers. Isopropanol can be prepared by any method suitable for its preparation. Various methods are known in the art, including:

[0029] - Indirect hydration, in which propylene reacts with sulfuric acid to form a sulfate ester, which is then hydrolyzed;

[0030] - Direct hydration, in which propylene reacts with water under high pressure in the presence of an acid catalyst; and

[0031] - Hydrogenation of acetone.

[0032] While these methods alone may not directly produce isopropanol with a purity of 99.0% or higher, methods for purifying isopropanol to obtain such purity are known in the art. Examples include distillation (e.g., as described in WO 01 / 94284 and the references discussed therein), extractive distillation (see, for example, US 5,897,750), ion exchange (e.g., as described in US 10,647,648), membrane separation (e.g., as described in US 5,585,527), solvent extraction (e.g., as described in US 4,399,000), and combinations thereof. An example of a method for producing 99.9% pure isopropanol is explained in WO 01 / 94284 (Figure 6 and pages 5, lines 14 through 6, lines 5).

[0033] In certain embodiments, the methods described herein include the step of preparing an isopropanol feedstock, preferably via one of the three methods described above, followed by purification. In other embodiments, isopropanol may be obtained from a waste stream, such as a waste isopropanol stream obtained from cleaning a semiconductor substrate. The waste stream may need to be treated using one or more purification methods known in the art to increase the purity of the isopropanol to 99.0% or higher.

[0034] The method of the present invention is characterized by subjecting the isopropanol feed to two or more distillation steps, at least one of which is a higher-pressure distillation at at least 6 bar. The inventors of this application have discovered that under such pressure, heavier molecules such as TBA and butanone (methyl ethyl ketone or MEK) can be separated from IPA via distillation. Since boiling point depends on pressure, pressure will determine the temperature required for distillation, but this can be determined by a person skilled in the art without undue burden. Typically, higher-pressure distillation is carried out at 6 to 20 bar, preferably 6 to 15 bar, more preferably 8 to 12 bar, for example, at about 10 bar. The inventors of this application have surprisingly found that pressures below 6 bar result in less efficient TBA removal, while higher pressures result in more efficient TBA removal. On the other hand, higher pressures require high temperatures, which are energy-intensive and may lead to excessive formation of impurities.

[0035] High-pressure distillation is performed using distillation columns known in the art (also referred to herein as "high-pressure distillation columns"). The high-pressure distillation column can be a tray column (also referred to as a plate column) configured with at least 30 trays, preferably at least 60 trays, at least 80 trays, more preferably at least 100 trays, such as about 110 trays. This high number of trays facilitates the efficient separation of heavier molecules such as TBA from IPA.

[0036] The isopropanol feed typically enters the high-pressure distillation column near the bottom, preferably at least below tray 20, or below tray 10 (where trays are counted from bottom to top). Those skilled in the art will understand that similar results can be obtained using a packed column with a similar number of theoretical trays. Furthermore, those skilled in the art will understand that similar results can be obtained with a column having fewer theoretical trays by appropriately recirculating the top fraction back into the column. As stated above, the inventors of this application have surprisingly discovered that higher pressures result in more efficient TBA removal. Therefore, those skilled in the art will understand that the required number of (theoretical) trays also depends on the applied pressure, with higher pressures requiring fewer trays than lower pressures.

[0037] The bottom fraction of a high-pressure distillation column is rich in heavier molecules such as TBA and can still be used as technical-grade isopropanol. Alternatively, the bottom fraction can be recovered and purified to form a new isopropanol feed for the method. The top fraction of the column contains a reduced amount of heavier molecules and is also referred to herein as the "high-pressure top fraction". Typically, the isopropanol feed is separated into 40-60 wt% bottom fraction and 40-60 wt% high-pressure top fraction. The terms "bottom fraction" and "top fraction" as used herein are relative and mean that the top fraction is collected at a higher point in the column than the bottom fraction. In certain embodiments, the bottom fraction does not necessarily have to be collected at the very bottom of the column, and / or the top fraction does not necessarily have to be collected at the very top of the column. Analysis of the (heavier) impurities present in the isopropanol can provide guidance on at which points in the column the bottom and top fractions can be collected. Sampling can be performed throughout the process. In a preferred embodiment, the top fraction is collected at or near the top of the column. In a preferred embodiment, the bottom fraction is collected at or near the bottom of the column.

[0038] The method of the present invention also includes lower-pressure distillation at a pressure lower than that used for higher-pressure distillation. Typically, lower-pressure distillation is carried out at pressures below 5 bar. The inventors of this application have discovered that molecules such as acetone and ethanol can be separated from IPA via distillation at such pressures. Preferably, the lower-pressure distillation is performed at pressures from 0.5 bar to 5 bar, more preferably from 0.5 bar to 3 bar, for example, about 2 bar.

[0039] A lower-pressure distillation is performed after a higher-pressure distillation step. The inventors of this application have discovered that some acetone may be formed during the higher-pressure distillation step. In certain embodiments, this may result in a high-pressure top fraction having a lower overall isopropanol content compared to the feed. Therefore, the bottom fraction of the higher-pressure distillation step can be "purified" in the sense that the concentration of at least one organic impurity (e.g., tert-butanol) is lower than the concentration of said organic impurity in the feed, but the fraction does not necessarily have a higher isopropanol content than the feed. However, purified isopropanol obtained via the method of the present invention (including both higher-pressure and lower-pressure distillation steps) has a higher isopropanol content than the feed.

[0040] Acetone formed during higher-pressure distillation can be removed by lower-pressure distillation following higher-pressure distillation. Lower-pressure distillation can be performed immediately after higher-pressure distillation, but in some embodiments, the high-pressure top fraction may undergo one or more additional purification steps (e.g., other distillation steps and / or ion exchange) prior to lower-pressure distillation.

[0041] Lower-pressure distillation is performed using distillation columns known in the art (also referred to herein as “low-pressure distillation columns” or “low-pressure columns”). Low-pressure distillation columns can be tray columns (also called plate columns) configured with at least 30 trays, preferably at least 60 trays, more preferably at least 75 trays, and even more preferably at least 90 trays, such as about 100 trays. Such a high number of trays facilitates the efficient separation of lighter molecules, such as acetone, from IPA. The isopropanol feed (i.e., the high-pressure top fraction, optionally purified via other purification steps) typically enters the column near the top, preferably between trays 80 and 100 (where trays are counted from bottom to top). As also noted above for higher-pressure distillation, the terms “bottom fraction” and “top fraction” are relative and mean that the top fraction is collected at a higher point in the column than the bottom fraction. Those skilled in the art will understand that similar results can be obtained using packed columns with a similar theoretical number of trays. Furthermore, technicians will understand that, with proper recirculation, similar results can be obtained with a column having fewer theoretical plates.

[0042] The top fraction of a low-pressure distillation column is rich in lighter molecules such as acetone and can still be used as a lower grade of isopropanol, or for its preparation. Alternatively, the top fraction can be recovered and purified to form a new isopropanol feed for the process. The bottom fraction of the column is rich in isopropanol and is also referred to herein as the "low-pressure isopropanol-rich fraction".

[0043] As mentioned above, the bottom fraction can be collected at or near the bottom of the distillation column. Therefore, a low-pressure isopropanol-rich fraction can be collected at or near the bottom of a low-pressure distillation column.

[0044] The inventors of this application have discovered that the bottom product of a low-pressure distillation column is not only rich in isopropanol, but can also have a (slightly) higher content of inorganic substances (e.g., metal content) compared to other fractions of the column. Therefore, in a particular embodiment, the low-pressure isopropanol-rich fraction can be collected as a vapor sidestream above (but near) the bottom of the distillation column, and typically also (far) below the location where the feed enters the low-pressure distillation column. In this way, an improved balanced feed stream with high isopropanol content and low metal content can be collected. In a particular embodiment, the low-pressure column has at least 75 trays, wherein the vapor sidestream is collected between trays 2 and 10, preferably between trays 2 and 5. The product collected at the bottom of the low-pressure distillation column (i.e., below the sidestream) is still suitable for use as a lower grade (e.g., technical grade) of isopropanol.

[0045] Alternatively, the low-pressure isopropanol-rich fraction can be a vapor side stream collected by a reboiler associated with the low-pressure column. The reboiler is used to generate vapor returned to the column to drive distillation separation by heating the bottom product of the distillation column by boiling the bottom fraction. A lower metal content is expected in the reboiler vapor side stream compared to the bottom product stream.

[0046] Typically, lower-pressure distillation produces 5-15% by weight of the top fraction and 85-95% by weight of the low-pressure isopropanol-rich fraction. When the low-pressure isopropanol-rich fraction is collected as a vapor sidestream above the bottom of the low-pressure column, lower-pressure distillation can produce 5-15% by weight of the top fraction, 70-85% by weight of the sidestream, and 5-15% by weight of the bottom fraction.

[0047] In certain embodiments, the methods described herein may include additional purification steps in addition to one or more distillation steps. In certain embodiments, the method may include an ion exchange step using an ion exchange resin. This can be used to (further) reduce the metal content in isopropanol, for example, to 100 ppt or less. The metal content can be determined via ICP-MS.

[0048] Ion exchange resins suitable for reducing the metal content in isopropanol are known in the art and may comprise a solid phase containing binding groups with positive or negative ionic charges, and replaceable exchangeable counterions.

[0049] Metallic impurities include all metal ions, such as sodium, potassium, calcium, and iron. Preferably, the ion exchange resin includes cation exchange resins, anion exchange resins, or mixtures thereof. An example of a suitable resin is Amberjet, sold by Rohm and Haas. TM UP6040 resin. If an acidic resin is used, cations are removed, including most metals expected to be present in isopropanol. In this case, the isopropanol can be subjected to additional treatment with an anion exchange resin to further remove anions. The cationic metal absorbs and releases anionic counterions, which can be absorbed by the anion exchange resin. Furthermore, the anion exchange resin is capable of removing trace amounts of acidic compounds that can cause cation release. The resin can be selected based on the substance to be removed. A single resin bed can be used alone or in various combinations. Additionally, the ion exchange resin can be a mixed device comprising a resin-impregnated filter or membrane.

[0050] The ion exchange step can be performed at any stage of the method, such as before or after higher-pressure distillation, between higher-pressure and lower-pressure distillation, or after higher-pressure and lower-pressure distillation. In a preferred embodiment, the ion exchange step is performed after the lower-pressure distillation step. In a particular embodiment, the isopropanol-rich fraction following the higher-pressure and lower-pressure distillation may undergo further purification.

[0051] In certain embodiments, the methods described herein may additionally include a filtration step, wherein isopropanol is filtered using a filtration device at any stage of the method. The filtration step may be used to remove particles (if present). The filtration step may be performed at any stage of the method. The filtration device may be any suitable device capable of removing particles from 0.05 μm to 10 μm in size. Suitable filtration devices include membranes (e.g., ceramic, polymer, or metal membranes), microfiltration devices or cartridges, ultrafiltration devices, or combinations thereof.

[0052] The purified isopropanol obtained by the method of the present invention preferably has a higher isopropanol content than the isopropanol feed. In a particular embodiment, the purified isopropanol obtained by the method may have a purity of at least 99.995%, preferably at least 99.999%. This makes the purified isopropanol suitable for even the most demanding semiconductor applications. Furthermore, the purified isopropanol may contain less than 100 ppm of water. In a particular embodiment, the purified isopropanol contains 40-100 ppm of water. The water content in the isopropanol can be determined by coulombic Karl Fischer titration according to ASTM E1064-16.

[0053] In a particular embodiment, the isopropanol feed comprises tert-butanol (TBA). Because TBA and IPA have very similar properties, it is extremely difficult to remove trace amounts of TBA from IPA using conventional purification methods. The inventors of this application have discovered that the method of the present invention is particularly suitable for reducing the TBA content of isopropanol to below 2 ppm, or even lower. Therefore, in a particular embodiment, the method described herein can be used to reduce the TBA content of the isopropanol feed. In these or other embodiments, the isopropanol feed may contain at least 5 ppm of TBA, at least 10 ppm of TBA, or even at least 20 ppm of TBA. In such embodiments, the purified isopropanol may contain less than 5 ppm of TBA, for example less than 2 ppm of TBA, or even less than 1.5 ppm of TBA.

[0054] As described above, the method described herein is particularly suitable for removing TBA impurities from isopropanol. The inventors of this application believe that the method allows for the reduction of the TBA content (if any) in isopropanol to levels that are extremely difficult to obtain using other purification methods such as extractive distillation, membrane filtration, adsorption, and crystallization. Therefore, this document provides a method for reducing the TBA content in IPA using a higher-pressure distillation step, as described herein.

[0055] Figure 1A method for purifying isopropanol according to a specific embodiment of the method described herein is illustrated. A feed (1) of technical-grade IPA with a purity of at least 99.0% by weight enters a 110-plate distillation column (2) at positions 7-11 for distillation at a pressure of at least 6 bar. The bottom fraction (3), enriched with heavier molecules such as TBA, can be used as technical-grade IPA and is returned to the distillation column (2) after passing through a reboiler (4), thereby supplying heat to the column. The top fraction (6) is partially recycled to the high-pressure column (2) via a condenser (7), and the remainder is moved via a drum (8) to a 100-plate distillation column (9). The fraction (6) enters a low-pressure column (9) at positions 90-95 for distillation at a pressure below 5 bar. The top fraction (10), enriched with low-boiling components such as acetone, is moved to a drum (12) after passing through a condenser (11). The top fraction can then be recycled back to column (9) and / or used as a lower grade of IPA. The bottom fraction (14) is rich in IPA and lean for organic impurities. Fraction (14) can be partially recovered to column (2) after passing through reboiler (19). The remainder of the bottom fraction (14) passes through cooler (15) and optionally through ion extraction unit (16) to remove metals and filter (17) to remove particulate matter, producing purified IPA (18).

[0056] Figure 2 An alternative embodiment of the isopropanol purification method according to the method described herein is shown. This embodiment is similar to... Figure 1 The illustrated implementation is identical except that the IPA-rich fraction is not collected at the bottom of the low-pressure column (9). Instead, the IPA-rich fraction is collected as a vapor side stream slightly above the bottom of the column (near tray 3), but well below the inlet point where the feed (6) enters the column (9). The vapor side stream passes through a condenser / cooler (20) and optionally undergoes further purification in an ion exchange unit (21) and a filter (22) to produce purified IPA (23). The use of the vapor side stream is particularly useful for obtaining IPA with a further reduced metal content. The actual bottom fraction (14) can still be used as lower-grade IPA (24) and is partially recovered to the column (9) after passing through a reboiler (19).

[0057] The following implementation scheme of the method described herein is also disclosed:

[0058] Implementation Scheme 1. A method for purifying isopropanol, comprising: (a) providing a feed comprising at least 99.0% by weight of isopropanol based on the total feed weight excluding water; and (b) subjecting the feed to two or more distillation steps, including higher pressure distillation at a pressure of at least 6 bar; and lower pressure distillation at a pressure of less than 5 bar, wherein the higher pressure distillation is performed prior to the lower pressure distillation; thereby obtaining purified isopropanol.

[0059] Implementation Scheme 2. The method according to Implementation Scheme 1, wherein the purified isopropanol obtained after the higher pressure distillation and the lower pressure distillation is 30% to 50% of the weight of the feed stream.

[0060] Implementation Scheme 3. The method according to Implementation Scheme 1 or 2, wherein the lower pressure distillation produces 85-95% by weight of a low-pressure isopropanol-rich fraction and 5-15% by weight of a low-pressure top fraction.

[0061] Implementation Scheme 4. The method according to any one of Implementation Schemes 1 to 3, wherein the lower pressure distillation is carried out at a pressure of 0.5 bar to 5 bar.

[0062] Implementation Scheme 5. The method according to Implementation Scheme 4, wherein the lower pressure distillation is carried out at a pressure of 0.5 bar to 3 bar.

[0063] Implementation Scheme 6. The method according to any one of Implementation Schemes 1 to 5, wherein the feed comprises at least 99.5% by weight of isopropanol based on the total weight of the feed after water removal.

[0064] Implementation Scheme 7. The method according to any one of Implementation Schemes 1 to 6, wherein the purified isopropanol comprises at least 99.8% by weight, and preferably at least 99.9% by weight, of the total weight of the purified isopropanol excluding water.

[0065] Implementation Scheme 8. The method according to Implementation Scheme 7, wherein the purified isopropanol comprises at least 99.99% by weight of isopropanol based on the total weight of the purified isopropanol excluding water.

[0066] Implementation Scheme 9. The method according to Implementation Scheme 8, wherein the purified isopropanol comprises at least 99.999% by weight of the total weight of the purified isopropanol excluding water.

[0067] Implementation Scheme 10. The method according to any one of Implementation Schemes 1 to 9, wherein the feed contains at least 5 ppm of tert-butanol.

[0068] Implementation Scheme 11. The method according to Implementation Scheme 10, wherein the purified isopropanol contains 2 ppm or less of tert-butanol.

[0069] Implementation Scheme 12. The method according to any one of Implementation Schemes 1 to 11, wherein the feed contains at least 20 ppm of organic matter other than isopropanol.

[0070] Implementation Scheme 13. The method according to any one of Implementation Schemes 1 to 12, wherein the higher pressure distillation is carried out at a pressure of 8 bar to 20 bar.

[0071] Implementation Scheme 14. The method according to any one of Implementation Schemes 1 to 12, wherein the higher pressure distillation is carried out at a pressure of 6 bar to 15 bar.

[0072] Implementation Scheme 15. The method according to any one of Implementation Schemes 1 to 14, wherein the higher pressure distillation is carried out at a pressure of 8 to 12 bar.

[0073] Implementation Scheme 16. The method according to any one of Implementation Schemes 1 to 15, wherein the purified isopropanol contains less than 100 ppm of water.

[0074] Implementation Scheme 17. The method according to any one of Implementation Schemes 1 to 16 further includes a metal removal step via ion exchange.

[0075] Implementation Scheme 18. The method according to any one of Implementation Schemes 1 to 17, wherein the higher pressure distillation produces 40-60% by weight of a high-pressure top fraction and 40-60% by weight of a high-pressure bottom fraction.

[0076] Implementation Scheme 19. The method according to any one of Implementation Schemes 1 to 18, comprising:

[0077] - The top fraction is obtained by distillation at the higher pressure;

[0078] - The top fraction, optionally after further purification, is fed as a low-pressure feed into a distillation column for the lower-pressure distillation;

[0079] - A side stream, preferably a vapor side stream, is collected from the distillation column at a location above the bottom of the distillation column but below the point where the low-pressure feed enters the distillation column, and optionally the side stream is further purified;

[0080] Thus, the purified isopropanol is obtained.

[0081] Implementation Scheme 20. A composition obtainable by any one of Implementation Schemes 1 to 19, said composition comprising at least 99.999% by weight of isopropanol based on the total organic matter weight of said composition; less than 2 ppm of tert-butanol; and optionally 40 ppm to 100 ppm of water.

[0082] Example

[0083] The following embodiments are provided to illustrate the present invention and are in no way intended and should be construed as limiting the scope of the invention.

[0084] An isopropanol feed with 99.99% purity is provided. The feed is prepared via indirect hydration. Sulfuric acid is removed by distillation, followed by water removal via azeotropic distillation. Further impurities are removed by additional distillation, yielding isopropanol with 99.99% purity. This isopropanol feed contains approximately 130 ppm water and 10 ppm TBA. Preliminary studies are conducted, in which the feed is first distilled at approximately 9 bar via three batches on a packed distillation column, equivalent to a single-pass distillation using a plate column with approximately 110 trays. Subsequently, the final top fraction from the third batch is distilled at approximately 2 bar via two batches on a packed distillation column, equivalent to a single-pass distillation using a plate column with approximately 70 trays. The bottom fraction is collected with an isopropanol purity greater than 99.999%, a water content less than 150 ppm, and a TBA content of 1 ppm. The relatively high water content can be explained by the highly hygroscopic nature of isopropanol, since no specific precautions were taken to avoid sample contamination.

[0085] In another experiment, an isopropanol feed of 99.99% purity was provided, containing approximately 150 ppm water and 8.5 ppm TBA. The feed was first distilled at approximately 16.5 bar via distillation in a packed distillation column (equivalent to a 35-plate column). The top fraction collected from this column had 99.99% isopropanol purity, 250 ppm water content, and 1.3 ppm TBA content. Subsequently, the top fraction was distilled at approximately 1.7 bar via distillation in a packed distillation column, equivalent to distillation using a plate column with approximately 35 plates. The bottom fraction was collected with 99.999% isopropanol purity, less than 100 ppm water content, and 2 ppm TBA content.

[0086] Without departing from the spirit or scope of this disclosure, any changes, modifications and variations will be readily apparent to those skilled in the art in light of the foregoing description, and when lower and upper limits of numerical values ​​are listed herein, the range from any lower limit to any upper limit is taken into account.

Claims

1. A method of purifying isopropanol, comprising: (a) providing a feed comprising at least 99.0 wt% isopropanol, based on the total feed weight excluding water; and (b) subjecting the feed to two or more distillation steps, comprising - a higher pressure distillation at a pressure of at least 6 bar; and - one or more further purification steps, comprising a lower pressure distillation at a pressure of below 5 bar, wherein the higher pressure distillation is performed prior to the lower pressure distillation; thereby obtaining purified isopropanol.

2. The method according to claim 1, wherein the lower pressure distillation results in a low pressure isopropanol-rich fraction of 85-95 wt% and a low pressure top fraction of 5-15 wt%.

3. The method according to claim 1 or 2, wherein the purified isopropanol comprises at least 99.9 wt% isopropanol, based on the total weight of the purified isopropanol excluding water.

4. The method according to any one of claims 1 to 3, wherein the feed contains tertiary butanol in an amount of at least 5 ppm.

5. The method according to claim 4, wherein the purified isopropanol contains tertiary butanol in an amount of 2 ppm or less.

6. The method according to any one of claims 1 to 5, wherein the feed contains an organic content other than isopropanol in an amount of at least 20 ppm.

7. The method according to any one of claims 1 to 6, wherein the higher pressure distillation is performed at a pressure of 8 to 20 bar.

8. The method according to any one of claims 1 to 6, wherein the higher pressure distillation is performed at a pressure of 8 to 12 bar.

9. The method according to any one of claims 1 to 8, wherein the purified isopropanol contains less than 100 ppm water.

10. The method according to any one of claims 1 to 9, wherein the purified isopropanol obtained after the higher pressure distillation and the lower pressure distillation is 30 to 50% by weight of the feed stream.

11. The method according to any one of claims 1 to 10, further comprising a metal removal step via ion exchange.

12. The method according to any one of claims 1 to 11, wherein the higher pressure distillation results in a high pressure top fraction of 40-60 wt% and a high pressure bottom fraction of 40-60 wt%.

13. The method according to any one of claims 1 to 12, wherein the lower pressure distillation is performed at a pressure of 0.5 to 5 bar.

14. The method according to any one of claims 1 to 13, comprising: - obtaining a top fraction from the higher pressure distillation; - subjecting the top fraction, optionally after further purification, as a low pressure feed to a distillation column for the lower pressure distillation; - collecting a side stream from the distillation column, above the bottom of the distillation column but below the position where the low pressure feed enters the distillation column, and optionally further purifying the side stream; thereby obtaining the purified isopropanol.

Images