Method and apparatus for simultaneously removing water and nitrogen-containing compounds from an alcohol-containing process stream and disposing the water contaminated with nitrogen-containing compounds

Abstract

Disclosed herein is a method for simultaneously removing water and nitrogen-containing compounds from an alcohol-containing process stream and disposing the water contaminated with nitrogen-containing compounds, and an apparatus for carrying out said method.

Description

[0001] 202200227 1

[0002] Method and apparatus for simultaneously removing water and nitrogen-containing compounds from an alcohol-containing process stream and disposing the water contaminated with nitrogencontaining compounds

[0003] TECHNICAL FIELD

[0004] The present disclosure concerns a method for simultaneously removing water and nitrogen-containing compounds from an alcohol-containing process stream and disposing the water contaminated with nitrogen-containing compounds, and an apparatus for carrying out said method.

[0005] BACKGROUND

[0006] Alcohols, such as, for instance, methanol, are used as solvent and / or diluent in various chemical reactions. For economic and ecologic reason, on an industrial scale it is desirable to recover the alcohol. However, in the course of a reaction, compounds, such as residual reactants, stabilizers of commercially available reactants, catalysts, cosolvents and / or (by-)products, may accumulate in the alcohol which have to be removed before the alcohol can be recycled into the process.

[0007] For instance, US 2004 / 110970 A1 shows that even rather small amounts of nitrogen-containing compounds in recycled methanol can poison a titanium zeolite catalyst used in the epoxidation of propylene to propylene oxide by hydrogen peroxide in methanol, resulting in reduced activity of the catalyst and more rapid catalyst deactivation.

[0008] EP 4166545 A1 describes an industrial process for making propylene oxide from propylene and hydrogen peroxide in the presence of a titanium zeolite catalyst and a nitrogen-containing compound, such as ammonia, using methanol as a solvent. After separating at least a part of the non-reacted propylene from the reaction mixture, the propylene-depleted reaction mixture is subjected to distillation in a distillation column to obtain an overhead product stream comprising propylene oxide and methanol and a bottoms product stream comprising methanol and water. To reduce the amount of nitrogen-containing compound in the overhead product stream, an acid is added to the propylene-depleted reaction mixture prior to feeding it to the distillation column or to the distillation column itself in an amount to provide an apparent pH in the bottoms product stream of from 3 to 4.5. The bottoms product stream is then separated in at least one further distillation stage to provide recovered methanol as an overhead product. Again, an acid may be added prior to or during said further distillation stage, this time in an amount to provide an apparent pH in the bottoms product stream of from 1.6 to 5.0, to reduce the amount of volatile organic amines in the recovered methanol. In both stages the acid added preferably is sulfuric acid and the amount added is controlled by the apparent pH in the bottoms product stream obtained after the respective distillation stage. The lower the pH in the bottoms product stream, the lower is the amount of nitrogen-containing compounds in the recovered methanol. However, sulfuric acid is highly corrosive, in particular at a pH of below 2.0, requiring the use of particular corrosion resistant materials in the apparatus. Further, at this low pH side reactions may occur due to the oxidizing properties of202200227 2

[0009] concentrated sulfuric acid. Accordingly, for practical and economic reasons, the apparent pH in the bottoms product of the further distillation stage is required to be not lower than 2.0. Due to inevitable fluctuations during operation, a pH not lower than 2.2 needs to be targeted. Using sulfuric acid at a pH of 2.2, however, it is not possible to consistently reduce the amount of total nitrogen in the recovered methanol to a value of less than 30 ppm. A further drawback of using sulfuric acid for removing nitrogencontaining compounds is the formation of sulfates which may precipitate in process stream fed to the distillation column: If they are insoluble, additional process steps are required for removing them, and even if they are soluble, additional cost intensive steps for treating the residual process water obtained as a bottoms product in the further distillation stage are required. Further, when wishing to combust the sulfur-containing waste from such processes, costly flue-gas desulfurization means are required.

[0010] Accordingly, there is a need for a method for removing nitrogen-containing compounds from an alcohol-containing process stream which avoids the above drawbacks associated to the use of sulfuric acid.202200227 3

[0011] SUMMARY

[0012] It has surprisingly been found that the above drawbacks can be avoided if an organic acid is used instead of sulfuric acid. Using a carboxylic acid, the bottoms product or at least a part thereof can be incinerated without the need for flue-gas desulfurization, while still maintaining or even improving the quality of the alcohol recovered in the process.

[0013] Accordingly, the present disclosure is directed to a method for simultaneously removing water and nitrogen-containing compounds from an alcohol containing process stream and disposing the water contaminated with nitrogen-containing compounds, wherein the process stream comprises less than 0.1 wt.% of hydrogen peroxide, based on the total weight of the process stream, the method comprising the steps of (a) distilling the process stream containing the alcohol and water in the presence of a carboxylic acid or an anhydride thereof to obtain an overhead product containing the alcohol depleted of nitrogencontaining compounds and a bottoms product of process water containing nitrogen-containing compounds; (b) separately withdrawing the overhead product containing the alcohol depleted of nitrogencontaining compounds and the bottoms product; and (c) incinerating at least a part of the bottoms product.

[0014] In contrast to sulfuric acid, the carboxylic acids can be incinerated to give carbon dioxide and water, thus avoiding the need for flue-gas desulfurization means.

[0015] Further disclosed is an apparatus for carrying out said method, the apparatus comprising: (i) a reactor or a series of reactors fluidly coupled to each other, the reactor or series of reactors being adapted to generate or process an alcohol-containing process stream which further comprises water and at least one nitrogen-containing compound; (ii) at least one distillation column fluidly coupled to the reactor or series of fluidly coupled reactors, the distillation column being adapted to allow separately withdrawing an overhead product containing the alcohol depleted of the at least one nitrogen-containing compound and a bottoms product of water containing the at least one nitrogen-containing compound; (iii) at least one inlet coupled to the distillation column itself or to a line fluidly coupled to the distillation column adapted to feed the carboxylic acid; and (iv) at least one incinerator adapted to incinerate at least a part of the bottoms product.

[0016] LIST OF FIGURES

[0017] Figure 1 shows the dependency of the amount of nitrogen in methanol recovered after distillation on the apparent pH of the bottoms product of the second methanol distillation column using sulfuric acid and maleic acid as described in Example 9.

[0018] Figure 2 shows the dependency of the amount of nitrogen in methanol recovered after distillation on the apparent pH of the feed to the first methanol distillation column using sulfuric acid and maleic acid as described in Example 9.202200227 4

[0019] DETAILED DESCRIPTION

[0020] The present disclosure is directed to a method for simultaneously removing water and nitrogen-containing compounds from an alcohol-containing process stream and disposing the water contaminated with nitrogen-containing compounds, wherein the process stream comprises less than 0.1 wt.% of hydrogen peroxide, based on the total weight of the process stream, the method comprising the steps of (a) distilling the process stream containing the alcohol and water in the presence of a carboxylic acid or an anhydride thereof at an apparent pH of equal to or below 7.5 to obtain an overhead product containing the alcohol depleted of nitrogen-containing compounds and a bottoms product of process water containing nitrogen-containing compounds; (b) separately withdrawing the overhead product containing the alcohol depleted of nitrogen-containing compounds and the bottoms product; and (c) incinerating at least a part of the bottoms product.

[0021] In the present method, the amount of nitrogen-containing compounds in the overhead product containing the alcohol obtained after distillation may be controlled by controlling the apparent pH of the process stream to be distilled, whereas in the process using sulfuric acid which is described in e.g., EP 4 165545 A1 , the amount of nitrogen-containing compounds in the overhead product containing the alcohol is controlled by controlling the apparent pH of bottoms product obtained after distillation. For carboxylic acids, such as maleic acid, an exponential dependency of the amount of nitrogen in the alcohol recovered after distillation on the apparent pH of the feed to the alcohol distillation was observed according to the formula shown below:

[0022] In(TlV)

[0023] pH(CA)' =

[0024] D

[0025] wherein pH(CA) refers to the apparent pH of the feed containing the carboxylic acid to the alcohol distillation, In(TN) refers to the natural logarithm of the total nitrogen in the alcohol recovered after distillation, and A and B are coefficients which depend on the actual process, including the carboxylic acid used, the amount of water in the feed, and the distillation apparatus used. If a series of distillation devices, e.g., two or more distillation columns, is used for distilling off the alcohol, pH(CA) refers to the apparent pH of the feed containing the carboxylic acid to the first distillation device.

[0026] The nitrogen-containing compounds may be organic or inorganic nitrogen-containing compounds or a mixture of organic or inorganic nitrogen-containing compounds, and may include, for instance, ammonia, hydrazine, hydrazones, aldimines as well as derivatives thereof, organic amines including alkanolamines and the corresponding amine oxides, carboxylic acid amides, and nitriles, as well as salts thereof.

[0027] For instance, in a process for the catalytic epoxidation of olefins, one or more nitrogen-containing compounds may be introduced at different stages of the process, both on purpose or unintentionally. An unintentional introduction of one or more nitrogen-containing compounds occurs if at least one of the starting materials, e.g., olefin and / or hydrogen peroxide, or a solvent used in the reaction contains a nitrogen-containing compound. For instance, commercially available hydrogen peroxide often contains a nitrogen-containing compound like an aminophosphonic acid as peroxide stabilizer or a nitrate salt as202200227 5

[0028] corrosion inhibitor. Nitrogen-containing compounds may also be introduced for a certain purpose.

[0029] Additives, such as ammonia or salts thereof, amines, amine oxides, carboxamides or nitrites may be introduced into the epoxidation reaction to improve epoxide selectivity. Nitrogen-containing chelating compounds may be introduced at the same stage to reduce peroxide decomposition. Nitrogen-containing compounds may also be introduced during work-up of the reaction mixture as additives of solvents, for example, in extraction or extractive distillation steps. For instance, nitrogen-containing compounds having at least one unsubstituted NH2 group, such as hydrazine, may be used during work-up to convert carbonyl compounds to less volatile products. In addition, these nitrogen-containing compounds may be converted to other nitrogen-containing compounds by chemical reactions within the process, e.g., by oxidation with hydrogen peroxide, converting ammonia to hydroxylamine, nitrite or nitrate, primary amines to substituted hydroxylamines, oximes or nitroalkanes, secondary amines to substituted hydroxylamines, and tertiary amines to amine oxides. Ammonia or primary amines may also react with epoxides to give amino alcohols which in turn can be further oxidized. Hydroxylamine may react with carbonyl compounds formed in side-reactions from the epoxide to give oximes. In a similar way hydrazine will react with carbonyl compounds to give hydrazones and azines. If the work-up of the reaction mixture contains a hydrogenation stage, oximes, hydrazones and azines may be converted to ammonia, primary amines, secondary, and / or tertiary amines.

[0030] The amount of nitrogen may be preferably determined with a nitrogen analyzer by combustion of the sample and measurement of formed NO by chemiluminescence according to DIN EN 12260:2003-12. It is also possible to determine the alkalinity, which is a measure for the total amount of nitrogen, by potentiometric titration of the sample with an acid, such as for example with hydrochloric acid.

[0031] The alcohol-containing process stream being subjected to distillation in step (a) of the present method comprises less than 0.1 wt.% of hydrogen peroxide, based on the total weight of the process stream. In particular, the alcohol-containing process stream may comprise of from 0 to less than 0.1 wt.% of hydrogen peroxide, or of from 0.0001 to 0.099 wt.% of hydrogen peroxide, based on the total weight of the process stream. If it is desired to remove nitrogen-containing compounds from an alcohol-containing process containing higher amounts of hydrogen peroxide, the process stream may be subjected to a catalytic hydrogenation as further described below before being subjected to distillation according to step (a) of the present method.

[0032] As used herein, the term "apparent pH" refers to a value determined by measurement with a glass electrode employing a commercial pH meter calibrated with aqueous buffer solutions of known pH for measuring dilute aqueous solutions. This apparent pH differs from the notional pH, i.e., the negative logarithm of the hydrogen ion activity, by a constant value because the normal potential of the glass electrode in the product stream, which comprises methanol, is different than the normal potential in pure water.

[0033] The distillation may be carried out in a distillation column, which may comprise trays, such as sieve trays or bubble cap trays, and / or packings to enhance separation of the components, a reboiler to provide202200227 6

[0034] vaporization for the distillation process, a condenser to cool and condense the vapor leaving the top of the column, and / or a reflux drum to hold the condensed vapor from the top of the column so that liquid (reflux) can be recycled back to the column. The distillation column may be operated batchwise or may be a continuously operated distillation column.

[0035] The distillation of step (a) may comprise two or more subsequent distillation stages, and preferably may comprise two subsequent distillation stages wherein the alcohol is withdrawn as the overhead product in both stages. Herein, one stage preferably may be operated at a higher pressure than the other stage to heat the other stage. Even more preferably, the second stage may be operated at a higher pressure than the first stage, and overhead product vapor from the second stage may be used for heating the bottom's evaporator of the first stage.

[0036] The carboxylic acid may be a monocarboxylic acid or a polycarboxylic acid. As used herein, the term polycarboxylic acid refers to dicarboxylic acids and higher carboxylic acids comprising more than two carboxyl groups per molecule. For instance, the carboxylic acid may be selected from the group consisting of acetic acid, propionic acid, citric acid, oxalic acid, malonic acid, and maleic acid. The use of a polycarboxylic acid, in particular a polycarboxylic acid comprising two or three carboxyl groups per molecule may be preferred. In particular, the carboxylic acid may be maleic acid. Anhydrides of any of the aforementioned carboxylic acids may be used as well, and in the following, unless explicitly stated to the contrary, a reference to a carboxylic acid is meant to also include a reference to an anhydride thereof.

[0037] In addition to the carboxylic acid or an anhydride thereof, corresponding salts of the carboxylic acids, such as alkaline or earth alkaline metal salts, may optionally be added to the process stream to adjust or buffer its apparent pH.

[0038] In addition to being less corrosive than sulfuric acid, the carboxylic acid preferably should not be too volatile so that it is not distilled off from the process stream together with methanol. Preferably, the free carboxylic acid, i.e., not necessarily the corresponding anhydride, has a vapor pressure of equal to or less than 50 Pa at 25 °C, more preferably of equal to or less than 10 Pa at 25 °C, even more preferably of equal to or less than 1 Pa at 25 °C, and still even more preferably of less than 0.1 Pa at 25 °C. Further, the acid or the salts formed therefrom with the nitrogen-containing compounds should be stable under the conditions employed during distillation, i.e., they should not decompose, forming, for instance, carbon dioxide or formic acid. Preferably, at atmospheric pressure (101 ,325 Pa) the carboxylic acid or the anhydride thereof does not decompose at temperatures of upto 125 °C or even 130 °C. To avoid premature precipitation, the carboxylic acid or the anhydride thereof and the salts formed therefrom with the nitrogen-containing compounds should be soluble in the alcohol-containing process stream under the conditions employed, so that e.g., at least 1 mol of the respective substance can be dissolved in 1 L of the process stream at 25 °C. The free carboxylic acid preferably may have a pKa being in the range of from 1 to 5, more preferably of from 1 to 3, and even more preferably of from 1.5 to 2.5 at 25 °C. In case of polycarboxylic acids, this value refers to the lower pKa (pKai). Finally, under the conditions employed, salt formation should prevail over formation of an ester with the alcohol in the process stream.202200227 7

[0039] In the method of the present disclosure, the carboxylic acid or an anhydride thereof may be added to the alcohol-containing process stream before the process stream is being distilled in step (a) and / or during said distillation. Herein, the carboxylic acid or an anhydride thereof may be added as a solid or as a solution in a suitable solvent, e.g., as an aqueous solution. Preferably, the carboxylic acid or an anhydride thereof may be added to the alcohol-containing process stream as an aqueous solution. Adding the carboxylic acid or an anhydride thereof as an aqueous solution rather than adding it as a solid or a nonaqueous alcoholic solution was found to reduce the formation of esters which may occur in particular when anhydrides are used. Said aqueous solution of the carboxylic acid or an anhydride thereof may be added to the alcohol-containing process stream before or while said process stream is subjected to distillation, e.g., at a feed point above a feed point for the alcohol-containing process stream and below the top of a distillation column, or to the reflux stream thereof. Preferably, the aqueous solution may be added in a separate step (a-0) before the alcohol-containing process stream is subjected to distillation in step (a). Upon addition, the aqueous solution of the carboxylic acid or an anhydride thereof and the alcohol-containing process stream preferably each independently may have a temperature above 50 °C. Preferably the temperature may be in the range of from 60 to 120 °C, more preferably of from 70 to 110 °C, and even more preferably of from 80 to 100 °C. Most preferably the aqueous solution of the carboxylic acid or an anhydride thereof and the alcohol-containing process stream both have a temperature being in the range of from 85 to 95 °C when the aqueous solution is added to the process stream.

[0040] The aqueous solution of the carboxylic acid or an anhydride thereof may be prepared by dissolving the carboxylic acid or an anhydride thereof in water, including tap water, distilled water, and deionized water, aqueous methanol, or a part of the bottoms product (process water) obtained in step (b). Preferably, the aqueous solution may be obtained by dissolving maleic anhydride in a part of the bottoms product obtained in step (b) of the present process, which has a temperature in the range of from 30 to 90 °C, more preferably of from 40 to 80 °C, even more preferably of from 50 to 70 °C, and still even more preferably of from 55 to 65 °C. When being withdrawn from the distillation process according to step (b), the bottoms product may have a temperature above said ranges, such as greater than 100 °C or even greater than 150 °C. In this case, the temperature of at least a part of the bottoms may be lowered using one or more heat exchangers. When having the desired temperature in the range of from 30 to 90 °C, preferably of from 40 to 80 °C, more preferably of from 50 to 70 °C, and even more preferably of from 55 to 65 °C, a partial stream of the bottoms may be fed to a dosing unit where the aqueous solution of the carboxylic acid or an anhydride thereof is prepared. Due to the heat of solution and also the heat of reaction, in case of anhydrides, the resulting solution may have a higher temperature than the partial stream of bottoms product fed to the dosing unit, allowing the use of concentrated solutions of the carboxylic acids, comprising, for instance, 20 wt.-% or more, preferably 25 wt.-% or more of the carboxylic acid, based on the total weight of the aqueous solution. Further, the temperature of the aqueous solution obtained may be such that the solution has about the same temperature as the alcohol-containing process stream to be distilled in step (a) of the present method, so that it can be contacted with said process stream without the need for prior heating or cooling it.202200227 8

[0041] The concentration of the carboxylic acid or an anhydride thereof in the aqueous solution used in step (a) preferably may be at least 0.1 mol / L, more preferably at least 1.0 mol / L, still more preferably at least 2.5 mol / L, even more preferably at least 3.0 mol / L, and still even more preferably at least 3.5 mol / L. In particular, the concentration of the carboxylic acid or an anhydride thereof in the aqueous solution used in step (a) preferably may be of from 0.1 to 10 mol / L, more preferably of from 1.0 mol / L to 9.0 mol / L, still more preferably of from 2.5 mol / L to 8.0 mol / L, even more preferably of from 3.0 mol / L to 7.5 mol / L, still even more preferably of from 3.5 mol / L to 7.0 mol / L. As generally known in the art, the solubility depends of the temperature, and a person skilled in the art knows to readily select a suitable temperature of the aqueous solution to provide a solution having a desired concentration of the carboxylic acid or anhydride thereof.

[0042] By adding the carboxylic acid or an anhydride thereof the apparent pH of the process stream in step (a) may be adjusted by to be equal to or below 7.5 and preferably to be in the range of from 2.0 to 7.5, more preferably of from 2.2 to 7.5 or of from 2.25 to 7.5, even more preferably of from 2.5 to 7.5, still even more preferably of from 2.75 to 7.5, still even more preferably of from 2.75 to 7.25, still even more preferably of from 2.75 to 6.75, still even more preferably of from 2.75 to 5.25, and still even more preferably of from 2.75 to 4.25. Preferably, the apparent pH of the process stream is adjusted prior to subjecting the stream to distillation according to step (a) of the present method.

[0043] As stated above, by controlling the apparent pH of the process stream to be distilled the present method allows to directly control the amount of nitrogen-containing compounds in the overhead product containing the alcohol which is obtained after distillation. Further, using the present method it is possible to reduce the amount of nitrogen-containing compound in the overhead product stream to less than 30 ppm without having to add large amounts of a highly corrosive inorganic acid, such as sulfuric acid, thus avoiding the need for particular corrosion resistant materials in the apparatus and special means for disposing sulfate containing salt waste and / or waste water and flue-gas desulfurization.

[0044] Using the present method, it is possible to control the overhead product obtained in step (b) to contain equal to or less than 70 ppm nitrogen-containing compounds, preferably equal to or less than 50 ppm, more preferably equal to or less than 30 ppm, even more preferably equal to or less than 20 ppm, and still even more preferably equal to or less than 10 ppm, based in the total weight of the overhead product. Lower contents of nitrogen-containing compounds also increase the time on stream for downstream ion exchangers which may optionally be used in further steps, such as step (d) described below, for refining the recovered methanol, e.g., by removing remaining nitrogen-containing compounds and / or aldehydes. In particular, using the present method, it is possible to control the overhead product obtained in step (b) to contain of from 0.1 to 70 ppm nitrogen-containing compounds, preferably of from 0.2 to 50 ppm, more preferably of from 0.3 to 30 ppm, even more preferably of from 0.4 to 20 ppm, and still even more preferably of from 0.5 to 10 ppm, based on the total weight of the overhead product.

[0045] The method further comprises a step (c) of incinerating at least a part of the bottoms product. As stated above, a partial stream of the bottoms product may be used to prepare an aqueous solution of the202200227 9

[0046] carboxylic acid or an anhydride thereof, said part then not being incinerated. In addition, the method may further comprise separating at least a part of a salt of the nitrogen-containing compound from the liquid phase of the bottoms product obtained in step (b) before at least a part of the bottoms product, in particular the separated salt-enriched phase, is incinerated according to step (c).

[0047] To separate salts, including those formed from the acid or an anhydride thereof and the nitrogencontaining compound removed from the alcohol containing process stream in the present method, any conventional technique and means known in the art for separating salts from industrial waste water can be used, including, but not limited to, distillation, spray evaporation, centrifugation, cyclonic separation, conventional filtration using strainers and / or filters, membrane separation including electrodialysis and nanofiltration, ion exchange separation, eutectic freezing, chemical processes, such as calcination, as well as combination thereof. Preferably, salt is separated in the present method using a falling film evaporator cascade and optionally further a so-called salt loop, which is a forced circulation evaporator.

[0048] A falling film evaporator is an evaporation device which represents a particular type of heat exchanger, wherein the fluid to be evaporated flows downwards by gravity as a continuous film, typically inside vertical tubes where it creates a film along the tube walls which is evaporated due to heat transfer from a heating medium placed on the outside of the tubes, such as condensing steam. Since evaporation takes place at very low mean temperature differences between the heating medium and liquid to be evaporated, falling film evaporators are particularly suitable for heat recovery in multi-stage processes, such as in a cascade of several falling film evaporators. Herein, the cascade or series of falling film evaporators may preferably be operated at progressively lower pressures, so that there is a resulting decrease in boiling temperature in successive stages. This allows the heating medium (condensing steam) as well as the vapor released from the evaporation of the liquid in one evaporator to be used as the heating medium for the next evaporator. The remaining liquid from one evaporator is then fed as more concentrated liquid feed to the next evaporator.

[0049] If desired, for further concentrating the liquid, e.g., to accelerate crystallization of the salt to be separated, a salt loop or forced circulation evaporator may be used. Herein, an impeller is mounted in a central unit of the evaporator, or a circulating pump is mounted outside an evaporator body, allowing maintenance of a good heat transfer rate even in highly concentrated, i.e., viscous liquids.

[0050] The liquid phase obtained after such salt separation comprises water and residual contaminants and may be subjected to a waste-water treatment before being disposed. Methods for treating industrial wastewater are known in the art. Preferably, the present method may comprise an anaerobic treatment followed by an aerobic treatment. Such combined processes are described, for instance, by Y. J. Chan et al. in Chemical Engineering Journal 2009, 155, 1-18.

[0051] Incinerators for incinerating salt-containing liquids are known in the art and are described, for instance, in Section 9.3.6 on pages 234 to 236 of The John Zink Hamworthy Combustion Handbook, Volume 3: Applications, 2ndEd., Baukal Jr., C.E. (Ed.), CRC Press, 2014. The incinerator usually has a vertical202200227 10

[0052] design with burner(s) mounted on the top and firing downward to prevent molten salt from accumulating on the refractory of the incinerator. The salt flows down the incinerator and can be discharged upon exit of the incinerator. The flue (exhaust) gas from the incineration may be further treated before being vented to the atmosphere, but due to the absence of sulfur-containing salts in the bottoms product of the present method, no flue-gas desulfurization is required.

[0053] The present method may further comprise a step of (d) contacting the overhead product containing the alcohol depleted of nitrogen-containing compounds obtained in step (b) with an ion exchange material.

[0054] For instance, the overhead product containing the alcohol depleted of nitrogen-containing compounds obtained in step (b) may be passed through a bed of an acidic ion exchanger. Both strongly acidic ion exchangers and weakly acidic ion exchangers may be used. Preferred are strongly acidic ion exchangers containing SO3H groups and weakly acidic ion exchangers containing COOH groups. The acidic ion exchanger is preferably based on an organic polymer, such as crosslinked polystyrene, or an organic inorganic hybrid polymer, such as a polysiloxane. The acidic ion exchanger may be a gel type solid or a macroporous solid. Preferably, two ion exchanger beds are arranged in parallel to allow regeneration of the ion exchanger without interrupting the methanol treatment.

[0055] Prior to the addition of the carboxylic acid or an anhydride thereof the alcohol-containing process stream may comprise alcohol and water in a weight ratio of from 70:30 to 90:10, preferably of from 75:25 to 85:15, and most preferably of 80:20. After completing step(s) (b) and (d), if present, the alcohol-containing process stream may comprise less than 5 wt.% water, based on the total weight of the process stream.

[0056] Preferably, the alcohol from which the nitrogen-containing compounds are removed by the present method may be methanol.

[0057] The present method may be part of a process for the continuous epoxidation of olefins, said process comprising the steps of: (i) reacting an olefin with hydrogen peroxide in an epoxidation reaction in the presence of a titanium-containing zeolite catalyst, at least one nitrogen-containing compound and an alcohol as a solvent to form a reaction product stream; (ii) recovering a stream containing the alcohol from the reaction product stream of step (i); (iii) hydrogenating the stream obtained in step (ii); (iv) removing nitrogen-containing compounds from the hydrogenated stream obtained in step (iii) according to the method comprising steps (a), (b) and optionally further (d) described above, to obtain an alcohol stream depleted of nitrogen-containing organic compounds; and (v) recycling at least part of the alcohol stream obtained in step (iv) to the epoxidation reaction of step (i).

[0058] Herein step (ii) of recovering the alcohol-containing stream from the reaction product stream of step (i) may comprise (1) separating at least a part of the unreacted olefin from the reaction product stream, followed by (2) separating the remainder of the reaction product stream by distillation into a first bottoms product stream containing alcohol, water, by-products, and unreacted peroxide and a first overhead202200227 11

[0059] product stream containing alkylene oxide and alcohol, (3) separating the alkylene oxide from the first overhead product stream by means of reactive distillation using one or more nitrogen-containing compounds to obtain a second overhead product stream containing purified alkylene oxide and a second bottoms product stream containing water, alcohol, and nitrogen-containing compounds, and (4) combining the first and second bottoms product stream.

[0060] The olefin preferably may be ethylene in which case the alkylene oxide is ethylene oxide, or propylene in which the alkylene oxide is propylene oxide, or butylene, i.e., 1-butylene, cis- or trans-2-butylene, isobutylene, or a mixture thereof, in which case the alkylene oxide is a butylene oxide. More preferably the olefin may be propylene and the alkylene oxide is propylene oxide.

[0061] Except for the particular method for removing nitrogen-containing compounds from an alcohol-containing process stream of the present disclosure, several aspects of such a method are described, in

[0062] EP 4166545 A1 and WO 2017 / 089079 A1 , the figures of the latter also illustrating details of a plant for carrying out the steps of such a method.

[0063] In step (i) of such as method, an olefin, e.g., propylene, is reacted with hydrogen peroxide in the presence of an alcohol solvent, such as methanol, a titanium-containing zeolite epoxidation catalyst and at least one nitrogen containing compound, such as ammonia.

[0064] The reaction is typically carried out using a molar excess of the olefin, such as propylene, to hydrogen peroxide, such as at a molar ratio of from 1.1:1 to 30:1, preferably of from 2:1 to 10:1 and more preferably of from 3:1 to 5:1. The olefin may be used in an excess sufficient to maintain an additional liquid phase rich in olefin throughout step (i). The olefin may contain the corresponding alkane, e.g., propylene may comprise propane, preferably with a molar ratio of alkane to olefin of from 0.001 to 0.20 and more preferably of from 0.08 to 0.12.

[0065] Hydrogen peroxide can be used as an aqueous solution, preferably containing from 30 to 75 wt.-% hydrogen peroxide and most preferably from 40 to 70 wt.-%. The aqueous hydrogen peroxide solution may preferably be made by an anthraquinone process.

[0066] The alcohol solvent, e.g., methanol, used can be of technical grade, a solvent stream recovered in the work-up of the epoxidation reaction mixture or a mixture of both. The solvent may comprise other solvents in minor amounts, e.g., minor amounts of ethanol if methanol is used as the solvent, with the amount of such other solvents preferably being less than 2 wt.-%. The solvent may also comprise water, preferably from 2 to 13 wt.-% water. The solvent is preferably used in the epoxidation in a weight ratio of 0.5 to 20 relative to the combined weight of water and hydrogen peroxide.

[0067] The titanium-containing zeolite epoxidation catalyst used in step (i) preferably may comprise titanium atoms on silicon lattice positions. Preferably, a titanium silicalite catalyst may be used, preferably with an MFI or MEL crystal structure. Most preferably a titanium silicalite-1 catalyst with MFI structure as known202200227 12

[0068] from EP 0 100 119 A1 , is used. The titanium silicalite catalyst is preferably employed as a shaped catalyst in the form of granules, extrudates or shaped bodies. For the shaping process the catalyst may contain 1 to 99% of a binder or carrier material, all binders and carrier materials being suitable that do not react with hydrogen peroxide or the alkylene oxide under the reaction conditions employed for the epoxidation, silica being preferred as binder. Extrudates with a diameter of 1 to 5 mm are preferably used as shaped catalysts. The amount of catalyst employed may be varied within wide limits and is preferably chosen so that a hydrogen peroxide consumption of more than 90%, preferably more than 95%, is achieved within 1 minute to 5 hours under the employed epoxidation reaction conditions.

[0069] The epoxidation reaction of step (i) may preferably be carried out at a temperature of 20 to 80°C, more preferably at 25 to 60°C. The epoxidation reaction may preferably be carried out at a pressure that is higher than the vapor pressure of olefin at the reaction temperature in order to maintain the olefin dissolved in the solvent or present as a separate liquid phase. The pressure in step (i) is preferably from 1.9 to 5.0 MPa, more preferably 2.1 to 3.6 MPa and most preferably 2.4 to 2.8 MPa. Using an excess of olefin at a high pressure provides high reaction rate and hydrogen peroxide conversion and at the same time high selectivity for the alkylene oxide.

[0070] The epoxidation reaction is carried out in the presence of a nitrogen-containing compound, such as ammonia, to improve epoxide selectivity as described in EP 0230949 A2. Ammonia may be used in an amount of from 100 to 3000 mg / kg of hydrogen peroxide, preferably in an amount of from 250 to 2000 mg / kg of hydrogen peroxide. The nitrogen-containing compound may preferably be added to a feed stream to step (i).

[0071] The epoxidation reaction of step (i) is preferably carried out continuously, more preferably in a fixed bed reactor by passing a mixture comprising the olefin, hydrogen peroxide and solvent over a fixed bed comprising a shaped titanium zeolite catalyst. The fixed bed reactor is preferably a tube bundle reactor and the catalyst fixed bed is arranged inside the reactor tubes. The fixed bed reactor is preferably equipped with cooling means and cooled with a liquid cooling medium. The temperature profile along the length of the catalyst fixed bed is preferably adjusted to keep the reaction temperature along 70 to 98%, preferably along 80 to 95%, of the length of the catalyst fixed bed within a range of less than 5 °C, preferably within a range of from 0.5 to 3 °C. The temperature of the cooling medium fed to the cooling means is preferably adjusted to a value 3 to 13 °C lower than the maximum temperature in the catalyst fixed bed. The epoxidation reaction mixture is preferably passed through the catalyst bed in down flow mode, preferably with a superficial velocity from 1 to 100 m / h, more preferably 5 to 50 m / h, most preferred 5 to 30 m / h. The superficial velocity is defined as the ratio of volume flow rate / cross section of the catalyst bed. Additionally, it is preferred to pass the reaction mixture through the catalyst bed with a liquid hourly space velocity (LHSV) from 1 to 20 h1, preferably 1.3 to 15 h-1. It is particularly preferred to maintain the catalyst bed in a trickle bed state during the epoxidation reaction. Suitable conditions for maintaining the trickle bed state during the epoxidation reaction are disclosed in WO 02 / 085873 A1 on page 8 line 23 to page 9 line 15. The epoxidation reaction is most preferably carried out with a catalyst fixed bed maintained in a trickle bed state at a pressure close to the vapor pressure of propylene at the202200227 13

[0072] reaction temperature, using an excess of olefin that provides a reaction mixture comprising two liquid phases, a solvent rich phase and an olefin rich liquid phase. Two or more fixed bed reactors may be operated in parallel or in series in order to be able to operate the epoxidation process continuously when regenerating the epoxidation catalyst.

[0073] In order to recover a stream containing the alcohol from the reaction product stream of step (i), in step (ii) of the method, all or a part of the non-reacted olefin may be separated from the reaction mixture of step (i) to provide an olefin depleted reaction mixture. Non-reacted olefin may be separated from the reaction mixture of step (i) by any method known from the prior art. Preferably, non-reacted olefin is separated from the reaction mixture of step (i) by a pressure reduction (step (ii-1)). Olefin vapor formed by the pressure reduction is preferably recompressed and cooled to recover the olefin by condensation. The pressure reduction is preferably carried out in at least two stages with corresponding stages of recompression as described in WO 2017 / 089079 A1 for propylene. The compressed olefin vapor is preferably fed to an olefin distillation column and separated into an overhead product comprising nonreacted olefin and a bottoms product containing compounds having a boiling point higher than the olefin, such as the alkylene oxide and methanol solvent. The overhead product comprising non-reacted olefin can be recycled to the epoxidation reaction. The alcohol-containing bottoms product can be combined with the olefin depleted reaction mixture remaining after the pressure reduction.

[0074] The olefin depleted reaction mixture obtained in step (ii-1) may then be subjected to a distillation in a distillation column which provides an overhead product stream comprising alkylene oxide and alcohol and a bottoms product stream comprising alcohol and water (step (ii-2)). In industrial context, such a distillation is usually performed continuously. The distillation column preferably has from 5 to 20 theoretical separation stages in the stripping section and preferably has less than 3 theoretical separation stages in a rectifying section. The distillation column is preferably operated without reflux and preferably without a rectifying section to minimize the residence time of propylene oxide in the distillation column. The distillation column is preferably operated at a pressure of from 0.16 to 0.3 MPa. The distillation column is preferably operated to provide an overhead product comprising from 20 to 60 % of the alcohol contained in the olefin depleted reaction mixture.

[0075] In a further step (step (ii-3)), the alkylene oxide may then be separated from this overhead product stream of step (ii-2), preferably by one or more distillations which are preferably carried out continuously.

[0076] Preferably, an extractive distillation in an extractive distillation column may be employed. The extractive distillation uses an aqueous extraction solvent to provide purified propylene oxide as an overhead product and a bottoms product comprising water and methanol. Additionally, a reactive compound containing at least one unsubstituted NH2 group and capable of reacting with a component having a carbonyl group, such as acetaldehyde, propionaldehyde and / or formaldehyde, which may form as by-products in the epoxidation reaction, at the conditions of said extractive distillation to form compounds with a boiling point higher than that of alkylene oxide is added to the extractive distillation either with a feed stream to the extractive distillation column or directly to the extractive distillation column at a feed point above a feed202200227 14

[0077] point for the crude alkylene oxide. Preferably, a crude alkylene oxide comprising from 15 to 97 wt.-% alkylene oxide and from 2 to 84 wt.-% alcohol is fed to the extractive distillation column.

[0078] The extractive distillation column may be a tray column containing discrete trays such as sieve trays or bubble cap trays. The extractive distillation column may also be a packed column and both random packings as well as structured packings, such as metal gauze packings may be used. The extractive distillation column may also combine sections with discrete trays and sections with packings. The extractive distillation column will in general also comprise at least one overhead condenser and at least one column reboiler. The extractive distillation column preferably has at least two feed points, a feed point A for feeding the crude propylene oxide in the middle section of the extractive distillation column and a feed point B for feeding aqueous extraction solvent located above feed point A. The feed points define three sections of the extractive distillation column, a stripping section between the column bottoms and feed point A, an extraction section between feed point A and feed point B and a rectifying section between feed point B and the top of the extractive distillation column. Preferably a distillation column is used that has a separation efficiency of 10 to 30 theoretical stages in the stripping section, a separation efficiency of 15 to 40 theoretical stages in the extraction section and a separation efficiency of 20 to 60 theoretical stages in the rectifying section, i.e. , feed point B is preferably located from 15 to 40 theoretical separation stages above feed point A and from 20 to 60 theoretical separation stages below the top of the extractive distillation column.

[0079] The aqueous extraction solvent preferably comprises more than 80 wt.-% water, more preferably more than 90 wt.-% water. Preferably, the aqueous extraction solvent comprises no further solvent in addition to water. The extractive distillation is preferably operated continuously and the extraction solvent is fed to the extractive distillation column at a rate providing a mass ratio of the extraction solvent relative to the amount of alcohol contained in the crude alkylene oxide feed of from 0.01 to 1, more preferably from 0.03 to 0.2. The use of such an amount of aqueous extraction solvent provides effective extraction of the alcohol and an alkylene oxide product with a low content of the alcohol and at the same time avoids hydrolysis of alkylene oxide in the extractive distillation column.

[0080] The reactive compound is preferably fed to the extractive distillation column admixed with the extraction solvent. The amount of the reactive compound fed to the distillation column is preferably chosen so that the molar ratio of the reactive compound relative to the compound having a carbonyl group is in the range of from 0.25 to 10. Preferably, said range extends from 0.5 to 10, more preferably from 3 to 8. The precise amount of the molar ratio depends on the number of actually reacting NH2 groups of the reactive compound: A reactive compound having several NH2 group needs to be added in a lower ratio to the carbonyl containing compound than a reactive component having only one NH2 group. However, even if the reactive compound bears several NH2 groups, not in every case every NH2 group reacts with the carbonyl component. Thus, the number of reacting NH2 groups governs the molar ratio of the reactive compound to the carbonyl containing compound. The use of such an amount of a reactive compound provides effective conversion of carbonyl compounds to high boiling compounds and provides an alkylene oxide product with a low content of carbonyl compounds, such as acetaldehyde. At the same time, by-202200227 15

[0081] product formation by reactions of the reactive compound with alkylene oxide can be kept at a low level. In a preferred embodiment, the reactive compound has a structure R1-Y-NH2, where Y is NR2, R1and R2independently of one another are hydrogen, an alkyl group or an aryl group, wherein the alkyl group or the aryl group may be optionally substituted with 1 , 2 or 3 NH2 group(s), or Y is absent. It is also possible that the reactive compound has a structure R1-(NR2)-Y, where Y is a hydroxyl group and R1and R2independently of one another are hydrogen, an alkyl group or an aryl group, wherein the alkyl group or the aryl group may be optionally substituted with 1 , 2 or 3 NH2 group(s). Salts of these reactive compounds with a protonated NH2 group may be used as well. Preferred compounds of structure R1-Y-NH2 are hydrazine, hydrazine monohydrate, and hydrazinium salts. Preferred compounds of structure R1-(NR2)-Y are hydroxylamine and hydroxylammonium salts. In an alternative preferred embodiment, the reactive compound is a diaminoalkane having from 2 to 6 carbon atoms, preferably 1 ,2-diaminoethane, 1 ,2-diaminopropane or 1 ,3-diaminopropane and most preferably 1 ,2-diaminoethane. The amount of reactive compound fed to the distillation column is then preferably chosen so that the molar ratio of the reactive compound relative to the carbonyl compounds such as acetaldehyde is in the range of from 0.5 to 10, more preferably from 3 to 8.

[0082] In a preferred embodiment, in step (ii-3) olefin may be stripped from the overhead product stream of step (ii-2) prior to the extractive distillation as described in the preceding paragraphs. Preferably, alkylene oxide and alcohol are condensed from the overhead product stream of step (ii-2) and olefin is stripped from the resulting condensate in an olefin stripping column which provides a bottom stream comprising alkylene oxide and methanol which is essentially free of olefin. The stripped olefin is preferably combined with the olefin vapor formed by the above-described pressure reduction step and is then recompressed.

[0083] Further, the overhead product stream of step (ii-2), optionally after stripping propylene, may be mixed with an aqueous alkaline solution and the resulting mixture may be reacted for 1 to 200 minutes, preferably for 1 to 60 minutes, at a temperature of from 20 to 100°C before the mixture is fed to the extractive distillation. The aqueous alkaline solution is preferably an aqueous solution of sodium hydroxide, potassium hydroxide, or sodium carbonate. Most preferred are aqueous sodium hydroxide solutions containing from 0.1 to 56 wt.-% sodium hydroxide. The amount of the aqueous alkaline solution is preferably chosen so that the molar ratio of hydroxide ions introduced with the aqueous alkaline solution relative to the amount of methyl formate contained in the crude alkylene oxide is in the range from 1.1 to 4. Reacting the overhead product stream of step (ii-2) with an aqueous alkaline solution converts methyl formate contained in the stream by hydrolyzing it to methanol and formate. It is also possible that the overhead product stream of step (ii-2), optionally after stripping of propylene, may be mixed with an aqueous alkaline solution in the extractive distillation column. The purified alkylene oxide obtained with these embodiments of the invention has a reduced content of methyl formate. Preferably the amount of aqueous alkaline solution is chosen to obtain a purified alkylene oxide having a content of methyl formate of less than 100 ppm by weight.

[0084] In step (iii) the bottoms product stream of step (ii) is preferably subjected to a catalytic hydrogenation before it is distilled for recovering methanol. The catalytic hydrogenation is preferably carried out at a202200227 16

[0085] hydrogen partial pressure of from 0.5 to 30 MPa, more preferably of from 1 to 25 MPa and most preferably of from 1 to 5 MPa. The temperature is preferably in the range of from 80 to 180 °C, more preferably from 90 to 150 °C. The catalytic hydrogenation is carried out in the presence of a hydrogenation catalyst, preferably a heterogeneous hydrogenation catalyst. Raney nickel and Raney cobalt may be used as hydrogenation catalyst. Preferably, a supported metal catalyst comprising one or more of metals selected from the group consisting of Ru, Rh, Pd, Pt, Ag, Ir, Fe, Cu, Ni and Co on a catalyst support is used. The metal is preferably platinum, palladium, iridium, ruthenium or nickel and most preferably ruthenium or nickel. The catalyst support can be any solid which is inert and does not deteriorate under the hydrogenation conditions. Suitable as catalyst support are activated carbon, the oxides SiO2, TiO2 , ZrO2 and AI2O3, and mixed oxides comprising at least two of silicon, aluminum, titanium and zirconium. SiO2, AI2O3 and mixed oxides of silicon and aluminum are preferably used as the catalyst support for the supported metal catalyst. The catalyst support is preferably shaped as spheres, pellets, tablets, granules or extrudates. Preferred are extrudates with a diameter of from 0.5 mm to 5 mm, especially from 1 mm to 3 mm, and a length of from 1 mm to 10 mm. The supported metal catalyst preferably comprises from 0.01 to 60 wt.% metal. Supported noble metal catalysts preferably comprise from 0.1 to 5 % metal. Supported nickel and cobalt catalysts preferably comprise from 10 to 60 % metal. The supported metal catalyst may be prepared by methods known in the art, preferably by impregnating the catalyst support with a metal salt followed by reducing the metal salt to the catalytically active metal. Suitable supported metal catalysts are commercially available, for example from Clariant under the NISAT® trade name and from Evonik Industries under the Octolyst® trade name. The catalytic hydrogenation converts unreacted hydrogen peroxide to water and the by-product peroxides to diol, e.g., in case of the olefin being propylene 1-hydroperoxy-2-propanol and 2-hydroperoxy-1 -propanol formed in step (i) to 1 ,2-propanediol and prevents by-product formation by peroxide decomposition in subsequent work-up stages. The catalytic hydrogenation is carried out to a conversion of hydrogen peroxide that provides a hydrogenated solvent mixture containing less than 0.1 wt.-% hydrogen peroxide. The hydrogenation also converts aldehyde and ketone by-products, such as acetaldehyde, to the corresponding alcohols, with the degree of conversion depending on the catalyst and the reaction conditions used. The conversion of the hydrogenation of acetaldehyde to ethanol can be adjusted by varying the reaction time and the hydrogen partial pressure and the temperature used in the catalytic hydrogenation and is preferably adjusted to provide a hydrogenated solvent mixture comprising from 1 to 1000 mg / kg of acetaldehyde.

[0086] If the method comprises an extractive distillation according to step (ii-3), in a further step (ii-4) the bottoms product of the extractive distillation is preferably combined with the bottoms product stream of step (ii-2) prior carrying out step (iv). Likewise, in this case the bottoms product of the extractive distillation according to step (ii-3) is preferably combined with the bottoms product stream of step (ii-2) prior to subjecting the bottoms product stream of step (ii-2) to a catalytic hydrogenation according to step (iii) of the present method. Reaction products resulting from the reaction of aldehydes and ketones with the reactive compound containing an NH2 group will then be hydrogenated, i.e., oximes and hydrazones will be hydrogenated with hydrogenolysis of the oxygen-nitrogen bond or the nitrogen-nitrogen bond and imines will be hydrogenated to the corresponding amines.202200227 17

[0087] In step (iv) the nitrogen-containing compounds are then removed from the hydrogenated stream obtained in step (iii) using the method comprising steps (a) and b) and optionally c) and / or d) described in detail above to obtain an alcohol stream depleted of nitrogen-containing compounds.

[0088] In a further step (v) at least a part of the alcohol stream obtained in step (iv) is then recycled to the epoxidation reaction of step (i).

[0089] An apparatus for carrying out the present method for removing nitrogen-containing compounds from an alcohol-containing process stream comprises:

[0090] (i) a reactor or a series of reactors fluidly coupled to each other, the reactor or series of reactors being adapted to generate or process an alcohol-containing process stream which further comprises water and at least one nitrogen-containing compound, (ii) at least one distillation column fluidly coupled to the reactor or series of fluidly coupled reactors, the distillation column being adapted to allow separately withdrawing an overhead product containing the alcohol depleted of the at least one nitrogen-containing compound and a bottoms product of water containing the at least one nitrogen-containing compound; (iii) at least one inlet coupled to the distillation column itself or to a line fluidly coupled to the distillation column adapted to feed the carboxylic acid; and (iv) at least one incinerator adapted to incinerate at least a part of the bottoms product.

[0091] When the inlet adapted to feed the carboxylic acid (iii) is coupled to a line fluidly coupled to the distillation column, downstream of said inlet but prior to the distillation column said line may further comprise one or more units for measuring the apparent pH of the alcohol-containing process stream and optionally controlling said apparent pH by adjusting the feed of the carboxylic acid to the process stream depending on the measured pH.

[0092] In addition, the apparatus may further comprise (iv) at least one a salt separation unit arranged between an outlet of the distillation column for withdrawing the bottoms product and the incinerator, wherein the salt separation unit is adapted to separate salts from the bottoms product, wherein said salts can be incinerated in the incinerator.

[0093] The apparatus may further comprise a waste-water treatment unit (v) to remove remaining contaminants from the bottoms product after salt has been removed in the salt separation unit (iv).

[0094] Suitable incinerators, salt separation units and waste-water treatment units are described above.

[0095] The following paragraphs summarize some aspects of the present disclosure.

[0096] A first aspect relates to a method for simultaneously removing nitrogen-containing compounds and water from an alcohol-containing process stream and disposing the water contaminated with nitrogencontaining compounds, wherein the process stream comprises less than 0.1 wt.% of hydrogen peroxide, based on the total weight of the process stream, the method comprising the steps of:202200227 18

[0097] (a) distilling the process stream containing the alcohol and water in the presence of a carboxylic acid or an anhydride thereof to obtain an overhead product containing the alcohol depleted of nitrogencontaining compounds and a bottoms product of process water containing nitrogen-containing compounds; and

[0098] (b) separately withdrawing the overhead product containing the alcohol depleted of nitrogencontaining compounds and the bottoms product; and

[0099] (c) incinerating at least a part of the bottoms product.

[0100] A second aspect relates to the method of the first aspect, wherein the alcohol-containing process stream comprises of from 0 to less than 0.1 wt.% of hydrogen peroxide.

[0101] A third aspect relates to the method of the second aspect, wherein the alcohol-containing process stream comprises of from 0.0001 to 0.099 wt.% of hydrogen peroxide.

[0102] A fourth aspect relates to the method of any of the preceding aspects, wherein the carboxylic acid is a polycarboxylic acid.

[0103] A fifth aspect relates to the method of any of the preceding aspects, wherein the carboxylic acid is selected from the group consisting of acetic acid, propionic acid, citric acid, oxalic acid, malonic acid and maleic acid.

[0104] A sixth aspect relates to the method of the fifth aspect, wherein the carboxylic acid is maleic acid.

[0105] A seventh aspect relates to the method of the any of the preceding aspects, wherein the carboxylic acid or an anhydride thereof is added to the alcohol-containing process stream before the process stream is subjected to distillation in step (a) and / or during said distillation step.

[0106] An eighth aspect relates to the method of the any of the preceding aspects, wherein an aqueous solution of the carboxylic acid or an anhydride thereof is added to the alcohol-containing process stream.

[0107] A ninth aspect relates to the method of the eighth aspect, wherein the aqueous solution is added in a separate step (a-0) before the alcohol-containing process stream is subjected to distillation in step (a) and upon addition the aqueous solution of the carboxylic acid or an anhydride thereof and the alcohol-containing process stream each independently have a temperature above 50 °C.

[0108] A tenth aspect relates to the method of the ninth aspect, wherein upon addition the aqueous solution of the carboxylic acid or an anhydride thereof and the alcohol-containing process stream each independently have a temperature in the range of from 60 to 120 °C.202200227 19

[0109] An eleventh aspect relates to the method of the tenth aspect, wherein upon addition the aqueous solution of the carboxylic acid or an anhydride thereof and the alcohol-containing process stream each independently have a temperature being in the range of from 70 to 110 °C.

[0110] A twelfth aspect relates to the method of the eleventh aspect, wherein upon addition the aqueous solution of the carboxylic acid or an anhydride thereof and the alcohol-containing process stream each independently have a temperature being in the range of from 80 to 100 °C.

[0111] A thirteenth aspect relates to the method of the twelfth aspect, wherein upon addition the aqueous solution of the carboxylic acid or an anhydride thereof and the alcohol-containing process stream both have a temperature being in the range of from 85 to 95 °C.

[0112] A fourteenth aspect relates to the method of any of the eighth to thirteenth aspect, wherein the aqueous solution of the carboxylic acid or an anhydride thereof is prepared by dissolving the carboxylic acid or an anhydride thereof in water, aqueous methanol, or a part of the bottoms product obtained in step (b)

[0113] A fifteenth aspect relates to the method of the fourteenth aspect, wherein the aqueous solution of the carboxylic acid or an anhydride thereof is prepared by dissolving maleic anhydride in a part of the bottoms product having a temperature in the range of from 30 to 90 °C.

[0114] A sixteenth aspect relates to the method of the fifteenth aspect, wherein the aqueous solution of the carboxylic acid or an anhydride thereof is prepared by dissolving maleic anhydride in a part of the bottoms product having a temperature in the range of from 40 to 80 °C.

[0115] A seventeenth aspect relates to the method of the sixteenth aspect, wherein the aqueous solution of the carboxylic acid or an anhydride thereof is prepared by dissolving maleic anhydride in a part of the process water having a temperature in the range of from 50 to 70 °C.

[0116] An eighteenth aspect relates to the method of the seventeenth aspect, wherein the aqueous solution of the carboxylic acid or an anhydride thereof is prepared by dissolving maleic anhydride in a part of the bottoms product having a temperature in the range of from 55 to 65 °C.

[0117] A nineteenth aspect relates to the method of any of the eighth to eighteenth aspects, wherein the concentration of the carboxylic acid or an anhydride thereof in the aqueous solution is at least 0.1 mol / L.

[0118] A twentieth aspect relates to the method of the nineteenth aspect, wherein the concentration of the carboxylic acid or an anhydride thereof in the aqueous solution is at least 1.0 mol / L.

[0119] A twenty-first aspect relates to the method of the twentieth aspect, wherein the concentration of the carboxylic acid or an anhydride thereof in the aqueous solution is at least 2.5 mol / L.202200227 20

[0120] A twenty-second aspect relates to the method of the twenty-first aspect, wherein the concentration of the carboxylic acid or an anhydride thereof in the aqueous solution is at least 3.0 mol / L.

[0121] A twenty-third aspect relates to the method of the twenty-second aspect, wherein the concentration of the carboxylic acid or an anhydride thereof in the aqueous solution is at least 3.5 mol / L.

[0122] A twenty-fourth aspect relates to the method of the nineteenth aspect, wherein the concentration of the carboxylic acid or an anhydride thereof in the aqueous solution is in the range of from 0.1 to 10 mol / L.

[0123] A twenty-fifth aspect relates to the method of the twenty-fourth aspect, wherein the concentration of the carboxylic acid or an anhydride thereof in the aqueous solution is in the range of from 1.0 to 9.0 mol / L.

[0124] A twenty-sixth aspect relates to the method of the twenty-fifth aspect, wherein the concentration of the carboxylic acid or an anhydride thereof in the aqueous solution is in the range of from 2.5 to 8.0 mol / L.

[0125] A twenty-seventh aspect relates to the method of the twenty-sixth aspect, wherein the concentration of the carboxylic acid or an anhydride thereof in the aqueous solution is in the range of from 3.0 to 7.5 mol / L.

[0126] A twenty-eighth aspect relates to the method of the twenty-seventh aspect, wherein the concentration of the carboxylic acid or an anhydride thereof in the aqueous solution is in the range of from 3.5 to 7.0 mol / L.

[0127] A twenty-ninth aspect relates to the method of any of the preceding aspects, wherein in step (a) the process stream is distilled at an apparent pH equal to or below 7.5.

[0128] A thirtieth aspect relates to the method of the twenty-ninth aspect, wherein the apparent pH of the process stream is adjusted by adding the carboxylic acid or an anhydride thereof to be equal to or below 7.5 prior to subjecting the stream to distillation according to step (a).

[0129] A thirty-first aspect relates to the method of the thirtieth aspect, wherein the apparent pH of the process stream is adjusted by adding the carboxylic acid or an anhydride thereof to be in the range of from 2.0 to 7.5 prior to subjecting the stream to distillation according to step (a).

[0130] A thirty-second aspect relates to the method of the thirty-first aspect, wherein the apparent pH of the process stream is adjusted by adding the carboxylic acid or an anhydride thereof to be in the range of from 2.2 to 7.5 prior to subjecting the stream to distillation according to step (a).

[0131] A thirty-third aspect relates to the method of the thirty-second aspect, wherein the apparent pH of the process stream is adjusted by adding the carboxylic acid or an anhydride thereof to be in the range of from 2.25 to 7.5 prior to subjecting the stream to distillation according to step (a).202200227 21

[0132] A thirty-fourth aspect relates to the method of the thirty-third aspect, wherein the apparent pH of the process streams is adjusted by adding the carboxylic acid or an anhydride thereof to be in the range of from 2.5 to 7.5 prior to subjecting the stream to distillation according to step (a).

[0133] A thirty-fifth aspect relates to the method of the thirty-fourth aspect, wherein the apparent pH of the process streams is adjusted by adding the carboxylic acid or an anhydride thereof to be in the range of from 2.75 to 7.5 prior to subjecting the stream to distillation according to step (a).

[0134] A thirty-sixth aspect relates to the method of the thirty-fifth aspect, wherein the apparent pH of the process streams is adjusted by adding the carboxylic acid or an anhydride thereof to be in the range of from 2.75 to 7.25 prior to subjecting the stream to distillation according to step (a).

[0135] A thirty-seventh aspect relates to the method of the thirty-sixth aspect, wherein the apparent pH of the process streams is adjusted by adding the carboxylic acid or an anhydride thereof to be in the range of from 2.75 to 6.75 prior to subjecting the stream to distillation according to step (a).

[0136] A thirty-eighth aspect relates to the method of the thirty-seventh aspect, wherein the apparent pH of the process streams is adjusted by adding the carboxylic acid or an anhydride thereof to be in the range of from 2.75 to 5.25 prior to subjecting the stream to distillation according to step (a).

[0137] A thirty-ninth aspect relates to the method of the thirty-eighth aspect, wherein the apparent pH of the process streams is adjusted by adding the carboxylic acid or an anhydride thereof to be in the range of from 2.75 to 4.25 prior to subjecting the stream to distillation according to step (a).

[0138] A fortieth aspect relates to the method of any of the preceding aspects, wherein the overhead product obtained in step (b) contains equal to or less than 70 ppm nitrogen-containing compounds.

[0139] A forty-first aspect relates to the method of the fortieth aspect, wherein the overhead product obtained in step (b) contains equal to or less than 50 ppm nitrogen-containing compounds.

[0140] A forty-second aspect relates to the method of the forty-first aspect, wherein the overhead product obtained in step (b) contains equal to or less than 30 ppm nitrogen-containing compounds.

[0141] A forty-third aspect relates to the method of the forty-second aspect, wherein the overhead product obtained in step (b) contains equal to or less than 20 ppm nitrogen-containing compounds.

[0142] A forty-fourth aspect relates to the method of the forty-third aspect, wherein the overhead product obtained in step (b) contains less 10 ppm nitrogen-containing compounds.

[0143] A forty-fifth aspect relates to the method of the fortieth aspect, wherein the overhead product obtained in step (b) contains of from 0.1 to 70 ppm nitrogen-containing compounds.202200227 22

[0144] A forty-sixth aspect relates to the method of the forty-fifth aspect, wherein the overhead product obtained in step (b) contains of from 0.2 to 50 ppm nitrogen-containing compounds.

[0145] A forty-seventh aspect relates to the method of the forty-sixth aspect, wherein the overhead product obtained in step (b) contains of from 0.3 to 30 ppm nitrogen-containing compounds.

[0146] A forty-eighth aspect relates to the method of the forty-seventh aspect, wherein the overhead product obtained in step (b) contains of from 0.4 to 20 ppm nitrogen-containing compounds.

[0147] A forty-ninth aspect relates to the method of the forty-eighth aspect, wherein the overhead product obtained in step (b) contains of from 0.5 to 10 ppm nitrogen-containing compounds.

[0148] A fiftieth aspect relates to the method of any of the preceding aspects,

[0149] wherein prior to the addition of the carboxylic acid or an anhydride thereof the alcohol-containing process stream comprises alcohol and water in a weight ratio of from 70:30 to 90:10.

[0150] A fifty-first aspect relates to the method of the fiftieth aspect,

[0151] wherein prior to the addition of the carboxylic acid or an anhydride thereof the alcohol-containing process stream comprises alcohol and water in a weight ratio of from 75:25 to 85:15.

[0152] A fifty-second aspect relates to the method of the fifty-first aspect, wherein prior to the addition of the carboxylic acid or an anhydride thereof the alcohol-containing process stream comprises alcohol and water in a weight ratio of 80:20.

[0153] A fifty-third aspect relates to the method of any of the preceding aspects, wherein the alcohol is methanol.

[0154] A fifty-fourth aspect relates to the method of any of the preceding aspects, further comprising the step of (d) contacting the overhead product containing the alcohol depleted of nitrogen-containing compounds obtained in step (b) with an ion exchange material.

[0155] A fifty-fifth aspect relates to the method of any of the preceding aspects, wherein at least a part of a salt of the nitrogen-containing compound is separated from the liquid phase of the bottoms product obtained in step (b) before at least a part of the bottoms product is incinerated according to step (c).

[0156] A fifty-sixth aspect relates to the method of any of the preceding aspects, wherein the distillation of step (a) comprises two subsequent distillation stages wherein the alcohol is withdrawn as the overhead product in both stages.

[0157] A fifty-seventh aspect relates to the method of the fifty-sixth aspect, wherein one stage is operated at a higher pressure than the other stage to heat the other stage.202200227 23

[0158] A fifty-eighth aspect relates to the method of the fifty-seventh aspect, wherein the second stage is operated at a higher pressure than the first stage, and overhead product vapor from the second stage is used for heating the bottom's evaporator of the first stage.

[0159] A fifty-ninth aspect relates to the method of any of the preceding aspects, wherein the method is part of a process for the continuous epoxidation of olefins, said process comprising the steps of:

[0160] (i) reacting an olefin with hydrogen peroxide in an epoxidation reaction in the presence of a titanium containing zeolite catalyst, at least one nitrogen-containing compound and an alcohol as a solvent to form a reaction product stream;

[0161] (ii) recovering a stream containing the alcohol from the reaction product stream of step (i);

[0162] (iii) hydrogenating the stream obtained in step (ii);

[0163] (iv) removing nitrogen-containing compounds from the hydrogenated stream obtained in step (iii) according to the method of any of the preceding claims to obtain an alcohol stream depleted of nitrogencontaining organic compounds; and

[0164] (v) recycling at least part of the alcohol stream obtained in step (iv) to the epoxidation reaction of step (i).

[0165] A sixtieth aspect relates to the method of the fifty-ninth aspect, wherein step (ii) of recovering the alcohol-containing stream from the reaction product stream of step (i) comprises (1) separating at least a part of the unreacted olefin from the reaction product stream, followed by (2) separating the remainder of the reaction product stream by distillation into a first bottoms product stream containing alcohol, water, byproducts, and unreacted peroxide and a first overhead product stream containing alkylene oxide and alcohol, (3) separating the alkylene oxide from the first overhead product stream by means of reactive distillation using one or more nitrogen-containing compounds to obtain a second overhead product stream containing purified alkylene oxide and a second bottoms product stream containing water, alcohol, and nitrogen-containing compounds, and (4) combining the first and second bottoms product stream.

[0166] A sixty-first aspect relates to the method of any of the preceding aspects, wherein the olefin is ethylene and the alkylene oxide is ethylene oxide.

[0167] A sixty-second aspect relates to the method of any of the first to sixtieth aspects, wherein the olefin is propylene and the alkylene oxide is propylene oxide.

[0168] A sixty-third aspect relates to the method of any of the first to sixtieth aspects, wherein the olefin is butylene and the alkylene oxide is a butylene oxide.

[0169] A sixty-fourth aspect relates to the method of any of the preceding aspects, wherein the method is a continuously operated method.202200227 24

[0170] A sixty-fifth aspect relates to the method of any of the preceding aspects, wherein the apparent pH of the process stream to be distilled is used as a control variable to control the amount of nitrogen-containing compounds in the overhead product containing the alcohol obtained after distillation in step (a).

[0171] A sixty-sixth aspect relates to an apparatus for carrying out the method of any of the preceding aspects, the apparatus comprising:

[0172] (i) a reactor or a series of reactors fluidly coupled to each other, the reactor or series of reactors being adapted to generate or process an alcohol-containing process stream which further comprises water and at least one nitrogen-containing compound,

[0173] (ii) at least one distillation column fluidly coupled to the reactor or series of fluidly coupled reactors, the distillation column being adapted to allow separately withdrawing an overhead product containing the alcohol depleted of the at least one nitrogen-containing compound and a bottoms product of water containing the at least one nitrogen-containing compound;

[0174] (iii) at least one inlet coupled to the distillation column itself or to a line fluidly coupled to the distillation column adapted to feed the carboxylic acid; and

[0175] (iv) at least one incinerator adapted to incinerate at least a part of the bottoms product.

[0176] A sixty-seventh aspect relates to the apparatus of the sixty-sixth aspect, wherein the inlet adapted to feed the carboxylic acid (iii) is coupled to a line fluidly coupled to the distillation column and wherein downstream of said inlet but prior to the distillation column said line further comprises one or more units for measuring the apparent pH of the alcohol-containing process stream and optionally controlling said apparent pH by adjusting the feed of the carboxylic acid to the process stream depending on the measured pH.

[0177] A sixty-eighth aspect relates to the apparatus of the sixty-sixth or sixty-seventh aspect, further comprising (iv) at least one a salt separation unit arranged between an outlet of the distillation column for withdrawing the bottoms product and the incinerator, wherein the salt separation unit is adapted to separate salts from the bottoms product, wherein said salts can be incinerated in the incinerator.

[0178] A sixty-ninth aspect relates to the apparatus of the sixty-eighth aspect, further comprising (v) a wastewater treatment unit to remove remaining contaminants from the bottoms product after salt has been removed in the salt separation unit (iv).

[0179] EXAMPLES

[0180] Examples 1 to 8: Epoxidation of propylene and recovery of methanol from the obtained reaction mixture using different acids for removing nitrogen-containing compounds

[0181] Propylene was epoxidized in a pilot plant reactor in a reaction tube equipped with a cooling jacket. A catalyst fixed bed of extruded titanium silicalite catalyst was arranged in the reaction tube. A mixture comprising 40 wt.-% propylene, 7.7 wt.-% hydrogen peroxide, 3.3 wt.-% water, 49 wt.-% methanol and202200227 25

[0182] 1000 ppm ammonia (96 g / h as 1 wt.-% aqueous solution) was fed to the top of the reaction tube and passed through the catalyst fixed bed in trickle mode. The pressure in the reactor was kept at 2.6 MPa (gauge) by introducing nitrogen. The temperature in the reactor was kept essentially constant at a temperature in the range of from 20 to 60 °C, adjusting the temperature during the epoxidation reaction to maintain an essentially constant conversion of hydrogen peroxide of >97%.

[0183] The reaction mixture exiting the reactor was depressurized to a pressure of 0.25 MPa and the depressurized liquid was fed to a distillation in a pre-separation column to provide an overhead product comprising propylene oxide, methanol and residual propylene, and a bottoms product comprising methanol, water and non-reacted hydrogen peroxide. Propylene oxide and methanol were condensed from the overhead product of the pre-separation column and propylene was stripped from the resulting condensate in a propylene stripping column to provide a crude propylene oxide as a bottom stream comprising propylene oxide and methanol.

[0184] 20 g / h of a 5 wt.-% aqueous solution of sodium hydroxide was added to the crude propylene oxide.

[0185] The crude propylene oxide was then fed to stage 42 (counted from top) of an extractive distillation column having a separation efficiency of 60 theoretical stages at a rate of 3870 g / h. 115 g / h of a 0.5 wt.-% aqueous solution of hydrazine hydrate was fed to stage 15 (counted from top) of the extractive distillation column. A purified propylene oxide was obtained as overhead product of the column.

[0186] The bottoms product of the extractive distillation column was combined with the bottom product obtained from the pre-separation column and subjected to continuous hydrogenation in a trickle-bed reactor. The reactor was filled with an extruded nickel hydrogenation catalyst comprising 50 wt.-% nickel. The hydrogenation was performed at 90 °C and 1.5 MPa at a hydrogen flow rate of 30 NL / h.

[0187] The hydrogenated solvent mixture was depressurized and an aqueous solution of one of the acids shown in Table 1 was added in each Example before the hydrogenated solvent mixture comprising methanol and water in a weight ratio of 80:20 was fed to stage 14 (counted from top) of a first methanol distillation column having 20 theoretical stages operated continuously at 0.5 MPa. Each acid was added in an amount of 1.17 mmol / h per 1 mmol / h total nitrogen feed (calculated as mmol / h ammonia + 2 x mmol / h hydrazine). The hydrogenated solvent mixture was fed at a rate of 7 kg / h. 2 kg / h of a first recovered methanol stream containing 96 wt.-% methanol and 4 wt.-% water was obtained as overhead product. The bottoms product was fed to a second methanol distillation column having 30 theoretical stages operated continuously at 1.0 MPa. 4.5 kg / h of a second recovered methanol stream containing 96 wt.-% methanol and 4 wt.-% water was obtained as overhead product. The apparent pH in the bottoms product of the second methanol distillation was determined using a pH electrode (Mettler-Toledo lnPro4800i (Mettler Toledo, Columbus, Ohio, USA) with offline regeneration and calibration) and is reported in Table 1. The alkalinity being a measure of the total amount of nitrogen present in the recovered methanol was determined by potentiometric titration of the combined overhead product of the first and second distillation column, using 0.01 M HCI (aq).202200227 26

[0188] Table 1 :

[0189] Example Acid pKa1 pKa2 pKa3 Apparent pH bottoms Alkalinity [ppm N]

[0190] product 2ndMeOH in overhead

[0191] column product

[0192] 1 Maleic Acid 1.9 6.5 3.5 7

[0193] 2 Citric acid 3.13 4.76 6.4 3.7 54

[0194] 3 Oxalic Acid 1.23 4.19 4.1 77

[0195] 4 Malonic acid 2.83 5.69 4.9 77

[0196] 5 Succinic acid 4.16 5.61 4.2 85

[0197] 6 Lactic acid 3.9 4.0 91

[0198] 7 Acetic acid 4.76 4.7 112

[0199] 8 Propionic acid 4.87 4.9 121

[0200]

[0201] Without adding any acid, the apparent pH in the bottoms product of the second methanol distillation is basic, and the alkalinity in the combined overhead products of the first and second distillation column is more than 200 ppm.

[0202] It can be seen that carboxylic acids, in particular polycarboxylic acids, can be used to reduce the amount of nitrogen-containing compounds in recovered methanol without the need for a pH in the bottoms product of the methanol distillation column of 2 or lower, when compared to sulfuric acid as depicted in Figure 1.

[0203] Example 9: Varying the amount of sulfuric acid and maleic acid

[0204] Following the general protocol given for Examples 1 to 8, the amount of maleic acid added to the hydrogenated solvent mixture before distilling off methanol was varied in the range of from 0.47 to 1.32 mmol acid per 1 mmol total nitrogen feed, calculated as mmol ammonia + 2 x mmol hydrazine, as described above. A comparative example was conducted using sulfuric acid in the range of from 0.43 to 0.72 mmol acid per 1 mmol total nitrogen feed, calculated as mmol ammonia + 2 x mmol hydrazine. The amount of nitrogen in the methanol recovered after distillation was determined with a nitrogen analyzer by combustion of the sample and measurement of formed NO by chemiluminescence according to DIN EN 12260:2003-12. The apparent pH of the feed to the first methanol distillation column and of the bottoms product of the second methanol distillation column was measured using a pH electrode as described above. The dependency of the amount of nitrogen in the methanol recovered after distillation on the apparent pH of the bottoms product of the second methanol distillation column and of the feed to the first methanol distillation column is shown in Figures 1 and 2, respectively.

[0205] It can be seen from Figure 1 that for sulfuric acid there is a linear dependency of the amount of nitrogen in the methanol recovered after distillation on the apparent pH of the bottoms product of the second methanol distillation. In contrast, for maleic acid the apparent pH of the bottoms product of the second202200227 27

[0206] methanol distillation remains more or less constant regardless of the amount of nitrogen in the covered methanol. This shows that the apparent pH of the bottoms product of the methanol distillation column cannot be used as a control variable for controlling the amount of nitrogen-containing compounds in the recovered methanol when using a carboxylic acid such as maleic acid. On the other hand, it can be seen from Figure 2 that for maleic acid there is an exponential dependency of the amount of nitrogen in the methanol recovered after distillation on the apparent pH of the feed to the first methanol distillation column according to the formula shown below:

[0207] In(TlV)

[0208] pH(CA)' =

[0209] D

[0210] wherein pH(CA) refers to the apparent pH of the feed containing the carboxylic acid to the first distillation column for distilling off the alcohol, In(TN) refers to the natural logarithm of the total nitrogen in the recovered alcohol determined as described above and A and B are coefficients which depend on the actual process, including the carboxylic acid used, the amount of water in the feed, and the distillation apparatus used. For the distillation of a feed comprising methanol and water in a weight ratio of 80:20 and maleic acid as described above and shown in Figure 2, A is 0.4291 and B is 0.6445.

[0211] Such an exponential dependency is not observed in case of sulfuric acid. The above shows that the apparent pH of the feed to the first methanol distillation column can be used as a control variable for controlling the amount of nitrogen-containing compounds in the recovered methanol when using a carboxylic acid such as maleic acid.

[0212] Example 10: Thermal treatment of a bottoms product obtained using sulfuric acid

[0213] 35 g of a sample of a bottoms product obtained from a comparative example using sulfuric acid as described above, having a theoretical maximum content of sulfuric acid of 150 mg, was concentrated by distillation. The remaining water was removed by from the sample by placing the sample on a heating plate overnight. The residue obtained was slowly heated in a muffle furnace to 500 °C, and then to 1000 °C for 2 h. The sample was allowed to cool to room temperature (23 °C) in a desiccator before being weighted. Only 50.9 mg residue was obtained (average of a determination in duplicate), which is clearly less than the expected amount of sulfates, and even less than the amount of sulfuric acid used. This indicates that a decomposition of the sulfates takes place during thermal treatment which makes flue gas desulfurization necessary when wishing to incinerate the bottoms product of a process using sulfuric acid.

Claims

202200227 28CLAIMS1. A method for simultaneously removing water and nitrogen-containing compounds from an alcohol-containing process stream and disposing the water contaminated with nitrogen-containing compounds, wherein the process stream comprises less than 0.1 wt.-% of hydrogen peroxide, based on the total weight of the process stream, the method comprising the steps of:(a) distilling the process stream containing the alcohol and water in the presence of a carboxylic acid or an anhydride thereof to obtain an overhead product containing the alcohol depleted of nitrogen-containing compounds and a bottoms product of water containing nitrogen-containing compounds;(b) separately withdrawing the overhead product containing the alcohol depleted of nitrogencontaining compounds and the bottoms product; and(c) incinerating at least a part of the bottoms product.

2. The method of claim 1 , wherein the carboxylic acid is a polycarboxylic acid.

3. The method of claim 1 or 2, wherein the carboxylic acid is selected from the group consisting of acetic acid, propionic acid, citric acid, oxalic acid, malonic acid and maleic acid, and preferably is maleic acid.

4. The method of any of the preceding claims, wherein the carboxylic acid or an anhydride thereof is added to the alcohol-containing process stream before the process stream is subjected to distillation in step (a) and / or during said distillation step.

5. The method of any of the preceding claims, wherein an aqueous solution of the carboxylic acid or an anhydride thereof is added to the alcohol-containing process stream.

6. The method of claim 5, wherein the aqueous solution is added in a separate step (a-0) before the alcohol-containing process stream is subjected to distillation in step (a) and upon addition the aqueous solution of a carboxylic acid or an anhydride thereof and the alcohol-containing process stream each independently have a temperature above 50 °C, preferably being in the range of from 60 to 120 °C, more preferably of from 70 to 110 °C, even more preferably of from 80 to 100 °C, and wherein most preferably the aqueous solution of a carboxylic acid or an anhydride thereof and the alcohol-containing process stream both have a temperature being in the range of from 85 to 95 °C.

7. The method of claim 5 or 6, wherein(a) the aqueous solution of a carboxylic acid or an anhydride thereof is prepared by dissolving the carboxylic acid or an anhydride thereof in water, aqueous methanol, or a part of the bottoms product obtained in step (b), preferably by dissolving maleic anhydride in a part of the202200227 29bottoms product having a temperature in the range of from 30 to 90 °C, more preferably of from 40 to 80 °C, even more preferably of from 50 to 70 °C, and still even more preferably of from 55 to 65 °C; and / or(b) the concentration of the carboxylic acid or an anhydride thereof in the aqueous solution is at least 0.1 mol / L, preferably at least 1.0 mol / L, more preferably at least 2.5 mol / L, still more preferably at least 3.0 mol / L, and even more preferably at least 3.5 mol / L; and / or(c) prior to the addition of the aqueous solution of a carboxylic acid or an anhydride thereof the alcohol-containing process stream comprises alcohol and water in a weight ratio of from 70:30 to 90:10, preferably of from 75:25 to 85:15, and most preferably of 80:20.

8. The method of any of the preceding claims, wherein the alcohol is methanol.

9. The method of any of the preceding claims, wherein the distillation of step (a) comprises two subsequent distillation stages wherein the alcohol is withdrawn as the overhead product in both stages, wherein preferably one stage is operated at a higher pressure than the other stage, wherein more preferably the second stage is operated at a higher pressure than the first stage, and overhead product vapor from the second stage is used for heating the bottom's evaporator of the first stage.

10. The method of any of the preceding claims, wherein the method is part of a process for the continuous epoxidation of olefins, said process comprising the steps of:(i) reacting an olefin with hydrogen peroxide in an epoxidation reaction in the presence of a titanium-containing zeolite catalyst, at least one nitrogen-containing compound and an alcohol as a solvent to form a reaction product stream;(ii) recovering a stream containing the alcohol from the reaction product stream of step (i); (iii) hydrogenating the stream obtained in step (ii);(iv) removing nitrogen-containing compounds from the hydrogenated stream obtained in step (iii) according to the method of any of the preceding claims to obtain an alcohol stream depleted of nitrogen-containing organic compounds; and(v) recycling at least part of the alcohol stream obtained in step (iv) to the epoxidation reaction step (i).

11. The method of claim 10, wherein step (ii) of recovering the alcohol-containing stream from the reaction product stream of step (i) comprises (1) separating at least a part of the unreacted olefin from the reaction product stream, followed by (2) separating the remainder of the reaction product stream by distillation into a first bottoms product stream containing alcohol, water, by-products, and unreacted peroxide and a first overhead product stream containing alkylene oxide and alcohol, (3) separating the alkylene oxide from the first overhead product stream by means of reactive distillation using one or more nitrogen-containing compounds to obtain a second202200227 30overhead product stream containing purified alkylene oxide and a second bottoms product stream containing water, alcohol, and nitrogen-containing compounds, and (4) combining the first and second bottoms product stream.

12. The method of claims 10 or 11 , wherein the olefin is ethylene and the alkylene oxide is ethylene oxide, or the olefin is propylene and the alkylene oxide is propylene oxide, or the olefin is a butylene and the alkylene oxide is a butylene oxide, wherein preferably the olefin is propylene and the alkylene oxide is propylene oxide.

13. An apparatus for carrying out the method of any of the preceding claims, the apparatus comprising:(i) a reactor or a series of reactors fluidly coupled to each other, the reactor or series of reactors being adapted to generate or process an alcohol-containing process stream which further comprises water and at least one nitrogen-containing compound,(ii) at least one distillation column fluidly coupled to the reactor or series of fluidly coupled reactors, the distillation column being adapted to allow separately withdrawing an overhead product containing the alcohol depleted of the at least one nitrogen-containing compound and a bottoms product of water containing the at least one nitrogen-containing compound;(iii) at least one inlet coupled to the distillation column itself or to a line fluidly coupled to the distillation column adapted to feed the carboxylic acid; and(iv) at least one incinerator adapted to incinerate at least a part of the bottoms product.

14. The apparatus of claim 13, wherein the inlet adapted to feed the carboxylic acid (iii) is coupled to a line fluidly coupled to the distillation column and wherein downstream of said inlet but prior to the distillation column said line further comprises one or more units for measuring the apparent pH of the alcohol-containing process stream and optionally controlling said apparent pH by adjusting the feed of the carboxylic acid to the process stream depending on the measured pH.

15. The apparatus of claim 13 or 14, further comprising a salt separation unit arranged between an outlet of the distillation column for withdrawing the bottoms product and the incinerator, wherein the salt separation unit is adapted to separate salts from the bottoms product, wherein said salts can be incinerated in the incinerator.

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