Process for purifying a reaction mixture obtained by an alkoxylation reaction

Abstract

A reaction mixture (1) is obtained by an alkoxylation reaction of a nitrogenous compound selected from ammonia and amines, with an alkylene oxide. The reaction mixture (1) contains nitrogenous alkoxylation products and unreacted nitrogenous compound. A process for purifying the reaction mixture (1) comprises the steps of (1) introducing the reaction mixture (1) into a distillation tower (101), (2) providing thermal energy to the distillation tower (101) via a bottom reboiler (102) heated by medium pressure pressurized steam (2), (3) providing additional thermal energy to the distillation tower (101) by heating and partially evaporating a liquid in a reboiler (103) heated by low pressure pressurized steam (3), and directing the heated, partially evaporated liquid (4) to the distillation tower (101), wherein the liquid is the reaction mixture (1) to be introduced into the distillation tower (101) and / or a liquid fraction (5) withdrawn from the distillation tower (101) via a sidedraw (104), (4) withdrawing an unreacted nitrogenous compound stream (6) at the top (105) of the distillation tower (101), and (5) withdrawing an alkoxylation products stream (7) at the bottom (106) of the distillation tower (101). The process can use low temperature level heat to contribute to the heating of the reaction mixture in the distillation tower.

Description

[0001] Process for purifying a reaction mixture obtained by an alkoxylation reaction

[0002] The present invention relates to a process for purifying a reaction mixture obtained by an alkoxylation reaction.

[0003] Alkanolamines and alkylalkanolamines are a versatile, chemically multifunctional group of chemicals used across a range of applications, including CO2capture; polyurethane catalysts; paints and coatings; fabric softeners; water treatment and paper manufacturing. Their large-scale production commonly involves alkoxylation of nitrogenous compounds such ammonia or amines with alkylene oxides such as ethylene oxide and propylene oxide.

[0004] Alkoxylation reactions of nitrogenous compounds such as ammonia or amines with alkylene oxides are processes well known in the art and, for example, described in EP 2 651 861 Bl.

[0005] M. Frauenkron et al., “Ethanolamines and Propanolamines”, in: Ullmann’s Encyclopedia of Industrial Chemistry, DOI: 10.1002 / 14356007. al0_001 describes a batchwise production of alkanolamines. For this purpose, a reaction kettle is filled with amine and water (as a catalyst), heated to the reaction temperature, followed by metering of ethylene oxide. After maintaining the reaction temperature for some time to ensure that the product discharged from the reactor is free of ethylene oxide, the reaction mixture is separated by fractional distillation. Unconverted amine and water are removed as the first fraction and recycled to the subsequent batch. Pure alkanolamines are obtained by distillation under reduced pressure.

[0006] CN 214553403 U describes producing methylethanolamine: Ethylene oxide is mixed and reacted with methylamine to obtain a mixture of methylethanolamine and methyldiethanolamine. The reaction mixture is then sent to a first distillation tower to remove unreacted methylamine. The removed methylamine is recycled. The remaining mixture after methylamine removal is sent to a second distillation tower where methylethanolamine is removed at the top. The bottom stream is sent to a third distillation tower where methyldiethanolamine is obtained.

[0007] WO 2009 / 147524 Al describes a method for producing a mono(lower alkyl)mono- alkanolamine by reacting a mono(lower al kyl)a mine (AA) and an alkylene oxide (AO). The method comprises feeding a mono(lower alkyl)amine (AA) and an alkylene oxide (AO) into a reaction tower to cause a reaction in a gas-liquid mixed phase state within the reaction tower, and separating a resultant reaction product in a liquid state from the reaction tower. The reaction tower can be a reaction distillation tower.

[0008] As outlined, the alkoxylation reactions yield reaction mixtures comprising unreacted nitrogenous compound, potential side product(s), alkoxylation product, and, if used as catalyst, water. For obtaining the alkoxylation product in essentially pure form, the alkoxylation reaction mixture has to be purified, e.g. by a series of distillations. For separation of compounds by distillation, sufficiently high temperatures are required which may, for example, be provided by electrical heating or medium pressure pressurized steam.

[0009] Energy for vaporizers may be supplied from a plant steam grid which draws heat from firing of fossil resources or from combustion of side-products that do warrant recovery and which are incinerated for their calorific value. Steam grids typically distribute steam at different pressure levels and, hence, temperature levels, to the consumers, most often including medium pressure pressurized steam and low pressure pressurized steam.

[0010] However, fossil resources are expensive and their firing is associated with inherent CO2emissions which should be reduced or avoided as far as possible, especially in view of climate change issues.

[0011] It is therefore an object of the present invention to provide a destil lative separation process for purifying a reaction mixture obtained by an alkoxylation reaction of a nitrogenous compound with an alkylene oxide in a manner that is more efficient and economical than heretofore known.

[0012] This object is solved by a process for purifying a reaction mixture obtained by an alkoxylation reaction of a nitrogenous compound selected from ammonia and amines, with an alkylene oxide, the reaction mixture containing nitrogenous alkoxylation products and unreacted nitrogenous compound. The process comprises the steps of

[0013] (1) introducing the reaction mixture into a distillation tower,

[0014] (2) providing thermal energy to the distillation tower via a bottom reboiler heated by medium pressure pressurized steam, (3) providing additional thermal energy to the distillation tower by heating and partially evaporating a liquid in a reboiler heated by low pressure pressurized steam, and directing the heated, partially evaporated liquid to the distillation tower, wherein the liquid is the reaction mixture to be introduced into the distillation tower and / or a liquid fraction withdrawn from the distillation tower via a sidedraw,

[0015] (4) withdrawing an unreacted nitrogenous compound stream at the top of the distillation tower, and

[0016] (5) withdrawing an alkoxylation products stream at the bottom of the distillation tower.

[0017] The process can use low temperature level heat to contribute to the heating of the reaction mixture in the distillation tower. It has been found that the inventive process for purifying a reaction mixture obtained by an alkoxylation reaction does not negatively impact the product quality when providing additional thermal energy to the distillation tower by heating and partially evaporating a liquid in a reboiler heated by low pressure pressurized steam, and directing the heated, partially evaporated liquid to the distillation tower. In other words, the inventive process allows for providing at least a part of the thermal energy to the distillation tower by low pressure pressurized steam. This is advantageous in comparison to state-of-the art processes in which the total amount of thermal energy is provided to the distillation tower by medium pressure pressurized steam. As a result, the inventive process may be operated at reduced energy consumption which allows for reducing CO2emissions. Furthermore, the process configuration additionally enables low capital costs. Even further, the inventive process is a process in which the concentration of unreacted nitrogenous compound (starting material) in the bottom product is very low, and in which the concentration of side products and / or alkoxylation products in the top product is economically adjustable.

[0018] All ratios specified herein with regard to particular streams (e.g. liquid streams, vapor streams, feed streams, bottom streams, top streams) are based on weight.

[0019] The process of the invention involves purifying a reaction mixture obtained by an alkoxylation reaction. Herein, alkoxylation reactions are chemical reactions which involve the addition of an alkylene oxide to a nitrogenous compound selected from ammonia and primary or secondary amines. The resulting alkoxylation reaction mixture to be purified at least contains nitrogenous alkoxylation products and unreacted nitrogenous compound, and may additionally contain alkoxylation side products and / or water, if used as catalyst in the alkoxylation reaction.

[0020] The alkoxylation reaction is known as such and may be carried out as described in the literature.

[0021] The nitrogenous compound is selected from ammonia and amines. The amine may be a compound of formula (I)

[0022] HN^R2

[0023] (I) wherein

[0024] R1is selected from H, Cj-Cg alkyl, and Cj-Cg hydroxyalkyl, and

[0025] R2is selected from Cj-Cg alkyl, and Cj-Cg hydroxyalkyl.

[0026] Preferably, R1is selected from H, C / -C4 alkyl, and C / -C4 hydroxyalkyl, and

[0027] R2is selected from C / -C4 alkyl.

[0028] For example, the amine may be selected from methylamine and dimethylamine.

[0029] The alkylene oxide may be selected from ethylene oxide and propylene oxide.

[0030] For example, reactions of ammonia as nitrogenous compound with ethylene oxide as alkylene oxide may yield the following nitrogenous alkoxylation product(s):

[0031] - monoethanolamine (MEOA)

[0032] - diethanolamine (DEOA)

[0033] - triethanolamine (TEOA)

[0034] For example, reactions of primary amines as nitrogenous compound with ethylene oxide as alkylene oxide may yield the following nitrogenous alkoxylation product(s):

[0035] - monomethylethanolamine (MMEOA, N-methylethanolamine) from methylamine as nitrogenous compound

[0036] For example, reactions of secondary amines as nitrogenous compound with ethylene oxide as alkylene oxide may yield the following nitrogenous alkoxylation product(s):

[0037] - dimethylethanolamine (DMEOA, N,N-dimethylethanolamine) from dimethylamine as nitrogenous compound

[0038] - methyldiethanolamine (MDEOA, N-methyldiethanolamine) from MMEOA as nitrogenous compound

[0039] - diethylethanolamine (DEEOA, N,N-diethylethanolamine) from diethylamine as nitrogenous compound

[0040] For example, reactions of ammonia as nitrogenous compound with propylene oxide as alkylene oxide may yield the following nitrogenous alkoxylation product(s):

[0041] - monoisopropanolamine (MIPOA)

[0042] - diisopropanolamine (DIPOA)

[0043] - triisopropanolamine (TIPOA)

[0044] The nitrogenous compound is commonly employed in a 1 to 20-fold molar excess, preferably a 1.5 to 5-fold molar excess, based on the alkylene oxide. The surplus of nitrogenous compound ensures a complete conversion of alkylene oxide and advantageously minimizes side product formation by, e.g., multiple alkylene oxide addition.

[0045] Suitable reaction conditions for the alkoxylation reaction(s) employ pressures in the range of from 10 to 30 bar absolute, preferably about 25 bar absolute, and reaction temperatures in the range of from 50 to 140 ° C, preferably about 100 ° C. For example, the reaction temperature may be provided to the mixture of nitrogenous compound and alkylene oxide by heating said mixture in a shell and tube heat exchanger using low pressure pressurized steam. The low pressure pressurized steam may have a pressure in the range of from 2 to 8 bar gauge, preferably about 4 bar gauge.

[0046] The alkoxylation reaction may be catalyzed by the addition of a proton donor compound, such as an organic acid or mineral acid. Water is a particularly preferred catalyst. Suitably amounts of water are in the range of 20 to 30 wt.-%, preferably about 25 wt.-%, based on the total amount of the alkoxylation reaction mixture.

[0047] The output mixture of these reactions, herein referred to as “reaction mixture”, predominantly comprises one or more nitrogenous alkoxylation product(s), i.e. one or more (a I ky I) a I ka n ol a m i n e(s) , and unreacted nitrogenous compound, i.e. ammonia or amine, and may additionally comprise side products and / or water, if used as catalyst. Said reaction mixture is suitably decompressed and outgassed, and subsequently sent to step (1) of the process of the invention.

[0048] Suitably, the reaction mixture comprises, based on the total weight of the reaction mixture, unreacted nitrogenous compound in the range of from 50 to 80 wt.-%, water in the range of from 10 to 30 wt.-%, and alkoxylation product(s) and alkoxylation side product(s) in the range of from 20 to 40 wt.-%.

[0049] The composition of the reaction mixture depends, of course, from the alkoxylation product that is the desired product of the reaction.

[0050] For example, for MDEOA as alkoxylation product, the reaction mixture comprises, based on the total weight of the reaction mixture, methylamine in the range of from 10 to 40 wt.-%, water in the range of from 15 to 25 wt.-%, MDEOA in the range of from 15 to 30 wt.-%, and MMEOA in the range of from 25 to 40 wt.-%.

[0051] For example, for DMEOA as alkoxylation product, the reaction mixture comprises, based on the total weight of the reaction mixture, dimethylamine in the range of from 45 to 60 wt.-%, water in the range of from 15 to 25 wt.-%, and DMEOA in the range of from 20 to 35 wt.-%.

[0052] The process of the invention for purifying the reaction mixture obtained by the alkoxylation reaction comprises an unreacted nitrogenous compound removal step, the unreacted nitrogenous compound removal step comprising five steps (1) to (5) which will be described in detail in the following.

[0053] Step (1) comprises introducing the reaction mixture into a distillation tower.

[0054] As outlined above, the alkoxylation reaction is commonly carried out at pressures in the range of from 10 to 30 bar absolute, preferably about 25 bar absolute, and the operating pressure of the distillation tower may suitably be in the range of from 3 to 6 bar absolute, for example about 4 bar absolute. Hence, introduction of the reaction mixture into the distillation tower may be accompanied by depressurization to the distillation tower pressure and partial evaporation of the reaction mixture.

[0055] Suitable configurations of distillation towers are known in the art. For example, the distillation tower may have 10 to 30, preferably 15 to 25, theoretical plates. The operating conditions of the distillation tower depends on the nature of the compounds to be separated. As the normal boiling points of the nitrogenous compound generally range between 50 ° C and negative temperatures, the distillation is suitably carried out under elevated pressure. For example, the operating pressure of the distillation tower may be in the range of from 3 to 6 bar absolute, for example about 4 bar absolute. Especially, for MDEOA or DMEOA as alkoxylation product, the operating pressure of the distillation tower may be about 4 bar absolute. Herein, the operating pressure is understood to mean the absolute pressure measured at the top of the distillation tower. The pressure in the distillation tower may be maintained by a N2-split range controller.

[0056] For example, the distillation tower may be equipped with structured packings or random packings, or may have separatory trays such as valve trays.

[0057] For example, the distillation tower may be operated at a pressure of about 4 bar absolute, and a bottom temperature in the range of from 130 to 180 ° C. For MDEOA as alkoxylation product, the distillation tower is suitably operated at a pressure of about 4 bar absolute, and a bottom temperature of about 164 ° C. For DMEOA as alkoxylation product, the distillation tower is suitably operated at a pressure of about 4 bar absolute, and a bottom temperature of about 146 ° C. These elevated temperatures may be achieved by providing thermal energy to the distillation tower via the bottom reboiler (step (2) of the inventive process), wherein the bottom reboiler is suitably heated by pressurized steam. For obtaining the desired bottom temperature in the distillation tower, the pressurized steam suitably has a temperature higher by 20 K than the desired bottom temperature of the distillation tower.

[0058] As outlined, the process of the invention involves heating a bottom reboiler by medium pressure pressurized steam, and heating a reboiler by low pressure pressurized steam. Generally, pressurized steam may be obtained form a steam network. For example, such a steam network is supplied with pressurized steam from a main boiler.

[0059] The medium pressure pressurized steam may have a pressure in the range of from 12 to 20 bar gauge, preferably about 16 bar gauge, and a temperature in the range of from 190 to 215 ° C, preferably about 205 ° C. The low pressure pressurized steam may have a pressure in the range of from 2 to 8 bar gauge, preferably about 4 bar gauge, and a temperature in the range of from 133 to 175 ° C, preferably about 151 ° C.

[0060] Thus, in order to obtain the desired bottom temperature as described above, providing thermal energy to the distillation tower via the bottom reboiler solely heated by low pressure pressurized steam is not sufficient. This is because, as outlined above, low pressure pressurized steam does not have a temperature higher by 20 K than the desired bottom temperature in order to ensure effective heat transfer. Thus, the inventive process requires providing at least a part of the thermal energy to the distillation tower via the bottom reboiler heated by medium pressure pressurized steam (i.e., step (2)).

[0061] Step (3) comprises providing additional thermal energy to the distillation tower by heating and partially evaporating a liquid in a reboiler heated by low pressure pressurized steam, and directing the heated, partially evaporated liquid to the distillation tower, wherein the liquid is the reaction mixture to be introduced into the distillation tower and / or a liquid fraction withdrawn from the distillation tower via a sidedraw.

[0062] Step (3) advantageously allows for substituting at least a part of the thermal energy provided to the distillation tower by low pressure pressurized steam instead of medium pressure pressurized steam as described in step (2). In other words, advantageously, less medium pressure pressurized steam is needed. For this purpose, two arrangements are possible:

[0063] (1) (A part of) the reaction mixture to be introduced into the distillation tower, herein referred to as “liquid”, is (pre-)heated and partially evaporated in a reboiler. The reboiler is heated by low pressure pressurized steam having a pressure as described above.

[0064] It will be appreciated that where introduction of the reaction mixture into the distillation tower is accompanied by depressurization to the distillation tower pressure, e.g. if the reaction mixture is released from the pressure prevailing in the alkoxylation reaction to the pressure prevailing in the distillation tower, the reaction mixture is partly evaporated. According to the invention, a part of the remaining liquid is evaporated in the reboiler. In this case, the reaction mixture is evaporated to a greater degree. (2) A liquid fraction is withdrawn from the distillation tower via a sidedraw, and said liquid fraction is (pre-)heated and partially evaporated in a reboiler. Again, the reboiler is heated by low pressure pressurized steam having a pressure as described above.

[0065] The liquid fraction withdrawn from the distillation tower via a sidedraw is taken at a height of from 8 to 12.

[0066] In an embodiment, directing the heated, partially evaporated liquid to the distillation tower comprises directing both a vapor phase and a liquid phase to the distillation tower. Preferably, the vapor phase of the heated, partially evaporated liquid is directed to distillation tower at a position located above the position where the liquid phase of the heated, partially evaporated liquid is directed to the distillation tower.

[0067] Suitably, 6 to 40% of the thermal energy provided to the distillation tower is provided via the reboiler heated by low pressure pressurized steam.

[0068] Suitably, in a case where methylamine is to be separated from a MDEOA containing alkoxylation reaction mixture, 7 to 36% of the thermal energy provided to the distillation tower is provided via the reboiler heated by low pressure pressurized steam.

[0069] Suitably, in a case where dimethylamine is to be separated from a DMEOA containing alkoxylation reaction mixture, 6 to 20% of the thermal energy provided to the distillation tower is provided via the reboiler heated by low pressure pressurized steam.

[0070] Step (4) comprises withdrawing an unreacted nitrogenous compound stream at the top of the distillation tower. If water is used as a catalyst, the unreacted nitrogenous compound stream may additionally comprise water. In other words, if water is used as a catalyst, at least a part of the water may be withdrawn at the top of the distillation tower together with the unreacted nitrogenous compound stream.

[0071] The unreacted nitrogenous compound stream withdrawn at the top of the distillation tower may be condensed in a condenser using cooling water to obtain the unreacted nitrogenous compound stream in liquid form. The unreacted nitrogenous compound stream may be collected in a collecting space. The collecting space may be arranged within the distillation tower or outside the distillation tower. The collecting space may be divided in a controlled manner by a fixed setting or a regulator at the top of the distillation tower. This arrangement allows for dividing the unreacted nitrogenous compound stream, e.g. in a stream to be withdrawn and a reflux stream to be sent back to the distillation tower.

[0072] In an embodiment, the process comprises recycling the unreacted nitrogenous compound stream at least partially to the alkoxylation reaction. Put otherwise, this embodiment encompasses recycling the above-mentioned withdrawn stream of unreacted nitrogenous compound stream back to the alkoxylation reaction.

[0073] Step (5) comprises withdrawing an alkoxylation products stream at the bottom of the distillation tower. The alkoxylation products stream comprises alkoxylation products and may additionally comprise alkoxylation side products, as described above. The alkoxylation products stream can be withdrawn at the bottom of the distillation tower in liquid form or in gaseous form, preferably in liquid form.

[0074] In an embodiment, the temperature of the medium pressure pressurized steam is higher than the bottom temperature by at least 20 ° C.

[0075] In an embodiment, it is envisaged to exploit the sensible heat contained in the medium pressure steam condensate. In this embodiment, the process comprises expanding the medium pressure steam condensate obtained from the bottom reboiler to obtain a low pressure pressurized steam, and heating the reboiler with the low pressure pressurized steam. For this purpose, the medium pressure steam condensate obtained from the bottom reboiler is introduced into a device suitable for expansion of a pressurized fluid and expanded. Devices suitable for expansion of pressurized fluids may be selected from flash drums. Expansion results in obtaining a low pressure pressurized steam besides a low pressure steam condensate. The low pressure steam condensate having a rather low energy content is usually not economically useful and may be expanded to ambient pressure in a further device suitable for expansion of pressurized fluids. On the other hand, the above-mentioned low pressure pressurized steam obtained from expansion carries an economically useful amount of energy as it is sufficiently heated and pressurized to act as the low pressure pressurized steam in the reboiler. Therefore, the above-mentioned low pressure pressurized steam obtained from expansion may suitably be directed to the reboiler to be used for heating the same.

[0076] This advantageously allows for further reducing or even completely avoiding the external demand of low pressure pressurized steam for heating the reboiler. As a result, the process of this embodiment is at least partially or may even be completely devoid of providing low pressure pressurized steam resulting in an even more energetically and economically favorable process.

[0077] In an embodiment, the process comprises subjecting the alkoxylation products stream to two or more distillations to remove water, and side products. Preferably, the process comprises subjecting the alkoxylation products stream to two or three distillations.

[0078] The alkoxylation reaction may either be an alkoxylation reaction (1) in which only minor amounts of (alkoxylation) side product are formed, or (2) in which an alkoxylation side product is a major component to be removed, and optionally recycled, or to be obtained as a (further) valuable compound.

[0079] For example, a case for (1) may be an alkoxylation reaction of a secondary amine such as dimethylamine and monomethylethanolamine (MMEOA) as nitrogenous compound with an alkylene oxide. In this case, the alkoxylation reaction mixture essentially comprises the alkoxylation product, unreacted secondary amine and water used as catalyst, besides minor amounts of side products (impurities) to be removed.

[0080] For example, a case for (2) may be an alkoxylation reaction of ammonia or a primary amine such as methylamine as nitrogenous compound with an alkylene oxide. In this case, the alkoxylation reaction mixture essentially comprises the alkoxylation product, alkoxylation side product(s), unreacted nitrogenous compound and water used as catalyst.

[0081] In both cases, the alkoxylation reaction mixture is first subjected to the distillation tower to remove unreacted nitrogenous compound and at least a part of the water used as catalyst, as described above. In case (1), the process additionally comprises subjecting the alkoxylation products stream comprising alkoxylation product, remaining water, and minor amounts of side products to be removed as impurities to two distillations. In case (2), the process additionally comprises subjecting the alkoxylation products stream comprising alkoxylation product, remaining water, and alkoxylation side products (in major amounts compared to step (1)) to three distillations.

[0082] In case (1), the alkoxylation products stream may be introduced into a second distillation tower to which thermal energy is provided, e.g. via a second bottom reboiler heated by medium pressure pressurized steam. The remaining water may be distilled off under a reduced pressure, withdrawn at the top of the second distillation tower and condensed in a condenser using cooling water. The obtained water may be recycled back to the alkoxylation reaction. An essentially water-free alkoxylation products stream comprising alkoxylation product and minor amounts of side products to be removed as impurities is withdrawn at the bottom of the second distillation tower. The pressures and temperatures applied in the second distillation tower depend on the nature of the produced alkoxylation product and are known to the skilled person.

[0083] Said essentially water-free alkoxylation products stream is subsequently introduced into a third distillation tower to which thermal energy is provided, e.g. via a third bottom reboiler. Low boiling side products may be distilled off under a reduced pressure, withdrawn at the top of the third distillation tower and condensed in a condenser using cooling water. High boiling side products may be withdrawn at the bottom of the third distillation tower. The purified alkoxylation product may be withdrawn via a side draw of the third distillation tower and condensed and cooled in a condenser using cooling water. The pressures and temperatures applied in the second distillation tower depend on the nature of the produced alkoxylation product and are known to the skilled person.

[0084] In case (2), i.e. in a case in which an alkoxylation side product is a major component to be removed or to be obtained as a (further) valuable compound, the process comprises subjecting the alkoxylation products stream to three distillations. Removal of remaining water in the second distillation tower and removal of impurities in the third distillation tower are carried out as described above. Additionally, a further distillation column is applied, arranged between the second distillation tower and the third distillation tower. The essentially water-free alkoxylation products stream from the first distillation tower is introduced into the further distillation tower to obtain the side product. For example, in case that methyldiethanolamine (MDEOA) is produced, the (intermediate) side product is methylmonoethanolamine (MMEOA). The pressures and temperatures applied in the further distillation tower depend on the nature of the produced alkoxylation product and are known to the skilled person.

[0085] The invention is further illustrated by the Figures and examples that follow.

[0086] Figure 1 depicts a state of the art process for purifying a reaction mixture obtained by an alkoxylation reaction.

[0087] Figure 2 depicts an embodiment of the inventive process for purifying a reaction mixture obtained by an alkoxylation reaction.

[0088] Figure 3 depicts an embodiment of the inventive process for purifying a reaction mixture obtained by an alkoxylation reaction.

[0089] Figure 4 depicts a preferred embodiment of the inventive process for purifying a reaction mixture obtained by an alkoxylation reaction.

[0090] Figure 5 depicts a preferred embodiment of the inventive process for purifying a reaction mixture obtained by an alkoxylation reaction.

[0091] Figures

[0092] Figure 1 depicts a state of the art process for purifying a reaction mixture obtained by an alkoxylation reaction. Alkoxylation reaction mixture 1 is introduced into distillation tower 101. At the top 105 of the distillation tower 101, unreacted nitrogenous compound stream 6 is withdrawn and condensed in condenser 107. The condensed unreacted nitrogenous compound stream 6 is either partly or fully withdrawn and / or recycled back into distillation tower 101. Alkoxylation products stream 7 comprising alkoxylation products, water (used as a catalyst) and potential side product(s) is withdrawn via the bottom 106 of distillation tower 101. Alkoxylation products stream 7 is either partly or fully discharged and / or introduced into bottom reboiler 102 where it is heated and introduced back into distillation tower 101 afterwards. Doing so allows for providing thermal energy to the distillation tower 101 via bottom reboiler 102. Bottom reboiler 102 is heated by medium pressure pressurized steam 2, thereby generating medium pressure steam condensate 2a.

[0093] Figure 2 depicts a process according to the invention as shown in Figure 1 with the difference that alkoxylation reaction mixture 1 is introduced into reboiler 103 (hereinafter also referred to as “auxiliary reboiler”) instead of direct introduction into distillation tower 101. Alkoxylation reaction mixture 1 (the “liquid”) is heated and partially evaporated in reboiler 103. In the process of Figure 2, the liquid is alkoxylation reaction mixture 1 to be introduced into the distillation tower 101. Reboiler 103 is heated by low pressure pressurized steam 3, thereby generating low pressure steam condensate 3a. The heated, partially evaporated liquid 4 is then directed to distillation tower 101, wherein the vapor phase 4a of the heated, partially evaporated liquid 4 is directed into distillation tower 101 at a position located above the position where the liquid phase 4b of the heated, partially evaporated liquid 4 is directed to the distillation tower 101. The process of Figure 2 allows for providing additional thermal energy to the distillation tower 101 via reboiler 103. In other words, at least a part of the thermal energy provided to the distillation tower 101 via bottom reboiler 102 heated by medium pressure pressurized steam 2 is substituted by the additional thermal energy provided via reboiler 103 heated by low pressure pressurized steam 3. As providing low pressure pressurized steam 3 is both energetically and economically more favorable, the resulting inventive process is energetically and economically more favorable, too.

[0094] Figure 3 depicts a process according to the invention as shown in Figure 1 with the difference that a liquid fraction 5 is withdrawn from the distillation tower 101 via sidedraw 104. Liquid fraction 5 (the “liquid”) is then introduced into reboiler 103 where it is heated and partially evaporated. Reboiler 103 is heated by low pressure pressurized steam 3, thereby generating low pressure steam condensate 3a. The heated, partially evaporated liquid 4 is then directed to distillation tower 101, wherein the vapor phase 4a of the heated, partially evaporated liquid 4 is directed into distillation tower 101 at a position located above sidedraw 104, and the liquid phase 4b of the heated, partially evaporated liquid 4 is directed into distillation tower 101 at a position located below sidedraw 104. The process of Figure 3 allows for providing additional thermal energy to the distillation tower 101 via reboiler 103. In other words, at least a part of the thermal energy provided to the distillation tower 101 via bottom reboiler 102 heated by medium pressure pressurized steam 2 is substituted by the additional thermal energy provided via reboiler 103 heated by low pressure pressurized steam 3. As providing low pressure pressurized steam 3 is both energetically and economically more favorable, the resulting inventive process is energetically and economically more favorable, too.

[0095] Figure 4 depicts an embodiment of the inventive process shown in Figure 2. In contrast to the process depicted in Figure 2, the medium pressure steam condensate 2a obtained from bottom reboiler 102 is introduced into flash drum 108 and expanded. As a result, low pressure pressurized steam 3 is obtained besides low pressure steam condensate 3a (whose energy content is rater low and thus usually not economically useful). The low pressure pressurized steam 3 is subsequently directed to reboiler 103 where it is used for heating the same. In addition to the advantages of the process described in Figure 2, the inventive process of Figure 4 allows for further reducing the demand of low pressure pressurized steam 3 as the low pressure pressurized steam 3 used for heating reboiler 103 at least partially and, preferably, fully originates from bottom reboiler 102 (after expansion in flash drum 108) and does therefore (at least partially) not have to be provided externally. In other words, the process described in Figure 4 is devoid of providing low pressure pressurized steam 3 which is even more energetically and economically favorable than the above-described embodiments of Figures 2 and 3. The process of Figure 4 provides the best Product Carbon Footprint (PCF).

[0096] Figure 5 depicts an embodiment of the inventive process with a combination of withdrawing a liquid fraction 5 from the distillation tower 101 via sidedraw 104 as shown in Figure 3 and obtaining low pressure pressurized steam 3 by expanding a medium pressure steam condensate 2a obtained from bottom reboiler 102 as shown in Figure 4. Reference signs remain unchanged compared to Figures 3 and 4.

[0097] Examples

[0098] Methods

[0099] For simulation calculations, BASF in-house software Chemasim was used; comparable results were obtained using commercially available software such as Aspen Plus (manufacturer: AspenTech, Burlington / Massachusetts, USA) or PRO II (Fullerton, USA). The set of parameters was based on comprehensive measurements, studies on laboratory set-ups and operating data from various plants. Example 1: Preparation of MDEOA

[0100] In example 1, a process according to Figure 2 is simulated. Methylamine as nitrogenous compound and ethylene oxide as alkylene oxide are reacted yielding methyldiethanolamine = MDEOA as alkoxylation product besides monomethylethanolamine = MMEOA as side product. The distillation tower pressure is 4 bar absolute and the bottom temperature is 164 ° C. The bottom reboiler (102 in Figure 2) is heated by medium pressure pressurized steam having a pressure of 16 bar gauge. The auxiliary reboiler (103 in Figure 2) is heated by low pressure pressurized steam having a pressure of 4 bar gauge.

[0101] In table 1, the amount of thermal energy provided to the distillation tower via the bottom reboiler is gradually reduced, while the amount of thermal energy provided to the distillation tower via the auxiliary reboiler is gradually increased, wherein the total amount of thermal energy provided to the distillation tower is kept constant (see table 1, column “ S 102 + 103”). Savings of medium pressure pressurized steam of up to 59.2% are achieved. As outlined above, providing low pressure pressurized steam requires less energy input than medium pressure pressurized steam. Thus, the process of example 1 is operated at reduced energy consumption which allows for reducing CO2emissions.

[0102] Table 1 further shows the concentration of side product MMEOA in the top product. At an auxiliary reboiler duty of 500 kW, a 10% increase of MMEOA is obtained at the top of the distillation tower. At an auxiliary reboiler duty of 800 kW, a 20% increase of MMEOA is obtained at the top of the distillation tower. This minor additional concentration of MMEOA in the top product is acceptable. Thus, the process of the invention advantageously allows for economically adjusting the concentration of alkoxylation side product (and / or alkoxylation product) removed overhead together with the amine (unreacted nitrogenous compound).

[0103] Table 1 further shows the concentration of methylamine in the bottom product. Up to an auxiliary reboiler duty of 1800 kW, the concentration of methylamine in the bottom product is reduced, at auxiliary reboiler duties above 1800 kW, similar concentrations of methylamine in the bottom product are obtained compared to a process with an auxiliary reboiler duty of 0 kW. Thus, the process of the invention advantageously allows for keeping the concentration of amine (unreacted nitrogenous compound) in the bottom product very low. In the present example, an auxiliary reboiler duty of up to 1200 kW is especially advantageous as up to 1200 kW, both the concentration of methylamine in the bottom product is reduced and the concentration of MMEOA in the top product is not excessively high.

[0104] Table 1 further shows the preferred auxiliary reboiler temperatures. The preferred auxiliary reboiler temperatures are in the range of from 90 and 130 ° C. The temperature difference ( A T) to low pressure pressurized steam having a pressure of 4 bar gauge and a temperature of 151.8 ° C is also shown in table 1.

[0105] Table 1 further shows the part of evaporated liquid, i.e. the part of the reaction mixture evaporated in the auxiliary reboiler. Without using an auxiliary reboiler, i.e. at an auxiliary reboiler duty of 0 kW, an amount of about 15 wt.-% of the liquid is evaporated. At an auxiliary reboiler duty of up to 2000 kW, an amount of the liquid in the range of from > 16 to 37 wt.-% is evaporated.

[0106] Table 1. ] Auxiliary reboiler (103 in Figure 2) [2] Savings of medium pressure pressurized steam

[0107] [3] T (low pressure pressurized steam having 4 bar gauge = 151.8 ° C) - T @ auxiliary reboiler 103 [4] Part of evaporated liquid in auxiliary reboiler 103

[0108] Example 2: Preparation of DMEOA

[0109] In example 2, an inventive process according to Figure 2 is simulated. Dimethylamine (DMA, (CH3)2NH) as nitrogenous compound and ethylene oxide as alkylene oxide are reacted yielding dimethylethanolamine = DMEOA as alkoxylation product. The distillation tower pressure is 4 bar absolute and the bottom temperature is 146 ° C. The bottom reboiler (102 in Figure 2) is heated by medium pressure pressurized steam having a pressure of 16 bar gauge. The auxiliary reboiler (103 in Figure 2) is heated by low pressure pressurized steam having a pressure of 4 bar gauge.

[0110] In table 2, the amount of thermal energy provided to the distillation tower via the bottom reboiler is gradually reduced, while the amount of thermal energy provided to the distillation tower via the auxiliary reboiler is gradually increased, wherein the total amount of thermal energy provided to the distillation tower is kept constant (see table 2, column “ S 102 + 103”). Savings of medium pressure pressurized steam of up to 51.9% are achieved. As outlined above, providing low pressure pressurized steam requires less energy input than medium pressure pressurized steam. Thus, the process of example 2 is operated at reduced energy consumption which allows for reducing CO2emissions.

[0111] Table 2 further shows the concentration of alkoxylation product DMEOA in the top product. At an auxiliary reboiler duty of 1000 kW, a 10% increase of DMEOA is obtained at the top of the distillation tower. At an auxiliary reboiler duty of 2000 kW, a 20% increase of DMEOA is obtained at the top of the distillation tower. These minor additional concentrations of DMEOA in the top product are acceptable. Thus, the process of the invention advantageously allows for economically adjusting the concentration of alkoxylation product removed overhead together with the amine (unreacted nitrogenous compound).

[0112] Table 2 further shows the concentration of dimethylamine in the bottom product. Up to an auxiliary reboiler duty of 1500 kW, the concentration of dimethylamine in the bottom product solely increases in an acceptable slight manner. Thus, the process of the invention advantageously allows for keeping the concentration of amine (unreacted nitrogenous compound) in the bottom product very low. In the present example, an auxiliary reboiler duty of up to 800 kW is especially advantageous as above 800 kW, the concentration of DMEOA in the top product becomes too high. Table 2 further shows the preferred auxiliary reboiler temperatures. The preferred auxiliary reboiler temperatures are in the range of from 85 and 105 ° C. The temperature difference ( A T) to low pressure pressurized steam having a pressure of 4 bar gauge and a temperature of 151.8 ° C is also shown in table 2. Table 2 further shows the part of evaporated liquid, i.e. the part of the reaction mixture evaporated in the auxiliary reboiler. Without using an auxiliary reboiler, i.e. at an auxiliary reboiler duty of 0 kW, an amount of about 30 wt.-% of the liquid is evaporated. Up to an auxiliary reboiler duty of 2000 kW, an amount of the liquid in the range of from > 31 to 54 wt.-% is evaporated.

[0113] Table 2. ] Auxiliary reboiler (103 in Figure 2) [2] Savings of medium pressure pressurized steam

[0114] [3] T (low pressure pressurized steam having 4 bar gauge = 151.8 ° C) - T @ auxiliary reboiler 103 [4] Part of evaporated liquid in auxiliary reboiler 103

[0115] List of reference signs

[0116] 1 (alkoxylation) reaction mixture

[0117] 2 medium pressure pressurized steam

[0118] 2a medium pressure steam condensate

[0119] 3 low pressure pressurized steam

[0120] 3a low pressure steam condensate

[0121] 4 heated, partially evaporated liquid

[0122] 4a vapor phase

[0123] 4b liquid phase

[0124] 5 liquid fraction

[0125] 6 unreacted nitrogenous compound stream

[0126] 7 alkoxylation products stream

[0127] 101 distillation tower

[0128] 102 bottom reboiler

[0129] 103 (auxiliary) reboiler

[0130] 104 sidedraw

[0131] 105 top

[0132] 106 bottom

[0133] 107 condenser

[0134] 108 flash drum

Claims

Claims1. A process for purifying a reaction mixture (1) obtained by an alkoxylation reaction of a nitrogenous compound selected from ammonia and amines, with an alkylene oxide, the reaction mixture (1) containing nitrogenous alkoxylation products and unreacted nitrogenous compound, the process comprising the steps of(1) introducing the reaction mixture (1) into a distillation tower (101),(2) providing thermal energy to the distillation tower (101) via a bottom reboiler (102) heated by medium pressure pressurized steam (2),(3) providing additional thermal energy to the distillation tower (101) by heating and partially evaporating a liquid in a reboiler (103) heated by low pressure pressurized steam (3), and directing the heated, partially evaporated liquid (4) to the distillation tower (101), wherein the liquid is the reaction mixture (1) to be introduced into the distillation tower (101) and / or a liquid fraction (5) withdrawn from the distillation tower (101) via a sidedraw (104),(4) withdrawing an unreacted nitrogenous compound stream (6) at the top (105) of the distillation tower (101), and(5) withdrawing an alkoxylation products stream (7) at the bottom (106) of the distillation tower (101).

2. The process of claim 1, wherein directing the heated, partially evaporated liquid (4) to the distillation tower (101) comprises directing both a vapor phase (4a) and a liquid phase (4b) to the distillation tower (101).

3. The process of claim 1 or 2, wherein the medium pressure pressurized steam (2) has a pressure in the range of from 12 to 20 bar, preferably about 16 bar.

4. The process of any one of the preceding claims, wherein the low pressure pressurized steam (3) has a pressure in the range of from 2 to 8 bar, preferably about 4 bar.

5. The process of any one of the preceding claims, wherein the temperature of the medium pressure pressurized steam (2) is higher than the bottom temperature by at least 20 ° C.

6. The process of any one of the preceding claims, comprising expanding the medium pressure steam condensate (2a) obtained from the bottom reboiler(102) to obtain a low pressure pressurized steam (3), and heating the reboiler(103) with the low pressure pressurized steam (3).

7. The process of any one of the preceding claims, comprising subjecting the alkoxylation products stream (7) to two or more distillations to remove water, and side products.

8. The process of any one of the preceding claims, wherein the alkylene oxide is selected from ethylene oxide and propylene oxide.

9. The process of any one of the preceding claims, wherein the amine is a compound of formula (I)HNR2R2(I) withR1selected from H, and Cj-Cg alkyl, and Cj-Cg hydroxyalkyl, and R2selected from Cj-Cg alkyl, and Cj-Cg hydroxyalkyl.

10. The process of any one of the preceding claims, comprising an alkoxylation reaction comprising reacting the nitrogenous compound and the alkylene oxide to obtain the alkoxylation reaction mixture (1), and recycling the unreacted nitrogenous compound stream (6) at least partially to the alkoxylation reaction.

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