Method for separating and recovering ammonia from an amination product mixture

Abstract

A method for separating and recovering ammonia from an amination product mixture comprises: a) introducing the amination product mixture into a first distillation tower operated at a pressure of 15 bara or higher, withdrawing from the first distillation tower an ammonia-rich overhead stream and a first bottoms stream; b) directing the first bottoms stream to a second distillation tower operated at a pressure of 8 bara or lower, withdrawing from the second distillation tower overhead vapors, an aqueous sidestream and a second bottoms stream, and at least partially condensing the overhead vapors to obtain at least one aqueous ammonia stream; c) partly returning the aqueous ammonia stream to the second distillation tower as a reflux and partly recycling the aqueous ammonia stream as a recycle to the first distillation tower. The method allows for recovering as much as possible of unconverted ammonia while optimizing the energy demand of the process.

Description

[0001] Method for separating and recovering ammonia from an amination product mixture The present invention relates to a method for separating and recovering ammonia from an amination product mixture. The reaction of ammonia with alcohols or with aldehydes over a heterogeneous catalyst in the presence ofhydrogen to yield amines is referred to as “reductive amination”. Typically, ammonia is used in excess in thereaction. The amination product mixture comprises unreacted ammonia, water, low-boilers having a lowerboiling point than that of the amine or amine / water azeotrope, and high-boilers having a higher boiling pointthan that of the product amine, for example higher-molecular-weight byproducts. For example, WO 2016 / 091643 A discloses a process for preparing a polyetheramine by reacting a polyether alcohol with ammonia in the presence of hydrogen and a catalyst in a reactor or plurality of reactors.After the effluent stream is removed from the reductive amination reactor, it can be subjected to a variety ofseparation steps for separating the various components. For example, the effluent stream may be subjected todistillation to remove water and ammonia. Typically, the amination mixture is first subjected to a primarypressure distillation during which at least the major part of the excess ammonia is recovered. The residue is thereafter subjected to a secondary distillation during which the remainder of excess ammonia, and at least part of the water contained therein, are recovered. The recovered ammonia can be used in any desired manner. For example, depending on the purity level of the recovered ammonia, the recovered ammonia may be recycled to another point in the process such as the inlet of one or more reactors. Advantageously, such recovered ammonia can be used as “make-up” ammonia forreactors where ammonia is consumed in a reaction or recycled to the amination reaction.EP 4151618 A1 discloses a method for producing an amine comprising distilling a composition comprising the amine, at least one compound having a lower boiling point than the amine and at least one other compoundhaving a higher boiling point than the amine in a thermally integrated distillation apparatus comprising a firstdistillation column, an evaporator-condenser and a second distillation column. The composition is introduced into the first distillation column operating at a pressure in the range from 1 to 23 bar(a), a bottoms liquid from the first distillation column is introduced into the evaporation space of the evaporator-condenser, is partially evaporated and is then separated into a gaseous feed, which is introduced into the second distillation column, and a residual stream. The second distillation column is operating at a head pressure between 0.05 to 3.8 bar(a) and at least 0.5 bar lower than the head pressure in the first distillation column. A first stream of vapors from the first distillation column is introduced into the condensing space of the evaporator-condenser, is at least partially condensed there so that a condensate forms and the condensation heat is used to evaporate the bottoms liquid of the first column in the evaporation space of the evaporator-condenser partially, and a product stream including the amine is removed as a side stream from the second column.US 2005 / 263385 discloses a process for the distillative separation of aqueous amine solutions from thehydrogenation of nitroaromatic compounds, comprising: a) carrying out distillation in at least two distillationcolumns connected in series and operated at different pressures; b) at least partially condensing vapors leavingthe distillation column operating at higher pressure and heating the bottom of the distillation column operatingat lower pressure with the heat released therefrom; c) feeding the amine solution into a first of the at least twodistillation columns connected in series, and at least partially removing bottom product from the first distillationcolumn and feeding the bottom product into the second distillation column, and d) removing purified amine asbottom product from a last distillation column connected in series. For economic reasons, it is desirable and therefore an object of the present invention to recover as much as possible of the unconverted ammonia. It is further desirable to recover as much as possible of the unconverted ammonia while optimizing the energy demand of the process. This object is solved by the method of the invention for separating and recovering ammonia from an amination product mixture comprising ammonia, water and at least one amination product, the method comprising:a) introducing the amination product mixture into a first distillation tower operated at a pressure of 15 bara orhigher, withdrawing from the first distillation tower an ammonia-rich overhead stream and a first bottoms stream;b) directing the first bottoms stream to a second distillation tower operated at a pressure of 8 bara or lower,withdrawing from the second distillation tower overhead vapors, an aqueous sidestream and a second bottoms stream, and at least partially condensing the overhead vapors to obtain at least one aqueous ammonia stream;c) partly returning the aqueous ammonia stream to the second distillation tower as a reflux and partlyrecycling the aqueous ammonia stream as a recycle to the first distillation tower.Step a) involves introducing the amination product mixture into a first distillation tower operated at a pressureof 15 bara or higher.For example, the first distillation tower may be equipped with structured packings or random packings, or mayhave separatory trays such as valve trays. Suitable configurations of distillation towers are known in the art. Forexample, the distillation tower may have 1 to 15, preferably 2 to 5 theoretical plates. Suitably, the aminationproduct mixture may be introduced via a sidefeed into the first distillation tower. The sidefeed may be introducedabove the lowermost and below the uppermost theoretical plate. The first distillation tower is operated at a pressure of 15 bara or higher. For example, the first distillation towermay be operated at a pressure in the range of from 15 to 24 bara, preferably 18 to 20 bara. Suitably, the firstdistillation tower may be operated at a bottoms temperature in the range of from 160 to 220 °C, preferably 175to 200 °C. Distillation of ammonia at high pressure allows for condensing out ammonia at a relatively hightemperature using readily available coolants, such as secondary cooling water. Preferably, a majority of theunconverted ammonia is recovered in step a).The method involves withdrawing an ammonia-rich overhead stream from the first distillation tower. For thispurpose, a gaseous overhead stream may be withdrawn from the first distillation tower via its head or upperpart of the distillation tower, and directed to a condenser to obtain an ammonia-rich condensate. Generally, thecondenser is cooled by a coolant. Suitably, the coolant has a supply temperature in the range of from 24 to38 °C. The skilled person will appreciate that the ammonia-rich condensate may be partly returned to the firstdistillation tower as reflux, i.e. to the upper part of the first distillation tower, in order to maintain liquid-vaporcontact and effect efficient fractionation in the upper section of the first distillation tower. The remainder iswithdrawn as the ammonia-rich overhead stream.In an embodiment, the method additionally comprises step d) directing at least a part of the ammonia-richoverhead stream to synthesis yielding the amination product mixture. This advantageously allows for recyclingammonia and reduces ammonia loss.The method involves withdrawing a first bottoms stream from the first distillation tower. Suitably, the first bottomsstream is withdrawn from the bottom of the first distillation tower or the reboiler recycle. The first bottoms streamis ammonia-depleted.Generally, the method comprises providing thermal energy to the first distillation tower via a bottom reboiler.For this purpose, the bottoms from the first distillation tower may be recycled via a bottom reboiler and heated.Energy for vaporizers such as bottom reboilers 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 high pressure pressurized steam, medium pressure pressurized steam and low pressure pressurized steam. However, fossil resources are expensive and their firing is associated with inherent CO2 emissions which should be reduced or avoided as far as possible, especially in view of climate change issues. The inventive method can use lower temperature level heat to contribute to the heating of the first distillation tower. It has been found that this does not negatively impact the amount of recoverable ammonia. While a lower bottoms temperature in the first distillation tower results in more ammonia in the first bottoms stream, recycle of aqueous ammonia from the second distillation tower to the first distillation tower avoids significant losses of ammonia via the aqueous ammonia. This is advantageous in comparison to state-of-the art processes in which thermal energy is provided to the first distillation tower by high pressure pressurized steam. Hence in an embodiment, the method comprises providing thermal energy to the first distillation tower via abottom reboiler heated by medium pressure pressurized steam. The medium pressure pressurized steam mayhave a pressure in the range of from 12 to 20 bar gauge, preferably about 16 bar gauge, and a temperature inthe range of from 190 to 215 °C, preferably about 205 °C.In an embodiment, the method comprises operating the first distillation tower at a pressure of 19 bara or higher.Increasing the pressure in the first distillation tower results in a higher condensation temperature of ammonia.Thus, one can use cooling water having a higher temperature, for example river water. It has been found thatthis does not negatively impact the amount of recoverable ammonia. While a higher pressure in the first distillation tower results in more ammonia in the first bottoms stream, recycle of aqueous ammonia from the second distillation tower to the first distillation tower avoids significant losses of ammonia via the aqueous ammonia.The first bottoms stream is directed to a second distillation tower (step b). Suitably, the first bottoms stream maybe introduced via a sidefeed into the second distillation tower. For example, the second distillation tower may be equipped with structured packings or random packings, ormay have separatory trays such as valve trays. Suitable configurations of distillation towers are known in theart. For example, the distillation tower may have 4 to 15, preferably 6 to 10theoretical plates. The sidefeed may be introduced above 10% and below 50% of the theoretical plates.The second distillation tower is operated at a pressure of 8 bara or lower. For example, the second distillationtower may be operated at a pressure in the range of from 1.5 to 8 bara, preferably 4 to 5 bara. Suitably, thesecond distillation tower may be operated at a bottoms temperature in the range of from 160 to 220 °C,preferably 180 to 200 °C.Step b) of the method of the invention further comprises withdrawing overhead vapors, an aqueous sidestreamand a second bottoms stream from the second distillation tower. The aqueous sidestream may primarily comprise water. It is suitably directed to wastewater treatment to be discarded. The second bottoms stream comprises the target amination product. Thus, in an embodiment, the methodadditionally comprises step d) separating the target amination product from the second bottoms stream.Suitably, separation may be carried out in at least one further distillation step known to the skilled person.Step b) further comprises at least partially condensing the overhead vapors to obtain at least one aqueousammonia stream. While the setting of the pressure is crucial for the setting of the temperatures, thetemperatures in the distillation are also affected by setting of a particular concentration. For instance, it is possible to increase the condensation temperature at the head by drawing off not only ammonia but also other components having a higher boiling point than ammonia, for example water, overhead as well. In other words,from the overhead vapors withdrawn from the second distillation tower, residual ammonia is condensed togetherwith water. This means that ammonia is absorbed into and dissolves in the condensed water. A further uncondensable stream may be obtained from the condenser.In this case, it is advantageous that condensing the overhead vapors occurs in a condenser which is configuredto enable a closed condensation, or in backmixed mode (called “closed condensation” by the person skilled inthe art), such that the condensation of the overhead vapors withdrawn from the second distillation tower to obtain an aqueous ammonia stream preferably takes place within a narrow temperature range. A suitable condenser for this type of condensation is one in which the condensation takes place in cocurrent with the outflow of the condensate, or a direct condenser in which cold liquid which is pumped in circulation is brought into contact with the vapors to be condensed. Hence, in an embodiment, the method comprises introducing the overhead vapors into passages of thecondenser for downward flow therein in indirect heat-exchange with a coolant supplied to the outside of thepassages, thereby effecting condensation of water on the walls of said passages, the condensed water forming a downwardly flowing liquid such that interaction takes place between the downwardly flowing overhead vapors and the downwardly flowing liquid such that the liquid becomes enriched in ammonia, and withdrawing the thus formed aqueous ammonia stream.Step c) of the inventive method comprises partly returning the aqueous ammonia stream to the seconddistillation tower as a reflux and partly recycling the aqueous ammonia stream as a recycle to the first distillation tower. The skilled person will appreciate that the aqueous ammonia stream may be partly returned to the seconddistillation tower as reflux in order to maintain liquid-vapor contact and effect efficient fractionation in the uppersection of the second distillation tower. A key feature of the invention resides in partly recycling the aqueous ammonia stream as a recycle to the first distillation tower. This feature allows for recovering higher proportions of ammonia, but also allows for implementation of energy savings without concomitant loss of recoverable ammonia. It may be energetically more efficient to use two condensers to condense overhead vapors withdrawn from the second distillation tower. Typically, one of the condensers is operated at a higher temperature than the other.In a preferred embodiment, the method comprises^ partially condensing the overhead vapors in a first condenser, to obtain a condensate and an uncondensedgas stream,^ partly returning the condensate as the reflux to the second distillation tower and partly directing thecondensate to a second condenser,^ directing the uncondensed gas stream to the second condenser such that ammonia contained in theuncondensed gas stream is absorbed by the condensate, i.e. such that the condensate becomes enriched in ammonia, to obtain the aqueous ammonia stream recycled to the first distillation tower.Preferably, the first condenser is cooled by a first coolant and the second condenser is cooled by a secondcoolant, the second coolant having a lower temperature than the first coolant. In other words, the secondcondenser is operated at a lower temperature than the first condenser. For example, the first coolant has atemperature in the range of from 50 to 120 °C, preferably 60 to 80 °C. For example, the second coolant has atemperature in the range of from 10 to 50 °C, preferably 25 to 38 °C.The inventive method can offer a number of areas where heat integration can use the condensation heat of theoverhead vapors from the second distillation tower. This advantageously allows for reducing steam consumption. In an embodiment, the method comprises^ partly withdrawing a liquid fraction from the first distillation tower, heat-exchanging the liquid fraction withthe overhead vapors to transfer heat from the overhead vapors to the withdrawn liquid fraction, and returning the heat-exchanged liquid fraction to the first distillation tower,^ at least partially condensing the heat-exchanged overhead vapors to obtain the aqueous ammonia stream.This allows for preventing loss of thermal energy and instead utilising the thermal energy of the overhead vaporsfor providing thermal energy to the first distillation tower via heating the liquid fraction withdrawn from the firstdistillation tower.Preferably, the combined mixture is introduced into the first distillation tower at a position close below the position from which the liquid fraction was withdrawn. In an embodiment, the method comprises^ heat-exchanging the overhead vapors with the liquid fraction, thereby partially condensing the overheadvapors to obtain a condensate and an uncondensed gas stream,^ partly returning the condensate as the reflux to the second distillation tower and partly directing thecondensate to a condenser,^ directing the uncondensed gas stream into the condenser such that ammonia contained in the uncondensedgas stream is absorbed by the condensate to obtain the aqueous ammonia stream recycled to the first distillation tower. For this embodiment, the preferences and advantages described above apply analogously.In an embodiment, the method comprises introducing the aqueous ammonia stream to be recycled to the firstdistillation tower into the low-temperature side of a heat-exchanger and combining the aqueous ammoniastream with the liquid fraction. Then, suitably, the combined mixture is introduced the to the first distillation towerat a position close below the position from which the liquid fraction was withdrawn. In an embodiment, the method comprises^ prior to introducing the amination product mixture into a first distillation tower, heat-exchanging the overheadvapors with the amination product mixture to transfer heat from the overhead vapors to the amination product mixture,^ at least partially condensing the heat-exchanged overhead vapors to obtain the aqueous ammonia stream.This allows for preventing loss of thermal energy and instead utilising the thermal energy of the overhead vapors for providing thermal energy to the amination product mixture to be introduced into the first distillation tower. In an embodiment, the method comprises^ heat-exchanging the overhead vapors with the amination product mixture, thereby partially condensing theoverhead vapors to obtain a condensate and an uncondensed gas stream,^ partly returning the condensate as the reflux to the second distillation tower and partly directing thecondensate to a condenser,^ directing the uncondensed gas stream into the condenser such that ammonia contained in the uncondensedgas stream is absorbed by the condensate to obtain the aqueous ammonia stream recycled to the first distillation tower. The method may further comprise introducing the aqueous ammonia stream to be recycled to the first distillationtower into the low-temperature side of a heat-exchanger and combining the aqueous ammonia stream with theamination product mixture. For these embodiments, the preferences and advantages described above apply analogously. Preferred amination products are polyetheramines. Generally, polyetheramines are obtained by reacting the respective alcohols with ammonia over a heterogeneous catalyst in the presence of hydrogen (also referred to as “reductive amination”). Typically, ammonia is used in excess in the reaction, e.g. in a 20-fold excess. Suitable heterogeneous catalyst are known in the art and include, for example, nickel rhenium type catalysts. Other transition metal catalysts such as Co, Cu, Ru, Rh, Pd, Pt, or mixtures thereof may also be useful. The catalysts are typically provided on a support, for example, an oxide support such as Al2O3, TiO2, ZrO2, or SiO2. Also useful are zeolite catalysts such as mordenites, faujasites, and chabazites.Suitably, the polyetheramines have a weight average molecular weight in the range of from 200 to 2500 g / mol.The present invention is further illustrated by the figures and examples that follow.Fig.1 depicts an embodiment of a method for separating and recovering ammonia from an amination productmixture according to the prior art.Figs. 2 to 6 depict embodiments of the inventive method for separating and recovering ammonia from an amination product mixture.In the method according to the prior art as shown in Fig.1, an amination product mixture 1 comprising ammonia,water and at least one amination product is introduced into a first distillation tower 101. The first distillation tower101 is operated at a pressure of 18 bara, and at a temperature of 210 °C.A gaseous overhead stream 2 is withdrawn from the first distillation tower 101 via its head 102, and directed toa condenser 104 and a vessel 105 to obtain at least partially condensed, ammonia-rich overhead streams 2a,2b. The condenser 104 is cooled by a coolant having a temperature of 30 °C. The ammonia-rich overheadstream 2a is directed to synthesis yielding the amination product mixture 1 (not shown). The ammonia-richoverhead stream 2b is returned to the first distillation tower 101.A first bottoms stream 3 is withdrawn from the first distillation tower 101 via its bottom 103. The first bottomsstream 3 is ammonia-depleted and directed to a bottom reboiler 106. The bottom reboiler 106 is heated by highpressure pressurized steam having a pressure of 40 bara and a temperature of 260 °C. The heated first bottoms stream 3 is partly returned to the first distillation tower 101 and partly directed to a second distillation tower 201.The second distillation tower 201 is operated at a pressure of 1.6 bara, and at a temperature of 200 °C.Overhead vapors 4 are withdrawn from the second distillation tower 201 via its head 202, and directed to acondenser 205a being cooled by a coolant having a temperature of 30 °C, and a vessel 206 for at least partiallycondensing the overhead vapors 4. At least partially condensed, aqueous ammonia streams 4a, 4b areobtained. The aqueous ammonia stream 4a is withdrawn and directed to wastewater treatment (not shown).The aqueous ammonia stream 4b is returned to the second distillation tower 201 as a reflux 4b.A second bottoms stream 6 is withdrawn from the second distillation tower 201 via its bottom 204, and directedto a bottom reboiler 207. The bottom reboiler 207 is heated by medium pressure pressurized steam having apressure of 20 bara and a temperature of 220 °C. The heated second bottoms stream 6 is partly returned tothe second distillation tower 201 and partly directed to further separation stages to separate the target aminationproduct from the second bottoms stream 6 (not shown).The embodiment of the inventive method as shown in Fig.2 is similar to the embodiment shown in Fig.1, withthe difference that from the overhead vapors 4, in addition to the at least partially condensed, aqueous ammoniastreams 4a, 4b, an uncondensable stream 4d is obtained and withdrawn. Instead of directing the aqueousammonia stream 4a to wastewater treatment, aqueous ammonia stream 4a is recycled to the first distillation tower 101.Furthermore, an aqueous sidestream 5 is withdrawn from the second distillation tower 201 via a sidedraw 203and directed to wastewater treatment (not shown).The embodiment of the inventive method as shown in Fig.3 is similar to the embodiment shown in Fig.2, withthe difference that the overhead vapors 4 are partially condensed in a first condenser 205a, to obtain a liquidcondensate 4AB and a gaseous, uncondensed gas stream 4AA. The condensate 4AB is directed to vessel 206from which the aqueous ammonia stream 4b is obtained alongside with a liquid condensate 4AC. The aqueous ammonia stream 4b is returned to the second distillation tower 201 as a reflux 4b. The condensate 4AC isdirected to a second condenser 205b. The first condenser 205a is cooled by a first coolant having a temperatureof 65 °C. The second condenser 205b is cooled by a second coolant having a temperature of 30 °C.The uncondensed gas stream 4AA is directed to the second condenser 205b such that ammonia contained in the uncondensed gas stream 4AA is absorbed by the condensate 4AC. From the second condenser 205b, an uncondensable stream 4d is obtained and withdrawn. Additionally, the aqueous ammonia stream 4a is obtained and recycled to the first distillation tower 101 as described above.In the embodiment of the inventive method as shown in Fig. 4, an amination product mixture 1 comprisingammonia, water and at least one amination product is introduced into a first distillation tower 101. The firstdistillation tower 101 is operated at a pressure of 20 bara, and at a temperature of 180 °C.A gaseous overhead stream 2 is withdrawn from the first distillation tower 101 via its head 102, and directed toa condenser 104 and a vessel 105 to obtain at least partially condensed, ammonia-rich overhead streams 2a,2b. The condenser 104 is cooled by a coolant having a temperature of 37 °C. The ammonia-rich overheadstream 2a is directed to synthesis yielding the amination product mixture 1 (not shown). The ammonia-rich overhead stream 2b is returned to the first distillation tower 101. A first bottoms stream 3 is withdrawn from the first distillation tower 101 via its bottom 103. The first bottomsstream 3 is ammonia-depleted and directed to a bottom reboiler 106. The bottom reboiler 106 is heated bymedium pressure pressurized steam having a pressure of 20 bara and a temperature of 220 °C. The heatedfirst bottoms stream 3 is partly returned to the first distillation tower 101 and partly directed to a second distillationtower 201. The second distillation tower 201 is operated at a pressure of 4.2 bara, and at a temperature of200 °C. Overhead vapors 4 are withdrawn from the second distillation tower 201 via its head 202.A liquid fraction is partly withdrawn from the first distillation tower 101 and heat-exchanged with the overhead vapors 4 to transfer heat from the overhead vapors 4 to the withdrawn liquid fraction. Heat-exchange occurs in a heat-exchanger 205a, wherein the overhead vapors 4 are introduced into the high-temperature side of the heat-exchanger 205a and the liquid fraction is introduced into the low-temperature side of the heat-exchanger 205a.The heat-exchanged overhead vapors 4 leaving the heat-exchanger 205a are directed to a condenser 205band a vessel 206 for at least partially condensing the heat-exchanged overhead vapors 4. The condenser 205bis cooled by a coolant having a temperature of 37 °C. At least partially condensed, aqueous ammonia streams4a, 4b are obtained. The aqueous ammonia stream 4b is returned to the second distillation tower 201 as a reflux 4b. The aqueous ammonia stream 4a to be recycled to the first distillation tower 101 is introduced into the low- temperature side of the heat-exchanger 205a and combined with the liquid fraction, followed by introducing the combined mixture to the first distillation tower 101 at a position close below the position from which the liquid fraction was withdrawn.A second bottoms stream 6 is withdrawn from the second distillation tower 201 via its bottom, and directed to abottom reboiler 207. The bottom reboiler 207 is heated by medium pressure pressurized steam having apressure of 20 bara and a temperature of 220 °C. The heated second bottoms stream 6 is partly returned tothe second distillation tower 201 and partly directed to further separation stages to separate the target amination product from the second bottoms stream 6 (not shown). Furthermore, an aqueous sidestream 5 is withdrawn from the second distillation tower 201 via a sidedraw 203and directed to wastewater treatment (not shown).The embodiment of the inventive method as shown in Fig.5 is similar to the embodiment shown in Fig.4, withthe difference that partial condensation of the overhead vapors 4 yields a liquid condensate 4AB and a gaseous,uncondensed gas stream 4AA. The condensate 4AB is partly returned as the reflux 4b to the second distillationtower 201, and the condensate 4AC is partly directed to the condenser 205b. The condenser 205b is cooled bya coolant having a temperature of 37 °C. The uncondensed gas stream 4AA is directed into the condenser205b such that ammonia contained in the uncondensed gas stream 4AA is absorbed by the condensate 4AC to obtain the aqueous ammonia stream 4a to be recycled to the first distillation tower 101.The aqueous ammonia stream 4a is directed to vessel 206 and subsequently introduced into the low-temperature side of the heat-exchanger 205a and combined with the liquid fraction, followed by introducing the combined mixture to the first distillation tower 101 at a position close below the position from which the liquid fraction was withdrawn.The embodiment of the inventive method as shown in Fig. 6 is a combination of the embodiments shown inFigs.4 and 5, with the difference that no liquid fraction is withdrawn from the first distillation tower 101. Furtherdifferently, prior to introducing the amination product mixture 1 into the first distillation tower 101, the overhead vapors 4 are heat-exchanged with the amination product mixture 1 to transfer heat from the overhead vapors 4 to the amination product mixture 1.The heat-exchanged overhead vapors 4 are at least partially condensed to obtain a condensate 4AB and anuncondensed gas stream 4AA which are treated as described above regarding Fig.5. The obtained aqueousammonia stream 4a to be recycled to the first distillation tower 101 is introduced into the low-temperature side of the heat-exchanger 205a and combined with the heat-exchanged amination product mixture 1. The combined mixture is then introduced into the first distillation tower 101. Examples Simulation methodReaction giving the amination product mixture: Reaction of polyetherol (weight average molecular weight:230 g / mol) with ammonia to yield polyetheramine (weight average molecular weight: 228 g / mol) and water.Conditions: temperature: 200 °C; pressure 110 bara. Amination product mixtures having the compositions asshown in tables 1 to 8 (stream 1) were used for the simulations of examples 1 to 8. For simulation calculations, commercially available software Aspen Plus (manufacturer: AspenTech, Burlington / Massachusetts, USA) was used. The set of parameters was based on comprehensive measurements, studies on laboratory set-ups and operating data from various plants.Example 1 – comparativeExample 1 is a simulation according to Fig. 1 (see detailed description above). The first distillation tower isoperated at a pressure of 18 bara, and at a bottom temperature of 210 °C. The second distillation tower isoperated at a pressure of 1.6 bara, and at a bottom temperature of 200 °C. Example 1 represents a prior artmethod. The simulation results are shown in table 1 below.Example 2 – according to the inventionExample 1 is a simulation according to Fig.2 (see detailed description above). The first distillation tower isoperated at a pressure of 18 bara, and at a bottom temperature of 210 °C. The second distillation tower isoperated at a pressure of 1.6 bara, and at a bottom temperature of 200 °C. Example 2 represents a methodaccording to the invention. The results are shown in table 2 below.Example 3 – according to the inventionExample 3 is a simulation according to Fig.2 (see detailed description above). The first distillation tower isoperated at a pressure of 19 bara, and at a bottom temperature of 180 °C. The second distillation tower isoperated at a pressure of 1.6 bara, and at a bottom temperature of 200 °C. Example 3 represents a methodaccording to the invention. The results are shown in table 3 below.Example 4 – according to the inventionExample 4 is a simulation according to Fig.2 (see detailed description above). The first distillation tower isoperated at a pressure of 20 bara, and at a bottom temperature of 180 °C. The second distillation tower isoperated at a pressure of 1.6 bara, and at a bottom temperature of 200 °C. Example 4 represents a methodaccording to the invention. The results are shown in table 4 below.Example 5 – according to the inventionExample 5 is a simulation according to Fig.2 (see detailed description above). The first distillation tower isoperated at a pressure of 20 bara, and at a bottom temperature of 180 °C. The second distillation tower isoperated at a pressure of 2.7 bara, and at a bottom temperature of 200 °C. Example 5 represents a methodaccording to the invention. The results are shown in table 5 below.Example 6 – according to the inventionExample 6 is a simulation according to Fig.2 (see detailed description above). The first distillation tower isoperated at a pressure of 20 bara, and at a bottom temperature of 180 °C. The second distillation tower isoperated at a pressure of 4.2 bara, and at a bottom temperature of 200 °C.The bottom reboiler (reference sign 106) of the first distillation tower was operated with the following specifications:^ H2O: 6450.0 kg / h^ Pressure: 14.0 bara^ Temperature: 203.0 °C^ Density: 6.9 kg / m3The bottom reboiler (reference sign 207) of the second distillation tower was operated with the following specifications:^ H2O: 3948.1 kg / h^ Pressure: 19.1 bara^ Temperature: 214.5 °C^ Density: 9.4 kg / m3Example 6 represents a method according to the invention. The results are shown in table 6 below.Example 7 – comparativeExample 7 is a simulation according to Fig.2 (see detailed description above). The first distillation tower isoperated at a pressure of 20 bara, and at a bottom temperature of 180 °C. The second distillation tower isoperated at a pressure of 8.2 bara, and at a bottom temperature of 200 °C. Example 7 represents a comparativeexample. The results are shown in table 7 below.Example 8 – according to the inventionExample 8 is a simulation according to Fig. 5 (see detailed description above). The first distillation tower isoperated at a pressure of 20 bara, and at a bottom temperature of 180 °C. The second distillation tower isoperated at a pressure of 4.2 bara, and at a bottom temperature of 200 °C. The bottom reboiler (reference sign 106) of the first distillation tower was operated with the following specifications:^ H2O: 2602.4 kg / h^ Pressure: 14.0 bara^ Temperature: 203.0 °C^ Density: 6.9 kg / m3The bottom reboiler (reference sign 207) of the second distillation tower was operated with the following specifications:^ H2O: 4099.6 kg / h^ Pressure: 19.1 bara^ Temperature: 214.5 °C^ Density: 9.4 kg / m3Example 8 represents a method according to the invention. The results are shown in table 8 below.

[0002] 6.3a.091.1.43.8 438 211 3 0.60 .7619.7.80 5.0.0 . .64 60 43 08.34 848 11 71 62 71 5.07.8.5 .202a0 0 0.427 30 1 4715796 8. . .80 5 .. .1 67 4 601. .2 8 30 45 9 82 52 1 667 1 5]h / g]] rk[ h a] / egb[ ]C3in k[°elte[om]] lehh p] / luh gehr / / inpgg / o mkg s[utrak[[komk[baa xr ty3a e2rlm iOe2 seHe epNyh th r nN Hu evittmeeeysDsarlToim erapPD P- m5, o3 c *.32.26 0 0. 66 0 3.09 55 2.65.104297 a401.6 2. 08 864.51.04 8.1 .5.39 4395.6.0 9.00.8 3 04807 .10163 ..26 81 0135 287a22..50126.8.57.2 .00 0 77134 27519.76.4 68.16 0.5.8.0.0 2281.4 37 165529586]h / gk[]h] / greab [ ] ]]ihnlok[eteC°3] ]h / h / g / ghp inlu[ erm / go kg s[utrk[ko[mk[baar ty3a2rlm iOe2 seHe pNyhh r nNtHu et meeeysDslTi om erPD P-5,3.39.26 0 0. 66 0 55 1 365.1.09.04297 a 5 4 0.94.880.1.2.41 70 .04 9.154 2485 3.71.3 49033 9..96 0.0.3 0369 .10822 5 157a21..1760 0 0.8.90 0178134.2759.6.8.1 1.0724286.4630.55.8 9.71165 2 5 086]h / gk[]]rehin / g alk[b[ ] teC°3] ]h] / hg / ]gh / oghe lu[ ekpri rm / [kon[ok[ sut gk 2 3 N Olm2marebHaar[ tyiN Hyh thetruep sem neie.myloss erT D 3 l D Pee -P b5a,T3.39.26 0 0. 66 0 55 1 365.1.09.04297 a 1 4 0.22.480.8.2.41 81 .04 9.154 1488 3.78.8 49063 9..96 0.0.3 0360 .20862 5 147a21..4040 0 0.8.07 0179144.1759.6.8.1 1.0724286.4630.55.8 9.71165 2 5 086]h / gk[]]rehin / g alk[b[ ] teC°3] ]h] / hg / ]gh / oghe lu[ ekpri rm / [kon[ok[ sut gk 2 3 N Olm2marebHaar[ tyiN Hyh thetruep sem neie.myloss erT D 4 l D Pee -P b5a,T3 3 6 0 0.13.467 0 ..05.11 2 365.205297 a 3.5.4 4 01400 3.50 5.20.5.118 4182. 1.8.0.0.3 3 05.53596 9.96316 02 0875 1472.2a2.021 .8.07.20 0 0 79144 17519.76.1. 468..60.5.8.00 228714 3165529586]h / gk[]eh] / grab [ ]C ] ]]ihn] lok[h e te °[3h / / g / ghp inluo erm / gkg s[utrk[ko[mk[baar ty3a2rlm iOe2 seHe pNyh th r nN Hu et meeeysDslToim erPD P-5,3 1 6 0 0.47.562 0 ..07.12 2 365.406297 a 4.9.1 4 04310 3.50 0.40.5.337 4086. 5.8.0.0.1 3 05.43616 9.96316 02 0885 1472.9a2.041 .8.07.20 0 0 79144 17519.76.1. 468..60.5.8.00 228714 3165529586]h / gk[]eh] / grab [ ]C ] ]]ihn] lok[h e te °[3h / / g / ghp inluo erm / gkg s[utrk[ko[mk[baar ty3a2rlm iOe2 seHe pNyh th r nN Hu et meeeysDslToim erPD P-5,3 1 0 0.07..762 0 87 3 365.8.05.02208 1 4 .0.14.330.0.3366.60 0.854 4972.71.80.8.033 46 0.0.8 8111 3602 0.885 1472..30022 0 0 0.89.07 7144.17519.6.8..0724860.5.8 21 .463529 .5087 165 6]h / gk[e]h] i / ra] ng]ok[b[ lteC°3] [ m e]h] / hg / g h[ / hekgkp inlu er / glp[roosutk[mamk[baar ty x3a e2rlm iOe2 seHe p eNyh th r nN Hu evittmeeeysDsarlToim erapPD P-5m, o3 c * 0 6 0 0.49.162 0 12.2 3.607.5.406297 a41 1 .0.76. 01.552 1.60 0.4 .593 9 4185. 1.8.5.0.0.3.3 07636900163602 0862 5 147a 2.72.0512 2 0 4.8.09.17.4.091447519.76.1. 468..26 0.5.8.08 30 45 9 82 52 1 667 1 5]h / g]] rk[ h a] / e gb[ ]C3in k[°lte[om]]ehh] / luh gehr / / inpgg / o kg s[utrk[ko[mk[baar ty3a2rlm iOe2 seHe pNyh th r nN Hu et meeeysDslToi.m erP8D P-le5,b3aTMinor shortage in the NH3 mass balance results from the fact that uncondensed gases of condensers 104 and / or205a, if present, were not covered in the simulations.As described above, in comparative example 1, the aqueous ammonia stream 4a is directed to wastewatertreatment, i.e., the ammonia contained in aqueous ammonia stream 4a of comparative example 1 is discarded.This results in a significant loss of ammonia via said stream 4a of 83.6 kg / h.In contrast thereto, aqueous ammonia stream 4a of inventive example 2 is recycled to the first distillation tower.In inventive example 2, trace amounts of ammonia are lost via streams 4d, 5 and 6 (total: 2.4 kg / h).Advantageously, compared to comparative example 1 (7140 kg / h), more ammonia is recovered via ammonia-rich overhead stream 2a in inventive example 2 (7221.5 kg / h), which can be directed to synthesis yielding theamination product mixture (recycle).Thus, advantageously, the method of the invention allows to recover high amounts of the unconverted ammonia while optimizing the energy demand of the process. The methods of inventive examples 2 to 4 differ in the temperature and pressure applied in the first distillationtower (18 bara, 210 °C vs. 19 bara, 180 °C vs. 20 bara, 180 °C, respectively). It can be seen in tables 2 to 4that increasing pressures and decreasing bottoms temperatures in the first distillation tower result in the firstbottoms stream 3 withdrawn from the first distillation tower having higher amounts of ammonia. However, saidammonia withdrawn from the first distillation tower via said stream 3 is recycled to the first distillation tower inthe examples according to the invention and can still be recovered via ammonia-rich overhead stream 2a.In example 4, 367.8 kg / h of ammonia are withdrawn from the first distillation tower via the first bottoms stream 3.In the second distillation tower operated at 1.6 bara and 200 °C, 76.2 kg / h of ammonia are lost viauncondensable stream 4d. Increasing the pressure in the second distillation tower to 2.7 bara (example 5) and4.2 bara (example 6) significantly reduces ammonia loss via said stream 4d to 3.9 kg / h and 0.9 kg / h,respectively.Increasing the pressure in the second distillation tower further leads to lower mass flows of aqueoussidestream 5, in turn resulting in increased amounts of water in the second bottoms stream 6 (see tables 4 to7, H2O in streams 5 and 6). These increasing amounts of water adversely effect the downstream purificationprocesses as more water needs to be handled and removed, e.g. in wastewater treatment. The drop of themass flow of stream 5 is significant for a pressure of > 8 bar in the second distillation tower (see comparativeexample 7, table 7). Thus, pressures of less than 8 bara in the second distillation tower are preferred.Without a heat-exchanging step, a total steam consumption in bottom reboilers 106 and 207 of 6450.0 kg / h +3948.1 kg / h = 10398.1 kg / h is necessary (see above, example 6). With a heat-exchanging step as of example 8,the total steam consumption advantageously drops to 2602.4 kg / h + 4099.6 kg / h = 6702 kg / h.List of reference signs1 amination product mixture2 gaseous overhead stream2a ammonia-rich overhead stream2b ammonia-rich overhead stream3 first bottoms stream4 overhead vapors4a aqueous ammonia stream4b aqueous ammonia stream reflux4d uncondensable stream4AA uncondensed gas stream4AB condensate4AC condensate5 aqueous sidestream6 second bottoms stream101 first distillation tower102 head103 bottom104 condenser105 vessel106 bottom reboiler201 second distillation tower202 head203 sidedraw204 bottom205a (first) condenser / heat-exchanger205b (second) condenser206 vessel207 bottom reboiler

Claims

Claims1. A method for separating and recovering ammonia from an amination product mixture comprisingammonia, water and at least one amination product, the method comprising:a) introducing the amination product mixture (1) into a first distillation tower (101) operated at apressure of 15 bara or higher, withdrawing from the first distillation tower (101) an ammonia-richoverhead stream (2a) and a first bottoms stream (3);b) directing the first bottoms stream (3) to a second distillation tower (201) operated at a pressure of8 bara or lower, withdrawing from the second distillation tower (201) overhead vapors (4), anaqueous sidestream (5) and a second bottoms stream (6), and at least partially condensing the overhead vapors (4) to obtain at least one aqueous ammonia stream (4a, 4b);c) partly returning the aqueous ammonia stream (4a, 4b) to the second distillation tower (201) as areflux (4b) and partly recycling the aqueous ammonia stream as a recycle (4a) to the first distillation tower (101).

2. The method according to claim 1, wherein condensing the overhead vapors (4) occurs in a condenser(205) which is configured to enable a closed condensation.

3. The method according to claim 1 or 2, comprising introducing the overhead vapors (4) into passages ofthe condenser (205) for downward flow therein in indirect heat-exchange with a coolant supplied to theoutside of the passages, thereby effecting condensation of water on the walls of said passages, the condensed water forming a downwardly flowing liquid such that interaction takes place between the downwardly flowing overhead vapors (4) and the downwardly flowing liquid such that the liquid becomes enriched in ammonia, and withdrawing the thus formed aqueous ammonia stream (4a, 4b).

4. The method according to claim 1, comprising^ partially condensing the overhead vapors (4) in a first condenser (205a), to obtain a condensate(4AB) and an uncondensed gas stream (4AA), ^partly returning the condensate (4AB) as the reflux (4b) to the second distillation tower (201) andpartly directing the condensate (4AC) to a second condenser (205b), ^directing the uncondensed gas stream (4AA) to the second condenser (205b) such that ammoniacontained in the uncondensed gas stream (4AA) is absorbed by the condensate (4AC) to obtain the aqueous ammonia stream (4a) recycled to the first distillation tower (101).

5. The method according to claim 4, wherein the first condenser (205a) is cooled by a first coolant andthe second condenser (205b) is cooled by a second coolant, the second coolant having a lowertemperature than the first coolant.

6. The method according to claim 1, comprising:^ partly withdrawing a liquid fraction from the first distillation tower (101), heat-exchanging in a heat-exchanger (205a) the liquid fraction with the overhead vapors (4) to transfer heat from theoverhead vapors (4) to the withdrawn liquid fraction, and returning the heat-exchanged liquid fraction to the first distillation tower (101), ^at least partially condensing the heat-exchanged overhead vapors (4) to obtain the aqueousammonia stream (4a, 4b).

7. The method according to claim 6, comprising^ heat-exchanging the overhead vapors (4) with the liquid fraction, thereby partially condensing theoverhead vapors (4) to obtain a condensate (4AB) and an uncondensed gas stream (4AA), ^partly returning the condensate as the reflux (4b) to the second distillation tower (201) and partlydirecting the condensate (4AC) to a condenser (205b), ^directing the uncondensed gas stream (4AA) into the condenser (205b) such that ammoniacontained in the uncondensed gas stream (4AA) is absorbed by the condensate (4AC) to obtain the aqueous ammonia stream (4a) recycled to the first distillation tower (101), and^ preferably, introducing the aqueous ammonia stream (4a) to be recycled to the first distillationtower (101) into the low-temperature side of the heat-exchanger (205a) and combining the aqueousammonia stream (4a) with the liquid fraction.

8. The method according to claim 1, comprising^ prior to introducing the amination product mixture (1) into a first distillation tower (101), heat-exchanging the overhead vapors (4) with the amination product mixture (1) to transfer heat from the overhead vapors (4) to the amination product mixture (1), ^at least partially condensing the heat-exchanged overhead vapors (4) to obtain the aqueousammonia stream (4a, 4b).

9. The method according to claim 8, comprising^ heat-exchanging in a heat-exchanger (205a) the overhead vapors (4) with the amination productmixture (1), thereby partially condensing the overhead vapors (4) to obtain a condensate (4AB) andan uncondensed gas stream (4AA), ^partly returning the condensate as the reflux (4b) to the second distillation tower (201) and partlydirecting the condensate (4AC) to a condenser (205b), ^directing the uncondensed gas stream (4AA) into the condenser (205b) such that ammoniacontained in the uncondensed gas stream (4AA) is absorbed by the condensate (4AC) to obtain the aqueous ammonia stream (4a) recycled to the first distillation tower (101).

10. The method according to claim 8 or 9, comprising introducing the aqueous ammonia stream (4a) to berecycled to the first distillation tower (101) into the low-temperature side of the heat-exchanger (205a)and combining the aqueous ammonia stream (4a) with the amination product mixture (1).

11. The method according to any one of the preceding claims, comprising providing thermal energy to thefirst distillation tower (101) via a bottom reboiler (106) heated by medium pressure pressurized steam.

12. The method according to any one of the preceding claims, comprising operating the first distillationtower (101) at a pressure of 19 bara or higher.

13. The method according to any one of the preceding claims, additionally comprising:d) directing the ammonia-rich stream (2a) to synthesis yielding the amination product mixture (1).

14. The method according to any one of the preceding claims, additionally comprising:e) separating a target amination product from the second bottoms stream (6).

15. The method according to any one of the preceding claims, wherein the amination product is apolyetheramine.

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