Process for drying 1,5-diaminopentane

Abstract

The invention relates to a process for drying 1,5-diaminopentane, comprising the following steps: a) providing at least one substance mixture containing 1,5-diaminopentane and water; b) distilling the substance mixture in at least one distillation column to obtain vapours and a dried 1,5-diaminopentane composition; characterised in that the distillation in step b) is carried out azeotropically using an entrainer containing monochlorobenzene.

Description

[0001] Process for drying 1,5-diaminopentane

[0002] The invention relates to a process for drying 1,5-diaminopentane comprising the following steps: a) providing at least one mixture of substances containing 1,5-diaminopentane and water and b) distilling the mixture of substances in at least one distillation column to obtain a dried 1,5-diaminopentane composition, as well as a process for preparing 1,5-diisocyanatopentane and the use of the 1,5-diisocyanatopentane for preparing oligomeric polyisocyanates.

[0003] 1,5-Diaminopentane (hereinafter also referred to as "pentamethylenediamine", "1,5-pentanediamine" or "PDA") is an important starting material for the production of polymers. It is used, for example, in the production of polyamides by polycondensation of the diamine with dicarboxylic acids. For example, polyamide 5,6 (PA56) is produced from 1,5-diaminopentane and adipic acid. Another important application is the phosgenation of the diamine to pentamethylene diisocyanate (hereinafter also referred to as "1,5-diisocyanatopentane", "1,5-pentanediisocyanate" or "PDI"), which can then be converted in a further step, for example, to polyurethanes, polyureas or polyisocyanurates. The phosgenation places particular demands on the purity of the aliphatic diamine. Since corrosive hydrochloric acid is formed from water and phosgene under phosgenation conditions, a very low water content is usually specified for amines used in phosgenation.For PDA used to produce pentamethylene diisocyanate, WO2016042125 states a water content of <500 ppm.

[0004] Since water content requirements in polyamide production are less stringent, commercially available PDA often contains more than 500 ppm of water and therefore requires further drying before use in isocyanate production. Due to the hygroscopic properties of PDA and the associated strong affinity for water, distillative drying of PDA is possible, but is associated with problems such as yield losses due to thermal decomposition of the PDA.

[0005] It is well known to those skilled in the art to dry organic substances by azeotropic distillation. Common entrainers are substances that form an azeotrope with water and are as immiscible as possible with water at low temperatures, such as toluene, xylene, or chloroform.

[0006] This approach is also taken up in CN216571619 U. There, an azeotropic distillation in the presence of o-dichlorobenzene (hereinafter also referred to as "ODB") is described to solve the problem. This azeotrope forms an azeotrope with water and thus facilitates its distillative separation from PDA. In this way, the temperature in the bottom of the distillation apparatus can be kept low and excessive decomposition of PDA can be avoided. The azeotrope is obtained as a distillate and, after condensation, is separated into an aqueous and an organic phase. After that, the organic phase is returned to the distillation apparatus as reflux, and the aqueous phase is removed from the system. The high density of ODB and thus the large difference to the density of water is described as advantageous for phase separation.

[0007] A disadvantage of this process is that part of the PDA is distilled overhead along with the azeotrope. Due to PDA's high solubility in water, only a portion of it remains in the organic phase, while the other part leaves the distillation apparatus with the aqueous phase and could only be recovered with considerable effort. Furthermore, the PDA acts as a solubilizer in the distillate, so that a higher proportion of ODB also remains in the water.

[0008] Other methods for drying organic substances are known to the person skilled in the art, but these methods themselves have disadvantages when used industrially to dry PDA.

[0009] Drying can be achieved, for example, by membrane processes. Zeolite membranes, for example, can be used for this purpose. Preferred processes are pervaporation or vapor permeation. Another option is treatment with drying agents. Preference is given to using solid drying agents that can be easily separated from the PDA to be dried by filtration. Preference is given to drying agents that can subsequently be regenerated, for example, thermally or by vacuum treatment, such as zeolites, especially molecular sieves. Molecular sieves with pore sizes of 3 Å to 4 Å, preferably 4 Å, are particularly suitable.Further possibilities include crystallizing the PDA, possibly recrystallizing it several times, introducing a stripping gas such as dry nitrogen, preferably previously warmed dry nitrogen, or performing extraction with an organic solvent. Combinations of these methods are also possible.

[0010] The object of the present invention was to provide an improved process for drying 1,5-diaminopentane, which avoids the disadvantages of the prior art and which can be easily applied and scaled up industrially.

[0011] This object was achieved by a process for drying 1,5-diaminopentane comprising the following steps: a) providing at least one mixture containing 1,5-diaminopentane and water, b) distilling the mixture in at least one distillation column to obtain a dried 1,5-diaminopentane composition, characterized in that the distillation in step b) is carried out azeotropically using an entraining agent containing monochlorobenzene. The process according to the invention has the following advantages:

[0012] The water azeotrope is essentially free of 1,5-diaminopentane

[0013] The water azeotrope forms two phases after condensation, with the aqueous phase containing only very small amounts of monochlorobenzene (hereinafter also referred to as “monochlorobenzene” or “MCB”)

[0014] Depending on the procedure, 1,5-diaminopentane can be obtained not only anhydrous but also free of monochlorobenzene.

[0015] According to the invention, the expressions “comprising” or “containing” preferably mean “consisting essentially of” and particularly preferably “consisting of”.

[0016] In the context of the present invention, content data for organic compounds refer to values ​​determined by gas chromatography, unless stated otherwise, and are based on the mass. Unless expressly stated otherwise, percentages are percentages by weight and ppm data are ppm by weight. The quantitative evaluation of gas chromatograms, optionally with the aid of an internal standard, is known to the person skilled in the art. Any necessary methods for determining the water content are likewise known to the person skilled in the art. The prior art methods can also be applied in the context of the present invention. In cases of doubt, the water content determined by Karl Fischer titration is decisive. The presence of amines can lead to sluggish endpoints. In such cases, the value determined by Karl Fischer titration after buffering with anhydrous benzoic acid is decisive.The method using buffering with benzoic acid is also known to those skilled in the art. For general information on Karl Fischer titration, see Jander, Jahr, Maßanalyse, 17th ed., de Gruyter, Berlin (2009), pp. 279 to 282.

[0017] "Distillation" is understood here as a thermal separation process used to obtain vaporizable substances, preferably liquids, from a mixture of substances. The separated vapors are then usually precipitated by condensation. The term specifically encompasses repeated evaporation and condensation using a column (distillation column) with multiple separation stages. Such processes, in which several distillation steps are connected in series in a column, are strictly speaking referred to as rectification, but will also be referred to as distillation for the sake of simplicity. The advantage of such processes is the high separation efficiency and the possibility of operating the plant continuously.

[0018] A "distillation apparatus" is an apparatus suitable for carrying out such a thermal separation process, for example, sieve-tray columns, packed columns, randomly packed columns, bubble-cap columns, or single-stage evaporators such as falling-film evaporators, thin-film evaporators, flash evaporators, multiphase spiral tube evaporators, natural or forced circulation evaporators. The individual process steps are explained in more detail below.

[0019] To carry out the process according to the invention, a mixture of substances comprising 1,5-diaminopentane (hereinafter also referred to as "PDA" or "pentamethylenediamine") and water is first provided. The provided mixture of substances preferably has a water content of more than 500 ppm, particularly preferably from 0.08 wt.% to 10.0 wt.%, very particularly preferably from 0.1 wt.% to 5.0 wt.%, and most preferably from 0.15 to 3.0 wt.%, based on the pentamethylenediamine present in the mixture of substances. The provided mixture of substances preferably contains > 30 wt.%, particularly preferably > 50 wt.%, very particularly preferably > 70 wt.%, and most preferably > 90 wt.% of pentamethylenediamine, based on the total weight of the mixture of substances.

[0020] The pentamethylenediamine in the provided mixture can, for example, originate from a recycling process for polyurethanes, polythiourethanes, polyureas, polyisocyanurates, or polyamides based on pentamethylene diisocyanate or pentamethylenediamine. Another example of the origin of pentamethylenediamine is its biotechnological production, for example, by fermentation of suitable precursor compounds. After the actual production of pentamethylenediamine, it usually undergoes distillative purification, optionally coupled with other types of processing, such as extraction or crystallization. Since a large portion of industrially produced PDA is used for polyamide production, for which less stringent water content requirements apply than for isocyanate production, complex drying down to water contents of <500 ppm is sometimes dispensed with.It is also possible that a previously dried PDA may reabsorb water through contact with, for example, atmospheric moisture, so that the water content ultimately exceeds the stated limit of 500 ppm and is no longer suitable for use in a phosgenation reaction. The present process can be used to reduce the water content of such a PDA to acceptable levels for phosgenation.

[0021] According to the invention, the distillation can be carried out discontinuously as a batch distillation or continuously, with an azeotrope containing water and monochlorobenzene preferably being withdrawn from the distillation apparatus as a gaseous vapor stream. The distillation is preferably carried out at a pressure of <250 kPa, preferably <101.3 kPa, particularly preferably <60 kPa, measured at the top of the distillation column.

[0022] It is essential to the invention that the distillation takes place in the presence of an entraining agent containing monochlorobenzene. For this purpose, it is possible, for example, to add the monochlorobenzene to the 1,5-pentanediamine before it is introduced into the distillation apparatus or to introduce the monochlorobenzene separately into the distillation apparatus so that contact between 1,5-pentanediamine and monochlorobenzene only occurs there. Preferably, essentially pure monochlorobenzene is used as the entraining agent. However, it is also possible for the entraining agent containing monochlorobenzene to be an entraining agent mixture of monochlorobenzene and at least one further solvent such as, for example, toluene, xylene or o-dichlorobenzene. In this case, entraining agent mixtures of monochlorobenzene and o-dichlorobenzene are preferred. The entraining agent preferably contains at least 5% by weight of monochlorobenzene, particularly preferably at least 20% by weight.-% monochlorobenzene, and very particularly preferably at least 40 wt.% monochlorobenzene. The use of such mixtures can be advantageous if subsequent phosgenation is also to take place in the presence of a corresponding solvent mixture. The entraining agent particularly preferably consists of at least technically pure monochlorobenzene. In this case, the corresponding mixtures can be easily adjusted after drying, if necessary.

[0023] To avoid or at least minimize thermal decomposition of the PDA, it is preferable to carry out the distillation at a bottom temperature of <200 °C, preferably <160 °C, more preferably <140 °C, and most preferably <130 °C. The bottom temperature can be adjusted via the pressure inside the column. The bottom temperature is preferably >80 °C, more preferably >100 °C, most preferably >110 °C, and most preferably >120 °C. This enables efficient condensation of the distillation vapors.

[0024] The vapors from the distillation are preferably at least partially condensed in a condenser after leaving the column. The temperature of the condensate is preferably in the range from 5 °C to 115 °C, more preferably in the range from 10 °C to 100 °C, and most preferably in the range from 20 °C to 70 °C. The constituents of the vapors condensed in this process are subsequently subjected to phase separation in at least one phase separation apparatus. In order to improve phase separation into a predominantly aqueous and a predominantly organic phase, it is preferable at higher condensation temperatures to cool the condensate to a temperature in the range from 5 °C to 65 °C, preferably in the range from 10 °C to 50 °C, and more preferably in the range from 15 °C to 45 °C, before entering the phase separation apparatus. All embodiments familiar to the person skilled in the art can be used as phase separation apparatus.The separation is preferably carried out in a gravity separator, such as a settler. If necessary, appropriate internals such as plates, coalescer pads, or electrophoresis cells can be used as coalescence aids, or additives such as salts can be added to the condensed liquid.

[0025] The organic phase obtained in the phase separation is at least partially, preferably completely, recycled as reflux to the distillation apparatus, while the resulting aqueous phase is at least partially, preferably completely, removed from the system and, if appropriate, further processed to recover valuable constituents or simplify disposal. The drying according to the invention can be carried out, for example, using a conventional distillation apparatus. This preferably comprises at least one, particularly preferably exactly one column, with 2 to 50, preferably 5 to 30, and particularly preferably 10 to 25 theoretical plates. Preferably, the at least one column contains so-called separating internals to increase the mass transfer area. These internals can, for example, be various types of mass transfer trays (bubble cap trays, sieve trays, valve trays, etc.).), packings with a random bed of random packings or so-called structured packings, the latter usually having a low pressure drop and are therefore preferred. Distillation is preferably carried out at a pressure < 250 kPa, preferably < 101.3 kPa, particularly preferably < 60 kPa, measured at the top of the distillation column. A low pressure enables distillation at lower temperatures and reduces the risk of yield losses due to side reactions of the 1,5-pentanediamine. However, it is always accompanied by a low gas density in the distillation apparatus, so that very large apparatus are required for high throughputs at low pressure. In addition, condensation of the vapors at low pressure requires lower temperatures, so that the effort required to cool the vapors increases.It is therefore preferred to operate the column at a pressure >5 kPa, particularly preferably >10 kPa and most preferably >20 kPa, measured at the top of the column.

[0026] If the drying is carried out as a discontinuous distillation (batch distillation), it is preferred if the mass ratio of monochlorobenzene to PDA in the mixture to be distilled at the start of the distillation is in the range from 1: 100 to 100: 1, preferably in the range from 1: 10 to 10: 1 and very particularly preferably in the range from 1: 2 to 2: 1. The distillation is then preferably carried out until the desired water content is reached in the distillation pot, in which a mixture of 1,5-pentanediamine and monochlorobenzene with a water content of less than 500 ppm, preferably less than 200 ppm and very particularly preferably less than 100 ppm, based on the pentamethylenediamine present, is then present. If a solvent-free pentamethylenediamine is required for the subsequent process, the distillation can be continued at reduced pressure and / or elevated temperature until the monochlorobenzene has also been separated overhead.

[0027] In a preferred embodiment of the process, drying takes place as a continuous distillation. In this embodiment, it is possible to introduce the mixture to be distilled directly into the column, and distillation takes place after a steady state has been reached under approximately constant conditions.

[0028] In a particularly advantageous embodiment of this continuous distillation, the column also comprises a stripping section in addition to the rectifying section, and a largely entraining agent-free dried 1,5-pentanediamine can be withdrawn very efficiently from the bottom of the column in one step. This is particularly advantageous if the dried 1,5-pentanediamine is subsequently to be converted to 1,5-pentane diisocyanate in a gas-phase phosgenation, in which case solvent is often initially omitted from the amine, for example, to avoid further chlorination of the solvent during the phosgenation. In this advantageous embodiment, the entraining agent circulates at the top of the distillation column, i.e., it leaves the column as an azeotrope with water at the top and is then returned to the column as reflux after condensation and phase separation.Losses of entrainer are minimal due to its low solubility in the aqueous phase, so a single initial filling of the system with the entrainer is essentially sufficient. Minor unavoidable losses can be compensated for by adding fresh monochlorobenzene to the recycle stream or simply introducing it into the phase separation apparatus.

[0029] To carry out the continuous azeotropic distillation, it is preferred if the ratio of the total mass flow of monochlorobenzene into the column to the mass flow of PDA which is fed into the column as feed is in the range from 100:1 to 1:100, particularly preferably in the range from 10:1 to 1:10 and very particularly preferably in the range from 1:1 to 1:5. The total mass flow of monochlorobenzene into the column comprises both monochlorobenzene which is fed into the column together with the PDA as feed and monochlorobenzene which is fed to the column as reflux, i.e. the organic phase from the phase separation after condensation of the vapors, as well as any monochlorobenzene-containing streams fed separately into the column.

[0030] The invention further provides a rectification system comprising at least one column with a stripping section and a rectifying section, a feed line for a 1,5-diaminopentane-containing feed stream, which opens into a liquid distributor or a feed tray between the rectifying section and the stripping section, at least one internal or external evaporator for heating the bottom contents of the column, an air cooler for at least partial condensation of the vapors obtained, optionally a post-condenser for condensing further vapors, a vacuum connection for reducing the internal pressure in the column, a liquid-liquid separator for separating the condensed vapors into a predominantly aqueous and a predominantly organic phase, a return line for returning the predominantly organic phase from the liquid-liquid separator to the upper part of the column,a withdrawal line for the predominantly aqueous phase from the liquid-liquid separator and a discharge line for the dried 1,5-diaminopentane composition obtained at the bottom of the column. Furthermore, the rectification system may optionally be associated with devices known from the prior art, with which operating parameters of the rectification system, such as temperatures, heat input, mass flows, or the pressure in the column, can be measured and / or modified.

[0031] It is possible to use azeotropic distillation in combination with at least one further drying process, wherein the at least one further drying process is preferably a membrane separation process, a treatment with solid drying agents, an extraction, a crystallization, and / or the passage of stripping gas. In this embodiment, drying is preferably carried out first by azeotropic distillation, and the dried 1,5-diaminopentane composition obtained in step b) is then further dried using the further drying process. In this way, 1,5-diaminopentane compositions with a particularly low water content are accessible. The process according to the invention is synonymous with a process for producing such a dried 1,5-diaminopentane composition.

[0032] The invention further relates to a process for the preparation of pentamethylene diisocyanate by reacting 1,5-pentanediamine with phosgene, characterized in that the 1,5-pentanediamine has previously been dried in an azeotropic distillation using an entraining agent containing monochlorobenzene.

[0033] The phosgenation of the 1,5-pentanediamine dried according to the invention can be carried out, for example, in the gas phase. Processes for the gas-phase phosgenation of aliphatic diamines in general, but also of 1,5-pentanediamine, are well known to those skilled in the art. The phosgenation is carried out at temperatures in the range of 200 to 600 °C with an excess of phosgene, optionally in the presence of an inert gas or vapors of an inert solvent. The phosgenation is preferably carried out as described in WO2016042125 A1.

[0034] After the reaction has taken place in a preferably cylindrical reaction space, the reaction mixture is freed from the pentamethylene diisocyanate formed, preferably by selective condensation in an inert solvent such as monochlorobenzene or o-dichlorobenzene, which is then processed into pure pentamethylene diisocyanate in a multi-stage distillation.

[0035] In a further embodiment, the phosgenation of the 1,5-diaminopentane dried according to the invention takes place in the liquid phase in step . The reaction can then be carried out in various ways. Either the diamine is reacted directly with an excess of phosgene in an inert liquid medium, preferably in a two-stage, so-called cold-hot phosgenation (base phosgenation), or the corresponding salt is first converted by reaction with hydrogen chloride gas or carbon dioxide in an inert liquid medium and then reacted with excess phosgene similarly to the hot phosgenation step of the base phosgenation (hydrochloride or carbamate phosgenation). The entraining agent used during drying is particularly suitable as a liquid medium.This results in the further advantage for the alternative embodiment of the process according to the invention that a smaller amount or no further monochlorobenzene needs to be added for the subsequent phosgenation and the process is more efficient. Thus, a likewise preferred subject of the invention is a process for preparing 1,5-diisocyanatopentane by liquid-phase phosgenation of the dried 1,5-diaminopentane composition prepared according to the invention. In both the base phosgenation and the amine hydrochloride or carbamate phosgenation, the remaining phosgene and hydrogen chloride gas are preferably blown out with an inert gas, preferably nitrogen, after the reaction has ended. If necessary, filtration can be carried out to remove any solids present, such as unreacted amine hydrochlorides.The pentamethylene diisocyanate formed is then preferably processed in a multi-stage distillation to produce pure pentamethylene diisocyanate.

[0036] Pentamethylene diisocyanate prepared in this way is ideally suited for the production of paint polyisocyanates, i.e., oligomeric polyisocyanates containing allophanate groups, biuret groups, isocyanurate groups, uretdione groups, urethane groups, and / or iminooxadiazinedione groups. Thus, the use of a 1,5-diisocyanatopentane prepared according to the invention for the production of oligomeric polyisocyanates containing allophanate groups, biuret groups, isocyanurate groups, uretdione groups, urethane groups, and / or iminooxadiazinedione groups is a further subject of the invention.

[0037] Examples

[0038] Example 1 (comparison example):

[0039] Based on the disclosure of CN216571619 U, a distillation apparatus consisting of a distillation pot, column, condenser, and separating flask was calculated as a model. A rectifying section with 20 separation stages was assumed for the column, and the temperature in the distillation pot was set at a maximum of 130 °C. Exceeding this temperature was prevented by reducing the pressure. A mixture consisting of 50.0 wt.% PDA, 1.0 wt.% water, and 49.0 wt.% ODB was distilled in batch mode until the water content in the distillation pot was reduced to 50 ppm by mass. The vapors withdrawn at the top of the column were condensed and subjected to phase separation, with the predominantly organic phase being returned to the column as reflux, and the predominantly aqueous phase being discharged. At the end of the distillation, a pressure of approximately 225 mbar(a) was established at the top of the column.The aqueous phase removed during distillation contained approximately 84.8 wt.% water, as well as approximately 8.0 wt.% ODB and 7.2 wt.% PDA. This corresponds to a loss of approximately 0.17 wt.% of the PDA used and approximately 0.2 wt.% of the amount of ODB entraining agent used.

[0040] Example 2 (according to the invention):

[0041] The model calculation from Example 1 was repeated, this time using a mixture consisting of 50.0 wt.% PDA, 1.0 wt.% water, and 49.0 wt.% MCB. In contrast to the calculation in Example 1, in this case a head pressure of 565 mbar(a) was obtained at the end of the distillation. The aqueous phase discharged during the distillation contained, in addition to 99.8 wt.% water, approximately 0.2 wt.% MCB and less than 1 wt. ppm of PDA. Thus, there was virtually no loss of PDA with the discharged water and only a very small loss of less than 0.01 wt.% of the amount of entrainer MCB used.

[0042] Example 3 (according to the invention)

[0043] The model calculation from Example 1 was repeated, this time using a mixture consisting of 94.3 wt.% PDA, 1.9 wt.% water, and 3.4 wt.% MCB. The distillation in this simulation proceeded similarly to Example 2, with the difference that the head pressure had to be reduced to 238 mbar at the end of the distillation in order not to exceed the bottom temperature of 130 °C. The aqueous phase discharged during the distillation contained, in addition to 99.9 wt.% water, approximately 0.1 wt.% MCB and less than 1 ppm by weight of PDA. Thus, there was virtually no loss of PDA with the discharged water and only a very small loss of less than 0.1 wt.% of the amount of entrainer MCB used. Due to the significantly lower amount of entrainer used, the absolute loss of entrainer was similar to that in Example 2. Example 4 (according to the invention)

[0044] The model calculation from Example 1 was repeated once again, this time using a mixture consisting of 50.0 wt.% PDA, 1.0 wt.% water, and 24.5 wt.% each of MCB and ODB. At the end of the distillation, a head pressure of 405 mbar(a) was established, and the aqueous phase discharged during the distillation contained, in addition to 99.8 wt.% water, approximately 0.2 wt.% MCB. It contained less than 1 wt. ppm of PDA and ODB. Thus, there was virtually no loss of PDA or ODB and only a very slight loss of less than 0.01 wt.% of the amount of entrainer MCB used.

[0045] Example 5 (comparison example)

[0046] The model calculation from Example 1 was repeated, this time assuming a rectifying section of 40 separation stages for the column. At the end of the distillation, a pressure of approximately 225 mbar(a) was restored at the top of the column. The aqueous phase discharged during the distillation contained, in addition to approximately 93.1 wt.% water, approximately 6.5 wt.% ODB and 0.4 wt.% PDA. This corresponds to a loss of approximately 0.01 wt.% of the PDA used and just over 0.1 wt.% of the ODB entraining agent used.

[0047] Example 6 (according to the invention)

[0048] In this example, the drying was calculated as a continuous azeotropic distillation. The input stream consisted of 50 wt.% MCB, 49 wt.% PDA, and 1 wt.% water. A column with an evaporator and 31 separation stages was used as the distillation device, with the feed introduced on the 15th stage. The vapors withdrawn at the top of the column were condensed at 50 °C and separated into an organic and an aqueous phase. The latter was discharged from the system, while the organic phase was fed to the top of the column as reflux. The heating capacity of the column evaporator was adjusted so that the product stream withdrawn at the bottom contained a water content of 100 wt. ppm based on the PDA contained. Furthermore, the column top pressure was reduced to 574 mbar(a), resulting in a temperature of 130 °C at the bottom. The discharged water stream contained less than 0.1 wt% of MCB and less than 1 wt%.-ppm to PDA.

[0049] Example 7 (comparison example)

[0050] In this example, the drying process was calculated as a continuous azeotropic distillation. The input stream consisted of 50 wt.% ODB, 49 wt.% PDA, and 1 wt.% water. A column with an evaporator and 31 separation stages was used as the distillation device, with the feed introduced on the 15th stage. The vapors withdrawn at the top of the column were condensed at 50 °C and separated into an organic and an aqueous phase. The latter was discharged from the system, while the organic phase was fed to the top of the column as reflux. The heating capacity of the column evaporator was adjusted so that the product stream withdrawn at the bottom contained a water content of 100 wt. ppm based on the PDA contained. The top pressure of the column had to be reduced to 227 mbar(a) in order to achieve the same low bottom temperature of 130 °C as in Example 6. The discharged water stream contained 94.3 wt.% water as well as approx.0.9 wt.% PDA, corresponding to approximately 0.02% of the amount used in the feed, and 4.8 wt.% ODB, corresponding to approximately 0.1% of the entraining agent ODB used in the feed.

[0051] Example 8 (according to the invention)

[0052] The model calculation from Example 6 was modified such that a PDA was taken from the bottom of the distillation apparatus that was practically free of water and the entraining agent MCB. To do this, the MCB was removed from the column feed stream, so that a mixture consisting of 98 wt.% PDA and 2 wt.% water was fed into the column at the 15th stage. For phase separation, an initial charge of MCB was assumed, so that the MCB entered the column via the reflux, evaporated there again, and ultimately an MCB cycle was formed at the top of the column via the phase separation. Losses of MCB were compensated by a small addition of MCB to the reflux stream to the column. The bottom product PDA contained a total of approximately 1 wt. ppm of water and MCB. To maintain the bottom temperature of 130 °C, the column top pressure was reduced to 214 mbar(a). The discharged water stream contained less than 0.1 wt.-% of MCB and less than 1 ppm by weight of PDA.

Claims

1. A process for drying 1,5-diaminopentane comprising the following steps: a) providing at least one mixture of substances containing 1,5-diaminopentane and water, b) distilling the mixture of substances in at least one distillation column to obtain vapors and a dried 1,5-diaminopentane composition, characterized in that the distillation in step b) is carried out azeotropically using an entraining agent containing monochlorobenzene.

2. Process according to claim 1, characterized in that the azeotropic distillation is carried out discontinuously or continuously.

3. Process according to one of claims 1 or 2, characterized in that the azeotropic distillation is carried out at a pressure of < 250 kPa, preferably < 101.3 kPa, particularly preferably < 60 kPa, measured at the top of the distillation column.

4. Process according to one of claims 1 to 3, characterized in that the entraining agent used contains at least 5% by weight, preferably at least 20% by weight and particularly preferably at least 40% by weight of monochlorobenzene or that the entraining agent consists of at least technically pure monochlorobenzene.

5. Process according to one of claims 1 to 4, characterized in that the bottom temperature is > 80 °C, preferably > 100 °C, particularly preferably > 110 °C and very particularly preferably > 120 °C.

6. Process according to one of claims 1 to 5, characterized in that the vapors from the distillation are at least partially condensed and the condensate obtained is separated into a predominantly aqueous and a predominantly organic phase at a temperature in the range from 5 °C to 65 °C, preferably in the range from 10 °C to 50 °C and particularly preferably in the range from 15 °C to 45 °C.

7. The process according to any one of claims 1 to 6, characterized in that the azeotropic distillation is used in combination with at least one further drying process, wherein the at least one further drying process is a membrane separation process, a treatment with solid drying agents, an extraction, a crystallization and / or the passage of stripping gas.

8. The method according to any one of claims 1 to 7, characterized in that the substance mixture provided in step a) has a water content of more than 500 ppm, preferably of 0.08 wt.% to 10 wt.%, particularly preferably from 0.1 wt.% to 5 wt.% and very particularly preferably from 0.15 wt.% to 3 wt.%, based on the pentamethylenediamine contained in the mixture.

9. The process according to any one of claims 1 to 8, characterized in that the 1,5-diaminopentane in the substance mixture provided in step a) originates from a recycling process and / or was produced biotechnologically.

10. The process according to any one of claims 1 to 9, characterized in that the substance mixture provided in step a) contains at least a portion of the monochlorobenzene used as entraining agent in step b).

11. A process for the preparation of 1,5-diisocyanatopentane, comprising liquid phase phosgenation or gas phase phosgenation, preferably liquid phase phosgenation, of the dried 1,5-diaminopentane composition prepared according to any one of claims 1 to 10.

12. Use of a 1,5-diisocyanatopentane prepared according to claim 11 for the preparation of oligomeric polyisocyanates containing allophanate groups, biuret groups, isocyanurate groups, uretdione groups, urethane groups and / or iminooxadiazinedione groups.

13. A rectification system comprising at least one column with a stripping section and a rectifying section, a feed line for a 1,5-diaminopentane-containing feed stream, which opens into a liquid distributor or a feed tray between the rectifying section and the stripping section, at least one internal or external evaporator for heating the bottom contents of the column, an air cooler for at least partially condensing the vapors obtained, optionally a post-condenser for condensing further vapors, a vacuum connection for reducing the internal pressure in the column, a liquid-liquid separator for separating the condensed vapors into a predominantly aqueous and a predominantly organic phase, a return line for returning the predominantly organic phase from the liquid-liquid separator to the upper part of the column,a withdrawal line for the predominantly aqueous phase from the liquid-liquid separator and a discharge line for the dried 1,5-diaminopentane composition obtained at the bottom of the column.

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