PROCESS FOR PRODUCING METHYLENEBIS(CYCLOHEXYLAMINE)

Abstract

The present invention provides a process for producing methylenebis(cyclohexylamine), comprising the steps of 1) catalytically hydrogenating MDA, 2) removing the catalyst and 3) subsequently distilling the product of the hydrogenation, in which at least one dividing-wall column is used in step 3). Exposure to high temperature and residence time of the product is reduced and problems due to crystallization do not occur. The methylenebis(cyclohexylamine) isomer ratio also may remain largely constant during the distillation.

Claims

1. A process for producing methylenebis(cyclohexylamine), comprising the steps of 1. catalytically hydrogenating MDA, 2. removing the catalyst and 3. subsequently distilling the product of the hydrogenation, wherein at least one dividing-wall column is employed in the distillation in step 3).

2. The process according to claim 1, wherein; a supported catalyst is used as catalyst during said catalytically hydrogenating MDA, said supported catalyst contains, an active metal in an amount of 0.01% to 20% by weight based on the supported catalyst, and wherein the active metal is ruthenium alone or ruthenium and at least one metal of subgroups I, VII or VIII of the periodic table of the elements.

3. The process according to claim 1, wherein the MDA comprises at least 70% by weight of 4,4-diaminodiphenylmethane and 0.01% to 2% by weight of N-methyl compounds, in each case based on the total mass of compounds having aromatic rings.

4. The process according to claim 1, wherein the distillation of the hydrogenation product in step 3) is carried out exclusively with a dividing-wall column.

5. The process according to claim 1, wherein the dividing wall of the at least one dividing-wall column is continuously present at a height of 15 to 80% of the dividing-wall column, measured from the lower end.

6. The process according to claim 1, wherein the dividing wall of the at least one dividing-wall column has an offset of 0 to 30% of the diameter from the middle towards the sidestream region or inflow region.

7. The Process according to claim 1, wherein the dividing wall of the at least one dividing-wall column is designed as an asymmetric dividing wall.

8. The process according to claim 1, wherein the distillation with at least one dividing-wall column in step 3) is operated such that: a) the inflow is located at the height of at least a portion of the dividing wall; b) the sidestream takeoff for drawing off purified methylenebis(cyclohexylamine) is located at the height of at least a portion of the dividing wall, on the other side of the dividing wall from the inflow; c) the distillate is withdrawn at the top of the dividing-wall column and partly discharged and partly returned to the dividing-wall column and d) the bottoms located at the base of the dividing-wall column is discharged.

9. The process according to claim 8, wherein the distillate is withdrawn in step c) such that: the distillate is withdrawn at the top of the dividing-wall column, it undergoes at least partial condensation in a connected condenser, and at least a portion of the condensate is returned to the top region of the dividing-wall column, and a low boilers stream possibly still present in volatile form downstream of the condenser is discharged together with non-returned condensate.

10. The process according to claim 1, wherein the inflow of the at least one dividing-wall column is present at a height of 25 to 66% of the height of the column, measured from the lower end.

11. The process according to claim 1, wherein the at least one dividing-wall column has a number of theoretical plates of from 10 to 90.

12. The process according to claim 1, wherein the at least one dividing-wall column is operated at a bottoms temperature of from 190 to 300 C.

13. The process according to claim 1, wherein the liquid load below the sidestream takeoff and above the bottoms and above the lower end of the dividing wall is less than or equal to 1.5 m.sup.3/(m.sup.2h).

14. Process according to claim 1, wherein the sidestream takeoff of the at least one dividing-wall column is located at a height of 30 to 60% of the column, measured from the lower end.

15. Process according to claim 1, wherein the packing beds of the at least one dividing-wall column are 2 to 7 metres in height.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0088] FIG. 1 shows a variant of the dividing wall which achieve favourable effects.

[0089] FIG. 2 shows another variant of the dividing wall which achieve favourable effects.

[0090] FIG. 3 shows another variant of the dividing wall which achieve favourable effects.

[0091] FIG. 4 shows another variant of the dividing wall which achieve favourable effects.

[0092] FIG. 5 shows another variant of the dividing wall which achieve favourable effects.

[0093] FIG. 6 shows a schematic design for the entire process.

[0094] These found that certain executions of the dividing wall achieve favourable effects. The various variants are depicted in FIGS. 1, 3, 4 and 5. The executions of the wall in FIGS. 1, 3, 4 can also be found in patent specification EP 2 569 274 B1. In contrast to the process in said patent, the process of the invention is characterized by a lower operating pressure, the consequently altered gas velocities and the low pressure drop in the column.

[0095] Particularly preferably, the process of the invention is a process using a dividing-wall column having at least one dividing wall with one of the following executions: [0096] a) The dividing wall may preferably extend from a dividing-wall-free bottoms region up to a dividing-wall-free top region. In this case, the feedstocks are able to pass across the entire cross section both in the top region and in the bottoms region. Further preferably, the dividing wall runs continuously from 10% to 90% of the height of the column, in each case measured from the lower end of the column. Further preferably, the dividing wall runs continuously from 20 to 80% of the height of the column, even more preferably from 25 to 75%. The position of the dividing wall in the regions mentioned above permits particularly efficient operation of the column with fulfilment of the high separation challenges.

[0097] The dividing wall is normally located in the middle of the column. To achieve advantageous properties, the dividing wall can in this execution also have an offset towards the inflow or towards the sidestream takeoff. Preferably, the offset of the dividing wall has a value of between 0 and 30% of the diameter from the centre towards the sidestream region (regions 4a, 4b in FIG. 1) or towards the inflow region (regions 3a, 3b in FIG. 1). This value is further preferably between 0 and 20%.

[0098] The inflow is further preferably located on one side of the dividing wall at a height between 25 and 66% of the height of the column, measured from the lower end of the column. Further preferably, above and below the inflow there are between 2 and 50 theoretical plates that are separated from the other side of the dividing wall.

[0099] The sidestream is in this execution preferably removed on the other side of the dividing wall at a height of 30 to 60%, further preferably at a height of 40 to 60%, even further preferably at a height of 45 to 55%, of the column height, measured from the lower end.

[0100] The dividing-wall column designed in this way is a particularly good solution for the purification of methylenebis(cyclohexylamine) that those skilled in the art had not anticipated for the specified considerations of the separation challenges and energy requirements of the requisite pressure drop, at particularly low temperatures, and with achievement of particularly high purity. This configuration makes it possible to separate low, medium and high boilers using just one condenser and just one evaporator. [0101] b) To achieve advantageous results, the dividing wall can also be designed such that the dividing wall closes off the lower end of the column but not the top region. In this case, the dividing wall preferably closes off the part of the column on the side of the sidestream takeoff (FIG. 3) or extends as far as the base of the bottoms.

[0102] The dividing wall is normally located in the middle of the column. To achieve advantageous properties, the dividing wall can in this execution also have an offset towards the inflow and towards the sidestream takeoff. Preferably, the offset of the dividing wall has a value of between 0 and 30% of the diameter from the middle towards the sidestream region or inflow region. This value is further preferably between 0 and 20%.

[0103] The inflow is further preferably located on one side of the dividing wall at a height between 25 and 66% of the height of the column, measured from the lower end of the column. Further preferably, above and below the inflow there are between 2 and 50 theoretical plates that are separated from the other side of the dividing wall.

[0104] The sidestream is in this execution further preferably removed on the other side of the dividing wall at a height between 30 and 60% of the column height, measured from the lower end.

[0105] The sidestream is preferably removed at the lower level of the sidestream region of the dividing wall than complete removal. Further preferably, a portion of the stream is transferred again to the gas phase by an evaporator and reintroduced at the same level as the sidestream takeoff. Where the dividing wall continues all the way to the bottom, this results in two independent bottoms. Preferably, the bottoms discharge is implemented with two evaporators and with plates, which in a) are present below the dividing wall across the whole diameter of the column, in equal number on either side. The sidestream is in this case removed as a second bottoms stream. [0106] c) To achieve advantageous results, the dividing wall can also be designed such that the dividing wall closes off the top region, but not the lower end of the column. Preferably, the dividing wall constitutes a barrier wall to the dividing-wall-free top region (FIG. 4) or a dividing wall that continues all the way to the top. The modifications in this concept too are similar to those in b). The sidestream is however preferably removed not as a second bottoms stream or in liquid form above the barrier wall, but as a second distillate or in condensed form below the barrier wall. In this concept, a second condenser is necessary. An advantage is that, above the dividing wall, no low boilers can pass into the sidestream region of the dividing-wall column and contaminate the sidestream. [0107] d) To achieve advantageous results, the dividing wall may also be designed as an asymmetric dividing wall (FIG. 5). An asymmetrically designed dividing wall has a horizontal offset. Further preferably, the horizontal offset is in this case designed such that the lower end of the dividing wall is closer to the sidestream takeoff than the upper end. As a consequence, the cross-sectional area below the sidestream takeoff is reduced there, whereas it is increased in the upper region on the side of the inflow. The advantage of this design is that the liquid load and gas distribution, and thus the pressure drop of the column, is optimized. Further preferably, the offset of the dividing wall above the inflow is 2 to 30% of the cross-sectional area of the column and the offset of the dividing wall below the sidestream is between 2 and 40% of the cross-sectional area of the column. This can have a particularly favourable effect on quality, yield and energy requirements.

[0108] FIG. 6 shows a preferred schematic design for the entire process, beginning with the reaction (24), subsequent catalyst removal (22), solvent removal (30) and subsequent purification in the dividing-wall column (31).

EXAMPLES

Example 1

[0109] In order to demonstrate the feasibility of separation in a dividing-wall column, experiments were carried out on a pilot scale. For this, a column having a diameter of 150 mm was operated that in the middle region was divided into two columns each having a diameter of 100 mm. The column had a total height of 19 metres, 9 metres of which were filled with a 500 m.sup.2/m.sup.3 fabric packing. The bottoms was made of metal and comprised a bottoms circuit and an evaporator (10).

[0110] The column built onto the bottoms was made of glass. A metal condenser (6) was built onto the glass column.

[0111] The glass column was subdivided into four regions: in the upper region (2) the column had two metres of fabric packing, in the inflow region (3a and 3b) four metres of fabric packing (the inflow was loaded in the middle of the inflow region), in the sidestream region four metres of packing (4a and 4b) and in the lower region (5) two metres of fabric packing. The distillate was partly returned to the column as a return flow (8) and partly discharged as a low boilers stream (7). The sidestream (9) was removed in the middle of region 4. The bottoms stream (11) was removed from the bottoms circuit.

Procedure

[0112] Methylenebis(cyclohexylamine) from the hydrogenation of MDA was after the removal of solvent separated with the above setup (see also FIG. 1). For this, in pilot tests 12 kg/h of methylenebis(cyclohexylamine) was loaded in the middle of the prefractionation region (3a and 3b) on an existing column. The temperature of the liquid inflow was here 170 C. The pressure at the top of the column was set at 7 to 10 mbar. The condensed vapour was partly discharged as a distillate discharge and partly returned to the column as a return flow. The amount of liquid obtained above the dividing wall was distributed between the two sides in a ratio of 25% (inflow region, above 3a) and 75% (sidestream region, above 4a). In the middle of the sidestream region (4a, 4b), the purified methylenebis(cyclohexylamine) is removed in purities of over 99.3%.

[0113] The bottoms flow was taken from the bottoms circuit so as to minimize losses of methylenebis(cyclohexylamine). The product streams and purities thereof are controlled by means of a closed-loop control concept (FIG. 2) that makes appropriate adjustments to the streams via filling level, temperature and flow controls.

Example 2

[0114] As an alternative to the experimental conditions in the previous experiment, the column was operated with a liquid split of 40% inflow region (3a, 3b) and 60% sidestream region (4a, 4b). In the event of changes to the inflow composition, the requirements for the liquid split between the two sides change and this must be altered in order to ensure an optimal separation, taking into consideration the energetic optimum.

Example 3

[0115] As an additional alternative, the load in the column was increased (about 40%) via a higher inflow stream (16.6 kg/h) but with the same liquid split as in experiment 1. The amount of energy was adhered to approximately here.

[0116] The results have shown that a high methylenebis(cyclohexylamine) purity can be achieved and at the same time a very high yield, with low losses in the bottoms stream and distillate streams.

[0117] The design as a glass column meant it was possible to look into the column during and after the experiments: no contaminants were detected.

[0118] Table 1 below summarizes the operating parameters and results for examples 1-3:

TABLE-US-00001 TABLE 1 No. 1 2 3 Top pressure mbar, a 7 9 8 Bottoms pressure mbar, a 13 18 16 Top temperature C. 127.5 140.7 138.5 Bottoms temperature C. 223.6 225.5 226.2 Liquid split 25/75 40/60 25/75 Return flow kg/h 13.69 21.39 18.87 Inflow temperature C. 170 170 170 Inflow kg/h 11.94 11.95 16.63 Distillate kg/h 0.11 0.13 0.18 Sidestream kg/h 10.00 9.91 13.94 Bottoms kg/h 1.83 1.91 2.51 Methylenebis(cyclohexylamine) wt % 11.92 20.84 22.07 in distillate Methylenebis(cyclohexylamine) wt % 99.49 99.43 99.09 in sidestream Methylenebis(cyclohexylamine) wt % 6.77 11.85 9.20 in bottoms Energy per kg kJ/kg 461 763 491 methylenebis(cyclohexylamine) in sidestream

LIST OF REFERENCE NUMERALS

[0119] 1Inflow [0120] 2Upper region/top [0121] 3Inflow region, prefractionation region, a above inflow, b below inflow [0122] 4Sidestream region, a above sidestream takeoff, b below sidestream takeoff [0123] 5Lower region/bottoms [0124] 6Condenser [0125] 7Low boilers stream [0126] 8Return flow [0127] 9Sidestream takeoff [0128] 10Evaporator [0129] 11Bottoms stream [0130] 12Distillate vessel [0131] 13Temperature control [0132] 14Filling level control [0133] 15Flow control [0134] 16Sidestream evaporator [0135] 17Sidestream evaporator recirculation [0136] 18Sidestream condenser [0137] 19Sidestream return flow [0138] 20Condenser/solvent column [0139] 21Inflow/solvent column [0140] 22Catalyst separator [0141] 23Reaction product [0142] 24Reactor [0143] 25Reaction reactants [0144] 26Solvent recirculation [0145] 27Catalyst recirculation [0146] 28Evaporator/solvent column [0147] 29Return flow/solvent column [0148] 30Solvent removal (column) [0149] 31Dividing-wall column