METHOD FOR CONTINUOUS PRODUCTION OF ADIPONITRILE

Abstract

A process for the continuous preparation of adiponitrile by hydrocyanation of 3-pentenenitrile is described, wherein a) 3-pentenenitrile is hydrocyanated to give a reaction output comprising adiponitrile, b) in a work-up 1, a mixture comprising cis-2-methyl-2-butenenitrile and cis-2-pentenenitrile is separated off as overhead product from the reaction output from the reactor R1 in a first distillation apparatus, c) the mixture comprising cis-2-methyl-2-butenenitrile and cis-2-pentenenitrile from step b) is continuously isomerized in the presence of aluminum oxide as catalyst in a reactor R2 to give a product mixture comprising 3-pentenenitrile, d) cis-2-methyl-2-butenenitrile is separated off as overhead product from the reaction output from the reactor R2 in a distillation apparatus in a work-up 2 and discharged.

Claims

1. A process for the continuous preparation of adiponitrile by hydrocyanation of 3-pentenenitrile, wherein a) 3-pentenenitrile or a mixture comprising 3-pentenenitrile is hydrocyanated by means of hydrocyanic acid in the presence of at least one nickel(0) complex as catalyst, free ligand, and at least one Lewis acid in a reactor R1 to give a reaction output comprising adiponitrile, 2-methylgiutaronitrile, the nickel(0) complex, free ligand, Lewis acid, catalyst degradation products, unreacted 3-pentenenitrile and, as secondary components, cis- and trans-2-methyl-2-butenenitrile and also cis- and trans-2-pentenenitrile, b) in a work-up 1, a mixture comprising cis-2-methyl-2-butenenitrile and cis-2-pentenenitrile is separated off as overhead product, a mixture comprising adiponitrile, nickel(0) complex, free ligand, at least one Lewis acid and catalyst degradation products is separated off as bottom product and a mixture comprising trans-2-methyl-2-butenenitrile, trans-2-pentenenitrile and 3-pentenenitrile is separated off at a side offtake from the reaction output from the reactor R1 in a first distillation apparatus, and the side offtake product is fractionated in a second distillation apparatus in such a way that trans-2-methyl-2-butenenitrile is separated off as overhead product and discharged and 3-pentenenitrile and trans-2-pentenenitrile are obtained as bottom product and recirculated to the 3-pentenenitrile hydrocyanation in step a), c) the mixture comprising cis-2-methyl-2-butenenitrile and cis-2-pentenenitrile from step b) is continuously isomerized in the presence of aluminum oxide as catalyst in a reaction zone in a reactive distillation column R2 to give a 3-pentenenitrile-comprising product mixture, where the isomerization is carried out at temperatures of from 150 to 220° C. and pressures of from 1 to 15 bar in the liquid phase and the aluminum oxide has a BET surface area of from 50 to 450 m.sup.2/g and a pH of from 7 to 10.5, and cis-2-methyl-2-butenenitrile is separated off as overhead product and discharged, unreacted cis-2-pentenenitrile is separated off from a side offtake and recirculated to the reactor R2 in step c) and the 3-pentenenitrile-comprising bottom product is recirculated to the 3-pentenenitrile hydrocyanation in step a).

2. A process for the continuous preparation of adiponitrile by hydrocyanation of 3-pentenenitrile, wherein a) 3-pentenenitrile or a mixture comprising 3-pentenenitrile is hydrocyanated by means of hydrocyanic acid in the presence of at least one nickel(0) complex as catalyst, free ligand, and at least one Lewis acid in a reactor R1 to give a reaction output comprising adiponitrile, 2-methylglutaronitrile, the nickel(0) complex, free ligand, Lewis acid, catalyst degradation products, unreacted 3-pentenenitrile and, as secondary components, cis- and trans-2-methyl-2-butenenitrile and also cis- and trans-2-pentenenitrile, b) in a work-up 1, only cis-2-methyl-2-butenenitrile is separated off as overhead product and all remaining compounds are separated off as bottom product from the reaction output from the reactor R1 in a first distillation apparatus and the bottom product from the first distillation apparatus is fractionated in a second distillation apparatus in such a way that cis-2-pentenenitrile is obtained as overhead product, 3-pentenenitrile, trans-2-pentenenitrile and trans-2-methyl-2-butenenitrile are obtained via a side offtake and crude adiponitrile, nickel(0) complex, free ligand, the at least one Lewis acid and catalyst degradation products are obtained as bottom product and the side offtake product from the second distillation apparatus is distilled in a third distillation apparatus in such a way that trans-2-methyl-2-butenenitrile is discharged as overhead product and a mixture comprising trans-2-pentenenitrile and 3-pentenenitrile is separated off as bottom product and recirculated to the 3-pentenenitrile hydrocyanation in step a), c) cis-2-pentenenitrile from step b) is continuously isomerized in the presence of aluminum oxide as catalyst in a reaction zone in a reactive distillation column R2 to give a 3-pentenenitrile-comprising product mixture, where the isomerization is carried out at temperatures of from 150 to 220° C. and pressures of from 1 to 15 bar in the liquid phase and the aluminum oxide has a BET surface area of from 50 to 450 m.sup.2/g and a pH of from 7 to 10.5, and unreacted cis-2-pentenenitrile is separated off as overhead product and recirculated to the reactor R2 in step c) and the 3-pentenenitrile-comprising bottom product is recirculated to the 3-pentenenitrile hydrocyanation in step a).

3. The process according to any of claim 1, wherein beta-, gamma-, chi-, kappa-, delta-, theta-, eta-aluminum oxide or mixtures of these aluminum oxides are used as catalyst as aluminum oxide in step c).

4. The process according to claim 1, wherein from 10 to 100% by weight of the aluminum oxides is made up of boehmite in step c).

5. The process according to claim 1, wherein the aluminumoxide is used as shaped bodies in step c).

6. The process according to claim 1, wherein the aluminum oxide in step c) comprises from 10 ppm by weight to 30% by weight of further compounds, based on the sum of aluminum oxide and such compounds.

7. The process according to claim 1, wherein the BET surface area of the aluminum oxide in step c) is from 100 to 420 m.sup.2/g.

8. The process according to claims 1, wherein the space velocity over the catalyst in step c) is from 0.05 to 50 kg of cis-2-pentenenitrile per liter of aluminum oxide per hour.

9. The process according to claims 1, wherein the cis-2-pentenenitrile isomerization in step c) is carried out in the upflow or downflow mode in a tube reactor.

10. The process according to claims 1, wherein the catalyst in step a) comprises bidentate or polydentate phosphites, phosphinites, phosphonites and/or phosphines as ligands.

11. The process according to claims 1, wherein the 3-pentenenitrile used in the process originates from the hydrocyanation of butadiene.

12. The process according to claim 2, wherein beta-, gamma-, chi-, kappa-, delta-, theta-, eta-aluminum oxide or mixtures of these aluminum oxides are used as catalyst as aluminum oxide in step c).

13. The process according to claim 2, wherein from 10 to 100% by weight of the aluminum oxides is made up of boehmite in step c).

14. The process according to claim 2, wherein the aluminum oxide is used as shaped bodies in step c).

15. The process according to claim 2, wherein the aluminum oxide in step c) comprises from 10 ppm by weight to 30% by weight of further compounds, based on the sum of aluminum oxide and such compounds.

16. The process according to claim 2, wherein the BET surface area of the aluminum oxide in step c) is from 100 to 420 m.sup.2/g.

17. The process according to claim 2, wherein the space velocity over the catalyst in step c) is from 0.05 to 50 kg of cis-2-pentenenitrile per liter of aluminum oxide per hour.

18. The process according to claim 2, wherein the cis-2-pentenenitrile isomerization in step c) is carried out in the upflow or downflow mode in a tube reactor.

19. The process according to claim 2, wherein the catalyst in step a) comprises bidentate or polydentate phosphites, phosphinites, phosphorites and/or phosphines as ligands.

20. The process according to claim 2, wherein the 3-pentenenitrile used in the process originates from the hydrocyanation of butadiene.

Description

EXAMPLES

Batchwise Isomerization of cis-2-pentenenitrile (Orienting Experiments, Not According to the Invention)

[0136] The batchwise isomerization of cis-2-pentenenitrile was carried out in a 250 ml multineck flask provided with stirrer, thermometer, condenser and septum for sampling. In each experiment, 120 g of cis-2-pentenenitrile from Merck (CAS 25899-50-7) were initially placed in the flask.

[0137] The cis-2-pentenenitrile was admixed with 10% by weight of Al.sub.2O.sub.3 powder (triturated to powder in a mortar) as per the following table and heated under reflux (from 126 to 144° C.) at atmospheric pressure for 7 hours. During the course of the isomerization, the temperature increased as a result of the formation of pentenenitriles having boiling points higher than that of cis-2-pentenenitrile.

[0138] After 15 and 30 minutes, then after one hour in each case, samples were taken and analyzed by gas chromatography to determine their content of pentenenitriles.

[0139] A CP-Wax52CB separation column was used as GC column. The GC temperature program was 5 minutes isothermal at 50° C., then 8° C. temperature increase per minute up to a final temperature of 240° C.

[0140] The pH values for the aluminum oxides are either taken from the product data sheets of the manufacturers or were measured.

[0141] For pH measurements in the laboratory, 5 g of catalyst powder were placed together with 45 g of water in a glass beaker and the resulting 10% strength by weight suspension was stirred at room temperature by means of a stirrer (5000 revolutions per minute). The pH was measured at various times (e.g. after 5 and 30 minutes) by means of a calibrated pH electrode (Blue Line 18 pH, SI. Analysis) until a constant value was obtained.

[0142] The table shows batchwise isomerization results in the presence of aluminum oxides as catalysts as a function of increasing BET surface area and increasing pH. The results show that the rate of isomerization increases with increasing BET surface area and increasing pH. However, increasing amounts of oligomers (including dimers) were observed at the same time.

TABLE-US-00003 BET surface Reaction c− + t − Example Al.sub.2O.sub.3 area time 3 PN + No. type Company pH [m.sup.2/g] [h] c-2 PN t-2 PN 4 PN Oligomers C1 alpha-Al.sub.2O.sub.3 NorPro 8.4-8.7.sup.2) 1 2 99.1 0 0.4 0 2 58A Sigma-   6 ± 0.5 150 7 59.5 19.6 19.8 0.13 Aldrich acidic 3 WN-3 Sigma- 7.0 ± 0.5.sup.1) 155 7 46.5 29.6 22.7 0.29 Prod. No. Aldrich Neutral 199974 4 W B-2 Sigma- 9.5 ± 0.5.sup.1) 155 7 40.8 34.8 23.2 0.35 Prod. No. Aldrich Basic 199443 5 WN-6 Sigma- 7.3-8.0  200 7 42.9 32.5 23.4 0.31 Aldrich Basic 6 F-200 BASF SE 9.6-9.7.sup.2) 350 7 39.6 34.2 23.9 1.45 Basic 7 AC 108-1000 Nanoscale 7.9-8.1.sup.2) 311 2 33.6 38.1 23.6 3.7 Basic 7 32.2 38.0 23.2 5.7 8 Pural Mg Sasol 9.7 271 2 37.7 30.5 23.4 7.6 30 Basic 7 34.3 33.5 22.8 8.5 MgO-Al.sub.2O.sub.3 .sup.1)from data sheet .sup.2)own measurements

[0143] It was determined by GC-MS coupling that the high boilers in the retention time range from 22.5 to 28 minutes are pentenenitrile dimers having a molecular weight of 162.

[0144] The oligomer content of the reaction outputs is reported in percent by area: (sum of the dimer areas divided by the sum of all areas)×100.

[0145] The qualitative composition of aluminum oxides was determined by XRD analysis:

[0146] The aluminum oxides 58A, WA-1, WN-3, WN-6 and WB-2 have the same XRD spectra. The crystallinity is low. gamma-Al.sub.2O.sub.3 (tetragonal) and chi-Al.sub.2O.sub.3 (cubic) were found as phases.

[0147] The Al.sub.2O.sub.3 catalyst F-200 likewise has a low crystallinity. Boehmite AlO (OH) (orthorhombic) was comprised as main phase, additionally as in the case of the preceding catalysts gamma-Al.sub.2O.sub.3 (tetragonal) and chi-Al.sub.2O.sub.3 (cubic).

Continuous Isomerization of cis-2-pentenenitrile (Operating Life Experiment)

[0148] The continuous isomerization of cis-2-pentenenitrile to give pentenenitrile isomer mixtures comprising 3-pentenenitrile was carried out in the presence of Al.sub.2O.sub.3 balls (3.2 mm diameter) of the type Alcoa F-200, which had a BET surface area of 350 m.sup.2/g, a pH of from 9.6 to 9.7 and a total pore volume of 0.59 ml/g.

[0149] The cis-2-pentenenitrile used had a purity of 98.8%, with the balance to 100% consisting of other unsaturated isomeric C5-nitriles.

[0150] The isomerization was carried out in the upflow mode in a 250 ml tube reactor (reactor geometry 25 mm×450 mm). 130.6 g of Al.sub.2O3 catalyst were placed in the reactor. This corresponds to 250 ml of catalyst. The reactor was then pressurized with 7 bar of argon and the pressure regulator was set to 10 bar.

[0151] Commencing at an isomerization temperature of 125° C. and a pressure of 10 bar, 31.2 ml/h (25 g/h) of cis-2-pentenenitrile (space velocity over the catalyst 0.1 kg of cis-2-pentenenitrile per liter of catalyst and hour=100 kg of cis-2-pentenenitrile per m.sup.3 of catalyst and hour) were fed into the reactor.

[0152] FIG. 3 shows that, at a constant space velocity over the catalyst, the temperature firstly increases to 200° C. (autogenous pressure at 200° C. about 4 bar) over a period of 1000 hours and the reaction was carried out under the same reaction conditions for a further 1800 hours.

[0153] After 2800 hours, the space velocity over the catalyst was increased to 0.2 kg of cis-2-pentenenitrile per liter of catalyst and hour, which led to a changed curve. The experiment was stopped after a total of 3200 hours. The Al.sub.2O.sub.3 catalyst could be removed from the reactor without problems.

[0154] FIG. 3 shows the amounts (Content in percent by area in the gas chromatogram) of cis- and trans-3-pentenenitrile (PN) formed as a function of temperature (T) and reaction time (L), The graph shows that no deactivation of the catalyst was observed over the entire period of 3200 hours. Blockages caused by high boilers (oligomers) did not occur.

[0155] Table 3 shows that amounts of cis-+trans-3-pentenenitrile of from 19.2 to 23.9% were achieved within from 1000 to 2800 hours reaction time; values of from 21.9 to 19.3% were achieved at higher space velocity within from 2800 to 3200 hours.

[0156] Amounts of oligomers in the range from 0.3 to 2.0% were measured by gas chromatography.

[0157] Since it is possible that not all oligomers are measurable by gas chromatography, 100 g of the isomerization output were in each case distilled at 120° C. and 5 mbar via a distillation bridge. The distillate receiver was cooled. The amount of nonvolatile residue was on average from 1.0 to 1.5 g per 100 g of isomerization output, and the amounts of distillate were in the range from 98.5 to 99 g. The amounts of oligomers determined by gas chromatography were thus confirmed.

TABLE-US-00004 TABLE 3 Continuous isomerization of cis-2-pentenenitrile c- + t-3PN + Total % Reaction time c-2PN t-2PN 4-PN Oligomers by area [h] GC-% by area 501 69.6 13.4 15.8 98.8 1006 50.5 25.7 21.2 97.4 1506 56.8 20.2 19.2 0.3 96.5 2011 43.8 29.2 23.4 1.0 97.4 2490 39.6 31.0 23.9 2.0 96.5 3017 50.3 26.0 21.9 0.7 98.9 3196 61.0 17.0 19.3 97.3