Inhibiting CPI formation from adiponitrile

Abstract

Disclosed is a method for inhibiting the formation of by-products from dinitriles, such as the formation of cyclopentylideneimine (CPI) from Adiponitrile (ADN), comprising adding an effective amount of a Brnsted acid to the ADN. Also disclosed is a method of refining a dinitrile compound by distillation the method comprising the steps of: (a) supplying (i) a feedstream comprising the dinitrile compound and (ii) a Brnsted acid to a distillation apparatus; and (b) withdrawing from the distillation apparatus an overhead distillate stream comprising the dinitrile compound.

Claims

1. A method of refining a dinitrile compound by distillation, the method comprising: (a) supplying (i) a feedstream comprising the dinitrile compound, wherein the dinitrile compound is adiponitrile and wherein the feedstream comprises a Lewis acid that is ZnX.sub.2, BX.sub.3, or AlX.sub.3, wherein X represents a halogen, trifluoromethanesulfonate, methanesulfonate, or toluenesulfonate, and (ii) a Brnsted acid to a distillation apparatus, wherein the Brnsted acid is supplied to the distillation apparatus in an amount of from 5 to 5,000 ppm by weight, based on the total weight of the dinitrile-containing feedstream and the Brnsted acid, the amount of the Brnsted acid supplied to the distillation apparatus is effective to inhibit the formation of 2-cyanocyclopentlideneimine (CPI) from the dinitrile compound in the distillation apparatus, and the Brnsted acid does not degrade in the distillation apparatus; and (b) withdrawing from the distillation apparatus an overhead distillate stream comprising the dinitrile compound and withdrawing the Brnsted acid from the distillation apparatus in a bottoms stream comprising the Brnsted acid.

2. A method according to claim 1, wherein the amount of Lewis acid present in the dinitrile-containing feedstream is in the range of from 50 to 10,000 ppm by weight based on the total weight of the dinitrile-containing feedstream.

3. A method according to claim 1, wherein the feedstream to the distillation apparatus in (a) comprises a reaction effluent from a process for the production of dinitriles via the hydrocyanation of unsaturated mononitriles.

4. A method according to claim 3, wherein the feedstream to the distillation apparatus in (a) comprises a reaction effluent from a process for the production of ADN via the hydrocyanation of 3PN.

5. A method according to claim 4 wherein the reaction effluent comprises a nickel (0) catalyst stabilized with phosphorus-containing ligands and/or excess phosphorus-containing ligands.

6. A method according to claim 1, wherein the Brnsted acid is selected from phosphoric acids, sulfuric acid, C.sub.4 to C.sub.12 alkanesulfonic acids and C.sub.7 to C.sub.18 alkylbenzenesulfonic acids.

7. A method according to claim 6, wherein the Brnsted acid is selected from phosphoric acid, polyphosphoric acid, pyrophosphoric acid, octanesulfonic acid, decanesulfonic acid, dodecanesulfonic acid, 4-toluenesulfonic acid, 4-ethylbenzenesulfonic acid, 4-butylbenzenesulfonic acid and 4-dodecylbenzenesulfonic acid.

8. A method according to claim 1, wherein the distillation apparatus is operated with a bottoms temperature in the range of from 150 to 200 C.

9. A method according to claim 1, wherein the distillation apparatus comprises a plurality of distillation columns and wherein the Brnsted acid is supplied to at least one of the distillation columns.

10. A method for inhibiting the formation of by-products from a dinitrile compound, the method comprising adding from 5 to 5,000 ppm by weight of a Brnsted acid to a composition comprising the dinitrile compound, based on the total weight of the dinitrile-containing composition and the Brnsted acid, wherein the dinitrile compound is adiponitrile, the composition comprises a Lewis acid that is ZnX.sub.2, BX.sub.3, or AlX.sub.3, wherein X represents a halogen, trifluoromethanesulfonate, methanesulfonate, or toluenesulfonate, the amount of the Brnsted acid supplied to the composition is effective to inhibit the formation of 2-cyanocyclopentylideneimine (CPI) from the dinitrile compound, and wherein the Brnsted acid has lower volatility than the dinitrile compound and the Brnsted acid does not degrade in the composition.

11. A method according to claim 10, for inhibiting the formation of CPI from ADN.

12. A method according to claim 10, comprising refining the dinitrile compound by distillation, wherein (i) a feedstream comprising the dinitrile compound and (ii) the Brnsted acid are supplied to a distillation apparatus; an overhead distillate stream comprising the dinitrile compound is withdrawn from the distillation apparatus; and the Brnsted acid is withdrawn from the distillation apparatus in a bottoms stream comprising the Brnsted acid; wherein the amount of the Brnsted acid supplied to the distillation apparatus is effective to inhibit the formation of 2-cyanocyclopentylideneimine (CPI) from the dinitrile compound in the distillation apparatus.

13. A method according to claim 10, wherein the method comprises adding 5 to 800 ppm by weight of the Brnsted acid to the composition comprising the dinitrile compound based on the total weight of the composition comprising the dinitrile compound and the Brnsted acid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a simplified theoretical mechanism illustrating formation of CPI from ADN, and subsequent reactions. The mechanism is presented for illustration only, and is not intended to limit the scope of the disclosure which is defined by the claims.

(2) FIG. 2 graphically shows the results of the Examples, in which the addition of an alkyl benzene sulfonic acid decreased formation of CPI.

(3) FIG. 3 graphically shows the results of Example 12, in which the addition of phosphoric acid decreased formation rate of CPI in a continuous process for refining adiponitrile by distillation as a function of the amount of phosphoric acid added.

EXAMPLES

(4) The following Examples demonstrate the disclosed method and its capability for use. The disclosed method is capable of other and different embodiments, and its several details are capable of modifications in various apparent respects, without departing from the spirit and scope of the present disclosure. Accordingly, the Examples are to be regarded as illustrative in nature and non-limiting. All parts and percentages are by weight unless otherwise indicated.

Example 1

(5) To a three-neck 100 mL round bottom flask equipped with an overhead condenser, supplied nitrogen, magnetic stirbar, digital stir plate, and a heating mantle was charged refined adiponitrile (25 grams). The material was heated to 180 C., samples were taken every hour for 4 hours, and analysis was performed by gas chromatography.

Example 2

(6) Example 1 was repeated, but zinc chloride (0.6 grams) was included.

Example 3

(7) Example 2 was repeated, but para-dodecylbenzenesulfonic acid (1.58 grams) was included.

Example 4

(8) Example 1 was repeated, but crude adiponitrile was used in place of refined adiponitrile, and the reaction temperature was 202 C. The composition of the crude adiponitrile was approximately: adiponitrile 95.4%, 2-methylglutaronitrile 3.8%, 2-ethylsuccinonitrile 0.4%, pentenenitriles 0.1%, and zinc 350 ppm.

Example 5

(9) Example 4 was repeated, but phosphoric acid, >85% (0.05 grams) was included.

Example 6

(10) Example 4 was repeated, but phosphoric acid, >85% (0.02 grams) was included.

Example 7

(11) Example 4 was repeated, but para-dodecylbenzenesulfonic acid (0.01 grams) was included.

Example 8

(12) Example 4 was repeated, but pyrophosphoric acid, 90% (0.01 grams) was included.

Example 9

(13) Example 4 was repeated, but para-dodecylbenzenesulfonic acid (0.0044 grams) was included.

Example 10

(14) Example 4 was repeated, but polyphosphoric acid (0.01 grams) was included.

Example 11

(15) Example 4 was repeated, but phosphoric acid (0.0025 grams) was included.

(16) TABLE-US-00001 TABLE 1 initial final Conc., Temp, CPI, CPI, Example Adiponitrile Additive ppm C. ppm ppm 1 refined None 0 180 13 17 2 refined + None 0 180 13 1522 added ZnCl.sub.2 3 refined + pDBSA 63200 180 13 202 added ZnCl.sub.2 4 crude None 0 202 252 537 5 crude H.sub.3PO.sub.4 2000 202 124 31 6 crude H.sub.3PO.sub.4 800 202 143 60 7 crude pDBSA 400 202 233 283 8 crude H.sub.4P.sub.2O.sub.7 400 202 213 152 9 crude pDBSA 176 202 269 400 10 crude PPA 400 202 277 397 11 crude H.sub.3PO.sub.4 100 202 249 287 CPI = 2-cyanocyclopentylideneimine Refined adiponitrile = refined adiponitrile, product of INVISTA. Crude adiponitrile = unrefined adiponitrile H.sub.3PO.sub.4 = Phosphoric acid, 85%, product of Sigma Aldrich. H.sub.4P.sub.2O.sub.7 = Pyrophosphoric acid, 90%, product of Sigma Aldrich. pDBSA = para-dodecylbenzenesulfonic acid, product of Stepan Company. PPA = polyphosphoric acid, 115% (based on H.sub.3PO.sub.4), product of Sigma Aldrich.

(17) The data presented in Table 1 show the effectiveness of various additives on the formation of CPI during the refining of adiponitrile. The data show that acidic additives inhibit CPI formation. Comparison of examples 1-3 shows that the presence of ZnCl.sub.2 increases the formation of CPI, but that the presence of the additive suppresses CPI formation. Comparison of examples 5-11 with example 4 demonstrate the effectiveness of various Brnsted acids for reducing CPI formation.

(18) Example 12 demonstrates the present disclosure and its capability for use in reducing the formation of CPI during the continuous refining of adiponitrile.

Example 12

(19) Phosphoric acid (84%) was added continuously to the feed of an adiponitrile distillation process to achieve a concentration of phosphoric acid delivered to the column in the feed, and the formation rate of CPI across the refining process was measured. The distillation was carried out in a column having 8 theoretical trays operating at an overhead temperature of 150 C., a reflux ratio of 0.5, with saturated liquid feed flowing to stage 2, counting the reboiler as the first stage.

(20) Data are presented in Table 2, and FIG. 3. In Table 2 and FIG. 3, the phosphoric acid concentration (in ppm by weight) is measured in the feed to adiponitrile distillation process.

(21) TABLE-US-00002 TABLE 2 Phosphoric acid, CPI generation rate, CPI generation rate, ppm kg per hour pph 0 95.3 210 50 38.6 85 75 22.7 50 100 18.1 40 125 13.6 30 150 9.1 20 pph = pounds of CPI generated per hour

(22) While the illustrative embodiments of the disclosure have been described with particularity, it will be understood that various other modifications will be apparent to and may be readily made by those skilled in the art without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the scope of the claims hereof be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the present disclosure, including all features which would be treated as equivalents thereof by those skilled in the art to which the disclosure pertains.