Method for Producing Linear Pentenenitrile

Abstract

A process is described for preparing 3-pentenenitrile, characterized by the following process steps: (a) isomerizing a reactant stream which comprises 2-methyl-3-butenenitrile over at least one dissolved or dispersed isomerization catalyst to give a stream 1 which comprises the at least one isomerization catalyst, 2-methyl-3-butenenitrile, 3-pentenenitrile and (Z)-2-methyl-2-butenenitrile, (b) distilling stream 1 to obtain a stream 2 as the top product which comprises 2-methyl-3-butenenitrile, 3-pentenenitrile and (Z)-2-methyl-2-butenenitrile, and a stream 3 as the bottom product which comprises the at least one isomerization catalyst, (c) distilling stream 2 to obtain a stream 4 as the top product which, compared to stream 2 , is enriched in (Z)-2-methyl-2-butenenitrile, based on the sum of all pentenenitriles in stream 2 , and a stream 5 as the bottom product which, compared to stream 2 , is enriched in 3-pentenenitrile and 2-methyl-3-butenenitrile, based on the sum of all pentenenitriles in stream 2, (d) distilling stream 5 to obtain a stream 6 as the bottom product which comprises 3-pentenenitrile and a stream 7 as the top product which comprises 2-methyl-3-butenenitrile.

1 . A process for preparing 3-pentenenitrile, comprising the following process steps:
 (a) isomerizing a reactant stream which comprises 2-methyl-3-butenenitrile over at least one dissolved or dispersed isomerization catalyst to give a stream  1  which comprises the at least one isomerization catalyst, 2-methyl-3-butenenitrile, 3-pentenenitrile and (Z)-2-methyl-2-butenenitrile,   (b) distilling stream  1  to obtain a stream  2  as the top product which comprises 2-methyl-3-butenenitrile, 3-pentenenitrile and (Z)-2-methyl-2-butenenitrile, and a stream  3  as the bottom product which comprises the at least one isomerization catalyst,   (c) distilling stream  2  to obtain a stream  4  as the top product which, compared to stream  2 , is enriched in (Z)-2-methyl-2-butenenitrile, based on the sum of all pentenenitriles in stream  2 , and a stream  5  as the bottom product which, compared to stream  2 , is enriched in 3-pentenenitrile and 2-methyl-3-butenenitrile, based on the sum of all pentenenitriles in stream  2 ,   (d) distilling stream  5  to obtain a stream  6  as the bottom product which comprises 3-pentenenitrile and a stream  7  as the top product which comprises 2-methyl-3-butenenitrile,   
     the (Z)-2-methyl-2-butenenitrile-depleted 2-methyl-3-butenenitrile being recycled. 
   
   
       2 . The process according to  claim 1 , wherein the reactant stream is obtained by the following process steps:
 (e) hydrocyanating 1,3-butadiene over at least one hydrocyanation catalyst using hydrogen cyanide to obtain a stream  8  which comprises the at least one hydrocyanation catalyst, 3-pentenenitrile, 2-methyl-3-butenenitrile, 1,3-butadiene and residues of hydrogen cyanide,   (f) distilling stream  8  one or more times to obtain a stream  9  which comprises 1,3-butadiene, a stream  10  which comprises the at least one hydrocyanation catalyst, and a stream  11  which comprises 3-pentenenitrile and 2-methyl-3-butenenitrile,   (g) distilling stream  11  to obtain a stream  12  as the bottom product which comprises 3-pentenenitrile, and a stream  13  as the top product which comprises 2-methyl-3-butenenitrile.   
   
   
       3 . The process according to  claim 2 , wherein process step (d) and (g) are carried out in the same distillation apparatus, in which case streams  6  and  12  and streams  7  and  13  coincide. 
   
   
       4 . The process according to  claim 2 , wherein process steps (c) and (g) are carried out in a common distillation column, in which case process step (d) is dispensed with, stream  2  from process step (b) and stream  11  from process step (f) are directed to process step (g), and, in process step (g), stream  4  is obtained as the top product comprising (Z)-2-methyl-2-butenenitrile, stream  12  as the bottom product comprising 3-pentenenitrile and stream  13  as a side draw stream comprising 2-methyl-3-butenenitrile. 
   
   
       5 . The process according to  claim 1 , wherein the at least one isomerization catalyst obtained in stream  3  in process step (b) is recycled into process step (a). 
   
   
       6 . The process according to  claim 1 , wherein process steps (b) and (c) are carried out together in one distillation apparatus, in which case stream  3  which comprises the at least one isomerization catalyst is obtained as the bottom product, stream  4  which comprises (Z)-2-methyl-2-butenenitrile as the top product, and stream  5  which comprises 3-pentenenitrile and 2-methyl-3-butenenitrile at a side draw of the column. 
   
   
       7 . The process according to  claim 1 , wherein process steps (a), (b) and (c) are carried out together in one distillation apparatus, in which case stream  4  which comprises (Z)-2-methyl-2-butenenitrile is obtained as the top product, and stream  5  which comprises 3-pentenenitrile and 2-methyl-3-butenenitrile at a side draw of the distillation apparatus, and the isomerization catalyst remains in the bottom of the distillation column. 
   
   
       8 . The process according to  claim 1 , wherein the isomerization catalyst contains nickel(0), a trivalent phosphorus-containing compound which complexes nickel(0) as a ligand and, optionally, a Lewis acid. 
   
   
       9 . The process according to  claim 1 , wherein pressure and temperature in process step (b) are set so that the isomerization catalyst is less active than in process step (a) or is inactive. 
   
   
       10 . The process according to  claim 2 , wherein the hydrocyanation catalyst and the isomerization catalyst are identical. 
   
   
       11 . A process for preparing 3-pentenenitrile, comprising the following process steps:
 (a*) isomerizing a reactant stream which comprises 2-methyl-3-butenenitrile over at least one dissolved or dispersed isomerization catalyst to give a stream  1  which comprises the at least one isomerization catalyst, 2-methyl-3-butenenitrile, 3-pentenenitrile and (Z)-2-methyl-2-butenenitrile,   (b*) distilling stream  1  to obtain a stream  2  as the top product which comprises 2-methyl-3-butenenitrile, 3-pentenenitrile and (Z)-2-methyl-2-butenenitrile, and a stream  3  as the bottom product which comprises the at least one isomerization catalyst,   (c*) distilling stream  2  to obtain a stream  4  as the top product which, compared to stream  2 , is enriched in (Z)-2-methyl-2-butenenitrile, based on the sum of all pentenenitriles in stream  2 , and a stream  5  as the bottom product which, compared to stream  2 , is enriched in 3-pentenenitrile and 2-methyl-3-butenenitrile, based on the sum of all pentenenitriles in stream  2 ,   (d*) distilling stream  5  to obtain a stream  6  as the bottom product which comprises 3-pentenenitrile and a stream  7  as the top product which comprises 2-methyl-3-butenenitrile,   (h*) catalyst regeneration to replenish the nickel(0) content of substream  14  from stream  3  and substream  16  from stream  10  to generate a stream  18 ,   (i*) optionally adding a diluent F to the stream  18  to generate stream  19 ,   (j*) extracting the stream  18 , with regard to the catalyst components and/or disruptive component(s) by adding a dinitrile stream  20  and hydrocarbon stream  21  to generate two nonmiscible phases  22  and  23 , stream  22  comprising the predominant proportion of the catalyst components and stream  23  the predominant proportion of the disruptive component,   (k*) distillatively removing the hydrocarbon from the catalyst components from the stream  22  to generate a stream  25  which comprises the predominant proportion of the catalyst components and, optionally, partly or fully recycling the stream  25  into process steps (a*) or (e*),   (e*) hydrocyanating 1,3-butadiene over at least one hydrocyanation catalyst using hydrogen cyanide to obtain a stream  8  which comprises the at least one hydrocyanation catalyst, 3-pentenenitrile, 2-methyl-3-butenenitrile, 1,3-butadiene and residues of hydrogen cyanide,   (f*) distilling the stream  8  one or more times to obtain a stream  9  which comprises 1,3-butadiene, a stream  10  which comprises the at least one hydrocyanation catalyst, and a stream  11  which comprises 3-pentenenitrile and 2-methyl-3-butenenitrile, and   (g*) distilling the stream  11  to obtain a stream  12  as the bottom product which comprises 3-pentenenitrile, and a stream  13  as the top product which comprises 2-methyl-3-butenenitrile.   
   
   
       12 . The process according to  claim 11 , wherein the replenishment of the nickel(0) catalyst content is carried out in process stage h*) by reductive catalyst regeneration. 
   
   
       13 . The process according to  claim 11 , wherein the catalyst system is operated as two separate catalyst circuits, one of the circuits including the stages e*) and f*) and the other circuit the stages a*), b*) and c*). 
   
   
       14 . The process according to  claim 11 , wherein stabilizer-containing butadiene is used as the feed stream to e*). 
   
   
       15 . The process according to  claim 11 , wherein the catalysts comprise phosphite ligands of the formula Ib
   P(O—R 1 ) x (O—R 2 ) y (O—R 3 ) z (O—R 4 ) p   (Ib)   
     where
 R 1 : aromatic radical having a C 1 -C 18 -alkyl substituent in the o-position to the oxygen atom which joins the phosphorus atom to the aromatic system, or having an aromatic substituent in the o-position to the oxygen atom which joins the phosphorus atom to the aromatic system, or having a fused aromatic system in the o-position to the oxygen atom which joins the phosphorus atom to the aromatic system, 
 R 2 : aromatic radical having a C 1 -C 18 -alkyl substituent in the m-position to the oxygen atom which joins the phosphorus atom to the aromatic system, or having an aromatic substituent in the m-position to the oxygen atom which joins the phosphorus atom to the aromatic system, or having a fused aromatic system in the m-position to the oxygen atom which joins the phosphorus atom to the aromatic system, the aromatic radical bearing a hydrogen atom in the o-position to the oxygen atom which joins the phosphorus atom to the aromatic system, 
 R 3 : aromatic radical having a C 1 -C 18 -alkyl substituent in the p-position to the oxygen atom which joins the phosphorus atom to the aromatic system, or having an aromatic substituent in the p-position to the oxygen atom which joins the phosphorus atom to the aromatic system, the aromatic radical bearing a hydrogen atom in the o-position to the oxygen atom which joins the phosphorus atom to the aromatic system, 
 R 4 : aromatic radical which bears substituents other than those defined for R 1 , R 2  and R 3  in the o-, m- and p-position to the oxygen atom which joins the phosphorus atom to the aromatic system, the aromatic radical bearing a hydrogen atom in the o-position to the oxygen atom which joins the phosphorus atom to the aromatic system, 
 x: 1 or 2, 
 y, z, p: each independently 0, 1 or 2, with the proviso that x+y+z+p=3. 
 
   
   
       16 . The process according to  claim 11 , wherein the catalysts comprise phosphite ligands of formula Ib
   P(O—R 1 ) x (O—R 2 ) y (O—R 3 ) z (O—R 4 ) p   (Ib)   where R 1 , R 2  and R 3  are each independently selected from o-isopropylphenyl, m-tolyl and p-tolyl, R 4  is phenyl; x is 1 or 2, and y, z, p are each independently 0, 1 or 2, with the proviso that x+y+z+p=3; and mixtures thereof.