A solvent is at least partially separated from a catalyst. The catalyst comprises nickel and a bidentate phosphorus-containing ligand. The method for separation involves distilling a catalyst solution. The ratio of 2-pentenenitrile to 3-pentenenitrile in distillation column bottoms is controlled to reduce the amount of 3-pentenenitrile which is isomerized to form 2-methyl-3-butenenitrile. Isomerization of 3-pentenenitrile to 2-methyl-3-butenenitrile and subsequent isomerization of 2-methyl-3-butenenitrile to 2-methyl-2-butenenitrile, and/or hydrocyanation of 2-methyl-3-butenenitrile to methylglutaronitrile represents a loss in adiponitrile yield in a process for making adiponitrile.