# Hydrogenation of Adiponitrile to Hexamethylenediamine over Raney Ni and Co Catalysts
## 3 Results and Discussion
### The Effect of Reaction Temperature, H\({}_{2}\) Pressure, Catalyst Loading, and ADN/HMDA Ratio  
The effects of reaction conditions (e.g., reaction temperature, H\({}_{2}\) pressure, ADN/HMDA ratio in the reactant, and catalyst loading) on the hydrogenation of ADN over the Raney Ni and Raney Co catalysts were investigated. Overall trends reveal that ADN hydrogenation is dependent on the reaction conditions, and that the Raney Co and Raney Ni catalysts followed similar trends regarding these reaction conditions, except for reaction temperature. For the Raney Ni catalyst, temperature variation in the range of 60 to 100 \({}^{\circ}\)C under a fixed H\({}_{2}\) pressure of 8 MPa, with an ADN/HMDA volumetric ratio of 0.2 and an ADN/catalyst weight ratio of 15, showed an increase in HMDA selectivity from 58 to \(>\)99% and a nearly quantitative conversion of ADN (\(>\)97%) with an increase in reaction temperature from 60 to 100 \({}^{\circ}\)C. However, in the case of the Raney Co catalyst, increasing the reaction temperature from 80 to 100 \({}^{\circ}\)C did not affect the HMDA selectivity of 85-87%. The conversion of ADN increased to \(>\)99% with an increase in H\({}_{2}\) pressure from 2.5 to 6 MPa at 80 \({}^{\circ}\)C, using a volumetric ADN/HMDA ratio of 0.2 and an ADN/catalyst weight ratio of 15 for 47 min. A higher hydrogen concentration also led to faster hydrogenation of the AHN intermediate to HMDA, increasing the HMDA selectivity at the expense of AHN selectivity. An increase in H\({}_{2}\) pressure from 6 MPa to 8 MPa further increased the HMDA selectivity to \(\sim\)90% at an AND conversion  
Figure 1: Adiponitrile (ADN) conversion and product selectivity for ADN hydrogenation over (**a**) Raney Ni and (**b**) Raney Co catalysts as a function of reaction time. Reaction conditions: 80 \({}^{\circ}\)C; 8 MPa H\({}_{2}\); ADN/Hexamethylenediamine (HMDA) = 0.2 (_v_/_v_); ADN/catalyst = 15 (_v_/_w_). Mean values of replicates (_n_ = 3) are reported with the standard deviations as error bars. Figure 2: Proposed reaction pathways for ADN hydrogenation. of \(>\)99%. A carbon balance loss of up to 13% was observed at a higher H\({}_{2}\) pressure (9 MPa) because of undetected products (vide supra). The dependence of ADN hydrogenation on the ADN/catalyst weight ratio in the range of 7.5 to 30 at 80 \({}^{\circ}\)C and under 8 MPa H\({}_{2}\). The HMDA selectivity (85-97%) and ADN conversion rate (\(>\)99%) remained high as the ADN/catalyst ratio increased from 7.5 to 15. However, upon further decreasing the catalyst loading (i.e., ADN/catalyst weight ratio of 30), low HMDA selectivity (56% for the Raney Ni catalyst and 46% for the Raney Co catalyst) was achieved at \(>\)90% ADN conversion, and a noticeable amount of AHN (33% for the Raney Ni catalyst and 43% for the Raney Co catalyst) remained in the mono-hydrogenated state. This indicates that a lower Ni concentration in the system results in the incomplete hydrogenation of the intermediate species, resulting in slower hydrogenation. It is notable to mention that ADN hydrogenation, without the addition of HMDA over the Raney Ni and Co catalysts, yielded \(<\)10% HMDA with carbon losses of \(>\)30%. Moreover, the low carbon balance is likely an indication of the formation of undetectable products. Therefore, the addition of HMDA to the reactant is required to achieve a high yield of HMDA via the hydrogenation of ADN over a Raney Ni or Raney Co catalyst. In light of these results, the impact of the ADN/HMDA volumetric ratio on ADN hydrogenation was explored. As more HMDA was added to the reactant, the more the selectivity toward HMDA increased. For both the Raney Ni and Raney Co catalysts, almost complete conversion of ADN into HMDA (i.e., \(>\)99% yield of HMDA) was achieved at 80 \({}^{\circ}\)C under an H\({}_{2}\) pressure of 8 MPa, an ADN/HMDA volumetric ratio of 0.06, and an ADN/catalyst weight ratio of 15.