# Hydrogenation of Adiponitrile to Hexamethylenediamine over Raney Ni and Co Catalysts
## 4 Conclusions  
In conclusion, herein the hydrogenation of ADN to HMDA over Raney Ni and Raney Co catalysts is reported. Moreover, AHN was identified as an intermediate species of HMDA during the hydrogenation of ADN over the two catalysts. Apart from AHN and HMDA, azacycloheptene and azepane were also produced as byproducts of the ADN hydrogenation reaction. The reaction temperature, H\({}_{2}\) pressure, catalyst loading (ADN/catalyst ratio), and ADN/HMDA ratio in the reactant had a strong influence on ADN conversion, product selectivity, and product yield. For both catalysts, a higher H\({}_{2}\) pressure, as well as lower ADN/catalyst and ADN/HMDA ratios, resulted in a higher HMDA yield. The dependence of the HMDA yield on the reaction temperature was highly associated with the kind of catalyst used. The HMDA yield increased from 56 to 100% for the Raney Ni catalyst as the temperature increased from 60 to 100 \({}^{\circ}\)C. For the Raney Co catalyst, increasing the temperature from 60 to 80 \({}^{\circ}\)C increased the HMDA yield from 56.4 to 87.4%, but a further increase in temperature from 80 to 100 \({}^{\circ}\)C did not change the HMDA yield. Among all tested reaction conditions, a 100% HMDA yield was only obtained for the Raney Ni catalyst at two conditions: (1) \(T\) = 100 \({}^{\circ}\)C; \(P_{\rm H2}\) = 8 MPa; ADN/catalyst weight ratio = 15; and ADN/HMDA volumetric ratio = 0.2 and (2) \(T\) = 80 \({}^{\circ}\)C; \(P_{\rm H2}\) = 8 MPa; ADN/catalyst weight ratio = 15; and ADN/HMDA volumetric ratio = 0.06. The results clearly indicated that reaction temperature and the addition of HMDA to the reactant are critical factors to achieve a high HMDA yield via ADN hydrogenation. Lastly, ICP-OES analysis of the product solution  
Figure 3: Yield of HMDA obtained via hydrogenation of ADN as functions of the following reaction conditions: (**a**) reaction temperature (reaction conditions: \(P_{\rm H2}\) = 8 MPa; ADN/catalyst (\(w\)/\(w\)) = 15; ADN/HMDA (\(v\)/\(v\)) = 0.2; \(t\) = 47 min); (**b**) H\({}_{2}\) pressure (reaction conditions: \(T\) = 80 \({}^{\circ}\)C; ADN/catalyst (\(w\)/\(w\)) = 15; ADN/HMDA (\(v\)/\(v\)) = 0.2; \(t\) = 47 min); (**c**) catalyst loading (reaction conditions: \(T\) = 80 \({}^{\circ}\)C; \(P_{\rm H2}\) = 8 MPa; ADN/HMDA (\(v\)/\(v\)) = 0.2; \(t\) = 47 min); and (**d**) ADN/HMDA ratio in the reactant (reaction conditions: \(T\) = 80 \({}^{\circ}\)C; \(P_{\rm H2}\) = 8 MPa; ADN/catalyst (\(w\)/\(w\)) = 15; \(t\) = 47 min). Mean values of replicates (\(n\) = 3) are reported with the standard deviations as error bars.  
proved that both the Raney Ni and Raney Co catalysts were stable and did not teach out during the hydrogenation reaction.  
The following are available online at [[http://www.mdpi.com/2076-3417/10/21/7506/s1](http://www.mdpi.com/2076-3417/10/21/7506/s1)]([http://www.mdpi.com/2076-3417/10/21/7506/s1](http://www.mdpi.com/2076-3417/10/21/7506/s1)). Table S1: Chemical composition of the Raney Ni and Co catalysts.  
Conceptualization, K.-Y.A.L. and J.L.; investigation, Y.L. and S.W.L.; validation, H.J.K. and Y.T.K.; visualization, K.-Y.A.L.; supervision, J.L.; writing--original draft preparation, Y.L. and J.L.; writing--review--editing, Y.L. and J.L. All authors have read and agreed to the published version of the manuscript.  
The APC was funded by the KRICT project (SI2011-30) of the Korea Research Institute of Chemical Technology.  
The authors declare no conflict of interest.