Investigation Of The Ni-Based Catalysts For Low Pressure Dinitrotoluene Hydrogenation

Toluenediamine(TDA),alternatively named diaminotoluene,is mainly used for the industrial production of toluene diisocyanate(TDI)and further for the production of polyurethane.In industry,TDA is synthesized by dinitrotoluene(DNT)liquid phase hydrogenation in the condition of organic solvent and catalyst.At the present,there are two industrial technology:the first one is dupont technology using noble metal of Pd/C and Pt/C et al.The catalyst has the advantage of low pressure(1 MPa)and high activity,but the price of which is expensive,and the catalyst is easy deactivation by coke and poisoning.The other technology is BASF technology using Raney-Ni catalyst,the price of the catalyst is low,but reaction pressure up to 2 MPa.The two technologies for DNT hydrogenation are blochaded by foreign techenology,simultaneously.Therefore,the development of low cost,high activity in the condition of low pressure(1 MPa)and independent intellectual property rights for DNT hydrogenation catalyst is of great signification.In this paper,the performance of Raney Ni and Ni-B amorphous alloy catalysts for DNT hydrogenation was investigated.The conversion of DNT and the selectivity of TDA are 100%in the condition of 1 MPa and 110 ? by optimizing the catalyst preparation process and the reaction conditions.The relationship between catalyst microstcture and hydrogenation properties were studied by the characterization of XRD,DSC,TG,TEM,XPS and H2-TPD.The main results as follows:1.The reaction of aluminum extraction has a significant impact on the performance of Raney-Ni for DNT hydrogenation during the preparation process of Raney-Ni.In this paper,the influences concentration of NaOH and NaOH/Al on the microstructure and the performance of DNT hydrogenation of Raney-Ni were studied.The results showed that the performance of Raney-Ni is best when the concentration of NaOH is 16 wt%and the NaOH/Al is 4.The conversion of DNT and the selectivity of TDA are 96.1%and 99.8%using ethanol and in the condition of 2 MPa and 110 ?.2.During of the preparation of Ni-Al original alloy power,one or more additives of Fe,Cr and Mo were introduced into Ni-Al to increase the DNT hydrogenation performance for Raney-Ni.The results show that the hydrogenation performance of Raney-Ni-Fe-Cr-Mo is optimal,the conversion of DNT and the selectivity of TDA are 98.23%and 100%,respectively.3.The KBH4/Ni has a significant impact on the microstructure of Ni-B and the performance for DNT hydrogenation in the preparation process.The increasing of KBH4/Ni led to the enhancement of degree of disorder of Ni-B and the formation of NiB2,so that the electron of B transfer to Ni,which led to the increasing of Ni electron and weaken the strength of Ni-H bond.When KBH4/Ni2+ is 4,the performance of Ni-B is best,the conversion of DNT and the selectivity of TDA are 95.4%and 100%in the condition of 2 MPa and 110 ?Further increasing of KBH4/Ni from 4 to 5 led to the covering of Ni active center by B and the decreasing of hydrogenation performance of Ni-B catalyst.4.The assistants of Mo,La,Zr and Co have a great effect on the microstructure and the performance of DNT hydrogenation.The introduction of Mo and La enhanced the extent of long-range disordered,reduce the particle diameter,weaken the strength of Ni-H bond,improve the thermal stability and antioxidation.The results showed that the conversion of DNT of Ni-Mo-B and Ni-La-B is 99.8%and 99.2%,respectively,and the selectivity of TDA is up to 100%,when the contents of Mo and La are 6 mol%.5.Ni-B amorphous alloy catalysts showed good catalytic performance in DNT hydrogenation,but the drawback of poor thermal stability and small specific surface area.The introduction of carrier has benefit to enhancement of specific surface area,thermal stability and hydrogenation performance.The results showed that the supported catalysts Ni-Mo-B/Si02 amophous alloy catalyst revealed good activity,when the nickel source is NiCl,carrier is SiO2 and the Ni loading is 6 wt%,the conversion of DNT and the selectivity of TDA are 98.7%and 100%.6.The conversion of DNT and the selectivity of TDA get further enhanced by optimizing the reaction condition of reaction temperature,catalyst amount and solvent.The investigation showed that Ni-Mo-B and Ni-La-B amorphous alloy catalysts,Raney-Ni-Mo and Raney-Ni-Mo-Fe-Cr exhibit good hydrogenation performance in the condition of 1 MPa and 110 ?,when the solvent is methanol and O-toluidine.Both of the conversion of DNT and the selectivity of TDA are 100%.The hydrogenation performances of Ni-Mo-B,Ni-La-B amorphous alloy catalyst,Raney-Ni-Mo and Raney-Ni-Mo-Fe-Cr catalyst is futher investigated without solvent.The influence of water on the catalytic performance of Ni-Mo-B and Ni-La-B is smaller in compared with Raney-Ni,the performance of Ni-Mo-B and Ni-La-B exihibited higher hydrogenation performance under productive condition.7.In the DNT hydrogenation using methanol as aolvent,Ni-Mo-B and Ni-La-B amorphous alloy catalyst run for 200 h at the condition of 1 MPa,both of the conversion of DNT and the selectivity of TDA reach 100%,and the deactivation of catalysts is not detected.In the DNT hydrogenation using methanol as aolvent,the Raney-Ni-Mo and Raney-Ni-Mo-Cr-Fe catalyst run for 200 h at the condition of 1 MPa,catalysts also exhibited deactivation,apparently,and the deactivation rate is 5.4%/h and 3.7%/h,respectively.8.The reaction course of Ni-Mo-B amorphous alloy catalyst is same to that of Pt/C.However,the 4-nitro was first hydrogenated to 4-hydroxy amino-2-nitrotolene and the tetraamino-dinitrotoluene reaction intermediate,and further hydrogenated to 2,4-TDA.The reaction rate of Pd/C and Ni-Mo-B is similar in DNT hydrogenation.Wherein,in the initial stage of the reaction,i.e.the process of transformation of DNT to the intermediate product,Pd/C catalysts show higher catalytic activity.During the further hydrogenation of intermediate product to TDA,the Ni-Mo-B catalyst exhibits higher catalytic activity.