Investigation On The One-pot Synthesis Of Methyl N-phenyl Carbamate From CO₂, Methanol And Aniline

CO₂ is the main gas to produce "greenhouse effect". The global warming caused by CO₂ emissions has raised people’s concern and so it is urgent to reduce the CO₂ emission. Methyl N-phenyl carbamate（MPC） is the intermediate for 4,4-diphenylmethane diisocyanate（MDI） synthesis. The synthesis MPC using aniline, CO₂ and methanol as raw materials has the great potential. Nowadays the homogeneous catalyst and liquid dehydrant were used in MPC synthesis, which has several drawbacks, such as separation difficulty, lower yield, etc. Therefore, in this paper, the synthesis of MPC was studied using 4A molecular sieve as dehydrant and CeO₂ based composite oxides as catalyst.The solid 4A molecular sieve use as dehydrant and Ce O₂-ZrO₂ as catalyst in the synthesis of MPC was studied.CeO₂-ZrO₂ catalyst exhibits the better catalytic activity at the nCe:nZr of 2 and the calcination temperature of 600℃.Compared with the CeO₂ and ZrO₂,CeO₂-ZrO₂ can improve the selectivity of MPC obviously,which was caused by the formation of CexZr1-xO₂.The optimal reaction conditions consist of a reaction temperature of 160℃,a reaction time of 8h,n苯胺:nCH₃OH of 100,mCeO₂-ZrO₂:m苯胺of 0.43（aniline0.46m L）,the initial CO₂ pressure of 4.0MPa and 4A molecular sieve amount of 0.2 g/mL methanol.Under these conditions,the aniline conversation is 7.8%and the MPC selectivity is 66.7%.Compared with 4A molecular sieve,the composite dehydrant CaCl₂/4A can increase the aniline conversion to 16.6%but decrease the MPC selectivity to 38.0%The CaCl₂/4A was used as dehydrant and K₂O-CeO₂+Zr O₂/SiO₂ as catalyst in the synthesis of MPC was studied. It was found that K doping in CeO₂ can increase amount of DMC. By the characterization of K₂O-CeO₂, it was found that K₂O-CeO₂ can form solid solution. There are two kinds of base sites with different base strength on the surface. The base strength and amount of K₂O-CeO₂ increases with doping amount of K. With the calcination temperature increasing, the particle size of K₂O-CeO₂ grain increases and the crystal lattice changed. Furthermore, the base strength of strong base site has dropped and the opposite for the weak base site. At the same time the base amount of catalyst has decreased. Compared with K₂O-CeO₂, the K₂O-CeO₂+ZrO₂/SiO₂ can improve the selectivity of MPC obviously. The aniline conversation is 14.8% and the selectivity of MPC is 51.7% when reaction is conducted at a reaction temperature of 160℃, a reaction time of 8h, m（K₂O-CeO₂（nCe:nk =2:1））:m（aniline） of 0.43,m（ZrO₂/SiO₂（10%））:m（aniline） of 0.64, n（aniline）:n（CH₃OH） of 1:100（aniline 0.46 m L）, 0.2 g/m L methanol CaCl₂/ 4A, initial CO₂ pressure of 4.0MPa.