Transition Metal Chlorides And 4A @ ZIF-8 Core-shell Materials For The Synthesis Of Dialkyl Carbonates

Dimethyl carbonate(DMC) and diethyl carbonate (DEC)are two kinds of the simplest dialkyl carbonate, and are also important and green raw, which acted as environment friendly organic agent. Nowadays, the synthesized methods of the dialkyl carbonate mainly included phosgene method, oxidatve carbonylation method, transesterification method, carbon dioxide and ethanol direct synthesis and alcoholysis of urea method. Moreover, the alcoholysis of urea method used inexpensive urea and ethanol as raw materials.Not only the by-product ammonia is just generated in the process,but also the final product can be separated easily, which is a greatly developing synthesis method. Alcoholysis of urea method makes up of two steps in the process, the first step is that one molar alcohol reacted with one molar urea to obtain dialkyl carbamate intermediate and ammonia.The second step is that one molar alcohol continually reacted with one molar intermediate to generate dialkyl carbonate and release ammonia, which is extremely inactive, so it is the rate-determining step.The yield of dialkyl carbonate synthesized by this method was low generally.and the synthesis of catalysts which can obtain higher yield was complex,the cost of which was high.Therefore, developing the catalyst with effect and environmental to improve the yield of final products is the one key of solving the current and exiting problems.This paper mainly study the catalytic activity of transition metal chlorides and porous material on the rate-determining of alcoholysis of dialkyl carbamate to dialkyl carbonate(DMC/DEC) reaction, and the Lewis acid active sites of transition metal chlorides and adsorption-separation performance of porous material are applied to improve the yield of final product. Specific studies are as following:1、The catalytic activity of five transition metal chlorides was investigated. The results showed their catalytic activity was poor(<15%), and the order of catalytic activity at DMC reaction is different from that of DEC.At the same time,almost all of them could transfer to the corresponding chloramines compound after the catalytic reaction which still keep some catalytic activity to the extend, but are worse than transition-metal chlorides.But this also shows transition-metal chlorides process catalytic activity and coordinate coupling effect.2、Five anhydrous transition metal chlorides reacted with ammonia in situ which generated from the alcoholysis of EC to DEC were investigated as the reaction condition changed. The results show ZnCI2 can directly convert to Zn(NH3)2Cl2 eight at the low temperature or at the high temperature. Other metal chlorides firstly transfer to one intermediate under low temperature, then transfer to the corresponding di-chloramine compounds under high temperature.The possible reaction mechanism of the alcoholysis of EC to DEC is put forward.3、The study of methanol and transition metal chlorides indicates that methanol have certain effect on transition metal chlorides,and have some effect on the coordinate of transition metal ions with ammonia, decreasing their catalytic activity.The force of methanol combined with MnCl2 is the strongest (292.3℃)on the basic of the final composition temperature.4、Dispersive uniformly and Size-controlled ZIF-8 particle was successfully synthesized by solvothermal method(100nm-1.2um).The results indicate that not only raw material ratio but also reaction temperature and surfactant have an effect on the ZIF-8 size.According to the characteristic results of XRD、IR、SEM show that 4A@ZIF-8 composite porous material with core-shell structure was synthesized successfully by lay-lay Assembly method, and the thickness of the shell can be controlled by repeating the assembly steps.The better crystallization condition is 50℃, 5h. Increasing growth temperature or time is bad for the synthesis of core-shell structure material.5、The catalytic activity of 4A@ZIF-8 core-shell material used to catalyze alcoholysis of EC to synthesis DEC was investigated. The results demonstrate that 4A@ZIF-8 does not possess a little catalytic activity for DEC synthesis reaction.The characteristic results of SEM indicate that the possible reasons include that firstly core-shell structure is not enough stable, broken undergo high pressure and then the force of pore to adsorb ammonia is worse and easy to be stripped under high pressure at high temperature.The last is that ethanol molecular take up some pores to some degree, which has an effect on the adsorption of ammonia.