Process Research On Urea Alcoholysis Reactions Catalyzed By Modified Fluor-hydroxyapatite

Calcium hydroxyapatite(Ca₁₀?PO₄?₆?OH?₂,HAP)with its excellent biocompatibility has been applied in the field of bioceramics,drug delivery carriers,adsorbent and coating material.As it is insoluable in water and most organic solvents,good hydrothermal stability,morphological controllablity,abundant surface ion exchange sites and acidic-basic sites,these make hydroxyapatite disperse and support metals and complex for catalytic purposes,and has gained more applications in catalytic practices.Fluorapatite(Ca₁₀?PO₄?₆F₂,FAP)with similar crystal structure and properties with HAP is considered as an more potential catalytic material due to its lower solubility in organic solvents as well as in water,higher hea-resistance than HAP.As the rapid consumption of non-renewable fossil resources and environmental problems are becoming more and more serious,the development of clean and renewable new energy sources is becoming extremely urgent.Urea can be used as raw material to prepare important ester chemical intermediates such as carbonate compounds and carbamate compounds by alcoholysis,the reaction process is clean,abundant and cheap materials,simpler operation and high efficiency,which can effectively reduce the production cost of these products,and the recovery and reuse of by-product ammonia gas can make the reaction system more efficient,achieving zero-emmision.However,the exploration of an efficient,green and stable catalyst is a key problem to be solved in the urea alcoholysis reaction.In this article,the controlled preparation of metal modified fluorapatite?metal=Ca,Co,Ni,Cu,Zn?and its catalytic activity change in a mumber of urea hydrolysis reactions were systematically investigated for the first time.The main experimental results were as follows.1 The aspherical shaped fluorapatite with larger specific surface area was successfully prepared by template method with?-cyclodextrin,and the specific surface area of increased from 17 m²/g to 46.4 m²/g,and morphology of fluorapatite changed from hexagonal prism to spheroid.2 Transition metal ions?Co,Ni,Cu,Zn?were introduced into fluorapatite by template-coprecipitation method,the controllable change of acdic-basic properties can be achieved by changing the types of transition metal and the ratio of transition metal to Ca²⁺in fluorapatite,this make it more suitable for acdic-basic catalyzed reactions.3 The catalytic activity change of metal modified fluorapatite?MCa₉?PO₄?₆F₂,M=Ca,Co,Ni,Cu,Zn?to catalyze the synthesis of dimethyl carbonate?DMC?from urea and methanol was investigated,and the thermodynamics of the process was analyzed the acdicity and basity has key effect on the activity of the catalyst.ZnCa₉?PO₄?₆F₂,exhibited the best catalytic performance with the conversion of urea of 87.6%,DMC yield of 34.8%,and the selectivity of 39.7%,at the optimal reaction conditions of 8 h,180?,urea 6.0 g,ratio of methnol to urea 20:1,catalyst 2.4 g.The catalyst shows stable activity for 5 times reuse.4 The catalytic activity change of metal modified fluorapatites to catalyze the synthesis of methyl carbamate?MC?by urea and methanol from urea and methanol was investigated,and the thermodynamics of the process was analyzed the basity of the catalysts has key effect on the activity of the catalyst.Zn₅Ca₅?PO₄?₆F₂,exhibited the best catalytic performance with the conversion of urea of 100.0%,MC yield of 98.5%at the optimal reaction conditions of 3 h,140?,urea 6.0 g,ratio of methnol to urea 10:1,catalyst0.3 g.The catalyst shows stable activity for 5 times reuse.5 The effect of process parameters on the synthesis of methyl N-phenyl carbamate?MPC?from aniline,urea and methanol catalyzed by ZnFAP was investigated,and the optimal conditions were determined as follows:180?,6 h,aniline 20 mmol,ratio of urea to anline 5:1,the ratio of methnol to aniline 2:1,catalyst 8.0 mmol,with aniline conversion of 94.4%and selectivity to MPC of 75.8%.These research achievements will be practically valuable in the controlled preparation of fluorapatites with adjustable acidity and basity and industrial applications,extending the application areas of the clean catalyst fluorapatite.