The Synthesis Of Urea Compounds In The Presence Of Carbon Dioxide

Carbon dioxide plays an important part in carbon chemistry as carbon monoxide does.Through proper ways to catalyze and active carbon dioxide, it can be used as a startingmaterial for organic synthesis, and then converted into organic fuel, bulk based chemicals ordirectly fixed as polymer materials，it is important to mitigate the greenhouse effect. Urea andits derivatives are a class of very useful fine chemicals, which can be widely used as animportant intermediate of herbicides, pesticides, agricultural plant growth regulator or thefield of medicine. At present, only in the presence of catalyst and dehydration agent, carbondioxide can be converted into urea. Because of the existence of catalyst anddehydration, leading to the synthesis of industrial complex, not easy purification ofproduct and production costs increase. Therefore, in the development of new technology ofusing carbon dioxide as raw material for the synthesis of urea and its derivatives become thefocus of current research. Based on the above analysis, this paper adopts the new preparationprocess, in the absence of catalyst, three kinds of urea derivatives were prepared materialsand amine reaction with carbon dioxide, and investigated its synthesis process, the specificcontents are as follows:Use supercritical carbon dioxide and hexamethylendiamine as materials to synthesizepolyurea without catalyst. The structure of polymer was characterized by infrared spectrum(FTIR) and the thermal stability of polyuria was studied by thermogravimetric(TG). Theoptimum reaction conditions were determined by orthogonal and optimization experiments:the reaction temperature was120℃, pressure was8MPa, time was8h, and the conversionrate of hexamethylenediamine into polyurea was89%.Based on the characteristics of high activity of hydrazine hydrate, the poly carbonyl ureawas synthesized with carbon dioxide and hydrazine hydrate as raw materials. The structure ofpoly carbonyl urea was characterized by infrared spectroscopy (FTIR) and nuclear magneticresonance (13C NMR), and gel permeation chromatography (GPC) to determine the averagemolecular weight of poly carbonyl urea, meanwhile calculate the degree of polymerization of poly carbonyl urea. Investigated three factors including temperature, time and pressure toaffect the hydrazine hydrate of carbon dioxide adsorption capacity, and through orthogonaland optimization test the best adsorption conditions were acquired: reaction temperature was100℃、reaction time was5h and reaction pressure5MPa, the carbon dioxide adsorption runup to0.62.Based on the characteristics of high activity of hydrazine hydrate, in the presence of carbondioxide, the biurea was synthesized under the condition of urea and hydrazine hydrate as rawmaterial. Through infrared spectroscopy (FTIR), nuclear magnetic resonance (1HNMR), thestructure of biurea was determined and the thermal stability of biurea was studied bythermogravimetry (TG). Through orthogonal and optimization experiment the best adsorptionconditions were acquired: temperature110℃, molar ratio (n (urea): n (hydrazine))=2.5:1,time was5h, pressure was3MPa, and the conversion rate was87%.