Simulation On The Decomposition For Condensation Of Dihydroxyl Methyl Urea Using The Reaxff Reactive Force Field

Nutrient release is an important index of Measure of slow/controlled release fertilizer forfertilizer efficiency. Fertilizer efficiency is mainly refering to nutrients absorbed by the plantin the way of chenicals which could be directly used in the effective process such asdissolution, hydrolyzation and degradation. Improve the nutrient release and promote thecrops to fully absorb the nutrient could help improve the quality of fertilizer efficiency. So toprobe the mechanism of degradation of the slow/controlled release fertilizer is an importantaspect of research. In this paper, using ReaxFF force field and Reactive molecular dynamics(RMD) simulations, the condensation of dihydroxy methyl urea was pyrolysed to explore themechanism in the high temperature. Direct at the pure, water and oxygen system, not onlypredict the reaction mechanism of the degradation, but also measure the kinetic parameters, inorder to provide theoretical guidance for slow-release fertilizer application.At first, pure condensation of dihydroxy methyl urea system was pyrolysed by theconstant temperature of3000K in RMD simulations, it shows that the main product are NH3,CO2, CHNO, H2O and so on. Thereinto the amounts of NH3and H2O are largeast. Then thesingle molecular chain was used to pyrolysed by increasing the temperature in RMDsimulation to reach the mechanism of the degradation. The whole pyrolysis process could bedivided into five stages, the first stage is the transformation of the molecular chain, mainlyabout the functional group C=O grabbed the H nearby the N and the C-N transformed into theC=N. the second stage is random degradation, C-O of the molecular chain was broke andproduced some of C3H7N2O2. In the third stage, large mounts of CH2O were produced and thecarbonic fragments like C2H5N2O were produced too. With the temperature increasing,thesingle bond C-N broke and produced CH2N2O, CH3N, CHNO and so on. In the forth stage,much more water molecules appeared with the combinations of-OH and-H. In the last stage,small molecules were produced such as NH3, CO2and H2O. In the heating simulations of multi molecular chains, the products of single molecule chain and multi molecular chains areconsistent, indicated that single molecule chain degradation mechanism applies to multimolecular chains system. At last the reaction activation energy of NH3and CH2O were alsocomputed, the value of them are15.73kJ/mol and47.25kJ/mol.In addition, this paper also probed the effect of water and oxygen to the condensation ofdihydroxy methyl urea. In the water system, it found that the water molecules inhibit therupture of C-O bond at the beginning and make the reaction activation energy of CH2Oincreased to20.03kJ/mol, later promote the breakage of C-N bond, producing large mounts ofNH3and computing the reaction activation energy of NH3as40.25kJ/mol. Obiously wateraccelerates the degradation. But in the oxygen system, the amounts of NH3decreesed,showing that the oxygen influenced the mechanism of degradation. The thermal degradationof oxygen system also divided into four stages, in the first stage, the functional group-CH2-was attacked by the oxygen and the H dropped out, the single bond C-N transformed intodouble bonds C=N. The second and the third stages are similar with the pure system. In theforth stage, the small molecular appeared largely like CHNO and H2O. Here also computedthe reaction activation energy of NH3and CHNO as18.07kJ/mol and28.77kJ/mol, which isobviouly lower than the water system, showing that the oxygen accelerate the process ofcondensation of dihydroxy methyl urea. The whole therory provided in above could be makeas the guidence for the slow/controlled release fertilizers.