Kinetics of calcium Cyanamid obtaining process from lime, carbon dioxide and ammonia

In Uzbekistan, the main range of nitrogen fertilizers produced is ammonium nitrate, carbamide and ammonium sulfate, the use of which has led to acidification of millions of hectares of land for many years, which negatively affects the receipt of high yields of agricultural crops.

straight line, the slope of which to the abscissa axis showed the order of the reaction for the component under study, i.e. the particular order of the reaction for carbon dioxide or ammonia.
During the experiments, the duration of the calcium cyanamide synthesis process varied from 25 to 105 minutes in 15-minute increments, the NH3:СО2 ratio ranged from 4:96 to 96: 4. The charge was prepared on the basis of natural limestone of the Jamansai deposit.
The temperature of 800 0 C was kept constant, which turned out to be optimal in the previous experiments, the volumetric velocity of the initial gas mixture was 6000 h -1 .
According to classical concepts, the reaction order can be 0, 1, 2, and 3, as well as fractional. In this regard, the experimental data obtained were checked by the known equations and diagrams, which showed their discrepancy. Therefore, from a theoretical point of view, the reaction is not three-molecular, apparently, it has an order associated with the complex mechanism of the reaction of formation of calcium cyanamide.
The first series of experiments to determine the order of the reaction with respect to carbon dioxide was carried out at a ratio of СО2:NH3 = 4:96, 7:93, 10:90.
The second series of experiments to determine the order of the reaction with respect to ammonia was given at the ratios of carbon dioxide to ammonia 96:4, 93:7, 90:10.
According to the results of experiments (Figs. 1 and 2), it can be concluded that with the same duration of the process, ammonia accelerates the formation of calcium cyanamide more than carbon dioxide. Figure: 1 Dependence of the nitrogen content in the product on the duration of the process and the concentration of ammonia in the gas mixture 1-4%, 2-7%, 3-10% Figure: 2 Dependence of the nitrogen content in the product on the duration of the process and the concentration of carbon dioxide in the gas mixture 1-Псо2=0,416, 2-ПNH3=0,425 Figure: 3 Dependence of the logarithms of the initial rates of the synthesis of calcium cyanamide on the logarithms of the concentration of carbon dioxide and ammonia in the initial gas mixture The determination of the particular orders (Fig. 3) shows that the order of the formation reaction for carbon dioxide is 0.416, and for ammonia -0.71205.
Since the reaction orders are fractional, this indicates that the process of chemical interaction of calcium oxide with ammonia and carbon dioxide is complex and its mechanism cannot be expressed by a simple stoichiometric equation.
Based on certain reaction orders, it can be considered that the heterogeneous process of the formation of calcium cyanamide from lime, ammonia and carbon dioxide is a complex process that includes a number of successive stages. In this regard, the overall speed will be determined by the speed of the slowest stage.
We put forward a hypothesis that the limiting stage of the studied process is the chemical interaction on the surface of a solid lime particle. To verify this, a number of experiments were carried out under optimal conditions for the synthesis of calcium cyanamide from lime, ammonia and carbon dioxide.
With the constancy of all other conditions of the experiment, changes were made: the duration of the process of exposure to the initial gas mixture from 15 to 120 minutes, as well as temperatures from 700 to 900 0 C.
Based on the experimental data (Fig. 4), graphs were constructed showing the effect of the temperature and duration of the process on the nitrogen content in calcium cyanamide.
The results of the analysis are in good agreement with the experimental data on the effect of temperature on the production of calcium cyanamide presented in this chapter.
The nature of the curves (Fig. 5) shows that in the initial period of the synthesis process they differ in steepness, which corresponds to the formation of a product at a high rate. With an increase in the duration of the synthesis process, the curves become flat, tending to a straight line, which reflects the achievement of an equilibrium yield of calcium cyanamide for the corresponding temperatures. Fig. 4 Influence of the duration and temperature of synthesis on the nitrogen content in the product Based on the research results, it can be concluded that the limiting stage of the process of obtaining calcium cyanamide from lime, carbon dioxide and ammonia is the diffusion of the initial gas components through the product layer.