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After having established in a previous paper that the synthesis of stoichiometric monochloramine is hazardous due to the high exothermicity of the reaction and the risk of decomposition of the solution from 36 °C, it appeared that the best solution for this synthesis is to use microreactor technology. A series of experiments carried out using a Doehlert experimental design provided access to a mathematical model describing, for an initial fixed composition ratio [NH4+]0/[OCl−]0, the evolution of the yield as a function of temperature, the flow rate of the reagents and the number of sodium hydroxide equivalent. Thus, the optimal conditions for the synthesis of stoichiometric chloramine using microreactor technology were established.

In this paper, we describe a new strategy developed for the synthesis of MMH using the Raschig process. For the first time, it consists in synthesizing chloramine under stoichiometric conditions which leads to a more economical process because it avoids the additional steps of extraction due to the presence of excess reagents. However, monochloramine is not very stable and, therefore, it is necessary to study its stability. The various batch tests show that the reaction must be strictly controlled. As shown from DSC analyses on stoichiometric chloramine solutions, a risk of decomposition is present from 36 °C. Thus, controlling the temperature rise requires efficient cooling in the synthesis reactor or synthesis at low temperature, in order to avoid any sudden decomposition of the synthesis solution.

The catalytic hydrogenation of both 1 and 2-pyrazoline was studied in order to obtain the pyrazolidine. Among the studied catalysts, the Pd/C type catalyst permitted to hydrogenate the 1-pyrazoline but did not hydrogenate 2-pyrazoline. A slow hydrogenation of 2-pyrazoline occurred with a Pt/C and a mixed Pd/Pt/C catalyst. We demonstrated that catalyst poisoning occurred, which is due to the presence of the NH link of the 2-pyrazoline, blocking the active centers of the catalyst. At least, the Rh/C catalyst permitted to hydrogenate the mixture of 1 and 2-pyrazolines with a quantitative yield. The experiments showed that it was possible to reduce the reaction time by using catalysts having different specific areas. The Raney nickel catalyst also gave good results but its use requires much more precautions. Two process schemes were then established, taking into account both the synthesis of the 1 and 2-pyrazolines and their hydrogenation.