A modular silicon micromixer is designed and fabricated for high-flow rapid mixing at a wide range of reaction conditions. The mixer operates by splitting two inlet flows into a large number of channels, interdigitating them, and constricting the laminated flow to create submicrometer diffusion lengths. Mixing is quantified using the Villermaux-Dushman method, with UV-vis detection of the photoactive species, and compared against a commercial micromixer. Micromixers and tubing are then used to perform a quantitative kinetic study of the direct two-step synthesis of sodium nitrotetrazolate (NaNT) by a Sandmeyer type reaction via a reactive diazonium intermediate. Orders of reactions and temperature dependence of both steps, as well as pH and ionic strength dependence of the second step, are evaluated. Successful production of 4.4 g/h of NaNT in solution is ultimately achieved in a compact footprint using the kinetic data, verifying the potential for scaling to typical production amounts.