Student Laboratory Module: Kinetics of Ammonia Cracking


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The Chemical and Biological Engineering (CBE) Department at the Colorado School of Mines is dedicated to the continual improvement of the laboratory resources made available to those undergraduates enrolled in courses which have major or minor laboratory components. One such course is Kinetics and Reaction Engineering (CBEN 418), offered to undergraduate seniors in the CBE department. Historically, this course has been delivered primarily as a series of traditional classroom lectures with an experimental module (usually one week at the end of the semester) with about 2 hours of participation time per student outside of normal class hours.

Previous experimental designs have involved the execution and study of homogeneous reactions (reversible and irreversible). So far, attempts to incorporate heterogeneous (surface) catalytic reactions have not come to fruition. In the previous two calendar years (2012 and 2013), the CBE department has acquired the appropriate hardware and analytical equipment that would allow for the successful design and building of such an experiment. This would be both an educational and challenging project for an undergraduate student that would be concurrently enrolled in CBEN 418 (thus putting classroom knowledge into immediate practice), and would benefit all future CBE students that would have hands-on access to a true catalytic gas reaction system – a rare opportunity for undergraduates in any chemical engineering curriculum in this country.

The student will put into practice the classical techniques of catalytic reactor design – including surface- and active-area catalyst characterization, reactor sizing (space-time calculation and turnover number studies in differential reaction mode), and preliminary data analysis using Langmuir–Hinshelwood (or, as appropriate, Eley-Rideal) mechanism suppositions. While several gas reactions will be possible with the final apparatus, the simple reversible reaction of ammonia and its elemental constituents has been selected.

The simple stoichiometry, absence of side reactions, and wide variation in thermal conductivity of hydrogen versus ammonia and nitrogen makes this an ideal reaction for an introductory experiment involving heterogeneous catalytic reactions. Finally, the student will have the advantage of the use of on-hand total surface area and active surface area measurement apparatus, gas mass flow controllers, pressure and temperature sensors, a reactor tube furnace with temperature control, and a thermal conductivity detector with a wide operation range (0 – 100% hydrogen in nitrogen/ammonia mixtures).