Hindawi Publishing Corporation Mathematical Problems in Engineering Volume 2011, Article ID 439785, 18 pages doi:10.1155/2011/439785 Research Article Digital Control of a Continuous Stirred Tank Reactor M. P.Di Ciccio, M. Bottini, and P. Pepe Department of Electrical and Information Engineering, University of L’Aquila, 67040 Poggio di Roio (AQ), Italy Correspondence should be addressed to P. Pepe, pierdomenico.pepe@univaq.it Received 4 August 2010; Revised 24 January 2011; Accepted 18 February 2011 Academic Editor: Maria do Ros´ ario de Pinho Copyright q 2011 M. P. Di Ciccio et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. We project a novel digital control law for continuous stirred tank reactors, based on sampled measures of temperatures and reactant concentration, as it happens in practice. The methodology of relative degree preservation under sampling is used. It is proved that a suitably approximated sampled system, obtained by Taylor series expansion and truncation, in closed loop with the projected control law, is asymptotically stable, provided that a condition on the sampling period is verified. Such condition allows for values of the sampling period larger than necessary in practical implementation with usual technology. Many simulations show the high performance of the proposed digital control law. 1. Introduction The control of the operation of chemical reactors has attracted the attention of researchers for a long time. The underlying motivation relies on the fact that industrial chemical reactors are frequently operated at unstable operating conditions, which often corresponds to optimal process performance 1–19. Polymerization processes 5 and bioreactors fermentors 18 are important examples of large-scale chemical reactors operated at unstable conditions. As well known, the measures of the reactant concentration cannot be achieved on continuous time. In practice, these measures are available at certain time intervals. It is therefore very important to project control laws which are piecewise constant and are updated at each measures update. That is, for practical use, a digital control law has to be projected. Applications of nonlinear digital control theory to some chemical reactors can be found in 20, 21. In 11 a discrete- time controller is obtained by linear approximations successively executed at each sampling time, and an application to a continuous stirred tank reactor is shown.