Automated chemical synthesis. Part 3: Temperature control systems

Research efforts have been directed towards constructing a fully automated microcomputer-controlled bench-scale 'batch-type' chemical reactor [1-6]. This fully automated reactor can execute repetitive experiments on an approximately 50 ml scale, providing important chemical reaction data during early stages of process development research programmes. The precision and accuracy of the reagent/solvent delivery systems, chemical analysis systems and temperature-control systems are, ofcourse, of fundamental concern. Fail-safe operation is an equally important design consideration if the apparatus is to be used in an unattended operation mode. Particular emphasis has been placed on both self-checking features (for example flow monitors verify proper solution movement through Teflon delivery lines) and fail-safe recovery (engineered into hardware and designed into the automation software). A key hardware element in the fail-safe construction, the opto-isolator interface, has been described previously [1 and 3-6]. With fail-safe operation considerations foremost in mind, a temperature-control system which is controlled by a Digital Equipment Corporation MINC LSI 11/2 computer system and its associated interfaces has been designed and constructed. To effect temperature control in the chemical reactor vessel the opposing actions of systems that remove and add heat to the vessel contents must be balanced. Since the intended application of the apparatus entails repetitive, statistically directed experimentation [7-9], the temperature-control systems must be capable of reaching the designated reaction temperature set-point as quickly as possible (to maximize ramping), thereby minimizing the overall experimentation time. The heating and cooling systems must respond quickly to computer control signals and must have sufficient heating/cooling capacity to effectively respond to and control thermal anomalies ofchemical reactions (for instance endotherms, exotherms).