Chemical reactors allow a controlled reaction to be run continuously. They are used to improve product quality, reduce capital costs per tonne and enable safer operations. In a tubular reactor fluids flow down a heated tube and react to form the desired chemical. There is little back mixing and the conditions are often referred to as plug flow.
Engineers designing industrial plants to manufacture chemicals must be able to accurately predict how much heat will be generated during a reaction. If too much heat is generated proteins denature, products burn and a reactor might explode. If too little heat is generated, the chemicals might not react or the wrong product may be produced. The basis of thermal calculations is the same for batch or continuous flow chemical reactors. It consists of the process stream and the exchanger fluid (the liquid used to cool the reactor). Heat flows from one to the other. The calculation involves estimating the outlet reaction and exchanger fluid temperatures using information on the reactor geometry, the fluids’ properties and their inlet and exit temperatures. Chemical engineers use a variety of tools for thermodynamic analysis and scale-up to make these predictions. Reaction calorimeters, provide scientists with accurate results quickly and allow them to investigate the impact of changing conditions on concentrations, temperatures or kinetics.
Depending on the chemical reaction type, mass transfer is important for cooling strongly exothermic reactions or to modify the effective reaction area for multiphase and interfacial processes. In the latter case, increased turbulence increases the effective mass transfer rate. Batch reactors are flexible and multipurpose but the limited heat and mass transfer rates hamper highly exothermic and fast reactions. Furthermore, solid catalyst particles are often crushed by the impeller during reaction resulting in low catalyst lifetime. Energy efficiency is poor because of the high amount of energy required every time a batch reactor is started up. Continuous stirred tank reactors (CSTRs) are agitated tanks that are continuously fed and emptied. They are well-characterized and available on a large scale with decades of performance and behaviour understanding. They are also versatile, allowing the residence time distribution to be adjusted by connecting multiple CSTRs in series, trading mechanical complexity for easy scale-up and superior mixing.
The extent to which reagents contact and interact in a chemical reactor has an important impact on local reaction rates, which in turn can impact the overall reaction yield. For this reason, mixing is of paramount importance when designing and scaling up chemical reactors.
Mixing in a chemical reactor is often a bottleneck, especially with complex reactions that require heating or cooling of the liquid mixture, dispersal of large particle solids, or high-speed reaction kinetics. To overcome these problems, continuous flow systems have developed that allow chemists to optimize the reaction conditions with precision heating and cooling instruments. The major advantage of flow chemistry is that the different reactants can be fed through individual lines and the residence time can be adjusted independently.
This makes it easy to fine-tune the reaction conditions and ensures the best possible results. Moreover, the separate handling of the different reagents reduces the risk for unwanted reactions and enables safer operation. For unbeatable deals on chemical reactors, click here or navigate to our official website.
