Choosing Reactors in the Chemical Industry for Complex Chemistries

Key Takeaways

• Choosing reactors for chemical industry settings requires a thorough understanding of your reaction process profile and operational requirements. 
• There are multiple reactor designs to choose from, many with overlapping capabilities and definitive key features. 
• Reasons to select one reactor over another are primarily rooted in operational nuances such as repeatability, thermal control, scale and safety.  

Selecting new reactors in the chemical industry for your complex processing applications is like picking any new process equipment, but with a few key differences. 

Let’s start with two definitions:

• Reactor: In chemical processing, a reactor is a piece of engineered equipment (typically a vessel) designed to facilitate chemical reactions by controlling ingredient flow, mixing, heat transfer, pressure and related process variables. 
• Complex chemistries: For this article, we’ll define complex chemistries as chemical products that require an advanced level of process operations and control to manufacture (like pharmaceutical ingredients and polymer bases). 

Next up, we’ll lay out the most common reactor types, followed by operational considerations that influence your selection. 

The Most Frequently Selected Reactor Designs

The most common reactors in the chemical industry include:    

• Batch and continuously stirred tank reactor: A batch reactor is a simple vertical vessel equipped with heat transfer jacketing (and agitation in the continuously stirred variant). Batch reactors are filled, sealed, heated/cooled and agitated (for CSTRs) until the reaction is finished, over and over. 
• Fluidized catalytic cracker: A continuous reactor type that vaporizes feed material and separates out valuable components. The specific reaction occurring is known as endothermic catalytic cracking, which breaks large hydrocarbon chains down into smaller, lighter molecules. 
• Plug flow reactors: A jacketed tubular reactor intended for continuous flow, the main benefit of a plug flow reactor is to keep products moving at a fixed speed and reaction rate without allowing any back-mixing. It’s mostly used for steam cracking, polymerization and hazardous reactions (like with ammonia). 
• Packed bed reactor: This reactor is a continuously flowing vertical column that incorporates media beds “packed” inside to increase surface area, promoting high conversion rates and controllable reaction times. Packed bed reactors are widely used for cracking, oxidation and fluid treatment reactions. 
• Fluid bed reactors: These reactors utilize a mechanically or hydraulically induced fluid bed (where solid particulates flow like a fluid) to mobilize a catalyst through a product volume. Fluid bed reactors are commonly used for cracking, gasification, combustion, granulation and drying of powders. 

Key Operational Factors to Consider for Complex Chemistries

In many cases, a given reaction can be performed in multiple types of reactors depending on how it’s operated. This is perhaps the most important detail about complex chemistries – that designing the ideal reaction process is less about the physical reactor (to a point), and more about operational factors such as:      

• Enthalpy: Chemical reactions are often exothermic (creating heat) or endothermic (absorbing heat), requiring very precise thermal control. A reaction’s enthalpy will heavily influence the selection of a reactor and its control system, especially for complex processes where runaway heat loads create hazards.  
• Reaction mechanics: The physical mechanics of complex chemical reactions can add many technical requirements into a reactor selection, such as multi-step kinetics, variable reaction rates and competing side reactions. In some cases, these mechanics require heavily customized or multiple sequential reactors.
• Reaction environments: Complex chemistries are sensitive to reaction fouling, which can occur from atmospheric gases, foreign materials, untreated cleaning water, high ambient temperature and even static electricity. Where needed, the overall reaction process must be contained in a controlled environment.    
• Reactor turnaround: When you evaluate reactors in the chemical industry, consider your requirements for the time spent between reactions. Cleaning, maintenance, inspection, calibration, catalyst replacement… All of these operational steps can be helped or hampered based on the selected reactor.  
• Production scale: Complex chemistry reactions often present different operational variables as they scale up from lab to production volumes. This involves both the physical reactor design itself, and also the performance and responsiveness of ancillary systems (like ingredient feed rates and steam ramp).

Finally, Remember Safety

Complex chemistry reactions are almost always classified as hazardous processes; if not by the materials themselves being explosive, corrosive or combustible, then by potential knockdown hazards created during production (like heat or off-gases). For help selecting the safest reactor for your application, please reach out to us here.