Reaction Kinetics and Reactors Review Greg Jarnutowski, Oliver Meade, Ben Brock, Kyle Patrick, James Stephen

Overview Reaction Kinetics Batch Reactors Continuous Stirred Tank Reactors Plug Flow Reactors Transient Processes

Main Kinetics Takeaways Kinetics, Reaction Rate, and Conversion Kinetics is important Profitability Safety Rate = Change in Molarity/sec r=k*Reactant1A*Reactant2B k=Rate constant Raghavan CHBE 440 Lecture 1

Zero, First, and Greater than First Order Rxns Rate [M]/s Time

Batch Reactor Kinetics Design Equations: Assumptions for a Batch Reactor: Closed System Uniform Mixing Constant Volume Constant Pressure ➜Constant Volume ➜Variable Volume Where C is concentration, N is moles, V is volume, v is stoichiometric coefficient, and r is rate https://en.wikipedia.org/wiki/Batch_reactor A batch reactor is a reactor that allows the reaction to take place with adding or removing anything throughout the reaction. The design equations are on the left of the slide, where C is concentration, N is moles, V is volume, v is stoichiometric coefficient, and r is rate. For the design equations, the following assumptions are made. The system is closed, this is because nothing is entering or leaving the reactor during the process. The system is assumed to be well-mixed to ensure the rate is constant throughout the reactor because it is dependent on concentration. The reactor also has constant volume and pressure. The reactor temperature is easily controlled with a heating and cooling jacket, which is important for processes that have very exothermic reactions.

Batch Reactors in Industry Usage in Industry: •Pharmaceutical Production •Fermentation •Smaller Scale Production High conversion per unit volume http://www.infors-ht.com/index.php/en/products/bioreactors Batch reactors are used in industry for a few applications. Batch reactors are used for pharmaceuticals because of the precise temperature control. They are also used in fermentation, like for making beer. The batch reactor is used for smaller scale production because the reaction takes longer to reach the desired conversion. The reactors allow for a high conversion per unit volume because the time in the reactor can be as high as desired. For large scale production, the batch reactor is less effective because of how long the process takes. https://en.wikipedia.org/wiki/Bioreactor

Continuous Stirred Tank Reactor Kinetics Design Equation: Assumptions in the CSTR Design Equation: •Steady state (no accumulation) •Well mixed with same concentration throughout Key Facts: •Concentration and rate of reaction is constant throughout a CSTR •CSTRs typically achieve a lower conversion than PFRs for the same reactor volume •Many CSTRs in series will behave similar to a single PFR with the same total volume Image source: wikipedia.com

The main advantage of CSTRs over PFRs is better temperature control Energy Balance: Heat removed by cooling jacket Heat removed by flow Heat generated or removed by reaction CSTR is a well-mixed reactor so the temperature is constant throughout •Constant heating/cooling rate over whole reactor •PFRs require different heating rates down the length of reactor PFRs require different heating rates down the length of reactor Image source: http://pubs.sciepub.com

Plug Flow Reactor Kinetics Design Equation: Assumptions in the PFR Design Equation: Plug FLow No Axial Mixing, Uniform concentration at a given Z Steady State CA is dependent on position in reactor. Key Facts: •Concentration and rate of reaction varies along the length of the reactor •Single pass conversion depends on reactor length

Plug Flow Reactors in Industry Pros: Large Processing Volume Low Maintenance Costs Creative Spacing Options More Effective Conversion/Volume Cons: More Difficult to Control Temperature Plug Flow not valid assumption, may get lower yields than expected http://encyclopedia.che.engin.umich.edu/Pages/Reactors/PFR/PFR.html

Transient Processes Processes often not at steady state (most of the time) Nonzero accumulation term Transient CSTR:

Transient CSTR ODE Solution: Time to reach steady state (99%) tss is k dependent: small for a large k, large for a small k

Semibatch Reactor Cross between a CSTR and a batch reactor Useful for maximizing selectivity, controlling exothermic temperature release Mass balance:

Questions?

Bibliography Batch Reactors, umich.edu/~elements/asyLearn/bits/batch/index.htm. https://myelms.umd.edu/courses/1215315/files/45013264?module_item_id=8743378 (Dr. Raghavan Slides) “Plug Flow Reactors.” Visual Encyclopedia of Chemical Engineering, encyclopedia.che.engin.umich.edu/Pages/Reactors/PFR/PFR.html.(PFR Image #1) library.automationdirect.com/wp-content/uploads/2015/07/Portable-Water-Treatment-Platform-3.jpg.(PFR Image #2) Woodard, Barney, et al. Fermentation Science and Biopharmaceutical Production. Vol. 2, Vandalay Publishing, 2017.