Scaling up Reactions for Application Flashcards
Cost drives everything in chemistry, what it the max cost per tonne a process can be before it is not economical on the bulk scale (10⁶)
~£200 per tonne
Cost drives everything in chemistry, what it the max cost per tonne a process can be before it is not economical on the fine scale (~10⁴-10⁵)
£2000 per tonne
Cost drives everything in chemistry, what it the max cost per tonne a process can be before it is not economical on the pharmacy scale (<10³)
£20,000 per kg
List 3 basic steps for scaling up a reaction
- Start with an optimised lab system
- Move to lab based scale up (£) and investigate/improve conditions
- Scale up to full size plant (£££) and make product to sell (£)
Why at large scale, liquids are preferred for ease of handling
- Equipment needed is complicated: Shovel? Excavator?
- Difficult to weigh at tonne scale
- Cannot tare a 10 tonne reactor
- Reagent packages/drums
- Static electricity problems
- Dust cloud is a problem
Why can exothermic reactions at industrial scale be an issue?
- Megajoules of energy coming out
- Solvent can boil
- Possibility of site exploding
Stored energy =
Pressure x Volume
(Stirred Tank Reactors are not suited where high pressures are required)
What are some requirements of mechanical agitation of an industrial scale reaction system?
- Overhead stirrer
- Driveshafts - pressure seals
- Very powerful motors
- Spark proof equipment - solvents
- Viscosity changes with temperature
- High solution viscosity
- Impeller and baffle design important
Reaction systems can fall under…
- Chemical limitation
- Diffusion limitation
Limitations by mass transport of reagents/products can be identified in varous ways….
- Reaction rate will not vary directly with mass of catalyst
- Rate will be increased by better gas/liquid mixing
- Activation energy of the reaction will be low (10-15 kJ/mol)
- Arrhenius plot can show distinctive kink at changeover:
In an exothermic process, loss of control can give side product and dangerous situations
How can this be controlled?
- Usually done by circulation of Heat Transfer Fluid (HTF) in jackets (glycol - iced water/salt - water - silicone oil)
- Can add extra coils inside near impellers to increase surface area
Temperature regulation essentially comes down to putting heat in and taking heat out
There is glass lining on reactors which is the insulating layer between reaction and heat transfer fluid
How can this be made more sustainable?
- Fridges at industrial scale are very expensive due to high energy requirements
- Therefore you can try to be more sustainable by using heat exchangers whenever possible
Failure in control measures can give runaway reactions
What are the two main types of runaway:
- Chain branch runaway
- Thermal runaway
Why are multi-tube reactors used?
- Instead of large stirrer tanks, use lots of tubes - many designs
- More challenging to manufacture
- Increased SA for thermal control
- Can give better mixing using baffles, etc
- Minimise part of the plant that must be under high pressure
What are the benefit of undertaking reactions using gases and liquids under continuous flow loops?
- Less catalyst needed
- Smaller reactor for heating or pressure containment
- Volume of product not restricted
- Reaction monitoring and control
What are the drawbacks of undertaking reactions using gases and liquids under continuous flow loops?
- Tend to be reaction specific
- Expensive (support systems)
- Difficult for solids (slurry)
Catalysts will loss activity due to deactivation processes
What will dictate the recharge/regeneration?
Economics will dictate the point at which reduced activity forces catalyst recharge and/or regeneration
Product seperation and purification is one of the single largest consumers of energy and material
Why is this complicated at an industrial scale?
- Large energy costs
- Mixture of compounds so could require further extraction
- Solvent still left in residue cake
- Reactor inside covered in material - difficult to access/clean
The best method is recovery external to a reactor
What are the issues with this however, on an industrial scale?
- Remove from reactor in solution (still hot)
- Crystalisation by cooling (controlled rate)
- Filtration from cold supernatant liquid
- Drying, typically under nitrogen
What are some defined emergency procedures in place surrounding engineering and construction?
- Engineering limit must be higher than service limit
- Expansion volumes for heating and cooling
- Must be able to handle worst case scenario
- Monitoring and feedback to maintain optimum conditions
