Solving process safety and scale up
In industries ranging from pharmaceuticals to fine chemicals, there is a need to take small, laboratory scale chemical reactions to mass manufacture of a product. Joe Willmot looks at how thermal and pressure hazards can be identified, assessed, and mitigated at each stage of product development.
See the original infographic on p20 of our digital issue of the September magazine.
Central to the risks involved with scale-up are the changes in heat loss behaviour with scale:
- Many reactions are exothermic and require cooling to ensure safe operation when performed on a large scale;
- Components in the reaction may become unstable under certain operating conditions, leading to additional thermal hazards.
It is necessary to identify and mitigate sources of risk during the process scale-up.
So, which safety tools are the right scale-up solutions for each process step?
Process Step: Discovery
PROBLEM: Are these materials safe to proceed with?
SOLUTION: Raw Material Hazard Screening
Hazard screening of raw materials early in development allows timely decisions to be made on how to develop a reaction or process.
- Identifying thermal and pressure hazards
Parameters such as the onset temperature of decomposition (Td) and rate of pressure increase can be determined, enabling an initial hazard assessment on the material.
If there is a need to characterize rapid thermal decompositions, higher resolution data on the rate of pressure change is required.
Process Step: Development
PROBLEM: What operating conditions are required to minimise risk?
SOLUTION: Reaction Calorimetry PLUS Reaction Mix Hazard Screening
Running a chemical process safely requires a thorough understanding of the main reactions and any possible, unintended, side reactions or decompositions.
Reaction calorimetry evaluates the main reactions. From this, operating conditions can be optimised to mitigate the hazards identified.
- Thermal properties of the desired reaction enable you to calculate the plant cooling capacity required to keep the reaction isothermal (Tp)
- Thermal runaway of the reaction is critical to understand the maximum temperature the main reaction will reach in the event of plant failure
Understanding if there are additional sources of thermal runaway risk within the reaction mixture is a further consideration of process development.
- Secondary thermal runaway risk; reaction mix hazard screening, combined with the data generated from reaction calorimetry, enables the criticality of the reaction to be classified, and identifies if further characterisation of exothermic events is required in order to define safe operating conditions.
Process Step: Scale-Up
PROBLEM: What is the extent of the thermal risk?
SOLUTION: Adiabatic Testing PLUS Hazard and Operability Assessment
When scaling up a process, accurate knowledge of an exothermic event is vital to ensure the magnitude of the thermal runaway risk is fully understood.
- Adiabatic calorimetry mimics the processes at large scale, while operating at laboratory volumes.
- Characterising the thermal runaway: adiabatic screening of a process collectively describes the magnitude of the thermal runaway risk by enabling accurate characterisation of:
- the onset temperature (Td)
- time to maximum rate (TMRd)
- adiabatic temperature rise (ΔTad,d)
- Plant-scale parameters from the laboratory: more advanced adiabatic screening during supports the use of low Phi factor test cells providing representative measurements of what would be expected to occur during a manufacturing scale incident, to include
- the rate of pressure increase
- the Time to Maximum Rate (TMR)
- adiabatic temperature rise (ΔTad)
- final temperature (Tend).
- Hazard and Operability Assessment: by directly comparing the impact of different operating scenarios using advanced adiabatic screening data, all necessary safety controls for manufacturing at scale can be selected
The ability to thoroughly simulate thermal runaway risks under manufacturing plant conditions, at the laboratory scale, is a valuable way of de-risking the process. Appropriate safety measures, such as emergency and evaporation cooling, quenching, controlled depressurisation and vent sizing can be designed and implemented before the final scale-up.
Author: Joe Willmot, Application Leader at H.E.L Group