Mastering ozonolysis: production from laboratory to ton scale in ...

safely evaluating and implementing technical processes. This
includes a Routine Safety Assessment of the process:
• Reaction calorimetric measurements (RC-1) (monitoring
of the whole process, including downstream processing).
• DSC measurements on starting materials, intermediary
compounds and products from the process.
Spectroscopic Methodologies:
• The handling of the primary product from conversion of
ozone with an olefinic substance requires precautions that
are very similar to the handling and processing of peroxides
with regard to the decomposition (E = 200–400kJ/mol).
• UV measurements for the determination of the ozone
consumption (ozone efficiency).
Table 1 shows typical RC-1 results for an ozonolysis reaction and a
following quench reaction. Clearly, the ozonolysis is highly
exothermic with a theoretical adiabatic temperature rise of more
than 386 K However, the mass transfer, fully controls the reaction,
leading to no heat accumulation and a reaction controlled by
the dosage of ozone (Note: the dosage can be interrupted at
any time). On the other hand, the quench reaction is less
exothermic (ΔT ad = 127 K) but a heat accumulation of 100
percent is observed. In case of lost control, it is imperative to
reduce this amount to its maximum possible limit.
Table 1. Typical heat characteristic of an ozonolysis process.
The key to controlling the handling of primary-generated
ozonides is embedding the ozonolysis in the required downstream
processing via a continuous process. Continuous operation
enables one to keep the stock of ozonides to its minimum and to
further process them once generated. In addition, the ozonolysis
should be performed in a confined area. This is accomplished at
Lonza by a dedicated laboratory and a bunker for large-scale
applications since ozone is a toxic gas.
CONTROL OF THE GAS-LIQUID MASS TRANSFER PROCESS
The safe implementation of ozonolysis at technical scale with a
throughput up to 8.5 Kg ozone/hour requires the perfect control of
the gas-liquid mass transfer process. Indeed, this process is
achieved on a small scale by using a gas-liquid loop reactor
integrated with a micro venturi injector. Knowledge of the process
conditions at laboratory scale with a throughput of 50 g ozone/
hour is the key to generating most of the criteria for later handling
at technical scale. The full picture of ozonolysis at laboratory scale
is carried out by applying a highly modular laboratory loop reactor
(150-1000 mL, T: -70 to 40°C) as depicted in Figure 2.
The loop-system consists of 4 main parts:
• Injector for Ozone / residence time module (conversion of
the substrate to the Ozonide)
• Gas/liquid separation / Heat transfer device (separation
of the gas phase from reaction solution)
• Pump (pulsation free)
• Ozone analyzer equipment (balance of the Ozone,
determination of reaction efficiency)
Determining the reaction criteria of an ozonolysis process can be
seen as a package that enables one to show the safe
implementation of the process at technical scale (Figure 3). The
development can be divided into four major parts, which are each
crucial for the safe handling of the process at technical scale.
FLOW CHEMISTRY
Figure 2. Schematic representation of the laboratory reactor.
Figure 3. The implementation scenarios for ozonolysis.
If the ozonolysis part of the process must be studied further,
Lonza is able to implement an additional scale-up step that
allows one to handle the ozonolysis in a kilogramscale.
The unit is an integral scale down of the plant
system, and it integrates the Sulzer SMV TM mixer
elements (Figure 4). These elements are then
combined in a shell-and-tube heat-exchange module
for isothermal operations. These mixing elements have
predictable k l a values (mass transfer coefficient) and
can be scaled-up in a straightforward manner.
The system depicted in Figure 5 is an exact scaled down version
of the final production reactor (scale factor of ca 1:500).
Formation of aerosol and operation with flammable solvents
The operation of ozonolysis in a classic plug flow manner would
lead to a huge imbalance of gas–to–liquid volume, resulting, in the
worst case, to a very critical situation: the dryness of ozonides (i.e.
solvent evaporation). Such operating conditions are only possible
Figure 4. Sulzer SMV static mixer elements for the laboratory from different
perspectives.
Figure 5. Lonza bench-scale unit that is an exact scale down the plant
system.
chimica oggi/Chemistry Today - vol 29 n 1 January/February 2011
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