Scale-up of Flame Spray Pyrolysis and Transfer to the Pulsation Reactor

In the flame spray pyrolysis reactor, a combustible solution – the precursor – is sprayed and ignited using a supporting flame – particles are formed, which are then collected by a filter above the flame. Typical process parameters in flame spray pyrolysis are the ratio of oxygen to fuel, dispersion pressure, residence time and throughput rate.

Usually this technology is applied in a University context, therefore it is a challenge to increase throughput rates, despite interesting development potentials.

A gas mixture is ignited in the combustion chamber, resulting in overpressure that discharges in the direction of the resonance tube. The inertia of the outgoing gas flow briefly causes a vacuum in the combustion chamber, which sucks in new fuel, which ignites and starts the cycle anew. Depending on the parameters and the design of the system, this cyclic combustion is the origin of the underlying frequency of the plant, between 1 and 500 Hz. The raw material is introduced at the beginning of the resonance tube; the air flow being cooled after treatment via cooling gas before the particles are separated with a cyclone or exhaust filter. [1]

One advantage of the pulsating gas flow is the homogeneous flow profile, which creates a very narrow distribution of the conditions under which the material is treated. The short residence time coupled with the precise control of the treatment temperature enables homogeneous product properties.

The challenge is to transfer the processes that were developed in flame spray pyrolysis to production scale in a pulsation reactor. We succeeded in doing so on behalf of a customer using zirconium oxide as an example.

The feed material consisted of a zirconium(IV) solution. First, the process was implemented on a laboratory scale with flame spray pyrolysis. After the desired product properties had been reached, we transferred the process to the pulsation reactor, achieving production scale.

The material content in the feed solution was increased, as well as the feed volume itself by 13 times, so that in the end a throughput rate 20 times as high as in laboratory flame spray pyrolysis was realized. Product properties in our pilot plant were in the same range as the comparison material from the FSP, with a slightly higher SSA and a slightly lower residual carbon content. Crystal structures were also comparable, with a slightly smaller particle size and very similar morphology on SEM and TEM images.

In addition to the already known advantages in the production of nanoscale powders with very specific properties that can be achieved using the pulsation reactor, this study shows that the transfer of flame spray pyrolysis processes from the laboratory to the production scale also offers a new possibility for the use of the pulsation reactor. For development projects of high-quality / innovative materials, this opens up a perspective for sampling or economic introduction. A further increase in throughput is possible on larger pulsation reactors.

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