Implementation of Process Intensification in Industry - Process Intensification for Green Chemistry - page 390

difficult start-up;
unreliable operation.
For RD, dividing wall columns and reverse flow combustors, the application range in the
oil refining and bulk chemical industries is high. Furthermore, they have a good fit with the
business drivers and all the hurdles mentioned have been overcome, mainly by technology
providers with a robust and easy to understand scale-up method. The number of
commercial-scale implementations for each of these technologies exceeds a hundred,
and it is ever increasing [6].
For microreactors, the business drivers mentioned are less fitting. In particular, the
economy of scale rule works against the application at the required large scale of oil
refining. This is probably why so far no commercial-scale applications have been reported
for the oil refining and bulk chemicals industries. Hydrogen production from methane in
microreactors may be the first candidate for commercial-scale implementation, as the
required production scale is relatively small and the economics look favourable [10].
For RPBs the applicability is very limited, the business drivers are not so fitting and the
scale-up certainty and reliability of operation are lower (due to the rotating equipment
involved) [6]. Dow Chemical has a commercial-scale RPB process in operation [11] and
China has several RPB processes that use the same technology as Dow [8].
In general, the scope for PI technology in the oil refining and bulk chemicals industries is
large for all technologies in which several functions are combined into a single vessel, such
as RD and dividing wall columns, because of the fit with the previously mentioned business
drivers and the methods available to reduce the uncertainties in commercial-scale
implementation.
16.3.2 Fine Chemicals and Pharmaceuticals Industries
The drivers for these industries are the lowest cost of feedstocks and rapid commercial-
scale implementation. Lower feedstock cost per mass of product can be obtained by
reducing byproduct formation. This in turn can be done by using short residence times
and perfect temperature control. The majority of reactors used in this industry belong to
the mechanically stirred type, which has an overhead vapour condenser for cooling, is
operated fed-batchwise and has a residence time of hours. This long residence time
is generally due to the limited cooling capacity of the reactor, by which slow fed-batch
feeding is needed in order to control the reaction temperature. Because of this reactor
type there is ample scope for PI.
Notably, there is a large application area for high heat-exchange rate microreactors
operated in batch or continuously. The reaction time of hours can then in most cases
be reduced to a few seconds, which often also greatly reduces byproduct formation.
An example of a microreactor for this type of application is provided by Zuidhof [12].
Moreover, the development time and the risk inherent in scale-up from laboratory-scale
experiments to commercial scale can be greatly reduced by these microreactors, as the
commercial-scale reactor is essentially the same as the laboratory-scale one, if it is brute-
force down-scaled.
There is also scope for a multifunctional PI, such as RD, in these industrial branches,
particularly where byproduct formation can be reduced by in situ removal of product from
the reactive phase, which is feasible using RD [13] or reactive extraction [14].