Spinning Disc Reactor for Green Processing and Synthesis - Process Intensification for Green Chemistry - page 79

Table 3.5 Comparison of static film and SDR film for n-butyl acrylate photopolymerization.
Reproduced from [ref 40] # 2003 American Chemical Society.

Film type UV intensity

(mW/cm 2 )

Exposure
time (s)

Conversion
(%)

M w M n PDI

Static 75 40 92 35 000 18 000 2.0

Static 25 10 30 52 000 28 000 1.8

SDR (dynamic) 25 2.1 90 70 000 33 000 2.1

These results have been benchmarked against photopolymerization in thin static films
(Table 3.5) [53]. It is apparent that thin, well-mixed film in the SDR generally outperforms
thin static film, in both conversion and molecular weight properties, when they are exposed
to identical UV intensities of 25 mW/cm 2 . To obtain polymers of similarly high conver-
sions above 90%, as in the SDR, it is necessary to illuminate the static films at a higher UV
intensity of 75mW/cm 2 and to extend the exposure time to 40 s. Clearly, the static film
photopolymerization process proceeds at a much slower rate, even with increased energy
input, due to the lack of mixing. It is also possible that temporal variations in the molecular
weight properties will exist across the static film thickness, leading to non-uniformity in the
polymer product.
The study demonstrates the exciting and industrially viable opportunity to perform
continuous photopolymerization of monomers in bulk in the SDR. With its enhanced
mixing, high heat-removal capabilities, sustainable thin-film flow for efficient UV
penetration and short, controllable residence time, the SDR offers the prospect of rapid
polymerization rates and improved polymer product quality. It is noteworthy that a related
investigation focusing on thermally-initiated, rather than UV-initiated, free-radical polym-
erization of styrene in bulk in the SDR has achieved similar benefits of rapid polymeriza-
tion and good control of molecular weight properties in single and multiple passes on the
rotating disc [54].

3.4.3 Heterogeneous Catalytic Organic Reaction in the SDR: An Example
of Application to the Pharmaceutical/Fine Chemicals Industry

Manufacturing in the pharmaceutical and fine/specialty chemicals sector has traditionally
been associated with the accumulation of excessive quantities of hazardous waste,
resulting not only from the large amounts of contaminated organic solvents [55-57]
but also from widespread use of mineral acids and Lewis acids in stoichiometric
proportions [58]. Low selectivity to the desired product, which translates into low
atom efficiency, is another factor that can produce significant amounts of unwanted
byproducts. In the past 2 decades serious efforts have been made in the search for
heterogeneous catalysts that will not only enhance reaction rates and product selectivity
but eliminate the problem of separating product from catalyst [46,59].
An important industrial example in the fine chemical industry typified by low-efficiency
processing and considerable environmental impact is the rearrangement reaction of
a -pinene oxide. The process can lead to the formation of more than 100 different products,
depending on the catalyst employed and the reaction conditions [60]. The main products
obtained from this reaction are shown in Scheme 3.3. One of these, campholenic aldehyde,