vanisal sodium (a chemical) and aspirin (a pharmaceutical), in
sequence on the same machine. Each reaction was run for 7
days, 24 h a day, interspersed by a cleaning stage.
this reactor design for long periods of operation, no data on
continuous multiproduct manufacturing or on cross-contamina-
tion matters when a single COBR is employed to produce
different chemical entities, testing its manufacturing versatility.
This was the first study of its kind.
A COBR is a mixing/reaction device consisting of a tube
with periodically spaced orifice baffles, perpendicularly orien-
tated in relation to the flow. The flow inside the tube is
superimposed with oscillatory motion, caused by a motor placed
at one or both ends of the reactor. Disruption of the flow occurs
when the fluid encounters a sharp restriction and eddies around
Experimental Section
Reaction Schemes. Vanisal Sodium. Vanillin is the molecule
that is normally used to evoke the smell of vanilla and that is
relatively stable in perfumes but not in soap formulations. Due
to the combination of light, heat, and basic conditions in soaps,
vanillin and its derivatives undergo chemical reactions that
rapidly transform them into polyphenols and other detergent
products. The outcome of these events is the discoloration of
soaps, from a light tone progressively to darker brown and
15,16
the annular baffles are formed.
This continuous generation
and cessation of eddies provides a vigorous axial and radial
17,18
mixing in the reactor.
Each baffled cell can be considered
as a perfectly mixed continuous stirred tank reactor (CSTR);
as a consequence of this the entire COBR behaves as a large
number of perfectly mixed CSTRs in series. Very sharp
residence time distributions, i.e. plug-flow characteristics, are
29,30
eventually black, as well as the loss of foaming power.
19
achieved using this reactor technology.
Vanisal sodium, the product of the treatment of vanillin with a
sulfiting agent, is the solution to this problem: it does not suffer
from discoloration when used in the composition of soaps and
Extensive studies using the COBR demonstrate that its
characteristics allow for a significant improvement in mixing
2
0
21
and heat and mass transfer rates. This reactor design has
shown success when tested for several industry-relevant pro-
30
retains the much appreciated vanilla scent. The reaction
scheme for the production of vanisal sodium is shown below;
it is a second-order reaction:
22
cesses, such as mixing and particle suspension, polymeriza-
tion, fermentation, crystallization, photooxidation, and
biodiesel production, just to name but a few.
Although there are industrial COBRs in use, there are
currently no published data on the robustness and reliability of
23
24
25
26
27
28
(
15) Brunold, C. R.; Hunns, J. C. B.; Mackley, M. R.; Thompson, J. W.
Experimental observations on flow patterns and energy losses for
oscillatory flow in ducts containing sharp edges. Chem. Eng. Sci. 1989,
4
4, 1227–1244.
(
16) Sommer de Gelicourt, Y. On single phase axial dispersion in oscillatory
baffled columns. M.Phil. thesis, Heriot-Watt University, Edinburgh,
U.K., 2000.
The experimental procedure is the following: vanillin and
water were mixed in a batch oscillatory baffled reactor (OBR)
that was preheated to 60 °C. Sodium hydrogen sulfite (40%
w/w) and the mixture were then separately fed into the COBR,
which was also heated and maintained at 60 °C. The COBR
was operated at laminar flow condition throughout the cam-
paign. Samples were taken every six hours. In this synthesis, a
constant temperature of 60 °C was used throughout the COBR.
Aspirin. More than a century after the Bayer pharmaceutical
company started selling aspirin, acetylsalicylic acid is still one
of the most widely used over-the-counter drugs in the world.
Nowadays, over 35,000 tons are produced and consumed
(
17) Nelson, G. A scale up study in suspension polymerisation of
methylmethacrylate in a pilot oscillatory baffled reactor. Ph.D. Thesis,
Heriot-Watt University: Edinburgh, U.K., http://worldcat.org/oclc/
5
3608706, 2001.
(
(
(
(
(
(
18) Mackley, M. R.; Ni, X.-W. Mixing and dispersion in a baffled tube
for steady laminar and pulsatile flow. Chem. Eng. Sci. 1991, 46 (12),
3
139–3151.
19) Ni, X.; Pereira, N. E. Parameters affecting fluid dispersion in a
continuous oscillatory baffled tube. Am. Inst. Chem. Eng. J. 2000, 46
(
1), 37–45.
20) Mackley, M. R.; Tweedle, G. M.; Wyatt, I. D. Experimental heat
transfer measurements for pulsatile flow in baffled tubes. Chem. Eng.
Sci. 1990, 45 (5), 1237–1242.
21) Hewgill, M. R.; Mackley, M. R.; Pandit, A. B.; Pannu, S. S.
Enhancement of gas-liquid mass transfer using oscillatory flow in a
baffled tube. Chem. Eng. Sci. 1993, 48 (4), 799–809.
31
annually, the equivalent to ∼100 billion tablets. The synthesis
22) Liu, S.; Ni, X.; Greated, C. A.; Fryer, P. J. Measurements of velocities
of single particles for steady and oscillatory flows in plain and baffled
tubes. Trans. Inst.Chem. Eng. 1995, 73 (A), 727–732.
of acetylsalicylic acid involves the acetylation of salicylic acid
by acetic anhydride in an acidic medium as shown below and
is again a second-order reaction:
23) Ni, X.; Zhang, Y.; Mustafa, I. Correction of Polymer Particle Size
with Droplet Size in Suspension Polymerisation of Methylmethacrylate
in a Batch Oscillatory Baffled Reactor. Chem. Eng. Sci. 1999, 54,
8
41–850.
(
(
(
(
24) Gaidhani, H. K.; McNeil, B.; Ni, X. Production of pullulan using an
oscillatory baffled bioreactor. J. Chem. Technol. Biotechnol. 2003, 78,
2
60–264.
25) Ni, X.-W.; Liao, A. Effects of Cooling Rate and Solution Concentration
on Solution Crystallization of L-Glutamic Acid in an Oscillatory
Baffled Crystallizer. Cryst. Growth Des. 2008, 8 (8), 2875–2881.
26) Gao, P.; Ching, W. H.; Herrmann, M.; Chan, C. K.; Yue, P. L.
Photooxidation of a model pollutant in an oscillatory flow reactor with
baffles. Chem. Eng. Sci. 2002, 58 (3-6), 1013–1020.
(29) Vidal, J.-P. Vanillin. In Kirk-Othmer Encyclopedia of Chemical
Technology; Kroschwitz, J., Ed.; John Wiley & Sons: Hoboken, NJ,
2006.
(30) Turin, L. Color-stabilization of Aromachemicals. WO/2007/013901,
2007.
(31) Classon, R. Spring Investor Conference (Bayer Healthcare), Le-
verkusen, Germany, March 18-19, 2004, Safe Harbor; Bayer AG:
Leverkusen, Germany, 2004.
27) Ni, X.; Mackley, M. R.; Harvey, A. P.; Stonestreet, P.; Baird, M. H. I.;
Rama Rao, N. V. Mixing through oscillations and pulsations: A guide
to achieving process enhancements in the chemical and process
industries. Trans. Inst. Chem. Eng. 2003, 81 (A), 373–383.
28) Laird, I., Nitech - The Company. PI Meeting, Grangemouth, U.K.,
April 26, 2007.
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