2.4 Continuous Flow Setup
The experimental setup used for micro-flow based photoisomerization and
in-flow separation process is presented in supporting information
(section S1). The solution is pumped from the inlet solution vessel
using an HPLC pump (Knauer Azura P4.1S). The outlet stream from the pump
is fed to FEP (fluorinated ethylenepropylene copolymer, IDEX 1548 L)
capillary tubular reactor (ID 0.02”, OD 1/16”, length 5 m) which is
wound around a cylindrical UV light source placed inside a closed oven.
Irradiation is carried out using a low-pressure amalgam lamp (TS23-212;
Dinies Technologies GmbH). The outlet then flows to the packed bed. The
packed bed (stainless steel, ID 4.5 mm, L 25 mm) is packed with 200-220
mg of AgNO3 impregnated silica gel (as packing or
adsorbent) with a mesh size of 230+ (Sigma-Aldrich). The
AgNO3/silica particles are mixed with 1 mm borosilicate
glass beads in a mass ratio 1.66:1 and then introduced to the packed bed
with a funnel. The inert glass beads are applied to prevent particle
agglomeration which results in channeling of the flow inside the packed
bed (for more information on micropacked beds and the assembling
process, we refer to [32]–[34]).The inlet and outlet of the
packed bed have attached separately two frits with a pore size of 10 μm
to keep the packing material inside the reactor. The outlet of the
packed bed is recycled to the inlet solution vessel through a 0.2 m long
FEP capillary tube. Samples are collected exactly before the recycle
stream enters the inlet solution vessel. The inlet solution vessel is
stirred with a magnetic stirrer bar to ensure a uniform concentration in
the vessel. In a general micro-flow based photoisomerization and an
in-flow separation experiment, cis -cyclooctene (0.06 g, 0.55
mmol), methyl benzoate as a singlet sensitizer (0.136 g, 1mmol) and
n-dodecane as the internal standard for GC analysis (0.017g, 0.1 mmol)
are dissolved in 25 ml n-hexane (with 1% diethyl ether) as solvent and
mixed in the same vessel (volumetric flask of 50 ml) and from this
vessel the solution is pumped to the flow setup.