THIN FILM REACTORS

This Thin film reactor is designed and best suited for irradiations of small volumes of reactant ranging from 50ml to 500ml and/or concentrated solutions where radiation only penetrates a fraction of a mm. The reactant solution is pumped from reservoir through a glass jet and thin film of liquid falls under gravity over quartz or borosilicate closed tube. A low pressure mercury lamp or phosphor-coated lamp mounted inside this tube ensures even irradiation of this falling film. By reversing the flow direction the reactor may be used for irradiation of 5 mm path-length of solution in a conventional flow reactor arrangement.

Five standard emission lamps are available for use in this reactor, all being of identical size and electrical characteristics. The spectral characteristics are shown in the figures or the 350nm, 410 nm and white lamps. The 254nm lamp has no phosphor coating and emits over 90% of its radiation at 254 nm.

Lamp type	Peak emission	Comments	Model
254	254 nm	Requires quartz tube (QW3)	TFQ3
350	350 nm	Use with borosilicate (BW3) or quartz (QW3) tube	TFB4
410	410 nm	Use with borosilicate (BW3) or quartz (QW3) tube	TFB5
White	See spectrum	Covers entire visible spectrum	TFB6
PAR	436, 650 nm	Strong emission at absorption, Bands of chlorophyll	TFB7

The 350 nm lamp (model TFB4) produces 4X1018 photons/s in the thin-film reactor as measured by benzophenone/isopropanol actinometry and representative spectral trace of changes with irradiation time is shown.

All these lamps my be used in a large immersion wells (models TFB7 and TFB5). The 254 nm lamp, for example, produces 2X1018 photons/s in the large quartz well as measured by ferrioxalate actinometry. The lamps are also used in the multilamp reactor (see page 6). Lamps have a nominal power consumption of 15 W, are 445 mm overall length and 25 mm diameter.

All lamps type TFQ3 - TFB7 operates from the same power supply which is built into the control unit for the thin-film photoreactor. The control unit operates the pump and lamp.

Double walled irradiation tubes (of quartz or borosilicate glass) are used in this reactor. Tubes are equipped with threaded glass entrance and exit ports to which are attached the liquid jet tube and exit tubing. In the reverse flow arrangement, the jet tube is removed.



Depending on the size of the jet and setting of the bypass control, flow rates through the jet may be varied from 0.1 to 1 ml/s. Film thickness depend on flow rate and the solvent used but are of the order of 0.1 to 0.3 mm.

A self-priming liquid pump, which is capable of handling mixtures of liquid and air, is used in this reactor. Being a diaphragm pump, the pumping solution is not contaminated by lubricants in the pump and is only in contact with stainless steel or PTFE tubing.

The standard flask supplied with this reactor is a 250ml capacity round- bottomed flask (see figure). The flask is equipped with one central port (29/32) and two side ports (14/23) Sockets provided with entrance tubes (and sinters) are used for connection to the pump and irradiation tube and an external gas cylinder (for studies under a reactive or inert atmosphere). Loss of solvent is prevented by use of a double surface condenser (model RC1), which fits into one of the side ports. The minimum usable volume is about 50 ml of solution. Flasks of larger capacity are also available.

The thin-film reactor is ideally suited for continuous monitoring of a photochemical reaction by changes produced (in reactant depletion or product formation) which may be monitored by UV/visible absorption spectroscopy or florescence spectroscopy.The reactor is simply positioned close to a spectrometer and the flow cell connected to the reactor with PTFE tubing. Two cuvettes are available, one a 10 mm pathlength far-UV quartz rectangular cell with three sides polished (for absorption or fluorescence) model 116 and the other a 2 mm pathlength far-UV quartz rectangular cell with two sides polished (for absorption), model 117.

The component parts of the reactor are housed in a robust metal housing (see figure) provided with a heavy metal base. A central metal support plate holds the irradiation tube on one side and the reservoir and pump assembly on the other. Connections are provided for (a) water-cooling for the reflux condenser,(b) gas-inlet and (c) flow-through connections for spectrometric monitoring (fluorescence on UV/visible absorption). Detachable covers are provided on both sides of the support plate. Electrical connections are provided between the reactor assembly and control unit. Power supply requirements 220 -250VAC, 100W.