Agitated photo reactors

Chem­i­cal reac­tions need acti­va­tion ener­gy. Cat­a­lysts reduce this ener­getic bar­ri­er, but the cat­a­lyst as an addi­tion­al com­po­nent is expen­sive, often tox­ic and pyrophor­ic. Light is an alter­na­tive source of the acti­va­tion ener­gy. Pho­to­chem­i­cal reac­tions can be ini­ti­at­ed by irra­di­a­tion with wave lengths of 200 to 700 nanome­ters. This allows low­er reac­tion tem­per­a­tures with final­ly less decom­po­si­tion or by-prod­ucts. Exam­ples of indus­tri­al pho­to reac­tions are chlo­ri­na­tions, sul­fona­tions, sul­fox­i­da­tions or nitro­sy­la­tions. The con­cept of the new agi­tat­ed reac­tor is ide­al for mul­ti­phase reac­tions with liq­uid, gas­es and solids. It com­bines high pro­duc­tiv­i­ty and flex­i­bil­i­ty with a reli­able oper­a­tion of the sub­merged light sources. Reac­tor sizes up to 50 m³ or beyond can be real­ized with the proven design.
The light sources are mer­cury or LED lamps sub­merged into the reac­tion mass inside a quartz glass tube. The glass tubes pass through noz­zles in the tank head, where they con­nect to the pow­er sup­ply and the cool­ing medi­um. They need a her­met­ic seal­ing and mon­i­tor­ing to ensure that the unex­pect­ed case of a glass break­age is imme­di­ate­ly detect­ed. Their sup­port must avoid local stress, allow for ther­mal expan­sion and pre­vent from vibra­tion ini­ti­at­ed by the intense agi­ta­tion. As the pow­er of the UV-lamps ranges from 5 to 60 kW each, the lamps need to be cooled inside the quartz tubes, oth­er­wise high sur­face tem­per­a­tures could dam­age the prod­ucts. Indus­tri­al reac­tors can be equipped with 4 to 20 of such quartz tubes.
The pen­e­tra­tion depth of the light into the reac­tion mass is short. Thus, the agi­ta­tor has to pro­vide high pump­ing rates and there­by a per­ma­nent renew­al of the reac­tants in the irra­di­a­tion zone. If one of the reac­tants is a gas as Cl₂, O₂ or SO₂, it must be effi­cient­ly dis­persed to achieve a max­i­mum mass trans­fer for high con­ver­sion rates. The homo­ge­neous sus­pen­sion of solids as poly­mers, and the removal of the reac­tion heat have to be con­sid­ered as well in the design of the agi­ta­tor and tank.
The seal­ing of the agi­ta­tor shaft towards the atmos­phere is a key ele­ment for a reli­able oper­a­tion. Dou­ble or triple act­ing mechan­i­cal seals or her­met­ic mag­net­ic dri­ves are applied. Mate­ri­als of con­struc­tion of agi­tat­ed pho­to reac­tors are steel with the option of glass lin­ing, alloys or titanium.