System/Product

Asia

Model/ModuleAll

Subject TypeHardware

Subject Version

1.0Author

Rory Parsons

Date

30/03/2016

1 Identifying the Source of Blockage
1.1 Visual Inspection
The Asia flow chemistry system is designed to allow the inspection of the majority of thereaction pathway visually. The first point of identifying where any potential blockage has
occurred is to visually inspect the flow pathway in sequence.
1)
2)
3)
4)
5)

Are the bottled reagents still in solution?
Are there any obvious particles observed in the syringes?
Are there any blockages in the tubing from the pump to the reactor?
Are there any blockages in the reactor itself?
Are there any blockages in the tubing from the reactor to the back pressure
regulator?
6) Are there any blockages in the tubing from the bpr to the collector (productcollector/automated collector)?

1.2 Pressure release
If you cannot see where the blockage occurs through a visual inspection then a systematic
inspection of the reaction pathway is required. This is done by releasing the connections insequence allowing you to see where the build-up of system pressure is released.
1) Start the pumps at a low flow rate to build up pressure in the system, if a blockage ispresent the system pressure will rise, switch off the pumps before the systemreaches the maximum pressure rating of the system to minimise damage.
2) Use the pressure reading shown either through Asia manager or the pump screen, if
the pressure drops when releasing the connection drops then the blockage is locatedin that position. Start from the last connection in your reaction pathway in thefollowing sequence;a. Release the connection to the Collector.
b. Release the connection to the Asia Pressure Controller
c. Release the connection to the input of the reactor (chip or tube). If more than
one reactor is connected in series release the connection to the last reactor
first to see which reactor contains the blockage.
d. Release the connection to the Asia Reagent Injector (if used).
Once the position of the blockage is identified then you can begin to resolve this. If theblockage is obvious then rectifying the issue should be straightforward.
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1.3 Common Sources of Blockages
If your reagent solutions are completely homogeneous at room temperature then it isprobably unlikely that they will be the problem and precipitate in the reagent bottles.
It is generally observed that most blockages occur when the reagents/reactants are mixed
i.e. when a reaction occurs. This can manifest itself in the formation of an insoluble product,by-product or salt formation.
This may occur either at the point of mixing, as the reaction occurs, as the reaction exits areactor (when it sees a change on temperature) or at a point of restriction.
With this in mind common points of blockages occur at:
1) The mixing section of a chip or tube reactor
2) The point of exit of chip or tube reactor
3) The BPR chip and diaphragm
Care should also be taken when using the Asia Reagent Injector. To avoid the reagent
coming out of solution in the injection loop a suitable compatible system solvent needs used
to be used. As aliquots are introduced from the injection loop the trailing end of the reagent
plug are exposed to the system solvent, if this is likely to cause the reagent to come out ofsolution a blockage is likely to form in the loop itself.

2 Unblocking the System
2.1 Choosing a Recovery Solvent
It is assumed that the chemistry being performed on the system is known and someunderstanding of possible products, by-products and salts is known. With this in mind asolvent can be selected that will have a high chance of dissolving any blockage that may beformed. This is known as the ‘recovery solvent’. It may be necessary to use more than one
recovery solvent to fully remove the blockage.
As a general guide the following tips can be followed to help in selecting the correct recovery
solvent.
1) Water - If the blockage is suspected to be an inorganic acid or base or salt2) Polar Organic Solvents – If the blockage is suspected to be organica. DCM/Methanolb. Acetonec. Acetonitriled. DMSO3) Acids – Useful for metal deposits from catalytic systems
a. 2M HCl/MeOH
Note however if using stainless steel reactors then strong acids are incompatible.

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2.2 Unblocking Tubing
If the blockage has been identified to be in a length of tubing connecting any two modules orreactors it should be straightforward in removing any blockage.
The simplest was to do this is to connect one end of the tubing to a luer lock syringe fitting
and push through the recovery solvent to remove the blockage. Care should be taken if notusing a luer lock syringe as the pressure generated in trying to push the solvent through may
cause the syringe and connector to fly off.
If the blockage is not easily removed replacing the length of tubing is the quickest solution.

2.3 Standard Chip Cleaning
The simplest way to clean chips after use is to leave the chip connected to the system anduse the pumps to pass a recovery solvent through them.
However, it will be necessary to purge the tubing prior to the chip with the recovery solvent
selected.
1) Replace the solvent or reagent solution with the recovery solvent you wish to use in
the Asia Pressurized Input Store, remove the reactor input tubing to the reactor andpump a suitable volume of solvent to waste to ensure the reactor input tubing iscompletely full with the recovery solvent.
2) Re-connect the reactor input and make sure the output is not connected to the BPR
begin pumping the recovery solvent at a low flow rate.
It is advisable to pump at low flow rates to avoid over pressurising the system. To avoid
over-pressurising the system when unblocking a reactor;
1) pump just one channel at a low flow rate2) ensure the BPR is not connected
3) set the over-pressurisation limit to that below the maximum operating pressure of thesyringe used
It may be necessary to reverse the flow through the reactor. To do this simply connect thetubing containing the recovery solvent to the output and connect a ‘spare’ length of tube tothe input.
The direction of the flow of solvent will depend on where the blockage has occurred. If theblockage is near the input then reversing the flow through the reactor may help pump thisout rather than pumping it ‘through’ the reactor.
If the blockage in a reactor is proving to be stubborn there are other techniques that may
assist in removing the issue;
1) Raising the reactor temperature to assist in solubility. Note however if you are raising
the temperature above the recovery solvent boiling point make sure the BPR isconnected and the Pressure Controller set to an appropriate setting.
2) Place the reactor in an ultrasound bath whilst pumping. This will aid in breaking up asolid blockage, helping its removal.
3) As a last resort it may be possible for chips only to pyrolize the contents of the chipusing the heater and then pumping NaOH (aq) to dissolve the contents.

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