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One of the things you have to consider when scaling up a chemical process is the composition of the wetted or exposedsurfaces in the reaction vessel, associated feed piping, gaskets,and overhead vapor spaces. Common materials of construction subject to wetting are steel (various types), glass, Hastelloy(s), tantalum, titanium, Teflon, Viton, and various polymers found in hoses.

Metal batch reactors are subject to erosion over time. Vessel walls can be tested for thickness periodically. This is done with metal surfaced vessels. Glass coated reactorsare very useful for their broad applicability to many kinds of reactions, but have drawbacks of their own. Glassed vessels are sensitive to very high and very low temperatures as well as thermal gradients across the vessel wall. It is possible to crack the glass coating and have it flake away, exposing the underlying metal to corrosion.

We are all trained to do chemistry in glass reactors, but it should be pointed out that much chemistry can be performed in steel vessels. While you want to give some thought to the use of hydrogen, for the most part metal pots are well suited for reaction under reducing conditions. That is, metal hydrides, Na,carbanionic species BuLi and RMgX, alkoxides, etc., are well tolerated in metal pots.

Oxidizing or acidic halide producing reaction systems are problematic for metal pots, however. Acid corrosive reaction mixtures can attack the wetted metal parts of the reactor system. It is especially problematic when you’re talking about tube and shell condensers. The tubes are often very thin for good heat transfer, leading to the possibility of the introduction of chiller fluids into the reactor if corrosion chews through the tubes. If the chiller fluids are protic and the pot is full of MeLi, then the batch may be lost or an unplanned reactive hazard eventmay take place.

Condenser surfaces may be subject to more corrosion that one may realize. This is the place where hot concentrated corrosive gases will condense, after all. To extend the life of the condenser, special materials of construction may be used. Tantalum and Teflon come to mind, but there are many other possibilities. With exotic materials of construction come exotic prices.

There is more to consider than corrosion. Plastic transfer lines may generate static electric hazards via the isolation of charge on nonconductive surfaces. Tranferring hydrocarbon solvents from a drum or cylinder to a reactor through nonconductive plumbing can generate significant hazardous energy and certainly enough to be incendive. Grounded or bonded metal piping can prevent part ofthis problem. However, discharging a flammable liquid into an air filled space may lead to an incendive discharge as well. It is important that all atmospheres over flammable liquids be inerted. While you may not be able to stop static discharges, you can certainly keep the fire triangle for being formed.

Operators are often frightened by the sight of a glassed reactor with stirring toluene in it generating sparks by discharge through the glass coating. While this may be hard on the glassing by forming pinholes, unless there is an explosive material in solution, the lack of a fire triangle means that the sparks cannot lead to ignition of the toluene.

Remember not to take your material to high viscosity or dryness in a large reactor. You might end up rolling your solid material into a giant bowling ball and bending your agitator shaft. Maybe even slamming it into the reactor wall, Very expensive mistake.


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