Wednesday, July 17, 2013

Process Wednesday: the 5 ways to get a liquid into a reactor

Our mentor-by-literature, Neal Anderson, tells us about how to get liquid (reagents, solvents, etc.) into a reactor in Practical Process Research and Development (the first edition):
There are five means to transfer a liquid: by gravity, siphoning, pumping, pressuring, or suctioning. The rate of transfer by gravity and siphoning is limited by the height of the liquid above the receiving vessel. Siphoning may be used conveniently on scale to remove a supernatant if dense solids separate from a suspension. Pumping is a faster means to transfer a liquid, and one of the fastest methods is to pressurize a liquid into the vessel using an inert gas. Transfer may also be carried out by applying suction ("partial vacuum") on the receiving vessel and by allowing the liquid to be drawn into the vessel. Transferring reactive materials by suction may be inherently safer than transferring by pressure; care must be taken to ensure that volatile solvents in the receiver are not lost when suction is applied. 
I've definitely used gravity in the lab and the kilo lab -- who hasn't? Addition funnels are basically gravity... but it's harder when you have larger amounts of liquid. We have done it in the plant (using gravity), but it is not something that is commonly performed. It seems that pumping and pressuring are the most common means of getting liquids from reactor to reactor and from reactor to equipment.

Suction seems to be a very common means of getting solvent for reactions into the reactor -- the reactor is pumped down to 20 torr and then that vacuum is used to pull the requisite amount of solvent into the reactor. I'm surprised that Anderson didn't mention the added safety factor, which is that (if you do it right, and don't pull a bunch of air into the reactor when your drum gets empty) there won't be any oxygen in your reactor when you're done pulling solvent in (and you still have a little vacuum left.)

1 comment:

  1. Yeah this use of vacuum transfer mode is one of those many basic realities of the plant that most new process chemists have to learn since is so rarely practiced at bench scales (almost always thinking push and never think pull). In fact it is generally easier done at scale since equipment design and controls are standard;y built in whereas in the lab do not typically have appropriate set ups and harder to acquire or assure what is required to execute.


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