Wednesday, March 21, 2012

Process Wednesday: glass-lined steel reactors

Credit: McIntyre, J., Osmonics
In an article addressing ways to clean the jacket of a glass-lined steel reactor, James McIntyre talks about the reasons why pharmaceutical process chemistry tends to use glass:
Glass-lined reactors are used in virtually all of the world's pharmaceutical manufacturing facilities.  There are several key reasons for their selection by design engineers. 
In a pharmaceutical process, cleanability is critical. Between batches, each reactor and its associated process equipment must be thoroughly cleaned in order to assure product quality and minimize heat transfer resistance caused by product buildup. Fortunately, glass has a high degree of surface smoothness which makes it easy to clean using noncorrosive, low pressure cleaning systems. 
Glass is also chemically resistant and as a result, can serve for many years in environments that would quickly render most metal vessels unserviceable. Aggressive reaction environments also tend to dissolve metals from unlined mild steel or alloy reactors. These metals can compromise product quality in an industry where purity is essential.  By comparison, the glass-lining protects the base metal so effectively that the relatively benign heat transfer fluids used in the jacket space will generally attack the jacket and reactor exterior long before the reaction environment compromises the glass-lined interior of the vessel.
As the article addresses, the glass/steel jacket around the reactor that does all of your heating and cooling needs to be maintained and cleaned. If you don't, you can get scale buildup from plant water (among other problems) which can limit the flow of the heating/cooling fluid.

Now that's not a problem you tend to have with a 3-necked round bottom flask in the lab! (A weird question: I've seen heating mantles for 72 liter flasks -- what's the largest heating mantle out there?)

14 comments:

  1. the earth's core certainly heats a lot of mantle.

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  2. I used to work with UHV; hydrogen diffusion through stainless steel is what often limits the base pressure. In fact, steels contain a surprisingly high partial pressure of atomic hydrogen.

    Does anyone make glass-coated aluminum reactors? I ask because aluminum contains less hydrogen. It also heats more uniformly because of its thermal conductivity, which is something like 10x greater. The UHV world is adopting aluminum more and more, and it surprises me that the same hasn't happened in your field.

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  3. Boiling concentrated NaOH solutions will etch your glass and make it harder to clean. At least on small scale for me in the lab. Problem on giant reactor scales?

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    1. Reactor boilouts tend to use the relevant organic solvent and lots of water. I don't know how Pfaudler reactors handle hot base, but I imagine the answer is: not well.

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  4. Re: Al/glass reactors - I would expect that the thermal expansion of Al would strip the glass coating. Steel has linear expansion coeff 10-13 (in 10^-6/deg) vs. 9-10 for soda lime glass. Al coeff is 23, aircraft aluminum (alloy 7075) coeff is 23.6. Too much difference in thermal expansion causes delamination.

    Re: cleaning, glass can stain permanently, too. Stained reactor is useless for pharma processes (it can't pass the "visually clean" test) even though there is nothing detectable leaching out of it.

    For me the biggest drawback of glass lining is its low thermal conductivity. If the scale-up depends on heat transfer then the uppper volume limit is a lot lower for GL than for alloy reactors.
    This kind of problem shows up in low temp reactions (Li chemistry at -40 C or lower) where power input from the agitator (viscous heating) can overwhelm the colling capacity of the jacket. When the agitator runs slower the heat transfer from the jacket slows down, too. Catch 22.

    There is also the sensitivity to fluoride, and mechanical fragility. Sales pitch for cheaper reactors with a couple of tantalum "plugs" in the glass is that they are as good as plug free originals. After having witnessed dissolving the steel shell around a plug in hot Br2/HBr (200 gal proces...) I stay away from them.

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    1. Thanks for adding your expertise, Anon.

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  5. You need to check for hairline cracks before use otherwise the materials scan leech through to the steel mantel.
    Happened to me once where the crack was right at the top near the stirrer joint. We only noticed it after we observed glass in the product. Somewhere I have a picture of the hole that the conc. HCl made!
    Since then I always insist on a conductivity check to make sure the glass is still intact.

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    1. Thanks for your comment, Quintus. (It's always a horrifying moment to find glass in the product! Someone is guaranteed to have a bad day/week/month/year.)

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    2. It is absolutely terrifying to find large flakes, but there is always a little bit of the reactor in the product. We just don't look for the ppm levels of tank materials, but they do enter the process. A good boilout in a 316 SS tank will pretty reliably boost Fe level in the solvent by a couple of ppm.

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  6. Can anyone explain, or provide a link on the glass lining process?
    I work in stainless manufacturing for chemical/pharmaceutical industries. We often are working on and around these vessels. Always wondered how they do it.

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  7. http://en.wikipedia.org/wiki/Vitreous_enamel

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  9. This comment has been removed by the author.

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  10. My company is looking to manufacture pressure vessels with glass lining. For incorporating Glass lining i require consultancy in terms of initial setup. If you have expertise for so, please contact me at kavan_4desai@yahoo.com.

    I don't wish to create a spam here but had needed a consultant and it appeared that people on this forum might have the knowledge

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