[Histonet] Off topic_recycling xylene

koellingr <@t> comcast.net koellingr <@t> comcast.net
Sun Mar 18 00:07:57 CDT 2007

     This post is an inquiry regarding recycling of xylene in histology labs but is kind of off topic so please simply delete at will.  I like to use the HistoNet for scientific inquiry and not debate.
     I fully support the concept of recycling of xylene in histology labs.  But for several years, I've read on the HistoNet many statements from users of various recycling instruments and am curious about their declarative statements.  I've read that with (name the brand) recycler, the xylene becomes "purer".  The xylene is "better".  All the impurities are completely removed.  You get purer xylene than you started with.  The xylene is absolutely pure.  All contaminants, even those that came in the bottle, are removed in recycling.  A whole set of declarations that I'm finding hard to accept at face value.
     When we went through a large study,  trying to figure out in a former lab if recycled xylene was good for us, we collected and had analyzed sample after sample from bottles, before recycling after recycling and after multiple recyclings.  Had them analyzed by gas chromatography at a good reference lab.  Although the recycling worked, we saw little in the change of the readout from pure to recycled.  A bit of a change but not much to affect anything.  So we recycled and were happy.
     It is my understanding that tens of millions of pounds of xylenes are produced every year.  Histologic grade mixed xylenes (o-, m- and p-) come with a good percentage of ethyl benzene and a minor percentage of various other hydrocarbon contaminants.  To remove ethylbenzene and these other contaminants to obtain pure xylenes (needed for upstream processes) requires 100 million dollar chemical plants, hydrogen atmospheres, catalysts and 200 foot high fractionation columns. 
     Do the people who are saying that their lab recyclers are removing these contaminants, follow this xylene stream with critical GC testing?  If the xylenes are "better" or "purer" why are there all the warnings to not use recycled xylene for certain procedures?  It is "too" pure?  Is there such a thing?   If this is so easy to accomplish it seems that one could buy a (your brand) recycler, find the cheapest mixed histologic grade xylene you can find, don't use it for histology but simply recycle it, bottle it in 25 or 100 ml bottles as ultrapure for HPLC or gold standard mass spec analysis for 100 times the cost of the original impure xylene and retire rich.
     I agree xylene recyling is cost-efficient, morally acceptable, environmentally friendly, useful, efficient and everything else.  I'm having a hard time accepting that these common lab recyclers do so easily what it takes massive chemical plants and incredible organic chemistry know how to do.
     If anyone has read this far, and you do recycling of xylene, I'd like to hear about your thoughts on the subject.

Raymond Koelling
Phenopath Laboratories
Seattle, WA

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