[Histonet] RE: Histonet Digest, Vol 96, Issue 33 xylene and ethanol recycling in lab

Steve McClain SteveM <@t> mcclainlab.com
Tue Nov 22 11:45:16 CST 2011

I am interested to learn more of your experience with isopropanol  as a clearing agent.
Does it take longer to clear than xylene?
For processing how many stations and how long are the times you use for clearing?
How often do you maintain or change isopropanol  - how many blocks per liter?
What about de-paraffinization or running down slides to water- what times are you using?
Are you recycling isopropanol ?
Having seen the devastating effects of a histolab fire during residency (Vermont) due to dioxane (flashpoint 18 degrees C), I am leery of isopropanol  alcohols  low flashpoint of 12 degrees C (vs 30 for xylene).  Does that concern you?

Yes xylene's properties, whether toxicity or carcinogenicity and flammability need to be considered, 
but it is still a valuable reagent, especially when one considers it can be recycled in the lab.
Techs need to be trained for the safe handling and monitoring badges worn.
The gasoline you pump at the gas station has xylene, benzene, and worse.

1. Modern recyclers (within the past 7-10 years) are computer controlled and when vented, xylene can be safely recycled (By vented I mean when connected to the same external fan-driven vents as the processors).
(If your lab is not vented, you should work on that first before tackling recycling -my opinion)
2. We have good experience with BR- CBGB is a reputable company also.  My experience is with the modern computer-controlled 5 gallon models ; the 20 year old glass-bottomed units held only 2 gallons if memory serves me.
a) we mounted our 2 retorts on plastic garbage can wheels with 2 plates of regular 3/4 inch plywood so the retorts can be easily swapped in and out of the still; separate retorts for xylene and alcohol.  I see no damage underneath after 7 years, either from heat or xylene.
3. Ethanol does take longer to recycle, and without strict attention the recycled alcohol may not be sufficiently pure- one can easily end up with 85-90% alcohol rather than 95%.  (see part 6 below)
4. The critical features for alcohol recycling are 
a) the alcohols being recycled should be reasonably clean and relatively concentrated and contain NO xylene at all; For alcohol we only recycle the 95 and 100% alcohols before the xylenes on the processors and stainers; 
xylene-contaminated alcohols do not work.  The rule of thumb I learned is that xylene can be distilled from xylene-alcohol mixtures, but not the other way around. 
b) the recycling program being run should be tailored and adjusted  to compensate for the purity of the alcohols.
c. The purity of the product needs to be monitored, e.g., we check the specific gravity, do the 50:50 mixing test, and send samples for analysis quarterly.
d) It takes longer to recycle alcohols- maybe 6-8 hours.
5.The statement about energy required for recycling ethanol is far off the mark in my experience.
To recycle 1 gallon of alcohol is about $0.40 or 1/50th of the waste expense to cart away 1 gallon ($18-20/gallon in NYS).  
6.  I have no experience yet I am told that isopropanol  alcohols  can be recycled, but may be even more finicky than reagent ethanol-methanol distillation.  
The chemistry suggests this is likely to be true.  For example, ethanol is a 4.5% azeotrope with water, meaning the maximum concentration one can distill to is 95.5%.
Isopropanol  is a 12.1% azeotrope, meaning once it is diluted/contaminated with more than 13% water, the maximum concentration recoverable is 87.9%.
Depending on how the isopropanol is used in the lab, recycled 87% isopropanol from the recycler may be less than suitable for your needs.  
I suppose if one recycled only the concentrated, less-contaminated isopropanol it might pretty well.
 See http://en.wikipedia.org/wiki/Azeotrope_(data)
Steve A. McClain, MD
631 361 4000
Hi Gudrun:
I never recycled ethanol because it takes too long, uses too much energy, and the final product is never 100% pure.
On the other hand I recycled xylene which a less time consuming operation, cheaper and renders a product that can be used directly in the tissue processor.
I used to recycle an average of 2,782 liters/year (about 11 liters/day).
The re-payment ratio was $537/month and at that rate the instrument (a B/R recycler) paid itself in 30 months.
The disadvantage is that you have to protect yourself from xylene fumes during recycling and this is one of the reasons why xylene should be totally substituted by 2-propanol in the general operation of the lab.
Ren? J.

More information about the Histonet mailing list