Note: With regard to solvent recycling xylene and xylene substitutes are nearly interchangeable. In this blog post everything that applies to xylene will also be true of xylene substitutes.
You’ve been using xylene for years and now you are thinking about recycling it. Great idea. It’s expensive to buy and to dispose of. It doesn’t take a lot of training or special knowledge to recycle xylene. But for those who are curious about the details of xylene recycling anyway, this post is for you.
Xylene is an aromatic hydrocarbon with 8 carbon atoms. Xylene comes in 3 different isomers (arrangements of atoms). Insert picture of isomers here. It is excellent for dissolving fat and paraffin. It also evaporates from slide quickly and so is useful for coverslipping.
High boiling contaminants in xylene include fat, paraffin, protein, and biological materials.
Xylene also gets cross contaminated with alcohol in the stainer. When slides move from alcohol stations to xylene stations, some alcohol gets carried over to the xylene where it accumulates.
Xylene contains both low boiling (alcohol/water) and high boiling (fat and wax) contaminants.
To recycle xylene you should choose a solvent recycler that uses fractional distillation by temperature.
Low boiling alcohol/water will distill over the fractional distillation column first. When the vapor temperature climbs to the boiling point of xylene, all the alcohol/water contamination will have been collected in the waste container.
The pure xylene will distill over next. Once all the useable xylene has been distilled into the pure xylene container the recycler will automatically stop and cool down.
Left behind in the boiler is a little xylene along with fat, paraffin, protein and some biological materials.
The xylene will be 99.9% pure. You can use it anywhere you would use new xylene including in the tissue processor, stainer and coverslipper.
The recovery rate for xylene is about 95%. Some xylene is lost in staining and tissue processing. Other xylene is left behind in the boiler so that it is not difficult to remove the fat and paraffin residue.
Since the recovery is 95%, you will still need to buy some xylene but it is about 1/20th of what you were buy before recycling.
The small xylene waste fraction and boiler residue contain some xylene. They should be disposed of in the same way you would dispose of waste xylene.
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