Recycling Solvents to Save Money (2024)

Solvents are used extensively in labs and chemical manufacturing as starting materials for a chemical process; the diluent for a product, starting material, or reaction; or in the analysis of a starting material or product for quality purposes. Often times after use, that solvent is then sent into a waste stream to be dealt with according to local regulations. The EPA estimates that nearly 35 million tons of hazardous waste, including solvents, is generated yearly and that number is projected to increase as more mandated testing is being required each year. For many organizations that is money that is being thrown away, and even worse that company has to pay to have the solvents disposed of properly.

One solution for organizations is to distill the solvents in order to reduce the amount of hazardous waste generated, and collect the solvent for use again within their process. But how would anyone know if the distilled solvent would be useable in the process again without contaminating the entire batch? This is where chromatography comes into play for organic contaminates.

Distillation essentially involves heating a solvent to different temperatures allowing it or other components in the solvent to evaporate, then collecting the solvent or other components by condensation. One very commonly used solvent is acetone, which has a boiling point of acetone is 56C, which means it is typically the component that is evaporated and then re-condensed, leaving higher boiling impurities behind. There are some commonly available distillation systems for both laboratory and manufacturing scale that can easily and affordably be implemented for acetone purification, and there is usually a fairly quick payback on implementing these solutions. When implementing solvent purification solutions, it is a good idea to have some sort of analytical tool to confirm whether or not the solvent is “pure”. A solvent will never truly be pure, or free of any level of other compounds, but you can reduce the contaminants in any solvent below a defined level, allowing you to use this solvent where high purity solvent is required. The Lucidity GC-FID is perfect for this application as we’ll show here.

For this study, we spiked high purity acetone with a BTEX standard containing 2,000ppm of each of 6 compounds (benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p-xylene). We only see 5 peaks in this standard, because the m-xylene and p-xylene co-elute in the same peak, which is expected and typical for GC-FID analysis. We then diluted this standard using acetone to create different levels of the “contaminants” in our acetone to mimic the resulting concentrations of contaminates after different numbers of distillations. We analyzed these different concentrations in the Lucidity GC-FID to demonstrate the viability of testing acetone (or just about any solvent) via this method to determine the level of contaminants in the solvent.

This is the GC-FID method we used to analyze the different acetone solutions.

The first thing we ran was a blank acetone. The acetone was poured from a 4 L bottle to a 50 mL beaker, from there it was vialed into a GC vial. As you can see there is a mystery peak at around 4:45.

Running this same sample in a GC-MS, we are able to determine the identity of this mystery contaminant. It appears to be 4-hydroxy-4-methyl-2-pentanone.

Up next was the BTEX standard. The chromatogram shows 5 fully resolved peaks at 2,000ppm concentration in acetone.

We then diluted the standard to 100ppm of each compound in acetone, which is representative of the levels one might find these or other compounds in acetone after acetone has been used in the laboratory. When we run this new acetone mixture on our GC-FID method, we are able to see 6 peaks, one for the compound already present in the acetone and the other 5 from the compounds added from the BTEX mixture. Even at 100ppm of concentration we are able to easily identify and quantify large peaks.

We then diluted the acetone mixture to 10ppm concentration of the BTEX compounds, and we’re still able to clearly see the 5 BTEX peaks and the additional compound that was initially present in the acetone, which is now of comparable size to the 10ppm BTEX peaks.

Lastly, we created a 2ppm mixture, with each of the BTEX compounds present in approximately 2ppm levels. We are still able to see peaks, although barely, for the BTEX compounds. This would seem to indicate that we can monitor levels of compounds like these down to around 2ppm using a GC-FID, which is consistent with what has been reported.

So, as we are running distillations on the acetone, we would run a sample of the distillate in the GC-FID to monitor the level of contaminants until they are below whatever level we determine to be acceptable, and once we are below these levels, our acetone (or whatever solvent we are purifying) is ready to be used again, thereby allowing us to reuse our solvents instead of having to dispose of them and purchase new solvents.