Purity in the solvents is crucial for a high quality product. In an extraction process, the solvent is being used to clean the material of it’s compounds. Commercial grade solvents are not desired for extractions, because the solvents themselves may contain sulfides and di-sulfides, otherwise known as mercaptans.
Heavy metals can also be present in hydrocarbons, and olefins, which can give the solvent a bad smell. These contaminants will affect the quality and quantity of essential oils that are produced.
You can ask for a COA, or Certificate of Analysis, from your provider in order to know how pure your solvents are.