Cosolvent Posted on 6th November 201522nd July 2021 by ThePD (The Project Definition) Cosolvent is a chemical added to a primary solvent used to improve the effectiveness of a primary solvent in a chemical process. Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window)Click to share on LinkedIn (Opens in new window) Related Posted in Substance and tagged chemistry. ThePD (The Project Definition) ThePD has been developing the Preferred Project Definitions based on the actual project execution and operation experiences and knowledge with the Project Language, and sharing with you daily basis.