When used at an elevated pH, aqueous cleaners are alkaline. In degreasing applications, some of these cleaners form oil emulsions and others clean without emulsifying oil. Emulsifying cleaners remove more types of contaminant but treatment of the waste water can be more difficult. Aqueous cleaning systems lead themselves to being easily closed loope through membrane technology. Semi-aqueous cleaners are emulsions of hydrocarbon solvents in water.
Terpenes are citrus based hydrocarbon solvents.
A semi-aqueous cleaning process may need to be supplemented by mechanical agitation, ultrasonics or elevated temperature to effectively compare with solvent cleaning. Semi-aqueous cleaning also requires rinsing and drying in most cases. Petroleum solvents are effective in removing resin oils and greases. The electronics industry often uses alcohol for defluxing operations. Petroleum solvents are compatible with most plastics, metals, and rubbers.