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Process for recovering high boiling solvents from a photolithographic waste stream comprising less than 10 percent by weight monomeric units

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A method of recovering solvents from an impure effluent stream of an industrial process. The effluent waste stream contains less than about 10 percent by weight of monomeric units that are reacted to form larger oligomers and polymers. The waste stream contains dissolved polymers polymeric particles and the hydrolysis oxidation and/or other decomposition products of one of the solvents. In one embodiment the first step involves filtering particulate matter from the waste stream. In another embodiment the filtering step is omitted. The filtered or unfiltered waste stream is fed to a first separation stage for separation into (i) a gaseous stream of water soluble gases and volatile contaminants and (ii) a suspension comprising the solvent water semi-volatile and non-volatile contaminants and photoresist products. Following the first separation stage the dewatered solvent-containing suspension is either distilled or evaporated to separate the solvent from photoresist products and other non-volatile contaminants. Then the solvent-containing suspension is separated into (i) a solvent vapor fraction which contains solvent and semi-volatile contaminants such as plasticizers and monomers and (ii) a sludge fraction which contains non-volatile contaminants such as polymer and benzoic acid. Thereafter the solvent vapor fraction is fed into a vapor stripper to strip the semi-volatile contaminants from the solvent vapor fraction using an organic solvent as a mass transfer medium. This removes the semi-volatiles from the solvent-containing vapor fraction and produces a solvent vapor fraction that is essentially pure.

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