| dc.description.abstract | Waste thinner (WT) is generated from TFT-LCD and IC manufacturing processes when unreacted photoresistor is removed from the products using photoresistor thinner (PT). The waste thinner has been retrieved by applying distillation. However, in distillation to recover the target constituents of PTs (i.e., Propylene Glycol Monomethyl Ether and Propylene Glycol Monomethyl Ether Acetate, referred to as PGME and PGMEA), the co-existing compounds in the WT may hinder the distillation and reduced the retrieval efficiency of the target compounds of PT. Therefore, it is desirable to identify the co-existing pounds and their hindering mechanism in order for possible improvement of the distillation process.
However, the compositions of the waste thinner may varied with the compositions of the parent PE and the manufacturing processes of TFT-LCD and IC. Furthermore, many recipes of the commercial PTs, unfortunately, are not revealed and the main PT compounds may or may not be available on the market. All this makes the identification of the co-existing compounds in the WTs and their mechanism to hinder the distillation more difficult even qualitative data from GC-MS analysis are available. Therefore, this study tried to identified the hindering compounds in the WT and their possible hindering mechanism by applying the qualitative data from GC-MS and multivariate analysis (i.e., Qualitative Theory Type I). Eighteen batches of WTs were conducted by column distillation apparatus, and the compositions of the WTs were determined before and after distillation; and the retrieval efficiency of target PT compounds were determined for each batch. By applying the Qualitative Theory Type I technique, the results indicate that in retrieving PGME, three compounds, n-Butyl acetate, Cyclopentanone, and Xylene were found to contribute to the hindering of distillation, while in retrieving PGMEA, two compounds, methyl amyl ketone and 2-hydroxyl methyl isobutyrate, were found of the main hindering compounds. The boiling points of the former two compounds fall between that of PGME and PGMEA (i.e, 120 oC-145 oC ) , and the azeotropic phenomenon is supposed to be the hindering mechanism of the distillation. The third compound in PGME retrieval has a boiling point much higher than 145 oC, the hindering mechanism is not clear. In PGMEA retrieval, the latter two compounds identified also have a boiling point close to that of PGMEA, and hindering in distillation is also supposed to be caused by the azeotropic effect. All the compounds found in this study are confirmed to be the main constituents of the common commercial PTs.
The results of this study may contribute to the waste PT recycling industry for how to improve their distillation process further to raise the retrieval efficiency.
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