An example of a waste chemical recycling process is to hydrolyze the production residue of TDI (toluene diisocyanate), which is a raw material for polyurethane, with subcritical water to recover TDA (toluenediamine). A chemical recycling plant that converts TDA to TDI started operation in 1998 in Kashima City, Chiba Prefecture, for the first time in the world. The sub-critical water treatment method is an environment-friendly method that can regenerate TDI, which has been incinerated in the past, using only water without using an alkaline catalyst.
This method utilizes the fact that the ion product of sub-critical water increases significantly and the hydrolysis reaction is likely to occur, as shown in Q.0. As shown in the figure on the right, the TDA recovery rate is high at temperatures with high ion product. The plant processes 7200 tonnes annually at 10MPa, 250 ° C, 1.8wt% water addition, and a residence time of 10-20 minutes.
In addition, Namhae Chemical Co., Ltd. of South Korea started a plant to hydrolyze urea, ammeline, ammelide, and biuret in residual water for melamine synthesis into ammonia and recycle it (2001). The processing amount is 3.4 tons / day.
Another company can recycle ε-caprolactam by 80% or more by hydrolyzing the distillation residue generated from the nylon 6 manufacturing process (18MPa, 330 ° C, residence time 20 minutes, water addition amount 2wt%).

The items shown below are also considered to be capable of chemical recycling by hydrolysis.