Deip in tdi products is diethyl isophthalate. According to the investigation related public information, in the production process of toluene diisocyanate (TDI) heavy solvent, diethyl isophthalate (DEIP), as a high-boiling inert solvent in the synthesis of TDI, can not only disperse in the reaction, but also protect TDI in the separation process, and it is evenly mixed with TDI, with few reaction by-products and high product purity.