Study On Seperation Of NCO From Recycle Solvent In TDI Production

Toluene diisocyanate (TDI) production process of heavy solvents, diethyl phthalate (DEIP) as the TDI since the synthesis of a high boiling point solvent inert solvent, both played in the reaction dispersion, but also protect the separation of the role of the process, and mixed, reaction is complete, less by-products, products of high purity. However, in the recycling process, because the side effects, such separation is not complete because there are not so DEIP removal of TDI, the compounds containing NCO groups, etc., in the production and the TDA reaction of NCO groups to reduce the TDI yield; prone to clogging. By joining the reaction with NCO groups of substances (such as PEG, ethanol), and with the reaction of NCO groups of substances of high boiling point substances, and then off to get rid of distillation. Experiment we can get:PEG reaction speed, reaction products with high boiling point, and DEIP separation easy, and good fluidity, easy to follow-up treatment. TDA and the NCO groups of floc formation is difficult to separate. Therefore, treatment agent selected PEG. After the first reaction by distillation approach.Response to intermittent,one-time investment in the material and the PEG reactor. Reaction product after completion of the reaction were separated into distillation unit, at the top are pure DEIP, tower reactor have been out of the NCO reaction components, as well as the reorganization of the original points. EG the greater the ratio of inputs,the reaction the better.Ratio of 1:0.5 in the experimental range the best. Raw materials for low NCO (NCO%=2500～3900ppm), light fraction can be reduced to 0.03% or less area, raw materials for high-NCO (NCO%= 13000～14000ppm), light components in the area can be reduced to 0.2%. Reaction temperature at 190℃to 205℃range of the best, raw materials for low NCO(NCO%= 2500-3900ppm),an area of light components can be reduced to 0.02%,raw materials for high-NCO (NCO%= 13000～14000ppm), light components in the area can be reduced to 0.25%. Higher than 205℃when the temperature increases the reaction rate and significantly reduced the extent of the reaction.Less than 190℃, with decreasing temperature, the reaction rate and degree of reaction is less and less. Two groups were compared to the results of low NCO material, the ratio of 1:0.5 is sufficient to light components in the raw materials down to very low levels; and high NCO of raw material, after reaction with a ratio of 1:0.5There exists a certain amount of light components. Material after the reaction distillation,at the top get DEIP meet the requirements. For the NCO%=14000ppm reaction and distillation of raw materials processed through the NCO%dropped to 300ppm.Moisture content of materials before and after the experiment to detect,verify the PEG reaction will not increase the water system.CBC fastest response,TDI slowest reaction,CLTDI between them,should minimize the content of recycle solvent in the TDI.High boiling stable to 56.7% of the concentration of liquidity is still good,aggregation does not occur,the phenomenon of blocking devices.