| Thin Film Transistor Liquid Crystal Display(TFT-LCD)is a very ideal digital information terminal,which is widely used in production and living.A large amount of waste water is generated in the production process,which cannot be directly discharged.The traditional harmless treatment of waste water not only causes the waste of resources,but also cannot meet the needs of production and living.Therefore,it is of great significance to carry out research on the recovery and utilization of TFT-LCD waste liquid.The recyclable waste liquid generated in the production process of TFT-LCD includes photoresist stripping waste liquid and etching waste liquid.Among of them,the etching waste liquid mainly includes ITO etching waste liquid and Al etching waste liquid.In this paper,the ITO etching waste liquid and photoresist stripping waste liquid were studied.The extraction and distillation processes were adopted to recycle the two waste liquids respectively,and the appropriate process conditions and feasibility of industrial application were discussed.The extraction process was adopted to recycle the metal indium from the ITO etching waste liquid.In this paper,suitable extractants were investigated for the ITO etching waste liquid of different acid systems,meanwhile other influence factors were also discussed such as the influence of time,extractant concentration,ratio of water phase to organic phase,and acidity on the extraction rate.The research results showed that both of the sulfuric and nitric ITO etching wastes liquid were suitable for extraction by the extraction agent P204,while the extraction condition was 6 minutes,extraction agent concentration was 20%,phase ratio was 4,acidity 1.3mol/L,and the extraction rate of indium was94.2% and 98.2%,respectively.The suitable extraction agent for the hydrochloric acid ITO etching waste liquid was TBP.The optimal extraction conditions were 6 min,80%extraction agent concentration,the ratio of water phase to organic phase is 1 and the acid concentration is 3 mol/L.After two extraction process,the extraction rate of indium was83.4%.The P204 indium-containing organic phase was back-extracted with 3mol/L hydrochloric acid,and the back-extraction efficiency could reach 88%.After extraction and back-extraction,the final recovery rates of indium in the sulfuric and nitric ITO etching waste solutions were 82.9% and 86.4%,respectively.Meanwhile,the separation of metal indium and tin in the reextraction process was achieved.The indium-carrying organic phase of TBP was back-extracted with 0.3 mol/L hydrochloric acid,and the back-extraction efficiency could reach 82.9%,the recovery rate of indium in the hydrochloric acid ITO etching waste liquid after extraction and back-extraction was 74.8%.At the same time,the separation of metal indium and tin was also reached in the back-extraction process.Except for a small amount of polymer resin,most of the photoresist stripping waste liquid is organic solvent which needs to be recycled and reused.In this paper,the vacuum distillation process was adopted to recover the mixture of NMF and MDG,which can be directly used for the preparation and reused of the stripping liquid.The effects of different pressure and reflux ratio on the mass fraction and recovery rate of NMF and MDG mixtures were explored.The experimental results showed that the appropriate recovery conditions was 10 k Pa,reflux ratio was 1,the purity of the mixture of NMF and MDG was98.15%,and the recovery rate was 91.23%.Aspen plus was used to simulate the process of stripping waste liquid vacuum distillation recovery process.The optimization simulation result was that the purity and yield of the mixture of NMF and MDG can reach99.60% and 94.20% respectively when the pressure was 10 k Pa and reflux ratio was 0.5.The simulation results were in accordance with the experimental results.The recovery conditions were optimized,and the feasibility of the vacuum distillation process was verified.Based on the result of the comprehensive experiment and simulation optimization result,a set of recycling processes by vacuum distillation with the annual processing of11,000 tons of photoresist stripping waste liquid were designed.And the process route,flow design,the material balance calculation,heat balance calculation,the main equipment design and selection were completed.The heat pump distillation technology can save 63% energy needed by the process.The Aspen plus software and NRTL physical property method was adopted to optimize the process.Among them,the dehydration tower had 10 trays,and the feedstock was entered in the fourth plate,the reflux ratio was 1.5,the recovery rate was 0.338,and the top pressure was 0.1 bar.The heat pump distillation tower had 12 trays,the feedstock was entered in the third plate,the pressure was 0.1 bar,the reflux ratio was 0.5,and the recovery rate was 0.942.The compressor motor consumed38.8k W of energy,and the material flow chart(PFD),pipeline and instrument flow chart(PID)and workshop layout were all drawn.The environmental and safety performance of the process had also been investigated.The process met the standards of energy saving and emission reduction,which can achieve good economic benefits and meet the requirements of green environmental development. |
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