Quality Improvement And Industrial Application For MDI-Oriented Aniline From Liquid Hydrogenation Of Nitrobenzene

As an important organic raw chemicals,aniline is widely used in the production of dye,medicine,powder,spices,rubber vulcanization accelerator,especially the MDI(4,4-diphenyl methane diisocyanate).With the rapid development of MDI market,the quality requirements for aniline have become higher than before,especially in quality index controlling of phenol,cyclohexanone and cyclohexylamine.Through operation optimization and process improvement of product refining for the nitrobenzene liquid hydrogenation process,this thesis accomplished quality improvement for generate controlling and separating the impurities,including cyclohexanone,cyclohexylamine and phenol.By computation simulation and laboratory experiment,the reaction orientation of unit,system effect of impurity gathering and distillation ability enhancement were studied to acquire a preliminary conclusion.Afterwards a unit-level experiment was carried out to verify this conclusion till it ended up with industrial application.The results are as follows:(1)The ASPEN simulation and laboratory scale experiment were carried out for the reaction mechanism of impurities production from liquid-bed hydrogenation of nitrobenzene.Besides,through unit-level experiment on reaction capacity?feed ratio,operational highest reaction temperature and catalyst activity,the highest reaction temperature was setted between 220-225?,the mole ratio of hydrogen and nitrobenzene was controlled within 14.5%-15% and production capacity was setted within 80-100%.Furthermore,the nitrobenzene in catalyst slurry of side reactor was controlled within 1000-2000 ppm.On the basis of keeping nitrobenzene's conversion percent above 99.8%,the content of cyclohexanone,phenol and cyclohexylamine in crude aniline were decreased by 20%,30% and 60%,meanwhile the catalyst consumption was reduced by 20%.(2)In the refining part,the reaction rate of cyclohexanone to Schiff base was increased and the product quality was improved by renovating the packing of dehydrating column.The conversion ratio of cyclohexanone to Schiff's base was improved from 50% to 75% in dehydrating column.The high boiling Schiff's base was eliminated in refining column to decrease the cyclohexanone in aniline from 30-40 ppm to 20 ppm.Due to the transformation of dehydrating column,the cyclohexylamine was gathered to the extent that reaction system abnormally fluctuated.As a emulsifier to affect the delamination for oil and water phases of aniline,the cyclohexylamine was decreased to within 10 ppm by adding a batched operation denaphtha column in the top.(3)In order to remove the phenol in refining column,first the whole regular packing was replaced to enhance the removing ability.Second a de-heavy oil column was added,together with increasing the extraction from the bottom of this column.By ASPEN simulation and unit-level experiment,these two methods were proved to be practicable.Through economic analysis we selected the first method and successfully decrease the phenol within 15 ppmw and save above 3millions' consumption per year.In conclusion,we decrease the impurities in aniline including phenol,cyclohexanone and cyclohexylamine by optimizing reaction parameters and improving refining process.This optimization helps to better adapt the requirements for MDI production and brings ideal profits.