Research On The Prepration Of 2, 4 (2,6)-dimethyl Nitrobenzene By M-xylene Nitrating

It was verificated the preparation technology of 2,4(2,6) - Dimethyl Nitrobenzene by m-Xylene Nitrating in lab research which was developed by a domestic chemical enginerring research institute.A pilot-plant equipment was designed according to the given technology and a series of pilot plant research was then conducted.In order to reduce the high content of dinitro complex that nitrifying from m-xylene in the pilot plant equipment,further lab research was then carried out to optimize the conditions of m-xylene nitration and a series of significant effects were then achieved in reduction of dinitro-generetion ratio.Pilot study on the nitration and distillation of m-xylene showed that the average conversion of m-xylene was 96.75%under following conditions: ratio of different phases was 2.68,nitration active factors of mixed acid(FNA) was 71%,ratio of nitric acid was 1.0,nitrification temperature ranged between 12 and 15℃,and reaction time ranged between 3 and 4 hours. Respectly,the ratio of the 2,4 - dimethyl-nitrobenzene and 2,6 -dimethyl-nitrobenzene generated was 82:18 in the nitration products;the average yield of 2,4(2,6) - dimethyl-nitrobenzene was 95.61%,but the content of dinitro complex was up to 1.5-4.0%.The ratio of different phases and FNA played a leading role in the generation of dinitro complex;and it was propitious to reduce the content of dinitro complex in the nitrifications by increasing the ratio of different phases and reducing FNA.M-xylene was separated in the batch distillation which was 6.4m high and packed by CY-700 filler.The contens of 2,4 - and 2,6 - dimethyl-nitrobenzene could be above 99%which operated on the reflux ratio of about 12;the residual tar in the distillation kettle could not be used repeatedly which was the main reason caused the the losses of 2,4 - dimethyl-nitrobenzene,and the tatol yield of 2,4(2,6)-dimethyl-nitrobenzene was 89.65%in the distillation process.Lab resarch on the optimization of nitrification of m-xylene showed that FAN was the most significant factor impacting the generation of dinitro complex.The lower FAN was,the fewer amount of dinitro complex was.The second factor was the ratio of different phases,the amount of dinitro complex would be less if it's value were higher.It also showed that higher nitrification temperature caused higher conversion of m-xylene,lower yields of 2,4(2,6)-dimethyl-nitrabenzene and larger amount of tar.In view of m-xylene was prone to be nitrified or nitrified in series,an idea was advanced that more attention could be focused on high selectivity than high one-through conversion,and a series of suitable conditions for nitrification was proposed as following:FNA was 68%,ratio of different phases was 4.5,nitrification temperature ranged between 10 and 15℃,reaction time ranged was 3 hours, respectly.Under these conditions,the conversion of m-xylene was above 75%, the tatol yield of 2,4(2,6) - dimethyl-nitrobenzene was above 97%,the ratio of 2,4- dimethyl-nitrobenzene and 2,6 - dimethyl-nitrobenzene generated was about 81.8:18.2,the amount dinitro complex generated could be controlled below 0.6%,and the integrated factorψcould be above 30.But the amout dinitro complex generated was up to 1.5-4.0%and the integrated factorψwas only 4-15 in the pilot plant condisions.So the ratio of dinitro complex generated was reduced significantly compared to the pilot plant condisions.