Study On Distillation Process Of Acetic Acid-Water System

On the basis of summarizing separation method of acetic acid-water system, we studied the azeotropic distillation process of acetic acid-water system, selecting butyl acetate, isobutyl acetate and isopropyl acetate as entrainers. The influence of packing height, ratio of water to entrainer and acetic acid initial concentration to separation effect of azeotropic distillation was studied in detail. Simulation calculations of general distillation and azeotropic distillation were carried out. The influence of reflux ratio, theoretical plate, feed position, feed temperature and feed concentration to distillation process were discussed. Preferred process operation parameter, which had guiding meaning to practical production of distillation process were obtained. Basic data for the process amplifying design of azeotropic distillation tower were provided. Invest and operation energy consumption of two distillation methods were compared. The elementary technical design of azeotropic distillation tower was carried out on the basis of result of simulation calculation. The type of major auxiliary equipments and inner parts of packed tower were selected.The research results are as follows: (1) Butyl acetate, isobutyl acetate and isopropyl acetate could be selected as entrainer, and separation effect was near. Acetic acid concentration of tower top was always very low. With the decrease of the ratio of water to entrainer or increase of acetic acid concentration of feed, acetic acid concentration of tower bottom increased. When butyl acetate and isobutyl acetate were selected as entrainer, tower bottom production contained entrainer, with the further decrease of the ratio of water to entrainer. When isopropyl acetate was selected as entrainer, isopropyl acetate didn't appear in the tower bottom production. Three entrainers rarely dissolve in the water and can be reclaimed. (2) When general distillation was simulated, the "chemical theory" was used to correct the nonideality of vapor phase and NRTL equation was used to calculate active coefficient in the liquid phase. The preferred condition of general distillation was obtained as follows: reflux ratio was 4.0~4.5 and the number of theoretical plate was 37~43; When azeotropic distillation was simulated, NRTL equation was used to calculate active coefficient in the liquid phase and Hayden-O'Connell equation was used to correct the nonideality of vapor phase with associated molecules. The preferred condition of azeotropic distillation was obtained as follows: reflux ratio was 3.0~3.5 and the number of theoretical plate was 30~35. (3) Compared with general distillation, the number of theoretical plate which azeotropic distillation needed was less under the same separation demand. The reflux ratio of azeotropic distillation could decrease. Equipment invest could be decreased 700000 yuan. Water vapor could be saved 36%. (4) Optimum feed positions of four feeds were confirmed. Optimum positions of general distillation were F1: 18, F2: 41, F3: 42 and F4: 39, when reflux ratio was 4.0;Optimum feed positions of azeotropic distillation were F1: 9, F2: 33, F3: 34 and F4: 30, when reflux ratio was 3.0. When feeds were situated in optimum positions, separation effect was best. Separation effect became worse when feed position rose or fell from optimum position. (5) With increasing of feeds temperature, acetic acid concentration of tower top increased and acetic acid concentration of tower bottom decreased. With increasing of initial concentration of acetic acid, acetic acid concentration of tower top and bottom increased. (6) Technical parameters of azeotropic distillation tower were obtained when reflux ratio was 3.0. Packing was 250Y titanium corrugated-plate packing. Diameter of tower was 4.0m, and height of packing was 25.92m. The pressure drop of packing was 2959.05Pa. Average flood point gas velocity of four parts of packed tower were 5.22m/s, 4.97 m/s, 3.63 m/s, 3.05 m/s. Average liquid holdup of four parts of packed tower were 0.025 m3/m3, 0.032 m3/m3, 0.044 m3/m3, 0.050...