Green Chemical Technology
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Distillation is undoubtedly the most common separation process used in the chemical industries. Although distillation is considered as a mature process, it should be noted that it is associated with high energy consumption. Distillation alone is reported to consume 40% of the energy used in the chemical industries worldwide. Distillation accounts for about 95% of the liquid and gas separation processes in the chemical industries. The energy consumption of distillation worldwide is estimated at 3% of the world energy consumption. Application of complex distillation column arrangements can substantially save energy. The DWC process is one of the most attractive methods for separating three or more component mixtures. Because this method can leads to significant savings in both energy consumption and investment cost. The activities in this study are divided into two parts of simulation and experimental. The feedstock contains three components of methanol, 2-propanol and n-butanol. In the simulation section, at first the simulation of two conventional systems consisting of two and three conventional distillation columns is performed in shortcut and rigorous methods, and the simulation of different parameters is performed by sensitivity analysis to reduce the heat duties of the boiler and condenser. The parameters studied can be divided into two categories: structural and process parameters. Structural parameters include the number of stages of the columns, feed stage number, and side product stage. Process parameters include the reflux ratio, the vapor split ratio, and the liquid split ratio. Distillation columns sizing have also been performed for optimal conditions. At optimal conditions for the first case including two distillation columns, first column speci ications are number of stages: 31, feed stage: 17, re lux ratio: 1.95 and second column speci ications are steps number: 13, feed stage: 7, re lux ratio: 0.67. For the second case consist of three distillation columns, the first column specifications are number of stages: 17, feed stage: 9, re lux ratio: 0.24, the second column speci ications are number of stages: 34, feed stage: 20, re lux ratio: 1.76, the third column specifications are number of stages: 17, feed stage: 10, re lux ratio: 2.13. To simulate the DWC process, a four-column model consisting of two absorbers, a rectifier and a stripper and two vapor and liquid splitters were used. In optimal conditions Absorber1 speci ications are number of stages: 16, feed stage number: 8, Absorber2 speci ications are number of stages: 16, side product stage number: 11, Recti ier speci ications are number of stages: 20, re lux ratio: 2, specifications of Stripper is number of stages: 6, liquid split ratio: 0.65 and vapor split ratio: 0.35. The results show that the DWC process in comparison with the conventional system consisting of two distillation columns have 19.95% energy savings for reboiler duty and 20.64% energy saving for condenser duty. Compared to the three distillation columns system DWC process has 37% energy saving for reboiler duty and 37.97% energy saving for condenser duty. In the experimental section, a pilot-plant DWC system has been designed, constructed, and installed at the department of chemical technologies. The system has four columns including pre-fractionator, side product column and rectifying and stripping columns, feed tank (including heating system), reboiler, glass packing, condenser, temperature sensors, peristaltic pumps, platform, piping and ittings. The diameters of the columns are 5 and 6 cm and the height with reboiler and the attachments is approximately 5 m. The column is made up of different sections with a length of 50 cm which can be changed if necessary. The glass packing used is Pyrex with 4-7 mm dimensions. The column is also made of stainless steel 316. The system was started up using a three-component feed of methanol, 2-propanol and n-butanol and the products were purified.‎
Iranian Research Organization for Science and Technology
Department of Chemical Technologies
Last updated on Aug - 16 2022
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