A chemical plant has a mixture of ethanol and water with a known composition. The plant wants to separate the mixture using a distillation column. As a chemistry student, design a feasible distillation column that can effectively separate the mixture with the given composition. You need to specify the height, diameter, number of trays, reflux ratio, and other necessary parameters needed for designing the column. You are also required to provide an explanation for the choice of each parameter.

Question

A chemical plant has a mixture of ethanol and water with a known composition. The plant wants to separate the mixture using a distillation column. As a chemistry student, design a feasible distillation column that can effectively separate the mixture with the given composition. You need to specify the height, diameter, number of trays, reflux ratio, and other necessary parameters

Answer 1

To design a feasible distillation column for separating a known mixture of ethanol and water, we need to consider several factors. Here, we will assume that the plant wants to obtain a high purity ethanol product  around 95% purity  and a separate water product. The following parameters will be specified: 1. Column Type: We will use a trayed distillation column, specifically a sieve tray column. Sieve trays are widely used in the industry and provide a good balance between efficiency and cost. 2. Number of trays: The number of trays required depends on the desired separation and the efficiency of the trays. We will assume a tray efficiency of 70%. Using the Fenske-Underwood-Gilliland method or a simulation software, we can estimate the number of theoretical trays required for the desired separation. For this example, let's assume we need 25 theoretical trays. Considering the tray efficiency, the actual number of trays required would be 25 / 0.7 = 36 trays  rounded up . 3. Column diameter: The diameter of the column is determined by the vapor and liquid flow rates, which depend on the feed flow rate and composition. The diameter should be large enough to avoid flooding but not too large to maintain good contact between the vapor and liquid phases. Using hydraulic design methods or simulation software, we can estimate the column diameter. For this example, let's assume a column diameter of 1.5 meters. 4. Column height: The height of the column depends on the number of trays and the tray spacing. Typical tray spacing ranges from 300 to 600 mm. For this example, let's assume a tray spacing of 500 mm. Therefore, the column height would be 36 trays * 0.5 m/tray = 18 meters. 5. Reflux ratio: The reflux ratio is the ratio of the liquid returned to the column  reflux  to the product withdrawn  distillate . A higher reflux ratio increases the purity of the product but also increases the energy consumption. The optimal reflux ratio can be determined using the minimum reflux ratio  R_min  calculated from the feed composition and desired product purity. For this example, let's assume a reflux ratio of 1.5 times the minimum reflux ratio  R_min . 6. Feed tray location: The feed tray location is determined by the feed composition and the desired product purities. For this example, let's assume the feed tray is located at tray number 18  midway in the column . 7. Operating pressure: The operating pressure of the column affects the boiling points of the components and the energy consumption. For ethanol-water separation, atmospheric pressure  1 atm  is a common choice as it provides a reasonable difference in boiling points  78.4°C for ethanol and 100°C for water . In summary, the designed distillation column has the following parameters: - Column type: Sieve tray column - Number of trays: 36 - Column diameter: 1.5 meters - Column height: 18 meters - Reflux ratio: 1.5 * R_min - Feed tray location: Tray 18 - Operating pressure: 1 atm These parameters can be further optimized using simulation software and considering the specific requirements of the plant, such as energy consumption, capital cost, and product quality.