• control scheme
• distillation
• dividing wall column
• dynamic simulation
• energy savings
• Petlyuk
• process intensification

The research discussed in the following master's thesis is focused on the simulation and experimentation in the field of Dividing Wall Columns (DWC) for distillation. In recent years, there has been an increasingly growing concern about energy consumption, and separations in the chemical industry account for 10-15% of global energy consumption, representing between 45-55% of energy consumed at the industrial level.
These separations, which are essential to produce chemical compounds of all kinds, face the challenge of having a high energy demand for their operation and are subject to high inefficiencies. Therefore, being a source of high operating and capital costs in the process industry, in recent years, there has been a drastic attempt to change the operating principle. This concept has led to the emergence of a new discipline in the early 2000s, known as Process Intensification, which aims to change the approach and mindset in the modeling and development of industrial equipment in the chemical field and plant design.
A specific separation technology that has been identified as a target for improving chemical processes through process intensification is distillation. Currently, there are approximately 40,000 operating distillation columns worldwide, collectively contributing to about 3% of globally consumed energy. Despite their flexibility and widespread use, they have the disadvantage of being energy-intensive.
In chemical processes, dealing with multicomponent mixtures is quite common, and in such cases, multiple distillation columns are essential to obtain individual pure products. Conventionally, the standard methodology for this type of separation involves the use of either a direct sequence column system (where the first separated component is the most volatile) or an indirect sequence system (where the first separated component is the heaviest). In the late '70s, researcher Y. Petlyuk proposed an alternative configuration for distillation columns in multicomponent mixtures, and it was subsequently demonstrated that the use of this configuration in a 3-component mixture requires a minimum energy equal to that required in the most challenging separation between the components of the ternary mixture (i.e., the separation of volatile-intermediate or heavy-intermediate components).
This type of configuration aims to minimize the energy consumption required for the separation of a ternary mixture, also reducing the complexity of the plant as two fewer heat exchangers are needed. In 1985, the first Divided Wall Column (DWC) was designed by BASF, where the additional step was to introduce the external column and the main column into a single column, dividing the two parts with a dividing wall.
Compared to classical designs of distillation columns, the advantages obtained are:
- High purity of all three or more streams exiting the distillation column
- High thermodynamic efficiency due to reduced remixing effects
- Lower capital cost due to the integration of multiple equipment into a single unit
- Lower energy requirement compared to conventional systems
- Reduced environmental impact due to the lower number of units
In this work, the objective is to demonstrate the feasibility of Divided Wall Columns (DWC) in the industrial field, promoting their development and growth for the future of distillation technologies in the process industry.
Specifically, the experimental activities were conducted at the University of Texas at Austin. The research group engaged in fluid separation at the same university made an experimental study to demonstrate the feasibility of separating a ternary mixture with a homogeneous azeotrope using a Dividing Wall Column.
The chemical system studied is an acetone-water-isopropanol mixture. It has a homogenous azeotrope water-isopropanol and the residue curve map has a boundary which delimitates the two different distillation zones. This is the first time that a mixture with a homogenous azeotrope has been separated with a Dividing Wall Column, as a third component. The feeds that have been tested in both the lab-scale and pilot plant setup are on the two different sides of the boundary, demonstrating the feasibility of the DWC configuration with all types of feeds.
The first step was to perform experiments on a laboratory-scale Oldershaw column to demonstrate its feasibility and a possible scale-up. Subsequently, the feasibility of DWC was demonstrated at the pilot scale, necessary for potential industrial applications.
To support the experimental campaign, simulations were conducted using Aspen Plus and Aspen Dynamics software, essential for setting process design parameters and comparing energy and economic consumption with other possible configurations.
The work goals were:
- Perform an experimental campaign on a laboratory-scale Dividing Wall Column (Oldershaw) to demonstrate its feasibility and a possible scale-up
- Perform an experimental campaign on a pilot-scale Dividing Wall Column to demonstrate its feasibility and a possible scale-up
- Conduct both experimental campaigns with two different feeds in the two different sides of the distillation boundary to demonstrate the potentiality of the dividing wall column with different feed composition
- Compare the experimental results obtained with the simulation results, to demonstrate the potentiality of modeling and simulation of Dividing Wall Columns with Aspen Plus
- Perform dynamic disturbances on the Dividing Wall Column pilot-scale with a dynamic model obtained with Aspen Dynamics, to demonstrate the potentiality of the control scheme used
- Compare the simulation results of the pilot Dividing Wall Column with the two-column configuration and analyze the economics of the three different configurations

Both experimental setups, the laboratory-scale Oldershaw column and the pilot-scale DWC column, are located at the J.J. Pickle Research Campus, managed by the University of Texas at Austin.
The experimental campaign, supported by simulation tools, has achieved all the set objectives. The simulation tools have proven to be extremely effective in selecting the operational parameters of the DWC (Dividing Wall Column) and in testing the control system used in the pilot-scale column. Furthermore, they have demonstrated the potential of DWC compared to the traditional double-column scheme, with an energy saving of approximately 30% and capital cost savings of about 15%. The experimental setup and the control scheme used in the pilot-scale experimental campaign have proven suitable for separating the chemical mixture on both sides of the residue curve map, achieving valid steady states and product purities within specifications, demonstrating the potential for scale-up to industrial scale. However, the laboratory-scale experimental setup has shown some difficulty in maintaining all imposed purity specifications. As this was the first time a laboratory-scale DWC with separate prefractioning and mainfractioning sections, as in an industrial DWC, was constructed, the results obtained nonetheless demonstrate the capabilities of this equipment and the potential for scale-up.