Using Response Surface Methodology for Modeling and Optimization of Propene/Propane Separation Column

Research Article

Austin Chem Eng. 2016; 3(4): 1041.

Using Response Surface Methodology for Modeling and Optimization of Propene/Propane Separation Column

Kazemi A*

Chemical Engineering Department, Isfahan University of Technology, Isfahan, Iran

*Corresponding author: Abolghasem Kazemi, Chemical Engineering Department, Isfahan University of Technology, Isfahan, Iran

Received: September 09, 2016; Accepted: September 27, 2016; Published: September 29, 2016


Propylene/Propane separation system is widely encountered in chemical and petrochemical processes. One of the conventional methods used for this separation is distillation. In this study a propylene/propane separation column with the capacity of purification of 70,000 tons/year of propylene has been considered. The primary aim of this study was the modeling and optimization of this column with the use of response surface methodology (RSM). Four input variables have been taken into account, which are columns reflux ratio, number of theoretical stages, condenser pressure and the recovery of propylene in the top product. A central composite design with 31 data points has been used, the data has been derived from simulation, and three different system responses have been studied and modeled which are propylene purity in the top product and condenser and reboiler duties. Based on the models derived and the surface plots of the models, several suggestions have been presented to enhance the system’s performance.

Keywords: Response Surface Methodology; Propane; Propylene; Optimization; Modeling


Propylene is a building block for the petrochemical industry and it is the base material for production of a wide range of other materials such as propylene oxide, polypropylene and acrylonitrile and the world propylene demand has been increasing in recent years [1-3]. Propylene can be produced via several different methods, while production of propylene in the FCC and Steam cracking of naphta process are the main sources for production of propylene [4, 5]. However nowadays a lot of other processes such as dehydrogenation of propane and methanol to propylene (MTP) are being developed for production of propylene [1,5]. The separation of propylene/ propane is required in each of the introduced propylene production processes. Since propylene and propane have close boiling points, the separation of these two gases is very energy consuming. Different methods like hybrid membrane distillation, cryogenic distillation, extractive distillation and adsorption can been used to separate these components [6-9]. In this study an ordinary distillation column is considered, modeled and optimized for separation of the two components. The response surface methodology has been used for modeling and optimization of this column.

The response surface methodology (RSM) is a method which can be used to find the relation between several input variables and system response (responses) [10]. RSM is extensively used in situations where several factors influence the response of the system and it is desired to optimize the performance of the system [11]. This method provides a way to choose some of the points of a design space, and having the system response at those points, it represents an estimation of the response at any other point in the design space. It uses a statistical approach for modeling and optimization of the system. The real relation between the input variables and the system response remains unknown, however the behavior of the system response is fitted by a polynomial in which variables are the input variables which have been selected for study [12]. The response surface methodology has been used in recent studies for a wide range of different systems like water and wastewater treatment, membrane systems, electronics and chemical systems like distillation [13-18]. The main of this study was the modeling and optimization of a propylene/propane distillation column with the use of response surface methodology.

Basis of Simulation

For the purpose of optimization of the propylene/ propane separation column, a feed of propylene/propane mixture based on production of 70,000 tons/year propylene has been taken into account. It has been assumed that the feed is available at a temperature of 173oC and a pressure of 500 psia. A distillation column model in Aspen HYSYS is selected for the modeling of the column [19].

Since the components in the feed mixture are hydrocarbons, and the pressure of the column doesn’t exceed 5,000 psia, the SRK property package is used for simulation of this process [20]. This property package exploits enhanced binary interactions for all library hydrocarbon-hydrocarbon systems [20]. As suggested by earlier studies and because of the close boiling point of the two components, this separation is a rather difficult separation process [21] and thus, in order to reach appropriate purities in the products, relatively high values of column reflux ratio and number of stages have been selected for the simulation. Figure 1 shows the simulated PFD of the separation process.