Romildo Pereira Brito

Optimization of the Design and Operation of Extractive Distillation Processes

The achievement of the optimal operating point of extractive distillation systems involves determining the values of the process variables, such as the solvent flowrate, the reflux ratio of the extractive, and recovery columns. From the point of view of design, the optimum involves defining the number of stages of extractive and recovery columns, as well as the feed stage positions of these columns. The above-mentioned columns are coupled through a recycle stream, which makes obtaining the optimal operating and design points a more complex task. This study arose from a new procedure for the analysis of extractive distillation columns, in which the solvent mole fraction in the solvent feed stage is the primary variable to be analyzed. The procedure allows for determining the values of the process and design variables that provide the global minimum for the total annual cost and the specific energy consumption of the extractive distillation processes (extractive and recovery columns). Furthermore, it is possible to determine the minimum solvent flowrate and the minimum reflux ratio for separation. Obtaining anhydrous ethanol using ethylene glycol as solvent is the case study of this work.

Effect of Solvent Content on the Separation and the Energy Consumption of Extractive Distillation Columns

This article sets out to evaluate the effect of solvent content in the extractive section on the separation efficiency and energy consumption of extractive distillation columns. Contrary to the classical approach, the proposed approach enables a simultaneous evaluation of the effect of the major decision variables (reflux ratio, solvent flow rate, and the number of stages of the extractive section [NSE]). The procedure allows calculating the minimum solvent flow rate for the separation and the minimum specific energy consumption. The results show that the minimum specific energy consumption is obtained for the minimum reflux ratio and not for the minimum solvent flow rate. Moreover, the results show that it is not always the case that a larger NSE results in lower energy consumption. Due to its industrial importance, the dehydration of aqueous mixtures of ethanol using ethylene glycol as solvent has been chosen as a case study.

Economic evaluation of energy saving alternatives in extractive distillation process

Abstract Until now, there has not been consensus about the superiority of thermally coupled sequence over the conventional sequence in the extractive distillation process. In this sense, the main goal of this paper is to analyze three approaches for saving energy in the extractive distillation process: optimization, thermal integration and thermal coupling. Three azeotropic mixtures were investigated: ethanol and water (M1); tetrahydrofuran and water (M2); and acetone and methanol (M3). The solvents were ethylene glycol for M1 and M2, and water for M3. The results are shown in terms of the total annual cost (TAC) and specific energy consumption (SEC), and revealed that a thermally coupled extractive distillation sequence with a side rectifier did not always present the best results. Taking the case studies from literature as a starting point (without thermal integration), the optimization procedure used in this work found that TACs are always lower. The inclusion of thermal integration in configurations led to reducing TAC for all mixtures under investigation when compared to the sequences without this integration. When comparing two modifications in the layout of extractive distillation, it can be seen that it is more advantageous to use the preheating of the azeotropic feed with the recycle stream from the recovery column of the conventional sequence than using a thermally coupled sequence.

Exergetic and economic analysis of an industrial distillation column

In this work, applications of exergy and economic concepts to compression, heat exchange, and separation processes were used for calculation of the irreversibility rate, thermodynamic efficiency, and internal rate of return (IRR) of the profitability. A case study based on a real process, the purification of 1,2-dichloroethane (DCE) in a high-purity distillation column, is presented. This column has the highest steam flow rate in any vinyl chloride monomer (VCM) plant. A configuration using a vapor compression heat pump is proposed for improvement of the energy efficiency without having to make important process modifications. Existing and proposed configurations were implemented using the Aspen Plus™ commercial simulator; the results of the existing configuration were validated with data extracted from the plant. The objective of this work was to compare the existing configuration with the proposed one, using a thermodynamic and an economic approach.

Control of an Extractive Distillation Column with Thermal Integration

Abstract Knowing the importance and necessity of the existence of a control system in chemical processes, this paper aims to investigate the control performance of an extractive column with thermal integration facing common process disturbances. The dehydration of ethanol using ethylene glycol as a solvent was used as a case study. The extractive column was simulated in steady and dynamic states using the commercial software Aspen Plus® and Aspen Plus Dynamics®, in which it was used a more rigorous model with decoupled condenser and reflux vessel. The technique of control by inference was adopted to control the overhead product composition. The results showed that it is possible to maintain the composition of ethanol near specification using a simple control structure, although the thermal integration lead to deviations in the solvent feed temperature of about 5 degrees, when disturbances in the azeotropic mixture feed flow rate are applied.

Auto Tuning Applied to Distillation Column Based on Armax Model Parameter Estimation

An auto-tuning procedure for PID controllers based on model ARMAX is the main subject of this paper. Such a model has been used in the on-line controller parameters estimation through the relay method, resulting in a smaller deviation between the model and process variables when utilized a normalized regression matrix. The procedure was applied to an Aspen Plus Dynamics® model of Naphtha Treatment Unit. The Aspen model takes into account the main control structures and the principal observed disturbances. The procedure has been developed in Visual Basic for Applications programming language, making possible a real-time connection with the Aspen model. The on-line identification of the ARMAX model was made using the RELS (PR), thereby allowing the estimation of the controllers parameters from classical tuning procedures in closed loop. With the use of this strategy, the updating of the controllers parameters has been possible, promoting a superior performance of the control structure.

Effect of Solvent Content on Controllability of Extractive Distillation Columns

Abstract This paper arose from a new approach to evaluating separation and energy consumption of extractive distillation columns using as primary analysis parameter the solvent content throughout the column. This new approach allows to find a range of possible solutions that contemplates the global optimal point of operation. In view of this, the objective of this paper is to investigate the influence of the solvent content throughout the column and the size (number of stages) of the column on controllability. The results showed that the columns with smaller number of stages operating with lower solvent content have a better controllability when applied disturbances in the composition of the azeotropic mixture that feeds the column. The production of anhydrous ethanol by extractive distillation using ethylene glycol as solvent was used as a case study for this work.

Joint Confidence Region for the Tuning Parameters of the PID Controller

Abstract The aim of this paper is to estimate the joint confidence region for the tuning parameters of the PID controller. Considerations on the statistical independence and the linear relationship between the tuning parameters for a more realistic scenario are taken into account. In order to capture the data necessary for the simulation, an appropriate structure was implemented, consisting of a process-model-based controller. By using the data resulting from the simulations, it was also possible to find the probability density function for each tuning parameter, as well the region of joint confidence of such parameters, which indicates a contraction of the region when compared with the standard level of significance. What is also shown is how to restore the joint confidence region by means of the Principal Components Technique.

Intelligent control system for extractive distillation columns

We developed and implemented an intelligent control system to be used in an extractive distillation column that produces anhydrous ethanol using ethylene glycol as solvent. The concept of artificial neural networks (ANN) was used to predict new setpoints after disturbances, and proved to be a fast and feasible solution. The developed control system receives data from temperature, flowrate and composition measurements of the azeotrope feed, and the ANN estimates the new set-points of the controllers to maintain 99.5 mol% of ethanol at the top and less than 0.1mol% at the bottom; feed composition was also estimated using an ANN. All ANN were trained to provide output data corresponding to an optimized operating condition. The results showed that the intelligent control system can predict a new operating condition for any disturbance in the column feed and presented superior performance when compared with the control system without ANN.

New Routes Study for Synthesis of Molecular Sieves Type Al-MCM-41 and Al-SBA-15

The areas of research, synthesis and catalytic application of zeolites as molecular sieves are a field of great development and prominence in recent decades. Needs of the industries of petrochemical and fine chemicals have been encouraging specific studies for the application of molecular sieves looking for technological, commercial, and more recently sustainable developments. In this work molecular sieves type Al-MCM-41 and Al-SBA-15 has been synthesized using new synthesis routes by replacing the silica source conventionally used by rice husk. The molecular sieves obtained were confirmed by X-ray diffraction. Through the thermograms the decomposition of the driver at different temperatures was noticed. According to SEM micrographs can be observed that the material shows an aggregate of relatively uniform short particles.