Effect of Solvent Content and Heat Integration on the Controllability of Extractive Distillation Process for Anhydrous Ethanol Production

Abstract

Considering that an analysis of both dynamic behavior and controllability of an extractive distillation process is important, and also taking into consideration the absence of studies in literature related to the influence of heat integration and solvent content on the controllability of this process, this work aims to investigate such aspects, or more specifically, investigate the dynamic responses in the presence of feed disturbances when operating at high, medium, and low solvent content. The production of anhydrous ethanol as the main product with ethylene glycol as solvent was the case study in this work, and a control scheme based on recent studies was used to perform this study. It was verified that the solvent content in the extractive section has an influence on top product composition when feed flow rate and composition disturbances are introduced in the azeotropic mixture feed stream; the system with high solvent content presented the highest offsets. The results also showed that the presence of heat integration causes considerable changes in the temperature of the recycled solvent stream when disturbances occur in the system feed flow rate, affecting the purity of the top product. A modification in the control scheme was proposed for the system with high solvent content, significantly improving the control of ethanol purity. The new control scheme includes two temperature control loops in the extractive column and a temperature control loop in the recycled solvent stream, using a bypass stream around the heat exchanger. It was also verified that the dimensions of the extractive column and reflux vessel are smaller when the system is configured to operate with a high solvent content.

A Novel Heat Integrated Extractive Dividing Wall Column for Ethanol Dehydration

“…For simulating the proposed processes, the feed (ethanol/ water) and solvent (ethylene glycol) conditions, such as temperature, composition, and flow rate are taken from the literature. 9 They are reported in Table 2.…”

“…To obtain the desired alcohol composition at low operational and capital cost, the extractive distillation (ED) is the most reliable technology. 9 The ED completes the separation in the presence of mass separating agent (MSA). The MSA features high boiling point, miscibility, and a tendency to form no azeotrope with either ethanol or water of the fermented product.…”

“…As stated, ethanol is produced via a trans-esterification reaction of fermentable sugar. This step yields dilute bioethanol with ethanol purity in the range of 5–12 wt % that needs to be further concentrated to more than 99.0–99.8 wt % (or above 99.5 mol %). , During the course of increasing ethanol concentration, a binary azeotrope of ethanol/water (95.63 wt % or 89.52 mol % of ethanol) is formed.…”

“…Figure shows the vapor–liquid equilibrium envelop, generated using the Aspen Plus, which confirms the existence of the ethanol/water azeotrope. To obtain the desired alcohol composition at low operational and capital cost, the extractive distillation (ED) is the most reliable technology . The ED completes the separation in the presence of mass separating agent (MSA).…”

Control Structures Evaluation for a Salt Extractive Distillation Pilot Plant: Application to Bio-Ethanol Dehydration

“…In this way, the control of azeotropic distillation columns is basically associated with multiple steady-states, and involves liquid-liquid equilibrium that imposes distillation boundaries limiting the operating range as well as the control of multiple-distillation columns with recycles [43]. The control of extractive distillation columns entails less difficulties and is the most frequently discussed in the literature [44][45][46][47][48][49]. The control of salt extractive distillation is still not an open research topic.…”