Article pubs.acs.org/IECR
HiGee Stripper-Membrane System for Decentralized Bioethanol Recovery and Purification Krishna Gudena, G. P. Rangaiah,* and S. Lakshminarayanan Department of Chemical & Biomolecular Engineering, National University of Singapore, Singapore 117576 ABSTRACT: Economic production of bioethanol from lignocellulosic feedstock is one of the important solutions to the rising environmental concerns and depleting crude-oil reserves. However, feedstock available for bulk production of bioethanol is spread over a wide horizon and is of low-energy density, and bioethanol produced in the fermentor is dilute (∼5 wt %), which significantly increases the energy required for and cost of bioethanol production. To address these issues, the present article introduces a process-intensified technology, namely, HiGee (short for high gravity) stripper combined with a membrane (HSM) process for concentrating bioethanol. The performance of HSM is compared with one of the best energy-efficient process for bioethanol purification in the literature. Design, optimization, and technoeconomic evaluation of both the processes are performed, and the HSM process is found to be compact, require lower capital and operating costs, and have a high turndown ratio over the conventional process. The size benefit of the HSM process is essential for transporting bioethanol separation units using commercial motor vehicles for decentralized and portable bioethanol recovery and purification.
1. INTRODUCTION The potential of bioethanol as an important solution to the rising environmental concerns and increasing crude oil prices has driven numerous works on this biofuel. Second-generation bioethanol obtained by the fermentation of lignocellulosic wastes, such as corn stover, sugar cane bagasse, and switchgrass, is of considerable interest within academia and the industrial community due to its abundance and as an effective solution to the “food versus fuel” conflict. Production of bioethanol from the lignocellulosic feedstock consists of the following main steps:1 (1) feed handling and storage, (2) pretreatment and detoxification, (3) enzymatic hydrolysis with cofermentation, (4) product recovery and purification, (5) wastewater treatment, (6) electricity and steam generation, and (7) storage. Typical concentration of lignocellulosic ethanol from the fermentation broth after step 3 is very dilute at about 5 wt %. Hence, concentration of ethanol to 99.7 wt % as per European Union standards (EN 15376)2 or 98.7 wt % as per American Society for Testing and Materials (ASTM) standards2,3 requires significant energy and is also costly. Several technologies, such as distillation, pervaporation, adsorption, and solvent−solvent extraction2 have been studied in the literature to attain these targeted concentrations of ethanol. The characteristic of ethanol to form an azeotrope with water at 95.6 wt % ethanol further increases the difficulty in its purification. Hence, distillation until the azeotropic limit of the ethanol−water mixture, followed by its further purification in a molecular-sieve adsorption system is widely studied and industrially applied.2,4 However, distillation−adsorption processes are energy-intensive, especially for dilute ethanol concentrations in the fermentation broths (
