Energy optimization of bioethanol production via hydrolysis of switchgrass

Abstract

Abstract.In this work, we propose the optimal flowsheet for the production of bioethanol from switchgrass, via hydrolysis. A superstructure embedding a number of alternatives is proposed. Two technologies are considered for switchgrass pretreatment, dilute acid and ammonia fibre explosion (AFEX) so that the structure of the grass is broken down. Next, enzymatic hydrolysis follows any of the pretreaments to obtain fermentable sugars, mainly xylose and glucose. Ethanol is obtained by fermentation of the sugars. In order to obtain fuel quality ethanol, water must be removed from the water-ethanol mixture. A number of dehydration technologies is considered including rectification, adsorption in corn grits, molecular sieves and pervaporation. The problem is formulated as an MINLP. The superstructure is optimized by decomposing the MINLP for each of the pretreaments. Then, multieffect columns and heat integration are used to reduce the energy consumption and cooling needs. Finally, an economic evaluation is performed. The optimal flowsheet consists of using dilute acid hydrolysis followed by molecular sieves as dehydration technology, which requires less energy and cooling and yielding a promising production price of 0.8 $/gal.

Combined production of biogas and ethanol at high solids loading from wheat straw impregnated with acetic acid: experimental study and techno-economic evaluation

“…A variety of raw materials, which require different process configurations, have been examined, including bagasse and sugar cane [21,22], switch grass [23,24], wood [25][26][27], and corn and corn stover [28][29][30]. However, to the best of the authors' knowledge, there are few reports on the technical and economic aspects of wheat straw biorefineries.…”

On the Systematic Synthesis of Sustainable Biorefineries

“…5,7,[69][70][71][72][73] In general, the similarity between the hydrolysis path and the first generation of bioethanol together with the lower investment cost compared to the thermalbased process has attracted the attention of many researchers. Martín & Grossmann 40,41 presented studies for gasification and hydrolysis of switchgrass based on superstructure optimization to evaluate a large number of alternatives in a systematic way using mathematical programming techniques. The NERL reports 7,69 and some academic papers 72,73 have evaluated the production of bioethanol from corn stover, wood chips or hybrid poplar through case studies using ASPEN as the simulation tool.…”

“…Martín & Grossmann 41 while Figure 7 presents the energy consumption and cooling needs of the process. The production of ethanol from hydrolysis is a more gentle process in terms of operating pressures and temperatures compared to the gasification process resulting in less than half the cooling requirements for the thermo-chemical process, (see Figure 7).…”

“…At this point there are still very few papers that have reported the use of process synthesis techniques with the explicit incorporation of sustainability issues. [31][32][33][34][35] Some of them have applied optimization methods to the molecular design of solvents and the synthesis of the associated separation processes [36][37] and more recently for the design of biorefineries as we show later in the paper [38][39][40][41] as well as integrating the different processes for the optimal operation of biorefineries. [42][43][44][45][46] In this paper we review the design of sustainable biorefineries from different raw materials such as corn, first generation of bioethanol, lignocelluslosic materials, second generation of biofuels or cooking and algae oil, second and third generation of biodiesel.…”

Optimal use of hybrid feedstock, switchgrass and shale gas for the simultaneous production of hydrogen and liquid fuels

“…Bioethanol production from switchgrass via thermochemical routes is becoming promising as a substitute for gasoline in terms of production cost [8], in spite of the higher investment required compared to the biochemical route [9]. Biodiesel from algae is also the focus of development by academia, government and industry; e.g.…”