The Efficiency of Nitrogen and Flue Gas as Operating Gases in Explosive Decompression Pretreatment

Merlin Raud,Vahur Rooni,Timo Kikas

doi:10.3390/en11082074

Abstract

As the pretreatment process is the most expensive and energy-consuming step in the overall second generation bioethanol production process, it is vital that it is studied and optimized in order to be able to develop the most efficient production process. The aim of this paper was to investigate chemical and physical changes in biomass during the process of applying the explosive decompression pretreatment method using two different gases—N2 and synthetic flue gas. The explosive decompression method is economically and environmentally attractive since no chemicals are used—rather it is pressure that is applied—and water is used to break down the biomass structure. Both pre-treatment methods were used at different temperatures. To be able to compare the effects of the pretreatment, samples from different process steps were gathered together and analysed. The results were used to assess the efficiency of the pretreatment, the chemical and physical changes in the biomass and, finally, the mass balances were compiled for the process during the different process steps of bioethanol production. The results showed that both pre-treatment methods are effective in hemicellulose dissolution, while the cellulose content decreases to a smaller degree. The high glucose and ethanol yields were gained with both explosive pretreatment methods at 175 °C (15.2–16.0 g glucose and 5.6–9.0 g ethanol per 100 g of dry biomass, respectively).

Highlights

The most common way of producing biofuels from lignocellulose is to convert the biomass into sugars and ferment the sugars into fuel, such as bioethanol
The most important property of biomass is high cellulose content, since bioethanol is produced from glucose that is formed during cellulose hydrolysis [16]
In order to investigate the effects of pretreatment upon chemical and physical changes in the biomass, The explosive decompression pretreatment method was studied and used with two different a traditional three-step bioethanol production process was used with pretreatment, hydrolysis and gases—nitrogen and synthetic flue gas

Summary

Introduction

The most common way of producing biofuels from lignocellulose is to convert the biomass into sugars and ferment the sugars into fuel, such as bioethanol. The low levels of accessibility of cellulose due to its rigid association with lignin and hemicellulose makes the degradation of cellulose difficult for cellulases. In order to increase the overall process efficiency, it is necessary to break down the lignin and hemicellulose seal in order to make cellulose more accessible for further processing [1]. Pretreatment is an essential step before the step involving hydrolysis of lignocellulosic biomass into sugars [2]. The most common are physical, chemical and physio-chemical methods, which combine the effect of both. The physical methods usually target biomass particle size reduction and are energy-intensive with low efficiency

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