Current Trends in Lignocellulosic Bioethanol Production

Lignocellulosic materials are raw materials with high cellulose content and they constitute the most abundant sources of biomass on planet. They are attractive for their low cost and high availability in diverse climates and places for the bioethanol production, however, the main impediment for its use is the appropriate selection from the technological and economic point of view of the stages of pretreatments and hydrolysis, that allow the breaking down of the lignocellulosic matrix to obtain the necessary substrates in the processes of fermentation. Pretreatment is an essential step in the enzymatic hydrolysis of biomass and subsequent production of bioethanol, which have been divided in three groups for its study in: physical-chemical, hydrothermal and biological. The aim of this paper is to analyze the potential of several pretreatment methods for bioethanol production from lignocellulosic materials.

Journal of Biofuels, 2010

Energy consumption has increased steadily as the world population has grown and more countries have become industrialized. The fossil fuels, such as Crude oil, Coal and natural gas have been the major resources to meet the increased energy demand. However, they are gradually being depleted to extinction because they are not renewable. Moreover, serious environmental and ecological problems have been aroused during their exploitation and use. Therefore, there is great interest in exploring alternative energy source to maintain the sustainable growth of society. Ethanol, a clean and renewable energy source, which can be produced through fermentation from renewable biomass, has drawn much attention from the government and researchers. Apart from an alternative to traditional energy sources, ethanol has been widely used as a solvent or feed stock in pharmaceutical and chemical industries. However, fermentative production of ethanol has been limited using current maize starch based technology because of raw material shortage and high cost. A potential method for low cost fermentative production of ethanol is to utilize lignocellulosic materials such as agricultural wastes. We would now discuss and cite out the rapid progress in the eld of bioethanol from lignocellulosic materials over the past few decades.

Energy, 2020

Regarding the supply of fossil fuels, greenhouse gasses emission, global warming, and increasing fuel price; there is a need to find alternative energy resources, which are renewable, environmentally sustainable, and economically viable. Agro-industrial biomass such as sugarcane bagasse, rice and wheat straw, corn stover, and switchgrass, named as lignocellulosic biomass (LCB) which is inexpensive, abundant, renewable, and provides a unique natural resource for large-scale and cost-effective bio-energy production. During the production of biofuels, pretreatment is a necessary step due to the recalcitrant structure of LCB. Various pretreatment methods were employed with a different mechanism of action, feasibility, and practicability to produce high yield biofuels. Since many years ago, the development of an effective pretreatment method has been challenging due to the existence of barriers and obstacles. Besides, each pretreatment method has its advantage and disadvantage, which should be investigated to obtain a higher yield of bioethanol. In this paper, the recent findings regarding the application of various pretreatment techniques such as chemical, physical and biological methods for bioethanol production from LCBs have been reviewed. The limitations of the mentioned methods based on the existing barriers were explained, and the future recommendations were discussed.

3 Biotech, 2015

Second-generation bioethanol can be produced from various lignocellulosic biomasses such as wood, agricultural or forest residues. Lignocellulosic biomass is inexpensive, renewable and abundant source for bioethanol production. The conversion of lignocellulosic biomass to bioethanol could be a promising technology though the process has several challenges and limitations such as biomass transport and handling, and efficient pretreatment methods for total delignification of lignocellulosics. Proper pretreatment methods can increase concentrations of fermentable sugars after enzymatic saccharification, thereby improving the efficiency of the whole process. Conversion of glucose as well as xylose to bioethanol needs some new fermentation technologies to make the whole process inexpensive. The main goal of pretreatment is to increase the digestibility of maximum available sugars. Each pretreatment process has a specific effect on the cellulose, hemicellulose and lignin fraction; thus, different pretreatment methods and conditions should be chosen according to the process configuration selected for the subsequent hydrolysis and fermentation steps. The cost of ethanol production from lignocellulosic biomass in current technologies is relatively high. Additionally, low yield still remains as one of the main challenges. This paper reviews the various technologies for maximum conversion of cellulose and hemicelluloses fraction to ethanol, and it point outs several key properties that should be targeted for low cost and maximum yield.

Frontiers in bioscience (Scholar edition), 2018

The future supply of energy to meet growing energy demand of rapidly exapanding populations is based on wide energy resources, particularly the renewable ones. Among all resources, lignocellulosic biomasses such as agriculture, forest, and agro-industrial residues are the most abundant and easily available bioresource for biorefineries to provide fuels, chemicals, and materials. However, pretreatment of biomass is required to overcome the physical and chemical barriers that exist in the lignin-carbohydrate composite and pretreatment facilitate the entry of biocatalysts for the conversion of biomass into fermentable sugars and other by-products. Therefore, pretreatment of the biomass is necessary prerequisite for efficient hydrolysis of lignocelluloses into different type of fermentable sugars. The physiochemical, biochemical and biological pretreatment methods are considered as most promising technologies for the biomass hydrolysis and are discussed in this review article. We also d...

Renewable and Sustainable Energy Reviews, 2013

Pretreatment technologies are aimed to increase enzyme accessibility to biomass and yields of fermentable sugars. In general, pretreatment methods fall into four different categories including physical, chemical, physico-chemical, and biological. This paper comprehensively reviews the lignocellulosic wastes to bioethanol process with a focus on pretreatment methods, their mechanisms, advantages and disadvantages as well as the combinations of different pretreatment technologies. Moreover, the new advances in plant "omics" and genetic engineering approaches to increase cellulose composition, reduce cellulose crystallinity, produce hydrolases and protein modules disrupting plant cell wall substrates, and modify lignin structure in plants have also been expansively presented.

The process of converting lignocellulosic biomass to ethanol involves pretreatment to disrupt the complex of lignin, cellulose, and hemicellulose, freeing cellulose and hemicellulose for enzymatic saccharification and fermentation. Determining optimal pretreatment techniques for fermentation is essential for the success of lignocellulosic energy production process. The purpose of this study was to evaluate energy cane for lignocellulosic ethanol production. Various pretreatment processes for energy cane variety L 79-1002 (type II) were evaluated including different concentrations of dilute acid hydrolysis and solid-state fungal pretreatment process using brown rot and white rot fungi. Pretreated biomass was enzymatically saccharified and fermented using a recombinant Escherichia coli. The results revealed that all pretreatment processes that were subjected to enzymatic saccharification and fermentation produced ethanol. However, the best result was observed in dilute acid hydrolysis of 3% sulfuric acid. Combination of fungal pretreatment with dilute acid hydrolysis reduced the acid requirement from 3% to 1% and this combined process could be more economical in a large-scale production system. Keywords: Dilute acid hydrolysis, energy cane, cellulose, hemicelluose, lignin, ethanol, fermentation

Biomass and Bioenergy, 2012

Biomass pretreatment aims at separating and providing easier access to the main biomass components (cellulose, hemicellulose and lignin), eventually removing lignin, preserving the hemicellulose, reducing the cellulose crystallinity and increasing the porosity of the material. Pretreatment is an essential step towards the development and industrialization of efficient 2nd generation lignocellulosic ethanol processes. The present work reviewed the main options available in pretreatment. Autohydrolysis and steam explosion were then selected for further investigation. Experimental work was carried out on batch scale reactors, using Miscanthus as biomass feedstock: the effects on sugar solubilization and degradation products generation have been examined for each of these two pretreatment systems. A new process using only water and steam as reacting media was then developed, experimentally tested, and results compared to those achieved by the autohydrolysis and steam explosion processes. Products obtained with the new pretreatment contained a lower amount of usual fermentation inhibitor compounds compared to that typically obtained in steam explosion. This result was achieved under operating conditions that at the same time allowed a good xylan yield, preventing degradation of hemicelluloses. The new pretreatment process was also able to act as an equalization step, as the solid material from the pretreatment phase had a similar composition even under different operating conditions. As regards the effect of pretreatment on enzymatic hydrolysis, the new process achieved yields similar to steam explosion on glucans: however, this was obtained reducing the formation of degradation products from sugars, mainly from C5 sugars. These results made the proposed pretreatment system suitable for further development and industrialization on pilot and industrial scale.

2017

Bioethanol production from lignocellulosic biomass has attracted a lot of attention as one of the most promising alternative to liquid fossil fuels. Over the last decades a lot of research has been done to find the optimal methods & devices to produce bioethanol from all kind of lignocellulosic biomass. A traditional three-step production process is used to produce bioethanol from lignocellulosic biomass – pretreatment, enzymatic hydrolysis, & fermentation. Today, the high cost of the pretreatment prevents bioethanol from competing with petrol. In this review article, the positive & negative aspects of different pretreatment methods & patented devices are investigated & analysed. Based on the analysis several options on how to lower lignocellulosic biomass pretreatment costs & how to increase the competitiveness of bioethanol are proposed.

IOP Conference Series: Earth and Environmental Science

The barrier to realising the potential of lignocellulosic bioethanol is the recalcitrance of cellulosic biomass. Overcoming this biomass recalcitrance is the key challenge to large scale production of lignocellulosic bioethanol. Pretreatment is an important and critical step that enables enzyme hydrolysis of lignocellulose conversion to ethanol. Finding a pretreatment method for reducing the high recalcitrance via cost-effective pretreatment methods would therefore be of great benefit. This study aims at investigating the effect of pretreatment on delignification process of sugarcane bagasse and oil palm trunk. Two methods of pretreatment were compared i.e. alkaline hydrogen peroxide pretreatment (1% and 5% H2O2) and subcritical water pretreatment (170°C, 2.2 MPa) for the effectiveness of reducing the lignin content. Scanning Electron Microscopy (SEM) analysis was also performed to investigate the effect of pretreatment on surface of lignocellulosic biomass. It was observed that alk...