Cellulosic ethanol and its co-products from different substrates,pretreatments,microorganisms and bioprocesses:A review

Cellulosic ethanol involves the following production steps: physical and/or chemical pretreatment, biological treatment, fermentation and distillation. First three steps are also the bottlenecks for the production of cellulosic ethanol and its co-products. Their production still pose some difficulties in terms of pretreatment, the high cost of enzymes for substrate hydrolysis, the formation of inhibitory compounds in the hydrolyzate, the lack of efficient and viable microorganisms for industrial fermentation of hexose and pentose among others. The solution or minimization of these difficulties may lead to numerous socio-environmental, political, and economic advantages for cellulosic ethanol production. This paper highlights the potential of different substrates, pretreatments, microorganisms and bioprocesses for cellulosic ethanol production.

Study on the Treatment of Cellulosic Ethanol

Wastewater from the production of cellulosic ethanol was treated by the processes of internal micro-electrolysis method ＋ABR＋UASB ＋MBR. The results of running indicated that, when COD is 12000 mg/L and HRT of UASB is 48 h, the COD removal rate reaches 72% and HRT of MBR is 20 h, COD removal rate is between 80.8% and 87.5%. The effluent COD concentration stabilized at 301- 537 mg/L, it indicates that the MBR system has a strong ability to resist impact load.

Technology and Production of Cellulosic Ethanol in a Pilot Plant in Taiwan

In concert with governmental policy for promoting the use of biofuels, the Institute of Nuclear Energy Research （INER） is dedicated to the research and development of technologies for cellulosic ethanol production. A pilot plant for cellulosic ethanol production with a capacity of one ton in dry biomass per day was established in 2007 and launched test-run operations for mass production in early 2010. The feedstock is focused on rice straw currently, but is also flexible for sugarcane bagasse and hardwood. The operative experiences and the experimental data will provide valuable information for the evaluation of production cost as well as the foundation for design of a commercial production plant in Taiwan. Additionally, this pilot plant will also serve as an important platform for validation of technologies related to cellulosic ethanol production and biorefinery operations. The biomass-to-ethanol process of this plant is based on the route of biochemical conversions. Developed and developing technologies, such as acid hydrolysis pretreatment, high solid to liquid ratio hydrolysis, in-house cellulase production, xylose fermentation, and the distillation and dehydration processes will be introduced.

Overview of biomass pretreatment for cellulosic ethanol production

Bioconversion of lignocellulosic biomass to ethanol is significantly hindered by the structural and chemical complexity of biomass,which makes these materials a challenge to be used as feedstocks for cellulosic ethanol production.Cellulose and hemicellulose,when hydrolyzed into their component sugars,can be converted into ethanol through well established fermentation technologies.However,sugars necessary for fermentation are trapped inside the crosslinking structure of the lignocellulose.Hence,pretreatment of biomass is always necessary to remove and/or modify the surrounding matrix of lignin and hemicellulose prior to the enzymatic hydrolysis of the polysaccharides(cellulose and hemicellulose)in the biomass.Pretreatment refers to a process that converts lignocellulosic biomass from its native form,in which it is recalcitrant to cellulase enzyme systems,into a form for which cellulose hydrolysis is much more effective.In general,pretreatment methods can be classified into three categories,including physical,chemical,and biological pretreatment.The subject of this paper emphasizes the biomass pretreatment in preparation for enzymatic hydrolysis and microbial fermentation for cellulosic ethanol production.It primarily covers the impact of biomass structural and compositional features on the pretreatment,the characteristics of different pretreatment methods,the pretreatment study status,challenges,and future research targets.

A Novel Approach to Ethanol Fuel Production using Rotary Collection of Forest Debris

In this article, the authors propose the production of ethanol from cellulose as an alternative to oil. Cellulosic-ethanol will reduce greenhouse gas emissions, and provide a means to prevent forest fires. This liquid dense fuel was selected because it： （1） easily transported and dispensed as a fuel; （2） can be handled by the existing fuel distribution infrastructure; and （3） unlike its commercial competitor, Me-OH （Methanol）, Et-OH （Ethanol）, is edible, thus being biodegradable and nontoxic. Forest residue ethanol is cheaper to produce and more environmentally friendly than other forms of ethanol fuel. Furthermore, forests would have less available ground fuel for fires. The potential decline of forest fires would then reduce the carbon footprint attributed directly to forest fires. In combination with ethanol fuel combustion, carbon emissions can be reduced by more than 70% compared to gasoline combustion. We used GREET （Greenhouse gases, Regulated Emissions, and Energy use in Transportation） software to assess the life cycles of different fuel pathways. In conclusion, cellulosic ethanol fuel is clearly an answer to decrease dependency on current oil imports and prevent forest fires.

An analysis of an ethanol-based, whole-crop refinery system in China

Bio-fuel can be used to help transition from a petroleum-based society to a bio-based society. Ever since the China Development and Reform Commission suspended the approval of crop processing programs, second-generation bio-ethanol research and industrialization processes have attracted significant attention. In 2020, bio-ethanol production is predicted to reach 10 million tons. Currently, there are a few domestic enterprises that have established different scaled pilot or demonstration bases for cellulosic ethanol, which reduce the cost of ethanol by continuously improving pretreatment and hydrolysis techniques. In the next three years, these enterprises will realize large-scale commercial production. Given the practical problems in cellulosic ethanol plant construction and operation(e.g., marketing price variation and difficulties in feedstock collection), this paper began with the concept of a "whole-crop refinery" and presented a solution to the integration of industry and agriculture as well as multi-crop refining. This paper then took the whole-crop refining system of corn as an example and presented an analysis of the logistics, energy flow, and economical efficiency of the system. The results demonstrated that the integrated system could properly reduce the required fixed investments in production equipment,shared utilities, and wastewater treatment facilities, as well as reduction of energy consumption. Although the proposed system has several problems, it brings the long-term goal of large-scale commercial application closer than ever.

A review on the chemo-catalytic conversion of cellulose to bio-ethanol

While the industry has produced sugar-derived ethanol from the conventional method of fermentation for hundreds of years,other effective routes involving the direct transformation of carbohydrates still remain extremely rare.Very recently,an innovative chemo-catalytic method driven by the aqueous-phase catalysis was created for the synthesis of cellulosic ethanol,making a great breakthrough in the common ways as it can theoretically utilize all of the carbon atoms in sugars with faster kinetics;up to now,results from the relevant studies have been accumulated to a certain extent,but the periodic conclusions in this field are unfortunately absent.For this reason,this work tries to offer an overview of the cellulosic ethanol produced by chemo-catalytic routes,highlighting the present knowledge in relation to the technical efficiency,catalytic mechanisms as well as practical applications.At first,the advanced progress on the increasing efficiency from a varied type of catalytic systems are extensively discussed,which involves the specific functions of hybrid components from different strategies;meanwhile,the general influences of processing conditions,such as the hydrothermal severity and aqueous environments,are also identified.Subsequently,possible mechanisms behind the chemo-catalytic processes are widely elaborated by analyzing a number of experimental cases associated with the reaction network and its kinetic models.After that,the actual effects of this technique on the real biomass are collected to identify the positive/negative interactions between multiple components,together with the potential solutions on the semi-continuous processes of pilot scale application.The techno-economic analysis(TEA)is also calculated and compared with other similar methods,such as fermentation and gasification.Finally,several proposals aimed at upgrading the whole chain of chemo-catalytic processes are clearly provided,which may function as a guideline for future studies on the production of bio-ethanol from lignocellulosic materials.

Effects of Chemical Pretreatment on Enzymatic Saccharification and Fermentation of Forages

[ Objective] To study the effect of pretreatment with chemical substances on enzymatic saccharification of affalfa （ Medic, ago sativa L. ）, sorghum hybrid sudan grass [ Sorghum bicolor （ L. ） Moench x Sorghum sudanese （Piper） Stapf], erect milkvetch （Astraga/us adsurgens Pall. ） and pearl millet （ Pennisetum americanum （ L. ） Leeke）. [ Method ] The forages were pretreated with sulfuric acid at different concentration, and then the content of cellulose, hemicellulose, and lignin were detected and compared with that before pretreatment. The concentration of glucose and ethanol after different fermentation time was also determined. [ Result] After pretreatment, the content of cellulose increased, while that of hemicel- lulose and lignin decreased. After treatment with 1.0% （W/V） sulfuric acid, the four kinds of forages all had the highest concentration of ethanol in the citric acid-sodium citrate buffer system （pH 4.8）. Dudng fermentation process, the concentration of glucose and ethanol first increased and then declined, peaking respectively at 24 h and 48 h post fermentation. [Condusion] Pretreatment promotes the enzymatic saccharification and fermen- tation of alfalfa, sorehum hvbrid sudan orass. Dead millet, and erect milkvetch, and their enerov performance decreases in order.

Nanostructural Evolution of Sugarcane Rind and Pith Submitted to Hydrothermal Pretreatments

Lignocellulose conversion into cellulosic ethanol and coproducts starts with a pretreatment step.Most current industrial plants of cellulosic ethanol use thermochemical pretreatments under hydrothermal conditions,with or without addition of acid catalyst.Such pretreatments modify biomass chemistry and morphology,particularly at the nanoscale.In this work,we use X-ray diffraction,dynamic vapor sorption and calorimetric thermoporometry to investigate the biomass nanostructural changes promoted by hydrothermal conditions.We compare and differentiate the rind and pith fractions of sugarcane stalks in order to contribute to the understanding of rind-pith contrasting recalcitrance.Moreover,for both cane fractions our results point consistently to cellulose co-crystallization,lignin aggregation,and opening of nanoscale pores as the main nanostructural phenomena occurring during hydrothermal treatments.

Characterization of Lignins Isolated from Alkali Treated Prehydrolysate of Corn Stover

Lignins were isolated and purified from alkali treated prehydrolysate of corn stover. The paper presents the structural features of lignins in a series purification processes. Fourier transform infrared spectroscopy, ultraviolet-vis spectroscopy and proton nuclear magnetic resonance spectroscopy were used to analyze the chemical structure. Thermogravimetric analysis was applied to follow the thermal degradation, and wet chemical method was used to determine the sugar content. The results showed that the crude lignin from the prehydrolysate of corn stover was a heterogeneous material of syringyl, guaiacyl and p-hydroxyphenyl units, containing associated polysaccharides, lipids, and melted salts. Some of the crude lignin was chemically linked to hemicelluloses （mainly xylan）. The lipids in crude lignin were probably composed of saturated and/or unsaturated long carbon chains, fatty acids, tdterpenols, waxes, and derivatives of aromatic. The sugar content of purified lignin was less than 2.11%, mainly composed of guaiacyl units. DTGmax of purified lignin was 359 ℃. The majority of the hydroxyl groups were phenolic hydroxyl groups. The main type of linkages in purified lignin was β-O-4. Other types of linkages included β-5, β-β and α-O-4.

Saccharification versus simultaneous saccharification and fermentation of kraft pulp

Enzymes are a significant cost in cellulosic ethanol production,minimizing their use would be desirable as long as ethanol yields and productivities are not reduced.The aim was to evaluate the effects of enzyme dosage on conversion of cellulose to ethanol.Kraft pulp,an intermediate in paper production,was used to represent a fractionated cellulose feedstock.Trials were conducted in a 5 L BioFlow bioreactor(2-3 L working volume)with agitation rate varied(80-900 r/m)to provide acceptable mixing.Based on survey of the literature,an average dosage for cellulase(34 FPU/g glucan)andβ-glucosidase(135 CBU/g glucan)was calculated,and these were set as the 100%dosages.Dosages of 1%,7%,13%,33%,67%,100%,133%were tested,using Novozyme Celluclast 1.5 L(cellulase)and Novozyme 188(β-glucosidase)in a 4.8%(dry mass)kraft pulp slurry.Novozymes recommended dosages are at the low end of this spectrum,at 12 g/g glucan for Celluclast 1.5 L(35%dosage)and 1.2 g/g glucan for Novozyme 188(0.9%dosage).Saccharification trials(50oC)showed a typical dosage response,with the 133%dosage achieving the highest sugar concentration(~59 g/L glucose)and saccharification rate(2.45 g/L/h),with a specific rate of 2.2×10-4 g glucose/unit enzyme/h.However the 13%enzyme dosage resulted in the highest specific saccharification rate(2.9×10-4 g glucose/unit enzyme/h).Simultaneous saccharification and fermentation(SSF)trials(35oC)were conducted using Saccharomyces cerevisiae or Candida molischiana to compare enzyme dosages of 33%,67%,100%,and 133%.Ethanol titers and productivities were similar for trials with 67%or more of the literature average enzyme dosage,however were lower at the 33%enzyme dosage.Thus enzyme dosage can be substantially reduced from levels typically cited in the literature,but cannot be reduced to levels recommended by the manufacturer,without reduction in ethanol yield and productivity.