Pretreatment technologies for an efficient bioethanol production process based on enzymatic hydrolysis: A review

Background Lignin, nature’s dominant aromatic polymer, is found in most terrestrial plants in the approximate range of 15 to 40% dry weight and provides structural integrity. Traditionally, most large-scale industrial processes that use plant polysaccharides have burned lignin to generate the power needed to productively transform biomass. The advent of biorefineries that convert cellulosic biomass into liquid transportation fuels will generate substantially more lignin than necessary to power the operation, and therefore efforts are underway to transform it to value-added products. Production of biofuels from cellulosic biomass requires separation of large quantities of the aromatic polymer lignin. In planta genetic engineering, enhanced extraction methods, and a deeper understanding of the structure of lignin are yielding promising opportunities for efficient conversion of this renewable resource to carbon fibers, polymers, commodity chemicals, and fuels. [Credit: Oak Ridge National Laboratory, U.S. Department of Energy] Advances Bioengineering to modify lignin structure and/or incorporate atypical components has shown promise toward facilitating recovery and chemical transformation of lignin under biorefinery conditions. The flexibility in lignin monomer composition has proven useful for enhancing extraction efficiency. Both the mining of genetic variants in native populations of bioenergy crops and direct genetic manipulation of biosynthesis pathways have produced lignin feedstocks with unique properties for coproduct development. Advances in analytical chemistry and computational modeling detail the structure of the modified lignin and direct bioengineering strategies for targeted properties. Refinement of biomass pretreatment technologies has further facilitated lignin recovery and enables catalytic modifications for desired chemical and physical properties. Outlook Potential high-value products from isolated lignin include low-cost carbon fiber, engineering plastics and thermoplastic elastomers, polymeric foams and membranes, and a variety of fuels and chemicals all currently sourced from petroleum. These lignin coproducts must be low cost and perform as well as petroleum-derived counterparts. Each product stream has its own distinct challenges. Development of renewable lignin-based polymers requires improved processing technologies coupled to tailored bioenergy crops incorporating lignin with the desired chemical and physical properties. For fuels and chemicals, multiple strategies have emerged for lignin depolymerization and upgrading, including thermochemical treatments and homogeneous and heterogeneous catalysis. The multifunctional nature of lignin has historically yielded multiple product streams, which require extensive separation and purification procedures, but engineering plant feedstocks for greater structural homogeneity and tailored functionality reduces this challenge.

https://lifelong.unt.edu/sites/default/files/EmeritusCollege/Spring2015/Handouts/Lignin%20co-products.pdf

Lignin valorization: improving lignin processing in the biorefinery.

Lignocelluloses are often a major or sometimes the sole components of different waste streams from various industries, forestry, agriculture and municipalities. Hydrolysis of these materials is the first step for either digestion to biogas (methane) or fermentation to ethanol. However, enzymatic hydrolysis of lignocelluloses with no pretreatment is usually not so effective because of high stability of the materials to enzymatic or bacterial attacks. The present work is dedicated to reviewing the methods that have been studied for pretreatment of lignocellulosic wastes for conversion to ethanol or biogas. Effective parameters in pretreatment of lignocelluloses, such as crystallinity, accessible surface area, and protection by lignin and hemicellulose are described first. Then, several pretreatment methods are discussed and their effects on improvement in ethanol and/or biogas production are described. They include milling, irradiation, microwave, steam explosion, ammonia fiber explosion (AFEX), supercritical CO2 and its explosion, alkaline hydrolysis, liquid hot-water pretreatment, organosolv processes, wet oxidation, ozonolysis, dilute- and concentrated-acid hydrolyses, and biological pretreatments.

/pdf/pretreatment-of-lignocellulosic-wastes-to-improve-ethanol-zbwx58h962.pdf

Pretreatment of lignocellulosic wastes to improve ethanol and biogas production: a review.

http://www.loewenlabs.com/peter/wp-content/themes/atahualpa/Manuscripts/BA_29_675.pdf

Biomass pretreatment: fundamentals toward application

Developments in nanotechnology are leading to a rapid proliferation of new materials that are likely to become a source of engineered nanoparticles (ENPs) to the environment, where their possible ecotoxicological impacts remain unknown. The surface properties of ENPs are of essential importance for their aggregation behavior, and thus for their mobility in aquatic and terrestrial systems and for their interactions with algae, plants and, fungi. Interactions of ENPs with natural organic matter have to be considered as well, as those will alter the ENPs aggregation behavior in surface waters or in soils. Cells of plants, algae, and fungi possess cell walls that constitute a primary site for interaction and a barrier for the entrance of ENPs. Mechanisms allowing ENPs to pass through cell walls and membranes are as yet poorly understood. Inside cells, ENPs might directly provoke alterations of membranes and other cell structures and molecules, as well as protective mechanisms. Indirect effects of ENPs depend on their chemical and physical properties and may include physical restraints (clogging effects), solubilization of toxic ENP compounds, or production of reactive oxygen species. Many questions regarding the bioavailability of ENPs, their uptake by algae, plants, and fungi and the toxicity mechanisms remain to be elucidated.

/pdf/environmental-behavior-and-ecotoxicity-of-engineered-3ivmobaxr6.pdf

Environmental behavior and ecotoxicity of engineered nanoparticles to algae, plants, and fungi

Production of ethanol by bioconversion of lignocellulosic biomass has attracted much interest in recent years. However, the pretreatment process for increasing the enzymatic digestibility of cellulose has become a key step in commercialized production of cellulosic ethanol. During the last decades, many pretreatment processes have been developed for decreasing the biomass recalcitrance, but only a few of them seem to be promising. From the point of view for integrated utilization of lignocellulosic biomass, organosolv pretreatment provides a pathway for biorefining of biomass. This review presents the progress of organosolv pretreatment of lignocellulosic biomass in recent decades, especially on alcohol, organic acid, organic peracid and acetone pretreatments, and corresponding action mechanisms. Evaluation and prospect of organosolv pretreatment were performed. Finally, some recommendations for future investigation of this pretreatment method were given.

Organosolv pretreatment of lignocellulosic biomass for enzymatic hydrolysis

Lignocellulosic biomass is recalcitrant to biodegradation due to the rigid and compact structure of plant cell wall The recalcitrance of biomass is mainly constructed by its chemical compositions that build a spatial network as a protective bulwark Generally, the factors affecting the accessibility of biomass cellulose can be divided into direct and indirect factors The direct factors refer to the accessible surface area, and the indirect factors include biomass structure-relevant factors (pore size and volume, particle size, and specific surface area), chemical compositions (lignin, hemicelluloses, and acetyl group), and cellulose structure-relevant factors (cellulose crystallinity and degree of polymerization) Pre-treatment is actually the process to alter indirect factors and improve direct factors thus enhancing the accessibility of cellulose In this review, we summarize the effects of chemical compositions and physical structures on the enzymatic digestibility of lignocellulosic biomass We suggest that future work should be focused on but not limited to the molecular mechanisms of biomass recalcitrance by investigating the microscale and nanoscale features as well as hydrogen bonds network of lignocellulosic biomass © 2012 Society of Chemical Industry and John Wiley & Sons, Ltd

Biomass recalcitrance. Part I: the chemical compositions and physical structures affecting the enzymatic hydrolysis of lignocellulose

Production of 2,5-furandicarboxylic acid (FDCA) from 5-hydroxymethylfurfural (HMF): recent progress focusing on the chemical-catalytic routes

Transesterification of oil feedstocks using immobilized lipase (IL) is a promising process for biodiesel production. However, the running cost of this process is still higher than that of conversional chemical-catalyzed approaches. To address this challenge, both upstream and downstream processes have to be optimized. This review provides an overview of recent progresses in improving IL-catalyzed biodiesel production, focusing on mid- and down-stream processing such as immobilization of lipase, bioreactors development, process optimization, simulation and techno-economic evaluation. The immobilization of lipase is a costly process. Most of the commercial ILs are prepared by adsorption of free lipase on polymeric materials. However, to further reduce cost, works should be focused on developing cheap carriers and strengthening the interaction between enzyme and carrier but without significant loss of lipase activity. Running cost of lipase also can be reduced by improving its lifetime during transesterification. To achieve this goal, solvents can be used to prevent lipase leaching and eliminate the inhibitive effects of alcohol (usually methanol) and glycerol. Downstream processing includes important units to purify biodiesel products. In this part, works should be focused on minimizing energy consumption and waste effluents. A global process integration and optimization with economic evaluation also should be figured out to improve the economic feasibility of Il-catalyzed production of biodiesel.

Lipase-catalyzed process for biodiesel production: Enzyme immobilization, process simulation and optimization

A number of pre-treatment methods have been developed during the last few decades to overcome bio- mass recalcitrance. Although the mechanisms of these pre-treatments are different, the fi nal objective is the same - increasing cellulose accessibility to cellulase enzymes. Generally, pre-treatment is the process to disrupt the compact structure of lignocellulosic biomass and expose cellulose fi bers, which can be achieved by mechanical comminu- tion, chemical modifi cations of biomass compositions, biological degradation, or a combination of these methods. After pre-treatment, the accessible surface area is increased resulting in the enhancement of cellulose digestibility. In this paper, we review the recent progress of the fundamental researches of various biomass pre-treatment proc- esses, especially on how these pre-treatments alter chemical composition and physically change cell wall struc- ture. Understanding these changes would be helpful to further optimize existing pre-treatments, and would aid in developing novel pre-treatment methods.© 2012 Society of Chemical Industry and John Wiley & Sons, Ltd

Xuebing Zhao

Papers

Organosolv pretreatment of lignocellulosic biomass for enzymatic hydrolysis

Biomass recalcitrance. Part I: the chemical compositions and physical structures affecting the enzymatic hydrolysis of lignocellulose

Production of 2,5-furandicarboxylic acid (FDCA) from 5-hydroxymethylfurfural (HMF): recent progress focusing on the chemical-catalytic routes

Lipase-catalyzed process for biodiesel production: Enzyme immobilization, process simulation and optimization

Biomass recalcitrance. Part II: Fundamentals of different pre-treatments to increase the enzymatic digestibility of lignocellulose