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Paper text:
lignocellulosic biomass is typically nonedible plant material composed primarily of the polysaccharides cellulose and hemicellulose .
the third major component is lignin , a phenolic polymer that provides structural strength to the plant .
technology for producing biofuels ( such as ethanol , butanol , or various hydrocarbons ) and biobased chemicals from lignocellulosic material is experiencing significant advances in an effort to meet global energy and chemical needs ( 1 , 2 ) . examples of lignocellulosic biomass materials considered as feedstocks for bioethanol production include crop residues such as corn stover and wheat straw , woody residues from forest thinning and paper production , cool- and warm - season grasses such as switchgrass and fescue , and crops such as sorghum .
accurate feedstock compositional analysis enables evaluation of conversion yields and process economics due to changes in feedstock or process design .
accurate measurement of biomass carbohydrate content is of prime importance because it is directly proportional to ethanol yield ( l mg ) in biochemical conversion processes ( 3 ) .
the minor components in biomass can include protein , ash , organic acids , and other nonstructural materials .
although these individual components may make up only a small fraction of the feedstock , their presence will become significant in the running of an industrial - scale biorefinery . quantifying minor components
the purpose of this paper is to review the history and lineage of biomass compositional analysis methods based on a sulfuric acid hydrolysis .
we describe them in this paper and relate how they have progressed over time and give special emphasis to changes to the hydrolysis conditions . however , we discuss improvements to the instrumental analysis of biomass - derived sugars as well .
the methods appear to have originated as wood lignin isolation procedures and evolved into summative compositional analysis methods for biomass feedstocks .
the methods reviewed here utilize a strong sulfuric acid solution ( typically 72 wt % ) in a primary hydrolysis , followed by dilution with water and a secondary high - temperature ( 100125 c ) hydrolysis .
this procedure hydrolyzes the polymeric carbohydrates into soluble monosaccharides , leaving behind a lignin - rich residue that is vacuum - filtered and measured gravimetrically .
the liberated sugars in the hydrolysate solution are measured as monomers to quantify the carbohydrate fraction of the sample .
this hydrolysis procedure , when combined with a suite of other tests , provides a quantitative summative compositional analysis of lignocellulosic biomass , ideally accounting for 100% of the original material .
the composition of different feedstocks can vary greatly due to the complex and heterogeneous nature of biomass .
the composition of corn stover , for example , has been shown to be variable .
factors such as harvest year , environment , and variety result in glucan , lignin , or xylan values ranging up to 10% on an absolute basis ( 4 ) .
similar variations in component concentrations have been seen within the same corn plant between its anatomical fractions ( see ref ( 5 ) , p 1467 ) .
feedstock variability will affect process economics ; therefore , robust and accurate analysis methods are crucial to determining the chemical composition of feedstocks .
as we show below , researchers have applied these methods to measure the lignin and structural carbohydrate content of woody materials , estimate the nutritional value of animal feed , analyze the dietary fiber content of human food , compare potential biofuels feedstocks , and measure the efficiency of biomass - to - biofuels processes .
researchers have also worked to improve the methods by speeding the hydrolysis steps , using smaller sample aliquots , and using better sugar detection techniques .
we trace changes to the biomass compositional analysis methods through time to the biomass methods currently used at the national renewable energy laboratory ( nrel ) .
we also present our current suite of analytical methods ( laboratory analytical procedures or laps ) used at nrel for biomass compositional analysis .
included is a brief outline of each lap , as well as major interferences or pitfalls .
it is important to note that these outlines are not intended to be a complete description of the procedures ; rather , they are intended only as an overview .
complete procedures are available in the supporting information or from nrel ( 6 ) , and updates are posted to the website when available .
ase , accelerated solvent extraction ; astm , american society for testing and materials ; fpl , forest products laboratory ; iea , international energy agency ; lap , laboratory analytical procedure ; nist , national institute of standards and technology ; nrel , national renewable energy laboratory ; aoac , association of official analytical chemists ; tappi , technical association of the pulp and paper industry ; usda , u.s .
as interest in lignocellulosic biomass feedstocks for conversion into transportation fuels grows , the summative compositional analysis of biomass , or plant - derived material , becomes ever more important . 
 the sulfuric acid hydrolysis of biomass has been used to measure lignin and structural carbohydrate content for more than 100 years . 
 researchers have applied these methods to measure the lignin and structural carbohydrate contents of woody materials , estimate the nutritional value of animal feed , analyze the dietary fiber content of human food , compare potential biofuels feedstocks , and measure the efficiency of biomass - to - biofuels processes . 
 the purpose of this paper is to review the history and lineage of biomass compositional analysis methods based on a sulfuric acid hydrolysis . 
 these methods have become the de facto procedure for biomass compositional analysis . 
 the paper traces changes to the biomass compositional analysis methods through time to the biomass methods currently used at the national renewable energy laboratory ( nrel ) . 
 the current suite of laboratory analytical procedures ( laps ) offered by nrel is described , including an overview of the procedures and methodologies and some common pitfalls . 
 suggestions are made for continuing improvement to the suite of analyses .