Swedish chemists analyze burning wood residue from celluosic ethanol.

Increased environmental concern worldwide has shown the need for alternatives to the use of fossil fuels for transportation. Ethanol produced from renewable resources has the potential to be a valuable substitute for or complement to gasoline. Sugarcane juice and starch-based materials, such as grains from maize, wheat, and barley, are major feedstocks for the present production of fuel ethanol.1 Lignocellulosic materials, such as wood and forest residues, could, however, provide an abundant alternative raw material for fuel ethanol production if the
challenges associated with the hydrolysis and fermentation processes can be overcome. The two-stage dilute acid hydrolysis process is known to be an efficient method to hydrolyze lignocellulose polysaccharides to fermentable sugars2, which then can be metabolized to ethanol using yeast.

However, when producing ethanol from lignocellulosic material, a large quantity of non-hydrolyzed material is produced. About 40-45% of a wood-based feedstock is presently obtained as a residue, which mainly includes the lignin in the wood. For overall process economy, a profitable use for this residue needs to be found.3 One possible use of this hydrolysis residue is as raw material for the production of fuel pellets, especially since the raw materials presently used for fuel pellet production (mainly sawdust, planer shavings, and dry chips from the wood working industry) already are in short supply.

Previous work has also shown that softwood hydrolysis residue has a low fuel-ash content and that the fuel-ash has a relatively high initial deformation temperature.4 These fuel properties could make it attractive as a pellet fuel to be used in small-scale (residential) combustion appliances. Earlier investigations have also proposed that lignin acts as a glue in the pelletizing process of woody biomass and therefore is supposed to be responsible for the important self-bonding mechanism.5 However, the combustion characteristics of biomass may vary considerably depending on the composition of the raw material used. Previous studies have found that lignin during pyrolysis gives higher char yields than cellulose and hemicellulose.6 As a result of the softening, melting, and carbonization of the lignin during thermal conversion, the pores in the produced chars might be partially blocked7 and may therefore also have lower reactivity compared to chars produced from other biomass constituents. Only a limited number of studies have previously been performed for combustion of hydrolysis residue4,8,9,10 and none of them deal with the possibilities of using pelletized hydrolysis residue specifically in residential pellet appliances.