Abstract
BackgroundSteam explosion pretreatment has been examined in many studies for enhancing the enzymatic digestibility of lignocellulosic biomass and is currently the most common pretreatment method in commercial biorefineries. The information available about the effect of the explosive decompression on the biochemical conversion is, however, very limited, and no studies prove that the latter is actually enhanced by the explosion. Hence, it is of great value to discern between the effect of the explosion on the one hand and the steaming on the other hand, to identify their particular influences on enzymatic digestibility.ResultsThe effect of the explosive decompression in the steam explosion pretreatment of spruce wood chips on their enzymatic cellulose digestibility was studied systematically. The explosion had a high influence on digestibility, improving it by up to 90 % compared to a steam pretreatment without explosion. Two factors were identified to be essentially responsible for the effect of the explosion on enzymatic digestibility: pretreatment severity and pressure difference of the explosion. A higher pretreatment severity can soften up and weaken the lignocellulose structure more, so that the explosion can better break up the biomass and decrease its particle size, which enhances its digestibility. In particular, increasing the pressure difference of the explosion leads to more defibration, a smaller particle size and a better digestibility. Though differences were found in the micro- and nanostructure of exploded and non-exploded biomass, the only influence of the explosion on digestibility was found to be the macroscopic particle size reduction. Steam explosion treatments with a high severity and a high pressure difference of the explosion lead to a comparatively high cellulose digestibility of the—typically very recalcitrant—softwood biomass.ConclusionsThis is the first study to show that explosion can enhance the enzymatic digestibility of lignocellulosic biomass. If the enhancing effect of the explosion is thoroughly exploited, even very recalcitrant biomass like softwood can be made enzymatically digestible.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0567-1) contains supplementary material, which is available to authorized users.
Highlights
Steam explosion pretreatment has been examined in many studies for enhancing the enzymatic digestibility of lignocellulosic biomass and is currently the most common pretreatment method in commercial biorefineries
Influence of pretreatment severity on the explosion effect The biomass loading in the reactor varied between 12 and 32 %w/w depending on the pretreatment time and temperature, showing the high loadings that are possible in steam explosion
The applied explosion pressure differences of 10 and 18 bar can achieve a good defibration if pretreatment severity is higher
Summary
Steam explosion pretreatment has been examined in many studies for enhancing the enzymatic digestibility of lignocellulosic biomass and is currently the most common pretreatment method in commercial biorefineries. A steam gun is well suited to deal with large biomass particles reducing their size during the explosion step in an energy-efficient way [6,7,8], and the process is related to sulfite pulping, a technically mature large-scale process For all these reasons, continuous steam explosion pretreatments are dominating on a commercial scale [8]. Continuous steam explosion pretreatments are dominating on a commercial scale [8] It is a flexible technology which has proven effective for a great variety of lignocellulosic feedstock, including hardwoods, grasses and agricultural residues such as corn stover, sugarcane bagasse and wheat straw [2, 4, 9, 10]. Reducing softwood recalcitrance via (uncatalyzed) cost-effective steam pretreatment methods would, be of great benefit
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