Analysis of by-product formation and sugar monomerization in sugarcane bagasse pretreated at pilot plant scale: differences between autohydrolysis, alkaline and acid pretreatment

Sugarcane bagasse is an interesting feedstock for the biobased economy since it contains a large fraction of polymerised sugars. A pretreatment is required to obtain the bagasse sugars in a fermentable state. In this research, three pretreatment conditions were used to acquire the bagasse sugars in their monomeric form: Autohydrolysis, Alkaline and Acid pretreatment. Experiments showed that Autohydrolysis and Alkaline pretreatment, followed by enzymatic treatment, monomerizes at least 65% of the sugars, while acid pretreatment monomerizes at least 80% of the sugars. By-products found after pretreatment included acetic-, glycolyic- and coumaric acid in concentrations up to 40, 21 and 2.5 g/kg dry weight bagasse respectively. Alkaline pretreated material contained up to 45 g/kg bagasse DW of sodium. Acid and autohydrolysis pretreatment results in a furan formation of 14 g/kg  and 25 g/kg DW bagasse respectively. These by-products can be inhibitory for micro-organisms during fermentation. Solid material was washed with superheated water to decrease the amount of by-products. Washing decreased organic acid, phenol and furan concentrations in solid material by at least 60%, without a major loss in sugar yield. All pretreatment methods were shown to have strengths and weaknesses. Overall, both acid and alkaline pretreatment combined with enzyme treatment were efficient in acquiring high amounts of monomeric sugars while limiting the amount of by-products formed.