Reactivity of glucan and xylan in sorghum feedstocks: Comparing wild versus reduced lignin content lines and dilute acid versus deacetylation followed by dilute acid pretreatment

For biofuel production processes to be economically efficient, it is essential to maximize the production of monomeric carbohydrates from glucan and xylan of feedstock. This can be achieved by identifying less recalcitrant feedstocks by screening or by genetic modifications such as the brown midrib (bmr) genes to get feedstocks with reduced lignin content. This can also be accomplished by using a pretreatment enhancing the reactivity such as deacetylation. It is a dilute NaOH pretreatment enabling to remove the acetyl groups of xylan.

A laboratory-scale screening (ASE350) and a pilot-scale (Zipperclave) tool working at relevant biofuel process conditions have been used to compare the reactivity of near-isogenic bmr sorghum (Sorghum bicolor L. Moench) mutants to their wild type. The ASE350 has also been used to evaluate the effect on the reactivity of these feedstocks made by the deacetylation before 1.0% sulfuric acid pretreatment.

These bmr sorghums had a reduced lignin content compared to wild type. bmr mutants compared to wild type, deacetylation before dilute acid pretreatment and higher temperature of dilute acid pretreatment significantly increased the reactivity. On the analyzed sorghum samples, the dilute acid pretreatment severity needs to be higher on the Zipperclave to have a reactivity approaching the results obtained on the ASE350. It is not recommended to deacetylate a feedstock with high non-structural carbohydrates content if they are not recovered.