(6d) Influence of Acids and Alkalis on Cellulose Pyrolysis Pathways and Kinetics

It has been suggested by a number of workers that cellulose pyrolysis proceeds (initially) by two competing, parallel reactions (β-elimination and transglycosylation). The mechanism shows the role of acid catalysis in the β-elimination (ring opening) reaction with the formation of levoglucosan solely via the alternative transglycosylation mechanism. It follows that if acids were present within the cellulose particles, during pyrolysis, the acids would tend to promote the ring-opening reactions (via β-elimination) at the expense of the transglycosylation pathway.

In this current work, we have studied the effects of acids (H₂SO₄, H₃PO₄ , H₃BO₃) and alkalis (Ca(OH)₂, NH₄OH) on the yields of levoglucosan and its derivatives levoglucosenone, 1,4:3,6-dianhydro-α-d-glucopyranose, anhydroglucofuranose, hydroxymethyl furfural, furfural and levulinic acid). Results indicate that generally higher acid loadings lowered levoglucosan production whilst, the alkali treatment increased the levoglucosan yield.

Kinetics experiments (via thermogravimetric analysis) have also been conducted to quantify the preference of β-elimination or transglycosylation by evaluating the respective pathway activation energies.