INFLUENCE OF ACID PRETREATMENT (H2SO4,HCL,HNO3) ON REACTION SELECTIVITY IN THE VACUUM PYROLYSIS OF CELLULOSE

Vacuum pyrolysis of acid-impregnated (H2SO4, HCl, HNO3) purified cellulose was carried out at a heating rate of 10-degrees-C min-1 and a constant final temperature (380-degrees-C). The average pressure was 130 Pa in the retort. The objective was to study the influence of inorganic ion content on the thermal decomposition of cellulose. The pH of the acid solutions (H2SO4, HCl, HNO3) used to impregnate the cellulose was adjusted (to 0.5, 1.0, 2.0, 4.0, or 7.0) to introduce 1-0.01 atoms of acid per 100 mol of anhydroglucose units of cellulose. The substrates and solid residues were characterized by X-ray scattering, elemental analysis, TGA and FT-IR. The qualitative analysis of the inorganic ion content of pretreated cellulose by X-ray scattering showed, in the case of H2SO4 and HCl pretreatments, that inorganic ions (SO42- and Cl-) were incorporated into the cellulose. Thermograms of pretreated cellulose showed that high contents of inorganic ions (SO42- and Cl-) accelerated the beginning of the weight loss and increased the char yield, whereas the weight loss profile for HNO3 pretreated celluloses was nearly the same at different pH values. The FT-IR spectra of H2SO4 and HCl pretreated celluloses showed that the bands corresponding to ring stretching increased at low pH (0.5), thus indicating that the pyranose ring was altered, No change was observed with the HNO3 pretreatment. Overall, the FT-IR information showed that the residual solids had an olefinic and carbonyl character. The carbonyl character of the residual solid was the same with the H2SO4 and HCl pretreatments at low pH (0.5, 1.0) and with all the HNO3 pretreatments. The anions (SO42- and Cl incorporated by the acid pretreatment into the cellulose induced the formation of high yields of char and water and low yields of pyrolytic oil. The inorganic ions favored the formation of hydroxyacetaldehyde, acetic acid and formic acid at the expense of levoglucosan. We observed no significant change in product yields for cellulose pretreated with HNO3.