Chemical Structure and Pyrolysis Characteristics of the Soda-Alkali Lignin Fractions

Abstract

In the present work, three different kinds of lignin fractions (L1, L2, and L3) were isolated from the alkali black liquor of Cunninghamia lanceolata by selective precipitation at the pH values of 8 (fraction L1), 5 (fraction L2), and 2 (fraction L3). Elemental analysis, gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT-IR), 31 P nuclear magnetic resonance ( 31 P-NMR), thermal gravimetric analysis (TG), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) were used to characterize the chemical structure and thermochemical properties of the three lignin fractions. The results showed that L1 presented higher heating value (HHV) and molecular weight compared with L2 and L3. The structures and functional group types were similar for the three lignin grades. However, there was more hydroxyl group in L1 than that in L2 and L3, and the L3 contained a higher amount of carboxylic hydroxyl. L1 exhibited the lowest weight loss value (47.8%) at 200 to 600 o C and the highest amount of charred residue (45.1%), which was exactly the opposite for L3. Phenols, the dominant pyrolysis products, constituted 92.17% of all the pyrolysis products for L1, 93.93% for L2, and 88.09% for L3.

Influence of reaction conditions on the composition of liquid products from two-stage catalytic hydrothermal processing of lignin

“…Literature shows that conversion of compounds with alcohol and ether functional groups to hydrocarbons often involves a dehydration step followed by a hydrogenation step [34][35]. Therefore, HDO of phenolics involves sequential hydrogenation-dehydration-hydrogenation steps and the conversion of aryl alcohols and ethers to hydrocarbons follow this mechanism.…”

Effect of Chemical Structure on Pyrolysis Behavior of Alcell Mild Acidolysis Lignin

“…This is because the reactive oxygen radicals generated from lignin degradation in the Alcell pulping process are easier to be shielded than those in soda pulping process. Though the total hydroxyl group content is slightly lower in Alcell than in Alkali MAL, it is higher than that in other reported lignins (Yang et al 2011;Li et al 2014). With high chemical activity, Alcell MAL and Alkali MAL could be further converted and utilized.…”

Analysis of Structural Units and Their Influence on Thermal Degradation of Alkali Lignins

“…The four alkali lignins isolated from the black liquors through the soda pulping in our laboratory (Li and Wu 2014) were poplar lignin (PL), fir lignin (FL), straw lignin (SL), and bagasse lignin (BL). The extraction process of lignins included mild acidolysis which put dilute acid solution into black liquor in order to adjust the pH to 2.0.…”

“…The initial degradation temperatures of PL and FL were higher than those of SL and BL. This is probably due to the higher degree of polymerization and molecular weight of wood alkali lignin (Parthasarathy et al 2013;Li and Wu 2014). The maximum devolatilization rate temperatures of the four alkali lignins were 403 °C for PL, 411 °C for FL, 336 °C for SL, and 383 °C for BL.…”