In this paper, the influence of some lignin features on its oxidative conversion to high-added-value phenolic aldehydes is discussed. Four softwood and three hardwood lignins are considered due to their different origins regarding the wood species, pulping process, and lignin isolation process. The lignins were characterized based on nitrobenzene oxidation (NO), frequency of phenolic hydroxyl (OHph) groups, and molecular weight determination, attempting to evaluate their potential to produce vanillin (V) and/or syringaldehyde (Sy) through the alkaline oxidation with oxygen. The raw-materials, Pinus spp. kraft lignin (LWest), Lignoboost kraft lignin (LBoostS), and Organosolv beech lignin (LOrgs) were selected to perform bench-scale oxidations with O2. These lignins contain lower content of nonlignin material and show higher yields of NO and high OHph groups content. In the oxidation with O2, LWest provide the highest production of V, 4.4% w/w (corresponding to 36% of NO yield). Considering the characteristics of LOrgs, an unexpected low Sy yield (2.5% w/w) was obtained (19% of the NO yield). The high reactivity of syringyl nuclei may be pointed out as the main reason for the faster production and degradation of Sy in oxidation. The concentration profile of products, the variation of pH in the reactive medium, and the variation of temperature with the reaction time of oxidation with O2 are shown and discussed with reference to the investigated lignins features.

No abstract

No abstract

Technologies and processes for lignocellulosic conversion in biorefineries are emergent subjects of research for which a reliable analysis of raw materials and quantification of yields of reaction products are required. This paper presents the development of an analytical method, using solid-phase extraction (SPE), for application to the reaction mixture of the oxidation of wood-derived lignin. The aim of the method is to extract the high value added aldehydes for quantification by high-performance liquid chromatography with ultraviolet detection (HPLC-UV). SPE and conventional liquid-liquid extraction (LLE) were evaluated and compared concerning recoveries and precision: (i) solutions of standard phenolic compounds (in alkaline medium and in lignin as matrix) and (ii) real samples and spiked real samples. The presence of lignin in the solutions decreases the recoveries of compounds from about 100% (no lignin) to 91% (for prepared solutions of lignin) and 94% (for real samples). This decrease was clearly evident with the increase of concentration of phenolic compounds in spiked real samples. The recovery averages and precision of SPE were higher than those of LLE and less affected by the presence of lignin. The results gathered and discussed in this work revealed SPE as an alternative to LLE: it is less time-consuming and has higher accuracy and precision for the quantification of phenolic compounds as reaction products of lignin oxidation.

No abstract