Evaluation of Analysis Methods for Formaldehyde, Acetaldehyde, and Furfural from Fast Pyrolysis Bio-oil

Fast pyrolysis bio-oil (FPBO), a second-generation liquid bioenergy carrier, is currently entering the market. FPBO is produced from biomass through the fast pyrolysis process and contains a large number of constituents, of which a significant part is still unknown. Various analytical methods have been systematically developed and validated for FPBO in the past; however, reliable methods for characterization of acetaldehyde, formaldehyde, and furfural are still lacking. In this work, different analysis methods with (HS-GC/ECD, HPLC, UV/Vis) and without derivatization (GC/MSD, HPLC) for the characterization of these components were evaluated. Five FPBO samples were used, covering a range of biomass materials (pine wood, miscanthus, and bark), storage conditions (freezer and room temperature), and after treatments (none, filtration, and vacuum evaporation). There was no difference among the methods for the acetaldehyde analysis. A significant difference among the methods for the determination of formaldehyde and furfural was observed. Thus, more data on the accuracy of the methods are required. The precision of all methods was below 10% with the exception of the HPLC analysis of acetaldehyde with an RSD of 14%. The concentration of acetaldehyde in the FPBO produced from the three different biomasses and stored in a freezer after production ranged from 0.24 to 0.60 wt %. Storage at room temperature and vacuum evaporation both decreased significantly the acetaldehyde concentration. Furfural concentrations ranged from 0.11 to 0.36 wt % for the five samples. Storage and after treatment affected the furfural concentration but to a lesser extent than for acetaldehyde. Storage at room temperature decreased formaldehyde similarly to acetaldehyde; however, after vacuum-evaporation the concentration of formaldehyde did not change. Thus, the analysis results indicated that in FPBO the equilibrium of formaldehyde and methylene glycol is almost completely on the methylene glycol side, as in aqueous solutions. All three methods employed here actually measure the sum of free formaldehyde and methylene glycol (FAMG)

Exploring Image Processing Tools To Unravel Complex ¹H-¹³C Heteronuclear Single-Quantum Correlation Nuclear Magnetic Resonance Spectra:A Demonstration for Pyrolysis Liquids

Pyrolysis liquids are very complex and heterogeneous in composition. This makes them hard to comprehensively analyze, which is one of the hurdles that could hinder further advances in science and technology toward their valorization. Recently, renewed interest grew for quantitative recording of two-dimensional 1H-13C heteronuclear single-quantum correlation (HSQC) nuclear magnetic resonance (NMR). This makes 1H-13C HSQC NMR a valuable tool to fingerprint and quantitatively assess these complex liquids. However, data analysis of complex 1H-13C HSQC spectra lacks behind on these recent experimental developments. That is, 1H-13C HSQC spectra are often manually and ad hoc analyzed. This work, therefore, seeks to automate data analysis from 1H-13C HSQC spectra. We explored the use of image processing tools and identified their much underestimated potential. Indeed, many of the existing tools (often built-in software) were found to be applicable for noise detection/removal, generation/comparison of regions of interest, etc. Moreover, pseudo-Voigt peaks were fitted to the 1H-13C HSQC spectra, with an average R2 of 0.94. These fitted spectral peaks allowed for the generation of a peak list, as an input for multivariate analysis. This allowed for pinpointing differences in the chemical composition of the samples. Overall, a new echelon for easy analysis of 1H-13C HSQC spectra has been explored and demonstrated.</p

Improving fast pyrolysis of lignin using three additives with different modes of action

Lignin holds the potential to obtain key monoaromatic compounds upon its depolymerization. Depolymerization of woody biomass by pyrolysis is well established but often unsuccessful for lignin due to a combination of its melting, agglomeration, and modest yields towards aromatics. Therefore, several lignin additives have been put forth to overcome one or more of these hurdles. Although some seem promising, a direct comparison is obscured by differences in applied technical lignin types, reactor configurations/scales, and product analyses. Moreover, the effects of additives have either been evaluated mostly on an analytical scale or their mode of action is not entirely understood. This work involves the addition of clays, calcium hydroxide and sodium formate to lignin, each having a different (putative) mode of action, in a well-defined and comparable manner. Organosolv lignin and lignin with additives were analysed by TGA/DSC and py-GC/MS. Pyrolysis was performed in a lab-scale reactor (350 g feeding). The pyrolysis liquids were characterised through elemental analysis, GCxGC-FID, GCxGC-HR-ToF-MS, GPC, and HSQC NMR analyses. All additives overcame melting issues and led to increased liquid yields but the most promising were attapulgite and calcium hydroxide. Lignin with attapulgite resulted in a heavy phase with the highest carbon yield (25.7%) and a substantial monomer yield (18.9%, mostly alkylphenols). Lignin with calcium hydroxide resulted in a heavy phase with the highest monomer yield (23.8%, mostly alkylphenols) at a substantial carbon yield (15.1%). The pyrolysis mechanisms for lignins with additives are elaborated and updated in this work

New insights into the base catalyzed depolymerization of technical lignins: A systematic comparison

A first systematic approach on the base catalyzed depolymerization (BCD) of five technical lignins derived from various botanical origins (herbaceous, hardwood and softwood) and covering the main three industrial pulping methods (soda, kraft and organosolv) is reported. This study provides a first of its kind in-depth quantification and structural characterization of two main BCD fractions namely lignin oil and lignin residue, describing the influence of the BCD process conditions. Depolymerization is evaluated in terms of lignin conversion, lignin oil yield, phenolic monomer selectivity and the production of lignin residue and char. Lignin oils were extensively characterized by size exclusion chromatography (SEC), GC-MS, GC-FID, 13C-NMR, HSQC NMR and elemental analysis. GC × GC-FID was used to identify and quantify distinct groups of monomeric compounds (methoxy phenols, phenols, dihydroxy-benzenes) in the lignin oil. The lignin oil yields (w/w) ranged from 20-31% with total monomer contents ranging from 48 to 57% w/w. SEC analysis indicated the presence of dimers/oligomers in the lignin oil, which through HSQC NMR analysis were confirmed to contain new, non-native interunit linkages. 13C NMR analyses of the lignin oils suggest the presence of diaryl type linkages (i.e. aryl-aryl, aryl C-O) evidencing deconstruction and recombination of lignin fragments during BCD. Irrespective of the lignin source, a residue, often regarded as ‘unreacted’ residual lignin was the main product of BCD (43 to 70% w/w). Our study highlights that this residue has different structural properties and should not be considered as unreacted lignin, but rather as an alkali soluble condensed aromatic material. HSQC, DEPT-135, 13C, and 31P NMR and SEC analyses confirm that the BCD residues are indeed more condensed, with increased phenolic hydroxyl content and lower molecular weights compared to all feed lignins. Subsequent BCD of solid residual fractions produced only low oil yields (6-9% w/w) with lower phenolic monomer yields (4% w/w) compared to original lignin, confirming the significantly more recalcitrant structure. Our study improves the overall understanding of the BCD process, highlights important feedstock-dependent outcomes and ultimately contributes to the complete valorization of BCD-derived lignin streams