Formaldehyde from Lignin Acidolysis Might Be Useful for In-Line Control of Industrial Biomass Processing

Abstract

Wood processing typically involves heating that generates lignin-borne formaldehyde, a well-known aspect of lignin acidolysis that played an important role in early efforts to elucidate lignin structure. Previously, we found that lignin-borne formaldehyde accounts for a small percentage of lignin acidolysis. This is explained by two competing lignin acidolysis pathways, C2 cleavage producing formaldehyde, and C3 cleavage (no formaldehyde). Here, the topic was studied with industrial-scale thermomechanical refining of Douglas fir wood, seeking correlations between refining energy and fiber chemistry and rheology. Refining caused substantial polysaccharide degradation accompanied by lignin acidolysis, the latter determined by nitrobenzene oxidation, titration of free phenols, and determination of formaldehyde captured in dried fiber. Formaldehyde generation (C2 cleavage) accounted for only 1% of the total loss of β-aryl ethers (C2 + C3 cleavage). This could imply that lignin-borne formaldehyde always results from lignocellulose thermal processing, raising possibilities for industrial process control using in-line formaldehyde monitoring. That requires future verification and correlation of formaldehyde generation with biomass properties. In this case, measured formaldehyde levels correlated with refining energy, reductions in the in situ lignin glass transition temperature, and reductions in lignin oxidative decomposition temperature.

Catalytic Acidolysis: Impact on In Situ Pine-Lignin Repolymerization

“…34−36 According to Martin-Sampedro et al, the second peak temperature indicates the state of in situ lignin cross-linking, where higher peak temperatures signify more lignin cross-linking, and vice versa. 37,38 Table 4 partially supports this claim where it shows that, relative to the unheated control, all heat treatments significantly increased the second peak temperature. It is recalled that DSC and SEC indicated significantly different cross-linking levels in MWL from pinewood heated with HCl or H 2 SO 4 , being the greatest in the latter.…”

“…Above the presumed dehydration near 100 °C, oxidative dTGA revealed two peaks, one near 350 °C (first peak) and another near 500 °C (second peak). Some have claimed that the first and second peaks, respectively, reflect the separate degradation of polysaccharides and lignin. , However, it has been shown that this interpretation is too simplistic, particularly for the second peak which reflects multiple events. − According to Martin-Sampedro et al, the second peak temperature indicates the state of in situ lignin cross-linking, where higher peak temperatures signify more lignin cross-linking, and vice versa. , Table partially supports this claim where it shows that, relative to the unheated control, all heat treatments significantly increased the second peak temperature. It is recalled that DSC and SEC indicated significantly different cross-linking levels in MWL from pinewood heated with HCl or H 2 SO 4 , being the greatest in the latter.…”

“…34−36 According to Martin-Sampedro et al, the second peak temperature indicates the state of in situ lignin cross-linking, where higher peak temperatures signify more lignin cross-linking, and vice versa. 37,38 SO 4 , being the greatest in the latter. Consequently, in this work, it seems that oxidative TGA can detect and distinguish low-to-moderate levels of in situ lignin cross-linking, but the highest levels cannot be differentiated.…”

Synthesis of a high-density jet fuel with creosol and formaldehyde

“…7 Third, formaldehyde can also be obtained from the acid hydrolysis of lignin. 8 In the previous work by our group, 9 it was found that jet fuel range polycycloalkanes could be obtained from the hydrodeoxygenation of bisphenols that may be produced with phenol, a model compound that can be obtained from the hydrogenolysis of lignin. To the best of our knowledge, there is no report about the synthesis of polycycloalkane from lignin-derived phenols that were connected with other functional groups (such as -OCH 3 group and alkyl group).…”