The influence of mass transfer intensity on the kinetics of the catalytic oxidation of flax shives with oxygen in alkaline media to aromatic aldehydes and pulp was studied. The process was carried out in two autoclaves, with moderate stirring (stirrer engine of 8 W) and intense stirring (stirrer engine of 200 W). The oxidation of flax shives into vanillin, syringaldehyde, and pulp was shown to proceed as a completely diffusion-controlled process under the studied conditions, both moderate and intense stirring. Depending on the process conditions, it can be limited by stages of oxygen transfer through the diffusion boundary layer near the gas–liquid interface (low intensity of mass transfer) as well as by reagents’ inner diffusion in the porous and solid matter of the flax shive particle (high intensity of mass transfer). The results on the influence of the stirring speed and volume of the reaction mass on the rates of oxygen consumption and vanillin accumulation were obtained. They were described using a known simple model connecting the intensity of mass transfer and the stirring power density in the bulk of the liquid phase in terms of algebra equations.

This research deals with a process of catalytic oxidation of flax shives to vanillin and pulp. Catalytic oxidation of flax shives with molecular oxygen allows two main products to be obtained—vanillin with a yield of up to 12 wt.% of lignin, and pulp. Final forms of the catalyst particles (Cu₂O and CuO) are agglomerates or monocrystals 0.5–5 µm in size. Acid prehydrolysis of the shives does not affect the oxidation, in contrast to pine-wood oxidation. Lignin prehydrolysis and oxidation was suggested as illustrate this difference. The dependence of the vanillin formation rate on stirring speed was studied. Minimum alkali consumption in the process was attained with a mild stirring speed of the reaction mass.

Agrotechnical wastes from processing herbaceous plants consist of lignin and polysaccharides, which can be processed into monomers – phenols and carbohydrates. The prospects of chemical processing of several agrotechnical waste types with a high lignin content (flax shives, sunflower seed husks and buckwheat husks) into vanillin, pulp, and glucose by oxidation and acid hydrolysis were studied. It has been shown that despite the distant phylogenetic relationship of the studied plants, their lignins have a similar structure: they contain a similar amount of methoxyl groups (10–13 wt.% per lignin) and give close yields of aromatic aldehydes upon oxidation with nitrobenzene (17–19%) and oxygen (14–16%). In general, the suitability of agrotechnical wastes for oxidation to aromatic aldehydes determines by the lignin content. Among the studied wastes, flax shives are the most promising feedstock for chemical processing into vanillin and glucose. Cellulose-containing solid residues of oxidation process are more easily hydrolyzed compared to the initial lignocellulosic biomass. The inversion of glucose oligomers during the hydrolysis of cellulose with H2SO4 is limited by the hydrolysis of the tetra- and octamers.

The growth-promoting activity of lignoacids (LA), by-products of the catalytic oxidation of flax shives into vanillin and cellulose, was studied. The growth-promoting activity of LA was estimated on radish seeds Raphanus sativus var radicula in laboratory conditions, as well as in soil in pots and open soil. It was shown that on filter paper low concentrations of LA (5–20 mg/l) significantly accelerate the germination of radish seeds, the average plant root and hypocotyl length are 1.5–3 times higher than with control solutions (water and sodium bicarbonate). The growth-promoting activity in pot experiments is preserved. In experiments on open soil the estimation of mass characteristics of plants and root crops was shown that the greatest growth-promoting effect is observed at a LA concentration 5 mg/l. The average values of plant mass increase by 70–180%, and root crop mass – by 140–150%.

The growth-promoting activity of lignoacids (LA), byproducts of the catalytic oxidation of pine and aspen wood to vanillin and cellulose, was studied. The use of LA opens the possibility of recycling wastewater from the catalytic processing of wood. The growth-promoting activity of LA was assessed on radish seeds Raphanus sativus var. radicula under laboratory conditions during germination on filter paper; germination energy, germination rate, and root and hypocotyl lengths were determined. The growth-promoting activity of LA was compared to radish seed germination in water and potassium bicarbonate solutions. It was shown that LA isolated during pine wood oxidation at concentrations of 5–40 mg/L exhibited a more pronounced growth-promoting effect compared to lignoacids isolated from aspen wood oxidation reaction solutions. It has been established that the growth-promoting effect increases in the order LCOsins < Pine LKS < Flax shives. This corresponds to a decrease in the content of methoxyl groups in various lignins. Lignoacids released during the oxidation of lignins from herbaceous plants and agricultural waste appear more promising for use as growth stimulants.

Kinetics of fir wood oxidation (Abies sibirica) in aqueous alkaline media were studied by measuring oxygen consumption rates. Oxidation of extracted wood conforms to the kinetics of non-branching chain mechanism. The same mechanism governs the initial stage of non-extracted wood oxidation, but a transition to degenerate branching mode soon occurs. This transition is probably caused by softwood's low hemicelluloses content and high content of propyl guaiacol lignin units that are prone to condensation involving phenolic hydroxyls. This leads to quick depletion of phenolic and uronic carboxylic groups; chain initiation by oxidizing the respective anions becomes impossible, and degenerate branching takes the lead. It is assumed that inert hydrophobic fir extractives physically shield hydroperoxides responsible for degenerate branching from alkali. This prevents alkali from causing heterolytic hydroperoxide cleavage that does result in chain branching. It is assumed that the catalyst accelerates the reaction of homolytic cleavage of the aforementioned hydroperoxides