P. K. Metreveli

Aromatic products of radiation-thermal degradation of lignin and chitin

Lignin and chitin degradation in the high-temperature radiolysis mode at ≤295°C has been investigated. Experimental conditions ensured the removal of low-molecular-weight products from the irradiation zone via volatilization. The formation of the low-molecular-weight aromatic products methoxyphenols and pyridine derivatives from lignin and chitin, respectively, has been shown. The yield of the distillable aromatic products was much higher than in the case of conventional dry distillation. It is noted that the mechanism of high-temperature radiolytic transformations of lignin and chitin differs from the mechanism of thermal transformations, which is due to the thermally stimulated degradation of radiation-induced radicals. It has been shown that high-temperature radiolysis opens a possibility for producing aromatic hydrocarbons at a lower dose rate and at lower temperature in comparison with conventional radiolysis and pyrolysis.

Radiation and postradiation distillation of biopolymers: Lignin and chitin

Lignin and chitin were decomposed in the regimes of postradiation dry distillation and distillation under conditions of radiation heating by accelerated electrons. The distilled off condensates consisted of two phases: brown viscous tar and lighter aqueous organic solution. The preliminary irradiation of lignin did not change the yield of distilled off tar, but it increased the fraction of alkoxyphenols in this tar. In the postradiation distillation of chitin, the yield of tar decreased with the dose. The effective distillation of biopolymers under radiation heating conditions was observed at dose rates higher than ∼1 kGy/s. The condensate distilled off at a dose rate of 1.5–2.5 kGy/s differed from the product of standard dry distillation in a higher yield of liquid organic products.

Formation of benzenediols upon electron-beam distillation of lignin mixtures with alkanes

In the process of the electron-beam distillation of lignin, its conversion into benzenediols increases in the presence of alkanes in the irradiated sample. An increase in the yield of benzenediols is accompanied by a decrease in the fractions of guaiacol, creosol, ethylguaiacol, and vinylguaiacol in the tar distilled off. It has been noted that alkanes serve as an additional source of atomic hydrogen and alkyl radicals, which, in turn, play a key role in the formation of benzenediols. In the presence of alkanes in the irradiated sample, guaiacol can be the main precursor of catechols; the proportion of guaiacol in the tar is almost three times below that in the case of distillation of individual lignin. It has been hypothesized that the chain decomposition of lignin can occur with the participation of •H and •CH3 radicals.

Effect of irradiation on aqueous dispersions of humic acids and lignin

The influence of electron-beam irradiation on the optical absorption of dilute aqueous solutions of lignin and humic acids has been studied. It has been shown that when the thickness of the irradiated layer of the solution is less than the electron range, preferential enlargement and precipitation of polyphenolic impurities observed. The most profound effect is achieved at doses of 5–15 kGy. When the irradiated-layer thickness is less than the electron range, the radiation-induced coagulation of impurities weakens. This effect can be due to the buildup of uncompensated charge of thermalizing electrons affecting the negatively charged micelles of polyphenolic impurities.

Phenolic products of the high-temperature radiolysis of lignin

The products of the radiation-stimulated dry distillation of coniferous hydrolytic lignin at a residual pressure of 1–5 torr have been obtained and analyzed. The tar distilled off under irradiation conditions predominantly contains phenols, including about 33% benzenediols. Among the benzenediols, the fraction of catechols is 69%. Phenoxyl radicals are considered to be direct precursors of the phenolic products. It has been found that the formation of benzenediols can be due to the rupture of the ether bond in the methoxy group. Among secondary processes, the reactions of the addition of •H and •CH3 radicals to the benzene ring have been considered.

Effect of absorbed dose on the postradiation dry distillation of cellulose and lignin

The postradiation dry distillation of cellulose and lignin has been studied. During the course of irradiation to 3 MGy, the weights of samples remained almost unchanged. The overpoints of lignin and cellulose irradiated at 2.2 MGy decrease by ∼80° and ∼100°, respectively. A third of the condensate from cellulose and almost a half that from lignin were distilled off at lower temperatures. Thermally unstable compounds are formed in cellulose; these compounds are predominantly converted into furans upon subsequent heating. The distillation of irradiated lignin affords a smaller amount of tar, but it is richer in methoxyphenols. The aqueous organic fraction distilled off has a higher concentration of soluble organic compounds.

Radiation-thermal transformations and distillation of lipids and disperse systems on their basis

The radiation-thermal transformations of rape oil under conditions of postradiation distillation, radiation heating, and electron-beam distillation with auxiliary heating were studied. Diesel hydrocarbons were predominant in the condensate distilled off upon combined heating. The concentration of oxygen atoms decreased as a result of radiation-induced decarboxylation and dehydration processes. The irradiation of oil as a constituent of disperse systems facilitated purposeful deoxygenation, a decrease in the viscosity, and an increase in the yield of the gasoline fraction.