Lignin In Aqueous Solution Research Articles

In Ukrainian

An important environmental problem is the removal of contaminants and the purification of domestic and industrial water from pollutants of various nature. There is a separate issue of cleaning the effluents of pharmaceutical enterprises. Various chemical and physical methods are used to solve these problems, such as settling, coagulation, filtration, and sorption techniques. Adsorption with using efficient and reusable adsorbents is the most effective and cheap. In recent years special attention has been paid to the use of sorption materials based on hydrolysis lignin, which has a high sorption activity in relation to ions of some heavy metals, dyes, organic compounds and pharmaceuticals. The use of lignin as an adsorbent simultaneously solves two problems: the disposal of paper production waste and the purification of sewage from various types of pollutants. The aim of this work was to study the sorption properties of hydroylysis lignin in aqueous solution in relation to some medical substances of different chemical nature, existing in solution in cationic, anionic or neutral forms. The point of zero charge of hydrolysis lignin was determined, which is equal to рНPZC = 4.95. The adsorption of rivanol, proflavin, doxorubicin, levofloxacin, furacilin, and salicylic acid by hydrolysis lignin was studied as dependence on the pH of the solutions and the concentration of adsorbates. It was found that adsorption largely depends on the structure of the pharmaceuticals and the pH values of the solutions. It is shown that the studied medical compounds, which exist in the solution in the form of cations, are adsorbed the best (rivanol, proflavin, doxorubicin). Adsorption of these substances occurs mainly due to electrostatic interaction with negatively charged surface groups. Adsorption of anionic form (salicylic acid) is the smallest and is observed only at quite low pH values. Levofloxacin is adsorbed mainly in the form of zwitter ions, and furacilin is in neutral form. The adsorption of these both compounds occupies an intermediate value of adsorption amount. The obtained adsorption isotherms are well lined up in Langmuir coordinates. Quantitative parameters of adsorption values - of maximum adsorption and equilibrium constants were calculated. Quite high values of these parameters indicate that hydrolysis lignin can be used as an adsorbent for the removal of these pharmaceuticals.

Selective Photocatalytic Transformation of Lignin to Aromatic Chemicals by Crystalline Carbon Nitride in Water–Acetonitrile Solutions

The photocatalytic conversion of lignin to aromatic compounds in aqueous solutions is a promising approach. We herein report a crystalline carbon nitride prepared by high-temperature thermal polymerization and alkali-metal molten salt treatment, which was then applied in the selective conversion of lignin to aromatic compounds. The results showed that the tri-s-tri-C3N4 presented a relatively high activity and selectivity for the conversion of lignin in aqueous solutions. In a 95% water-acetonitrile solution, it achieved a relatively high conversation rate of lignin, reaching 62.00%, and the selectivity of the C-C bond cleavage was high, at 86.8%. The characterization results obtained by TEM, UV-vis/DRS, PL, and transient photocurrent response showed that the ultra-high activity of tri-s-tri-C3N4 was mainly due to the improvements in crystallinity and light absorption. Mechanism studies showed that the dispersion of the catalyst and the combination of lignin and catalyst in aqueous solvents with different acetonitrile ratios were the main factors affecting lignin conversion. As the water content in the solutions increased, the primary active sites were converted from h+ to ·O2-. This study revealed the interactions between lignin, photocatalysts, and reaction solutions, providing a theoretical basis for the photocatalytic conversion of lignin in aqueous solutions.

Synthesis of lignin-poly(N-methylaniline)-reduced graphene oxide hydrogel for organic dye and lead ions removal

Lignin is one of the major contents of lignocellulose and can be used as feedstock for adsorbent materials for wastewater treatment. Here, a lignin-poly(N-methylaniline)-graphene oxide (lignin-PNMA-rGO) hydrogel has been prepared by a two-step method, microspheres of lignin-PNMA was synthesis by the polymerization of NMA monomer in the presence of lignin in aqueous solution, and then they were encapsulated by the as-prepared reduced graphene oxide (GO) hydrogel via a reduction induced self-assembly of the GO nanosheets.The scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and UV–Vis studies have been carried out and revealed that the formation of the 3D porous nanocomposite hydrogel with multilevel structures and sufficient active sites. The lignin-PNMA-rGO adsorbent exhibited high adsorption capacity for both organic dye methylene blue (MB, 201.7 mg/g) and Pb2+ ion (753.5 mg/g). The new lignin-based adsorbent is a low-cost, environmentally benign, which is an attractive adsorbent for wastewater treatment.

Hydrotropy and Cosolvency in Lignin Solubilization with Deep Eutectic Solvents

The mechanisms responsible for the good solubility of lignin in aqueous solutions of deep eutectic solvents are here investigated using both monomer model compounds and technical lignins (kraft and...

The aggregation structure regulation of lignin by chemical modification and its effect on the property of lignin/styrene–butadiene rubber composites

ABSTRACTThe aggregation structure of lignin in aqueous solution had an important effect on the dispersion of lignin and the properties of lignin/styrene–butadiene rubber (SBR) composites. This article revealed the relationship between aggregation structure and chemical structure of modified lignin. Unmodified lignin was amorphous; however, our results showed that aldehyde‐modified lignin was transformed into spherical aggregates, while propylene‐oxide‐modified lignin self‐aggregated into supramolecular domains. The relationships between aggregation structure, filler dispersion, filler–rubber interaction, and performance were also studied by investigating the microstructure, viscoelastic behavior, and mechanical properties of lignin/SBR composites. Meanwhile, a solution to improve the coprecipitation efficiency of lignin and SBR latex was proposed. In this article, epoxidized natural rubber (ENR) was also used as compatibilizer to improve the interfacial adhesion between polar lignin and nonpolar SBR. The results showed better lignin dispersion for the ENR‐containing rubber composites, as well as superior wet skid resistance and lower rolling resistance. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45759.

Influence of Temperature on Microstructure and Physicochemical Properties of Alkali Lignin in Aqueous Solution

Influence of Temperature on Microstructure and Physicochemical Properties of Alkali Lignin in Aqueous Solution

Kinetic Modelling of Hydrothermal Lignin Depolymerisation

Although lignin is one of the most abundant renewable organic materials in the world, it is principally a waste product of the paper industry which is used for the production of heat and power. Hydrothermal lignin depolymerisation aids in facilitating the valorization of lignin in aqueous solutions or suspensions. For the recovery of valuable phenolic products from lignin it is crucial to understand the main reaction pathways of lignin degradation and the reaction kinetics. Batch experiments were carried out for studying the depolymerisation of an enzymatic hydrolysis lignin from spruce wood in near critical water. Phenolic products were extracted from the aqueous phase and quantified via gas chromatography. The main reaction products were grouped (lumped), the main reaction pathways of hydrothermal lignin depolymerisation were discovered and formal kinetic rate coefficients were determined. Optimization of these formal kinetic parameters yielded a satisfying approximation of the experimental yields of phenolic products and describes the most important tendencies over temperature and residence time of solid residue and gas. The model is validated by the comparison with other kinetic studies of the degradation of lignin as well as the decomposition of intermediate phenolics, such as catechols and methoxyphenols.

Mechanism of the catalytic ozonization of lignin in the presence of Mn(II) ions

The reaction between ozone and lignin in aqueous solutions catalyzed by Mn(II) ions is studied. The rate of destruction for aromatic structures of lignin is found to increase in the presence of Mn(II) ions. However, the greatest catalytic effect is observed upon the transformation of aliphatic acids that are difficult to oxidize with ozone. The introduction of catalyst raises the total consumption of ozone from 3 to 7 mol per each structural unit of lignin. A scheme is proposed for the transformation of phenol fragments of lignin using ozone with the participation of Mn(II) ions: at the initial stage, we observe the ozone oxidation of lignin and Mn(II) to Mn(III) ions stabilized with products of lignin oxidation and accompanied by the formation of chelate complexes, and the Mn(III) chelate complexes act as low-molecular mediators, attacking phenol structures and initiating radical processes.

Characteristics and Properties of Soda Lignin Obtained from Aspen Wood By-Products

In the work, soda lignin was obtained under laboratory alkaline delignification conditions from aspen sawdust. The chemical composition and the surface-active properties of this lignin in aqueous solutions were studied. The high indices of Klason lignin and the content of methoxyl groups indicated the insignificant presence of non-lignin admixtures, including lignocarbohydrate complexes, in the purified lignin. It was shown that aspen lignin was a surface active substance, the surface activity of which at the water-air interface grew with falling the solution рН values. Simultaneously, with decreasing рН, the particle sizes of aspen lignin in the aqueous solutions increased, but zeta potential of the lignin particles had the tendency to decrease.

On the homogeneous catalysis of the photochemical and thermal O2-degrading of lignin in aqueous solution. Mechanistic observations on the processes catalyzed by AlIII(phthalocyaninetetrasulfonate)3− and CoIIIdimethylglyoximate complexes

We have explored in this work the photo- and thermally-induced degradations of water soluble lignin in aqueous homogeneous media. Coordination complexes, Al(III) phthalocyaninetetrasulfonate ([AlIII(tspc)]3− and tspc6−=phthalocyaninetetrasulfonate) and CoIII/II dimethylglyoximate (dimethylglyoximate=DMG−) were used as catalysts of degrading processes with different mechanisms. The photodegradation was induced with visible light, λexc⩾470nm, and [AlIII(tspc)]3− as the photosensitizer of the (3Σg−)O2 to (1Δg)O2 conversion. (1Δg)O2 was the primary active species of the degrading process. [Co(DMG)2(SO3)2]3− and [Co(DMG)2Cl2]− in the presence and absence of SO32− were used as catalysts of the thermal lignin degrading process. Differences in the mechanisms of the photo and thermally induced processes lead to some diversity of products. Adducts formed in solutions containing [AlIII(tspc)]3− and lignin have the absorption spectrum of phthalocyanine oligomers and could be located in pockets of the lignin. Under a steady state irradiation, the attack of lignin by (1Δg)O2 was followed by changes in the spectrum of the solution and by the formation of various products. The participation of O2·− radicals in the mechanism photodegrading process was investigated with the pulse radiolysis technique. Different lignin radicals were produced when pulse radiolytically generated O2·− and N3· radicals reacted with lignin. The CoIII/II dimethylglyoximate catalyzed lignin degrading process was investigated in the presence and absence of SO32−. Although the presence SO32− in the medium is not essential, it accelerates the degrading process. This observation shows the participation of inorganic S(V) radicals, e.g., SO3·−, as active species in the mechanism when SO32− is present. Moreover, the pulse radiolysis experiments demonstrate that O2·− can be an active species when SO32− is absent.

Water delignification by advanced oxidation processes: Homogeneous and heterogeneous Fenton and H2O2 photo-assisted reactions

The oxidation of lignin in synthetic aqueous solutions as well as in the biologically treated pulp-and-paper mill wastewater with hydrogen peroxide was studied in various methods: hydrogen peroxide UV-photolysis, homogeneous, heterogeneous and UV-assisted heterogeneous Fenton reactions, catalysed by FeZSM-5 zeolite. Contrasting the low-molecular organic contaminants, the oxidation of lignin in aqueous solutions was drastically slowed down in presence of heterogeneous FeZSM-5 zeolite, showing the superior performance of acidic homogeneous Fenton and hydrogen peroxide photolysis. This is explained by steric hindrance in oxidation of lignin with OH radicals on the catalyst surface and possible deactivation of lignin molecules adsorbed on the zeolite. The hydrogen peroxide photolysis among the studied delignification methods appeared to be the most efficient one in a wide range of pH.

Reaction between lead oxide and lignin in aqueous solution

The reaction between lignin and the surface oxide layer on Pb plates was studied by dipping experiments in ultra pure water with lignin, anodic polarograms in sulfuric acid solution with or without lignin and also scanning electron microscopy (SEM) observations of the sample surface after anodic polarization. It is found that the lignin reacts with the surface oxide on the Pb plates in ultra pure water with lignin to reaction products containing Pb and the lignin and they grew preferentially at the interface between Pb and the surface oxide. The deposits formed on the surface suppress to passivate the Pb surface under sulfuric acid solution.

Degradation of phenol, Asulam and lignin in aqueous solution by Ozonation

Abstract Phenol, the herbicide asulam (methylsulfanilyl carbamate) and lignin were degraded by ozonation. The addition of Fe3+ did not affect the disappearance rates of phenol and asulam appreciably, whereas UV illumination accelerated the disappearance rate. Fe3+ under UV illumination showed only a slight effect on the disappearance rate, but a fairly large effect on TOC elimination. The degradation of the intermediate compounds of asulam including aromatic compounds and organic acids, under UV illumination was accelerated by the addition of Fe3+. A possible degradation process of asulam by ozonation was proposed on the basis of intermediate and final products identified.

The radiation-induced degradation of lignin in aqueous solutions

Sodium ligno sulfonate in aqueous solution was easily degraded by gamma irradiation in the presence of oxygen, as evidenced by the disappearance of the characteristic absorption bands at 202.5 and 280 nm. The rate of their disappearance was accelerated by addition of N 2O. The total organic carbon (TOC) reduction was much larger for the oxygen-saturated solution than for the nitrogen-saturated solution. The TOC reduction increased linearly with dose in the early stages, for all dose rates in the range from 3 × 10 5 to 1.1 × 10 6 rad/hr. The pH of the oxygen-saturated solution dropped steeply at first with dose, and then became gradually higher above about 2 × 10 6 rad. In the presence of enough oxygen, the sodium ligno sulfonate molecule was degraded to lower molecular weight compounds, such as organic acids, and finally to carbon dioxide. An anomalous increase in visible color was observed in the oxygen-saturated solution with doses up to 2 × 10 6 rad; it decreased with further irradiation.