N-modified compounds were obtained on the basis of previously isolated tannins from larch (T). The estimated composition of the compounds obtained was analyzed by FTIR spectroscopy and elemental analysis. The thermal degradation of larch tannin and its nitrated compounds, such as nitrile azotannin (ATN) and cationic azotannin (CAT), has been studied using thermogravimetry at three heating rates of 5, 10 and 20 degrees/min. Thermal stability of N-modified tannins depends on the nature of the introduced azogroups. The introduction of the azo group-N=N-into the aromatic structure of tannin increases its thermal stability. On the contrary, the presence of a quaternary ammonium group makes the structure of tannin decrease its thermal stability. The main stages, kinetics, and proposed mechanism of pyrolysis during the period of intensive release of volatile substances were determined. Kinetic analysis was performed using both model-free and model-based methods. The results of the study indicate the inaccuracy of model-free methods, in contrast to model-based methods, in relation to the description of the kinetics of thermal decomposition of tannin. The model-based method of Coats-Redfern revealed that within the temperature range of 200-350 degrees C, the thermal decomposition of the initial tannin is constrained by a chemical reaction, likely of the second order (E = 118 kJ/mol). The thermal decomposition of the ATN sample at the second stage of thermolysis (260-340 degrees C) also takes place under conditions of a chemical reaction, most likely of the first order (E = 53 kJ/mol). For the CAT sample, it is challenging to select a decomposition model unambiguously within the temperature range of 280-340 degrees C. Models of chemical interaction, diffusion, and nucleus growth show similar high regression coefficients (R-2 > 0.99).

The influence of the method of thermal- alkaline activation of biochars from larch bark with NaOH on the formation of the porous structure of active carbons was established. A comparison was made of the textural characteristics and sorption properties of the active carbon samples obtained by thermal- alkaline activation of the original and carbonized larch bark. The possibility of regulation of the textural, morphological and sorption properties of active carbons by varying the method of thermal alkaline activation of the bark is shown. The most effective development of the porous structure of active carbons was observed after thermal- alkaline activation (800 degrees C, 20 % NaOH) of larch bark subjected to carbonization at temperatures 400 degrees C and 600 degrees C. The specific surface area of these samples reaches to 546 m2/g and 501 m2/g, respectively. Active carbons obtained by thermal- alkaline activation (800 degrees C, 10 % and 20 % NaOH) of the original bark have less developed specific surface area (260 and 380 m2/g, respectively). Pre- carbonization of the bark also helps to increase more than double the yield of active adsorption capacity in relation to benzene (350 mg/g) is demonstrated by a sample of active carbon obtained by thermal- alkaline activation of bark, pre- carbonized at 400 degrees C, and in terms of methylene blue sorption (94 mg/g) - by a sample obtained from bark pre- carbonized at 600 degrees C.

We report on the kinetics of pyrolysis of bark wood of four coniferous tree species: fir (Abies sibirica), larch (Larix sibirica), spruce (Picea obovata), and cedar (Pinus sibirica) denoted as FB, LB, SB, and CB, respectively. Thermogravimetry (TG) and differential scanning calorimetry (DSC) methods were used to study the influence of KCl and K3PO4 compounds on the process of thermal decomposition of fir bark and determine the main thermal effects accompanying this process. As a result of the studies carried out, it was found that KCl additives practically do not affect the decomposition of hemicelluloses, but they shift the maximum decomposition of the cellulose peak in the direction of decreasing temperature to 340.9 °C compared to untreated bark (357.5 °C). K3PO4 promotes the simultaneous decomposition of hemicelluloses and cellulose in the temperature range with a maximum of 277.8 °C. In both cases, the additions of KCl and K3PO4 reduce the maximum rate of weight loss, which leads to a higher yield of carbon residues: the yield of char from the original fir bark is 28.2%, in the presence of K3PO4 and KCl it is 52.6 and 65.0%, respectively. Using the thermogravimetric analysis in the inert atmosphere, the reaction mechanism has been established within the Criado model. It is shown that the LB, SB, and CB thermal decomposition can be described by a two-dimensional diffusion reaction (D2) in a wide range (up to 0.5) of conversion values followed by the reactions with orders of three (R3). The thermal decomposition of the FB occurs somewhat differently. The diffusion mechanism (D2) of the FB thermal decomposition continues until a conversion value of 0.6. As the temperature increases, the degradation of the FB sample tends to R3. It has been found by the thermogravimetric analysis that the higher cellulose content prevents the degradation of wood. The bark wood pyrolysis activation energy has been calculated within the Coats–Redfern and Arrhenius models. The activation energies obtained within these models agree well and can be used to understand the complexity of biomass decomposition.

A suitable and relatively low-cost route for synthesizing pine polyphenol-based carbon xerogels is reported. It is proposed to produce porous carbon xerogels by carbonization of organic xerogels synthesized primarily by polycondensation of pine-derived polyphenols (tannins and organosolv ethanol lignin) with furfuryl alcohol. The effect of the tannin:furfuryl alcohol weight ratio on the structural porosity, apparent density, and adsorption capacity of the carbon gels has been established. The carbon gel obtained at a tannin/furfuryl alcohol ratio of 1:1.5 is shown to have the largest BET surface area (585 m2/g) and pore volume (0.7 cm3/g). It has been found that this sample is capable of adsorbing up to 0.83 g/g of benzene vapour at a temperature of 25 degrees C. Using scanning electron microscopy, it has been established that the addition of lignin into the tannin/furfuryl organic xerogel increases the size of particles forming the carbon gel matrix and the pore size.

The paper describes a promising route for the synthesis of novel organic xerogels from naturally occurring, renewable resources using pine-derived polyphenols as suitable initial precursors with relatively low cost. Methods of organic xerogels synthesis based on the use of condensed tannins and ethanol lignin isolated respectively from pine bark and wood are proposed. The effect of cross linking agent nature - formaldehyde or furfuryl alcohol on the porous structure of resulting organic tannin (lignin)-formaldehyde and tannin (lignin)-furfuryl xerogels was established. Denser tannin formaldehyde xerogels are subjected to shrinkage (up to 50 %) in processes of drying, and their bulk density ranges in 0.73-0.80 g/cm(3). Porous tannin-furfuryl xerogels almost do not shrink at drying and have bulk density 0.30-0.42 g/cm(3). The addition of ethanol lignin to the reaction mixture decreases the shrinkage of organic xerogels, whereas the addition of surfactant has a weak effect on the shrinkage. The chemical and porous structure of organic xerogels was investigated by FTIR, BET and SEM methods. FTIR results showed that lignin-containing xerogel possesses more numerous surface functional groups due to an inclusion of ethanol lignin in the gel structure. According to SEM, the three-dimensional network is characteristic for tannin-formaldehyde xerogels which is built from crosslinked polymer chains formed by globular particles with size about 40-50 nm. The tannin-furfuryl xerogels structure is formed by large agglomerates of particles with size up to 100-150 nm.

For the first time, it was proposed to obtain carbon gels by carbonization of organic gels synthesized by sol-gel condensation of formaldehyde with larch bark tannins and pine cellulose. According to the BET method, the introduction of cellulose into the composition of an organic tannin- -formaldehyde gel changes such characteristics of the porous structure of the obtained carbon gels as specific surface area, total pore volume, micropore surface area, micro-and mesopore volume, and average pore diameter. The development of the porous structure of carbon gels obtained with the use of dissolved cellulose additives (10 and 20 wt%) occurs as a result of the formation of mesopores with an average diameter of 22.83 and 21.54 nm. The introduction of cellulose aerogel powder into the original organic gel promotes the formation of micropores in the resulting carbon gel. The most developed microporous structure has a carbon gel obtained by carbonization of an organic tannin-cellulose gel containing 20 wt% cellulose aerogel (specific surface 754 m2/g, of which 80 % (606 m2/g) relates to the surface of micropores). Using scanning electron microscopy, it was found that the surface morphology of carbon gels obtained by carbonization of organic tannin-cellulose gels may be controlled by varying both the concentration of cellulose and its state (cellulose solution or cellulose aerogel powder) during the synthesis of the initial organic gel.

A new method for the synthesis of mixed organic gels based on larch bark tannins and pine wood cellulose, and formaldehyde as a crosslinking agent has been developed. The effect of cellulose content on the morphology, porous structure, thermochemical and adsorption properties of tannin -cellulose gels was studied by thermogravimetry, SEM and BET methods.The isotherms of nitrogen adsorption-desorption on tannin-cellulose gels correspond to materials with a predominantly mesoporous structure. In the case of samples prepared using a cellulose solution, the porous structure of the gels is represented by mesopores uniform in shape, with predominant sizes from 10 to 30 nm. In mixed gels prepared using cellulose powder, the predominant number of mesopores has 5-10 nm in size. The introduction of a cellulose solution in an amount of 10 and 20 wt% during the synthesis of tannin -formaldehyde gels increase their specific surface area from 4 m2/g to 87 and 118 m2/g, the volume of mesopores up to 0.39 and 0.50 cm3/g, and decrease their apparent density from 0.60 to 0.21 and 0.24 g/ cm3, respectively. According to scanning electron microscopy data, the gel containing 10 wt% cellulose has a more uniform three-dimensional structure than the sample containing 20 wt% cellulose. The rate of thermal decomposition of tannin-cellulose gel in the temperature range of 280-380 degrees C (-6.4 %/ min) is significantly higher than that of a cellulose -free tannin-formaldehyde gel sample (-1.4 %/min).

Organic xerogels based on lignin and tannins isolated from pine bark and wood were for the first time obtained by condensation with formaldehyde and furfuryl alcohol in the presence of hydrochloric acid. Sulfated pine ethanol lignin made it possible to obtain the first sulfur-containing (up to 1.3 wt

Firstly, the structure and properties of cellulose aerogels produced from birch-wood and cottoncellulose and of, and products of their sulfation with a non-toxic sulfamic acid-urea complex in an environmentally safe solvent – a mixture of polyethylene glycol and sodium hydroxide are compared. Aerogels based on birch and cotton celluloses have similar values of apparent density (0,071–0,078 г/см3) and porosity (near 95 %). The products of sulfating of cellulose aerogels, in contrast to the originalbirch and cotton celluloses, are completely soluble in water. Their yield and degree of substitution are higher when using birch cellulose aerogel. By drying the dissolved products of sulfating of cellulose aerogels, smooth and transparent films were produced. The structure and morphology of the obtained aerogels and films were established by metods of scanning electron microscopy and atomic force microscopy. Birch cellulose aerogel (BCA) has a reticular microfibrillated porous structure, and cotton cellulose aerogel (CCA) has a spongy structure in which more cavities and cracks are observed than in the case of CCA. The surface of the film of sulfated BCA is formed by particles with a length 100–200 nm and width of 50–70 nm, and the films of sulfated CCA is formed by spherical particles with a diameter of 70–100 nm. The developed methods for obtaining sulfated cellulose films can be used in medicine to oreate anticoagulant coatings

Porous carbon tannin–lignin/formaldehyde and tannin–lignin/furfuryl gels were prepared by carbonization of organic gels synthesized by sol–gel condensation of larch bark tannins and hydrolysis lignin with formaldehyde and furfuryl alcohol. The effect of lignin addition on the porous structure formation, apparent density, and adsorption and electrochemical properties of carbon gels was determined. Analysis by the Brunauer–Emmett–Teller method shows that the carbon gels are microporous materials with high specific surface area. Introduction of lignin into the initial organic tannin–formaldehyde gel favors an increase in the specific surface area of the carbon gel from 237 to 407 m2 g–1, to a decrease in the apparent density from 0.61 to 0.37 g cm–3, and to a decrease in the fraction of micropores in the total pore volume from 88 to 85.6%. The specific surface area of carbon tannin–lignin/furfuryl gels is somewhat higher than that of tannin–lignin/formaldehyde gels and reaches 512 m2 g–1 in a sample with 20% lignin content. The density of tannin–lignin/furfuryl gels increases from 0.17 to 0.32 g cm–3 with an increase in their lignin content from 10 to 30 wt %. Examination by scanning electron microscopy shows that the structure of carbon gels is a three-dimensional network of interconnected sphere-like particles of size varying from 20 to 100 nm. The tannin–formaldehyde and tannin–furfuryl gels with 10% lignin content are capable to adsorb 35.6 and 55.2 mg g–1 Methylene Blue, respectively. The tannin–lignin/furfuryl gel containing 10 wt % lignin shows the highest performance in benzene sorption (513 mg g–1). Electrochemical trials show that the tannin–lignin/formaldehyde gel with 30% lignin content exhibits the highest ability to accumulate the electric charge.

For the first time, tannin-lignin-formaldehyde and tannin-lignin-furfuryl organic gels were obtained on the basis of larch bark tannins and hydrolysis lignin by sol-gel condensation with formaldehyde and furfuryl alcohol. Their physico-chemical properties were studied by varying the content of lignin (from 5 to 30 wt%) and a fixed mass ratio of polyphenolic substances to the crosslinking reagent (1 : 1.5). With an increase in the lignin content the density of tannin-lignin formaldehyde gels decreases from 0.83 to 0.53 g/ cm3, and that of tannin-lignin-furfuryl gels is from 0.32 to 0.14 g / cm3. According to the FTIR data, the structures of tannin-lignin-formaldehyde and tannin-lignin-furfuryl gels are formed by aromatic fragments cross-linked with methylene and methylene-ether bridges. Scanning electron microscopy shows that the addition of appropriate amounts of lignin to tannins (up to 10 wt% when using formaldehyde and up to 20 wt% when using furfuryl alcohol) promotes the formation of gels with a more developed porous structure. In the case of tannin-lignin-formaldehyde gel, the specific surface area and sorption of methylene blue are 12 m2 / g and 43 mg / g and for tannin-lignin-furfuryl gel – 72 m2 / g and 114.5 mg/g, respectively. It was found that an increase in the lignin content in the gel composition over 20 wt.% is accompanied by the phase localization of lignin (precipitation), which reduces the strength of the resulting gel and reduces its specific surface area.

Methods of organic and carbon xerogels synthesis based on the use of condensed tannins isolated from abies bark were developed. Organic gels were synthesized by sol-gel condensation of tannins with formaldehyde in a solution of ethanol in the presence of catalysts (NaOH or HCl). The final gelation products were dried by alternating low (-18 – -40 °C) and room temperature to obtain tanninformaldehyde (TF) xerogels. FTIR study indicates that the formation of xerogels was accompanied by crosslinking reactions mainly due to the formation of carbon-carbon and alkyl ether bonds. Using the method of thermogravimetry, it was found that organic TF xerogels are thermally stable up to a temperature of 295 °C and they are resistant to ignition in air at temperatures up to 600 °C and can be used as thermo- and fire-retardant materials. Carbon tannin-formaldehyde xerogels were obtained by carbonization of organic xerogels at 800 °C in an argon atmosphere. The porous structure and surface morphology of organic and carbon xerogels was studied by BET- and SEM–methods. A significant development of the specific surface area (to 483–524 m2/g)as a result of the organic xerogels carbonization was established. Using SEM, it was shown that in carbon gels a spatially cross-linked structure of polymer chains consisting of 5-10 nmsized globule particles forming nanometer-sized pores is retained

The porous structure and sorption properties of carbon materials produced by thermochemical activation of the bast of birch bark with potassium hydroxide at 800°C have been studied. The effect of the amount of introduced KOH on the specific surface area of carbon materials obtained from bast was established. The selection of the optimal conditions for the preliminary carbonization of the bast was carried out, providing after thermal activation with KOH the formation of porous carbon materials with a specific surface of up to 2469 m2 g–1, a total pore volume of up to 1.085 cm3 g–1, a micropore volume of up to 0.84 cm3 g–1, and an average size pores less than 2.0 nm. It is shown that preliminary carbonization of bast at 500–580°С and subsequent activation with KOH at 800°С shifts the pore distribution in the resulting carbon materials towards smaller sizes (0.5–1.0 nm). It was found that carbon materials produced from heat-treated birch bast have a sorption activity for benzene, which exceeds the performance of foreign industrial carbon sorbents by 2.4 times and domestic active carbons of SKT-3 and SKT-10 grades by 3.4 times. Pre-carbonization of birch bast increases the yield of porous carbon materials by a factor of 3–4 compared to their yield when using untreated bast.

Carbon tannin-lignin-formaldehyde (TLF) gels were obtained for the first time by carbonization of organic xerogels synthesized by sol-gel condensation of formaldehyde with polyphenolic substances isolated from abies wood and bark – ethanol lignin and condensed tannins. The effect of the mass ratio of the tannins/lignin (T/L) components in the range 1:0 – 1:2 on the specific surface areas, porous volume, apparent density, and microstructure of carbon tannin-lignin-formaldehyde gels has been studied. It was found that the density of the carbon gels increases from 0.52 to 0.60 g/cm3 with a rises in the T/L ratio from 1:0 to 1:0.2 and 1:0.5 in the initial gel and then decreases to 0.20 and 0.13 g/cm3 with an increase in the lignin content to T/L ratios of 1:1 and 1:2, respectively. The study of the porous structure of carbon gels by the BET method showed that the carbon TLF gel obtained at a T/L ratio 1:2 is characterized by the highest specific surface area (538 m2/g). Using scanning electron microscopy, the structures of TF and TLF carbon gels have been studied. It has been established that the size of globular particles has a decisive influence on the structure of gels. The size of the globule particles increases with increasing of lignin content in the composition of the tannin-lignin-formaldehyde gel that leads to the formation of a less ordered structure of the carbon gel. The porous structure of TLF carbon gels obtained from abies polyphenolic substances can be regulated by varying the ratio of tannins:lignin. The obtained carbon gels can be used as sorbents and catalyst supports

The kinetic parameters of the pyrolysis of Siberian fir bark were estimated by thermogravimetric analysis. The thermochemical conversion of the bark biomass was performed at heating rates of 5, 10, and 20 deg/min in an inert (argon) medium. The results of thermogravimetric and differential thermogravimetric analyses were studied by model-fitting (Arrhenius and Coats–Redfern) and model-free (Friedman and Ozawa–Flynn–Wall) kinetic methods. The most reliable values of the activation energy were obtained by the model-free Ozawa–Flynn–Wall and Friedman methods (159 and 156 kJ/mol, respectively). It was shown that using these kinetic models enables one to determine more accurate temperature ranges of decomposition of biomass components under pyrolysis conditions.

Thermogravimetric (TG/DTG) methods have been used to study the thermal destruction of fir and aspen ethanol lignins at different heating rates in an inert (argon) medium. For each of the lignins, the main stages of thermal degradation were found under conditions of programmed heating of samples from 298 to 1173 K at heating rates of 5, 10, and 20 K/min. It was found that with an increase in the heating rate, the ranges of the main degradation of lignins expand. Shifts toward higher temperatures were 13.8 K for fir lignin and 21.1 K for aspen lignin. At the same temperatures, ethanol lignin from aspen showed a greater weight loss than fir lignin. Using the Ozawa–Flynn–Wall, Broido, and Redfern–Coats kinetic models, the results of the thermogravimetric analysis of the studied lignins are analyzed and the values ​​of the activation energy are calculated. The most reliable values of ​​the activation energy were obtained by the Ozawa–Flynn–Wall isoconversion method for the main temperature range of degradation (from ~569 to ~725 K): 113 kJ/mol for fir ethanol lignin and 106 kJ/mol for aspen ethanol lignin.