N. V. Chesnokov

Lignin conversion in supercritical ethanol in the presence of solid acid catalysts

The effects of sulfated ZrO2 and ZrO2-Al2O3 catalysts and acidic zeolite catalysts with various Si/Al ratios on the thermal conversion of alkali lignin in supercritical ethanol at 300–400°C and on the composition of the resulting products have been investigated. All of the catalysts enhance lignin conversion into liquid products. The strongest effect with the catalysts based on sulfated ZrO2 is attained at 400°C; with the zeolites, at 350°C. The catalysts diminish the concentration of phenol and its derivatives and increase the concentration of ethers (mainly the 1,1-diethoxyethane concentration) in the liquid products. The zeolite catalysts are preferable, since the reaction over the ZrO2-containing catalysts produces gaseous compounds in higher yields. The maximum lignin conversion and a high yield of low-boiling liquid products are achieved at 350°C with the zeolite catalyst with Si/Al = 30, which contains a high concentration of acid sites that are stable at elevated temperatures. The most abundant phenolic liquid products of lignin conversion over the zeolite catalysts at 350°C are methoxyphenols and their methylated and ethylated derivatives.

New methods of heterogeneous catalysis for lignocellulosic biomass conversion to chemicals

This review deals with the use of solid catalysts for the enhancement of the efficiency and the development of a new generation of environmentally friendly, energy and resource efficient processes for the deep processing of lignocellulosic biomass to desired chemicals. The oxidative delignification of wood with hydrogen peroxide in the presence of the suspended TiO2 catalyst, the oxidation of wood with molecular oxygen in the presence of copper catalysts, the acidcatalyzed conversion of cellulose to glucose and levulinic acid, and the thermal conversion of lignin to fuel additives on solid acid catalysts are analyzed. New integrated processes based on the heterogeneous catalytic oxidation are suitable for the complex processing of lignocellulosic biomass to produce valuable chemicals and engine fuel components without the use of toxic and corrosion-active reagents.

Formation of the pore structure of brown coal upon thermolysis with potassium hydroxide

The pore-structure characteristics of active carbons prepared by the thermolysis (800°C) of brown coal impregnated with potassium hydroxide were studied. The dependence of the specific surface area, total pore volume, micropore volume, micropore fraction, and micropore size distribution on the KOH/coal weight ratio RKOH ≤ 1.0 g/g was found. Condensation processes with the formation of a low-porosity material were predominant at low ratios of RKOH ≤ 0.1 g/g. The development of a micropore structure was observed at RKOH ≥ 0.1 g/g, and it increased as RKOH was increased to 1.0 g/g. It was hypothesized that pore formation was due to the thermally initiated reactions of the structural fragments of coal with KOH molecules, which occurred within the framework of coal.

Synthesis of porous carbon materials from birch sawdust modified with ZnCl2

Carbonization of birch sawdust modified with zinc chloride and selected properties of the resulting porous carbon materials were studied.

Porous carbon materials produced by the chemical activation of birch wood

It was established that the main factors responsible for the yield and specific surface area of porous carbon materials obtained by the chemical activation of the wood of birch are the nature of a modifying agent and the temperature of pyrolysis. The additional opening of the porous structure of the product of the chemical activation of wood occurs at the stage of its water treatment as a result of the removal of water-soluble compounds. The conditions of the carbonization of birch wood modified with H3PO4, KOH, and ZnCl2 were chosen in order to provide the significant development of the porous structure of carbon materials. The porous carbon material with the highest specific surface area (more than 2560 m2/g) was obtained by the water washing of the product of the carbonization of birch wood modified H3PO4 at 400°C.

Production and properties of porous carbon materials from chemically modified microcrystalline cellulose

Certain fundamental aspects of how the porous structure is formed in carbon materials produced by pyrolysis of microcrystalline cellulose modified with phosphoric acid, potassium hydroxide, and zinc chloride were determined. The above chemical promoters shift the onset of the process of intense thermal transformation of cellulose to lower temperatures and promote formation of porous carbon materials. Water treatment of porous carbon materials produced by pyrolysis of microcrystalline cellulose with high content of a promoter leads to additional pore opening due to the removal of the excess amount of the promoter and soluble products formed in its interaction with cellulose, which makes it possible to obtain porous carbon materials with specific surface area of up to 1500 m2 g−1.

Formation of the porous structure of carbon materials during carbonization of microcrystalline cellulose modified by phosphoric acid and potassium hydroxide

Formation of the porous structure of carbon material obtained by carbonization of microcrystalline cellulose (MCC) in the presence of modifying additives KOH and H3PO4 has been investigated. The optimal conditions for the synthesis of porous carbon materials (PCMs) from chemically activated MCC have been revealed. The highest specific surface area (about 1500 m2/g) is observed for water-washed carbon products obtained by carbonization at 800°C of MCC containing 50 wt % KOH and by carbonization at 400°C of MCC with the addition of 50 wt % H3PO4.

Chemical transformations of a SiO2-supported [Fe5RhC(CO)16]− cluster and catalysis of propylene hydroformylation

Chemical transformations of SiO2-supported [Fe5RhC(CO)16]− and [Fe4RhC(CO)14]− clusters in Ar, CO, and synthesis gas are studied by IR spectroscopy, Mössbauer spectroscopy, and transmission electron microscopy. It is shown that partial transformation of the [Fe5RhC(CO)16]− cluster to the [Fe4RhC(CO)14]− cluster occurs immediately after its deposition on the substrate surface with the simultaneous formation of Fe2+ ions. The complete conversion of the supported [Fe5RhC(CO)16]− cluster to [Fe4RhC(CO)14]− is observed at 323 K in the synthesis gas. At 373 to 423 K [Fe5RhC(CO)16]− transforms into a mixture of Fe4Rh2C(CO)16, [Fe4RhC(CO)14]−, and [Fe53Rh3C(CO)15]− clusters. In the 523 to 623 K range, the supported [Fe5RhC(CO)16]− cluster decarbonylates completely to form bimetallic species Å 5 Å in size. Silica-supported FeRh clusters are active in propylene hydroformylation at 423 to 473 K and form a mixture of butyl alcohols and butyraldehydes.

Thermal transformation of betulin by alkaline activation

Carbonization of betulin (betulinol) as an individual carbon precursor was studied in the temperature range of 400–800°C in the presence of KOH. Differential thermal analysis and IR spectroscopy were used to determine the influence of KOH on major structural changes and the chemical composition of betulin, which occur at 400–500°C. It was shown by scanning electron microscopy and BET analysis that KOH promoted the formation of a developed specific surface (SBET 1350–2100 m2/g) at temperatures of 600–800°C and had the greatest influence on the textural and adsorption properties of the resulting porous carbon adsorbents. It has been found that the formation of microporous carbon materials with a pore size of 1.92 nm and a specific micropore surface area of 1275 m2/g is possible upon the activation of betulin with KOH at 800°C. Betulin may be proposed to control the porosity of the carbon carriers derived from birch wood.

Production of porous carbon materials from bark

The effect of the conditions of consecutive carbonization–activation of the bark of larch, fir tree, and birch in a fluidized bed reactor on the yield, textural characteristics, and sorption properties of the resulting porous carbon materials was studied. The rate of temperature increase at the stage of the pyrolysis of bark exerted the greatest effect on the specific surface area, total pore volume, and sorption capacity of porous carbon materials for iodine and methylene blue. The porous carbon materials obtained by the slow pyrolysis (5 K/min) of larch bark with an isothermal exposure for 60 min at 600°C and the subsequent activation with CO2 at 850°C for 30 min were characterized by a maximum sorption activity. The porous carbon materials obtained from bark by consecutive carbonization–activation in a fluidized bed were similar to commercial powder sorbents from wood in their characteristics.