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The paper presents a research on the disposal of the toxic waste of pulp and paper mill (sludge-lignin with the empirical formula CH1.51N0.05S0.03Cl0.01O0.54through its oxidation in supercritical water-oxygen fluid, including the case of using methane as a co-fuel. The experiments were carried out with a flow reactor of original design at a pressure of 25 MPa, temperature gradient along the vertical axis (from top to bottom: 390–600°C), and variation in the flow rate of the sludge-lignin (with the addition of NaOH, 1.6 wt %), oxygen, and methane. The experiments yielded data on the content of phenols in the water and the composition of the gaseous products collected at the outlet of the reactor versus the oxygen excess ratio. From these data, as well as the time dependences of the reactor wall temperature and the power of the ohmic heaters, it follows that using distributed supply of methane to compensate for the energy for heating of the reagents is preferable as compared with local inlet of methane to the upper part of the reactor. It has been shown that the addition of methane makes it possible to reduce the oxygen excess required for complete oxidation of the organic components of sludge-lignin.

The paper presents the results of investigation of the products of oxidation of sludge-lignin (waste from the Baikal pulp and paper mill) in H$$_{2}$$O/O$$_{2}$$ mixture in the autoclave and semi-flow modes at uniform heating of the reactor up to 750 K. The time dependencies of the reactor wall temperature and the power of ohmic heaters imply that the oxidation starts at 440 K and the maximum oxidation rate is realized at 583-643 K. Mass spectrometry measurements of the composition of the volatile products yielded the temperature dependency of the degree of removal of carbon occurring in CO and CO$$_{2}$$ from sludge-lignin. Using physical and chemical methods of analysis it was shown that Al$$_{2}$$O$$_{3}$$ (AlOOH in the autoclave mode), Fe$$_{2}$$O$$_{3}$$, SiO$$_{2}$$, AlPO$$_{4}$$, and CaSO$$_{4}$$ were major components of the residue after the sludge-lignin conversion. Formation of HCl and H$$_{2}$$SO$$_{4}$$ in the course of oxidation of chlorine- and sulfur-containing organic compounds was found to cause corrosion of stainless steel.

—The combustion of hydrogen in its stoichiometric mixtures with oxygen diluted with water vapor, carbon dioxide, and nitrogen at 2.6 MPa was studied. The experiments were performed in a slowly and uniformly heated (1 K/min) tubular stainless steel reactor. The process occurred via conjugate heterogeneous (on the reactor wall) and homogeneous (in the reaction mixture) oxidations. The heterogeneous oxidation of H2 prevailed in N2 and CO2, while the homogeneous oxidation was predominant in H2O. Based on the time dependences of temperature rise caused by the exothermic oxidation of hydrogen, it was found that the self-ignition temperature of the Н2/О2/N2 and Н2/О2/H2O mixtures was ~30 K lower than that of the Н2/О2/СО2 mixture. A small water addition to the H2/O2/N2 and H2/O2/CO2 mixtures led to a decrease in the self-ignition temperature.

The paper presents investigation results on propane combustion in argon, carbon dioxide, and water vapor under the conditions of O2 deficiency and high reagent density when they are uniformly heated up to 620 K. Based on time dependences of reaction mixture temperature, the self-ignition temperature of propane was determined. It has been established that the oxidation of propane in an Ar and H2O medium proceeds according to the mechanism of chain-thermal explosion. The results of mass spectrometric analysis showed that oxidation in a CO2 medium is characterized by the lowest degree of propane conversion. It was also found that at a low density of water vapor, the oxidation of propane is accompanied by a high yield of H2. The mechanisms of CO2 and H2O molecule participation in the oxidation of propane are discussed in the paper.

The effect of supercritical water and pyrite on the transformations of propylene upon the uniform heating (1.5 K/min) of reagents to 718 K is studied. The products are analyzed by IR and 1H NMR spectroscopy, mass-spectrometry and gas chromatography/mass-spectrometry. It is established based on the temperature dependences of the pressure of reagents that the addition of pyrite in the absence of water gives rise to a decrease in the starting temperature of propylene oligomerization. In the absence of pyrite, the addition of water suppresses propylene oligomerization. A synergetic effect of supercritical water and pyrite on the degree of conversion of propylene is revealed. It is shown that hydrogen sulfide, thiols, and methyl-derivatives of thiophene are formed in the presence of pyrite, as well as the yield of aromatic and polyaromatic hydrocarbons increases. The mechanisms of the observed processes are discussed.

The oxidation of isobutane at high density of reagents in a mixture of i-C4H10/O2/H2O and i-C4H10/O2/CO2 with oxygen deficiency (a molar ratio [O2]0/[i-C4H10]0 = 3.5–5.8) has been studied for the first time. The experiments were carried out in a tubular reactor under uniform heating (1 K/min) to 590 K. Data on the kinetics, auto-ignition temperature, and the products of isobutane conversion have been obtained. The auto-ignition was found to be a two-stage process and begin at a temperature of 510–522 K. The heat capacity of the reaction mixture suppressed the autoacceleration of the oxidation. Mass spectrometric analysis of the reactants revealed a difference in the mechanisms of isobutane conversion in water vapor and carbon dioxide. In water vapor, the oxidation is dominant and is realized with the participation of vibrationally excited O*2 molecules, which appear mainly from resonant exchange with H2O* molecules. In the CO2 medium, the oxidation proceeds against the background of intense isobutane dissociation, initiated by the vibrational pumping of i-C4H10 molecules in their resonant excitation by CO*2 molecules.

The composition of volatile and solid products of oxidation of hydrogen sulfide and stainless steel in gas mixtures containing H2S, O2, H2O, and CO2 has been determined using mass spectrometry, x-ray diffraction analysis, and scanning electron microscopy. It has been shown that holding an H2S–O2 mixture at 301 K results in prevailing formation of elemental sulfur and iron sulfides in the form of porous hygroscopic crust on the reactor wall surface. Formation of gas-phase sulfur causes self-acceleration of the oxidation of hydrogen sulfide; the resulting water triggers corrosion of the reactor wall. Heating of the resulting sulfur-sulfide crust in O2 medium is accompanied by formation of SO2 and heat release at T > 508 K. After heating of the H2S–CO2 mixture to 615 K, H2 and COS were found in the volatile reactants; no noticeable corrosion of the reactor wall has been detected. It has been established that addition of O2 to the H2S–CO2 mixture and its heating to 673 K leads to formation of ferrous sulfates. The mechanisms of the observed processes are discussed.

The oxidation of brown coal continuously fed as part of a coal–water slurry into a counterflowing stream of a supercritical water–oxygen fluid at a temperature difference along the reactor axis of 673–873 K and a pressure of 30 MPa has been studied. It has been found that, in the case of a partial combustion of coal (under conditions of O2 deficiency), the yield of hydrogen-enriched products increases owing to heat evolution. Under conditions of excess O2, coal undergoes complete oxidation. In this case, the heat evolved per unit volume of furnace space is about 1.0 MW/m3. It has been shown that the heat consumed for the implementation of the process using external sources can be partially or completely compensated for by heat evolution during homogeneous and heterogeneous combustion coupled with coal thermolysis.

The article reports the conversion of tar (empirical formula CH1.47N0.01S0.007) continuously introduced into a counter flow of supercritical water (SCW) at 30 MPa in a tubular reactor with a temperature gradient along its vertical axis (450°C at the top and 650°C at the bottom). The yields of liquid products and volatile (C1–C9) hydrocarbons are 41.4 and 28.4%, respectively, relative to the weight of tar supplied into the reactor. Methane is the major component (40.5 mol %) of the volatile products, and the liquid products are dominated by oils (74.4 wt %). Deasphaltization and desulfurization of tar conversion products are observed. The average rate of water decomposition calculated from the quantity of O atoms in the conversion products is 0.24 g/min. Use of counter flows of the reactants in combination with a temperature gradient along the reactor axis affords a higher yield of low-boiling hydrocarbons than in the case of SCW pumping through a tar layer.

The paper represents results on investigation of methane oxidation in supercritical water (SCW) in autoclave and flow conditions. In the autoclave, oxidation is realized under uniform heating of a CH4/O2/H2O and CH4/O2/N2 mixture to 873 K (the water and nitrogen density ≈ 3.2 mmol/cm3, the molar ratio [O2]0/[CH4]0 ≈ 1 and 2). In the composition of the oxidation products we detected H2 (only at [O2]0/[CH4]0 ≈ 1), CO and CO2. Based on time dependences of the reaction mixture temperature we have found that temperature of the onset of self-heating of the CH4/O2/H2O mixture is lower by 23 K than that of the CH4/O2/N2 mixture and grows as the CH4 concentration decreases. For comparable values of self-heating the average power in CH4 combustion in the H2O medium has appeared to be about two orders lower than in the N2 medium, which evidences inhibition of SCWmethane oxidation. In the boiler-reactor, oxidation was realized while mixing CH4 and O2 in counter-propagating jets in the cocurrent upflow of SCW at 673–874 K, 30 MPa (molar ratio [O2]/[CH4] ≈ 2.2). Unsteady combustion was observed only at a reaction mixture temperature of 678 K, which became steady at 700 K after a series of flashes. The carbon-bearing methane oxidation products in the boiler-reactor contain only CO2 (≥ 97.5%) and CO (≤ 2.5%mole).

The autothermal regime of partial oxidation of carbonized coal residue in a stream of water-oxygen fluid at 923 K and 30 MPa is implemented for the first time. It is revealed that the oxidation of coal residue and the formation of combustible gases (hydrogen content in the products is increased by 26% with respect to its amount in the original sample) occur simultaneously and are caused by the participation of the H2O molecules in the redox reactions.

The presence of a constant electric field (300 kV m–1) and variation of CO2 concentration in the fluid affected the morphology of ZnO nanocrystals and the internal structure of ZnO layer obtained on interacting zinc anode with supercritical H2O/CO2 at 673 K and 35 MPa. The electric field favors the formation of zinc oxalate and carbonate, the thermal decomposition of which forms the pore structured of ZnO. Moreover, a fraction of elongated nanocrystals in the surface layer of ZnO is increased due to the action of the electric field.

The yield and composition of conversion products are investigated in a layout that provides countersupply of reagents (brown coal, supercritical water (SCW), and O2) into a vertical tubular reactor and drain of reactants into replaceable collectors under isobaric conditions (30 MPa). The coal (gross formula CH0.96N0.01S0.002O0.31) incorporated into coal-water slurry (CWS) stabilized by starch addition (1 wt.%), was supplied through the top end of the reactor, while SCW and SCW/O2 fluids were supplied through the bottom end. Based on the results of elemental analysis of liquid products and solid residue of conversion, and mass spectrometric analysis of volatile products, we obtained gross reactions of brown coal conversion in SCW and SCW/O2 fluids. It was found that addition of O2 to SCW leads to autothermal conversion conditions and an increase in the contribution from heterogeneous reactions between carbon and water, which provides additional yield of H2 and CH4.

The paper deals with the gasification of thiophene in supercritical water (SCW) at a molar ratio of H2O:C4H4S = 1:0.107, a temperature of 873–1023 K, a pressure of 30 MPa, and a holding time of 150–600 s in a batch reactor. The gases of CO2, CO, H2, CH4, and H2S were detected in the composition of SCW gasification products. The maximum degree of thiophene gasification (>99.9%) was achieved at 1023 K and 600 s. The conversion of thiophene in SCW is described by a pseudo-first-order macro kinetic equation. It was revealed that the oxidation of thiophene in H2O/O2 mixture at uniform heating of the reactor (1 K·min−1) begins at T ≈ 400 K. The lack of O2 results in the formation of soot. It is shown that the formation of sulfuric acid during the oxidation of thiophene in the H2O/O2 mixture causes corrosion of stainless steel.

Formation of zinc sulfide nanoparticles was detected during interaction of bulk samples with hydrogen sulfide at supercritical parameters. Synthesis proceeds with liberation of H2 by the reaction nZn + nH2S = (ZnS)n + nH2. It has been found by the X-ray diffraction method, scanning electron microscopy, and mass spectrometry that the addition of water stimulates coupled reactions of nanoparticle synthesis nZn + nH2O = (ZnO)n + nH2 and (ZnO)n + nH2S = (ZnS)n + nH2O and brings about an increase in the synthesis rate and morphological changes of (ZnS)n nanoparticles.

The work has detected an influence of a constant electric field (up to E = 300 kV/m) on the structure of a nanocrystalline layer of zinc oxide, formed on the surface of a planar zinc anode in water under supercritical (673 K and 23 MPa) and near-critical (673 K and 17. 5 MPa) conditions. The effect of an increase of zinc oxidation rate with an increase in E is observed under supercritical conditions and is absent at near-critical ones. Increase in the field strength leads to the formation of a looser structure in the inner part of the zinc oxide layer.

It is established that the rate of oxidation of a massive zinc plate by supercritical water (SCW) at 673 K and 23 MPa increases and the morphology of obtained ZnO nanocrystals changes when strength E of the constant electric field applied perpendicular to the plate increases from 0 to 286 kV/m. A decrease in the SCW density at the same temperature results in the formation of a more compact nanostructured ZnO layer, while the increase in E leads to loosening of structure in the inner part of the ZnO layer.

The composition of liquid and volatile products and residue of bitumen conversion in supercritical water (SCW) flow at 400°C and 30 MPa with and without addition of zinc savings to bitumen is investigated. The yield of liquid products upon bitumen SCW conversion reaches 47.3%. The data on oxygen and hydrogen balance in the initial bitumen, products, and conversion residue indicate the chemical participation of H2O molecules in the conversion. The yield of liquid products is increased up to 62.3% if zinc is added to the initial bitumen with a simultaneous increase of the H/C atomic ratio in the products. Hydrogenation is due to hydrogen evolution during zinc oxidation by supercritical water. Under these conditions, ZnO nanoparticles with a size of 50–100 nm are formed. The data of transmission electronic microscopy and X-ray diffraction analysis of oxidized zinc demonstrate the presence of about 0.5 wt % of ZnS and about 1.2 wt % of metal zinc clusters (up to 10-nm size) in the samples. According to the sulfur atoms’ balance accounting products and conversion residue, 12.6 wt % of bitumen sulfur participates in the formation of zinc sulfide.

Oxidation of bulk samples of tungsten (923 K) and zirconium (773 and 873 K) by H2O/CO2 supercritical fluid (molar ratio [CO2]/[H2O] = 0.17–0.26) at a pressure of about 300 atm is investigated. Oxidation produces monoclinic WO3, monoclinic W19O55, monoclinic ZrO2, H2, CO, CH4, and carbon (on the surface of tungsten oxide). Differences in oxidation mechanisms for tungsten and zirconium are revealed. CO2 molecules take part in the oxidation of tungsten only after oxide formation in reaction with H2O. Zirconium is oxidized fully, and oxidation of tungsten terminates in the formation of the oxide layer at the metal surface.

Two new conversion methods of brown coals in water steam and supercritical water (SCW) are proposed and investigated. In the first method, water steam or SCW is supplied periodically into the array of coal particles and then is ejected from the reactor along with dissolved conversion products. The second method includes the continuous supply of water-coal suspension (WCS) into the vertically arranged reactor from above. When using the proposed methods, agglomeration of coal particles is excluded and a high degree of conversion of coal into liquid and gaseous products is provided. Due to the removal of the main mass of oxygen during conversion in the composition of CO2, the high heating value of fuels obtained from liquid substantially exceeds this characteristic of starting coal. More than half of the sulfur atoms transfer into H2S during the SCW conversion already at a temperature lower than 450°C.

It was found that bulk samples of molybdenum 〈Mo〉 are oxidized by supercritical water forming nanoparticles of monocline MoO2. The average size of nanoparticles obtained at uniform heating of 〈Mo〉 with supercritical water was about 27 nm, and the size of agglomerates of nanoparticles was ≤ 1 μm. From time dependence of the amount of formed H2nH2(t), we have determined kinetic parameters of 〈Mo〉 transition to MoO2 particles. The dependence dnH2/dt is characterized by the presence of two pronounced maxima. This is explained by the change of mutual diffusion of H2 and H2O molecules along with the growth of thickness of the layer of MoO2 nanoparticles.

Special features of the tungsten wire (TW) heat transfer in supercritical water at P = 25 MPa and T ≤ 923 K are investigated, including the conditions of (WO3)n nanoparticle formation on the tungsten wire surface with the reaction kn〈W〉 + 3knH2O = k(WO3)n + 3knH2. Values of the heat transfer coefficient as a function of oxidation time and temperature were determined using the method of electric current flash heating of the tungsten wire. It has been found that due to WO3 dissolution in supercritical water, there occurs oxide recondensation from the tungsten wire surface onto other design elements of the setup, which is accompanied by formation of monoclinic and rhombic WO3, and also monoclinic FeWO4.

It is found out that the rate of oxidation of a massive zirconium plate by supercritical water at 823 K and ∼25 MPa increases under the action of constant electric field of ∼300 kV/m. The formed oxide layer undergoes strong destructions of a top part and strong inhomogeneity in oxygen distribution along the layer. At interaction between Zr and H2O/CO2 supercritical fluid under the action of electric field, a decrease in the mass increment of the sample is observed. It can be caused by the fact that the electric field impedes formation of zirconium carbonate as a result of the polarization effects at the sample surface.

The conversion of brown coal in sub- and supercritical water at 310–460°C and pressures up to 30 MPa in the cyclic pressurization and depressurization modes is studied. The temperature dependences of coal organic matter (COM) conversion and the yield of volatile and condensed products are obtained. The temperature dependence of the yield of condensed substances has a maximum at 370°C. The fraction of high-molecular substances in condensed products is increased with increasing temperature. The cumulative conversion of COM into volatile and condensed products upon heating to 460°C was 31.4 and 8.6%, respectively. According to the data of mass spectrometry analysis of volatile products and the elemental analysis of the initial coal, carbonaceous residue after the conversion, and condensed products, 82.3% of oxygen and 74.7% of sulfur, are removed from COM. CO2 and H2S are the main products of the conversion of oxygen- and sulfur-containing groups.

Wide application of water supercritical fluid (SCF) as an operating fluid in thermal and nuclear power plants,1,2 involvement of natural resources of supercritical H2O and H2O/CO2 into power production, 3 as well as the develop ment of the plants with reactors based on supercritical water to dispose toxic wastes4,5 and convert low grade fuels6,7 have generated the interest to research on corro sion of structural materials in supercritical media.8 Nano particles of iron oxide are also extensively used in medi cine, bioengineering, in manufacturing of magnetic mem ory devices, and in catalysis.9 Various methods9,10 includ ing hydrothermal techniques11,12 are applied to synthesize iron oxide nanoparticles. In this work, the oxidation of iron (Fe) particles in supercritical H2O and H2O/CO2 at different temperatures T is described (Table 1). The initial pressure of SCF in the reactor P0 (see Table 1) containing iron particles was gen erated by injecting SCF from a mixer with the volume approximately 20 times larger that of the reactor. The reactor with Fe particles was preliminary evacuated and heated up to operating temperature. The Fe particles were evenly placed at the bottom of a flat cell located along the axis of

It is established that iron is oxidized by supercritical water (SCW) with the formation of H2 and nanoparticles of iron oxides (Fe3O4, FeO, and γ-Fe2O3). The kinetics of H2 production and iron oxidation has been studied by SCW injection at T = 673, 723, 773, 823, and 873 K into a reactor with iron particles. Data of X-ray diffraction and transmission electron microscopy show that the phase composition and morphology of synthesized oxide nanoparticles depend on the SCW temperature.

The new technique of usage of supercritical water (SCW) for brown coals conversion into both liquid (condensed), and solid and gas (volatile) fuels is proposed. The method consists in cyclic filling of SCW up to the given pressure (pressurization) into the tubular reactor, filled with coal particles, and fast discharging of conversion products dissolved in SCW (depressurization). The dynamics and composition of conversion products in a mode of stepwise temperature (310–460 °C) and pressure (9–31 MPa) rise at cyclic filling and discharging of, first, the water vapor (T < 374 °C), and then of SCW have been investigated. The vapor stage of conversion has prevented agglomeration of coal particles at the stage of SCW conversion. The maximum yield of the condensed products is obtained at 390 °C, 29.0 MPa. High heating value of combustible products of conversion and solid residue appeared to be much more than that of initial coal because of removal of a great bulk (up to 85.2%) of native oxygen as CO2. H/C atomic ratio in the volatile combustible and condensed products is much higher than in the conversion residue because of redistribution of native hydrogen in coal organic matter (COM). It has been established that sulfur is mainly removed from COM as H2S (up to 77.2%) and nitrogen is concentrated (up to 67.2%) in the solid conversion residue.

The possibility of low-temperature oxidation of a solid carbonized coal residue in a mixture of NH4NO3 and supercritical water (723 K and 30 MPa) is shown for the first time and its mechanism is described. Conjugate processes of oxidation of the carbonized residue and formation of combustible gases H2 and CH4 caused by the participation of H2O in redox reactions was found. It was established that the ash residue has a high porosity and consists of agglomerated nanoparticles of silicon and metal oxides.

Massive aluminum samples were oxidized by sub- and supercritical water with the formation of (AlOOH) n and (Al2O3) n nanoparticles. The release of H2 began at 523 K when the reagents were heated uniformly to 700 K. The time lag of the beginning of oxidation was 140 s when supercritical water was injected into a reactor with aluminum samples at 665 K and 23.1 MPa. Oxidized aluminum powders were analyzed using a transmission electron microscope. Predominantly large (300–400 nm) α-Al2O3 particles were formed when supercritical water was injected into a reactor with aluminum. Smaller (20–50 nm) γ-Al2O3 particles were also observed in samples oxidized by water vapor under temperature increase conditions. Kinetic equations describing the rate of H2 formation in the reaction of H2O with aluminum were obtained. Possible nanostructuring mechanisms are discussed.

The paper deals with the investigation of the hydrogen combustion in mixtures of H2/O2/H2O (0.70/0.35/1.64 mol L−1), H2/O2/N2 (0.72/0.34/1.61 mol L−1), and H2/O2/N2/H2O (0.72/0.34/1.64/0.03 mol L−1) under uniform heating at a rate of 1 K min−1 in a tubular reactor. Based on the comparison of the time-dependent variations of the reaction mixture temperature and the temperature of the reactor wall, the self-ignition temperature is determined as well as the effect of diluent on the nature of heat release was revealed. The contributions of homogeneous and heterogeneous combustion of hydrogen and their effect on heat release in the reaction mixture are discussed. The possibility of hydrogen oxidation enhancement in the H2O medium, associated with the involvement of vibrationally excited O2* molecules, generated from the resonant exchange of vibrational energy with the H2O* molecules, are considered.

We have discovered that massive samples of solid zirconium (Zr)s are completely oxidized by supercritical water (SCW, T > 647 K, P > 22.1 MPa) with the formation of zirconium oxide nanoparticles (ZrO2)n. The particle size distribution, morphology, and features of the nanostructure formation depend on the process conditions. The kinetics of H2 production and zirconium oxidation has been determined using the method of SCW injection into a reactor with (Zr)s at various temperatures. The dependence of the oxidation induction time on the SCW parameters has been studied.

Oxidation of solid and liquid zinc by water (temperature 335–648 °C, pressure 13.7–31.2 MPa, water density 0.045–0.420 g/cm3), supercritical CO2 (514–600 °C, 7.1–24.4 MPa, 0.041–0.158 g/cm3), mixture of H2O/CO2 (140–600 °C, 30 MPa, water density 0.026–0.569 g/cm3, initial ratio of [H2O]0/[CO2]0 = 0.46–2.75 mol/mol) has been studied. In pure CO2, besides CO, carbons are formed and in mixtures H2O/CO2 along with H2 and CO, paraffin and aromatic hydrocarbons, alcohols and formaldehyde are synthesized. Combustible products composition depends on the temperature and ratio of [H2O]/[CO2] in the mixture. In every experiment ZnO nanoparticles formation was observed. Cluster mechanism of nanostructured ZnO generation has been proposed and kinetic parameters of this process have been revealed. Temperature dependence of the rate constant of Zn reacting with H2O is described by the equation kW(T) = 1.09 × 10−4 exp(−53.23 (kJ/mol)/RT). At the same temperature rate constant of Zn reacting with CO2 is 44 times less than kW, and the rate constant of Zn reacting with H2O/CO2 mixture is 25.4% less than kW.

Oxidation of solid and liquid zinc by water (temperature 335–648 °C, pressure 13.7–31.2 MPa, water density 0.045–0.420 g/cm 3 ), supercritical CO 2 (514–600 °C, 7.1–24.4 MPa, 0.041–0.158 g/cm 3 ), mixture of H 2 O/CO 2 (140–600 °C, 30 MPa, water density 0.026–0.569 g/cm 3 , initial ratio of [H 2 O] 0 /[CO 2 ] 0 = 0.46–2.75 mol/mol) has been studied. On the basis of scanning and transmission of electron microscopy data, we have demonstrated that depending on the process conditions nanoparticles with the size of 2–100 nm, nanorods and nanowhiskers with the diameter of 10–100 nm and length of up to 50 μm, mechanically solid nanostructured ceramics are synthesized. The presence of (Zn) n clusters with the size below 5 nm has been found in ZnO nanoparticles synthesized in supercritical water and H 2 O/CO 2 mixture. Higher level perfection of nanocrystals formed at zinc oxidation by subcritical water has been revealed by means of room temperature photoluminescence study.

The conversion of the organic matter of municipal sewage sludge in water under supercritical conditions (T≤750°C; P≤30 MPa) was studied. According to mass-spectrometric data, CO2, H2, CH4, and NH3 were predominant among volatile conversion products. The kinetic parameters of conversion were determined. It was found that the rate of the process increased with temperature and mainly depended on the interaction of water molecules with sewage sludge carbon T > 600°C.

A study was made of the conversion of single spherical coal particles of diameter 1–5 mm in a supercritical H2O/O2 fluid with an oxygen mass fraction of 0–6.6% in a semibatch reactor at a pressure of 30 MPa and a temperature of 673–1023 K. A decrease in the particle mass was observed in two parallel processes: gasification of coal with water and oxidation of coal with oxygen. An activation energy 19 ± 7 kJ/mole and a pre-exponential factor 10−2±0.4 sec−1 were obtained under the assumption of zero order for the concentration H2O and an Arrhenius dependence for the rate of gasification with water. The oxidation with oxygen at a temperature above 780 K was found to be limited by the rate of O2 diffusion to the coal organic matter. Below 780 K, the rate of heterogeneous oxidation with oxygen is described by a first-order reaction for the concentration of O2 and a zero-order reaction for the concentration of H2O with an activation energy of 150 ± 27 kJ/mole and a pre-exponential factor of 107.6±1.9 cm3/(g · sec).

The product composition of the dynamic conversion of brown coal, which was continuously supplied as a water-coal slurry to a flow reactor at 30 MPa, was studied. The temperature of water and coal particles was increased from room temperature to 400°C (top part of the reactor). The conversion of the organic matter of coal was ∼48%, and the products collected at the reactor outlet consisted of solid tar components, substances dissolved and emulsified in water, and volatile substances, whose major constituent was CO2. The composition of solid tar components and oils was determined.

A test bench was developed and the conversion of the organic matter of coal (OMC) in supercritical water (SCW) was studied under conditions of a continuous supply of a water-coal suspension to a vertical flow reactor at 390–760°C and a pressure of 30 MPa. From 44 to 63% OMC was released as liquid and gaseous products from coal particles (from the water-coal supension) during the time of fall to the reactor. This stage was referred to as the dynamic conversion of coal. The particles passed through the stage of the dynamic conversion of coal did not agglomerate in the reactor in the subsequent process of batch conversion in a coal layer at T = 550–760°C. The volatile products of the overall process of the dynamic and batch conversion of coal included saturated hydrocarbons (CH4 and C2H6), aromatic hydrocarbons (C6H6, C7H8, and C8H10), synthesis gas (H2 and CO), and CO2. At T < 600°C, CO2 and CO were the degradation products of oxygen-containing OMC fragments, whereas they also resulted from the decomposition of water molecules at higher temperatures in accordance with the reaction (C) + H2O = CO + H2. The mechanisms were considered, and the parameters responsible for the dynamic conversion of coal were calculated.

The conversion of an array of coal particles in supercritical water (SCW) was studied in a semibatch reactor at a pressure of 30 MPa, 500–750°C, and a reaction time of 1–12 min. The bulk conversion, surface conversion, and random pore models were used to describe the conversion. The quantitative composition of reaction products was determined, and the dependence of the rate of reaction on the degree of coal conversion, reaction time, and reaction temperature was obtained on the assumption of a first-order reaction and the Arrhenius function (E = 103 kJ/mol; A 0 = 7.7 × 104 min−1). It was found that the gasification of coal under SCW conditions without the addition of oxidizing agents is a weakly endothermic process. The addition of CO2 to SCW decreased the rate of conversion and increased the yield of CO. It was found that, at a 90% conversion of the organic matter of coal (OMC) in a flow of SCW in a time of 2 min, the process power was 26 W/g per gram of OMC.

dT/dt = 2 K min -1 . A cell with a specified amount of water and a cell with the 〈W〉 sample were loaded in the reactor. In entries 2—4, only a cell with the 〈W〉 sample was loaded in the reactor and water at the supercritical parameters (Т > 647 K, P > 22.1 MPa) was sprayed in the preheated reactor through a highperformance gate from a prereac� tor. After water was sprayed, the temperature of the reac� tor was maintained constant. The volume of the prereac� tor is ∼20 times of the volume (VR) of the reactor occupied with water. The pressure (P) was measured by membrane tensiosensors, whose accuracy in the range from 1 to 40 MPa was 0.25%. The temperature regime of the reactor was established by a thermoregulator using ohmic heaters and chromel—alumel thermocouples. The temperature dependence of the hydrogen pressure was measured in en� try 1, and the time dependence of the hydrogen pressure was measured in entries 2—4. At the end of experiments the reactor was rapidly cooled. Water and Н 2 , which was formed upon oxidation, were collected in a collector cooled with liquid nitrogen. The amount of hydrogen NH2 was determined from the results of measurements of the H2 pressure in a volumetric cylinder of a known volume, and the gas composition in the cylinder was measured on a quadrupole mass spectrometer. 6 In addition, the weights m0 of the 〈W〉 samples were measured before and after oxidation, and the difference indicated the weight increase Δm. The values of the above parameters are given in Table 1

Fe3O4, FeO, and traces of γ-Fe2O3 are obtained by supercritical fluid oxidation of Fe particles using H2O or a H2O/CO2 mixture in a horizontal tubular stainless steel reactor.

Bulk solid (Zn)S and liquid zinc (Zn)L samples are oxidized by water with the formation of nanodimensional ZnO. The rate of this process, called chemical recondensation (CR) by water, increases with temperature and water density rise. The CR process begins with the formation of (ZnO)n clusters via the reaction (Zn)S,L + nH2O = [(Zn)S,Lmiddot(ZnO)n] + nH2, followed by their growth at n > 4. The CR of solid Zn leads predominantly to the formation of nanowires and nanorods, while the CR of liquid Zn practically always proceeds with the formation of nanoparticles. The complete CR of solid Zn cylinders results in the formation of highly porous nanostructural ceramics.

The synthesis of nanoparticles (ZnO)n was found out at study of liquid zinc (Zn)L oxidizing by supercritical CO2. This process called as chemical recondensation (CR). It was determined that depending on CR conditions the nanoparticles with size of 5-50 nm and the nanoneedles with diameter of 25.100 nm, length of up to 50 mum are synthesized. For CR of (Zn)L in CO2 the cluster mechanism is suggested and kinetic parameters are estimated. Besides (ZnO)n at zinc CR in CO2 carbon and CO are formed.

At oxidizing of liquid zinc by H2O/CO2 mixture at supercritical parameters it is found the formation of nanoparticles (ZnO)n with size from 1.5 to 100 nm and combustible substances: H2, CO, lower paraffin and aromatic hydrocarbons, alcohols and formaldehyde. Composition of combustible products depends on H2O/CO2 ratio in mixture. Synthesized ZnO samples were studied by methods of scanning and transmission electron microscopy, thermal analysis.