S. A. Psarov

The effect of thermal explosion in a supercritical water

The conversion of hydrocarbons (eicosane, naphthalene, and synthetic bitumen) dissolved in super-critical water (SCW) was studied in a batch reactor at a pressure of P=30 MPa and a range of temperatures from 450 to 75°C. It was established that water participates in the conversion process on a chemical level: in particular, oxygen from water molecules is involved in the formation of carbon oxides. Even in the absence of added molecular oxygen, the process of naphthalene and bitumen conversion in a certain temperature interval exhibited an exothermal character. Upon adding O2 into SCW, the oxidation reaction may proceed in a burning regime with self-heating of the mixture. Under certain conditions, the self-heating process may lead to the thermal explosion effect accompanied by ejection of the substance from the reactor, which is explained by the high rate of hydrocarbon burning in SCW.

Coal gasification with water under supercritical conditions

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; A0 = 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.

Naphthalene oxidation in supercritical water

Characteristic features of naphthalene oxidation and the kinetics of naphthalene pyrolysis in supercritical water (SCW) were studied using a batch reactor under isobaric conditions at a pressure of 30 MPa, in the temperature range from 660 °C to 750 °C, and for different levels of oxygen supply, varying from 0 to 2.5 moles of O2 per mole of naphthalene. The pyrolysis produces benzene, toluene, methane, hydrogen, soot, and carbon oxides. The rate constant for naphthalene pyrolysis in SCW was found to be k = 1012.3±0.2exp(–E/T) s–1 where E = 35400±500 K. For T > 660 °C, water participates in the chemical reactions of naphthalene conversion, particularly, in the formation of carbon oxides. The conversion of naphthalene in pure SCW is accompanied by heat evolution. Molecular oxygen oxidizes a part of naphthalene completely, i.e., to CO2 and H2O, this reaction being so prompt that in some cases, self-heating of the mixture and thermal explosion in the reactor were observed.

The explosive oxidation of hydrocarbons in a supercritical water

The kinetics of oxidation of naphthalene and a heavy oil residue (upon vacuum distillation) by oxygen dissolved in supercritical water is studied in a wide range of temperatures (663 K≤T≤1075 K) and pressures (31MPa≤P≤67MPa). It is established that the oxidation process exhibits an explosive (blow-up) character. The kinetic constants characterizing the thermal explosion are determined. For naphthalene, the heat evolution rate during the explosive oxidation obeys the law WN=1013.10±0.30exp((170.4±1.0 kJ/mol)/RT)×[C10H8]0.46±0.01[O2]0.63±0.01[H2O]1.66±0.03kJ/(l s).

Brown coal conversion under the action of supercritical water

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 combustion of benzene in a supercritical water

We have studied the kinetics of benzene combustion in an aqueous solution at supercritical temperatures (663 K≤T≤1075 K) and pressures (28 MPa≤P≤90 MPa). The oxidative combustion exhibits an explosive character and can develop according to either thermal or branched-chain mechanisms. The conditions for these mechanisms are established and the corresponding kinetic constants are determined.

Product composition of the dynamic conversion of brown coal in supercritical water

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.