Mesut Akgün

The effect of premixing on the floatation of oxidized Amasra coal

Abstract In this study factors affecting the floatation efficiency of oxidized Amasra coal containing high quantities of inorganic materials were examined under laboratory conditions. The Amasra coal samples were oxidized by exposing them to atmospheres for a long time with the aim of obtaining coal having a lower ash content. Premixing is applied to condensed pulp containing 60% coal and 40% water to remove the oxidized layer on the coal surface. The oxidized layer is removed as a result of friction between particles during mixing. Premixing periods were 1, 2, 3, 4, 5, 10, 15 and 20 min, and floatation tests were done after each premixing. Some relations were obtained between frothing period, calorific value, combustible matter recovery, and ash content. The relation between premixing and floatation efficiency was another subject of examination. The effect of oxidized coal on floatation was also examined after oxidized coal was exposed to thermal treatment in inert milieu. From the results obtained at the end of an average frothing period of 20–25 min, it was observed that the quantity of product increased and the ash content in the product reached a minimum value. At the same time, the calorific value of the coal and the recovery of combustible matter reached their highest value.

Treatment of whey wastewater by supercritical water oxidation

Whey wastewater is a by-product of cheese industry, which causes environmental pollution problems due to its containment of heavy organic pollutants. Conventional methods such as biological treatment and physico-chemical treatment are insufficient or ineffective. In this paper, the treatment of cheese whey wastewater has been carried out by supercritical water oxidation, using hydrogen peroxide as oxidant. The reaction conditions ranged between temperatures of 400-650°C and residence times of 6-21 s under a pressure of 25 MPa. Treatment efficiencies based on TOC removal were obtained between 75.0% and 99.81%. An overall reaction rate model, which consists of the hydrothermal and the oxidation reactions, was determined for the hydrothermal decomposition of the wastewater with an activation energy of 50.022 (±1.7) kJmol(-1) and a pre-exponential factor of 107.72 (±4.1) s(-1). The oxidation reaction rate orders for the TOC and the oxidant were 1.2 (±0.4) and 0.4 (±0.1) respectively, with an activation energy of 20.337 (±0.9) kJmol(-1), and a pre-exponential factor of 1.86 (±0.5) mmol(-0.6)L(0.6)s(-1) in a 95% confidence level.

Supercritical Fluid Extraction of Lavandula stoechas L. ssp. cariensis (Boiss.) Rozeira

Abstract The flowers of Lavandula stoechas L. ssp. cariensis (Boiss.) Rozeira were extracted in both a batch and semi-continuous system by supercritical CO2. In the first stage, experiments were performed in a batch system based on response surface methodology (RSM). Parameters used were pressure, temperature, mixing speed and extraction time, and were coded as, X1, X2, X3 and X4, respectively. These parameters were investigated at three levels (-1,0 and 1). The dependent variable, Y, was taken as the volatile concentrate yield of supercritical fluid extraction. It was calculated with respect to the yield of solvent extraction by dichloromethane. In the second stage, experiments were carried out in a semi-continuous system at constant pressure and temperature, and different CO2 flow rates. Concentrations of volatile components were determined as a function of extraction time and CO2 residence time

In situ gas fuel production during the treatment of textile wastewater at supercritical conditions

Supercritical water gasification has recently received much attention as a potential alternative to energy conversion methods applied to aqueous/non-aqueous biomass sources, industrial wastes or fossil fuels such as coal because of the unique physical properties of water above its critical conditions (i.e. 374.8 °C and 22.1 MPa). This paper presents the results obtained for the hydrothermal gasification of textile wastewater at supercritical conditions. The experiments were carried out at five reaction temperatures (between 450 and 650 °C) and five reaction times (between 30 and 150 s), under a constant pressure of 25 MPa. It was found that the gaseous products contained considerable amounts of hydrogen, carbon monoxide, carbon dioxide, and C(1)-C(4) hydrocarbons, such as methane, ethane, propane and propylene. The maximum amount of the obtained gaseous product was 1.23 mL per mL textile wastewater, at a reaction temperature of 600 °C, with a reaction time of 150 s. At this state, the product comprised 13.02% hydrogen, 38.93% methane, 4.33% ethane, 0.10% propane, 0.01% propylene, 7.97% carbon monoxide, 27.22% carbon dioxide and 8.00% nitrogen. In addition, a 62.88% decrease in the total organic carbon (TOC) content was observed and the color of the wastewater was removed. Moreover, for the hydrothermal decomposition of the textile wastewater, a first-order reaction rate was designated with an activation energy of 50.42 (±2.33) kJ/mol and a pre-exponential factor of 13.29 (±0.41) s(-1).

Equilibrium and kinetic study on the adsorption of basic dye (BY28) onto raw Ca-bentonite

AbstractThe adsorption of Basic Yellow 28 (BY28) onto bentonite in a batch system was carried out at temperatures of 20 and 40°C. The initial dye concentrations were in the range of 100 and 300 mg/L based on the total organic carbon (TOC) content of the dye solution. The effects of contact time, initial pH, and initial dye concentration on BY28 adsorption by the bentonite have been studied. BY28 removal was observed to increase until equilibrium, with increasing contact time and initial dye concentration, and the adsorption capacity of bentonite was seen to increase with increasing pH from 3 to 8. Adsorption efficiencies up to about 98.1% were obtained based on the TOC at various adsorption conditions. The adsorption process was determined to follow the pseudo-second-order adsorption kinetics. Kinetic parameters, rate constants, equilibrium adsorption capacities, and correlation coefficients of the adsorption kinetic models were calculated and discussed. The experimental isotherm data were analyzed using ...

Hydrogen Production by Supercritical Water Gasification of Biomass

It is widely accepted that hydrogen energy can sustainably provide the world’s growing energy needs. Currently, hydrogen is produced from mainly nonrenewable feedstocks through biochemical and thermochemical technologies. However, to achieve a genuinely sustainable, economic, viable, and environmentally benign technology, hydrogen will need to be produced from renewable energy sources through innovative production processes. This chapter focuses on one of these technologies that provide a novel approach for hydrogen production: supercritical water gasification of biomass. The process has significant potential for the conversion of biomass to produce hydrogen and other combustible gases. It also has major advantages when compared with other processes, such as eliminating the necessity for drying of the feedstock, providing high gasification efficiency and hydrogen selectivity, enabling the formation of clean gaseous products, and producing much lower amounts of tars and chars. To increase the hydrogen selectivity, the use of catalysts is common, with the preferred catalysts being alkaline salts, some metals, and metal oxides. The supercritical water gasification process can exhibit different gas compositions or activities with respect to the feedstock, reaction conditions, or catalyst used. Therefore, in this chapter, hydrogen production from various biomass sources by supercritical water gasification is comparatively discussed with examples from the literature. The term biomass covered in this chapter includes model compounds (such as glucose, cellulose, and lignin), alcohols, and real biomass (such as industrial wastewaters and sewage sludge). The effects of reaction time, system temperature and pressure, biomass concentration, oxidant concentration, catalyst use, and the kind of catalyst on the hydrogen yield are investigated.

Supercritical Water Oxidation (SCWO) for Wastewater Treatment

Water behaves as an acidic and alkaline precursor for acidic or basic reactions, since the formation of both H3O+ and OH– ions takes place in accordance with the self-dissociation of water at near-critical and above supercritical (Tc = 374 °C, Pc = 22.1 MPa) conditions. Therefore, supercritical water is considered both as a solvent for organic materials and as a reactant at processes such as the oxidative treatment of wastewaters, the gasification of aqueous organic solutions and the production of fine metal oxide particles. Supercritical water oxidation is a very efficient method for wastewater treatment, which is based on oxidation of organic compounds in aqueous media above critical temperature and pressure conditions of pure water.