Zeki Aktas

Effect of addition of surface active agent on the viscosity of a high concentration slurry of a low-rank British coal in water

Abstract Coal–water mixtures (CWM) are concentrated suspensions of coal particles in water. The rheological properties of CWM depend on a number of factors such as the type of coal, the solid content and its size distribution, the temperature, the pH and the presence of electrolytes and chemical additives. The slurry viscosity was influenced significantly by initial surfactant loading, the particle size distribution and the ash content of the feeds. CWS of up to 60% prepared from Bickershaw coal samples with low ash contents (4.0% and 6.86%) could be produced at acceptable viscosities in the presence of a non-ionic surfactant, Triton X-405. To produce pumpable slurries with more than 60% solid, it will be necessary first to achieve a significant level of demineralisation, and to use high levels of reagent addition. The viscosities of the slurries with low ash content were significantly reduced by the surfactant addition which also altered the rheological characters of these slurries from non-Newtonian towards Newtonian fluids. However, sample containing very fine particles with a high ash content (24.5%) showed non-Newtonian behaviour even in the presence of reagent.

Effect of various bridging liquids on coal fines agglomeration performance

Abstract Oil agglomeration is a surface property based on the differences in the surface properties of the organic and inorganic constituents of coal. A bituminous coal was agglomerated using kerosene, diesel oil, Kirkuk Crude Petroleum, extract fractions (obtained from Soxhlet extraction)—kerosene or toluene mixtures and toluene. The amounts of bridging oils were varied from 5% to 30% of the initial coal loading. Centrifugal float–sink separations of the coal in dense media were conducted and the results of their grade recovery performances were compared with those of the agglomeration of the particles. Factors affecting the agglomeration performance, such as the amount of bridging oils and washing water, type of bridging oil, solid content of the slurry and finer particles, were determined. The relationship between the agglomerate sizes and their ash content was also determined. Higher recovery values (>95%) were obtained from the agglomeration tests. Extract-oil fraction of the coal extract at various ratios in kerosene decreased the agglomeration recovery from 98.99% to 88.44%. A sharp decrease (from 90.52% to 56.01%) in the recovery was observed for asphaltane fraction of the coal extract in toluene. Increase in finer particle portion in the bulk solids decreased the grade values of the final product.

Centrifugal float-sink separation of fine Turkish coals in dense media

Abstract Zonguldak bituminous coal, Tuncbilek and Soma–Merkez lignites were each separated into two sub-fractions, coal rich and mineral matter rich, using a centrifugal float–sink separation technique in heavy media. An isopropyl alcohol (IPA)–carbon tetrachloride (CCl 4 ) mixture and a zinc chloride (ZnCl 2 ) solution, with a specific gravity of 1.40 g cm −3 at 25°C were used as dense medium liquids. The addition of surface active agents (Triton X-100 and Brij-35) to the zinc chloride solution improved the removal of minerals. The recovery and purity of the final product (float) obtained from the heavy media separation depend on such parameters as the density of the medium, rotor speed and centrifugation time. The separation efficiency of each coal differed significantly. Particle size distributions of the coals and their float and sink fractions were analysed using a Laser Particle Size Analyser. A Scanning Electron Microscope (SEM) was used to interpret the liberation of minerals from the coal particles.

Adsorption of Aromatic Hydrocarbons on BTEA–bentonites

Organobentonites were synthesized using benzyltrimethyl-ammonium bromide (BTEA) with five different exchange degrees. At low concentrations, the amounts of BTEA exchanged did not reach the value of the cation-exchange capacity (CEC) of the bentonite. To obtain full displacement, it was necessary to add an amount of BTEA four-times greater than the CEC. Synthesized organobentonites were characterized by X-ray diffraction, particlesizeanalysis and infrared spectroscopy. The basal spacings of the organobentonites increased slightly with increasing amounts of BTEA cations. Particle-size analyses of the original bentonite and organobentonites showed that the organobentonites contained a greater number of coarse particles than present in the original bentonite. Toluene and xylenes were used as solutes to determine the adsorption properties of the BTEA–bentonites. The 4BTEA–bentonite was evaluated as an adsorbent of water-soluble aromatic hydrocarbons including toluene and xylenes.

Supercritical toluene extraction of a reduced Turkish lignite

Elbistan-Afsin lignite, 64.2% C (daf), was reduced with lithium in THF in the presence of purified naphthalene as an electron transfer agent. The reduced lignite was then extracted with supercritical toluene. Even under comparatively mild conditions, 340°C, relatively large yields of supercritical extract were obtained, almost all of which dissolved in benzene. The n-pentane-soluble and benzene-soluble fractions of the extract were eluted using column chromatography. Less than half of the originally soluble material could be eluted with n-pentane or benzene, the total methanol eluates amounting to 56.1% of the initial extract. The eluates were analysed by gas chromatography/mass spectrometry. The amount of phenol was 23.6% of the original benzene soluble fraction. It was concluded that bond cleavage had taken place during the reduction of the lignite. The naphthalene used as an electron transfer agent participated in side reactions.

Examination of gas and solid products during the preparation of activated carbon using phosphoric acid

Activating agents play significant roles in the preparation of activated carbon (AC) from biomasses and their wastes, which are widely used in AC production. Application methods are also important for the production process. Products give remarkable ideas regarding the method and heat treatment process. The activated carbon was produced from waste tea in accordance with either the conventional method or microwave energy pretreated method using phosphoric acid (H3PO4) as activating agent. The yields of the activated carbons were 51.8% for conventional method and 46.0% for microwave pretreated method. The acid suppressed the formation of tar and promoted the amount of solid and aromatic structure accordance to sp2 hybridisation. Additionally, the waste tea was directly carbonised (without H3PO4) and the yield was 36.3%. Major gas (H2, CH4, C2H6, C2H4, CO2 and CO) products obtained during heat treatment process in a conventional furnace were examined in terms of quantity and quality. The solid products were characterised in terms of surface area, pore size and surface properties. The result of gas analysis showed that phosphoric acid affected formation of activated carbon mechanism and significant reactions occurred during microwave pretreatment process.

Waste tea derived activated carbon/polyaniline composites as supercapacitor electrodes

Activated carbon-polyaniline composite samples were prepared via the polymerisation of aniline monomer into the pores of the activated carbon sample derived from waste tea. The composites were used as electrode materials for supercapacitors in an aqueous electrolyte. The effects of polyaniline content of the electrodes on the electrochemical performances of the supercapacitors were examined. The highest specific capacitance of 228 F/g at 1.5 mA/cm2 in an aqueous electrolyte was obtained for the electrode containing equal mass amount of the activated carbon and polyaniline.