Yazar "Demirbas, A" seçeneğine göre listele
Listeleniyor 1 - 20 / 68
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Adsorption of Cr(III) and Cr(VI) ions from aqueous solutions on to modified lignin(TAYLOR & FRANCIS INC, 2005) Demirbas, AThe aim for this research is to study inexpensive and effective metal ion adsorbents from biomass sources of modified lignin to offer these adsorbents as replacements for existing commercial materials. The Cr(III) and Cr(VI) binding properties of modified lignin from wood sawdust were studied. The maximum amounts of adsorption are 9.3 and 25.0 mg/g lignin for Cr(VI) and Cr(III) ions for 240 min at 290 K, respectively. As the pH of the solution increases from 2.0 to 6.0, Cr(III) ions show an increase in adsorption to the lignin with optimum adsorption occurring between pH 4.5 and 5.5. The maximum adsorption percentage is 39.5 for Cr(VI) for 240 min at 330 K, and is 67.8 for Cr(III) for 240 min at 330 K.Öğe Adsorption of lead and cadmium ions in aqueous solutions onto modified lignin from alkali glycerol delignication(ELSEVIER SCIENCE BV, 2004) Demirbas, AAdsorptions of toxic metal ions (Pb(II) and Cd(II)) onto modified lignin from beech and poplar woods by alkali glycerol delignification are presented in this paper. The material exhibits good adsorption capacity and the adsorption data follow the Langmuir model. The maximum adsorption capacities are 8.2-9.0 and 6.7-7.5 mg/g of the modified lignin for Pb(II) and Cd(II), respectively. The maximum adsorption percentage is 95.8 for Pb(II) for 4 h at 330 K and is 95.0 for Cd(II) for 10 h at 290 K. The adsorption of both the metal ions increased with increasing temperature indicating endothermic nature of the adsorption process. The maximum adsorption percentages of Pb(II) and Cd(II) ions decrease with time till 48 and 42 h and then again increase slightly with time. The adsorption of both heavy metal ions increases with pH. The adsorption of Pb(II) ions reached a maximum at a 5.0 value of pH. (C) 2004 Elsevier B.V. All rights reserved.Öğe Anaerobic digestion of agricultural solid residues(TAYLOR & FRANCIS INC, 2004) Demirbas, A; Ozturk, TAgricultural residues can be converted to methane-rich gas mixture. Anaerobic biomethane production is an effective process for conversion of a broad variety of agricultural residues to methane to substitute natural gas and medium calorific value gases. Methane generating bacteria (methanogens) and other microbes that help digest dying plants in anaerobic conditions. Agricultural solid residues (ASR) represent a potential energy resource if they can be properly and biologically converted to methane.Öğe beta-Glucan and mineral nutrient contents of cereals grown in Turkey(ELSEVIER SCI LTD, 2005) Demirbas, AMixed-linked (1-->3), (1-->4)-beta-D-glucan contents of 14 selected cereal grains grown in Turkey, such as barley (Hordeum vulgaria), beans, canary seed (Tropaeolum peregrinum), corn/maize (Zea mays), flax, lentil (Lens culinaris), millet (Panicum miliaceum), oat (Avena sativa), peas, rice, rye (Secale cereale), spelt (Triticum spelta), spring wheat and winter wheat, were determined quantitatively using enzymatic methods. By using pure beta-D-glucanase and beta-D-glucosidase in the experiments, (1-->3), (1-->4)-glycosidic bonds of linear polysaccharides found in cell-wall endosperm of plant seeds were hydrolyzed and the resulting beta-D-glucans were determined by using glucose oxidase/peroxidase solution and measuring the absorbances at 510 nm in a UV-spectrophotometer. The nutrient mineral contents of the 14 selected cereal grains were studied. Some macronutrients such as K, Ca, Mg, N, P and S, and some micronutrients, such as Zn, Cu, Fe, Mn, Mo, and B, were analyzed by using atomic absorption spectrometric (AAS) methods. A flame photometer was used for determination of potassium. After oven drying of the samples, P was determined by a colorimetric method. (C) 2004 Elsevier Ltd. All rights reserved.Öğe Biodiesel impacts on compression ignition engine (CIE): Analysis of air pollution issues relating to exhaust emissions(TAYLOR & FRANCIS INC, 2005) Demirbas, AIn cities across the globe, the personal automobile is the single greatest polluter as emissions from millions of vehicles on the road add up to a planet-wide problem. Vegetable oils have become more attractive recently because of their environmental benefits and the fact that they are made from renewable resources. With recent increases in petroleum prices and uncertainties concerning petroleum availability, there is renewed interest in vegetable oil fuels for diesel engines. The biodiesel impacts oil exhaust emissions varied depending on the type of biodiesel and oil the type of conventional diesel. Blends of up to 20% biodiesel mixed with petroleum diesel fuels can be used in nearly all diesel equipment and are compatible with most storage and distribution equipment. Using biodiesel in a conventional diesel engine substantially reduces emissions of unburned hydrocarbons, carbon monoxide, sulfates, polycyclic aromatic hydrocarbons, nitrated polycyclic aromatic hydrocarbons, and particulate matter. These reductions increase as the amount of biodiesel blended into diesel fuel increases. In general, biodiesel increases NOX emissions when used asjuel in a diesel engine. The fact that NOX emissions increase with increasing biodiesel concentration could be a detriment in areas that are out of attaininentfor ozone.Öğe Biodiesel production from vegetable oils by supercritical methanol(NATL INST SCIENCE COMMUNICATION, 2005) Demirbas, ATransesterification of vegetable oils in supercritical methanol are carried out without using any catalyst. Methyl esters of vegetable oils or biodiesels have several outstanding advantages among other new-renewable and clean engine fuel alternatives and can be used in any diesel engine without modification. The most important variables affecting the methyl ester yield during the transesterification reaction are molar ratio of alcohol to vegetable oil and reaction temperature. Compared to no. 2 Diesel fuel, all vegetable oils are more viscous, while the methyl esters of vegetable oils are slightly more viscous. Biodiesel has become more attractive because of its environmental benefits. The cost of biodiesel, however, is the main obstacle to commercialization. With cooking oils as raw material, viability of a continuous transesterification process and recovery of high quality glycerol as a biodiesel by-product are primary options to be considered to lower the cost of biodiesel. Supercritical methanol has a high potential for both transesterification of triglycerides and methyl esterification of free fatty acids to methyl esters for diesel fuel substitute. In supercritical methanol transesterification method, yield of conversion rises 95% in 10 min. Viscosity of vegetable oils (27.2-53.6 mm(2)/s) get reduced in vegetable oil methyl esters (3.59-4.63 mm(2)/s). The flash point values of vegetable oil methyl esters are highly lower than those of vegetable oils. All increase in density from 860 to 885 k-/m(3) for vegetable oil methyl esters increases the viscosity from 3.59 to 4.63 mm(2)/s.Öğe Biodiesel production from vegetable oils via catalytic and non-catalytic supercritical methanol transesterification methods(PERGAMON-ELSEVIER SCIENCE LTD, 2005) Demirbas, AThis paper reviews the production and characterization of biodiesel (BD or 13) as well as the experimental work carried out by many researchers in this field. BD fuel is a renewable substitute fuel for petroleum diesel or petrodiesel (PD) fuel made from vegetable or animal fats. BD fuel can be used in any mixture with PD fuel as it has very similar characteristics but it has lower exhaust emissions. BD fuel has better properties than that of PD fuel such as renewable, biodegradable, non-toxic, and essentially free of sulfur and aromatics. There are more than 350 oil bearing crops identified, among which only sunflower, safflower, soybean, cottonseed, rapeseed and peanut oils are considered as potential alternative fuels for diesel engines. The major problem associated with the use of pure vegetable oils as fuels, for Diesel engines are caused by high fuel viscosity in compression ignition. Dilution, micro-emulsification, pyrolysis and transesterification are the four techniques applied to solve the problems encountered with the high fuel viscosity. Dilution of oils with solvents and microemulsions of vegetable oils lowers the viscosity, some engine performance problems still exist. The viscosity values of vegetable oils vary between 27.2 and 53.6 mm(2)/S whereas those of vegetable oil methyl esters between 3.59 and 4.63 mm(2)/S. The viscosity values of vegetable oil methyl esters highly decreases after transesterification process. Compared to no. 2 diesel fuel, all of the vegetable oil methyl esters were slightly viscous. The flash point values of vegetable oil methyl esters are highly lower than those of vegetable oils. An increase in density from 860 to 885 kg/m(3) for vegetable oil methyl esters or biodiesels increases the viscosity from 3.59 to 4.63 mm(2)/s and the increases are highly regular. The purpose of the transesterification process is to lower the viscosity of the oil. The transesterfication of triglycerides by methanol, ethanol, propanol and butanol, has proved to be the most promising process. Methanol is the commonly used alcohol in this process, due in part to its low cost. Methyl esters of vegetable oils have several outstanding advantages among other new-renewable and clean engine fuel alternatives. The most important variables affecting the methyl ester yield during the transesterification reaction are molar ratio of alcohol to vegetable oil and reaction temperature. Biodiesel has become more attractive recently because of its environmental benefits. Biodiesel is an environmentally friendly fuel that can be used in any diesel engine without modification. (c) 2005 Elsevier Ltd. All rights reserved.Öğe Bioenergy, global warming, and environmental impacts(TAYLOR & FRANCIS INC, 2004) Demirbas, ABioenergy is one of the forms of renewable energy. Bioenergy, the energy from biomass, has been used for thousands of years, ever since people started burning wood to cook food, and today wood is still our largest biomass resource for bioenergy. The use of bioenergy has the potential to greatly reduce our greenhouse gas emissions. Replacing fossil fuels with energy from biomass has several distinct environmental implications. If biomass is harvested at a rate that is sustainable, using it for energy purposes does not result in any net increase in atmospheric carbon dioxide, a greenhouse gas. States have played a leading role in protecting the environment by reducing emissions of greenhouse gasses (GHGs), and state emissions are significant on a global scale. CO2 and CO are the main greenhouse gases associated with global warning. At the present time, coal is responsible for 30-40% of world CO2 emissions from fossil fuels. SO2 and NOx contribute to acid rain. Carbon assessments can play an important role in a strategy to control carbon dioxide emissions while raising revenue.Öğe Bioethanol from cellulosic materials: A renewable motor fuel from biomass(TAYLOR & FRANCIS INC, 2005) Demirbas, AEthanol is the most widely used liquid biofuel. It is an alcohol and is fermented from sugars, starches or from cellulosic biomass. Cellulosic materials can be used to produce bioethanol. Bioethanol represents an important, renewable liquid fuel for motor vehicles. Production of bioethanol from biomass is one way to reduce both the consumption of crude oil and environmental pollution. Conversion technologies for producing ethanol from cellulosic biomass resources such as forest materials, agricultural residues and urban wastes are under development and have not yet been demonstrated commercially. In order to produce bioethanol from cellulosic biomass, a pretreatment process is used to reduce the sample size, break down the hemicelluloses to sugars, and open up the structure of the cellulose component. The cellulose portion is hydrolyzed by acids or enzymes into glucose sugar that is fermented to bioethanol. The sugars from the hemicelluloses are also fermented to bioethanol. The use of bioethanol as a motor fuel has as long a history as the car itself. It began with the use of ethanol in the internal combustion engine.Öğe Biomass co-firing for boilers associated with environmental impacts(TAYLOR & FRANCIS INC, 2005) Demirbas, AThis article is presented to discuss general combustion and emissions issues with biomass co-firing, as well as specific issues with particular biomass fuels, such as fouling. The tests of co-firing were carried out in a lab-scale bubbling fluidized bed combustor. Biomass is an attractive and sustainable renewable fuel to supplement coal combustion in utility boilers. Coal and biomass fuels are quite different in composition. Ash composition for the biomass is fundamentally different from ash composition for coal. Chlorine in the biomass may affect operation by corrosion. Ash deposits reduce heat transfer and may also result in severe corrosion at high temperatures. Biomass and coal blend combustion is a promising combustion technology; however, significant development work is required before large-scale implementation can be realized. Coal co-firing was successful with up to a 20% biomass mix boilers. Issues related to successful implementation of coal biomass blend combustion are identified. Co-firing of coal and biomass is an effective method of control NOx. Formation of NOx decreases with the increase of biomass fraction. This study focuses on five of the critical fireside issues associated with co-firing: ash deposition, SO2 emission, NOx formation, corrosion, and carbon burnout.Öğe Bounding of carbon dioxide in flue gases via carbonation process(MULTI SCIENCE PUBL CO LTD, 2004) Demirbas, ACarbonation is a stabilization of carbon dioxide (CO2) by solidification process. In order to prevent rapid climate change, it will be necessary to stabilize CO2 as carbonate by the carbonation process. Carbonation of the widely occurring mineral olivine (Mg2SiO4) converts CO2 into an environmentally benign mineral magnesite (MgCO3). The availability of a CO2 fixation technology would serve as insurance in case global warming causes severe restrictions on CO2 emissions. The yield of carbonation increased with increasing temperature. The rate of carbonation conversion sharply increased in initial 20 min and then reduced and reached a plateau value after about 40 min. The carbonation conversion with MgO is higher than that of CaO.Öğe Briquetting properties of biomass waste materials(TAYLOR & FRANCIS INC, 2004) Demirbas, A; Sahin-Demirbas, A; Demirbas, AHIn this study, some briquetting properties such as moisture content, shatter index, compressive strength, water resistance, heating value, and combustion of briquettes from pulping reject and spruce wood sawdust were determined. The strongest briquettes ( shatter index 20500, compressive strength 49.5 MPa) produced using spruce wood sawdust were achieved with a moisture content of 15% at a briquetting pressure of 350 MPa. The effect of the moisture content on the compressive strength and the shatter index of the briquette samples from pulping reject and spruce sawdust were studied. The results suggest that as the moisture content of the briquette samples increased significantly, the compressive strength and shatter index of the briquettes also increased.Öğe Characterization of products from two lignite samples by supercritical fluid extraction(TAYLOR & FRANCIS INC, 2004) Demirbas, ASupercritical fluid extractions (SFEs) of Ilgin and Tuncbilek lignites from Turkish resources using toluene as solvent were investigated. Experiments were performed in a batch autoclave at 633 K. The yields of extracts from supercritical toluene extractions of Ilgin and Tuncbilek lignites were 14.8%, 22.9%, 24.6%, 26.8% and 17.3%, 268%, 29.4%, 31.3% at 11.8, 15.1, 20.0, 27.5 MPa runs, respectively. Extracts recovered from SFEs were fractionated into petroleum ether solubles and benzene solubles by solvent extraction. Petroleum ether solubles were fractionated into hexane, benzene, methanol and tetrahydrofuran eluats. Benzene solubles were separated into phenols + acids, bases and neutrals fractions.Öğe Combustion characteristics of different biomass fuels(PERGAMON-ELSEVIER SCIENCE LTD, 2004) Demirbas, ABiomass energy is one of humanity's earliest sources of energy particularly in rural areas where it is often the only accessible and affordable source of energy. Worldwide biomass ranks fourth as an energy resource, providing approximately 14% of the world's energy needs all human and industrial processes produce wastes, that is, normally unused and undesirable products of a specific process. Generation and recovery of solid wastes varies dramatically from country to country and deserves special mention. The burning velocity of pulverized biomass fuels is considerably higher than that of coals. The use of biomass fuels provides substantial benefits as far as the environment is concerned. Biomass absorbs carbon dioxide during growth, and emits it during combustion. Utilization of biomass as fuel for power production offers the advantage of a renewable and CO2-neutral fuel. Although the structural, proximate and ultimate analyses results of biomass and wastes differ considerably, some properties of the biomass samples such as the hydrogen content, the sulfur content and the ignition temperatures changed in a narrow interval. (C) 2004 Elsevier Ltd. All rights reserved.Öğe Competition potential of wind power plants(TAYLOR & FRANCIS INC, 2005) Demirbas, AIn Turkey, wind energy has great potential. According to the Organization for Economic Cooperation and Development (OECD), Turkey theoretically has 160 terrawatt hours a year of wind potential. Substantial potential of wind energy in Turkey is important with respect to the economic, financing, and environmental benefits. Therefore, the evaluation of the substitution potential of wind energy is becoming an important task by generation planning of power systems. Wind energy is among the fastest developing energy sources in Turkey. The Marmara, southeast Anatolian and Aegean regions are highly suitable for wind power generation since wind speeds exceed 3 m/s in most of these areas. Old windmills found in the Marmara and Aegean regions are good indicators of the wind energy potential for these regions. While the average density of wind power is below the 40 W/m(2) in 89.3% of Turkey's total domain, it is over 40 W/m(2) in 10.7% and it exceeds 100 W/m(2) in 0.8%. There are also some regions of Turkey where average density of wind power reaches 294.1 W/m(2) level.Öğe Conversion of agricultural residues to fuel products via supercritical fluid extraction(TAYLOR & FRANCIS INC, 2004) Demirbas, AIn this study, various agricultural residues such as wheat straw, corncob, corn stover, tobacco stalk, tobacco leaf, olive waste, walnut shell, and almond shell were subjected to supercritical fluid extraction (SFE) using acetone, methanol, and water as solvent. The highest yield (59.3%) of SFE was obtained from OW with water solvent at 678 K. While carbon content of the selected samples varies from about 41.2% to 53.6%, carbon content of the extracts from SFEs varies from 52.8% to 67.8%. The hydrogen content of the extracts varies from 6.8% to 8.8%. The oxygen content of the extracts ranges from 21.7% to 38.1%, and nitrogen content ranges from 0.4% to 2.3%. Decreases of oxygen content in the supercritical fluid extracts range from 38.9% to 13.8%. The supercritical fluid extracts were fractionated into water soluble, acetone soluble, phenolic, fatty acid, polar, nonpolar, and basic fractions.Öğe Degradation of poplar and spruce wood chips using alkaline glycerol(TAYLOR & FRANCIS INC, 2005) Demirbas, A; Celik, APoplar and spruce wood chips were degraded by using glycerol as a solvent and alkaline glycerol with and without alkali media at different temperatures: 440, 450, 460, 470, 480, 490, and 500 K, then the results were compared with the other organic solvent systems. The degradation reactions were mainly occurred as delignification and partly decomposition of cellulose. The effects of solvent, temperature, catalyst, delignification time and wood species on the yield of delignification were discussed. Major byproducts from delignification rections of wood chips include lignin degradation products. Lignin and its degradation products can be utilized as fuels.Öğe Determination of calorific values of bio-chars and pyro-oils from pyrolysis of beech trunkbarks(ELSEVIER SCIENCE BV, 2004) Demirbas, AIn this study, the beech trunkbark was pyrolyzed to obtain bio-char and pyro-oil for determining their calorific values. Experiments were designed to investigate the effects of both the heating rate and temperature of pyrolysis on pyro-oil and bio-char yields and their characteristics. The temperature was maintained at 550, 600, 650, 700, 750 and 800 K, while the heating rates were 2, 5, 10, 20, 40 and 100 K/s. The maximum pyro-oil yield of 34% was obtained at a final pyrolysis temperature of 750 K. It was concluded that both the temperature and heating rate had a significant effect on both yield of pyro-oil and bio-char resulting from pyrolysis of beech trunkbark. The yield of pyro-oil increases from 24 to 27% for 2 K/s run and it increases from 27 to 34% for 100 K/s run as the final temperature was raised from 550 to 800 K. The yield of bio-char decreases from 59 to 42% for 2 K/s run and it decreases from 43 to 29% for 100 K/s run as the final temperature was raised from 550 to 800 K. (C) 2004 Elsevier B.V. All rights reserved.Öğe Direct and catalytic liquefaction of wood species in aqueous solution(TAYLOR & FRANCIS INC, 2005) Demirbas, A; Balat, M; Bozbas, KDirect and catalytic liquefaction of wood kinds picea orientalis, quersus pedunculate and fagus orientalis were carried out in an autoclave in the reaction temperature range of 550-650 K in the aqueous medium. NaOH was used as catalyst in the catalytic liquefaction runs. The maximum liquid yields obtained from direct and catalytic runs were 49% and 82% for the picea orientalis wood at 650 K, respectively. It is clear that the yield of liquid products increase with increasing liquefaction temperature for each wood sample. hi general, composition of liquefaction products depends on structural composition of the sample. The yield of acetone insoluble fraction decreases with increasing liquefaction temperature for all of runs.Öğe A discussion of the paper "Performance of rice husk ash produced using a new technology as a mineral admixture in concrete" by M. Nehdi, J. Duquette, and A. El Damatty(PERGAMON-ELSEVIER SCIENCE LTD, 2004) Demirbas, A[Abstract not Available]
