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Öğe Adsorption of Sulfur Dioxide From Coal Combustion Gases on Natural Zeolite(Taylor & Francis Inc, 2006) Demirbas, AyhanIn this study, better efficiency of SO2 removal in flue gas from lignite coal combustion by adding of NZ in the gas phase was achieved. Natural zeolite was exposed to flue gas containing sulfur dioxide at varying conditions of relative humidity and temperature. It was found that the amount of sulfate on the zeolite increased with increasing relative humidity and temperature. The percents of adsorbed sulfur dioxide were 86, 74, 56, and 35, while the values of relative humidity (RH) were 75, 60, 45, and 30% for 40 minutes, respectively. The percents of adsorbed sulfur dioxide sharply increased within the first 40 min for the values of RH were 75 and 60, and after 40 min, slightly increased, then reached a plateau. In general, as increasing the RH increased the amount of sulfur dioxide adsorbed by natural zeolite. The amounts of adsorbed sulfur dioxide increased with exposure time. It increased and reached 30.2 mg/g for 40 min. After 40 min, it slightly increased and then reached a plateau. The NZ adsorbs 35.1 mg SO2 per gram adsorbent with 75% RH at 298 K from a simulated coal combustion flue gas. The amounts of adsorbed sulfur dioxide increased with increasing temperature. The NZ adsorbs 71.5 mg SO2 per gram adsorbent with 75% RH for 100 min exposure time from the flue gas mixture.Öğe Adsorption Thermodynamics of Stearic Acid Onto Bentonite(Elsevier, 2006) Demirbas, Ayhan; Sarı, Ahmet; Isıldak, ÖmerAdsorption equilibrium of stearic acid onto natural bentonite with Turkish origin was studied at the temperatures of 298, 308 and 318 K. SEM and XRD analysis show that the bentonite used as adsorbent is composed of microcrystal and porous structure. The specific surface area was determined by BET method as 38.6 m(2)/g. The adsorption of stearic acid onto bentonite was conformed to the Langnmuir and Freundlich isotherms. The equilibrium parameter, R-L revealed that the bentonite is a good adsorbent for stearic acid. The sorption capacity of bentonite studied decreases with increasing temperature. However, it is concluded that the adsorption capacity of bentonite for the stearic acid under the same experimental conditions is in comparable level in terms of that of the rice husk ash given in literature. Thermodynamic parameters, Delta G degrees(ads), was calculated to be between -21.8 and -22.8 kJ mol(-1). Delta H degrees(ads) and Delta S degrees(ads) were found to be -9.2 kJ mol(-1) and 42.4 J mol(-1) K-1, respectively. These parameters obtained as a function of temperature indicate that the adsorption of stearic acid onto bentonite was a spontaneous and an exothermic process. An FT-IR study on the adsorbed material was used to verify the interaction of the stearic molecule with bentonite after adsorption process.Öğe Alternative Fuels for Transportation(Multi Science Publ Co Ltd, 2006) Demirbas, AyhanThere are four alternative fuels that can be relatively easily used in conventional Cl engines: Vegetable oil, bio-diesel, Fischer-Tropsch (F-T), and dimethyl ether (DME). Both F-T and DME can be manufactured from natural gas and are, therefore, not limited by feedstock availability. The main advantage of the diesel engine is that the level of efficiency is greater than in the Otto cycle engine. Gasoline is a blend of hydrocarbons with some contaminants, including sulfur, nitrogen, oxygen, and certain metals. The four major constituent groups of gasoline are olefins, aromatics, paraffins, and napthenes. The main alternative fuels include alcohol, liquefied petroleum gas, compressed natural gas, hydrogen, and electricity for operation gasoline type vehicles.Öğe Biodiesel from sunflower oil in supercritical methanol with calcium oxide(PERGAMON-ELSEVIER SCIENCE LTD, 2007) Demirbas, AyhanIn this study, sunflower seed oil was subjected to the transesterification reaction with calcium oxide (CaO) in supercritical methanol for obtaining biodiesel. Methanol is used most frequently as the alcohol in the transesterification process. Calcium oxide (CaO) can considerably improve the transesterification reaction of sunflower seed oil in supercritical methanol. The variables affecting the methyl ester yield during the transesterification reaction, such as the catalyst content, reaction temperature and the molar ratio of soybean oil to alcohol, were investigated and compared with those of non-catalyst runs. The catalytic transesterification ability of CaO is quite weak under ambient temperature. At a temperature of 335 K, the yield of methyl ester is only about 5% in 3 h. When CaO was added from LUX) to 3.0%, the transesterification speed increased evidently, while when the catalyst content was further enhanced to 5%, the yield of methyl ester slowly reached to a plateau. It was observed that increasing the reaction temperature had a favorable influence on the methyl ester yield. In addition, for molar ratios ranging from I to 41, as the higher molar ratios of methanol to oil were charged, the greater transesterification speed was obtained. When the temperature was increased to 525 K, the transesterification reaction was essentially completed within 6 min with 3 wt% CaO and 41:1 methanol/oil molar ratio. (c) 2006 Elsevier Ltd. All rights reserved.Öğe Calculation of higher heating values of hydrocarbon compounds and fatty acids(TAYLOR & FRANCIS INC, 2018) Demirbas, Ayhan; Ak, Namik; Aslan, Avni; Sen, NejdetHydrocarbon compounds are formed by carbon and hydrogen elements. The higher heating values (HHVs) of the hydrocarbon compounds can be calculated based on the carbon (C) and hydrogen (H) contents of the chemical structures. HHVs (MJ / kg) as a function of the carbon (C) and hydrogen (H) fractions of N-saturated hydrocarbons can be calculated by the following equation: According to this Equation, the HHV is a function of the percentages of the carbon (C) and hydrogen (H) of pure n-saturated hydrocarbon compounds. This Equation represents the correlation obtained by means of regression analysis. It is found that the calculated values shows mean difference of 0.18%. The correlation coefficient is 0.9955.HHVs as a function of the iodine value (IV) and the saponification value (SV) of fatty acids can be calculated by the following equation: HHV(MJ/kg) = 49.43 - 0.015(IV)-0.041(SV)Öğe Gasoline- and diesel-like products from heavy oils via catalytic pyrolysis(TAYLOR & FRANCIS INC, 2017) Demirbas, Ayhan; Al-Ghamdi, Khalid; Sen, Nejdet; Aslan, Avni; Alalayah, Walid M.Heavy oil is less expensive than light crude oil, but heavy oil is more expensive to obtain light oil products. Conventional light crude oil resources are decreasing, therefore heavy oil resources will be needed more in the future. There are huge differences from field to field for heavy oil deposits. In terms of final productive use, heavy oil is considered as an unconventional resource. Heavy oil upgrading depends on four important factors: catalyst selection, heavy oil classification, process design, and production economics. Heavy and extra-heavy oils are unconventional reservoirs of oil. Globally, 21.3% of total oil reserves are heavy oil. Heavy oil is composed of long chain organic molecules called heavy hydrocarbons. The thermal degradation of the heavy hydrocarbons in heavy oil generates liquid and gaseous products. All kinds of heavy oils contain asphaltenes, and therefore are considered to be very dense material. The most similar technologies for upgrading of heavy oils are pyrolysis and catalytic pyrolysis, thermal and catalytic cracking, and hydrocracking. The amount of liquid products obtained from pyrolysis of heavy oil was dependent on the temperature and the catalyst. Pyrolytic oil contains highly valuable light hydrocarbons as gasoline and diesel components range. The constant increase in the use of crude oils has raised prices of the most common commercial conventional products and consequently seeking for new alternative petroleum resources, like some unconventional oil resources, becomes an interesting issue. The mass contents of gasoline, diesel, and heavy oil in the crude oil are 44.6%, 38.3%, and 17.1%, respectively. The gasoline yield from the heavy oil catalytic (Na2CO3) pyrolysis is higher than the diesel efficiency for all conditions. The yield of gasoline products increases with increasing pyrolysis temperature (from 230 degrees C to 350 degrees C) and percentage of catalyst (from 5% to 10%). The yields of gasoline-like product are from 21.5% to 39.1% in 5% catalytic run and from 32.5% to 42.5% in 10% catalytic run. The yields of diesel-like product are from 9.3% to 29.8% in 5% catalytic run and from 15.5% to 33.7% in 10% catalytic run.Öğe Hazardous emissions, global climate change and environmental precautions(TAYLOR & FRANCIS INC, 2006) Demirbas, AyhanIt has been recognized worldwide that the utilization of an enormous amount of fossil fuel has created various adverse effects on the environment, including acid rain and global warming. An increase in average global temperatures of approximately 0.56 K has been measured over the past century. This increase is called global climate change or global warming. The gases with three or more atoms that have higher heat capacities than those of O-2 and N-2 cause the greenhouse effect. Carbon dioxide (CO2) is a main greenhouse gas associated with global climate change. Nitrous oxide (N2O), chlorofluorocarbons (CFCs), methane (CH4) are other important greenhouse gases. Collectively, they are projected to contribute, directly, about as much potential global warming over the next 60 years as CO2. Three trace gases, HFCs, PFCs, and SF6, would be regulated under the 1997 Kyoto Protocol because of their global warming potential and for their potential growth of concentrations in the atmosphere. HFCs have been widely approved as substitutes for CFCs.Öğe Oily products from mosses and algae via pyrolysis(TAYLOR & FRANCIS INC, 2006) Demirbas, AyhanIn this study, the fuel properties of mosses and algae, and the effect of pyrolysis temperature on the yield of bio-oil from moss and alga samples, were investigated. The yield of bio-oil from pyrolysis of the samples increased with temperature. The yields were increased up to 750 K in order to reach the plateau values at 775 K. The maximum yields were 39.1, 34.3, 33.6, 37.0, 35.4, 48.2 and 55.3% of the sample for Polytrichum commune, Dicranum scoparium, Thuidium tamarascinum, Sphagnum palustre, Drepanocladus revolvens, Cladophora fracta and Chlorella protothecoides, respectively. The bio-oil yield for Chlorella protothecoides (a microalga sample) rose from 5.7 to 55.3% as the temperature rose from 525 to 775 K, and then gradually decreased to 51.8% and was obtained at 875 K with a heating rate of 10 K/s. Formulas can be developed to calculate higher heating value (HHV) of different moss and alga samples. The calculated HHV using these new correlations showed mean differences ranging from -2.3% to +0.06%. The equation developed in this study showed good agreement with experimental results on moss and algae samples. The HHVs for bio-oils from mosses 21.5-24.8 MJ/kg and the HHVs for bio-oils from algae and microalga 32.5 and 39.7 MJ/kg, respectively, were obtained at temperature ranging from 775 to 825 K. In general, algae bio-oils are of higher quality than bio-oils from mosses. In general, microalgae bio-oils are higher quality than bio-oil from wood.Öğe Progress and recent trends in biodiesel fuels(PERGAMON-ELSEVIER SCIENCE LTD, 2009) Demirbas, AyhanFossil fuel resources are decreasing daily. Biodiesel fuels are attracting increasing attention worldwide as blending components or direct replacements for diesel fuel in vehicle engines. Biodiesel fuel typically comprises lower alkyl fatty acid (chain length C-14-C-22), esters of short-chain alcohols, primarily, methanol or ethanol. Various methods have been reported for the production of biodiesel from vegetable oil, such as direct use and blending, microemulsification, pyrolysis, and transesterification. Among these, transesterification is an attractive and widely accepted technique. The purpose of the transesterification process is to lower the viscosity of the oil. The most important variables affecting methyl ester yield during the transesterification reaction are the molar ratio of alcohol to vegetable oil and the reaction temperature. 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 over other new-renewable and clean engine fuel alternatives. Biodiesel fuel is a renewable substitute fuel for petroleum diesel or petrodiesel fuel made from vegetable or animal fats; it can be used in any mixture with petrodiesel fuel. as it has very similar characteristics, but it has lower exhaust emissions. Biodiesel fuel has better properties than petrodiesel fuel; it is renewable, biodegradable, non-toxic, and essentially free of sulfur and aromatics. Biodiesel seems to be a realistic fuel for future: it 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) 2008 Elsevier Ltd. All rights reserved.Öğe Progress and recent trends in biofuels(PERGAMON-ELSEVIER SCIENCE LTD, 2007) Demirbas, AyhanIn this paper, the modern biomass-based transportation fuels such as fuels from Fischer-Tropsch synthesis, bioethanol, fatty acid (m)ethylester, biomethanol, and biohydrogen are briefly reviewed. Here, the term biofuel is referred to as liquid or gaseous fuels for the transport sector that are predominantly produced from biomass. There are several reasons for biofuels to be considered as relevant technologies by both developing and industrialized countries. They include energy security reasons, environmental concerns, foreign exchange savings, and socioeconomic issues related to the rural sector. The term modern biomass is generally used to describe the traditional biomass use through the efficient and clean combustion technologies and sustained supply of biomass resources, environmentally sound and competitive fuels, heat and electricity using modern conversion technologies. Modern biomass can be used for the generation of electricity and heat. Bioethanol and biodiesel as well as diesel produced from biomass by Fischer-Tropsch synthesis are the most modern biomass-based transportation fuels. Bio-ethanol is a petrol additive/substitute. It is possible that wood, straw and even household wastes may be economically converted to bio-ethanol. Bio-ethanol is derived from alcoholic fermentation of sucrose or simple sugars, which are produced from biomass by hydrolysis process. Currently crops generating starch, sugar or oil are the basis for transport fuel production. There has been renewed interest in the use of vegetable oils for making biodiesel due to its less polluting and renewable nature as against the conventional petroleum diesel fuel. Biodiesel is a renewable replacement to petroleum-based diesel. Biomass energy conversion facilities are important for obtaining bio-oil. Pyrolysis is the most important process among the thermal conversion processes of biomass. Brief summaries of the basic concepts involved in the thermochemical conversions of biomass fuels are presented. The percentage share of biomass was 62.1 % of the total renewable energy sources in 1995. The reduction of greenhouse gases pollution is the main advantage of utilizing biomass energy. (c) 2006 Elsevier Ltd. All rights reserved.Öğe Recovery of energy and chemicals from carbonaceous materials(TAYLOR & FRANCIS INC, 2006) Demirbas, Ayhan; Ozturk, Temel; Demirbas, M. FatihBiomass is the most common form of carbonaceous materials, widely used in the third world. In this study, methods of recovery of organic wastes are evaluated. These methods are mainly hydrogenation, pyrolysis, thermal and/or catalytic cracking, gasification and bioconversion. These methods are compared with each other. During these processes, the polymeric structure is broken down, producing smaller intermediate species, which can further react and produce a mixture of smaller hydrocarbon molecules, liquids and gases. These hydrocarbons could be used as fuel or as chemical raw materials for several industries. Thus, plastic wastes are recovered by using alternative energy sources.Öğe Sustainable biomass production(TAYLOR & FRANCIS INC, 2006) Demirbas, AyhanThis study aims to estimate, identify and evaluate the biomass production options, estimate the sustainable biomass production for energy, and estimate the energy potential of biomass production in Turkey. Within the framework of sustainable development, Turkey today faces the challenge of balancing economic growth with environmental progress. Sustainable biomass production potential mainly depends on the productivity and surplus land available for biomass production. Based on the surplus land available for plantation, the plantation options and biomass productivity, the sustainable biomass potential for energy is estimated. Among the biomass energy sources, fuelwood seems to be one of the most interesting because its share of the total energy production of Turkey is high at 21%. The total biomass energy potential of Turkey is about 32 Mtoe. The amount of usable biomass potential of Turkey is approximately 17 Mtoe. The electrical production from usable biomass has a net impact of $4.4 billion in personal and corporate income and represented more than 160,000 jobs.
