Fatma Karaca

Coprocessing of a Turkish lignite with a cellulosic waste material. 1. The effect of coprocessing on liquefaction yields at different reaction temperatures

Abstract In recent years, the liquefaction potential of waste materials has been investigated to increase the yield of coal conversion processes and the quality of liquid fuels from coal. The results have shown that the coprocessing of coal with biowaste materials increases liquefaction yields. In this study, the effects of liquefaction of Soma lignite with sawdust as a coprocessing agent, on total conversion, oil+gas total yields, asphaltene yields and preasphaltene yields were investigated at five different temperatures, 300, 325, 350, 375 and 400°C, 40 atm initial cold pressure, 1/1 (wt/wt) sawdust/lignite ratio and 3/1 (vol/wt) tetralin/(lignite+sawdust) ratio values.

Coprocessing of a Turkish lignite with a cellulosic waste material: 2. The effect of coprocessing on liquefaction yields at different reaction pressures and sawdust/lignite ratios

Abstract Most of the research works done for alternative energy sources have shown that, in general, coprocessing of coal with biomass-type wastes has a positive effect on the liquefaction yields and these materials are increasingly studied as coliquefaction agents for the conversion of coal to liquid fuels. Addition of biomass waste materials to coal is known to be synergetic in that it improves the yields and quality of liquid products produced from coal under relatively mild conditions of temperature and pressure. This paper reports the coprocessing of a Turkish lignite with sawdust in the category of biomass-type waste material. The experiments have been conducted in a stainless-steel reactor, and temperature and tetralin/(lignite+sawdust) ratio were kept constant at 350 °C and 3:1 (vol/wt), respectively. This is the first time that the influence of reaction pressures on coliquefaction yields was investigated. In addition, the influence of the sawdust/lignite ratios on coprocessing conversion and product distribution was also investigated under the same reaction conditions. The runs were carried out at 10, 25, 40, 55, and 70 atm initial cold hydrogen pressure values and at 0.5:1, 0.75:1, 1:1, 1.25:1, and 1.5:1 sawdust/lignite (wt/wt) ratio values.

Molecular mass ranges of coal tar pitch fractions by mass spectrometry and size-exclusion chromatography

A coal tar pitch was fractionated by solvent solubility into heptane-solubles, heptane-insoluble/toluene-solubles (asphaltenes), and toluene-insolubles (preasphaltenes). The aim of the work was to compare the mass ranges of the different fractions by several different techniques. Thermogravimetric analysis, size-exclusion chromatography (SEC) and UV-fluorescence spectroscopy showed distinct differences between the three fractions in terms of volatility, molecular size ranges and the aromatic chromophore sizes present. The mass spectrometric methods used were gas chromatography/mass spectrometry (GC/MS), pyrolysis/GC/MS, electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) and laser desorption time-of-flight mass spectrometry (LD-TOFMS). The first three techniques gave good mass spectra only for the heptane-soluble fraction. Only LDMS gave signals from the toluene-insolubles, indicating that the molecules were too involatile for GC and too complex to pyrolyze into small molecules during pyrolysis/GC/MS. ESI-FTICRMS gave no signal for toluene-insolubles probably because the fraction was insoluble in the methanol or acetonitrile, water and formic acid mixture used as solvent to the ESI source. LDMS was able to generate ions from each of the fractions. Fractionation of complex samples is necessary to separate smaller molecules to allow the use of higher laser fluences for the larger molecules and suppress the formation of ionized molecular clusters. The upper mass limit of the pitch was determined as between 5000 and 10,000 u. The pitch asphaltenes showed a peak of maximum intensity in the LDMS spectra at around m/z 400, in broad agreement with the estimate from SEC. The mass ranges of the toluene-insoluble fraction found by LDMS and SEC (400-10,000 u with maximum intensity around 2000 u by LDMS and 100-9320 u with maximum intensity around 740 u by SEC) are higher than those for the asphaltene fraction (200-4000 u with maximum intensity around 400 u by LDMS and 100-2680 u with maximum intensity around 286 u by SEC) and greater than values considered appropriate for petroleum asphaltenes (300-1200 u with maximum intensity near 700 u).

Economic analysis and comparison of chemical heat pump systems

Over the last years great interest has been shown in chemical heat pump systems. Chemical heat pumps represent a new technology with great potential to reduce the energy consumption in very different sectors. They can provide the ability to capture the rejected low-grade heat and to reuse it at increased temperature levels in various industrial processes. Heat can be removed from a heat source at low-temperature by an endothermic reaction and can be boosted to a heat sink at high-temperature by an exothermic reaction. Since chemical heat pumps can operate without compression, with less electrical power and at higher temperature levels compared to conventional heat pumps, they can afford high performance advantages. As an additional advantage, energy storage can also be accomplished so that intermittent energy sources can be utilized in a chemical heat pump system. The objective of this work was to study methanol–formaldehyde–hydrogen, ethanol–acetaldehyde– hydrogen, i-propanol–acetone–hydrogen and n-butanol–butyraldehyde–hydrogen chemical heat pump systems based on catalytic dehydrogenation of alcohols at low-temperature and hydrogenation of aldehydes and a ketone at high-temperature. On the base of economic analysis, the quantity of waste-heat that must be supplied to produce the benefits of the process heat and also the improvement in the net gain reached were determined and compared. � 2002 Elsevier Science Ltd. All rights reserved.

Coprocessing of a Turkish lignite with a cellulosic waste material: 3. A statistical study on product yields and total conversion

The objectives of this study were to evaluate statistically the effects of coprocessing parameters on liquefaction yields, to determine the key process variables affecting the oil+gas, oil and asphaltene yields and total conversion. A statistical experimental design based on Second Order Central Composite Desing was planned fixing the liquefaction period at 1 h. Parameters such as temperature, initial cold pressure, tetralin/(lignite+sawdust) and sawdust/lignite ratios coded as x1, x2, x3 and x4, respectively, were used. The parameters were investigated at five levels (−2, −1, 0, 1 and 2). The effects of these factors on dependent variables, namely, oil+gas, oil and asphaltene yields and total conversion were investigated. To determine the significance of effects, the analysis of variance with 99.9% confidence limits was used. It was shown that within the experimental ranges examined, temperature and sawdust/lignite ratio were the variables of highest significance for oil+gas yields, oil yields and total conversion.

Direct liquefaction of pistachio nut shells—Effects of parameters on product yields

ABSTRACT Direct liquefaction is a technique for obtaining clean biofuel from biomass in the presence of a solvent at moderate conditions. The aim of this work was to investigate the effects of various experimental parameters on direct liquefaciton yields of a biomass waste material, namely, pistachio nut shells. Experiments were carried out in an autoclave at the conditions of temperature range 300–400°C, pressure 10–30 atmosphere, and tetralin to solvent mixture ratio 0/1–1/1. A Box–Behnken experimental design was used fixing the liquefaction period to 45 min. The effects of these parameters on oil+gas, asphaltene, and preasphaltene yields and total conversion as dependent variables were evaluated, and the model equations for these dependent variables were obtained. Desirability function was used to find the optimal solution for the liquefaction process. Fourier-transform infrared analysis and heating values were also determined for the oil and solid products obtained at the conditions where the maximum oil+gas yield was obtained.

Pyrolysis of waste polypropylene and characterisation of tar

Waste polypropylene (PP) has been pyrolysed to obtain mainly a liquid tar product of high yield (83.5%) with the balance as gas (15.5%) and a little residue (1.0%). The elemental composition of the PP tar was: C: 87.1%, H: 12.6% and O+others: 0.4% (by difference). The tar samples have been characterised by gas chromatography/mass spectrometry, heated-probe mass spectrometry and laser desorption mass spectrometry (LD-MS), to give molecular mass distributions for comparison with molecular mass ranges indicated by size-exclusion chromatography (SEC). About 50% of the tar was soluble in 1-methyl-2-pyrrolidinone, the solvent used for SEC. It appeared to consist mostly of low molecular mass materials with elution time at 20–27 min. Mass ranges from SEC and LD-MS agreed approximately in showing the upper mass limit of the tar to be about 1200 u, consisting of aromatics, alkenes, dialkenes and only minor quantities of alkanes.

The Liquefaction of Sunflower Seed Hulls

Liquefaction of a biomass waste material, namely, sunflower seed hulls, was studied in a laboratory scale stainless-steel reactor. The key parameters investigated were temperature, cold hydrogen pressure, and tetralin to solvent mixture ratio within the ranges of 325–375°C, 10–30 atm., and 0/1–1/1, respectively. A Box-Behnken experimental design was used fixing the liquefaction period at 45 minutes. The effects of parameters on dependent variables, namely, oil + gas, asphaltene, and preasphaltene yields and total conversion were evaluated, and the model equations for dependent variables were developed. It was shown that temperature and tetralin to solvent mixture ratio were the variables of highest significance on liquefaction yields. An optimization study was also done by using the desirability function approach.

Chemical exergy calculations for petroleum and petroleum–derived liquid fractions

This work focused on the chemical exergy calculation methods that can be applied to petroleum and petroleum–derived liquid fuels. The importance of thermodynamic data in the calculation of chemical exergies, and the limitations due to the absence of this kind of data to the methods to be applied, were also determined in this work. Chemical exergy values were calculated for some petroleum derived fuels for which thermodynamic data were available, using the methods given in literature. Further, chemical exergy values were also calculated and tabulated for the components of these petroleum–derived fuels.