Emir H. Şimşek

Flash pyrolysis of polystyrene wastes in a free-fall reactor under vacuum

Abstract Plastic waste minimization and recycling are important for both economical and environmental reasons. In this flash pyrolysis study, polystyrene wastes were degraded in a free-fall reactor under vacuum to regain the monomer. A set of experiments varied the temperature between 700 and 875°C and determined its effects on the phase yields, the benzene, styrene, toluene, and naphthalene distribution of the liquid output and C1–C4 content of the gaseous output. The liquid yield maximized around 750°C and the styrene yield at 825°C. In general, operating at higher temperatures lessened the solid residue and increased the gaseous yield and total conversion. Employing waste particles in four size ranges, a second set of runs indicated that the finer the waste particles fed the higher the gaseous yield and total conversion. This recycling method can be made more promising if the feed particles are allowed more time for degradation and the removal of the primary products speeded up thereby preventing their decomposition. Ways are suggested to obviate these residence time problems.

Liquefaction of Turkish coals in tetralin with microwaves

Abstract The effect of the ratio of solvent to coal (S/C) and the period of heating by microwave on the solubilization of Turkish Coals (Beypazari, Bolu-Goynuk, Mugla-Yatagan, Soma-Merkez, Tuncbilek lignites and Zonguldak coal) in tetralin have been investigated. For the investigation of the effect of the S/C ratios with values of 4/1, 5/1, 6/1, 7/1 and 8/1, the coal samples were heated by microwave for 10 min. The results indicated that the optimum S/C ratio depends on the coal type to obtain the highest yields of THF solubles. The effect of microwave heating period was investigated at the values of 4/1 and 8/1 of S/C ratios and the heating period was changed from 2 to 10 min at 2-min intervals. The yield of THF solubles decreased with increasing heating period at the value of S/C ratio of 4/1, they increased with increasing heating period when the value of S/C ratio was 8/1. The yield of THF soluble coal products after 10 min of microwave heating period changed from 13% to 23%, depending on the coal type.

Investigation of dissolution mechanism of six Turkish coals in tetralin with microwave energy

Abstract Rates of formation of oil, asphaltenes, and preasphaltenes during liquefaction of six Turkish coals in tetralin with microwave heating have been experimentally determined. Five reaction mechanisms have been proposed and tested to estimate the rates of formation of products. Proposed mechanisms are based on assumptions that the reactions are irreversible and pseudo-first order with respect to the reacting species. Pseudo-first order rate constants for each of the indicated mechanistic steps have been calculated by multivariable non-linear regression analysis. The best fit between experimental data and models suggested was obtained from model 3 (this model suggests that oils, asphaltenes and preasphaltenes formed directly from coal) with Tuncbilek and Zonguldak, from model 4 (this model assumes oils to be produced directly from preasphaltenes in addition to being formed from coal according to model 3) with Mugla–Yatagan and Soma–Merkez, and from model 5 (this model describes conversion of coal to solvent fractionation products incorporating both series and parallel reactions) with Bolu–Goynuk and Beypazari coals. The results indicated that the reaction mechanism of coal liquefaction depends on the coal type.

The effect of preswelling and/or pretreatment of some Turkish coals on the supercritical fluid extract yield☆

Abstract The effects of preswelling, and/or pretreatment with 1N HCl of four Turkish coals (Bolu-Goynuk, Seyitomer, Tuncbilek and Soma-Merkez) on the supercritical toluene extract yields have been investigated. Methanol, 1,4-dioxane, THF (tetrahydrofuran), pyridine and EDA (ethylenediamine) were used as swelling agents. Solvent swelling and pretreatment with 1N HCl of coals significantly enhanced the liquid yields. The effectiveness of the swelling solvents in enhancing the liquid yield is in the same order as their swelling ratios. Swelling in EDA and pyridine were more effective for the extraction of coals. The highest improved liquid yields in supercritical toluene for each coal was obtained by the combined effects of pretreatment and preswelling of coals. No simple trend in reactivity increment with properties of coals was observed.

Thermal Degradation Mechanism of Low-Density Polyethylene Plastic Wastes in Cyclohexane

The thermal LDPE degradation mechanism harnessing a high-pressure autoclave surrounded by a furnace was investigated in this work. Rates of formation of gas, liquid, and solid during degradation of PE plastic wastes in cyclohexane as solvent at 400 and 425°C have been experimentally determined. Four reaction mechanisms have been proposed and tested to estimates of gas, liquid, and solid. Proposed mechanisms are based on the assumption that the reactions are pseudo-first-order with respect to the reacting species. Pseudo-first-order rate constants for each of the indicated mechanistic steps have been calculated by nonlinear regression analysis. The best fit was obtained by model 2 (pure parallel reaction mechanism), and its activation energy was determined.

RELATION BETWEEN SWELLING OF LIGNITES AND THE CHARACTERISTICS OF SWELLING AGENTS

Abstract Relation between swelling ratio of lignites and lignite and solvent characteristics was developed using a third level factorial design with three variables; percent carbon content, particle size of the lignite and electron donor number of the solvent. The results indicate that particle size of the lignite does not affect the swelling ratio. While swelling ratio of the lignites decreases slightly with increasing carbon content of the lignites electron donor number of the solvent has a noticeable effect on the swelling ratio.

The effect of swelling pretreatment on the coal liquefaction in tetralin with microwave energy

Three Turkish coals, a Zonguldak coal and Tunçbilek and Beypazari lignites were used to examine the effect of solvent swelling pretreatment on the solubilization and dissolution behavior. Methanol, THF (tetrahydrofuran) and TBAH (tetrabutylammonium hydroxide) were used as swelling agents. For the investigation of dissolution behavior of coals, the microwave heating period was changed from 10 to 30 min at 5 min intervals. While solvent pretreatment enhanced the THF solubles yields for the Zonguldak coal, solvent treatment decreased the THF solubles yields for the Tunçbilek and Beypazari lignites. The data obtained in this study indicated that the formation mechanism of AS (asphaltenes), PAS (preasphaltenes) and oils depend on the coal and swelling agent type.

EFFECT OF PRESWELLING ON SOXHLET AND SUPERCRITICAL GAS EXTRACTION OF A TURKISH LIGNITE

ABSTRACT Preswelling of Mugla-Yatagan lignite with THF (Tetrahydrofuran) followed by removal of the swelling agents results in higher extract yields, probably because the solvent molecules had easier access to the expanded pore structure of the swollen lignite. On the other hand, the yields of supercritical THF extract of the same lignite sample indicated that during removal of the swelling agent the expanded pore structure had collapsed. The results show that higher extract yields might have been obtained by the combined effect of the expanded pore structure of the swollen lignite and the solvent power of the mixed solvent,i.e., of the mixture of swelling agent and supercritical extraction fluid.

USE OF CYCLOHEXANE AS SOLVENT IN THERMAL DEGRADATION OF LOW DENSITY POLYETHYLENE WASTES

Thermal degradation of low density polyethylene (LDPE) wastes was investigated in this study as a step in chemical recycling. The effects of the degradation temperature, the solvent–LDPE ratio, and the reaction time were researched in the respective ranges 375–450°C, 0:1–6:1, and 30–120 min. Experiments at a cyclohexane:LDPE ratio of 6:1 showed that up to 425°C the solid residue decreased whereas the liquid yield and the total conversion increased. There were no significant changes thereafter. Solventless degradation at 425°C gave the weight percentages of 4.7, 75.6, and 19.7 for solid, liquid, and gaseous products, respectively. The use of cyclohexane as a solvent brought about approximately 20% gain in liquid yield and diminished the solid residue to negligible levels. Alkanes, alkenes, and cycloalkanes were the identified compounds in the light liquid products of degradation. The solvent reacted with the products. Reactions between alkanes and alkenes also contributed to cyclization that increased with temperature. The gas chromatography analyses identified methane and C2–C4 in the gaseous products. Reaction time tests showed unimportant changes in yield figures.

Photocatalytic Dissolution of Two Turkish Lignites in Tetralin: Effects of UV Irradiation, TiO2 and ZnO as Photocatalyst

The effects of ultraviolet (UV) irradiation, photocatalyst, and reaction time on the dissolution of two Turkish lignites (Beypazarı and Tunçbilek lignites) in tetralin have been investigated under ambient conditions. Lignites samples were irradiated in the presence or absence of added photocatalysts (TiO 2 and ZnO) at varying reaction times (1–10 days), constant irradiation power (180 W), and constant solvent/lignite ratio (5/1). The solubility of lignites increased with reaction time under UV light. The liquefaction behaviors of the lignites are different from each other. As the maximum solubility (45%) with Tunçbilek lignite has been achieved at shorter reaction times, it has been reached at longer reaction times for Beypazarı lignite (32%). The solubility values obtained from noncatalytic liquefaction are higher than those obtained from liquefaction with TiO 2 and ZnO.