Ali Karaduman

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.

Pyrolysis of Polystyrene Plastic Wastes with Some Organic Compounds for Enhancing Styrene Yield

Pyrolysis of polystyrene (PS) plastic waste was investigated in this experimental work harnessing a pressured autoclave surrounded by a furnace. PS was thermally degraded with various organic compounds, such as phenol, quinone, naphthalene, and diphenylamine. Experiments varied the temperature between 350 and 450°C. The main products of PS waste pyrolysis were mainly styrene monomer, ethyl benzene, toluene, and methyl styrene. The product spectrum can be described as a function of pyrolysis temperature and used organic compounds. The yield styrene of liquid products at various temperatures and at 400°C and 60 min with organic compounds were about from 60 to 74%. The optimum pyrolysis temperature to maximize styrene monomer yield (about 60%) was 400°C, and the maximum styrene yield was obtained with naphthalene as 74% in this study. The amount of styrene was found to increase in the following order: diphenylamine < thermal < phenol < quinone < naphthalene.

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.

Flash Vacuum Pyrolysis of Low Density Polyethylene in a Free-Fall Reactor

Polyethylene (PE) is the principal component of postconsumer plastic wastes. It is important to develop chemical techniques to decompose PE with a view to recycling and production of compounds that are valuable as fuel or industrial raw materials. The most common reactors in polymer pyrolysis are fluidized-bed types. Free-fall reactors do not suffer the disadvantages of fluidized beds related to inert gas employment. This flash pyrolysis study has shown that low density polyethylene (LDPE) can be continuously degraded in a free-fall reactor under vacuum to give a product quality superior to other methods. The total conversion (i.e., the sum of liquid and gas yield) is 43% at 875°C when the feed is 150–75 μm LDPE particles. Over 99% of the gaseous product is C1 to C4, the ethylene monomer exceeding 64%. The bulk of the liquid product is paraffinic; 96% of which is below C40, while over 55% is C12–C20. As is known, C12–C20 hydrocarbons are essential raw materials for the production of fatty acids, fatty alcohols, and detergents. Reduction in operation temperature down to 750°C causes the total conversion to fall from 40% to 25%. This is accompanied by a slight increase (from about 64% to 67%) in the ethylene monomer yield. Thus higher temperatures should be preferred. On the other hand, indications are that lowering the particle size down to −75 μm favorably influences the total conversion, with a gain of about 20%.

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.

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.

The Effect of Moisture on the Liquefaction of Some Turkish Coals in Tetralin with Microwave Energy

The effect of the moisture content of coals, solvent/coal ratio, and the heating period by microwave energy on solubilization of Turkish coals (Bolu-Göynük, Beypazari, Mu < la-Yata < an, Tunçbilek, Aydi n-Yeniçeltek lignites, and Zonguldak coal) in tetralin has been investigated. The yields of tetrahydrofuran (THF) solubles and oils were increased with increasing moisture content of coals. When solvent/coal ratio increased from 2/1 to 4/1, the yield of oils increased. However, the yields of asphaltenes and preasphaltenes decreased. The yields of THF solubles and oils did not change considerably with reaction time. While the yields of asphaltenes and preasphaltenes decreased with reaction time at the value of 2/1 of solvent/coal ratio and increased with reaction time at the value of 4/1 of solvent/coal ratio, the yields are lower than at the value of 2/1 of solvent/coal ratio.

Simple Model Predictive Control Studies on a Batch Polymerization Reactor

A single step control algorithm has been developed and implemented for the temperature control of a batch styrene polymerization reactor. The algorithm is based on the energy balance of the system with assumed linear dependency of the overall heat transfer coefficient on feed flow rate through the cooling jacket. The heat generation term in the energy equation is treated as an inferentially measured process disturbance and predicted by on-line process measurements. The algorithm was tested in real-time runs and resulted in a good performance for maintaining the reactor temperature at its set point during the isothermal reaction stage.